Has Tranexamic Acid in Total Knee Arthroplasty Made Tourniquet Use Obsolete?

The application of tranexamic acid (TXA) in total joint arthroplasty has dramatically improved peri-operative blood management. In light of these benefits, a study by Huang et al., “Intravenous and Topical Tranexamic Acid Alone Are Superior to Tourniquet Use for Primary Total Knee Arthroplasty,” evaluates the need for continued use of the intra-operative tourniquet, which remains a routine practice with documented benefits and adverse effects. This review evaluates the study’s design and critically interprets its findings for clinical practice. Through a prospective, randomized trial, Huang et al. demonstrated that among selected patients undergoing primary total knee arthroplasty, the use of a tourniquet results in no reduction in blood loss beyond that provided by TXA alone. Moreover, the use of TXA without a tourniquet led to improved early clinical outcomes such as reduced post-operative swelling, improved knee range of motion at discharge, and enhanced patient satisfaction. As medicine is practiced in an increasingly value-driven environment, this study provides a useful method for evaluating the utility of commonly used interventions. Its findings highlight the need for future investigations into the optimal administration of TXA in total knee arthroplasty.     

Comparative electrophysiological evaluation of hippocampal function following repeated inhalation exposures to JP-8, Jet A,JP-5, and the synthetic Fischer Tropsch fuel

Exposure to fuels continues to be a concern in both military and general populations. The aim of this study was to examine effects of in vivo rat repeated exposures to different types of jet fuel utilizing microelectrode arrays for comparative electrophysiological (EP) measurements in hippocampal slices. Animals were exposed to increasing concentrations of four jet fuels, Jet Propellant (JP)-8, Jet A, JP-5, or synthetic Fischer Tropsch (FT) fuel via whole-body inhalation for 20 d (6 hr/d, 5 d/week for 28 d) and synaptic transmission as well as behavioral performance were assessed. Our behavioral studies indicated no significant changes in behavioral performance in animals exposed to JP-8, Jet A, or JP-5. A significant deviation in learning pattern during the Morris water maze task was observed in rats exposed to the highest concentration of FT (2000 mg/m³). There were also significant differences in the EP profile of hippocampal neurons from animals exposed to JP-8, Jet A, JP-5, or FT compared to control air. However, these differences were not consistent across fuels or dose dependent. As expected, patterns of EP alterations in brain slices from JP-8 and Jet A exposures were more similar compared to those from JP-5 and FT. Further longitudinal investigations are needed to determine if these EP effects are transient or persistent. Such studies may dictate if and how one may use EP measurements to indicate potential susceptibility to neurological impairments, particularly those that result from inhalation exposure to chemicals or mixtures.     

Determination of Tedizolid susceptibility interpretive criteria for gram-positive pathogens according to clinical and laboratory standards institute guidelines

For effective antibacterial therapy, physicians require qualitative test results using susceptibility breakpoints provided by clinical microbiology laboratories. This article summarizes the key components used to establish the Clinical Laboratory Standards Institute (CLSI) breakpoints for tedizolid. First, in vitro studies using recent surveillance and clinical trial isolates ascertained minimal inhibitory concentration (MIC) distributions against pertinent organisms, including staphylococci, streptococci, and enterococci. Studies in animal models of infection determined rates of antibacterial efficacy and survival following administration of tedizolid phosphate at doses equivalent to those in humans. Pharmacokinetic and pharmacodynamic analyses examined the relationship between plasma concentrations and MICs against the target organism. Finally, clinical trials assessed clinical and microbiologic outcomes by MIC. All these data were evaluated and combined to obtain the ratified CLSI susceptibility criteria for tedizolid of ≤0.5 μg/mL for Staphylococcus aureus, Streptococcus pyogenes, Streptococcus agalactiae, and Enterococcus faecalis and ≤0.25 μg/mL for Streptococcus anginosus group.     

Activity of CD101, a long-acting echinocandin,against clinical isolates of Candida auris

CD101 is a new echinocandin with a prolonged half-life. CD101 was tested by broth microdilution against 100 isolates of the emerging yeast Candida auris. It showed activity against most isolates, including some that were resistant to other echinocandins.     

Melatonin excretion with affect disorders over age 60

Numerous studies have reported low melatonin secretion in depression, but other studies have suggested no deficit or an increase. Alterations of circadian phase or duration of melatonin secretion have also been described. Since melatonin secretion decreases as we age, it seemed interesting to examine melatonin and depression in an aging sample. Volunteers who complained of mood or sleep problems were recruited for studies in which fractional urine specimens were collected for 24 h, both at home and in the laboratory. The major metabolite, 6-sulfatoxymelatonin (aMT6s), was determined by radioimmunoassay. Of 72 volunteers aged 60-78 years, seven had current major depression and 55% had a lifetime history of an affective disorder. A 55-fold range of home aMT6s excretion rates was observed. A lifetime history of any affective disorder was significantly associated with greater log(10)[mesor] aMT6s excretion in home collections and laboratory collections, but current affective disorders were neither significantly related to melatonin excretion nor to aMT6s acrophase timing, onset, offset or duration. These results are only weakly consistent with a photoperiodic hypothesis of depression.     

Dynamin 2–dependent endocytosis is required for sustained S1PR1 signaling

Sphingosine-1-phosphate (S1P) receptor 1 (S1PR1) is critical for lymphocyte egress from lymphoid organs. Lymphocytes encounter low S1P concentrations near exit sites before transmigration, yet S1PR1 signaling is rapidly terminated after exposure to S1P. How lymphocytes maintain S1PR1 signaling in a low S1P environment near egress sites is unknown. Here we identify dynamin 2, an essential component of endocytosis, as a novel regulator of T cell egress. Mice with T cell–specific dynamin 2 deficiency had profound lymphopenia and impaired egress from lymphoid organs. Dynamin 2 deficiency caused impaired egress through regulation of S1PR1 signaling, and transgenic S1PR1 overexpression rescued egress in dynamin 2 knockout mice. In low S1P concentrations, dynamin 2 was essential for S1PR1 internalization, which enabled continuous S1PR1 signaling and promoted egress from both thymus and lymph nodes. In contrast, dynamin 2–deficient cells were only capable of a pulse of S1PR1 signaling, which was insufficient for egress. Our results suggest a possible mechanism by which T lymphocytes positioned at exit portals sense low S1P concentrations, promoting their egress into circulatory fluids.The egress of T lymphocytes from lymphoid organs is essential for adaptive immune responses. The exit of mature single-positive (SP) thymocytes from the thymus into blood establishes a pool of naive T cells with a diverse repertoire in peripheral organs. Egress from lymph nodes into lymph is required for the recirculation of T cells through secondary lymphoid organs and for immune surveillance. Egress from lymphoid organs is critically dependent on the binding of sphingosine-1-phosphate (S1P) to S1P receptor 1 (S1PR1) that is expressed on T cells (Matloubian et al., 2004; Pappu et al., 2007; Zachariah and Cyster, 2010; Cyster and Schwab, 2012). Sensing of S1P gradients that exist between lymphoid tissues (interstitial S1P concentration in low nanomolar range) and blood or lymph (plasma S1P concentration ∼100–1,000 nM) is required for egress (Schwab et al., 2005; Pappu et al., 2007; Cyster and Schwab, 2012). Beyond a requirement for S1PR1, the lymphocyte-intrinsic molecular mechanisms that regulate egress remain incompletely defined.S1PR1 is a G protein–coupled receptor (GPCR) with unique properties (Lee et al., 1996, 1998; Windh et al., 1999; Rivera et al., 2008; Rosen et al., 2009; Spiegel and Milstien, 2011; Cyster and Schwab, 2012). It is highly sensitive to desensitization and internalization in the continued presence of its ligand S1P (Liu et al., 1999; Schwab et al., 2005; Oo et al., 2007, 2011; Pappu et al., 2007; Arnon et al., 2011), particularly when compared with chemokine receptors and even when compared with members of the same receptor family, such as S1PR5 (Jenne et al., 2009). Receptor desensitization is mediated by GPCR kinase 2 (GRK2), which phosphorylates serine residues in the cytoplasmic tail of S1PR1 (Watterson et al., 2002; Arnon et al., 2011). Receptor phosphorylation recruits β-arrestins that sterically uncouple the receptor from heterotrimeric G proteins, thereby leading to the rapid loss of receptor responsiveness (“desensitization”). Arrestin binding also leads to GPCR internalization via clathrin-mediated endocytosis and either receptor degradation or recycling back to the cell surface (Ferguson, 2001; Pierce et al., 2002; Sorkin and von Zastrow, 2009). Receptor internalization can restore GPCR responsiveness (“resensitization”) as has been shown for the β₂-adrenergic receptor (Zhang et al., 1997).Although large S1P gradients exist between blood/lymph and lymphoid tissue, several data indicate that lymphocytes encounter small S1P gradients that likely instruct migration toward exit portals within lymphoid tissues. For example, thymocytes are attracted to egress sites at corticomedullary junctions in response to S1P produced locally by pericytes that ensheath thymic blood vessels (Zachariah and Cyster, 2010). Furthermore, S1PR1 signaling enforces internalization of the surface molecule CD69 (Shiow et al., 2006; Bankovich et al., 2010; Cyster and Schwab, 2012), a molecular timer which delays egress (Zachariah and Cyster, 2010). A prediction from these observations is the presence of an intrathymic gradient of low S1P concentration that guides thymocytes to exit sites, although technical limitations have not yet allowed direct visualization of S1P gradients within tissue (Cyster and Schwab, 2012). Given the rapid and sensitive down-regulation of S1PR1 signaling upon S1P engagement, this prediction also implies that S1PR1, after exposure to intrathymic S1P, maintains S1P responsiveness to promote thymocyte egress. However, the molecular requirements for, and the functional significance of, S1PR1 resensitization for T cell egress have not been defined.Intravital microscopy of S1PR1-deficient lymphocytes revealed that T cells approach lymph node egress sites (cortical lymphatic sinuses) efficiently, but S1PR1 is critical for the transendothelial migration step (Grigorova et al., 2009). The data on lymph node egress are consistent with a model in which a pulse of S1PR1 signaling, as opposed to sustained signaling, is sufficient for lymphocyte egress. Alternatively, egress requires sustained S1PR1 signaling, and therefore, lymphocytes need to maintain S1PR1 responsiveness even in the presence of low S1P concentrations. The latter mode of egress would predict that rapid S1PR1 resensitization mechanisms are essential for egress to occur.Binding of S1P to S1PR1 triggers both signaling through the receptor and its endocytosis (Liu et al., 1999; Oo et al., 2007, 2011), yet whether and how endocytosis regulates S1PR1 signaling are unclear. Given the critical role for dynamins in promoting the membrane scission step during endocytosis (Praefcke and McMahon, 2004; McMahon and Boucrot, 2011; Schmid and Frolov, 2011; Ferguson and De Camilli, 2012), we used mice genetically deficient in dynamin 2 (Dnm2; Ferguson et al., 2009), the dynamin isoform expressed in immune cells, to investigate the physiological function of endocytosis in T lymphocytes. We report here that dynamin 2 is critical for T cell egress from thymus and lymph nodes by directly regulating S1PR1 signaling. Surprisingly, dynamin 2–dependent endocytosis was not required for termination of S1PR1 signaling. Instead, dynamin 2 was required for S1PR1 resensitization in T lymphocytes, thereby promoting sustained S1PR1 signaling in vivo. We propose that dynamin 2–dependent endocytosis enables continuous S1PR1 signaling in T lymphocytes that are positioned near exit sites in a low S1P environment and promotes their egress into blood and lymph. Overall, our findings identify a previously unknown mechanistic link between endocytosis and T lymphocyte egress.