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Pectin Isolated From Prickly Pear (Opuntia sp.) Modifies Low Density Lipoprotein Metabolism in Cholesterol-Fed Guinea Pigs^{1, 2,}

Department of Nutrition and Food Science, and Nutritional Sciences Program, University of Arizona, Tucson, AZ 85721 ^* CIIDIR-IPN, Unidad Michoacan, Justo Sierra #28 Ote. Jiquilpan de Juarez, Michoacan, Mexico 59510

The effect of prickly pear soluble fiber on low density lipoprotein (LDL) metabolism was investigated by feeding male guinea pigs either a nonpurified diet containing 0.25% cholesterol (HC diet) or the HC diet + 1% prickly pear pectin (HC-P diet). Plasma cholesterol levels were significantly decreased by the HC-P diet, with a 33% decrease in LDL levels (p < 0.02) and an increase in LDL density. Hepatic free and esterified cholesterol levels were reduced 40 and 85%, respectively (p < 0.002), by the HC-P diet. Hepatic microsomal 3-hydroxy-3-methylglutaryl coenzyme A reductase levels were not different. ¹²⁵I-LDL binding to hepatic membranes was increased 1.7-fold by the HC-P diet (p < 0.001), with receptor affinity (K_d) being unaltered and receptor number (B_max) being significantly increased (p < 0.001). These data suggest that prickly pear pectin may act by a mechanism similar to that of bile acid-binding resins in lowering plasma cholesterol levels. The observed reduction in LDL and hepatic cholesterol levels and increase in LDL density and hepatic apolipoprotein B/E receptors are responses suggesting an increased demand on hepatic cholesterol from increased excretion of bile acids and interruption of the enterohepatic circulation.

KEY WORDS: • pectin • dietary cholesterol • low density lipoprotein • hepatic HMG-CoA reductase • guinea pigs

¹ These studies were supported in part by a grant-in-aid from the American Heart Association, Arizona Affiliate (G-2-15-87), a grant from the National Dairy Council, and funds provided by the University of Arizona Biomedical Research Support Grant Program.

² Paper no. 7179 from the University of Arizona Agricultural Experiment Station.

³ Postdoctoral fellow of the American Heart Association, Arizona Affiliate.

Manuscript received 14 December 1989. Revision accepted 4 May 1990.