Effects of deteriorated frying oil and dietary protein levels on liver microsomal enzymes in rats

Abstract

This study was conducted to investigate the effects of deteriorated used frying oil (DUFO) and dietary protein levels upon the hepatic microsomal drugmetabolizing enzyme system. Fresh soybean oil was subjected to a deep-frying process at 205 __ 5°C for four six-hr periods. The resultant DUFO was incorporated into high protein (HU} (27% lactalbumin) or low protein (LU) (8% lactalbumin) test diets at a 15% level. High protein (HF) and low protein (LF) diets containing fresh soybean oil served as the control. Male Long-Evans young rats fed the test diets for eight weeks showed decreased fat absorption and increased red blood cell {RBC) in vitro hemolysis. The activities of hepatic aminopyrine N-demethylase (AD), aniline hydroxylase (AH), NADPH-cytochrome C reductase (NCD), UDP-glucuronyl transferase (UDPGT) and glutathione S-transferase (GST) as well as cytochrome P-450 content were significantly increased in rats fed the HU diet. However, the AD, AH and GST activities, as well as the cytochrome P-450 content of the LU group, were increased to a lesser extent and significantly lower than those of the HU group. Rats fed the LU diet were the only group that showed significantly elevated serum GOT {E.C. 2.6.1.1, glutamate-oxaloacetate transaminase) and GPT (E.C. 2.6.1.2, glutamatepyruvate transaminase) values. Supplementation of 0.3% DL-methionine to the HU diet further increased GST activity. Unexpectedly, rats fed the low protein control diet (LF) also had raised levels of AD, AH and UDPGT activities as well as in vitro RBC hemolysis. It was concluded that rat hepatic microsomal enzymes are induced by dietary DUFO and that the level of induction is influenced by dietary protein level.

A high oxidised frying oil content diet is less adipogenic, but induces glucose intolerance in rodents

“…In addition, hydrolysis of non-oxidised triacylglycerol by pancreatic lipase is also negatively affected by the presence of large amounts of thermoxidised compounds in the lumen (González-Muñoz et al 1998). In our previous studies, a mild reduction (5-10 %) in fat absorption was observed in OFO-fed rats (Huang et al 1988;Liu & Huang, 1995). However, a greater reduction would be expected in this study since the OFO was fed at a higher level (20 v. 15 % level for this study and the previous ones).…”

Peroxisome Proliferation in Liver of Rats Fed Oxidized Frying Oil

“…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).…”

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

“…The vitamin E-stripped fresh soybean oil, fresh soybean oil, and OFO were analyzed for acid value, TBA value, carbonyl values, and UV absorbance at 233 nm [3]. The vitamin E content of the test oils was analyzed by HPLC as described below for plasma and liver homogenate.…”

“…The effects of oxidized frying oil (OFO) on animals has been widely studied. 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.…”