P Cavallo Perin

SYMPATHETIC NERVOUS SYSTEM, DIABETES, AND HYPERTENSION

Hypertension is twice as frequent in diabetic patients than in the general population. Its prevalence is higher in Type 2 than in Type 1 diabetes: in the former, the onset of hypertension often precedes the diagnosis of diabetes, whereas, in the latter it is strictly related to the presence of nephropathy. Sympathetic nerve overactivity is crucial in the pathogenesis of hypertension in diabetes. It can be related to the activation of the renin-angiotensin-aldosterone (RAA) system in Type 1 diabetic patients with chronic renal failure, or to a condition of insulin resistance/hyperinsulinemia in Type 2 patients with the metabolic syndrome. In patients with early autonomic neuropathy, vagal impairment can lead to a relative predominance of sympathetic activity in the sympatho-vagal balance. In these patients, the onset of hypertension is frequently preceded by reduced nocturnal dipping. Sympathetic overactivity stimulates RAA activity, promotes sodium reabsorption, and increases heart rate, stroke volume and peripheral vascular resistance, thus inducing hypertension and increasing cardiovascular risk. A number of drugs acting either directly or indirectly on sympathetic activity are available for the treatment of hypertension in diabetic subjects. Opinions on the potential advantages of the metabolic profile of some of these drugs are as yet conflicting.

The ghrelin gene products and exendin-4 promote survival of human pancreatic islet endothelial cells in hyperglycaemic conditions, through phosphoinositide 3-kinase/Akt, extracellular signal-related kinase (ERK)1/2 and cAMP/protein kinase A (PKA) signalling pathways.

Aims/hypothesisPancreatic islet microendothelium exhibits unique features in interdependent relationship with beta cells. Gastrointestinal products of the ghrelin gene, acylated ghrelin (AG), unacylated ghrelin (UAG) and obestatin (Ob), and the incretin, glucagon-like peptide-1 (GLP-1), prevent apoptosis of pancreatic beta cells. We investigated whether the ghrelin gene products and the GLP-1 receptor agonist exendin-4 (Ex-4) display survival effects in human pancreatic islet microendothelial cells (MECs) exposed to chronic hyperglycaemia.MethodsIslet MECs were cultured in high glucose concentration and treated with AG, UAG, Ob or Ex-4. Apoptosis was assessed by DNA fragmentation, Hoechst staining of the nuclei and caspase-3 activity. Western blot analyses and pharmacological inhibition of protein kinase B (Akt) and extracellular signal-related kinase (ERK)1/2 pathways, detection of intracellular cAMP levels and blockade of adenylyl cyclase (AC)/cAMP/protein kinase A (PKA) signalling were performed. Levels of NO, IL-1β and vascular endothelial growth factor (VEGF)-A in cell culture supernatant fractions were measured.ResultsIslet MECs express the ghrelin receptor GHS-R1A as well as GLP-1R. Treatment with AG, UAG, Ob and Ex-4 promoted cell survival and significantly inhibited glucose-induced apoptosis, through activation of PI3K/Akt, ERK1/2 phosphorylation and intracellular cAMP increase. Moreover, peptides upregulated B cell lymphoma 2 (BCL-2) and downregulated BCL-2-associated X protein (BAX) and CD40 ligand (CD40L) production, and significantly reduced the secretion of NO, IL-1β and VEGF-A.Conclusions/interpretationThe ghrelin gene-derived peptides and Ex-4 exert cytoprotective effects in islet MECs. The anti-apoptotic effects involve phosphoinositide 3-kinase (PI3K)/Akt, ERK1/2 and cAMP/PKA pathways. These peptides could therefore represent a potential tool to improve islet vascularisation and, indirectly, islet cell function.

Antiangiogenic and immunomodulatory effects of rapamycin on islet endothelium: Relevance for islet transplantation

Donor intra‐islet endothelial cells contribute to neovascularization after transplantation. Several factors may interfere with this process and ultimately influence islet engraftment. Rapamycin, a central immunosuppressant in islet transplantation, is an mTOR inhibitor that has been shown to inhibit cancer angiogenesis. The aim of this study was to evaluate the effects of rapamycin on islet endothelium. Rapamycin inhibited the outgrowth of endothelial cells from freshly purified human islets and the formation of capillary‐like structures in vitro and in vivo after subcutaneous injection within Matrigel plugs into SCID mice. Rapamycin decreased migration, proliferation and angiogenic properties of human and mouse islet‐derived endothelial cell lines with appearance of apoptosis. The expression of angionesis‐related factors VEGF, αVβ3 integrin and thrombospondin‐1 on islet endothelium was altered in the presence of rapamycin. On the other hand, rapamycin decreased the surface expression of molecules involved in immune processes such as ICAM‐1 and CD40 and reduced the adhesion of T cells to islet endothelium. Our results suggest that rapamycin exerts dual effects on islet endothelium inducing a simultaneous inhibition of angiogenesis and a down‐regulation of receptors involved in lymphocyte adhesion and activation.

Expression of nephrin by human pancreatic islet endothelial cells

Aims/hypothesisThe islet microcirculation has morphological characteristics resembling those of renal glomeruli. Transcription of the nephrin gene, a highly specific barrier protein of the slit diaphragm of podocyte foot processes, has been reported in the pancreas, although its cellular localisation and function remain to be defined. In this study, we purified and characterised microvascular endothelial cells (MECs) isolated from human islets and investigated the expression and distribution of nephrin on these cells.MethodsHuman islet MECs were extracted and purified using anti-CD105-coated immunomagnetic beads and their endothelial characteristics were confirmed by expression of classical endothelial markers and basal high-level expression of intercellular adhesion molecule-1 and TNF-α-inducible vascular cell adhesion molecule-1. Nephrin expression was assessed by immunofluorescence, flow cytometric analysis and western blotting on cell lysates, as well as by RT-PCR.ResultsImmunofluorescence studies detected nephrin in a fine, punctate, diffuse pattern on cultured islet MECs, and also in human pancreatic islet sections. In both cases nephrin colocalised with endothelial markers. TNF-α treatment induced a marked reduction and redistribution of the protein in one or multiple aggregates. Nephrin expression was confirmed by flow cytometry, western blotting and RT-PCR studies. In contrast, nephrin could not be detected at the protein or mRNA level in human macro- and microvascular cells from other sites.Conclusions/interpretationNephrin is expressed at protein and mRNA levels in islet microendothelium, supporting the hypothesis that islet MECs exhibit distinctive morphological characteristics that indicate functional specialisation of potential pathophysiological importance.

Is autonomic neuropathy a risk factor for severe hypoglycaemia ? The EURODIAB IDDM Complications Study

Summary The hypothesis that diabetic patients with autonomic neuropathy are at increased risk of severe hypoglycaemia was examined in an epidemiological study of over 3000 IDDM patients in Europe (EURODIAB IDDM Complications Study). Autonomic function was assessed by two standard cardiovascular tests: change in heart rate and systolic blood pressure on standing. Severe hypoglycaemia was defined as an attack serious enough to require the help of another person. Compared to patients (68 %) reporting no attacks in the last year, those reporting one or more attacks were older (34.0 ± 10.7 vs 32.1 ± 9.9 years, mean ± SD, p < 0.0001), had had diabetes for a longer period (16.6 ± 9.5 vs 13.8 ± 9.1 years, p < 0.0001), had better glycaemic control (HbA1c 6.4 ± 1.8 vs 6.9 ± 1.9 %, p < 0.0001) and were more likely (p = 0.002) to have abnormal responses to both autonomic tests (13.0 vs 7.7 %). A single abnormal autonomic response was not associated with an increased risk of severe hypoglycaemia. The odds ratio for severe hypoglycaemia in people with abnormal responses to both autonomic tests, compared to those with normal responses, was 1.7 (95 % confidence interval 1.3, 2.2) after controlling for age, duration of diabetes, glycaemic control and study centre. In conclusion, a combined autonomic deficit in heart rate and blood pressure responses to standing is associated with only a modest increase in the risk of severe spontaneous hypoglycaemia. Although the increase in risk is not large, severe hypoglycaemia was a frequently reported event in this study. IDDM patients with deficient autonomic responses who strive for tight glycaemic control may therefore be at particular risk of severe hypoglycaemia. [Diabetologia (1996) 39: 1372–1376]

Does Abnormal QT Interval Prolongation Reflect Autonomic Dysfunction in Diabetic Patients? QTc Interval Measure Versus Standardized Tests in Diabetic Autonomic Neuropathy

The question as to whether the QTc interval correlates with five cardiovascular tests (deep breathing test, 30/15 ratio test, lying to standing test, cough test, and postural blood pressure test) for the diagnosis of diabetic autonomic neuropathy (DAN) was investigated in 168 (38 Type 1, 130 Type 2) consecutive outpatients (mean age 54.9 ± 11.2 years). QT interval was measured on an ECG recorded at rest and QTc calculated according to Bazetts formula. The percentage of patients with a QTc greater than 0.440 s was: absent DAN = 11% (n = 7), probable DAN = 7% (n = 4), definite DAN = 23% (n = 12) (p < 0.05), and the mean (± SD) QTc values were 0.403 ± 0.028 s, 0.405 ± 0.023 s, and 0.421 ± 0.026 s, respectively. A significant correlation between QTc duration and DAN score of autonomic cardiovascular test results (r = 0.34, p < 0.0001) was observed. The calculated specificity, sensitivity, positive and negative predictive values were 89%, 15%, 70% and 37%, respectively. In conclusion, QTc can be considered as an additional specific test in the assessment of diabetic autonomic neuropathy, but cannot replace the standard battery of cardiovascular tests.

Acute effect of prednisone and deflazacort on glucose tolerance in prediabetic subjects

SummaryThe diabetogenic effect of deflazacort (DF), an oxazolinic synthetic corticosteroid, was studied in 12 healthy adult subjects with a positive family history of diabetes mellitus. Three oral glucose tests (oGTT) were performed at 9.00 a. m., after a 12 h fast, following randomized administration of Placebo (PL), or Deflazacort (DF 36+36 mg) or Prednisone (PN 30+30 mg) 12 and 2 h before the test. Plasma glucose (BG), insulin (IRI), non-esterified fatty acids (NEFA), total cholesterol (CL), HDL-cholesterol (HDL-CL) and triglycerides (TG) were measured at time 0, and BG, IRI, NEFA were again measured 30, 60, 90 and 120 min after oGTT. PN was followed by a significant increase in BG over the PL values in accordance with the prediabetic state of these subjects, and there was also an increase in IRI values. No change in CL, HDL-CL and TG was found. After DF administration, there was a small increase only in BG and IRI over PL values. The differences between DF-PL were not significant, but those between PL-PN and DF-PN were significant at p<0.05 (Scheffes test). The lesser metabolic effect of DF on glucose balance by comparison with PN, as shown by these results, is consistent with previous reports of its lower osteopaenic effect. Thus, DF may be more suitable than PN and similar corticosteroids for corticosteroid therapy in prediabetic and diabetic subjects.

Autonomic neuropathy and QT interval in hemodialysed patients.

Abstract.Background QT interval prolongation increases the risk of ventricular arrhythmias and sudden death in diabetic autonomic neuropathy and ischemic heart disease. In end–stage renal disease (ESRD), the effects of hemodialysis on QT interval are diverse and the influence of autonomic neuropathy has yet to be clearly defined.MethodsSixty–nine ERSD patients (age 64 ± 14) were studied. Prior to the dialysis session, patients underwent four standard autonomic cardiovascular tests; before and after the dialysis session, a 12–lead ECG was recorded. Corrected QT intervals (QTc) were measured and QT dispersion (QTd) was calculated. Twelve subjects (age 59 ± 6) with normal renal function served as control group.ResultsCompared to controls, ESRD patients showed a longer QTc (434 ± 26 vs 414 ± 28ms; p = 0.016) and a similar QTd (35 ± 13 vs 37 ± 14ms; p = 0.54).QTc was > 440ms in 33.3% of the patients. No difference in the prevalence or score of autonomic neuropathy was observed between the subgroups with and without a prolonged QTc. After the hemodialysis session, QTc increased in 56% and decreased in 43% of the patients, and QTd increased in 45 % and decreased in 55% of the patients. QTc and QTd changes were not related to the presence of autonomic neuropathy.ConclusionsA large variability in QTc and QTd response was observed after hemodialysis. Autonomic neuropathy did not contribute to QTc and QTd length, nor to QTc and QTd change after dialysis.

Sex-differences in prevalence of electrocardiographic left ventricular hypertrophy in Type 2 diabetes: The Casale Monferrato Study

Aims  Although left ventricular hypertrophy (LVH) defined by either standard 12‐lead ECG or echocardiography strongly predicts cardiovascular mortality, its prevalence in Type 2 diabetes is largely unknown. We have assessed prevalence of ECG‐LVH and its relationship with clinical and metabolic variables in an Italian population‐based cohort of subjects with Type 2 diabetes.

The influence of autonomic neuropathy on hypotension during hemodialysis.

Abstract Many patients with chronic renal failure experience profound hypotension during hemodialysis. This phenomenon may be caused by hypovolemia, autonomic or cardiac dysfunction, vascular resistance defects or vasoactive substances such as nitric oxide or adrenomedullin. The aim of the study was to evaluate the influence of autonomic neuropathy on the occurrence of hypotension during hemodialysis. Fifty-three patients with chronic renal failure on maintenance hemodialysis underwent a standard battery of cardiovascular tests for the diagnosis of autonomic neuropathy. The study population was then divided into two groups, with (AN+) and without (AN−) autonomic neuropathy. Blood pressure (BP) was recorded before, during and after hemodialysis for 10 consecutive dialysis sessions and the mean value was calculated. Results Of the patients, 38 % were AN+. During hemodialysis, systolic BP was lower in AN+ than in AN− patients at the third hour (110.0 ± 17.5 vs 128.0 ± 26.2; p = 0.049). Systolic BP reduction during hemodialysis was greater in AN+ than AN− patients (−21.2 ± 10.9 vs −13.5 ± 10.6 % change, p = 0.013). Conclusion The presence of autonomic neuropathy is associated with a more severe BP fall during hemodialysis. Routine evaluation of autonomic function may be helpful in defining patients at risk for dialysis-induced hypotension.