Yong-Soon Choi

Interaction of dietary protein, cholesterol and age on lipid metabolism of the rat.

1. Male rats at 1 (young) and 9 months (adult) of age were fed on purified diets, supplemented with or without cholesterol, containing 200 g protein/kg (casein (CAS), whey protein (WHY) or soya-bean protein (SOY] for 4 weeks. 2. SOY exerted a hypocholesterolaemic effect in young rats regardless of dietary cholesterol, whereas in adult rats it was observed only when a cholesterol-enriched diet was given. WHY was also hypocholesterolaemic in rats of both ages given cholesterol. SOY tended to reduce the liver cholesterol both in young and adult rats. 3. The liver hydroxymethylglutaryl-CoA reductase (NADPH) (EC 1.1.1.34) activity tended to be lower in the vegetable-protein groups than in the animal-protein groups in young rats, but the age-related reduction was observed only in the latter groups. 4. There was no significant age-related difference in the activity of liver cholesterol 7 alpha-monooxygenase (EC 1.14.13.17) in response to diets. However, when cholesterol was given, activity tended to decrease with age. Rats given SOY excreted more faecal steroids than those given casein, particularly adult rats. 5. The fatty acid profile of phosphatidylcholine and the delta 6-desaturase activity of liver microsomes indicated the reduced desaturation of linoleate in the SOY and WHY groups compared with the CAS groups. 6. The results thus showed a complex interaction of protein type, cholesterol and age on cholesterol homeostasis.

Effects of Dietary Alpha- and Gamma-Linolenic Acid on Lipid Metabolism in Young and Adult Rats

The effect of age on lipid metabolism was studied in rats fed diets containing safflower oil (SFO, 78% linoleic acid), evening primrose oil (EPO, 9.4% gamma-linolenic acid and 70% linoleic acid) or the mixture of safflower and linseed oil (SLO, 10.2% alpha-linolenic acid and 68% linoleic acid). The activity of hepatic HMG-CoA reductase declined with age in all groups. In adult rats, the reductase activity was high in the EPO group and low in the SLO group. The activity of hepatic cholesterol 7 alpha-hydroxylase was independent of the diet or age. Hepatic delta 6-desaturase activity was low in adult rats fed EPO. In liver microsomal phospholipids, the percentage of 22:5 n-6 decreased while that of 22:6 n-3 increased with age. The ratio of linoleate metabolites to linoleate was high in the EPO group and low in the SLO group. Liver and serum cholesterol increased with age only in rats fed the SLO diet. Thus, the results indicated an enhanced susceptibility to dietary fats with age.

Effects of short-term cholestyramine feeding on cholesterol metabolism in differently aged rats

The effects of short-term (7 days) feeding of a diet containing cholestyramine (5%) on the cholesterol metabolism were studied in male Sprague-Dawley rats at ages of 5 weeks (young) and 9-10 months (adult). Cholestyramine significantly enhanced the activities of hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase and cholesterol 7 alpha-hydroxylase both in young and adult rats; however, the absolute values were significantly higher in the former. The time-courses of changes in the activities of these enzymes after cessation of cholestyramine were comparable in both groups of rats. The rate of incorporation of mevalonate into sterol was also higher in young than in adult rats, while the stimulating effect of cholestyramine was markedly greater in adult rats. Hepatic acyl-CoA:cholesterol acyltransferase activity was comparable, but cholestyramine significantly decreased it only in adult rats. In adult rats hepatic cholesterol was decreased significantly by the resin while it remained uninfluenced in young rats. The serum cholesterol level tended to be higher in adult rats regardless of the dietary manipulation. The results indicate an appreciable age-dependent change in the hepatic cholesterol metabolism in response to the interruption of enterohepatic circulation of bile acids.

Sex-difference in the age related change of cholesterol metabolism in rats.

In Sprague-Dawley rats at the ages of 5 weeks (young) and 9 months (adult), the activity of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase in age-matched animals was significantly higher in females than in males. The magnitude of the age-related decrease in the reductase activity was also greater in female rats. When rats were fed a cholesterol-enriched (1%) diet for 30 h as cholesterol challenge, the reduction of reductase activity depended more on sex than on age. The activity of cholesterol 7 alpha-hydroxylase was also higher in female than in male rats and it apparently remained unchanged with age in female rats while it decreased in male rats. With a cholesterol-enriched diet, the hydroxylase exhibited a significant age- and sex-dependent difference and it increased only in young males and adult females. In male rats, the concentration of hepatic cholesterol was significantly higher in adult than in young rats while it was comparable in female rats. The increase in hepatic cholesterol with dietary cholesterol was observed only in male adult rats. A significant age-related difference was observed in the concentration of serum cholesterol. The results suggest an existence of sex-dependent compensatory mechanism for maintenance of hepatic cholesterol homeostasis with age.

Isolation of rice allergenic cDNA clones from a rice cDNA library by immunoscreening with a polyclonal antibody specific to 16 kD rice allergenic protein

Clinical cases of type-1 hypersensitive reaction to rice (Oryza sativa) have been reported in western countries as well as in Japan. Among rice proteins, 14-16 kD globulin proteins encoded by multiple gene family have been identified as major rice allergens. In this study, a rice cDNA library was constructed using λ UniZap vector and screened with a rat anti-16 kD globulin protein polyclonal antibody in order to isolate Korean rice allergenic cDNA clones. Five independent cDNA clones, termed RAK1-5, were obtained after second rounds of plaque assay and immunoblot analysis. These clones encoded 13-19 kD recombinant proteins upon IPTG induction, which were identified by the polyclonal antibody in immunoblot analysis. DNA sequencing analysis showed that RAK1-4 have 99% sequence homology with RA5b, and RAK5 is closely related with RA14c. This result indicated that RA5b gene is widely distributed in our cDNA library among other possible rice allergenic genes, and more study is needed to isolate heterogeneous or novel rice allergen genes.

Comparative Effects of Dietary Palm Oil, Perilla Oil, and Soybean Oil on Lipid Profiles in Differently Aged Rats Fed on Hypercholesterolemic Diets

The effects of palm oil, soybean oil, and perilla oil on the lipid profiles of liver and serum were compared in young (1 month old) and adult (8 months old) rats fed on hypercholesterolemic diets. In young rats, the concentration of serum cholesterol was highest in the order of palm oil (PAO), soybean oil (SBO), and perilla oil (PEO), whereas it was comparable among the groups of adult rats, resulting in an age-dependent increase in the rats fed on PEO. In young rats, but not in adult rats, the ratio of HDL-/total-cholesterol was significantly increased with an increase in the degree of unsaturation of dietary fats. Dietary PAO, when compared with SBO or PEO, prevented the accumulation of liver cholesterol in adult rats, when expressed as mg per liver. No fat-effect on liver cholesterol was seen in young rats. SBO amd PEO, when compared with PAO, markedly enhanced fecal output of bile acids in adult rats. The concentration of serum triacylglycerol showed a fat-dependent response, whereas that of liver triacylglycerol showed both an ageand fat-dependent response. Thus, PAO showed an effect similar to that of SBO on the serum cholesterol level in adult animals fed on a hypercholesterolemic diet.