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Metformin, an antihyperglycemic, is widely used in the treatment of type 2 diabetes mellitus (DM). A rare, but important complication associated with this drug is the development of lactic acidosis: Overall mortality of lactic acidosis is approximately 50%. Certain subsets of patients taking metformin are at greater risk of developing lactic acidosis. This report discusses the development of metformin-associated lactic acidosis in four older adults admitted to an institution during a 2-month period, treatments, and outcomes. We recommend an aggressive treatment strategy of hemodialysis followed by peritoneal dialysis, continuous bicarbonate infusion, and tight glucose control. We review the cautions and contraindications of metformin use for the treatment of type 2 DM and report an educational plan for residents and staff instituted to improve drug complication awareness and reduce mortality.

Activities of the anti-oxidative enzymes, superoxide dismutase (SOD), glutathione peroxidase (GPx) and catalase were studied in rat tissues to determine the ability of detergents both to solubilize the enzymes and also to stabilize enzyme activity. Rat brain, heart and liver were homogenized in 0.1M KCl, 0.1% sodium dodecyl sulfate, 0.1% lubrol, or 0.1% cetyl-trimethylammonium bromide. In general lubrol was more effective than the other solutions in solubilizing GPx and catalase. Lubrol and 0.1M KCl were equally effective in solubilizing SOD. The highest enzyme activities were (1) SOD: 2484 ng/mg (brain), 2501 ng/mg (heart), and 5586 ng/mg (liver); (2) GPx: 224 mU/mg (brain), 1870 mU/mg (heart), and 7332 mU/mg (liver); (3) catalase: 2.8 mU/mg (brain), 10.6 mU/mg (heart), and 309 mU/mg (liver). While cetyl trimethylammonium bromide is marginally better than sodium dodecyl sulfate in solubilizing active enzyme, neither ionic detergent has any advantage over lubrol or 0.1M KCl. For catalase and GPx, enzyme activity loss with time is biphasic. After initial, rapid activity loss (1-5 days for GPx and 7-10 days for catalase) the differences noted among the homogenizing solutions disappear and very little if any activity loss is noted over the next 2-3 weeks. For catalase and GPx, only baseline enzyme activity from t = 0-3 weeks is found in the most chaotropic solution, 0.1% sodium dodecyl sulfate while biphasic activity loss is most pronounced in 0.1% lubrol. These results may indicate active GPx and catalase species stabilized by a lipid-like environment. Correlating in vitro catalase or GPx measurements with in vivo anti-oxidative protection may underestimate tissue defences.

When isolated rat heart mitochondria are subject to xanthine/xanthine oxidase generated free radicals, nmol quantities of ADP are phosphorylated to ATP. This effect is proportional to xanthine oxidase concentration, and is relatively independent of ADP concentration. Exogenous superoxide dismutase partially suppresses the phosphorylation. Micromolar concentrations of iron salts completely eliminate the phosphorylation. Catalase has no effect. The likely electron source, then, is superoxide radicals. The reduced minus oxidised spectra of superoxide-bombarded mitochondria show that superoxide enters the electron transport chain by reducing cytochrome c and complex IV. Mitochondria retain their ability to phosphorylate ADP in more traditional ways under the experimental conditions described. Superoxide under physiological conditions in vivo may be a source of electrons for the oxidative phosphorylation of ADP.

The ultraviolet (uv) difference spectra of M(II)-apocarbonic anhydrase at pH 5-9 are reported. For Zn(II) at all pH's and Co(II) at pH greater than or equal to 7.65 identical protein difference spectra are seen and a positive 300 nm feature is interpreted as consistent with interaction of a metal-bound hydroxyl with a Trp chromophore near the active site. Hg(II), Cu(II), and Cd(II) do not provoke a positive 300 nm band even at alkaline pH (although a Cd(II) spectral band at 300 nm becomes less negative, i.e., more like the holoenzyme with increasing pH) and the 280-292 nm spectral region is generally different from that of Zn(II) and high pH Co(II). A specific orientation of M-OH and, hence, an ordered solvent structure in the enzyme site is implied for enzyme activation. Ni(II) appears to bind to the vacated zinc site slowly, at low pH, in a manner similar to zinc. At higher pH's Ni(II) may be displaced toward a Tyr residue in the active site of apocarbonic anhydrase.

The interaction of lead (Pb2+) ions with apocarbonic anhydrase is studied by u.v. difference spectroscopy. The Pb2+ results are compared with those of Zn2+ interacting with apocarbonic anhydrase. The results of both metals interacting with apoenzyme are related to the difference spectra of Pb2+ and Zn2+ with Trp and Tyr model compounds. The interaction of Pb2+ with apocarbonic anhydrase containing an acetylated tyrosine residue is examined. Evidence is presented that Pb2+ is located in the active site cavity of apocarbonic anhydrase, but displaced from the zinc His ligands, interacting with Tyr 7. An attempt is made to rationalize the metal-chromophore micro-environment based on analysis of the 270-295 nm u.v. region of the difference spectra.

Lead-substituted bovine carbonic anhydrase is investigated and the return to the holoenzyme form with exchange of Pb2+ by Zn2+ is followed by uv difference spectroscopy and by esterase activity methods. Equimolar amounts of Pb2+ added to apocarbonic anhydrase release one hydronium ion per molecule below pH 6. Above this pH there is a net gain of hydronium ions by the enzyme, due to Pb(OH)+----Pb(OH2)2+, when the metal is bound within the active site of the enzyme molecule. The reduced hydrolysis by lead when it is bound to the enzyme is relevant to the theory of Zn2+ hydrolysis as a mechanism for carbon dioxide hydration by the holoenzyme and to the idea of an altered pKhydrolysis when Zn2+ is bound in the enzyme active site cavity. Lead appears to be bound to a His residue in the active site and to interact with a Tyr residue nearby. The Tyr interaction is disrupted by a high concentration of chloride ions, (also by lower concentrations of cyanide ions), but such anions do not displace lead from the enzyme. At pH 8.0 the buffer-free exchange of Pb2+ by Zn2+ is found to be consistent with a second-order process with an effective beta = (95 +/- 7) M-1 sec-1. Thus lead is more rapidly replaced by zinc than is Mn2+ or VO2+, whose replacement kinetics have been reported by others. Comparison of esterase-activation and spectral curves with second-order models shows that the effective beta is both large and buffer dependent, indicating that a proton transfer process or buffer anion effects may be rate limiting in the buffer-free case.