Acute oral toxicity study of Thymus serrulatus and Thymus schimperi from Ethiopia

Abstract

Thymus serrulatus and Thymus schimperi both endemic to Ethiopia are used by the public as tea and food additives. They are claimed to have some sort of toxicity. However, no toxicity test has been conducted to date. So the present study aimed to test the acute oral toxicities of their Essential Oils (EOs). T. serrulatus was collected from Ofla (Ofl), Alamata (Ala), and Yilmana Densa (Yil) and T. schimperi from Tarmaber (Tar), Butajira (Buta), and Bale (Bal). The control group (Group I) mice were administered with calculated amounts of 0.1% Tween-80 in normal saline. Experimental group (Groups II to VI), on the other hand, were delivered with 2000 μL/Kg body weight of Ofl, Ala, Yil, Tar, Buta and Bal EOs respectively. Treated and control mice were observed, and changes were recorded for 14 days. On the 14th day, after mice were humanely killed by heart puncture method, their organs were weighed, organ to body weight ratios were calculated and packed cell volumes (PCVs) were determined. Growth rate decrease was observed in mice treated with Yil and Buta EOs (carvacrol chemotypes) than in those treated with the thymol chemotypes (Ofl, Ala, Tar, and Bal). The organ to body weight ratios of the control group were either significantly higher than or comparable to that of the treatment groups implying that the EOs had no any inflammatory effects on the organs. The % PCVs of mice treated with the EOs were either significantly higher than or comparable to the control mice. The median lethal dose (LD50) of each EO was between 2000 μL/kg to 5000 μL/kg body weight. The LD50 values of the dry weights of thyme were calculated based on their EO yields that were approximated to be around 278g /kg bw (Bal), 313g /kg bw (Yil, Tar, and Buta) and 500g /kg bw (Ofl and Ala). Since the aerial parts, not the EOs, of thyme are used in the form of tea and food additives (not their EOs), this value is so high that these plants are not toxic. However, cautions should be taken for vulnerable groups.

Key words: Acute Toxicity, Thymus serrulatus, Thymus schimperi, Essential oils