Abstract
Rhamnus prinoides L’Herit (R. prinoides) has long been widely consumed as folk medicine in Kenya and other Africa countries. Previous studies indicated that polyphenols were abundant in genus Rhamnus and exhibited outstanding antioxidant and anti-inflammatory activities. However, there are very few studies on such pharmacological activities and the polyphenol profile of this plant up to now. In the present study, the antioxidant activities of the crude R. prinoides extracts (CRE) and the semi-purified R. prinoides extracts (SPRE) of polyphenol enriched fractions were evaluated to show the strong radical scavenging effects against 1,1-diphenyl-2- picrylhydrazyl radical 2,2-diphenyl-1-(2,4,6-trinitrophenyl) hydrazyl (DPPH) (0.510 ± 0.046 and 0.204 ± 0.005, mg/mL), and 2,2′-azinobis-(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) (0.596 ± 0.005 and 0.096 ± 0.004, mg/mL), respectively. Later, the SPRE with higher contents of polyphenols and flavonoids displayed obvious anti-inflammatory activities through reducing the NO production at the dosage of 11.11 − 100 μg/mL, and the COX-2 inhibitory activity with an IC50 value at 20.61 ± 0.13 μg/mL. Meanwhile, the HPLC-UV/ESI-MS/MS analysis of polyphenol profile of R. prinoides revealed that flavonoids and their glycosides were the major ingredients, and potentially responsible for its strong antioxidant and anti-inflammatory activities. For the first time, the present study comprehensively demonstrated the chemical profile of R. prinoides, as well as noteworthy antioxidant and anti-inflammatory activities, which confirmed that R. prinoides is a good natural source of polyphenols and flavonoids, and provided valuable information on this medicinal plant as folk medicine and with good potential for future healthcare practice.
Highlights
Rhamnus prinoides L’Herit (R. prinoides), belonging to family Rhamnaceae, and commonly known as dogwood or Gesho in Amharic, is widely distributed in many countries of eastern, central, and southern Africa [1]
Based on the yields of crude R. prinoides extracts (CRE) (11.72%) and semi-purified R. prinoides extracts (SPRE) (1.36%) to the R. prinoides powders, the higher total phenolic content (TPC) and total flavonoids content (TFC) values in SPRE in this study demonstrated the effective application of polyamide resin for the enrichment of the polyphenols
The CRE (352.25 ± 10.95 mg RE/g extract) and SPRE (958.21 ± 21.18 mg RE/g extract) in this study obtained from R. prinoides in Kenya communities presented higher TFC values than that of the methanol extract (51.17 mg quercetin equivalent (QE)/g extract), aqueous extract (24.09 mg QE/g extract) and traditional boiling aqueous extract (12.03 mg QE/g extract) of Rhamnus alaternus bark from Algeria [25], and ethyl acetate (EA) extract (108.03 ± 3.09 mg catechin equivalent (CE)/g extract) of Rhamnus lycioides leaves from Algeria [26]
Summary
Rhamnus prinoides L’Herit (R. prinoides), belonging to family Rhamnaceae, and commonly known as dogwood or Gesho in Amharic, is widely distributed in many countries of eastern, central, and southern Africa [1]. An in vitro anti-plasmodium study on many plants used in Kisii, Kenya, displayed that aqueous extracts from the root bark of R. prinoides exerted distinct antimalarial effects against both chloroquine (CQ)-sensitive and Plasmodium falciparum with an IC50 values less than 30 μg/mL [9]. In another effort on in vivo antimalarial activities in Kenya, the hot water extracts of R. prinoides root barks exhibited high chemo suppression of 51% at the dosage of 500 mg/kg in mice on the CQ-resistant Plasmodium berghei NK65. The sonicated aqueous extracts of R. prinoides root exhibited distinct acetylcholinesterase (ACE) inhibition with an IC50 value at 0.201 mg/mL, and showed potential utility in the treatment of Alzheimer’s disease [11]
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