Acetaminophen-induced Hepatotoxicity Research Articles

Deletion of Glyoxalase 1 Exacerbates Acetaminophen-Induced Hepatotoxicity in Mice

Deletion of Glyoxalase 1 Exacerbates Acetaminophen-Induced Hepatotoxicity in Mice

Hepatoprotective effects of safranal on acetaminophen-induced hepatotoxicity in rats

Abstract This research aimed to explore the protective and therapeutic properties of safranal in mitigating inflammation and oxidative stress induced by elevated acetaminophen (APAP) doses in a rat model. The protective and therapeutic effects of safranal were determined by histopathologically and examining some biochemical parameters such as aspartate transaminase (AST), alanine transaminase (ALT), glutathione, glutathione peroxidase, catalase, malondialdehyde, interleukin-6, tumor necrosis factor-α, and interleukin-1β. Male Wistar–Albino rats were subject to random allocation, forming five groups, each comprising seven rats (n = 7) in the study. Group 1 was the control group. APAP was administered in Group 2 to induce hepatotoxicity. Rats in Groups 3, 4, and 5 received intraperitoneal injections of safranal at doses of 0.025, 0.05, and 0.1 mL/kg/day for 14 days, respectively. On the 15th day, to induce APAP-induced hepatotoxicity, four groups (Groups 2, 3, 4, and 5) acquired a single intraperitoneal injection of 600 mg/kg APAP. The presence of APAP-induced hepatotoxic effect was proven by elevated AST and ALT levels, which are typical biomarkers of liver function in addition to the demonstration of histopathological changes. The findings suggest that pre-treatment with safranal may offer a protective effect against hepatotoxicity by attenuating oxidative stress and the inflammatory response.

Kaempferol sophoroside glucoside mitigates acetaminophen-induced hepatotoxicity: Role of Nrf2/NF-κB and JNK/ASK-1 signaling pathways

APAP (Acetaminophen)-induced hepatic injury is a major public health threat that requires continuous searching for new effective therapeutics. KSG (Kaempferol-3-sophoroside-7-glucoside) is a kaempferol derivative that was separated from plant species belonging to different genera. This study explored the protective effects of KSG on ALI (acute liver injury) caused by APAP overdose in mice and elucidated its possible mechanisms. The results showed that KSG pretreatment alleviated APAP-induced hepatic damage as it reduced hepatic pathological lesions as well as the serum parameters of liver injury. Moreover, KSG opposed APAP-associated oxidative stress and augmented hepatic antioxidants. KSG suppressed the inflammatory response as it decreased the genetic and protein expression as well as the levels of inflammatory cytokines. Meanwhile, KSG enhanced the mRNA expression and level of anti-inflammatory cytokine, IL-10 (interleukin-10). KSG repressed the activation of NF-κB (nuclear-factor kappa-B), besides it promoted the activation of Nrf2 signaling. Additionally, KSG markedly hindered the elevation of ASK-1 (apoptosis-signal regulating-kinase-1) and JNK (c-Jun-N-terminal kinase). Furthermore, KSG suppressed APAP-induced apoptosis as it decreased the level and expression of Bax (BCL2-associated X-protein), and caspase-3 concurrent with an enhancement of anti-apoptotic protein, Bcl2 in the liver. More thoroughly, Computational studies reveal indispensable binding affinities between KSG and Keap1 (Kelch-like ECH-associated protein-1), ASK1 (apoptosis signal-regulating kinase-1), and JNK1 (c-Jun N-terminal protein kinase-1) with distinctive tendencies for selective inhibition. Taken together, our data showed the hepatoprotective capacity of KSG against APAP-produced ALI via modulation of Nrf2/NF-κB and JNK/ ASK-1/caspase-3 signaling. Henceforth, KSG could be a promising hepatoprotective candidate for ALI.

Phytic acid attenuates acetaminophen-induced hepatotoxicity via modulating iron-mediated oxidative stress and SIRT-1 expression in mice.

Introduction: Administration of high doses of acetaminophen (APAP) results in liver injury. Oxidative stress and iron overload play roles in the pathogenesis of APAP-induced hepatotoxicity. The present study assessed the potential hepatoprotective effects of phytic acid (PA), a natural antioxidant and iron chelator, on APAP-induced hepatotoxicity and the possible underlying mechanism through its effects on CYP2E1 gene expression, iron homeostasis, oxidative stress, and SIRT-1 expression levels. Methods: Twenty-four adult male albino mice were used in this study. Mice were divided into four groups (six mice in each group): control, APAP-treated, PA-treated and APAP + PA-treated groups. Liver function tests, serum and liver tissue iron load were evaluated in all the study groups. Hepatic tissue homogenates were used to detect oxidative stress markers, including malondialdehyde (MDA) and reduced glutathione (GSH). Histological hepatic evaluation and immunohistochemistry of SIRT-1 were performed. Quantitative real-time PCR was used for the assessment of CYP2E1 and SIRT-1 gene expressions. APAP-induced biochemical and structural hepatic changes were reported. Results: PA administration showed beneficial effects on APAP-induced hepatotoxicity through improvements in liver functions, decreased CYP2E1 gene expression, decreased serum and liver iron load, decreased MDA, increased GSH, increased SIRT-1 expression level and improvement in hepatic architecture. Conclusion: Conclusively, PA can be considered a potential compound that can attenuate acetaminophen-induced hepatotoxicity through its role as an iron chelator and antioxidant, as well as the up-regulation of SIRT-1 and down-regulation of CYP2E1.

Autonomous circadian rhythms in the human hepatocyte regulate hepatic drug metabolism and inflammatory responses.

Critical aspects of physiology and cell function exhibit self-sustained ~24-hour variations termed circadian rhythms. In the liver, circadian rhythms play fundamental roles in maintaining organ homeostasis. Here, we established and characterized an in vitro liver experimental system in which primary human hepatocytes display self-sustained oscillations. By generating gene expression profiles of these hepatocytes over time, we demonstrated that their transcriptional state is dynamic across 24 hours and identified a set of cycling genes with functions related to inflammation, drug metabolism, and energy homeostasis. We designed and tested a treatment protocol to minimize atorvastatin- and acetaminophen-induced hepatotoxicity. Last, we documented circadian-dependent induction of pro-inflammatory cytokines when triggered by LPS, IFN-β, or Plasmodium infection in human hepatocytes. Collectively, our findings emphasize that the phase of the circadian cycle has a robust impact on the efficacy and toxicity of drugs, and we provide a test bed to study the timing and magnitude of inflammatory responses over the course of infection in human liver.

Novel fast dissolving freeze dried sublingual baicalin tablets for enhanced hepatoprotective effect: in-vitro characterization, cell viability, and in-vivo evaluation

Baicalin (BG), a natural product, has been used in the prevention and treatment of drug-induced liver injury (DILI); however, its poor solubility and extensive liver metabolism limit its pharmacological use. The aim of the present study was the formulation of fast-dissolving freeze-dried sublingual tablets (FFSTs) to increase BG dissolution, avoid first-pass metabolism, and overcome swallowing difficulties. FFSTs were prepared following a 23 factorial design. The effect of three independent variables namely matrix former, Maltodextrin, concentration (4%, and 6%), binder concentration (2%, and 3%), and binder type (Methocel E5, and Methocel E15) on the FFSTs’ in-vitro disintegration time and percentage dissolution was studied along with other tablet characteristics. Differential scanning calorimetry, scanning electron microscopy, in-vitro HepG2 cell viability assay, and in-vivo characterization were also performed. F8 (6% Maltodextrin, 2% Mannitol, 2% Methocel E5), with desirability of 0.852, has been furtherly enhanced using 1%PEG (F10). F10 has achieved an in-vitro disintegration time of 41 secs, and 60.83% in-vitro dissolution after 2 min. Cell viability assay, in-vivo study in rats, and histopathological studies confirmed that pretreatment with F10 has achieved a significant hepatoprotective effect against acetaminophen-induced hepatotoxicity. The outcome of this study demonstrated that FFSTs may present a patient-friendly dosage form against DILI.

Ameliorative Potentials of Persea americana Mill (Avocado) Seed Extract on Acetaminophen-induced Hepatic Insufficiency in Rats

Aim: The ability of ethylacetate extract of Persea americana Mill (avocado) seed to ameliorate the hepatotoxic effect of acetaminophen in rats was assessed. Methodology: Thirty experimental rats were placed in 6 groups of 5 animals per group. Two animal groups received distilled water and the drug vehicle, dimethyl sulphoxide (DMSO). Four other groups received acetaminophen (750 mg/kg bw/day) in DMSO for 3 days with 3 of the 4 groups receiving, after 3 days of acetaminophen administration and for 11 days, Persea americana seed extracts (150-, 350 mg/kg bw) and silymarin (200 mg/kg bw). Animals were sacrificed and both serum and liver tissue analysed for markers of liver integrity (AST, ALT, ALP), liver function (total protein, albumin, total cholesterol, triglyceride), antioxidant status (SOD, Catalase) and liver architecture. Results: The result showed induction of hepatotoxicity by acetaminophen with increased AST, ALT, ALP and decreased SOD and CAT activities. Hepatotoxicity was also observed as increase in total and conjugated bilirubin and decrease in total cholesterol and triglyceride. Administration of Persea americana seed ethylacetate extract reversed the status of the parameters towards normal (except for AST, total protein and albumin). Also the liver architecture which hitherto revealed inflammation, fatty changes and hepatocyte necrosis also reversed to mild inflammation to normal histology. The action of the extract was dose dependent and its effectiveness comparable to silymarin (200 mg/kg bw). Conclusion: The ethylacetate extract of Persia americana showed ameliorative effect against acetaminophen-induced hepatotoxicity at higher dose, with potentials to reverse disruptions in liver integrity and function, and restore balance in endogenous antioxidant system.

Effects of gossypin on acetaminophen-induced hepatotoxicity in mice

Liver injury from paracetamol (acetaminophen) (APAP) is common worldwide. To prevent intoxication with a drug with high poisoning, treatment can be made possible with an easily accessible and harmless substance. This study aimed to investigate the hepatoprotective ef-fects of Gossypin (GOS) in mice exposed to an overdose of APAP -the possible mechanism of action. Specifically, serum [alanine aminotransferase (ALT), aspartate transaminase (AST), and hepatic biochemical parameters (glutathione (GSH), malondialdehyde (MDA) and super-oxide dismutase (SOD)] were evaluated. Protein and mRNA levels of inflammatory, apoptot-ic, and cytochrome factors, including TNF-α, IL-1β, IL-6, NF-kB, and CYP2E1, were ana-lyzed using real-time PCR. Pretreatment with GOS significantly reduced APAP-induced he-patic injury via oxidative stress. Along with potent antioxidant activity, GOS promoted APAP hepatic detoxification by regulating AST, ALT, GSH, MDA, and SOD activities and mRNA levels of the cytochrome CYP2E1 gene. The anti-inflammatory activity of GOS in-creases its production. TNF-α, IL-1β and IL-6, through possible NF-kB blockade, are also responsible for its hepatoprotective effect. Taken together, GOS has the potential to be devel-oped as a preventive agent to be administered to patients suffering from APAP overdose.

PROTECTIVE EFFECTS OF VITAMIN C ON ACETAMINOPHEN-INDUCED LIVER AND KIDNEY TOXICITY IN MALE RATS

Acetaminophen (paracetamol) is a widely used over-the-counter analgesic and antipyretic medication known for its efficacy and safety when administered within recommended doses. However, overdose or prolonged use of acetaminophen can lead to severe hepatotoxicity and nephrotoxicity, posing a significant public health concern. This study aims to investigate the protective effects of vitamin C on acetaminophen-induced hepatotoxicity and nephrotoxicity in male Wistar rats. Six rats were randomly assigned to seven groups, with Group 1 designated as the control. Groups 2, 4, and 6 were given daily single oral doses of 100, 200, and 400 mg/kg of acetaminophen, respectively. Meanwhile, Groups 3, 5, and 7 received daily single oral doses of 100, 200, and 400 mg/kg of acetaminophen, followed by intraperitoneal administration of 100 mg/kg of vitamin C daily, for 14 days. Liver function markers (AST, ALT, total bilirubin, and total protein) and renal function indicators (urea and creatinine levels) were assessed, alongside antioxidant status in liver and kidney tissues through antioxidant assays (SOD, CAT, GSH, and MDA). The results demonstrated the protective influence of vitamin C on liver and kidney tissues, as indicated by the modulation of biochemical markers. These findings suggest that vitamin C may play a pivotal role in alleviating acetaminophen-induced liver and kidney damage across different dosage regimens, potentially serving as a therapeutic intervention for preventing or treating drug-induced organ injuries. Further investigations are essential to elucidate the underlying mechanisms and validate the translational potential of vitamin C as a protective agent against acetaminophen toxicity.

Hepatoprotective effect of amifostine and WR-1065 on acetaminophen-induced liver toxicity on Wistar rats.

The most important problem with acetaminophen is its hepatotoxicity. N-acetylcysteine (NAC) is used to treat the hepatotoxicity of acetaminophen. Due to the structural similarities of this compound with amifostine, we decided to test the effect of this substance and its metabolite, WR-1065, on the hepatotoxicity of acetaminophen. The single-dose method contained 1. Control; 2. Acetaminophen (1 g/kg, gavage); 3-5. Acetaminophen + amifostine (100, 200, 400 mg/kg, i.p.); 6-8. Acetaminophen + WR-1065 (50, 100, 200 mg/kg, i.p.); and 9. Acetaminophen + NAC (100, 200 mg/kg, i.p.). The multiple-dose method included the same groups: amifostine (50, 100, 200 mg/kg), WR-1065 (25, 50, 100 mg/kg), and NAC (100 mg/kg). Then, animals were sacrificed, and blood samples were collected for measuring ALT, AST, ALP, and T-Bil, liver tissue for histopathological examination, MDA, and GSH amounts. Acetaminophen increased the levels of MDA, T-Bil, ALT, AST, and ALP, decreased GSH levels, and augmented necrosis, neutrophils, lymphocytes, and macrophages in the port space in single-dose and multiple-dose studies. Amifostine and WR-1065 significantly reduced the levels of MDA, T-Bil, ALT, AST, ALP, increased GSH content, and ameliorated histopathological alterations in a single-dose and multiple-dose method compared to the acetaminophen group. Moreover, NAC caused a significant decrease in the levels of MDA, T-Bil, ALT, AST, and ALP, and reduced GSH amounts in single-dose and multiple-dose studies. Amifostine and WR-1065 as antioxidant and hepatoprotective compounds are effective in reducing acetaminophen-induced hepatotoxicity with a similar effect to NAC and can be administered as an adjunct in the treatment of acetaminophen overdose.

Hepatoprotective effects of Elaeagnus latifolia fruit extract against acetaminophen-induced hepatotoxicity in mice: Mechanistic insights

Elaeagnus latifolia fruit extract (EE) has been reported to contain antioxidant and anti-inflammatory phytochemicals. The present study aimed to examine the anti-hepatotoxic effects of EE in acetaminophen (APAP)-injected mice. Pretreatment with EE for 7 days in APAP mice showed significant reductions in the levels of AST and ALT and necrotic area, accompanied by decreases in liver oxidative stress, nitric oxide, and infiltrating inflammatory cells, compared to the APAP-only group. EE markedly down-regulated expression of CYP2E1, JNK, Bax, NOX subunit, and NF-κB target genes, and up-regulated expression of Bcl-2 and Nrf2 target genes in the livers. Furthermore, EE effectively lowered serum and hepatic lipids, and down-regulated expression of SREBP-1c/2 genes. EE was found to contain phenolic compounds, flavonoids, and proanthocyanidins. Therefore, mechanistic insights into EE's anti-hepatotoxic effects may be associated with preventing the abnormal expression of genes involved in toxic metabolite generation, hepatotoxic signaling, apoptosis, oxidative stress, inflammation, and lipid synthesis.

The discovery of gut microbial metabolites as modulators of host susceptibility to acetaminophen-induced hepatotoxicity.

The mammalian gut microbiota plays diverse and essential roles in modulating host physiology. Key mediators determining the outcome of the microbiota-host interactions are the small molecule metabolites produced by the gut microbiota. The liver is the organ massively exposed to gut microbial metabolites, and it serves as the nexus, maintaining healthy interactions between the gut microbiota and host. At the same time, the liver is the primary target of harmful gut microbial metabolites. This review provides an up-to-date list of gut microbial metabolites identified to increase or decrease host susceptibility to APAP-induced liver injury. Signaling pathways and molecular factors involved in the progression of APAP-induced hepatotoxicity are well-established, and we propose that the mouse model of APAP-induced hepatotoxicity serves as an excellent system for uncovering gut microbial metabolites of previously unknown function. Moreover, we envision that gut microbial metabolites identified to alter APAP-induced hepatotoxicity likely have broader implications in other liver diseases. Significance Statement This review provides an overview of recent discoveries from investigating whether and how the gut microbiota modulates the host susceptibility to APAP-induced liver injury. It focuses on the roles of gut bacterial small molecule metabolites as mediators of the interaction between the gut microbiota and the liver. It also illustrates the utility of APAP-induced liver injury as a model to identify gut microbial metabolites with biological function.

Safety and Hepatoprotective Assessments of Polyherbal Formulation in Lead and Acetaminophen-induced Hepatotoxicity in Rats

Safety and Hepatoprotective Assessments of Polyherbal Formulation in Lead and Acetaminophen-induced Hepatotoxicity in Rats

Effect of ethanolic extract of Petroselinum crispum (Mill.) Fuss (Apiaceae) strand on acetaminophen-induced hepatotoxicity in wistar rat

Effect of ethanolic extract of Petroselinum crispum (Mill.) Fuss (Apiaceae) strand on acetaminophen-induced hepatotoxicity in wistar rat

Serine synthesis via reversed SHMT2 activity drives glycine depletion and acetaminophen hepatotoxicity in MASLD

Metabolic dysfunction-associated steatotic liver disease (MASLD) affects one-third of the global population. Understanding the metabolic pathways involved can provide insights into disease progression and treatment. Untargeted metabolomics of livers from mice with early-stage steatosis uncovered decreased methylated metabolites, suggesting altered one-carbon metabolism. The levels of glycine, a central component of one-carbon metabolism, were lower in mice with hepatic steatosis, consistent with clinical evidence. Stable-isotope tracing demonstrated that increased serine synthesis from glycine via reverse serine hydroxymethyltransferase (SHMT) is the underlying cause for decreased glycine in steatotic livers. Consequently, limited glycine availability in steatotic livers impaired glutathione synthesis under acetaminophen-induced oxidative stress, enhancing acute hepatotoxicity. Glycine supplementation or hepatocyte-specific ablation of the mitochondrial SHMT2 isoform in mice with hepatic steatosis mitigated acetaminophen-induced hepatotoxicity by supporting de novo glutathione synthesis. Thus, early metabolic changes in MASLD that limit glycine availability sensitize mice to xenobiotics even at the reversible stage of this disease.

Antioxidant and hepatoprotective effects of hypericum sampsonii

Hypericum sampsonii or Sampson’s St John’s Wort is a species of flowering plant in the Hypericaceae family. Our previous study revealed the diverse and bioactive chemical constituents of the plant. This study investigates the antioxidant activity and potential hepatoprotective of Hypericum sampsonii extract (BLD1 extract) in vitro and in vivo. The in vitro experiment was carried out with DPPH (1, 1-diphenyl-2-picrylhydrazyl) radical scavenging assay to assess the antioxidant properties of BLD1 extract. In the in vivo experiment, the hepatoprotective activity of BLD1 extract was evaluated on an acetaminophen-induced hepatotoxicity mouse model. The in vitro assay demonstrated that the extract exhibited antioxidant activity in a dose-dependent manner. In the in vivo experiments, BLD1 extract at both doses (3.6 g/kg b.w day and 10.8 g/kg b.w day) reflected the decrease in serum ALT, AST and MDA level. Hepatic histology was also investigated post-mortem to assess the degree of liver injury. The overall findings of this study demonstrate the potential hepatoprotective effect of Hypericum sampsonii in acetaminophen-induced oxidative stress and liver toxicity in mice. This study has established the efficacy of Hypericum sampsonii, which should warrant further clinical trials and applications.

Therapeutic potentials of N-acetylcysteine immobilized polyrhodanine nanoparticles toward acetaminophen-induced acute hepatotoxicity in rat.

N-acetylcysteine (NAC) is a recommended drug for treating acetaminophen (APAP) intoxication. Due to NAC's low bioavailability, this study aimed to use polyrhodanine (PR) nanoparticles (NPs) as a drug carrier to improve the effectiveness of NAC. After preparation and characterization of NAC loaded on PR, 30 rats were randomly divided into five groups of six. The first group (control) received normal saline. Groups 2-5 were treated with normal saline, PR, NAC, and NAC loaded on PR, respectively. The treatments were started 4 h after oral administration of APAP (2000 mg kg-1 ). After 48 h, the animals were anesthetized, and liver function indices and oxidative stress were measured in tissue and serum samples. The APAP administration can increase aminotransferases and alkaline phosphatase enzymes in serum, decreasing the total antioxidant capacity and thiol groups and increasing lipid peroxidation in liver tissue. Administration of PR-NAC could effectively improve the level of serum-hepatic enzymes, total antioxidant capacity and thiol groups, lipid peroxidation, and pathological changes in liver tissue in animals poisoned with APAP. PR-NAC has a significant therapeutic effect on preventing acute hepatotoxicity caused by APAP, and its effectiveness can be associated with an improvement in the oxidant/antioxidant balance of liver tissue.

The influence of acetaminophen on human health

In pain management, acetaminophen, a widely used analgesic and antipyretic, holds a central position. The metabolic pathways can lead to acetaminophen-induced hepatotoxicity, elucidating from glucuronidation to the cytochrome P450 system. It meticulously details the complexities of acetaminophen metabolism, culminating in the formation of the toxic metabolite, n-acetyl-p-benzoquinone imine (NAPQI). Providing a holistic understanding guiding clinical practice, it explores risk factors, clinical implications, and management strategies. Transitioning to respiratory risks, potential associations between acetaminophen use and asthma, rhinoconjunctivitis, and eczema in adolescents is investigated. The study offers nuanced insights, urging caution in acetaminophen use during adolescence. In addition, the role of drug metabolism in acetaminophen-induced hepatic necrosis is also analyzed. Despite its temporal origins, the studys identification of cytochrome P450 as a catalyst for NAPQI formation remains foundational, contributing mechanistic insights to drug-induced liver injury knowledge. Synthesizing these studies reveals a delicate balance between acetaminophen metabolism and detoxification, crucial in determining its hepatotoxic potential. This nuanced understanding informs clinical practice and beckons researchers to bridge gaps, embarking on further explorations. In essence, this synthesis becomes a compass guiding the scientific community toward a profound comprehension of acetaminophen, epitomizing the standards expected in high-quality, peer-reviewed literature.

Jujuboside B alleviates acetaminophen-induced hepatotoxicity in mice by regulating Nrf2-STING signaling pathway

BackgroundJujuboside B (JuB) is the main bioactive saponin component of Chinese anti-insomnia herbal medicine Ziziphi Spinosae Semen, which has been reported to possess varied pharmacological functions. Even though it has been traditionally used to treat inflammation- and toxicity-related diseases, the effects of JuB on acetaminophen (APAP) overdose-induced hepatotoxicity have not been determined yet. MethodsC57BL/6 J mice were pre-treated with JuB (20 or 40 mg/kg) for seven days before APAP (400 mg/kg) injection. After 24 h of APAP treatment, serum, and liver tissues were collected to evaluate the therapeutic effects. To investigate whether the Nrf2-STING signaling pathway is involved in the protective effects of JuB against APAP-induced hepatotoxicity, the mice received the DMXAA (the specific STING agonist) or ML385 (the specific Nrf2 inhibitor) during the administration of JuB, and Hematoxylin-eosin staining, Real-time PCR, immunohistochemical, and western blot were performed. ResultsJuB pretreatment reversed APAP-induced CYP2E1 accumulations and alleviated APAP-induced acute liver injury. Furthermore, JuB treatment significantly inhibited oxidative stress and the pro-inflammatory cytokines, as well as alleviated hepatocyte apoptosis induced by APAP. Besides, our result also demonstrated that JuB treatment upregulated the levels of total Nrf2, facilitated its nuclear translocation, upregulated the expression of HO-1 and NQO-1, and inhibited the APAP-induced STING pathway activation. Finally, we verified that the beneficial effects of JuB were weakened by DMXAA and ML385. ConclusionOur study suggested that JuB could ameliorate APAP-induced hepatic damage and verified a previously unrecognized mechanism by which JuB prevented APAP-induced hepatotoxicity through adjusting the Nrf2-STING pathway.

Hepatoprotective activity of herbal extracts and other compounds against acetaminophen-induced hepatotoxicity by various mechanisms: A narrative review

Hepatoprotective activity of herbal extracts and other compounds against acetaminophen-induced hepatotoxicity by various mechanisms: A narrative review