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  • br Conclusion S chirata and ursolic acid showed very


    Conclusion S. chirata and ursolic 86 5 showed very less inhibition on both CYP3A4 and CYP2D6 isozymes which was insignificant as compared to their known inhibitors (ketoconazole and quinidine). The tested heavy metals and trace elements present in S. chirata were within the prescribed limit. The extract showed the inhibitory activity against two CYP450 isozymes (CYP3A4 and CYP2D6) in a dose dependent manner. Therefore it may be safe to use S. chirata traditionally in respect to two tested key CYP450 isozymes. Some factors (co-administration of herb and drug, mechanism based enzyme inhibition, undesirable interactions with proteins, enzyme etc.) need to be addressed in future for better understanding of herb-drug interaction.
    Conflict of interest
    Acknowledgment The authors would like to express their gratitude to the National Medicinal Plant Board (NMPB), Ministry of AYUSH (Ayurveda, Yoga, Unani, Siddha and Homeopathy), Government of India, New Delhi, India (F.No. Z.18017/187/CSS/R&D/WB-01/2009-10-NMPB) for providing financial support to School of Natural Product Studies, Jadavpur University, Kolkata for this work.
    Introduction Gamma-aminobutyric acid type A (GABAA) receptors are the major inhibitory neurotransmitter receptors in the central nervous system (CNS). Many CNS active drugs, such as benzodiazepines, exert their action via enhancement of the GABAergic neuronal inhibition. However, the therapy with GABAA modulatory drugs possesses various side-effects which largely result from their lack of GABAA receptor subtype selectivity. Therefore, drug discovery has been directed towards identifying subtype specific GABAA receptor modulators to overcome the limitations of existing drugs [1]. In a screening of natural products for GABAA modulatory properties, the alkaloid piperine was identified as a positive allosteric modulator [2]. However the most interesting aspects of this compound were that i) it interacted with a benzodiazepine-independent binding site which has not been identified until now and ii) was compliant with Lipinski’s rule of five, as shown by in silico calculations [2]. Given that piperine is also an activator of TRPV1 (transient receptor potential vanilloid type 1) receptors involved in pain signaling and thermoregulation [3], systematic structural modifications of the parent structure were carried out in several cycles of optimization, aiming at separating GABAA modulatory from TRPV1 activity. A first analog, SCT-66 (Fig. 1), did not activate TRPV1 receptors while maintaining GABAA receptor modulatory properties in vitro and in vivo[4]. Subsequently, a library of 76 piperine analogs was prepared and examined using Xenopus laevis oocytes and the two electrode voltage-clamp technique [5]. Among those, SCT-64 and SCT-29 showed the highest potency and efficacy at GABAA receptors, and anxiolytic activity in mice upon intraperitoneal administration [5]. Based on snapshot pharmacokinetic data, SCT-29 was selected for the next cycle of medicinal chemistry optimization [5]. All analogs synthesized up to this point contained a 1,3-benzodioxole moiety which is susceptible to metabolic degradation to an ortho-catechol that can be oxidized to a reactive ortho-quinone [6], [7]. Therefore, a library of 15 aryl-modified analogs was synthesized, of which LAU 397 and LAU 399 showed the highest efficacy and potency in vitro[8]. Given that to this point no experimental drug metabolism data had been recorded, we here evaluated metabolic stability and metabolite formation in microsomal incubations of piperine and selected analogs from the three cycles of optimization (SCT-29, LAU 397 and LAU 399) to guide further structural modifications. In addition, reaction phenotyping was carried out to identify major CYP450 isoenzymes involved in the oxidative metabolism of these compounds, and unbound fraction in whole blood was determined with the aid of rapid equilibrium dialysis. Furthermore, the hepatic extraction ratio was calculated to classify the compounds into low, medium, or high extraction categories.