Assembly of an active enzyme by the linkage of two protein modules

BACKGROUND & AIMS: Oxidative stress mediates activation and stimulates collagen production of cultured hepatic stellate (Ito) cells. The aim of this study was to assess whether oxidative stress contributes to hepatic fibrogenesis in chronic hepatitis C. METHODS: In liver biopsy specimens of patients with chronic hepatitis C, the following fibrogenesis cascade was analyzed: (1) oxidative stress, determined by the presence of malondialdehyde protein adducts; (2) activation of stellate cells as indicated by their expression of alpha-smooth muscle actin; (3) stimulation of c-myb expression in stellate cells, a critical step in the activation of these cells; and (4) induction of collagen gene expression as detected by in situ hybridization. RESULTS: Treatment with d-alpha-tocopherol (1200 IU/day for 8 weeks) in 6 of these patients, who were refractory to interferon therapy, prevented the fibrogenesis cascade observed before antioxidant treatment. In addition, d-alpha-tocopherol treatment significantly decreased the carbonyl modifications of plasma proteins, a sensitive index of oxidative stress. However, 8 weeks of d-alpha-tocopherol treatment did not significantly affect serum alanine aminotransferase levels, hepatitis C virus titers, or histological degree of hepatocellular inflammation or fibrosis. CONCLUSIONS: These data suggest that enhanced oxidative stress initiates a fibrogenesis cascade in the liver of patients with chronic hepatitis C.     

Molecular interaction of [2,3-14C] acrylonitrile with DNA in gastric tissue of rat

Acrylonitrile (VCN) is used extensively in polymer industries, and is known to induce gastric cancer following oral administration. A paucity of information exists regarding the mechanism(s) by which acrylonitrile induces gastric neoplasia. The time course for uptake of radioactivity by gastric tissue and covalent binding of [2,3-14C] VCN or its metabolites to gastric DNA were determined following a single oral dose of 46.5 mg/kg. The rates of DNA synthesis and repair, as measured by unscheduled DNA synthesis in the gastric tissue of VCN-treated rats, were also studied. Maximum tissue uptake and covalent binding of radioactivity to gastric DNA were observed at 15 minutes following [2,3-14C] VCN administration. At 6 hours following VCN administration, significant inhibition (37% of control) in gastric replicative DNA synthesis was observed. A rebound followed by an increase (211% of control) in replicative DNA synthesis was observed at 24 hours. A three-fold elevation in unscheduled DNA synthesis was observed at 24 hours following treatment with VCN. These results indicate that VCN or its metabolites irreversibly interact with gastric DNA, causing DNA damage. The results also indicate that the delayed VCN-induced DNA repair, determined as unscheduled DNA synthesis, is inefficient for the removal of the resulting DNA lesions.     

Visualisation of mass transport of small organic molecules and metal ions through articular cartilage by magnetic resonance imaging

Magnetic resonance imaging of water has been used to visualise the migration of three paramagnetic species, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (4-hydroxy-TEMPO, 1), Cu2+ ions, and copper ethylenediamine-tetraacetate (CuEDTA, 2) through cartilage on the femoral condyle of the chicken knee. The migration of copper ions is dominated by strong binding with the cartilage. In contrast, both 1 and 2 bind weakly, and their diffusion can be followed as a progressive wave through the cartilage and subsequently into the trabecular bone structure.