Incorporating SPACES recommendations to the COVID-19 ward care approach at the Royal Bournemouth Hospital

The British Thoracic Society have published SPACES (Sharing Patient Assessments Cuts Exposure for Staff) guidance recommending the use of telecommunications as a means of inpatient clinical assessment during the COVID-19 pandemic. The aim of this audit was to reduce face-to-face exposure time during inpatient care of patients with suspected/confirmed COVID-19 using a telecommunications-based approach. 76 patients were included in the audit. 46 patients were included in cycle 1, which measured the average face-to-face time for clinical consultation per patient. 30 patients were included in cycle 2, whereby history-taking was conductedusing telecommunications and, if required, face-to-face physical examination.Average face-to-face exposure time was reduced to a median of 0 seconds (IQR 0-146.3 seconds) in the telecommunications group, from a median of 312.5 seconds (IQR 178.8-442.3 seconds) in the comparator group (p<0.0001). Patient satisfaction was high with individuals' responses revealing a perception of improved safety by maintaining social distancing. No adverse events were noted.The audit confirms telecommunications can be integrated successfully into the daily inpatient ward round structure, reducing face-to-face exposure time while maintaining patient satisfaction and safety.

A Case Series of Patients with Isolated IgG4-related Hypophysitis Treated with Rituximab

Context

The acute presentation of immunoglobulin G4 (IgG4)-related hypophysitis can be indistinguishable from other forms of acute hypophysitis, and histology remains the diagnostic gold standard. The high recurrence rate necessitates long-term immunosuppressive therapy. Rituximab (RTX) has been shown to be effective in systemic IgG4-related disease (IgG4-RD), but experience with isolated pituitary involvement remains limited.

Case Description

We report 3 female patients with MRI findings suggestive of hypophysitis. All patients underwent transsphenoidal biopsy and fulfilled diagnostic criteria for IgG4-related hypophysitis. Treatment with glucocorticoids (GCs) resulted in good therapeutic response in Patients 1 and 2, but the disease recurred on tapering doses of GCs. GC treatment led to emotional lability in Patient 3, necessitating a dose reduction. All 3 patients received RTX and Patients 2 and 3 received further courses of treatment when symptoms returned and B-cells repopulated. Patient 3 did not receive RTX until 12 months from the onset of symptoms. Patient 1 was not able to have further RTX treatments due to an allergic reaction when receiving the second dose. Rituximab treatment resulted in sustained remission and full recovery of anterior pituitary function in Patients 1 and 2, with complete resolution of pituitary enlargement. By contrast, Patient 3 only showed a symptomatic response following RTX treatment, but pituitary enlargement and hypofunction persisted.

Conclusion

Rituximab treatment for IgG4-related hypophysitis resulted in sustained remission in 2 patients treated early in the disease process but only achieved partial response in a patient with chronic disease, suggesting that early therapeutic intervention may be crucial in order to avoid irreversible changes.

Minimally Invasive Repair of Sacroiliac Luxation

Sacroiliac fracture-luxation is a common injury that is associated with ilial and acetabular fractures of the opposite hemipelvis. Sacroiliac fracture-luxation results in an unstable pelvis and potentially collapse of the pelvic canal. A minimally invasive approach to the reduction and insertion of a screw for fixation of sacroiliac fracture-luxation using fluoroscopic guidance is viable. The advantages of using this technique are that a small incision is made with minimal soft tissue disruption and the surgical time is short. Recent publications have documented that this technique provided superior repair of sacroiliac fracture-luxations.

Evidence for a protective role for the rs805305 single nucleotide polymorphism of dimethylarginine dimethylaminohydrolase 2 (DDAH2) in septic shock through the regulation of DDAH activity

BACKGROUND

Dimethylarginine dimethylaminohydrolase 2 (DDAH2) regulates the synthesis of nitric oxide (NO) through the metabolism of the endogenous inhibitor of nitric oxide synthase, asymmetric dimethylarginine (ADMA). Pilot studies have associated the rs805305 SNP of DDAH2 with ADMA concentrations in sepsis. This study explored the impact of the rs805305 polymorphism on DDAH activity and outcome in septic shock.

METHODS

We undertook a secondary analysis of data and samples collected during the Vasopressin versus noradrenaline as initial therapy in septic shock (VANISH) trial. Plasma and DNA samples isolated from 286 patients recruited into the VANISH trial were analysed. Concentrations of L-Arginine and the methylarginines ADMA and symmetric dimethylarginine (SDMA) were determined from plasma samples. Whole blood and buffy-coat samples were genotyped for polymorphisms of DDAH2. Clinical data collected during the study were used to explore the relationship between circulating methylarginines, genotype and outcome.

RESULTS

Peak ADMA concentration over the study period was associated with a hazard ratio for death at 28 days of 3.3 (95% CI 2.0-5.4), p < 0.001. Reduced DDAH activity measured by an elevated ADMA:SDMA ratio was associated with a reduced risk of death in septic shock (p = 0.03). The rs805305 polymorphism of DDAH2 was associated with reduced DDAH activity (p = 0.004) and 28-day mortality (p = 0.02). Mean SOFA score and shock duration were also reduced in the less common G:G genotype compared to heterozygotes and C:C genotype patients (p = 0.04 and p = 0.02, respectively).

CONCLUSIONS

Plasma ADMA is a biomarker of outcome in septic shock, and reduced DDAH activity is associated with a protective effect. The polymorphism rs805305 SNP is associated with reduced mortality, which is potentially mediated by reduced DDAH2 activity.

TRIAL REGISTRATION

ISRCTN Registry, ISRCTN20769191 . Registered on 20 September 2012.

Motion-corrected multiparametric renal arterial spin labelling at 3 T: reproducibility and effect of vasodilator challenge

OBJECTIVES

We investigated the feasibility and reproducibility of free-breathing motion-corrected multiple inversion time (multi-TI) pulsed renal arterial spin labelling (PASL), with general kinetic model parametric mapping, to simultaneously quantify renal perfusion (RBF), bolus arrival time (BAT) and tissue T₁.

METHODS

In a study approved by the Health Research Authority, 12 healthy volunteers (mean age, 27.6 ± 18.5 years; 5 male) gave informed consent for renal imaging at 3 T using multi-TI ASL and conventional single-TI ASL. Glyceryl trinitrate (GTN) was used as a vasodilator challenge in six subjects. Flow-sensitive alternating inversion recovery (FAIR) preparation was used with background suppression and 3D-GRASE (gradient and spin echo) read-out, and images were motion-corrected. Parametric maps of RBF, BAT and T₁ were derived for both kidneys. Agreement was assessed using Pearson correlation and Bland-Altman plots.

RESULTS

Inter-study correlation of whole-kidney RBF was good for both single-TI (r² = 0.90), and multi-TI ASL (r² = 0.92). Single-TI ASL gave a higher estimate of whole-kidney RBF compared to multi-TI ASL (mean bias, 29.3 ml/min/100 g; p <0.001). Using multi-TI ASL, the median T₁ of renal cortex was shorter than that of medulla (799.6 ms vs 807.1 ms, p = 0.01), and mean whole-kidney BAT was 269.7 ± 56.5 ms. GTN had an effect on systolic blood pressure (p < 0.05) but the change in RBF was not significant.

CONCLUSIONS

Free-breathing multi-TI renal ASL is feasible and reproducible at 3 T, providing simultaneous measurement of renal perfusion, haemodynamic parameters and tissue characteristics at baseline and during pharmacological challenge.

KEY POINTS

• Multiple inversion time arterial spin labelling (ASL) of the kidneys is feasible and reproducible at 3 T. • This approach allows simultaneous mapping of renal perfusion, bolus arrival time and tissue T ₁ during free breathing. • This technique enables repeated measures of renal haemodynamic characteristics during pharmacological challenge.

Regulation of fluid reabsorption in rat or mouse proximal renal tubules by asymmetric dimethylarginine and dimethylarginine dimethylaminohydrolase 1

Nitric oxide prevents hypertension yet enhances proximal tubule Na⁺ reabsorption. Nitric oxide synthase is inhibited by asymmetric dimethylarginine (ADMA) that is metabolized by dimethylarginine dimethylaminohydrolase (DDAH) whose type 1 isoform is expressed abundantly in the proximal tubule (PT). We hypothesize that ADMA metabolized by DDAH-1 inhibits fluid reabsorbtion (Jv) by the proximal tubule. S2 segments of the PT were microperfused between blocks in vivo to assess Jv in anesthetized rats. Compared with vehicle, microperfusion of ADMA or N^ω-nitro-l-arginine methyl ester (l-NAME) in the proximal tubule reduced Jv dose dependently. At 10^-4 mol/l both reduced Jv by ~40% (vehicle: 3.2 ± 0.7 vs. ADMA: 2.1 ± 0.5, P < 0.01 vs. l-NAME: 1.9 ± 0.4 nl·min^-1·mm^-1, P < 0.01; n = 10). Selective inhibition of DDAH-1 in rats with intravenous L-257 (60 mg/kg) given 2 h before and L-257 (10^-5 mol/l) perfused in the proximal tubule for 5 min reduced Jv by 32 ± 4% (vehicle: 3.2 ± 0.5 vs. L-257: 2.2 ± 0.5 nl·min^-1·mm^-1; P < 0.01) and increased plasma ADMA by ≈50% (vehicle: 0.46 ± 0.03 vs. L-257: 0.67 ± 0.03 µmol/l, P < 0.0001) without changing plasma symmetric dimethylarginine. Compared with nontargeted control small-interference RNA, knock down of DDAH-1 in mice by 60% with targeted small-interference RNAs (siRNA) reduced Jv by 29 ± 5% (nontargeted siRNA: 2.8 ± 0.20 vs. DDAH-1 knockdown: 1.9 ± 0.31 nl·min^-1·mm^-1, P < 0.05). In conclusion, fluid reabsorption in the proximal tubule is reduced by tubular ADMA or by blocking its metabolism by DDAH-1. L-257 is a novel regulator of proximal tubule fluid reabsorption.

NRF2 prevents hypertension, increased ADMA, microvascular oxidative stress, and dysfunction in mice with two weeks of ANG II infusion

Nuclear factor erythyroid factor 2 (Nrf2) transcribes genes in cultured endothelial cells that reduce reactive oxygen species (ROS) and generate nitric oxide (NO) or metabolize asymmetric dimethylarginine (ADMA), which inhibits NO synthase (NOS). Therefore, we undertook a functional study to test the hypothesis that activation of Nrf2 by tert-butylhydroquinone (tBHQ) preserves microvascular endothelial function during oxidative stress. Wild-type CB57BL/6 (wt), Nrf2 wt (+/+), or knockout (-/-) mice received vehicle (Veh) or tBHQ (0.1%; activator of Nrf2) during 14-day infusions of ANG II (to induce oxidative stress) or sham. MAP was recorded by telemetry. Mesenteric resistance arterioles were studied on isometric myographs and vascular NO and ROS by fluorescence microscopy. ANG II increased the mean arterial pressure (112 ± 5 vs. 145 ± 5 mmHg; P < 0.01) and excretion of 8-isoprostane F_2α (2.8 ± 0.3 vs. 3.8 ± 0.3 ng/mg creatinine; P < 0.05) at 12-14 days. However, 12 days of ANG II reduced endothelium-derived relaxation (27 ± 5 vs. 17 ± 3%; P < 0.01) and NO (0.38 ± 0.07 vs. 0.18 ± 0.03 units; P < 0.01) but increased microvascular remodeling, endothelium-derived contractions (7.5 ± 0.5 vs. 13.0 ± 1.7%; P < 0.01), superoxide (0.09 ± 0.03 vs. 0.29 ± 0.08 units; P < 0.05), and contractions to U-46,619 (87 ± 6 vs. 118 ± 3%; P < 0.05), and endothelin-1(89 ± 4 vs. 123 ± 12%; P < 0.05). tBHQ prevented all of these effects of ANG II at 12-14 days in Nrf2^+/+ mice but not in Nrf2^-/- mice. In conclusion, tBHQ activates Nrf2 to prevent microvascular endothelial dysfunction, remodeling, and contractility, and moderate ADMA and hypertension at 12-14 days of ANG II infusion, thereby preserving endothelial function and preventing hypertension.

New ways of working; delivering better care for people with long-term conditions

Background

The cost-effectiveness of the traditional outpatient model for specialist care provision is increasingly being questioned in view of the changing patient needs, workforce challenges and technological advances.

Setting

This report summarises two RCGP London events showcasing new ways of delivering care for long-term conditions.

Questions

What are the alternative approaches to the traditional outpatient model and do they have common themes? What are the challenges and opportunities of these new models of care?

Methods

Presentation of examples of new ways of long-term condition care delivery and round-table facilitative discussion and reflection on the challenges and solutions around service re-design and implementation, the commissioning and funding of new models of care, the facilitation of system-wide learning and the collection of data for evaluation.

Results

Different ways of delivering care for people with Chronic Kidney Disease (CKD) and Chronic Obstructive Pulmonary Disease (COPD) were presented. Most of the interventions included virtual clinics (during which patient care was reviewed by a specialist remotely without the need for a face-to-face consultation), improved communication between primary and secondary care clinicians, an element of referral triage/prioritisation, the use of trigger tools to identify people at risk of deterioration, patient education and a multi-disciplinary approach.

Discussion-conclusions

Different models to the traditional outpatient long-term condition care are feasible and can result in improvements in the quality of care and staff satisfaction. However, such initiatives require careful planning, close collaboration between health care professionals and allocation of appropriate resources and training within primary care. There is also a need for systematic evaluation of such pilots to assess their cost-effectiveness and their acceptability to clinicians and patients. This requires systematic collection of population level data, agreement on the key outcomes for evaluation and a commitment of all stakeholders to sharing learning and resources to enable continuous improvement.

Abstract P344: Nuclear Factor E2-related Factor 2 (nrf2) Causes Early Microvascular Endothelial Dysfunction and Increased Adma by Activation of the Cox2/tp Receptor Pathway in Mice Infused With Angiotensin II for Three Days

Background: Activation of Nrf2 by tert-buthylhydroquinone (tBHQ) prevents hypertension, oxidative stress, endothelial dysfunction and ADMA in mice infused with angiotensin II (Ang II) for 12 days. However, Nrf2 activation with bardoxolone methyl increased cardiovascular events in diabetic patients within one week. Since we found that tBHQ activated cyclooxygenase (COX)-2 within 3 days, we tested the hypothesis that short-term tBHQ administration to Ang II infused mice increases microvascular dysfunction via COX dependent of PGs and TxA 2 that activate thromboxane-prostanoid receptors (TP-Rs).

Methods: Mesenteric resistance arterioles(MRAs)were isolated from mice infused for 3 days with ANG II (400 ng/kg/min) or vehicle and given oral tBHQ (0.1% of water) or vehicle (n=6 mice/group). Endothelial derived relaxation factor (EDRF) was assessed by a myograph and NO and ROS by RatioMaster TM .

Results: Compared to vehicle, Ang II infused mice given tBHQ had increased (P<0.05) conscious mean arterial pressure (135±6 vs 115±7 mmHg), urinary 8-Iso prostane (1.5±0.4 vs 1.1±0.2ng/mg creatinine), and decreased EDRF (17± 3 vs 23± 2%) and NO (0.23 ± 0.02 vs 0.35 ± 0.02 Δunits), and enhanced ( P<0.05, ) cellular ROS (0.27 ± 0.02 vs 0.12 ± 0.03 Δunits), mitochondria ROS (0.24 ± 0.02 vs 0.1 ± 0.02 Δunit) and microvascular asymmetric dimethylarginine (ADMA, 77 ± 6 vs 55 ± 7 nmol/mg protein). All these effects of tBHQ were prevented in COX-1 knockout mice drinking parecoxib (COX-2 inhibitor) and in TPR and Nrf2 knockout mice.

Conclusions: Activation of Nrf2 increases short term Ang II-induced increases in BP, oxidative stress, ADMA and endothelial dysfunction. These depend on signaling via COX 1 + 2 and TP receptors. Our studies reveal novel dual effects of Nrf2 in Ang II infused mice: increased BP, ROS, ADMA and endothelial dysfunction within 3 days secondary to activation of COX/TPR signaling follow by the opposite effects of Nrf2 on BP, ADMA and vascular function within 12 days. Therefore, blockade of COX-2/TPRs pathway during initiation of Nrf2 therapy may prevent the devastating early adverse effects that have prevented its use in hypertension or diabetes.

"Take-home" box trainers are an effective alternative to virtual reality simulators

BACKGROUND

Practice on virtual reality simulators (VRSs) has been shown to improve surgical performance. However, VRSs are expensive and usually housed in surgical skills centers that may be inaccessible at times convenient for surgical trainees to practice. Conversely, box trainers (BT) are inexpensive and can be used anywhere at anytime. This study assesses "take-home" BTs as an alternative to VRS.

METHODS

After baseline assessments (two simulated laparoscopic cholecystectomies, one on a VRS and one on a BT), 25 surgical trainees were randomized to two groups. Trainees were asked to practice three basic laparoscopic tasks for 6 wk (BT group using a "take-home" box trainer; VR group using VRS in clinical skills centers). After the practice period, all performed two laparoscopic cholecystectomy, one on a VRS and one on a BT; (i.e., posttraining assessment). VRS provided metrics (total time [TT], number of movements instrument tip path length), and expert video assessment of cholecystectomy in a BT (Global Operative Assessment of Laparoscopic Skills [GOALS] score) were recorded. Performance during pretraining and posttraining assessment was compared.

RESULTS

The BT group showed a significant improvement for all VRS metrics (P = 0.008) and the efficiency category of GOALS score (P = 0.03). Only TT improved in the VRS group, and none of the GOALS categories demonstrated a statistically significant improvement after training. Finally, the improvement in VRS metrics in the BT group was significantly greater than in the VR group (TT P = 0.005, number of movements P = 0.042, path length P = 0.031), although there were no differences in the GOALS scores between the groups.

CONCLUSIONS

This study suggests that a basic "take-home" BT is a suitable alternative to VRS.

Perceptions About the Present and Future of Surgical Simulation: A National Study of Mixed Qualitative and Quantitative Methodology

OBJECTIVES

Assess expert opinion on the current and future role of simulation in surgical education.

DESIGN

Expert opinion was sought through an externally validated questionnaire that was disseminated electronically.

PARTICIPANTS

Heads of Schools of Surgery (HoS) (and deputies) and Training Program Directors (TPD) (and deputies).

RESULTS

Simulation was considered a good training tool (HoS: 15/15, TPD: 21/21). The concept that simulation is useful mostly to novices and for basic skills acquisition was rejected (HoS: 15/15, TPDs: 21/21; HoS: 13/15, TPDs: 18/21). Further, simulation is considered suitable for teaching nontechnical skills (HoS: 13/15, TPDs: 20/21) and re-enacting stressful situations (HoS: 14/15, TPDs: 15/21). Most respondents also felt that education centers should be formally accredited (HoS: 12/15, TPDs: 16/21) and that consultant mentors should be appointed by every trust (HoS: 12/15, TPDs: 19/21). In contrast, there were mixed views on its use for trainee assessment (HoS: 6/15, TPDs: 14/21) and whether it should be compulsory (HoS: 8/15, TPDs: 11/21).

CONCLUSION

The use of simulation for the acquirement of both technical and nontechnical skills is strongly supported while views on other applications (e.g., assessment) are conflicting. Further, the need for center accreditation and supervised, consultant-led teaching is highlighted.

Managing Developmental Dysplasia of the Hip

Developmental dysplasia of the hip (DDH) involves a spectrum of hip disorders that affect hip anatomy and development and can range from mild anatomical deformity with a reduced but subluxatable hip to a frankly dislocated hip. It was previously known as congenital dislocation of the hip (CDH) but this name is no longer used due to the fact that the hip may be anatomically abnormal whilst not being dislocated. The key aim of clinical management of DDH is early diagnosis and referral as this can often mean less invasive treatment is possible, and outcomes are significantly improved if treatment is initiated at an early stage and certainly before 6 wk of age.

Abstract P623: Endothelial Dysfunction and Abnormal Perivascular Adipose Tissue Signaling in Subcutaneous Vessels from HIV-infected individuals

Objective: Perivascular adipose tissue (PVAT) normally promotes vascular endothelial function, whereas is impaired by reactive oxygen species (ROS) in CVD. But PVAT effects on microvessels in HIV are unexplored. We previously reported endothelial dysfunction in living subcutaneous microvascular arterioles (SMAs) dissected from a gluteal biopsy in HIV infected individuals. We test hypothesis that HIV increases microvascular ROS and asymmetric dimethylarginine (ADMA) leading to impair microvascular function and PVAT signaling.

Methods: Isolated SMAs with or without PVAT were prepared from young African American HIV-infected (n=8) and matched HIV-uninfected women (n=6) enrolled in the DC Women’s Interagency HIV Study (DC-WIHS). HIV-infected participants were virally suppressed on HAART without identified CVD risk factors (except obesity). SMA’s acetylcholine (ACh)-induced endothelium dependent relaxation (EDR), nitric oxide (NO) activity (DAF-FM), ACh-induced endothelium dependent contractions (EDC) and ROS generation (temp-9AC), plasma L-arginine, ADMA and adipose adipokines and malondialdehyde (MDA) were measured.

Results: HIV-infected participants had significantly ( p <0.05) reduced plasma ratio of L-arginine : ADMA (99 ± 13 vs 182 ± 32 μmol/μmol), increased adipose MDA (15.1 ± 2.5 vs 10.9 ± 2.6 ng/mg protein) and leptin (40 ± 9 vs 28 ± 7 ng/mg protein); and reduced adiponectin in plasma (14 ± 2 vs 23 ± 2 ng/ml) and in adipose (2.1 ± 0.3 vs 4.6 ± 1.3 ng/mg protein). ACh-induced EDR (57 ± 4 vs 71± 4%) and NO (0.20 ± 0.03 vs 0.58 ± 0.07 Δfluoresce unit) were significantly attenuated (p<0.05) in vessels from HIV-infected participants, whereas EDC (22 ± 2 vs 7 ± 2%) and O 2 - (0.17 ± 0.02 vs 0.09 ± 0.02 Δfluoresce unit) were significantly increased ( p <0.05) . PVAT significantly increased ( p <0.05) EDR (87 ± 3 vs 72 ± 4%) and NO (0.84 ± 0.09 vs 0.58 ± 0.08 Δfluoresce unit) only in control vessels.

Conclusion: HIV-infected individuals have reductions in NO synthase substrate: inhibitor ratio (L-arginine:ADMA) and consequent increased intrinsic vascular effects of ROS leading to disruption of the beneficial microvascular PVAT signaling pathway. Therapeutic targets for vascular dysfunction in HIV should include ROS and its extravascular actions on ADMA and PVAT.

Retrospective Evaluation of Horses Diagnosed with Neuroborreliosis on Postmortem Examination: 16 Cases (2004-2015)

BACKGROUND

Equine neuroborreliosis (NB), Lyme disease, is difficult to diagnose and has limited description in the literature.

OBJECTIVE

Provide a detailed description of clinical signs, diagnostic, and pathologic findings of horses with NB.

ANIMALS

Sixteen horses with histologically confirmed NB.

METHODS

Retrospective review of medical records at the University of Pennsylvania and via an ACVIM listserv query with inclusion criteria requiring possible exposure to Borrelia burgdorferi and histologic findings consistent with previous reports of NB without evidence of other disease.

RESULTS

Sixteen horses were identified, 12 of which had additional evidence of NB. Clinical signs were variable including muscle atrophy or weight loss (12), cranial nerve deficits (11), ataxia (10), changes in behavior (9), dysphagia (7), fasciculations (6), neck stiffness (6), episodic respiratory distress (5), uveitis (5), fever (2), joint effusion (2), and cardiac arrhythmias (1). Serologic analysis was positive for B. burgdorferi infection in 6/13 cases tested. CSF abnormalities were present in 8/13 cases tested, including xanthochromia (4/13), increased total protein (5/13; median: 91 mg/dL, range: 25-219 mg/dL), and a neutrophilic (6/13) or lymphocytic (2/13) pleocytosis (median: 25 nucleated cells/μL, range: 0-922 nucleated cells/μL). PCR on CSF for B. burgdorferi was negative in the 7 cases that were tested.

CONCLUSION AND CLINICAL IMPORTANCE

Diagnosis of equine NB is challenging due to variable clinical presentation and lack of sensitive and specific diagnostic tests. Negative serology and normal CSF analysis do not exclude the diagnosis of NB.

Hypoxia causes increased monocyte nitric oxide synthesis which is mediated by changes in dimethylarginine dimethylaminohydrolase 2 expression in animal and human models of normobaric hypoxia

BACKGROUND

Tissue hypoxia is a cardinal feature of inflammatory diseases and modulates monocyte function. Nitric oxide is a crucial component of the immune cell response. This study explored the metabolism of the endogenous inhibitor of nitric oxide production asymmetric dimethylarginine(ADMA) by monocyte dimethylarginine dimethylaminohydrolase 2(DDAH2), and the role of this pathway in the regulation of the cellular response and the local environment during hypoxia.

METHODS

Peritoneal macrophages were isolated from a macrophage-specific DDAH2 knockout mouse that we developed and compared with appropriate controls. Cells were exposed to 3% oxygen followed by reoxygenation at 21%. Healthy volunteers underwent an 8 h exposure to normobaric hypoxia with an inspired oxygen percentage of 12%. Peripheral blood mononuclear cells were isolated from blood samples taken before and at the end of this exposure.

RESULTS

Intracellular nitrate plus nitrite(NOx) concentration was higher in wild-type murine monocytes after hypoxia and reoxygenation than in normoxia-treated cells (mean(SD) 13·2(2·4) vs 8·1(1·7) pmols/mg protein, p = 0·009). DDAH2 protein was 4·5-fold (SD 1·3) higher than in control cells (p = 0·03). This increase led to a 24% reduction in ADMA concentration, 0·33(0.04) pmols/mg to 0·24(0·03), p = 0·002). DDAH2-deficient murine monocytes demonstrated no increase in nitric oxide production after hypoxic challenge. These findings were recapitulated in a human observational study. Mean plasma NOx concentration was elevated after hypoxic exposure (3·6(1.8)μM vs 6·4(3·2), p = 0·01), which was associated with a reduction in intracellular ADMA in paired samples from 3·6(0.27) pmols/mg protein to 3·15(0·3) (p < 0·01). This finding was associated with a 1·9-fold(0·6) increase in DDAH2 expression over baseline(p = 0·03).

DISCUSSION

This study shows that in both human and murine models of acute hypoxia, increased DDAH2 expression mediates a reduction in intracellular ADMA concentration which in turn leads to elevated nitric oxide concentrations both within the cell and in the local environment. Cells deficient in DDAH2 were unable to mount this response.