Synergism between particle-based multiplexing and microfluidics technologies may bring diagnostics closer to the patient.

In the field of medical diagnostics there is a growing need for inexpensive, accurate, and quick high-throughput assays. On the one hand, recent progress in microfluidics technologies is expected to strongly support the development of miniaturized analytical devices, which will speed up (bio)analytical assays. On the other hand, a higher throughput can be obtained by the simultaneous screening of one sample for multiple targets (multiplexing) by means of encoded particle-based assays. Multiplexing at the macro level is now common in research labs and is expected to become part of clinical diagnostics. This review aims to debate on the "added value" we can expect from (bio)analysis with particles in microfluidic devices. Technologies to (a) decode, (b) analyze, and (c) manipulate the particles are described. Special emphasis is placed on the challenges of integrating currently existing detection platforms for encoded microparticles into microdevices and on promising microtechnologies that could be used to down-scale the detection units in order to obtain compact miniaturized particle-based multiplexing platforms.

Development of a dual glow-signal firefly and Renilla luciferase assay reagent for the analysis of G-protein coupled receptor signalling.

Several reporter gene assays have been described where gene transcription is activated as a consequence of a specific signal transduction event, such as activation of adenylyl cyclase (1.2). Reporter genes typically consist of specific responsive elements placed upstream of a minimal promoter, which together control the expression of a readily detectable reporter protein, such as luciferase. We have developed a dual glow-signal firefly and Renilla luciferase assay, which allows the simultaneous measurement of two reporter genes in the same well of a 96-well plate. In this report we demonstrate the use of this assay for the simultaneous analysis of agonist activity at two G-protein coupled receptors which signal through activation of the G-protein alpha sub-unit, G alpha S. Chinese hamster ovary (CHO) cells stably transfected with a cAMP responsive firefly luciferase reporter were further transfected with the human Vasopressin V2 receptor. Similarly, CHO cells stably transfected with a cAMP responsive Renilla luciferase reporter were further transfected with the human beta 2-adrenoceptor. The two cell lines were mixed in individual wells of a 96-well plate and a number of compounds were screened to determine their activity at both receptors. Stimulation with vasopressin and beta 2-adrenoceptor agonists resulted in the activation of the firefly and Renilla luciferases respectively. Stimulation with forskolin, which directly stimulates adenylyl cyclase, caused the activation of both reporter genes, and stimulation with a range of further compounds with no activity at either receptor did not generate a reporter response. The dual luciferase assay allows the simultaneous screening of two receptors in a 96-well format resulting in significant time and cost savings.

Protective effects of the lazaroid U-74389G against hyperoxia in rat type II pneumocytes.

The aims of this study were to investigate the effect of hyperoxia on O2(-.), H2O2 and .NO generation and iNOS mRNA levels in rat type II pneumocytes in vitro and the possible protective effect of the lazaroid U-74389G. Rat type II pneumocytes were exposed, 36 h after isolation, to air, 60% or 85% O2 for 48 h. At the beginning of the experiment and 24 h later, the cells were exposed for 30 min to either 30 microM U-74389G or only the vehicle for the lazaroid (control). Exposure to 60% and 85% O2 decreased nitrite production 2.9-fold and 3.9-fold, and increased O2(-.) and H2O2 generation 4.6-fold and 6.7-fold, respectively. In the 85% O2-exposed cells, hyperoxia increased lipid peroxidation (thiobarbituric acid reactive substances, TBARS production) 2-fold and iNOS mRNA production 5.4-fold. U-74389G prevented the decrease in nitrite and the rise in O2(-.) and H2O2 production, the increase in TBARS and the rise in iNOS mRNA after hyperoxia. We conclude that exposure of type II pneumocytes in vitro to subtoxic oxygen levels leads to a disturbance in the .NO-O2(-.) balance despite increased iNOS mRNA levels. The lazaroid U-74389G appears to be a useful compound in the protection of hyperoxic lung injury by restoration of this .NO-O2(-.) balance and prevention of TBARS formation.

Involvement of an NAD(P)H oxidase-like enzyme in superoxide anion and hydrogen peroxide generation by rat type II cells.

BACKGROUND: Although alveolar macrophages are considered to be the primary cellular mediators of host defence in the lung, there is increasing evidence that type II cells may also play an active role in host defence. A study was undertaken to investigate whether type II cells generate O2-. and H2O2 via an NADPH oxidase-like system and whether exposure of the type II cells to soluble or particulate stimuli known to activate NADPH oxidase in macrophages also leads to increased production of H2O2. METHODS: Rat type II cells and alveolar macrophages were exposed to 10, 100, or 1000 nM phorbol-12-myristate-13-acetate (PMA) and the production of O2-. and H2O2 was determined by chemiluminescence. Thirty minutes before stimulation with 1 microM PMA type II cells were also exposed to the same concentrations of a protein kinase C (PKC) antagonist GF109203x, the non-selective protein kinase inhibitor staurosporine (1, 10, or 100 nM), or the NADPH oxidase inhibitor diphenyliodonium chloride (DPI) (1, 10, 100, or 1000 microM). The effects of arachidonic acid, zymosan and Staphylococcus aureus on H2O2 production were determined. Cell membrane fractions from type II cells and macrophages were assayed for NADPH oxidase activity. RESULTS: After exposure to 1 microM PMA, O2-. and H2O2 generation increased 6.3-fold and 9.0-fold, respectively, in type II cells and 2.4-fold and 5.2-fold, respectively, in macrophages. In contrast to the macrophages, the increase in O2-. and H2O2 generation by type II cells was completely prevented by 1 mM KCN. Preexposure to GF109203x, staurosporine, or DPI completely prevented the rise in O2-. and H2O2 generation. Mean (SD) NADPH oxidase activity of 138 (38) nmol O2-./min/mg protein was found in membrane fraction I of the type II cells, and 102 (31) nmol O2-./min/mg protein in fraction II. Macrophages showed higher NADPH oxidase activity in membrane fraction II. In type II cells exposure to arachidonic acid led to a significant 5.3-fold increase in H2O2 generation, exposure to zymosan increased H2O2 generation 46-fold, and exposure to S aureus 25-fold with a maximum 30-50 minutes after addition of the bacteria. CONCLUSIONS: Type II cells generate O2-. and H2O2 via a PKC-mediated activation of an NAD(P)H oxidase-like membrane bound enzyme. Arachidonic acid, zymosan, and bacteria also give rise to increased H2O2 production. Type II cells might thus play an active role in host defence.

Accelerating the pace of luciferase reporter gene assays.

Luciferase reporter gene assays have gained more importance because of their easy readout, high sensitivity and lack of environmental waste disposal problems. However, several obstacles remain that have prohibited a wider use and the implementation of this type of assay in high-throughput screening programs: (i) Measurements need to be carried out within an active enzyme reaction, and the assessment of such reactions are time-dependent; (ii) the signal produced has a "flash" type characteristic and therefore requires specialized equipment for measurement; and (iii) side-reactions can occur that interact with the signal readout of the assay in a non-reproducible way. These hurdles make an otherwise convenient assay principle troublesome for larger-scale screening use. We have attempted to overcome these problems by different means, leading to the development of LucLite, a stable signal homogeneous reagent system. This system allows use in a higher throughput screening capacity and enables the use of standard scintillation/luminescence instruments.

Platelets augment granulocyte aggregation and cytotoxicity: uncovering of their effects by improved cell separation techniques using Percoll gradients.

The 'standard' technique of granulocyte preparation for in vitro studies uses dextran removal of erythrocytes and Ficoll-Hypaque gradient centrifugation to increase granulocyte purity. The procedure is lengthy, approximately 150 min in our hands, and provides granulocytes significantly contaminated with platelets (approx. 5 platelets/PMN). We report a technique that replaces dextran with hydroxy-ethylstarch and Ficoll-Hypaque with Percoll. Preparation time is reduced by approximately 40% and platelet contamination by more than 80%. Granulocytes, so prepared, function metabolically (O2-generation, chemiluminescence, HMP-shunt maxima) and, in motility/phagocytosis assays, identically to 'standard' preparations. However, an augmentatory effect of platelets in granulocyte aggregation responses and their mediation of cytotoxicity is uncovered. Ficoll-Hypaque purified cells (platelet-rich) aggregate to a significantly greater degree with FMLP or activated complement lectins and excessively kill 51Cr-labelled target cells when compared to Percoll-preparations (platelet-poor). Re-addition of purified platelets or of platelet release supernatants to the latter reproduces results using the 'standard' preparations.

Complement activation and adult respiratory distress syndrome during intermittent flow apheresis procedures.

We observed complement (C) activation during intermittent flow apheresis procedures (Haemonetics model 30) in four subjects, two of whom developed adult respiratory distress syndrome (ARDS). Actual C3 conversion during apheresis was illustrated by the finding of significantly elevated C3d levels (p less than 0.05) and of significantly increased alpha-1-antitrypsin/C3 ratios (p less than 0.05) in postapheresis serums. Similarly, marked granulocyte aggregating activity was found in these serums, indicative of the generation of significant amounts of the C-derived anaphylatoxin, C5a or C5a desarginine. A mean decrease of 59.75 percent in neutrophil count during the four procedures suggested sequestration of aggregated granulocytes in the pulmonary vasculature. Moreover, granulocytes activated by apheresis serums induced significant 51Cr leak from cultured human endothelial cells is vitro (p less than 0.001). We conclude that inflammatory C components produced during apheresis procedures may provoke granulocyte aggregation and embolization, leading to plugging of the pulmonary vasculature, and that apheresis-activated granulocytes may induce endothelial cytotoxicity, leading to the capillary leakage syndrome, characteristic of ARDS. Individual variability in C5a generation capacity or alterations in normal C5a clearing mechanisms may account for the low incidence of clinical C activation and true ARDS during apheresis. In these instances, high-dose steroids, which interfere with granulocyte-C interactions, may be beneficial.

Protective effect of vitamin E on immune triggered, granulocyte mediated endothelial injury.

The effect of alfa-tocopherol on the cell-cell interactions at the vessel wall were studied, using an in vitro model of human umbilical vein endothelial cell cultures (HUEC). Immune triggered granulocytes (PMN) will adhere to and damage HUEC and platelets enhance this PMN mediated endothelial injury. When HUEC are cultured in the presence of vitamin E, 51Cr-leakage induced by complement stimulated PMN is significantly decreased and the enhanced cytotoxicity by platelets is completely abolished (p less than 0.001). The inhibition of PMN induced endothelial injury is directly correlated to a diminished adherence of PMN to vitamin E-cultured HUEC (p less than 0.001), which may be mediated by an increase of both basal and stimulated endogenous prostacyclin (PGI2) from alfa-tocopherol-treated HUEC (p less than 0.025). The vitamin E-effect is abolished by incubation of HUEC with the irreversible cyclo-oxygenase inhibitor, acetylsalicylic acid, but the addition of exogenous PGI2 could not reproduce the vitamin E-mediated effects. We conclude that vitamin E exerts a protective effect on immune triggered endothelial damage, partly by increasing the endogenous anti-oxidant potential, partly by modulating intrinsic endothelial prostaglandin production. The failure to reproduce vitamin E-protection by exogenously added PGI2 may suggest additional, not yet elucidated vitamin E-effects on endothelial metabolism.

Effect of beta-blocking drugs on red cell adhesive and rheological properties.

Abnormal cell-cell interactions at the vessel wall play an important role in the development of microvascular occlusions. Since beta-blocking drugs have been implicated in the long-term and short-term prevention of myocardial infarction, we investigated the possibility that these drugs might exert their action by interfering with red cell-endothelial interactions. 51Cr-labeled, washed erthrocytes were added to confluent monolayers of cultured human vascular endothelial cells. After incubation at 37 degrees C, the nonadherent red cells were removed by sequential washing. When red cells were pretreated by cardioselective or noncardioselective beta-blocking drugs (e.g., metoprolol and propranolol), significantly fewer erythrocytes remained adherent to the endothelial monolayers after repeated washing. Pretreatment of the endothelium did not result in decreased adherence, indicating that the inhibitory action of beta-blockers is exerted on the red cell itself. The specificity of red cell-endothelial interactions is illustrated by the finding that erythrocytes adhere significantly less to plastic surfaces. In parallel studies, we have shown that beta-blockers significantly both diminish erythrocyte viscosity and increase erythrocyte deformability. The precise mechanisms of cellular action by which beta-blockers exert these actions remain unknown. Differences in beta-receptor subtypes do not seem to be involved, but complex metabolic changes leading to alterations in physiological properties of the red cell membrane cannot be excluded. Finally, our results suggest that the presumed beneficial effects of beta-blockade in various prethrombotic conditions (e.g., hypertension, angina pectoris, reinfarction) may be partly due to the interference of these drugs with the normal and abnormal adhesive and rheological properties of human erythrocytes.

Blood neutrophil function in primary myelodysplastic syndromes.

Ten different tests of blood neutrophil function were studied in 20 patients with primary myelodysplastic syndromes (PMDS). The patients were selected according to the new diagnostic criteria for PMDS of the FAB-cooperation group. Impairments of granulocyte functions were found in all patients. Moreover, several steps in the mobilization of granulocytes at the site of injury seemed to be affected: decreased adhesion (P less than 0.05), deficient chemotaxis (P less than 0.05), decreased enzyme content (P less than 0.001), 'slower' chemiluminescence (P less than 0.005), decreased phagocytosis (P less than 0.05) and impaired microbicidal capacity (P less than 0.025). No significant correlation between disease category and severity of granulocyte dysfunction was discerned, though an increasing number of blasts was associated with more severe granulocytic disability. Results in seven patients with abnormal karyotypes were not significantly different from 13 others with normal karyotypes. Our results indicate that defects in blood neutrophil function are a common feature in PMDS and might account for the increased frequency of infection in these patients.

Mechanisms of vascular damage in gout and oxalosis: crystal induced, granulocyte mediated, endothelial injury.

Immune triggered granulocyte (PMN)-endothelial interactions have been implicated in the pathogenesis of vascular diseases. While hyperuricemia and gout are associated with an increased risk of atherogenesis, we studied the modulation by monosodium-urate (MSU) crystals of PMN-endothelial interactions in vitro. The relationship between calcium oxalate (COX) crystals - implicated in the vasculitis of primary oxalosis - and immunologically mediated endothelial injury was also explored. Both MSU- and COX-crystal treated sera stimulate PMN to adhere to and induce significant 51Cr-release from endothelial cells in vitro. Platelets significantly increase crystal-triggered PMN endothelial cell adherence and 51Cr-release. This platelet augmenting effect depends on the release of platelet constituents (e.g. serotonin). Microcrystalline material present in vessel walls, thus may cause C-activation and may trigger PMN and platelets to damage endothelium in vitro and in vivo. These findings may have relevance to the understanding of the accelerated atherogenesis of hyperuricemia and the fulminant vasculitis of oxalosis or ethylene glycol poisoning.

Enkephalins modify granulocyte-endothelial interactions by stimulating prostacyclin production.

Granulocyte (PMN)-endothelial interactions have been implicated in the primary events of vascular injury and atherogenesis. We now present data which show that endogenous opioid peptides, e.g. enkephalins (ENK), dampen immune-triggered, granulocyte-induced endothelial damage by enhancing prostacyclin production. Concurrent exposure of human umbilical vein endothelial cells (HUEC) to Met5-enkephalin increased arachidonic acid (AA, 20 muM) and thrombin (T, 10 U/ml) induced 6-keto-PGF1 alpha-release to respectively 197.2 +/- 28.1% and 204.1 +/- 17.8% (mean +/- SEM) of base line stimulation (p less than 0.025). The increases noted were significant at ENK-concentrations as low as 10(-12)M. Simultaneous addition of naloxone with ENK completely abolished the enhanced 6-keto-PGF1 alpha-release. Addition of a protease resistant enkephalin analogue significantly (p less than 0.01 over several different concentrations) reduced PMN adherence to HUEC; concomitantly 51Cr-leakage from HUEC that had been exposed to PMN plus activated serum complement was decreased. The even further enhanced 51Cr-leakage that occurs when platelet release products (e.g. serotonin) are included is also decreased by added enkephalin. These data suggest that endogenous neurotransmitters may affect endothelial prostaglandin metabolism, and by so doing provide a protective effect during in vitro, and perhaps in vivo, PMN mediated endothelial injury. This link between neurohumoral and inflammatory systems might enhance our understanding of stress-related phenomena in inflammation and vascular diseases.