Renoprotective therapy in patients with nondiabetic nephropathies

Endothelin: 30 Years From Discovery to Therapy

Discovered in 1987 as a potent endothelial cell-derived vasoconstrictor peptide, endothelin-1 (ET-1), the predominant member of the endothelin peptide family, is now recognized as a multifunctional peptide with cytokine-like activity contributing to almost all aspects of physiology and cell function. More than 30 000 scientific articles on endothelin were published over the past 3 decades, leading to the development and subsequent regulatory approval of a new class of therapeutics-the endothelin receptor antagonists (ERAs). This article reviews the history of the discovery of endothelin and its role in genetics, physiology, and disease. Here, we summarize the main clinical trials using ERAs and discuss the role of endothelin in cardiovascular diseases such as arterial hypertension, preecclampsia, coronary atherosclerosis, myocardial infarction in the absence of obstructive coronary artery disease (MINOCA) caused by spontaneous coronary artery dissection (SCAD), Takotsubo syndrome, and heart failure. We also discuss how endothelins contributes to diabetic kidney disease and focal segmental glomerulosclerosis, pulmonary arterial hypertension, as well as cancer, immune disorders, and allograft rejection (which all involve ET_A autoantibodies), and neurological diseases. The application of ERAs, dual endothelin receptor/angiotensin receptor antagonists (DARAs), selective ET_B agonists, novel biologics such as receptor-targeting antibodies, or immunization against ET_A receptors holds the potential to slow the progression or even reverse chronic noncommunicable diseases. Future clinical studies will show whether targeting endothelin receptors can prevent or reduce disability from disease and improve clinical outcome, quality of life, and survival in patients.

Endothelin: 20 years from discovery to therapy

Since its identification as an endothelial cell-derived vasoconstrictor peptide in 1988, endothelin-1, the predominant member of the endothelin peptide family, has received considerable interest in basic medical science and in clinical medicine, which is reflected by more than 20 000 scientific publications on endothelin research in the past 20 years. The story of endothelin is unique as the gene sequences of endothelin receptors and the first receptor antagonists became available within only 4 years of the identification of the peptide sequence. The first clinical study in patients with congestive heart failure was published only 3 years thereafter. Yet, despite convincing experimental evidence of a pathogenetic role for endothelin in development, cell function, and disease, many initial clinical studies on endothelin antagonism were negative. In many of these studies, study designs or patient selection were inadequate. Today, for diseases such as pulmonary hypertension, endothelin antagonist treatment has become reality in clinical medicine, and ongoing clinical studies are evaluating additional indications, such as renal disease and cancer. Twenty years after the discovery of endothelin, its inhibitors have finally arrived in the clinical arena and are now providing us with new options to treat disease and prolong the lives of patients. Possible future indications include resistant arterial hypertension, proteinuric renal disease, cancer, and connective tissue diseases.

Angiotensin-converting enzyme inhibition and renal protection in nondiabetic patients: the data of the meta-analyses

ESRD represents a major health problem. The number of patients who enter kidney replacement programs has increased at an average of 7% per year in the past 10 yr. A large number of experimental and clinical studies have demonstrated that chronic nephropathies share common pathogenic mechanisms that contribute to renal disease progression, even independent of the original cause. Clinical studies found a significant correlation between the extent of urinary protein excretion and the rate of GFR decline in both diabetic and nondiabetic chronic nephropathies. Randomized trials, in particular the Ramipril Efficacy In Nephropathy (REIN) study, also showed that treatments that reduce proteinuria (namely angiotensin-converting enzyme [ACE] inhibitors) are renoprotective and limit progression to ESRD. Meta-analyses of randomized clinical trials also evaluated the role of proteinuria and of ACE inhibition therapy in chronic renal disease progression. Their findings were consistent with those of the REIN study and confirmed in larger series of patients the predictive value of proteinuria and the renoprotective effect of proteinuria reduction by ACE inhibition therapy. Thus, the meta-analyses may confirm and extend previous findings generated by randomized clinical trials. Conceivably, well-designed studies in properly selected and carefully monitored patients who are at increased risk continue to be the best approach to test novel hypotheses. The meta-analyses, however, represent a valuable tool to evaluate the consistency and generalizability of trial results to larger cohorts of patients.

Proteinuria predicting outcome in renal disease: nondiabetic nephropathies (REIN)

About two thirds of patients on renal replacement therapy irreversibly lose their kidney function because of progressive nephropathies, such as diabetic nephropathy and nondiabetic chronic renal disease. Halting the progression of these patients to end-stage renal disease (ESRD) is instrumental to substantially decrease the need and cost for renal replacement therapy. A large number of experimental studies have demonstrated that chronic nephropathies share common pathogenic mechanisms that contribute to renal disease progression, even independently of the original etiology. Actually, a variety of insults may result in a common pathway of systemic hypertension, increased glomerular pressure and protein ultrafiltration, glomerular and tubular protein overload, chronic inflammation and, ultimately, scarring. Experimental and clinical data converge to indicate that in chronic renal disease increased protein traffic is nephrotoxic, proteinuria predicts disease progression, and proteinuria reduction is renoprotective. Initial clinical trials, mostly in patients with no or mild proteinuria, failed to demonstrate that ACE inhibition therapy is renoprotective in nondiabetic chronic nephropathies. Consistently, meta-analyses based on data generated by these trials failed to detect a specific, blood pressure-independent, renoprotective effect of ACE inhibition therapy. The Ramipril Efficacy In Nephropathy (REIN) study found that ACE inhibitors, by reducing urinary proteins, may contribute to improve the outcome of nondiabetic renal disease, and reduce the risk of progression to ESRD by about 50%. Cumulative meta-analyses, including the REIN study results, confirmed and extended these findings. Thus, well-designed trials in properly selected and carefully monitored study populations continue to be the best approach to test the efficacy of novel treatments. The meta-analyses may help confirming the consistency of these findings and their generalizability to larger cohorts of patients.

Calcium channel blockers in the prevention of end stage renal disease: a review

Hypertension and high levels of proteinuria are independent risk factors for accelerated progression of renal failure. There is increasing evidence that strict control of both blood pressure (BP) and proteinuria are beneficial in slowing the rate of progression of chronic renal disease in diabetic as well as non-diabetic nephropathy. The angiotensin-converting enzyme inhibitors (ACE-I) and angiotensin 2 receptor blockers (ARB) have clearly demonstrated their beneficial effect on both reduction of BP and proteinuria. The calcium channel blockers (CCB) have individual pharmacological and therapeutic properties that may vary, but as a group they are effective antihypertensive agents in patients with renal disease. Their effects on the kidney may extend beyond BP reduction alone. Current studies suggest that CCB do not worsen the progression of renal disease but may rather provide benefit when systemic BP has been tightly normalised. The non-dihydropyridine calcium channel blockers (NDHP), diltiazem and verapamil, slow the progression of type 2 diabetic nephropathy with overt proteinuria almost to a similar extent as observed with ACE-I. The dihydropyridine calcium channel blockers (DHP) have a variable effect on proteinuria. Pharmaceutical compounds, which inhibit the renin-angiotensin system (RAAS), remain the drugs of first choice in the treatment of hypertension and/or proteinuria in chronic nephropathy. However, a combination of two or more drugs is almost always required to attain sufficient BP reduction. CCB may have an advantage in combination with ACE-I and/or ARB.

Is it time to measure microalbuminuria in hypertension?

Former guidelines on hypertension never made a commitment to the detection of microalbuminuria for screening or follow-up of hypertensive patients. On the other hand, growing evidence support the contributory role of microalbuminuria in the prediction of absolute cardiovascular risk in hypertension and document the potential relevance of this parameter to the initial choice of antihypertensive treatment. Upcoming new guidelines and diagnostic algorithms in hypertension need to underscore the clinical positioning of microalbuminuria for stratification of risk and follow-up purposes.

Combined effects of low-dose oral spironolactone and captopril therapy in a rat model of spontaneous hypertension and heart failure

The effects of low-dose oral spironolactone (SPIRO) in a rat model of hypertensive heart failure (spontaneously hypertensive heart failure rat) were compared with its effects when combined with captopril (CAP). Twenty-six spontaneously rats with hypertensive heart failure were treated with either placebo (CON), SPIRO (20 mg/kg/d by mouth), CAP (100 mg/kg/d by mouth), or both SPIRO and CAP for 12 weeks. This dose of oral SPIRO did not affect blood pressure, left ventricular end-diastolic diameter, left ventricular ejection fraction, plasma atrial natriuretic peptide concentration, or cardiac fibrosis; however, in combination with CAP, it exerted a significant depressor effect after 12 weeks of treatment that was accompanied by increased urine output and decreased urinary protein excretion. These effects were significantly greater than those with CAP treatment alone. A significant increase in plasma aldosterone level was observed only in CON (174 +/- 21%). These data suggest that the addition of low-dose SPIRO to angiotensin I-converting enzyme inhibitor treatment may prevent progression into end-stage congestive heart failure through synergistic effects on diuresis and renoprotection.

Blood pressure response to conventional and low-dose enalapril in chronic renal failure

AIMS

In chronic renal failure, the clearance of most ACE inhibitors including enalapril is reduced. Hence, with conventional dosage, plasma enalaprilat may be markedly elevated. It is unclear whether this excess of drug exposure affords an improved control of blood pressure. The aim of the present study was to evaluate short-term blood pressure response to two different plasma levels of enalaprilat.

METHODS

As part of an open, randomized, controlled trial of the effect of high and low dosage of enalapril on the progression of renal failure, short-term blood pressure response was evaluated. Data were analysed in all patients completing 3 months of follow-up. The patients were allocated to two trough plasma concentrations of enalaprilat, either above 50 ng ml(-1) (high) (n = 17) or below 10 ng ml(-1) (low) (n = 18), and the daily dose of enalapril titrated accordingly.

RESULTS

Median (range) glomerular filtration rate (GFR) at baseline was 18 (7.9) in the high enalaprilat concentration group and 17 (7.3) ml min(-1) 1.73 m(2) in the low concentration group (NS). Nine patients in each group were on treatment with enalapril at baseline with a median daily dose of 5 mg in both the high (5-10) and low (2.5-20) concentration group. At 3 months' follow-up, the dose was 10 (2.5-30) and 1.9 (1.25-5) mg (P < 0.0001), respectively. After 3 months median trough concentrations of enalaprilat were 82.5 (22-244) ng ml(-1) and 9.1 (2.5-74.8) ng ml(-1) (P < 0.002). At baseline the median systolic blood pressures in the two groups were 140 (110-200) and 133 (110-165), in the high and low enalaprilat concentration groups, respectively, and after 3 months they were 135 (105-170) and 130 (105-170) mmHg (NS). Median diastolic blood pressure was 80 mmHg in each group both at baseline (65-100) and at follow-up (60-95) (NS). There was no difference between the groups in concomitant antihypertensive treatment (number of patients treated, mean daily dose) during the observation period. Proteinuria remained stable during the study period in both groups; patients in the high concentration group had higher plasma potassium concentrations at day 90 and patients in the low group experienced a slight increase in GFR.

CONCLUSIONS

In moderate to severe chronic renal insufficiency the same degree of blood pressure control was achieved on low as well as moderate daily doses of enalapril. This was irrespective of concomitant antihypertensive treatment.

Type 2 diabetes: RENAAL and IDNT--the emergence of new treatment options

The Reduction in End Points in NIDDM with the Angiotensin II Antagonist Losartan (RENAAL) study and the Irbesartan Diabetic Nephropathy Trial (IDNT) are two recently reported trials with hard end points, conducted in patients in advanced stages of diabetic nephropathy. Two other studies--the Irbesartan Microalbuminuria Study (IRMA)-2 and the Microalbuminuria Reduction with Valsartan study (MARVAL)--were trials conducted in patients with type 2 diabetes with microalbuminuria, a cardiovascular risk factor associated with early-stage diabetic nephropathy. These trials all had a common theme--that is, does an angiotensin receptor blocker (ARB) interfere with the natural history of diabetic nephropathy in a blood pressure-independent fashion? Without question, the results of these trials legitimatize the use of the ARB class in forestalling the deterioration in renal function, which is almost inevitable in the patient with untreated diabetic nephropathy. These data can now be added to the vast array of evidence supporting angiotensin-converting enzyme (ACE) inhibitor use in patients with nephropathy associated with type 1 diabetes. It now appears a safe conclusion that the patient with diabetic nephropathy should receive therapy with an agent that interrupts the renin-angiotensin system. These studies have not resolved the question as to whether an ACE inhibitor or an ARB is the preferred agent in people with nephropathy from type 1 diabetes, though the optimal doses of these drugs remain to be determined. Head-to-head studies comparing ACE inhibitors to ARBs in diabetic nephropathy are not likely to occur, so it is unlikely that comparable information will be forthcoming with ACE inhibitors. An evidence-based therapeutic approach derived from these trials would argue for ARBs to be the foundation of therapy in the patient with type 2 diabetes and nephropathy.