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.

Circulating prorenin: its molecular forms and plasma concentrations.

The renin-angiotensin-aldosterone system plays pivotal roles in the maintenance of fluid homeostasis and in the pathophysiology of major human diseases. However, the molecular forms of plasma renin/prorenin have not been fully elucidated, and measurements of plasma prorenin levels are still unavailable for clinical practice. We attempted to evaluate the molecular forms of human plasma prorenin and to directly measure its concentration without converting it to renin to determine its activity. Polyacrylamide gel electrophoresis and subsequent immunoblotting using antibodies that specifically recognise prosegment sequences were used to analyse its molecular forms in plasma. We also created a sandwich enzyme-linked immunosorbent assay suitable for directly quantifying the plasma concentration. The plasma level in healthy people was 3.0-13.4 µg/mL, which is from 3 to 4 orders of magnitude higher than the levels reported thus far. Plasma immunoreactive prorenin consists of three major distinct components: a posttranslationally modified full-length protein, an albumin-bound form and a smaller protein truncated at the common C-terminal renin/prorenin portion. In contrast to plasma renin activity, plasma prorenin concentrations were not affected by the postural changes of the donor. Hence, plasma prorenin molecules may be posttranslationally modified/processed or bound to albumin and are present in far higher concentrations than previously thought.

Molecular form and concentration of serum α2-macroglobulin in diabetes.

α2-Macroglobulin is a highly abundant serum protein involved in the development of atherosclerosis and cardiac hypertrophy. However, its circulating molecular form and exact concentrations in human health/diseases are not known. Blue native-polyacrylamide gel electrophoresis of human serum was used to confirm the native conformation of α2-macroglobulin. We created an enzyme-linked immunosorbent assay suitable for quantifying its circulating molecular form and undertook a cross-sectional study to measure its serum levels in 248 patients with diabetes mellitus and 59 healthy volunteers. The predominant circulating molecular form of α2-macroglobulin was the tetramer, whereas its dimer was detectable in patients with high serum levels of α2-macroglobulin. The serum α2-macroglobulin concentration was not associated with glycated hemoglobin or any other glycemic variable as evaluated from 48-h continuous glucose monitoring, but showed close correlation with left ventricular posterior wall thickness, carotid artery intima-media thickness, urinary albumin:creatinine ratio (ACR) and brachial-ankle pulse wave velocity (baPWV). Multivariate analysis revealed only the ACR and baPWV to be independent variables influencing serum levels of α2-macroglobulin. Thus, an increased ACR and baPWV are associated with higher serum concentrations of α2-macroglobulin, and the latter may contribute to the mechanism by which albuminuria increases the risk of developing cardiovascular diseases.