Exposure to traffic-related fine particulate matter 2.5 causes respiratory damage via peroxisome proliferator-activated receptor gamma-regulated inflammation.

Exposure to particulate matter 2.5 (PM2.5) potentially triggers airway inflammation. Peroxisome proliferator-activated receptor gamma (PPARγ) has been reported to regulate inflammatory responses in diverse cell types. Therefore, this work investigated the mechanisms of PPARγ in regulating traffic-related PM2.5-induced airway inflammation. Using the diffusion flame burner soot generation, traffic-related PM2.5 was generated and adsorbed. BALB/c male mice and human bronchial epithelial cells (16-HBE) were exposed to PM2.5 alone or co-treatment with rosiglitazone (RSG), an agonist of PPARγ. To the end of exposure, bronchoalveolar lavage fluid (BALF), venous blood and arterial blood, trachea, bronchus and lung tissues were collected. The levels of IL-1ß, IL-6, and IL-17 were detected by ELISA, and the cell types in BALF were counted. Hematoxylin-eosin (H&E) assay were used to analyze the pathological conditions of lung, bronchus, and pulmonary artery. Apoptosis was detected by TUNEL, and PPARγ expression in lung and bronchus was detected by immunohistochemical (IHC) staining. Western Blot was used to detect PPARγ, NF-kB, AP-1 and STAT3 expression in lung and bronchus. The viability was detected by MTT method. PM2.5 exposure caused pathological damage to the lung, bronchus and pulmonary artery tissue, which induced apoptosis of bronchial epithelial cells. PM2.5 exposure caused local inflammation of the whole body and airway. PPARγ expression increased after PM2.5 exposure. PM2.5 exposure regulated the downstream signaling pathways to affect the inflammatory response through PPARγ. Exposure to traffic-related PM2.5 caused respiratory damage via PPARγ-regulated inflammation.

Use of a non-hepatic cell line highlights limitations associated with cell-based assessment of metabolically induced toxicity.

Metabolically induced drug-toxicity is a major cause of drug failure late in drug optimization phases. Accordingly, in vitro metabolic profiling of compounds is being introduced at earlier stages of the drug discovery pipeline. An increasingly common method to obtain these profiles is through overexpression of key CYP450 metabolic enzymes in immortalized liver cells, to generate competent hepatocyte surrogates. Enhanced cytotoxicity is presumed to be due to toxic metabolite production via the overexpressed enzyme. However, metabolically induced toxicity is a complex multi-parameter phenomenon and the potential background contribution to metabolism arising from the use of liver cells which endogenously express CYP450 isoforms is consistently overlooked. In this study, we sought to reduce the potential background interference by applying this methodology in kidney-derived HEK293 cells which lack endogenous CYP450 expression. Overexpression of CYP3A4 resulted in increased HEK293 proliferation, while exposure to four compounds with reported metabolically induced cytotoxicity in liver-derived cells overexpressing CYP3A4 resulted in no increase in cytotoxicity. Our results indicate that overexpression of a single CYP450 isoform in hepatic cell lines may not be a reliable method to discriminate which enzymes are responsible for metabolic induced cytotoxicity.

Evaluation of Uracil, Sodium Ascorbate, and Rosiglitazone as Promoters of Urinary Bladder Transitional Cell Carcinomas in Male Sprague-Dawley Rats.

The purpose of this study was to establish a 2-stage model of urinary bladder carcinogenesis in male Sprague-Dawley rats to identify tumor promoters. In phase 1 of the study, rats ( n = 170) were administered 100 mg/kg of the tumor initiator, N-butyl-N-(4-hydroxybutyl)-nitrosamine (BBN), twice weekly by oral gavage (po) for a period of 6 weeks. Phase 2 consisted of dividing rats into 4 groups ( n = 40 per group) and administering one of the following for 26 weeks to identify putative tumor promoters: (1) vehicle po, (2) 25 mg/kg/day rosiglitazone po, (3) 5% dietary sodium l-ascorbate, and (4) 3% dietary uracil. Rats were necropsied after 7.5 months, and urinary bladders were evaluated by histopathology. BBN/vehicle treatments induced the development of urothelial hyperplasia (83%) and papillomas (15%) but no transitional cell carcinomas (TCCs). Rosiglitazone increased the incidence and severity of papillomas (93%) and resulted in TCC in 10% of treated rats. Uracil was the most effective tumor promoter in our study and increased the incidence of papillomas (90%) and TCC (74%). Sodium ascorbate decreased the incidence of urothelial hyperplasia (63%) and did not increase the incidence of urothelial papillomas or TCC. These data confirm the capacity of our 2-stage model to identify urinary bladder tumor promoters.

Comparison of transcriptomic profiles between HFPO-DA and prototypical PPARα, PPARγ, and cytotoxic agents in mouse, rat, and pooled human hepatocytes.

Like many per- or polyfluorinated alkyl substances (PFAS), toxicity studies with HFPO-DA (ammonium, 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)-propanoate), a short-chain PFAS used in the manufacture of some types of fluorinated polymers, indicate that the liver is the primary target of toxicity in rodents following oral exposure. Although the current weight of evidence supports the PPARα mode of action (MOA) for liver effects in HFPO-DA-exposed mice, alternate MOAs have also been hypothesized including PPARγ or cytotoxicity. To further evaluate the MOA for HFPO-DA in rodent liver, transcriptomic analyses were conducted on samples from primary mouse, rat, and pooled human hepatocytes treated for 12, 24, or 72 h with various concentrations of HFPO-DA, or agonists of PPARα (GW7647), PPARγ (rosiglitazone), or cytotoxic agents (ie, acetaminophen or d-galactosamine). Concordance analyses of enriched pathways across chemicals within each species demonstrated the greatest concordance between HFPO-DA and PPARα agonist GW7647-treated hepatocytes compared with the other chemicals evaluated. These findings were supported by benchmark concentration modeling and predicted upstream regulator results. In addition, transcriptomic analyses across species demonstrated a greater transcriptomic response in rodent hepatocytes treated with HFPO-DA or agonists of PPARα or PPARγ, indicating rodent hepatocytes are more sensitive to HFPO-DA or PPARα/γ agonist treatment. These results are consistent with previously published transcriptomic analyses and further support that liver effects in HFPO-DA-exposed rodents are mediated through rodent-specific PPARα signaling mechanisms as part of the MOA for PPARα activator-induced rodent hepatocarcinogenesis. Thus, effects observed in mouse liver are not appropriate endpoints for toxicity value development for HFPO-DA in human health risk assessment.

Molecular toxicological alterations in the mouse hearts induced by sub-chronic thiazolidinedione drugs administration.

Thiazolidinediones are well-known anti-diabetic drugs. However, they are not widely used due to their cardiotoxic effects. Therefore, in this study, we aimed to determine the molecular toxicological alterations induced in the mouse hearts after thiazolidinedione administration. Balb/c mice received doses clinically equivalent to those given to humans of the most commonly used thiazolidinediones, pioglitazone, and rosiglitazone for 30 days. After that, RNA samples were isolated from the hearts. The mRNA expression of cytochrome (cyp) p450 genes that synthesize the cardiotoxic 20-hydroxyeicosatetraenoic acid (20-HETE) in addition to 92 cardiotoxicity biomarker genes were analyzed using quantitative polymerase chain reaction array technique. The analysis demonstrated that thiazolidinediones caused a significant upregulation (p < 0.5) of the mRNA expression of cyp1a1, cyp4a12, itpr1, ccl7, ccr1, and b2 m genes. In addition, thiazolidinediones caused a significant (p < 0.05) downregulation of the mRNA expression of adra2a, bsn, col15a1, fosl1, Il6, bpifa1, plau, and reg3b genes. The most affected gene was itpr1 gene, which was upregulated by pioglitazone and rosiglitazone by sevenfold and 3.5-fold, respectively. In addition, pioglitazone caused significant upregulation of (p < 0.05) hamp, ppbp, psma2, sik1, timp1, and ucp1 genes, which were not affected significantly (p > 0.05) by rosiglitazone administration. In conclusion, this study showed that thiazolidinediones induce toxicological molecular alterations in the mouse hearts, such as the induction of cyp450s that synthesize 20-HETE, chemokine activation, inflammatory responses, blood clotting, and oxidative stress. These findings may help us understand the mechanism of cardiotoxicity involved in thiazolidinedione administration.

Protracted rosiglitazone treatment exacerbates inflammation in white adipose tissues of adipocyte-specific Nfe2l1 knockout mice.

Nuclear factor-erythroid 2-related factor 1 (NFE2L1, also known as NRF1) belongs to the CNC-bZIP family and is a master regulator of cellular adaptive responses to various stresses in many cells and tissues. Rosiglitazone (RGZ), a thiazolidinedione agonist of PPARγ, is widely used in the treatment of type 2 diabetes mellitus by stimulating genes which favor storage of triglycerides. Our previous studies demonstrated that loss of Nfe2l1 in adipocytes [Nfe2l1(f)-KO] resulted in diminished subcutaneous white adipose tissue (WAT) mass with adipocyte hypertrophy and severe adipose inflammation, which might be attributed, at least in part, to impaired lipolysis. However, the exact mechanism underlying this phenotype remains unclear. To further clarify the regulatory role of NFE2L1 in adipocyte lipid metabolism, we used protracted RGZ treatment to facilitate lipid accumulation in mice. In Nfe2l1flox/flox control mice, three weeks of RGZ treatment significantly downregulated mRNA levels of a group of inflammation-related genes in WAT. In contrast, the phenotype of Nfe2l1(f)-KO mice was aggravated showing increased transcript expression related to inflammation and pyroptosis in their shrunk WAT. These findings provide deeper insight into the mechanisms by which NFE2L1 regulates the expression of a set of lipolysis-related genes and controls WAT plasticity and global energy homeostasis.

GATA3, HDAC6, and BCL6 Regulate FOXP3+ Treg Plasticity and Determine Treg Conversion into Either Novel Antigen-Presenting Cell-Like Treg or Th1-Treg.

We conducted an experimental database analysis to determine the expression of 61 CD4+ Th subset regulators in human and murine tissues, cells, and in T-regulatory cells (Treg) in physiological and pathological conditions. We made the following significant findings: (1) adipose tissues of diabetic patients with insulin resistance upregulated various Th effector subset regulators; (2) in skin biopsy from patients with psoriasis, and in blood cells from patients with lupus, effector Th subset regulators were more upregulated than downregulated; (3) in rosiglitazone induced failing hearts in ApoE-deficient (KO) mice, various Th subset regulators were upregulated rather than downregulated; (4) aortic endothelial cells activated by proatherogenic stimuli secrete several Th subset-promoting cytokines; (5) in Treg from follicular Th (Tfh)-transcription factor (TF) Bcl6 KO mice, various Th subset regulators were upregulated; whereas in Treg from Th2-TF GATA3 KO mice and HDAC6 KO mice, various Th subset regulators were downregulated, suggesting that Bcl6 inhibits, GATA3 and HDAC6 promote, Treg plasticity; and (6) GATA3 KO, and Bcl6 KO Treg upregulated MHC II molecules and T cell co-stimulation receptors, suggesting that GATA3 and BCL6 inhibit Treg from becoming novel APC-Treg. Our data implies that while HDAC6 and Bcl6 are important regulators of Treg plasticity, GATA3 determine the fate of plastic Tregby controlling whether it will convert in to either Th1-Treg or APC-T-reg. Our results have provided novel insights on Treg plasticity into APC-Treg and Th1-Treg, and new therapeutic targets in metabolic diseases, autoimmune diseases, and inflammatory disorders.