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      Metformin overdose: time to move on

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      Journal: Critical Care
      Publisher: BioMed Central

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          Abstract

          Does metformin-associated lactic acidosis really exist? Despite an old controversy, there is no doubt about it. But do we understand what is going on? Laboratory findings raised several hypotheses explaining the pathophysiology of this disease. The main cause could be an inhibition of either gluconeogenesis or mitochondrial respiratory chain complex I. From bench to bedside, one hypothesis is now confirmed in humans. Metformin poisoning involves, at least partially, a mitochondrial dysfunction.

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          Dimethylbiguanide inhibits cell respiration via an indirect effect targeted on the respiratory chain complex I.

          Daniel V Nogueira, L. M. Mir, N Avéret … (2000)
          We report here a new mitochondrial regulation occurring only in intact cells. We have investigated the effects of dimethylbiguanide on isolated rat hepatocytes, permeabilized hepatocytes, and isolated liver mitochondria. Addition of dimethylbiguanide decreased oxygen consumption and mitochondrial membrane potential only in intact cells but not in permeabilized hepatocytes or isolated mitochondria. Permeabilized hepatocytes after dimethylbiguanide exposure and mitochondria isolated from dimethylbiguanide pretreated livers or animals were characterized by a significant inhibition of oxygen consumption with complex I substrates (glutamate and malate) but not with complex II (succinate) or complex IV (N,N,N',N'-tetramethyl-1, 4-phenylenediamine dihydrochloride (TMPD)/ascorbate) substrates. Studies using functionally isolated complex I obtained from mitochondria isolated from dimethylbiguanide-pretreated livers or rats further confirmed that dimethylbiguanide action was located on the respiratory chain complex I. The dimethylbiguanide effect was temperature-dependent, oxygen consumption decreasing by 50, 20, and 0% at 37, 25, and 15 degrees C, respectively. This effect was not affected by insulin-signaling pathway inhibitors, nitric oxide precursor or inhibitors, oxygen radical scavengers, ceramide synthesis inhibitors, or chelation of intra- or extracellular Ca(2+). Because it is established that dimethylbiguanide is not metabolized, these results suggest the existence of a new cell-signaling pathway targeted to the respiratory chain complex I with a persistent effect after cessation of the signaling process.
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            Methyl succinate antagonises biguanide-induced AMPK-activation and death of pancreatic beta-cells through restoration of mitochondrial electron transfer.

            Peter Y. Cai, G A Martens, D G Pipeleers … (2007)
            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.
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              Oxygen consumption is depressed in patients with lactic acidosis due to biguanide intoxication

              Alessandro Protti, Riccarda Russo, Paola Tagliabue … (2010)
              Introduction Lactic acidosis can develop during biguanide (metformin and phenformin) intoxication, possibly as a consequence of mitochondrial dysfunction. To verify this hypothesis, we investigated whether body oxygen consumption (VO2), that primarily depends on mitochondrial respiration, is depressed in patients with biguanide intoxication. Methods Multicentre retrospective analysis of data collected from 24 patients with lactic acidosis (pH 6.93 ± 0.20; lactate 18 ± 6 mM at hospital admission) due to metformin (n = 23) or phenformin (n = 1) intoxication. In 11 patients, VO2 was computed as the product of simultaneously recorded arterio-venous difference in O2 content [C(a-v)O2] and cardiac index (CI). In 13 additional cases, C(a-v)O2, but not CI, was available. Results On day 1, VO2 was markedly depressed (67 ± 28 ml/min/m2) despite a normal CI (3.4 ± 1.2 L/min/m2). C(a-v)O2 was abnormally low in both patients either with (2.0 ± 1.0 ml O2/100 ml) or without (2.5 ± 1.1 ml O2/100 ml) CI (and VO2) monitoring. Clearance of the accumulated drug was associated with the resolution of lactic acidosis and a parallel increase in VO2 (P < 0.001) and C(a-v)O2 (P < 0.05). Plasma lactate and VO2 were inversely correlated (R2 0.43; P < 0.001, n = 32). Conclusions VO2 is abnormally low in patients with lactic acidosis due to biguanide intoxication. This finding is in line with the hypothesis of inhibited mitochondrial respiration and consequent hyperlactatemia.
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                Author and article information

                Contributors
                Jean-Christophe Orban
                Eric Fontaine
                Carole Ichai
                Journal
                Journal ID (nlm-ta): Crit Care
                Journal ID (iso-abbrev): Crit Care
                Title: Critical Care
                Publisher: BioMed Central
                ISSN (Print): 1364-8535
                ISSN (Electronic): 1466-609X
                Publication date (Print): 2012
                Publication date (Electronic): 25 October 2012
                Publication date PMC-release: 25 October 2013
                Volume: 16
                Issue: 5
                Page: 164
                Affiliations
                [1 ]Service de Réanimation Médico-chirurgicale, Hôpital Saint-Roch, Centre Hospitalier Universitaire de Nice, 5 rue Pierre Dévoluy, 06006 Nice, France
                [2 ]IRCAN, Faculté de Médecine, Université de Nice, Avenue de Valombrose, 06107 Nice, France
                [3 ]INSERM, U1055, 2280 rue de la piscine, 38041 Grenoble, France
                Article
                Publisher ID: cc11664
                DOI: 10.1186/cc11664
                PMC ID: 3682282
                PubMed ID: 23110819
                SO-VID: f2a62a5f-3a27-4750-a1b0-5e2e29ef42a4
                Copyright © Copyright ©2012 BioMed Central Ltd
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                Subject: Commentary

                ScienceOpen disciplines: Emergency medicine & Trauma
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                ScienceOpen disciplines: Emergency medicine & Trauma

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