Pharmacological characterization of 3-azabicyclo[3,2,1] octane-1-yl-l-leucyl-d-tryptophanyl-d-4-Cl-phenylalanine: A novel ETA receptor-selective antagonist

Comprehensive Update on Synthetic Aspects of Bosentan Derivatives

Bosentan and its analogues were first reported as endothelin (ET) receptor antagonists in US patent No. 5, 292,740 in 1994. Bosentan synthesis has been reported by employing different methods from the reaction between (4,6-dichloro-5-(2-methoxyphenoxy)-2,2'-bipyrimidine and 4- (tert-butyl) benzenesulfonamide and 4-(tert-butyl)-N-(6-chloro-5-(2-methoxyphenoxy)-[2,2'- bipyrimidin]-4-yl) benzenesulfonamide in the form of different salts like potassium salt, ammonium salt, sodium salt, and free, on its reaction with ethylene glycol. Several changes have been observed in the chemistry of the involved intermediate synthesis, particularly coupling chemistry, to produce bosentan derivatives with high purity and yield.

Phenylalanine induces pulmonary hypertension through calcium-sensing receptor activation

Phenylalanine levels are associated with pulmonary hypertension in metabolic profiling clinical studies. However, the pathophysiological role of phenylalanine on pulmonary circulation is still unclear. We experimentally addressed the direct impact of phenylalanine on pulmonary circulation in rats and explored the underlying molecular pathway. Phenylalanine was injected intraperitoneally into Sprague-Dawley rats (400 mg/100 g body wt) as a single dose or daily in a chronic manner for 2, 3, and 4 wk. Chronic injection of phenylalanine induced pulmonary hypertension with time-dependent severity, evidenced by elevated pulmonary artery pressure and pulmonary vascular resistance as well as pulmonary artery and right ventricular hypertrophy. Using tandem mass spectrometry analysis, we found a quick twofold increase in blood level of phenylalanine 2 h following injection. This increase led to a significant accumulation of phenylalanine in lung after 4 h, which remained sustained at up to a threefold increase after 4 wk. In addition, a cellular thermal shift assay with lung tissues from phenylalanine-injected rats revealed the binding of phenylalanine to the calcium-sensing receptor (CaSR). In vitro experiments with cultured pulmonary arterial smooth muscle cells showed that phenylalanine activated CaSR, as indicated by an increase in intracellular calcium content, which was attenuated or diminished by the inhibition or knockdown of CaSR. Finally, the global knockout or lung-specific knockdown of CaSR significantly attenuated phenylalanine-induced pulmonary hypertension. Chronic phenylalanine injection induces pulmonary hypertension through binding to CaSR and its subsequent activation. Here, we demonstrate a pathophysiological role of phenylalanine in pulmonary hypertension through the CaSR. This study provides a novel animal model for pulmonary hypertension and reveals a potentially clinically significant role for this metabolite in human pulmonary hypertension as a marker, a mediator of disease, and a possible therapeutic target.

Risk factors for hypertensive retinopathy in a Chinese population with hypertension: The Beijing Eye study

Hypertensive retinopathy (HRP) is a clinical feature and systemic manifestation of hypertension. There have been few reports on the risk factors for hypertensive retinopathy in China. The aim of the present study was to describe risk factors associated with HRP in a population-based sample of Chinese patients with hypertension in Beijing. The clinical data of 228 hypertensive patients was retrospectively studied, including 112 patients with retinopathy for the HRP group and 116 patients without retinopathy for the NO-HRP group. Basic clinical data and plasma clinical indicators of the two groups were compared. Logistic regression models were used to assess risk factors associated with HRP. Duration of hypertension, smoking habits, family history of hypertension, plasma level of endothelin-1 (ET-1) and systolic and diastolic blood pressure were significantly increased in the HRP group compared with the NO-HRP group (P<0.05). No significant differences were identified between the two groups for other factors. Logistic regression models indicated that hypertension duration (P<0.001, 95% CI: 0.962-0.988) and ET-1 level (P<0.001, 95% CI: 1.144-1.278) were significantly associated with HRP. The diagnostic threshold of ET-1 to diagnosis HRP was 43.5 ng/l. Of the factors studied, longer hypertension duration and elevated ET-1 level were identified to be risk factors for HRP in patients with hypertension from Beijing. Detecting the plasma level of ET-1 in patients with hypertension may be a useful diagnostic indicator for HRP.

The principal pathways involved in the in vivo modulation of hypoxic pulmonary vasoconstriction, pulmonary arterial remodelling and pulmonary hypertension

Hypoxic pulmonary vasoconstriction (HPV) serves to optimize ventilation-perfusion matching in focal hypoxia and thereby enhances pulmonary gas exchange. During global hypoxia, however, HPV induces general pulmonary vasoconstriction, which may lead to pulmonary hypertension (PH), impaired exercise capacity, right-heart failure and pulmonary oedema at high altitude. In chronic hypoxia, generalized HPV together with hypoxic pulmonary arterial remodelling, contribute to the development of PH. The present article reviews the principal pathways in the in vivo modulation of HPV, hypoxic pulmonary arterial remodelling and PH with primary focus on the endothelin-1, nitric oxide, cyclooxygenase and adenine nucleotide pathways. In summary, endothelin-1 and thromboxane A₂ may enhance, whereas nitric oxide and prostacyclin may moderate, HPV as well as hypoxic pulmonary arterial remodelling and PH. The production of prostacyclin seems to be coupled primarily to cyclooxygenase-1 in acute hypoxia, but to cyclooxygenase-2 in chronic hypoxia. The potential role of adenine nucleotides in modulating HPV is unclear, but warrants further study. Additional modulators of the pulmonary vascular responses to hypoxia may include angiotensin II, histamine, serotonin/5-hydroxytryptamine, leukotrienes and epoxyeicosatrienoic acids. Drugs targeting these pathways may reduce acute and/or chronic hypoxic PH. Endothelin receptor antagonists and phosphodiesterase-5 inhibitors may additionally improve exercise capacity in hypoxia. Importantly, the modulation of the pulmonary vascular responses to hypoxia varies between species and individuals, with hypoxic duration and age. The review also define how drugs targeting the endothelin-1, nitric oxide, cyclooxygenase and adenine nucleotide pathways may improve pulmonary haemodynamics, but also impair pulmonary gas exchange by interference with HPV in chronic lung diseases.

Inhibition of endothelin-1 and hypoxia-induced pulmonary pressor responses in the rat by a novel selective endothelin-A receptor antagonist, di-n-butylaminocarbamyl-L-leucyl-D-tryptophanyl-D-4-chloro-Phe

Pulmonary hypertension is a kind of disease associated with a very high rate of mortality, and there are not many effective drugs for the treatment. Today, endothelin (ET)-1 receptor antagonists were proved to be effective in the treatment of pulmonary hypertension. Aiming at developing new endothelin-A receptor (ETA) antagonist for treatment of pulmonary hypertension, di-n-butylaminocarbamyl-L-leucyl-D-tryptophanyl-D-4-chloro-Phe, named GF063, was synthesized at base of selective ETA receptor antagonist BQ485 and selected for the further pharmacological characterization. The preliminary pharmacodynamics of GF063 was evaluated by radioligand receptor binding assay and test of antivasoconstriction effects in vitro and in vivo. The integrative pharmacodynamics was evaluated in hypoxia-induced rat pulmonary hypertension. In vitro, GF063 bound to ETA receptor with 100,000-fold higher affinity than to ETB receptor. GF063 concentration dependently inhibited contraction of isolated rat aortic ring induced by ET-1 and shifted the cumulative concentration-contraction response curve to right with no change in the maximal response. In vivo, GF063 inhibited the increase of mean systemic arterial pressure induced by ET-1 in anesthetized rat. In hypoxia-induced rat pulmonary hypertension model, pretreatment with GF063 (40 mg/kg, s.c.) significantly decreased pulmonary artery pressure and right ventricular hypertrophy, also significantly inhibited the increase of ET-1 level in lung, improved hemodynamics, and alleviated the wall thickness of pulmonary vessels. This study indicated that GF063, as a selective ETA receptor antagonist, could inhibit vasoconstriction effects in vivo and in vitro, could prevent pulmonary hypertension induced by hypoxia, and may have great potential to be developed as a new drug of antipulmonary hypertension.

Involvement of tissue transglutaminase in endothelin 1-induced hypertrophy in cultured neonatal rat cardiomyocytes

A potential link between tissue-type transglutaminase (tTG) and cardiac hypertrophy was suggested recently. However, whether tTG is implicated in hypertrophic agonist-induced cardiac hypertrophy is not yet known. The purpose of this study was to investigate the effects of tTG on cardiomyocyte hypertrophy induced by endothelin (ET) 1. Real-time quantitative RT-PCR and Western blot analysis demonstrated that ET-1 increased the expression of tTG mRNA and protein in cardiomyocytes by activating ET(A) receptors. ET-1 failed to cause increases in cell size and [(3)H]leucine uptake, sarcomere reorganization, and gene induction of the atrial natriuretic factor when cardiomyocytes were treated with monodansylcadaverine, a competitive inhibitor of tTG. Furthermore, the effects of ET-1 on multifunctional activities of tTG were determined by evaluating the incorporation of [(3)H]putrescine into N,N'-dimethylated casein and charcoal absorption, respectively. The results showed that ET-1 did not influence the basal transglutaminase activity of cardiomyocytes but significantly inhibited the 0.1-mmol/L Ca(2+)-stimulated transglutaminase activity. Otherwise, ET-1 elevated the activity of GTPase in a concentration- and time-dependent manner. In vivo, right ventricular hypertrophy induced by 2 weeks of chronic hypoxia was depressed by the tTG inhibitor cystamine (10 to 30 mg/kg, 2 times per day, IP) in a dose-dependent manner. Taken together, our data strongly supported the notion that tTG may act as a positive regulator of the hypertrophic program in response to ET-1. This is probably attributable to the signaling activity of tTG rather than transglutaminase activity.