Thymol dietary supplementation mitigates microplastic-induced hematological disturbances, oxidative stress, immunosuppression, gene dysregulation, and histopathological alterations in Nile tilapia.

Abstract

Pollution of aquatic bodies with microplastics is a main concern endangering aquatic life and aquaculture. This study highlights the potential protective benefits of thymol (TML) supplementation against polystyrene microplastics (PS-MPs) exposure in Oreochromis niloticus (Nile tilapia). Over a 60-d, fish (n = 160; 27.62 ± 0.20 g) were split into four groups (40 fish/group; 4 replicates per group). The control (C) and TML groups were consumed basal diets augmented with 0 and 2 g TML/kg without exposure to PS-MPs. Conversely, the PS-MPs and TML + PS-MPs groups received the same diets as the C and TML groups and were exposed to 0.1 mg/L PS-MPs. PS-MPs exposure induced hematological abnormalities (reduced red blood cells count, hemoglobin, packed cell volume, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, and white blood cells and their differential counts, while increasing mean corpuscular volume). Additionally, PS-MPs increased malondialdehyde and decreased immunological (nitric oxide, complement 3, and lysozyme) and antioxidant (superoxide dismutase, catalase, glutathione reductase, and reduced glutathione) responses. PS-MPs elevated serum inflammatory markers (tumor necrosis factor-α and interferon-gamma) and caused pathological alterations in the spleen. The pro-inflammatory cytokines (tumor necrosis factor-α, interferon-gamma, interleukin-1β, interleukin-6, and interleukin-8) and cellular stress kinases (p38 and mapk-1) expression were up-regulated, but anti-inflammatory cytokine (interleukin-10) was down-regulated as a result of PS-MPs exposure. Conversely, hematological, antioxidant responses, and immunological functions were considerably enhanced by TML supplementation. Additionally, TML enhanced the expression of anti-inflammatory cytokine while modulating the expression of pro-inflammatory cytokines and cellular stress kinases. As a result, TML may be considered a helpful nutritional additive for lessening the negative impacts of PS-MPs in Nile tilapia.