Benchmark dose-response analyses for multiple endpoints in drug safety evaluation

Comparison of sensitivity between blood parameters and a genotoxic biomarker at low blood Pb levels: A population-based study

BACKGROUND

Previous studies reported that lead (Pb) exposure induced adverse health effects at high exposure concentrations, however, there have been limited data on sensitivity comparisons among different health outcomes at low blood Pb levels.

OBJECTIVES

To compare sensitivity between blood parameters and a genotoxic biomarker among workers exposed to low blood Pb levels (< 20 µg/dl), and to estimate a benchmark dose (BMD).

METHODS

Pb-exposed workers were recruited from a lead-acid storage battery plant. Their blood lead levels (BLLs) were measured. Blood parameters and micronuclei (MN) frequencies were determined. Multivariate linear or Poisson regression was used to analyze relationships between blood parameters or MN frequencies with BLLs. Two BMD software were used to calculate BMD and its 95 % lower confidence limit (BMDL) for BLLs.

RESULTS

The median BLL for 611 workers was 10.44 µg/dl with the 25th and 75th percentile being 7.37 and 14.62 µg/dl among all participants. There were significantly negative correlations between blood parameters and BLLs. However, MN frequencies correlated positively with BLLs (all P<0.05). Results from the two BMD software revealed that the dichotomous model was superior to the continuous model, and the BMDL for BLL derived from red blood cell (RBC) was 15.11 µg/dl, from hemoglobin (HGB) was 8.50 µg/dl, from mean corpuscular hemoglobin (MCH) was 7.87 µg/dl, from mean corpuscular hemoglobin concentration (MCHC) was 3.98 µg/dl, from mean corpuscular volume (MCV) was 11.44 µg/dl, and from hematocrit (HCT) was 6.65 µg/dl. The conservative BMDL obtained from the MN data was 7.52 µg/dl.

CONCLUSION

Our study shows that low dose Pb exposure caused decrease of blood parameters and increase of MN frequencies. The genotoxic biomarker was more sensitive than most blood parameters. BMDLs for BLL derived from MN frequencies and the red blood cell indicators should be considered as new occupational exposure limits. Our results suggest that MN assay can be considered as a part of occupational health examination items.

Hepatotoxicity of oral exposure to 2-methyl-4-nitroaniline: toxicity prediction and in vivo evaluation

2-Methyl-4-nitroaniline (MNA), an intermediate in the synthesis of azo dyes, is widely distributed in various environmental media and organisms. Although there is speculation regarding MNA's potential to be hepatotoxic, the underlying mechanisms of its hepatotoxicity and its definitive diagnostic process remain largely unexplored. In this research. In the present study, we initially predicted the toxicity and possible toxic effect pathways of MNA using ProTox-II, and found that MNA binds to the PPARγ receptor (binding energy －6.118 kcal/mol) with a potential PPARγ agonist effect. Subsequently, in vivo exposure evaluation was conducted on Wistar rats to assess the impact of MNA after a 90-day exposure period, by detecting serum biochemical indexes, hematological indexes, urinary indexes, inflammatory factors, liver histopathological observations and liver tissue PPARγ mRNA expression. The results showed that MNA causes liver function abnormalities, liver histopathological changes and inflammatory response, along with a pronounced increase in PPARγ mRNA levels. This study suggests that the hepatotoxic mechanism of MNA may be related to its possible upregulation of PPARγ expression, increased liver dysfunction and inflammatory responses. Based on these results, the benchmark dose lower limit (BMDL) of 1.503 mg/kg for male Wistar rats was also established, providing a vital benchmark for determining the safety threshold of MNA. Our data highlight the hepatotoxic mechanism of MNA and contribute to a better understanding of its potential etiological diagnosis.

3D multi-cell-type liver organoids: A new model of non-alcoholic fatty liver disease for drug safety assessments

The development of in vitro models that recapitulate critical liver functions is essential for accurate assessments of drug toxicity. Although liver organoids can be used for drug discovery and toxicology, they are limited by (i) the lack of expression and activity of xenobiotic-metabolizing enzymes, and (ii) the difficulty of mimicking non-alcoholic fatty liver disease (NAFLD, which influences the expression of these enzymes) in vitro. Here, we generated three-dimensional multi-cell-type liver organoids (hereafter "HML organoids") from HepaRG cells, primary human macrophages, and hepatic-stellate-cell-derived LX-2 cells. We also developed an NAFLD model by culturing HML organoids for 9 days with a mixture of stearic and oleic acids. The exposed organoids showed typical features of steatosis and expressed fibrosis markers. We subsequently used HML and NAFLD-HML organoids to model drug-induced liver injury. By estimating the IC50 and benchmark doses, we were able to improve the in vitro detection of drugs likely to be toxic in fatty livers. Thus, HML and NAFLD-HML organoids exhibited most of the liver's functions and are relevant in vitro models of drug metabolism, drug toxicity, and adverse drug event in NAFLD.