Evaluation of omeprazole genotoxicity in a battery of in vitro and in vivo assays.

Omeprazole, a proton pump inhibitor of wide use in the treatment of gastric acid-related disorders, was evaluated for its genotoxic effects in both rat and human cultured cells and in the intact rat. DNA repair synthesis, as revealed by autoradiography, was detected in primary cultures of metabolically competent rat hepatocytes exposed to concentrations ranging from 10 to 100 mg/l, but the responses cannot be considered as clearly positive. Under the same experimental conditions any significant evidence of DNA repair was absent in primary hepatocytes from two human donors. At the same concentrations a modest but dose-related increase of micronucleated cells, that reached the level of statistical significance at 33 mg/l, was present in primary rat hepatocytes and in one of two human donors. In human lymphocytes exposed to subtoxic concentrations ranging from 0.78 to 12.5 mg/l a reproducible concentration dependent clastogenic effect was absent. In partially hepatectomized female rats treated with a single p.o. dose of 1000 mg/kg, the frequency of micronucleated cells was 5.2-fold higher than in controls in the liver, but only 2.0-fold higher in polychromatic erythrocytes of the bone marrow. In rats of the same sex given azoxymethane as initiator of colon carcinogenesis the oral administration for 8 successive weeks of 10 mg/kg omeprazole on alternate days increased the response to azoxymethane, as indicated by the occurrence in colon mucosa of a modest but statistically significant increase in both the average number and size of aberrant crypt foci. Taken as a whole, our results suggest that omeprazole behaves as a weak genotoxic agent for the rat liver. Reliable information about the potential genotoxic risk to humans requires further studies on primary cells from a wide number of donors.

Induction of micronuclei and initiation of enzyme-altered foci in the liver of female rats treated with cyproterone acetate, chlormadinone acetate, or megestrol acetate.

The synthetic anti-androgen and progestin cyproterone acetate (CPA), recently found to be genotoxic for the liver, and two structurally similar progestins, chlormadinone acetate (CMA) and megestrol acetate (MGA), have been compared for clastogenic and tumor-initiating activities in female rats. In the micronucleus assay, carried out in rats given a single p.o. dose of 100 mg/kg, CPA induced the maximum increase in the frequency of micronucleated hepatocytes (6.6-fold as compared to controls) when treatment was performed 3 days before partial hepatectomy and cell sampling 2 days later. Under the same experimental conditions the clastogenic potencies of CMA and MGA were 69% and 36% of that of CPA respectively. In the liver foci assay, p.o. dosing with 100 mg/kg CPA once a week for 6 successive weeks induced, as compared to controls, a significant increase in the number and area of gamma-glutamyltranspeptidase-positive foci. At the same dosage schedule the tumor-initiating activity of CMA and MGA was 7- to 10-fold lower than that of CPA. These findings suggest that the 1,2 alpha-methylene group, present in CPA but absent in both CMA and MGA, favours the activation to a reactive species and/or hinders the biotransformation to non-toxic metabolites.

Cinnamaldehyde-induced micronuclei in rodent liver.

Cinnamaldehyde, a widely used flavoring agent, has so far been subjected to a limited range of genotoxicity tests, mainly carried out in vitro, which produced contradictory results. Therefore we have examined cinnamaldehyde using additional in vivo genotoxicity end-points. In Sprague-Dawley rats, a single oral dose equal to 1/2 LD50 did not induce DNA fragmentation in liver and gastric mucosa as evaluated by the alkaline elution technique, increased the frequency of micronucleated hepatocytes but not of bone marrow micronucleated polychromatic erythrocytes, and gave rise to a significantly higher incidence of total nuclear anomalies but not of micronucleated cells in forestomach mucosa. In Swiss mice, the equitoxic dose of cinnamaldehyde caused the same clastogenic effect in the liver, whilst a negative response was observed in both bone marrow and forestomach mucosa. Finally, in rats initiated with N-nitrosodiethylamine the administration of 500 mg/kg/day cinnamaldehyde for 14 successive days produced a modest but statistically significant increase of the average diameter and area of gamma-glutamyltranspeptidase-positive foci that, together with changes observed in other parameters, might be considered indicative of a potential promoting activity. Taken as a whole, these findings confirm that high doses of cinnamaldehyde may induce genetic alterations at the chromosomal level, and suggest that the liver is the preferential target of its undesirable effects.

Oral administration of chlordiazepoxide plus sodium nitrite investigated for tumor initiating activity in the rat liver.

Chlordiazepoxide (CDE) reacts with sodium nitrite at acid pH yielding the genotoxic derivative N-nitrosochlordiazepoxide (NO-CDE). In the present study oral administration of CDE plus NaNO2, previously found to produce DNA fragmentation in the rat liver, was examined for its ability to initiate hepatocarcinogenesis. The oral treatment for 6 successive weeks with CDE + NaNO2, added to the diet at the levels of 290 + 270 and 870 + 800 ppm, did not significantly increase the number or volume of gamma-glutamyltranspeptidase-positive foci (putative preneoplastic lesions). These findings are in agreement with the negative results previously obtained in rodent carcinogenesis assays and indicate that NO-CDE belongs to the progressively expanding list of genotoxic non-carcinogens.