Aldose Reductase Inhibition by Orthosiphon stamineus Extracts and Constituents Suggests Antioxidant Potential

Aldose reductase (AR) plays a crucial role in the accumulation of oxidative factors that lead to oxidative stress-related neuroinflammation. This study aims to find a novel agent from natural sources that can inhibit AR.

Different extracts of Orthosiphon stamineus Benth (OS) leaves and its active constituents, eupatorin (EUP), rosmarinic acid (RA), sinensetin (SEN) and 3-hydroxy-5,6,7,4-tetramethoxyflavone (TMF), were used to identify the potential inhibition effect of AR. A new high-performance liquid chromatography (HPLC) method was developed to determine these phytochemicals using the Shimadzu LC-20AD HPLC system. In addition, the in vitro inhibition effect of OS ethanol extracts (95% and 50%) and OS components EUP, RA, and SEN was investigated in recombinant AR (AKR1B1).

In this study, the developed HPLC method was precise and accurate, and demonstrated clear separation of the four compounds-EUP, RA, SEN, and TMF-in the ethanolic extract. The contents of the four selected compounds-EUP, RA, SEN, and TMF-in 95% ethanolic extract were 2.35, 11.91, 0.94, and 0.18%, respectively. RA showed the highest concentration among the selected compounds, indicating that RA is the major constituent of this plant. The in vitro assay showed significant inhibition of the AR enzyme by RA and OS ethanol extracts 95% and 50% (IC₅₀: 41.42 µM; 63.42 µg/mL and 93.22 µg/mL, respectively).

The ethanolic extract of OS and RA could be a promising therapeutics option for the treatment of oxidative stress-related neuroinflammation disorders by inhibiting AR.