Evidence for marked sensitivity to the antilipolytic action of insulin in obese maturity-onset diabetics.

Changes in plasma free fatty acids (FFA) observed during oral glucose tolerance tests in 12 obese maturity-onset diabetic Pima Indians with insulin response to oral glucose averaging only 7 ± 19 μU/ml above fasting were compared to those of 11 obese nondiabetic Pima Indians and 10 obese nondiabetic Caucasions who had mean insulin responses of 252 ± 34 and 73 ± 18 μU/ml, respectively. Fasting free fatty acid levels in the diabetics were higher, but they showed decreases similar to controls (278 ± 55 versus 284 ± 32 for nondiabetic Pima controls and 262 ± 43 μeq/liter below fasting for nondiabetic Caucasions). Plasma glycerol levels showed decreases parallel to those of free fatty acids, indicating that the FFA changes in the diabetics were attributable to inhibition of lipolysis rather than to increased removal. During intravenous glucose tolerance tests (IVGTT) in these diabetics, insulin levels decreased initially and there was no decline in FFA. In a second group of less severe diabetics (N = 6), whose increments in insulin during intravenous glucose tolerance tests averaged 15 ± 4.1 μU/ml above fasting, FFA decreases were again comparable to Pima and Caucasion nondiabetics (214 ± 53, 234 ± 37, and 183 ± 51 μeq/liter below fasting, respectively). These findings demonstrate marked sensitivity to the antilipolytic effects of insulin in individuals considered to be resistant to its glucose-lowering action.     

Glycosylphosphatidylinositol-anchored proteins coordinate lipolysis inhibition between large and small adipocytes

In response to palmitate, the antidiabetic sulfonylurea drug glimepiride, phosphoinositoglycans, or H₂O₂, the release of the glycosylphosphatidylinositol-anchored and cyclic adenosine monophosphate-degrading phosphodiesterase Gce1 from adipocytes into small vesicles (adiposomes) and its translocation from adiposomes to cytoplasmic lipid droplets (LD) of adipocytes have been reported. Here the role of Gce1-harboring adiposomes in coordinating lipolysis between differently sized adipocytes was studied. Separate or mixed populations of isolated epididymal rat adipocytes of small and large size and native adipose tissue pieces from young and old rats were incubated with exogenous adiposomes or depleted of endogenous adiposomes and then analyzed for translocation of Gce1 and lipolysis in response to above antilipolytic stimuli. Large compared with small adipocytes are more efficient in releasing Gce1 into adiposomes but less efficient in translocating Gce1 from adiposomes to LDs. Maximal lipolysis inhibition by above antilipolytic stimuli, but not by insulin, was observed with mixed populations of small and large adipocytes (1:1 to 1:2) rather than with separate populations. In mixed adipocyte populations and adipose tissue pieces from young, but not old, rats, lipolysis inhibition by above antilipolytic stimuli, but not by insulin, was dependent on the function of Gce1-harboring adiposomes. Inhibition of lipolysis in rat adipose tissue in response to palmitate, glimepiride, and H₂O₂ is coordinated via the release of adiposome-associated and glycosylphosphatidylinositol-anchored Gce1 from large “donor” adipocytes and their subsequent translocation to the LDs of small “acceptor” adipocytes. This transfer of antilipolytic information may be of pathophysiologic relevance.     

Mechanisms of metformin inhibiting lipolytic response to isoproterenol in primary rat adipocytes

The mobilization of free fatty acids (FFA) from adipose tissue to the bloodstream primarily depends on triacylglycerol lipolysis in adipocytes. Catecholamines are major hormones that govern lipolysis through elevating cellular cAMP production and activating protein kinase, cAMP dependent, catalytic, alpha (PKA) and mitogen-activated protein kinase 1/2 (MAPK1/3). Obesity and type 2 diabetes are associated with elevated levels of systemic FFA, which restricts glucose utilization and induces insulin resistance. The biguanide metformin exerts its antihyperglycemic effect by enhancing insulin sensitivity, which is associated with decreased levels of circulating FFA. In this study, we examined the characteristics and basis of the inhibitory effect of metformin on adrenergic-stimulated lipolysis in primary rat adipocytes. We measured the release of FFA and glycerol as an index of lipolysis and examined the major signalings of the lipolytic cascade in primary rat adipocytes. Metformin at 250-500 microM efficiently attenuated FFA and glycerol release from the adipocytes stimulated with 1 microM isoproterenol. To elucidate the basis for this antilipolytic action, we showed that metformin decreased cellular cAMP production, reduced the activities of PKA and MAPK1/3, and attenuated the phosphorylation of perilipin during isoproterenol-stimulated lipolysis. Further, metformin suppressed isoproterenol-promoted lipase activity but did not affect the translocation of lipase, hormone-sensitive from the cytosol to lipid droplets in adipocytes. This study provides evidence that metformin acts on adipocytes to suppress the lipolysis response to catecholamine. This antilipolytic effect could be a cellular basis for metformin decreasing plasma FFA levels and improving insulin sensitivity.     

Evidence of insulin resistant lipid metabolism in adipose tissue in familial combined hyperlipidemia,but not type 2 diabetes mellitus

In patients with familial combined hyperlipidemia (FCHL) and type 2 diabetes (DM2) organ-specific differences in insulin resistance may exist. In FCHL and DM2 in vivo insulin mediated muscle glucose uptake and inhibition of lipolysis were studied by euglycemic hyperinsulinemic clamp. Insulin mediated glucose uptake was impaired to the same extent in both FCHL and DM2. Only FCHL subjects showed no reduction in plasma glycerol concentrations during insulin infusion and incomplete suppression of plasma free fatty acid (FFA) concentrations combined. This finding indicated that insulin-induced suppression of lipolysis, or glycerol/FFA utilization, or both, were impaired in FCHL, in contrast to DM2 or control subjects. To analyze these possibilities in more detail, control, FCHL, and DM2 adipocytes were studied in vitro. In contrast to adipocytes from DM2 or control subjects, no reduction in medium FFA concentration was detected with FCHL adipocytes after incubation with insulin. This finding indicated impaired intracellular FFA utilization, most likely impaired FFA re-esterification. Genetic linkage analysis in 18 Dutch families with FCHL revealed no evidence for involvement of LIPE, the hormone sensitive lipase gene, indicating that genetic variation in adipocyte lipolysis by LIPE is not the key defect in FCHL. In conclusion, FCHL as well as DM2 subjects exhibited in vivo insulin resistance to glucose disposal, which occurs mainly in muscle. FCHL subjects showed insulin resistant adipose tissue lipid metabolism, in contrast to DM2 and controls. The different pattern of organ-specific insulin resistance in FCHL versus DM2 advances our understanding of differences and similarities in phenotypes between these disorders.     

DPP-IV inhibition enhances the antilipolytic action of NPY in human adipose tissue

Context: Dipeptidyl peptidase IV (DPP‐IV) inactivates the incretin hormone glucagon‐like peptide. It can also affect the orexigenic hormone neuropeptide Y (NPY_1–36) which is truncated by DPP‐IV to NPY_3–36, as a consequence NPY’s affinity changes from receptor Y1, which mediates the antilipolytic function of NPY, to other NPY receptors. Little is known whether DPP‐IV inhibitors for the treatment of type 2 diabetic (T2DM) patients could influence these pathways. Aims: To investigate the in vitro effects of NPY with DPP‐IV inhibition in isolated abdominal subcutaneous (AbdSc) adipocytes on fat metabolism, and assessment of NPY receptor and DPP‐IV expression in adipose tissue (AT). Methods: Ex vivo human AT was taken from women undergoing elective surgery (body mass index: 27.5 (mean ± s.d.) ± 5 kg/m², age: 43.7 ± 10 years, n = 36). Isolated AbdSc adipocytes were treated with human recombinant (rh)NPY (1–100 nM) with and without DPP‐IV inhibitor (1 M); glycerol release and tissue distribution of DPP‐IV, Y1 and Y5 messenger RNA (mRNA) were measured and compared between lean and obese subjects. Results and conclusion: rhNPY reduced glycerol release, an effect that was further enhanced by co‐incubation with a DPP‐IV inhibitor [control: 224 (mean ± s.e.) ± 37 μmol/l; NPY, 100 nM: 161 ± 27 μmol/l**; NPY 100 nM/DPP‐IV inhibitor, 1 M: 127 ± 14 μmol/l**; **p < 0.01, n = 14]. DPP‐IV was expressed in AbdSc AT and omental AT with relative DPP‐IV mRNA expression lower in AbdSc AT taken from obese [77 ± 6 signal units (SU)] vs. lean subjects (186 ± 29 SU*, n = 10). Y1 was predominantly expressed in fat and present in all fat depots but higher in obese subjects, particularly the AbdSc AT‐depot (obese: 1944 ± 111 SU vs. lean: 711 ± 112 SU**, n = 10). NPY appears to be regulated by AT‐derived DPP‐IV. DPP‐IV inhibitors augment the antilipolytic effect of NPY in AT. Further studies are required to show whether this explains the lack of weight loss in T2DM patients treated with DPP‐IV inhibitors.     

Lowering plasma free fatty acids with Acipimox mimics the antidiabetic effects of the beta 3-adrenergic agonist CL-316243 in obese Zucker diabetic fatty rats

We previously reported that long-term treatment of Zucker diabetic fatty (ZDF) rats with the selective beta(3) agonist CL-316243 normalizes glycemia, decreases plasma free fatty acids (FFA) concentration, improves insulin responsiveness, and increases glucose uptake, not only in brown and white adipose tissues, but also in skeletal muscles. Because muscles do not express typical beta(3) adrenoceptors, we postulated that the muscle effect was indirect and that it was possibly mediated by an activation of the glucose-fatty acid cycle. To test this hypothesis, we investigated the effects of Acipimox, a potent inhibitor of lipolysis in adipose tissue. Similar to CL-316243, Acipimox (150 mg/kg orally) markedly decreased plasma FFA, glucose, and insulin concentrations and improved glucose tolerance while reducing the insulin response in obese (350 to 400 g) ZDF rats. Plasma FFA concentrations were significantly correlated with plasma glucose and insulin concentrations (r =.72 and.83, respectively; P <.01), indicating strong metabolic relationships between these parameters. Euglycemic-hyperinsulinemic clamps combined with the 2-[(3)H]deoxyglucose method revealed that Acipimox markedly improved insulin responsiveness and significantly increased glucose uptake (Rg') in the diaphragm, the heart, and various skeletal muscles. Unlike CL-316243, Acipimox did not increase glucose use in brown or white adipose tissues. This selectivity shows that it is possible to improve diabetes in obese ZDF rats without necessarily stimulating thermogenesis in adipose tissues. Thus, decreasing plasma FFA with 2 drugs (Acipimox or CL-316243) that act via different mechanisms (acute inhibition of lipolysis or chronic stimulation of FFA oxidation) is associated with increased glucose uptake in muscles and enhanced insulin responsiveness. These observations support the hypothesis that CL-316243 may indirectly stimulate glucose uptake in muscles of type II diabetic rats by first stimulating brown adipose tissue (increasing uncoupling protein content and fatty acid oxidation) and progressively decreasing the levels of circulating FFA, resulting in activation of the glucose-fatty acid cycle or other mechanisms regulating insulin responsiveness in skeletal muscles.     

W-5 and quin 2-AM reverse the inhibitory effect of insulin on lipolysis due to dibutyryl cAMP.

The effects of W-5, a weak calmodulin antagonist, and quin 2-AM, a cell permeant calcium chelator, on lipolysis and antilipolytic activity of insulin were studied in isolated rat adipocytes. We have previously shown that W-7, a strong calmodulin antagonist, suppresses the inhibitory effect of insulin on lipolysis due to dibutyryl cAMP (Bt2cAMP) in a dose-dependent manner [H. Goko, A. Matsuoka, Diabetes Res. Clin. Prac. 19 (1993) 177-181] and verapamil, a calcium antagonist, potentiates lipolysis due to Bt2cAMP. Like W-7, W-5 suppressed the antilipolytic action of insulin on lipolysis due to Bt2cAMP in a dose-dependent manner. However, when lipolysis was potentiated with 3-isobutyryl-1-methylxanthine (IBMX), W-5 did not suppress the antilipolytic action of insulin. At the same time, like verapamil, W-5 also potentiated lipolysis due to Bt2cAMP in a dose-dependent manner. Thus W-5 has the pharmaceutical effects of both W-7 and verapamil. The chelation of intracellular Ca2+ in adipocytes with quin 2-AM also produced a dose-dependent potentiation of lipolysis due to Bt2cAMP and suppression of the antilipolytic action of insulin on lipolysis due to Bt2cAMP. These effects of quin 2-AM are the same as those of W-5. Therefore, our results suggest that the cytoplasmic Ca2+ plays a pivotal role in mediating the potentiation of lipolysis and antilipolytic action of insulin when lipolysis is induced by Bt2cAMP in rat adipocytes and that W-5 appears to exert its pharmaceutical effects through the inhibition of intracellular calcium-dependent steps other than calmodulin.     

Effects of age and adenosine in the modulation of insulin action on rat adipocyte metabolism

The age-related declines in the antilipolytic and lipogenic actions of insulin were studied in adipocytes from rats aged 2, 6, 12, and 24 months. Since adenosine modulates insulin action, its concentration was controlled by treatment of adipocytes with adenosine deaminase and addition of the non-metabolizable adenosine analog, N6-[(R)-(-)1-methyl-2-phenethyl] adenosine (PIA). Inhibition of isoproterenol-stimulated lipolysis by PIA increased significantly by 6 months of age. Decreasing the concentration of PIA rendered the adipocytes from the 6-, 12-, and 24-mo-old rats less sensitive to the antilipolytic effect of insulin. Basal and insulin-stimulated lipogenesis decreased with aging. PIA increased insulin-stimulated lipogenesis at 0.2 ng/ml insulin only in the 2-month-old rats. PIA reduced insulin-stimulated lipogenesis at higher insulin doses in the oldest rats. These results suggest that aging causes quantitative declines in maximal lipolysis and basal and maximal lipogenesis. Maturation may cause a decline in sensitivity to insulin, but adenosine in sufficient concentration reverses the acquired resistance to the antilipolytic effect of insulin.     

Metformin reduces lipolysis in primary rat adipocytes stimulated by tumor necrosis factor-alpha or isoproterenol

In patients with type 2 non-insulin-dependent diabetes mellitus (NIDDM), the biguanide, metformin, exerts its antihyperglycemic effect by improving insulin sensitivity, which is associated with decreased level of circulating free fatty acids (FFA). The flux of FFA and glycerol from adipose tissue to the blood stream primarily depends on the lipolysis of triacylglycerols in the adipocytes. Adipocyte lipolysis is physiologically stimulated by catecholamine hormones. Tumor necrosis factor-alpha (TNF-alpha), a cytokine largely expressed in adipose tissue, stimulates chronic lipolysis, which may be associated with increased systemic FFA and insulin resistance in obesity and NIDDM. In this study, we examined the role of metformin in inhibiting lipolytic action upon various lipolytic stimulations in primary rat adipocytes. Treatment with metformin attenuated TNF-alpha-mediated lipolysis by suppressing phosphorylation of extracellular signal-related kinase 1/2 and reversing the downregulation of perilipin protein in TNF-alpha-stimulated adipocytes. The acute lipolytic response to adrenergic stimulation of isoproterenol was also restricted by metformin. A high concentration of glucose in the adipocyte culture promoted the basal rate of glycerol release and significantly enhanced the lipolytic action stimulated by either TNF-alpha or isoproterenol. Metformin not only inhibits the basal lipolysis simulated by high glucose, but also suppresses the high glucose-enhanced lipolysis response to TNF-alpha or isoproterenol. The antilipolytic action in adipocytes could be the mechanism by which cellular action by metformin reduces systemic FFA concentration and thus improves insulin sensitivity in obese patients and the hyperglycemic conditions of NIDDM.     

Regional differences in triglyceride breakdown in human adipose tissue: effects of catecholamines, insulin, and prostaglandin E2

Regional variation of adipose tissue triglyceride breakdown (lipolysis) has been suggested to play a role for the health consequences of some forms of obesity. Thus, in the present study we investigated the regulation of lipolysis in isolated adipocytes obtained from different fat depots in females. Intra-abdominal adipose tissue (omental) and subcutaneous abdominal adipose tissue were obtained from the same individuals undergoing abdominal surgery (n = 9); in addition, adipocytes from the subcutaneous gluteal region (n = 12) and from mammary adipose tissue (n = 5) were investigated. The lipolytic/antilipolytic properties of epinephrine (EPI), insulin, clonidine, and prostaglandin E2 (PGE2) were investigated. The most prominent observation was that EPI had none or only minor lipolytic effect in adipocytes from the subcutaneous regions, but significantly enhanced lipolysis by approximately 500% in omental adipocytes (P less than .001). In the presence of the alpha 2-adrenergic antagonist, yohimbine, EPI had similar stimulatory effects (fourfold to fivefold) in all fat depots. The antilipolytic compounds, insulin and clonidine, had greatly reduced antilipolytic properties in omental adipocytes as compared with subcutaneous adipocytes (P less than .01 and P less than .05, respectively). On the other hand, PGE2 had similar antilipolytic properties in adipocytes from the various depots. In conclusion, we found great regional variation in the regulation of lipolysis. Particularly, EPI was much more lipolytic in omental adipocytes than in subcutaneous adipocytes, mainly due to an enhanced functional alpha 2-receptor activity in subcutaneous adipocytes. These in vitro data suggest that free fatty acids (FFA) are more readily mobilized from omental adipose tissue than from subcutaneous adipose tissue.     

Lipolysis and the antilipolytic effect of insulin in adipocytes from rats adapted to a high-protein diet

Free fatty acid (FFA) mobilization during fasting was investigated in rats fed a high-protein, carbohydrate-free (HP) diet (70% casein, 8% fat, wt/wt) or a balanced diet (66% carbohydrate, 17% casein, 8% fat) for 30 to 40 days. In vivo, rats on the HP diet showed reduced rates of plasma FFA increase during fasting. Their blood sugar remained unchanged and was higher than that of control rats 24 hours after removal of food. In the fed state, serum insulin levels were smaller in HP-fed rats but did not differ significantly in the two experimental groups during fasting. In vitro, the rates of glycerol and FFA release by epididymal fat pads obtained from fasted rats were similar in rats consuming the HP diet. Fat cells isolated from rats on the HP diet also had reduced rates of basal lipolysis. Furthermore, they showed a significant increase in responsiveness to the lipolytic action of noradrenaline and an increase in both sensitivity and responsiveness to the inhibitory effect of insulin on noradrenaline-stimulated lipolysis. Adipocytes from HP-fed and control rats had mean diameters of 51 and 60 mu, respectively, and estimated average volumes of 90 and 142 pL. On the basis of existing data on the correlation between size and lipolytic activity of fat cells, the smaller size of the adipocytes from HP-fed rats might account for the lower rate of basal lipolysis but not for the increased response to the hormones. The increased sensitivity of fat cells to the antilipolytic action of insulin may have been an important factor in the reduced lipomobilization during fasting in rats under the high-protein regimen.     

Sensitivity of chicken and rat adiopocytes and hepatocytes to isologous and heterologous pancreatic hormones

Isolated chicken and rat adipocytes and hepatocytes were used to compare chicken vs mammalian pancreatic hormones in regulating glucose and lipid metabolism. Porcine glucagon is twice as potent as chicken glucagon in eliciting lipolysis in both rat and chicken adipocytes. A less but marked bignificant difference exists between the two glucagon hormologs when glucose release by isolated hepatocytes is measured. Chicken adipocytes respond to lower concentrations (1 ng/ml) of glucagon than rat adipocytes (5 ng/ml). Hepatocytes from both animal species responded to glucagon at concentrations of 1 ng/ml. Chicken insulin is slightly more potent than porcine insulin both in inducing glucose utilization and in inhibiting glucagon-stimulated lipolysis in rat adipocytes. Glucose utilization, basal lipolysis, and the rate of glucagon-stimulated lipolysis of the chicken adipocyte are unaltered by insulin concentrations which are 1000 times greater than those required to affect rat adipocytes. The antilipolytic action of avian pancreatic polypeptide (APP) was compared with the bovine homolog of APP, namely bovine pancreatic polypeptide (BPP). BPP is not was effective as APP in inhibiting glucagon-stimulated lipolysis in the chicken adipocyte, and neither APP nor BPP inhibit glucagon-stimulated lipolysis in the rat adipocyte.     

Lipolytic patterns in isolated adipocytes of continuously endotoxemic rats

Lipolytic patterns were studied in adipocytes isolated from rats after 6 and 30 hr of continuous Escherichia coli endotoxin (ET) or saline infusion via a subcutaneously implanted osmotic pump. By 6 hr, ET cells responded to norepinephrine (NE) stimulation with significantly greater increase above basal rates of glycerol and free fatty acid (FFA) release than did control adipocytes. By 30 hr of continuous infusion, basal glycerol release was enhanced; the in vitro lipolytic response evoked by NE was significantly reduced in ET cells compared to rates on the previous day, and NE-stimulated lipolysis in ET cells was significantly below that of controls. At the same time, the in vitro antilipolytic effect of insulin was attenuated. We conclude that 1) an initial metabolic response can be observed within a few hours of a continuous, low dose ET infusion, 2) the biphasic nature of the sequential changes in lipolysis is likely to reflect alterations in the hormonal environment in vivo, and 3) these features are consonant with some aspects of the metabolic profile of septic patients.     

Adipokines in type 1 diabetes after successful pancreas transplantation: normal visfatin and retinol‐binding‐protein‐4, but increased total adiponectin fasting concentrations

Objective In type 1 diabetes mellitus (T1DM), the release of many hormones, not only from beta‐cells, but also from adipocytes (adipokines) may be altered. After successful pancreas–kidney‐transplantation (PKTx), T1DM patients can revert to a nondiabetic metabolism, but it is unclear whether alterations of adipokines are still present after PKTx. Design, patients and measurements Concentrations of adipokines [visfatin, retinol‐binding protein‐4 (RBP‐4), adiponectin, high molecular weight (HMW) adiponectin] were measured at fasting in 10 PKTx and in 19 T1DM. Nondiabetic healthy controls (CON, n = 9) and six nondiabetic patients after kidney transplantation (KTx) were examined as control groups. In PKTx, KTx and CON, indices of insulin sensitivity (OGIS) and beta cell function (adaptation index, AI) were calculated from 75 g oral glucose tolerance test (OGTT) data. Results Fasting serum visfatin (T1DM: 56 ± 4 μg/l, PKTx: 42 ± 6 μg/l, KTx: 39 ± 3 μg/l, CON: 40 ± 3 μg/l) and RBP‐4 (T1DM: 490 ± 26 μg/l, PKTx: 346 ± 39 μg/l, KTx: 401 ± 13 μg/l, CON: 359 ± 36 μg/l) was increased by 40% and 36%, respectively (each P < 0·03) in T1DM only. Levels were positively correlated with HbA1c in all subjects (visfatin: r = 0·43, P < 0·004; RBP‐4: r = 0·46, P < 0·03). Fasting plasma adiponectin was 80% higher in T1DM and in PKTx (T1DM: 18 ± 2 mg/l, PKTx: 18 ± 3 mg/l, KTx: 12 ± 3 mg/l, CON: 10 ± 1 mg/l; P < 0·04) and was positively correlated with diabetes duration (r = 0·37, P < 0·02). HMW/total adiponectin ratio was increased in T1DM (P < 0·02). PKTx displayed a normoglycaemic metabolism as insulin sensitive as CON, but AI was lower than in CON and KT (P < 0·01). Conclusions T1DM after successful PKTx show normal fasting visfatin and RBP‐4 levels and HMW‐adiponectin/adiponectin‐ratio, which are elevated in T1DM, whereas total adiponectin levels are similarly increased in T1DM and PKTx patients.     

Rosiglitazone and pioglitazone similarly improve insulin sensitivity and secretion, glucose tolerance and adipocytokines in type 2 diabetic patients

Objective: We examined the effects of rosiglitazone treatment on profiles of adipocytokines levels, postprandial insulin and glucose excursion, lipids levels, comparing with those of pioglitazone treatment in patients with type 2 diabetes mellitus (T2DM). Methods: Changes in body weight, haemoglobin A_1c (HbA_1c), glucose/insulin/C‐peptide/free fatty acid (FFA) during 75 g oral glucose tolerance test (OGTT), HDL‐/LDL‐cholesterol, triglyceride (TG) and adipocytokines [tumour necrosis factor (TNF)‐α, leptin and adiponectin] were measured in T2DM patients treated with rosiglitazone, 8 mg/day (n = 35), or pioglitazone, 45 mg/day (n = 21), for 3 months. Results: After rosiglitazone or pioglitazone treatment, HbA_1c (8.6–7.2 vs. 8.3–6.9%, rosiglitazone vs. pioglitazone), fasting plasma glucose (190–144 vs. 178–140 mg/dl), fasting FFA (729–595 vs. 641–526 μEq/l), mean plasma glucose‐OGTT (292–229 vs. 285–233 mg/dl) and mean FFA‐OGTT (580–430 vs. 488–377 μEq/l) decreased similarly and all were statistically significant (p < 0.01). The insulinogenic index (ΔI_0–120/ΔG_0–120) (0.19–0.30 vs. 0.17–0.26) and Matsuda index of insulin sensitivity (2.0–3.1 and 2.7–4.3) increased (p < 0.01) similarly, despite increase in body weight (85–88 vs. 81–84 kg). TNF‐α (3.8–3.4 vs. 5.2–4.5 pg/ml) decreased (p < 0.05) and adiponectin (6.3–17.8 vs. 7.1–16.4 μg/ml) increased (p < 0.01), while leptin did not change following either treatment. After rosiglitazone treatment, plasma HDL‐cholesterol (34–38 mg/dl) and LDL‐cholesterol (103–120 mg/dl) increased (p < 0.01), while TGs (177–167 mg/dl) did not change significantly. After pioglitazone treatment, plasma HDL‐cholesterol (34–37 mg/dl) increased (p < 0.05), while LDL‐cholesterol (104–105 mg/dl) did not change and TGs (153–106 mg/dl) decreased (p < 0.01). Conclusions: Rosiglitazone and pioglitazone have similar beneficial effects on glycaemic control insulin sensitivity, insulin secretion and plasma adipocytokine levels. However, pioglitazone has a more beneficial effect on the plasma lipid profile than rosiglitazone.     

Interaction of indomethacin with the antilipolytic effect of prostaglandin E2 in rat adipocytes

The interaction of indomethacin with the antilipolytic effect of prostaglandin E2 (PGE2) was investigated in rat adipocytes in order to reveal a possible role of endogenous PGs in adipose tissue. Adipocytes isolated from rats treated in vivo for 5 days with indomethacin were compared with non-treated control rats. The sensitivity of the antilipolytic effect of exogenous PGE2 was significantly enhanced in adipocytes from indomethacin-treated rats (IC50 of PGE2: 0.45 +/- 0.05 nM vs. 1.2 +/- 0.1 nM, P less than 0.01). This enhanced antilipolytic effect of exogenous PGE2 could be related to the reduced endogenous PGE2 formation in adipocytes from the indomethacin-treated rats (PGE2 formation was reduced by more than 90%). In agreement with that observation the [p3H]PGE2 receptor binding was enhanced by 58% in adipocytes treated with indomethacin. Thus, indomethacin via inhibition of endogenous PG formation could modulate some properties of lipolysis in adipocytes. However, indomethacin treatment had no significant effects on basal or isoproterenol-stimulated lipolysis.     

Melatonin ameliorates low‐grade inflammation and oxidative stress in young Zucker diabetic fatty rats

The aim of this study was to investigate the effects of melatonin on low‐grade inflammation and oxidative stress in young male Zucker diabetic fatty (ZDF) rats, an experimental model of metabolic syndrome and type 2 diabetes mellitus (T2DM). ZDF rats (n = 30) and lean littermates (ZL) (n = 30) were used. At 6 wk of age, both lean and fatty animals were subdivided into three groups, each composed of 10 rats: naive (N), vehicle treated (V), and melatonin treated (M) (10 mg/kg/day) for 6 wk. Vehicle and melatonin were added to the drinking water. Pro‐inflammatory state was evaluated by plasma levels of interleukin‐6 (IL‐6), tumor necrosis factor‐α (TNF‐α), and C‐reactive protein (CRP). Also, oxidative stress was assessed by plasma lipid peroxidation (LPO), both basal and after Fe²⁺/H₂O₂ inducement. ZDF rats exhibited higher levels of IL‐6 (112.4 ± 1.5 pg/mL), TNF‐α (11.0 ± 0.1 pg/mL) and CRP (828 ± 16.0 µg/mL) compared with lean rats (IL‐6, 89.9 ± 1.0, P < 0.01; TNF‐α, 9.7 ± 0.4, P < 0.01; CRP, 508 ± 21.5, P < 0.001). Melatonin lowered IL‐6 (10%, P < 0.05), TNF‐α (10%, P < 0.05), and CRP (21%, P < 0.01). Basal and Fe²⁺/H₂O₂‐induced LPO, expressed as malondialdehyde equivalents (µmol/L), were higher in ZDF rats (basal, 3.2 ± 0.1 versus 2.5 ± 0.1 in ZL, P < 0.01; Fe²⁺/H₂O₂‐induced, 8.7 ± 0.2 versus 5.5 ± 0.3 in ZL; P < 0.001). Melatonin improved basal LPO (15%, P < 0.05) in ZDF rats, and Fe²⁺/H₂O₂‐ induced LPO in both ZL (15.2%, P < 0.01) and ZDF rats (39%, P < 0.001). These results demonstrated that oral melatonin administration ameliorates the pro‐inflammatory state and oxidative stress, which underlie the development of insulin resistance and their consequences, metabolic syndrome, diabetes, and cardiovascular disease.     

Melatonin induces browning of inguinal white adipose tissue in Zucker diabetic fatty rats

Melatonin limits obesity in rodents without affecting food intake and activity, suggesting a thermogenic effect. Identification of brown fat (beige/brite) in white adipose tissue (WAT) prompted us to investigate whether melatonin is a brown‐fat inducer. We used Zücker diabetic fatty (ZDF) rats, a model of obesity‐related type 2 diabetes and a strain in which melatonin reduces obesity and improves their metabolic profiles. At 5 wk of age, ZDF rats and lean littermates (ZL) were subdivided into two groups, each composed of four rats: control and those treated with oral melatonin in the drinking water (10 mg/kg/day) for 6 wk. Melatonin induced browning of inguinal WAT in both ZDF and ZL rats. Hematoxylin–eosin staining showed patches of brown‐like adipocytes in inguinal WAT in ZDF rats and also increased the amounts in ZL animals. Inguinal skin temperature was similar in untreated lean and obese rats. Melatonin increased inguinal temperature by 1.36 ± 0.02°C in ZL and by 0.55 ± 0.04°C in ZDF rats and sensitized the thermogenic effect of acute cold exposure in both groups. Melatonin increased the amounts of thermogenic proteins, uncoupling protein 1 (UCP1) (by ~2‐fold, P < 0.01) and PGC‐1α (by 25%, P < 0.05) in extracts from beige inguinal areas in ZL rats. Melatonin also induced measurable amounts of UCP1 and stimulated by ~2‐fold the levels of PGC‐1α in ZDF animals. Locomotor activity and circulating irisin levels were not affected by melatonin. These results demonstrate that chronic oral melatonin drives WAT into a brown‐fat‐like function in ZDF rats. This may contribute to melatonin′s control of body weight and its metabolic benefits.     

Antilipolytic action of insulin in adipocytes from starved and diabetic rats during adenosine-controlled incubations

Insulin action on adipocytes induces two major metabolic effects: stimulation of glucose transport and inhibition of lipolysis. Previously, we have shown that incubated isolated adipocytes from starved (S), and streptozotocin-treated diabetic (D) rats show insulin resistance on glucose transport. It is not known whether insulin resistance is also present on antilipolysis. In this study the antilipolytic action of insulin was investigated. Since basal lipolysis was low, lipolysis was first stimulated by isoproterenol (ISO). This showed that differences existed in sensitivity for ISO among control (C), S, and D adipocytes. We investigated whether changes in adenosine accumulation could attribute to the differences in ISO action and thereby influence insulin action. When endogenous accumulating adenosine was removed by adenosine deaminase and replaced by a fixed concentration (200 nM) of the nonhydrolyzable adenosine analog phenylisopropyladenosine, the differences in ISO action disappeared. This indicates that the sensitivity of C, S, and D adipocytes for ISO is strongly influenced by endogenous adenosine release. The dose-response relationship between insulin and inhibition of ISO-stimulated lipolysis showed that insulin sensitivity was increased and responsiveness unaltered in S and D compared to C adipocytes for incubations with both uncontrolled and controlled adenosine concentrations. This indicates that during S and D states, endogenous adenosine release has no major effect on insulin action. The increased sensitivity for insulin of S and D adipocytes was paralleled by an increased binding of [125I]iodoinsulin. The unaltered responsiveness for insulin indicates that there is no insulin resistance at the postbinding level for antilipolysis, i.e. intracellular processes for antilipolysis are intact. This is in contrast to glucose transport, where insulin resistance exists at the postbinding level during S and D. Thus, insulin resistance is no general phenomenon, but is confined to specific effector systems.     

Lack of central autonomic regulation of substrate during early fasting in man

To determine whether centrally mediated adrenergic tone modulates lipolysis, ketogenesis, or insulinopenia during starvation, four lean male subjects with complete cervical cord transection and six lean healthy male volunteers were fasted for 48 hr.Plasma glucose and insulin levels decreased to comparable levels in both groups. Plasma free fatty acid (FFA) and β-hydroxybutyrate concentrations rose to peak levels 1.23 ± 0.08 mmoles/liter and 4.2 ± 1.0 mmoles/liter at 36 and 48 hr in normals, respectively. Cord-sectioned subjects had similar peak FFA (1.2 ± 0.12) and β-hydroxybutyrate (5.6 ± 0.3) concentrations. Urinary catecholamine excretion in four normal subjects failed to increase during the fast.Since normal glucose, free fatty acid, β-hydroxybutyrate, and insulin relationships were maintained in sympathectomized subjects, it appears that central adrenergic mechanisms are not essential for initiation of lipolysis, ketonemia, or the hypoinsulinemia of early starvation. These results provide additional evidence that these metabolic events are primarily related to insulinopenia.