Characterization, in vitro and in vivo biological activities of P. equisetiforme extract powder, and preformulation studies for hard gelatin capsules

Abstract

The aim of this study was to evaluate the influence of two extraction solvents, ethanol (EtOH) and water (AQ), on the chemical composition (HPLC-DAD and GC-MS) and in vitro biological properties of P. equisetiforme aerial parts. Biological activities included antixanthine oxidase (anti-XOD), antiacetylcholinesterase (anti-AChE), anti-5-lipoxygenase (anti-5-LOX), anti-α-glucosidase, anti-α-amylase, as well as cytotoxic activity was evaluated. Subsequently, the in vivo hepatoprotective effect of the bioactive extract was also assessed. Finally, we made powder capsules with two different excipients, microcrystalline cellulose (MCC) and starch, and proceeded to characterize each formulation to optimize hard gelatin capsules. The results revealed that the ethanolic extract is more active than the aqueous extract, notably in DPPH (IC₅₀ = 6.52 μg/mL), ABTS (IC₅₀ = 3.13 μg/mL) tests, anti-AChE (IC₅₀ = 15.63 μg/mL), and antidiabetic activities via the α-glucosidase (IC₅₀ = 5.96 μg/mL) and α-amylase (IC₅₀ = 21.19 μg/mL) enzymes. This extract is also the most concentrated in polyphenols (427.72 GAE/g DW) and flavonoids (36.43 RE/g DW). For the in vivo part, results showed that pretreatment with P. equisetiforme EtOH extract significantly attenuated nickel (Ni)-induced elevated liver marker and lipid levels in rats. In addition, antioxidant enzyme activities and TBARS levels were significantly corrected by pretreatment with EtOH extract. The starch-based (F1) and MCC-based (F2) capsules maintained a considerable amount of bioactivity, despite the pure extract exhibiting greater anti-α-glucosidase and antioxidant properties. The polyphenol content and bioactive characteristics of the extract were retained by both formulations, according to stability tests conducted over a 30-day period. The results obtained support the use of starch and MCC as suitable excipients for the stable and efficient encapsulation of the ethanolic extract of P. equisetiforme.