Prevention of diabetic nephropathy with enalapril in normotensive diabetics with microalbuminuria

Treatment with atenolol prevents progression of microalbuminuria in type I diabetic patients

Nine patients with Type I diabetes mellitus, diastolic blood pressure of 90 to 100 mmHg and persistent microalbuminuria of greater than or equal to 30 micrograms/min were treated with 50 to 100 mg atenolol daily for 3 years in an uncontrolled pilot study to assess the effect of long-term reduction of blood pressure on microalbuminuria. Treatment with atenolol prevented progression of microalbuminuria with a median (range) urinary albumin excretion rate before treatment of 74 (33 to 196) micrograms/min and 50 (5 to 123) micrograms/min after 3 years of therapy (p less than 0.05). Blood pressure was significantly reduced from 156 (121 to 187) mmHg systolic and 95 (90 to 100) mmHg diastolic before treatment to 143 (112 to 168) mmHg systolic (p less than 0.04) and 82 (66 to 84) mmHg diastolic (p less than 0.0003) at 3 years. Measurements of renal function and diabetic control remained unchanged throughout the study period. These results suggest that early and prolonged use of antihypertensive therapy is beneficial in slowing down progression of microalbuminuria.

Diabetic nephropathy: new directions in management

Approximately 6 million people in the United States are known to be diabetic, with an estimated 4 million individuals having undiagnosed diabetes mellitus. The metabolic derangements of both insulin-dependent diabetes mellitus (IDDM) and noninsulin-dependent diabetes mellitus (NIDDM) result in widespread end-organ damage, including progressive kidney failure. Since its initial description in 1936, the incidence of diabetic nephropathy has progressively increased, and it is now the most common cause of newly diagnosed end-stage renal disease (ESRD) requiring renal replacement therapy in the United States. While basic research efforts into pathogenesis continue, there is significant interest in clinical interventions that may slow the progression of diabetic renal disease. In addition, the options available for renal replacement therapy have increased and improved substantially in recent years.

Management of mild hypertension. Selecting an antihypertensive regimen

This discussion was selected from the weekly staff conferences in the Department of Medicine, University of California, San Francisco. Taken from a transcription, it has been edited by Homer A. Boushey, MD, Professor of Medicine, and Nathan M. Bass, MD, PhD, Associate Professor of Medicine, under the direction of Lloyd H. Smith, Jr, MD, Professor of Medicine and Associate Dean in the School of Medicine.

Do glomerular hemodynamic adaptations influence the progression of human renal disease?

Although experiments in the rat suggest that glomerular hemodynamic alterations following a reduction of renal mass may be implicated in the progression of chronic renal failure, we argue that the deleterious effects of similar adaptations in human renal disease are unproven. In the otherwise normal solitary kidney the supranormal glomerular filtration rate (GFR) remains stable over the longterm, and in early diabetic nephropathy which is also accompanied by hyperfiltration, renal deterioration cannot be dissociated from a rise in systemic blood pressure. In patients with miscellaneous renal diseases and a depressed basal GFR there is indirect evidence that hyperfiltration might occur in some of the remnant glomeruli. However, at present there is little conclusive evidence to indicate that therapies which might normalize glomerular hemodynamics, e.g., dietary protein restriction, have any effect on progression of renal disease, or that angiotensin converting-enzyme inhibitors, which lower glomerular capillary pressure, have any advantage over other antihypertensive agents which are equally efficacious in lowering systemic blood pressure.

Effect of dietary protein restriction on functional renal reserve in diabetic nephropathy

PURPOSE, PATIENTS, AND METHODS

Functional renal reserve in patients with insulin-dependent diabetes mellitus, as determined by the glomerular filtration rate (GFR) response test, is a measure of the capacity of the kidney to increase glomerular filtration in response to the stimulus of a protein meal or amino acid infusion. This 12-month study evaluated the changes in functional renal reserve in eight patients with insulin-dependent diabetes mellitus with nephropathy (micro-albuminuria [greater than or equal to 30 micrograms/minute]) who chronically decreased their dietary protein intake to a mean of 0.6 g/kg/day (Group 1) compared with a group of similar patients (n = 7) who maintained their unusual dietary protein intake (1.0 g/kg/day, Group 2). Patients were evaluated and measurements taken at 3-, 6-, and 12-month intervals. Absolute and percent increases in GFR were calculated from three averaged 1-hour measurements after an 80-g protein test meal.

RESULTS

Although the initial absolute mean rise (14 +/- 12 versus 18 +/- 13 mL/minute/1.73 m2) in GFR and maximal percent rise (16% +/- 16% versus 32% +/- 27%) after the meal did not differ significantly between the two groups, at 12 months, values in the lower protein group increased (27.8 +/- 9.5 mL/minute/1.73 m2 and 54.7% +/- 48.8%), whereas those in the normal protein intake group declined significantly (3.7 +/- 3.6 mL/min-ute/1.73 m2 and 6.5% +/- 6.5%) (p less than 0.05). Both urine urea and microalbuminuria decreased significantly (p less than 0.05) in the low protein group. Unstimulated GFR at the end of 12 months was significantly less (p less than 0.05) in Group 2 (47 +/- 2 mL/minute/1.73 m2) than in Group 1 (71 +/- 21 mL/minute/1.73 m2). The rate of decline in GFR was significantly greater (p less than 0.05) in the normal protein intake group than in the low protein intake group (0.68 +/- 0.4 versus 0.28 +/- 0.15 mL/minute/1.73 m2/month).

CONCLUSIONS

This study indicates that sustained dietary protein restriction can help to preserve renal function, decrease albuminuria, and lower the baseline GFR while maintaining functional renal reserve in patients with insulin-dependent diabetes mellitus.

Enalapril reduces microalbuminuria in young normotensive type 1 (insulin-dependent) diabetic patients irrespective of its hypotensive effect

The effect of enalapril on albumin excretion rate was studied in two groups of age- and sex-matched Type 1 (insulin-dependent) diabetic patients, aged 15-20 years, with persistent microalbuminuria greater than 20 micrograms/min. Group 1 contained six patients with systolic blood pressure greater than or equal to 75th percentile for age and sex, group 2 six normotensive patients. Enalapril (10-20 mg/day) was given for six months. Albumin excretion rate, glomerular filtration rate, renal plasma flow, blood pressure at rest and during exercise, and angiotensin converting enzyme activity were measured before, after three weeks' and six months' treatment and six months after treatment withdrawal. Albumin excretion rate decreased in all patients after three weeks' (mean decreases 55% in group 1, 65% in group 2) and six months' treatment (35% in group 1, 61% in group 2). Systolic blood pressure remained unchanged in both groups. Diastolic pressure was reduced after three weeks in group 1 (p = 0.001). No reduction in increment in systolic pressure during exercise test occurred in any group during treatment. Angiotensin converting enzyme activity decreased in all patients after three weeks (p = 0.001) and six months (p = 0.003). This correlated to the decrease in albumin excretion rate after three weeks (r = 0.79, p = 0.05) and six months (r = 0.59, p = 0.04). HbA1c, mean blood glucose and glomerular filtration rate remained unchanged during the study in both groups. Renal plasma flow tended to increase after three weeks' and six months' treatment in group 2 (p = 0.06, respectively) but not in group 1.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin converting enzyme inhibitor therapy to decrease microalbuminuria in normotensive children with insulin-dependent diabetes mellitus

It has been proposed that lowering glomerular pressure in children with insulin-dependent diabetes mellitus will reduce microalbuminuria and that this reduction may preserve renal function. We therefore conducted a double-blind, placebo-controlled, crossover trial to compare 3 months of treatment with the angiotensin converting enzyme inhibitor captopril (0.9 mg/kg/day), and 3 months of placebo administration to 12 normotensive adolescents with insulin-dependent diabetes mellitus, 11 with microalbuminuria (albumin excretion rate of 15 to 200 micrograms/min) and one with early overt nephropathy. Mean age (+/- SD) was 14.4 +/- 1.7 years, and disease duration was 5.1 +/- 2.5 years. Albumin excretion rate decreased significantly during captopril therapy (baseline 78 +/- 114 micrograms/min; mean of monthly measurements 38 +/- 55 micrograms/min vs placebo 78 +/- 140 micrograms/min; p less than 0.001). During captopril therapy, albumin excretion was reduced by 41 +/- 44% and decreased in 10 of 12 subjects, but was unchanged in two, one with a borderline albumin excretion rate (16.3 micrograms/min) and one with diabetes of short duration (2.9 years). Plasma renin activity rose significantly during captopril therapy, and mean arterial pressure decreased slightly (placebo 81 +/- 7 mm Hg; captopril 76 +/- 5 mm Hg; p = 0.004). After 3 months of captopril treatment, glomerular filtration rate and renal plasma flow did not change significantly. Hemoglobin Alc values remained stable during the study. The only side effect of captopril was diarrhea in one patient. We conclude that, in the short term, captopril is effective in decreasing albumin excretion rate in normotensive children with insulin-dependent diabetes mellitus and microalbuminuria, without significant side effects. Longer trials are indicated in an attempt to delay or prevent overt nephropathy.

Renal haemodynamic changes in response to moderate hyperglycaemia in type 1 (insulin-dependent) diabetes mellitus

The prevailing blood-glucose level has been found to influence renal haemodynamics in type 1 (insulin-dependent) diabetes mellitus. In a group of 48 type 1 diabetic patients with normal serum creatinine (less than 120 mumol l-1) and without persistent proteinuria, no relationship was present between blood glucose, corrected to near normoglycaemia (6.8 [6.2 to 7.3] mmol l-1 (median [95% confidence interval]), and glomerular filtration rate (GFR), effective renal plasma flow (ERPF) determined with 125I-iothalamate and 131I-hippuran respectively. GFR tended to increase (2 [-1 to +4] ml min-1 1.73 m-2, 0.05 less than P less than 0.10) and ERPF did not change after a blood glucose rise of 7.9 (7.0 to 8.9) mmol l-1, achieved by an intravenous glucose load in 31 patients. The individual changes in GFR and ERPF were correlated (r = 0.60, P less than 0.005). The changes in GFR were inversely related to baseline blood glucose (r = -0.45, P less than 0.02), but not to baseline GFR. GFR increased (3.5 [0 to +12] ml min-1 1.73 m-2, P less than 0.01) if baseline blood glucose was less than or equal to 6.8 mmol l-1 (n = 16) but ERPF did not. Achievement of near normoglycaemia before measurement of kidney function in type 1 diabetes appears to reduce the influence of variation in glycaemia on renal haemodynamics and thus would improve comparison between and within individuals. Moderate hyperglycaemia can cause a small rise in the glomerular filtration rate.

Blood glucose control determines the renal haemodynamic response to angiotensin converting enzyme inhibition in type 1 diabetes

Elevation of glomerular filtration rate (GFR) is a feature of diabetes mellitus in humans and in animal models. Angiotensin II has been implicated as a mediator of GFR in diabetes. The acute effect of inhibition of angiotensin converting enzyme with captopril on renal haemodynamic and endocrine parameters was therefore studied in 14 normotensive male Type 1 diabetic patients, and the responses compared with those in five normal male control subjects. Following captopril 12.5 mg orally the diabetic patients exhibited an acute fall in GFR from 122 +/- 3.8 to 113 +/- 4.5 ml min-1 1.73-m-2 (p less than 0.02) and a rise in renal plasma flow (RPF) from 670 +/- 57 to 797 +/- 46 ml min-1 1.73-m-2 (p less than 0.01) which resulted in a fall in filtration. This did not occur in normal control subjects. Natriuresis occurred only in normal control subjects. There was no change in urinary excretion of PGE2 or kallikrein in either group but excretion of 6-keto-PGF1 alpha fell in the diabetic patients. There was a significant correlation between glycosylated haemoglobin and baseline RPF (rs = -0.79, p less than 0.001) and filtration fraction (rs = 0.83, p less than 0.001) that persisted when the change in these variables following captopril was analysed. Our results are compatible with the response to ACE inhibition in diabetic patients being secondary to inhibition of angiotensin II and suggest that this response may be related to blood glucose control.

Perindopril safety and tolerance in at-risk patients

The angiotensin-converting enzyme (ACE) inhibitors are effective in the treatment of hypertension and congestive heart failure. They improve the quality of life when compared with other conventional antihypertensive drugs. Perindopril, a new ACE inhibitor, is well tolerated and associated with fewer side effects than other types of antihypertensive agents. Moreover, it does not induce adverse metabolic changes such as hyperglycaemia and/or alterations in the blood lipid profile that could negate the benefits of lowering blood pressure. In hypertensive diabetic patients, perindopril decreases microalbuminuria without affecting the quality of glycaemic control and thereby may delay the progression of nephropathy. Therefore, perindopril appears to be an alternative first-line antihypertensive agent which may be useful in hypertensive diabetics.

Protective effect of captopril on the blood-retina barrier in normotensive insulin-dependent diabetic patients with nephropathy and background retinopathy

The effect of 18 months' inhibition of angiotensin-converting enzyme by captopril on the leakage of fluorescein through the blood-retina barrier was examined in a prospective, randomized control study of 20 normotensive insulin-dependent diabetic patients with nephropathy and background retinopathy. After 18 months, 15 patients remained in the study. Fluorescein leakage remained nearly unchanged in the captopril-treated group, being 4.1 +/- 4.1 (mean +/- SD) x 10(-7) cm/s at baseline and 4.2 +/- 4.1 x 10(-7) cm/s after 18 months' treatment. The permeability increased significantly (P less than 0.01) from 3.3 +/- 2.2 x 10(-7) cm/s to 5.6 +/- 3.5 x 10(-7) cm/s at 18 months in the control group. Arterial blood pressure was nearly constant in both groups throughout the study. The results indicate that angiotensin-converting enzyme inhibition with captopril can arrest or delay a progressive breakdown of the blood-retina barrier in normotensive insulin-dependent diabetic patients with nephropathy and background retinopathy.

Concerns about diabetic nephropathy in the treatment of diabetic hypertensive patients

Diabetic nephropathy ultimately develops in approximately, 40 percent of patients with insulin-dependent diabetes mellitus, as well as in a significant fraction of those with non-insulin-dependent diabetes. Consequently, diabetic nephropathy represents the most common single cause of end-stage renal failure in adults. Recent studies indicate that the subset of insulin-dependent diabetic patients who develop nephropathy may have a genetic susceptibility to renal injury resulting from the abnormal physiologic milieu associated with diabetes. This is perhaps due to abnormal glomerular hemodynamic responses resulting in glomerular capillary hypertension. Diabetic nephropathy progresses through a prolonged subclinical stage characterized by abnormal urinary albumin excretion rates (30 to 250 mg/24 hours, "microalbuminuria") and small, but significant, increases in arterial blood pressure. This stage of incipient diabetic nephropathy represents the earliest point at which patients destined to develop overt diabetic nephropathy (albumin excretion rate of more than 250 mg/24 hours, hypertension, and decreased glomerular filtration rate) can be identified, and targets a population that may benefit from therapy aimed at preventing progression of renal failure. Hypertension is intimately related to the development and progression of diabetic nephropathy. Control of hypertension has been clearly shown to slow or arrest the progression of diabetic nephropathy and represents the most important therapeutic option available. Preliminary studies suggest that treatment consisting of strict metabolic control and selective antihypertensive agents during the stage of incipient nephropathy could potentially prevent the development of overt nephropathy. Although control of hypertension with any regimen is most likely beneficial, those agents endowed with selective protective effects on the glomerulus may confer optimal preservation of renal function. Patients with diabetes mellitus, whether insulin-dependent or non-insulin-dependent, are at increased risk for developing systemic arterial hypertension. The treatment of hypertension in diabetic patients takes on importance beyond the usual concerns for reducing blood pressure in other hypertensive patients. In diabetic patients, hypertension is directly linked to the development and progression of nephropathy. If this devastating complication is to be minimized or prevented, then control of arterial hypertension must be a major goal of therapy from the earliest stages of the disease process.

Albuminuria in type 2 (non-insulin-dependent) diabetes mellitus and impaired glucose tolerance in Pima Indians

The prevalence of abnormal urinary albumin excretion, defined by a urine albumin to creatinine ratio greater than or equal to 30 mg/g (approximately equivalent to an albumin excretion rate of greater than or equal to 30 mg/24 h), was determined in 2728 Pima Indians aged greater than or equal to 15 years from the Gila River Indian Community in Arizona, a population with a high prevalence of Type 2 (non-insulin-dependent) diabetes mellitus. Excessive albumin excretion was present in 8% of subjects with normal glucose tolerance, 15% of those with impaired glucose tolerance, and 47% of subjects with diabetes. The intermediate prevalence of abnormal albuminuria in those with impaired glucose tolerance suggests that hyperglycaemia even at levels below those diagnostic of diabetes is associated with renal abnormalities in some subjects and that these abnormalities may precede the onset of diabetes. Abnormal albuminuria at levels not reliably detected by the usual dipstick methods was commonly observed in Pima Indians with diabetes, even those with diabetes of recent onset. Associations were found with age, duration of diabetes, level of glycaemia, blood pressure, and treatment with insulin.

The epidemiology of diabetic nephropathy

Many areas of information in the epidemiology of diabetic nephropathy are lacking, but multiple studies designed specifically to answer these questions are currently being conducted. In the next 5-10 years, our current understanding of the epidemiology of diabetic nephropathy may either be confirmed or discredited. In the meantime, clinicians should use the data available to make decisions about treatment and should focus on the modifiable factors of glucose and blood pressure control in both IDDM and NIDDM, especially in patients with low-level albuminuria or clinical proteinuria.

Short and long term effects of antihypertensive therapy in the diabetic rat

To compare the impact of differing antihypertensive regimens on the development of renal injury, studies were performed in three groups of moderately hyperglycemic diabetic rats, and one group of non-diabetic control (C) rats. One diabetic group (DM) received no therapy except insulin. The remaining diabetic groups received insulin and either the angiotensin I converting enzyme inhibitor captopril (CAP), or triple therapy (TRX) with reserpine, hydralazine and hydrochlorothiazide. CAP and TRX modestly and comparably lowered blood pressure. At 6 to 10 weeks, DM rats exhibited elevation of the single nephron glomerular filtration rate (SNGFR), due to elevations of the glomerular capillary plasma flow rate (QA) and the glomerular capillary hydraulic pressure (PGC). In both DM/CAP and DM/TRX rats, blood pressure reduction was associated with selective normalization of PGC, without change in SNGFR or QA. In long-term (70 weeks) studies, DM rats exhibited progressive albuminuria and marked glomerular sclerosis. CAP limited albuminuria and injury to values even lower than those in C rats, whereas TRX served only to delay, but not to prevent, the increase in albuminuria. TRX reduced glomerular sclerosis, but was less effective than CAP. At 70 weeks, CAP and TRX still reduced systemic blood pressure; PGC remained at normal levels with CAP but was no longer controlled with TRX. These results confirm the clinical observation that antihypertensive therapy slows diabetic glomerulopathy, but also suggest that CAP affords superior long-term protection as compared to the other antihypertensive drug regimen studied.

Effect of captopril on blood pressure and kidney function in normotensive insulin dependent diabetics with nephropathy

OBJECTIVE

To assess whether inhibition of angiotensin converting enzyme protects kidney function in diabetic nephropathy.

DESIGN

Open, randomised follow up study of normotensive insulin dependent diabetics with nephropathy either treated or not with captopril for one year.

SETTING

Outpatient diabetic clinic in a tertiary referral centre.

PATIENTS

32 Normotensive patients with insulin dependent diabetes complicated by nephropathy who were randomised either to the treatment group (n = 15) or to the control group (n = 17).

INTERVENTIONS

The treatment group was given captopril (25-100 mg/day) for 12 months, the average dose during the second six months of the study being 40 mg daily. Controls were not treated.

MAIN OUTCOME MEASURES

Albuminuria, arterial blood pressure, and the glomerular filtration rate.

RESULTS

Mean arterial blood pressure fell by 3 (SE 2) mm Hg in the captopril treated group and rose by 6 (1) mm Hg in the controls. In addition, albuminuria declined by 11% in the captopril treated group and rose by 55% in the controls, fractional albumin clearance fell by 17% in the captopril treated group and increased by 66% in the controls, and the glomerular filtration rate declined by 3.1 (2.8)ml/min/1.73 m2 with captopril and by 6.4 (3.1) ml/min/1.73 m2 in the controls.

CONCLUSION

Inhibition of angiotensin converting enzyme arrests the progressive rise in albuminuria in normotensive insulin dependent diabetics with nephropathy.