Gene T. Yocum

Neurocognitive Performance in Hypertensive Patients after Spine Surgery

Background:Cognitive dysfunction is fairly common after noncardiac surgery and may be related to intraoperative blood pressure management. The authors present an analysis of risk factors for cognitive deterioration after spine surgery in older patients, with particular emphasis on intraoperative blood pressure in normotensive and hypertensive patients. Methods:This is a post hoc cohort analysis of 45 patients enrolled before undergoing lumbar laminectomy or microdiscectomy. The patients underwent a battery of 5 neuropsychometric tests preoperatively, and 1 day and 1 month postoperatively. Computerized anesthesia records were used to obtain intraoperative mean arterial pressure (MAP) data. Simple linear regressions between intraoperative MAP and postoperative cognitive performance were performed, and multivariate linear regression models of postoperative cognitive performance were constructed to analyze potential risk factors for cognitive decline after surgery. Results:Twenty-one normotensive patients (mean age, 62.4 yr) and 24 hypertensive patients (mean age, 67.9 yr) were included in this analysis. There was a significant positive relationship between minimum intraoperative MAP values and 1-day cognitive performance by simple linear regression in hypertensive (P = 0.003), but not normotensive, patients. In multivariate linear regression analysis of cognitive performance, there was a significant interaction between hypertension and minimum intraoperative MAP at 1 day and 1 month. Conclusions:In hypertensive patients, there was a significant relationship between minimum intraoperative MAP and decline in cognitive function 1 day and 1 month after surgery. A prospective controlled trial of intraoperative blood pressure control, especially during induction of anesthesia when MAP values typically drop, is needed to confirm these findings.

Inducible Nitric Oxide Synthase Promoter Polymorphism Affords Protection Against Cognitive Dysfunction After Carotid Endarterectomy

BACKGROUND AND PURPOSE Cognitive dysfunction occurs in 9% to 23% of patients during the first month after carotid endarterectomy (CEA). A 4-basepair (AAAT) tandem repeat polymorphism (either 3 or 4 repeats) has been described in the promoter region of inducible nitric oxide synthase (iNOS), a gene with complex roles in ischemic injury and preconditioning against ischemic injury. We investigated whether the 4-repeat variant (iNOS(+)) affects the incidence of cognitive dysfunction after CEA. METHODS One-hundred eighty-five CEA and 60 spine surgery (control) subjects were included in this nested cohort analysis. Subjects underwent a battery of 7 neuropsychometric tests before and 1 day and 1 month after surgery. Multivariate logistic regression analyses were performed to determine if the iNOS promoter variant was independently associated with the incidence of cognitive dysfunction at 1 day and 1 month. Further, all right-hand-dominant CEA subjects were grouped by operative side and performance on each test was compared between iNOS(+) and iNOS(-) groups. RESULTS Forty-four of 185 CEA subjects had at least 1 iNOS promoter allele containing 4 copies of the tandem repeat (iNOS(+)). iNOS(+) status was significantly protective against moderate/severe cognitive dysfunction 1 month after CEA. Right-hand-dominant iNOS(+) CEA subjects undergoing left-side CEA performed significantly better than iNOS(-) subjects on a verbal learning test and those undergoing right-side CEA performed significantly better on a test of visuospatial function. CONCLUSIONS We demonstrate an iNOS promoter polymorphism variant provides protection against moderate/severe cognitive dysfunction 1 month after CEA. Further, this protection appears to involve cognitive domains localized ipsilateral to the operative carotid artery.

Targeting the γ-Aminobutyric Acid A Receptor α4 Subunit in Airway Smooth Muscle to Alleviate Bronchoconstriction

We previously demonstrated that airway smooth muscle (ASM) cells express γ-aminobutyric acid A receptors (GABA(A)Rs), and that GABA(A)R agonists acutely relax ASM. Among the GABA(A)R α subunits, human ASM cells express only α4 and α5, providing the opportunity for selective pharmacologic targeting. Novel GABA(A)R-positive allosteric modulators designed for enhanced α4/α6 subunit selectivity were synthesized using iterative computational analyses (CMD-45 and XHe-III-74). Studies using oocyte heterologous expression systems confirmed that CMD-45 and XHe-III-74 led to significantly greater augmentation of currents induced by a 3% maximal effective concentration (EC3) of GABA [EC3]-induced currents in oocytes expressing α4 or α6 subunits (along with β3 and γ2) compared with other α subunits. CMD-45 and XHe-III-74 also led to greater ex vivo relaxation of contracted wild-type mouse tracheal rings compared with tracheal rings from GABA(A)R α4 subunit (Gabra4) knockout mice. Furthermore, CMD-45 and XHe-III-74 significantly relaxed precontracted human ASM ex vivo, and, at a low concentration, both ligands led to a significant leftward shift in albuterol-mediated ASM relaxation. In vivo, inhaled XHe-III-74 reduced respiratory system resistance in an asthmatic mouse model. Pretreatment of human ASM cells with CMD-45 and XHe-III-74 inhibited histamine-induced increases in intracellular calcium concentrations in vitro, an effect that was lost when calcium was omitted from the extracellular buffer, suggesting that inhibition of calcium influx due to alterations in plasma membrane potential may play a role in the mechanism of ASM relaxation. Selective targeting of the GABA(A)R α4 subunit with inhaled ligands may be a novel therapeutic pathway to treat bronchoconstriction, while avoiding sedative central nervous system effects, which are largely mediated by α1-3 subunit-containing GABA(A)Rs in the brain.

Development of GABAA Receptor Subtype-Selective Imidazobenzodiazepines as Novel Asthma Treatments

Recent studies have demonstrated that subtype-selective GABAA receptor modulators are able to relax precontracted human airway smooth muscle ex vivo and reduce airway hyper-responsiveness in mice upon aerosol administration. Our goal in this study was to investigate systemic administration of subtype-selective GABAA receptor modulators to alleviate bronchoconstriction in a mouse model of asthma. Expression of GABAA receptor subunits was identified in mouse lungs, and the effects of α4-subunit-selective GABAAR modulators, XHE-III-74EE and its metabolite XHE-III-74A, were investigated in a murine model of asthma (ovalbumin sensitized and challenged BALB/c mice). We observed that chronic treatment with XHE-III-74EE significantly reduced airway hyper-responsiveness. In addition, acute treatment with XHE-III-74A but not XHE-III-74EE decreased airway eosinophilia. Immune suppressive activity was also shown in activated human T-cells with a reduction in IL-2 expression and intracellular calcium concentrations [Ca(2+)]i in the presence of GABA or XHE-III-74A, whereas XHE-III-74EE showed only partial reduction of [Ca(2+)]i and no inhibition of IL-2 secretion. However, both compounds significantly relaxed precontracted tracheal rings ex vivo. Overall, we conclude that the systemic delivery of a α4-subunit-selective GABAAR modulator shows good potential for a novel asthma therapy; however, the pharmacokinetic properties of this class of drug candidates have to be improved to enable better beneficial systemic pharmacodynamic effects.

Role of transient receptor potential vanilloid 1 in the modulation of airway smooth muscle tone and calcium handling

Asthma is a common disorder characterized, in part, by airway smooth muscle (ASM) hyperresponsiveness. Transient receptor potential vanilloid 1 (TRPV1) is a nonselective cation channel expressed on airway nerve fibers that modulates afferent signals, resulting in cough, and potentially bronchoconstriction. In the present study, the TRPV1 transcript was detected by RT-PCR in primary cultured human ASM cells, and the TRPV1 protein was detected in ASM of human trachea by immunohistochemistry. Proximity ligation assays suggest that TRPV1 is expressed in the sarcoplasmic reticulum membrane of human ASM cells in close association with sarco/endoplasmic reticulum Ca2+-ATPase-2. In guinea pig tracheal ring organ bath experiments, the TRPV1 agonist capsaicin led to ASM contraction, but this contraction was significantly attenuated by the sodium channel inhibitor bupivacaine (n = 4, P < 0.05) and the neurokinin-2 receptor antagonist GR-159897 (n = 4, P < 0.05), suggesting that this contraction is neutrally mediated. However, pretreatment of guinea pig and human ASM in organ bath experiments with the TRPV1 antagonist capsazepine inhibited the maintenance phase of an acetylcholine-induced contraction (n = 4, P < 0.01 for both species). Similarly, capsazepine inhibited methacholine-induced contraction of peripheral airways in mouse precision-cut lung slice (PCLS) experiments (n = 4-5, P < 0.05). Although capsazepine did not inhibit store-operated calcium entry in mouse ASM cells in PCLS (n = 4-7, P = nonsignificant), it did inhibit calcium oscillations (n = 3, P < 0.001). These studies suggest that TRPV1 is expressed on ASM, including the SR, but that ASM TRPV1 activation does not play a significant role in initiation of ASM contraction. However, capsazepine does inhibit maintenance of contraction, likely by inhibiting calcium oscillations.

Alleviation of Multiple Asthmatic Pathologic Features with Orally Available and Subtype Selective GABAA Receptor Modulators

We describe pharmacokinetic and pharmacodynamic properties of two novel oral drug candidates for asthma. Phenolic α4β3γ2 GABAAR selective compound 1 and acidic α5β3γ2 selective GABAAR positive allosteric modulator compound 2 relaxed airway smooth muscle ex vivo and attenuated airway hyperresponsiveness (AHR) in a murine model of asthma. Importantly, compound 2 relaxed acetylcholine contracted human tracheal airway smooth muscle strips. Oral treatment of compounds 1 and 2 decreased eosinophils in bronchoalveolar lavage fluid in ovalbumin sensitized and challenged mice, thus exhibiting anti-inflammatory properties. Additionally, compound 1 reduced the number of lung CD4+ T lymphocytes and directly modulated their transmembrane currents by acting on GABAARs. Excellent pharmacokinetic properties were observed, including long plasma half-life (up to 15 h), oral availability, and extremely low brain distribution. In conclusion, we report the selective targeting of GABAARs expressed outside the brain and demonstrate reduction of AHR and airway inflammation with two novel orally available GABAAR ligands.

GABAA receptor α4-subunit knockout enhances lung inflammation and airway reactivity in a murine asthma model

Emerging evidence indicates that hypnotic anesthetics affect immune function. Many anesthetics potentiate γ-aminobutyric acid A receptor (GABAAR) activation, and these receptors are expressed on multiple subtypes of immune cells, providing a potential mechanistic link. Like immune cells, airway smooth muscle (ASM) cells also express GABAARs, particularly isoforms containing α4-subunits, and activation of these receptors leads to ASM relaxation. We sought to determine if GABAAR signaling modulates the ASM contractile and inflammatory phenotype of a murine allergic asthma model utilizing GABAAR α4-subunit global knockout (KO; Gabra40/0 ) mice. Wild-type (WT) and Gabra4 KO mice were sensitized with house dust mite (HDM) antigen or exposed to PBS intranasally 5 days/wk for 3 wk. Ex vivo tracheal rings from HDM-sensitized WT and Gabra4 KO mice exhibited similar magnitudes of acetylcholine-induced contractile force and isoproterenol-induced relaxation (P = not significant; n = 4). In contrast, in vivo airway resistance (flexiVent) was significantly increased in Gabra4 KO mice (P < 0.05, n = 8). Moreover, the Gabra4 KO mice demonstrated increased eosinophilic lung infiltration (P < 0.05; n = 4) and increased markers of lung T-cell activation/memory (CD62L low, CD44 high; P < 0.01, n = 4). In vitro, Gabra4 KO CD4+ cells produced increased cytokines and exhibited increased proliferation after stimulation of the T-cell receptor as compared with WT CD4+ cells. These data suggest that the GABAAR α4-subunit plays a role in immune cell function during allergic lung sensitization. Thus GABAAR α4-subunit-specific agonists have the therapeutic potential to treat asthma via two mechanisms: direct ASM relaxation and inhibition of airway inflammation.

A Novel Orally Available Asthma Drug Candidate That Reduces Smooth Muscle Constriction and Inflammation by Targeting GABAA Receptors in the Lung

We describe lead compound MIDD0301 for the oral treatment of asthma based on previously developed positive allosteric α5β3γ2 selective GABAA receptor (GABAAR) ligands. MIDD0301 relaxed airway smooth muscle at single micromolar concentrations as demonstrated with ex vivo guinea pig tracheal rings. MIDD0301 also attenuated airway hyperresponsiveness (AHR) in an ovalbumin murine model of asthma by oral administration. Reduced numbers of eosinophils and macrophages were observed in mouse bronchoalveolar lavage fluid without changing mucous metaplasia. Importantly, lung cytokine expression of IL-17A, IL-4, and TNF-α were reduced for MIDD0301-treated mice without changing antiinflammatory cytokine IL-10 levels. Automated patch clamp confirmed amplification of GABA induced current mediated by α1-3,5β3γ2 GABAARs in the presence of MIDD0301. Pharmacodynamically, transmembrane currents of ex vivo CD4+ T cells from asthmatic mice were potentiated by MIDD0301 in the presence of GABA. The number of CD4+ T cells observed in the lung of MIDD0301-treated mice were reduced by an oral treatment of 20 mg/kg b.i.d. for 5 days. A half-life of almost 14 h was demonstrated by pharmacokinetic studies (PK) with no adverse CNS effects when treated mice were subjected to sensorimotor studies using the rotarod. PK studies also confirmed very low brain distribution. In conclusion, MIDD0301 represents a safe and improved oral asthma drug candidate that relaxes airway smooth muscle and attenuates inflammation in the lung leading to a reduction of AHR at a dosage lower than earlier reported GABAAR ligands.