|Year : 2013 | Volume
| Issue : 4 | Page : 347-351
Association of amylin in the development of impaired fasting glucose and impaired glucose tolerance
Md Abdur Rashid1, MO Faruque1, Mahmuda Haque2, MR Karim3
1 Department of Biochemistry and Cell Biology, Biomedical Research Group, BIRDEM, Dhaka 1000, Bangladesh
2 Department of Pharmacy, Southeast University, Dhaka 1213, Bangladesh
3 Department of Biochemistry and Molecular Biology, Rajshahi University, Rajshahi 6205, Bangladesh
|Date of Submission||01-May-2013|
|Date of Acceptance||29-May-2013|
|Date of Web Publication||15-Oct-2013|
Md Abdur Rashid
Lab of Molecular Signaling, National Institute on Alcohol Abuse and Alcoholism, 5625 Fisher Lane, Room # 3S-O2, MD 20852, USA
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Objective: The present study was planned to explore the role of amylin in the pathogenesis of impaired fasting glucose (IFG) and impaired glucose tolerance (IGT) subjects. Subjects and Methods: In this study, 20 IFG and 25 IGT subjects along with 30 healthy subjects were included. Plasma glucose (fasting and 2 h after 75 g glucose) was measured by glucose oxidase method, serum triglyceride and total cholesterol, high density lipoprotein (HDL) and low density lipoprotein (LDL) by enzymatic method. Serum insulin and amylin were measured by the enzyme-linked immunosorbent assay method. B-cell secretory capacity (Homeostasis model assessment [HOMA] %B) and insulin sensitivity (HOMA %S) were estimated by HOMA-CIGMA software. Results: Age and body mass index were matched among control and the hyperglycemic groups (IFG, IGT). Fasting total cholesterol, HDL and LDL was significantly higher in IGT subjects compared with control and IFG subjects. Plasma insulin was significantly higher in IFG and IGT compared with control subjects (median [range], pmol/l; control, 38 [28-55]; IFG, 49 [40-56] and IGT, 60 [20-91]). HOMA %B was significantly lower in IFG and significantly higher in IGT subjects compared with the controls (median [range], %; control, 81 [53-156]; IFG, 52 [40-63] and IGT, 95 [33-195]). HOMA %S was significantly decreased in IGT and also in IFG compared to controls (median (range), %; control, 137 [95-187]; IFG, 104 [88-127] and IGT, 86 [57-255]). Plasma amylin was significantly raised in IFG and IGT compared to control subjects (mean ± standard deviation, pmol/l; control, 5.0 ± 0.63; IFG, 6.43 ± 0.67 and IGT, 8.0 ± 1.18). In binary logistic regression analysis, it has been found that plasma amylin concentration is positively associated with impaired glucose regulation and in bivariate correlation analysis it has been found that plasma amylin is positively associated with HOMA %B and negatively associated with fasting glucose. Conclusion: The present data suggested that increased amylin concentration may be contributed to the development of pre-diabetic condition or vice versa.
Keywords: Amylin, impaired fasting glucose, impaired glucose tolerance, type 2 diabetes
|How to cite this article:|
Rashid MA, Faruque M O, Haque M, Karim M R. Association of amylin in the development of impaired fasting glucose and impaired glucose tolerance. Int J Nutr Pharmacol Neurol Dis 2013;3:347-51
|How to cite this URL:|
Rashid MA, Faruque M O, Haque M, Karim M R. Association of amylin in the development of impaired fasting glucose and impaired glucose tolerance. Int J Nutr Pharmacol Neurol Dis [serial online] 2013 [cited 2020 Jan 19];3:347-51. Available from: http://www.ijnpnd.com/text.asp?2013/3/4/347/119842
| Introduction|| |
Type 2 diabetes mellitus (DM) is characterized by beta-cell dysfunction manifest in part as a reduction in insulin release.  Although the changes in insulin sensitivity and beta-cell function have been demonstrated to exist once hyperglycemia is present, it has been debated as to when during the development of the disease these changes occur. A number of studies suggest that insulin resistance exists in individuals who are at high risk of developing diabetes and have normal glucose tolerance, beta-cell function has not diminished  or if beta-cell dysfunction is present, this dysfunction is only mild and is present only when impaired glucose tolerance (IGT) exists.  Two intermediate groups at risk for diabetes are impaired fasting glucose (IFG) and IGT. Patients with IFG and/or IGT are now referred to as having "pre-diabetes" by American Diabetes Association or "impaired glucose regulation (IGR)" by World Health Organization (WHO). IFG and IGT refer to a metabolic state intermediate between normal glucose homeostasis and diabetes. They are not interchangeable and represent different abnormalities of glucose regulation, one in the fasting state and one postprandial. Both IFG and IGT are thought to be part of the natural history of diabetes. As insulin resistance and impaired insulin secretion are the basic pathophysiological features of DM, these are also conceived to be the mediators of other forms of glucose intolerance. However, it is uncertain, which defect(s) is (are) clearly related to IFG and IGT.
In addition to impaired insulin secretion, it is apparent that a decrease in the release of the more recently described beta-cell peptide known as amylin or islet amyloid polypeptide (IAPP) can also be demonstrated in subjects with type 2 diabetes.  Amylin is a 37 amino acid peptide that is produced by pancreatic beta-cells and is co-secreted with insulin in response to glucose and non-glucose secretagogues administered orally or intravenously. It is isolated from the islet amyloid of type 2 diabetic subjects, might play a potential role in the pathogenesis of type 2 DM. In vitro and in vivo studies show that amylin has an effect of insulin secretion as well as on insulin sensitivity. Islet amyloid has been shown to be present in animal models of type 2 diabetes at a stage when these animals have IGT. Although it is clear that islet amyloid deposits are present in almost all individuals with type 2 diabetes, the role of this lesion on the pathogenesis of type 2 diabetes remain somewhat controversial.  It has been shown that increased amylin release may contribute to the pathogenesis of type 2 diabetes by leading to the formation of islet amyloid and/or by inducing insulin resistance and diminished insulin secretion. Limited human studies suggested that amylin levels are increased with obesity and that it is present in plasma of individuals with type 2 diabetes at concentrations that are lower, similar or higher than control subjects. Autopsy studies in humans have demonstrated that islet amyloid is associated with the loss of beta-cell mass, but a direct role for amyloid in the pathogenesis of type 2 diabetes cannot be inferred from such studies. 
IFG and IGT are two conditions, which may be considered as pre-diabetic stage. The rising prevalence of IGT is assumed to increase from 8.2% to 9.0% world-wide and 7.1-7.8% in Bangladesh from 2003 to 2025 in adults (20-79 years age groups). The 40-59 age groups currently have the greatest number of persons with IGT.  IGT is more prevalent than IFG, ≤50% of people with IFG has IGT and 20-30% with IGT also has IFG. IFG is subsequently more common among men and IGT slightly more common among women. The prevalence of IFG tends to plateau in middle age, whereas the prevalence of IGT rises into old age.  From Diabetes Epidemiology: Collaborative analysis of Diagnostic criteria in Asia study, it was found that IGT was more prevalent than impaired fasting glycemia in all Asian populations studied for all age-groups.  The rising prevalence rate of IGT may be mainly due to diabetogenic life-style factors that lead to obesity and increasing life expectancy. Interestingly, there is a tendency for the prevalence rates of IGT to decline as those of diabetes rise, perhaps suggesting that areas with a high ratio of IGT: Diabetes are at an earlier stage of the diabetes epidemic and thus may be a particular target for preventive strategies.  Although amylin was studied in type 2 diabetic subjects, but there are few studies exists where amylin explored in IFG and IGT subjects. In a few immunostaining studies in cats performed at a time when they have islet amyloid and IGT suggest that amylin production may be increased during the pathogenesis of type 2 diabetes syndrome in these animals. Thus, although it is certain that amylin is important in islet amyloidogenesis, it is unclear whether increased amylin secretion occurs in type 2 diabetes either when the disease is fully established or during its development. Measurement of serum amylin in IFG and IGT subjects may help in understanding the association of serum amylin with insulin resistance and insulin secretion in different stages of the natural history of type 2 DM.
| Subjects and Methods|| |
This cross-sectional observational study was conducted in the Research Division, Bangladesh Institute of Research and Rehabilitation in Diabetes, Endocrine and Metabolic Disorders (BIRDEM), Dhaka, Bangladesh. A group of 20 IFG and 25 IGT subjects were recruited purposively from the out-patient department of BIRDEM, along with a group of 30 age-, sex- and body mass index (BMI)- matched healthy subjects without a family history of diabetes as controls from the friend circle of the IGR subjects considering the same socio-economic status. Subjects were considered as IFG and IGT using the WHO guidelines.  Written consent was taken from all the volunteers; clinical examination was performed by a registered physician using a pre-designed questionnaire. Anthropometric measurements were taken using standard methods. Subjects were requested to come on a prescheduled morning after overnight fasting for the fasting blood sample in an ethylenediaminetetraacetic acid (EDTA) containing tubes. Then, patient was given 75 g of glucose in 250-300 ml of water and advised to drink in 5 min. Patient was advised not to smoke, not to take any food and to take rest in a chair for 2 h. Then blood samples were drawn into tubes containing EDTA and kept on ice before being separated. After 15 min blood sample was centrifuged for 10 min at 3,000 rpm to obtain plasma. Subjects were finally selected from fasting and 2 h plasma glucose values that fulfilled the inclusion criteria of this study. The plasma of selected subjects was aliquoted and kept frozen at −70°C until analysis.
Fasting and postprandial plasma glucose was measured using the glucose-oxidase method; fasting plasma lipid profile (cholesterol, triglyceride and high density lipoprotein (HDL)) was determined by enzymatic-colorimetric method (Randox Laboratories Ltd., UK). Serum low density lipoprotein (LDL) was calculated using the formula of Friedewald et al. Fasting plasma insulin and amylin levels were determined through the enzyme-linked immunosorbent assay method (Linco Research Inc., USA). Insulin secretory capacity (Homeostasis model assessment [HOMA] %B) and insulin sensitivity (HOMA %S) were calculated from fasting glucose and fasting insulin using the HOMA-CIGMA software. 
Statistical analysis was performed using Statistical Package for Social Science (SPSS) software for Windows version 11 (SPSS Inc., Chicago, Illinois, USA). All data were expressed as mean ± standard deviation (SD), median (range) and/or percentage (%) as appropriate. The statistical significance of differences between the values was assessed by analysis of variance or Mann-Whitney U test (as appropriate). Binary logistic regressions were performed in the parameters. A two-tailed P < 0.05 was considered as statistically significant.
| Results|| |
Age and BMI were matched among control and the pre-diabetic groups. The mean ± SD, fasting plasma glucose was significantly higher in IFG and IGT groups compared with control, but 2 h plasma glucose was significantly raised in IFG and IGT compared with control [Table 1].
The fasting total cholesterol, HDL and LDL was significantly higher in IGT subjects compared to control and IFG [Table 1].
HOMA %B was significantly lower in IFG and significantly higher in IGT compared to Controls (Median [range], %; control, 81 (53-156); IFG, 52 (40-63) and IGT, 95 (33-195)). HOMA %S was significantly decreased in IGT and also in IFG compared to control (Median [range], %; control, 137 (95-187); IFG, 104 (88-127) and IGT, 86 (57-255)) [Table 1].
Plasma amylin was significantly raised in IFG and IGT compared to control (mean ± SD, pmol/l; control, 5.0 ± 0.63; IFG, 6.43 ± 0.67 and IGT, 8.0 ± 1.18). Plasma insulin was significantly higher in IFG and IGT compared to control (median [range], pmol/l; control, 38 (28-55); IFG, 49 (40-56) and IGT, 60 (20-91)) [Table 1].
In Binary logistic regression analysis, it has been found that plasma amylin concentration is positively associated with IGR [Table 2] and in bivariate correlation analysis it has been found that plasma amylin is positively associated with HOMA %B and negatively associated with fasting glucose [Table 3].
|Table 2: Binary regression of amylin in IGR subjects considering control as reference|
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|Table 3: Correlations of plasma amylin with other biochemical parameters|
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| Discussion|| |
Type 2 diabetes develops through the stage of IFG and/or IGT, which are a symptomatic and unassociated with any manifested morbidity. Their sole significance lies in the fact that they predict future diabetes or cardiovascular disease.  Recently, it has been found that insulin resistance and insulin secretory defect appears in the pre-diabetes stage i.e., before the onset of diabetes.  A number of studies suggest that insulin resistance exists in individuals who are at high risk of developing diabetes and have normal glucose tolerance, beta-cell function has not diminished  or if beta-cell dysfunction is present, this dysfunction is only mild and is present only when IGT exists.  However, these assessments have not accounted for the fact that insulin sensitivity is an important modulator of the beta-cell response to secretagogues and therefore reduced beta-cell function may easily be overlooked. Thus, when the effect of insulin sensitivity on beta-cell function is accounted for a comparable insulin response could in fact be considered inappropriately low in insulin resistance.  Although it is clear that islet amyloid deposits are present in almost all individuals with type 2 diabetes, the role of this lesion on the pathogenesis of type 2 diabetes remains somewhat controversial.  As both IFG and IGT are known to be intermediate stages in the natural history of type 2 diabetes, this study was planned to explore the role of amylin in the pathogenesis of type 2 diabetes and also to determine whether increased or decreased level of amylin in type 2 diabetes. This is for the first time the issue has been addressed in a Bangladeshi population.
Measurement of plasma amylin and insulin is a central issue in the present study. In the present study, it was found that plasma amylin and insulin was significantly higher in IFG and IGT subjects compared with the healthy control subjects. It has been reported that amylin levels are increased with obesity.  In the present study, BMI values were similar in all three groups though there was an increasing tendency of amylin in IFG and IGT in comparison with controls. Immunostaining studies in cats performed at a time when they have islets and IGT suggest that amylin production may increase during the pathogenesis of type 2 diabetes syndromes in these animals.  Thus, although it is certain that amylin is important in islets amyloidgenesis, it is unclear whether increased amylin secretion occurs in type 2 diabetes either when the disease is fully established or during its developments. The present study suggests that increased amylin release may contribute to the development of IFG and IGT leading to the formation of type 2 diabetes. In binary logistic regressions when both the IFG and IGT were considered as IGR, it has been found that amylin is positively associated with IGR adjusted with age and BMI. In bivariate correlation analysis, it has been found that amylin is positively associated with HOMA %B and negatively associated with fasting glucose levels. Therefore, increased concentration of amylin, which was known in diabetes, in the present study, it indicates that increased amylin concentrations starts before the initiation of diabetes i.e., in the pre-diabetes stage.
Insulin secretion and insulin sensitivity are the crucial issue in the present study and it was found that insulin secretion (HOMA %B) was significantly lower in IFG and significantly higher in IGT compared with control subjects and insulin sensitivity (HOMA %S) was significantly lower in IGT and in IFG compared to control subjects. Similar results were found in the same population in a previous study.  IFG subjects showed significantly lower level of HOMA %B as compared to control in IGT. This finding reflects that insulin secretory capacity is compromised in IFG subjects. So in IFG, there is beta-cells failure along with a tendency of insulin resistance evident by compromised HOMA %B and HOMA %S. Due to beta-cells failure, there is a relatively lower insulin level in IFG subjects. In another study showed that insulin sensitivity has been shown to be an important modulator of IAPP release by the beta-cell. Thus, IAPP levels are elevated in conditions associated with insulin resistance, such as obesity and pregnancy.  Conversely, in disease states associated with reduced beta-cell peptide release namely IGT and both type 1 and type 2 diabetes, IAPP release has been shown to be diminished in response to both oral and iv stimulation, paralleling the reduction in insulin release.  In the present study, it was found that serum cholesterol and LDL level was significantly higher in IGT compared to IFG and control subjects, which indicates that dyslipidemia starts earlier than diabetes.
From the above context, it may be concluded that the pathogenesis of IFG and IGT are not similar at least in the Bangladeshi population; increased amylin concentration may contribute to the development of pre-diabetic condition leading to the formation of type 2 diabetes.
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[Table 1], [Table 2], [Table 3]