The In Vitro Multifaceted Biological Activity of Catechins in Relation to Their Oxidation Potentials

In this study, the rank of multifaceted activity of catechin (C), epicatechin (EC), epigallocatechin (EGC), epicatechin-3-gallate (ECG) and epigallocatechin-3-gallate (EGCG) was addressed. Their antioxidant activity was determined by the differential pulse voltammetry (DPV), whereas their ability to inhibit angiotensin-converting enzyme (ACE) activity, acetylcholinesterase activity (AChE), and formation of the advanced glycation end-products (AGEs) was performed in a model system to show their importance against hypertension, Alzheimer-type dementia, and diabetic’s complication, respectively. The order of the antioxidant potential of catechins in comparision to gallic acid (GA) was EGCG > ECG > EC > EGC ≈ C > GA, whereas the order of the ACE inhibitory activity was EGCG > ECG > EGC > EC > C, thus indicating the importance of the structure–activity relationship. The correlation between IC50 for ACE inhibition of catechins and their antioxidant activity had the value r = −0.60. The order of the AChE enzyme inhibitory activity was EGCG ≈ EGC > ECG > EC > C, and the weak positive correlation between IC50 and the first anodic peak potential (Epa1) values was noted (r = 0.67). The ranking of the anti-AGE activities was EGCG ≈ ECG > EGC > EC > C, and a negative correlation between the inhibitory activity of catechins against AGE formation and their antioxidant activity was r = −0.82, whereas a positive correlation (r = 0.88) was noted between their first anodic peak potential (Epa1) values. The provided results expand our knowledge on the multifaceted activity of catechins, indicating EGCG and ECG as the most active antioxidants against inhibition of ACE and AChE as well as towards AGE formation.