Mutations in the amiloride‐sensitive epithelial sodium channel in patients with cystic fibrosis‐like disease

We investigated whether mutations in the genes that code for the different subunits of the amiloride‐sensitive epithelial sodium channel (ENaC) might result in cystic fibrosis (CF)‐like disease. In a small fraction of the patients, the disease could be potentially explained by an ENaC mutation by a Mendelian mechanism, such as p.V114I and p.F61L in SCNN1A. More importantly, a more than three‐fold significant increase in incidence of several rare ENaC polymorphisms was found in the patient group (30% vs. 9% in controls), indicating an involvement of ENaC in some patients by a polygenetic mechanism. Specifically, a significantly higher number of patients carried c.–55+5G>C or p.W493R in SCNN1A in the heterozygous state, with odds ratios (ORs) of 13.5 and 2.7, respectively.The p.W493R‐SCNN1A polymorphism was even found to result in a four‐fold more active ENaC channel when heterologously expressed in Xenopus laevis oocytes. About 1 in 975 individuals in the general population will be heterozygous for the hyperactive p.W493R‐SCNN1A mutation and a cystic fibrosis transmembrane conductance regulator (CFTR) gene that results in very low amounts (0–10%) functional CFTR. These ENaC/CFTR genotypes may play a hitherto unrecognized role in lung diseases. Hum Mutat 30:1–11, 2009. © 2009 Wiley‐Liss, Inc.     

Cross talk of cAMP and flavone in regulation of cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel and Na+/K+/2Cl- cotransporter in renal epithelial A6 cells

We have reported that in renal epithelial A6 cells flavones stimulate the transepithelial Cl- secretion by activating the cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel and/or the Na+/K+/2Cl- cotransporter. On the other hand, it has been established that cAMP activates the CFTR Cl- channel and the Na+/K+/2Cl- cotransporter. However, no information is available on the interaction between cAMP and flavones on stimulation of the CFTR Cl- channel and the Na+/K+/2Cl- cotransporter. To clarify the interaction between cAMP and flavones, we studied the regulatory mechanism of the CFTR Cl- channel and the Na+/K+/2Cl- cotransporter by flavones (apigenin, luteolin, kaempherol, and quercetin) under the basal and cAMP-stimulated conditions in renal epithelial A6 cells. Under the basal (cAMP-unstimulated) condition, these flavones stimulated the Cl- secretion by activating the Na+/K+/2Cl- cotransporter without any significant effects on the CFTR Cl- channel activity. On the other hand, these flavones diminished the activity of the cAMP-stimulated Na+/K+/2Cl- cotransporter without any significant effects on the CFTR Cl- channel activity. Interestingly, the level of the flavone-induced Cl- secretion under the basal condition was identical to that under the cAMP-stimulated condition. Based on these results, it is suggested that although both cAMP and flavones activate the Na+/K+/2Cl- cotransporter, these flavones have more powerful effects than cAMP on the Na+/K+/2Cl- cotransporter.     

Nonclinical safety assessment of SPX-101, a novel peptide promoter of epithelial sodium channel internalization for the treatment of cystic fibrosis

Background: ENaC inhibition has long been an attractive therapeutic target for the treatment of cystic fibrosis. However, previous attempts at developing ENaC inhibitors have been unsuccessful due to complications arising from systemic circulation of the compounds. Here, we describe the preclinical toxicology assessment of a new inhaled peptide promoter of ENaC internalization delivered as a nebulized aerosol.

Methods: Preclinical assessment of SPX-101 safety was determined using an in vitro hERG assay, bolus injection of SPX-101 in a canine cardiovascular and respiratory safety pharmacology model and 28-day inhalation toxicology studies of nebulized drug in rats and dogs.

Results: SPX101 had no effects on the respiratory, cardiac or central nervous systems. The 28-day inhalation toxicology studies of nebulized SPX-101 in rats and dogs revealed no drug-related adverse events. Plasma levels of SPX-101 peaked less than 1?h after the end of treatment in rats and were below the limit of detection in canine models.

Conclusions: SPX-101, a novel peptide promoter of ENaC internalization, elicited no adverse effects at doses up to the MFD and in excess of the highest preclinical efficacious and expected clinical doses. In contrast to channel blockers like amiloride and derivative small molecules, SPX-101 does not achieve significant systemic circulation, thus doses are not limited due to toxic side effects like hyperkalemia and weight loss.     

The oral mucosa as a therapeutic target for xerostomia

Autoimmune disorders, medical interventions, and aging are all known to be associated with salivary gland hypofunction, which results in the uncomfortable feeling of dry mouth (xerostomia) and significantly diminished oral health. The current therapeutic regimen includes increasing oral hydration using over‐the‐counter oral comfort agents and the use of systemic cholinergic drugs to stimulate salivary output. However, these approaches produce very transient relief or are associated with uncomfortable side‐effects. Thus, new treatments that provide long‐lasting relief from discomfort and improve oral health with minimal side‐effects would benefit the therapy of this disease. The processes that mediate fluid loss from the oral cavity, such as the absorption of fluid from the oral mucosa, represent novel therapeutic targets for xerostomia. Preventing fluid absorption from the oral cavity is predicted to improve oral hydration and alleviate the clinical symptoms and discomfort associated with dry mouth. Furthermore, therapeutic strategies that prevent fluid absorption should complement current approaches that increase salivary output. This review discusses the current understanding of oral fluid balance and how these processes may be manipulated to provide relief for those suffering from dry mouth.     

肺气虚证模型大鼠肾组织钠离子转运相关蛋白表达变化研究

目的检测肺气虚大鼠肾脏组织与钠离子转运相关蛋白表达,为中医学肺肾相关理论提供实验依据。方法复制肺气虚大鼠模型,应用免疫组化方法检测肾小管上皮性Na^＋：通道（ENaC）、Na^＋-K^＋-2Cl^-转运体（rBSC1）蛋白表达,放免方法测定血浆与肺组织中醛固酮（ALD）、心房钠尿素（ANP）含量。结果与对照组比较,模型组大鼠肾小管ENaC、rBSC1蛋白表达明显上调,同时血浆与肺组织中ALD水平升高而ANP水平下降。结论肺组织通过释放ALD和ANP调节肾小管上皮细胞ENaC、rBSC1蛋白表达,从而调节肾小管对Na^＋与水的重吸收而影响机体水液代谢过程。     

上皮细胞钠离子通道ENaC及其基因研究现状

人类上皮细胞钠离子通道（hENaC）由α、β、γ3个亚单位组成,分别由CNN1A、SCNN1B、SCNN1G基因所编码。ENaC负责钠离子的限速重吸收,对于维持钠的自身平衡、细胞外液量和血压起重要作用。功能获得性ENaC基因突变可引起一种罕见的遗传性高血压——Liddle综合征;而功能丧失性ENaC基因突变可引起一种遗传性低血压——假性低醛固酮血症;原发性高血压是受遗传因素和环境因素共同影响的复杂性疾病,由于ENaC的维持钠的自身平衡和血压的重要作用,因此ENaC基因作为原发性高血压的候选基因而备受关注。     

高盐饮食影响骨骼质量的中医理论基础及现代医学研究

高盐饮食对骨健康的影响日益受到人们的关注,越来越多的证据表明长期摄入大量钠盐会引起骨丢失,但其具体机制尚未完全清楚。本文从“咸入肾、肾主骨、过咸伤骨”理论以及“咸伤血”后瘀血对骨骼质量的影响两方面详细论述了中医学对高盐饮食影响骨骼质量的病机认识,并对其可能的现代医学机制如钙磷代谢紊乱、代谢性酸中毒、RAAS和ENaC对骨骼质量的影响进行了综述。对高盐饮食与骨代谢紊乱之间的内在联系与可能机制加以分析,以期为研究高盐饮食对骨骼质量的影响提供新思路。     

Staphylococcus aureus in chronic rhinosinusitis: the effect on the epithelial chloride channel (cystic fibrosis transmembrane conductance regulator,CFTR) and the epithelial sodium channel (ENaC) physiology

Background: Chronic rhinosinusitis (CRS) is an inflammatory disease of the nose and the paranasal sinuses, often associated with an infection by Staphylococcus aureus (S. aureus). Disturbance in the function of ion channels is regarded as an etiological factor for pathogenesis of CRS.

Aims: The study aims to measure the mRNA expression of the ENaC and CFTR ion channels in nasal epithelial cells (NECs) and to investigate the effect of both the budesonide and S. aureus on these ion channels.

Materials and method: NECs biopsies obtained from healthy volunteers and patients with CRS. NECs were infected with S. aureus strains and/or budesonide to study the mRNA expression levels of the ENaC and CFTR ion channels.

Results: The mRNA expression level of CFTR was increased while that of ENaC was decreased. S. aureus infection and budesonide treatment induced a significant modulation of ENaC and CFTR ion channels expression.

Conclusion: The CFTR and ENaC ion channel physiology are of importance in the pathogenesis of CRS. Exposure to S. aureus infection and treatment with budesonide modulated the mRNA expression of CFTR and ENaC ion channels.

Significance: Better understanding of the pathophysiology of CRS.     

Ca<Superscript>2+</Superscript> regulation of endocochlear potential in marginal cells

We examined the effect of the cytosolic Ca²⁺ concentration ([Ca²⁺]_c) in marginal cells on the asphyxia- or furosemide-induced decrease in the endocochlear potential (EP) by perfusing the endolymph with or without a Ca²⁺ chelator or inhibitors of Ca²⁺-permeable channels or Ca²⁺-pump during transient asphyxia or intravenous administration of furosemide. We obtained the following results. (1) Endolymphatic administration of SKF96365 (an inhibitor of TRPC and L-type Ca²⁺ channels) or EGTA-acetoxymethyl ester (EGTA-AM) significantly inhibited both the transient asphyxia-induced decrease in EP (TAID) and the furosemide-induced decrease in EP (FUID). (2) Endolymphatic perfusion with nifedipine significantly inhibited the TAID but not the FUID. (3) The recovery from the FUID was significantly suppressed by perfusing the endolymph with EGTA-AM, nifedipine, or SKF96365. (4) Endolymphatic administration of thapsigargin inhibited both the FUID and TAID. (5) The recovery rate from the FUID was much slower than that from the TAID, indicating that furosemide may inhibit the Ca²⁺-pump. (6) A strong reaction in immunohistochemical staining for TRPC channels was observed in the luminal and basolateral membranes of marginal cells. (7) A positive staining reaction for the γ subunit of epithelial Na⁺ channels was observed in the luminal and basolateral membranes of marginal cells. (8) Positive EP was diminished toward 0 mV by the endolymphatic perfusion with 10 μM amiloride or 10 μM phenamil. Taken together, these findings suggest that [Ca²⁺]_c regulated by endoplasmic Ca²⁺-pump and Ca²⁺-permeable channels in marginal cells may regulate the positive EP, which is partly produced by the diffusion potential of Na⁺ across the basolateral membrane in marginal cells.     

钠盐及其调控因素对骨骼影响的研究进展

高盐的摄入可以引发高血压已有很多研究,随着研究的深入,越来越多的证据表明高盐的摄入还引起骨量丢失,导致骨质疏松和骨折。Na+在生理和病理过程中起着很重要的作用,细胞凋亡、肿瘤生长以及离子转运都与细胞内外的Na+有关,而且Na+与骨骼的关系目前越来越受到关注。该文综述了钠盐及其调控因素:Na+,K+-ATP酶、钠氯共同转运体(NCC)、上皮钠离子通道(ENaC)、肾素-血管紧张素-醛固酮系统(RAAS)对骨骼的影响。