α- or ß-Adrenergic blockade does not affect transplanted islet cell responses to hypoglycemia in type 1 diabetes.

Type 1 diabetes recipients of intrahepatic islet transplantation exhibit glucose-dependent suppression of insulin and activation of glucagon secretion in response to insulin-induced hypoglycemia associated with clinical protection from hypoglycemia. Whether sympathetic activation of adrenergic receptors on transplanted islets is required for these responses in defense against hypoglycemia is not known. To evaluate the adrenergic contribution to post-transplant glucose counterregulation, we performed a randomized, double-blind crossover study of responses during a hyperinsulinemic euglycemic-hypoglycemic clamp under phentolamine (α-adrenergic blockage), propranolol (ß-adrenergic blockage), or placebo infusion. Participants (5 female/4 male) were median (range) age 53 (34-63) years, diabetes duration 29 (18-56) years, post-transplant 7.0 (1.9-8.4) years, HbA1c 5.8 (4.5-6.8)%, insulin in-/dependent 5/4, all on tacrolimus-based immunosuppression. During the clamp, blood pressure was lower with phentolamine and heart rate lower with propranolol vs. placebo (P <0.05). There was no difference in suppression of endogenous insulin secretion (derived from C-peptide measurements) during the euglycemic or hypoglycemic phases, and while levels of glucagon were similar with phentolamine or propranolol vs. placebo, the increase in glucagon from eu- to hypoglycemia was greater with propranolol vs. placebo (P < 0.05). Pancreatic polypeptide was greater with phentolamine vs. placebo during the euglycemic phase (P < 0.05), and free fatty acids were lower and the glucose infusion rate higher with propranolol vs. placebo during the hypoglycemic phase (P < 0.05). These results indicate that neither physiologic α- nor ß-adrenergic blockade attenuates transplanted islet responses to hypoglycemia, suggesting sympathetic re-innervation of the islet graft is not necessary for post-transplant glucose counterregulation.

Validating and Establishing a Diagnostic Threshold for the Hypoglycemia Awareness Questionnaire Impaired Awareness Subscale.

OBJECTIVE: To evaluate the discriminant and convergent validities of the Hypoglycemia Awareness Questionnaire Impaired Awareness (HypoA-Q IA) subscale and establish a diagnostic threshold for the classification of impaired awareness of hypoglycemia (IAH) in adults with type 1 diabetes (T1D). METHODS: Twenty-one adults with T1D (male, 48%; median age, 36 years; and T1D duration, 21 years) completed the HypoA-Q IA subscale, Clarke, and hypoglycemia severity (HYPO) scores, continuous glucose monitoring, and hyperinsulinemic hypoglycemic clamp testing. Those with IAH defined by a Clarke score of ≥4 (n = 10) and who experienced severely problematic hypoglycemia and/or marked glycemic lability started automated insulin delivery as part of an 18-month intervention study with the 6-monthly paired assessment of the HypoA-Q IA subscale, Clarke score, HYPO score and continuous glucose monitoring, and hypoglycemic clamp testing at baseline and 6 and 18 months. RESULTS: The HypoA-Q IA subscale discriminated between those with and without IAH defined by the Clarke score (W = 110.5; P <.001). During intervention, the HypoA-Q IA subscale demonstrated convergent validity via significant relationships with the Clarke (r = 0.72; P <.001) and HYPO (r = 0.60; P <.001) scores; hypoglycemia exposure below 70 (r = 0.53; P <.01), 60 (r = 0.50; P <.01), and 54 (r = 0.48; P <.01) mg/dL; and autonomic symptom (r = -0.53; P <.05), epinephrine (r = -0.68; P <.001), and pancreatic polypeptide (r = -0.52; P <.05) responses to insulin-induced hypoglycemia. The receiver operating characteristic curve analysis revealed that the HypoA-Q IA subscale was an excellent predictor of an abnormal symptom response to insulin-induced hypoglycemia (area under the curve, 0.86) with a score of 12, which was the optimal threshold for IAH classification (sensitivity, 83%; specificity, 80%). CONCLUSION: These findings support the validity of the HypoA-Q IA subscale and propose a HypoA-Q IA diagnostic threshold to identify IAH in both clinical and research settings.

Automated Insulin Delivery for Hypoglycemia Avoidance and Glucose Counterregulation in Long-Standing Type 1 Diabetes with Hypoglycemia Unawareness.

Objective: Automated insulin delivery (AID) may benefit individuals with long-standing type 1 diabetes where frequent exposure to hypoglycemia impairs counterregulatory responses. This study assessed the effect of 18 months AID on hypoglycemia avoidance and glucose counterregulatory responses to insulin-induced hypoglycemia in long-standing type 1 diabetes complicated by impaired awareness of hypoglycemia. Methods: Ten participants mean ± standard deviation age 49 ± 16 and diabetes duration 34 ± 16 years were initiated on AID. Continuous glucose monitoring was paired with actigraphy to assess awake- and sleep-associated hypoglycemia exposure every 3 months. Hyperinsulinemic hypoglycemic clamp experiments were performed at baseline, 6, and 18 months postintervention. Hypoglycemia exposure was reduced by 3 months, especially during sleep, with effects sustained through 18 months (P ≤ 0.001) together with reduced glucose variability (P < 0.01). Results: Hypoglycemia awareness and severity scores improved (P < 0.01) with severe hypoglycemia events reduced from median (interquartile range) 3 (3-10) at baseline to 0 (0-1) events/person·year postintervention (P = 0.005). During the hypoglycemic clamp experiments, no change was seen in the endogenous glucose production (EGP) response, however, peripheral glucose utilization during hypoglycemia was reduced following intervention [pre: 4.6 ± 0.4, 6 months: 3.8 ± 0.5, 18 months: 3.4 ± 0.3 mg/(kg·min), P < 0.05]. There were increases over time in pancreatic polypeptide (Pre:62 ± 29, 6 months:127 ± 44, 18 months:176 ± 58 pmol/L, P < 0.01), epinephrine (Pre: 199 ± 53, 6 months: 332 ± 91, 18 months: 386 ± 95 pg/mL, P = 0.001), and autonomic symptom (Pre: 6 ± 2, 6 months: 6 ± 2, 18 months: 10 ± 2, P < 0.05) responses. Conclusions: AID led to a sustained reduction of hypoglycemia exposure. EGP in response to insulin-induced hypoglycemia remained defective, however, partial recovery of glucose counterregulation was evidenced by a reduction in peripheral glucose utilization likely mediated by increased epinephrine secretion and, together with improved autonomic symptoms, may contribute to the observed clinical reduction in hypoglycemia.

Evaluation of Clinical Metrics for Identifying Defective Physiologic Responses to Hypoglycemia in Long-Standing Type 1 Diabetes.

Repeated hypoglycemia exposure leads to impaired awareness of hypoglycemia (IAH) and the development of defective counterregulatory responses. To date, only pancreas or islet transplantation has demonstrated normalization of hypoglycemia awareness and the endogenous glucose production (EGP) response to defend against insulin-induced hypoglycemia in long-standing type 1 diabetes (T1D). This study aims to validate clinical metrics of IAH (Clarke score), hypoglycemia severity (HYPO score), glycemic lability (lability index), and continuous glucose monitoring (CGM) as predictors of absent autonomic symptom (AS) recognition and defective glucose counterregulation during insulin-induced hypoglycemia, thus enabling early identification of individuals with compromised physiologic defense against clinically significant hypoglycemia. Forty-three subjects with mean ± standard deviation age 43 ± 13 years and T1D duration 28 ± 13 years, including 32 with IAH and 11 with hypoglycemia awareness (Aware), and 12 nondiabetic control subjects, underwent single-blinded randomized-paired hyperinsulinemic-euglycemic and hypoglycemic clamp experiments. Receiver operating characteristic (ROC) curves and sensitivity analyses were performed to assess metric prediction of absent AS recognition and defective EGP responses to hypoglycemia. Clarke score and CGM measures of hypoglycemia exposure demonstrated good ability to predict absent AS recognition (area under the curve ≥0.80). A composite threshold of IAH-Clarke ≥4 with ROC curve-derived thresholds for CGM measures of hypoglycemia exposure showed high specificity and predictive value in identifying an absent AS response during the hypoglycemic clamp. Metrics demonstrated poor ability to predict defective glucose counterregulation by the EGP response, which was impaired even in the Aware group. Screening for IAH alongside assessment of CGM data can increase the specificity for identifying individuals with absent hypoglycemia symptom recognition who may benefit from further intervention.

Continuous Glucose Monitoring for Hypoglycemia Avoidance and Glucose Counterregulation in Long-Standing Type 1 Diabetes.

Context: Patients with long-standing type 1 diabetes (T1D) are at increased risk for severe hypoglycemia because of defects in glucose counterregulation and recognition of hypoglycemia symptoms, in part mediated through exposure to hypoglycemia. Objective: To determine whether implementation of real-time continuous glucose monitoring (CGM) as a strategy for hypoglycemia avoidance could improve glucose counterregulation in patients with long-standing T1D and hypoglycemia unawareness. Design, Setting, Participants, and Intervention: Eleven patients with T1D disease duration of ∼31 years were studied longitudinally in the Clinical & Translational Research Center of the University of Pennsylvania before and 6 and 18 months after initiation of CGM and were compared with 12 nondiabetic control participants. Main Outcome Measure: Endogenous glucose production response derived from paired hyperinsulinemic stepped-hypoglycemic and euglycemic clamps with infusion of 6,6-2H2-glucose. Results: In patients with T1D, hypoglycemia awareness (Clarke score) and severity (HYPO score and severe events) improved (P < 0.01 for all) without change in hemoglobin A1c (baseline, 7.2% ± 0.2%). In response to insulin-induced hypoglycemia, endogenous glucose production did not change from before to 6 months (0.42 ± 0.08 vs 0.54 ± 0.07 mg·kg-1·min-1) but improved after 18 months (0.84 ± 0.15 mg·kg-1·min-1; P < 0.05 vs before CGM), albeit remaining less than in controls (1.39 ± 0.11 mg·kg-1·min-1; P ≤ 0.01 vs all). Conclusions: Real-time CGM can improve awareness and reduce the burden of problematic hypoglycemia in patients with long-standing T1D, but with only modest improvement in the endogenous glucose production response that is required to prevent or correct low blood glucose.

Long-Term Improvement in Glucose Control and Counterregulation by Islet Transplantation for Type 1 Diabetes.

CONTEXT: Islet transplantation has been shown to improve glucose counterregulation and hypoglycemia symptom recognition in patients with type 1 diabetes (T1D) complicated by severe hypoglycemia episodes and symptom unawareness, but long-term data are lacking. OBJECTIVE: To assess the long-term durability of glucose counterregulation and hypoglycemia symptom responses 18 months after intrahepatic islet transplantation and associated measures of glycemic control during a 24-month follow-up period. DESIGN, SETTING, AND PARTICIPANTS: Ten patients with T1D disease duration of approximately 27 years were studied longitudinally before and 6 and 18 months after transplant in the Clinical & Translational Research Center of the University of Pennsylvania and were compared to 10 nondiabetic control subjects. INTERVENTION: All 10 patients underwent intrahepatic islet transplantation according to the CIT07 protocol at the Hospital of the University of Pennsylvania. MAIN OUTCOME MEASURES: Counterregulatory hormone, endogenous glucose production, and autonomic symptom responses derived from stepped hyperinsulinemic-hypoglycemic and paired hyperinsulinemic-euglycemic clamps with infusion of 6,6-2H2-glucose. RESULTS: Near-normal glycemia (HbA1c ≤ 6.5%; time 70-180 mg/dL ≥ 95%) was maintained for 24 months in all patients, with one returning to low-dose insulin therapy. In response to insulin-induced hypoglycemia, glucagon secretion was incompletely restored at 6 and 18 months, epinephrine was improved at 6 months and normalized at 18 months, and endogenous glucose production and symptoms, absent before, were normalized at 6 and 18 months after transplant. CONCLUSIONS: In patients with T1D experiencing problematic hypoglycemia, intrahepatic islet transplantation can lead to long-term improvement of glucose counterregulation and hypoglycemia symptom recognition, physiological effects that likely contribute to glycemic stability after transplant.

Restoration of Glucose Counterregulation by Islet Transplantation in Long-standing Type 1 Diabetes.

Patients with long-standing type 1 diabetes (T1D) may exhibit defective glucose counterregulation and impaired hypoglycemia symptom recognition that substantially increase their risk for experiencing severe hypoglycemia. The purpose of this study was to determine whether intrahepatic islet transplantation improves endogenous glucose production (EGP) in response to hypoglycemia in T1D patients experiencing severe hypoglycemia. We studied longitudinally subjects (n = 12) with ∼30 years, disease duration before and 6 months after intrahepatic islet transplantation using stepped hyperinsulinemic-hypoglycemic and paired hyperinsulinemic-euglycemic clamps with infusion of 6,6-(2)H2-glucose and compared the results with those from a nondiabetic control group (n = 8). After islet transplantation, HbA1c was normalized, and time spent while hypoglycemic (<70 mg/dL) was nearly abolished as indicated by continuous glucose monitoring. In response to insulin-induced hypoglycemia, C-peptide (absent before transplant) was appropriately suppressed, glucagon secretion was recovered, and epinephrine secretion was improved after transplantation. Corresponding to these hormonal changes, the EGP response to insulin-induced hypoglycemia, which was previously absent, was normalized after transplantation, with a similar effect seen for autonomic symptoms. Because the ability to increase EGP is ultimately required to circumvent the development of hypoglycemia, these results provide evidence that intrahepatic islet transplantation can restore glucose counterregulation in long-standing T1D and support its consideration as treatment for patients with hypoglycemia unawareness experiencing severe hypoglycemia.

Insulin sensitivity index in type 1 diabetes and following human islet transplantation: comparison of the minimal model to euglycemic clamp measures.

Insulin sensitivity is impaired in type 1 diabetes (T1D) and may be enhanced by islet transplantation, an effect best explained by improved metabolic control. While the minimal model index of insulin sensitivity, SI, has been used in studies of T1D, it has not before been evaluated against gold-standard measures derived from the euglycemic clamp. We sought to determine how well minimal model SI derived from an insulin-modified frequently sampled intravenous glucose tolerance (FSIGT) test compared with total body and peripheral insulin sensitivity estimates derived from the hyperinsulinemic-euglycemic clamp in subjects with T1D and following islet transplantation. Twenty-one T1D subjects were evaluated, including a subgroup (n = 12) studied again after intrahepatic islet transplantation, with results compared with normal controls (n = 11 for the FSIGT). The transplant recipients received 9,648 ± 666 islet equivalents/kg with reduction in HbA1c from 7.1 ± 0.2 to 5.5 ± 0.1% (P < 0.01) and 10/12 were insulin independent. FSIGT-derived SI was reduced in T1D pre- compared with posttransplant and with normal [1.76 ± 0.45 vs. 4.21 ± 0.34 vs. 4.45 ± 0.81 × 10(-4)(µU/ml)(-1)·min(-1); P < 0.01 for both]. Similarly, clamp-derived total body, and by the isotopic dilution method with [6,6-(2)H2]glucose, peripheral insulin sensitivity increased in T1D from pre- to posttransplant (P < 0.05 for both). The predictive power (r(2)) between volume-corrected SIC and measures of total and peripheral insulin sensitivity was 0.66 and 0.70, respectively (P < 0.00001 for both). That the minimal model SIC is highly correlated to the clamp-derived measures indicates that the FSIGT is an appropriate methodology for the determination of insulin sensitivity in T1D and following islet transplantation.

Improvement in insulin sensitivity after human islet transplantation for type 1 diabetes.

CONTEXT: Islet transplantation can improve metabolic control for type 1 diabetes (T1D), an effect anticipated to improve insulin sensitivity. However, current immunosuppression regimens containing tacrolimus and sirolimus have been shown to induce insulin resistance in rodents. OBJECTIVE: The objective of the study was to evaluate the effect of islet transplantation on insulin sensitivity in T1D using euglycemic clamps with the isotopic dilution method to distinguish between effects at the liver and skeletal muscle. DESIGN, SETTING, AND PARTICIPANTS: Twelve T1D subjects underwent evaluation in the Clinical and Translational Research Center before and between 6 and 7 months after the transplant and were compared with normal control subjects. INTERVENTION: The intervention included intrahepatic islet transplantation according to a Clinical Islet Transplantation Consortium protocol under low-dose tacrolimus and sirolimus immunosuppression. MAIN OUTCOME MEASURES: Total body (M/Δinsulin), hepatic (1/endogenous glucose production ·basal insulin) and peripheral [(Rd - endogenous glucose production)/Δinsulin] insulin sensitivity assessed by hyperinsulinemic (1 mU·kg(-1)·min(-1)) euglycemic (∼90 mg/dL) clamps with 6,6-(2)H2-glucose tracer infusion were measured. RESULTS: Glycosylated hemoglobin was reduced in the transplant recipients from 7.0% ± 0.3% to 5.6% ± 0.1% (P < .01). There were increases in total (0.11 ± 0.01 to 0.15 ± 0.02 dL/min·kg per microunit per milliliter), hepatic [2.3 ± 0.1 to 3.7 ± 0.4 × 10(2) ([milligrams per kilogram per minute](-1)·(microunits per milliliter)(-1))], and peripheral (0.08 ± 0.01 to 0.12 ± 0.02 dL/min·kg per microunit per milliliter) insulin sensitivity from before to after transplantation (P < .05 for all). All insulin sensitivity measures were less than normal in T1D before (P ≤ .05) and not different from normal after transplantation. CONCLUSIONS: Islet transplantation results in improved insulin sensitivity mediated by effects at both the liver and skeletal muscle. Modern dosing of glucocorticoid-free immunosuppression with low-dose tacrolimus and sirolimus does not induce insulin resistance in this population.

Improvement in ß-cell secretory capacity after human islet transplantation according to the CIT07 protocol.

The Clinical Islet Transplantation 07 (CIT07) protocol uses antithymocyte globulin and etanercept induction, islet culture, heparinization, and intensive insulin therapy with the same low-dose tacrolimus and sirolimus maintenance immunosuppression as in the Edmonton protocol. To determine whether CIT07 improves engrafted islet ß-cell mass, our center measured ß-cell secretory capacity from glucose-potentiated arginine tests at days 75 and 365 after transplantation and compared those results with the results previously achieved by our group using the Edmonton protocol and normal subjects. All subjects were insulin free, with CIT07 subjects receiving fewer islet equivalents from a median of one donor compared with two donors for Edmonton protocol subjects. The acute insulin response to glucose-potentiated arginine (AIRpot) was greater in the CIT07 protocol than in the Edmonton protocol and was less in both cohorts than in normal subjects, with similar findings for C-peptide. The CIT07 subjects who completed reassessment at day 365 exhibited increasing AIRpot by trend relative to that of day 75. These data indicate that engrafted islet ß-cell mass is markedly improved with the CIT07 protocol, especially given more frequent use of single islet donors. Although several peritransplant differences may have each contributed to this improvement, the lack of deterioration in ß-cell secretory capacity over time in the CIT07 protocol suggests that low-dose tacrolimus and sirolimus are not toxic to islets.

Effect of a low-carbohydrate diet versus a low-fat, calorie-restricted diet on adipokine levels in obese, diabetic participants.

The effect of dietary macronutrient composition on adipokine concentrations remains unclear. Greater reductions in leptin have been reported in participants who followed low-carbohydrate versus low-fat diets, although these studies did not adjust for the important effects of weight loss on adipokines. We investigated the effect of macronutrient composition on adipokine levels in 144 obese, diabetic participants who were randomly assigned to a low- carbohydrate (< 30 g/day) or low-fat diet (≤ 30% of calories from fat with a deficit of 500 kcal/day). Weight, adipokines, and dietary intake were assessed at baseline and 6 months. Complete data were available for 79 participants. At month 6, weight, leptin, adiponectin, and tumor necrosis factor-α concentrations did not differ significantly between groups (P > 0.05 for all variables). However, significant changes in leptin and adiponectin occurred over time (P < 0.001 and P < 0.012, respectively). Modest weight loss, rather than macronutrient composition, likely accounted for the favorable changes observed in leptin and adiponectin over time.

Effects of a low-intensity intervention that prescribed a low-carbohydrate vs. a low-fat diet in obese, diabetic participants.

Low-carbohydrate diets have been associated with significant reductions in weight and HbA(1c) in obese, diabetic participants who received high-intensity lifestyle modification for 6 or 12 months. This investigation sought to determine whether comparable results to those of short-term, intensive interventions could be achieved over a 24-month study period using a low-intensity intervention that approximates what is feasible in outpatient practice. A total of 144 obese, diabetic participants were randomly assigned to a low-carbohydrate diet (<30 g/day) or to a low fat diet (