Signaling steps in the induction of genomic damage by insulin in colon and kidney cells

Modified Citrus Pectin (MCP) Confers a Renoprotective Effect on Early-Stage Nephropathy in Type-2 Diabetic Mice

Diabetic nephropathy (DN) is a significant global health concern with a high morbidity rate. Accumulating evidence reveals that Galectin-3 (Gal-3), a β-galactoside-binding lectin, is a biomarker in kidney diseases. Our study aimed to assess the advantageous impacts of modified citrus pectin (MCP) as an alternative therapeutic strategy for the initial and ongoing progression of DN in mice with type 2 diabetes mellitus (T2DM). The animal model has been split into four groups: control group, T2DM group (mice received intraperitoneal injections of nicotinamide (NA) and streptozotocin (STZ), T2DM+MCP group (mice received 100 mg/kg/day MCP following T2DM induction), and MCP group (mice received 100 mg/kg/day). After 4 weeks, kidney weight, blood glucose level, serum kidney function tests, histopathological structure alterations, oxidative stress, inflammation, apoptosis, and fibrosis parameters were determined in renal tissues. Our findings demonstrated that MCP treatment reduced blood glucose levels, renal histological damage, and restored kidney weight and kidney function tests. Additionally, MCP reduced malondialdehyde level and restored glutathione level, and catalase activity. MCP demonstrated a notable reduction in inflammatory and apoptosis mediators TNF-α, iNOS, TGF-βRII and caspase-3. Overall, MCP could alleviate renal injury in an experimental model of DN by suppressing renal oxidative stress, inflammation, fibrosis, and apoptosis mediators.

Comparative phytochemical analysis of five Egyptian strawberry cultivars (Fragaria × ananassa Duch.) and antidiabetic potential of Festival and Red Merlin cultivars

This work aims to explore the differences in phytochemical composition and biological properties of five strawberry hybrids (Fragaria × ananassa Duch.), and highlights the non-edible part (byproduct) as a source of self-remedy natural herb along with fruits. HPLC/DAD/HRESIMS technique was used in the dereplication of ten ethanolic extracts of five strawberry cultivars leaves and fruits (Festival, Red Merlin, Suzana, Tamar and Winter Dawn). Total phenolic and total flavonoid contents were established using Folin–Ciocalteu and aluminum chloride colorimetric assays, respectively. Ethanolic extracts of leaves and fruits from Festival and Red Merlin cultivars were selected to investigate their anti-hyperglycemic activity using streptozotocin-induced diabetic rats. Oxidative stress markers, lipid profile and kidney and liver function tests were assessed. The results revealed different chemical profiles of ten samples with the identification of 37 metabolites, represented mainly as flavonoids and phenolic acid derivatives. Phytochemical investigation resulted in the isolation of seven known phenolic compounds; quercetin, kaempferol, p-coumaric acid, p-tyrosol, methyl gallate, trans-tiliroside and eutigoside A. Suzana cultivar was the richest cultivar with flavonoids and total phenolics except for the total flavonoid content in leaves referred to Festival cultivar. Ethanolic extract of leaves, especially Festival cultivar was the most bioactive one. The results established the role of strawberry leaves along with fruits as an antioxidant and hypoglycemic natural remedy.

This work aims to explore the differences in phytochemical composition and biological properties of five strawberry hybrids (Fragaria × ananassa Duch.), and highlights the non-edible part (byproduct) as a source of self-remedy natural herb along with fruits.

Colon Carcinogenesis: The Interplay Between Diet and Gut Microbiota

Colorectal cancer (CRC) incidence increases yearly, and is three to four times higher in developed countries compared to developing countries. The well-known risk factors have been attributed to low physical activity, overweight, obesity, dietary consumption including excessive consumption of red processed meats, alcohol, and low dietary fiber content. There is growing evidence of the interplay between diet and gut microbiota in CRC carcinogenesis. Although there appears to be a direct causal role for gut microbes in the development of CRC in some animal models, the link between diet, gut microbes, and colonic carcinogenesis has been established largely as an association rather than as a cause-and-effect relationship. This is especially true for human studies. As essential dietary factors influence CRC risk, the role of proteins, carbohydrates, fat, and their end products are considered as part of the interplay between diet and gut microbiota. The underlying molecular mechanisms of colon carcinogenesis mediated by gut microbiota are also discussed. Human biological responses such as inflammation, oxidative stress, deoxyribonucleic acid (DNA) damage can all influence dysbiosis and consequently CRC carcinogenesis. Dysbiosis could add to CRC risk by shifting the effect of dietary components toward promoting a colonic neoplasm together with interacting with gut microbiota. It follows that dietary intervention and gut microbiota modulation may play a vital role in reducing CRC risk.

Malic enzyme 1 (ME1) in the biology of cancer: it is not just intermediary metabolism

Malic enzyme 1 (ME1) is a cytosolic protein that catalyzes the conversion of malate to pyruvate while concomitantly generating NADPH from NADP. Early studies identified ME1 as a mediator of intermediary metabolism primarily through its participatory roles in lipid and cholesterol biosynthesis. ME1 was one of the first identified insulin-regulated genes in liver and adipose and is a transcriptional target of thyroxine. Multiple studies have since documented that ME1 is pro-oncogenic in numerous epithelial cancers. In tumor cells, the reduction of ME1 gene expression or the inhibition of its activity resulted in decreases in proliferation, epithelial-to-mesenchymal transition and in vitro migration, and conversely, in promotion of oxidative stress, apoptosis and/or cellular senescence. Here, we integrate recent findings to highlight ME1's role in oncogenesis, provide a rationale for its nexus with metabolic syndrome and diabetes, and raise the prospects of targeting the cytosolic NADPH network to improve therapeutic approaches against multiple cancers.

Overlapping mechanism of the induction of genomic damage by insulin and adrenaline in human promyelocytic HL-60 cells

Endogenous hormones systemically regulate the growth and metabolism and some prior studies have shown that their imbalance can have a potential to induce genomic damage in in vitro and animal models. Some conditions that are associated with elevated levels of endogenous hormones are hyperinsulinemia and intense exercise-induced stress causing increased adrenaline. In this study we test whether these two hormones, could cause an additive increase in genomic damage and whether they have an overlapping mechanism of action. For this, we use the human promyelocytic HL60 cells, as they express the receptors for both hormones. At doses taken from the saturation level of the individual dose response curves, no additivity in genomic damage was detected through micronucleus induction. This hints towards a common step in the pathway, which is under these conditions fully activated by each of the individual hormone. To investigate this further, individual and common parts in insulin and adrenaline signalling such as their respective hormone receptors, the downstream protein AKT and the involvement of mitochondria and NADPH oxidase (NOX) enzymes were studied. The results indicate no additive effect of high hormone concentrations in genomic damage in the in vitro model, which may be due to exhaustion of the NOX 2-mediated reactive oxygen production. It remains to be determined whether a similar situation may occur in in vivo situations.

Direct toxicity of insulin on the human placenta and protection by metformin

OBJECTIVE

To study the effects of insulin and metformin on primary trophoblasts from early pregnancies.

DESIGN

Experimental in vitro study.

SETTING

Academic research institute.

PATIENT(S)

Trophoblasts from healthy patients undergoing first trimester elective termination of pregnancy and primary lung fibroblasts (IMR-90).

INTERVENTION(S)

Culture and treatment with insulin and metformin of primary trophoblasts and primary lung fibroblasts (IMR-90).

MAIN OUTCOME MEASURE(S)

DNA damage measured by expression of γ-H2AX with immunofluorescence and Western blot. Apoptosis measured by expression of cleaved caspase-3 by Western blot. Cell survival measured by cell proliferation assay.

RESULT(S)

Culture of purified primary trophoblast cells in the presence of insulin at levels as low as 1 nM resulted in a 386% increase in the number of cell with elevated γ-H2AX expression, a 66% reduction in cell survival and a marked increase of cleaved caspase-3 expression. Pretreatment of trophoblasts with therapeutic doses of metformin prevented the detrimental effects of insulin. Treatment with insulin and/or metformin had no effects on primary fibroblasts.

CONCLUSION(S)

Elevated insulin levels are directly toxic to first trimester trophoblasts and result in increased DNA damage, apoptosis, and decreased cell survival. These effects are prevented by metformin. Trophoblast cells from early pregnancy are uniquely vulnerable to elevated levels of insulin. These findings, if confirmed in vivo, suggest that there may be a role for insulin resistance screening before attempting pregnancy and for focusing on prevention of hyperinsulinemia during early pregnancy.

NOX4, a new genetic target for anti-cancer therapy in digestive system cancer

Oxidative stress has been implicated as an important factor in tumorigenesis and tumor progression. The nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunit 4 (NOX4), a substrate of NADPH that can generate H₂ O₂ reactive oxygen species, has been reported to be highly expressed in gastrointestinal tumors. In this review we summarize the available evidence on the biological function of NOX4 in digestive system tumors by focusing on its correlation with classical cell signaling pathways, including VEGF, MAPK and PI3K/AKT, and with biochemical mediators, such as nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), activator protein (AP)-1 and transforming growth factor (TGF)-β. According to the clinical and database studies on tumors of the digestive system, such as colorectal, gastric and pancreatic cancer, there are significant associations between NOX4 expression and tumor prognosis as well as patient's survival. Animal studies using NOX4 inhibitors such as diphenylene iodonium and GKT137831, which selectively block NOX4, indicate their potential as therapeutic agents for targeting cancer cells.

Protective effects of tricetinidin against oxidative stress inducers in rat kidney cells: A comparison with delphinidin and standard antioxidants

The potential protective effect of tricetinidin as novel antioxidant is investigated and compared with selected known antioxidant substances in vitro. Dihydroethidium staining was performed to detect intracellular ROS formation and the protective effect of the antioxidant substances in combination with the superoxide-inducer antimycin a (AMA). Glutathione level, mitochondrial membrane potential and HO-1 expression were analysed for further characterization of the cellular response. The cytokinesis block micronucleus test was applied to investigate the anti-genotoxic effect of the substances against insulin induced genomic damage. AMA treatment caused a significant increase in intracellular ROS formation and insulin treatment induced a significant micronucleus induction in NRK cells. Combination of the antioxidant substances with AMA or insulin protected from the oxidative stress and the micronucleus-induction. All analysed antioxidants showed comparable effects on GSH production and mitochondrial membrane potential. Only delphinidin and tricetinidin caused an increase in HO-1 expression. Tricetinidin and delphinidin might be good candidates for development as an antioxidant supplement. Further research is necessary to show possible therapeutic and preventive effects of tricetinidin and delphinidin in vivo.

Decreased Chromosomal Damage in Lymphocytes of Obese Patients After Bariatric Surgery

The number of bariatric surgeries being performed worldwide has markedly risen. While the improvement in obesity-associated comorbidities after bariatric surgery is well-established, very little is known about its impact on cancer risk. The peripheral lymphocyte micronucleus test is a widely used method for the monitoring of chromosomal damage levels in vivo, and micronucleus frequency positively correlates with cancer risk. Therefore, the aim of this study was to compare the micronucleus frequency before and after bariatric surgery in obese subjects. Peripheral blood mononuclear cells were collected from 45 obese subjects before and at two time-points after bariatric surgery (6 and 12 months) to assess spontaneous micronucleus frequency. Consistent with the increased cancer risk previously shown, bariatric surgery-induced weight loss led to a significant reduction in lymphocyte micronucleus frequency after 12 months. Interestingly, comorbidities such as type 2 diabetes mellitus and metabolic syndrome further seemed to have an impact on the lymphocyte micronucleus frequency. Our findings may indicate a successful reduction of cancer risk in patients following weight loss caused by bariatric surgery.

Gallic acid, a common dietary phenolic protects against high fat diet induced DNA damage

Purpose

Aim of the study was to find out if gallic acid (GA), a common phenolic in plant foods, prevents obesity induced DNA damage which plays a key role in the induction of overweight associated cancer.

Methods

Male and female C57BL6/J mice were fed with a low fat or a high fat diet (HFD). The HFD group received different doses GA (0, 2.6–20 mg/kg b.w./day) in the drinking water for 1 week. Subsequently, alterations of the genetic stability in blood and inner organs were monitored in single cell gel electrophoresis assays. To elucidate the underlying molecular mechanisms: oxidized DNA bases, alterations of the redox status, lipid and glucose metabolism, cytokine levels and hepatic NF-κB activity were monitored.

Results

HFD fed animals had higher body weights; increased DNA damage and oxidation of DNA bases damage were detected in colon, liver and brain but not in blood and white adipose tissue. Furthermore, elevated concentrations of insulin, glucose, triglycerides, MCP-1, TNF-α and NF-κB activity were observed in this group. Small amounts of GA, in the range of human consumption, caused DNA protection and reduced oxidation of DNA bases, as well as biochemical and inflammatory parameters.

Conclusions

Obese animals have increased DNA damage due to oxidation of DNA bases. This effect is probably caused by increased levels of glucose and insulin. The effects of GA can be explained by its hypoglycaemic properties and indicate that the consumption of GA-rich foods prevents adverse health effects in obese individuals.

Electronic supplementary material

The online version of this article (10.1007/s00394-018-1782-2) contains supplementary material, which is available to authorized users.

Impact of obesity and overweight on DNA stability: Few facts and many hypotheses

Health authorities are alarmed worldwide about the increase of obesity and overweight in the last decades which lead to adverse health effects including inflammation, cancer, accelerated aging and infertility. We evaluated the state of knowledge concerning the impact of elevated body mass on genomic instability. Results of investigations with humans (39 studies) in which DNA damage was monitored in lymphocytes and sperm cells, are conflicting and probably as a consequence of heterogeneous study designs and confounding factors (e.g. uncontrolled intake of vitamins and minerals and consumption of different food types). Results of animal studies with defined diets (23 studies) are more consistent and show that excess body fat causes DNA damage in multiple organs including brain, liver, colon and testes. Different molecular mechanisms may cause genetic instability in overweight/obese individuals. ROS formation and lipid peroxidation were found in several investigations and may be caused by increased insulin, fatty acid and glucose levels or indirectly via inflammation. Also reduced DNA repair and formation of advanced glycation end products may play a role but more data are required to draw firm conclusions. Reduction of telomere lengths and hormonal imbalances are characteristic for overweight/obesity but the former effects are delayed and moderate and hormonal effects were not investigated in regard to genomic instability in obese individuals. Increased BMI values affect also the activities of drug metabolizing enzymes which activate/detoxify genotoxic carcinogens, but no studies concerning the impact of these alterations of DNA damage in obese individuals are available. Overall, the knowledge concerning the impact of increased body weight and DNA damage is poor and further research is warranted to shed light on this important issue.

The protective effect of shikonin on renal tubular epithelial cell injury induced by high glucose

Hyperglycemia-induced oxidative stress is thought to play a critical role in the pathogenesis of diabetic nephropathy (DN). Treating high-glucose (HG)-induced proximal tubule injury has become a patential therapeutic option to attenuate the onset and progression of DN. The present study aimed to investigate the renoprotective effect of shikonin, the chief active compound extracted from the roots of the traditional Chinese herb Lithospermum erythrorhizon, on HG-induced cytotoxicity in NRK-52E cells. Treating cells with HG significantly reduce cell viability while also significantly increasing content of reactive oxygen species (ROS). Treating the cells with shikonin improved these changes induced by HG. Shikonin strongly stabilized mitochondrial membrane potential in HG-induced NRK-52E cells. In addition, treatment with shikonin upregulated antioxidant system in response to ROS by increasing levels of SOD and CAT. Furthermore, shikonin also strongly decreased the levels of activated caspase-3, Bax and p-GSK-3β while increased the p-AKT level. These findings provide that the renoprotective effects of shikonin against HG-induced cytotoxicity in NRK-52E cells may be mediated in inhibiting oxidative stress through activating of the AKT signalling pathway.

Effects of Resveratrol, Lovastatin and the mTOR-Inhibitor RAD-001 on Insulin-Induced Genomic Damage In Vitro

Diabetes mellitus (DM) is one of the major current health problems due to lifestyle changes. Before diagnosis and in the early years of disease, insulin blood levels are elevated. However, insulin generates low levels of reactive oxygen species (ROS) which are integral to the regulation of a variety of intracellular signaling pathways, but excess levels of insulin may also lead to DNA oxidation and DNA damage. Three pharmaceutical compounds, resveratrol, lovastatin and the mTOR-inhibitor RAD-001, were investigated due to their known beneficial effects. They showed protective properties against genotoxic damage and significantly reduced ROS after in vitro treatment of cultured cells with insulin. Therefore, the selected pharmaceuticals may be attractive candidates to be considered for support of DM therapy.

Insulin Receptor Isoforms in Physiology and Disease: An Updated View

The insulin receptor (IR) gene undergoes differential splicing that generates two IR isoforms, IR-A and IR-B. The physiological roles of IR isoforms are incompletely understood and appear to be determined by their different binding affinities for insulin-like growth factors (IGFs), particularly for IGF-2. Predominant roles of IR-A in prenatal growth and development and of IR-B in metabolic regulation are well established. However, emerging evidence indicates that the differential expression of IR isoforms may also help explain the diversification of insulin and IGF signaling and actions in various organs and tissues by involving not only different ligand-binding affinities but also different membrane partitioning and trafficking and possibly different abilities to interact with a variety of molecular partners. Of note, dysregulation of the IR-A/IR-B ratio is associated with insulin resistance, aging, and increased proliferative activity of normal and neoplastic tissues and appears to sustain detrimental effects. This review discusses novel information that has generated remarkable progress in our understanding of the physiology of IR isoforms and their role in disease. We also focus on novel IR ligands and modulators that should now be considered as an important strategy for better and safer treatment of diabetes and cancer and possibly other IR-related diseases.

Diabetes-induced mechanophysiological changes in the small intestine and colon

The disorders of gastrointestinal (GI) tract including intestine and colon are common in the patients with diabetes mellitus (DM). DM induced intestinal and colonic structural and biomechanical remodeling in animals and humans. The remodeling is closely related to motor-sensory abnormalities of the intestine and colon which are associated with the symptoms frequently encountered in patients with DM such as diarrhea and constipation. In this review, firstly we review DM-induced histomorphological and biomechanical remodeling of intestine and colon. Secondly we review motor-sensory dysfunction and how they relate to intestinal and colonic abnormalities. Finally the clinical consequences of DM-induced changes in the intestine and colon including diarrhea, constipation, gut microbiota change and colon cancer are discussed. The final goal is to increase the understanding of DM-induced changes in the gut and the subsequent clinical consequences in order to provide the clinicians with a better understanding of the GI disorders in diabetic patients and facilitates treatments tailored to these patients.

Zeaxanthin ameliorates high glucose-induced mesangial cell apoptosis through inhibiting oxidative stress via activating AKT signalling-pathway

Oxidative stress is a critical factor in the pathophysiology of diabetic kidney disease. Previous study shows that hyperglycaemia aggravates renal injury through oxidative stress in diabetic model, and antioxidants have beneficial effect on diabetic kidney disease. However, the role of antioxidants in the progression of diabetic kidney disease is poorly understood. The aim of this study was to clarify whether zeaxanthin, an antioxidant, could ameliorate mesangial cell injury and if so, identify the related mechanism underlying this protective effect. To that end, superoxide dismutase (SOD) activity and methane dicarboxylic aldehyde (MDA) levels were measured by an assay kit, and mesangial cell apoptosis and ROS levels were assessed using flow cytometry analysis. Furthermore, The levels of a phosphorylated ser/thr protein kinase (p-AKT), phosphorylated glycogen synthase kinase-3 beta (p-GSK-3β), Bcl-2 associated X protein (Bax) and cleaved cysteinyl aspartate-specific proteinase-3 (caspase-3) were detected by western blot. We found that zeaxanthin decreases MDA levels and increased SOD activity, as well as inhibits apoptosis and decreases ROS levels in mesangial cells in a high sugar environment. Furthermore, zeaxanthin increased p-AKT levels while decreased the levels of p-GSK-3β, Bax and cleaved-caspase-3. In addition, LY294002 reversed the protective effect of zeaxanthin on mesangial cells. In conclusion, zeaxanthin ameliorated mesangial cell apoptosis may be involved in inhibiting oxidative stress through activating of the AKT signalling pathway.

Highly Potent and Isoform Selective Dual Site Binding Tankyrase/Wnt Signaling Inhibitors That Increase Cellular Glucose Uptake and Have Antiproliferative Activity

Compounds 13 and 14 were evaluated against 11 PARP isoforms to reveal that both 13 and 14 were more potent and isoform selective toward inhibiting tankyrases (TNKSs) than the "standard" inhibitor 1 (XAV939)⁵, i.e., IC₅₀ = 100 pM vs TNKS2 and IC₅₀ = 6.5 μM vs PARP1 for 14. In cellular assays, 13 and 14 inhibited Wnt-signaling, enhanced insulin-stimulated glucose uptake, and inhibited the proliferation of DLD-1 colorectal adenocarcinoma cells to a greater extent than 1.

Role of PTEN in Oxidative Stress and DNA Damage in the Liver of Whole-Body Pten Haplodeficient Mice

Type 2 diabetes (T2DM) and obesity are frequently associated with non-alcoholic fatty liver disease (NAFLD) and with an elevated cancer incidence. The molecular mechanisms of carcinogenesis in this context are only partially understood. High blood insulin levels are typical in early T2DM and excessive insulin can cause elevated reactive oxygen species (ROS) production and genomic instability. ROS are important for various cellular functions in signaling and host defense. However, elevated ROS formation is thought to be involved in cancer induction. In the molecular events from insulin receptor binding to genomic damage, some signaling steps have been identified, pointing at the PI3K/AKT pathway. For further elucidation Phosphatase and Tensin homolog (Pten), a tumour suppressor phosphatase that plays a role in insulin signaling by negative regulation of PI3K/AKT and its downstream targets, was investigated here. Dihydroethidium (DHE) staining was used to detect ROS formation in immortalized human hepatocytes. Comet assay and micronucleus test were performed to investigate genomic damage in vitro. In liver samples, DHE staining and western blot detection of HSP70 and HO-1 were performed to evaluate oxidative stress response. DNA double strand breaks (DSBs) were detected by immunohistostaining. Inhibition of PTEN with the pharmacologic inhibitor VO-OHpic resulted in increased ROS production and genomic damage in a liver cell line. Knockdown of Pten in a mouse model yielded increased oxidative stress levels, detected by ROS levels and expression of the two stress-proteins HSP70 and HO-1 and elevated genomic damage in the liver, which was significant in mice fed with a high fat diet. We conclude that PTEN is involved in oxidative stress and genomic damage induction in vitro and that this may also explain the in vivo observations. This further supports the hypothesis that the PI3K/AKT pathway is responsible for damaging effects of high levels of insulin.

Enhancement of anti-proliferative activities of Metformin, when combined with Celecoxib, without increasing DNA damage

Pathophysiological changes in diabetes like hyperglycemia, oxidative stress, insulin resistance and compensatory hyperinsulinemia predispose cells to malignant transformation and damage DNA repair mechanism. This study was designed to explore the potential synergistic toxic effects of anti-diabetic drug (Metformin), and an analgesic drug (Celecoxib) at cellular level. MTT assay run on Vero cell line revealed that the combinations of Metformin and Celecoxib augment the anti-proliferative effects, whereas Single cell gel electrophoresis spotlighted that Metformin produce non-significant DNA damage with the threshold concentration of 400μg/ml in peripheral blood mononuclear cells (lymphocytes and monocytes), while Celecoxib produced significant (P<0.05) DNA damage (class III comets) above the concentration of 75μg/ml, however the DNA damage or DNA tail protrusions by combinations of both drugs were less than what was observed with Celecoxib alone. Metformin or Celecoxib did not appear mutagenic against any mutant strains (TA 100 and TA 98) but their combination exhibited slight mutagenicity at much higher concentration. The results obtained at concentrations higher than the therapeutic level of drugs and reflect that Metformin in combination with Celecoxib synergistically inhibits the cell proliferation in a concentration dependent pattern. Since, this increase in cytotoxicity did not confer an increase in DNA damage; this combination could be adopted to inhibit the growth of malignant cell without producing any genotoxic or mutagenic effects at cellular level.

Metformin Protects Kidney Cells From Insulin-Mediated Genotoxicity In Vitro and in Male Zucker Diabetic Fatty Rats

Hyperinsulinemia is thought to enhance cancer risk. A possible mechanism is induction of oxidative stress and DNA damage by insulin, Here, the effect of a combination of metformin with insulin was investigated in vitro and in vivo. The rationales for this were the reported antioxidative properties of metformin and the aim to gain further insights into the mechanisms responsible for protecting the genome from insulin-mediated oxidative stress and damage. The comet assay, a micronucleus frequency test, and a mammalian gene mutation assay were used to evaluate the DNA damage produced by insulin alone or in combination with metformin. For analysis of antioxidant activity, oxidative stress, and mitochondrial disturbances, the cell-free ferric reducing antioxidant power assay, the superoxide-sensitive dye dihydroethidium, and the mitochondrial membrane potential-sensitive dye 5,5',6,6'tetrachloro-1,1',3,3'-tetraethylbenzimidazol-carbocyanine iodide were applied. Accumulation of p53 and pAKT were analyzed. As an in vivo model, hyperinsulinemic Zucker diabetic fatty rats, additionally exposed to insulin during a hyperinsulinemic-euglycemic clamp, were treated with metformin. In the rat kidney samples, dihydroethidium staining, p53 and pAKT analysis, and quantification of the oxidized DNA base 8-oxo-7,8-dihydro-2'-deoxyguanosine were performed. Metformin did not show intrinsic antioxidant activity in the cell-free assay, but protected cultured cells from insulin-mediated oxidative stress, DNA damage, and mutation. Treatment of the rats with metformin protected their kidneys from oxidative stress and genomic damage induced by hyperinsulinemia. Metformin may protect patients from genomic damage induced by elevated insulin levels. This may support efforts to reduce the elevated cancer risk that is associated with hyperinsulinemia.