Effect of zinc supplementation on immunotoxicity induced by subchronic oral exposure to glyphosate-based herbicide (GOBARA®) in Wistar rats

Abstract

Objectives: To evaluate the effect of zinc supplementation on immunotoxicity induced by subchronic oral exposure to glyphosate-based herbicide (GBH).

Methods: Sixty adult male Wistar rats randomly divided equally into six groups were exposed to GBH by gavage daily for 16 weeks with or without zinc pretreatment. Group DW rats received distilled water (2 mL/kg), group Z rats received zinc (50 mg/kg), and group G1 and G2 rats received 187.5 and 375 mg/kg GBH, respectively. Group ZG1 and ZG2 rats were pretreated with 50 mg/kg zinc before exposure to 187.5 and 375 mg/kg GBH, respectively. Tumor necrosis factor alpha (TNF-α) and immunoglobulin (IgG, IgM, IgE) levels were measured by enzyme-linked immunosorbent assay. Spleen, submandibular lymph node, and thymus samples were processed for histopathology.

Results: Exposure to GBH (G1 and G2) significantly increased serum TNF-α concentrations and significantly decreased serum IgG and IgM concentrations compared with the control levels. Moderate-to-severe lymphocyte depletion occurred in the spleen, lymph nodes, and thymus in the GBH-exposed groups. Zinc supplementation mitigated the immunotoxic effects of GBH exposure.

Conclusions: GBH exposure increased pro-inflammatory cytokine responses, decreased immunoglobulin production, and depleted lymphocytes in lymphoid organs in rats, but zinc supplementation mitigated this immunotoxicity.

Keywords: Glyphosate; cytokine; herbicide; immunoglobulin; immunotoxicity; subchronic toxicity; zinc supplementation.

Figure 1.

Effect of oral zinc pretreatment on serum TNF-α concentrations (a) and IL-1β concentrations (b) in rats orally exposed to glyphosate-based herbicide on daily basis for 16 weeks. Treatment groups: DW, control (2 mL/kg distilled water); Z, zinc chloride (50 mg/kg); G1, glyphosate (187.5 mg/kg); G2, glyphosate (375 mg/kg); ZG1, zinc chloride (50 mg/kg) with glyphosate (187.5 mg/kg); and ZG2, zinc chloride (50 mg/kg) with glyphosate (375 mg/kg). Letters indicate increases in the G1 (b, P = 0.0043) and G2 (a, P = 0.0426) groups compared with the DW group. TNF-α, tumor necrosis factor alpha; IL-1β, interleukin-1 beta.

Figure 2.

Effect of oral zinc pretreatment on serum immunoglobulin concentrations (IgG, IgM, IgE) concentrations in rats orally exposed to glyphosate-based herbicide daily for 16 weeks. Treatment groups: DW, control (2 mL/kg distilled water); Z, zinc chloride (50 mg/kg); G1, glyphosate (187.5 mg/kg); G2, glyphosate (375 mg/kg); ZG1, zinc chloride (50 mg/kg) with glyphosate (187.5 mg/kg); and ZG2, zinc chloride (50 mg/kg) with glyphosate (375 mg/kg). IgG: the letter (a) indicates decreases in the Z (P = 0.0130), G1 (P = 0.0142), and G2 (P = 0.0229) groups versus the DW group. IgM: letters indicate decreases in the G1 (a, P = 0.0139) and G2 (b, P = 0.0031) groups versus the DW group, a decrease in the G1 (a, P = 0.0243) group versus the Z group, and an increase in the ZG2 (b, P = 0.0455) group versus the G2 group. IgE: letters indicate decreases in the G1 (b, P = 0.001) and G2 (c, P = 0.0003) groups versus the ZG2 group, a decrease in the G1 (a, P = 0.0238) group versus the ZG1 group, and an increase in the ZG2 (a, P = 0.0287) group versus the ZG1 group. IgG, immunoglobulin G; IgM, immunoglobulin M; IgE, immunoglobulin E.

Figure 3.

Hematoxylin and eosin staining of tissues in rats treated with glyphosate-based herbicide daily for 16 weeks with zinc pretreatment. (a) Photomicrographs of the spleens of rats. No lymphocyte depletion was observed in the DW (i) and Z groups (ii), moderate lymphocyte depletion (ld) was detected in the G1 group (iii), severe lymphocyte depletion (ld) was observed in the G2 group (iv), and no lymphocyte depletion was detected in the ZG1 (v) and ZG2 groups (vi). (b) Photomicrographs of the submandibular lymph nodes of rats. Severe lymphocyte depletion (ld) was present in the G1 (iii) and G2 groups (iv), but no lymphocyte depletion was observed in the DW (i), Z (ii), ZG1 (v), and ZG2 groups (vi). (c) Photomicrographs of the thymi of rats. No lymphocyte depletion was detected in the DW (i), Z (ii), ZG1 (v), and ZG2 groups (vi), but moderate and severe lymphocyte depletion (ld) was detected in the G1 (v) and G2 groups (vi), respectively. Treatment groups: DW, control (2 mL/kg distilled water); Z, zinc chloride (50 mg/kg); G1, glyphosate (187.5 mg/kg); G2, glyphosate (375 mg/kg); ZG1, zinc chloride (50 mg/kg) with glyphosate (187.5 mg/kg); and ZG2, zinc chloride (50 mg/kg) with glyphosate (375 mg/kg).