The inhibitory effects of lycopene and thymoquinone on angiotensin converting enzyme from human plasma (An in vitro study)

Angiotensin converting enzyme (ACE, EC 3.4.15.1) is an important enzyme responsible for regulating blood pressure. Inhibition of this enzyme is an important treatment approach in the treatment of hypertension, and natural or synthetic ACE inhibitors are often used for this purpose. In this study, the preventive effect of two important antioxidant compounds, lycopene (LYC) and thymoquinone (TQ) on ACE activity in human plasma was investigated. Human plasma was used as ACE source. ACE activity was calculated absorbance at 345 nm after incubation for 30 minutes at 35 degrees C. TQ and LYC showed inhibitory effect on ACE activity. IC50 values for TQ and LYC were determined as 314 mu M and 182 mu M, respectively. Type of inhibition for TQ and lycopene from plot Line weaver-Burk was designated as noncompetitive inhibition. The Ki constants of TQ and LYC were determined to be 707 mu M and 167 mu M, respectively. It was concluded that TQ and LYC may have significant potential as ACE inhibitors.