Faculty Bibliography

Dietary fat absorption takes place in the intestine, and the liver mobilizes endogenous fat to other tissues by synthesizing lipoproteins that require apoB and microsomal triglyceride transfer protein (MTP). Dietary fat triggers the synthesis of oleoylethanolamide (OEA), a regulatory fatty acid that signals satiety to reduce food intake mainly by enhancing neural PPARα activity, in enterocytes. We explored OEA's roles in the assembly of lipoproteins in WT and Ppara ^-/- mouse enterocytes and hepatocytes, Caco-2 cells, and human liver-derived cells. In differentiated Caco-2 cells, OEA increased synthesis and secretion of triacylglycerols, apoB secretion in chylomicrons, and MTP expression in a dose-dependent manner. OEA also increased MTP activity and triacylglycerol secretion in WT and knockout primary enterocytes. In contrast to its intestinal cell effects, OEA reduced synthesis and secretion of triacylglycerols, apoB secretion, and MTP expression and activity in human hepatoma Huh-7 and HepG2 cells. Also, OEA reduced MTP expression and triacylglycerol secretion in WT, but not knockout, primary hepatocytes. These studies indicate differential effects of OEA on lipid synthesis and lipoprotein assembly: in enterocytes, OEA augments glycerolipid synthesis and lipoprotein assembly independent of PPARα. Conversely, in hepatocytes, OEA reduces MTP expression, glycerolipid synthesis, and lipoprotein secretion through PPARα-dependent mechanisms.

Circadian rhythms controlled by clock genes affect plasma lipids. Here we show that global ablation of Bmal1 in Apoe^-/- and Ldlr^-/- mice and its liver-specific ablation in Apoe^-/- (L-Bmal1^-/-Apoe^-/-) mice increases, whereas overexpression of BMAL1 in L-Bmal1^-/-Apoe^-/- and Apoe^-/-mice decreases hyperlipidaemia and atherosclerosis. Bmal1 deficiency augments hepatic lipoprotein secretion and diminishes cholesterol excretion to the bile. Further, Bmal1 deficiency reduces expression of Shp and Gata4. Reductions in Shp increase Mtp expression and lipoprotein production, whereas reductions in Gata4 diminish Abcg5/Abcg8 expression and biliary cholesterol excretion. Forced SHP expression normalizes lipoprotein secretion with no effect on biliary cholesterol excretion, while forced GATA4 expression increases cholesterol excretion to the bile and reduces plasma lipids in L-Bmal1^-/-Apoe^-/- and Apoe^-/- mice. Thus, our data indicate that Bmal1 modulates lipoprotein production and biliary cholesterol excretion by regulating the expression of Mtp and Abcg5/Abcg8 via Shp and Gata4.

High plasma cholesterol levels are a major risk factor for atherosclerosis. Plasma cholesterol can be reduced by inhibiting lipoprotein production; however, this is associated with steatosis. Previously we showed that lentivirally mediated hepatic expression of microRNA-30c (miR-30c) reduced hyperlipidemia and atherosclerosis in mice without causing hepatosteatosis. Because viral therapy would be formidable, we examined whether a miR-30c mimic can be used to mitigate hyperlipidemia and atherosclerosis without inducing steatosis. Delivery of a miR-30c mimic to the liver diminished diet-induced hypercholesterolemia in C57BL/6J mice. Reductions in plasma cholesterol levels were significantly correlated with increases in hepatic miR-30c levels. Long term dose escalation studies showed that miR-30c mimic caused sustained reductions in plasma cholesterol with no obvious side effects. Furthermore, miR-30c mimic significantly reduced hypercholesterolemia and atherosclerosis in Apoe(-/-) mice. Mechanistic studies showed that miR-30c mimic had no effect on LDL clearance but reduced lipoprotein production by down-regulating microsomal triglyceride transfer protein expression. MiR-30c had no effect on fatty acid oxidation but reduced lipid synthesis. Additionally, whole transcriptome analysis revealed that miR-30c mimic significantly down-regulated hepatic lipid synthesis pathways. Therefore, miR-30c lowers plasma cholesterol and mitigates atherosclerosis by reducing microsomal triglyceride transfer protein expression and lipoprotein production and avoids steatosis by diminishing lipid syntheses. It mitigates atherosclerosis most likely by reducing lipoprotein production and plasma cholesterol. These findings establish that increasing hepatic miR-30c levels is a viable treatment option for reducing hypercholesterolemia and atherosclerosis.

The microbial fuel cell (MFC) was evaluated as an alternative way to recover electricity from canteen based food waste. Characteristics of the organics in food waste before and after the MFC treatment were analyzed to investigate how the organic matters were biodegraded and transformed during the MFC treatment. A maximum power density of 5.6W/m(3) and an average output voltage of 0.51V were obtained. During the MFC operation, the hydrophilic and acidic fractions were more readily degraded, compared to the neutral fractions. Additionally, aromatic compounds in the hydrophilic fraction were more preferentially removed than non-aromatic compounds. The MFC could easily remove the tryptophan protein-like substances in all fractions and aromatic proteins in hydrophilic and hydrophobic neutral fractions. Additionally, the hydrophobic amide-1 proteins and aliphatic components were readily hydrolyzed and biodegraded in the MFC. These findings may facilitate the pretreatment and posttreatment choices for MFC system fed with food waste.

AIMS/HYPOTHESIS/OBJECTIVE:Recent studies have suggested that determination of HDL function may be more informative than its concentration in predicting its protective role in coronary artery disease (CAD). Apolipoprotein AI (apoAI), the major protein of HDL, is nitrosylated in vivo to nitrated apoAI (NT-apoAI) that might cause dysfunction. We hypothesized that NT-apoAI/apoAI ratio might be associated with diabetes mellitus (DM) in CAD patients. METHODS:We measured plasma NT-apoAI and apoAI levels in 777 patients with coronary artery disease (CAD) by ELISA. Further, we measured plasma cholesterol efflux potential in subjects with similar apoAI but different NT-apoAI levels. RESULTS:We found that median NT-apoAI/apoAI ratio was significantly higher in diabetes mellitus (DM) (n = 327) versus non-diabetic patients (n = 450). Further analysis indicated that DM, thiobarbituric acid-reactive substances and C-reactive protein levels were independent predictors of higher NT-apoAI/apoAI ratio. There was negative correlation between NT-apoAI/apoAI and use of anti-platelet and lipid lowering drugs. The cholesterol efflux capacity of plasma from 67 individuals with differing NT-apoAI but similar apoAI levels from macrophages in vitro was negatively correlated with NT-apoAI/apoAI ratio. CONCLUSIONS:Higher NT-apoAI/apoAI ratio is significantly associated with DM in this relatively large German cohort with CAD and may contribute to associated complications by reducing cholesterol efflux capacity.

Various intestinal functions exhibit circadian rhythmicity. Disruptions in these rhythms as in shift workers and transcontinental travelers are associated with intestinal discomfort. Circadian rhythms are controlled at the molecular level by core clock and clock-controlled genes. These clock genes are expressed in intestinal cells, suggesting that they might participate in the circadian regulation of intestinal functions. A major function of the intestine is nutrient absorption. Here, we will review absorption of proteins, carbohydrates, and lipids and circadian regulation of various transporters involved in their absorption. A better understanding of circadian regulation of intestinal absorption might help control several metabolic disorders and attenuate intestinal discomfort associated with disruptions in sleep-wake cycles.

Among all the metabolites present in the plasma, lipids, mainly triacylglycerol and diacylglycerol, show extensive circadian rhythms. These lipids are transported in the plasma as part of lipoproteins. Lipoproteins are synthesized primarily in the liver and intestine and their production exhibits circadian rhythmicity. Studies have shown that various proteins involved in lipid absorption and lipoprotein biosynthesis show circadian expression. Further, intestinal epithelial cells express circadian clock genes and these genes might control circadian expression of different proteins involved in intestinal lipid absorption. Intestinal circadian clock genes are synchronized by signals emanating from the suprachiasmatic nuclei that constitute a master clock and from signals coming from other environmental factors, such as food availability. Disruptions in central clock, as happens due to disruptions in the sleep/wake cycle, affect intestinal function. Similarly, irregularities in temporal food intake affect intestinal function. These changes predispose individuals to various metabolic disorders, such as metabolic syndrome, obesity, diabetes, and atherosclerosis. Here, we summarize how circadian rhythms regulate microsomal triglyceride transfer protein, apoAIV, and nocturnin to affect diurnal regulation of lipid absorption.

OBJECTIVES/OBJECTIVE:ω-3 Fatty acids (FAs), natural ligands for the peroxisome proliferator-activated receptor-α (PPAR-α), attenuate parenteral nutrition-associated liver disease (PNALD). However, the mechanisms underlying the protective role of ω-3 FAs are still unknown. The aim of this study was to determine the effects of ω-3 FAs on hepatic triglyceride (TG) accumulation in a murine model of PNALD and to investigate the role of PPAR-α and microsomal triglyceride transfer protein (MTP) in this experimental setting. METHODS:129S1/SvImJ wild-type or 129S4/SvJaePparatm/Gonz/J PPAR-α knockout mice were fed chow and water (controls); oral, fat-free PN solution only (PN-O); PN-O plus intraperitoneal (IP) ω-6 FA-predominant supplements (PN-ω-6); or PN-O plus IP ω-3 FA (PN-ω-3). Control and PN-O groups received sham IP injections of 0.9% NaCl. Hepatic histology, TG and cholesterol, MTP activity, and PPAR-α messenger RNA were assessed after 19 days. RESULTS:In all experimental groups, PN feeding increased hepatic TG and MTP activity compared with controls. Both PN-O and PN-ω-6 groups accumulated significantly greater amounts of TG when compared with PN-ω-3 mice. Studies in PPAR-α null animals showed that PN feeding increases hepatic TG as in wild-type mice. PPAR-α null mice in the PN-O and PN-ω-6 groups demonstrated variable degrees of hepatic steatosis, whereas no evidence of hepatic fat accumulation was found after 19 days of oral PN plus IP ω-3 FAs. CONCLUSIONS:PN induces TG accumulation (steatosis) in wild-type and PPAR-α null mice. In PN-fed wild-type and PPAR-α null mice given IP ω-3 FAs, reduced hepatic TG accumulation and absent steatosis are found. Prevention of steatosis by ω-3 FAs results from PPAR-α-independent pathways.

Adsorptive fouling of microbial extracellular polymeric substances (EPS) greatly influences the fouling behavior and membrane characteristics in a membrane bioreactor (MBR). In this study, adsorptive fouling of the EPS on different membrane materials was compared and adsorptive mechanism between membranes and EPS was investigated by thermodynamic analysis. The results suggested that both the absolute and relative changes of hydraulic resistances should be considered to evaluate fouling of membranes with different materials, and Sips isotherm was the most suitable model to describe the EPS carbohydrate and protein adsorptions on membranes. Thermodynamic analysis showed that both EPS carbohydrate and protein adsorptions were spontaneous (ΔrG(θ) < 0), endothermic (ΔrH(θ) > 0), and entropy driven (ΔrS(θ) > 0). Decreasing ΔrG(θ) values with temperature suggested that EPS adsorptive fouling can be limited by reducing temperature. In addition, physisorption processes and hydrogen bonding interactions between EPS and membranes might play a relatively major role in the adsorption mechanism of EPS on the membrane surface. Atomic force microscopy (AFM) and contact angle analysis confirmed that the adsorptive fouling modified the membrane surface, making the membrane surface more heterogeneous and more hydrophobic.

ApoB-crescent, an endoplasmic reticulum (ER)-lipid droplet amalgamation structure, is a useful marker to indicate aberrant lipidated apolipoprotein B accumulation in the hepatocyte ER. Blockade of the ER-to-Golgi transport by either vesicle transport inhibitors or dominant-negative Arf1 caused a significant increase in ApoB-crescents. However, a low concentration of Brefeldin A induced the same result without affecting protein secretion, suggesting ADP-ribosylation as an additional mechanism. ADP-ribosylation inhibitors not only suppressed the increase of ApoB-crescents, but also rapidly dissolved existing ApoB-crescents. These results implicate the involvement of ADP-ribosylation in the ApoB-crescent formation and maintenance process at the ER.