Are Sodium Transporters in Urinary Exosomes Reliable Markers of Tubular Sodium Reabsorption in Hypertensive Patients?

Abstract

absorption and urinary exosomal excretion of sodium transporters, and (2) the profile of sodium transporter excretion related to blood pressure (BP) changes with salt intake. A 24-hour ambulatory BP monitoring and a 24-hour urine collection were performed after 1 week on a low-and 1 week on a high-salt diet. Results: Animal studies: urinary NKCC2 and NCC excretion rates correlated well with their abundance in the kidney. Human studies: 6 patients (15%) were classified as salt sensitive. The NKCC2 and NCC abundance did not decrease after the high-salt period, when the urinary sodium reabsorption decreased from 99.7 to 99.0%. In addition, the changes in BP with salt intake were not associated with a specific profile of exosomal excretion. Conclusions: Our results do not support the idea that excretion levels of NKCC2 and NCC via urinary exosomes are markers of tubular sodium reabsorption in hypertensive patients.Copyright © 2010 S. Karger AG, Basel Key WordsExosomes ؒ Na-Cl cotransporter ؒ Na-K-2Cl cotransporter ؒ Renal sodium transporters ؒ Salt sensibility ؒ Urine biomarkers Abstract Background: Altered renal sodium handling has a major pathogenic role in salt-sensitive hypertension. Renal sodium transporters are present in urinary exosomes. We hypothesized that sodium transporters would be excreted into the urine in different amounts in response to sodium intake in salt-sensitive versus salt-resistant patients. Methods: Urinary exosomes were isolated by ultracentrifugation, and their content of Na-K-2Cl cotransporter (NKCC2) and Na-Cl cotransporter (NCC) was analyzed by immunoblotting. Animal studies: NKCC2 and NCC excretion was measured in 2 rat models to test whether changes in sodium transporter excretion are indicative of regulated changes in the kidney tissue. Human studies: in hypertensive patients (n = 41), we investigated: (1) a possible correlation between sodium re-

The Phosphorylated Sodium Chloride Cotransporter in Urinary Exosomes Is Superior to Prostasin as a Marker for Aldosteronism

“…Of interest, the increase in NCC in urinary exosomes we observed in this study with a low-sodium diet was similar to the increase Esteva-Font et al found for NCC in a separate study. 10 Our study suggests that pNCC was better than prostasin as a marker of aldosteronism, which could be explained by several factors. First, although prostasin is sensitive to aldosterone and can activate ENaC, this does not necessarily render it a direct marker of ENaC activity and, as such, it may not be a direct marker of distal sodium reabsorption.…”

“…Esteva-Font et al, however, found no difference in the abundance of NCC in urinary exosomes of patients with salt-sensitive hypertension. 10 Recently, it has become clear that the phosphorylated form of NCC (pNCC) represents the active form of NCC and that trafficking and phosphorylation of NCC can be regulated independently.…”

Clinical and Physiological Aspects of Salt Sensitive Hypertension

“…In another human study 41 patients with mild-moderate hypertension underwent 1 week of low and then 1 week of a high sodium diet [217]. 24 hour sodium excretion was 44mmol/24h at the end of the low sodium diet and 162mmol/24h at the end of the high sodium diet respectively.…”

“…In a 2008 paper they used this new technique of urinary exosome analysis with western blot to quantify NCC expression in 8 subjects with FHHT and 8 family member controls, finding that expression of NCC was approximately 4 fold higher in FHHT subjects than related controls [187]. Other groups have used exosome analysis to quantify NCC expression in response to high and low salt diets [217], and in limited fashion pNCC in patients with primary aldosteronism [216]. A recent study looked at NCC and NKCC2 expression in patients with Gitelman and Bartter syndrome [228].…”

“…Corbetta et al used standard amounts of protein on their gels, but expressed density per mg of creatinine to standardise [228]. Esteva-Font et al normalised human samples to creatinine and animal samples to time in one study [217], as did the study by van der Lubbe et al [216]. Van der Lubbe reported subsequently that normalising to time, creatinine or total protein yielded similar results [248], and Isobe et al reported an experiment in which 5 different samples were collected at different time points in 3 subjects, but levels corrected for creatinine were almost the same within patients [193].…”