Depression of gelsolin levels and detection of gelsolin-actin complexes in plasma of patients with acute lung injury

Actin is the major protein of muscle and nonmuscle cells and is one of the most abundant body proteins. Physiologic or pathologic cell death may therefore result in the liberation of large amounts of this fibrous protein into the extravascular space. The potential for long actin filaments to increase plasma viscosity and change the rheology of the microvasculature are potentially obviated by the presence of 2 recently recognized plasma actin-binding proteins, vitamin-D-binding protein, and plasma gelsolin. As part of our initial evaluation of this newly recognized physiologic system in humans, we measured levels of gelsolin in plasma samples from patients with extensive lung injury. Gelsolin levels were depressed in 25 of 25 patients with the adult respiratory distress syndrome (ARDS), a disease characterized by massive cellular injury, as determined by either of 2 functional assays for gelsolin. Mean total gelsolin concentration of 20 patients with ARDS was 89.2 +/- 33 micrograms/ml (normal levels, approximately 240 micrograms/ml; p less than 0.001) and the mean free gelsolin concentration 69.6 +/- 29 micrograms/ml (normal levels, approximately 240 micrograms/ml; p less than 0.001). Gelsolin concentrations of 6 patients with bacterial pneumonias were also depressed, but to a lesser degree (mean total level, 117 +/- 21 micrograms/ml). Direct demonstration of the presence of actin in these plasmas (but not in normal plasmas) was performed by precipitating actin directly with DNase-Sepharose beads, or indirectly with antigelsolin-Sepharose beads, as confirmed with immunoblotting. Actin was found in 18 of 19 patients using DNase beads and in 7 of 19 using antigelsolin beads.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cost analysis of a patient navigation system to increase screening colonoscopy adherence among urban minorities

BACKGROUND:

Patient navigation (PN) is being used increasingly to help patients complete screening colonoscopy (SC) to prevent colorectal cancer. At their large, urban academic medical center with an open‐access endoscopy system, the authors previously demonstrated that PN programs produced a colonoscopy completion rate of 78.5% in a cohort of 503 patients (predominantly African Americans and Latinos with public health insurance). Very little is known about the direct costs of implementing PN programs. The objective of the current study was to perform a detailed cost analysis of PN programs at the authors' institution from an institutional perspective.

METHODS:

In 2 randomized controlled trials, average‐risk patients who were referred for SC by primary care providers were recruited for PN between May 2008 and May 2010. Patients were randomized to 1 of 4 PN groups. The cost of PN and net income to the institution were determined in a cost analysis.

RESULTS:

Among 395 patients who completed colonoscopy, 53.4% underwent SC alone, 30.1% underwent colonoscopy with biopsy, and 16.5% underwent snare polypectomy. Accounting for the average contribution margins of each procedure type, the total revenue was $95,266.00. The total cost of PN was $14,027.30. Net income was $81,238.70. In a model sample of 1000 patients, net incomes for the institutional completion rate (approximately 80%), the historic PN program (approximately 65%), and the national average (approximately 50%) were compared. The current PN program generated additional net incomes of $35,035.50 and $44,956.00, respectively.

CONCLUSIONS:

PN among minority patients with mostly public health insurance generated additional income to the institution, mainly because of increased colonoscopy completion rates. Cancer 2013. © 2012 American Cancer Society.     

Plasma Gelsolin and Circulating Actin Correlate with Hemodialysis Mortality

Plasma gelsolin (pGSN) binds actin and bioactive mediators to localize inflammation. Low pGSN correlates with adverse outcomes in acute injury, whereas administration of recombinant pGSN reduces mortality in experimental sepsis. We found that mean pGSN levels of 150 patients randomly selected from 10,044 starting chronic hemodialysis were 140 ± 42 mg/L, 30 to 50% lower than levels reported for healthy individuals. In a larger sample, we performed a case-control analysis to evaluate the relationship of pGSN and circulating actin with mortality; pGSN levels were significantly lower in 114 patients who died within 1 yr of dialysis initiation than in 109 survivors (117 ± 38 mg/L versus 147 ± 42 mg/L, P < 0.001). pGSN levels had a graded, inverse relationship with 1-yr mortality, such that patients with pGSN <130 mg/L experienced a >3-fold risk for mortality compared with those with pGSN ≥150 mg/L. The 69% of patients with detectable circulating actin had lower pGSN levels than those without (127 ± 45 mg/L versus 141 ± 36 mg/L, P = 0.026). Compared with patients who had elevated pGSN and no detectable actin, those with low pGSN levels and detectable actin had markedly increased mortality (odds ratio 9.8, 95% confidence interval 2.9 to 33.5). Worsening renal function correlated with pGSN decline in 53 subjects with CKD not on dialysis. In summary, low pGSN and detectable circulating actin identify chronic hemodialysis patients at highest risk for 1-yr mortality.Although chronic hemodialysis has markedly reduced the acute mortality of ESRD patients, these patients still die at a markedly accelerated rate, principally from cardiovascular events and recurrent infections.^1–3 Patients with ESRD exhibit muscle depletion, malnutrition, hypoalbuminemia, and manifestations of diffuse tissue injury, and these parameters strongly correlate with early mortality.^4–10 However, the specific factors linking wasting and inflammation with accelerated mortality remain under investigation.¹¹The extracellular actin binding proteins include vitamin D binding protein and plasma gelsolin (pGSN).¹² pGSN also inactivates bioactive lipid mediators including lysophosphatidic acid,¹³ lipopolysaccharide endotoxin,¹⁴ and platelet-activating factor.¹⁵ pGSN is measurable in healthy individuals (approximately 190 to 300 mg/L, Supplementary Table 2) as a secreted variant of a cellular protein involved in the regulation of changes in cell shape.^16,17 Many cell types secrete pGSN, but striated muscle accounts for most pGSN production.¹⁸ pGSN contributes to removing actin when injected into the circulation of experimental animals, and levels of pGSN fall after acute injuries, consistent with the release of actin in circulation after tissue damage.^12,19–22A highly evolutionarily conserved actin- and inflammatory mediator-binding protein present in diverse species from Drosophila to humans suggests that it functions to localize inflammatory and immune reactions to sites of injury.²³ Local depletion of pGSN due to tissue damage and exposure of cytoplasmic actin, one of the most abundant body proteins, enables inflammatory mediators to locally exert adaptive defense and repair functions, whereas a reservoir of circulating pGSN prevents these mediators from injuring organs away from the primary site of insult.Extensive injuries, however, may compromise the inflammation-localizing function of pGSN by depleting it because of excessive actin exposure. Consistent with this hypothesis, critical extents of pGSN level reductions predict adverse clinical outcomes, including death, in patients subjected to acute injuries such as major trauma or surgery, burns, or hematopoietic stem cell transplantation.^20–21 Here we report that a critical level of pGSN depletion, measured at the initiation of chronic hemodialysis, correlates with the highest risk for 1-yr mortality in patients initiating chronic hemodialysis and that the presence of circulating actin markedly increases this risk. In addition, pGSN concentrations decline with deteriorating renal function in chronic kidney disease. These findings potentially link the pathophysiologies of protein-energy wasting, inflammation, and tissue injury and mortality in ESRD via low circulating muscle-derived pGSN. Because partial or complete repletion of depleted pGSN stores alleviates inflammatory manifestations and reduces mortality in experimental tissue injury,^24–26 pGSN depletion is a potentially modifiable risk factor in this setting.     

Kinetics of actin monomer exchange at the slow growing ends of actin filaments and their relation to the elongation of filaments shortened by gelsolin

Summary The kinetics of actin monomer exchange with the slow growing pointed ends of actin filaments have been determined by measuring rates of monomer addition to or loss from filaments with their fast-growing barbed ends blocked by the protein gelsolin. Direct measurements of filament length by electron microscopy confirmed that each gelsolin acts as a nucleus for an actin filament. The rate constants ascertained arek _–=0.03s^–1;k ₊=0.06 m ^–1 s^–1 at 23° C andk _–=0.11 s^–1;k ₊=0.09 m ^–1s^–1 at 37° C. They are approximately independent of pH from 7.0 to 8.0 at both temperatures. These rates are far slower than those reported on the basis of some electron microscopic studies of filaments assembled on to actin bundles. The rate constants also predict a higher critical monomer concentration for the pointed end at 37° C than at room temperature, consistent with direct measurements of this quantity. The relative slowness of the monomer exchange at the pointed end suggests that actin filaments with blocked barbed ends are relatively stable. The rate of redistribution of actin monomers from filaments stabilized at their barbed ends by the gelsolin-calcium complex to longer filaments was measured following removal of Ca²⁺, which decreases the capacity of gelsolin to nucleate filaments. The elongation occurs at a rate consistent with the measured rates of monomer exchange and is quantitatively described by Hill's model for filament elongation by random exchange of monomers from one end.