Complement factor H and hemolytic uremic syndrome

Factor H is a 150 kDa single chain plasma glycoprotein that plays a pivotal role in the regulation of the alternative pathway of complement. Primary sequence analysis reveals a structural organization of this plasma protein, in 20 homologous units, called Short Consensus Repeats (SCRs), each about 60 amino acids long. Biochemical and genetic studies show an association between factor H deficiency and human diseases, including Systemic Lupus Erythematosus, susceptibility to pyogenic infection and a form of membranoproliferative glomerulonephropathy. More recently, factor H deficiency has also been associated with susceptibility to Hemolytic Uremic Syndrome (HUS), a disease consisting of microangiopathic hemolytic anemia, thrombocytopenia and acute renal failure, caused by platelet thrombi which mainly, but not exclusively, form in the microcirculation of the kidney. In this review, we summarize recent genetic and biochemical data, which indicate a critical role for factor H in the pathogenesis of HUS and suggest an important role of the most C-terminal domain, i.e. SCR 20, in the disease. In addition, we discuss the physiological consequences of these findings, as novel functional data show a particular essential role of SCR 20 of factor H as the central discriminatory and regulatory site of this multidomain, multifunctional plasma protein.

The molecular basis of familial hemolytic uremic syndrome: mutation analysis of factor H gene reveals a hot spot in short consensus repeat 20

The aim of the present study was to clarify whether factor H mutations were involved in genetic predisposition to hemolytic uremic syndrome, by performing linkage and mutation studies in a large number of patients from those referred to the Italian Registry for Recurrent and Familial HUS/TTP. PCR and Western blot analyses were conducted to characterize the biochemical consequences of the mutations. Five mutations in the factor H gene were identified. Three, identified in two families and in a sporadic case, are heterozygous point mutations within the most C-terminal short consensus repeat 20 (SCR20) of factor H, resulting in single amino acid substitutions. The other two mutations introduce premature stop codons that interrupt the translation of factor H. A heterozygous nonsense mutation was identified in SCR8 in one family, and a homozygous 24-bp deletion within SCR20 was identified in a Bedouin family with a recessive mode of inheritance. Reverse transcription-PCR analysis of cDNA from peripheral blood leukocytes from the Bedouin family showed that the deletion lowered factor H mRNA levels. Although heterozygous mutations were associated with normal factor H levels and incomplete penetrance of the disease, the homozygous mutation in the Bedouin family resulted in severe reduction of factor H levels accompanied by very early disease onset. These data provide compelling molecular evidence that genetically determined deficiencies in factor H are involved in both autosomal-dominant and autosomal-recessive hemolytic uremic syndrome and identify SCR20 as a hot spot for mutations in the disease. The mutations identified here give an important hint to the relevance of the C-terminus of factor H in the control of the alternative complement activation pathway.

17beta-estradiol corrects hemostasis in uremic rats by limiting vascular expression of nitric oxide synthases

Conjugated estrogens shorten the prolonged bleeding time in uremic patients and are similarly effective in a rat model of uremia. We have previously demonstrated that the shortening effect of a conjugated estrogen mixture or 17beta-estradiol on bleeding time was abolished by the nitric oxide (NO) precursor L-arginine, suggesting that the effect of these drugs on hemostasis in uremia might be mediated by changes in the NO synthetic pathway. The present study investigated the biochemical mechanism(s) by which conjugated estrogens limit the excessive formation of NO. 17beta-estradiol (0.6 mg/kg), given to rats made uremic by reduction of renal mass, significantly reduced bleeding time within 24 h and completely normalized plasma concentrations of the NO metabolites, nitrites and nitrates, and of NO synthase (NOS) catalytic activity, determined by NADPH-diaphorase staining in the thoracic aorta. Endothelial NOS (ecNOS) and inducible NOS (iNOS) immunoperoxidase staining in the endothelium of uremic aortas of untreated rats was significantly more intense than in control rats, while in uremic rats receiving 17beta-estradiol staining was comparable to controls. Thus 17beta-estradiol corrected the prolonged bleeding time of uremic rats and fully normalized the formation of NO by reducing the expression of ecNOS and iNOS in vascular endothelium. These results provide a possible biochemical explanation of the well-known effect of estrogens on primary hemostasis in uremia, in experimental animals and humans.

Thymic dendritic cells express inducible nitric oxide synthase and generate nitric oxide in response to self- and alloantigens

Thymocytes maturing in the thymus undergo clonal deletion/apoptosis when they encounter self- or allo-Ags presented by dendritic cells (DCs). How this occurs is a matter of debate, but NO may play a role given its ability of inducing apoptosis of these cells. APC (a mixed population of macrophages (Mphi) and DCs) from rat thymus expressed high levels of inducible NO synthase (iNOS) and produced large amounts of NO in basal conditions whereas iNOS expression and NO production were very low in thymocytes. Analysis by FACS and by double labeling of cytocentrifuged preparations showed that DCs and MPhi both express iNOS within APC. Analysis of a purified preparation of DCs confirmed that these cells express high levels of iNOS and produce large amounts of NO in basal conditions. The capacity of DCs to generate NO was enhanced by exposure to rat albumin, a self-protein, and required a fully expressed process of Ag internalization, processing, and presentation. Peptides derived from portions of class II MHC molecules up-regulate iNOS expression and NO production by DCs as well, both in self and allogeneic combinations, suggesting a role of NO in both self and acquired tolerance. We also found that NO induced apoptosis of rat double-positive thymocytes, the effect being more evident in anti-CD3-stimulated cells. Altogether, the present findings might suggest that DC-derived NO is at least one of the soluble factors regulating events, in the thymus, that follow recognition of self- and allo-Ags.

Physiology and pathophysiology of nitric oxide in chronic renal disease

Nitric oxide (NO), an L-arginine derivative, exerts a variety of renal and extrarenal physiological and pathophysiological effects. NO is generated by three isoforms of nitric oxide synthases (NOS): two acutely responsive, constitutive isoforms, neuronal NOS (nNOS) and endothelial NOS (ecNOS), and the slower, more persistent, inducible NOS (iNOS). NO regulates glomerular ultrafiltration; tubular reabsorption, and intrarenal renin secretion. A number of recent studies, most of them in the experimental model of renal mass reduction (RMR) in rats, have raised the hypothesis that an impaired NO synthetic pathway could have a key role in mediating the complex renal hemodynamic and nonhemodynamic disorders associated with the progression of renal disease. Thus, kidneys from rats with RMR produce less NO than normal rats, and NO generation negatively correlates with markers of renal damage. The abnormality is due to a defect in iNOS in the kidney. Data are also available showing that drugs capable of enhancing renal NO activity may be renoprotective in a variety of experimental renal diseases, particularly those characterized by derangements of glomerular hemodynamics. Fewer studies are available in humans and these have shown less than conclusive results.

Increased fragmentation of von Willebrand factor, due to abnormal cleavage of the subunit, parallels disease activity in recurrent hemolytic uremic syndrome and thrombotic thrombocytopenic purpura and discloses predisposition in families. The Italian Registry of Familial and Recurrent HUS/TTP

We investigated here the changes in von Willebrand factor (vWF) multimers in recurrent, sporadic and familial forms of hemolytic uremic syndrome (HUS)/thrombotic thrombocytopenic purpura (TTP) to see whether they are actually proteolyzed in vivo in these patients. Molecular determinants of fragments in vWF were also characterized to identify possible sites of cleavage of the subunit. Unusually large vWF multimers were found in blood of 8 of 10 patients with recurrent HUS/TTP, both in the acute phase and in remission, but never in familial and sporadic cases. Instead, all of the groups showed evidence of enhanced fragmentation of vWF multimers during the acute phase. Increased fragmentation was also shown by decrease in native 225-kD vWF subunit. In recurrent and sporadic HUS/TTP, enhanced fragmentation normalized at remission, but the abnormality persisted in familial HUS/TTP patients. The latter findings suggest that patients with familial HUS/TTP may have a congenital abnormality in vWF processing. Analysis with specific monoclonal antibodies showed the presence of the normal vWF fragments with apparent molecular mass of 189, 176, and 140 kD in all patients; however, in 6 recurrent and in 5 familial cases, novel fragments that differed in size from normal ones were found. The size of these abnormal fragments differed from one patient to another and none of them was ever found in normal plasma. These results documented, for the first time in HUS/TTP, an abnormal cleavage of the vWF subunit that might account for the increased fragmentation observed in these patients.

Interleukin-6 and RANTES in Takayasu arteritis: a guide for therapeutic decisions?

BACKGROUND

In patients with Takayasu arteritis, circulating lymphocytes are activated, and histological findings indicate that cell-mediated immunity plays an important role in the pathogenetic sequence leading to vascular lesions.

METHODS AND RESULTS

To delineate the profile of inflammatory and chemoattractant cytokines involved in T-cell activation in Takayasu arteritis, we measured by ELISA serum levels of interleukin (IL)-6, IL-1beta, and RANTES in 18 patients. Subsequently, we wanted to establish whether any of these molecules could be used as a marker to monitor the clinical course of the disease and to predict disease exacerbations. We found that all patients with Takayasu arteritis studied during an active phase of the disease have increased serum concentration of IL-6 compared with healthy control subjects (P<0.01). Enhanced IL-6 serum levels paralleled disease activity to the extent that its serum concentrations were comparable to those of control subjects when patients were studied in remission. RANTES concentrations were also higher than normal in the serum of all patients with Takayasu arteritis (P<0.01) studied during an active phase of the disease. RANTES serum levels tended to normalize in remission, but values remained higher than those of control subjects (P<0.05). In contrast, serum concentrations of IL-1beta were below the detection limit of ELISA in both healthy subjects and all patients with Takayasu arteritis. A positive correlation was found between either IL-6 (rho=0.705, P<0.01) or RANTES (rho=0.607, P<0.05) serum level and disease activity.

CONCLUSIONS

The close correlation of serum IL-6 and RANTES levels with disease activity suggests that these cytokines contribute to vasculitic lesions in Takayasu arteritis and raises the possibility that their monitoring in serum helps clinicians find adequate treatment adjustments in individual patients.

Nitric oxide/L-arginine in uremia

Nitric oxide (NO), a gaseous free radical derived from L-arginine, is a potent modulator of vascular tone and platelet functions. A number of recent studies, both in the experimental model of renal mass reduction (RMR) in rats and in uremic patients, have raised the hypothesis that abnormalities of NO synthetic pathway could have a key role in mediating the complex hemodynamic and hemostatic disorders associated to the progression of renal disease. Thus, kidneys from rats with RMR produce less NO than normal rats and NO generation negatively correlates with markers of renal damage. The abnormality is due to a strong defect of inducible NO synthase (iNOS) content in the kidney. Recent in vitro and in vivo data have raised the possibility that excessive renal synthesis of the potent vasoconstrictor and promitogenic peptide endothelin-1 (ET-1) is a major determinant for progressive iNOS loss in the kidney of RMR rats. In contrast, uremia is associated with excessive systemic NO release, both in experimental model and in human beings. In the systemic circulation of uremic rats, as well as uremic patients, NO is formed in excessive amounts. Possible cause of the increased NO levels is higher release from systemic vessels due to the augmented expression of both iNOS and endothelial NOS. A putative cause for excessive NO production in uremia can be guanidinosuccinate, an uremic toxin that accumulates in the circulation of uremic patients and upregulates NO synthesis from cultured endothelial cells. Upregulation of systemic NO synthesis might be a defense mechanism against hypertension of uremia. On the other hand, more NO available to circulating cells may sustain the bleeding tendency, a well-known complication of uremia.

Renoprotection by nitric oxide donor and lisinopril in the remnant kidney model

Previous studies showed a renoprotective effect of l-arginine in experimental uremia. Whether this was caused by an increased nitric oxide (NO) release or depended on l-arginine per se is not clear. Here, we evaluated whether chronic administration of an NO donor, molsidomine, controlled systemic blood pressure and renal disease progression and prolonged survival in rats with renal mass reduction (RMR). Rats with RMR received the following daily in the drinking water: group 1 (n = 21), no specific therapy (vehicle); group 2 (n = 12), molsidomine, 120 mg/L; group 3 (n = 9), lisinopril, 25 mg/L; and group 4 (n = 12), reserpine, 5 mg/L, hydralazine, 80 mg/L, and hydrochlorothiazide, 25 mg/L, from day 21 after surgery, when rats had hypertension and proteinuria, until the death of the vehicle-treated rats. Molsidomine normalized systemic hypertension, only partially reduced proteinuria and serum creatinine levels, but significantly prolonged animal survival, particularly in the early stage of the disease. Lisinopril at a similar systemic blood pressure was even better than molsidomine in limiting proteinuria, preserving renal function, and prolonging survival, but triple therapy, despite being effective on blood pressure, offered no renoprotection or prolonged survival. Endothelin-1 (ET-1) levels, formed in excessive amounts by the kidneys of these animals, were reduced by molsidomine and lisinopril, but not by triple therapy. The prolongation of survival by NO donor could be attributed to its effect of reducing ET levels, which in turn may limit the smooth muscle cell proliferation and matrix accumulation responsible for organ and, especially, myocardial fibrosis in uremia.

Hypocomplementemia discloses genetic predisposition to hemolytic uremic syndrome and thrombotic thrombocytopenic purpura: role of factor H abnormalities. Italian Registry of Familial and Recurrent Hemolytic Uremic Syndrome/Thrombotic Thrombocytopenic Purpura

Familial hemolytic uremic syndrome (HUS) and thrombotic thrombocytopenic purpura (TTP) carry a very poor outcome and have been reported in association with decreased serum levels of the third complement component (C3). Uncontrolled consumption in the microcirculation, possibly related to genetically determined deficiency in factor H--a modulator of the alternative pathway of complement activation--may account for decreased C3 serum levels even during disease remission and may predispose to intravascular thrombosis. In a case-control study by multivariate analysis, we correlated putative predisposing conditions, including low C3 serum levels, with history of disease in 15 cases reporting one or more episodes of familial HUS and TTP, in 25 age- and gender-matched healthy controls and in 63 case-relatives and 56 control-relatives, respectively. The relationship between history of disease, low C3, and factor H abnormalities was investigated in all affected families and in 17 controls. Seventy-three percent of cases compared with 16% of controls (P < 0.001), and 24% of case-relatives compared with 5% of control-relatives (P = 0.005) had decreased C3 serum levels. At multivariate analysis, C3 serum level was the only parameter associated with the disease within affected families (P = 0.02) and in the overall study population (P = 0.01). Thus, subjects with decreased C3 serum levels had a relative risk of HUS or TTP of 16.56 (95% confidence interval [CI], 1.66 to 162.39) within families and of 27.77 (95% CI, 2.44 to 314.19) in the overall population, compared to subjects with normal serum levels. Factor H abnormalities were found in four of the cases, compared with three of the healthy family members (P = 0.02) and none of the controls (P = 0.04) and, within families, factor H abnormalities were correlated with C3 reduction (P < 0.05). Reduced C3 clusters in familial HUS and TTP is likely related to a genetically determined deficiency in factor H and may predispose to the disease. Its demonstration may help identify subjects at risk in affected families.

Effect of acetate, bicarbonate dialysis, and acetate-free biofiltration on nitric oxide synthesis: implications for dialysis hypotension

The effect of acetate dialysis (AD), bicarbonate dialysis (BD), and acetate-free biofiltration (AFB) on nitric oxide (NO) synthesis and the implications for dialysis hypotension was studied. The finding that uremic plasma is a potent inducer of NO synthesis by endothelial cells in vitro suggested that the cardiovascular instability of dialysis patients might result from excessive NO formation. Cardiovascular instability is more frequent in patients undergoing AD than BD. To see whether these differences were attributable to NO, we studied the NO synthetic pathway ex vivo in patients undergoing different dialysis procedures. Five patients were treated, in a random order, with AD, BD, and AFB, a technique using a buffer-free dialysate and postdilution of a sterile bicarbonate solution. Each type of dialysis was used for 1 week, comprising three dialysis sessions. A polyacrylonitrile dialyzer was used for all three methods. Before and after the third dialysis, plasma was collected, added to [3H]L-arginine, and incubated with human umbilical vein endothelial cells (HUVECs) for 24 hours. NO synthesis was evaluated as [3H]L-citrulline formation. Plasma concentrations of interleukin-1beta (IL-1beta), a potent inducer of inducible NO synthase (iNOS) in endothelial cells, were also measured. Plasma collected from patients after AD stimulated endothelial NO synthesis more than plasma from the same patients before the dialysis session (pre-AD, 0.173+/-0.028 nmol/10(5) cells v post-AD, 0.280+/-0.093 nmol/10(5) cells; P < 0.05). A slight, although not significant, increase was also observed when HUVECs were incubated with plasma drawn after BD (pre-BD, 0.151+/-0.014 nmol/10(5) cells; post-BD, 0.230+/-0.055 nmol/10(5) cells). AFB did not aggravate the stimulatory effect of uremic plasma on endothelial NO synthesis (pre-AFB, 0.184+/-0.038 nmol/10(5) cells; post-AFB, 0.189+/-0.040 nmol/10(5) cells). Plasma IL-1beta was greater (P < 0.01) after AD than after BD and AFB (post-AD, 0.234+/-0.028 pg/mL; post-BD, 0.124+/-0.019 pg/mL; post-AFB, 0.120+/-0.013 pg/mL). With AD, there was a greater intradialytic decrease in systolic blood pressure than with BD or AFB. Weight and blood volume loss and sodium balance were similar in AD, BD, and AFB. These data were consistent with the possibility that NO and cytokines, released in excessive amounts during AD, may contribute to hemodynamic instability.

Upregulation of renal and systemic cyclooxygenase-2 in patients with active lupus nephritis

In lupus nephritis (LN), renal thromboxane A2 (TXA2) production is increased, and inhibition of TXA2 activity improves renal function. In patients with LN, renal function depends very much on vasodilatory prostaglandins, and indeed inhibiting the prostaglandin-forming enzyme cyclooxygenase (COX) with aspirin or related compounds was detrimental on renal hemodynamics in these patients. There are no data so far on whether the excessive TXA2 production in LN derives from upregulation of type I or type II isoforms of COX. It was found that TXB2 synthesis and COX-2 gene expression were higher in peripheral blood mononuclear cells from patients with active LN compared to patients in the inactive form of the disease and to healthy subjects. Unlike COX-2, levels of COX-1 mRNA were comparable in lupus patients and control subjects and were not influenced by the disease activity. Immunoperoxidase studies on kidney biopsies showed COX-1 staining in glomerular arterioles and other renal vessels, with no evident difference between lupus biopsies and control specimens taken from either individuals who were free of renal disease or patients with non-lupus nephropathies. In contrast, COX-2 staining was definitely stronger in specimens from patients with active LN than control specimens. In active LN, COX-2-specific staining was localized mainly in the glomeruli, with a weaker signal on tubuli and in the interstitium. Double-staining studies with an antibody against the macrophage marker CD68 and an anti-COX-2 antibody definitely showed that COX-2 and CD68 often colocalized on the same cell, with only occasional glomerular COX-2-stained mesangial areas. Patients with non-lupus nephropathies had no increase in renal COX-2 expression. These results indicate that COX-2 upregulation is a specific finding of active LN and that monocytes infiltrating the glomeruli contribute to the exaggerated local synthesis of TXA2. If this is correct, COX-2 may soon become a target for therapeutic intervention in this disease.

Identification of a novel gene--SSK1--in human endothelial cells exposed to shear stress

To identify transcriptionally regulated genes potentially involved in the effect of shear stress on endothelial gene expression, we performed a differential display analysis of mRNAs from human umbilical vein endothelial cell (HUVEC) exposed to laminar shear stress (12 dynes/cm2) in comparison to HUVEC maintained in static condition. We identified a cDNA fragment overexpressed by laminar shear stress. The full-length, SSK1, was 3653 long and encoded for a novel protein of 1050 amino acids. Northern blot demonstrates that SSK1 mRNA is expressed at high levels also in placenta, a weak transcript was present in heart, skeletal muscle, kidney and pancreas. Homology searches of the protein databases showed that SSK1 is related to numerous serine-threonine kinases. The highest homology was found with a very recently described gene, BUBR1, an analogue of BUB1, which is a kinase involved in the regulation of cell cycle. The most conserved residues in catalytic domains II, III, VIb, VII, VIII and IX of serine-threonine protein kinases were found in the C terminal region of SSK1 which further supports the kinase nature of the new protein. The putative serine-threonine kinase SSK1 may represent a tool by which mechanical forces regulates phosphorylation events within endothelial cells.

Nitric oxide/endothelin balance after nephron reduction

Nitric oxide (NO), an L-arginine derivative, is implicated in neuronal transmission, immune response and vasodilation, besides acting as a platelet function modulator. A number of recent studies in the experimental model of renal mass reduction (RMR) in rats have proposed the hypothesis that abnormalities of the NO synthetic pathway could have a key role in mediating the complex hemodynamic and hemostatic disorders associated with the progression of renal disease. Thus, renal NO generation is lower than normal in rats with RMR seven days after surgery, and progressively worsens with time in close correlation with signs of renal injury. This abnormality is due to a strong defect of inducible NO synthase (iNOS) content in the kidney. In the same model, administration of either the NO precursor, L-arginine, or a NO-releasing compound reduces proteinuria, slows renal disease progression and prolongs survival. On the other hand RMR is associated with a progressive increase of renal synthesis of the potent vasoconstrictor peptide, endothelin-1 (ET-1), whose mRNA is expressed in excessive amounts in cortical tubules early after surgical ablation. In this setting, a marked reduction of NO, in the face of continuous local generation of ET-1, may well contribute to intraglomerular capillary hypertension and cell proliferation. Actually, administration of a selective ETA receptor antagonist to RMR rats reduced abnormal permeability to proteins and prevented renal function deterioration. In the same model the ETA receptor antagonist also corrected the impaired renal NO synthesis, suggesting that excessive ET-1 bioactivity might also be responsible for the progressive reduction of renal NO. In keeping with this possibility are recent in vitro data that ET-1 inhibits iNOS transcription, a process mediated by interaction of the peptide with subtype A receptors. Nitric oxide and ET-1 have profound and opposite effects on glomerular and tubular function. Thus, abnormalities of renal NO and ET-1 synthetic pathways, as documented in the RMR model, likely have major and complementary roles in promoting alteration in renal hemodynamics and functions in progressive nephropathies.

Nitric oxide synthesis and L-arginine in uremia

Nitric oxide (NO), an L-arginine derivative, is implicated in neuronal transmission, immune response and vasodilation, and acts as a modulator of platelet function. Recent studies in the experimental model of renal mass reduction (RMR) in rats have generated the hypothesis that abnormalities in the NO synthetic pathway could play a key role in mediating the complex hemodynamic and hemostatic disorders associated with the progression of renal disease. Thus, renal NO generation is lower than normal in rats with RMR 7 days after surgery and progressively worsens with time in close correlation with signs of renal injury. This abnormality is due to a major defect in inducible NO synthase (iNOS) content in the kidney. In the same model, administration of either the NO precursor, L-arginine, or a NO-releasing compound reduces proteinuria, slows renal disease progression, and prolongs survival. In contrast, in the systemic circulation of uremic rats, NO is formed in excessive amounts, possibly caused by higher release from systemic vessels due to the augmented expression of both iNOS and endothelial NOS. Up-regulation of systemic NO synthesis might be a defense mechanism against uremic hypertension. On the other hand, a greater availability of NO to circulating cells may sustain the bleeding tendency, a well-known complication of uremia.

Platelet-activating factor mediates angiotensin II-induced proteinuria in isolated perfused rat kidney

Isolated kidney preparations (IPK) from male Sprague Dawley rats perfused at constant pressure were used to evaluate the effect of angiotensin II (AII) and platelet-activating factor (PAF) on renal function and urinary protein excretion. Compared with basal, intrarenal infusion of AII at 8 ng/min caused a progressive increase in protein excretion (11 +/- 6 versus 73 +/- 21 micrograms/min) in parallel with a decline in renal perfusate flow (RPF) (29 +/- 3 versus 18 +/- 3 ml/min). Addition to the perfusate of PAF at 50 nM final concentration also induced proteinuria (9 +/- 4 versus 55 +/- 14 micrograms/min) but did not change RPF (29 +/- 3 versus 30 +/- 3 ml/min). Preexposure of isolated kidneys to the PAF receptor antagonist WEB 2086 prevented the increase in urinary protein excretion induced by AII infusion (basal: 13 +/- 6; post-AII: 12 +/- 7 micrograms/min) but failed to prevent the vasoactive effect of AII (RPF, basal: 30 +/- 2; post-AII: 21 +/- 3 ml/min). In additional experiments, dexamethasone reduced the proteinuric effect of PAF remarkably. These results indicate that in isolated kidney preparation: (1) AII infusion induced proteinuria and decreased RPF; and (2) the effect of AII in enhancing urinary protein excretion was completely prevented by a specific PAF receptor antagonist, which, however, did not influence the AII-induced fall in RPF. It is suggested that PAF plays a major role in AII-induced changes in the permselective function of the glomerular capillary barrier.

Emergency department use of aspirin in patients with possible acute myocardial infarction

BACKGROUND

Efforts have been made to improve the suboptimal use of aspirin after hospitalization.

OBJECTIVE

To assess the frequency and timing of aspirin administration in emergency department patients with possible myocardial infarction.

DESIGN

Retrospective record review.

SETTING

Emergency departments of four hospitals affiliated with the same university.

PATIENTS

All patients who were admitted to the four hospitals in 1994 for evaluation and treatment of suspected acute myocardial infarction.

MEASUREMENTS

The frequency and timing of aspirin administration and the definitive diagnosis established before discharge from the hospital.

RESULTS

Aspirin was not given to 253 of 463 emergency department patients (55%) who had a definitive diagnosis of acute myocardial infarction. Seventy-eight percent of patients who did receive aspirin received it more than 30 minutes after arrival in the emergency department.

CONCLUSION

Aspirin therapy is underutilized as the first intervention in patients who are admitted with suspected myocardial infarction.

Renal and systemic nitric oxide synthesis in rats with renal mass reduction

In rats undergoing renal mass reduction (RMR) oral supplementation with the nitric oxide (NO) precursor L-arginine increases glomerular filtration rate and ameliorates signs of glomerular injury, suggesting that chronic renal failure in the rats is a condition of low NO formation in the kidney. On the contrary, data are available that in the systemic circulation of uremics, both rats and human beings, NO is formed in excessive amounts and may contribute to platelet dysfunction and bleeding tendency, well-known complications of uremia. The present study was designed to clarify the pathophysiology of renal and systemic NO synthesis in uremia. We showed that renal ex vivo NO generation, measured as the conversion of [3H] L-arginine to [3H] L-citrulline, was lower than normal in RMR rats, seven days after surgery, and progressively worsened with time in close correlation with signs of renal injury. Consistent with these results, urinary excretion of the stable NO metabolites, NO2-/NO3-, significantly decreased in rats with RMR. To go deeper into the cellular origin and biochemical nature of this abnormality we used two histochemical approaches that could locate either NO synthase (NOS) catalytic activity (NADPH-diaphorase) or NOS isoenzyme expression (immunoperoxidase). NADPH-diaphorase documented a progressive loss of renal NOS activity in RMR rats that co-localized with a strong progressive decrease of inducible NOS isoenzyme (iNOS) immunostaining. At variance with iNOS, endothelial cell NOS (ecNOS) staining was rather comparable in RMR and control kidneys. At variance to the kidney, in the systemic circulation of RMR rats the synthesis of NO increased as reflected by higher than normal plasma NO2-/NO3- concentrations. High systemic NO likely derives from vessels as documented by the increased NOS activity and higher expression of both iNOS and ecNOS in the aorta of RMR rats. Up-regulation of systemic NO synthesis might be an early defense mechanism against hypertension of uremia. On the other hand, more NO available to circulating cells may sustain the bleeding tendency, a well-known complication of uremia.

Sequential monitoring of urine-soluble interleukin 2 receptor and interleukin 6 predicts acute rejection of human renal allografts before clinical or laboratory signs of renal dysfunction

BACKGROUND

The significance of noninvasive techniques to the early diagnosis of acute rejection in kidney transplants remains elusive. In this study, we examined whether an early posttransplant increase in serum- and urine-soluble interleukin (IL) 2 receptor (sIL-2R) and IL-6 levels predicted acute rejection.

METHODS

Sequential determinations of serum and urine sIL-2R and IL-6 were performed in the first 30 postoperative days in 40 renal transplant patients. Changes during the posttransplant period observed in 26 patients who had one or more episodes of acute rejection (group A) were compared with those recorded in 14 patients who did not experience acute rejection of their graft (group B).

RESULTS

Serum sIL-2R was higher than normal in patients of groups A and B without statistical differences between the two groups. In the first 3 days after transplantation, urinary sIL-2R was higher than normal in group A but not in group B. Urinary sIL-2R at days 2 and 3 was significantly higher (P<0.05) in group A than in group B. In the first 5 days after transplantation, urinary IL-6 was persistently higher than normal in group A, whereas it progressively decreased to normal value on day 4 in group B. Sudden increases (doubling within 24 hr) in urine IL-6 preceded clinical diagnosis of acute rejection by a mean period of 2 days, with an 87% sensitivity and a 64% specificity, and also predicted recurrent rejection episodes.

CONCLUSIONS

Sequential monitoring of urinary sIL-2R and IL-6 levels does allow very early diagnosis of rejection without invasive procedures. Specifically, high urinary sIL-2R in the first 5 posttransplant days identifies the subgroup of patients at risk. In the subsequent days, a sudden increase in urinary IL-6 occurs in those of the above patients who will indeed reject their graft.

Systemic and fetal-maternal nitric oxide synthesis in normal pregnancy and pre-eclampsia

OBJECTIVE

To investigate systemic and fetal-placental nitric oxide synthesis by biochemical and molecular biology means in normal human pregnancy and pre-eclampsia.

DESIGN AND PARTICIPANTS

Three groups of women were studied: healthy pregnant women (n = 8), pregnant women with pre-eclampsia (n = 8), and age-matched nonpregnant controls (n = 8). Pre-eclamptic patients were treated with nifedipine (30-60 mg/day) for severe hypertension. Systemic nitric oxide synthesis was assessed in normal pregnant women at weeks 18-21, 29-32 and 38-39 and in pre-eclamptic women on admission to the hospital (29-32 weeks, 30 on average), before the morning nifedipine administration. Nonpregnant women were studied twice at four-week intervals as controls. The pattern of nitric oxide biosynthesis in fetal-placental circulation was studied in normal and pre-eclamptic women at the delivery.

SETTING

Mario Negri Institute for Pharmacological Research, Bergamo, and the Division of Obstetrics and Gynaecology of the University of Brescia.

MAIN OUTCOME MEASURES

Plasma cGMP levels and platelet nitric oxide synthesis, assessed by measuring the conversion of [3H]L-arginine to [3H]L-citrulline as well as intracellular cGMP, were evaluated. Constitutive nitric oxide synthase (EC-NOS) gene expression by Northern blot analysis and nitric oxide release by the conversion of [3H]L-arginine to [3H]L-citrulline were assessed in umbilical vein endothelial cells (HUVEC) and in placenta. Inducible nitric oxide synthase activity was also evaluated in HUVEC exposed to tumour necrosis factor alpha (TNF alpha) and in placenta homogenates incubated in calcium free medium.

RESULTS

Plasma cGMP was higher in both normal pregnant and pre-eclamptic women than in nonpregnant controls. In normal pregnancy cGMP rose as early as 18-21 weeks and remained elevated throughout pregnancy. [3H]L-citrulline production and intracellular cGMP were comparable in platelets from all women. EC-NOS gene expression and nitric oxide synthesis were identical in HUVEC and placenta from normal pregnant and pre-eclamptic women.

CONCLUSIONS

Systemic levels of CGMP, the nitric oxide second messenger, are increased in normal pregnancy. Excessive nitric oxide production does not derive from platelets. Pre-eclampsia is not associated with changes in fetal-placental nitric oxide synthesis.