S.H. Zaidi

Some new perspectives on the biological effects of asbestos.

Abstract A brief review of recent biochemical investigations conducted on the biological effects of asbestos is presented along with a critical appraisal of the likely mechanisms involved. Involvement of intracellular organelles such as lysosomes and mitochondria, along with changes in various tissue constituents, helps us to understand the biochemical basis of asbestosis. The central role for α-ketoglutarate metabolism and related biochemical aspects are pointed out, and a few areas where further work is needed are suggested.

Effect of ascorbic acid on pulmonary silicosis of guinea pigs.

The role of ascorbic acid on developing pulmonary silicosis of normal and scorbutic guinea pigs was studied for 115 days. In normal silicotic guinea pigs an increasing concentration of ascorbic acid in lungs with the advancement of silicosis was observed. The increase of ascorbic acid was directly related to collagen percentage. Adrenal ascorbic acid showed an increase with lapse of time, and blood ascorbic acid did not show any alteration. In scorbutic silicotic guinea pigs the collagen fiber formation was retarded but the hydroxyproline contents and acid mucopolysaccharide remained the same as in normal silicotics.

Experimental infective manganese pneumoconiosis in guinea pigs

Abstract In order to study the role of an infective factor in the course of manganese pneumoconiosis, guinea pigs were intratracheally inoculated only with Candida albicans, a common commensal of upper respiratory tract of miners, manganese dioxide alone or with the combination of C. albicans and manganese dioxide dust. The histopathological studies revealed that at the termination of the experiment (180 days) the combined effect of dust and organism produced thick reticulin and collagen fibrosis in the lungs, manganese dioxide alone produced fibrotic reaction comprised of only thick reticulin fibers while the organisms alone produced slight lymphoid hyperplasia and no fibrosis.

Effect of silicic acid and polyvinyl pyrrolidone on lysosomal ribonuclease of rat lungs.

Abstract Incubation of freshly prepared rat lung homogenate with silicic acid led to abolition of the latency of ribonuclease activity, as evident from the decrease in activation on detergent treatment. Preincubation of the homogenate with polyvinyl pyrrolidone abolished this effect. The release of the enzyme from lysosomes caused by silicic acid was also prevented by the polymer. Such a mechanism of interaction of silicic acid with biomembranes is likely to be responsible for the effect of silica and silicate dusts on membrane structures and, hence, in the etiology of pneumoconiosis.

Wood dust toxicity:In vivo andin vitro studies

Abstract The relationship between in vitro cytotoxicity, hemolytic activity, and in vivo fibrogenicity of wood dusts. Dalbergia sissoo (Sheesham) and Mangifera indica (Mango), were examined. It was observed that hemolytic activity may be indicative of the degree of acute toxicity and macrophage cytotoxicity of the fibrogenicity of the dusts. It has been suggested that these two parameters may be useful for assessing a wood dust for its acute toxicity and fibrogenicity.

Early biochemical response of pulmonary tissue to manganese dioxide.

The biochemical response of pulmonary tissue to MnO2 dust burden of 30 days duration was studied in rats. The activities of enzymes from isolated fractions of rat lungs were not significantly altered, even though manganese content was increased significantly in tissues remote from lungs, indicating translocation of the dust from its intrapulmonary location.

Changes in mitochondrial enzyme activity of rat lung during the development of silicosis

Abstract Significant changes occurred in the activities of enzymes in silicotic rat lung at 30, 90 and 150 days after intratracheal injection of quartz dust. The pattern of changes indicated that the mitochondrial metabolism in silicosis is altered significantly indicating disturbances in bioenergetics. Increase in activity of cytochrome- c -oxidase and NADH-cytochrome- c -reductase at the early stage and a significant decline at the advanced stage of the disease suggest that metabolic changes in silicosis during the initial and the advanced stage of the disease are distinctly different. Besides, enhanced rate of glycolysis is also observed at the early stages of silicosis.

Effect of intratracheal injection of mica dust on the lymph nodes of guinea pigs

Histopathological changes in the tracheo-bronchial lymph nodes were studied up to 365 days in guinea pigs following intratracheal injection of a suspension of mica dust. In general, the cytotoxic effect provoked by dust was not pronounced as the majority of the swollen dust-laden macrophages retained their normal structure at the termination of the experiment and fibrotic lesions were limited to the formation of thick reticulin fibers. The poor fibrogenic response of mica dust has been attributed to its low cytotoxicity.

Amino acid changes and pulmonary response of rats to silica dust

Abstract The effect of intratracheal injection of quartz on the free amino acids of lung, serum, and liver and the bound amino acids of lung was studied in rats, at intervals preceding and following the formation of collagen. The studies revealed that amino acid metabolism is significantly altered in silicotic rat lung. Changes in the body pool of amino acids seem to be related to both collagen and noncollagen formation in silicotic lung. It appears that some of the amino acid residues for collagen formation in lung in response to silica exposure are made available by the in situ formation from available precursors, while others are contributed by other organs, especially liver. A central role for glutamic acid metabolism in the genesis of pulmonary fibrosis is discussed.

Fibrogenic response in murine lungs to asbestos.

Pulmonary fibrogenic response was investigated in mice following intratracheal inoculation of amosite, anthophylite and tremolite varieties of Indian asbestos and studies were made over a period of 150 days. At early periods all the varieties produced acute inflammatory reaction in the lungs. Thick reticulum fibers were encountered at later periods with amosite, while only thin reticulum fibers developed with anthophyllite or tremolite variety. The formation of asbestos bodies did not take place with any of the asbestos varieties even at 150 days. The deviation in the pulmonary fibrogenic response in mice has been attributed to species difference.