Histopathologic and ultrastructural alterations of white liver disease in sheep experimentally depleted of cobalt.

Many cobalt-deficient sheep develop liver lesions known as ovine "white liver" disease, but the etiology of these changes is controversial. It has been suggested that cofactors are required for development of liver damage in cobalt-deficient sheep. In this study, one group of lambs (n = 5) was fed a diet low in cobalt (4.5 micrograms/kg) while a group of control lambs (n = 4) received the same diet after it had been supplemented with cobalt (1000 micrograms/kg). All cobalt-depleted lambs had reduced growth rate, anorexia, lacrimation, and alopecia, and they eventually became emaciated (mean body weight at end of study: 83% of initial body weight). Plasma concentrations of bilirubin and serum activity of glutamate-oxaloacetate transferase were elevated in these animals, while plasma concentrations of vitamin B12 were reduced (less than 220 pmol/L from day 42). Fatty degeneration of the liver associated with reduced concentrations of vitamin B12 (14.5 pmol/g) was seen in these animals at necropsy at 196 days. Microscopic liver lesions included accumulation of lipid droplets and lipofuscin particles in hepatocytes, dissociation and necrosis of hepatocytes, and sparse infiltration by neutrophils, macrophages, and lymphocytes. Ultrastructural hepatocytic alterations included swelling, condensation and proliferation of mitochondria, hypertrophy of smooth endoplasmic reticulum, vesiculation and loss of arrays of rough endoplasmic reticulum, and accumulation of lipid droplets and lipofuscin granules in cytoplasm of hepatocytes. No liver lesions were seen in control lambs. The results of this study indicate that cofactors are not a prerequisite to development of hepatic damage in cobalt-deficient sheep. Reduced activities of the vitamin B12-dependent enzymes, methylmalonyl CoA mutase and methionine synthase, and lipid peroxidation are of likely pathogenetic importance in the development of the lesions.

Dietary folate affects the response of rats to nickel deprivation.

Because vitamin B12 and Ni are known to interact and because of the similar metabolic roles of vitamin B12 and folate, an experiment was performed to determine the effect of dietary folate on Ni deprivation in rats. A 2 x 2 factorially arranged experiment used groups of nine weanling Sprague-Dawley rats. Dietary variables were Ni, as NiCl(2) 6H(2)0, 0 or 1 mu g/g; and folic acid, 0 or 2 mg/kg. The basal diet, based on skim milk, contained less than 20 ng Ni/g. After 54 d, an interaction between dietary Ni and folate affected several variables including erythrocyte folate, plasma amino acids, and femur trace elements. For example, folate deprivation decreased erythrocyte folate; folate supplementation to the Ni-supplemented rats caused a larger increase in erythrocyte folate concentration than did folate supplementation to the Ni-deprived rats. Also, dietary Ni affected several plasma amino acids important in one-carbon metabolism (e.g., Ni deprivation increased the plasma concentrations of glycine and serine). This study shows that dietary Ni, folate, and their interaction can affect variables associated with one-carbon metabolism. This study does not show a specific site of action of Ni but it indicates that Ni may be important in processes related to the vitamin B12-dependent pathway in methionine metabolism, possibly one-carbon metabolism.

Heterozygous mutations at the mut locus in fibroblasts with mut0 methylmalonic acidemia identified by polymerase-chain-reaction cDNA cloning.

Genetic defects in the enzyme methylmalonyl CoA mutase cause a disorder of organic acid metabolism termed "mut methylmalonic acidemia." Various phenotypes of mut methylmalonic acidemia are distinguished by the presence (mut-) or absence (mut0) of residual enzyme activity. The recent cloning and sequencing of a cDNA for human methylmalonyl CoA mutase enables molecular characterization of mutations underlying mut phenotypes. We identified compound heterozygous mutations in a mut0 fibroblast cell (MAS) line by cloning the methylmalonyl CoA mutase cDNA by using the polymerase chain reaction (PCR), sequencing with internal primers, and confirming the pathogenicity of observed mutations by DNA-mediated gene transfer. Both mutations alter amino acids common to the normal human, mouse, and Propionibacterium shermanii enzymes. This analysis points to evolutionarily preserved determinants critical for enzyme structure or function. The application and limitation of cDNA cloning by PCR for the identification of mutations are discussed.

Methylmalonyl-CoA mutase activity of leukocytes in variants and heterozygotes of methylmalonic acidemia.

An assay method for the methylmalonyl-CoA mutase of leukocytes obtained from 3 ml of blood was established. The enzyme activity which was measured with or without the in vitro addition of 5'-deoxyadenosylcobalamin was found to be of value for the diagnosis of two variants of methylmalonic acidemia (vitamin B12 responsive and unresponsive), and also for the detection of heterozygotes with the vitamin B12 unresponsive type.

Detection of errors in methylmalonyl-CoA metabolism by using amniotic fluid.

We report a method for rapid prenatal detection of methylmalonic acidemia, consisting of measuring methylmalonly-CoA mutase (EC 5.4.99.2) activity in non-cultured amniotic cells and measuring the concentration of methylmalonate in the amniotic fluid. Immediate stabilization of the mutase activity in the non-cultured amniotic cell by its coenzyme adenosycobalamin, and use of methylmalonyl-CoA with high specific activity gives mutase activity comparable to that of cultured amniotic cells or normal fibroblasts. Consequently, findings of low mutase activity and a hight concentration of methylmalonate in the amniotic fluid allows accurate diagnosis of the vitamin B12-nonresponsive form of methylmalonic acidemia. These results can be obtained in two days. For the vitamin B12-responsive form, the correct diagnosis depends upon finding amniotic fluid methylmalonate, because cells from these patients will display normal methylmalony-CoA mutase activity after adenosylcobalamin is added. Problems in interpreting data on bloody samples and the limitations of the method are discussed.