Covalent hemoglobin binding to membranes leads to band 3 (AE1) clustering and the removal of erythrocytes from the circulation; it is also implicated in blood storage lesions. Damaged hemoglobin, with the heme being in a redox and oxygen-binding inactive hemichrome form, has been implicated as the binding species. However, previous studies used strong non-physiological oxidants. In vivo hemoglobin is constantly being oxidised to methemoglobin (ferric), with around 1% of hemoglobin being in this form at any one time. In this study we tested the ability of the natural oxidised form of hemoglobin (methemoglobin) in the presence or absence of the physiological oxidant hydrogen peroxide to initiate membrane binding. The higher the oxidation state of hemoglobin (from Fe(III) to Fe(V)) the more binding was observed, with approximately 50% of this binding requiring reactive sulphydryl groups. The hemoglobin bound was in a high molecular weight complex containing spectrin, ankyrin and band 4.2, which are common to one of the cytoskeletal nodes. Unusually, we showed that hemoglobin bound in this way was redox active and capable of ligand binding. It can initiate lipid peroxidation showing the potential to cause cell damage. In vivo oxidative stress studies using extreme endurance exercise challenges showed an increase in hemoglobin membrane binding, especially in older cells with lower levels of antioxidant enzymes. These are then targeted for destruction. We propose a model where mild oxidative stress initiates the binding of redox active hemoglobin to the membrane. The maximum lifetime of the erythrocyte is thus governed by the redox activity of the cell; from the moment of its release into the circulation the timer is set.
Introduction: Rheumatoid arthritis (RA) is a systemic disease of unknown cause. A variety of pulmonary disorders have been described in association with RA. Among the most common are interstitial lung disease
(ILD) and bronchiectasis.
Objectives: This study aims to determine the characteristics of RA patients with lung disease in relation to clinical characteristics, pulmonary function test (PFT) and high resolution computed tomography (HRCT) thorax.
Method: This is a 6-months cross-sectional study involving 63 consecutive RA patients in an outpatient rheumatology clinic. Patients had a mean disease duration of 5 years and above. Disease activity and severity
was assessed by Disease Activity Score 28 (DAS28), Health Assessment Questionnaire (HAQ) and Rheumatoid Arthritis Articular Damage (RAAD) score. Full pulmonary function test (PFT) and HRCT of thorax were performed.
Conclusions: The prevalence of RA-ILD is 44% and 67% of patients are asymptomatic. There was significant higher proportion (68%) in patients of Chinese ethnicity who have ILD. Diffusion capacity of carbon monoxide
was abnormal in all patients and forced expiratory flow (FEF)25–75% was low in 16%. Restrictive pattern was 66.7% by PFT. The most common HRCT findings were reticulation (46%) followed by ground glass opacities
(38.1%) and bronchiectasis (28.6%). There was no association between ILD and male gender, duration of the disease, smoking, rheumatoid factor, extra-articular manifestations, disease activity or severity.
Key words: high resolution computed tomography, interstitial lung disease, lung function test, rheumatoid arthritis.
Study site: Rheumatology clinic, Pusat Perubatan Universiti Kebangsaan Malaysia (PPUKM), Kuala Lumpur, Malaysia