Aristolochic acid I induced oxidative DNA damage associated with glutathione depletion and ERK1/2 activation in human cells

Unveiling correlations between aristolochic acids and liver cancer: spatiotemporal heterogeneity phenomenon

Aristolochic acids are a class of naturally occurring compounds in Aristolochiaceae that have similar structural skeletons and chemical properties. Exposure to aristolochic acids is a risk factor for severe kidney disease and urinary system cancer. However, the carcinogenicity of aristolochic acids to the liver, which is the main site of aristolochic acid metabolism, is unclear. Although the characteristic fingerprint of aristolochic acid-induced mutations has been detected in the liver and aristolochic acids are known to be hepatotoxic, whether aristolochic acids can directly cause liver cancer is yet to be verified. This review summarizes the findings of long-term carcinogenicity studies of aristolochic acids in experimental animals. We propose that spatiotemporal heterogeneity in the carcinogenicity of these phytochemicals could explain why direct evidence of aristolochic acids causing liver cancer has never been found in adult individuals. We also summarized the reported approaches to mitigate aristolochic acid-induced hepatotoxicity to better address the associated global safety issue and provide directions and recommendations for future investigation.

SGLT2 inhibitor dapagliflozin protects the kidney in a murine model of Balkan nephropathy

Proximal tubular uptake of aristolochic acid (AA) forms aristolactam (AL)-DNA adducts, which cause a p53/p21-mediated DNA damage response and acute tubular injury. Recurrent AA exposure causes kidney function loss and fibrosis in humans (Balkan endemic nephropathy) and mice and is a model of (acute kidney injury) AKI to chronic kidney disease (CKD) transition. Inhibitors of the proximal tubule sodium-glucose transporter SGLT2 can protect against CKD progression, but their effect on AA-induced kidney injury remains unknown. C57BL/6J mice (15-wk-old) were administered vehicle or AA every 3 days for 3 wk (10 and 3 mg/kg ip in females and males, respectively). Dapagliflozin (dapa, 0.01 g/kg diet) or vehicle was initiated 7 days prior to AA injections. All dapa effects were sex independent, including a robust glycosuria. Dapa lowered urinary kidney-injury molecule 1 (KIM-1) and albumin (both normalized to creatinine) after the last AA injection and kidney mRNA expression of early DNA damage response markers (p53 and p21) 3 wk later at the study end. Dapa also attenuated AA-induced increases in plasma creatinine as well as AA-induced up-regulation of renal pro-senescence, pro-inflammatory and pro-fibrotic genes, and kidney collagen staining. When assessed 1 day after a single AA injection, dapa pretreatment attenuated AL-DNA adduct formation by 10 and 20% in kidney and liver, respectively, associated with reduced p21 expression. Initiating dapa application after the last AA injection also improved kidney outcome but in a less robust manner. In conclusion, the first evidence is presented that pretreatment with an SGLT2 inhibitor can attenuate the AA-induced DNA damage response and subsequent nephropathy.NEW & NOTEWORTHY Recurrent exposure to aristolochic acid (AA) causes kidney function loss and fibrosis in mice and in humans, e.g., in the form of the endemic Balkan nephropathy. Inhibitors of the proximal tubule sodium-glucose transporter SGLT2 can protect against CKD progression, but their effect on AA-induced kidney injury remains unknown. Here we provide the first evidence in a murine model that pretreatment with an SGLT2 inhibitor can attenuate the AA-induced DNA damage response and subsequent nephropathy.

An unprecedented free radical mechanism for the formation of DNA adducts by the carcinogenic N-sulfonated metabolite of aristolochic acids

The carcinogenicity of aristolochic acids (AAs) has been attributed mainly to the formation of stable DNA-aristolactam (DNA-AL) adducts by its reactive N-sulfonated metabolite N-sulfonatooxyaristolactam (N-OSO3--AL). The most accepted mechanism for such DNA-AL adduct formation is via the postulated but never unequivocally-confirmed aristolactam nitrenium ion. Here we found that both sulfate radical and two ALI-derived radicals (N-centered and C-centered spin isomers) were produced by N-OSO3--ALI, which were detected and unequivocally identified by complementary applications of ESR spin-trapping, HPLC-MS coupled with deuterium-exchange methods. Both the formation of the three radical species and DNA-ALI adducts can be significantly inhibited (up to 90%) by several well-known antioxidants, typical radical scavengers, and spin-trapping agents. Taken together, we propose that N-OSO3--ALI decomposes mainly via a new N-O bond homolysis rather than the previously proposed heterolysis pathway, yielding reactive sulfate and ALI-derived radicals, which are together and in concert responsible for forming DNA-ALI adducts. This study presents strong and direct evidence for the production of free radical intermediates during N-OSO3--ALI decomposition, providing an unprecedented free radical perspective and conceptual breakthrough, which can better explain and understand the molecular mechanism for the formation of DNA-AA adducts, the carcinogenicity of AAs and their potential prevention.

Aristolochic acid-associated cancers: a public health risk in need of global action

Aristolochic acids (AAs) are a group of naturally occurring compounds present in many plant species of the Aristolochiaceae family. Exposure to AA is a significant risk factor for severe nephropathy, and urological and hepatobiliary cancers (among others) that are often recurrent and characterized by the prominent mutational fingerprint of AA. However, herbal medicinal products that contain AA continue to be manufactured and marketed worldwide with inadequate regulation, and possible environmental exposure routes receive little attention. As the trade of food and dietary supplements becomes increasingly globalized, we propose that further inaction on curtailing AA exposure will have far-reaching negative effects on the disease trends of AA-associated cancers. Our Review aims to systematically present the historical and current evidence for the mutagenicity and carcinogenicity of AA, and the effect of removing sources of AA exposure on cancer incidence trends. We discuss the persisting challenges of assessing the scale of AA-related carcinogenicity, and the obstacles that must be overcome in curbing AA exposure and preventing associated cancers. Overall, this Review aims to strengthen the case for the implementation of prevention measures against AA's multifaceted, detrimental and potentially fully preventable effects on human cancer development.

Nephrotoxicity induced by natural compounds from herbal medicines - a challenge for clinical application

Herbal medicines (HMs) have long been considered safe and effective without serious toxic and side effects. With the continuous use of HMs, more and more attention has been paid to adverse reactions and toxic events, especially the nephrotoxicity caused by natural compounds in HMs. The composition of HMs is complex and various, especially the mechanism of toxic components has been a difficult and hot topic. This review comprehensively summarizes the kidney toxicity characterization and mechanism of nephrotoxic natural compounds (organic acids, alkaloids, glycosides, terpenoids, phenylpropanoids, flavonoids, anthraquinones, cytotoxic proteins, and minerals) from different sources. Recommendations for the prevention and treatment of HMs-induced kidney injury were provided. In vitro and in vivo models for evaluating nephrotoxicity and the latest biomarkers are also included in this investigation. More broadly, this review may provide theoretical basis for safety evaluation and further comprehensive development and utilization of HMs in the future.

Curcumin alleviates aristolochic acid nephropathy based on SIRT1/Nrf2/HO-1 signaling pathway

Aristolochic acid I (AA-I), presenting in a variety of natural medicinal plants, which could cause tubular epithelial cell injury. Curcumin (CUR), a polyphenolic substance isolated from turmeric, is a natural antioxidant. The aim of this experiment was to investigate whether CUR attenuated AA-I-induced renal injury in rats through the SIRT1/Nrf2/HO-1 signaling pathway. SD rats were treated with AA-I (10 mg/kg) or/and CUR (200 mg/kg) for 28 days to assess the protective effect of CUR on AA-I-induced renal injury in vivo. NRK-52E cells were treated with AA-I (40 μ M) or/and CUR (20 μ M) for 24 h in vitro. The intervention pathway of CUR against oxidative stress injury induced by AA-I was assessed by observing pathological changes, oxidative stress status, apoptosis and the expression of SIRT1/Nrf2/HO-1 signaling pathway-related factors. The results showed that AA-I exposure increased the contents of BUN, Cr, KIM-1, NGAL, ALT and AST in serum. It increased the content of MDA, decreased the activities of SOD, GST, GSH and the content of ATP in renal tissue. Pathological changes such as inflammatory cell infiltration and mitochondrial injury occurred in renal tissue. AA-I exposure resulted in a substantial rise in the levels of BAX, Ccaspase-9, Cleaved Caspase-9, Caspase-3, Cleaved Caspase-3 and a significant decrease in mRNA and protein expression levels of Bcl-2, SIRT1, Nrf2, NQO1, HO-1 and Keap1. However, these changes were reversed by CUR intervention. In summary, AA-I exposure caused mitochondrial dysfunction and triggered apoptosis through the oxidative stress pathway. However, CUR could reduce AA-I-induced renal injury by activating the SIRT1/Nrf2/HO-1 signaling pathway.

Aristolochic acid I exposure decreases oocyte quality

Oocyte quality is a determinant of a successful pregnancy. The final step of oocyte development is oocyte maturation, which is susceptible to environmental exposures. Aristolochic acids (AAs), widely existing in Aristolochia and Asarum plants that have been used in traditional medicine, can result in a smaller ovary and fewer superovulated oocytes after in vivo exposure to mice. However, whether AAs affect oocyte maturation and the underlying mechanism(s) are unclear. In this study, we focused on the effect of Aristolochic acid I (AAI), a major compound of AAs, on the maturation of in vitro cultured mouse oocytes. We showed that AAI exposure significantly decreased oocyte quality, including elevated aneuploidy, accompanied by aberrant chiasma patterns and spindle organization, and decreased first polar body extrusion and fertilization capability. Moreover, embryo development potential was also dramatically decreased. Further analyses revealed that AAI exposure significantly decreased mitochondrial membrane potential and ATP synthesis and increased the level of reactive oxygen species (ROS), implying impaired mitochondrial function. Insufficient ATP supply can cause aberrant spindle assembly and excessive ROS can cause premature loss of sister chromatid cohesion and thus alterations in chiasma patterns. Both aberrant spindles and changed chiasma patterns can contribute to chromosome misalignment and thus aneuploidy. Therefore, AAI exposure decreases oocyte quality probably via impairing mitochondrial function.

Aristolochic Acid Nephropathy: A Novel Suppression Strategy of Carbon Dots Derived from Astragali Radix Carbonisata

Despite strict restrictions on the use of aristolochic acids (AAs)-containing merchandise or drugs in many countries, a substantial amounts of occurrences aristolochic acid nephropathy (AAN) had been accounted worldwide. Clinically, there is no effective incurable therapy regimen to reverse the progression of AAN. Although carbon dots have shown surprising bioactivity, research on the acute kidney injury caused by AAs is lacking. Here, a novel biomass-carbon dots from Astragali Radix (AR) as precursors was synthesized through one-step pyrolysis treatment. The ARC-carbon dots (ARC-CDs) was demonstrated in detail for its inhibitory effect on aristolochic acid nephropathy in a mice model. The indexes of inflammatory cytokines as well as oxidative stress were significantly reduced by the ARC-CDs in kidney tissue cells. Additionally, the ARC-CDs administration resulted in a large decrease in positive apoptotic cells according to TUNEL labeling and western blotting, which may be connected to the ARC-CDs’ modulation of the protein in the Akt/Mdm2/p53 signaling pathway. These findings show that ARC-CDs have remarkable anti-inflammatory, antioxidant, and anti-apoptotic capabilities against acute kidney injury spurred by aristolochic acids via the AKT/Mdm2/p53 signaling pathway.

Aristolochic acid I induces proximal tubule injury through ROS/HMGB1/mt DNA mediated activation of TLRs

Aristolochic acids (AAs) are extracted from certain plants as folk remedies for centuries until their nephrotoxicity and carcinogenicity were recognized. Aristolochic acid I (AAI) is one of the main pathogenic compounds, and it has nephrotoxic, carcinogenic and mutagenic effects. Previous studies have shown that AAI acts mainly on proximal renal tubular epithelial cells; however, the mechanisms of AAI‐induced proximal tubule cell damage are still not fully characterized. We exposed human kidney proximal tubule cells (PTCs; HK2 cell line) to AAI in vitro at different time/dose conditions and assessed cell proliferation, reactive oxygen species (ROS) generation, nitric oxide (NO) production, m‐RNA/ protein expressions and mitochondrial dysfunction. AAI exposure decreased proliferation and increased apoptosis, ROS generation / NO production in PTCs significantly at 24 h. Gene/ protein expression studies demonstrated activation of innate immunity (TLRs 2, 3, 4 and 9, HMGB1), inflammatory (IL6, TNFA, IL1B, IL18, TGFB and NLRP3) and kidney injury (LCN2) markers. AAI also induced epithelial‐mesenchymal transition (EMT) and mitochondrial dysfunction in HK2 cells. TLR9 knock‐down and ROS inhibition were able to ameliorate the toxic effect of AAI. In conclusion, AAI treatment caused injury to PTCs through ROS‐HMGB1/mitochondrial DNA (mt DNA)‐mediated activation of TLRs and inflammatory response.

Experimental Aristolochic Acid Nephropathy: A Relevant Model to Study AKI-to-CKD Transition

Aristolochic acid nephropathy (AAN) is a progressive tubulointerstitial nephritis caused by the intake of aristolochic acids (AA) contained in Chinese herbal remedies or contaminated food. AAN is characterized by tubular atrophy and interstitial fibrosis, characterizing advanced kidney disease. It is established that sustained or recurrent acute kidney injury (AKI) episodes contribute to the progression of CKD. Therefore, the study of underlying mechanisms of AA-induced nephrotoxicity could be useful in understanding the complex AKI-to-CKD transition. We developed a translational approach of AKI-to-CKD transition by reproducing human AAN in rodent models. Indeed, in such models, an early phase of acute tubular necrosis was rapidly followed by a massive interstitial recruitment of activated monocytes/macrophages followed by cytotoxic T lymphocytes, resulting in a transient AKI episode. A later chronic phase was then observed with progressive tubular atrophy related to dedifferentiation and necrosis of tubular epithelial cells. The accumulation of vimentin and αSMA-positive cells expressing TGFβ in interstitial areas suggested an increase in resident fibroblasts and their activation into myofibroblasts resulting in collagen deposition and CKD. In addition, we identified 4 major actors in the AKI-to-CKD transition: (1) the tubular epithelial cells, (2) the endothelial cells of the interstitial capillary network, (3) the inflammatory infiltrate, and (4) the myofibroblasts. This review provides the most comprehensive and informative data we were able to collect and examines the pending questions.

Fetal exposure of Aristolochic Acid I undermines ovarian reserve by disturbing primordial folliculogenesis

The primordial follicle pool established in early life determines the ovarian reserve in the female reproductive lifespan. Premature exhaustion of primordial follicles contributes to primary ovarian insufficiency (POI), that is dependent by the initial size of the primordial follicle pool and by the rate of its activation and depletion. AAI, a powerful nephrotoxin with carcinogenic potential, is present in the Aristolochiaceae species, which can release AAI into soil as a persistent pollutant. In order to assess the potential risk of Aristolochic Acid I (AAI) exposure on mammalian oogenesis, we uncovered its adverse effect on primordial folliculogenesis in the neonatal mouse ovary and its effect on female fertility in adulthood. Pregnant mice were orally administrated with doses of AAI without hepatic or renal toxicity during late-gestation. Ovaries from offspring of administered female displayed gross aberrations during primordial folliculogenesis. Also, unenclosed oocytes in germ-cell cysts showed increased DNA damage. Furthermore, several key factors, including NANOS3, SOX9, KLF4, that govern early gonad's differentiation were abnormally expressed in the exposed ovary, while the follicle formation was partially restored by knockdown of Nanos3 or sox9. In adulthood, these aberrations evolved into a significant reduction in offspring number and impaired ovarian reserve. Together, our results show that AAI influences primordial folliculogenesis and, importantly, affected female fertility. This study shows that administration of drugs herbs or consumption of vegetables that contain AAs during pregnancy may adversely influence the fertility of offspring.

Macrophage interferon regulatory factor 4 deletion ameliorates aristolochic acid nephropathy via reduced migration and increased apoptosis

Aristolochic acid (AA) is the causative nephrotoxic alkaloid in aristolochic acid nephropathy, which results in a tubulointerstitial fibrosis. AA causes direct proximal tubule damage. There is also an influx of macrophages, although their role in the pathogenesis is poorly understood. Here we demonstrate that AA directly stimulates migration, inflammation, and reactive oxygen species (ROS) production in macrophages ex vivo. Cells lacking interferon regulatory factor 4 (IRF4), a known regulator of macrophage migration and phenotype, had a reduced migratory response, though effects on ROS production and inflammation were preserved or increased relative to wild-type cells. Macrophage-specific IRF4 knockout mice were protected from both acute and chronic kidney effects of AA administration based on functional and histological analysis. Renal macrophages from kidneys of AA-treated macrophage-specific IRF4 knockout mice demonstrated increased apoptosis and ROS production compared with wildtype controls, indicating that AA directly polarizes macrophages to a promigratory and proinflammatory phenotype. However, knockout mice had reduced renal macrophage abundance following AA administration. While macrophages lacking IRF4 can adopt a proinflammatory phenotype upon AA exposure, their inability to migrate to the kidney and increased rates of apoptosis upon infiltration provide protection from AA in vivo. These results provide evidence of direct AA effects on macrophages in AAN and add to the growing body of evidence that supports a key role of IRF4 in modulating macrophage function in kidney injury.

Cyclophilin D Promotes Acute, but Not Chronic, Kidney Injury in a Mouse Model of Aristolochic Acid Toxicity

The plant-derived toxin, aristolochic acid (AA), is the cause of Chinese Herb Nephropathy and Balkan Nephropathy. Ingestion of high dose AA induces acute kidney injury, while chronic low dose ingestion leads to progressive kidney disease. Ingested AA is taken up by tubular epithelial cells of the kidney, leading to DNA damage and cell death. Cyclophilin D (CypD) participates in mitochondrial-dependent cell death, but whether this mechanism operates in acute or chronic AA-induced kidney injury is unknown. We addressed this question by exposing CypD-/- and wild type (WT) mice to acute high dose, or chronic low dose, AA. Administration of 5 mg/kg AA to WT mice induced acute kidney injury 3 days later, characterised by loss of kidney function, tubular cell damage and death, and neutrophil infiltration. All of these parameters were significantly reduced in CypD-/- mice. Chronic low dose (2 mg/kg AA) administration in WT mice resulted in chronic kidney disease with impaired renal function and renal fibrosis by day 28. However, CypD-/- mice were not protected from AA-induced chronic kidney disease. In conclusion, CypD facilitates AA-induced acute kidney damage, but CypD does not contribute to the transition of acute kidney injury to chronic kidney disease during ongoing AA exposure.

Co-Exposure to Aristolochic Acids I and II Increases DNA Adduct Formation Responsible for Aristolochic Acid I-Mediated Carcinogenicity in Rats

The plant extract aristolochic acid (AA), containing aristolochic acids I (AAI) and II (AAII) as major components, causes aristolochic acid nephropathy (AAN) and Balkan endemic nephropathy (BEN), unique renal diseases associated with upper urothelial cancer. Recently (Chemical Research in Toxicology 33(11), 2804–2818, 2020), we showed that the in vivo metabolism of AAI and AAII in Wistar rats is influenced by their co-exposure (i.e., AAI/AAII mixture). Using the same rat model, we investigated how exposure to the AAI/AAII mixture can influence AAI and AAII DNA adduct formation (i.e., AA-mediated genotoxicity). Using ³²P-postlabelling, we found that AA-DNA adduct formation was increased in the livers and kidneys of rats treated with AAI/AAII mixture compared to rats treated with AAI or AAII alone. Measuring the activity of enzymes involved in AA metabolism, we showed that enhanced AA-DNA adduct formation might be caused partially by both decreased AAI detoxification as a result of hepatic CYP2C11 inhibition during treatment with AAI/AAII mixture and by hepatic or renal NQO1 induction, the key enzyme predominantly activating AA to DNA adducts. Moreover, our results indicate that AAII might act as an inhibitor of AAI detoxification in vivo. Consequently, higher amounts of AAI might remain in liver and kidney tissues, which can be reductively activated, resulting in enhanced AAI DNA adduct formation. Collectively, these results indicate that AAII present in the plant extract AA enhances the genotoxic properties of AAI (i.e., AAI DNA adduct formation). As patients suffering from AAN and BEN are always exposed to the plant extract (i.e., AAI/AAII mixture), our findings are crucial to better understanding host factors critical for AAN- and BEN-associated urothelial malignancy.

c-Jun Amino Terminal Kinase Signaling Promotes Aristolochic Acid-Induced Acute Kidney Injury

Aristolochic acid (AA) is a toxin that induces DNA damage in tubular epithelial cells of the kidney and is the cause of Balkan Nephropathy and Chinese Herb Nephropathy. In cultured tubular epithelial cells, AA induces a pro-fibrotic response via the c-Jun amino terminal kinase (JNK) signaling pathway. This study investigated the in vivo role of JNK signaling with a JNK inhibitor (CC-930) in mouse models of acute high dose AA-induced kidney injury (day 3) and renal fibrosis induced by chronic low dose AA exposure (day 22). CC-930 treatment inhibited JNK signaling and protected from acute AA-induced renal function impairment and severe tubular cell damage on day 3, with reduced macrophage infiltration and expression of pro-inflammatory molecules. In the chronic model, CC-930 treatment inhibited JNK signaling but did not affect AA-induced renal function impairment, tubular cell damage including the DNA damage response and induction of senescence, or renal fibrosis; despite a reduction in the macrophage pro-inflammatory response. In conclusion, JNK signaling contributes to acute high dose AA-induced tubular cell damage, presumably via an oxidative stress-dependent mechanism, but is not involved in tubular atrophy and senescence that promote chronic kidney disease caused by ongoing DNA damage in chronic low dose AA exposure.

Integration of transcriptomic, proteomic and metabolomic data to reveal the biological mechanisms of AAI injury in renal epithelial cells

Overexposure to aristolochic acid I (AAI) can induce aristolochic acid nephropathy (AAN). However, the comprehensive mechanisms of AAI-induced nephrotoxicity have not been entirely explicated. To investigate the toxicological mechanisms by which AAI induces renal injury, human kidney cells (HK-2 cells) were subjected to comprehensive transcriptomic, proteomic and metabolomic analyses. The transcriptomic analysis identified a total of 7749 differentially expressed genes (DEGs) after AAI treatment, while the proteomic analysis found 598 differentially expressed proteins (DEPs) after AAI treatment. The metabolomic analysis revealed 49 and 42 differentially expressed metabolites (DEMs) in the positive and negative ion modes, respectively. Gene Ontology (GO) functional annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis were performed on these DEGs, DEPs and DEMs. The results of the comprehensive analyses of transcripts, proteins, and metabolites indicated that the DEGs, DEPs, and DEMs were jointly regulated in three ways. These genes, proteins and metabolites and their related dysregulated pathways may be promising targets for research on the mechanisms of AAI injury in human renal epithelial cells. This study provides large-scale omics data that can be used to formulate new strategies for the prevention, rapid diagnosis, and treatment of AAI injury.

Local and Systemic Oxidative Stress in Balkan Endemic Nephropathy Is Not Associated with Xanthine Oxidase Activity

Balkan endemic nephropathy (BEN) represents a chronic tubulointerstitial nephropathy which is followed by the progression of kidney fibrosis to end-stage kidney failure. The critical involvement of poisons in food (aristolochic acid (AA), ochratoxin, and heavy metals) and selenium deficiency are among nutritive factors which contribute to the pathogenesis of BEN, due to reactive oxygen species (ROS) liberation and/or decreased antioxidative defence system. The aim of the study is to distinguish a possible systemic and local origin of ROS through the measurement of xanthine oxidase (XO) activity in urine and plasma, along with the determination of the oxidative changes in lipids and proteins. The study included 50 patients with BEN and 38 control healthy subjects. We noted increased levels of both thiobarbituric acid-reactive substances (TBARS) and advanced oxidation protein products (AOPPs) in the plasma of patients with BEN, compared to the control group (p < 0.001). The urinary levels of AOPPs were higher in patients with BEN in comparison to the control (p < 0.001). The specific activity of XO was significantly lower in plasma and urine in BEN samples, compared to controls (p < 0.005). Based on these results, we hypothesize that XO might not be considered a direct systemic or local contributor to ROS production in BEN, most probably because of the diminished kidney functional tissue mass and/or AA-induced changes in purine nucleotide conformation. The increased AOPP and TBARS level in both plasma and urine in BEN may predict ROS systemic liberation with toxic local effects.

The protective role of Nrf2 against aristolochic acid-induced renal tubular epithelial cell injury

Aristolochic acid nephropathy is a rapidly progressive tubulointerstitial disease induced by aristolochic acid (AA) and effective treatment is lacking. Nuclear factor erythroid 2-related factor 2 (Nrf2) has been proven to be protective in acute kidney injury and chronic kidney disease progression. But its role in AA-induced renal tubular epithelial cell injury has not been determined. This study aimed to investigate the role of Nrf2 in AA-induced renal tubular epithelial cell injury in vitro. NRK-52E cells were incubated with 5-50 μM AA to evaluate cell viability, reactive oxygen species (ROS) production, cell apoptosis/necrosis, and Nrf2 signaling pathway protein levels. We found that AA reduced cell viability and induced cell apoptosis in a time-dependent manner, accompanied by increased production of intracellular ROS. Meanwhile, the expression of Nrf2 signaling pathway proteins was significantly decreased. Downregulation of Nrf2 by Nrf2 siRNA decreased its downstream antioxidant proteins HO-1 and NQO1 and resulted in increased AA-induced ROS production and cell death. On the contrary, overexpression of Nrf2 increased HO-1 and NQO1 expression and resulted in decreased cell death. In conclusion, Nrf2 plays an important role in AA-induced injury. Enhanced Nrf2 signaling pathway could ameliorate AA-induced renal tubular epithelial cell injury, while downregulation of Nrf2 signaling exacerbated the injury.

Aristolochic Acid-Induced Genotoxicity and Toxicogenomic Changes in Rodents

Aristolochic acid (AA) is a group of structurally related nitrophenanthrene carboxylic acids found in many plants that are widely used by many cultures as traditional herbal medicines. AA is a causative agent for Chinese herbs nephropathy, a term replaced later by AA nephropathy. Evidence indicates that AA is nephrotoxic, genotoxic, and carcinogenic in humans; and it also induces tumors in the forestomach, kidney, renal pelvis, urinary bladder, and lung of rats and mice. Therefore, plants containing AA have been classified as carcinogenic to humans (Group 1) by the International Agency for Research on Cancer. In our laboratories, we have conducted a series of genotoxicity and toxicogenomic studies in the rats exposed to AA of 0.1–10 mg/kg for 12 weeks. Our results demonstrated that AA treatments induced DNA adducts and mutations in the kidney, liver, and spleen of rats, as well as significant alteration of gene expression in both its target and nontarget tissues. AA treatments altered mutagenesis- or carcinogenesis-related microRNA expression in rat kidney and resulted in significant changes in protein expression profiling. We also applied benchmark dose (BMD) modeling to the 3-month AA-induced genotoxicity data. The obtained BMDL₁₀ (the lower 95% confidence interval of the BMD₁₀ that is a 10% increase over the background level) for AA-induced mutations in the kidney of rats was about 7 μg/kg body weight per day. This review constitutes an overview of our investigations on AA-induced genotoxicity and toxicogenomic changes including gene expression, microRNA expression, and proteomics; and presents updated information focused on AA-induced genotoxicity in rodents.

Characterization of cytotoxic effects of aristolochic acids on the vascular endothelium

Aristolochic acid nephropathy (AAN) is characterized by interstitial fibrosis, proximal tubular atrophy, and hypoxia. A correlation between a reduced peritubular capillary density and the severity of fibrosis has been demonstrated. As calcium, redox and energetic homeostasis are crucial in maintaining endothelial cell function and survival, we aimed to investigate AA-induced disturbances involved in endothelial cell injury. Our results showed a cytotoxic effect of AA on EAhy926 endothelial cells. Exposure of aortic rings to AA impaired vascular relaxation to Acetylcholine (ACh). Increased levels of intracellular reactive oxygen species (ROS) were observed in cells exposed to AA. Pre-treatment with antioxidant N-acetyl cysteine inhibited AA-induced cell death. Superoxide dismutase resulted in restoring ACh-induced relaxation. An increase in intracellular calcium level ([Ca²⁺]_i) was observed on endothelial cells. Calcium chelators BAPTA-AM or APB, a specific inhibitor of IP₃R, improved cell viability. Moreover, AA exposure led to reduced AMP-activated protein kinase (AMPK) expression. AICAR, an activator of AMPK, improved the viability of AA-intoxicated cells and inhibited the rise of cytosolic [Ca²⁺]_i levels. This study provides evidence that AA exposure increases ROS generation, disrupts calcium homeostasis and decreases AMPK activity. It also suggests that significant damage observed in endothelial cells may enhance microcirculation defects, worsening hypoxia and tubulointerstitial lesions.

Aristolochic Acid-Induced Nephrotoxicity: Molecular Mechanisms and Potential Protective Approaches

Aristolochic acid (AA) is a generic term that describes a group of structurally related compounds found in the Aristolochiaceae plants family. These plants have been used for decades to treat various diseases. However, the consumption of products derived from plants containing AA has been associated with the development of nephropathy and carcinoma, mainly the upper urothelial carcinoma (UUC). AA has been identified as the causative agent of these pathologies. Several studies on mechanisms of action of AA nephrotoxicity have been conducted, but the comprehensive mechanisms of AA-induced nephrotoxicity and carcinogenesis have not yet fully been elucidated, and therapeutic measures are therefore limited. This review aimed to summarize the molecular mechanisms underlying AA-induced nephrotoxicity with an emphasis on its enzymatic bioactivation, and to discuss some agents and their modes of action to reduce AA nephrotoxicity. By addressing these two aspects, including mechanisms of action of AA nephrotoxicity and protective approaches against the latter, and especially by covering the whole range of these protective agents, this review provides an overview on AA nephrotoxicity. It also reports new knowledge on mechanisms of AA-mediated nephrotoxicity recently published in the literature and provides suggestions for future studies.

Mitochondrial dysfunction is involved in aristolochic acid I-induced apoptosis in renal proximal tubular epithelial cells

Aristolochic acid (AA) is a compound extracted from the Aristolochia species of herbs. AA exposure is associated with kidney injury known as aristolochic acid nephropathy (AAN). Proximal tubular epithelial cell (PTEC) is the primary target of AA and rich in mitochondria. Recently, increasing evidence suggests that mitochondrial dysfunction plays a critical role in the pathogenesis of kidney disease. However, the status of mitochondrial function in PTEC after exposure to AA remains largely unknown. The aim of this study was to explore the effect of aristolochic acid I (AAI) on cell apoptosis and mitochondrial function in PTEC. Normal rat kidney-52E (NRK-52E) cells were exposed to different concentrations of AAI for different time periods. Cell viability was detected by 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide, cell apoptosis was analyzed by flow cytometry, and the expression of cleaved caspase-3 by Western blotting. Mitochondrial function was evaluated by reactive oxygen species (ROS), mitochondrial membrane potential (MMP), mitochondrial DNA (mtDNA) copy number, and adenosine triphosphate (ATP). It was found that AAI reduced cell viability and increased cell apoptosis in a dose- and time-dependent manner. In parallel to increased apoptosis, NRK-52E cell manifested signs of mitochondrial dysfunction in response to AAI treatment. The data indicated that AAI could increase ROS level, lower MMP, decrease mtDNA copy number, and reduce ATP production. In addition, Szeto-Schiller 31, a mitochondria-targeted antioxidant peptide, attenuated AAI-induced mitochondrial dysfunction and apoptosis. Our study depicted significant aberrant of mitochondrial function in AAI-treated NRK-52E cell, which suggested that mitochondrial dysfunction may be involved in AAI-induced apoptosis in PTEC.

Protective Effects of Melatonin Against Aristolochic Acid-Induced Nephropathy in Mice

Melatonin, a pineal hormone, is well known to regulate the sleep–wake cycle. Besides, the hormone has been shown to display pleiotropic effects arising from its powerful anti-oxidant and anti-inflammatory activities. Recent studies have reported that melatonin exerts protective effects in animal models of kidney disease. However, the potential effects of melatonin on aristolochic acid (AA)-induced nephropathy (AAN) have not yet been investigated. Here, we found that the administration of melatonin ameliorated AA-induced renal dysfunction, as evidenced by decreased plasma levels of blood urea nitrogen and creatinine and histopathological abnormalities such as tubular dilatation and cast formation. The upregulation of tubular injury markers after AA injection was reversed by melatonin. Melatonin also suppressed AA-induced oxidative stress, as evidenced by the downregulation of 4-hydroxynonenal and reduced level of malondialdehyde, and modulated expression of pro-oxidant and antioxidant enzymes. In addition, p53-dependent apoptosis of tubular epithelial cells, infiltration of macrophages and CD4⁺ T cells into damaged kidneys, and renal expression of cytokines and chemokines were inhibited by melatonin. Moreover, melatonin attenuated AA-induced tubulointerstitial fibrosis through suppression of the tumor growth factor-β/Smad signaling pathway. These results suggest that melatonin might be a potential therapeutic agent for AAN.

Carbon monoxide: An emerging therapy for acute kidney injury

Treating acute kidney injury (AKI) represents an important unmet medical need both in terms of the seriousness of this medical problem and the number of patients. There is also a large untapped market opportunity in treating AKI. Over the years, there has been much effort in search of therapeutics with minimal success. However, over the same time period, new understanding of the underlying pathobiology and molecular mechanisms of kidney injury have undoubtedly helped the search for new therapeutics. Along this line, carbon monoxide (CO) has emerged as a promising therapeutic agent because of its demonstrated cytoprotective, and immunomodulatory effects. CO has also been shown to sensitize cancer, but not normal cells, to chemotherapy. This is particularly important in treating cisplatin-induced AKI, a common clinical problem that develops in patients receiving cisplatin therapies for a number of different solid organ malignancies. This review will examine and make the case that CO be developed into a therapeutic agent against AKI.

Bioactivation mechanisms of N-hydroxyaristolactams: Nitroreduction metabolites of aristolochic acids

Aristolochic acids (AAs) are human nephrotoxins and carcinogens found in concoctions of Aristolochia plants used in traditional medicinal practices worldwide. Genotoxicity of AAs is associated with the formation of active species catalyzed by metabolic enzymes, the full repertoire of which is unknown. Recently, we provided evidence that sulfonation is important for bioactivation of AAs. Here, we employ Salmonella typhimurium umu tester strains expressing human N-acetyltransferases (NATs) and sulfotransferases (SULTs), to study the role of conjugation reactions in the genotoxicities of N-hydroxyaristolactams (AL-I-NOH and AL-II-NOH), metabolites of AA-I and AA-II. Both N-hydroxyaristolactams show stronger genotoxic effects in umu strains expressing human NAT1 and NAT2, than in the parent strain. Additionally, AL-I-NOH displays increased genotoxicity in strains expressing human SULT1A1 and SULT1A2, whereas AL-II-NOH shows enhanced genotoxicity in SULT1A1/2 and SULT1A3 strains. 2,6-Dichloro-4-nitrophenol, SULTs inhibitor, reduced umuC gene expression induced by N-hydroxyaristolactams in SULT1A2 strain. N-hydroxyaristolactams are also mutagenic in parent strains, suggesting that an additional mechanism(s) may contribute to their genotoxicities. Accordingly, using putative SULT substrates and inhibitors, we found that cytosols obtained from human kidney HK-2 cells activate N-hydroxyaristolactams in aristolactam-DNA adducts with the limited involvement of SULTs. Removal of low-molecular-weight reactants in the 3.5-10 kDa range inhibits the formation of aristolactam-DNA by 500-fold, which could not be prevented by the addition of cofactors for SULTs and NATs. In conclusion, our results demonstrate that the genotoxicities of N-hydroxyaristolactams depend on the cell type and involve not only sulfonation but also N,O-acetyltransfer and an additional yet unknown mechanism(s). Environ. Mol. Mutagen. 2019. © 2019 Wiley Periodicals, Inc.

Systematic Overview of Aristolochic Acids: Nephrotoxicity, Carcinogenicity, and Underlying Mechanisms

Aristolochic acids (AAs) are a group of toxins commonly present in the plants of genus Aristolochia and Asarum, which are spread all over the world. Since the 1990s, AA-induced nephropathy (AAN) and upper tract urothelial carcinoma (UTUC) have been reported in many countries. The underlying mechanisms of AAN and AA-induced UTUC have been extensively investigated. AA-derived DNA adducts are recognized as specific biomarkers of AA exposure, and a mutational signature predominantly characterized by A→T transversions has been detected in AA-induced UTUC tumor tissues. In addition, various enzymes and organic anion transporters are involved in AA-induced adverse reactions. The progressive lesions and mutational events initiated by AAs are irreversible, and no effective therapeutic regimen for AAN and AA-induced UTUC has been established until now. Because of several warnings on the toxic effects of AAs by the US Food and Drug Administration and the regulatory authorities of some other countries, the sale and use of AA-containing products have been banned or restricted in most countries. However, AA-related adverse events still occur, especially in the Asian and Balkan regions. Therefore, the use of AA-containing herbal remedies and the consumption of food contaminated by AAs still carry high risk. More strict precautions should be taken to protect the public from AA exposure.

Nephrotoxicity: Topical issue

Drug-induced kidney injury is one of the most significant adverse events and dose limiting factor in chemotherapy as well a major cause of prospective drug attrition during pharmaceutical development. Moreover, kidney injury can also occur as a consequence of exposures to environmental xenobiotics such as heavy metals, fungal toxins and nanomaterials. The lack of adequate in vitro human kidney models that mimic more realistically the in vivo conditions and the absence of suitable and robust, cost-effective and predictive cell-based in vitro assays contribute to an underestimation of the kidney toxic potential of new drugs and xenobiotics. Therefore, a rapid screening system capable to detect potential nephrotoxicity at early stages of drug discovery is an urgent need. Here we provide an overview of human cell lines currently used as a surrogate in vitro kidney models in nephrotoxicity studies, including their advantages and limitations. In addition, the capacity of the single cell gel electrophoresis (SCGE)/comet assay as a potential tool in kidney toxicants screening is discussed. Despite a limited number of studies using the comet assay to evaluate the drug-induced kidney damage potential, a considerable variability in SCGE methodology (e.g. lysis, unwinding, and electrophoresis conditions) has been observed. Before the comet assay can be included in nephrotoxicity testing, a basic guideline has to be developed. To test its feasibility, additional in vitro experiments including inter-laboratory validation studies based on this guideline have to be performed.

Philosophical thinking of Chinese Traditional Medicine

Traditional medicine is often an integration of ancient philosophy, clinical experiences, primitive knowledge of medicine, regional cultures and religious beliefs. Chinese Traditional Medicine (CTM) is the general appellation of all the traditional medicines of different ethnicities in China, which share great similarities of basic concept and philosophical basis, and conform to the development of empirical medicine, among which the medicine of Han ethnicity (Han medicine) is the most mature. The development of CTM is totally different from that of modern medicine, always revolving around the center of disease diagnosis and treatment, establishing the core theoretical system of Yin and Yang, Five Elements, Zang and Fu and Humoralism with the theoretical foundation of ancient Chinese philosophy, which represents the highest achievement of worldwide empirical medicine and philosophy form at that time. In general, the basic structure of CTM mainly consists of three parts as follows: the part that has already reached consensus with modern medicine, the part that is unconsciously ahead of modern medicine, and the part that needs to be reconsidered or abandoned.

Vitamin E (α‑tocopherol) ameliorates aristolochic acid‑induced renal tubular epithelial cell death by attenuating oxidative stress and caspase‑3 activation

Aristolochic acid (AA) is a component identified in traditional Chinese remedies for the treatment of arthritic pain, coughs and gastrointestinal symptoms. However, previous studies have indicated that AA can induce oxidative stress in renal cells leading to nephropathy. α-tocopherol exists in numerous types of food, such as nuts, and belongs to the vitamin E isoform family. It possesses antioxidant activities and has been used previously for clinical applications. Therefore, the aim of the present study was to determine whether α-tocopherol could reduce AA-induced oxidative stress and renal cell cytotoxicity, determined by cell survival rate, reactive oxygen species detection and apoptotic features. The results indicated that AA markedly induced H₂O₂ levels and caspase-3 activity in renal tubular epithelial cells. Notably, the presence of α-tocopherol inhibited AA-induced H₂O₂ and caspase-3 activity. The present study demonstrated that antioxidant mechanisms of α-tocopherol may be involved in the increased survival rates from AA-induced cell injury.

An Integrated View of Aristolochic Acid Nephropathy: Update of the Literature

The term “aristolochic acid nephropathy” (AAN) is used to include any form of toxic interstitial nephropathy that is caused either by ingestion of plants containing aristolochic acids (AA) as part of traditional phytotherapies (formerly known as “Chinese herbs nephropathy”), or by the environmental contaminants in food (Balkan endemic nephropathy). It is frequently associated with urothelial malignancies. Although products containing AA have been banned in most of countries, AAN cases remain regularly reported all over the world. Moreover, AAN incidence is probably highly underestimated given the presence of AA in traditional herbal remedies worldwide and the weak awareness of the disease. During these two past decades, animal models for AAN have been developed to investigate underlying molecular and cellular mechanisms involved in AAN pathogenesis. Indeed, a more-in-depth understanding of these processes is essential to develop therapeutic strategies aimed to reduce the global and underestimated burden of this disease. In this regard, our purpose was to build a broad overview of what is currently known about AAN. To achieve this goal, we aimed to summarize the latest data available about underlying pathophysiological mechanisms leading to AAN development with a particular emphasis on the imbalance between vasoactive factors as well as a focus on the vascular events often not considered in AAN.

Protective Roles of N-acetyl Cysteine and/or Taurine against Sumatriptan-Induced Hepatotoxicity

Purpose: Triptans are the drug category mostly prescribed for abortive treatment of migraine. Most recent cases of liver toxicity induced by triptans have been described, but the mechanisms of liver toxicity of these medications have not been clear. Methods: In the present study, we obtained LC₅₀ using dose-response curve and investigated cell viability, free radical generation, lipid peroxide production, mitochondrial injury, lysosomal membrane damage and the cellular glutathione level as toxicity markers as well as the beneficial effects of taurine and/or N-acetyl cysteine in the sumatriptan-treated rat parenchymal hepatocytes using accelerated method of cytotoxicity mechanism screening. Results: It was revealed that liver toxicity induced by sumatriptan in in freshly isolated parenchymal hepatocytes is dose-dependent. Sumatriptan caused significant free radical generation followed by lipid peroxide formation, mitochondrial injury as well as lysosomal damage. Moreover, sumatriptan reduced cellular glutathione content. Taurine and N-acetyl cysteine were able to protect hepatocytes against sumatriptan-induced harmful effects. Conclusion: It is concluded that sumatriptan causes oxidative stress in hepatocytes and the decreased hepatocytes glutathione has a key role in the sumatriptan-induced harmful effects. Also, N-acetyl cysteine and/or taurine could be used as treatments in sumatriptan-induced side effects.

Alpha-Actinin-4 is a Possible Target Protein for Aristolochic Acid I in Human Kidney Cells In Vitro

Aristolochic acid I (AA-I) is a strong nephrotoxin, carcinogen, and mutagen found in plants such as the Aristolochia species. The mechanisms underlying AA-I toxicity in the kidneys are poorly understood. In this study, we aimed to gain insight into the mechanism of AA-I nephrotoxicity by analyzing the uptake, subcellular distribution, and intracellular targets of AA-I in the human kidney cell line HK-2 using immunocytochemistry, immunoprecipitation, and LC-MS/MS. In HK-2 cells incubated with 20[Formula: see text][Formula: see text]g/mL AA-I for different periods of time (up to 12[Formula: see text]h), AA-I was detected by a specific monoclonal antibody (MAb) against AA-I, both in the cytoplasm and nuclei. Nuclear localization depended on the exposure time. A protein with the molecular weight of 100 kDa was immunoprecipitated with the anti-AA-I MAb from the AA-I-treated cell lysates and was identified by LC-MS/MS as [Formula: see text]-actinin-4 after digestion of the protein, and was confirmed by immunoblotting with a specific anti-[Formula: see text]-actinin-4 MAb. This evidence shows, for the first time, that [Formula: see text]-actinin-4 is a protein targeted by AA-I in kidney cells. Our findings strongly suggest an association between [Formula: see text]-actinin-4 and AA-I nephrotoxic activity.

Balkan endemic nephropathy: an update on its aetiology

Balkan endemic nephropathy (BEN) is a unique, chronic renal disease frequently associated with upper urothelial cancer (UUC). It only affects residents of specific farming villages located along tributaries of the Danube River in Bosnia-Herzegovina, Croatia, Macedonia, Serbia, Bulgaria, and Romania where it is estimated that ~100,000 individuals are at risk of BEN, while ~25,000 have the disease. This review summarises current findings on the aetiology of BEN. Over the last 50 years, several hypotheses on the cause of BEN have been formulated, including mycotoxins, heavy metals, viruses, and trace-element insufficiencies. However, recent molecular epidemiological studies provide a strong case that chronic dietary exposure to aristolochic acid (AA) a principal component of Aristolochia clematitis which grows as a weed in the wheat fields of the endemic regions is the cause of BEN and associated UUC. One of the still enigmatic features of BEN that need to be resolved is why the prevalence of BEN is only 3-7 %. This suggests that individual genetic susceptibilities to AA exist in humans. In fact dietary ingestion of AA along with individual genetic susceptibility provides a scenario that plausibly can explain all the peculiarities of BEN such as geographical distribution and high risk of urothelial cancer. For the countries harbouring BEN implementing public health measures to avoid AA exposure is of the utmost importance because this seems to be the best way to eradicate this once mysterious disease to which the residents of BEN villages have been completely and utterly at mercy for so long.

Metabolomics insights into activated redox signaling and lipid metabolism dysfunction in chronic kidney disease progression

Early detection is critical in prevention and treatment of kidney disease. However currently clinical laboratory and histopathological tests do not provide region-specific and accurate biomarkers for early detection of kidney disease. The present study was conducted to identify sensitive biomarkers for early detection and progression of tubulo-interstitial nephropathy in aristolochic acid I-induced rats at weeks 4, 8 and 12. Biomarkers were validated using aristolochic acid nephropathy (AAN) rats at week 24, adenine-induced chronic kidney disease (CKD) rats and CKD patients. Compared with control rats, AAN rats showed anemia, increased serum urea and creatinine, progressive renal interstitial fibrosis, activation of nuclear factor-kappa B, and up-regulation of pro-inflammatory, pro-oxidant, and pro-fibrotic proteins at weeks 8 and 12. However, no significant difference was found at week 4. Metabolomics identified 12-ketodeoxycholic acid, taurochenodesoxycholic acid, LPC(15:0) and docosahexaenoic acid as biomarkers for early detection of tubulo-interstitial nephropathy. With prolonging aristolochic acid I exposure, LPE(20:2), cholic acid, chenodeoxycholic acid and LPC(17:0) were identified as biomarkers for progression from early to advanced AAN and lysoPE(22:5), indoxyl sulfate, uric acid and creatinine as biomarkers of advanced AAN. These biomarkers were reversed by treatment of irbesartan and ergone in AAN rats at week 24 and adenine-induced CKD rats. In addition, these biomarkers were also reversed by irbesartan treatment in CKD patients.

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Tubulo-interstitial nephropathy (TIN) is a common cause of chronic kidney disease.

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Plasma biomarker discovery and validation was performed by UPLC-based metabolomics.

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CKD progression associated with activated redox signaling and lipid dysfunction.

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TIN was associated with abnormal amino acids, purine and phospholipid metabolisms.

Biomarkers of oxidative damage and antioxidant enzyme activities in pre-dialysis Balkan endemic nephropathy patients

AIM

To obtain more insight into molecular mechanisms underlying oxidative stress in Balkan endemic nephropathy (BEN), biomarkers of oxidative stress and antioxidant enzyme activities were studied in 38 pre-dialysis BEN patients, 21 healthy BEN family members and 36 healthy subjects from non-endemic areas.

METHODS

Protein thiol groups (P-SH), antioxidant enzyme activities [superoxide dismutase (SOD) and glutathione peroxidase (GPX)], were determined in plasma spectrophotometrically, while malondialdehyde adducts (MDA) by enzyme immunoassay.

RESULTS

BEN patients had significantly lower plasma GPX activity in comparison with values for both control groups (p = 0.016), gradually decreasing with kidney function impairment estimated by glomerular filtration rate (r = 0.53, p = 0.002). GPX activity was inversely correlated with serum urea (r = -0.627, p < 0.001), creatinine (r = -0.53, p < 0.05), urinary excretion of protein and α1-microglobulin (r = -0.44, p = 0.012; r = -0.50, p < 0.007). Significant upregulation of SOD activity was observed in healthy BEN family members (p < 0.05). While the concentration of MDA adducts was similar in all three groups, BEN patients and healthy BEN family members exhibited increased protein damage, based on fewer P-SH groups in comparison with subjects from non-BEN areas (p = 0.085; p = 0.014, respectively).

CONCLUSIONS

Based on our results on increased oxidative protein damage in both pre-dialysis BEN patients and healthy BEN family members, it can be speculated that individuals from BEN areas, in general, are chronically exposed to some prooxidant environmental compounds. Moreover, decrease in plasma GPX activity, as a consequence of impaired kidney function, could further affect oxidative status in BEN patients.

Vitamin C attenuates the toxic effect of aristolochic acid on renal tubular cells via decreasing oxidative stress‑mediated cell death pathways

Aristolochic acid (AA) is a component of Chinese medicinal herbs, including asarum and aristolochia and has been used in Traditional Chinese Medicine for a long time. Recent studies found that AA has a cytotoxic effect resulting in nephropathy. These studies indicated that AA‑induced cytotoxicity is associated with increases in oxidative stress and caspase‑3 activation. The present study further demonstrated that AA mainly elevates the H2O2 ratio, leading to increases in oxidative stress. Furthermore, the results indicated that AA induces cell death can via caspase‑dependent and ‑independent pathways. It is desirable to identify means of inhibiting AA‑induced renal damage; therefore, the present study applied an anti‑oxidative nutrient, vitamin C, to test whether it can be employed to reduce AA‑induced cell cytotoxicity. The results showed that vitamin C decreased AA‑induced H2O2 levels, caspase‑3 activity and cytotoxicity in renal tubular cells. In conclusion, the present study was the first to demonstrate that AA‑induced increases of the H2O2 ratio resulted in renal tubular cell death via caspase‑dependent and ‑independent pathways, and that vitamin C can decrease AA‑induced increases in H2O2 levels and caspase‑3 activity to attenuate AA‑induced cell cytotoxicity.

Prediction of drug-induced nephrotoxicity and injury mechanisms with human induced pluripotent stem cell-derived cells and machine learning methods

The renal proximal tubule is a main target for drug-induced toxicity. The prediction of proximal tubular toxicity during drug development remains difficult. Any in vitro methods based on induced pluripotent stem cell-derived renal cells had not been developed, so far. Here, we developed a rapid 1-step protocol for the differentiation of human induced pluripotent stem cells (hiPSC) into proximal tubular-like cells. These proximal tubular-like cells had a purity of >90% after 8 days of differentiation and could be directly applied for compound screening. The nephrotoxicity prediction performance of the cells was determined by evaluating their responses to 30 compounds. The results were automatically determined using a machine learning algorithm called random forest. In this way, proximal tubular toxicity in humans could be predicted with 99.8% training accuracy and 87.0% test accuracy. Further, we studied the underlying mechanisms of injury and drug-induced cellular pathways in these hiPSC-derived renal cells, and the results were in agreement with human and animal data. Our methods will enable the development of personalized or disease-specific hiPSC-based renal in vitro models for compound screening and nephrotoxicity prediction.

Protective effect of Wuzhi tablet (Schisandra sphenanthera extract) against cisplatin-induced nephrotoxicity via Nrf2-mediated defense response

Cisplatin is a potent anti-cancer agent for various types of tumors. However, the clinical use of cisplatin is often limited by its nephrotoxicity. This study reports that WZ tablet (WZ, a preparation of an ethanol extract of Schisandra sphenanthera) mitigates cisplatin-induced toxicity in renal epithelial HK-2 cells and in mice. Pretreatment of HK-2 cells with WZ ameliorated cisplatin-induced cytotoxicity caused by oxidative stress, as was demonstrated by reductions in the levels of reactive oxygen species (ROS) and increased levels of glutathione (GSH). WZ facilitated the nuclear accumulation of the transcription factor NF-E2-related factor 2 (Nrf2) and the subsequent expression of its target genes such as

NAD(P)H

quinine oxidoreductase 1 (NQO1), heme oxygenase-1 (HO-1) and glutamate cysteine ligase (GCL). Protective effects of WZ on cisplatin-induced nephrotoxicity were also observed in mice. WZ attenuated cisplatin-induced renal dysfunction, structural damage and oxidative stress. The nuclear accumulation of Nrf2 and its target genes were increased by WZ treatment. Taken together, these findings demonstrated WZ have a protective effect against cisplatin-induced nephrotoxicity by activation of the Nrf2 mediated defense response, which is of significant importance for therapeutic intervention in cisplatin induced renal injury.

Localization of Aristolochic Acid in Mouse Kidney Tissues by Immunohistochemistry Using an Anti-AA-I and AA-II Monoclonal Antibody

Aristolochic acids (AAs) are found in herbal medicines of Aristolochiaceae plants, including Aristolochia and Asarum species. AAs are associated with a rapidly progressive interstitial nephritis, which is called aristolochic acid nephropathy (AAN). However, the in-situ localization of AAs in the target organ, the kidney, has not been investigated yet. In the present study, the accumulation of aristolochic acid I (AA-I) in mouse kidney was revealed by immunoperoxidase light microscopy as well as colloidal gold immunoelectron microscopy (IEM) based on an anti-AA-I and AA-II monoclonal antibody (mAb). Male BALB/c mice were treated with 1.25 or 2.50 mg kg-1 of AA-I per day for 5 days. Paraffin sections and ultra-thin sections of kidney tissue were respectively prepared. Under light microscopy, the apical surface of proximal tubules was strongly stained for AA-I, whereas no obvious immunostaining was found in the distal tubules and glomerulus, which remained relatively intact. Under electron microscopy, epithelial cells of the proximal tubules, distal tubules and collecting tubules were broken to various degrees. Gold labeling in the proximal and distal tubules was stronger than that in the collecting tubules. In renal tubules, immunogold signals of AA-I tended to accumulate in the mitochondria and peroxisomes, though the signals could be observed all over the cell. Gold signals were also found in the erythrocytes of glomeruli. The MAb against AA-I and AA-II provides a clue for the identification of proteins or factors which might interact with AA-I and thus induce targeted damage of kidney.

Aristolochic acid induced suicidal erythrocyte death

BACKGROUND/AIMS

Aristolochic Acid, a component of Aristolochia plants, has been shown to cause acute kidney injury, renal aristolochic acid nephropathy, Balkan endemic nephropathy, and urothelial carcinoma. Aristolochic acid nephropathy may be associated with severe anemia. The anemia could theoretically be due to stimulation of eryptosis, the suicidal death of erythrocytes characterized by cell shrinkage and cell membrane scrambling with translocation of phosphatidylserine to the erythrocyte cell membrane surface. Signalling involved in the stimulation of eryptosis include increase of cytosolic Ca(2+)-activity ([Ca(2+)]i) and formation of ceramide.

METHODS

Cell volume was estimated from forward scatter, phosphatidylserine-exposure from annexin V binding, [Ca(2+)]i from Fluo3 fluorescence, and ceramide abundance from binding of fluorescent antibodies in flow cytometry.

RESULTS

A 48 hours exposure to Aristolochic Acid (≥ 75 µg/ml) was followed by a significant decrease of forward scatter and increase of annexin-V-binding. The effects were paralleled by a significant increase of [Ca(2+)]i and significantly blunted, but not abrogated by removal of extracellular Ca(2+). Aristolochic Acid further significantly increased ceramide abundance.

CONCLUSIONS

Aristolochic Acid triggers eryptosis, an effect at least in part due to entry of extracellular Ca(2+) and ceramide formation.

The influence of ochratoxin A on DNA adduct formation by the carcinogen aristolochic acid in rats

Exposure to the plant nephrotoxin and carcinogen aristolochic acid (AA) leads to the development of AA nephropathy, Balkan endemic nephropathy (BEN) and upper urothelial carcinoma (UUC) in humans. Beside AA, exposure to ochratoxin A (OTA) was linked to BEN. Although OTA was rejected as a factor for BEN/UUC, there is still no information whether the development of AA-induced BEN/UUC is influenced by OTA exposure. Therefore, we studied the influence of OTA on the genotoxicity of AA (AA-DNA adduct formation) in vivo. AA-DNA adducts were formed in liver and kidney of rats treated with AA or AA combined with OTA, but no OTA-related DNA adducts were detectable in rats treated with OTA alone or OTA combined with AA. Compared to rats treated with AA alone, AA-DNA adduct levels were 5.4- and 1.6-fold higher in liver and kidney, respectively, of rats treated with AA combined with OTA. Although AA and OTA induced

NAD(P)H

quinone oxidoreductase (NQO1) activating AA to DNA adducts, their combined treatment did not lead to either higher NQO1 enzyme activity or higher AA-DNA adduct levels in ex vivo incubations. Oxidation of AA I (8-methoxy-6-nitrophenanthro[3,4-d]-1,3-dioxole-5-carboxylic acid) to its detoxification metabolite, 8-hydroxyaristolochic acid, was lower in microsomes from rats treated with AA and OTA, and this was paralleled by lower activities of cytochromes P450 1A1/2 and/or 2C11 in these microsomes. Our results indicate that a decrease in AA detoxification after combined exposure to AA and OTA leads to an increase in AA-DNA adduct formation in liver and kidney of rats.

The influence of dicoumarol on the bioactivation of the carcinogen aristolochic acid I in rats

Aristolochic acid I (AAI) is the major toxic component of the plant extract AA, which leads to the development of nephropathy and urothelial cancer in human. Individual susceptibility to AAI-induced disease might reflect variability in enzymes that metabolise AAI. In vitro

NAD(P)H

quinone oxidoreductase (NQO1) is the most potent enzyme that activates AAI by catalyzing formation of AAI-DNA adducts, which are found in kidneys of patients exposed to AAI. Inhibition of renal NQO1 activity by dicoumarol has been shown in mice. Here, we studied the influence of dicoumarol on metabolic activation of AAI in Wistar rats in vivo. In contrast to previous in vitro findings, dicoumarol did not inhibit AAI-DNA adduct formation in rats. Compared with rats treated with AAI alone, 11- and 5.4-fold higher AAI-DNA adduct levels were detected in liver and kidney, respectively, of rats pretreated with dicoumarol prior to exposure to AAI. Cytosols and microsomes isolated from liver and kidney of these rats were analysed for activity and protein levels of enzymes known to be involved in AAI metabolism. The combination of dicoumarol with AAI induced NQO1 protein level and activity in both organs. This was paralleled by an increase in AAI-DNA adduct levels found in ex vivo incubations with cytosols from rats pretreated with dicoumarol compared to cytosols from untreated rats. Microsomal ex vivo incubations showed a lower AAI detoxication to its oxidative metabolite, 8-hydroxyaristolochic acid (AAIa), although cytochrome P450 (CYP) 1A was practically unchanged. Because of these unexpected results, we examined CYP2C activity in microsomes and found that treatment of rats with dicoumarol alone and in combination with AAI inhibited CYP2C6/11 in liver. Therefore, these results indicate that CYP2C enzymes might contribute to AAI detoxication.

The induction of biochemical changes in Daphnia magna by CuO and ZnO nanoparticles

Whilst a considerable number of studies have been reported on the acute toxicity of nanoparticles (NPs) on invertebrates such as Daphnia magna, few studies have been reported on the biochemical change (biomarkers) induction on these species by NPs, especially metal oxide NPs. The aim of this study was to investigate some biomarkers in D. magna induced by copper oxide (CuO) and zinc oxide (ZnO) NPs under controlled laboratory conditions. We exposed the 5 day old D. magna for 72 h to sublethal concentration of CuO and ZnO NPs in synthetic moderately hard water (MHW) with and without dissolved natural organic matter (NOM) and estimated the glutathione-S-transferase (GST) activity, formation of oxidized glutathione (GSSG), and amounts of thiobarbituric acid reacting substances (TBARS) and metallothionein (MT). Additionally, complementary short term dissolution studies on CuO and ZnO NPs were conducted. The results showed inactivation of GST enzyme by both metal oxide NPs. The results also showed increased production of oxidized GSH, increased generation of TBARS and increased induction of MT. In the presence of NOM, significant reduction (p<0.05) in these biochemical changes was observed. These results indicated that oxidative stress is one of the toxicity mechanisms for these metal oxide NPs. Furthermore, the results suggest that these metal oxide NPs compromise the health of D. magna, and possibly other aquatic organisms, and therefore have potential to affect ecosystem stability. The short term dissolution studies showed that the proportion of dissolved NPs is higher (1.2% and 70% of initial concentration for dissolved Cu and Zn, respectively) at low particle concentration and is lower (0.4% and 17% of initial concentration for dissolved Cu and Zn, respectively) at higher particle concentration. These results suggest that the observed toxicity may be caused by both metal oxide nanoparticles and metal ions dissociated from the nanoparticles.