Quantification and characterization of aortic cholesterol in rabbits fed a high-cholesterol diet

Determination of fat percentage of aortic intimal area stained by Sudan III is useful as an index of atherosclerosis in the rabbit animal model. However, the determination of sudanophilic area of the thoracic aorta is two-dimensional and does not measure the third dimension of depth. The objective of the present study was to quantify and characterize aortic lipids using the gas–liquid chromatographic (GLC) technique and to determine whether elevated measurements of total cholesterol and cholesteryl esters was correlated with increased measurements of sudanophilic area staining of the thoracic aorta in rabbits given either a normal chow or a 1% cholesterol diet. The GLC results showed that there was a mean accumulation of 10.9 mg of cholesterol per gram of aortic tissue in the rabbits given a cholesterol diet (mean sudanophilic area of 23.8%). In contrast, rabbits on a normal chow diet had only a deposition of 0.58 mg of cholesterol per gram of the aortic tissue diet (mean sudanophilic area of 1.4%). The present study suggests that quantification of the aortic lipids can be performed by using GLC techniques and that it could be used as an alternative to the measurement of sudanophilic area when assessing the severity of atherosclerosis.     

Quantification and characterization of aortic cholesterol in rabbits fed a high-cholesterol diet

Determination of fat percentage of aortic intimal area stained by Sudan III is useful as an index of atherosclerosis in the rabbit animal model. However, the determination of sudanophilic area of the thoracic aorta is two-dimensional and does not measure the third dimension of depth. The objective of the present study was to quantify and characterize aortic lipids using the gas-liquid chromatographic (GLC) technique and to determine whether elevated measurements of total cholesterol and cholesteryl esters was correlated with increased measurements of sudanophilic area staining of the thoracic aorta in rabbits given either a normal chow or a 1% cholesterol diet. The GLC results showed that there was a mean accumulation of 10.9 mg of cholesterol per gram of aortic tissue in the rabbits given a cholesterol diet (mean sudanophilic area of 23.8%). In contrast, rabbits on a normal chow diet had only a deposition of 0.58 mg of cholesterol per gram of the aortic tissue diet (mean sudanophilic area of 1.4%). The present study suggests that quantification of the aortic lipids can be performed by using GLC techniques and that it could be used as an alternative to the measurement of sudanophilic area when assessing the severity of atherosclerosis.     

Effects of dietary calcium on atherosclerosis, aortic calcification, and icterus in rabbits fed a supplemental cholesterol diet

Background  

Vascular calcification is implicated in myocardial infarction, instability and rigidity of the aortic wall, and bioprosthetic failures. Although an increase in the calcium (Ca) content in atherogenic diets has been shown to decrease atherosclerosis in rabbits, whether Ca supplementation and deficiency can affect atherosclerosis-related aortic calcification remains unknown.     

Plasma lipids and lipoproteins in normo- and in hyperlipidemic rabbits fed plant protein diets

The effect of a diet based on a plant protein mixture, on plasma lipids and lipoproteins was evaluated in normo-and in hyperlipidemic rabbits. The proteins comprising the experimental diet consisted of equal amounts of soy protein, cottonseed protein and wheat gluten, and was supplemented with lysine, methionine and threonine to their respective levels in casein which was the control diet. Each diet was served with (0.25%) and without cholesterol. The normolipidemic rabbits were fed the various diets for 55 days. When rendered hyperlipidemic, animals were pre-fed for 20 days the cholesterol containing casen diet and subsequently given the experimental diets for an additional 35 day period. The plant protein diet had a marked hypocholesterolemic effect, and induced a reduction in the cholesterol and in the protein VLDL + LDL to HDL ratios that were used as atherogenic parameters.     

Effect of curcumin on LDL oxidation in vitro, and lipid peroxidation and antioxidant enzymes in cholesterol fed rabbits

In this study we examined the antioxidant effect of curcumin on lipid oxidation in vitro and in vivo. In vitro, curcumin at 5 microgM concentration completely prevented low-density lipoprotein (LDL) oxidation by CuS0(4), indicating that curcumin is an effective antioxidant in vitro. In vivo, feeding a pure cholesterol (PC)-rich diet to rabbits significantly increased the plasma and liver lipids as well as thiobarbituric acid reactive substances (TBARS) levels. Addition of curcumin to the PC diet did not show any effect on either plasma lipid and TBARS or liver lipids. Liver TBARS tended to decrease but that decrease was not significant. Erythrocyte glutathione peroxidase (GSH-Px) activity was significantly decreased while catalase activity was significantly increased in rabbits fed a PC diet. The addition of curcumin to a PC diet did not show any significant effect on erythrocyte enzyme activities compared to the rabbits fed a PC diet. The liver GSH-Px and catalase activities were significantly decreased in rabbits fed a PC diet, but the addition of curcumin to the PC diet enhanced the liver GSH-Px activity, which became nonsignificantly different from the control group. These results were discussed considering that curcumin may not be well absorbed and it did not reach a level high enough in vivo to overcome the severe hypercholesterolemia and oxidative stress produced by the PC-rich diet.     

Hawthorn fruit is hypolipidemic in rabbits fed a high cholesterol diet.

The present study examined the hypolipidemic activity of hawthorn fruit. New Zealand white rabbits were fed one of three diets, a reference diet with no cholesterol added (NC), a high cholesterol diet (1 g/100 g, HC) and a HC diet supplemented with 2 g/100 g hawthorn fruit powder (HC-H). After 12 wk, serum total cholesterol (TC) and triacylglycerols (TG) were 23.4 and 22.2% lower, respectively, in the hawthorn fruit group compared with the HC rabbits (P < 0.05). Hawthorn supplementation led to 50.6% less cholesterol accumulation in aorta (P < 0.05) and 23-95% greater excretion of neutral and acidic sterols (P < 0.05). Supplementation of hawthorn fruit did not affect the activities of hepatic 3-hydroxy-3-methyl glutaryl coenzyme A reductase (HMG-CoA-R) or cholesterol 7alpha-hydroxylase (CH) but it suppressed the activity of intestinal acyl CoA:cholesterol acyltransferase (ACAT, P < 0.05). The results suggest that the mechanism by which hawthorn fruit decreases serum cholesterol involves, at least in part, the inhibition of cholesterol absorption mediated by down-regulation of intestinal ACAT activity.     

Trans fatty acids and cholesterol metabolism: mechanistic studies in rats and rabbits fed semipurified diets

Studies were conducted in rabbits and rats to investigate the effects of diets rich in oleic (CIS diet), palmitic (SAT diet) and trans fatty acids (TRANS diet) on plasma lipids and lipoprotein metabolism. An important difference between these species is that rabbits possess plasma cholesteryl ester transfer protein (CETP) activity while rats are devoid of transfer activity. In the presence of dietary cholesterol (0.2% w/w) the change in plasma low density lipoprotein-cholesterol (LDL-C) concentration from baseline was significantly higher in rabbits fed the TRANS diet compared with those fed the CIS diet (P < 0.01). Despite this difference, the hepatic LDL-receptor activity was similar in all groups. Also, the fatty acid composition of hepatic phospholipids was affected by diet with lower proportion of palmitic (11%) and higher (19%) linoleic acid despite a similar content in the diet. These effects may represent the maintenance of membrane fluidity within narrow limits to ensure optimal function. The studies in rats showed that the plasma total cholesterol concentration was 20% lower (P < 0.01) in TRANS-fed rats compared with those fed the CIS diet. The results of an in vivo assay of reverse cholesterol transport (RCT) suggested that the three diets gave rise to high density lipoprotein (HDL) particles with similar capacity to accept cellular cholesterol. The differential effects of dietary trans fatty acids in these animal models provide another line of evidence that reinforces the significant role of CETP activity in determining the distribution of plasma cholesterol in response to dietary trans fatty acids.     

Trans fatty acids and cholesterol metabolism: mechanistic studies in rats and rabbits fed semipurified diets

Studies were conducted in rabbits and rats to investigate the effects of diets rich in oleic (CIS diet), palmitic (SAT diet) and trans fatty acids (TRANS diet) on plasma lipids and lipoprotein metabolism. An important difference between these species is that rabbits possess plasma cholesteryl ester transfer protein (CETP) activity while rats are devoid of transfer activity. In the presence of dietary cholesterol (0.2% w/w) the change in plasma low density lipoprotein-cholesterol (LDL-C) concentration from baseline was significantly higher in rabbits fed the TRANS diet compared with those fed the CIS diet (P < 0.01). Despite this difference, the hepatic LDL-receptor activity was similar in all groups. Also, the fatty acid composition of hepatic phospholipids was affected by diet with lower proportion of palmitic (11%) and higher (19%) linoleic acid despite a similar content in the diet. These effects may represent the maintenance of membrane fluidity within narrow limits to ensure optimal function. The studies in rats showed that the plasma total cholesterol concentration was 20% lower (P < 0.01) in TRANS-fed rats compared with those fed the CIS diet. The results of an in vivo assay of reverse cholesterol transport (RCT) suggested that the three diets gave rise to high density lipoprotein (HDL) particles with similar capacity to accept cellular cholesterol. The differential effects of dietary trans fatty acids in these animal models provide another line of evidence that reinforces the significant role of CETP activity in determining the distribution of plasma cholesterol in response to dietary trans fatty acids.     

Erythrocyte lipid peroxidation and (Na+ + K+)-ATPase activity in cholesterol fed rabbits

Cholesterol, phospholipid and lipid peroxide levels in plasma and erythrocytes as well as membrane-bound (Na+ + K+)-ATPase activity were determined in rabbits fed a high-cholesterol diet for 3 months. While cholesterol feeding caused an increase in lipid peroxide levels, (Na+ + K+)-ATPase activity was found to be reduced. According to this, we can assume that, in high-cholesterol fed rabbits, elevated lipid peroxides may be one of the responsible factors for the decreased erythrocyte (Na+ + K+)-ATPase activity.     

Influence of eicosapentaenoic acid and vitamin E on hepatic hydroxyproline content in rabbits fed cholesterol-rich diet

The effect of eicosapentaenoic acid (EPA) and vitamin E on hepatic hydroxyproline content, as an index of collagen was examined in rabbits receiving cholesterol rich diets for a period of 45 days. Rabbits were divided as control (A) and cholesterol fed groups (B, C, D). Group C received 80 mg. of EPA and group D received 100 IU of vitamin E daily in addition to the cholesterol rich diet (2% w/w) which was solely given to group B. The maintenance of rabbits on high cholesterol diets resulted in significantly increased liver cholesterol concentrations. This effect was most pronounced in rabbits receiving cholesterol alone. Hepatic triglyceride levels remained unchanged in all cholesterol-fed rabbits, but total phospholipid levels in liver significantly decreased in EPA and vitamin E supplemented rabbits. An interesting finding was the increase in hepatic hydroxyproline content in rabbits following the administration of EPA and vitamin E to cholesterol rich diet.     

Effects of dietary calcium on blood and tissue lipids, tissue phospholipids, calcium and magnesium levels in rabbits fed diets containing beef tallow.

Levels of lipids, calcium and magnesium in blood and tissue were examined in rabbits to determine the effects of 20% beef tallow diets containing three levels of calcium, less than 0.02, 0.8 or 1.6%. In plasma, the calcium-deficient (less than 0.02%) diet contributed to elevated cholesterol and phospholipid, but had no effect on triglyceride levels. Plasma calcium decreased in the calcium-deficient group and plasma magnesium decreased in the high-calcium (1.6%) group of rabbits. Lipid levels of some tissues varied with the level of dietary calcium. Cholesterol, total phospholipid, sphingomyelin and phosphatidylethanolamine were generally elevated in livers of calcium-deficient rabbits, but the individual phospholipids were decreased in skeletal muscle. Lungs of the calcium-deficient group also had lower phospholipid levels than the high-calcium group. Liver, kidneys, brain and adipose tissue triglyceride levels were highest in the high-calcium group. The calcium level of skeletal muscle was lower in the calcium-deficient group than in the high-calcium group. Calcium in brain and adipose tissue were highest in the calcium-deficient group. Except for adipose tissue, magnesium levels of the tissues studied were not affected by dietary calcium.     

Uptake, toxicity, and effects on detoxication enzymes of atrazine and trifluoroacetate in embryos of zebrafish

The uptake, toxicity, and elimination of atrazine and trifluoroacetate (TFA) were studied in early life stages of the zebrafish (Danio rerio). Furthermore, the effects of these xenobiotics on soluble (s) and microsomal (m) glutathione S-transferases (GST) of zebrafish embryos were investigated using 1-chloro-2,4-dinitrobenzene (CDNB), 1,2-dichloro-4-nitrobenzene (DCNB), and [(14)C]atrazine. [(14)C]Atrazine was taken up by the embryos within seconds, unhindered by the chorions. It accumulated in the embryos by a factor of 19 after 24 h of exposure time. LC(50) (48 h) was determined at 36.8 mg/L. At a level of 5 mg/L atrazine, activities of s and m GSTs were elevated in most stages, especially in prim 6 and long pec stage (24, 48 h after fertilization, respectively). GST activity toward atrazine was detectable only in untreated D. rerio eggs, increasing with developmental time. [(14)C]Atrazine was eliminated from the embryos between 24 and 48 h, indicating a possible metabolism to a more hydrophilic GSH conjugate. [(14)C]TFA was taken up by embryos, reaching at maximum fivefold the concentration of the incubation medium after 10 h. The chorions served no physiological protection. TFA (1 g/L) caused low elevation of the GST activity. No acute toxic effects (48 h) were observed up to 4 g/L TFA.     

Uptake,metabolism, and effects on detoxication enzymes of isoproturon in spawn and tadpoles of amphibians

Using ring-(14)C-labeled isoproturon (1 microg/L), the uptake into spawn and tadpoles of Bombina bombina and Bombina variegata was investigated. Two percent of the applied radioactivity was found per gram fresh weight in the embryo after 24h. Results indicate that the jelly mass of the spawn does not act as a sufficient physical barrier for protection against the uptake and influence of isoproturon (IPU) on the embryo. In vivo metabolism of ring-14C-labeled IPU by the cytochrome P-450 system was analyzed in tadpoles. Different metabolites of IPU, such as N-demethylated and C-hydroxylated derivatives, and the olefinic metabolite were detected. In tadpoles of B. variegata, the activity of microsomal and soluble glutathione-S-transferase (sGSTs) toward different model substrates was measured after treatment with IPU. Activities of sGST increased corresponding to elevated stress by IPU dependent on exposure time and dose. Compared to the pure active ingredient IPU, the commercial phenyl-urea herbicide Tolkan Flo, consisting of IPU and an emulsifier, also caused significantly elevated enzymatic response.