Angiotensin I-converting enzyme in isolated human glomeruli.

Area of Science:

• Nephrology
• Biochemistry
• Pharmacology

Background:

• The glomerulus is a key site for kidney function.
• Angiotensin I-converting enzyme (ACE) plays a critical role in the renin-angiotensin system.
• The presence and activity of ACE within human glomeruli require detailed investigation.

Purpose of the Study:

• To quantify Angiotensin I-converting enzyme (ACE) activity in isolated human glomeruli.
• To characterize the binding of a novel ACE inhibitor, S9780, to human glomeruli.
• To confirm the identity of the ACE binding site in human glomeruli.

Main Methods:

• Measurement of ACE activity using hippurylhistidylleucine substrate in isolated human glomeruli.
• Competitive inhibition assays with S9780, S9490, and Captopril.
• Radioligand binding studies using [3H]S9780 to determine binding affinity (Kd) and site density.
• Immunohistochemical validation using anti-human ACE antibodies.

Main Results:

• Significant ACE activity was detected in human glomeruli (2.2 +/- 0.47 mIU/mg protein).
• The novel ACE inhibitor S9780 demonstrated potent inhibition (85% at 0.3 microM) and specific binding to glomeruli (Kd = 23 nM, 83 fmol/mg).
• Binding was inhibited by anti-ACE antibodies, confirming the target's identity.

Conclusions:

• Angiotensin I-converting enzyme (ACE) is demonstrably present and active within human adult glomeruli.
• The novel inhibitor S9780 exhibits specific binding to glomerular ACE, suggesting potential therapeutic applications.
• These findings provide direct evidence for glomerular ACE localization and offer insights into its role in renal physiology.