The OGTT as test for beta cell function?

The clinical value of glycosylated hemoglobin level in newly diagnosed ketosis-prone type 2 diabetes

Objective

To evaluate the clinical value of glycosylated hemoglobin (HbA1c) in newly diagnosed ketosis-prone type 2 diabetes (KPD).

Methods

A total of 330 patients with newly diagnosed type 2 diabetes (T2DM) hospitalized in our department with an average age of 48.72 ± 13.07 years old were selected and divided into T2DM group (193 cases) and KPD group (137 cases) according to whether they were combined with ketosis. According to the quartile level of HbA1c, they were divided into group A (HbA1c < 8.90%, 84 cases), group B (8.90%≤HbA1c < 10.70%, 86 cases), group C (10.70%≤HbA1c ≤ 12.40%, 85 cases) and group D (HbA1c > 12.40%, 75 cases). The general clinical features, laboratory indicators and islet function of each group were compared. Spearman correlation analysis was used to explore the correlation between HbA1c and β- Hydroxybutyric acid (β- HB) and islet function. ROC curve was used to analyze the sensitivity and specificity of HbA1c in diagnosing KPD, and the optimal tangent point was obtained.

Results

HbA1c, β-HB, FFA, RBG, insulin dosage, GSP, OGTT (0, 0.5, 1, 2, 3h) in KPD group were significantly higher than those in T2DM group (P< 0.001). HDL-C, IRT (0, 0.5, 1, 2, 3h), HOMA-β, HOMA-IR, HOMA-IS, ΔC30/ΔG30, AUC insulin were significantly lower than those in T2DM group (P< 0.001). With the increase of HbA1c level, the incidence of ketosis, β-HB, FFA and insulin dosage increased, while IRT (0, 0.5, 1, 2, 3h), ΔC30/ΔG30, AUC insulin, HOMA-β and HOMA-IS decreased accordingly (P< 0.001). In all newly diagnosed T2DM patients, Spearman correlation analysis showed that HbA1c was positively correlated with β-HB (r=0.539, P < 0.001), and was negatively correlated with HOMA-β (r=-0.564, P < 0.001), HOMA-IS (r=-0.517, P < 0.01, P < 0.001), HOMA-IR (r=-0.177, P < 0.001), ΔC30/ΔG30 (r=-0.427, P < 0.01) and AUC insulin (r=-0.581, P < 0.001). In ROC curve analysis, the optimal threshold for the diagnosis of KPD was 10.15%, Youden index was 0.616, area under the curve (AUC) was 0.882, sensitivity = 92.70%, specificity = 70.50%.

Conclusion

In newly diagnosed T2DM patients, if HbA1c > 10.15%, it is more likely to develop KPD. Monitoring HbA1c level is conducive to timely detection of high-risk individuals with KPD and taking appropriate measures to prevent the occurrence and development of the disease.

Effects of Combined High-Protein Diet and Exercise Intervention on Cardiometabolic Health in Middle-Aged Obese Adults: A Randomized Controlled Trial

Background: Obesity is the main risk factor of cardiovascular diseases (CVD) and metabolic diseases. The middle-aged population is the age group with the highest prevalence of obesity. Thus, improving cardiometabolic health is important to prevent CVD and metabolic diseases in middle-aged obese adults. The aim of this study was to examine the effects of exercise alone or in combination with a high-protein diet on markers of cardiometabolic health in middle-aged adults with obesity.

Methods: Sixty-nine middle-aged adults with obesity were assigned randomly to the control group (C; n = 23), exercise group (E; n = 23), or exercise combined with high-protein diet group (EP; n = 23). Individuals in the E and EP groups received supervised exercise training and individuals in the EP group received high-protein diet intervention. Body composition (assessed by dual-energy X-ray absorptiometry), oral glucose tolerance test (OGTT), lipid profiles, and inflammatory markers were determined before and after 12 weeks of intervention. Insulin sensitivity index (ISI_0,120) was calculated from values of fasting and 2-h insulin and glucose concentration of OGTT. Insulin-peak-time during the OGTT was recorded to reflect β-cell function. Analysis of covariance with baseline values as covariates was used to examine the effects of the intervention. The significant level was set at 0.05.

Results: After 12 weeks of intervention, the E group had a greater percentage of individuals with early insulin-peak-time during the OGTT than that in the C and EP groups (p = 0.031). EP group had lower total cholesterol and triglycerides than that in the C group (p = 0.046 and 0.014, respectively). Within-group comparisons showed that the 2-h glucose of OGTT and C-reactive protein decreased in the EP group (p = 0.013 and 0.008, respectively) but not in the E and C groups; insulin sensitivity improved in the EP group (p = 0.016) and had a trend to improve in the E group (p = 0.052); and abdominal fat mass and total body fat mass decreased in both intervention groups (p < 0.05).

Conclusion: Combined high-protein diet and exercise intervention significantly decreased fat mass and improved lipid profiles, insulin sensitivity, glucose tolerance, and inflammation in middle-aged adults with obesity.

Clinical Trial Registration: Thai Clinical Trials Registry, TCTR20180913003, 13-09-2018.

An Acute, Placebo-Controlled, Single-Blind, Crossover, Dose-Response, Exploratory Study to Assess the Effects of New Zealand Pine Bark Extract (Enzogenol®) on Glycaemic Responses in Healthy Participants

An acute, placebo-controlled, single-blind, crossover, dose-response, exploratory study was designed to investigate the hypoglycaemic effects of New Zealand pine bark extract (Enzogenol®). Twenty-five healthy participants categorised into having a monophasic or complex (biphasic or triphasic) glucose curve shape at the control visit consumed a placebo and Enzogenol® (50 and 400 mg) on three separate occasions before an oral glucose tolerance test (OGTT). In the monophasic group, 50 and 400 mg of Enzogenol® significantly reduced the mean glucose incremental area under the curve (iAUC) compared to control 241.3 ± 20.2 vs. 335.4 ± 34.0 mmol/L·min, p = 0.034 and 249.3 ± 25.4 vs. 353.6 ± 31.5 mmol/L·min, p = 0.012, respectively. The 400 mg dose further reduced the percentage increment of postprandial glucose (%PG) 31.4% ± 7.9% vs. 47.5% ± 8.6%, p = 0.010, glucose peak 7.9 ± 0.3 vs. 8.9 ± 0.3 mmol/L, p = 0.025 and 2h-OGTT postprandial glucose (2hPG) 6.1 ± 0.3 vs. 6.7 ± 0.3 mmol/L, p = 0.027. Glucose iAUC was not significantly different in the complex group, except for reductions in %PG 28.7% ± 8.2% vs. 43.4% ± 5.9%, p = 0.012 after 50 mg dose and 27.7% ± 5.4% vs. 47.3% ± 7.2%, p = 0.025 after 400 mg dose. The results suggest that Enzogenol® may have hypoglycaemic effects in healthy participants, especially those exhibiting monophasic shapes.

Rethinking the accuracy of 75g glucose used in the oral glucose tolerance test in the diagnosis and management of diabetes

AIMS

We investigated the specificity of the 75g oral glucose tolerance test (OGTT) and the clinical usefulness of the 2h post loading glucose (2h PLG) value in the clinical care of diabetes patients.

METHODS

The 75g OGTT data of 1755 subjects were analyzed. The relationships and degrees of consistency among 2h PLG, fasting plasma glucose (FPG), and HbA1c values were assessed. We also investigated the degree of contribution of 2h PLG in the prescription of glucose-lowering agents and in the pitfall group for use of 75g OGTT.

RESULTS

Among 595 subjects with normal FPG, only 329 (55.3%) showed normal 2h PLG level, and 66 (11.1%) patients could be considered as having diabetes. Among 454 diabetes patients (based on FPG and HbA1c), 409(90.1%) showed 2h PLG values in the range of diabetes, 45 (9.9%) subjects did not exhibit diabetes. Pitfall group who used 75g OGTT for diagnosis diabetes (lower 2h PLG value compared to fasting and upper 2h PLG value compared to fasting) showed differences in body weight and height.

CONCLUSIONS

Based on OGTT results, around 10% patients cannot be diagnosed with diabetes based solely on the 2h PLG value. Further studies on differences in glucose loading according to body weight, individual life pattern, and calorie requirement are needed for improvement of the specificity of the OGTT in the clinical management of diabetes.

The 1h post glucose value best predicts future dysglycemia among normal glucose tolerance subjects

AIM

To analyse the OGTT glycemic parameters - fasting, 1h and 2h plasma glucose values singly and in various combinations; with respect to their prediction of future dysglycemia in subjects with normal glucose tolerance (NGT).

METHODS

Electronic medical records of individuals who underwent an OGTT between 1991 and 2016 at a tertiary diabetes centre were analysed. NGT subjects who had at least one more follow up OGTT (n=1356) were selected for the study. Regarding their prediction of future dysglycemia, the glycemic parameters-Fasting plasma glucose (FPG), 1h plasma glucose (1HrPG) and 2h plasma glucose (2HrPG) were analysed separately and also in different combinations. HbA1c and the combined use of HbA1c and FPG were also compared. Receiver operating characteristic (ROC) curve analysis was performed to assess the capability of various glycemic parameters to discriminate between NGT and dysglycemia. The WHO criteria were used to define dysglycemia as the presence of prediabetes (Impaired fasting glucose and/or Impaired glucose tolerance) or diabetes.

RESULTS

318(23.4%) developed prediabetes (median follow up 3.5years) and 134(10%) developed diabetes (median follow up 5.6years). The 1hrPG had a significantly higher AUC (0.684, 0.716) compared to FPG (0.560 and 0.593) and 2hrPG (0.644 and 0.618) for prediabetes and diabetes respectively. Adding the FPG or the 2hrPG to the 1HrPG did not significantly improve the AUC beyond 1HrPG alone. The 1HrPG also predicted diabetes better than HbA1c as well as the combined use of HbA1c and FPG.

CONCLUSION

The 1HrPG value during OGTT is a good predictor of future dysglycemia among NGT subjects.

Functional high-intensity training improves pancreatic β-cell function in adults with type 2 diabetes

Type 2 diabetes (T2D) is characterized by reductions in β-cell function and insulin secretion on the background of elevated insulin resistance. Aerobic exercise has been shown to improve β-cell function, despite a subset of T2D patients displaying "exercise resistance." Further investigations into the effectiveness of alternate forms of exercise on β-cell function in the T2D patient population are needed. We examined the effect of a novel, 6-wk CrossFit functional high-intensity training (F-HIT) intervention on β-cell function in 12 sedentary adults with clinically diagnosed T2D (54 ± 2 yr, 166 ± 16 mg/dl fasting glucose). Supervised training was completed 3 days/wk, comprising functional movements performed at a high intensity in a variety of 10- to 20-min sessions. All subjects completed an oral glucose tolerance test and anthropometric measures at baseline and following the intervention. The mean disposition index, a validated measure of β-cell function, was significantly increased (PRE: 8.4 ± 3.1, POST: 11.5 ± 3.5, P = 0.02) after the intervention. Insulin processing inefficiency in the β-cell, expressed as the fasting proinsulin-to-insulin ratio, was also reduced (PRE: 2.40 ± 0.37, POST: 1.78 ± 0.30, P = 0.04). Increased β-cell function during the early-phase response to glucose correlated significantly with reductions in abdominal body fat (R² = 0.56, P = 0.005) and fasting plasma alkaline phosphatase (R² = 0.55, P = 0.006). Mean total body-fat percentage decreased significantly (Δ: -1.17 0.30%, P = 0.003), whereas lean body mass was preserved (Δ: +0.05 ± 0.68 kg, P = 0.94). We conclude that F-HIT is an effective exercise strategy for improving β-cell function in adults with T2D.

The oral glucose tolerance test (OGTT) revisited

The oral glucose tolerance test (OGTT) has been the mainstay for diagnosing diabetes for decades. Recently, the American Diabetes Association (ADA) suggested abandoning the OGTT, while resorting to a simpler screening test, exclusively based on baseline fasting blood glucose concentration. This review article rewinds the history of OGTT and its recent advancements, and compares its power in detecting early diabetes with that of fasting blood glucose alone. The key point is that there are more diabetics originating from a population with normal fasting blood glucose than from subjects with impaired fasting glucose, those who can be detected by the new ADA recommendations. Conversely, the OGTT detects more efficiently early diabetes as well as subjects with IGT, as the glycemia at the second hour seems crucial as a diagnostic tool. We discuss the different significance of fasting versus second hour glycemia during OGTT, according to different mechanisms of glucose homeostasis. Finally, we provide recent evidence on very simple additional information that can be obtained from the OGTT, which renders this test even more useful, discussing pathophysiologic significance.

Associations of age with serum insulin, proinsulin and the proinsulin-to-insulin ratio: a cross-sectional study

BACKGROUND

Insulin responses and insulin levels seem to decline with age. However, the question of beta cell impairment attributable to ageing has been sparsely addressed in population-based studies. Non-fasting insulin levels are determined by the ambient degree of insulin resistance together with the capacity of beta cells to compensate by insulin secretion to prevent hyperglycaemia. A raised proinsulin-to-insulin ratio (proinsulin/insulin) due to impaired processing of proinsulin is an early marker of beta cell dysfunction. We hypothesised that in a general population, signs of beta cell failure with advancing age manifest not only by decreases in random insulin, but also with a corresponding increase in its precursor proinsulin.

METHODS

In the Tromsø Study 1994-95 we measured insulin and proinsulin concentrations in random blood samples from 6212 persons without self-reported diabetes mellitus and plotted the levels as percentiles according to age. In regression analyses we assessed the relationships between age and insulin, proinsulin, and proinsulin/insulin, while adjusting for the concomitant measurements of glucose and other metabolic variables, and the time since the last meal.

RESULTS

Median insulin concentrations declined significantly with advancing age group in men, but not in women. Proinsulin levels and proinsulin/insulin increased across age groups in both genders. After adjustment, greater age was associated with lower log10(insulin) and higher log10(proinsulin) and log10(proinsulin/insulin) (p = 0.0001 for all).

CONCLUSIONS

Negative associations of age with random insulin levels, together with positive associations of age with proinsulin and proinsulin/insulin, point towards a loss of beta cell function inherent in the ageing process.

Comparison of composite whole body insulin sensitivity index derived from mixed meal test and oral glucose tolerance test in insulin resistant obese subjects

Apart from fasting blood glucose (FBG) and insulin (FBI), oral glucose tolerance test (OGTT) is also used in calculating insulin sensitivity. During OGTT, insulin secretion may not reflect normal physiological insulin secretion. Based on this idea, hepatic and whole body insulin sensitivity rates were tested during OGTT and mixed meal test (MMT) in obese subjects. Thirty-one women with Quantitative Insulin Sensitivity Check Index (QUICKI) values below 0.350 and body mass index (BMI) >or=30 were included into the study. OGTT with 75-g glucose and MMT 300 kcal were applied to all cases. Data obtained from OGTT and MMT were used in the assessment of insulin sensitivity with Hemostasis of Model Assessment-Insulin Resistance (HOMA-IR) and Matsuda's Composite Whole Body Insulin Sensitivity Index (Matsuda's ISI). Mean BMI, FBG, and FBI were 36.8 +/- 3.9 kg/m(2), 100.5 +/- 0.10 mg/dl, 16.2 +/- 5.3 microg/ml, respectively. QUICKI was 0.31 +/- 0.01 and HOMA-IR was 3.71 +/- 0.88. Matsuda's ISI derived from OGTT was 6.96 +/- 3.35 and from MMT was 11.32 +/- 6.61. In analysis, it was demonstrated that there was a correlation between HOMA-IR, QUICKI, and Matsuda's ISIs derived from OGTT and MMT. Comparing the time periods separately, it was detected that despite similar increment in insulin levels, glucose levels were higher in OGTT than MMT at 15 and 30 min. Consequently, Matsuda's ISI was demonstrated to be effectively used with the data of MMT, as used with OGTT. Moreover, MMT was shown to be in parallel to physiologic insulin secretion and reflect pancreatic functions better compared to OGTT.

Assessing the shape of the glucose curve during an oral glucose tolerance test

OBJECTIVE

The oral glucose tolerance test (OGTT) is used to define the status of glucose tolerance based on the plasma glucose level at 120 min. The purpose of the present study was to identify parameters that determine the shape of the plasma glucose course measured at 0, 30, 60, 90, and 120 min during an OGTT.

RESEARCH DESIGN AND METHODS

OGTT data from 551 subjects (485 with normal glucose tolerance [NGT] and 66 with impaired glucose tolerance [IGT]) were analyzed. We distinguished between "monophasic," "biphasic," and unclassified glucose shapes. A "shape" index based on the extent and the direction of the plasma glucose change in the second hour allowed us to treat shape as a continuous variable.

RESULTS

In the biphasic group, the NGT-to-IGT ratio was slightly higher (173/20 vs. 209/40, P = 0.08) and the male-to-female ratio was lower (60/133 vs. 120/129, P = 0.0003). Subjects with a biphasic shape had significantly lower age, BMI, waist-to-hip ratio (WHR), HbA(1c), plasma glucose, and area under the insulin curve (insulin(AUC)) and a better estimated insulin sensitivity and secretion (using validated indexes) than monophasic subjects (all P < 0.05). By adjusting this shape index for glucose(AUC) (as continuous measure of glucose tolerance), correlations with age, BMI, WHR, HbA(1c), and insulin(AUC) were completely abolished. The adjusted shape index was still higher in female than in male subjects but lower in IGT than in NGT subjects (both P = 0.0003). Finally, we tested common polymorphisms in insulin receptor substrate (IRS)-1, IRS-2, calpain-10, hepatic lipase, and peroxisome proliferator-activated receptor-gamma for association with the shape index.

CONCLUSIONS

We conclude that the plasma glucose shape during an OGTT depends on glucose tolerance and sex. In addition, genetic factors seem to play a role. The shape index may be a useful metabolic screening parameter in epidemiological and genetic association studies.