Masoprocol decreases serum triglyceride concentrations in rats with fructose-induced hypertriglyceridemia

Anti-hyperlipidaemic effects of synthetic analogues of nordihydroguaiaretic acid in dyslipidaemic rats

BACKGROUND AND PURPOSE

Previous studies have shown that Creosote bush-derived nordihydroguaiaretic acid (NDGA) exerts beneficial actions on the key components of metabolic syndrome including dyslipidaemia, insulin resistance and hypertension in several relevant rodent models. Here, we synthesized and screened a total of 6 anti-hyperlipidaemic analogues of NDGA and tested their efficacy against hepatic lipid metabolism in a high-fructose diet (HFrD) fed dyslipidaemic rat model.

EXPERIMENTAL APPROACH

HFrD fed Sprague-Dawley rats treated with NDGA or one of the six analogues were used. Serum samples were analysed for blood metabolites, whereas liver samples were quantified for changes in various mRNA levels by real-time RT-PCR.

KEY RESULTS

Oral gavage of HFrD-fed rats for 4 days with NDGA analogues 1 and 2 (100 mg·kg^-1 ·day^-1 ) suppressed the hepatic triglyceride content, whereas the NDGA analogues 2, 3 and 4, like NDGA, decreased the plasma triglyceride levels by 70-75%. qRT-PCR measurements demonstrated that among NDGA analogues 1, 2, 4 and 5, analogue 4 was the most effective at inhibiting the mRNA levels of some key enzymes and transcription factors involved in lipogenesis. All four analogues almost equally inhibited the key genes involved in triglyceride synthesis and fatty acid elongation. Unlike NDGA, none of the analogues affected the genes of hepatic fatty acid oxidation or transport.

CONCLUSIONS AND IMPLICATIONS

Our data suggest that NDGA analogues 1, 2, 4 and 5, particularly analogue 4, exert their anti-hyperlipidaemic actions by negatively targeting genes of key enzymes and transcription factors involved in lipogenesis, triglyceride synthesis and fatty acid elongation. These analogues have therapeutic potential.

Creosote Bush (Larrea tridentata) Improves Insulin Sensitivity and Reduces Plasma and Hepatic Lipids in Hamsters Fed a High Fat and Cholesterol Diet

Creosote bush, Larrea tridentata (Sesse y Moc. Ex DC, Zygophyllaceae) is a shrub found in the deserts of Northern Mexico and Southwestern United States. In traditional medicine, it is used to treat a variety of illnesses including type 2 diabetes. The present study aims to investigate the effects of creosote bush ethanolic extract on plasma and liver parameters associated with the metabolic syndrome in hamsters fed a high fat and cholesterol diet (HFD), comparing them with those induced by ezetimibe (EZ). Seven groups of six hamsters each were formed. Six groups were fed HFD for 2 weeks. The following 2 weeks, the HFD groups received: (1) only HFD, (2) HFD + 3 mg% EZ, (3) HFD + 0.2% creosote bush ethanolic extract, (4) only standard diet (Std Diet), (5) Std Diet + 3 mg% EZ, (6) Std Diet + 0.2% creosote bush ethanolic extract. The beneficial effects of creosote bush ethanolic extract in the HFD hamster model were a reduction of insulin resistance, associated with lower serum insulin and leptin, lower hepatic lipid peroxidation and higher liver antioxidant capacity. Plasma and liver lipids tended or were reduced to values closer to those of animals fed standard diet. A similar effect on lipids was induced by EZ, although with even lower hepatic cholesterol and total lipids concentrations. In general, the change from HFD to standard diet plus ethanolic extract induced the same but deeper changes, including a reduction in plasma glucose and an increase in the percentage of HDL cholesterol. Unlike creosote bush extract, EZ increased food consumption and neutral fecal steroids, with no significant effect on body weight, epididymal fat pads, liver peroxidation or antioxidant capacity. Also EZ did not modify serum insulin and leptin. However, insulin sensitivity improved to values similar to those induced by the extract. This suggests that the mechanism of action of creosote bush ethanolic extract is different to inhibition of cholesterol absorption or increase excretion. The ethanolic extract of L. tridentata could be useful in the treatment of the metabolic syndrome.

Effect of Creosote Bush-Derived NDGA on Expression of Genes Involved in Lipid Metabolism in Liver of High-Fructose Fed Rats: Relevance to NDGA Amelioration of Hypertriglyceridemia and Hepatic Steatosis

Nordihydroguaiaretic acid (NDGA), the main metabolite of Creosote bush, has been shown to have profound effects on the core components of the metabolic syndrome (MetS), lowering blood glucose, free fatty acids (FFA) and triglyceride (TG) levels in several models of dyslipidemia, as well as improving body weight (obesity), insulin resistance, diabetes and hypertension, and ameliorating hepatic steatosis. In the present study, a high-fructose diet (HFrD) fed rat model of hypertriglyceridemia was employed to further delineate the underlying mechanism by which NDGA exerts its anti-hypertriglyceridemic action. In the HFrD treatment group, NDGA administration by oral gavage decreased plasma levels of TG, glucose, FFA, and insulin, increased hepatic mitochondrial fatty acid oxidation and attenuated hepatic TG accumulation. qRT-PCR measurements indicated that NDGA treatment increased the mRNA expression of key fatty acid transport (L-FABP, CD36), and fatty acid oxidation (ACOX1, CPT-2, and PPARα transcription factor) genes and decreased the gene expression of enzymes involved in lipogenesis (FASN, ACC1, SCD1, L-PK and ChREBP and SREBP-1c transcription factors). Western blot analysis indicated that NDGA administration upregulated hepatic insulin signaling (P-Akt), AMPK activity (P-AMPK), MLYCD, and PPARα protein levels, but decreased SCD1, ACC1 and ACC2 protein content and also inactivated ACC1 activity (increased P-ACC1). These findings suggest that NDGA ameliorates hypertriglyceridemia and hepatic steatosis primarily by interfering with lipogenesis and promoting increased channeling of fatty acids towards their oxidation.

Eicosanoids, β-cell function, and diabetes

Arachidonic acid (AA) is metabolized by cyclooxygenase (COX), lipoxygenase (LOX), and cytochrome P450 (CYP) enzymes into eicosanoids, which are involved in diverse diseases, including type 1 and type 2 diabetes. During the last 30 years, evidence has been accumulated that suggests important functions for eicosanoids in the control of pancreatic β-cell function and destruction. AA metabolites of the COX pathway, especially prostaglandin E(2) (PGE(2)), appear to be significant factors to β-cell dysfunction and destruction, participating in the pathogenesis of diabetes and its complications. Several elegant studies have contributed to the sorting out of the importance of 12-LOX eicosanoids in cytokine-mediated inflammation in pancreatic β cells. The role of CYP eicosanoids in diabetes is yet to be explored. A recent publication has demonstrated that stabilizing the levels of epoxyeicosatrienoic acids (EETs), CYP eicosanoids, by inhibiting or deleting soluble epoxide hydrolase (sEH) improves β-cell function and reduces β-cell apoptosis in diabetes. In this review we summarize recent findings implicating these eicosanoid pathways in diabetes and its complications. We also discuss the development of animal models with targeted gene deletion and specific enzymatic inhibitors in each pathway to identify potential targets for the treatment of diabetes and its complications.

Metabolic effects of dietary cholesterol in an animal model of insulin resistance and hepatic steatosis

Although the atherogenic role of dietary cholesterol has been well established, its diabetogenic potential and associated metabolic disturbances have not been reported. Diet-induced hamster models of insulin resistance and dyslipidemia were employed to determine lipogenic and diabetogenic effects of dietary cholesterol. Metabolic studies were conducted in hamsters fed diets rich in fructose (40%), fat (30%), and cholesterol (0.05-0.25%) (FFC) and other test diets. Short-term feeding of the FFC diet induced insulin resistance, glucose intolerance, hypertriglyceridemia, and hypercholesterolemia. Prolonged feeding (6-22 wk) of the FFC diet led to severe hepatic steatosis, glucose intolerance, and mild increases in fasting blood glucose, suggesting progression toward type 2 diabetes, but did not induce beta-cell dysfunction. Metabolic changes induced by the diet, including dyslipidemia and insulin resistance, were cholesterol concentration dependent and were only markedly induced on a high-fructose and high-fat dietary background. There were significant increases in hepatic and plasma triglyceride with FFC feeding, likely due to a 10- to 15-fold induction of hepatic stearoyl-CoA desaturase compared with chow levels (P < 0.03). Hepatic insulin resistance was evident based on reduced tyrosine phosphorylation of the insulin receptor-beta, IRS-1, and IRS-2 as well as increased protein mass of protein tyrosine phosphatase 1B. Interestingly, nuclear liver X receptor (LXR) target genes such as ABCA1 were upregulated on the FFC diet, and dietary supplementation with an LXR agonist (instead of dietary cholesterol) worsened dyslipidemia, glucose intolerance, and upregulation of target mRNA and proteins similar to that of dietary cholesterol. In summary, these data clearly implicate dietary cholesterol, synergistically acting with dietary fat and fructose, as a major determinant of the severity of metabolic disturbances in the hamster model. Dietary cholesterol appears to induce hepatic cholesterol ester and triglyceride accumulation, and diet-induced LXR activation (via cholesterol-derived oxysterols) may possibly be one key underlying mechanism.

Momordica charantia (bitter melon) reduces plasma apolipoprotein B-100 and increases hepatic insulin receptor substrate and phosphoinositide-3 kinase interactions

Aqueous extracts or juice from unripened fruit of Momordica charantia (bitter melon) has traditionally been used in the treatment of diabetes and its complications. Insulin resistance is characterized by significant down-regulation of hepatic insulin signalling as documented by attenuated phosphorylation of insulin receptor (IR), IR substrates 1 and 2, phosphoinositide-3 kinase, protein kinase B, and over-expression of phosphotyrosine phosphatase 1B. We recently demonstrated that bitter melon juice (BMJ) is a potent inhibitor of apoB secretion and TAG synthesis and secretion in human hepatoma cells, HepG2, that may be involved in plasma lipid- and VLDL-lowering effects observed in animal studies. The aim of this study was to evaluate the effects of BMJ on plasma apoB levels and hepatic insulin signalling cascade in mice fed high-fat diet (HFD). Female C57BL/6 mice (4–6 weeks old) were randomized into three groups receiving regular rodent chow, HFD and HFD+BMJ. The data indicate that BMJ not only improves glucose and insulin tolerance but also lowers plasma apoB-100 and apoB-48 in HFD-fed mice as well as modulates the phosphorylation status of IR and its downstream signalling molecules. Investigating the biochemical and molecular mechanisms involved in amelioration of diabetic dyslipidaemia by BMJ may lead to identification of new molecular targets for dietary/alternative therapies.

Eicosanoids and renal damage in cardiometabolic syndrome

BACKGROUND

Obesity, hypertension and Type 2 diabetes are major contributing factors to the increase in the number of patients that have chronic kidney disease. The clustering of visceral obesity and cardiovascular risk factors has been designated metabolic syndrome or cardiometabolic syndrome. Cardiometabolic syndrome is associated with a complex systemic inflammatory state that has been implicated in medically important complications, including endothelial dysfunction. Inflammation, endothelial dysfunction and insulin resistance are interrelated and have reciprocal relationships that link cardiovascular and metabolic diseases. Ultimately, cardiometabolic syndrome increases the risk for cardiovascular events and end-organ damage. Although the number of patients with cardiometabolic syndrome is escalating, therapeutic approaches have not been developed that provide protection to the kidney.

OBJECTIVE

The objective of this review is to provide an overview of the contribution of eicosanoids to renal damage in cardiometabolic syndrome.

RESULTS/CONCLUSION

Eicosanoids are altered in cardiometabolic syndrome and contribute to the progression of renal injury. The antihypertensive and anti-inflammatory actions of epoxides and soluble epoxide hydrolase inhibitors make these attractive eicosanoid therapeutic targets for chronic kidney disease in patients with cardiometabolic syndrome.

Nordihydroguaiaretic acid inhibits insulin-like growth factor signaling, growth, and survival in human neuroblastoma cells

Neuroblastoma is a common pediatric malignancy that metastasizes to the liver, bone, and other organs. Children with metastatic disease have a less than 50% chance of survival with current treatments. Insulin-like growth factors (IGFs) stimulate neuroblastoma growth, survival, and motility, and are expressed by neuroblastoma cells and the tissues they invade. Thus, therapies that disrupt the effects of IGFs on neuroblastoma tumorigenesis may slow disease progression. We show that NVP-AEW541, a specific inhibitor of the IGF-I receptor (IGF-IR), potently inhibits neuroblastoma growth in vitro. Nordihydroguaiaretic acid (NDGA), a phenolic compound isolated from the creosote bush (Larrea divaricata), has anti-tumor properties against a number of malignancies, has been shown to inhibit the phosphorylation and activation of the IGF-IR in breast cancer cells, and is currently in Phase I trials for prostate cancer. In the present study in neuroblastoma, NDGA inhibits IGF-I-mediated activation of the IGF-IR and disrupts activation of ERK and Akt signaling pathways induced by IGF-I. NDGA inhibits growth of neuroblastoma cells and induces apoptosis at higher doses, causing IGF-I-resistant activation of caspase-3 and a large increase in the fraction of sub-G0 cells. In addition, NDGA inhibits the growth of xenografted human neuroblastoma tumors in nude mice. These results indicate that NDGA may be useful in the treatment of neuroblastoma and may function in part via disruption of IGF-IR signaling.

Eicosanoids and renal vascular function in diseases

Arachidonic acid metabolites are vital for the proper control of renal haemodynamics and, when not properly controlled, can contribute to renal vascular injury and end-stage renal disease. Three major enzymatic pathways, COX (cyclo-oxygenase), CYP450 (cytochrome P450) and LOX (lipoxygenase), are responsible for the metabolism of arachidonic acid metabolites to bioactive eicosanoids. These eicosanoids can dilate or constrict the renal vasculature and maintain vascular resistance in the face of changing vasoactive hormones. Renal vascular generation of eicosanoids is altered in pathophysiological conditions such as hypertension, diabetes, metabolic syndrome and acute renal failure. Experimental evidence supports the concept that altered eicosanoid metabolism contributes to renal haemodynamic alterations and the development and progression of nephropathy. The possible beneficial renal vascular actions of enzymatic inhibitors, eicosanoid analogues and receptor antagonists have been examined in hypertension, diabetes and metabolic syndrome. This review highlights the roles of renal vascular eicosanoids in the pathogenesis of nephropathy and therapeutic targets for renal disease related to hypertension, diabetes, metabolic syndrome and acute renal failure.

Citrus polymethoxylated flavones improve lipid and glucose homeostasis and modulate adipocytokines in fructose-induced insulin resistant hamsters

The present study was undertaken to determine whether supplementation with polymethoxylated flavones (PMFs) could ameliorate the fructose-induced hypertriglyceridemia and other metabolic abnormalities associated with insulin resistance (IR) in hamsters. Following feeding with the fructose diet, hamsters were supplemented orally with PMF-L or PMF-H (62.5 and 125 mg/kg/day) for 4 weeks. Both PMF-treated groups showed a statistically significant (p<0.05) decrease in serum triglyceride (TG) and cholesterol levels compared to the fructose-fed control group. The fructose control group at the end of the study showed elevated serum insulin and impaired insulin sensitivity (glucose intolerance). On the other hand, PMF-supplemented groups showed a reversal in these metabolic defects, including a decrease in insulin level and an improvement in glucose tolerance. PMF supplementation also reduced TG contents in the liver and heart and was able to regulate adipocytokines by significantly suppressing TNF-alpha, INF-gamma, IL-1beta and IL-6 expression and increasing adiponectin in IR hamsters. The mechanism of PMF on the activation of peroxisome proliferator-activated receptors (PPAR) was also explored. PMF-H supplementation significantly increased PPARalpha and PPARgamma protein expression in the liver. This is the first report of positive effects of PMF on adipocytokine production and on PPAR expression in IR hamsters. This study suggests that PMF can ameliorate hypertriglyceridemia and its anti-diabetic effects may occur as a consequence of adipocytokine regulation and PPARalpha and PPARgamma activation.

Green tea leaf extract improves lipid and glucose homeostasis in a fructose-fed insulin-resistant hamster model

The present study evaluated the effect of green tea (Camellia sinensis L.) leaf extract on triglyceride and glucose homeostasis in a fructose-fed hypertriglyceridemic, insulin-resistant hamster model. There was a significant decrease in plasma triglyceride levels following supplementation of the green tea epigallocatechin gallate-enriched extract (42% at 150 mg/(kg day) to 62% at 300 mg/(kg day) for 4 weeks). Compared to baseline, the fructose control group at the end of the study showed elevated serum insulin and apolipoprotein B levels, and decreased serum adiponectin levels. The fructose/green tea extract group showed a reversal in all of these metabolic defects, including an improvement in glucose levels during a glucose tolerance test. Triglyceride content was also examined in various tissues and compared to the control fructose group; supplementation of the green tea extract (300 mg/kg) reduced triglyceride content in liver and heart tissues. There was molecular evidence of improved lipid and glucose homeostasis based on peroxisome proliferator-activated receptor (PPAR) protein expression. Compared to the control fructose group, supplementation of the green tea extract (300 mg/kg) significantly increased PPARalpha and PPARgamma protein expression. In summary, the data suggest that intake of the green tea extract ameliorated the fructose-induced hypertriglyceridemia and the insulin-resistant state in part through PPAR.

Reversal of high dietary fructose-induced PPARalpha suppression by oral administration of lipoxygenase/cyclooxygenase inhibitors

High fructose feeding causes diet-induced alterations of lipid metabolism and decreased insulin sensitivity, hallmark of which is a rapid and profound hypertriglyceridemia. One of the mechanisms that contribute to serum hypertriglyceridemia in this model is suppression of hepatic PPARα. HMG-CoA inhibitors, which reduce serum triglycerides in these animals, also elevate/restore hepatic PPARα. Previously we demonstrated that two known lipoxygenase/cyclooxygenase inhibitors reversed diet-induced hypertriglyceridemia in this model and that reversal of certain inflammatory markers in the liver correlated with the metabolic benefit. In this paper we extended these studies by examining the impact of these compounds on expression of PPARα, both at the level of transcription and expression. Our data show that diet-induced suppression of hepaic PPARα is reversed upon treatment with lipoxygenase/cyclooxygenase compounds. We then tested one of these compounds, BW-755c, over a range of doses from 10 mg/kg to 100 mg/kg to establish a dose-response relationship with the reduction of serum hypertriglyceridemia in this model. These experiments support the concept of using anti-inflammatory medications as one method to correct metabolic dysfunction.

Larrea tridentata (Creosote bush), an abundant plant of Mexican and US-American deserts and its metabolite nordihydroguaiaretic acid

Although controversial, Creosote bush, Larrea tridentata (Sesse and Moc. ex DC) Coville, is used to treat a variety of illnesses including infertility, rheumatism, arthritis, diabetes, gallbladder and kidney stones, pain and inflammation. Recently, it has been used as a nutritional supplement. The primary product extracted from this common plant of the arid regions of northern Mexico and Southwestern United States is the potent antioxidant nordihydroguaiaretic acid (NDGA). It was widely used during the 1950s as a food preservative and to preserve naturals fibers. Later it was banned after reports of toxicity during the early 1960s. Renal and hepatotoxicity are also reported for chronic use of creosote bush and NDGA. This article reviews traditional and contemporary uses and pharmacology, including toxicology of this plant widely used in Mexican traditional medicine.

Increased diacylglycerol acyltransferase activity is associated with triglyceride accumulation in tissues of diet-induced insulin-resistant hyperlipidemic hamsters

Over-accumulation of triglyceride (TG) in insulin-sensitive tissues is associated with the development of insulin resistance. We investigated whether enhanced de novo lipogenesis via diacylglycerol acyltransferase (DGAT) may contribute to the over-accumulation of TG in various tissues (liver, adipose, muscle, and intestine) using 2 well-characterized hyperlipidemic, insulin-resistant hamster models. In general, a marked increase in TG accumulation was noted in most tissues. Interestingly, the increase in TG accumulation corresponded to an increase in microsomal DGAT activity which ranged from 114% to 575% in all of the examined tissues (n = 7 per group). To delineate the mechanism for the increase in DGAT activity, we measured the expression of DGAT-1 and DGAT-2 messenger RNA by relative reverse transcriptase polymerase chain reaction (RT-PCR). In general, DGAT gene expression changed with DGAT-1 changing the most in the liver and adipose tissue, whereas DGAT-2 showed responses mainly in muscle and intestine. The increases in messenger RNA expression were not remarkable (averaging 35%; n = 4 per group) indicating that posttranscriptional mechanism(s) may play a larger role in regulating DGAT activity. In summary, the data suggest that elevated DGAT activity/expression and the subsequent increase in de novo lipogenesis could in part induce the insulin-resistant state.

Lipoxygenase inhibitors inhibit heparin-releasable lipoprotein lipase activity in 3T3-L1 adipocytes and enhance body fat reduction in mice by conjugated linoleic acid

The t10c12 isomer of conjugated linoleic acid (CLA) reduces lipid accumulation in adipocytes in part by inhibiting heparin-releasable lipoprotein lipase (LPL) activity. We now show that inhibitors of lipoxygenase (LOX) activity (2-[12-hydroxydodeca-5,10-diynyl]-3,5,6-trimethyl-p-benzoquinone; 5,8,11,14-eicosatetraynoic acid; salicylhydroxamic acid; indomethacin; nordihydroguaiaretic acid (NDGA)) produce a similar inhibitory effect on LPL activity in cultured 3T3-L1 mouse adipocytes. Additionally the LOX inhibitors had no effect on, or inhibited, lipolysis in this cell system (measured as glycerol release). Growing mice fed diet containing 0.1% NDGA for 4 weeks displayed 21% reduction in body fat, which was similar to 23% reduction in body fat produced by feeding diet containing a suboptimal amount of CLA (0.1%) for 4 weeks. Feeding diet containing both 0.1% NDGA and 0.1% CLA resulted in 51% reduction in body fat which was accompanied by significant increases in whole body water and protein. Aspirin, an inhibitor of cyclooxygenase 1 and 2, had no effect on LPL activity in 3T3-L1 adipocytes, did not affect body composition when fed to growing mice, and failed to influence the effects of CLA on LPL activity in 3T3-L1 cells or body composition in mice. These findings appear to provide new perspectives and insights into the relationships between CLA, eicosanoids, the control of lipid accumulation in adipocytes, and effects of CLA on the immune system.