Effects Of Biguanides Research Articles

A laboratory investigation on the effect of biguanide- and pyridine-derived antiseptics on the adhesion of resin composites to dentin.

Optimal bonding of adhesive restorations to dentin is crucial to prevent microleakage and enhance the survival of root-filled teeth. The aim of this study was to investigate the effect of chlorhexidine (CHX), alexidine (ALX) and octenidine dihydrochloride (OCT) on the bond strength of resin composites to coronal dentin. Human coronal dentin specimens were treated with 2% CHX, 0.1% ALX, 0.1% OCT or saline then restored with traditional or bulk-fill resin composites. The adhesion strength between the resin and dentin was measured using the microtensile bond strength and failure mode was determined using a stereomicroscope. Treatment with ALX and OCT resulted in significantly greater μTBS compared with CHX and saline, irrespective of the resin composite used. Alexidine treatment predominantly resulted in mixed failure, while adhesive failures were frequently observed in CHX and saline-treated dentin. In conclusion, final irrigation with ALX or OCT improved the bonding of resin composites to dentin.

Sulfonylureas or biguanides is associated with a lower risk of rheumatoid arthritis in patients with diabetes: A nationwide cohort study.

ObjectiveDiabetes mellitus (DM) is associated with immune dysregulation, while sulfonylureas or biguanides have been linked to anti-inflammatory mechanisms. In this study, we aimed to examine the occurrence rate of rheumatoid arthritis (RA) among DM patients and its incidence rate between different treatments.MethodsThis cohort study used the Taiwan National Health Insurance Research Database between 1997 and 2013 to evaluate the primary outcomes of the preventive role of sulfonylureas or biguanides in the development of RA. We used the Chi-square test for categorical variables and Cox proportional hazard regression and log-rank test to explore the time for development of RA in DM patients. Logistic regression was adopted to estimate the odds ratio of RA in different dosages of medication exposure.ResultsOur cohort study included 94,141 DM cases. The risk of RA development of non-sulfonylureas/biguanides users among the DM group in each analysis was set as the reference, and the adjusted hazard ratio of RA in DM patients who were using sulfonylureas or biguanides was 0.73 (95% confidence interval 0.60–0.90). Within 1 year before the index date, compared with no-biguanides users, patients with more than 180 days of prescription of biguanides had a significantly lower RA risk. Similarly, the significantly lower risk of RA was still observed in DM patients who had more than 365 days of prescription of sulfonylurea within 2 or 3 years before the index date of first RA visit (all p < 0.05).ConclusionOur data suggest that sulfonylureas or biguanides are associated with a lower rate of RA development in patients with DM; the effect of biguanides appeared more rapid than that of sulfonylureas, but the sulfonylureas might have a longer effect on lowering RA development incidence.

A calibration approach to transportability and data-fusion with observational data.

Two important considerations in clinical research studies are proper evaluations of internal and external validity. While randomized clinical trials can overcome several threats to internal validity, they may be prone to poor external validity. Conversely, large prospective observational studies sampled from a broadly generalizable population may be externally valid, yet susceptible to threats to internal validity, particularly confounding. Thus, methods that address confounding and enhance transportability of study results across populations are essential for internally and externally valid causal inference, respectively. These issues persist for another problem closely related to transportability known as data-fusion. We develop a calibration method to generate balancing weights that address confounding and sampling bias, thereby enabling valid estimation of the target population average treatment effect. We compare the calibration approach to two additional doubly robust methods that estimate the effect of an intervention on an outcome within a second, possibly unrelated target population. The proposed methodologies can be extended to resolve data-fusion problems that seek to evaluate the effects of an intervention using data from two related studies sampled from different populations. A simulation study is conducted to demonstrate the advantages and similarities of the different techniques. We also test the performance of the calibration approach in a motivating real data example comparing whether the effect of biguanides vs sulfonylureas-the two most common oral diabetes medication classes for initial treatment-on all-cause mortality described in a historical cohort applies to a contemporary cohort of US Veterans with diabetes.

A dual-functional buformin-mimicking poly(amido amine) for efficient and safe gene delivery

Biguanides (i.e. metformin, phenformin and buformin) are antidiabetic drugs with potential antitumor effects. Herein, a polycationic polymer, N,N′-bis(cystamine)acrylamide-buformin (CBA-Bu), containing multiple biodegradable disulphide bonds and buformin-mimicking side chains was synthesised. CBA-Bu was equipped with high efficiency and safety profile for gene delivery, meanwhile exhibiting potential antitumor efficacy. As a gene vector, CBA-Bu was able to condense plasmid DNA (pDNA) into nano-sized (<200 nm), positively-charged (>30 mV) uniform polyplexes that were well resistant to heparin and DNase I. Due to the reduction responsiveness of the disulphide bonds, CBA-Bu/pDNA polyplexes could release the loaded pDNA in the presence of dithiothreitol, and induce extremely low cytotoxicity in NIH/3T3 and U87 MG cells. The transfection results showed that CBA-Bu had a cellular uptake efficiency comparable to 25 kDa PEI, while a significantly higher gene expression level. Additionally, CBA-Bu had a lower IC50 value than its non-biguanide counterpart in two cancer cell lines. Furthermore, CBA-Bu could activate AMPK and inhibit mTOR pathways in U87 MG cells, a mechanism involved in the antitumor effect of biguanides. Taken together, CBA-Bu represented an advanced gene vector combining desirable gene delivery capability with potential antitumor activity, which was promising to achieve enhanced therapeutic efficacy in antitumor gene therapy.

A STUDY ON EFFECT OF DRUG DURING IN CLINICAL MANAGEMENT OF DIABETES

Diabetes is defined as a state in which homeostasis of carbohydrate, protein and lipid metabolism is improperly regulated as a consequence of a relative or absolute deficiency of insulin secretion, resistance to insulin action or both at one or more center in tedious pathways of hormones activity. Diabetes is deadly disease in both developed and developing countries. In 2000, there were a probable 175 million people with diabetes universal and by 2030, the projected estimate of diabetes is 354 million. The most widely recognized unfavorable responses to insulin are weight addition and hypoglycaemia (Henry et al, 1993; Kudlacek et al, 1992). Weight increase in the wake of beginning insulin treatment for uncontrolled diabetes is an inescapable outcome and is the consequence of expanded truncal fat and muscle mass and severe side effects of biguanides include diarrhoea, abdominal discomfort, nausea, metallic taste, and anorexia.&#x0D; Keywords: Diabetes, Insulin, Biguanides and Hypoglycaemia

Abstract P3-06-16: Synergistic effect of biguanides and fatty acid β-oxidation inhibitor in triple-negative breast cancers

Abstract Triple negative breast cancer (TNBC) is one of non-targetable cancers which are still poorly understood for the driver pathways and therapeutic targets. Over the past decade, cancer metabolism researches have a huge advance. Thus, it has enhanced our understanding on metabolic reprogramming in cancer therapy. We have previously shown that metabolic reprogramming to fatty acid β-oxidation (FAO) is a key energy metabolic pathway in TNBC. Moreover, we reported that FAO regulates c-Src, one of the frequently upregulated oncopathways in TNBC via autophosphorylation of Src at Y419. However, single treatment by FAO inhibitor alone cannot effectively control the tumor progression in TNBC because of metabolic reprogramming and flexibility of tumors. Therefore, proper combination therapies with other metabolic targets are necessary. Recently increasing studies demonstrate that anti-diabetic biguanides have attractive anti-cancer effect in various cancer types including breast cancer (BC). However, its significance as an anti-cancer drug is not well established due to parallel metabolic pathways that support tumor growth. Biguanide like metformin is the most widely administered anti-diabetic agent worldwide. Phenformin, a biguanide derivative similar to metformin, has a greater potency than metformin. Like metformin, phenformin also inhibits mitochondrial electron transport chain (ETC) through complex I inhibition. In addition, biguanides lead to the activation of AMPK, which plays a important role in insulin signaling and energy sensing. Importantly, AMPK is an upstream regulator of FAO pathway because it can phosphorylate ACC to activate FAO. Considering the dependency of TNBC to FAO, we evaluated the therapeutic significance of the combination of biguanides (ETC inhibitors) and FAO inhibitors in TNBC progression and metastasis. And we investigated that targeting both ‘arms’ of the pathway can provide more effective and durable responses in TNBC treatments. Our various in vitro and in vivo studies using TNBC cell lines and PDX models suggest that the combination of both inhibitors can provide better therapeutic benefits in TNBCs. This is a rationale and cost-effective metabolic approach to overcome the currently non-targetable TNBCs. Further study toward the clinical effectiveness of this combination may offer better treatment opportunities for TNBC patients. Citation Format: Jun Hyoung Park, Kwang Hwa Jung, Dongya Jia, Benny A Kaipparettu. Synergistic effect of biguanides and fatty acid β-oxidation inhibitor in triple-negative breast cancers [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-06-16.

Abstract 381: Uptake of biguanides in mitochondria appears to be related to increased glucose uptake and medium acidification but not necessarily related to inhibition of growth of bladder and colon cancer cells

Abstract Biguanides including metformin have been used in the treatment of Type 2 diabetes and they are under investigation as anti-cancer agents. Investigation on the mechanism of action of biguanides has largely focused on inhibition of complex 1 in the mitochondrial electron transport chain with subsequent activation of AMP-dependent protein kinase. Studies by Bridges et al. (BMC Biology 14:65, 2016) indicate that inhibitory effects on complex 1 in cells require uptake of biguanides into the mitochondria. In the present work the action of two biguanides that enter the mitochondria (buformin and phenformin) were compared with the action of two biguanides with poor uptake (phenyl biguanide and proguanil). Effects on growth, glucose uptake and medium acidification were studied with two human colon cancer cells (Caco-2 and HT29) and seven bladder cancer cell lines (5637, HT1197, HT1376, RT4, T24, TCCSUP and UM-UC-3). After incubation for 72 hours with 25 µM and 50 µM concentrations of the biguanides, growth inhibition was greatest with proguanil followed by phenformin and with little or no growth inhibition at these concentrations with buformin and phenylbiguanide. In contrast, increased glucose uptake and acidification of the medium was observed with buformin and phenformin with no change or decreased medium acidification with phenyl biguanide and proguanil. Studies with buformin over a concentration range from 10 µM to 500 µM indicated that there was generally growth inhibition at concentrations greater than 50 µM. Studies on medium acidification and glucose uptake revealed biphasic responses with increases at lower concentrations that were reversed at higher concentrations of buformin where growth inhibition was observed. The data suggested that the effect of biguanides on glucose metabolism requires mitochondrial uptake while the mechanism for growth inhibition by biguanides remains to be established. Citation Format: Michael A. Lea, Haneulsol Kim, Charles desBordes. Uptake of biguanides in mitochondria appears to be related to increased glucose uptake and medium acidification but not necessarily related to inhibition of growth of bladder and colon cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 381.

Abstract 1274: Effects of diet on lung adenoma carcinogenesis in metformin treated A/J mice

Abstract There has been considerable interest in the effects of biguanides, utilized to treat type 2 diabetes, on human carcinogenesis. Several population studies established diabetes patients treated with metformin and other type 2 diabetes agents experience decreased cancers in several organ systems. However, the effects are not universal in all organ systems and metabolically complex. In the present study, we utilized a dosing regimen of dietary metformin in benzo[a]pyrene treated mice known to reduce lung adenoma formation in A/J mice by approximately 50% over controls. For the duration of this study we used several animal diets commonly employed for mouse chemoprevention experiments with and without 850 mg/kg/day metformin added to the diet. These included AIN93M, AIN76A, D62 (Dr. Lee Wattenberg's chemoprevention diet), a modification of D62 with added maltodextrin and sucrose, and Teklad 4% fat pellets from Envigo. At the conclusion of the study, animals were sacrificed and surface adenoma counts were performed on fresh lungs from each group of animals. We found 850 mg/kg/day metformin for 16 weeks reduced adenoma formation by 35-60% in the diets we employed for the study. Interestingly, the Teklad diet which contains dehulled soybean meal had significantly reduced tumor formation in the control animals, demonstrating some animal diets provide chemoprevention efficacy independent of any pharmaceutical effects. There was no observed toxicity of metformin in the animals; however we have observed significant differences in the average end weights of animals treated with metformin. We conclude metformin is an efficacious agent in lung adenoma chemoprevention and similar reductions in adenoma formation occurred in several of the diets commonly employed for chemoprevention studies in B[a]P treated mice. However, attention to diet formulation is vital due to potential chemoprevention and metabolic effects independent of metformin treatment. Citation Format: Vannesa Souksavong, Beverly R. Wuertz, Donna Seabloom, Frank G. Ondrey. Effects of diet on lung adenoma carcinogenesis in metformin treated A/J mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1274.

Peripheral 5-HT3 Receptors Are Involved in the Antinociceptive Effect of Bunodosine 391.

Bunodosine 391 (BDS 391), a low molecular weight compound isolated from the sea anemone Bunodosoma cangicum, increases the nociceptive threshold and inhibits inflammatory hyperalgesia. Serotonin receptors are involved in those effects. In this study, we have expanded the characterization of the antinociceptive effect of BDS 391 demonstrating that, in rats: (a) the compound inhibits (1.2–12 ng/paw) overt pain, in the formalin test, and mechanical hyperalgesia (0.6–6.0 ng/paw) detected in a model of neuropathic pain; (b) intraplantar administration of ondansetron, a selective 5-HT3 receptor antagonist, blocks the effect of BDS 391, whereas ketanserin, a 5-HT2 receptor antagonist, partially reversed this effect, indicating the involvement of peripheral 5-HT2 and 5-HT3 receptors in BDS 391 antinociception; and (c) in binding assay studies, BDS 391 was not able to displace the selective 5-HT receptor antagonists, suggesting that this compound does not directly bind to these receptors. The effect of biguanide, a selective 5-HT3 receptor agonist, was also evaluated. The agonist inhibited the formalin’s nociceptive response, supporting an antinociceptive role for 5-HT3 receptors. Our study is the first one to show that a non-peptidic low molecular weight compound obtained from a sea anemone is able to induce antinociception and that activation of peripheral 5-HT3 receptors contributes to this effect.

Abstract 1216: Effects of phenformin in LKB1/KRAS mutated non-small cell lung cancer patient derived xenograft

Abstract Metformin is an oral antidiabetic drug of the biguanide class. Several epidemiological and case-control studies reported that diabetics using metformin may have lower cancer risk in comparison to those using other antidiabetic medications. Recent studies in experimental models suggest that another biguanide, phenformin, has higher anticancer activity compared with metformin. The aim of this study was to evaluate the effects of metformin and phenformin in Non-Small Cell Lung Cancer (NSCLC) models. In particular, the effects of these compounds in LKB1 or LKB1/KRAS mutated compared to wild type models have been investigated. NSCLC cell lines (A549, H460, H1299, LT73) have been treated with either metformin or phenformin to evaluate in vitro dose/response depending on the different mutational status of KRAS and LKB1 genes. The effects of the two biguanide have been investigated also in vivo models, exploiting the panel of Patient Derived Xenografts (PDXs) directly generated from NSCLC patients in our Institute. In vitro experiments indicated that cell lines with already impaired metabolism (LKB1 and/or KRAS mutated) were more sensitive to phenformin treatment. Interestingly, treatments of these cell lines with r phenformin resulted in a 50% decrease in the amount of CD133+ Tumor Initiating Cells (TIC). Moreover, high doses of phenformin (LD75) did not result in the increase of TIC previously observed after Cisplatin treatment. In vivo, early treatments (Tumor Volume = 50-100mm3) of an LKB1 mutated PDX model resulted in a significant reduction of tumor volume (300 ± 50 mm3 in phenformin treated vs 750 ± 100 mm3 in vehicle treated tumors) already after three weeks of treatment (100mg/Kg/day). Importantly, no regrowth was observed in responding tumors even after the end of treatments. No effects were observed in LKB1 wild type PDX treated with phenformin. Taken together, these preliminary data indicate a selective action of phenformin on LKB1 mutated lung adenocarcinoma models in vitro and in vivo. Interestingly, this compound seems to be more active in TIC than normal chemotherapeutic drugs (i.e. cisplatin). Effects of biguanide on TIC could be the cause of the lack of tumor regrowth after treatment, thus making these compounds potentially useful in counteracting disease recurrence and/or metastasis formation. Further investigations are needed to elucidate the different effects of metformin and phenformin in double mutated (LKB1 and KRAS) PDXs models. Citation Format: Massimo Moro, Luca Roz, Roberto Caserini, Ugo Pastorino, Gabriella Sozzi. Effects of phenformin in LKB1/KRAS mutated non-small cell lung cancer patient derived xenograft. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1216. doi:10.1158/1538-7445.AM2014-1216

Effects of biguanides on oxidative phosphorylation

Metformin, and the related biguanides buformin and phenformin, have been proposed to act by inhibiting respiratory complex I, causing the cellular energetic stress that activates AMP-kinase and initiates a multitude of cell-lineage-specific effects, including inhibition of gluconeogenesis in hepatocytes. However, the molecular mechanism of biguanide action on complex I is not known, limiting understanding of pharmacological effects on this proposed primary target. Biguanides have also been proposed to affect reactive oxygen species production in cells, a respiratory-chain linked effect - but there is no consensus even on whether they increase or decrease it. In this talk I will discuss the results of experiments on a hierarchy of systems, from purified respiratory enzymes and membrane preparations, to mitochondria and cells, to define the functional effects of biguanides on the oxidative phosphorylation system. The aim is to define and link the molecular effects of biguanides on specific enzymes to their known effects on cellular and signalling pathways.

Energy balance at the organism and cellular level: effects of biguanides

Metformin, an inhibitor of OXPHOS, is widely used for treatment of type II diabetes (T2D). A key site of action in diabetes treatment is liver, where the drug achieves a relatively high concentration following oral administration, leading to inhibition of gluconeogenesis and reduction of the hyperglycemia and hyperinsulinemia of T2D. As high levels of insulin have been associated with poor prognosis of prostate, breast, and colon cancer and as early retrospective pharmaco-epidemiologic studies suggested reduced cancer burden among diabetics treated with metformin relative to other diabetes treatments, the hypothesis that metformin or other biguanides could be useful in cancer prevention or treatment has received considerable attention. However, it is not clear if metformin at conventional anti-diabetic doses administered to non-diabetic subjects has effects of sufficient magnitude on levels of insulin or other candidate mediators to influence cancer biology. Drugs used for androgen deprivation in prostate cancer treatment and most PI3K inhibitors provide examples of therapies that induce hyperinsulinemia which may attenuate therapeutic benefit, justifying study of combinations of each of these with biguanides. The separate hypothesis that biguanides can directly influence cancer cell metabolism is attractive, as this mechanism has been shown to operate in many laboratory models - yet there is uncertainty if metformin administered at conventional anti diabetic doses achieves sufficient concentrations in extra-hepatic tissues or cancers to perturb their cellular energy metabolism. Therefore, studies of maximally tolerated doses of biguanides with more favourable pharmacokinetic properties than metformin may be necessary if the “direct action” hypothesis is to be clinically tested. Recent work is identifying contexts where ‘direct’ actions of biguanides as inhibitors of OXPHOS may be of particular therapeutic benefit. For example, there is evidence that tumours using glutamine as a carbon source are relatively sensitive to biguanides, that high ambient glucose levels are associated with reduced sensitivity, and that serine deficiency enhances the anti-proliferative actions of biguanides.

Modulation of Cardiomyocyte and Hepatocyte Bioenergetics by Biguanides

Biguanides (metformin, buformin and phenformin) have been developed for oral treatment of non-insulindependent diabetes mellitus. Metformin, the drug of choice in this class, controls blood glucose primarily by lowering hepatic gluconeogenesis (e.g., decreasing glucagon-mediated hepatic glucose output). Its mode-of-action, however, is more complex and may involve “refining” cellular bioenergetics (improving energy efficiency) in various cell types including myocytes. Buformin and phenformin presumably have similar mechanisms of action. The main purpose of this in vitro study was to assess the effects of these drugs on bioenergetics - cellular respiration (mitochondrial O2 consumption) and ATP content - in tissue fragments from the heart muscle (cardiomyocytes) and liver (hepatocytes) of C57BL/6 mice. Cardiomyocyte respiration decreased by 10-26% in the presence of 100 μM metformin (p=0.093), buformin (p=0.028) or phenformin (p=0.015). Similar effects on cardiomyocyte respiration were noted with 1.0 mM drugs. Cardiomyocyte ATP, on the other hand, increased by 17-31% in the presence of 100 μM metformin (p=0.093), buformin (p=0.445) or phenformin (p=0.093). Hepatocyte respiration and ATP decreased by 11-26% and 8-25%, respectively in the presence of 1.0 mM drugs. Decreased respiration and ATP were also noted in hepatocytes exposed to 100 μM metformin for 1 ≤ t ≤ 6 hours (13% and 5%, respectively). Thus, the effects of biguanides on cardiomyocyte bioenergetics differed from that on hepatocyte bioenergetics. These findings suggest that biguanides regulate cardiomyocyte energy conversion, favoring better fuel efficiency (↓respiration/↑ATP). The drug effects in hepatocyte are ↓respiration/↓ATP, favoring less fuel production (↓hepatic gluconeogenesis). Biguanide activities in various tissues may be coupled.

Abstract 4069: 2-deoxyglucose and compound C reversed acidification but enhanced growth inhibition in colon cancer cells treated with metformin and phenformin

Abstract A report that effects of butyrate on some cells may be mediated by activation of AMP-dependent kinase (AMPK) prompted us to examine if other AMPK activators can induce differentiation and inhibit proliferation of colon cancer cells in a manner similar to butyrate. Using induction of alkaline phosphatase as a marker, we observed that compound C, an AMPK inhibitor, could decrease the differentiating effect of butyrate or valproate on SW1116 and Caco-2 colon cancer cells. On the other hand, A769662, an activator of AMPK did not increase alkaline phosphatase activity and decreased the induction seen with butyrate. Metformin was observed to be less effective than butyrate in the induction of alkaline phosphatase but was more effective as a growth inhibitor. Phenformin was found to be a more potent growth inhibitor than metformin and both compounds cause acidification of the medium when incubated with colon cancer cells. pH changes were monitored with a pH electrode and by the decrease in absorbance of phenol red at 560 nm. Coincubation with compound C decreased the acidification caused by the biguanides. Combined incubation of 2-deoxyglucose with either of the biguanides prevented the acidification of the medium but enhanced the growth inhibitory effects. Growth inhibitory effects of biguanides appeared less with a tetrazolium reduction assay than with thymidine incorporation but supported the conclusion that combination with 2-deoxyglucose could increase growth inhibition caused by biguanides. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4069. doi:10.1158/1538-7445.AM2011-4069

Effects of biguanides on oxidative status of rat tissues after cerebral ischemia/reperfusion

We studied the effects of synthetic biguanide derivatives on the intensity of free-radical processes and catalase activity in rat tissues after cerebral ischemia/reperfusion. We found that administration of phenylethyl-biguanide or (2,4-dimethoxyphenyl)biguanide in this pathology decreased the lactate/pyruvate ratio, an index of cell metabolism impairment, as compared to this index in rats with pathology. In the brain of rats and their blood serum, we observed a decrease in biochemiluminescence parameters, which was enhanced after ischemia/reperfusion and reflected the intensity of free radical processes. We also found a decrease in the mobilization rate of the antioxidant system as compared to the rate observed after pathology. These data show that the biguanide derivatives studied had antioxidant and protective properties in ischemic brain damage accompanied by oxidative stress.

Methyl succinate antagonises biguanide‐induced AMPK‐activation and death of pancreatic β‐cells through restoration of mitochondrial electron transfer

Two mechanisms have been proposed to explain the insulin-sensitising properties of metformin in peripheral tissues: (a) inhibition of electron transport chain complex I, and (b) activation of the AMP activated protein kinase (AMPK). However the relationship between these mechanisms and their contribution to beta-cell death and dysfunction in vitro, are currently unclear. The effects of biguanides (metformin and phenformin) were tested on MIN6 beta-cells and primary FACS-purified rat beta-cells. Cell metabolism was assessed biochemically and by FACS analysis, and correlated with AMPK phosphorylation state and cell viability, with or without fuel substrates. In MIN6 cells, metformin reduced mitochondrial complex I activity by up to 44% and a 25% net reduction in mitochondrial reducing potential. In rat beta-cells, metformin caused NAD(P)H accumulation above maximal glucose-inducible levels, mimicking the effect of rotenone. Drug exposure caused phosphorylation of AMPK on Thr(172) in MIN6 cell extracts, indicative of kinase activation. Methyl succinate, a complex II substrate, appeared to bypass metformin blockade of complex I. This resulted in reduced phosphorylation of AMPK, establishing a link between biguanide-induced mitochondrial inhibition and AMPK activation. Corresponding assessment of cell death indicated that methyl succinate decreased biguanide toxicity to beta-cells in vitro. AMPK activation can partly be attributed to metformin's inhibitory action on mitochondrial complex I. Anaplerotic fuel metabolism via complex II rescued beta-cells from metformin-associated toxicity. We propose that utilisation of anaplerotic nutrients may reconcile in vitro and in vivo effects of metformin on the pancreatic beta-cell.

Increased alanine uptake and lipid synthesis from alanine in isolated hepatocytes of Wistar-Kyoto fatty rats: an inhibitory effect of biguanides

To examine the pathophysiological characteristics of non-insulin-dependent diabetes mellitus, alanine metabolism in isolated hepatocytes of male Wistar-Kyoto (WKY) fatty rats (genetically obese and hyperglycemic) and their lean littermates was investigated. The effects of glucagon and the biguanides, metformin and buformin, on alanine metabolism were also studied by measuring alanine uptake and lipid synthesis from alanine. WKY fatty rats showed higher plasma insulin and lipid concentrations than lean rats at 5 as well as at 12 weeks of age. Alanine uptake into hepatocytes was increased in fatty rats only at 12 weeks of age compared with lean rats. Lipid synthesis from alanine in hepatocytes was increased in fatty rats at 5 and 12 weeks of age compared with lean rats. Glucagon increased alanine uptake into hepatocytes but did not affect lipid synthesis from alanine in both fatty and lean rats. Low concentrations (0.1 mM) of biguanides decreased lipid synthesis from alanine only in fatty rats without inhibiting alanine uptake into hepatocytes. These observations suggest that lipid synthesis from alanine in hepatocytes of WKY fatty rats is accelerated prior to the onset of diabetes mellitus, which might be associated with the development of diabetes, and that an inhibitory effect on increased lipid synthesis is one of the pharmacodynamic actions of biguanides.

Increased alanine uptake and lipid synthesis from alanine in isolated hepatocytes of Wistar-Kyoto fatty rats: an inhibitory effect of biguanides

Increased alanine uptake and lipid synthesis from alanine in isolated hepatocytes of Wistar-Kyoto fatty rats: an inhibitory effect of biguanides

The Effects of Biguanides and Bradykinin on Glucose Transport System in Rat Adipocytes

The Effects of Biguanides and Bradykinin on Glucose Transport System in Rat Adipocytes

Metformin treatment in elderly type II diabetic patients

Pharmacological treatment in elderly patients with type II, non-insulin dependent diabetes mellitus (NIDDM) is becoming a growing and complex problem in the clinical practice, since longevity in almost every population is increasing, and the prevalence of NIDDM also rises with age. It is generally indicated that age over 65-70 years represents a specific contraindication against the administration of the biguanides since the risk of the drug-associated lactic acidosis increases with age. However very few data exist in literature about the effect of biguanides, particularly metformin, in aging patients. Therefore, we aimed to evaluate the effects of adding metformin to poorly controlled sulfonylurea-treated elderly diabetic subjects for a one year period. Eighty-four type II diabetic patients aged more than 70 years and with a poor glycemic control were recruited after an informed consent. All diabetic patients were treated with various sulfonylureas at medium doses and presented renal and liver biochemical function tests within normal ranges and were free of severe macroangiopathy and respiratory or congestive heart failure. Metformin treatment was added to the previous sulfonylurea dosages in order to achieve a satisfactory glycemic control. All patients showed a marked improvement in the glycemic control with no significant modification in fasting blood lactate and a mild increase in the post-prandial lactate peak which, however, always felt largely within the normal ranges. Metformin also improved some metabolic vascular risk factors such as plasma cholesterol levels that were reduced, circulating HDL-cholesterol levels that mildly but significantly increased and uric acid that was lowered. In conclusion our data further support the opinion that metformin has not to be denied to diabetic patients on the sole basis of their age.