Does fried high-oleic sunflower oil impact plasma lipid profile and liver enzymatic activity in rat?

Introduction: Deep-fat frying is one of the most important and widely spread cooking methods. The characteristics of the oil bath play a preponderant role on frying performance, as well as on the level of neoformation compounds generated by this cooking treatment. Over the past few years, palm oil and its fractions have been widely used as frying oil, due to its stability, low cost and positive impact on the sensory properties of fried food. However, due to its sustainability, process contaminants and health effects, it has been widely replaced with other vegetable oils (such as high-oleic sunflower oil, HOS) or palm-free frying mixtures in the catering sector, which are more unsaturated and thus more prone to oxidation than palm oil. Considering that vegetable oils that oxidize during frying can exert various toxicological effects, it would be interesting to assess the in vivo impact of fried HOS on rat lipid profile and liver Phase I, II and antioxidant enzymatic activity. Materials and Methods: Twenty-two male Sprague Dawley rats aged 9 weeks and weighing 170-200 g, were housed under 12h-light/12h-dark cycle, 22°C, 60% humidity, and fed ad libitum. After 10-day adaptation, the rats were randomly split into four experimental units: HOS group daily treated with 2.6 g of fresh oil for 7 days; 2) HOS-7F group daily treated for 7 days with 2.6 g of 5-day fried oil (3 cycles at 180°C/day); 3) HOS-14 group daily treated with 2.6 g of fresh oil for 14 days; 4) HOS-14F group daily treated for 14 days with 2.6 g of 5-day fried oil (as described above). The animals were treated by gavage. Rats were fasted 16 h prior to sacrifice, which occurred 24 h after the last treatment, in accordance with approved Ministerial procedures appropriate to the species. Immediately prior to the sacrifice, a blood sample was collected from each animal. The liver was rapidly removed and processed separately. Results: Only HSO-14F had a significant impact on the animal body weight (5.5% gain, p<0.01 vs HOS-14). HSO-7F group displayed a considerable inactivation of CYP2B1/2 isoform (40% loss, p<0.05 vs. HSO), while an increase (up to 45%, p<0.05 vs. HSO) of QNO1 activity was registered. Concerning plasma lipids, an increase of free cholesterol in fried-oil groups was denoted. On the other hand, no significant changes were observed in the fatty acid composition of both triacylglycerol and phospholipid fractions. In general, the level of cholesterol oxidation products (COPs) in plasma was higher in the fried-oil groups, while a significant reduction of 24-hydroxycholesterol (24-HC) was found in HSO-7F. Conclusions: Dietary supplementation of fried HSO by gavage did not significantly affect liver Phase I, II and antioxidant enzymes, and fatty acid composition of plasma in rats regardless of the treatment length, so HSO could be considered a valid alternative to palm oil as frying oil. However, the higher presence of COPs in plasma, and in particular the reduction of 24-HC level, could suggest that fried HSO could exert some effect at brain level. A deeper investigation is thus needed to better clarify this result.