A single gene of a commensal microbe affects host susceptibility to enteric infection.

Indigenous microbes inside the host intestine maintain a complex self-regulating community. The mechanisms by which gut microbes interact with intestinal pathogens remain largely unknown. Here we identify a commensal Escherichia coli strain whose expansion predisposes mice to infection by Vibrio cholerae, a human pathogen. We refer to this strain as 'atypical' E. coli (atEc) because of its inability to ferment lactose. The atEc strain is resistant to reactive oxygen species (ROS) and proliferates extensively in antibiotic-treated adult mice. V. cholerae infection is more severe in neonatal mice transplanted with atEc compared with those transplanted with a typical E. coli strain. Intestinal ROS levels are decreased in atEc-transplanted mice, favouring proliferation of ROS-sensitive V. cholerae. An atEc mutant defective in ROS degradation fails to facilitate V. cholerae infection when transplanted, suggesting that host infection susceptibility can be regulated by a single gene product of one particular commensal species.

Orotic acid induces hypertension associated with impaired endothelial nitric oxide synthesis.

Orotic acid (OA) is an intermediate of pyrimidine nucleotide biosynthesis. Hereditary deficiencies in some enzymes associated with pyrimidine synthesis or the urea cycle induce OA accumulation, resulting in orotic aciduria. A link between patients with orotic aciduria and hypertension has been reported; however, the molecular mechanisms remain elusive. In this study, to elucidate the role of OA in vascular insulin resistance, we investigated whether OA induced endothelial dysfunction and hypertension. OA inhibited insulin- or metformin-stimulated nitric oxide (NO) production and endothelial NO synthase (eNOS) phosphorylation in human umbilical vein endothelial cells. A decreased insulin response by OA was mediated by impairment of the insulin-stimulated phosphoinositide 3-kinase (PI3K)-protein kinase B (PKB/Akt) signaling pathway in cells overexpressing the p110-PI3K catalytic subunit. Impaired effects of metformin on eNOS phosphorylation and NO production were reversed in cells transfected with constitutively active AMP-activated protein kinase. Moreover, experimental induction of orotic aciduria in rats caused insulin resistance, measured as a 125% increase in the homeostasis model assessment, and hypertension, measured as a 25% increase in systolic blood pressure. OA increased the plasma concentration of endothelin-1 by 201% and significantly inhibited insulin- or metformin-induced vasodilation. A compromised insulin or metformin response on the Akt/eNOS and AMP-activated protein kinase/eNOS pathway was observed in aortic rings of OA-fed rats. Taken together, we showed that OA induces endothelial dysfunction by contributing to vascular and systemic insulin resistance that affects insulin- or metformin-induced NO production, leading to the development of hypertension.

Protective effect of resveratrol derivatives on high-fat diet induced fatty liver by activating AMP-activated protein kinase.

Non-alcoholic fatty liver disease is associated with inhibited AMP-activated kinase (AMPK) and activation of sterol regulatory element binding protein 1 (SREBP-1). AMPK phosphorylation inhibits SREBP-1, a major transcription factor of de novo lipogenesis, by inhibiting the liver X receptor (LXR) or by direct phosphorylation. Resveratrol, a polyphenol, has regulatory effects on hepatic lipid metabolism as a potent AMPK activator. In this study, we evaluated the anti-steatogenic effects of resveratrol and its derivatives and identified the molecular mechanism in vitro and in vivo. Resveratrol and its derivatives decreased lipid accumulation by free fatty acids (FFA mixture; 0.5 mM, oleic acid:palmitic acid = 2: 1) in H4IIEC3 cells. Synthesized derivatives of resveratrol had lower cytotoxicity than the parental molecule with similar potency. SY-102 suppressed SREBP-1 maturation by T0901317, an LXR agonist, and decreased SRE luciferase activity and the mRNA levels of lipogenic genes. Inhibition of AMPK by pre-treatment with compound C completely blocked the effects of SY-102. To evaluate their efficacy in vivo, mice were fed a high-fat diet for 5 days, and resveratrol or SY-102 was administered orally for the last 2 days. Oral administration of the SY-102 increased AMPK phosphorylation, followed by reduced hepatic triglyceride accumulation to a similar extent as resveratrol. These data demonstrate that SY-102, a synthesized derivative of resveratrol, might provide a promising therapeutic effect against fatty liver disease.

Uric acid induces endothelial dysfunction by vascular insulin resistance associated with the impairment of nitric oxide synthesis.

Endothelial dysfunction is defined as impairment of the balance between endothelium-dependent vasodilation and constriction. Despite evidence of uric acid-induced endothelial dysfunction, a relationship with insulin resistance has not been clearly established. In this study, we investigated the role of vascular insulin resistance in uric acid-induced endothelial dysfunction. Uric acid inhibited insulin-induced endothelial nitric oxide synthase (eNOS) phosphorylation and NO production more substantially than endothelin-1 expression in HUVECs, with IC50 of 51.0, 73.6, and 184.2, respectively. Suppression of eNOS phosphorylation and NO production by uric acid was PI3K/Akt-dependent, as verified by the transfection with p110. Treatment of rats with the uricase inhibitor allantoxanamide induced mild hyperuricemia and increased mean arterial pressure by 25%. While hyperuricemic rats did not show systemic insulin resistance, they showed impaired vasorelaxation induced by insulin by 56%. A compromised insulin response in terms of the Akt/eNOS pathway was observed in the aortic ring of hyperuricemic rats. Coadministration with allopurinol reduced serum uric acid levels and blood pressure and restored the effect of insulin on Akt-eNOS pathway and vasorelaxation. Taken together, uric acid induced endothelial dysfunction by contributing to vascular insulin resistance in terms of insulin-induced NO production, potentially leading to the development of hypertension.-Choi, Y.-J., Yoon, Y., Lee, K.-Y., Hien, T. T., Kang, K. W., Kim, K.-C., Lee, J., Lee, M.-Y., Lee, S. M., Kang, D.-H., Lee, B.-H. Uric acid induces endothelial dysfunction by vascular insulin resistance associated with the impairment of nitric oxide synthesis.

Functional screening of a metagenomic library reveals operons responsible for enhanced intestinal colonization by gut commensal microbes.

Evidence suggests that gut microbes colonize the mammalian intestine through propagation as an adhesive microbial community. A bacterial artificial chromosome (BAC) library of murine bowel microbiota DNA in the surrogate host Escherichia coli DH10B was screened for enhanced adherence capability. Two out of 5,472 DH10B clones, 10G6 and 25G1, exhibited enhanced capabilities to adhere to inanimate surfaces in functional screens. DNA segments inserted into the 10G6 and 25G1 clones were 52 and 41 kb and included 47 and 41 protein-coding open reading frames (ORFs), respectively. DNA sequence alignments, tetranucleotide frequency, and codon usage analysis strongly suggest that these two DNA fragments are derived from species belonging to the genus Bacteroides. Consistent with this finding, a large portion of the predicted gene products were highly homologous to those of Bacteroides spp. Transposon mutagenesis and subsequent experiments that involved heterologous expression identified two operons associated with enhanced adherence. E. coli strains transformed with the 10a or 25b operon adhered to the surface of intestinal epithelium and colonized the mouse intestine more vigorously than did the control strain. This study has revealed the genetic determinants of unknown commensals (probably resembling Bacteroides species) that enhance the ability of the bacteria to colonize the murine bowel.

Effects of Medicinal herb Extracts and their Components on Steatogenic Hepatotoxicity in Sk-hep1 Cells.

Herbal medicines are widely used in many countries for the treatment of many diseases. Although the use of herb extracts as alternative medicine is growing, their toxicological properties have not been thoroughly investigated. In this study, we have investigated the effects of water and ethanol extracts of 18 herbs on the hepatic lipid metabolism and steatogenic hepatotoxicity. Ethanol extracts of Cirsium japonicum, Carthamus tinctorius, Rehmanniae glutinosa (preparata), Polygala tenuifolia, Foeniculum vulgare, Polygonum multiflorum, and Acorus gramineus and water extracts of Polygonum multiflorum and Rehmanniae glutinosa induced lipid accumulation in Sk-hep1 human hepatoma cells as determined by Nile red staining. These extracts increased the luciferase activity of sterol regulatory element (SRE) and decreased that of peroxisome proliferator response element (PPRE), indicating the possibilities of enhanced fatty acid synthesis and decreased fatty acid oxidation. To identify the components responsible for the fat accumulation, we tested 50 chemicals isolated from the nine herbs. Apigenin, luteolin, pectolinarin and lupeol from Cirsium japonicum, 8-methoxypsoralen and umbelliferone from Foeniculum vulgare and pomonic acid and jiocerebroside from Rehmanniae glutinosa significantly increased the accumulation of lipid droplets. These results suggest that ethanol extracts of Cirsium japonicum, Carthamus tinctorius, Rehmanniae glutinosa (preparata), Polygala tenuifolia, Foeniculum vulgare, Polygonum multiflorum, and Acorus gramineus and water extracts of Polygonum multiflorum and Rehmanniae glutinosa can cause fatty liver disease by decreasing ß-oxidation of fatty acid and increasing lipogenesis.