Composition of the Essential Oil Thymus schimperi and Evaluation of Its Acute and Subacute Toxicity in Wistar Albino Rats: In Silico Toxicity Studies
Authors: Adane Fentahun , Asres Kaleab , Ergete Wondwossen , Woldekidan Samuel , Abebe Abiy , Lengiso Boki , Seyoum Girma 
Published: July 2021

Background. In Ethiopian traditional medicine, the aerial part of Thymus schimperi is widely used to treat diseases such as gonorrhea, cough, liver disease, kidney disease, hypertension, stomach pain, and fungal skin infections. However, there is insufficient investigation on the toxic effect of the essential oil of T. schimperi. The aim of this study was, therefore, to evaluate the acute, subacute, and in silico toxicity of Thymus schimperi essential oil in the Wistar albino rats. Method. Essential oil of the aerial part of T. schimperi extracted by hydrodistillation was analyzed by GC-MS. The oil was subjected to toxicity studies. In the acute toxicity study, rats were randomly divided into seven groups (n = 5). The control group received only distilled water with 2% of tween 80, whereas the experimental groups received single doses of 300, 600, 900, 1200, 1500, and 2 000 mg/kg of the oil. In the subacute toxicity study, rats were randomly divided into four groups (n = 10). The control group received distilled water with 2% of tween 80, whereas the experimental groups received 65 mg/kg, 130 mg/kg, and 260 mg/kg of the oil orally for 28 days. At the end of the experiment, blood samples were collected for hematology and clinical chemistry evaluation. Gross pathology and histopathology of the liver and the kidneys were also evaluated. For the in silico toxicity study, PubChem CID numbers of GC-MS identified bioactive compounds in the essential oil of T. schimperi obtained from PubChem. Chemdraw (8.0) was used to construct two-dimensional structures of the compounds. The Swiss ADMET web tool was used to convert the two-dimensional structures into a simplified molecular-input line input system (SMILES). In addition, the toxicity parameters were predicted via vNN and ADMET servers. Results. In this study, the LD50 of the essential oil of T. schimperi was found to be 1284.2 mg/kg. According to the World Health Organization, the oil is classified as moderately hazardous in its oral administration. In the subacute toxicity study, rats showed no significant changes in behavioral indices, gross pathology, body weight, biochemical, and most hematological parameters. However, hematological profiles showed a significant decrement in WBC counts and a significant increment of MCV in high dose (260 mg/kg) groups as compared to the control group. Furthermore, no significant differences were observed between the control and essential oil-treated groups, observed in the gross histopathology of the liver and the kidneys. In the in silico toxicity study, all compounds derived from the essential oil showed no cardiac toxicity (h-ERG Blocker), AMES (Ames Mutagenicity), and cytotoxicity via ADMET and vNN-ADMET toxicity predictors. However, by using these servers, about 8.6% of the compounds showed hepatotoxicity, only 3.45% caused drug-induced liver injury, and only 1.75% were potentially toxic to the mitochondrial membrane. Conclusion. From the results of this study, oral administration of the essential oil T. schimperi up to a dose of 130 mg/kg is not harmful. However, in the high-dose (260 mg/kg) group, the WBC count was significantly decreased and the MCV was significantly increased. In the in silico toxicity study, most of the components of the oil were found to be nontoxic, although a few of the compounds showed hepatotoxicity and mitochondrial membrane potential toxicity. It is, therefore, essential to conduct chronic toxicity of the essential oil as well as its components, which showed toxicity in the in silico study before using preparations containing the essential oil of T. schimperi.