K16ApoE is a brain-targeted drug carrier that can deliver drugs throughout the brain and maintain sustained activity during delivery. However, related studies have revealed that K16ApoE has acute and high toxicity, and its toxicological mechanism remains unknown. Our previous experiments found that K16ApoE affects the blood state of mice. Thus, we performed a hemolysis assay to investigate whether K16ApoE could induce hemolysis, but we found that K16ApoE was unable to lyse red blood cells at lethal doses. Then, we monitored cerebral blood flow and perfusion after the mice received incremental doses of K16ApoE and found that K16ApoE could suddenly interrupt the blood flow and reduce the perfusion in the brain. K16ApoE could also disrupt the consistency of cerebral perfusion. Last, we examined the blood cells under the microscope and found that K16ApoE caused the cells to clump in the plasma and increase blood viscosity. Based on these findings, we confirmed that the toxicity of K16ApoE is mainly in the blood. The mechanism is that K16ApoE induces blood cell aggregation and interrupts blood flow.

Covalent binding of chemicals to skin proteins represents the Molecular Initiating Event (MIE) of the skin sensitization process. We attempted to construct in silico models for predicting the reactivities of chemicals to cysteine measured by the Direct Peptide Reactivity Assay (DPRA) as a screening tool for skin sensitization potential of chemicals since there was no readily available in silico prediction model for reactivity classes of the DPRA. We used a dataset of 211 chemicals compiled based on the chemical reactivity to cysteine in the DPRA for model construction, and each chemical was classified as “Minimal-Low” or “Moderate-High” reactivity according to the percent cysteine depletion value in the DPRA. We constructed two independent classification models using two machine learning algorithms named Random Forest (RF) and Graph Convolutional Network (GCN), and a consensus model adopting prediction results when both of the GCN-based and the RF-based models were matched was also constructed. Performance evaluation showed that the RF-based model showed higher specificity than the GCN-based model and the GCN-based model showed higher sensitivity than the RF-based model. The consensus model showed high accuracy and high specificity of over 0.9. Comparison of the reactivity class predicted by the consensus model and the skin sensitization potential for humans revealed that all chemicals classified into the “Moderate-High” class were human skin sensitizers. In conclusion, the consensus model we constructed here may be a promising in silico screening tool to predict cysteine reactivity measured by the DPRA and skin sensitization potential of chemicals.

The amidine compound 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) is a strong organic base, is non-nucleophilic, and has been widely used in the organic synthesis of pharmaceuticals as a base catalyst. In the present study, we propose the permitted daily exposure (PDE) values of DBU by the oral, parenteral, and inhalation routes based on toxicological information in animals from the database of the European Chemicals Agency (ECHA). DBU exhibited mainly stomach toxicity caused by the corrosive effect of this strong alkali in rats. Although it is unlikely that stomach toxicity is induced in patients by DBU contamination of pharmaceuticals because most pharmaceutical products are adjusted to a near neutral pH, we calculated the PDE values conservatively based on the dosage at which no stomach-related findings were observed because no other noteworthy findings caused by systemic exposure were included in toxicity studies. By applying adjustment factors to the no-observed-adverse-effect-level (NOAEL) (120 mg/kg/day) in animal studies during the longest treatment period (3 months), we estimated the PDE values for oral, parenteral, and inhalation routes as 24, 12, and 6 mg/day, respectively. Derivation of the PDE was performed according to the concepts described by the International Conference on Harmonisation (ICH) Q3C(R8) and Q3D(R2) guidelines.

p-tert-butyl phenol (ptBP) is an alkylphenol organic compound that is used in the production of polycarbonates, phenolic resins, epoxy resins, etc., as a polymer chain terminator. However, it can occasionally be an impurity contaminant during the chemical synthesis of active pharmaceutical ingredients. Some alkylphenols are known as carcinogens or endocrine modulators, therefore controlling the impurity level to below the permitted daily exposure (PDE) value based on the toxicological risk assessment of ptBP should be considered. Here, we propose the PDE using toxicological information primarily obtained from OECD Existing Chemicals Database. Four scenarios for the oral PDE calculation were investigated, and the lowest value, 2 mg/day, was proposed as the most appropriate control criterion of ptBP based on the depigmentation toxicity seen in black mice. The PDE for the parenteral route was concluded to be 1 mg/day by applying a default bioavailability of 50% per ICH Q3D guideline.

Trifluoroacetic acid (TFA) has been used for production of pharmaceuticals including recently emerging middle size peptides. TFA has severe local toxicity like skin and respiratory tract irritation due to the strong acidity. Because almost all pharmaceutical products are prepared at neutral pH, derivation of permitted daily exposure (PDE) of TFA from the information with neutralized form could provide useful information on the risk management for protection of patients and production of pharmaceuticals. Sodium TFA caused hepatotoxicity in a rat 90-day. Based on the results of the 90-day study, we respectively proposed PDE for oral, parenteral and inhalation routes as 1.7, 0.005 and 0.84 mg/person/day. The derivation of PDE was done according to the concept described in ICH Q3C(R8) and Q3D(R2).