Regulation of hormone-sensitive lipase in streptozotocin-induced diabetic rats

Nrf2 Signaling Pathway as a Key to Treatment for Diabetic Dyslipidemia and Atherosclerosis

Diabetes mellitus (DM) is a chronic endocrine disorder that affects more than 20 million people in the United States. DM-related complications affect multiple organ systems and are a significant cause of morbidity and mortality among people with DM. Of the numerous acute and chronic complications, atherosclerosis due to diabetic dyslipidemia is a condition that can lead to many life-threatening diseases, such as stroke, coronary artery disease, and myocardial infarction. The nuclear erythroid 2-related factor 2 (Nrf2) signaling pathway is an emerging antioxidative pathway and a promising target for the treatment of DM and its complications. This review aims to explore the Nrf2 pathway's role in combating diabetic dyslipidemia. We will explore risk factors for diabetic dyslipidemia at a cellular level and aim to elucidate how the Nrf2 pathway becomes a potential therapeutic target for DM-related atherosclerosis.

Ilex paraguariensis A.St.-Hil. improves lipid metabolism in high-fat diet-fed obese rats and suppresses intracellular lipid accumulation in 3T3-L1 adipocytes via the AMPK-dependent and insulin signaling pathways

Background

Obesity is closely associated with several chronic diseases, and adipose tissue plays a major role in modulating energy metabolism.

Objective

This study aimed to determine whether Mate, derived from I. paraguariensis A.St.-Hil., ameliorates lipid metabolism in 3T3-L1 adipocytes and high-fat diet (HFD)-fed obese Sprague-Dawley (SD) rats.

Design

3T3-L1 adipocytes were cultured for 7 days, following which intracellular lipid accumulation and expression levels of lipid metabolism-related factors were examined. Dorsomorphin was used to investigate the potential pathways involved, particularly the adenosine monophosphate-activated protein kinase (AMPK)- dependent pathway. Mate was administered to rat HFD-fed obese SD models for 8 consecutive weeks. The expression of lipid metabolism-related factors in the organs and tissues collected from dissected SD rats was evaluated.

Results

Mate suppressed intracellular lipid accumulation in 3T3-L1 adipocytes, increased the protein and gene expression levels of AMPK, hormone sensitive lipase (HSL), calmodulin kinase kinase (CaMKK), liver kinase B1 (LKB1), protein kinase A (PKA), CCAAT/enhancer binding protein β (C/EBPβ), insulin receptor b (IRβ), and insulin receptor substrate 1 (IRS1) (Tyr465), and decreased those of sterol regulatory element binding protein 1C (Srebp1c), fatty acid synthase (FAS), peroxisome-activated receptor γ (PPARγ), and IRS1 (Ser1101). Furthermore, an AMPK inhibitor abolished the effects exerted by Mate on intracellular lipid accumulation and HSL and FAS expression levels. Mate treatment suppressed body weight gain and improved serum cholesterol levels in HFD-fed obese SD rats. Treatment with Mate increased the protein and gene expression levels of AMPK, PKA, Erk1/Erk2 (p44/p42), and uncoupling protein 1 and reduced those of mammalian target of rapamycin, S6 kinase, Srebp1c, ap2, FAS, Il6, Adiponectin, Leptin, and Fabp4 in rat HFD-fed obese SD models.

Discussion and conclusions

Mate suppressed intracellular lipid accumulation in 3T3-L1 adipocytes and improved lipid metabolism in the epididymal adipose tissue of HFD-fed obese SD rats via the activation of AMPK-dependent and insulin signaling pathways.

Postprandial Hyperlipidemia: Its Pathophysiology, Diagnosis, Atherogenesis, and Treatments

Postprandial hyperlipidemia showing postprandial increases in serum triglyceride (TG) is associated with the development of atherosclerotic cardiovascular disease (ASCVD). To diagnose postprandial hyperlipidemia, the oral fat loading test (OFLT) should be performed; however, this test is very time-consuming and is difficult to perform. Elevated serum TG levels reflect an increase in TG-rich lipoproteins (TRLs), such as chylomicrons (CM), very low-density lipoproteins (VLDL), and their remnants (CM remnants [CMRs] and VLDL remnants [VLDLRs]). Understanding of elevation in CMR and/or VLDLR can lead us to understand the existence of postprandial hyperlipidemia. The measurement of apo B48, which is a constituent of CM and CMR; non-fasting TG, which includes TG content in all lipoproteins including CM and CMR; non-high-density lipoprotein cholesterol (non-HDL-C), which includes TRLs and low-density lipoprotein; and remnant cholesterol are useful to reveal the existence of postprandial hyperlipidemia. Postprandial hyperlipidemia is observed in patients with familial type III hyperlipoproteinemia, familial combined hyperlipidemia, chronic kidney disease, metabolic syndrome and type 2 diabetes. Postprandial hyperlipidemia is closely related to postprandial hyperglycemia, and insulin resistance may be an inducing and enhancing factor for both postprandial hyperlipidemia and postprandial hyperglycemia. Remnant lipoproteins and metabolic disorders associated with postprandial hyperlipidemia have various atherogenic properties such as induction of inflammation and endothelial dysfunction. A healthy diet, calorie restriction, weight loss, and exercise positively impact postprandial hyperlipidemia. Anti-hyperlipidemic drugs such pemafibrate, fenofibrate, bezafibrate, ezetimibe, and eicosapentaenoic acid have been shown to improve postprandial hyperlipidemia. Anti-diabetic drugs including metformin, alpha-glucosidase inhibitors, pioglitazone, dipeptidyl-peptidase-4 inhibitors and glucagon-like peptide 1 analogues have been shown to ameliorate postprandial hyperlipidemia. Although sodium glucose cotransporter-2 inhibitors have not been proven to reduce postprandial hyperlipidemia, they reduced fasting apo B48 and remnant lipoprotein cholesterol. In conclusion, it is important to appropriately understand the existence of postprandial hyperlipidemia and to connect it to optimal treatments. However, there are some problems with the diagnosis for postprandial hyperlipidemia. Postprandial hyperlipidemia cannot be specifically defined by measures such as TG levels 2 h after a meal. To study interventions for postprandial hyperlipidemia with the outcome of preventing the onset of ASCVD, it is necessary to define postprandial hyperlipidemia using reference values such as IGT.

Plin5, a New Target in Diabetic Cardiomyopathy

Abnormal lipid accumulation is commonly observed in diabetic cardiomyopathy (DC), which can create a lipotoxic microenvironment and damage cardiomyocytes. Lipid toxicity is an important pathogenic factor due to abnormal lipid accumulation in DC. As a lipid droplet (LD) decomposition barrier, Plin5 can protect LDs from lipase decomposition and regulate lipid metabolism, which is involved in the occurrence and development of cardiovascular diseases. In recent years, studies have shown that Plin5 expression is involved in the pathogenesis of DC lipid toxicity, such as oxidative stress, mitochondrial dysfunction, endoplasmic reticulum (ER) stress, and insulin resistance (IR) and has become a key target of DC research. Therefore, understanding the relationship between Plin5 and DC progression as well as the mechanism of this process is crucial for developing new therapeutic approaches and exploring new therapeutic targets. This review is aimed at exploring the latest findings and roles of Plin5 in lipid metabolism and DC-related pathogenesis, to explore possible clinical intervention approaches.

Characteristics and molecular mechanisms through which SGLT2 inhibitors improve metabolic diseases: A mechanism review

Metabolic diseases, such as diabetes, gout and hyperlipidemia are global health challenges. Among them, diabetes has been extensively investigated. Type 2 diabetes mellitus (T2DM), which is characterized by hyperglycemia, is a complex metabolic disease that is associated with various metabolic disorders. The newly developed oral hypoglycemic agent, sodium-glucose cotransporter 2 (SGLT2) inhibitor, has been associated with glucose-lowering effects and it affects metabolism in various ways. However, the potential mechanisms of SGLT2 inhibitors in metabolic diseases have not fully reviewed. Many of the effects beyond glycemic control must be considered off-target effects. Therefore, we reviewed the effects of SGLT2 inhibition on metabolic diseases such as obesity, hypertension, hyperlipidemia, hyperuricemia, fatty liver disease, insulin resistance, osteoporosis and fractures. Moreover, we elucidated their molecular mechanisms to provide a theoretical basis for metabolic disease treatment.

Molecular Biological and Clinical Understanding of the Statin Residual Cardiovascular Disease Risk and Peroxisome Proliferator-Activated Receptor Alpha Agonists and Ezetimibe for Its Treatment

Several randomized, double blind, placebo-controlled trials (RCTs) have demonstrated that low-density lipoprotein cholesterol (LDL-C) lowering by using statins, including high-doses of strong statins, reduced the development of cardiovascular disease (CVD). However, among the eight RCTs which investigated the effect of statins vs. placebos on the development of CVD, 56-79% of patients had the residual CVD risk after the trials. In three RCTs which investigated the effect of a high dose vs. a usual dose of statins on the development of CVD, 78-87% of patients in the high-dose statin arms still had the CVD residual risk after the trials. An analysis of the characteristics of patients in the RCTs suggests that elevated triglyceride (TG) and reduced high-density lipoprotein cholesterol (HDL-C), the existence of obesity/insulin resistance, and diabetes may be important metabolic factors which determine the statin residual CVD risk. To understand the association between lipid abnormalities and the development of atherosclerosis, we show the profile of lipoproteins and their normal metabolism, and the molecular and biological mechanisms for the development of atherosclerosis by high TG and/or low HDL-C in insulin resistance. The molecular biological mechanisms for the statin residual CVD risk include an increase of atherogenic lipoproteins such as small dense LDL and remnants, vascular injury and remodeling by inflammatory cytokines, and disturbed reverse cholesterol transport. Peroxisome proliferator-activated receptor alpha (PPARα) agonists improve atherogenic lipoproteins, reverse the cholesterol transport system, and also have vascular protective effects, such as an anti-inflammatory effect and the reduction of the oxidative state. Ezetimibe, an inhibitor of intestinal cholesterol absorption, also improves TG and HDL-C, and reduces intestinal cholesterol absorption and serum plant sterols, which are increased by statins and are atherogenic, possibly contributing to reduce the statin residual CVD risk.

Effects of a Novel Selective Peroxisome Proliferator-Activated Receptor α Modulator, Pemafibrate, on Metabolic Parameters: A Retrospective Longitudinal Study

The modulation of peroxisome proliferator-activated receptors (PPARs), the superfamily of steroid–thyroid–retinoid nuclear receptors, is expected to induce an amazing crosstalk between energy-demanding organs. Here, we aimed to study the effects of the novel selective PPARα modulator, pemafibrate, on metabolic parameters in patients with dyslipidemia. We retrospectively studied patients who had taken pemafibrate and compared metabolic parameters at baseline with the data at 3, 6 and 12 months after the start of pemafibrate. Serum triglyceride significantly decreased and high-density lipoprotein-cholesterol significantly increased at 3, 6 and 12 months after the start of pemafibrate. Serum aspartate aminotransferase levels significantly decreased at 3 and 6 after the start of pemafibrate as compared with baseline. Serum alanine aminotransferase and gamma-glutamyl transferase significantly decreased and albumin significantly increased after 3, 6 and 12 months. HbA1c levels significantly decreased after 3 months. Further, serum uric acid significantly decreased after 12 months. Such metabolic favorable changes due to pemafibrate were significantly correlated with changes in serum lipids. In conclusion, we observed a significant improvement of liver function, HbA1c and serum uric acid along with an amelioration of dyslipidemia after the start of pemafibrate.

Dapagliflozin elevates plasma high-density lipoprotein levels and influences visceral fat gene expression in streptozotocin-induced diabetes mellitus

OBJECTIVES

Dapagliflozin (Dapa) could potentially be used to treat type 1 diabetes mellitus. We tested the hypothesis that it would influence blood lipid levels and visceral fat accumulation in a rodent diabetic model.

METHODS

We used three groups of male Wistar rats: Controls, streptozotocin (STZ)-treated rats and STZ-treated orally with Dapa (STZ+Dapa), 10 mg/kg/day for six weeks. Blood glucose and serum lipids levels were determined. Plasma levels of lipases (hormone-sensitive lipase, HSL and lipoprotein lipase, LPL), adipokines (leptin and adiponectin) and proinflammatory cytokines [tumour necrosis factor-alpha (TNFα) and interleukin-6 (IL-6)] were determined by ELISA assays. mRNA levels in the perirenal fat were determined by real-time PCR.

KEY FINDINGS

Dapa suppressed STZ-related hyperglycemia by 20% (P < 0.05) and increased serum HDL when compared to the controls and the STZ-only treated rats (both P < 0.05). STZ treatment caused elevations of other serum lipids that were resistant to Dapa treatment. Dapa treatment also increased both plasma and visceral fat mRNA levels of leptin, LPL and IL-6, while decreasing plasma and fat expressions of HSL and TNFα compared to the STZ-only treated rats (all P < 0.05).

CONCLUSIONS

Our results suggest that Dapa, in addition to its antidiabetic effect, also influences the function of adipose tissue which could be beneficial in the treatment of diabetes.

Multi-Organ Protective Effects of Sodium Glucose Cotransporter 2 Inhibitors

Sodium glucose cotransporter 2 inhibitors (SGLT2i) block the reabsorption of glucose by inhibiting SGLT2, thus improving glucose control by promoting the renal excretion of glucose, without requiring insulin secretion. This pharmacological property of SGLT2i reduces body weight and improves insulin resistance in diabetic patients. Such beneficial metabolic changes caused by SGLT2i are expected to be useful not only for glucose metabolism, but also for the protection for various organs. Recent randomized controlled trials (RCTs) on cardiovascular diseases (EMPA-REG OUTCOME trial and CANVAS program) showed that SGLT2i prevented cardiovascular death and the development of heart failure. RCTs on renal events (EMPA-REG OUTCOME trial, CANVAS program, and CREDENCE trial) showed that SGLT2i suppressed the progression of kidney disease. Furthermore, SGLT2i effectively lowered the liver fat content, and our study demonstrated that SGLT2i reduced the degree of hepatic fibrosis in patients at high-risk of hepatic fibrosis. Such promising properties of SGLT2i for cardiovascular, renal, and hepatic protection provide us the chance to think about the underlying mechanisms for SGLT2i-induced improvement of multiple organs. SGLT2i have various mechanisms for organ protection beyond glucose-lowering effects, such as an increase in fatty acids utilization for hepatic protection, osmotic diuresis for cardiac protection, an improvement of insulin resistance for anti-atherogenesis, and an improvement of tubuloglomerular feedback for renal protection.

Maintaining Myocardial Glucose Utilization in Diabetic Cardiomyopathy Accelerates Mitochondrial Dysfunction

Cardiac glucose uptake and oxidation are reduced in diabetes despite hyperglycemia. Mitochondrial dysfunction contributes to heart failure in diabetes. It is unclear whether these changes are adaptive or maladaptive. To directly evaluate the relationship between glucose delivery and mitochondrial dysfunction in diabetic cardiomyopathy, we generated transgenic mice with inducible cardiomyocyte-specific expression of the GLUT4. We examined mice rendered hyperglycemic following low-dose streptozotocin prior to increasing cardiomyocyte glucose uptake by transgene induction. Enhanced myocardial glucose in nondiabetic mice decreased mitochondrial ATP generation and was associated with echocardiographic evidence of diastolic dysfunction. Increasing myocardial glucose delivery after short-term diabetes onset exacerbated mitochondrial oxidative dysfunction. Transcriptomic analysis revealed that the largest changes, driven by glucose and diabetes, were in genes involved in mitochondrial function. This glucose-dependent transcriptional repression was in part mediated by O-GlcNAcylation of the transcription factor Sp1. Increased glucose uptake induced direct O-GlcNAcylation of many electron transport chain subunits and other mitochondrial proteins. These findings identify mitochondria as a major target of glucotoxicity. They also suggest that reduced glucose utilization in diabetic cardiomyopathy might defend against glucotoxicity and caution that restoring glucose delivery to the heart in the context of diabetes could accelerate mitochondrial dysfunction by disrupting protective metabolic adaptations.

White adipose tissue mitochondrial metabolism in health and in obesity

White adipose tissue is one of the largest organs of the body. It plays a key role in whole-body energy status and metabolism; it not only stores excess energy but also secretes various hormones and metabolites to regulate body energy balance. Healthy adipose tissue capable of expanding is needed for metabolic well-being and to prevent accumulation of triglycerides to other organs. Mitochondria govern several important functions in the adipose tissue. We review the derangements of mitochondrial function in white adipose tissue in the obese state. Downregulation of mitochondrial function or biogenesis in the white adipose tissue is a central driver for obesity-associated metabolic diseases. Mitochondrial functions compromised in obesity include oxidative functions and renewal and enlargement of the adipose tissue through recruitment and differentiation of adipocyte progenitor cells. These changes adversely affect whole-body metabolic health. Dysfunction of the white adipose tissue mitochondria in obesity has long-term consequences for the metabolism of adipose tissue and the whole body. Understanding the pathways behind mitochondrial dysfunction may help reveal targets for pharmacological or nutritional interventions that enhance mitochondrial biogenesis or function in adipose tissue.

Acer okamotoanum inhibits adipocyte differentiation by the regulation of adipogenesis and lipolysis in 3T3‑L1 cells

Acer okamotoanum is reported to have various antioxidant, anti‑inflammatory and beneficial immune system effects. The anti‑adipocyte differentiation effects and mechanisms of the ethyl acetate (EtOAc) fraction of an A. okamotoanum extraction was investigated in 3T3‑L1 adipocyte cells. Treatment with differentiation inducers increased the level of triglycerides (TGs) in 3T3‑L1 adipocyte cells compared with an untreated control. However, the EtOAc fraction of A. okamotoanum significantly decreased TGs. Treatment with 1, 2.5 and 5 µg/ml showed weak activity, but TG production was inhibited at 10 µg/ml compared with the control. In addition, A. okamotoanum caused a significant downregulation of proteins related to adipogenesis, such as γ‑cytidine‑cytidine‑adenosine‑adenosine‑thymidine/enhancer binding protein‑α, ‑β and peroxisome proliferator‑activated receptor‑γ, compared with the untreated control. Furthermore, A. okamotoanum significantly upregulated lipolysis related protein, hormone‑sensitive lipase and the phosphorylation of adenosine monophosphate‑activated protein kinase (AMPK). Therefore, these results indicate that A. okamotoanum suppressed adipogenesis and increased lipolysis and the activation of AMPK, suggesting a protective role in adipocyte differentiation.

The effect of endurance training with crocin consumption on the levels of MFN2 and DRP1 gene expression and glucose and insulin indices in the muscle tissue of diabetic rats

This study aimed to investigate the effect of crocin consumption, high-intensity interval training (HIIT), and low-intensity continuous training (LICT) and their interactive effect on the gene expression of Mfn2 and Drp1 in the skeletal muscle and serum glucose and insulin indices in high-fat diet (HFD) and streptozotocin (STZ)-induced diabetic rats. Fifty-six adult rats were divided into eight groups of seven subjects: crocin consumption, HIIT, LICT, HIIT with crocin, LICT with crocin, diabetic control, healthy control, and sham (placebo). At the end of the course (5 months), metabolic indices were measured. Moreover, the Mfn2 and Drp1 gene expression levels in all groups were measured using RT-PCR. The statistical analysis showed that in the exercise training (HIIT and LICT) and the crocin consumption groups, the glucose and insulin indices significantly improved (p = .005). Moreover, in these groups, the levels of gene expression of Mfn2 and Drp1 significantly increased and decreased, respectively (p = .001). Exercise training and crocin consumption appear to, either in combination or individually, have a beneficial effect on mitochondrial dynamics and diabetes by improving the mitochondrial fusion and fission indices (Mfn2 and Drp1), and by modifying the insulin resistance index and glucose homeostasis. PRACTICAL APPLICATIONS: Mfn2 and Drp1, as the main regulators of the mitochondrial fusion and fission, play an important role in maintaining mitochondrial dynamics and type 2 diabetes. Thus, the regulation of mitochondrial dynamics is an intricate process that retains the balance between mitochondrial fission and fusion, and any disturbance in this balance can lead to mitochondrial-associated diseases including insulin resistance and T2D. There is evidence that herbal antioxidants Including crocin and exercise training help improve the mitochondrial activity and insulin sensitivity in T2D. Considering the importance of the two Drp1 and Mfn1 genes in the mitochondrial dynamic pathway and coding the proteins that play a key role in relation to T2D, this study primarily examined the interactive effects of endurance training (HIIT and LICT) along with crocin consumption on the expression the genes mentioned above; the results obtained in this study can provide a new approach to the treatment of HFD + STZ-induced diabetic rats.

Diabetic dyslipidemia: evaluation and mechanism

Diabetes is one of the well-established independent risk factors for cardiovascular diseases. Diabetes induces dyslipidemia which is characterized by elevated fasting triglyceride (TG) and reduced high-density lipoprotein-cholesterol (HDL-C), and such diabetic dyslipidemia is a crucial determinant for atherogenesis and atherosclerotic progression in patients with diabetes. Previous measurement methods of lipoproteins have problems including time-consuming (ultracentrifugation) and inaccurate and impossible measurements of TG-rich lipoproteins such as chylomicron, intermediate-density lipoprotein (IDL) and very low-density lipoprotein (VLDL). Our developed anion-exchange high-performance liquid chromatography (AEX-HPLC) can measure all fractions of lipoproteins accurately. Our studies using AEX-HPLC showed that IDL and VLDL in type 2 diabetes were higher than non-diabetic subjects, and IDL and VLDL were higher in the order of type 2 diabetic patients with obesity, type 2 diabetic patients without obesity, and non-diabetic subjects. Here, we also describe the underlying mechanisms for development of diabetic dyslipidemia.

Beneficial Effects of Adiponectin on Glucose and Lipid Metabolism and Atherosclerotic Progression: Mechanisms and Perspectives

Circulating adiponectin concentrations are reduced in obese individuals, and this reduction has been proposed to have a crucial role in the pathogenesis of atherosclerosis and cardiovascular diseases associated with obesity and the metabolic syndrome. We focus on the effects of adiponectin on glucose and lipid metabolism and on the molecular anti-atherosclerotic properties of adiponectin and also discuss the factors that increase the circulating levels of adiponectin. Adiponectin reduces inflammatory cytokines and oxidative stress, which leads to an improvement of insulin resistance. Adiponectin-induced improvement of insulin resistance and adiponectin itself reduce hepatic glucose production and increase the utilization of glucose and fatty acids by skeletal muscles, lowering blood glucose levels. Adiponectin has also β cell protective effects and may prevent the development of diabetes. Adiponectin concentration has been found to be correlated with lipoprotein metabolism; especially, it is associated with the metabolism of high-density lipoprotein (HDL) and triglyceride (TG). Adiponectin appears to increase HDL and decrease TG. Adiponectin increases ATP-binding cassette transporter A1 and lipoprotein lipase (LPL) and decreases hepatic lipase, which may elevate HDL. Increased LPL mass/activity and very low density lipoprotein (VLDL) receptor and reduced apo-CIII may increase VLDL catabolism and result in the reduction of serum TG. Further, adiponectin has various molecular anti-atherosclerotic properties, such as reduction of scavenger receptors in macrophages and increase of cholesterol efflux. These findings suggest that high levels of circulating adiponectin can protect against atherosclerosis. Weight loss, exercise, nutritional factors, anti-diabetic drugs, lipid-lowering drugs, and anti-hypertensive drugs have been associated with an increase of serum adiponectin level.

The effect of Psidium guajava aqueous leaf extract on liver glycogen enzymes, hormone sensitive lipase and serum lipid profile in diabetic rats

Diabetes mellitus is characterized by hyperglycaemia that results from defects in insulin secretion or insulin action and is accompanied by general disturbances metabolism. Psidium guajava (PG) leaf is known to have antidiabetic effects that include lowering of blood glucose. The aim of the study was to investigate the effect of PG leaf extract on tissue activity of glycogen synthase (GS) and glycogen phosphorylase (GP); tissue activity of hormone sensitive lipase (HSL); serum lipid profile; and serum enzyme biomarkers of tissue damage. Diabetes was induced in male Sprague-Dawley rats with a single dose of 40 mg/kg body weight streptozotocin. The aqueous extract of PG leaves was used to treat both normal and diabetic animals (400 mg/kg body weight) for 2 weeks while control animals were treated with the vehicle. At the end of the treatment period, blood, liver and adipose tissue samples were collected from the euthanized animals. The results show that PG extract significantly decreased (P < 0.05) HSL activity in adipose tissue and liver of diabetic animals which was accompanied by increased glycogen levels, reduced serum triglycerides, total cholesterol, LDL-cholesterol and increased HDL-cholesterol. This study demonstrates that P. guajava has significant anti-diabetic effects that include increased glycogen storage and reduced HSL activity in the liver and adipose tissue with an improved serum lipid profile.

An Improvement of Cardiovascular Risk Factors by Omega-3 Polyunsaturated Fatty Acids

An epidemiological survey in the Northwest Greenland reported that the Greenlanders have a lower frequency of acute myocardial infarction and diabetes mellitus. The very low incidence of ischemic heart disease in the Greenlanders was explained by consumption of a diet rich in omega-3 polyunsaturated fatty acids (PUFAs). Possible anti-atherothrombotic effects of omega-3 PUFA include an improvement of lipid metabolism such as a reduction of triglyceride and an increase of high-density lipoprotein-cholesterol (HDL-C), and glucose metabolism, anti-platelet activity, anti-inflammatory effects, an improvement of endothelial function and stabilization of atherosclerotic plaque. The present study reviews an improvement of cardiovascular risk factors such as dyslipidemia and diabetes due to consumption of omega-3 PUFA. A sufficient number of studies suggest that omega-3 PUFA supplementation reduces serum triglyceride and increases HDL-cholesterol. The mechanisms for omega-3 PUFA-mediated improvements of lipid metabolism have been partially elucidated. The studies using experimental animals, part of trials in humans, have shown the beneficial effects of omega-3 PUFA on glucose metabolism and insulin sensitivity. The meta-analysis showed that omega-3 PUFA might prevent development of diabetes in part of population. Further studies should be performed to elucidate the association of omega-3 PUFA supplementation with diabetes, in the future.

Gelidium amansii extract ameliorates obesity by down-regulating adipogenic transcription factors in diet-induced obese mice

BACKGROUND/OBJECTIVES

In this study, we investigated whether Gelidium amansii extract (GAE) ameliorates obesity in diet-induced obese (DIO) mice.

MATERIALS/METHODS

The mice were maintained on a high-fat diet (HD) for 5 weeks to generate the DIO mouse model. And then mice fed HD plus 0.5% (GAE1), 1% (GAE2) or 2% (GAE3) for 8 weeks.

RESULTS

After the experimental period, GAE-supplemented groups were significantly lower than the HD group in body weight gain and liver weight. GAE supplemented groups were significantly lower than the HD group in both epididymal and mesenteric adipose tissue mass. The plasma leptin level was significantly higher in the HD group than in GAE-supplemented groups. The leptin level of HD+GAE3 group was significantly lower than that of the HD+conjugated linoleic acid (CLA) group. In contrast, plasma adiponectin level of the HD group was significantly lower than those of HD+GAE2 and HD+GAE3 groups. The expression levels of adipogenic proteins such as fatty acid synthase, sterol regulatory element-binding protein-1c, peroxisome proliferator-activated receptor γ, and CCAAT/enhancer binding protein α in the GAE supplemented groups were significantly decreased than those in HD group, respectively. In addition, the expression levels of HD+GAE2 and HD+GAE3 groups are significantly decreased compared to those of HD+CLA group. On the contrary, the expression levels of hormone-sensitive lipase and phospho-AMP-activated protein kinase, proteins associated with lipolysis, were significantly increased in the GAE supplemented groups compared to those in the HD group. HD+GAE3 group showed the highest level among the GAE supplemented groups.

CONCLUSIONS

These results suggested that GAE supplementation stimulated the expressions of lipid metabolic factors and reduced weight gain in HD-fed C57BL/6J obese mice.

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.

Therapeutic potential of HDL in cardioprotection and tissue repair

Epidemiological studies support a strong association between high-density lipoprotein (HDL) cholesterol levels and heart failure incidence. Experimental evidence from different angles supports the view that low HDL is unlikely an innocent bystander in the development of heart failure. HDL exerts direct cardioprotective effects, which are mediated via its interactions with the myocardium and more specifically with cardiomyocytes. HDL may improve cardiac function in several ways. Firstly, HDL may protect the heart against ischaemia/reperfusion injury resulting in a reduction of infarct size and thus in myocardial salvage. Secondly, HDL can improve cardiac function in the absence of ischaemic heart disease as illustrated by beneficial effects conferred by these lipoproteins in diabetic cardiomyopathy. Thirdly, HDL may improve cardiac function by reducing infarct expansion and by attenuating ventricular remodelling post-myocardial infarction. These different mechanisms are substantiated by in vitro, ex vivo, and in vivo intervention studies that applied treatment with native HDL, treatment with reconstituted HDL, or human apo A-I gene transfer. The effect of human apo A-I gene transfer on infarct expansion and ventricular remodelling post-myocardial infarction illustrates the beneficial effects of HDL on tissue repair. The role of HDL in tissue repair is further underpinned by the potent effects of these lipoproteins on endothelial progenitor cell number, function, and incorporation, which may in particular be relevant under conditions of high endothelial cell turnover. Furthermore, topical HDL therapy enhances cutaneous wound healing in different models. In conclusion, the development of HDL-targeted interventions in these strategically chosen therapeutic areas is supported by a strong clinical rationale and significant preclinical data.

Treatment with a melanocortin agonist improves abnormal lipid metabolism in streptozotocin-induced diabetic mice

Impairments in leptin-melanocortin signaling are associated with insulin-deficient diabetes and leptin treatment has been shown to be effective in reversing hyperglycemia in animal models of type 1 diabetes. Therefore, we hypothesized that enhanced central melanocortin signaling reverses the metabolic impairments associated with type 1 diabetes. To address this hypothesis, streptozotocin (STZ)-induced diabetic mice were treated with daily intracerebroventricular injection of MTII, a melanocortin agonist, for 11days. STZ-induced hyperglycemia and glucose intolerance were not improved by MTII treatment. MTII treatment did not alter expression levels of genes encoding gluconeogenic enzymes including glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK), in the liver of diabetic mice. Skeletal muscle and white adipose tissue glucose transporter 4 (GLUT4) mRNA levels were not altered by MTII treatment in diabetic mice. In contrast, serum nonesterified fatty acid (NEFA) levels were significantly increased in STZ-induced diabetic mice compared to non-diabetic control mice and MTII treatment significantly reduced serum NEFA levels in diabetic mice. MTII treatment also significantly reduced expression levels of hormone sensitive lipase (HSL) and adipose triglyceride lipase (ATGL) mRNA in white adipose tissue of diabetic mice without a significant change in serum insulin levels. Expression levels of lipoprotein lipase (LPL) and fatty acid translocase (FAT/CD36) mRNA in white adipose tissue and skeletal muscle were not changed by MTII treatment. These data suggest that central melanocortin signaling regulates lipid metabolism and that enhancing central melanocortin signaling is effective in reversing abnormal lipid metabolism, but not carbohydrate metabolism, at least partly by reducing lipolysis in type 1 diabetes.

Effect of starvation on activities and mRNA expression of lipoprotein lipase and hormone-sensitive lipase in tilapia (Oreochromis niloticus x O. areus)

A 4-week study was conducted to determine the effect of starvation on activities and mRNA expression of lipoprotein lipase (LPL) and hormone-sensitive lipase (HSL) in hybrid tilapia (Oreochromis niloticus x O. areus). The tissue samples were sampled once a week. Results showed that body weight (BW) and hepatosomatic index (HSI) were decreased significantly (P < 0.05) during starvation. The percentages of crude fat and crude protein in the whole body and the fat content in muscle decreased significantly (P < 0.05), while the rate of moisture and crude ash increased significantly (P < 0.05). The response of LPL, HSL activities and mRNA expression in tissues was tissue dependent. The activities of LPL and HSL in muscle at day 7 were elevated by 2.5 times (P < 0.05) and 11.8 times (P < 0.05) of the value at day 0, respectively, and both then decreased to pre-starvation levels at day 14 and finally stabilized at a certain level afterward. LPL and HSL mRNA abundance in muscle remained relatively stable between 0 and 14 day; then, a significant increase was seen after 14 days. In the liver, LPL activity maintained a significantly increasing trend during starvation, while HSL activity rose dramatically at day 7 of starvation by 2.35 times (P < 0.05) and finally stabilized at a certain level. The mRNA abundance of liver LPL increased significantly during the whole process of starvation (P < 0.05), whereas the mRNA abundance of liver HSL decreased significantly at day 7 of starvation, elevating significantly afterward (P < 0.05).

Berberine attenuates cAMP-induced lipolysis via reducing the inhibition of phosphodiesterase in 3T3-L1 adipocytes

Berberine, a hypoglycemic agent, has been shown to decrease plasma free fatty acids (FFAs) level in insulin-resistant rats. In the present study, we explored the mechanism responsible for the antilipolytic effect of berberine in 3T3-L1 adipocytes. It was shown that berberine attenuated lipolysis induced by catecholamines, cAMP-raising agents, and a hydrolyzable cAMP analog, but not by tumor necrosis factor α and a nonhydrolyzable cAMP analog. Unlike insulin, the inhibitory effect of berberine on lipolysis in response to isoproterenol was not abrogated by wortmannin, an inhibitor of phosphatidylinositol 3-kinase, but additive to that of PD98059, an extracellular signal-regulated kinase kinase inhibitor. Prior exposure of adipocytes to berberine decreased the intracellular cAMP production induced by isoproterenol, forskolin, and 3-isobutyl-1-methylxanthine (IBMX), along with hormone-sensitive lipase (HSL) Ser-563 and Ser-660 dephosphorylation, but had no effect on perilipin phosphorylation. Berberine stimulated HSL Ser-565 as well as adenosine monophosphate-activated protein kinase (AMPK) phosphorylation. However, compound C, an AMPK inhibitor, did not reverse the regulatory effect of berberine on HSL Ser-563, Ser-660, and Ser-565 phosphorylation, nor the antilipolytic effect of berberine. Knockdown of AMPK using RNA interference also failed to restore berberine-suppressed lipolysis. cAMP-raising agents increased AMPK activity, which was not additive to that of berberine. Stimulation of adipocytes with berberine increased phosphodiesterase (PDE) 3B and PDE4 activity measured by hydrolysis of (3)[H]cAMP. These results suggest that berberine exerts an antilipolytic effect mainly by reducing the inhibition of PDE, leading to a decrease in cAMP and HSL phosphorylation independent of AMPK pathway.

Cardiac overexpression of hormone-sensitive lipase inhibits myocardial steatosis and fibrosis in streptozotocin diabetic mice

Intracellular lipid accumulation (steatosis) and resultant lipotoxicity are key features of diabetic cardiomyopathy. Since cardiac hormone-sensitive lipase (HSL) is activated in diabetic mice, we sought to explore a pathophysiological function of cardiac HSL in the development of diabetic cardiomyopathy. Transgenic (Tg) mice with heart-specific HSL overexpression were generated, and cardiac histology, function, lipid profile, and gene expressions were analyzed after induction of diabetes by streptozotocin. Electron microscopy showed numerous lipid droplets in wild-type (Wt) hearts after 3 wk of diabetes, whereas Tg mice showed no lipid droplet accumulation. Cardiac content of acylglycerides was increased approximately 50% with diabetes in Wt mice, whereas this was blunted in Tg hearts. Cardiac lipid peroxide content was twofold lower in Tg hearts than in Wt hearts. The mRNA expressions for peroxisome proliferator-activated receptor-alpha, genes for triacylglycerol synthesis, and lipoprotein lipase were increased with diabetes in Wt hearts, whereas this induction was absent in Tg hearts. Expression of genes associated with lipoapoptosis was decreased, whereas antioxidant protein metallothioneins were increased in diabetic Tg hearts. Diabetic Wt hearts showed interstitial fibrosis and increased collagen content. However, Tg hearts displayed no overt fibrosis, concomitant with decreased expression of collagens, transforming growth factor-beta, and matrix metalloproteinase 2. Notably, mortality during the experimental period was approximately twofold lower in diabetic Tg mice compared with Wt mice. In conclusion, since HSL overexpression inhibits cardiac steatosis and fibrosis by apparently hydrolyzing toxic lipid metabolites, cardiac HSL could be a therapeutic target for regulating diabetic cardiomyopathy.

Adipose triglyceride lipase and hormone-sensitive lipase protein expression is decreased in the obese insulin-resistant state

AIM/HYPOTHESIS

Obesity is associated with increased triacylglycerol (TAG) storage in adipose tissue and insulin resistance. The mobilization of stored TAG is mediated by hormone-sensitive lipase (HSL) and the recently discovered adipose triglyceride lipase (ATGL). The aim of the present study was to examine whether ATGL and HSL mRNA and protein expression are altered in insulin-resistant conditions. In addition, we investigated whether a possible impaired expression could be reversed by a period of weight reduction.

METHODS

Adipose tissue biopsies were taken from obese subjects (n = 44) with a wide range of insulin resistance, before and just after a 10-wk hypocaloric diet. ATGL and HSL protein and mRNA expression was determined by Western blot and quantitative RT-PCR, respectively.

RESULTS

Fasting insulin levels and the degree of insulin resistance (using the homeostasis model assessment index for insulin resistance) were negatively correlated with ATGL and HSL protein expression, independent of age, gender, fat cell size, and body composition. Both mRNA and protein levels of ATGL and HSL were reduced in insulin-resistant compared with insulin-sensitive subjects (P < 0.05). Weight reduction significantly decreased ATGL and HSL mRNA and protein expression. A positive correlation between the decrease in leptin and the decrease in ATGL protein level after weight reduction was observed. Finally, ATGL and HSL mRNA and protein levels seem to be highly correlated, indicating a tight coregulation and transcriptional control.

CONCLUSIONS

In obese subjects, insulin resistance and hyperinsulinemia are strongly associated with ATGL and HSL mRNA and protein expression, independent of fat mass. Data on weight reduction indicated that also other factors (e.g. leptin) relate to ATGL and HSL protein expression.

Placental triglyceride accumulation in maternal type 1 diabetes is associated with increased lipase gene expression

Maternal diabetes can cause fetal macrosomia and increased risk of obesity, diabetes, and cardiovascular disease in adulthood of the offspring. Although increased transplacental lipid transport could be involved, the impact of maternal type 1 diabetes on molecular mechanisms for lipid transport in placenta is largely unknown. To examine whether maternal type 1 diabetes affects placental lipid metabolism, we measured lipids and mRNA expression of lipase-encoding genes in placentas from women with type 1 diabetes (n = 27) and a control group (n = 21). The placental triglyceride (TG) concentration and mRNA expression of endothelial lipase (EL) and hormone-sensitive lipase (HSL) were increased in placentas from women with diabetes. The differences were more pronounced in women with diabetes and suboptimal metabolic control than in women with diabetes and good metabolic control. Placental mRNA expression of lipoprotein lipase and lysosomal lipase were similar in women with diabetes and the control group. Immunohistochemistry showed EL protein in syncytiotrophoblasts facing the maternal blood and endothelial cells facing the fetal blood in placentas from both normal women and women with diabetes. These results suggest that maternal type 1 diabetes is associated with TG accumulation and increased EL and HSL gene expression in placenta and that optimal metabolic control reduces these effects.

Antiobesity Effect ofKochujang(Korean Fermented Red Pepper Paste) Extract in 3T3-L1 Adipocytes

Kochujang (Korean fermented red pepper paste) is a mixture of fermented soybeans, wheat, and red pepper powder. Kochujang has been reported to reduce body fat gain and lipid levels of adipose tissues and serum in rats. We studied the inhibitory effect of Kochujang on lipid accumulation and investigated the molecular mechanism of the action in 3T3-L1 adipocytes by measuring the expression levels of adipocyte-specific genes by real-time reverse transcription-polymerase chain reaction. When 3T3-L1 adipocytes were treated with Kochujang extract (KE), the sizes of adipocytes and leptin secretion were decreased. Hormone-sensitive lipase (HSL) was transcriptionally up-regulated at 4 hours, and glycerol secretion was increased at both 4 hours and 24 hours. Moreover, mRNA expression levels of both sterol regulatory element-binding protein 1-c (SREBP-1c) and peroxisome proliferator-activated receptor-gamma (PPAR-gamma), which are critical transcription factors for adipogenesis, were markedly down-regulated. Tumor necrosis factor-alpha (TNF-alpha) is reported to impair pre-adipocyte differentiation and induce lipolysis and apoptosis. KE treatment of 3T3-L1 adipocytes decreased TNF-alpha mRNA levels, but had no apparent affect on apoptosis. Taken together, our study shows that Kochujang decreased lipid accumulation in 3T3-L1 adipocytes by inhibiting adipogenesis through down-regulation of SREBP-1c and PPAR-gamma and by stimulation of lipolysis due to increased HSL activity. TNF-alpha might not be involved in the reduction of lipid accumulation by KE.

Adipose triglyceride lipase: function, regulation by insulin, and comparison with adiponutrin

Adipose triglyceride lipase (ATGL) is a recently described adipose-enriched protein with triglyceride-specific lipase activity. ATGL shares the greatest sequence homology with adiponutrin, a nutritionally regulated protein of unclear biological function. Here we present a functional analysis of ATGL and adiponutrin and describe their regulation by insulin. Retroviral-mediated overexpression of ATGL in 3T3-L1 adipocytes increased basal and isoproterenol-stimulated glycerol and nonesterified fatty acid (NEFA) release, whereas siRNA-mediated knockdown of ATGL had the opposite effect. In contrast, siRNA-mediated knockdown of adiponutrin in 3T3-L1 adipocytes had no effect on glycerol or NEFA release. In mice, both ATGL and adiponutrin are nutritionally regulated in adipose tissue, with ATGL being upregulated and adiponutrin being downregulated by fasting. In 3T3-L1 adipocytes, insulin decreased ATGL and increased adiponutrin expression in a dose- and time-dependent manner, suggesting that insulin directly mediates this nutritional regulation. In addition, adipose expression of ATGL was increased by insulin deficiency and decreased by insulin replacement in streptozotocin-induced diabetic mice and was increased in fat-specific insulin receptor knockout mice, whereas adiponutrin showed the opposite pattern. These data suggest that murine ATGL but not adiponutrin contributes to net adipocyte lipolysis and that ATGL and adiponutrin are oppositely regulated by insulin both in vitro and in vivo.

Isoproterenol, TNFalpha, and insulin downregulate adipose triglyceride lipase in 3T3-L1 adipocytes

Recently, adipose triglyceride lipase (ATGL, also called desnutrin and calcium-independent phospholipase A2 [iPLA(2)] zeta) was isolated as a novel adipose-expressed triglyceride lipase which is downregulated in obesity and may contribute to obesity-associated metabolic disorders such as hyperlipidemia and insulin resistance. To clarify expression and regulation of this fat-derived lipase, ATGL mRNA was measured in 3T3-L1 adipocytes by quantitative real-time reverse transcription-polymerase chain reaction after treatment with isoproterenol, tumor necrosis factor (TNF) alpha, insulin, and growth hormone (GH) which have been shown to influence lipolysis and insulin sensitivity profoundly. Interestingly, treatment of adipocytes with 100 nM isoproterenol, 30 ng/ml TNF alpha, and 100 nM insulin for 16 h significantly decreased ATGL mRNA to 74%, 17%, and 49% of control levels, respectively. GH did not influence ATGL synthesis. The effect of isoproterenol, TNFalpha, and insulin on ATGL expression was time- and dose-dependent. Similarly, HSL mRNA was downregulated by the three hormones. Furthermore, signaling studies suggested that activation of Gs-protein-coupled pathways by forskolin and cholera toxin is sufficient to significantly downregulate ATGL mRNA. Moreover, p44/42 mitogen-activated protein kinase appears to partly mediate the negative effect of insulin but not TNFalpha on ATGL. Taken together, downregulation of ATGL by isoproterenol, TNFalpha, and insulin might contribute to dysregulated expression and function of this lipase in obesity, hyperlipidemia, and insulin resistance.

Function of hormone-sensitive lipase in diacylglycerol-protein kinase C pathway

To explore the functional effects of hormone-sensitive lipase (HSL) in diacylglycerol (DAG) metabolism, Chinese hamster ovary cells were stably transfected with rat HSL cDNA (wt-HSL), inactive mutant S423A-HSL cDNA (S423A) and pcDNA3 vector alone (Ct). [(14)C]Glucose-incorporation into triglyceride (TG) was 75% lower in the presence or absence of insulin in cells expressing wt-HSL compared to Ct or S423A. [(14)C]Glucose-incorporation into DAG was 33% lower without insulin and 51% lower with insulin in cells expressing wt-HSL compared to Ct or S423A. Insulin stimulated glucose-incorporation into DAG 2.2-fold in S423A and Ct cells, whereas only a 50% increase was observed in cells expressing wt-HSL. Phospholipase C-mediated release of DAG from membrane phospholipids was reduced 70% in cells expressing wt-HSL compared to Ct or S423A. Western blot analysis showed that membrane-bound protein kinase C (PKC)-alpha and -epsilon were decreased 40-50% in cells expressing wt-HSL grown in high glucose with insulin. These data show that HSL potentially hydrolyzes cellular DAG generated either by de novo synthesis from glucose or release from membrane phospholipids by phospholipase C, resulting in a reduction in the translocation of DAG-sensitive PKCs.

The effect of thyroid hormones on blood insulin level and metabolic parameters in diabetic rats

The effect of exogenous thyroid hormones on blood insulin and metabolic parameters in diabetic rats was investigated. Three groups of rats were treated with streptozotocin (STZ; 50 mg/kg b.w., intravenously) and one group receiving only saline served as control. Beginning with the third day after STZ treatment, until the last day before decapitation, i.e. for 11 days, two groups of diabetic rats were treated with T3 (50 microg/kg b.w., i.p.) or T4 (250 microg/kg b.w., i.p.). After two weeks, STZ injected rats had lower body weight, hyperglycemia with a simultaneous drop in blood insulin and decrease of T3 and T4 concentrations in comparison to control animals. Liver glycogen content was also reduced, whereas serum lactate, free fatty acids, triglycerides and cholesterol were elevated. Exogenous thyroid hormones given to diabetic rats substantially attenuated hyperglycemia without any significant changes in blood insulin concentration. An additional reduction of body weight gain and depletion in liver glycogen stores were also observed. Thyroid hormones augmented serum lactate and cholesterol and had no beneficial effect on elevated free fatty acids and triglycerides. It can be concluded that in spite of partial restriction of hyperglycemia, thyroid hormones evoked several unfavourable changes strongly limiting their potential use in diabetes.

Synthesis and Structure−Activity Relationship for a Novel Class of Potent and Selective Carbamoyl-Triazole Based Inhibitors of Hormone Sensitive Lipase

The central role of the intracellular enzyme hormone-sensitive lipase (HSL) in regulating fatty acid metabolism makes it an interesting pharmacological target for the treatment of insulin resistant and dyslipidemic disorders where a decrease in delivery of fatty acids to the circulation is desirable, e.g., in individuals with type 2 diabetes, metabolic syndrome, or impaired glucose tolerance. On the basis of a lead structure from high throughput screening, we have identified a very potent type of carbamoyl-triazole inhibitors of HSL. As part of the lead optimization program, four new classes of carbamoyl-triazoles were synthesized and tested with respect to potency, efficacy and selectivity. Methyl-phenyl-carbamoyl-triazoles were identified as potent and efficacious HSL inhibitors. These compounds do not inhibit other hydrolases such as hepatic lipase, lipoprotein lipase, pancreatic lipase, and butyrylcholine esterase. However, the inhibitors 4b and 4g with IC(50) values for HSL of 0.17 and 0.25 microM, respectively, were the only inhibitors selective against acetylcholine esterase. A reversible pseudosubstrate inhibition mechanism is proposed for this class of inhibitors.

Cholesteryl ester transfer protein expression is down-regulated in hyperinsulinemic transgenic mice

Cholesteryl ester transfer protein (CETP) mediates cholesteryl ester (CE) and triglyceride redistribution among plasma lipoproteins. In this work, we investigated whether varying levels of insulin regulate the CETP expression in vivo. Insulin deficiency [streptozotocin (STZ) injection], and hyperinsulinemia (insulin injections, 14 days) were induced in transgenic mice expressing a human CETP minigene flanked by its natural regulatory sequences. Glucose supplementation was provided to the hyperinsulinemic group (INS+GLUC) and to an extra group of mice (GLUC). In the STZ group, endogenous CE transfer rate, plasma CETP, and hepatic CETP mRNA levels were enhanced 3.0-, 1.5-, and 2.5-fold, respectively, as compared with controls. Insulin replacement in STZ mice normalized their glycemia and liver mRNA levels. Higher plasma CETP levels were observed in GLUC mice, which were decreased in INS+GLUC mice. Hepatic CETP mRNA was not altered in GLUC mice and was reduced by one-third in INS+GLUC mice. These results show that: 1) STZ treatment increases CETP plasma levels and liver mRNA expression; 2) diet glucose supplementation increases plasma CETP levels but does not change liver mRNA abundance; and 3) daily insulin injections blunt the glucose-stimulated CETP expression by reducing its liver mRNA levels. These data suggest that insulin down-regulates CETP gene expression.

Differences in the expression of lipolytic-related genes in rat white adipose tissues

We have investigated in vivo whether the gene expression of the beta3-adrenergic receptor (beta3-AR), perilipin A, hormone-sensitive lipase (HSL), and adipocyte lipid-binding protein (ALBP/aP2) is regulated in a site-specific manner. To induce lipolysis and discriminate between short- and long-term modifications, rats were submitted to an experimental fast for one or five days followed or not by refeeding. The mRNA encoding beta3-AR in retroperitoneal adipose tissue (RP) was significantly increased by one and five days of fasting (4-fold) and then lowered by one day of refeeding (2-fold) compared to fed rats. The reverse trend was observed for perilipin A expression in one day fasted rats. HSL mRNA concentrations were significantly induced (2.2-fold) by five days of fasting relative to fed animals and remained high after refeeding. ALBP/aP2, peroxisome proliferator-activated receptor gamma, and CAAT/enhancer binding protein alpha mRNA levels were essentially unaffected by dietary manipulations. Fasting and/or refeeding were similarly ineffective at regulating gene expression in SC. These data provide a molecular basis for regional differences at different steps of the lipolytic process.

Characteristics of the epidermis and stratum corneum of hairless mice with experimentally induced diabetes mellitus

Diabetes mellitus induces many pathophysiologic changes in the skin. Even so, dermatologists still lack an animal model of diabetes that enables the direct evaluation of the various functional properties of the skin. Our group induced two types of an experimental type 1 diabetes model in hairless mice by administering either streptozotocin or alloxan, in order to examine the properties of the stratum corneum and epidermis of these animals. The plasma glucose concentrations of the mice at 3 wk after their i.v. injection were significantly higher than those of control mice (streptozotocin, 3.2-fold; alloxan, 3.7-fold). The stratum corneum water content was significantly reduced in both types of diabetic mice, whereas the transepidermal water loss remained unchanged. The amino acid content with normal epidermal profilaggrin processing was either normal or elevated in the stratum corneum of the streptozotocin-treated mice. In contrast, the stratum corneum triglyceride content in the streptozotocin-treated mice was significantly lower than the control level, even though the levels of ceramides, cholesterols, and fatty acids in the stratum corneum were all higher than the control levels. The streptozotocin-treated group also exhibited decreases in basal cell proliferation and epidermal DNA content linked with an increase in the number of corneocyte layers in the stratum corneum, suggesting that the rates of epidermal and stratum corneum turnover were slower in the streptozotocin-treated animals than in the normal controls. In contrast, there were no remarkable changes in any of the epidermal differentiation marker proteins examined. This finding in diabetic mice, namely, reduction in both the epidermal proliferation and stratum corneum water content without any accompanying impairment in the stratum corneum barrier function, is similar to that found in aged human skin. Our new animal model of diabetes will be useful for the study of diabetic dermopathy as well as the mechanisms of stratum corneum moisturization.

Hormone-sensitive lipase: control of intracellular tri-(di-)acylglycerol and cholesteryl ester hydrolysis

Hormone-sensitive lipase (HSL) is an intracellular neutral lipase that is capable of hydrolyzing triacylglycerols, diacylglycerols, monoacylglycerols, and cholesteryl esters, as well as other lipid and water soluble substrates. HSL activity is regulated post-translationally by phosphorylation and also by pretranslational mechanisms. The enzyme is highly expressed in adipose tissue and steroidogenic tissues, with lower amounts expressed in cardiac and skeletal muscle, macrophages, and islets. Studies of the structure of HSL have identified several amino acids and regions of the molecule that are critical for enzymatic activity and regulation of HSL. This has led to important insights into its function, including the interaction of HSL with other intracellular proteins, such as adipocyte lipid binding protein. Accumulating evidence has defined important functions for HSL in normal physiology, affecting adipocyte lipolysis, steroidogenesis, spermatogenesis, and perhaps insulin secretion and insulin action; however, direct links between abnormal expression or genetic variations of HSL and human disorders, such as obesity, insulin resistance, type 2 diabetes, and hyperlipidemia, await further clarification. The published reports examining the regulation, and function of HSL in normal physiology and disease are reviewed in this paper.

Insulin and rosiglitazone regulation of lipolysis and lipogenesis in human adipose tissue in vitro

Lipolysis is an important process determining fuel metabolism, and insulin regulates this process in adipose tissue. The aim of this study was to investigate the long-term effects of insulin, an insulin enhancer (rosiglitazone [RSG]), and insulin in combination with RSG on the regulation of lipolysis and lipogenesis in human abdominal subcutaneous fat. Lipolysis and lipogenesis were assessed by protein expression studies of hormone-sensitive lipase (HSL) (84 kDa) and lipoprotein lipase (LPL) (56 kDa), respectively. In addition, lipolytic rate was assessed by glycerol release assay and tumor necrosis factor (TNF)-alpha release measured by enzyme-linked immunosorbent assay (n = 12). In subcutaneous adipocytes, increasing insulin doses stimulated LPL expression, with maximal stimulation at 100 nmol/l insulin (control, 1.0 +/- 0.0 [mean +/- SE, protein expression relative to control]; 1 nmol/l insulin, 0.87 +/- 0.13; 100 nmol/l insulin, 1.68 +/- 0.19; P < 0.001). In contrast, insulin at the 100 nmol/l dose reduced the expression of HSL (100 nmol/l insulin, 0.49 +/- 0.05; P < 0.05), while no significant reduction was observed at other doses. Higher doses of insulin stimulated both HSL (1,000 nmol/l insulin, 1.4 +/- 0.07; P < 0.01) and LPL (control 1.00 +/- 0.0; 1,000 nmol/l insulin, 2.66 +/- 0.27; P < 0.01) protein expression. Cotreatment with RSG induced an increased dose response to insulin for LPL and HSL (P < 0.05); RSG alone also increased LPL and HSL expression (P < 0.05). Insulin stimulated TNF-alpha secretion in a dose-dependent manner (P < 0.01); the addition of RSG (10(-8) mol/l) reduced TNF-alpha secretion (P < 0.05). In summary, chronic treatment of human adipocytes with insulin stimulates lipolysis and LPL protein expression. The addition of RSG reduced the lipolytic rate and TNF-alpha secretion. The increase in lipolysis is not explained by changes in HSL expression. These data, therefore, may explain in part why hyperinsulinemia coexists with increased circulating nonesterified free fatty acids and increased adiposity in obese and/or type 2 diabetic patients.

The regulation of HSL and LPL expression by DHT and flutamide in human subcutaneous adipose tissue

Clinical observations suggest a role for testosterone in the accumulation of central adiposity and with an associated increased risk of disease. To date, no human study has analysed the role of dihydrotestosterone (DHT) on adipose tissue mass regulation in vitro. This study investigated the role of DHT and androgen receptors (AR) in the regulation of lipolysis and lipogenesis by examining the key enzymes hormone sensitive lipase (HSL) and lipoprotein lipase (LPL) respectively. Isolated abdominal subcutaneous adipocytes (Scad) (n = 15) were treated with either DHT (10(-7)-10(-9) m), an antiandrogen, flutamide (FLT: 10(-7)-10(-9) m) or a combination of DHT (10(-7)-10(-9) m) with FLT (10(-8) m). Relative protein expression of HSL, LPL and AR was determined. In Scad, DHT inhibited HSL expression maximally at 10(-9) m (0.7 +/- 0.4**; p < 0.01**) compared with control (control: 1.0 +/- (s.e.m.) 0.0), whereas LPL protein expression was stimulated at DHT10(-9) m (2.22 +/- 0.48*; p < 0.05*). Glycerol release assay results correlated with HSL expression data. LPL expression was reduced at all doses with combinations of DHT + FLT compared with DHT alone. Androgen receptor expression studies showed an inverse correlation with DHT, whereas DHT + FLT reduced AR expression. These studies indicate that DHT may alter HSL and LPL expression, whereas only LPL expression appears mediated by AR. These findings suggest a physiological role for DHT in the control of adipose tissue mass in women, and indicate that androgens may also play an important role in regulating lipid metabolism.

Transcriptional regulation of adipocyte hormone-sensitive lipase by glucose

Hormone-sensitive lipase (HSL) catalyzes the rate-limiting step in the mobilization of fatty acids from adipose tissue, thus determining the supply of energy substrates in the body. HSL mRNA was positively regulated by glucose in human adipocytes. Pools of stably transfected 3T3-F442A adipocytes were generated with human adipocyte HSL promoter fragments from -2,400/+38 to -31/+38 bp linked to the luciferase gene. A glucose-responsive region was mapped within the proximal promoter (-137 bp). Electromobility shift assays showed that upstream stimulatory factor (USF)-1 and USF2 and Sp1 and Sp3 bound to a consensus E-box and two GC-boxes in the -137-bp region. Cotransfection of the -137/+38 construct with USF1 and USF2 expression vectors produced enhanced luciferase activity. Moreover, HSL mRNA levels were decreased in USF1- and USF2-deficient mice. Site-directed mutagenesis of the HSL promoter showed that the GC-boxes, although contributing to basal promoter activity, were dispensable for glucose responsiveness. Mutation of the E-box led to decreased promoter activity and suppression of the glucose response. Analogs and metabolites were used to determine the signal metabolite of the glucose response. The signal is generated downstream of glucose-6-phosphate in the glycolytic pathway before the triose phosphate step.

Subcellular localization of insulin receptor substrate family proteins associated with phosphatidylinositol 3-kinase activity and alterations in lipolysis in primary mouse adipocytes from IRS-1 null mice

To clarify the roles of insulin receptor substrate (IRS) family proteins in phosphatidylinositol (PI) 3-kinase activation and insulin actions in adipocytes, we investigated the intracellular localization of IRS family proteins and PI 3-kinase activation in response to insulin by fractionation of mouse adipocytes from wild-type and IRS-1 null mice. In adipocytes from wild-type mice, tyrosine-phosphorylated IRS-1 and IRS-2, which were found to associate with PI 3-kinase in response to insulin, were detected in the plasma membrane (PM) and low-density microsome (LDM) fractions. By contrast, tyrosine-phosphorylated IRS-3 (pp60), which was found to associate with PI 3-kinase, was predominantly localized in the PM fraction. In adipocytes from IRS-1-null mice, insulin-stimulated PI 3-kinase activity in anti-phosphotyrosine (alphaPY) immunoprecipitates in the LDM fraction was almost exclusively mediated via IRS-2 and was reduced to 25%; however, insulin-stimulated PI 3-kinase activity in the PM fraction was primarily mediated via IRS-3 and was reduced to 60%. To determine the potential functional impact of the distinct subcellular localization of IRSs and associating PI 3-kinase activity on adipocyte-specific metabolic actions, we examined lipolysis in IRS-1 null mice. The level of isoproterenol-induced lipolysis was increased 5.1-fold in adipocytes from IRS-1 null mice as compared with wild-type mice. Moreover, hormone-sensitive lipase (HSL) protein was increased 4.3-fold in adipocytes from IRS-1-null mice compared with wild-type mice, and HSL mRNA expression was also increased. The antilipolytic effect of insulin in IRS-1 null adipocytes, however, was comparable to that in wild-type mice. Thus, discordance between these two insulin actions as well as the transcriptional and translational effect (HSL mRNA and protein regulation) and the PM effect (antilipolysis) of insulin may be explained by distinct roles of both PI 3-kinase activity associated with IRS-1/IRS-2 and PI 3-kinase activity associated with IRS-3 in insulin actions related to their subcellular localization.

Soluble receptors for tumor necrosis factor-alpha (TNF-R p55 and TNF-R p75) in familial combined hyperlipidemia

We investigated the potential role of the 75 kD receptor for tumor necrosis factor-alpha (TNF-alpha) (TNFRSF1B, located on chromosome 1 band p36.2) as a modifier gene in familial combined hyperlipidemia (FCH), based on previous linkage and association data. Age-corrected values for the soluble (s) extracellular domain of TNF-R p75 were lower in 156 well-characterized hyperlipidemic (HL) FCH relatives than in 168 normolipidemic (NL) relatives (P<0.01). Plasma concentrations of the soluble domain of the 55 kD receptor (sTNF-R p55, the other TNF-alpha receptor) did not differ between HL and NL relatives. In conditional logistic regression analysis, plasma sTNF-R p75 concentration was the only non-lipid variable that contributed significantly to prediction of affected FCH status (regression coefficient=-0.413, P=0.01). The present findings have potentially important diagnostic and therapeutic implications in FCH.