why do statins work and what on?

Statins work because they are antimicrobial. Stopping the microbial process results in there not being what they call cholesterol from being used to repair the microbial damage. We also call it scar tissue.

1. Bacteria
2. Archaea
3. Fungi
4. Protazoa
5. Algae
6. Viruses

If you have use for statins in your body it is because you have one, some or all of these overgrowing in or on your person. So not really a waste of time if you have one of these living in or on you.

Just sayin…Statins might be the lesser of the evils.

Unexpected antimicrobial effect of statins

Is There Potential for Repurposing Statins as Novel Antimicrobials?

How do statin drugs affect aging?

https://www.ncbi.nlm.nih.gov/pubmed/29085751

Mood, Personality, and Behavior Changes During Treatment with Statins: A Case Series

~Content Source – PDF: Mood, Personality, and Behavior Changes During Treatment with Statins

ABSTRACT

Psychiatric adverse drug reactions (ADRs) have been reported with statin use, but the literature regarding statin-associated mood/behavioral changes remains limited. We sought to elicit information germane to natural history and characteristics of central nervous system/behavioral changes in apparent connection with statin and/or cholesterol-lowering drug use, and delineate mechanisms that may bear on an association. Participants (and/or proxies) self-referred with behavioral and/or mood changes in apparent association with statins completed a survey eliciting cholesterol-lowering drug history, character and impact of behavioral/mood effect, time-course of onset and recovery in relation to drug use/modification, co-occurrence of recognized statin-associated ADRs, and factors relevant to ADR causality determination. Naranjo presumptive ADR causality criteria were assessed. Participants (n = 12) reported mood/behavior change that commenced following statin initiation and persisted or progressed with continued use. Reported problems included violent ideation, irritability, depression, and suicide. Problems resolved with drug discontinuation and recurred with rechallenge where attempted. Eight met presumptive criteria for “probable” or “definite” causality; others had additional factors not considered in Naranjo criteria that bear on casual likelihood. (1) Simvastatin 80 mg was followed in 5 days by irritability/depression culminating in suicide in a man in his 40s (Naranjo criteria: possible causality). (2) Simvastatin 10 mg was followed within 2 weeks by depression in a woman in her 50s (probable causality). (3) Atorvastatin 20 mg was followed in ~1 month by depression and irritability/aggression in a male in his 50s (probable causality). (4) Atorvastatin 10 mg was followed in several months by aggression/irritability and depression culminating in suicide in a man in his 40s (possible causality). (5) Fenofibrate + rosuvastatin (unknown dose), later combined with atorvastatin were followed in 1 month by aggression/irritability in a male in his 30s (probable causality). (6) Lovastatin (unknown dose and time-course to reaction) was followed by depression, dyscontrol of bipolar disorder, and suicide attempts in a male in his 40s (possible causality). (7) Atorvastatin 20 mg was followed within 2 weeks by cognitive compromise, and nightmares, depression, and anxiety culminating in suicide in a man in his teens (definite causality). (8) Simvastatin 10 mg was followed (time-course not recalled) by depression, aggression/irritability culminating in suicide in a man in his 60s (possible causality). (9) Simvastatin 20 mg then atorvastatin 10 mg were followed (time-course not provided) by irritability/aggression in a man in his 60s (definite causality). (10) Atorvastatin 10 then 20 then 40 mg were followed shortly after the dose increase by violent ideation and anxiety in a man in his 30s (probable causality). (11) Atorvastatin 20 mg and then simvastatin 20 mg were followed in 2 weeks by aggression/irritability in a man in his 50s (definite causality). (12) Lovastatin, rosuvastatin, atorvastatin, and simvastatin at varying doses were followed as quickly as 1 day by aggression, irritability, and violent ideation in a man in his 40s (definite causality). Most had risk factors for statin ADRs, and co-occurrence of other, recognized statin ADRs. ADRs had implications for marriages, careers, and safety of self and others. These observations support the potential for adverse mood and behavioral change in some individuals with statin use, extend the limited literature on such effects, and provide impetus for further investigation into these presumptive ADRs. Potential mechanisms are reviewed, including hypothesized mechanisms related to oxidative stress and bioenergetics.

KEY POINTS

Psychiatric adverse effects, altering mood, personality, and behavior, sometimes arise in patients receiving statins.

Statin psychiatric effects can include irritability/aggression, anxiety or depressed mood, violent ideation, sleep problems including nightmares, and possibly suicide attempt and completion.

INTRODUCTION

Most adverse drug reaction (ADR) reporting focuses on non-behavioral health risks to the medication-taking individual; however, attention is increasingly given to drug-induced behavioral and mood changes that may affect self or others. Drugs and medications with behavioral concerns include alcohol (best recognized) [], but also varenicline [], loratadine [], mefloquine [], tramadol [], isotretinoin [], tricyclics [], benzodiazepines [], and selective serotonin reuptake inhibitors (SSRIs) [], among others []. Emerging evidence suggests such problems may occasionally arise with cholesterol-lowering drugs []. These drugs are widely prescribed and most prominently include statins (3-hydroxy-3-methylglutaryl coenzyme-A reductase inhibitors), which held the place of best-selling class of prescription drugs in the world and include the best-selling prescription drug in history [].

Neuropsychiatric ADRs of statins, including suicide and aggression, have been reported in pharmacovigilance databases [] and in adverse event reports and series []. Moreover, adverse behaviors have been reported in settings of low cholesterol []; and of lower omega-3 fatty acid levels (the omega-3 to omega-6 ratio is reportedly reduced with statins) []. Both naturally low cholesterol and randomized assignment to cholesterol reduction in the pre-statin era have been reported to be linked to increased violent deaths [], though statin randomization has not []. Recent randomized controlled trial (RCT) evidence indicating that statins can have bidirectional effects on aggression may be germane here: different mediating factors, including increased sleep problems and perhaps reduced testosterone, appear to drive effects in differing directions, and bidirectional effects on oxidative stress may also be speculated to do so. Nonetheless, the literature relating mood and behavioral changes to cholesterol-lowering drugs, and depicting the character and potential implications of adverse psychiatric effects with statins, remains relatively sparse []. Here we present 12 cases of mood and behavioral change apparently associated with lipid-lowering agents.

METHODS

A total of 12 subjects and/or their family members (if the subject was deceased) who reportedly experienced mood and behavioral changes while receiving one or more statin, as identified by the subject and/or by family members, contacted our study group and provided survey information. Written informed consent was obtained from each participant (or proxy for deceased subjects) for inclusion of their case in this case series. These 12 represent a convenience sample, chosen because the neuropsychiatric problem was the primary complaint, because the nature or severity appeared to warrant representation in the literature, because the participant or proxy was amenable to inclusion (with proper de-identification), and because the aggregate number, 12, was small enough to allow inclusion of some individual detail, yet sufficient to illustrate a suite of potential issues.

Elicited information included demographic characteristics, drug(s) used (statin and concomitant medications), dose(s), time-course of mood and behavior change relative to drug use (onset, duration, recovery), character of symptoms, and open-ended narrative of the impact of behavior, mood, and/or personality changes. We inquired whether a modification to the treatment regimen occurred—such as changes in dose, drug discontinuation, and drug rechallenge—and the impact on symptoms. Recognized risk factors for statin ADRs, and development of other recognized statin ADRs, were also elicited. Information for each case is presented in tabular form.

Cases were assessed for adherence to presumptive causality criteria using the published Naranjo drug ADR causality classification. This employs a point system of positive and negative causality points to estimate the probability of an ADR, with a score ≥9 deemed to indicate “definite” ADR causality, 5–8 “probable”, 1–4 “possible”, and ≤0 “doubtful” []. For all participants, adverse event causality was at least “possible”, since psychiatric and behavioral reactions to statins or cholesterol reduction bear biological plausibility and prior reports. “Probable” causality was limited to those who experienced occurrence following drug initiation, had the drug discontinued, and improved following drug discontinuation. “Definite” causality assignments were limited to those who, in addition to recovery with discontinuation, were rechallenged with the drug, and experienced symptom recurrence.

RESULTS

Information on drug, drug dose, reported mood and behavioral effect, factors supporting a causal connection, other statin symptoms, family history of psychiatric problems associated with statin use, and presence of risk factors for statin adverse effects are listed in Table 1. Cases commonly involved more than one psychiatric element (Table 2). An expanded description of each case is provided (Table 3). Marked change in mood and/or behavior was commonly noted, in some instances leading to tragic consequences. In some cases, proximal mood or behavioral changes arising with cholesterol-lowering agents led to the addition of psychiatric medications, and a role for these psychotropic medications in behavioral sequelae cannot be excluded. Behavioral/mood findings often accompanied muscle, cognitive, or other better recognized statin adverse effects []. Some participants had family members who also had experienced psychiatric adverse effects attributed to statins. Several participants exhibited compelling on-off-on reproducibility of findings.

Based on Naranjo presumptive criteria for ADR causality, eight cases qualified as bearing a “probable” or “definite” causality designation. The four cases designated “possible” are included because of factors not considered in Naranjo criteria that bear on likelihood of a causal connection. (As was said for a drug bearing a similar spectrum of behavioral adverse behaviors, “the clear temporal relationship, lack of prior history of this behavior, and unusual nature of these events strengthens the accumulating scientific evidence” []). Each patient exhibited persistent absence of the symptom prior to administration of the statin, followed by persistent presence while receiving the statin (days to years). One possible exception was a man with bipolar disorder; however, he had manifested years of stability and good control since initiation of lithium until statin initiation, which resulted in loss of psychiatric stability persisting for the years he was receiving statins until his death. Prospects for a causal connection were buttressed by an adverse behavioral change while receiving statins in a first-degree relative who also experienced dechallenge–rechallenge support (family history and genetics are risk factors for statin problems) []. A total of 75 % of cases were accompanied by other symptoms with a confirmed relation to statin use, including muscle symptoms [], cognitive problems [], and dermatologic reactions []. Additionally, 50 % of cases had factors previously shown to be linked to an elevated risk of statin ADRs, such as thyroid conditions [].

Discussion

Summary

Behavioral and psychiatric changes in the cases presented range from violent nightmares to aggression, mood/personality change, violent or homicidal ideation (in some instances culminating in suicide), each in apparent association with statin use. The temporal association between the drug initiation and mood and behavior change, and again between drug discontinuation and resolution of symptoms where this occurred, suggests a causal connection in a number of these cases. Notable mood and behavioral changes for all patients or introduction of serious psychiatric events began after drug initiation. The latency profile is consistent with that for other statin ADRs that share common mechanisms [], and bear RCT support []. Symptoms persisted or progressed with continued use in all cases. Those able to discontinue the drug experienced resolution of symptoms. For those in whom rechallenge was possible, symptoms recurred. The presence of ADRs and risk factors with a confirmed relation to statin ADRs is consistent with common pathophysiological factors, hypothesized to underlie many statin adverse effects, extending to behavioral effects []. (12 cases are included; for those interested in knowledge of other cases of this kind, a 13th case, involving a physician with behavioral changes while receiving statins and leading to professional review, is planned for inclusion in a separate manuscript on statin adverse effects in physicians).

Explanation of Findings; Comparison/Contrast with Other Findings in Literature

Though a relation of statins to instances of behavior alteration may seem counterintuitive, it fits with a body of existing literature. Observationally, lower cholesterol has been linked to greater violence (including aggression, suicide, homicide, violence) in many studies, including prospective longitudinal studies []. Behavioral consequences of lipid-lowering medications have been reported for non-statin treatments, including fibrates [] (implicated in case 5), with support extending to meta-analyses of RCTs showing significantly increased violent death []. RCT meta-analysis in the statin era did not support an increase in violent death on average (indeed the point estimate was lower, though not significantly) []. RCT patient selection may be one factor: excess violent deaths on pre-statin lipid drugs were preferentially evident in those with risk factors for violence—e.g., alcohol, psychiatric history, and non-compliance []. Of note, there was no evidence of more patients with these characteristics in the cholesterol-lowering group, but the excess of events emphasized these patients. Psychiatric histories, alcohol/substance use, and low conscientiousness are risk factors for lower compliance, so may lead to exclusion with compliance run-ins, but are also risk factors for adverse behaviors, so vulnerable individuals might be preferentially excluded []. Relative exclusion may affect detection of risk in two ways. First, the same fractional (relative) risk change will lead to a greater number affected, and more power to show a change, in those at higher risk (a doubling of nothing is still nothing) []. Second, the fractional risk change itself may be greater in a behaviorally vulnerable subset (effect modification): illustrating this point, the odds ratios risk of psychiatric events with mefloquine use was reported to be 3.8 among those without a psychiatric history, versus apparently double that (8.0) in those with a psychiatric history [].

Other factors may also explain this. Randomized trial evidence examining statin effects on aggression provides potential insights: statins (vs. placebo) promoted both average significant increases and reduction in aggression, in different groups []. Typical effects in men (particularly in men who were both younger and less aggressive at baseline) were toward reduced aggression [], with older age and female sex shifting the distribution. Simvastatin has been shown to both significantly lower testosterone [] and worsen sleep problems on average []. (It may also promote sleep apnea in some []). For men receiving simvastatin, the magnitude of each of these effects significantly predicted the change in aggression, in opposite directions []. Sleep problems and sleep apnea are elsewhere linked to irritability [], as well as aggression and violence []. Lower testosterone in some settings is linked to lower aggression and violence [].

Other mechanisms may be theorized. Low central serotonin has been linked to low cholesterol and to aggression []. However, whole blood serotonin (which correlates inversely to central serotonin) did not predict aggression in mediation analysis within a randomized trial []. We also hypothesize that effects on aggression, and perhaps mood problems on statins, may be linked to oxidative stress [] and inter-related mitochondrial dysfunction (which has been linked to temper disorders) []. The explanation accords with our finding that behavioral adverse effects commonly co-occur with better known statin adverse effects, with the documented relation of better known statin adverse effects to oxidative stress and mitochondrial dysfunction [], and with the documented connection of mitochondrial dysfunction to a range of psychiatric problems [].

Other hypothetical mechanisms of potential relevance, such as the role of cholesterol in synapse formation or membrane function, and myelin production have been reviewed elsewhere [], but in contrast to mechanisms cited above, triangulating evidence for a role is currently lacking.

The explanation accords with our finding that behavioral adverse effects commonly co-occur with better known statin adverse effects, for which a relation to oxidative stress and mitochondrial dysfunction has been elucidated []. Mitochondrial dysfunction has a documented connection to a range of psychiatric problems [], and may also contribute to behavioral change with statin-induced oxidative damage.

More lipophilic statins have better brain penetration [], though all statins have some ability to cross the blood–brain barrier []. Whether this is important for central effects of the kinds described is unknown, since peripheral effects can have central consequences—and since prooxidant effects of statins, which are linked to the occurrence of statin adverse effects [], also raise blood–brain barrier penetrability []. Each of the patients in our report experienced problems while receiving at least one of simvastatin, atorvastatin, or lovastatin, which are lipophilic statins. However, most involved atorvastatin and simvastatin, which have also historically been the most frequently prescribed statins. This, and the lack of a defined base population in which statin prescribing rates are known, obviates our ability to comment on whether lipophilicity is relevant to these effects.

Limitations

This study has the limitations inherent to all case series: data are observational, which constrains causal inference. However, a profound change in state while receiving a drug, particularly with dechallenge–rechallenge support, strengthens the case for causality. There is no defined base population or control group, precluding calculation of rates and risk ratios, and occurrence of adverse neuropsychiatric effects in these cases, even if presumed causal, has no inherent implications for usual effects of statins on the outcomes reported—nor do usual effects have necessary implications to individual ones. Rather, this case series underscores that statins may in specific individuals promote adverse behavioral, mood, and personality changes, irrespective of whether behavioral (or mood) effects are on average favorable, adverse, or neutral. Even reporting rates relative to other ADRs may be a challenge to gauge meaningfully for neuropsychiatric problems, because these may be particularly sensitive, and may go unreported. In an analysis of emails abstracting statin ADRs mentioned spontaneously, mood or personality problems were spontaneously related as part of the ADR complex in a minority, but in a survey directly asking about each of a list of symptoms the participant attributed to statins, among those self-selected for having at least one such symptom, a majority cited a neuropsychiatric effect. (However, in the latter, there is no gauge of severity; and physical problems can themselves contribute to some level of psychic distress).

Some of our participants had underlying conditions (such as a psychiatric disorder) that can themselves lead to an adverse outcome; however, as above, the odds ratios for risk of psychiatric events due to a drug can be magnified in the presence of a psychiatric history []. Consistent with this, most of the excess cases of violent death arising in the active treatment, cholesterol-lowering arms in a pre-statin-era analysis of randomized trials had other risk factors for violent death []; since those risk factors themselves were not shown to be increased in the active treatment group, this underscores that individuals with such issues may represent a vulnerable subgroup (as with mefloquine). As a further analogy, an analysis of rhabdomyolysis cases in the San Diego area showed that typical instances involved the confluence of more than one risk factor—consistent again with an increase in the odds of an event “due to” each agent, in the presence of the other []. In our cases, factors such as the temporal relation to statin use, and concurrence of other statin-compatible ADRs increases the prospects for causality with statins.

Data rely on self-report. However, patient self-reports of ADRs can be a valuable and reliable tool [], and—if heeded—may hasten recognition of important ADRs []; such benefits have led to standardized implementation of patient reporting for EU-based pharmacovigilance databases []. Self-selection of participants is inherent to studies with volunteer patients; however, for studying those with ADRs, whether or not they reflect typical effects, observed effects are important.

Conclusions

Though statins are widely tolerated, they may be among the growing list of prescription agents that, in some participants, may increase the risk of serious psychiatric events and/or behavioral changes. In the cases cited here, these adverse experiences posed risks to the safety of self and others—sometimes, tragically, adversely affecting marriages and careers, or culminating in death. The possibility of such ADRs, even if rare, should be recognized by physicians who prescribe cholesterol-lowering drugs, such that if personality or behavior changes arise, the drug can be included in considerations of etiology and treatment. This series extends the modest literature on behavior and psychiatric changes apparently associated with cholesterol-lowering treatment. These findings further the evidence that cholesterol-lowering drugs should be added to the list of agents that bear consideration when new irritability, or aggressive or violent behavioral changes arise.

Candida albicans-Endothelial Cell Interactions: a Key Step in the Pathogenesis of Systemic Candidiasis

~ Content Source – PDF Candida albicans-Endothelial Cell Interactions-0332-08

Candida albicans is a normal commensal organism of the oral cavity, gastrointestinal tract, and vagina. Under certain circumstances, C. albicans is capable of causing host damage (or disease) leading to oral, vaginal, cutaneous, or systemic candidiasis. The latter is a serious infection with a high mortality range of 33% to 54% and high morbidity in those who survive. In fact, in recent years, systemic candidal infections have become the fourth most frequent cause of nosocomial bloodstream infections in the United States, giving rise to an enormous associated personal and economic cost. Systemic candidiasis involves the hematogenous spread of C. albicans to multiple organs, including the brain, kidneys, heart, liver, and lungs. Histologically, infection of these organs is characterized by ramifying candidal hyphae and accompanying yeast forms that produce multiple necrotic nodules or abscesses that result in extensive organ damage leading to organ failure. Risk factors for systemic candidiasis include neutropenia, intravascular catheters, hemodialysis, total parenteral nutrition, abdominal surgery, burns, broad-spectrum antibiotics, and corticosteroids. Systemic innate immune responses by phagocytic cells, particularly neutrophils and macrophages, appear to play a critical role in the host defense against systemic Candida infections, and consequently, the majority of candidal infections occur in patients with neutropenia or defects in neutrophil or macrophage function.

MORPHOGENETIC CONVERSIONS AND C. ALBICANS VIRULENCE

C. albicans is a polymorphic organism that is capable of converting between yeast, pseudohyphal, and hyphal forms. The conventional view was that yeast forms were associated with commensal carriage, whereas hyphal forms were associated with disease. This was based on evidence showing that mutant forms of C. albicans that were locked into the yeast form were avirulent. However, this notion was challenged by Braun et al., who found that a tup1-deficient C. albicans strain that was constitutively pseudohyphal was avirulent in a murine model of systemic candidiasis. Although the precise nature of the association between fungal morphogenesis and host invasion is a hotly debated topic, it is now widely accepted that it is the ability to undergo morphogenetic conversion, rather than the morphological form itself, that is the primary determinant of pathogenicity.

The dissemination of fungal organisms in systemic candidiasis starts with their entry into the bloodstream. Given the known risk factors for systemic candidiasis, this is most likely to occur in susceptible individuals by seeding from contaminated intravascular devices, by persorption of C. albicans across the gastrointestinal mucosa, by invasion of epithelially denuded surfaces, or via trauma or surgically related inoculation. Exit from the circulation is thought to occur by adhesion and then penetration into the endothelial lining of blood vessels, except possibly in the kidney, where direct adhesion to exposed extracellular matrix components within glomerular regions may occur. Animal studies suggest that candidal trafficking from the circulation into the tissues occurs rapidly. This review discusses the two critical steps in the migration of C. albicans cells from the circulation into the tissues, which are (i) candidal adhesion to endothelial cells lining the blood vessels and (ii) transmigration of C. albicans across the endothelium into the tissues.

ADHESION OF C. ALBICANS TO ENDOTHELIAL CELLS

During hematogenous dissemination of C. albicans, organisms must first adhere to the endothelial lining of blood vessels before transmigrating across the endothelium to invade the tissues. However, little is known about the mechanisms involved in either process. What is known is complicated further by conflicting evidence concerning the roles played by yeast, pseudohyphal, and hyphal forms of C. albicans and the role of morphogenetic change in the adhesion and transmigration processes.

There are currently two different theories as to how C. albicans adheres to the endothelium. The first theory proposes that cells must first undergo morphogenetic conversion to hyphal forms, which then bind to and damage the endothelial lining of blood vessels before undergoing transmigration from the circulation into the tissues. However, more recent data indicate a second possibility in which morphogenetic change is not necessary for C. albicans invasion of the tissues. In this scenario, yeast cells adhere to the endothelium and then transmigrate into the tissues without undergoing morphogenetic conversion.

The basis of the first theory is morphogenetic conversion of C. albicans to the hyphal form, and there are many lines of evidence to support this hypothesis. These include the observations that germination of C. albicans is necessary for the organism to damage endothelial cells and that substances that inhibit germination block C. albicans-induced endothelial cell damage. Moreover, the time course of candidal germination and germ tube elongation on endothelial cells parallels the time course of endothelial cell damage. Further evidence has come from experiments using genetically engineered forms of C. albicans with filamentation defects. The ability of these organisms to damage and invade endothelial cells is severely impaired compared to that of wild-type parent strains.

Studies showing that germinated C. albicans cells exhibit much greater adherence to epithelial cells than do yeast forms prompted suggestions that C. albicansadherence to endothelial cells might also be hypha dependent. Indeed, there is some evidence to suggest that germinated candidal forms exhibit greater endothelial cell adhesion than do yeast forms of C. albicans. However, it is also possible that yeast forms adhere to the endothelial surface, germinate there, and then penetrate and damage the endothelium during transmigration or that yeast forms adhere and are then endocytosed before germinating within the endothelial cell to cause damage. Taken together, the data suggest that morphogenetic transformation is involved in endothelial cell adhesion but, more particularly, in the subsequent trans-endothelial cell migration.

Conversely, there is also evidence to suggest that morphogenetic change may not be necessary for C. albicans invasion, and this is the basis for the alternative hypothesis. In animal studies in which mice were intravenously inoculated with different mutant strains, Bendel et al. found that cells from a C. albicans mutant strain locked into the yeast form were able to leave the circulation and enter the tissues in greater numbers than those of the wild-type control. However, once cells were in the tissues, the ability of the wild-type strain to undergo hyphal transformation was associated with higher mortality, despite the lower fungal burden in the tissues than that with mutant yeast forms. Further evidence to support this theory has come from in vivo experiments investigating tissue invasion and damage, performed by Saville et al. using a genetically engineered strain of C. albicans (SSY50-B). This study demonstrated that yeast cells are capable of extravasating from blood vessels into the tissues without undergoing morphogenetic change. However, once cells were in the tissues, morphogenetic conversion from yeast to hyphal forms was crucial in causing tissue damage leading to death.

Such observations have led to a hypothesis in which circulating yeast cells bind to the endothelium and then transmigrate into the tissues before undergoing the hyphal transformation that results in tissue damage. In support of this, C. albicans migration from the circulation is very rapid (80 to 90% migration within 5 min), whereas hyphal transformation and endothelial cell damage may take several hours. Furthermore, because of their more compact shape and size, yeast cells may be better adapted for free dissemination within the circulation. In addition, the emergence of C. glabrata and C. parapsilosis as contenders for the second most common cause of disseminated candidiasis, after C. albicans, indicates that the ability to form true hyphae may not be essential for tissue adhesion, invasion, and pathogenesis among Candida species.

CANDIDATE CANDIDA ADHESINS AND THEIR ENDOTHELIAL LIGANDS

The cell wall of C. albicans is composed primarily of an inner structural layer of β1,3- and β1,6-glucans and chitin (a β1,4-linked polymer of N-acetylglucosamine) and a matrix primarily consisting of proteins (mannoproteins) that are heavily glycosylated with mannose-containing polysaccharides, sometimes called mannans. These take the form of short, linear, O-linked mannan side chains that stabilize the protein in the cell wall and large, highly branched N-linked mannans. It is this outermost layer that represents the first point of contact between C. albicans and the endothelium, although not at bud scars, where the components of the inner layers of the cell wall are exposed. Proteins and carbohydrates in these outer layers may have a number of functions, including the ability to act as adhesion molecules, and over recent years several C. albicans cell wall components with the potential to mediate adhesion to the endothelium have been identified. These include proteins with integrin-like properties, Candida agglutinin-like sequence (ALS) gene products, and mannans.

Cell wall protein adhesin candidates. (i) Integrin αMβ2-like adhesin.

Integrin analogues first gained interest in 1991, when Gustafson et al. found that adhesion of yeast forms of C. albicans to cultured monolayers of human endothelial cells was mediated in part by a candidal protein antigenically and structurally related to the leukocyte integrin αMβ2 (Mac-1, CD11b/CD18, CR3, or iC3b receptor) (). They demonstrated the expression of the αMβ2-like molecule on yeast forms of C. albicans and showed that expression was increased by growth in 20 mM d-glucose, as opposed to 20 mM l-glutamine (). Furthermore, the adhesion of yeast forms of C. albicans to endothelial cells was significantly reduced by anti-αMβ2 antibodies or pretreatment of the Candida cells with purified iC3b. Expression of this ligand may be altered at different temperatures and in different morphogenetic forms of C. albicans (), and this may affect the ability of C. albicans to adhere to endothelium (). αMβ2 has many different ligands, including iC3b, fibrinogen, factor X, urokinase receptor, CD14, CD23, CD54 (ICAM-1), CD102 (ICAM-2), CD242 (ICAM-4), heparin, haptoglobin, kininogen, and various microbial proteins (). Of these molecules, only ICAM-1 and -2 are widely expressed on endothelial cells, although CD14 was recently identified on primary, but not passaged, cultures of human umbilical vein endothelial cells (). There are no data on the role of CD14, CD102, or CD242 as a possible endothelial ligand for C. albicans adhesion, but Yokomura et al. () have shown that anti-CD54 monoclonal antibodies can partially inhibit the adhesion of yeast forms of C. albicans to rat pulmonary artery endothelial cells in vitro and significantly prolong the survival of rats injected intravenously with C. albicans. In certain circumstances, it is also possible that αMβ2 ligands such as fibrinogen, heparin and iC3b could in turn bind to endothelial cells and act as an intermediary in Candida-endothelial cell adhesion.

(ii) Integrin αvβ3– and αvβ5-like adhesins.

Two other integrin-like adhesins that may play a role in candidal adhesion to endothelium have been identified. They are homologs of the vitronectin-binding integrins αvβ3 (CD51/CD61) and αvβ5 (). Spreghini et al. () reported the expression of both of these adhesins on yeast forms of C. albicans, while Santoni et al. () showed that transformation to germ tubes was associated with a marked reduction in αvβ5-like integrin expression and an increase in αvβ3-like integrin expression. They also showed that adhesion of C. albicans germ tubes to endothelium was partially inhibited by anti-αvβ3 antibodies or an RGD sequence peptide. Heparin also inhibited germ tube adhesion, and when heparin treatment was combined with either anti-αvβ3 antibody or RGD peptide, the reduction in adhesion was greater still (). More recently, it was shown that a candidal focal adhesion kinase-like protein may be involved in regulating yeast cell adhesion to endothelium via the αvβ3– or αvβ5-like adhesins () or in mediating intracellular signaling following ligand binding, much as focal adhesion kinase proteins are involved in integrin-mediated signaling in mammalian cells (). Like its human counterpart, the candidal αvβ3-like adhesin has been shown to bind to vitronectin (), but other ligands for αvβ3 include CD31 (PECAM-1), fibronectin, fibrinogen, thrombospondin, von Willebrand factor, and RGD sequence peptides (). CD31 is expressed by endothelial cells and could act as a direct ligand for Candida adhesion (), while in certain circumstances it is possible that other ligands could act as a bridge in Candida-endothelial cell binding. Like its human counterpart, the αvβ5-like adhesin on C. albicans also binds vitronectin and RGD peptides (), but αvβ5 lacks a known endothelial cell target ligand and thus may not be involved directly with adherence to the endothelium.

(iii) ALS gene family.

The ALS (agglutinin-like sequence) gene family encodes a group of large glycosylphosphatidylinositol-linked cell surface glycoproteins (). To date, eight ALS genes have been identified, including ALS1 to ALS7 and ALS9, all of which appear to have differing roles in adhesion and transmigration. These genes have gained particular interest recently, and evidence shows that ALS1-transformed Saccharomyces cerevisiae exhibits up to 100-fold greater adherence to endothelial cells (), while Als1-deficient C. albicans hyphae exhibit reduced adhesion to endothelial cells (). Similarly, S. cerevisiae transformed with ALS3 shows increased adhesion (), while Als3-deficient hyphal forms of C. albicans exhibit defective adhesion to endothelial cells (). The loss of Als9 from yeast forms of C. albicans () or the loss of Als4 and decreased expression of Als2 from 1-hour-old germ tubes () also inhibit the adhesion of mutant C. albicans strains to endothelial cells. In contrast, mutational analysis has shown that deletion of ALS5ALS6, or ALS7 results in increased adhesion of yeast forms of C. albicans to endothelial cells, suggesting an antiadhesive role for these proteins (). On the other hand, the protein Als5 has been found to mediate adhesion, along with Als1, when expressed in S. cerevisiae (). To date, the only ligand for the ALSgene products that has been found on endothelial cells is N-cadherin, which binds to Als3 on C. albicans hyphae ().

(iv) C4BP.

The complement protein regulator C4b binding protein (C4BP) is able to bind to both yeast and hyphal forms of C. albicans and is predominantly localized at the tip of the germ tube on hyphae (). This binding is normally regarded as a survival mechanism that inhibits complement activation and the attachment of opsonins to the microbial surface. However, it may also enhance the adhesion of yeast forms of C. albicans to endothelial cells. It is not clear if this enhancement of adhesion by the C4BP coating occurs by activating other Candidaadhesins or by acting as a bridge.

Cell wall carbohydrate adhesin candidates.

The outer cell wall proteins of Candida are heavily glycosylated with N- or O-linked mannosyl residues and have been found to be strongly involved in the recognition of C. albicans by the innate immune system. Indeed, some of these sugar residues provide conserved Candida-associated chemical signatures, known as pathogen-associated molecular patterns, by which the host is able to recognize the presence of the pathogen via host pattern recognition receptors (PRRs). In recent years, it has become apparent that specific host PRRs bind to and recognize specific mannosyl residues on C. albicans. For example, the mannose receptor (MR) recognizes and binds to N-linked mannosyl residues, while Toll-like receptor 4 (TLR-4) binds O-linked mannosyl residues. Similarly, TLR-2 recognizes and binds phospholipomannan, and galectin-3 binds β-mannosides. As these mannosyl residues are part of the structure of the cell wall, they are expressed on all three different morphological forms of C. albicans. However, there is evidence to suggest that there are differences in the recognition of yeast and hyphae by TLR-2 and TLR-4.

Although these PRRs are principally involved in the recognition of C. albicans by components of the host immune response, it is also possible that they are used by C. albicans to adhere to and transmigrate across the endothelial lining of blood vessels. Indeed, several studies have demonstrated the important role of the TLRs in experimental models of disseminated candidiasis. Netea et al. showed that TLR-4-defective C3H/HeJ mice have an increased susceptibility to disseminated candidiasis, and mice deficient in the universal TLR adaptor protein myeloid differentiation factor 88 (MyD88) are extremely susceptible to C. albicans infection. However, it has also been shown that TLR-4-deficient mice are more resistant to disseminated Candida infection. This is also the case for TLR-2-deficient mice, which have also been shown to be more resistant to disseminated candidiasis. However, the majority of the literature on knockout mice and disseminated candidiasis looks at susceptibility to infection and correlates it with the immune response without focusing on receptor expression on endothelial cells. To date, endothelial cells have been shown to express a number of PRRs, including the MR, TLRs, and galectins. The MR was the first receptor on the surfaces of macrophages to be described as a mannan receptor, and it recognizes oligosaccharides that terminate in mannose, fucose, and N-acetylglucosamine. It is also expressed on subtypes of dendritic cells and endothelial cells from certain vascular beds, including human dermal microvascular endothelial cells but not human umbilical vein endothelial cells. So far, 10 TLRs have been found, of which 7 or 8 are expressed on unstimulated endothelial cells. However, upon stimulation with proinflammatory cytokines, all 10 TLRs are expressed. Perhaps most importantly for interactions with C. albicans, endothelial cells express TLR-2 and TLR-4. TLR-4 is expressed constitutively at a higher level than that of TLR-2 by endothelial cells. However, the expression of both is significantly upregulated by stimulation with gamma interferon or bacterial lipopolysaccharide. It is also notable that the expression of TLR-2 on endothelial cells is strongly affected by the effects of flow on the endothelial cells. The galectins are a family of 15 carbohydrate binding proteins with high affinities for β-galactosides, extracellular glycoproteins, and glycolipids. So far, expression of galectin-1, -3, and -9 has been found on cultured endothelial cells, but only galectin-3 has been found to recognize C. albicans. Other PRRs that have been found to be involved in the recognition of C. albicans include DC-SIGN, αMβ2, FcγR, and dectin-1, but so far these receptors have not been found to be expressed on endothelial cells.

With so many different cell wall components having the potential to mediate adhesion of C. albicans to the endothelium, it seems that there could be a number of different mechanisms of adhesion. This may have consequences for the development of therapies aimed at blocking adhesion, because with so many molecules potentially playing a role, blocking only one could simply result in its role being taken up by other molecules. However, to investigate this further, more research is needed on the molecules involved in adhesion of C. albicans to the endothelial lining of blood vessels.

STATIC VERSUS FLOW ADHESION ASSAYS

The majority of the above studies that have directly explored candidal adhesion to endothelium were performed by using static in vitro assays where C. albicans was left in prolonged contact with cultured monolayers of endothelial cells. This is very different from the fleeting interactions C. albicans has with endothelial cells under the conditions of shear stress and flow that occur in blood vessels in vivo. Numerous studies with other cells and microorganisms have shown that static assays do not replicate the dynamic interactions that occur with endothelium under conditions of flow and are poor at elucidating the contributions of specific adhesion molecules. Only a few studies have attempted to study candidal adhesion to synthetic substrata under conditions of flow. These have shown that there are significant differences in the adhesion of Candida to the same substrata when the assays are performed under static and flow conditions. To date, only one study has attempted to examine the adhesion of Candida to endothelium under conditions of flow. Glee et al. found that under shear flow, C. albicans formed rapid, tight adhesions in less than 67 ms. This is much quicker than in static assays and is comparable to the rapid adhesion interactions that occur between leukocytes and endothelial cells. In view of this, it is difficult to fully evaluate the contributions of the mechanisms and adhesion molecules discussed above to the adhesion of C. albicans to endothelium in vivo, as none have been studied under conditions of flow.

TRANSMIGRATION

After adhesion of C. albicans to the endothelial lining of blood vessels, the second step in the migration of C. albicans from the circulation into the tissues is transmigration across the endothelial barrier. This step may involve some of the same molecules used for adhesion but could involve others. Transmigration is hard to research in isolation, which explains why there is little information on specific methods of Candida-endothelial cell transmigration. Even so, there are several proposed mechanisms for Candida transmigration across the endothelium. The first mechanism proposes that endothelial cells endocytose adherent organisms and allow their passage through to the abluminal surface of the endothelial cell layer. It is this mechanism that has gained the most interest and for which a model has evolved to explain how candidal hyphae adhere to and then induce endothelial cells to endocytose them. In this model, C. albicanshyphae bind to N-cadherin and other, as yet unidentified proteins on the endothelial cell surface via the candidal protein Als3. This adhesive interaction induces tyrosine phosphorylation of unidentified intracellular endothelial cell proteins, causing microfilament rearrangement to produce pseudopods, which initiate the endocytosis of adherent hyphal forms of C. albicans. However, endothelial endocytosis of C. albicans is not restricted to hyphal forms, and strains that do not undergo hyphal change and cause little endothelial cell damage are endocytosed to a significant degree. Since the Als3 protein is predominantly expressed on candidal hyphae, this could involve other adhesin-endothelial ligand pairs. There is also evidence that suggests that adherent yeast forms could penetrate endothelial cells, damaging them in the process, without undergoing morphogenetic change allowing them to cross the endothelial barrier. Another proposed mechanism of trans-endothelial cell migration of adherent C. albicans involves the extension of penetrating hyphal processes through the endothelial cells, likely destroying them in the process, much as fungal hyphae ramify through other tissues. Alternatively, a further proposal suggests that adherent C. albicans cells may pass between adjacent endothelial cells as a result of translocation and cyclical switching of adhesion molecules at the junction between endothelial cells, in a manner similar to that of leukocyte and tumor cell trans-endothelial cell migration.

Two alternative methods of transmigration across the endothelium that may not require prior adhesion of C. albicans to the endothelial cell surface have also been proposed. The first mechanism proposes that organisms phagocytosed by leukocytes are transported across the endothelial barrier inside the leukocytes. It is well known that leukocytes are able to cross the endothelium, between adjacent endothelial cells, by diapedesis and cyclical switching of adhesion molecules. Furthermore, there is evidence of C. albicans being found inside circulating leukocytes in systemic candidiasis. However, it is unlikely that this represents the only mechanism for candidal transmigration, since neutropenia is a major risk factor for invasive disease. The second mechanism, which may or may not require prior adhesion, suggests that circulating Candida cells simply pass through endothelial fenestrations between adjacent endothelial cells in vascular beds such as the kidney.

Some of these mechanisms may operate only for the yeast, pseudohyphal, or hyphal form of C. albicans, some may work for all forms, and others may require morphogenetic change for transmigration to occur. As with C. albicans adhesion to endothelial cells, there is clearly much more research required in order to elucidate the precise mechanism by which C. albicans migrates across the endothelium and into the tissues. Additionally, as with leukocyte and tumor cell transmigration, the validity of these mechanisms may become apparent only when transmigration is studied in vivo or in situations where the endothelium is subject to conditions of flow.

CONCLUSION

In summary, the interaction of C. albicans with the endothelial lining of blood vessels and its invasion of the tissues involve a complex series of processes that is further complicated by the role played by the morphogenetic conversion of C. albicans. There is still a large amount of work required to clarify these processes. Furthermore, it is important that this work be performed under conditions that replicate the fleeting contacts of C. albicans with the endothelium and the dynamic conditions of flow that occur in vivo. Nonetheless, understanding these mechanisms may be critical in identifying a means for preventing Candida invasion of the tissues and its lethal sequelae in systemic candidiasis.

Statin Therapy and Decreased Incidence of Positive Candida Cultures Among Patients With Type 2 Diabetes Mellitus Undergoing Gastrointestinal Surgery

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OBJECTIVE

To assess whether statin therapy decreases the incidence of cultures positive for Candida species among high-risk hospitalized patients with type 2 diabetes mellitus (DM).

PATIENTS AND METHODS

We performed a retrospective cohort study analyzing the records of all patients with type 2 DM who were admitted to Massachusetts General Hospital for lower gastrointestinal tract surgery between January 1, 2001, and May 1, 2008. We defined statin exposure as the filling of at least 1 prescription of statins during the 6 months before hospitalization or during the current hospital stay. The primary outcome was a culture positive for Candida species during hospitalization. Clinical information on a wide range of covariates was collected. Logistic regression analysis was used to adjust for possible confounders.

RESULTS

Of the 1019 patients who were eligible for the study, 493 (48%) were receiving statins. A total of 139 patients (14%) had at least 1 culture positive for Candida species during hospitalization. An adjusted multivariate model based on a backward stepwise elimination procedure showed that statin therapy significantly decreased the incidence of cultures positive for Candida species (odds ratio, 0.60; 95% confidence interval [CI], 0.38-0.96; P=.03) with a statistically significant prolonged time to event compared with no statin therapy (adjusted hazard ratio, 0.62; 95% CI, 0.44-0.88; P=.01). The benefit of statins was more prominent in patients with type 2 DM who had greater comorbidities (Charlson Comorbidity Index ≥2) (adjusted odds ratio, 0.47; 95% CI, 0.27-0.79; P=.01).

CONCLUSION

Among patients with type 2 DM who underwent gastrointestinal surgery, use of statins correlated with a decreased incidence of cultures positive for Candida species.