Oral 3-hydroxybutyrate ingestion decreases endogenous glucose production, lipolysis, and hormone-sensitive lipase phosphorylation in adipose tissue in men: a human randomized, controlled, crossover trial.

AIMS: To test whether oral administration of D/L-3-hydroxybutyrate as a sodium salt inhibits lipolysis and intracellular lipid signalling, in particular, hormone-sensitive lipase, and whether D/L-3-hydroxybutyrate alters endogenous glucose production. METHODS: We studied six young men in a randomized, controlled, crossover study after ingestion of Na-D/L-3-hydroxybutyrate (hyperketotic condition) or saline (placebo control). We quantified lipolysis and endogenous glucose production using [9,10-3 H]-palmitate and [3-3H]glucose tracers, and adipose tissue biopsies were collected to investigate key lipolytic enzymes. RESULTS: After ingestion, D/L-3-hydroxybutyrate increased by more than 2.5 mmol/l, free fatty acid concentrations decreased by >70%, and palmitate rate of appearance was halved. Protein kinase A phosphorylation of perilipin was reduced and hormone-sensitive lipase 660 phosphorylation in adipose tissue biopsies was 70-80% decreased in the hyperketotic condition and unchanged in the control. Compared to the control, endogenous glucose production was reduced by close to 20% (P<0.05) after 3-hydroxybutyrate ingestion. CONCLUSION: We conclude that oral D/L-Na-3-hydroxybutyrate increases D/L-3-hydroxybutyrate concentrations within half an hour, decreases free fatty acid concentrations, lowers lipolysis and endogenous glucose production, and dephosphorylates hormone-sensitive lipase. Collectively these phenomena may be viewed as an orchestrated feedback loop, controlling endogenous glucose production, lipolysis and ketogenesis. Such effects would be beneficial in insulin-resistant states. (www.clinicaltrials.gov ID number: NCT02917252).

Metformin treatment affects adipocytokine secretion and lipid composition in adipose tissues of diet-induced insulin-resistant rats.

OBJECTIVES: Adipose tissue plays a central role in the pathogenesis of insulin resistance (IR) and type 2 diabetes. However, the molecular changes that promote these diseases are not completely understood. Several studies demonstrated that ceramide (Cer) and diacylglycerol (DAG) accumulation in muscle is associated with IR. The aim of this study was to explain whether a high-fat diet (HFD) leads to bioactive lipid accumulation in adipose tissue and how metformin affects the lipid content in adipocytes and the concentration of plasma adipocytokines. METHODS: The experiments were conducted on male Wistar rats divided into three groups: control, HFD-fed, and HFD-fed and treated with metformin. Cer and DAGs were analyzed by liquid chromatography tandem mass spectrometry. Phosphorylation of hormone-sensitive lipase (HSL) was analyzed by Western blot. Oral glucose tolerance and insulin tolerance tests were also performed. Plasma adiponectin and tumor necrosis factor (TNF)-α concentration were measured by enzyme-linked immunosorbent assay. RESULTS: HFD induced IR and elevated DAGs and Cer content in subcutaneous and visceral adipose tissues, which was accompanied by an increased phosphorylation of HSL. Metformin improved insulin sensitivity, decreased Cer and DAG levels, and attenuated the phosphorylation of HSL in both fat depots. Furthermore, we observed a strong correlation between adiponectin (negative) and TNF-α (positive) and bioactive lipids in both fat tissues. CONCLUSIONS: These results indicated that bioactive lipids accumulation in adipose tissue influences the induction of IR and, at least in part, answered the question of what the insulin-sensitizing effect of metformin at the level of adipose tissue is.

Pik3r1 Is Required for Glucocorticoid-Induced Perilipin 1 Phosphorylation in Lipid Droplet for Adipocyte Lipolysis.

Glucocorticoids promote lipolysis in white adipose tissue (WAT) to adapt to energy demands under stress, whereas superfluous lipolysis causes metabolic disorders, including dyslipidemia and hepatic steatosis. Glucocorticoid-induced lipolysis requires the phosphorylation of cytosolic hormone-sensitive lipase (HSL) and perilipin 1 (Plin1) in the lipid droplet by protein kinase A (PKA). We previously identified Pik3r1 (also called p85α) as a glucocorticoid receptor target gene. Here, we found that glucocorticoids increased HSL phosphorylation, but not Plin1 phosphorylation, in adipose tissue-specific Pik3r1-null (AKO) mice. Furthermore, in lipid droplets, the phosphorylation of HSL and Plin1 and the levels of catalytic and regulatory subunits of PKA were increased by glucocorticoids in wild-type mice. However, these effects were attenuated in AKO mice. In agreement with reduced WAT lipolysis, glucocorticoid- initiated hepatic steatosis and hypertriglyceridemia were improved in AKO mice. Our data demonstrated a novel role of Pik3r1 that was independent of the regulatory function of phosphoinositide 3-kinase in mediating the metabolic action of glucocorticoids. Thus, the inhibition of Pik3r1 in adipocytes could alleviate lipid disorders caused by excess glucocorticoid exposure.

Berberine increases adipose triglyceride lipase in 3T3-L1 adipocytes through the AMPK pathway.

BACKGROUND: Obesity is closely related to the metabolism of triacylglycerol (TG) in adipocytes. Adipose triglyceride lipase (ATGL) and hormone-sensitive lipase (HSL) are rate-limiting enzymes that control the hydrolysis of TG. Effects on ATGL and HSL to increase lipolysis may counteract obesity. Berberine (BBR) is a compound derived from the Chinese medicine plant Coptis chinensis. In the present study we show the effects of BBR on ATGL and HSL and explore the potential underlying mechanisms of these effects. METHODS: The TG content in cells was measured using a colorimetric assay. The expressions of HSL, ATGL and GPAT3 were evaluated by Western-blotting. The expression of ATGL was also evaluated by real-time PCR and radioimmunoassay. Compound C, an inhibitor of AMP-activated protein kinase (AMPK), was used to explore the possible pathway that involved in the effect of BBR on ATGL. RESULTS: TG content of differentiated 3T3-L1 cells was significantly decreased by more than 10% after treated with BBR. In differentiated 3T3-L1 adipocytes, BBR increased the expression of p-HSL and ATGL, and these effects were time-depended (p <0.01). The effect of BBR on ATGL expression could be abolished by Compound C which suggested that AMPK pathway was involved in the effects of BBR on p-HSL and ATGL. CONCLUSIONS: BBR could increase the expression of ATGL and therefore stimulate basal lipolysis in mature adipocytes through the associated mechanisms related to the AMPK pathway.

Tofogliflozin Improves Insulin Resistance in Skeletal Muscle and Accelerates Lipolysis in Adipose Tissue in Male Mice.

Sodium glucose cotransporter 2 inhibitors have attracted attention as they exert antidiabetic and antiobesity effects. In this study, we investigated the effects of tofogliflozin on glucose homeostasis and its metabolic consequences and clarified the underlying molecular mechanisms. C57BL/6 mice were fed normal chow containing tofogliflozin (0.005%) for 20 weeks or a high-fat diet containing tofogliflozin (0.005%) for 8 weeks ad libitum. In addition, the animals were pair-fed in relation to controls to exclude the influence of increased food intake. Tofogliflozin reduced the body weight gain, mainly because of fat mass reduction associated with a diminished adipocyte size. Glucose tolerance and insulin sensitivity were ameliorated. The serum levels of nonesterified fatty acid and ketone bodies were increased and the respiratory quotient was decreased in the tofogliflozin-treated mice, suggesting the acceleration of lipolysis in the white adipose tissue and hepatic ß-oxidation. In fact, the phosphorylation of hormone-sensitive lipase and the adipose triglyceride lipase protein levels in the white adipose tissue as well as the gene expressions related to ß-oxidation, such as Cpt1α in the liver, were significantly increased. The hepatic triglyceride contents and the expression levels of lipogenic genes were decreased. Pair-fed mice exhibited almost the same results as mice fed an high-fat diet ad libitum. Moreover, a hyperinsulinemic-euglycemic clamp revealed that tofogliflozin improved insulin resistance by increasing glucose uptake, especially in the skeletal muscle, in pair-fed mice. Taken together, these results suggest tofogliflozin ameliorates insulin resistance and obesity by increasing glucose uptake in skeletal muscle and lipolysis in adipose tissue.

Cyclopia maculata (honeybush tea) stimulates lipolysis in 3T3-L1 adipocytes.

We have previously, for the first time, demonstrated that hot water extracts of Cyclopia maculata and Cyclopia subternata, endemic South African plants that are consumed as herbal teas, inhibit adipogenesis in 3T3-L1 adipocytes. The aim of this study was to extend the anti-obesity investigations of these plants by quantifying lipolysis in mature 3T3-L1 adipocytes. Glycerol concentration in culture supernatants was used as a marker of adipocyte lipolysis. Isoproterenol, a ß-adrenergic agonist and a known lipolytic agent, was used as a positive control in our assays. Lipolysis was stimulated by all extracts, although statistical significance was noted for fermented (oxidised) C. maculata only. A concentration of 80µg/ml of C. maculata extract induced maximal lipolysis (1.8-fold, p<0.001). The increased lipolysis was accompanied by an increase in the expression of hormone sensitive lipase (1.6-fold, p<0.05) and perilipin (1.6-fold, p<0.05). The plant extracts, at the concentration range assayed (0-100µg/ml), were not cytotoxic in terms of mitochondrial dehydrogenase and adenosine-5'-triphosphate activity. These results showed that C. maculata stimulates lipolysis in mature 3T3-L1 adipocytes, providing further support for the anti-obesity effects of Cyclopia spp.

Influence of large molecular polymeric pigments isolated from fermented Zijuan tea on the activity of key enzymes involved in lipid metabolism in rat.

Influence of large molecular polymeric pigments (LMPP) isolated from fermented Zijuan tea on the activity and mRNA expression of key enzymes involved in lipid metabolism in rat was explored. The results show that intragastric infusion of high-dose LMPP (1.215 g/kg body weight) effectively suppressed the elevation in TC and LDL-C (p<0.05), and prevented the reduction in HDL-C (p<0.05), compared with the hyperlipidemia model group. LMPP significantly enhanced the activity of HL and HSL, and increased the HSL mRNA expression in the liver tissue and adipose tissue. High-LMPP treatment significantly reduced the HMG-CoA reductase expression by 56.5% in the liver compared with hyperlipidemia model group. In contrast, LDL-R expression was increased by 120% in the presence of high-LMPP treatment. These results suggest that LMPP have the hypolipidemic effect to some extent and significantly enhance HSL mRNA expression in the liver and adipose tissue, thereby increasing HSL activity in rat.

Dietary cystine level affects metabolic rate and glycaemic control in adult mice.

Plasma total cysteine (tCys) is strongly and independently associated with obesity in large human cohorts, but whether the association is causal is unknown. Dietary cyst(e)ine increases weight gain in some rodent models. We investigated the body composition, metabolic rate and metabolic phenotype of mature C3H/HeH mice assigned to low-cystine (LC) or high-cystine (HC) diets for 12 weeks. Compared to LC mice, HC mice gained more weight (P=.004 for 12-week weight gain %), with increased fat mass and lean mass, and lowered O2 consumption and CO2 production by calorimetry. The HC mice had 30% increase in intestinal fat/body weight % (P=.003) and ∼twofold elevated hepatic triglycerides (P=.046), with increased expression of hepatic lipogenic factors, peroxisome proliferator-activated receptor-γ and sterol regulatory element binding protein-1. Gene expression of both basal and catecholamine-stimulated lipolytic enzymes, adipose triglyceride lipase and hormone-sensitive lipase was inhibited in HC mice adipose tissue. The HC mice also had elevated fasting glucose (7.0 vs. 4.5 mmol/L, P<.001) and a greater area under the curve (P<.001) in intraperitoneal glucose tolerance tests, with enhanced expression of the negative regulator of insulin signaling, protein tyrosine phosphatase-1B, in liver and adipose tissue. Overall, high cystine intake promotes adiposity and an adverse metabolic phenotype in mice, indicating that the positive association of plasma tCys with obesity in humans may be causal.

Effects of trans-10,cis-12 conjugated linoleic acid on cholesterol metabolism in hypercholesterolaemic hamsters.

BACKGROUND: Conjugated linoleic acid (CLA) has received great attention in recent years because of its pleiotropic biological activities, but considerably fewer studies have been published addressing its role in serum lipids and atherosclerosis compared to other topics covered. AIMS OF THE STUDY: The aim of the present study was to assess the effects of the trans-10,cis-12 isomer of CLA on cholesterolaemia and on several metabolic pathways involved in cholesterol metabolism in hamsters. METHODS: Animals were fed atherogenic diets supplemented with 0.5% linoleic acid, 0.5% trans-10,cis-12 CLA or 1.0% trans-10,cis-12 CLA, for 6 weeks. Serum lipoproteins were separated by FPLC. Cholesterol in serum and liver, as well as triacylglycerols and phospholipids in liver were assessed by spectrophotometry. 3-Hydroxy-3-methylglutaryl coenzyme A reductase (HMGCoAR), acyl-coenzyme A:cholesterol acyltransferase (ACAT) and cholesteryl ester hydrolase (CEH) activities were measured by radiometry, and LDL receptors were determined by Western blot. RESULTS: trans-10,cis-12 CLA feeding did not modify food intake nor final body weight. Although serum total cholesterol remained unchanged, when cholesterol fractions were analyzed a significant decrease in VLDL-cholesterol was observed in CLA-fed animals, without changes in HDL-cholesterol or LDL-cholesterol. trans-10,cis-12 CLA decreased cholesterol ester content and increased free cholesterol in liver. The activity of HMGCoAR was not modified. In contrast, ACAT activity was reduced by both CLA doses and CEH was increased by the high CLA dose. LDL receptors were significantly reduced by trans-10,cis-12 feeding when expressed as arbitrary units per mg of protein, however, the total receptor mass remained unchanged. CONCLUSIONS: These results suggest that, under the present experimental conditions, trans-10,cis-12 CLA feeding reduces cholesterol esterification in liver and decreases the minority serum VLDL-cholesterol fraction, but it does not show a hypocholesterolaemic effect. A dose-response effect was not observed.

Alterations of lipid metabolism and gene expression in rat adipocytes during chronic olanzapine treatment.

Although antipsychotics are established drugs in schizophrenia treatment, they are admittedly known to induce side effects favoring the onset of obesity and worsening its complications. Despite potential involvement of histamine receptor antagonism, or of other neurotransmitter systems, the mechanism by which antipsychotic drugs increase body weight is not elucidated. The aim of the present study was to investigate whether chronic antipsychotic treatments can directly alter the regulation of two main functions of white adipose tissue: lipolysis and glucose utilization. The influence of a classical antipsychotic (haloperidol) was compared to that of two atypical antipsychotics, one known to favor weight gain (olanzapine), the other not (ziprasidone). Cell size, lipolytic capacity and glucose transport activity were determined in white adipocytes of rats subjected to 5-week oral treatment with these antipsychotics. Gene expression of adipocyte proteins involved in glucose transport or fat storage and mobilization, such as glucose transporters (GLUT1 and GLUT4), leptin, matrix metallo-proteinase-9 (MMP9), hormone-sensitive lipase (HSL) and fatty acid synthase (FAS) was also evaluated. Adipocytes from chronic olanzapine-treated rats exhibited decreased lipolytic activity, lowered HSL expression and increased FAS expression. These changes were concomitant to enlarged fat deposition and adipocyte size. Alterations were observed in adipocytes from olanzapine-treated rats whereas the other antipsychotics did not induce any notable disorder. Our results therefore show evidence of an effect of chronic antipsychotic treatment on rat adipocyte metabolism. Thus, impairment of fat cell lipolysis should be considered as a side effect of certain antipsychotics, leading, along with the already documented hyperphagia, to the excessive weight gain observed in patients under prolonged treatment..

Bile salt-stimulated lipase from human milk binds DC-SIGN and inhibits human immunodeficiency virus type 1 transfer to CD4+ T cells.

A wide range of pathogens, including human immunodeficiency virus type 1 (HIV-1), hepatitis C virus, Ebola virus, cytomegalovirus, dengue virus, Mycobacterium, Leishmania, and Helicobacter pylori, can interact with dendritic cell (DC)-specific ICAM3-grabbing nonintegrin (DC-SIGN), expressed on DCs and a subset of B cells. More specifically, the interaction of the gp120 envelope protein of HIV-1 with DC-SIGN can facilitate the transfer of virus to CD4+ T lymphocytes in trans and enhance infection. We have previously demonstrated that a multimeric LeX component in human milk binds to DC-SIGN, preventing HIV-1 from interacting with this receptor. Biochemical analysis reveals that the compound is heat resistant, trypsin sensitive, and larger than 100 kDa, indicating a specific glycoprotein as the inhibitory compound. By testing human milk from three different mothers, we found the levels of DC-SIGN binding and viral inhibition to vary between samples. Using sodium dodecyl sulfate-polyacrylamide gel electrophoresis, Western blotting, and matrix-assisted laser desorption ionization analysis, we identified bile salt-stimulated lipase (BSSL), a Lewis X (LeX)-containing glycoprotein found in human milk, to be the major variant protein between the samples. BSSL isolated from human milk bound to DC-SIGN and inhibited the transfer of HIV-1 to CD4+ T lymphocytes. Two BSSL isoforms isolated from the same human milk sample showed differences in DC-SIGN binding, illustrating that alterations in the BSSL forms explain the differences observed. These results indicate that variations in BSSL lead to alterations in LeX expression by the protein, which subsequently alters the DC-SIGN binding capacity and the inhibitory effect on HIV-1 transfer. Identifying the specific molecular interaction between the different forms may aid in the future design of antimicrobial agents.

Peptides derived from serum amyloid A prevent, and reverse, aortic lipid lesions in apoE-/- mice.

Macrophages (Mphi) at sites of acute tissue injury accumulate and export cholesterol quickly. This metabolic activity is likely dependent on the physiological function of a major acute-phase protein, serum amyloid A 2.1 (SAA2.1), that is synthesized by hepatocytes as part of a systemic response to acute injury. Our previous studies using cholesterol-laden J774 mouse Mphi showed that an N-terminal domain of SAA2.1 inhibits acyl-CoA:cholesterol acyltransferase activity, and a C-terminal domain enhances cholesteryl ester hydrolase activity. The net effect of this enzymatic regulation is to drive intracellular cholesterol to its unesterified state, the form readily exportable to an extracellular acceptor such as HDL. Here, we demonstrate that these domains from mouse SAA2.1, when delivered in liposomal formulation, are effective at preventing and reversing aortic lipid lesions in apolipoprotein E-deficient mice maintained on high-fat diets. Furthermore, mouse SAA peptides, in liposomal formulation, are effective at regulating cholesterol efflux in THP-1 human Mphi, and homologous domains from human SAA are effective in mouse J774 cells. These peptides operate at the level of the foam cell in the reverse cholesterol pathway and therefore may be used in conjunction with other agents that act more distally in this process. Such human peptides, or small molecule mimics of their structure, may prove to be potent antiatherogenic agents in humans.

Suppression of plasma free fatty acids upregulates peroxisome proliferator-activated receptor (PPAR) alpha and delta and PPAR coactivator 1alpha in human skeletal muscle, but not lipid regulatory genes.

Fatty acids are an important ligand for peroxisome proliferator-activated receptor (PPAR) activation and transcriptional regulation of metabolic genes. To examine whether reduced plasma free fatty acid (FFA) availability affects the mRNA content of proteins involved in fuel metabolism in vivo, the skeletal muscle mRNA content of various transcription factors, transcriptional coactivators and genes encoding for lipid regulatory proteins were examined before and after 3 h of cycle exercise with (NA) and without (CON) pre-exercise ingestion of nicotinic acid (NA). NA resulted in a marked (3- to 6-fold) increase (P<0.05) in PPARalpha, PPARdelta and PPAR coactivator 1alpha (PGC1alpha) mRNA, but was without effect on nuclear respiratory factor-1 and Forkhead transcription factor, fatty acid transcolase/CD36, carnitine palmitoyl transferase 1, hormone sensitive lipase (HSL) and pyruvate dehydrogenase kinase 4. Exercise in CON was associated with increased (P<0.05) PPARalpha, PPARdelta and PGC1alpha mRNA, which was similar in magnitude to levels observed with NA at rest. Exercise was generally without effect on the mRNA content of lipid regulatory proteins in CON and did not affect the mRNA content of the measured subset of transcription factors, transcriptional co-activators and lipid regulatory proteins during NA. To determine the possible mechanisms by which NA might affect PGC1alpha expression, we measured p38 MAP kinase (MAPK) and plasma epinephrine. Phosphorylation of p38 MAPK was increased (P<0.05) by NA treatment at rest, and this correlated (r2=0.84, P<0.01) with increased PGC1alpha. Despite this close relationship, increasing p38 MAPK in human primary myotubes was without effect on PGC1alpha mRNA content. Plasma epinephrine was elevated (P<0.05) by NA at rest (CON: 0.27+/-0.06, NA: 0.72+/-0.11 nM) and throughout exercise. Incubating human primary myotubes with epinephrine increased PGC1alpha independently of changes in p38 MAPK phosphorylation. Hence, despite the fact that NA ingestion decreased FFA availability, it promoted the induction of PPARalpha/delta and PGC1alpha gene expression to a similar degree as prolonged exercise. We suggest that the increase in PGC1alpha may be due to the elevated plasma epinephrine levels. Despite these changes in transcription factors/coactivators, the mRNA content of lipid regulatory proteins was generally unaffected by plasma FFA availability.

Comparison of the changes in lipid metabolism between hepatoma-bearing and lipopolysaccharide-treated rats.

To elucidate the mechanism for hyperlipidemia in the hepatoma-bearing state, changes in some parameters related to the lipid metabolism and serum tumor necrosis factor-alpha (TNF-alpha) level were examined in Donryu rats that had been subcutaneously implanted with an ascites hepatoma cell line of AH109A. These parameters were also examined in rats that had been given a single injection of lipopolysaccharide (LPS), a model for acute infection with TNF-alpha secretion into the blood circulation. The serum triglyceride and total cholesterol (Ch) levels were significantly higher in both the hepatoma-implanted and LPS-injected rats than in normal rats. The level of adipose tissue lipoprotein lipase was decreased by hepatoma implantation and LPS injection, while the hormone-sensitive lipase activity was increased by the same treatments. Fatty acid (FA) oxidation and Ch synthesis were also stimulated by both treatments. The serum TNF-alpha level was noticably elevated by hepatoma implantation and greatly by the LPS injection. This LPS injection increased hepatic FA synthesis. The serum high-density lipoprotein Ch level and hepatic Ch 7alpha-hydroxylase activity were not changed by the LPS injection. Hepatoma implantation led to hyperlipidemia and elevated the serum TNF-alpha level, as did the LPS injection.

The in-vitro influence of serum amyloid A isoforms on enzymes that regulate the balance between esterified and un-esterified cholesterol.

The intracellular balance between un-esterified and esterified cholesterol is regulated by two enzyme activities, cholesterol ester hydrolases, which drive the balance in favor of un-esterified cholesterol, and acyl-CoA:cholesterol acyl transferase (ACAT) which acts in the opposite direction. During acute inflammation apo-serum amyloid A (apoSAA) isoforms 1.1 and 2.1 become major constituents of high density lipoprotein and this complex is internalized by macrophages. Mixtures of the two isoforms have been shown to enhance cholesterol esterase activity. Using a purified form of the pancreatic enzyme we have explored the mechanism by which apoSAA may accomplish this stimulation. The pancreatic esterase cleaves cholesteryl-oleate with a Km of 0.255 mM, releasing both cholesterol and oleate. Cholesterol exhibits a product inhibition which is relieved by isoform 2.1 but not 1.1 nor apolipoprotein A-I. The NH2-terminal 16 residues of isoform 2.1 had no effect on the esterase, but the 80 residue peptide constituting its COOH-terminus possessed the stimulatory property. Purified isoforms 1.1, 2.1, 2.2, apolipoprotein A-I, the NH2-terminal 16 residues and COOH-terminal 80 residues of isoform 2.1 were also examined for their effects on macrophage ACAT activity. Isoforms 2.1 and 2.2 produced dose dependent inhibitions of up to 50%, (p<0.001). Isoform 1.1, and apoA-I had no effect on ACAT activity. The NH2-terminal 16 residue peptide of isoform 2.1 reduced the ACAT activity in a dose dependent manner by 74% (p<0.001), whereas the COOH-terminal 80 residues, in contrast to its enhancing effect on the esterase, had no inhibitory effect on ACAT. Such complementary but opposite effects of isoform 2.1 on ACAT and the esterase are consistent with a role for this protein in shifting the balance between unesterified (transportable) and esterified (storage) forms of cholesterol in favor of the latter. They suggest that apoSAA2.1 may mediate cholesterol mobilization at sites of tissue injury.

Mechanism of intracellular calcium ([Ca2+]i) inhibition of lipolysis in human adipocytes.

We investigated the mechanisms responsible for the anti-lipolytic effect of intracellular Ca2+ ([Ca2+]i) in human adipocytes. Increasing [Ca2+]i inhibited lipolysis induced by b-adrenergic receptor activation, A1 adenosine receptor inhibition, adenylate cyclase activation, and phosphodiesterase (PDE) inhibition, as well as by a hydrolyzable cAMP analog, but not by a nonhydrolyzable cAMP analog. This finding indicates that the anti-lipolytic effect of [Ca2+]i may be mediated by the activation of adipocyte PDE. Consistent with this theory, [Ca2+]i inhibition of isoproterenol-stimulated lipolysis was reversed completely by the nonselective PDE inhibitor isobutyl methylxanthine and also by the selective PDE 3B inhibitor cilostamide, but not by selective PDE 1 and 4 inhibitors. In addition, phosphatidylinositol-3 kinase inhibition with wortmannin completely prevented insulin's anti-lipolytic effect but only minimally blocked [Ca2+]i's effect, which suggests that [Ca2+]i and insulin may activate PDE 3B via different mechanisms. In contrast, the antilipolytic effect of [Ca2+]i was not affected by inhibitors of calmodulin, Ca2+/calmodulin-dependent kinase, protein phosphatase 2B, and protein kinase C. Finally, [Ca2+]i inhibited significantly isoproterenol-stimulated increases in cAMP levels and hormone-sensitive lipase phosphorylation in human adipocytes. In conclusion, increasing [Ca2+]i exerts an antilipolytic effect mainly by activation of PDE, leading to a decrease in cAMP and HSL phosphorylation and, consequently, inhibition of lipolysis.

Masoprocol decreases rat lipolytic activity by decreasing the phosphorylation of HSL.

Masoprocol (nordihydroguaiaretic acid), a lipoxygenase inhibitor isolated from the creosote bush, has been shown to decrease adipose tissue lipolytic activity both in vivo and in vitro. The present study was initiated to test the hypothesis that the decrease in lipolytic activity by masoprocol resulted from modulation of adipose tissue hormone-sensitive lipase (HSL) activity. The results indicate that oral administration of masoprocol to rats with fructose-induced hypertriglyceridemia significantly decreased their serum free fatty acid (FFA; P < 0.05), triglyceride (TG; P < 0.001), and insulin (P < 0.05) concentrations. In addition, isoproterenol-induced lipolytic rate and HSL activity were significantly lower (P < 0.001) in adipocytes isolated from masoprocol compared with vehicle-treated rats and was associated with a decrease in HSL protein. Incubation of masoprocol with adipocytes from chow-fed rats significantly inhibited isoproterenol-induced lipolytic activity and HSL activity, associated with a decrease in the ability of isoproterenol to phosphorylate HSL. Masoprocol had no apparent effect on adipose tissue phosphatidylinositol 3-kinase activity, but okadaic acid, a serine/threonine phosphatase inhibitor, blocked the antilipolytic effect of masoprocol. The results of these in vitro and in vivo experiments suggest that the antilipolytic activity of masoprocol is secondary to its ability to inhibit HSL phosphorylation, possibly by increasing phosphatase activity. As a consequence, masoprocol administration results in lower serum FFA and TG concentrations in hypertriglyceridemic rodents.

Inhibition of adipocyte lipolysis by papaverine: papaverine can inhibit the redistribution of hormone-sensitive lipase.

Papaverine, despite being a potent phosphodiesterase inhibitor, actually blocks adipocyte lipolysis. The present study was designed to clarify the mechanism of the inhibitory effect of papaverine on lipolysis. Lipolysis, stimulated by either 10 microM isoproterenol or 5 mM dibutyryl cAMP, was significantly inhibited by papaverine (100 microM and above). Papaverine, however, did not affect the isoproterenol-induced increase in the protein kinase A (A-kinase) activity ratio. In cell-free extract from non-stimulated adipocytes, cAMP-stimulated A-kinase activities were almost completely blocked by H-89, a potent inhibitor of A-kinase, but not by papaverine. Thus, the inhibitory effect of papaverine on lipolysis could be responsible for a deficit in step(s) distal to A-kinase activity. Hormone-sensitive lipase activities in the infranatant fraction of centrifuged homogenates of cells, which were maximally stimulated with isoproterenol were significantly reduced. This result indicates that hormone-sensitive lipase redistributes from cytosol to its substrate in lipolytically stimulated cells. Papaverine completely blocked the isoproterenol-induced decrease in lipase activity in the infranatant fraction. These results suggest that papaverine blocks lipolysis through its inhibitory effect on the redistribution of hormone-sensitive lipase.