Basu, Rita

Early postprandial glucagon concentrations are higher in type 1 diabetes (T1D) than in individuals with no diabetes (ND). To determine the cause, we infused stable [13C9, 15N1]glucagon before, during, and after a mixed meal in 16 ND and 16 T1D individuals to measure glucagon turnover. In a subcohort of 9 ND and 12 T1D individuals, we estimated [13C9, 15N1]glucagon kinetics during steady state. A linear, single-compartment model described [13C9, 15N1]glucagon kinetics and allowed precise estimation of the volume of distribution (VD) and clearance rate (CL). Model parameters were similar between groups, with the VD of [13C9, 15N1]glucagon at 42.1 ± 3.3 mL/kg, implying that [13C9, 15N1]glucagon distributes in a single compartment and with VD approximating the plasma volume and CL at 10.6 ± 0.9 mL/kg/min. Higher early (0–120 min after meal ingestion) postprandial glucagon concentrations (1,907.9 ± 373.4 vs. −93.6 ± 240.5 pg/mL · 120 min P < 0.001) observed in T1D was due to higher rates of glucagon appearance (3.39 ± 2.8 vs. −3.95 ± 2.0 ng/kg · 120 min, P < 0.04) and disappearance (2.13 ± 2.6 vs. −5.28 ± 2.1 ng/kg · 120 min, P < 0.04) compared with ND. We have determined postprandial glucagon turnover in humans and have demonstrated that changes in postprandial glucagon concentrations in T1D are due to increased rates of glucagon turnover during the early postprandial period. Article Highlights This study was conducted to determine postprandial glucagon metabolism in people with and without type 1 diabetes. We wanted to determine the cause for higher early postprandial glucagon concentrations in type 1 diabetes. We found that higher early postprandial glucagon turnover is the cause of higher early postprandial glucagon concentrations in type 1 diabetes Strategies that decrease early post prandial glucagon fluxes could improve postprandial glucose concentrations in type 1 diabetes.

Circulating glucagon concentrations differ between individuals with no diabetes (ND) and those with type 1 diabetes (T1D). We combined an isotope dilution technique using stable tracers [6,22-13C9,15N1]glucagon and [6,14,19,22-13C9,15N1]glucagon with splanchnic and leg catheterization in participants with ND (n = 8; age 23.1 ± 2.9 years, BMI 26.6 ± 3.5 kg/m2, HbA1c 5.0 ± 0.2% [31 ± 2 mmol/mol]) and T1D (n = 6; 29.0 ± 8.8 years, BMI 26.3 ± 5.0 kg/m2, HbA1c 7.9 ± 0.8% [63 ± 8 mmol/mol]) in the overnight fasted state. After baseline period, exogenous glucagon was infused at rates designed to achieve plasma glucagon concentrations spanning the physiological ranges, to determine the effects of rising glucagon concentrations on splanchnic and leg glucagon balance. At baseline, splanchnic glucagon extraction (SGE) was similar (30.7 ± 2.7 vs. 29.1 ± 2.9%) but leg glucagon extraction (LGE) was lower (27.0 ± 4.2 vs. 40.6 ± 3.1%) in participants with T1D versus those with ND. However, with increasing plasma glucagon concentrations, while SGE remained unchanged within and between groups, LGE fell in participants with ND (41 vs. 31 vs. 24%) but did not change in those with T1D. Despite a numerically lower net splanchnic glucagon production in participants with T1D than in those with ND, no changes were observed with increasing glucagon concentrations within the physiological range in both groups. This is the first human study applying novel glucagon isotopes that describes regional glucagon metabolism in participants with ND and T1D. Our observations provide translational relevance for dual hormone closed-loop systems and provide tools for probing the effects of GLP-1, dual, and triple receptor agonists on pancreatic α-cell functions. Article Highlights This study was conducted to assess splanchnic and leg glucagon metabolism in humans using stable glucagon isotopes. We wanted to evaluate whether splanchnic and leg glucagon metabolism differed between participants with no diabetes (ND) and those with type 1 diabetes (T1D) at glucagon concentrations spanning the physiological range. Whereas splanchnic glucagon extraction did not differ between participants with ND and those with T1D, leg glucagon extraction fell in those with ND but did not change in those with T1D as glucagon concentrations increased. Net splanchnic glucagon production did not change with exogenous glucagon infusion. Our study has implications for dual hormone closed-loop control in T1D where glucagon is infused for prevention of hypoglycemia and for investigating the effects of emerging GLP-1, glucose-dependent insulinotropic polypeptide, and glucagon receptor agonists on endogenous glucagon secretion and clearance.

Abstract Context Higher gluconeogenesis (GNG) contributes to higher nocturnal endogenous glucose production (EGP) in type 2 diabetes (T2D). Studies using 13C magnetic resonance spectroscopy (MRS) have confirmed lower hepatic glycogen content in subjects with T2D than in subjects with no diabetes (ND). Objective We determined the role of glycogen loading (GL) vs nonglycogen loading (NGL) on the contribution of GNG to nocturnal EGP in T2D. Methods In total, 14 subjects with T2D and 15 matched subjects with ND were studied on 2 occasions, with GL (60% carbohydrate) vs NGL (40% carbohydrate) isocaloric meals for 3 days, in random order in the overnight state. [6,6-2H2] glucose was infused to measure EGP, deuterium labelled water was used to measure GNG, and 13C MRS scans were performed in fed and fasted states to measure hepatic glycogen content. Results Hepatic glycogen content and nocturnal EGP were higher (P < .05) in GL vs NGL in both cohorts. The % GNG to EGP averaged ∼50% in subjects with ND throughout the night after both meals. In contrast, % GNG to nocturnal EGP in T2D was lower with GL vs NGL and matched the pattern observed in subjects with ND with GL lowering overnight rates of GNG in subjects with T2D. Conclusion Selective targeting of GNG at night with appropriate medications could reduce nocturnal and early morning fasting hyperglycemia and hepatic insulin resistance in people with T2D.

Abstract Context Circulating lactate concentration is an important determinant of exercise tolerance. Objective This work aimed to determine the role of hyperglycemia on lactate metabolism during exercise in individuals with type 1 diabetes (T1D). Methods The protocol at the University of Virginia compared 7 T1D participants and 7 participants without diabetes (ND) at euglycemia (5.5 mM) or hyperglycemia (9.2 mM) in random order in T1D and at euglycemia in ND. Intervention included [1-13C] lactate infusion, exercise at 65% maximal oxygen uptake (VO2max), euglycemia, and hyperglycemia visits. The main outcome measure was lactate turnover before, during, and after 60 minutes of exercise at 65% VO2max. Results A 2-compartment model with loss only from the peripheral compartment described lactate kinetics. Volume of distribution of the accessible compartment was similar between T1D and ND individuals (P = .76) and concordant with plasma volume (∼40 mL/kg). Circulating lactate concentrations were higher (P < .001) in T1D participants during exercise at hyperglycemia than euglycemia. Exercise-induced lactate appearance did not differ (P = .13) between hyperglycemia and euglycemia. However, lactate clearance (CL) was lower (P = .03) during hyperglycemia than euglycemia in T1D participants. There were no differences in any of the aforementioned parameters between T1D and ND participants during euglycemia. Conclusion Hyperglycemia modulates lactate metabolism during exercise by lowering CL, leading to higher circulating lactate concentrations in T1D individuals. This novel observation implies that exercise during hyperglycemia can lead to higher circulating lactate concentrations thus increasing the likelihood of reaching the lactate threshold sooner in T1D, and has high translational relevance both for providers and recreationally active people with T1D.

Glucose production is inappropriately increased in people with type 2 diabetes both before and after food ingestion. Excessive postprandial glucose production occurs in the presence of decreased and delayed insulin secretion and lack of suppression of glucagon release. These abnormalities in hormone secretion, coupled with impaired insulin-induced suppression of glucose production and stimulation of splanchnic glucose uptake, likely account in large part for the excessive amounts of glucose that reach the systemic circulation for disposal by peripheral tissues following food ingestion. In contrast, when adequate basal insulin concentrations are present, neither glucagon-induced stimulation of glucose production nor glucose-induced suppression of glucose production differs in diabetic and nondiabetic subjects matched for gender, age, and degree of obesity. However, when insulin secretion is defective, lack of suppression of glucagon can cause substantial hyperglycemia by enhancing rates of glucose production. Therefore, normalization of hepatic glucose metabolism in people with type 2 diabetes mellitus likely will require normalization of insulin and glucagon secretion as well as hepatic insulin action.

To assess the diurnal patterns of postprandial glucose tolerance and insulin sensitivity, 19 subjects with type 2 diabetes (8 women; 60 ± 11 years; BMI 32 ± 5 kg/m2) and 19 anthropometrically matched subjects with no diabetes (ND; 11 women; 53 ± 12 years; BMI 29 ± 5 kg/m2) were studied during breakfast (B), lunch (L), and dinner (D) with identical mixed meals (75 g carbohydrates) on 3 consecutive days in a randomized Latin square design. Three stable isotopes of glucose were ustilized to estimate meal fluxes, and mathematical models were used in estimating indices of insulin action and β-cell function. Postmeal glucose excursions were higher at D versus B and at D versus L in type 2 diabetes (P < 0.05), while in ND they were higher at D versus B (P = 0.025) and at L versus B (P = 0.04). The insulin area under the curve was highest at B compared with L and D in type 2 diabetes, while no differences were observed in ND. Disposition index (DI) was higher at B than at L (P < 0.01) and at D (P < 0.001) in ND subjects, whereas DI was low with unchanging pattern across B-L-D in individuals with type 2 diabetes. Furthermore, between-meal differences in β-cell responsivity to glucose (F) and insulin sensitivity (SI) were concurrent with changes in the DI within groups. Fasting and postmeal glucose, insulin, and C-peptide concentrations, along with estimates of endogenous glucose production (EGP), Rd, SI, F, hepatic extraction of insulin, insulin secretion rate, extracted insulin, and DI, were altered in type 2 diabetes compared with ND (P < 0.011 for all). The data show a diurnal pattern of postprandial glucose tolerance in overweight otherwise glucose-tolerant ND individuals that differs from overweight individuals with type 2 diabetes. The results not only provide valuable insight into management strategies for better glycemic control in people with type 2 diabetes, but also improved understanding of daytime glucose metabolism in overweight individuals without impaired glucose tolerance or overt diabetes.

Abstract Aim To evaluate whether short‐term treatment with a selective 11β‐Hydroxysteroid dehydrogenase‐1 (11β‐HSD1) inhibitor, AZD4017, would block hepatic cortisol production and thereby decrease hepatic fat in patients with nonalcoholic fatty liver disease (NAFLD)/nonalcoholic steatohepatitis (NASH), with or without type 2 diabetes (T2D). Materials and Methods This was a randomized, double‐blind, placebo‐controlled, phase 2 study conducted at two sites. Key inclusion criteria were the presence of NAFLD or NASH on magnetic resonance imaging (MRI) or recent biopsy positive for NASH. Enrolled patients were randomly assigned (1:1) to AZD4017 or placebo for 12 weeks. Primary outcomes were between‐group differences in mean change from baseline to week 12 in liver fat fraction (LFF) and conversion of 13 C cortisone to 13 C cortisol in the liver. Results A total of 93 patients were randomized; 85 patients completed treatment. The mean (standard deviation [SD]) change in LFF was −0.667 (5.246) and 0.139 (4.323) in the AZD4017 and placebo groups ( P = 0.441). For patients with NASH and T2D, the mean (SD) change in LFF was significantly improved in the AZD4017 versus the placebo group (−1.087 [5.374] vs. 1.675 [3.318]; P = 0.033). Conversion of 13 C cortisone to 13 C cortisol was blocked in all patients in the AZD4017 group. There were no significant between‐group differences (AZD4017 vs. placebo) in changes in fibrosis, weight, levels of liver enzymes or lipids, or insulin sensitivity. Conclusion Although the study did not meet one of the primary outcomes, AZD4017 blocked the conversion of 13 C cortisone to 13 C cortisol in the liver in all patients who received the drug. In patients with NASH and T2D, AZD4017 improved liver steatosis versus placebo.

Background Hypoglycemia results in a reduction in spontaneous cardiac baroreflex sensitivity (scBRS) and a shift in the baroreflex working range to higher heart rates; this effect may be mediated by the carotid chemoreceptors. We hypothesized changes in baroreflex control of heart rate with hypoglycemia would be blunted in carotid body resected patients when compared with healthy controls. Methods Five patients (3M/2F) with bilateral carotid body resection for glomus tumors and ten healthy controls (7M/3F) completed a 180‐min hyperinsulinemic, hypoglycemic (~3.3 µmol/mL) clamp. Changes in heart rate, blood pressure, and scBRS were assessed. Results scBRS was reduced from baseline during hypoglycemia (p<0.01) and was lower in carotid body resected patients when compared with controls (p=0.01). Hypoglycemia‐mediated reductions in systolic and mean blood pressure were significantly greater in patients when compared with controls (p<0.05). Despite lower blood pressures, increases in heart rate with hypoglycemia were blunted in patients (p<0.01). Conclusion Reductions in scBRS with hypoglycemia cannot be exclusively attributed to the carotid chemoreceptors; however, the chemoreceptors play a role in resetting the baroreflex working range to higher heart rates during hypoglycemia such that a rise in heart rate is not observed in carotid body resected patients. These data support a contribution of the carotid chemoreceptors to baroreflex control of blood pressure during hypoglycemia and highlight potential widespread effects of carotid body resection in humans. Funding DK090541, HL120570

Cardio‐vagal tone (CVT) and heart rate variability (HRV) are reduced during hypoglycemia. Carotid body (CB) peripheral chemoreceptors are multi‐modal; therefore we hypothesized a correlation between CB activity and CVT during hypoglycemia. Seven healthy adults (4M/3F) underwent two 180 min hyperinsulemic (2mU/kg FFM/min), hypoglycemic (3.33 mmol/L) clamps one week apart, randomized to normoxia (arterial P O2 (P a O 2 ) 111 ± 6.3 mmHg) or hyperoxia (P a O 2 345 ± 80.6 mmHg) to desensitize the CB. CVT was assessed via the high frequency (HF) component of HRV from 5 min periods of 5‐lead ECG recording under baseline (euglycemia) and hypoglycemia. HF values decreased significantly from baseline during hypoglycemia, however this reduction was attenuated under hyperoxia (Normoxia (N): −69% vs. Hyperoxia (H): −41%, p=0.04). Heart rate increased significantly during hypoglycemia (N: 59.7 bpm ± 2.4 vs. 71.9 ± 4.0; H: 60.6 bpm ± 1.9 vs. 68.5 ± 3, p<0.001), however, this increase was not different between normoxia and hyperoxia, despite differences in CVT and HRV. These data indicate that the CB chemoreceptors may be partially responsible for the reduction in CVT associated with hypoglycemia, and they provide evidence for a role of the CB chemoreceptors in parasympathetic tone to the heart. Future studies are required to determine whether inhibition of the CB may serve to improve CVT function during hypoglycemia. T32 DK07352, F32 DK84624‐01 A1, CTSA 1 UL 1 RR024150 , R01DK 29953