Citreoviridin inhibits cell proliferation and enhances apoptosis of human umbilical vein endothelial cells

In some areas of China, citreoviridin (CIT) is considered one of the risk factors for development of cardiovascular disease (CVD). Apoptosis of endothelial cell may induce vascular endothelium injury and atherosclerosis, which result in CVD probably. In this study, we investigated the effect of CIT on apoptosis and proliferation of human umbilical vein endothelial cells (HUVECs). The MTT assay was used to determinate HUVECs proliferation. Distribution of the cell cycle was analyzed by flow cytometry. The Annexin-V/PI staining was used to investigate cell apoptosis. Western blotting analysis was used to indicate changes in the expression level of apoptosis-related proteins. The results indicated that CIT inhibited HUVECs proliferation and the cells were arrested at G0/G1 phase, which is associated with decreased levels of cyclinD1 and increased expression of p53 and p21. The apoptosis rate of HUVECs was improved by CIT. The expression of Bcl-2 were down-regulated after CIT treatment, whereas the levels of Bax was significantly up-regulated. Furthermore, CIT-induced apoptosis was accompanied by the activation of caspase-3, -9. These findings demonstrate that CIT inhibits cell proliferation via DNA synthesis reduction and induces caspase-dependent apoptosis in HUVECs. CIT plays a pivotal role in the process of endothelial cell apoptosis, may thereby play an important role in the improvement of CVD in areas of China that have a high prevalence of CIT contamination.     

力达霉素抑制内皮细胞增殖和诱导细胞凋亡

目的研究力达霉素(lidamyein,LDM)对内皮细胞的增殖抑制作用和诱导细胞凋亡作用。方法用MTT测定法和[^2H]胸苷掺入测定法观察LDM对内皮细胞的增殖抑制；用流式细胞分析、形态观察、蛋白质印迹分析等方法研究LDM诱导内皮细胞凋亡及对相关调节蛋白的影响。结果 LDM呈浓度依赖性抑制内皮细胞增殖和诱导内皮细胞凋亡。LDM浓度1～10nmol／L可将内皮细胞阻断在G2／M期。LDM可导致内皮细胞中的游离钙增高，可使Bcl-2和PCNA蛋白的表达下调，但对Bax蛋白的表达无影响。结论 力达霉素抑制内皮细胞增殖与诱导内皮细胞凋亡。可进一步说明其抑制血管生成的相关机制。     

Nitric oxide dynamics and endothelial dysfunction in type II model of genetic diabetes

Although diabetes is a major risk factor for vascular diseases, e.g., hypertension and atherosclerosis, mechanisms that underlie the "risky" aspects of diabetes remain obscure. The current study is intended to examine the notion that diabetic endothelial dysfunction stems from a heightened state of oxidative stress induced by an imbalance between vascular production and scavenging of reactive oxygen/nitrogen species. Goto-Kakizaki (GK) rats were used as a genetic animal model for non-obese type II diabetes. Nitric oxide (NO) bioavailability and O2- generation in aortic tissues of GK rats were assessed using the Griess reaction and a lucigenin-chemiluminescence-based technique, respectively. Organ chamber-based isometric tension studies revealed that aortas from GK rats had impaired relaxation responses to acetylcholine whereas a rightward shift in the dose-response curve was noticed in the endothelium-independent vasorelaxation exerted by the NO donor sodium nitroprusside. An enhancement in superoxide (O2-) production and a diminuation in NO bioavailability were evident in aortic tissues of GK diabetic rats. Immunoblotting and high-performance liquid chromatography (HPLC)-based techniques revealed, respectively, that the above inverse relationship between O2- and NO was associated with a marked increase in the protein expression of nitric oxide synthase (eNOS) and a decrease in the level of its cofactor tetrahydrobiopterin (BH4) in diabetic aortas. Endothelial denudation by rubbing or the addition of pharmacological inhibitors of eNOS (e.g. N(omega)-nitro-L-arginine methyl ester (L-NAME)), and NAD(P)H oxidase (e.g. diphenyleneiodonium, apocynin) strikingly reduced the diabetes-induced enhancement in vascular O2- production. Aortic contents of key markers of oxidative stress (isoprostane F2alpha III, protein-bound carbonyls, nitrosylated protein) in connection with the protein expression of superoxide generating enzyme NAD(P)H oxidase (e.g. p47phox, pg91phox), a major source of reactive oxygen species in vascular tissue, were elevated as a function of diabetes. In contrast, the process involves in the vascular inactivation of reactive oxygen species exemplified by the activity of CuZnSOD was reduced in this diseased state. Our studies suggest that diabetes produces a cascade of events involving production of reactive oxygen species from the NADPH oxidase leading to oxidation of BH4 and uncoupling of NOS. This promotes the oxidative inactivation of NO with subsequent formation of peroxynitrite. An alteration in the balance of these bioactive radicals in concert with a defect in the antioxidant defense counteracting mechanism may favor a heightened state of oxidative stress. This phenomenon could play a potentially important role in the pathogenesis of diabetic endothelial dysfunction.     

Diallyl trisulfide activates NADPH oxidase by inducing the expression of NADPH oxidase subunits and translocation of both Rac2 and p67phox subunit in HL-60 cells

Objective To explore the effect and mechanism of diallyl trisulfide on the activity of NADPH oxidase in Hl-60 cells.Methods HL-60 cells were treated with DATS at a indicated concentration for 0,1,3,6,12 hours,respectively.The activity of NADPH oxidase was measured by the reduction of the yellow dye nitroblue tetrazolium(NBT).The mRNA expression of NADPH oxidase subunits,including gp91phox,p47 phox,p22 phox,Rac2 and Rac1,was detected by RT-PCR.The protein expression of p67 phox,gp91 phox and Rac2 was analyzed by Western blot.The cell membrane fractions were prepared according to the instruction of Mem-PER kit from Pierce Corp.Results The results showed that reduction ability of HL-60 cells for NBT markedly increased in a concentration-dependent manner following DATS incubation for 3 and 6 hours(P<0.05).HL-60 cells treated by DATS at a concentration of 150 μM for 3 hours have a maximal reduction effect for NBT.The results from RT-PCR indicated that mRNA expression of NADPH oxidase subunits,including p47phox,gp91 phox,p22 phox,Rac2 and Rac1,significantly increased in a concentration-dependent manner in HL-60 cells treated by DATS.The results from western blot showed that HL-60 cells following DATS incubation have a higher level expression of Rac2 and gp91phox,compared with untreated-HL-60 cells.Our results also indicated that a maximal expression level of p47phox,gp91 phox,p22 phox,Rac2 and Rac1in HL-60 cells is present at 3 hours following DATS incubation.We found that levels of both Rac2 and p67phox was reduced in the cytosolic fraction and meanwhile increased in the membrane fraction following HL-60 exposed to DATS,Which is dependent on the concentration and time of DATS treatment.Furthermore,the level of both Rac2 and p67phox located to the plasma membrane translocation was maximized following 150 μM of DATS incubation for 3 hours.Conclusions DATS induce the activation of NADPH oxidase by both up-regulating the expression of NADPH oxidase subunit and translocating the cytosolic Rac2 and p67 phox subunit to the plasma membrane in HL-60 cells.     

Comparative pharmacology of chemically distinct NADPH oxidase inhibitors

BACKGROUND AND PURPOSE

Oxidative stress [i.e. increased levels of reactive oxygen species (ROS)] has been suggested as a pathomechanism of different diseases, although the disease-relevant sources of ROS remain to be identified. One of these sources may be NADPH oxidases. However, due to increasing concerns about the specificity of the compounds commonly used as NADPH oxidase inhibitors, data obtained with these compounds may have to be re-interpreted.

EXPERIMENTAL APPROACH

We compared the pharmacological profiles of the commonly used NADPH oxidase inhibitors, diphenylene iodonium (DPI), apocynin and 4-(2-amino-ethyl)-benzolsulphonyl-fluoride (AEBSF), as well as the novel triazolo pyrimidine VAS3947. We used several assays for detecting cellular and tissue ROS, as none of them is specific and artefact free.

KEY RESULTS

DPI abolished NADPH oxidase-mediated ROS formation, but also inhibited other flavo-enzymes such as NO synthase (NOS) and xanthine oxidase (XOD). Apocynin interfered with ROS detection and varied considerably in efficacy and potency, as did AEBSF. Conversely, the novel NADPH oxidase inhibitor, VAS3947, consistently inhibited NADPH oxidase activity in low micromolar concentrations, and interfered neither with ROS detection nor with XOD or eNOS activities. VAS3947 attenuated ROS formation in aortas of spontaneously hypertensive rats (SHRs), where NOS or XOD inhibitors were without effect.

CONCLUSIONS AND IMPLICATIONS

Our data suggest that triazolo pyrimidines such as VAS3947 are specific NADPH oxidase inhibitors, while DPI and apocynin can no longer be recommended. Based on the effects of VAS3947, NADPH oxidases appear to be a major source of ROS in aortas of SHRs.     

NADPH氧化酶在大鼠心肌梗死后左室重构中的作用

目的探讨还原型辅酶Ⅱ(NADPH)氧化酶在大鼠心肌梗死后左室重构中的作用。方法 25只SD大鼠随机分为四组:心肌梗死组(A组,7只)、心肌梗死+夹竹桃麻素15mg.kg-1.d-1组(B组,6只)、假手术组(C组,6只)和假手术+生理盐水组(D组,6只)。6周后处死大鼠,称取心脏和左室重量,ELISA法检测胶原蛋白Ⅰ、Ⅲ含量,TUNEL法检测心肌细胞凋亡并分析其与左室射血分数(LVEF)的关系。结果与A组相比,B、C、D组心脏及左室重量指数、胶原蛋白Ⅰ含量及Ⅰ/Ⅲ比值、心肌细胞凋亡指数均明显降低(P<0.05或P<0.01),而LVEF则显著增高(P<0.01)。心肌细胞凋亡指数与LVEF呈负相关(r=-0.757,P<0.01)。结论心肌梗死后NADPH氧化酶激活可能是导致左室重构的重要原因之一。     

Mechanism of apoptosis induced by apigenin in hepg2 human hepatoma cells: involvement of reactive oxygen species generated by NADPH oxidase

Although plant-derived flavonoids have been reported to have anti-cancer activities, the exact mechanism of these actions is not completely understood. In this study we investigated the role for reactive oxygen species (ROS) as a mediator of the apoptosis induced by apigenin, a widespread flavonoid in plant, in HepG2 human hepatoma cells. Apigenin reduced cell viability, and induced apoptotic cell death in a dose-dependent manner. In addition, it evoked a dose-related elevation of intracellular ROS level. Treatment with various inhibitors of the NADPH oxidase (diphenylene iodonium, apocynin, neopterine) significantly blunted both the generation of ROS and induction of apoptosis induced by apigenin. These results suggest that ROS generated through the activation of the NADPH oxidase may play an essential role in the apoptosis induced by apigenin in HepG2 cells. These results further suggest that apigenin may be valuable for the therapeutic management of human hepatomas.     

The PPARgamma ligand, rosiglitazone, reduces vascular oxidative stress and NADPH oxidase expression in diabetic mice

Oxidative stress plays an important role in diabetic vascular dysfunction. The sources and regulation of reactive oxygen species production in diabetic vasculature continue to be defined. Because peroxisome proliferator-activated receptor gamma (PPARgamma) ligands reduced superoxide anion (O(2)(-.)) generation in vascular endothelial cells in vitro by reducing NADPH oxidase and increasing Cu/Zn superoxide dismutase (SOD) expression, the current study examined the effect of PPARgamma ligands on vascular NADPH oxidase and O(2)(-.) generation in vivo. Lean control (db(+)/db(-)) and obese, diabetic, leptin receptor-deficient (db(-)/db(-)) mice were treated with either vehicle or rosiglitazone (3 mg/kg/day) by gavage for 7-days. Compared to controls, db(-)/db(-) mice weighed more and had metabolic derangements that were not corrected by treatment with rosiglitazone for 1-week. Aortic O(2)(-.) generation and mRNA levels of the NADPH oxidase subunits, Nox-1, Nox-2, and Nox-4 as well as Nox-4 protein expression were elevated in db(-)/db(-) compared to db(+)/db(-) mice, whereas aortic Cu/Zn SOD protein and PPARgamma mRNA levels were reduced in db(-)/db(-) mice. Treatment with rosiglitazone for 1-week significantly reduced aortic O(2)(-.) production and the expression of Nox-1, 2, and 4 but failed to increase Cu/Zn SOD or PPARgamma in aortic tissue from db(-)/db(-) mice. These data demonstrate that the vascular expression of Nox-1, 2, and 4 subunits of NADPH oxidase is increased in db(-)/db(-) mice and that short-term treatment with the PPARgamma agonist, rosiglitazone, has the potential to rapidly suppress vascular NADPH oxidase expression and O(2)(-.) production through mechanisms that do not appear to depend on correction of diabetic metabolic derangements.     

NADPH氧化酶在氟诱导小胶质细胞氧化应激中的作用

目的：观察NADPH氧化酶在氟引起的小胶质细胞氧化应激中的作用,为进一步研究氟致中枢神经系统损伤机制提供实验依据.方法：用1,5,10,25,50,100 mg/L的氟化钠处理BV-2小胶质细胞6,12,24h后,检测细胞活力、细胞内活性氧（ROS）含量,以及NADPH氧化酶抑制剂API处理后的小胶质细胞ROS水平变化情况.结果：BV-2小胶质细胞细胞氟化钠染毒后,细胞活力显著降低,差异有统计学意义（P＜0.05）.染毒组细胞内ROS含量显著高于对照组,差异有统计学意义（P＜0.05）.与单独染氟组相比,NADPH氧化酶抑制剂API能够显著降低氟化钠诱导的BV-2细胞内活性氧（ROS）含量.结论：氟能引起小胶质细胞氧化应激,NADPH氧化酶在氟诱导的ROS产生中起一定作用。     

NADPH氧化酶对自发性高血压大鼠体内氧化应激的影响

目的考察NADPH氧化酶对自发性高血压大鼠体内氧化应激的影响。方法22wk龄自发性高血压大鼠(SHR)和正常血压WKY大鼠,采用尾套法测定血压,Greiss反应测定血清一氧化氮分泌量,ABTS和FRAP法进行血清总抗氧化能力测定,血管环舒缩测定来评价超氧阴离子清除剂超氧化物歧化酶(SOD)和NADPH氧化酶抑制剂夹竹桃麻素(Apo)对大鼠腹主动脉内皮依赖性舒张反应;采用RT-PCR考察内皮型一氧化氮合酶(eNOS)、NADPH氧化酶亚基p22phox以及NADPH氧化酶亚基gp91phox类似物nox4mRNA表达。结果与WKY大鼠相比,SHR血压升高,而血清总抗氧化水平及NO分泌量均降低。PCR显示SHR胸主动脉中eNOS及p22phoxmRNA表达与WKY大鼠相比差异无显著性,而nox4表达则升高。SHR腹主动脉内皮依赖性舒张反应与WKY相比降低,SOD或Apo均能明显逆转该变化。结论结果提示SHR体内氧化应激状态与NADPH氧化酶gp91phox类似物nox4mRNA过表达有关;NADPH氧化酶依赖性的氧化应激参与了SHR内皮功能障碍的发生发展;药理调节NADPH氧化酶功能或应用抗氧化治疗可明显改善SHR内皮依赖性舒张反应。     

溶血卵磷脂对血管内皮细胞增殖及凋亡的影响

目的观测溶血卵磷脂(LPC)对血管内皮细胞增殖及凋亡的影响,从而探讨动脉硬化发生的机制。方法取体外培养的人脐静脉内皮细胞(HUVECs),在含不同浓度LPC(5、10、20mg/L)的培养基中分别培养6、12、24、48h,用四甲基偶氮唑蓝(MTT)比色法、流式细胞仪、荧光显微镜观测血管内皮细胞增殖及凋亡的变化。结果与正常对照组比较,LPC抑制内皮细胞增殖,促进细胞凋亡,且其作用呈时间-效应、浓度-效应依赖关系,但随着LPC浓度增加,细胞凋亡增加的同时细胞死亡比例也增加。结论LPC抑制血管内皮细胞增殖,促进细胞凋亡,可能是其致动脉粥样硬化机制之一。     

Novel isoforms of NADPH oxidase in vascular physiology and pathophysiology

1. Vascular cells have evolved to use reactive oxygen species (ROS), such as superoxide and hydrogen peroxide, as signalling molecules. Under physiological conditions, ROS are important regulators of cell cycle, protein kinase activity and gene expression. However, in vascular disease states, such as hypertension and hypercholesterolaemia, excessive production of ROS may overwhelm the anti-oxidant defence mechanisms of cells, resulting in 'oxidative stress', damage to the artery wall and, ultimately, development of atherosclerotic plaques. 2. The primary source of ROS in the vasculature is NADPH oxidase. There appear to be at least three isoforms of NADPH oxidase expressed in the vascular wall, each differing with respect to the flavin-containing catalytic subunit it uses to transfer electrons from NADPH to molecular oxygen. Thus, although endothelial cells and adventitial fibroblasts express a gp91phox-containing NADPH oxidase similar to that originally identified in phagocytes, vascular smooth muscle cells may rely on novel homologues of gp91phox, namely Nox1 and Nox4, to produce superoxide. 3. Controversy remains over which isoform(s) of NADPH oxidase is responsible for the oxidative stress associated with vascular diseases. We and others have shown that although gp91phox mRNA expression is upregulated during atherogenesis in human and animal models, expression of the Nox4 subunit remains unchanged. Nox1 expression is also likely to be increased in diseased arteries; however, its relative level of expression, at least at the mRNA level, appears to be markedly lower than that of the other gp91phox homologues, even after upregulation. 4. Whether these findings suggest that a gp91phox-containing NADPH oxidase is more important than either Nox4 or Nox1 in vascular disease awaits studies examining relative protein expression and enzyme kinetics of each subunit, as well as the effects of targeted gene deletion of each of these gp91phox homologues on atherogenesis.     

NecroX-7 prevents oxidative stress-induced cardiomyopathy by inhibition of NADPH oxidase activity in rats

Oxidative stress is one of the causes of cardiomyopathy. In the present study, NecroXs, novel class of mitochondrial ROS/RNS scavengers, were evaluated for cardioprotection in in vitro and in vivo model, and the putative mechanism of the cardioprotection of NecroX-7 was investigated by global gene expression profiling and subsequent biochemical analysis. NecroX-7 prevented tert-butyl hydroperoxide (tBHP)-induced death of H9C2 rat cardiomyocytes at EC₅₀ = 0.057 μM. In doxorubicin (DOX)-induced cardiomyopathy in rats, NecroX-7 significantly reduced the plasma levels of creatine kinase (CK-MB) and lactate dehydrogenase (LDH) which were increased by DOX treatment (p < 0.05). Microarray analysis revealed that 21 genes differentially expressed in tBHP-treated H9C2 cells were involved in ‘Production of reactive oxygen species’ (p = 0.022), and they were resolved by concurrent NecroX-7 treatment. Gene-to-gene networking also identified that NecroX-7 relieved cell death through Ncf1/p47phox and Rac2 modulation. In subsequent biochemical analysis, NecroX-7 inhibited NADPH oxidase (NOX) activity by 53.3% (p < 0.001). These findings demonstrate that NecroX-7, in part, provides substantial protection of cardiomyopathy induced by tBHP or DOX via NOX-mediated cell death.     

NADPH oxidase and ERK1/2 are involved in cadmium induced-STAT3 activation in HepG2 cells

The molecular mechanism of Cd-induced signal transduction is not well understood. The aims of this study were to determine the system that generates reactive oxygen species in response to Cd that contribute to intracellular signaling on the activation of the STAT3 pathway in HepG2 cells and to address the participation of STAT3 in the production of Hsp70. Cadmium induced a significant increase in STAT3 DNA-binding after 1 h treatment. Serine phosphorylation of STAT3 was observed as a result of cadmium treatment while no tyrosine phosphorylation was detected. Cells were pretreated with inhibitors for several ROS generating systems, only diphenylen iodonium, an inhibitor of NADPH oxidase, decreased STAT3 activation. Cd induced 2.6-fold NADPH oxidase activity. Antioxidant treatment with pegylated-catalase reduced STAT3 activation. Cells were pretreated with different MAPK's inhibitors. ERK contributes in approximately 60%, and JNK in a small proportion, while p38 does not contribute in STAT3 activation. Cells were pretreated with a specific STAT3 peptide inhibitor that decreased the Cd-induced Hsp70 expression. Data suggest that STAT3 is phosphorylated at serine 727 by a Cd stress-activated signaling pathway inducing NADPH oxidase activity which produced ROS, leading ERK activation. MAPK promotes STAT3 phosphorylation that could induce a protective mechanism against Cd toxicity.     

老年大鼠角膜和晶状体上皮细胞NADPH氧化酶表达的研究

目的研究NADPH氧化酶在青年和老年大鼠角膜和晶状体上皮细胞中的表达。方法实验分为青年组(3月龄)和老年组(16月龄),比色法测定血清中超氧化物歧化酶(SOD)活性和丙二醛(MDA)含量,HE染色观察角膜和晶状体上皮细胞病理形态学变化,免疫组化检测角膜和晶状体上皮细PKCα、P47phox和NOX2的表达。结果与青年组大鼠比较,老年组大鼠血清SOD活性明显降低,MDA含量明显增加。病理结果显示,老年组角膜和晶状体上皮细胞核固缩、核深染细胞增多。免疫组化结果表明,老年组大鼠角膜和晶状体上皮细胞PKCα、P47phox和NOX2的表达明显增加。结论老年大鼠角膜和晶状体上皮细胞NADPH氧化酶表达明显增加,NADPH氧化酶介导的活性氧可能与老龄大鼠角膜和晶状体退行性变有关。     

β-eudesmol,a sesquiterpene from Teucrium ramosissimum,inhibits superoxide production,proliferation, adhesion and migration of human tumor cell

Reactive oxygen species are well-known mediators of various biological responses. Recently, new homologues of the catalytic subunit of NADPH oxidase have been discovered in non phagocytic cells. These new homologues (Nox1–Nox5) produce low levels of superoxides compared to the phagocytic homologue Nox2/gp91phox. In this study we examined the effect of β-eudesmol, a sesquiterpenoid alcohol isolated from Teucrium ramosissimum leaves, on proliferation, superoxide anion production, adhesion and migration of human lung (A549) and colon (HT29 and Caco-2) cancer cell lines. Proliferation of tumor cells was inhibited by β-eudesmol. It also significantly inhibited superoxide production in A549 cells. Furthermore, β-eudesmol inhibited adhesion and migration of A549 and HT29 cell. These results demonstrate that β-eudesmol may be a novel anticancer agent for the treatment of lung and colon cancer by different ways: by inhibition of superoxide production or by blocking proliferation, adhesion and migration.     

Protective effects of diphenyleneiodonium,an NADPH oxidase inhibitor,on lipopolysaccharide‐induced acute lung injury

NADPH oxidase (NOX) plays an important role in inflammatory response by producing reactive oxygen species (ROS). The inhibition of NOX has been shown to induce anti‐inflammatory effects in a few experimental models. The aim of this study was to investigate the effects of diphenyleneiodonium (DPI), a NOX inhibitor, on lipopolysaccharide (LPS)‐induced acute lung injury (ALI) in a rat model. Sprague‐Dawley rats were intraperitoneally administered by DPI (5 mg/kg) 30 minutes after intratracheal instillation of LPS (3 mg/kg). After 6 hours, bronchoalveolar lavage fluid (BALF) and lung tissue were collected. The NOX activity in lung tissue was significantly increased in LPS‐treated rats. It was significantly attenuated by DPI. DPI‐treated rats showed significant reduction in the intracellular ROS, the number of inflammatory cells, and cytokines (TNF‐α and IL‐6) in BALF compared with LPS‐treated rats. In lung tissue, DPI‐treated rats showed significantly decreased malondialdehyde content and increased activity of glutathione peroxidase and superoxide dismutase compared with LPS‐treated rats. Lung injury score, myeloperoxidase activity, and inducible nitric oxide synthase expression were significantly decreased in DPI‐treated rats compared with LPS‐treated animals. Western blotting analysis demonstrated that DPI significantly suppressed LPS‐induced activation of NF‐κB and ERK1/2 and SAPK/JNK in MAPK pathway. Our results suggest that DPI may have protective effects on LPS‐induced ALI thorough anti‐oxidative and anti‐inflammatory effects which may be due to inactivation of the NF‐κB, ERK1/2, and SAPK/JNK pathway. These results suggest the therapeutic potential of DPI as an anti‐inflammatory agent in ALI.     

The NADPH oxidase inhibitor diphenyleneiodonium is also a potent inhibitor of cholinesterases and the internal Ca2+ pump

Background and purpose:

Diphenyleneiodonium (DPI) is often used as an NADPH oxidase inhibitor, but is increasingly being found to have unrelated side effects. We investigated its effects on smooth muscle contractions and the related mechanisms.

Experimental approach:

We studied isometric contractions in smooth muscle strips from bovine trachea. Cholinesterase activity was measured using a spectrophotometric assay; internal Ca²⁺ pump activity was assessed by Ca²⁺ uptake into smooth muscle microsomes.

Key results:

Contractions to acetylcholine were markedly enhanced by DPI (10⁻⁴ M), whereas those to carbachol (CCh) were not, suggesting a possible inhibition of cholinesterase. DPI markedly suppressed contractions evoked by CCh, KCl and 5-HT, and also unmasked phasic activity in otherwise sustained responses. Direct biochemical assays confirmed that DPI was a potent inhibitor of acetylcholinesterase and butyrylcholinesterase (IC₅₀∼8 × 10⁻⁶ M and 6 × 10⁻⁷ M, respectively), following a readily reversible, mixed non-competitive type of inhibition. The inhibitory effects of DPI on CCh contractions were not mimicked by another NADPH oxidase inhibitor (apocynin), nor the Src inhibitors PP1 or PP2, ruling out an action through the NADPH oxidase signalling pathway. Several features of the DPI-mediated suppression of agonist-evoked responses (i.e. suppression of peak magnitudes and unmasking of phasic activity) are similar to those of cyclopiazonic acid, an inhibitor of the internal Ca²⁺ pump. Direct measurement of microsomal Ca²⁺ uptake revealed that DPI modestly inhibits the internal Ca²⁺ pump.

Conclusions and implications:

DPI inhibits cholinesterase activity and the internal Ca²⁺ pump in tracheal smooth muscle.