Plasma prorenin as an early marker of nephropathy in diabetic (IDDM) adolescents

Plasma and serum prorenin concentrations in diabetes, hypertension, and renal disease

Although the renin-angiotensin-aldosterone system plays a crucial role in fluid homeostasis and cardiovascular disease pathophysiology, measurements of plasma prorenin levels are still unavailable in clinical practice. We previously found that prorenin molecules in human blood underwent significant posttranslational modifications and were undetectable using immunological assays that utilized antibodies specifically recognizing unmodified recombinant prorenin. Using a sandwich enzyme-linked immunosorbent assay that captures posttranslationally modified prorenins with their prosegment antibodies, we measured plasma and serum prorenin concentrations in 219 patients with diabetes mellitus, hypertension and/or renal disease and compared them with those of 40 healthy controls. The measured values were not significantly different from those of the healthy controls and were 1,000- to 100,000-fold higher than previously reported levels determined using conventional assay kits. Multiple regression analyses showed that body weight, serum albumin levels, and serum creatinine levels negatively correlated with plasma prorenin levels, while the use of loop diuretics was associated with elevated plasma prorenin levels. Blood pressure, HbA1c, and plasma renin activity were not independent variables affecting plasma prorenin levels. In contrast, serum prorenin levels were unaffected by any of the above clinical parameters. The association of the plasma prorenin concentration with indices reflecting body fluid status suggests the need to scrutinize its role as a biomarker, while serum prorenins are less likely to have immediate diagnostic value.

Prorenin and active renin levels in paediatrics: a bioanalytical review

As part of the extended renin-angiotensin-aldosterone system, active renin and its precursor prorenin have been an area of research interest for decades. Although several studies showed a correlation with disease, other studies found no significant association, e.g. attributed to limited sample size or pharmacological effects of antihypertensive drugs. Since the measurement of both proteins has typically been carried out in adult populations, the data in paediatrics is limited. This review aimed to collate the current data on plasma renin and prorenin levels in children and compare the levels of healthy vs. the diseased state. A literature search using Medline resulted in 213 publications of which 15 studies were classified as relevant. In the extant studies in the literature, an age-dependent decline of renin plasma concentration was observed in newborns compared to adolescents. For children with cardiovascular disease, five studies were identified that provide limited insight into the pathophysiological regulation of renin. In general, sample handling is still a crucial step, which might particularly affect measured active renin concentrations due to conformational changes of its precursor prorenin. A reliable assessment for prorenin levels in the maturating population is yet not possible due to the low number of available publications. Three different approaches to quantify prorenin were found and raise the question on the comparability of these methods. The review emphazised several weaknesses and highlights the need for an accurate procedure to determine levels of active renin as well as prorenin in its closed and open form.

Homeostatic effect of laughter on diabetic cardiovascular complications: The myth turned to fact

AIMS

Laughter has been used for centuries to alleviate pain in morbid conditions. It was not until 1976 that scientists thought about laughter as a form of therapy that can modulate hormonal and immunological parameters that affect the outcome of many serious diseases. Moreover, laughter therapy was shown to be beneficial in type 2 diabetes mellitus (T2DM) by delaying the onset of many diabetic complications. Laughter is also described to influence the cardiovascular and endothelial functions and thus may protect against diabetic cardiovascular complications. In this review, we outline the different biochemical, physiological and immunological mechanisms by which laughter may influence the overall state of wellbeing and enhance disease prognosis. We also focus on the biological link between laughter therapy and diabetic cardiovascular complications as well as the underlying mechanisms involved in T2DM.

METHODS

Reviewing all the essential databases for "laughter" and "type 2 diabetes mellitus".

RESULTS

Although laughter therapy is still poorly investigated, recent studies show that laughter may retard the onset of diabetic complications, enhance cardiovascular functions and rectify homeostatic abnormalities associated with T2DM.

CONCLUSIONS

Laughter therapy is effective in delaying diabetic complications and should be used as an adjuvant therapy.

Expression and functional role of the prorenin receptor in the human adrenocortical zona glomerulosa and in primary aldosteronism

OBJECTIVES

Prorenin can be detected in plasma of hypertensive patients. If detected in patients with primary aldosteronism could implicate prorenin in the development of primary aldosteronism. To address this issue, we measured the plasma prorenin levels in primary aldosteronism patients, the expression of the prorenin receptor (PRR) in the normal human adrenocortical zona glomerulosa and aldosterone-producing adenoma (APA), and we investigated the functional effects of PRR activation in human adrenocortical cells.

METHOD

Plasma renin activity, aldosterone, and active and total trypsin-activated renin were measured in primary aldosteronism patients, essential hypertensive patients, and healthy individuals, and then prorenin levels were calculated. Localization and functional role of PRR were investigated in human and rat tissues, and aldosterone-producing cells.

RESULTS

Primary aldosteronism patients had detectable plasma levels of prorenin. Using digital-droplet real-time PCR, we found a high PRR-to-porphobilinogen deaminase ratio in both the normal adrenal cortex and APAs. Marked expression of the PRR gene and protein was also found in HAC15 cells. Immunoblotting, confocal, and immunogold electron microscopy demonstrated PRR at the cell membrane and intracellularly. Renin and prorenin significantly triggered both CYP11B2 expression (aldosterone synthase) and ERK1/2 phosphorylation, but only CYP11B2 transcription was prevented by aliskiren.

CONCLUSION

The presence of detectable plasma prorenin in primary aldosteronism patients, and the high expression of PRR in the normal human adrenal cortex, APA tissue, CD56+ aldosterone-producing cells, along with activation of CYP11B2 synthesis and ERK1/2 phosphorylation, suggest that the circulating and locally produced prorenin may contribute to the development or maintenance of human primary aldosteronism.

(Pro)renin receptor and vacuolar H(+)-ATPase

The (pro)renin receptor [(P)RR] is a molecule that binds prorenin and renin in tissues, leading not only to their activation, but also carrying out intracellular signaling. As a key player in the tissue renin-angiotensin system, (P)RR activation plays an important role in the development of end-organ damage in hypertension and diabetes. One fragment of (P)RR is also known as ATP6AP2 because it is associated with vacuolar H(+)-ATPase (V-ATPase). V-ATPase is a multi-subunit proton pump involved in diverse and fundamental aspects of cellular physiology, including receptor-mediated endocytosis and recycling, processing of proteins and signaling molecules, membrane sorting and trafficking, and activation of lysosomal/autophagosomal enzymes. The role of (P)RR in the function of V-ATPase has been investigated in recent studies using conditional knockout mice. Furthermore, the novel function of (P)RR as an adaptor protein between the Wnt receptor complex and V-ATPase has been demonstrated. Thus, (P)RR is a multi-functional molecule that has complex structure and functionality. This review focuses on current insights into the possibility of (P)RR acting as a modulator of V-ATPase and future perspectives in translational research.

Renin as a biomarker of cardiovascular disease in clinical practice

The search for novel circulating blood biomarkers as predictors of cardiovascular (CV) risk and prognosis is a continuing field of interest in clinical medicine. Biomarkers from several pathophysiological pathways, including markers of organ damage, of inflammation, of the atherosclerotic process and of the coagulation pathway, have been investigated in the last decades. A particular interest has been raised for neurohormonal factors. The role of the activation of the sympathetic system and the renin-angiotensin-aldosterone system (RAAS) in the development of CV diseases has been extensively explored. Renin is the first limiting step of the RAAS and its role as a biomarker to improve CV risk stratification still remains a topic of debate. Several studies have shown that elevated plasma renin activity is associated with increased morbidity and mortality in patients with CV disease. The aim of this paper is to critically evaluate the evidence on the role of renin as a biomarker of CV risk and prognosis. With the new advances of pharmacological treatment acting on the RAAS, the effect of elevated levels of renin on the prognosis of these patients becomes even more intriguing.

Dual renin-angiotensin-aldosterone system blockade for diabetic kidney disease

Blockade of the renin-angiotensin-aldosterone system (RAAS) prevents the development and progression of diabetic kidney disease (DKD). It is controversial whether the simultaneous use of two RAAS inhibitors (ie, dual RAAS blockade) further improves renal outcomes. This review examines the scientific rationale and current clinical evidence addressing the use of dual RAAS blockade to prevent and treat DKD. It is concluded that dual RAAS blockade should not be routinely applied to patients with low or moderate risk of progressive kidney disease (normoalbuminuria or microalbuminuria with preserved glomerular filtration rate). For patients with high risk of progressive kidney disease (substantial albuminuria or impaired glomerular filtration rate), clinicians should carefully weigh the potential risks and benefits of dual RAAS blockade on an individual basis until ongoing clinical trials provide further insight.

The pathogenesis of diabetic nephropathy

Between 20% and 40% of patients with diabetes ultimately develop diabetic nephropathy, which in the US is the most common cause of end-stage renal disease requiring dialysis. Diabetic nephropathy has several distinct phases of development and multiple mechanisms contribute to the development of the disease and its outcomes. This Review provides a summary of the latest published data dealing with these mechanisms; it focuses not only on candidate genes associated with susceptibility to diabetic nephropathy but also on alterations in various cytokines and their interaction with products of advanced glycation and oxidant stress. Additionally, the interactions between fibrotic and hemodynamic cytokines, such as transforming growth factor beta1 and angiotensin II, respectively, are discussed in the context of new information concerning nephropathy development. We touch on the expanding clinical data regarding markers of nephropathy, such as microalbuminuria, and put them into context; microalbuminuria reflects cardiovascular and not renal risk. If albuminuria levels continue to increase over time then nephropathy is present. Lastly, we look at advances being made to enable identification of genetically predisposed individuals.

Enhancing the Predictive Value of Urinary Albumin for Diabetic Nephropathy

Diabetic nephropathy (DN) is a growing cause of ESRD despite widely known recommendations for improved glycemic and BP control. Perhaps earlier identification of patients who have diabetes and are at high risk for DN could reverse these epidemiologic trends. Albumin excretion rate (AER), the mainstay of early detection of DN, is not a sufficiently precise predictor of DN risk. Careful family history, smoking history, consideration of absolute versus categorical AER values, more frequent AER measures, ambulatory BP monitoring, precise GFR measurements, diabetic retinopathy assessments, and plasma lipid levels all can add to predictive accuracy for DN. Thus, although further research in DN biomarkers and predictors is greatly needed, a careful integrated evaluation of currently available parameters can improve our ability to predict DN risk in individual patients.

Prediction, progression and prevention of diabetic nephropathy. The Minkowski Lecture 2005

Diabetic nephropathy is a major problem for patients and health care systems. The costs of treatment remain high. To confront the ongoing challenge, we need to identify individuals at high risk for initiation and progression of this devastating complication. Risk factors include genetic markers; constitutional factors such as low birthweight; haemodynamic factors, including activation of the RAS system and hypertension; metabolic factors such as glycaemia; and additional factors such as urinary AER and smoking. Modifiable risk factors should be treated aggressively. Potential new markers of risk include indices of increased inflammation, changes in coagulation, endothelial dysfunction, growth factors and cytokines. Application of such markers may in time improve risk assessment and allow new treatment targets to be identified. Interventions that aim to achieve strict glycaemic control and blockade of the renin-angiotensin system have been shown to be effective in clinical trials and are feasible in clinical practice. The 'natural history' of diabetic nephropathy can be transformed if these strategies of intensive screening and care are applied, leading both to a lower incidence of diabetic nephropathy and to an improved outcome, with survival exceeding 20 years from onset of overt proteinuria.

Sex difference and possible relationship to microvascular complications of serum prorenin levels in type 2 diabetic patients, measured by a novel antibody-activating direct enzyme kinetic assay

Prorenin, a precursor of renin, was measured in sera from normal subjects and type 2 diabetic patients, using a newly developed antibody-activating direct enzyme kinetic assay. Levels of prorenin were examined in relationship to diabetic microangiopathies. The levels of antibody-activating direct prorenin (AAD-PR) were approximately 1.5-fold higher than levels of prorenin measured by a conventional enzyme-activating method. AAD-PR levels were significantly higher in males than in females and in diabetic patients than in normal subjects. Moreover, AAD-PR levels were higher in diabetic patients with microalbuminuria and even higher in those with macroalbuminuria. In normoalbuminuric diabetic patients, AAD-PR levels were higher in those with retinopathy. Furthermore, a significant positive correlation was seen between the AAD-PR levels and HbA(lc) in normoalbuminuric diabetic subjects without retinopathy. Thus, the determination of circulating serum prorenin measured as AAD-PR is related to glycemia and in type 2 diabetic patients may be a risk marker of diabetic microangiopathy. More studies are necessary to determine whether AAD-PR may actually predict the development of microangiopathy.

Transmural pressure control of prorenin processing and secretion in diabetic rat juxtaglomerular cells

In diabetic patients, the elevation of plasma prorenin levels or arterial pressure is correlated with the severity of diabetic nephropathy. This study was designed to assess the effects of transmural pressure on prorenin regulation in juxtaglomerular (JG) cells from diabetes rats. The JG cells, harvested from rats intraperitoneally injected with streptozotocin 7 (early-diabetic) or 28 (late-diabetic) days previously, were exposed to atmospheric pressure (AP) and AP+40 mmHg for 12 h, and the renin secretion rate (RSR), prorenin secretion rate (PRSR), active renin content (ARC), prorenin content (PRC), and total renin content (TRC) were determined. Exposure of control JG cells to AP+40-mmHg significantly decreased RSR, PRSR, and ARC and significantly increased PRC without affecting TRC, suggesting the occurrence of pressure-mediated inhibition of prorenin processing and secretion. Exposure of early-diabetic and late-diabetic cells to AP+40-mmHg significantly decreased ARC and significantly increased PRC without affecting RSR, PRSR, or TRC. The changes in ARC and PRC were similar in the control and early-diabetic cells, but greater changes were observed in late-diabetic cells. However, when streptozotocin-treated rats were continuously treated with insulin (9 U/kg/day), the transmural pressure control of prorenin in JG cells was similar to that observed in the JG cells from control rats. In late-diabetic cells, treatment with a phospholipase C inhibitor did not alter the pressure control of ARC or PRC; however, treatment with a phospholipase D inhibitor did inhibit the changes in ARC and PRC with transmural pressure. Thus, pressure-mediated inhibition of prorenin secretion from JG cells has already been impaired in early diabetes. Pressure-induced inhibition of prorenin processing in JG cells via phospholipase D-dependent pathways is enhanced in late diabetes.

ACE inhibitor intervention in Type 1 diabetes with low grade microalbuminuria

Several clinical trials have consistently shown that antihypertensive treatment, particularly with angiotensin-converting enzyme inhibitors (ACE-I) reduces albuminuria in Type 1 diabetic patients. More recently, data on the beneficial effects of ACE-I on the preservation of glomerular filtration rate and renal ultrastructure have emerged. However, in general, these trials have recruited a wide spectrum of diabetics, including some patients with severe albuminuria. Thus, the question of the ideal stage at which to instigate what is likely to be lifelong therapy in young people still remains unanswered. Exercise is known to significantly increase both blood pressure (BP) and urinary albumin excretion (UAE), both of which are important determinants of progression of nephropathy in diabetes. Thus, it is possible that exercise may have an adverse effect on diabetic renal disease. The effects of ACE-I on exercise-BP and exercise-UAE in microalbuminuric Type 1 diabetic patients has not been examined in long-term placebo-controlled studies. In the second part of this two-part review, we examine the effects of the ACE-I, lisinopril, 20 mg o.d. for two years, in comparison with placebo, on UAE, 24-hour ambulatory BP, exercise-BP, exercise-UAE and renal haemodynamics in 22 patients with Type 1 diabetes and low-grade microalbuminuria. We further discuss the effects of ACE-I on nephropathy and other complications of diabetes.

ACE-I and ARBs in early diabetic nephropathy

INTRODUCTION

Antihypertensive treatment of patients with clinical manifestations of diabetic nephropathy, and especially, renin-angiotensin system (RAS) inhibition, slows, but may not fully arrest progression towards end-stage renal disease. Studies using hard endpoints such as doubling of serum creatinine, dialysis, or death that are initiated before emergence of any renal functional abnormalities in diabetes, would be of impractical length and size. We therefore undertook a primary prevention study (The Renin-Angiotensin System Study or RASS) to determine if inhibition of the RAS could slow the development of a key diabetic glomerulopathy structural endpoint, increase in mesangial fractional volume (Vv[Mes/glom]).

METHODS

This is a parallel group, double-blind, placebo-controlled trial with 285 patients with Type 1 diabetes mellitus (95 per group) randomised to receive the angiotensin-converting enzyme inhibitor, enalapril, the angiotensin II receptor blocker, losartan, or placebo. All patients are normotensive, normoalbuminuric and have normal or increased glomerular filtration rates at study entry. The study is based on primary endpoint of change in Vv(Mes/glom) from baseline to the five-year renal biopsy, with baseline and interval measures of albumin excretion rate, glomerular filtration rate, blood pressure, and glycaemia. Baseline, mid-point, and five-year retinal fundus photography are also performed.

RESULTS

One thousand and sixty-five patients were interviewed, 707 refused participation and 73 were excluded. The target of 285 subjects were randomised and their clinical and demographic characteristics are described. Biopsy complications occurred in 17 (6%), only one of which required hospitalisation. There were no permanent biopsy-related sequelae.

CONCLUSIONS

Renal structural variables are reasonable surrogate endpoints for studies of progression of early diabetic nephropathy. Although requiring substantial recruitment effort, diabetic nephropathy primary prevention trials based on change in renal structure are feasible.

Prorenin concentration in the hypertensive disorders in pregnancy

OBJECTIVE

To evaluate the plasma prorenin levels during the three trimesters of normal pregnancy, their prognostic value, and their correlation with hypertensive disorders of pregnancy.

DESIGN

A prospective study in which plasma prorenin and renin levels were measured in 55 healthy pregnant women and 66 who developed gestational hypertension or preeclampsia. The patients were classified as mild preeclampsia (mild PE), severe preeclampsia (severe PE), chronic hypertension and superimposed preeclampsia upon chronic hypertension (superimposed PE).

METHOD

Venous blood samples were collected in the first, second and third trimesters and during delivery or cesarean. Plasma renin concentration (PRC) was measured by radioinmmunoassay before and after incubation with trypsin solution. The difference gave plasma prorenin concentration (PProRC).

RESULTS

PRC and PProRC were significantly higher in pregnant women compared with healthy non-pregnant. PRC was significantly increased in the first trimester in the chronic hypertension group and a lower value was found in the first trimester in the superimposed PE compared with those in healthy pregnant women. No differences in other groups were found. PProRC showed a significant lower value in the first and third trimesters in the severe PE group. In the superimposed PE a low value of PProRC similar to those of non-pregnant women was found.

CONCLUSIONS

The results show that the different types of hypertension in pregnancy have different profiles of PProRC and PRC in relation to development of preeclampsia. The absence of increase of PProRC in the first trimester of superimposed PE may have a prognostic value.

Functional significance of prorenin internalization in the rat heart

Intracardiac renin is considered to be involved in the pathogenesis of cardiac hypertrophy, fibrosis, and myocardial infarction. Cardiac renin is predominantly derived from the circulation, because preprorenin is not expressed locally and uptake of renin has been demonstrated. One mechanism of internalization recently described involves the mannose-6-phosphate receptor and requires glycosylation of renin. Based on previous observations, we considered the existence of another pathway of uptake, not requiring glycosylation and predominantly involving prorenin. This hypothesis and its functional consequences were investigated in vitro and in vivo. We demonstrate that isolated adult cardiomyocytes internalize unglycosylated prorenin, which is followed by the generation of angiotensins. We further show that transgenic rats, expressing the ren-2(d) renin gene in an inducible manner, exhibit markedly enhanced levels of unglycosylated renin within intracellular compartments in the heart as a consequence of the induction of hepatic transgene expression and the rise of circulating unglycosylated prorenin levels. Because in this model severe cardiac damage occurs as a consequence of the rise of circulating prorenin levels, internalization of prorenin into cardiac cells is likely to play a key role in this process.

High plasma concentrations of prorenin in a transgenic animal model of nephropathy with overexpression of transforming growth factor-beta1 in the kidneys

1. Plasma concentrations of prorenin were determined in a transgenic animal model of nephropathy induced by overexpression of transforming growth factor (TGF)-beta1 in the juxtaglomerular apparatus. 2. In both female and male mice, plasma concentrations of prorenin were higher in transgenic than in non-transgenic animals. In sexually mature mice, plasma prorenin concentrations were higher in males than in females in both transgenic and non-transgenic animals in accordance with a sexual dimorphism of the plasma concentration of prorenin. 3. The results indicate that TGF-beta1-like androgens increase prorenin secretion in the kidneys and may explain the increased plasma prorenin concentrations in patients with diabetic nephropathy.

High plasma prorenin in non diabetic siblings of non insulin-dependent diabetes mellitus patients

In a large cohort (no. = 361) of NIDDM probands and their concordant/discordant siblings from no. = 132 families we studied: 1. the levels of plasma prorenin in non affected siblings of NIDDM probands as opposed to normal subjects without family history of diabetes, and 2. whether plasma prorenin raises in parallel to urinary protein loss in NIDDM patients. Prorenin (solid-phase trypsin) and micro-macroalbuminuria (radioimmunoassay) were evaluated. Plasma prorenin was higher in NIDDM probands and siblings than in non NIDDM siblings (37+/-31 vs. 25+/-15 ng/ml/h, p<0.0005) who, in turn, showed higher plasma prorenin than non diabetic controls without family history of diabetes (25+/-15 vs. 17+/-8 ng/ml/h, p<0.005). Plasma prorenin was higher in NIDDM siblings of micro-macroalbuminuric probands than in NIDDM siblings of non micro-macroalbuminuric probands (40+/-26 vs. 29+/-20 ng/ml/h, mean +/- SD, p = 0.0058) whereas no difference was found among non diabetic siblings (24+/-14 vs. 22+/-11 ng/ml/h, NS). Our data confirm that plasma prorenin is elevated in NIDDM patients, and show: 1. that the raise of plasma prorenin in non-NIDDM siblings of a diabetic patient does not depend entirely from the presence of diabetes, and 2. that plasma prorenin in NIDDM probands and their concordant siblings goes along with micro-macroalbuminuria.

Plasma renin and prorenin and renin gene variation in patients with insulin-dependent diabetes mellitus and nephropathy

BACKGROUND

The most striking abnormality in the renin angiotensin system in diabetic nephropathy (DN) is increased plasma prorenin. Renin is thought to be low or normal in DN. In spite of altered (pro)renin regulation the renin gene has not been studied for contribution to the development of DN.

METHODS

We studied plasma renin, prorenin, and four polymorphic markers of the renin gene in 199 patients with IDDM and DN, and in 192 normoalbuminuric IDDM controls matched for age, sex, and duration of diabetes. Plasma renin and total renin were measured by immunoradiometric assays. Genotyping was PCR-based.

RESULTS

Plasma renin was increased in patients with nephropathy (median (range), 26.3 (5.2-243.3) vs 18.3 (4.2-373.5) microU/ml in the normoalbuminuric group, P<0.0001). Prorenin levels were elevated out of proportion to renin levels in nephropathic patients (789 (88-5481) vs 302 (36-2226) microU/ml, P<0.0001). Proliferative retinopathy had an additive effect on plasma prorenin, but not on renin. DN was associated with a BglI RFLP in the first intron of the renin gene (bb-genotype: n=106 vs 82 in DN and normoalbuminuric patients respectively, P=0.037), but not with three other polymorphisms in the renin gene. A trend for association of higher prorenin levels with the DN-associated allele of this renin polymorphism was observed in a subgroup of patients with DN (bb vs Bb+BB, P=0.07).

CONCLUSIONS

The results indicate that in DN there is an increase in both renin and prorenin levels. A renin gene polymorphism may contribute weakly to DN. Although speculative, one of the renin gene alleles could lead to increased renin gene expression, leading to higher renin and prorenin levels. These may play a role in the pathogenesis of DN.

Serum total renin is increased before microalbuminuria in diabetes

Serum prorenin is increased in patients with insulin dependent diabetes mellitus (IDDM) with microvascular complications. The present longitudinal study investigated whether increases in serum total renin concentration (TRC, active+prorenin) can predict the development of microalbuminuria in IDDM patients over a 10 year period. TRC and albumin excretion rates (AER) were determined in 78 IDDM patients who were followed longitudinally for 10.4 +/- 0.2 (mean +/- SE) years. Twelve patients had progressively increasing albuminuria (progressors), and these were compared to 66 patients in whom albuminuria did not rise (non-progressors). The two groups had similar duration of diabetes, age, follow-up, glycemic control and blood pressure at the start of the study. Serum TRC was increased in progressors [350 (1.1) mIU/liter, geometric mean (tolerance factor)] compared to non-progressors [189 (1.2)] after 5 to 10 years duration of diabetes, and continued to rise in this group, reaching a mean of 923 mIU/liter (normal range 131 to 170) after 20 years of diabetes. When serial measurements of TRC and AER were compared in individual progressors, a significant increase in TRC was apparent up to five years before the onset of microalbuminuria. Microalbuminuria in patients with IDDM is preceded by a substantial increase in serum TRC, suggesting that serum TRC may predict the subsequent development of incipient nephropathy.

New monoclonal antibodies directed against the propart segment of human prorenin as a tool for the exploration of prorenin conformation

Six monoclonal antibodies (MAbs) directed against human prorenin were produced by immunizing BALB/c mice with a peptide corresponding to the sequence (-17 to +9) of prorenin. The new MAbs were screened for their ability to first bind to the immobilized peptide and then to prorenin previously captured by an anti-total renin MAb. The specificity of the MAbs was confirmed by the total lack of binding to active renin. Using BIAcore technology, equilibrium affinity constants of the MAbs were determined and ranged from 3.2 x 10(8) to 5.7 x 10(9) l/mol. Immunoradiometric assays (IRMA) for prorenin were performed using the anti-total renin MAb and the anti-prorenin MAbs. The best results were obtained when an anti-prorenin MAb was immobilized and the anti-total renin MAb was used as tracer in a one-step procedure. Moreover, the signal was significantly increased by the presence of the renin inhibitor SR 43845 suggesting that the inhibitor-induced conformational change of prorenin could be detected by the MAbs.