Unique Regulation of Intestinal Villus Epithelial Cl−/HCO3− Exchange by Cyclooxygenase Pathway Metabolites of Arachidonic Acid in a Mouse Model of Spontaneous Ileitis

Electrolytes (NaCl) and fluid malabsorption cause diarrhea in inflammatory bowel disease (IBD). Coupled NaCl absorption, mediated by Na+/H+ and Cl−/HCO3− exchanges on the intestinal villus cells brush border membrane (BBM), is inhibited in IBD. Arachidonic acid metabolites (AAMs) formed via cyclooxygenase (COX) or lipoxygenase (LOX) pathways are elevated in IBD. However, their effects on NaCl absorption are not known. We treated SAMP1/YitFc (SAMP1) mice, a model of spontaneous ileitis resembling human IBD, with Arachidonyl Trifluoro Methylketone (ATMK, AAM inhibitor), or with piroxicam or MK-886, to inhibit COX or LOX pathways, respectively. Cl−/HCO3− exchange, measured as DIDS-sensitive 36Cl uptake, was significantly inhibited in villus cells and BBM vesicles of SAMP1 mice compared to AKR/J controls, an effect reversed by ATMK. Piroxicam, but not MK-886, also reversed the inhibition. Kinetic studies showed that inhibition was secondary to altered Km with no effects on Vmax. Whole cell or BBM protein levels of Down-Regulated in Adenoma (SLC26A3) and putative anion transporter-1 (SLC26A6), the two key BBM Cl−/HCO3− exchangers, were unaltered. Thus, inhibition of villus cell Cl−/HCO3− exchange by COX pathway AAMs, such as prostaglandins, via reducing the affinity of the exchanger for Cl−, and thereby causing NaCl malabsorption, could significantly contribute to IBD-associated diarrhea.

Mechanism of Dyslipidemia in Obesity—Unique Regulation of Ileal Villus Cell Brush Border Membrane Sodium–Bile Acid Cotransport

In obesity, increased absorption of dietary fat contributes to altered lipid homeostasis. In turn, dyslipidemia of obesity leads to many of the complications of obesity. Bile acids are necessary for the absorption of dietary fat. In the mammalian intestine, apical sodium-dependent bile acid cotransporter (ASBT; SLC10A2) is exclusively responsible for the reabsorption of bile acids in the terminal ileum. In rat and mice models of obesity and importantly in obese humans, ASBT was increased in ileal villus cells. The mechanism of stimulation of ASBT was secondary to an increase in ASBT expression in villus cell brush border membrane. The stimulation of ASBT was not secondary to the altered Na-extruding capacity of villus cells during obesity. Further, increased Farnesoid X receptor (FXR) expression in villus cells during obesity likely mediated the increase in ASBT. Moreover, enhanced FXR expression increased the expression of bile-acid-associated proteins (IBABP and OSTα) that are responsible for handling bile acids absorbed via ASBT in villus cells during obesity. Thus, this study demonstrated that in an epidemic condition, obesity, the dyslipidemia that leads to many of the complications of the condition, may, at least in part, be due to deregulation of intestinal bile acid absorption.

Non-invasive prenatal testing of pregnancies at risk for phenylketonuria

BackgroundPhenylketonuria (PKU) is a common metabolic disorder caused predominately by mutations in the phenylalanine hydroxylase (PAH) gene. The aim of the study was to design and validate the performance of a non-invasive prenatal test (NIPT) for PKU using circulating single molecule amplification and resequencing technology (cSMART).MethodsA total of 18 couples at genetic risk for having a child with PKU were recruited to the study. Gold standard invasive prenatal diagnosis (IPD) was performed on amniocyte or villus cell DNA by Sanger sequencing, targeting the known parental PAH mutations. Retrospectively, NIPT was also performed on stored maternal plasma samples from the 18 pregnancies by a multiplex cSMART assay designed to target all known DNA variants in the PAH gene.ResultsBenchmarking against IPD results, NIPT correctly genotyped all fetuses, including six compound heterozygotes with PKU, four normal non-carriers of PKU and eight heterozygote carriers of PKU comprising five cases of a maternally inherited mutation and three cases of a paternally inherited mutation.ConclusionsThe NIPT cSMART PKU assay was highly sensitive and specific for mutation detection and correct assignment of fetal genotypes. Based on comprehensive mutation coverage across the PAH gene, the assay may initially have clinical utility as a pregnancy screening test for high-risk carrier couples.