The mCK-5 multiprobe RNase protection assay kit can yield erroneous results for the murine chemokines IP-10 and MCP-1

The ribonuclease protection assay (RPA) represents a sensitive method to detect and quantify RNA levels. It can be adapted to allow the simultaneous analysis of more than 10 different mRNAs. The multiprobe RPA kit mCK-5 from PharMingen was used to analyze the expression of chemokines in CCR5 chemokine receptor knockout mice. Upon careful analysis it was found that the mCK-5 kit is defective and can lead to false results for the chemokines IP-10 and MCP-1. The problem is caused by a long-known sequence polymorphism within the 3'-untranslated region of the murine IP-10 gene. This polymorphism leads to a protected IP-10 fragment approximately 20 nucleotides shorter than expected, yielding a length similar to the protected MCP-1 fragment from the mCK-5 kit. Since the identification of specific transcripts with this kit is based exclusively on the size of the various protected fragments, false-negative results for IP-10 together with false-positive results for MCP-1 can be obtained. Interestingly, the polymorphism was found not only in 129/CD-1 mice, but also in MRL and SJL/J mice. To facilitate troubleshooting in the future, all templates from the mCK-5 set were isolated and sequenced.

Role of reactive oxygen species in the signalling cascade of cyclosporine A-mediated up-regulation of eNOS in vascular endothelial cells

1. Cyclosporine A (CsA) increases eNOS mRNA expression in bovine cultured aortic endothelial cells (BAEC). As some effects of CsA may be mediated by reactive oxygen species (ROS), present experiments were devoted to test the hypothesis that the CsA-induced eNOS up-regulation could be dependent on an increased synthesis of ROS. 2. CsA induced a dose-dependent increase of ROS synthesis, with the two fluorescent probes used, DHR123 (CsA 1 microM: 305+/-7% over control) and H2DCFDA (CsA 1 microM: 178+/-6% over control). 3. Two ROS generating systems, xanthine plus xanthine oxidase (XXO) and glucose oxidase (GO), increased the expression of eNOS mRNA in BAEC, an effect which was maximal after 8 h of incubation (XXO: 168+/-21% of control values. GO: 208+/-18% of control values). The ROS-dependent increased eNOS mRNA expression was followed by an increase in eNOS activity. 4. The effect of CsA on eNOS mRNA expression was abrogated by catalase, and superoxide dismutase (SOD). In contrast, the antioxidant PDTC augmented eNOS mRNA expression, both in basal conditions and in the presence of CsA. 5. The potential participation of the transcription factor AP-1 was explored. Electrophoretic mobility shift assays were consistent with an increase in AP-1 DNA-binding activity in BAEC treated with CsA or glucose oxidase. 6. The present results support a role for ROS, particularly superoxide anion and hydrogen peroxide, as mediators of the CsA-induced eNOS mRNA up-regulation. Furthermore, they situate ROS as potential regulators of gene expression in endothelial cells, both in physiological and pathophysiological situations.

Cyclosporin A-induced hydrogen peroxide synthesis by cultured human mesangial cells is blocked by exogenous antioxidants

Cyclosporin A (CsA) is the immunosupressor most widely used in transplanted patients for preventing organ rejection, but it has some toxic side effects in vascular beds and kidney. The purpose of this work was to study if H2O2, a reactive oxygen species, is involved in the CsA-induced toxic effects on kidney in vitro. Human mesangial cells (HMC) in culture were incubated in presence of CsA (10[-5]-10[-8]M) and H2O2 was measured by flow cytometry. The specificity of the probe used in this method was demonstrated as fluorescence was not detected when superoxide anion generated through a Xanthine-Xanthine oxidase system was present, but fluorescence was noted when H2O2 was present in the incubation medium, both directly and after addition of superoxide dismutase to the medium thus promoting H2O2 synthesis. CsA induced a significant dose and time-response increased H2O2 synthesis by cultured HMC. This increase appeared 5 min after CsA addition, being maximal between 15-45 min at CsA concentration of 10(-7)M. When HMC were preincubated with antioxidants as vitamin E or selenium, the CsA-induced H2O2 production was partially blocked. In addition, selenium also induced an increased activity of glutathion peroxidase in HMC after 24 hours of incubation, suggesting that it exerted its H2O2 scavenging action through the modulation of the activity of this enzyme.

Involvement of phospholipase A2 in gentamicin-induced rat mesangial cell activation

The role of the phospholipase A2 (PLA2) activation in the gentamicin (Gent)-induced rat mesangial cell activation has been studied. Gent (10(-5) M) induced a time-dependent mesangial planar cell surface area reduction that was significantly inhibited by the PLA2 inhibitors aristolochic acid (AA) and quinacrine, by the platelet-activating factor (PAF) blocker BN-52021 (BN), and by verapamil. These substances also inhibited Gent-induced [3H]thymidine incorporation into DNA (AA, 504 +/- 20; quinacrine, 555 +/- 66; BN, 1,126 +/- 120; and verapamil, 896 +/- 109; vs. 1,818 +/- 35 cpm/well in cells treated with Gent alone) and the Gent-induced increase in cell number (AA, 20,116 +/- 2,696; quinacrine, 24,687 +/- 1,481; BN, 26,122 +/- 1,016; and verapamil, 27,566 +/- 1,214; vs. 47,486 +/- 1,124 cells/well in cells treated with Gent alone). Gent induced a twofold increase in [3H]acetate incorporation into PAF (27 +/- 3 vs. 12 +/- 2 cpm/microgram protein in control conditions) that was completely blocked by AA, BN, or verapamil. Gent increased thromboxane B2 and prostaglandin E2 (PGE2) production, with both increases inhibited by either AA or verapamil. BN only inhibited the Gent-induced mesangial PGE2 production. In addition, Gent increased PLA2 activity (measured as [3H]arachiodonic acid release, 29,849 +/- 2,151 vs. 20,104 +/- 2,308 cpm/well in basal conditions), an effect that was blocked by AA (11,804 +/- 684 cpm/well). These data suggest a major role for PLA2 activation in Gent-induced mesangial cell contraction, proliferation and prostanoid secretion.

Thromboxane A2 and platelet-activating factor decrease in the platelet-mesangial cell interactions

To analyze the metabolisms of platelet-activating factor (PAF) and Thromboxane A2 (TxA2) when platelets and mesangial cells (MC) interact, immunoreactive thromboxane B2 (TxB2) and PAF were measured after incubation of cultured rat MC with platelets (P) and with platelet supernatants (PS). In both cases, TxB2 significantly decreased with respect to the P synthesis and to the PS content, suggesting an increased degradation of this metabolite or even the existence of a specific effect of MC upon platelet TxB2. When immunoreactive PAF was measured, results were comparable to those observed for TxB2. Moreover, when intrinsic mesangial cell synthesis of PAF was assessed by analyzing the [3H]-acetate incorporation by prelabeled MC in the HPLC fraction coeluting with cold PAF standards, it was possible to demonstrate that P or PS did not modify PAF synthesis in these cells. In summary, present results support the existence of a specific effect of mesangial cells upon platelet TxA2 and PAF.

A possible role for platelet-activating factor in the hydrogen peroxide-induced TXB2 and PGE2 glomerular synthesis

Hydrogen peroxide stimulates both prostanoid and platelet-activating factor (PAF) biosynthesis in cultured rat mesangial cells and isolated rat glomeruli. The present experiments were designed to try to establish some relationship between prostanoid and PAF synthesis in these renal structures, in the presence of hydrogen peroxide. Cells and glomeruli were incubated with hydrogen peroxide under different experimental conditions, and thromboxane B2 (TXB2), the stable metabolite of thromboxane A2 (TXA2), and prostaglandin E2 (PGE2) concentrations were measured in the supernatants of the cells or glomeruli. Moreover, H2O2-dependent PAF synthesis was measured by high performance liquid chromatography (HPLC) ([3H]acetate incorporation) and radioimmunoassay. H2O2 induced increased TXB2 and PGE2 production in cultured rat mesangial cells and isolated rat glomeruli. This effect was blocked by incubation in the presence of a PAF-receptor antagonist, BN-52021. This antagonist has no intrinsic effect either in basal prostanoid synthesis or in arachidonic acid-stimulated glomerular TXB2 synthesis. Alprazolam, another PAF antagonist, nonchemically related to BN-52021, also completely blocked the H2O2-induced production of TXB2 by isolated rat glomeruli. Moreover, H2O2 was also able to induce an increased [3H]acetate incorporation into a fraction comigrating with a PAF standard in HPLC in isolated glomeruli, and this effect was dependent on the H2O2 concentration tested. Moreover, H2O2 was also able to induce an increased [3H]acetate incorporation and increased synthesis of radioimmunoassayable PAF in cultured mesangial cells. These results suggest that the increased synthesis of PGE2 and TXB2 induced by H2O2 could be dependent on platelet-activating factor production.