Complications Associated with Low Position versus Good Position Umbilical Venous Catheters in Neonates of ≤32 Weeks' Gestation.

OBJECTIVE: This study aimed to determine the incidence of umbilical venous catheter associated infection (UVCAI) in very preterm infants based on UVC tip position. STUDY DESIGN: In this retrospective cohort study, infants born at ≤32 weeks were divided into groups with a UVC tip in either a low-lying or good position. The primary outcome was UVCAI. Survival analysis represented time to infection between groups. Subgroup analyses were based on duration of UVC indwelling time. RESULTS: Of 1,983 infants, 1,638 infants were eligible; 33% had low-lying UVC and 67% had good position UVC. Survival analyses suggested a significantly higher probability of infection was associated with low UVC (adjusted hazard ratio [HR]: 1.9, 95% confidence interval [CI]: 1.1-3.2; p = 0.001). The risk of infection was higher for UVC of >7 days duration (adjusted HR: 2.2, 95% CI: 1.1-4.2). Extravasation as a complication was significantly higher in the low UVC versus good position UVC (1.3 vs. 0.1%; odds ratio: 14.4, 95% CI: 1.8-119). CONCLUSION: Low-lying UVC was associated with higher risk of infection and extravasation. KEY POINTS: · Low-lying UVC are at higher risk of UVCAI.. · Presence of UVC in situ for > 7 days carries higher risk of UVCAI.. · There was a higher risk of UVC extravasation with low UVCs..

Magnetic particles assisted capture and release of rare circulating tumor cells using wavy-herringbone structured microfluidic devices.

A wavy-herringbone (wavy-HB) structured microfluidic device was used to effectively and selectively capture and release circulating tumor cells (CTCs) by using immunoaffinity and magnetic force. This device was designed to create passive turbulence and increase the possibility of tumor cells colliding with the device wall. Under an external magnetic field, magnetic particles (MPs) coated with anti-EpCAM against a tumor cell surface protein (EpCAM) were immobilized over the wavy-HB surface to capture tumor cells. After removing the magnetic field, the captured cells with surplus MPs were released from the device and collected; thus, these cells could be re-cultured for further analysis. Under optimized conditions, the capture efficiency of the tumor cells can be as high as 92% ± 2.8%. Capture experiments were also performed on whole blood samples, and the capture efficiency was in a high range of 81-95%, at different tumor cell concentrations. Such a method can potentially be used for CTC sorting from patient blood samples, CTC concentration monitoring, therapeutic guidance and drug dosage choice, and further study of tumors, such as drug screening and tumor mutations.

Iatrogenic Spinal Cord Injury in a Trauma Patient with Ankylosing Spondylitis.

BACKGROUND: The recommended practice for over 30 years has been to routinely immobilize patients with unstable cervical spinal injuries using cervical spinal collars. It is shown that patients with Ankylosing spondylitis (AS) are four times more likely to suffer a spinal fracture compared to the general population and have an eleven-fold greater risk of spinal cord injury. Current protocols of spinal immobilization were responsible for secondary neurologic deterioration in some of these patients. OBJECTIVE: To describe an iatrogenic injury resulting from the use of a rigid spinal board and advocate for the use of alternative immobilization methods or no immobilization at all. CASE: We present our case here of a 68-year-old male with a history of AS. The patient was ambulatory on scene after a low speed car accident, but immobilized with a rigid backboard by paramedics. He developed back pain and paraplegia suddenly when the backboard was lifted for transport to the hospital. A CT scan revealed an extension fraction of T10 to T11 with involvement of the posterior column. Emergency spinal fusion was performed. Patient died of complications in the hospital. CONCLUSION: This case shows that spinal immobilization should be avoided in cases of ambulatory patients without a clear indication. Alternative transport methods such as vacuum mattresses should be considered when spinal immobilization is indicated, especially for patients with predispositions to spinal injury, particularly AS, to maintain the natural alignment of the spinal curvature.

Carbon Monoxide Poisoning: The Great Imitator.

Carbon Monoxide (CO) is one of the leading causes of poison deaths in the United States. Signs and symptoms are clinically variable secondary to inconsistent targeting of highly metabolic tissues by the gas. We report a case of a man in his early to mid-30's presenting to the emergency department with mental status changes, fatigue, headache, and flu-like symptoms for three days. The patient had been working on his motor vehicles in the garage during this time, using a portable diesel powered space heater to keep warm. Subsequent neurology and cardiology workup demonstrated bilateral globus pallidus (GP) lesions on brain imaging, increased non-myocardial infarction troponin levels, carboxyhemoglobin (COHb) level of 3.8%, elevated liver enzymes, and acute kidney failure. In this setting of his delayed presentation as a smoker with carbon monoxide poisoning, carboxyhemoglobin levels alone become less reliable. This report investigates the use of bilateral GP lesions, the most frequently affected structure, as well as damage preference to highly metabolic tissues to assist in diagnosis and prognosis for CO poisoning. Our observations can be used for further study of the relationship between bilateral GP necrosis and initial presentation and outcome of patients experiencing CO poisoning leading to earlier recognition, treatment, and decreased morbidity/mortality.

Cys palmitoylation of the beta subunit modulates gating of the epithelial sodium channel.

The epithelial Na(+) channel (ENaC) is comprised of three homologous subunits (α, ß, and γ) that have a similar topology with two transmembrane domains, a large extracellular region, and cytoplasmic N and C termini. Although ENaC activity is regulated by a number of factors, palmitoylation of its cytoplasmic Cys residues has not been previously described. Fatty acid-exchange chemistry was used to determine whether channel subunits were Cys-palmitoylated. We observed that only the ß and γ subunits were modified by Cys palmitoylation. Analyses of ENaCs with mutant ß subunits revealed that Cys-43 and Cys-557 were palmitoylated. Xenopus oocytes expressing ENaC with a ß C43A,C557A mutant had significantly reduced amiloride-sensitive whole cell currents, enhanced Na(+) self-inhibition, and reduced single channel P(o) when compared with wild-type ENaC, while membrane trafficking and levels of surface expression were unchanged. Computer modeling of cytoplasmic domains indicated that ß Cys-43 is in proximity to the first transmembrane α helix, whereas ß Cys-557 is within an amphipathic α-helix contiguous with the second transmembrane domain. We propose that ß subunit palmitoylation modulates channel gating by facilitating interactions between cytoplasmic domains and the plasma membrane.

Novel determinants of epithelial sodium channel gating within extracellular thumb domains.

Activity of the epithelial Na(+) channel (ENaC) is modulated by Na(+) self-inhibition, an allosteric down-regulation of channel open probability by extracellular Na(+). We searched for determinants of Na(+) self-inhibition by analyzing changes in this inhibitory response resulting from specific mutations within the extracellular domains of mouse ENaC subunits. Mutations at gammaMet(438) altered the Na(+) self-inhibition response in a substitution-specific manner. Fourteen substitutions (Ala, Arg, Asp, Cys, Gln, Glu, His, Ile, Phe, Pro, Ser, Thr, Tyr, and Val) significantly suppressed Na(+) self-inhibition, whereas three mutations (Asn, Gly, and Leu) moderately enhanced the inhibition. Met to Lys mutation did not alter Na(+) self-inhibition. Mutations at the homologous site in the alpha subunit (G481A, G481C, and G481M) dramatically increased the magnitude and speed of Na(+) self-inhibition. Mutations at the homologous betaAla(422) resulted in minimal or no change in Na(+) self-inhibition. Low, high, and intermediate open probabilities were observed in oocytes expressing alphaG481Mbetagamma, alphabetagammaM438V, and alphaG481M/betagammaM438V, respectively. This pair of residues map to thealpha5 helix in the extracellular thumb domain in the chicken acid sensing ion channel 1 structure. Both residues likely reside near the channel surface because both alphaG481Cbetagamma and alphabetagammaM438C channels were inhibited by an externally applied and membrane-impermeant sulfhydryl reagent. Our results demonstrate that alphaGly(481) and gammaMet(438) are functional determinants of Na(+) self-inhibition and of ENaC gating and suggest that the thumb domain contributes to the channel gating machinery.

Defining an inhibitory domain in the alpha-subunit of the epithelial sodium channel.

Epithelial sodium channels (ENaC) are processed by proteases as they transit the biosynthetic pathway. We recently observed that furin-dependent processing of the alpha-subunit of ENaC at two sites within its extracellular domain is required for channel activation due to release of a 26-residue inhibitory domain. While channels with alpha-subunits lacking the furin sites are not cleaved and have very low activity, channels lacking the furin consensus sites as well as the tract between these sites (alphaD206-R231) are active. We analyzed channels with a series of deletions in the tract alphaD206-R231 and lacking the alpha-subunit furin consensus sites in Xenopus laevis oocytes. We found an eight-residue tract that, when deleted, restored channel activity to the level found in oocytes expressing wild-type ENaC. A synthetic peptide, LPHPLQRL, representing the tract alphaL211-L218, inhibited wild-type ENaC expressed in oocytes with an IC(50) of 0.9 microM, and inhibited channels expressed in collecting duct cells and human primary airway epithelial cells with an IC(50)s of between approximately 50 and 100 microM. Analyses of peptides with deletions within this inhibitory tract indicate that eight residues is the minimal backbone length that is required for ENaC inhibition. Analyses of 8-mer peptides with conserved and nonconserved substitutions suggest that L(1), P(2), H(3), P(4), and L(8) are required for inhibitory activity. Our findings suggest that this eight-residue tract is a key conserved inhibitory domain that provides epithelial cells with a reserve of inactive channels that can be activated as required by proteases.

Epithelial sodium channel exit from the endoplasmic reticulum is regulated by a signal within the carboxyl cytoplasmic domain of the alpha subunit.

Epithelial sodium channels (ENaCs) are assembled in the endoplasmic reticulum (ER) from alpha, beta, and gamma subunits, each with two transmembrane domains, a large extracellular loop, and cytoplasmic amino and carboxyl termini. ENaC maturation involves transit through the Golgi complex where Asn-linked glycans are processed to complex type and the channel is activated by furin-dependent cleavage of the alpha and gamma subunits. To identify signals in ENaC for ER retention/retrieval or ER exit/release, chimera were prepared with the interleukin alpha subunit (Tac) and each of the three cytoplasmic carboxyl termini of mouse ENaC (Tac-Ct) or with gamma-glutamyltranspeptidase and each of the three cytoplasmic amino termini (Nt-GGT). By monitoring acquisition of endoglycosidase H resistance after metabolic labeling, we found no evidence of ER retention of any chimera when compared with control Tac or GGT, but we did observe enhanced exit of Tac-alphaCt when compared with Tac. ER exit of ENaC was assayed after metabolic labeling by following the appearance of cleaved alpha as cleaved alpha subunit, but not non-cleaved alpha, is endoglycosidase H-resistant. Interestingly ER exit of epitope-tagged and truncated alpha (alphaDelta624-699-V5) with full-length betagamma was similar to wild type alpha (+betagamma), whereas ER exit of ENaC lacking the entire cytoplasmic carboxyl tail of alpha (alphaDelta613-699-V5 +betagamma) was significantly reduced. Subsequent analysis of ER exit for ENaCs with mutations within the intervening sequence (613)HRFRSRYWSPG(623) within the context of the full-length alpha revealed that mutation alphaRSRYW(620) to AAAAA significantly reduced ER exit. These data indicate that ER exit of ENaC is regulated by a signal within the alpha subunit carboxyl cytoplasmic tail.

Functional role of extracellular loop cysteine residues of the epithelial Na+ channel in Na+ self-inhibition.

The epithelial Na(+) channel (ENaC) is typically formed by three homologous subunits (alpha, beta, and gamma) that possess a characteristic large extracellular loop (ECL) containing 16 conserved cysteine (Cys) residues. We investigated the functional role of these Cys residues in Na(+) self-inhibition, an allosteric inhibition of ENaC activity by extracellular Na(+). All 16 Cys residues within alpha and gamma ECLs and selected beta ECL Cys residues were individually mutated to alanine or serine residues. The Na(+) self-inhibition response of wild type and mutant channels expressed in Xenopus oocytes was determined by whole cell voltage clamp. Individual mutation of eight alpha (Cys-1, -4, -5, -6, -7, -10, -13, or -16), one beta (Cys-7), and nine gamma (Cys-3, -4, -6, -7, -10, -11, -12, -13, or -16) residues significantly reduced the magnitude of Na(+) self-inhibition. Na(+) self-inhibition was eliminated by simultaneous mutations of either the last three alpha ECL Cys residues (Cys-14, -15, and -16) or Cys-7 within both alpha and gamma ECLs. By analyzing the Na(+) self-inhibition responses and the effects of a methanethiosulfonate reagent on channel currents in single and double Cys mutants, we identified five Cys pairs within the alphaECL (alphaCys-1/alphaCys-6, alphaCys-4/alphaCys-5, alphaCys-7/alphaCys-16, alphaCys-10/alphaCys-13, and alphaCys-11/alphaCys-12) and one pair within the gammaECL (gammaCys-7/gammaCys-16) that likely form intrasubunit disulfide bonds. We conclude that approximately half of the ECL Cys residues in the alpha and gamma ENaC subunits are required to establish the tertiary structure that ensures a proper Na(+) self-inhibition response, likely by formation of multiple intrasubunit disulfide bonds.

Epithelial Na+ channels are fully activated by furin- and prostasin-dependent release of an inhibitory peptide from the gamma-subunit.

Epithelial sodium channels (ENaC) are expressed in the apical membrane of high resistance Na(+) transporting epithelia and have a key role in regulating extracellular fluid volume and the volume of airway surface liquids. Maturation and activation of ENaC subunits involves furin-dependent cleavage of the ectodomain at two sites in the alpha subunit and at a single site within the gamma subunit. We now report that the serine protease prostasin further activates ENaC by inducing cleavage of the gamma subunit at a site distal to the furin cleavage site. Dual cleavage of the gamma subunit is predicted to release a 43-amino acid peptide. Channels with a gamma subunit lacking this 43-residue tract have increased activity due to a high open probability. A synthetic peptide corresponding to the fragment cleaved from the gamma subunit is a reversible inhibitor of endogenous ENaCs in mouse cortical-collecting duct cells and in primary cultures of human airway epithelial cells. Our results suggest that multiple proteases cleave ENaC gamma subunits to fully activate the channel.

Distinct structural elements in the first membrane-spanning segment of the epithelial sodium channel.

Epithelial Na+ channels (ENaCs) comprise three subunits that have been proposed to be arranged in either an alpha2betagamma or a higher ordered configuration. Each subunit has two putative membrane-spanning segments (M1 and M2), intracellular amino and carboxyl termini, and a large extracellular loop. We have used the TOXCAT assay (a reporter assay for transmembrane segment homodimerization) to identify residues within the transmembrane segments of ENaC that may participate in important structural interactions within ENaC, with which we identified a candidate site within alphaM1. We performed site-directed mutagenesis at this site and found that, although the mutants reduced channel activity, ENaC protein expression at the plasma membrane was unaffected. To deduce the role of alphaM1 in the pore structure of ENaC, we performed tryptophan-scanning mutagenesis throughout alphaM1 (residues 110-130). We found that mutations within the amino-terminal part of alphaM1 had effects on activity and selectivity with a periodicity consistent with a helical structure but no effect on channel surface expression. We also observed that mutations within the carboxyl-terminal part of alphaM1 had effects on activity and selectivity but with no apparent periodicity. Additionally, these mutants reduced channel surface expression. Our data support a model in which the amino-terminal half of alphaM1 is alpha-helical and packs against structural element(s) that contribute to the ENaC pore. Furthermore, these data suggest that the carboxyl-terminal half of alphaM1 may be helical or assume a different conformation and may be involved in tertiary interactions essential to proper channel folding or assembly. Together, our data suggest that alphaM1 is divided into two distinct regions.