Chromosomal Aberration Test in Human Lymphocytes.

Human peripheral lymphocytes (HPL) are non-cycling primary cells (G0 cells). They are easily collectable by venipuncture. In the presence of suitable culture media and stimulants in vitro HPL enter the cell cycle and divide mitotically. Metaphase-like stages can be arrested using the spindle fiber poison colcemid and prepared on microscopic slides. Following appropriate staining, chromosomal aberrations can be analyzed in the microscope. These aberrations may either be induced in vivo by environmental or occupational influences or in vitro after experimentally controlled manipulations in order to detect or to test the mutagenic potency of various agents.

Chromosomal aberration test in human lymphocytes.

Human peripheral lymphocytes (HPL) are non-cycling primary cells (G0 cells). They are easily collectable by venipuncture. In the presence of suitable culture media and stimulants in vitro HPL enter the cell cycle and divide mitotically. Metaphase-like stages can be arrested using the spindle fiber poison colcemid and prepared on microscopic slides. Following appropriate staining, chromosomal aberrations can be analyzed in the microscope. These aberrations may be induced either in vivo by environmental or occupational influences or in vitro after experimentally controlled manipulations in order to detect or to test the mutagenic potency of various agents.

The number and not the molecular structure of DNA double-strand breaks is more important for the formation of chromosomal aberrations: a hypothesis.

DNA double-strand breaks (DSB) are known to cause chromosomal aberrations (CA). The ends of DSB have different molecular structures depending on the inducing agent. Restriction endonucleases, DNase I and benzon nuclease produce DSB with 3'-OH and 5'-phosphate ends which should be easily rejoinable ("clean" DSB). Other DSB-inducing agents, such as neocarzinostatin, bleomycin and ionizing radiation induce DSB with chemically modified ends ("dirty" DSB) which are not religatable before enzymatic pruning to make them "clean". Both "clean" and "dirty" DSB lead to CA whose quantities and distributions are quite similar. We conclude that the number and not the molecular structures of DSB are essential for the production of CA. All DSB-inducing agents discussed in this review induce exchange events in the G1 phase of the cell cycle which look like sister chromatid exchanges (SCE) and are therefore called "false" SCE. "False" SCE seem to be mainly intrachanges and would therefore outweigh the frequencies of interchanges. Consequently, the factor F of inter- to intrachanges would then be <1, indicating that the majority of DSB would lead to CA inside the chromosome domains in which they were induced and not between different chromosomes.

Controversial cytogenetic observations in mammalian somatic cells exposed to extremely low frequency electromagnetic radiation: a review and future research recommendations.

During the years 1990-2003, a large number of investigations were conducted using animals, cultured rodent and human cells as well as freshly collected human blood lymphocytes to determine the genotoxic potential of exposure to nonionizing radiation emitted from extremely low frequency electromagnetic fields (EMF). Among the 63 peer reviewed scientific reports, the conclusions from 29 studies (46%) did not indicate increased damage to the genetic material, as assessed from DNA strand breaks, incidence of chromosomal aberrations (CA), micronuclei (MN), and sister chromatid exchanges (SCE), in EMF exposed cells as compared with sham exposed and/or unexposed cells, while those from 14 investigations (22%) have suggested an increase in such damage in EMF exposed cells. The observations from 20 other studies (32%) were inconclusive. This study reviews the investigations published in peer reviewed scientific journals during 1990-2003 and attempts to identify probable reason(s) for the conflicting results. Recommendations are made for future research to address some of the controversial observations.

Controversial cytogenetic observations in mammalian somatic cells exposed to radiofrequency radiation.

During the years 1990-2003 a large number of investigations were conducted using rodents, cultured rodent and human cells, and freshly collected human blood lymphocytes to determine the genotoxic potential of exposure to radiofrequency (RF) radiation. The results of most of these studies (58%) did not indicate increased damage to the genetic material (assessed from DNA strand breaks, incidence of chromosomal aberrations, micronuclei and sister chromatid exchanges) in cells exposed to RF radiation compared to sham-exposed and/or unexposed cells. Some investigations (23%) reported an increase in such damage in cells exposed to RF radiation. The observations from other studies (19%) were inconclusive. This paper reviews the investigations published in scientific journals during 1990-2003 and attempts to identify probable reason(s) for the conflicting results. Recommendations are made for future research to address some of the controversial observations.

Effect of microcystin-LR and cyanobacterial extract from Polish reservoir of drinking water on cell cycle progression, mitotic spindle, and apoptosis in CHO-K1 cells.

Microcystin-LR is a cyanobacterial toxin possessing a potent tumor-promoting activity mediated through inhibition of protein phosphatases PP1 and PP2A. Because these enzymes are involved in fundamental cell processes, we decided to examine the influence of microcystin-LR on cell cycle progression, onset of anaphase, segregation of chromosomes by the mitotic spindle, and apoptosis in Chinese hamster ovary (CHO-K1) cells. Cells were incubated with 25, 50, and 100 microM of pure microcystin-LR and a cyanobacterial extract for 14, 18, and 22 h. Giemsa staining of cells treated with these toxins revealed a dose- and time-dependent increase of mitotic indices, accumulation of abnormal G(2)/M figures with hypercondensed chromosomes, abnormal anaphases with defective chromosome separation, and polyploid cells. Because spindle checkpoint is a fundamental regulatory mechanism that assures the onset of anaphase and subsequent exit from mitosis, we examined the spindle organization in microcystin-treated cells. The majority of the mitotic cells showed monopolar and multipolar mitotic spindles (multiple asters). Microtubule bundles were present in interphase cells. Our results indicate that microcystin-LR induces apoptosis and necrosis in a dose- and time-dependent manner and that the frequency of dead cells cells is positively correlated with the frequency of polyploid cells.