Cytochrome P-450 isozyme pattern is related to individual susceptibility to diethylnitrosamine-induced liver cancer in rats

A systematic review on multipotent carcinogenic agent, N-nitrosodiethylamine (NDEA), its major risk assessment, and precautions

The International Agency for Research on Cancer has classified N-nitrosodiethylamine (NDEA) as a possible carcinogen and mutagenic substances, placing it in category 2A of compounds that are probably harmful to humans. It is found in nature and tobacco smoke, along with its precursors, and is also synthesized endogenously in the human body. The oral or parenteral administration of a minimal quantity of NDEA results in severe liver and kidney organ damage. The NDEA required bioactivation by CYP450 enzyme to form DNA adduct in the alkylation mechanism. Thus, this bioactivation directs oxidative stress and injury to cells due to the higher formation of reactive oxygen species and alters antioxidant system in tissues, whereas free radical scavengers guard the membranes from NDEA-directed injury in many enzymes. This might be one of the reasons in the etiology of cancer that is not limited to a certain target organ but can affect various organs and organ systems. Although there are various possible approaches for the treatment of NDEA-induced cancer, their therapeutic outcomes are still very dismal. However, several precautions were considered to be taken during handling or working with NDEA, as it considered being the best way to lower down the occurrence of NDEA-directed cancers. The present review was designed to enlighten the general guidelines for working with NDEA, possible mechanism, to alter the antioxidant line to cause malignancy in different parts of animal body along with its protective agents. Thus, revelation to constant, unpredictable stress situations even in common life may remarkably augment the toxic potential through the rise in the oxidative stress and damage of DNA.

Nanocapsulated quercetin downregulates rat hepatic MMP-13 and controls diethylnitrosamine-induced carcinoma

AIMS

The aims of our work were to investigate the controlling role and the efficacy of nanocapsulated quercetin drug delivery system on the decrement of inflammatory mediators such as MMP-13 in diethyl nitrosamine (DEN)-induced hepatocarcinogenesis.

MATERIALS & METHODS

Hepatocellular carcinoma was developed in the Swiss albino rats by the exposure of DEN. DEN administration caused the generation of reactive oxygen species, upregulation of TNF-α, IL-6, activation of MMP-13, severe oxidative damage, hyperplastic nodules with preneoplastic lesions and the histopathological changes in rat liver.

RESULTS & CONCLUSION

Nanocapsulated quercetin treatment restricted all alterations in DEN-mediated development of hepatocarcinogenesis. Therefore, it may be concluded that nanocapsulated quercetin may be accepted as a potent therapeutic formulation in preventing DEN-mediated hepatocarcinogenesis.

Differential effects of partial hepatectomy and carbon tetrachloride administration on induction of liver cell foci in a model for detection of initiation activity

Differential effects of partial hepatectomy (PH) and carbon tetrachloride (CCl(4)) administration on induction of glutathione S-transferase placental form (GST-P)-positive foci were investigated in a model for detection of initiation activity. Firstly, we surveyed cell proliferation kinetics and fluctuation in cytochrome P450 (CYP) mRNA levels by means of relative-quantitative real-time reverse transcriptase-polymerase chain reaction (RT-PCR) and CYP 2E1 apoprotein amount by immunoblotting (experiment I) after PH or CCl(4) administration. Next, to assess the interrelationships among cell proliferation, fluctuation of CYPs after PH or CCl(4) administration and induction of liver cell foci, the non-hepatocarcinogen, 1,2-dimethylhydrazine (DMH) was administered to 7-week-old male F344 rats and initiated populations were selected using the resistant hepatocyte model (experiment II). In experiment I, the values of all CYP isozyme mRNAs after PH or CCl(4) administration were drastically decreased at the 12-h time point. From 72 h, mRNAs for all CYP isozymes began increasing, with complete recovery after 7 days. The CYP 2E1 apoprotein content in the PH group fluctuated weakly, whereas in the CCl(4) group it had decreased rapidly after 12 h and was still low at the 48 h point. In experiment II, induction of GST-P-positive foci was related to cell kinetics in the PH group, with about a 6-h time lag between time for carcinogen administration giving greatest induction of GST-P-positive foci and peaks in bromodeoxyuridine (BrdU) labeling, presumably due to the necessity for bioactivation of DMH. With CCl(4) administration, induction of foci appeared dependent on the recovery of CYP 2E1. In conclusion, PH was able to induce cell proliferation with maintenance of CYP 2E1, therefore being advantageous for induction of liver cell foci in models to detect initiation activity.

Role of hypoxia and constitutionally different resistance to hypoxia/stress as the determiners of individual profile of cytochrome P450 isozyme activity

The hepatic cytochromes P450 1A1, 1A2, 2B1, and 2E1 activities have been investigated in the sublines of Wistar rats with principally different (high or low) resistance to hypoxia/stress. Repeated measurements in normoxic conditions showed a significant prevalence of total cytochrome P450 content, CYP 1A1, and CYP 2E1 activities in rats with low-resistance (LR) to hypoxia compared to rats with high-resistance to hypoxia (HR), whereas in HR rats the CYP 1A2 activity was 63% higher (p < 0.001) than in LR rats. In the conditions of acute hypobaric hypoxia these differences were manifested distinctly: in HR rats an enhancement of CYP 1A2 activity by 49% of aerobic value (p < 0.01) was observed, in LR rats the total P450 content, CYP 1A1 and 2E1 activities (p < 0.05-0.001) were increased. The 30-min total liver ischemia formed an individual response of the drug-metabolizing system: in HR rats CYP 1A2 and 2B1 activities were decreased in the early postischemic period and were not restored by the 21st day, whereas in LR rats CYP 1A2 activity was not affected and was induced more than 2-fold of aerobic value in the late post-ischemic period. The CYP 2B1 activity was induced almost 1.5-fold during the whole postischemic period. These data suggest that acute hypoxia and individual resistance to hypoxia/stress, one of the cardinal constitutional features, provide an individual reaction of drug-metabolizing system and enzymes of P450, in particular. The individual constitutional resistance to hypoxia/stress may be a serious criterion for an individual approach in pharmacotherapy of hypoxic states, diseases, as well as for prognosis and prevention of early and distant complications of irrational pharmacotherapy.

The detection of cytochrome P450 2E1 and its catalytic activity in rat testis

Cytochrome P450 2E1 participates in the bioactivation of a wide variety of environmental and occupational pollutants. Such reactions may lead to the production of active carcinogenic metabolites. The presence of P450 2E1 in the testis and prostate has not yet been reported. In the present study, cytochrome P450 2E1 mRNA has been identified in the rat prostate and testis by reverse transcription PCR, southern blotting, and DNA sequencing. P450 2E1 protein from rat testis could be detected with immunoblot analysis, but was not detected in the prostate. The hydroxylation of p-nitrophenol, known to be mediated by P450 2E1, was demonstrated by HPLC measurement of product formation in microsomal fractions from the rat testis, but again not from prostate. Exposure of rats to pyridine resulted in a 2.9-fold increase of p-nitrophenol hydroxylation by testicular microsomes. Diethyldithiocarbamate, a selective mechanism-based inhibitor of P450 2E1, or a P450 2E1 monoclonal antibody, caused marked inhibition of testicular microsomal p-nitrophenol hydroxylase activity. These results indicate that cytochrome P450 2E1 is present in the rat testis, and that it is elevated by the treatment of the animals with pyridine. Thus, the presence and inducibility of cytochrome P450 2E1 in the testis may be of significance in the bioactivation of environmental chemicals to genotoxic metabolites.

Drug metabolism in rats with cancer induced by N-nitrosodiethylamine and phenobarbital

The metabolism of R- and S-warfarin in vivo and in vitro, bufuralol in vitro, and antipyrine and debrisoquine in vivo were studied in rats with cancer induced by N-nitrosodiethylamine and phenobarbital treatment. Microsomal cytochrome P-450 content was greatly reduced in both healthy and cancerous parts of the livers of tumour-bearing animals. The specific activities of R-warfarin and bufuralol 1'-hydroxylases were significantly elevated in rats with cancer. The activities of S-warfarin hydroxylases expressed per mg microsomal protein were reduced in animals with cancer, whereas those of R-warfarin and bufuralol 1'-hydroxylases were not. The urinary excretion of R-7-hydroxywarfarin was increased and those of S-6- and S-4'-hydroxywarfarin decreased in rats with cancer. The correlations between microsomal formation and urinary excretion of all warfarin metabolites were poor, except for R-7-hydroxywarfarin. Antipyrine oxidation was increased in the cancerous state but the urinary metabolic profiles were similar in rats with cancer and in controls. The metabolism of debrisoquine was decreased in tumour-bearing animals. Antipyrine metabolism did not show any correlation with either warfarin or debrisoquine metabolism, whereas several relationships were observed between warfarin and debrisoquine metabolism and between warfarin and bufuralol metabolism.