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Invasive mechanical ventilation is a lifesaving intervention for patients with severe acute hypoxic respiratory failure (AHRF), but it is associated with neuromuscular, cognitive, and infectious complications. Noninvasive ventilation (NIV) may provide sufficient respiratory support without these complications. The helmet interface for NIV could address concerns raised for the use of NIV as first-line therapy in AHRF. This review will summarize and appraise the current evidence for helmet NIV in AHRF.There are only six randomized controlled trials comparing helmet NIV to standard nasal cannula, facemask NIV, or high-flow nasal oxygen in patients with AHRF. Lower rates of endotracheal intubations and fewer days of mechanical ventilation were reported, with inconsistent findings on patient survival. Facemask NIV may worsen preexisting lung injury, delay intubations, and be inferior at delivering lung protective ventilation strategies compared with mechanical ventilation. The helmet interface could circumvent some of these concerns through the delivery of higher positive end expiratory pressure and more uniform distribution of negative pleural pressure.There is limited evidence to support or refute the use of helmet NIV in AHRF. Further studies investigating the interface of helmet in NIV as a separate clinical entity are needed.

Medical Procedure Services (MPS) may represent a solution to the educational gap in procedural training among internal medicine residents and the unmet need for the clinical provision of non-urgent inpatient procedures. However, there is little guidance available to help launch an MPS. Furthermore, procedural outcomes from a newly initiated MPS, including those comparing trainees versus attending physicians, are lacking.To describe the blueprint used in the design, implementation, and ongoing oversight of an MPS and to report its procedural outcomes.Vanderbilt University Medical Center (VUMC), Nashville, Tennessee.The launch of an MPS at a large tertiary academic hospital.6,152 procedural consultations resulting in 5,320 attempted procedures over a four-and-a-half year period.The primary proceduralist was a supervised resident in 58.7% (3124 /5,320) and an attending in 41.3% (2,196/5,320) of procedures. The overall success rate was 91.1% (95% CI: 90.3-91.9%) and the major complication rate was 0.7% (95% CI: 0.5-1.0%). There was no difference in the mean number of attempts required to complete a procedure (1.6 vs 1.5 attempts, p=0.68) and the complication rates between supervised residents and attending proceduralists, respectively (20/3,124 vs 20/2,196, p=0.26).At a tertiary academic medical center, the implementation and maintenance of MPS is feasible, safe, and results in high rates of successful procedures performed by supervised residents. Procedures performed by supervised residents require comparable number of attempts for completion and carry similar risks as those performed alone by attendings.

BACKGROUND: Invasive mechanical ventilation in critically ill adults involves adjusting the fraction of inspired oxygen to maintain arterial oxygen saturation. The oxygen-saturation target that will optimize clinical outcomes in this patient population remains unknown. METHODS: In a pragmatic, cluster-randomized, cluster-crossover trial conducted in the emergency department and medical intensive care unit at an academic center, we assigned adults who were receiving mechanical ventilation to a lower target for oxygen saturation as measured by pulse oximetry (Spo(2)) (90%; goal range, 88 to 92%), an intermediate target (94%; goal range, 92 to 96%), or a higher target (98%; goal range, 96 to 100%). The primary outcome was the number of days alive and free of mechanical ventilation (ventilator-free days) through day 28. The secondary outcome was death by day 28, with data censored at hospital discharge. RESULTS: A total of 2541 patients were included in the primary analysis. The median number of ventilator-free days was 20 (interquartile range, 0 to 25) in the lower-target group, 21 (interquartile range, 0 to 25) in the intermediate-target group, and 21 (interquartile range, 0 to 26) in the higher-target group (P = 0.81). In-hospital death by day 28 occurred in 281 of the 808 patients (34.8%) in the lower-target group, 292 of the 859 patients (34.0%) in the intermediate-target group, and 290 of the 874 patients (33.2%) in the higher-target group. The incidences of cardiac arrest, arrhythmia, myocardial infarction, stroke, and pneumothorax were similar in the three groups. CONCLUSIONS: Among critically ill adults receiving invasive mechanical ventilation, the number of ventilator-free days did not differ among groups in which a lower, intermediate, or higher Spo(2) target was used. (Supported by the National Heart, Lung, and Blood Institute and others; PILOT ClinicalTrials.gov number, NCT03537937.)

BACKGROUND AND AIMS: The number of procedures performed by internal medicine residents in the United States (US) is declining. An increasing proportion of residents do not feel confident performing essential invasive bedside procedures and, upon graduation, desire additional training. Several residency programs have utilized the medical procedure service (MPS) to address this issue. We aim to summarize the current state of evidence by systematically evaluating the effect of the MPS on resident education, comfort, and training, as well as patient safety and procedural outcomes in the US. METHODS: We conducted a systematic review of all studies reporting the use of an MPS with supervision from a board-certified physician in internal medicine residencies in the US. Database search was performed on PubMed, Embase, ERIC, and Cochrane Library from January 2000 to November 2020 for relevant studies. Quality of evidence assessment and random-effects proportion meta-analyses were performed. RESULTS: A total of nine studies reporting on 3879 procedures performed by MPS were identified. Procedures were safely performed, with a pooled complication rate of 2.1% (95% CI: 1.0–3.5) and generally successful, with a pooled success rate of 94.7% (95% CI: 90.8–97.7). The range of procedures performed by residents under MPS was 6.7–72.8 procedures per month (n = 9) compared to 4.3–64.4 procedures (n = 4) without MPS. MPS significantly increased confidence, comfort, and use of appropriate safety measures among residents. CONCLUSION: There are a limited number of published studies on MPS supervised by a board-certified physician in US internal medicine residencies. Procedures performed by MPS are generally successfully completed and safe. MPS benefits internal medicine residents training by improving competency, comfort, and confidence. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s11606-020-06526-2.

We report a case of a 31-year-old immunocompetent male who presented with altered mental status and agitation requiring intubation. As sedation was weaned, he demonstrated choreiform movements with associated hemiballismus of the right upper and lower extremities, and he was ultimately diagnosed with cryptococcal meningitis. The patient’s chorea did not terminate after the completion of induction antifungal therapy and all pharmacologic options for the management of chorea were ineffective. He underwent a successful unilateral pallidotomy using standard stereotactic methodology targeting the posterior-ventral pallidum, and his choreiform movements dramatically improved post-operatively within 48 hours.

Objectives Neurocysticercosis (NCC) and human immunodeficiency virus (HIV) have high disease burden and are prevalent in overlapping low- and middle-income areas. Yet, treatment guidance for people living with HIV/AIDS (PLWH/A) co-infected with NCC is currently lacking. This study aims to scope the available literature on HIV/AIDS and NCC co-infection, focusing on epidemiology, clinical characteristics, diagnostics, and treatment outcomes. Methods The scoping literature review methodological framework, and the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were followed. A total of 16,969 records identified through database searching and 45 additional records from other sources were reduced to 52 included studies after a standardised selection process. Results Two experimental studies, ten observational studies, 23 case series/case reports and 17 reviews or letters were identified. Observational studies demonstrated similar NCC seroprevalence in PLWH/A and their HIV-negative counterparts. Of 29 PLWH/A and NCC co-infection, 17 (59%) suffered from epileptic seizures, 15 (52%) from headaches, and 15 (52%) had focal neurological deficits. Eighteen (62%) had viable vesicular cysts and six (21%) had calcified cysts. Fifteen (52%) were treated with albendazole, of which 11 (73%) responded well to treatment. Five individuals potentially demonstrated an immune-reconstitution inflammatory syndrome after commencing anti-retroviral therapy, although this was in the absence of immunological and neuroimaging confirmation. Conclusions There is a paucity of evidence to guide treatment of PLWH/A and NCC co-infection. There is a pressing need for high-quality studies in this patient group to appropriately inform diagnostic and management guidelines for HIV-positive patients with NCC.

Rationale: Respiratory support (noninvasive ventilation or high-flow nasal cannula) applied at the time of extubation has been reported to reduce reintubation rates, but concerns regarding effectiveness have limited uptake into practice. Objectives: To determine if providing postextubation respiratory support to all patients undergoing extubation in a medical ICU would decrease the incidence of reintubation. Methods: We conducted a pragmatic, two-armed, cluster–crossover trial of adults undergoing extubation from invasive mechanical ventilation between October 1, 2017, and March 31, 2019, in the medical ICU of an academic medical center. Patients were assigned to either protocolized postextubation respiratory support (a respiratory therapist–driven protocol in which patients with suspected hypercapnia received noninvasive ventilation and patients without suspected hypercapnia received high-flow nasal cannula) or usual care (postextubation management at the discretion of treating clinicians). The primary outcome was reintubation within 96 hours of extubation. Measurements and Main Results: A total of 751 patients were enrolled. Of the 359 patients assigned to protocolized support, 331 (92.2%) received postextubation respiratory support compared with 66 of 392 patients (16.8%) assigned to usual care, a difference driven by differential use of high-flow nasal cannula (74.7% vs. 2.8%). A total of 57 patients (15.9%) in the protocolized support group experienced reintubation compared with 52 patients (13.3%) in the usual care group (odds ratio, 1.23; 95% confidence interval, 0.82 to 1.84; P = 0.32). Conclusions: Among a broad population of critically ill adults undergoing extubation from invasive mechanical ventilation at an academic medical center, protocolized postextubation respiratory support, primarily characterized by an increase in the use of high-flow nasal cannula, did not prevent reintubation compared with usual care. Clinical trial registered with www.clinicaltrials.gov (NCT0328831).

Background: The optimal timing for the de-escalation of broad-spectrum antibiotics with activity against Pseudomonas aeruginosa and resistant Gram-negative rods (GNRs) in critically ill adults remains unknown. Research Question: We tested the hypothesis that cultures will identify GNRs that ultimately demonstrate resistance to ceftriaxone within 48 hours, potentially allowing safe de-escalation at this time point. Study Design and Methods: We conducted a secondary analysis of data from the Isotonic Solutions and Major Adverse Renal Events Trial: a pragmatic, cluster-randomized, multiple-crossover trial comparing balanced crystalloids versus saline for intravenous fluid administration in 15,802 critically ill adults at 5 intensive care units (ICUs) at Vanderbilt University Medical Center in Nashville, TN, USA. The primary endpoint was the time-to-positivity of respiratory and blood cultures that ultimately demonstrated growth of GNRs resistant to ceftriaxone. Multivariable logistic regression modeling was used to examine risk factors for the growth of cultures after 48 hours. Results: A total of 524 respiratory cultures had growth of GNRs, of which 284 (54.2%) had resistance to ceftriaxone. A total of 376 blood cultures grew GNRs, of which 70 (18.6%) had resistance to ceftriaxone. At 48 hours, 87% of respiratory cultures and 85% of blood cultures that ultimately grew GNRs resistant to ceftriaxone had demonstrated growth. Age, gender, predicted risk of inpatient mortality and prior use of antibiotics did not predict the growth of cultures after 48 hours. Interpretation: Among a cohort of critically ill adults, 13% of respiratory cultures and 15% of blood cultures that ultimately grew GNRs resistant to ceftriaxone did not demonstrate growth until at least 48 hours after collection. Further work is needed to determine the ideal time for critically ill adults to de-escalate from broad-spectrum antibiotics targeting Pseudomonas aeruginosa and extended-spectrum β-lactamase-producing gram-negative pathogens.

Introduction Age-related immunosenescence influences the presentation of tuberculosis (TB) in older patients. Here, we explore the clinical and radiological presentation of TB in the elderly and the factors associated with time to treatment for TB. Methods This is a retrospective cohort study comparing the clinical, radiological and demographic characteristics of TB patients aged ≥65 years with TB patients aged 18–64 years in a large cohort of TB patients in the UK. Factors associated with the time to presentation and time to treatment were identified using a multivariable analysis model. Results 1023 patients were included in the analyses: 679 patients aged 18–64 years and 344 patients aged ≥65 years. “Classical” symptoms of TB (cough, haemoptysis, fever, nights sweats and weight loss) were less common among older patients with pulmonary TB (PTB) (p, A retrospective UK study in patients with TB shows only age remains an independent predictor of time to treatment in a multivariable model. Older patients have fewer of the “classical” clinical and radiological features of TB compared with younger patients. http://bit.ly/2yHc0OL

IntroductionFollowing extubation from invasive mechanical ventilation, nearly one in seven critically ill adults requires reintubation. Reintubation is independently associated with increased mortality. Postextubation respiratory support (non-invasive ventilation or high-flow nasal cannula applied at the time of extubation) has been reported in small-to-moderate-sized trials to reduce reintubation rates among hypercapnic patients, high-risk patients without hypercapnia and low-risk patients without hypercapnia. It is unknown whether protocolised provision of postextubation respiratory support to every patient undergoing extubation would reduce the overall reintubation rate, compared with usual care.Methods and analysisThe Protocolized Post-Extubation Respiratory Support (PROPER) trial is a pragmatic, cluster cross-over trial being conducted between 1 October 2017 and 31 March 2019 in the medical intensive care unit of Vanderbilt University Medical Center. PROPER compares usual care versus protocolized post-extubation respiratory support (a respiratory therapist-driven protocol that advises the provision of non-invasive ventilation or high-flow nasal cannula based on patient characteristics). For the duration of the trial, the unit is divided into two clusters. One cluster receives protocolised support and the other receives usual care. Each cluster crosses over between treatment group assignments every 3 months. All adults undergoing extubation from invasive mechanical ventilation are enrolled except those who received less than 12 hours of mechanical ventilation, have ‘Do Not Intubate’ orders, or have been previously reintubated during the hospitalisation. The anticipated enrolment is approximately 630 patients. The primary outcome is reintubation within 96 hours of extubation.Ethics and disseminationThe trial was approved by the Vanderbilt Institutional Review Board. The results will be submitted for publication in a peer-reviewed journal and presented at one or more scientific conferences.Trial registration numberNCT03288311.

ObjectiveThe aim of this study was to determine the occurrence of latent tuberculosis infections (LTBI) and active TB in a cohort of patients with inflammatory bowel disease (IBD) treated with biologics. We also examined the effects of immunosuppressive drugs on indeterminate interferon-gamma release assays (IGRA) in LTBI screening.DesignRetrospective study of patients treated with biologics between March 2007 and November 2015.SettingSt Mark’s Hospital, North West London, UK.Patients732 patients with IBD who were screened for LTBI using either tuberculin skin test or IGRA before starting a biologic treatment.MethodsRetrospective case note review of all patients with IBD who were screened for LTBI prior to initiating biologics. Patients who developed active TB were identified from the London TB register.ResultsOf 732 patients with IBD, 31 (4.2%) were diagnosed with and treated for LTBI with no significant side effects. Six of 596 patients (1.0%) who received biologic treatment developed active TB. There was a higher proportion of indeterminate IGRA in the immunosuppressive medication group compared with the non-immunosuppressive group (33% (59/181) compared with 9% (6/66), pConclusionsThis study highlights the challenges of LTBI screening prior to commencing biologic therapy and demonstrates the risk of TB in patients who have been screened and who are receiving prolonged and continuing doses of antitumour necrosis factor.

There are an estimated 35 million people living with human immunodeficiency virus (HIV) globally, 19 million of whom are unaware of their HIV status and, in the absence of antiretroviral therapy (ART), will have a shortened life expectancy. Although ART remains the "gold standard" for treatment of HIV infection, the requirement for lifelong treatment poses multiple challenges for the patient. These include stigma, an untenable pill burden, side effects, and the threat of viral resistance in the case of non-compliance. This review evaluates the challenges of accessing, delivering, and sustaining ART for people living with HIV and will discuss the case for pursuing a goal of HIV cure, the potential benefits of such a cure for the individual patient, and the current potential candidates for such a cure.

Background: Scientific literature can contain errors. Discrepancies, defined as two or more statements or results that cannot both be true, may be a signal of problems with a trial report. In this study, we report how many discrepancies are detected by a large panel of readers examining a trial report containing a large number of discrepancies. Methods: We approached a convenience sample of 343 journal readers in seven countries, and invited them in person to participate in a study. They were asked to examine the tables and figures of one published article for discrepancies. 260 participants agreed, ranging from medical students to professors. The discrepancies they identified were tabulated and counted. There were 39 different discrepancies identified. We evaluated the probability of discrepancy identification, and whether more time spent or greater participant experience as academic authors improved the ability to detect discrepancies. Results: Overall, 95.3% of discrepancies were missed. Most participants (62%) were unable to find any discrepancies. Only 11.5% noticed more than 10% of the discrepancies. More discrepancies were noted by participants who spent more time on the task (Spearman’s ρ = 0.22, P

Empyema necessitans is a complication of a pleural space infection that dissects through the pleura into the soft tissues of the chest and skin. Due to the widespread availability of antibiotics, empyema necessitans is rare in modern medicine and is most commonly caused by Mycobacterium tuberculosis. A 38-year-old immunocompetent male presented with left shoulder pain and his chest radiograph revealed a mass in the upper left lung and/or pleural space. He underwent multiple debridements of the chest wall due to a left chest wall abscess and empyema necessitans. All operative samples were positive for Streptococcus agalactiae (Group B Streptococcus). The patient's clinical course was complicated by septic arthritis of the left sternoclavicular joint and first rib, vertebral osteomyelitis/discitis, and pelvic abscesses. This case report illustrates the pathogenic process of empyema necessitans and summarizes the clinical management for practicing clinicians. It also documents the second case of Streptococcus agalactiae-associated empyema necessitans, to our knowledge, with significantly greater disease extension than the first.

IntroductionCauda equina syndrome (CES) is a neurosurgical emergency. Early diagnosis with MRI and subsequent surgical decompression surgery can prevent permanent neurological dysfunction. Charing Cross Hospital (CXH) is a tertiary neurosurgical referral centre where in the emergency department (ED), current practice mandated a neurosurgery review prior to requesting MRI.HypothesisIt was hypothesised that a new clinical pathway, with better coordination from the ED, radiology and neurosurgical teams could reduce the time of presentation to diagnosis or exclusion of CES.MethodRetrospective case-note analysis of patients presenting with back pain to CXH ED over a 3-month period was performed. The primary outcome was the time interval between the patient’s arrival to the ED and the MRI preliminary report.ResultsThe baseline primary outcome was recorded at 8 hours and 16 min (n=30). A new clinical pathway was designed empowering ED senior decision makers to order MRIs prior to neurosurgical review. Two Plan-Do-Study-Act (PDSA) cycles were performed, each measured over a 2-month period. The first PDSA cycle was performed after the pathway was initially launched (n=17), while the second PDSA cycle measured the effect of staff education and active promotion of the pathway (n=17). MRI was requested earlier, waiting and reporting time for MRI were reduced. The exclusion or diagnosis of CES was reduced to 5 hours and 54 min in PDSA 1 and 5 hours 17 min in PDSA 2, a 29% and 36% reduction (p=0.048 and p=0.012, respectively).ConclusionThe clinical protocol was a cost-neutral and sustainable intervention that effectively reduced the time taken to diagnose or exclude CES and ED waiting times.

ATP is a known mediator of inflammatory and neuropathic pain. However, the mechanisms by which specific purinergic receptors contribute to chronic pain states are still poorly characterized. Here, we demonstrate that in response to peripheral nerve injury, P2X4receptors (P2X4R) are expressedde novoby activated microglia in the spinal cord. Usingin vitroandin vivomodels, we provide direct evidence that P2X4R stimulation leads to the release of BDNF from activated microglia and, most likely phosphorylation of the NR1 subunit of NMDA receptors in dorsal horn neurons of the spinal cord. Consistent with these findings, P2X4-deficient mice lack mechanical hyperalgesia induced by peripheral nerve injury and display impaired BDNF signaling in the spinal cord. Furthermore, ATP stimulation is unable to stimulate BDNF release from P2X4-deficient mice microglia in primary cultures. These results indicate that P2X4R contribute to chronic pain through a central inflammatory pathway. P2X4R might thus represent a potential therapeutic target to limit microglia-mediated inflammatory responses associated with brain injury and neurodegenerative disorders.

This is a study of the HTLV-1/HIV-1 co-infected cohort attending the National Centre for Human Retrovirology in London. In a retrospective analysis, demographic, clinical, immunological and virological data was described. A subgroup of patients on combination antiretroviral therapy (cART) for more than twelve months with an undetectable HIV viral load was identified and compared to a matched HTLV-1 mono-infected group. In an ongoing prospective study, HIV-1 mono-infected patients are recruited and virological and immunological parameters compared to the HTLV/HIV co-infected and HTLV mono-infected groups. 29 co-infected patients had a median age of 47 years, 55% were male and over 80% identified with the Black – African/Caribbean ethnic group. The median time on cART was 6 months. CD4/CD4% cell counts were lower in stable co-infected patients (508 cells/mm3, p=0.2 / 27.9%, p

Cell fusion is a central phenomenon during the immune response that leads to formation of large elements called multinucleated giant cells (MGCs) of common occurrence at sites of granulomatous inflammation. We have previously reported on the involvement in this event of a novel receptor expressed to high level by mononuclear phagocytes, the purinergic P2X7receptor. Herein, we show that blockade of this receptor by a specific monoclonal antibody prevents fusion in vitro. In contrast, cell fusion is stimulated by addition of enzymes that destroy extracellular ATP (i.e., apyrase or hexokinase). Experiments performed with phagocytes selected for high (P2X7hyper) or low (P2X7hypo) P2X7expression show that fusion only occurs between P2X7hyper/P2X7hyper and not between P2X7hyper/P2X7hypo or P2X7hypo/P2X7hypo. During MGCs formation we detected activation of caspase 3, an enzyme that is powerfully stimulated by P2X7. Finally, we observed that during MGCs formation, the P2X7receptor is preferentially localized at sites of cell-to-cell contact. These findings support the hypothesis originally put forward by our group that the P2X7receptor participates in multinucleated giant cell formation.

P2X receptors are membrane proteins that incorporate a cation-selective ion channel that can be opened by the binding of extracellular ATP. They associate as hetero- and homo-multimers of currently unknown stoichiometry. In this study, we have used Xenopus laevis oocytes to express rat P2X(2) receptor subunits, which carry a cysteine mutation at position 336. ATP-induced currents at this mutant receptor subunit were blocked by more than 90% when exposed to [2-(trimethylammonium) ethyl] methanethiosulfonate (MTSET), whereas currents from wild-type subunits were not affected. To compare mutant and wild-type channel expression, we introduced an epitope in their extracellular domains and found for both channels a similar linear relationship between antibody binding and currents induced by ATP. To study the contribution of the individual subunits to the block by MTSET, we coinjected different mixtures of wild-type and mutant-encoding mRNAs. We found that the inhibition by MTSET depended linearly on the proportion of mutant subunits, which was clearly contrary to the hypothesis that a single mutant subunit could act in a dominant fashion. Subsequent concatenation of wild-type and mutant-encoding cDNAs resulted in an inhibition by MTSET that also depended linearly on the number of mutant subunits and was independent of the position of the mutant subunit, as long as only two or three P2X(2) subunits were joined. With four or six subunits joined, however, the inhibition by MTSET became strongly position-dependent. The present results show that a "per-subunit" channel block causes the blocking effects of MTSET and they suggest that not four but maximally three subunits actively participate in the channel formation.

Signaling by extracellular nucleotides through P2 purinergic receptors affects diverse macrophage functions; however, its role in regulating antimicrobial radicals during bacterial infection has not been investigated. Mycobacterium tuberculosis-infected macrophages released ATP in a dose-dependent manner, which correlated with nitrite accumulation. P2 receptor inhibitors, including oxidized ATP, blocked NO synthase (NOSII) up-regulation and NO production induced by infection with M. tuberculosis or bacille Calmette-Guérin, or treatment with LPS or TNF-α. Oxidized ATP also inhibited oxygen radical production and activation of NF-κB and AP-1 in response to infection and inhibited NO-dependent killing of bacille Calmette-Guérin by macrophages. Experiments using macrophages derived from P2X7 gene-disrupted mice ruled out an essential role for P2X7 in NOSII regulation. These data demonstrate that P2 receptors regulate macrophage activation in response to bacteria and proinflammatory stimuli, and suggest that extracellular nucleotides released from infected macrophages may enhance production of oxygen radicals and NO at sites of infection.

The P2X3 receptor subunit, a member of the P2X family of ATP-gated ion channels, is almost exclusively localized in sensory neurons. In the present study, we sought to gain insight into the role of P2X3 and P2X3-containing neurons in sensory transmission, using immunohistochemical approaches. In rat dorsal root ganglia (DRG), P2X3-immunoreactivity (-ir) was observed in small- and medium-sized neurons. Approximately 40% of DRG neuronal profiles in normal rats contained P2X3-ir. In rats that had received neonatal capsaicin treatment, the number of P2X3-positive neurons was decreased by approximately 70%. Analysis of the colocalization of P2X3-ir with cytochemical markers of DRG neurons indicated that approximately 94% of the P2X3-positive neuronal profiles were labelled by isolectin B4 from Bandeiraea simplicifolia, while only 3% contained substance P-ir, and 7% contained somatostatin-ir. In dorsal horn of rat spinal cord, P2X3-ir was observed in the inner portion of lamina II and was reduced subsequent to dorsal rhizotomy, as well as subsequent to neonatal capsaicin treatment. Finally, P2X3-ir accumulated proximal to the site of sciatic nerve ligation, and was seen in nerve fibres in skin and corneal epithelium. In summary, our results suggest that P2X3 is expressed by a functionally heterogeneous population of BSI-B4-binding sensory neurons, and is transported into both central and peripheral processes of these neurons.

Studies made during the past four years have reported the cDNA cloning of P2X receptors and their electrophysiologic evaluation. More recently, mutagenesis and protein biochemistry approaches have begun to assign functions to specific regions in these proteins. These functions include the agonist and antagonist binding profiles of different P2X receptors and their ability to form nonselective cationic channels. The work has also shed light on how the physiologic ligand for P2X receptors, extracellular ATP, can have effects in both the nervous and immune systems. One member of the P2X receptor family, i.e., P2X7, is selectively expressed in the immune system. This receptor is a bifunctional molecule, generating both a cationic channel and a macromolecular pore, whose activation can result in permeabilization of the cell. Drug Dev. Res. 45:125–129, 1998. © 1998 Wiley-Liss, Inc.

A cDNA was isolated from a human monocyte library that encodes the P2X7 receptor; the predicted protein is 80% identical to the rat receptor. Whole cell recordings were made from human embryonic kidney cells transfected with the human cDNA and from human macrophages. Brief applications (1-3 s) of ATP and 2′,3′-(4-benzoyl)-benzoyl-ATP elicited cation-selective currents. When compared with the rat P2X7 receptor, these effects required higher concentrations of agonists, were more potentiated by removal of extracellular magnesium ions, and reversed more rapidly on agonist removal. Longer applications of agonists permeabilized the cells, as evidenced by uptake of the propidium dye YO-PRO1, but this was less marked than for cells expressing the rat P2X7 receptor. Expression of chimeric molecules indicated that some of the differences between the rat and human receptor could be reversed by exchanging the intracellular C-terminal domain of the proteins.

Mouse and human macrophages express a plasma membrane receptor for extracellular ATP named P2Z/P2X7. This molecule, recently cloned, is endowed with the intriguing property of forming an aqueous pore that allows transmembrane fluxes of hydrophylic molecules of molecular weight below 900. The physiological function of this receptor is unknown. In a previous study we reported experiments suggesting that the P2Z/P2X7 receptor is involved in the formation of macrophage-derived multinucleated giant cells (MGCs; Falzoni, S., M. Munerati, D. Ferrari, S. Spisani, S. Moretti, and F. Di Virgilio. 1995. J. Clin. Invest. 95:1207– 1216). We have selected several clones of mouse J774 macrophages that are characterized by either high or low expression of the P2Z/P2X7 receptor and named these clones P2Zhyper or P2Zhypo, respectively. P2Zhyper, but not P2Zhypo, cells grown to confluence in culture spontaneously fuse to form MGCs. As previously shown for human macrophages, fusion is inhibited by the P2Z/P2X7 blocker oxidized ATP. MGCs die shortly after fusion through a dramatic process of cytoplasmic sepimentation followed by fragmentation. These observations support our previous hypothesis that the P2Z/P2X7 receptor is involved in macrophage fusion.

ATP-gated ion channels (P2X receptors) are abundantly expressed in both neuronal and nonneuronal tissues, where they can serve as postsynaptic receptors. The response to ATP shows marked desensitization in some tissues but not others. Currents induced by ATP in Xenopus oocytes expressing cloned P2X 1 (or P2X 3 ) receptors had strong desensitization, whereas currents in cells expressing P2X 2 receptors desensitized relatively little (90% vs. 14% decline of current in a 10-s application). In chimeric receptors, substitution into the P2X 1 receptor of either one of two 34-residue segments from the P2X 2 receptor removed the desensitization; these segments included the first or the second hydrophobic domain. In contrast, desensitization was introduced into the P2X 2 receptor only by providing both these segments of the P2X 1 (or P2X 3 ) receptor. This suggests that desensitization requires interaction between the two hydrophobic domains of the receptor, and supports the view that these are membrane-spanning segments.

Previous reports indicate that intestinal intraluminal ethanol increases mucosal permeability (an index of mucosal injury) and histamine release by mast cells, and that the released histamine plays a role in mediating the increased permeability. In the present study, we investigated whether reactive oxygen metabolites and their major sources (xanthine oxidase and leukocytes) were involved in these ethanol effects. In rabbits, segments of the jejunum were perfused with a control solution or with 6% ethanol. In these segments, mucosal permeability was assessed by determining jejunal clearance of i.v. administered 51Cr-ethylenediaminetetraacetate (51Cr-EDTA) and 125I-bovine serum albumin (125I-BSA), and mast cell histamine release was estimated from the histamine concentration of the gut effluent. Ethanol increased 51Cr-EDTA clearance, 125I-BSA clearance, and histamine release. These ethanol effects decreased when the animals were given superoxide dismutase plus catalase (scavenger of O2- and H2O2, respectively), allopurinol, or oxypurinol (xanthine oxidase inhibitors). Administration of a monoclonal antibody (R15.7) against leukocyte adhesion molecule, CD18, inhibited completely the ethanol-induced increased 51Cr-EDTA and 125I-BSA clearances and histamine release. These and supplementary data suggest that (a) ethanol-induced mucosal injury and mast cell histamine release are mediated primarily by leukocytes, and (b) oxy radicals, especially those generated by xanthine oxidase, mediate these ethanol effects mainly by promoting leukocyte infiltration.

New exciting developments on the occurrence and functional role of purinoceptors in mammalian brain were presented at the session Purinoceptors in the central nervous system chaired by Flaminio Cattabeni and Tom Dunwiddie at the Purines '96 international conference. The focus of the session were topics of recent interest, including the sources and mechanisms involved in ATP and adenosine release during physiological neurotransmission in hippocampus, the brain expression of the recently cloned P2 receptors, and the role of the various adenosine receptor subtypes in brain protection from neurodegeneration associated with trauma-, ischemia- and excessive excitatory amino acid neurotransmission. New important insights into the mechanisms responsible for the formation and release of adenosine into the extracellular space were provided by data obtained by Dunwiddie and coworkers in hippocampal pyramidal neurons. These data may have functional implications for the role of purines in modulation of synaptic plasticity and long-term potentiation in this brain area, and hence in cognitive functions. Buell provided an updated overview on the cloning, molecular characteristics and brain expression of various ligand-gated P2X purinoceptors; although the functional role of these receptors in mammalian brain still awaits elucidation, their widespread distribution in the nervous system strongly suggests that ATP-mediated events are more prevalent and important in brain than expected. Pedata presented data on the functional interrelationships between adenosine and glutamate in the brain, and also provided evidence for alterations of the reciprocal regulation between these two systems in aged brain, which may have important implications for both ischemia- and trauma-associated neurodegenerative events and senescence-associated cognitive impairment. Finally, von Lubitz provided novel data on the molecular mechanisms likely to be at the basis of the brain protective effects associated with the chronic stimulation of the adenosine A 3 receptor, further confirming that this receptor represents a crucial target for the development of new antiischemic and antineurodegenerative therapeutic agents.

In the immune system, apoptosis is involved in intrathymic elimination of self-reactive thymocytes and in peripheral T cell tolerance to exogenous antigens. Here, we describe the role in T cell apoptosis of P(2x1), a nonselective cation channel activated by ATP. P(2X1) molecules are up-regulated in thymocytes during dexamethasone-induced apoptosis, and antagonists to these receptors protect thymocytes from cell death. Moreover, P(2X1) mRNA and protein levels increase in thymocytes induced to die in vivo by the superantigen staphylococcal enterotoxin B. In contrast, T cells undergoing apoptosis in the periphery do not express P(2X1). The demonstration that P(2X1) ion channels play a role in the apoptosis of thymocytes but not peripheral T cells illustrates a novel mechanism contributing to thymocyte cell death and opens new possibilities for investigating clonal deletion in the thymus.

Several P2X receptor subunits were recently cloned; of these, one was cloned from the rat vas deferens (P2X1) and another from pheochromocytoma (PC12) cells differentiated with nerve growth factor (P2X2). Peptides corresponding to the C-terminal portions of the predicted receptor proteins (P2X1 391-399 and P2X2 460-472) were used to generate antisera in rabbits. The specificities of antisera were determined by staining human embryonic kidney cells stably transfected with either P2X1 or P2X2 receptors and by absorption controls with the cognate peptides. In the vas deferens and the ileal submucosa, P2X1 immunoreactivity (ir) was restricted to smooth muscle, whereas P2X2-ir was restricted to neurons and their processes. Chromaffin cells of the adrenal medulla and PC12 cells contained both P2X1- and P2X2-ir. P2X1-ir was also found in smooth muscle cells of the bladder, cardiac myocytes, and nerve fibers and terminals in the superficial dorsal horn of the spinal cord. In contrast, P2X2-ir was observed in scattered cells of the anterior pituitary, neurons in the hypothalamic arcuate and paraventricular nuclei, and catecholaminergic neurons in the olfactory bulb, the substantia nigra, ventral tegmental area, and locus coeruleus. A plexus of nerve fibers and terminals in the nucleus of the solitary tract contained P2X2-ir. This staining disappeared after nodose ganglionectomy, consistent with a presynaptic function. The location of the P2X1 subunit in smooth muscle is consistent with its role as a postjunctional receptor in autonomic transmission, while in neurons, these receptors appear in both postsynaptic and presynaptic locations.

The P2Z receptor is responsible for adenosine triphosphate (ATP)-dependent lysis of macrophages through the formation of membrane pores permeable to large molecules. Other ATP-gated channels, the P2X receptors, are permeable only to small cations. Here, an ATP receptor, the P2X7 receptor, was cloned from rat brain and exhibited both these properties. This protein is homologous to other P2X receptors but has a unique carboxyl-terminal domain that was required for the lytic actions of ATP. Thus, the P2X7 (or P2Z) receptor is a bifunctional molecule that could function in both fast synaptic transmission and the ATP-mediated lysis of antigen-presenting cells.