Comparison of the immunomodulatory effects of the plant sterol beta-sitosterol to simvastatin in peripheral blood cells from multiple sclerosis patients.

Statins as hypocholesterolimic drugs have recently shown to have ant-inflammatory properties and thus are being assessed for the treatment of multiple sclerosis (MS). Dietary phytosterols such as beta-sitosterol (SIT) are also hypocholesterolemic compounds and from preliminary studies they appear to have also anti-inflammatory properties. In this communication, we report on studies to investigate the immunomodulatory effects of SIT on proliferation and release of key cytokines from peripheral blood mononuclear cells (PBMC) of MS patients. In PBMC of MS patients, 16 microM SIT had no effect on cell proliferation; however simvastatin (SV) at 10 and 20 microM reduced cell proliferation by as much as 60%. SIT (4 microM) reduced TNF-alpha release by 24% in PBMC of MS patients whereas 10 microM SV reduced TNF-alpha release by 94%. SIT reduced IL-12 release in MS patients at 4 and 16 microM by 27% and 30%, respectively. In healthy subjects, 16 microM SIT increased the anti-inflammatory cytokine IL-10 by 47% whereas 10 microM SV decreased IL-10 by 30%. In PBMC of MS patients, SIT had no effect on IL-10 release whereas 10 microM SV reduced IL-10 by 62%. SIT (4 microM) reduced IL-5 release by 47% in MS patients while 10 microM SV reduced IL-5 by 89%. The results show that SIT is effective in modulating the secretion of pro/anti-inflammatory cytokines and suggest a potential beneficial effect of SIT in MS management without the side effects associated with statin therapy.

beta-Sitosterol enhances tamoxifen effectiveness on breast cancer cells by affecting ceramide metabolism.

The objective of this study was to investigate the effects of the dietary phytosterol beta-sitosterol (SIT) and the antiestrogen drug tamoxifen (TAM) on cell growth and ceramide (CER) metabolism in MCF-7 and MDA-MB-231 human breast cancer cells. The MCF-7 and MDA-MB-231 cell lines were studied as models of estrogen receptor positive and estrogen receptor negative breast cancer cells. Growth of both cell lines as determined using the sulforhodamine B assay was inhibited by treatment with 16 microM SIT but only MCF-7 cell growth was inhibited by treatment with 1 microM TAM. The combination of SIT and TAM further inhibited growth in both cell lines, most significantly in MDA-MB-231 cells. CER is a proapoptotic signal and CER levels were increased in both MCF-7 and MDA-MB-231 cells by individual treatment with SIT and TAM and the combined treatment raised cellular CER content even further. SIT and TAM raised CER levels by different means. SIT potently activated de novo CER synthesis in both MCF-7 and MDA-MB-231 cells by stimulating serine palmitoyltransferase activity; whereas TAM promoted CER accumulation in both cell types by inhibiting CER glycosylation. These results suggest that the combination regimen of dietary SIT and TAM chemotherapy may be beneficial in the management of breast cancer patients.

beta-Sitosterol stimulates ceramide metabolism in differentiated Caco2 cells.

Previous studies from our laboratory on tumor cells suggest that phytosterols stimulate ceramide production, which was associated with cell growth inhibition and stimulation of apoptosis. The objective of the present study was to examine the effect of phytosterols on ceramide metabolism in small intestinal cells that represent the first cells in contact with dietary phytosterols. Caco(2) cells, an accepted model for human intestinal epithelial cells, were used in this study. Ceramide and ceramide-containing lipids were examined by labeling the ceramide pool with (3)H-serine. Cells were supplemented with 16 microM of sterols (cholesterol, beta-sitosterol or campesterol) for 16 days postconfluence and continued to differentiate. Of the two phytosterols, beta-sitosterol, but not campesterol, induced more than double the serine labeling when compared with cholesterol. This increase was uniform in sphingomyelin (SM), ceramide and sphingosine labeling. Sterols had no effect on SM concentration in the cells. In addition, sterol had no effect on the activity of SM synthase or sphingomyelinases. There was an inhibition of ceramidases with campesterol supplementation. These data suggest that the observed increases in SM and sphingosine labeling were due to an increase in ceramide turnover. The increase in ceramide turnover with beta-sitosterol supplementation was not associated with growth inhibition but was with increases in ceramide glycosylation products such as cerebrosides and gangliosides. It was concluded that beta-sitosterol has no effect on differential Caco(2), a model of normal small intestinal cells. The increase in the glycosylated ceramide products may offer a means to protect the cells from the harmful effect of ceramide by excreting them with lipoproteins.

Effect of resveratrol and beta-sitosterol in combination on reactive oxygen species and prostaglandin release by PC-3 cells.

The objective of this project was to identify some possible mechanisms by which two common phytochemicals, resveratrol and beta-sitosterol, inhibit the growth of human prostate cancer PC-3 cells. These mechanisms include the effect of the phytochemicals on apoptosis, cell cycle progression, prostaglandin synthesis and the production of reactive oxygen species (ROS). Prostaglandins have been known to play a role in regulating cell growth and apoptosis. PC-3 cells were supplemented with 50 microM resveratrol or 16 microM beta-sitosterol alone or in combination for up to 5 days. Phytochemical supplementation resulted in inhibition in cell growth. beta-Sitosterol was more potent than resveratrol and the combination of the two resulted in greater inhibition than supplementation with either alone. Long-term supplementation with resveratrol or beta-sitosterol elevated basal prostaglandin release but beta-sitosterol was much more potent than resveratrol in this regard. beta-Sitosterol was more effective than resveratrol in inducing apoptosis and the combination had an intermediate effect after 1 day of supplementation. Cells supplemented with resveratrol were arrested at the G1 phase and at the G2/M phase in the case of beta-sitosterol while the combination resulted in cell arrest at the two phases of the cell cycle. beta-Sitosterol increased ROS production while resveratrol decreased ROS production. The combination of the two phytochemicals resulted in an intermediate level of ROS. The observed changes in prostaglandin levels and ROS production by these two phytochemicals may suggest their mediation in the growth inhibition. The reduction in ROS level and increase by resveratrol supplementation in PC-3 cells reflects the antioxidant properties of resveratrol. It was concluded that these phytochemicals may induce the inhibition of tumor growth by stimulating apoptosis and arresting cells at different locations in the cell cycle and the mechanism may involve alterations in ROS and prostaglandin production.

Combination of phytosterols and omega-3 fatty acids: a potential strategy to promote cardiovascular health.

Phytosterols and omega-3 fatty acids (n-3) are natural food ingredients with potential cardiovascular benefits. Phytosterols inhibit cholesterol absorption, thereby reducing total cholesterol (TC) and LDL-cholesterol levels. Numerous clinical studies have shown that a daily intake of 1.5-2.0 g of phytosterols can result in a 10-15 % reduction in LDL levels, while consumption of n-3 is associated with a significant reduction in plasma triglyceride (TG) concentrations. Furthermore, n-3 may also beneficially modify a number of other risk factors of coronary heart disease (CHD). Thus, it is reasonable to suggest that combination of phytosterols and n-3 may further reduce cardiovascular risk factors. Esterification of phytosterols with non-n-3 fatty acids has substantially improved their incorporation into a variety of foods without affecting the efficacy of phytosterols. Therefore, it is assumed that esterification of phytosterols with n-3 may have advantages for both food industry and health. Evidence suggests that this combination is effective in reducing the levels of several cardiovascular risk factors including TC and TG concentrations, pro-aggregatory factors, arrhythmic eicosanoid and thromboxane A2 levels. In this mini-review, we have critically reviewed and summarized data from clinical and animal studies in which phytosterols and n-3, alone or in combination, were used. We have also provided information on structure-function relationship for these two natural compounds. Biological properties of several phytosterol derivatives including phytosterol-glucoside have been also discussed. Although the animal studies are supportive of this combination therapy, human studies are needed to address its long term effects.

Phytosterols decrease prostaglandin release in cultured P388D1/MAB macrophages.

Cardiovascular disease (CVD) remains the leading cause of death in Western societies. Atherosclerosis is a major cardiovascular related disorder that is responsible for 50% of all mortality in the United States. Several epidemiological studies suggest that consumption of a plant-based diet is associated with a decreased incidence of cardiovascular abnormalities. Phytosterols, especially beta-sitosterol, are plant sterols that have been shown to exert protective effects against cardiovascular diseases as well as many types of cancer. Monocyte/macrophage cells are involved with the inflammatory process. Accumulation of these cells in arteries is one of the initial events leading to atherosclerosis. Macrophages are capable of supplying the atherosclerotic vessel with substantial amounts of prostaglandins. Prostaglandins have been shown by numerous studies to play a key role in the atherosclerosis process. They can affect platelet aggregation, vasodilation or constriction of blood vessels, and the adherence of monocytes to the vessel walls. The purpose of this study was to examine the effect of phytosterols on the release of PGE(2) and PGI(2) from lipopolysaccharide (LPS)-stimulated P388D(1)/MAB macrophage cells. P388D(1)/MAB cells were supplemented with 16 microM cholesterol, beta-sitosterol or campesterol using cyclodextrin as a vehicle. Phytosterol supplementation led to a significant decrease in cellular growth at various time points throughout a 7-day treatment period, especially after 3 days of treatment. Macrophages incorporated the supplemented phytosterols into their membranes which accounted for 26% of total membrane sterols. Cholesterol supplementation at 16 microM however, had no effect on membrane sterols. Supplementation with 16 microM concentration of beta-sitosterol or campesterol resulted in a significant inhibition of PGE(2) and PGI(2) release from macrophage cells as compared to the vehicle control. Of the two phytosterols, beta-sitosterol supplementation exhibited a greater inhibitory effect. PGE(2) release was decreased 68% by beta-sitosterol and 55% by campesterol, while cholesterol supplementation was not as effective, as it led to a 37% decrease. Similarly, release of PGI(2) from macrophages was inhibited 67% by beta-sitosterol and 52% by campesterol treatment, while enrichment of the cells with cholesterol, led to a 35% decrease in PGI(2) release. The decrease in prostaglandin release was not due to alteration in the expression of cPLA(2) and COX-2 enzymes which suggests that alterations in the activities of these enzymes may be responsible for the observed changes in prostaglandin release. It was concluded that phytosterol incorporation into macrophages may offer protection from atherosclerosis by reducing their prostaglandin release and thus slowing down the atheroma development.

A plant food-based diet modifies the serum beta-sitosterol concentration in hyperandrogenic postmenopausal women.

Plant sterols or phytosterols are common components of plant foods, especially plant oils, seeds and nuts, cereals and legumes. The most common phytosterols are campesterol, beta-sitosterol and stigmasterol. Phytosterols have anticarcinogenic properties. Previous studies have suggested that populations with low breast cancer incidence often consume diets high in phytosterols. The present study evaluated whether consumption of a plant food-based diet, low in animal fat, may increase serum phytosterol levels in postmenopausal women. One hundred and four women volunteers were randomized to dietary intervention or control groups. The dietary intervention included intensive dietary counseling to replace animal products with plant-based foods. Subjects in the dietary intervention group participated twice a week for 18 wk in workshops about the preparation and consumption of a plant food-based diet. The absolute change in serum total phytosterol concentration was greater in the dietary intervention group than in the control group. The percent change tended to differ between groups (P = 0.06). However, only for beta-sitosterol did the absolute and percent changes within a group differ significantly between groups (P = 0.0017). The decrease in serum total cholesterol in the dietary intervention group (-14%) was greater than that in the control group (-4%; P = 0.0005). The results of this study show that circulating levels of phytosterols can be affected by dietary modification. These findings indicate that phytosterols, in particular beta-sitosterol, can be used as biomarkers of exposure in observational studies or as compliance indicators in dietary intervention studies of cancer prevention.

Effect of phytosterols on cholesterol metabolism and MAP kinase in MDA-MB-231 human breast cancer cells.

Epidemiological studies suggest that dietary phytosterols may offer protection form some types of cancer including breast cancer. In an attempt to investigate the mechanism by which phytosterols offer this protection, we investigated the effect of the two most common dietary phytosterols, beta-sitosterol and campesterol, on the mevalonate and MAP Kinase (MAPK) pathways in MDA-MB-231 cells. These pathways play a role in cell growth and apoptosis. MDA-MB-231 cell line was used in this study since it is a hormone-insensitive tumor cell line which represents the majority of advanced breast cancer cases. Cells grown in the presence of 16 microM beta-sitosterol or campesterol for 3 days exhibited a 70% and 6% reduction in cell growth, respectively, while cholesterol treatment had no effect on growth as compared to the control. Studies investigating the effect of sterol supplementation on the relative and total sterol composition of cells, showed that cells supplemented with cholesterol contained 23% more cholesterol than the control. Cells supplemented with campesterol had almost one-half the cholesterol of controls but accumulated campesterol to account for 40% of the total sterols. In the case of cells supplemented with beta-sitosterol, cells had only 25% of their sterols as cholesterol and the rest was in the form of beta-sitosterol. All sterols tested equally inhibited de novo cholesterol synthesis using 14C-acetate as substrate. beta-Sitosterol supplemented cells had reduced cholesterol synthesis when using 3H-mevalonolactone as substrate, which suggests that the inhibition in this pathway is downstream of mevalonate where processes such as isoprenylation of proteins may take place. Mevalonate supplementation to cells treated with beta-sitosterol did not completely correct the observed growth inhibition by beta-sitosterol. There was no effect of sterols on the concentrations of both low (21-26 kDa) or high (44-74 kDa) molecular weight isoprenylated proteins in these cells. On the other hand, both the quantity and activity of MAPK was elevated in the cells supplemented with beta-sitosterol. These data suggest that the down regulation of cholesterol synthesis from mevalonate and stimulation of the MAPK pathway may play roles in the inhibition of MDA-MB-231 cell growth by beta-sitosterol.

Beta-sitosterol, a plant sterol, induces apoptosis and activates key caspases in MDA-MB-231 human breast cancer cells.

The objective of the present study was to evaluate the effect of beta-sitosterol, a plant sterol that induces apoptosis in breast cancer cells, on two pathways leading to apoptosis. These pathways are classified based on the localization of the initiated signal, extrinsic and intrinsic pathways. Extrinsic and intrinsic pathways are catalyzed by caspases 8 and 9, respectively, which leads to the activation of the executioner caspase 3. The results of the present study indicate that beta-sitosterol supplementation at 16 microM for 3 days to MDA-MB-231 cells induces 39% and 80% increases in the activities of caspases 8 and 9, respectively, compared to cholesterol supplemented cells or controls. There was also a 3-fold increase in the activity of caspase 3. Sterol treatment had no effect on the quantities of the enzymes. It is concluded that beta-sitosterol may induce apoptosis through the two pathways but was more pronounced on the intrinsic pathway.