Alfonso Oriente

Oxygen radicals inhibit human plasma acetylhydrolase, the enzyme that catabolizes platelet-activating factor.

Platelet-activating factor (PAF) can exert profound inflammatory effects at very low concentrations. In plasma, PAF is hydrolyzed to lyso-PAF by acetylhydrolase, an enzyme that circulates bound to LDL. Previous studies suggest that oxygen radicals may act synergistically with PAF to potentiate tissue injury. However, mechanisms underlying this interaction have not been elucidated. In this study we investigated whether oxygen radicals may inactivate PAF acetylhydrolase. PAF acetylhydrolase activity was measured in human plasma and purified LDL before and after exposure to radicals (10-20 nmol/min per ml) generated by xanthine/xanthine oxidase. Oxygen radicals induced > 50% loss of PAF acetylhydrolase activity within 60 s and almost complete inactivation by 10 min. This phenomenon was irreversible and independent of oxidative modification of LDL. Inactivation occurred without changes in the affinity constant of the enzyme (Km was 17.9 microM under control conditions and 15.1 microM after exposure to oxygen radicals). Inactivation was prevented by the scavengers superoxide dismutase or dimethylthiourea or by the iron chelator deferoxamine. Thus, superoxide-mediated, iron-catalyzed formation of hydroxyl radicals can rapidly and irreversibly inactivate PAF acetylhydrolase. Since concomitant production of PAF and oxygen radicals can occur in various forms of tissue injury, inactivation of acetylhydrolase might represent one mechanism by which oxygen radicals may potentiate and prolong the proinflammatory effects of PAF.

Histamine Induces Exocytosis and IL-6 Production from Human Lung Macrophages Through Interaction with H1 Receptors

Increasing evidence suggests that a continuous release of histamine from mast cells occurs in the airways of asthmatic patients and that histamine may modulate functions of other inflammatory cells such as macrophages. In the present study histamine (10−9–10−6 M) increased in a concentration-dependent fashion the basal release of β-glucuronidase (EC50 = 8.2 ± 3.5 × 10−9 M) and IL-6 (EC50 = 9.3 ± 2.9 × 10−8 M) from human lung macrophages. Enhancement of β-glucuronidase release induced by histamine was evident after 30 min and peaked at 90 min, whereas that of IL-6 required 2–6 h of incubation. These effects were reproduced by the H1 agonist (6-[2-(4-imidazolyl)ethylamino]-N-(4-trifluoromethylphenyl)heptane carboxamide but not by the H2 agonist dimaprit. Furthermore, histamine induced a concentration-dependent increase of intracellular Ca2+ concentrations ([Ca2+]i) that followed three types of response, one characterized by a rapid increase, a second in which [Ca2+]i displays a slow but progressive increase, and a third characterized by an oscillatory pattern. Histamine-induced β-glucuronidase and IL-6 release and [Ca2+]i elevation were inhibited by the selective H1 antagonist fexofenadine (10−7–10−4 M), but not by the H2 antagonist ranitidine. Inhibition of histamine-induced β-glucuronidase and IL-6 release by fexofenadine was concentration dependent and displayed the characteristics of a competitive antagonism (Kd = 89 nM). These data demonstrate that histamine induces exocytosis and IL-6 production from human macrophages by activating H1 receptor and by increasing [Ca2+]i and they suggest that histamine may play a relevant role in the long-term sustainment of allergic inflammation in the airways.

Secretory Phospholipases A2 Induce β-Glucuronidase Release and IL-6 Production from Human Lung Macrophages

Secretory phospholipases A2 (sPLA2s) are a group of extracellular enzymes that release fatty acids at the sn-2 position of phospholipids. Group IIA sPLA2 has been detected in inflammatory fluids, and its plasma level is increased in inflammatory diseases. To investigate a potential mechanism of sPLA2-induced inflammation we studied the effect of group IA (from cobra venom) and group IIA (human synovial) sPLA2s on human macrophages. Both sPLA2s induced a concentration- and Ca2+-dependent, noncytotoxic release of β-glucuronidase (16.2 ± 2.4% and 13.1 ± 1.5% of the total content with groups IA and IIA, respectively). Both sPLA2s also increased the rate of secretion of IL-6 and enhanced the expression of IL-6 mRNA. Preincubation of macrophages with inhibitors of the hydrolytic activity of sPLA2 or cytosolic PLA2 did not influence the release of β-glucuronidase. Incubation of macrophages with p-aminophenyl-mannopyranoside-BSA (mp-BSA), a ligand of the mannose receptor, also resulted in β-glucuronidase release. However, while preincubation of macrophages with mp-BSA had no effect on β-glucuronidase release induced by group IIA sPLA2, it enhanced that induced by group IA sPLA2. A blocking Ab anti-mannose receptor inhibited both mp-BSA- and group IIA-induced β-glucuronidase release. Taken together, these data indicate that group IA and IIA sPLA2s activate macrophages with a mechanism independent from their enzymatic activities and probably related to the activation of the mannose receptor or sPLA2-specific receptors. The secretion of enzymes and cytokines induced by sPLA2s from human macrophages may play an important role in inflammation and tissue damage associated with the release of sPLA2s.

Secretory phospholipases A2 induce cytokine release from blood and synovial fluid monocytes.

Secretory phospholipases A2 (sPLA2) are released in the blood of patients with various inflammatory diseases and exert proinflammatory activities by releasing arachidonic acid (AA), the precursor of eicosanoids. We examined the ability of four sPLA2 to activate blood and synovial fluid monocytes in vitro. Monocytes were purified from blood of healthy donors or from synovial fluid of patients with rheumatoid arthritis by negative immunoselection and by adherence to plastic dishes, respectively. The cells were incubated with group IA, IB, IIA and III sPLA2 and the release of TNF‐α, IL‐6 and IL‐12 was determined by ELISA. Group IA, IB and IIA sPLA2 induced a concentration‐dependent release of TNF‐α and IL‐6 from bloodmonocytes. These sPLA2 activated IL‐12 production only in monocytes preincubated with IFN‐γ. Group IA and IIA sPLA2 also induced TNF‐α and IL‐6 release from synovial fluid monocytes. TNF‐α and IL‐6 release paralleled an increase in their mRNA expression and was independent from the capacity of sPLA2 to mobilize AA. These results indicate that sPLA2 stimulate cytokine release from blood and synovial fluid monocytes by a mechanism at least partially unrelated to their enzymatic activity. This effect may concur with the generation of AA in theproinflammatory activity of sPLA2 released during inflammatory diseases.

Short-term and long-term role of platelet activating factor as a mediator of in vivo platelet aggregation.

BACKGROUND Platelet activating factor (PAF) is a phospholipid released upon stimulation by a variety of cells and has been implicated in several pathophysiological events such as asthma and inflammatory diseases. However, although the ability to aggregate platelets in vitro was the first biological activity ascribed to PAF, its role in contributing to the in vivo formation of arterial thrombi has not been thoroughly clarified. METHODS AND RESULTS Intravascular platelet aggregation was initiated in two different animal models of arterial stenosis and endothelial injury. An external constrictor was positioned around rabbit carotid arteries and canine coronary arteries. After placement of the constrictor, a typical pattern of flow developed in the stenotic vessels. This pattern of flow, characterized by progressive reductions of carotid or coronary blood flow followed by spontaneous or induced restorations of flow (cyclic flow variations, CFVs), is related to recurrent platelet aggregation at the site of the stenosis followed by dislodgment of the thrombus. After observing CFVs for 30 minutes, BN52021 (up to 1.2 mg/kg), a potent and selective PAF antagonist, was given intravenously to rabbits (n = 12) and dogs (n = 10). BN52021 completely inhibited CFVs in 10 of 12 rabbits, whereas it was relatively ineffective in abolishing CFVs in dogs (only 2 of 10 animals inhibited). This different effect of BN52021 was not explained by too small a dose of the drug to achieve a complete blockade of PAF receptors in dogs, since ex vivo platelet aggregation was completely inhibited in both rabbits and dogs in response to exogenous PAF at concentrations up to 10(-5) mol/L. In a second group of 10 dogs, the hypothesis that PAF may become an important mediator of CFVs in dogs only several hours after endothelial injury was tested. After 30 minutes of baseline CFVs, these animals received a bolus of BN52021 up to 1.2 mg/kg. After this treatment, CFVs were completely abolished in 2 of 10 animals. The remaining 8 dogs were followed for an additional 8-hour period, at the end of which a second bolus of BN52021 was given. At this time, BN52021 was effective, as CFVs were abolished in 6 of 8 animals. These effects of BN52021 at 8 hours were not the consequence of a cumulative dose of the compound, since ex vivo platelet aggregation in response to PAF returned to baseline values immediately before administering the second dose. To identify possible sources of PAF other than aggregating platelets at the site of arterial stenosis, dogs in a third group were killed after 30 minutes (n = 7) and after 8 hours (n = 8) of CFVs. Histological sections of the stenotic coronary artery showed a marked leukocyte infiltration in these arterial segments after 8 hours of CFVs, whereas sections from dogs killed after 30 minutes showed only moderate or no infiltration. CONCLUSIONS These data demonstrate that PAF plays an important role as a mediator of platelet aggregation in vivo in rabbits and dogs. In the canine model, PAF appears to become more important after leukocyte infiltration of the arterial wall, as it may contribute to initiating enough platelet activation to lead to cyclic flow variations at sites of arterial stenosis and endothelial injury. Data from the present study suggest that PAF antagonists may be used as antiplatelet agents.

Is the involvement of the distal interphalangeal joint in psoriatic patients related to nail psoriasis

The aim of this study was to investigate the relationship between onychopathy and distal interphalangeal (DIP) joint involvement in psoriatic patients. Twenty-five consecutive unselected, unrelated patients with psoriatic onychopathy and 25 consecutive unselected, unrelated patients with psoriatic arthritis without onychopathy, were enrolled in the study. X-ray films of the hands were taken to identify DIP arthritic involvement and/or bone changes of the distal phalanx, which were categorized into five classes (0: no lesions; 1: tuftal minimal erosions; 2: tuftal bone resorption; 3: tuftal periosteal osteitis; 4: overlap of erosive and osteitic changes). Ten psoriatic patients with onychopathy and 8 without showed DIP arthritis, with no statistical differences in this distribution (p=0.556). Bone changes of the distal phalanx were found in all 25 psoriatic patients with onychopathy and in 18 without. The distribution of patients in different categories of involvement of the distal phalanx showed that patients without onychopathy were markedly distributed in the categories with no or minimal lesions, whereas patients with onychopathy had structural changes prevailing included in categories with more severe bone changes (osteitis and overlap of erosive and osteitic changes) (p=0.002). Onychopathic patients with DIP arthritis were older than those without (p<0.0001) and showed a longer duration of onychopathy (p<0.0001). Although the occurrence of DIP arthritis seems to depend on the duration of nail involvement, no statistical difference has been found in the distribution of DIP arthritis in psoriatic patients with or without onychopathy. In contrast, a topographical association between bone changes of the distal phalanx and dystrophy of the adjacent nail may be advanced.

Biochemical Functions of a Pool of Arachidonic Acid Associated with Triglycerides in Human Inflammatory Cells

The distribution of arachidonic acid (AA) within intracellular lipid pools of inflammatory cells is thought to be an important factor regulating the production of eicosanoids. We have recently identified a pool of AA associated with triglycerides (TGs) in human lung macrophages. This pool is also present in other human inflammatory cells (mast cells, eosinophils, monocytes and platelets) and it contains a percentage of total cellular AA ranging from 10 to 45%. Kinetic studies of AA incorporation have shown that TG are the first acceptor pool for exogenous AA that is subsequently transferred to phospholipid pools. During cell activation, AA is released from phospholipids; however, a large amount of AA is rapidly reincorporated into TGs. The TG pool also supplies AA to the phospholipid pools once these have been depleted during cell activation. These data suggest that TGs are not only a storage site for AA but may also be important as regulators of AA metabolism and eicosanoid biosynthesis in human inflammatory cells.

Fragility Fractures in Patients with Psoriatic Arthritis

Psoriatic arthritis (PsA) can have peculiar effects on bone, including mechanisms of bone loss such as erosions, but also of bone formation, such as ankylosis or periostitis. The aim of the present study was to describe the prevalence of fractures in patients with PsA as compared to healthy controls and to investigate determinants of fractures among cases. For both cases and controls, radiographs were read to identify vertebral fractures (VF), and the presence of femoral neck or other nonvertebral fractures was obtained from patients’ medical history. The prevalence of fragility fractures on radiographic readings did not differ between cases and controls. The number of subjects showing a VF was 33 (36%) among PsA patients and 36 (36%) among controls, with a prevalence of severe VF of 8% among cases and 4% among controls. Controlling for covariates in a logistic model, the only variables showing a significant correlation with the presence of nonvertebral fractures (NVF) were disease duration (p = 0.02), age (p = 0.03), and bone mineral density at femoral neck (inverse correlation, p = 0.04). Fractures should be carefully considered when evaluating the global picture of the patient with PsA for their contribution to the “fragility” profile.

Serum A1 and B apolipoprotein determination: comparison of an immunoturbidimetric method with a monoclonal-antibody-based radial immunodiffusion assay

SummaryEpidemiological and clinical evidence have indicated that apolipoprotein A1 and B determination can better define the lipoprotein pattern in normal subjects and in subjects with coronary heart disease. In this paper, a recent immunoturbidimetric method for routine apolipoprotein A1 and B measurement (using the Turbitimer system and commercially available antisera) has been evaluated. The precision and the accuracy of the method have been previously considered. Within-run and between-run coefficients of variation (ranging from 1.67% to 5.04%) for both assays indicate good precision of the method. Accuracy was evaluated on 2 consecutive days (n=10 each run) using a standard serum for apolipoprotein A1 and B. The bias obtained was 3.79% for apolipoprotein A1 and 2.30% for B. Apolipoproteins A1 and B were then measured in 100 normal and hyperlipemic sera with the immunoturbidimetric assay and radial immunodiffusion (using the monoclonal antibodies). The data obtained were evaluated by linear regression analysis (A1,r=0.893; B,r=0.862). The good correlation between the two methods suggests that the immunoturbidimetric assay can be usefully performed for routine apolipoprotein A1 and B determination because of its lower cost, rapidity, and simplicity.

Sources of Arachidonic Acid in Human Lung Macrophages

The aim of this study was to define the lipid pools in which arachidonic acid (AA) is stored and from which it is released upon activation of human lung macrophages (HLM). HLM incorporate exogenous AA