Features of Hepatic and Skeletal Muscle Insulin Resistance Unique to Type 1 Diabetes
ABSTRACT Type 1 diabetes is known to be a state of insulin resistance; however, the tissues involved in whole-body insulin resistance are less well known. It is unclear whether insulin resistance is due to glucose toxicity in the post-Diabetes Control and Complications Trial era of tighter glucose control.
We performed this study to determine muscle and liver insulin sensitivity individuals with type 1 diabetes after overnight insulin infusion to lower fasting glucose concentration.
Fifty subjects [25 controls without and 25 individuals with type 1 diabetes (diabetes duration 22.9 ± 1.7 yr, without known end organ damage] were frequency matched on age and body mass index by group and studied. After 3 d of dietary control and overnight insulin infusion to normalize glucose, we performed a three-stage hyperinsulinemic/euglycemic clamp infusing insulin at 4, 8, and 40 mU/m(2) · min. Glucose metabolism was quantified using an infusion of [6,6-(2)H(2)]glucose. Hepatic insulin sensitivity was measured using the insulin IC(50) for glucose rate of appearance (Ra), whereas muscle insulin sensitivity was measured using the glucose rate of disappearance during the highest insulin dose.
Throughout the study, glucose Ra was significantly greater in individuals compared with those without type 1 diabetes. The concentration of insulin required for 50% suppression of glucose Ra was 2-fold higher in subjects with type 1 diabetes. Glucose rate of disappearance was significantly lower in individuals with type 1 diabetes during the 8- and 40-mU/m(2) · min stages.
Insulin resistance in liver and skeletal muscle was a significant feature in type 1 diabetes. Nevertheless, the etiology of insulin resistance was not explained by body mass index, percentage fat, plasma lipids, visceral fat, and physical activity and was also not fully explained by hyperglycemia.
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ABSTRACT: Insulin resistance (IR) increases cardiovascular morbidity and is associated with mitochondrial dysfunction. IR is now recognized to be present in type 1 diabetes, however its relationship to mitochondrial function is unknown. We determined the relationship between IR and muscle mitochondrial function in type 1 diabetes using the hyperinsulinemic euglycemic clamp and 31Phosphorus magnetic resonance spectroscopy before, during and after near-maximal isometric calf exercise. Volunteers included 21 non-obese adolescents with type 1 diabetes and 17 non-diabetic controls with similar age, sex, BMI, Tanner stage and activity levels. We found that youth with type 1 diabetes were more IR (median glucose infusion rate 10.1 vs. 18.9 mg/kglean/min; p<0.0001) and had a longer time constant of the curve of ADP conversion to ATP (23.4±5.3 vs. 18.8±3.9 seconds, p<0.001), and a lower rate of oxidative phosphorylation (median 0.09 vs. 0.21 mmol/L/sec, p<0.001). The ADP time constant (β=-0.36, p=0.026) and oxidative phosphorylation (β=0.02, p<0.038) were related to IR, but not HbA1c. Normal weight youth with type 1 diabetes demonstrated slowed post-exercise ATP re-synthesis and were more IR than controls. The correlation between skeletal muscle mitochondrial dysfunction in type 1 diabetes and IR suggests a relationship between mitochondrial dysfunction and IR in type 1 diabetes.Diabetes 08/2014; DOI:10.2337/db14-0765 · 8.47 Impact Factor
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ABSTRACT: There is a paucity of literature describing metabolic and histological data in adult-onset autoimmune diabetes. This subgroup of diabetes mellitus affects at least 5% of clinically diagnosed type 2 diabetic patients (T2DM) and it is termed Latent Autoimmune Diabetes in Adults (LADA). We evaluated indexes of insulin secretion, metabolic assessment, and pancreatic pathology in clinically diagnosed T2DM patients with and without the presence of humoral islet autoimmunity (Ab). A total of 18 patients with at least 5-year duration of clinically diagnosed T2DM were evaluated in this study. In those subjects we assessed acute insulin responses to arginine, a glucose clamp study, whole-body fat mass and fat-free mass. We have also analyzed the pancreatic pathology of 15 T2DM and 43 control cadaveric donors, using pancreatic tissue obtained from all the T2DM organ donors available from the nPOD network through December 31, 2013. The presence of islet Ab correlated with severely impaired β-cell function as demonstrated by remarkably low acute insulin response to arginine (AIR) when compared to that of the Ab negative group. Glucose clamp studies indicated that both Ab positive and Ab negative patients exhibited peripheral insulin resistance in a similar fashion. Pathology data from T2DM donors with Ab or the autoimmune diabetes associated DR3/DR4 allelic class II combination showed reduction in beta cell mass as well as presence of autoimmune-associated pattern A pathology in subjects with either islet autoantibodies or the DR3/DR4 genotype. In conclusion, we provide compelling evidence indicating that islet Ab positive long-term T2DM patients exhibit profound impairment of insulin secretion as well as reduced beta cell mass seemingly determined by an immune-mediated injury of pancreatic β-cells. Deciphering the mechanisms underlying beta cell destruction in this subset of diabetic patients may lead to the development of novel immunologic therapies aimed at halting the disease progression in its early stage.PLoS ONE 09/2014; 9(9):e106537. DOI:10.1371/journal.pone.0106537 · 3.53 Impact Factor
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ABSTRACT: Despite improvements in glucose, lipids and blood pressure control, vascular complications remain the most important cause of morbidity and mortality in patients with type 1 diabetes. For that reason, there is a need to identify additional risk factors to utilize in clinical practice or translate to novel therapies to prevent vascular complications. Reduced insulin sensitivity is an increasingly recognized component of type 1 diabetes that has been linked with the development and progression of both micro- and macrovascular complications. Adolescents and adults with type 1 diabetes have reduced insulin sensitivity, even when compared to their non-diabetic counterparts of similar adiposity, serum triglycerides, high-density lipoprotein cholesterol, level of habitual physical activity, and in adolescents, pubertal stage. Reduced insulin sensitivity is thought to contribute both to the initiation and progression of macro- and microvascular complications in type 1 diabetes. There are currently clinical trials underway examining the benefits of improving insulin sensitivity with regards to vascular complications in type 1 diabetes. Reduced insulin sensitivity is an increasingly recognized component of type 1 diabetes, is implicated in the pathogenesis of vascular complications and is potentially an important therapeutic target to prevent vascular complications. In this review, we will focus on the pathophysiologic contribution of insulin sensitivity to vascular complications and summarize related ongoing clinical trials.