Steven V. Edelman

Decreased effect of insulin to stimulate skeletal muscle blood flow in obese man. A novel mechanism for insulin resistance.

Obesity is characterized by decreased rates of skeletal muscle insulin-mediated glucose uptake (IMGU). Since IMGU equals the product of the arteriovenous glucose difference (AVGd) across muscle and blood flow into muscle, reduced blood flow and/or tissue activity (AVGd) can lead to decreased IMGU. To examine this issue, we studied six lean (weight 68 +/- 3 kg, mean +/- SEM) and six obese (94 +/- 3 kg) men. The insulin dose-response curves for whole body and leg IMGU were constructed using the euglycemic clamp and leg balance techniques over a large range of serum insulin concentrations. In lean and obese subjects, whole body IMGU, AVGd, blood flow, and leg IMGU increased in a dose dependent fashion and maximal rates of all parameters were reduced in obese subjects compared to lean subjects. The dose-response curves for whole body IMGU, leg IMGU, and AVGd were right-shifted in obese subjects with an ED50 two- to threefold higher than that of lean subjects for each parameter. Leg blood flow increased approximately twofold from basal 2.7 +/- 0.2 to 4.4 +/- 0.2 dl/min in lean, P less than 0.01, and from 2.5 +/- 0.3 to 4.4 +/- 0.4 dl/min in obese subjects, P less than 0.01. The ED50 for insulins effect to increase leg blood flow was about fourfold higher for obese (957 pmol/liter) than lean subjects (266 pmol/liter), P less than 0.01. Therefore, decreased insulin sensitivity in human obesity is not only due to lower glucose extraction in insulin-sensitive tissues but also to lower blood flow to these tissues. Thus, in vivo insulin resistance can be due to a defect in insulin action at the tissue level and/or a defect in insulins hemodynamic action to increase blood flow to insulin sensitive tissues.

Double‐blind randomized trial of tramadol for the treatment of the pain of diabetic neuropathy

Objective The objective of this study was to evaluate the efficacy and safety of tramadol in treating the pain of diabetic neuropathy. Background The pain of diabetic neuropathy is a major cause of morbidity among these patients and treatment, as with other small-fiber neuropathies, is often unsatisfactory. Tramadol is a centrally acting analgesic for use in treating moderate to moderately severe pain. Methods This multicenter, outpatient, randomized, double-blind, placebo-controlled, parallel-group study consisted of a washoutlscreening phase, during which all analgesics were discontinued, and a 42-day double-blind treatment phase. A total of 131 patients with painful diabetic neuropathy were treated with tramadol (n = 65) or placebo (n = 66) tramadol, which were administered as identical capsules in divided doses four times daily. The primary efficacy analysis compared the mean pain intensity scores in the tramadol and placebo groups obtained at day 42 of the study or at the time of discontinuation. Secondary efficacy assessments were the pain relief rating scores and a quality of life evaluation based on daily activities and sleep characteristics. Results Tramadol, at an average dosage of 210 mg/day, was significantly (p < 0.001) more effective than placebo for treating the pain of diabetic neuropathy. Patients in the tramadol group scored significantly better in physical (p = 0.02) and social functioning (p = 0.04) ratings than patients in the placebo group. No statistically significant treatment effects on sleep were identified. The most frequently occurring adverse events with tramadol were nausea, constipation, headache, and somnolence. Conclusions The results of this placebo-controlled trial showed that tramadol was effective and safe in treating the pain of diabetic neuropathy.

Impaired Insulin-Mediated Skeletal Muscle Blood Flow in Patients With NIDDM

Patients with non-insulin-dependent diabetes metlitus (NIDDM) exhibit decreased rates of skeletal muscle insulin-mediated glucose uptake (IMGU). Because IMGU is equal to the product of the arteriovenous glucose difference (AVGΔ) across and blood flow (F) into muscle (IMGU = AVGΔ × F), reduced tissue permeability (AVGΔ) and/or glucose and insulin delivery (F) can potentially lead to decreased IMGU. The components of skeletal muscle IMGU were studied in six obese NIDDM subjects (103 ± 9 kg) and compared with those previously determined in six lean (weight 68 ± 3 kg), and six obese (94 ± 3 kg) with normal glucose tolerance. The insulin dose-response curves for whole body and leg muscle IMGU were constructed using the combined euglycemic clamp and leg balance techniques during sequential insulin infusions (range of serum insulin 130–80,000 pmol/L). In lean, obese, and NIDDM subjects, whole body IMGU, femoral AVGΔ, and leg IMGU increased in a dose-dependent fashion over the range of insulin with an ED50 of 400–500 pmol/L in lean, 1000–1200 pmol/L in obese, and 4000–7000 pmol/L in NIDDM subjects (P < 0.01 lean vs. obese and NIDDM). In lean and obese subjects, maximally effective insulin concentrations increased leg blood flow ∼2-fold from basal with an ED50 of 266 pmol/L and 957 pmol/L, respectively (P < 0.01 lean vs. obese). In contrast, leg F did not increase from the basal value in NIDDM subjects (2.7 ± 0.1 vs. 3.5 ± 0.5 dl/min, NS). In the physiological range of insulin concentrations NIDDM subjects had lower body IMGU, leg F, femoral AVGΔ, and leg IMGU than obese and lean subjects, but at maximally effective insulin concentrations, femoral AVGA did not differ between obese and NIDDM subjects. Thus, 1) both reduced skeletal muscle tissue permeability and blood flow are found in NIDDM subjects and 2) impaired insulin-mediated augmentation of skeletal muscle blood flow in obese NIDDM patients is due to the diabetic state per se and not to the obesity status. Whether reduced skeletal muscle blood flow is the result or the cause of insulin resistance in patients with NIDDM remains to be elucidated.

Maintenance of the long-term effectiveness of tramadol in treatment of the pain of diabetic neuropathy

OBJECTIVE The objective of this study was to evaluate the efficacy and safety of tramadol in a 6-month open extension following a 6-week double-blind randomized trial. RESEARCH DESIGN AND METHODS Patients with painful diabetic neuropathy who completed the double-blind study were eligible for enrollment in an open extension of up to 6 months. All patients received tramadol 50-400 mg/day. Self-administered pain intensity scores (scale 0-4; none to extreme pain) and pain relief scores (scale -1-4; worse to complete relief) were recorded the first day of the open extension (last day of the double-blind phase) and at 30, 90, and 180 days. RESULTS A total of 117 patients (56 former tramadol and 61 former placebo) entered the study. On the first day of the study, patients formerly treated with placebo had a significantly higher mean pain intensity score (2. 2+/-1.02 vs. 1.4+/-0.93, P<0.001) and a lower pain relief score (0. 9+/-1.43 vs. 2.2+/-1.27, P<0.001) than former tramadol patients. By Day 90, both groups had mean pain intensity scores of 1.4, which were maintained throughout the study. Mean pain relief scores (2. 4+/-1.09 vs. 2.2+/-1.14) were similar after 30 days in the former placebo and former tramadol groups, respectively and were maintained for the duration of the study. Four patients discontinued therapy due to ineffective pain relief; 13 patients discontinued due to adverse events. The most common adverse events were constipation, nausea, and headache. CONCLUSIONS Tramadol provides long-term relief of the pain of diabetic neuropathy.

INSULIN THERAPY IN TYPE 2 DIABETES

Type 2 diabetes is a common disorder often accompanied by numerous metabolic abnormalities leading to a high risk of cardiovascular morbidity and mortality. Results from the UKPDS have confirmed that intensive glucose control delays the onset and retards the progression of microvascular disease and possibly of macrovascular disease in patients with type 2 diabetes. In the early stages of the disease, insulin resistance plays a major role in the development of hyperglycemia and other metabolic abnormalities, and patients with type 2 diabetes often benefit from measures to improve insulin sensitivity such as weight loss, dietary changes, and exercise. Later, the use of oral insulin secretagogues and insulin sensitizers as monotherapy and in combination helps maintain glycemia for varying periods of time. Ultimately, because of the progressive nature of the disease and the progressive decline in pancreatic beta-cell function, insulin therapy is almost always obligatory to achieve optimal glycemic goals. Not all patients are candidates for aggressive insulin management; therefore, the goals of therapy should be modified, especially in elderly individuals and those with co-morbid conditions. Candidates for intensive management should be motivated, compliant, and educable, without other major medical conditions and physical limitations that would preclude accurate and reliable HGM and insulin administration. In selected patients, combination therapy with insulin and oral antidiabetic medications can be an effective method for normalizing glycemia without the need for rigorous multiple-injection regimens. The patients for whom combination therapy is most commonly successful are those who do not achieve adequate glycemic control using daytime oral agents but who still show some evidence of responsiveness to the medications. Bedtime intermediate-acting or predinner premixed intermediate- and rapid-acting insulin is administered and progressively increased until the FPG concentration is normalized. If combination therapy is not successful, a split-mixed regimen of intermediate- and rapid-acting insulin equally divided between the prebreakfast and pre-dinner periods is advised for oese patients, and more intensive regimens are advised for thin patients. Insulin therapy is invariably associated with weight gain and hypoglycemia. The use of metformin or glitazones in combination with insulin has been demonstrated to have insulin-sparing properties. Also, metformin use may ameliorate weight gain. The use of continuous subcutaneous insulin infusion pumps can be particularly beneficial in treating patients with type 2 diabetes mellitus who do not respond satisfactorily to more conventional treatment strategies. Intraperitoneal insulin delivery systems hold considerable promise in type 2 diabetes because of their more physiologic delivery of insulin and their ability to inhibit hepatic glucose production selectively, with less peripheral insulinemia than with subcutaneous insulin injections. Newer insulin analogues such as the rapidly acting Lispro insulin and the peakless, long-acting glargine insulin are increasingly being used because of their unique physiologic pharmacokinetics. New developments such as inhaled and buccal insulin preparations will also make it easier for many patients to initiate and maintain a proper insulin regimen. Finally, a new generation of gut peptides such as amylin and GLP-1 will add a new dimension to glycemic control through modification of nutrient delivery and other mechanisms; however, the ultimate goal in the management of type 2 diabetes is the primary prevention of the disease. The Diabetes Prevention Program (DPP) sponsored by the National Institutes of Health has currently randomly assigned more than 3000 persons with impaired glucose tolerance and at high risk of developing diabetes into three treatment arms: metformin arm, an intensive lifestyle-modification arm, and a placebo arm. The study will conclude in 2002 after all participants have been followed for 3 to 6 years.

Serum 1,5-Anhydroglucitol (GlycoMark™): A Short-Term Glycemic Marker

1,5-Anhydroglucitol (1,5-AG), the 1-deoxy form of glucose, has been measured and used clinically in Japan for over a decade to monitor short-term glycemic control. Evaluation of glucose control otherwise requires measuring plasma glucose or glycated proteins whose levels reflect average glucose concentration over the half-life of the protein analyzed. Hemoglobin A1c measurements reflect blood glucose levels over that past 2-3 months, while fructosamine can be used to evaluate glycemic control over 10-14 days. In contrast, 1,5-AG levels in blood respond within 24 h as a result of glucoses competitive inhibition of 1,5-AG reabsorption in the kidney tubule. When glucose levels rise, even transiently, urinary loss of 1,5-AG occurs, and circulating levels fall. Because of changes in renal hemodynamics in normal pregnancies, 1,5-AG appears of limited usefulness in evaluation of gestational diabetes. However, the characteristics of 1,5-AG levels in patients with moderate to near-normal glycemic control suggest that it may be a valuable complement to frequent self-monitoring or continuous monitoring of plasma glucose to confirm stable glycemic control. Measurements performed daily or weekly in a given patient would suggest that overall glycemic control has been stable or improved if 1,5-AG levels are stable or increasing. If 1,5-AG levels fall, greater attention to glucose monitoring and both lifestyle and medical management could be prescribed to correct the glycemic excursions that would underlie such changes. The behavior of this analyte is different from all others used in the management of diabetes, creating potential opportunities for its use in clinical practice.

Exploring the Potential of the SGLT2 Inhibitor Dapagliflozin in Type 1 Diabetes: A Randomized, Double-Blind, Placebo-Controlled Pilot Study

OBJECTIVE Insulin adjustments to maintain glycemic control in individuals with type 1 diabetes often lead to wide glucose fluctuations, hypoglycemia, and increased body weight. Dapagliflozin, an insulin-independent sodium–glucose cotransporter 2 (SGLT2) inhibitor, increases glucosuria and reduces hyperglycemia in individuals with type 2 diabetes. The primary objective of this study was to assess short-term safety of dapagliflozin in combination with insulin; secondary objectives included pharmacokinetic, pharmacodynamic, and efficacy parameters. RESEARCH DESIGN AND METHODS A 2-week, dose-ranging, randomized, double-blind, placebo-controlled proof-of-concept study randomly assigned 70 adults with type 1 diabetes (HbA1c 7–10%), who were receiving treatment with stable doses of insulin, to one of four dapagliflozin doses (1, 2.5, 5, or 10 mg) or placebo. The insulin dose was not proactively reduced at randomization but could be adjusted for safety reasons. RESULTS Sixty-two patients (88.6%) completed the study. Any hypoglycemia was common across all treatments (60.0–92.3%); one major event of hypoglycemia occurred with dapagliflozin 10 mg. No diabetic ketoacidosis occurred. Pharmacokinetic parameters were similar to those observed in patients with type 2 diabetes. Glucosuria increased by 88 g/24 h (95% CI 55 to 121) with dapagliflozin 10 mg and decreased by −21.5 g/24 h (95% CI −53.9 to 11.0) with placebo. Changes from baseline with dapagliflozin 10 mg by day 7 were as follows: −2.29 mmol/L (95% CI −3.71 to −0.87 [−41.3 mg/dL; 95% CI −66.9 to −15.7]) for 24-h daily average blood glucose; −3.77 mmol/L (95% CI −6.09 to −1.45 [−63.1 mg/dL; 95% CI −111.5 to −14.8]) for mean amplitude of glycemic excursion; and −16.2% (95% CI −29.4 to −0.5) for mean percent change in total daily insulin dose. Corresponding changes with placebo were as follows: −1.13 mmol/L (95% CI −3.63 to 1.37), −0.45 mmol/L (95% CI −4.98 to 4.08), and 1.7% (95% CI −22.8 to 33.9), respectively. However, for every efficacy parameter, the 95% CIs for all dapagliflozin doses overlapped those for placebo. CONCLUSIONS This exploratory study of dapagliflozin in adults with type 1 diabetes demonstrated acceptable short-term tolerability and expected pharmacokinetic profiles and increases in urinary glucose excretion. Within the dapagliflozin groups, dose-related reductions in 24-h glucose, glycemic variability, and insulin dose were suggested, which provide hope that SGLT2 inhibition may prove in larger randomized controlled trials to be efficacious in reducing hyperglycemia in type 1 diabetes.

Reduced capacity and affinity of skeletal muscle for insulin-mediated glucose uptake in noninsulin-dependent diabetic subjects. Effects of insulin therapy.

We have estimated the capacity and affinity of insulin-mediated glucose uptake (IMGU) in whole body and in leg muscle of obese non-insulin-dependent diabetics (NIDDM, n = 6) with severe hyperglycemia, glycohemoglobin (GHb 14.4 +/- 1.2%), lean controls (ln, n = 7) and obese nondiabetic controls (ob, n = 7). Mean +/- SEM weight (kg) was 67 +/- 2 (ln), 100 +/- 7 (ob), and 114 +/- 11 (NIDDM), P = NS between obese groups. NIDDM were also studied after 3 wk of intensive insulin therapy, GHb post therapy was 10.1 +/- 0.9, P less than 0.01 vs. pretherapy. Insulin (120 mu/m2 per min) was infused and the arterial blood glucose (G) sequentially maintained at approximately 4, 7, 12, and 21 mmol/liter utilizing the G clamp technique. Leg glucose uptake (LGU) was calculated as the product of the femoral arteriovenous glucose difference (FAVGd) and leg blood flow measured by thermodilution. Compared to ln, ob and NIDDM had significantly lower rates of whole body IMGU and LGU at all G levels. Compared to ob, the NIDDM exhibited approximately 50% and approximately 40% lower rates of whole body IMGU over the first two G levels (P less than 0.02) but did not differ at the highest G, P = NS. LGU was 83% lower in NIDDM vs. ob, P less than 0.05 at the first G level only. After insulin therapy NIDDM were indistinguishable from ob with respect to whole body IMGU or LGU at all G levels. A significant correlation was noted between the percent GHb and the EG50 (G at which 1/2 maximal FAVGd occurs) r = 0.73, P less than 0.05. Thus, (a) insulin resistance in NIDDM and obese subjects are characterized by similar decreases in capacity for skeletal muscle IMGU, but differs in that poorly controlled NIDDM display a decrease in affinity for skeletal muscle IMGU, and (b) this affinity defect is related to the degree of antecedent glycemic control and is reversible with insulin therapy, suggesting that it is an acquired defect.

Kinetics of In Vivo Muscle Insulin-Mediated Glucose Uptake in Human Obesity

The kinetics of in vivo insulin-mediated glucose uptake in human obesity have not been previously studied. To examine this, we used the glucose-clamp technique to measure whole-body and leg muscle glucose uptake in seven lean and six obese men during hyperinsulinemia (∼2000 pM) at four glucose levels (∼4.5, ∼8.3, ∼13.5, and ∼23.5 mM). To measure leg glucose uptake, the femoral artery and vein were catheterized, and blood flow was measured by thermodilution (leg glucose uptake = arteriovenous glucose difference × blood flow). With this approach, we found that rates of whole-body and leg glucose uptake were significantly lower in obese than in lean subjects at each glucose plateau. Leg blood flow rates increased from 4.3 ± 0.4 to 6.5 ± 0.8 dl/min over the range of glucose in lean subjects (P < 0.05) but remained unchanged in obese subjects. The apparent maximal capacity (Vmax), based on whole-body and leg glucose uptake, was reduced in obese compared with lean subjects, but the apparent Km was similar in the lean and obese subjects (6-9 mM, NS). To assess the affinity of muscle for glucose extraction independent of changes in muscle plasma flow, we determined the mean half-maximal effective glucose concentration (EG50) and found it was similar in the lean and obese subjects (6.0 ± 0.3 vs. 6.0 ± 0.8 mM, NS). We conclude that 1) the kinetics of in vivo insulin-mediated glucose uptake in skeletal muscle in human obesity are characterized by reduced Vmax but normal Km; 2) the EG50 for insulin-mediated glucose extraction in skeletal muscle was 6 mM in both lean and obese subjects, consistent with a Km characteristic of the glucose-transport system; 3) obese subjects were unable to generate increases in blood flow in response to hyperglycemia under hyperinsulinemic conditions, and this contributed significantly to lower rates of leg and whole-body glucose uptake.

Kinetics of Insulin-Mediated and Non-Insulin-Mediated Glucose Uptake in Humans

The kinetics of insulin-mediated glucose uptake (IMGU) and non-insulin-mediated glucose uptake (NIMGU) in humans have not been well defined. We used the glucose-clamp technique to measure rates of wholebody and leg muscle glucose uptake in six healthy lean men during hyperinsulinemia (∼460 pM) to study IMGU and during somatostatin-induced insulinopenia to study NIMGU at four glucose levels (4.5, 9,12, and 21 mM). To measure leg glucose uptake, the femoral artery and vein were catheterized, and blood flow was measured by thermodilution (leg glucose uptake = arteriovenous glucose difference [A-VG] × blood flow). With this approach, we found that, during hyperinsulinemia, both whole-body and leg glucose uptake increased in a curvilinear fashion at every glucose level, the highest glucose uptake values obtained being 139 ± 17 μmol · kg−1 · min−1 and 3656 ± 931 μmol · min−1 · leg−1, respectively. Leg blood flow increased twofold from 6.0 ± 1.7 to 11.7 ± 3.1 dl/min (P < 0.01) over the range of glucose and was correlated with whole-body glucose uptake (r = 0.55, P < 0.005). Leg muscle glucose extraction, independent of changes in blood flow, which is reflected by the A-VG, saturated over the range of glucose (1.28 ± 0.12, 2.22 ± 0.30, 2.92 ± 0.42, 3.02 ± 0.41 mM, NS between last 2 values) with a halfmaximal effective glucose concentration (EGS0) of 5.3 ± 0.4 mM. During insulinopenia, both whole-body and leg glucose uptake increased in a near-linear fashion; however, glucose uptake remained significantly lower than that seen with insulin stimulation, the highest glucose uptake values obtained being 22 ± 2 μmol · kg−1 · min−1 and 260 ± 34 μmol · min−1 · leg1, respectively. Leg blood flow was unchanged from the basal value (4.15 ± 0.63 dl/min) over the range of glucose studied, and A-VG increased at all glucose levels: 0.094 ± 0.010, 0.28 ± 0.03, 0.38 ± 0.04, and 0.59 ± 0.03 mM (P < 0.05 between any 2 consecutive values), with an EG50 of 10.0 ± 0.4 mM (P < 0.001 vs. IMGU). We conclude that 1) insulin increases the capacity for muscle A-VQ approximately fivefold; 2) muscle IMGU, independent of blood flow, displays an EG50 similar to the Km characteristic of the glucose-transport system (∼5–6 mM); 3) in contrast, NIMGU is a low-affinity glucoseuptake system; and 4) blood flow to insulin-sensitive tissue increases with insulin and glucose infusions and is an important determinant of the rate of in vivo glucose uptake.