Peroxisome Proliferation in Liver of Rats Fed Oxidized Frying Oil

Abstract

SummaryOxidized frying oil (OFO) activates peroxisome proliferator-activated receptor a (PPAR a) in vitro and in vivo. As most PPARa activators are also peroxisome proliferators (PP), this study was aimed at exploring whether OFO induces peroxisome proliferation in the liver of rats. Four groups of male weanling Sprague-Dawley rats were fed the following diets for 6 wk: a basal diet containing 5g/100 g fresh soybean oil (LSB), high-fat diets con taining 20g/100g of fresh soybean oil (HSB as a control), OFO (HO) or fish oil (HF, as a pos itive control). Hepatomegaly and peroxisome proliferation in the liver of the HO group of rats were higher than those of the HF group. In addition, the acyl-CoA oxidase (ACO) activity, as well as cytochrome P450 4A (CYP4A) protein content in the livers of the HO group were 6 fold those of the HSB group, but were 2.5 fold in those of the HF group. These results indi cated that dietary OFO induced typical responses to PPARa signaling. Moreover, as a dietary source, the OFO prepared under our frying conditions appears to be a more potent peroxi some proliferator than fish oil. Key Words oxidized frying oil, fish oil, acyl-CoA oxidase, cytochrome P450 4A, peroxi some proliferation Fat samples oxidized under more realistic cooking practices (frying) as part of a nutritional balanced diet gave rise to mild symptoms, such as: less body weight gain and feed intake, and enlargement of liver and kid ney, in long term animal studies (1, 2). The modest bio logical effect could be attributed to a decreased diges tion and absorption of the dimerized and polymerized TG (3, 4) as well as an effective detoxifying capability by the liver microsomal enzymes, including cytochrome P450 monoxygenase and phase II conjugation enzymes (5). The enlarged liver was thus speculated to be related to the increased microsomal protein since routine histo pathological examination did not reveal significant alterations (Cheung and Huang, unpublished data).

Dietary moderately oxidized oil induces expression of fibroblast growth factor 21 in the liver of pigs

“…Studies in rodents have shown that many of the effects induced by administration of FGF21 such as a reduction of liver and plasma TAG concentrations [10-12,18,19,31], a reduction of plasma cholesterol [10,13,31-33], an increase in HDL-cholesterol concentration [31], a reduction of adipose mass [15], or an increase of insulin sensitivity [34] are also induced by dietary oxidized fat. Previous studies have shown that dietary oxidized fats can even prevent an alcohol induced steatosis or the development of atherosclerosis [16,35].…”

Gestational Ingestion of Oxidized Frying Oil by C57BL/6J Mice Differentially Affects the Susceptibility of the Male and Female Offspring to Diet-Induced Obesity in Adulthood

“…OFO was prepared by frying dough sheets in soybean oil (President) at 205 6 5°C for four 6-h periods as previously described (1)(2)(3). The extent of oxidation was evaluated by the acid value (OFO, 2.841; SO, 0.056 KOH mg/g) and conjugated diene amounts (OFO, 3560; SO, 504 OD 233 units/g oil), values very similar to those obtained in our previous studies (1)(2)(3)7,8).…”

“…Although frequent consumption of fried food, inevitably accompanied by high fat intake, is causally related with obesity, cardiovascular disease, and cancer, we and others have shown that, in both in vitro and in vivo, oxidized frying oil (OFO) 4 is more potent than fresh oil in activating PPARa (1)(2)(3)(4). Accordingly, when rodents fed diets with equal amounts of OFO or fresh oil are compared, lower plasma and liver lipid concentrations (1,5,6), less adiposity (7,8), and lower proinflammatory responses in the vasculature (9) are observed in the OFO-fed group.…”

Effects of Oxidized Frying Oil on Proteins Related to α-Tocopherol Metabolism in Rat Liver

“…Catalase is a peroxisome enzyme which cleaves hydrogen peroxide. OFO causes peroxisome proliferation by activating PPARα [5] and this could be the cause of the increased levels of catalase protein in OFO-fed rats.…”

“…The induction of total cytochrome P450 monooxygenase (CYP) activity [3] by OFO suggests that OFO contains substances that need to be metabolized by CYPs in the liver. CYP1A1 [4] and CYP4A1 [5] protein levels and CYP4A1 and CYP2E1 mRNA levels [6] are also increased when rats are fed thermally oxidized dietary fat.…”