Bitter taste TAS2R14 activation by intracellular tastants and cholesterol.

Bitter taste receptors, particularly TAS2R14, play central roles in discerning a wide array of bitter substances, ranging from dietary components to pharmaceutical agents1,2. TAS2R14 is also widely expressed in extragustatory tissues, suggesting its extra roles in diverse physiological processes and potential therapeutic applications3. Here we present cryogenic electron microscopy structures of TAS2R14 in complex with aristolochic acid, flufenamic acid and compound 28.1, coupling with different G-protein subtypes. Uniquely, a cholesterol molecule is observed occupying what is typically an orthosteric site in class A G-protein-coupled receptors. The three potent agonists bind, individually, to the intracellular pockets, suggesting a distinct activation mechanism for this receptor. Comprehensive structural analysis, combined with mutagenesis and molecular dynamic simulation studies, elucidate the broad-spectrum ligand recognition and activation of the receptor by means of intricate multiple ligand-binding sites. Our study also uncovers the specific coupling modes of TAS2R14 with gustducin and Gi1 proteins. These findings should be instrumental in advancing knowledge of bitter taste perception and its broader implications in sensory biology and drug discovery.

Deep whole-genome analysis of 494 hepatocellular carcinomas.

Over half of hepatocellular carcinoma (HCC) cases diagnosed worldwide are in China1-3. However, whole-genome analysis of hepatitis B virus (HBV)-associated HCC in Chinese individuals is limited4-8, with current analyses of HCC mainly from non-HBV-enriched populations9,10. Here we initiated the Chinese Liver Cancer Atlas (CLCA) project and performed deep whole-genome sequencing (average depth, 120×) of 494 HCC tumours. We identified 6 coding and 28 non-coding previously undescribed driver candidates. Five previously undescribed mutational signatures were found, including aristolochic-acid-associated indel and doublet base signatures, and a single-base-substitution signature that we termed SBS_H8. Pentanucleotide context analysis and experimental validation confirmed that SBS_H8 was distinct to the aristolochic-acid-associated SBS22. Notably, HBV integrations could take the form of extrachromosomal circular DNA, resulting in elevated copy numbers and gene expression. Our high-depth data also enabled us to characterize subclonal clustered alterations, including chromothripsis, chromoplexy and kataegis, suggesting that these catastrophic events could also occur in late stages of hepatocarcinogenesis. Pathway analysis of all classes of alterations further linked non-coding mutations to dysregulation of liver metabolism. Finally, we performed in vitro and in vivo assays to show that fibrinogen alpha chain (FGA), determined as both a candidate coding and non-coding driver, regulates HCC progression and metastasis. Our CLCA study depicts a detailed genomic landscape and evolutionary history of HCC in Chinese individuals, providing important clinical implications.

Investigation of the applicability of the zebrafish model for the evaluation of aristolochic acid-related nephrotoxicity.

BACKGROUND: The risk of compounds/drugs, including aristolochic acid-induced nephrotoxicity remains high and is a significant public health concern. Therefore, it is particularly important to select reasonable animal models for rapid screening and evaluation of different samples with complex chemical systems. The zebrafish (Danio rerio) has been used to study chemical-induced renal toxicity. However, most of the published literature was performed on individual components or drugs, and the key evidence confirming the applicability of zebrafish larvae for the evaluation of aristolochic acid-related nephrotoxicity in complex chemical systems, such as in traditional Chinese medicine (TCM), was insufficient. METHODS: High-performance liquid chromatography (HPLC) was used to determine the content of aristolochic acid (AA) in herbs and Chinese patent medicines. The zebrafish larvae at 4 days post-fertilization (dpf) were used to evaluate the nephrotoxicity of various samples, respectively, based on the phenotype of the kidney and histological, and biochemical. Transcriptome technology was used to investigate the related signaling pathways and potential mechanisms after treatment with AA, which was verified by RT-PCR technology. RESULTS: The results showed that the total amounts of AAI, AAII, and ALI ranged from 0.0004 to 0.1858 g·g-1( %) from different samples, including Aristolochia debilis, Fibraurea recisa, Asarum, Wantongjingu tablets, Jiuweiqianghuo granules, and Xiaoqinglong granules in descending order. Moreover, compared with the negative/blank control, substantial changes in phenotype, histomorphology and biochemical parameters of renal function were observed in the groups challenged with the sublethal concentration of drugs. The transcriptomics results showed the upregulation of most genes in PERK/ATF4/CHOP, ATM/Chk2/p53, Caspase/Bax/Bcl-2a, TGF/Smad/ERK, PI3K/Akt, induced by aristolochic acid analogues, which were essentially consistent with those of the q-RT-PCR experiments, highlighting the similar toxicity response to the previously published article with the other traditional evaluation model. CONCLUSION: The stability, accuracy and feasibility of the zebrafish larval model in screening and evaluating the nephrotoxicity of TCM were validated for the first time on the AAs-related drugs in a unified manner, confirming and promoting the applicability of zebrafish in assessing nephrotoxicity of samples with complex chemical character.

Differences in p38-STAT3-S100A11 signaling after the administration of aristolochic acid I and IVa may account for the disparity in their nephrotoxicity.

BACKGROUND: The safety of herbs containing aristolochic acids (AAs) has become a widespread concern. Previous reports indicate that AAs are highly nephrotoxic and carcinogenic, although there are more than 170 analogues of aristolochic acid. Not all AAs have the same degree of nephrotoxicity or carcinogenicity. Previous studies have found that aristolochic acid IVa (AA-IVa), the principal component of AAs within members of the Aristolochiaceae family, especially Asarum, a commonly used herb in China, has essentially no significant nephrotoxicity. However, several studies, including ours, have shown that aristolochic acid I (AA-I) is clearly nephrotoxic. PURPOSE: The focus of the study was to elucidate the molecular mechanism responsible for the difference in nephrotoxicity between the AA-I and AA-IVa. STUDY DESIGN/METHOD: Mice were administered with AA-I or AA-IVa for 22 weeks through the oral route, followed by a 50-week recovery time. The kidney tissues of mice were extracted at the end of 22 weeks. Pathological examination and proteomic detection (tandem mass tagging (TMT) and phosphorylated proteomics) were performed on the kidney tissue to investigate the key signaling pathways and targets of AAs-induced renal interstitial fibrosis (RIF). The key signaling pathways and targets were verified by Western blot (WB), siRNA transfection, and luciferase assays. RESULTS: AA-I caused severe nephrotoxicity, high mortality, and extensive RIF. However, the same AA-IVa dosage exhibited almost no nephrotoxicity and does not trigger RIF. The activation of the p38-STAT3-S100A11 signaling pathway and upregulated expression of α smooth muscle actin (α-SMA) and Bcl2-associated agonist of cell death (Bad) proteins could be the molecular mechanism underlying AA-I-induced nephrotoxicity. On the other hand, AA-IVa did not regulate the activation of the p38-STAT3-S100A11 signaling pathway and had relatively little effect on the expression of α-SMA and Bad. Consequently, the difference in the regulation of p38-STAT3-S100A11 pathway, α-SMA, and Bad proteins between AA-I and AA-IVa may be responsible for the divergence in their level of nephrotoxicity. CONCLUSION: This is the first study to reveal the molecular mechanism underlying the difference in nephrotoxicity between AA-I and AA-IVa. Whether STAT3 is activated or not may be the key factor leading to the difference in nephrotoxicity between AA-I and AA-IVa.

Bioaccumulation and DNA Adduct Formation of Aristolactam I: Unmasking a Toxicological Mechanism in the Pathophysiology of Aristolochic Acid Nephropathy.

Prolonged exposure to aristolochic acid (AA) through AA-containing herbal medicines or AA-tainted food is putting a large portion of the global population at risk of developing renal fibrosis and tumors of the upper urinary tract. In an effort to better understand the organotropic property of AA, we studied the cytotoxicity, absorption, oxidative-stress inducing potential, and DNA adduct formation capability of aristolactam I (ALI), one of the major urinary metabolites of aristolochic acid I (AAI) in human cells. Despite ALI having a slightly lower cytotoxicity than that of AAI, the analysis revealed, for the first time, that ALI is bioaccumulated 900 times more than that of AAI inside cultured kidney cells. Furthermore, ALI induced a significantly larger glutathione depletion than that of AAI in the exposed cells. Together with the formation of ALI-DNA adduct at a reasonably high abundance, results of this study unmasked a previously disregarded causative role of ALI in the organotropic tumor-targeting property of AA.

Involvement of 5-HT2 serotonin receptors in cognitive defects induced by aristolochic acid I in mice.

Aristolochic acids (AAs) are a natural bioactive substance found in Chinese herbs, which are widely used for treating diseases. Many studies have demonstrated that AAs have various pharmacological function, while increasing reports indicated its toxicity. However, the role AAs in cognition remains poorly understood. This study explored the neurotoxic effect of aristolochic acid I (AAI), the most toxic component of the AAs family, on hippocampal synaptic plasticity and spatial cognition in mice. C57BL/6 mice were exposed to 5 mg/kg AAI for 4 weeks. After chronic treatment, AAI considerably increased the level of anxiety and the degree of behavioral despair in mice. Working and reference error rates were higher in the AAI exposed mice than in the control. This was further validated by the molecular docking studies, which AAI might interact with 5-HT2 serotonin receptor (5-HT2AR). Mechanism investigation indicated that AAI triggered inflammation in the hippocampus of mice through increasing the activity of Tnf-α-NF-κB-IL-6 signaling pathway. Conclusively, chronic AAI administration causes inflammation, and it possibly also serves as a potential antagonist of 5-HT2AR to influence the cognition function in C57BL/6 mice.

In Vivo Metabolism of Aristolochic Acid I and II in Rats Is Influenced by Their Coexposure.

The plant extract aristolochic acid (AA), containing aristolochic acid I (AAI) and II (AAII) as major components, causes aristolochic acid nephropathy and Balkan endemic nephropathy, unique renal diseases associated with upper urothelial cancer. Differences in the metabolic activation and detoxification of AAI and AAII and their effects on the metabolism of AAI/AAII mixture in the plant extract might be of great importance for an individual's susceptibility in the development of AA-mediated nephropathies and malignancies. Here, we investigated in vivo metabolism of AAI and AAII after ip administration to Wistar rats as individual compounds and as AAI/AAII mixture using high performance liquid chromatography/electrospray ionization mass spectrometry. Experimental findings were supported by theoretical calculations using density functional theory. We found that exposure to AAI/AAII mixture affected the generation of their oxidative and reductive metabolites formed during Phase I biotransformation and excreted in rat urine. Several Phase II metabolites of AAI and AAII found in the urine of exposed rats were also analyzed. Our results indicate that AAI is more efficiently metabolized in rats in vivo than AAII. Whereas AAI is predominantly oxidized during in vivo metabolism, its reduction is the minor metabolic pathway. In contrast, AAII is mainly metabolized by reduction. The oxidative reaction only occurs if aristolactam II, the major reductive metabolite of AAII, is enzymatically hydroxylated, forming aristolactam Ia. In AAI/AAII mixture, the metabolism of AAI and AAII is influenced by the presence of both AAs. For instance, the reductive metabolism of AAI is increased in the presence of AAII while the presence of AAI decreased the reductive metabolism of AAII. These results suggest that increased bioactivation of AAI in the presence of AAII also leads to increased AAI genotoxicity, which may critically impact AAI-mediated carcinogenesis. Future studies are needed to explain the underlying mechanism(s) for this phenomenon.

Replication of the Aristolochic Acid I Adenine Adduct (ALI-N6-A) by a Model Translesion Synthesis DNA Polymerase: Structural Insights on the Induction of Transversion Mutations from Molecular Dynamics Simulations.

Exposure to aristolochic acid I and II (AAI and AAII) has been implicated in aristolochic acid nephropathy and urothelial carcinoma. The toxicological effects of AAs are attributed to their ability to form aristolacatam (AL)-purine DNA adducts. Among these lesions, the AL-adenine (ALI-N6-A and ALII-N6-A) adducts cause the "signature" A → T transversion mutations associated with AA genotoxicity. To provide the currently missing structural basis for the induction of these signature mutations, the present work uses classical all-atom molecular dynamics simulations to examine different (i.e., preinsertion, insertion, and postextension) stages of replication past the most abundant AA adduct (ALI-N6-A) by a representative lesion-bypass DNA polymerase (Dpo4). Our analysis reveals that, before dNTP incorporation (i.e., preinsertion step), ALI-N6-A adopts a nearly planar conformation at the N6-linkage and the ALI moiety intercalates within the DNA helix. Since this conformation occupies the dNTP binding site, the same planar lesion conformation results in a significant distortion of the polymerase active site at the insertion step and therefore replication will likely not be successful. However, if ALI-N6-A undergoes a small conformational change to introduce non-planarity at the N6-linkage during the insertion step, minimal distortion occurs in the Dpo4 active site upon incorporation of dATP. This insertion and subsequent extension would initially lead to A:A mismatches and then result in A → T transversion mutations during the second round of replication. In contrast, if a large conformation flip of the ALI moiety occurs at the insertion step to reorient the bulky moiety from an intercalated position into the major groove, dTTP (non-mutagenic) incorporation will be favored. Molecular dynamics (MD) simulations on postextension complexes reveal that damaged DNA will likely further rearrange during later replication steps to acquire a base-displaced intercalated conformation that is similar to that previously reported for (unbound) ALI-N6-A adducted DNA, with the exception of slight non-planarity at the lesion site. Overall, our results provide a structural explanation for both the successful non-mutagenic lesion bypass and the preferential misincorporation of dATP opposite ALI-N6-A and thereby rationalize the previously reported induction of A → T signature transversion mutations associated with AAs. This work should thereby inspire future biochemical experiments and modeling studies on the replication of this important class of DNA lesions by related human translesion synthesis polymerases.

Biotransformation and Toxicities of Aristolochic Acids.

Environmental and iatrogenic exposures contribute significantly to human diseases, including cancer. The list of known human carcinogens has recently been extended by the addition of aristolochic acids (AAs). AAs occur primarily in Aristolochia herbs, which are used extensively in folk medicines, including Traditional Chinese Medicine. Ingestion of AAs results in chronic renal disease and cancer. Despite importation bans imposed by certain countries, herbal remedies containing AAs are readily available for purchase through the internet. With recent advancements in mass spectrometry, next generation sequencing, and the development of integrated organs-on-chips, our knowledge of cancers associated with AA exposure, and of the mechanisms involved in AA toxicities, has significantly improved. DNA adduction plays a central role in AA-induced cancers; however, significant gaps remain in our knowledge as to how cellular enzymes promote activation of AAs and how the reactive species selectively bind to DNA and kidney proteins. In this review, I describe pathways for AAs biotransformation, adduction, and mutagenesis, emphasizing novel methods and ideas contributing to our present understanding of AA toxicities in humans.

The impact of p53 on aristolochic acid I-induced nephrotoxicity and DNA damage in vivo and in vitro.

Exposure to aristolochic acid (AA) is associated with human nephropathy and urothelial cancer. The tumour suppressor TP53 is a critical gene in carcinogenesis and frequently mutated in AA-induced urothelial tumours. We investigated the impact of p53 on AAI-induced nephrotoxicity and DNA damage in vivo by treating Trp53(+/+), Trp53(+/-) and Trp53(-/-) mice with 3.5 mg/kg body weight (bw) AAI daily for 2 or 6 days. Renal histopathology showed a gradient of intensity in proximal tubular injury from Trp53(+/+) to Trp53(-/-) mice, especially after 6 days. The observed renal injury was supported by nuclear magnetic resonance (NMR)-based metabonomic measurements, where a consistent Trp53 genotype-dependent trend was observed for urinary metabolites that indicate aminoaciduria (i.e. alanine), lactic aciduria (i.e. lactate) and glycosuria (i.e. glucose). However, Trp53 genotype had no impact on AAI-DNA adduct levels, as measured by 32P-postlabelling, in either target (kidney and bladder) or non-target (liver) tissues, indicating that the underlying mechanisms of p53-related AAI-induced nephrotoxicity cannot be explained by differences in AAI genotoxicity. Performing gas chromatography-mass spectrometry (GC-MS) on kidney tissues showed metabolic pathways affected by AAI treatment, but again Trp53 status did not clearly impact on such metabolic profiles. We also cultured primary mouse embryonic fibroblasts (MEFs) derived from Trp53(+/+), Trp53(+/-) and Trp53(-/-) mice and exposed them to AAI in vitro (50 µM for up to 48 h). We found that Trp53 genotype impacted on the expression of NAD(P)H:quinone oxidoreductase (Nqo1), a key enzyme involved in AAI bioactivation. Nqo1 induction was highest in Trp53(+/+) MEFs and lowest in Trp53(-/-) MEFs; and it correlated with AAI-DNA adduct formation, with lowest adduct levels being observed in AAI-exposed Trp53(-/-) MEFs. Overall, our results clearly demonstrate that p53 status impacts on AAI-induced renal injury, but the underlying mechanism(s) involved remain to be further explored. Despite the impact of p53 on AAI bioactivation and DNA damage in vitro, such effects were not observed in vivo.

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.

Untargeted LC-MS-based metabonomics revealed that aristolochic acid I induces testicular toxicity by inhibiting amino acids metabolism, glucose metabolism, ß-oxidation of fatty acids and the TCA cycle in male mice.

As the main toxic component of aristolochic acid, aristolochic acid I (AAI) is primarily found in Aristolochiaceae plants such as Aristolochia, Aristolochia fangchi and Caulis aristolochiae manshuriensis. AAI has been proven to be carcinogenic, mutagenic and nephrotoxic. Although the role of AAI in testicular toxicity has been reported, its mechanism of action is unknown. Using metabonomics and molecular biology techniques, we tried to identify the differential endogenous metabolites of AAI that may affect the changes in testicular function in mice, map the network of metabolic pathways, and systematically reveal the molecular mechanism of AAI-induced testicular toxicity. We found that AAI inhibited amino acid metabolism in mouse testicular cells, impeded the uptake and oxidative decomposition of fatty acids, prevented normal glucose uptake by testicular cells, which inhibited glycolysis and gluconeogenesis, affected the mitochondrial tricarboxylic acid (TCA) cycle, which impaired the ATP energy supply, decreased the number of spermatogenic cells and sperm in the testes, induced changes in the mitochondrial state of spermatogonial cells, and ultimately led to physiological and pathological changes in the testes. AAI also regulated the testicular physiological activity by regulating the androgen receptor and hormone levels. This study used metabonomics and other methods to elucidate the mechanism of AAI-induced testicular toxicity from a new angle.

Aristolochic acid I determine the phenotype and activation of macrophages in acute and chronic kidney disease.

Acute and chronic kidney injuries are multifactorial traits that involve various risk factors. Experimental animal models are crucial to unravel important aspects of injury and its pathophysiological mechanisms. Translating knowledge obtained from experimental approaches into clinically useful information is difficult; therefore, significant attention needs to be paid to experimental procedures that mimic human disease. Herein, we compared aristolochic acid I (AAI) acute and chronic kidney injury model with unilateral ischemic-reperfusion injury (uIRI), cisplatin (CP)- or folic acid (FA)-induced renal damage. The administration of AAI showed significant changes in serum creatinine and BUN upon CKD. The number of neutrophils and macrophages were highly increased as well as AAI-induced CKD characterized by loss of tubular epithelial cells and fibrosis. The in vitro and in vivo data indicated that macrophages play an important role in the pathogenesis of AA-induced nephropathy (AAN) associated with an excessive macrophage accumulation and an alternative activated macrophage phenotype. Taken together, we conclude that AA-induced injury represents a suitable and relatively easy model to induce acute and chronic kidney injury. Moreover, our data indicate that this model is appropriate and superior to study detailed questions associated with renal macrophage phenotypes.

Reengineering the ligand sensitivity of the broadly tuned human bitter taste receptor TAS2R14.

BACKGROUND: In humans, bitterness perception is mediated by ~25 bitter taste receptors present in the oral cavity. Among these receptors three, TAS2R10, TAS2R14 and TAS2R46, exhibit extraordinary wide agonist profiles and hence contribute disproportionally high to the perception of bitterness. Perhaps the most broadly tuned receptor is the TAS2R14, which may represent, because of its prominent expression in extraoral tissues, a receptor of particular importance for the physiological actions of bitter compounds beyond taste. METHODS: To investigate how the architecture and composition of the TAS2R14 binding pocket enables specific interactions with a complex array of chemically diverse bitter agonists, we carried out homology modeling and ligand docking experiments, subjected the receptor to point-mutagenesis of binding site residues and performed functional calcium mobilization assays. RESULTS: In total, 40 point-mutated receptor constructs were generated to investigate the contribution of 19 positions presumably located in the receptor's binding pocket to activation by 7 different TAS2R14 agonists. All investigated positions exhibited moderate to pronounced agonist selectivity. CONCLUSIONS: Since numerous modifications of the TAS2R14 binding pocket resulted in improved responses to individual agonists, we conclude that this bitter taste receptor might represent a suitable template for the engineering of the agonist profile of a chemoreceptive receptor. GENERAL SIGNIFICANCE: The detailed structure-function analysis of the highly promiscuous and widely expressed TAS2R14 suggests that this receptor must be considered as potentially frequent target for known and novel drugs including undesired off-effects.

Fermentation of Aristolochia debilis by six different medicinal fungi and identification of aristolochic acid derivates in their products by HPLC-ESI-TOF-MS.

To analyze the content change of the nephrotoxic substances, aristolochic acid derivates (AAs) in the roots of Aristolochia debilis and the products generated from the solid-state fermentation of six different medicinal fungi by HPLC-ESI-TOF-MS, the chromatographic separation was carried out on C18 column at 30°C with the DAD detector. The elution was performed using the mobile phase of acetonitrile (A) and 0.2% acetic acid (B). Several new peaks were found in the scale of 0-20 min elution of HPLC diagram in the fermentation products. The ESI-MS detection (negative ion mode) was carried out by post-column flow splitting method following the automatic injection. Seven AAs in the fermentation products and A. debilis were deduced, which were recognized as AAIa or IIIa (1), AAVIa (2), AAIVa, Va, VIIa or VIIIa (3); AAII (4); AAIII (5); AAI (6); AAIV or VII (7). The areas of almost all these seven components existing originally in the corresponding crude drug decreased after the fermentation process, suggesting that fermentation is an effective way of lowering the nephrotoxicity induced by AAs in Chinese medicines similar with A. debilis. In addition, Optimized HPLC-MS method is helpful to AAs content identification.

Drosophila Gr64e mediates fatty acid sensing via the phospholipase C pathway.

Animals use taste to sample and ingest essential nutrients for survival. Free fatty acids (FAs) are energy-rich nutrients that contribute to various cellular functions. Recent evidence suggests FAs are detected through the gustatory system to promote feeding. In Drosophila, phospholipase C (PLC) signaling in sweet-sensing cells is required for FA detection but other signaling molecules are unknown. Here, we show Gr64e is required for the behavioral and electrophysiological responses to FAs. GR64e and TRPA1 are interchangeable when they act downstream of PLC: TRPA1 can substitute for GR64e in FA but not glycerol sensing, and GR64e can substitute for TRPA1 in aristolochic acid but not N-methylmaleimide sensing. In contrast to its role in FA sensing, GR64e functions as a ligand-gated ion channel for glycerol detection. Our results identify a novel FA transduction molecule and reveal that Drosophila Grs can act via distinct molecular mechanisms depending on context.

Structural Insight into Binding Mode of 9-Hydroxy Aristolochic Acid, Diclofenac and Indomethacin to PLA2.

Phospholipase A2 (PLA2) catalyzes the hydrolysis of phospholipids into arachidonic acid and lysophospholipids. Arachidonic acid is modified by cyclooxygenases into active compounds called eicosanoids that act as signaling molecules in a number of physiological processes. Excessive production of eicosanoids leads to several pathological conditions such as inflammation. In order to block the inflammatory effect of these compounds, upstream enzymes such as PLA2 are valid targets. In the present contribution, molecular dynamic analysis was performed to evaluate the binding of diclofenac, 9-hydroxy aristolochic acid (9-HAA) and indomethacin to PLA2. Obtained results revealed that 9-HAA could form a more stable complex with PLA2 when compared to diclofenac and indomethacin. Furthermore, analysis of intermolecular binding energy components indicated that hydrophobic interactions were dominant in binding process. On the basis of obtained data, inhibitors bearing fused rings with hydrogen acceptor/donor substituent(s) interacted with His48 and Asp49 residues of the active site. More affinity toward PLA2 might be envisaged through negatively charged moieties via interaction with Trp31, Lys34 and Lys69.

DNA Adducts Formed by Aristolochic Acid Are Unique Biomarkers of Exposure and Explain the Initiation Phase of Upper Urothelial Cancer.

Aristolochic acid (AA) is a plant alkaloid that causes aristolochic acid nephropathy (AAN) and Balkan endemic nephropathy (BEN), unique renal diseases frequently associated with upper urothelial cancer (UUC). This review summarizes the significance of AA-derived DNA adducts in the aetiology of UUC leading to specific A:T to T:A transversion mutations (mutational signature) in AAN/BEN-associated tumours, which are otherwise rare in individuals with UCC not exposed to AA. Therefore, such DNA damage produced by AA-DNA adducts is one rare example of the direct association of exposure and cancer development (UUC) in humans, confirming that the covalent binding of carcinogens to DNA is causally related to tumourigenesis. Although aristolochic acid I (AAI), the major component of the natural plant extract AA, might directly cause interstitial nephropathy, enzymatic activation of AAI to reactive intermediates capable of binding to DNA is a necessary step leading to the formation of AA-DNA adducts and subsequently AA-induced malignant transformation. Therefore, AA-DNA adducts can not only be utilized as biomarkers for the assessment of AA exposure and markers of AA-induced UUC, but also be used for the mechanistic evaluation of its enzymatic activation and detoxification. Differences in AA metabolism might be one of the reasons for an individual's susceptibility in the multi-step process of AA carcinogenesis and studying associations between activities and/or polymorphisms of the enzymes metabolising AA is an important determinant to identify individuals having a high risk of developing AA-mediated UUC.

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.