HDL cholesterol is an independent predictor of ß-cell function decline and incident type 2 diabetes: A longitudinal study.

BACKGROUND: Experimental evidence indicates that high-density lipoprotein (HDL) may stimulate glucose uptake and improve ß-cell function. The aim of this study was to evaluate whether lower levels of HDL may affect the risk to develop type 2 diabetes. METHODS: Incident rate of type 2 diabetes and changes in insulin sensitivity and ß-cell function over 5.5-year follow-up were examined in 670 non-diabetic subjects stratified in tertiles according to basal HDL levels. RESULTS: As compared to the highest tertile of HDL, individuals with lower levels of HDL have an increased risk to develop type 2 diabetes independently from several cardiometabolic risk factors (odds ratio: 2.88, 95% confidence interval: 1.05-7.91), and exhibited a greater deterioration of ß-cell function, estimated by the disposition index, over 5.5-year follow-up. Conversely, changes in Matsuda index of insulin sensitivity over the follow-up were not significantly different amongst the three HDL groups. In a multivariable regression analysis model including age, sex, waist circumference, triglycerides, total cholesterol, C-reactive protein, fasting and 2-hour post-load glucose, family history of type 2 diabetes and smoking habit, HDL concentration at baseline was an independent predictor of ß-cell function decline over the follow-up (ß = .30, P = .0001). Mediation analysis showed that the association between lower HDL levels at baseline and increased risk of incident diabetes was mediated by ß-cell function deterioration during the follow-up (t = -3.32, P = .001). CONCLUSIONS: Subjects with lower levels of HDL have an increased risk to develop type 2 diabetes likely due to a greater ß-cell function decline over time.

The polymorphism rs35767 at IGF1 locus is associated with serum urate levels.

Previous studies suggested that the IGF-1/IGF-1 receptor signaling pathway may contribute to regulate uric acid levels. To confirm this hypothesis, we assessed the effects of the IGF-1-raising genetic variant rs35767 on urate levels in serum and urine, and we investigated IGF-1 ability to modulate the expression of transporters involved in reabsorption and secretion of uric acid in the kidney. The study population included 2794 adult Whites. 24-hour urinary uric acid concentration was available for 229 subjects. rs35767 polymorphism was screened using TaqMan genotyping assays. HEK293 (human embryonic kidney-293) cell line was treated with IGF-1 (1, 5, 10, 50 nM) for 24-hours, and differences in the expression of urate transporters were evaluated via Western Blot and real time rtPCR. Individuals carrying the IGF-1-raising allele (rs35767 T) exhibited significantly lower levels of serum urate according to both additive and recessive models, after correction for gender, age, BMI, glucose tolerance, glomerular filtration rate, and anti-hypertensive treatment. TT genotype carriers displayed higher uricosuria than C allele carriers did, after adjusting for confounders. Exposure of HEK293 cells to IGF-1 resulted in a dose-dependent increase of uric acid transporters deputed to uric acid excretion (MRP4, NPT1 and BCRP), and reduction of GLUT9 expression, the major mediator of uric acid reabsorption, both at mRNA and protein level. We observed a significant association between the functional polymorphism rs35767 near IGF1 with serum urate concentrations and we provide a mechanistic explanation supporting a causal role for IGF-1 in the regulation of uric acid homeostasis.

A polymorphism at IGF1 locus is associated with carotid intima media thickness and endothelium-dependent vasodilatation.

OBJECTIVE: Whether IGF-1 has a protective or a detrimental role in vascular homeostasis remains unsettled. There is evidence that the C/T polymorphism rs35767 near the promoter region of the IGF1 gene located in chromosome 12 is associated with plasma IGF-1 levels. We investigated the effects of this polymorphism on circulating IGF-1 levels, carotid intima media thickness (cIMT) and endothelial-dependent vasodilation. METHODS: Two samples of adult nondiabetic Whites were studied. Sample 1 comprised 1124 individuals in whom cIMT was measured by ultrasonography. Sample 2 included 162 drug-naïve hypertensive individuals in whom endothelium-dependent and endothelium-independent vasodilation were assessed by intra-arterial infusion of acetylcholine (ACh), and sodium nitroprusside (SNP), respectively. IGF-1 was determined by chemiluminescent immunoassay. rs35767 polymorphism was screened using a TaqMan allelic discrimination assay. RESULTS: In sample 1, IGF-1 levels were higher in subjects carrying the T allele compared with CC carriers (178 ± 78 vs. 166 ± 60 ng/mL, respectively; P = 0.007 adjusted for age, gender, and BMI). cIMT was lower in subjects carrying the T allele compared with CC carriers (0.71 ± 0.20 vs. 0.76 ± 0.22 mm, respectively; P < 0.0001 adjusted for age, gender, and BMI). In sample 2, maximally ACh-stimulated forearm blood flow was higher in subjects carrying the T allele compared with CC carriers (343 ± 191 vs. 281 ± 125%, respectively; P = 0.02 adjusted for age, gender, and BMI). CONCLUSION: Subjects carrying the T allele exhibited significantly higher levels of circulating IGF-1, lower values of cIMT, and higher endothelium-dependent vasodilatation compared with CC carriers. These findings support the idea that IGF-1 plays a role in the pathogenesis of atherosclerosis.

Differences in insulin clearance between metabolically healthy and unhealthy obese subjects.

Metabolically healthy obese (MHO) are relatively insulin sensitive and have a favorable cardio-metabolic risk profile compared with metabolically abnormal obese (MAO). To evaluate whether MAO individuals have a decreased insulin clearance compared with MHO individuals, 49 MHO, 147 MAO, and 172 non-obese individuals were analyzed in this cross-sectional study. Insulin clearance and insulin sensitivity were assessed through euglycemic hyperinsulinemic clamp. MHO subjects exhibited significant lower triglycerides, total cholesterol, 2-h post-challenge glucose, fasting and 2-h post-challenge insulin, steady-state plasma insulin, alanine aminotransferase, aspartate aminotransferase, and gamma-glutamyltransferase as compared with MAO individuals. Disposition index was higher in MHO subjects as compared with MAO individuals after adjusting for gender and age (P = 0.04). Insulin clearance was significantly lower in MAO individuals as compared with MHO and non-obese individuals. The difference between the two obese subgroups remained significant after adjusting for gender, age, waist circumference, fat mass, and insulin-stimulated glucose disposal (P = 0.03). The hepatic insulin extraction (C-peptide/insulin) in the fasting state was significantly higher in MHO subjects as compared with MAO individuals (P < 0.0001). In univariate analysis adjusted for gender and age, insulin clearance was correlated with hepatic insulin extraction (P = 0.01). In conclusion, insulin clearance differs among obese subjects with different metabolic phenotypes. Impaired insulin clearance may contribute to sustained fasting and post-meal hyperinsulinemia observed in MAO individuals.

A functional variant of the dimethylarginine dimethylaminohydrolase-2 gene is associated with chronic kidney disease.

OBJECTIVE: Studies reported a relationship between elevated asymmetric dimethylarginine (ADMA) concentrations and adverse renal outcomes. There is evidence that the rs9267551 variant in the DDAH2 gene has a functional impact with the C allele having a higher transcriptional activity resulting in increased expression of DDAH2 in endothelial cells and lower plasma ADMA levels in C allele carriers. METHODS: To address whether this variant is associated with chronic kidney disease (CDK), 2852 White European were studied. CKD was defined as estimated glomerular filtration rate (eGFR) <60 ml/min/1.73 m(2). RESULTS: The proportion of subjects with CKD was significantly lower in C allele carriers than in GG genotype carriers (OR 0.49, 95%CI 0.25-0.97; P = 0.03). In a logistic regression model adjusted for age, gender, BMI, blood pressure, total and HDL cholesterol, triglyceride, and fasting plasma glucose, C allele carriers have a lower risk of CKD compared with GG genotype carriers (OR 0.38, 95%CI 0.18-0.78; P = 0.008). This association was maintained after addition to the logistic regression model of other confounders including glucose tolerance status, presence of dyslipidemia, anti-hypertensive and antidiabetic drugs (OR 0.35, 95%CI 0.15-0.80; P = 0.01). CONCLUSION: The rs9267551 functional variant of the DDAH2 gene is associated with CKD with carriers of the C allele having a lower risk of renal dysfunction independently from several confounders. Because ADMA predicted progression of renal disease, it is possible that, in GG carriers, ADMA may accumulate at the renal level causing endothelial dysfunction as a consequence of reduced nitric oxide availability and potentiating micro-vascular damage.

Insulin clearance is associated with carotid artery intima-media thickness.

OBJECTIVE: The aim of this study was to investigate whether insulin clearance is independently associated with carotid artery intima-media thickness (IMT), a well-recognized index of vascular damage. METHODS: 361 Non-diabetic Caucasian subjects were subjected to euglycemic hyperinsulinemic clamp to assess insulin sensitivity, and insulin clearance. IMT of the common carotid was measured by ultrasonography. RESULTS: Among the study group, 270 subjects had normal glucose tolerance, 33 had impaired fasting glucose, and 58 had impaired glucose tolerance. Univariate correlations showed that age, BMI, waist, blood pressure, triglycerides, fasting and 2-h post-load glucose and insulin levels were positively correlated with carotid IMT whereas HDL, insulin clearance, and insulin-stimulated glucose disposal were negatively correlated with IMT. A multivariate regression analysis in a model including, in addition to insulin clearance, age, gender, BMI, waist, blood pressure, triglycerides, HDL, fasting and 2-h post-load glucose, insulin-stimulated glucose disposal, fasting and 2-h post-load insulin showed that the traits independently associated with carotid IMT were BMI (ß = 0.42, P < 0.0001), insulin clearance (ß = -0.29, P < 0.0001), age (ß = 0.19, P < 0.0001), waist (ß = 0.18, P = 0.01), diastolic blood pressure (ß = 0.17, P = 0.01), and 2-h post-load glucose (ß = 0.12, P = 0.03). These factors explained 26% of the variance in carotid IMT. Subjects in the lowest tertile of insulin clearance had a 4.06-fold higher odds of having vascular damage (IMT > 0.9 mm) as compared with those in the highest tertile (OR 4.06, 95%CI 1.15-13.24). CONCLUSIONS: Insulin clearance is independently associated with carotid IMT in adult non-diabetic subjects. Individuals with lower levels of insulin clearance have a higher odds of vascular damage.

A fasting insulin-raising allele at IGF1 locus is associated with circulating levels of IGF-1 and insulin sensitivity.

BACKGROUND: A meta-analysis of genome-wide data reported the discovery of the rs35767 polymorphism near IGF1 with genome-wide significant association with fasting insulin levels. However, it is unclear whether the effects of this polymorphism on fasting insulin are mediated by a reduced insulin sensitivity or impaired insulin clearance. We investigated the effects of the rs35767 polymorphism on circulating IGF-1 levels, insulin sensitivity, and insulin clearance. METHODOLOGY/PRINCIPAL FINDINGS: Two samples of adult nondiabetic white Europeans were studied. In sample 1 (n=569), IGF-1 levels were lower in GG genotype carriers compared with A allele carriers (190±77 vs. 218±97 ng/ml, respectively; P=0.007 after adjusting for age, gender, and BMI). Insulin sensitivity assessed by euglycaemic-hyperinsulinemic clamp was lower in GG genotype carriers compared with A allele carriers (8.9±4.1 vs. 10.1±5.1 mg x Kg(-1) free fat mass x min(-1), respectively; P=0.03 after adjusting for age, gender, and BMI). The rs35767 polymorphism did not show significant association with insulin clearance. In sample 2 (n=859), IGF-1 levels were lower in GG genotype carriers compared with A allele carriers (155±60 vs. 164±63 ng/ml, respectively; P=0.02 after adjusting for age, gender, and BMI). Insulin sensitivity, as estimated by the HOMA index, was lower in GG genotype carriers compared with A allele carriers (2.8±2.2 vs. 2.5±1.3, respectively; P=0.03 after adjusting for age, gender, and BMI). CONCLUSION/SIGNIFICANCE: The rs35767 polymorphism near IGF1 was associated with circulating IGF-1 levels, and insulin sensitivity with carriers of the GG genotype exhibiting lower IGF-1 concentrations and insulin sensitivity as compared with subjects carrying the A allele.

Cardiometabolic risk profiles and carotid atherosclerosis in individuals with prediabetes identified by fasting glucose, postchallenge glucose, and hemoglobin A1c criteria.

OBJECTIVE: We evaluated whether cardiometabolic risk profiles differ for subjects identified as having prediabetes by A1C, fasting glucose (FPG), or 2-h postchallenge glucose (2-PG) criteria. RESEARCH DESIGN AND METHODS: Atherosclerosis risk factors, oral glucose tolerance test, and ultrasound measurement of carotid intima-media thickness (IMT) were analyzed in 780 nondiabetic individuals. RESULTS: Poor agreement existed for A1C and FPG criteria for identification of subjects with prediabetes (κ coefficient = 0.332). No differences in cardiometabolic risk profiles were observed among the three groups of individuals with prediabetes by A1C only, FPG only, and both A1C and FPG. Poor agreement also existed for A1C and 2-PG criteria for identification of individuals with prediabetes (κ coefficient = 0.299). No significant differences in cardiometabolic risk factors were observed between IGT-only and individuals with prediabetes by A1C and 2-PG. Compared with subjects with prediabetes identified by A1C only, IGT-only individuals exhibited a worse cardiometabolic risk profile, with significantly higher systolic blood pressure, pulse pressure, 2-h postchallenge insulin, triglycerides, high-sensitivity C-reactive protein, and carotid IMT, and lower HDL cholesterol levels and insulin sensitivity. CONCLUSIONS: These results suggest that considerable discordance between A1C, FPG, and 2-PG exists for the identification of individuals with prediabetes and that the cardiometabolic risk profile of these individuals varies by metabolic parameter, with 2-PG showing the stronger association with cardiometabolic risk factors and subclinical atherosclerosis than FPG or A1C.

Insulin sensitivity, ß-cell function, and incretin effect in individuals with elevated 1-hour postload plasma glucose levels.

OBJECTIVE: Individuals with normal glucose tolerance (NGT), whose 1-h postload plasma glucose is ≥155 mg/dL (NGT 1h-high), have an increased risk of type 2 diabetes. The purpose of this study was to characterize their metabolic phenotype. RESEARCH DESIGN AND METHODS: A total of 305 nondiabetic offspring of type 2 diabetic patients was consecutively recruited. Insulin secretion was assessed using both indexes derived from oral glucose tolerance test (OGTT) and intravenous glucose tolerance test (IVGTT). Insulin sensitivity was measured by hyperinsulinemic-euglycemic clamp. RESULTS: Compared with individuals with a 1-h postload plasma glucose <155 mg/dL (NGT 1h-low), NGT 1h-high individuals exhibited lower insulin sensitivity after adjustment for age, sex, and BMI. Insulin secretion estimated from the OGTT did not differ between the two groups of individuals. By contrast, compared with NGT 1h-low individuals, the acute insulin response during an IVGTT and the disposition index were significantly reduced in NGT 1h-high individuals after adjustment for age, sex, and BMI. Incretin effect, estimated as the ratio between total insulin responses during OGTT and IVGTT, was higher in NGT 1h-high individuals compared with NGT 1h-low individuals. CONCLUSIONS: NGT 1h-high individuals may represent an intermediate state of glucose intolerance between NGT and type 2 diabetes characterized by insulin resistance and reduced ß-cell function, the two main pathophysiological defects responsible for the development of type 2 diabetes. Postload hyperglycemia is the result of an intrinsic ß-cell defect rather than impaired incretin effect.

Xantomatosis cerebrotendinosa. A Propósito de un Caso / Cerebrotendinous xanthomatosis. A case report

La xantomatosis cerebrotendinosa (XCT) es un raro desorden del almacenamiento de los lípidos, que se transmite en forma autosómica recesiva y se caracteriza por el depósito de colesterol y colestanol en diferentes tejidos, con preferencia por los tendones, los cristalinos y el sistema nervioso central. El diagnóstico de la enfermedad se confirma con la presencia de β–colestanol en sangre y de alcoholes biliares en orina. Obedece a una mutación del gen CYP27A1 (responsable de la síntesis de la enzima esterol 27-hidrolasa) que mapea en el brazo largo del cromosoma 2. Se manifiesta clínicamente por un deterioro neurológico progresivo, además de la presencia de xantomas tendinosos, cataratas juveniles, arterioesclerosis y diarrea crónica. Las alteraciones aparecen en las primeras dos décadas de la vida, pero el diagnóstico definitivo suele hacerse tardíamente (entre la tercera y la cuarta décadas). La terapéutica consiste en la administración de ácido quenodesoxicólico asociado a pravastatina o simvastatina. El tratamiento temprano y prolongado podría detener la progresión de la enfermedad. Se presenta un paciente de 40 años con esta enfermedad y se hace una descripción actualizada de la misma.

Insulin secretion in metabolically obese, but normal weight, and in metabolically healthy but obese individuals.

Metabolically obese but normal-weight (MONW) individuals present metabolic disturbances typical of obese individuals. Additionally, metabolically healthy but obese (MHO) individuals have been identified who are relatively insulin sensitive and have a favorable cardiovascular risk profile. We compared insulin secretion patterns of MONW and MHO with those of two age-matched groups comprising nonobese individuals or obese insulin-resistant subjects, respectively. To this end, 110 nonobese subjects and 87 obese subjects were stratified into quartile based on their insulin-stimulated glucose disposal (M(FFM)). Insulin secretion was estimated by acute insulin response (AIR) during an intravenous glucose-tolerance test (IVGTT), and the disposition index was calculated as AIR x M(FFM). We found that, as defined, M(FFM) was lower in MONW, who exhibited higher triglycerides, free-fatty acid (FFA), and 2-h postchallenge glucose levels compared to normal nonobese group. Insulin secretion was higher in MONW than in normal nonobese subjects, but disposition index was lower in MONW. Disposition index did not differ between MONW and insulin-resistant obese. M(FFM) was higher in MHO who exhibited lower waist circumference, blood pressure (BP), triglycerides, FFA, insulin levels, and higher high-density lipoprotein (HDL) cholesterol compared to insulin-resistant obese. Insulin secretion did not differ between insulin-resistant obese and MHO, but disposition index was lower in the former group. In conclusion, MONW and insulin-resistant obese showed decreased compensatory insulin secretion compared to normal nonobese and MHO subjects, respectively. Because these subjects also exhibited a worse metabolic risk profile, these findings may account for their increased risk for type 2 diabetes.

Plasma interleukin-6 levels are independently associated with insulin secretion in a cohort of Italian-Caucasian nondiabetic subjects.

We have investigated the relationships between plasma interleukin-6 (IL-6) levels and insulin sensitivity and insulin secretion in a cohort of Italian-Caucasian glucose-tolerant subjects. Insulin sensitivity was assessed by euglycemic-hyperinsulinemic clamp, and first-phase insulin secretion was measured by intravenous glucose tolerance test. Fasting plasma IL-6 concentration was negatively correlated with the rate of insulin-stimulated glucose disposal (M) (P = 0.001). The correlation remained statistically significant, while attenuated, after adjusting for sex, age, and BMI (P < 0.03); after an additional adjustment for free fatty acids (FFAs), a further attenuation was observed, but statistical significance was maintained (P < 0.044). Fasting plasma IL-6 concentration was positively correlated with first-phase insulin secretion assessed as acute insulin response (AIR) (P = 0.001). The correlation remained significant after adjusting for sex, age, and BMI (P = 0.003). To estimate the independent contribution of plasma IL-6 levels to AIR, we carried out forward stepwise linear regression analysis in a model that included sex, age, BMI, waist-to-hip ratio, FFAs, and insulin-stimulated glucose disposal. Only insulin sensitivity and plasma IL-6 concentration were independently associated with AIR, accounting, respectively, for 19.0 and 5.2% of its variation. These data indicate that IL-6 is associated in a reciprocal manner with the two pathophysiological components of type 2 diabetes, i.e., insulin resistance and insulin secretion.