Hypertension and nephropathy in diabetes mellitus: what is inherited and what is acquired?

Update on blood pressure control and renal outcomes in diabetes mellitus

Diabetic nephropathy (DN) is associated with a high incidence of cardiovascular (CV) morbidity and mortality. Although relationships between hypertension and diabetic nephropathy are complex, blood pressure (BP) control is an important management strategy in the prevention of onset and progression of DN in patients with diabetes mellitus (DM). Recent guidelines recommend less stringent BP targets among patients with type 2 DM and chronic kidney disease. These recommendations are based mostly on lack of benefit in CV outcomes with a low BP target. We review the current information on efficacy of BP control in improving renal outcomes in patients with type 2 DM. Presently, although intensive BP control has been was beneficial in decreasing albuminuria, it has not translated into reductions in risks of hard renal endpoints, such as progression to end-stage renal disease, the need for renal replacement therapy, and mortality from renal causes.

Prevalence and risk factors of diabetic nephropathy in omani type 2 diabetics in Al-dakhiliyah region

OBJECTIVE

To assess the prevalence and risk factors of diabetic nephropathy among Omani type 2 diabetics in Al-Dakhiliyah region of the Sultanate of Oman.

METHODS

A cross-sectional and a case control study designs were used to assess the prevalence and risk factors respectively. For the prevalence study a sample of 699 diabetic subjects were selected randomly from two polyclinics in Al-Dakhiliyah region; Sumail and Nizwa polyclinics. For the case control study, a sample consisting of 215 cases and 358 controls were randomly selected from those who were included in the cross-sectional study. A well designed questionnaire has been used to collect data regarding the disease and risk factors. Data was analyzed using SPSS19 statistical program.

RESULTS

Total prevalence of diabetic nephropathy was calculated as 42.5% (95% C.I: 38.83% - 46.15%). The difference in the prevalence in the two polyclinic catchment area was not significant. The prevalence was significantly higher among males (51.6%) compared to females (36.5%). Crude analysis of the risk factors showed significant association between diabetic nephropathy and the following factors; male gender, decreased literacy, long duration of diabetes mellitus, hypertension, retinopathy, neuropathy, family history of diabetic nephropathy, poor glycemic control (high HbA1c), and hypertriglyceridemia. Multivariate analysis showed the following factors to be independent risk factors; male gender, decreased literacy, long duration of diabetes, family history of diabetic nephropathy and poor glycaemic control (high HbA1c).

CONCLUSION

The prevalence of diabetic nephropathy in this study was 42.5% and the significant risk factors associated with it included male gender, decreased literacy, long duration of diabetes, family history of diabetic nephropathy and poor glycemic control (high HbA1c).

Heritability of proliferative diabetic retinopathy

OBJECTIVE

Diabetic nephropathy clusters in families, suggesting that genetic factors play a role in its pathogenesis. We investigated whether similar clustering exists for proliferative retinopathy in families with two or more siblings with type 1 diabetes.

RESEARCH DESIGN AND METHODS

The FinnDiane Study has characterized 20% (4,800 patients) of adults with type 1 diabetes in Finland. In 188 families, there were at least two siblings with type 1 diabetes. Ophthalmic records were obtained for 369 of 396 (93%) and fundus photographs for 251 of 369 (68%) patients. Retinopathy was graded based on photographs and/or repeated ophthalmic examinations using the Early Treatment of Diabetic Retinopathy grading scale.

RESULTS

Mean age at onset of diabetes was 14.3 +/- 10.2 years, and mean duration was 25.9 +/- 11.8 years. Proliferative retinopathy was found in 115 of 369 patients (31%). The familial risk of proliferative retinopathy was estimated in 168 of 188 sibships, adjusted for A1C, duration, and mean blood pressure. Proliferative retinopathy in the probands (48 of 168) was associated with an increased risk (odds ratio 2.76 [95% CI 1.25- 6.11], P = 0.01) of proliferative retinopathy in the siblings of probands (61 of 182). The heritability of proliferative retinopathy was h(2) = 0.52 +/- 0.31 (P < 0.05).

CONCLUSIONS

We found a familial clustering of proliferative retinopathy in patients with type 1 diabetes. The observation cannot be accounted for by conventional risk factors, suggesting a genetic component in the pathogenesis of proliferative retinopathy in type 1 diabetes.

Late diabetes complications and non-dipping phenomenon in patients with Type 1 diabetes

BACKGROUND

Cardiovascular autonomic neuropathy (CAN) has been thought to underlie the loss of normal nocturnal blood pressure dipping, which is associated with a higher risk for nephropathy in Type 1 diabetes. Previous analyses also suggest however that nephropathy is a major predictor of subsequent CAN.

OBJECTIVE

To investigate links between non-dipping phenomenon (NDP) and complications, particularly CAN and nephropathy.

METHODS

24-h ambulatory blood pressure monitoring was performed on 61 consecutively recruited subjects (mean age: 38.5+/-8.1, mean duration: 29.5+/-8.2 years) from the Pittsburgh Epidemiology of Diabetes Complications cohort (658 subjects with childhood onset Type 1 diabetes diagnosed between 1950 and 80). NDP was diagnosed if nocturnal fall of both systolic and diastolic blood pressure was <10% of the average daytime blood pressure. CAN was detected by abnormal (<or=1.1) expiration/inspiration heart rate ratio. Proteinuria was established by abnormal (>20 microg/min) albumin excretion rate (AER) in at least two of three timed urines.

RESULTS

Non-dippers (n=17) had greater LDLc (p=0.012) and AER (p=0.052) and a higher frequency of nephropathy (OR=3.6, 95% CI=1.0-12.6) and proliferative retinopathy (OR=5.1, 95% CI=1.3-20.3) compared to the 44 dippers. CAN and NDP were not associated. In multivariate analyses, adjusting for CAN, proteinuria was significantly related to NDP (OR=3.6, 95% CI=1.0-12.6), an association that further modeling suggests was related to interactions between nephropathy, LDLc and hypertension.

CONCLUSIONS

These data suggest a strong link between NDP and proteinuria which is independent of CAN and may be modified by LDLc and hypertension.

Cellular basis of diabetic nephropathy: III. In vitro GLUT1 mRNA expression and risk of diabetic nephropathy in type 1 diabetic patients

AIMS/HYPOTHESIS

Altered glucose transporter expression has been implicated in the pathogenesis of diabetic nephropathy. There is increasing evidence that genetic factors convey risk of, or protection from, diabetic nephropathy and that the behaviour of cultured skin fibroblasts from type 1 diabetic patients may reflect these genetic influences. This study aimed to compare GLUT1 mRNA expression levels in skin fibroblasts from type 1 diabetic patients with either rapid ("fast-track", n=25) or slow ("slow-track", n=25) development of diabetic nephropathy and from non-diabetic normal control subjects (controls, n=25).

METHODS

Skin fibroblasts were cultured in Dulbecco's Modified Eagle's Medium with 25 mmol/l glucose for 36 h. Total RNA was isolated, and GLUT1 mRNA levels were estimated by microarray analysis and RT-PCR.

RESULTS

Levels of GLUT1 mRNA expression in skin fibroblasts from "slow-track" patients were greater than those from "fast-track" patients (p=0.02), as initially detected by microarray. GLUT1 mRNA expression levels were confirmed by RT-PCR to be higher in skin fibroblasts from "slow-track" patients (4.59+/-2.04) than in those from "fast-track" patients (3.34+/-1.2, p=0.02), and were also higher than in skin fibroblasts from control subjects (3.52+/-1.66, p=0.03). There was no statistically significant difference between levels of expression in the "fast-track" patients and the control subjects.

CONCLUSIONS/INTERPRETATION

This finding is consistent with the presence of cellular protection factors against diabetic nephropathy in the "slow-track" patients. These factors could be associated with the regulation of the GLUT1 pathway and may be genetically determined.

Genetics for targeting disease prevention: diabetes

This article provides an overview of current thinking regarding genetics and diabetes (type 1, type 2, and gestational diabetes mellitus),including a selective look at a few implicated gene variants. This article explores how this information might be applied in current and future clinical practice to (1) predict who is at risk for diabetes and its complications, (2) identify and intervene to prevent or delay the development of diabetes in persons at risk, (3) identify patients with diabetes in an early stage and intervene to prevent later complications,and (4) individualize therapy for patients with diabetes to improve outcomes. The article concludes with some general thoughts about genetics and diabetes prevention in the future.

Nephropathy in type 1 diabetes: a manifestation of insulin resistance and multiple genetic susceptibilities? Further evidence from the Pittsburgh Epidemiology of Diabetes Complication Study

BACKGROUND

The pathogenesis of diabetic nephropathy remains unclear, although previous reports implicate a wide range of putative genetic and metabolic factors.

METHODS

Incident and prevalent cases of overt nephropathy (ON), defined as an albumin excretion rate>200 microg/min in at least two of the three timed urines, from the Pittsburgh Epidemiology of Diabetes Complication Study (a prospective epidemiologic study of an incident cohort of childhood onset type 1 diabetic subjects) were studied.

RESULTS

Incidence analyses reveal differences in univariate baseline risk factors that predict ON within 5 years of measurement [low-density lipoprotein (LDL) cholesterol, triglycerides, white blood cell count, and hypertension] and those that predict in the long-term, that is, 6 to 10 years after baseline, hemoglobin A1 (Hb A1). Estimated glucose disposal rate (calculated using a formula derived from euglycemic-hyperinsulinemic clamp studies), however, strongly (P < 0.001) predicted ON throughout follow-up. Comparing individuals who were most susceptible to ON (those with an onset before 20 years duration of type 1 diabetes and before the development of other advanced complications) with the least susceptible (late or no occurrence of ON despite the development of other advanced complications) revealed otherwise undetected genetic associations [that is, apolipoprotein E (Apo E), angtiotensin-converting enzyme insertion/deletion (ACE I/D), and lipoprotein lipase (LPL) HindIII polymorphism) with odds ratios ranging from 2.9 to 7.1.

CONCLUSIONS

In type 1 diabetes insulin resistance is an underlying risk state for ON, which may be accelerated by other disturbances (for example, hypertension and dyslipidemia). A novel approach to classifying (that is, phenotyping) subjects, which compares those at the extremes of susceptibility, reveals strong genetic associations and important interactions with other risk factors not otherwise apparent.

Cyclooxygenase-2 inhibitor blocks expression of mediators of renal injury in a model of diabetes and hypertension

BACKGROUND

We previously reported that renal cortical cyclooxygenase (COX-2) expression increased following subtotal nephrectomy, and chronic treatment with a selective COX-2 inhibitor, SC58236, reduced proteinuria and retarded the development of glomerulosclerosis. The present studies were designed to examine the effects of COX-2 inhibition in a model of diabetic nephropathy.

METHODS

Rats were divided into three groups: control, diabetic (streptozotocin-induced diabetic animals with superimposed DOCA/salt hypertension; right nephrectomy and DOCA treatment), and treated (administration of the selective COX-2 inhibitor, SC58236, to a subset of diabetic/DOCA/salt rats). Insulin was administered to maintain blood glucose in the 200 to 300 mg/dL range.

RESULTS

Systolic blood pressure in the two diabetic groups was elevated within one week and remained elevated until sacrifice at six weeks (control, 108 +/- 2 mm Hg; diabetic, 158 +/- 4 mm Hg; treated, 156 +/- 7 mm Hg). When measured at six weeks, immunoreactive COX-2 expression in the renal cortex of the diabetic rats was 2.5 +/- 0.3-fold of control animals (N = 7). Immunohistochemical localization indicated increased expression in macula densa and surrounding cortical thick ascending limb of Henle (cTALH). The COX-2 inhibitor decreased COX-2 expression in diabetic rats to 1.3 +/- 0.1-fold control. In addition, SC58236 decreased expression of PAI-1 (diabetic vs. treated, 3.2 +/- 0.5 vs. 1.7 +/- 0.2-fold control, N = 7, P < 0.05), vascular endothelial growth factor (VEGF; 2.0 +/- 0.2 vs. 1.2 +/- 0.2; N = 7, P < 0.05), fibronectin (2.4 +/- 0.3 to 1.3 +/- 0.1; N = 7, P < 0.05) and transforming growth factor-beta (TGF-beta; 2.1 +/- 0.2 vs. 1.3 +/- 0.2; N = 7, P < 0.05). Proteinuria at six weeks was decreased in the SC58236-treated rats (149 +/- 8 vs. 92 +/- 8 mg/24 h; N = 7, P < 0.01). The mesangial sclerosis index, defined as increases in extracellular matrix within the mesangial space, was determined at six weeks; the control group had an index of 0.06 +/- 0.01, the diabetic group was 2.7 +/- 0.04 and the treated group was 0.6 +/- 0.03 (P < 0.0001 compared to the diabetic group).

CONCLUSIONS

These results suggest that in an experimental model of diabetes and hypertension, inhibition of COX-2 expression decreases potential mediators of glomerular and tubulointerstitial injury and also decreases biochemical, functional and structural markers of renal injury.

Endothelial dysfunction in children with type 1 diabetes mellitus

Endothelial dysfunction is defined as the loss of endothelium properties, e.g. alteration of protein synthesis, increased vascular tone and permeability, acquisition of prothrombotic and antifibrinolytic properties. Endothelium, a primary target of unbalanced glycaemic control, is involved in the pathogenesis of vascular complications in patients with type 1 diabetes mellitus (DM). Vascular endothelium damage is characterised by an increase of endothelium-derived regulatory proteins. vWF and t-PA may be useful to investigate early endothelium involvement. However, impaired endothelium-dependent vasodilatation may be a more sensitive marker. Abnormal markers of endothelial cell activation and impaired endothelium-dependent vasodilatation have been observed in young patients with type I DM. Hyperglycaemia may alter normal endothelium functions, either directly or indirectly, by inducing different metabolic pathways. Complete understanding of the pathophysiology of endothelial dysfunction may lead to timely therapeutic intervention to prevent its development and to slow the progression of diabetic complications.

Approaches to understanding susceptibility to nephropathy: from genetics to genomics

The incidence of end-stage renal disease (ESRD) is increasing worldwide despite efforts to slow the progression of chronic renal failure (CRF) by controlling blood pressure and hyperglycemia. Two available therapies for ESRD, dialysis and transplantation, are expensive and are at best palliative. Recently, data from several laboratories have demonstrated that ESRD is under substantial genetic control, and efforts to identify these genetic determinants are underway. Identifying genes for ESRD pathogenesis has several goals. First, understanding the genetic basis of ESRD offers a means to clarify the mechanisms that result in kidney pathobiology. Second, better and new treatments for prevention of progression of CRF to ESRD may be developed. Third, individuals at risk could be identified early in their course and targeted for intensive therapy. Finally, the products of genes causing disease become target molecules for gene therapy. In this article, we discuss data from our laboratories, which employ two different molecular genetic strategies for identifying ESRD pathogenesis genes. In contrast to traditional experimental design, both approaches are hypothesis generating, identifying candidate molecules for further study, rather than hypothesis driven and may provide novel insights into mechanisms of renal disease progression.

Lipid and blood pressure treatment goals for type 1 diabetes: 10-year incidence data from the Pittsburgh Epidemiology of Diabetes Complications Study

OBJECTIVE

Subjects with type 1 diabetes are at high risk for many long-term complications, including early mortality and coronary artery disease (CAD). Few data are available on which to base goal levels for two major risk factors, namely blood pressure and lipid/lipoproteins. The objective of this study was to determine at which levels of LDL and HDL cholesterol, triglycerides, and blood pressure the relative risks of type 1 diabetic complications increase significantly.

RESEARCH DESIGN AND METHODS

Observational prospective study of 589 patients with childhood-onset type 1 diabetes (<17 years) aged > or =18 years at baseline; 10-year incidence of mortality, CAD, lower-extremity arterial disease, proliferative retinopathy, distal symmetric polyneuropathy, and overt nephropathy. Relative risks were determined using traditional groupings of blood pressure and lipid/lipoproteins, measured at baseline, using the lowest groupings (<100 mg/dl [2.6 mmol/l] LDL cholesterol, <45 mg/dl [1.1 mmol/l] HDL cholesterol, <100 mg/dl [1.1 mmol/l] triglycerides, <110 mmHg systolic blood pressure, and <80 mmHg diastolic blood pressure) as reference. Adjustments for age, sex, and glycemic control were examined.

RESULTS

Driven mainly by strong relationships (RR range 1.8-12.1) with mortality, CAD, and overt nephropathy, suggested goal levels are as follows: LDL cholesterol <100 mg/dl (2.6 mmol/l), HDL cholesterol >45 mg/dl (1.1 mmol/l), triglycerides <150 mg/dl (1.7 mmol/l), systolic blood pressure <120 mmHg, and diastolic blood pressure <80 mmHG: Age, sex, and glycemic control had little influence on these goals.

CONCLUSIONS

Although observational in nature, these data strongly support the case for vigorous control of lipid levels and blood pressure in patients with type 1 diabetes.

Urinary albumin excretion in families with type 2 diabetes is heritable and genetically correlated to blood pressure

Urinary albumin excretion in families with type 2 diabetes is heritable and genetically correlated to blood pressure.

BACKGROUND

Levels of urinary albumin excretion (UAE) are used to define both the diagnosis of diabetic nephropathy and its progression. Predisposition to high blood pressure is also a risk factor for susceptibility to nephropathy, but its relationship with UAE in type 2 diabetes remains unclear. In this study, we have estimated heritabilities of UAE and blood pressure and their correlation attributable to genetic effects using 96 large families ascertained for type 2 diabetes.

METHODS

In these families, 630 individuals with type 2 diabetes and 639 individuals with normoglycemia were examined. All of them had a determination of UAE as the urinary albumin creatinine ratio (ACR), a convenient index of UAE, together with blood pressure and other variables, such as age, sex, and body mass index. A variance components approach was used to estimate heritability and genetic correlations for ACR and systolic and diastolic blood pressures (SBP and DBP) after adjustment for relevant covariates.

RESULTS

In the 96 pedigrees, 6481 usable pairs of relatives were identified. In the total collection of pairs, heritability for ACR (h2 = 0.27, P < 0.001) was similar to that for blood pressure. When only pairs of diabetic relatives were analyzed (N = 1732), the estimates of heritability increased slightly for ACR (h2 = 0.31), SBP (h2 = 0.33), and DBP (h2 = 0.23). A significant genetic correlation was found between ACR and SBP (rg 0.27) and DBP (rg 0.26) in all pairs of relatives (P < 0.001). In pairs of diabetic relatives, these values were higher for SBP and DBP, 0.38 and 0.52, respectively.

CONCLUSION

In families with type 2 diabetes, UAE is a heritable trait, with a heritability similar to that for blood pressure. A significant genetic correlation between UAE and blood pressure, particularly in the presence of diabetes, indicates that these traits share common genetic determinants.