Early autonomic dysfunction in type 1 diabetes: a reversible disorder?

AIMS/HYPOTHESIS

Cardiac autonomic neuropathy is associated with increased morbidity and mortality rates in patients with type 1 diabetes. The prevalence of early autonomic abnormalities is relatively high compared with the frequency of manifest clinical abnormalities. Thus, early autonomic dysfunction could to some extent be functional and might lead to an organic disease in a subgroup of patients only. If this is true, manoeuvres such as slow deep-breathing, which can improve baroreflex sensitivity (BRS) in normal but not in denervated hearts, could also modify autonomic modulation in patients with type 1 diabetes, despite autonomic dysfunction.

METHODS

We compared 116 type 1 diabetic patients with 36 matched healthy control participants and 12 heart-transplanted participants with surgically denervated hearts. Autonomic function tests and spectral analysis of heart rate and blood pressure variability were performed. BRS was estimated by four methods during controlled (15 breaths per minute) and slow deep-breathing (six breaths per minute), and in supine and standing positions.

RESULTS

Conventional autonomic function tests were normal, but resting spectral variables and BRS were reduced during normal controlled breathing in patients with type 1 diabetes. However, slow deep-breathing improved BRS in patients with type 1 diabetes, but not in patients with surgically denervated hearts. Standing induced similar reductions in BRS in diabetic and control participants.

CONCLUSIONS/INTERPRETATION

Although we found signs of increased sympathetic activity in patients with type 1 diabetes, we also observed a near normalisation of BRS with a simple functional test, indicating that early autonomic derangements are to a large extent functional and potentially correctable by appropriate interventions.

Pre-eclampsia but not pregnancy-induced hypertension is a risk factor for diabetic nephropathy in type 1 diabetic women

AIMS/HYPOTHESIS

Our aim was to study whether pre-eclampsia and pregnancy-induced hypertension are predictors of diabetic nephropathy in type 1 diabetic women.

MATERIALS AND METHODS

A total of 203 type 1 diabetic women, who were pregnant between 1988 and 1996 and followed at the Department of Obstetrics and Gynaecology in Helsinki, were re-assessed after an average of 11 years within the nationwide, multi-centre Finnish Diabetic Nephropathy Study. Diabetic nephropathy was defined as microalbuminuria, macroalbuminuria or end-stage renal disease.

RESULTS

Patients with prior pre-eclampsia had diabetic nephropathy more often than patients with a normotensive pregnancy (diabetic nephropathy vs normal albumin excretion rate: 41.9% vs 8.9%; p<0.001), whereas patients with a history of pregnancy-induced hypertension did not (10.3% vs 8.9%; p=0.81). CHD was more prevalent in patients with a history of pre-eclampsia than in patients with a normotensive pregnancy (12.2% vs. 2.2%; p=0.03). Pre-eclampsia (odds ratio [OR] 7.7, 95% CI 1.6-36.1; p=0.01) and HbA(1c) (OR 2.0, 95% CI 1.1-3.8; p<0.05) were associated with incident diabetic nephropathy even when adjusted for follow-up time, BMI, smoking, diabetes duration and age.

CONCLUSIONS/INTERPRETATION

These data suggest that a history of pre-eclamptic pregnancy but not pregnancy-induced hypertension is associated with an elevated risk of diabetic nephropathy.

The AT2 gene may have a gender-specific effect on kidney function and pulse pressure in type I diabetic patients

Diabetic nephropathy shows a higher incidence in male subjects, which may in part be owing to genetic factors. The angiotensin II type 2 receptor (AT2), present in the renal glomerulus, may oppose the deleterious effects of the type I receptor (AT1) through vasodilatation and growth inhibition. We determined whether the functional intronic G1675A or A1818T polymorphism of the X-chromosomal AT2 gene is associated with blood pressure levels or with kidney function. We genotyped 996 (538 female/458 male subjects) Finnish patients with type I diabetes from the FinnDiane-study in a cross-sectional study. DNA samples were amplified using standard polymerase chain reaction protocol and the genotypes were determined by the minisequencing method. Male patients with the AA haplotype had a lower glomerular filtration rate (83 +/- 32 vs 94 +/- 34 ml min(-1) 1.73 m(-2), P = 0.008) and a higher pulse pressure (PP) (62 +/- 18 vs 57 +/- 15 mm Hg, P = 0.002; P < 0.05 after adjustment for age) than did those with the GT haplotype. No differences between the genotypes or haplotypes and these variables were evident in females. In males, the G1675A was also an independent variable in a linear regression analysis with PP (r(2) = 0.16, coefficient=3.64, s.e.m.=1.38, P < 0.01) as the dependent variable. These data suggest a gender-specific association between the AT2 gene and kidney function and premature aging of the arterial tree in patients with type I diabetes.

Polymorphisms in the gene encoding angiotensin I converting enzyme 2 and diabetic nephropathy

AIMS/HYPOTHESIS

Substantial evidence exists for the involvement of the renin-angiotensin system (RAS) in diabetic nephropathy. Angiotensin I converting enzyme 2 (ACE2), a new component of the RAS, has been implicated in kidney disease, hypertension and cardiac function. Based on this, the aim of the present study was to evaluate whether variations in ACE2 are associated with diabetic nephropathy.

MATERIALS AND METHODS

We used a cross-sectional, case-control study design to investigate 823 Finnish type 1 diabetic patients (365 with and 458 without nephropathy). Five single-nucleotide polymorphisms (SNPs) were genotyped using TaqMan technology. Haplotypes were estimated using PHASE software, and haplotype frequency differences were analysed using a chi(2)-test-based tool.

RESULTS

None of the ACE2 polymorphisms was associated with diabetic nephropathy, and this finding was supported by the haplotype analysis. The ACE2 polymorphisms were not associated with blood pressure, BMI or HbA(1)c.

CONCLUSIONS/INTERPRETATION

In Finnish type 1 diabetic patients, ACE2 polymorphisms are not associated with diabetic nephropathy or any studied risk factor for this complication. Further studies are necessary to assess a minor effect of ACE2.

Increased levels of mannan-binding lectin in type 1 diabetic patients with incipient and overt nephropathy

AIMS/HYPOTHESIS

Diabetic nephropathy is associated with insulin resistance, and low-grade inflammation and activation of the complement system may contribute to this cascade. Mannan-binding lectin (MBL) activates the complement system, and elevated MBL concentrations have been observed in normoalbuminuric type 1 diabetic patients. The aim of this study was to assess whether MBL is associated with diabetic nephropathy in type 1 diabetes, and whether there is an association between MBL and low-grade inflammatory markers or insulin resistance.

METHODS

A total of 191 type 1 diabetic patients from the Finnish Diabetic Nephropathy Study were divided into three groups based upon their AER. Patients with normal AER (n=67) did not take antihypertensive medication, while patients with microalbuminuria (n=62) or macroalbuminuria (n=62) were all treated with an ACE inhibitor. As a measure of insulin sensitivity we used estimated glucose disposal rate. MBL was measured by an immunofluorometric assay, C-reactive protein by a radioimmunoassay and IL-6 by high-sensitivity enzyme immunoassay.

RESULTS

Patients with normal AER (median [interquartile range]: 1,154 microg/l [180-2,202 microg/l]) had lower levels of MBL than patients with microalbuminuria (1,713 microg/l [724-2,760 microg/l]; p=0.029) or macroalbuminuria (1,648 microg/l [568-3,394 microg/l]; p=0.019). There was a significant correlation between MBL and estimated glucose disposal rate, but not between MBL and C-reactive protein or IL-6 levels in univariate analysis. However, in a multiple regression analysis, HbA1c was the single variable independently associated with MBL (beta+/-SEM: 0.26+/-0.08; p=0.003).

CONCLUSIONS/INTERPRETATION

MBL concentrations are increased in type 1 diabetic patients with diabetic nephropathy. MBL was not associated with low-grade inflammatory markers.

Diabetic nephropathy is associated with low-grade inflammation in Type 1 diabetic patients

AIMS/HYPOTHESIS

Increased concentrations of C-reactive protein and interleukin-6, a finding suggestive of the presence of inflammation, have been observed in Type 2 diabetes. In such patients, C-reactive protein was predictive of diabetic nephropathy. Studies on low-grade inflammatory markers and nephropathy in Type 1 diabetic patients have shown conflicting results. Therefore we studied whether low-grade inflammation is associated with diabetic nephropathy in Type 1 diabetic patients.

METHODS

We divided 194 Type 1 diabetic patients into three groups from the Finnish Diabetic Nephropathy Study based upon their albumin excretion rate. Patients with normoalbuminuria (n=67) had no antihypertensive medication or signs of cardiovascular disease, while patients with microalbuminuria (n=64) or macroalbuminuria (n=63) were all treated with an angiotensin-converting enzyme inhibitor, a drug that could attenuate low-grade inflammation. As a measure of insulin sensitivity we used estimated glucose disposal rate. C-reactive protein was measured by radioimmunoassay and interleukin-6 by high sensitivity enzyme immunoassay.

RESULTS

C-reactive protein was higher in micro- and macroalbuminuric patients compared to normoalbuminuric patients (normoalbuminuria 2.0+/-1.7, microalbuminuria 2.6+/-1.7, macroalbuminuria 2.9+/-2.5 mg/l; p=0.016), while interleukin-6 increased in parallel with the severity of the renal disease (1.9+/-1.5, 2.9+/-3.3, 3.6+/-3.1 ng/l; p<0.0001). In multiple regression analysis albumin excretion rate was the only variable independently associated with C-reactive protein (p=0.03), whereas albumin excretion rate (p=0.0003), HDL-cholesterol (p=0.0135) and duration of diabetes (p=0.0176) were independently associated with interleukin-6.

CONCLUSIONS/INTERPRETATION

Low-grade inflammatory markers are associated with diabetic nephropathy in Type 1 diabetic patients. The predictive value needs to be assessed.

Factors associated with progression of IgA nephropathy are related to renal function--a model for estimating risk of progression in mild disease

BACKGROUND

A number of factors are linked to the outcome of IgA nephropathy (IgAN). However, it has been difficult to compare results of studies since patient populations have varied greatly. There were 3 aims in the study reported here, namely to compare factors associated with renal outcome in IgAN patients with different levels of renal function on diagnosis; to determine factors which were independently associated with progression of renal disease in initially mild IgAN; and to create a model for the estimation of the risk of progression in individual IgAN patients with normal renal function on diagnosis.

METHODS

Two hundred and fifty-nine IgAN patients who had been followed on average for 9.1 (SD 4.5) after diagnosis were divided into 2 groups on the basis of renal function on diagnosis. In group 1 (98 patients), Ccr (creatinine clearance, estimated by the Cockcroft-Gault formula) was < 85 ml/min, in group 2 (161 patients) > or = 85 ml/min. Univariate analyses were used to find significant differences between progressors and non-progressors in both groups. Logistic regression analysis was used to determine factors independently associated with progression in group 2.

RESULTS

Several factors were found to be associated with outcome in both groups, such as hypertension, level of Ccr, serum cholesterol, proteinuria, and also histopathological changes. Factors associated with progression in patients with initially decreased renal function (group 1), were predictable, such as male sex, absence of episodes of macroscopic hematuria, serum urate level and degree of tubular atrophy. Surprisingly, in patients with initially normal renal function (group 2), numbers of urinary erythrocytes were associated with outcome. The factors independently associated with progression in this group were number of urinary erythrocytes, existence of hypertension and in histopathology arteriolosclerosis and the level of glomerular score. A model for estimating risk of progression on the basis of various combinations of factors found to be independently associated with outcome is presented.

CONCLUSIONS

We concluded that association between variable and outcome in IgAN depends partly on renal function at the time of assessment of the factor. Since there are factors which are independently associated with the outcome of early and apparently mild disease, early diagnosis of IgAN is desirable: outcome in mild IgAN can be predicted reliably on the basis of factors found to be independently associated with outcome.

Mutations and variants of the epithelial sodium channel gene in Liddle's syndrome and primary hypertension

Liddle's syndrome is a rare monogenic form of hypertension caused by truncating or missense mutations in the C termini of the epithelial sodium channel beta- or gamma-subunits. These mutations delete or alter a conserved proline-rich amino acid sequence referred to as the PY-motif. We report here a Liddle's syndrome family with a betaArg564X mutation with a premature stop codon deleting the PY-motif of the beta-subunit. This family shows marked phenotypic variation in blood pressure, serum potassium levels, and age of onset of hypertension. Given the similarity with primary hypertension, changes in the C termini of the beta- or gamma-subunits may contribute to the development of primary hypertension or to hypertension associated with diabetic nephropathy. Accordingly, the coding sequences for the cytoplasmic C termini of the beta- and gamma-subunits were screened for mutations with the use of polymerase chain reaction, single-strand conformation polymorphism, and direct DNA sequencing in 105 subjects with primary hypertension and 70 subjects with diabetic nephropathy. One frequent polymorphism was identified, but its frequency did not differ among subjects with primary hypertension, subjects with diabetic nephropathy, or control subjects. Two of the 175 subjects with primary hypertension or diabetic nephropathy showed variants that were not present in 186 control subjects. None of the variants changed the PY-motif sequence. In conclusion, a betaArg564X mutation is the likely cause of Liddle's syndrome in this Swedish family, but it is unlikely that mutations in the beta- and gamma-subunit genes of the epithelial sodium channel play a significant role in the pathogenesis of primary hypertension or diabetic nephropathy.

Hyperreactivity to nitrovasodilators in forearm vasculature is related to autonomic dysfunction in insulin-dependent diabetes mellitus

BACKGROUND

The link between diabetes and vascular disease is poorly understood. Data regarding endothelial function in vivo in patients with insulin-dependent diabetes mellitus (IDDM) have been inconsistent with in vitro studies demonstrating hyperglycemia-induced impairments in endothelium-dependent vasodilation.

METHODS AND RESULTS

We determined whether alterations in neural control of the vascular tone might contribute to blood flow responses to intrabrachial infusions of acetylcholine (ACh), sodium nitroprusside (SNP), and L-N-monomethyl-arginine (L-NMMA) in 22 men with IDDM (12 with normoalbuminuria. HbA1c = 8.6 +/- 0.3%; 10 with macroalbuminuria, HbA1c = 8.6 +/- 0.3%) and 11 matched normal men. Autonomic function was assessed from reflex vasoconstriction to cold, the blood pressure response to standing and hand grip, and heart rate variation, including spectral analysis, during controlled breathing, and the Valsalva maneuver. IDDM with macroalbuminuria exhibited hyperresponsiveness to both ACh and SNP compared with the patients with normoalbuminuria or normal subjects. Reflex sympathetic vasoconstriction to cold was severely impaired in the IDDM patients with macroalbuminuria (-19 +/- 6%) compared with normoalbuminuric patients (-39 +/- 5%, P < .05) and normal subjects (-54 +/- 7%, P < .001). The macroalbuminuric patients also had evidence of autonomic dysfunction during controlled and deep breathing tests and during the Valsalva maneuver. Within the group of IDDM patients, neither the urinary albumin excretion rate nor other parameters such as HbA1c or serum cholesterol correlated with forearm blood flow during the vasoactive drug infusions. There were, however, significant inverse correlations between several measures of both sympathetic and parasympathetic autonomic functions and vascular hyperresponsiveness to SNP and ACh. For example, the Valsalva ratio was inversely correlated with the increase in blood flow in response to infusion of 3 (r = -.74, P < .001) and 10 (r = -.73, P < .001) micrograms/min SNP and 7.5 (r = -.73, P < .001) and 15 (r = -.75, P < .001) micrograms/min ACh.

CONCLUSIONS

These data are consistent with idea that altered neurotransmission is an important determinant of vascular reactivity of diabetic blood vessels to nitrovasodilators in vivo.

Chronic hyperglycemia impairs endothelial function and insulin sensitivity via different mechanisms in insulin-dependent diabetes mellitus

BACKGROUND

We explored whether chronic hyperglycemia is associated with defects in endothelium-dependent vasodilatation in vivo and whether defects in the hemodynamic effects of insulin explain insulin resistance.

METHODS AND RESULTS

Vasodilator responses to brachial artery infusions of acetylcholine, sodium nitroprusside, and NG-monomethyl-L-arginine and, on another occasion, in vivo insulin sensitivity (euglycemic insulin clamp combined with the forearm catheterization technique) were determined in 18 patients with insulin-dependent diabetes mellitus (IDDM) and 9 normal subjects. At identical glucose and insulin levels, insulin stimulation of whole-body and forearm glucose uptake was 57% reduced in the IDDM patients compared with normal subjects (P < .001). The defect in forearm glucose uptake was attributable to a defect in glucose extraction (glucose AV difference, 1.1 +/- 0.2 versus 1.9 +/- 0.2 mmol/L, P < .001, IDDM versus normal subjects), not blood flow. Within the group of IDDM patients, hemoglobin A1c was inversely correlated with forearm blood flow during administration of acetylcholine (r = -.50, P < .02) but not sodium nitroprusside (r = .07). The ratio of endothelium-dependent to endothelium-independent blood flow was approximately 40% lower in patients with poor glycemic control than in normal subjects or patients with good or moderate glycemic control.

CONCLUSIONS

We conclude that chronic hyperglycemia is associated with impaired endothelium-dependent vasodilatation in vivo and with a glucose extraction defect during insulin stimulation. These data imply that chronic hyperglycemia impairs vascular function and insulin action via distinct mechanisms. The defect in endothelium-dependent vasodilatation could contribute to the increased cardiovascular risk in diabetes.