Oxytetracycline-Protein Complex: The Dark Side of Pet Food

Background: Worldwide antibiotic abuse represents a huge burden, which can have a deep impact on pet and human health through nutrition and medicalization representing another way of antibiotic resistance transmission. Objective: We aimed our research to determine a possible complex formation between biological bone substrates, such as proteins, and Oxytetracycline (OTC), an approved antibiotic for use in zootechny, which might determine a toxic effect on K562 cells. Method: Cell viability and HPLC-ESI/QqToF assays were used to assess potential toxicity of bone extract derived from OTC-treated chickens according to standard withdrawal times and from untreated chickens at 24, 48 and 72h of incubation. Results: Cell culture medium with ground bone from chickens reared in the presence of OTC (OTC-CCM) resulted significantly cytotoxic at every incubation time regardless of the bone concentration while cell culture medium with ground bone from chickens reared without OTC (BIO-CCM) resulted significantly cytotoxic only after 72h of incubation. HPLC-ESI/QqToF assay ruled out the possible presence of OTC main derivatives possibly released by bone within culture medium until 1 μg/mL. Conclusion: The presence of a protein complex with OTC is able to exert a cytotoxic effect once released in the medium after 24-48h of incubation.