Lionel Gil

Inhibitors of cytochrome P-450-dependent arachidonic acid metabolism.

A new generation of heteroatom analogs of arachidonic acid are documented as powerful and selective inhibitors of the cytochrome P-450-dependent arachidonic acid oxygenase reaction (IC50, 5-10 microM) with little effect on either cyclooxygenase or soybean lipoxidase at 100 microM. The imidazole derivatives, ketoconazole and clotrimazole, are potent and selective inhibitors of the arachidonic acid epoxygenase and lipoxidase-like activities of phenobarbital-induced rat liver microsomal fractions (IC50, 2.0 and 0.3 microM, respectively). In contrast, the w/w-1 oxygenase activity of ciprofibrate-induced microsomal fractions was relatively resistant to inhibition by these compounds (IC50, 50 and 25 microM for ketoconazole and clotrimazole, respectively). Nordihydroguaiaretic acid (NDGA), eicosatetraynoic acid (ETYA), and indomethacin, extensively utilized inhibitors of the cyclooxygenase and lipoxygenase branches of the arachidonate cascade, also inhibit cytochrome P-450-dependent arachidonic acid metabolism. In decreasing order of potency, they were NDGA, ETYA, and indomethacin (IC50, 15, 40, and 70 microM, respectively).

Arsenic Exposure and the Induction of Human Cancers

Arsenic is a metalloid, that is, considered to be a human carcinogen. Millions of individuals worldwide are chronically exposed through drinking water, with consequences ranging from acute toxicities to development of malignancies, such as skin and lung cancer. Despite well-known arsenic-related health effects, the molecular mechanisms involved are not fully understood; however, the arsenic biotransformation process, which includes methylation changes, is thought to play a key role. This paper explores the relationship of arsenic exposure with cancer development and summarizes current knowledge of the potential mechanisms that may contribute to the neoplastic processes observed in arsenic exposed human populations.

Susceptibility and exposure biomarkers in people exposed to PAHs from diesel exhaust

Xenobiotic metabolizing enzymes, especially CYP1A1 and GSTM1, are involved in the activation and conjugation of PAHs and are controlled by polymorphic genes. PAHs released from diesel emissions in many cities of the world, especially in developing countries, contribute significantly to the toxic effects of airborne inhalable particles. We have evaluated the gene-environment interaction in Santiago of Chile, studying the contribution of CYP1A1 and GSTM1 polymorphisms on 1-OH-P urinary levels used as the PAHs exposure biomarker. The study was performed on 59 diesel exposed (38 diesel revision workers and 21 subjects working in an urban area as established street vendors) and 44 non-exposed subjects living in a rural area. The 1-OH-P urinary levels of the urban (P=0.043) and rural (P=0.040) populations showed, without considering the genotypes, significant differences between smokers and non-smokers, but no significant differences were found between smokers and non-smokers among the diesel plant workers (P=0.33). Non-smoking subjects of the diesel plants and the urban area showed similar 1-OHP levels (P=0.466) which were significantly higher than those of the subjects living in the rural area (P<0.05). When 1-OH-P levels were related with genotypes, an association was observed for the CYP1A1*2A genotype, so that the diesel-exposed workers carrying the CYP1A1*2A allele showed significantly higher 1-OH-P levels than the subjects from the rural area with the same genotype (P=0.008). On the other hand, there was no significant correlation between urinary 1-OH-P levels and GSTM1 null genotype, although higher levels of the urinary metabolite were found in individuals carrying the combined CYP1A1*2A and GSTM1 null genotype (P=0.055). These results may suggest an association between levels of the exposure biomarker 1-OH-P and presence of the CYP1A1*2A genotype, a potential genetic susceptibility biomarker which might be useful in identifying individuals at higher risk among people exposed to high PAH levels in diesel exhaust.

Chilean pilot study on the risk of lung cancer associated with codon 72 polymorphism in the gene of protein p53.

The p53 gene has a polymorphism at codon 72 that presents the arginine or proline genotype, although this polymorphism has been associated with genetically determined susceptibility to lung cancers, the literature has not been consistent with this association. In Chile lung cancer represents the second cause of mortality from cancer. p53 codon 72 polymorphism frequency was studied in a Chilean subpopulation of 133 healthy controls and 111 lung cancer patients. The allelic distribution of the three genotypes (ArgArg, ArgPro, ProPro) in healthy normal controls was 41, 44 and 15%, respectively, which differs slightly from that of lung cancer patients, which was 38, 40 and 22%. A relation between the presence of the Pro allele and lung cancer risk in male smokers was observed. Relative risks were O.R.=2.47 (95% CI: 1.34-4.54) for one single nucleotide polymorphic allele (Pro) and O.R.=3.88 (95% CI: 1.16-13.39) for ProPro genotype.

Arsenic Biotransformation as a Cancer Promoting Factor by Inducing DNA Damage and Disruption of Repair Mechanisms

Chronic exposure to arsenic in drinking water poses a major global health concern. Populations exposed to high concentrations of arsenic-contaminated drinking water suffer serious health consequences, including alarming cancer incidence and death rates. Arsenic is biotransformed through sequential addition of methyl groups, acquired from s-adenosylmethionine (SAM). Metabolism of arsenic generates a variety of genotoxic and cytotoxic species, damaging DNA directly and indirectly, through the generation of reactive oxidative species and induction of DNA adducts, strand breaks and cross links, and inhibition of the DNA repair process itself. Since SAM is the methyl group donor used by DNA methyltransferases to maintain normal epigenetic patterns in all human cells, arsenic is also postulated to affect maintenance of normal DNA methylation patterns, chromatin structure, and genomic stability. The biological processes underlying the cancer promoting factors of arsenic metabolism, related to DNA damage and repair, will be discussed here.

Mutagenicity of organic extracts from Santiago (Chile) airborne particulate matter.

The Ames test has been used to detect the mutagenic activity of organic extracts from Santiago (Chile) airborne particles collected in 1990 and 1991 in one of the monitoring net system stations (MACAM). The samples were assayed with the strains TA98, TA98-NR, and TA98/1,8-DNP6 of Salmonella typhimurium, in the presence and in the absence of liver S9 fraction obtained from rats treated with Aroclor 1254. With the strain TA98 all the samples showed a very high mutagenic response either in the presence or in the absence of S9 fraction, suggesting that Santiago airborne particles contain both indirect-acting (polycyclic aromatic hydrocarbons) and direct-acting mutagenic agents. The mutagenicity of Santiago airborne particles was much higher than that reported in studies performed in other countries. Results obtained with the strains TA98-NR and TA98/1,8-DNP6 suggest that the extracts also contain mononitro and dinitroarenes. These nitroarenes have been described as very potent mutagenic agents, that can be generated by photochemical reactions under certain atmospheric conditions, or in the combustion of fuel, especially of diesel motors. The presence of polycyclic aromatic hydrocarbons and nitroarenes in Santiago airborne particles, as well as the high levels of mutagenicity detected, suggest that the inhabitants permanent exposure to these kinds of compounds represents a high risk for human health.

Some properties of the microsomal system metabolizing DDT in Triatoma infestans

Abstract 1. 1. Microsomes prepared from Triatoma infestans fifth-instar larvae metabolize DDT to a compound similar to Kelthane (metabolite No. 3), and to a derivative of apparently a phenolic nature (metabolite No. 2). 2. 2. The production of both metabolites requires either NADPH or NADH, but only the formation of metabolite No. 3 is nicotinamide—and magnesium— dependent. 3. 3. Optimum pH for the formation of metabolite No. 3 is 8·5, while it is 9·0 for metabolite No. 2. The K m values for each activity were also slightly different. 4. 4. The activity for each metabolite was increased by pretreatment with phenobarbital, but the induction kinetics was different in each case. 5. 5. These observations suggest that two rather than one microsomal enzyme are involved in DDT metabolism in T. infestans .

CYP1A1 and GSTM1 genetic polymorphisms in lung cancer populations exposed to arsenic in drinking water

Region II of Chile is the most important copper mining area in the world and it shows the highest lung cancer mortality rate in the country (35/100 000). The population in Antofagasta, the main city of Region II, was exposed from 1958 to 1970 to 860 µg m−3 arsenic (As) in drinking water and has currently been declining to 40 µg m−3. Glutathione serves as a reducing agent and glutathione S-transferase (GST) may have an important role in As methylation capacity and body retention. In the current study, the null genotype of GSTM1 and the MspI polymorphism of CYP450 1A1 were investigated in lung cancer patients and in healthy volunteers of Region II. In males, the 2A genotype of MspI represented a highly significant estimated relative lung cancer risk (OR = 2.60). Relative lung cancer risk for the combined 2A/null GSTM1 genotypes was 2.51, which increased with the smoking habit (OR = 2.98). In Region II, the cancer mortality rate for As-associated cancers at least partly might be related to differences in As biotransformation. Genetic biomarkers such as 2A and GSTM1 polymorphisms in addition to DR70 as screening biomarkers might provide relevant information to identify individuals with a high risk for lung cancer as prevention and protection actions to protect public health.

The effect of benzo[a]pyrene on DNA synthesis and DNA polymerase activity of rat liver mitochondria.

and methods The circular, double-stranded, covalentlyclosed mitochondrial genome has proved to be a target of choice for some carcinogenic drugs. When animal cells are incubated with radioactively labeled benzo[a]- pyrene (B[a]P), metabolites of the drug are found covalently linked to both nuclear and mitochondrial DNA, although the amount of derivative/pg DNA is higher in the organelle genome

Nutritionally triggered alterations in the regiospecificity of arachidonic acid oxygenation by rat liver microsomal cytochrome P450.

Cytochrome P450-dependent oxidation of arachidonic acid was studied in liver microsomes from normal fed, protein-energy malnourished, and refed rats. The overall rate of arachidonic acid oxidation was very similar in microsomes from the three groups, but microsomes from malnourished rats showed a higher turnover rate than microsomes from normal fed and refed rats. The regiospecificity of cytochrome P450 oxidation of arachidonic acid was drastically altered by the animal nutritional status. Thus, protein-energy malnutrition results in a clear stimulation of total omega and omega-1 hydroxylation, concomitant with a marked decrease in olefin epoxidation and allyllic oxidations. These changes, as well as the documented biological activity of some of the cytochrome P450 arachidonate metabolites, suggest that protein-energy deficiency might help to select P450 isozymes which are probably involved in key monooxygenation reactions of physiological substrates.