Evolving strategies for renoprotection: diabetic nephropathy

Effects of dual blockade of the renin-angiotensin system in primary proteinuric nephropathies

BACKGROUND

Blockade of the renin-angiotensin system (RAS) with angiotensin converting enzyme (ACE) inhibitors or with angiotensin II type 1 (AT1) receptor blockers has been shown to reduce proteinuria and to slow down the progression of renal disease in diabetic and non-diabetic primary proteinuric nephropathies. Additionally, this beneficial effect is not dependent on blood pressure control.

METHODS

To assess and compare the effects of lisinopril (up to 40 mg/day), candesartan (up to 32 mg/day) and combination therapy (lisinopril up to 20 mg/day plus candesartan up to 16 mg/day) on urinary protein excretion, 45 patients with primary proteinuric nephropathies (urinary protein/creatinine ratio 3.8+/-2.4 g/g) and normal or slightly reduced renal function (CCr 95+/-33 mL/min) were enrolled in a six month multicenter, prospective, open, randomized, active-controlled and parallel-group trial with 1:1:1 allocation. Blood pressure goal was set at or below 125/75 mm Hg for all patients, with additional antihypertensive medication prescribed if required.

RESULTS

Renal function, estimated by creatinine clearance, remained stable throughout the study. Hyperkalemia (K>5.5 mmol/L) was detected in 3.1% of all measurements in follow-up, and was more frequent in patients treated with lisinopril alone or lisinopril plus candesartan (P<0.001) than in those on candesartan alone. No other relevant adverse event was recorded. The blood pressure goal (<125/75 mm Hg) was achieved by week 4 in all treatment groups (P<0.005 when compared to baseline), and afterwards the mean systolic and diastolic blood pressure remained below these values until the end of the trial with no statistically significant differences between groups. Urinary protein/creatinine ratio (percentage reduction 95% confidence intervals CI) decreased in patients treated with lisinopril alone to -33% (CI -12-56) to -31% (CI 0-68) and to -50% (CI -9-90), in patients treated with candesartan to -28% (CI -12-45), to -41% (CI -30-52) and to -48% (CI -32-63), in patients treated with the combination of both to -60% (CI -44-77) to -54% (CI -38-69) and to -70% (CI -57-83) at two, three, and six months, respectively. All comparisons with baseline achieved statistical significance and treatment with combination therapy was statistically more effective in proteinuria reduction than treatment with candesartan alone at two and six months (P=0.004 and P=0.023, respectively) and than treatment with lisinopril only at two months (P=0.03).

CONCLUSION

Dual blockade of the renin-angiotensin system with ACE inhibitors and AT1 receptor blockers produces a beneficial antiproteinuric effect that could not be explained only by the systemic blood pressure reduction. All treatments were well tolerated.

Angiotensin blockade in type 2 diabetic renal disease

The available evidence on renal protection in type 2 diabetes mellitus favors the administration of an angiotensin receptor blocker (ARB) more than that of an angiotensin converting enzyme inhibitor (ACEi). This evidence is based on recent studies showing that losartan and irbesartan can prevent the development of overt diabetic nephropathy in microalbuminuric type 2 diabetic patients as well as slow the velocity of progression to end-stage renal disease in patients with overt type 2 diabetic nephropathy. These studies do not deny the possibility that ACEi are equally effective, but studies of an adequate magnitude are lacking. These findings on ARB administration do not preclude the importance of strict control of blood pressure and proteinuria and/or albuminuria to avoid or retard renal damage in type 2 diabetic patients.

Prediction of renal insufficiency in Pima Indians with nephropathy of type 2 diabetes mellitus

BACKGROUND

A high prevalence and early onset of type 2 diabetes in Pima Indians is well known. Our objective is to use several statistical models to identify predictors of glomerular filtration rate (GFR) deterioration and develop an algorithm to predict GFR 4 years after the initial evaluation.

METHODS

All records (n = 86) were randomly assigned to a training set (n = 60) and a testing set (n = 26). Linear regression, generalized additive, tree-based, and artificial neural network models were used to identify predictors of outcome and develop a prediction algorithm.

RESULTS

Proteinuria remained the single most important predictor of long-term renal function; other predictors included baseline GFR, blood pressure, plasma renin activity, lipid profile, age, weight/body mass index, and diabetes duration. All four models achieved a good correlation (r = 0.73 to 0.78) between observed and predicted 4-year GFRs on a separate (testing) data set. Best results in predicting the value of GFR were achieved using a tree-based model with six terminal nodes (r = 0.78; root mean squared prediction error = 38.9). The tree-based and generalized additive models achieved high positive (91%) and negative (100%) predictive values in identifying subjects, who developed depressed GFRs in 4 years. An artificial neural network achieved the highest area under the receiver operating characteristic curve (0.91).

CONCLUSION

GFR depression within 4 years can be predicted with a precision that suggests potential clinical utility. A tree-based model with six terminal nodes has shown the best results in predicting the actual value of GFR, whereas an artificial neural network is the model of choice to identify the group of patients that will develop renal insufficiency.

Long-term renal consequences of hypertension for normal and diseased kidneys

Substantial evidence indicates that the adverse effects of hypertension on the kidney depend on the degree to which systemic blood pressure elevations are transmitted to the renal microvasculature. Such blood pressure transmission and consequent susceptibility to hypertensive renal damage is markedly exacerbated in states characterized by preglomerular vasodilation and an impairment of the normally protective renal autoregulatory mechanisms, e.g. diabetes or chronic renal disease. Moreover, this pathophysiology gives rise to the prediction that prevention of hypertension-induced barotrauma will require blood pressure to be reduced well into the normotensive range in such patients, as is being recognized in the currently recommended blood pressure goals. Agents that block the renin-angiotensin system should be preferred as initial therapy as they may provide additional risk reductions and minimize the potassium and magnesium depletion associated with the diuretic use usually necessary to achieve the lower blood pressure targets. The current failure to achieve optimal blood pressure reductions may be contributing not only to the still escalating incidence of end-stage renal disease in diabetic patients, but also to their greatly increased cardiovascular morbidity and mortality.

Diabetic Renal Disease in Patients with Type 2 Diabetes Mellitus

Over the last 35 years an increasing number of patients with type 2 diabetes mellitus have developed advanced renal disease and the need for dialysis. At present in the US, about 50% of the patients in dialysis units have type 2 diabetes mellitus. The explanation for the increase in the number of patients with type 2 diabetes mellitus in end-stage renal disease programs is not completely clear, but the overall number of patients with this type of diabetes is rapidly increasing - and is expected to continue to increase over the next years. The diagnosis of renal disease in type 2 diabetes mellitus is usually straightforward, and is mainly dependent upon measurements of urinary albumin or urinary protein excretion as well as serum creatinine measurements. Renal biopsies or exact glomerular filtration rate measurements are rarely necessary. Microalbuminuria is the first sign of renal disease in diabetes mellitus. It predicts overt nephropathy and cardiovascular disease. Several studies document that albuminuria and microalbuminuria can be reduced by treatment with antihypertensives, especially agents that block the renin angiotensin system. New studies show that end-stage renal disease can be postponed by the use of angiotensin II receptor antagonists. ACE inhibitors are also useful, and dual blockade of the renin angiotensin system has been utilized as well. However, generally speaking, patients with proteinuria have a poor prognosis. Screening for microalbuminuria is therefore proposed, and glycemic control and blood pressure should be optimized.