Effects of 2-[1-(ethoxyimino)propyl]-3-hydroxy-5-(2,4,6-trimethylphenyl) cyclohex-2-enone on hepatic haem biosynthesis: species differences in hepatic porphyria.

2-[1-(Ethoxyimino)propyl]-3-hydroxy-5-(2,4,6-trimethylphenyl) cyclohex-2-enone (ETC) is a novel alkyl ketone herbicide. Continuous administration of ETC to mice for 28 days resulted in marked liver enlargement and severe intrahepatic cholestasis. These effects have been shown to result directly from a rapid and marked accumulation of porphyrin in the liver. The porphyrin which accumulates in the liver has been identified as protoporphyrin IX and dose response and time course studies confirm prior inhibition of mitochondrial ferrochelatase as the causal lesion. ETC was a very potent porphyrinogenic compound in mice, with a no-effect level for a single oral dose of 1 mg/kg. Rats and hamsters were insensitive to this type of hepatotoxicity following single oral doses of up to 750 mg/kg or following repeated, and indeed prolonged administration. The sensitivity of different species to ETC-induced porphyria correlated with the effect of ETC on hepatic ferrochelatase activity. The inhibition of ferrochelatase activity and the hepatic porphyria in mice were both found to be readily reversible upon withdrawal of ETC.

Comparison of the effects of griseofulvin and dihydropyridines on ferrochelatase activity and porphyrin accumulation in primary cultures of mouse and rat hepatocytes.

The ability of 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC), 3,5-diethoxycarbonyl-4-ethyl-1,4-dihydro-2,6-dimethyl pyridine (EDDC) and griseofulvin to induce porphyria in primary cultures of mouse and rat hepatocytes was determined. Exposure of mouse hepatocytes to DDC, EDDC or griseofulvin (5-100 mum) for 4 days resulted in a marked inhibition of ferrochelatase activity (up to 95%). However, whereas exposure of rat hepatocytes to DDC or EDDC (5-100 mum) for 4 days also resulted in marked inhibition of ferrochelatase activity (up to 96%), exposure to griseofulvin (5-100 mum) had no effect. DDC, EDDC and griseofulvin induced porphyrin accumulation in both mouse and rat hepatocyte cultures. In mouse hepatocyte cultures exposed to each xenobiotic the porphyrin that accumulated was predominantly protoporphyrin. In rat hepatocyte cultures exposed to DDC or EDDC the porphyrin that accumulated was also predominantly protoporphyrin, whereas following exposure to griseofulvin it was coproporphyrin. Time course studies confirmed that in rat hepatocyte cultures exposed to griseofulvin (25 or 100 mum) over a 4-day exposure period, ferrochelatase activity was not inhibited and coproporphyrin was always the predominant porphyrin accumulating (45-72% of total). Addition of 5-aminolaevulinic acid to mouse or rat hepatocyte cultures (10-1000 mum) also resulted in marked accumulation of porphyrin but whereas uroporphyrin accumulated in mouse hepatocyte cultures, coproporphyrin accumulated in rat hepatocyte cultures. These studies demonstrated that the hepatic porphyrias produced by the dihydropyridines and griseofulvin can be modelled in vitro in primary cultures of hepatocytes. Furthermore, the species differences in sensitivity of mouse and rat hepatocyte cultures in vitro to inhibition of ferrochelatase activity by griseofulvin mirrors, and therefore probably explains, the species differences in porphyria observed in vivo.

Evolution of antibody structure and effector functions: comparative hemolytic activities of monomeric and tetrameric IgM from rainbow trout, Salmo gairdnerii.

Monomeric and tetrameric IgM anti-haptin antibodies isolated from the sera of rainbow trout (S. gairdnerii) by immunoaffinity chromatography were compared both immunochemically and with regard to their functional abilities to lyse haptenated trout erythrocytes in the presence of trout complement. The two populations had similar binding affinities for hapten and apparently identical L chains, but differed in H chain peptide maps and immunoreactivity with rabbit anti-trout H chain serum. These differences could not be attributed to J-chain. The abilities of the two antibody subpopulations to activate C to lyse haptenated trout erythrocytes also differed dramatically. Such functional differences are not simply explained by the greater avidity of the tetrameric form since preliminary studies show that the monomeric form of trout IgM activates C via an alternative pathway mechanism while the tetrameric form activates both classical and alternative pathway mechanisms. Results suggest divergent evolution of antibody structures involved in the familiar effector functions (C activation, transport, etc.).

Immunological block to synthetic alpha-melanocyte-stimulating hormone: melanocyte interaction by antibodies isolated from cell-column immunoadsorbents.

Antibodies to formalin-fixed, syngeneic melanoma cells were prepared in mice, purified by immunoaffinity chromatography, and tested for binding activity to viable melanoma cells. The radiolabeled antibodies detected congruent to 9 X 10(6) melanoma antigenic sites/cell. The calculated average association constant (Ka) for the antibody population was 7 to 10 X 10(7) M-1. The antibody was shown to block the binding of melanocyte-stimulating hormone in competitive cell surface binding studies. Results are discussed conceptually in terms of the potentially important role that the humoral immune response may play in the phenomenon of tumor progression.

Protracted circulating lifetimes of mannose-terminated glycoproteins and aggregated albumin in mice infected with LDH-elevating virus.

Several macromolecular homeostasis-regulating mechanisms were tested for functional integrities in mice during acute and early chronic phases of infection with lactic dehydrogenase-elevating virus (LDV). Fractional catabolic rates of carbodiimide-aggregated albumin and immunoglobulin G were studied to evaluate glomerular filtration and hepatic Kupffer cell phagocytic activities. Several glycoproteins (fetuin, IgG antibodies, and ovalbumin) were also compared with their deglycosylated counterparts for fractional catabolic rates and organ distributions as a basis for evaluating virus-induced modifications of saccharide-binding "receptor functions" in vivo. Findings were that normal hepatic clearance of aggregated albumin and of ovalbumin is slowed from the onset of viremia. Fractional catabolic rates of amannosyl-ovalbumin and amannosyl-IgG are similar in uninfected animals to those seen with native ovalbumin or with mannose-terminated IgG in LDV-infected animals. Ovalbumin and aggregated albumin were also found to be mutually competitive for hepatic uptake in uninfected animals. It is proposed that LDV, which replicates in cells of the mononuclear phagocyte system (reticuloendothelial system), alters the clearance functional state of fixed tissue macrophage, thereby explaining in part the protracted circulatory longevity of several enzymes, aggregated albumin and mannose-terminated ovalbumin, and IgG in LDV-infected mice.