Gossypin up-regulates LDL receptor through activation of ERK pathway: a signaling mechanism for the hypocholesterolemic effect

Gossypin induces apoptosis and autophagy via the MAPK/JNK pathway in HT‑29 human colorectal cancer cells

Gossypin, a flavone found in Hibiscus vitifolius, exhibits antioxidant, antidiabetic, anti‑inflammatory and anticancer effects. The present study investigated the potential of gossypin to induce apoptosis and autophagy in HT‑29 human colorectal cancer (CRC) cells, and assessed its association with the MAPK/JNK pathway. Cell viability assays, DAPI staining, flow cytometry, acridine orange staining, western blotting, hematoxylin and eosin staining, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining and immunohistochemistry were performed. The results revealed an increased number of apoptotic bodies, higher apoptosis rates and enhanced autophagy in gossypin‑treated HT‑29 cells. To investigate autophagy during cell death, the effects of the early autophagy inhibitor 3‑methyladenine (3‑MA) and the late autophagy inhibitor hydroxychloroquine on cell viability and the expression of apoptosis‑related proteins were assessed. Significant increases in cell viability were observed following 3‑methyladenine pretreatment, as well as a decrease in the expression levels of Bcl‑2 and an increase in Bax. The analysis of MAPK pathway proteins following treatment with gossypin revealed that the levels of phosphorylated (p‑)JNK and p‑p38 were significantly increased in a concentration‑dependent manner. The JNK inhibitor SP600125 was used to confirm the role of the JNK pathway in gossypin‑induced apoptosis and autophagy. Moreover, gossypin reduced the volume of HT‑29 tumors in mice, and western blotting indicated the induction of apoptosis and autophagy in these tumors in vivo. Finally, TUNEL and immunohistochemistry experiments confirmed the induction of apoptosis and p‑JNK upregulation in these tumors in vivo. In conclusion, the present study suggested that gossypin may induce MAPK/JNK‑mediated apoptosis and autophagy in HT‑29 CRC cells, highlighting the potential of gossypin as an anticancer agent.

MicroRNA-34a Mediates High-Fat-Induced Hepatic Insulin Resistance by Targeting ENO3

The etiology of numerous metabolic disorders is characterized by hepatic insulin resistance (IR). Uncertainty surrounds miR-34a's contribution to high-fat-induced hepatic IR and its probable mechanism. The role and mechanism of miR-34a and its target gene ENO3 in high-fat-induced hepatic IR were explored by overexpressing/suppressing miR-34a and ENO3 levels in in vivo and in vitro experiments. Moreover, as a human hepatic IR model, the miR-34a/ENO3 pathway was validated in patients with non-alcoholic fatty liver disease (NAFLD). The overexpression of hepatic miR-34a lowered insulin signaling and altered glucose metabolism in hepatocytes. In contrast, reducing miR-34a expression significantly reversed hepatic IR indices induced by palmitic acid (PA)/HFD. ENO3 was identified as a direct target gene of miR-34a. Overexpression of ENO3 effectively inhibited high-fat-induced hepatic IR-related indices both in vitro and in vivo. Moreover, the expression patterns of members of the miR-34a/ENO3 pathway in the liver tissues of NAFLD patients was in line with the findings of both cellular and animal studies. A high-fat-induced increase in hepatic miR-34a levels attenuates insulin signaling and impairs glucose metabolism by suppressing the expression of its target gene ENO3, ultimately leading to hepatic IR. The miR-34a/ENO3 pathway may be a potential therapeutic target for hepatic IR and related metabolic diseases.

LncRNA Gm12664-001 ameliorates nonalcoholic fatty liver through modulating miR-295-5p and CAV1 expression

Background

Our study aims to investigate the mechanisms of lncRNA Gm12664–001 improved hepatic lipid accumulation-initiated NAFLD via regulating miR-295-5p and CAV1 in AML12 cells.

Methods

The animals were divided into normal control (NC) group and high fat diet (HFD) group (20 mice per group) for 8w. The steatotic liver was measured by hematoxylin eosin (HE) staining and kits. We performed systematical analyses on hepatic expression profiles of long noncoding RNAs (lncRNAs) and microRNAs in a high-fat diet (HFD)-induced steatotic animal model. The expression profile of targets was confirmed by bioinformatics analysis, luciferase assay, RT-PCR and western blot in AML12 cells.

Results

HFD treatment markedly observed hepatic fatty degeneration with primarily fat vacuoles, and increased TG level compared with control. According to microarray data, we found that transfection of Gm12664–001 siRNA (siRNA-118,306) obviously enhanced TG accumulation and repressed CAV1 in AML12 cells. Furthermore, the TG accumulation markedly increased by siRNA-mediated knockdown of CAV1 in AML12 cells. By bioinformatics prediction, AML12 cells were transfected of siRNA-118,306 obviously upregulated miR-295-5p. Transfection of miR-295-5p mimics significantly increased TG accumulation and obviously suppressed the target CAV1.

Conclusions

The results revealed that lncRNA Gm12664–001 attenuated hepatic lipid accumulation through negatively regulating miR-295-5p and enhancing CAV1 expression in AML12 cells.

Mangiferin Improved Palmitate-Induced-Insulin Resistance by Promoting Free Fatty Acid Metabolism in HepG2 and C2C12 Cells via PPARα: Mangiferin Improved Insulin Resistance

Elevated free fatty acid (FFA) is a key risk factor for insulin resistance (IR). Our previous studies found that mangiferin could decrease serum FFA levels in obese rats induced by a high-fat diet. Our research was to determine the effects and mechanism of mangiferin on improving IR by regulating FFA metabolism in HepG2 and C2C12 cells. The model was used to quantify PA-induced lipid accumulation in the two cell lines treated with various concentrations of mangiferin simultaneously for 24 h. We found that mangiferin significantly increased insulin-stimulated glucose uptake, via phosphorylation of protein kinase B (P-AKT), glucose transporter 2 (GLUT2), and glucose transporter 4 (GLUT4) protein expressions, and markedly decreased glucose content, respectively, in HepG2 and C2C12 cells induced by PA. Mangiferin significantly increased FFA uptake and decreased intracellular FFA and triglyceride (TG) accumulations. The activity of the peroxisome proliferator-activated receptor α (PPARα) protein and its downstream proteins involved in fatty acid translocase (CD36) and carnitine palmitoyltransferase 1 (CPT1) and the fatty acid β-oxidation rate corresponding to FFA metabolism were also markedly increased by mangiferin in HepG2 and C2C12 cells. Furthermore, the effects were reversed by siRNA-mediated knockdown of PPARα. Mangiferin ameliorated IR by increasing the consumption of glucose and promoting the FFA oxidation via the PPARα pathway in HepG2 and C2C12 cells.

Epigallocatechin gallate improves insulin resistance in HepG2 cells through alleviating inflammation and lipotoxicity

AIMS

High levels of circulating free fatty acids (FFAs), inflammation and oxidative stress are important causes for insulin resistance (IR) and type 2 diabetes mellitus. The aim of this study was to investigate the mechanisms of EGCG in alleviating IR in HepG2 cells.

METHODS

HepG2 cells were treated with 25 mM glucose, 0.25 mM palmitic acid (PA), or 50 μM EGCG for 24 h.

RESULTS

EGCG increased glucose uptake and decreased glucose content. EGCG markedly decreased the levels of inflammatory and oxidative stress factors including nuclear factor κB (NF-κB), tumor necrosis factor-α, interleukin-6, reactive oxygen species, malondialdehyde and p53 protein, and markedly increased superoxide dismutases (SOD), glutathione peroxidase and SOD2 protein. EGCG significantly downregulated the levels of FFAs, triacylglycerol and cholesterol in HepG2 cells. The glucose transporter 2 (GLUT2) protein and its downstream proteins peroxisome proliferator-activated receptor γ coactivator (PGC)-1β were significantly increased, and sterol regulatory element-binding-1c (SREBP-1c) protein, and fatty acid synthase (FAS) were significantly decreased by EGCG in HepG2. Moreover, the foregoing effects were reversed by siRNA-mediated knockdown of GLUT2.

CONCLUSION

Our data demonstrated that EGCG improved IR, possibly through ameliorating glucose (25 mM) and PA (0.25 mM)-induced inflammation, oxidative stress, and FFAs via the GLUT2/PGC-1β/SREBP-1c/FAS pathway in HepG2 cells.

Elevated microRNA-34a contributes to trophoblast cell apoptosis in preeclampsia by targeting BCL-2

Preeclampsia (PE) is one of the most common pregnancy-specific pathologic complications, and is characterised by onset of hypertension and proteinuria. Placental trophoblast cell apoptosis is generally accepted as a major cause of PE. However, the details of the mechanism underlying the condition remain unclear. Here, we aimed to investigate a possible association between microRNA (miR)-34a and human trophoblast cell apoptosis during PE. We evaluated miR-34a expression in placentas from patients with PE compared with those from healthy pregnant individuals. Furthermore, we measured apoptosis rate after miR-34a mimic and/or inhibitor transfection in vitro, and identified B-cell CLL/lymphoma 2 (BCL-2) as a target of miR-34a. We found that miR-34a levels were significantly higher in placental tissues from patients with PE than in normal placentas. Upregulation of miR-34a induced trophoblast cell apoptosis in PE by inhibiting expression of BCL-2 protein. miR-34a inhibition reversed miR-34a-induced apoptosis in the HTR-8/SVneo human trophoblast cell line. Our findings indicate that miR-34a may be linked to the occurrence of PE via effects on BCL-2 in the human placenta, and may therefore provide a potential therapeutic target for PE.

Maternal Prenatal Folic Acid Supplementation Programs Offspring Lipid Metabolism by Aberrant DNA Methylation in Hepatic ATGL and Adipose LPL in Rats

The effects of maternal prenatal folic acid supplementation (FAS) on offspring lipid metabolism in adulthood remains unclear, although prenatal FAS is compulsively suggested in many countries. Female Sprague-Dawley rats were fed with control (CON) or FAS diets before and during pregnancy. Male offspring of CON and FAS dams were further divided into two groups at seven weeks for CON and high-fat (HF) diet interventions for eight weeks in adulthood (n = 10). The interactive effects of maternal prenatal FAS and offspring HF in adulthood on lipid metabolism and DNA methylation of genes involved in lipids metabolism were assessed. The male offspring of FAS dams had elevated serum and liver triglyceride level when fed with HF compared to the male offspring of CON dams. The mRNA and protein expression levels of hepatic ATGL and adipose LPL were significantly decreased in offspring of FAS dams than in offspring of CON dams. Furthermore, maternal prenatal FAS resulted in elevated DNA methylation levels in the promoter and first exon region of hepatic ATGL and adipose LPL in offspring. Maternal FAS exacerbated the adverse effects of HF on lipid metabolism in offspring through inducing aberrant DNA methylation levels of hepatic ATGL and adipose LPL.

Chronic vitamin A-enriched diet feeding regulates hypercholesterolaemia through transcriptional regulation of reverse cholesterol transport pathway genes in obese rat model of WNIN/GR-Ob strain

Background & objectives:

Hepatic scavenger receptor class B1 (SR-B1), a high-density lipoprotein (HDL) receptor, is involved in the selective uptake of HDL-associated esterified cholesterol (EC), thereby regulates cholesterol homoeostasis and improves reverse cholesterol transport. Previously, we reported in euglycaemic obese rats (WNIN/Ob strain) that feeding of vitamin A-enriched diet normalized hypercholesterolaemia, possibly through hepatic SR-B1-mediated pathway. This study was aimed to test whether it would be possible to normalize hypercholesterolaemia in glucose-intolerant obese rat model (WNIN/GR/Ob) through similar mechanism by feeding identical vitamin A-enriched diet.

Methods:

In this study, 30 wk old male lean and obese rats of WNIN/GR-Ob strain were divided into two groups and received either stock diet or vitamin A-enriched diet (2.6 mg or 129 mg vitamin A/kg diet) for 14 wk. Blood and other tissues were collected for various biochemical analyses.

Results:

Chronic vitamin A-enriched diet feeding decreased hypercholesterolaemia and normalized abnormally elevated plasma HDL-cholesterol (HDL-C) levels in obese rats as compared to stock diet-fed obese groups. Further, decreased free cholesterol (FC) and increased esterified cholesterol (EC) contents of plasma cholesterol were observed, which were reflected in higher EC to FC ratio of vitamin A-enriched diet-fed obese rats. However, neither lecithin-cholesterol acyltransferase (LCAT) activity of plasma nor its expression (both gene and protein) in the liver were altered. On the contrary, hepatic cholesterol levels significantly increased in vitamin A-enriched diet fed obese rats. Hepatic SR-B1 expression (both mRNA and protein) remained unaltered among groups. Vitamin A-enriched diet fed obese rats showed a significant increase in hepatic low-density lipoprotein receptor mRNA levels, while the expression of genes involved in HDL synthesis, namely, ATP-binding cassette protein 1 (ABCA1) and apolipoprotein A-I, were downregulated. No such response was seen in vitamin A-supplemented lean rats as compared with their stock diet-fed lean counterparts.

Interpretation & conclusions:

Chronic vitamin A-enriched diet feeding decreased hypercholesterolaemia and normalized HDL-C levels, possibly by regulating pathways involved in HDL synthesis and degradation, independent of hepatic SR-B1 in this glucose-intolerant obese rat model.

Elevated circulating stearic acid leads to a major lipotoxic effect on mouse pancreatic beta cells in hyperlipidaemia via a miR-34a-5p-mediated PERK/p53-dependent pathway

AIMS/HYPOTHESIS

Serum stearic acid (C18:0) is elevated in individuals with hyperlipidaemia and type 2 diabetes. However, the lipotoxicity induced by increased stearic acid in beta cells has not been well described. This study aimed to examine the adverse effects of stearic acid on beta cells and the potential mechanisms through which these are mediated.

METHODS

Three groups of C57BL/6 mice were fed a normal diet or a high-stearic-acid/high-palmitic-acid diet for 24 weeks, respectively. The microRNA (miR) profiles of islets were determined by microarray screening. Islet injury was detected with co-staining using the TUNEL assay and insulin labelling. A lentiviral vector expressing anti-miRNA-34a-5p oligonucleotide (AMO-34a-5p) was injected into mice via an intraductal pancreatic route.

RESULTS

In both mouse islets and cultured rat insulinoma INS-1 cells, stearic acid exhibited a stronger lipotoxic role than other fatty acids, owing to repression of B cell CLL/lymphoma 2 (BCL-2) and BCL-2-like 2 (BCL-W) by stearic acid stimulation of miR-34a-5p. The stearic-acid-induced lipotoxicity and reduction in insulin secretion were alleviated by AMO-34a-5p. Further investigations in INS-1 cells revealed that p53 was involved in stearic-acid-induced elevation of miR-34a-5p, owing in part to activation of protein kinase-like endoplasmic reticulum kinase (PERK). Conversely, silencing PERK alleviated stearic-acid-induced p53, miR-34a-5p and lipotoxicity.

CONCLUSIONS/INTERPRETATION

These findings provide new insight for understanding the molecular mechanisms underlying not only the deleterious impact of stearic-acid-induced lipotoxicity but also apoptosis in beta cells and progression to type 2 diabetes.

Synergetic cholesterol-lowering effects of main alkaloids from Rhizoma Coptidis in HepG2 cells and hypercholesterolemia hamsters

AIMS

Hyperlipidemia contributes to the progression of cardiovascular diseases. Main alkaloids from Rhizoma Coptidis including berberine (BBR), coptisine (COP), palmatine (PAL), epiberberine (EPI) and jatrorrhizine (JAT), improved dyslipidemia in hypercholesterolemic hamsters to a different degree. In this study, HepG2 cells and hypercholesterolemic hamsters were used to investigate the synergetic cholesterol-lowering efficacy of these five main alkaloids.

MAIN METHODS

The cellular lipid and cholesterol accumulation and in HepG2 cells were evaluated by Oil Red O staining and HPLC analysis. LDL receptor, 3-Hydroxy-3-methylglutaryl CoA reductase (HMGCR) and cholesterol 7-alpha-hydroxylase (CYP7A1) that involving cholesterol metabolism in HepG2 cells were measured by qRT-PCR, western blot and immunofluorescence analysis. The serum profiles including total cholesterol (TC), triglyceride (TG), low-density lipoprotein cholesterol (LDL-c) and high-density lipoprotein cholesterol (HDL-c), as well as TC and total bile acids (TBA) of feces in hypercholesterolemic hamsters were also measured.

KEY FINDING

As compared to single alkaloids, the combination of five main alkaloids (COM) reduced the lipid and cholesterol accumulation in HepG2 cells more effectively and performed an advantageous effect on controlling TC, TG, LDL-c and HDL-c in hypercholesterolemic hamsters. More effective reduction of TBA and TC levels in feces of hamsters were achieved after the administration of COM. These effects were derived from the up-regulation of LDL receptor and CYP7A1, as well as HMGCR downregulation.

SIGNIFICANCE

Our results demonstrated that COM showed a synergetic cholesterol-lowering efficacy, which was better than single alkaloids and it might be considered as a potential therapy for hypercholesterolemia.

Ursolic acid increases energy expenditure through enhancing free fatty acid uptake and β-oxidation via an UCP3/AMPK-dependent pathway in skeletal muscle

SCOPE

Ursolic acid (UA) is a triterpenoid compound with multifold biological functions. Our previous studies have reported that UA protects against high-fat diet-induced obesity and improves insulin resistance (IR). However, the potential mechanisms are still undefined. Free fatty acid (FFA) metabolism in skeletal muscle plays a central role in obesity and IR. Therefore, in this study, we investigated the effect and the potential mechanisms of UA on skeletal muscle FFA metabolism.

METHODS AND RESULTS

In diet-induced obese rats, 0.5% UA supplementation for 6 weeks markedly reduced body weight, increased energy expenditure, decreased FFA level in serum and skeletal muscle and triglyceride content in skeletal muscle. In vitro, the data provided directly evidence that UA significantly increased fluorescently labeled FFA uptake and (3) H-labeled palmitic acid β-oxidation. UA-activated AMP-activated protein kinase (AMPK) and downstream targets were involved in the increase of FFA catabolism. Moreover, upregulated uncoupling protein 3 (UCP3) by UA contributed to AMPK activation via elevating adenosine monophosphate/adenosine triphosphate ratio.

CONCLUSION

UA increases FFA burning through enhancing skeletal muscle FFA uptake and β-oxidation via an UCP3/AMPK-dependent pathway, which provides a novel perspective on the biological function of UA against obesity and IR.

Myricetin derived from Hovenia dulcis Thunb. ameliorates vascular endothelial dysfunction and liver injury in high choline-fed mice

The present study was conducted to explore the protective effects of myricetin (MYR) purified from Hovenia dulcis Thunb. against vascular endothelial dysfunction and liver injury in mice fed with 3% dietary choline water.

Maternal vitamin D deficiency during pregnancy results in insulin resistance in rat offspring, which is associated with inflammation and Iκbα methylation

AIMS/HYPOTHESIS

We aimed to investigate the impact of maternal vitamin D deficiency during pregnancy on insulin resistance in male offspring and examine its mechanism.

METHODS

Pregnant Sprague-Dawley rats were maintained on a vitamin-D-free diet with ultraviolet-free light during pregnancy (early-VDD group). Insulin resistance in the male offspring was assessed by HOMA-IR, OGTT and euglycaemic clamp. NEFA, oxidative stress and inflammation levels were estimated as risk factors for insulin resistance. DNA methylation was examined by bisulfate sequencing PCR analysis. Luciferase reporter assay was performed to validate the effect of DNA methylation.

RESULTS

The offspring in the early-VDD group had significantly higher fasting insulin and HOMA-IR levels, markedly reduced glucose tolerance and significantly lower tissue sensitivity to exogenous insulin at 16 weeks (all p < 0.05) compared with control offspring. Significantly higher serum and liver IL-1β, IL-6, IL-8 and TNF-α concentrations were observed in the offspring of the early-VDD group at 0, 3, 8 and 16 weeks. Expression of hepatic Iκbα (also known as Nfkbia) mRNA and nuclear factor κB inhibitor α (IκBα) protein was persistently lower in the early-VDD offspring at all time points, and their hepatic Iκbα methylation levels at the cytosine phosphate guanine site +331 were significantly higher at 0 and 16 weeks (all p < 0.01). Methylation at Iκbα first exon +331 markedly decreased the luciferase activity (p < 0.05).

CONCLUSIONS/INTERPRETATION

Maternal vitamin D deficiency during pregnancy results in insulin resistance in the offspring, which is associated with persistently increased inflammation. Persistently decreased Iκbα expression, potentially caused by changes in Iκbα methylation, plays an important role in persistent inflammation.

Therapeutic role of ursolic acid on ameliorating hepatic steatosis and improving metabolic disorders in high-fat diet-induced non-alcoholic fatty liver disease rats

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is one of the most prevalent liver diseases around the world, and is closely associated with obesity, diabetes, and insulin resistance. Ursolic acid (UA), an ubiquitous triterpenoid with multifold biological roles, is distributed in various plants. This study was conducted to investigate the therapeutic effect and potential mechanisms of UA against hepatic steatosis in a high-fat diet (HFD)-induced obese non-alcoholic fatty liver disease (NAFLD) rat model.

METHODOLOGY/PRINCIPAL FINDINGS

Obese NAFLD model was established in Sprague-Dawley rats by 8-week HFD feeding. Therapeutic role of UA was evaluated using 0.125%, 0.25%, 0.5% UA-supplemented diet for another 6 weeks. The results from both morphologic and histological detections indicated that UA significantly reversed HFD-induced hepatic steatosis and liver injury. Besides, hepatic peroxisome proliferator-activated receptor (PPAR)-α was markedly up-regulated at both mRNA and protein levels by UA. Knocking down PPAR-α significantly inhibited the anti-steatosis role of UA in vitro. HFD-induced adverse changes in the key genes, which participated in hepatic lipid metabolism, were also alleviated by UA treatment. Furthermore, UA significantly ameliorated HFD-induced metabolic disorders, including insulin resistance, inflammation and oxidative stress.

CONCLUSIONS/SIGNIFICANCE

These results demonstrated that UA effectively ameliorated HFD-induced hepatic steatosis through a PPAR-α involved pathway, via improving key enzymes in the controlling of lipids metabolism. The metabolic disorders were accordingly improved with the decrease of hepatic steatosis. Thereby, UA could be a promising candidate for the treatment of NAFLD.

The polyphenol extract from Sechium edule shoots inhibits lipogenesis and stimulates lipolysis via activation of AMPK signals in HepG2 cells

Fatty liver may have implications for metabolic syndrome, such as obesity, hypertension, and diabetes. Therefore, the development of pharmacological or natural agents to reduce fat accumulation in the liver is an important effort. The Sechium edule shoots have already been verified to decrease serum lipids and cholesterol and prevent atherosclerosis. However, how Sechium edule shoots modulate hepatic lipid metabolism is unclear. This study was designed to investigate the effects and mechanisms of polyphenol extracts (SPE) of Sechium edule shoots in reducing lipid accumulation in oleic acid-treated HepG2 cells. We found that water extracts (SWE) of Sechium edule shoots could decrease serum and hepatic lipid contents (e.g., triacylglycerol and cholesterol). Furthermore, SWE and SPE through the AMPK (AMP-activating protein kinase) signaling pathway could decrease lipogenic relative enzymes, such as FAS (fatty acid synthase), HMGCoR (HMG-CoA reductase), and SREBPs (sterol regulatory element binding proteins), and increase the expression of CPT-I (carnitine palmitoyltransferase I) and PPARα (peroxisome proliferators activated receptor α), which are critical regulators of hepatic lipid metabolism. These observations suggested that Sechium edule shoots have potential for developing health foods for preventing and remedying fatty liver.

Calcium supplementation increases circulating cholesterol by reducing its catabolism via GPER and TRPC1-dependent pathway in estrogen deficient women

BACKGROUND

Limited studies have addressed the effects of calcium supplementation (CaS) on serum total cholesterol (TC) in postmenopausal women and the results are inconclusive. Moreover, the potential mechanisms through which CaS regulates cholesterol metabolism in the absence of estrogen are still sealed for the limitation of human being study.

METHODS

Cross-sectional survey, animal and in vitro experiments were conducted to investigate the effect of CaS on endogenous cholesterol metabolism in estrogen deficiency and identify its potential mechanisms. Ovariectomized rats were used to mimic estrogen deficiency. In vitro, HepG2 cell line was exposed to estradiol and/or calcium treatment.

RESULTS

We demonstrated that CaS significantly increased serum TC and the risk of hypercholesterolemia and myocardial infarction in postmenopausal women. Increased serum TC in estrogen deficiency was caused mainly by decreased cholesterol catabolism rather than increased synthesis. This was mediated by reduced 7α-hydroxylase resulting from increased liver intracellular Ca(2+) concentrations, reduced intracellular basal cAMP and subsequent up-regulation of SREBP-1c and SHP expression. Estrogen had a protective role in preventing CaS-induced TC increase by activating the G-protein coupled estrogen receptor, which mediated the estrogen effect through the transient receptor potential canonical 1 cation channel.

CONCLUSIONS

CaS increases endogenous serum TC via decreasing hepatic cholesterol catabolism in estrogen deficiency. G-protein coupled estrogen receptor is shown to be a key target in mediating CaS-induced TC increase. CaS should be monitored for the prevention of serum TC increase during menopause.

Sterol regulatory element-binding protein-1c mediates increase of postprandial stearic acid, a potential target for improving insulin resistance, in hyperlipidemia

Elevated serum free fatty acids (FFAs) levels play an important role in the development of insulin resistance (IR) and diabetes. We investigated the dynamic changes and the underlying regulatory mechanism of postprandial FFA profile in hyperlipidemia (HLP) and their relation with insulin sensitivity in both humans and mice. We found that serum stearic acid (SA) is the only fatty acid that is increased dramatically in the postprandial state. The elevation of SA is due to increased insulin-stimulated de novo synthesis mediated by sterol regulatory element-binding protein-1c (SREBP-1c)/acetyl-CoA carboxylase/fatty acid synthase/elongation of long-chain fatty acid family member 6 (ELOVL6) and the elongation of palmitic acid (PA) catalyzed by ELOVL6. Downregulation of SREBP-1c or ELOVL6 by small interfering RNA can reduce SA synthesis in liver and serum SA level, followed by amelioration of IR in HLP mice. However, inhibition of SREBP-1c is more effective in improving IR than suppression of ELOVL6, which resulted in accumulation of PA. In summary, increased postprandial SA is caused by the insulin-stimulated SREBP-1c pathway and elongation of PA in HLP. Reduction of postprandial SA is a good candidate for improving IR, and SREBP-1c is potentially a better target to prevent IR and diabetes by decreasing SA.

Hibiscus vitifolius (Linn.) root extracts shows potent protective action against anti-tubercular drug induced hepatotoxicity

ETHNOPHARMACOLOGICAL RELEVANCE

The roots of Hibiscus vitifolius Linn. (Malvaceae) is used for the treatment of jaundice in the folklore system of medicine in India. This study is an attempt to evaluate the hepatoprotective activity of the roots of Hibiscus vitifolius against anti-tubercular drug induced hepatotoxicity.

MATERIALS AND METHODS

Hepatotoxicity was induced in albino rats of either sex by oral administration of a combination of three anti-tubercular drugs. Petroleum ether, chloroform, methanol and aqueous extracts of roots of Hibiscus vitifolius (400mg/kg/day) were evaluated for their possible hepatoprotective potential.

RESULTS

All the extracts were found to be safe up to a dose of 2000mg/kg. Among the four extracts studied, oral administration of methanol extract of Hibiscus vitifolius at 400mg/kg showed significant difference in all the parameters when compared to control. There was a significant (P<0.001) reduction in the levels of serum aspartate amino transaminase, alanine amino transferase, alkaline phosphatase, lactate dehydrogenase, total and direct bilirubin, where as an increase was found in the levels of total cholesterol, total protein and albumin. Liver homogenate studies showed a significant increase in the levels of total protein, phospholipids and glycogen, and a reduction in the levels of total lipids, triglycerides, and cholesterol against control animals. In the tissue anti-oxidant studies, we found a significant increase in the levels of catalase and superoxide dismutase, whereas there was marked reduction in the levels of thiobarbituric acid reactive substances, as compared to control. Histology of liver sections of the animals treated with the extracts showed significant reduction of necrosis and fatty formation when compared with control specimens.

CONCLUSION

These findings suggest that the root extracts of Hibiscus vitifolius have potent hepatoprotective activity, thereby justifying its ethnopharmacological claim.

Antidiabetic activity of gossypin, a pentahydroxyflavone glucoside, in streptozotocin-induced experimental diabetes in rats

BACKGROUND

Most of the currently available oral hypoglycemic drugs for the treatment of diabetes mellitus elicit detrimental side effects. Hence, the search for plant-derived products for the treatment of diabetes continues. Gossypin, a pentahydroxy flavone glucoside found in the flowers of Hibiscus vitifolius, has many biological properties, including as an antioxidant, anti-inflammatory and anticancer agent. The aim of the present study was to evaluate the effect of gossypin in streptozotocin (STZ)-induced experimental diabetes in rats.

METHODS

Diabetic rats were administered 20 mg/kg per day gossypin orally for 30 days. On the 28th day, rats were subjected to an oral glucose tolerance test. In addition, blood glucose, plasma insulin, hemoglobin, and HbA1c levels were determined, as was the glycogen content of the liver and muscles. Plasma protein and blood urea were also estimated.

RESULTS

Oral administration of gossypin to diabetic rats resulted in improved glucose tolerance. Increased blood glucose and HbA1c levels and the reduced plasma insulin and hemoglobin levels in diabetic rats were significantly reversed to near normal after oral administration of gossypin. Furthermore, the glycogen content of the liver and muscles was significantly improved after gossypin treatment of diabetic rats, and plasma protein and blood urea levels were almost normalized. The data obtained in gossypin-treated rats were comparable with those obtained following gliclazide treatment of rats, a standard reference drug for diabetes.

CONCLUSIONS

The results of the present study indicate that gossypin has potent antidiabetic activity in STZ-induced experimental diabetes in rats.

The calcium-sensing receptor promotes adipocyte differentiation and adipogenesis through PPARγ pathway

Adipocyte differentiation and adipogenesis are closely related to obesity and obesity-induced metabolic disorders. The calcium-sensing receptor (CaSR) has been reported to play an antilipolytic role in human adipocyte and regulate cell differentiation in many tissues. However, the effects of CaSR on adipocyte differentiation and adipogenesis have not been clarified. In the study, we observed that activation of CaSR significantly promoted adipocyte differentiation and adipogenesis in human SW872 adipocytes. Gene expression analysis revealed that the CaSR activation increased the transcription factor proliferator-activated receptor γ (PPARγ) and its downstream genes including CCAAT element binding protein α (C/EBPα), adipose fatty acid-binding protein (aP2), and lipoprotein lipase. The activity of glycerol-3-phosphate dehydrogenase was also increased after the stimulation of CaSR. In addition, levels of cyclic AMP and calcium which have been shown to regulate PPARγ gene expression were significantly affected by the activation of CaSR. These effects could be suppressed by CaSR small interfering RNA (CaSR-siRNA). In conclusion, our findings suggest that activation of CaSR promotes differentiation and adipogenesis in adipocytes, which might be achieved by upregulating PPARγ and its downstream gene expressions. Therefore, CaSR in adipocytes may be involved in the pathogenesis of obesity by promoting adipocyte differentiation and adipogenesis.

Rutin inhibits oleic acid induced lipid accumulation via reducing lipogenesis and oxidative stress in hepatocarcinoma cells

Excessive lipid accumulation within liver has been proposed to cause obesity, hyperlipidemia, diabetes, and fatty liver disease. Rutin, a common dietary flavonoid that is consumed in fruits, vegetables, and plant-derived beverages, has various biological functions, including antioxidant, anti-inflammatory, and anticancer effects. However, a hypolipidemic effect of rutin on fatty liver disease has not been reported. In this study, we examined the effect of rutin on reducing lipid accumulation in hepatic cells. Hepatocytes were treated with oleic acid (OA) containing with or without rutin to observe the lipid accumulation by Nile red stain. The result showed rutin suppressed OA-induced lipid accumulation and increased adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) activity in hepatocytes. The expression of critical molecule involved in lipid synthesis, sterol regulatory element binding proteins-1 (SREBP-1), was attenuated in rutin-treated cells. Moreover, long-term incubation of rutin inhibited the transcriptions of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase (HMGCR), glycerol-3-phosphate acyltransferase (GPAT), fatty acid synthase (FAS), and acetyl-coenzyme carboxylase (ACC). Besides, we also found out the antioxidative effect of rutin by increasing the expression of peroxisome proliferator-activated receptor (PPAR)-α and antioxidative enzymes. Taken together, our findings suggest rutin could attenuate lipid accumulation by decreasing lipogenesis and oxidative stress in hepatocyte.

Ursolic acid stimulates lipolysis in primary-cultured rat adipocytes

Ursolic acid (UA) is a pentacyclic triterpenic acid with many biological functions naturally existing in many kinds of food. To investigate whether UA can accelerate lipolysis, primary-cultured rat adipocytes were treated with UA, and glycerol release in the culture medium was measured. UA stimulated lipolysis significantly. Furthermore, the lipolytic effect of UA was inhibited by the protein kinase A (PKA) specific inhibitor H89, suggesting that UA exerted its lipolytic function through the cAMP-dependent PKA pathway. Downstream targets of the PKA pathway, hormone-sensitive lipase (HSL) and perilipin A were checked, UA enhanced lipolysis by promoting the translocation of HSL from the cytosol to the lipid droplets and inhibiting the expression of perilipin A. Additionally, adipose triglyceride lipase (ATGL), a novel rate-limiting lipase in the lipolytic catabolism, was upregulated by UA. UA-induced expression of ATGL could not be blocked by H89, suggesting that ATGL upregulation is not regulated by the PKA pathway. These findings suggest that UA significantly stimulates lipolysis by translocating HSL, decreasing perilipin A expression by the PKA pathway, and up-regulating ATGL in primary cultured adipocytes. Thus, UA is a promising candidate for the treatment of obesity.

Effects of mulberry (Morus alba L.) extracts on lipid homeostasis in vitro and in vivo

The objective of this study was to investigate the lipid-lowering effects of mulberry water extracts (MWEs). To evaluate the hypolipidemic effect of MWEs, hamsters were fed with either high fat/cholesterol diets (HFCD) or HFCD supplemented with 1 and 2% MWEs for 12 weeks. Plasma total cholesterol (TC) and triglyceride (TG) levels of hamsters fed HFCD with MWEs were significantly reduced by about 30-37% and 16-35%, respectively, as compared to those without MWEs. Similar results were also measured in hepatic TC and TG of hamsters fed HFCD with MWEs. Low-density lipoprotein receptor (LDLR) gene expression and the uptake ability of low-density lipoprotein (LDL) in HepG2 cells were also upregulated by additions of MWEs. MWEs also decreased the gene expressions of enzymes involved in the TG and TC biosyntheses. Results suggest that hypolipidemic effects of MWEs are via an enhancement of LDLR gene expression and the clearance ability of LDL and a decrease in the lipid biosynthesis. Therefore, MWEs could be used as a natural agent against hyperlipidemia.