Developmental and reproductive toxicity hazard characterization of 2-amino-2-methyl-1-propanol (AMP).

2-Amino-2-methyl-1-propanol (AMP™) is a widely used pH stabilizer in personal care products (PCPs); thus, the safety implications of dermal AMP exposure remain of interest. We have previously reported that exposure to AMP in PCPs when used as intended is not anticipated to result in an increased risk of hepatotoxicity (primarily steatosis and altered phospholipid homeostasis). The current study focuses on AMP in PCP's potential for developmental and reproductive toxicity (DART) in humans, based on data from animal studies. Animal studies suggest that exposure to AMP can result in post-implantation loss. However, such effects occur at maternally toxic doses, posing a challenge for determining appropriate hazard classifications in the context of relevant consumer use scenarios. Our assessment concluded that human exposure to AMP in PCPs is not anticipated to result in DART at non-maternally toxic doses. Further, mode of action (MOA) analysis elucidated the potential biological pathways underlying DART effects observed in high-dose animal studies, such that perturbation of uterine choline synthesis was the most well-supported MOA hypothesis. Downstream uterine effects might reflect choline-dependent changes in epigenetic control of pathways important for implantation maintenance and uterine cell energetics. Since AMP-induced post-implantation loss occurs at doses higher than pathology related to liver toxicity, maintaining AMP exposures from exceeding the onset dose for maternal liver effects will also be protective of DART effects. Furthermore, dermal exposure to AMP expected from the use of PCPs is highly unlikely to result in toxicologically significant systemic AMP concentrations; thus, DART is not anticipated.

Acceptable intakes (AIs) for 11 small molecule N-nitrosamines (NAs).

Low levels of N-nitrosamines (NAs) were detected in pharmaceuticals and, as a result, health authorities (HAs) have published acceptable intakes (AIs) in pharmaceuticals to limit potential carcinogenic risk. The rationales behind the AIs have not been provided to understand the process for selecting a TD50 or read-across analog. In this manuscript we evaluated the toxicity data for eleven common NAs in a comprehensive and transparent process consistent with ICH M7. This evaluation included substances which had datasets that were robust, limited but sufficient, and substances with insufficient experimental animal carcinogenicity data. In the case of robust or limited but sufficient carcinogenicity information, AIs were calculated based on published or derived TD50s from the most sensitive organ site. In the case of insufficient carcinogenicity information, available carcinogenicity data and structure activity relationships (SARs) were applied to categorical-based AIs of 1500 ng/day, 150 ng/day or 18 ng/day; however additional data (such as biological or additional computational modelling) could inform an alternative AI. This approach advances the methodology used to derive AIs for NAs.

Dose and exposure route analyses inform relationships between liver steatosis and 2-amino-2-methyl-1-propanol: Implications for hazard characterization.

2-Amino-2-methyl-1-propanol (AMP™) is widely used as a neutralizer/pH stabilizer in personal care products (PCPs); however, the potential health implications of dermal AMP exposure remain to be fully elucidated. Consequently, an in-depth analysis was performed to determine if PCPs containing AMP pose an elevated risk in humans under the intended use conditions. Animal studies have shown that at high doses, oral AMP exposure could lead to liver steatosis; thus, this study focused on hepatotoxicity. Our assessment revealed that the derived margin of exposure (MoE) values for AMP-containing PCPs were above 100, indicating that dermal exposure to AMP is unlikely to present an elevated risk of hepatotoxicity. Further, mode of action (MOA) analysis was conducted to elucidate the potential mechanisms underlying the observed hepatotoxicity in animal studies. Our analysis proposed that AMP interferes with the CDP-choline pathway in hepatocytes via the inhibition of one or more enzymes integral to the pathway and/or the replacement of choline in the assembly of the phospholipid unit. Ultimately, these events halt the lipid export via very low-density lipoproteins, which can subsequently develop into fatty liver accompanied by hepatotoxicity and other pathological changes if AMP exposure persists at sufficiently high doses. MOA analysis corroborated that dermal exposure to AMP expected from use of PCPs is highly unlikely to result in toxicologically significant systemic concentrations of AMP and thus hepatotoxicity. We concluded that dermal exposure to AMP in PCPs is not anticipated to result in an increased risk of hepatotoxicity.

Opposite regulation of cholesterol levels by the phosphatase and hydrolase domains of soluble epoxide hydrolase.

Soluble epoxide hydrolase (sEH) is a bifunctional enzyme with two catalytic domains: a C-terminal epoxide hydrolase domain and an N-terminal phosphatase domain. Epidemiology and animal studies have attributed a variety of cardiovascular and anti-inflammatory effects to the C-terminal epoxide hydrolase domain. The recent association of sEH with cholesterol-related disorders, peroxisome proliferator-activated receptor activity, and the isoprenoid/cholesterol biosynthesis pathway additionally suggest a role of sEH in regulating cholesterol metabolism. Here we used sEH knock-out (sEH-KO) mice and transfected HepG2 cells to evaluate the phosphatase and hydrolase domains in regulating cholesterol levels. In sEH-KO male mice we found a approximately 25% decrease in plasma total cholesterol as compared with wild type (sEH-WT) male mice. Consistent with plasma cholesterol levels, liver expression of HMG-CoA reductase was found to be approximately 2-fold lower in sEH-KO male mice. Additionally, HepG2 cells stably expressing human sEH with phosphatase only or hydrolase only activity demonstrate independent and opposite roles of the two sEH domains. Whereas the phosphatase domain elevated cholesterol levels, the hydrolase domain lowered cholesterol levels. Hydrolase inhibitor treatment in sEH-WT male and female mice as well as HepG2 cells expressing human sEH resulted in higher cholesterol levels, thus mimicking the effect of expressing the phosphatase domain in HepG2 cells. In conclusion, we show that sEH regulates cholesterol levels in vivo and in vitro, and we propose the phosphatase domain as a potential therapeutic target in hypercholesterolemia-related disorders.

Distribution and expression of soluble epoxide hydrolase in human brain.

Epoxyeicosatrienoic acids (EETs) are cytochrome P450 metabolites of arachidonic acid, which function in the brain to regulate cerebral blood flow and protect against ischemic brain injury. EETs are converted by soluble epoxide hydrolase (sEH) to the corresponding inactive diol metabolites. Previous animal studies have indicated that sEH gene deletion or treatment with sEH inhibitors results in increased levels of EETs and protection against stroke-induced brain damage. To begin elucidating the underlying mechanism for these effects, we sought to determine the distribution, expression, and activity of sEH in human brain samples obtained from patients with no neurological changes/pathologies. Immunohistochemical analyses showed the distribution of sEH mainly in the neuronal cell bodies, oligodendrocytes, and scattered astrocytes. Surprisingly, in the choroid plexus, sEH was found to be highly expressed in ependymal cells. Vascular localization of sEH was evident in several regions, where it was highly expressed in the smooth muscles of the arterioles. Western blot analysis and enzyme assays confirmed the presence of sEH in the normal brain. Our results indicate differential localization of sEH in the human brain, thus suggestive of an essential role for this enzyme in the central nervous system. This manuscript contains online supplemental material at http://www.jhc.org. Please visit this article online to view these materials.