Vitamin E protects human lymphocytes from genotoxicity induced by oxaliplatin

Cilostazol protective effect on nedaplatin-induced genotoxicity in cultured human lymphocytes

Background

Nedaplatin has demonstrated remarkable efficacy in combating various malignancies. However, the administration of nedaplatin has been associated with the induction of DNA damage within normal cells. Cilostazol is a phosphodiesterase III inhibitor with an antioxidant mechanism that could protect cells from genotoxicity. We aimed to evaluate the genotoxic effect of nedaplatin on cultured human lymphocytes and the potential protective effect of cilostazol on chromosomal damage induced by nedaplatin.

Methods

The proposed nedaplatin's genotoxic effect was studied in vitro by evaluating the frequencies of sister chromatid exchanges (SCEs) in human cultured lymphocytes. Both the mitotic and proliferative indices (MI and PI, respectively) were used to assess the cytotoxic effects of nedaplatin.

Results

Nedaplatin significantly increased the frequency of SCEs compared to control and cilostazol-treated cells. The chromosomal injury induced by nedaplatin was significantly reduced by pretreatment of cells with cilostazol (P < 0.0001). Treating with cilostazol alone also reduced the frequency of SCEs, MI, and PI compared to the control group. Nedaplatin induced significant decreases in the MI and PI compared to the control group. Pretreatment with cilostazol partially debilitated the nedaplatin-induced changes in MI but not PI.

Conclusion

Cilostazol ameliorated the genotoxicity of nedaplatin in cultured human lymphocytes.

Analgesic and neuroprotective effect of a lipid transfer protein isolated from Morinda citrifolia L. (noni) seeds on oxaliplatin-induced peripheral sensory neuropathy in mice

Oxaliplatin, a 3rd-generation platinum compound, has a dose-limiting effect: neurotoxicity manifests as peripheral sensory neuropathy (PNS). Many studies have assessed the different pharmacological properties of a lipid transfer protein isolated from Morinda citrifolia L. (McLTP1) seeds. This study aimed to evaluate the analgesic and neuroprotective effects of McLTP1 on oxaliplatin-induced peripheral sensory neuropathy in mice and the mechanisms involved. Male Swiss mice received oxaliplatin twice a week for 28 days. McLTP1 (1 to 4 mg/kg, p.o.) was administered 60 min before oxaliplatin injection. Mechanical and cold allodynia were assessed once a week via electronic von Frey and acetone tests. TRPA1 and TRPM8 receptor agonists were applied intraplantarly to the hind paw to evaluate their involvement in the antiallodynic mechanism of McLTP1. ATF3 and c-Fos expression was assessed in the dorsal root ganglia (DRG) or spinal cord (SC) to investigate nociceptive pathway activation and neurotoxic injury. MDA and GSH assays were performed in the sciatic nerve and spinal cord, and histological analysis was performed in the sciatic nerve. Total and differential leukocyte counts were analyzed in the peripheral blood. McLTP1 prevented the mechanical and cold allodynia and increase in c-Fos and ATF3 expression induced by oxaliplatin in the DRG and SC, possibly involving TRPM8 receptors. McLTP1 prevented the oxidative stress caused by oxaliplatin in the sciatic nerve and spinal cord and the histological changes associated with oxaliplatin in the sciatic nerve. McLTP1 inhibited leukopenia, mainly lymphopenia caused by oxaliplatin. McLTP1 prevents oxaliplatin-induced peripheral sensory neuropathy through its antiallodynic, antioxidant and neuroprotective properties.

Cilostazol geno-protective effects mitigate carbamazepine-induced genotoxicity in human cultured blood lymphocytes

Background

Carbamazepine is one of the most widely used antiepileptic drugs. Carbamazepine has been shown to be toxic to cells. Cilostazol, an antiplatelet agent, has known antioxidant, antiproliferative, anti-inflammatory, and anti-tumor effects.

Objective

This study aimed to explore whether carbamazepine and cilostazol exert genotoxic and/or cytotoxic effects in human cultured blood lymphocytes and the impact of combining both drugs on such effects.

Methods

Genotoxicity was examined using sister chromatid exchange (SCE) assay, while cytotoxicity was evaluated by cell kinetic assays (mitotic and proliferative indices).

Results

Study findings have revealed that carbamazepine markedly increased SCEs (p<0.01), while cilostazol significantly decreased their frequencies (p<0.01). In addition, the frequency of SCEs of the combination of both drugs was similar to that of the control group (p>0.05). Carbamazepine increased the cell proliferative index (p<0.01) while cilostazol decreased it (p<0.01). The proliferative index was normalized to the control level when both drugs were combined.

Conclusion

We suggest that cilostazol has the potential to protect human lymphocytes from carbamazepine-induced toxic effects.

Guidance for the use and interpretation of assays for monitoring anti-genotoxicity

Since DNA damage can occur spontaneously or be produced by the environmental genotoxins in living cells, it is important to investigate compounds that can reverse or protect DNA damage. An appropriate methodology is essential for the responsive identification of protection offered against DNA damage. This review includes information on the current state of knowledge on prokaryotic cell-based assays (SOS chromotest, umu test, vitotox assay) and cytogenetic techniques (micronucleus assay, chromosome aberration test and sister chromatid exchange assay) with an emphasis on the possibility to explore genoprotective compounds. Throughout the last decade, studies have extrapolated the scientific methodologies utilized for genotoxicity to assess genoprotective compounds. Therefore, shortcomings of genotoxicity studies are also mirrored in antigenotoxicity studies. While regulatory authorities around the world (OECD, US-EPA and ICH) continue to update diverse genotoxic assay strategies, there are still no clear guidelines/approaches for efficient experimental design to screen genoprotective compounds. As a consequence, non-synergetic and inconsistent implementation of the test method by the researchers to execute such simulations has been adopted, which inevitably results in unreliable findings. The review has made the first attempt to collect various facets of experimentally verified approaches for evaluating genoprotective compounds, as well as to acknowledge potential significance and constraints, and further focus on the assessment of end points which are required to validate such action. Henceforth, the review makes an incredible commitment by permitting readers to equate several components of their test arrangement with the provided simplified information, allowing the selection of convenient technique for the predefined compound from a central repository.

Vitamin B12 Protects against Genotoxicity Induced by Cisplatin

BACKGROUND

Cisplatin is an effective synthetic chemotherapeutic drug used for cancer treatment. Vitamin B12 has been shown to possess anti-genotoxic activity. This study aimed to investigate the effect of vitamin B12 on chromosomal damage induced by cisplatin.

METHODS

The level of sister chromatid exchanges (SCEs) and chromosomal aberrations (CAs) were measured in cultured human blood lymphocytes treated with cisplatin and/or vitamin B12.

RESULTS

The results showed a significantly elevated frequency of CAs and SCEs of cisplatin-treated cultures compared to the control (P < 0.05). The CAs and SCEs induced by cisplatin were significantly lowered by pretreatment of cell cultures with vitamin B12. In addition, cisplatin caused a slight reduction in the mitotic index (MI), while vitamin B12 did not modulate the effect of cisplatin on MI.

CONCLUSION

Vitamin B12 can protect human lymphocytes against genotoxicity associated with cisplatin.

Evaluation of toxicity and mutagenicity of oxaliplatin on germ cells in an alternative in vivo model Caenorhabditis elegans

The platinum compound oxaliplatin is a widely used chemotherapeutic drug that shows a broad spectrum of activity in various human tumors. While the treatment-related side effects of oxaliplatin on directly treated individuals have been well-documented, little is known about the influence of oxaliplatin on germ cells and non-exposed progenies. Here we investigated the reproductive toxicity of oxaliplatin in a 3R-compliant in vivo model Caenorhabditis elegans, and evaluated the germ cell mutagenicity of oxaliplatin by using whole genome sequencing. Our results indicated that oxaliplatin treatment significantly disrupts development of spermatids and oocytes. By treating parental worms with oxaliplatin for three successive generations, sequencing data unveiled the clear mutagenic effects of oxaliplatin on germ cells. Analysis of genome-wide mutation spectra showed the preferentially induction of indels by oxaliplatin. In addition, we uncovered the involvement of translesion synthesis polymerase ζ in modulating mutagenic effects of oxaliplatin. These findings suggest that germ cell mutagenicity is worthy of consideration for the health risk assessment of chemotherapeutic drugs, while the combined use of alternative in vivo models and next generation sequencing technology appears to be a promising way for the preliminary safety assessment of various drugs.

Reduction of Genotoxicity of Carbamazepine to Human Lymphocytes by Pre-treatment with Vitamin B12

BACKGROUND

Carbamazepine (CBZ) is widely used as an anti-epileptic drug. Vitamin B12 has been shown to protect against DNA damage caused by several mutagenic agents.

OBJECTIVE

This study aimed to investigate the effect of vitamin B12 on CBZ-induced genotoxicity in cultured human lymphocytes.

METHODS

Sister chromatid exchanges (SCEs) and chromosomal aberrations (CAs) genotoxic assays were utilized to achieve the study objective.

RESULTS

The results showed significantly higher frequencies of CAs and SCEs in the CBZ-treated cultures (12 μg/mL) compared to the control group (P<0.01). The genotoxic effects of CBZ were reduced by pre-treatment of cultures with vitamin B12 (13.5μg/ml, P<0.05). Neither CBZ nor vitamin B-12 showed any effects on mitotic and proliferative indices.

CONCLUSION

CBZ is genotoxic to lymphocyte cells, and this genotoxicity can be reduced by vitamin B12.

Genotoxicity of nedaplatin in cultured lymphocytes: modulation by vitamin E

Nedaplatin is a chemotherapeutic agent used widely in cancer therapy. Nedaplatin has been shown to cause DNA damage to cells via the induction of oxidative stress. Vitamin E (Vit E) has an anti-mutagenic activity that can protect cells from DNA damaging agents. The objective of this study is to examine the genotoxic and cytotoxic effects of nedaplatin in human cultured lymphocytes. In addition, modulation of such effects by Vit E was also examined. The frequencies of sister chromatid exchange (SCE) and chromosomal aberrations (CAs) were used as an indicator for genotoxicity. The mitotic and proliferative indices were used to examine the cytotoxic effects of nedaplatin. The results showed that nedaplatin significantly elevated SCE and CA frequencies in human lymphocytes (p ˂ 0.01). The increases in the frequencies of SCE and CA caused by nedaplatin were lowered by pretreatment treatment with Vit E (p < 0.05). Nedaplatin significantly lowered mitotic index but Vit E pretreatment did not modulate this effect. These results suggest that Vit E has the potential to ameliorate the genotoxicity of nedaplatin in cultured lymphocytes.

Modulatory effect of myricitrin against chromosome instability and cytostasis induced by bleomycin and oxaliplatin in CHO-K1 cells

Myricitrin (MYR), a flavonol consumed in the leaves and fruits of plants of the Myrtaceae family, presents anti-proliferative, anti-inflammatory, anti-diabetic, and antioxidant properties in humans. However, there are few studies regarding the cyto-genotoxicity and the chemopreventive potential of MYR. Using the in vitro Micronucleus test, the cytostasis, mutagenicity, and modulatory effect of MYR in CHO-K1 cells were assessed. The concentrations of 39 and 78 µg/mL (p < 0.001.) of MYR decrease the cytokinesis-block proliferation index (CBPI) in the short exposure treatment (4 h), while in the extended treatment (24 h), concentrations of 4.8, 9.7, 19.5, 39 and 78 µg/mL (p < 0.001.) decreased the CBPI. MYR associated with oxaliplatin decreased CBPI at all tested concentrations in the pre-(p < 0.001) and post-treatments (p < 0.001), but there was no decrease when associated with bleomycin. As for chromosome instability, MYR did not increase the frequency of micronuclei (MNi), nucleoplasmic bridges (NPBs), or nuclear buds (NBUDs) in the 4 h exposure time, however, in the 24 h treatment, MYR increased the frequency of MNi and NPBs at concentration 19.5 µg/mL (p < 0.001). As for the modulatory effect, MYR associated with bleomycin decreased the frequency of MNi, NPBs, and NBUDs at all concentrations in the pretreatment (MNi and NPBs p < 0.001, NBUDs p < 0.05) and simultaneously (MNi, NPBs and NBUDs p < 0.001). When associated with oxaliplatin, the simultaneous treatment decreased the frequency of MNi (p < 0.001) and NBUDs (p < 0.01) at all concentrations, however, in the post-treatment, MYR increased MNi (p < 0.001) and NPBs p < 0.05) in CHO-K1 cells, when compared to oxaliplatin alone. The results demonstrated that MYR could modulate the mutagenic and cytostatic actions of bleomycin and oxaliplatin, demonstrating distinct behaviors, depending on the mechanism of action of the chemotherapeutic agent.

The genotoxic effects of perchloroethylene in human peripheral blood lymphocytes and the possible ameliorative role of α-tocopherol

Perchloroethylene (PCE), also known as tetrachloroethylene, is a commercially important chlorinated solvent commonly used in dry cleaning, textile processing, and metal degreasing industries. According to the available studies, the potential genotoxic impacts of this chlorinated solvent on human beings are still controversial. The present work was carried out to determine the genotoxic effects of PCE on human peripheral blood lymphocytes (PBLs) using chromosome aberrations (CAs) and cytokinesis-block micronucleus (CBMN) tests. Additionally, the antigenotoxic potential of α-tocopherol (α-Toc), a well-known antioxidant agent, on human lymphocytes treated with PCE in vitro was assessed. The cells were exposed for 48 h to PCE (25, 50, 100, and 150 μg/mL) alone as well as in combination with α-Toc (100 μg/mL). The findings of the study suggested that, relative to solvent control, PCE significantly increased the structural CA and MN formation for all concentrations. However, simultaneous treatment of PCE and α-Toc caused a significant reduction of CAs and MNi as compared to cultures treated with PCE alone. Besides, the results showed that PCE has cytotoxic effects on human PBLs as indicated by the significant decrease in mitotic index (MI) and nuclear division index (NDI). Nevertheless, the co-treatment of α-Toc with PCE did not reduce the cytotoxicity of PCE at a significant level. In conclusion, it can be suggested that PCE is genotoxic and cytotoxic in human PBLs, and α-Toc has an antigenotoxic effect on PCE-induced genotoxicity but has no significant effect on the cytotoxicity triggered by PCE.

The Protective Effect of Cilostazol in Genotoxicity Induced by Methotrexate in Human Cultured Lymphocytes

BACKGROUND

Methotrexate is an antagonist of folic acid that has been shown to be genotoxic to healthy body cells via induction of oxidative stress. Cilostazol is a phosphodiesterase III inhibitor and a potent antioxidant drug.

OBJECTIVE

To evaluate the potential protective effect of cilostazol on methotrexate genotoxicity.

METHODS

The genotoxic effect of methotrexate by measuring the frequency of chromosomal aberrations (CAs) and sister chromatid exchanges (SCEs) in human cultured lymphocytes was studied.

RESULTS

Methotrexate significantly increased the frequency of CAs and SCEs (p < 0.0001) as compared to control cultures. This chromosomal damage induced by methotrexate was considerably decreased by pretreatment of the cells with cilostazol (P < 0.01). Moreover, the results showed that methotrexate resulted in a notable reduction (P < 0.01) in cells kinetic parameters, the mitotic index (MI) and the proliferative index (PI). Similarly, cilostazol significantly reduced the mitotic index, which could be related to the anti-proliferative effect (P < 0.01).

CONCLUSION

Methotrexate is genotoxic, and cilostazol could prevent the methotrexate-induced chromosomal damage with no modulation of methotrexate-induced cytotoxicity.

In vitro genotoxicity assessment of functional ingredients: DHA, rutin and α-tocopherol

The in vitro genotoxicity of three compounds widely used as functional ingredients, docosahexaenoic acid (DHA), rutin and α-tocopherol, was assessed. A miniaturized version of the Ames test in Salmonella typhimurium TA97a, TA98, TA100, TA102, and TA1535 strains (following the principles of OECD 471), and the in vitro micronucleus test in TK6 cells (OECD 487) were performed. This strategy is recommended by the European Food Safety Authority for the in vitro genotoxicity assessment of food and feed. In addition, this approach was complemented with the in vitro standard and enzyme-modified comet assay (S9-/S9+) using hOGG1, EndoIII and hAAG in order to assess potential premutagenic lesions in TK6 cells. Rutin showed an equivocal response in the in vitro micronucleus test and also was a potent Salmonella typhimurium revertant inductor in the Ames test. DHA showed equivocal results in the in vitro micronucleus test. In this regard, DHA and rutin seemed to interact with the DNA at a chromosomal level, but rutin is also capable of producing frameshift mutations. No genotoxicity was observed in cells treated with α-tocopherol. This article complements the evidence already available about the genotoxicity of these compounds. However, more studies are needed in order to elucidate the consequences of their use as functional ingredients in human health.

A review on the protective effects of naringenin against natural and chemical toxic agents

Naringenin (NRG), as a flavanone from flavonoids family, is widely found in grapefruit, lemon tomato, and Citrus fruits. NRG has shown strong anti-inflammatory and antioxidant activities in body organs via mechanisms such as enhancement of glutathione S-transferase (GST), superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and catalase (CAT) activity, but reduction of serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), lactate dehydrogenase (LDH), and malondialdehyde (MDA). Furthermore, NRG anti-apoptotic potential was indicated to be mediated by regulating B-cell lymphoma (Bcl-2), Bcl-2-associated X protein (Bax) and caspase3/9. Overall, these properties make NRG a highly fascinating compound with beneficial pharmacological effects. Based on the literature, NRG-induced protective effects against toxicities produced by natural toxins, pharmaceuticals, heavy metals, and environmental chemicals, were mainly mediated via suppression of lipid peroxidation, oxidative stress (through boosting the antioxidant arsenal), and inflammatory factors (e.g., TNF-α, interleukin [IL]-6, IL-10, and IL-12), and activation of PI3K/Akt and MAPK survival signaling pathways. Despite considerable body of evidence on protective properties of NRG against a variety of toxic compounds, more well-designed experimental studies and particularly, clinical trials are required before reaching a concrete conclusion. The present review discusses how NRG protects against the above-noted toxic compounds.

Vitamin E prevents the cognitive impairments in post-traumatic stress disorder rat model: behavioral and molecular study

RATIONALE

Post-traumatic stress disorder (PTSD) is a psychiatric disorder developed after an exposure to severe traumatic events. Patients with PTSD suffer from different symptoms including memory impairment. In addition, PTSD is associated with oxidative stress. Vitamin E, a fat-soluble vitamin, possesses cognition protective effects via its antioxidative properties.

OBJECTIVES

To investigate the impact of vitamin E on memory impairment induced by PTSD in animals.

METHODS

A rat model of PTSD-like behavior and the radial arm water maze (RAWM) for testing of learning and memory paradigm were used. Rats were divided into 4 groups: control, vitamin E, PTSD, and vitamin E + PTSD.

RESULTS

In the learning phase, results showed no significant differences among experimental groups, indicating that PTSD-like behavior did not impair learning ability in rats. However, memory tests in the RAWM showed that PTSD-like animals had impairment in both short-term and long-term memories. Vitamin E, on the other hand, prevented this impairment of memory. With respect to oxidative stress, significant decreases were detected in reduced glutathione/oxidized glutathione (GSH/GSSG) ratio, glutathione peroxidase (GPx) and catalase enzyme activities, global histone 3 acetylation, and brain derived neurotrophic factor (BDNF) levels in the PTSD-like animals group compared with other groups (P < 0.05). Vitamin E protected the reduction of these oxidative stress biomarkers, global histone 3 acetylation, and BDNF levels.

CONCLUSIONS

Vitamin E prevented memory impairment associated with PTSD-like behavior in animals, probably via its antioxidative properties, and preservation of epigenetic changes induced in PTSD-like animals.

Vitamin E protects against cisplatin-induced genotoxicity in human lymphocytes

Cisplatin is an anticancer drug that is widely used in treatments of human malignancies such as ovaries,' testes,' and solid tumors of the head and neck. However, the use of cisplatin in the treatments can be associated with DNA damage and high risk to the development of secondary malignancies. Vitamin E is a strong lipophilic antioxidant that has the ability to protect normal cells from chromosomal damage and promote the repair of the damaged DNA. In the current study, the possible protective effect of vitamin E on DNA damage induced by cisplatin was investigated. For that, chromosomal aberrations (CAs) frequency and the number of sister chromatid exchanges (SCEs) were measured in cultured human lymphocytes. Results showed that cisplatin statistically significant increases in the number of cells with CAs (P < 0.05) and in the frequency of SCEs (P < 0.05) as compared to the control group. These increases were significantly lowered by pretreatment of cells with vitamin E. Additionally, cisplatin reduced mitotic index at used concentrations (P < 0.05), which was normalized by vitamin E. Therefore, we conclude that vitamin E can prevent the genotoxicity of cisplatin on cultured human lymphocyte.

Evaluation of mutagenic activity of platinum complexes in somatic cells of Drosophila melanogaster

Cisplatin, carboplatin, and oxaliplatin are some of the most often used alkylating chemotherapeutic agents. In view of the paucity of data on the genotoxicity of oxaliplatin, this study compares the mutagenic activity of cisplatin (0.006, 0.012, 0.025, 0.05 mM), carboplatin (0.1, 0.2, 0,5, 1.0 mM), and oxaliplatin (0.1, 0.2, 0,5, 1.0 mM) using the somatic mutation and recombination test (SMART) in Drosophila melanogaster. Standard and high-bioactivation crosses of the drosophilid were used, which present basal and high levels of cytochrome P450 (CYP450) metabolization enzymes, respectively. All concentrations of cisplatin and carboplatin induced lesions in genetic material in both crosses, while oxaliplatin was mutagenic only to high bioactivation flies treated with 0.1, 0.5 and 1 mM of the compound. No significant differences were observed between genotoxicity values of cisplatin and carboplatin. However, CYP450 enzymes may have affected the mutagenic action of oxaliplatin. Carboplatin induced mainly mutation events, while cisplatin triggered mostly mutation and recombination events when low and high doses were used. Most events induced by oxaliplatin were generated by somatic recombination. Important differences were observed in genotoxic potential of platinum chemotherapeutic compounds, possibly due to the origin and type of the lesions induced in DNA and the repair mechanisms involved.

Assessment of Genotoxicity of Levosimendan in Human Cultured Lymphocytes

BACKGROUND AND OBJECTIVE

Levosimendan is a positive inotropic and a vasodilator agent with pleotropic characteristics that include antioxidation, anti-inflammation and smooth muscle vasodilation.

METHODS

In this study, the effects of levosimendan (0, 0.1, 1, 10, and 20 µg/ml) on oxidative DNA damage and sister-chromatid exchanges (SCEs) were evaluated in human cultured lymphocytes.

RESULTS

The results showed that levosimendan increased the frequency of SCEs in all examined concentrations (P<0.01) except for 0.1 µg/ml. On the other hand, levosimendan did not induce oxidative DNA damage as measured by the 8-OHdG biomarker (P > 0.05). In addition, neither mitotic arrest nor proliferation index was affected by levosimendan at all examined doses (P > 0.05).

CONCLUSION

In conclusion, levosimendan might be associated with increases in sister-chromatid exchanges in cultured human lymphocytes. In vivo studies are required to confirm the present findings.

Effects of α-tocopherol on bone marrow mesenchymal cells derived from type II diabetes mellitus rats

It is widely accepted that vitamin E (VE) acts as an antioxidant and is involved in various metabolic systems including the regulation of gene expression and inhibition of cell proliferation. The most predominant isoform of VE in the living body is α-tocopherol. However, the influence of α-tocopherol on bone marrow mesenchymal cells (BMMCs) in a background of type II diabetes mellitus (DM) has not been investigated. The focus of the present study was to clarify the effect of α-tocopherol on BMMCs derived from rats with type II DM and the underlying mechanisms involved. BMMCs were isolated from rats with type II DM. The BMMCs were either untreated or exposed to α-tocopherol at concentrations of 1.0, 10, and 100 μM, and the resulting effects of α-tocopherol on cell proliferation, H₂O₂ activity, and antioxidant and inflammatory cytokine production were examined. At 100 μM, α-tocopherol had no effect on cell proliferation, but H₂O₂ activity was significantly increased. At 10 μM, α-tocopherol increased the gene expression of IL-1β, and markedly promoted that of TNF-α. Expression of catalase in the presence of 100 μM α-tocopherol was lower than for the other concentrations. At a low concentration, α-tocopherol exerted good antioxidant and anti-inflammatory effects on BMMCs. The study suggests that maintaining α-tocopherol at a low concentration might promote the recovery of BMMCs from oxidative stress.

Vitamin B12 protects against DNA damage induced by hydrochlorothiazide

DNA damage induced by hydrochlorothiazide was previously reported in cultured human lymphocytes. In this study, we aimed to investigate the harmful effects of hydrochlorothiazide on DNA by measuring the spontaneous frequency of sister chromatid exchanges (SCEs) in cultured human lymphocytes. We also aimed to investigate the possible protection of that damage by vitamin B12. The results showed that hydrochlorothiazide (5 µg/mL) significantly increased the frequency of sister chromatid exchanges (P < 0.001) in human lymphocytes in comparison with control. Additionally, the frequency of hydrochlorothiazide-induced SCEs was significantly decreased by co-treatment with vitamin B12 at concentration of 13.5 µg/mL (P < 0.001). In conclusion, hydrochlorothiazide is genotoxic to human lymphocytes and its toxicity is reduced by vitamin B12.