Chai Siah Ku

Eliciting the mitochondrial unfolded protein response by nicotinamide adenine dinucleotide repletion reverses fatty liver disease in mice

With no approved pharmacological treatment, nonalcoholic fatty liver disease (NAFLD) is now the most common cause of chronic liver disease in Western countries and its worldwide prevalence continues to increase along with the growing obesity epidemic. Here, we show that a high‐fat high‐sucrose (HFHS) diet, eliciting chronic hepatosteatosis resembling human fatty liver, lowers hepatic nicotinamide adenine dinucleotide (NAD+) levels driving reductions in hepatic mitochondrial content, function, and adenosine triphosphate (ATP) levels, in conjunction with robust increases in hepatic weight, lipid content, and peroxidation in C57BL/6J mice. To assess the effect of NAD+ repletion on the development of steatosis in mice, nicotinamide riboside, a precursor of NAD+ biosynthesis, was added to the HFHS diet, either as a preventive strategy or as a therapeutic intervention. We demonstrate that NR prevents and reverts NAFLD by inducing a sirtuin (SIRT)1‐ and SIRT3‐dependent mitochondrial unfolded protein response, triggering an adaptive mitohormetic pathway to increase hepatic β‐oxidation and mitochondrial complex content and activity. The cell‐autonomous beneficial component of NR treatment was revealed in liver‐specific Sirt1 knockout mice (Sirt1hep−/−), whereas apolipoprotein E‐deficient mice (Apoe−/−) challenged with a high‐fat high‐cholesterol diet affirmed the use of NR in other independent models of NAFLD. Conclusion: Our data warrant the future evaluation of NAD+ boosting strategies to manage the development or progression of NAFLD. (Hepatology 2016;63:1190–1204)

Aronia melanocarpa (chokeberry) polyphenol–rich extract improves antioxidant function and reduces total plasma cholesterol in apolipoprotein E knockout mice

We hypothesized that a polyphenol-rich chokeberry extract (CBE) would modulate hepatic lipid metabolism and improve antioxidant function in apolipoprotein E knockout (apoE(-/-)) mice. ApoE(-/-) mice were fed diets containing 15% fat with 0.2% cholesterol alone or supplemented with 0.005% or 0.05% CBE for 4 weeks. CBE polyphenol content was determined by the total phenols, 4-dimethylaminocinnamaldehyde, and ultra high-performance liquid chromatography-mass spectrometry methods. The 0.05% CBE diet provided mice with mean daily doses of 1.2 mg gallic acid equivalents of total phenols, 0.19 mg anthocyanins, 0.17 mg phenolic acids, 0.06 mg proanthocyanidins (as catechin-equivalents), and 0.02 mg flavonols. The 0.05% CBE group had 12% less plasma total cholesterol concentrations than the control. Despite the hypocholesterolemic effect of CBE, hepatic mRNA levels of low-density lipoprotein receptor, hydroxyl-3-methylglutaryl coenzyme A reductase and cholesterol 7α-hydroxylase in CBE-fed mice were not significantly different from controls. Dietary CBE did not alter hepatic lipid content or the hepatic expression of genes involved in lipogenesis and fatty acid β-oxidation such as fatty acid synthase, carnitine palmitoyltransferase 1 and acyl-CoA oxidase. Plasma paraoxonase and catalase activities were significantly increased in mice fed 0.05% CBE. Both CBE diets increased hepatic glutathione peroxidase (GPx) activity but the 0.05% CBE group had 24% less proximal intestine GPx activity relative to controls. Thus, dietary CBE lowered total cholesterol and improved plasma and hepatic antioxidant function at nutritionally-relevant doses in apoE(-/-) mice. Furthermore, the CBE cholesterol-lowering mechanism in apoE(-/-) mice was independent of hepatic expression of genes involved in cholesterol metabolism.

Edible blue-green algae reduce the production of pro-inflammatory cytokines by inhibiting NF-κB pathway in macrophages and splenocytes.

BACKGROUND Chronic inflammation contributes to the development of pathological disorders including insulin resistance and atherosclerosis. Identification of anti-inflammatory natural products can prevent the inflammatory diseases. METHODS Anti-inflammatory effects of blue-green algae (BGA), i.e., Nostoc commune var. sphaeroides Kützing (NO) and Spirulina platensis (SP), were compared in RAW 264.7 and mouse bone marrow-derived macrophages (BMM) as well as splenocytes from apolipoprotein E knockout (apoE(-/-)) mice fed BGA. RESULTS When macrophages pretreated with 100μg/ml NO lipid extract (NOE) or SP lipid extract (SPE) were activated by lipopolysaccharide (LPS), expression and secretion of pro-inflammatory cytokines, such as tumor necrosis factor α (TNFα), interleukin 1β (IL-1β), and IL-6, were significantly repressed. NOE and SPE also significantly repressed the expression of TNFα and IL-1β in BMM. LPS-induced secretion of IL-6 was lower in splenocytes from apoE(-/-) fed an atherogenic diet containing 5% NO or SP for 12weeks. In RAW 264.7 macrophages, NOE and SPE markedly decreased nuclear translocation of NF-κB. The degree of repression of pro-inflammatory gene expression by algal extracts was much stronger than that of SN50, an inhibitor of NF-κB nuclear translocation. Trichostatin A, a pan histone deacetylase inhibitor, increased basal expression of IL-1β and attenuated the repression of the gene expression by SPE. SPE significantly down-regulated mRNA abundance of 11 HDAC isoforms, consequently increasing acetylated histone 3 levels. CONCLUSION NOE and SPE repress pro-inflammatory cytokine expression and secretion in macrophages and splenocytes via inhibition of NF-κB pathway. Histone acetylation state is likely involved in the inhibition. GENERAL SIGNIFICANCE This study underscores natural products can exert anti-inflammatory effects by epigenetic modifications such as histone acetylation.

Health Benefits of Blue-Green Algae: Prevention of Cardiovascular Disease and Nonalcoholic Fatty Liver Disease

Blue-green algae (BGA) are among the most primitive life forms on earth and have been consumed as food or medicine by humans for centuries. BGA contain various bioactive components, such as phycocyanin, carotenoids, γ-linolenic acid, fibers, and plant sterols, which can promote optimal health in humans. Studies have demonstrated that several BGA species or their active components have plasma total cholesterol and triglyceride-lowering properties due to their modulation of intestinal cholesterol absorption and hepatic lipogenic gene expression. BGA can also reduce inflammation by inhibiting the nuclear factor κ B activity, consequently reducing the production of proinflammatory cytokines. Furthermore, BGA inhibit lipid peroxidation and have free radical scavenging activity, which can be beneficial for the protection against oxidative stress. The aforementioned effects of BGA can contribute to the prevention of metabolic and inflammatory diseases. This review provides an overview of the current knowledge of the health-promoting functions of BGA against cardiovascular disease and nonalcoholic fatty liver disease, which are major health threats in the developed countries.

Unsaturated fatty acids repress expression of ATP binding cassette transporter A1 and G1 in RAW 264.7 macrophages

Reverse cholesterol transport (RCT), a process to deliver excess cholesterol from the periphery to the liver for excretion from body, is a major atheroprotective property of high-density lipoproteins. As major transporters for cholesterol efflux in macrophages, ATP-binding cassette transporter A1 (ABCA1) and G1 (ABCG1) are critical for RCT. We investigated mechanisms for the regulation of ABCA1 and ABCG1 expression by fatty acids (FA) in RAW264.7 macrophages. Cells were incubated with 100 μmol/L of palmitic, oleic, linoleic, linolenic or eicosapentaenoic acids in the absence or presence of T0901317, a liver X receptor (LXR) agonist. Unsaturated FA, but not saturated FA, significantly reduced ABCA1 and ABCG1 mRNA without the agonist. Trichostatin A (TSA), a histone deacetylase inhibitor, not only increased basal ABC transporter expression but abrogated the transcriptional repression by unsaturated FA. The increased basal ABCA1 and ABCG1 mRNA by TSA paralleled the increased peroxisome proliferator-activated receptor γ (PPARγ) and PPARγ coactivator 1α expression, whereas LXRα and PGC-1β expression was significantly lowered. Although the repressive effect of ABCA1 and ABCG1 mRNA by unsaturated FA was abolished by T0901317, protein levels remained diminished. Chemical and genetic deficiency of protein kinase C δ did not abolish the repressive effect of linoleic acid on ABCA1 and ABCG1. In conclusion, unsaturated FA repressed ABCA1 and ABCG1 expression by two distinct mechanisms in RAW 264.7 macrophages: LXR-dependent transcriptional repression possibly by modulating histone acetylation state and LXR-independent posttranslational inhibition.

Astaxanthin lowers plasma TAG concentrations and increases hepatic antioxidant gene expression in diet-induced obesity mice

Non-alcoholic fatty liver disease (NAFLD) is significantly associated with hyperlipidaemia and oxidative stress. We have previously reported that astaxanthin (ASTX), a xanthophyll carotenoid, lowers plasma total cholesterol and TAG concentrations in apoE knockout mice. To investigate whether ASTX supplementation can prevent the development of NAFLD in obesity, male C57BL/6J mice (n 8 per group) were fed a high-fat diet (35%, w/w) supplemented with 0, 0.003, 0.01 or 0.03% of ASTX (w/w) for 12 weeks. The 0.03% ASTX-supplemented group, but not the other groups, exhibited a significant decrease in plasma TAG concentrations, suggesting that ASTX at a 0.03% supplementation dosage exerts a hypotriacylglycerolaemic effect. Although there was an increase in the mRNA expression of fatty acid synthase and diglyceride acyltransferase 2, the mRNA levels of acyl-CoA oxidase 1, a critical enzyme in peroxisomal fatty acid β-oxidation, exhibited an increase in the 0.03% ASTX-supplemented group. There was a decrease in plasma alanine transaminase (ALT) and aspartate transaminase (AST) concentrations in the 0.03% ASTX-supplemented group. There was a significant increase in the hepatic mRNA expression of nuclear factor erythroid 2-related factor 2 and its downstream genes, which are critical for endogenous antioxidant mechanism, in the 0.03% ASTX-supplemented group. Furthermore, there was a significant decrease in the mRNA abundance of IL-6 in the primary splenocytes isolated from the 0.03% ASTX-supplemented group upon lipopolysaccharide (LPS) stimulation when compared with that in the splenocytes isolated from the control group. In conclusion, ASTX supplementation lowered the plasma concentrations of TAG, ALT and AST, increased the hepatic expression of endogenous antioxidant genes, and rendered splenocytes less sensitive to LPS stimulation. Therefore, ASTX may prevent obesity-associated metabolic disturbances and inflammation.

Polyphenol-rich blackcurrant extract exerts hypocholesterolaemic and hypoglycaemic effects in mice fed a diet containing high fat and cholesterol

Obesity is associated with an increased risk of metabolic abnormalities, such as hyperlipidaemia and hyperglycaemia. We investigated whether polyphenol-rich blackcurrant extract (BCE) can prevent high fat/high cholesterol (HF/HC) diet-induced metabolic disturbances in mice. Male C57BL/6J mice were fed a modified AIN-93M diet containing HF/HC (16% fat, 0·25% cholesterol, w/w) or the same diet supplemented with 0·1% BCE (w/w) for 12 weeks. There were no differences in total body weight and liver weight between groups. Plasma total cholesterol (TC) and glucose levels were significantly lower in BCE group than in controls, while plasma TAG levels were not significantly different. There was a decreasing trend in hepatic TAG levels, and histological evaluation of steatosis grade was markedly lower in the livers of mice fed BCE. Although the mRNA levels of major regulators of hepatic cholesterol metabolism, i.e. 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMGR) and LDL receptor (LDLR), were not significantly altered by BCE supplementation, protein expression of mature sterol-regulatory element-binding protein and LDLR was significantly increased with no change in HMGR protein. The expression of proprotein convertase subtilisin/kexin type 9 that facilitates LDLR protein degradation, as well as one of its transcriptional regulators, i.e. hepatocyte nuclear factor 4α, was significantly decreased in the livers of mice fed BCE. Taken together, BCE supplementation decreased plasma TC and glucose, and inhibited liver steatosis, suggesting that this berry may be consumed to prevent metabolic dysfunctions induced by diets high in fat and cholesterol.

Unsaturated fatty acids repress the expression of ATP-binding cassette transporter A1 in HepG2 and FHs 74 Int cells

Adenosine triphosphate-binding cassette transporter A1 (ABCA1) plays a critical role in the formation and metabolism of high-density lipoproteins (HDLs). Adenosine triphosphate-binding cassette transporter A1 in the liver and small intestine, in particular, accounts for approximately 90% of plasma HDL cholesterol. Therefore, any alterations in the hepatic and intestinal expression of ABCA1 could have a large impact on HDL biogenesis. We tested the hypothesis that ABCA1 expression is regulated differentially by different types of fatty acids in the liver and small intestine. Human hepatoma HepG2 and human small intestine epithelial FHs 74 Int cells were used as an in vitro model. Cells were incubated with saturated and unsaturated fatty acids in the presence or absence of T0901317, a synthetic agonist of liver X receptor. Unsaturated fatty acids decreased ABCA1 protein levels at 100 μmol/L of concentration regardless of the agonist with a minimal effect on messenger RNA abundance. Incubation of HepG2 and FHs 74 Int cells with rottlerin, a protein kinase C δ (PKCδ) inhibitor, increased ABCA1 protein but did not abolish linoleic acid-induced decrease in ABCA1 protein levels. Depletion of PKCδ using small interfering RNA showed decreased ABCA1 protein levels in control, palmitic acid-, and linoleic acid-treated cells; but the repressive effect of linoleic acid was sustained. In conclusion, our results indicate that unsaturated fatty acids regulate ABCA1 expression in HepG2 and FHs 74 Int cells at the posttranscriptional level and PKCδ is likely to be involved in maintaining ABCA1 protein levels.

Astaxanthin inhibits inflammation and fibrosis in the liver and adipose tissue of mouse models of diet-induced obesity and nonalcoholic steatohepatitis

The objective of this study was to determine if astaxanthin (ASTX), a xanthophyll carotenoid, can prevent obesity-associated metabolic abnormalities, inflammation and fibrosis in diet-induced obesity (DIO) and nonalcoholic steatohepatitis (NASH) mouse models. Male C57BL/6J mice were fed a low-fat (6% fat, w/w), a high-fat/high-sucrose control (HF/HS; 35% fat, 35% sucrose, w/w), or a HF/HS containing ASTX (AHF/HS; 0.03% ASTX, w/w) for 30 weeks. To induce NASH, another set of mice was fed a HF/HS diet containing 2% cholesterol (HF/HS/HC) a HF/HS/HC with 0.015% ASTX (AHF/HS/HC) for 18 weeks. Compared to LF, HF/HS significantly increased plasma total cholesterol, triglyceride and glucose, which were lowered by ASTX. ASTX decreased hepatic mRNA levels of markers of macrophages and fibrosis in both models. The effect of ASTX was more prominent in NASH than DIO mice. In epididymal fat, ASTX also decreased macrophage infiltration and M1 macrophage marker expression, and inhibited hypoxia-inducible factor 1-α and its downstream fibrogenic genes in both mouse models. ASTX significantly decreased tumor necrosis factor α mRNA in the splenocytes from DIO mice upon lipopolysaccharides stimulation compared with those from control mice fed an HF/HS diet. Additionally, ASTX significantly elevated the levels of genes that regulate fatty acid β-oxidation and mitochondrial biogenesis in the skeletal muscle compared with control obese mice, whereas no differences were noted in adipose lipogenic genes. Our results indicate that ASTX inhibits inflammation and fibrosis in the liver and adipose tissue and enhances the skeletal muscles capacity for mitochondrial fatty acid oxidation in obese mice.

Blueberry, blackberry, and blackcurrant differentially affect plasma lipids and pro-inflammatory markers in diet-induced obesity mice

BACKGROUND/OBJECTIVES Evidence indicates that berry anthocyanins are anti-atherogenic, antioxidant, and anti-inflammatory. However, berries differ vastly in their anthocyanin composition and thus potentially in their biological and metabolic effects. The present study compared hypolipidemic, antioxidant, and anti-inflammatory properties of blueberry (BB), blackberry (BK), and blackcurrant (BC) in a diet-induced obesity (DIO) mouse model. MATERIALS/METHODS Male C57BL/6J mice were fed a high fat (HF; 35% fat, w/w) control diet or a HF diet supplemented with freeze-dried 5% BB, 6.3% BK or 5.7% BC for 12 weeks (10 mice/group) to achieve the same total anthocyanin content in each diet. Plasma lipids, antioxidant status and pro-inflammatory cytokines were measured. The expression of genes involved in antioxidant defense, inflammation, and lipid metabolism was determined in the liver, epididymal adipose tissue, proximal intestine, and skeletal muscle. Histological analysis was performed to identify crown-like structure (CLS) in epididymal fat pads to determine macrophage infiltration. RESULTS No differences were noted between the control and any berry-fed groups in plasma levels of liver enzymes, insulin, glucose, ferric reducing antioxidant power, superoxide dismutase, and tumor necrosis factor α. However, BK significantly lowered plasma triglyceride compared with the HF control and other berries, whereas BC significantly reduced F4/80 mRNA and the number of CLS in the epididymal fat pad, indicative of less macrophage infiltration. CONCLUSIONS The present study provides evidence that BB, BK and BC with varying anthocyanin composition differentially affect plasma lipids and adipose macrophage infiltration in DIO mice, but with no differences in their antioxidant capacity and anti-inflammatory potential.