Overexpression of sirtuin 1 attenuates calcium oxalate-induced kidney injury by promoting macrophage polarization.

Sirtuin 1 (SIRT1) protein is involved in macrophage differentiation, while NOTCH signaling affects inflammation and macrophage polarization. Inflammation and macrophage infiltration are typical processes that accompany kidney stone formation. However, the role and mechanism of SIRT1 in renal tubular epithelial cell injury caused by calcium oxalate (CaOx) deposition and the relationship between SIRT1 and the NOTCH signaling pathway in this urological disorder are unclear. This study investigated whether SIRT1 promotes macrophage polarization to inhibit CaOx crystal deposition and reduce renal tubular epithelial cell injury. Public single-cell sequencing data, RT-qPCR, immunostaining approaches, and Western blotting showed decreased SIRT1 expression in macrophages treated with CaOx or exposed to kidney stones. Macrophages overexpressing SIRT1 differentiated towards the anti-inflammatory M2 phenotype, significantly inhibiting apoptosis and alleviating injury in the kidneys of mice with hyperoxaluria. Conversely, decreased SIRT1 expression in CaOx-treated macrophages triggered Notch signaling pathway activation, promoting macrophage polarization towards the pro-inflammatory M1 phenotype. Our results suggest that SIRT1 promotes macrophage polarization towards the M2 phenotype by repressing the NOTCH signaling pathway, which reduces CaOx crystal deposition, apoptosis, and damage in the kidney. Therefore, we propose SIRT1 as a potential target for preventing disease progression in patients with kidney stones.

microRNA-486-5p is implicated in the cisplatin-induced apoptosis and acute inflammation response of renal tubular epithelial cells by targeting HAT1.

The proinflammatory property of cisplatin is potentially destructive and contributes to the pathogenesis of acute kidney injury (AKI). The role and upstream regulatory mechanism of histone acetyltransferase 1 (HAT1) in acute kidney inflammation are still unknown. We performed RNA sequencing to filter differentially expressed microRNAs (miRNAs) in the kidney tissue of mice with AKI induced by cisplatin and ischemia-reperfusion. Here, we found that miR-486-5p was upregulated and that the expression of HAT1 was reduced in AKI mouse models and injured human renal proximal tubular epithelial cell (HK-2) model induced by cisplatin. miR-486-5p is implicated in cisplatin-induced kidney damage in vivo. Bioinformatics analysis predicted a potential binding site between miR-486-5p and HAT1. The Luciferase reporter assay and Western blot confirmed that miR-486-5p directly targeted the 3'-untranslated region of HAT1 mRNA and inhibited its expression in the cytoplasm of HK-2 cells. In the in vitro study, inhibiting miR-486-5p reduced apoptosis, and the expression of proinflammatory mediators was induced by cisplatin in HK-2 cells. Simultaneously, the downregulation of miR-486-5p inhibited the activation of the toll-like receptor 4 (TLR4) and nuclear factor-kappa B (NF-κB). We further found that HAT1 could inhibit apoptosis and the activation of cisplatin on the TLR4/NF-κB pathway and that the upregulation of miR-486-5p reversed this effect. Therefore, the upregulation of miR-486-5p targeting HAT1 promoted the cisplatin-induced apoptosis and acute inflammation response of renal tubular epithelial cells by activating the TLR4/NF-κB pathway, providing a new basis to highlight the potential intervention of regulating the miR-486-5p/HAT1 axis.

Adsorption Performances and Electrochemical Properties of Methyl Blue onto CoFe2O4 Nanoparticles.

Magnetic CoFe2O4 nanoparticles were successfully manufactured through the process of nitrate combustion using anhydrous ethanol as fuel, they together with their intermediate were characterized by thermo gravimetric (TG) analysis, selected area electron diffraction (SAED), transmission electron microscope (TEM), vibrating sample magnetometer (VSM), and X-ray diffraction (XRD). These results indicated a phenomenon that the magnetic CoFe2O4 nanoparticles could be formed at 400 °C, the average grain size, the specific magnetization, and the specific surface area of magnetic CoFe2O4 nanoparticles fabricated at 400 °C for 2 h with 30 mL anhydrous ethanol were corresponding 20 nm, 78.0 Am²/kg and 83.2 m²/kg. Magnetic CoFe2O4 nanoparticles were in application to adsorb methyl blue (MB) of wastewater, and their adsorption performances and electrochemical properties were investigated, the adsorption process data well agreed with the pseudo-second-order kinetics model in concentration ranging from 100 mg/L to 400 mg/L of MB. Compared with Freundlich model, Langmuir model (correlation coefficient R² = 0.9976) could evaluate the adsorption equilibrium state of MB onto CoFe2O4 nanoparticles at indoor temperature, so the monomolecular layer adsorption mechanism was demonstrated to be the mechanism of the MB molecules' adsorption onto CoFe2O4 nanoparticles.

[Effect of testicular autophagy on spermatogenic cells in varicocele rats].

OBJECTIVE: To study the effect of different levels of autophagy in the testis on the apoptosis of spermatogenic cells in the rat model of varicocele (VC). METHODS: We randomly divided 54 SD male rats into six groups, blank control (n = 6), rapamycin control (n = 6), chloroquine control (n = 6), VC model control (n = 12), VC + rapamycin (n = 12), and VC + chloroquine (n = 12). We observed the histomorphological changes of the testis and epididymis by HE staining, obtained the scores on spermatogenesis in the testis and epididymis, calculated the apoptosis index (AI) of the testicular spermatogenic cells by TUNEL, and determined the expressions of LC3-Ⅱ, LC3-Ⅰ, p62, Bax and Bcl-2 proteins in the testis tissue by Western blot. RESULTS: There were no significant morphological changes in the testis and epididymis of the rats in the blank control, rapamycin control and chloroquine control groups, or significant differences in the scores on testicular and epididymal spermatogenesis and AI of the testicular spermatogenic cells (P>0.05). The animals in the VC model control group exhibited significant pathological damage in the testicular and epididymal tissues, with remarkably decreased scores on spermatogenesis (P<0.01) and increased AI (P<0.01), which were markedly improved in the VC + rapamycin group and slightly aggravated in the VC + chloroquine group compared with the VC model controls. In comparison with the rats in the blank control group, those in the VC model control group showed significantly up-regulated expressions of the autophagy-related protein LC3 (including the LC3-Ⅱ/LC3-Ⅰ ratio) and the pro-apoptotic protein Bax in testicular tissue (P<0.01) but down-regulated expression of the anti-apoptotic protein Bcl-2 (P<0.01). The expressions of LC3 and Bcl-2 in the testis tissue were significantly higher in the VC + rapamycin (P<0.01) but lower in the VC + chloroquine group (P<0.01), while those of p62 and Bax remarkably lower in the VC + rapamycin (P<0.01) but higher in the VC + chloroquine group than in the VC model controls (P<0.01). CONCLUSIONS: Varicocele induces autophagy in the testis and apoptosis of spermatogenic cells in rats. Up-regulating autophagy can inhibit while blocking autophagy can promote the apoptosis of spermatogenic cells.

Dihydroquercetin protects against renal fibrosis by activating the Nrf2 pathway.

BACKGROUND: Dihydroquercetin (DHQ) is an antifibrotic agent. However, whether DHQ can prevent renal fibrosis remains unknown. PURPOSE: This study aimed to investigate the effects of DHQ on tubulointerstitial fibrosis and its underlying mechanisms in unilateral ureteral obstruction (UUO) mice in vivo and NRK-49F cells in vitro. METHODS: In vivo, UUO mice received vehicle or DHQ treatment. In vitro, NRK-49F cells were pretreated with DHQ and exposed to transforming growth factor-ß1 (TGF-ß1). Changes in fibroblast activation, collagen synthesis, oxidative stress, and related signaling pathways were assessed by immunohistochemical staining, Western blot analysis, real-time reverse transcription-PCR, and fluorescence microscopy. RESULTS: UUO induced tubular atrophy, inflammation, fibroblast differentiation into myofibroblast, and collagen deposition, whereas DHQ ameliorated these effects. UUO also resulted in decreased levels of nuclear factor-erythroid-2-related factor 2 (Nrf2), catalase, and heme oxygenase-1, but increased H2O2 and malondialdehyde levels. DHQ treatment corrected these changes. In vitro, the intracellular Nrf2 level of NRK-49F exposed to TGF-ß1 decreased. However, DHQ rescued intracellular Nrf2 level and promoted nuclear translocation of Nrf2. DHQ scavenged TGF-ß1-induced accumulation of reactive oxygen species, inhibited TGF-ß1-induced Smad3 phosphorylation, and prevented TGF-ß1-induced fibroblast activation and collagen synthesis in NRK-49F. Nrf2 knockdown could suppress the DHQ-mediated inhibitory effects on oxidative stress, Smad3 phosphorylation, fibroblast activation, and collagen deposition. Furthermore, DHQ ameliorated established renal fibrosis in UUO mice. CONCLUSIONS: DHQ posed remarkable preventive and therapeutic effects on UUO-induced renal fibrosis and suppressed fibroblast activation by reducing oxidative stress and Smad3 phosphorylation via Nrf2 signaling. This study provided a mechanistic basis for the clinical application of DHQ in renal fibrosis treatment.

Ursolic acid inhibits epithelial-mesenchymal transition in vitro and in vivo.

CONTEXT: Ursolic acid (UA; 3ß-hydroxy-urs-12-en-28-oic acid), one of the pentacyclic triterpenoids found in various plants and herbs, possesses some beneficial effects under pathological conditions, including combating hepatic fibrosis. OBJECTIVE: This study investigates the effects of UA on renal tubulointerstitial fibrosis in vivo and in vitro. MATERIALS AND METHODS: In vivo, 24 male C57BL6 mice were divided into four groups. Eighteen mice were subjected to unilateral ureteral obstruction (UUO) and the remaining six sham-operated mice served as control. UUO mice received either vehicle or UA (50 or 100 mg/kg) by gastric gavage for 6 days. In vitro, HK-2 cells were treated with 10 or 50 µM UA and 10 ng/mL recombinant human transforming growth factor-ß1 (TGF-ß1). The molecular mechanisms of fibrosis were investigated. RESULTS: UUO induced marked interstitial collagen I and fibronectin deposition and epithelial-mesenchymal transition (EMT), as evidenced by increased α-smooth muscle actin (α-SMA) and decreased E-cadherin. However, UA treatment significantly reduced collagen I and fibronectin accumulation in the fibrotic kidney. UA treatment also decreased α-SMA and preserved E-cadherin in vivo. In vitro, TGF-ß1-treated HK-2 cells demonstrated elevated α-SMA, snail1, slug, TGF-ß1, and p-smad3, as well as diminished E-cadherin. UA pretreatment prevented E-cadherin loss and diminished α-SMA expression in HK-2 cells. UA downregulated mRNA expression of snail1 and slug. UA also lowered TGF-ß1 protein expression and p-Smad3 in HK-2 cells. CONCLUSIONS: UA attenuated renal tubulointerstitial fibrosis by inhibiting EMT, and such inhibition may be achieved by decreasing profibrotic factors. UA may be a novel therapeutic agent for renal fibrosis.

Cryptotanshinone hinders renal fibrosis and epithelial transdifferentiation in obstructive nephropathy by inhibiting TGF-ß1/Smad3/integrin ß1 signal.

Recent studies have reported that CTS can alleviate cardiac fibrosis. However, the effects of CTS on kidney fibrosis and EMT are still unknown. This study explored whether CTS could attenuate tubulointerstitial fibrosis as well as EMT, and investigated the potential underlying mechanisms. In this study, an in vivo UUO mouse model and an in vitro TGF-ß1 stimulated normal renal tubular kidney epithelial cell model were established. In UUO model, administration of 50 mg kg-1 day-1 CTS markedly decreased the occurrence of kidney injury and the accumulation of fibronectin and collagen-1. In addition, CTS reduced the expression level of α-SMA but retained E-cadherin in obstructed kidneys. In vitro, CTS suppressed the expression of fibronectin, collagen-1 and α-SMA but retained that of E-cadherin. Furthermore, CTS selectively abolished the activation of Smad3 and suppressed the nuclear translocation of Smad2, Smad3 and Smad4. CTS could block the promoter activity of integrin ß1 induced by Smad3. Furthermore, CTS inhibited Smad3 binding to integrin ß1 promoter sequences. These data suggest that CTS can ameliorate kidney fibrosis and EMT, at least in part, by inhibiting the TGF-ß1/Smad3/integrin ß1 signaling pathway.

Astragalus membranaceus ameliorates renal interstitial fibrosis by inhibiting tubular epithelial-mesenchymal transition in vivo and in vitro.

Epithelial-mesenchymal transition (EMT) induces the progression of renal tubulointerstitial fibrosis. Astragalus membranaceus (AM) is a traditional Chinese herbal medicine that has been demonstrated to exert anti-inflammatory and anti-cancer effects, in addition to protecting and supporting the immune system. The present study investigated the effects of AM on renal fibrosis. A mouse model of unilateral ureteral obstruction (UUO) was established and treated with various concentrations of AM (100, 200 or 400 mg/kg/day). Interstitial fibrosis markedly increased in the UUO mice. AM significantly reduced the obstruction-induced upregulation of α-smooth muscle actin (α-SMA) and downregulation of E-cadherin in the kidneys of the UUO mice (P<0.05). Furthermore, AM treatment significantly inhibited the induction of EMT and the deposition of extracellular matrix. In addition, a transforming growth factor (TGF)-ß1-stimulated murine renal proximal tubule cell line (NRK-52E) was treated with various concentrations of AM (10, 20, and 40 µg/ml). E-cadherin expression levels significantly decreased and those of α-SMA significantly increased in NRK-52E cells stimulated with TGF-ß1 in vitro (P<0.05). Co-treatment with AM reversed these effects (P<0.05), and AM treatment reduced TGF-ß1-induced expression and Smad2/3 phosphorylation (P<0.05). These results suggested that AM antagonizes tubular EMT by inhibiting the Smad signaling pathway.

Baicalein ameliorates renal interstitial fibrosis by inducing myofibroblast apoptosis in vivo and in vitro.

OBJECTIVE: To investigate the anti-fibrotic effects of baicalein and its influence on myofibroblasts in vivo and in vitro. MATERIALS AND METHODS: An in vivo unilateral ureteric obstruction (UUO) mouse model and an in vitro transforming growth factor ß1 (TGF-ß1) activated normal rat kidney (NRK)-49F cell model were established. Baicalein treatment was then investigated in these models to assess its anti-fibrotic effects and potential mechanisms of action. RESULTS: Baicalein attenuated renal fibrosis by ameliorating kidney injury, reducing deposition of fibronectin and collagen type 1, and inducing apoptosis in myofibroblasts in the UUO mouse model. Baicalein also induced apoptosis of TGF-ß1-activated myofibroblasts in vitro in a dose-dependent manner. Furthermore, baicalein triggered a cascade of mitochondrion-associated apoptosis by upregulating cleaved-caspase-3, Bcl2-associated X protein (Bax), and cleaved-caspase-9 while downregulating the protein expression of B-cell lymphoma 2 (Bcl-2). Additionally, down-regulation of phosphorylated protein kinase B (pAkt) was found in the baicalein-induced pro-apoptotic components. CONCLUSIONS: The present findings show that baicalein can ameliorate tubulointerstitial fibrosis by inducing myofibroblast apoptosis through the mitochondrion-associated intrinsic pathway, which may be mediated by the inhibition of the phosphoinositide-3-kinase/Akt (PI3k/Akt) pathway.

Baicalein attenuates renal fibrosis by inhibiting inflammation via down-regulating NF-κB and MAPK signal pathways.

Baicalein is a natural flavonoid that possesses notable anti-inflammatory effects. In this study, we detected whether baicalein protects against inflammatory response in unilateral ureteral obstruction mice model to ameliorate tubulointerstitial fibrosis. Baicalein treatment significantly attenuated tubulointerstitial fibrosis by markedly reducing fibronectin and collagen-I. The downregulation of alpha-smooth muscle actin and upregulation of E-cadherin indicated that the epithelial-mesenchymal transition process was suppressed. Furthermore, baicalein administration blocked the infiltration of macrophages and lymphocytes, as evidenced by the significantly reduced CD68 and CD3 positive cells. Meanwhile, the mRNA expression of the pro-inflammatory cytokines tumor necrosis factor-α, interleukin-1ß, and monocyte chemotactic protein in baicalein-treated groups was markedly reduced compared with the vehicle-treated group. More importantly, unilateral ureteral obstruction induced the activation of NF-κB and mitogen-activated protein kinase signal pathways to switch on inflammatory response to aggravate kidney fibrosis, but these effects were mitigated by baicalein. These data demonstrate that baicalein could inhibit inflammatory process via inactivation of NF-κB and MAPK signal pathways to execute its anti-fibrotic actions in obstructive kidney disease.

In vitro dissolution of calcium oxalate stones with ethylenediaminetetraacetic acid and snake venom thrombin-like enzyme.

OBJECTIVE: The aim of this study was to determine the feasibility of using snake venom thrombin-like enzyme (SVTLE) and/or ethylenediaminetetraacetic acid (EDTA) to dissolve calcium oxalate stones in vitro. METHODS: Seven calcium oxalate stones were incubated with various chemolytic agents [EDTA, Tris-HCl/EDTA (TE) buffer or SVTLE diluted in TE buffer]. The pH, calcium concentration, stone weight and stone surface integrity were recorded, as well as related pathological changes to bladder mucosae. RESULTS: Compared to all other solutions, those containing SVTLE and buffered EDTA had higher concentrations of mobilized calcium and caused significantly more stone weight loss, stone fragility and gaps in the calcium crystals. Also, there were no adverse pathological effects on rabbit bladder mucosae from any of the solutions. CONCLUSIONS: The data indicate that buffered EDTA and SVTLE can be used to dissolve calcium oxalate stones and, at the concentrations used here, do not damage tissue.

[Expression of insulin-like factor 3 in the testis of flutamide-induced cryptorchidism mice and its significance].

OBJECTIVE: To study the changes in the mRNA expression of insulin-like factor 3 (INSL-3) in the testis of mouse models of flutamide-induced cryptorchidism. METHODS: We randomized pregnant BALB/c mice to groups A (control) , B, C, D and E to receive continuous gavage of flutamide at 0, 150, 300, 500 and 700 mg/kg body weight, respectively, from gestation day 12 to 21. We detected the expression of INSL-3 mRNA in the testis of the neonates by real-time PCR at 4 and 8 postnatal weeks. RESULTS: No cryptorchidism was found in group A; unilateral cryptorchidism was seen in groups B (10.0%) and C (25.0%); and bilateral cryptorchidism was observed in groups D (21.1%) and E (40.0%). The expression of INSL-3 mRNA was reduced with the increased dose of flutamide, not significantly changed in groups B and C (P > 0.05) but remarkably decreased in D and E as compared with A (P < 0.05). CONCLUSION: Administration of flutamide to pregnant mice can induce unilateral cryptorchidism at 150 and 300 mg/kg and bilateral cryptorchidism at 500 and 700 mg/kg in their male offspring, which may be related with its reducing effect on the expression of INSL-3 in the testis of the mice.

Biological implications of oxidation and unidirectional chiral inversion of D-amino acids.

Recent progress in chiral separation of D- and L-amino acids by chromatography ascertained the presence of several free Damino acids in a variety of mammals including humans. Unidirectional chiral inversion of many D-amino acid analogs such as exogenous NG-nitro-D-arginine (D-NNA), endogenous D-leucine, D-phenylanine and D-methionine have been shown to take place with inversion rates of 4-90%, probably dependent on various species D-amino acid oxidase (DAAO) enzymatic activities. DAAO is known to catalyze the oxidative deamination of neutral and basic D-amino acids to their corresponding α-keto acids, hydrogen peroxide and ammonia, and is responsible for the chiral inversion. This review provides an overview of recent research in this area: 1) oxidation and chiral inversion of several D-amino acid analogs in the body; 2) the indispensable but insufficient role of DAAO particularly in the kidneys and brain for the oxidation and chiral inversion of D-amino acids analogs; and 3) unidentified transaminase(s) responsible for the second step of chiral inversion. The review also discusses the physiological significance of oxidation and chiral inversion of D-amino acids, which is still a subject of dispute.

Histone deacetylation directs DNA methylation in survivin gene silencing.

DNA methylation and histone acetylation are major epigenetic modifications in gene silencing. In our previous research, we found that the methylated oligonucleotide (SurKex) complementary to a region of promoter of survivin could induce DNA methylation in a site-specific manner leading to survivin silencing. Here, we further studied the role of histone acetylation in survivin silencing and the relationship between histone acetylation and DNA methylation. First we observed the levels of histone H4 and H4K16 acetylation that were decreased after SurKex treatment by using the chromatin immunoprecipitation (ChIP) assay. Next, we investigated the roles of histone acetylation and DNA methylation in survivin silencing after blockade of histone deacetylation with Trichostatin A (TSA). We assessed survivin mRNA expression by RT-PCR, measured survivin promoter methylation by bisulfite sequencing and examined the level of histone acetylation by the ChIP assay. The results showed that histone deacetylation blocked by TSA reversed the effects of SurKex on inhibiting the expression of survivin mRNA, inducing a site-specific methylation on survivin promoter and decreasing the level of histone acetylation. Finally, we examined the role of histone acetylation in the expression of DNA methyltransferase 1 (DNMT1) mRNA. The results showed that histone deacetylation blocked by TSA reversed the increasing effect of histone deacetylation on the expression of survivin mRNA. This study suggests that histone deacetylation guides SurKex-induced DNA methylation in survivin silencing possibly through increasing the expression of DNMT1 mRNA.

Induced epigenetic modifications of the promoter chromatin silence survivin and inhibit tumor growth.

Anti-apoptotic survivin is over-expressed in a variety of human carcinomas and is considered as a therapeutic target in cancers. Suppression of survivin mRNA by RNAi and anti-sense nucleotides has proved to be a powerful anti-tumor therapy in both animal models and human investigations. In this communication, we tested an alternative approach to silence survivin by knocking down its gene transcription through a short methylated oligonucleotide (SurKex) that is complementary to the survivin gene promoter. Treatment of NCI-H460 cells with SurKex significantly suppressed the production of survivin mRNA and its oncoprotein. DNA bisulfite sequencing showed that SurKex induced site-specific de novo CpG methylation in the complementary region of survivin promoter. Chromatin immunoprecipitation assay also demonstrated that SurKex induced histone hypermethylation at histone H3K9 and H3K27 as well as deacetylation of histone H4 in the same regulatory region. SurKex remarkably inhibited tumor growth in nude mice bearing xenograft tumors. This study demonstrates that the synthetic methylated oligonucleotide SurKex inhibits tumor growth by silencing the survivin gene using a mechanism of altering the epigenotype in the survivin promoter. Thus, targeted epigenetic modification in the gene promoter may offer a new general strategy to silence tumor-related genes in tumor therapy.

Spinal D-amino acid oxidase contributes to neuropathic pain in rats.

D-amino acid oxidase (DAO) is an enzyme catalyzing oxidative deamination of neutral and polar d-amino acids and is expressed in the kidneys, liver, and central nervous system (CNS) including the spinal cord. We have previously demonstrated that DAO gene deletion/mutation by using mutant ddY/DAO(-/-) mice and systemic administration of the DAO inhibitor sodium benzoate blocked formalin-induced hyperalgesia in mice. In this study, we further investigated the potential role of DAO in neuropathic pain in a rat model of tight L(5)/L(6) spinal nerve ligation. After L(5)/L(6) spinal nerve ligation, the mRNA expression (measured by real-time quantitative polymerase chain reaction) and enzyme activity (measured by a colorimetric method) of DAO in the lumbar spinal cord were markedly increased, in agreement with the development of neuropathic pain (mechanical allodynia). Intraperitoneal injection of sodium benzoate (400 mg/kg) specifically blocked mechanical allodynia in neuropathic rats and formalin-induced hyperalgesia but did not suppress acute pain responses in the tail-flick test or formalin test. Systemic injection of sodium benzoate also inhibited DAO activity in the lumbar spinal cord of rats. Furthermore, direct intrathecal (spinal cord) injection of benzoate (30 mug/rat) specifically blocked spinal nerve ligation-induced mechanical allodynia in neuropathic rats and formalin-induced hyperalgesia (but not acute pain) in the formalin test. Based on the above results, we conclude that spinal DAO plays a pronociceptive (rather than an antinociceptive) role and might be a target molecule for the treatment of chronic pain of neuropathic origin.

Inhibition of D-amino-Acid oxidase activity induces pain relief in mice.

(1). We investigated the effects of inhibiting D: -amino-acid oxidase (DAO) activity on nociceptive responses through the use of mutant ddY/DAO(-) mice, which lack DAO activity, and through the application of a selective inhibitor of DAO, sodium benzoate, in the tail flick test, hot-plate test, formalin test, and acetic acid-induced writhing test. (2). Compared with normal ddY/DAO+ mice, ddY/DAO(- )mice showed significantly prolonged tail withdrawal latency in the tail flick test and licking/jumping latency in the hot-plate test, as well as significantly reduced duration of licking/biting in the late phase of the formalin test and the number of abdominal writhing in the acetic acid-induced writhing test. (3). In addition, we investigated the effects of sodium benzoate in Kunming mice having normal DAO activity. (4). Intravenous administration of sodium benzoate (400 mg/kg) significantly inhibited pain responses of the late phase of the formalin test and abdominal writhing responses in the acetic acid-induced writhing test, with no effects on the early phase flinch responses in the formalin test, nociceptive responses in the tail flick test, or hot-plate test. (5). These results suggest that DAO acts as a pro-nociceptive factor in pain, particularly chronic pain, transmission and modulation, and may be a target for pain treatment.

D-dopa is unidirectionally converted to L-dopa by D-amino acid oxidase, followed by dopa transaminase.

1. Many studies have shown that administration of d-3, 4-dihydroxyphenylalanine (D-dopa) produces contralateral rotation in hemi-parkinsonian animals comparable to L-dopa, with less potency and slower onset. It was postulated that D-dopa was converted to L-dopa to produce these effects. 2. To investigate the postulated chiral inversion of D-dopa to L-dopa and the related mechanism, an enantiomeric separation method for D- and L-dopa using HPLC was first established. Then, rat kidney homogenates containing D-dopa or L-dopa were incubated and subjected to HPLC to detect traces of respective enantiomer generation. The mechanism of the chiral inversion of d-dopa was explored by direct measurement of the production of L-dopa in kidney homogenates. D-dopa incubations containing different concentrations of an inhibitor of D-amino acid oxidase (DAAO) and an inhibitor of dopa transaminase were measured for L-dopa generation using HPLC. The role of DAAO in the chiral inversion of D-dopa to L-dopa was further investigated by using purified DAAO and mutant ddY/DAAO- mouse kidney lacking DAAO activity. 3. In rat kidney homogenate, D-dopa was, indeed, converted to L-dopa, whereas L-dopa was not converted to D-dopa. Sodium benzoate, a selective inhibitor of DAAO, blocked L-dopa generation in a concentration-dependant manner. In contrast with kidney homogenates of wild-type ddY/DAAO+ mice, those of mutant ddY/DAAO- mice lacking DAAO activity did not convert D-dopa to L-dopa unless exogenous DAAO protein was added. Conversely, when carbidopa, an inhibitor of dopa transaminase, was added to the homogenates, significant inhibition of L-dopa production was noted. 4. These results prove the proposal that d-dopa undergoes unidirectional chiral inversion and further suggest that D-dopa is first oxidatively deaminated by DAAO to its alpha-keto acid and then transaminated by dopa transaminase to L-dopa.

Renal D-amino acid oxidase mediates chiral inversion of N(G)-nitro-D-arginine.

N(G)-nitro-d-arginine (d-NNA), i.v. injected into rats, produced a pressor response, and was presumed to act via chiral inversion into N(G)-nitro-l-arginine (l-NNA), an inhibitor of nitric oxide synthase. We examined the possible role of renal d-amino acid oxidase (DAAO) in the chiral inversion of d-NNA to l-NNA. In pentobarbital-anesthetized rats, l-NNA was detected via capillary electrochromatography in the blood immediately after i.v. injection of d-NNA. The time course of appearance of l-NNA paralleled the increase in blood pressure elicited by d-NNA. Unilateral renal ligation partially, and bilateral ligation completely, blocked the pressor response as well as the conversion of d-NNA to l-NNA. Furthermore, injection into conscious rats of sodium benzoate, a selective DAAO inhibitor, completely blocked the pressor response to naive d-NNA, but not pressor response to d-NNA preincubated with homogenates of the kidney. Homogenates of the kidneys, liver (lesser degree), and brain (much lesser degree) converted d-NNA to l-NNA, and the chiral inversion was blocked by the addition of benzoate. Moreover, d-NNA chiral inversion correlates with the activity of DAAO. Our results reveal a novel pathway of chiral inversion of d-amino acids where the renal DAAO plays an essential role that accounts for the biological activity of d-NNA.