Pectin-bile acid binding

Judd and Truswell (19) observed no difference in lipid response between the high and low methoxyl pectin and suggested that the ability of pectin to lower cholesterol lies in its gelling properties. Binding of bile acids or cholesterol to pectin has been reported in animal studies (10) and may reduce available cholesterol and lipids for absorption. 

Role of Pectin in Binding of Bile Acids to Carrot Fiber... 

We have proposed that the binding of bile acids to carrot fiber, or cell wall residue rich in pectin, may involve salt linkages between calcium pectate and the carboxylate group of the bile acid. This report presents studies that furnish additional evidence that calcium pectate does have a role in the binding of bile acids to carrot fiber. 

The release of the stronger carboxylate groups of pectin that this equation produces would account for the drop in pH that is observed upon binding of bile acids to carrot AAIR. 

Soluble fiber has certain health benefits, including binding of bile acids in the small intestine, leading to reduced serum cholesterol levels. However, extrusion-induced solubilization may not offer the same health benefits. This new soluble fiber is chemically distinct from naturally soluble fiber compounds such as pectin and gums. Extrusion nearly doubled soluble fiber in potato peels, and significantly more cholic acid and deoxycholic acid were bound by peels extruded at the lower temperature studied (Camire et al., 1994). 

Other dietary interventions or diet supplements may be useful in certain patients with lipid disorders. Increased intake of soluble fiber in the form of oat bran, pectins, certain gums, and psyllium products can result in useful adj unctive reductions in total and LDL cholesterol, but these dietary alterations or supplements should not be substimted for more active forms of treatment. Total daily fiber intake should be about 20 to 30 g/day, with about 25%, or 6 g/day, being soluble fiber. Studies with psyllium seed in doses of 10 to 15 g/day show reductions in total and LDL cholesterol ranging from about 5% to 20% They have little or no effect on HDL cholesterol or triglyceride concentrations. These products also may be useful in managing constipation associated with the bile acid sequestrants. Psyllium binds cholesterol in the gut but also reduces hepatic production and clearance. Fish... 

Carrot fiber, prepared as an alcohol-acetone insoluble residue of cell wall material, binds deoxycholate and chenodeoxycholate under physiological conditions with the release of protons. Removal of calcium pectate from this material by extraction with ammonium oxalate reduces the capacity of carrot fiber to bind bile acids. Calcium carboxymethyl cellulose exhibits similar binding activity, whereas free carboxymethyl cellulose shows no binding. Calcium pectate prepared from citrus pectin and dissolved in water was found to bind bile acids under conditions used with carrot fiber. These results suggest that binding occurs through formation of salt linkage between calcium pectate in the cell wall residue and a bile acid. 

During the course of bile acid binding assays of carrot AAIR it was noted that a peak emerged at the void volume during HPLC of the solution of bile acid that had been in contact with the fiber. We therefore suspected that the bile acid solution was solubilizing some small fraction of the AAIR. Accordingly, carrot AAIR was then extracted with sodium deoxycholate and a pectin fraction was isolated by alcohol precipitation of the... 

Dietary pectin affects lipid metabolism, especially that of cholesterol. One of the explanations proposed to explain an action of pectin on cholesterol metabolism is through its ability to bind bile acids and bile salts. However, pectin also has the property of forming a gel in water. This gel lowers the intestinal absorption of cholesterol and thereby decreases liver cholesterol. Recently, evidence has been obtained that the presence of pectin in a cholesterol diet increases the excretion of cholesterol esters. Results from the administration of cholesterol-4-l C in the diet showed that the presence of pectin slows gastric emptying and results in more labeled cholesterol as well as cholesterol esters in all segments of the gut. 

Pectin also increase bile acid excretion in rats[22j. Kelley et al.[23] observed that rats fed 15% cellulose as part of a semi-purified diet excreted 2.52 mg of bile acids per gm of faces and the ratio of fecal cholic-chenodeoxycholic acid (C/CD) was 1.04. When cellulose was replaced by alfalfa the fecal bile acid concentration rose to 3.75 mg/gm and the C/CD ratio became 0.64. Substitution of whole ground oats for cellulose increased fecal bile acid concentration to 6.16 mg/gm and the C/CD ratio was 0.67. A similar effect of fiber on bile acid spectrum was seen in studies in which baboons were fed commercial or semipurified rations[24]. The effect of fiber on bile acid metabolism is a function of the type of fiber used. Binding may be one mechanism by which fiber increases bile acid excretion. 

Does Citrus Pectin Bind Bile Salts A possible mechanism by which dietary pectin may cause lowering of cholesterol levels in rats has been reported (1 9). In these in vitro studies, pectin was found to inhibit the transport of taurocholic acid from everted sacs of rat intestine. The absorption of labelled cholesterol was depressed by the addition of 5% pectin to the diet as evidenced by increased excretion of labelled cholesterol and diminished cholesterol deposition in the liver. It was concluded from these studies that pectin lowers cholesterol levels in cholesterol-fed rats primarily by binding bile salts and, consequently, by impairing cholesterol absorption. Results similar to those obtained with dietary pectin and described have also been reported for other non-nutritive substances such as guar gum, psyllium seed colloid and seruglucan (20). 

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