Frederick S. Southwick

Multifactorial Index of Cardiac Risk in Noncardiac Surgical Procedures

To determine which preoperative factors might affect the development of cardiac complications after major noncardiac operations, we prospectively studied 1001 patients over 40 years of age. By multivariate discriminant analysis, we identified nine independent significant correlates of life-threatening and fatal cardiac complications: preoperative third heart sound or jugular venous distention; myocardial infarction in the preceding six months; more than five premature ventricular contractions per minute documented at any time before operation; rhythm other than sinus or presence of premature atrial contractions on preoperative electrocardiogram; age over 70 years; intraperitoneal, intrathoracic or aortic operation; emergency operation; important valvular aortic stenosis; and poor general medical condition. Patients could be separated into four classes of significantly different risk. Ten of the 19 postoperative cardiac fatalities occurred in the 18 patients at highest risk. If validated by prospective application, the multifactorial index may allow preoperative estimation of cardiac risk independent of direct surgical risk.

Sphenoid sinusitis. A review of 30 cases.

We studied 30 patients with infectious sphenoid sinusitis (15 acute cases and 15 chronic cases) in an effort to characterize the clinical presentation, bacteriology, and associated complications of this frequently misdiagnosed infection. Severe frontal, temporal, or retro-orbital headache that radiated to the occipital regions or pain in the trigeminal (V1 to V3) distribution or both were the most prominent presenting symptoms. In acute cases, purulent exudate was frequently seen in the middle and superior nasal turbinates. Computerized axial tomography or sinus tomography and cannulation of the sphenoid sinus proved to be the most useful diagnostic studies. Organisms detected in acute cases included streptococci other than Streptococcus pneumoniae (41 per cent), Staphylococcus aureus (29 per cent), and Str. pneumoniae (17 per cent). In chronic infections, gram-negative bacilli (43 per cent) and staphylococcal species (24 per cent) were the predominant organisms. In acute disease, early diagnosis and aggressive therapy, including surgical drainage, were important. Delay in treatment was always associated with serious morbidity or mortality. Fatal complications included cavernous sinus thrombosis and bacterial meningitis.

Profilin Promotes Barbed-end Actin Filament Assembly without Lowering the Critical Concentration

The mechanism of profilin-promoted actin polymerization has been systematically reinvestigated. Rates of barbed-end elongation onto Spectrin·4.1·Actin seeds were measured by right angle light scattering to avoid confounding effects of pyrenyl-actin, and KINSIM was used to analyze elongation progress curves. Without thymosin-β4, both actin and Profilin·Actin (P·A) are competent in barbed-end polymerization, and kinetic simulations yielded the same bimolecular rate constant (∼10 × 106 m −1 s−1) for actin monomer or Profilin·Actin. When measured in the absence of profilin, actin assembly curves over a 0.7–4 μmthymosin-β4 concentration range fit a simple monomer sequestering model (1 μm K D for Thymosin-β4·Actin). The corresponding constant for thymosin-β4·pyrenyl-Actin, however, was significantly higher (∼9–10 μm), suggesting that the fluorophore markedly weakens binding to thymosin-β4. With solutions of actin (2 μm) and thymosin-β4 (2 or 4 μm), the barbed-end assembly rate rose with increasing profilin concentration (0.7–2 μm). Actin assembly in presence of thymosin-β4 and profilin fit a simple thermodynamic energy cycle, thereby disproving an earlier claim (D. Pantaloni and M.-F. Carlier (1993)Cell 75, 1007–1014) that profilin promotes nonequilibrium filament assembly by accelerating hydrolysis of filament-bound ATP. Our findings indicate that profilin serves as a polymerization catalyst that captures actin monomers from Thymosin-β4·Actin and ushers actin as a Profilin·Actin complex onto growing barbed filament ends.

Comparisons of CapG and gelsolin-null macrophages: demonstration of a unique role for CapG in receptor-mediated ruffling, phagocytosis, and vesicle rocketing

Capping the barbed ends of actin filaments is a critical step for regulating actin-based motility in nonmuscle cells. The in vivo function of CapG, a calcium-sensitive barbed end capping protein and member of the gelsolin/villin family, has been assessed using a null Capg allele engineered into mice. Both CapG-null mice and CapG/gelsolin double-null mice appear normal and have no gross functional abnormalities. However, the loss of CapG in bone marrow macrophages profoundly inhibits macrophage colony stimulating factor–stimulated ruffling; reintroduction of CapG protein by microinjection fully restores this function. CapG-null macrophages also demonstrate ∼50% impairment of immunoglobulin G, and complement-opsonized phagocytosis and lanthanum-induced vesicle rocketing. These motile functions are not impaired in gelsolin-null macrophages and no additive effects are observed in CapG/gelsolin double-null macrophages, establishing that CapG function is distinct from, and does not overlap with, gelsolin in macrophages. Our observations indicate that CapG is required for receptor-mediated ruffling, and that it is a major functional component of macrophage phagocytosis. These primary effects on macrophage motile function suggest that CapG may be a useful target for the regulation of macrophage-mediated inflammatory responses.

Anthrax Lethal Toxin Paralyzes Neutrophil Actin-Based Motility

Bacillus anthracis causes high-level bacteremia, strongly suggesting paralysis of the innate immune system. We have examined the effects of anthrax lethal toxin (LT) on human neutrophil chemotaxis, a process that requires actin filament assembly. Polymorphonuclear neutrophils (PMNs) treated with a sublethal concentration of LT (50 ng/mL) for 2 h demonstrated insignificant apoptosis or necrosis. However, this same concentration slowed human PMN formylmethionylleucylphenylalanine (FMLP)-stimulated chemokinesis by >60%, markedly reduced polar morphology, and rendered PMNs incapable of responding to a chemotactic gradient. These changes were accompanied by a >50% reduction in FMLP-induced actin filament assembly. One hour of exposure to LT failed to impair polarity or actin assembly, and the effects of LT were independent of mitogen-activated protein kinase kinase 1 inhibition. We conclude that 2 h of exposure to LT markedly impairs PMN actin assembly, and reductions in actin filament content are accompanied by a profound paralysis of PMN chemotaxis.

A Variant of Chronic Granulomatous Disease: Deficient Oxidative Metabolism Due to a Low-Affinity NADPH Oxidase

OUR defense against bacterial infections depends in part on the action of phagocytic leukocytes, which encounter and kill potentially pathogenic microorganisms. A severe reduction in the number or ...

Importance of free actin filament barbed ends for Arp2/3 complex function in platelets and fibroblasts

We investigated the effect of actin filament barbed end uncapping on Arp2/3 complex function both in vivo and in vitro. Arp2/3 complex redistributes rapidly and uniformly to the lamellar edge of activated wild-type platelets and fibroblasts but clusters in marginal actin filament clumps in gelsolin-null cells. Treatment of gelsolin-null platelets with the negative dominant N-WASp C-terminal CA domain has no effect on their residual actin nucleation activity, placing gelsolin actin filament severing, capping, and uncapping function upstream of Arp2/3 complex nucleation. Actin filaments capped by gelsolin or the gelsolin homolog CapG fail to enhance Arp2/3 complex nucleation in vitro, but uncapping of the barbed ends of these actin filaments restores their ability to potentiate Arp2/3 complex nucleation. We conclude that Arp2/3 complex contribution to actin filament nucleation in platelets and fibroblasts importantly requires free barbed ends generated by severing and uncapping.

Anthrax lethal toxin paralyzes actin‐based motility by blocking Hsp27 phosphorylation

Inhalation of anthrax causes fatal bacteremia, indicating a meager host immune response. We previously showed that anthrax lethal toxin (LT) paralyzes neutrophils, a major component of innate immunity. Here, we have found that LT also inhibits actin‐based motility of the intracellular pathogen Listeria monocytogenes. LT inhibition of actin assembly is mediated by blockade of Hsp27 phosphorylation, and can be reproduced by treating cells with the p38 mitogen‐activated protein (MAP) kinase inhibitor SB203580. Nonphosphorylated Hsp27 inhibits Listeria actin‐based motility in cell extracts, and binds to and sequesters purified actin monomers. Phosphorylation of Hsp27 reverses these effects. RNA interference knockdown of Hsp27 blocks LT inhibition of Listeria actin‐based motility. Rescue with wild‐type Hsp27 accelerates Listeria speed in knockdown cells, whereas introduction of Hsp27 mutants incapable of phosphorylation or dephosphorylation causes slowing down. We propose that Hsp27 facilitates actin‐based motility through a phosphorylation cycle that shuttles actin monomers to regions of new actin filament assembly. Our findings provide a previously unappreciated mechanism for LT virulence, and emphasize a central role for p38 MAP kinase‐mediated phosphorylation of Hsp27 in actin‐based motility and innate immunity.

A direct-transfer polymerization model explains how the multiple profilin-binding sites in the actoclampin motor promote rapid actin-based motility☆

The high actin-based motility rates observed in nonmuscle cells require the per-second addition of 400-500 monomers to the barbed ends of growing actin filaments. The chief polymerization-competent species is profilin.actin.ATP (present at 5-40 microM intracellular concentrations), whereas G-actin.ATP is much less abundant ( approximately 0.1-1 microM). While earlier studies unambiguously demonstrated that profilin.actin is highly concentrated within the polymerization zone, profilin-actin localization on the motile surface cannot increase the local solution-phase concentration of polymerizable actin. To explain these high rates of actin polymerization, we present and analyze a novel polymerization model in which monomers are directly transferred to growing filament ends in the actoclampin motor. This direct-transfer polymerization mechanism endows the polymerization zone with properties unavailable to bulk-phase actin monomers, and our model also indicates why profilin is the ideal mobile carrier for actin monomers.

The Potential Influence of Common Viral Infections Diagnosed during Hospitalization among Critically Ill Patients in the United States

Viruses are the most common source of infection among immunocompetent individuals, yet they are not considered a clinically meaningful risk factor among the critically ill. This work examines the association of viral infections diagnosed during the hospital stay or not documented as present on admission to the outcomes of ICU patients with no evidence of immunosuppression on admission. This is a population-based retrospective cohort study of University HealthSystem Consortium (UHC) academic centers in the U.S. from the years 2006 to 2009. The UHC is an alliance of over 90% of the non-profit academic medical centers in the U.S. A total of 209,695 critically ill patients were used in this analysis. Eight hospital complications were examined. Patients were grouped into four cohorts: absence of infection, bacterial infection only, viral infection only, and bacterial and viral infection during same hospital admission. Viral infections diagnosed during hospitalization significantly increased the risk of all complications. There was also a seasonal pattern for viral infections. Specific viruses associated with poor outcomes included influenza, RSV, CMV, and HSV. Patients who had both viral and bacterial infections during the same hospitalization had the greatest risk of mortality RR 6.58, 95% CI (5.47, 7.91); multi-organ failure RR 8.25, 95% CI (7.50, 9.07); and septic shock RR 271.2, 95% CI (188.0, 391.3). Viral infections may play a significant yet unrecognized role in the outcomes of ICU patients. They may serve as biological markers or play an active role in the development of certain adverse complications by interacting with coincident bacterial infection.