Commentary

Hepatotoxic metabolic activation of paracetamol and its derivatives phenacetin and benorilete: Oxygenation or electron transfer?

A series of diclofenac hybrid molecules were synthesized and evaluated for their NO-inhibitory ability in LPS-induced RAW 264.7 macrophage cells. Among them, compound 1 showed the highest NO-inhibitory ability (approximately 66%) and no significant cytotoxicity. Compound 1 exhibited superior NF-κB-inhibitory ability compared to diclofenac through the activation of Nrf2/HO-1 signaling pathway in RAW 264.7. 20 mg/kg compound 1 resulted in remarkable colitis improvement in dextran sulfate sodium (DSS)-induced mice model by up-regulating HO-1 and down-regulating phosphorylation level of NF-κB p65. Moreover, 50 mg/kg dose of compound 1 showed a lower ulcerogenic potential compared to diclofenac in rats. The diclofenac-eugenol hybrid (compound 1) may serve as a novel anti-inflammatory agent based on its role in inhibiting the NF-κB signaling pathway and activating HO-1 expression with no toxicity in vitro and in vivo.

Geranylgeranylacetone (GGA), an anti-ulcer drug, has been reported to induce heat shock protein (HSP) 70 in several animal organs. The present study was performed to determine whether GGA protects mouse liver against acetaminophen (APAP)-induced injury and whether it has potential as a therapeutic agent for APAP overdose. Hepatic damage was induced by single oral administration of APAP (500 mg/kg). GGA at 400 mg/kg was given orally 4 or 8 h before, or 0.5 h after APAP administration. Treatment of mice with GGA 4 h before or 0.5 h after APAP administration suppressed increases in transaminase activities and ammonia content in blood as well as hepatic necrosis. Such GGA treatment significantly increased hepatic HSP70 accumulation after APAP administration. Furthermore, GGA inhibited increases in hepatic lipid peroxide content and hepatic myeloperoxidase activity after APAP administration. In contrast, GGA neither inhibited hepatic cytochrome P450 2E1 activity nor suppressed hepatic glutathione depletion after APAP administration. The protective effect of GGA treatment 4 h before APAP on hepatotoxicity induced by APAP was completely inhibited with quercetin, known as an HSP inhibitor. In conclusion, GGA has been identified as a new antidote to APAP injury, acting by induction of HSP70. The potential of GGA as a therapeutic tool is strongly supported by its ability to inhibit hepatic injury even when administered after ingestion of APAP.

Quantum chemistry calculations at the B3LYP theory level, together with the 6-31G* basis set were employed to obtain energy (E), ionization potential (IP), bond dissociation energies (BDE), and spin-density distribution for paracetamol (PAR) and 3,5-disubstituted analogues of PAR. Calculations of spin densities were performed for radical formed by hydrogen abstraction from the phenolic hydroxyl group. The unpaired electron remains is localized on the O₇ phenolic oxygen (31–40%), C₃ and C₅ carbon atoms at the ortho (17–27 and 21–27%) and C₁ carbon atom at the para (25–33%) positions. The correlation between analgesic activity, cytotoxicity, and electronic properties was obtained by using correlation matrix. The IP, and BDE_O–H are significant related with the in vitro inhibition of cyclooxygenase, while BDE_O–H, BDE_N–H and IP are significant related with the cytotoxicity (LDH).

In this study we used a peroxidase model system (glucose/glucose oxidase and horseradish peroxidase) to investigate the effect of extracellularly generated reactive metabolites of 3,5-Me₂-acetaminophen on cell viability and on cellular thiol levels. Incubation of hepatocytes with 3,5-Me₂-acetaminophen in the presence of glucose/glucose oxidase and horseradish peroxidase caused a concentration-dependent loss of cell viability. Loss of viability was associated with decreased protein thiol levels. Addition of the reducing agent DTT, but not catalase, during the incubation restored cellular protein thiol levels and arrested the cell killing. Protein thiol depletion occurred selectively to the mitochondrial and microsomal fractions and was specific for a very limited number of protein bands. The data suggest that the oxidative modification of individual protein cysteine residues within the latter two organelle fractions is critically involved in the mechanism of toxicity.