Safety and efficacy of ethoxyquin (6‐ethoxy‐1,2‐dihydro‐2,2,4‐trimethylquinoline) for all animal species

Determination of ethoxyquin by ultra-high performance liquid chromatography with tandem mass spectrometry and a Singapore survey of ethoxyquin residues in eggs, egg products and poultry

In this study, an advanced ultra-high performance liquid chromatography with tandem mass spectrometry (UPLC-MS/MS) method was developed for quantifying ethoxyquin (EQ). The approach employed a distinctive antioxidant added extraction step designed to prevent ethoxyquin decomposition and maintain analytical precision. This method effectively determines residue levels of EQ in eggs, processed egg products, poultry muscle, salmon, and liquid milk. The method was shown to have a limit of quantitation (LOQ) for eggs, milk, salmon, and chicken muscle of 1.5 µg/kg, 1.9 µg/kg, 2.1 µg/kg, and 1.2 µg/kg, respectively. The recoveries of EQ ranged from 79.2% to 107.6%, with a relative standard deviation (RSD) below 8.4%. A surveillance study for the presence of EQ in different types of eggs and poultry muscle available in Singapore was conducted and a total of 140 samples were tested. EQ residues in all samples were found to be below the U.S. Food and Drug Administration (FDA) MRLs of 500 µg/kg. Some samples of salted and preserved eggs from China were detected with higher concentration of EQ.

Probing the interaction between encapsulated ethoxyquin and its β-cyclodextrin inclusion complex with bovine serum albumin

Ethoxyquin (EQ) is a synthetic antioxidant that is derived from quinolines and found in many meat products. EQ is strictly regulated in feed due to its potential health implications. An investigation of the interaction mechanism between EQ and transporter protein before and after β-cyclodextrin (β-CD) encapsulation was conducted with the use of multi-spectroscopy, cyclic voltammetry, and molecular docking. EQ formed complexes with bovine serum albumin (BSA), and affected secondary structure and microenvironment polarity of BSA. However, at 298 K, EQ's fluorescence quenching constants decreased from (9.81 ± 0.05) × 103 L mol-1 to (4.94 ± 0.09) × 103 L mol-1, binding constants decreased from (10.28 ± 0.02) × 103 L mol-1 to (2.08 ± 0.07) × 103 L mol-1, after encapsulation in β-CD as well as the binding distance increased. β-CD contains part of EQ in its hydrophobic cavity, inhibiting its binding to BSA. β-CD inclusion complex prevented adverse effects of EQ on BSA conformation. However, β-CD encapsulation had no effect on EQ's antioxidant activity.

Monitoring the exposure to ethoxyquin between 2000 and 2021 in urine samples from the German Environmental Specimen Bank

Human Biomonitoring (HBM) of emerging chemicals gained increasing attention within the EU in recent years. After evaluating the metabolism, we established a new HBM method for ethoxyquin (EQ), a feed additive, which was banned in 2017 due to concerns regarding the possible exposure of the general population to it and its highly toxic precursor p-phenetidine. The method was applied to 250 urine samples from the Environmental Specimen Bank collected between 2000 and 2021. The major metabolite EQI was quantified in the majority of the study samples illustrating the ubiquitous exposure of the non-occupationally exposed population. A rather constant exposure was observed until 2016 with a significant decline from 2016 to 2021. This drop falls within the EU wide ban of the chemical as a feed additive from June 2017 which led to a gradual removal until its complete suspension in June 2020. The daily intake (DI) was evaluated with respect to the reported derived no-effect level (DNEL) to estimate the potential health risks from EQ exposure. The median DI of 0.0181 µg/kg bw/d corresponds to only 0.01 % of the DNEL. Even the observed maxima up to 13.1 µg/kg bw/d only accounted for 10 % of the DNEL. Nevertheless, the values suggest a general exposure with the risk of higher burden in a low fraction of the population. In regard to the EQ associated intake of the carcinogen and suspected mutagen p-phenetidine, this level of exposure cannot be evaluated as safe. The recent decrease and the broad exposure substantiate the need for future HBM campaigns in population representative studies to further investigate the observed reductions, potentially find highly exposed subgroups and clarify the impact of the ban as feed additive on EQ exposure.

1-benzoyl-6-hydroxy-2,2,4-trimethyl-1,2-dihydroquinoline exerts a neuroprotective effect and normalises redox homeostasis in a rat model of cerebral ischemia/reperfusion

Ischemia is one of the main etiological factors of stroke and is associated with the development of energy deficiency, oxidative stress, and inflammation. An abrupt restoration of blood flow, called reperfusion, can worsen the effects of ischemia. In our study, we assessed the neuroprotective potential of 1-benzoyl-6-hydroxy-2,2,4-trimethyl-1,2-dihydroquinoline (BHDQ) in cerebral ischemia/reperfusion (CIR) in rats. Wistar rats, divided into 4 groups were used in the study: sham-operated animals; animals with CIR caused by occlusion of the common carotid arteries and subsequent removal of the occlusions; rats treated with BHDQ at a dose of 50 mg/kg in the presence of pathology; sham-operated animals treated with BHDQ. The analysis of the state of energy metabolism in the brain, the level of the S100B protein and the histological assessment of the brain tissue were carried out. The antioxidant potential of BHDQ was assessed by measuring biochemiluminescence parameters, analysing the level of 8-isoprostane, products of lipid and protein oxidation, concentration of α-tocopherol and citrate, and aconitate hydratase activity during CIR in rats. A study of the effect of BHDQ on the regulation of the enzymatic antioxidant system and the inflammatory processes was performed. We demonstrated that BHDQ has a neuroprotective effect in CIR, reducing histopathological changes in the brain, normalizing pyruvate and lactate concentrations, and the transcripts level of Hif-1α gene. The positive effect of BHDQ was probably due to its antioxidant and anti-inflammatory activity, manifested in a decrease in the parameters of the oxidative stress, decreased mRNA of proinflammatory cytokines and NF-κB factor genes. In addition, BHDQ reduced the load on antioxidant protection enzymes, contributing to a change in their activities, decreased the level of antioxidant gene transcripts and expression of Nrf2 and Foxo1 factors toward control. Thus, BHDQ exhibited a neuroprotective effect due to a decrease in the level of oxidative stress and inflammation and the normalization of redox homeostasis on CIR in rats.

Safety and efficacy of a feed additive consisting of ethoxyquin (6-ethoxy-1,2-dihydro-2,2,4-trimethylquinoline) for all animal species (FEFANA asbl)

Ethoxyquin is synthetised from p-phenetidine, a possible mutagen, which remains in the additive as an impurity at concentrations of < 2.5 mg/kg additive. Ethoxyquin is considered safe for all animal species at the proposed inclusion level of 50 mg/kg complete feed. However, owing the presence of p-phenetidine, no safe level of the additive in feed for long-living and reproductive animals could be identified. The FEEDAP Panel derived a health-based guidance value of 0.006 mg ethoxyquin dimer (EQDM)/kg bw per day and applied it to the sum of ethoxyquin and its transformation products. A maximum total concentration of 50 mg ethoxyquin/kg complete feed for all animal species, except dairy ruminants, would not pose a risk for the consumer. However, in the absence of data on p-phenetidine residues in tissues and products of animal origin, no conclusion on the safety for the consumer could be drawn. The conclusions on consumer safety assume that the maximum total concentration of 50 mg EQ/kg feed is expressed as the sum of EQ, EQDM, EQI and DHEQ. Exposure of the unprotected user to p-phenetidine via inhalation should be minimised. No safety concerns for groundwater are expected. It is not possible to conclude on the safety of EQ for the terrestrial compartment. A risk for the aquatic compartment cannot be excluded when ethoxyquin is used in terrestrial animals. Unacceptable risk is not expected for freshwater sediment-dwelling organisms. A risk of secondary poisoning via the terrestrial food chain is not expected, whereas a risk via the aquatic food chain cannot be excluded. No concerns for aquatic organisms are expected for ethoxyquin used in fish farmed in land-based system, a risk cannot be excluded for marine sediment dwelling organisms when ethoxyquin is used in sea-cages. Ethoxyquin is considered efficacious in the range 25-50 mg/kg complete feed.

Microfluidic Electrochemistry Meets Trapped Ion Mobility Spectrometry and High-Resolution Mass Spectrometry-In Situ Generation, Separation, and Detection of Isomeric Conjugates of Paracetamol and Ethoxyquin

Over the last 3 decades, electrochemistry (EC) has been successfully applied in phase I and phase II metabolism simulation studies. The electrochemically generated phase I metabolite-like oxidation products can react with selected reagents to form phase II conjugates. During conjugate formation, the generation of isomeric compounds is possible. Such isomeric conjugates are often separated by high-performance liquid chromatography (HPLC). Here, we demonstrate a powerful approach that combines EC with ion mobility spectrometry to separate possible isomeric conjugates. In detail, we present the hyphenation of a microfluidic electrochemical chip with an integrated mixer coupled online to trapped ion mobility spectrometry (TIMS) and time-of-flight high-resolution mass spectrometry (ToF-HRMS), briefly chipEC-TIMS-ToF-HRMS. This novel method achieves results in several minutes, which is much faster than traditional separation approaches like HPLC, and was applied to the drug paracetamol and the controversial feed preservative ethoxyquin. The analytes were oxidized in situ in the electrochemical microfluidic chip under formation of reactive intermediates and mixed with different thiol-containing reagents to form conjugates. These were analyzed by TIMS-ToF-HRMS to identify possible isomers. It was observed that the oxidation products of both paracetamol and ethoxyquin form two isomeric conjugates, which are characterized by different ion mobilities, with each reagent. Therefore, using this hyphenated technique, it is possible to not only form reactive oxidation products and their conjugates in situ but also separate and detect these isomeric conjugates within only a few minutes.

Development of EQ-6, a Novel Analogue of Ethoxyquin to Prevent Chemotherapy-Induced Peripheral Neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a common and often dose-limiting side effect of many cancer drugs. Because the onset of neuronal injury is known, it is an ideal clinical target to develop neuroprotective strategies. Several years ago, we had identified ethoxyquin as a potent neuroprotective drug against CIPN through a phenotypic drug screening and demonstrated a novel mechanism of action, inhibition of chaperone domain of heat shock protein 90. To improve its drug-like properties we synthesized a novel analogue of ethoxyquin and named it EQ-6 (6-(5-amino)-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline hydrochloride). Here we show that EQ-6 prevents axon degeneration in primary dorsal root ganglion neurons in vitro, and this axon protection is associated with preserved levels of nicotinamide adenine dinucleotide, a key metabolite in programmed axon degeneration pathway. We also found that EQ-6 prevents loss of epidermal nerve fibers in a mouse model of CIPN induced by paclitaxel and that doses of EQ-6 that provide neuroprotection are associated with reduced tissue levels of SF3B2, a potential biomarker of target engagement. Furthermore, we show that EQ-6 is safe in vitro and in mice with daily administration for a month. We found that oral bioavailability is about 10%, partly due to rapid metabolism in liver, but EQ-6 appears to be concentrated in neural tissues. Given these findings, we propose EQ-6 as a first-in-class drug to prevent CIPN.

Development of a human biomonitoring method for assessing the exposure to ethoxyquin in the general population

Ethoxyquin (EQ) is commonly used as an antioxidant in animal feeds. Although EQ is not permitted for usage in food products for humans within the EU, residues of EQ and its transformation products could be determined in food of animal origin. Despite its widespread use and concerns on its toxicological profile, no information about the systemic exposure to EQ in the general population is available. Hence, we developed a human biomonitoring (HBM) method for EQ. Our approach included a metabolism study with five subjects, who were administered an oral dose of 0.005 mg EQ/kg body weight. Unchanged EQ and the major metabolite 2,2,4-trimethyl-6(2H)-quinolinone (EQI) were identified as urinary excretion products of EQ. While small amounts of EQ could be determined in high concentrated samples from the metabolism study only, 28.5% of the orally applied EQ dose could be recovered as EQI. Toxicokinetic parameters were determined for EQI, the potential biomarker of exposure. In addition, an analytical method for EQI (LOQ = 0.03 µg/L) in urine based on UHPLC-MS/MS comprising enzymatic glucuronide hydrolysis and salt-assisted liquid-liquid extraction was developed, validated and applied to 53 urine samples from the general population. EQI could be quantified in 11 (21%) of the samples in levels up to 1.7 µg/L urine, proving the suitability of the developed method for the intended purpose.

Determination of the Synthetic Antioxidant Ethoxyquin and Its Metabolites in Fish and Fishery Products Using Liquid Chromatography-Fluorescence Detection and Stable-Isotope Dilution Analysis-Liquid Chromatography-Tandem Mass Spectrometry

The use of the synthetic antioxidant ethoxyquin (1,2-dihydro-6-ethoxy-2,2,4-trimethylquinoline, EQ) as a flame retardant in fish meal transported by sea is required by international authorities to prevent self-ignition. Because of extensive carry-over within the food chain, selective and sensitive analytical methods are required for investigations on human exposure and the safety of EQ and its metabolites. Therefore, a simple, fast, and rugged liquid-chromatography (LC) method was developed for the detection of EQ and its metabolites in fish and fishery products after liquid-liquid extraction using QuEChERS. For screening purposes, a fluorescence detector was used (LC-FLD) with the EQ-analogue methoxyquin serving as an internal standard. For stable-isotope dilution analysis by liquid chromatography-tandem mass spectrometry (SIDA-LC-MS/MS), deuterated analogues of EQ and its metabolites were synthesized for the first time and allowed for sensitive quantification and thus confirmation of screening results. Both methods were validated and successfully applied to commercially available fish samples.