Dietary docosahexaenoic acid-induced production of tissue lipid peroxides is not suppressed by higher intake of ascorbic acid in genetically scorbutic Osteogenic Disorder Shionogi/Shi-od/od rats

In previous studies, we showed that docosahexaenoic acid (DHA) ingestion enhanced the susceptibility of rat liver and kidney to lipid peroxidation, but did not increase lipid peroxide formation to the level expected from the relative peroxidizability index (P-index) of the total tissue lipids. The results suggested the existence of some suppressive mechanisms against DHA-induced tissue lipid peroxide formation, as increased tissue ascorbic acid (AsA) and glutathione levels were observed. Therefore, we focused initially on the role of AsA for the suppressive mechanisms. For this purpose, we examined the influence of different levels of dietary AsA (low, moderate, high and excessive levels were 100, 300 (control), 600 and 3000 mg/kg diet respectively) on the tissue lipid peroxide and antioxidant levels in AsA-requiring Osteogenic Disorder Shionogi/Shi-od/od (ODS) rats fed DHA (6·4 % total energy) for 32 or 33 d. Diets were pair-fed to the DHA- and 100 mg AsA/kg diet-fed group. We found that the lipid peroxide concentrations of liver and kidney in the DHA-fed group receiving 100 mg AsA/kg diet were significantly higher or tended to be higher than those of the DHA-fed groups with AsA at more than the usual control level of 300 mg/kg diet. Contrary to this, the liver α-tocopherol concentration was significantly lower or tended to be lower in the DHA and 100 mg AsA/kg diet-fed group than those of the other DHA-fed groups. However, tissue lipid peroxide formation and α-tocopherol consumption were not suppressed further, even after animals received higher doses of AsA. The present results suggest that higher than normal concentrations of tissue AsA are not necessarily associated with the suppressive mechanisms against dietary DHA-induced tissue lipid peroxide formation.

Benzophenone-Sensitized Peroxidation in Compressed Lipid Monolayers at Air-Water Interface

The paper reports on a study of radical-type lipid peroxidation of biomembrane lipid constituents in compressed monolayers, with incorporated lipoidic benzophenone photosensitizers. Their triplets abstract allylic and double-allylic hydrogen atoms from hydrophobic moieties of the lipid molecules. The results confirmed the H abstraction occurrence (and thus the initiation of the peroxidizing chain mechanism), and absence of lipid peroxide formation at the same time. The reason is in the "cage effect": highly restricted spatial area of compressed lipid monolayers limits mobility of the formed radicals (lipid and ketyl radicals) and leads to their recombination, preventing the propagation step of the chain mechanism. With certain approximation, one may conclude that these results have clear implication for real biomembranes: their structure is one of the main factors in prevention of spreading of the chain reaction, and lipid peroxide formation.