Synergism between insulin and low concentrations of isoproterenol in the stimulation of leptin release by cultured human adipose tissue

Influence of intermittent fasting on autophagy in the liver

Studies have found that intermittent fasting (IF) can prevent diabetes, cancer, heart disease, and neuropathy, while in humans it has helped to alleviate metabolic syndrome, asthma, rheumatoid arthritis, Alzheimer's disease, and many other disorders. IF involves a series of coordinated metabolic and hormonal changes to maintain the organism's metabolic balance and cellular homeostasis. More importantly, IF can activate hepatic autophagy, which is important for maintaining cellular homeostasis and energy balance, quality control, cell and tissue remodeling, and defense against extracellular damage and pathogens. IF affects hepatic autophagy through multiple interacting pathways and molecular mechanisms, including adenosine monophosphate (AMP)-activated protein kinase (AMPK), mammalian target of rapamycin (mTOR), silent mating-type information regulatory 2 homolog-1 (SIRT1), peroxisomal proliferator-activated receptor alpha (PPARα) and farnesoid X receptor (FXR), as well as signaling pathways and molecular mechanisms such as glucagon and fibroblast growth factor 21 (FGF21). These pathways can stimulate the pro-inflammatory cytokines interleukin 6 (IL-6) and tumor necrosis factor α (TNF-α), play a cytoprotective role, downregulate the expression of aging-related molecules, and prevent the development of steatosis-associated liver tumors. By influencing the metabolism of energy and oxygen radicals as well as cellular stress response systems, IF protects hepatocytes from genetic and environmental factors. By activating hepatic autophagy, IF has a potential role in treating a variety of liver diseases, including non-alcoholic fatty liver disease, drug-induced liver injury, viral hepatitis, hepatic fibrosis, and hepatocellular carcinoma. A better understanding of the effects of IF on liver autophagy may lead to new approaches for the prevention and treatment of liver disease.

Blocking β-adrenergic signaling attenuates reductions in circulating leptin, cancellous bone mass, and marrow adiposity seen with dietary energy restriction

We tested whether β-adrenergic blockade attenuates bone loss and increased marrow adiposity during energy restriction (ER) and whether such an effect is associated with changes in serum leptin and leptin expression in bone and marrow tissues. Female 4-mo-old Sprague-Dawley rats were assigned into four groups (n = 10 each): two groups of 40% ER treated with vehicle (ERVEH; saline) or β-blocker (ERBB; DL-propranolol; 250 μg · kg(-1) · h(-1)) during 12 wk, and two groups of ad libitum-fed controls treated with the same two agents (CONVEH, CONBB, respectively). Over 84 days, CONVEH and CONBB rats gained but ERVEH and ERBB rats lost body fat mass; lean mass did not change in any group. Reduction in serum leptin in ERVEH rats was mitigated in ERBB rats (-5.32 vs. -1.15 ng/ml, respectively). The decline in proximal tibia cancellous vBMD observed in ERVEH rats was attenuated in ERBB rats (-85.24 vs. -53.94 mg/cm(3), respectively). Adipocyte number in ERVEH rats was dramatically higher vs. CON rats at week 12, but this increment was abolished by β-blockade in ERBB animals. The number of osteoblastic cells and marrow adipocytes staining positively for leptin in ERVEH rats tended to be lower vs. that of both CON groups, but β-blockade appears to reverse this effect in ERBB rats. In summary, β-adrenergic blockade mitigated metaphyseal bone loss and bone marrow adiposity during energy restriction and attenuated reductions in serum leptin. These data suggest an important role for β-adrenoreceptor signaling pathway in the cancellous bone and marrow fat response to energy restriction.

Dopamine receptors in human adipocytes: expression and functions

Introduction

Dopamine (DA) binds to five receptors (DAR), classified by their ability to increase (D1R-like) or decrease (D2R-like) cAMP. In humans, most DA circulates as dopamine sulfate (DA-S), which can be de-conjugated to bioactive DA by arylsulfatase A (ARSA). The objective was to examine expression of DAR and ARSA in human adipose tissue and determine whether DA regulates prolactin (PRL) and adipokine expression and release.

Methods

DAR were analyzed by RT-PCR and Western blotting in explants, primary adipocytes and two human adipocyte cell lines, LS14 and SW872. ARSA expression and activity were determined by qPCR and enzymatic assay. PRL expression and release were determined by luciferase reporter and Nb2 bioassay. Analysis of cAMP, cGMP, leptin, adiponectin and interleukin 6 (IL-6) was done by ELISA. Activation of MAPK and PI3 kinase/Akt was determined by Western blotting.

Results

DAR are variably expressed at the mRNA and protein levels in adipose tissue and adipocytes during adipogenesis. ARSA activity in adipocyte increases after differentiation. DA at nM concentrations suppresses cAMP, stimulates cGMP, and activates MAPK in adipocytes. Acting via D2R-like receptors, DA and DA-S inhibit PRL gene expression and release. Acting via D1R/D5R receptors, DA suppresses leptin and stimulates adiponectin and IL-6 release.

Conclusions

This is the first report that human adipocytes express functional DAR and ARSA, suggesting a regulatory role for peripheral DA in adipose functions. We speculate that the propensity of some DAR-activating antipsychotics to increase weight and alter metabolic homeostasis is due, in part, to their direct action on adipose tissue.

Thirty years of personal experience in hyperglycemic crises: diabetic ketoacidosis and hyperglycemic hyperosmolar state

CONTEXT

Diabetic ketoacidosis (DKA) and hyperglycemic hyperosmolar state (HHS) cause major morbidity and significant mortality in patients with diabetes mellitus. For more than 30 yr, our group, in a series of prospective, randomized clinical studies, has investigated the pathogenesis and evolving strategies of the treatment of hyperglycemic crises. This paper summarizes the results of these prospective studies on the management and pathophysiology of DKA.

SETTING

Our earliest studies evaluated the comparative efficacy of low-dose vs. pharmacological amounts of insulin and the use of low-dose therapy by various routes in adults and later in children. Subsequent studies evaluated phosphate and bicarbonate therapy, lipid metabolism, ketosis-prone type 2 patients, and use of rapid-acting insulin analogs as well as leptin status, cardiac risk factors, proinflammatory cytokines, and the mechanism of activation of T lymphocytes in hyperglycemic crises.

MAIN OUTCOME

The information garnered from these studies resulted in the creation of the 2001 American Diabetes Association (ADA) technical review on DKA and HHS as well as the ADA Position and Consensus Paper on the therapy for hyperglycemic crises.

CONCLUSIONS

Areas of future research include prospective randomized studies to do the following: 1) establish the efficacy of bicarbonate therapy in DKA for a pH less than 6.9; 2) establish the need for a bolus insulin dose in the initial therapy of DKA; 3) determine the pathophysiological mechanisms for the absence of ketosis in HHS; 4) investigate the reasons for elevated proinflammatory cytokines and cardiovascular risk factors; and 5) evaluate the efficacy and cost benefit of using sc regular insulin vs. more expensive insulin analogs on the general ward for the treatment of DKA.

Pinealectomy alters adipose tissue adaptability to fasting in rats

This study investigated the effects of pinealectomy and fasting on rat adipose tissue metabolism, as well as on profiles of the hormones directly involved in its regulation (insulin, leptin, and corticosterone). Pinealectomized (PINX) and sham-operated (CONTROL) adult male Wistar rats were killed 6 weeks after surgery, in either fed or fasted (12 and 36 hours) states. Blood samples (for glucose and hormone determinations) and peri-epididymal adipocytes (for in vitro insulin-stimulated glucose uptake, oxidation, and incorporation into lipids) were collected. Pineal ablation decreased insulin-stimulated glucose uptake in adipocytes of both fed and fasted animals without affecting insulin-binding capacity. Pinealectomy attenuated the reduction in the ability to oxidize glucose in both basal and insulin-stimulated states during fasting. This alteration in the ability of adipocytes to oxidize glucose appeared together with a decrease in insulin-induced glucose incorporation into lipids in PINX animals. Additionally, pinealectomized rats showed higher corticosterone levels in both fed and fasted states, and a lower leptinemia with 36 hours of fasting, in comparison to CONTROLs. In conclusion, our data reinforce the hypothesis that the pineal gland has a role in the modulation of adipocyte metabolism, and its absence alters metabolic adaptation to fasting in rats.

Dual effects of pituitary adenylate cyclase-activating polypeptide and isoproterenol on lipid metabolism and signaling in primary rat adipocytes

Pituitary adenylate cyclase-activating peptide (PACAP) is a neuropeptide that exerts its effects throughout the body by elevating the intracellular amounts of cAMP. In adipocytes, an increased amount of cAMP is associated with increased lipolysis. In this work we evaluated the effects of PACAP38 on triglyceride metabolism in primary rat adipocytes. Stimulation of adipocytes with PACAP (0.1-100 nm) resulted in stimulation of lipolysis to the same extent as isoproterenol. Lipolysis was blocked by 25 microm of the protein kinase A inhibitor H-89 and potentiated in the presence of 10 microm OPC3911, a phosphodiesterase 3 inhibitor. In addition, PACAP38 induced activation of protein kinase A. Insulin efficiently inhibited PACAP38-induced lipolysis in a phosphatidyl inositol 3-kinase and phosphodiesterase 3-dependent manner. Interestingly, we also found that PACAP38, as well as isoproterenol, induced potentiation of lipogenesis in the presence of insulin. These results show that PACAP38 and isoproterenol mediate catabolic as well as anabolic effects in adipocytes, depending on the concentration of insulin present. We speculate that in the early postprandial state and during fasting, when insulin levels are low, PACAP and beta-adrenergic catecholamines induce lipolysis, whereas when higher levels of insulin are present, these agents potentiate the anabolic effect of insulin, i.e. storage of triglycerides.

Regulation of leptin release by insulin, glucocorticoids, G(i)-coupled receptor agonists, and pertussis toxin in adipocytes and adipose tissue explants from obese humans in primary culture

The basal release of leptin by adipocytes from massively obese human subjects incubated for 48 hours in serum-free suspension culture was comparable to that by explants of subcutaneous adipose tissue from the same obese individuals. There was no stimulation due to dexamethasone or insulin alone of leptin release by adipocytes. However, the combination of insulin and dexamethasone doubled leptin release by adipocytes. The release of leptin was also stimulated by agonists of G(i)-coupled receptors (prostaglandin E(2) [PGE(2)], brimonidine [an alpha(2) catecholamine agonist] and cyclopentyladenosine [CPA]) in the presence of dexamethasone. Leptin release by these agents was further enhanced by insulin in both adipocytes and adipose tissue. Pertussis toxin, which irreversibly inactivates G(i) heterotrimers, inhibited leptin release and abolished the stimulatory effects of G(i)-coupled receptor agonists. However, pertussis toxin did not block the stimulation of leptin release by insulin in either adipose tissue or adipocytes. These data indicate that the release of leptin by human adipocytes cultured for 48 hours in a serum-free medium is comparable to that by explants of adipose tissue except that dexamethasone stimulation of leptin release requires the presence of insulin.

Effects of Trecadrine, a beta3-adrenergic agonist, on leptin secretion, glucose and lipid metabolism in isolated rat adipocytes

OBJECTIVE

Leptin, a hormone produced in adipocytes, is a key signal in the regulation of food intake and energy expenditure. Beta-adrenergic agonists have been shown to inhibit leptin gene expression and leptin secretion. The mechanisms underlying the inhibitory effects of beta-adrenergic agonists have not been established. In this study, we examined the effects of Trecadrine, a novel beta3-adrenergic agonist, on basal and insulin-stimulated leptin secretion in isolated rat adipocytes. Because insulin-stimulated glucose metabolism is an important regulator of leptin expression and secretion by the adipocytes, the effects of Trecadrine on indices of adipocyte metabolism were also examined.

MEASUREMENTS

Isolated adipocytes were incubated with Trecadrine (10(-8)-10(-4) M) in the absence or presence of insulin (1.6 nM). Leptin secretion, glucose utilization, lactate production, glucose incorporation into CO(2) and triglyceride, as well as lipolysis (glycerol release) were determined.

RESULTS

Trecadrine induced a concentration-dependent inhibition of basal leptin secretion. Trecadrine also decreased insulin-stimulated leptin secretion; however, the effect was not as pronounced as in the absence of insulin. Treatment of adipocytes with Trecadrine increased basal glucose utilization and produced a further increase in insulin-stimulated glucose utilization. Basal lactate production was also increased by Trecadrine; however, the proportion (percentage) of glucose carbon released as lactate was unaffected. In the presence of insulin, absolute lactate production was unaffected by Trecadrine at 96 h. However, the percentage of glucose carbon released as lactate was significantly decreased by insulin treatment, and was further decreased by the co-treatment with Trecadrine. Trecadrine induced a dose-dependent increase of the absolute amount of glucose incorporated into triglyceride. However, the percentage of glucose utilized that was incorporated into triglyceride was unaffected by Trecadrine. Trecadrine did not modify the proportion of glucose utilized that was oxidized to CO(2). Trecadrine increased glycerol release after 96 h of treatment. Glycerol release was negatively correlated with leptin secretion.

CONCLUSIONS

These results suggest that alterations of glucose metabolism are not directly involved in the effects of beta3-adrenergic agonists to inhibit leptin expression and secretion. The inverse relationship between leptin secretion and the increase of glycerol levels, which is an index of the activation of cAMP-dependent protein kinases, suggests that activation of the cAMP signaling pathway mediates the inhibitory effects of Trecadrine on leptin gene expression and secretion.

Effects of a beta3-adrenergic agonist on glucose uptake and leptin expression and secretion in cultured adipocytes from lean and overweight (cafeteria) rats

The increase in body and white adipose tissue weights induced by a high-fat diet were prevented by treatment with the beta3-adrenergic agonist Trecadrine. Plasma insulin levels were slightly elevated in overweight rats, while a decrease was observed in Trecadrine-treated groups. Insulin-dependent glucose uptake was impaired in adipocytes of the overweight rats in relation to lean animals. The beta3-adrenergic agonist induced an increase in insulin-stimulated glucose uptake by adipocytes as compared to the nontreated animals. In fact, Trecadrine treatment was able to restore to control values the impairment in insulin-mediated glucose uptake induced by the cafeteria diet, suggesting that Trecadrine prevents the development of insulin resistance in overweight animals. Basal leptin secretion was increased in adipocytes of the overweight rats in relation to lean animals. Trecadrine treatment induced a decrease in basal leptin secretion compared to the untreated animals. Insulin-stimulated leptin secretion reached similar levels in adipocytes of the overweight rats as in lean animals. There was a trend for insulin-induced leptin secretion to be lower at 24 h in Trecadrine-treated rats, but it did not reach statistical significance. In conclusion, adipocytes of diet-induced overweight animals have a higher basal leptin secretion, which is reduced by treatment with Trecadrine. However, neither the cafeteria diet nor the Trecadrine treatment significantly alters the ability of adipocytes to increase leptin secretion in response to insulin.

Regulation of leptin release by troglitazone in human adipose tissue

In pieces of human subcutaneous adipose tissue incubated in primary culture for 48 hours, the release of leptin was stimulated by 50% in the presence of 3.3 micromol/L troglitazone. Insulin (0.1 nmol/L) and dexamethasone (200 nmol/L) stimulated leptin release by 30% and 300%, respectively. Troglitazone in combination with either insulin or dexamethasone had no effect on leptin release. Instead, troglitazone inhibited leptin release in the presence of both dexamethasone and insulin. The stimulatory effect of troglitazone on leptin release was also mimicked by 1 micromol/L 15-deoxy-delta(12-14)prostaglandin J2 (dPGJ2). However, if the concentration of dPGJ2 was increased to 10 micromol/L in the presence of dexamethasone, there was a decrease in leptin release, as well as of lactate formation and lipolysis. These data indicate that both stimulatory and inhibitory effects of troglitazone and dPGJ2 can be seen on leptin release by human adipose tissue.