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Couch CA, Piccinini F, Fowler LA, Garvey WT, Gower BA. Proinsulin-to-C-Peptide Ratio as a Marker of β-Cell Function in African American and European American Adults. Diabetes Care 2023; 46:2129-2136. [PMID: 36787895 PMCID: PMC10698211 DOI: 10.2337/dc22-1763] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/09/2022] [Accepted: 01/17/2023] [Indexed: 02/16/2023]
Abstract
OBJECTIVE The primary purpose of the current study was to test the hypothesis that the proinsulin-to-C-peptide (PI-to-CP) ratio, as an index of proinsulin secretion, would be higher and associated with indices of β-cell function in African American adults relative to European American adults without type 2 diabetes. RESEARCH DESIGN AND METHODS Participants were 114 African American and European American adult men and women. A 2-h oral glucose tolerance test was conducted to measure glucose, insulin, C-peptide, and proinsulin and derive indices of β-cell response to glucose. The Matsuda index was calculated as a measure of insulin sensitivity. The disposition index (DI), the product of insulin sensitivity and β-cell response, was calculated for each phase of β-cell responsivity. Pearson correlations were used to investigate the relationship of the PI-to-CP ratio with each phase of β-cell response (basal, Φb; dynamic, Φd; static, Φs; total, Φtot), disposition indices (DId, DIs, DItot), and insulin sensitivity. Multiple linear regression analysis was used to evaluate independent contributions of race, BMI, and glucose tolerance status on PI-to-CP levels before and after adjustment for insulin sensitivity. RESULTS African American participants had higher fasting and 2-h PI-to-CP ratios. The fasting PI-to-CP ratio was positively associated with Φb, and the fasting PI-to-CP ratio and 2-h PI-to-CP ratio were inversely associated with DId and insulin sensitivity only in African American participants. CONCLUSIONS The PI-to-CP ratio could be useful in identifying African American individuals at highest risk for β-cell dysfunction and ultimately type 2 diabetes.
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Affiliation(s)
- Catharine A. Couch
- Department of Nutrition Sciences, University of Alabama at Birmingham, Birmingham, AL
| | - Francesca Piccinini
- Department of Nutrition Sciences, University of Alabama at Birmingham, Birmingham, AL
| | - Lauren A. Fowler
- Department of Nutrition Sciences, University of Alabama at Birmingham, Birmingham, AL
| | - W. Timothy Garvey
- Department of Nutrition Sciences, University of Alabama at Birmingham, Birmingham, AL
| | - Barbara A. Gower
- Department of Nutrition Sciences, University of Alabama at Birmingham, Birmingham, AL
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Skytte MJ, Samkani A, Astrup A, Frystyk J, Rehfeld JF, Holst JJ, Madsbad S, Burling K, Fenger M, Thomsen MN, Larsen TM, Krarup T, Haugaard SB. Effects of carbohydrate restriction on postprandial glucose metabolism, β-cell function, gut hormone secretion, and satiety in patients with Type 2 diabetes. Am J Physiol Endocrinol Metab 2021; 320:E7-E18. [PMID: 33103448 DOI: 10.1152/ajpendo.00165.2020] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Dietary carbohydrate restriction may improve the phenotype of Type 2 diabetes (T2D) patients. We aimed to investigate 6 wk of carbohydrate restriction on postprandial glucose metabolism, pancreatic α- and β-cell function, gut hormone secretion, and satiety in T2D patients. Methods In a crossover design, 28 T2D patients (mean HbA1c: 60 mmol/mol) were randomized to 6 wk of carbohydrate-reduced high-protein (CRHP) diet and 6 wk of conventional diabetes (CD) diet (energy-percentage carbohydrate/protein/fat: 30/30/40 vs. 50/17/33). Twenty-four-hour continuous glucose monitoring (CGM) and mixed-meal tests were undertaken and fasting intact proinsulin (IP), 32,33 split proinsulin concentrations (SP), and postprandial insulin secretion rates (ISR), insulinogenic index (IGI), β-cell sensitivity to glucose (Bup), glucagon, and gut hormones were measured. Gastric emptying was evaluated by postprandial paracetamol concentrations and satiety by visual analog scale ratings. A CRHP diet reduced postprandial glucose area under curve (net AUC) by 60% (P < 0.001), 24 h glucose by 13% (P < 0.001), fasting IP and SP concentrations (both absolute and relative to C-peptide, P < 0.05), and postprandial ISR (24%, P = 0.015), while IGI and Bup improved by 31% and 45% (both P < 0.001). The CRHP diet increased postprandial glucagon net AUC by 235% (P < 0.001), subjective satiety by 18% (P = 0.03), delayed gastric emptying by 15 min (P < 0.001), decreased gastric inhibitory polypeptide net AUC by 29% (P < 0.001), but had no significant effect on glucagon-like-peptide-1, total peptide YY, and cholecystokinin responses. A CRHP diet reduced glucose excursions and improved β-cell function, including proinsulin processing, and increased subjective satiety in patients with T2D.
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Affiliation(s)
- Mads J Skytte
- Department of Endocrinology, Copenhagen University Hospital, Bispebjerg, Denmark
| | - Amirsalar Samkani
- Department of Endocrinology, Copenhagen University Hospital, Bispebjerg, Denmark
| | - Arne Astrup
- Department of Nutrition, Exercise and Sports, University of Copenhagen, Copenhagen, Denmark
| | - Jan Frystyk
- Department of Clinical Medicine, Aarhus University, Aarhus, Denmark
| | - Jens F Rehfeld
- Department. of Clinical Biochemistry, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark
| | - Jens J Holst
- Novo Nordisk Foundation Center for Basic Metabolic Research and Department of Biomedical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Sten Madsbad
- Department of Endocrinology, Copenhagen University Hospital Hvidovre, Copenhagen, Denmark
| | - Keith Burling
- Core Biochemical Assay Laboratory, Cambridge University Hospitals National Health Service Foundation Trust, Cambridge, United Kingdom
| | - Mogens Fenger
- Department of Clinical Biochemistry, Copenhagen University Hospital Hvidovre, Copenahagen, Denmark
| | - Mads N Thomsen
- Department of Endocrinology, Copenhagen University Hospital, Bispebjerg, Denmark
| | - Thomas M Larsen
- Department of Nutrition, Exercise and Sports, University of Copenhagen, Copenhagen, Denmark
| | - Thure Krarup
- Department of Endocrinology, Copenhagen University Hospital, Bispebjerg, Denmark
| | - Steen B Haugaard
- Department of Endocrinology, Copenhagen University Hospital, Bispebjerg, Denmark
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Smith SA, Porter LE, Biswas N, Freed MI. Rosiglitazone, but not glyburide, reduces circulating proinsulin and the proinsulin:insulin ratio in type 2 diabetes. J Clin Endocrinol Metab 2004; 89:6048-53. [PMID: 15579757 DOI: 10.1210/jc.2004-0705] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/12/2023]
Abstract
An elevation in the ratio of proinsulin (PI) to immunoreactive insulin (IRI) is inversely related to beta-cell function in type 2 diabetes, and increased PI is an independent risk factor for coronary heart disease. An objective of the present studies was to assess the effects of the thiazolidinedione insulin sensitizer, rosiglitazone, on indirect markers of beta-cell function and cardiovascular risk in people with type 2 diabetes by measuring plasma PI and the PI:IRI ratio. Parameters of insulin processing, including plasma PI and PI:IRI ratios, were determined in type 2 diabetes patients enrolled in two randomized double-blind studies comparing the effects of rosiglitazone (4 or 8 mg/d) with placebo (study 1, 26-wk treatment) or the sulfonylurea glyburide (study 2, 52-wk treatment). Treatment with rosiglitazone for 26 wk (study 1) produced significant dose-dependent decreases in both plasma PI concentrations (18-29%) and the PI:IRI ratio compared with baseline (7-14%) and placebo (19-29%) (P < 0.001). A significant increase in the PI:IRI ratio in placebo-treated patients occurred (P < 0.001). In study 2, rosiglitazone also significantly reduced both plasma PI and the PI:IRI ratio compared with baseline (P < 0.001). In contrast, glyburide significantly increased both plasma PI (45%; P < 0.001) and the PI:IRI ratio (10%) (P < 0.05 vs. baseline). These results show that rosiglitazone and glyburide have differential effects on absolute PI levels and the PI:IRI ratio in people with type 2 diabetes.
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Affiliation(s)
- Stephen A Smith
- Scientific Affairs, Diabetes, GlaxoSmithKline, Harlow, Essex, CM19 5AW, United Kingdom.
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Petrie HJ, Chown SE, Belfie LM, Duncan AM, McLaren DH, Conquer JA, Graham TE. Caffeine ingestion increases the insulin response to an oral-glucose-tolerance test in obese men before and after weight loss. Am J Clin Nutr 2004; 80:22-8. [PMID: 15213023 DOI: 10.1093/ajcn/80.1.22] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
BACKGROUND Caffeine ingestion decreases the insulin sensitivity index (ISI) for an oral-glucose-tolerance test (OGTT) and decreases insulin-induced glucose disposal in lean male subjects during a hyperinsulinemic clamp. OBJECTIVE We examined the effects of caffeine ingestion on insulin and glucose homeostasis in obese men before and after a nutrition and exercise intervention. DESIGN Nine sedentary, obese [body mass index (in kg/m(2)): 34.0 +/- 1.0] men who had refrained from exercise and caffeine ingestion for 48 h underwent 2 oral-glucose-tolerance tests (OGTTs). The subjects randomly received caffeine (5 mg/kg) or placebo 1 h before each OGTT. After a 12-wk nutrition and exercise intervention, during which time the subjects avoided dietary caffeine, the OGTTs were repeated. RESULTS The intervention resulted in decreases (P < or = 0.05) in body weight (8.5 +/- 1.5 kg), percentage body fat (2.8 +/- 0.7%), and fasting glucose, insulin, and proinsulin concentrations and increases in the ISI for the placebo OGTT (P < or = 0.05). Caffeine caused a greater (P < or = 0.05) OGTT insulin response and a lower (P < or = 0.05) ISI both before and after weight loss. The proinsulin-insulin ratio indicated that neither weight loss nor caffeine affected the nature of the beta cell secretion of insulin. CONCLUSIONS A nutrition and exercise intervention improved, whereas caffeine ingestion impaired, insulin-glucose homeostasis in obese men. The results are consistent with previous findings that caffeine ingestion contributes to insulin resistance.
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Affiliation(s)
- Heather J Petrie
- Department of Human Biology and Nutritional Sciences, University of Guelph, Ontario, Canada
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Hanley AJG, McKeown-Eyssen G, Harris SB, Hegele RA, Wolever TMS, Kwan J, Zinman B. Cross-sectional and prospective associations between abdominal adiposity and proinsulin concentration. J Clin Endocrinol Metab 2002; 87:77-83. [PMID: 11788626 DOI: 10.1210/jcem.87.1.8139] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/12/2023]
Abstract
The objective of this study was to investigate the associations of total and abdominal obesity with variation in proinsulin concentration in a Native Canadian population experiencing an epidemic of type 2 diabetes mellitus (DM). Between 1993 and 1995, 728 members of a Native Canadian community participated in a population-based survey to determine the prevalence and risk factors for type 2 DM. Samples for glucose, C-peptide, and proinsulin were drawn after an overnight fast, and a 75-g oral glucose tolerance test was administered. Type 2 DM and impaired glucose tolerance (IGT) were diagnosed using World Health Organization criteria. Height, weight, waist circumference, and percent body fat were measured. In 1998, 95 individuals who, at baseline, had IGT or normal glucose tolerance with an elevated 2-h glucose level (> or = 7.0 mM) participated in a follow-up evaluation using the same protocol. After adjustment for age, sex, C-peptide concentration, per cent body fat, and waist circumference, proinsulin was found to be significantly elevated in diabetic subjects, relative to subjects with both impaired and normal glucose tolerance (both P < 0.0001); and the concentration in those with IGT was higher, compared with normals (P < 0.0001). Among nondiabetic subjects, proinsulin showed significant univariate associations with percent body fat, body mass index, and waist circumference (r = 0.34, 0.45, 0.41, respectively, all P < 0.0001). After adjustment for body fat and other covariates, waist circumference remained significantly associated with proinsulin concentration in nondiabetic subjects (r = 0.20, P < 0.0001). In prospective analysis, adjusted for covariates (including baseline IGT and follow-up glucose tolerance status), baseline waist circumference was positively associated with both follow-up and change in proinsulin concentration (r = 0.27, P = 0.01; r = 0.24, P = 0.03, respectively). These data highlight the detrimental effects of abdominal obesity on beta-cell function, and support the hypothesis that beta-cell dysfunction occurs early in the natural history of glucose intolerance.
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Affiliation(s)
- Anthony J G Hanley
- Department of Public Health Sciences, University of Toronto, Ontario M5S 1A8, Canada.
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Hanley AJ, McKeown-Eyssen G, Harris SB, Hegele RA, Wolever TM, Kwan J, Connelly PW, Zinman B. Cross-sectional and prospective associations between proinsulin and cardiovascular disease risk factors in a population experiencing rapid cultural transition. Diabetes Care 2001; 24:1240-7. [PMID: 11423509 DOI: 10.2337/diacare.24.7.1240] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
OBJECTIVE To examine cross-sectional and prospective associations between proinsulin and cardiovascular disease risk factors using data from a population-based study of type 2 diabetes among Native Canadians. RESEARCH DESIGN AND METHODS Between 1993 and 1995, 72% of eligible members of a Native Canadian community participated in a baseline diabetes prevalence survey. Fasting samples were collected for glucose, C-peptide, proinsulin, lipids, and apolipoproteins. A 75-g oral glucose tolerance test was administered, and a second sample for glucose was drawn after 120 min. Blood pressure and waist circumference were determined. In the present study, subjects with normal glucose tolerance (NGT) (n = 505) and impaired glucose tolerance (IGT) (n = 74) were included in cross-sectional analyses. In 1998, 95 individuals who had IGT or NGT at baseline with an elevated 2-h glucose concentration (> or = 7.0 mmol/l) participated in a follow-up evaluation using the protocol used at baseline. Cross-sectional and prospective associations between proinsulin and cardiovascular risk factors were assessed using correlation and multiple linear regression analyses. RESULTS After adjustment for covariates including age, sex, C-peptide, waist circumference, and glucose tolerance status, fasting proinsulin concentration was significantly associated with concurrently measured lipid and apolipoprotein concentrations (triglycerides: r = 0.18, P < 0.0001; total cholesterol: r = 0.10, P = 0.02; LDL cholesterol: r = 0.11, P = 0.01; HDL cholesterol: r = -0.16, P = 0.0002; apolipoprotein (apo) B: r = 0.17, P < 0.0001; apoAI: r = -0.11, P = 0.008). In the adjusted prospective analysis, baseline triglycerides, HDL cholesterol, and apoB were associated with changes over time in proinsulin (r = 0.23, P = 0.04; r = -0.30, P = 0.01; r = 0.23, P = 0.04; respectively). CONCLUSIONS These results confirm previously reported cross-sectional associations between proinsulin and lipid concentrations. In addition, an unexpected association between baseline lipids and proinsulin change was documented.
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Affiliation(s)
- A J Hanley
- Department of Public Health Sciences, University of Toronto, Toronto, Ontario, Canada
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8
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MacNamara CM, Barrow BA, Manley SE, Levy JC, Clark A, Turner RC. Parallel changes of proinsulin and islet amyloid polypeptide in glucose intolerance. Diabetes Res Clin Pract 2000; 50:117-26. [PMID: 10960722 DOI: 10.1016/s0168-8227(00)00188-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Elevated proinsulin secretion and islet amyloid deposition are both features of Type 2 diabetes but their relationship to beta-cell dysfunction is unknown. To determine if islet amyloid polypeptide (IAPP) secretion is disproportionate with other beta-cell products at any stage of glucose intolerance, 116 subjects were studied. Non-diabetic subjects with equivalent body mass index (BMI) were assigned to three groups, (i) normal fasting glucose, fpg<5.5 mmol l(-1); (ii) intermediate fasting glucose, fpg> or =5.5<6.15 mmol l(-1); (iii) impaired fasting glucose (IFG), fpg> or =6.1<7.0 mmol l(-1). Diabetic subjects were divided according to therapy (9 diet, 19 tablet, and 11 insulin). IAPP, C-peptide and proinsulin were measured fasting and at the end of a 1-h glucose infusion. Fasting C-peptide, IAPP and proinsulin were significantly elevated in the IFG group compared with the other non-diabetic groups (P<0.02); fasting IAPP/C-peptide and proinsulin/C-peptide were 1-2% in all non-diabetic groups. Fasting and 1-h proinsulin and proinsulin/C-peptide were higher in diabetic compared with non-diabetic subjects (P<0.01). IAPP and IAPP/C-peptide in diabetic groups were similar to that in non-diabetic subjects but reduced in the insulin-treated group (P<0.01). Proinsulin was disproportionately increased compared with C-peptide and IAPP in Type 2 diabetes particularly in severe beta-cell failure implying more than one concurrent beta-cell pathology.
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Affiliation(s)
- C M MacNamara
- Diabetes Research Laboratories, Radcliffe Infirmary, Woodstock Road, OX2 6HE, Oxford, UK
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Piemonti L, Bertuzzi F, Nano R, Leone BE, Socci C, Pozza G, Di Carlo V. Effects of cryopreservation on in vitro and in vivo long-term function of human islets. Transplantation 1999; 68:655-62. [PMID: 10507485 DOI: 10.1097/00007890-199909150-00011] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
BACKGROUND The possibility of performing transplantation several days after explant seems to be a peculiarity of islet grafts, and the opportunity to cryopreserve human islets may permit an indefinite period for modulating the recipient immune system. The aim of the present study was the evaluation of in vitro and in vivo functional properties of cryopreserved human islets. METHODS We used six consecutive human islet preparations not suitable for an immediate transplantation in diabetic patients because the limited islet mass separated. The in vitro function of cryo and fresh islets was studied by determination of insulin and glucagon secretion in response to such classical stimuli as glucose (16.7 mM), glucose (16.7 mM) + 3-isobutyl-1-methylxanthine (0.1 mM), arginine (10 mM), and tolbutamide (100 microM). In vivo islet function was assessed through intravenous glucose tolerance tests performed at 15, 30, 60, and 90 days after transplantation of 1000 hand-picked fresh or cryopreserved islets in nude mice. RESULTS Basal secretion of true insulin was significantly higher in cryopreserved islets than in fresh ones. The response of cryopreserved islets to arginine and glucose + isobutyl-1-methylxanthine seemed partially impaired. Proinsulin-like molecule secretion seemed higher in cryopreserved than in fresh islets in response to all secretagogues used, and the difference was statistically significant for arginine. The capacity of human cryopreserved islets to maintain a correct metabolic control in diabetic nude mice was progressively lost in 3 months. CONCLUSIONS These findings showed that cryopreservation affects the function of isolated human islets, maintaining in vivo function for a limited period of time.
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Affiliation(s)
- L Piemonti
- Department of Surgery, Istituto Scientifico San Raffaele, Università degli Studi di Milano, Milan, Italy.
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Babazono T, Teraoka S, Tomonaga O, Iwamoto Y, Omori Y. Circulating proinsulin levels in insulin-dependent diabetic patients after whole pancreas-kidney transplantation. Metabolism 1998; 47:1325-30. [PMID: 9826207 DOI: 10.1016/s0026-0495(98)90299-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Disproportional hyperproinsulinemia is a sensitive marker for beta-cell dysfunction. The objective of this study was to assess the proinsulin profile in persons with insulin-dependent diabetes mellitus (IDDM) after pancreas-kidney transplantation. We determined serum insulin, C-peptide, and proinsulin concentrations during an oral glucose challenge in five pancreas-kidney transplant recipients, nine nondiabetic kidney transplant recipients, and 17 normal subjects. Basal proinsulin concentrations were significantly increased in pancreas-kidney recipients (geometric mean [+/-1 SE range], 6.0 [5.5 to 6.4] pmol/L) and kidney recipients (6.4 [5.4 to 7.5] pmol/L) compared with the normal subjects (2.8 [2.5 to 3.2] pmol/L). Integrated proinsulin concentrations during the oral glucose load were also higher in pancreas-kidney recipients (1.4 [1.1 to 1.8] nmol/L x min) and kidney recipients (1.5 [1.2 to 2.0] nmol/L x min) versus normal subjects (0.8 [0.7 to 0.9] nmol/L x min). There was no difference in basal or integrated proinsulin concentrations between the two transplant groups. Even after adjustment for the glomerular filtration rate (GFR), basal and incremental proinsulin concentrations continued to be higher in the transplant groups than in the normal subjects. Proinsulin to C-peptide molar ratios both before and after the glucose load were similar in the three groups. From these findings, we conclude that pancreas-kidney transplantation provokes proportional hyperproinsulinemia, which is closely associated with its reduced clearance in the kidneys.
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Affiliation(s)
- T Babazono
- Department of Medicine, Diabetes Center, Tokyo Women's Medical College, Japan
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Harvey J, Ashford ML. Insulin occludes leptin activation of ATP-sensitive K+ channels in rat CRI-G1 insulin secreting cells. J Physiol 1998; 511 ( Pt 3):695-706. [PMID: 9714853 PMCID: PMC2231169 DOI: 10.1111/j.1469-7793.1998.695bg.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
1. Using whole-cell and cell-attached recording configurations, the effects of insulin on leptin activation of ATP-sensitive K+ (KATP) channels were examined in the CRI-G1 insulinoma cell line. 2. Whole-cell recordings demonstrated that the leptin-induced hyperpolarization and increased potassium conductance are completely occluded by prior exposure to insulin (1-50 nM). In cell-attached recordings, insulin prevented leptin activation of tolbutamide-sensitive KATP channels. Furthermore, insulin (50 nM) slowly and completely reversed the effects of leptin (10 nM), an action not attributable to direct inhibition of KATP channels per se. 3. Low concentrations of insulin-like growth factor-1 (IGF-1; 10-100 nM) failed to prevent leptin activation of KATP channels, although higher concentrations (1 microM) did inhibit leptin actions. 4. The action of insulin was specific for leptin, as the hyperglycaemic agent diazoxide activated KATP channels following prior exposure to insulin. 5. Wortmannin (1-10 nM) and LY 294002 (10 microM) prevented leptin activation of KATP channels, indicating an involvement of phosphoinositide 3-kinase (PI 3-kinase). 6. In conclusion, leptin activation of KATP channels is counter-regulated by insulin in the CRI-G1 insulinoma cell line. This feedback mechanism may be important in the local integration of hormonal signals which regulate insulin secretion and in alterations of metabolic homeostasis associated with obesity and non-insulin dependent diabetes mellitus (NIDDM).
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Affiliation(s)
- J Harvey
- Department of Biomedical Sciences, Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, UK
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12
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Snehalatha C, Ramachandran A, Satyavani K, Vijay V, Haffner SM. Specific insulin and proinsulin concentrations in nondiabetic South Indians. Metabolism 1998; 47:230-3. [PMID: 9472976 DOI: 10.1016/s0026-0495(98)90226-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The study was performed to determine plasma levels of proinsulin (PI) and specific insulin (SI) in normoglycemic (NGT) Asian Indians and to assess the effect of obesity and impaired glucose tolerance (IGT) on these concentrations. Blood samples from 151 adult nondiabetic South Indian subjects were collected during an epidemiological survey of diabetes. Plasma SI and PI levels were measured in fasting and 30-minute and 120-minute samples of a glucose tolerance test (World Health Organization criteria) using monospecific antibodies. The total insulin (TI) level was also measured by the nonspecific assay. The molar ratio of PI to SI (PI/SI) was calculated. Correlations of the peptides with anthropometry, serum lipids, and blood pressure (BP) were studied by univariate and multivariate analyses. Comparisons were also made in NGT versus IGT groups. As expected, TI values were higher than SI values, but the patterns of response were similar for both. SI and PI responses in NGT were similar to the values found in Mexican-Americans who had a higher body mass index (BMI). Asian Indians were thus found to have a high SI response despite a low BMI. Obesity and IGT produced an increased response of both PI and SI, with normal PI/SI ratios thus showing an absence of hyperproinsulinemia in either condition. Fasting PI showed a strong association with serum triglycerides, and proinsulin at 120 minutes was associated with cholesterol. None of the peptides showed a correlation with BP. Using specific assays for insulin and PI, it is shown that Asian Indians with NGT have a hyperinsulinemic response despite a low BMI. Obesity and mild hyperglycemia in IGT produce a simultaneous increase in PI and SI with no alteration in the PI/SI ratio.
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Affiliation(s)
- C Snehalatha
- Diabetes Research Centre, Royapuram, Madras, India
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Affiliation(s)
- A A Alzaid
- Riyadh Armed Forces Hospital, Kingdom of Saudi Arabia
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14
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Seaquist ER, Kahn SE, Clark PM, Hales CN, Porte D, Robertson RP. Hyperproinsulinemia is associated with increased beta cell demand after hemipancreatectomy in humans. J Clin Invest 1996; 97:455-60. [PMID: 8567967 PMCID: PMC507037 DOI: 10.1172/jci118435] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The cause of disproportionate hyperproinsulinemia in patients with type II diabetes is controversial. To examine whether increased beta cell demand might contribute, we measured proinsulin and insulin concentrations in clinically healthy humans who had undergone hemipancreatectomy for the purpose of organ donation, a procedure previously demonstrated to increase beta cell demand and diminish insulin secretory reserve capacity. Subjects were studied at least 1 yr after hemipancreatectomy. Seven donors were followed prospectively and serves as their own controls. Nine additional donors were matched with normal controls (cross-sectional group). Fasting serum concentrations of intact proinsulin and conversion intermediates (total) were measured by a two-step radioimmunoassay; independent determinations of intact proinsulin and 32,33 split proinsulin were performed using an immunoradiometric assay. Serum total proinsulin values were significantly greater in hemipancreatectomized groups than controls (prospective group: predonation = 6.24 +/- 1.14 pM, postdonation = 34.63 +/- 17.47 pM, P < 0.005; cross-sectional group: controls = 5.78 +/- 1.12 pM, donors = 15.22 +/- 5.20 pM, P < 0.025). The ratio of total proinsulin to immunoreactive insulin was directly correlated with fasting plasma glucose and showed a significant inverse relationship to secretory reserve capacity. Both absolute and relative hyperproinsulinemia is found in hemipancreatectomized donors. These data demonstrate that partial pancreatectomy with its associated increase in beta cell demand raises measures of proinsulin in humans.
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Affiliation(s)
- E R Seaquist
- Department of Medicine, University of Minnesota, Minneapolis 55455, USA
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Mykkänen L, Haffner SM, Kuusisto J, Pyörälä K, Hales CN, Laakso M. Serum proinsulin levels are disproportionately increased in elderly prediabetic subjects. Diabetologia 1995; 38:1176-82. [PMID: 8690169 DOI: 10.1007/bf00422366] [Citation(s) in RCA: 54] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Insulin resistance and impaired insulin secretion are thought to be the primary defects in the pathogenesis of non-insulin-dependent diabetes mellitus (NIDDM). Disproportionately increased proinsulin relative to insulin levels are suggested to be an early indicator of a failing pancreas. We examined the relationship of fasting specific insulin, proinsulin, and 32, 33 split proinsulin concentrations, and the proinsulin: insulin ration to the risk of developing NIDDM 3.5 years later in 65-74-year-old non-diabetic Finnish subjects participating in a population-based study (n=892) on diabetes and heart disease. Altogether 69 subjects developed NIDDM over a 3.5-year follow-up (cases). The cases were compared to randomly-selected gender-matched control subjects (n=69) and control subjects matched for gender, glucose tolerance status (normal or impaired), and body mass index (n=69). There were no differences in insulin concentrations between cases and random or matched control subjects [median and interquartile range: 123 (77-154), 108 (74-143), 118 (83-145) pmol/l, p=0.271]. Random control subjects had lower proinsulin and 32, 33 split proinsulin concentrations and split proinsulin: insulin ratios compared to cases [5.7 (3.8-9.0) vs 7.3 (4.8-10.0) pmol/l, p=0.005; 7.3 (4.5-13.0 vs 10.4 (7.1-18.0) pmol/l, p=0.002; 0.073 (0.057-0.110) vs 0.097 (0.060- 0.135), p=0.003]. Matched control subjects had lower proinsulin concentrations and proinsulin: insulin ratios compared to cases [5.9 (4.0-7.7) vs 7.3 (4.8-10.0) pmol/l, p=0.019; 0.048 (0.035-0.071) vs 0.064 (0.045-0.100), p=0.008]. When cases were compared to matched control subjects a 1 SD increase in baseline proinsulin: insulin ratio was associated with a 1.37-fold risk (p=0.020) of developing diabetes. Moreover, this association was independent of fasting glucose concentration at baseline. Thus, in elderly prediabetic subjects disproportionately increased proinsulin concentration, an indicator of defective insulin secretion, is associated with conversion to diabetes over a short time period.
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Affiliation(s)
- L Mykkänen
- Department of Medicine, University of Kuopio, Finland
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Kumakura S, Iwamoto Y, Kuzuya T, Shiraishi I, Matsuda A, Saito T. Elevated ratio of summed serum proinsulin to insulin response after oral glucose load in type 2 diabetes decreases following sulfonylurea treatment. Diabetes Res Clin Pract 1995; 29:107-12. [PMID: 8591697 DOI: 10.1016/0168-8227(95)01127-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
We showed previously that the disproportionate elevation of serum proinsulin at fasting and after glucose ingestion in Type 2 diabetes is reduced to nearly normal after improvement of glycemic control by diet therapy. In this study, we investigated the effect of sulfonylurea (SU) treatment on serum proinsulin levels and proinsulin/insulin ratio (PI/I) during oral glucose tolerance test in patients with Type 2 diabetes. Thirteen diabetic patients (age 56 +/- 9 years, body mass index 22.4 +/- 1.9 kg/m2, mean +/- SD) were examined by 75 g oral glucose tolerance test (OGTT) before and after glycemic control by SU therapy. Mean interval of two OGTTs was 126 days. Serum proinsulin was measured by the radioimmunoassay using a human proinsulin-specific antiserum. When glycemic control improved after SU therapy (mean fasting plasma glucose 11.5 and 6.0 mmol/l, before and after SU treatment), fasting insulin, proinsulin and PI/I ratio did not change significantly. Insulin response during OGTT markedly increased after SU therapy. Summed value of insulin (sigma I) increased from 634 to 1064 pmol/l after SU (P < 0.01), whereas summed proinsulin (sigma PI) did not change significantly (146 and 159 pmol/l), resulting in a significant decrease in sigma PI/sigma I (23.6-15.1%, P < 0.05). We conclude that the disproportionate elevation of proinsulin during OGTT in patients with Type 2 diabetes can be reduced after glycemic control by SU treatment, chiefly by a selective increase in insulin response.
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Affiliation(s)
- S Kumakura
- Division of Endocrinology and Metabolism, Jichi Medical School, Tochigi-ken, Japan
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Monti LD, Sandoli EP, Phan VC, Piatti PM, Costa S, Secchi A, Pozza G. A sensitive and reliable method for assaying true human insulin without interaction with human proinsulin-like molecules. Acta Diabetol 1995; 32:57-63. [PMID: 7612920 DOI: 10.1007/bf00581048] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
In the present study our interests focused on the evaluation of a high capacity assay (MEIA) which allows true insulin determinations in the absence of cross-reactivity with proinsulin-like molecules. This method was compared to a commercially available radioimmunoassay (RIA) for insulin determination. As the latter gives insulin levels which represent a mixture of insulin and proinsulin-like molecules, the proinsulin-like molecules were quantitated by subtracting the true insulin levels measured using MEIA from the total insulin levels obtained using RIA. These methods were applied for the analysis of blood samples drawn in 63 normal subjects, 16 obese subjects, 3 patients submitted to islet transplantation and 4 patients with insulinoma. The MEIA was precise, fully automated and time-saving, making its application on a routine basis particularly attractive. MEIA and RIA were equally able to correctly quantify human insulin molecules. On the contrary, the antibody present in the true insulin assay did not interact with proinsulin-like molecules, which were recognized even in the presence of increasing insulin levels. In normal subjects, the true and total insulin levels in the fasting state and at the time peak after glucose- or arginine-induced endogenous insulin release were well correlated at r = 0.88 and 0.89, respectively. Interestingly, total insulin values were overestimated by 10%-16% as compared with true insulin levels, which represent proinsulin values superimposable on previously reported data. Proinsulin-like molecules made up 50% of the total insulin in obese and transplanted patients, and about 70% in patients with insulinoma.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- L D Monti
- Department of Medicine, Istituto Scientifico H. San Raffaele, Milan, Italy
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Pontiroli AE, Calderara A, Pozza G. Secondary failure of oral hypoglycaemic agents: frequency, possible causes, and management. DIABETES/METABOLISM REVIEWS 1994; 10:31-43. [PMID: 7956674 DOI: 10.1002/dmr.5610100104] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- A E Pontiroli
- Istituto Scientifico San Raffaele, Università degli Studi di Milano, Italy
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Schmidli RS, Hagan C, Scott RS, Livesey J, Forbes LV. Plasma proinsulin in recently diagnosed type 2 diabetes mellitus. Diabetes Res Clin Pract 1993; 20:133-8. [PMID: 8375266 DOI: 10.1016/0168-8227(93)90007-r] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
We measured levels of immunoreactive insulin (IRI) and proinsulin using a sensitive and specific immunoradiometric assay (IRMA), in non-obese recently diagnosed type 2 diabetic subjects. The proinsulin IRMA showed full cross reaction with intact proinsulin, des 31-32 proinsulin and des 64-65 proinsulin, but no reaction with insulin or C-peptide. In a group of 41 recently diagnosed non-obese Caucasian type 2 diabetic subjects (study group), mean fasting proinsulin levels were greater than that of 40 age and body mass index (BMI) matched controls (study group 17.4 +/- 2.0, controls 10.1 +/- 0.9 pmol-1, P < 0.001). Following a standard test meal, 30 and 60 min levels were not significantly different between groups but 90- and 120-min proinsulin levels were elevated in the study group. The maximum proinsulin to IRI ratio was 20% in the fasting state and did not differ between study and control groups. Proinsulin profiles were similar in subjects receiving oral hypoglycaemic agents and those on dietary treatment alone. Proinsulin did not correlate with indices of glycaemic control, total cholesterol, triglycerides or HDL cholesterol, but a relationship was observed with IRI before and after the meal. These results suggest that increased secretion of insulin precursors of low biological activity occurs in non obese recently diagnosed type 2 diabetic subjects under reasonably good glycaemic control; in such individuals the elevated levels of these precursors are approximately in proportion to the increase in IRI and are less than those reported in some previous studies.
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Affiliation(s)
- R S Schmidli
- Burnet Clinical Research Unit, Walter and Eliza Hall Institute of Medical Research, Melbourne, Victoria, Australia
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Abstract
Cigarette smoking is associated with increases in plasma triglycerides and decreases in plasma high density-lipoprotein-cholesterol concentration. These changes not only increase risk of coronary heart disease but also are secondary to resistance to insulin-stimulated glucose uptake or hyperinsulinaemia. To see whether there is a relation between cigarette smoking and insulin-mediated glucose uptake we measured plasma lipid and lipoprotein concentrations, plasma glucose and insulin response to an oral glucose challenge, and insulin-mediated glucose uptake in 40 matched healthy volunteers (20 non-smokers, 20 smokers). Smokers had significantly higher mean (SEM) very-low-density-lipoprotein triglycerides (0.66 [0.10] vs 0.39 [0.03] mmol/l, p less than 0.02) and cholesterol (0.45 [0.06] vs 0.23 [0.04] mmol/l, p less than 0.005) concentrations and lower high-density-lipoprotein cholesterol concentrations (1.16 [0.05] vs 1.51 [0.08] mmol/l, p less than 0.001). Although plasma glucose concentrations in response to the oral glucose load were similar in the two groups, plasma insulin response of the smokers was significantly higher (p less than 0.001). Finally, smokers had higher steady-state plasma glucose concentrations in response to a continuous infusion of glucose, insulin, and somatostatin (8.4 [0.2] vs 5.0 [0.3] mmol/l, p less than 0.001), despite similar steady-state plasma insulin concentrations. The findings show that chronic cigarette smokers are insulin resistant, hyperinsulinaemic, and dyslipidaemic compared with a matched group of non-smokers, and may help to explain why smoking increases risk of coronary heart disease.
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Affiliation(s)
- F S Facchini
- Department of Medicine, Stanford University School of Medicine, California
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