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Biomedical subjects

E L Bierman

Publications and source records attributed to E L Bierman.

At least 19 recordsLinked to original sources
PubMed1993

Cyclic AMP stimulates efflux of intracellular sterol from cholesterol-loaded cells.

The interaction of high density lipoprotein with its putative receptor stimulates translocation and efflux of intracellular sterols by a process involving activation of protein kinase C. This study shows that activation of cAMP-dependent protein kinase also stimulates efflux of intracellular sterols. When intracellular sterol pools of cholesterol-loaded cultured human skin fibroblasts and bovine aortic endothelial cells were radiolabeled with the biosynthetic precursor [3H]mevalonolactone, high density lipoprotein3 (HDL3)-mediated 3H-sterol efflux was enhanced by addition of the adenylylcyclase activator forskolin, the phosphodiesterase inhibitors theophylline and 3-isobutyl-1-methylxanthine, and the cAMP analogues N6-benzoyl-cAMP (N6-cAMP) and 8-thiomethyl-cAMP. The effect of N6-cAMP was abolished by an inhibitor of cAMP-dependent protein kinase (H8). The enhanced sterol efflux was independent of receptor binding of HDL3, as similar effects were observed in the presence of tetranitromethane-modified HDL3, which lacks receptor binding activity. N6-cAMP stimulated efflux of several subspecies of newly synthesized sterols, including cholesterol. Elevation of cAMP levels increased the proportion of radiosterols that were accessible to treatment of cells with the enzyme cholesterol oxidase, suggesting that activation of cAMP-dependent protein kinase stimulates translocation of sterols from intracellular compartments to the plasma membrane where they desorb from the cell surface. Thus, at least two distinct protein kinase signalling pathways modulate transport of intracellular sterols in cholesterol-loaded cells.

1-Methyl-3-isobutylxanthine↗
PubMed1992

The effect of probucol on HDL-mediated sterol translocation and efflux from cells.

It has been suggested that the antioxidant drug probucol can prevent arterial cholesterol accumulation in part by promoting HDL-mediated cholesterol removal from cells. In this study, the effect of probucol in vitro on the interaction of HDL3 with cultured skin fibroblasts, bovine aortic endothelial cells and human monocyte-derived macrophages was tested. Treatment of cholesterol-loaded cells with up to 20 microM probucol had no effect on [3H]cholesterol efflux from plasma membranes. No effect of probucol on HDL3-mediated efflux of labeled sterol was seen after intracellular sterol was labeled either with the biosynthetic precursor [3H]mevalonolactone or after incubation with lipoprotein-associated [3H]cholesterol linoleate. Further, no effect of probucol on cell cholesterol mass efflux was observed. Thus these results demonstrate that probucol does not affect movement of sterol from different cellular radiolabeled sterol pools. Within the limitations of cell culture studies, it is suggested that the proposed antiatherogenic effect of probucol in vivo is not likely to be the result of modulation of major cellular pathways for removal of cholesterol.

Animals↗
PubMed1992

Effect of glyburide and omega 3 fatty acid dietary supplements on glucose and lipid metabolism in patients with non-insulin-dependent diabetes mellitus.

Using a random crossover design, we examined the effects of glyburide for 4 wk on glucose, insulin, lipid, and lipoprotein metabolism in 10 men with non-insulin-dependent diabetes (NIDDM) receiving dietary fish-oil concentrates containing omega 3 (n-3) fatty acids (8 g/d). Compared with glyburide alone, fasting plasma glucose concentrations increased with fish oil. Although glyburide with fish oil decreased fasting glucose concentrations, they did not return to baseline. Basal insulin concentrations were unaltered by fish oil without or with glyburide; however, postprandial insulin concentrations were decreased by fish oil. Although total cholesterol and triglyceride concentrations were unchanged, very-low-density-lipoprotein cholesterol concentrations decreased and low-density-lipoprotein cholesterol rose and apolipoprotein B concentrations trended higher. Thus, glyburide only partially rectified the impaired fuel homeostasis associated with fish-oil supplements in patients with NIDDM. Therefore, we do not recommend intake of fish oil concentrates containing n-3 fatty acids in patients with NIDDM.

Aged↗
PubMed1991

Protein kinase C as a mediator of high density lipoprotein receptor-dependent efflux of intracellular cholesterol.

The interaction of high density lipoproteins (HDL) with the HDL receptor stimulates the translocation of cholesterol from intracellular pools to the plasma membrane where the cholesterol becomes available for removal by appropriate acceptors. The role of signal transduction through protein kinase C in HDL receptor-dependent cholesterol translocation and efflux was examined using cholesterol-loaded cultured human skin fibroblasts. Treatment of cells with HDL3 activated protein kinase C, demonstrated by a transient increase in membrane associated kinase activity. Kinase activation appeared to be dependent on binding of HDL3 to the HDL receptor, since tetranitromethane-modified HDL3, which does not bind to the receptor, was without effect. Translocation of intracellular sterol to the plasma membrane was stimulated by treatment of cells with the protein kinase C activators, dioctanoylglycerol and phorbol myristic acetate, and the calcium ionophore A23187. Conversely, treatment of cells with sphingosine, a protein kinase C inhibitor, reduced HDL3-mediated translocation and efflux of intracellular sterols. However, sphingosine had no effect on efflux of labeled cholesterol derived from the plasma membrane. Down-regulation of cellular protein kinase C activity by long term incubation with phorbol esters also inhibited HDL3-mediated efflux of intracellular sterols and abolished the ability of sphingosine to further inhibit HDL3-mediated efflux. These studies support the conclusion that HDL receptor-mediated translocation and efflux of intracellular cholesterol occurs through activation of protein kinase C.

Apolipoprotein A-I↗
PubMed1991

High glucose levels do not directly impair cellular binding of HDL3 or HDL-mediated efflux of cholesterol from human skin fibroblasts.

The excess risk of atherosclerosis that is associated with diabetes mellitus cannot be completely accounted for by other known risk factors. Recent studies have suggested that increased glycation of high density lipoproteins (HDL) at high glucose concentrations causes functional abnormalities that might contribute to accelerated atherosclerosis. Other investigators also have shown that elevated glucose concentrations can stimulate the activity of protein kinase C in cultured cells. Because protein kinase C appears to be involved in HDL receptor-mediated efflux, the hypothesis that a high glucose concentration in vitro might modulate HDL-mediated efflux of cholesterol from human fibroblasts was tested. These studies indicate that a high glucose level alone does not affect the interaction of normal HDL3 with cultured human skin fibroblasts.

Carrier Proteins↗
PubMed1991

Potential role of insulin in the clearance of remnant lipoproteins in dysbetalipoproteinaemia.

Dysbetalipoproteinaemia is a genetic disorder characterized by accumulation of lipoprotein remnant particles in the plasma, accelerated atherosclerosis, and the abnormal apoprotein E2. Uncontrolled diabetes mellitus can aggravate the hyperlipidaemia associated with this disorder, presumably by increasing triglyceride synthesis and reducing very low density lipoprotein catabolism by lipoprotein lipase. This report documents the gradual amelioration of dysbetalipoproteinaemia in uncontrolled diabetes mellitus following therapy with exogenous insulin alone. Although the beneficial effects of insulin therapy in this patient may include inhibition of triglyceride synthesis and improved triglyceride catabolism, we propose that insulin may also stimulate clearance of atherogenic remnant lipoprotein particles.

Adult↗
PubMed1991

Nonenzymatic glycosylation of HDL and impaired HDL-receptor-mediated cholesterol efflux.

Previous studies have shown that nonenzymatic glycosylation of high-density lipoprotein (HDL) inhibits high-affinity binding to cultured cells and the candidate HDL-receptor protein. Because binding of HDL to its receptor is required for HDL-receptor-mediated cholesterol efflux from cells, we hypothesized that glycosylated HDL3 would have reduced ability to remove cholesterol from cells. HDL3 was glycosylated in vitro to achieve up to 40-50% reductions in free-lysine residues. Glycosylated HDL3 had a slightly greater ability than control HDL3 to sequester cholesterol directly from the plasma membrane, as predicted by changes in lipid composition. This process is independent of HDL-receptor binding and should not be influenced by reduced binding of HDL3. In contrast, efflux of intracellular cholesterol from cells, which is HDL-receptor dependent, was reduced 25-40%. The ability of glycosylated HDL3 to diminish cholesterol esterification was significantly reduced, indicating reduced net cholesterol efflux. Steady-state efflux of LDL-derived cholesterol was also markedly reduced. These findings suggest that nonenzymatically glycosylated HDL is functionally abnormal and might contribute to the accelerated development of atherosclerosis in patients with diabetes mellitus.

Carrier Proteins↗
PubMed1991

Role of the protein kinase C signaling pathway in high-density lipoprotein receptor-mediated efflux of intracellular cholesterol.

These studies provide evidence that binding of HDL3 to the HDL receptor stimulates translocation and efflux of intracellular cholesterol through mechanisms involving the activation of protein kinase C. This conclusion is supported by data demonstrating that HDL is able to increase cell diacylglycerol levels and activate protein kinase C. Sphingosine, a protein kinase C inhibitor, was able to inhibit HDL3-mediated cholesterol translocation and efflux, further suggesting a role for protein kinase C in HDL receptor-dependent cholesterol efflux. Inhibition of HDL-mediated diacylglycerol formation by pertussis toxin suggests the possible involvement of a G protein-activated phospholipase. Further studies are needed to understand how activation of protein kinase C promotes cholesterol translocation and to identify the target proteins for protein kinase C phosphorylation.

Biological Transport, Active↗
PubMed1990

Nonenzymatic glycosylation of HDL resulting in inhibition of high-affinity binding to cultured human fibroblasts.

Nonenzymatic glycosylation of plasma proteins may contribute to the excess risk of developing atherosclerosis in patients with diabetes mellitus. Because high-density lipoprotein (HDL) is believed to protect against atherosclerosis and is glycosylated at increased levels in diabetic individuals, the effects of nonenzymatic glycosylation of HDL3 on binding of HDL3 to cultured fibroblasts and to the candidate HDL-receptor protein were examined. HDL3 was glycosylated in vitro with glucose alone or in combination with sodium cyanoborohydride. With this catalyst, up to 40-50% of the lysine residues could be glycosylated, resulting in a progressive drop to nearly 60% in high-affinity binding to cultured fibroblasts at 4 degrees C. Binding to the 110,000-Mr candidate HDL-receptor protein was reduced by almost 75%. At levels of HDL glycosylation equivalent to the 3-5% observed in diabetes, high-affinity binding to fibroblasts at 4 degrees C was diminished by up to 15-20%. Binding kinetic studies paradoxically suggested that glycosylated HDL3 binds with higher affinity to a reduced number of binding sites. The findings in this study suggest that nonenzymatically glycosylated HDL may be functionally abnormal and might contribute to the development of atherosclerosis in patients with diabetes mellitus.

Animals↗
PubMed1990

The relationship between sex hormones and high-density lipoprotein cholesterol levels in healthy adult men.

The objective of this study was to clarify the complex and uncertain relationship between endogenous sex hormones and high-density lipoprotein (HDL) cholesterol levels in healthy men. Fifty-five healthy adult men were consecutively recruited from an ongoing cross-sectional study of cardiovascular disease risk factors from a lipid research clinic at the University of Washington, Seattle. Subjects receiving medication were excluded. Multiple linear regression analysis identified several factors that correlated highly significantly with HDL cholesterol levels, including alcohol intake; frequency of strenuous exercise; age; levels of total cholesterol, low-density lipoprotein cholesterol, and triglyceride; and carbohydrate intake. Nearly 80% of the heterogeneity in HDL cholesterol levels could be accounted for by these factors. Despite finding significant correlations with factors known to influence HDL cholesterol levels, no correlation with estradiol level, testosterone level, or the ratio of estradiol to testosterone levels was apparent. In conclusion, endogenous sex hormones do not appear to influence HDL cholesterol levels in healthy adult men. Alternatively, a large proportion of the heterogeneity in HDL levels in this group of men can be accounted for by environmental factors. The disparity between this conclusion and others may be partially due to differences in accounting for these confounding variables.

Adult↗
PubMed1989

Intracellular transport of cholesterol in type C Niemann-Pick fibroblasts.

The purpose of this study was to determine the capacity of Niemann-Pick type C (NPC) fibroblasts to transport cholesterol from the cell surface to intracellular membranes. This is relevant in light of the observations that NPC cells display a sluggish metabolism of LDL-derived cholesterol, a phenomenon which could be explained by a defective intracellular transport of cholesterol. Treatment of NPC cells for 4 h with 0.1 mg/ml of LDL failed to increase the incorporation of [14C]oleic acid into cholesterol [14C]oleate, an observation consistent with previous reports on this cell type (Pentchev et al. (1985) Proc. Natl. Acad. Sci. USA 82, 8247). Normal fibroblasts, however, displayed the classical upregulation (6-fold over control) of the endogenous esterification reaction in response to LDL exposure. Incubation of normal or NPC fibroblasts with sphingomyelinase (100 mU/ml; Staphylococcus aureus) led to a rapid and marked increase (9- and 10-fold for normal and NPC fibroblasts, respectively, after 4 h) in the esterification of plasma-membrane-derived [3H]cholesterol suggesting that sphingomyelin degradation forced a net transfer of cholesterol from the cell surface to the endoplasmic reticulum. The similar response in normal and mutant fibroblasts to the degradation of sphingomyelin suggests that plasma membrane cholesterol can be transported into the substrate pool of ACAT to about the same extent in these two cell types. Degradation of cell sphingomyelin in NPC fibroblasts also resulted in the movement of 20-25% of the cellular cholesterol from a cholesterol oxidase susceptible pool into oxidase-resistant pools, implying that a substantial amount of plasma membrane cholesterol was internalized after sphingomyelin degradation. This cholesterol internalization was not accompanied by an increased rate of membrane internalization, as measured by [3H]sucrose uptake. Although NPC cells showed a relative accumulation of unesterified cholesterol and a sluggish esterification of LDL-derived cholesterol when exposed to LDL, these cells responded like normal fibroblasts with regard to their capacity to transport cholesterol from the cell surface into intracellular sites in response to sphingomyelin degradation. It therefore appears that NPC cells, in contrast to the impaired intracellular movement of lipoprotein-derived cholesterol, do not display a general impairment of cholesterol transport between the cell surface and the intracellular regulatory pool of cholesterol.

Cell Line↗
PubMed1989

Downregulation of high-density lipoprotein receptor in human fibroblasts by insulin and IGF-I.

High-density lipoprotein (HDL3) particles bind to a cell surface receptor, thereby promoting the efflux of cholesterol from extrahepatic nonsteroidogenic cells. This receptor appears to be upregulated by increased cell cholesterol content and also may be responsive to the growth state of cells. Because insulin can be mitogenic, the effect of insulin on HDL-receptor function was tested. HDL-receptor activity of cholesterol-loaded fibroblasts was inhibited by insulin treatment. Insulin decreased HDL binding in a log-dose fashion (-25% at 67 nM insulin) in association with increases in [3H]thymidine incorporation into DNA. HDL-mediated cholesterol efflux from cholesterol-loaded cells was diminished by insulin treatment of cells in parallel with decreased HDL binding. Insulin induced reciprocal changes in HDL- and low-density lipoprotein (LDL)-receptor activity. In cells in which these receptors were upregulated by varying cell cholesterol content, insulin increased LDL binding (+88%) and decreased HDL binding (-24%). Insulin-like growth factor I (IGF-I, 100 ng/ml) also significantly decreased HDL binding and HDL-mediated cholesterol efflux to a comparable degree. Pooled human serum similarly induced a reduction in HDL binding to its receptor. These results are consistent with the hypothesis that growth factors in general, and insulin and IGF-I in particular, decrease HDL-receptor activity, possibly to promote retention of cholesterol needed for new membrane synthesis during cell proliferation. Such a mechanism could be partly responsible for accumulation of cholesteryl esters in arterial wall cells during atherogenesis in diabetes mellitus.

Carrier Proteins↗
PubMed1989

Elevated plasma glucose and lowered triglyceride levels from omega-3 fatty acid supplementation in type II diabetes.

We studied the effect of omega-3 fatty acids (omega 3FA) on glucose homeostasis and lipoprotein levels in eight type II (non-insulin-dependent)-diabetic subjects ingesting 8 g/day omega 3FA for 8 wk as marine-lipid concentrate capsules. After omega 3FA supplementation, fasting plasma glucose levels increased 22% (P = .005) and meal-stimulated glucose increased 35% (P = .036). The percentage of glucose elevation correlated with percentage ideal body weight (r = .73, P = .04). No significant changes were seen in fasting or meal-stimulated plasma insulin, glucose disposal, or insulin-to-glucagon ratios. Very-low-density lipoprotein cholesterol and triglyceride (TG) levels showed consistent reductions of 56% (P less than .001) and 42% (P less than .001), respectively, after omega 3FA supplementation. Total cholesterol levels decreased 7% (P less than .05) without alteration in low- or high-density lipoprotein cholesterol. Thus, omega 3FA supplementation at a dose of 8 g/day significantly improves plasma TG levels but increases fasting and meal-stimulated glucose concentrations in the type II diabetic patient not treated with insulin or sulfonylurea agents. Marine-lipid concentrate capsules supplying large amounts of omega 3FAs should be used cautiously in the type II diabetic patient.

Aged↗