Increased urinary excretion of thromboxane B2 and 2,3-dinor-TxB2 in cyclosporin A nephrotoxicity

New insights into the obligatory nature of cyclooxygenase-2 and PGE2 during early chick embryogenesis

Temporal expression patterns and activity of two cyclooxygenase (COX-1 and COX-2) isoforms were analysed during early chick embryogenesis to evaluate their roles in development. COX-2 inhibition with etoricoxib resulted in significant structural anomalies such as anophthalmia (born without one or both eyes), phocomelia (underdeveloped or truncated limbs), and gastroschisis (an opening in the abdominal wall), indicating its significance in embryogenesis. Furthermore, the levels of PGE₂, PGD₂, PGF_2α, and TXB₂ were assessed using quantitative LC-MS/MS to identify which effector prostanoid (s) had their synthesis initiated by COX-2. COX-2 inhibition was only shown to reduce the level of PGE₂ significantly_, and hence it could be inferred that the later could be largely under the regulation of activated COX-2 in chick embryos. The compensatory increase in the activity of COX-1 observed in the etoricoxib-treated group helped to maintain the levels of PGD₂, PGF_2α, and TXB₂. Though the roles of these three prostanoids in embryogenesis need to be further clarified, it appears that their contribution to the observed developmental anomalies is minimal. This study has shown that COX-2 is functionally active during chick embryogenesis, and it plays a central role in the structural configuration of several organs and tissues through its downstream effector molecule PGE₂.

Attenuation of Cyclosporine-Induced Renal Dysfunction by Catechin: Possible Antioxidant Mechanism

One of great use of immunosuppressant, Cyclosporine-A (CsA) is in the solid organ transplantation; however the extensive use of this is cautionable due to its toxic effect in renal tissue, characterized by the tubular atrophy, interstitial fibrosis, and progressive renal impairment. However, there are many mediators are associated with pathogenesis of nephrotoxicity of CsA, the exact mechanism is still in debate. Recent studies indicate that Reactive Oxygen Species (ROS) induced oxidative stress and lipid peroxidations are the important mechanisms implicated in the pathophysiology of nephrotoxicity with CsA. In the present study we examined effect of dietary flavonoid catechin on oxidative damage in cyclosporine-A induced nephrotoxicity. Chronic administration of CsA (20 mg/kg/day) subcutaneously for 21 days significantly decreased the body weight as compared with vehicle treated rats. CsA (20 mg/kg/day) administration for 21 days significantly decreased the renal function by increase in the serum creatinine, blood urea nitrogen, and decrease in the creatinine and urea clearance as compared with vehicle treated rats. Catechin (100 mg/kg/day) for 21 days along with CsA significantly reversed the changed renal parameters, however lower dose of catechin (50 mg/kg/day) restored only increased serum creatinine levels as compared with CsA alone treated group. Biochemical analysis revealed that chronic administration of CsA (20 mg/kg/day) for 21 days significantly induced lipid peroxidation and decreased the glutathione levels in the kidney homogenate of rats. It is also observed that chronic CsA administered rats showed decrease in antioxidant defense enzyme superoxide dismutase and increase in the catalase activity as compared with vehicle treated rats. Co-administration of catechin (100 mg/kg/day) orally along with CsA for 21 days significantly reduced the lipid peroxidation and restored the decreased glutathione levels as compared with CsA alone group, but lower dose of catechin (50 mg/kg/day) restored only decreased glutathione levels induced by CsA. Co-administration of only higher dose of catechin (100 mg/kg/day) along with CsA significantly increased the superoxide dismutase (SOD) levels as compared with CsA alone treated group. It is also observed that catechin (100 mg/kg/day) along with CsA further increased the catalase levels as compared with CsA alone treated group, but not with lower dose of catechin. Animals administered with catechin (100 mg/kg/day) alone for 21 days showed significant increase in the catalase levels as compared with vehicle treated group. The major findings of the present study suggest that oxidative stress might play a significant role in CsA-induced nephrotoxicity. In conclusion, dietary administration of flavonoid catechin could be a useful component for the prevention/treatment of CsA-induced nephrotoxicity.

Nephrotoxic aspects of cyclosporine

Over the last 20 years cyclosporine (CsA) has improved the survival of kidney, heart, and liver transplants. However, with increasing use, evidence has accumulated that CsA therapy carries a variety of side effects, the most important being renal toxicity. CsA can lead to a wide spectrum of renal function impairments, including a marked and rapidly reversible decrease in renal hemodynamics (acute CsA nephrotoxicity), and a chronic form of renal damage that potentially progress irreversibly to end-stage renal disease (chronic CsA nephrotoxicity). All these manifestations are the consequence of the drug toxic effects on renal vessels and the tubulointerstitium. A proper diagnosis of CsA toxicity at early stages, the combination of low CsA doses with non-nephrotoxic immunosuppressants, and the development of more feasible strategies to monitor daily CsA exposure may contribute to a better CsA management, improve quality of life of transplant recipients, and prolong graft survival.

New morphological changes induced by FK506 in a short period in the rat kidney and the effect of superoxide dismutase and OKY-046 on THEM: the relationship of FK506 nephrotoxicity to lipid peroxidation and change in production of thromboxane A2 in the kidney

Juxtaglomerular (JG) hyperplasia and tubular damage along with a decrease in the urine creatinine level induced by FK506 in rat kidney have already been reported in previous paper by us. In this paper, we document the relationship of FK506 nephrotoxicity to the change in the production of thromboxane (Tx) A2 and the lipid peroxidation of the cellular membrane in the rat kidney in order to clarify its morphogenesis. The urinary excretion of TxB2 increased with FK506 administration even on day 1 (P < 0.02). Histologically, OKY-046 (thromboxane synthetase inhibitor) decreased tubular damage, although JG hyperplasia was not eradicated, while biochemically the excretion of TxB2 decreased significantly (P < 0.02), and both the decrease in the urine creatinine level and the increase in the N-acetyl-beta,D-glucosaminidase (NAG) index were relatively smaller. Although the FK506-induced morphological and biochemical changes could not be prevented by the continuous administration of superoxide dismutase (SOD) 30,000 U/kg daily, the malondialdehyde content in renal tissue removed 1 h after FK506 administration had increased. These data suggest that FK506 nephrotoxicity is related to the change in the production of TxA2 and lipid peroxidation of the cellular membrane. However, other mechanisms such as the involvement of sympathomimetic effects of FK506 and other vasoconstrictive factors cannot be ruled out.

Role for thromboxane A2 from glomerular thrombi in nephropathy with type 2 diabetic rats

We used rats (the Otsuka Long-Evans Tokushima Fatty strain) as a model of type 2 diabetes to find whether thromboxane (TX) A2 is involved in diabetic nephropathy, and if so, to identify where it is synthesized. We measured urinary excretion of TXB2 and 2,3-dinor-TXB2 in rats up to 60 weeks of age as markers of renal and platelet synthesis of TXA2, respectively. Some diabetic rats were given daily oral doses of OKY-046 (100 mg/kg), a TXA2 synthase inhibitor, starting when they were 10 weeks of age. Healthy Long-Evans Tokushima Otsuka rats served as the controls. Urinary excretion of protein was greater in diabetic rats at 26 weeks than in controls, and the difference increased with age. Urinary excretion of TXB2 by diabetic rats was about 150% that of controls at 14 weeks, and remained at that level. In diabetic rats, urinary excretion of 2,3-dinor-TXB2 increased with age in parallel to increases in proteinuria, but in controls, excretion of these metabolites did not change with age. In diabetic rats, OKY-046 prevented the increase in urinary excretion of both metabolites, and decreased the proteinuria. Histologic examination at 60 weeks showed intraglomerular thrombi in diabetic rats but not in controls. OKY-046 reduced intraglomerular thrombi formation and the score for glomerulosclerosis. When platelet aggregation began, more TXA2 than before was released from the thrombi that formed, and the TXA2 contributed to the progress of nephropathy in this rat model of type 2 diabetes.

Determinants of enhanced thromboxane biosynthesis in renal transplantation

BACKGROUND

Despite great improvement in patient and graft survival, the long-term morbidity and mortality in renal transplant recipients (RTRs) are still significant, with a high incidence of cardiovascular disease-related deaths.

METHODS

We investigated thromboxane (TXA2) biosynthesis and endothelial and coagulative activation in 65 patients who received a renal transplant.

RESULTS

The rate of TXA2 biosynthesis (urinary 11-dehydro-TXB2 excretion largely reflects platelet TXA2 production in vivo) was significantly (P < 0.0001) higher in RTRs than in healthy subjects. Plasma von Willebrand factor (vWF) and thrombin-antithrombin (TAT) complexes were significantly higher (P < 0.001) in RTRs compared with controls. Urinary 11-dehydro-TXB2 directly correlated with plasma vWF and cholesterol. We next examined the relative influence of cyclosporine A (CsA) on TXA2 biosynthesis and endothelial activation, comparing a group of RTRs not receiving CsA with an age- and sex-matched group of patients treated with CsA. Urinary excretion of 11-dehydro-TXB2 and plasma levels of vWF were significantly increased in RTRs who received CsA compared with those who did not. After an overall follow-up of 120 months, RTRs who experienced cardiovascular events had a higher frequency of abnormal plasma levels of vWF than patients who remained event free.

CONCLUSION

Renal transplantation is associated with in vivo platelet activation highly related to endothelial activation. This is particularly evident in CsA-treated patients. Administration of drugs that are able to reduce or eliminate thromboxane-dependent platelet activation in vivo may be beneficial to reduce the risk of cardiovascular events in RTRs.

Effect of 6 weeks of vitamin E administration on renal haemodynamic alterations following a single dose of neoral in healthy volunteers

BACKGROUND

A single oral dose of cyclosporin-A (CsA) transiently reduces renal plasma flow (RPF) and glomerular filtration rate (GFR) in transplant patients and, in some patients, chronic administration of CsA leads to renal impairment and fibrosis. Based on experimental studies, several mediators including free radicals have been proposed to account for CsA-nephrotoxicity. We have previously reported that administration of the antioxidant vitamin E in a rat model of chronic CsA-nephrotoxicity reduces renal fibrosis and maintains renal function.

METHODS

In the present study, the effect on renal haemodynamics of a single dose of the new oral formulation of CsA (neoral) was assessed before and after 6 weeks of vitamin E (800 IU/day, 2-fold increase in serum vitamin E). GFR (inulin clearance) and RPF (para-amino hippuric acid clearance) were measured before and after a single dose of 5 mg/kg of neoral in 12 healthy subjects under standardised conditions.

RESULTS

Although the mean area under the curve of the CsA levels was 21% lower after the vitamin E period, the peak CsA level at 120 min after neoral was similar both before and after vitamin E administration. At 120 min after neoral, a transient reduction in RPF and GFR was noted both before and after vitamin E administration. The nadir of the reductions in RPF (-81 +/-27 ml/min) and GFR (-14 +/- 6 ml/min) at 120 min compared with baseline tended to be lower before than after the treatment with vitamin E (-51 +/- 33 ml/min of RPF and -12 +/- 8, ml/min of GFR, respectively). Plasma and urine levels of F2-isoprostanes (free radical-catalysed vasoconstrictive prostanoids (F2-iso) at 120 min after the administration of neoral were not different from the pre-neoral levels.

CONCLUSION

The findings demonstrate that a single oral dose of neoral causes transient, yet significant, reductions in RPF and GFR, and suggest that F2-iso might not be involved in the CsA-induced acute renal vasoconstriction. The tendency for a lower reduction in RPF and GFR following CsA during the vitamin E period in healthy humans warrants additional studies in transplant patients.

A role for leukotrienes in cyclosporine nephrotoxicity

BACKGROUND

Nephrotoxicity associated with cyclosporine A (CsA) administration is characterized by marked renal vasoconstriction, interstitial fibrosis, and arteriolar hypertrophy. While the molecular mechanisms of CsA toxicity are not well characterized, previous studies have demonstrated that altered arachidonic acid (AA) metabolism plays a role its pathogenesis. Using a rat renal transplant model, the purpose of this study was to examine the effects of CsA on the 5-lipoxygenase (5-LO) pathway of AA metabolism.

METHODS

The PVG (RT1c) strain of rats underwent kidney transplantation, and recipients of nonrejecting kidney transplants were treated with either 50 mg/kg/day CsA or vehicle (N = 24). To determine the physiologic significance of increased leukotriene (LT) production, the peptidoleukotriene receptor antagonist SKF 106203 was administered to CsA-treated animals for six days.

RESULTS

CsA caused a substantial reduction in glomerular filtration rate (GFR) in the transplanted rats compared with the vehicle-treated controls (1.5 +/- 0.6 vs. 4.1 +/- 0.8 mL/min/kg, P < 0.05). The reduction in renal function was associated with enhanced urinary excretion of the peptidoleukotriene metabolites LTE4 (1431 +/- 207 vs. 953 +/- 125 pg/24 h, P < 0.05) and N-acetyl-LTE4 (4411 +/- 848 vs. 463 +/- 70 pg/24 h, P < 0.001). LT receptor blockade had a significant protective effect on renal transplant function in CsA-treated animals (GFR, 4.8 +/- 1.1 vs. 1.7 +/- 0.9 mL/min/kg, P < 0.05), such that CsA-treated animals that received SKF106203 maintained GFR at levels similar to controls that never received CsA (4.1 +/- 0.8 mL/min/kg). Peptidoleukotriene receptor blockade also prevented the histomorphological abnormalities caused by CsA, including tubular vacuolization.

CONCLUSIONS

These studies identify a critical role for LTs in the pathophysiology of CsA nephrotoxicity and suggest that LT antagonists may be useful in preventing CsA-associated kidney toxicity.

Effects of nitric oxide blockade and cyclosporin A on cardiovascular and renal function in normal man

OBJECTIVE

The present study investigated whether the nitric oxide (NO) system is involved in cyclosporin A (CsA)-induced changes in cardiovascular and renal function in man.

SUBJECTS AND METHODS

Ten healthy volunteers were investigated twice--with and without intake of a single dose of CsA (8 mg/kg). N(G)-monomethyl-L-arginine (L-NMMA; 3 mg/kg) was injected 4 h after study start on each day.

RESULTS

There was no change in glomerular filtration rate (GFR) on the day without CsA. CsA alone did not change GFR, but after L-NMMA injection, GFR decreased significantly from 101 +/- 4 to 91 +/- 4 ml/min. L-NMMA increased renal vascular resistance with no difference between the two study days. CsA increased significantly the diastolic blood pressure (BP) by 8 +/- 2% and the heart rate (HR) by 30 +/- 4%, without changes in cardiac output L-NMMA further increased BP by around 8%, and decreased HR by 11% and cardiac output by 20% on both study days. L-NMMA decreased urinary flow rate by around 25% and renal sodium clearance from 1.1 to approximately 0.6 ml/min on both study days. CsA decreased plasma renin significantly and increased the urinary excretion rate of prostaglandin E2 (PgE2), 6-keto-prostaglandin F1alpha (6-keto-PgF1alpha) and thromboxane B2(TxB2) when compared to the control day. The urinary excretion rate of NOx and cGMP declined gradually on the control day. In contrast, there was a minor, non-significant increase in NOx and cGMP excretion after CsA, followed by a decrease (29 +/- 2 and 16 +/- 4%, respectively) after L-NMMA in parallel with the decrease in GFR.

CONCLUSION

The present findings suggest that NO does not play a major role during acute CsA-induced changes in cardiovascular function and renal haemodynamics in man. Renal NO synthesis, however, may attenuate the acute CsA-induced decrease in GFR.

Cyclosporine increases local glomerular synthesis of reactive oxygen species in rats: effect of vitamin E on cyclosporine nephrotoxicity

BACKGROUND

We report an investigation of the effects of cyclosporine (CsA) on kidney function, the glomerular synthesis of reactive oxygen species, the peroxidation of lipids, and the levels of thromboxane B2 (TXB2). The effect of the simultaneous administration of the antioxidant vitamin E (Vit E) and CsA in rats was also evaluated.

METHODS

Adult male Wistar rats were treated for 30 days with CsA (30 mg/kg/day), with Vit E (0.05 mg/ml), with CsA plus Vit E, or with the vehicle used for administration of CsA, namely 12.6% ethanol.

RESULTS

CsA induced kidney failure and increased the glomerular synthesis of superoxide anion, H2O2, malonyldialdehyde, and TXB2. Vit E minimized the adverse effects of CsA on kidney function and the glomerular synthesis of these compounds.

CONCLUSIONS

Our results suggest that the acute decrease in glomerular filtration rate induced by CsA might be mediated by the synthesis of reactive oxygen species and subsequent peroxidation of lipids, which increases the levels of TXB2. Treatment with Vit E prevented these effects, suggesting a possible role for antioxidants in the prevention of CsA nephrotoxicity.

Cyclosporine A nephrotoxicity: role of thromboxane and reactive oxygen species

The main adverse effect of cyclosporine A (CyA) is nephrotoxicity. CyA increases urinary concentrations of thromboxane A2 (TXA2), a potent vasoconstrictor that can be involved in kidney failure induced by CyA. Furthermore, it has been postulated that a relationship exists between oxygen free radicals and the synthesis of arachidonate metabolites in experimental models of CyA nephrotoxicity. We studied the effect of vitamin E (VitE), an oxygen free radical scavenger, on renal function, on glomerular synthesis of thromboxane B2 (TXB2), and on free radicals in rats treated with CyA. Four groups of male Wistar rats were studied: (1) a control group; (2) a group given VitE at 0.05 mg/dl in drinking water for 25 days; (3) a group given CyA at 50 mg/kg body weight/day orally for 10 days; and (3) a group given Vit E + CyA, in which rats were provided with drinking water containing VitE for 15 days and afterwards were treated with VitE and CyA for 10 days. Renal function parameters and glomerular synthesis of TXB2, superoxide anion (02.-), malondialdehyde (MDA), and hydrogen peroxide (H202) were evaluated. CyA decreased body weight, caused deterioration of kidney function and increased glomerular synthesis of TXB2, O2.-, MDA, and H202. Pretreatment with VitE prevented the effects of CyA on kidney function and decreased glomerular synthesis of these mediators. In conclusion, CyA induced glomerular synthesis of reactive oxygen species (ROS) and TxB2. Pretreatment with VitE inhibited acute renal failure induced by CyA, probably by scavenging free radicals and by inhibiting the synthesis of TXB2.

Cyclosporine impairs the ability of human platelets to mediate vasodilation

Cyclosporine causes various platelet abnormalities. Whether it affects the ability of platelets to mediate vasodilation is unknown. Platelets were isolated from healthy volunteers and 13 heart transplant patients on cyclosporine. When perfused through preconstricted normal rabbit carotid arteries, activated platelets from transplant patients failed to cause vasorelaxation, whereas normal platelets produced significant vasodilation (-4.0 +/- 1.9% versus 30 +/- 3% [P < .0001] change in vessel diameter, respectively). When normal platelets were exposed to cyclosporine in vitro, they lost their ability to cause vasodilation in a dose- and time-dependent fashion. However, when activated and perfused through quiescent, N omega-nitro-L-arginine-pretreated arteries, platelets from transplant patients and normal platelets caused similar degrees of vasoconstriction. The amount of adenosine triphosphate in the supernatant from activated cyclosporine-exposed and control platelets was similar (1.7 +/- 0.4 versus 1.5 +/- 0.3 mumol/L [P = NS], respectively). However, concomitant perfusion of activated platelets from transplant patients impaired acetylcholine-mediated, endothelium-dependent vasodilation but perfusion of normal platelets did not. Although cyclosporine-exposed platelets showed an impaired ability to produce vasorelaxation, supernatant from the same platelets caused near normal vasodilation. Human platelets exposed to cyclosporine have an impaired ability to mediated vasodilation. This is not due to increased platelet-mediated vasoconstriction or a decrease in the release of platelet-derived nucleotides but rather to a short-acting compound released by cyclosporine-exposed platelets that interferes with endothelium-dependent vasodilation.

Lazaroids prevent acute cyclosporine-induced renal vasoconstriction

BACKGROUND

Cyclosporine (CsA)-induced nephrotoxicity may be due to intrarenal vasoconstriction and glomerular hypoperfusion. Several factors, including endothelin and prostanoids, are suggested mediators of this response. Recent evidence suggests that CsA leads to increased oxygen-derived free radical (ODFR) production and lipid peroxidation in renal tissue. Whether this leads to alterations in renal vessel reactivity is unclear. Lazaroids, such as U74389G, are radical-quenching antioxidants that inhibit ODFR-induced lipid peroxidation and may improve renal function after ischemia and reperfusion. We hypothesized that ODFRs contribute to CsA-induced alterations of the renal microcirculation.

METHODS

Rat hydronephrotic kidneys were studied by video microscopy. Interlobular arteriolar diameter and flow, afferent and efferent arteriolar diameters, and cardiac output were measured at 15-min intervals for 120 min. U74389G or its vehicle was infused 15 min before topical application of CsA to the kidney. The results were compared with U74389G alone and normal saline.

RESULTS

CsA administration caused renal microvascular vasoconstriction (10-25% below baseline) and hypoperfusion (35% below baseline). Both vasoconstriction and hypoperfusion were significantly attenuated by U74389G (5-8% and 20% below baseline, respectively).

CONCLUSIONS

Inhibition of lipid peroxidation by U74389G maintained renal blood flow during acute CsA administration. These data suggest that ODFRs are involved in the renal microvascular response to CsA. Inhibition of ODFR-induced lipid peroxidation may help prevent CsA-induced glomerular hypoperfusion. Lazaroids may prove an effective adjunct in reducing CsA-induced nephrotoxicity.

Cyclosporin A inhibits prostaglandin E2 production by fetal amnion cells in response to various stimuli

Use of cyclosporin A as part of an immunosuppressive regimen in pregnant transplant patients is not uncommon. Although successful pregnancies have been reported with the use of various immunosuppressive agents including cyclosporin A, the concern for fetal outcome still remains. Our purpose was to evaluate the effects of immunosuppressive cyclosporin A on prostaglandin E2 (PGE2) production by human fetal amnion. Amnion cells were isolated from term placentae obtained at elective cesarean section before the onset of labor. Cells were grown to confluence and then incubated for 16 hours with cyclosporin A (1-1000 ng/ml) in the presence and absence of interleukin 1 beta (IL-1 beta, 1 ng/ml), phorbol 12-myristate 13-acetate (PMA, 10(-7) M) and ionomycin (0.5 microM). PGE2 was measured by radioimmunoassay and cellular protein determined. IL-1 beta, PMA and ionomycin all stimulated amnion cell PGE2 production as expected. However, these stimulatory actions were attenuated by at least 50% when cells were co-incubated with cyclosporin A (1000 ng/ml). Concentrations of cyclosporin A tested included the therapeutic range (250-1000 ng/ml). Our results indicate that cyclosporin A does not stimulate amnion cell PGE2 production and is probably unrelated to preterm labor and delivery in allograft recipients.

Cyclosporine enhances leukocyte adhesion to vascular endothelium under physiologic flow conditions

We investigated the effect of cyclosporine (CyA) on leukocyte adhesion to endothelium under flow conditions. Confluent human umbilical vein endothelial cells (HUVECs) were incubated for 24 hours with CyA (1, 5, and 10 micromol/L) and then exposed to a total human leukocyte suspension in a parallel plate flow chamber under laminar flow (1.5 dynes/cm2. Human umbilical vein endothelial cells stimulated with interleukin-1beta (20 U/mL) were used as a positive control. Adherent cells were measured by digital image analysis. Results showed that CyA dose-dependently increased the number of leukocytes adhering to HUVECs compared with control cells. Leukocyte adhesion markedly increased on HUVECs incubated with interleukin-lbeta, one of the most potent inducers of endothelial cell adhesiveness. Exposure of endothelial cells to CyA did not affect the number of rolling leukocytes, which was similar to control values. To examine the role of adhesion molecules in CyA-induced leukocyte adhesion, HUVECs were incubated with monoclonal antibodies against intercellular adhesion molecule-1 (ICAM-1), vascular adhesion molecule-1 (VCAM-1), and E-selectin before adhesion assay. Functional blocking of ICAM-1, VCAM-1, and E-selectin on endothelial cells significantly inhibited CyA (10 micromol/L)-induced leukocyte adhesion. Confocal fluorescence microscopy studies showed that CyA induced an increase in the endothelial surface expression of ICAM-1, VCAM-1, and E-selectin. Pretreatment of leukocytes with the platelet activating factor receptor antagonist L659,989 significantly reduced the number of leukocytes adhering to CyA-treated HUVECs. We suggest that CyA enhances leukocyte adhesion to endothelium by upregulating adhesive proteins on endothelial surface membrane. Blocking leukocyte receptor for platelet-activating factor partially prevents adhesion, suggesting a role for endothelial cell-associated platelet-activating factor in the interaction between leukocytes and CyA-treated endothelium.

Kinetic and structural evidence for the identification of 11-hydroxythromboxane B2 dehydrogenase as cytosolic aldehyde dehydrogenase

We have recently purified 11-hydroxythromboxane B2 dehydrogenase from porcine kidney and identified it as cytosolic aldehyde dehydrogenase (EC 1.2.1.3) based on amino acid analysis and other protein characteristics. In the present paper we have studied the catalytic interaction of thromboxane B2 (TXB2) with different aldehyde substrates and a potent aldehyde dehydrogenase inhibitor, disulfiram. TXB2 was a competitive inhibitor of the aldehyde dehydrogenase reaction in assays with 3,4-dihydroxyphenylacetaldehyde, a high affinity substrate. The conversion of TXB2 to 11-dehydro-TXB2 was also inhibited by propanal and disulfiram. The protein characteristics of the enzyme have also been further studied. The native enzyme is a tetramer and has an isoelectric point of 7.0 which is comparable with that of cytosolic aldehyde dehydrogenases from other species. Taken together the present data further indicate that 11-hydroxythromboxane B2 dehydrogenase is identical with cytosolic aldehyde dehydrogenase and that substrates and inhibitors of aldehyde dehydrogenase interact with thromboxane metabolism in vitro.

Effect of DP-1904, a thromboxane A2 synthase inhibitor, administered from the autologous phase on crescentic-type anti-GBM nephritis in rats

The antinephritic effect of DP-1904 [6-(1-imidazolylmethyl)-5,6,7,8-tetrahydronaphthalene-2-carboxylic acid hydrochloride], a thromboxane (TX) A2 synthase inhibitor, was compared with that of OKY-046 and azathioprine, using an experimental model of nephritis, crescentic-type anti-glomerular basement membrane (GBM) nephritis. Test drugs were given p.o. once daily from an autologous phase in which proteinuria was already fully developed. DP-1904 (15 and 45 mg/kg per day) and OKY-046 (20 mg/kg per day), another TXA2 synthase inhibitor, significantly inhibited the development of glomerular alteration as well as the elevation of proteinuria. On the other hand, azathioprine (20 mg/kg per day), an immunosuppressive agent, failed to suppress the proteinuria. A single administration of DP-1904 or OKY-046 inhibited glomerular TXB2 production and increased glomerular prostaglandin (PG) E2 and 6-keto PGF1 alpha production in nephritic rats. Both drugs apparently decreased the depositions of both rabbit immunoglobulin (Ig) G and rat IgG on GBM in nephritic rats, but azathioprine inhibited only the deposition of rat IgG. These results suggest that DP-1904 may be an effective agent for the treatment of proliferative glomerulonephritis and its antinephritic effect may be due to the amelioration of abnormal metabolism of arachidonic acid.

Dietary fatty acids and the glomerular hemodynamic response to cyclosporine in borderline hypertensive rats

We have recently reported that cyclosporine A (CsA) decreases glomerular filtration rate in the borderline hypertensive rat (BHR), but that the glomerular filtration rate is normal when the rats are maintained on a diet supplemented with evening primrose (EP) oil. The current studies were designed to determine the glomerular hemodynamic changes responsible for this effect. A first group (PLAC-SAFF) received a diet supplemented with safflower oil (SAFF) (10% of calories) and placebo (PLAC). A second group (CsA-SAFF) received a diet supplemented with SAFF and CsA (10 mg/kg/day). A third group (CsA-EP) also received CsA, but the diet was supplemented with EP oil (10% of calories). Routine micropuncture studies were performed after five to nine weeks of treatment. Single nephron glomerular filtration rate (SNGFR) was lower in CsA-SAFF than in PLAC-SAFF (36 +/- 2 vs. 46 +/- 1 nl/min, p < 0.05). Maintenance of SNGFR in CsA-EP compared to CsA-SAFF (48 +/- 2 nl/min vs. 36 +/- 2 nl/min, P < 0.05) was due to higher values for single nephron plasma flow rate (156 +/- 16 vs. 118 +/- 9off/min, P < 0.05), and higher values for the glomerular capillary ultrafiltration coefficient (0.091 +/- 0.013 vs. 0.054 +/- 0.010 nl/s/mm Hg, P < 0.05). Since dietary fatty acids can affect prostaglandin (PG) production, we measured PGE production in isolated glomeruli. Mean values for basal production rates of PGE were greater in rats maintained on EP than in rats maintained on SAFF (3958 +/- 105 vs. 3378 +/- 146 pg PGE/mg glomerular protein, P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Serotonergic measures in cyclosporine A treated rats

Whole blood and plasma serotonin (5-HT), its major metabolite--5-hydroxyindoleacetic acid (5-HIAA), renal cortical blood flow, serum creatinine and whole blood cyclosporine A (CyA) levels were investigated in rats administered with CyA at a dose of 5 mg/kg b.w. or 10 mg/kg b.w. for 14 consecutive days. Serum creatinine remained unaltered during CyA treatment and no apparent changes in excised kidneys were found. Dose-dependent increases in whole blood and plasma 5-HT as well as whole blood 5-HIAA levels were observed. Renal cortical blood flow declined significantly and correlated inversely with whole blood 5-HT and 5-HIAA as well as with plasma 5-HT. Whole blood 5-HT was positively related to whole blood CyA levels. Taking all these data into account and considering the fact that 5-HT is a potent vasoconstrictor, a possible role of this amine in the pathogenesis of renal ischemia during CyA administration is suggested.

Role of nitric oxide in renal hemodynamic abnormalities of cyclosporin nephrotoxicity

To evaluate the participation of nitric oxide (NO) in chronic cyclosporin A (CsA) nephrotoxicity, the glomerular hemodynamic response to NO inhibition with N-nitro-L-arginine-methyl-ester (NAME) and stimulation of NO production with L-arginine was studied in uninephrectomized rats. Chronic CsA administration produced renal vasoconstriction, characterized by increased afferent (AR) and efferent (ER) resistances, decrease of glomerular plasma flow (QA) and ultrafiltration coefficient (Kf) that resulted in a 53% fall of single-nephron glomerular filtration rate (SNGFR). NAME infusion in vehicle group (V) elevated mean arterial pressure (MAP), AR and ER, reduced qA and Kf, and increased glomerular capillary pressure (PGC), resulting in a 28.9% fall of SNGFR. In the CsA group, NAME also increased MAP, but renal vasoconstriction was more intense; a greater rise of AR lowered PGC (P < 0.05 vs. V) further decreasing SNGFR by 38.9%. In control rats, L-arginine infusion induced a vasodilatory response of AR and ER, and elevation of QA and Kf, which resulted in a 72.6% increase in SNGFR. In the CsA group, greater vasodilation was observed and SNGFR rose by 114.9%. NO2-/NO3- urinary excretion was similar in CsA and V groups, and it was not modified by NAME in either group, but it increased five- to sixfold during L-arginine infusion in both groups. In conclusion, in CsA nephrotoxicity NO production seems to be normal and the ability of the renal endothelium to produce NO is maintained. Therefore renal vasoconstriction associated with CsA is not mediated by NO deficiency, although NO appears to attenuate it.

Effect of DP-1904, a thromboxane A2 synthetase inhibitor, on crescentic nephritis in rats

The antinephritic effect of DP-1904 [6-(1-imidazolylmethyl)-5,6,7,8-tetrahydronaphthalene-2-carboxylic acid hydrochloride], a thromboxane A2 synthetase inhibitor, was compared with that of OKY-046, using an experimental model of nephritis, crescentic-type anti-glomerular basement membrane nephritis. Test drugs were given p.o. once daily from the day after the the development of glomerular alteration as well as the elevation of proteinuria and plasma cholesterol. On the other hand, OKY-046 (20 mg/kg per day), a thromboxane A2 synthetase inhibitor, significantly inhibited only deterioration in the glomeruli. DP-1904 and OKY-046 inhibited glomerular thromboxane B2 production and increased glomerular prostaglandin E2 and 6-keto prostaglandin F1 alpha production in normal and nephritic rats. Both drugs inhibited the increase in platelet aggregability, restored decreased renal tissue blood flow to a near-normal level and decreased the deposition of rat immunoglobulin G on glomerular basement membrane in nephritic rats. These results suggest that DP-1904 may be an effective agent for the treatment of proliferative glomerulonephritis.

Urinary excretion of 2,3-dinor-thromboxane B1, a major metabolite of thromboxane B2 in the rat

Urinary 2,3-dinor-thromboxane B2 (2,3-dinor-TXB2), an enzymatic degradation product of TXB2, is currently measured for evaluating in vivo thromboxane biosynthesis in rats. We simultaneously measured 2,3-dinor-TXB2 and 2,3-dinor-TXB1, another product of TXB2 metabolism, in the urine of rats by immunoaffinity extraction/gas chromatography negative ion chemical ionization mass spectrometry (GC-NICIMS). In rats under basal conditions, urinary excretion of 2,3-dinor-TXB1 was much higher than that of 2,3-dinor-TXB2 (19.22 +/- 4.86 and 1.64 +/- 0.29 ng/24 h, respectively). The relative abundance of the two metabolites in each animal was fairly constant (91.9 +/- 1.6 and 8.1 +/- 1.6% of their sum, respectively). Urinary excretion of both 2,3-dinor-TXB1 and 2,3-dinor-TXB2 increased in rats undergoing in vivo hepatic ischemia-reperfusion. Other thromboxane metabolites, including 11-dehydro-TXB2 and 11-dehydro-2,3-dinor-TXB2, were measured by GC-NICIMS in selected urines. The resulting profile was: 2,3,4,5-tetranor-TXB1 > 2,3-dinor-TXB1 >> 11-dehydro-TXB2 > 2,3-dinor-TXB2 = TXB2. This study shows that urinary 2,3-dinor-TXB1 is a suitable parameter of TXB2 biosynthesis in vivo in rats. The possible cross-reactivity of 2,3-dinor-TXB1 in immunoassays of urinary 2,3-dinor-TXB2 or even TXB2 in rats should be considered in future studies.

Effects of KW-3635, a specific thromboxane A2-receptor antagonist, on the development of lupus nephritis in NZB x NZW F1 mice

We examined the effect of KW-3635, a specific thromboxane A2 (TXA2)-receptor antagonist, on the development of lupus nephritis in NZB x NZW F1 mice. KW-3635 was orally given once a day for 33 weeks beginning at eight weeks of age. In the control group, the mice began to die at 39 weeks of age, showing severe proteinuria and histopathologic abnormality in the renal glomeruli. Administration of KW-3635 (30 mg/kg/day) significantly reduced urinary protein excretion (1.7 +/- 0.9 vs. 8.5 +/- 2.4 mg/6 hr/mouse, P < 0.01), mortality (1/18 vs. 6/19, P < 0.05) and the histopathologic score of the kidney examined at 41 weeks of age. Thus, chronic administration of KW-3635 markedly attenuated the renal disease in NZB x NZW F1 mice, suggesting that TXA2 is an important mediator of the pathogenesis in this murine model of lupus nephritis.

Tacrolimus. A review of its pharmacology, and therapeutic potential in hepatic and renal transplantation

Tacrolimus (FK 506) is a macrolide immunosuppressant which possesses similar but more potent immunosuppressant properties compared with cyclosporin, inhibiting cell-mediated and humoral immune responses. Like cyclosporin, tacrolimus demonstrates considerable interindividual variation in its pharmacokinetic profile. This has caused difficulty in defining the optimum dosage regimen and has highlighted the usefulness of therapeutic drug monitoring. Most clinical studies with tacrolimus have neither been published in their entirety nor subjected to extensive peer review; there is also a paucity of published randomised investigations of tacrolimus versus cyclosporin, particularly in renal transplantation. Despite these drawbacks, tacrolimus has shown notable efficacy as a rescue or primary immunosuppressant therapy when combined with corticosteroids in adult and paediatric recipients following liver or kidney transplantation. Indeed, graft salvage rates in patients experiencing rejection or drug-related toxicity were > or = 50%, although data in renal transplantation are limited. Compared with cyclosporin as a primary immunosuppressant, tacrolimus showed comparable or greater patient/graft survival rates in liver allograft recipients (where cost savings associated with reduced hospitalisation costs were evident in one study), and comparable patient/graft survival in patients following kidney transplantation. Worthy of note was the efficacy of tacrolimus as a primary immunosuppressant in patients who received en bloc kidney allografts. The incidence of rejection was largely reduced following rescue therapy with tacrolimus and was generally lower (notably for refractory rejection) than that observed for cyclosporin, at least in liver allograft recipients. This was reflected in less need for adjunct immunotherapy including antilymphocyte preparations for the treatment of rejection episodes. The potential for reduction or withdrawal of corticosteroid therapy with tacrolimus appears to be a distinct advantage compared with cyclosporin, and this may be enhanced by the reduced incidence of infectious complications and of hypertension and hypercholesterolaemia reported by some investigators. In other respects, however, the tolerability profile of tacrolimus appears to be broadly similar to that of cyclosporin. Against this background, preliminary data indicate that tacrolimus provides a valuable therapeutic alternative to retransplantation in patients experiencing liver or kidney graft rejection or drug-related toxicity. Pending confirmation of initial randomised studies and preliminary results from large randomised investigations, tacrolimus may well be considered as an alternative primary immunosuppressant to cyclosporin in hepatic (particularly) and renal transplantation. Furthermore, the steroid-sparing effects of tacrolimus, although of benefit to all patient groups, may prove to be of particular worth in children and in en bloc kidney recipients. In these patients tacrolimus may well emerge as the drug of choice.(ABSTRACT TRUNCATED AT 400 WORDS)

Cyclosporin A attenuates increased prostaglandin and thromboxane production in response to various stimuli in human decidua

PROBLEM

This study was undertaken to evaluate the effects of cyclosporin A on prostanoid (prostaglandin and thromboxane) production by human decidua.

METHOD

Decidual cells were isolated from term placentae obtained at elective cesarean section before the onset of labor. Cells were grown to confluence and then incubated for 16 h with cyclosporin A (0.1-100 ng/ml) in the presence and absence of interleukin 1 beta (IL-1 beta, 10 ng/ml), phorbol 12-myristate 13-acetate (PMA, 10(-7) M) and ionomycin (0.5 micron). Prostaglandin E2 (PGE2) and thromboxane B2 (TXB2) were measured by radioimmunoassay, and cellular protein was determined.

RESULTS

IL-1 beta, PMA, and ionomycin all stimulated decidual PGE2 and TXB2 production as expected. However, these stimulatory actions were attenuated by 20% when cells were coincubated with cyclosporin A (100 ng/ml). All concentrations of cyclosporin A tested were within the therapeutic range.

CONCLUSIONS

Our results indicate that cyclosporin A does not stimulate decidual prostanoid production and is probably unrelated to preterm labor and delivery in allograft recipients.

De novo hypertension after liver transplantation

Hypertension develops in most patients after transplantation when immunosuppression is based on cyclosporine and prednisone. The pathogenesis appears to be multifactorial but involves rapidly rising vasoconstrictor tone in renal and systemic vascular beds. Much of this tone reflects abnormal vascular function, characterized by impaired prostacyclin and EDRF effects, in conjunction with increased vasoconstriction due to endothelin and possibly other factors. Effective management of the transplant recipient depends on preventing excessive vasoconstriction, usually with calcium channel blocking agents.

Cellular signaling by cyclosporine A in contractile cells: interactions with atrial natriuretic peptide

Immunosuppressive therapy with cyclosporine A (CyA) may be associated with severe side effects such as nephrotoxicity and arterial hypertension. The partial reversibility of these effects suggests that they are at least in part functional. The present study examined the effects of CyA on cellular signaling in vascular smooth muscle cells and in glomerular mesangial cells and the interactions with the endogenous vasodilator atrial natriuretic peptide (ANP). Intracellular free calcium concentrations ([Ca2+]i) were measured using Fura-2. 45Ca2+ was used to measure Ca2+ efflux and cellular Ca2+ influx. In the presence of cyclosporine (10 micrograms/ml), the Ca(2+)-mobilizing effects of angiotensin II (10(-8)M) in smooth muscle cells and of arginine vasopressin (AVP) in mesangial cells were significantly enhanced. CyA significantly stimulated cellular Ca2+ uptake in both cell types. ANP blocked the Ca2+ mobilization by angiotensin II and AVP and also completely inhibited the potentiating effect of CyA on angiotensin II- and AVP-induced Ca2+ mobilization. ANP also completely blocked the CyA-stimulated Ca2+ uptake. These findings suggest that CyA stimulates transmembrane Ca2+ influx, thereby increasing vasopressor-sensitive intracellular Ca2+ stores and augmenting vasopressor-induced Ca2+ mobilization. This cellular effect of CyA in vitro was markedly diminished by ANP. The effects of CyA on intracellular signaling may directly enhance the contractile response of smooth muscle and the glomerular mesangium to vasopressor stimuli and may also contribute to other disturbances of cell metabolism associated with CyA.

Cyclophilin-dependent stimulation of transcription by cyclosporin A

Exposure to cyclosporin A (CspA) increased laccase (lac-1) transcript accumulation in the chestnut blight fungus Cryphonectria parasitica. This response was suppressed by compounds that interfere with calcium-dependent signal transduction and by the presence of a virulence-attenuating mycovirus. CspA stimulated the accumulation of mRNA from a nonhomologous reporter fused to the lac-1 promoter, indicating that the increased transcript levels resulted from an increase in promoter activity. Based on the current model for the regulation of lac-1 transcription, these results suggest that CspA interferes with a negative regulatory pathway that normally constrains lac-1 promoter activity. Significantly, CspA did not stimulate lac-1 transcription in mutant strains deficient in CspA binding activity, directly demonstrating a requirement for the interaction of CspA and cyclophilin in the modulation of lac-1 transcription. Our results establish that CspA treatment can stimulate gene transcription and that cyclophilin is the cellular receptor that mediates this activity.

Early sequential ultrastructural renal alterations induced by 2-bromoethylamine hydrobromide in the Swiss ICR mouse

Thirty-two male Swiss ICR mice were injected intraperitoneally with 300 mg 2-bromoethylamine hydrobromide/kg body weight, anesthetized, and perfused with glutaraldehyde-paraformaldehyde solution at 5, 15, 30, 60, 90, 120, 150, and 180 minutes after treatment. Eight control mice were injected intraperitoneally with sterile diluent, and one was perfused at each of the same time periods as the treated mice. Proximal tubule epithelial alterations progressed over time from increased secondary lysosome and myeloid body formation to cellular and mitochondrial swelling and eventually cell necrosis. The glomerular, peritubular, and vasa recta capillaries had endothelial cell swelling and desquamation and platelet aggregation. Bromoethylamine nephrotoxicosis in the male Swiss ICR mouse is an ischemic necrosis of the proximal tubules and papilla initiated by endothelial cell damage and makes an excellent model of chemically induced damage to endothelial cells and tubular necrosis.

Thromboxane synthesis and action within the kidney

PGH2 and TxA2 exert their actions via tissue specific, receptor isoforms. PGH2/TxA2-dependent platelet aggregation and contraction of vascular and bronchial smooth muscle and of glomerular mesangial cells occur via receptors linked to activation of phospholipase C. Although PGH2/TxA2 appear to be of little importance in the maintenance of renal function under physiological circumstances, increased renal TxA2 biosynthesis has been documented in a variety of animal models of renal disease and in some clinical disorders (Table 2). The effects of this eicosanoid on renal tissues in vitro and of pharmacological manipulation of TxA2 synthesis and action in vivo suggest that such interventions will provide new drugs for the treatment of human kidney disease.

Protection of glomerular filtration rate by the thromboxane receptor antagonist L655,240 during low dose cyclosporine administration

Cyclosporin A (CsA) alters the production of prostaglandins (PG) by the kidney. CsA causes an increase in renal vascular resistance, a decrease in renal blood flow, a decrease in glomerular filtration rate (GFR), and increases the renal production of the vasoconstrictor thromboxane. Recently, low dose CsA has been utilized in the treatment of refractory autoimmune diseases. To determine if low dose CsA administration could produce renal hemodynamic alterations and to determine if the thromboxane receptor antagonist L655,240 could prevent these alterations, we administered groups of rats either CsA, 5 mg/kg, subcutaneously and the L655,240 vehicle NaHCO3 (CsA-NaHCO3), or CsA and L655,240 (CsA-L655,240), or CsA vehicle and L655,240. The rats were administered the drugs for 7 days and then subjected to inulin and PAH clearances or kidneys were harvested for prostaglandin production studies. CsA significantly depressed GFR and renal plasma flow when compared to the L655,240 treated groups. There was no difference in inulin or PAH clearance between the CsA-L655,240 and CsA vehicle L655,240 groups. Glomerular prostaglandin production including thromboxane was depressed by CsA administration. No histologic alterations were noted in the glomeruli or the medullary portions of the kidney. We conclude that administration of low dose CsA, 5 mg/kg, for 7 days results in a decrease in renal blood flow and GFR without histologic alterations. Administration of the thromboxane receptor antagonist L655,240 prevents the renal hemodynamic alterations induced by CsA in this rat model.

Cyclosporin A abolishes renal reserve capacity

Renal functional reserve (RFR) was investigated in a group of renal transplant recipients taking cyclosporin A (CyA) immunosuppressive therapy. Nine patients received a 93 g oral protein load containing 5983 mg of glycine. GFR and ERPF were measured using isotope infusions of 51Cr EDTA and 125I OIH, respectively, before and for 3 h after the meal. Patients studied demonstrated a wide range of baseline GFRs (20.9-89.5 mL/min, mean 50.09 mL/min). However, few patients demonstrated an individual RFR, regardless of original level of function. Overall, no significant change in either GFR or ERPF was demonstrated after the protein stimulus. CyA is known to alter intrarenal prostanoid synthesis in favor of vasoconstriction and RFR is thought to be mediated by prostanoids. Therefore a mechanism for the absence of RFR in patients receiving CyA therapy is suggested.

Effects of thromboxane synthase inhibition with CGS 13080 in human cyclosporine nephrotoxicity

Cyclosporine is a potent immunosuppressive agent, however, its use is limited by nephrotoxicity. Increased production of the potent vasoconstrictor thromboxane A2 contributes to cyclosporine nephrotoxicity in animal models, but the role of thromboxane in human cyclosporine nephrotoxicity has not been established. We therefore studied cyclosporine-treated renal allograft recipients who had evidence of toxicity manifested by decreased renal function. We measured GFR and PAH clearance (CPAH) before, during, and one week after a 48-hour intravenous infusion of the thromboxane synthase inhibitor CGS 13080. At baseline, the urinary excretion of TXB2 and 2,3-dinor-TXB2 was elevated in the study patients compared to healthy subjects. CGS 13080 infusion caused selective and nearly complete inhibition of thromboxane metabolite excretion in all patients. Mean CPAH improved 33% from 223 +/- 45 to 298 +/- 59 ml/min/m2 (P = 0.055) during infusion, while mean GFR improved 9% from 50.1 +/- 3.9 at baseline to 54.6 +/- 4.5 ml/min/1.73 m2 (P = 0.111). The effect on GFR occurred primarily in those patients taking calcium channel blockers. The mean increase in GFR in these 5 patients was 10.0 +/- 2.8 versus -1.0 +/- 2.8 ml/min/m2 in the remainder. We conclude that thromboxane synthase inhibitors may be useful in attenuating the nephrotoxic effects of cyclosporine following renal transplantation.

Contribution of platelet thromboxane production to enhanced urinary excretion and glomerular production of thromboxane and to the pathogenesis of albuminuria in the streptozotocin-diabetic rat

Previous studies have demonstrated that urinary thromboxane B2 (TXB2) excretion (UTXB2) and glomerular production of TXB2 are enhanced in experimental diabetes and that selective inhibitors of TX synthesis prevent or delay the development of albuminuria. The present study was conducted to examine the contribution of platelet TXB2 production to the enhancement of UTXB2 and glomerular TXB2 production and to the pathogenesis of albuminuria in the partially insulin-treated moderately hyperglycemic (blood glucose, 200 to 400 mg/dL) streptozotocin-diabetic rat (SDR). Treatment of control rats or of SDR with diabetes of 5 months' duration with antiplatelet serum for 4 consecutive days reduced circulating platelet counts and serum TXB2 generation, an index of platelet cyclooxygenase activity, by 80% or greater, but reduced UTXB2 excretion by only 30%. UTXB2 and glomerular production of TXB2 of thrombocytopenic SDR remained markedly elevated compared with corresponding values from age-matched thrombocytopenic or platelet-replete, nondiabetic controls. Similarly, treatment of rats for 180 days with a dose of aspirin (ASA), which selectively inhibited platelet versus renal cyclooxygenase activity, reduced UTXB2 of both SDR and controls by 25% to 35%. The absolute reductions in UTXB2 induced by either ASA or thrombocytopenia in SDR were significantly greater than the absolute decrements in corresponding controls, suggesting that increased platelet TXB2 production in SDR may contribute to the enhanced UTXB2. However, as in the thrombocytopenic SDR, UTXB2 and glomerular production of TXB2 of SDR treated with ASA remained clearly above corresponding control values. Moreover, chronic ASA treatment failed to prevent the development of albuminuria in SDR.(ABSTRACT TRUNCATED AT 250 WORDS)

Therapeutic implications of arachidonic acid metabolism in transplant-associated acute renal failure

Acute renal failure is common in kidney transplantation due to immunologic, nephrotoxic, and ischemic events. In this paper the subject of posttransplant acute renal failure is reviewed in relation to arachidonic acid metabolism. Although experimental abnormalities noted in ischemia, rejection, and cyclosporin nephrotoxicity are discussed separately, it is obvious that in the clinical situation there is great overlap. The effects of altering the substrate arachidonic acid by feeding of dietary omega-3 fatty acids, both experimentally and clinically, are discussed. Finally, the limited clinical trials of prostaglandin analogues in renal transplant patients show conflicting conclusions as regards beneficial effects on rejection and renal function. Careful clinical studies of compounds with proven efficacy in animals are needed if acute renal failure posttransplant is to be modified or prevented.

Prostanoids in paediatric kidney diseases

Prostanoids belong to the growing family of eicosanoids, which are all derived from arachidonic acid. Prostanoids act as modulators and mediators in a large spectrum of physiological and pathophysiological processes within the kidney. On the one hand, the potent vasoconstrictor and platelet-aggregating thromboxane (TX) A2 is involved in the pathophysiology of a variety of glomerular diseases, such as haemolytic-uraemic syndrome and immune-mediated glomerulopathies. Prostaglandin (PG) E2, on the other hand, interferes with tubular electrolyte and water handling. Clinical data support the hypothesis that this member of the prostanoid family contributes to the pathophysiology of Bartter's syndrome, hyperprostaglandin E syndrome, idiopathic hypercalciuria and renal diabetes insipidus. Both prostanoids, TXA2 and PGE2, are involved in the pathophysiology of obstructive uropathies. The physiological and protective role of renal vasodilator prostanoids (PGI2 and PGE2) has been studied during treatment with non-steroidal anti-inflammatory drugs. Part of the pharmacological effects of frusemide and converting enzyme inhibitors is mediated by PGI2 and PGE2. The role of renal prostanoids in cyclosporine toxicity is still equivocal. Future investigations on the physiological and pathophysiological role of renal prostanoids will have to consider the multiple interactions between prostanoids on the one hand, and classical hormones and other mediators (e.g. cytokines) on the other hand.

Cyclosporin A augments human platelet sensitivity to aggregating agents by increasing fibrinogen receptor availability

Clinical use of cyclosporin A (CsA) has been associated with platelet hypersensitivity and an increased incidence of thrombotic and vasoactive events. The purpose of this study was (1) to confirm that CsA enhances platelet sensitivity to the soluble agonists, adenosine diphosphate (ADP) and epinephrine (EPI), and (2) to determine if this enhancement is mediated by alteration in the availability of platelet surface fibrinogen receptors, a final mediator of platelet activation. Mean log dose of ADP required to achieve complete second-wave platelet aggregation in vitro decreased from 1.90 to 1.49 microM (n = 19, paired t test, P less than 0.05) and 2.86 to 2.11 microM (n = 16, P less than 0.05) following a 15-min and 3-hr incubation in the absence (saline) and presence of CsA (1000 ng/ml), respectively. At the threshold dose of ADP, concurrent thromboxane B2 levels at 15 min were 245 +/- 44 ng/ml (n = 12, saline) and 265 +/- 54 ng/ml (n = 9, CsA; P greater than 0.05). At 3 hr respective levels were 333 +/- 57 and 442 +/- 81 ng/ml (P greater than 0.05). Similar results were obtained with EPI. The number of fibrinogen binding sites in response to 50 microM ADP was determined in washed platelets in the absence and presence of CsA by radioligand binding. In 6 of 7 volunteers, CsA increased fibrinogen receptors from 26,635 +/- 4841 to 35,925 +/- 7290 sites/platelet (means +/- SEM; P less than 0.05). No change in receptor affinity was noted. In conclusion, cyclosporine does augment platelet reactivity.(ABSTRACT TRUNCATED AT 250 WORDS)

Is cyclophilin involved in the immunosuppressive and nephrotoxic mechanism of action of cyclosporin A?

In this report we have approached two questions relating to the mechanism of action of cyclosporin A (CsA). First, we address whether the major cytosolic protein for CsA, cyclophilin, is directly involved in mediating the immunosuppressive activity of this drug, and, in particular, whether inhibition of this protein's peptidyl-prolyl cis-trans isomerase (PPIase) activity results in inhibition of murine T cell activation. Second, we ask whether the nephrotoxicity observed with CsA is related to inhibition of PPIase-dependent pathways in cells other than lymphocytes. Using a series of 61 cyclosporin analogues, we generally found a good correlation between cyclophilin binding and immunosuppressive activity for the majority of analogues analyzed. However, a number of compounds of distinct structural classes were found that could interact with cyclophilin but were much less immunosuppressive than expected. The inability of these analogues to inhibit lymphocyte activation could not be explained by their failure to enter the cell and bind to cyclophilin under the conditions used in the cellular assays. Surprisingly, a nonimmunosuppressive analogue, MeAla-6, which bound well to cyclophilin and was active as a PPIase inhibitor, did not induce renal pathology in vivo. Furthermore, another analogue, MeBm2t, which was immunosuppressive in vitro, possessed little or no activity as a PPIase inhibitor. These findings pose serious questions concerning a direct role of cyclosporin in mediating CsA's immunosuppressive and nephrotoxic activities. In addition, they raise doubts about whether PPIase has a direct function in lymphocyte signal transduction.

Arteriolosclerosis of the human renal allograft: morphology, origin, life history and relationship to cyclosporine therapy

In the decade 1979-1988, 658 biopsies were collected from 568 cadaveric renal allografts. In 118 grafts a non-proliferative insudative vasculopathy (IVA) was found in afferent vessels. Immunosuppression was based on azathioprine (AZA) or on cyclosporin A (CsA), from 1983. The prevalence and extent of IVA has increased significantly since 1984. Light microscopy showed fibrinoid and hyaline masses of varying extent; transmural insudative "knobs", intimal oedema with metachromasia, and microthrombosis were also seen with CsA. The ultrastructure of the insudates was unremarkable but CsA grafts displayed early oedema and hypergranulation of endothelial cells with a disarray of smooth muscle cell (SMC) microfibrils, and pronounced degenerative changes of SMC. Rebiopsy showed stationary IVA in AZA grafts and progression in one-half of CsA-treated patients. Nephrectomy specimens revealed, however, a marked predominance of late rejection endarteritis; in only 3 cases was IVA and/or microthrombosis the possible cause of nephrectomy. The mean donor age was higher in severe IVA in CsA grafts and the mean post-transplantation interval at the time of diagnosis of IVA was significantly shorter in CsA-treated patients. No important differences in cumulative graft survival were seen between grafts with absent, moderate or severe IVA. Unused cadaveric donors' kidneys of comparable age exhibited normal arterioles or a slight focal insudative or hyaline lesion.

The pathophysiology of Sandimmune (cyclosporine) in man and animals

Part II: The side-effects of Sandimmune that have also been observed clinically include hepatic dysfunction, glucose intolerance, thrombo-embolic complications and nervous system disorders. To determine the cause and significance of such effects, the actions of Sandimmune on the liver, the pancreas, on hematostasis and the nervous system were examined. Comparisons were made between animal and human data obtained in vivo and in vitro, and the clinical setting under which the side-effects occur was analyzed. The actions of Sandimmune on the liver seem to reflect mostly a cholestasis with a small depression in protein synthesis and a mild disturbance in lipid metabolism of uncertain origin. The action of Sandimmune on the pancreas suggests insulin resistance and possibly a secretory disturbance, with no evidence for depressed insulin synthesis, except in animals at high doses. Sandimmune does not seem to promote thromboembolism in man, although fibrinolysis may be depressed and platelet aggregation can be enhanced. The effects of Sandimmune on the nervous system are unclear, for tremor is common but of uncertain origin, whereas seizures and encephalopathy are rare and invariably associated with other risk factors.

The pathophysiology of Sandimmune (cyclosporine) in man and animals

Part I: The side-effects of Sandimmune that have been of most significance clinically are renal dysfunction, renal vascular damage and arterial hypertension. To examine the nature and the origin of such effects, the actions of Sandimmune on the renal tubule, the renal vessels and systemic vessels have been analyzed. To evaluate whether common vasoconstrictory systems may be involved, changes in the renin-angiotensin-aldosterone system and prostaglandin-thromboxane system have been assessed. Comparison between animal and human data obtained in vivo and in vitro shows the actions of Sandimmune on the renal tubule to be modest and involve only a few specific effects. The major action of Sandimmune is on the vessels, vasoconstriction being the major cause of renal dysfunction and also the cause of arterial hypertension. Neither the circulating renin-angiotension-aldosterone system nor the prostaglandin-thromboxane system is clearly responsible for vasoconstriction. Although not itself a vasoconstrictor, Sandimmune seems to modulate the constrictory and dilatory response to other agents in several vascular beds.

Current concepts for a drug-induced inhibition of formation and action of thromboxane A2

Urinary and plasma metabolites of thromboxane A2 (TxA2) indicate an increased TxA2 synthesis in a number of diseases, whereby TxA2 is assumed to contribute to the underlying pathomechanisms by its profound effects on platelet aggregation and smooth muscle contraction. In some clinical situations the increment in TxA2 biosynthesis is accompanied by an increased formation of prostacyclin (PGI2) which is one of the most potent inhibitors of platelet activation and smooth muscle contraction. Therefore, drugs are being developed which suppress the formation or action of TxA2 without interfering with its functional antagonist PGI2. Low doses of acetylsalicyclic acid (ASA) preferentially inhibit cyclooxygenase activity in platelets and the synthesis of TxA2 in vivo. However, neither low doses (approximately 300 mg/day) nor very low doses spare the formation of PGI2 completely. Despite its limited selectivity, very low dose ASA (approximately 40 mg/day) provides an attractive perspective in TxA2 pharmacology. Although thromboxane synthase inhibitors selectively suppress TxA2 biosynthesis PGH2 can accumulate instead of TxA2 and substitute for TxA2 at their common TxA2/PGH2 receptors. Thromboxane synthase inhibitors can only exert platelet-inhibiting and vasodilating effects if PGH2 rapidly isomerizes to functional antagonists like PGI2 that can be formed from platelet-derived PGH2 by the vessel wall. TxA2/PGH2 receptor antagonists provide a specific and effective approach for inhibition of TxA2. These inhibitors do not interfere with the synthesis of PGI2 and other prostanoids but prevent TxA2 and PGH2 from activating platelets and inducing smooth muscle contractions. Most of the available TxA2/PGH2 receptor antagonists produce a competitive antagonism that can be overcome by high agonist concentrations. Since in certain disease states very high local TxA2 concentrations are to be antagonized, non-competitive receptor antagonists may be of particular interest. Some recent TxA2/PGH2 receptor antagonists produce such a non-competitive type of inhibition due to their low dissociation rate constant. As a consequence, agonists like TxA2 or PGH2 only reach a hemiequilibrium state at their receptors, previously occupied by those antagonists. A combination of a thromboxane synthase inhibitor with a TxA2/PGH2 receptor antagonist presents a very high inhibitory potential that utilizes the dual activities of the synthase inhibitor to increase PGI2 formation and of the receptor antagonist to antagonize PGH2 and TxA2. Such combinations or dual inhibitors, combining both moieties in one compound, prolong the skin bleeding time to a greater extent than thromboxane synthase inhibitors and even more than low dose ASA or TxA2/PGH2 receptor antagonists.

Cyclosporin reduces renal blood flow through vasoconstriction of arcuate arteries in the hydronephrotic rat model

Besides its beneficial effects in organ transplantation cyclosporin (CyA) exhibits nephrotoxic (and other) side effects. CyA nephrotoxicity is associated with a decrease in glomerular filtration rate. Two mechanisms of action have emerged. First, tubular destruction with secondary reduction in renal blood flow and glomerular filtration rate; second, decrease in renal blood flow with secondary interstitial fibrosis. We studied the effect of an acute infusion of CyA in the hydronephrotic rat kidney model, which lacks tubular structures completely. Hence, only the direct vascular effects of CyA were determined. Five groups (G) of rats were studied by television microscopy. G I (n = 7) received CyA (30 mg/kg, i.v.) dissolved in cremophore/plasma; G II (n = 5), time control 1, received cremophore/plasma instead of CyA; G III (n = 8), received CyA 30 mg/kg followed by 20 mg/kg CyA i.v. dissolved in an ethanol/tween solution; G IV (n = 3), time control 2 received ethanol/tween alone in the experimental period; in G V, CyA was applied locally onto the surface of the kidney with concentrations increasing from 10(-7) to 10(-5) M. CyA caused profound reduction in the diameter of arcuate arteries in groups I and III, in contrast to the time control groups II and IV. The vasoconstriction could be partially reversed by the calcium-channel blocker nitrendipine, and completely reversed with acetyl-choline. Glomerular blood flow decreased due to CyA and could not be completely normalized by either drug. Increasing the dosage from 30 to 50 mg/kg was not associated with further reduction in blood flow. Local application of CyA (G V) did not demonstrate vasoconstriction.(ABSTRACT TRUNCATED AT 250 WORDS)