Annexin A1 as a potential prognostic biomarker for COVID-19 disease: Case-control study

BACKGROUND

Annexin A1 (AnxA1) is an important endogenous glucocoticoid protein that contributes to the suppression of inflammation by limiting the production of neutrophil and pro-inflammatory cytokines. This study aims to determine the clinical predictivity value of blood AnxA1 levels in patients with mild and severe-critical pneumonia induced by COVID-19.

METHODS

This study employed a prospective, case-control study design and was conducted at Ankara Training and Research hospital between 10 February 2021 and 15 March 2021. A total of 74 patients (42 of whom had moderate and 32 of whom had severe/critical cases of COVID-19 disease according to World Health Organization guidelines) and 50 nonsymptomatic healthy volunteers participated in the study. Blood samples were taken from patients at the time of hospital admission, after which serum was isolated. Following the isolation of serum, AnxA1 levels were evaluated using the enzyme-linked immunosorbent assay method.

RESULTS

The serum AnxA1 levels were measured as 25.5 (18.6-38.6) ng/ml in the control group, 21.2 (14.7-32) ng/ml in the moderate disease group, and 14.8 (9.7-26.8) ng/ml in the severe/critical disease group. Serum AnxA1 levels were significantly lower in the severe/critical disease group compared with the control and moderate disease groups (P = .01 and P = .0001, respectively). Using receiver operating characteristic analysis, a larger area under the curve (AUC) for the serum AnxA1 levels of the control group (AUC = 0.715, 95% CI = 0.626-0.803; P = .0001) was calculated compared with the COVID-19 patient group for the diagnosis of COVID-19 disease. The AnxA1 level was found to be 80% sensitive and 54.1% specific at a cut-off level of 18.5 ng/ml for the diagnosis of COVID-19 disease. Moreover, the AnxA1 level was found to be 69.8% sensitive and 58.1% specific at a cut-off level of 17.2 ng/ml in predicting the need for intensive care unit (ICU) treatment.

CONCLUSION

AnxA1 levels may be a beneficial biomarker in the diagnosis of COVID-19 pneumonia and in predicting the need for ICU treatment in patients with COVID-19 pneumonia at the time of admission to the emergency department.

Annexin A1 attenuates microvascular complications through restoration of Akt signalling in a murine model of type 1 diabetes

AIMS/HYPOTHESIS

Microvascular complications in the heart and kidney are strongly associated with an overall rise in inflammation. Annexin A1 (ANXA1) is an endogenous anti-inflammatory molecule that limits and resolves inflammation. In this study, we have used a bedside to bench approach to investigate: (1) ANXA1 levels in individuals with type 1 diabetes; (2) the role of endogenous ANXA1 in nephropathy and cardiomyopathy in experimental type 1 diabetes; and (3) whether treatment with human recombinant ANXA1 attenuates nephropathy and cardiomyopathy in a murine model of type 1 diabetes.

METHODS

ANXA1 was measured in plasma from individuals with type 1 diabetes with or without nephropathy and healthy donors. Experimental type 1 diabetes was induced in mice by injection of streptozotocin (STZ; 45 mg/kg i.v. per day for 5 consecutive days) in C57BL/6 or Anxa1 ^-/- mice. Diabetic mice were treated with human recombinant (hr)ANXA1 (1 μg, 100 μl, 50 mmol/l HEPES; 140 mmol/l NaCl; pH 7.4, i.p.) or vehicle (100 μl, 50 mmol/l HEPES; 140 mmol/l NaCl; pH 7.4, i.p.).

RESULTS

Plasma levels of ANXA1 were elevated in individuals with type 1 diabetes with/without nephropathy compared with healthy individuals (66.0 ± 4.2/64.0 ± 4 ng/ml vs 35.9 ± 2.3 ng/ml; p < 0.05). Compared with diabetic wild-type (WT) mice, diabetic Anxa1 ^-/- mice exhibited a worse diabetic phenotype and developed more severe cardiac (ejection fraction; 76.1 ± 1.6% vs 49.9 ± 0.9%) and renal dysfunction (proteinuria; 89.3 ± 5.0 μg/mg vs 113.3 ± 5.5 μg/mg). Mechanistically, compared with non-diabetic WT mice, the degree of the phosphorylation of mitogen-activated protein kinases (MAPKs) p38, c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK) was significantly higher in non-diabetic Anxa1 ^-/- mice in both the heart and kidney, and was further enhanced after STZ-induced type 1 diabetes. Prophylactic treatment with hrANXA1 (weeks 1-13) attenuated both cardiac (ejection fraction; 54.0 ± 1.6% vs 72.4 ± 1.0%) and renal (proteinuria; 89.3 ± 5.0 μg/mg vs 53.1 ± 3.4 μg/mg) dysfunction associated with STZ-induced diabetes, while therapeutic administration of hrANXA1 (weeks 8-13), after significant cardiac and renal dysfunction had already developed, halted the further functional decline in cardiac and renal function seen in diabetic mice administered vehicle. In addition, administration of hrANXA1 attenuated the increase in phosphorylation of p38, JNK and ERK, and restored phosphorylation of Akt in diabetic mice.

CONCLUSIONS/INTERPRETATION

Overall, these results demonstrate that ANXA1 plasma levels are elevated in individuals with type 1 diabetes independent of a significant impairment in renal function. Furthermore, in mouse models with STZ-induced type 1 diabetes, ANXA1 protects against cardiac and renal dysfunction by returning MAPK signalling to baseline and activating pro-survival pathways (Akt). We propose ANXA1 to be a potential therapeutic option for the control of comorbidities in type 1 diabetes.

Identification of two phosphorylation sites essential for annexin A1 in blood-brain barrier protection after experimental intracerebral hemorrhage in rats

Annexin A1 has been reported to exert a blood-brain barrier protection. This study was designed to examine the role of annexin A1 in intracerebral hemorrhage-induced blood-brain barrier dysfunction. A collagenase intracerebral hemorrhage model was performed in adult male Sprague Dawley rats. First, a possible relationship between annexin A1 and intracerebral hemorrhage pathology was confirmed by a loss of annexin A1 in the cerebrovascular endothelium and serum of intracerebral hemorrhage rats, and the rescue effects of i.v. administration of human recombinant annexin A1 in vivo and annexin A1 overexpression in vitro on the barrier function of brain microvascular endothelial cells exposed to intracerebral hemorrhage stimulus. Second, we found that intracerebral hemorrhage significantly increased the phosphorylation ratio of annexin A1 at the serine/threonine residues. Finally, based on site-specific mutagenesis, we identified two phosphorylation sites (a) annexin A1 phosphorylation at threonine 24 is required for its interaction with actin cytoskeleton, and (b) phosphorylation at serine27 is essential for annexin A1 secretion, both of which were essential for maintaining cytoskeleton integrity and paracellular permeability. In conclusion, annexin A1 prevents intracerebral hemorrhage-induced blood-brain barrier dysfunction in threonine 24 and serine27 phosphorylation-dependent manners. Annexin A1 phosphorylation may be a self-help strategy in brain microvascular endothelial cells after intracerebral hemorrhage; however, that was almost completely abolished by the intracerebral hemorrhage-induced loss of annexin A1.

Inflammation in Sickle Cell Disease: Differential and Down-Expressed Plasma Levels of Annexin A1 Protein

Sickle cell disease (SCD) is an inherited hemolytic anemia whose pathophysiology is driven by polymerization of the hemoglobin S (Hb S), leading to hemolysis and vaso-occlusive events. Inflammation is a fundamental component in these processes and a continuous inflammatory stimulus can lead to tissue damages. Thus, pro-resolving pathways emerge in order to restore the homeostasis. For example there is the annexin A1 (ANXA1), an endogenous anti-inflammatory protein involved in reducing neutrophil-endothelial interactions, accelerating neutrophil apoptosis and stimulating macrophage efferocytosis. We investigated the expression of ANXA1 in plasma of SCD patients and its relation with anemic, hemolytic and inflammatory parameters of the disease. Three SCD genotypes were considered: the homozygous inheritance for Hb S (Hb SS) and the association between Hb S and the hemoglobin variants D-Punjab (Hb SD) and C (Hb SC). ANXA1 and proinflammatory cytokines were quantified by ELISA in plasma of SCD patients and control individuals without hemoglobinopathies. Hematological and biochemical parameters were analyzed by flow cytometry and spectrophotometer. The plasma levels of ANXA1 were about three-fold lesser in SCD patients compared to the control group, and within the SCD genotypes the most elevated levels were found in Hb SS individuals (approximately three-fold higher). Proinflammatory cytokines were higher in SCD groups than in the control individuals. Anemic and hemolytic markers were higher in Hb SS and Hb SD genotypes compared to Hb SC patients. White blood cells and platelets count were higher in Hb SS genotype and were positively correlated to ANXA1 levels. We found that ANXA1 is down-regulated and differentially expressed within the SCD genotypes. Its expression seems to depend on the inflammatory, hemolytic and vaso-occlusive characteristics of the diseased. These data may lead to new biological targets for therapeutic intervention in SCD.

Human Blood Autoantibodies in the Detection of Colorectal Cancer

Colorectal cancer (CRC) is the second most common malignancy in the western world. Early detection and diagnosis of all cancer types is vital to improved prognosis by enabling early treatment when tumours should be both resectable and curable. Sera from 3 different cohorts; 42 sera (21 CRC and 21 matched controls) from New York, USA, 200 sera from Pittsburgh, USA (100 CRC and 100 controls) and 20 sera from Dundee, UK (10 CRC and 10 controls) were tested against a panel of multiple tumour-associated antigens (TAAs) using an optimised multiplex microarray system. TAA specific IgG responses were interpolated against the internal IgG standard curve for each sample. Individual TAA specific responses were examined in each cohort to determine cutoffs for a robust initial scoring method to establish sensitivity and specificity. Sensitivity and specificity of combinations of TAAs provided good discrimination between cancer-positive and normal serum. The overall sensitivity and specificity of the sample sets tested against a panel of 32 TAAs were 61.1% and 80.9% respectively for 6 antigens; p53, AFP, K RAS, Annexin, RAF1 and NY-CO16. Furthermore, the observed sensitivity in Pittsburgh sample set in different clinical stages of CRC; stage I (n = 19), stage II (n = 40), stage III (n = 34) and stage IV (n = 6) was similar (73.6%, 75.0%, 73.5% and 83.3%, respectively), with similar levels of sensitivity for right and left sided CRC. We identified an antigen panel of sufficient sensitivity and specificity for early detection of CRC, based upon serum profiling of autoantibody response using a robust multiplex antigen microarray technology. This opens the possibility of a blood test for screening and detection of early colorectal cancer. However this panel will require further validation studies before they can be proposed for clinical practice.

Alterations in the profile of blood neutrophil membrane receptors caused by in vivo adrenocorticotrophic hormone actions

Elevated levels of adrenocorticotrophic hormone (ACTH) mobilize granulocytes from bone marrow into the blood, although these neutrophils are refractory to a full migratory response into inflamed tissues. Here, we investigated the dependence of glucocorticoid receptor activation and glucocorticoid-regulated protein annexin A1 (ANXA1) on ACTH-induced neutrophilia and the phenotype of blood neutrophil after ACTH injection, focusing on adhesion molecule expressions and locomotion properties. ACTH injection (5 μg ip, 4 h) induced neutrophilia in wild-type (WT) mice and did not alter the elevated numbers of neutrophils in RU-38486 (RU)-pretreated or ANXA1(-/-) mice injected with ACTH. Neutrophils from WT ACTH-treated mice presented higher expression of Ly6G⁺ANXA1(high), CD18(high), CD62L(high), CD49(high), CXCR4(high), and formyl-peptide receptor 1 (FPR1(low)) than those observed in RU-pretreated or ANXA1(-/-) mice. The membrane phenotype of neutrophils collected from WT ACTH-treated mice was paralleled by elevated fractions of rolling and adherent leukocytes to the cremaster postcapillary venules together with impaired neutrophil migration into inflamed air pouches in vivo and in vitro reduced formyl-methionyl-leucyl-phenylalanine (fMLP) or stromal-derived factor-1 (SDF-1α)-induced chemotaxis. In an 18-h senescence protocol, neutrophils from WT ACTH-treated mice had a higher proportion of ANXAV(low)/CXCR4(low), and they were less phagocytosed by peritoneal macrophages. We conclude that alterations on HPA axis affect the pattern of membrane receptors in circulating neutrophils, which may lead to different neutrophil phenotypes in the blood. Moreover, ACTH actions render circulating neutrophils to a phenotype with early reactivity, such as in vivo leukocyte-endothelial interactions, but with impaired locomotion and clearance.

Dysregulation of anti-inflammatory annexin A1 expression in progressive Crohns Disease

Background

Development of inflammatory bowel disease (IBD) involves the interplay of environmental and genetic factors with the host immune system. Mechanisms contributing to immune dysregulation in IBD are not fully defined. Development of novel therapeutic strategies is focused on controlling aberrant immune response in IBD. Current IBD therapy utilizes a combination of immunomodulators and biologics to suppress pro-inflammatory effectors of IBD. However, the role of immunomodulatory factors such as annexin A1 (ANXA1) is not well understood. The goal of this study was to examine the association between ANXA1 and IBD, and the effects of anti-TNF-α, Infliximab (IFX), therapy on ANXA1 expression.

Methods

ANXA1 and TNF-α transcript levels in PBMC were measured by RT PCR. Clinical follow up included the administration of serial ibdQs. ANXA1 expression in the gut mucosa was measured by IHC. Plasma ANXA1 levels were measured by ELISA.

Results

We found that the reduction in ANXA1 protein levels in plasma coincided with a decrease in the ANXA1 mRNA expression in peripheral blood of IBD patients. ANXA1 expression is upregulated during IFX therapy in patients with a successful intervention but not in clinical non-responders. The IFX therapy also modified the cellular immune activation in the peripheral blood of IBD patients. Decreased expression of ANXA1 was detected in the colonic mucosa of IBD patients with incomplete resolution of inflammation during continuous therapy, which correlated with increased levels of TNF-α transcripts. Gut mucosal epithelial barrier disruption was evident by increased plasma bacterial 16S levels.

Conclusion

Loss of ANXA1 expression may support inflammation during IBD and can serve as a biomarker of disease progression. Changes in ANXA1 levels may be predictive of therapeutic efficacy.

Plasma levels in sepsis patients of annexin A1, lipoxin A4, macrophage inflammatory protein-3a, and neutrophil gelatinase-associated lipocalin

BACKGROUND

The relationship between the various cytokine responses that occur during sepsis remains controversial. Emerging evidence indicates that the proinflammatory and anti-inflammatory responses are regulated simultaneously from the beginning of sepsis. However, the roles of the novel anti-inflammatory mediators annexin (Anx)A1 and lipoxin (LX)A4 and the proinflammatory cytokines neutrophil gelatinase-associated lipocalin (NGAL) and macrophage inflammatory protein (MIP)-3a have been studied.

METHODS

In this study, the plasma levels of AnxA1, LXA4, NGAL, MIP-3a, interleukin (IL)-8 and IL-6 in patients with sepsis were determined on admission to the intensive care unit. The patients were classified into survivors and non-survivors based on their outcome on day 28.

RESULTS

AnxA1 and LXA4 levels were decreased in sepsis patients compared with control patients, whereas the levels of the proinflammatory cytokines MIP-3a, NGAL, IL-8, and IL-6 were elevated. Furthermore, a significantly higher level of MIP-3a was detected in nonsurviving patients compared with surviving patients (p < 0.05), whereas there were no significant differences between these two groups for the levels of the other mediators. Correlation analysis demonstrated that only NGAL level was closely correlated with the level of IL-6. Univariate analysis indicated that the levels of MIP-3a and IL-8 were independent factors associated with patient survival, but this was not confirmed by the multivariate analysis.

CONCLUSION

AnxA1 and LXA4 plasma levels were found to be decreased in sepsis patients, whereas the levels of MIP-3a and NGAL were found to be elevated. This warrants further study in order to determine the clinical implications of these changes.

Correlation between the antiinflammatory protein annexin 1 (lipocortin 1) and serum cortisol in subjects with normal and dysregulated adrenal function

Annexin 1 (ANXA1), a Ca(2+) and phospholipid binding protein, is an important mediator of the antiinflammatory actions of glucocorticoids. However, although inflammatory responses in man are sensitive to alterations in adrenocortical function, the relationship between endogenous cortisol and ANXA1 expression has not been explored. Accordingly, we measured serum cortisol levels and ANXA1 expression in peripheral blood leukocytes from subjects with normal and dysregulated cortisol secretion before and 30 min after a standard corticotrophin (ACTH) test. Our data demonstrate a highly significant correlation between the serum cortisol concentration and the expression of ANXA1 in neutrophils, both before and after ACTH treatment, and thus suggest that ANXA1 may serve as a marker of glucocorticoid sensitivity. They also reveal a correlation between ANXA1 and the serum gonadotrophins, LH and FSH, and an age-related reduction in ANXA1 expression in lymphocytes.

Detection of annexins I and IV in bronchoalveolar lavage fluids from calves inoculated with bovine herpes virus-1

Annexins are phospholipid-binding proteins and are abundant in the lung. Annexins I and IV, but not II and VI, have been detected in bronchoalveolar lavage (BAL) fluids from calves inoculated with Pasteurella haemolytica, the pathogen for calf pneumonia. In this study, BAL fluids from calves with experimental pneumonia induced by inoculation to right lung lobes of bovine herpes virus-1 (BHV-1), the major viral pathogen for pneumonia, were examined for detection of annexins I and IV. Of 6 calves inoculated with BHV-1, annexins I and IV were coincidentally detected in BAL fluids from right lung lobes of 4 calves, but not in BAL fluids from left lung lobes of 6 inoculated calves or those from left and right lung lobes of 3 control calves. Annexin II and VI were not found in any BAL fluids examined. These results, together with previous findings on calves inoculated with Pasteurella haemolytica, suggest that the release of annexins I and IV onto the alveolar surface is an essential event occurring in response to pulmonary infections of BHIV-1 and Pasteurella haemolytica.

Modulation of cellular annexin I in human leukocytes infiltrating DTH skin reactions

Based on our previous studies showing endogenous annexin I being depleted from migrated neutrophils (PMN) in vitro, we have tested whether the levels of this glucocorticoid-regulated protein in PMN and mononuclear cells (PBMC) were modified after adhesion to endothelial monolayers in vitro and extravasation into skin blisters in vivo. In vitro, annexin I levels were depleted more significantly (-70%) in post-adherent PMNs than in monocytes (-25%) and lymphocytes (-50%, only in the positive fraction). In vivo, a significant time-dependent increase (approximately threefold, P < 0.05) in cell-associated annexin I was measured in PBMCs recovered from the blisters, whereas no significant changes were detected in extravasated PMNs. This was associated with annexin I release in the blister fluids (approximately 35 ng/mL), whereas no detectable protein was found in matched-paired plasmas. In conclusion, we report for the first time an activation of the annexin I pathway during an ongoing experimental inflammatory response in humans, which is differently regulated between PMNs and PBMCs.

Differential modulation of annexin I binding sites on monocytes and neutrophils

Specific binding sites for the anti-inflammatory protein annexin I have been detected on the surface of human monocytes and polymorphonuclear leukocytes (PMN). These binding sites are proteinaceous in nature and are sensitive to cleavage by the proteolytic enzymes trypsin, collagenase, elastase and cathepsin G. When monocytes and PMN were isolated independently from peripheral blood, only the monocytes exhibited constitutive annexin I binding. However PMN acquired the capacity to bind annexin I following co-culture with monocytes. PMN incubation with sodium azide, but not protease inhibitors, partially blocked this process. A similar increase in annexin I binding capacity was also detected in PMN following adhesion to endothelial monolayers. We propose that a juxtacrine activation rather than a cleavage-mediated transfer is involved in this process. Removal of annexin I binding sites from monocytes with elastase rendered monocytes functionally insensitive to full length annexin I or to the annexin I-derived pharmacophore, peptide Ac2-26, assessed as suppression of the respiratory burst. These data indicate that the annexin I binding site on phagocytic cells may have an important function in the feedback control of the inflammatory response and their loss through cleavage could potentiate such responses.

Autoantigen components recognizable by scleroderma sera are exported via ectocytosis of fibroblasts

Previously, we have demonstrated that ectocytosis, a unique cell trafficking process to export a specific subset of cellular proteins in the form of membrane vesicles, can be triggered from human skin fibroblasts cultured in a three-dimensional collagen lattice upon stress relaxation. The same culturing system was employed in the present study using fibroblasts isolated from patients with systemic sclerosis (SSc). To see whether any putative intracellular autoantigens causing SSc might escape out of cells by way of ectocytosis, the same stress-relaxation method was used to induce a synchronized ectocytosis among cultured cells. Membrane vesicles released by scleroderma fibroblasts were subsequently isolated, resolved on SDS-PAGE and immunoblotted with sera from 89 patients with various autoimmune diseases and 11 normal volunteers. Three major polypeptides with apparent mol. wts of 12-14, 32-34 and 70-80 kDa are prominent bands on both SDS-PAGE and immunoblots. The 32-34 kDa polypeptide has been further identified as a member of the annexin protein family, while the 70-80 kDa protein has been shown to be topoisomerase I, as judged by its reactivity to patients' sera and a rabbit polyclonal antibody, and as also judged by a functional assay. In conclusion, our results suggest that ectocytosis might be one of the potential pathways for cells to export intracellular antigens and subsequently cause autoimmune reactions.

Exacerbation of adjuvant arthritis by adrenalectomy is associated with reduced leukocyte lipocortin 1

OBJECTIVE

Lipocortin 1 is a mediator of the antiinflammatory actions of therapeutic glucocorticoids. ENdogenous glucocorticoids modulate inflammatory arthritides including rheumatoid and adjuvant arthritis (AA), but the role of lipocortin 1 in this phenomenon is not known. We studied the effects of endogenous glucocorticoids on adjuvant arthritis and leukocyte lipocortin 1 content.

METHODS

Adrenalectomy of sham adrenalectomy was performed 2 days before adjuvant injection in 170 g inbred Sprague-Dawley rats. Peripheral blood was obtained and disease severity assessed by delta paw volume and clinical score 14 days later. Leukocyte subset lipocortin 1 content was determined by double labeling permeabilization flow cytometry using specific monoclonal antibodies.

RESULTS

Lipocortin 1 fluorescence was readily detected in control rat peripheral blood cells labeled with OX-1 (pan-leukocyte), OX-19 (CD5), W3/25 (CD4), and OX-8 (CD8). Lipocortin 1 fluorescence was significantly greater in polymorphonuclear leukocytes (PMN) (RP3; p < 0.01). Induction of AA was accompanied by significant increases in lipocortin 1 (p < 0.001) in all subsets. Sham adrenalectomy induced no significant change in AA rat leukocyte lipocortin 1. Adrenalectomy induced significant exacerbation of AA disease severity compared to sham operation (delta paw volume 1.43 +/- 0.1 vs 1.13 +/- 0 ml; p < 0.05). Adrenalectomy was also associated with significant reduction in lipocortin 1 content in all leukocyte subsets except PMN. Leukocyte lipocortin 1 content exhibited significant negative correlation with clinical disease severity (R2 = -0.55; p < 0.05).

CONCLUSION

Endogenous glucocorticoids modulate leukocyte expression of lipocortin 1 in inflammatory disease, and reduced lipocortin 1 may be involved in the exacerbation of AA by adrenalectomy.

Translocation of annexin I to plasma membranes and phagosomes in human neutrophils upon stimulation with opsonized zymosan: possible role in phagosome function

Annexin I in the cytosol of resting neutrophils was translocated to the plasma membranes upon addition of opsonized zymosan (OZ). Maximum translocation could be detected 1 min after stimulation with OZ, and decreased thereafter. Subcellular fractionation studies demonstrated that annexin I could not be detected in the granule fractions in either resting or activated cells, but was found in association with the phagosome fraction. The marked translocation of annexin I was unique to OZ, since formyl-Met-Leu-Phe induced only slight translocation of annexin I to the plasma membranes, and phorbol 12-myristate 13-acetate had no effect at all. The mechanism regulating the translocation of annexin I is not clear. Annexin I is not phosphorylated in resting or stimulated cells. The correlation between the elevation in the intracellular calcium ion concentration ([Ca2+]i) and the degree of translocation of annexin I to the plasma membranes induced by the different stimuli, together with the inhibition of these processes by the addition of EGTA, indicate that the translocation of annexin I can probably be attributed to the rise in [Ca2+]i. However, this cannot be the sole mechanism since ionomycin, which caused an increase in [CA2+]i similar to that induced by OZ, was less efficient than OZ in inducing translocation of annexin I. The induction of annexin I translocation to the plasma membrane by OZ, which was the only agent that induced phagosome formation, and the detection of annexin I in the phagosome fraction, suggest that annexin I participates in phagosome function.

Leukocyte transmigration, but not rolling or adhesion, is selectively inhibited by dexamethasone in the hamster post-capillary venule. Involvement of endogenous lipocortin 1

This study investigates the effect of dexamethasone on leukocyte extravasation in the post-capillary venules of the hamster cheek pouch, using an intravital microscopy technique, and seeks to clarify the potential involvement of the steroid-inducible protein lipocortin 1. Topical application of FMLP (10 nmol), or substance P (10 nmol), to the superfused cheek pouch induced at the level of the post-capillary venules the three characteristic phenomena of leukocyte rolling, adhesion, and transmigration. Pretreatment of hamsters with an anti-inflammatory dose of dexamethasone (1 mg/kg) increased lipocortin 1 levels in circulating leukocytes as assessed by flow cytometry, but did not modify either leukocyte rolling or the number of adherent cells; however approximately 65% of the adherent leukocytes subsequently detached and returned to the blood stream, whereas those that entered into the diapedesis process exhibited a long latency (approximately three- to fourfold longer than in control animals) before transmigration. In hamsters passively immunized with a polyclonal anti-lipocortin 1 serum, leukocyte diapedesis started at similar times in both control and dexamethasone-treated animals, whereas a significant prolongation was observed in those animals treated with a non-immune sheep serum. These observations indicate that 1) lipocortin 1 is elevated in circulating leukocytes following dexamethasone treatment; 2) the step of leukocyte extravasation affected by dexamethasone in the actual transmigration process, and 3) this specific effect upon leukocyte diapedesis is mediated by endogenous lipocortin 1.

Virtual lack of annexins in human platelets argues against a role in phospholipase A2 regulation and platelet secretion

Annexins are calcium-phospholipid binding proteins which share structural similarities and common biochemical properties. These proteins seem to be involved in different pathways of cell activation such as regulation of phospholipase A2 activity, membrane-cytoskeleton interaction, and exocytosis. The aim of this study was to attempt to characterize annexins in human platelets. Our results were based on specific EGTA extraction of proteins from platelet homogenates, immunodetection with specific antibodies raised against annexins I, II, V and VI, and measurement of phospholipase A2 inhibition. Antibodies raised against annexins I, V and VI revealed only trace amounts of these proteins in platelet EGTA extracts which did not promote phospholipase A2 inhibition in an in vitro assay. In addition, upon precipitation of membranes in the presence of calcium followed by EGTA extraction, the main substrate of protein kinase C (40-47-kDa protein) displayed a behaviour strictly different from that of annexins. Although one cannot exclude that a small amount of annexin(s) becomes phosphorylated in activated human platelets, these data argue against a role of annexins in the regulation of intracellular phospholipase A2 or in the processes of exocytosis in activated human platelets.

Lipocortin I is not accessible for protein kinase C bound to the cytoplasmic surface of the plasma membrane in streptolysin-O-permeabilized pig granulocytes

We previously observed a 38 kDa protein that was a major protein component of the cytosolic extract of pig granulocytes and the dominant substrate of protein kinase C at supra-physiological Ca2+ concentrations. The purified 38 kDa protein itself required Ca2+ to be phosphorylated by protein kinase C. Now we demonstrate that this protein, which is also present in human granulocytes, is identical to lipocortin I. The identification is based on the chromatographic properties and immunoblot of the purified protein which is also a good substrate for tissue transglutaminase. Phosphorylation of lipocortin I by protein kinase C was investigated in granulocytes permeabilized with streptolysin-O. At physiological intracellular Ca2+ concentrations lipocortin I was not phosphorylated at all. At supra-physiological Ca2+ concentrations (0.5 mM), lipocortin I was also not phosphorylated when protein kinase C was translocated to the membrane by treatment of the cells with phorbol myristate acetate. Its phosphorylation was detectable only in control experiments when protein kinase C was activated in the cytosol by the addition of dioleoylglycerol and phosphatidylserine to the permeabilized cells. The data presented show that, in permeabilized granulocytes, Ca(2+)-lipocortin is not formed at physiological Ca2+ concentrations, and at supra-physiological Ca2+ concentrations the Ca(2+)-lipocortin I is not accessible to protein kinase C bound to the cytoplasmic surface of the plasma membrane.

Presence of lipocortins I and IV, but not II and VI, in human platelets

The present investigation revealed the presence of lipocortins I and IV, but not lipocortins II and VI, in human platelets. Lipocortin I was found in the Triton-soluble fraction of both resting and thrombin-activated platelets and was not covalently bound to skeletal components. Without detergents, when resting platelets were lysed and fractionated in the absence of Ca2+, lipocortin I was found only in the cytosolic fraction, whereas, in the presence of Ca2+, lipocortin I was associated only with the crude particulate and not with the membrane nor the cytosolic fractions.

Evidence for the presence and location of annexins in human platelets

In this study the identity of annexins in human platelets has been determined together with their ability to be released by agents which induce platelet degranulation. The presence of proteins cross-reacting to antibodies against annexins I and V was detected in human platelets. However, the study provided evidence that these annexins are not located on the surface of the plasma membrane in a Ca++ dependent manner. Moreover, activation of platelets with several agents which induced platelet degranulation did not cause release of annexins I or V as determined by both immunoblotting and ELISA.