Leena Seppo

Dietary habits affect the susceptibility of low-density lipoprotein to oxidation

Objective: To study, if there are differences in the fatty acid composition of low‐density lipoprotein (LDL) in people eating three different long‐standing habitual diets: vegetarian, high fish intake, or high saturated fat (milk fat) diet as a control group, and to study if these differences influence the oxidation susceptibility of LDL.Design: Cross‐sectional study using blood samples and a validated dietary frequency questionnaire with illustrations.Setting: Helsinki University Central Hospital, Finland.Subjects: The effect of three different types of long‐standing diets of different fatty acid content (a strict vegetarian diet, n=11; a high fish intake diet, n=9; and a high saturated fat (milk fat) diet, controls, n=7) on the serum and LDL fatty acid content, and on the susceptibility of LDL to oxidation in vitro, was studied in healthy normocholesterolemic volunteers who had been on these diets for years. Oxidation of LDL was carried out by using CuSO4 as a pro‐oxidant.Results: There were no statistically significant differences in the serum lipids or lipoproteins, though the vegetarian group exhibited lowest mean values of total, high‐density lipoprotein (HDL) and LDL cholesterol levels. Both the serum and LDL eicosapentaenoic, docosapentaenoic and docosahexaenoic acid proportions were highest in the fish and lowest in the vegetarian groups. Linoleic acid was highest among the vegetarians. In the fish group, the vitamin A concentration in serum was higher than in vegetarians and controls and β-carotene lower than in controls, but in α‐tocopherol, or lycopene concentrations there were no statistically significant differences. The lag phase of LDL oxidation was shortest (116 min) in the fish group and longest (165 min) in the vegetarian group, and the control group was between them (129 min). The mean oxidation percentage after 2.5 h of copper‐induced oxidation was highest (44%) in the fish group and lowest (22%) in the vegetarian group and intermediate (31%) in the control group.Conclusion: Long‐term dietary habits predict the fatty acid composition of serum and LDL, and influence the susceptibility of LDL to oxidation. In the fish group with the highest content of omega‐3 fatty acids in LDL, the oxidation susceptibility of LDL was highest. In the vegetarian group with less omega‐3 fatty acids in LDL, the LDL was more resistant to oxidation.Sponsorship: Helsinki University Central Hospital.

Can primary hypolactasia manifest itself after the age of 20 years? A two-decade follow-up study

Objective. The age at manifestation of primary hypolactasia varies between ethnic groups. Many people report experiencing the first symptoms of lactose intolerance at adult age. The purpose of this study was to investigate whether primary hypolactasia can appear after the age of 20 among the Finnish population and to investigate the outcome of different diagnostic methods of lactose maldigestion. Material and methods. Lactose digestion status was assessed by the lactose tolerance test with ethanol (LTTE) in 42 subjects (38–71 years) who reported having gastrointestinal symptoms after the ingestion of 20 g or less of lactose and who were diagnosed as lactose digesters in earlier studies. Thirteen of the study subjects underwent upper gastrointestinal endoscopy, and 35 gave a blood sample for DNA analysis. Results. Only one of the 42 subjects studied had the genotype C/C−13910 indicating hypolactasia. Lactase activity was higher in those with the genotype T/T (69.2 U/g protein) than in those with the heterozygous genotype C/T (36.3 U/g protein) (p=0.017). Conclusions. Although primary hypolactasia normally appears before the age of 20 years, the decline in lactase activity may on rare occasions continue after that age. Genotyping of the C/T−13910 variant was found to be a reliable diagnostic approach in defining the lactase persistence/non-persistence status of the study subjects.

Effects of vitamin E on the toxicity of oxidized LDL on endothelial cells in vitro in smokers vs nonsmokers on diets rich in fish

Objective:To clarify whether supplementation of vitamin E can alter the low density lipoprotein (LDL) oxidation properties and thereby affect endothelial cell function and prostacyclin production in smokers compared to nonsmokers on diets rich in fish in a pilot study.Design:The LDL of six smokers and six nonsmokers on habitual high fish diet was isolated before and after an 8-week supplementation of vitamin E (800 IU/day). LDL was oxidized by incubation with CuSO4. Cytotoxicity of LDL oxidized to different degrees on endothelial cells was investigated in vitro in these two groups.Setting:Helsinki University Central Hospital; Institute of Biomedicine, Pharmacology, University of Helsinki.Results:At baseline, the rate of oxidation was higher in nonsmokers than in smokers. The lag phase increased significantly after the supplementation of vitamin E both in smokers and nonsmokers. Native LDL dose dependently tended to reduce the viability of endothelial cells in vitro more markedly when isolated from smokers than from nonsmokers. Vitamin E supplementation had no beneficial effect on the cytotoxicity of oxidized LDLs in endothelial cell culture. On the other hand, simultaneous administration of Trolox®, the water-soluble analogue of vitamin E, attenuated the LDL cytotoxicity on endothelial cells. The vitamin E supplementation to LDL donors attenuated the increase in prostacyclin production both in smokers and nonsmokers.Conclusion:Supplementation of LDL donors (healthy male volunteers on habitual fish diet) with vitamin E increased the lag phase of LDL oxidation, but, on the other hand, did not influence in vitro cytotoxicity of LDL, or prostacyclin production.Sponsorship:Helsinki University Central Hospital and Biomed 2.