Protective Action of Cannabidiol on Tiamulin Toxicity in Humans—In Vitro Study

The growing awareness and need to protect public health, including food safety, require a thorough study of the mechanism of action of veterinary drugs in consumers to reduce their negative impact on humans. Inappropriate use of veterinary drugs in animal husbandry, such as tiamulin, leads to the appearance of residues in edible animal tissues. The use of natural substances of plant origin, extracted from hemp (Cannabis sativa L.), such as cannabidiol (CBD), is one of the solutions to minimize the negative effects of tiamulin. This study aimed to determine the effect of CBD on the cytotoxicity of tiamulin in humans. The cytotoxic activity of tiamulin and the effect of its mixtures with CBD were tested after 72 h exposure to three human cell lines: SH-SY5Y, HepG2 and HEK-293. Cytotoxic concentrations (IC50) of the tested drug and in combination with CBD were assessed using five biochemical endpoints: mitochondrial and lysosomal activity, proliferation, cell membrane integrity and effects on DNA synthesis. Oxidative stress, cell death and cellular morphology were also assessed. The nature of the interaction between the veterinary drug and CBD was assessed using the combination index. The long-term effect of tiamulin inhibited lysosomal (SH-SY5SY) and mitochondrial (HepG2) activity and DNA synthesis (HEK-293). IC50 values for tiamulin ranged from 2.1 to >200 µg/mL (SH-SY5SY), 13.9 to 39.5 µg/mL (HepG2) and 8.5 to 76.9 µg/mL (HEK-293). IC50 values for the drug/CBD mixtures were higher. Reduced levels of oxidative stress, apoptosis and changes in cell morphology were demonstrated after exposure to the mixtures. Interactions between the veterinary drug and CBD showed a concentration-dependent nature of tiamulin in cell culture, ranging from antagonistic (low concentrations) to synergistic effects at high drug concentrations. The increased risk to human health associated with the presence of the veterinary drug in food products and the protective nature of CBD use underline the importance of these studies in food toxicology and require further investigation.