Contribution of acetaminophen-cysteine to acetaminophen nephrotoxicity in CD-1 mice: I. Enhancement of acetaminophen nephrotoxicity by acetaminophen-cysteine

Spatial analysis of renal acetaminophen metabolism and its modulation by 4-methylpyrazole with DESI mass spectrometry imaging

Acute kidney injury (AKI) is a common complication in acetaminophen (APAP) overdose patients and can negatively impact prognosis. Unfortunately, N-acetylcysteine, which is the standard of care for the treatment of APAP hepatotoxicity does not prevent APAP-induced AKI. We have previously demonstrated the renal metabolism of APAP and identified fomepizole (4-methylpyrazole, 4MP) as a therapeutic option to prevent APAP-induced nephrotoxicity. However, the kidney has several functionally distinct regions, and the dose-dependent effects of APAP on renal response and regional specificity of APAP metabolism are unknown. These aspects were examined in this study using C57BL/6J mice treated with 300-1200 mg/kg APAP and mass spectrometry imaging (MSI) to provide spatial cues relevant to APAP metabolism and the effects of 4MP. We find that renal APAP metabolism and generation of the nonoxidative (APAP-GLUC and APAP-SULF) and oxidative metabolites (APAP-GSH, APAP-CYS, and APAP-NAC) were dose-dependently increased in the kidney. This was recapitulated on MSI which revealed that APAP overdose causes an accumulation of APAP and APAP GLUC in the inner medulla and APAP-CYS in the outer medulla of the kidney. APAP-GSH, APAP-NAC, and APAP-SULF were localized mainly to the outer medulla and the cortex where CYP2E1 expression was evident. Interestingly, APAP also induced a redistribution of reduced GSH, with an increase in oxidized GSH within the kidney cortex. 4MP ameliorated these region-specific variations in the formation of APAP metabolites in renal tissue sections. In conclusion, APAP metabolism has a distinct regional distribution within the kidney, the understanding of which provides insight into downstream mechanisms of APAP-induced nephrotoxicity.

The Emerging Roles of γ-Glutamyl Peptides Produced by γ-Glutamyltransferase and the Glutathione Synthesis System

L-γ-Glutamyl-L-cysteinyl-glycine is commonly referred to as glutathione (GSH); this ubiquitous thiol plays essential roles in animal life. Conjugation and electron donation to enzymes such as glutathione peroxidase (GPX) are prominent functions of GSH. Cellular glutathione balance is robustly maintained via regulated synthesis, which is catalyzed via the coordination of γ-glutamyl-cysteine synthetase (γ-GCS) and glutathione synthetase, as well as by reductive recycling by glutathione reductase. A prevailing short supply of L-cysteine (Cys) tends to limit glutathione synthesis, which leads to the production of various other γ-glutamyl peptides due to the unique enzymatic properties of γ-GCS. Extracellular degradation of glutathione by γ-glutamyltransferase (GGT) is a dominant source of Cys for some cells. GGT catalyzes the hydrolytic removal of the γ-glutamyl group of glutathione or transfers it to amino acids or to dipeptides outside cells. Such processes depend on an abundance of acceptor substrates. However, the physiological roles of extracellularly preserved γ-glutamyl peptides have long been unclear. The identification of γ-glutamyl peptides, such as glutathione, as allosteric modulators of calcium-sensing receptors (CaSRs) could provide insights into the significance of the preservation of γ-glutamyl peptides. It is conceivable that GGT could generate a new class of intercellular messaging molecules in response to extracellular microenvironments.

Hepatic pyruvate and alanine metabolism are critical and complementary for maintenance of antioxidant capacity and resistance to oxidative insult

OBJECTIVE

Mitochondrial pyruvate is a critical intermediary metabolite in gluconeogenesis, lipogenesis, and NADH production. As a result, the mitochondrial pyruvate carrier (MPC) complex has emerged as a promising therapeutic target in metabolic diseases. Clinical trials are currently underway. However, recent in vitro data indicate that MPC inhibition diverts glutamine/glutamate away from glutathione synthesis and toward glutaminolysis to compensate for loss of pyruvate oxidation, possibly sensitizing cells to oxidative insult. Here, we explored this in vivo using the clinically relevant acetaminophen (APAP) overdose model of acute liver injury, which is driven by oxidative stress.

METHODS

We used pharmacological and genetic approaches to inhibit MPC2 and alanine aminotransferase 2 (ALT2), individually and concomitantly, in mice and cell culture models and determined the effects on APAP hepatotoxicity.

RESULTS

We found that MPC inhibition sensitizes the liver to APAP-induced injury in vivo only with concomitant loss of alanine aminotransferase 2 (ALT2). Pharmacological and genetic manipulation of neither MPC2 nor ALT2 alone affected APAP toxicity, but liver-specific double knockout (DKO) significantly worsened APAP-induced liver damage. Further investigation indicated that DKO impaired glutathione synthesis and increased urea cycle flux, consistent with increased glutaminolysis, and these results were reproducible in vitro. Finally, induction of ALT2 and post-treatment with dichloroacetate both reduced APAP-induced liver injury, suggesting new therapeutic avenues.

CONCLUSIONS

Increased susceptibility to APAP toxicity requires loss of both the MPC and ALT2 in vivo, indicating that MPC inhibition alone is insufficient to disrupt redox balance. Furthermore, the results from ALT2 induction and dichloroacetate in the APAP model suggest new metabolic approaches to the treatment of liver damage.

Cysteine conjugates of acetaminophen and p-aminophenol are potent inducers of cellular impairment in human proximal tubular kidney HK-2 cells

Acetaminophen (APAP) belong among the most used analgesics and antipyretics. It is structurally derived from p-aminophenol (PAP), a potent inducer of kidney toxicity. Both compounds can be metabolized to oxidation products and conjugated with glutathione. The glutathione-conjugates can be cleaved to provide cysteine conjugates considered as generally nontoxic. The aim of the present report was to synthesize and to purify both APAP- and PAP-cysteine conjugates and, as the first study at all, to evaluate their biological effects in human kidney HK-2 cells in comparison to parent compounds. HK-2 cells were treated with tested compounds (0-1000 µM) for up to 24 h. Cell viability, glutathione levels, ROS production and mitochondrial function were determined. After 24 h, we found that both APAP- and PAP-cysteine conjugates (1 mM) were capable to induce harmful cellular damage observed as a decrease of glutathione levels to 10% and 0%, respectively, compared to control cells. In addition, we detected the disappearance of mitochondrial membrane potential in these cells. In the case of PAP-cysteine, the extent of cellular impairment was comparable to that induced by PAP at similar doses. On the other hand, 1 mM APAP-cysteine induced even larger damage of HK-2 cells compared to 1 mM APAP after 6 or 24 h. We conclude that cysteine conjugates with aminophenol are potent inducers of oxidative stress causing significant injury in kidney cells. Thus, the harmful effects cysteine-aminophenolic conjugates ought to be considered in the description of APAP or PAP toxicity.

Detection of Distinct Distributions of Acetaminophen and Acetaminophen-Cysteine in Kidneys up to 10 μm Resolution and Identification of a Novel Acetaminophen Metabolite Using an AP-MALDI Imaging Mass Microscope

Drug distribution studies in tissue are crucial for understanding the pharmacokinetics and potential toxicity of drugs. Recently, matrix-assisted laser desorption ionization-mass spectrometry imaging (MALDI-MSI) has gained attention for drug distribution studies due to its high sensitivity, label-free nature, and ability to distinguish between parent drugs, their metabolites, and endogenous molecules. Despite these advantages, achieving high spatial resolution in drug imaging is challenging. Importantly, many drugs and metabolites are rarely detectable by conventional vacuum MALDI-MSI because of their poor ionization efficiency. It has been reported that acetaminophen (APAP) and one of its major metabolites, APAP-Cysteine (APAP-CYS), cannot be detected by vacuum MALDI-MSI without derivatization. In this context, we showed the distribution of both APAP and APAP-CYS in kidneys at high spatial resolution (25 and 10 μm) by employing an atmospheric pressure-MALDI imaging mass microscope without derivatization. APAP was highly accumulated in the renal pelvis 1 h after drug administration, while APAP-CYS exhibited characteristic distributions in the outer medulla and renal pelvis at both 30 min and 1 h after administration. Interestingly, cluster-like distributions of APAP and APAP-CYS were observed in the renal pelvis at 10 μm spatial resolution. Additionally, a novel APAP metabolite, tentatively coined as APAP-butyl sulfate (APAP-BS), was identified in the kidney, brain, and liver by combining MSI and tandem MSI. For the first time, our study revealed differential distributions of APAP, APAP-CYS (in kidneys), and APAP-BS (in kidney, brain, and liver) and is believed to enhance the understanding of the pharmacokinetics and potential nephrotoxicity of this drug.

Critical Roles of the Cysteine-Glutathione Axis in the Production of γ-Glutamyl Peptides in the Nervous System

γ-Glutamyl moiety that is attached to the cysteine (Cys) residue in glutathione (GSH) protects it from peptidase-mediated degradation. The sulfhydryl group of the Cys residue represents most of the functions of GSH, which include electron donation to peroxidases, protection of reactive sulfhydryl in proteins via glutaredoxin, and glutathione conjugation of xenobiotics, whereas Cys-derived sulfur is also a pivotal component of some redox-responsive molecules. The amount of Cys that is available tends to restrict the capacity of GSH synthesis. In in vitro systems, cystine is the major form in the extracellular milieu, and a specific cystine transporter, xCT, is essential for survival in most lines of cells and in many primary cultivated cells as well. A reduction in the supply of Cys causes GPX4 to be inhibited due to insufficient GSH synthesis, which leads to iron-dependent necrotic cell death, ferroptosis. Cells generally cannot take up GSH without the removal of γ-glutamyl moiety by γ-glutamyl transferase (GGT) on the cell surface. Meanwhile, the Cys-GSH axis is essentially common to certain types of cells; primarily, neuronal cells that contain a unique metabolic system for intercellular communication concerning γ-glutamyl peptides. After a general description of metabolic processes concerning the Cys-GSH axis, we provide an overview and discuss the significance of GSH-related compounds in the nervous system.

A review: Systematic research approach on toxicity model of liver and kidney in laboratory animals

Therapeutic experiments are commonly performed on laboratory animals to investigate the possible mechanism(s) of action of toxic agents as well as drugs or substances under consideration. The use of toxins in laboratory animal models, including rats, is intended to cause toxicity. This study aimed to investigate different models of hepatotoxicity and nephrotoxicity in laboratory animals to help researchers advance their research goals. The current narrative review used databases such as Medline, Web of Science, Scopus, and Embase and appropriate keywords until June 2021. Nephrotoxicity and hepatotoxicity models derived from some toxic agents such as cisplatin, acetaminophen, doxorubicin, some anticancer drugs, and other materials through various signaling pathways are investigated. To understand the models of renal or hepatotoxicity in laboratory animals, we have provided a list of toxic agents and their toxicity procedures in this review.

Tanshinone IIA prevents acetaminophen-induced nephrotoxicity through the activation of the Nrf2-Mrp2/4 pathway in mice

It's known that APAP overdose often leads to hepatotoxicity and nephrotoxicity. In the present study, we investigated the preventative effect of Tan IIA on APAP-induced nephrotoxicity. Mice were orally administrated with Tan IIA (10 or 30 mg/kg/day) for 1 week and subsequently gavaged with 200 mg/kg of APAP. Tan IIA reduced APAP-induced nephrotoxicity as evidenced by histopathological evaluation and serum creatinine levels. Tan IIA pretreatment promoted the efflux of the toxic intermediate metabolite N-acetyl-p-benzoquinone imine (NAPQI), thus reduced its injury to mouse kidney. After Tan IIA pretreatment, a remarkable increase in mRNA and protein expression of Nrf2 and its target genes Mrp2 and Mrp4 was observed in Nrf2^+/+ mice kidneys, however, no obvious change of Mrp2 and Mrp4 mRNA and protein expression was detected in Nrf2^-/- mice kidneys. HK-2 cells were used for exploring the roles of Tan IIA in the Nrf2-MRPs pathway in vitro. Consistently, Tan IIA up-regulated the Nrf2-MRPs pathway and promoted the nuclear Nrf2 accumulation in HK-2 cells. Collectively, our findings suggested that Tan IIA facilitated the clearance of toxic intermediate metabolite NAPQI from the kidney through upregulation of the Nrf2-MRP2/4 pathway, thereby, performing preventive effects against APAP-induced nephrotoxicity.

Construction of N-CDs and Calcein-Based Ratiometric Fluorescent Sensor for Rapid Detection of Arginine and Acetaminophen

In our study, a unique ratiometric fluorescent sensor for the rapid detection of arginine (Arg) and acetaminophen (AP) was constructed by the integration of blue fluorescent N-CDs and yellowish-green fluorescent calcein. The N-CD/calcein ratiometric fluorescent sensor exhibited dual emission at 435 and 519 nm under the same excitation wavelength of 370 nm, and caused potential Förster resonance energy transfer (FRET) from N-CDs to calcein. When detecting Arg, the blue fluorescence from the N-CDs of the N-CD/calcein sensor was quenched by the interaction of N-CDs and Arg. Then, the fluorescence of our sensor was recovered with the addition of AP, possibly due to the stronger association between AP and Arg, leading to the dissociation of Arg from N-CDs. Meanwhile, we observed an obvious fluorescence change from blue to green, then back to blue, when Arg and AP were added, exhibiting the “on–off–on” pattern. Next, we determined the detection limits of the N-CD/calcein sensor to Arg and AP, which were as low as 0.08 μM and 0.02 μM, respectively. Furthermore, we discovered that the fluorescence changes of the N-CD/calcein sensor were only responsible for Arg and AP. These results suggested its high sensitivity and specificity for Arg and AP detection. In addition, we have successfully achieved its application in bovine serum samples, indicating its practicality. Lastly, the logic gate was generated by the N-CD/calcein sensor and presented its good reversibility. Overall, we have demonstrated that our N-CD/calcein sensor is a powerful sensor to detect Arg and AP and that it has potential applications in biological analysis and imaging.

Comparing N-acetylcysteine and 4-methylpyrazole as antidotes for acetaminophen overdose

Acetaminophen (APAP) overdose can cause hepatotoxicity and even liver failure. N-acetylcysteine (NAC) is still the only FDA-approved antidote against APAP overdose 40 years after its introduction. The standard oral or intravenous dosing regimen of NAC is highly effective for patients with moderate overdoses who present within 8 h of APAP ingestion. However, for late-presenting patients or after ingestion of very large overdoses, the efficacy of NAC is diminished. Thus, additional antidotes with an extended therapeutic window may be needed for these patients. Fomepizole (4-methylpyrazole), a clinically approved antidote against methanol and ethylene glycol poisoning, recently emerged as a promising candidate. In animal studies, fomepizole effectively prevented APAP-induced liver injury by inhibiting Cyp2E1 when treated early, and by inhibiting c-jun N-terminal kinase (JNK) and oxidant stress when treated after the metabolism phase. In addition, fomepizole treatment, unlike NAC, prevented APAP-induced kidney damage and promoted hepatic regeneration in mice. These mechanisms of protection (inhibition of Cyp2E1 and JNK) and an extended efficacy compared to NAC could be verified in primary human hepatocytes. Furthermore, the formation of oxidative metabolites was eliminated in healthy volunteers using the established treatment protocol for fomepizole in toxic alcohol and ethylene glycol poisoning. These mechanistic findings, together with the excellent safety profile after methanol and ethylene glycol poisoning and after an APAP overdose, suggest that fomepizole may be a promising antidote against APAP overdose that could be useful as adjunct treatment to NAC. Clinical trials to support this hypothesis are warranted.

Kidney Injury Following Ibuprofen and Acetaminophen: A Real-World Analysis of Post-Marketing Surveillance Data

Background: Although kidney injury has been reported as a serious adverse effect in patients treated with ibuprofen or acetaminophen (APAP), there are still few real-world studies to compare the specific differences in the adverse effects of nephrotoxicity.

Methods: Disproportionality analysis and Bayesian analysis were devoted to data-mining of the suspected kidney injury after using ibuprofen and APAP based on the FDA’s Adverse Event Reporting System (FAERS) from January 2004 to March 2021. The times to onset, fatality, and hospitalization rates of ibuprofen-associated kidney injury and APAP-associated kidney injury were also investigated.

Results: 2,453 reports of ibuprofen-associated kidney injury and 1,288 reports of APAP-associated kidney injury were identified. Ibuprofen appeared to affected more middle-aged patients than elderly ones (27.76 vs 16.53%) while APAP appeared to affected more young patients than middle-aged patients (45.24 vs 29.10%) and elderly patients were fewer (13.99%). Compared to ibuprofen, APAP had the higher association with renal injury based on the higher reporting odds ratio (ROR = 2.45, 95% two-sided CI = 2.36–2.56), proportional reporting ratio (PRR = 2.39, χ² = 2002.94) and empirical Bayes geometric mean (EBGM = 2.38, 95% one-sided CI = 2.3). In addition, APAP-associated kidney injury had earlier onset (32.74 vs 115.82 days, p < 0.0001) and a higher fatality rate (44.43 vs 7.36%, p < 0.001) than those of ibuprofen-associated kidney injury.

Conclusion: The analysis of FAERS data provides a more accurate profile on the incidence and prognosis of kidney injury after ibuprofen and acetaminophen treatment, enabling continued surveillance and timely intervention in patients at risk of kidney injury using these drugs.

4-methylpyrazole protects against acetaminophen-induced acute kidney injury

Acetaminophen (APAP) hepatotoxicity is the most common cause of acute liver failure in the United States, and while a significant percentage of APAP overdose patients develop kidney injury, molecular mechanisms involved in APAP-induced nephrotoxicity are relatively unknown. We have shown that 4-methylpyrazole (4MP, Fomepizole) protects against APAP-induced liver injury by inhibiting reactive metabolite formation through Cyp2E1, and analysis of data from APAP overdose patients indicated that kidney dysfunction strongly correlated with severe liver injury. Since Cyp2E1 is also expressed in the kidney, this study explored protection by 4MP against APAP-induced nephrotoxicity. Male C57BL/6 J mice were treated with either 300 or 600 mg/kg APAP with or without 4MP for 2, 6 or 24 h, followed by measurement of APAP metabolism and tissue injury. Interestingly, levels of APAP and its non-oxidative metabolites were significantly higher in kidneys when compared to the liver. APAP-protein adducts were present in both tissues within 2 h, but were absent in kidney mitochondria, unlike in the liver. While GSH depletion was seen in both tissues, activation of c-jun N-terminal kinase and its translocation to the mitochondria, which is a critical feature of APAP-induced liver injury, was not detected in the kidney. Treatment with 4MP attenuated APAP oxidative metabolite generation, GSH depletion as well as kidney injury indicating its potential use in protection against APAP-induced nephrotoxicity. In conclusion, since reactive metabolite formation seems to be common in both liver and kidney, 4MP mediated inhibition of Cyp2E1 protects against APAP-induced nephrotoxicity. However, downstream mechanisms of APAP-induced nephrotoxicity seem distinct from the liver.

Comparative biochemical and histopathological evaluations proved that receptacle is the most effective part of Cynara scolymus against liver and kidney damages

ETHNOPHARMACOLOGICAL RELEVANCE

The liver and kidney are among the most important organs in the body, where metabolic and elimination functions take place. During this process, liver and kidneys may suffer damage due to ingestion or formation of toxic metabolites leading to organ loss and even death. Artichoke (Cynara scolymus L.) leaf has long been recognized as a popular herbal remedy in traditional medicines with beneficial effects on liver.

AIM OF THE STUDY

In phytotherapy leaves are the part used to support the liver functions and for treatment of damage induced by various toxins, while fleshy receptacle is cooked as meal to support liver homeostasis. However, effects of other plant parts on liver such as stems, bracts have not much attracted the attention of scientific community so far. In this study we investigated comparatively the hepatoprotective and nephroprotective effects of different plant parts of artichoke, i.e. receptacles, outer bracts, inner bracts, and stems with that of leaves upon paracetamol-induction in rats.

MATERIALS AND METHODS

Aqueous ethanol (80%) extracts obtained from the different parts of artichoke were administered for five consecutive days after paracetamol induction to rats. At the end of experimental period blood samples from the experimental animals were taken for biochemical tests, while livers and kidneys were removed for further histopathological evaluation.

RESULTS

The histopathological examinations of liver and kidney tissues revealed that the receptacle and stem extracts of the artichoke were the most effective parts by improving the experimentally induced pathology in both liver and kidney. Biochemical tests also supported the histopathological data; receptacle, stem and bract extracts reduced serum alanine transaminase (ALT) and aspartate transaminase (AST) levels, but not alkaline phosphatase (ALP), creatinine and blood urea nitrogen (BUN) levels.

CONCLUSIONS

Histopathological and biochemical studies have shown that receptacle and stem extracts of artichoke were found to exert higher protective activity on liver and kidney damage induced by paracetamol comparing to its bract and leaf extracts, the latest is officially recognized as herbal remedy.

Evaluation of hepatic and renal effects in rat dams and their offspring after exposure to paracetamol during gestation and lactation

Paracetamol (PAR) is the analgesic and antipyretic of choice for pregnant and nursing women. PAR may reach the fetus and/or neonate through the placenta and/or milk and effect development. This study evaluated possible hepatic and renal effects in rat dams and their offspring exposed to PAR using a human-relevant route of administration and doses from Gestational Day 6 to Postnatal Day (PND) 21. Dams were gavaged daily with PAR (35 or 350mg kg-1) or water (CON). Dams and pups were killed on PND21 and 22 respectively, and blood was collected for biochemical analysis (aspartate aminotransferase (AST), alanine aminotransferase (ALT), urea and creatinine). The kidneys and liver were isolated and processed for histopathological assessment and evaluation of oxidative stress markers. Compared with the CON groups, pups exposed to 350mg kg-1 PAR had increased renal reduced glutathione (GSH), whereas dams exposed to both doses of PAR increased serum AST. PAR administration did not affect parameters of general toxicity or renal and hepatic oxidative stress. In conclusion, maternal exposure to human-relevant doses of PAR by gavage was not associated with hepatic or renal toxicity in the pups or dams, but PAR was not devoid of effects. Exposure to PAR increased renal GSH in pups, which could suggest an adaptive antioxidant response, and affected maternal serum AST activity.

The mercapturomic profile of health and non-communicable diseases

The mercapturate pathway is a unique metabolic circuitry that detoxifies electrophiles upon adducts formation with glutathione. Since its discovery over a century ago, most of the knowledge on the mercapturate pathway has been provided from biomonitoring studies on environmental exposure to toxicants. However, the mercapturate pathway-related metabolites that is formed in humans—the mercapturomic profile—in health and disease is yet to be established. In this paper, we put forward the hypothesis that these metabolites are key pathophysiologic factors behind the onset and development of non-communicable chronic inflammatory diseases. This review goes from the evidence in the formation of endogenous metabolites undergoing the mercapturate pathway to the methodologies for their assessment and their association with cancer and respiratory, neurologic and cardiometabolic diseases.

Inter-individual and inter-organ variability in the bioactivation of paracetamol by human liver and kidney tissues

Paracetamol (PAR) overdose is associated with massive hepatic injury; it may induce kidney toxicity as well. It is essential to measure organ-specific activities of related CYPs for evaluating the overdose cases. Available HPLC-based methods require high amounts of tissue samples. In order to develop liquid chromatography mass spectrometry (LC-MS)-based methods to process small amounts of human tissues, liver and kidney samples were obtained. Individual microsomes were prepared and incubated with PAR (for quantifying bioactivation), with nifedipine (for measuring CYP3A4 activity) and with p-nitrophenol (for measuring CYP2E1 activity). The small amount of tissue microsomes was sufficient to measure both the formation of NAPQI and the activities of CYP enzymes. Although the sample size in group was relatively low, both NAPQI formation and activity of CYP2E1 were significantly higher in males compared to females in kidney. Considerable variations in the metabolic capacity of individuals were observed for both organs.

Protective effect of an L-type calcium channel blocker, amlodipine, on paracetamol-induced hepatotoxicity in rats

Paracetamol (P), one of the most popular and commonly used analgesic and antipyretic agents, causes hepatotoxicity in overdoses. Amlodipine (AML), an L-type calcium channel blocker, has been shown to have anti-inflammatory activity by reversing the effect of calcium in the inflammation pathogenesis. In this study, the hepatoprotective activity of AML on P-induced hepatotoxicity was evaluated. Thirty male albino Wistar rats were divided into five groups: (1) control, (2) 2 g/kg of P, (3) 2 g/kg of P + 5 mg/kg of AML, (4) 2 g/kg of P + 10 mg/kg of AML, and (5) 10 mg/kg of AML. Some liver enzymes, oxidative parameters, cytokine mRNA expressions, histopathology, and immunohistochemical studies were performed in liver and blood samples. The serum levels of alanine aminotransferase and aspartate aminotransferase and the mRNA expression of tumor necrosis factor-alpha (TNF-α) and transforming growth factor-beta in the liver tissues were significantly increased in the group treated with P. The superoxide dismutase and glutathione parameters decreased and malondialdehyde levels increased in the livers of the rats treated with P. All these parameters were increased with both doses of the AML similar to the control group. A histopathological examination of the liver showed that AML administration ameliorated the P-induced inflammatory liver damage. In immunohistochemical staining, the expression of TNF-α in the cytoplasm of the hepatocytes was increased in the P group but not in other treatment groups when compared to the control. In conclusion, AML treatment showed significant protective effects against P-induced hepatotoxicity by increasing the activity of antioxidants and reducing inflammatory cytokines.

Extrahepatic toxicity of acetaminophen: critical evaluation of the evidence and proposed mechanisms

Research on acetaminophen (APAP) toxicity over the last several decades has focused on the pathophysiology of liver injury, but increasingly attention is paid to other known and possible adverse effects. It has been known for decades that APAP causes acute kidney injury, but confusion exists regarding prevalence, and the mechanisms have not been well investigated. More recently, evidence for pulmonary, endocrine, neurological, and neurodevelopmental toxicity has been reported in a number of published experimental, clinical, and epidemiological studies, but the quality of those studies has varied. It is important to view those data critically due to implications for regulation and clinical practice. Here, we review evidence and proposed mechanisms for extrahepatic adverse effects of APAP and weigh weaknesses and strengths in the available data.

Nephrotoxicity of sodium valproate and protective role of L-cysteine in rats at biochemical and histological levels

BACKGROUND

This study investigated whether the combination of sodium valproate (SV) with L-cysteine (LC) can decrease the SV toxicity of kidneys. SV caused alternation in oxidative/antioxidant balance.

METHODS

Biochemical estimations included the determination of oxidative stress markers like thiobarbituric acid-reactive substances in kidney tissue, and enzymatic antioxidant activities such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase as well as total antioxidant capacity were evaluated in renal tissues. Creatinine and uric acid levels in the serum were also determined to assess kidney function. Pathological examination of the kidney was also performed.

RESULTS

Increasing the levels of lipid peroxidation and decreasing the enzymatic activity (SOD, CAT, and GPx) as well as total antioxidant capacity of rats was shown with different doses of SV. Impairment in renal function tests suggests a decreased glomerular filtration rate, as serum creatinine was elevated. Histopathological changes of kidney tissue treated with SV reveal the proximal and the distal convoluted tubules that show hydropic changes (small white vacuoles within the cytoplasm and the glomeruli show hypercellularity).

CONCLUSIONS

The concurrent administration of LC with SV significantly had beneficial effects on the kidney and all the above parameters have been improved.

Characterization of Acetaminophen Toxicity in Human Kidney HK-2 Cells

Acetaminophen (APAP) overdose causes liver injury, but in some cases it is associated also with renal impairment. While several studies exist in relation to acetaminophen nephrotoxicity, no reports have been published describing intracellular changes related to APAP nephrotoxicity in vitro. Because proximal tubular cells are considered to constitute a secondary site of drug-induced injury after hepatocytes, our study's aim was to estimate the toxicity in the human HK-2 cell line. We used a range of APAP concentrations (1-10 mM) to examine toxicity in the cells (1-48 h). We evaluated cell viability using the WST-1 and LDH tests. Cells impairment was also determined by monitoring ROS production, glutathione levels. We proved that HK-2 cells are able to metabolize acetaminophen. We observed moderate impairment of cells already after 1 h of treatment based on a finding of increased ROS production and decreased cell viability. After 24 h, the results showed significant cellular impairment at all tested concentrations except for 1 mM APAP, but no glutathione depletion was found. We conclude that HK-2 cells are susceptible to acetaminophen toxicity but, unlike hepatocytes, it might be not linked to glutathione depletion.

Thearubigins protect against acetaminophen-induced hepatic and renal injury in mice: biochemical, histopathological, immunohistochemical, and flow cytometry study

CONTEXT

Acetaminophen toxicity is used as a model for studying chemical toxicity. N-acetylcysteine (NAC) is used for the treatment of hepatotoxicity; however, there is no specific therapy for nephrotoxicity.

OBJECTIVE

This study was designed to investigate the potential protective effect of black tea extract (BTE) and its main phenolic pigment, thearubigins (TRs), against acetaminophen (APAP)-induced hepatic and renal injury in mice.

MATERIALS AND METHODS

Besides control groups, six groups (n = 8) were given intraperitoneally APAP (300 mg/kg) and then after 1.5 hours were treated intraperitoneally as follows: NAC (318 mg/kg), BTE (3%, 4.5%), and TRs (50, 60, and 70 mg/kg). Six hours post-APAP injection, blood was collected for biochemical measurements. Later, liver and kidneys were removed for histopathological, immunohistochemical, and flow cytometry studies.

RESULTS

APAP increased alanine aminotransferase and malondialdehyde and decreased glutathione levels in blood. Treatments significantly reversed these changes mostly with NAC and TRs70. TRs showed dose-dependent significant differences. The APAP-induced central lobular hepatic necrosis and increased TUNEL positivity were mild with co-administration of NAC and TRs (60, 70) while moderate with co-administration of BTE (3, 4.5) and TRs50. The APAP-increased serum creatinine level was significantly reversed by treatments (mostly TRs60, 70). The APAP-induced renal tubular epithelial degeneration and necrosis were mild with co-administration of TRs (60, 70) while moderate with co-administration of NAC, BTE (3, 4.5), and TRs50. The APAP-accumulated apoptotic cells in sub-G1 phase were significantly decreased by treatments, mostly by NAC and TRs70 in the liver and TRs (60, 70) in kidneys.

CONCLUSION

Thearubigins protected against acetaminophen-induced hepatotoxicity and nephrotoxicity in mice possibly through their antioxidant activity.

A novel defensive mechanism against acetaminophen toxicity in the mouse lateral nasal gland: role of CYP2A5-mediated regulation of testosterone homeostasis and salivary androgen-binding protein expression

To identify novel factors or mechanisms that are important for the resistance of tissues to chemical toxicity, we have determined the mechanisms underlying the previously observed increases in resistance to acetaminophen (APAP) toxicity in the lateral nasal gland (LNG) of the male Cyp2g1-null/Cyp2a5-low mouse. Initial studies established that Cyp2a5-null mice, but not a newly generated strain of Cyp2g1-null mice, were resistant to APAP toxicity in the LNG; therefore, subsequent studies were focused on the Cyp2a5-null mice. Compared with the wild-type (WT) male mouse, the Cyp2a5-null male mouse had intact capability to metabolize APAP to reactive intermediates in the LNG, as well as unaltered circulating levels of APAP, APAP-GSH, APAP-glucuronide, and APAP-sulfate. However, it displayed reduced tissue levels of APAP and APAP-GSH and increased tissue levels of testosterone and salivary androgen-binding protein (ABP) in the LNG. Furthermore, we found that ABP was able to compete with GSH and cellular proteins for adduction with reactive metabolites of APAP in vitro. The amounts of APAP-ABP adducts formed in vivo were greater, whereas the amounts of APAP adducts formed with other cellular proteins were substantially lower, in the LNG of APAP-treated male Cyp2a5-null mice compared with the LNG of APAP-treated male WT mice. We propose that through its critical role in testosterone metabolism, CYP2A5 regulates 1) the bioavailability of APAP and APAP-GSH (presumably through modulation of the rates of xenobiotic excretion from the LNG) and 2) the expression of ABP, which can quench reactive APAP metabolites and thereby spare critical cellular proteins from inactivation.

Diabetes and hypertriglyceridemia modify the mode of acetaminophen-induced hepatotoxicity and nephrotoxicity in rats and mice

Certain disease conditions can modify drug-induced toxicities, which, in turn, may cause a medication-related health crisis. Therefore, preclinical investigations into the alterations in drug-induced toxicities using appropriate disease animal models are very important. This paper reviews the reported data related to the effects of diabetes and hypertriglyceridemia, common lifestyle-related diseases in a modern society, on acetaminophen (APAP)-induced hepatotoxicity and nephrotoxicity in rats and mice. It has generally been reported that diabetes protects rats and mice from APAP-induced hepatotoxicity and there are several reports that help to speculate on the effects of diabetes on APAP-induced nephrotoxicity. In fructose-induced hypertriglyceridemic rats, hepatotoxicity of APAP becomes apparently less severe, whereas nephrotoxicity of APAP becomes significantly more severe. The mechanisms of alteration of APAP-induced hepatorenal toxicity under diabetic and hypertriglyceridemic conditions are also discussed in this paper.

Proteomic Study of Hepatic Nuclear Extracts in an Adaptive Acetaminophen Tolerance Model

Introduction

Variability in response to acetaminophen (APAP)-induced aseptic inflammation and tolerance to the impending hepatic damage has been described. To understand the mechanism of adaptive tolerance, we investigated the proteomic profiles of crude nuclear lysates in a mouse model. We hypothesized that pretreatment with low doses of APAP prior to a toxic dose results in differential protein expression.

Materials and Methods

Mice (BALB/C) were separated into three groups: the pretreated (PT) group received incremental doses of APAP while the last dose only (LD) and naïve groups were given saline vehicle. A toxic dose of APAP was administered on the seventh day to the PT and LD animals only and all groups were euthanized 3 h postdose. Total protein from crude hepatic nuclear lysates were applied to protein arrays and analyzed by immunoaffinity mass spectrometry.

Results and Discussion

Comparative data analyses of protein peaks revealed a protein that was significantly increased at m/z of 60,030 (p60) in the LD animals vs the other two groups. The closest match for the preliminary identification of the p60 protein based on a Swiss-Prot/TagIdent database search using the approximate isoelectric point and molecular weight information was Ccr4–Not complex subunit-2. This protein is a subunit of a multiprotein complex and serves as a transcriptional suppressor involved in controlling mRNA synthesis and degradation. Preliminary identification was also supported by Western blot analysis using anti-CNOT2 antibody.

Conclusion

Considering the APAP tolerance model, we conclude that toxicogenomic approaches such as nuclear profiling are useful tools in assessing differential expression of transcriptional factors involved in inflammatory response and adaptive tolerance to toxins.

Acetaminophen-induced nephrotoxicity: pathophysiology, clinical manifestations, and management

Acetaminophen-induced liver necrosis has been studied extensively, but the extrahepatic manifestations of acetaminophen toxicity are currently not described well in the literature. Renal insufficiency occurs in approximately 1-2% of patients with acetaminophen overdose. The pathophysiology of renal toxicity in acetaminophen poisoning has been attributed to cytochrome P-450 mixed function oxidase isoenzymes present in the kidney, although other mechanisms have been elucidated, including the role of prostaglandin synthetase and N-deacetylase enzymes. Paradoxically, glutathione is considered an important element in the detoxification of acetaminophen and its metabolites; however, its conjugates have been implicated in the formation of nephrotoxic compounds. Acetaminophen-induced renal failure becomes evident after hepatotoxicity in most cases, but can be differentiated from the hepatorenal syndrome, which may complicate fulminant hepatic failure. The role of N-acetylcysteine therapy in the setting of acetaminophen-induced renal failure is unclear. This review will focus on the pathophysiology, clinical features, and management of renal insufficiency in the setting of acute acetaminophen toxicity.

CASE

A 47-year-old female was found lethargic at home and brought by ambulance to an emergency department. History from family members suggested an inadvertent acetaminophen overdose, and she had last been seen a few hours earlier. She reportedly ingested 18 tablets of 500 mg acetaminophen (APAP) over the previous two days because she had run out of her prescription pain medication. Her past medical history was significant for fibromyalgia, arthritis, and a prior gastric bypass procedure. She had no history of alcohol abuse or renal insufficiency. She was lethargic. Vital signs: BP 128/96 mmHg, pulse 112/min, respirations 32/min; pulse oximetry 98% on 2L nasal cannula oxygen. Laboratory studies: BUN 9 mg/dL, creatinine 0.9 mg/dl, acetaminophen 12 mcg/mL, AST 5409 u/L and ALT 1085 u/L. A urinalysis was negative for blood with trace protein and ketones. A urine drug screen was positive for marijuana and opioid metabolites. At the initial hospital, she was treated with N-acetylcysteine (NAC) orally. Subsequently, she developed fulminant hepatic failure with elevated transaminases, hypoglycemia, and coagulopathy (Tables 1A and 1B). She was transferred to our facility two days after initial presentation for liver transplant evaluation. At that time, her APAP level was 2.0 mg/L. Oral NAC therapy was continued after transfer. The patient's liver function subsequently improved and she ultimately did not require transplantation. She did develop acute renal failure during the course of her hospitalization, with a creatinine of 2.3 mg/dL on transfer, which increased to 8.1 mg/dL nine days later (approximately 11-13 days post-ingestion). Medical toxicology was consulted by the intensive care unit team to address whether this was acetaminophen-induced renal failure and if there was a role for NAC in this setting.

Profound metabolic acidosis and oxoprolinuria in an adult

INTRODUCTION

Profound metabolic acidosis in critically ill adults sometimes remains unexplained despite extensive evaluation.

CASE REPORT

A 58-year-old female presented in a confused state to the emergency department; she had been confused for several days. Laboratory evaluation revealed a high anion gap metabolic acidosis and modestly elevated acetaminophen level. Lactic acid was only modestly elevated. There was no evidence of ketoacids, salicylate, methanol, or ethylene glycol. A urine sample submitted on day 1 of hospitalization revealed a markedly elevated level of 5-oxoproline.

DISCUSSION

Originally described in children with an inherited defect of glutathione synthetase, 5-oxoproline is an unusual cause of metabolic acidosis. More recently this disturbance has been recognized in critically ill adults without a recognized inherited metabolic disorder. In most of these cases there has been the concomitant use of acetaminophen. Any causal relationship between acetaminophen and this disturbance is speculative.

CONCLUSION

In critically ill adults with unexplained metabolic acidosis, 5-Oxoproline should be considered in the differential.

Identification of novel toxicity-associated metabolites by metabolomics and mass isotopomer analysis of acetaminophen metabolism in wild-type and Cyp2e1-null mice

CYP2E1 is recognized as the most important enzyme for initiation of acetaminophen (APAP)-induced toxicity. In this study, the resistance of Cyp2e1-null mice to APAP treatment was confirmed by comparing serum aminotransferase activities and blood urea nitrogen levels in wild-type and Cyp2e1-null mice. However, unexpectedly, profiling of major known APAP metabolites in urine and serum revealed that the contribution of CYP2E1 to APAP metabolism decreased with increasing APAP doses administered. Measurement of hepatic glutathione and hydrogen peroxide levels exposed the importance of oxidative stress in determining the consequence of APAP overdose. Subsequent metabolomic analysis was capable of constructing a principal components analysis (PCA) model that delineated a relationship between urinary metabolomes and the responses to APAP treatment. Urinary ions high in wild-type mice treated with 400 mg/kg APAP were elucidated as 3-methoxy-APAP glucuronide (VII) and three novel APAP metabolites, including S-(5-acetylamino-2-hydroxyphenyl)mercaptopyruvic acid (VI, formed by a Cys-APAP transamination reaction in kidney), 3,3'-biacetaminophen (VIII, an APAP dimer), and a benzothiazine compound (IX, originated from deacetylated APAP), through mass isotopomer analysis, accurate mass measurement, tandem mass spectrometry fragmentation, in vitro reactions, and chemical treatments. Dose-, time-, and genotype-dependent appearance of these minor APAP metabolites implied their association with the APAP-induced toxicity and potential biomarker application. Overall, the oxidative stress elicited by CYP2E1-mediated APAP metabolism might significantly contribute to APAP-induced toxicity. The combination of genetically modified animal models, mass isotopomer analysis, and metabolomics provides a powerful and efficient technical platform to characterize APAP-induced toxicity through identifying novel biomarkers and unraveling novel mechanisms.

Effect of acetaminophen administration to rats chronically exposed to depleted uranium

The extensive use of depleted uranium (DU) in both civilian and military applications results in the increase of the number of human beings exposed to this compound. We previously found that DU chronic exposure induces the expression of CYP enzymes involved in the metabolism of xenobiotics (drugs). In order to evaluate the consequences of these changes on the metabolism of a drug, rats chronically exposed to DU (40mg/l) were treated by acetaminophen (APAP, 400mg/kg) at the end of the 9-month contamination. Acetaminophen is considered as a safe drug within the therapeutic range but in the case of overdose or in sensitive animals, hepatotoxicity and nephrotoxicity could occur. In the present work, plasma concentration of APAP was higher in the DU group compared to the non-contaminated group. In addition, administration of APAP to the DU-exposed rats increased plasma ALT (p<0.01) and AST (p<0.05) more rapidly than in the control group. Nevertheless, no histological alteration of the liver was observed but renal injury characterized by incomplete proximal tubular cell necrosis was higher for the DU-exposed rats. Moreover, in the kidney, CYP2E1 gene expression, an important CYP responsible for APAP bioactivation and toxicity, is increased (p<0.01) in the DU-exposed group compared to the control group. In the liver, CYP's activities were decreased between control and DU-exposed rats. These results could explain the worse elimination of APAP in the plasma and confirm our hypothesis of a modification of the drug metabolism following a DU chronic contamination.