Tissue distribution and plasma protein binding of [14C]phenol in rats

Miniaturized screening and performance prediction of tailored subcutaneous extended-release formulations for preclinical in vivo studies

Microencapsulation of active pharmaceutical ingredients (APIs) for preparation of long acting injectable (LAI) formulations is an auspicious technique to enable preclinical characterization of a broad variety of APIs, ideally independent of their physicochemical and pharmacokinetic (PK) characteristics. During early API discovery, tunable LAI formulations may enable pharmacological proof-of-concept for the given variety of candidates by tailoring the level of plasma exposure over the duration of various timespans. Although numerous reports on small scale preparation methods for LAIs utilizing copolymers of lactic and glycolic acid (PLGA) and polymers of lactic acid (PLA) highlight their potential, application in formulation screening and use in preclinical in vivo studies is yet very limited. Transfer from downscale formulation preparation to in vivo experiments is hampered in early preclinical API screening by the large number of API candidates with simultaneously very limited available amount in the lower sub-gram scale, lack of formulation stability and deficient tunability of sustained release. We hereby present a novel comprehensive platform tool for tailored extended-release formulations, aiming to support a variety of preclinical in vivo experiments with ranging required plasma exposure levels and timespans. A novel small-scale spray drying process was successfully implemented by using an air brush based instrument for preparation of PLGA and PLA based formulations. Using Design of Experiments (DoE), required API amount of 250 mg was demonstrated to suffice for identification of dominant polymer characteristics with largest impact on sustained release capability for an individual API. BI-3231, a hydrophilic and weakly acidic small compound with good water solubility and permeability, but low metabolic stability, was used as an exemplary model for one of the many candidates during API discovery. Furthermore, an in vitro to in vivo correlation (IVIVC) of API release rate was established in mice, which enabled the prediction of in vivo plasma concentration plateaus after single subcutaneous injection, using only in vitro dissolution profiles of screened formulations. By tailoring LAI formulations and their doses for acute and sub-chronic preclinical experiments, we exemplary demonstrate the practical use for BI-3231. Pharmacological proof-of-concept could be enabled whilst circumventing the need of multiple administration as result of extensive hepatic metabolism and simultaneously superseding numerous in vivo experiments for formulation tailoring.

Discovery of a Novel Potent and Selective HSD17B13 Inhibitor, BI-3231, a Well-Characterized Chemical Probe Available for Open Science

Genome-wide association studies in patients revealed HSD17B13 as a potential new target for the treatment of nonalcoholic steatohepatitis (NASH) and other liver diseases. However, the physiological function and the disease-relevant substrate of HSD17B13 remain unknown. In addition, no suitable chemical probe for HSD17B13 has been published yet. Herein, we report the identification of the novel potent and selective HSD17B13 inhibitor BI-3231. Through high-throughput screening (HTS), using estradiol as substrate, compound 1 was identified and selected for subsequent optimization resulting in compound 45 (BI-3231). In addition to the characterization of compound 45 for its functional, physicochemical, and drug metabolism and pharmacokinetic (DMPK) properties, NAD⁺ dependency was investigated. To support Open Science, the chemical HSD17B13 probe BI-3231 will be available to the scientific community for free via the opnMe platform, and thus can help to elucidate the pharmacology of HSD17B13.

Combining in vitro embryotoxicity data with physiologically based kinetic (PBK) modelling to define in vivo dose-response curves for developmental toxicity of phenol in rat and human

In vitro assays are often used for the hazard characterisation of compounds, but their application for quantitative risk assessment purposes is limited. This is because in vitro assays cannot provide a complete in vivo dose-response curve from which a point of departure (PoD) for risk assessment can be derived, like the no observed adverse effect level (NOAEL) or the 95 % lower confidence limit of the benchmark dose (BMDL). To overcome this constraint, the present study combined in vitro data with a physiologically based kinetic (PBK) model applying reverse dosimetry. To this end, embryotoxicity of phenol was evaluated in vitro using the embryonic stem cell test (EST), revealing a concentration-dependent inhibition of differentiation into beating cardiomyocytes. In addition, a PBK model was developed on the basis of in vitro and in silico data and data available from the literature only. After evaluating the PBK model performance, effective concentrations (ECx) obtained with the EST served as an input for in vivo plasma concentrations in the PBK model. Applying PBK-based reverse dosimetry provided in vivo external effective dose levels (EDx) from which an in vivo dose-response curve and a PoD for risk assessment were derived. The predicted PoD lies within the variation of the NOAELs obtained from in vivo developmental toxicity data from the literature. In conclusion, the present study showed that it was possible to accurately predict a PoD for the risk assessment of phenol using in vitro toxicity data combined with reverse PBK modelling.

Disposition of phenol in rat after oral, dermal, intravenous, and intratracheal administration

The absorption and elimination of [14C]-phenol (63.5 nmol) after oral, dermal, intratracheal, or intravenous administration in rat was rapid and extensive. Urinary elimination of radioactivity predominated, with a range of 75-95% of the dose detected in urine by 72 h post-exposure. Washing the dermal site 72 h post-exposure removed 14% of the dose. Two per cent of the dose was detected in the skin. The urinary metabolites at 4 and 8 h after administration by the four routes included phenyl sulphate and lower amounts of phenyl glucuronide. Phenol was poorly retained in the body after administration by the four routes. Phenol remaining in the body was widely distributed, with accumulation primarily in the liver, lung, and kidney.

A multidisciplinary approach to toxicological screening: III. Neurobehavioral toxicity

The neurobehavioral effects of 10 known toxicants were examined as part of a multidisciplinary screening battery. The toxicants included carbaryl (CAR), triadimefon (TDM), heptachlor (HEP), chlordane (CDN), diethylhexyl phthalate (DEHP), carbon tetrachloride (CCl4), phenol, trichloroethylene (TCE), tetrachloroethylene (PER or perchlorethylene), and dichloromethane (DCM or methylene chloride). A functional observational battery and motor activity measurements were conducted before exposure, at specified times after an acute exposure, and during and after 14-d exposure. Severity scoring analysis was used to generate profiles of effect. The pesticides, CAR, TDM, HEP, and CDN, displayed the most acute neurotoxicity and were active at lower proportions of their respective acute LD50 values than were the solvents or the industrial chemicals. Although CAR and TDM showed little or no neurobehavioral effects with repeated dosing, cumulative neurotoxicity and lethality were evident with HEP and CDN. Phenol produced acute convulsive effects, and the most prominent finding with repeated exposure was lethality. DEHP displayed no neurobehavioral toxicity. The organic solvents, TCE, PER, CCl4, and DCM, produced various degrees of general nervous system depression following acute administration of high dose levels. Repeated dosing produced little or no effect with TCE or PER, marked physiological changes with CCl4, and cumulative toxicity and lethality with DCM. Some results of these studies were unexpected and should provide impetus for further research. Overall, these findings illustrate the utility of these screening methods.

Protein binding of benzene under ambient exposure conditions

Based on examination of exposure monitoring studies, we speculate that under ambient conditions benzene binds appreciably to plasma proteins. The binding capacity, n*[beta], is estimated to be on the order of 10(-9) chi M (90.0 ng/L) and the association constant, Kas, on the order of 2 X 10(10) M-1 (.3 L/ng). These values indicate that protein binding of benzene is characterized by a very small capacity with a very large affinity. We predict that steady-state exposure to ambient benzene air concentrations in the range of 10 ppb to 1 ppb will result in 35 to 80 percent of benzene in blood being bound to plasma proteins.

Summary review of the health effects associated with phenol

Phenol, a monohydroxy derivative of benzene, occurs naturally in animal waste and by decomposition of organic wastes. It is also produced by man, originally by fractional distillation of coal tar, but more recently by cumene hydroperoxidation and toluene oxidation. As a result of large production volume and natural sources, occupational and environmental exposure to phenol is likely. Phenol poisoning can occur by skin absorption, vapor inhalation, or ingestion, and, regardless of route of exposure, can result in detrimental health effects. Acute toxicity has been observed in man and experimental animals, resulting in muscle weakness, convulsions, and coma. In addition, studies have shown that although teratogenic effects have not been associated with exposure to phenol by either inhalation or oral route, high doses of phenol are fetotoxic. This paper addresses these studies and others in an attempt to determine if human health is at risk to those levels of phenol present in the environment and workplace. However, because data are limited, further research is necessary to analyze the mutagenic and carcinogenic potential of this chemical.