Outcomes of COVID-19 re-infections: a single-center cohort of 167 patients with systemic rheumatic diseases.

Data on COVID-19 re-infections in patients with systemic rheumatic diseases (SRDs) are lacking. We aimed to describe the course and outcomes of COVID-19 re-infections in these patients versus controls. In this single-center retrospective study, we included 167 consecutive SRD patients with at least one COVID-19 re-infection (mean age 47.3 years, females 70.7%). SRD patients were compared in terms of patient-perceived COVID-19 re-infection severity and hospitalizations/deaths with 167 age/sex-matched non-SRD controls. Logistic regression analysis was performed to assess potential milder re-infection versus primary infection severity, adjusting for study group, demographics (age, sex), vaccination status, body mass index, smoking, and comorbidities. 23 and 7 out of 167 re-infected SRD patients experienced two and three re-infections, respectively, which were comparable to the re-infection rates in controls (two: 32; and three: 2) who also had comparable COVID-19 vaccination history (89% and 95% vaccinated, respectively). In the initial infection, patients with SRDs were hospitalized (7.2% versus 1.8%, p = 0.017), and had received antiviral treatment (16.1% versus 4.7%, p < 0.001) more frequently than controls. However, hospitalizations (1.8% vs 0.6%) and antiviral treatment (7.8% vs 3.5%) did not differ (p > 0.05) between patients and controls at the first re-infection, as well as during the second and third re-infection; no deaths were recorded. Perceived severity of re-infections was also comparable between patients and controls (p = 0.847) and among those on biologic DMARDs or not (p = 0.482). In multivariable analysis, neither SRDs presence nor demographics or comorbidities were associated with COVID-19 re-infection severity. COVID-19 re-infection severity (patient-perceived/hospitalizations/deaths) did not differ between SRDs and controls.

Glucocorticoid discontinuation rate and risk factors for relapses in a contemporary cohort of patients with giant cell arteritis.

The rates of relapses and therapy discontinuation in patients with giant cell arteritis (GCA) in the modern therapeutic era have not been defined. We aimed to evaluate the glucocorticoid (GC) discontinuation rate and the factors associated with relapses in a contemporary GCA cohort. Patient and treatment data were collected cross-sectionally at first evaluation and 2 years later (second evaluation), in a multicenter, prospective GCA cohort. Predictors of relapses were identified by logistic regression analyses. 243 patients with GCA were initially included (67% women, mean age at diagnosis: 72.1 years, median disease duration: 2 years) while 2 years later complete data for 160 patients were available and analyzed. All patients had received GCs at diagnosis (mean daily prednisolone dose: 40 mg) while during follow-up, 37% received non-biologic and 16% biologic agents, respectively. At second evaluation, 72% of patients were still on therapy (GCs: 58% and/or GC-sparing agents: 29%). Relapses occurred in 27% of patients during follow-up; by multivariable logistic regression analysis, large vessel involvement at diagnosis [odds ratio (OR) = 4.22], a cardiovascular event during follow-up (OR = 4.60) and a higher initial GC daily dose (OR = 1.04), were associated with these relapses. In this large, real-life, contemporary GCA cohort, the rates of GC discontinuation and relapses were 40% and 27%, respectively. Large vessel involvement, a higher GC dose at diagnosis and new cardiovascular events during follow-up were associated with relapses.

Augmented oxidative stress, accumulation of DNA damage and impaired DNA repair mechanisms in thrombotic primary antiphospholipid syndrome.

Antiphospholipid syndrome (APS) is a rare autoimmune disorder with complex pathogenesis. Studies have shown that oxidative stress may contribute to APS pathophysiology. In peripheral blood mononuclear cells (PBMCs) from thrombotic Primary APS (thrPAPS) patients and age/sex-matched healthy controls (HC), as well as a control group of asymptomatic antiphospholipid antibody (aPL) positive individuals without APS (aPL+/non-APS), we examined oxidative stress, abasic (apurinic/apyrimidinic) sites, and DNA damage response (DDR)-associated parameters, including endogenous DNA damage (single- and double-strand breaks) and DNA repair mechanisms, namely nucleotide excision repair (NER) and double-strand breaks repair (DSB/R). We found that thrPAPS patients exhibited significantly higher levels of endogenous DNA damage, increased oxidative stress and abasic sites, as well as lower NER and DSB/R capacities versus HC (all P < 0.001) and versus aPL+/non-APS subjects (all P < 0.05). Our findings demonstrate that oxidative stress and decreased DNA repair mechanisms contribute to the accumulation of endogenous DNA damage in PBMCs from thrPAPS patients and, if further validated, may be exploited as therapeutic targets and potential biomarkers.

Deregulated DNA damage response network in Behcet's disease.

Behcet's disease (BD) is a chronic, relapsing systemic vasculitis of unknown etiology. Since the DNA repair enzyme NEIL1 has been identified as one of the two genetic risk factors for BD by whole exome study, we examined the potential involvement of the DNA damage response (DDR) network in BD. Peripheral blood mononuclear cells from 26 patients and 26 age-/sex-matched healthy controls were studied. Endogenous DNA damage levels were increased in active BD patients compared to controls or patients in remission. In parallel, BD patients had defective nucleotide excision repair capacity. RNA-sequencing revealed reduced expression of NEIL1 that negatively correlated with DNA damage accumulation. On the other hand, expression of genes involved in senescence and senescence-associated secretory phenotype positively correlated with individual endogenous DNA damage levels. We conclude that deregulated DDR contributes to the proinflammatory environment in BD.

Systemic Lupus Erythematosus and COVID-19.

PURPOSE OF REVIEW: To describe the current state of knowledge regarding COVID-19 in patients with systemic lupus erythematosus (SLE). We focus on (i) SARS-CoV-2 vaccination uptake, immunogenicity and safety, and (ii) outcomes of COVID-19 in patients with SLE and pertinent risk factors for adverse sequelae. RECENT FINDINGS: Notwithstanding the potential concern of patients about possible post-vaccination side-effects, the safety of anti-SARS-CoV-2 vaccines in patients with SLE has been undisputedly confirmed in numerous studies. Humoral immunogenicity is generally attained in SLE, although affected by the use of background immunosuppressive drugs, especially rituximab. The latter has also clearly been implicated with adverse COVID-19 outcomes in SLE, including need for hospitalization, mechanical ventilation and death. Although the wide adoption of vaccination has significantly improved COVID-19 outcomes, patients with SLE continue to pose challenges during the pandemic, mainly owing to administered immunosuppressive medications.

Higher frequency but similar recurrence rate of uveitis episodes in axial spondylarthritis compared to psoriatic arthritis. A multicentre retrospective study.

BACKGROUND/OBJECTIVE: Data on risk factors predicting uveitis development in spondyloarthritis (SpA) is scarce. Our aim was to examine associations between demographic, clinical and/or laboratory characteristics of SpA with the occurrence and the course of uveitis, including ocular damage and recurrence rate. METHODS: Characteristics (at disease diagnosis and ever-present) from axSpA and Psoriatic arthritis (PsA) patients followed in 3 tertiary rheumatology-clinics were retrospectively recorded. Comparisons were made between patients with and without uveitis, as well as between those with uveitis-rate [episodes/year] above the median uveitis-rate in the whole cohort ("recurrent"-uveitis) and the remaining uveitis patients ("non-recurrent uveitis"). In multivariable models, age, gender and variables significantly different in univariate analyses were included. RESULTS: 264 axSpA and 369 PsA patients were enrolled. In axSpA, uveitis occurred in 11.7% and was associated with HLA-B27 (OR = 4.15, 95%CI 1.16-14.80, p = 0.028) and ever-present peripheral arthritis (OR = 3.05 (1.10-8.41, p = 0.031). In contrast, uveitis in PsA occurred only in 2.7% of patients and was associated with SpA family-history (OR = 6.35 (1.29-31.27), p = 0.023) axial disease at diagnosis (OR = 5.61 [1.01-28.69], p = 0.038) and disease duration (OR = 1.12 [1.04-1.21], p = 0.004). Median uveitis recurrence rate was comparable between axSpA and PsA (0.205 and 0.285 episodes/year, respectively). No associations were found between recurrent uveitis and demographic/clinical/laboratory characteristics. Ocular damage (e.g. synechiae) was seen in 16.1% of axSpA and 30% of PsA patients, all of them with recurrent uveitis. CONCLUSION: Uveitis occurred more commonly in axSpA than in PsA patients, while uveitis recurrence rate was similar. Permanent ocular damage may occur more often in PsA than axSpA.

Chronological Age and DNA Damage Accumulation in Blood Mononuclear Cells: A Linear Association in Healthy Humans after 50 Years of Age.

Aging is characterized by the progressive deregulation of homeostatic mechanisms causing the accumulation of macromolecular damage, including DNA damage, progressive decline in organ function and chronic diseases. Since several features of the aging phenotype are closely related to defects in the DNA damage response (DDR) network, we have herein investigated the relationship between chronological age and DDR signals in peripheral blood mononuclear cells (PBMCs) from healthy individuals. DDR-associated parameters, including endogenous DNA damage (single-strand breaks and double-strand breaks (DSBs) measured by the alkaline comet assay (Olive Tail Moment (OTM); DSBs-only by γH2AX immunofluorescence staining), DSBs repair capacity, oxidative stress, and apurinic/apyrimidinic sites were evaluated in PBMCs of 243 individuals aged 18-75 years, free of any major comorbidity. While OTM values showed marginal correlation with age until 50 years (rs = 0.41, p = 0.11), a linear relationship was observed after 50 years (r = 0.95, p < 0.001). Moreover, individuals older than 50 years showed increased endogenous DSBs levels (γH2Ax), higher oxidative stress, augmented apurinic/apyrimidinic sites and decreased DSBs repair capacity than those with age lower than 50 years (all p < 0.001). Results were reproduced when we examined men and women separately. Prospective studies confirming the value of DNA damage accumulation as a biomarker of aging, as well as the presence of a relevant agethreshold, are warranted.

Better outcomes of COVID-19 in vaccinated compared to unvaccinated patients with systemic rheumatic diseases.

OBJECTIVE: Τo report outcomes of breakthrough COVID-19 in comparison with COVID-19 in unvaccinated patients with systemic rheumatic diseases (SRDs). METHODS: Patients with SRD with COVID-19 (vaccinated and unvaccinated) were included by their rheumatologists in a registry operated by the Greek Rheumatology Society in a voluntarily basis. Type, date and doses of SARS-CoV-2 vaccines were recorded, and demographics, type of SRD, concurrent treatment, comorbidities and COVID-19 outcomes (hospitalisation, need for oxygen supplementation and death) were compared between vaccinated and unvaccinated patients. RESULTS: Between 1 March 2020 and 31 August 2021, 195 patients with SRD with COVID-19 were included; 147 unvaccinated and 48 vaccinated with at least one dose of a SARS-CoV-2 vaccine (Pfizer n=38 or AstraZeneca n=10). Among vaccinated patients, 29 developed breakthrough COVID-19 >14 days after the second vaccine dose (fully vaccinated), while 19 between the first and <14 days after the second vaccine dose (partially vaccinated). Despite no differences in demographics, SRD type, treatment or comorbidities between unvaccinated and vaccinated patients, hospitalisation and mortality rates were higher in unvaccinated (29.3% and 4.1%, respectively) compared with partially vaccinated (21% and 0%) or fully vaccinated (10.3% and 0%) patients. CONCLUSIONS: Vaccinated patients with SRD with breakthrough COVID-19 have better outcomes compared with unvaccinated counterparts with similar disease/treatment characteristics.

Axial psoriatic arthritis and ankylosing spondylitis: same or different? A real-world study with emphasis on comorbidities.

OBJECTIVES: Axial involvement affects 25-70% of psoriatic arthritis (PsA) patients, depending on the criteria used for its definition. Efforts are underway to clarify the similarities and differences between axial-PsA and ankylosing spondylitis (AS). We aimed to compare, in a real-world setting, axial-PsA and AS, in terms of demographic, radiologic and clinical (musculoskeletal and extra-articular) characteristics, with a focus on comorbidities. METHODS: All AS (New York criteria, n=128) and PsA patients (CASPAR criteria, n=78) with axial involvement who were regularly followed-up in the outpatients' rheumatology clinics from two tertiary hospitals (December 2018-July 2020) were included. Demographic, radiologic and clinical characteristics were recorded and compared between the two groups. For comorbidities (coronary disease, cerebrovascular accidents, hypertension, diabetes mellitus, dyslipidaemia, depression, osteoporosis, and malignancies), adjustments were made for relevant confounders. RESULTS: AS patients were younger (p=0.05) and were diagnosed at a younger age (p=0.002), more frequently of male gender (p=0.04), had lower BMI (p=0.006) and they were more frequently HLA-B27-positive (p=0.006). In AS patients, peripheral arthritis, dactylitis and nail involvement were less common (p=0.001 for all), in contrast to eye (p=0.001) and bowel involvement (p=0.004). Frequency of radiologic abnormalities in the spine was similar between the two groups while sacroiliitis was more often bilateral in AS and unilateral in axial-PsA. Comorbidities, including cardiovascular-related ones, were comparable between AS and axial-PsA, apart from depression which was more frequent in axial-PsA (p=0.07 in logistic regression). CONCLUSIONS: AS and axial-PsA have certain clinical and radiologic differences. Comorbidities were comparable, while depression was more common in axial-PsA.

COVID-19 vaccine safety and nocebo-prone associated hesitancy in patients with systemic rheumatic diseases: a cross-sectional study.

OBJECTIVE: To describe the rate and type of adverse effects (AEs) and the frequency of disease flares after COVID-19 vaccination and to assess the reasons for vaccination hesitancy (non-vaccination) in SRD patients. METHODS: Telephone interviews were conducted of SRD patients consecutively enrolled (15/06/2021-1/7/2021). Participants were asked about the type of AEs and disease flare after vaccination. Reasons for vaccination hesitancy were recorded. Univariate and mutivariable analyses examined associations of demographic, clinical and other features, with occurrence of AEs, disease flare and non-vaccination. For the latter, association with negative vaccination behaviour (not influenza vaccinated for the last 2 years) and nocebo-prone behaviour (denoting AEs attributed to negative expectations [Q-No questionnaire]) was also tested. RESULTS: 561 out of 580 contacted patients were included in the study. 441/561 (78.6%) patients were vaccinated [90% (Pfizer, Moderna), 10% (Astra-Zeneca)]. AEs were reported by 148/441 (33.6%), with rates being comparable between the three vaccines. AEs were more common in females and those with chronic obstructive pulmonary disease [OR, 95% CI; females: 2.23 (1.30-3.83); COPD: 3.31 (1.24-8.83)]. Disease flare was reported in 9/441 (2%) patients. For those unvaccinated, fear that the vaccine would be harmful (53.3%), could cause disease flare (24.2%) and/or could cause thrombosis (21.7%) were the main reasons to do so. Multivariable analysis identified as independent variables for non-vaccination: nocebo-prone behaviour (OR; 95% CI, 3.88; 1.76-8.55), negative vaccination behaviour (6.56; 3.21-13.42) and previous COVID-19 infection (2.83; 1.13-7.05). Higher educational status was protective (0.49; 0.26-0.92). CONCLUSION: No new safety signals for COVID-19 vaccination were observed. Vaccination campaign should target SRD patients with nocebo-prone and negative influenza vaccination behaviour.

Effective DNA damage response after acute but not chronic immune challenge: SARS-CoV-2 vaccine versus Systemic Lupus Erythematosus.

Whether and how an acute immune challenge may affect DNA Damage Response (DDR) is unknown. By studying vaccinations against Influenza and SARS-CoV-2 (mRNA-based) we found acute increases of type-I interferon-inducible gene expression, oxidative stress and DNA damage accumulation in blood mononuclear cells of 9 healthy controls, coupled with effective anti-SARS-CoV-2 neutralizing antibody production in all. Increased DNA damage after SARS-CoV-2 vaccine, partly due to increased oxidative stress, was transient, whereas the inherent DNA repair capacity was found intact. In contrast, in 26 patients with Systemic Lupus Erythematosus, who served as controls in the context of chronic immune activation, we validated increased DNA damage accumulation, increased type-I interferon-inducible gene expression and induction of oxidative stress, however aberrant DDR was associated with deficiencies in nucleotide excision repair pathways. These results indicate that acute immune challenge can indeed activate DDR pathways, whereas, contrary to chronic immune challenge, successful repair of DNA lesions occurs.

Adenosine-to-inosine RNA editing contributes to type I interferon responses in systemic sclerosis.

OBJECTIVE: Adenosine deaminase acting on RNA-1 (ADAR1) enzyme is a type I interferon (IFN)-stimulated gene (ISG) catalyzing the deamination of adenosine-to-inosine, a process called A-to-I RNA editing. A-to-I RNA editing takes place mainly in Alu elements comprising a primate-specific level of post-transcriptional gene regulation. Whether RNA editing is involved in type I IFN responses in systemic sclerosis (SSc) patients remains unknown. METHODS: ISG expression was quantified in skin biopsies and peripheral blood mononuclear cells derived from SSc patients and healthy subjects. A-to-I RNA editing was examined in the ADAR1-target cathepsin S (CTSS) by an RNA editing assay. The effect of ADAR1 on interferon-α/ß-induced CTSS expression was assessed in human endothelial cells in vitro. RESULTS: Increased expression levels of the RNA editor ADAR1, and specifically the long ADAR1p150 isoform, and its target CTSS are strongly associated with type I IFN signature in skin biopsies and peripheral blood derived from SSc patients. Notably, IFN-α/ß-treated human endothelial cells show 8-10-fold increased ADAR1p150 and 23-35-fold increased CTSS expression, while silencing of ADAR1 reduces CTSS expression by 60-70%. In SSc patients, increased RNA editing rate of individual adenosines located in CTSS 3' UTR Alu elements is associated with higher CTSS expression (r = 0.36-0.6, P < 0.05 for all). Similar findings were obtained in subjects with activated type I IFN responses including SLE patients or healthy subjects after influenza vaccination. CONCLUSION: ADAR1p150-mediated A-to-I RNA editing is critically involved in type I IFN responses highlighting the importance of post-transcriptional regulation of proinflammatory gene expression in systemic autoimmunity, including SSc.

Increased influenza vaccination rates in patients with autoimmune rheumatic diseases during the Covid-19 pandemic: a cross-sectional study.

To assess non-compliance and potential changes in seasonal flu vaccination coverage before and during the Covid-19 pandemic in patients with autoimmune rheumatic diseases (ARDs). Consecutive patients with ARDs followed-up in 2 tertiary hospitals were telephone-interviewed (December 12-30, 2020) regarding seasonal flu vaccination during the 2019/20 and 2020/21 time periods. Self-reported disease flares that occurred after flu vaccination, as well as reasons for non-vaccination were recorded. One thousand fifteen patients were included. The rate of flu vaccination increased from 76% before to 83% during the COVID-19 pandemic (p = 0.0001). The rate of self-reported disease flares was < 1% among vaccinated patients. Reasons for not vaccination in both periods, respectively, included: 'was not recommended by their rheumatologists' (35.0vs.12.2%, p < 0.0001), 'did not feel that they would have any benefit' (36.9 vs. 32.6%), felt unsafe to do so (27.5 vs. 30.2%), or other reasons (18.9 vs. 23.8%). By multivariate analysis, age [OR = 1.03 (95% CI 1.02-1.04)] vs. [1.04 (95% CI 1.02-1.05)] and treatment with biologics [OR = 1.66 (95% CI 1.22-2.24) vs. [1.68 (95% CI 1.19-2.38)] were independent factors associated with vaccination in both periods. These findings, although are temporally encouraging, emphasize the need for continuous campaigns aiming at increasing patients' and physicians' awareness about the benefits of vaccination.

The Effects of Muscle Cell Aging on Myogenesis.

The process of myogenesis gradually deteriorates as the skeletal muscle ages, contributing to muscle mass loss. The aim of this study is to investigate the effect of senescence/aging on skeletal myogenesis, in vitro. A model of multiple cell divisions of C2C12 myoblasts was used to replicate cell senescence. Control and aged myoblasts were investigated during myogenesis, i.e., at days 0, 2, and 6of differentiation. SA-ß-gal activity and comet assay were used as markers of aging and DNA damage. Flow cytometry was performed to characterize potential differences in cell cycle between control and aged cells. Alterations in the mRNA and/or protein expression of myogenic regulatory factors (MRFs), IGF-1 isoforms, apoptotic, atrophy, inflammatory, metabolic and aging-related factors were evaluated. Compared with the control cells, aged myoblasts exhibited G0/G1 cell cycle arrest, DNA damage, increased SA-ß-gal activity, and increased expression of aging-related factors p16 and p21 during differentiation. Moreover, aged myoblasts showed a reduction in the expression of MRFs and metabolic/anabolic factors, along with an increased expression of apoptotic, atrophy and inflammatory factors. A diminished differentiation capacity characterized the aged myoblasts which, in combination with the induction of apoptotic and atrophy factors, indicated a disrupted myogenic lineage in the senescent muscle cells.

DNA damage accumulation, defective chromatin organization and deficient DNA repair capacity in patients with rheumatoid arthritis.

We investigated the DNA damage response and repair network in 18 patients with active rheumatoid arthritis and tested the hypothesis that treatment influences this network. A 3-fold increase of endogenous DNA damage (single- and double-strand breaks) was detected in patient-derived peripheral blood mononuclear cells than controls (alkaline comet assay; mean ±â€¯SD Olive Tail Moment of 11.8 ±â€¯7.3 versus 4.3 ±â€¯2.2, p < .001). Patients exhibited significantly higher formation of DNA damage (oxidative stress and abasic sites), deficient global genome repair and more condensed chromatin structure than controls. Twelve weeks following treatment, chromatin structure loosened, global genome repair capacity was restored, oxidative stress and abasic sites decreased and levels of endogenous DNA damage reached control values in all 8 patients examined. We conclude that deregulated chromatin organization, deficient DNA repair capacity and augmented formation of DNA damage, which are reversible after treatment, contribute to the accumulation of endogenous DNA damage in rheumatoid arthritis.

DNA Damage Response and Oxidative Stress in Systemic Autoimmunity.

The DNA damage response and repair (DDR/R) network, a sum of hierarchically structured signaling pathways that recognize and repair DNA damage, and the immune response to endogenous and/or exogenous threats, act synergistically to enhance cellular defense. On the other hand, a deregulated interplay between these systems underlines inflammatory diseases including malignancies and chronic systemic autoimmune diseases, such as systemic lupus erythematosus, systemic sclerosis, and rheumatoid arthritis. Patients with these diseases are characterized by aberrant immune response to self-antigens with widespread production of autoantibodies and multiple-tissue injury, as well as by the presence of increased oxidative stress. Recent data demonstrate accumulation of endogenous DNA damage in peripheral blood mononuclear cells from these patients, which is related to (a) augmented DNA damage formation, at least partly due to the induction of oxidative stress, and (b) epigenetically regulated functional abnormalities of fundamental DNA repair mechanisms. Because endogenous DNA damage accumulation has serious consequences for cellular health, including genomic instability and enhancement of an aberrant immune response, these results can be exploited for understanding pathogenesis and progression of systemic autoimmune diseases, as well as for the development of new treatments.

Arabidopsis CPR5 regulates ethylene signaling via molecular association with the ETR1 receptor.

The plant hormone ethylene plays various functions in plant growth, development and response to environmental stress. Ethylene is perceived by membrane-bound ethylene receptors, and among the homologous receptors in Arabidopsis, the ETR1 ethylene receptor plays a major role. The present study provides evidence demonstrating that Arabidopsis CPR5 functions as a novel ETR1 receptor-interacting protein in regulating ethylene response and signaling. Yeast split ubiquitin assays and bi-fluorescence complementation studies in plant cells indicated that CPR5 directly interacts with the ETR1 receptor. Genetic analyses indicated that mutant alleles of cpr5 can suppress ethylene insensitivity in both etr1-1 and etr1-2, but not in other dominant ethylene receptor mutants. Overexpression of Arabidopsis CPR5 either in transgenic Arabidopsis plants, or ectopically in tobacco, significantly enhanced ethylene sensitivity. These findings indicate that CPR5 plays a critical role in regulating ethylene signaling. CPR5 is localized to endomembrane structures and the nucleus, and is involved in various regulatory pathways, including pathogenesis, leaf senescence, and spontaneous cell death. This study provides evidence for a novel regulatory function played by CPR5 in the ethylene receptor signaling pathway in Arabidopsis.

Synthesis of quinoline/naphthalene-containing azaphenothiazines and their potent in vitro antioxidant properties.

New tetracyclic and pentacyclic azaphenothiazines containing one or two quinoline rings instead of benzene rings were obtained in the original reactions of isomeric diquinodithiins, dichlorodiquinolinyl sulfides, and disulfide with aromatic amines. The type of ring fusion in the azaphenothiazine system was concluded from the 1H NMR spectra. The obtained azaphenothiazines were evaluated in vitro for their antioxidant activity on rat hepatic microsomal membranes for protection of non-enzymatic lipid peroxidation promoted by the Fe2+/ascorbic acid redox system. Most compounds exhibited a very significant antioxidant activity with IC50 values between 1 and 23 µM. The degree of antioxidant activity depends on the lipophilicity and molecular size as well as the (non)substitution of the thiazine nitrogen atom and type of ring system fusion. It is the first time to our knowledge that azaphenothiazines are shown to exhibit such potent antioxidant activity.