Biological activity studies on some Sideritis L. species

In this thesis, seven endemic Sideritis species growing in Turkey. S. arguta Boiss. & Heldr., S. brevibracteata P.H. Davis, S. congesta P.H. Davis & Hub.-Mor., S. hololeuca Boiss. & Heldr., S. rubriflora Hub.-Mor., S. stricta Boiss. & Heldr. apud Bentham, ve S. tmolea P.H.Davis were investigated for their in vitro tyrosinase (TYR) and cholinesterase (ChE) inhibitory activities as well as total phenolic content and DPPH• radical scavenging effects. Methanolic (MeOH) extracts were prepared from the aerial parts of plants and the highest total phenolic content was found in S. stricta (253.53 ± 4.37 GAE/g) while the highest DPPH• radical scavenging activity was detected in S. arguta (IC50=20.37 ± 0.32 μg/mL). Considering the inhibitory effects on acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes associated with Alzheimer's disease (AD), S. rubriflora and S. stricta showed the highest inhibition values against AChE (Inhibition%=52.855 ± 1.923) and BChE (Inhibition%=41.275±1.949), respectively. In the experiment of inhibition of the TYR enzyme, associated with Parkinson's disease (PD), it was determined that S. stricta had the highest inhibitory effect (IC50=288.5 ± 9.17 µg/mL). Following S. stricta, S. congesta (IC50=895.45 ± 7.83 µg/mL) and S. hololeuca (IC50=1565.25 ± 17.59 µg/mL) exhibited significant TYR inhibitory effects. Phenolic content, antioxidant, TYR, AChE and BChE inhibitory properties showed that Sideritis species are important natural resources that can be utilized in the pharmaceutical, cosmetics and food industries.