Maria Luz Fernandez

Dietary fat-mediated changes in hepatic apoprotein B/E receptor in the guinea pig: effect of polyunsaturated, monounsaturated, and saturated fat.

These studies investigated the effects of dietary fat quality on guinea pig plasma total and low-density lipoprotein (LDL) cholesterol and triglyceride levels; LDL composition, density, and binding affinity to hepatic apolipoprotein (apo) B/E receptors; and hepatic apo B/E receptor levels. Animals were fed semi-synthetic diets containing 7.5% (weight per weight) fat--either corn oil (CO), olive oil (OL), or lard. Plasma cholesterol levels were significantly lower on the CO diet compared with the OL and lard diets. The isolated LDL had mean peak densities that ranged from 1.071 for LDL from lard-fed animals to 1.075 for LDL from CO- and OL-fed animals. The cholesterol ester to protein ratio of the LDL particle decreased in CO-fed guinea pigs. Binding studies showed that these compositional changes of the LDL had no effect on the binding affinity of the particles to a standardized hepatic membrane preparation. Membrane phospholipid fatty acid compositions were significantly different among the three dietary fat groups. When hepatic membranes were incubated with 125I-labeled LDL, the receptor-mediated binding of LDL to membranes from CO-fed animals increased 1.5-fold compared with binding to membranes from OL- and lard-fed guinea pigs. Scatchard plots indicated an increase of 50% in receptor number in membranes of animals fed the CO diet, whereas the affinity of the hepatic apo B/E receptor for LDL (Kd) was virtually identical for all membranes.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiovascular consequences of new-onset hyperglycemia after kidney transplantation.

Background New-onset diabetes after transplantation (NODAT) is associated with high cardiovascular (CV) risk and reduced patient survival. It is unclear whether this risk is newly acquired or represents preexisting CV disease in patients with this complication. Methods Included are 1146 adults, recipients of first kidney transplants from 1984 to 2008 treated with modern immunosuppressants. Results One year after transplantation, 29.8% of patients experienced impaired fasting glycemia and 13.4% NODAT. The risk of NODAT related to recipient variables include the following: older age, male gender, higher body mass index, higher pretransplantation glucose and triglyceride levels, and lower high-density lipoprotein level. Increasing fasting glucose levels at 1, 4, or 12 months after transplantation, independent of other factors, related to reduced patient survival (12 months hazard ratio [HR]=1.146 [1.132–1.161], P<0.0001 for 10mg/dL increase in glucose), and this was primarily because of an increase in CV deaths. Hyperglycemia related to all major CV events (MCVE), cardiac (HR=1.113 [1.094–1.132], P<0.0001), vascular (HR=1.168 [1.140–1.197], P<0.0001), and strokes (HR=1.156 [1.123–1.191], P=0.003). These relations were statistically independent of other risk factors. The increased risk of MCVE was noted particularly in patients without MCVE before transplantation (HR=1.145 [1.126–1.165], P<0.0001). Furthermore, among patients with after transplantation MCVE (n=123, 11%), hyperglycemia increases the risk of death (NODAT: HR=2.410 [1.125–5.162], P=0.024). Conclusions After transplantation hyperglycemia is a strong independent risk factor for MCVE and death, mainly from CV causes. This risk is independent of the presence of CV disease identified before transplantation.

Whole body and hepatic cholesterol synthesis rates in the guinea-pig: effect of dietary fat quality.

The effects of polyunsaturated, monounsaturated and saturated dietary fat on total and hepatic cholesterol synthesis were studied in the guinea-pig. Male Hartley guinea-pigs were fed semi-synthetic diets containing 7.5% (w/w) of either corn oil (CO), olive oil (OL) or lard for a period of 5 weeks and rates of endogenous cholesterol synthesis were determined from the incorporation of [3H]water into digitonin-precipitable sterols (DPS) and by measurement of sterol balance. In addition, total and expressed 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activities were determined in hepatic microsomes. Rates of whole body cholesterol synthesis determined by incorporation of [3H]water into DPS were significantly lower for guinea-pigs on the CO diet with values of 18.7 +/- 1.8 mumol/h (n = 4) vs. 26.7 +/- 4.8 and 24.6 +/- 1.8 mumol/h for animals on the OL (n = 4) and lard (n = 3) diets (P less than 0.001), respectively. Hepatic cholesterol synthesis rates were significantly decreased in animals on the OL diet, whether determined from incorporation of [3H]water into DPS or by analysis of HMG-CoA reductase activity. Hepatic total and free cholesterol levels were not different for animals on the three dietary fats; however, cholesteryl ester levels were 35% lower in guinea-pigs fed the lard diet (P less than 0.02). Sterol balance measurements indicated that whole body cholesterol synthesis rates were not affected by dietary fat quality (51.9 +/- 12.2, 42.8 +/- 7.6 and 51.2 +/- 20.2 mg/kg per day for animals on the CO, OL and lard diets, respectively). This is in striking contrast to the observed reduction in cholesterol synthesis rates for animals on the polyunsaturated CO diet as determined by incorporation of [3H]water into DPS. One possible explanation for the discrepancy between the sterol balance and [3H]water incorporation data is a polyunsaturated fat-mediated effect on energy utilization, which affects the equilibration of NADPH with the body water pool such that the [3H]NADPH has a lower specific activity than body [3H]water.

Nutritional evaluation of chickpea and germinated chickpea flours

The ability of seed germination to increase the nutritional quality of chickpea was studied. Chickpea flours germinated for 0, 24 and 48 h were evaluated nutritionally by determination of protein efficiency ratio (PER), net protein ratio (NPR), digestibility and essential amino acid availability “in vivo”. A significant increase in ascorbic acid was observed during germination. PER and NPR values indicated that germinated chickpea flours compared favorably to casein. Protein digestibility decreased as germination time increased. Essential amino acid availability did not change after 24 h of germination, but a small decrease was observed after 48 h. The increase in some amino acids during germination may account for the observed increase in PER for the germinated flours. Seed germination enhanced significantly the nutritional quality of chickpea protein and substantially increased the ascorbic acid level.

Dietary fat saturation modifies the metabolism of LDL subfractions in guinea pigs.

The effects of dietary fat saturation on the metabolism of low-density lipoprotein (LDL) subfractions were measured in adult male guinea pigs fed semipurified diets containing 15% (wt/wt) corn oil (CO; 58% linoleic acid), lard (24% palmitic/14% stearic acid), or palm kernel oil (PK; 52% lauric/18% myristic acid). Animals fed the CO diet had lower plasma total cholesterol levels than guinea pigs fed the PK or lard diets (P < .01). Plasma LDL-1 (d = 1.019 to 1.05 g/mL) concentrations were 3.5- and 2.4-fold higher in animals fed the PK diet compared with the CO and lard groups, respectively, while LDL-2 (d = 1.05 to 1.09 g/mL) concentrations were not different among groups. For all dietary fat groups LDL-1 had a higher molecular weight and a larger diameter than LDL-2. LDL fractional catabolic rates (FCRs) varied, depending on both the diet and the LDL subfraction. Animals fed the polyunsaturated CO diet had a more rapid LDL FCR than animals from the other two groups (P < .01). Within the same diet group, LDL-2 exhibited a slower turnover rate than LDL-1 in animals fed the PK diet, while no differences in LDL subfraction FCR were found in the CO and lard groups. Animals fed the PK and lard diets did not exhibit significant modifications in the density distribution of LDL subfractions over a period of 33 hours. In contrast, animals fed the CO diet exhibited a shift of more buoyant to denser LDL particles, suggesting that differences in LDL intravascular processing are mediated by dietary fat saturation. In vitro LDL binding to hepatic membranes confirmed the in vivo data with an increased expression of apolipoprotein B/E receptors (Bmax) in animals fed the CO diet (P < .01). Hepatic apolipoprotein B/E receptors exhibited less affinity for LDL-2 in the PK group, a result consistent with the less rapid turnover of LDL-2 in PK-fed animals. The results suggest that dietary fatty acids varying in saturation and composition have distinctive atherogenic potentials. The lowest plasma LDL cholesterol concentrations mediated by CO intake could in part be explained by induced changes in the composition and processing of LDL subfractions, resulting in faster LDL turnover rates in addition to increased expression of hepatic apolipoprotein B/E receptors.(ABSTRACT TRUNCATED AT 400 WORDS)

Exercise improves plasma lipid profiles and modifies lipoprotein composition in guinea pigs

These studies were conducted to determine the effects of exercise training on plasma lipoprotein levels and metabolism in the guinea pig to evaluate potential utilization of this model for studies of exercise-mediated effects on the regulation of sterol and lipoprotein metabolism and atherosclerosis regression. Male guinea pigs (n = 5 per group) were randomly assigned to either a control or an exercise group. The exercise protocol consisted of a 7-week training program, 5 days/wk on a rodent treadmill. Final speed and duration were 33 meters/min for 30-40 min per session. Guinea pigs in the exercise group had 33% lower plasma triacylglycerol concentrations (P < 0.01), 66% higher HDL cholesterol levels (P < 0.05) and 31% lower plasma free fatty acids (P < 0.05) than guinea pigs from the non-exercised group. In addition, lipoprotein lipase activity in the heart was 50% higher (P < 0.025) in guinea pigs allocated to the exercise protocol. Exercise training resulted in modifications in composition and size of lipoproteins. The concentrations of free cholesterol in LDL and HDL were higher in the exercised guinea pigs. The LDL peak density values were lower in guinea pigs from the exercise group compared to controls suggesting that exercise training resulted in larger LDL particles. In contrast, no significant effects due to exercise were observed in hepatic cholesterol concentrations, hepatic HMG-CoA reductase activity or LDL binding to guinea pig hepatic membranes. These data indicate that exercise had a more pronounced effect on the intravascular processing of lipoproteins than on hepatic cholesterol metabolism. In addition, the pattern of changes in guinea pig lipoprotein metabolism, in response to exercise training, was similar to reported effects in humans.

Carbohydrate-fat exchange and regulation of hepatic cholesterol and plasma lipoprotein metabolism in the guinea pig

Adult female guinea pigs were fed semipurified diets containing increasing concentrations of saturated fat (2.5%, 7.5%, 15%, and 25% wt/wt) to determine effects of exchanging fat-carbohydrate calories on lipoprotein metabolism. Plasma very-low-density lipoprotein (VLDL) and high-density lipoprotein (HDL) did not vary but plasma low-density lipoprotein (LDL) concentrations increased with increasing fat calories. LDL cholesterol values were 42 +/- 25, 61 +/- 17, 92 +/- 25, and 98 +/- 21 mg/dL (mean +/- SD, n = 5), respectively. The relative proportion of cholesteryl ester increased and triacylglycerol (TAG) decreased for VLDL, LDL, and HDL as dietary fat increased. Plasma lecithin cholesterol acyltransferase (LCAT) activity was positively correlated with HDL cholesteryl ester content. Hepatic cholesterol and TAG concentrations were highest in animals fed 25% fat (P < .01). Hepatic apolipoprotein (apo) B/E receptor maximal binding capacity (Bmax) was 30% higher in animals fed 2.5% and 7.5% fat as compared with those fed 15% and 25% fat (P < .01) and inversely correlated with plasma LDL (r = -.85, P < .01). In contrast, HDL binding to guinea pig hepatic membranes exhibited a significant positive correlation with dietary fat quantity (r = .98, P < .001), consistent with a dose-response with increasing fat calories. The activity of hepatic 3-hydroxy-3-methyl glutaryl coenzyme A (HMG CoA) reductase was not affected by the amount of dietary fat, whereas the activity of acyl CoA:cholesterol acyltransferase (ACAT) was significantly increased in animals fed 25% fat (P < .05). Hepatic free-cholesterol and ACAT activity exhibited a positive correlation for all dietary groups (r = .75, P < .001). These results demonstrate that exchange of saturated dietary fat for carbohydrate calories results in significant modifications in the regulation of metabolic pathways that determine plasma LDL concentrations and hepatic cholesterol homeostasis.

Vitamin C level and dietary fat saturation alter hepatic cholesterol homeostasis and plasma LDL metabolism in guinea pigs

This study addressed the independent and interactive effects of vitamin C status and dietary fat saturation on hepatic cholesterol and LDL metabolism in guinea pigs. Animals were fed adequate (500 mg/kg) or marginal (50 mg/kg) vitamin C with diets high in polyunsaturated (POLY), monounsaturated (MONO), or saturated (SAT) fatty acids during 6 weeks. Plasma cholesterol, triacylglycerol (TAG), and apo B concentrations were higher in animals fed vitamin C-deficient compared with Vit C-adequate diets (P < 0.02). SAT fat intake also resulted in more elevated plasma cholesterol and apo B concentrations (P < 0.001). The susceptibility of LDL to oxidation was highest in animals fed POLY diets and marginal levels of vitamin C (P < 0.001). Intake of adequate levels of vitamin C significantly reduced TBARS formation by 64% in animals fed POLY diets indicating an interactive effect between POLY fat intake and the level of vitamin C. Hepatic Acyl CoA cholesterol acyltransferase (ACAT) activity was higher by SAT fat intake (P < 0.01) and marginal intake of vitamin C (P < 0.05), whereas cholesterol 7α-hydroxylase activity was lower in vitamin C-deficient groups (P < 0.01). LDL fractional catabolic rates (FCR) were 42 to 67% faster and LDL apo B flux slower in animals fed POLY and MONO diets compared with the SAT group (P < 0.001). Animals fed marginal levels of vitamin C had higher LDL apo B flux (P < 0.05). These data suggest that the higher plasma LDL concentrations induced by SAT diets are caused by both slower LDL FCR and higher LDL apo B flux, whereas the hypercholesterolemia and hypetriglyceridemia induced by vitamin C deficiency with POLY and MONO diets is mainly caused by alterations in hepatic cholesterol homeostasis, which result in higher LDL apo B flux.

Differential effects of simple vs. complex carbohydrates on VLDL secretion rates and HDL metabolism in the guinea pig

Guinea pigs were fed isocaloric diets containing 52% (w/w) carbohydrate, either sucrose or starch, to investigate effects of simple vs. complex carbohydrates on plasma VLDL and HDL metabolism. Plasma cholesterol concentrations were not different between dietary groups while plasma triacylglycerol (TAG) and VLDL cholesterol levels were significantly increased in animals fed the sucrose diet (P < 0.05). Hepatic VLDL TAG secretion rates measured following intravenous injection of Triton WR-1339 were not affected by carbohydrate type whereas the rate of apo B secretion was 1.9-fold higher in sucrose fed animals (P < 0.02). Nascent VLDL from the sucrose group contained less TAG per apo B suggesting that the higher plasma TAG in animals fed simple carbohydrates results from increased secretion of VLDL particles with lower TAG content. Sucrose fed animals exhibited higher concentrations of hepatic free cholesterol (P < 0.01) while hepatic TAG levels and acyl CoA:cholesterol acyltransferase (ACAT) activity were not different between groups. Plasma HDL cholesterol concentrations and composition, and plasma lecithin cholesterol acyltransferase (LCAT) activity were not affected by diet yet there was a positive correlation between HDL cholesteryl ester content and LCAT activities (r = 0.70, P < 0.05). Hepatic membranes from the sucrose group had a higher hepatic HDL binding protein number (Bmax) with no changes in the dissociation constant (Kd). These results suggest that at the same carbohydrate energy intake, simple sugars induce modest changes in HDL metabolism while VLDL metabolism is affected at multiple sites, as indicated by the higher concentrations of hepatic cholesterol, dissociation in the synthesis rates of VLDL components, and compositional changes in nascent and mature VLDL.

Characterization of high-density lipoprotein binding to guinea pig hepatic membranes: Effects of dietary fat quality and cholesterol feeding☆☆☆

The effects of dietary fat quality and cholesterol intake on expression of guinea pig hepatic membrane high-density lipoprotein (HDL) binding sites were studied. Animals were fed semisynthetic diets containing 7.5% (wt/wt) of either corn oil (CO), olive oil (OL), or lard. The cholesterol diet was prepared by incorporating 0.25% recrystallized cholesterol into standard guinea pig chow. Plasma cholesterol levels of guinea pigs on the CO diet were significantly lower (P less than .02) than animals on the OL or lard diets. HDL cholesterol levels did not differ between the polyunsaturated, monounsaturated, and saturated dietary fat groups. Guinea pigs on the high cholesterol diet had increased total and HDL cholesterol levels compared with animals on the chow diet (P less than .01). Initial studies demonstrated that HDL binding to hepatic membranes was temperature-dependent. A threefold increase in binding was observed when assays were performed at 37 degrees C, as compared with 4 degrees C, for all membrane preparations. Dietary fat quality and dietary cholesterol intake significantly altered HDL binding to hepatic membranes with increased HDL binding to membranes of animals fed polyunsaturated fat and the high cholesterol diet. At 37 degrees C, HDL binding to hepatic membranes of CO-fed animals was 26% and 46% higher than for membranes of OL- and lard-fed guinea pigs, respectively. A high cholesterol intake increased HDL binding by 24% at both 4 degrees C and 37 degrees C. Scatchard analysis demonstrated that while membrane affinity for HDL (Kd) was not affected by diet, changes did occur in the total number of HDL binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)