Search PubMed⌕ Search

Biomedical subjects

D S Goodman

Publications and source records attributed to D S Goodman.

186 records · Page 11Linked to original sources
PubMedDate not supplied

Biochemical characteristics of isolated rat liver stellate cells.

Hepatic stellate cells play a quantitatively important role in hepatic retinoid metabolism and storage in rats maintained under normal nutritional conditions. Studies were conducted to further explore the biochemical characteristics of hepatic stellate cells. Stellate cells were isolated in high purity and yield from the livers of normal rats. The isolated cells had the morphology expected (on electron micrographs) for stellate cells, and were enriched in retinoids and in the intracellular retinoid-binding proteins. The composition of the stellate cell lipid droplets was examined. These lipid droplets were isolated in high purity and integrity from frozen and thawed stellate cell preparations by differential centrifugation. We estimate that the lipid composition of stellate cell lipid droplets consisted of approximately 42% retinyl ester, 28% triglyceride, 13% cholesterol (total) and 4% phospholipid. Thus, stellate cell lipid droplets contain substantial levels of both cholesterol and triglyceride, in addition to retinyl esters. Stellate cell homogenates were assayed for both retinol-binding protein and transthyretin by specific radioimmunoassays. Within the detection limits of these radioimmunoassays, we were unable to detect the presence of either retinol-binding protein (less than 9 ng per 10(6) cells) or transthyretin (less than 11 ng per 10(6) cells) in the stellate cell preparations. Total RNA, prepared from the isolated stellate cells, was examined by Northern blot analysis for retinol-binding protein mRNA and transthyretin mRNA, using cDNA probes for retinol-binding protein and transthyretin. Within the sensitivity of these assays, retinol-binding protein mRNA and transthyretin mRNA were not detected in stellate cells. These findings suggest that stellate cells do not synthesize or accumulate retinol-binding protein.

Animals↗
PubMedDate not supplied

Inhibition of LDL degradation in cultured human fibroblasts induced by endothelial cell-conditioned medium.

Cultured porcine aortic endothelial cells (EC) secrete a potent mitogen into their serum-free culture medium which stimulates DNA synthesis in quiescent human fibroblasts. Previous work has shown that endothelial cell-conditioned medium (ECCM) also stimulates parallel, concentration-dependent increases in low density lipoprotein (LDL) cell surface binding and internalization. LDL degradation, however, was inhibited in ECCM-treated cells. Studies were conducted to determine whether the EC-derived growth factor (EDGF) and the endothelial-derived inhibitor of LDL degradation (EDID) are separate and distinct components, and to further delineate some of the characteristics of EDID. Time-course studies showed that the mitogenic activity released by EC into ECCM increased steadily during the first 24 hours and came to a plateau at about 48 hours of conditioning, whereas inhibitory activity increased linearly in ECCM for at least 6 days. Mitogenic activity in ECCM was stable under the same conditions. Ultrafiltration experiments showed that EDGF activity has an apparent molecular weight in excess of 30,000; in contrast EDID activity was not retained by filters with a 2000 dalton retention limit. EDID activity also failed to bind to a Blue Sepharose affinity column, while EDGF was bound and could be eluted with 1M NaCl in the presence of ethylene glycol. The ammonium ion concentration in ECCM was measured to determine the possible contribution of this ion to EDID activity. Confluent cultures of porcine aortic EC in serum-free culture medium produced substantial amounts of NH4+. After 96 hours of conditioning, the level of NH4+ in ECCM rose from near zero to 2-4 mM. When equivalent amounts of NH4Cl were added to fresh nonconditioned medium, a level of inhibitory (EDID) activity similar to that found with ECCM was observed. These studies indicate that EDGF and EDID activities are distinct and separate components of ECCM. Since NH4+ ion is present in ECCM in concentrations that are sufficient to account for all the observed EDID activity, it is likely that NH4+ is responsible for this activity.

Ammonia↗
PubMedDate not supplied

Effects of platelet-derived growth factor on 3-hydroxy-3-methylglutaryl coenzyme A reductase activity in cultured human fibroblasts.

Studies were conducted to delineate in detail the effects of platelet-derived growth factor (PDGF) upon 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase activity in cultured human fibroblasts. PDGF has a variety of coordinated effects on low density lipoprotein (LDL) and cholesterol metabolism and on DNA synthesis in these cells. We have previously shown that there is a critical time period, 10 to 20 hours after PDGF addition to quiescent cells, when mevalonate (MVA) is required for DNA synthesis to occur. The present studies demonstrate that PDGF produces a biphasic stimulation of reductase activity in cultured fibroblasts: a peak at 4 to 6 hours, followed by a decline, and then a second smaller peak at 24 hours, concurrent with DNA synthesis. The stimulation of both peaks was PDGF concentration-dependent, although quantitative differences were observed. Proportionally similar, LDL concentration-dependent reductions in both peaks of reductase activity were also seen. PDGF stimulated cholesterol synthesis from acetate in intact cells reaching peak values after 24 to 28 hours. The two peaks of reductase activity stimulated by PDGF neither coincide with the critical time period when mevalonate is needed for later DNA synthesis to occur, nor reflect the pattern of cholesterol synthesis within the cells.

Cell Cycle↗