Bromocriptine alters hormone rhythms and lipid metabolism in swine

Current Views on Dopaminergic Drugs Affecting Glucose Homeostasis

BACKGROUND

For more than three decades, it has been known that manipulation of dopaminergic system could affect glucose homesotasis in experimental animals. The notion that glucose homeostasis in human might be influenced by dopaminergic drugs has attracted a great deal of attention in the past two decades. In spite of rapid advancements in revealing involvement of dopaminergic neurotransmission in insulin release, glucose up-take and pancreatic beta cell function in general through centrally and peripherally controlled mechanisms, there are discrepancies among observations on experimental animals and human subjects.

CONCLUSION

With the expansion of pharmacotherapy in psychotic conditions, depression and endocrine abnormalities along with a sharp increase in prevalence of type two diabetes and disturbances of glucose homeostasis as a major risk factor for many cardiovascular complications and associated mortalities; it seems a critical analysis of recent investigations on drugs which act as agonists or antagonists of dopaminergic receptors in various tissues and organs may provide better insight into how safe and efficient these medicines could be prescribed. Furthermore, the other main objective of present review is to compare clinical data on significance of changes in blood glucose and insulin levels during short term and after long term treatment with these agents. This in turn would be beneficial for determining adequate strategies to combat or to avoid adverse effects associated with dopaminergic drug therapy.

Effects of cabergoline on blood glucose levels in type 2 diabetic patients: A double-blind controlled clinical trial

BACKGROUND

Cabergoline is a long-acting agonist of dopamine, which has a high affinity to dopamine receptors (type 2). Treatment using a dopaminergic agonist reduces hypothalamic stimulation that increases during liver gluconeogenesis, lipids synthesis, and insulin resistance. Our aim was to evaluate the effects of cabergoline on blood glucose levels in patients with type 2 diabetes mellitus (DM).

METHODS

This study was a double-blind, controlled clinical trial in patients with type 2 DM. The patients received treatments of a placebo (control group; n = 20) or cabergoline 0.5 mg (cabergoline group; n = 20) using the sequential method, once per week for 3 months, while using previously prescribed glucose-lowering drugs. All tests, such as levels of fasting blood glucose, 2-hour post-prandial glucose, complete lipid profile, prolactin, alanine amino transferase, aspartate amino transferase, creatinine, blood urea nitrogen, and serum insulin, and homeostasis model assessment insulin resistance were measured at baseline and at 3-month follow-up.

RESULTS

The fasting blood sugar levels were significantly different between placebo and cabergoline groups after 3 months of treatment (P = 0.004). The prolactin levels were significantly different from beginning of the treatment to 6 months later (P = 0.001). In the cabergoline group, there was a significant decrease in glycosylated hemoglobin (HbA1C) levels after 3 months (P = 0.003). Overall, 65%and 45% patients in the cabergoline and control groups, respectively, responded to treatment (HbA1C<7%).

CONCLUSION

Cabergoline may be useful as a long-acting antidiabetic agent in patients with type 2 diabetes mellitus.

Bromocriptine-QR therapy for the management of type 2 diabetes mellitus: developmental basis and therapeutic profile summary

An extended series of studies indicate that endogenous phase shifts in circadian neuronal input signaling to the biological clock system centered within the hypothalamic suprachiasmatic nucleus (SCN) facilitates shifts in metabolic status. In particular, a diminution of the circadian peak in dopaminergic input to the peri-SCN facilitates the onset of fattening, insulin resistance and glucose intolerance while reversal of low circadian peak dopaminergic activity to the peri-SCN via direct timed dopamine administration to this area normalizes the obese, insulin resistant, glucose intolerant state in high fat fed animals. Systemic circadian-timed daily administration of a potent dopamine D2 receptor agonist, bromocriptine, to increase diminished circadian peak dopaminergic hypothalamic activity across a wide variety of animal models of metabolic syndrome and type 2 diabetes mellitus (T2DM) results in improvements in the obese, insulin resistant, glucose intolerant condition by improving hypothalamic fuel sensing and reducing insulin resistance, elevated sympathetic tone, and leptin resistance. A circadian-timed (within 2 hours of waking in the morning) once daily administration of a quick release formulation of bromocriptine (bromocriptine-QR) has been approved for the treatment of T2DM by the U.S. Food and Drug Administration. Clinical studies with such bromocriptine-QR therapy (1.6 to 4.8 mg/day) indicate that it improves glycemic control by reducing postprandial glucose levels without raising plasma insulin. Across studies of various T2DM populations, bromocriptine-QR has been demonstrated to reduce HbA1c by -0.5 to -1.7. The drug has a good safety profile with transient mild to moderate nausea, headache and dizziness as the most frequent adverse events noted with the medication. In a large randomized clinical study of T2DM subjects, bromocriptine-QR exposure was associated with a 42% hazard ratio reduction of a pre-specified adverse cardiovascular endpoint including myocardial infarction, stroke, hospitalization for congestive heart failure, revascularization surgery, or unstable angina. Bromocriptine-QR represents a novel method of treating T2DM that may have benefits for cardiovascular disease as well.

Therapeutic interventions to reduce the risk of progression from prediabetes to type 2 diabetes mellitus

Clinical trials have demonstrated that it is possible to prevent diabetes through lifestyle modification, pharmacological intervention, and surgery. This review aims to summarize the effectiveness of these various therapeutic interventions in reducing the risk of progression of prediabetes to diabetes, and address the challenges to implement a diabetes prevention program at a community level. Strategies focusing on intensive lifestyle changes are not only efficient but cost-effective and/or cost-saving. Indeed, lifestyle intervention in people at high risk for type 2 diabetes mellitus (T2DM) has been successful in achieving sustained behavioral changes and a reduction in diabetes incidence even after the counseling is stopped. Although prediabetes is associated with health and economic burdens, it has not been adequately addressed by interventions or regulatory agencies in terms of prevention or disease management. Lifestyle intervention strategies to prevent T2DM should be distinct for different populations around the globe and should emphasize sex, age, ethnicity, and cultural and geographical considerations to be feasible and to promote better compliance. The translation of diabetes prevention research at a population level, especially finding the most effective methods of preventing T2DM in various societies and cultural settings remains challenging, but must be accomplished to stop this worldwide epidemic.

Bromocriptine: old drug, new formulation and new indication

Bromocriptine is an ergot alkaloid dopamine D(2) receptor agonist that has been used extensively in the past to treat hyperprolactinaemia, galactorrhoea and Parkinsonism. It is known that hypothalamic hypodopaminergic states and disturbed circadian rhythm are associated with the development of insulin resistance, obesity and diabetes in animals and humans. When administered in the early morning at the start of the light phase, a new quick release (QR) formulation of bromocriptine appears to act centrally to reset circadian rhythms of hypothalamic dopamine and serotonin and improve insulin resistance and other metabolic abnormalities. Phase II and III clinical studies show that QR-bromocriptine lowers glycated haemoglobin by 0.6-1.2% (7-13 mmol/mol) either as monotherapy or in combination with other antidiabetes medications. Apart from nausea, the drug is well tolerated. The doses used to treat diabetes (up to 4.8 mg daily) are much lower than those used to treat Parkinson's disease and have not been associated with retroperitoneal fibrosis or heart valve abnormalities. QR-bromocriptine (Cycloset™) has recently been approved in the USA for the treatment of type 2 diabetes mellitus (T2DM). Thus, a QR formulation of bromocriptine timed for peak delivery in the early morning may provide a novel neurally mediated approach to the control of hyperglycaemia in T2DM.

Bromocriptine approved as the first medication to target dopamine activity to improve glycemic control in patients with type 2 diabetes

Type 2 diabetes mellitus (T2DM) continues to rise in prevalence in the United States and worldwide. Despite advances in medical treatments for T2DM, many patients remain uncontrolled. By targeting centrally mediated pathways of glucose metabolism, bromocriptine represents a novel therapeutic option in T2DM. Several small clinical trials demonstrate improvements in insulin resistance and glycemic control. After the submission of data from four recent, large clinical trials, the US Food and Drug Administration has approved the use of bromocriptine in T2DM. We review the available data from these four trials and other published studies. Bromocriptine is a promising therapy for diabetes patients and demonstrates modest improvements in glycemic control.

A randomized, double-blind, placebo-controlled trial to assess safety and tolerability during treatment of type 2 diabetes with usual diabetes therapy and either Cycloset or placebo

BACKGROUND

Cycloset is a quick-release formulation of bromocriptine mesylate, a dopamine agonist, which in animal models of insulin resistance and type 2 diabetes acts centrally to reduce resistance to insulin- mediated suppression of hepatic glucose output and tissue glucose disposal. In such animals, bromocriptine also reduces hepatic triglyceride synthesis and free fatty acid mobilization, manifesting decreases in both plasma triglycerides and free fatty acids. In clinical trials, morning administration of Cycloset either as monotherapy or adjunctive therapy to sulfonylurea or insulin reduces HbA1c levels relative to placebo by 0.55-1.2. Cycloset therapy also reduces plasma triglycerides and free fatty acid by approximately 25% and 20%, respectively, among those also receiving sulfonylurea therapies. The effects of once-daily morning Cycloset therapy on glycemic control and plasma lipids are demonstrable throughout the diurnal portion of the day (7 a.m. to 7 p.m.) across postprandial time points.

METHODS/DESIGN

3,095 individuals were randomized in a 2:1 ratio into a one year trial aimed to assess the safety and efficacy of Cycloset compared to placebo among individuals receiving a variety of treatments for type 2 diabetes. Eligibility criteria for this randomized placebo controlled trial included: age 30-80, HbA1c <or= 10%, diabetes therapeutic regimen consisting of diet or no more than two hypoglycemic agents or insulin with or without one additional oral agent (usual diabetes therapy; UDT). The primary safety endpoint will test the hypothesis that the rate of all-cause serious adverse events after one year of usual diabetes therapy (UDT) plus Cycloset is not greater than that for UDT plus placebo by more than an acceptable margin defined as a hazard ratio of 1.5 with a secondary endpoint analysis of the difference in the rate of serious cardiovascular events, (myocardial infarction, stroke, coronary revascularization or hospitalization for or angina or congestive heart failure). Efficacy analyses will evaluate effects of Cycloset versus placebo on change from baseline in HbA1c, fasting glucose, body weight, waist circumference, blood pressure and plasma lipids.

DISCUSSION

This study will extend the current data on Cycloset safety, tolerability and efficacy in individuals with type 2 diabetes to include its effects in combination with thiazolodinediones, insulin secretagogues, metformin, alpha-glucosidase inhibitors and exogenous insulin regimens.

TRIAL REGISTRATION

clinical trials.gov NCT00377676.

Association of the antidiabetic effects of bromocriptine with a shift in the daily rhythm of monoamine metabolism within the suprachiasmatic nuclei of the Syrian hamster

Bromocriptine, a dopamine D2 agonist, inhibits seasonal fattening and improves seasonal insulin resistance in Syrian hamsters. Alterations in daily rhythms of neuroendocrine activities are involved in the regulation of seasonal metabolic changes. Changes in circadian neuroendocrine activities that regulate metabolism are believed to be modulated by central circadian oscillators within the hypothalamic suprachiasmatic nuclei (SCN) of seasonal animals. We examined the association of metabolic responses to bromocriptine with its effects on the daily rhythms of metabolic hormones and daily monoamine profiles within the SCN, a primary circadian pacemaker known to regulate metabolism, in Syrian hamsters. Obese glucose-intolerant male Syrian hamsters (body weight [BW] 185 +/- 10 g) held on 14h daily photoperiods were treated at light onset with bromocriptine (800 microg/animal/day, ip) or vehicle for 2 weeks. Animals were then subjected to a glucose tolerance test (GTT) (3 g/kg BW, ip). Different subsets of animals (n = 6) from each treatment group were sacrificed at 0h/24h, 5h, 10h, 15h, or 20h after light onset for analyses of SCN monoamines, plasma insulin, prolactin, cortisol, thyroxin (T4), triiodothyronine (T3), glucose, and free fatty acids (FFAs). Compared with control values, bromocriptine treatment significantly reduced weight gain (14.9 vs. -2.9 g, p < .01) and the areas under the GTT glucose and insulin curves by 29% and 48%, respectively (p < .05). Basal plasma insulin concentration was markedly reduced throughout the day in bromocriptine-treated animals without influencing plasma glucose levels. Bromocriptine reduced the daily peak in FFA by 26% during the late light span (p < .05). Bromocriptine significantly shifted the daily plasma cortisol peak from the early dark to the light period of the day, reduced the plasma prolactin (mean 1.8 vs. 39.4 ng/dL) and T4 throughout the day (mean 1.6 vs. 3.8 microg/dL), and selectively reduced T3 during the dark period of the day (p < .01). Concurrently, bromocriptine treatment significantly reduced SCN dopamine turnover during the light period and shifted daily peaks of SCN serotonin and 5-hydroxy-indoleacetic acid (5-HIAA) content by 12h from the light to the dark period of the day (p < .05). This was confirmed by a further in vivo microdialysis study in which bromocriptine increased SCN extracellular 5-HIAA of glucose-intolerant hamsters during the dark phase (47% increase, p < .05) toward levels observed in normal glucose-tolerant hamsters. Thus, bromocriptine-induced resetting of daily patterns of SCN neurotransmitter metabolism is associated with the effects of bromocriptine on attenuation of the obese insulin-resistant and glucose-intolerant condition. A large body of corroborating evidence suggests that such bromocriptine-induced changes in SCN monoamine metabolism may be functional in its effects on metabolism.

Bromocriptine/SKF38393 treatment ameliorates obesity and associated metabolic dysfunctions in obese (ob/ob) mice

It has been postulated that dopaminergic activities comprise a major functional component of a central regulatory system for metabolism which can be manipulated by dopamine modulating drugs. The present study is aimed at delineating the role and importance of pharmacological dopaminergic activation in the regulation of metabolism during obesity and diabetes. We treated C57BL/6J ob/ob mice for 2 weeks with bromocriptine (dopamine D2 agonist), SKF38393 (dopamine D1 agonist), both drugs combined or vehicle and monitored the effects of such treatment on body composition, food consumption, and serum metabolites. Bromocriptine and SKF38393 individually produced moderate improvements in obesity, hyperglycemia, and hyperinsulinemia. However, a combination of bromocriptine plus SKF38393 resulted in major reductions in body weight (7.5 g), body fat (40%), food consumption (42%), and serum concentrations of glucose (59%), triglyceride (37%), free fatty acid (45%) and insulin (49%) while increasing protein mass (8%). These results indicate that regulatory components of metabolism in the ob/ob mouse are modulated by and/or are comprised of dopaminergic activities. Importantly, dopaminergic D1/D2 receptor coactivation maximizes this dopaminergic response (i.e., improvement of metabolic abnormalities) in these mice.

Bromocriptine redirects metabolism and prevents seasonal onset of obese hyperinsulinemic state in Syrian hamsters

Bromocriptine redirects metabolism and prevents seasonal onset of the obese hyperinsulinemic state in Syrian hamsters. Metabolic and hormonal effects of bromocriptine were studied in seasonally obese female Syrian hamsters, Mesocricetus auratus. Daily injections of bromocriptine and vehicle (controls) were made at light onset (10:14-h light-dark cycle) for 10 wk. After 9 wk of treatment blood samples were taken every 4 h during a day for assays of hormones, glucose, triglyceride, and fatty acids, and after 10 wk of treatment, tests were carried out to measure insulin-stimulated glucose disposal during a hyperinsulinemic clamp, lipid mobilization (rate of glycerol appearance), protein turnover (lysine flux and deamination), and body composition (deuterium dilution). Bromocriptine reduced percent body fat by 53% and increased percent lean body mass by 8%. It also decreased triglyceride levels by 52% and plasma free fatty acid concentration during the dark-near light onset by 49% and glycerol appearance by 25%. Protein synthesis and catabolism were increased by 62 and 56%, respectively, and deamination of amino acid was decreased by 53% by bromocriptine. Bromocriptine reduced plasma concentration of insulin throughout the day, especially at light onset, by 78% without change in baseline glucose level and markedly decreased steady state plasma glucose (by 40%) during a continuous infusion of insulin and glucose. It also reduced the nocturnal plasma concentration of prolactin by 90%, cortisol by 70%, and thyroid hormones (thyroxine and triiodothyronine) by 50% and dramatically altered the circadian profiles of these hormones and insulin.(ABSTRACT TRUNCATED AT 250 WORDS)

Timed bromocriptine administration reduces body fat stores in obese subjects and hyperglycemia in type II diabetics

Obese postmenopausal female volunteers were given timed daily oral dosages of bromocriptine, and tested for reduction of body fat stores. This dopamine agonist has been shown to reset circadian rhythms that are altered in obese animals and to reduce body fat levels in several animal models. The participants were instructed not to alter their existing exercise and eating behavior during treatment. Skinfold measurements were taken on 33 subjects as indices of body fat. The measurements (e.g., suprailiac) were reduced after six weeks by about 25%, which represents a reduction of 11.7% of the total body fat. These dramatic decreases in body fat, which are equivalent to that produced by severe caloric restriction, were accompanied by more modest reductions of body weight (2.5%), indicating a possible conservation of protein that is usually lost as a consequence of such caloric restriction. The effects of bromocriptine treatment on body fat and hyperglycemia were also examined in non-insulin dependent diabetics being treated with oral hypoglycemics (7 subjects) or insulin (7 subjects). Total body fat was reduced by 10.7% and 5.1% in diabetics on oral hypoglycemics and insulin, respectively, without any significant reductions in body weight. Hyperglycemia was reduced in most of the 15 diabetic subjects treated leading to euglycemia and even cessation of hypoglycemic drugs in 3 of the 7 subjects during 4-8 weeks of bromocriptine treatment. These findings support the hypothesis that obesity and type II diabetes may be treated effectively with bromocriptine when administered at the proper times and dosages.

Bromocriptine inhibits the seasonally occurring obesity, hyperinsulinemia, insulin resistance, and impaired glucose tolerance in the Syrian hamster, Mesocricetus auratus

Seasonally obese-hyperinsulinemic female Syrian hamsters were injected daily with bromocriptine or saline for a period of 34 days to test for effects of bromocriptine on body fat store levels, hepatic triglyceride secretion, glucose tolerance, and plasma insulin and glucose concentrations. The effects of bromocriptine on body fat store levels, as well as on plasma insulin and glucose concentrations, in seasonally obese hamsters were compared with the levels of body fat, plasma insulin, and plasma glucose observed in seasonally lean hamsters. Bromocriptine treatment substantially improved glucose intolerance and reduced the total and stimulated areas under the glucose tolerance curve by 33% after 14 days of treatment. After 34 days of treatment, bromocriptine reduced body fat store levels by 36% and hepatic triglyceride secretion by 40% without any concurrent change in food consumption. Furthermore, bromocriptine reduced the plasma insulin level by 70%, while slightly reducing plasma glucose concentration (ie, 68% reduction in the insulin to glucose ratio). The reductions of body fat, plasma insulin, and plasma insulin to glucose ratio produced by bromocriptine in seasonally obese hamsters are equivalent to those observed in seasonally lean hamsters. Shifts in phase relationships of circadian neuroendocrine rhythms have been demonstrated to regulate annual cycles of metabolism in vertebrates, including the Syrian hamster. The effects of bromocriptine can also be explained as an alteration of such a circadian mechanism.