Chronic ventromedial hypothalamic infusion of norepinephrine and serotonin promotes insulin resistance and glucose intolerance

Brain Dopamine-Clock Interactions Regulate Cardiometabolic Physiology: Mechanisms of the Observed Cardioprotective Effects of Circadian-Timed Bromocriptine-QR Therapy in Type 2 Diabetes Subjects

Despite enormous global efforts within clinical research and medical practice to reduce cardiovascular disease(s) (CVD), it still remains the leading cause of death worldwide. While genetic factors clearly contribute to CVD etiology, the preponderance of epidemiological data indicate that a major common denominator among diverse ethnic populations from around the world contributing to CVD is the composite of Western lifestyle cofactors, particularly Western diets (high saturated fat/simple sugar [particularly high fructose and sucrose and to a lesser extent glucose] diets), psychosocial stress, depression, and altered sleep/wake architecture. Such Western lifestyle cofactors are potent drivers for the increased risk of metabolic syndrome and its attendant downstream CVD. The central nervous system (CNS) evolved to respond to and anticipate changes in the external (and internal) environment to adapt survival mechanisms to perceived stresses (challenges to normal biological function), including the aforementioned Western lifestyle cofactors. Within the CNS of vertebrates in the wild, the biological clock circuitry surveils the environment and has evolved mechanisms for the induction of the obese, insulin-resistant state as a survival mechanism against an anticipated ensuing season of low/no food availability. The peripheral tissues utilize fat as an energy source under muscle insulin resistance, while increased hepatic insulin resistance more readily supplies glucose to the brain. This neural clock function also orchestrates the reversal of the obese, insulin-resistant condition when the low food availability season ends. The circadian neural network that produces these seasonal shifts in metabolism is also responsive to Western lifestyle stressors that drive the CNS clock into survival mode. A major component of this natural or Western lifestyle stressor-induced CNS clock neurophysiological shift potentiating the obese, insulin-resistant state is a diminution of the circadian peak of dopaminergic input activity to the pacemaker clock center, suprachiasmatic nucleus. Pharmacologically preventing this loss of circadian peak dopaminergic activity both prevents and reverses existing metabolic syndrome in a wide variety of animal models of the disorder, including high fat-fed animals. Clinically, across a variety of different study designs, circadian-timed bromocriptine-QR (quick release) (a unique formulation of micronized bromocriptine-a dopamine D2 receptor agonist) therapy of type 2 diabetes subjects improved hyperglycemia, hyperlipidemia, hypertension, immune sterile inflammation, and/or adverse cardiovascular event rate. The present review details the seminal circadian science investigations delineating important roles for CNS circadian peak dopaminergic activity in the regulation of peripheral fuel metabolism and cardiovascular biology and also summarizes the clinical study findings of bromocriptine-QR therapy on cardiometabolic outcomes in type 2 diabetes subjects.

Therapeutic potential of dopamine agonists in the treatment of type 2 diabetes mellitus

Diabetes is a global health concern that has affected almost 415 million people globally. Bromocriptine is a dopamine D2 agonist, which is a Food and Drug Administration (FDA)-approved drug to treat type 2 diabetes mellitus (T2DM) patients. However, it is considered that a novel treatment therapy is required which can be used in the treatment of diabetes with or without other antidiabetic agents. Dopamine agonists are usually used in neurological disorders like Parkinson's disease (PD), restless leg syndrome, and hyperprolactinemia. However, dopamine agonists including bromocriptine and cabergoline are also effective in reducing the glycemic level in T2DM patients. Bromocriptine was formerly used for the treatment of PD, hyperprolactinemia, and restless leg syndrome, but now it is used for improving glycemic levels as well as reducing free fatty acids and triglycerides. In addition, cabergoline has been found to be effective in glycemic control, but this drug is yet to be approved by the FDA due to its limitations and lack of study. Findings of the clinical trials of bromocriptine have suggested that it reduces almost 0.4-0.8% glycated hemoglobin and cardiovascular risk by 40% in insulin-resistant patients. Moreover, the safe use of bromocriptine in obese T2DM patients makes it a more attractive option as it causes weight loss. Indeed, bromocriptine is a novel therapy for T2DM patients, as its mechanism of action is unique in T2DM patients with minimal adverse effects. This review summarizes the potential of dopamine agonists in the treatment of T2DM.

Experimental dopaminergic neuron lesion at the area of the biological clock pacemaker, suprachiasmatic nuclei (SCN) induces metabolic syndrome in rats

BACKGROUND

The daily peak in dopaminergic neuronal activity at the area of the biological clock (hypothalamic suprachiasmatic nuclei [SCN]) is diminished in obese/insulin resistant vs lean/insulin sensitive animals. The impact of targeted lesioning of dopamine (DA) neurons specifically at the area surrounding (and that communicate with) the SCN (but not within the SCN itself) upon glucose metabolism, adipose and liver lipid gene expression, and cardiovascular biology in normal laboratory animals has not been investigated and was the focus of this study.

METHODS

Female Sprague-Dawley rats received either DA neuron neurotoxic lesion by bilateral intra-cannula injection of 6-hydroxydopamine (2-4 μg/side) or vehicle treatment at the area surrounding the SCN at 20 min post protriptyline ip injection (20 mg/kg) to protect against damage to noradrenergic and serotonergic neurons.

RESULTS

At 16 weeks post-lesion relative to vehicle treatment, peri-SCN area DA neuron lesioning increased weight gain (34.8%, P < 0.005), parametrial and retroperitoneal fat weight (45% and 90% respectively, P < 0.05), fasting plasma insulin, leptin and norepinephrine levels (180%, 71%, and 40% respectively, P < 0.05), glucose tolerance test area under the curve (AUC) insulin (112.5%, P < 0.05), and insulin resistance (44%-Matsuda Index, P < 0.05) without altering food consumption during the test period. Such lesion also induced the expression of several lipid synthesis genes in adipose and liver and the adipose lipolytic gene, hormone sensitive lipase in adipose (P < 0.05 for all). Liver monocyte chemoattractant protein 1 (a proinflammatory protein associated with metabolic syndrome) gene expression was also significantly elevated in peri-SCN area dopaminergic lesioned rats. Peri-SCN area dopaminergic neuron lesioned rats were also hypertensive (systolic BP rose from 157 ± 5 to 175 ± 5 mmHg, P < 0.01; diastolic BP rose from 109 ± 4 to 120 ± 3 mmHg, P < 0.05 and heart rate increase from 368 ± 12 to 406 ± 12 BPM, P < 0.05) and had elevated plasma norepinephrine levels (40% increased, P < 0.05) relative to controls.

CONCLUSIONS

These findings indicate that reduced dopaminergic neuronal activity in neurons at the area of and communicating with the SCN contributes significantly to increased sympathetic tone and the development of metabolic syndrome, without effect on feeding.

Bromocriptine mesylate improves glucose tolerance and disposal in a high-fat-fed canine model

Bromocriptine mesylate treatment was examined in dogs fed a high fat diet (HFD) for 8 wk. After 4 wk on HFD, daily bromocriptine (Bromo; n = 6) or vehicle (CTR; n = 5) injections were administered. Oral glucose tolerance tests were performed before beginning HFD (OGTT1), 4 wk after HFD began (Bromo only), and after 7.5 wk on HFD (OGTT3). After 8 wk on HFD, clamp studies were performed, with infusion of somatostatin and intraportal replacement of insulin (4× basal) and glucagon (basal). From 0 to 90 min (P1), glucose was infused via peripheral vein to double the hepatic glucose load; and from 90 to 180 min (P2), glucose was infused via the hepatic portal vein at 4 mg·kg^-1·min^-1, with the HGL maintained at 2× basal. Bromo decreased the OGTT glucose ΔAUC_0-30 and ΔAUC_0-120 by 62 and 27%, respectively, P < 0.05 for both) without significantly altering the insulin response. Bromo dogs exhibited enhanced net hepatic glucose uptake (NHGU) compared with CTR (~33 and 21% greater, P1 and P2, respectively, P < 0.05). Nonhepatic glucose uptake (non-HGU) was increased ~38% in Bromo in P2 (P < 0.05). Bromo vs. CTR had higher (P < 0.05) rates of glucose infusion (36 and 30%) and non-HGU (~40 and 27%) than CTR during P1 and P2, respectively. In Bromo vs. CTR, hepatic 18:0/16:0 and 16:1/16:0 ratios tended to be elevated in triglycerides and were higher (P < 0.05) in phospholipids, consistent with a beneficial effect of bromocriptine on liver fat accumulation. Thus, bromocriptine treatment improved glucose disposal in a glucose-intolerant model, enhancing both NHGU and non-HGU.

Circadian-timed dopamine agonist treatment reverses high-fat diet-induced diabetogenic shift in ventromedial hypothalamic glucose sensing

INTRODUCTION

Within the ventromedial hypothalamus (VMH), glucose inhibitory (GI) neurons sense hypoglycaemia while glucose excitatory (GE) neurons sense hyperglycaemia to initiate counter control mechanisms under normal conditions. However, potential electrophysiological alterations of these two neuronal types in vivo in insulin-resistant states have never been simultaneously fully documented. Further, the anti-diabetic effect of dopamine agonism on this VMH system under insulin resistance has not been studied.

METHODS

This study examined the impact of a high-fat diet (HFD) on in vivo electrophysiological recordings from VMH GE and GI neurons and the ability of circadian-timed dopamine agonist therapy to reverse any adverse effect of the HFD on such VMH activities and peripheral glucose metabolism.

RESULTS

HFD significantly inhibited VMH GE neuronal electrophysiological response to local hyperglycaemia (36.3%) and augmented GI neuronal excitation response to local hypoglycaemia (47.0%). Bromocriptine (dopamine agonist) administration at onset of daily activity (but not during the daily sleep phase) completely reversed both VMH GE and GI neuronal aberrations induced by HFD. Such timed treatment also normalized glucose intolerance and insulin resistance. These VMH and peripheral glucose metabolism effects of circadian-timed bromocriptine may involve its known effect to reduce elevated VMH noradrenergic activity in insulin-resistant states as local VMH administration of norepinephrine was observed to significantly inhibit VMH GE neuronal sensing of local hyperglycaemia in insulin-sensitive animals on regular chow diet (52.4%).

CONCLUSIONS

HFD alters VMH glucose sensing in a manner that potentiates hyperglycaemia and this effect on the VMH can be reversed by appropriately circadian-timed dopamine agonist administration.

Norepinephrine protects against apoptosis of mesenchymal stem cells induced by high glucose

In diabetes, the number of bone mesenchymal stem cells (MSCs) decreases and their differentiation is impaired. However, the exact mechanism is unclear. Patients with diabetes often experience sympathetic nerve injury. Norepinephrine (NE), a major mediator of the sympathetic nervous system, influences rat MSC migration in culture and in vivo. The present study aimed to investigate the effect of NE on MSCs under high glucose conditions; therefore MSCs were treated with high glucose and NE. High glucose-induced MSCs apoptosis, which was reversed by NE. To verify the effect of NE, mice underwent sympathectomy and were used to establish a diabetic model. Diabetic mice with sympathectomy had a higher apoptosis rate and higher levels of reactive oxygen species in their bone marrow-derived cells than diabetic mice without sympathectomy. High glucose inhibited p-AKT production and B-Cell CLL/Lymphoma 2 expression, and promoted BAX and caspase-3 expression. NE reversed these effects of high glucose. An AKT inhibitor enhanced the effects of high glucose. Thus, NE had a protective effect on MSC apoptosis induced by high glucose, possibly via the AKT/BCL-2 pathway.

Circadian peak dopaminergic activity response at the biological clock pacemaker (suprachiasmatic nucleus) area mediates the metabolic responsiveness to a high-fat diet

Among vertebrate species of the major vertebrate classes in the wild, a seasonal rhythm of whole body fuel metabolism, oscillating from a lean to obese condition, is a common biological phenomenon. This annual cycle is driven in part by annual changes in the circadian dopaminergic signalling at the suprachiasmatic nuclei (SCN), with diminution of circadian peak dopaminergic activity at the SCN facilitating development of the seasonal obese insulin-resistant condition. The present study investigated whether such an ancient circadian dopamine-SCN activity system for expression of the seasonal obese, insulin-resistant phenotype may be operative in animals made obese amd insulin resistant by high-fat feeding and, if so, whether reinstatement of the circadian dopaminergic peak at the SCN would be sufficient to reverse the adverse metabolic impact of the high-fat diet without any alteration of caloric intake. First, we identified the supramammillary nucleus as a novel site providing the majority of dopaminergic neuronal input to the SCN. We further identified dopamine D2 receptors within the peri-SCN region as being functional in mediating SCN responsiveness to local dopamine. In lean, insulin-sensitive rats, the peak in the circadian rhythm of dopamine release at the peri-SCN coincided with the daily peak in SCN electrophysiological responsiveness to local dopamine administration. However, in rats made obese and insulin resistant by high-fat diet (HFD) feeding, these coincident circadian peak activities were both markedly attenuated or abolished. Reinstatement of the circadian peak in dopamine level at the peri-SCN by its appropriate circadian-timed daily microinjection to this area (but not outside this circadian time-interval) abrogated the obese, insulin-resistant condition without altering the consumption of the HFD. These findings suggest that the circadian peak of dopaminergic activity at the peri-SCN/SCN is a key modulator of metabolism and the responsiveness to adverse metabolic consequences of HFD consumption.

Sex differences in the effects of androgens acting in the central nervous system on metabolism

One of the most sexually dimorphic aspects of metabolic regulation is the bidirectional modulation of glucose and energy homeostasis by testosterone in males and females. Testosterone deficiency predisposes men to metabolic dysfunction, with excess adiposity, insulin resistance, and type 2 diabetes, whereas androgen excess predisposes women to insulin resistance, adiposity, and type 2 diabetes. This review discusses how testosterone acts in the central nervous system, and especially the hypothalamus, to promote metabolic homeostasis or dysfunction in a sexually dimorphic manner. We compare the organizational actions of testosterone, which program the hypothalamic control of metabolic homeostasis during development, and the activational actions of testosterone, which affect metabolic function after puberty. We also discuss how the metabolic effect of testosterone is centrally mediated via the androgen receptor.

Impact of bromocriptine-QR therapy on cardiovascular outcomes in type 2 diabetes mellitus subjects on metformin

OBJECTIVES

Type 2 diabetes mellitus (T2DM) is associated with a substantially increased risk of cardiovascular disease (CVD). Bromocriptine-QR (B-QR), a quick release sympatholytic dopamine D₂ receptor agonist, is a FDA-approved therapy for T2DM which may provide CVD risk reduction. Metformin is considered to be an agent with a potential cardioprotective benefit. This large placebo controlled clinical study assessed the impact of B-QR addition to existing metformin therapy on CVD outcomes in T2DM subjects.

METHODS

1791 subjects (1208 B-QR; 583 placebo) on metformin ± another anti-diabetes therapy at baseline derived from the Cycloset Safety Trial, a 12-month, randomized, multicenter, placebo-controlled, double-blind study in T2DM, were included in this study. The primary CVD endpoint evaluated was treatment impact on CVD event rate, prespecified as a composite of time to first myocardial infarction, stroke, coronary revascularization, or hospitalization for unstable angina/congestive heart failure. Impact on glycemic control was evaluated as a secondary analysis.

RESULTS

The composite CVD end point occurred in 16/1208 B-QR treated (1.3%) and 18/583 placebo treated (3.1%) subjects resulting in a 55% CVD hazard risk reduction (intention-to-treat, Cox regression analysis; HR: 0.45 [0.23-0.88], p = 0.028). Kaplan-Meier curves demonstrated a significantly lower cumulative incidence rate of the CVD endpoint in the B-QR treatment group (Log-Rank p = 0.017). In subjects with poor glycemic control (HbA1c ≥ 7.5) at baseline, B-QR therapy relative to placebo resulted in a significant mean %HbA1c reduction of -0.59 at week 12 and -0.51 at week 52 respectively (p < 0.001 for both) and a 10 fold higher percent of subjects achieving HbA1c goal of ≤7% by week 52 (B-QR 30%, placebo 3%; p = 0.003).

CONCLUSION

These findings suggest that in T2DM subjects on metformin, BQR therapy may represent an effective strategy for reducing CVD risk. Cycloset Safety Trial registration: ClinicalTrials.gov Identifier: NCT00377676.

Evidence-based practice use of quick-release bromocriptine across the natural history of type 2 diabetes mellitus

OBJECTIVES

To provide an evidence-based practice overview on the clinical use of bromocriptine-quick release (QR) across the natural history of type 2 diabetes mellitus (T2DM).

METHODS

Articles for inclusion were selected after a comprehensive literature search of English-language PubMed articles and identification of other relevant references through other sources. Inclusion criteria were animal studies examining the mechanism of action and efficacy of bromocriptine, and clinical studies examining the safety and efficacy of bromocriptine-QR in patients with T2DM, without a time limitation.

RESULTS

The brain plays a key role in total body metabolism, in particular ensuring that sufficient levels of glucose are available for proper neural functioning. The hypothalamic suprachiasmatic nucleus (SCN), the body's biological clock, plays a key role in the regulation of seasonal and diurnal variations of insulin sensitivity. A daily surge of dopaminergic activity in the SCN upon waking enables insulin sensitivity throughout the day. When this is disrupted (e.g. by a high fat/sugar diet, stress, altered [diminished] exercise, altered sleep/wake cycle, diabetes), insulin resistance persists throughout the day and overnight. Improving the morning surge in dopaminergic activity with the short-acting dopamine D2 receptor agonist bromocriptine-QR can safely and effectively improve glycemic control, while improving cardiovascular disease risk factors and related adverse events, and reducing sympathetic tone, as demonstrated by 5 reports of the Cycloset Safety Trial and 3 additional clinical studies of bromocriptine-QR.

CONCLUSIONS

In patients with T2DM, the dopamine D2 receptor agonist bromocriptine-QR has been shown to be well tolerated, efficacious, and a logical treatment option.

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.

Impact of Bromocriptine-QR Therapy on Glycemic Control and Daily Insulin Requirement in Type 2 Diabetes Mellitus Subjects Whose Dysglycemia Is Poorly Controlled on High-Dose Insulin: A Pilot Study

BACKGROUND

The concurrent use of a postprandial insulin sensitizing agent, such as bromocriptine-QR, a quick release formulation of bromocriptine, a dopamine D2 receptor agonist, may offer a strategy to improve glycemic control and limit/reduce insulin requirement in type 2 diabetes (T2DM) patients on high-dose insulin. This open label pilot study evaluated this potential utility of bromocriptine-QR.

METHODS

Ten T2DM subjects on metformin (1-2 gm/day) and high-dose (TDID ≥ 65 U/day) basal-bolus insulin were enrolled to receive once daily (morning) bromocriptine-QR (1.6-4.8 mg/day) for 24 weeks. Subjects with at least one postbaseline HbA1c measurement (N = 8) were analyzed for change from baseline HbA(1c), TDID, and postprandial glucose area under the curve of a four-hour mixed meal tolerance test (MMTT).

RESULTS

Compared to the baseline, average HbA1c decreased 1.76% (9.74 ± 0.56 to 7.98 ± 0.36, P = 0.01), average TDID decreased 27% (199 ± 33 to 147 ± 31, P = 0.009), and MMTT AUC(60-240) decreased 32% (P = 0.04) over the treatment period. The decline in HbA(1c) and TDID was observed at 8 weeks and sustained over the remaining 16-week study duration.

CONCLUSION

In this study, bromocriptine-QR therapy improved glycemic control and meal tolerance while reducing insulin requirement in T2DM subjects poorly controlled on high-dose insulin therapy.

Timed Bromocriptine-QR Therapy Reduces Progression of Cardiovascular Disease and Dysglycemia in Subjects with Well-Controlled Type 2 Diabetes Mellitus

BACKGROUND

Type 2 diabetes (T2DM) patients, including those in good glycemic control, have an increased risk of cardiovascular disease (CVD). Maintaining good glycemic control may reduce long-term CVD risk. However, other risk factors such as elevated vascular sympathetic tone and/or endothelial dysfunction may be stronger potentiators of CVD. This study evaluated the impact of bromocriptine-QR, a sympatholytic dopamine D2 receptor agonist, on progression of metabolic disease and CVD in T2DM subjects in good glycemic control (HbA1c ≤ 7.0%).

METHODS

1834 subjects (1219 bromocriptine-QR; 615 placebo) with baseline HbA1c ≤ 7.0% derived from the Cycloset Safety Trial (this trial is registered with ClinicalTrials.gov Identifier: NCT00377676), a 12-month, randomized, multicenter, placebo-controlled, double-blind study in T2DM, were evaluated. Treatment impact upon a prespecified composite CVD endpoint (first myocardial infarction, stroke, coronary revascularization, or hospitalization for angina/congestive heart failure) and the odds of losing glycemic control (HbA1c >7.0% after 52 weeks of therapy) were determined.

RESULTS

Bromocriptine-QR reduced the CVD endpoint by 48% (intention-to-treat; HR: 0.52 [0.28-0.98]) and 52% (on-treatment analysis; HR: 0.48 [0.24-0.95]). Bromocriptine-QR also reduced the odds of both losing glycemic control (OR: 0.63 (0.47-0.85), p = 0.002) and requiring treatment intensification to maintain HbA1c ≤ 7.0% (OR: 0.46 (0.31-0.69), p = 0.0002).

CONCLUSIONS

Bromocriptine-QR therapy slowed the progression of CVD and metabolic disease in T2DM subjects in good glycemic control.

Neuroendocrine and metabolic components of dopamine agonist amelioration of metabolic syndrome in SHR rats

BACKGROUND

The hypertensive, pro-inflammatory, obese state is strongly coupled to peripheral and hepatic insulin resistance (in composite termed metabolic syndrome [MS]). Hepatic pro-inflammatory pathways have been demonstrated to initiate or exacerbate hepatic insulin resistance and contribute to fatty liver, a correlate of MS. Previous studies in seasonally obese animals have implicated an important role for circadian phase-dependent increases in hypothalamic dopaminergic tone in the maintenance of the lean, insulin sensitive condition. However, mechanisms driving this dopaminergic effect have not been fully delineated and the impact of such dopaminergic function upon the above mentioned parameters of MS, particularly upon key intra-hepatic regulators of liver inflammation and lipid and glucose metabolism have never been investigated.

OBJECTIVE

This study therefore investigated the effects of timed daily administration of bromocriptine, a potent dopamine D2 receptor agonist, on a) ventromedial hypothalamic catecholamine activity, b) MS and c) hepatic protein levels of key regulators of liver inflammation and glucose and lipid metabolism in a non-seasonal model of MS - the hypertensive, obese SHR rat.

METHODS

Sixteen week old SHR rats maintained on 14 hour daily photoperiods were treated daily for 16 days with bromocriptine (10 mg/kg, i.p.) or vehicle at 1 hour before light offset and, subsequent to blood pressure recordings on day 14, were then utilized for in vivo microdialysis of ventromedial hypothalamic catecholamine activity or sacrificed for the analyses of MS factors and regulators of hepatic metabolism. Normal Wistar rats served as wild-type controls for hypothalamic activity, body fat levels, and insulin sensitivity.

RESULTS

Bromocriptine treatment significantly reduced ventromedial hypothalamic norepinephrine and serotonin levels to the normal range and systolic and diastolic blood pressures, retroperitoneal body fat level, plasma insulin and glucose levels and HOMA-IR relative to vehicle treated SHR controls. Such treatment also reduced plasma levels of C-reactive protein, leptin, and norepinephrine and increased that of plasma adiponectin significantly relative to SHR controls. Finally, bromocriptine treatment significantly reduced hepatic levels of several pro-inflammatory pathway proteins and of the master transcriptional activators of lipogenesis, gluconeogenesis, and free fatty acid oxidation versus control SHR rats.

CONCLUSION

These findings indicate that in SHR rats, timed daily dopamine agonist treatment improves hypothalamic and neuroendocrine pathologies associated with MS and such neuroendocrine events are coupled to a transformation of liver metabolism potentiating a reduction of elevated lipogenic and gluconeogenic capacity. This liver effect may be driven in part by concurrent reductions in hyperinsulinemia and sympathetic tone as well as by reductions in intra-hepatic inflammation.

Effect of bromocriptine-QR on glycemic control in subjects with uncontrolled hyperglycemia on one or two oral anti-diabetes agents

OBJECTIVE

To investigate the effect of Bromocriptine-QR on glycemic control in patients with type 2 diabetes whose glycemia is poorly controlled on one or two oral anti-diabetes agents.

METHODS

Five hundred fifteen Type 2 Diabetes Mellitus (T2DM) subjects (ages 18 to 80 and average body mass index [BMI] of 32.7) with baseline HbA1c ≥ 7.5 and on one or two oral anti-diabetes (OAD) medications (metformin, sulfonylurea, and/or thiazolidinediones) were randomized 2:1 to bromocriptine-QR (1.6 to 4.8 mg/day) or placebo for a 24 week treatment period. Study investigators were allowed to adjust, if necessary, subject anti-diabetes medications during the study to attempt to achieve glycemic control in case of glycemic deterioration. The impact of bromocriptine-QR treatment intervention on glycemic control was assessed in subjects on any one or two OADs (ALL treatment category) (N = 515), or on metformin with or without another OAD (Met/OAD treatment category) (N = 356), or on metformin plus a sulfonylurea (Met/SU treatment category) (N = 245) 1) by examining the between group difference in change from baseline a) concomitant OAD medication changes during the study, and b) HbA1c and 2) by determining the odds of reaching HbA1c of ≤ 7.0% on bromocriptine-QR versus placebo.

RESULTS

Significantly more patients (approximately 1.5 to 2-fold more; P<.05) intensified concomitant anti-diabetes medication therapy during the study in the placebo versus the bromocriptine-QR arm. In subjects that did not change the intensity of the baseline diabetes therapy (72%), and that were on any one or two OADs (ALL), or on metformin with or without another OAD (Met/OAD), or on metformin plus sulfonylurea (Met/SU), the HbA1c change for bromocriptine-QR versus placebo was -0.47 versus +0.22 (between group delta of -0.69, P<.0001), -0.55 versus +0.26 (between group delta of -0.81, P<.0001) and -0.63 versus +0.20 (between group delta of -0.83, P<.0001) respectively, after 24 weeks on therapy. The odds ratio of reaching HbA1c of ≤ 7.0% was 6.50, 12.03 and 11.45 (P<.0002) for these three groups, respectively.

CONCLUSION

In T2DM subjects whose hyperglycemia is poorly controlled on one or two oral agents, bromocriptine-QR therapy for 24 weeks can provide significant added improvement in glycemic control relative to adding placebo.

Novel therapies for the management of type 2 diabetes mellitus: part 1. pramlintide and bromocriptine-QR

Several classes of antidiabetic agents have been introduced into the market place over the past dozen years. As our understanding of the underlying pathophysiology of type 2 diabetes has advanced, attempts have been made to address these defects specifically. This brief review focuses on our experience with two such pharmacological approaches: (i) a synthetic amylin analog addressing amylin deficiency; and (ii) a dopaminergic agonist, focused on enhancing the lowered dopaminergic tone in patients with type 2 diabetes. Importantly, the use of these agents is not associated with hypoglycemia or weight gain.

Leptin signaling and circuits in puberty and fertility

Leptin is an adipocyte-derived hormone involved in a myriad of physiological process, including the control of energy balance and several neuroendocrine axes. Leptin-deficient mice and humans are obese, diabetic, and display a series of neuroendocrine and autonomic abnormalities. These individuals are infertile due to a lack of appropriate pubertal development and inadequate synthesis and secretion of gonadotropins and gonadal steroids. Leptin receptors are expressed in many organs and tissues, including those related to the control of reproductive physiology (e.g., the hypothalamus, pituitary gland, and gonads). In the last decade, it has become clear that leptin receptors located in the brain are major players in most leptin actions, including reproduction. Moreover, the recent development of molecular techniques for brain mapping and the use of genetically modified mouse models have generated crucial new findings for understanding leptin physiology and the metabolic influences on reproductive health. In the present review, we will highlight the new advances in the field, discuss the apparent contradictions, and underline the relevance of this complex physiological system to human health. We will focus our review on the hypothalamic circuitry and potential signaling pathways relevant to leptin’s effects in reproductive control, which have been identified with the use of cutting-edge technologies of molecular mapping and conditional knockouts.

Why does quick-release bromocriptine decrease cardiac events?

A placebo-controlled prospective safety study of quick-release bromocriptine in patients with type 2 diabetes has shown a 40% reduction in cardiovascular events. Possible explanations for this decrease are that through re-establishing diurnal variation a decrease in insulin resistance and its associated risk factors occurs. In addition, a decrease in the activity of the sympathetic nervous and renin-angiotensin systems and re-establishment of diurnal variations in the pituitary-adrenal axis may play a role. However, the most probable explanation is that because of the lowering of insulin resistance there are decreases in hepatic glucose production and an increased uptake of glucose leading to decreased levels of postprandial glucose, free fatty acids and triglycerides, which cause decreases in inflammation, oxidative stress and accumulation of atheroma.

Bromocriptine in type 2 diabetes mellitus

Bromocriptine mesylate quick-release was approved by the Food and Drug Administration (FDA) in May 2009, for the treatment of type 2 diabetes. Bromocriptine is thought to act on the circadian neuronal activities in the hypothalamus, to reset an abnormally elevated hypothalamic drive for increased plasma glucose, free fatty acids, and triglycerides in insulin-resistant patients. Randomized controlled trials have shown that bromocriptine-QR lowers glycated hemoglobin by 0.4 - 0.8% either as monotherapy or in combination with other anti-diabetes medications. The doses used to treat diabetes (up to 4.8 mg daily) are much lower than those used to treat Parkinson's disease, and apart from nausea, the drug is well-tolerated. The novel mechanism of action, good side effect profile, and its effects to reduce cardiovascular event rates make it an attractive option for the treatment of type 2 diabetes.

Bromocriptine--unique formulation of a dopamine agonist for the treatment of type 2 diabetes

IMPORTANCE TO THE FIELD

There is a large unmet need for new therapies to treat type 2 diabetes (T2DM) which reduce fasting and postprandial glucose without increasing insulin levels and which are not associated with weight gain or hypoglycemia. The quick-release formulation of bromocriptine (bromocriptine-QR; Cycloset) represents such a therapy.

AREAS COVERED IN THE REVIEW

Bromocriptine-QR's proposed mechanism of action, unique formulation and clinical efficacy and safety will be discussed. A Medline search was conducted using the terms: bromocriptine quick-release, circadian rhythms, treatment type 2 diabetes, insulin resistance, beta-cell dysfunction (years 1985 - 2009).

WHAT THE READER WILL GAIN

The reader will gain an understanding of the importance of the brain as a target for the treatment of type 2 diabetes. In addition the safety, efficacy and indication for use of a first-in-class dopamine agonist as a treatment option for type 2 diabetes are discussed.

TAKE HOME MESSAGE

Bromocriptine-QR is indicated to be used alone or in conjunction with all available treatments for type 2 diabetes. Although the mechanism of action is not fully understood, bromocriptine-QR's action points to a central target in the brain (hypothalamus) which may explain the observed peripheral improvements in metabolic parameters.

Lower central serotonergic responsivity is associated with preclinical carotid artery atherosclerosis

BACKGROUND AND PURPOSE

Central nervous system serotonergic neurotransmission appears to play a role in mood disorders, eating habits, and sleep, and also modulates blood pressure and metabolism. This investigation tested a hypothesized association between central serotonergic functioning and preclinical atherosclerosis.

METHODS

Subjects were 244 adults 30 to 55 years of age and free of clinically evident vascular disease (52% men, 84% white). Central serotonergic responsivity was measured as the rise in serum prolactin concentration (area under the curve) over 2.5 hours, adjusted for baseline prolactin, after citalopram administered intravenously at 0.33 mg/kg lean body weight. Carotid artery morphology served as a marker of preclinical atherosclerosis, and carotid artery intima-media thickness and plaque occurrence were determined by B-mode ultrasonography.

RESULTS

In linear regression models including age, gender, race, and citalopram concentration, a 1 SD lower prolactin response was associated with greater maximum intima-media thickness (+0.016 mm; P=0.006) and with greater mean intima-media thickness (+0.009 mm; P=0.03). The odds ratio for carotid artery plaque corresponding to a 1 SD decrease in prolactin response, adjusted for age, race, sex, and citalopram concentration, was 1.47 (95% CI, 0.98 to 2.19; P=0.06). The metabolic syndrome mediated (P<0.01), but did not fully account for, the association between lower prolactin response and greater maximum intima-media thickness.

CONCLUSIONS

In this young and relatively healthy sample, blunted prolactin response to citalopram was associated with carotid artery thickening, suggesting that individual differences in central serotonergic responsivity are inversely related to preclinical vascular disease.

Central nervous system circuitry involved in the hyperinsulinism syndrome

Raised plasma levels of insulin, glucose and glucagon are found in patients affected by 'hyperinsulinism'. Obesity, hypertension, mammary plus ovary cysts and rheumatic symptoms are frequently observed in these patients. Sleep disorders and depression are also present in most subjects affected by this polysymptomatic disorder. The simultaneous increases of glucose, insulin and glucagon plasma levels seen in these patients indicate that the normal crosstalk between A cells, B cells and D cells is disrupted. With respect to this, it is well known that glucose excites B cells (which secrete insulin) and inhibits A cells (which secrete glucagon), which in turn excites D cells (which secrete somatostatin). Gastrointestinal hormones (incretins) modulate this crosstalk both directly and indirectly throughout pancreatic and hepatobiliary mechanisms. The above factors depend on autonomic nervous system mediation. For instance, acetylcholine released from parasympathetic nerves excites both B and A cells. Noradrenaline released from sympathetic nerves and adrenaline secreted from the adrenal glands inhibit B cells and excite A cells, which are crowded with beta(2)- and alpha(2)-receptors, respectively. Noradrenaline released from sympathetic nerves also excites A cells by acting at alpha(1)-receptors located at this level. According to this, the excessive release of noradrenaline from these nerves should provoke an enhancement of glucagon secretion which will result in overexcitation of insulin secretion from B cells. That is the disorder seen in the so-called 'hyperinsulinism', in which raised plasma levels of glucose, insulin and glucagon coexist. Taking into account that neural sympathetic activity is positively correlated to the A5 noradrenergic nucleus and median raphe serotonergic neurons, and negatively correlated to the A6 noradrenergic, the dorsal raphe serotonergic and the C1 adrenergic neurons, we postulate that this unbalanced central nervous system circuitry is responsible for the hyperinsulinism syndrome.

Reduced dopaminergic tone in hypothalamic neural circuits: expression of a "thrifty" genotype underlying the metabolic syndrome?

The thrifty genotype hypothesis postulates that the genetically determined ability to grow obese and insulin resistant in times of food abundance confers a survival advantage in times of famine. Obviously, this ability poses a major health threat in modern times, where food is always available in large quantities. In the last 10-15 years, many genes encoding pathways that orchestrate energy balance and fuel flux have been discovered. This paper summarizes the evidence that diminished dopaminergic tone in hypothalamic nuclei contributes to the "thrifty" genotype/phenotype. Reduced dopaminergic neurotransmission in the suprachiasmatic nucleus of seasonally obese animals appears to drive noradrenalin and NPY mediated transmissions in other nuclei to induce the obesity syndrome at the appropriate time of year. Treatment with dopamine D(2) receptor agonists can fully reverse the metabolic syndrome in these animals. Similar mechanisms are operative in non-seasonal obese animal models. In man, treatment with dopamine D(2) receptor antagonists induces obesity and type 2 diabetes mellitus, whereas dopamine D(2) receptor activation ameliorates the metabolic profile in obese nondiabetic and diabetic humans. Various loss of function mutations of the dopamine D(2) receptor gene are associated with overweight in humans. In concert, the data support the notion that diminution of dopaminergic (dopamine D(2) receptor mediated) transmission in relevant hypothalamic nuclei sets the stage for efficient partitioning of ingested nutrients to contribute to a phenotype that is not so thrifty anymore.

Blood glucose is correlated with cerebrospinal fluid neurotransmitter metabolites

Medications which influence monoaminergic neurotransmission can also have an effect on glucose regulation. In order to better understand the role of central monoaminergic neurotransmission in blood glucose homeostasis, we explored the relation between blood glucose and cerebrospinal fluid metabolite concentrations of monoaminergic neurotransmitters. Under stringently controlled resting conditions, we measured fasting blood glucose and performed lumbar punctures on 41 healthy participants. Peripheral blood glucose concentrations were significantly correlated with the cerebrospinal fluid concentrations of the dopamine metabolite, homovanillic acid and the noradrenaline metabolite, 3-methoxy-4-hydroxyphenylglycol. These correlations may represent a homeostatic relation between brain neurotransmitter activity and blood glucose.

Modulation of Monoaminergic Neural Circuits

A plethora of data from experimental animals provide strong support for the concept that reduced dopaminergic neuronal activity and enhanced noradrenergic tone in specific hypothalamic nuclei are involved in the pathogenesis of the metabolic syndrome. The available information on these neurotransmitter systems in insulin-resistant humans with obesity is in keeping with the postulate that analogous mechanisms may underlie their adverse metabolic profile. Treatment with bromocriptine, which has dopaminergic (D2 receptor agonist) and sympatholytic (alpha2-adrenoceptor agonistic and an alpha1-adrenoceptor antagonistic) actions, can reverse the metabolic anomalies in a variety of obese mammalian species. Combined D1/D2 receptor activation appears to exert even more powerful effects on fuel metabolism in various animal models of the metabolic syndrome. The currently available data on the metabolic effects of bromocriptine in humans with obesity and type 2 diabetes mellitus point in the same direction. Bromocriptine favorably affects glucose metabolism and various other components of the metabolic syndrome simultaneously to ameliorate the risk of damage to eyes, neural tissue, kidneys and the cardiovascular system in patients with type 2 diabetes mellitus. Moreover, a substantial number of studies indicate that bromocriptine lowers blood pressure in animals and humans with hypertension via its sympatholytic capacities. However, the effects of bromocriptine alone are relatively modest, the metabolic mechanism of action in humans remains uncertain, and the long-term efficacy and safety profiles of this compound are unknown. It seems important to seek for ways to boost the action of bromocriptine, by combining dopaminergic D2 and D1 receptor activation, for example. Notably, there is no antidiabetic drug that acts through central (dopaminergic) mechanisms. This novel approach may, therefore, result in synergistic actions with other available agents to favorably impact the risk of tissue damage in patients with type 2 diabetes mellitus.

Increased responsiveness to the hyperglycemic, hyperglucagonemic and hyperinsulinemic effects of circulating norepinephrine in ob/ob mice

OBJECTIVE

Several studies have implicated increased sympathetic tone as a contributing factor to the hyperglycemia and hyperglucagonemia of ob/ob mice. However, the responsiveness of plasma glucose, insulin and glucagon to circulating norepinephrine (NE) in ob/ob vs normal lean mice has never been described. Therefore, the present study investigated the effect of a 15 min intravenous NE infusion (1 pmol/min/g) on plasma glucose, insulin and glucagon in anesthetized lean, ob/ob, ob/ob-concurrent yohimbine (alpha(2) antagonist) treated, and ob/ob-chronically sympatholytic dopamine agonist treated (for 14 days prior to infusion) mice. In an effort to gain insight into a possible relation between norepinephrine, hyperglucagonemia and hyperinsulinemia in ob/ob mice, this study also examined the isolated islet responses to NE and glucagon in lean, ob/ob and ob/ob-sympatholytic dopamine agonist treated mice.

RESULTS

Basal humoral values of glucose, insulin and glucagon were all elevated in ob/ob vs lean mice (by 63, 1900 and 63%, respectively, P<0.01). However, NE infusion further increased levels of glucose, insulin and glucagon in ob/ob (by 80, 90 and 60%, respectively, P<0.05) but not in lean mice (between group difference for all parameters P<0.05). Acute concurrent yohimbine treatment as well as chronic prior sympatholytic dopamine agonist treatment (bromocriptine plus SKF38393) simultaneously strongly aborgated or abolished all these humoral hypersensitivity responses to intravenous NE in ob/ob mice (P<0.05). Clamping the plasma glucose level in untreated ob/ob mice at a high level (30 mM) established by NE infusion did not significantly alter the plasma insulin level, suggesting that some other influence of NE was responsible for this insulin effect. Direct NE administration at 1 microM to islets from lean and ob/ob mice inhibited 15 mM glucose-stimulated insulin secretion in both groups, but at 0.1 microM it was inhibitory only in islets from ob/ob mice. However, glucagon (10 nM) increased 15 mM glucose-stimulated insulin secretion in ob/ob (by 170%, P<0.05) but not lean mice (between group difference P<0.05).

CONCLUSION

These findings suggest that hypersensitivity to circulating NE may potentiate hyperglycemia and hyperglucagonemia in ob/ob mice, and the subsequent hyperglucagonemia coupled with increased islet beta-cell insulin secretory responsiveness to glucagon in ob/ob mice may support hyperinsulinemia, thus explaining the increased plasma insulin level response to intravenous NE in these animals. These findings further support a role for increased peripheral noradrenergic activities in the development and maintenance of the hyperglycemic, hyperglucagonemic and hyperinsulinemic state, characteristic of type 2 diabetes.

Hypothalamic adrenergic receptor changes in the metabolic syndrome of genetically obese (ob/ob) mice

The genetically, seasonally, and diet-induced obese, glucose-intolerant states in rodents, including ob/ob mice, have each been associated with elevated hypothalamic levels of norepinephrine (NE). With the use of quantitative autoradiography on brain slices of 6-wk-old obese (ob/ob) and lean mice, the adrenergic receptor populations in several hypothalamic nuclei were examined. The binding of [(125)I]iodocyanopindolol to beta(1)- and beta(2)-adrenergic receptors in ob/ob mice was significantly increased in the paraventricular hypothalamic nucleus (PVN) by 30 and 38%, in the ventromedial hypothalamus (VMH) by 23 and 72%, and in the lateral hypothalamus (LH) by 10 and 15%, respectively, relative to lean controls. The binding of [(125)I]iodo-4-hydroxyphenyl-ethyl-aminomethyl-tetralone to alpha(1)-adrenergic receptors was also significantly increased in the PVN (26%), VMH (67%), and LH (21%) of ob/ob mice. In contrast, the binding of [(125)I]paraiodoclonidine to alpha(2)-adrenergic receptors in ob/ob mice was significantly decreased in the VMH (38%) and the dorsomedial hypothalamus (17%) relative to lean controls. This decrease was evident in the alpha(2A)- but not the alpha(2BC)-receptor subtype. Scatchard analysis confirmed this decreased density of alpha(2)-receptors in ob/ob mice. Together with earlier studies, these changes in hypothalamic adrenergic receptors support a role for increased hypothalamic NE activity in the development of the metabolic syndrome of ob/ob mice.

Hyperinsulinemia increases norepinephrine metabolism in the ventromedial hypothalamus of rats

Numerous studies have implicated increased ventromedial hypothalamic (VMH) norepinephrine (NE) activity as a contributing factor to the obese, hyperinsulinemic, glucose intolerant condition. However, factors contributing to the increased VMH NE activity remain unknown. This study therefore investigated in normal rats the effect of a hyperinsulinemic-euglycemic clamp on VMH monoamine turnover and utilization via simultaneous VMH microdialysis to establish a role for hyperinsulinemia in the stimulation of VMH NE activity. Within 20 min of initiation of the hyperinsulinemic-euglycemic clamp, VMH extracellular methoxyhydroxy phenylglycol (metabolite of NE) level increased by 54% and remained approximately at this level for the 100 min duration of the clamp relative to control values (p<0.05). Hyperinsulinemia did not affect VMH dopamine or serotonin metabolism. Subsequent establishment of a hyperinsulinemic-hypoglycemic camp did not alter the VMH monoamine metabolism profile relative to the hyperinsulinemic-euglycemic clamp. Infusion of saline (as control) in a separate group of rats over the entire clamp period induced no changes in any monoamine metabolic profile relative to baseline. Hyperinsulinemia can feedback to stimulate VMH NE activity and, as a result, may contribute to the initiation and/or perpetuation of the obese, hyperinsulinemic, glucose-intolerant state.

Chronic infusion of norepinephrine into the VMH of normal rats induces the obese glucose-intolerant state

Increases in ventromedial hypothalamic (VMH) norepinephrine (NE) levels and/or activities have been observed in a variety of animal models of the obese insulin-resistant condition. This study examined the metabolic effects of chronic NE infusion (25 nmol/h) into the unilateral VMH of normal rats. Within 4 days, VMH NE infusion significantly increased plasma insulin (140%), glucagon (45%), leptin (300%), triglyceride (100%), abdominal fat pad weight (50%), and white adipocyte lipogenic (100%) and lipolytic (100%) activities relative to vehicle-infused rats. Furthermore, isolated islet insulin secretory response to glucose (15 mM) within 4 days of such treatment was increased over twofold (P < 0.05). Among treated animals, fat stores continued to increase over time and plateaued at approximately 2 wk (3-fold increase), remaining elevated to the end of the study (5 wk). By week 4 of treatment, NE infusion induced glucose intolerance as evidenced by a 32% increase in plasma glucose total area under the glucose tolerance test curve (P < 0.01). Whole body fat oxidation rate measured after 5 wk of infusion was significantly increased among treated animals as evidenced by a reduced respiratory quotient (0.87 +/- 0.01) relative to controls (0. 90 +/- 0.01). VMH NE infusion induced hyperphagia (30%) only during the first week and did not affect body weight over the 5-wk period. Increases in VMH NE activity that are common among obese insulin-resistant animal models can cause the development of this obese glucose-intolerant (metabolic) syndrome.