Structural features of mammalian histidine decarboxylase reveal the basis for specific inhibition

Gout and pain are synonymous, and a study in this issue of the BJP reports a novel anti-nociceptive effect of allopurinol, the drug most commonly used to treat gout. Allopurinol works by inhibiting xanthine oxidase (XO), the enzyme responsible for converting hypoxanthine to uric acid which is deposited as crystals in the joints of gout sufferers. Hypoxanthine is a metabolite of, and a possible precursor to, adenosine. Schmidt et al., find that acute inhibition of XO with allopurinol produces a modest adenosine A₁ receptor-mediated anti-nociceptive effect in common tests of chemical and thermal nociception in mice. A concomitant increase in cerebrospinal fluid levels of adenosine supports their hypothesis that inhibiting XO increases adenosine levels via salvage from hypoxanthine. Elevating endogenous adenosine levels by inhibiting metabolism is a well-established strategy for producing anti-nociception in many preclinical models, but inhibiting XO is likely to be particularly beneficial in some chronic pain states because of the pro-nociceptive reactive oxygen species that are produced by XO activity. Thus, allopurinol may have unexpected benefits in pain associated with chronic inflammation, diabetes and vascular dysfunction.     

Therapeutic voyage of synthetic and natural xanthine oxidase inhibitors

Xanthine oxidase (XO) inhibitors are commonly used to treat gout, nephropathy, and renal stone diseases related to hyperuricemia. However, recent research has shown that these inhibitors may also have potential benefits in preventing vascular diseases, including those affecting the cerebrovasculature. This is due to emerging evidence suggesting that serum uric acid is involved in the growth of cardiovascular disease, and XO inhibition can reduce oxidative stress in the vasculature. There is a great interest in the development of new XO inhibitors for the treatment of hyperuricemia and gout. The present review discusses the many synthetic and natural XO inhibitors that have been developed which are found to have greater potency.     

Role of xanthine oxidase in dexamethasone-induced hypertension in rats

1. Glucocorticoid-induced hypertension (GC-HT) in the rat is associated with nitric oxide-redox imbalance. 2. We studied the role of xanthine oxidase (XO), which is implicated in the production of reactive oxygen species, in dexamethasone-induced hypertension (dex-HT). 3. Thirty male Sprague-Dawley rats were divided randomly into four treatment groups: saline, dexamethasone (dex), allopurinol plus saline, and allopurinol plus dex. 4. Systolic blood pressures (SBP) and bodyweights were recorded each alternate day. Thymus weight was used as a marker of glucocorticoid activity, and serum urate to assess XO inhibition. 5. Dex increased SBP (110 +/- 2-126 +/- 3 mmHg; P < 0.001) and decreased thymus (P < 0.001) and bodyweights (P" < 0.01). Allopurinol decreased serum urate from 76 +/- 5 to 30 +/- 3 micromol/L (P < 0.001) in saline and from 84 +/- 13 to 28 +/- 2 micromol/L in dex-treated (P < 0.01) groups. 6. Allopurinol did not prevent dex-HT. This, together with our previous findings that allopurinol failed to prevent adrenocorticotrophic hormone induced hypertension, suggests that XO activity is not a major determinant of GC-HT in the rat.     

A method for determination of the inhibition of xanthine oxidase activity in plasma during allopurinol treatment

Summary A micromethod suitable for measuring the combined blood levels of allopurinol and alloxanthine has been developed. The two compounds display marked inhibition of xanthine oxidase activity (K_i=6.3×10^–10 and 5.4×10^–10 M), so the amounts found in 20 µl serum from allopurinol-treated patients can cause marked inhibition of xanthine oxidase activity in vitro under appropriate conditions. If the concentrations of compounds acting in an allopurinol-like manner are expressed in terms of allopurinol, activity equivalent values are obtained which reflect the effective drug concentration during therapy. The procedure is simple and suitable for serial examinations. It also satisfies the demands of the clinician, in that it can reveal any disturbance in the absorption of allopurinol and in excretion of the drug and its active metabolite, alloxanthine.     

Mechanisms involved in the antinociception induced by systemic administration of guanosine in mice

Background and purpose:

It is well known that adenine-based purines exert multiple effects on pain transmission. However, less attention has been given to the potential effects of guanine-based purines on pain transmission. The aim of this study was to investigate the effects of intraperitoneal (i.p.) and oral (p.o.) administration of guanosine on mice pain models. Additionally, investigation into the mechanisms of action of guanosine, its potential toxicity and cerebrospinal fluid (CSF) purine levels were also assessed.

Experimental approach:

Mice received an i.p. or p.o. administration of vehicle (0.1 mM NaOH) or guanosine (up to 240 mg·kg⁻¹) and were evaluated in several pain models.

Key results:

Guanosine produced dose-dependent antinociceptive effects in the hot-plate, glutamate, capsaicin, formalin and acetic acid models, but it was ineffective in the tail-flick test. Additionally, guanosine produced a significant inhibition of biting behaviour induced by i.t. injection of glutamate, AMPA, kainate and trans-ACPD, but not against NMDA, substance P or capsaicin. The antinociceptive effects of guanosine were prevented by selective and non-selective adenosine receptor antagonists. Systemic administration of guanosine (120 mg·kg⁻¹) induced an approximately sevenfold increase on CSF guanosine levels. Guanosine prevented the increase on spinal cord glutamate uptake induced by intraplantar capsaicin.

Conclusions and implications:

This study provides new evidence on the mechanism of action of the antinociceptive effects after systemic administration of guanosine. These effects seem to be related to the modulation of adenosine A₁ and A_2A receptors and non-NMDA glutamate receptors.     

Nitric oxide, adenosine deaminase, xanthine oxidase and superoxide dismutase in patients with panic disorder: alterations by antidepressant treatment

OBJECTIVE: In the present study, we aimed to investigate whether nitric oxide (NO) levels and activities of xanthine oxidase (XO), superoxide dismutase (SOD), and adenosine deaminase (ADA) are associated with Panic disorder (PD) as well as impact of psychopharmacological treatments on NO, SOD, ADA, and XO levels in PD. METHOD: In this study, 32 patients and 20 healthy controls were included. The serum levels of NO, XO, SOD, and ADA were measured in the patients and controls. The patients were treated with antidepressant. RESULTS: ADA and XO levels of the patients were significantly higher than the controls. SOD levels of the patients were significantly lower than the controls but the difference was not statistically significant. Although NO levels of the patients were higher than the controls, the difference was not statistically significant. There was no correlation between PAS and the parameters studied (SOD, ADA, XO, and NO) of the patients. After 8 weeks of antidepressant treatment, ADA and SOD activities were increased whereas NO and XO levels decreased significantly. CONCLUSION: ADA, XO activity may have a pathophysiological role in PD, and prognosis of PD. Activity of these enzymes may be used to monitor effects of the antidepressant treatment.     

Fructose-1,6-bisphosphate reduces inflammatory pain-like behaviour in mice: role of adenosine acting on A1 receptors

Background and purpose:

D-Fructose-1,6-bisphosphate (FBP) is an intermediate in the glycolytic pathway, exerting pharmacological actions on inflammation by inhibiting cytokine production or interfering with adenosine production. Here, the possible antinociceptive effect of FBP and its mechanism of action in the carrageenin paw inflammation model in mice were addressed, focusing on the two mechanisms described above.

Experimental approach:

Mechanical hyperalgesia (decrease in the nociceptive threshold) was evaluated by the electronic pressure-metre test; cytokine levels were measured by elisa and adenosine was determined by high performance liquid chromatography.

Key results:

Pretreatment of mice with FBP reduced hyperalgesia induced by intraplantar injection of carrageenin (up to 54%), tumour necrosis factor α (40%), interleukin-1 β (46%), CXCL1 (33%), prostaglandin E₂ (41%) or dopamine (55%). However, FBP treatment did not alter carrageenin-induced cytokine (tumour necrosis factor α and interleukin-1 β) or chemokine (CXCL1) production. On the other hand, the antinociceptive effect of FBP was prevented by systemic and intraplantar treatment with an adenosine A₁ receptor antagonist (8-cyclopentyl-1,3-dipropylxanthine), suggesting that the FBP effect is mediated by peripheral adenosine acting on A₁ receptors. Giving FBP to mice increased adenosine levels in plasma, and adenosine treatment of paw inflammation presented a similar antinociceptive mechanism to that of FBP.

Conclusions and implications:

In addition to anti-inflammatory action, FBP also presents an antinociceptive effect upon inflammatory hyperalgesia. Its mechanism of action seems dependent on adenosine production but not on modulation of hyperalgesic cytokine/chemokine production. In turn, adenosine acts peripherally on its A₁ receptor inhibiting hyperalgesia. FBP may have possible therapeutic applications in reducing inflammatory pain.     

Febuxostat: a non-purine,selective inhibitor of xanthine oxidase for the management of hyperuricaemia in patients with gout

Febuxostat is a non-purine, selective inhibitor of xanthine oxidase being developed for the management of hyperuricaemia in patients with gout. With febuxostat 10 – 120 mg, the pharmacokinetics are linear. No dose adjustment appears to be necessary in those with renal insufficiency or mild-to-moderate hepatic impairment. Febuxostat 10 – 120 mg/day rapidly and sustainably reduces serum uric acid by 25 – 70% in uric acid underexcretors and overproducers. Prophylaxis with colchicine or a non-steroidal anti-inflammatory drug can mitigate the gout-flare risk from the rapid urate lowering after febuxostat initiation. Febuxostat is well tolerated, the majority of treatment-related adverse events are transient and mild-to-moderate in severity. Febuxostat can broaden the therapeutic options for urate-lowering therapy in those with gout.     

Hypouricemic effect of allopurinol and the novel xanthine oxidase inhibitor TEI-6720 in chimpanzees

The hypouricemic effect of a newly synthesized xanthine oxidase / xanthine dehydrogenase inhibitor, TEI-6720, 2-(3-cyano-4-isobutoxyphenyl)-4-methyl-5-thiazolecarboxylic acid, was investigated and compared with that of allopurinol in male chimpanzees (n = 3). When allopurinol (10 mg/kg) was administered orally once a day for three consecutive days, it cumulatively reduced serum urate levels by 29.7, 50.1 and 60.2%, 24, 48 and 72 h, respectively, after the initial dose. This effect was dose dependent at doses of 3 and 10 mg/kg. At 3 mg/kg, the mean serum urate levels were 3.1, 2.4, 2.5 and 2.3 mg/dl before and 24, 48 and 72 h, respectively, after the initial dose. Animals treated with 10 mg/kg of allopurinol showed serum urate levels of 3.3, 2.3, 1.6 and 1.3 mg/dl, respectively. The urate-lowering effect of TEI-6720 was then comapred with that of allopurinol at a daily dose of 5 mg/kg (n = 3). Both compounds caused striking reductions in serum and urinary uric acid levels accompanied by an increase in urinary xanthine levels. These effects of TEI-6720 were more potent than those of allopurinol. TEI-6720 reduced serum urate levels by 55.9, 69.6 and 73.6%, 24, 48 and 72 h, respectively, after the first dose, whereas, the corresponding values after allopurinol were 28.1, 41.6 and 45.1%. These results suggest that the hypouricemic effect of TEI-6720 may be more potent than that of allopurinol in the treatment of hyperuricemia and gout, and that TEI-6720 may become an effective alternative drug.     

芬太尼对C6胶质瘤细胞黄嘌呤氧化还原酶基因表达的影响

<正> 芬太尼同吗啡是较强的μ受体激动剂,许多实验已经表明μ受体介导了吗啡的依赖、耐受作用。芬太尼是常用于心脑血管外科手术的麻醉镇痛剂。芬大尼在细胞水平对核苷酸代谢相关酶的基因表达还不清楚。本文采用了高度灵敏的RT-PCR-Southern杂交方法检测芬太尼对C6胶质瘤细胞黄嘌呤脱氢酶(Xanthine dehydrogenase,XD)/黄嘌呤氧化酶(Xanthine oxidase,XO)基因表达的影响。     

槲皮素与黄嘌呤氧化酶相互作用的紫外光谱性质研究

目的：研究了槲皮素与黄嘌呤氧化酶相互作用的紫外光谱性质及孵育时间对酶抑制性的影响。方法：紫外光谱法。结果：槲皮素与黄嘌呤氧化酶相互作用导致了槲皮素的紫外光谱的Ⅱ带红移。吸收峰升高;I带兰移,吸收峰下降。另外,随着两者孵育时间的增加,紫外光谱吸收峰下降。结论：槲皮素对黄嘌呤氧化酶有抑制性．并随着抑制时间的增加而增加。     

Natural compounds with xanthine oxidase inhibitory activity: A review

Hyperuricemia (HUA), a disease due to an elevation of body uric acid level and responsible for various diseases such as gout, cardiovascular disorders, and renal failure, is a major ground debate for the medical science these days. Considering the risk factors linked with allopathic drugs for the treatment of this disease, the debate has now become a special issue. Previously, we critically discussed the role of dietary polyphenols in the treatment of HUA. Besides dietary food plants, many researchers figure out the tremendous effects of medicinal plants‐derived phytochemicals against HUA. Keeping in mind all these aspects, we reviewed all possible managerial studies related to HUA through medicinal plants (isolated compounds). In the current review article, we comprehensively discussed various bioactive compounds, chemical structures, and structure–activity relationship with responsible key enzyme xanthine oxidase.     

Xanthine oxidase inhibition by allopurinol affects the reliability of urinary caffeine metabolic ratios as markers for N-acetyltransferase 2 and CYP1A2 activities

Objectives: To evaluate the in vivo effect of xanthine oxidase (XO) inhibition by allopurinol on the determination of polymorphic N-acetyltransferase 2 (NAT2) and cytochrome P450 1A2 (CYP1A2) with urinary caffeine metabolic ratios. Methods: In an open, prospective study involving 21 healthy subjects (eight fast, 13 slow NAT2 acetylators) allopurinol (300 mg perday) was administered orally on trial days 1–8, followed by a wash-out period of 8 days. Urinary caffeine tests (200 mg caffeine p.o.) were performed repetitively. Urine was collected for 8 h and venous blood samples for the determination of allopurinol, oxypurinol and uric acid were drawn. The urinary caffeine metabolites 1-methyluric acid (1MU), 1-methylxanthine (1MX), 1,7-dimethyluric acid (17MU), 1,7-dimethylxanthine (17MX), 5-acetylamino-6-formylamino-3-methyluracil (AFMU), plasma allopurinol and oxypurinol were analysed using high-performance liquid chromatography (HPLC). Results: During XO inhibition by allopurinol, the formation of 1MU from 1MX and therefore the XO ratio 1MU/1MX decreased to 15.9 (1.2)% [mean with (SEM)] of baseline values (P < 0.005). The NAT2 ratio AFMU/1MX decreased likewise to 56.7 (6.3)% (P < 0.005). AFMU/(AFMU + 1MX + 1MU), an alternative NAT2 ratio, remained constant, but the CYP1A2 ratio (AFMU + 1MX + 1MU)/17MU, used to express CYP1A2 activity, transiently increased to 167 (13)% (P < 0.005). The NAT2 phenotype did not influence CYP1A2 and XO ratios or plasma oxypurinol pharmacokinetics. Conclusions: Several caffeine metabolic ratios are commonly used to express the activities of NAT2, CYP1A2 and XO both in healthy volunteers and in polymedicated patients, although their reliability has not been evaluated thoroughly during concurrent drug administration. The findings of this study suggest that NAT2 phenotyping should be performed using the ratio AFMU/(AFMU + 1MX + 1MU) if an XO inhibitor may be present. It also shows that the determination of CYP1A2 activity with caffeine as a metabolic probe is considerably altered under these conditions. Thus, concomitant drug administration may impair the robustness of multiple pathways of the complex caffeine test. This points to the need for alternative probes, designed to assess only the activity of a single enzyme because, in contrast to healthy volunteers, in patients known or unknown drug interactions may often be present. Received: 10 August 1998 / Accepted in revised form: 5 October 1998     

染料木素等5种黄酮类物质对小鼠血清尿酸水平及黄嘌呤氧化酶活性的影响

目的探讨黄酮类化合物染料木素、芹菜素、槲皮素、芦丁和落新妇苷体外对黄嘌呤氧化酶活性的影响,对正常小鼠血清和肝脏黄嘌呤氧化酶活性的影响,同时评价对小鼠血清尿酸水平的作用。方法采用改良的紫外分光光度法测定染料木素、芹菜素、槲皮素、芦丁和落新妇苷体外对黄嘌呤氧化酶的抑制作用,采用分光光度法研究对小鼠血清和肝脏黄嘌呤氧化酶活性的影响,以磷钨酸法测定对小鼠血清尿酸水平的作用。结果体外实验表明黄酮类化合物染料木素、芹菜素、槲皮素、芦丁和落新妇苷体外对黄嘌呤氧化酶活性无明显影响。体内实验观察到这5种黄酮类化合物能够显著升高或降低黄嘌呤氧化酶的活性;而且,血清尿酸水平与血清黄嘌呤氧化酶活性密切相关,与肝脏黄嘌呤氧化酶活性无明显关联。用这些黄酮类化合物给药的小鼠血清尿酸水平都高于正常对照组。结论这5种黄酮类化合物不能够作为替代别嘌醇的药物用来降低血清尿酸水平。     

华山松松节的化学成分及黄嘌呤氧化酶抑制活性研究

目的：研究华山松松节的化学成分和黄嘌呤氧化酶抑制活性。方法通过各种柱色谱方法分离化合物,通过理化性质和波谱数据进行结构鉴定,对提取物和分离得到的化合物通过紫外分光光度法测定黄嘌呤氧化酶抑制活性。结果从松节提取物的石油醚部分共分离得到8个化合物,分别鉴定为异海松-7-烯-18-酸（1）,唐松酸（2）,3β,21α-二甲氧基锯齿石松-14-烯（3）,3β-甲氧基-21α-乙酰氧基-锯齿石松-14-烯（4）,3-甲氧基-锯齿石松-14-烯-21-酮（5）,β-谷甾醇（6）,胆甾醇肉豆蔻酸酯（7）和山嵛酸（8）。结论化合物3为首次从该植物中分离得到,并首次报道了该化合物的碳谱数据;化合物1和2具有一定的黄嘌呤氧化酶抑制作用。     

4-Amino-6-hydroxypyrazolo [3,4-d]pyrimidine (AHPP) conjugated PEG micelles: Water soluble polymeric xanthine oxidase inhibitor

Xanthine oxidase (XO) is the major source of superoxide anion (O₂^?) that is associated with various reactive oxygen species (ROS) related diseases. 4-amino-6-hydroxypyrazolo[3,4-d]pyrimidine (AHPP) is a potent XO inhibitor discovered in Maeda’s laboratory, which is now being developed for the treatment of ischemia reperfusion injury and inflammatory diseases. However, the poor aqueous solubility of AHPP at physiological pH hampers its clinical development. To overcome this drawback, in the present study water soluble polyethyleneglycol conjugated AHPP (AHPP-PEG) was synthesized via two different approaches, which resulted in two derivatives of AHPP-PEG, namely, mono-AHPP-PEG and bis-(AHPP)-PEG depending on the number of AHPP on PEG chain. We characterized both conjugates by UV, FTIR spectroscopy and elemental analysis. Dynamic light scattering and Sephadex G-100 chromatography studies revealed mean particle size of 164.1 and 218.8?nm and Mw. equivalent to 107 and 126?kDa for mono-AHPP-PEG and bis-(AHPP)-PEG, respectively. Further, XO inhibitory activity for mono-AHPP-PEG and bis-(AHPP)-PEG were found with Ki of 0.23?±?0.03 and 0.21?±?0.03 µM, respectively. In vivo pharmacokinetic study showed longer circulation time of AHPP-PEG conjugates compared to free AHPP. These results indicate AHPP-PEG conjugates have better potentials with supramolecular assemblies in aqueous medium and may become a good candidate for the treatment of ROS related diseases.     

The role of adenosine A1 receptors in the nucleus accumbens during morphine withdrawal

Opioids are effective analgaesic agents, but serious adverse effects such as tolerance and withdrawal contribute to opioid dependence and limit their use. Opioid withdrawal is a common occurrence in human opiate addicts that is not life-threatening. Studies have shown that the mesocorticolimbic system, especially the nucleus accumbens, is an important region in drug addiction and adenosine receptors play a modulatory role in the mechanism of action of drug dependence and withdrawal. The aim of this study was to investigate the effects of the selective A₁ receptor agonist CPA (N⁶-cyclopentyladenosine) on withdrawal symptoms, and the concentration of dopamine and noradrenaline in the nucleus accumbens and locomotor activity behaviour during naloxone-precipitated withdrawal in morphine-dependent rats. The local administration of CPA (1.5, 3.0, and 6.0 mmol/L bilateral 250 nL) into the nucleus accumbens decreased the Gellert–Holtzman withdrawal scale, and increased concentrations of dopamine and noradrenaline in the same region during naloxone-induced withdrawal. Our findings suggest that administration of the A₁ receptor agonist significantly decreased withdrawal behaviours and increased dopamine and noradrenaline concentrations in opioid withdrawal in a dose-dependent manner. These results demonstrate that adenosine receptors should be examined as a potential mechanism that could be exploited for the treatment of morphine withdrawal.     

奥美拉唑、兰索拉唑和泮托拉唑对黄嘌呤氧化酶活性的影响

目的:探讨奥美拉唑、兰索拉唑和泮托拉唑对药物代谢酶黄嘌呤氧化酶(XO)活性的影响,预测奥美拉唑、兰索拉唑和泮托拉唑与常用药物的相互作用,指导临床医师合理用药。方法:以咖啡因作为药物代谢酶XO的探针药物,以高效液相色谱法测定90名受试者分别服用奥美拉唑、兰索拉唑和泮托拉唑前后尿液内咖啡因2种主要代谢产物的相对含量,采用代谢物的比率评价药物代谢酶XO活性的变化。结果:服用奥美拉唑、兰索拉唑和泮托拉唑3种质子泵抑制剂前XO平均活性分别为(0.42±0.11),(0.37±0.13),(0.45±0.06);服药后活性分别为(0.40±0.09),(0.39±0.08),(0.43±0.08),服药前后药物代谢酶XO活性差异无显著性(P>0.05)。结论:短期内服用治疗剂量的奥美拉唑、兰索拉唑和泮托拉唑不会影响与之合用的需经XO代谢的药物疗效。     

An updated patent review: xanthine oxidase inhibitors for the treatment of hyperuricemia and gout (2011-2015)

Introduction: Xanthine oxidase (XO) is a versatile molybdoflavoprotein, widely distributed, occurring in milk, kidney, lung, heart, and vascular endothelium. Catalysis by XO to produce uric acid and reactive oxygen species leads to many diseases. Anti hyperuricemic therapy by xanthine oxidase inhibitors has been mainly employed for the treatment of gout.

Area covered: This review covers the patent literature (2011–2015) and also presents the interesting strategies/rational approaches employed for the design of xanthine oxidase inhibitors reported recently.

Expert opinion: Recent literature indicates that various non purine scaffolds have been extensively investigated for xanthine oxidase inhibition. The significant potential endowed by heteroaryl based compounds, in particularly fused heterocycles clearly highlights their clinical promise and the need for detailed investigation. Studies by various research groups have also revealed that the flavone framework is open for isosteric replacements and structural modifications for yielding potent non purine xanthine oxidase inhibitors. In addition, various plant extracts recently reported to possess significant xanthine oxidase inhibitory potential presents enough promise to initiate a screening program for the identification of other plant extracts and phytoconstituents possessing inhibitory potential towards the enzyme.     

以黄嘌呤氧化酶为靶点的新型非嘌呤类抗痛风及高尿酸血症药物研究进展

黄嘌呤氧化酶（XO）催化黄嘌呤生成尿酸及次黄嘌呤生成黄嘌呤的过程,是抗高尿酸血症或痛风药物研究的关键靶点。黄嘌呤氧化酶抑制剂由于作用机制明确、疗效显著而倍受关注,研发新型XO抑制剂具有广阔的应用前景。XO的结构生物学及分子模拟技术为新一代非嘌呤类XO抑制剂的合理药物设计奠定了基础。本文综述了以黄嘌呤氧化酶为靶标的新型非嘌呤类小分子杂环化合物及天然产物来源的活性分子在抗高尿酸血症或痛风药物研究领域中的进展。