Sergio Gambardella

Relationship Between the Circadian Rhythms of Blood Pressure and Sympathovagal Balance in Diabetic Autonomic Neuropathy

In diabetic autonomic neuropathy, abnormal circadian patterns of blood pressure and sympathovagal balance with reduced fall of blood pressure and prevalence of sympathetic activity during the night have been described. To correlate the abnormalities of blood pressure to those of sympathovagal balance, we simultaneously performed 24-h noninvasive monitoring of blood pressure and ECG in 25 diabetic patients (45.6 ± 13.6 yr of age with a 17.6 ± 9.1 yr duration of diabetes) with various degrees of cardiovascular reflex impairment. Autoregressive power spectrum analysis of RR interval variability was applied to 24-h ECG recordings to obtain for day and night periods the mean power of low- (0.03–0.15 Hz) and high-frequency (0.18–0.40 Hz) components, which are relative markers of sympathetic and vagal activity, respectively, and their ratio (low frequency/high frequency), assumed as index of sympathovagal balance. Diabetic patients showed a lower percentage of day-night change in systolic blood pressure (9 ± 5.48 vs. 11.6 ± 4.78%, P < 0.037), a lower day low frequency (5.9 ± 0.81 vs. 6.62 ± 0.73 In-ms2 P < 0.001), a lower night high frequency (6.06 ± 0.71 vs. 6.52 ± 0.85 In-ms2 P < 0.05), a lower day low frequency:high frequency ratio (1.82 ± 1.77 vs. 3.05 ± 1.82, P < 0.01), and a lower percentage of day-night change in low-frequency:high frequency ratio (– 13.4 ± 109.9 vs. 28.7 ± 29.7%, P < 0.05), when compared with control subjects. Day-night change in low frequency:high frequency ratio correlated to day-night change in systolic blood pressure (r = 0.52, P < 0.01) and diastolic blood pressure (r = 0.48, P < 0.015). In conclusion, in diabetic patients the degree of loss in day-night rhythm of blood pressure is associated with a proportional nocturnal sympathetic predominance. Decreased blood pressure fall combined with relative sympathetic prevalence during the night might represent a risk factor for cardiovascular accidents and could modify the circadian pattern of cardiovascular events in the diabetic population.

Relationship between autonomic neuropathy, 24-h blood pressure profile, and nephropathy in normotensive IDDM patients.

OBJECTIVE To evaluate the relationship between autonomic neuropathy, nephropathy, and 24-h blood pressure (BP) pattern in insulin-dependent diabetes mellitus (IDDM). RESEARCH DESIGN AND METHODS We studied 30 normotensive IDDM patients without overt nephropathy, divided into two groups and matched for age, duration of diabetes, and HbA1 according to the presence of cardiovascular autonomic neuropathy. We simultaneously measured 24-h BP and urinary albumin excretion rate (UAE) on urine collections timed overnight and at 2-h intervals during the day. RESULTS Mean day and night systolic and diastolic BP values did not significantly differ between the groups. Mean night albuminuria was significantly higher in patients with autonomic neuropathy than in those without (61.4 ± 104.6 [mean ± SD] vs. 16 ± 25.2 μg/min, P < 0.04). The percentages day-night changes in systolic BP, diastolic BP, and UAE were significantly lower in neuropathic patients (systolic BP: 2.4 ± 7.7 vs. 9.6 ± 4.2%, P < 0.001; diastolic BP: 8.4 ± 6.9 vs. 15.5 ± 5.4%, P < 0.002; UAE: – 8 ± 99.4 vs. 49.3 ± 29.4%, P < 0.02) and were inversely related to autonomic score, index of autonomic neuropathy degree (r = –0.54, P < 0.002; r = –0.58, P < 0.001; and r = –0.53, P < 0.005, respectively). In patients with autonomic neuropathy, 2-h day periods and day and night UAE were more strongly related, respectively, to mean 2-h day periods (r = 0.58, P < 0.0001), day systolic BP (r = 0.67, P < 0.04), and night systolic BP (r = 0.69, P < 0.04) than in patients without autonomic neuropathy (2-h day periods: r = 0.32, P < 0.001; day: r = 0.37, NS; night: r = 0.35, NS). CONCLUSIONS Autonomic neuropathy in IDDM patients is associated with reduced nocturnal falls in BP and UAE and with a stronger relationship of UAE to systolic BP. We suggest a pathogenetic role of autonomic neuropathy in the development of diabetic nephropathy through changes in nocturnal glomerular function and by enhanced kidney vulnerability to hemodynamic effects of BP.

Early autonomic dysfunction in glucose-tolerant but insulin-resistant offspring of type 2 diabetic patients.

Abstract— In type 2 diabetes, both insulin resistance and hyperglycemia are considered responsible for autonomic dysfunction, but the specific role of these two abnormalities is not clear. To test the specific role of insulin resistance on autonomic dysfunction, we studied 69 glucose‐tolerant offspring of type 2 diabetic patients, comparing the most insulin‐resistant tertile (IR) with the most insulin‐sensitive tertile (IS) and comparable control subjects, all undergoing the oral glucose tolerance test, impedentiometry, 24‐hour blood pressure and ECG monitoring, and an intravenous glucose tolerance test (IVGTT) followed by a euglycemic hyperinsulinemic clamp, with continuous blood pressure and ECG measurements. Sympathovagal balance was evaluated as low‐ to high‐frequency ratio (LF:HF) by spectral analysis on R‐R intervals. The change of systolic and diastolic blood pressure was calculated as [(day‐night/d)]×100. In IR, the changes of systolic and diastolic blood pressure were significantly lower versus IS (9.2±5.0% versus 12.4±3.6%, P <0.02; 13.2±6.5% versus 17.4±5.2%, P <0.02). During the night, LF:HF fall was reduced in IR (43.1±21.0 versus 61.4±16.9, P <0.02). Hyperinsulinemia (IVGTT) rapidly and significantly increased LF:HF in IR (4.9±3.3 versus basal: 2.3±1.4, P =0.03) but not in IS. In offspring of type 2 diabetic patients with normal glucose tolerance and normal blood pressure values, insulin resistance is associated with abnormal control of blood pressure and sympathetic activation. Insulin resistance may therefore be responsible for some early derangements of the autonomic nervous tone control and thus contributes to increase the incidence of arterial hypertension and/or diabetes.

Renal Hemodynamics and Urinary Excretion of 6-Keto-Prostaglandin F1α and Thromboxane B2 in Newly Diagnosed Type I Diabetic Patients

We have studied the functional importance of renal eicosanoids in renal hemodynamics of seven newly diagnosed insulin-dependent diabetes mellitus (IDDM) patients by treatment with two structurally unrelated inhibitors of cyclooxygenase (i.e., piroxicam and sulindac). Glomerular filtration rate (GFR), renal plasma flow (RPF), daily urinary excretion of 6-keto-prostaglandin F1α (6-keto-PGF1α, the stable hydrolysis product of prostacyclin), and thromboxane B2 (TXB2, the stable hydrolysis product of thromboxane A2) were measured before, during, and after piroxicam (all patients) or sulindac (3 patients) treatment. Urinary excretion of 6-keto-PGF1α was significantly increased (P < .01) in diabetic patients compared with seven healthy subjects, whereas urinary excretion of TXB2 was unchanged. The baseline value of GFR was significantly (P < .01) higher in diabetic compared with normal volunteers, whereas baseline RPF was comparable in both groups. Piroxicam (20 mg/day) reduced urinary excretion of 6-keto-PGF1α and TXB2 by 65.7 ± 26 and 64.6 ± 33%, respectively. These biochemical changes were temporally associated with the ∼ 19% decrease in GFR (P < .01). A week after discontinuation of the drug, GFR and urinary excretion of 6-keto-PGF1α were still significantly (P < .05) reduced, whereas urinary excretion of TXB2 returned to control values. In contrast, urinary excretion of eicosanoids and renal function were not affected by sulindac (0.4 g/day) treatment. No functional changes were detected in healthy subjects despite a similar suppression of renal cyclooxygenase activity when they were treated with piroxicam.We conclude that altered GFR in newly diagnosed IDDM patients may depend, at least partially, on altered renal synthesis of vasodilator prostacyclin.

Effects of Insulin on Cholesterol Synthesis in Type II Diabetes Patients

OBJECTIVE To evaluate the effects of intensive insulin therapy and subsequent optimized metabolic control on daily urinary mevalonic acid (MVA) excretion, an index of whole-body cholesterol synthesis, and the acute effects of insulin on plasma MVA concentrations in type II diabetes. RESEARCH DESIGN AND METHODS Ten (five men and five postmenopausal women) nonobese, normolipidemic (total cholesterol < 6.2 mmol/l, triglycerides < 2.82 mmol/l), type II diabetic patients in poor metabolic control (HbA1c > 10%, fasting plasma glucose > 11 mmol/l) and receiving sulfonylurea treatment were selected. The 24-h urinary MVA excretion and plasma lipid values were determined before and after intensive insulin therapy. The acute effects of insulin on plasma MVA concentrations were also evaluated during a 3-h euglycemic hyperinsulinemic clamp study. RESULTS Urinary MVA excretion rates (μmol/24h) were 1.82 ± 0.21 in control subjects and 2.49 ± 0.35 (P < 0.01 vs. control subjects) and 1.78 ± 0.28 in patients before and after intensive insulin therapy, respectively. Total cholesterol, low-density-lipoprotein (LDL) cholesterol, and triglycerides decreased by 9, 8, and 12%, respectively, after blood glucose optimization. Acute insulin infusion during the euglycemic clamp studies reduced mean plasma MVA concentrations at 120 and 180 min by 29 and 38%, respectively (P < 0.01 for both vs. baseline). CONCLUSIONS Our study demonstrates that in nonobese, normolipidemic, type II diabetic patients under poor metabolic control, an increased cholesterol synthesis is normalized by insulin therapy. Hyperinsulinemia in the presence of euglycemia acutely decreases the circulating levels of MVA, the immediate product of hydroxymethylglutaryl-CoA reductase activity and an index of whole-body cholesterol synthesis.

Carbohydrate metabolism in hypertension: influence of treatment.

Epidemiologic studies suggest a close association between hypertension, obesity, and diabetes. It has been demonstrated that essential hypertension, per se, is an insulin-resistant state. However, the pathogenesis of the association between insulin resistance and hypertension is poorly understood. Elevated plasma insulin levels may contribute to the development of hypertension through renal sodium reabsorption. the sympathetic nervous system, the transmembranous cation transport, the renin-angiotensin system, the cardiovascular reactivity, and the atrial natriuretic peptide. Diuretics. β-blockers. calcium antagonists, angiotensin-converting enzyme (ACE) inhibitors, and α1-antagonists are first-choice drugs in the management of hypertension. Diuretics, except indapamide, impair insulin sensitivity and glucose tolerance. The same negative effects, exerted by β-blockers, are reduced employing those with selective activity. With few exceptions, calcium antagonists have no adverse influence on carbohydrate metabolism. ACE inhibitors and α1-antagonists do not influence or even improve glucose metabolism.

Regression of microalbuminuria in type II diabetic, hypertensive patients after long-term indapamide treatment

The influence of hypertension on the progression of persistent microalbuminuria in type II diabetes has not yet been clarified. We have studied the effects of 36 months of indapamide treatment (2.5 mg once daily) on blood pressure (BP), albumin excretion rate (AER), urinary immunoglobulin G4 (IgG4), and glomerular filtration rate (GFR) in 10 patients who were mildly hypertensive and had type II microalbuminuric diabetes (AER greater than 30 mg/24 hours and less than 300 mg/24 hours). BP, AER, and IgG4 significantly decreased after 6 months until the end of the study. Mean GFR was 94.4 +/- 7.5 ml/min/1.73 m2 in the baseline and did not change significantly throughout the course of the antihypertensive therapy. AER and IgG4 were directly related (r = 0.57; p less than 0.004), whereas BP did not relate to GFR, AER, or IgG4. The nephropathy index (45.5 +/- 4 in the baseline) significantly decreased at 12 months (38.7 +/- 2.1), 24 months (35.4 +/- 1.6), and 36 months (36.5 +/- 1.5) (at least p less than 0.01). Long-term indapamide treatment reduced BP and urinary protein loss without affecting GFR. These results indicate a potential role of this drug in the long-term renal protection of patients with type II diabetes, mild hypertension, and microalbuminuria.

New Parameters to Monitor the Progression of Diabetic Nephropathy

The possible differential elimination of the anionic IgG4 and of the other cationic IgG molecules whose pH differs but whose other characteristics are similar, has been hypothesized as a possibly useful parameter in monitoring preclinical diabetic nephropathy. An enzyme-linked immunosorbent assay method has been developed, based on a sandwich technique with subclass-specific antiimmunoglobulin monoclonal antibodies, which detects about 2 ng/mL IgG4. A sensitive radioimmunoassay method has been used to detect IgG. Normoalbuminuric, microalbuminuric, and macroalbuminuric patients, together with normal control subjects, were included in the cross-sectional study. Whereas IgG levels were elevated, as expected, in macroalbuminuric patients, it was interesting to note that IgG4, but not total IgG, levels were elevated in microalbuminuric patients. The IgG4/IgG ratio was increased almost to the same extent in microalbuminuric and macroalbuminuric patients. These findings are strongly in favor of the selective elimination of the acid medium-sized protein, IgG4, in incipient diabetic nephropathy. The measurement of immunoglobulin subclasses in the urine appears to be a promising parameter to characterize and subgroup diabetic patients with preclinical diabetic nephropathy.

Nonenzymic glycation of isolated human glomerular basement membrane changes its physicochemical characteristics and binding properties.

The chronic hyperglycemia in diabetes mellitus enhances the nonenzymic glycation of structural proteins possibly increasing the formation of highly reactive advanced glycation end products (AGE). These protein changes might be involved in tissue-damaging mechanisms leading to diabetic complications, including diabetic nephropathy. To simulate these events, an in vitro model, based on isolated human glomerular basement membrane (hGBM), has been developed. In this study we have investigated the extent of AGE formation and the binding changes induced by the nonenzymic glycation of hGBM. An enriched fraction of hGBM was isolated from normal human kidneys and glycated in vitro by incubation with glucose (500 mmol/l) at 37 degrees C for 10 days. The presence of AGE was investigated by two methods - spectrofluorescence and the diazonium salt reaction - both specific for this type of chemical entity. The binding capacity of glycated hGBM was tested by a 10-day incubation with human insulin, albumin, immunoglobulin G and fibrinogen. Higher relative spectrofluorescence values at 440 nm emission (20.0 +/- 2.0 vs. 12.5 +/- 5.0) and higher absorbance values at 492 nm (0.798 +/- 0.063 vs. 0.429 +/- 0.228) indicated the presence of increased levels of AGE in glycated vs. native hGBM. Insulin and the three proteins were bound to hGBM in increased amounts after its glycation (p less than 0.05). The results obtained in this in vitro model confirm that enhanced nonenzymic glycation of hGBM induces the formation of AGE and possibly, through these compounds, alters its physicochemical and binding properties. This reaction might contribute to the mechanisms eventually leading to diabetic nephropathy.

The selective elimination of anionic immunoglobulins as a parameter of kidney damage in diabetes and diabetic pregnancy

IgG1 and IgG4 have similar molecular weights but differ in pH (about 9 and 4.6, respectively). Their different rates of excretion in the urine of diabetic patients may indicate an impairment of charge selectivity in the kidney filter. Working on this hypothesis, a sensitive new ELISA for the detection of urinary IgG4 has been developed. This method can detect less than 1 ng/ml of this immunoglobulin; total IgG was detected by a RIA method developed by our laboratory. Twenty-eight Type I diabetic patients with or without clinical nephropathy were included in a cross-sectional study. An additional seven diabetic patients were followed over time, and eight diabetic pregnant women were studied during the different trimesters of pregnancy. Whereas both IgG4 and total IgG values were increased in clinically nephropathic patients, levels of IgG4, but not IgG1-3, were enhanced in patients without clinical nephropathy. In the latter group as well, IgG4-positive patients were microalbuminuric; all but one of the remaining patients were IgG4 and albumin negative. There was no significant variation in IgG4 values with time on repeated samples. The increased glomerular filtration rate in diabetic pregnancy did not significantly modify the levels of IgG4 in the urine. These results are in accordance with a selective excretion of this medium to large sized anionic protein (IgG4) in incipient (or stage III) diabetic nephropathy. Urinary IgG4 could be an additional useful marker when studying diabetic patients with early and pre-clinical stages of diabetic nephropathy.