A. H. M. Terpstra

Thermally oxidised sunflower-seed oil increases liver and serum peroxidation and modifies lipoprotein composition in rats.

Peroxidation of LDL and other lipoproteins is thought to play a central role in atherogenesis. Dietary thermally oxidised oils may increase atherogenic risk in consumers by increasing their oxidative status. The present paper compares the effects of two diets containing unused sunflower-seed oil (US) or sunflower-seed oil repeatedly used in frying (FS) (both 15 g/100 g diet) on weight gain, food efficiency ratio, serum lipid levels and lipoprotein composition, and the content of thiobarbituric acid-reactive substances (TBARS) in the liver, serum, and lipoproteins in growing Wistar rats. After sixty potato fryings the FS contained 27.7 g polar material/100 g oil and 16.6 g oligomers/100 g oil. The FS-fed rats had a significantly lower weight gain and food efficiency ratio. Liver-TBARS increased due to the consumption of the highly altered oil and showed a significant linear relationship (all r > 0.68; P < 0.002) with the ingestion of thermally oxidised compounds. Serum-, VLDL-, LDL- and HDL-TBARS were significantly higher in the FS-fed rats (all P < 0.001). Concentrations of serum total and non-esterified cholesterol and phospholipids were significantly higher in the FS-fed rats (P < 0.05, P < 0.05, and P < 0.001, respectively). Serum triacylglycerol concentrations did not vary between the two dietary groups. Total and esterified cholesterol and phospholipid levels increased significantly in the HDL fraction (P < 0.05, P < 0.05, and P < 0.001, respectively) of the FS-fed rats. HDL-cholesterol and HDL-phospholipids were significantly correlated with liver-TBARS (r > 0.747; P < 0.0001), VLDL-TBARS (r > 0.642; P < 0.003), LDL-TBARS (r > 0.475; P < 0.04), and HDL-TBARS (r > 0.787; P < 0.0001). The data suggest that the rat increases HDL as a protecting mechanism against the peroxidative stress induced by the consumption of a diet containing the thermally oxidised oil.

The effect of six different C18 fatty acids on body fat and energy metabolism in mice

We studied the effects of five high-fat semi-purified diets varying at a 4% (w/w) level in either stearic, oleic, linoleic, alpha-linolenic, or gamma-linolenic acid on body fat and energy metabolism in BALB/c mice. A diet containing caprylic, capric, lauric, and myristic acid was used as a reference diet and a diet with 4% conjugated linoleic acid (CLA) was used as a positive control as it is known to effectively lower body fat in mice. The diets were fed for 35 d. Body fat was significantly lower in the CLA group than in the other groups but was not significantly different among the non-CLA groups. Among the non-CLA groups, the linoleic acid group tended to have the highest and the alpha-linolenic acid group the lowest proportion of body fat. In energy-balance studies, the percentage of energy intake that was stored in the body was significantly lower in the CLA group compared with the other dietary groups. The percentage of energy intake eliminated in excreta was highest in the stearic acid group followed by the gamma-linolenic acid group. These results were reflected in apparent fat digestibility, which was lowest in the stearic acid group. The percentage of energy intake expended as heat was highest in the CLA-fed mice. The results of the present study suggest that body fat and energy accretion in mice fed diets containing different C18 fatty acids is by far the lowest with CLA and that linoleic acid produced the highest fat intake and energy accretion.

Hypocholesterolemic Effect of Dietary Psyllium in Female Rats

We fed cholesterol-enriched (1% cholesterol and 0.2% cholic acid) semipurified diets containing either 3% cellulose or psyllium to 2 groups of female Wistar rats for a period of 8 weeks. The feeding of the cholesterol-enriched semipurified diets resulted in a progressive increase in plasma cholesterol levels in both groups during the 8 weeks of the experiment. The rats fed psyllium, however, had significantly lower plasma cholesterol concentrations than the animals fed cellulose throughout the experimental period (at 8 weeks, 8.92 ± 4.42 and 16.47 ± 8 mmol/l, respectively, means ± SD, n = 14, p < 0.01). Most of the plasma cholesterol in both groups at the end of the study was located in the very low-density lipoprotein (VLDL) fraction (91%) and differences in total plasma cholesterol concentrations were predominantly reflected in differences in VLDL cholesterol. Plasma triglyceride concentrations were not significantly different between the 2 groups. Liver cholesterol concentrations paralleled the concentrations of plasma cholesterol and were significantly lower (p < 0.001) in the psyllium-fed rats (90.31 ± 13.81 µmol/g liver) than in the cellulose-fed rats (60.49 ± 15.25 µmol/g liver). Substitution of psyllium for cellulose resulted in an increase in the excretion of fecal bile acids by 26%, and this increase was predominantly caused by an increased excretion of β-muricholic acid and the bile acids derived from β-muricholic acid (ω-muricholic acid and hyodeoxycholic acid).

The hypercholesterolemic effect of cafestol in coffee oil in gerbils and rats

Coffee beans contain the diterpene cafestol, which raises plasma cholesterol concentrations in humans. Daily consumption of 2 g coffee oil, which provides approximately 60 mg cafestol (equivalent to 5.7 mg cafestol/MJ), increases plasma cholesterol concentrations by 28%. We studied the effect of cafestol in coffee oil on gerbils and rats to determine whether the pathways that lead to cafestol-induced hypercholesterolemia in humans are also present in other species. We fed coffee oil from the same batch used in humans to female gerbils and rats. Gerbils were fed a semipurified diet containing 0.5% or 5% (w/w) coffee oil (equivalent to 8.7 and 86.8 mg cafestol/MJ, respectively) in the presence or absence of 0.05% (w/w) cholesterol for a period of 10 weeks. When compared with the gerbils fed no coffee oil, the addition of 0.5% coffee oil to the diets did not affect plasma cholesterol. Plasma cholesterol was significantly higher only when 5% coffee oil was fed, both in the absence (1.01 mmol/L, 33% higher) and presence (1.87 mmol/L, 70% higher) of dietary cholesterol. Liver weight was also significantly higher when 5% coffee oil was fed. Rats were also fed diets containing 0.5% or 5% coffee oil (equivalent to 8.7 and 86.8 mg cafestol/MJ) with and without 0.05% cholesterol for 8 weeks. Feeding 0.5% coffee oil compared with no coffee oil resulted in significantly higher plasma cholesterol levels throughout the study both in the absence (0.46 mmol/L, 27% higher) and presence (0.28 mmol/L, 15% higher) of dietary cholesterol. Diets containing 5% coffee oil appeared to be toxic. Thus, coffee oil diterpenes can result in higher plasma cholesterol in gerbils and rats. The failure to observe these effects in previous studies may be due to doses that were too low.

Decreasing dietary fat saturation lowers HDL-cholesterol and increases hepatic HDL binding in hamsters.

In order to study the mechanism by which increasing unsaturation of dietary fat lowers HDL-cholesterol levels, we studied various measures of HDL metabolism in hamsters fed with fats with different degrees of saturation. Hamsters were fed on a cholesterol-enriched (1 g/kg) semipurified diet containing 200 g/kg of maize oil, olive oil, or palm oil for 9 weeks. Increasing saturation of dietary fat resulted in increasing concentrations of total plasma cholesterol (4.29 (SD 0.51), 5.30 (SD 0.67) and 5.58 (SD 0.76) mmol/l respectively, n 12) and HDL-cholesterol (3.31 (SD 0.50), 3.91 (SD 0.12) and 3.97 (SD 0.43) mmol/l) and these concentrations were significantly higher (P < 0.05) in the palm-oil and olive-oil-fed hamsters compared with the maize-oil group. Total plasma triacylglycerol levels also increased with increasing fat saturation (1.01 (SD 0.59), 1.56 (SD 0.65) and 2.75 (SD 1.03) mmol/l) and were significantly higher (P < 0.05) in the palm-oil group compared with the olive-oil and maize-oil-fed hamsters. The three diets did not have differential effects on plasma activity levels of lecithin: cholesterol acyltransferase (LCAT) and cholesteryl ester transfer protein (CETP). Levels of phospholipid transfer protein (PLTP) tended to be higher with increasing fat saturation but this effect was not significant. The capacity of liver membranes to bind human HDL3 was significantly higher (P < 0.05) in the hamsters fed with maize oil (810 (SD 100) ng HDL3 protein/mg membrane protein, n 4) compared with those fed on palm oil (655 (SD 56) ng/mg), whereas the olive-oil group had intermediate values (674 (SD 26) ng/mg). The affinity of HDL3 for the binding sites was not affected by the type of dietary fat. Hepatic lipase (EC 3.1.1.3) activity, measured in liver homogenates, increased with increasing fat saturation. We conclude that dietary maize oil, when compared with either olive oil or palm-oil, may lower HDL-cholesterol concentrations by enhancing HDL binding to liver membranes.

Intact pectin and its polygalacturonic acid regions have similar hypocholesterolemic properties in hybrid F1B hamsters.

We fed cholesterol-enriched (0.1% w/w) semipurified diets containing 3% of lemon pectin or 3% of the polygalacturonic acid regions fraction (smooth regions fraction) of the lemon pectin to hybrid F1B hamsters for a period of 8 weeks. A control group was fed cellulose and a positive control group was fed psyllium. The feeding of the semipurified diets resulted in an increase of plasma cholesterol levels in all the dietary groups when compared with initial values. The hamsters fed the psyllium, pectin, or the polygalacturonic acid regions fraction had significantly (P < 0.05) lower plasma cholesterol levels than the cellulose fed group throughout the experimental period. Plasma cholesterol levels in the hamsters fed the psyllium, pectin, or polygalacturonic acid regions fraction were not significantly different. Liver cholesterol concentrations were also lower in the hamsters fed the psyllium, pectin, or the polygalacturonic acid regions fraction than in the hamsters fed the cellulose, but this effect reached statistical significance only in the hamsters fed the polygalacturonic acid regions fraction. The results of these studies suggest that the polygalacturonic acid regions of the pectin molecule is responsible for the cholesterol-lowering properties of the pectin.