Effects of age and sex on postprandial glucose metabolism: differences in glucose turnover, insulin secretion, insulin action, and hepatic insulin extraction

Visual Predictive Check in Models with Time-Varying Input Function

The nonlinear mixed effects models are commonly used modeling techniques in the pharmaceutical research as they enable the characterization of the individual profiles together with the population to which the individuals belong. To ensure a correct use of them is fundamental to provide powerful diagnostic tools that are able to evaluate the predictive performance of the models. The visual predictive check (VPC) is a commonly used tool that helps the user to check by visual inspection if the model is able to reproduce the variability and the main trend of the observed data. However, the simulation from the model is not always trivial, for example, when using models with time-varying input function (IF). In this class of models, there is a potential mismatch between each set of simulated parameters and the associated individual IF which can cause an incorrect profile simulation. We introduce a refinement of the VPC by taking in consideration a correlation term (the Mahalanobis or normalized Euclidean distance) that helps the association of the correct IF with the individual set of simulated parameters. We investigate and compare its performance with the standard VPC in models of the glucose and insulin system applied on real and simulated data and in a simulated pharmacokinetic/pharmacodynamic (PK/PD) example. The newly proposed VPC performance appears to be better with respect to the standard VPC especially for the models with big variability in the IF where the probability of simulating incorrect profiles is higher.

Hepatic insulin sensitivity in healthy and prediabetic subjects: from a dual- to a single-tracer oral minimal model

Recently, a model was proposed to assess hepatic insulin sensitivity during a meal, i.e., the ability of insulin to suppress glucose production (EGP), SI (P). The model was developed on EGP data obtained from a triple-tracer meal and the tracer-to-tracee clamp technique and validated against the euglycemic hyperinsulinemic clamp. The aim of this study was to assess whether SI (P) can be obtained from plasma concentrations measured after a single-tracer meal by incorporating the above EGP model into the oral glucose minimal model by describing both glucose production and disposal (OMM(PD)). Triple-tracer meal data of two databases (20 healthy and 60 healthy and prediabetic subjects) were used. Virtually model-independent EGP estimates were calculated. OMM(PD) was identified on exogenous and endogenous glucose concentrations, providing indices of SI (P), disposal insulin sensitivity (SI (D)), and EGP. The model fitted the data well, and SI (P) and SI (D) were estimated with precision in both databases (SI (P) = 5.48 ± 0.54 10(-4) dl·kg(-1)·min(-1) per μU/ml and SI (D) = 9.93 ± 2.18 10(-4) dl·kg(-1)·min(-1) per μU/ml in healthy; SI (P) = 5.41 ± 3.55 10(-4) dl·kg(-1)·min(-1) per μU/ml and SI (D) = 5.34 ± 6.17 10(-4) dl·kg(-1)·min(-1) per μU/ml, in healthy and prediabetic subjects). Estimated SI (P) and that derived from the triple-tracer EGP model were very similar on average. Moreover, the time course of EGP normalized to basal EGP (EGPb), and EGP/EGPb agreed with the results obtained using the triple-tracer method. In this study, we have demonstrated that SI (P), SI (D), and EGP/EGPb time course can be estimated reliably from a single-tracer meal protocol in both healthy and prediabetic subjects.

Severe disturbance of glucose metabolism in peripheral blood mononuclear cells of schizophrenia patients: a targeted metabolomic study

Background

Schizophrenia is a widespread and debilitating mental disorder. However, the underlying molecular mechanism of schizophrenia remains largely unknown and no objective laboratory tests are available to diagnose this disorder. The aim of the present study was to characterize the alternations of glucose metabolites and identify potential diagnostic biomarkers for schizophrenia.

Methods

Gas chromatography/mass spectrometry based targeted metabolomic method was used to quantify the levels of 13 glucose metabolites in peripheral blood mononuclear cells (PBMCs) derived from healthy controls, schizophrenia and major depression subjects (n = 55 for each group).

Results

The majority (84.6%) of glucose metabolites were significantly disturbed in schizophrenia subjects, while only two (15.4%) glucose metabolites were differently expressed in depression subjects relative to healthy controls in both training set (n = 35/group) and test set (n = 20/group). Antipsychotics had only a subtle effect on glucose metabolism pathway. Moreover, ribose 5-phosphate in PBMCs showed a high diagnostic performance for first-episode drug-naïve schizophrenia subjects.

Conclusion

These findings suggested disturbance of glucose metabolism may be implicated in onset of schizophrenia and could aid in development of diagnostic tool for this disorder.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-015-0540-y) contains supplementary material, which is available to authorized users.

Additional benefit of higher dose green tea in lowering postprandial blood glucose

Background: Green tea contains catechins that have inhibitory effects on amylase, sucrase, and sodium-dependent glucose transporter (SGLT) which result in lowering of postprandial blood glucose (PBG). This beneficial effect has been widely demonstrated using the usual dose (UD) of green tea preparation. Our study was aimed to explore futher lowering of PBG using high dose (HD) of green tea in healthy adolescents. Methods: 24 subjects received 100 mL infusion of either 0.67 or 3.33 grams of green tea with test meal. Fasting, PBG at 30, 60, 120 minutes were measured. Subjects were cross-overed after wash out. PBG and its incremental area under the curve (IAUC) difference between groups were analyzed with paired T-test. Cathecin contents of tea were measured using high-performance liquid chromatography (HPLC). Results: The PBG of HD group was lower compared to UD (at 60 minutes =113.70 ± 13.20 vs 124.16 ± 8.17 mg/dL, p = 0.005; at 120 minutes = 88.95 ± 6.13 vs 105.25 ± 13.85 mg/dL, p < 0.001). The IAUC of HD was also found to be lower compared to UD (2055.0 vs 3411.9 min.mg/dL, p < 0.001). Conclusion: Additional benefit of lowering PBG can be achieved by using higher dose of green tea. This study recommends preparing higher dose of green tea drinks for better control of PBG.

Effect of Galactose Ingestion Before and During Exercise on Substrate Oxidation, Postexercise Satiety, and Subsequent Energy Intake in Females

OBJECTIVE

To examine the effects of consuming a galactose carbohydrate (CHO) drink on substrate oxidation, postexercise satiety, and subsequent energy intake.

METHODS

Nine recreationally active eumenorrheic females undertook 3 trials, each consisting of running for 60 minutes at 65% VO(2peak) followed immediately by a 90-minute rest period. Prior to (300 ml) and at 15-minute intervals during exercise (150 ml), participants consumed either a glucose (GLU: GI 89) or galactose (GAL: GI 20) drink, each of which contained 45 g of CHO, or an artificially sweetened placebo (PLA). Following the rest period, participants were provided with an ad libitum test lunch and asked to record food intake for the remainder of the day.

RESULTS

Plasma glucose was significantly greater throughout exercise and rest following the GLU trial compared with the GAL and PLA trials (P < 0.05); however there were no differences in CHO oxidation. Hunger was significantly lower (P < 0.05) throughout the GAL compared to the GLU and PLA trials. There were no significant differences between trials for energy intake during the postexercise meal. Overall net energy balance for the 24 hours was negative in both the GAL (-162 ± 115 kcal; P < 0.05 vs GLU) and PLA trials (-49 ± 160 kcal).

CONCLUSIONS

Results demonstrate that ingesting a solution containing GAL before and during exercise can positively impact postexercise satiety and energy balance throughout the day, compared to a more readily available and widely consumed form of CHO. Despite this, there appears to be no apparent benefit in consuming a CHO beverage on fuel utilization for this moderate exercise intensity and duration.

Advancing our understanding of the glucose system via modeling: a perspective

The glucose story begins with Claude Bernard's discovery of glycogen and milieu interieur, continued with Banting's and Best's discovery of insulin and with Rudolf Schoenheimer's paradigm of dynamic body constituents. Tracers and compartmental models allowed moving to the first quantitative pictures of the system and stimulated important developments in terms of modeling methodology. Three classes of multiscale models, models to measure, models to simulate, and models to control the glucose system, are reviewed in their historical development with an eye to the future.

Randomized, double-blind, placebo-controlled, clinical study on the effect of Diabetinol(®) on glycemic control of subjects with impaired fasting glucose

BACKGROUND

This study investigated the efficacy of Diabetinol(®) in people with diabetes on medication but not meeting the American Association of Clinical Endocrinologists and American Diabetes Association glycemic, blood pressure, and lipid targets.

SUBJECTS AND METHODS

Fifty subjects, aged 18-75 years, with fasting blood glucose ≤15.4 mmol/L, hemoglobin A1c levels ≤12%, and a body mass index between 25 and 40 kg/m(2), were enrolled in a 24-week, randomized, double-blind, placebo-controlled, parallel study. Diabetinol(®) or placebo was administered as 2×525 mg capsules/day.

RESULTS

In the Diabetinol(®) group, 14.3% versus 0% in the placebo group, 33.3% versus 15.4% in placebo, 20.0% versus 12.5% in placebo, and 83.3% versus 60% in placebo achieved the American Association of Clinical Endocrinologists and American Diabetes Association targets for hemoglobin A1c, low-density lipoprotein, total cholesterol, and systolic blood pressure, respectively. There was no difference in the maximum concentration (Cmax) of serum glucose or area under the curve (AUC)0-240 minutes. The time to Cmax was longer for participants on Diabetinol(®) than placebo group at week 12 (P=0.01). Fasting blood glucose increased from baseline to week 24 in both groups; however, this increase was 14.3 mg/dL lower in the Diabetinol(®) group versus placebo. The Diabetinol(®) group showed an increase of 5.53 mg/dL in fasting insulin at week 12 (P=0.09) and 3.2 mg/dL at week 24 (P=0.41) over and above the placebo group. A decrease of 1.5% in total cholesterol, 5.8% in low-density lipoprotein, and a 1.6% increase in high-density lipoprotein concentrations were seen in the Diabetinol(®) group. Diabetinol(®) improved 6-month oral glucose tolerance test and 2-hour postprandial glucose profiles in participants between 40 and 60 years of age.

CONCLUSION

The current study suggests a role for Diabetinol(®) as an adjunctive therapy for glycemic maintenance and for decreasing the risk of diabetes-associated comorbidities in type 2 diabetic patients on conventional therapies.

Sex differences in the genome-wide DNA methylation pattern and impact on gene expression, microRNA levels and insulin secretion in human pancreatic islets

Background

Epigenetic factors regulate tissue-specific expression and X-chromosome inactivation. Previous studies have identified epigenetic differences between sexes in some human tissues. However, it is unclear whether epigenetic modifications contribute to sex-specific differences in insulin secretion and metabolism. Here, we investigate the impact of sex on the genome-wide DNA methylation pattern in human pancreatic islets from 53 males and 34 females, and relate the methylome to changes in expression and insulin secretion.

Results

Glucose-stimulated insulin secretion is higher in female versus male islets. Genome-wide DNA methylation data in human islets clusters based on sex. While the chromosome-wide DNA methylation level on the X-chromosome is higher in female versus male islets, the autosomes do not display a global methylation difference between sexes. Methylation of 8,140 individual X-chromosome sites and 470 autosomal sites shows sex-specific differences in human islets. These include sites in/near AR, DUSP9, HNF4A, BCL11A and CDKN2B. 61 X-chromosome genes and 18 autosomal genes display sex-specific differences in both DNA methylation and expression. These include NKAP, SPESP1 and APLN, which exhibited lower expression in females. Functional analyses demonstrate that methylation of NKAP and SPESP1 promoters in vitro suppresses their transcriptional activity. Silencing of Nkap or Apln in clonal beta-cells results in increased insulin secretion. Differential methylation between sexes is associated with altered levels of microRNAs miR-660 and miR-532 and related target genes.

Conclusions

Chromosome-wide and gene-specific sex differences in DNA methylation associate with altered expression and insulin secretion in human islets. Our data demonstrate that epigenetics contribute to sex-specific metabolic phenotypes.

Electronic supplementary material

The online version of this article (doi:10.1186/s13059-014-0522-z) contains supplementary material, which is available to authorized users.

Can bread processing conditions alter glycaemic response?

Bread is a staple food that is traditionally made from wheat flour. This study aimed to compare the starch digestibility of western baked bread and oriental steamed bread. Four types of bread were prepared: western baked bread (WBB) and oriental steamed bread (OSB), modified baked bread (MBB) made with the OSB recipe and WBB processing, and modified steamed bread (MSB) made with the WBB recipe and OSB processing. MBB showed the highest starch digestibility in vitro, followed by WBB, OSB and MSB. A similar trend was observed for glycaemic response in vivo. MBB, WBB, OSB and MSB had a glycaemic index of 75±4, 71±5, 68±5 and 65±4, respectively. Processing differences had a more pronounced effect on starch digestibility in bread, and steamed bread was healthier in terms of glycaemic response. The manipulation of processing conditions could be an innovative route to alter the glycaemic response of carbohydrate-rich foods.

A low glycaemic load breakfast can attenuate cognitive impairments observed in middle aged obese females with impaired glucose tolerance

BACKGROUND AND AIMS

There has been no systematic investigation of the individual and combined effects of impaired glucose tolerance (IGT) and obesity on cognitive function in the absence of ageing. The aims were to examine the effects of IGT and increased waist circumference on cognitive function in ostensibly healthy adults, and to investigate whether a low glycaemic load (GL) breakfast can attenuate cognitive impairments in these populations.

METHODS AND RESULTS

Sixty five females aged 30-50 years were classified into one of four groups following waist circumference (WC) measurements and an oral glucose tolerance test: NGT/low WC (n = 25), NGT/high WC (n = 22), IGT/low WC (n = 9), IGT/high WC (n = 9). Memory, psychomotor and executive functions were examined 30 and 120 min after consuming low GL, high GL and water breakfasts according to a randomised, crossover, counterbalanced design. IGT was associated with impairment of verbal and spatial memory, and psychomotor function relative to females with NGT, independent of waist circumference. Increased waist circumference was associated with impairment of verbal memory and executive function relative to females with low WC, independent of IGT. Consumption of the LGL breakfast attenuated verbal memory impairment in the IGT/high WC group relative to the HGL breakfast and no energy control.

CONCLUSION

Increased central adiposity and abnormalities in glucose tolerance preceding type 2 diabetes can have demonstrable negative effects on cognitive function, even in ostensibly healthy, middle-aged females. The potential for GL manipulations to modulate glycaemic response and cognitive function in type 2 diabetes and obesity merits further investigation.

Evaluation of intragastric vs intraperitoneal glucose tolerance tests in the evaluation of insulin resistance in a rodent model of burn injury and glucagon-like polypeptide-1 treatment

Evaluation of glucose tolerance in rodent models is usually performed after intraperitroneal administration of glucose (intraperitoneal glucose tolerance test [IPGTT]), whereas in humans the test is performed with oral glucose. Hyperglycemia is a major clinical manifestation of burn injury. Our previous studies using IPGTT have demonstrated burn injury-induced insulin resistance and the beneficial effects of glucagon-like polypeptide-1 (GLP-1) in improving insulin resistance. The goal of the present study is to compare the results of these two procedures under 1) burn injury-induced insulin resistance and 2) GLP-1 treatment after burn. Male CD rats were divided into three groups: sham burn, burn, and burn with GLP-1. Blood glucose and plasma insulin levels were measured during intragastric glucose tolerance test (IGGTT) on day 6 after 40% of full-thickness burn injury. The results were compared with our previous IPGTT. Blood glucose curves for IGGTT and IPGTT showed a similar pattern. However, IGGTT demonstrated a significant lower level of maximal blood glucose when compared with IPGTT. This was accompanied by higher peak insulin levels in sham burn and burn groups. In contrast, peak insulin levels of each burn with GLP-1 group were similar. 1) Both IPGTT and IGGTT demonstrated burn injury-induced insulin resistance and the efficacy of GLP-1 for reducing hyperglycemia after burn injury. 2) The observed differences in the plasma glucose and insulin levels between IGGTT and IPGTT suggest that endogenously produced GLP-1 during the IGGTT may play a role in ameliorating insulin resistance after burn injury.

Effects of delayed gastric emptying on postprandial glucose kinetics, insulin sensitivity, and β-cell function

Controlling meal-related glucose excursions continues to be a therapeutic challenge in diabetes mellitus. Mechanistic reasons for this need to be understood better to develop appropriate therapies. To investigate delayed gastric emptying effects on postprandial glucose turnover, insulin sensitivity, and β-cell responsivity and function, as a feasibility study prior to studying patients with type 1 diabetes, we used the triple tracer technique C-peptide and oral minimal model approach in healthy subjects. A single dose of 30 μg of pramlintide administered at the start of a mixed meal was used to delay gastric emptying rates. With delayed gastric emptying rates, peak rate of meal glucose appearance was delayed, and rate of endogenous glucose production (EGP) was lower. C-peptide and oral minimal models enabled the assessments of β-cell function, insulin sensitivity, and β-cell responsivity simultaneously. Delayed gastric emptying induced by pramlintide improved total insulin sensitivity and decreased total β-cell responsivity. However, β-cell function as measured by total disposition index did not change. The improved whole body insulin sensitivity coupled with lower rate of appearance of EGP with delayed gastric emptying provides experimental proof of the importance of evaluating pramlintide in artificial endocrine pancreas approaches to reduce postprandial blood glucose variability in patients with type 1 diabetes.

O-GlcNAc transferase and O-GlcNAcase: achieving target substrate specificity

O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA) catalyze the dynamic cycling of intracellular, post-translational O-GlcNAc modification on thousands of Ser/Thr residues of cytosolic, nuclear, and mitochondrial signaling proteins. The identification of O-GlcNAc modified substrates has revealed a functionally diverse set of proteins, and the extent of O-GlcNAcylation fluctuates in response to nutrients and cellular stress. As a result, OGT and OGA are implicated in widespread, nutrient-responsive regulation of numerous signaling pathways and transcriptional programs. These enzymes are required for normal embryonic development and are dysregulated in metabolic and age-related disease states. While a recent surge of interest in the field has contributed to understanding the functional impacts of protein O-GlcNAcylation, little is known about the upstream mechanisms which modulate OGT and OGA substrate targeting. This review focuses on elements of enzyme structure among splice variants, post-translational modification, localization, and regulatory protein interactions which drive the specificity of OGT and OGA toward different subsets of the cellular proteome. Ongoing efforts in this rapidly advancing field are aimed at revealing mechanisms of OGT and OGA regulation to harness the potential therapeutic benefit of manipulating these enzymes' activities.

Impact of sex on insulin secretion in cystic fibrosis

CONTEXT

Cystic fibrosis-related diabetes is primarily due to a defect in insulin secretion. Women with cystic fibrosis (CF) are at higher risk of developing CF-related diabetes.

OBJECTIVE

The objective of the study was to examine sex differences in insulin and glucose homeostasis. We hypothesized that in CF, women would display lower insulin secretion than men.

DESIGN

This was a study based on an ongoing observational CF cohort with a mean follow-up of 19.9 ± 5.2 months.

SETTING

The study was conducted at the CF clinic of the Centre Hospitalier de l'Université de Montréal (Québec, Canada).

PATIENTS

From 230 adults with CF (123 men, 107 women) of similar age and functional pulmonary status, 104 retested after the follow-up. Age-matched healthy individuals (25 men, 19 women) were included in the study.

INTERVENTIONS

Participants underwent a 2-hour oral glucose tolerance test with 30-minute interval sample measurements.

MAIN OUTCOME MEASURE

Plasma insulin and glucose levels were measured.

RESULTS

Women with CF had higher overall insulin secretion as compared with men with CF (P ≤ .05) but similar to healthy women (P = .606). Men with CF had lower overall insulin secretion than healthy men (P = .020) and higher insulin sensitivity (P = .009) than women with CF. PATIENTS with CF displayed higher overall glucose excursions than healthy patients. Sex-related differences were still observed in the CF cohort after follow-up.

CONCLUSIONS

Surprisingly, in CF, adult women presented higher insulin secretion than adult men at a comparable level with what is observed in healthy individuals. Potential implications of this sex dimorphism in CF remain to be established.

Sexually dimorphic actions of glucocorticoids: beyond chromosomes and sex hormones

Sexual dimorphism is a well-documented phenomenon that is observed at all levels of the animal kingdom. Historically, sex hormones (testosterone and estrogen) have been implicated as key players in a wide array of pathologies displaying sexual dimorphism in their etiology and progression. While these hormones clearly contribute to sexually dimorphic diseases, other factors may be involved in this phenomenon as well. In particular, the stress hormone cortisol exerts differential effects in both males and females. The underlying molecular basis for the sexually dimorphic actions of glucocorticoids is unknown but clearly important to understand, since synthetic glucocorticoids are the most widely prescribed medication for the treatment of chronic inflammatory diseases and hematological cancers in humans.

The oral minimal model method

The simultaneous assessment of insulin action, secretion, and hepatic extraction is key to understanding postprandial glucose metabolism in nondiabetic and diabetic humans. We review the oral minimal method (i.e., models that allow the estimation of insulin sensitivity, β-cell responsivity, and hepatic insulin extraction from a mixed-meal or an oral glucose tolerance test). Both of these oral tests are more physiologic and simpler to administer than those based on an intravenous test (e.g., a glucose clamp or an intravenous glucose tolerance test). The focus of this review is on indices provided by physiological-based models and their validation against the glucose clamp technique. We discuss first the oral minimal model method rationale, data, and protocols. Then we present the three minimal models and the indices they provide. The disposition index paradigm, a widely used β-cell function metric, is revisited in the context of individual versus population modeling. Adding a glucose tracer to the oral dose significantly enhances the assessment of insulin action by segregating insulin sensitivity into its glucose disposal and hepatic components. The oral minimal model method, by quantitatively portraying the complex relationships between the major players of glucose metabolism, is able to provide novel insights regarding the regulation of postprandial metabolism.

Sex-specific differences in lipid and glucose metabolism

Energy metabolism in humans is tuned to distinct sex-specific functions that potentially reflect the unique requirements in females for gestation and lactation, whereas male metabolism may represent a default state. These differences are the consequence of the action of sex chromosomes and sex-specific hormones, including estrogens and progesterone in females and androgens in males. In humans, sex-specific specialization is associated with distinct body-fat distribution and energy substrate-utilization patterns; i.e., females store more lipids and have higher whole-body insulin sensitivity than males, while males tend to oxidize more lipids than females. These patterns are influenced by the menstrual phase in females, and by nutritional status and exercise intensity in both sexes. This minireview focuses on sex-specific mechanisms in lipid and glucose metabolism and their regulation by sex hormones, with a primary emphasis on studies in humans and the most relevant pre-clinical model of human physiology, non-human primates.

The association between the serum C-peptide level and bone mineral density

Objective

Although serum C-peptide was previously considered biologically inactive, a growing number of recent studies have shown that it is an active peptide with important physiologic functions. The present study aimed to investigate the association of serum C-peptide level with bone mineral density (BMD) in residents of the United States.

Methods

The study included 6,625 participants aged 12–85 years. Total and regional BMD were measured using dual-energy X-ray absorptiometry. Stratified multiple linear regression analysis was performed to determine the association of the serum C-peptide level with BMD. Three regression models were produced for each stratum. All models were adjusted for ethnicity, height, weight, education level, physical activity, smoking status, alcohol use, triglycerides and creatinine level, and models 2 and 3 were further adjusted for the fasting plasma glucose (FPG) and alkaline phosphatase (ALP) levels, respectively.

Results

Sex-specific results showed a significant association between the serum C-peptide level and total BMD in both sexes. Stratified analyses based on age and body mass index showed that serum C-peptide levels were significantly negatively associated with most regional BMD, and most of these associations remained significant after stratification based on the serum insulin level.

Conclusion

The serum C-peptide level was significantly negatively associated with the total and most regional BMD. These findings suggest that serum C-peptide may have biological activity associated with bone metabolism and therefore serum C-peptide control is advisable in order to reduce the risk of low bone mineral density.

The abundance of fecal Faecalibacterium prausnitzii in relation to obesity and gender in Chinese adults

The influence of gender and obesity on the abundance of human colonic Feacalibacterium prausnitzii is currently unclear. We collected fecal samples from 54 obese and 54 sex- and age-matched normal-weight Chinese adults and quantified the fecal F. prausnitzii as percentage of 16S rRNA gene copies of F. prausnitzii accounting to that of total gut bacteria with quantitative PCR. The fecal F. prausnitzii amount was not significantly different between obese and lean subjects. Men possessed significantly lower level of fecal F. prausnitzii than women, and the significant and positive correlation of fecal F. prausnitzii quantity with fasting glucose level was observed in men, not in women. Our results suggest that the gender effect, in addition to other factors including the geographic location, ethnicity, diet and gut transit times of study subjects, has to be considered when studying the relationship between gut F. prausnitzii and diseases.

β-Cell dysfunction is associated with metabolic syndrome severity in adults

BACKGROUND

Metabolic syndrome is prevalent in adults characterized by increased visceral adiposity and insulin resistance (IR). However, the link between pancreatic β-cell function and metabolic syndrome severity in adults across the glucose spectrum is unknown. We hypothesized that poor β-cell function would independently predict a higher metabolic syndrome Z-score (i.e., severity).

METHODS

Seventy (12 normal glucose tolerant, 37 prediabetic, 21 type 2 diabetic) obese adults [62.4±1.1 year; 34.6±0.6 kg/m(2); data are mean±standard error of the mean (SEM)] participated in this cross-sectional study. A 2-hr 75-gram oral glucose tolerance test (OGTT) was administered, and insulin and glucose area under the curve was determined for calculations of insulin action. Fasting and glucose-stimulated insulin secretion was calculated using homeostasis model assessment of insulin secretion (HOMA-B) and the insulinogenic index (i.e., I(0-30)/Glc(0-30) or I(60-120)/Glc(60-120)), respectively. Fasting and postprandial insulin sensitivity was assessed by HOMA-IR and the Matsuda Index, respectively. β-cell function was estimated using the disposition index via HOMA-B/HOMA-IR, I(0-30)/Glc(0-30) or I(60-120)/Glc(60-120) × Matsuda Index, which represents basal, first-, and second-phase insulin release, respectively. Body composition (via computerized tomography and dual X-ray absorptiometry) and sex-specific metabolic syndrome Z-scores were calculated from waist circumference, blood pressure, fasting glucose, triglycerides, and high-density lipoproteins.

RESULTS

Compared to those with normal glucose tolerance, visceral fat and IR were higher and β-cell function was lower in adults with glucose intolerance and type 2 diabetes mellitus. Elevated visceral fat and IR (HOMA-IR and Matsuda Index) correlated with elevated Z-scores (r=0.51, r=0.54, r=-0.49; all P<0.002, respectively). Basal, first-, and second-phase β-cell function correlated with low Z-scores (r=-0.59, r=-0.51, and r=-0.43, all P<0.001). Insulin secretion significantly predicted the Z-score independent of sex, body fat, blood lipids, blood pressure, IR, and glucose metabolism (P<0.005).

CONCLUSION

β-cell dysfunction is highly correlated with the severity of metabolic syndrome in adults. Future work is warranted to elucidate the mechanism by which cardiometabolic disturbances influence insulin secretion.

Insulin resistance and fasting plasma glucose in first degree relatives of patients with type 1 diabetes

BACKGROUND

We analyzed the relationship between fasting plasma glucose (FPG), the presence of autoantibodies, first phase of insulin secretion and insulin resistance in the first degree relatives of patients with type 1 diabetes.

MATERIALS AND METHODS

The group studied consisted of 90 healthy relatives, divided into two groups: "high-normal" FPG group (≥88mg/dl) and "low-normal" FPG group (<88/mg/dl). All subjects underwent an intravenous glucose tolerance test, and the 1st phase insulin response (FPIR) and FPIR-to-HOMA-IR-ratio were calculated. Additionally, islet autoantibodies (GADA, IAA and IA-2A) were determined by radioimmunoassays.

RESULTS

The subjects with "high-normal" FPG were older (p=0.0009), had higher BMI (p<0.0001) and lower HOMA%B (p=0.0004), FPIR (p=0.006) and FPIR-to-HOMA-IR-ratio (p=0.004) in comparison with the "low-normal" FPG group. Autoantibodies were present in 40.9% and in 21.7% of the subjects with "high-normal" and "low-normal" FPG, respectively. In the "high-normal" FPG group, FPG correlated positively with GADA (r=0.31, p=0.04), and HOMA-IR (r=0.19, p=0.02), and negatively with HOMA%B (r=-0.36, p=0.001), whereas FPIR correlated positively with HOMA%B (r=0.55, p=0.0001) and BMI (r=0.30, p=0.04). After an adjustment for BMI, the difference in FPIR between the "high-normal" and "low-normal" FPG groups remained significant (p=0.025), whereas the difference in FPIR-to-HOMA-IR-ratio became insignificant.

CONCLUSIONS

Our results suggest that taking into account the impact of age and BMI on insulin sensitivity, it would be expected that the relatives of patients with type 1 diabetes with "high-normal" glucose levels would become gradually unable to compensate for increasing insulin resistance.

Race and sex differences in small-molecule metabolites and metabolic hormones in overweight and obese adults

In overweight/obese individuals, cardiometabolic risk factors differ by race and sex categories. Small-molecule metabolites and metabolic hormone levels might also differ across these categories and contribute to risk factor heterogeneity. To explore this possibility, we performed a cross-sectional analysis of fasting plasma levels of 69 small-molecule metabolites and 13 metabolic hormones in 500 overweight/obese adults who participated in the Weight Loss Maintenance trial. Principal-components analysis (PCA) was used for reduction of metabolite data. Race and sex-stratified comparisons of metabolite factors and metabolic hormones were performed. African Americans represented 37.4% of the study participants, and females 63.0%. Of thirteen metabolite factors identified, three differed by race and sex: levels of factor 3 (branched-chain amino acids and related metabolites, p<0.0001), factor 6 (long-chain acylcarnitines, p<0.01), and factor 2 (medium-chain dicarboxylated acylcarnitines, p<0.0001) were higher in males vs. females; factor 6 levels were higher in Caucasians vs. African Americans (p<0.0001). Significant differences were also observed in hormones regulating body weight homeostasis. Among overweight/obese adults, there are significant race and sex differences in small-molecule metabolites and metabolic hormones; these differences may contribute to risk factor heterogeneity across race and sex subgroups and should be considered in future investigations with circulating metabolites and metabolic hormones.

Selective slow wave sleep but not rapid eye movement sleep suppression impairs morning glucose tolerance in healthy men

Shortened nocturnal sleep impairs morning glucose tolerance. The underlying mechanism of this effect is supposed to involve a reduced fraction of slow wave sleep (SWS). However, it remains unanswered if impaired glucose tolerance occurs due to specific SWS reduction or a general disturbance of sleep. Sixteen healthy men participated in three experimental conditions in a crossover design: SWS suppression, rapid eye movement (REM)-sleep disturbance, and regular sleep. Selective sleep stage disturbance was performed by means of an acoustic tone (532Hz) with gradually rising sound intensity. Blood concentrations of glucoregulatory parameters were measured upon an oral glucose tolerance test the next morning. Our data show that morning plasma glucose and serum insulin responses were significantly increased after selective SWS suppression. Moreover, SWS suppression reduced postprandial insulin sensitivity up to 20%, as determined by Matsuda Index. Contrastingly, disturbed REM-sleep did not affect glucose homeostasis. We conclude that specifically SWS reduction is critically involved in the impairment of glucose tolerance associated with disturbed sleep. Therefore, glucose metabolism in subjects predisposed to reduced SWS (e.g. depression, aging, obstructive sleep apnea, pharmacological treatment) should be thoroughly monitored.

High fasting blood glucose and obesity significantly and independently increase risk of breast cancer death in hormone receptor-positive disease

PURPOSE

We investigated the effect of fasting blood glucose and body mass index (BMI) at diagnosis on risk of breast cancer death for cases diagnosed in five Italian cancer registries in 2003-2005 and followed up to the end of 2008.

METHODS

For 1607 Italian women (≥15 years) with information on BMI or blood glucose or diabetes, we analysed the risk of breast cancer death in relation to glucose tertiles (≤84.0, 84.1-94.0, >94.0 mg/dl) plus diabetic and unspecified categories; BMI tertiles (≤23.4, 23.5-27.3, >27.3 kg/m(2), unspecified), stage (T1-3N0M0, T1-3N+M0 plus T4anyNM0, M1, unspecified), oestrogen (ER) and progesterone (PR) status (ER+PR+, ER-PR-, ER and PR unspecified, other), age, chemotherapy and endocrine therapy, using multiple regression models. Separate models for ER+PR+ and ER-PR- cases were also run.

RESULTS

Patients often had T1-3N0M0, ER+PR+ cancers and received chemotherapy or endocrine therapy; only 6% were M1 and 17% ER-PR-. Diabetic patients were older and had more often high BMI (>27 kg/m(2)), ER-PR-, M1 cancers than other patients. For ER+PR+ cases, with adjustment for other variables, breast cancer mortality was higher in women with high BMI than those with BMI 23.5-27.3 kg/m(2) (hazard ratio (HR)=2.9, 95% confidence interval (CI) 1.2-6.9). Breast cancer mortality was also higher in women with high (>94 mg/dl) blood glucose compared to those with glucose 84.1-94.0mg/dl (HR=2.6, 95% CI 1.2-5.7).

CONCLUSION

Our results provide evidence that in ER+PR+ patients, high blood glucose and high BMI are independently associated with increased risk of breast cancer death. Detection and correction of these factors in such patients may improve prognosis.

Postprandial glucose fluxes and insulin sensitivity during exercise: a study in healthy individuals

Quantifying the effect size of acute exercise on insulin sensitivity (SI(exercise)) and simultaneous measurement of glucose disappearance (R(d)), endogenous glucose production (EGP), and meal glucose appearance in the postprandial state has not been developed in humans. To do so, we studied 12 healthy subjects [5 men, age 37.1 ± 3.1 yr, body mass index 24.1 ± 1.1 kg/m², fat-free mass (FFM) 50.9 ± 3.9 kg] during moderate exercise at 50% V(O₂max) for 75 min, 120-195 min after a triple-tracer mixed meal consumed at time 0. Tracer infusion rates were adjusted to achieve constant tracer-to-tracee ratio and minimize non-steady-state errors. Glucose turnover was estimated by accounting for the nonstationary kinetics introduced by exercise. Insulin sensitivity index was calculated in each subject both in the absence [time (t) = 0-120 min, SI(rest)] and presence (t = 0-360 min, SI(exercise)) of physical activity. EGP at t = 0 min (13.4 ± 1.1 μM·kg FFM⁻¹·min⁻¹) fell at t = 120 min (2.4 ± 0.4 μM·kg FFM⁻¹·min⁻¹) and then rapidly rose almost eightfold at t = 180 min (18.2 ± 2.6 μM·kg FFM⁻¹·min⁻¹) before gradually falling at t = 360 min (10.6 ± 0.9 μM·kg FFM⁻¹·min⁻¹). R(d) rapidly peaked at t = 120 min at the start of exercise (89.5 ± 11.6 μM·kg FFM⁻¹·min⁻¹) and then gradually declined at t = 195 min (26.4 ± 3.3 μM·kg FFM⁻¹·min⁻¹) before returning to baseline at t = 360 min. SI(exercise) was significantly higher than SI(rest) (21.6 ± 3.7 vs. 12.5 ± 2.0 10⁻⁴ dl·kg⁻¹·min⁻¹ per μU/ml, P < 0.0005). Glucose turnover was estimated for the first time during exercise with the triple-tracer technique. Our results, applying state-of-the-art techniques, show that moderate exercise almost doubles postprandial insulin sensitivity index in healthy subjects.

Sex-specific association of fetuin-A with type 2 diabetes in older community-dwelling adults: the Rancho Bernardo study

OBJECTIVE

This study evaluated the sex-specific association of plasma fetuin-A levels with prevalent and incident type 2 diabetes in community-dwelling older adults.

RESEARCH DESIGN AND METHODS

Participants were 684 men and 1,058 women (median age, 71 years) whose fetuin-A levels, diabetes prevalence, and diabetes risk factors were evaluated in 1992-1996. The participants were followed for incident diabetes through 2010 (median follow-up, 9 years).

RESULTS

Women with impaired glucose tolerance had elevated fetuin-A levels compared with women with normal glucose tolerance (P = 0.019), but fetuin-A levels were not elevated in women with impaired fasting glucose. Fetuin-A did not vary by glucose tolerance status in men. There were significant interactions of fetuin-A by sex for prevalent (P = 0.007) and incident (P = 0.020) diabetes. For women, each SD (0.10 g/L) higher fetuin-A level was associated with a higher odds of prevalent diabetes (odds ratio [OR] 1.79, 95% CI 1.47-2.17) and greater risk of incident diabetes (hazard ratio [HR] 1.66, 95% CI 1.18-2.34), adjusting for age and estrogen therapy. These associations were not materially altered by adjustment for diabetes risk factors but were attenuated by adjusting for postchallenge glucose levels. Among men, although positive associations with prevalent (OR 1.15 [0.94-1.41]) and incident (HR 1.24 [0.93-1.65]) diabetes were suggested in age-adjusted models, risk estimates attenuated to one after multivariable adjustment.

CONCLUSIONS

Higher fetuin-A concentrations were independently associated with an increased risk of developing type 2 diabetes in older women but were not related to diabetes risk in older men. Fetuin-A may provide novel insights into mechanisms underlying sex differences in glucose homeostasis and diabetes risk in old age.

Sex, sex steroids, and diabetic cardiomyopathy: making the case for experimental focus

More than three decades ago, the Framingham study revealed that cardiovascular risk is elevated for all diabetics and that this jeopardy is substantially accentuated for women in particular. Numerous studies have subsequently documented worsened cardiac outcomes for women. Given that estrogen and insulin exert major regulatory effects through common intracellular signaling pathways prominent in maintenance of cardiomyocyte function, a sex-hormone:diabetic-disease interaction is plausible. Underlying aspects of female cardiovascular pathophysiology that exaggerate cardiovascular diabetic risk may be identified, including increased vulnerability to coronary microvascular disease, age-dependent impairment of insulin-sensitivity, and differential susceptibility to hyperglycemia. Since Framingham, considerable progress has been made in the development of experimental models of diabetic disease states, including a diversity of genetic rodent models. Ample evidence indicates that animal models of both type 1 and 2 diabetes variably recapitulate aspects of diabetic cardiomyopathy including diastolic and systolic dysfunction, and cardiac structural pathology including fibrosis, loss of compliance, and in some instances ventricular hypertrophy. Perplexingly, little of this work has explored the relevance and mechanisms of sexual dimorphism in diabetic cardiomyopathy. Only a small number of experimental studies have addressed this question, yet the prospects for gaining important mechanistic insights from further experimental enquiry are considerable. The case for experimental interrogation of sex differences, and of sex steroid influences in the aetiology of diabetic cardiomyopathy, is particularly compelling-providing incentive for future investigation with ultimate therapeutic potential.

Retinol binding protein 4 and incident diabetes--the Atherosclerosis Risk in Communities Study (ARIC Study)

BACKGROUND

Retinol binding protein 4 (RBP4) has been described as a link between impaired glucose uptake in adipocytes and systemic insulin sensitivity.

OBJECTIVE

To determine whether RBP4 fasting levels predict the development of type 2 diabetes.

METHODS

Using a case-cohort design, we followed 543 middle-aged individuals who developed diabetes and 537 who did not over ~9 years within the population-based Atherosclerosis Risk in Communities Study. Weighted Cox proportional hazards analyses permitted statistical inference of the RBP4 - incident diabetes associations to the entire cohort.

RESULTS

Women in the highest tertile of RBP4 presented greater risk of developing diabetes (HR = 1.74; 95%CI 1.03 - 2.94) in analyses adjusted for age, ethnicity, study center, parental history of diabetes, hypertension, glomerular filtration rate, body mass index, waist-hip ratio, nonesterified fatty acids, adiponectin, leptin, triglycerides and HDL-C. When additionally adjusted for fasting insulin, this association's significance became borderline (HR = 1.68; 95%CI 1.00 - 2.82). No association between RBP4 levels and incident diabetes was found in men.

CONCLUSION

These findings suggest that RBP4 levels may be directly involved in the pathogenesis of type 2 diabetes in women.

Assessment of insulin action on carbohydrate metabolism: physiological and non-physiological methods

Carbohydrate metabolism in humans is regulated by insulin secretion from pancreatic β-cells and glucose disposal by insulin-sensitive tissues. Insulin facilitates glucose utilization in peripheral tissues and suppresses hepatic glucose production. Any defects in insulin action predispose an individual to glucose intolerance and Type 2 diabetes mellitus. Early detection of defects in insulin action could provide opportunities to prevent or delay progression of the disease state. There are different approaches to assess insulin action. Initial methods, such as peripheral insulin concentration and simple indices, have several limitations. Subsequently, researchers developed methodologies using intravenous glucose infusion to determine glucose fluxes. However, these methodologies are limited by being non-physiological. Newer, innovative techniques that have been developed are more sophisticated and physiological. By modelling glucose kinetics using isotope dilution techniques, several robust parameters can be obtained that are physiologically relevant and sound. This brief review summarizes most of the non-physiological and physiological methodologies used to measure the variables of insulin action.

Absorption patterns of meals containing complex carbohydrates in type 1 diabetes

AIMS/HYPOTHESIS

Successful postprandial glycaemia management requires understanding of absorption patterns after meals containing variable complex carbohydrates. We studied eight young participants with type 1 diabetes to investigate a large low-glycaemic-load (LG) meal and another eight participants to investigate a high-glycaemic-load (HG) meal matched for carbohydrates (121 g).

METHODS

On Visit 1, participants consumed an evening meal. On follow-up Visit 2, a variable-target glucose clamp was performed to reproduce glucose and insulin levels from Visit 1. Adopting stable-label tracer dilution methodology, we measured endogenous glucose production on Visit 2 and subtracted it from total glucose appearance measured on Visit 1 to obtain meal-attributable glucose appearance.

RESULTS

After the LG meal, 25%, 50% and 75% of cumulative glucose appearance was at 88 ± 21, 175 ± 39 and 270 ± 54 min (mean ± SD), whereas glucose from the HG meal appeared significantly faster at 56 ± 12, 100 ± 25 and 153 ± 39 min (p < 0.001 to 0.003), and resulted in a 50% higher peak appearance (p < 0.001). Higher apparent bioavailability by 15% (p = 0.037) was observed after the LG meal. We documented a 20 min deceleration of dietary mixed carbohydrates compared with dietary glucose for the HG meal and a twofold deceleration for the LG meal.

CONCLUSIONS/INTERPRETATION

Absorption patterns may be influenced by glycaemic load and/or meal composition, affecting optimum prandial insulin dosing in type 1 diabetes.

MATLAB-implemented estimation procedure for model-based assessment of hepatic insulin degradation from standard intravenous glucose tolerance test data

Present study provides a novel MATLAB-based parameter estimation procedure for individual assessment of hepatic insulin degradation (HID) process from standard frequently-sampled intravenous glucose tolerance test (FSIGTT) data. Direct access to the source code, offered by MATLAB, enabled us to design an optimization procedure based on the alternating use of Gauss-Newton's and Levenberg-Marquardt's algorithms, which assures the full convergence of the process and the containment of computational time. Reliability was tested by direct comparison with the application, in eighteen non-diabetic subjects, of well-known kinetic analysis software package SAAM II, and by application on different data. Agreement between MATLAB and SAAM II was warranted by intraclass correlation coefficients ≥0.73; no significant differences between corresponding mean parameter estimates and prediction of HID rate; and consistent residual analysis. Moreover, MATLAB optimization procedure resulted in a significant 51% reduction of CV% for the worst-estimated parameter by SAAM II and in maintaining all model-parameter CV% <20%. In conclusion, our MATLAB-based procedure was suggested as a suitable tool for the individual assessment of HID process.

Modeling hepatic insulin sensitivity during a meal: validation against the euglycemic hyperinsulinemic clamp

Recently, we proposed a model describing the suppression of endogenous glucose production (EGP) during a meal. It assumes that EGP suppression depends on glucose concentration and its rate of change and on delayed insulin action. Hepatic insulin sensitivity (S(I)(Lmeal)) can be derived from EGP model parameters. This model was shown to adequately describe EGP profiles measured with multiple tracer techniques; however, S(I)(Lmeal) has never been compared directly with its euglycemic hyperinsulinemic clamp counterpart (S(I)(Lclamp)). To do so, 62 subjects with different degrees of glucose tolerance underwent a triple-tracer mixed meal. Fifty-seven subjects also underwent a labeled ([3-(3)H]glucose) euglycemic hyperinsulinemic clamp. From the triple-tracer meal data, virtually model-independent estimates of EGP were obtained using the tracer-to-tracee clamp technique, and the EGP model was identified in each subject. Model fit was satisfactory, and S(I)(Lmeal) was estimated with good precision. Correlation between S(I)(Lclamp) and S(I)(Lmeal) was good (r = 0.72, P < 0.001); however, S(I)(Lmeal) was lower than S(I)(Lclamp) (4.60 ± 0.64 vs. 8.73 ± 1.07 10(-4) dl·kg(-1)·min(-1) per μU/ml, P < 0.01). This difference may be due to different ranges of insulin explored during the two tests (ΔI(clamp) = 15.60 ± 1.61 vs. ΔI(meal)= 83.37 ± 10.71 μU/ml) as well as steady- vs. non-steady-state glucose and insulin profiles. In conclusion, the new EGP model provides an estimate of hepatic insulin sensitivity during a meal that is in good agreement with that derived in the same individuals with a hyperinsulinemic clamp. When used in conjunction with the minimal model, the approach potentially enables estimation of hepatic insulin sensitivity from a single-tracer labeled meal or oral glucose tolerance test.

Systemic and local impact of glucose and glucose degradation products in peritoneal dialysis solution

The main osmotic agent used in the peritoneal dialysis (PD) solution is glucose because of its great osmotic power, simple metabolism, and safety. Once into the systemic circulation, however, glucose can be a cause for metabolic complications including hyperglycemia, obesity, and dyslipidemia. The glucose absorbed from peritoneal cavity leads to insulin resistance and hyperglycemia, which is associated with oxidative stress. Long-term exposure of peritoneal membrane to glucose in PD solution also has local effects such as functional and structural changes leading to peritoneal membrane failure. Moreover, the intraperitoneal glucose absorption induces conditions similar to postprandial hyperglycemia, which is a proven independent risk factor of coronary artery disease in patients with type 2 diabetes. Though speculative, glucose toxicity might explain a higher mortality of PD patients after the first few years compared with those on hemodialysis. Glucose degradation products (GDPs) induce apoptosis of peritoneal mesothelial cells (PMCs), renal tubular epithelial cells, and endothelial cells, and facilitating epithelial mesenchymal transition of PMCs. GDPs provide a stronger reactivity than glucose in the formation of advanced glycation end-products, a known cause for microvascular complications and arteriosclerosis. Unfortunately, clinical studies using a low-GDP PD solution have provided mixed results on the residual renal function, peritonitis, peritoneal membrane function, and mortality; consistent outcome data are not readily available at present.

Diurnal pattern to insulin secretion and insulin action in healthy individuals

Evaluation of the existence of a diurnal pattern of glucose tolerance after mixed meals is important to inform a closed-loop system of treatment for insulin requiring diabetes. We studied 20 healthy volunteers with normal fasting glucose (4.8 ± 0.1 mmol/L) and HbA(1c) (5.2 ± 0.0%) to determine such a pattern in nondiabetic individuals. Identical mixed meals were ingested during breakfast, lunch, or dinner at 0700, 1300, and 1900 h in randomized Latin square order on 3 consecutive days. Physical activity was the same on all days. Postprandial glucose turnover was measured using the triple tracer technique. Postprandial glucose excursion was significantly lower (P < 0.01) at breakfast than lunch and dinner. β-Cell responsivity to glucose and disposition index was higher (P < 0.01) at breakfast than lunch and dinner. Hepatic insulin extraction was lower (P < 0.01) at breakfast than dinner. Although meal glucose appearance did not differ between meals, suppression of endogenous glucose production tended to be lower (P < 0.01) and insulin sensitivity tended to be higher (P < 0.01) at breakfast than at lunch or dinner. Our results suggest a diurnal pattern to glucose tolerance in healthy humans, and if present in type 1 diabetes, it will need to be incorporated into artificial pancreas systems.

Insulin-mediated FFA suppression is associated with triglyceridemia and insulin sensitivity independent of adiposity

CONTEXT

A central/visceral fat distribution and excess free fatty acid (FFA) availability are associated with dyslipidemia and insulin resistance. However, these two characteristics often coexist, making it difficult to detect the independent contributions of each. Whether FFA suppression is more closely linked to metabolic abnormalities is not clear.

OBJECTIVE

The aim of the study was to examine the relationship between FFA suppression, body fat distribution, and fitness as contributors toward insulin resistance and hypertriglyceridemia.

DESIGN

We measured systemic palmitate turnover using an iv infusion of [9,10-(3)H]palmitate; upper body sc adipose tissue (UBSQ) and visceral adipose tissue (VAT) with dual-energy x-ray absorptiometry and a single-slice abdominal computed tomography scan; fitness with a graded exercise treadmill test; and insulin sensitivity with both the iv glucose tolerance test (IVGTT) (SI(IVGTT)) and mixed meal tolerance test (SI(Meal)).

SETTING

The study was conducted at a General Clinical Research Center.

PARTICIPANTS

Baseline data were obtained from 140 elderly adults (age, 60-88 yr; 83 males) and 60 young adults (age, 18-31 yr; 31 males) who participated in a previously published trial assessing the effects of 2-yr supplementation of dehydroepiandrosterone or testosterone on body composition, glucose metabolism, and bone density.

INTERVENTIONS

There were no interventions.

MAIN OUTCOME MEASURES

We measured fasting plasma triglyceride (TG) concentrations, SI(IVGTT), and SI(Meal).

RESULTS

Using multivariate regression analysis, the strongest combined predictors of TG concentrations were VAT, postmeal nadir FFA concentrations, sex, and age. The best predictors of SI(IVGTT) were IVGTT nadir palmitate concentration, VAT, UBSQ fat, fitness, and age, whereas the best predictors of SI(Meal) were meal nadir palmitate concentration, UBSQ fat, fitness, and sex.

CONCLUSIONS

FFA suppression is associated with both fasting TG concentrations and insulin sensitivity, independent of measures of adiposity.

The disposition index: from individual to population approach

To correctly evaluate the glucose control system, it is crucial to account for both insulin sensitivity and secretion. The disposition index (DI) is the most widely accepted method to do so. The original paradigm (hyperbolic law) consists of the multiplicative product of indices related to insulin sensitivity and secretion, but more recently, an alternative formula has been proposed with the exponent α (power function law). Traditionally, curve-fitting approaches have been used to evaluate the DI in a population: the algorithmic implementations often introduce some critical issues, such as the assumption that one of the two indices is error free or the effects of the log transformation on the measurement errors. In this work, we review the commonly used approaches and show that they provide biased estimates. Then we propose a novel nonlinear total least square (NLTLS) approach, which does not need to use the approximations built in the previously proposed alternatives, and show its superiority. All of the traditional fit procedures, including NLTLS, account only for uncertainty affecting insulin sensitivity and secretion indices when they are estimated from noisy data. Thus, they fail when part of the observed variability is due to inherent differences in DI values between individuals. To handle this inevitable source of variability, we propose a nonlinear mixed-effects approach that describes the DI using population hyperparameters such as the population typical values and covariance matrix. On simulated data, this novel technique is much more reliable than the curve-fitting approaches, and it proves robust even when no or small population variability is present in the DI values. Applying this new approach to the analysis of real IVGTT data suggests a value of α significantly smaller than 1, supporting the importance of testing the power function law as an alternative to the simpler hyperbolic law.

Developmental programming of aging of isolated pancreatic islet glucose-stimulated insulin secretion in female offspring of mothers fed low-protein diets in pregnancy and/or lactation

Diabetes predisposition is determined by pancreatic islet insulin secretion and insulin resistance. We studied female rat offspring exposed to low-protein maternal diet (50% control protein diet) in pregnancy and/or lactation at postnatal days 36, 110 and 450. Rats were fed either control 20% casein diet (C) or restricted diet (R – 10% casein) during pregnancy. After delivery, mothers received either C or R diet until weaning to provide four offspring groups: CC, RR, CR and RC (first letter denoting maternal pregnancy diet and the second lactation diet). Serum glucose, insulin and homeostatic model assessment (HOMA) were measured. Pancreatic islets were isolated and in vitro insulin secretion quantified in low glucose (5 mM) and high glucose (11 mM). Serum glucose, insulin and HOMA were similar in all groups at 36 and 110 postnatal days. HOMA was only higher in RR at 450 postnatal days. Only CC demonstrated differences in glucose sensitivity of β-cells to high and low doses at the three ages studied. At 36 days, RR, CR and RC and at 450 days RR and RC groups did not show glucose-stimulated insulin secretion differences between low and high glucose. Aging-associated glucose-stimulated insulin secretion loss was affected by maternal dietary history, indicating that developmental programming must be considered a major factor in aging-related development of predisposition to later-life dysfunctional insulin metabolism. Female offspring islets’ insulin secretion was higher than previously reported in males.

Glycemic index and glycemic load are associated with some cardiovascular risk factors among the PREMIER study participants

BACKGROUND

The clinical significance of glycemic index (GI) and glycemic load (GL) is inconclusive.

OBJECTIVE

This study was conducted to examine the association of GI and GL with clinical cardiovascular disease (CVD) risk factors including body weight, blood pressure (BP), serum lipids, fasting glucose, insulin and homocysteine over time among the PREMIER participants.

DESIGN

PREMIER was an 18-month randomized lifestyle intervention trial, conducted from 2000 to 2002, designed to help participants reduce BP by following the Dietary Approaches to Stop Hypertension (DASH) dietary pattern, losing weight, reducing sodium and increasing physical activity. GI and GL were estimated from 24 h diet recall data at baseline, 6 and 18 months after intervention. PROC MIXED model was used to examine the association of changes in GI or GL with changes in CVD risk factors.

RESULTS

A total of 756 randomized participants, 62% females and 34% African Americans and who averaged 50.0±0.3 years old and 95.3±0.7 kg, were included in this report. Neither GI nor GL changes was associated with changes in any risk factors at 6 months. At 18 months, however, the GI change was significantly and positively associated with total cholesterol (TC) change only (p<0.05, β=23.80±12.11 mg/dL or 0.62±0.31 mmol/L) with a significant age interaction. The GL change was significantly associated with TC (p=0.02, β=0.28±0.15 mg/dL or 0.01±0.00 mmol/L) positively and with low density lipoprotein cholesterol (LDL-C) changes negatively (p=0.03, β=-0.01±0.00 mg/dL or -0.00±0.00 mmol/L), and significant age interactions were observed for both.

CONCLUSIONS

GI and GL was associated with TC and LDL-C after controlling for energy, fat and fiber intake and other potential confounders and the associations were modified by age. Further investigation into this relationship is important because of its potential clinical impact.

Levels of C-peptide, body mass index and age, and their usefulness in classification of diabetes in relation to autoimmunity, in adults with newly diagnosed diabetes in Kronoberg, Sweden

OBJECTIVE

C-peptide is a main outcome measure in treatment trials of diabetes. C-peptide also has a role in the classification of diabetes, which is often difficult in adults and this is also increasingly recognised in adolescents and elders.

AIM

We aimed to describe the levels of C-peptide in relation to age and body mass index (BMI) in a large population-based cohort of adults with newly diagnosed diabetes and compare the capabilities of C-peptide, age and BMI to discriminate between autoimmune and non-autoimmune diabetes.

SUBJECTS AND METHODS

Blood samples from 1180 patients were analysed regarding islet cell antibody, glutamic acid decarboxylase antibody and fasting C-peptide (FCP). Receiver operating characteristics (ROC) curves were analysed to check the ability of age, BMI and C-peptide to discriminate between autoantibody-positive (Ab(+)) and -negative (Ab(-)) diabetes.

RESULTS

Mean FCP was 0.73±0.5 (range 0.13-1.80) nmol/l in the Ab(+) and 1.42±0.9 (range 0.13-8.30) nmol/l in the Ab(-). FCP was 0.02 nmol/l higher per year increase in age at diagnosis of diabetes. Mean BMI was 26.0±4.8 (range 18.0-39.0) kg/m(2) in the Ab(+) and 28.9±5.3 (range 15.5-62.6) kg/m(2) in the Ab(-). FCP increased with age also within each BMI group. The highest area under the curve (AUC) in the ROC analysis was found for C-peptide, followed by age and BMI (0.78, 0.68 and 0.66 respectively).

CONCLUSIONS

At diagnosis of diabetes, C-peptide was superior to age and BMI in discriminating between autoimmune and non-autoimmune diabetes. C-peptide increased significantly with BMI and age, latter also within each BMI group. Most of the adults had normal or high levels of C-peptide at presentation of diabetes among the autoimmune patients.

β-cell dysfunction in adolescents and adults with newly diagnosed type 2 diabetes mellitus

OBJECTIVE

To compare β-cell function in adolescents and adults with newly diagnosed type 2 diabetes (T2DM).

STUDY DESIGN

Thirty-nine adolescents with T2DM, 38 age- and weight-matched control subjects, and 19 adults with T2DM were studied. The adolescent subjects with diabetes were divided on the basis of whether they needed insulin to control their initial hyperglycemia. The primary outcome variable was the disposition index, computed from the acute insulin response to glucose corrected for insulin sensitivity (1/Homeostatic model assessment of insulin resistance).

RESULTS

The disposition index was significantly reduced in all 3 diabetic groups (control n=3360, adolescents with T2DM without insulin n=630, adolescents with T2DM with insulin n=120, adults with T2DM n=200; P<.001), and the adolescents with more severe hyperglycemia at diagnosis had lower disposition index than those with a more modest presentation (P<.05).

CONCLUSION

At the time of diagnosis, adolescents with T2DM have significant β-cell dysfunction, comparable with adults newly diagnosed with T2DM. Thus, severe β-cell impairment can develop within the first two decades of life and is likely to play a central role in the pathogenesis of T2DM in adolescents.

Pathophysiology of postprandial hyperglycaemia in women with type 1 diabetes during pregnancy

AIMS/HYPOTHESIS

Although maternal hyperglycaemia is associated with increased risk of adverse pregnancy outcome, the mechanisms of postprandial hyperglycaemia during pregnancy are poorly understood. We aimed to describe glucose turnover in pregnant women with type 1 diabetes, according to stage of gestation (early vs late gestation).

METHODS

The rates of systemic glucose appearance (R(a)) and glucose disposal (R(d)) were measured in ten pregnant women with type 1 diabetes during early (12-16 weeks) and late (28-32 weeks) gestation. Women ate standardised meals--a starch-rich 80 g carbohydrate dinner and a sugar-rich 60 g carbohydrate breakfast--and fasted between meals and overnight. Stable-label isotope tracers ([6,6-(2)H(2)]glucose and [U-(13)C]glucose) were used to determine R(a), R(d) and glucose bioavailability. Closed-loop insulin delivery maintained stable glycaemic conditions.

RESULTS

There were no changes in fasting R(a) (10 ± 2 vs 11 ± 2 μmol kg(-1) min(-1); p = 0.32) or fasting R(d) (11 ± 2 vs 11 ± 1 μmol kg(-1) min(-1); p = 0.77) in early vs late gestation. There was increased hepatic insulin resistance (381 ± 237 vs 540 ± 242 μmol kg(-1) min(-1) × pmol/l; p = 0.04) and decreased peripheral insulin sensitivity (0.09 ± 0.04 vs 0.05 ± 0.02 μmol kg(-1) min(-1) per pmol/l dinner, 0.11 ± 0.05 vs 0.07 ± 0.03 μmol kg(-1) min(-1) per pmol/l breakfast; p = 0.002) in late gestation. It also took longer for insulin levels to reach maximal concentrations (49 [37-55] vs 71 [52-108] min; p = 0.004) with significantly delayed glucose disposal (108 [87-125] vs 135 [110-158] min; p = 0.005) in late gestation.

CONCLUSIONS/INTERPRETATION

Postprandial glucose control is impaired by significantly slower glucose disposal in late gestation. Early prandial insulin dosing may help to accelerate glucose disposal and potentially ameliorate postprandial hyperglycaemia in late pregnancy.

TRIAL REGISTRATION

ISRCTN 62568875

FUNDING

Diabetes UK Project Grant BDA 07/003551. H.R. Murphy is funded by a National Institute for Health Research (NIHR) research fellowship (PDF/08/01/036). Supported also by the Juvenile Diabetes Research Foundation (JDRF), Abbott Diabetes Care (Freestyle Navigator CGM and sensors free of charge), Medical Research Council Centre for Obesity and Related Metabolic Diseases and NIHR Cambridge Biomedical Research Centre.

Impact of time since last caloric intake on blood glucose levels

Blood glucose (BG) is usually measured after a caloric restriction of at least 8 h; however evidence-based recommendations for the duration of a fasting status are missing. Here we analyze the effect of fasting duration on levels of BG to determine the minimal fasting duration to achieve comparable BG levels to conventional fasting measurements. We used data of a cross-sectional study on primary care patients, performed in October 2005. We included 28,024 individuals (age-range 18–99 years; 63% women) without known diabetes mellitus and without missing data for BG and fasting status. We computed general linear models, adjusting for age, sex, time of blood withdrawal, systolic blood pressure, waist circumference, total- and HDL-cholesterol, physical activity, smoking, intake of beta-blocker and alcohol. We tested the intra-individual variability with respect to fasting status. Overall, the mean BG differed only slightly between individuals fasting ≥8 h and those fasting <8 h (men: 5.1 ± 0.8 mmol/L versus 5.2 ± 1.2 mmol/L; women: 4.9 ± 0.7 mmol/L, 5.0 ± 1.0 mmol/L). After 3 h of fasting differences of BG diminished in men to −0.08 mmol/L (95%-CI: −0.15; −0.01 mmol/L), in women to −0.07 mmol/L (−0.12; −0.03 mmol/L) compared to individuals fasting ≥8 h. Noteworthy, age, time of day of blood withdrawal, physical activity, and intake of hard liquor influenced BG levels considerably. Our data challenge the necessity for a fasting duration of ≥8 h when measuring blood glucose, suggesting a random sampling or a fasting duration of 3 h as sufficient. Rather, our study indicates that essentially more effort on the assessment of additional external/internal factors on BG levels is necessary.

A hierarchical whole-body modeling approach elucidates the link between in Vitro insulin signaling and in Vivo glucose homeostasis

Type 2 diabetes is a metabolic disease that profoundly affects energy homeostasis. The disease involves failure at several levels and subsystems and is characterized by insulin resistance in target cells and tissues (i.e. by impaired intracellular insulin signaling). We have previously used an iterative experimental-theoretical approach to unravel the early insulin signaling events in primary human adipocytes. That study, like most insulin signaling studies, is based on in vitro experimental examination of cells, and the in vivo relevance of such studies for human beings has not been systematically examined. Herein, we develop a hierarchical model of the adipose tissue, which links intracellular insulin control of glucose transport in human primary adipocytes with whole-body glucose homeostasis. An iterative approach between experiments and minimal modeling allowed us to conclude that it is not possible to scale up the experimentally determined glucose uptake by the isolated adipocytes to match the glucose uptake profile of the adipose tissue in vivo. However, a model that additionally includes insulin effects on blood flow in the adipose tissue and GLUT4 translocation due to cell handling can explain all data, but neither of these additions is sufficient independently. We also extend the minimal model to include hierarchical dynamic links to more detailed models (both to our own models and to those by others), which act as submodules that can be turned on or off. The resulting multilevel hierarchical model can merge detailed results on different subsystems into a coherent understanding of whole-body glucose homeostasis. This hierarchical modeling can potentially create bridges between other experimental model systems and the in vivo human situation and offers a framework for systematic evaluation of the physiological relevance of in vitro obtained molecular/cellular experimental data.

A closed-loop artificial pancreas based on risk management

BACKGROUND

Control algorithms that regulate blood glucose (BG) levels in individuals with type 1 diabetes mellitus face several fundamental challenges. Two of these are the asymmetric risk of clinical complications associated with low and high glucose levels and the irreversibility of insulin action when using only insulin. Both of these nonlinearities force a controller to be more conservative when uncertainties are high. We developed a novel extended model predictive controller (EMPC) that explicitly addresses these two challenges.

METHOD

Our extensions to model predictive control (MPC) operate in three ways. First, they explicitly minimize the combined risk of hypoglycemia and hyperglycemia. Second, they integrate the effect of prediction uncertainties into the risk. Third, they understand that future control actions will vary if measurements fall above or below predictions. Using the University of Virginia/Padova Simulator, we compared our novel controller (EMPC) against optimized versions of a proportional-integral-derivative (PID) controller, a traditional MPC, and a basal/bolus (BB) controller, as well as against published results of an independent MPC (IMPC). The BB controller was optimized retrospectively to serve as a bound on the possible performance.

RESULTS

We tuned each controller, where possible, to minimize a published blood glucose risk index (BGRI). The simulated controllers (PID/MPC/EMPC/BB) provided BGRI values of 2.99/3.05/2.51/1.27 as compared to the published IMPC BGRI value of 4.10. These correspond to 73/79/84/92% of BG values lying in the euglycemic range (70-180 mg/dl), respectively, with mean BG levels of 151/156/147/140 mg/dl.

CONCLUSION

The EMPC strategy extends MPC to explicitly address the issues of asymmetric glycemic risk and irreversible insulin action using estimated prediction uncertainties and an explicit risk function. This controller reduces the avoidable BGRI by 56% (p < .05) relative to a published MPC algorithm studied on a similar population.