TOXICOLOGICAL EFFECTS OF THYMOL and Ocimum gratissimum L. OIL IN ALBINO RATS

Abstract

There is a progressive shift from the use of synthetic pesticides to botanical pesticides because of the problems of toxicity to the environment, non-target organisms and most importantly negative effects on human health. However, to reduce the burden of pests control and management, there is a need for continuous research to establish the safety of these botanicals on the environment and human health. In this study, acute and sub-chronic toxicity of the essential oil of Thymol and Ocimum gratissimum, Linn., Lamiaceae (Ocimum oil), were investigated using albino rats. The acute oral toxicity study was performed according to guidelines of Organisation for Economic Cooperation and Development (OECD), Guideline 420, using fixed doses of 5, 50, 300, and 2000 mg/kg body weight (bw). The animals were observed individually after administration of the doses, for acute toxicity signs and behavioural changes. Toxic signs including twitching, disturbed fur, itching and weakness were recorded for 14 days post treatment. The sub-chronic toxicity study was also carried out with six test groups each consisting of five animals. Groups I and II were administered olive oil (negative control) and 2,2-dichlorovinyl dimethyl phosphate (DDVP; standard), respectively while groups III-VI were administered 1.33 and 2.65mg/kg bw of thymol, and 55.00 and 110.00mg/kg bw of O. gratissimum oil. Blood samples were collected for analysis at the end of the 28-day treatment period. Results obtained showed that the lethal doses 50 (LD50) from probit analyses were 26.50 and 1100.00mg/kg for Thymol and Ocimum oil, respectively. In the sub-chronic toxicity study, all the rats in each of the treatment groups except the thymol groups recorded geometric increase in their weekly weight. However, the % weight gain results showed that the rats administered olive oil (negative control) recorded the highest % weight gain value (73.78±0.86g), followed by the animals administered 55mg/kg bw O. gratissimum essential oil (64.93±9.00g), while the animals administered 1.33mg/kg bw of thymol recorded the least % weight gain value (19.13±3.58g). Data analyses of serum biochemical markers; Alanine Aminotransferase (ALT), Alkaline Phosphatase (ALP), Aspartate Aminotransferase (AST), Total Protein (TP), Urea, and Creatinine showed significant differences between control and treated groups. These revealed that both Thymol and Ocimum oil are capable of inducing liver and kidney injury on persistent administration. Elevated levels of ALT, AST, ALP and TP in circulation were indicative of a hepatic and renal injury after the administration of 1.33mg/kg (AST-182.90±14.72U/l; ALP-362.20±32.13U/l; ALT-78.02±6.17U/l; TP-8.06±0.22g/dl), 2.65mg/kg (AST-297.20±32.45U/l; ALP-328.89±27.46U/l; ALT-61.76±22.32 U/l; TP-9.47±0.22g/dl) bw of thymol and 110mg/kg bw (AST-258.86±9.49U/l; ALP-453.32±57.95U/l; ALT-123.13±9.99 U/l; TP-9.41±1.18 g/dl) of Ocimum oil. However, only 55mg/kg bw of Ocimum oil was observed not to inhibit the activities of these markers in the rats (AST-162.92±5.10U/l; ALP-211.26±3.06U/l; ALT-53.73±6.17U/l; TP-7.16±0.23 g/dl), suggesting it to be safe, followed by DDVP (AST-188.98±18.76 U/l; ALP-241.59±20.00 U/l; ALT-72.58±4.66U/l; TP-9.28±0.60g/dl) while Thymol showed the highest toxic effect. Based on the results of this study, 55.00 mg/kg concentration of Ocimum oil suggests to be safe.