A longitudinal study of glucose tolerance in cystic fibrosis: the central role of beta cell functional mass.

CONTEXT: The pathophysiological mechanisms underlying the natural history of glucose intolerance and its fluctuations in subjects with cystic fibrosis (CF) are still unclear. OBJECTIVE: To investigate the relationship between longitudinal changes in glucose tolerance and concomitant changes in the main parameters of insulin secretion/metabolism/action determining glucose regulation in CF subjects. METHODS: Insulin sensitivity and glucose-stimulated insulin secretion (GSIS, a biomarker of beta cell functional mass), as estimated by the Oral Glucose Sensitivity Index (OGIS) and by a sophisticated mathematical model, respectively, and insulin clearance were assessed in 127 CF subjects, aged 10-25 years, who underwent two OGTT tests over at least 1-year follow-up period. Subjects were classified a posteriori as regressors (improved glucose tolerance), stable, or progressors (worsened glucose tolerance). The interplay between beta cell compensatory action and insulin sensitivity over time was analyzed by vector plots of insulin clearance adjusted GSIS (PCadj) versus OGIS. RESULTS: OGIS decreased in progressors and stable. Insulin clearance decreased in both regressors and progressors. GSIS (beta cell functional mass) improved in regressors and worsened in progressors, whereas it did not change in stable. Vector plot analysis confirmed that glucose regulation changed differently in each group. Multinomial logistic regression analysis showed that baseline glucose tolerance and GSIS changes were the only significant predictors of the changes in glucose tolerance (p<0.02, R2Nagelkerke=0.55), whereas age, gender, z-BMI, CF genotypes, and baseline PCadj were not. CONCLUSIONS: In CF subjects, changes in beta cell functional mass are associated with favorable or detrimental changes of glucose tolerance over time.

Crosstalk between genetic variability of adiponectin and leptin, glucose-insulin system and subclinical atherosclerosis in patients with newly diagnosed type 2 diabetes. The Verona Newly Diagnosed Type 2 Diabetes Study 14.

AIM: To evaluate the relationship of genetic variability of adiponectin (ADIPOQ), leptin (LEP) and leptin receptor (LEPR) genes with glucose-insulin system and markers of subclinical atherosclerosis (ATS) in patients with newly diagnosed type 2 diabetes. MATERIALS AND METHODS: In 794 subjects we performed: 1) euglycemic hyperinsulinemic clamp to assess insulin sensitivity; 2) mathematical modelling of a 5h-OGTT to estimate ß-cell function; 3) resting ECG; 4) carotid artery and lower limb artery eco-doppler sonography to identify ATS; 5) genotyping of tag-SNPs within ADIPOQ, LEP and LEPR gene. RESULTS: Regression analyses showed: 1) adiponectin levels were negatively associated with BMI, waist-to-hip ratio and triglycerides and positively with HDL and insulin sensitivity (p-all<0.03); 2) leptin levels were positively associated with BMI, HDL-cholesterol and plasma triglycerides and negatively with insulin sensitivity (p-all<0.001). Two SNPs (rs1501299 and rs2241767) within ADIPOQ gene were associated with circulating levels of adiponectin. The ADIPOQ-GAACA haplotype was associated with plasma adiponectin (p=0.034; ß=-0.24), ECG abnormalities (p=0.012; OR=2.76), carotid ATS (p=0.025; OR=2.00) and peripheral limb artery ATS (p=0.032; OR=1.90). The LEP-CTA haplotype showed an association with ischemic ECG abnormalities (p=0.017; OR=2.24). Finally, LEPR-GAACGG was associated with circulating leptin (p=0.005; ß=-0.31) and worst ß-cell function (p=0.023; ß=-15.10). Omnibus haplotype analysis showed that ADIPOQ haplotypes were associated with levels of adiponectin and common carotid artery ATS, LEP with peripheral limb artery ATS, whereas LEPR haplotypes influenced circulating levels of leptin. CONCLUSIONS: Results of this study reinforce knowledge on adipokines' role in regulating glucose metabolism; in particular highlighted the potential atherogenic role of leptin and the anti atherogenic role of adiponectin.

Impact of CFTR Modulators on Beta-Cell Function in Children and Young Adults with Cystic Fibrosis.

BACKGROUND: To date, no consistent data are available on the possible impact of CFTR modulators on glucose metabolism. The aim of this study was to test the hypothesis that treatment with CFTR modulators is associated with an improvement in the key direct determinants of glucose regulation in children and young adults affected by Cystic Fibrosis (CF). METHODS: In this study, 21 CF patients aged 10-25 underwent oral glucose tolerance test (OGTT) before and after 12-18 months of treatment with Lumacaftor/Ivacaftor or Elexacaftor-Ivacaftor-Tezacaftor. ß-cell function (i.e., first and second phase of insulin secretion measured as derivative and proportional control, respectively) and insulin clearance were estimated by OGTT mathematical modelling. Insulin sensitivity was estimated by the Oral Glucose Sensitivity Index (OGIS). The dynamic interplay between ß-cell function, insulin clearance and insulin sensitivity was analysed by vector plots of glucose-stimulated insulin bioavailability vs. insulin sensitivity. RESULTS: No changes in glucose tolerance occurred after either treatment, whereas a significant improvement in pulmonary function and chronic bacterial infection was observed. Beta cell function and insulin clearance did not change in both treatment groups. Insulin sensitivity worsened in the Lumacaftor/Ivacaftor group. The analysis of vector plots confirmed that glucose regulation was stable in both groups. CONCLUSIONS: Treatment of CF patients with CFTR modulators does not significantly ameliorate glucose homeostasis and/or any of its direct determinants.

Insulin resistance and beta-cell dysfunction in newly diagnosed type 2 diabetes: Expression, aggregation and predominance. Verona Newly Diagnosed Type 2 Diabetes Study 10.

AIMS: We investigated quantitative expression, mutual aggregation and relation with hyperglycemia of insulin resistance (IR) and beta-cell dysfunction (BCD) in newly diagnosed type 2 diabetes. METHODS: We assessed IR with euglycemic hyperinsulinemic clamp and BCD with modelled glucose/C-peptide response to oral glucose in 729 mostly drug-naïve patients. We measured glycated hemoglobin, pre-prandial, post-prandial and meal-related excursion of blood glucose. RESULTS: IR was found in 87.8% [95% confidence intervals 85.4-90.2] and BCD in 90.0% [87.8-92.2] of subjects, ranging from mild to moderate or severe. Approximately 20% of subjects had solely one defect: BCD 10.8% [8.6-13.1] or IR 8.6% [6.6-10.7]. Insulin resistance and BCD aggregated in most subjects (79.1% [76.2-82.1]). We arbitrarily set nine possible combinations of mild, moderate or severe IR and mild, moderate or severe BCD, finding that each had a similar frequency (∼10%). In multiple regression analyses parameters of glucose control were related more strongly with BCD than with IR. CONCLUSIONS: In newly-diagnosed type 2 diabetes, IR and BCD are very common with a wide range of expression but no specific pattern of aggregation. Beta-cell dysfunction is likely to play a greater quantitative role than IR in causing/sustaining hyperglycemia in newly-diagnosed type 2 diabetes.

Exploring the determinants of ethnic differences in insulin clearance between men of Black African and White European ethnicity.

AIM: People of Black African ancestry, who are known to be at disproportionately high risk of type 2 diabetes (T2D), typically exhibit lower hepatic insulin clearance compared with White Europeans. However, the mechanisms underlying this metabolic characteristic are poorly understood. We explored whether low insulin clearance in Black African (BA) men could be explained by insulin resistance, subclinical inflammation or adiponectin concentrations. METHODS: BA and White European (WE) men, categorised as either normal glucose tolerant (NGT) or with T2D, were recruited to undergo the following: a mixed meal tolerance test with C-peptide modelling to determine endogenous insulin clearance; fasting serum adiponectin and cytokine profiles; a hyperinsulinaemic-euglycaemic clamp to measure whole-body insulin sensitivity; and magnetic resonance imaging to quantify visceral adipose tissue. RESULTS: Forty BA (20 NGT and 20 T2D) and 41 WE (23 NGT and 18 T2D) men were studied. BA men had significantly lower insulin clearance (P = 0.011) and lower plasma adiponectin (P = 0.031) compared with WE men. In multiple regression analysis, ethnicity, insulin sensitivity and plasma adiponectin were independent predictors of insulin clearance, while age, visceral adiposity and tumour necrosis factor alpha (TNF-α) did not significantly contribute to the variation. CONCLUSION: These data suggest that adiponectin may play a direct role in the upregulation of insulin clearance beyond its insulin-sensitising properties.

Ethnic differences in beta cell function occur independently of insulin sensitivity and pancreatic fat in black and white men.

INTRODUCTION: It is increasingly recognized that type 2 diabetes (T2D) is a heterogenous disease with ethnic variations. Differences in insulin secretion, insulin resistance and ectopic fat are thought to contribute to these variations. Therefore, we aimed to compare postprandial insulin secretion and the relationships between insulin secretion, insulin sensitivity and pancreatic fat in men of black West African (BA) and white European (WE) ancestry. RESEARCH DESIGN AND METHODS: A cross-sectional, observational study in which 23 WE and 23 BA men with normal glucose tolerance, matched for body mass index, underwent a mixed meal tolerance test with C peptide modeling to measure beta cell insulin secretion, an MRI to quantify intrapancreatic lipid (IPL), and a hyperinsulinemic-euglycemic clamp to measure whole-body insulin sensitivity. RESULTS: Postprandial insulin secretion was lower in BA versus WE men following adjustment for insulin sensitivity (estimated marginal means, BA vs WE: 40.5 (95% CI 31.8 to 49.2) × 103 vs 56.4 (95% CI 48.9 to 63.8) × 103 pmol/m2 body surface area × 180 min, p=0.008). There was a significantly different relationship by ethnicity between IPL and insulin secretion, with a stronger relationship in WE than in BA (r=0.59 vs r=0.39, interaction p=0.036); however, IPL was not a predictor of insulin secretion in either ethnic group following adjustment for insulin sensitivity. CONCLUSIONS: Ethnicity is an independent determinant of beta cell function in black and white men. In response to a meal, healthy BA men exhibit lower insulin secretion compared with their WE counterparts for their given insulin sensitivity. Ethnic differences in beta cell function may contribute to the greater risk of T2D in populations of African ancestry.

Glucose Tolerance Stages in Cystic Fibrosis Are Identified by a Unique Pattern of Defects of Beta-Cell Function.

OBJECTIVE: We aimed to assess the order of severity of the defects of 3 direct determinants of glucose regulation-beta-cell function, insulin clearance, and insulin sensitivity-in patients with cystic fibrosis (CF), categorized according their glucose tolerance status, including early elevation of mid-level oral glucose tolerance test (OGTT) glucose values (>140 and <200 mg/dL), referred to as AGT140. METHODS: A total of 232 CF patients aged 10 to 25 years underwent OGTT. Beta-cell function and insulin clearance were estimated by OGTT mathematical modeling and OGTT-derived biomarkers of insulin secretion and sensitivity were calculated. The association between glucometabolic variables and 5 glucose tolerance stages (normal glucose tolerance [NGT], AGT140, indeterminate glucose tolerance [INDET], impaired glucose tolerance [IGT], cystic fibrosis-related diabetes CFRD]) was assessed with a general linear model. RESULTS: Beta-cell function and insulin sensitivity progressively worsened across glucose tolerance stages (P < 0.001), with AGT140 patients significantly differing from NGT (all P < 0.01). AGT140 and INDET showed a degree of beta-cell dysfunction similar to IGT and CFRD, respectively (all P < 0.01). Insulin clearance was not significantly associated with glucose tolerance stages (P = 0.162). Each stage of glucose tolerance was uniquely identified by a specific combination of defects of the direct determinants of glucose regulation. CONCLUSIONS: In CF patients, each of the 5 glucose tolerance stages shows a unique pattern of defects of the direct determinants of glucose regulation, with AGT140 patients significantly differing from NGT and being similar to IGT. These findings suggest that AGT140 should be recognized as a distinct glucose tolerance stage and that reconsideration of the grade of glucometabolic deterioration across glucose tolerance stages in CF is warranted.

Chronic complications in patients with newly diagnosed type 2 diabetes: prevalence and related metabolic and clinical features: the Verona Newly Diagnosed Type 2 Diabetes Study (VNDS) 9.

INTRODUCTION: We explored the presence of chronic complications in subjects with newly diagnosed type 2 diabetes referred to the Verona Diabetes Clinic. Metabolic (insulin secretion and sensitivity) and clinical features associated with complications were also investigated. RESEARCH DESIGN AND METHODS: The comprehensive assessment of microvascular and macrovascular complications included detailed medical history, resting ECG, ultrasonography of carotid and lower limb arteries, quantitative neurological evaluation, cardiovascular autonomic tests, ophthalmoscopy, kidney function tests. Insulin sensitivity and beta-cell function were assessed by state-of-the-art techniques (insulin clamp and mathematical modeling of glucose/C-peptide curves during oral glucose tolerance test). RESULTS: We examined 806 patients (median age years, two-thirds males), of whom prior clinical cardiovascular disease (CVD) was revealed in 11.2% and preclinical CVD in 7.7%. Somatic neuropathy was found in 21.2% and cardiovascular autonomic neuropathy in 18.6%. Retinopathy was observed in 4.9% (background 4.2%, proliferative 0.7%). Chronic kidney disease (estimated glomerular filtration rate <60 mL/min/1.73 m2) was found in 8.8% and excessive albuminuria in 13.2% (microalbuminuria 11.9%, macroalbuminuria 1.3%).Isolated microvascular disease occurred in 30.8%, isolated macrovascular disease in 9.3%, a combination of both in 9.1%, any complication in 49.2% and no complications in 50.8%.Gender, age, body mass index, smoking, hemoglobin A1c and/or hypertension were independently associated with one or more complications. Insulin resistance and beta-cell dysfunction were associated with macrovascular but not microvascular disease. CONCLUSIONS: Despite a generally earlier diagnosis for an increased awareness of the disease, as many as ~50% of patients with newly diagnosed type 2 diabetes had clinical or preclinical manifestations of microvascular and/or macrovascular disease. Insulin resistance might play an independent role in macrovascular disease. TRIAL REGISTRATION NUMBER: NCT01526720.

Central role of the ß-cell in driving regression of diabetes after liver transplantation in cirrhotic patients.

BACKGROUND & AIMS: Diabetes occurring as a direct consequence of loss of liver function is usually characterized by non-diabetic fasting plasma glucose (FPG) and haemoglobin A1c (HbA1c) levels and should regress after orthotopic liver transplantation (OLT). This observational, longitudinal study investigated the relationship between the time-courses of changes in all 3 direct determinants of glucose regulation, i.e., ß-cell function, insulin clearance and insulin sensitivity, and diabetes regression after OLT. METHODS: Eighty cirrhotic patients with non-diabetic FPG and HbA1c levels underwent an extended oral glucose tolerance test (OGTT) before and 3, 6, 12 and 24 months after OLT. The OGTT data were analysed with a mathematical model to estimate derivative control (DC) and proportional control (PC) of ß-cell function and insulin clearance (which determine insulin bioavailability), and with the Oral Glucose Insulin Sensitivity (OGIS)-2 h index to estimate insulin sensitivity. RESULTS: At baseline, 36 patients were diabetic (45%) and 44 were non-diabetic (55%). Over the 2-year follow-up, 23 diabetic patients (63.9%) regressed to non-diabetic glucose regulation, whereas 13 did not (36.1%); moreover, 4 non-diabetic individuals progressed to diabetes (9.1%), whereas 40 did not (90.9%). Both DC and PC increased in regressors (from month 3 and 24, respectively) and decreased in progressors, whereas they remained stable in non-regressors and only PC decreased in non-progressors. Insulin clearance increased in all groups, apart from progressors. Likewise, OGIS-2 h improved at month 3 in all groups, but thereafter it continued to improve only in regressors, whereas it returned to baseline values in the other groups. CONCLUSIONS: Increased insulin bioavailability driven by improved ß-cell function plays a central role in favouring diabetes regression after OLT, in the presence of a sustained improvement of insulin sensitivity. LAY SUMMARY: Diabetes occurring in cirrhosis as a direct consequence of loss of liver function should regress after transplantation of a new functioning liver, though the pathophysiological mechanisms are unclear. This is the first study evaluating the contribution of all 3 direct determinants of insulin-dependent glucose regulation using a sophisticated mathematical model. Results show that ß-cell function is the key process governing favourable or detrimental changes in glucose regulation in cirrhotic patients undergoing transplantation, pointing to the need to develop therapies to sustain ß-cell function in these individuals. TRIAL REGISTRATION: ClinicalTrials.gov, NCT02038517.

Contribution of ß-cell dysfunction and insulin resistance to cirrhosis-associated diabetes: Role of severity of liver disease.

BACKGROUND & AIMS: This study evaluated the contribution of ß-cell dysfunction and insulin resistance to cirrhosis-associated diabetes. METHODS: One-hundred and sixty cirrhotic patients with normal fasting plasma glucose (FPG), three with impaired fasting glucose and seven with untreated diabetes mellitus (DM) underwent an extended oral glucose tolerance test (OGTT). The OGTT data were analyzed with a Minimal Model to estimate dynamic (derivative) control (DC) and static (proportional) control (PC) of ß-cell function, and with the Oral Glucose Insulin Sensitivity (OGIS)-2h index to estimate insulin sensitivity. RESULTS: Twenty-six patients (15.6%) had normal glucose tolerance (NGT), 60 (35.8%) had impaired glucose tolerance (IGT), and 84 (48.6%) had DM. DC was significantly reduced in DM vs. NGT and IGT patients. PC was significantly impaired in DM and IGT vs. NGT patients and in DM vs. IGT subjects. The OGIS-2h index was significantly reduced to a similar extent in DM and IGT vs. NGT patients. Patients with Child-Pugh class B and C cirrhosis had reduced DC and PC, but not OGIS-2h values, as compared with subjects in class A. Moreover, Child-Pugh class/score was an independent predictor of ß-cell function even after adjustment for glucose tolerance. CONCLUSIONS: Abnormalities of glucose tolerance occur frequently in cirrhosis even in patients with normal FPG, thereby supporting the importance of performing an OGTT. Transition from IGT to DM is driven primarily by ß-cell dysfunction. Insulin secretion worsens in parallel with the severity of liver disease, thus suggesting a detrimental effect of liver failure on pancreatic islets on its own.

Variants of GCKR affect both ß-cell and kidney function in patients with newly diagnosed type 2 diabetes: the Verona newly diagnosed type 2 diabetes study 2.

OBJECTIVE: In genome-wide association studies, performed mostly in nondiabetic individuals, genetic variability of glucokinase regulatory protein (GCKR) affects type 2 diabetes-related phenotypes, kidney function, and risk of chronic kidney disease (CKD). We tested whether GCKR variability affects type 2 diabetes or kidney-related phenotypes in newly diagnosed type 2 diabetes. RESEARCH DESIGN AND METHODS: In 509 GAD-negative patients with newly diagnosed type 2 diabetes, we 1) genotyped six single nucleotide polymorphisms in GCKR genomic region: rs6717980, rs1049817, rs6547626, rs780094, rs2384628, and rs8731; 2) assessed clinical phenotypes, insulin sensitivity by the euglycemic insulin clamp, and ß-cell function by state-of-the-art modeling of glucose/C-peptide curves during an oral glucose tolerance test; and 3) estimated glomerular filtration rate (eGFR) by the Modification of Diet in Renal Disease formula. RESULTS: The major alleles of rs6717980 and rs2384628 were associated with reduced ß-cell function (P < 0.05), with mutual additive effects of each variant (P < 0.01). The minor alleles of rs1049817 and rs6547626 and the major allele of rs780094 were associated with reduced eGFR according to a recessive model (P < 0.03), but with no mutual additive effects of the variants. Additional associations were found between rs780094 and 2-h plasma glucose (P < 0.05) and rs8731 and insulin sensitivity (P < 0.05) and triglycerides (P < 0.05). CONCLUSIONS: Our findings are compatible with the idea that GCKR variability may play a pathogenetic role in both type 2 diabetes and CKD. Genotyping GCKR in patients with newly diagnosed type 2 diabetes might help in identifying patients at high risk for metabolic derangements or CKD.