Low exogenous lactate clearance as an early predictor of mortality in normolactatemic critically ill septic patients

OBJECTIVE: To evaluate the prognostic value of lactate clearance and lactate production in severely ill septic patients with normal or mildly elevated blood lactate concentration.DESIGN Prospective, observational study. SETTING: Nineteen-bed mixed medicosurgical intensive care unit. PATIENTS: Fifty-six patients with severe sepsis and blood lactate concentration <3 mmol/L. MEASUREMENTS AND MAIN RESULTS: Lactate metabolism was evaluated in all patients. Lactate clearance was measured by modeling the change in arterial blood lactate over time induced by an infusion of 1 mmol/kg sodium lactate for 15 mins. Lactate production was calculated as the product of lactate clearance times the blood lactate concentration before the infusion. Outcome was taken to be mortality at 28 days after the beginning of the septic episode. A logistic regression model taking into account different risk factors was constructed. Among the 56 patients, 17 (30.3%) died before the 28th day. Basal blood lactate concentration was not different between survivors and nonsurvivors, whereas lactate clearance and production were higher in survivors (0.86 +/- 0.32 vs. 0.58 +/- 0.18 L/hr/kg, p < .005, and 1.19 +/- 0.63 vs. 0.89 +/- 0.24 mmol/hr/kg, p = .055, respectively). An increase in blood lactate 45 mins after the end of the lactate infusion (Deltalact-T60) > or = 0.6 mmol/L was predictive of 28-day mortality with 53% sensitivity and 90% specificity. Multivariate analysis showed that only three factors were independently and significantly correlated with 28-day mortality: presence of more than two organ failures (odds ratio, 27; p = .04), age >70 yrs (odds ratio, 5.7; p = .032), and Deltalact-T60 > or =0.6 mmol/L (odds ratio, 14.2; p = .042). CONCLUSION: Low lactate clearance in severely ill septic patients with normal or mildly elevated blood lactate is predictive of poor outcome independently of other known risk factors such as age and number of organ failures.     

α7 Nicotinic Acetylcholine Receptor Regulates Airway Epithelium Differentiation by Controlling Basal Cell Proliferation

Airway epithelial basal cells are known to be critical for regenerating injured epithelium and maintaining tissue homeostasis. Recent evidence suggests that the α7 nicotinic acetylcholine receptor (nAChR), which is highly permeable to Ca²⁺, is involved in lung morphogenesis. Here, we have investigated the potential role of the α7 nAChR in the regulation of airway epithelial basal cell proliferation and the differentiation of the human airway epithelium. In vivo during fetal development and in vitro during the regeneration of the human airway epithelium, α7 nAChR expression coincides with epithelium differentiation. Inactivating α7 nAChR function in vitro increases cell proliferation during the initial steps of the epithelium regeneration, leading to epithelial alterations such as basal cell hyperplasia and squamous metaplasia, remodeling observed in many bronchopulmonary diseases. The regeneration of the airway epithelium after injury in α7^−/− mice is delayed and characterized by a transient hyperplasia of basal cells. Moreover, 1-year-old α7^−/− mice more frequently present basal cells hyperplasia. Modulating nAChR function or expression shows that only α7 nAChR, as opposed to heteropentameric α_xβ_y nAChRs, controls the proliferation of human airway epithelial basal cells. These findings suggest that α7 nAChR is a key regulator of the plasticity of the human airway epithelium by controlling basal cell proliferation and differentiation pathway and is involved in airway remodeling during bronchopulmonary diseases.The respiratory epithelium, which is constantly exposed to airborne pollutants, is frequently injured, which results in altered epithelial functions. To restore these functions, the respiratory epithelium must undergo rapid repair via epithelial cell spreading and migration and regenerate its structure via basal cell proliferation and differentiation.¹ These processes are tightly controlled to restore the pseudostratified architecture of the normal mucociliary epithelium. However, in most respiratory diseases, alterations of the regeneration processes induce epithelial remodeling such as hyperplasia, metaplasia, and fibrosis. Understanding the sequence of processes involved in cell proliferation and differentiation is therefore of crucial importance. Both in vivo and in vitro, human airway basal cells are able to proliferate and reconstitute a fully differentiated and functional epithelium.² These cells are such considered as progenitors of the human airway epithelium and important actors of the airway epithelium regeneration.The nonneuronal cholinergic system is thought to be involved in the regulation of cell functions such as cell-cell interaction, apoptosis, and proliferation.³ It is now established that human bronchial epithelial cells contain all of the machinery for the production, storage, secretion, and degradation of acetylcholine, which acts as an autocrine or paracrine hormone.^4,5 Acetylcholine exerts its effects through muscarinic and nicotinic acetylcholine receptors. Nicotinic acetylcholine receptors (nAChRs) are composed of five subunits, arranged as α/β heteromeric or α homomeric nAChRs, and assembled around a central ion channel, mediating the influx of Ca²⁺.⁶ The airway epithelium expresses α3, α4, α5, α7, α9, β2, and β4 subunits for nAChRs.^7,8,9α7 nAChR is characterized by an elevated Ca²⁺ permeability¹⁰ and has been involved in several important biological processes such as cell proliferation, apoptosis, and angiogenesis in cancer.^11,12 Prenatal nicotine exposure significantly increases pulmonary α7 nAChR expression and alters fetal lung development¹³ and subsequently pulmonary function in newborn.¹⁴ In particular, alteration of lung branching morphogenesis induced by nicotine is mediated by α7 nAChR.¹⁵ Altogether, these observations led us to investigate whether the α7 nAChR could be involved in the differentiation of the respiratory epithelium. In the human airway epithelium, we observed α7 nAChR expression in basal cells, which play a critical role in the epithelial regeneration. Both in vivo and in vitro, the α7 nAChR expression is associated with the airway epithelium differentiation. Moreover, in vitro inactivating α7 nAChR or in vivo disrupting genetic α7 nAChR expression induces airway epithelium remodeling by modulating basal cell proliferation. This study thus provides several lines of evidence that α7 nAChR is significant for airway epithelial differentiation and suggests that α7 nAChR is a key regulator of the plasticity of the airway epithelium.     

A regulatory role for the cohesin loader NIPBL in nonhomologous end joining during immunoglobulin class switch recombination

DNA double strand breaks (DSBs) are mainly repaired via homologous recombination (HR) or nonhomologous end joining (NHEJ). These breaks pose severe threats to genome integrity but can also be necessary intermediates of normal cellular processes such as immunoglobulin class switch recombination (CSR). During CSR, DSBs are produced in the G1 phase of the cell cycle and are repaired by the classical NHEJ machinery. By studying B lymphocytes derived from patients with Cornelia de Lange Syndrome, we observed a strong correlation between heterozygous loss-of-function mutations in the gene encoding the cohesin loading protein NIPBL and a shift toward the use of an alternative, microhomology-based end joining during CSR. Furthermore, the early recruitment of 53BP1 to DSBs was reduced in the NIPBL-deficient patient cells. Association of NIPBL deficiency and impaired NHEJ was also observed in a plasmid-based end-joining assay and a yeast model system. Our results suggest that NIPBL plays an important and evolutionarily conserved role in NHEJ, in addition to its canonical function in sister chromatid cohesion and its recently suggested function in HR.DNA double strand breaks (DSBs) pose a severe threat to genome integrity, but can also be a necessary part of normal cellular processes, such as meiosis and Ig class switch recombination (CSR). Depending on cell cycle phase and DSB structure, different strategies are used for repair. Homologous recombination (HR) depends on a homologous DNA template for repair, preferentially the identical sister chromatid, and is therefore mainly active during the S and G2 phases. Nonhomologous end joining (NHEJ), however, is active throughout the cell cycle and is the principal pathway during the G1 phase, when there is no immediate close template for homologous repair. The classical NHEJ pathway requires not only the key components of the NHEJ machinery, i.e., Ku70/Ku80, DNA-PKcs, Artemis, XLF (Cernunnos), XRCC4, and DNA ligase IV, but also several DNA damage sensors or adaptors, such as ATM, γH2AX, 53BP1, MDC1, RNF168, and the Mre11–Rad50–NBS1 complex.Cohesin is an evolutionarily conserved multisubunit complex consisting of a heterodimer of two structural maintenance of chromosomes (SMC) proteins, SMC1A and SMC3, one kleisin protein RAD21 (MCD1 or SCC1) and SA (STAG1/2 or SCC3). The SMC proteins fold back on themselves in the hinge region to form long antiparallel coiled-coil arms, with the amino and carboxyl termini coming together to create head domains that contain ATPases. RAD21 bridges the two head domains to facilitate the formation of the proposed ring-like structure of the complex, and it also interacts with the SA subunit. The cohesin complex ensures correct chromosome segregation through cohesion between sister chromatids (Nasmyth and Haering, 2009). In addition to this canonical role, cohesin and its loading complex NIPBL/MAU2 have also been suggested to be important for regulation of gene expression and repair of DSBs through HR, presumably by facilitating proximity between the broken DNA ends and the repair template (Sjögren and Nasmyth, 2001; Vrouwe et al., 2007; Nasmyth and Haering, 2009). Smc1, the yeast SMC1A orthologue, has furthermore been suggested to coordinate the HR and NHEJ processes (Schär et al., 2004).Cornelia de Lange syndrome (CdLS) is a developmental disorder characterized by growth retardation, severe intellectual disability, gastrointestinal abnormalities, malformations, of the upper limbs and characteristic facial dysmorphisms. Heterozygous loss-of-function mutations in NIPBL, encoding the cohesin loader NIPBL, are the major cause of CdLS (Liu and Baynam, 2010). In addition, mutations in the SMC1A, SMC3, PDS5B, RAD21, and HDAC8 encoding genes, all being part of the cohesion pathway, have been found in selected CdLS patients. The multisystem dysfunctions connected to the syndrome implicate defective gene regulation during fetal development and current evidence suggests that CdLS may be caused by alterations in cohesin chromatin-binding dynamics (Liu et al., 2009). In addition, cell lines established from CdLS patients have an increased sensitivity to DNA damage that has been suggested to be caused by defective HR-mediated repair (Vrouwe et al., 2007).Here, we show an increased DNA damage sensitivity, especially after exposure to γ-rays, in B-lymphoblastoid (LCLs) and fibroblast cell lines (FBs) from NIPBL-deficient CdLS patients. However, we also observed that the majority of the patient and control cells studied were in the G1 phase of the cell cycle, where NHEJ is the principle DSB repair mechanism. We therefore investigated whether defective NHEJ could underlie the DNA damage sensitivity observed in the patient cells.     

Up-regulation of tRNA biosynthesis affects translational readthrough in maf1-delta mutant of Saccharomyces cerevisiae

Maf1p is a negative effector of RNA polymerase III in yeast. The maf1-delta mutation caused an increase in the level of cellular tRNAs, but a decrease of translational readthrough at nonsense codons. Using the lacZ- luc dual gene reporter system, we detected an almost twofold diminution of UAA and UAG readthrough in maf1-delta compared with the parental strain. The maf1-delta mutation did not affect the rate of protein biosynthesis and growth at standard conditions, but resulted in temperature-sensitive growth on non-fermentable carbon sources. We examined the correlation of the temperature sensitive and antisuppression phenotypes of maf1- Delta using a colour phenotype assay in the ade2-1 SUP11 strain. Antisuppression, but not the temperature-sensitive growth defect, was compensated either by increased dosage of SUP11or by [PSI(+)], the prion form of the translation termination factor Sup35p. Summarizing, the elevated tRNA levels in maf1- Delta increase translational fidelity and, independently, affect growth under special conditions.     

Effect of zidovudine resistance mutations on virologic response to treatment with zidovudine or stavudine,each in combination with lamivudine and indinavir

The authors studied the effect of zidovudine (ZDV) resistance mutation on virologic response to treatment with ZDV or stavudine (d4T) each in combination with lamivudine and indinavir. Viral genotyping was performed on plasma HIV-1 RNA at study entry and concerned 155 patients previously treated with ZDV, didanosine, or zalcitabine and enrolled in the NOVAVIR (Agence National de Recherche sur le SIDA [ANRS] 073) trial. Three virologic responses were investigated: early response (<50 copies/mL at week 24), late response (<500 copies/mL at week 80), and virologic failure (two HIV-1 RNA >5000 copies/mL). Patients were classified as resistant or susceptible to ZDV according to the ANRS algorithm. Plasma viral RNA from 123 of 155 patients had two or more ZDV resistance mutations. The number of ZDV resistance mutations was positively correlated with the duration of prior antiviral therapy (p <.001). At week 24, 74% and 77% of patients with virus classified as resistant were responders in the d4T and ZDV arm, respectively. Similar results were found at week 80. Virologic failure was reached in 7 of 24 patients with virus classified as susceptible and in 26 of 131 patients with resistant virus (p =.29). In the ZDV arm, patients classified as resistant had longer times to virologic failure than those classified as susceptible (p =.003). In conclusion, sustained virologic response despite presence of ZDV resistance mutations implies that these mutations do not preclude an early and durable response to treatment with a potent three-drug regimen in these patients. Patients susceptible to ZDV had lower median mean corpuscular volumes and lower random indinavir levels, suggesting that adherence was the main reason for failure.     

Chromogranin B P413L variant as risk factor and modifier of disease onset for amyotrophic lateral sclerosis

Recently, chromogranins were reported to interact specifically with mutant forms of superoxide dismutase that are linked to amyotrophic lateral sclerosis (ALS). This interaction led us to analyze the frequencies of sequence variants of the CHGB gene in ALS patients and matched controls from three different countries. Of particular interest was the finding of the P413L CHGB variant present in 10% of ALS patients (n = 705) as compared to 4.5% in controls (n = 751), conferring a 2.2-fold greater relative risk to develop the disease (P < 0.0001). This effect was mainly contributed by the samples of French origin that yielded a frequency of the P413L variation at 17% in ALS (n = 289) and 5% in controls (n = 448), conferring a 3.3-fold greater risk to develop ALS. Furthermore, the P413L CHGB variant is associated with an earlier age of onset by almost a decade in both sporadic ALS and familial ALS cases. Genetic variation influencing age of onset in ALS had not previously been reported. Expression of fusion CHGB-EGFP constructs in SHSY-5Y cells revealed that the P413L variation can cause defective sorting of CHGB into secretory granules. The finding that CHGB may act as a susceptibility gene and modifier of onset in ALS is consistent with the emerging view that dysfunction of the secretory pathway may contribute to increased vulnerability of motor neurons.     

Disseminated arterial occlusions revealing bilateral venous thrombosis with paradoxical embolisms

Paradoxical embolism is a diagnosis of exclusion. Clinical triad associates deep venous thrombosis with or without pulmonary embolism, arterial embolism, and intracardiac communication with right-to-left shunt. The intracardiac communication is generally related to a patent foramen ovale (PFO). We report a 75-year-old patient, who presented with bilateral deep venous thrombosis of the legs, complicated by massive pulmonary embolism and paradoxical embolisms through a PFO. This resulted in cerebral, mesenteric, splenic and bilateral kidney infarctions. A promptly initiated anticoagulant treatment allowed a favourable outcome.