Influence of vitamin C on hydroxylation and side chain oxidation of cholesterol in vitro

The addition of ascorbic acid (20–160 μg) to mitochondrial preparations of rat or guinea pig liver has no effect upon the oxidation of [26-¹⁴C]-cholesterol to¹⁴CO₂. The 7α-hydroxylation of cholesterol by rat liver microsomes is also unaffected by addition of ascorbic acid. Hydroxylation by guinea pig liver microsomes is increased in the presence of ascorbic acid, but the results are not statistically significant.     

Solubilization of vitamin C in fish oil and synergistic effect with vitamin E in retarding oxidation

Antioxidative effects of ascorbic acid and δ-tocopherol on the oxidation of sardine oil stored at 30°C in the dark has been investigated. It was found from phase diagrams and peroxide values of fish oil/lecithin/water systems that the desirable levels of lecithin and water to solubilize ascorbic acid in the oil were 0.3% (w/w) and 0.1% (w/w), respectively. When ascorbic acid (0.02%) and δ-tocopherol (0.4%) were used together, the induction period of fish oil could be lengthened 22-fold, due to their synergism. They could inhibit the production of carbonyl and volatile compounds and oxidative polymerization.     

The effect of vitamin C on in vivo lipid peroxidation in guinea pigs as measured by pentane and ethane production

Measurements of pentane and ethane as indices of in vivo lipid peroxidation were made on samples of breath from vitamin C-sufficient and vitamin C-deficient guinea pigs injected with 23 μl carbon tetrachloride (CCl₄)/100 g body wt. Vitamin C-deficient animals produced significantly more pentane and ethane after CCl₄ treatment than did vitamin C-sufficient guinea pigs. Pretreatment of vitamin C-deficient animals with 75 mg ascorbic acid/100 g body wt significantly lowered both pentane and ethane evolution. Protection against in vivo lipid peroxidation similar to that provided by ascorbic acid was also found when vitamin C-deficient guinea pigs were pretreated with isoascorbic acid, reduced glutathione, α-tocopherol or β-carotene. When animals were pretreated with the radical scavenger mannitol, a protective effect was also observed as measured by pentane evolution.     

Plasma cholesterol levels in suckling and weaned kittens,puppies, and guinea pigs

Plasma cholesterol levels in kittens and puppies were low at birth, rose during the suckling period, and then decreased at about the time of weaning. The increase during the suckling period was much greater in puppies than in kittens. No significant differences in plasma cholesterol levels were observed in puppies fed two different types of diet, horse meat or dog chow, after weaning. Guinea pigs had lower plasma cholesterols than either kittens or puppies. The level was highest on the first day after birth, decreased during the next 3 wk, and then remained fairly constant after the animals were weaned.     

Effect of dietary cholesterol on bile-acid composition of gall bladder bile from guinea pigs

The composition of gall bladder bile acids from control and cholesterol-fed, anemic guinea pigs was analyzed by thinlayer-chromatographic and colorimetric techniques. In both control and cholesterol-fed animals, the gall bladder bile acids constituted about one third of the total bile solids. The main component of the bile acids of both groups of animals was chenodexycholic acid, which was predominantly conjugated with glycine. No cholic acid was present although this is the main bile acid in most mammals. The major difference in bile composition between control and cholesterol-fed animals was the conjugation pattern of chenodeoxycholic acid. The ratio of glycochenodeoxycholic to taurochenode-oxycholic acid was high, 6.4, for control animals, and decreased to 2.4 for the cholesterol-fed, anemic animals. Impaired liver function, limited availability of glycine, and greater efficiency of taurocholanic acids for the disposal of excess cholesterol may be involved in the mechanism for this phenomenon. Material in this paper has been submitted in partial satisfaction of the requirements for the degree of Master of Science in Nutition in the Graduate Division of the University of California, Berkeley. A portion of this material was presented at the 7th International Congress of Biochemistry in Tokyo, Japan, August, 1967.     

Effect of dietary vitamin C on adrenal cholesteryl ester content in the guinea pig

Male guinea pigs fed a vitamin C-deficient diet for 3 weeks had lower concentrations of cholesteryl esters in their adrenals than did control animals fed the recommended intake of the vitamin. Not all esters were affected to the same degree, and the fatty acid profiles of the esters from control and deficient guinea pigs differed; there was proportionately more palmitic and linoleic acids and less docosatetraenoic acid [22∶4 (n−6)] in the deficient guinea pig adrenal esters. [Fatty acids are designated as X∶Y (n−Z), where X and Y are the numbers of carbon atoms and olefinic bonds in the acid and Z is the number of carbon atoms after the terminal olefinic bond.] A 100-fold excess of vitamin C in the diet also resulted in lower concentrations of adrenal cholesteryl esters than did the control diet, but they were not as low as in the deficient animals. Fatty acid profiles were similar for esters from control and excessively supplemented guinea pigs. Vitamin C deficiency apparently imposes a long term stress which results in a depletion of adrenal cholesteryl esters, possibly specific esters, to meet the requirements for glucocorticoid synthesis.     

Sparing effects of selenium and ascorbic acid on vitamin C and E in guinea pig tissues

Background

Selenium (Se), vitamin C and vitamin E function as antioxidants within the body. In this study, we investigated the effects of reduced dietary Se and L-ascorbic acid (AA) on vitamin C and α-tocopherol (AT) status in guinea pig tissues.

Methods

Male Hartley guinea pigs were orally dosed with a marginal amount of AA and fed a diet deficient (Se-D/MC), marginal (Se-M/MC) or normal (Se-N/MC) in Se. An additional diet group (Se-N/NC) was fed normal Se and dosed with a normal amount of AA. Guinea pigs were killed after 5 or 12 weeks on the experimental diets at 24 and 48 hours post AA dosing.

Results

Liver Se-dependent glutathione peroxidase activity was decreased (P < 0.05) in guinea pigs fed Se or AA restricted diets. Plasma total glutathione concentrations were unaffected (P > 0.05) by reduction in dietary Se or AA. All tissues examined showed a decrease (P < 0.05) in AA content in Se-N/MC compared to Se-N/NC guinea pigs. Kidney, testis, muscle and spleen showed a decreasing trend (P < 0.05) in AA content with decreasing Se in the diet. Dehydroascorbic acid concentrations were decreased (P < 0.05) in several tissues with reduction in dietary Se (heart and spleen) or AA (liver, heart, kidney, muscle and spleen). At week 12, combined dietary restriction of Se and AA decreased AT concentrations in most tissues. In addition, restriction of Se (liver, heart and spleen) and AA (liver, kidney and spleen) separately also reduced AT in tissues.

Conclusion

Together, these data demonstrate sparing effects of Se and AA on vitamin C and AT in guinea pig tissues.     

Cholesterol oxidation in heated lard enriched with two levels of cholesterol

Cholesterol oxidation in lard containing two levels of added cholesterol was monitored using capillary gaschromatography. Loss of cholesterol and formation of cholesterol oxidation products (COPs) were measured. Lard samples with 10 times (Test I) and 2 times (Test II) the amount of cholesterol originally found in each batch of lard were heated at 180°C for 10 hr a day for 240 and 160 hr, respectively. Cholesterol steadily decreased throughout the heating period in both tests. Cholesterol loss followed a first-order reaction rate, with a rate constant (k) of −1.18×10⁻³ h⁻¹ for Test I and −9.45×10⁻³ h⁻¹ for Test II. The COPs accumulated during both heating tests. But the amount of COPs formed did not total the amount of cholesterol lost. During heating, thermal degradation of cholesterol likely occurred, and those products were not detected. During cooling, hydroperoxides formed, which further oxidized into the COPs that were detected. The 7-ketocholesterol and 5α,6α-epoxycholesterol were the predominant COPs formed. The isomeric 7α-and 7β-hydroxycholesterols also accumulated in the heating tests. The 3β,5α,6β-cholestantriol was found in very small amounts and the 25-hydroxycholesterol was not detected. Presented in part at the 80th AOCS Annual Meeting, Cincinnati, OH, in May, 1989.     

Biokinetics of dietaryRRR-α-tocopherol in the male guinea pig at three dietary levels of vitamin C and two levels of vitamin E. Evidence that vitamin C does not “spare” vitamin Ein vivo

The net rates of uptake of “new” and loss of “old”2R,4′ R,8′ R-α-tocopherol (RRR-α-TOH, which is natural vitamin E) have been measured in the blood and in nine tissues of male guinea pigs over an eight week period by feeding diets containing deuterium-labelled α-tocopheryl acetate (d ₆-RRR-α-TOAc). There was an initial two week “lead-in” period during which 24 animals [the “high” vitamin E (HE) group] received diets containing 36 mg of unlabelled (d ₀)RRR-α-TOAc and 250 mg of ascorbic acid per kg diet, while another 24 animals [the “low” vitamin E (LE) group] received diets containing 5 mgd ₀-RRR-α-TOAc and 250 mg ascorbic acid per kg diet. The HE group was then tivided into three equal subgroups, which were fed diets containing 36 mgd ₆-RRR-α-TOAc and 5000 mg [the “high” vitamin C (HEHC) subgroup], 250 mg [the “normal” vitamin C (HENC) subgroup] and 50 mg [the “low” vitamin C (HELC) subgroup] ascorbic acid per kg diet. One animal from each group was sacrificed each week and the blood and tissues were analyzed ford ₀- andd ₆-RRR-α-TOH by gas chromatography-mass spectrometry. The LE group was similarly divided into three equal subgroups with animals receiving diets containing 5 mgd ₆-RRR-α-TOAc and 5,000 mg (LEHC), 250 mg (LENC) and 50 mg (LELC) ascorbic acid per kg diet with a similar protocol being followed for sacrifice and analyses. In the HE group the totald ₀-+d ₆-)RRR-α-TOH concentrations in blood and tissues remained essentially constant over the eight week experiment, whereas in the LE group the totalRRR-α-TOH concentrations declined noticeably (except in the brain, an organ with a particularly slow turnover of vitamin E). There were no significant differences in the concentrations of “old”d ₀-RRR-α-TOH nor in the concentrations of “new”d ₆-RRR-α-TOH found in any tissue at a particular time between the HEHC, HENC and HELC subgroups, nor between the LEHC, LENC and LELC subgroups. We conclude that the long-postulated “spring” action of vitamin C on vitamin E, which is well documentedin vitro, is of negligible importancein vivo in guinea pigs that are not oxidatively stressed in comparison with the normal metabolic processes which consume vitamin E (e.g., by oxidizing it irreversibly) or elminate it from the body. This is true both for guinea pigs with an adequate, well-maintained vitamin E status and for guinea pigs which are receiving insufficient vitamin E to maintain their body stores. The biokinetics of vitamin E uptake and loss in the HE guinea pigs are compared with analogous data for rats reported previously (Lipids 22, 163–172, 1987). For most guinea pig tissues the uptake of vitamin E under “steadystate” conditions was faster than for the comparable rat tissues. However, the brain was an exception with the turnover of vitamin E occurring at only one-third of the rate for the rat. NRCC Publication No. 30775.     

豚鼠对EB病毒的易感性分析

目的建立豚鼠感染EB病毒(Epstein-Barr virus,EBV)动物模型,分析EBV对豚鼠的易感性。方法将EBV经鼻腔和口腔感染豚鼠,建立感染EBV动物模型。提取分离的豚鼠淋巴细胞总RNA,巢式PCR法检测EBNA1及BcLF1基因mRNA的表达水平;ELISA法检测豚鼠血清中抗EBV IgG抗体水平的变化。取豚鼠肝脏、肺、脾脏、腮腺进行病理分析。结果10只模型组豚鼠中有6只检测到BcLF1基因mRNA的表达,其中有4只同时检测到了EBNA1和BcLF1基因mRNA的表达;经双酶切及测序鉴定,扩增的EBNA1及BcLF1基因大小与预期相符。10只豚鼠血清中VCA IgG和EBNA-IgG抗体水平均有所升高。模型组中有5只豚鼠的肝脏、肺、脾脏、腮腺的组织发生不同程度的病变。结论豚鼠可作为EBV感染动物模型的备选动物。     

Lipoprotein lipase in cholesterol-fed and control guinea pigs

A study of the in vitro activity of lipoprotein lipase of guinea pigs has shown that (a) the lipolytic activity of activated post-heparin serum is depressed in hypercholesteremic guinea pigs compared to the serum of normocholesteremic guinea pigs; and (b) this depressed lipolytic activity in hypercholesteremic guinea pigs is not due to the presence of an inhibitor.     

Gamma-irradiation of individual cholesterol oxidation products

Cholesterol and seven of its oxidation products in aqueous suspensions of multilamellar vesicles or sonicated aqueous suspensions were subjected individually to γ-radiation (10 KGy) at 0–4°C in air, N₂ or N₂O. All compounds underwent some changes under the influence of radiation. β-Epoxide (cholesterol 5β,6β-epoxide) and, to a much lesser extent, α-epoxide (cholesterol 5α,6α-epoxide) were converted in low yield to 6-ketocholestanol (5α-cholestan-3β-ol-6-one). 7β-Hydroxycholesterol (cholest-5-ene-3β,7β-diol) and, to a lesser extent, 7α-hydroxycholesterol (cholest-5-ene-3β,7α-diol) gave low yields of 7-ketocholestanol (5α-cholestan-3β-ol-7-one). The latter compound also was obtained by irradiation of 7-ketocholesterol (cholest-5-ene-3β-ol-7-one). 6-Ketocholestanol and 7-ketocholestanol are potential biomarkers for irradiated meat and poultry.     

Wide variations of plasma triglyceride concentrations in guinea pigs

Guinea pigs have varying plasma triglyceride concentrations ranging from 28 to 1392 mg/dl, with relatively uniform plasma cholesterol and phospholipid levels. To understand why the animals exhibit such wide variations of plasma triglyceride concentrations, we have explored the triglyceride hydrolyzing system by measuring tissue lipoprotein lipase activities and plasma activator for the enzyme. Lipoprotein lipase activities of epididymal adipose tissue of these animals were 759±117 (mean±SE) n moles FFA·min⁻¹·g wet tissue⁻¹, markedly low compared with those of rats. There were no relationships between plasma triglyceride concentrations and tissue lipase activities. Plasma activator for lipoprotein lipase was lacking in this animal. Guinea pigs with ascorbic acid deficiency for 2 weeks also showed marked variations of plasma triglyceride concentrations, without any changes in tissue lipoprotein lipase activities. Low adipose tissue lipoprotein lipase activities with deficient plasma activator for the enzyme suggest that the lipoprotein lipase-mediated triglyceride degradation could be impaired in this animal, and this may account for the marked variation of plasma triglyceride concentrations.     

Maternal vitamin D deficiency associated with neonatal hypocalcaemic convulsions

Maternal vitamin D insufficiency is not uncommon. Infants born to mothers who are deficient in vitamin D and or calcium, usually due to cultural modifications in their diets or clothing habits, and in addition are breastfed, are at risk of developing vitamin D deficiency and hypocalcaemia. We present a case of neonatal hypocalcaemic seizures secondary to vitamin D deficiency.     

In vitro oxidation of vitamins C and E,cholesterol, and thiols in rat brain synaptosomes

Free radical-induced oxidation of vitamins C, E, sulfhydryl compounds, and cholesterol in brain synaptosomes from Fisher 344 rats was studied. The synaptosomes were incubated at 37°C with 2,2′-abobis-(2-amidinopropane) dihydrochloride (AAPH), which undergoes thermal decomposition to yield free radicals. After incubation, the synaptosomes were sedimented, saponified, and extracted with hexane to isolate tocopherol and cholesterol. Ascorbate and tocopherol were assayed by liquid chromatography, cholesterol by gas chromatography, and total sulfhydryls by spectrophotometry. Under thein vitro conditions used in this study, the approximate order for the ease of oxidation of the various compounds was: ascorbate ≫tocopherol>sulfhydryl compounds⋙cholesterol. However, tocopherol and sulfhydryl oxidation occurred even before all of the ascorbate had been consumed. Therefore, the fate of a specific antioxidant at a particular cellular location cannot be predicted with complete accuracy using thein vitro order for ease of oxidation shown here. Ascorbate may play a major role in protecting brain against oxidative damage because: (i) ascorbate concentration is high in brain, (ii) it can regenerate vitamin E from its radical oxidation product, and (iii) it is one of the first antioxidants to be consumed during oxidative reactions.     

Cholesterol esterifying capacity of various organs in cholesterol-fed guinea pigs

In guinea pigs fed a diet enriched with 1% cholesterol, the liver, adrenals, spleen, and small intestine accumulated cholesterol much more than the lungs and kidneys. The cholesterol content of the aorta, stomach and colon was not increased by the diet. Cholesteryl ester was the predominant form of cholesterol deposited in the organs richest in this sterol and the total cholesterol content of a tissue tended to increase with the proportion of cholesteryl ester. Cholesterol esterifying activity (ACAT) was found in most tissues and paralleled the cholesteryl ester content of these tissues, being highest in the adrenals, liver, spleen and the proximal part of the small intestine. ACAT activity was enhanced by the cholesterol diet and its elevation was fairly well correlated with the increase in the cholesterol content of the organs. However, the liver and adrenals tended to accumulate more cholesterol than anticipated from their cholesteryl ester content and their ACAT activity. Cholesterol esterification may play a major role in the ability of organs to accumulate cholesterol.     

Enzyme-resistant fractions of beans lowered serum cholesterol and increased sterol excretions and hepatic mRNA levels in rats

Feeding rats beans with resistant starch reduces their serum cholesterol concentration; however, the mechanism by which this occurs is not fully understood. We examined the effects of enzyme-resistant fractions of adzuki (Vigna angularis) and tebou (Phaseolus vulgaris, var.) beans on serum cholesterol and hepatic mRNA in rats. Rats were fed a cholesterol-free diet with 50 g of cellulose powder (CP)/kg, 50 g of an enzyme-resistant fraction of adzuki starch (AS)/kg, or 50 g of an enzyme-resistant fraction of tebou starch (TS)/kg diet for 4 wk. There were no significant differences in body weight, liver weight, and cecum contents among the groups, nor was there a significant difference in food intake among the groups. The levels of serum total cholesterol, VLDL + intermediate density lipoprotein + LDL-cholesterol, and HDL cholesterol in the AS and TS groups were significantly (P<0.05) lower than in the CP group throughout the feeding period. Total hepatic cholesterol in the CP group was significantly (P<0.05) lower than in the AS and TS groups, fecal cholesterol excretion in the TS group was significantly (P<0.05) greater than in the CP and AS groups, and the fecal total bile acid concentrations in the AS and TS groups were significantly (P<0.05) higher than in the CP group. Cecal acetate, propionate, and n-butyrate concentrations in the AS and TS groups were significantly (P<0.05) higher than in the CP group. The level of hepatic scavenger receptor class B1 (SR-B1) mRNA in the TS group was significantly (P<0.05) higher than in the CP group, and the levels of hepatic cholesterol 7α-hydroxylase mRNA in the AS and TS groups were significantly (P<0.05) higher than in the CP group. These results suggest that AS and TS have a serum cholesterol-lowering function due to the enhanced levels of hepatic SR-B1 and cholesterol 7α-hydroxylase mRNA.     

Effects of dietary cholesterol upon bile acid metabolism in guinea pig

Cholesterol fed guinea pigs develop a hemolytic anemia accompanied by high cholesterol concentrations in the liver, plasma, and red cells. We have studied the bile acid metabolism of guinea pigs fed a diet with or without cholesterol in a search for the factor(s) which prevent adequate control of their body cholesterol pool and, therefore, its pathological consequences. The results show that in the cholesterol fed guinea pig the synthesis (and excretion) of bile acids was at least three times greater than in controls. This is the result of a doubling of the fractional turnover rate and a smaller increase in the pool size. The major increase of the bile acid pool was in the liver. The main bile acid in gall bladder bile and small intestines was chenodeoxycholic acid, with smaller amounts of 7-ketolithocholic and ursodeoxycholic acids. In the caecum, large intestines, and feces, the major bile acid was lithocholic acid.     

Perineal scent gland of wild and domestic guinea pigs

Wild and domestic male guinea pigs (Cavia aperea andCavia porcellus) prefer the perineal secretion from males of the same species to that of males of the other species. Gas chromatographic-mass spectroscopic analyses of the volatile components of the secretions show complex mixtures comprised primarily of fatty acids, alcohols, and ketones. Inter-species differences in the composition of the volatiles are evident. The possible role of bacteria in odor production is discussed.Camille and Henry Dreyfus Teacher-Scholar, 1978–1983.     

Effect of dietary taurine on bile acid metabolism in guinea pigs

The effect of oral administration of taurine (200–300 mg daily) on the metabolism of bile acids was studied in male guinea pigs which have predominantly glycine conjugated bile acids. The results were summarized as follows: (a) oral administration of taurine for 10 days increased taurine-conjugated bile acids and the ratio of glycine-to taurine-conjugated bile acids (G:T ratio) shifted from 3.95 to 0.19; (b) in taurine fed guinea pigs, the half-life of chenodeoxycholic acid (CDC) was about 40% shorter than that in controls and the fractional turnover rate increased by 70%; (c) the synthetic rate (mg/day/500 g body weight) of bile acids increased from 4.28 to 7.27 by taurine feeding; (d) hepatic cholesterol 7α-hydroxylase activity was increased 2.4-fold by taurine feeding; (e) the total pool size of bile acids did not change significantly but the amount of lithocholic acid in the caecum and large intestine increased by about 40%; (f) neither free cholesterol nor cholesterol ester levels in liver and serum changed significantly. Results of this study suggest that changing the G:T ratio in the bile acid conjugation pattern may influence the rate of hepatic bile acid synthesis. This paper is Part IX of a series entitled “Metabolism of Bile Acids”. Part VIII: ref. 12.