Impaired fasting glucose with or without impaired glucose tolerance: progressive or parallel states of prediabetes?

Prediabetes and Cardiometabolic Risk: The Need for Improved Diagnostic Strategies and Treatment to Prevent Diabetes and Cardiovascular Disease

The progression from prediabetes to type-2 diabetes depends on multiple pathophysiological, clinical, and epidemiological factors that generally overlap. Both insulin resistance and decreased insulin secretion are considered to be the main causes. The diagnosis and approach to the prediabetic patient are heterogeneous. There is no agreement on the diagnostic criteria to identify prediabetic subjects or the approach to those with insufficient responses to treatment, with respect to regression to normal glycemic values or the prevention of complications. The stratification of prediabetic patients, considering the indicators of impaired fasting glucose, impaired glucose tolerance, or HbA1c, can help to identify the sub-phenotypes of subjects at risk for T2DM. However, considering other associated risk factors, such as impaired lipid profiles, or risk scores, such as the Finnish Diabetes Risk Score, may improve classification. Nevertheless, we still do not have enough information regarding cardiovascular risk reduction. The sub-phenotyping of subjects with prediabetes may provide an opportunity to improve the screening and management of cardiometabolic risk in subjects with prediabetes.

Hyperinsulinemia is a probable trigger for weight gain and hyperphagia in individuals with Prader-Willi syndrome

Objective

Prader-Willi syndrome (PWS) is the most frequently diagnosed genetic cause of early childhood obesity. Individuals with PWS typically progress through 7 different nutritional phases during their lifetime. The main objective of this study was to assess potential factors, particularly insulin, that may be responsible for the weight gains in sub-phase 2a and their role in the subsequent increase in fat mass and obesity in sub-phase 2b and insatiable appetite in phase 3.

Methods

Fasting plasma insulin levels were measured in children with PWS between the ages of 0-12 years and in age-matched non-PWS participants with early-onset major (clinically severe) obesity (EMO) and in healthy-weight sibling controls (SC).

Results

Participants with PWS in nutritional phases 1a and 1b had plasma insulin levels comparable to SC. However, the transition from phase 1b up to phase 3 in the PWS group was accompanied by significant increases in insulin, coinciding in weight gains, obesity, and hyperphagia. Only individuals with PWS in phase 3 had comparable insulin levels to the EMO group who were higher than the SC group at any age.

Conclusions

Elevated insulin signaling is a probable trigger for weight gain and onset of hyperphagia in children with Prader-Willi syndrome. Regulating insulin levels early in childhood before the onset of the early weight gain may be key in modulating the onset and severity of obesity and hyperphagia in individuals with PWS, as well as in other young children with non-PWS early-onset obesity. Preventing or reversing elevated insulin levels in PWS with pharmacological agents and/or through diet restrictions such as a combined low carbohydrate, low glycemic-load diet may be a viable therapeutic strategy in combating obesity in children with PWS and others with early childhood obesity.

Diagnosis and Management of Prediabetes: A Review

Importance

Prediabetes, an intermediate stage between normal glucose regulation and diabetes, affects 1 in 3 adults in the US and approximately 720 million individuals worldwide.

Observations

Prediabetes is defined by a fasting glucose level of 100 to 125 mg/dL, a glucose level of 140 to 199 mg/dL measured 2 hours after a 75-g oral glucose load, or glycated hemoglobin level (HbA1C) of 5.7% to 6.4% or 6.0% to 6.4%. In the US, approximately 10% of people with prediabetes progress to having diabetes each year. A meta-analysis found that prediabetes at baseline was associated with increased mortality and increased cardiovascular event rates (excess absolute risk, 7.36 per 10 000 person-years for mortality and 8.75 per 10 000 person-years for cardiovascular disease during 6.6 years). Intensive lifestyle modification, consisting of calorie restriction, increased physical activity (≥150 min/wk), self-monitoring, and motivational support, decreased the incidence of diabetes by 6.2 cases per 100 person-years during a 3-year period. Metformin decreased the risk of diabetes among individuals with prediabetes by 3.2 cases per 100 person-years during 3 years. Metformin is most effective for women with prior gestational diabetes and for individuals younger than 60 years with body mass index of 35 or greater, fasting plasma glucose level of 110 mg/dL or higher, or HbA1c level of 6.0% or higher.

Conclusions and Relevance

Prediabetes is associated with increased risk of diabetes, cardiovascular events, and mortality. First-line therapy for prediabetes is lifestyle modification that includes weight loss and exercise or metformin. Lifestyle modification is associated with a larger benefit than metformin.

Impaired fasting glucose levels in overweight or obese subjects for screening of type 2 diabetes in Korea

BACKGROUND/AIMS

We examined the concordance rate among fasting plasma glucose (FPG), 2-hour post-challenge glucose (2hr PG), and hemoglobin A1c (HbA1c) in the diagnosis of diabetes in a population with a high-risk for type 2 diabetes mellitus (T2DM) in Korea.

METHODS

Among the participants from the Korean Diabetes Prevention Study, individuals with FPG ≥ 100 mg/dL, body mass index (BMI) ≥ 23.0 kg/m2, and no previous history of T2DM were consecutively enrolled after a 75 g glucose tolerance test. We analyzed the differences in the clinical characteristics in subjects with stage 1 (FPG, 100 to 109 mg/dL) and stage 2 (FPG, 110 to 125 mg/dL) impaired fasting glucose (IFG).

RESULTS

Of 1,637 participants, 27.2% had T2DM and 59.3% had IFG and/or impaired glucose tolerance (IGT). The mean age was 55.0 ± 8.1 years and the mean BMI was 26.3 ± 2.7 kg/m2. Based on FPG criteria, 515 (31.4%) and 352 (21.5%) subjects were classified as having stage 1 and stage 2 IFG, respectively. The 19.0% of stage 1 and 43.5% of stage 2 subjects showed 2hr PG levels in the diabetic range. Even for those in the normal FPG range, 63 (9.5%) participants showed a 2hr PG level of ≥ 200 mg/dL. Of 446 subjects with newly-diagnosed diabetes, 340 (76.2%) showed FPG levels < 126 mg/dL.

CONCLUSION

The oral glucose tolerance test should be actively considered for Korean adults who are overweight or obese with the IFG range (FPG, 100 to 125 mg/ dL) to allow for early detection of diabetes and prompt intervention.

Type 2 diabetes: one disease, many pathways

Diabetes is a chronic, progressive disease that calls for longitudinal data and analysis. We introduce a longitudinal mathematical model that is capable of representing the metabolic state of an individual at any point in time during their progression from normal glucose tolerance to type 2 diabetes (T2D) over a period of years. As an application of the model, we account for the diversity of pathways typically followed, focusing on two extreme alternatives, one that goes through impaired fasting glucose (IFG) first and one that goes through impaired glucose tolerance (IGT) first. These two pathways are widely recognized to stem from distinct metabolic abnormalities in hepatic glucose production and peripheral glucose uptake, respectively. We confirm this but go beyond to show that IFG and IGT lie on a continuum ranging from high hepatic insulin resistance and low peripheral insulin resistance to low hepatic resistance and high peripheral resistance. We show that IFG generally incurs IGT and IGT generally incurs IFG on the way to T2D, highlighting the difference between innate and acquired defects and the need to assess patients early to determine their underlying primary impairment and appropriately target therapy. We also consider other mechanisms, showing that IFG can result from impaired insulin secretion, that non-insulin-dependent glucose uptake can also mediate or interact with these pathways, and that impaired incretin signaling can accelerate T2D progression. We consider whether hyperinsulinemia can cause insulin resistance in addition to being a response to it and suggest that this is a minor effect.

A CROSS-SECTIONAL STUDY OF THE ASSOCIATION BETWEEN THE 1-HOUR ORAL GLUCOSE TOLERANCE TEST AND THE METABOLIC SYNDROME IN A HIGH-RISK SAMPLE WITH IMPAIRED FASTING GLUCOSE

Objective: The aim of this study was to evaluate the association between the 1-hour oral glucose tolerance test (OGTT) (≥155 mg/dL) and metabolic syndrome (MS) in a sample with previous impaired fasting glucose (IFG). Methods: Three hundred and twenty four Peruvian subjects with a history of IFG ≥100 mg/dL were selected for a cross-sectional study. They underwent a 75 g OGTT and were assigned to different groups according to the result. We evaluated the association between 1-hour OGTT and MS. Results: The mean age was 56.5 ± 12.6 years and 191 (61.5%) were female. During the OGTT, we found 28 (8.6%) subjects with diabetes, 74 (22.8%) with IGT, and 222 (68.5%) with a normal glucose tolerance test with a 2-hour glucose <140 mg/dL (NGT). In the NGT group, 124 (38.3%) had 1-hour glucose levels <155 mg/dL, while 98 (30.2%) had 1-hour glucose levels ≥155 mg/dL. Evaluating the association between the 1-hour value in the OGTT and MS, we found that subjects with a 1-hour glucose ≥155 mg/dL were more than twice as likely to have MS as those with a 1-hour glucose <155 mg/dL (odds ratio = 2.64, 95% confidence interval: 1.52 to 4.57). In addition, body mass index, fasting glycemia, triglycerides, and waist circumferences were significantly higher in subjects with 1-hour glucose levels ≥155 mg/dL compared to those with 1-hour glucose levels <155 mg/dL (P<.05). Conclusion: Among subjects with IFG, performing an OGTT was helpful to identify subjects with 1-hour glucose levels ≥155 mg/dL and NGT who were significantly more likely to have MS and a worse cardiometabolic risk profile. Abbreviations: AST = aspartate aminotransferase; BMI = body mass index; CI = confidence interval; IFG = impaired fasting glucose; IGT = impaired glucose tolerance; LDL = low-density lipoprotein; MS = metabolic syndrome; NGT = normal glucose tolerance; OGTT = oral glucose tolerance test; OR = odds ratio; T2DM = type 2 diabetes; TG = triglycerides.

The Natural Course of Impaired Fasting Glucose

Impaired glucose regulation, including diabetes and prediabetes, poses a huge global problem not only in health but also in the epidemiological and economic areas. These disorders are often detected too late or remain unrecognized. The article aims to provide a review of the prevalence, etiology, and natural history of impaired fasting glucose (IFG). We focus on the progression of isolated IFG to full-fledged type 2 diabetes and the factors conducive to the development of diabetes. The knowledge about it could help design an optimal management program for the prevention of diabetes in patients with IFG; a program that would be patient-tailored and based on the underlying pathophysiology.

Obesity Alters the Muscle Protein Synthetic Response to Nutrition and Exercise

Improving the health of skeletal muscle is an important component of obesity treatment. Apart from allowing for physical activity, skeletal muscle tissue is fundamental for the regulation of postprandial macronutrient metabolism, a time period that represents when metabolic derangements are most often observed in adults with obesity. In order for skeletal muscle to retain its capacity for physical activity and macronutrient metabolism, its protein quantity and composition must be maintained through the efficient degradation and resynthesis for proper tissue homeostasis. Life-style behaviors such as increasing physical activity and higher protein diets are front-line treatment strategies to enhance muscle protein remodeling by primarily stimulating protein synthesis rates. However, the muscle of individuals with obesity appears to be resistant to the anabolic action of targeted exercise regimes and protein ingestion when compared to normal-weight adults. This indicates impaired muscle protein remodeling in response to the main anabolic stimuli to human skeletal muscle tissue is contributing to poor muscle health with obesity. Deranged anabolic signaling related to insulin resistance, lipid accumulation, and/or systemic/muscle inflammation are likely at the root of the anabolic resistance of muscle protein synthesis rates with obesity. The purpose of this review is to discuss the impact of protein ingestion and exercise on muscle protein remodeling in people with obesity, and the potential mechanisms underlining anabolic resistance of their muscle.

Glucose-Mediated Glucose Disposal at Baseline Insulin Is Impaired in IFG

OBJECTIVE

To quantify glucose-mediated glucose disposal with and without basal insulin replacement and insulin-mediated glucose disposal in subjects with impaired fasting glucose (IFG).

RESEARCH DESIGN AND METHODS

We used the hyperglycemic/pancreatic clamp and stepped euglycemic clamp techniques to quantify glucose disposal and suppression of endogenous glucose production (EGP) in those with normal glucose tolerance (NGT; n = 14) and those with IFG (n = 14).

RESULTS

Total body glucose-mediated glucose uptake, measured with the hyperglycemic/pancreatic clamp, was not significantly affected by the basal plasma insulin levels in subjects with IFG and those with NGT. Compared with subjects with NGT, those with IFG had significantly lower glucose-mediated glucose uptake (by 15%) during the hyperglycemic clamp performed with and without basal insulin replacement. In contrast, insulin-mediated glucose disposal was comparable in both groups. The suppression of EGP by hyperglycemia was similar in both groups. However, the suppression of EGP by insulin was attenuated in those with IFG compared with those with NGT.

CONCLUSIONS

The results of the present study have demonstrated that (i) glucose-mediated glucose disposal is impaired in those with IFG; (ii) insulin-mediated glucose uptake in IFG is normal; and (iii) insulin action to suppress EGP is impaired.

Prevalence of Pre-Diabetes across Ethnicities: A Review of Impaired Fasting Glucose (IFG) and Impaired Glucose Tolerance (IGT) for Classification of Dysglycaemia

Prediabetes can be defined by the presence of impaired fasting glucose (IFG) and/or impaired glucose tolerance (IGT), or glycated haemoglobin (Hb_A1c) to identify individuals at increased risk of developing type 2 diabetes (T2D). The World Health Organization (WHO, 1999) and the American Diabetes Association (ADA, 2003) utilise different cut-off values for IFG (WHO: 6.1–6.9 mmol/L; ADA: 5.6–6.9 mmol/L) but the same cut-off values for IGT (7.8–11.0 mmol/L). This review investigates whether there are differences in prevalence of IFG, IGT, and combined IFG&IGT between ethnicities, in particular Asian Chinese and European Caucasians. In total, we identified 19 studies using the WHO₁₉₉₉ classification, for which the average proportional prevalence for isolated (i)-IFG, i-IGT, and combined IFG&IGT were 43.9%, 41.0%, and 13.5%, respectively, for Caucasian and 29.2%, 49.4%, and 18.2%, respectively, for Asian. For the 14 studies using ADA₂₀₀₃ classification, the average proportional i-IFG, i-IGT, and combined IFG&IGT prevalences were 58.0%, 20.3%, and 19.8%, respectively, for Caucasian; 48.1%, 27.7%, and 20.5%, respectively, for Asian. Whilst not statistically different, there may be clinically relevant differences in the two populations, with our observations for both classifications indicating that prevalence of i-IFG is higher in Caucasian cohorts whilst i-IGT and combined IFG&IGT are both higher in Asian cohorts.

Decreased basal hepatic glucose uptake in impaired fasting glucose

AIMS/HYPOTHESIS

This research aimed to define the pathophysiological defects responsible for the elevated fasting plasma glucose (FPG) concentration and excessive rise in post-load plasma glucose observed in individuals with impaired fasting glucose (IFG).

METHODS

We used tracer techniques to quantify basal splanchnic (primarily hepatic) glucose uptake and glucose fluxes following glucose ingestion in individuals with normal glucose tolerance (NGT; n = 10) and IFG (n = 10).

RESULTS

Individuals with IFG had a comparable basal rate of hepatic glucose production to those with NGT (15.2 ± 0.2 vs 18.0 ± 0.8 μmol min^-1 [kg lean body mass (LBM)]^-1; p = 0.09). However, they had a significantly reduced glucose clearance rate during the fasting state compared with NGT (2.64 ± 0.11 vs 3.62 ± 0.20 ml min^-1 [kg LBM]^-1; p < 0.01). The difference between the basal rate of glucose appearance measured with [3-³H]glucose and [1-¹⁴C]glucose, which represent basal splanchnic glucose uptake, was significantly reduced in IFG compared with NGT (1.39 ± 0.28 vs 3.16 ± 0.44 μmol min^-1 [kg LBM]^-1; p = 0.02). Following glucose ingestion, the total amount of exogenous glucose that appeared in the systemic circulation was not significantly different between groups. However, suppression of endogenous glucose production (EGP) was markedly impaired in individuals with IFG.

CONCLUSIONS/INTERPRETATION

These results demonstrate that decreased tissue (liver) glucose uptake, not enhanced EGP, is the cause for elevated FPG concentration in individuals with IFG, while the excessive rise in plasma glucose concentration following a glucose load in these individuals is the result of impaired suppression of hepatic glucose production.

Prediabetes as a toxic environment for the initiation of microvascular and macrovascular complications

Prediabetes is a state characterized by impaired fasting glucose or impaired glucose tolerance. Evidence is increasingly demonstrating that prediabetes is a toxic state, in addition to being a harbinger of future development of diabetes mellitus. This minireview discusses the pathophysiology and clinical significance of prediabetes, and approach to its management, in the context of the worldwide diabetes epidemic. The pathophysiologic defects underlying prediabetes include insulin resistance, β cell dysfunction, increased lipolysis, inflammation, suboptimal incretin effect, and possibly hepatic glucose overproduction. Recent studies have revealed that the long-term complications of diabetes may manifest in some people with prediabetes; these complications include classical microvascular and macrovascular disorders, and our discussion explores the role of glycemia in their development. Finally, landmark intervention studies in prediabetes, including lifestyle modification and pharmacologic treatment, are reviewed.

Prediabetes: A Worldwide Epidemic

Prediabetes, defined by blood glucose levels between normal and diabetic levels, is increasing rapidly worldwide. This abnormal physiologic state reflects the rapidly changing access to high-calorie food and decreasing levels of physical activity occurring worldwide, with resultant obesity and metabolic consequences. This is particularly marked in developing countries. Prediabetes poses several threats; there is increased risk of developing type 2 diabetes mellitus (T2DM), and there are risks inherent to the prediabetes state, including microvascular and macrovascular disease. Studies have helped to elucidate the underlying pathophysiology of prediabetes and to establish the potential for treating prediabetes and preventing T2DM.

Exercise resistance across the prediabetes phenotypes: Impact on insulin sensitivity and substrate metabolism

Prediabetes is a heterogeneous term that encompasses different origins of insulin resistance and insulin secretion that contribute to distinct patterns of hyperglycemia. In fact, prediabetes is an umbrella term that characterizes individuals at high risk for developing type 2 diabetes (T2D) and/or cardiovascular disease (CVD). Based on current definitions there are at least 3 distinct phenotypes of prediabetes: impaired fasting glucose (IFG), impaired glucose tolerant (IGT), or the combination of both (IFG + IGT). Each phenotype is clinically relevant as they are uniquely recognized as having different levels of risk for progressing to T2D and CVD. Herein, we discuss the underlying pathophysiology that characterizes IFG, IGT and the combination, as well as examine how some of these phenotypes appear resistant to traditional exercise interventions. We propose that substrate metabolism differences between the prediabetes phenotypes may be a unifying mechanism that explains the inter-subject variation in response to exercise seen across obese, metabolic syndrome, pre-diabetic and T2D patients in the current literature. Ultimately, a better understanding of the pathophysiologic mechanisms that govern disturbances responsible for fasting vs. postprandial hyperglycemia and the combination of both is important for designing optimal and personalized exercise treatment strategies that treat and prevent hyperglycemia and CVD risk.

Relationship between insulin resistance and β-cell dysfunction in subphenotypes of prediabetes and type 2 diabetes

CONTEXT

There is little overlap between diabetes diagnosed by glycated hemoglobin (HbA1c) and blood glucose, and it is unclear which pathophysiological defects are captured when using HbA1c for diagnosis.

OBJECTIVE

We examined and compared the relationship between insulin sensitivity and β-cell function in different subphenotypes of prediabetes and type 2 diabetes (T2D).

DESIGN, SETTING, AND PARTICIPANTS

A cross-sectional analysis of the Danish ADDITION-PRO study was performed (n = 1713). Participants without known diabetes were classified into subgroups of prediabetes and T2D based on fasting or 2-hour glucose criteria or HbA1c. Insulin sensitivity and insulin release were determined from glucose and insulin concentrations during the oral glucose tolerance test, and disposition indices were calculated.

RESULTS

Individuals with prediabetes or T2D diagnosed by fasting glucose had lower absolute insulin release (P ≤ .01) and higher insulin sensitivity in response to glucose intake (P ≤ .01) but a similar disposition index (P ≥ .36), compared with individuals with elevated 2-hour glucose concentrations. Individuals with HbA1c-defined T2D or prediabetes had a mixture of the pathophysiological defects observed in the glucose-defined subgroups, and individuals with normoglycemia by HbA1c had worse pathophysiological abnormalities than individuals with normoglycemia by the glucose criteria.

CONCLUSIONS

On average, the diagnostic HbA1c criteria for diabetes and prediabetes identified individuals with a mixture of the pathophysiological characteristics found when using the glucose criteria, but the diversity and pathophysiology captured by the oral glucose tolerance test cannot be captured when applying the more simple HbA1c criteria. Whether the disease progression and prognosis will differ in individuals diagnosed by fasting glucose, 2-hour glucose, or HbA1c should be examined in longitudinal studies.

The Early Diabetes Intervention Program--is early actually late?

This Commentary briefly reviews the background of prediabetes including its definition and pathophysiology and describes as well the natural course of glycemic deterioration as it follows a continuum. Research efforts in identifying glucose and other biomarkers for the early detection of high-risk individuals are summarized.

Hepatic glucose sensing is impaired, but can be normalized, in people with impaired fasting glucose

OBJECTIVE

Abnormal endogenous glucose production (EGP) is a characteristic feature in people with impaired fasting glucose (IFG). We sought to determine whether impaired hepatic glucose sensing contributes to abnormal EGP in IFG and whether it could be experimentally restored.

METHODS

Glucose production (rate of appearance; Ra) and flux (glucose cycling) were assessed during a hyperglycemic-euinsulinemic somatostatin clamp with an infusion of [6,6-(2)H2-]glucose and [2-(2)H]glucose before and after enhanced hepatic glucokinase activity via an infusion of low-dose fructose in people with IFG and normal glucose tolerance (NGT).

RESULTS

During euglycemia, neither endogenous glucose production [(6,6-(2)H2)-glucose Ra; P = 0.53] or total glucose output (TGO; [2-(2)H]-glucose Ra; P = .12) was different between groups, but glucose cycling ([2-(2)H]glucose Ra to [6,6-(2)H2-]glucose Ra; a surrogate measure of hepatic glucokinase activity in the postabsorptive state) was lower in IFG than NGT (P = .04). Hyperglycemia suppressed EGP more in NGT than IFG (P < .01 for absolute or relative suppression, NGT vs IFG), whereas TGO decreased similarly in both groups (P = .77). The addition of fructose completely suppressed EGP in IFG (P < .01) and tended to do the same to TGO (P = .01; no such changes in NGT, P = .39-.55). Glucose cycling (which reflects glucose-6-phosphatase activity during glucose infusion) was similar in IFG and NGT (P = .51) during hyperglycemia and was unchanged and comparable between groups with the addition of fructose (P = .24).

CONCLUSIONS

In summary, glucose sensing is impaired in IFG but can be experimentally restored with low-dose fructose. Glucokinase activation may prove to be a novel strategy for the prevention of diabetes in this high-risk group.

Approaching pre-diabetes

As the global epidemic of type 2 diabetes continues to rise, the time has come to revisit our approach to pre-diabetes. Recently, much ado has been made about screening, diagnosis, pathophysiology and clinical interventions in pre-diabetes, and all for good reason as the key to reversing the diabetes epidemic likely lies therein. The somewhat controversial term "pre-diabetes" represents collective dysglycemic states intermediate between normal glucose regulation (NGR) and diabetes. Not all people with pre-diabetes will develop diabetes, but the majority will. In fact, up to 70% of those with pre-diabetes may acquire the disease over their lifetime. Furthermore, even when overt diabetes is delayed or prevented, both micro- and macrovascular disease appears more prevalent in those with pre-diabetes compared to their normoglycemic peers. Hence, there is growing consensus that NGR should be the goal for people with pre-diabetes. Nevertheless, there is much to consider in that pursuit. Herein, we provide an update on the global burden of pre-diabetes, its underlying pathophysiology and discuss clinical considerations in these individuals at high risk of developing diabetes.

Trajectories of cardiometabolic risk factors before diagnosis of three subtypes of type 2 diabetes: a post-hoc analysis of the longitudinal Whitehall II cohort study

BACKGROUND

Most clinicians acknowledge that type 2 diabetes is multifactorial and has heterogeneous characteristics, but neither prevention nor treatment is systematically stratified. To address the heterogeneity of the disease, we examined whether patients diagnosed on the basis of fasting glucose concentrations, those diagnosed on the basis of 2 h concentrations, and those diagnosed on the basis of both criteria differed in terms of pathogenesis or cardiovascular risks.

METHODS

Retrospectively, we analysed trajectories of cardiometabolic risk factors and 10 year cardiovascular risks in the prospective Whitehall II study cohort by use of multilevel longitudinal modelling. Participants were diagnosed by 75 g oral glucose-tolerance tests. We classified those diagnosed with type 2 diabetes into three subgroups: diagnosed on the basis of fasting glucose concentrations, diagnosed on the basis of 2 h glucose concentrations, and diagnosed on the basis of both concentrations. We also developed a classification tree for identification of individuals who are likely to have high fasting and 2 h glucose concentrations, but for whom only fasting concentrations are available.

RESULTS

Median follow-up was 14·2 years with 15,826 person-examinations (1991-2009). Of 10,308 individuals, 6843 were included and 6569 remained diabetes free. 274 cases of type 2 diabetes were identified: 55 had high fasting glucose concentrations only, 148 had high 2 h concentrations only, and 71 had high fasting and 2 h concentrations. At diagnosis, participants with high fasting and 2 h glucose concentrations had higher mean body-mass indices (30·9 kg/m(2) [SD 5·7]) than did those with high fasting concentrations (28·4 kg/m(2) [4·4]; p=0·0009) or 2 h concentrations (27·9 kg/m(2) [4·9]; <0·0001). Mean glycated haemoglobin A1c concentrations were also higher in the fasting and 2 h subgroup (7·4% [1·6]) than in the fasting (5·9% [0·5]; <0·0001) or 2 h (5·9% [0·6]; <0·0001) sugroups. Additionally, the fasting and 2 h subgroup had a higher proportion of individuals with moderate or high risk of cardiovascular disease than did the fasting subgroup (p=0·02). A classic pattern of β-cell decompensation before diagnosis was noted only in the fasting and 2 h subgroup. Additionally, glucose concentrations and insulin resistance accelerated more substantially before diagnosis in the fasting and 2 h subgroup than in the fasting subgroup or the 2 h subgroup.

INTERPRETATION

Patients with type 2 diabetes diagnosed on the basis of increased fasting glucose concentrations or 2 h glucose concentrations, or both, have distinct cardiometabolic risk development before diagnosis.

FUNDING

UK Medical Research Council, UK Economic and Social Research Council, British Heart Foundation, UK Health and Safety Executive, UK Department of Health, US National Heart Lung and Blood Institute, US National Institute on Aging, US Agency for Health Care Policy Research, and John D and Catherine T MacArthur Foundation.

Mild fasting hyperglycemia shifts fuel reliance toward fat during exercise in adults with impaired glucose tolerance

Impaired glucose tolerance (IGT) is characterized by decreased oxidative capacity and reduced carbohydrate utilization during exercise. However, it is unclear if the presence of impaired fasting glucose (IFG) affects fuel utilization during exercise in adults with IGT. We tested the hypothesis that the presence of IFG in adults with IGT decreases reliance on carbohydrate during exercise. Middle-aged, obese, sedentary individuals (n = 6, IGT and n = 6, IFG+IGT) were compared during exercise at 60% peak O2 consumption for 45 min on a cycle ergometer. Glucose rates of appearance and disposal and muscle glycogen were assessed by stable isotope dilution methods, and fat utilization was estimated via indirect calorimetry. A 75-g oral glucose tolerance test was used to determine fasting and 2-h glucose concentrations. A glucose intolerance severity z-score was calculated from the oral glucose tolerance test. Glucose flux (i.e., rates of appearance and disposal) was not different between groups. However, individuals with IFG+IGT had lower muscle glycogen use (P < 0.05) and elevated fat oxidation (P < 0.01) during exercise compared with those with isolated IGT. Plasma nonesterified fatty acids and glucose were significantly higher during exercise in subjects with IFG+IGT vs. IGT alone (P < 0.05). Fat utilization during exercise correlated with fasting glucose (r = 0.57, P = 0.05), glucose intolerance severity z-score (r = 0.66, P = 0.01), and nonesterified fatty acids (trend; r = 0.55, P = 0.08). The presence of IFG shifts fuel selection toward increased fat oxidation and decreased muscle glycogen utilization during exercise in adults with IGT. Whether these differences in substrate use contribute to, or are the result of, movement along the continuum from prediabetes to type 2 diabetes awaits further work.

Pathogenesis of prediabetes: role of the liver in isolated fasting hyperglycemia and combined fasting and postprandial hyperglycemia

CONTEXT

People with prediabetes are at high risk of developing diabetes.

OBJECTIVE

The objective of this study was to determine the pathogenesis of fasting and postprandial hyperglycemia in prediabetes.

DESIGN

Glucose production, gluconeogenesis, glycogenolysis, and glucose disappearance were measured before and during a hyperinsulinemic clamp using [6,6-(2)H2]glucose and the deuterated water method corrected for transaldolase exchange.

SETTING

The study was conducted at the Mayo Clinic Clinical Research Unit.

PARTICIPANTS

Subjects with impaired fasting glucose (IFG)/normal glucose tolerance (NGT) (n = 14), IFG/impaired glucose tolerance (IGT) (n = 18), and normal fasting glucose (NFG)/NGT (n = 16) were studied.

INTERVENTION

A hyperinsulinemic clamp was used.

OUTCOME MEASURES

Glucose production, glucose disappearance, gluconeogenesis, and glycogenolysis were measured.

RESULTS

Fasting glucose production was higher (P < .0001) in subjects with IFG/NGT than in those with NFG/NGT because of increased rates of gluconeogenesis (P = .003). On the other hand, insulin-induced suppression of glucose production, gluconeogenesis, glycogenolysis, and stimulation of glucose disappearance all were normal. Although fasting glucose production also was increased (P = .0002) in subjects with IFG/IGT, insulin-induced suppression of glucose production, gluconeogenesis, and glycogenolysis and stimulation of glucose disappearance were impaired (P = .005).

CONCLUSIONS

Fasting hyperglycemia is due to excessive glucose production in people with either IFG/NGT or IFG/IGT. Both insulin action and postprandial glucose concentrations are normal in IFG/NGT but abnormal in IFG/IGT. This finding suggests that hepatic and extrahepatic insulin resistance causes or exacerbates postprandial glucose intolerance in IFG/IGT. Elevated gluconeogenesis in the fasting state in IFG/NGT and impaired insulin-induced suppression of both gluconeogenesis and glycogenolysis in IFG/IGT suggest that alteration in the regulation of these pathways occurs early in the evolution of type 2 diabetes.

Does insulin resistance drive the association between hyperglycemia and cardiovascular risk?

Background

Several studies have shown associations between hyperglycemia and risk of cardiovascular disease (CVD) and mortality, yet glucose-lowering treatment does little to mitigate this risk. We examined whether associations between hyperglycemia and CVD risk were explained by underlying insulin resistance.

Methods

In 60 middle-aged individuals without diabetes we studied the associations of fasting plasma glucose, 2-hour post oral glucose tolerance test plasma glucose, insulin sensitivity as well as body fat percentage with CVD risk. Insulin sensitivity was measured as the glucose infusion rate during a euglycemic hyperinsulinemic clamp, body fat percentage was measured by dual X-ray absorptiometry, and CVD risk was estimated using the Framingham risk score. Associations of fasting plasma glucose, 2-hour plasma glucose, insulin sensitivity and body fat percentage with the Framingham risk score were assessed in linear regression models.

Results

Both fasting and 2-hour plasma glucose levels were associated with higher Framingham risk score (fasting glucose: r² = 0.21; 2-hour glucose: r² = 0.24; P<0.001 for both), and insulin sensitivity with lower Framingham risk score (r² = 0.36; P<0.001). However, adjustment for insulin sensitivity and 2-hour glucose made the effect of fasting glucose non-significant (P = 0.060). Likewise, when adjusting for insulin sensitivity and fasting glucose, the association between 2-hour glucose and Framingham risk score disappeared (P = 0.143). In contrast, insulin sensitivity was still associated with Framingham risk score after adjusting for glucose levels (P<0.001). Body fat was not associated with Framingham risk score when taking insulin sensitivity into account (P = 0.550).

Conclusion

The association between plasma glucose levels and CVD risk is mainly explained by insulin resistance, which raises the question of whether glucose lowering per se without changes in the processes that underlie hyperglycemia should be the sole clinical paradigm in the treatment of type 2 diabetes or its prevention.

Fatty acids impair endothelium-dependent vasorelaxation: a link between obesity and arterial stiffness in very old Zucker rats

To analyze age-related interactions between obesity, its associated metabolic disorders, and macrocirculation, we studied large artery stiffness and fatty acid responsiveness in lean and obese Zucker rats, aged 25 (adult) and 80 weeks (very old). Systolic arterial pressure was higher in old obese than in old lean rats (178 ± 10 vs 134 ± 8 mmHg, respectively). Carotid elastic modulus-wall stress curves showed increased age-dependent arterial stiffening, which was greater in obese animals. Old obese exhibited endothelial dysfunction with increased systemic oxidative stress. Adult obese had elevated plasma free fatty acid levels (1,866 ± 177 vs 310 ± 34 μg/μL in lean animals). In old obese, linoleate and palmitate increased contractility to phenylephrine and reduced relaxation to acetylcholine. Thus, obesity at 25 weeks appears to trigger accelerated arterial aging observed at 80 weeks. The early increase in free fatty acids may be a key effector in the severe arterial stiffness of the aged obese Zucker model.

The prediabetic period: review of clinical aspects

Hyperglycemia that does not satisfy the diagnostic criteria for diabetes mellitus (DM) is generally called prediabetes (preDM). The global prevalence of preDM has been increasing progressively in the past few decades, and it has been established that preDM status is a strong risk factor for DM and cardiovascular disease. Currently, preDM status is classified into two subtypes: impaired fasting glucose and impaired glucose tolerance. Currently, preDM is not regarded as an independent clinical entity, but only as a risk factor for others. In this article, we review various clinical aspects of preDM in terms of the working definition, changes in criteria over the years, epidemiology, and pathophysiological characteristics, and its clinical significance in current medicine.

Incretin action maintains insulin secretion, but not hepatic insulin action, in people with impaired fasting glucose

AIMS

To determine whether altered GLP-1 activity contributes to the abnormal endogenous glucose production (EGP) and insulin secretion characteristic of people with impaired fasting glucose (IFG).

METHODS

People with IFG (n=10) and normal glucose tolerance (NGT; n=13) underwent assessment of EGP (via [6,6-(2)H(2)]-glucose infusion). Parameters of whole body insulin action and secretion were estimated by IVGTT and OGTT. Measures of EGP and insulin secretion were made before and after sitagliptin administration.

RESULTS

EGP was not different at baseline (glucose R(a); 1.47+/-0.08 vs. 1.46+/-0.05mg/kg/min, IFG vs. NGT, p=0.93). However, when differences in circulating insulin were accounted for (EGPXSSPI; 20.2+/-2.1 vs. 14.4+/-1.0AU, vs. NGT, p=0.03) the hepatic insulin resistance index was significantly higher in IFG. Baseline insulin action (S(i); 2.3+/-0.1x10(-4)/microU/ml vs. 3.5+/-0.4x10(-4)/microU/ml, p=0.01, IFG vs. NGT) and secretion (DI; 587+/-81x10(-4)/min vs. 1171+/-226x10(-4)/min, p=0.04, IFG vs. NGT) were impaired in IFG when evaluated by the IVGTT, but not by OGTT (insulin sensitivity 4.52+/-1.08x10(-4)dl/kg/min vs. 6.73+/-1.16x10(-4)dl/kg/min, IFG vs. NGT, p=0.16; indices of basal (Phi(b)), static (Phi(s)), dynamic (Phi(d)), and total (Phi(t)) insulin secretion, p>0.07). Sitagliptin did not change EGP or insulin secretion in either group.

CONCLUSIONS

Incretin action maintained insulin secretion, but not hepatic insulin action, in people with IFG.

From pre-diabetes to type 2 diabetes in obese youth: pathophysiological characteristics along the spectrum of glucose dysregulation

OBJECTIVE

Impaired fasting glucose (IFG) and impaired glucose tolerance (IGT) are considered pre-diabetes states. There are limited data in pediatrics in regard to their pathophysiology. We investigated differences in insulin sensitivity and secretion among youth with IFG, IGT, and coexistent IFG/IGT compared with those with normal glucose tolerance (NGT) and type 2 diabetes.

RESEARCH DESIGN AND METHODS

A total of 24 obese adolescents with NGT, 13 with IFG, 29 with IGT, 11 with combined IFG/IGT, and 30 with type 2 diabetes underwent evaluation of hepatic glucose production ([6,6-(2)H(2)]glucose), insulin-stimulated glucose disposal (R(d), euglycemic clamp), first- and second-phase insulin secretion (hyperglycemic clamp), body composition (dual-energy X-ray absorptiometry), abdominal adiposity (computed tomography), and substrate oxidation (indirect calorimetry).

RESULTS

Adolescents with NGT, pre-diabetes, and type 2 diabetes had similar body composition and abdominal fat distribution. R(d) was lower (P = 0.009) in adolescents with type 2 diabetes than in those with NGT. Compared with adolescents with NGT, first-phase insulin was lower in those with IFG, IGT, and IFG/IGT with further deterioration in those with type 2 diabetes (P < 0.001), and β-cell function relative to insulin sensitivity (glucose disposition index [GDI]) was also lower in those with IFG, IGT, and IFG/IGT (40, 47, and 47%, respectively), with a further decrease (80%) in those with type 2 diabetes (P < 0.001). GDI was the major determinant of fasting and 2-h glucose levels.

CONCLUSIONS

Obese adolescents who show signs of glucose dysregulation, including abnormal fasting glucose, glucose intolerance or both, are more likely to have impaired insulin secretion rather than reduced insulin sensitivity. Given the impairment in insulin secretion, they are at high risk for progression to type 2 diabetes. Further deterioration in insulin sensitivity or secretion may enhance the risk for this progression.

Indices of insulin sensitivity and secretion from a standard liquid meal test in subjects with type 2 diabetes, impaired or normal fasting glucose

Background

To provide an initial evaluation of insulin sensitivity and secretion indices derived from a standard liquid meal tolerance test protocol in subjects with normal (NFG), impaired fasting glucose (IFG) or type 2 diabetes mellitus.

Methods

Areas under the curve (AUC) for glucose, insulin and C-peptide from pre-meal to 120 min after consumption of a liquid meal were calculated, as were homeostasis model assessments of insulin resistance (HOMA2-IR) and the Matsuda index of insulin sensitivity.

Results

Subjects with NFG (n = 19), IFG (n = 19), and diabetes (n = 35) had mean ± SEM HOMA2-IR values of 1.0 ± 0.1, 1.6 ± 0.2 and 2.5 ± 0.3 and Matsuda insulin sensitivity index values of 15.6 ± 2.0, 8.8 ± 1.2 and 6.0 ± 0.6, respectively. The log-transformed values for these variables were highly correlated overall and within each fasting glucose category (r = -0.91 to -0.94, all p < 0.001). Values for the product of the insulin/glucose AUC ratio and the Matsuda index, an indicator of the ability of the pancreas to match insulin secretion to the degree of insulin resistance, were 995.6 ± 80.7 (NFG), 684.0 ± 57.3 (IFG) and 188.3 ± 16.1 (diabetes) and discriminated significantly between fasting glucose categories (p < 0.001 for each comparison).

Conclusion

These results provide initial evidence to support the usefulness of a standard liquid meal tolerance test for evaluation of insulin secretion and sensitivity in clinical and population studies.

Site-specific GlcNAcylation of human erythrocyte proteins: potential biomarker(s) for diabetes

OBJECTIVE

O-linked N-acetylglucosamine (O-GlcNAc) is upregulated in diabetic tissues and plays a role in insulin resistance and glucose toxicity. Here, we investigated the extent of GlcNAcylation on human erythrocyte proteins and compared site-specific GlcNAcylation on erythrocyte proteins from diabetic and normal individuals.

RESEARCH DESIGN AND METHODS

GlcNAcylated erythrocyte proteins or GlcNAcylated peptides were tagged and selectively enriched by a chemoenzymatic approach and identified by mass spectrometry. The enrichment approach was combined with solid-phase chemical derivatization and isotopic labeling to detect O-GlcNAc modification sites and to compare site-specific O-GlcNAc occupancy levels between normal and diabetic erythrocyte proteins.

RESULTS

The enzymes that catalyze the cycling (addition and removal) of O-GlcNAc were detected in human erythrocytes. Twenty-five GlcNAcylated erythrocyte proteins were identified. Protein expression levels were compared between diabetic and normal erythrocytes. Thirty-five O-GlcNAc sites were reproducibly identified, and their site-specific O-GlcNAc occupancy ratios were calculated.

CONCLUSIONS

GlcNAcylation is differentially regulated at individual sites on erythrocyte proteins in response to glycemic status. These data suggest not only that site-specific O-GlcNAc levels reflect the glycemic status of an individual but also that O-GlcNAc site occupancy on erythrocyte proteins may be eventually useful as a diagnostic tool for the early detection of diabetes.