The role of calcium in paracetamol (acetaminophen) cytotoxicity in PC12 cells transfected with CYP4502E1

Toxicity of the acetyl-para-aminophenol group of medicines to intact intervertebral disc tissue cells

The present study aimed to investigate the effects of paracetamol, an analgesic and antipyretic that is used in emergency departments and neurosurgery departments for postoperative pain management on intervertebral disc tissue. Paracetamol-treated human primary cell cultures and untreated cell cultures were compared using molecular analyses. Cell proliferation and gene expression were statistically analyzed. Cell proliferation was suppressed on days 10 (P=0.05) and 20 (P<0.05) in the paracetamol-treated groups. Gene expression of chondroadherin, matrix metalloproteinase (MMP)-7, MMP-13 and MMP-19 was higher in the paracetamol-treated samples while gene expression of Cartilage Oligomeric Matrix Protein and interleukin-1β was lower (P<0.05). Paracetamol, which appears innocuous compared with many analgesics, may increase the expression of MMPs, which serve a significant role in catabolic reactions and suppress the proliferation of intact intervertebral disc tissue cells.

Identification of Novel Regulatory Genes in APAP Induced Hepatocyte Toxicity by a Genome-Wide CRISPR-Cas9 Screen

Acetaminophen (APAP) is a commonly used analgesic responsible for more than half of acute liver failure cases. Identification of previously unknown genetic risk factors would provide mechanistic insights and novel therapeutic targets for APAP-induced liver injury. This study used a genome-wide CRISPR-Cas9 screen to evaluate genes that are protective against, or cause susceptibility to, APAP-induced liver injury. HuH7 human hepatocellular carcinoma cells containing CRISPR-Cas9 gene knockouts were treated with 15 mM APAP for 30 minutes to 4 days. A gene expression profile was developed based on the 1) top screening hits, 2) overlap of expression data from APAP overdose studies, and 3) predicted affected biological pathways. We further demonstrated the implementation of intermediate time points for the identification of early and late response genes. This study illustrated the power of a genome-wide CRISPR-Cas9 screen to systematically identify novel genes involved in APAP-induced hepatotoxicity and to provide potential targets to develop novel therapeutic modalities.

Acetaminophen inhibits intestinal p-glycoprotein transport activity

Repeated acetaminophen (AP) administration modulates intestinal P-glycoprotein (P-gp) expression. Whether AP can modulate P-gp activity in a short-term fashion is unknown. We investigated the acute effect of AP on rat intestinal P-gp activity in vivo and in vitro. In everted intestinal sacs, AP inhibited serosal-mucosal transport of rhodamine 123 (R123), a prototypical P-gp substrate. R123 efflux plotted against R123 concentration adjusted well to a sigmoidal curve. Vmax decreased 50% in the presence of AP, with no modification in EC50, or slope, ruling out the possibility of inhibition to be competitive. Inhibition by AP was absent at 0°C, consistent with interference of the active transport of R123 by AP. Additionally, AP showed no effect on normal localization of P-gp at the apical membrane of the enterocyte and neither affected paracellular permeability. Consistent with absence of a competitive inhibition, two further strategies strongly suggested that AP is not a P-gp substrate. First, serosal-mucosal transport of AP was not affected by the classical P-gp inhibitors verapamil or Psc 833. Second, AP accumulation was not different between P-gp knock-down and wild-type HepG2 cells. In vivo intestinal absorption of digoxin, another substrate of P-gp, was assessed in the presence or absence of AP (100 μM). Portal digoxin concentration was increased by 214%, in average, by AP, as compared with digoxin alone. In conclusion, AP inhibited P-gp activity, increasing intestinal absorption of digoxin, a prototypical substrate. These results suggest that therapeutic efficacy of P-gp substrates can be altered if coadministered with AP.

Development of a high-throughput screening assay for chemical effects on proliferation and viability of immortalized human neural progenitor cells

There is considerable public concern that the majority of commercial chemicals have not been evaluated for their potential to cause developmental neurotoxicity. Although several chemicals are assessed annually under the current developmental neurotoxicity guidelines, time, resource, and animal constraints prevent testing of large numbers of chemicals using this approach. Thus, incentive is mounting to develop in vitro methods to screen chemicals for their potential to harm the developing human nervous system. As an initial step toward this end, the present studies evaluated an automated, high-throughput method for screening chemical effects on proliferation and viability using ReNcell CX cells, a human neural progenitor cell (hNPC) line. ReNcell CX cells doubled in approximately 36 h and expressed the neural progenitor markers nestin and SOX2. High-throughput assays for cell proliferation (5-bromo-2'-deoxyuridine incorporation) and viability (propidium iodide exclusion) were optimized and tested using known antiproliferative compounds. The utility of this in vitro screen was evaluated further using a set of compounds containing eight known to cause developmental neurotoxicity and eight presumably nontoxic compounds. Six out of eight developmental neurotoxicants significantly inhibited ReNcell CX cell proliferation and/or viability, whereas two out of eight nontoxic chemicals caused only minimal effects. These results demonstrate that chemical effects on cell proliferation and viability can be assessed via high-throughput methods using hNPCs. Further development of this approach as part of a strategy to screen compounds for potential effects on nervous system development is warranted.

Acetaminophen alters microsomal ryanodine Ca2+ channel in HepG2 cells overexpressing CYP2E1

Acetaminophen hepatotoxicity is mediated by an initial metabolic activation and covalent binding of drug metabolites to liver proteins. Acetaminophen metabolites have been shown to affect rat liver microsomal Ca2+ stores, but the mechanism is not well understood. The aim of the current work was to find out if the metabolism of acetaminophen by CYP2E1 affects ryanodine-sensitive Ca2+ stores in the endoplasmic reticulum of transduced HepG2 cells. Five millimoles acetaminophen decreased proliferation of CYP2E1-overexpressing HepG2 cells, increased cytosolic Ca2+ levels and produced significant cytotoxicity, while only little, mostly anti-proliferative effects were found in HepG2 cells lacking CYP2E1. CYP2E1 inhibitor-4-methylpyrazole decreased drug cytotoxicity in transduced cells and normalized elevated Ca2+ levels. Acetaminophen cytotoxicity was significantly higher in CYP2E1 expressing cells with depleted glutathione. In the cells engineered to overexpress CYP2E1, an increased [3H]ryanodine affinity (by 45%) and increased ligand maximal binding to ryanodine receptors (by 64%) was observed, most probably due to increased association rate of [3H]ryanodine. Ca2+ loading was decreased by about 53% in microsomal fractions isolated from transduced cells treated with acetaminophen and by 92% in glutathione depleted transfected cells treated with the drug. Ca2+/Mg2+-ATPase activity was unchanged in all microsomal fractions. Such effects were not observed in cells lacking CYP2E1. Our results confirm significant role of CYP2E1 in metabolic activation of acetaminophen and indicate that ryanodine receptors located in the liver endoplasmic reticulum are sensitive targets for acetaminophen metabolites.