Brain serotonin (5-HT) neuroendocrine function in patients taking cholesterol-lowering drugs

The pharmacological bases for repurposing statins in depression: a review of mechanistic studies

Statins are commonly prescribed medications widely investigated for their potential actions on the brain and mental health. Pre-clinical and clinical evidence suggests that statins may play a role in the treatment of depressive disorders, but only the latter has been systematically assessed. Thus, the physiopathological mechanisms underlying statins' putative antidepressant or depressogenic effects have not been established. This review aims to gather available evidence from mechanistic studies to strengthen the pharmacological basis for repurposing statins in depression. We used a broad, well-validated search strategy over three major databases (Pubmed/MEDLINE, Embase, PsychINFO) to retrieve any mechanistic study investigating statins' effects on depression. The systematic search yielded 8068 records, which were narrowed down to 77 relevant papers. The selected studies (some dealing with more than one bodily system) described several neuropsychopharmacological (44 studies), endocrine-metabolic (17 studies), cardiovascular (6 studies) and immunological (15 studies) mechanisms potentially contributing to the effects of statins on mood. Numerous articles highlighted the beneficial effect of statins on depression, particularly through positive actions on serotonergic neurotransmission, neurogenesis and neuroplasticity, hypothalamic-pituitary axis regulation and modulation of inflammation. The role of other mechanisms, especially the association between statins, lipid metabolism and worsening of depressive symptoms, appears more controversial. Overall, most mechanistic evidence supports an antidepressant activity for statins, likely mediated by a variety of intertwined processes involving several bodily systems. Further research in this area can benefit from measuring relevant biomarkers to inform the selection of patients most likely to respond to statins' antidepressant effects while also improving our understanding of the physiopathological basis of depression.

Revisiting the serotonin-aggression relation in humans: a meta-analysis

The inverse relation between serotonin and human aggression is often portrayed as "reliable," "strong," and "well established" despite decades of conflicting reports and widely recognized methodological limitations. In this systematic review and meta-analysis, we evaluate the evidence for and against the serotonin deficiency hypothesis of human aggression across 4 methods of assessing serotonin: (a) cerebrospinal fluid levels of 5-hydroxyindoleacetic acid (CSF 5-HIAA), (b) acute tryptophan depletion, (c) pharmacological challenge, and (d) endocrine challenge. Results across 175 independent samples and over 6,500 total participants were heterogeneous, but, in aggregate, revealed a small, inverse correlation between serotonin functioning and aggression, anger, and hostility (r = -.12). Pharmacological challenge studies had the largest mean weighted effect size (r = -.21), and CSF 5-HIAA studies had the smallest (r = -.06). Potential methodological and demographic moderators largely failed to account for variability in study outcomes. Notable exceptions included year of publication (effect sizes tended to diminish with time) and self- versus other-reported aggression (other-reported aggression was positively correlated to serotonin functioning). We discuss 4 possible explanations for the pattern of findings: unreliable measures, ambient correlational noise, an unidentified higher order interaction, and a selective serotonergic effect. Finally, we provide 4 recommendations for bringing much needed clarity to this important area of research: acknowledge contradictory findings and avoid selective reporting practices; focus on improving the reliability and validity of serotonin and aggression measures; test for interactions involving personality and/or environmental moderators; and revise the serotonin deficiency hypothesis to account for serotonin's functional complexity.

Lovastatin potentiates the antidepressant efficacy of fluoxetine in rats

BACKGROUND

Cholesterol may have a role in the pathophysiology of depression. Lowering cholesterol levels with statins reduces risks for cardiovascular events, and there is clinical evidence that statins exert neuroprotective properties not fully explained by their effects on serum cholesterol levels. Altered cholesterol levels can affect serotonergic neurotransmission, which might be involved in the clinical efficacy of standard antidepressants.

METHODS

We examined interactions between a statin (lovastatin) and a selective serotonin reuptake inhibitor (fluoxetine) using the forced swim test (FST) in rats, a behavioral assay that identifies treatments with antidepressant effects in humans. Specifically, we determined if the addition of lovastatin to the diet would increase the efficacy of a subeffective dose of fluoxetine.

RESULTS

Rats maintained on a lovastatin-enriched diet for 30 days were more sensitive to the antidepressant-like effects of a low (subthreshold) dose of fluoxetine. The behavior of rats treated with this combination resembled that normally seen with higher doses of fluoxetine. No effects were observed in rats maintained on a lovastatin-enriched diet for 3 days.

CONCLUSIONS

Lovastatin can augment the antidepressant-like effects of a low dose of fluoxetine in rats, raising the possibility that statins could be used to facilitate the effects of antidepressants in humans.

Combined biological tests for suicide prediction

Disturbances in serotonin neuroregulation and in hypothalamic-pituitary-adrenal axis activity are both likely, and possibly independent, factors in the genesis of suicidal behavior. This analysis considers whether clinically accessible measures of these two disturbances have additive value in the estimation of risk for suicide. Seventy-four inpatients with RDC major or schizoaffective depressive disorders entered a prospective follow-up study from 1978-1981, underwent a dexamethasone suppression test (DST) and had fasting serum cholesterol levels available in the medical record. As reported earlier, patients who had had an abnormal DST result were significantly more likely to commit suicide during follow-up. Serum cholesterol concentrations did not differ by DST result and low cholesterol values were associated with subsequent suicide when age was included as a covariate. These results indicate that, with the use of age-appropriate thresholds, serum cholesterol concentrations may be combined with DST results to provide a clinically useful estimate of suicide risk.

Clinical assessment of suicide risk in depressive disorder

Efforts to identify clinical risk factors for complete suicide through the follow-up of depressed patients have yielded relatively few robust predictors. Those identified by at least three studies are (in order of decreasing frequency) suicidal plans/attempts, male sex, being single or living alone, inpatient status, and hopelessness. Because the best established of these predictors has only modest sensitivity and specificity, the need for other robust tools is clear. A rich body of research has identified two biological risk factors for suicide in depressive disorder: hypothalamic-pituitary-adrenal axis hyperactivity and deficits in serotonin function. Moreover, there is now considerable evidence that the dexamethasone suppression test and measures of serum cholesterol concentrations, respectively, may provide a clinically useful reflection of these two mechanisms. Observations that these measures appear to be additive, both with each other and with other clinical risk factors, indicate that a substantial improvement in the clinician's ability to assess suicide risk is possible.

Cholesterol-lowering therapy evokes time-limited changes in serotonergic transmission

A number of studies have reported an increased risk for violent deaths and depression in subjects with reduced serum cholesterol concentrations. Links with hypothesized impairment of serotonin neurotransmission have not been satisfactorily tested. In this investigation, the serum and membrane cholesterol, microviscosity of erythrocyte membranes, platelet serotonin uptake, and clinical parameters were determined during pharmacotherapy of 17 hypercholesterolemic patients. A significant decrease in serum cholesterol and a nonsignificant decrease in membrane cholesterol concentration were found after 2 months of simvastatin therapy. Serotonin transporter (SERT) activity was significantly increased following 1 month of simvastatin; the tendency to decrease the initial increase in SERT activity was evident following 2 months of therapy. Both membrane cholesterol and SERT activity returned to pre-treatment levels after more than 1 year of therapy. Microviscosity of plasma membranes, impulsivity, empathy, adventure, sensation seeking, and depressed mood were not markedly changed. These data indicate that long-term therapy has different effects on serotonin transmission from short-term (1- to 2-month) therapy. A significant increase in SERT activity was detected only during the first month of simvastatin therapy. This finding suggests that within this period some patients could be vulnerable to depression, violence, or suicide.

Conceptual foundations of the UCSD Statin Study: a randomized controlled trial assessing the impact of statins on cognition, behavior, and biochemistry

BACKGROUND

Statin cholesterol-lowering drugs are among the most prescribed drugs in the United States. Their cardiac benefits are substantial and well supported. However, there has been persistent controversy regarding possible favorable or adverse effects of statins or of cholesterol reduction on cognition, mood, and behavior (including aggressive or violent behavior).

METHODS

The literature pertaining to the relationship of cholesterol or statins to several noncardiac domains was reviewed, including the link between statins (or cholesterol) and cognition, aggression, and serotonin.

RESULTS

There are reasons to think both favorable and adverse effects of statins and low cholesterol on cognition may pertain; the balance of these factors requires further elucidation. A substantial body of literature links low cholesterol level to aggressive behavior; statin randomized trials have not supported a connection, but they have not been designed to address this issue. A limited number of reports suggest a connection between reduced cholesterol level and reduced serotonin level, but more information is needed with serotonin measures that are practical for clinical use. Whether lipophilic and hydrophilic statins differ in their impact should be assessed.

CONCLUSION

There is a strong need for randomized controlled trial data to more clearly establish the impact of hydrophilic and lipophilic statins on cognition, aggression, and serotonin, as well as on other measures relevant to risks and quality-of-life impact in noncardiac domains.

No evidence for an association between serum cholesterol and the course of depression and suicidality

In a number of previous reports, an association of altered, in most cases lower, serum cholesterol levels with depression, suicidal ideation and current or past suicidal behavior has been suggested. In this investigation, the course of serum cholesterol concentrations was measured in depressed patients during treatment. Ninety-two inpatients with a major depressive episode were included. Serum lipid concentrations were assessed at admission, after 1 week and after 4 weeks of antidepressant treatment. Degrees of depression and suicidality were measured with the Hamilton Depression Rating Scale. Although there was a significant reduction in depression and suicidality scores, neither a significant change in serum cholesterol levels nor a correlation between cholesterol levels and clinical improvement was found. Further, there were no significant differences in lipid levels between patients with and without a history of attempted suicide. In patients who had used a violent method, there was a trend for lower total cholesterol levels compared to those who had poisoned themselves. The results of this study do not support the hypothesis of an association of serum cholesterol with the course of depression and suicidal ideation. Cholesterol levels do not appear to be an appropriate biological marker for suicidality during the first 4 weeks of treatment in patients with a major depressive episode.

Chronic administration of the cholesterol reducing drug gemfibrozil fails to alter 5-HT1A and 5-HT2A mediated receptor behaviours in rats

Some studies have suggested that reductions in plasma cholesterol might be associated with suicidal behaviour. Serotonergic systems are thought to be involved in suicidal ideation and behaviour and links with altered 5-HT1A and 5-HT2A receptors have been proposed. We have therefore examined the effects of cholesterol reduction using gemfibrozil, upon 5-HT2A and 5-HT1A receptor-related behaviours in rats. Rats were treated chronically (57 days) with gemfibrozil (50 mg/kg p.o.) or gum acacia vehicle and challenged sequentially with the 5-HT1A agonist 8-hydroxy-d-n-aminopropyl tetralin, to elicit 5-HT1A syndrome behaviours, and the 5-HT2 receptor agonist 1-(2,5-dimethoxy-4-iodophenyl)2-amino-propane to establish their head-shake frequency. Significant cholesterol reduction, within the clinical range, failed to induce any changes in either 5-HT1A or 5-HT2A mediated behaviours. These data suggest that cholesterol reduction fails to induce changes in 5-HT1A and 5-HT2A receptor tone suggesting that the reduction of plasma cholesterol, within the human clinical range, does not result in neuroplasticity of the 5-HT1A and 5-HT2A receptors in rats.

Total serum cholesterol in relation to psychological correlates in parasuicide

BACKGROUND

Low cholesterol may act as a peripheral marker for parasuicide.

AIMS

To examine the relationship between total serum cholesterol and psychological parameters in parasuicide.

METHOD

Total serum cholesterol and self-rated scores for impulsivity, depression and suicidal intent were measured in 100 consecutive patients following parasuicide, pair-matched with normal and psychiatric control groups.

RESULTS

Backward, stepwise multiple regression analysis revealed a significantly lower mean cholesterol in the parasuicide population (P < 0.01). Across all groups there was an independent significant (P < 0.01) negative correlation between cholesterol and self-reported scores of impulsivity. No correlation existed between cholesterol and scores for depression or suicidal intent.

CONCLUSIONS

The data confirm previous reports of low cholesterol in parasuicide. This is the first reported investigation of the construct of impulsivity in relation to cholesterol. We hypothesise that the reported increased mortality in populations with low cholesterol may derive from increased suicide and accident rates consequent on increased tendencies to impulsivity in these populations.

Differences between morning and afternoon hormonal responses to D-fenfluramine in healthy humans

The prolactin (PRL) and cortisol responses to oral D-fenfluramine (30 mg) and placebo were measured in seven healthy subjects (two women and five men) in the morning and in the afternoon. As compared to placebo, D-fenfluramine significantly increased plasma PRL levels in both the morning and the afternoon, with no significant circadian difference. On the contrary, D-fenfluramine significantly enhanced plasma cortisol levels in the afternoon, but not in the morning. These data suggest that the time of the day at which the D-fenfluramine challenge test is carried out may be an important variable in determining the glucocorticoid response to the 5-HT releasing agent in humans.