M. Cassone-Faldetta

Influence of reduced glutathione infusion on glucose metabolism in patients with non—insulin-dependent diabetes mellitus

To evaluate the relationship between oxidative stress and glucose metabolism, insulin sensitivity and intraerythrocytic reduced glutathione (GSH)/oxidized glutathione (GSSG) ratio were measured in 10 non-insulin-dependent diabetes mellitus (NIDDM) patients and 10 healthy subjects before and after the intravenous administration of GSH. In particular, after baseline insulin sensitivity was assessed by a 2-hour euglycemic hyperinsulinemic clamp, either glutathione (1.35 g x m2 x min(-1)) or placebo (saline) were infused over a period of 1 hour. The same protocol was repeated at a 1-week interval, in cross-over, according to a randomized, single-blind design. In healthy subjects, baseline intraerythrocytic GSH/GSSG ratio (P < .0005) and total glucose uptake (P < .005) were significantly higher than in NIDDM patients. In the same subjects, GSH infusion significantly increased total glucose uptake (from 37.1 +/- 6.7 micromol kg(-1) x min(-1) to 39.5 +/- 7.7 micromol x kg(-1) x min(-1), P < .05), whereas saline infusion was completely ineffective. In addition, the mean intraerythrocytic GSH/GSSG ratio significantly increased after GSH infusion (from 21.0 +/- 0.9 to 24.7 +/- 1.3, P < .05). Similar findings were found in diabetic patients, in whom GSH infusion significantly increased both total glucose uptake (from 25.3 +/- 9.0 micromol x kg(-1) x min(-1) to 31.4 +/- 10.0 micromol x kg(-1) x min(-1), P < .001) and intraerythrocytic GSH/GSSG ratio (from 14.8 +/- 4.1 to 21.7 +/- 6.7, P < .01). Pooling diabetic patients and controls, significant correlations were found between intraerythrocytic GSH/GSSG ratio and total glucose uptake (r = .425, P < .05), as well as between increments of the same variables after GSH infusion (r = .518, P < .05). In conclusion, our data support the hypothesis that abnormal intracellular GSH redox status plays an important role in reducing insulin sensitivity in NIDDM patients. Accordingly, intravenous GSH infusion significantly increased both intraerythrocytic GSH/GSSG ratio and total glucose uptake in the same patients.

Polyol pathway activation and glutathione redox status in non-insulin-dependent diabetic patients.

The current study aimed to evaluate whether nicotinamide adenine dinucleotide phosphate (NADPH) alteration in erythrocytes from patients with non-insulin-dependent diabetes mellitus (NIDDM) is responsible for the impaired glutathione (GSH) redox status, and to assess if short-term inhibition of the polyol pathway normalizes NADPH levels and GSH redox status via an amelioration of the NADPH/total NADP (tNADP) ratio. For this purpose, erythrocyte NADPH and GSH levels were measured in 18 NIDDM patients at baseline and then after 1 week of random double-blind assignment to treatment with either tolrestat (an aldose reductase inhibitor, 200 mg daily) (n = 12) or placebo (n = 6). A group of 16 healthy volunteers served as the control. In the basal condition, mean GSH (P < .0001) and NADPH (P < .0001) levels and NADPH/tNADP (P < .0001) and GSH/ glutathione disulfide (GSSG) (P < .005) ratios were lower in NIDDM patients than in control subjects. Tolrestat treatment increased GSH levels (P < .05 v placebo and baseline) and the NADPH/tNADP ratio (P < .05 v placebo and baseline). Interestingly, tolrestat-induced changes in GSH and NADPH levels and in GSH/GSSG and NADPH/tNADP ratios were significant only in patients who showed a decreased NADPH/tNADP ratio at baseline (n = 8). In these latter patients, we also found a direct correlation between percentage increments in GSH levels and NADPH/tNADP ratios after tolrestat treatment (r = .71, P < .05). In conclusion, our findings support the hypothesis that polyol pathway activation decreases NADPH and GSH levels. Accordingly, short-term inhibition of this enzymatic route increased both the GSH level and the NADPH/tNADP ratio. These changes were observable only in the subgroup of patients with an abnormal NADPH/tNADP ratio at baseline. Polyol pathway inhibition could be useful for decreasing oxidative stress in NIDDM.

Gliclazide improves anti‐oxidant status and nitric oxide‐mediated vasodilation in Type 2 diabetes

Aims To evaluate the effects of gliclazide on oxidative status and vascular response to systemic administration of L‐arginine, the natural precursor of nitric oxide (NO), in Type 2 diabetic patients.

Role of Plasma and Urinary Endothelin-1 in Early Diabetic and Hypertensive Nephropathy

To evaluate the role of circulating and renal endothelin-1 (ET-1) in early diabetic nephropathy, plasma ET-1 levels and urinary ET-1 excretion were evaluated in lean, normotensive patients affected by non-insulin-dependent diabetes (NIDDM) either with (n = 9, NIDDM+) or without microalbuminuria (n = 18, NIDDM-); in never-treated, lean, essential hypertensive patients with (n = 12, EH+) or without microalbuminuria (n = 10, EH-); and in healthy volunteers (n = 12). Results showed higher plasma ET-1 levels in NIDDM+ (1.97 +/- 0.58 pg/mL) than in NIDDM- (1.59 +/- 0.14 pg/mL, P = .013), EH+ (1.40 +/- 0.21 pg/mL, P = .005), EH- (0.91 +/- 0.19 pg/mL, P < .0001), and controls (0.60 +/- 0.10 pg/mL, P < .0001). The circulating ET-1 concentration was also higher in EH+ than EH- and controls (P < .0001). Urinary ET-1 excretion did not differ (P = .387, NS) between NIDDM+ (48.5 +/- 20.1 pg/min) and NIDDM- (40.9 +/- 21.6 pg/min), but was significantly reduced (P < .0001) in both groups compared with controls (70.0 +/- 15.5 pg/min). Similar findings were observed in hypertensive subgroups. No correlations were found between urinary ET-1 and other variables, including plasma ET-1 levels, in all groups. In conclusion, NIDDM+ is accompanied by a significant increase in plasma ET-1 levels. A significant elevation of circulating ET-1 concentration was evident also in NIDDM-, suggesting that early abnormalities of ET-1 production might precede the microalbuminuric phase of diabetes-related renal damage.

Circulating catecholamines and metabolic effects of captopril in NIDDM patients

OBJECTIVE To evaluate the effects of captopril on circulating catecholamine levels in NIDDM patients and the possible relationship between captopril-related changes in circulating catecholamine levels and insulin sensitivity. RESEARCH DESIGN AND METHODS Fourteen nonobese normotensive NIDDM men (aged 44.5 ± 5.1 years) underwent a 2-h euglycemic-hyperinsulinemic clamp (40 mU·m−2 · min−1). Baseline evaluation of insulin sensitivity was followed by the random assignment of each patient to either captopril or placebo treatment, according to a crossover double-blind design. Euglycemic-hyperinsulinemic clamp studies were then repeated for all patients after both placebo and captopril treatments. Plasma norepinephrine (NE) and epinephrine (E) levels were assessed before, during, and after each clamp. RESULTS Resulting data showed that plasma catecholamine levels increased during baseline euglycemic-hyperinsulinemic clamp (NE: +23.6% time 0 vs. time 120 min, P < 0.05; E: +24.8% time 0 vs. time 120 min, P < 0.05). Captopril treatment significantly increased total glucose uptake (from 19.0 ± 9.0 to 26.8 ± 10.1 mmol·kg−1 · min−1, P < 0.05) and reduced baseline plasma NE (P < 0.001) and E (P < 0.05) levels. However, the magnitude of the NE (+25.7% time 0 vs. time 120 min, P < 0.001) and E (+27.2% time 0 vs. time 120 min, P < 0.05) increments during euglycemic hyperinsulinemia were not affected by the drug. Percentage changes in the ratio of total body glucose uptake to circulating insulin levels and corresponding decrements of baseline plasma E levels after captopril therapy were negatively correlated (r = −0.57, P < 0.05). CONCLUSIONS The reduction of circulating catecholamines could contribute, at least in part, to the captopril-related amelioration of insulin sensitivity.

Ambulatory blood pressure recording in diabetic patients with abnormal responses to cardiovascular autonomic function tests

The aim of our study was to analyse the 24-h periodic pattern of blood pressure (BP) in diabetic patients with abnormal responses to cardiovascular reflexes, in order to evaluate the extent of the initial autonomic damage. We studied 44 patients with diabetes mellitus (14 insulin-dependent, 30 non-insulin-dependent; mean duration of disease 6.5±1.8 years) in good metabolic control (fasting glycaemia <140 mg/dl, postprandial glycaemia <180 mg/dl, fructosamine <285 mg/dl), divided into two subgroups, containing 21 normotensives (13 males and 8 females aged 28–72 years) and 23 hypertensives (13 males and 10 females aged 32–70 years) respectively. All patients showed abnormal responses to at least two out of four tests: deep breathing, lying to standing, Valsalva manœuvre and postural hypotension. Two sex-and age-matched control groups were recruited, comprising 20 normotensive and 20 hypertensive diabetic patients without dysautonomia, respectively. The reference group consisted of 248 normotensives (135 males and 113 females, aged 18–76 years) and 212 mild-moderate hypertensives (130 males and 82 females, aged 27–66 years). Each patient underwent ambulatory BP monitoring for at least 24 h, using an auscultatory automatic device. Data concerning biological rhythms were analysed by means of periodic functions. We limited the Fourier partial sums to the first three harmonics. In the diabetic normotensive groups, we observed that the absolute systolic and diastolic BP minima during the night occurred very rapidly and that the increase to the morning maximum was markedly slowed in patients with abnormal responses to cardiovascular tests in comparison with the controls (nocturnal BP decrease −5.8/−4.7 vs −3.8/−4.0 mm Hg/h; increase 4.7/3.6 vs 5.9/6.1 mm Hg/h). The same phenomenon was observed in both hypertensive groups but the differences were more marked (nocturnal BP decrase −7.7/−7.1 vs −4.3/−3.9 mm Hg/h; increase 3.2/2.1 vs 5.8/4.3 mm Hg/h). Diabetic patients without dysautonomia had similar patterns to those in the normotensive and hypertensive reference groups. Since alterations in circadian rhythm are preceded by an intermediate smoothed BP curve during the early morning, which is well defined by Fourier analysis and related “speeds”, this method makes it possible to quantify the extent of the initial autonomic damage.

Effect of aprotinin on insulin sensitivity in non-insulin-dependent diabetes mellitus

It has been suggested that kallikrein‐kinin system may influence carbohydrate metabolism via a kinin‐mediated increment of insulin‐mediated glucose uptake. To evaluate the effect of acute inhibition of the kallikrein‐kinin system on insulin sensitivity, a randomized, placebo‐controlled, double‐blind study was performed in 15 male non‐insulin‐dependent diabetic patients. After basal evaluation of insulin sensitivity with a 2‐h euglycaemic hyperinsulinaemic clamp (40 mU m−2 min−1), patients were infused either with aprotinin (200 000 U.I.C. as intravenous bolus injection) or placebo (10 ml isotonic saline) in a cross‐over fashion, at 1 week intervals. After both saline and aprotinin infusions, insulin sensitivity was reassessed by continuing the euglycaemic hyperinsulinaemic clamp for a further 1 h. Resulting data showed that aprotinin significantly improved total glucose uptake (from 16.2 ± 2.9 μmol kg min−1 to 20.6 ± 4.9 μmol kg min−1, p<0.01), and decreased metabolic clearance rate of insulin (from 586 ± 57 ml m−2 min−1 to 442 ± 155 ml m−2 min−1, p<0.05). Thus, in spite of the suggested positive effects of kinins on insulin‐mediated glucose uptake, acute inhibition of the kallikrein‐kinin system resulted in a paradoxical increment of insulin sensitivity, which was probably mediated by the reduced metabolic clearance rate of insulin.

Early nocturnal blood pressure changes in diabetic autonomic neuropathy assessed by Fourier series

The 24 h periodic pattern of blood pressure was studied in 44 patients with diabetes mellitus (14 type 1, 30 type 2; mean duration of disease 6.5 ± 1.8 years) in good metabolic control but with abnormal cardiovascular reflex responses; of these 21 were normotensive and 23 hypertensive. All had abnormal responses to at least two out of four tests: deep breathing, lying to standing, Valsalva manoeuvre and postural hypotension. Two sex- and agematched groups, consisting of 20 normotensive and 20 hypertensive diabetic patients without dysautonomia, were studied as controls. Each patient underwent ambulatory blood pressure monitoring for at least 24 h, using an auscultatory automatic device. Data were analysed using the sum of three periodic functions (Fourier partial sum). In the diabetic normotensive groups, the absolute blood pressure fell to its night-time minimum more rapidly, and increased to its morning maximum more slowly, in those with abnormal cardiovascular reflexes than in the controls (nightly blood pressure decrease −5.8/−4.7 vs. −3.8/−4.0 mmHg/h; increase 4.7/3.6 vs. 5.9/6.1 mmHg/h). The same behaviour was found in both hypertensive groups but the amplitude of the differences was more marked (blood pressure nocturnal decrease −7.7/−7.1 vs. −4.3/−3.9 mmHg/h; increase 3.2/2.1 vs. 5.8/4.3 mmHg/h). This analysis of 24 h ambulatory blood pressure data may be of value in diagnosis and evaluation of autonomic deficits.