Amit H. Trivedi

DNA repair proficiency in breast cancer patients and their first-degree relatives

Defective DNA repair capacity as measured by enumerating chromatid aberrations induced in G2 phase by X‐irradiation may explain increased risk of breast cancer among relatives of patients. In the present study, chromatid damage was determined in peripheral blood lymphocytes (PBL) following in vitro exposure to 50R X‐irradiation in G2 phase from 14 breast cancer (BrCa) patients, 19 first‐degree relatives (FDR) of BrCa patients and 17 control women who had no family history of cancer for the last 3 generations. Controls, BrCa patients and their FDR had comparable frequency of gaps and breaks when cells were arrested with Colcemid (30 min) after X‐irradiation. A steep decline in chromatid damage was observed in cells of controls when arrested after 30, 90 and 120 min of X‐irradiation. BrCa patients and their FDR showed higher frequencies of lymphocytic chromatid damage as compared to controls. Chromatid damage (95 gaps + breaks per 100 cells) observed among controls at 90 min post X‐irradiation was considered as the optimal level of efficient DNA repair. Thirty‐five percent of controls, 93% of BrCa patients and 79% of FDR showed sub‐optimal DNA repair. Amongst the FDR, the likelihood of having suboptimal DNA repair was 7 times higher and the risk of developing breast cancer was 2.7 times higher as compared to controls. Moreover, in the BrCa patients, there was frequent involvement of chromosomes 1 and 2, and chromosomes of B, D and E groups, while in FDR, involvement of chromosome 2 and chromosomes of B, D and E groups was more frequent. Int. J. Cancer 73:20–24, 1997.

Assessment of genotoxicity of nicotine employing in vitro mammalian test system

Genotoxicity of nicotine was evaluated employing Chinese hamster ovary (CHO) cells. Two cytogenetic endpoints, viz. frequency of sister chromatid exchange (SCE) and chromosome aberration (CA) were considered. Nicotine was found to induce CA and SCE frequency in a dose and duration dependent manner. Statistically significant elevations in CA frequency were observed only with higher concentrations of nicotine, whereas, SCE frequencies were increased significantly by all the doses utilized. It was genotoxic at the concentration, comparable to the saliva levels of nicotine achieved during tobacco chewing. The results obtained by continuous and pulse treatments with nicotine explain the harmful effects of chronic tobacco consumption.

In vitro genotoxic effects of areca nut extract and arecoline

SummaryThe genotoxic potential of the aqueous extract of areca nut as well as arecoline, the major alkaloid of the areca nut, was tested with the help of cytogenetic markers such as sister-chromatid exchanges and chromosome aberrations, utilizing Chinese hamster ovary (CHO) cells. The continuous-treatment and pulse-treatment schedules yielded dose-dependent elevations in the frequencies of sister-chromatid exchange and chromosomal aberration in CHO cells, indicating a genotoxic effect of both the extract and arecoline. The results also imply that, besides arecoline, there may be some other water-extractable substances in the areca nut that make the extract more genotoxic. The chromosome damage was found to be more severe on treating the cells with low concentrations and for longer duration, which mimic the effects of chronic areca nut consumption.

Spontaneous Chromosomal Instability in Breast Cancer Families

Spontaneous chromosomal instability has been correlated with cancer predisposition. In the present study, the phenomenon has been evaluated using two cytogenetic markers, namely, frequency of spontaneous sister chromatid exchanges (SCE) and spontaneous chromosomal aberrations (CA) in peripheral blood lymphocytes of hereditary breast cancer (HBC) patients (n = 11) and healthy blood relatives (HBR, n = 36). A statistically significant difference was observed for both the endpoints between HBC patients and controls (P < 0.001), HBC patients and HBR (P < 0.001), as well as HBR and controls (P < 0.001). Thus, 63.64% of the HBC patients and 25% of HBR showed a mean CA/cell value higher than the highest mean CA/cell value of the controls (0.11 CA/cell). Similarly, 81.81% of the HBC patients and 61.11% of HBR showed a mean SCE/cell value higher than the highest mean SCE/cell value of the controls (9.60 SCE/cell). Chromosomal aberrations were more frequently observed in the B and E group of chromosomes in HBC patients and HBR. These findings primarily indicate the high level of chromosomal instability in breast cancer families, and might be one of the predisposing factors for high risk of cancer in HBR.

Spontaneous and induced sister chromatid exchange frequencies and cell cycle progression in lymphocytes of patients with carcinoma of the uterine cervix

Thirteen healthy females and thirteen untreated patients with carcinoma of the uterine cervix were studied for spontaneous and mitomycin C (MMC)-induced rates of sister chromatid exchange (SCE) and cell cycle progression. The mean values of spontaneous as well as MMC-induced SCE rates showed no statistically significant difference between groups. For studying cell cycle progression, cells in the M1, M2, and M3 stages were scored from the same samples. The percent values of cells in these stages, identified by the nature of differential sister chromatid staining, were found to be almost identical in normal as well as MMC-treated cultures in controls and patients. It was concluded that the presence of carcinoma of the uterine cervix in human females has no bearing either on spontaneous and MMC-induced SCE rates or on cell cycle progression in PHA-stimulated cultures of peripheral blood lymphocytes.

Chromosome damaging effects of pan masala

Effects of aqueous extracts of a popular brand of pan masala with and without tobacco (PM-T and PM) were studied for short duration treatment employing an in vitro system. Metabolic activation with S9 mix was also included. Frequency of all the three cytogenetic endpoints viz., chromosome aberration (CA); sister chromatid exchange (SCE) and % micronucleated cells (% MNC) were found to be elevated significantly in a dose-dependent manner in cultures without metabolic activation. However, addition of S9 activation system resulted in suppression of chromosomal damage. Our findings indicate that pan masalas contain water soluble direct acting mutagens.

Genotoxic effects of nicotine in combination with arecoline on CHO cells

Genotoxic effects of nicotine and arecoline, major alkaloids of tobacco and areca nut, respectively, were analysed in combination on CHO cells utilising two different cytogenetic end points, namely chromosome aberration frequency and sister chromatid exchange frequency. Statistically significant elevation in the values of both markers compared with controls, as well as nicotine alone, clearly indicated a more clastogenic and genotoxic effect following the addition of areca nut to tobacco. The effects observed following the treatment with a low dose for a longer duration are of relevance to the condition of oral mucosa of the chewers of tobacco with areca nut.

Heteromorphism of C-band positive chromosomal regions in CML patients

The heteromorphism of constitutive heterochromatin in chromosomes #1, #9, and #16 was investigated in 44 chronic myelocytic leukemia patients and 44 controls using bone marrow and peripheral blood lymphocyte cultures. A significant increase in the length of C-band region in all the three chromosome pairs as well as a statistically significant difference in the homologs of chromosome #1 was observed in chronic myelocytic leukemia patients when compared with the controls. The frequency of inversions was also greater in the patients than in the controls. A random translocation of 22q was found on either homolog of chromosome #9.

Pan masala — a genotoxic menace

Cytogenetic markers such as chromosome aberration (CA), sister-chromatid exchange (SCE) and micronucleated cells (MNC) were used to assess the genotoxic potential of dimethyl sulphoxide (DMSO) extract of pan masala with and without tobacco (PM-T and PM). Using in vitro short-term assays, the extracts were tested in the presence or absence of metabolic activation. In cultures without metabolic activation the extracts were found to increase the frequency of all the three parameters tested significantly, however those with activation elicited a weak response, implying that pan masalas contain solvent (DMSO)-soluble direct-acting mutagen.

Genotoxic effects of tobacco extract on Chinese hamster ovary cells

Genotoxic effects of an aqueous extract of Nicotiana tabacum, a variety commonly used in India for chewing purposes, were analysed on CHO cells utilizing two different cytogenetic end-points, namely, chromosome aberration frequency and sister chromatid exchange frequency. Statistically significant elevations in the values of both the markers clearly indicated chromosome damaging effects of the extract. Elevations in chromosome aberration and sister chromatid exchange frequencies are suggestive of intrastrand and interstrand DNA cross-links following exposure to tobacco. The effects observed following treatment with low dose for longer duration are of relevance to the condition of the oral mucosa of the chronic smokeless tobacco users.