Cytotoxic effects of oxytetracycline residues in the bones of broiler chickens following therapeutic oral administration of a water formulation

Abstract

Tetracyclines, which represent one of the most commonly used antibiotics for poultry, are known to be deposited in bones, where they can remain, despite the observation of appropriate withdrawal times. The aim of the study was to determine the concentration of oxytretracycline (OTC) residues in the bone and muscle of chickens, following the oral administration of a commercially available liquid formulation, and to test their cytotoxic effects on an in vitro cell culture model. Seventy-two 1-day-old broiler chickens were randomly allotted into 2 groups (control and treated animals). OTC (40 mg/kg BW) was administered via drinking water during the 1 to 5 and 20 to 25 days of life periods. At the end of the trial, the birds were slaughtered and the OTC residues in the target tissues were measured by means of liquid chromatography (LC) - tandem mass spectrometry (MS/MS). Cytotoxicity was assessed by evaluating the pro-apoptotic effect of the bone residues on the K562 erythroleukemic line and on the peripheral blood mononuclear cells (PBMC). In all the animals, the OTC residues in the muscle were far below the established MRL of 100 μg/kg. The OTC levels in the bones of the treated animals were instead found in the parts per million (ppm) range. Cell cytotoxicity was assessed by evaluating the pro-apoptotic effect of OTC bone residues on the haematopoietic cell system. This in vitro system has revealed a significant pro-apoptotic effect on both the K562 cell line and PBMC cultures. This result suggests potential human and animal health risks due to the entry of tetracycline residues contained in the bones of treated livestock into the food-chain. This could be of concern, particularly for canine and feline diets, as meat, bone meal, and poultry by-products represent some of the main ingredients of pet foods, especially in the case of dry pet food. Further studies are needed to define the underlying mechanisms of cytotoxicity and to evaluate the in vivo toxicological implications due to the observed in vitro effects.

Nutrition: From the First Medicine to the First Poison

“…This antibiotic, apparently harmless to chickens, turkeys, pigs, and cows, becomes unexpectedly toxic once bound to the bone, promoting apoptosis and inlammatory processes related to the increased pro-inlammatory cytokine release. The overall result is the onset of several immune-mediated pathologies in dogs and cats [10,14,24]. It is worth noting that a rapid disappearance of clinical symptoms (otitis, conjunctivitis, keratitis, gingivitis, stomatitis, dermatitis, hot spot, pyoderma, gastritis, enterocolitis, colitis, enteritis, nephritis, cystitis, pancreatitis, and other inlammatory processes) with a privation diet without oxytetracycline and without therapy is a clear demonstration of our researches.…”

“…Therefore, we claim that the immune system is absolutely involved in the inlammatory and deregulatory process induced by OTC rather than in the allergic one [10,14].…”

“…It is worth noting that a rapid disappearance of clinical symptoms (otitis, conjunctivitis, keratitis, gingivitis, stomatitis, dermatitis, hot spot, pyoderma, gastritis, enterocolitis, colitis, enteritis, nephritis, cystitis, pancreatitis, and other inlammatory processes) with a privation diet without oxytetracycline and without therapy is a clear demonstration of our researches. Thus, OTC toxicity is exerted through apoptosis induction and interferon-γ release [7,10]. We just listed that there are many inlammatory and reactive processes induced by OTC (generally those related to the intolerances), which can involve each organ.…”

“…Moreover, current regulatory authorities do not contemplate the evaluation of bone because considered not eatable, while widely present in most of meat meals [10].…”

“…It is important to point out that in vitro experiments showed a cytotoxicity of OTC even at lower concentrations with respect to minimal residual limits [7,10,12].…”