Clinical pharmacokinetic evaluation of Withania somnifera (L.) Dunal root extract in healthy human volunteers: A non-randomized, single dose study utilizing UHPLC-MS/MS analysis

Ethnopharmacological relevance: Withania somnifera (L.) Dunal; (Solanaceae), commonly known as Ashwagandha, is one of the most significant medicinal herbs in 'Ayurveda', a traditional Indian medicine used for centuries with evidence in scriptures. Ashwagandha was mentioned in old Ayurvedic medical literature such as Charaka Samhita and Sushruta Samhita for improving weight and strength, with multiple citations for internal and exterior usage in emaciation and nourishing the body. Ethnopharmacological evidence revealed that it was used to relieve inflammation, reduce abdominal swelling, as a mild purgative, and treat swollen glands. The root was regarded as a tonic, aphrodisiac, and emmenagogue in the Unani tradition of the Indian medicinal system. Further, Ashwagandha has been also described as an Ayurvedic medicinal plant in the Ayurvedic Pharmacopoeia of India extending informed therapeutic usage and formulations. Despite the widespread ethnopharmacological usage of Ashwagandha, clinical pharmacokinetic parameters are lacking in the literature; hence, the findings of this study will be relevant for calculating doses for future clinical evaluations of Ashwagandha root extract.

Aim: This study aimed to develop a validated and highly sensitive bioanalytical method for quantifying withanosides and withanolides of the Ashwagandha root extract in human plasma to explore its bioaccessibility. Further to apply a developed method to perform pharmacokinetics of standardized Withania somnifera (L.) Dunal root extract (WSE; AgeVel®/Witholytin®) capsules in healthy human volunteers.

Methods: A sensitive, reliable, and specific ultra-high pressure liquid chromatography-mass spectrometry (UHPLC-MS/MS) method was developed and validated for the simultaneous quantification of five major withanosides and withanolides (withanoside IV, withanoside V, withanolide A, withaferin A, and 12-deoxy-withastramonolide) in human plasma. Further for the study, eighteen healthy male volunteers (18-45 years) were enrolled in a non-randomized, open-label, single period, single treatment, clinical pharmacokinetic study and given a single dose (500 mg) of WSE (AgeVel®/Witholytin®) capsules containing not less than 7.5 mg of total withanolides under fasting condition. Later, pharmacokinetic profiles were assessed using the plasma concentration of each bioactive constituent Vs. time data.

Results: For all five constituents, the bioanalytical method demonstrated high selectivity, specificity, and linearity. There was no carryover, and no matrix effect was observed. Furthermore, the inter-day and intra-day precision and accuracy results fulfilled the acceptance criteria. Upon oral administration of WSE capsules, C_max was found to be 0.639 ± 0.211, 2.926 ± 1.317, 2.833 ± 0.981, and 5.498 ± 1.986 ng/mL for withanoside IV, withanolide A, withaferin A, and 12-deoxy-withastramonolide with T_max of 1.639 ± 0.993, 1.361 ± 0.850, 0.903 ± 0.273, and 1.375 ± 0.510 h respectively. Further, withanoside V was also detected in plasma; but its concentration was found below LLOQ.

Conclusion: The novel and first-time developed bioanalytical method was successfully applied for the quantification of five bio-active constituents in human volunteers following administration of WSE capsules, indicating that withanosides and withanolides were rapidly absorbed from the stomach, have high oral bioavailability, and an optimum half-life to produce significant pharmacological activity. Further, AgeVel®/Witholytin® was found safe and well tolerated after oral administration, with no adverse reaction observed at a 500 mg dose.