Concept of Diabetes Mellitus: Diabetes mellitus is a group of diseases associated with various metabolic disorders, the main feature of which is chronic hyperglycemia due to insufficient insulin action. Its pathogenesis involves both genetic and environmental factors. The long-term persistence of metabolic disorders can cause susceptibility to specific complications and also foster arteriosclerosis. Diabetes mellitus is associated with a broad range of clinical presentations, from being asymptomatic to ketoacidosis or coma, depending on the degree of metabolic disorder. Classification ( Tables 1 and 2 , and Figure 1 ): Table 1. Etiological classification of diabetes mellitus and glucose metabolism disorders I. Type 1 (destruction of pancreatic β-cells, usually leading to absolute insulin deficiency) A. Autoimmune B. Idiopathic II. Type 2 (ranging from predominantly insulin secretory defect, to predominantly insulin resistance with varying degrees of insulin secretory defect) III. Due to other specific mechanisms or diseases (see Table 2 for details) A. Those in which specific mutations have been identified as a cause of genetic susceptibility (1) Genetic abnormalities of pancreatic β-cell function (2) Genetic abnormalities of insulin action B. Those associated with other diseases or conditions (1) Diseases of exocrine pancreas (2) Endocrine diseases (3) Liver disease (4) Drug- or chemical-induced (5) Infections (6) Rare forms of immune-mediated diabetes (7) Various genetic syndromes often associated with diabetes IV. Gestational diabetes mellitus Note: Those that cannot at present be classified as any of the above are called unclassifiable. The occurrence of diabetes-specific complications has not been confirmed in some of these conditions. Table 2. Diabetes mellitus and glucose metabolism disorders due to other specific mechanisms and diseases A. Those in which specific mutations have been identified as a cause of genetic susceptibility B. Those associated with other diseases or conditions (1) Genetic abnormalities of pancreatic β-cell functionInsulin gene (abnormal insulinemia, abnormal proinsulinemia, neonatal diabetes mellitus) HNF 4α gene (MODY1) Glucokinase gene (MODY2) HNF 1α gene (MODY3) IPF-1 gene (MODY4) HNF 1β gene (MODY5) Mitochondria DNA (MIDD) NeuroD1 gene (MODY6) Kir6.2 gene (neonatal diabetes mellitus) SUR1 gene (neonatal diabetes mellitus) AmylinOthers(2) Genetic abnormalities of insulin actionInsulin receptor gene (type A insulin resistance, leprechaunism, Rabson–Mendenhall syndrome etc.) Others (1) Diseases of exocrine pancreasPancreatitisTrauma/pancreatectomyNeoplasmHemochromatosisOthers(2) Endocrine diseasesCushing’s syndromeAcromegalyPheochromocytomaGlucagonomaAldosteronismHyperthyroidismSomatostatinomaOthers(3) Liver diseaseChronic hepatitisLiver cirrhosis Others(4) Drug- or chemical-inducedGlucocorticoidsInterferonOthers(5) InfectionsCongenital rubellaCytomegalovirusOthers(6) Rare forms of immune-mediated diabetesAnti-insulin receptor antibodiesStiffman syndromeInsulin autoimmune syndromeOthers(7) Various genetic syndromes often associated with diabetesDown syndromePrader-Willi syndromeTurner syndromeKlinefelter syndromeWerner syndromeWolfram syndromeCeruloplasmin deficiencyLipoatrophic diabetes mellitusMyotonic dystrophyFriedreich ataxiaLaurence-Moon-Biedl syndromeOthers The occurrence of diabetes-specific complications has not been confirmed in some of these conditions. Figure 1 Open in figure viewer PowerPoint A scheme of the relationship between etiology (mechanism) and patho-physiological stages (states) of diabetes mellitus. Arrows pointing right represent worsening of glucose metabolism disorders (including onset of diabetes mellitus). Among the arrow lines, indicates the condition classified as ‘diabetes mellitus’. Arrows pointing left represent improvement in the glucose metabolism disorder. The broken lines indicate events of low frequency. For example, in type 2 diabetes mellitus, infection can lead to ketoacidosis and require temporary insulin treatment for survival. Also, once diabetes mellitus has developed, it is treated as diabetes mellitus regardless of improvement in glucose metabolism, therefore, the arrow lines pointing left are filled in black. In such cases, a broken line is used, because complete normalization of glucose metabolism is rare. The classification of glucose metabolism disorders is principally derived from etiology, and includes staging of pathophysiology based on the degree of deficiency of insulin action. These disorders are classified into four groups: (i) type 1 diabetes mellitus; (ii) type 2 diabetes mellitus; (iii) diabetes mellitus due to other specific mechanisms or diseases; and (iv) gestational diabetes mellitus. Type 1 diabetes is characterized by destruction of pancreatic β-cells. Type 2 diabetes is characterized by combinations of decreased insulin secretion and decreased insulin sensitivity (insulin resistance). Glucose metabolism disorders in category (iii) are divided into two subgroups; subgroup A is diabetes in which a genetic abnormality has been identified, and subgroup B is diabetes associated with other pathologic disorders or clinical conditions. The staging of glucose metabolism includes normal, borderline and diabetic stages depending on the degree of hyperglycemia occurring as a result of the lack of insulin action or clinical condition. The diabetic stage is then subdivided into three substages: non-insulin- requiring, insulin-requiring for glycemic control, and insulin-dependent for survival. The two former conditions are called non-insulin-dependent diabetes and the latter is known as insulin-dependent diabetes. In each individual, these stages may vary according to the deterioration or the improvement of the metabolic state, either spontaneously or by treatment. Diagnosis ( Tables 3–7 and Figure 2 ): Table 3. Criteria of fasting plasma glucose levels and 75 g oral glucose tolerance test 2-h value Normal range Diabetic range Fasting value <110 mg/dL (6.1 mmol/L) ≥126 mg/dL (7.0 mmol/L) 75 g OGTT 2-h value <140 mg/dL (7.8 mmol/L) ≥200 mg/dL (11.1 mmol/L) Evaluation of OGTT Normal type: If both values belong to normal range *Diabetic type: If any of the two values falls into diabetic range Borderline typeNeither normal nor diabetic types *Casual plasma glucose ≥200 mg/dL (≥11.1 mmol/L) and HbA_1c≥6.5% are also regarded as to indicate diabetic type. Even for normal type, if 1-h value is 180 mg/dL (10.0 mmol/L), the risk of progression to diabetes mellitus is greater than for <180 mg/dL (10.0 mmol/L) and should be treated as with borderline type (follow-up observation, etc.). Fasting plasma glucose level of 100–109 mg/dL (5.5–6.0 mmol/L) is called ‘high-normal’: within the range of normal fasting plasma glucose. Plasma glucose level after glucose load in oral glucose tolerance test (OGTT) is not included in casual plasma glucose levels. The value for HbA_1c (%) is indicated with 0.4% added to HbA_1c (JDS) (%). Table 4. Procedures for diagnosing diabetes mellitus Clinical diagnosis (1) At initial examination, a ‘diabetic type’ is diagnosed if any of the following criteria are met: (i) fasting plasma glucose level ≥126 mg/dL (7.0 mmol/L), (ii) 75 g OGTT 2-h value ≥200 mg/dL (11.1 mmol/L), (iii) casual plasma glucose level ≥200 mg/dL (11.1 mmol/L) or (iv) *HbA_1c≥6.5%. Re-examination is carried out at another date and diabetes mellitus is diagnosed if ‘diabetic type’ is confirmed again**. However, diagnosis cannot be made on the basis of a repeated HbA_1c test alone. If the same blood sample is confirmed to be diabetic type by both plasma glucose and HbA_1c levels (any of [i] to [iii] plus [iv]), then diabetes mellitus can be diagnosed from the initial test (2) If plasma glucose level shows diabetic type (any of [i] to [iii]) and either of the following conditions exists, diabetes mellitus can be diagnosed immediately at the initial examination• The presence of typical symptoms of diabetes mellitus (thirst, polydipsia, polyuria, weight loss)• The presence of definite diabetic retinopathy (3) If it can be confirmed that either of the above conditions 1 or 2 existed in the past, diabetes mellitus must be diagnosed or suspected even if present test values do not meet the above conditions (4) If diabetes mellitus is suspected but the diagnosis cannot be made by the above (1) to (3), the patient should be followed-up (5) The following points should be kept in mind when selecting the method of determination in initial examination and re-examination• If HbA_1c is used at initial examination, another method of determination is required for diagnosis at re-examination. As a rule, both plasma glucose level and HbA_1c should be measured• If casual plasma glucose level is ≥200 mg/dL (11.1 mmol/L) at the initial test, a different test method is desirable for re-examination• In the case of disorders and conditions in which HbA_1c may be inappropriately low, plasma glucose level should be used for diagnosis (Table 5) Epidemiological study For the purpose of estimating the frequency of diabetes mellitus, determination of ‘diabetic type’ from a single test can be considered to represent ‘diabetes mellitus’. Whenever possible, the criteria to be used are HbA_1c≥6.5% or OGTT 2-h value ≥200 mg/dL (11.1 mmol/L) Health screening It is important to detect diabetes mellitus and identify high risk groups without overlooking anyone. Therefore, besides measuring plasma glucose and HbA_1c, clinical information such as family history and obesity should be referred *The value for HbA_1c (%) is indicated with 0.4% added to HbA_1c (JDS) (%). **Hyperglycemia must be confirmed in a non-stressful condition. OGTT, oral glucose tolerance test. Table 5. Disorders and conditions associated with low HbA_1c values Anemia Liver disease Dialysis Major hemorrhage Blood transfusion Chronic malaria Hemoglobinopathy Others Table 6. Situations where a 75-g oral glucose tolerance test is recommended Strongly recommended (suspicion of present diabetes mellitus cannot be ruled out) Fasting plasma glucose level is 110–125 mg/dL (6.1–6.9 mmol/L) Casual plasma glucose level is 140–199 mg/dL (7.8–11.0 mmol/L) *HbA_1c is 6.0–6.4% (excluding those having overt symptoms of diabetes mellitus) Testing is desirable (high risk of developing diabetes mellitus in the future;Testing is especially advisable for patients with risk factors for arteriosclerosis such as hypertension, dyslipidemia and obesity.) Fasting plasma glucose level is 100–109 mg/dL (5.5–6.0 mmol/L) *HbA_1c is 5.6–5.9% Strong family history of diabetes mellitus or present obesity regardless of above criteria *The value for HbA_1c (%) is indicated with 0.4% added to HbA_1c (JDS) (%). Table 7. Definition and diagnostic criteria of gestational diabetes mellitus Definition of gestational diabetes mellitus Glucose metabolism disorder with first recognition or onset during pregnancy, but that has not developed into diabetes mellitus Diagnostic criteria of gestational diabetes mellitus Diagnosed if one or more of the following criteria is met in a 75 g OGTT Fasting plasma glucose ≥92 mg/dL (5.1 mmol/L) 1-h value ≥180 mg/dL (10.0 mmol/L) 2-h value ≥153 mg/dL (8.5 mmol/L) However, diabetes mellitus that is diagnosed according to ‘Clinical diagnosis’ outlined in Table 4 is excluded from gestational diabetes mellitus (IADPSG Consensus Panel, Reference 42, partly modified with permission of Diabetes Care). Figure 2 Open in figure viewer PowerPoint Flow chart outlining steps in the clinical diagnosis of diabetes mellitus. *The value for HbA_1c (%) is indicated with 0.4% added to HbA_1c (JDS) (%). Categories of the State of Glycemia: Confirmation of chronic hyperglycemia is essential for the diagnosis of diabetes mellitus. When plasma glucose levels are used to determine the categories of glycemia, patients are classified as having a diabetic type if they meet one of the following criteria: (i) fasting plasma glucose level of ≥126 mg/dL (≥7.0 mmol/L); (ii) 2-h value of ≥200 mg/dL (≥11.1 mmol/L) in 75 g oral glucose tolerance test (OGTT); or (iii) casual plasma glucose level of ≥200 mg/dL (≥11.1 mmol/L). Normal type is defined as fasting plasma glucose level of <110 mg/dL (<6.1 mmol/L) and 2-h value of <140 mg/dL (<7.8 mmol/L) in OGTT. Borderline type (neither diabetic nor normal type) is defined as falling between the diabetic and normal values. According to the current revision, in addition to the earlier listed plasma glucose values, hemoglobin A_1c (HbA_1c) has been given a more prominent position as one of the diagnostic criteria. That is, (iv) HbA_1c≥6.5% is now also considered to indicate diabetic type. The value of HbA_1c, which is equivalent to the internationally used HbA_1c (%) (HbA_1c [NGSP]) defined by the NGSP (National Glycohemoglobin Standardization Program), is expressed by adding 0.4% to the HbA_1c (JDS) (%) defined by the Japan Diabetes Society (JDS). Subjects with borderline type have a high rate of developing diabetes mellitus, and correspond to the combination of impaired fasting glucose (IFG) and impaired glucose tolerance (IGT) noted by the American Diabetes Association (ADA) and WHO. Although borderline cases show few of the specific complications of diabetes mellitus, the risk of arteriosclerosis is higher than those of normal type. When HbA_1c is 6.0–6.4%, suspected diabetes mellitus cannot be excluded, and when HbA_1c of 5.6–5.9% is included, it forms a group with a high risk for developing diabetes mellitus in the future, even if they do not have it currently. Clinical Diagnosis: 1 If any of the criteria for diabetic type (i) through to (iv) is observed at the initial examination, the patient is judged to be ‘diabetic type’. Re-examination is conducted on another day, and if ‘diabetic type’ is reconfirmed, diabetes mellitus is diagnosed. However, a diagnosis cannot be made only by the re-examination of HbA_1c alone. Moreover, if the plasma glucose values (any of criteria [i], [ii], or [iii]) and the HbA_1c (criterion [iv]) in the same blood sample both indicate diabetic type, diabetes mellitus is diagnosed based on the initial examination alone. If HbA_1c is used, it is essential that the plasma glucose level (criteria [i], [ii] or [iii]) also indicates diabetic type for a diagnosis of diabetes mellitus. When diabetes mellitus is suspected, HbA_1c should be measured at the same time as examination for plasma glucose. 2 If the plasma glucose level indicates diabetic type (any of [i], [ii], or [iii]) and either of the following conditions exists, diabetes mellitus can be diagnosed immediately at the initial examination. • The presence of typical symptoms of diabetes mellitus (thirst, polydipsia, polyuria, weight loss) • The presence of definite diabetic retinopathy 3 If it can be confirmed that the above conditions 1 or 2 existed in the past, diabetes mellitus can be diagnosed or suspected regardless of the current test results. 4 If the diagnosis of diabetes cannot be established by these procedures, the patient is followed up and re-examined after an appropriate interval. 5 The physician should assess not only the presence or absence of diabetes, but also its etiology and glycemic stage, and the presence and absence of diabetic complications or associated conditions. Epidemiological Study: For the purpose of estimating the frequency of diabetes mellitus, ‘diabetes mellitus’ can be substituted for the determination of ‘diabetic type’ from a single examination. In this case, HbA_1c≥6.5% alone can be defined as ‘diabetes mellitus’. Health Screening: It is important not to misdiagnose diabetes mellitus, and thus clinical information such as family history and obesity should be referred to at the time of screening in addition to an index for plasma glucose level. Gestational Diabetes Mellitus: There are two hyperglycemic disorders in pregnancy: (i) gestational diabetes mellitus (GDM); and (ii) diabetes mellitus. GDM is diagnosed if one or more of the following criteria is met in a 75 g OGTT during pregnancy: 1 Fasting plasma glucose level of ≥92 mg/dL (5.1 mmol/L) 2 1-h value of ≥180 mg/dL (10.0 mmol/L) 3 2-h value of ≥153 mg/dL (8.5 mmol/L) However, diabetes mellitus that is diagnosed by the clinical diagnosis of diabetes mellitus defined earlier is excluded from GDM. (J Diabetes Invest, doi: 10.1111/j.2040-1124.2010.00074.x, 2010)

Gastric inhibitory polypeptide (GIP) and glucagon‐like peptide‐1 (GLP‐1) are the two primary incretin hormones secreted from the intestine on ingestion of glucose or nutrients to stimulate insulin secretion from pancreatic β cells. GIP and GLP‐1 exert their effects by binding to their specific receptors, the GIP receptor (GIPR) and the GLP‐1 receptor (GLP‐1R), which belong to the G‐protein coupled receptor family. Receptor binding activates and increases the level of intracellular cyclic adenosine monophosphate in pancreatic β cells, thereby stimulating insulin secretion glucose‐dependently. In addition to their insulinotropic effects, GIP and GLP‐1 play critical roles in various biological processes in different tissues and organs that express GIPR and GLP‐1R, including the pancreas, fat, bone and the brain. Within the pancreas, GIP and GLP‐1 together promote β cell proliferation and inhibit apoptosis, thereby expanding pancreatic β cell mass, while GIP enhances postprandial glucagon response and GLP‐1 suppresses it. In adipose tissues, GIP but not GLP‐1 facilitates fat deposition. In bone, GIP promotes bone formation while GLP‐1 inhibits bone absorption. In the brain, both GIP and GLP‐1 are thought to be involved in memory formation as well as the control of appetite. In addition to these differences, secretion of GIP and GLP‐1 and their insulinotropic effects on β cells have been shown to differ in patients with type 2 diabetes compared to healthy subjects. We summarize here the similarities and differences of these two incretin hormones in secretion and metabolism, their insulinotropic action on pancreatic β cells, and their non‐insulinotropic effects, and discuss their potential in treatment of type 2 diabetes. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2010.00022.x, 2010)

Aims: To assess the efficacy and safety of once‐daily lixisenatide versus placebo in Asian patients with type 2 diabetes insufficiently controlled on basal insulin ± sulfonylurea. Methods: In this 24‐week, randomized, double‐blind, placebo‐controlled, parallel‐group, multicentre study, participants (mean baseline HbA _1c 8.53%) from Japan, Republic of Korea, Taiwan and the Philippines received lixisenatide (n = 154) or placebo (n = 157) in a stepwise dose increase to 20 µg once daily. The primary endpoint was HbA _1c change from baseline to week 24. Results: Once‐daily lixisenatide significantly improved HbA _1c versus placebo ( LS mean difference vs. placebo = −0.88% [95% CI = −1.116, −0.650]; p < 0.0001), and allowed more patients to achieve HbA _1c <7.0% (35.6 vs. 5.2%) and ≤6.5% (17.8 vs. 1.3%). Lixisenatide also significantly improved 2‐h postprandial plasma glucose and glucose excursion, average 7‐point self‐monitored blood glucose and fasting plasma glucose. Lixisenatide was well tolerated; 86% of patients on lixisenatide completed the study versus 92% on placebo. Ten (6.5%) lixisenatide and 9 (5.7%) placebo patients experienced serious adverse events. More lixisenatide patients [14 (9.1%)] discontinued for adverse events versus placebo [5 (3.2%)], mainly with gastrointestinal causes. Nausea and vomiting were reported in 39.6 and 18.2% of patients on lixisenatide versus 4.5 and 1.9% on placebo. Symptomatic hypoglycaemia was more frequent with lixisenatide (42.9%) versus placebo (23.6%), but was similar between groups (32.6 vs. 28.3%, respectively), in those not receiving sulfonylureas. No severe hypoglycaemia was reported. Conclusions: In an Asian type 2 diabetes population insufficiently controlled by basal insulin ± sulfonylurea, once‐daily lixisenatide significantly improved glycaemic control, with a pronounced postprandial effect, and was well tolerated.

Glucose‐dependent insulinotropic polypeptide (GIP) and glucagon‐like peptide‐1 (GLP‐1) are the two primary incretin hormones secreted from the intestine on ingestion of various nutrients to stimulate insulin secretion from pancreatic β‐cells glucose‐dependently. GIP and GLP‐1 undergo degradation by dipeptidyl peptidase‐4 (DPP‐4), and rapidly lose their biological activities. The actions of GIP and GLP‐1 are mediated by their specific receptors, the GIP receptor (GIPR) and the GLP‐1 receptor (GLP‐1R), which are expressed in pancreatic β‐cells, as well as in various tissues and organs. A series of investigations using mice lacking GIPR and/or GLP‐1R, as well as mice lacking DPP‐4, showed involvement of GIP and GLP‐1 in divergent biological activities, some of which could have implications for preventing diabetes‐related microvascular complications (e.g., retinopathy, nephropathy and neuropathy) and macrovascular complications (e.g., coronary artery disease, peripheral artery disease and cerebrovascular disease), as well as diabetes‐related comorbidity (e.g., obesity, non‐alcoholic fatty liver disease, bone fracture and cognitive dysfunction). Furthermore, recent studies using incretin‐based drugs, such as GLP‐1 receptor agonists, which stably activate GLP‐1R signaling, and DPP‐4 inhibitors, which enhance both GLP‐1R and GIPR signaling, showed that GLP‐1 and GIP exert effects possibly linked to prevention or treatment of diabetes‐related complications and comorbidities independently of hyperglycemia. We review recent findings on the extrapancreatic effects of GIP and GLP‐1 on the heart, brain, kidney, eye and nerves, as well as in the liver, fat and several organs from the perspective of diabetes‐related complications and comorbidities.

Type 2 diabetes in East Asians is characterized primarily by β‐cell dysfunction, and with less adiposity and less insulin resistance compared with that in Caucasians. Such pathophysiological differences can determine the appropriate therapeutics for the disease. Incretins, glucose‐dependent insulinotropic polypeptide and glucagon‐like peptide‐1, are secreted in response to meal ingestion, and enhance insulin secretion glucose‐dependently. Incretin‐based drugs, dipeptidyl peptidase‐4 inhibitors (DPP‐4i) and glucagon‐like peptide‐1 receptor agonists, that ameliorate β‐cell dysfunction with limited hypoglycemia risk are now widely used in type 2 diabetes management. Recent meta‐analyses of clinical trials on DPP‐4i and glucagon‐like peptide‐1 receptor agonists found that the drugs were more effective in Asians, most likely because of amelioration of β‐cell dysfunction. In addition, we found increased glycated hemoglobin‐lowering effects of DPP‐4i to be associated with intake of fish in type 2 diabetes, which suggests that dietary customs of East Asians might also underlie the greater efficacy of DPP‐4i. Despite the limited risk, cases of severe hypoglycemia were reported for DPP‐4i/sulfonylureas combinations. Importantly, hypoglycemia was more frequent in patients also receiving glibenclamide or glimepiride, which activate exchange protein directly activated by cyclic adenosine monophosphate 2, a critical mediator of incretin signaling, and was less frequent in patients receiving gliclazide, which does not activate exchange protein directly activated by cyclic adenosine monophosphate 2. Prevention of insulin‐associated hypoglycemia by DPP‐4i has gained attention with regard to the enhancement of hypoglycemia‐induced glucagon secretion by insulinotropic polypeptide, but remains to be investigated in East Asians. Despite the safety issues, which are paramount and must be carefully monitored, the incretin‐based drugs could have potential as a first choice therapy in East Asian type 2 diabetes patients.