Dietary oxidised frying oil causes oxidative damage of pancreatic islets and impairment of insulin secretion, effects associated with vitamin E deficiency

Abstract

We previously reported that, in rodents, a diet with a high oxidised frying oil (OFO) content leads to glucose intolerance associated with a reduction in insulin secretion. The present study aimed at investigating the impairment of pancreatic islets caused by dietary OFO. C57BL/6J mice were divided into three groups to receive a low-fat basal diet containing 5 g/100 g of fresh soyabean oil (LF group) or a high-fat diet containing 20 g/100 g of either fresh soyabean oil (HF group) or OFO (HO group). After 8 weeks, mice in the HO group showed glucose intolerance and hypoinsulinaemia, and their islets showed impaired glucose-stimulated insulin secretion (P,0·05; HO group v. LF and HF groups). Significantly higher oxidative stress and a lower mitochondrial membrane potential were observed in the islets in the HO group compared with the LF and HF groups. Immunoblots showed that the reduction in insulin levels in HO islets was associated with activation of the c-Jun NH 2 -terminal kinase and a reduction in levels of pancreatic and duodenal homeobox factor-1. In a second study, when dietary OFO-induced tissue vitamin E depletion was prevented by large-dose vitamin E supplementation (500 IU(1·06 mmol all-rac-a-tocopherol acetate)/kg diet; HO þ E group), the OFO-mediated reduction in islet size and impairment of glucose tolerance and insulin secretion were significantly attenuated (P, 0·05; HO group v. HO þ E group). We conclude that a high level of dietary OFO ingestion impairs glucose metabolism by causing oxidative damage and compromising insulin secretion in pancreatic islets, and that these effects can be prevented by vitamin E supplementation.Key words: Oxidised frying oil: Glucose-stimulated insulin secretion: Vitamin E: Pancreatic and duodenal homeobox factor-1: c-Jun NH 2 -terminal kinase Deep-frying is a common cooking practice, and the safety of oxidised frying oil (OFO) ingested with fried food is a concern. During the deep-frying process, a series of reactions, including auto-oxidation, thermal oxidation, polymerisation, cyclisation and fission, occur in the frying oil (1) . Generally, OFO prepared using normal cooking practices as part of a nutritionally balanced diet is regarded as safe due to the induction of detoxifying cytochrome P450 enzymes and the limited absorption of toxic polymers produced during the deep-frying process (2,3) . However, animal studies have revealed that some nutritional and metabolic effects related to OFO ingestion are noteworthy.We (4 -6) and others (7,8) have shown that, in rats and mice, OFO ingestion can influence lipid metabolism through the activation of PPARa in the liver, leading to increased fatty acid catabolism. Paradoxically, impairment of glucose metabolism, i.e. glucose intolerance, is observed in OFO-fed rodents (9) . When OFO-induced effects were compared with conjugated linoleic acid-induced lipodystrophic diabetes in mice, we found that, although both are characterised by body fat loss and glucose intolerance, OFO-mediated glucose intolerance is due to ...

The Effects of Heated Oils Used in Fast Food Restaurants on Metabolic, Inflammatory and Oxidative Stress Markers, Blood Pressure, and Liver Histology in Sprague-Dawley Rats

“…Similarly, in previous studies, heated oils by increasing production of reactive oxygen species caused glucose intolerance, pancreatic beta cell destruction, and reduced insulin secretion (11,22). In this study, no significant difference was found in HDL-C level between the groups yet TG and total cholesterol levels increased at the end of the study.…”

“…Likewise, heating soybean oil for 3 hours increased fat mass while it reduced body weight of mice (7). Also, 8-week ingestion of high oxidized frying oil (205°C for four 6-hour periods) deteriorated insulin secretion from pancreatic islets (11).…”

n-3 PUFA added to high-fat diets affect differently adiposity and inflammation when carried by phospholipids or triacylglycerols in mice

“… a Considering the difference observed in tocopherols in lipid mixtures, which can affect their metabolic impact [31], care was taken to supplement lipid mixtures with α-tocopherol during formulation to achieve iso-tocopherol diets.…”

Potential Adverse Public Health Effects Afforded by the Ingestion of Dietary Lipid Oxidation Product Toxins: Significance of Fried Food Sources

“…The molecular nature, toxicities and health hazards potentially presented by aldehydic LOP toxins have been previously explored in some detail, as have analytical strategies available for their determination and monitoring, e.g., in fried food sources, and human/animal biofluids and tissues, for probing their in vivo absorption, biodistribution, metabolism and urinary excretion (an example of the 1 H NMR analysis of aldehydes, specifically LOPs and vanillin, in a typical non-fried food product is shown in Figure 4). Indeed, the toxicological and pathogenic properties conceivably arising from the ingestion of aldehydic LOP-containing COs heated according to standard frying practices (in the form of CO-absorbing fried foods for humans), and also aldehyde model systems, include their potential roles in the development and perpetuation of cardiovascular diseases [54][55][56], their carcinogenic [57][58][59][60][61], gastropathic [62], pro-inflammatory [63], and teratogenic properties [64], contributions towards neurodegenerative disorders [65], their hypertensive effects [66]; the development and perpetuation of diabetes [67];and respiratory and pulmonary complications, the latter especially for acrolein [68]; this list is inexhaustive. The inhalation of volatile aldehydes and other carbonyl compounds by workers employed in poorly-ventilated fast-food/restaurant retail outlets is also considered to pose a major threat to human health [69], particularly with reference to established links between an increased incidence of lung cancer and cooking oil fume inhalation amongst such personnel [13,[70][71][72].…”