Jialin Xu

Enhanced Nrf2 Activity Worsens Insulin Resistance, Impairs Lipid Accumulation in Adipose Tissue, and Increases Hepatic Steatosis in Leptin-Deficient Mice

The study herein determined the role of nuclear factor erythoid 2–related factor 2 (Nrf2) in the pathogenesis of hepatic steatosis, insulin resistance, obesity, and type 2 diabetes. Lepob/ob-Keap1-knockdown (KD) mice, which have increased Nrf2 activity, were generated. Markers of obesity and type 2 diabetes were measured in C57Bl/6J, Keap1-KD, Lepob/ob, and Lepob/ob-Keap1-KD mice. Lepob/ob-Keap1-KD mice exhibited less lipid accumulation, smaller adipocytes, decreased food intake, and reduced lipogenic gene expression. Enhanced Nrf2 activity impaired insulin signaling, prolonged hyperglycemia in response to glucose challenge, and induced insulin resistance in Lepob/ob background. Nrf2 augmented hepatic steatosis and increased lipid deposition in liver. Next, C57Bl/6J and Keap1-KD mice were fed a high-fat diet (HFD) to determine whether Keap1 and Nrf2 impact HFD-induced obesity. HFD-induced obesity and lipid accumulation in white adipose tissue was decreased in Keap1-KD mice. Nrf2 activation via Keap1-KD or sulforaphane suppressed hormone-induced differentiation and decreased peroxisome proliferator–activated receptor-γ, CCAAT/enhancer–binding protein α, and fatty acid–binding protein 4 expression in mouse embryonic fibroblasts. Constitutive Nrf2 activation inhibited lipid accumulation in white adipose tissue, suppressed adipogenesis, induced insulin resistance and glucose intolerance, and increased hepatic steatosis in Lepob/ob mice.

UDP-Glucuronosyltransferase Expression in Mouse Liver Is Increased in Obesity- and Fasting-Induced Steatosis

UDP-glucuronosyltransferases (Ugt) catalyze phase II conjugation reactions with glucuronic acid, which enhances chemical polarity and the elimination from the body. Few studies have addressed whether Ugt expression and activity are affected by liver disease, such as steatosis. The purpose of this study was to determine whether steatosis induced by obesity or fasting could affect liver Ugt mRNA expression and activity. Male C57BL/6J and Lepob/ob (ob/ob) mice were fed ad libitum or food was withheld for 24 h. In steatotic livers of ob/ob mice, Ugt1a1, -1a6, -1a9, -2a3, -3a1, and -3a2 mRNA expression increased. Fasting, which also induced steatosis, increased hepatic Ugt1a1, -1a6, -1a7, -1a9, -2b1, -2b5, -2a3, -3a1, and -3a2 mRNA expression in mouse liver. Likewise, acetaminophen glucuronidation increased by 47% in hepatic microsomes from ob/ob mice compared with that in C57BL/6J mice, but not after fasting. In both steatosis models, Ugt induction was accompanied by increased aryl hydrocarbon receptor, constitutive androstane receptor (CAR), peroxisome proliferator-activated receptor (PPAR)-α, pregnane X receptor, nuclear factor (erythroid-derived 2)-like 2 (Nrf2), and peroxisome proliferator-activated receptor-γ coactivator-1α mRNA expression. In addition, fasting increased CAR, PPAR, and Nrf2 binding activity. The work points to hepatic triglyceride concentrations corresponding with nuclear receptor and Ugt expression. The findings indicate that steatosis significantly alters hepatic Ugt expression and activity, which could have a significant impact on determining circulating hormone levels, drug efficacy, and environmental chemical clearance.

Keap1 knockdown increases markers of metabolic syndrome after long-term high fat diet feeding

The nuclear factor E2-related factor 2 (Nrf2)-Kelch-like ECH-associated protein 1 (Keap1) pathway upregulates antioxidant and biotransformation enzyme expression to counter cellular oxidative stress. The contributions of Nrf2 to other cellular functions, such as lipid homeostasis, are emerging. This study was conducted to determine how enhanced Nrf2 activity influences the progression of metabolic syndrome with long-term high-fat diet (HFD) feeding. C57BL/6 and Keap1-knockdown (Keap1-KD) mice, which exhibit enhanced Nrf2 activity, were fed a HFD for 24 weeks. Keap1-KD mice had higher body weight and white adipose tissue mass compared to C57BL/6 mice on HFD, along with increased inflammation and lipogenic gene expression. HFD feeding increased hepatic steatosis and inflammation to a greater extent in Keap1-KD mice compared to C57BL/6 mice, which was associated with increased liver Cd36, fatty acid-binding protein 4, and monocyte chemoattractant protein 1 mRNA expression, as well as increased acetyl-CoA carboxylase 1 and stearoyl-CoA desaturase-1 protein expression. The HFD altered short-term glucose homeostasis to a greater degree in Keap-KD mice compared to C57BL/6 mice, which was accompanied by downregulation of insulin receptor substrate 1 mRNA expression in skeletal muscle. Together, the results indicate that Keap1 knockdown, on treatment with HFD, increases certain markers of metabolic syndrome.

Antidiabetic ellagitannins from pomegranate flowers: inhibition of α-glucosidase and lipogenic gene expression.

Two new ellagitannins containing a rare 3-oxo-1,3,3a,8b-tetrahydrofuro[3,4-b]benzofuran moiety, namely punicatannins A (1) and B (2), were isolated from pomegranate (Punica granatum) flowers. Their structures with absolute configuration were determined by detailed analysis of spectroscopic data, electronic circular dichroism (ECD) calculation, and chemical hydrolysis. A plausible biogenetic route involving a key enzymatic 1,4-Michael addition is proposed. Punicatannin A showed potent inhibition of α-glucosidase and lipogenic gene expression.

Effects of Developmental Deltamethrin Exposure on White Adipose Tissue Gene Expression

Deltamethrin, a type II pyrethroid, is a widely used insecticide. The purpose of this study was to determine whether perinatal deltamethrin exposure altered the expression of adipogenic and lipogenic genes in white adipose tissue (WAT) in adult pups. C57BL/6 pregnant mice were administered 0, 1, or 3 mg/kg of deltamethrin orally every 3 days throughout gestation and lactation. Offspring were weaned on postnatal day 25, and WAT was collected from 5‐month‐old male mice. Perinatal deltamethrin exposure decreased the mRNA expression of adipogenesis‐related transcription factors Pparγ, Cebpα, and lipogenic genes Srebp1c, Acc‐1, Cd36, Lpl, Scd‐1; along with Nrf2 and target genes Nqo1 and Gclc at the 1 mg/kg treatment. Cytokine expression of Fas/Tnf‐R and Cd209e at the 1 mg/kg treatment was significantly decreased, and expression of Tnf, Cd11c, and Fas/Tnf‐R was decreased at the 3 mg/kg treatment. Developmental deltamethrin exposure did not overtly affect body weight or adipose weight, but decreased mRNA expression of specific genes that may potentially disrupt normal adipogenesis and lipid and glucose metabolism if the offspring are challenged by changes in diet or environment.

Urolithins Attenuate LPS-Induced Neuroinflammation in BV2Microglia via MAPK, Akt, and NF-κB Signaling Pathways

Emerging data suggest that urolithins, gut microbiota metabolites of ellagitannins, contribute toward multiple health benefits attributed to ellagitannin-rich foods, including walnuts, red raspberry, strawberry, and pomegranate. However, there is limited data on whether the potential neuroprotective effects of these ellagitannin-rich foods are mediated by urolithins. Herein, we evaluated the potential mechanisms of antineuroinflammatory effects of urolithins (urolithins A, B, and C; 8-methyl-O-urolithin A; and 8,9-dimethyl-O-urolithin C) in BV2 murine microglia in vitro. Nitrite analysis and qRT-PCR suggested that urolithins A and B reduced NO levels and suppressed mRNA levels of pro-inflammatory genes of TNF-α, IL-6, IL-1β, iNOS, and COX-2 in LPS-treated microglia. Western blot revealed that urolithins A and B decreased phosphorylation levels of Erk1/2, p38 MAPK, and Akt, prevented IκB-α phosphorylation and degradation, and inhibited NF-κB p65 subunit phosphorylation and nuclear translocation in LPS-stimulated microglia. Our results indicated that urolithins A and B attenuated LPS-induced inflammation in BV2 microglia, which may be mediated by inhibiting NF-κB, MAPKs (p38 and Erk1/2), and Akt signaling pathway activation. The antineuroinflammatory activities of urolithins support their role in the potential neuroprotective effects reported for ellagitannin-rich foods warranting further in vivo studies on these ellagitannin gut microbial derived metabolites.

Effect of Caloric Restriction and AMPK Activation on Hepatic Nuclear Receptor, Biotransformation Enzyme, and Transporter Expression in Lean and Obese Mice

PurposeFatty liver alters liver transporter expression. Caloric restriction (CR), the recommended therapy to reverse fatty liver, increases Sirtuin1 deacetylase activity in liver. This study evaluated whether CR and CR mimetics reversed obesity-induced transporter expression in liver and hepatocytes.MethodsmRNA and protein expression was determined in adult lean (lean) and leptin-deficient obese (OB) mice fed ad libitum or placed on 40% (kCal) reduced diet. Hepatocytes were isolated from lean and OB mice, treated with AMP Kinase activators, and gene expression was determined.ResultsCR decreased Oatp1a1, Oatp1b2, and Abcb11 mRNA expression in lean, but not OB mice. CR increased Abcc2 mRNA OB livers, whereas protein expression increased in both genotypes. CR increased Abcc3 protein expression increased in OB livers. CR did not alter Abcc1, 4 and 5 mRNA expression in lean mice but decreased expression in livers of OB mice. CR increased Abcc4 protein in lean, but not OB mice.ConclusionsCR restriction reversed the expression of some, but not all transporters in livers of OB mice. Overall, these data indicate a potential for CR to restore some hepatic transporter changes in OB mice, but suggest a functional leptin axis is needed for reversal of expression for some transporters.