Antigenotoxic effect of allicin against methyl methanesulphonate induced genotoxic damage.

Allicin, one of the sulfur compounds especially thiosulphonates of garlic (Allium sativum), possesses antioxidant and thioldisulphide exchange activity and is also shown to cause a variety of actions potentially useful for human health. In this investigation we determined its antigenotoxic potential using chromosomal aberrations (CAs) and sister chromatid exchanges (SCEs) induced by methyl methanesulphonate (MMS) as genotoxic end points both in the presence as well as absence of rat liver microsomal activation system (S9 mix) in cultured human lymphocytes. We tested the effect of 5, 10 and 20 microM of allicin on the damage exerted by 60 microM of MMS. The levels of CAs and SCEs were lowered suggesting an antigenotoxic role of allicin against genotoxic damage both in the presence as well as absence of metabolic activation.

2-Deoxy-D-glucose induced modulation of DNA damage repair, survival, mutagenesis and recombinogenesis in 8-MOP+UVA treated yeast.

Cellular and genomic effects of post-treatment repair modulation by 2-deoxy-D-glucose (2-DG) and yeast extract were studied in 8-MOP + UVA treated cells of Saccharomyces cerevisiae. The type of lesions and their repair in phosphate buffer glucose (PBG) differed with UVA dose. At low UVA dose (1.4 kJ/m2), lesions were sublethal and mutagenic and did not repair by recombinogensis. The fraction of potentially lethal lesions and lesions repaired by recombinogenesis increased with UVA dose. Cellular repair in PBG was largely error-free and was inhibited by 2-DG. Yeast extract enhanced cellular repair and also recombinogensis; 2-DG in presence of yeast extract promoted error-prone repair. Pulsed-field gel electrophoresed chromosomal DNA bands did not show observable alterations immediately after 8-MOP + UVA treatment. On post-treatment incubation in PBG, the intensity ratio (rho n), of each band altered in a biphasic manner showing decrease first, followed by either increase or no change upto 24 hr depending upon UVA exposure dose. Presence of 2-DG in PBG inhibited decrease in rho n in a concentration dependent manner. Yeast extract reduced the time of first phase of DNA repair. 2-DG and yeast extract together reduced the time of first phase of repair and also inhibited the subsequent increase in rho n, which was observed in the case of yeast extract in PBG. It is proposed that (i) 2-DG in PBG inhibits excision of DNA damage and error-free repair; (ii) yeast extract stimulates the error-prone repair associated with cell cycle and recombinogenesis; (iii) 2-DG in presence of yeast extract allows excision of damage but inhibits build up through recombinogenesis inducing instead, cell cycle associated error-prone repair. A simple schematic model has been proposed to explain these events.

Effect of nalidixic acid on recombination and DNA repair of Escherichia coli K-12 strains.

Bacterial DNA gyrase enzyme plays a role in replication, transcription, recombination and repair. Escherichia coli gyrase enzyme is composed of two types of subunit, the gyr A and gyr B gene products called subunit A and B. Each type of subunit can be inhibited with temperature-sensitive mutations or by treating cells with specific antibiotic. Quinolones class of drugs such as nalidixic acid, oxonilic acid and norfloxacin affect gyr A protein. This effect due to inactivation of gyrase arises from the change in DNA superhelical tension. Mutant bacteria resistant to nalidixic acid show structural alterations in subunit A. Nalidixic acid resistant mutants of E. coli strains showed lower recombination efficiency, linkage, DNA repair, and mutation frequency than their wild types.

Modification by chloramphenicol of diethyl sulphate-induced male recombination frequency in Drosophila melanogaster.

To study the effect of chloramphenicol (CPL, an inhibitor of protein synthesis) on diethyl sulphate (DES, a potent mutagen) induced male recombination frequency, the F1 (+/aristaless dumpy black cinnabar, al dp b cn) larvae of D. melanogaster were given a pre- or post-treatment of CPL with DES during the first or second half of larval life. In order to determine sensitivity of different germ cell stages to the induction and modification of male recombination frequency, five 3-day broods were taken from every F1 male. DES showed toxic effect on egg-to-adult development. DES was found to be a potent recombinogen. Several cases of non-reciprocal male recombination were recorded. The most frequent recombinant phenotype observed was b cn followed by cn and al. Majority of the recombinants appeared in clusters suggesting their pre-meiotic origin. DES produced male recombination at a stage where only primary spermatocytes were present in the larval testes. CPL when given as a pre- or post-treatment with DES revealed highest frequency of male recombination in broods that represented effect of treatment on spermatogonia predominantly. CPL enhanced the overall level of male recombination produced by DES in both pre- and post-treatments. The results suggested the role of protein synthesis in induction of male recombination in D. melanogaster. In addition, the present experiments give a methodology of enhancing the frequency of chemically-induced male recombination.

Gradual decline of formaldehyde-induced male recombination in successive generations of Drosophila melanogaster.

Transmission of formaldehyde (FA)-induced male recombination was studied in D. melanogaster for three generations. Among recombinants, al dp was the most and b pr the next most frequent phenotype in the progenies of F1, TC1, TC2 and TC3 males of genotype + /al dp br. Non-reciprocal male recombination for dp-b and b-pr regions whereas reciprocal male recombination for al-dp region were noted. Percentages of recombinants observed in TC1 (1.052), TC2 (0.876), TC3 (0.698) and TC4 (0.497) progenies of D. melanogaster males were not statistically different from each other in any two successive generations. A continuous but gradual decline in the frequency of FA-induced male recombination was observed in the three subsequent generations studied.

Evaluación de la actividad genética de los medicamentos meprobamato y pirimetamina en Aspergillus nidulans / Evaluation of genetic activity of meprobamate and pirimetamine on Aspergillus nidulans

El objetivo de este trabajo es estudiar la actividad genética como inductores de recombinación mitótica y de delecciones, de dos medicamentos: meprobamato y pirimetamina, utilizando el ascomiceto Aspergillus nidulans como organismo de ensayo. Para el primer caso se utilizó una cepa diploide heterocigótica para marcadores del color de los conidios, y en el segundo caso, la cepa llevaba una duplicación de parte del genoma en el grupo de ligamento II. Para cada medicamento se probaron varias concentraciones diferentes; 6 para el meprobamato y 4 para la pirimetamina. Los resultados obtenidos indican que el meprobamato induce delecciones a las dosis de 10mM, 5mM y 2,5mM. La pirimetamina, a su vez, presentó un efecto positivo como inductora de recombinación mitótica a la dosis de 50*g/ml. Estos resultados indican que estos medicamentos, de amplio uso en nuestro país, presentan cierto tipo de actividad genética, detectada en las condiciones experimentales usadas por nosotros en este trabajo