Delayed graft function in the kidney transplant.

Acute kidney injury occurs with kidney transplantation and too frequently progresses to the clinical diagnosis of delayed graft function (DGF). Poor kidney function in the first week of graft life is detrimental to the longevity of the allograft. Challenges to understand the root cause of DGF include several pathologic contributors derived from the donor (ischemic injury, inflammatory signaling) and recipient (reperfusion injury, the innate immune response and the adaptive immune response). Progressive demand for renal allografts has generated new organ categories that continue to carry high risk for DGF for deceased donor organ transplantation. New therapies seek to subdue the inflammatory response in organs with high likelihood to benefit from intervention. Future success in suppressing the development of DGF will require a concerted effort to anticipate and treat tissue injury throughout the arc of the transplantation process.

RGS4 controls renal blood flow and inhibits cyclosporine-mediated nephrotoxicity.

Calcineurin inhibitors (CNI) are powerful immunomodulatory agents that produce marked renal dysfunction due in part to endothelin-1-mediated reductions in renal blood flow. Ligand-stimulated Gq protein signaling promotes the contraction of smooth muscle cells via phospholipase Cbeta-mediated stimulation of cytosolic calcium release. RGS4 is a GTPase activating protein that promotes the deactivation of Gq and Gi family members. To investigate the role of G protein-mediated signaling in the pathogenesis of CNI-mediated renal injury, we used mice deficient for RGS4 (rgs4(-/-)). Compared to congenic wild type control animals, rgs4(-/-) mice were intolerant of the CNI, cyclosporine (CyA), rapidly developing fatal renal failure. Rgs4(-/-) mice exhibited markedly reduced renal blood flow after CyA treatment when compared to congenic wild type control mice as measured by magnetic resonance imaging (MRI). Hypoperfusion was reversed by coadministration of CyA with the endothelin antagonist, bosentan. The MAPK/ERK pathway was activated by cyclosporine administration and was inhibited by cotreatment with bosentan. These results show that endothelin-1-mediated Gq protein signaling plays a key role in the pathogenesis of vasoconstrictive renal injury and that RGS4 antagonizes the deleterious effects of excess endothelin receptor activation in the kidney.

Preanalytical factors in human plasma ascorbate assay.

Estimation of vitamin C (ascorbic acid) in various samples of fresh and frozen human plasma has shown that freezing in a regular freezer at -25 degrees C causes an approximately 14% loss of ascorbate in the sample. Freezing the same samples in a deep freezer at -75 degrees C causes less of an ascorbate loss amounting to about 9%. On the other hand, using the dry ice alcohol bath freezing, which shortens the freezing process to a fraction of seconds produced loss of ascorbate by 3.5% only. The storage time of previously frozen samples at -25 degrees C or -75 degrees C, from 2 to 14 days does not produce noticeable differences in the sample ascorbate concentration. Loss of ascorbate in samples frozen in the dry ice alcohol bath may be acceptable assuming analytical variability of ascorbate assay amounting to about 4% and broad biological variability of ascorbate concentration in various clinical conditions. Use of frozen plasma samples for ascorbate assays may essentially facilitate running this analysis in clinical laboratories.

Chronic electroconvulsive treatment increases the activity of nitric oxide synthase in the rat brain.

Activation of the NMDA receptor complex increases the intracellular free Ca2+ concentration, which in turn influences a nitric oxide synthase (NOS) activity. In this study we investigated the NOS activity after acute and chronic electroconvulsive treatment in different rat brain regions. Chronic (10 daily treatments) but not acute (single treatment) significantly increased the NOS activity by 60% in the cerebral cortex and by 20-30% in hippocampus and cerebellum. The increased NOS activity might be a compensatory mechanism which balanced the reduced NMDA receptor complex reactivity. In fact, the adaptation of the NMDA receptor complex induced by chronic electroconvulsive treatment (and antidepressant drugs) measured at the receptor level, suggests the subsensitivity of that complex. Present results support the hypothesis of the critical role of the NMDA receptor pathway in the mechanism of antidepressant action.

Influence of oxy-LDL and interleukin-8 on the platelet/PMNs adhesion and on chemotaxis-mediated induction of iNOS in neutrophils.

Selectin-P expression on platelets stimulated with thrombin was measured in terms of formation of "rosettes" according to Jungi et al. [9]. Selectin-P-mediated platelet/PMNs adhesion was inhibited by iloprost (IC50 = 5.0 nM), sodium nitroprusside (NaNP, IC50 = 0.93 microM) and interleukin-8 (IL-8, IC50 = 88 ng/ml), but activated dose-dependently by oxy-LDL (3-15 micrograms/ml). Glycogen-induced peritonitis in rats up-regulated the iNOS activity measured by the 2,3-[3H]-citrulline formation by the abdominal cavity PMNs up to 6 h after insult. Pretreatment with IL-8 (3 micrograms/300 g iv) decreased the amount of PMNs in ascites as well as its iNOS activity. Chemotaxis mediated iNOS gene expression of PMNs were measured by Northern blot hybridization. IL-8 (100 ng/ml) did not influence the PMNs iNOS gene expression induced by chemotaxis. We conclude that the decrease in iNOS activity by IL-8 involves postranslational modification of the enzyme activity.

An inhibitory effect of camonagrel-a new thromboxane synthase inhibitor, on P-selectin-mediated platelet/PMN adhesion.

P-selectin (PADGEM protein, GMP-140 or CD 62) is a glycoprotein of platelet a-granules and endothelial Weibel-Palade bodies that, by mediating cellular adhesion, initiates recruitment of leukocytes and lymphocytes into injured tissue. Both of the endothelial antiplatelet autacoids prostacyclin (PGI(2)) and nitric oxide (NO) have been demonstrated to inhibit P-selectin expression. Prostaglandin endoperoxides PGG(2)/PGH(2) that are generated by activated platelets have been demonstrated to be used by endothelium for generation of prostacyclin. In an experimental model in vitro that resembles vessel wall/platelet/PMN interaction in vivo, we found that aspirin (100 µM), a COX inhibitor, but not L-NMMA (100 µM) and a NO-synthase inhibitor, reversed the inhibitory effect of arterial wall on P-selectin mediated platelet/PMN adhesion. The anti-adhesive potency of vessel wall reversed by aspirin was dose-dependently restored by camonagrel (3-100 µM), a new TXA(2) synthase inhibitor. We conclude that selective TXA(2)-synthase inhibitors may inhibit P-selectin mediated platelet/PMN adhesion by augmenting formation of prostacyclin by vessel walls.

Effects of prolonged L-arginine administration on blood pressure in patients with essential hypertension (EH).

L-arginine (L-Arg) was administered intravenously through 4 consecutive days to 20 males (40-63 years old) with essential hypertension (EH). Significant decrease (p < 0.02) of systolic blood pressure (SBP) was observed only during the first day of the therapy and tachyphylaxis against L-Arg was noticed. The reduction of diastolic blood pressure (DBP) was more marked (p < 0.001). Significant changes in cGMP plasma level and the nitrite/nitrate urine concentration were not observed. L-Arg caused a significant activation of fibrinolysis (p < 0.005). The decrease of platelet activity, measured by the ADP-induced aggregation, after L-Arg administration was not statistically significant. Therefore, L-Arg may play only a secondary role in the treatment of EH.