Ashim K. Bhattacharyya

Sluggish sitosterol turnover and hepatic failure to excrete sitosterol into bile cause expansion of body pool of sitosterol in patients with sitosterolemia and xanthomatosis.

Sitosterolemia and xanthomatosis are characterized by the development of tendon and tuberous xanthomas at an early age and premature atherosclerosis despite normal plasma cholesterol concentrations. The reason(s) for the xanthoma formation and premature atherosclerosis are not clearly understood. The accumulation of sitosterol in the tissues of these patients could be due to increased uptake of low density lipoprotein (LDL) via LDL receptors because of an expanded sitosterol pool caused by sluggish turnover and decreased excretion of sitosterol into bile and feces coupled with the hyperabsorption of sitosterol. We have studied sitosterol and cholesterol turnovers, the biliary and fecal excretion of neutral and acidic steroids, and the response of plasma sterol (sitosterol and cholesterol) levels to either a sterol-free formula or low plant sterol diet in three patients. The average half-life of the first exponential (tA1/2) for sitosterol was 9.2 +/- 3.3 (mean +/- SD) days, which was more than twice that in normal humans. The second exponential (tB1/2) was 156 +/- 108 days, which was nearly 10 times longer than that for normal humans. The average cholesterol production rate in pool A was 0.87 g/day, which is about 40% of that in normal humans. Cholesterol synthesis measured by the sterol balance technique was also found to be about 70% lower than that for normal humans. In two patients fed a sterol-free formula diet, by 25 days their plasma sitosterol and cholesterol levels had decreased by 42% and 36%, respectively. However, in one patient plasma sitosterol and cholesterol concentrations remained unchanged while on the low plant sterol-mixed food diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorbability of plant sterols and their distribution in rabbit tissues.

Rabbits were fed a low cholesterol diet containing 2% plant sterols for 10 weeks to determine the absorbability of these sterols and their deposition in the tissues. We found campesterol and beta-sitosterol in the blood and tissues. The plasma campesterol levels were 4.34--13.3 mg/100 ml, whereas, beta-sitosterol levels were 0.41--1 mg/100 ml. Stigmasterol was not detected. The total plasma plant sterol concentration was about 10% of the total plasma sterol. The mean terminal plasma cholesterol concentration averaged 60% higher (55 vs. 88 mg/100 ml, P less than 0.001) than the mean initial value. Campesterol was the preponderant sterol in all tissues studied, including the aorta. Sitosterol was found in small amounts in the tissues of the abdominal organs. Stigmasterol was not detected in any tissue studied. Esterified campesterol and sitosterol were detected in trace amounts in most tissues. Campesterol and sitosterol, particularly the former, accumulated in the tissues including the aorta.

The masai, milk and the yogurt factor: An alternative explanation

I read with great interest the letter by Dr. Alan N. Howard on the subject “The Masai, Milk and the Yogurt Factor An Alternative Explanation” [l]. In this respect, I would like to draw attention to a study [2] in which 11 male students were fed in a switch back pattern, diets containing either saturated fat or polyunsaturated fat, each with two different levels of calcium (254 mg and 2355 mg per day). The results showed that addition of 2 g calcium daily to the basal low calcium-saturated fat diet produced a decrease in the serum cholesterol level by 8 mg/dl (P < 0.05). However, a change in the serum cholesterol level was observed when the same amount of calcium was added to the basal low calcium-polyunsaturated fat diet. Since milk contains between 55 to 59% saturated fatty acids, it may not be only calcium, as suggested by Dr. Howard, but possibly the combination of calcium and saturated fatty acids in the milk may be the hypocholesterolemic factor.

Long-term induction and regression of diet-induced atherosclerotic lesions in rhesus monkeys. I. Morphological and chemical evidence for regression of lesions in the aorta and carotid and peripheral arteries.

Atherosclerotic lesions were induced in rhesus monkeys by feeding a high-saturated fatty acid and high-cholesterol diet. After 5.4 years the extent of fatty streaks and raised lesions was evaluated in one group of animals (group P) by visual estimation in 10 arterial segments and chemically in four arterial segments. The remaining animals were switched to a basal regression diet low in cholesterol but high in saturated fatty acids for up to 3.7 years. Regression of lesions was evaluated in one group for 1.9 years (group R4) and in another for 3.7 years (group R5) after deleting cholesterol from the diet. The atherogenic diet increased serum cholesterol levels in all animals from a mean of 150 mg/dL to a mean of about 430 mg/dL. The atherogenic diet produced lesions in group P in all arterial segments (involving up to 50% of the arterial intimal surface) and increased cholesterol content in four arterial segments (varying between 443 and 506 micrograms/cm2). Switching to the basal regression diet decreased serum cholesterol levels to normal after 12 to 18 weeks. The switch to the basal diet significantly decreased the extent of fatty streaks in most arterial segments in both groups. Although differences in the mean extent of raised lesions among groups were not statistically significant, 7 of 10 arterial segments in group R4 and 9 of 10 segments in group R5 showed a lesser extent of raised lesions than in group P. Cholesterol content was lower (P < .05) in all four arterial segments in group R5 than in group P.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationships between dietary cholesterol, cholesterol absorption, cholesterol synthesis, and plasma cholesterol in rhesus monkeys

The relationships between the cholesterol content of the diet, plasma cholesterol concentration, cholesterol absorption, and cholesterol synthesis (measured indirectly by desmosterol suppression technique) are explored in groups of high- and low-responding rhesus monkeys fed diets containing 0.02, 0.15 and 0.75 mg cholesterol/kcal. The cholesterol content of the diet (expressed as mg/kcal) is positively correlated with plasma cholesterol concentration and is negatively correlated with percent cholesterol absorption in both groups. Also the cholesterol content of the diet is negatively correlated (r = -0.66) with cholesterol synthesis only in low-responders but not in high-responders. Similarly, the correlation between percent cholesterol absorption and cholesterol synthesis is significant in the low-responders (r = 0.82, P less than 0.01) but not in the high-responders (r = 0.12, P greater than 0.1). Further, a negative correlation (r = -0.61) is observed between cholesterol synthesis and plasma cholesterol concentration in the low-responders but in the high-responders, there is no relationship between the parameters. From these correlations we conclude that the higher cholesterol absorption in the high-responders than in the low-responders is one important mechanism responsible for the development of severe hypercholesterolemia in the high-responding monkeys fed cholesterol. The results also suggest that there might be a lower sensitivity in the feedback inhibition mechanism of cholesterol biosynthesis in the high-responding than in the low-responding rhesus monkeys.

Effects of feeding cholesterol and mixed plant sterols on the fecal excretion of acidic steroids in rhesus monkeys

The effects of feeding diets with high or low amounts of cholesterol and with low or high levels of mixed plant sterols (sitosterol: campesterol: stigmasterol, 60:35:5) on the daily fecal excretion of acidic steroids were studied in rhesus monkeys. During periods of low dietary plant sterol, total fecal acidic steroid excretion was 43% lower (P less than 0.01) during low dietary cholesterol than during high dietary cholesterol. During periods of high dietary plant sterols the fecal acidic steroid excretion was 113% higher (P less than 0.01) with low dietary cholesterol than with high dietary cholesterol. Addition of mixed plant sterols to the low-cholesterol diet produced nearly a 2-fold increase (P less than 0.005) whereas, such an addition to the high cholesterol diet produced a significant decrease by about 53% (P less than 0.025) in the total fecal acidic steroid excretion. The results suggest that the effect of cholesterol feeding on fecal acidic steroid excretion depends on the level of plant sterols in the diet. This interaction of the effects of cholesterol and plant sterols on the fecal acidic steroid excretion is probably related to the inhibitory effect of plant sterols on cholesterol absorption.

Long-term induction and regression of diet-induced atherosclerotic lesions in rhesus monkeys. II. Morphometric evaluation of lesions by light microscopy in coronary and carotid arteries.

Atherosclerotic lesions were induced in rhesus monkeys (Macaca mulatta) by feeding them a high-saturated fatty acid and high-cholesterol diet. After 5.4 years the extent of lesions in three major coronary arteries and the right carotid artery was evaluated morphometrically by light microscopy in one group of animals (group P). The remaining animals were switched to a low-cholesterol diet that remained high in saturated fatty acids and provided the same percentage of total calories as did the atherogenic diet. Lesion regression was then evaluated in one group of monkeys 1.9 years (group R4) and in another group of monkeys 3.7 years (group R5) after withdrawal of cholesterol alone from the diet. In group P, the mean intimal thickness varied between 26 and 47 microns, maximum intimal thickness between 70 and 92 microns, and luminal reduction between 9% and 12% in the three major coronary arteries. Luminal reduction varied between 1% and 11% in right carotid artery segments. After 1.9 years of consuming the basal diet, group R4 animals were no different from group P animals with respect to morphometric measures. Total intimal and medial areas of the left anterior descending (LAD) coronary artery in groups P and R4 were also similar. In contrast, after 3.7 years of consuming the basal diet, group R5 animals showed consistently although not statistically significantly lower values than those in group P for the morphometric measures in coronary arteries and total intimal area in the LAD. Similar results were obtained for the common carotid and external carotid arteries. Thus, our study shows that long-term diet-induced lesions in coronary arteries and in common and external segments of the right carotid artery regressed only when the animals were fed the basal diet for 3.7 years. We conclude that atherosclerotic lesions induced in coronary and carotid arteries can regress toward normal to a certain extent, but they require a longer time for regression than do other arterial segments. These findings support the results of clinical trials in human subjects.

Effect of cholesterol feeding on lipolytic activities in high- and low-responding rhesus monkeys.

We compared the activities of llpoproteln llpase (LPL) and hepatic llpase (HL) in postheparln plasma in groups of highand low-responding rhesus monkeys fed a low cholesterol diet followed by a high cholesterol diet Cholesterol feeding resulted In a two-phase response In lipolytic activities: an Initial phase lasting about 21 days that was similar in the two groups, followed by the second phase In which major differences became apparent between the groups. In the initial phase, LPL and HL activities Increased along with plasma cholesterol and high density llpoproteln (HDL) cholesterol, but there was no change In plasma triglycerldes or apollpoproteln (apo) A-l levels. These changes suggest that both high and low responders respond In a similar manner to metabolize an Increased llpid load and that both groups continue to remove triglycerlde efficiently while cholesterol accumulation begins. The second phase (between 21 and 42 days and thereafter) In high responders was characterized by a decrease In LPL and HL activities along with plasma HDL cholesterol and apo A-l levels, continued Increase In plasma cholesterol, and a slow Increase In plasma triglycerldes. In low responders, LPL activity was maintained at a high level, HL activity decreased to the basal level, and plasma llplds were unchanged. All changes occurred simultaneously, suggesting metabolic relationships between plasma lipolytic activities, plasma llplds, and apollpoproteln.

Absorbability of Plant Sterols in the Rhesus Monkeys

High- and low-responding rhesus monkeys were fed a semisynthetic high or low cholesterol diet with 2% plant sterols for 6 weeks to determine the absorbability of the plant sterols. No plant sterols were detected in the plasma of either high- or low-responding animals fed either high or low cholesterol diet containing low levels of plant sterols. After addition of 2% plant sterols to either of the diets, only campesterol was found in the plasma of all animals. The final plasma campesterol concentrations in the high-responders on high and low cholesterol diets containing high levels of plant sterols were 0.91 ± 0.14(SE)and 1.16 ± 0.27 mg/dl, respectively. Similar values in the low-responders were 0.51 ± 0.06 and 0.24 ± 0.16 mg/dl, respectively. Sitosterol was occasionally detected in trace amounts in some animals of both groups on either high or low cholesterol diet. Stigmasterol was not detected in the plasma of any animals. We conclude, based on the plasma sterol levels, that rhesus monkeys absorb campesterol and probably do not absorb sitosterol or stigmasterol in any significant amount. The study also shows that the high-responders absorb higher amounts of campesterol than the low-responders; a finding similar in respect to cholesterol absorption in the high-responders.

Studies on the mechanism of high intestinal absorption of cholesterol and campesterol in high-responding rhesus monkeys

To understand better the mechanism of higher absorption of cholesterol and campesterol in high-responding than in low-responding rhesus monkeys, we measured the concentrations of the two sterols in the micellar fraction isolated from small intestinal content, and also determined their rates of esterification by cholesterol esterase prepared from the small intestinal mucosa. The results show that the concentrations of both cholesterol and campesterol in the micellar fraction were significantly higher in the high- than in low- and intermediate-responding rhesus monkeys. Also the rates of esterification of both sterols are higher in the proximal segment of the small intestine in high-responders than the other two groups. We conclude that the two necessary steps in the process of sterol absorption, namely, the amounts of sterols solubilized in micelles and their esterification within mucosal cells which are higher in high- than in low-responders are responsible for the higher absorption of the sterols in the high-responding rhesus monkeys.