A pharmacologic increase in activity of plasma transaminase derived from small intestine in animals receiving an acyl CoA: diacylglycerol transferase (DGAT) 1 inhibitor

Diacylglycerol O-acyltransferase 1 inhibitor increases plasma alanine aminotransferase and aspartate aminotransferase activities via a shedding of the intestinal villi and an increase in intestinal permeability in rats

Diacylglycerol O-acyltransferase 1 (DGAT1) is a key enzyme for fat absorption step in the enterocytes. We previously reported that DGAT1 inhibition increased plasma alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities in corn oil-loaded rats via protein kinase C (PKC) activation. In the present study, we investigated the mechanism with respect to the morphology and permeability of the small intestine, focusing on PKC function, and found that shortening of the intestinal villi and a decrease in the number of tdT-mediated dUTP-biotin nick-end labeling-positive cells in the tips of the villi were observed in the jejunum of DGAT1 inhibitor-treated rats loaded with corn oil. These results suggested that the tips of the villi were shed into the intestinal lumen. Next, fluorescein isothiocyanate-dextran, 110 kDa (FD-110) was administered intraduodenally to DGAT1 inhibitor-treated rats loaded with corn oil and we found that plasma FD-110 concentrations increased, indicating that the intestinal permeability to molecules with a molecular weight of approximately 110,000 (e.g., ALT and AST) increased. Taken together, the present results suggested that DGAT1 inhibitor-treatment in combination with corn oil causes ALT and AST to leak from the enterocytes into the blood by shedding the tips of the intestinal villi and increasing intestinal permeability.

Transcriptome and iTRAQ-Based Proteome Reveal the Molecular Mechanism of Intestinal Injury Induced by Weaning Ewe's Milk in Lambs

Early feeding regime has a substantial lifelong effect on lambs and weaning ewe's milk can lead to the intestinal injury of lambs. To explore the molecular regulatory mechanism of intestinal injury of lambs under weaning stress, the jejunum was conducted transcriptome and then integrated analyzed with our previous proteome data. A total of 255 upregulated genes and 285 downregulated genes were significantly identified. These genes showed low overlapping with differentially expressed proteins identified by isobaric tags for relative and absolute quantification (iTRAQ). However, according to their functions, the differentially expressed genes (DEGs) and proteins with the same expression trend were enriched for the similar Gene Ontology (GO) terms and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, such as intestinal lipid absorption, urea cycle, peroxisome proliferator-activated receptor (PPAR) signaling pathway, and ferroptosis. Furthermore, the DEGs, including FABP2, ACSL3, APOA2, APOC3, and PCK1, might play essential roles in intestinal lipid absorption and immune response through the PPAR signaling pathway and ferroptosis. This study could provide new insights into early lamb breeding at the molecular level.

Acyl-CoA:diacylglycerol acyltransferase 1 inhibition in the small intestine increases plasma transaminase activity via the activation of protein kinase C pathway

Acyl-CoAdiacylglycerol acyltransferase 1 (DGAT1) is a key enzyme in the fat absorption step in enterocytes. We previously reported that the pharmacological inhibition of DGAT1 increased plasma alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activity in corn oil-loaded rats without any sign of hepatotoxicity. In this study, we investigated this mechanism. We found that this elevation occurred only during the pharmacologically active period of a DGAT1 inhibitor and the magnitude did not depend on the volume of corn oil. In addition, this elevation was not accompanied by increases in ALT or AST mRNA levels in the small intestine and liver. To clarify a lipid component responsible for this elevation, rats were treated with free fatty acids instead of corn oil and no plasma ALT elevation was observed. Next, rats were pretreated with inhibitors of monoacylglycerol acyltransferase 2 and intestinal microsomal triglyceride transfer protein instead of the DGAT1 inhibitor, but no plasma ALT elevation was observed after corn oil loading. Since the results suggested a possible role of diacylglycerol (DAG), which activates protein kinase C (PKC), we measured PKC activity in the small intestine and found that the activity was increased by treatment with the DGAT1 inhibitor and corn oil. Moreover, rats pretreated with a PKC inhibitor in combination with the DGAT1 inhibitor showed suppression of plasma ALT elevation. Taken together, the present results suggest that DAG accumulation induced by pharmacological DGAT1 inhibition and resultant PKC activation in enterocytes are involved in the increase in plasma ALT and AST activity in rats.

Effects of 1,25(OH)2 D3 on lipid droplet growth in adipocytes

This study aimed to explore the effects of 1,25(OH)2 D3 on lipid droplet (LD) growth in 3T3-L1 adipocytes of hypertrophy model. Cocktail method was used to induce differentiation in 3T3-L1 cells. After 8 days, the cells were modeled by 100, 300, 600, and 900 μM palmitic acid (PA) for 24 hr. The best concentration of modeling was screened by MTT results and triglycerides (TG) content. The model cells were intervened by 1, 10, and 100 nM 1,25(OH)2 D3 for 24 hr. Then, the TG content of cells were detected and stained by oil red O. The diameter and quantity of LDs were analyzed. mRNA relative expression levels of genes related to LD (CIDE-a, Fsp27, PLIN-1), upstream response factor (PPAR-α, PPAR-γ, and VDR), and TG metabolism (long chain acyl-CoA synthetase 3, 1-acylglycerol-3-phosphate O-acyltransferase 1, adipose triglyceride lipase, diacylglycerol acyltransferase 1, diacylglycerol acyltransferase 2, glycerol-3-phosphate O-acyltransferase 3, glycerol-3-phosphate O-acyltransferase 4, hormone-sensitive lipase, mannosyl (alpha-1,3-)-glycoprotein beta-1,2-N-acetyl glucosaminyl transferase, phosphatidic acid phosphatase, and uncoupling protein-1) were detected by RT-qPCR. A total of 300 μM PA was selected as the optimum concentration. Compared with model group, 10 and 100 nM 1,25(OH)2 D3 decreased the average diameter, increased the quantity of LDs, upregulated PPAR-α and PLIN-1 mRNA expression levels, and downregulated CIDE-a and Fsp27 mRNA expression levels significantly (p < .05). However, 1 nM 1,25(OH)2 D3 did not alter LD morphology and TG content. mRNA expression levels of long chain acyl-CoA synthetase 3, 1-acylglycerol-3-phosphate O-acyltransferase 1, diacylglycerol acyltransferase 2, glycerol-3-phosphate O-acyltransferase 3, and glycerol-3-phosphate O-acyltransferase 4 in 10 and 100 nM groups were significantly lower than those in the model group (p < .05); mRNA expression levels of adipose triglyceride lipase, diacylglycerol acyltransferase 1, hormone-sensitive lipase, mannosyl (alpha-1,3-)-glycoprotein beta-1,2-N-acetyl glucosaminyl transferase, phosphatidic acid phosphatase, and uncoupling protein-1 were significantly increased in the 100 nM group (p < .05). The 10 and 100 nM 1,25(OH)2 D3 can inhibit LD fusion, promote LD decomposition, reduce LD volume, and inhibit lipogenesis through the PPAR-α signaling pathway.

Specificity of transaminase activities in the prediction of drug-induced hepatotoxicity

The activities of the transaminases (aminotransferases) alanine aminotransferase and aspartate aminotransferase in the blood (serum or plasma) are widely used as sensitive markers of possible tissue damage and, in particular for liver toxicity. On the other hand, an increase in transaminase activities is not always accompanied by findings suggestive of hepatotoxicity. Transaminases are some of the key enzymes in the gluconeogenesis and glycolysis pathways and exist in many organs and tissues which have high activities of the gluconeogenesis and glycolysis. The activities of transaminases are altered not only in the liver but also in other organs by modification of gluconeogenesis by nutritional or hormonal factors and this phenomenon leads to alteration of transaminase activity in the blood. Drugs, which are considered to directly or secondarily modify gluconeogenesis through lowering blood glucose levels or activating lipid metabolism, such as α-glucosidase inhibitors and fibrates, slightly increase transaminase activities in the blood but there is little evidence that the phenomenon is related to drug-induced liver injury (DILI). This type of elevations can be called pharmacology-related elevation. The pharmacology-related elevation of transaminase activities sometimes makes it difficult to assess precisely the potential hepatotoxicity of new investigational drugs. Considering the characteristic of transaminases, concomitant use of new biomarkers more specific to hepatic injury is needed in the assessment of DILI both in non-clinical and clinical studies. In this review, we will discuss the specificity of transaminases to DILI and future perspectives for transaminases in the estimation of risk of DILI.