Epidemiology/Health Services/Psychosocial Research ORIGINAL ARTICLE Insulin and Amylin Release Are Both Diminished in First-Degree Relatives of Subjects With Type 2 Diabetes NEGAR G. KNOWLES, MA WILFRED Y. FUJIMOTO, MD ease these changes occur. A number of MELINDA A. LANDCHILD, MA STEVEN E. KAHN, MB, CHB studies have been largely interpreted to suggest that whereas insulin resistance exists in individuals who are at high risk of developing diabetes and have normal glucose tolerance, ␤-cell function is not OBJECTIVE — To determine whether first-degree relatives of individuals with type 2 diabe- ␤ ␤ diminished (6–9), or if -cell dysfunction tes, who are at high risk of subsequently developing hyperglycemia, manifest alterations in -cell is present, this dysfunction is only mild function including an alteration in the co-release of insulin and amylin. and is present only when impaired glu- RESEARCH DESIGN AND METHODS — In 30 first-degree relatives and 24 matched cose tolerance exists (10,11). However, subjects with no family history of diabetes, ␤-cell function was measured as the intravenous these assessments have not accounted for glucose–induced acute insulin response (AIRg) and acute amylin response (AARg). The insulin the fact that insulin sensitivity is an im- sensitivity index (SI) was quantified and used to account for the role of insulin sensitivity to portant modulator of the ␤-cell response ␤ ϫ␤ modulate -cell function (SI -cell function). to secretagogues, and therefore reduced ␤-cell function may easily be overlooked RESULTS — Fasting plasma glucose (5.3 Ϯ 0.1 vs. 5.1 Ϯ 0.1 mmol/l; means Ϯ SEM), Ϯ Ϯ (12,13). Thus, when the effect of insulin immunoreactive insulin (IRI) (68 7 vs. 57 6 pmol/l) and amylin-like immunoreactivity ␤ (ALI) (5.5 Ϯ 0.6 vs. 4.7 Ϯ 0.7 pmol/l) were similar in relatives and control subjects, respectively. sensitivity on -cell function is accounted Ϯ Ϯ for, a comparable insulin response could Relatives were insulin resistant compared with control subjects (SI: 4.86 0.63 vs. 7.20 ϫ Ϫ5 Ϫ1 ⅐ Ϫ1 ⅐ Ϫ1 ϭ Ϯ Ϯ 0.78 10 min pmol l , P 0.01), but their AIRg (392 59 vs. 386 50 pmol/l) in fact be considered inappropriately low Ϯ Ϯ ␤ and AARg (5.9 0.9 vs. 6.1 0.8 pmol/l) did not differ. When -cell function was determined in the face of insulin resistance. Using this ϫ Ϯ relative to insulin sensitivity, in the first-degree relatives, both AIRg (SI AIRg: 1.60 0.23 vs. approach, it is now being recognized that Ϯ ϫ Ϫ2 Ϫ1 Ͻ ϫ Ϯ Ϯ ϫ 2.44 0.31 10 min , P 0.05) and AARg (SI AARg: 2.39 0.35 vs. 4.06 0.56 ␤-cell function is relatively decreased in 10Ϫ4 minϪ1, P Ͻ 0.05) were reduced. The molar proportion of ALI to IRI was not altered in Ϯ Ϯ some groups at high risk of developing high-risk subjects (1.75 0.16 vs. 1.71 0.15%). hyperglycemia (14–18). Amylin is a 37–amino acid peptide CONCLUSIONS — First-degree relatives of subjects with type 2 diabetes have diminished ␤ ␤-cell function at a time when they are not hyperglycemic, and this reduction affects insulin and that is produced by the -cell and is co- amylin responses proportionally. Thus, an altered amylin-to-insulin ratio is not likely to identify secreted with insulin in response to glucose individuals at high risk of developing type 2 diabetes. and nonglucose secretagogues adminis- tered orally or intravenously (4,5,19,20). Diabetes Care 25:292–297, 2002 It is the unique constituent of the islet amyloid deposits found in the vast major- ity of subjects with type 2 diabetes (21– he pathogenesis of type 2 diabetes ␤-cell peptide known as amylin or islet 23). We and others have hypothesized includes reductions in insulin sensi- amyloid polypeptide can also be demon- that alterations in the handling of this T tivity and ␤-cell function (1). The strated in subjects with type 2 diabetes peptide by the ␤-cell may underlie the change in ␤-cell function has been dem- (3–5). propensity of diabetic individuals to de- onstrated to include a reduction in insulin Although the changes in insulin sen- posit amyloid, resulting in a reduction in secretion in response to glucose (2). In sitivity and ␤-cell function have been ␤-cell mass and the loss of ␤-cell secretory addition to this reduction in insulin re- demonstrated to exist once hyperglyce- capacity (24). In keeping with a reduction lease, it is apparent that a decrease in the mia is present, it has been debated as to in ␤-cell secretory capacity, we have ob- release of the more recently described when during the development of the dis- served reductions in insulin and amylin responses in individuals with impaired ●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●● glucose tolerance (5). Others have found From the Division of Metabolism, Endocrinology and Nutrition, Department of Medicine, VA Puget Sound that the amylin response is increased un- Health Care System, and the University of Washington, Seattle, Washington. Address correspondence and reprint requests to Steven E. Kahn, MB, ChB, VA Puget Sound Health Care der conditions associated with insulin System (151), 1660 S. Columbian Way, Seattle, WA 98108. E-mail: [email protected]. resistance, such as obesity (4,25) and Received for publication 27 July 2001 and accepted in revised form 4 November 2001. pregnancy (26), including in women with Abbreviations: AARg, intravenous glucose–induced acute amylin response; AIRg, intravenous glucose– gestational diabetes who are at high risk induced acute insulin response; ALI, amylin-like immunoreactivity; GEZI, glucose effectiveness at zero for subsequently developing type 2 diabe- insulin; IRI, immunoreactive insulin; SG, glucose effectiveness; SI, insulin sensitivity index. A table elsewhere in this issue shows conventional and Syste`me International (SI) units and conversion tes. Thus, changes in amylin have been factors for many substances. observed under scenarios that are associ- 292 DIABETES CARE, VOLUME 25, NUMBER 2, FEBRUARY 2002 Knowles and Associates ated with an increased risk of developing Table 1—Demographic characteristics and fasting plasma glucose, IRI, and ALI concentra- type 2 diabetes. tions in first-degree relatives of type 2 diabetic subjects and in control subjects First-degree relatives of subjects with type 2 diabetes are at increased risk of First-degree relatives Control subjects developing hyperglycemia. They there- fore provide an ideal group to study to n 30 24 determine the magnitude of changes in Age (years) 39.8 Ϯ 1.7 42.0 Ϯ 3.1 insulin sensitivity and ␤-cell function that BMI (kg/m2) 29.2 Ϯ 1.2 26.7 Ϯ 0.8 may be present in such high-risk individ- Fasting glucose (mmol/l) 5.3 Ϯ 0.1 5.1 Ϯ 0.1 uals. Furthermore, as they are at increased Fasting IRI (pmol/l) 68 Ϯ 757Ϯ 6 risk of developing hyperglycemia, they Fasting ALI (pmol/l) 5.5 Ϯ 0.6 4.7 Ϯ 0.7 also represent an appropriate cohort for Data are means Ϯ SEM. examining whether amylin responses are altered in high-risk subjects. Therefore, were obtained 2, 3, 4, 5, 6, 8, 10, 12, 14, as the insulin sensitivity index (SI) and we have examined a group of first-degree 16, 19, 22, 23, 24, 25, 27, 30, 35, 40, 50, glucose effectiveness at basal insulin (SG) relatives of subjects with type 2 diabetes 60, 70, 80, 90, 100, 120, 140, 160, 180, (28). Glucose effectiveness at zero insulin ϭ Ϫ ϫ and a control group and quantified insu- 200, 220, and 240 min after glucose ad- [GEZI SG (SI fasting IRI)] was cal- lin sensitivity and both insulin and amylin ministration. The administration of tol- culated as a measure of insulin-indepen- responses as measures of ␤-cell function butamide and the prolonged sampling dent glucose disposal (31). The in these individuals to determine whether schedule served to improve the ability to intravenous glucose–induced acute insu- these variables are altered in these high- identify the parameters (27) when the lin (AIRg) and acute amylin (AARg)re- risk subjects. In the process, we also ex- glucose and insulin data were analyzed sponses were calculated as the mean amined whether differential alterations in using the minimal model of glucose kinet- incremental response above basal from insulin and amylin responses may pro- ics developed by Bergman et al. (28). All the samples drawn during the first 10 min vide an additional useful marker for sub- samples were assayed for glucose and in- after intravenous glucose administration. jects at high risk of developing type 2 sulin, whereas only the basal samples and The percentile ranking for each individu- diabetes. those drawn up to 10 min after glucose al’s product of SI and AIRg (disposition injection were assayed for amylin. index) was determined using the formula RESEARCH DESIGN AND ␣ϭ ϫ ϩ METHODS Assays Z [ln(SI AIRg) 3.802]/0.5613 All blood samples were drawn into tubes Subjects containing EDTA, kept on ice before sep- which was originally determined by our The groups consisted of 30 (9 males/21 aration, and subsequently stored at Ϫ70°C group in a cohort of 93 apparently healthy females) individuals with at least one first- before being assayed. Plasma glucose was subjects (13). degree relative with a known diagnosis of measured by an automated glucose oxi- The glucose disappearance constant type 2 diabetes and 24 (14 males/10 fe- dase method. Plasma immunoreactive was calculated as the slope of the regres- males) subjects who had no known family insulin (IRI) was measured by a radioim- sion line relating the natural log of the history of type 2 diabetes.