Rivaroxaban in patients with symptomatic peripheral artery disease after lower extremity bypass surgery with venous and prosthetic conduits.

BACKGROUND: Patients with peripheral artery disease (PAD) requiring lower extremity revascularization (LER) have a high risk of adverse limb and cardiovascular events. The results from the VOYAGER PAD (efficacy and safety of rivaroxaban in reducing the risk of major thrombotic vascular events in subjects with symptomatic peripheral artery disease undergoing peripheral revascularization procedures of the lower extremities) trial have demonstrated that rivaroxaban significantly reduced this risk with an overall favorable net benefit for patients undergoing surgical revascularization. However, the efficacy and safety for those treated by surgical bypass, including stratification by bypass conduit (venous or prosthetic), has not yet been described. METHODS: In the VOYAGER PAD trial, patients who had undergone surgical and endovascular infrainguinal LER to treat PAD were randomized to rivaroxaban 2.5 mg twice daily or placebo on top of background antiplatelet therapy (aspirin 100 mg to be used in all and clopidogrel in some at the treating physician's discretion) and followed up for a median of 28 months. The primary end point was a composite of acute limb ischemia, major amputation of vascular etiology, myocardial infarction, ischemic stroke, and cardiovascular death. The principal safety outcome was major bleeding using the TIMI (thrombolysis in myocardial infarction) scale. The index procedure details, including conduit type (venous vs prosthetic), were collected at baseline. RESULTS: Among 6564 randomized patients, 2185 (33%) had undergone surgical LER. Of these 2185 patients, surgical bypass had been performed for 1448 (66%), using a prosthetic conduit for 773 patients (53%) and venous conduit for 646 patients (45%). Adjusting for the baseline differences and anatomic factors, the risk of unplanned limb revascularization in the placebo arm was 2.5-fold higher for those receiving a prosthetic conduit vs a venous conduit (adjusted hazard ratio [HR], 2.53; 95% confidence interval [CI], 1.65-3.90; P < .001), and the risk of acute limb ischemia was three times greater (adjusted HR, 3.07; 95% CI, 1.84-5.11; P < .001). The use of rivaroxaban reduced the primary outcome for the patients treated with bypass surgery (HR, 0.78; 95% CI, 0.62-0.98), with consistent benefits for those receiving venous (HR, 0.66; 95% CI, 0.49-0.96) and prosthetic (HR, 0.87; 95% CI, 0.66-1.15) conduits (Pinteraction = .254). In the overall trial, major bleeding using the TIMI scale was increased with rivaroxaban. However, the numbers for those treated with bypass surgery were low (five with rivaroxaban vs nine with placebo; HR, 0.55; 95% CI, 0.18-1.65) and not powered to show statistical significance. CONCLUSIONS: Surgical bypass with a prosthetic conduit was associated with significantly higher rates of major adverse limb events relative to venous conduits even after adjustment for patient and anatomic characteristics. Adding rivaroxaban 2.5 mg twice daily to aspirin or dual antiplatelet therapy significantly reduced this risk, with an increase in the bleeding risk, but had a favorable benefit risk for patients treated with bypass surgery, regardless of conduit type. Rivaroxaban should be considered after lower extremity bypass for symptomatic PAD to reduce ischemic complications of the heart, limb, and brain.

Effect of Rivaroxaban and Aspirin in Patients With Peripheral Artery Disease Undergoing Surgical Revascularization: Insights From the VOYAGER PAD Trial.

BACKGROUND: Patients with peripheral artery disease requiring lower extremity revascularization (LER) are at high risk of adverse limb and cardiovascular events. The VOYAGER PAD trial (Vascular Outcomes Study of ASA [Acetylsalicylic Acid] Along With Rivaroxaban in Endovascular or Surgical Limb Revascularization for PAD) demonstrated that rivaroxaban significantly reduced this risk. The efficacy and safety of rivaroxaban has not been described in patients who underwent surgical LER. METHODS: The VOYAGER PAD trial randomized patients with peripheral artery disease after surgical and endovascular LER to rivaroxaban 2.5 mg twice daily plus aspirin or matching placebo plus aspirin and followed for a median of 28 months. The primary end point was a composite of acute limb ischemia, major vascular amputation, myocardial infarction, ischemic stroke, or cardiovascular death. The principal safety outcome was Thrombolysis in Myocardial Infarction major bleeding. International Society on Thrombosis and Haemostasis bleeding was a secondary safety outcome. All efficacy and safety outcomes were adjudicated by a blinded independent committee. RESULTS: Of the 6564 randomized, 2185 (33%) underwent surgical LER and 4379 (67%) endovascular. Compared with placebo, rivaroxaban reduced the primary end point consistently regardless of LER method (P-interaction, 0.43). After surgical LER, the primary efficacy outcome occurred in 199 (18.4%) patients in the rivaroxaban group and 242 (22.0%) patients in the placebo group with a cumulative incidence at 3 years of 19.7% and 23.9%, respectively (hazard ratio, 0.81 [95% CI, 0.67-0.98]; P=0.026). In the overall trial, Thrombolysis in Myocardial Infarction major bleeding and International Society on Thrombosis and Haemostasis major bleeding were increased with rivaroxaban. There was no heterogeneity for Thrombolysis in Myocardial Infarction major bleeding (P-interaction, 0.17) or International Society on Thrombosis and Haemostasis major bleeding (P-interaction, 0.73) on the basis of the LER approach. After surgical LER, the principal safety outcome occurred in 11 (1.0%) patients in the rivaroxaban group and 13 (1.2%) patients in the placebo group; 3-year cumulative incidence was 1.3% and 1.4%, respectively (hazard ratio, 0.88 [95% CI, 0.39-1.95]; P=0.75) Among surgical patients, the composite of fatal bleeding or intracranial hemorrhage (P=0.95) and postprocedural bleeding requiring intervention (P=0.93) was not significantly increased. CONCLUSIONS: The efficacy of rivaroxaban is associated with a benefit in patients who underwent surgical LER. Although bleeding was increased with rivaroxaban plus aspirin, the incidence was low, with no significant increase in fatal bleeding, intracranial hemorrhage, or postprocedural bleeds requiring intervention. Registration: URL: http://www.clinicaltrials.gov; Unique Identifier: NCT02504216.

Rivaroxaban and Aspirin in Peripheral Artery Disease Lower Extremity Revascularization: Impact of Concomitant Clopidogrel on Efficacy and Safety.

BACKGROUND: The VOYAGER PAD trial (Vascular Outcomes Study of ASA Along With Rivaroxaban in Endovascular or Surgical Limb Revascularization for Peripheral Artery Disease) demonstrated superiority of rivaroxaban plus aspirin versus aspirin to reduce major cardiac and ischemic limb events after lower extremity revascularization. Clopidogrel is commonly used as a short-term adjunct to aspirin after endovascular revascularization. Whether clopidogrel modifies the efficacy and safety of rivaroxaban has not been described. METHODS: VOYAGER PAD was a phase 3, international, double-blind, placebo-controlled trial in patients with symptomatic PAD undergoing lower extremity revascularization randomized to rivaroxaban 2.5 mg twice daily plus 100 mg aspirin daily or rivaroxaban placebo plus aspirin. The primary efficacy outcome was a composite of acute limb ischemia, major amputation of a vascular cause, myocardial infarction, ischemic stroke, or cardiovascular death. The principal safety end point was TIMI (Thrombolysis in Myocardial Infarction) major bleeding, with International Society on Thrombosis and Haemostasis major bleeding a secondary safety outcome. Clopidogrel use was allowed at the discretion of the investigator for up to 6 months after the qualifying revascularization. RESULTS: Of the randomized patients, 3313 (50.6%) received clopidogrel for a median duration of 29.0 days. Over 3 years, the hazard ratio for the primary outcome of rivaroxaban versus placebo was 0.85 (95% CI, 0.71-1.01) with clopidogrel and 0.86 (95% CI, 0.73-1.01) without clopidogrel without statistical heterogeneity (P for interaction=0.92). Rivaroxaban resulted in an early apparent reduction in acute limb ischemia within 30 days (hazard ratio, 0.45 [95% CI, 0.14-1.46] with clopidogrel; hazard ratio, 0.48 [95% CI, 0.22-1.01] without clopidogrel; P for interaction=0.93). Compared with aspirin, rivaroxaban increased TIMI major bleeding similarly regardless of clopidogrel use (P for interaction=0.71). With clopidogrel use >30 days, rivaroxaban was associated with more International Society on Thrombosis and Haemostasis major bleeding within 365 days (hazard ratio, 3.20 [95% CI, 1.44-7.13]) compared with shorter durations of clopidogrel (P for trend=0.06). CONCLUSIONS: In the VOYAGER PAD trial, rivaroxaban plus aspirin reduced the risk of adverse cardiovascular and limb events with an early benefit for acute limb ischemia regardless of clopidogrel use. The safety of rivaroxaban was consistent regardless of clopidogrel use but with a trend for more International Society on Thrombosis and Haemostasis major bleeding with clopidogrel use >30 days than with a shorter duration. These data support the addition of rivaroxaban to aspirin after lower extremity revascularization regardless of concomitant clopidogrel, with a short course (≤30 days) associated with less bleeding. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT02504216.

Rivaroxaban in Peripheral Artery Disease after Revascularization.

BACKGROUND: Patients with peripheral artery disease who have undergone lower-extremity revascularization are at high risk for major adverse limb and cardiovascular events. The efficacy and safety of rivaroxaban in this context are uncertain. METHODS: In a double-blind trial, patients with peripheral artery disease who had undergone revascularization were randomly assigned to receive rivaroxaban (2.5 mg twice daily) plus aspirin or placebo plus aspirin. The primary efficacy outcome was a composite of acute limb ischemia, major amputation for vascular causes, myocardial infarction, ischemic stroke, or death from cardiovascular causes. The principal safety outcome was major bleeding, defined according to the Thrombolysis in Myocardial Infarction (TIMI) classification; major bleeding as defined by the International Society on Thrombosis and Haemostasis (ISTH) was a secondary safety outcome. RESULTS: A total of 6564 patients underwent randomization; 3286 were assigned to the rivaroxaban group, and 3278 were assigned to the placebo group. The primary efficacy outcome occurred in 508 patients in the rivaroxaban group and in 584 in the placebo group; the Kaplan-Meier estimates of the incidence at 3 years were 17.3% and 19.9%, respectively (hazard ratio, 0.85, 95% confidence interval [CI], 0.76 to 0.96; P = 0.009). TIMI major bleeding occurred in 62 patients in the rivaroxaban group and in 44 patients in the placebo group (2.65% and 1.87%; hazard ratio, 1.43; 95% CI, 0.97 to 2.10; P = 0.07). ISTH major bleeding occurred in 140 patients in the rivaroxaban group, as compared with 100 patients in the placebo group (5.94% and 4.06%; hazard ratio, 1.42; 95% CI, 1.10 to 1.84; P = 0.007). CONCLUSIONS: In patients with peripheral artery disease who had undergone lower-extremity revascularization, rivaroxaban at a dose of 2.5 mg twice daily plus aspirin was associated with a significantly lower incidence of the composite outcome of acute limb ischemia, major amputation for vascular causes, myocardial infarction, ischemic stroke, or death from cardiovascular causes than aspirin alone. The incidence of TIMI major bleeding did not differ significantly between the groups. The incidence of ISTH major bleeding was significantly higher with rivaroxaban and aspirin than with aspirin alone. (Funded by Bayer and Janssen Pharmaceuticals; VOYAGER PAD ClinicalTrials.gov number, NCT02504216.).

Sources and sinks of chloromethane in a salt marsh ecosystem: constraints from concentration and stable isotope measurements of laboratory incubation experiments.

Chloromethane (CH3Cl) is the most abundant long-lived chlorinated organic compound in the atmosphere and contributes significantly to natural stratospheric ozone depletion. Salt marsh ecosystems including halophyte plants are a known source of atmospheric CH3Cl but estimates of their total global source strength are highly uncertain and knowledge of the major production and consumption processes in the atmosphere-halophyte-soil system is yet incomplete. In this study we investigated the halophyte plant, Salicornia europaea, and soil samples from a coastal salt marsh site in Sardinia/Italy for their potential to emit and consume CH3Cl and using flux measurements, stable isotope techniques and Arrhenius plots differentiated between biotic and abiotic processes. Our laboratory approach clearly shows that at least 6 different production and consumption processes are active in controlling atmospheric CH3Cl fluxes of a salt marsh ecosystem. CH3Cl release by dried plant and soil material was substantially higher than that from the fresh material at temperatures ranging from 20 to 70 °C. Results of Arrhenius plots helped to distinguish between biotic and abiotic formation processes in plants and soils. Biotic CH3Cl consumption rates were highest at 30 °C for plants and 50 °C for soils, and microbial uptake was higher in soils with higher organic matter content. Stable isotope techniques helped to distinguish between formation and degradation processes and also provided a deeper insight into potential methyl moiety donor compounds, such as S-adenosyl-l-methionine, S-methylmethionine and pectin, that might be involved in the abiotic and biotic CH3Cl production processes. Our results clearly indicate that cycling of CH3Cl in salt marsh ecosystems is a result of several biotic and abiotic processes occurring simultaneously in the atmosphere-plant-soil system. Important precursor compounds for biotic and abiotic CH3Cl formation might be methionine derivatives and pectin. All formation and degradation processes are temperature dependent and thus environmental changes might affect the strength of each source and sink within salt marsh ecosystems and thus considerably alter total fluxes of CH3Cl from salt marsh ecosystems to the atmosphere.

Chloromethane Degradation in Soils: A Combined Microbial and Two-Dimensional Stable Isotope Approach.

Chloromethane (CHCl, methyl chloride) is the most abundant volatile halocarbon in the atmosphere and involved in stratospheric ozone depletion. The global CHCl budget, and especially the CHCl sink from microbial degradation in soil, still involves large uncertainties. These may potentially be resolved by a combination of stable isotope analysis and bacterial diversity studies. We determined the stable isotope fractionation of CHCl hydrogen and carbon and investigated bacterial diversity during CHCl degradation in three soils with different properties (forest, grassland, and agricultural soils) and at different temperatures and headspace mixing ratios of CHCl. The extent of chloromethane degradation decreased in the order forest > grassland > agricultural soil. Rates ranged from 0.7 to 2.5 µg g dry wt. d for forest soil, from 0.1 to 0.9 µg g dry wt. d for grassland soil, and from 0.1 to 0.4 µg g dry wt. d for agricultural soil and increased with increasing temperature and CHCl supplementation. The measured mean stable hydrogen enrichment factor of CHCl of -50 ± 13‰ was unaffected by temperature, mixing ratio, or soil type. In contrast, the stable carbon enrichment factor depended on CHCl degradation rates and ranged from -38 to -11‰. Bacterial community composition correlated with soil properties was independent from CHCl degradation or isotope enrichment. Nevertheless, increased abundance after CHCl incubation was observed in 21 bacterial operational taxonomical units (OTUs at the 97% 16S RNA sequence identity level). This suggests that some of these bacterial taxa, although not previously associated with CHCl degradation, may play a role in the microbial CHCl sink in soil.

Chloromethane formation and degradation in the fern phyllosphere.

Chloromethane (CH3Cl) is the most abundant halogenated trace gas in the atmosphere. It plays an important role in natural stratospheric ozone destruction. Current estimates of the global CH3Cl budget are approximate. The strength of the CH3Cl global sink by microbial degradation in soils and plants is under discussion. Some plants, particularly ferns, have been identified as substantial emitters of CH3Cl. Their ability to degrade CH3Cl remains uncertain. In this study, we investigated the potential of leaves from 3 abundant ferns (Osmunda regalis, Cyathea cooperi, Dryopteris filix-mas) to produce and degrade CH3Cl by measuring their production and consumption rates and their stable carbon and hydrogen isotope signatures. Investigated ferns are able to degrade CH3Cl at rates from 2.1 to 17 and 0.3 to 0.9µggdw-1day-1 for C. cooperi and D. filix-mas respectively, depending on CH3Cl supplementation and temperature. The stable carbon isotope enrichment factor of remaining CH3Cl was -39±13‰, whereas negligible isotope fractionation was observed for hydrogen (-8±19‰). In contrast, O. regalis did not consume CH3Cl, but produced it at rates ranging from 0.6 to 128µggdw-1day-1, with stable isotope values of -97±8‰ for carbon and -202±10‰ for hydrogen, respectively. Even though the 3 ferns showed clearly different formation and consumption patterns, their leaf-associated bacterial diversity was not notably different. Moreover, we did not detect genes associated with the only known chloromethane utilization pathway "cmu" in the microbial phyllosphere of the investigated ferns. Our study suggests that still unknown CH3Cl biodegradation processes on plants play an important role in global cycling of atmospheric CH3Cl.

Chloromethane emissions in human breath.

Chloromethane (CH3Cl), currently the most abundant chlorinated organic compound in the atmosphere at around ~550 parts per trillion by volume (pptv), is considered responsible for approximately 16% of halogen-catalyzed stratospheric ozone destruction. Although emissions of CH3Cl are known to occur from animals such as cattle, formation and release of CH3Cl from humans has not yet been reported. In this study a pre-concentration unit coupled with a gas chromatograph directly linked to a mass spectrometer was used to precisely measure concentrations of CH3Cl at the pptv level in exhaled breath from 31 human subjects with ages ranging from 3 to 87years. We provide analytical evidence that all subjects exhaled CH3Cl in the range of 2.5 to 33 parts per billion by volume, levels which significantly exceed those of inhaled air by a factor of up to 60. If the mean of these emissions was typical for the world's population, then the global source of atmospheric CH3Cl from humans would be around 0.66Ggyr-1 (0.33 to 1.48Ggyr-1), which is less than 0.03% of the total annual global atmospheric source strength. The observed endogenous formation of a chlorinated methyl group in humans might be of interest to biochemists and medical scientists as CH3Cl is also known to be a potent methylating agent and thus, could be an important target compound in future medical research diagnostic programs.

Renal tubular NEDD4-2 deficiency causes NCC-mediated salt-dependent hypertension.

The E3 ubiquitin ligase NEDD4-2 (encoded by the Nedd4L gene) regulates the amiloride-sensitive epithelial Na+ channel (ENaC/SCNN1) to mediate Na+ homeostasis. Mutations in the human ß/γENaC subunits that block NEDD4-2 binding or constitutive ablation of exons 6-8 of Nedd4L in mice both result in salt-sensitive hypertension and elevated ENaC activity (Liddle syndrome). To determine the role of renal tubular NEDD4-2 in adult mice, we generated tetracycline-inducible, nephron-specific Nedd4L KO mice. Under standard and high-Na+ diets, conditional KO mice displayed decreased plasma aldosterone but normal Na+/K+ balance. Under a high-Na+ diet, KO mice exhibited hypercalciuria and increased blood pressure, which were reversed by thiazide treatment. Protein expression of ßENaC, γENaC, the renal outer medullary K+ channel (ROMK), and total and phosphorylated thiazide-sensitive Na+Cl- cotransporter (NCC) levels were increased in KO kidneys. Unexpectedly, Scnn1a mRNA, which encodes the αENaC subunit, was reduced and proteolytic cleavage of αENaC decreased. Taken together, these results demonstrate that loss of NEDD4-2 in adult renal tubules causes a new form of mild, salt-sensitive hypertension without hyperkalemia that is characterized by upregulation of NCC, elevation of ß/γENaC, but not αENaC, and a normal Na+/K+ balance maintained by downregulation of ENaC activity and upregulation of ROMK.

Mutations of the serine protease CAP1/Prss8 lead to reduced embryonic viability, skin defects, and decreased ENaC activity.

CAP1/Prss8 is a membrane-bound serine protease involved in the regulation of several different effectors, such as the epithelial sodium channel ENaC, the protease-activated receptor PAR2, the tight junction proteins, and the profilaggrin polypeptide. Recently, the V170D and the G54-P57 deletion mutations within the CAP1/Prss8 gene, identified in mouse frizzy (fr) and rat hairless (fr(CR)) animals, respectively, have been proposed to be responsible for their skin phenotypes. In the present study, we analyzed those mutations, revealing a change in the protein structure, a modification of the glycosylation state, and an overall reduction in the activation of ENaC of the two mutant proteins. In vivo analyses demonstrated that both fr and fr(CR) mutant animals present analogous reduction of embryonic viability, similar histologic aberrations at the level of the skin, and a significant decrease in the activity of ENaC in the distal colon compared with their control littermates. Hairless rats additionally had dehydration defects in skin and intestine and significant reduction in the body weight. In conclusion, we provided molecular and functional evidence that CAP1/Prss8 mutations are accountable for the defects in fr and fr(CR) animals, and we furthermore demonstrate a decreased function of the CAP1/Prss8 mutant proteins. Therefore, fr and fr(CR) animals are suitable models to investigate the consequences of CAP1/Prss8 action on its target proteins in the whole organism.

Low expression of the beta-ENaC subunit impairs lung fluid clearance in the mouse.

Transepithelial alveolar sodium (Na+) transport mediated by the amiloride-sensitive epithelial sodium channel (ENaC) constitutes the driving force for removal of fluid from the alveolar space. To define the role of the beta-ENaC subunit in vivo in the mature lung, we studied a previously established mouse strain harboring a disruption of the beta-ENaC gene locus resulting in low levels of beta-ENaC mRNA expression. Real-time RT-PCR experiments confirmed that beta-ENaC mRNA levels were decreased by >90% in alveolar epithelial cells from homozygous mutant (m/m) mice. beta-ENaC protein was undetected in lung homogenates from m/m mice by Western blotting, but alpha- and gamma-ENaC proteins were increased by 83% and 45%, respectively, compared with wild-type (WT) mice. At baseline, Na+-driven alveolar fluid clearance (AFC) was significantly reduced by 32% in m/m mice. Amiloride at the concentration 1 mM inhibited AFC by 75% and 34% in WT and m/m mice, respectively, whereas a higher concentration (5 mM) induced a 75% inhibition of AFC in both groups. The beta2-agonist terbutaline significantly increased AFC in WT but not in m/m mice. These results show that despite the compensatory increase in alpha- and gamma-ENaC protein expression observed in mutant mouse lung, low expression of beta-ENaC results in a moderate impairment of baseline AFC and in decreased AFC sensitivity to amiloride, suggesting a possible change in the stoichiometry of ENaC channels. Finally, adequate beta-ENaC expression appears to be required for AFC stimulation by beta2-agonists.

beta-Liddle mutation of the epithelial sodium channel increases alveolar fluid clearance and reduces the severity of hydrostatic pulmonary oedema in mice.

Transepithelial sodium transport via alveolar epithelial Na(+) channels and Na(+),K(+)-ATPase constitutes the driving force for removal of alveolar oedema fluid. Decreased activity of the amiloride-sensitive epithelial Na(+) channel (ENaC) in the apical membrane of alveolar epithelial cells impairs sodium-driven alveolar fluid clearance (AFC) and predisposes to pulmonary oedema. We hypothesized that hyperactivity of ENaC in the distal lung could improve AFC and facilitate the resolution of pulmonary oedema. AFC and lung fluid balance were studied at baseline and under conditions of hydrostatic pulmonary oedema in the beta-Liddle (L) mouse strain harbouring a gain-of-function mutation (R(566)(stop)) within the Scnn1b gene. As compared with wild-type (+/+), baseline AFC was increased by 2- and 3-fold in heterozygous (+/L) and homozygous mutated (L/L) mice, respectively, mainly due to increased amiloride-sensitive AFC. The beta(2)-agonist terbutaline stimulated AFC in +/+ and +/L mice, but not in L/L mice. Acute volume overload induced by saline infusion (40% of body weight over 2 h) significantly increased extravascular (i.e. interstitial and alveolar) lung water as assessed by the bloodless wet-to-dry lung weight ratio in +/+ and L/L mice, as compared with baseline. However, the increase was significantly larger in +/+ than in L/L groups (P=0.01). Volume overload also increased the volume of the alveolar epithelial lining fluid in +/+ mice, indicating the presence of alveolar oedema, but not in L/L mice. Cardiac function as evaluated by echocardiography was comparable in both groups. These data show that constitutive ENaC activation improved sodium-driven AFC in the mouse lung, and attenuated the severity of hydrostatic pulmonary oedema.

Activation of epithelial sodium channels by mouse channel activating proteases (mCAP) expressed in Xenopus oocytes requires catalytic activity of mCAP3 and mCAP2 but not mCAP1.

Mouse channel activating proteases 1, 2, and 3 (mCAP1, mCAP2, and mCAP3) were described recently as regulators of the epithelial sodium channel (ENaC). The mCAP are membrane-bound serine proteases that are synthesized as inactive proenzymes. To mature into active proteases, they undergo intramolecular cleavage by auto- and/or heterocatalytic processing. Specific antibodies against each mCAP were developed to distinguish between proenzyme and active protease by Western blot analysis. Various point mutations were introduced in the catalytic or protein-protein interacting domains of mCAP and wild-type and mutant enzymes were expressed in the Xenopus oocyte expression system to test for ability to activate ENaC. In mCAP3, an intact catalytic triad was necessary for activation of ENaC but not for intramolecular cleavage of the protease. This suggests a heterocatalytic mechanism. Mutating the catalytic triad of mCAP2 not only abolished ENaC activation completely but also impeded cleavage of the protease. Processing of mCAP2 therefore seems to be autocatalytic. Furthermore, mutations in conserved residues of mCAP2 located in two protein-protein interacting domains significantly modulated ENaC activation. Surprisingly, mCAP1 catalytically inactive mutants were still able to fully activate ENaC, and no evidence of mCAP1 intramolecular cleavage was seen. The presence of an intact glycosylphosphatidylinositol anchor, however, was required. It is concluded that auto- and heterocatalytic requirements are specific for each CAP and that endogenous partners are a necessity for activation of ENaC by mCAP in the Xenopus oocyte expression system.

A novel TMPRSS3 missense mutation in a DFNB8/10 family prevents proteolytic activation of the protein.

Pathogenic mutations in TMPRSS3, which encodes a transmembrane serine protease, cause non-syndromic deafness DFNB8/10. Missense mutations map in the low density-lipoprotein receptor A (LDLRA), scavenger-receptor cysteine-rich (SRCR), and protease domains of the protein, indicating that all domains are important for its function. TMPRSS3 undergoes proteolytic cleavage and activates the ENaC sodium channel in a Xenopus oocyte model system. To assess the importance of this gene in non-syndromic childhood or congenital deafness in Turkey, we screened for mutations affected members of 25 unrelated Turkish families. The three families with the highest LOD score for linkage to chromosome 21q22.3 were shown to harbor P404L, R216L, or Q398X mutations, suggesting that mutations in TMPRSS3 are a considerable contributor to non-syndromic deafness in the Turkish population. The mutant TMPRSS3 harboring the novel R216L missense mutation within the predicted cleavage site of the protein fails to undergo proteolytic cleavage and is unable to activate ENaC, thus providing evidence that pre-cleavage of TMPRSS3 is mandatory for normal function.

Mineralocorticoid versus glucocorticoid receptor occupancy mediating aldosterone-stimulated sodium transport in a novel renal cell line.

Aldosterone controls sodium balance by regulating an epithelial sodium channel (ENaC)-mediated sodium transport along the aldosterone-sensitive distal nephron, which expresses both mineralocorticoid (MR) and glucocorticoid receptors (GR). Mineralocorticoid specificity is ensured by 11beta-hydroxysteroid dehydrogenase type 2, which metabolizes cortisol or corticosterone into inactive metabolites that are unable to bind MR and/or GR. The fractional occupancy of MR and GR by aldosterone mediating the sodium transport response in the aldosterone-sensitive distal nephron cannot be studied in vivo. For answering this question, a novel mouse cortical collecting duct cell line (mCCD(cl1)), which expresses significant levels of MR and GR and a robust aldosterone sodium transport response, was used. Aldosterone elicited a biphasic response: Low doses (K(1/2) = approximately 0.5 nM) induced a transient and early increase of sodium transport (peaking at 3 h), whereas high doses (K(1/2) = approximately 90 nM) entailed an approximately threefold larger, long-lasting response. At 3 h, the corticosterone dose-response curve was shifted to the right compared with that of aldosterone by more than two log concentrations, an effect that was fully reverted in the presence of the 11beta-hydroxysteroid dehydrogenase type 2 inhibitor carbenoxolone. Low doses of dexamethasone (0.1 to 1 nM) failed to induce an early response, but high doses elicited a long-lasting response (K(1/2) = approximately 8 nM), similar to that observed for high aldosterone concentrations. Equilibrium binding assays showed that both aldosterone and corticosterone bind to a high-affinity, low-capacity site, whereas dexamethasone binds to one site. Within the physiologic range of aldosterone concentrations, sodium transport is predicted to be controlled by MR occupancy during circadian cycles and by MR and GR occupancy during salt restriction or acute stress.

Collecting duct-specific gene inactivation of alphaENaC in the mouse kidney does not impair sodium and potassium balance.

Aldosterone controls the final sodium reabsorption and potassium secretion in the kidney by regulating the activity of the epithelial sodium channel (ENaC) in the aldosterone-sensitive distal nephron (ASDN). ASDN consists of the last portion of the distal convoluted tubule (late DCT), the connecting tubule (CNT), and the collecting duct (CD) (i.e., the cortical CD [CCD] and the medullary CD [MCD]). It has been proposed that the control of sodium transport in the CCD is essential for achieving sodium and potassium balance. We have tested this hypothesis by inactivating the alpha subunit of ENaC in the CD but leaving ENaC expression in the late DCT and CNT intact. Under salt restriction or under aldosterone infusion, whole-cell voltage clamp of principal cells of CCD showed no detectable ENaC activity, whereas large amiloride-sensitive currents were observed in control littermates. The animals survive well and are able to maintain sodium and potassium balance, even when challenged by salt restriction, water deprivation, or potassium loading. We conclude that the expression of ENaC in the CD is not a prerequisite for achieving sodium and potassium balance in mice. This stresses the importance of more proximal nephron segments (late DCT/CNT) to achieve sodium and potassium balance.

A novel vasopressin-induced transcript promotes MAP kinase activation and ENaC downregulation.

In the principal cell of the renal collecting duct, vasopressin regulates the expression of a gene network responsible for sodium and water reabsorption through the regulation of the water channel and the epithelial sodium channel (ENaC). We have recently identified a novel vasopressin-induced transcript (VIT32) that encodes for a 142 amino acid vasopressin-induced protein (VIP32), which has no homology with any protein of known function. The Xenopus oocyte expression system revealed two functions: (i) when injected alone, VIT32 cRNA rapidly induces oocyte meiotic maturation through the activation of the maturation promoting factor, the amphibian homolog of the universal M phase trigger Cdc2/cyclin; and (ii) when co-injected with the ENaC, VIT32 cRNA selectively downregulates channel activity, but not channel cell surface expression. In the kidney principal cell, VIP32 may be involved in the downregulation of transepithelial sodium transport observed within a few hours after vasopressin treatment. VIP32 belongs to a novel gene family ubiquitously expressed in oocyte and somatic cells that may be involved in G to M transition and cell cycling.

Synergistic activation of ENaC by three membrane-bound channel-activating serine proteases (mCAP1, mCAP2, and mCAP3) and serum- and glucocorticoid-regulated kinase (Sgk1) in Xenopus Oocytes.

Sodium balance is maintained by the precise regulation of the activity of the epithelial sodium channel (ENaC) in the kidney. We have recently reported an extracellular activation of ENaC-mediated sodium transport (I(Na)) by a GPI-anchored serine protease (mouse channel-activating protein, mCAP1) that was isolated from a cortical collecting duct cell line derived from mouse kidney. In the present study, we have identified two additional membrane-bound serine proteases (mCAP2 and mCAP3) that are expressed in the same cell line. We show that each of these proteases is able to increase I(Na) 6-10-fold in the Xenopus oocyte expression system. I(Na) and the number (N) of channels expressed at the cell surface (measured by binding of a FLAG monoclonal I(125)-radioiodinated antibody) were measured in the same oocyte. Using this assay, we show that mCAP1 increases I(Na) 10-fold (P < 0.001) but N remained unchanged (P = 0.9), indicating that mCAP1 regulates ENaC activity by increasing its average open probability of the whole cell (wcP(o)). The serum- and glucocorticoid-regulated kinase (Sgk1) involved in the aldosterone-dependent signaling cascade enhances I(Na) by 2.5-fold (P < 0.001) and N by 1.6-fold (P < 0.001), indicating a dual effect on N and wcP(o). Compared with Sgk1 alone, coexpression of Sgk1 with mCAP1 leads to a ninefold increase in I(Na) (P < 0.001) and 1.3-fold in N (P < 0.02). Similar results were observed for mCAP2 and mCAP3. The synergism between CAPs and Sgk1 on I(Na) was always more than additive, indicating a true potentiation. The synergistic effect of the two activation pathways allows a large dynamic range for ENaC-mediated sodium regulation crucial for a tight control of sodium homeostasis.

Activation of the amiloride-sensitive epithelial sodium channel by the serine protease mCAP1 expressed in a mouse cortical collecting duct cell line.

This study examines whether serine proteases can activate the amiloride-sensitive sodium channel (ENaC) in mammalian kidney epithelial cells. The transepithelial sodium transport assessed by amiloride-sensitive short-circuit current appears to be sensitive to aprotinin, a protease inhibitor in a mouse cortical collecting duct cell line (mpkCCD(c14)). This result indicated that serine proteases may be implicated in the regulation of ENaC-mediated sodium transport. Using degenerated oligonucleotides to a previously isolated serine protease from Xenopus, xCAP1 (channel activating protease), a novel full-length serine protease (mCAP1), has been isolated and characterized. RNA analysis showed a broad pattern of expression in tissues (kidney, lung, colon, and salivary glands) expressing ENaC. Reverse transcription-PCR experiments also showed that mCAP1 was abundantly expressed in proximal tubule cells and was also expressed in intact and cultured collecting duct cells. Coexpression of the Xenopus, rat, or human alpha-, beta-, and gamma-ENaC subunits in Xenopus oocytes also showed that mCAP1 induces a significant increase in ENaC-mediated current accompanied by a decrease of channel molecules at the cell surface. It is proposed that this novel mouse channel activating protease may act as a regulator of ENaC within the kidney.