Apolipoprotein A-V: a novel apolipoprotein associated with an early phase of liver regeneration.

Liver regeneration in response to various forms of liver injury is a complex process, which ultimately results in restoration of the original liver mass and function. Because the underlying mechanisms that initiate this response are still incompletely defined, this study was aimed to identify novel factors. Liver genes that were up-regulated 6 h after 70% hepatectomy (PHx) in the rat were selected by cDNA subtractive hybridization. Besides known genes associated with cell proliferation, several novel genes were isolated. The novel gene that was most up-regulated was further studied. Its mRNA showed a liver-specific expression and encoded a protein comprising 367 amino acids. The mouse and human cDNA analogues were also isolated and appeared to be highly homologous. The human gene analogue was located at an apolipoprotein gene cluster on chromosome 11q23. The protein encoded by this gene had appreciable homology with apolipoproteins A-I and A-IV. Maximal expression of the gene in the rat liver and its gene product in rat plasma was observed 6 h after PHx. The protein was present in plasma fractions containing high density lipoprotein particles. Therefore, we have identified a novel apolipoprotein, designated apolipoprotein A-V, that is associated with an early phase of liver regeneration.

Analysis of a positional candidate gene for inflammatory bowel disease: NRAMP2.

Genome scans have identified a region spanning 40 cM on the long arm of chromosome 12 as a susceptibility locus for inflammatory bowel disease (IBD). This locus contains several candidate genes for IBD, one of which is the gene for the natural resistance associated macrophage protein 2 (NRAMP2). This protein is a divalent cation transporter and is expressed in many cells and tissues. The putative role of this protein in innate immunity prompted us to investigate a possible relationship between NRAMP2 and IBD. We assessed the frequency of four restriction fragment length polymorphisms (IVS2+11A/G, IVS4+44C/A, 1254T/C, and IVS15Ex16-16C/G) in a group of 155 Crohn's disease (CD) patients, 114 ulcerative colitis (UC) patients, and 189 healthy controls. Linkage analysis was performed in a group of 70 families with multiple members suffering from IBD. We searched for additional intragenic markers and mutations by sequence analysis of the natural resistance-associated macrophage 2 gene of 33 CD patients, with a positive family history for IBD. We identified one novel restriction fragment length polymorphism in intron 15 of the gene. The frequency of the rare allele is: 0.08 in our control population. An increased frequency of this allele was found in CD patients but this difference did not reach statistical significance. A weak association between CD and homozygosity for the G allele of the IVS2+11A/G was found (OR [odds ratio] = 2.2, CI [confidence interval] = 1.3-3.9, chi2 = 8.4, p = 1.013). Nonparametric linkage analysis and transmissions disequilibrium tests did not provide evidence for linkage of NRAMP2 to IBD, UC, or CD. Sequence analysis of the exons and the iron-responsive element in a panel of 33 CD patients did not reveal any mutations in NRAMP2. Our association, linkage, and sequence analysis in IBD shows that the putative genetic risk factor on chromosome 12 likely is not NRAMP2. The weak association between the G/G genotype of IVS2+11A/G and CD may be due to linkage disequilibrium with a nearby disease-causing gene.

Inflammatory bowel disease and the genes for the natural resistance-associated macrophage protein-1 and the interferon-gamma receptor 1.

The genes for the interferon-gamma receptor 1 and the natural resistance-associated macrophage protein 1 (NRAMP1) control the immune response to intracellular microbial pathogens. Such pathogens, in particular Mycobacterium paratuberculosis, have been implicated in the pathogenesis of Crohn's disease. We studied markers in the genes for NRAMP1 and two mutations in the interferon-gamma receptor in relation to inflammatory bowel disease (IBD) in the following groups: 270 healthy individuals, 74 patients with Crohn's disease, 72 patients with ulcerative colitis, and 40 patients with primary sclerosing cholangitis. We studied the allele frequencies of two restriction fragment length polymorphisms in the gene for NRAMP1 and the prevalence of two mutations in the interferon-gamma receptor 1 gene. The markers in the NRAMP1 gene were not associated with inflammatory bowel disease. Also, the mutations in the interferon-gamma receptor 1 were not found in the 186 IBD patients. Genetic markers in NRAMP1 are thus not associated with IBD. Therefore this gene is not likely to play a role in the pathogenesis of IBD. The mutation in the interferon-gamma receptor was not found in our IBD patients group.

Cell-swelling-induced taurine release from isolated perfused rat liver.

Astrocytes and lymphocytes are able to release significant amounts of taurine during periods of hypotonicity to reduce the increase in cell volume. To investigate this mechanism in the liver, we studied the release of free amino acids from isolated perfused rat liver during hypotonicity. The osmolarity of the perfusion medium was reduced from 305 to 255 or 205 mosM by decreasing the NaCl concentration 25 or 50 mM, respectively. This induced an 6-8% increase in liver mass and was associated with a specific 1.7-fold (-50 mosM) and 14-fold (-100 mosM) increase of the taurine release. None of the other amino acids measured showed a significant increase in their concentration in the effluent. The increase in taurine release occurred within 30 s after exposure to hypotonicity (maximal after 1-1.5 min) and followed closely the changes in liver mass. The taurine release declined gradually during successive exposures of the isolated liver to -100 mosM. This release was 29 and 17% of the original during the second and third exposure, respectively.

A fast reliable method for the measurement of intraperitoneal dextran 70, used to calculate lymphatic absorption.

The use of intraperitoneally administered dextran 70 was investigated for measurement of lymphatic absorption in CAPD patients. For this purpose a fast, highly accurate HPLC method was developed, that was not influenced by the high glucose concentration in peritoneal dialysate, nor by the inulin that was added to the dialysate for the measurement of residual volume. Pretreatment of the samples consisted of deproteinization with trichloroacetic acid, followed by incubation at 45 degrees C to hydrolyze inulin. This was followed by a further rinsing step using a Sephadex G-25 PD-10 column. The HPLC was performed on a Bio-Gel XL guard column with refractive index detection. Because of the short guard column the chromatographic analysis was only 5 minutes for one sample. With the method described lymphatic absorption rate was measured in 30 CAPD patients and was found to range from 0.1 to 3.5 mL/min, median 1.0 mL/min.