Diagnostic significance of antibodies to glutamic acid decarboxylase in Japanese diabetic patients with secondary oral hypoglycemic agents failure

Antibodies against glutamic acid decarboxylase and indices of insulin resistance and insulin secretion in nondiabetic adults: a cross-sectional study

BACKGROUND

Autoimmunity against insulin-producing beta cells from pancreatic islets is a common phenomenon in type 1 diabetes and latent autoimmune diabetes in adults. Some reports have also related beta-cell autoimmunity to insulin resistance (IR) in type 2 diabetes. However, the extent to which autoimmunity against components of beta cells is present and relates to IR and insulin secretion in nondiabetic adults is uncertain.

AIM

To explore the association between antibodies against glutamic acid decarboxylase (GADA), a major antigen from beta cells, and indices of whole-body IR and beta-cell capacity/insulin secretion in adults who do not have diabetes.

METHODS

We studied 81 adults of both sexes aged 30-70, without known diabetes or any autoimmune disease. Participants underwent an oral glucose tolerance test (OGTT) with determination of plasma glucose and insulin at 0, 30, 60, 90, and 120 minutes. From these results we calculated indices of insulin resistance (homeostasis model assessment of insulin resistance [HOMA-IR] and incremental area under the insulin curve [iAUCins]) and insulin secretion (corrected insulin response at 30 minutes and HOMA beta-cell%). GADAs were measured in fasting plasma using immunoenzymatic methods.

RESULTS

We found an overall prevalence of GADA positivity of 21.3%, without differences by sex and no correlation with age. GADA titers did not change monotonically across quartiles of any of the IR or insulin secretion indices studies. GADA did not correlate linearly with fasting IR expressed as HOMA-IR (Spearman's r=-0.18, p=0.10) or postabsorptive IR expressed as iAUCins (r=-0.15, p=0.18), but did show a trend toward a negative correlation with insulin secretory capacity expressed by the HOMA-beta cell% index (r=-0.20, p=0.07). Hemoglobin A1c, body mass index, and waist circumference were not associated with GADA titers.

CONCLUSION

GADA positivity is frequent and likely related to impaired beta-cell function among adults without known diabetes.

Autoimmunity, insulin resistance and Beta cell function in subjects with low body weight type 2 diabetes mellitus

In developing countries like India, the majority of Type 2 diabetics are non-obese, and many are "lean" with a body mass index (BMI) below 18.5. This type is referred to as "Low Body Weight Type 2 DM" (LB Type 2 DM). LB Type 2 DM are confused with Type 1 DM or late autoimmune diabetes in adults (LADA) due to their high blood glucose levels and early insulin-requiring state. We assessed pancreatic islet cell autoimmunity by using both glutamic acid decarboxylase 65 antibody (GADA) and anti-IA(2) antibody estimation in 23 patients with LB Type 2 DM and 10 age-matched normal weight (NW) Type 2 DM. Fasting blood glucose (FBG) and 2 hr postchallenge blood glucose (PGBG2) were significantly higher in LB (p < 0.05), while mean values of fasting insulin (24.47 +/- 73.15 muIU/mL vs. 13.4 +/- 16.54 muIU/mL, p > 0.7) and fasting C-peptide (180.81 +/- 357.08 pM/mL vs. 279.83 +/- 281.38 pM/mL, p > 0.5) in LB and NW respectively were not statistically different. All 23 LB and 10 NW subjects were GADA negative while IA(2) positivity was found in 1/23 and 1/10 cases, respectively. LB Type 2 DM revealed good beta cell function with homeostasis model assessment beta cells (HOMAB) values of 57.41 +/- 153.18 as compared to 44.74 +/- 56.24 (p > -0.2) in NW Type 2 DM. Insulin resistance as assessed by homeostasis model assessment insulin resistant (HOMA IR) was 13.50 +/- 42.83 and 5.68 +/- 6.90 (p > 0.6) in LB and NW Type 2 DM, respectively, suggesting that LB Type 2 DM are a phenotypic variant of Type 2 DM.

The role of sulphonylureas in the management of type 2 diabetes mellitus

The sulphonylureas act by triggering insulin release from the pancreatic beta cell. A specific site on the adenosine triphosphate (ATP)-sensitive potassium channels is occupied by sulphonylureas leading to closure of the potassium channels and subsequent opening of calcium channels. This results in exocytosis of insulin. The meglitinides are not sulphonylureas but also occupy the sulphonylurea receptor unit coupled to the ATP-sensitive potassium channel. Glibenclamide (glyburide), gliclazide, glipizide and glimepiride are the primary sulphonylureas in current clinical use for type 2 diabetes mellitus. Glibenclamide has a higher frequency of hypoglycaemia than the other agents. With long-term use, there is a progressive decrease in the effectiveness of sulphonylureas. This loss of effect is the result of a reduction in insulin-producing capacity by the pancreatic beta cell and is also seen with other antihyperglycaemic agents. The major adverse effect of sulphonylureas is hypoglycaemia. There is a theoretical concern that sulphonylureas may affect cardiac potassium channels resulting in a diminished response to ischaemia. There are now many choices for initial therapy of type 2 diabetes in addition to sulphonylureas. Metformin and thiazolidinediones affect insulin sensitivity by independent mechanisms. Disaccharidase inhibitors reduce rapid carbohydrate absorption. No single agent appears capable of achieving target glucose levels in the majority of patients with type 2 diabetes. Combinations of agents are successful in lowering glycosylated haemoglobin levels more than with a single agent. Sulphonylureas are particularly beneficial when combined with agents such as metformin that decrease insulin resistance. Sulphonylureas can also be given with a basal insulin injection to provide enhanced endogenous insulin secretion after meals. Sulphonylureas will continue to be used both primarily and as part of combined therapy for most patients with type 2 diabetes.

Clinical evaluation of a radioimmunoprecipitation assay for IA-2 antibody and comparison of GAD antibody in type 1 diabetes mellitus

We evaluated a insulinoma-associated protein (IA-2) antibody assay kit using 125I-labelled recombinant IA-2. IA-2 antibodies were present in patients with early-onset type 1 diabetes mellitus (DM) at frequencies of 74%, 67%, 57%, and 50% for respective periods <1 year, 1 < or =years<2, 2< or =years<3, and 3< or =years<4 after onset. IA-2 antibody frequency was low throughout the DM course as compared with glutamic acid decarboxylase (GAD) antibody frequency. No one had IA-2 antibody, but 29% still had positive GAD antibody titers after 11 years. Of the patients with 0<years<7 duration, 42% had IA-2 Ab+/GAD Ab+, 9% IA-2 Ab+/GAD Ab-, and 24% IA-2 Ab-/GAD Ab+. Prevalence of IA-2 and GAD antibody in 1243 patients with type 2 DM were 1.5% and 3.1%, respectively, and 1.1% had both. This new IA-2 antibody kit is easy to use and provides a specific, sensitive method for making routine assays. Furthermore, the combined analysis of GAD antibody provides high detection of type 1 DM.