Repeated-dose toxicity and toxicokinetic study of isobutylparaben in rats subcutaneously treated for 13 weeks

Parabens have historically served as antimicrobial preservatives in a range of consumables such as food, beverages, medications, and personal care products due to their broad-spectrum antibacterial and antifungal properties. Traditionally, these compounds were believed to exhibit low toxicity, causing minimal irritation, and possessing limited sensitization potential. However, recent evidence suggests that parabens might function as endocrine-disrupting chemicals (EDCs). Consequently, extensive research is underway to elucidate potential human health implications arising from exposure to these substances. Among these parabens, particular concerns have been raised regarding the potential adverse effects of iso-butylparaben (IBP). Studies have specifically highlighted its potential for inducing hormonal disruption, significant ocular damage, and allergic skin reactions. This study aimed to evaluate the prolonged systemic toxicity, semen quality, and estrus cycle in relation to endocrine disruption endpoints, alongside assessing the toxicokinetic behavior of IBP in Sprague-Dawley rats following a 13-week repeated subcutaneous administration. The rats were administered either the vehicle (4% Tween 80) or IBP at dosage levels of 2, 10, and 50 mg/kg/day for 13 weeks. Blood collection for toxicokinetic study was conducted on three specified days: day 1 (1st), day 30 (2nd), and day 91 (3rd). Systemic toxicity assessment and potential endocrine effects were based on various parameters including mortality rates, clinical signs, body weights, food and water consumption, ophthalmological findings, urinalysis, hematological and clinical biochemistry tests, organ weights, necropsy and histopathological findings, estrus cycle regularity, semen quality, and toxicokinetic behavior. The findings revealed that IBP induced local irritation at the injection site in males at doses ≥ 10 mg/kg/day and in females at 50 mg/kg/day; however, systemic toxicity was not observed. Consequently, the no-observed-adverse-effect level (NOAEL) for IBP was determined to be 50 mg/kg/day in rats of both sexes, indicating no impact on the endocrine system. The toxicokinetics of IBP exhibited dose-dependent systemic exposure, reaching a maximum dose of 50 mg/kg/day, and repeated administration over 13 weeks showed no signs of accumulation.

Pharmacokinetic profile of propyl paraben in humans after oral administration

Parabens are commonly used as antimicrobial preservatives in consumer products. Because of their possible endocrine-disrupting activities, their safety has become a public concern. Although pharmacokinetic studies on parabens have been conducted in animals, limited information exists on their pharmacokinetic profiles in humans. In the present study, we determined the pharmacokinetic characteristics of propyl paraben (PP) in humans following a single oral administration of 0.6 mg/kg bw of deuterium labeled-PP. We also conducted experiment with similar design but different exposure amount (2.5 mg/kg bw) to verify the validity of the model to be developed. Blood and urine were collected at several intervals over the course of 48 h to measure levels of PP and its metabolites (conjugates and hydrolysates) in 12 male volunteers. The unconjugated parent compound (free PP), glucuronide and sulfate conjugates, p-hydroxybenzoic acid, and p-hydroxyhippuric acid were measured using HPLC-MS/MS. It was found that PP was rapidly absorbed via ingestion within 2 h and quickly eliminated (terminal half-life, 2.9 h). The fraction of administered dose excreted in the urine was 0.05% for free PP, 8.6% for total PP (free + conjugates), 23.2% for p-hydroxyhippuric acid, and 7.0% for p-hydroxybenzoic acid. Utilizing this pharmacokinetic profile, we successfully constructed a multi-compartment model where the disposition of PP was well described with two compartments and that of its metabolites was explained with first-order reactions. The present pharmacokinetic model provides insights into the kinetic properties of the disposition of PP and its metabolites in humans, and it can be used for risk assessment with biomonitoring of PP.