苯丙酮尿症杂合子高危人群基因型与生化表型相关性

目的:用分子生物学方法对可疑PKU/HPA杂合子进行PAH突变基因分析,以验证生化筛查PKU/HPA杂合子方法的可行性。方法:利用PCR、SSCP和DNA测序等方法对152例已知PKU/HPA杂合子(阳性组)和29例可疑PKU/HPA杂合子(可疑组)的PAH基因部分外显子进行分析。并与健康体检者对照(对照组)结果:152例已知PKU/HPA杂合子中发现26种基因突变,突变检出率为80.9%(123/152)。29例可疑“PKU/HPA杂合子”发现5例突变,检出率为17.2%(5/29)。对照组与可疑PKU/HPA杂合子组间差异有统计学意义(P<0.05)。结论:生化方法与分子生物学方法有一定相关性,提示生化筛查法用作PKU杂合子的初筛是可行的。     

Sapropterin dihydrochloride, 6-R-L-erythro-5,6,7,8-tetrahydrobiopterin, in the treatment of phenylketonuria

Sapropterin dihydrochloride, 6-R-L-erythro-5,6,7,8-tetrahydrobiopterin (BH4) is being introduced in the US for treatment of phenylketonuria (PKU). This compound has been in use in Europe to treat mild forms of PKU. Tetrahydrobiopterin is the cofactor in the hydroxylation reaction of the three aromatic amino acids phenylalanine, tyrosine and tryptophan. It is also involved in other reactions, which are not the focus of this review. The cofactor BH4 is synthesized in many tissues in the body. The pathway of BH4 biosynthesis is complex, and begins with guanosine triphosphate (GTP). The first reaction that commits GTP to form pterins is GTP cyclohydrolase. Several reactions follow resulting in the active cofactor BH4. During the hydroxylation reaction BH4 is oxidized to quinonoid-BH2, which is recycled by dihydropteridine reductase, resulting in the active cofactor. It was discovered that some patients with PKU had a decline in blood phenylalanine after oral intake of BH4. This response to BH4 is not the result of change in the synthesis or regeneration of the cofactor, but rather an effect on the mutant enzyme phenylalanine hydroxylase either by accommodating the higher K(m) of the mutant enzyme or by acting as a chaperone for the mutant enzyme. This response has become of intense interest in the treatment of PKU.     

Sapropterin dihydrochloride, 6-R-L-erythro-5,6,7,8-tetrahydrobiopterin,in the treatment of phenylketonuria

Sapropterin dihydrochloride, 6-R-L-erythro-5,6,7,8-tetrahydrobiopterin (BH4) is being introduced in the US for treatment of phenylketonuria (PKU). This compound has been in use in Europe to treat mild forms of PKU. Tetrahydrobiopterin is the cofactor in the hydroxylation reaction of the three aromatic amino acids phenylalanine, tyrosine and tryptophan. It is also involved in other reactions, which are not the focus of this review. The cofactor BH4 is synthesized in many tissues in the body. The pathway of BH4 biosynthesis is complex, and begins with guanosine triphosphate (GTP). The first reaction that commits GTP to form pterins is GTP cyclohydrolase. Several reactions follow resulting in the active cofactor BH4. During the hydroxylation reaction BH4 is oxidized to quinonoid-BH2, which is recycled by dihydropteridine reductase, resulting in the active cofactor. It was discovered that some patients with PKU had a decline in blood phenylalanine after oral intake of BH4. This response to BH4 is not the result of change in the synthesis or regeneration of the cofactor, but rather an effect on the mutant enzyme phenylalanine hydroxylase either by accommodating the higher K_m of the mutant enzyme or by acting as a chaperone for the mutant enzyme. This response has become of intense interest in the treatment of PKU.     

Disorders of tetrahydrobiopterin metabolism and their treatment

Tetrahydrobiopterin (BH4) deficiencies are disorders affecting phenylalanine metabolism in liver and neurotransmitters biosynthesis in brain. BH4 is the essential cofactor in the enzymatic hydroxylation of 3 aromatic amino acids (phenylalanine, tyrosine, and tryptophan). BH4 is synthesized from guanosine triphosphate (GTP) catalyzed by GTP cyclohydrolase I (GTPCH), 6-pyruvoyl-tetrahydropterin synthase, and sepiapterin reductase (SPR), and in aromatic amino acids hydoxylating system is regenerated by pterin-4a-carbinolamine dehydratase (PCD) and dihydropteridine reductase (DHPR). To date, 4 enzyme deficiencies (GTPCH, PTPS, DHPR, PCD) have been reported and they all follow an autosomal recessive mode of inheritance. The incidence of BH4 deficiency is at 1 in 1,000,000, except that in Taiwanese (much higher than in Japanese and Caucasians). BH4 deficiency has been diagnosed in patients with hyperphenylalaninemia (HPA) by neonatal mass-screening based on BH4 oral loading tests, analysis of urinary or serum pteridines, and measurement of dihydropterindine reductase (DHPR) activity in blood from a Guthrie card. BH4 deficiency without treatment causes combined symptoms of HPA and neurotransmitter (dopamine, norepinephrine, epinephrine, and serotonin) deficiency, such as red hair, psychomotor retardation, and progressive neurological deterioration. Treatment of BH4 deficiencies consists of BH4 supplementation (2-20 mg/kg per day) or diet to control blood phenylalanine concentration and replacement therapy with neurotransmitters precausers (L-dopa/CarbiDOPA and 5-hydroxytryptophan), and supplements of folinic acid in DHPR deficiency.     

Tetrahydrobiopterin binding to aromatic amino acid hydroxylases. Ligand recognition and specificity

The three aromatic amino acid hydroxylases (phenylalanine, tyrosine, and tryptophan hydroxylase) and nitric oxide synthase (NOS) all utilize (6R)-l-erythro-5,6,7,8-tetrahydrobiopterin (BH(4)) as cofactor. The pterin binding site in the three hydroxylases is well conserved and different from the binding site in NOS. The structures of phenylalanine hydroxylase (PAH) and of NOS in complex with BH(4) are still the only crystal structures available for the reduced cofactor-enzyme complexes. We have studied the enzyme-bound and free conformations of BH(4) by NMR spectroscopy and molecular docking into the active site of the three hydroxylases, using endothelial NOS as a comparative probe. We have found that the dihydroxypropyl side chain of BH(4) adopts different conformations depending on which hydroxylase it interacts with. All the bound conformations are different from that of BH(4) free in solution at neutral pH. The different bound conformations appear to result from specific interactions with nonconserved amino acids at the BH(4) binding sites of the hydroxylases, notably the stretch 248-251 (numeration in PAH) and the residue corresponding to Ala322 in PAH, i.e., Ser in TH and Ala in TPH. On the basis of analysis of molecular interaction fields, we discuss the selectivity determinants for each hydroxylase and explain the high-affinity inhibitory effect of 7-tetrahydrobiopterin specifically for PAH.     

唐山市苯丙酮尿症患儿筛查及PAH基因突变情况分析

摘要：目的　分析唐山市苯丙酮尿症（PKU）患儿筛查结果及苯丙氨酸羟化酶（PAH）基因突变的情况。方法　选取2015年1月—2018年12月唐山市新生儿303 777例,通过茚三酮免疫荧光法检测新生儿足跟血中苯丙氨酸（PA）含量。再利用聚合酶链反应（PCR）和基因测序的方法对筛查出的PKU患儿PAH基因进行检测。结果　303 777例新生儿初步筛查共发现609例可疑阳性,召回其中411例（67.49%）进行复查,确诊42例（13.8/10万）。42例PKU患者的PAH基因测序显示,在84条染色体上共检测到62个（73.81%）12种突变,其中错义突变8种,无义突变2种,缺失突变1种,剪接突变1种。患者PAH基因突变分布在第2、3、6、7、9外显子上,其中第7外显子最多（35个,56.45%）,其次为第3外显子（14个,22.58%）。最常见的突变基因为Exon7-R243Q（18个,29.03%）和Exon3-R111X（10个,16.13%）、Exon7-R261Q（10个,16.13%）。筛查中发现1例典型PKU患儿,该患儿在PAH基因外显子区域同时发现2处杂合突变：c.208-210delTCT（缺失突变）和c.964G＞A（鸟嘌呤＞腺嘌呤）。结论　唐山市新生儿PKU发病率略高于全国,PAH基因突变以错义突变为主,第7外显子是唐山市患儿PAH基因高频突变位点。     

New insights into tetrahydrobiopterin pharmacodynamics from Pah, a mouse model for compound heterozygous tetrahydrobiopterin-responsive phenylalanine hydroxylase deficiency

Phenylketonuria (PKU), an autosomal recessive disease with phenylalanine hydroxylase (PAH) deficiency, was recently shown to be a protein misfolding disease with loss-of-function. It can be treated by oral application of the natural PAH cofactor tetrahydrobiopterin (BH₄) that acts as a pharmacological chaperone and rescues enzyme function in vivo. Here we identified Pah^enu1/2 bearing a mild and a severe mutation (V106A/F363S) as a new mouse model for compound heterozygous mild PKU. Although BH₄ treatment has become established in clinical routine, there is substantial lack of knowledge with regard to BH₄ pharmacodynamics and the effect of the genotype on the response to treatment with the natural cofactor. To address these questions we applied an elaborate methodological setup analyzing: (i) blood phenylalanine elimination, (ii) blood phenylalanine/tyrosine ratios, and (iii) kinetics of in vivo phenylalanine oxidation using ¹³C-phenylalanine breath tests. We compared pharmacodynamics in wild-type, Pah^enu1/1, and Pah^enu1/2 mice and observed crucial differences in terms of effect size as well as effect kinetics and dose response. Results from in vivo experiments were substantiated in vitro after overexpression of wild-type, V106A, and F263S in COS-7 cells. Pharmacokinetics did not differ between Pah^enu1/1 and Pah^enu1/2 indicating that the differences in pharmacodynamics were not induced by divergent pharmacokinetic behavior of BH₄. In conclusion, our findings show a significant impact of the genotype on the response to BH₄ in PAH deficient mice. This may lead to important consequences concerning the diagnostic and therapeutic management of patients with PAH deficiency underscoring the need for individualized procedures addressing pharmacodynamic aspects.     

A structural approach into human tryptophan hydroxylase and its implications for the regulation of serotonin biosynthesis

Tryptophan hydroxylase (TPH) catalyzes the 5-hydroxylation of tryptophan, which is the first step in the biosynthesis of indoleamines (serotonin and melatonin). Serotonin functions mainly as a neurotransmitter, whereas melatonin is the principal hormone secreted by the pineal gland. TPH belongs to the family of the aromatic amino acid hydroxylases, including phenylalanine hydroxylase (PAH) and tyrosine hydroxylase (TH), which all have a strict requirement for dioxygen, non-heme iron (II) and tetrahydrobiopterin (BH4). During the last three years there has been a formidable increase in the amount of structural information about PAH and TH, which has provided new insights into the active site structure, the binding of substrates, inhibitors and pterins, as well as on the effect of disease-causing mutations in these hydroxylases. Although structural information about TPH is not yet available, the high sequence homology between the three mammalian hydroxylases, notably at the catalytic domains, and the similarity of the reactions that they catalyze, indicate that they share a similar 3D-structure and a common catalytic mechanism. Thus, we have prepared a model of the structure of TPH based on the crystal structures of TH and PAH. This structural model provides a frame for understanding the specific interactions of TPH with L-tryptophan and substrate analogues, BH4 and cofactor analogues, L-DOPA and catecholamines. The interactions of these ligands with the enzyme are discussed focusing on the physiological and pharmacological regulation of serotonin biosynthesis, notably by tryptophan supplementation therapy and substitution therapy with tetrahydrobiopterin analogues (positive effects), as well as the effect of catecholamines on TPH activity in L-DOPA treated Parkinson's disease patients (enzyme inhibition).     

Alternative therapies to address the unmet medical needs of patients with phenylketonuria

Standard therapy for phenylketonuria (PKU), the most common inherited disorder in amino acid metabolism, is an onerous phenylalanine-restricted diet. Adherence to this stringent diet regimen decreases as patients get older, and this lack of adherence is directly associated with cognitive and executive dysfunction and psychiatric issues. These factors emphasize the need for alternative pharmacological therapies to help treat patients with PKU. Sapropterin dihydrochloride is a synthetic form of tetrahydrobiopterin, the cofactor of phenylalanine hydroxylase that in pharmacological doses can stabilize and increase residual enzyme activity in some patients with PKU. About one-third of all patients with PKU respond to oral sapropterin. Phenylalanine ammonia lyase (PAL) is a prokaryotic enzyme that converts phenylalanine to ammonia and trans-cinnamic acid. Phase I and II trials have shown that injectable recombinant Anabaena variabilis PAL produced in Escherichia coli conjugated with PEG can reduce phenylalanine levels in subjects with PKU. The most frequently reported adverse events were injection-site reactions, dizziness and immune reactions. Additionally, oral administration of PAL and delivery of enzyme substitution therapies by encapsulation in erythrocytes are being investigated. Novel therapies for patients with PKU appear to be options to reduce phenylalanine levels, and may reduce the deleterious effects of this disorder.     

Structural and mechanistic implications of incorporating naturally occurring aberrant mutations of human dihydropteridine reductase into a rat model

Phenylketonuria (PKU) is a debilitating hereditary disorder related to an individual's inability to convert phenylalanine to its usual tyrosine product. The genetic errors occur in three regions: in the cooperative enzymes phenylalanine hydroxylase (PAH) and dihydropteridine reductase (DHPR), and in the biosynthetic pathway from GTP to the hydroxylation cofactor, tetrahydrobiopterin (BH₄). Many instances of naturally occurring defects in DHPR metabolism have been identified, and in most cases the error has been equated with an altered enzyme gene sequence. Using computer graphics, this report analyses the altered structural characteristics of eight of the enzymes encoded by mutant gene sequence and provides logical explanations for their diminished enzyme activities. In one instance, that of a threonine insertion, a mutant construct of the rat analog has been expressed in Escherichia coli and the DHPR isolated and characterised, confirming the marked changes this insert can create.     

5-Hydroxytryptophan during critical postnatal period improves cognitive performances and promotes dendritic spine maturation in genetic mouse model of phenylketonuria

Although phenylketonuria (PKU) is the most common genetic cause of mental retardation, the cellular mechanisms underlying impaired brain function are still unclear. Using PAHenu2 mice (ENU2), the genetic mouse model of PKU, we previously demonstrated that high phenylalanine levels interfere with brain tryptophan hydroxylase activity by reducing the availability of serotonin (5-hydroxytryptamine, 5-HT), crucial for maturation of neuronal connectivity in the prefrontal cortex (PFC), around the third postnatal week, a critical period for cortical maturation. 5-Hydroxytryptophan (5-HTP), the product of tryptophan hydroxylation, is known to be a better treatment to increase brain 5-HT levels. In this study we investigated the role of 5-HT during the early postnatal period in cognitive disturbances and in cortical dendritic alterations of PKU subjects by restoring temporarily (postnatal days 14-21) physiological brain levels of 5-HT in ENU2 through 5-HTP treatment. In adult ENU2 mice early 5-HTP treatment reverses cognitive deficits in spatial and object recognition tests accompanied by an increase in spine maturation of pyramidal neurons in layer V of the prelimbic/infralimbic area of the PFC, although locomotor deficits are not recovered by treatment. Taken together, our results support the hypothesis that mental retardation in PKU depends on reduced availability of brain 5-HT during critical developmental periods that interferes with cortical maturation and point to 5-HTP supplementation as a highly promising additional tool to heal PKU patients.     

潍坊市2000~2014年苯丙酮尿症筛查资料回顾分析

目的 了解潍坊市2000~2014年苯丙酮尿症(PKU)的筛查和确诊患儿情况。方法 查阅潍坊市15年来新生儿疾病筛查年报和患儿病历档案,对PKU筛查和确诊患儿情况进行统计分析。结果 潍坊市PKU筛查覆盖率呈逐年上升趋势,2012年达到最高的99.15%;共确诊患儿136例,检出率为1.22/万,以经典型为主,男性居多,农村患儿数多于城市;规范治疗率69.85%,患儿治疗前后的血苯丙氨酸水平差异有统计学意义(P<0.05)。结论 潍坊市PKU筛查推广工作取得了明显成效,但需加强资料统计工作,实施安全有效治疗、规范随访,可较好改善患儿预后。     

Treatment of pulmonary arterial hypertension in connective tissue disease

Pulmonary arterial hypertension (PAH) is a group of distinct disorders that includes idiopathic PAH (IPAH), familial PAH and PAH associated with other conditions (APAH) such as connective tissue disease (CTD-APAH) or congenital heart disease. PAH is characterized by increased pulmonary arterial pressure and pulmonary vascular resistance. If left untreated, PAH can lead to right heart failure and premature death. CTD-APAH represents an important clinical subgroup of APAH that has a higher risk of death than IPAH. The European treatment guidelines advocate the use of PAH-targeted therapies including bosentan, ambrisentan, sildenafil, inhaled iloprost, intravenous epoprostenol (I-A recommendations), tadalafil or treprostinil (I-B recommendations) for patients in WHO functional class II-III. Not all randomized clinical studies of the approved PAH-targeted therapies have included patients with CTD-APAH. The purpose of this review is to describe the clinical characteristics of CTD-APAH and discuss the approved pharmacological treatments, with a focus on data specific to this subgroup where possible.     

Phenylalanine 4-monooxygenase and the S-oxidation of S-carboxymethyl-L-cysteine in HepG2 cells

The role of phenylalanine 4-monooxygenase (PAH) in the S-oxidation of S-carboxymethyl-L-cysteine (SCMC) in the rat has now been well established in rat cytosolic fractions in vitro. However, the role of PAH in the S-oxidation of SCMC in human cytosolic fractions or hepatocytes has yet to be investigated. The aim of this investigation was to analyse the kinetic parameters of PAH oxidation of both L-phenylalanine (Phe) and SCMC in the human HepG2 cell line in order to investigate the use of these cells as a model for the cellular regulation of SCMC S-oxidation. The experimentally determined Km and V(max) were 7.14 +/- 0.32 mM and 0.85 +/- 0.32 nmole Tyr formed min(-1) x mg protein(-1) using Phe as substrate. For SCMC the values were 25.24 +/- 5.91 mM and 0.79 +/- 0.09 nmole SCMC (RIS) S-oxides formed min(-1) x mg protein(-1). The experimentally determined Km and V(max) for the cofactor BH4 were 6.81 +/- 0.21 microM and 0.41 +/- 0.004 nmole Tyr formed min(-1) x mg protein(-1) for Phe and 7.24 +/- 0.19 microM and 0.42 +/- 0.002 nmole SCMC (R/S) S-oxides formed min(-1) x mg protein(-1) for SCMC. The use of various PAH inhibitors confirmed that HepG2 cells contained PAH and that the enzyme was capable of converting SCMC to its (R) and (S) S-oxide metabolites in an in vitro PAH assay. Thus HepG2 cells have become a useful additional tool for the investigation of the cellular regulation of PAH in the S-oxidation of SCMC.     

Pulmonary hypertension: role of combination therapy

Over the past decade different effective treatment options for use in pulmonary arterial hypertension (PAH) have been developed. Due to multiple pathophysiological pathways in PAH and unsatisfactory overall results with the use of monotherapy in a substantial number of PAH patients, there is a pharmacological rationale for combination therapy. The currently approved substances target the prostacyclin, the endothelin and the NO (nitric oxide) -pathways. Those agents have shown a varying degree of improvement in different categories of PAH associated limitations like hemodynamics, exercise capacity, functional class, and quality of life. However, clinical worsening over time is still significant in most patients irrespective of the treatment utilized. The recently published ESC-ERS (European Society of Cardiology and European Respiratory Society) guidelines on pulmonary hypertension suggest the use of combination therapy in patients who do not respond adequately to monotherapy.This article reviews and critically discusses the available data on combination therapy in PAH.     

Assessment of the dexamethasone/CRH test as a state-dependent marker for hypothalamic-pituitary-adrenal (HPA) axis abnormalities in major depressive episode: a Multicenter Study.

There is compelling evidence for the involvement of hypothalamic-pituitary-adrenal (HPA) axis abnormalities in depression. Growing evidence has suggested that the combined dexamethasone (DEX)/corticotropin-releasing hormone (CRH) test is highly sensitive to detect HPA axis abnormalities. We organized a multicenter study to assess the DEX/CRH test as a state-dependent marker for major depressive episode in the Japanese population. We conducted the DEX/CRH test in 61 inpatients with major depressive episode (Diagnostic and Statistical Manual of Mental Disorders 4th edition (DSM-IV)) and 57 healthy subjects. In all, 35 patients were repeatedly assessed with the DEX/CRH test on admission and before discharge. The possible relationships between clinical variables and the DEX/CRH test were also examined. Significantly enhanced pituitary-adrenocortical responses to the DEX/CRH test were observed in patients on admission compared with controls. Such abnormalities in patients were significantly reduced after treatment, particularly in those who underwent electroconvulsive therapy (ECT) in addition to pharmacotherapy. Age and female gender were associated with enhanced hormonal responses to the DEX/CRH test. Severity of depression correlated with DEX/CRH test results, although this was explained, at least in part, by a positive correlation between age and severity in our patients. Medication per se was unrelated to DEX/CRH test results. These results suggest that the DEX/CRH test is a sensitive state-dependent marker to monitor HPA axis abnormalities in major depressive episode during treatment. Restoration from HPA axis abnormalities occurred with clinical responses to treatment, particularly in depressed patients who underwent ECT.     

Bosentan

Bosentan (Tracleer), an orally administered dual endothelin (ET)(A) and ET(B) receptor antagonist, is indicated in the treatment of pulmonary arterial hypertension (PAH).The efficacy of oral bosentan 125 mg twice daily in improving exercise capacity has been demonstrated in well designed trials in adult patients with idiopathic PAH or PAH associated with connective tissue disease or congenital systemic-to-pulmonary shunts, and in other trials in patients with idiopathic PAH or PAH associated with congenital heart disease or HIV infection. The beneficial effects of first-line bosentan treatment may be maintained for up to 1 year in patients with idiopathic PAH or PAH associated with connective tissue disease. Despite the potential for treatment-related teratogenicity and hepatotoxicity, long-term data indicate that bosentan is generally well tolerated at the approved dosages. Although well designed trials are required to establish the efficacy of bosentan versus or in combination with other specific PAH therapies, especially sildenafil, the convenient oral administration and lack of serious injection-related adverse effects may render bosentan preferable to other PAH therapies. Preliminary data indicate that bosentan may be effective in pediatric PAH patients, although randomized trials are required. Furthermore, bosentan may be a useful option for the prevention of digital ulcer development in patients with systemic sclerosis. Thus, in accordance with current clinical guidelines, bosentan is a convenient, effective, and generally well tolerated agent for use in the first-line treatment of class III PAH or second-line treatment of class IV PAH.     

Biochemical analysis of Centaurea depressa phenylalanine ammonia lyase (PAL) for biotechnological applications in phenylketonuria (PKU)

Context: Phenylketonuria (PKU) is the most common hereditary defect of phenylalanine hydroxylase (PAH) enzyme achieving the hydroxylation of phenylalanine (Phe). Phenylalanine ammonia lyase (PAL) converts Phe to a harmless metabolite, trans-cinnamic acid (TCA) in plants and PAL enzyme activity is fairly high in plants rich in flavonoids.

Objective: The study aimed the biochemical analysis of PAL form Centaurea depressa BIEB. (Asteraceae) a flavonoid rich plant. This study may form the main frame of future research efforts for the development of a plant preparation aimed for oral intake in PKU patients in an attempt to enrich their diet by allowing them to ingest some food stuff containing Phe without being exposed to complications.

Materials and methods: PAL was partially purified from the leaves of C. depressa. Enzyme activity was determined in comparison with that of other herbs that reportedly have a high PAL activity. Enzyme optimization was achieved and the PAL protein was detected by western blotting.

Results: C. depressa PAL demonstrated high activity (34.9?±?0.6?U/mg protein). The enzyme was purified by 1.92-fold, which resulted in an activity of 53.30?±?0.2?U/mg protein. The high-performance liquid chromatography analyzes of the PAL activity both before and after purification were in agreement. Western blot of PAL exhibited a 70?kDa protein band. The optimum pH and temperature are pH 8.8 and 37?°C. The optimum activities under gastric and intestinal digestion conditions were observed at pH 4.0 and pH 8.0, respectively.

Discussion and conclusion: PAL activity of C. depressa is high, and does not disappear under different environmental conditions. This enzyme could be used for the development of dietary foods and biotechnological products for patients with PKU.     

Sitaxsentan: a selective endothelin-A receptor antagonist, for the treatment of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a progressive, life-threatening condition. Sitaxsentan, a selective endothelin-A receptor antagonist, is an effective, safe and well-tolerated endothelin receptor antagonist for the treatment of PAH in adult patients. Multi-center, randomized, placebo-controlled clinical trials have demonstrated that sitaxsentan has beneficial effects on exercise capacity (i.e., 6-min walk distance), functional class and hemodynamic parameters in PAH patients. Sitaxsentan has a low incidence of acute hepatotoxicity. Patients on concomitant warfarin require a decrease in warfarin dose to maintain a therapeutic international normalized ratio. The demonstration of clinical efficacy and low incidence of acute hepatotoxicity support the potential use of sitaxsentan for the treatment of PAH.     

Tadalafil for the treatment of pulmonary arterial hypertension

Background: Tadalafil, a long-acting phosphodiesterase-5 inhibitor (PDE-5) is the most recent oral agent to receive FDA approval for the treatment of pulmonary arterial hypertension (PAH). Objective: With several new agents emerging for the treatment of PAH, this article reviews tadalafil, the compound and its properties, clinical evidence supporting its use, and the role of tadalafil in the current treatment approach for patients with PAH. Methods: A broad PubMed literature search was performed to identify the most current data on the use of tadalafil for PAH. Results: Tadalafil received FDA approval in 2009 following the recently published pivotal trial that demonstrated that the use of tadalafil 40 mg once daily was well tolerated, improved exercise capacity and quality of life measures and reduced time to clinical worsening in PAH patients. As the second PDE-5 inhibitor to gain approval for PAH, clinical properties such as its long half-life leading to once-daily dosing and possibly improved compliance, as well as potential cost benefit, may distinguish tadalafil from sildenafil in the widespread treatment of PAH.