Protective Effect of Thymus serrulatus Essential Oil on Cadmium-Induced Nephrotoxicity in Rats, through Suppression of Oxidative Stress and Downregulation of NF-κB, iNOS, and Smad2 mRNA Expression

The purpose of the research was to examine the protective effect of essential oil from Thymus serrulatus Hochst. ex Benth. (TSA oil) against cadmium (Cd)-induced renal toxicity. The experimental protocol was designed using 30 healthy adult Wistar albino rats allocated into five groups containing six animals in each group. Group 1 was treated as normal control and groups 2, 3, 4, and 5 were treated with cadmium chloride (CdCl2, 3 mg/kg, IP) for 7 days. Group 3 was also treated with silymarin (100 mg/kg, PO) as a standard group, while groups 4 and 5 were administered with TSA oil at doses of 100 and 200 mg/kg PO, respectively. The nephrotoxicity was measured with various parameters such as kidney function markers, oxidative stress markers (glutathione (GSH) and malondialdehyde (MDA)), and messenger ribonucleic acid (mRNA) expression levels of inflammatory factors. The histological studies were also evaluated in the experimental protocol. The CdCl2-treated groups showed a significant increase in the levels of serum kidney function markers along with MDA levels in kidney homogenate. However, renal GSH level was found to be reduced significantly. It was found that CdCl2 significantly upregulated the nuclear factor levels of kappaB (NF-κB p65), inducible nitric oxide synthase (iNOS), and small mothers against decapentaplegic (Smad2) as compared to the normal control group. On the other hand, TSA oil significantly improved the increased levels of serum kidney function markers, non-enzymatic antioxidants, and lipid peroxidation. In addition, TSA oil significantly downregulated the increased expression of NF-κB p65, iNOS, and Smad2 in Cd-intoxicated rats. Moreover, the histological changes in the tissue samples of the kidney of Cd-treated groups were significantly ameliorated in the silymarin- and TSA-oil-treated groups. The present study reveals that TSA oil ameliorates Cd-induced renal injury, and it is also proposed that the observed nephroprotective effect could be due to the antioxidant potential of TSA oil and healing due to its anti-inflammatory action.