Imipramine effect on hypothalamic-pituitary-adrenal axis response to hypoglycemia

Imipramine activates FAM3A-FOXA2-CPT2 pathway to ameliorate hepatic steatosis

Mitochondrial FAM3A has been revealed to be a viable target for treating diabetes and nonalcoholic fatty liver disease (NAFLD). However, its distinct mechanism in ameliorating hepatic steatosis remained unrevealed. High-throughput RNA sequencing revealed that carnitine palmityl transferase 2 (CPT2), one of the key enzymes for lipid oxidation, is the downstream molecule of FAM3A signaling pathway in hepatocytes. Intensive study demonstrated that FAM3A-induced ATP release activated P2 receptor to promote the translocation of calmodulin (CaM) from cytoplasm into nucleus, where it functioned as a co-activator of forkhead box protein A2 (FOXA2) to promote the transcription of CPT2, increasing free fatty acid oxidation and reducing lipid deposition in hepatocytes. Furthermore, antidepressant imipramine activated FAM3A-ATP-P2 receptor-CaM-FOXA2-CPT2 pathway to reduce lipid deposition in hepatocytes. In FAM3A-deficient hepatocytes, imipramine failed to activate CaM-FOXA2-CPT2 axis to increase lipid oxidation. Imipramine administration significantly ameliorated hepatic steatosis, hyperglycemia and obesity of obese mice mainly by activating FAM3A-ATP-CaM-FOXA2-CPT2 pathway in liver and thermogenesis in brown adipose tissue (BAT). In FAM3A-deficient mice fed on high-fat-diet, imipramine treatment failed to correct the dysregulated lipid and glucose metabolism, and activate thermogenesis in BAT. In conclusion, imipramine activates FAM3A-ATP-CaM-FOXA2-CPT2 pathway to ameliorate steatosis. For depressive patients complicated with metabolic disorders, imipramine may be recommended in priority as antidepressive drug.

The effect of antidepressants on glucose homeostasis and insulin sensitivity: synthesis and mechanisms

OBJECTIVE

To synthesise results from investigations reporting on the effect of antidepressants on glucose-insulin homeostasis.

METHOD

The authors conducted a MedLine search of all English language articles from 1966 to October 2005 using the keywords: bipolar disorder, major depressive disorder, diabetes mellitus, glucose homeostasis, and the name of each antidepressant that has been indicated for major depression in Canada and the US up to October 2005. The search was supplemented with a manual review of relevant references. Both preclinical and clinical investigations were reviewed.

RESULTS

Some serotonergic antidepressants (e.g., fluoxetine) reduce hyperglycaemia, normalise glucose homeostasis and increase insulin sensitivity, whereas some noradrenergic antidepressants (e.g., desipramine) exert opposite effects. Dual-mechanism antidepressants (e.g., duloxetine and venlafaxine) do not appear to disrupt glucose homeostatic dynamics, whereas nonselective hydrazine monoamine oxidase inhibitors (e.g., phenelzine) are associated with hypoglycaemia and an increased glucose disposal rate.

CONCLUSION

Some antidepressants exert a clinically significant effect on metabolism relevant to both therapeutic outcome and adverse events.

The inhibition of GLUT1 glucose transport and cytochalasin B binding activity by tricyclic antidepressants

Under normal metabolic conditions glucose is an important energy source for the mammalian brain. Positron Emission Tomography studies of the central nervous system have demonstrated that tricyclic antidepressant medications alter cerebral metabolic function. The mode by which these drugs perturb metabolism is unknown. In the present study the interactions of tricyclic antidepressants with the GLUT1 glucose transport protein is examined. Amitriptyline, nortriptyline, desipramine, and imipramine all inhibit the influx of 3-O-methyl glucose into resealed erythrocytes. This inhibition is observed with drug concentrations in the millimolar range. All four antidepressants also noncompetitively displace cytochalasin B binding to GLUT1. The K(I) for this displacement ranges from 0.56 to 1.43 millimolar. This value is in a range greater than that associated with clinical doses and this effect may not be directly applicable to side effects observed with normal use. The observed interaction of these drugs with GLUT1 may reflect an affinity for other glucose-transport or glucose-binding proteins, and may possibly contribute to tricyclic antidepressant toxicity.

Enhanced neuroendocrine response to insulin tolerance test performed under increased ambient temperature

The hypothesis that an increase in ambient temperature modulates neuroendocrine response in clinically used provocative pituitary function tests was verified. Healthy male volunteers were subjected to insulin tolerance tests in two randomized trials. In the first trial hypoglycemia was induced by a bolus injection of insulin (0.1 U per kg of BW, i.v.) at room temperature. In the second trial, the subjects were exposed to increased ambient temperature for 45 min before insulin injection and for 45 min thereafter. The environmental temperature was selected to increase body temperature less than 1C. Under conditions of increased temperature basal hormone levels as measured in antecubital venous blood samples failed to be modified and the hypoglycemia was less severe. Nevertheless, the responses of most (beta-endorphin, ACTH, prolactin, catecholamines), but not all (growth hormone, cortisol), hormones to hypoglycemia were exaggerated. The remarkable increase in ACTH and beta-endorphin release was not accompanied by concomitant increase of plasma cortisol response. The sympathetic-adrenomedullary system was significantly activated, which was manifested particularly by enhanced norepinephrine release. Growth hormone response to hypoglycemia was not modified, while that of prolactin was enhanced. Thus during evaluation of neuroendocrine function under clinical conditions, changes in ambient and body temperature should not be underestimated.

Effects of nortriptyline on depression and glycemic control in diabetes: results of a double-blind, placebo-controlled trial

OBJECTIVE

Depression is a prevalent and chronic condition in diabetes and is associated with poor glucose regulation and poor compliance with diabetes treatment. This investigation evaluated the effects of nortriptyline on depression and glycemic control to see whether depression in diabetes is treatable and whether restoring mental health contributes to improved medical outcome.

METHOD

Sixty-eight diabetic patients with poor glycemic control, 28 of whom had active major depression (DSM-IIIR), completed a randomized, placebo-controlled, double-blind trial involving 8 weeks of treatment with nortriptyline targeted to therapeutic plasma levels (50-150 ng/ml). Depression improvement was determined with the Beck Depression Inventory; glucose control was measured by glycated hemoglobin levels. Compliance behavior was assessed using medication dispensing devices and glucometers equipped with electronic memory.

RESULTS

The reduction in depression symptoms was significantly greater in depressed patients treated with nortriptyline compared with those receiving placebo (-10.2 vs -5.8, p = .03). Nortriptyline was not statistically superior to placebo in reducing glycated hemoglobin of the depressed subjects (p = .5). However, path analysis indicated that the direct effect of nortriptyline was to worsen glycemic control whereas depression improvement had an independent beneficial effect on glycated hemoglobin. These findings were not explained by the relationships of nortriptyline treatment to weight change (r = -0.21, p = .31) or depression improvement to compliance with the protocol for self-monitoring of blood glucose (r = 0.01, p = .97).

CONCLUSIONS

Major depression in diabetic patients can be effectively treated with nortriptyline at the expense of a direct hyperglycemic effect. Path analysis demonstrated a treatment-independent effect of depression improvement on glycemic control, suggesting that a more ideal antidepressant agent may both restore mental health and improve medical outcome.

Physiopharmacological interactions between stress hormones and central serotonergic systems

The present review tries to delineate some mechanisms through which the sympathetic nervous system (SNS) and the hypothalamo-pituitary-adrenal (HPA) interact with central serotonergic systems. The recent progress in 5-hydroxytryptamine (5-HT) receptor pharmacology has helped to define the means by which central serotonergic activity may alter the respective activities of the SNS (sympathetic nerves and adrenomedulla) and of the HPA axis. These pharmacological findings have also helped to characterize the differential effects of central 5-HT upon different branches of the SNS and the numerous sites at which 5-HT exerts stimulatory influences upon the HPA axis. Although relevant to stress-related neuroendocrinology, the extent to which these interactions are involved in the antidepressant/anxiolytic properties of some serotonergic agents still remains to be clarified. Beside these findings, there is also abundant evidence for a tight control of central serotonergic systems by stress hormones. Activation of the SNS increases, by numerous means, central availability of tryptophan, whereas glucocorticoids exert differential actions upon the intra- and the extraneuronal regulation of 5-HT function. Actually, a significant number of these mechanisms is involved in the maintenance of homeostasis during stressful events, thereby conferring to these mechanisms a key role in adaptation processes.