Metformin's performance in in vitro and in vivo genetic toxicology studies

Metformin counters oxidative stress and mitigates adverse effects of radiation exposure: An overview

Metformin (1,1-dimethylbiguanidine hydrochloride) (MF) is a drug that has long been in use for the treatment of type 2 diabetes mellitus and recently is coming into use in the radiation therapy of cancer and other conditions. Exposure to ionizing radiation disturbs the redox homeostasis of cells and causes damage to proteins, membranes, and mitochondria, destroying a number of biological processes. After irradiation, MF activates cellular antioxidant and repair systems by signaling to eliminate the harmful consequences of disruption of redox homeostasis. The use of MF in the treatment of the negative effects of irradiation has great potential in medical patients after radiotherapy and in victims of nuclear accidents or radiologic terrorism.

High-dose metformin induces a low-glucose dependent genotoxic stress

Epidemiological studies have demonstrated that metformin (a cornerstone of diabetes treatment) has anticancer activity, but the underlying mechanism remains elusive. We aimed to investigate whether metformin elicits anticancer activity via increasing genotoxic stress, a state of increased genome damage that becomes tumor-suppressing if it goes beyond an intolerable threshold. We found that metformin (1-16 mM) suppressed proliferation and colony formation in a panel of cancer cell lines (HeLa, A375, A549 and QGY). Metformin induced a dose-dependent increase of genotoxic stress (including micronucleus, nucleoplasmic bridge and nuclear bud) and the increase of genotoxic stress correlated well with metformin's anticancer potential. Metformin deregulated the expression of BUBR1 and MAD2, two core genes of spindle assembly checkpoint (SAC) that surveillances chromosome segregation. Metformin had weakened antiproliferative effect and a corresponding attenuated genotoxic effect in HeLa cells cultured in high glucose (16 mg/ml). Meanwhile, metformin significantly increased genotoxicity in non-cancer cells (NCM460 and HUVECs). Metformin became non-genotoxic to HUVECs in high-glucose (8 and 16 mg/ml) conditions and reduced the genotoxicity of high glucose. Overall, these results infer a new mechanism of high-dose metformin, whereby low-glucose dependent genotoxic stress derived from SAC dysfunction might mediate some of the anticancer effect of this drug.

Metformin as a Potential Adjuvant Antimicrobial Agent Against Multidrug Resistant Bacteria

Introduction

The continuous increase in the incidence of bacterial resistance to existing antibiotics represents a worldwide health burden. A surrogate strategy to combat such crisis is to find compounds that restore the antimicrobial activity of the already existing antibiotics against multidrug resistant bacteria. Metformin is a commonly used antidiabetic medication. It has proven benefits in other diseases including cancer, aging-related and infectious diseases. In this study, the potential effect of metformin as an adjuvant therapy to antibiotics was investigated.

Methods

Two multidrug resistant bacterial strains were used; methicillin-resistant Staphylococcus aureus (MRSA; ATCC 33,591) and multidrug resistant Pseudomonas aeruginosa (ATCC BAA-2114). To assess its efficacy, metformin was combined with several antibiotics: levofloxacin, chloramphenicol, rifampicin, ampicillin, and doxycycline. The antibacterial effect of metformin was tested using the micro broth dilution method. The minimum inhibitory concentration (MIC) was also measured. Cytotoxicity studies were also performed on mammalian cells to assess its safety.

Results

Metformin exhibited an antibacterial effect when combined with the antibiotics on the two tested strains. It also showed low toxicity on the mammalian cells. Moreover, synergetic studies showed that metformin enhanced the effect of the combined antibiotics, as these combinations provide either a synergistic or additive effect with significant reduction in the MIC.

Conclusion

Metformin exerts an adjuvant antibacterial effect; thus, it could be a possible candidate as an adjuvant therapy to reduce antimicrobial resistance.

Cytogenetic effects of antidiabetic drug metformin

Metformin (MET) is the first-choice antidiabetic drug for type 2 diabetes mellitus treatment. In this study, the genotoxic potential of MET was evaluated by using chromosome aberrations (CAs), sister chromatid exchanges (SCEs), and micronucleus (MN) assays in human peripheral lymphocytes as well as comet assay in isolated lymphocytes. Human lymphocytes were treated with different concentrations of MET (12.5, 25, 50, 75, 100, and 125 µg/mL) for 24 h and 48 h. A negative and a positive control (Mitomycin-C-MMC, 0.20 μg/mL, for CA, SCE, and MN tests; hydrogen peroxide-H₂O₂, 100 µM, for comet assay) were also maintained. MET significantly increased the frequency of CAs at 48 h exposure (except 12.5 µg/mL) compared to the negative control. MET increased SCEs/cells in both treatment periods (except 12.5 µg/mL at 24 h). MET only increased the frequency of MN at 125 µg/mL. While MET significantly increased the comet tail length (CTL) at four concentrations (25, 75, 100, and 125 µg/mL), it did not affect comet tail intensity (CTI) (except 125 µg/mL) and comet tail moment (CTM) at all the treatments. All these data showed that MET had a mild genotoxic effect, especially at a long treatment period and higher concentrations in human lymphocytes in vitro. However, further in vitro and especially in vivo studies should be conducted to understand the detailed genotoxic potential of MET.HighlightsMetformin increased the frequency of CAs and SCEs, especially at 48-h exposure time in human lymphocytes.This antidiabetic drug increased the frequency of MN only at the highest concentration tested (125 µg/mL).Metformin significantly increased the comet tail length in all treatments (except 50 µg/mL).The drug did not significantly affect the comet tail intensity (except 125 µg/mL) and comet tail moment in all treatments.

Benefits of Metformin in Attenuating the Hallmarks of Aging

Biological aging involves an interplay of conserved and targetable molecular mechanisms, summarized as the hallmarks of aging. Metformin, a biguanide that combats age-related disorders and improves health span, is the first drug to be tested for its age-targeting effects in the large clinical trial-TAME (targeting aging by metformin). This review focuses on metformin's mechanisms in attenuating hallmarks of aging and their interconnectivity, by improving nutrient sensing, enhancing autophagy and intercellular communication, protecting against macromolecular damage, delaying stem cell aging, modulating mitochondrial function, regulating transcription, and lowering telomere attrition and senescence. These characteristics make metformin an attractive gerotherapeutic to translate to human trials.

Environmental monitoring and the developmental origins of health and disease

Early-life chronic exposure to environmental contaminants, such as bisphenol-A, particulate matter air pollution, organophosphorus pesticides, and pharmaceutical drugs, among others, may affect central tissues, such as the hypothalamus, and peripheral tissues, such as the endocrine pancreas, causing inflammation and apoptosis with severe implications to the metabolism. The Developmental Origins of Health and Disease (DOHaD) concept articulates events in developmental phases of life, such as intrauterine, lactation, and adolescence, to later-life metabolism and health. These developmental phases are more susceptible to environmental changes, such as those caused by environmental contaminants, which may predispose individuals to obesity, metabolic syndrome, and chronic noncommunicable diseases later in life. Alterations in the epigenome are explored as an underlying mechanism to the programming effects on metabolism, as the expression of key genes related with central and peripheral metabolic functions may be altered in response to environmental disturbances. Studies show that environmental contaminants may affect gene expressions in mammals, especially when exposed to during the developmental phases of life, leading to metabolic disorders in adulthood. In this review, we discuss the current obesity epidemics, the DOHaD concept, pollutants' toxicology, environmental control, and the role of environmental contaminants in the central and peripheral programming of obesity and metabolic syndrome. Improving environmental monitoring may directly affect the quality of life of the population and help protect the future generations from metabolic diseases.

Metformin attenuates cisplatin-induced genotoxicity and apoptosis in rat bone marrow cells

Metformin is widely used as an oral hypoglycemic drug in the management of type 2 diabetes mellitus. This study evaluated the possible protective effects of metformin against cisplatin-induced genotoxicity and apoptosis in rat bone marrow cells. Two different doses of metformin (50 and 100 mg/kg b.w.) were administered orally to experimental animals for seven consecutive days. On the seventh day, the rats were exposed to cisplatin (5 mg/kg, i.p.) 1 h after the last oral metformin administration. Rats in the control group were treated orally with 10 ml/kg PBS for 7 consecutive days and a single intraperitoneal injection of saline (0.9%) on the 7th day. The antagonistic effects of metformin against cisplatin were evaluated using micronucleus assay, reactive oxygen species (ROS) level analysis, hematological analysis, and flow cytometry. Treatment with 50 and 100 mg/kg metformin before cisplatin injection produced a significant reduction in the frequencies of micronucleated polychromatic erythrocytes (MnPCEs) and micronucleated normochromatic erythrocytes (MnNCEs) 24 h after cisplatin treatment with a corresponding increase in the PCE/(PCE + NCE) ratio. Moreover, metformin markedly elevated the levels of both red and white blood cells in peripheral blood and decreased the percentage of apoptotic cells and the ROS level in bone marrow cells of rats treated with cisplatin. The data suggest that metformin has potential chemoprotective properties in rat bone marrow after cisplatin treatment, which support its candidature as a potential chemoprotective agent for cancer patients undergoing chemotherapy.

A preclinical overview of metformin for the treatment of type 2 diabetes

Type 2 diabetes (T2D) is the most common type of diabetes mellitus and is mainly characterized by insulin resistance, β-cell dysfunction, and elevated hepatic glucose output. Metformin is a first-line antihyperglycemic agent that works mainly by regulating hepatic glucose production and peripheral insulin sensitivity. Metformin has been clinically applied for more than half a century, although the underlying pharmacological mechanisms remain elusive. This current review mainly focused on the development history of metformin and related preclinical studies on structural modification, pharmacological mechanisms for treatment of T2D, toxicology, pharmacokinetics, and pharmaceutics. The pharmacological function of metformin in lowering hyperglycemia suggests that multi-targeting could be an effective strategy for the discovery of new anti-diabetic drugs. A number of discoveries have revealed the pharmacologic mechanisms of metformin; however, precise mechanisms remain unclear. Deeper investigations on the biological features of metformin are expected to provide more rational applications and indications of this evergreen anti-T2D agent, which will in turn help to better understand the complicated pathogenesis of T2D.

Metformin prolongs survival rate in mice and causes increased excretion of cell-free DNA in the urine of X-irradiated rats

An antidiabetic drug metformin has anticarcinogenic and geroprotective effects and has been used in combination with radiation cancer therapy. The present work is devoted to the study of the effect of metformin on survival in mice, the frequency of micronuclei in mouse bone marrow cells and excretion of cell-free nuclear and mitochondrial DNA in the urine of X-ray-exposed rats. The survival rate and the frequency of micronuclei in mice and excretion of DNA into rat urine were determined after administration of the drug before and after irradiation of animals. The DNA content was measured by qRT-PCR. Metformin shows a radioprotective effect only when administered to mice after the radiation exposure. On the 11th day after irradiation, we observed 100% mortality in the control group; 78% of mice remained alive if metformin was given. Twenty percent of the mice in this group survived for 30 days after irradiation. Metformin has the same effect on the frequency of micronuclei; its reduction is observed, when the drug is administered to the mice after irradiation. Metformin promotes the excretion of nuclear and mitochondrial DNA with the urine of irradiated rats. The results show that metformin acts as a radiomitigation effector. Metformin promotes the active excretion of DNA of dying cells from the tissues of irradiated animals.

Assessment of bendamustine-induced genotoxicity in eukaryotic cells

Bendamustine, an anticancer drug with alkylating properties, is widely used to treat hematological malignancies. Since the nitrogen mustard family alkylators induce DNA damages and have been associated with an elevated risk of second malignancy, current study evaluates the cytotoxic, mutagenic, and recombinogenic effects of bendamustine by using, respectively the mitotic index assay, the in vitro mammalian cell micronucleus test (Mnvit) and the chromosome aberration (CA) test in human peripheral lymphocytes, and the in vivo homozygotization assay in Aspergillus nidulans, which detects the loss of heterozygosity (LOH) due to somatic recombination. Bendamustine (6.0 µg/ml, 9.0 µg/ml, and 12.0 µg/ml) induced a statistically significant concentration-related increase in the frequencies of micronuclei and a significant reduction in the cytokinesis block proliferation index (CBPI) rates when compared to negative control. In the CA test, bendamustine significantly increased the frequencies of structural aberrations at the three tested concentrations when compared to the negative control. Aspergillus nidulans diploids, obtained after bendamustine treatment (6.0 µg/ml, 12.0 µg/ml, and 24.0 µg/ml), produced, after haploidization, homozygotization index (HI) rates higher than 2.0 and significantly different from the negative control. Since bendamustine showed genotoxic effects in all tested concentrations, two of them corresponding to the peak plasma concentrations observed in cancer patients treated with bendamustine, data provided in the current research work may be useful to identify the most appropriate dosage regimen to achieve the efficacy and safety of this anticancer medication.

Metformin: Prevention of genomic instability and cancer: A review

The diabetes drug metformin can mitigate the genotoxic effects of cytotoxic agents and has been proposed to prevent or even cure certain cancers. Metformin reduces DNA damage by mechanisms that are only incompletely understood. Metformin scavenges free radicals, including reactive oxygen species and nitric oxide, which are produced by genotoxicants such as ionizing or non-ionizing radiation, heavy metals, and chemotherapeutic agents. The drug may also increase the activities of antioxidant enzymes and inhibit NADPH oxidase, cyclooxygenase-2, and inducible nitric oxide synthase, thereby limiting macrophage recruitment and inflammatory responses. Metformin stimulates the DNA damage response (DDR) in the homologous end-joining, homologous recombination, and nucleotide excision repair pathways. This review focuses on the protective properties of metformin against genomic instability.

Increased Micronuclei Frequency in Oral and Lingual Epithelium of Treated Diabetes Mellitus Patients

Diabetes mellitus (DM) is a metabolic disease characterized by persistent high levels of glucose in plasma. Chronic hyperglycemia is thought to increase oxidative stress and the formation of free radicals that in turn damage cells. Thus, we decided to determine the frequency of nuclear abnormalities in epithelial cells from cheek and tongue mucosa of DM patients with type 1 (DM1, treated only with insulin) and type 2 (DM2, treated with metformin) using the buccal micronucleus cytome (BMCyt) assay. Micronuclei frequency in cheek epithelial cells was higher in both DM1 (0.75 ± 0.31, P < 0.001) and DM2 (0.52 ± 0.27, P < 0.001) patients, as compared to healthy controls (0.07  ±  0.06). Similarly, micronuclei frequency in tongue epithelium was increased in DM1 (0.81  ±  0.22, P < 0.001) and DM2 (0.41  ±  0.21, P < 0.001) groups, in comparison to controls (0.06  ±  0.05). Besides, we found a positive correlation between micronuclei frequency and the onset time of DM2 in both cheek (ρ = 0.69, P < 0.001) and tongue epithelial cells (ρ = 0.71, P < 0.001), but not with onset time of DM1 or age of the patients. Considering all this, we pose that BMCyt could serve as a fast and easily accessible test to assess genotoxic damage during dental visits of DM patients, helping to monitor their disease.

X-rays and metformin cause increased urinary excretion of cell-free nuclear and mitochondrial DNA in aged rats

Activation of cell death in mammals can be assessed by an increase of an amount of cell-free DNA (cf-DNA) in urine or plasma. We investigated the excretion of cf nuclear DNA (nDNA) and cf mitochondrial DNA (mtDNA) in the urine of rats 3 and 24 months in age after X-irradiation and metformin administration. Analyses showed that prior to treatment, the amount of cf-nDNA was 40% higher and cf-mtDNA was 50% higher in the urine of aged rats compared to that of young animals. At 12 h after irradiation, the content of cf-nDNA and cf-mtDNA in the urine of young rats was increased by 200% and 460%, respectively, relative to the control, whereas in the urine of aged rats, it was 250% and 720% higher. After 6 h following metformin administration, the amount of cf-nDNA and cf-mtDNA in the urine of young rats was elevated by 25% and 55% and by 50% and 160% in the urine of aged rats. Thus, these preliminary data suggest that X-rays and metformin cause a significant increase of cf-DNA in the urine of older rats caused by the active cell death in tissues. These results also suggest that metformin possibly initiates the death of the cells containing structural and functional abnormalities.

The radioprotective effect of metformin against cytotoxicity and genotoxicity induced by ionizing radiation in cultured human blood lymphocytes

Metformin is a widely prescribed drug used in the treatment of patients with type 2 diabetes. In this study, the radioprotective effect of metformin was investigated against cytotoxicity and genotoxicity induced by ionizing radiation (IR) in human peripheral blood lymphocytes. Human lymphocytes were treated with metformin at concentrations 10 and 50μM for 2h and irradiated with 6MV X-rays. The radiation antagonistic potential of metformin was assessed by MTT [3-(4,5-dimethyl-2-thiaozolyl)-2,5-diphenyl-2H tetrazolium bromide] assay, chromosomal aberration (CA) analysis, cytokinesis blocked micronucleus (CBMN) assay, and flow cytometry. Observations demonstrated a radiation-dose-dependent decrease in the percentage of cell viability after 24h. It was found that pretreatment with metformin (10 and 50μM) increased the percentage of cell viability. A highly significant dose modifying factor (DMF) 1.35 and 1.42 was observed for 10 and 50μM metformin, respectively. Metformin (10 and 50μM) pretreatment significantly decreased the frequency of dicentrics (DCs), acentric fragments (AFs), rings (RIs), micronuclei (MN), and nucleoplasmic bridges (NPBs) in irradiated human peripheral blood lymphocytes. Also, treatment with metformin (10 and 50μM) without irradiation did not increase the number of MN, NPBs, DCs, AFs, RIs, and did not show a cytostatic effect in the human peripheral blood lymphocytes. On the other hand, metformin treatment (10 and 50μM) 2h prior to irradiation significantly reduced X-radiation-induced apoptotic incidence in human lymphocytes. The present study demonstrates metformin to be an effective radioprotector against DNA damage and apoptosis induced by IR in human lymphocytes. These data have an important application for the protection of lymphocytes from the genetic damage and side-effects induced by radiotherapy in cancer patients.

Assessment of in vivo and in vitro genotoxicity of glibenclamide in eukaryotic cells

Glibenclamide is an oral hypoglycemic drug commonly prescribed for the treatment of type 2 diabetes mellitus, whose anti-tumor activity has been recently described in several human cancer cells. The mutagenic potential of such an antidiabetic drug and its recombinogenic activity in eukaryotic cells were evaluated, the latter for the first time. The mutagenic potential of glibenclamide in therapeutically plasma (0.6 μM) and higher concentrations (10 μM, 100 μM, 240 μM and 480 μM) was assessed by the in vitro mammalian cell micronucleus test in human lymphocytes. Since the loss of heterozygosity arising from allelic recombination is an important biologically significant consequence of oxidative damage, the glibenclamide recombinogenic activity at 1 μM, 10 μM and 100 μM concentrations was evaluated by the in vivo homozygotization assay. Glibenclamide failed to alter the frequency of micronuclei between 0.6 μM and 480 μM concentrations and the cytokinesis block proliferation index between 0.6 μM and 240 μM concentrations. On the other hand, glibenclamide changed the cell-proliferation kinetics when used at 480 μM. In the homozygotization assay, the homozygotization indices for the analyzed markers were lower than 2.0 and demonstrated the lack of recombinogenic activity of glibenclamide. Data in the current study demonstrate that glibenclamide, in current experimental conditions, is devoid of significant genotoxic effects. This fact encourages further investigations on the use of this antidiabetic agent as a chemotherapeutic drug.