ETHNOBOTANY, PHYTOCHEMISTRY, AND TOXICITY OF ALOE SPECIES FROM EAST AND SOUTH OF THE GREAT RIFT VALLEY IN ETHIOPIA

Abstract

Interest in the ethnomedicinal and biocultural values, and phytochemical profile of Aloe species have been raise over the years, due to its popularity as an ingredient in pharmaceuticals, cosmetic formulations, and food supplements. In view of the broad number of Aloe species, 560 species and 21 infraspecific taxa, only few have been cultivated and commercialized at the global level and none from the 46 Ethiopian Aloe species with 67.3% endemism. This might be due to the limited knowledge of their valuable bioactive compounds and safety concerns since some species have been reported as potentially toxic. Therefore, ethnobotanical investigation, phytochemical characterization, quantification, and toxicological evaluation were conducted on targeted Aloe species of Ethiopia that could allow exploitation of enormous potential of the Genus for emerging cosmetic and pharmaceutical industries in the country. A total of 210 respondents (152 men and 58 women) were involved to provide information in the analysis of ethnomedicinal and bio-cultural values. Interviews, focus group discussion (FGD), and guided field walks were methods used to retrieve the knowledge. Relative frequency of citation (RFCs), informants’ consensus factor (icF), use value (UVs), relative importance index (RIs), and cultural value index (CV) were analyzed. Non-parametric Kruskal Wallis and Wilcoxon tests were performed using R software. Phytochemical profiles of 17 Aloe species were quantified using fully automated high-performance thin layer chromatography (HPTLC) and ultra-high pressure liquid chromatography–mass spectrometry (UHPLC-MS) coupled with ultraviolet-photodiode array detector (UV-PDAD). Data were analyzed using visionCATS and Masslynx (version 4.2) softwares. Oral acute toxicity test from leaf exudates of 17 Aloe species were conducted using Swiss albino mice (n=5/cage) following OECD 423 guide. A single oral dose of 300 and 2000mg/kg body weight at a rate of 10 mL/kg administered and major toxicity signs were monitored; and relative body and organs weights were measured on a daily base for 14 days. Data were analyzed using one-way ANOVA followed by Tukey’s post hoc test for multiple comparisons. Twenty-three Aloe species were recorded in the study areas with 196 use-reports (UR) and 2158 citations, grouped into six major use categories (NUC=6). Medicinal use categories accounted for 149 use-reports (76%) with 1607 citations. Aloe megalacantha subsp. alticola, A. trichosantha subsp. longiflora and A. calidophila were species with the highest numbers of UR (23, 20 and 18, respectively). Higher proportion of medicinal UR (87%, 75% and 61.1% respectively) was recorded for all the three species than other uses. Aloe calidophila has highest values in all indices UV (11.72), RFC (0.68), RI (0.89), and CV (6.2). With regard to use per plant parts, leaf exudate accounted for 111 UR (49.1%) of which 92.9% was used for xix medicinal purposes. Aloe retrospiciens and A. ruspoliana were reported poisonous to carnivores. Fic values of the six major use categories ranged from 0.86 to 0.22. Elderly people (>60) had better knowledge than 25-40 and 41-60 age groups (Kruskal-Wallis chi-squared=12.17, df=3, p=0.006) and there was a significant difference in depth of ethnomedicinal knowledge between age groups (p< .001). The UHPLC-MS chromatogram of 14 Aloe species resulted in 56 peaks corresponds to compounds among which 35 (62.5%) were isolated and characterized. Anthrones and chromones were found dominant compound classes accounting for 23 compounds (65.7%) among the isolated and characterized compounds. The most common compounds were aloin A/B isolated from 11 species, aloinoside A/B from 11 species, and microdontin A/B from eight species. In addition, a number of unique compounds like, 7-O-methylaloesin, trihydroxy octadecenoic acid, 7-hydroxy-8-O-methylaloin B, deacetyllitoraloin, 6'-O-coumaroyl aloesin, 7-O-methyl-2'-feruloylaloesin, 1-hexanol-pentosyl hexoside, 1-O-methylplicalaloside, isorabichromone, and caffeoyl ester of aloesin were isolated and characterized from Ethiopian endemic Aloe species. The phytochemical characterization of A. pirottae, A. megalacantha subsp. alticola, A. trichosantha subsp. longiflora were done and resulted in unique characteristic compounds. In acute oral toxicity test, mice groups treated with exudates of Aloe calidophila, A. trichosantha subsp. longiflora, A. megalacantha subsp. alticola, A. megalacantha subsp. megalacantha, A. otallensis, A. pubescens, A. rivae, A. rugosifolia, A. secundiflora, A. tewoldei and A. yavellana did not show any sign of toxicity at both dose levels. Median Lethal Oral Dose (LD50 value) of these groups was estimated to be >2000mg/kg body weight. Groups treated with A. harlana, A. mcloughlinii, A. pirottae and unidentified/AHU53 showed overt signs of toxicity and significance difference (P<.05) of percentage change in body weight, relative liver weight, and food consumption compared to control group. Aloe ruspoliana and A. retrospiciens treatment groups showed severe level of toxicity signs and mortality of mice at both doses, in which LD50 value was >300mg/kg body weight. These findings will assist emerging cosmetic and pharmaceutical industries in selecting specific Ethiopian Aloe species for resource exploitation through wide-scale farming in marginal and non-agricultural croplands suitable for Aloe cultivation.