M. C. Marescotti

Differential effects of hyperinsulinemia and hyperaminoacidemia on leucine-carbon metabolism in vivo. Evidence for distinct mechanisms in regulation of net amino acid deposition.

The effects of physiologic hyperinsulinemia and hyperaminoacidemia, alone or in combination, on leucine kinetics in vivo were studied in postabsorptive healthy subjects with primed-constant infusions of L-[4,5-3H]leucine and [1-14C]alpha-ketoisocaproate (KIC) under euglycemic conditions. Hyperinsulinemia (approximately 100 microU/ml) decreased (P less than 0.05 vs. baseline) steady state Leucine + KIC rates of appearance (Ra) from proteolysis, KIC (approximately leucine-carbon) oxidation, and nonoxidized leucine-carbon flux (leucine----protein). Hyperaminoacidemia (plasma leucine, 210 mumol/liter), with either basal hormone replacement or combined to hyperinsulinemia, resulted in comparable increases in leucine + KIC Ra, KIC oxidation, and leucine----protein (P less than 0.05 vs. baseline). However, endogenous leucine + KIC Ra was suppressed only with the combined infusion. Therefore, on the basis of leucine kinetic data, hyperinsulinemia and hyperaminoacidemia stimulated net protein anabolism in vivo by different mechanisms. Hyperinsulinemia decreased proteolysis but did not stimulate leucine----protein. Hyperaminoacidemia per se stimulated leucine----protein but did not suppress endogenous proteolysis. When combined, they had a cumulative effect on net leucine deposition into body protein.

Defective suppression by insulin of leucine-carbon appearance and oxidation in type 1, insulin-dependent diabetes mellitus. Evidence for insulin resistance involving glucose and amino acid metabolism.

To determine whether a resistance to insulin in type 1, insulin-dependent diabetes mellitus (IDDM) is extended to both glucose and amino acid metabolism, six normal subjects and five patients with IDDM, maintained in euglycemia with intravenous insulin administration, were infused with L-[4,5-3H]leucine (Leu) and [1-14C]alpha ketoisocaproate (KIC). Steady-state rates of leucine-carbon appearance derived from protein breakdown (Leu + KIC Ra) and KIC (approximately leucine) oxidation were determined at basal and during sequential euglycemic, hyperinsulinemic (approximately 40, approximately 90 and approximately 1,300 microU/ml) clamps. In the euglycemic postabsorptive diabetic patients, despite basal hyperinsulinemia (24 +/- 6 microU/ml vs. 9 +/- 1 microU/ml in normals, P less than 0.05), Leu + KIC Ra (2.90 +/- 0.18 mumol/kg X min), and KIC oxidation (0.22 +/- 0.03 mumol/kg X min) were similar to normal values (Leu + KIC Ra = 2.74 +/- 0.25 mumol/kg X min) (oxidation = 0.20 +/- 0.02 mumol/kg X min). During stepwise hyperinsulinemia, Leu + KIC Ra in normals decreased to 2.08 +/- 0.19, to 2.00 +/- 0.17, and to 1.81 +/- 0.16 mumol/kg X min, but only to 2.77 +/- 0.16, to 2.63 +/- 0.16, and to 2.39 +/- 0.08 mumol/kg X min in the diabetic patients (P less than 0.05 or less vs. normals at each clamp step). KIC oxidation decreased in normal subjects to a larger extent than in the diabetic subjects. Glucose disposal was reduced at all insulin levels in the patients. In summary, in IDDM: (a) Peripheral hyperinsulinemia is required to normalize both fasting leucine metabolism and blood glucose concentrations. (b) At euglycemic hyperinsulinemic clamps, lower glucose disposal rates and a defective suppression of leucine-carbon appearance and oxidation were observed. We conclude that in type 1 diabetes a resistance to the metabolic effects of insulin on both glucose and amino acid metabolism is present.

Optimized glycaemic control achieved with add-on basal insulin therapy improves indexes of endothelial damage and regeneration in type 2 diabetic patients with macroangiopathy: a randomized crossover trial comparing detemir versus glargine

Aims: In diabetes, endothelial damage promotes macroangiopathy and endothelial regeneration is impaired, owing to reduced endothelial progenitor cells (EPCs). Given that insulin influences endothelial biology, we compared the effects of add‐on basal insulin analogues on endothelial damage and regeneration in type 2 diabetes (T2D).

Effect of insulin replacement on intermediary metabolism in diabetes secondary to pancreatectomy

SummaryPatients with diabetes due to pancreatectomy have metabolic features different from Type 1 (insulin-dependent) diabetes after insulin withdrawal. Whether or not glucagon by itself or combined glucagon-insulin absence are responsible for this metabolic behaviour is unknown. This study was carried out to evaluate the ability of insulin replacement to abolish differences between patients with Type 1 diabetes and patients with diabetes due to pancreatectomy. We studied the diurnal patterns of intermediary metabolites, free insulin, and glucagon using the Biostator (glucose-controlled insulin infusion system) and intensive subcutaneous insulin therapy in five patients after total pancreatectomy, five after partial pancreatectomy and seven patients with Type 1 diabetes. All were studied for 24 h after an overnight period of normoglycaemia. Insulin requirement was lower in the patients with total pancreatectomy than in patients with partial pancreatectomy or Type 1 diabetes during both types of insulin treatment (p< 0.05). Blood glucose and free insulin were similar in all the groups in both conditions. Immunoreactive glucagon was higher in the patients with diabetes secondary to pancreatectomy than in Type 1 diabetic patients. However, glucagon levels did not increase after arginine infusion in the patients with total pancreatectomy, and column chromatography of blood samples from two totally pancreatectomized patients showed no significant levels of immunoreactive pancreatic glucagon. Non-esterified fatty acids and ketone bodies were similar during Biostator and intensive subcutaneous insulin therapy. By contrast, gluconeogenic precursors (lactate, pyruvate, alanine and glycerol) were higher in patients with total pancreatectomy than in patients with partial pancreatectomy and Type 1 diabetes. In particular, alanine was significantly higher in the patients with total pancreatectomy (400±50 μmol/l during Biostator; 437±62 μmol/l during intensive subcutaneous insulin therapy) than in patients with partial pancreatectomy (207±13 μmol/l, p<0.005 and 226±14 μmol/l, p<0.005) and in Type 1 diabetic patients (191±11 μmol/l, p<0.005 and 216±10 μmol/l, p<0.005). Our data show that the high levels of gluconeogenic precursors, already reported in patients with diabetes due to total pancreatectomy after insulin withdrawal, do not become normal even in the presence of insulin. This finding shows that gluconeogenesis is primarily dependent on pancreatic glucagon and confirms the role of glucagon in the development of diabetic hyperglycaemia.

Mechanisms of fasting hypoglycemia and concomitant insulin resistance in insulinoma patients

To gain further insight into the pathogenesis of fasting hypoglycemia in patients with insulin-secreting adenoma of the pancreas, we studied seven patients affected by insulinoma (age, 42 +/- 7 years; body mass index [BMI], 27 +/- 2 kg/m2) and seven normal subjects. In insulinoma patients, hepatic glucose production (HGP) and glucose utilization (Rd) were evaluated by infusion of 3-3H-glucose at spontaneous fasting plasma glucose concentration, after restoration of euglycemia and during euglycemic insulin clamp (40 mU/m2/min). In insulinoma patients, fasting plasma glucose concentration (2.8 +/- 0.2 v 4.5 +/- 0.1 mmol/L; P < .001), HGP, and glucose Rd (7.8 +/- 1.1 v 12.0 +/- 0.3 mumol/kg/min; P < .01) were lower than in normal subjects, while plasma insulin level was higher (138 +/- 19 v 38 +/- 3 pmol/L; P < .001). In insulinoma patients after attainment of euglycemia (4.7 +/- 0.2 mmol/L) by exogenous glucose infusion, insulin level increased slightly (174 +/- 18 pmol/L; P < .01) and glucose Rd was similar to that of normal individuals (12.8 +/- 0.6 v 12.0 +/- 0.3 mumol/kg/min). During the clamp studies, glucose Rd was lower in insulinoma patients (18.7 +/- 1.2 v 33.8 +/- 3.1 mumol/kg/min; P < .01) despite higher plasma insulin concentration (612 +/- 48 v 420 +/- 12 pmol/L). Therefore, glucose Rd/I x 100 ratio (where I is plasma insulin concentration) was much lower in insulinoma patients (3.1 +/- 0.9 v 8.0 +/- 0.7; P < .01), suggesting a marked degree of insulin resistance.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms of acute and chronic hypoglycemic action of gliclazide.

Abstract An extrapancreatic effect of sulfonylureas has been postulated. However, in vivo results have been disputed because the amelioration of insulin action that follows sulfonylurea may represent the relief from glucose toxicity rather than a direct effect of the drug. Therefore, we studied the hypoglycemic action of gliclazide acutely and after 2 months of therapy in seven type 2 diabetic patients. All patients received a 240-minute IV glucose infusion with [3-3H]glucose. In a random order, 160 mg gliclazide (study 1) or placebo (study2) was given orally before glucose infusion. Finally, the effect of 160 mg gliclazide was reassessed after a two-month treatment with the same sulfonylurea (80 mg t. i. d.). Basal plasma glucose, insulin, C-peptide and endogenous glucose production (EGP) were similar before the two initial studies. During glucose infusion, EGP was more suppressed after gliclazide in spite of comparable increase in plasma insulin and C-peptide. After the two-month therapy, basal plasma glucose levels and HbA1c were lower while plasma insulin and C-peptide were higher with respect to baseline (p < 0.05). Gliclazide further reduced plasma glucose, the incremental area above baseline, and EGP during glucose infusion, while plasma insulin and C-peptide achieved higher plateaus (p < 0.05). When data were pooled, plasma glucose concentration and EGP correlated both in the basal state (r = 0.71) and during the last hour of glucose infusion (r = 0.84; both p < 0.05). These data suggest that gliclazide enhances the suppression of EGP induced by insulin and that this effect is greater with chronic treatment because of concomitant improvement of insulin secretion.

Surgical removal of insulinoma restores glucose recovery from hypoglycaemia but does not normalize insulin action

Abstract. In the present study we have evaluated the effects of chronic hyperinsulinaemia secondary to insulinoma, on insulin sensitivity and on counter‐regulatory responses to hypoglycaemia. We studied six patients (M/F = 3/3; age = 40 ± years), before and 6–9 months after surgical ablation of the neoplasia, by means of an euglycaemic‐hyperinsulinaemic clamp (1 mUkg‐1min‐1). Seven normal subjects (M/F = 4/ 3; age = 38 ± 6 years) underwent the same experimental study as the control subjects. In insulinoma patients after 100 min of the euglycaemic‐hyperinsulinaemic clamp, glycaemia was allowed to drop to a minimum value of l.9mmol L‐1, and recovery evaluated after interrupting insulin infusion. During the entire study, 3‐3H‐glucose was infused to determine hepatic glucose production and glucose utilization. Surgical removal of the pancreatic adenoma was followed by a reduction in body weight (BMI=25.7 ±l.9vs. 23.0 ± 1.6 kgm‐2; P0.005), normalization of fasting plasma levels of glucose (2.94 ±0.16 vs. 4.83± 0.11 mmol L‐1), insulin (162 ± 24 vs. 48 ±12 pmol L‐1) and of basal hepatic glucose production (7.6 ± 0.7 vs. 12.2 ± 1.11μmol kg‐1min‐1). Before the operation, insulin‐mediated glucose disposal was significantly lower than in the controls (30.8 ±3.1 vs. 4.91± 3.1 μmol kg‐1min‐1). Six to nine months after surgical removal of the adenoma, glucose utilization was unchanged (30.5 ±3.3 μmol kg‐1min‐1) and still significantly lower than in controls (P<0.0). After the euglycaemic phase, the plasma glucose level dropped to the same hypoglycaemic nadir (2.0±0.1 vs. 2.2 ±0.2 mmol L‐1) in both studies. Upon withdrawal of insulin infusion, recovery from hypoglycaemia was much slower before than after removal of the insulinoma (0.66±0.16vs. 2.50 ± 0.38 μmol min‐1; P<0.01). The impaired recovery from hypoglycaemia was associated with a sluggish rise in plasma glucagon concentration (+ 49 ± 15vs. +95 ±27 ng L‐1), growth hormone (+16±6vs.+ 30±3*mu;g L‐1), and cortisol (+156 ±41 vs. +361 ±62nmol L‐1; all P<0.05–0.005). In contrast to that found after adenoma removal, hepatic glucose production in insulinoma patients remained suppressed even after induction of hypoglycaemia. Our data suggest that in hyperinsulinaemic insulinoma patients restoration of normal insulin levels (a) ameliorates the response of some parameters of the counter‐regulation to acute hypoglycaemia; but (b) is not able to restore normal insulin sensitivity.

Development of metabolic syndrome and electrocardiographic features of left ventricular hypertrophy in middle-aged working subjects

Background and aims: Metabolic syndrome (MS) leads to excess cardiovascular disease, including heart failure. Left ventricular hypertrophy (LVH) is common in MS patients, but it is unknown whether onsets of MS and LVH coincide. Herein, we tested the association between development of MS and of electrocardiographic LVH in a cohort of middle-aged individuals. Methods: We included 303 working subjects (mean age 43.0±6.2; 41% males), follo wed-up for 4.3±0.8 yr. ATP-III MS components were determined. Electrocardiographic LVH features were assessed by Sokolow and Cornell voltage indexes and Romhilt-Estes (RE) score. Results: At baseline, Cornell index was significantly higher in subjects with (no.=55; 18.2%) than in those without MS (12.8±6.4 vs 10.9±5.4 mm; p=0.023), while Sokolow index and RE score were not different. At follow-up, individuals who developed (no.=51) compared to those who did not develop MS showed a significant increase in Cornell voltage index (1.0±0.6 vs −0.55±0.3 mm; p=0.035) and RE score (0.17±0.17 vs −0.08±0.04; p=0.028). The change in Cornell index over time was directly correlated with the change in the number of MS components (r=0.133; p=0.02) and in homeostasis model assessment of insulin resistance (r=0.117; p=0.046). The association between MS onset and the increase in Cornell index/RE score was independent from confounders. Conclusions: In a young population of working subjects, the development of MS is associated with worsening features of LVH. Early LVH electrocardiographic screening in young subjects who develop MS should be considered and performed using Cornell voltage index.