Pharmacology and therapeutic implications of current drugs for type 2 diabetes mellitus Abd A. Tahrani1,2, Anthony H. Barnett1,2 and Clifford J. Bailey3 Abstract |6[RG|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|TGEGRVQT ).24 CIQPKUVUFKRGRVKF[N RGRVKFCUG| &22 KPJKDKVQTUCPFUQFKWOINWEQUGEQVTCPURQTVGT|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ype 2 diabetes mellitus (T2DM) is a global epidemic with an dysfunction, as well as precipitating microvascular com- estimated worldwide prevalence of 415 million people in plications and contributing to macrovascular disease, 2015, which is projected to rise to 642 million people which are major causes of morbidity and mortality21. The by 2040 (REF. 1). The very considerable health, social and results of several randomized controlled trials (RCTs) economic burdens caused by T2DM1–3 present a major have demonstrated the short-term and long-term bene- challenge to health-care systems around the world. fits of improving glycaemic control in delaying the onset 1Centre of Endocrinology, Diabetes and Metabolism, T2DM is a complex endocrine and metabolic disorder and reducing the severity of diabetes-related outcomes, 2nd Floor, Institute of in which the interaction between genetic and environ- particularly retinopathy, nephropathy, neuropathy and Biomedical Research, mental factors generates a heterogeneous and progressive cardiovascular disease, and also mortality22–25. Attaining University of Birmingham, pathology with varying degrees of insulin resistance and normal (or nearly normal) levels of blood glucose (where Birmingham, B15 2TT, UK. 2Department of Diabetes dysfunction of pancreatic β cells and α cells, as well as practical) is a major aim of T2DM treatment. Several 4–14 and Endocrinology, other endocrine disturbances (FIG. 1). Insulin resist- strategies are available for this purpose: lifestyle changes, Heart of England NHS ance results from deficits in signalling pathways at the including dietary prudence, weight loss and physical Foundation Trust, level of the insulin receptor and downstream, and T2DM activity, remain the cornerstones of management, but Birmingham, B9 5SS, UK. emerges when β cells can no longer secrete sufficient because of the progressive nature of T2DM and the dif- 3School of Life and Health 4,15–17 Sciences, Aston University, insulin to overcome insulin resistance . Overweight ficulty in maintaining lifestyle changes in the long term, Birmingham, B4 7ET, UK. and obesity are major risk factors for the development of most patients also require oral therapies and (eventually) 4,5,16,18–20 26 Correspondence to A.A.T. insulin resistance . injectable treatments . [email protected] Hyperglycaemia is the fundamental biochemical fea- For more than four decades, only two classes of oral doi:10.1038/nrendo.2016.86 ture of T2DM, causing oxidative and nitrosative stress glucose-lowering medications were available (biguanides and activation of inflammatory pathways and endothelial and sulfonylureas), but in the past 20 years many more Key points Biguanides The only biguanide available in clinical practice is met- • )TGCVGTWPFGTUVCPFKPIQHVJGEQORNGZCPFOWNVKHCEVQTKCNRCVJQIGPGUKUQHV[RG| formin (dimethylbiguanide)37. Other biguanides (phen- FKCDGVGUOGNNKVWU 6&/ JCUKPHQTOGFVJGFGXGNQROGPVQHUGXGTCNPGYENCUUGUQH formin and buformin) have been withdrawn because of INWEQUGNQYGTKPIVJGTCRKGU risks of lactic acidosis38. Biguanides were derived from • /GVHQTOKPTGOCKPUVJGHKTUVNKPGRJCTOCEQVJGTCR[HQTRCVKGPVUYKVJ6&/YJGTGCU the guanidine-rich herb Galega officinalis (French lilac), VJGWUGQHQVJGTYGNNGUVCDNKUJGFCIGPVUUWEJCUUWNHQP[NWTGCUOGINKVKPKFGU which was used in traditional medicine in Europe37,39. pioglitazone and INWEQUKFCUGKPJKDKVQTUXCTKGUKPFKHHGTGPVTGIKQPU α Metformin was introduced into clinical practice in • #IGPVUVJCVGPJCPEGKPETGVKPCEVKXKV[ &22KPJKDKVQTU UWRRNGOGPVGPFQIGPQWU Europe in 1957 and in the USA in 1995, and has become ).2 ).2TGEGRVQTCIQPKUVU QTKPETGCUGWTKPCT[INWEQUGGNKOKPCVKQP 5).6 the most prescribed agent for T2DM worldwide37,39. KPJKDKVQTU JCXGNQYTKUMQHJ[RQIN[ECGOKCCPFECPCUUKUVYGKIJVEQPVTQN • 6TGCVOGPVYKVJVYQQTVJTGGCIGPVUYKVJFKHHGTGPVOQFGUQHCEVKQPECPDGTGSWKTGFCU Mechanism of action 6&/CFXCPEGUCPFKPUWNKPVJGTCR[KUTGSWKTGFKHQVJGTCIGPVUCTGWPCDNGVQOCKPVCKP CFGSWCVGIN[ECGOKEEQPVTQN Metformin enters cells mainly via solute carrier family 22 member 1 (also known as organic cation • )N[ECGOKEVCTIGVUCPFVJGEJQKEGQHINWEQUGNQYGTKPICIGPVUUJQWNFDGEWUVQOK\GF VQOGGVVJGPGGFUCPFEKTEWOUVCPEGUQHKPFKXKFWCNRCVKGPVUYJKEJEQWNFDGHCEKNKVCVGF transporter 1 (hOCT1)) and exerts multiple insulin- D[HWVWTGFGXGNQROGPVUKPRJCTOCEQIGPQOKEU dependent and insulin-independent actions according to the level of drug exposure and the control of nutri- • #NVJQWIJVJGDCNCPEGQHDGPGHKVUCPFTKUMUHQTFKHHGTGPVCIGPVUXCTKGUDGVYGGP 28,37,40–42 (FIG. 2) KPFKXKFWCNRCVKGPVUGCTN[GHHGEVKXGCPFUWUVCKPGFIN[ECGOKEEQPVTQNFGNC[UVJGQPUGV ent metabolism within different tissues . CPFTGFWEGUVJGUGXGTKV[QHJ[RGTIN[ECGOKCTGNCVGFEQORNKECVKQPU During treatment, the gut is exposed to high concen- trations of metformin42, which interrupt the mito- chondrial respiratory chain at complex I, and increase treatment options have been introduced26,27 (TABLE 1). glucose utilization, anaerobic glycolysis and lactate In this Review, we provide an evaluation of the thera- production; some of the lactate can be converted back pies available for the management of hyperglycaemia in to glucose in the liver43. Lactate–glucose turn over patients with T2DM. causes energy dissipation, which might contribute to the weight neutrality (lack of weight gain or weight Glycaemic control and targets in T2DM loss) observed in metformin-treated patients28,42. In the The treatment needs of patients with T2DM, and the liver, metformin increases insulin signalling, reduces responses to treatments, are highly variable, reflecting the glucagon action and reduces gluconeogenesis and complexity and variability of the pathogenic process28,29, glyco genolysis28. Metformin can inhibit the mitochon- so decisions must be made for each patient regarding the drial redox shuttle enzyme glycerol-3-phosphate dehy- choice of therapy and glycaemic targets. Factors for con- drogenase, altering the hepatocellular redox state and sideration include patient age, weight, duration of T2DM, resulting in reductions in the ATP:AMP ratio, hepatic risk of hypoglycaemia, cardiovascular risk, concomitant gluconeogenesis and the conversion of lactate and treatments, presence of complications and concomitant glycerol to glucose, and activation of AMP-activated life-limiting illness. Other aspects, which are more diffi- protein kinase (AMPK)44. In addition, metformin treat- cult to quantify in clinical practice, include the reserve ment results in a shift toward the utilization of glucose capacity for insulin secretion, genetic factors that might relative to fatty acids as a cellular source of energy in affect responses to therapies, the risk of developing future the liver37. In muscle, metformin promotes insulin- complications and the rate of disease progression30. mediated glucose uptake via solute carrier family 2, The long-term benefits of intensive glycaemic control facilitated glucose transporter member 4 (GLUT-4)28. on T2DM-related complications and mortality are well As delayed-release formulations of metformin have known, particularly when initiated promptly after diag- achieved similar efficacies at lower doses compared with nosis in young patients who do not yet have comorbid ‘regular’ formulations, it seems that the gut is a major site complications22–25. However, intensive glycaemic control of metformin action at therapeutic doses45. Metformin is not without risks, such as hypoglycaemia, weight gain can increase circulating levels of glucagon-like peptide-1 and possible cardiovascular events and mortality in high- (GLP-1) from pretreatment levels, even in the absence risk individuals. These risks might relate, at least in part, of an oral glucose load and in individuals with and to the choice of glycaemic target and medications22,31–36, without T2DM46–50, by mechanisms that could include so an individualized management strategy is prefera- inhibition of sodium-dependent bile-acid transporters, ble36. The difficulty lies in the identification of patients in which increase the availability of ileal bile acids to acti- whom the risks associated with intensive glycaemic con-