Xiang Xue

Baicalin inhibits macrophage activation by lipopolysaccharide and protects mice from endotoxin shock.

Baicalin (BA) exhibits anti-inflammatory effect in vivo and in vitro and is used to treat inflammatory diseases. Here, we report that BA inhibits the activation of macrophage and protects mice from macrophage-mediated endotoxin shock. The experiments in vitro showed BA suppressed the increased generation of nitric oxide (NO) and expression of inducible nitric oxide synthase (iNOS) induced by LPS or Interferon-gamma (IFN-gamma) without directly affecting iNOS activity in RAW264.7 cells and peritoneal macrophages. Similarly, BA inhibited the production of reactive oxidative species (ROS), whereas augmented the level of intracellular superoxide dismutase (SOD). Moreover, BA inhibited the production of inflammatory mediators including tumor necrosis factor (TNF)-alpha, endothelin (ET)-1 and thromboxane A2 (TXA2) induced by lipopolysaccharide (LPS) in RAW264.7 cells. In animal model, BA protected mice from endotoxin shock induced by d-galactosamine (D-GalN)/LPS possibly through inhibiting the production of cytokine and NO. Collectively, BA inhibited the production of inflammatory mediators by macrophage and may be a potential target for treatment of macrophage-mediated diseases.

Hepatic cytochrome P450s metabolize aristolochic acid and reduce its kidney toxicity

Cytochrome P450s metabolize the naturally occurring nephrotoxin aristolochic acid. Using liver-specific cytochrome P450 reductase-null mice we found that a low but lethal dose of aristolochic acid I was ineffective in wild-type mice. Induction of hepatic CYP1A by 3-methylcholanthrene pretreatment markedly increased the survival rate of wild type mice given higher doses and these mice were protected from aristolochic acid I-induced renal injury. Clearance of aristolochic acid I in null mice was slower compared to control and the 3-methylcholanthrene-pretreated wild type mice. The levels of aristolochic acid I in the kidney and liver were much higher in null mice but much lower in 3-methylcholanthrene-treated compared to control wild type mice. Hepatic microsomes from 3-methylcholanthrene-treated wild type mice had greater activity compared to untreated mice. Finally, aristolochic acid I was more cytotoxic than its major metabolite aristolactam I and this cytotoxicity was decreased in human renal tubular epithelial HK2 cells in the presence of a reconstituted hepatic microsome-cytosol (S9) system. These results indicate that hepatic P450s play an important role in metabolizing aristolochic acid I into less toxic metabolites and thus have a detoxification role in aristolochic acid I-induced kidney injury.

Emodin Triggers DNA Double-Strand Breaks by Stabilizing Topoisomerase II-DNA Cleavage Complexes and by Inhibiting ATP Hydrolysis of Topoisomerase II

Emodin, an anthraquinone derived from a plant and fungi, has been reported to possess potential genotoxicity, but the mechanism is not entirely clear. Here, we report that emodin causes DNA double-strand breaks (DSBs) through stabilization of topoisomerase (Topo) II-DNA cleavage complexes and inhibition of ATP hydrolysis. In our study, emodin did not induce mutagenecity in the salmonella mutation assay but caused genotoxicity in the thymidine kinase gene mutation assay and in the micronucleus test. Moreover, emodin induced DNA DSBs demonstrated by induction of comet tails, the expression of phosphorylated histone H2AX, and phosphorylation of ataxia telangiectasia mutated. Our studies also revealed that emodin exerted strong inhibitory activity against Topo II in the supercoiled pBR322 relaxation assay and in Topo II-mediated kinetoplast DNA decatenation, similar to the previous report. We also showed that the inhibitory effect of emodin on Topo II was because of its ability to stabilize Topo II-DNA complexes and to inhibit the ATP hydrolysis of Topo II. Furthermore, emodin was found to trigger DNA DSBs in a Topo II-dependent manner using the Topo II catalytic inhibitor aclarubicin and in Topo II-deficient mitoxantrone-resistant variant HL-60/MX2 cells. Together, these results suggest that in emodin-induced DNA DSBs and genotoxicity, stabilization of Topo II-DNA cleavage complexes and inhibition of ATP hydrolysis play an important role.

Baicalin protects mouse from Concanavalin A-induced liver injury through inhibition of cytokine production and hepatocyte apoptosis

Background: Baicalin (BA) exhibits an anti‐inflammatory effect in vivo and in vitro and is used to treat chronic hepatitis. However, the mechanism by which BA exerts the liver‐protective effect remains largely unknown.

Critical role of organic anion transporters 1 and 3 in kidney accumulation and toxicity of aristolochic acid I.

Ingestion of aristolochic acid (AA), especially its major constituent aristolochic acid I (AAI), results in severe kidney injury known as aristolochic acid nephropathy (AAN). Although hepatic cytochrome P450s metabolize AAI to reduce its kidney toxicity in mice, the mechanism by which AAI is uptaken by renal cells to induce renal toxicity is largely unknown. In this study, we found that organic anion transporters (OATs) 1 and 3, proteins known to transport drugs from the blood into the tubular epithelium, are responsible for the transportation of AAI into renal tubular cells and the subsequent nephrotoxicity. AAI uptake in HEK 293 cells stably transfected with human OAT1 or OAT3 was greatly increased compared to that in the control cells, and this uptake was dependent on the AAI concentration. Administration of probenecid, a well-known OAT inhibitor, to the mice reduced AAI renal accumulation and its urinary excretion and protected mice from AAI-induced acute tubular necrosis. Further, AAI renal accumulation and severe kidney lesions induced by AAl in Oat1 and Oat3 gene knockout mice all were markedly suppressed compared to those in the wild-type mice. Together, our results suggest that OAT1 and OAT3 have a critical role in AAl renal accumulation and toxicity. These transporters may serve as a potential therapeutic target against AAN.

Induction of P450 1A by 3-methylcholanthrene protects mice from aristolochic acid-I-induced acute renal injury

BACKGROUNDnCytochrome P450 1A, an enzyme known to metabolize polycyclic aromatic hydrocarbons (PAHs), participates in the metabolism of aristolochic acid I (AAI) in liver and kidney microsomes isolated from humans and rodents. This study was designed to investigate whether P450 1A plays a role in AAI-induced renal injury in C57BL/6 mice.nnnMETHODSnSeparate groups of mice were given AAI (10 mg/kg and 20 mg/kg) or pretreatment with 3-methylcholanthrene (3-MC, an agent known to induce P450 1A expression in many species including rodents) at 60 mg/kg given at 24 h before AAI injection. Renal function and histopathology were determined at the 3rd day following the high dose of AAI and at the 14th day following the low dose of AAI treatment. For both doses, we determined in vivo AAI clearances and pharmacokinetic parameters. We also determined in vitro P450 1A1/2 activity and the ability of liver microsomes from 3-MC-treated and vehicle-treated mice to metabolize AAI. Finally, the effect of 3-MC on protein levels of P450 1A1/2 in both liver and kidney was measured by western blotting.nnnRESULTSnPretreatment with 3-MC greatly protected mice against renal failure induced by AAI. In vivo AAI clearance was more rapid in 3-MC-pretreated mice than in the vehicle-pretreated mice. In addition, the P450 1A1/2 activity and the ability to metabolize AAI in hepatic microsomes isolated from 3-MC-treated mice were much greater than in vehicle-treated mice. Western blotting showed that protein levels of hepatic P450 1A1/2 were greatly increased in 3-MC-treated mice than in vehicle-treated mice.nnnCONCLUSIONnThese results demonstrated that the induction of hepatic P450 1A1/2 protected against AAI-induced kidney injury through faster in vivo clearance of AAI and suggested an important role for hepatic P450s in the detoxification of AAI-induced renal injury.

Inhibition of renal NQO1 activity by dicoumarol suppresses nitroreduction of aristolochic acid I and attenuates its nephrotoxicity

Aristolochic acid I (AAI) is the major toxic component of aristolochic acid that causes aristolochic acid nephropathy and Balkan endemic nephropathy. Nitroreduction is an essential metabolic process for AAI rapid clearance in different species including humans. However, which enzyme participates in AAI nitroreduction in vivo and whether this metabolic process contributes to AAI nephrotoxicity are unclear. Here, we showed that NAD(P)H:quinone oxidoreductase 1 (NQO1) was highly expressed in mouse renal tubular epithelial cells. Inhibition of NQO1 activity by dicoumarol pretreatment significantly decreased renal aristolactam I (ALI) levels, a major reductive metabolite of AAI, whereas it increased renal AAI and its major oxidative metabolite 8-hydroxy-aristolochic acid I (AAIa) levels in male C57BL/6 mice. Similar changes in renal ALI, AAI, and AAIa levels were also observed in mice pretreated with another NQO1 inhibitor, phenindione. Consistent with higher levels of renal AAI and AAIa found in dicoumarol-pretreated mice, their serum clearance was much slower compared with vehicle-pretreated mice. The survival rate of mice pretreated with dicoumarol was markedly increased when higher doses of AAI were given. Similarly, pretreatment of mice with phenindione also attenuated AAI-induced nephrotoxicity. These results indicate that NQO1 plays an important role in renal AAI nitroreduction and may thus contribute to AAI-induced nephrotoxicity.

Roles of reactive oxygen species and MAP kinases in the primary rat hepatocytes death induced by toosendanin

Toosendanin (Tsn), a triterpenoid extracted from Melia toosendan Sieb et Zucc, possesses different pharmacological effects in human and important values in agriculture. However, liver injury has been reported when toosendanin or Melia-family plants, which contain toosendanin are applied. The mechanism by which toosendanin induces liver injury remains largely unknown. Here we reported that toosendanin induced primary rat hepatocytes death by mitochondrial dysfunction and caspase activation. Toosendanin led to decrease of mitochondrial membrane potential, fall in intracellular ATP level, release of cytochrome c to cytoplasm, activation of caspase-8, 9, and 3 and ultimately cell death. Level of reactive oxygen species (ROS) was also increased in hepatocytes after incubation with toosendanin. Catalase, the H2O2-decomposing enzyme, can prevent the reduction in ATP level and protect hepatocytes from toosendanin-induced death. The ERK1/2 (p44/42 MAP kinases) and JNK (c-Jun N-terminal kinase) were activated, but p38 MAPK was not activated by toosendanin. Inhibition of ERK1/2 activation sensitized hepatocytes to death and increased activity of caspase-9 and 3 in response to toosendanin. Inhibition of JNK attenuated toosendanin-induced cell death. These results suggested that toosendanin causes death of primary rat hepatocytes by mitochondrial dysfunction and caspase activation. Generation of ROS and MAP kinases activation might be involved in this process.

beta-Naphthoflavone protects mice from aristolochic acid-I-induced acute kidney injury in a CYP1A dependent mechanism.

AbstractAim:The role of CYP1A in the protection of aristolochic acid (AA)I-induced nephrotoxicity has been suggested. In the present study we investigated the effects of β-naphthoflavone (BNF), a non-carcinogen CYP1A inducer, on AAI-induced kidney injury.Methods:Mice were pretreated with 80 mg/kg BNF by daily intraperitoneal injection (ip) for 3 days followed by a single ip of 10 mg/kg AAI. AAI and its major metabolites in blood, liver and kidney, the expression of CYP1A1 and CYP1A2 in microsomes of liver and kidney, as well as the nephrotoxicity were evaluated.Results:BNF pretreatment prevented AAI-induced renal damage by facilitating the disposal of AAI in liver. BNF pretreatment induced the expression of CYP1A1 in both liver and kidney; but the induction of CYP1A2 was only observed in liver.Conclusion:BNF prevents AAI-induced kidney toxicity primarily through CYP1A induction.

Comparative 28-day repeated oral toxicity of Longdan Xieganwan, Akebia trifoliate (Thunb.) koidz., Akebia quinata (Thunb.) Decne. and Caulis aristolochiae manshuriensis in mice

ETHNOPHARMACOLOGICAL RELEVANCEnLongdan Xieganwan, which contains Aristolochia species, is a traditional Chinese prescription. It has been used for thousands of years to enhance liver. However, many cases of Longdan Xieganwan induced nephropathy were reported recently.nnnAIM OF THE STUDYnThis study was designed to compare the possible toxic effects of Longdan Xieganwan and three different Aristolochia species, i.e. Akebia trifoliate (Thunb.) koid (Akebia trifoliate), Akebia quinata (Thunb.) Decne. (Akebia quinata) and Caulis aristolochiae manshuriensis (Aristolochia manshuriensis).nnnMATERIALS AND METHODSnMice were orally administered these drugs for 28 days. Clinical signs, body weights, serum biochemistry, organ weights and histopathology were examined.nnnRESULTSnSignificantly decreased body weights and obvious nephropathy were noticed in the Aristolochia manshuriensis groups at doses higher than 0.24 g/kg/d. A few endothelial cell degenerations in renal glomerulus were observed in the Akebia trifoliate group at a high-dose of 2.00 g/kg/d. No significant changes were observed in the other groups.nnnCONCLUSIONSnThe no-observed-adverse-effect levels (NOAELs) for Aristolochia manshuriensis, Akebia trifoliate, Akebia quinata and Longdan Xieganwan in this study for mice were 0.06 g/kg/d, 0.40 g/kg/d, higher than 3.00 g/kg/d and higher than 10.00 g/kg/d, which were equivalent to 0.25 times, 5 times, 25 times and 10 times of normal human dose in clinical prescription, respectively.