Glucose uptake saturation explains glucose kinetics profiles measured by different tests

Cooked rice- and wheat-based food structure influenced digestion kinetics and glycemic response in growing pigs

BACKGROUND

How starch-based food structure can impact the rate and extent of digestion in the small intestine and resulting glycemic response is not properly understood. One possible explanation is that food structure influences gastric digestion, which subsequently determines digestion kinetics in the small intestine and glucose absorption. However, this possibility has not been investigated in detail.

OBJECTIVES

Using growing pigs as a digestion model for adult humans, this study aimed to investigate how physical structure of starch-rich foods impacts small intestinal digestion and glycemic response.

METHODS

Male growing pigs (21.7 ± 1.8 kg, Large White × Landrace) were fed one of six cooked diets (250-g starch equivalent) with varying initial structures (rice grain, semolina porridge, wheat or rice couscous, or wheat or rice noodle). The glycemic response, small intestinal content particle size and hydrolyzed starch content, ileal starch digestibility, and portal vein plasma glucose were measured. Glycemic response was measured as plasma glucose collected from an in-dwelling jugular vein catheter for up to 390 min postprandial. Portal vein blood samples and small intestinal content were measured after sedation and euthanasia of the pigs at 30, 60, 120, or 240 min postprandial. Data were analyzed with a mixed-model ANOVA.

RESULTS

The plasma glucose Δmax_overall and iAUC_overall for couscous and porridge diets (smaller-sized diets) were higher than intact grain and noodle diets (larger-sized diets); 29.0 ± 3.2 vs. 21.7 ± 2.6 mg/dL and 5659 ± 727 vs. 2704 ± 521 mg/dL.min, for the smaller- and larger-sized diets, respectively (p < 0.05). Ileal starch digestibility was not significantly different between diets (p ≥ 0.05). The iAUC_overall was inversely related to the starch gastric emptying half-time of the diets (r = -0.90, p = 0.015).

CONCLUSIONS

Starch-based food structure affected the glycemic response and starch digestion kinetics in the small intestine of growing pigs.

ALDH2 rs671 Is Associated With Elevated FPG, Reduced Glucose Clearance and Hepatic Insulin Resistance in Japanese Men

CONTEXT

A recent meta-analysis of genome-wide association studies data from East Asians identified aldehyde dehydrogenase 2 (ALDH2) rs671 as a susceptibility variant for type 2 diabetes in males.

OBJECTIVE

To investigate the association between ALDH2 rs671 and metabolic characteristics.

METHODS

We studied 94 nonobese, nondiabetic, Japanese men. Using a 2-step hyperinsulinemic-euglycemic clamp, we evaluated insulin sensitivity in muscle and liver. Intrahepatic lipid and fat distribution were measured using 1H-magnetic resonance spectroscopy and magnetic resonance imaging, respectively. We divided participants into a risk-carrying group with ALDH2 rs671 G/G (n = 53) and a nonrisk-carrying group with ALDH2 rs671 G/A or A/A (n = 41).

RESULTS

The risk-carrying group had significantly higher levels of alcohol consumption (18.4 [interquartile range, IQR, 10.4-48.9]) vs 12.1 (IQR, 1.3-29.0) g/day; P = .003), elevated fasting plasma glucose (FPG) (97.5 ± 7.9 vs 93.5 ± 6.2 mg/dL; P = .010), lower hepatic insulin sensitivity (61.7 ± 20.5% vs 73.1 ± 15.9%; P = .003), and lower fasting glucose clearance (0.84 ± 0.8 dL·m-2·min-1 vs 0.87 ± 0.09 dL·m-2·min-1; P = .047) than the nonrisk-carrying group, while insulin resistance in muscle and body fat distribution were similar. The single linear correlation analysis revealed significant correlations between alcohol consumption and hepatic insulin sensitivity (r = -0.262, P = .011), fasting glucose clearance (r = -0.370, P < .001), or FPG (r = 0.489, P < .001). The multiple regression analysis revealed that both ALDH2 rs671 G/G genotype and alcohol consumption were significant independent correlates for hepatic insulin sensitivity, whereas only alcohol consumption was a significant independent correlate for fasting glucose clearance.

CONCLUSION

Our data suggest that high-alcohol intake-dependent and independent hepatic insulin resistance and reduced fasting glucose clearance due to high alcohol intake could be a relatively upstream metabolic abnormality in ALDH2 rs671 G/G carriers.

Mathematical Modeling for the Physiological and Clinical Investigation of Glucose Homeostasis and Diabetes

Mathematical modeling in the field of glucose metabolism has a longstanding tradition. The use of models is motivated by several reasons. Models have been used for calculating parameters of physiological interest from experimental data indirectly, to provide an unambiguous quantitative representation of pathophysiological mechanisms, to determine indices of clinical usefulness from simple experimental tests. With the growing societal impact of type 2 diabetes, which involves the disturbance of the glucose homeostasis system, development and use of models in this area have increased. Following the approaches of physiological and clinical investigation, the focus of the models has spanned from representations of whole body processes to those of cells, i.e., from in vivo to in vitro research. Model-based approaches for linking in vivo to in vitro research have been proposed, as well as multiscale models merging the two areas. The success and impact of models has been variable. Two kinds of models have received remarkable interest: those widely used in clinical applications, e.g., for the assessment of insulin sensitivity and β-cell function and some models representing specific aspects of the glucose homeostasis system, which have become iconic for their efficacy in describing clearly and compactly key physiological processes, such as insulin secretion from the pancreatic β cells. Models are inevitably simplified and approximate representations of a physiological system. Key to their success is an appropriate balance between adherence to reality, comprehensibility, interpretative value and practical usefulness. This has been achieved with a variety of approaches. Although many models concerning the glucose homeostasis system have been proposed, research in this area still needs to address numerous issues and tackle new opportunities. The mathematical representation of the glucose homeostasis processes is only partial, also because some mechanisms are still only partially understood. For in vitro research, mathematical models still need to develop their potential. This review illustrates the problems, approaches and contribution of mathematical modeling to the physiological and clinical investigation of glucose homeostasis and diabetes, focusing on the most relevant and stimulating models.

A Model-Informed Drug Discovery and Development Strategy for the Novel Glucose-Responsive Insulin MK-2640 Enabled Rapid Decision Making

A model‐informed drug discovery and development strategy played a key role in the novel glucose‐responsive insulin MK‐2640’s early clinical development strategy and supported a novel clinical trial paradigm to assess glucose responsiveness. The development and application of in silico modeling approaches by leveraging substantial published clinical insulin pharmacokinetic–pharmacodynamic (PKPD) data and emerging preclinical and clinical data enabled rapid quantitative decision making. Learnings can be applied to define PKPD properties of novel insulins that could become therapeutically meaningful for diabetic patients.

Dynamics of Intrinsic Glucose Uptake Kinetics in Human Mesenchymal Stem Cells During Chondrogenesis

Chondrogenesis of human mesenchymal stem cells (hMSCs) is an important biological process in many applications including cartilage tissue engineering. We investigated the glucose uptake characteristics of aggregates of hMSCs undergoing chondrogenesis over a 3-week period both experimentally and by using a mathematical model. Initial concentrations of glucose in the medium were varied from 1 to 4.5 g/L to mimic limiting conditions and glucose uptake profiles were obtained. A reaction-diffusion mathematical model was implemented and solved to estimate kinetic parameters. Experimental glucose uptake rates increased with culture time for aggregates treated with higher initial glucose concentrations (3 and 4.5 g/L), whereas they decreased or remained constant for those treated with lower initial glucose concentrations (1 and 2 g/L). Lactate production rate increased by as much as 40% for aggregates treated with higher initial glucose concentrations (2, 3 and 4.5 g/L), whereas it remained constant for those treated with 1 g/L initial glucose concentration. The estimated DNA-normalized maximum glucose uptake rate decreased by a factor of 9 from day 0-2 (12.5 mmol/s/g DNA) to day 6-8 (1.5 mmol/s/g DNA), after which it started to increase. On day 18-20, its value (17.5 mmol/s/g DNA) was about 11 times greater than its lowest value. Further, the extracellular matrix levels of aggregates at day 14 and day 21 correlated with their overall glucose uptake and lactate production. The results suggest that during chondrogenesis, for optimal results, cells require increasing amounts of glucose. Our results also suggest that diffusion limitations play an important role in glucose uptake even in the smaller size aggregate model of chondrogenesis. Further, the results indicate that glucose uptake or lactate production can be a tool for predicting the end quality of tissue during the process of chondrogenesis. The estimated kinetic parameters can be used to model glucose requirements in cartilage tissue engineering applications.

Insulin sensitivity across the lifespan from obese adolescents to obese adults with impaired glucose tolerance: Who is worse off?

OBJECTIVE

Youth type 2 diabetes mellitus (T2DM) occurs decades earlier than adult T2DM and is characterized by high therapeutic failure rates and decreased response to insulin sensitizers suggesting a more severe disease process than in adults. To explain these observations, we hypothesized that insulin resistance is worse in obese youth than adults with impaired glucose tolerance (IGT), a state of high-risk for T2DM. As proof-of-concept, we compared insulin sensitivity between BMI-, sex-, and race-matched obese youth vs adults with IGT.

METHODS

This retrospective analysis of IGT youth and adults included 34 obese adolescents matched (2:1) for BMI, sex, and race to 17 adults. Hepatic and peripheral insulin sensitivity were measured by [6,6-² H₂ ]glucose and hyperinsulinemic-euglycemic clamp. Body composition (DEXA) and serum lipid profile were examined.

RESULTS

Despite similar percent body fat, obese adolescents had 2-fold higher fasting insulin concentration, lower hepatic (~53%) and peripheral (~42%) insulin sensitivity and lower HDL compared with adults (all P < .01). Surrogate estimate of insulin sensitivity, 1/fasting insulin was lower and HOMA-IR was higher in adolescents vs adults. Adults had a more atherogenic lipid profile with higher total-, LDL-, and non-HDL cholesterol.

CONCLUSIONS

Obese youth and adults with IGT differ in that youth are more insulin resistant than adults in spite of similar adiposity. This could potentially explain the earlier onset of T2DM in youth through an early and amplified burden on a β-cell destined to decompensate, and explicate their lower therapeutic response to insulin sensitizers.

Effect of exenatide on postprandial glucose fluxes, lipolysis, and ß-cell function in non-diabetic, morbidly obese patients

AIMS

To investigate the effect of exenatide on glucose disposal, insulin secretion, ß-cell function, lipolysis and hormone concentrations in non-diabetic, morbidly obese subjects under physiological conditions.

MATERIALS AND METHODS

Patients were assigned to exenatide 10 µg twice daily (EXE, n = 15) or control (CT, n = 15) for 3 months. Patients received a meal test/tracer study (MTT) to measure endogenous glucose production (EGP), rate of oral glucose appearance (RaO), insulin secretion rate (ISR), ß-cell function, hepatic insulin resistance (HIR) and adipose tissue insulin resistance (AT-IR) and insulin sensitivity (IS).

RESULTS

Post treatment, the EXE group showed a significant reduction in body weight ( P < .001). The postmeal time-course of glucose, insulin and ISR showed a lower peak between 60 and 180 minutes in phase with a reduction in RaO ( P < .01). After an initial similar suppression, EGP resumed at higher rates between 60 and 180 minutes ( P = .02) in EXE vs CT, while total RaO and EGP were similar throughout the MTT. In EXE, the postmeal glucagon, GLP1 and GIP responses were reduced ( P < .05). Fasting and postprandial lipolysis and ß-cell function were unaltered by active treatment. HIR, AT-IR and IS were all improved after exenatide treatment ( P < .05).

CONCLUSIONS

In morbidly obese non-diabetic subjects, exenatide causes weight loss, decreased postprandial glycaemia and glucagon response without changes in ß-cell function. These effects are consequent upon delayed oral glucose appearance in the circulation. Exenatide treatment is also associated with an improvement in hepatic, adipose tissue and whole-body IS with no influence on postprandial lipolysis.