Epidemiology/Health Services/Psychosocial Research ORIGINAL ARTICLE Fasting Intact Proinsulin Is a Highly Specific Predictor of Insulin Resistance in Type 2 Diabetes 1,2 1 ANDREAS PFUTZNER¨ , MD, PHD SABINE PAHLER, MSC sulin is a commonly secreted by-product 3 4 THOMAS KUNT, MD THOMAS KONRAD, MD of ␤-cell secretion in later stages of type 2 1 5 CLOTH HOHBERG, MD GEORG L¨UBBEN, MD 1 1 diabetes and is involved in the develop- AGNES MONDOK, MD THOMAS FORST, MD ment of macrovascular disease, whereas des64,65 is usually not present in the cir- culation (11,12). Assays that try to differentiate be- OBJECTIVE — In later stages of type 2 diabetes, proinsulin and proinsulin-like molecules are tween intact proinsulin and the specific secreted in increasing amounts with insulin. A recently introduced chemiluminescence assay is and unspecific proinsulin derivatives able to detect the uncleaved “intact” proinsulin and differentiate it from proinsulin-like mole- were used in cross-sectional and prospec- cules. This investigation explored the predictive value of intact proinsulin as an insulin resistance marker. tive follow-up studies to investigate the real relation of immunoreactive insulin RESEARCH DESIGN AND METHODS — In total, 48 patients with type 2 diabetes (20 with coronary risk and to explore and women and 28 men, aged 60 Ϯ 9 years [means Ϯ SD], diabetes duration 5.1 Ϯ 3.8 years, BMI confirm the important role of intact pro- Ϯ 2 Ϯ 31.2 4.8 kg/m , and HbA1c 6.9 1.2%) were studied by means of an intravenous glucose insulin in the prediction and diagnosis of tolerance test and determination of fasting values of intact proinsulin, insulin, resistin, adiponec- type 2 diabetes (13,14). Recent presenta- tin, and glucose. Insulin resistance was determined by means of minimal model analysis (MMA) tions indicate a potential value for fasting (as the gold standard) and homeostatis model assessment (HOMA). intact proinsulin to become a marker of insulin resistance, e.g., to identify patients RESULTS — There was a significant correlation between intact proinsulin values and insulin eligible for an insulin sensitizer therapy resistance (MMA P Ͻ 0.05 and HOMA P Ͻ 0.01). Elevation of intact proinsulin values above the reference range (Ͼ10 pmmol/l) showed a very high specificity (MMA 100% and HOMA 92.9%) (15), or to monitor treatment success dur- and a moderate sensitivity (MMA 48.6% and HOMA 47.1%) as marker for insulin resistance. ing sensitizer treatment (16). Summariz- Adiponectin values were slightly lower in the insulin resistant group, but no correlation to ing all scientific literature, there is a great insulin resistance could be detected for resisitin in the cross-sectional design. likelihood that intact and/or total proin- sulin may become an important diagnos- CONCLUSIONS — Elevated intact proinsulin seems to indicate an advanced stage of ␤-cell tic tool in type 2 diabetes. exhaustion and is a highly specific marker for insulin resistance. It might be used as arbitrary The following cross-sectional study marker for the therapeutic decision between secretagogue, sensitizer, or insulin therapy in type describes the relationship between intact 2 diabetes. proinsulin as measured by means of a re- cently introduced, very specific chemilu- Diabetes Care 27:682–687, 2004 minescence method (17) and several other clinical and biochemical markers of insulin resistance in a well-characterized n the past decades, insulin resistance proinsulin, which was present in many group of 48 patients with dietary and and cardiovascular disease in type 2 di- assays for insulin measurement. Rela- orally treated type 2 diabetes. I abetic patients have been linked to hy- tively few and contradicting data are perinsulinemia as an independent risk available on the relation of proinsulin to factor (1–3). However, many studies were insulin resistance, cardiovascular disease, RESEARCH DESIGN AND not able to confirm the negative impact of and atherosclerosis (6–8). Prospective METHODS — The study was con- insulin on cardiovascular risk (4–6). One studies have demonstrated that the deter- ducted at the Institute for Clinical Re- explanation for this overall confusing data mination of the proinsulin-to-insulin ra- search and Development (Mainz, may be found in the cross-reactivity be- tio may be used to predict deterioration in Germany) in accordance with Good Clin- tween insulin and its precursor molecule, glucose tolerance (9,10). Des31,32 proin- ical Practice Guidelines and was approved ●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●● by the responsible local ethics review committee. In total, 48 patients on oral From the 1Institute for Clinical Research and Development, Mainz, Germany; the 2University of Applied Sciences, Rheinbach, Germany; the 3Department of Internal Medicine, Al Zayed Hospital Abu Dhabi, United anti-diabetic treatment were enrolled in Arab Emirates; the 4Institute for Metabolic Research Frankfurt, Frankfurt, Germany; and 5Takeda Pharma the investigation (20 women and 28 men, Aachen, Germany. aged 60 Ϯ 9 years [means Ϯ SD], diabetes Address correspondence and reprint requests to Andreas Pfu¨ tzner, MD, PhD, Institute for Clinical Re- duration 5.1 Ϯ 3.8 years, BMI 31.2 Ϯ 4.8 search and Development (IKFE) Parcusstr. 8, D-55116 Mainz, Germany. E-mail: [email protected]. 2 Ϯ Received for publication 5 June 2003 and accepted in revised form 11 December 2003. kg/m , and HbA1c 6.9 1.2%). Abbreviations: HOMA, homeostatis model assessment; MMA, minimal model analysis. The patients arrived in the morning of © 2004 by the American Diabetes Association. the study day after an overnight fast, and 682 DIABETES CARE, VOLUME 27, NUMBER 3, MARCH 2004 Pfu¨tzner and Associates Table 1—Patient characteristics for insulin-resistant and insulin-sensitive patients according estimate was expressed as fractional SD to MMA and HOMA analysis (the ratio between the SD of the estimate and the estimated value expressed as a Insulin resistant Insulin sensitive P percentage). Estimation of Si with frac- MMA tional SD Ͼ25% were excluded from fur- n 35 13 ther evaluation. Insulin resistance was Ϫ4 Ϫ1 Age (years) 59 Ϯ 960Ϯ 6NSdefined as values Ͻ1.5 ϫ 10 ⅐ min ⅐ Ϫ1 Ϫ1 Disease duration (months) 54 Ϯ 42 65 Ϯ 46 NS ␮U ⅐ ml (20). Body weight (kg) 94 Ϯ 19 85 Ϯ 13 NS, 0.118 Homeostatis model assessment BMI (kg/m2) 31.8 Ϯ 5.2 29.5 Ϯ 3.3 NS, 0.145 (HOMA) score calculation was applied as Hypertension (number, %) 28 (80%) 10 (77%) NS a second measure for insulin resistance Ϯ Ϯ Ͻ HbA1c (%) 7.1 1.2 6.2 0.6 0.05 analysis as previously described (21). The Fasting glucose (mg/dl) 119 Ϯ 33 102 Ϯ 22 NS, 0.093 estimate of insulin resistance by HOMA Fasting insulin (␮U/ml) 13.1 Ϯ 6.6 9.4 Ϯ 3.9 NS, 0.063 score was calculated with the following Fasting intact proinsulin (pmol/l) 19.9 Ϯ 11.7 6.0 Ϯ 2.6 Ͻ0.01 formula: fasting serum insulin (␮U/ml) ϫ Proinsulin/insulin ratio (pmol/mU) 1.21 Ϯ 0.70 0.71 Ϯ 0.36 Ͻ0.05 fasting plasma glucose (mmol/l)/22.5. As Fasting resistin (ng/l) 0.07 Ϯ 0.12 0.11 Ϯ 0.18 NS described by Hedblad et al. (22), patients Fasting adiponectin (␮/ml) 7.05 Ϯ 4.43 9.70 Ϯ 5.66 NS, 0.095 with HOMA score values exceeding the Fibrinogen (mg/dl) 2.9 Ϯ 0.9 2.6 Ϯ 0.6 NS 75th percentile (i.e., 2.0) were considered HOMA analysis to have insulin resistance. n 34 14 Glucose levels were determined using Age (years) 58 Ϯ 962Ϯ 6 NS, 0.92 a standard laboratory reference method Disease duration (months) 54 Ϯ 34 63 Ϯ 59 NS (glucose oxidase method) (Super GL RLT, Body weight (kg) 96 Ϯ 17 81 Ϯ 14 Ͻ0.01 Mo¨hnesee, Germany). Lipid values (tri- BMI (kg/m2) 32.3 Ϯ 4.9 28.5 Ϯ 3.5 Ͻ0.05 glycerides, total cholesterol, and HDL Hypertension (%) 27 (79%) 11 (79%) NS cholesterol) were determined using stan- Ϯ Ϯ Ͻ HbA1c (%) 7.2 1.2 6.2 0.8 0.05 dard dry chemistry methods. Fasting glucose (mg/dl) 126 Ϯ 29 86 Ϯ 13 Ͻ0.001 Insulin and proinsulin were deter- Fasting insulin (␮U/ml) 14.6 Ϯ 5.5 6.0 Ϯ 1.7 Ͻ0.001 mined by means of specific chemilumi- Fasting intact proinsulin (pmol/l) 15.4 Ϯ 11.6 5.3 Ϯ 2.1 Ͻ0.005 nescence tests (MLT insulin [intra- and Proinsulin/insulin ratio (pmol/mU) 1.58 Ϯ 0.66 0.66 Ϯ 0.36 Ͻ0.001 interassay coefficient of variation {CV} 3.8 Fasting resistin (ng/l) 0.08 Ϯ 0.15 0.08 Ϯ 0.11 NS and 2.3%, reference range Ͻ30 ␮U/ml] Fasting adiponectin (␮g/ml) 6.95 Ϯ 4.33 9.77 Ϯ 5.68 NS, 0.068 and MLT Intact Proinsulin [intra- and in- Fibrinogen (mg/dl) 2.8 Ϯ 0.9 2.7 Ϯ 0.6 NS terassay CV 5.2 and 8.6%, reference range Ͻ Data are means Ϯ SD unless otherwise indicated. 10 pmol/l]; Sciema Diagnostics, Mainz, Germany). The tests were carried out as blood samples were taken for the deter- cording to Bergmann by means of the previously described (17). mination of insulin, intact proinsulin, SAAM 1.2 software package (SAAM Insti- Resistin concentrations were deter- glucose, resisitin, adiponectin, and lipids. tute, Seattle, WA). Precision parameters mined by means of a clinical research Thereafter, a standardized modified fre- quently sampled intravenous glucose tol- erance test was performed for the determination of insulin resistance by means of the minimal model analysis (MMA) according to Bergman et al.