Experimental Methyl Mercury Neurotoxicity: Locus of Mercurial Inhibition of Brain Protein Synthesis In Vivo and In Vitro

Brain cell-free protein synthesis is inhibited by methyl mercury chloride (MeHg) following in vivo or in vitro administration. In this report, we have identified the locus of mercurial inhibition of translation. Intraperitoneal injection of MeHg (40 nmol/g body wt) induced variable inhibition of amino acid incorporation into the post-mitochondrial supernatant (PMS) harvested from the brain of young (10-20-day-old) rats. No mercurial-induced disaggregation of brain polyribosomes nor change in the proportion of 80S monoribosomes was detected on sucrose density gradients. No difference in total RNA was found in the PMS. Initiation complex formation was stimulated by MeHg, as detected by radiolabelled methionine binding to 80S monoribosomes following continuous sucrose density gradient centrifugation. After micrococcal nuclease digestion of endogenous mRNA, both in vivo and in vitro MeHg inhibited polyuridylic acid-directed incorporation of [3H]phenylalanine. However, the in vivo inhibition was no longer observed when [3H]phenylalanyl-tRNAPhe replaced free [3H]phenylalanine in the incorporation assay. The formation of peptidyl[3H]puromycin revealed no difference from controls. There was significant mercurial inhibition of phenylalanyl-tRNA Phe synthetase activity in pH 5 enzyme fractions derived from brain PMS of MeHg-poisoned rats. These experiments revealed that the apparent MeHg inhibition of brain translation in vivo and in vitro is due primarily to perturbation in the aminoacylation of tRNA and is not associated with defective initiation, elongation, or ribosomal function.     

Mapping parathyroid hormone, β-globin,insulin, and LDH-A genes within the human chromosome 11 short arm by spot blotting sorted chromosomes

Summary Rearranged human chromosomes carrying segments of chromosome 11 were separated from the normal chromosome 11 by high-resolution chromosome sorting. Sorted chromosomes were tested with parathyroid hormone, -globin, insulin, and LDH-A gene-specific probes to determine the genes carried by each chromosome segment. Based on the gene content and karyotypes of these abnormal chromosomes, the parathyroid hormone, -globin, insulin, and LDH-A genes and the unique restriction fragment ADJ-762 are all located on the terminal band of the short arm of human chromosome 11 (band 11p15), with LDH-A proximal to the other loci.     

Host defense deficiency in newborn nonhuman primate lungs

We have investigated two major aspects of the pulmonary host defense mechanism--alveolar macrophage function as a "first line of bacterial defense" and induced neutrophil migration into the lung as a "back-up defense." Chemotactic and phagocytic/killing assays revealed a functional deficiency in the alveolar macrophages of newborn primates. Serial bronchoalveolar lavage investigations revealed diminished neutrophil migration into the newborn primate lung. The overall pulmonary host defense capability in newborn primates was deficient. The results of this investigation may have direct clinical relevance to the susceptibility of newborns to infections and pneumonia.     

Stimulation of hexose transport in L6 rat myoblasts by antibody and by glucose starvation.

Treatment of glucose-grown L6 rat myoblasts with rabbit or sheep anti-(L6-rat myoblast) antibody for 35 min or glucose starvation for at least 8 h results in a 2-fold increase in the Vmax. of 2-deoxy-D-glucose (dGlc) and 3-O-methyl-D-glucose uptake. In both cases, apparent transport affinities were not affected. Furthermore, once stimulation has occurred, further increases in hexose uptake could not be produced. Assays of antibody binding to whole cells suggested that the antibody is not internalized but remains bound on the cell surface. To elucidate the site and mechanism of antibody action, plasma-membrane vesicles from L6 cells were prepared. Anti-L6 antibody was found to cause a time- and dosage-dependent stimulation of dGlc transport in these vesicles. Maximum activation was achieved after 30 min exposure. This antibody-mediated activation could be inhibited by treatment of vesicles with various proteinase inhibitors. Treatment of vesicles with trypsin was also found to activate dGlc transport to levels observed with antibody. These results are virtually identical with those obtained with whole cells and suggest that antibody-mediated activation of hexose transport results from interaction of antibody with a specific membrane component(s).     

Exophiala pisciphila

Exophiala pisciphila is a dematiaceous fungus that belongs to a group of fungi known as the black yeasts. It was isolated from the skin lesions of a smooth dogfish, Mustelus canis Mitchill, that had been born in the shark exhibit tank of the New York Aquarium. The different stages of development of this fungus were studied by light microscopy and scanning electron microscopy to illustrate the morphology and surface structures of conidia and mycelium. The list of marine and fresh water fish, which have been infected by Exophiala spp. and Exophiala-like fungi has been up-dated. Potato Dextrose Agar and Malt Agar proved to be the best growth media, while Corn Meal Agar proved to be the best medium for studying the morphological features of the conidia and mycelial development of E. pisciphila, which exhibited polymorphic conidiogenesis.     

Rifampin alone or with trimethoprim for contacts of children with Haemophilus influenzae type b infections.

We carried out a nonrandomized, unblinded study to compare the efficacy of rifampin alone with that of rifampin in combination with trimethoprim in the eradication of the Haemophilus influenzae type b (HIB) carrier state among contacts of patients with invasive HIB infection. The study population comprised 17 index patients admitted to hospital with severe HIB infections and 233 contacts, 43 of whom had nasopharyngeal colonization with HIB of the same biotype as that of the index patient. Rifampin in a daily dose of 20 mg/kg (maximum 600 mg) for 4 days eradicated the carrier state in 86% of cases, as did the combination of rifampin at the same dosage and trimethoprim in a daily dose of 5 mg/kg (maximum 160 mg) for 4 days.     

Rates of peptidoglycan turnover and cell growth of Bacillus subtilis are correlated

Peptidoglycan turnover was measured by the decrease of trichloroacetic acid-precipitable label in cells labeled with N-acetyl-D-[14C]glucosamine. The rate of turnover was reduced strongly by the inhibition of RNA or protein synthesis and weakly by the inhibition of lipid, peptidoglycan, or DNA synthesis. It increased with the growth rate (which was controlled by the concentration of oxomethylvalerate limiting the intracellular isoleucine supply) to the same degree in stringent (rel+) and isogenic relaxed (relA) strains. In these and all other strains tested, the turnover rate (k) increased with the growth rate (g) according to the equation, k = 0.70 X g1.38, even when the growth rate was systematically altered by changes in the temperature or in the composition of the medium.     

Phagocytosis of hydroxyapatite or calcium pyrophosphate dihydrate crystals by rabbit articular chondrocytes stimulates release of collagenase, neutral protease, and prostaglandins E2 and F2 alpha

Synthetic hydroxyapatite (HA) and calcium pyrophosphate dihydrate (CPPD) microcrystals are phagocytosed by rabbit articular-cartilage chondrocytes in primary culture. The ingestion of crystals greatly stimulated the release of collagenase, neutral protease, and prostaglandins E2 and F2 alpha into the ambient medium. Lactate dehydrogenase was not released by either crystal despite electron microscopic evidence of cell damage by HA crystals (partial loss of phagolysosomal membrane and increased myelin figures). HA, but not CPPD crystals, stimulated release of beta-glucuronidase. HA crystal concentrations from 50 to 200 micrograms ml-1 induced a dose-dependent release of collagenase and of extracellular protein. Both phagocytosis and collagenase release were greatly attenuated when HA crystals were added to the chondrocyte monolayers in the absence of serum. As HA and CPPD crystals have been identified in human articular cartilage in association with degenerative changes, it is possible that the cell-crystal interaction described here may be pathogenetically important.