Mary E. Dempsey

The Effect of Beta Sitosterol on the Serum Lipids of Young Men with Arteriosclerotic Heart Disease

Previous studies in human beings on unrestricted diets have indicated that the plant sterols (beta or gamma sitosterol) cause decreases in serum cholesterol. In this study, 15 young men with previous myocardial infarction were given 12 to 18 Gm./day of beta sitosterol with resultant sustained reductions of serum cholesterol and beta lipoprotein lipid. Lipoprotein lipid fractionation was performed by paper electrophoresis. These changes occurred irrespective of initial serum cholesterol or content of diet. Control observations of the effects of diet, weight maintenance, and the inclusion of placebos brought about increased confidence that the changes were due to the administered sitosterol.

The role of a carrier protein in cholesterol and steroid hormone synthesis by adrenal enzymes

Squalene and sterol carrier protein (SCP) of liver, known to be required for cholesterol synthesis by liver microsomal enzymes, functions with adrenal microsomal enzymes (Δ7-sterol Δ5-dehydrogenase and Δ5,7-sterol Δ7-reductase) catalyzing cholesterol synthesis from sterol precursors. Adrenal preparations contain a heat-stable protein which functions similarly to liver-SCP with adrenal and liver enzymes. Liver-SCP also can participate with an adrenal enzyme (solubilized from an acetone powder of mitochondria) in the conversion of cholesterol to pregnenolone. These findings indicate that an SCP-like protein not only participates in cholesterol synthesis and transport in the adrenal, but also in the initial steps of cholesterol metabolism to steroid hormones.

Purification and characterization of a naturally occurring activator of cholesterol biosynthesis from Δ5, 7-cholestadienol and other precursors☆☆☆

Abstract The reduction of Δ 5, 7 -cholestadienol to cholesterol by the microsomal fraction of rat liver homogenates is specifically stimulated 4-fold or greater, in the presence of excess NADPH, by an activator isolated from the high speed supernatant fraction. This activator was purified by heat treatment, (NH 4 ) 2 SO 4 fractionation, and gel filtration. It is inactivated by trypsin hydrolysis. The results demonstrate that the activator is a heat stable protein capable of binding Δ 5, 7 -cholestadienol, which in bound form is readily converted to cholesterol by microsomal Δ 5, 7 -sterol Δ 7 -reductase. Similar findings were obtained with other precursors of cholesterol and suggest a unique biosynthetic function for the protein as a vehicle for water insoluble precursors of cholesterol.

Regulation of Lipid Metabolism by a Lipid-Carrying Protein

The overall conclusion to be made from the information presented here is that for many reasons SCP is a highly unusual protein. Some of these reasons are, first, SCP serves as cofactor for a number of different membrane-bound enzymes catalyzing specific steps in lipid metabolism. Second, SCP is involved in intracellular transport or movement of both cholesterol and fatty acids. Third, SCP is remarkably abundant and ubiquitous; its structure is conserved throughout nature. Fourth, SCP is exported to the blood stream from its site of synthesis by some, perhaps unique, mechanism and then rapidly taken up by specific tissues, e.g., the adrenal. Fifth, SCP is free in the cytosol and can also move to the inner mitochondrial membrane, where it is tightly bound. Sixth, SCP undergoes a dramatic diurnal variation in amount, reflecting changes in synthetic rate. Its half-life is less than an hour. Seventh, the diurnal variation in amount is triggered by feeding and influenced by several hormones. The diurnal variation is lost but a high level of SCP is maintained in the face of debilitating conditions, i.e., starvation, diabetes. Eighth, malignant cells exhibit defects in the uptake, synthesis, or turnover of SCP. Ninth, the synthesis of SCP is regulated by the efficiency of translation of its ever abundant mRNA. Tenth, there is much more to be learned about the functions and regulation of SCP.

Blood lipids and lipoproteins in a Minnesota urban population

Abstract The distributions are described of lipids and lipoprotein cholesterol in a randomly selected sample from a Minneapolis, Minnesota, suburb. There are large differences in these levels in different age, sex and hormone use groups. Total plasma cholesterol, the low-density and very-low-density lipoprotein fractions, and plasma triglycerides rise steadily for ages 10–49 in both men and women. The level continues to rise in women during ages 50–59 but falls in men. High-density lipoprotein cholesterol, however, decreases from sexual equality at ages 10–11 to low levels in adult men. High levels are maintained in adult women. Exogenous hormones apparently affect lipids. Oral contraceptive use is associated with higher levels of each of the lipids except high-density lipoprotein cholesterol; post-menopausal supplementary estrogen use is associated, however, with decreased total and low-density lipoprotein cholesterol levels, while the high-density fraction is higher.

Studies of sterol synthesis, synthesis regulation and transport in cultured human kidney☆

Abstract Cellular sterol content and sterol metabolism were studied in diploid human kidney cells in early passages in culture. Cholesterol, the main cellular sterol, was present at levels similar to those reported for other cultured mammalian kidneys. Cholesterol biosynthesis was characterized by a slow conversion of sterol precursors with accumulation of lanosterol and 27 carbon-atom sterols. In the absence of exogenous cholesterol, kidney cells grew slowly and intracellular cholesterol decreased; however, sterol formation from labelled acetate was stimulated. These results suggest that the cholesterol concentration in the culture medium influences the rate of sterol formation by the kidney cell. Furthermore, cholesterol appears to be essential to cultured human kidney and de novo synthesis by the cells in culture is not adequate to meet their requirements for growth.

Two major regulatory steps in cholesterol synthesis by human renal cancer cells.

Abstract Two major mechanisms regulating cholesterol biosynthesis exist in a human renal cancer cell line, Caki-1. Caki-1 is a newly established cell line whose characteristics of rapid growth and active cholesterol synthesis qualify it as a potentially valuable tool for elucidation of regulatory mechanism of cholesterol synthesis and transport. In the absence of exogenous cholesterol, cholesterol is the dominant sterol arising from labeled acetate and mevalonate. As expected, in the presence of exogenous cholesterol, the conversion of acetate to cholesterol and the activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase (EC 1.1.1.34) is markedly reduced and this inhibition is released when cholesterol is removed from the medium. An unexpected and possibly unique finding is the inhibition of the conversion of mevalonate to cholesterol in the presence of exogenous cholesterol. This second major control process results in the accumulation of squalene and may involve additional late steps in cholesterol biosynthesis or metabolism. The occurrence of two major mechanisms regulating cholesterol synthesis may be a unique property of renal cancer cells or a previously unrecognized characteristic of a variety of cultured cells.

Role of sterol carrier protein in cholesterol metabolism

This report summarizes our recent studies on the protein known as sterol carrier protein (SCP) or fatty acid binding protein (FABP). SCP is a highly abundant, ubiquitous protein with multifunctional roles in the regulation of lipid metabolism and transport. SCP in vitro activates membrane-bound enzymes catalyzing cholesterol synthesis and metabolism, as well as those catalyzing long chain fatty acid metabolism. SCP also binds cholesterol and fatty acids with high affinity and rapidly penetrates cholesterol containing model membranes. Studies in vivo showed SCP undergoes a remarkable diurnal cycle in level and synthesis, induced by hormones and regulated in liver by translational events. SCP rapidly responds in vivo to physiological events and manipulations affecting lipid metabolism by changes in level. Thus SCP appears to be an important regulator of lipid metabolism. Preliminary evidence is presented that SCP is secreted by liver and intestine into blood and then taken up by tissues requiring SCP but incapable of adequate SCP synthesis.

Correlation of tumor metastasis with sterol carrier protein and plasma membrane sterol levels

Squalene and sterol carrier protein (SCP) levels and sterol/phospholipid molar ratios of whole cells and plasma membranes were measured in cultured primary tumor and metastatic cell lines. SCP is abundant in all cell lines. However, metastatic lines have significantly lower SCP levels and plasma membrane sterol/phospholipid ratios than do primary lines. The results indicate that extremely malignant, metastatic cells are unable to produce or maintain adequate levels of both SCP and plasma membrane sterols when grown in lipoprotein deficient media. This defect, in vivo, probably causes excess uptake of SCP and lipid.

Sterol Synthesis in Cultured Human Renal Cell Cancer

Studies on sterol synthesis in cultured human renal cell carcinoma were conducted in an attempt to elucidate the mechanism by which clear cell tumors accumulate cholesterol in the cytoplasm. Cultured renal cell carcinoma requires serum lipoproteins for optimal growth. In some renal cell carcinomas cellular cholesterol content was significantly higher than that present in cultured kidney cells under similar conditions. Renal cell carcinoma synthesizes sterols from labeled acetate. The rate of sterol synthesis is inversely proportional to the levels of exogenous cholesterol in the growth medium, suggesting the presence of a negative feedback mechanism. In addition, the conversion of 27-carbon-atom sterol precursors to cholesterol appears to be slow and inefficient under the presnt conditions. We conclude that an aberrant regulation of cholesterol synthesis cannot be invoked necessarily to explain cholesterol accumulation in renal cell carcinoma.