Reduction of Acute Inhalation Toxicity Testing in Rats: The Contact Angle of Organic Pigments Predicts Their Suffocation Potential

Abstract

Determination of acute inhalation toxicity is requested for hazard assessment of substances. In the regulatoryrequired test, otherwise toxicologically inert solid (dust) aerosols have to be tested up to a very high concentration limit of 5 mg/L of air. By testing a series of organic pigments at this concentration, we found that some pigments were well tolerated (hence, resulting in an LC 50 >5 mg/L). For other pigments, we identified obstruction of the airways with subsequent suffocation as the cause of death at this concentration. In these cases, Organization for Economic Cooperation and Development TG 436 requires that additional animals are tested at 1 mg/L air. However, the mortality of animals at the high concentration could have been avoided if the suffocation by obstruction of the airways was predictable. Hence, we investigated the correlation of several physicochemical characteristics with the observed mortality. Test substances with the highest contact angle, a measure of hydrophobicity, produced mortality at high concentrations, whereas the more hydrophilic compounds did not. Therefore, the contact angle of test substances may serve as a predictive parameter for suffocation potential. We propose conducting this characterization before in vivo testing to reduce the number and suffering of animals until further in vitro and in silico approaches are developed to completely replace animal testing.

Physical Obstruction of Nasal Cavities With Subsequent Asphyxia, Causes Lethality of Rats in an Acute Inhalation Study With Hydrophobic HMDZ Surface-Treated Synthetic Amorphous Silica (SAS)

“…Settlement of the test item in the larynx of one animal may be considered supportive of asphyxia caused by obstruction of the nasal cavities as demonstrated in this study. However, it is not possible to determine exactly at which concentration the physical obstruction of the nasal cavity for the respective hydrophobic particulate substance occurs, e.g., some hydrophobic organic pigments show 4 h LC50-value above 1,000 mg/m 3 (12). In this study, mortality is discussed as a consequence of the limited wettability of the test material.…”

“…Figure 1 shows the contact angle of the test material as measured according to DIN 55660-2 (11) and Hofmann et al (12). The measurement was performed using a contact angle instrument, the DSA100 Drop Shape Analyzer and ADVANCE software (KRÜSS Scientific, Germany).…”

Safety and Toxicity Implications of Multifunctional Drug Delivery Nanocarriers on Reproductive Systems In Vitro and In Vivo

“…Also, fewer available reproductive toxicity research reports sometimes do not indicate the nanoparticles’ impacts on the male or female fertilities or developmental stages of the fetus, e.g., silica nanoparticles. Likewise, the presently at-hand in vitro as well as in vivo reports have not been pointing to the non-intentional permeabilities and systemic bioavailabilities of cutaneously or sub-cutaneously applied nanoparticles, like those nanoparticles employed in sun-screen lotion or creams ( Wolterbeek et al, 2015 ; Landsiedel et al, 2017 ; Hofmann et al, 2018 ).…”

In vitro Alternatives to Acute Inhalation Toxicity Studies in Animal Models—A Perspective

“…Also, rat airway diameter is smaller than human one. Thus, insoluble solid aerosols can lead to an obstruction of the rat airways and, subsequently, to animal death, at the highest tested doses, even when the compound under investigation is non-toxic to humans (Hofmann et al, 2018).…”

“…Indeed, inadequate physicochemical characterization of the test compound and dosimetry can also lead to unpredictive results in inhalation toxicity tests. However, our manuscript does not address issues associated with exposure technology, test compound characterization and dosimetry, as these have already been identified and described in detail elsewhere (Dorato and Wolff, 1991;Oberdorster, 1996;Pauluhn, 2003Pauluhn, , 2005Wong, 2007;Phalen and Mendez, 2009;Clippinger et al, 2018b;Hofmann et al, 2018).…”