The effects of cryopreservation on sperm morphology, motility and mitochondrial function

BACKGROUND

The effects of cryoinjury were determined simultaneously on the mitochondrial function, motility, morphology and viability of ejaculated human sperm.

METHOD

Rhodamine 123 (R123) uptake (% of sperm) and stain intensity were used to determine sperm mitochondrial activity before and after cryopreservation from the semen of 50 men attending for infertility investigation. Morphology was assessed using Tygerberg's strict criteria and viability was assessed by eosin Y. Sperm motility was measured using computer-assisted semen analysis (CASA).

RESULTS

Freeze-thawing caused a 37% (P = 0.001) reduction in normal morphological forms of sperm. All CASA sperm motility parameters except amplitude of lateral head displacement were similarly reduced. R123 uptake and intensity within sperm mitochondria decreased by 36 and 47% respectively (both P = 0.001). In addition, there was a similar significant decrease (31%, P = 0.001) in the viability of the sperm.

CONCLUSIONS

Sperm morphology, motility, mitochondrial activities and viability are equally susceptible to cryopreservation-induced damage. R123 intensity is a novel and robust indicator of mitochondrial function before and after such trauma.

Altered metabolism of the amyloid beta precursor protein is associated with mitochondrial dysfunction in Down's syndrome

Most Down's syndrome (DS) patients develop Alzheimer's disease (AD) neuropathology. Astrocyte and neuronal cultures derived from fetal DS brain show alterations in the processing of amyloid beta precursor protein (AbetaPP), including increased levels of AbetaPP and C99, reduced levels of secreted AbetaPP (AbetaPPs) and C83, and intracellular accumulation of insoluble Abeta42. This pattern of AbetaPP processing is recapitulated in normal astrocytes by inhibition of mitochondrial metabolism, consistent with impaired mitochondrial function in DS astrocytes. Intracellular Abeta42 and reduced AbetaPPs are also detected in DS and AD brains. The survival of DS neurons is markedly increased by recombinant or astrocyte-produced AbetaPPs, suggesting that AbetaPPs may be a neuronal survival factor. Thus, mitochondrial dysfunction in DS may lead to intracellular deposition of Abeta42, reduced levels of AbetaPPs, and a chronic state of increased neuronal vulnerability.

Genetic models meet trophic mechanisms: EGF family members are gliatrophins in Drosophila

Trophic survival mechanisms are crucial for the determination of cell numbers in the developing vertebrate nervous system, but important neurotrophic factor families such as the neurotrophins have not yet been found in either Drosophila or C. elegans. Two independent studies on distinct glial populations in Drosophila have now shown that their survival is regulated by EGF family members secreted by adjacent neurons. Fly genetics thus promises new insights on trophic signaling mechanisms and confirms that trophic regulation of cell survival is an evolutionarily ancient mechanism for building the nervous system.

Growth hormone can act as a cytokine controlling survival and proliferation of immune cells: new insights into signaling pathways

While growth hormone (GH) is classically defined as a peptide hormone, recent evidence supports a role for GH acting as a cytokine in the immune system under conditions of stress, counteracting immunosuppression by glucocorticoids. Lymphoid cells express the GH receptor, which belongs to the cytokine receptor superfamily, and GH can be produced by immune tissues, suggesting an autocrine/paracrine mode of action of GH. GH can act as a cytokine, promoting cell cycle progression of lymphoid cells and preventing apoptosis. These effects of GH were shown to be mainly mediated by the PI-3 kinase/Akt pathway and the transcription factor NF-kappaB. Expression of several cell cycle mediators, as well as Bcl-2, c-Myc and cyclin proteins were found to be regulated by GH. Survival of immune cells under conditions of stress was promoted by NF-kappaB. Thus, GH acts not only as a hormone but also as a cytokine, playing a potentially important role in immune system cells. Lastly, in this mini-review, we will discuss whether the discovery of these molecules in GH signaling pathways offers new insights into additional mechanisms of action whereby GH regulates apoptosis, proliferation and neoplastic transformation of cells of the immune system.

Cells bearing mutations causing Leber's hereditary optic neuropathy are sensitized to Fas-Induced apoptosis

Three prevalent mitochondrial DNA pathogenic mutations at positions 11778, 3460, and 14484, which affect different subunits of Complex I, cause retinal ganglion cell death and optic nerve atrophy in Leber's hereditary optic neuropathy (LHON). The cell death is painless and without inflammation, consistent with an apoptotic mechanism. We have investigated the possibility that the LHON mutation confers a pro-apoptotic stimulus and have tested the sensitivity of osteosarcoma-derived cybrid cells carrying the most common and severe mutations (11778 and 3460) to cell death induced by Fas. We observed that LHON cybrids were sensitized to Fas-dependent death. Control cells that bear the same mitochondrial genetic background (the J haplogroup) without the pathogenic 11778 mutation are no more sensitive than other controls, indicating that increased Fas-dependent death in LHON cybrids was induced by the LHON pathogenic mutations. The type of death was apoptotic by several criteria, including induction by Fas, inhibition by the caspase inhibitor zVAD-fmk (zVal-Ala-Asp-fluoro-methyl ketone), activation of DEVDase activity (Asp-Glu-Val-Asp protease), specific cleavage of caspase-3, DNA fragmentation, and increased Annexin-V labeling. These data indicate that the most common and severe LHON pathogenic mutations 11778 and 3460 predispose cells to apoptosis, which may be relevant for the pathophysiology of cell death in LHON, and potential therapy.

Effect of p53 status on tumor response to antiangiogenic therapy

The p53 tumor suppressor gene is inactivated in the majority of human cancers. Tumor cells deficient in p53 display a diminished rate of apoptosis under hypoxic conditions, a circumstance that might reduce their reliance on vascular supply, and hence their responsiveness to antiangiogenic therapy. Here, we report that mice bearing tumors derived from p53(-/-) HCT116 human colorectal cancer cells were less responsive to antiangiogenic combination therapy than mice bearing isogenic p53(+/+) tumors. Thus, although antiangiogenic therapy targets genetically stable endothelial cells in the tumor vasculature, genetic alterations that decrease the vascular dependence of tumor cells can influence the therapeutic response of tumors to this therapy.

Polichlorinated biphenyls (PCB126 and PCB 153) action on proliferation and progesterone secretion by cultured in vitro porcine luteal cells

SUMMARY

To characterise PCBs action on luteal cell steroidogenesis and cell viability two PCB congeners were selected as model substances. PCB 126 because of its dioxin-like configuration and high toxicity while 153 because it is one of the most commonly detected congeners in breast milk. Luteal cells collected from mature corpora lutea were cultured in M199 medium at 37 degrees C. Control cultures were maintained in that medium alone, while other cultures were supplemented with either PCB 126 (5, 10, 50 and 100 pg/ml) or PCB 153 (5, 10, 50 and 100 ng/ml). After 24 h, 48 h and 72 h of culture media were collected for P4 content analysis. Cell viability was measured using LDH cytotoxicity test. Exposure of luteal cells to all doses of PCB 126 for 24 h had no effect on progesterone secretion while longer, 48 h and 72 h exposure decreased progesterone secretion in a statistically significant manner. Concentration dependent decrease in progesterone secretion by luteal cells was seen after 24 h and 48 h exposure to PCB153 while concentration dependent increase in progesterone secretion was noted after 72 h exposition to this congener. The toxic effect of both congeners was observed only after 72 h exposition to 50 pg/ml and 100 pg/ml in the case of PCB 126 and 50 ng/ml and 100 ng/ml in the case of PCB 153. In conclusion, these results suggest that there are differences in PCB 153 and 126 action in luteal cells. Since information concerning mechanism of PCBs action on luteal cells is scarce, these preliminary experiments are of pioneering character.

Biocompatibility of dental materials in two human cell lines

It was the aim of this study to investigate the biocompatibility of metallic (titan, gold, amalgam) and ceramic dental materials in contact with gingival (GF) and epithelial tumour cells (EpiCa). The cells were incubated with the test specimens (5 mg/piece) over a period of six days. Cellular proliferation rate, protein synthesis, and prostaglandin release (PGE2) served as parameters to determine the biocompatibility of the materials. - The investigations showed that the protein values were subject to slight variations following contact with the dental materials. Incubation of the cells with the test materials resulted in material dependent increases in PGE2-values (GF/EpiCa: titan: 187.4%, 131.0%; ceramic: 151.5%, 176.4%; gold: 114.5%, 123.8%; amalgam 150.6%, 159.8%). A comparison of control cells and cells of the test series (GF/EpiCa) after cell stimulation with 10-5M arachidonic acid (AA) showed the following changes in PGE2 on contact with titan (110.0%, 167.5%), ceramic (98.7%, 188.9%), gold (119.5%, 153.1%), and amalgam (68.9%, 179.5%). - Measurement of the proliferation rate (24 hours) further demonstrated that the dental materials used exerted an influence on the growth rates. While amalgam was associated with a marked reduction in the proliferation rate, titan, gold and ceramic induced only slight changes in the growth rate. - The results of the present study demonstrate that the cell culture systems used represent suitable in vitro models for the investigation of the biocompatibility of dental materials. The level of cell irritation was shown to be lowest for titan, closely followed by ceramic and gold. Cell culture; prostaglandin release; titan; ceramic; amalgam

Efficient in-vitro transfer of a 60-Mb mammalian artificial chromosome into murine and hamster cells using cationic lipids and dendrimers

Non-integrating artificial chromosomes represent a potentially promising approach to ex-vivo and in-vivo gene therapy applications. These large vectors require an efficient means for delivery to target cells. We have evaluated a panel of twenty-one commercially available transfection agents for their ability to mediate the in-vitro transfer of a 60-Mb murine artificial chromosome consisting of mouse major satellite DNA and a payload including a marker gene (hygromycin B) and a reporter gene (lacZ). A rapid screening procedure utilizing iododeoxyuridine-incorporated artificial chromosomes facilitated the assessment of different transfection conditions. The results were confirmed by cytogenetic analysis of positively transfected clones. By transfecting both hamster lung fibroblast cells (V79-4) and murine connective tissue cells [L-M(TK-)], the best results were obtained using either Superfect (cationic dendrimer) or LipofectAMINE 2000 (cationic lipid) with protocols adapted for metaphase chromosome preparation. Transfection efficiencies of 10(-4)-10(-2) (0.01-1%) were routinely observed, and recipient cells were able to maintain expression of the reporter gene over the total length of the experiment. This represents a significant advance over our previous attempts at mass-transfection of artificial chromosomes using microcell fusion, where we routinely achieved efficiencies at least two orders of magnitudes less than reported here. These data are particularly noteworthy given that lipid-mediated gene transfer typically involves transfecting millions of plasmids (1 microg of DNA from a 5 kb plasmid is approximately 1.2 x 10(11) copies) to each cell whereas the much larger artificial chromosomes comprise only a one-to-one ratio, yet achieve transfection efficiencies of (10(-2)-10(-1)), that is, comparable to our results. These data suggest that artificial chromosomes containing therapeutic genes can be successfully delivered to target cells in vitro using well-established transfection agents.

Evaluation of mouse preimplantation embryos cultured in media enriched with insulin-like growth factors I and II, epidermal growth factor and tumor necrosis factor alpha

Culture of preimplantation embryos is complex and requires strictly defined culture media to sustain their viability and quality. In the current study, an effort was made to evaluate comprehensively the quality of mice embryos, grown in media enriched with IGF I, IGF II, EGF and TNFalpha. For that purpose, critically chosen and thoroughly described, complex morphological methods based on contrast-phase, fluorescent and confocal microscopy were used. The study evaluated blastulation and hatching rates, total blastocyst cells, inner cell mass cell numbers (differential staining) as well as identified embryo cells with positive reactions for necrosis or apoptosis (TUNEL). The critical evaluation of the effects of the studied cytokines allowed for simultaneous, meticulous assessment of the applied study methods. Significantly more blastocysts were found in culture media enriched with IGF-I, IGF II and EGF. Significantly more hatched blastocysts were found in media with IGF-I and IGF II. Additionally, IGF I and II increased inner cell mass and total blastocyst cell numbers. Very few cells with necrosis and apoptosis were found in the culture media enriched with IGF I, IGF II and EGF. TNFalpha produced negative effects. The observed effects were dose-dependent.

Validation of flow cytometry for assessment of viability and acrosomal integrity of dog spermatozoa and for evaluation of different methods of cryopreservation

The aims of the present study were: (i) to validate the accuracy of flow cytometry for assessment of viability and acrosomal status of canine spermatozoa; and (ii) to evaluate the cryopreservation protocols currently used for dog spermatozoa using flow cytometry. Data obtained by flow cytometry analysis of fresh dog spermatozoa stained with carboxyfluorescein diacetate (CFDA) and propidium iodide, or with fluorescein isothiocyanate (FITC)-conjugated Pisum sativum agglutinin (PSA) and propidium iodide, were compared with those obtained by microscopic evaluation. The results demonstrated that flow cytometry is a precise method for evaluating the viability and acrosomal status of fresh samples of dog semen. A new triple staining procedure, using carboxy-SNARF-1, propidium iodide and FITC-PSA, was developed and was an efficient method for evaluating the following aspects of cryopreservation protocols for dog spermatozoa: (i) addition of 0.5% (v/v) Equex STM paste to a Tris-egg yolk-based extender; (ii) dilution of the semen in one or two steps; (iii) freezing semen by placing 0.5 ml straws horizontally above liquid nitrogen in a styrofoam box or lowering them vertically into a liquid nitrogen tank; (iv) thawing semen at two different rates; (v) packaging semen at different sperm concentrations; and (vi) diluting semen at different rates after thawing. The highest sperm survival and longevity was obtained when Equex was present in the semen extender, the semen dilution was performed in two steps to obtain a concentration of 2.0 x 10(8) spermatozoa ml-1, the freezing was carried out using the styrofoam box, the straws were thawed at 70 degrees C for 8 s and the semen was diluted 1:4 after thawing.

Vital and ultrastructural changes in dog spermatozoa during cyopreservation

The exact nature of cryo-injury to dog semen and the stage of cryopreservation at which it occurs have not been evaluated fully and were investigated in the present study. Semen samples were examined immediately before and after addition of semen extender, cooling and freeze-thawing in a Tris-based medium. Vital and ultrastructural assessments were made immediately after each treatment and after incubation for 4 h at 39 degrees C after each treatment. Addition of semen extender produced no significant ultrastructural changes in spermatozoa; however, cooling resulted in an immediate increase in the number of acrosomal abnormalities and a subsequent decrease in sperm viability. Freeze-thawing caused both an immediate and a delayed decrease in sperm viability. This effect may have been an exacerbation of the effects of cooling as many acrosomal abnormalities were present or it may have been the result of initially unrecognized damage. Cooling and freezing of dog spermatozoa may have both immediate and delayed effects on the ultrastructure of spermatozoa. The immediate effects of cooling and freezing may either kill spermatozoa or render them incapable of fertilization by damaging the acrosome, whereas delayed effects may reduce sperm longevity by altering plasma membrane structure.

Effect of prostatic fluid on motility, viability and acrosome integrity of chilled and frozen-thawed dog spermatozoa

Sperm preservation has become a routine procedure in dog breeding. In this study, the influence of prostatic fluid on sperm characteristics after preservation (either chilling or freezing) was investigated. The sperm-rich fractions of 20 ejaculates from five dogs were either extended without centrifugation or centrifuged and resuspended either directly in extender or in prostatic fluid before dilution with extender. Aliquots were processed for storage at 4 degrees C for 6 h or for freezing. Storage at 4 degrees C did not affect sperm motility, viability or acrosome integrity, irrespective of the dilution treatment. However, sperm motility and viability decreased significantly after freezing and thawing, particularly in the samples with additional prostatic fluid. In contrast, the acrosome morphology of viable spermatozoa was not affected by either the dilution method or by chilling or freezing and thawing. It is concluded that addition of prostatic fluid during semen processing adversely affects the motility and viability of frozen-thawed spermatozoa. However, prostatic fluid does not appear to affect the motility and viability of chilled spermatozoa or to alter acrosome integrity in either system of preservation.

The radiation-induced lesions which trigger the bystander effect

The ionizing radiation induced bystander effect is initiated by damage to a cellular molecule which then gives rise to a signal exported to other cells. The nature of this damage is considered with the understanding that it may not be the same as that responsible for the traditional cellular effects of radiation. Consideration is give to amounts of endogenous damage and to radiation yields of the various candidate lesions.

Interactions between double positive thymocytes and high affinity ligands presented by cortical epithelial cells generate double negative thymocytes with T cell regulatory activity

Previous studies on thymocyte differentiation by using reaggregate cultures (RC) of double positive T cell receptor (TCR) transgenic thymocytes and the thymic epithelial cell line ANV indicated that low concentrations of high affinity ligands for the TCR were efficient inducers of thymocyte maturation to CD4 single positive (SP) functional cells. In this study, it is demonstrated that, when high concentrations of high affinity ligands are used in this RC system, double positive (DP) cells down-modulate expression of both coreceptors and that, as a result, large numbers of double negative (DN) cells are generated. These DN cells proliferated modestly in response to stimulation by antigen, and this response was considerably augmented by the addition of IL-2 to the cultures. Notably, these antigen-stimulated DN cells produced large amounts of IL-10. When the DN cells generated in RC were cocultured with naive TCR transgenic T cells in the presence of antigen, they suppressed the proliferative response of the naive T cells. Thus, high affinity ligands, when presented to DP thymocytes by cortical thymic epithelial cells in reaggregate cultures, rather than causing deletion of the immature thymocytes, induce their differentiation into immunoregulatory DN cells, suggesting a distinct mechanism by which self tolerance may be maintained.

Differential sensitivity to apoptosis between the human small and large intestinal mucosae: linkage with segment-specific regulation of BCL-2 homologs and involvement of signaling pathways

The small and large intestines differ in their expression profiles of Bcl-2 homologs. Intestinal segment-specific Bcl-2 homolog expression profiles are acquired as early as by mid-gestation (18-20 weeks) in man. In the present study, we examined the question whether such distinctions underlie segment-specific control mechanisms of intestinal cell survival. Using mid-gestation human jejunum and colon organotypic cultures, we analyzed the impact of growth factors (namely insulin; 10 microg/ml) and pharmacological compounds that inhibit signal transduction molecules/pathways (namely tyrosine kinases, Fak, P13-K/Akt, and MEK/Erk) on cell survival and Bcl-2 homolog expression (anti-apoptotic: Bcl-2, Bcl-X(L), Mcl-1; pro-apoptotic: Bax, Bak, Bad). The relative activation levels of p125Fak, p42Erk-2, and p57Akt were analyzed as well. Herein, we report that (1) the inhibition of signal transduction molecules/pathways revealed striking differences in their impact on cell survival in the jejunum and colon (e.g., the inhibition of p125Fak induced apoptosis with a significantly greater extent in the jejunum [approximately 43%] than in the colon [approximately 24%]); (2) sharp distinctions between the two segments were noted in the modulatory effects of the various treatments on Bcl-2 homolog steady-state levels (e.g., inhibition of tyrosine kinase activities in the jejunum down-regulated all anti-apoptotics analyzed while increasing Bax, whereas the same treatment in the colon down-regulated Bcl-X(L) only and increased all pro-apoptotics); and (3) in addition to their differential impact on cell survival and Bcl-2 homolog expression, the MEK/Erk and P13-K/Akt pathways were found to be distinctively regulated in the jejunum and colon mucosae (e.g., insulin in the jejunum increased p42Erk-2 activation without affecting that of p57Akt, whereas the same treatment in the colon decreased p42Erk-2 activation while increasing that of p57Akt). Altogether, these data show that intestinal cell survival is characterized by segment-specific susceptibilities to apoptosis, which are in turn linked with segmental distinctions in the involvement of signaling pathways and the regulation of Bcl-2 homolog steady-state levels. Therefore, these indicate that cell survival is subject to segment-specific control mechanisms along the proximal-distal axis of the intestine.

Clusterin expression is significantly enhanced in prostate cancer cells following androgen withdrawal therapy

INTRODUCTION AND OBJECTIVES

Progression of prostate cancer to androgen independence (AI) results in part from the upregulation of anti-apoptotic genes following androgen withdrawal, and androgen-independent disease remains the primary obstacle to improved survival. Testosterone-repressed prostate message-2 (TRPM-2) encodes the anti-apoptotic protein clusterin, which is upregulated in response to cellular compromise as observed in normal and malignant tissues undergoing apoptosis. Systemic administration of antisense clusterin oligonucleotides in prostate cancer xenograft models delays progression to AI and enhances chemosensitivity. The objective of this study was to define changes in clusterin expression following neoadjuvant hormone therapy (NHT) in prostate cancer patients.

MATERIALS AND METHODS

Archival radical prostatectomy (RP) specimens were obtained for 128 patients who received either no NHT or treatment for 2-8 weeks, 3 months, or 8 months. Paired needle biopsy specimens were acquired for 30 patients and all tissues were subjected to clusterin immunohistochemistry. Western blot analysis was performed on frozen tissue from 5 untreated and 5 treated patients.

RESULTS

Clusterin expression in malignant prostatic tissue was significantly greater in patients who underwent preoperative NHT (P < 0.001). Needle biopsies obtained prior to NHT consistently demonstrated lower staining intensity than corresponding RP specimens (P < 0.001). Western blot analysis confirmed clusterin levels increased 17-fold beginning within 4 weeks after androgen withdrawal.

CONCLUSIONS

Upregulation of clusterin levels following androgen ablation therapy may represent an adaptive cell survival response following apoptotic signals like androgen withdrawal. These findings support clusterin as a valid therapeutic target in strategies employing novel multimodality therapy for advanced prostate cancer.

Modulation of DNA single-strand breaks by intracellular glutathione in human lung cells exposed to asbestos fibers

We investigated the role of glutathione and nitric oxide synthase (NOS) in fiber-induced cell and DNA toxicity using alkaline (pH 13) single-cell gel electrophoresis (the Comet assay). Transformed cultured human pleural mesothelial (MeT-5A) cells and alveolar epithelial cells (A549) were exposed to crocidolite asbestos fibers (1-10 microg/cm(2)) in the presence of buthionine sulfoximine (BSO) or L-arginine-methyl ester (L-NAME). BSO inhibits gamma-glutamylcysteine synthetase (gamma-GCS) and causes glutathione depletion, and L-NAME inhibits nitric oxide generation. Studies were also conducted to assess the expression of the heavy and light subunits of gamma-GCS in human pleural mesothelium and bronchial epithelium in vivo and the induction of inducible NOS (iNOS) by asbestos fibers. Asbestos fibers caused DNA single-strand breaks, and the process was significantly enhanced by BSO (69% compared to the non-treated cells). A549 cells had a 3.5-fold glutathione content compared to MeT-5A cells, which was consistent with the higher resistance of these cells against oxidants and fibers. Flow cytometry of iNOS showed no change of iNOS by the fibers in either cell type in vitro. L-NAME had no effects on the DNA single-strand breaks in the Comet assay, either. Studies on lung biopsies showed that the immunoreactivities of both gamma-GCS subunits were very low in healthy human mesothelium in vivo. We conclude that glutathione may play an essential role in protecting intact cells against fiber-induced oxidative DNA alterations, and low gamma-GCS reactivity in pleural mesothelium may be associated with the high sensitivity of mesothelial cells to fiber-induced toxicity.

Prevalent loss of mitotic spindle checkpoint in adult T-cell leukemia confers resistance to microtubule inhibitors

Human T-cell leukemia virus type I (HTLV-I) is the causative agent for adult T-cell leukemia (ATL). Molecularly, ATL cells have extensive aneugenic abnormalities that occur, at least in part, from cell cycle dysregulation by the HTLV-I-encoded Tax oncoprotein. Here, we compared six HTLV-I-transformed cells to Jurkat and primary peripheral blood mononuclear cells (PBMC) in their responses to treatment with microtubule inhibitors. We found that both Jurkat and PBMCs arrested efficiently in mitosis when treated with nocodazole. By contrast, all six HTLV-I cells failed to arrest comparably in mitosis, suggesting that ATL cells have a defect in the mitotic spindle assembly checkpoint. Mechanistically, we observed that in HTLV-I Tax-expressing cells human spindle assembly checkpoint factors hsMAD1 and hsMAD2 were mislocated from the nucleus to the cytoplasm. This altered localization of hsMAD1 and hsMAD2 correlated with loss of mitotic checkpoint function and chemoresistance to microtubule inhibitors.

Free radicals-mediated induction of oxidized DNA bases and DNA-protein cross-links by nickel chloride

Using the comet assay, we showed that nickel chloride at 250-1000 microM induced DNA damage in human lymphocytes, measured as the change in comet tail moment, which increased with nickel concentration up to 500 microM and then decreased. Observed increase might follow from the induction of strand breaks or/and alkali-labile sites (ALS) by nickel, whereas decrease from its induction of DNA-DNA and/or DNA-protein cross-links. Proteinase K caused an increase in the tail moment, suggesting that nickel chloride at 1000 microM might cross-link DNA with nuclear proteins. Lymphocytes exposed to NiCl(2) and treated with enzymes recognizing oxidized and alkylated bases: endonuclease III (Endo III), formamidopyrimidine-DNA glycosylase (Fpg) and 3-methyladenine-DNA glycosylase II (AlkA), displayed greater extent of DNA damage than those not treated with these enzymes, indicating the induction of oxidized and alkylated bases by nickel. The incubation of lymphocytes with spin traps, 5,5-dimethyl-pyrroline N-oxide (DMPO) and PBN decreased the extent of DNA damage, which might follow from the production of free radicals by nickel. The pre-treatment with Vitamin C at 10 microM and Vitamin E at 25 microM decreased the tail moment of the cells exposed to NiCl(2) at the concentrations of the metal causing strand breaks or/and ALS. The results obtained suggest that free radicals may be involved in the formation of strand breaks or/and ALS in DNA as well as DNA-protein cross-links induced by NiCl(2). Nickel chloride can also alkylate DNA bases. Our results support thesis on multiple, free radicals-based genotoxicity pathways of nickel.