Red blood cell aggregation in nephrotic syndrome

[Thromboembolic complications in nephrotic syndrome]

This review devoted to the nephrotic syndrome (NS) subsequent thrombotic outcomes. The pathogenesis of hypercoagulation disorders that cause venous and arterial vascular system thrombosis are studied. Discussed procoagulant and anticoagulant mechanisms imbalance due to the anticoagulants natural urinal loss, affected by disfunction of the glomerular filter selective permeability, leading to high molecular weight liver-derived proteins (at least of the albumin size) leakage, fibrinolysis depression, excessive liver synthesis of plasma clotting cascade factors and platelet activation. Presented new data on the thrombogenesis at NS concerning the role of endothelial microparticles with high prothrombogenic activity that go from damaged glomerulus endothelial capillary cells into the systemic circulation, which can turn the local renal hypercoagulation (concomitant to the kidney immune inflammation process) into the generalized, working towards the thrombosis development. The most frequent adverse variants of arterial and venous thromboses are studied, specified their basic and general risk factors, as well as individual, varying in different patients. Indications and prophylactic anticoagulant therapy regimen and thrombosis treatment duration in patients with NS are discussed. It also stressed that the decision on time and method of anticoagulant therapy for a NS patients is still a challenge for healthcare providers.

Prescribing Dialysate Bicarbonate Concentrations for Hemodialysis Patients

A rearranged equation of Sargent and Gotch (1) was used to determine dialysate bicarbonate concentrations for hemodialysis patients. Parameters in this equation include an estimate of the acid generated by each patient between treatments, an estimate for the dialyzer dialysance for bicarbonate, ultrafiltration rate, blood flow rate and a targeted mid-dialysis plasma bicarbonate concentration of 25 mEq/L. Nine patients were studied over a 35 week period to verify this method of determining each patient's dialysate bicarbonate concentration. Prescribed dialysate bicarbonate concentrations for the nine patients varied from 29 to 38 mEq/L with five patients having a prescribed value of 35 mEq/L. After a baseline period of five weeks, five patients switched from a 37 mEq/L acetate dialysate to their prescribed dialysate bicarbonate concentration. Four patients who had already been on bicarbonate dialysis at a concentration of 35 mEq/L were dialyzed with their prescribed dialysate bicarbonate concentrations. Patients were then followed for a study period of 30 weeks. The prescribed dialysate bicarbonate concentration resulted in more normal acid/base chemistries for both groups of patients. The results also demonstrate that chronic hemodialysis patients require individualization of dialysate bicarbonate concentrations.

Urea, Creatinine and Phosphate Kinetic Modeling during Dialysis: Application to Pediatric Hemodialysis

The kinetics of urea, creatinine and phosphate removal during dialysis were investigated in pediatric patients using a two-pool model taking into account fluid shifts and mass transfer between the two compartments. It is found that even urea must be described by a two-pool model since it presents a post dialysis rebound due to equilibration between the two compartments. Phosphate plasma concentration drops very sharply during the first hour of dialysis and rises rapidly during the rebound period. This pattern cannot be accounted for by the classical two-pool model with constant generation rate and mass transfer coefficients, but corresponds to a large time-dependent phosphate influx from the intracellular compartment in which phosphate is generated by biochemical reactions or liberated from the bones. This influx was calculated for four patients representing 8 dialysis sessions and was found to reach a plateau after 90 minutes of dialysis, dropping rapidly during the rebound period.

Alteration of Blood Flow in a Venular Network by Infusion of Dextran 500: Evaluation with a Laser Speckle Contrast Imaging System

This study examined the effect of dextran-induced RBC aggregation on the venular flow in microvasculature. We utilized the laser speckle contrast imaging (LSCI) as a wide-field imaging technique to visualize the flow distribution in venules influenced by abnormally elevated levels of RBC aggregation at a network-scale level, which was unprecedented in previous studies. RBC aggregation in rats was induced by infusing Dextran 500. To elucidate the impact of RBC aggregation on microvascular perfusion, blood flow in the venular network of a rat cremaster muscle was analyzed with a stepwise reduction of the arterial pressure (100 → 30 mmHg). The LSCI analysis revealed a substantial decrease in the functional vascular density after the infusion of dextran. The relative decrease in flow velocity after dextran infusion was notably pronounced at low arterial pressures. Whole blood viscosity measurements implied that the reduction in venular flow with dextran infusion could be due to the elevation of medium viscosity in high shear conditions (> 45 s-1). In contrast, further augmentation to the flow reduction at low arterial pressures could be attributed to the formation of RBC aggregates (< 45 s-1). This study confirmed that RBC aggregation could play a dominant role in modulating microvascular perfusion, particularly in the venular networks.

Primary Nephrotic Syndrome in Adults as a Risk Factor for Pulmonary Embolism: An Up-to-Date Review of the Literature

Patients with nephrotic syndrome are at an increased risk for thrombotic events; deep venous thrombosis, renal vein thrombosis, and pulmonary embolism are quite common in patients with nephrotic syndrome. It is important to note that nephrotic syndrome secondary to membranous nephropathy may impose a greater thrombotic risk for unclear reasons. Increased platelet activation, enhanced red blood cell aggregation, and an imbalance between procoagulant and anticoagulant factors are thought to underlie the excessive thrombotic risk in patients with nephrotic syndrome. The current scientific literature suggests that patients with low serum albumin levels and membranous nephropathy may benefit from primary prophylactic anticoagulation. A thorough approach which includes accounting for all additional thrombotic risk factors is, therefore, essential. Patient counseling regarding the pros and cons of anticoagulation is of paramount importance. Future prospective randomized studies should address the question regarding the utility of primary thromboprophylaxis in patients with nephrotic syndrome.

Two-phase model for prediction of cell-free layer width in blood flow

This study aimed to develop a numerical model capable of predicting changes in the cell-free layer (CFL) width in narrow tubes with consideration of red blood cell aggregation effects. The model development integrates to empirical relations for relative viscosity (ratio of apparent viscosity to medium viscosity) and core viscosity measured on independent blood samples to create a continuum model that includes these two regions. The constitutive relations were derived from in vitro experiments performed with three different glass-capillary tubes (inner diameter=30, 50 and 100 μm) over a wide range of pseudoshear rates (5-300 s(-1)). The aggregation tendency of the blood samples was also varied by adding Dextran 500 kDa. Our model predicted that the CFL width was strongly modulated by the relative viscosity function. Aggregation increased the width of CFL, and this effect became more pronounced at low shear rates. The CFL widths predicted in the present study at high shear conditions were in agreement with those reported in previous studies. However, unlike previous multi-particle models, our model did not require a high computing cost, and it was capable of reproducing results for a thicker CFL width at low shear conditions, depending on aggregating tendency of the blood.

Procoagulant activity of erythrocytes and platelets through phosphatidylserine exposure and microparticles release in patients with nephrotic syndrome

Recent studies showed that an imbalance of prothrombotic and antithrombotic factors and impaired thrombolytic activity contribute to the thrombophilia of the nephrotic syndrome (NS). However, it is not clear whether blood cell injury and/or activation is involved in hypercoagulability in NS patients. Our objectives were to study the increase in microparticle (MP) release and phosphatidylserine (PS) exposure on the outer membrane of MP-origin cells in NS patients, and to evaluate their procoagulant activity (PCA). The subjects were patients with membranous nephropathy (MN), minimal change nephrotic syndrome (MCNS) and healthy controls. Analyses of MPs and PS exposure were performed using a flow cytometer. PCA was determined by clotting time and purified coagulation complex assays. We found that lactadherin+ MPs, which derived from red blood cells (RBC), platelet and endothelial cell, increased in NS patients. Moreover, PS exposure on RBCs and platelets in each NS group, especially in MN, are higher than that in controls. MP shedding and PS exposure of RBCs/platelets were highly procoagulant in NS patients. However, blockade of PS with lactadherin inhibited over 90% of PCA while an anti-tissue factor antibody had no significant inhibition effect. Our results demonstrate that the thrombophilic susceptibility of NS may be partly ascribed to MP release and PS exposure of RBCs, platelets and endothelial cells. Lactadherin is a sensitive probe for PS that has high anticoagulant activity.

Epidemiology and pathophysiology of nephrotic syndrome-associated thromboembolic disease

After infections, thromboembolism is considered by many experts to be the most significant life-threatening complication of nephrotic syndrome. The purpose of this review is to summarize the epidemiology, clinical and molecular pathophysiology, and management of this complication. Children (2.8%) are less likely than adults (26.7%) with nephrotic syndrome to develop thromboembolism. However, infants and children aged >12 years are at much greater risk. Membranous histologic changes increase thromboembolic risk at all ages; in particular, adults with membranous nephropathy have the highest reported risk (37.0%) and children with membranous histology have a rate (25%) that approaches the overall adult rate. There are striking, but variable, pathologic alterations of molecular hemostasis associated with nephrotic syndrome. No clear molecular therapeutic targets have been identified, but most studies show that the major pathologic changes involve antithrombin, fibrinogen, and factors V and VIII. There is inadequate evidence to support routine prophylactic therapy. Therapy includes anticoagulation in all cases, with thrombolysis reserved for those with the most severe thromboembolic disease. Future hemostatic research in nephrotic syndrome should focus on identifying cohorts at highest risk for thrombosis through the use of clinical markers and biomarkers as well as searching for molecular targets to correct the prothrombotic pathophysiology of this disease.

Transient Ischemic Attack and Nephrotic Syndrome: Case Report and Review of Literature

Thrombotic complications in patients with nephrotic syndrome are attributed to a hypercoagulable state. Venous thrombosis is common, but arterial thrombosis occurs less frequently in adult nephrotic patients. We report a case of recurrent transient ischemic attacks as an initial manifestation of nephrotic syndrome due to early-stage membranous glomerulonephritis, review the literature for similar cases, and briefly discuss this potentially life-threatening condition. We observed that transient ischemic attack or ischemic stroke could be the initial manifestation of nephrotic syndrome. Our observation may serve as reminder to consider nephrotic syndrome as a possible contributor when evaluating patients with transient ischemic attacks with no other discernable clues. A high index of suspicion alone avoids the unnecessary withholding of prophylaxis or treatment that can be life saving.

Blood rheology and albumin excretion in diabetic pregnancy

Blood rheology is altered in diabetes and also in non-diabetic pregnant women. The cumulative effect of hyperfiltration, abnormal rheology of pregnancy, and diabetes could be one mechanism contributing to increased intraglomerular pressure and albuminuria in diabetic pregnancy. We conducted a prospective study of 22 Type 1 (insulin-dependent) diabetic patients and 22 non-diabetic women to determine if there was an association of altered blood rheology on glomerular function in diabetic pregnancy. Albumin excretion showed no increment with increasing gestation and was similar in diabetic and non-diabetic women throughout pregnancy (first trimester: 5.0 (3.0-14.0) vs 5.8 (3.7-10.7) mg l-1, p = 0.89; second trimester: 6.0 (5.0-12.0) vs 5.1 (3.6-10.4) mg l-1, p = 0.25; third trimester: 7.5 (3.5-16.0) vs 4.9 (2.9-7.3) mg l-1, p = 0.18). Red cell aggregation index increased in both groups between the first and third trimesters (diabetic patients: mean difference 2.0; Cl: 1.0-2.9, p = 0.003, and control patients: mean difference 2.3, Cl: 1.0-3.5, p = 0.002). Fibrinogen levels were significantly higher between the third and first trimesters in diabetic patients (mean difference 0.7, Cl: 0.2-1.3 g l-1, p = 0.006). Pregnancy, therefore, was associated with increased red cell aggregation, related in part to increased fibrinogen levels but the extent of change was similar in diabetic and nondiabetic women and appeared to have no adverse effect on glomerular function in pregnant insulin-dependent diabetic women.

Arterial thrombosis in the nephrotic syndrome

Thrombosis is a frequent cause of morbidity and mortality in patients with the nephrotic syndrome. Venous thrombotic complications are well recognized but arterial complications are rare. Thrombosis is multifactorial, and has been attributed to a hypercoaguable state due to alterations in blood levels of the various factors involved in the coagulation and fibrinolytic systems, alterations in platelet function, venous stasis, haemoconcentration, increased blood viscosity and possibly the administration of steroids. Thrombosis in general and arterial thrombosis in particular is a significant and potentially serious problem in nephrotic patients. Awareness of the condition and its pathogenesis is needed. Assessment for the risk factors is required to allow appropriate prophylactic measures to be taken.

Mathematical modelling of haemodialysis in children

The single-pool urea kinetic model (UKM), utilising "Kt/V" (the normalised whole body urea clearance), is widely used to help assess the adequacy of haemodialysis in adults. In the presence of an adequate dietary protein intake, a value of unity is acceptable for thrice weekly dialysis. Children could benefit from this approach but, with their relatively higher protein intakes and dialysis needs, this model may not be applicable. Urea kinetics, studies in six children with chronic renal failure by serial timed blood urea measurements during and after haemodialysis, were compared with the kinetics of a one-pool and a two-pool UKM. The two-pool UKM with intra- and extracellular pools best fitted the observed data, re-equilibration between pools accounting for the marked rebound increase in blood urea seen in the 1st h after dialysis (mu 17%, SD 5). Kt/V calculated using the end-dialysis blood urea was higher (mu 21%, SD 5) than when the more correct equilibrated value was used. The post-dialysis rebound indicates significant disequilibrium between the two pools at the end of dialysis. Dialysis efficiency may be substantially overestimated unless this is allowed for by using the rebounded post-dialysis blood urea when calculating Kt/V.

Peroxidative damage of the erythrocyte membrane in children with nephrotic syndrome

The structural composition of erythrocyte ghosts was analysed in children affected by steroid-responsive (SRNS) and unresponsive nephrotic syndrome (SUNS). No variation of either intrinsic or extrinsic ghost proteins was found by discontinuous SDS-electrophoresis associated with a very sensitive double staining technique. By contrast, the composition of inner-layer phospholipids--phosphatidyl ethanolamine (PE) and phosphatidyl serine (PS)--was altered in SRNS with minor changes also involving phosphatidic acid, phosphatidyl inositol and lysophosphatidyl choline. Signs of peroxidative damage were present in both SRNS and SUNS ghosts and inside the cells; these included high levels of fluorescent amino-iminopropene derivates of PE and PS, increased intraerythrocytic amounts of malonyldialdehyde and decreased levels of reduced glutathione. Taken together these results support the concept that in SRNS and SUNS erythrocytes are target cells for peroxidative damage. In SRNS peroxidation of membrane lipids results in a marked alteration of the phospholipid composition of erythrocyte ghosts.

Blood rheology in general medicine and surgery

Traditionally, blood rheology tests have been used in diagnosis and monitoring of infection, rheumatic diseases and malignancy, and are still of clinical value in these conditions. In the last twenty years, clinical and epidemiological studies have shown that the haematological determinants of blood flow resistance (haematocrit, fibrinogen, white cell count and altered red and white cell rigidity) are also associated with nutritional, metabolic, endocrine and vascular disorders. Decreased red cell deformability may contribute to reduced red cell survival and anaemia in burns, malaria, liver disease and kidney failure. In trauma and inflammatory disease, overt hyperviscosity is usually prevented by vasodilatation and reduction in the haematocrit. However, low-flow states may arise systemically from haemoconcentration (contracted plasma volume, Chapter 3) in severe burns, inappropriate red cell transfusion, or dehydration due to illness; systemically in circulatory shock; and locally in venous thrombosis or arterial disease. In such circumstances, the intrinsic flow resistance of blood may perpetuate flow disturbance, ischaemia and thrombosis. Conversely, optimal levels of haematocrit, fibrinogen and white cell count may be lower than normal in low-flow states. Haemodilution by colloid infusion is beneficial in burns, shock, major surgery, prevention of postoperative venous thrombosis, chronic stable claudication and possibly in acute stroke and retinal vein thrombosis. Plasma exchange may be beneficial in severe Raynaud's phenomenon. Defibrination with ancrod is effective in prevention and treatment of venous thrombosis but its role in arterial disease is unproven. The benefits of streptokinase therapy in venous thrombo-embolism and acute myocardial infarction may be partly rheological, due to fibrinogen depletion. Drugs with rheological effects may be beneficial in intermittent claudication.

The nephrotic syndrome and its complications

Modern views of the pathogenesis and natural history of nephrotic syndrome have changed substantially since the early studies by Cotugno and Bright. Contrary to beliefs held 20 years ago, we do not possess a unique satisfying explanation for the induction, maintenance, and resolution of nephrotic edema, and many concepts firmly established as "classic" are now being revised or reconsidered. These include the relationship between urinary protein losses and hypoalbuminemia, which is complicated by several factors such as daily protein intake, albumin catabolism, and the possible role of albumin loss at extrarenal sites. The influence of lowered plasma albumin on the decrease in plasma volume is also quite complex, due to technical difficulties in measuring plasma volume and turnover of radio-labeled albumin. The most contentious areas are how sodium and water retention are initiated and maintained and the relationship between hypoalbuminemia, plasma oncotic pressure, and edema. While aldosterone excretion and plasma concentrations are elevated in nephrotic patients, data on the renin-angiotensin system are controversial and the renal handling of sodium is related to a host of factors including glomerular filtration rate, altered proximal tubular reabsorption, and the role of vasodilators or vasoconstrictors. The complications of nephrotic syndrome are protean and relatively common. Among those are acute renal failure, thrombosis, infections, and hyperlipidemia. Since the introduction of percutaneous biopsy, the spectrum of lesions underlying nephrotic syndrome has widened considerably, the most common being minimal change, especially in children. There are very few prognostic indicators by which response to treatment may be predicted and these include persistent microscopic hematuria.

Changes in blood rheology in patients with stable angina pectoris as a result of coronary artery disease

We investigated several rheologic variables in 17 patients (11 men, six women, mean age = 52.1 +/- 9.8 years) with chronic stable angina. None took any medication except for sublingual nitroglycerin for 2 weeks before the study, and all had angiographically proven coronary artery disease with no history of myocardial infarction. Rheologic measurements included hematocrit, whole blood and plasma viscosity (750 and 1500 sec-1), degree of red cell aggregation via the zeta sedimentation ratio, and the extent and rate of red cell aggregation after stasis (Myrenne aggregometer). Compared with normal control donors, salient observations in the patients as a group included: a small (6%) but significant increase in hematocrit, a significant elevation in plasma viscosity (9%), significant increases in whole blood viscosity at both shear rates (14% and 16%), significant increases in the degree (12%), the extent (41%), and the rate (28% faster time constant) of red cell aggregation, an elevated alpha 2 level (15% increase) and a significantly increased fibrinogen concentration (25% increase), both of which correlated with the enhanced red cell aggregation. Rheologic abnormalities were evident when patients with disease in either one vessel or two to three vessels were compared with controls, but differences between these subgroups of patients were not significant. We conclude that patients with angina have rheologic abnormalities that are compatible with disturbed blood flow and an enhanced tendency for coronary arterial thrombosis.

Steroid-responsive nephrotic syndrome: a generalised disorder of membrane negative charge

A simple chemical test, based on the binding of the cationic dye alcian-blue 8GX (AB), has been devised to measure negative charge on cell membranes. The test has demonstrated that AB binding to red blood cells and platelets is significantly less in children with steroid-responsive nephrotic syndrome (SRNS) or nephrotic syndrome associated with focal segmental glomerulosclerosis than in normal controls. However, the sialic acid content of the nephrotic cell membrane is normal. This suggests that a generalised loss of membrane negative charge occurs in SRNS and that this is due to neutralisation rather than absence of anionic groups.

Elevated plasma fibronectin levels in nephrotic syndrome

In nine patients with nephrotic syndrome the behaviour of plasma fibronectin was studied. Of nine patients seven showed elevated plasma fibronectin levels while the plasma fibrinogen level was increased in eight of the nine investigated patients. A positive correlation was found between plasma fibronectin levels and fibrinogen (P less than 0.01), cholesterol (P less than 0.01) and proteinuria (P less than 0.05). The results indicate that elevated plasma fibronectin levels could be an additional factor responsible for hypercoagulability in nephrotic syndrome.

Erythrocyte aggregation during normal pregnancy

Red blood cell aggregation induced by fibrinogen is a major determinant of the non-Newtonian flow behavior of blood and has been suggested as a possible contributing factor for thrombogenesis. Given the elevated fibrinogen levels and the incidence of thrombotic accidents in pregnancy, a study was designed to assess red blood cell aggregation at selected gestational periods. Three separate in vitro aggregation assays were used: (1) aggregation half time, (2) zeta sedimentation ratio, and (3) microscopic aggregation index. Our results indicate that red blood cell aggregation is increased throughout normal pregnancy (i.e., at 10, 25, and 36 weeks and during labor) in comparison to that in nonpregnant women. Significant correlations between plasma fibrinogen concentration and zeta sedimentation ratio (p less than 0.001) or aggregation half time (p less than 0.02) were demonstrated, but the correlation coefficient for the microscopic aggregation index technique did not reach significance (p greater than 0.20). Type O-positive red blood cells suspended in plasma from pregnant women also exhibited increased aggregation (p less then 0.001), thus suggesting plasma rather than cellular factors for the enhanced aggregation. Possible influences of abnormal fibrinogen structure during pregnancy are considered and the implications of increased red blood cell aggregation vis-à-vis altered blood viscosity are discussed.