Publications

Lipid aldehydes have been proposed as mediators of hepatic fibrosis in alcoholics. In this study we examined whether hepatic lipocytes, the principal matrix-producing cells in liver, exhibit enhanced collagen synthesis in response to the lipid aldehyde malondialdehyde. Lipocytes isolated from normal rat liver and plated in primary culture for 3 days were not affected by malondialdehyde in concentrations ranging from 2 to 200 microM. Cells cultured for 7 days displayed a modest increase in collagen synthesis (137% of control levels) in response to malondialdehyde, but only at a concentration of 200 microM. The malondialdehyde-induced increase in collagen synthesis was paralleled by a rise in type I procollagen mRNA. Subcultured rat fibroblasts at confluent density responded better to malondialdehyde than did 7-day lipocytes. The results indicate that lipocytes respond to the fibrogenic effects of malondialdehyde only after activation in primary culture. This delayed response suggests that lipid aldehydes may enhance, but do not initiate, alcoholic liver fibrosis in vivo.

The porphyrinogenic agent 3,5-dicarbethoxy-2,6-dimethyl-4-ethyl-1,4-dihydropyridine (DDEP) is known to inactivate hepatic cytochrome P450 (P450) enzymes 2C11, 2C6, and 3A1 [Correia et al. (1987) Arch. Biochem. Biophys. 258, 436-451] by different mechanisms. The inactivation of P450 2C11 and 2C6 appears to be due to the ethylation of the heme in the active sites of the enzymes [Augusto et al. (1982) J. Biol. Chem. 257, 11288-11295], whereas the inactivation of P450 3A1 appears to involve the covalent binding of the heme to the apoprotein [Correia et al. (1987)]. Moreover, we have found that DDEP inactivates horseradish peroxidase (HRP) pretreated with hydrogen peroxide. In this system, DDEP was oxidized predominately to 3,5-dicarbethoxy-2,6-dimethyl-4-ethylpyridine (EDP) under weakly acidic conditions and predominately to 3,5-dicarbethoxy-2,6-dimethylpyridine (DP) under basic conditions. The loss of heme and the formation of altered heme products were also pH-dependent and were correlated with the formation of DP and the inactivation of HRP. Thus the inactivation of HRP appears to depend on the formation of an ethyl radical, which presumably reacts with the heme in the active site of the enzyme. Similar product ratios were obtained for the oxidation of DDEP by K3Fe(CN)6, indicating that product ratios of DP over EDP are mainly determined by the pH of buffer. These results, in addition to semiemperical calculations (AM1) for the oxidation of DDEP in the gas phase, are consistent with the idea that the inhibitor undergoes a single-electron oxidation to form the DDEP radical cation, the fate of which depends on the environment of the active site of the enzyme. The proposed formation of a radical cation by the abstraction of an electron from nitrogen is consistent with the finding of low intramolecular isotope effects of the metabolism of 3,5-dicarbethoxy-2,6-dimethyl-[4-2H,4-1H]-1,4-dihydropyridine by P450 2C11 and 3A4. Under basic or aprotic conditions, the radical dissociates to form DP and the ethyl radical, which reacts with the heme, thereby inactivating the enzyme. Under acidic or polar conditions, the radical undergoes an additional one-electron oxidation to form EDP.(ABSTRACT TRUNCATED AT 400 WORDS)

The long-term success of heart transplantation for end-stage heart disease has been hindered by the problems associated with acute and chronic graft rejection, opportunistic infections and potentially fatal complications of intensive immunosuppression. A more complete understanding of the biology of transplant rejection should provide the basis for the development of improved methods for controlling and monitoring rejection. Cytokines, the soluble factors which regulate the immune response, are central to the rejection process. The objective of this study was to analyse cytokine mRNA transcripts in 99 biopsy samples and 89 blood samples from 65 and 35 Stanford Medical Center cardiac transplant recipients, respectively, gathered between January 1990 and January 1992. Following RNA extraction and conversion to cDNA, samples were amplified with cytokine-specific primers for interleukins (IL) 1 to 8, TNF-beta (tumour necrosis factor-beta) and IFN-gamma (interferon-gamma) and were analysed by gel electrophoresis and Southern blot hybridization. Our results demonstrate that despite chronic immunosuppressive therapy, the peripheral blood of transplant recipients expressed a higher combined percentage of different cytokine transcripts than did peripheral blood obtained from normal volunteers. In transplant patients, detection of cytokine transcripts for IL-1 alpha, IL-1 beta and IL-2 increased with time after transplantation. Intragraft IL-7 gene expression was significantly increased in biopsies diagnosed with mild (grade 1) rejection when compared to those with no evidence of rejection or with moderate to severe rejection. Implications of these results in light of possible mechanisms of rejection and of new approaches to immunotherapy are discussed.

The interaction of B7-related molecules on antigen-presenting cells with CD28 or CTLA-4 antigens on T cells provides a second signal for T cell activation. Selection inhibition of the B7-CD28 or B7-CTLA-4 interactions produces antigen-specific T cell unresponsiveness in vitro and suppresses immune function in vivo. To determine whether selective inhibition of the B7-CD28 or B7-CTLA-4 interactions could suppress spontaneous autoimmune disease, a B7-binding protein was generated by genetic fusion of the extracellular domain of murine CTLA-4 to the Fc portion of a mouse immunoglobulin G2a monoclonal antibody (muCTLA4Ig). In lupus-prone NZB/NZW filial generation (F1) mice, treatment with muCTLA4Ig blocked autoantibody production and prolonged life, even when treatment was delayed until the most advanced stage of clinical illness. These findings suggest a possible role for human CTLA4Ig in the treatment of autoimmune diseases in humans.