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Dietary saponins and serum lipids
Fd Chem. Toxic. Vol. 24, No. 5, p. 441, 1986
0278-6915/86 $3.00+0.00 Pergamon Journals Ltd
Printed in Great Britain
LETTER TO THE EDITOR DIETARY SAPONINS A N D SERUM LIPIDS
Sir,--Saponins are widely distributed throughout the plant kingdom and are found in many foods consumed by man. An important commercial source of saponin is obtained from the bark of the quillaja tree (L. Quillaja saponaria, Rosaceae). In view of the emphasis being placed on increasing the consumption of plant foods in our diet to combat such chronic diseases as cancer and heart disease, the intake of saponins is expected to increase as well. Dietary saponins may play an important beneficial role in human nutrition since they have been shown to lower serum cholesterol concentrations in several species of animals (Oakenfull, Fd Chem. 1981, 6, 19), to stimulate immune response in animals and possibly humans (Bomford, Int. ,4rchs Allergy appl. Immun. 1982, 67, 127) and to possess anti-tumorigenic properties (Huang et al. Acta pharm, sin. 1982, 3, 286). However, they are strongly surface-active compounds, which readily interact with lipids and may be toxic to cell membranes as well as to the entire organism. In order to evaluate the effect on serum lipid composition of feeding quillaja saponin to rats for up to 24 weeks, weanling male Fischer (F-344) rats were maintained on a semi-purified AIN-76A diet. The test diet was prepared by the addition of food-grade quillaja saponin extract 2F (obtained from Meet Corporation, North Bergen, NJ) at a level of 7.5 g/kg diet. Animals were maintained on their respective diets for either 8 or 24 weeks. This study demonstrated that 0.75% quillaja saponin added to the diet of rats was well tolerated and had no adverse effects on food consumption and body weight. No gross changes were observed in the saponin-fed rats at autopsy. In contrast to the findings of Gaunt et al. (Fd Cosmet. Toxicol. 1974, 12, 641), who reported significant increases in the caecal weights of rats fed 4% quillaja saponin, no such differences were observed in our study even after saponin feeding for 24 weeks. We did, however, observe a significant increase in the relative weight of the small intestine in rats fed the saponin. A similar finding was also reported previously (Phillips et al. Fd Cosmet. Toxicol. 1979, 17, 23). Serum lipid analysis showed no difference in the triglyceride and cholesterol concentrations at the end of the 8 weeks. However these levels were reduced significantly, compared with the controls, after 24 weeks on the 0.75% saponin diet. Saponin treatment reduced serum cholesterol levels to 75 + l0 mg/dl from control levels of 8 5 + 12mg/dl ( P < 0 . 0 5 ) and triglyceride concentrations were reduced to 116+22 from 172 + 65 mg/dl (P < 0.01) for controls. It appears that saponins may have to be consumed over a long period of time before serum lipids are significantly altered. Most of the studies to date have shown a similar lowering of serum cholesterol by saponins only when cholesterol was incorporated into the diet. Saponins are thought to bind to exogenous cholesterol and prevent its absorption. However, in our study a significant reduction in serum cholesterol was observed although additional cholesterol was not incorporated into the diet. This supports the hypothesis that saponins, by binding to bile acids, prevent their reabsorption. Endogenous cholesterol is then metabolized to bile acids to maintain an adequate supply. As a result, over a period of time, serum cholesterol levels would be lowered. We did observe a significant increase in the faecal excretion of total bile acids in rats maintained on diets containing saponin. Not all saponins would affect serum cholesterol status similarly. Sapogenins that contain carboxylic groups, such as alfalfa and quillaja saponins bind cholesterol/n vitro (Gestetner et al. Biochim. biophys. Acta 1972, 270, 181) and may modify cholesterol metabolism m vivo. Evidence is accumulating to suggest that saponins, which were previously regarded as 'antinutrients', may have a beneficial role in human nutrition and health. However, the benefits must be weighed against possible toxic effects before specific recommendations can be made concerning the intake levels and the appropriate type of saponins. It would seem from our study that quillaja bark saponin is well tolerated in rats at a level of 0.75% in the diet. Although a significant reduction in the serum cholesterol and triglyceride levels was obtained after 24 weeks, a careful evaluation has to be undertaken to assess the effects of saponins on the absorption of fat-soluble vitamins. Investigations should also be undertaken to evaluate the effects of saponins from common dietary sources such as the legumes. A . V. RAO arid C. W .
KENDALL,
Department of Nutritional Sciences, University of Toronto, Toronto, Ontario, Canada
441
0278-6915/86 $3.00+0.00 Pergamon Journals Ltd
Printed in Great Britain
LETTER TO THE EDITOR DIETARY SAPONINS A N D SERUM LIPIDS
Sir,--Saponins are widely distributed throughout the plant kingdom and are found in many foods consumed by man. An important commercial source of saponin is obtained from the bark of the quillaja tree (L. Quillaja saponaria, Rosaceae). In view of the emphasis being placed on increasing the consumption of plant foods in our diet to combat such chronic diseases as cancer and heart disease, the intake of saponins is expected to increase as well. Dietary saponins may play an important beneficial role in human nutrition since they have been shown to lower serum cholesterol concentrations in several species of animals (Oakenfull, Fd Chem. 1981, 6, 19), to stimulate immune response in animals and possibly humans (Bomford, Int. ,4rchs Allergy appl. Immun. 1982, 67, 127) and to possess anti-tumorigenic properties (Huang et al. Acta pharm, sin. 1982, 3, 286). However, they are strongly surface-active compounds, which readily interact with lipids and may be toxic to cell membranes as well as to the entire organism. In order to evaluate the effect on serum lipid composition of feeding quillaja saponin to rats for up to 24 weeks, weanling male Fischer (F-344) rats were maintained on a semi-purified AIN-76A diet. The test diet was prepared by the addition of food-grade quillaja saponin extract 2F (obtained from Meet Corporation, North Bergen, NJ) at a level of 7.5 g/kg diet. Animals were maintained on their respective diets for either 8 or 24 weeks. This study demonstrated that 0.75% quillaja saponin added to the diet of rats was well tolerated and had no adverse effects on food consumption and body weight. No gross changes were observed in the saponin-fed rats at autopsy. In contrast to the findings of Gaunt et al. (Fd Cosmet. Toxicol. 1974, 12, 641), who reported significant increases in the caecal weights of rats fed 4% quillaja saponin, no such differences were observed in our study even after saponin feeding for 24 weeks. We did, however, observe a significant increase in the relative weight of the small intestine in rats fed the saponin. A similar finding was also reported previously (Phillips et al. Fd Cosmet. Toxicol. 1979, 17, 23). Serum lipid analysis showed no difference in the triglyceride and cholesterol concentrations at the end of the 8 weeks. However these levels were reduced significantly, compared with the controls, after 24 weeks on the 0.75% saponin diet. Saponin treatment reduced serum cholesterol levels to 75 + l0 mg/dl from control levels of 8 5 + 12mg/dl ( P < 0 . 0 5 ) and triglyceride concentrations were reduced to 116+22 from 172 + 65 mg/dl (P < 0.01) for controls. It appears that saponins may have to be consumed over a long period of time before serum lipids are significantly altered. Most of the studies to date have shown a similar lowering of serum cholesterol by saponins only when cholesterol was incorporated into the diet. Saponins are thought to bind to exogenous cholesterol and prevent its absorption. However, in our study a significant reduction in serum cholesterol was observed although additional cholesterol was not incorporated into the diet. This supports the hypothesis that saponins, by binding to bile acids, prevent their reabsorption. Endogenous cholesterol is then metabolized to bile acids to maintain an adequate supply. As a result, over a period of time, serum cholesterol levels would be lowered. We did observe a significant increase in the faecal excretion of total bile acids in rats maintained on diets containing saponin. Not all saponins would affect serum cholesterol status similarly. Sapogenins that contain carboxylic groups, such as alfalfa and quillaja saponins bind cholesterol/n vitro (Gestetner et al. Biochim. biophys. Acta 1972, 270, 181) and may modify cholesterol metabolism m vivo. Evidence is accumulating to suggest that saponins, which were previously regarded as 'antinutrients', may have a beneficial role in human nutrition and health. However, the benefits must be weighed against possible toxic effects before specific recommendations can be made concerning the intake levels and the appropriate type of saponins. It would seem from our study that quillaja bark saponin is well tolerated in rats at a level of 0.75% in the diet. Although a significant reduction in the serum cholesterol and triglyceride levels was obtained after 24 weeks, a careful evaluation has to be undertaken to assess the effects of saponins on the absorption of fat-soluble vitamins. Investigations should also be undertaken to evaluate the effects of saponins from common dietary sources such as the legumes. A . V. RAO arid C. W .
KENDALL,
Department of Nutritional Sciences, University of Toronto, Toronto, Ontario, Canada
441