Mechanisms of fat-related modulation of N-nitrosodiethylamine-induced tumors in rats: organ distribution, blood lipids, enzymes and pro-oxidant state

Abstract

Groups of rats, either dosed with N-nitrosodiethylamine (NDEA) for 10 weeks (from the age of 7 to 17 weeks) or untreated, were fed diets containing either 2% (low fat, LF) or 30% polyunsaturated fat (high fat, HF) on an equicaloric basis from 5 weeks until rats were 43 weeks old. Biochemical parameters were measured during and at the end of the experiment in various organs, blood, urine and exhaled air, for correlation with the presence or absence of tumors. The HF diet tended to increase the number of hepatic tumors induced by NDEA, while the number of extrahepatic tumors was higher in rats fed on the LF diet; also the overall tumor incidence was higher in the LF group. In the HF/NDEA group, only two benign extrahepatic tumors were found. Plasma total and free cholesterol and triglyceride concentrations were lower in the HF than the LF group without NDEA treatment. In animals bearing liver and/or extrahepatic tumors all plasma lipid concentrations were lower than in tumor-free animals. Only minor or no changes were detected in blood catalase activity, malondialdehyde level, reduced glutathione (GSH) level or GSH-related enzymes and excretion of thioethers in the urine due to dietary modulation or NDEA. Changes in the liver that were associated with the HF diet were: (i) increased amounts of some polyunsaturated fatty acids and of total phospholipids in liver microsomes; (ii) an enhanced level of lipid peroxidation in liver; (iii) a decrease in liver glutathione levels during NDEA treatment, with a simultaneous adaptive increase in superoxide dismutase levels, and a decrease in renal glutathione levels in both treated and untreated groups; (iv) enhanced microsomal induction of aminopyrine N-demethylase and epoxide hydrolase activities by NDEA, and (v) decreased hexose monophosphate shunt (HMS) activity. All mono-oxygenase activities were lower, and the activities of epoxide hydrolase, UDP-glucuronosyltransferase and HMS were higher, in liver tumors than in non-tumorous liver of similarly-treated rats. Neither diet nor NDEA had a major effect on drug-metabolizing enzyme activities in lung and kidney. HF diet significantly increased ethane exhalation (an indicator of the whole-body pro-oxidant state) over those on the LF diet: in rats on either diet, it was further increased when NDEA was given. Ethane exhalation was still elevated 30 weeks after the cessation of NDEA treatment. Our results suggest an association between the observed changes in biochemical parameters, notably oxidative stress, due to dietary modulation and the altered tumor incidence and organ distribution of tumors induced by NDEA.

Nitrosamine exposure exacerbates high fat diet-mediated type 2 diabetes mellitus, non-alcoholic steatohepatitis, and neurodegeneration with cognitive impairment

“…In contrast, neither the NDEA exposure nor the chronic HFD feeding caused hyperlipidemia, indicating that seemingly favorable serum lipid profiles can exist in the context of peripheral insulin resistance or T2DM. These findings are similar to those in a previous report in which the experimental model was generated with much higher doses of NDEA than used herein [62]. One possible interpretation of these seemingly paradoxical results is that homeostasis may have shifted toward increased storage of lipids/triglycerides in adipose tissue, skeletal muscle, and/or liver.…”

Early limited nitrosamine exposures exacerbate high fat diet-mediated type 2 diabetes and neurodegeneration

“…Although chronic HFD feeding and limited NDEA exposure increased body weight and caused T2DM/peripheral insulin resistance with fasting hyperglycemia, hyper-insulinemia, and hyper-leptinemia [99,100], the rats were not obese and they did not have hyper-lipidemia. Instead, the serum lipid profile was favorable, consistent with a previous report of a related experimental model [84]. …”

“…In contrast, neither the NDEA exposure nor the chronic HFD feeding caused hyper-lapidarian, indicating that seemingly favorable serum lipid profiles can exist in the context of peripheral insulin resistance or T2DM. Similar results have been reported previously, in which the investigators generated models with much higher doses of NDEA [84]. One potential explanation for this paradox is that homeostatic mechanisms may have shifted toward increased storage of lipids/triglycerides in adipose tissue, skeletal muscle, and perhaps liver.…”

Chemopreventive effects of β-ionone and geraniol during rat hepatocarcinogenesis promotion: distinct actions on cell proliferation, apoptosis, HMGCoA reductase, and RhoA

“…To our knowledge, this is the first study to report the chemopreventive activities of βI and GOH specifically during promotion of hepatocarcinogenesis. It is noteworthy that, in our study, these isoprenoids presented inhibitory effects when dissolved in corn oil, a dietary fat shown to enhance carcinogenesis in several organs, including rat liver [23,24]. Considering the scarcity of isoprenoid chemopreventive studies with an experimental design similar to the present one, emphasis should be given on further investigations that would address the protective potential of these compounds during the promotion phase of hepatocarcinogenesis.…”