Zoltan Trizna

Glutathione S-transferase genotypes as risk factors for head and neck cancer

BACKGROUNDnSeveral enzymatic systems, including glutathione S-transferases, are involved in the metabolism of environmental agents. The absence of glutathione S-transferases mu (GSTM1) and theta (GSTT1) results in decreased detoxification of carcinogens, for example, chemicals in cigarette smoke. These metabolic deficiencies may predispose individuals to the development of smoking-related tumors, such as cancers of the lung, head and neck, and bladder.nnnMETHODSnThe glutathione S-transferase genotypes of 186 previously untreated patients with squamous cell carcinoma of the head and neck and 42 healthy controls were determined with polymerase chain reaction (PCR) methodologies. Lymphocytes separated from heparinized peripheral blood or whole blood extracts served as sources of genomic DNA. The presence or absence of the gene-specific PCR products revealed the positive or negative genotypes, respectively.nnnRESULTSnThe absence of the GSTM1 genotype conferred an odds ratio of 2.37, and the 95% confidence interval (CI) was 1.20 to 4.67. The absence of the GSTT1 gene conferred an odds ratio of 1.47 (CI 0.71 to 3.02). In the population of 42 patients and their matched 42 controls, the absence of the GSTM1 and GSTT1 genotypes conferred odds ratios of 3.10 (CI 1.24 to 7.75) and 2.18 (CI 0.91 to 5.23), respectively.nnnCONCLUSIONSnDespite the small study size, our preliminary data suggest that genetically determined factors of carcinogen metabolism may be associated with increased risk for head and neck cancer.

Effects of N-acetyl-l-cysteine and ascorbic acid on mutagen-induced chromosomal sensitivity in patients with head and neck cancers

The protective effect of N-acetyl-L-cysteine (NAC) and ascorbic acid on mutagen-induced chromosomal breakage was determined using human lymphoblastoid cell lines as well as freshly cultured lymphocytes from patients with head and neck malignancies and healthy control subjects. Mutagen sensitivity was determined using the previously described bleomycin exposure assay. The toxicities of different concentrations of NAC and ascorbic acid, as well as both the preincubation and dose-dependent protective effects of these two agents, were analyzed. Both test drugs proved to be effective in diminishing mutagen-induced chromatid breakage in established lymphocyte cell lines. In freshly cultured lymphocytes, NAC given in doses ranging from 0.1 to 10 mmol/L decreased the number of mutagen-induced breaks per cell in a range from 23% to 73%, and ascorbic acid decreased chromosomal breakage by 21% to 58% in a dose range from 0.01 to 1 mmol/L. The results of this study demonstrate the protective effect mediated in vitro by both NAC and ascorbic acid against mutagen-induced chromosomal damage. A similar in vivo phenomenon may explain the differences in occurrence of head and neck cancer between populations with different dietary backgrounds.

Epidemiology, biology, and chemoprevention of aerodigestive cancer.

Cancers of the aerodigestive tract are a major cause of worldwide morbidity and mortality. Long term survival rates for these epithelial cancers have not improved substantially in the past 20 years despite intensive efforts to improve the prevention and therapy of these diseases. Therefore, new approaches are needed. One new investigative approach is chemoprevention, the chemical prevention of cancer. Chemoprevention studies in the upper aerodigestive tract have focused on the reversal of pre‐malignant lesions and the prevention of second primary tumors. These chemoprevention efforts have resulted from an understanding of the multistep nature of epithelial carcinogenesis and the diffuse epithelial injury that results from carcinogen exposure. Ongoing research efforts are attempting to define these processes. The interaction between carcinogen exposure and host susceptibility in the development of cancers of the aerodigestive tract is being evaluated (e.g., with an assay of chromosomal sensitivity to the clastogen bleomycin). This review discusses several new aspects of the epidemiology, biology, and chemoprevention of aerodigestive tract carcinogenesis.

Mutagen sensitivity in humans: A comparison between two nomenclature systems for recording chromatid breaks

Currently, there are two systems in use for recording chromatid breaks, either spontaneously occurring or induced by mutagens: The International System for Human Cytogenetic Nomenclature (ISCN) and the Chatham Barrs Inn Conference (CBIC) recommendation. The former system considers that a chromatid break is recognized only when the chromatid fragment is displaced to the other side of its sister chromatid, while all others, regardless of the distance between the two broken ends, are called chromatid gaps. The CBIC system recognizes a chromatid break when the intervening achromatic segment is longer than or equal to the diameter of the chromatid, whether the fragment is displaced or not. Minor lesions are called chromatid gaps. We conducted experiments using bleomycin treatment of human cells (primary cultures or lymphoblastoid cell lines) and read the chromatid lesions both ways. We conclude that the CBIC system appears to have more direct biologic relevance than the ISCN system.

Anticlastogenic Effects of 13-cis-Retinoic Acid in vitro

The anticlastogenic effects of 13-cis-retinoic acid were studied in four human lymphoblastoid cell lines and in primary lymphocyte cultures derived from the peripheral blood of 11 study subjects. Cells were pre-incubated with 13-cis-retinoic acid in the concentration range of 10(-8)-10(-5) mol/l for 24 h and the numbers of chromatid breaks per cell induced by bleomycin were determined. The presence of 13-cis-retinoic acid decreased the number of breaks per cell by 13.0 to 59.5% in lymphoblastoid cell lines and by 0 to 57.4% in primary lymphocyte cultures (in the concentration ranges of 10(-8)-10(-6) mol/l and of 10(-8)-10(-5) mol/l, respectively). Regression analysis showed that there was a statistically significant correlation between the presence of 13-cis-retinoic acid and protection against bleomycin-induced clastogenicity. These data give additional information to the knowledge of possible chemopreventive mechanisms of action of 13-cis-retinoic acid.