The concentration of serum lipid hydroperoxides of male rats of the Wistar strain that had received thermal injury on their backs was measured by the hemoglobin-methylene blue (Hb-MB) method. The concentration increased significantly 0.5h after the injury, was higher than that of the normal level until 5h, and decreased to the normal concentration by 7h after the injury. The lipid peroxide level measured by the thiobarbituric acid (TBA) method increased up to 5h after the injury, and then maintained at a higher level than normal for 48h. Thus, the measurement of the total concentration of serum lipid hydroperoxides by the Hb-MB method is useful to detect lipid peroxidation in the early period after the injury, and serum lipid peroxide level measured by the TBA method may reflect the progress of systemic dysfunction.
Effect of long-chain fatty acids on peroxisomal β-oxidation in rat hepatocytes was examined. Out of four long-chain fatty acids, linoleic acid (C 18:2) increased the β-oxidation activity 1.7-2.7 fold without cell toxicity. Total fatty acid content in linoleic acid-treated hepatocytes was increased more than twofold. Addition of nafenopin to the culture medium, instead of linoleic acid, produced a reciprocal relation between the β-oxidation activity and the fatty acid content with a coefficient r=0.906. Cycloheximide inhibited the increase in peroxisomal β-oxidation activity by linoleic acid to 50% of that in cultures without cycloheximide. Results of these experiments suggest that the increase in fatty acid content in hepatocytes may have a significant role in the induction of peroxisomal β-oxidation and that the enzyme proteins in the peroxisomal β-oxidation system induced by linoleic acid were the result of de novo synthesis.
The effect of dietary essential fatty acid (EFA) deficiency on the lipid composition of peroxisomal extracts was studied in Wistar rats. After 21 days of EFA deficiency, no difference was noted in protein levels, but a significant change had occurred in the level of phospholipids and fatty acid composition of phospholipids. In EFA-deficient rat peroxisomes, phosphatidylcholine and phosphatidylinositol were both significantly higher than in controls. This alteration was more marked in peroxisomes than in microsomes. The peroxisomal fatty acid composition was markedly affected as well. In EFA-deficient rats, linoleic (18:2 n-6), arachidonic (C20:4 n-6), and docosahexaenoic (C22:6 n-3) acids were lower whereas oleic (C18:1 n-9), octadecenoic (C18:1 n-7), and eicosatrienoic (C20:3 n-9) acids were higher than in controls. This alteration was also more prominent in the peroxisomal than the microsomal extracts. Catalase activity was weakly reduced, whereas dihydroxyacetone-phosphate acyltransferase activity was strongly increased in EFA-deficient rats. We conclude that the composition of phospholipids and fatty acids may be a factor contributing to peroxisome function and that a diet poor in essential fatty acids or defective unsaturated fatty acid metabolism could amplify peroxisomal dysfunction of genetic origin.
The effect of ascorbic acid on serum lipids and lipid peroxidation has been studied in guinea pigs kept on a high cholesterol diet for 6 and 16 weeks. After 6 weeks, total cholesterol (TC), low-density lipoprotein (LDL), very-low-density lipoprotein (VLDL), and triglycerides (TG) decreased significantly (p<0.001) in ascorbic acid-treated (groups 3 and 4) guinea pigs in comparison to their levels in hypercholesterolemic guinea pigs (group 2). Similar results for TC, LDL, and VLDL were observed after 16 weeks. However, the TG levels showed a nonsignificant decrease (NS) in group 3 and a significant decrease in group 4 (p<0.05) in comparison to those in group 2, after the 16 weeks study. The high-density lipoprotein (HDL) level after both 6 and 16 weeks showed a significant increase in the ascorbic acid-treated animals. The serum lipid peroxide level of animals fed both cholesterol and ascorbic acid showed a significant decrease (p<0.01). These results suggest that ascorbic acid lowers the serum level of cholesterol and protects lipids against peroxidative damage induced by hypercholesterolemia.
In vitro digestibility of stevioside, a natural sweetener, by various digestive enzymes was investigated. Stevioside was incubated with salivary α-amylase, pancreatic α-amylase, saliva, pepsin, gastric secretion, pancreatin and intestinal brush border membrane enzymes of mice, rats, and hamsters as well as with intestinal microflora of mice, rats, hamsters and humans. None of these enzymes digested stevioside except the microflora of the rat and hamster cecal contents, which hydrolyzed it to steviol, and the microflora of mouse cecal content and human feces, which hydrolyzed it to both steviol and steviol-16, 17α-epoxide. Steviol-16, 17α-epoxide was then completely converted back into steviol. These results suggest that steviol might be the only metabolite produced by the intestinal microflora from various animal species and humans.
We evaluated the relationship between the removal rate (K2) of fat emulsion and serum lipids or apolipoproteins of apoA-I, A-II, and B to assess fat emulsion metabolism in subjects who were apoE3/3 homozygotes of wild-type apoE3. K2 of fat emulsion, Intralipid®, was determined by the intravenous fat emulsion tolerance test (FETT) in 184 subjects with apoE phenotype 3/3, including normolipidemic subjects and those with primary hyperlipidemia. Other subjects (n=47) with normolipidemia or primary hyperlipidemia were also evaluated for comparison; they consisted of individuals with apoE phenotype 3/2 and 4/3. In subjects with apoE phenotype 3/3, when a single correlation coefficient was calculated, there were significant correlations between K2 and the serum level of triglyceride (TG) (r=-0.48), total cholesterol (r=-0.15), apoB (r=-0.27), HDL cholesterol (r=0.42), and apoA-I (r=0.26). Multiple regression analysis for elimination of internal correlations revealed significant correlations between K2 and the serum level of TG (r=-0.46, p<0.001) or apoA-I (r=0.23, p<0.01: multiple correlation coefficient=0.51, p<0.001). No significant correlations between K2 and serum lipids or apolipoproteins were observed in subjects with apoE phenotypes other than 3/3. We suggest that K2 is strongly related to serum TG and apoA-I in subjects with apoE phenotype 3/3 and that this relationship is unique and specific to subjects with this phenotype.
The total proteins and collagenase activity in tears as well as α2-macroglobulin (anticollagenase) and vitamin A levels in serum, were estimated in 35 malnourished children with corneal lesions, in 30 malnourished controls (age matched) without corneal lesions, and in 19 normal children. Also eye swabs from some of the children were cultured for bacteria. Significant decreases in the serum vitamin A and α2-macroglobulin levels and in tear total protein levels were observed in malnourished children when compared with the normal values. Further, the reduction was more pronounced in children with corneal lesions than in those without them. Interestingly, the tear collagenase activity was significantly elevated in malnourished children with corneal lesions as compared with that in those without lesions or in normal children. Similarly, more bacteria could be cultured in samples from malnourished children (with/without corneal lesions) than in those from normal children. These observations clearly indicate that the elevated levels of anterior segment collagenase may play an important role in the pathogenesis of corneal lesions.