Bioactivity of Essential Oils of Thymus Serrulatus and Thymus Schimperi from Ethiopia: Hepatoprotective, Dental Caries Protective, Mosquitocidal and Acute Oral Toxicity
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Date
2016-01
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Addis Ababa University
Abstract
This study was conducted to investigate; the ethnobotanical information, chemical composition, bioassays (antibacterial, mosquitocidal, larvicidal, and oviposition deterrent, hepatoprotective) and acute oral toxicity of the essential oils (EOs) of Thymus species collected from six localities in Ethiopia. Ethnobotanical information was collected using semistructured questionnaires, antibacterial test using disk diffusion technique, mosquitocidal activity using fumigation test, hepatoprotective activity in male Wistar rats and acute oral toxicity in female albino mice. Thymus species collected from Ofla (Ofl), Alamata (Ala), and Yilmana Densa (Yil) were identified as Thymus serrulatus and those collected from Tarmaber (Tar), Butajira (Buta), and Bale (Bal) as Thymus schimperi. Both species which are endemic to Ethiopia are traditionally used to treat different illnesses like blood pressure, general pain syndrome, liver diseases, influenza, abdominal pain, and against intestinal parasites. The major compounds in Ofl EO were thymol (49.55%), carvacrol (36.34%), and p-cymene (3.06%). In Ala EO, thymol was the dominant component (65.63%) followed by carvacrol (6.68%) and thymol methyl ether (6.55%). Yil EO on the other hand had carvacrol (80.84%), thymol (6.52%), and p-cymene (3.65) as its major components. Tar was the EO with thymol (48.84%), carvacrol (42.12%), and linalool (2.97%) as its major components. In the same way, the major components of Buta EO were (71.83%), thymol (15.77%), and p-cymene (3.75%). The predominant components of the last EO, Bal were thymol (53.57%), carvacrol (34.55%), and p-cymene (3.20%). Four of the EOs (Ofl, Ala, Tar, and Bal) were found to be thymol and the rest two (Yil and Buta) carvacrol chemotypes. All the essential oils inhibited cariogenic bacteria (Streptococcus mutans and Lactobacillus). The minimum inhibitory
concentration (MIC) and minimum bactericidal concentration (MBC) of the Bal EO against S. mutans was found to be 0.25 μL/mL and the MIC/MBC of all the rest EOs against this bacterium was 0.5 μL/mL. On the other hand, the MIC and MBC of all the EOs against Lactobacillus was at the dose of 0.5 μL/mL. Paracetamol-induced hepatotoxicity in Wistar rats was prevented by the application of EOs at 200 μL/Kg body weight. This was demonstrated by the reduced serum levels of marker enzymes; alkaline phosphatase (ALP), alanine aminotransferase (ALT), and aspartate aminotransferase (AST). In addition, it was seen from the histopathological tests that Thymus EOs prevented paracetamol-induced necrosis. Thymus EOs too showed larvicidal, mosquitocidal (fumigation test) and oviposition detterent activities against the mosquito Anophelus arabiensis. The essential oil concentrations that resulted in mortality of 50% of larvae (LD50) were: (60.75 μL/L, Ala); (44 μL/L, Yil); and (41.75 μL/L, Tar). The LD50 values for the fumigation test, on the other hand, were: (17.19 μL/L, Ala); (14.92 μL/L, Yil); and (13.20 μL/L, Tar). The 200 μL/L, 100 μL/L, and 50 μL/L doses of Tar; the 200 μL/L and 100 μL/L doses of Ala; and the 200 μL/L dose of Yil resulted in complete oviposition detterent activity. Except some irritation responses, all the test EOs were found to be non-toxic to mice and had LD50 values in the range of 2000μL/kg body weight to 5000μL/kg body weight with corrected acute toxicity point (LD50) estimate of 2500μL/kg body weight. In conclusion, the different chemotypes of T. serrulatus and T. shimperi EOs resulted in antibacterial activities, hepatoprotective activities, mosquitocidal activities and were not toxic.
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Keywords
Bioactivity, Toxicity, Thymus Serrulatus, Thymus Schimperi, Hepatoprotective, Caries Causing (Cariogenic) Bacteria, Mosquitocidal.