Increased urinary angiotensin-converting enzyme 2 in renal transplant patients with diabetes

Angiotensin-converting enzyme 2 (ACE2) is expressed in the kidney and may be a renoprotective enzyme, since it converts angiotensin (Ang) II to Ang-(1-7). ACE2 has been detected in urine from patients with chronic kidney disease. We measured urinary ACE2 activity and protein levels in renal transplant patients (age 54 yrs, 65% male, 38% diabetes, n = 100) and healthy controls (age 45 yrs, 26% male, n = 50), and determined factors associated with elevated urinary ACE2 in the patients. Urine from transplant subjects was also assayed for ACE mRNA and protein. No subjects were taking inhibitors of the renin-angiotensin system. Urinary ACE2 levels were significantly higher in transplant patients compared to controls (p = 0.003 for ACE2 activity, and p≤0.001 for ACE2 protein by ELISA or western analysis). Transplant patients with diabetes mellitus had significantly increased urinary ACE2 activity and protein levels compared to non-diabetics (p<0.001), while ACE2 mRNA levels did not differ. Urinary ACE activity and protein were significantly increased in diabetic transplant subjects, while ACE mRNA levels did not differ from non-diabetic subjects. After adjusting for confounding variables, diabetes was significantly associated with urinary ACE2 activity (p = 0.003) and protein levels (p<0.001), while female gender was associated with urinary mRNA levels for both ACE2 and ACE. These data indicate that urinary ACE2 is increased in renal transplant recipients with diabetes, possibly due to increased shedding from tubular cells. Urinary ACE2 could be a marker of renal renin-angiotensin system activation in these patients.

Urinary clearance of angiotensin II in Pekin ducks

To quantify the renal excretion of angiotensin II (AII) in birds, synthetic AII was intravenously infused into conscious Pekin ducks at rates of 5, 15 and 45 ng/kg/min for 30 min and the relationships between plasma and urine AII concentrations were monitored by radioimmunoassay. The infusions of AII produced dose-dependent elevations in the plasma concentrations of the hormone, however, urinary concentrations and excretion rates did not change significantly from the basal values of 11.6 +/- 1.2 pg/ml and 4.3 +/- 1.0 pg/min, respectively. The metabolic clearance rate of AII remained constant at each infusion dose (approximately 120 ml/min/kg). The urinary clearance rates (< 0.3 ml/min/kg) indicated that the fraction of AII cleared from the blood via the urine was less than 0.2%. Clearly, excretion of intact AII via this route is not a quantitatively important means of elimination for this hormone in birds.