Makindo Medical Notes

📖 About Angiotensin-Converting Enzyme (ACE)

• Biochemistry: ACE is a zinc-containing dipeptidyl carboxypeptidase.
• Genetics: Encoded by a single gene on chromosome 17.
• Distribution: Found on vascular endothelial cells (especially in lungs), renal epithelium, and other tissues.

⚙️ Physiological Action

• Converts angiotensin I → angiotensin II (potent vasoconstrictor, stimulates aldosterone release, ↑ BP).
• Most angiotensin I conversion occurs in the pulmonary endothelium due to large surface area.
• Also degrades bradykinin (a vasodilator). ACE inhibition therefore increases bradykinin → enhances nitric oxide (NO) release, vasodilation, but can cause dry cough or angioedema.

🧪 Measurement

• Reference range: typically < 40 mcg/L (varies by lab and method).
• Serum ACE can be affected by genetics, treatment (e.g., corticosteroids, ACE inhibitors), and comorbidities.
• Interpret in the clinical context — not diagnostic in isolation.

📊 Clinical Significance

Serum ACE is sometimes used as a supportive marker in diagnosis and monitoring of granulomatous disease, especially sarcoidosis. However, it has limited sensitivity and specificity and should never be used alone for diagnosis.

⬆️ Raised ACE Levels

• Granulomatous diseases: Sarcoidosis, Tuberculosis, Histoplasmosis, Coccidioidomycosis.
• Infections: HIV, Leprosy.
• Other conditions: Gaucher disease, Hyperthyroidism, Diabetes, Lymphoma, Asbestosis, Silicosis, COPD (variable).
• Normal variation: Some healthy individuals may have higher ACE levels without pathology.

⬇️ Low ACE Levels

• Medication effect: Corticosteroids or ACE inhibitors (reduce measurable ACE activity).
• Endocrine/metabolic: Hypothyroidism, Anorexia nervosa.
• Organ disease: Chronic liver disease, COPD (in some cases).

💊 Clinical Link — ACE Inhibitors

• Widely used in hypertension, heart failure, post-MI, and diabetic nephropathy.
• Mechanism: block conversion of angiotensin I → II, and prevent bradykinin breakdown → vasodilation, ↓ BP, renal protection.
• Adverse effects: dry cough, angioedema, hyperkalaemia, renal impairment.