The antioxidative effects of lactic acid bacteria on lipid peroxidation in the colonic mucosa were investigated. Among 49 strains of lactic acid bacteria, Streptococcus thermophilus YIT 2001 showed the highest inhibitory activity against lipid peroxidation in liposomes induced by ferrous iron. Feeding a diet containing 0.4% St. thermophilus YIT 2001 (2 x 10(8) colony-forming units per mouse per day) for 2 weeks caused a significant decrease of lipid peroxide (thiobarbituric acid reactive substance) in the colonic mucosa of iron-overloaded mice (0.07% Fe in the diet). The mucosal lipid peroxide level did not correlate with the soluble iron concentration of the cecal contents. Therefore, it is suggested that the antioxidative effect of St. thermophilus YIT 2001 in the colonic mucosa was not due to the removal of ferrous iron from the reaction system of lipid peroxidation.

The antioxidative effects of live bifidobacteria on lipid peroxidation in the colonic mucosa were investigated. Bifidobacterium bifidum strain Yakult, which has been used for production of fermented milk, most effectively inhibited lipid peroxidation catalyzed by ferrous iron in liposomes among 10 species of bifidobacteria from human intestinal flora. Oral administration of B. bifidum strain Yakult for 2 wk significantly decreased the level of lipid peroxide (thiobarbituric acid reactive substance) in the colonic mucosa of iron-overload mice (Fe 0.07% in diet). The iron concentrations in plasma and cecum contents were not affected by administration of B. bifidum strain Yakult. Bifidobacterium bifidum strain Yakult had no chelating or incorporating activity for ferrous iron in vitro. Therefore, the antioxidative effect of B. bifidum strain Yakult in the colonic mucosa was not thought to be based on the removal of ferrous iron from the reaction system of lipid peroxidation. These results suggested that B. bifidum strain Yakult protected the colonic mucosa from oxidative injury without inhibiting iron absorption.

The cellular components involved in the hypocholesterolemic activity of Kluyveromyces marxianus YIT 8292 were examined in rats fed on a high-cholesterol diet. Whole cells (KM) were heated at 115 degrees C for 10 minutes and fractionated into water-soluble extract 1 and the insoluble residue (KM-CW). After mechanical disruption by glass beads, KM-CW was separated into the cell wall (KM-W) and water-soluble extract 2. Plasma total cholesterol was decreased by feeding KM-CW or KM-W, but was not changed by feeding extract 1 or extract 2. Feeding KM-CW and KM-W increased the fecal sterol excretion and concentration of short-chain fatty acids (SCFA) in the cecum. The hypocholesterolemic activity of KM-CW was completely abolished by the enzymatic degradation of alpha-mannan and beta-glucan. These results suggest that alpha-mannan and beta-glucan were the major active components of KM, and that its hypocholesterolemic activity may be attributable to the increasing fecal sterol excretion and/or production of SCFA.

It is known that macrophages recognize and take up oxidized low density lipoprotein (LDL) and this macrophage recognition has been suggested to be due to modification of the lysine (Lys) residues of apoprotein B (apo B). In order to determine whether such modification is involved in recognition, delipidated apo B was modified with lipid peroxidation products and the macrophage recognition of the modified apo B was examined. When delipidated apo B was treated with linoleic acid 13-mono-hydroperoxide (LOOH) and trans-2-octenal (octenal), apo B became fluorescent and its Lys and histidine (His) residues were decreased. When delipidated apo B, partially methylated at the epsilon-amino groups of Lys residues, was treated with LOOH and octenal, fluorescence was not produced and the free Lys residues were not decreased. LOOH- and octenal-modified delipidated apo B were recognized by mouse peritoneal macrophages. The macrophage recognition of the modified apo B was prevented by maleyl bovine serum albumin, indicating that the scavenger receptor was involved in recognition. Neither methyl apo B nor methyl apo B, modified with LOOH or octenal, was recognized by macrophages. Neutralization of positively charged Lys residues of apo B by modification with LOOH and octenal may be requisite for recognition. Bovine serum albumin modified with LOOH and octenal prevented the recognition of the modified apo B, indicating that none of the intrinsic structure of apo B is required for recognition.

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