RRx-001 Increases Erythrocyte Preferential Adhesion to the Tumor Vasculature.

Red blood cells (RBCs) serve a variety of functions beyond mere oxygen transport both in health and pathology. Notably, RRx-001, a minimally toxic pleiotropic anticancer agent with macrophage activating and vascular normalization properties currently in Phase III trials, induces modification to RBCs which could promote vascular adhesion similar to sickle cells. This study assessed whether RBCs exposed to RRx-001 adhere to the tumor microvasculature and whether this adhesion alters tumor viability. We next investigated the biomechanics of RBC adhesion in the context of local inflammatory cytokines after treatment with RRx-001 as a potential mechanism for preferential tumor aggregation. Human HEP-G2 and HT-29 tumor cells were subcutaneously implanted into nu/nu mice and were infused with RRx-001-treated and Technetium-99m (99mTc)-labeled blood. RBC adhesion was quantified in an in vitro human umbilical vein endothelial cell (HUVEC) assay under both normoxic and hypoxic conditions with administration of either lipopolysaccharide (LPS) or Tumor necrosis alpha (TNFα) to mimic the known inflammation in the tumor microenvironment. One hour following administration of 99mTc labeled RBCs treated with 10 mg/kg RRx-001, we observed an approximate 2.0-fold and 1.5-fold increase in 99mTc-labeled RBCs compared to vehicle control in HEPG2 and HT-29 tumor models, respectively. Furthermore, we observed an approximate 40% and 36% decrease in HEP-G2 and HT-29 tumor weight, respectively, following treatment with RRx-001. To quantify RBC adhesive potential, we determined τ50, or the shear stress required for 50% disassociation of RBCs from HUVECs. After administration of TNF-α under normoxia, τ50 was determined to be 4.5 dynes/cm2 (95% CI: 4.3-4.7 dynes/cm2) for RBCs treated with 10 µM RRx-001, which was significantly different (p < 0.05) from τ50 in the absence of treatment. Under hypoxic conditions, the difference of τ50 with (4.8 dynes/cm2; 95% CI: 4.6-5.1 dynes/cm2) and without (2.6 dynes/cm2; 95% CI: 2.4-2.8 dynes/cm2) 10 µM RRx-001 treatment was exacerbated (p = 0.05). In conclusion, we demonstrated that RBCs treated with RRx-001 preferentially aggregate in HEP-G2 and HT-29 tumors, likely due to interactions between RRx-001 and cysteine residues within RBCs. Furthermore, RRx-001 treated RBCs demonstrated increased adhesive potential to endothelial cells upon introduction of TNF-α and hypoxia suggesting that RRx-001 may induce preferential adhesion in the tumor but not in other tissues with endothelial dysfunction due to conditions prevalent in older cancer patients such as heart disease or diabetic vasculopathy.

Mixing commonly used crystalloid solutions with red blood cells in five common additives does not negatively impact hemolysis, aggregometry, or deformability.

BACKGROUND: Literature is beginning to challenge the belief that it is unsafe to coinfuse red blood cells (RBCs) with solutions other than isotonic saline. We recently showed that additive-free RBCs tolerated coincubation with Plasma-Lyte or catecholamines dissolved in normal saline (NS), though 5% dextrose in water (D5W) promoted hemolysis. Herein, we evaluate the effect of coincubating crystalloids on additive-preserved RBC hemolysis, aggregation, and membrane deformability. STUDY DESIGN AND METHODS: RBCs were coincubated 5 minutes with plasma, NS, Plasma-Lyte, lactated Ringer's (LR) or D5W (1 mL PRBC +131.3 µL solution). Samples were then assessed for hemolysis (free hemoglobin), aggregation (critical shear stress [mPa]), and membrane deformability (elongation index [EI]). Significance (P ≤ .05) by t test or ANOVA with post-hoc Tukey-Kramer test. RESULTS: Additive-prepared RBCs coincubated with crystalloid instead of plasma demonstrated: (a) no increase in hemolysis as indicated by plasma free hemoglobin levels that is likely to be clinically relevant; (b) no increase, but in some cases a decrease, in aggregation as indicated by critical shear stress; and (c) in some combinations, a deterioration in deformability. When present, the deformability decrease was likely clinically insignificant in degree, and always returned to normal when the crystalloid was subsequently diluted out with plasma. CONCLUSION: Our data suggest that additive-prepared RBCs coincubated for 5 minutes with any of four common crystalloids demonstrate no clinically relevant increased lysis, increased aggregation, or decreased deformability.

Silica nanomaterials induce organ injuries by Ca2+-ROS-initiated disruption of the endothelial barrier and triggering intravascular coagulation.

BACKGROUND: The growing use of silica nanoparticles (SiNPs) in many fields raises human toxicity concerns. We studied the toxicity of SiNP-20 (particle diameter 20 nm) and SiNP-100 (100 nm) and the underlying mechanisms with a focus on the endothelium both in vitro and in vivo. METHODS: The study was conducted in cultured human umbilical vein endothelial cells (HUVECs) and adult female Balb/c mice using several techniques. RESULTS: In vitro, both SiNP-20 and SiNP-100 decreased the viability and damaged the plasma membrane of cultured HUVECs. The nanoparticles also inhibited HUVECs migration and tube formation in a concentration-dependent manner. Both SiNPs induced significant calcium mobilization and generation of reactive oxygen species (ROS), increased the phosphorylation of vascular endothelial (VE)-cadherin at the site of tyrosine 731 residue (pY731-VEC), decreased the expression of VE-cadherin expression, disrupted the junctional VE-cadherin continuity and induced F-actin re-assembly in HUVECs. The injuries were reversed by blocking Ca2+ release activated Ca2+ (CRAC) channels with YM58483 or by eliminating ROS with N-acetyl cysteine (NAC). In vivo, both SiNP-20 and SiNP-100 (i.v.) induced multiple organ injuries of Balb/c mice in a dose (range 7-35 mg/kg), particle size, and exposure time (4-72 h)-dependent manner. Heart injuries included coronary endothelial damage, erythrocyte adhesion to coronary intima and coronary coagulation. Abdominal aorta injury exhibited intimal neoplasm formation. Lung injuries were smaller pulmonary vein coagulation, bronchiolar epithelial edema and lumen oozing and narrowing. Liver injuries included multifocal necrosis and smaller hepatic vein congestion and coagulation. Kidney injuries involved glomerular congestion and swelling. Macrophage infiltration occurred in all of the observed organ tissues after SiNPs exposure. SiNPs also decreased VE-cadherin expression and altered VE-cadherin spatial distribution in multiple organ tissues in vivo. The largest SiNP (SiNP-100) and longest exposure time exerted the greatest toxicity both in vitro and in vivo. CONCLUSIONS: SiNPs, administrated in vivo, induced multiple organ injuries, including endothelial damage, intravascular coagulation, and secondary inflammation. The injuries are likely caused by upstream Ca2+-ROS signaling and downstream VE-cadherin phosphorylation and destruction and F-actin remodeling. These changes led to endothelial barrier disruption and triggering of the contact coagulation pathway.

Extracellular histones induce erythrocyte fragility and anemia.

Extracellular histones have been shown to play an important pathogenic role in many diseases, primarily through their cytotoxicity toward nucleated cells and their ability to promote platelet activation with resultant thrombosis and thrombocytopenia. In contrast, little is known about the effect of extracellular histones on erythrocyte function. We demonstrate in this study that histones promote erythrocyte aggregation, sedimentation, and using a novel in vitro shear stress model, we show that histones induce erythrocyte fragility and lysis in a concentration-dependent manner. Furthermore, histones impair erythrocyte deformability based on reduced passage of erythrocytes through an artificial spleen. These in vitro results were mirrored in vivo with the injection of histones inducing anemia within minutes of administration, with a concomitant increase in splenic hemoglobin content. Thrombocytopenia and leukopenia were also observed. These findings suggest that histones binding to erythrocytes may contribute to the elevated erythrocyte sedimentation rates observed in inflammatory conditions. Furthermore, histone-induced increases in red blood cell lysis and splenic clearance may be a significant factor in the unexplained anemias seen in critically ill patients.

Effects of Ankaferd Hemostat on red blood cell aggregation: a hemorheological study

Background/aim: Ankaferd hemostat (ABS; Ankaferd blood stopper, Istanbul, Turkey) is a prohemostatic agent affecting erythrocytes. The hemostatic action of ABS depends upon fibrinogen gamma chain, prothrombin, and red blood cells. The aim of this study was to assess the effects of ABS on erythrocyte aggregation via hemorheological analyses. Materials and methods: To measure erythrocyte aggregation, blood samples were obtained from healthy, nonsmoker volunteers who had not taken any medication in the previous 10 days. One mL of blood was placed into the laser-assisted optical rotational cell analyzer (LORCA), into the chamber formed by the gap between two concentric glass cylinders. The solution prepared with ABS and saline was added to blood in incremental amounts of 10 µL, 20 µL, 30 µL, 40 µL, 50 µL, 60 µL, 70 µL, and 100 µL. Erythrocyte aggregation was determined by laser-assisted optical rotational cell analyzer at 37 °C Results: AMPwas found to be 17.7 ± 2.1 au in the blood without ABS, whereas it was lower in the blood with ABS. AMP was 16.0 ± 3.3 in the ABS-added blood group. RBC aggregates did not form faster when cells contacted ABS. The t t½ value was 4.6 ± 2.6 in the ABS-added blood group and 1.9 ± 0.20 in the control group. Aggregation was faster in the control group (P = 0.03). AI, which is a combination of AMP and t½, was lowered in the ABS group (48.7 ± 12.3) compared to the control group (65.8 ± 1.6) (P = 0.02). It was notable that the γIsc max (sec-1) value of the control was higher (200 ± 106) than the ABS-added blood group (141 ± 51.0). Conclusion: ABS has antierythroid aggregation effect. ABS inhibits pathological aggregation of red blood cells. Antithrombotic clinical effects of ABS may be ascribed to the antierythroid aggregan actions of the drug.

Effects of Histidine-rich glycoprotein on erythrocyte aggregation and hemolysis: Implications for a role under septic conditions.

The apoptotic process of erythrocytes is known as eryptosis, and is characterized by phosphatidylserine (PS) expression on the outer membrane. PS-positive erythrocytes are increased in sepsis, and PS is believed to facilitate coagulation of erythrocytes and activate macrophages. However, the relationship between eryptosis and abnormal coagulation in sepsis is still not fully understood. Histidine-rich glycoprotein (HRG) inhibits immunothrombus formation by regulating neutrophils and vascular endothelial cells. In the present study, we subjected isolated erythrocytes to Zn2+ stimulation, which activated their aggregation and PS expression. We then determined the Zn2+ contents in septic lung and kidney tissues, and found that they were elevated, suggesting that eryptosis was enhanced in these tissues. Erythrocyte adhesion to endothelial cells was also significantly increased after Zn2+ stimulation, and this effect was inhibited by HRG. Finally, we examined HRG treatment in septic model mice, and found that HRG decreased hemolysis, possibly due to its ability to bind heme. Our study demonstrated a novel Zn2+-initiated aggregation/thrombus formation pathway. We also showed the regulatory role of HRG in this pathway, together with the ability of HRG to inhibit hemolysis under septic conditions. HRG supplementation might be a novel therapeutic strategy for inflammatory disorders, especially sepsis.

The Impact of Two Combined Oral Contraceptives Containing Ethinyl Estradiol and Drospirenone on Whole Blood Clot Viscoelasticity and the Biophysical and Biochemical Characteristics of Erythrocytes.

Venous thrombosis is associated with combined oral contraceptive (COC) use. We investigated the impact of two ethinyl estradiol (EE) and drospirenone (DRSP) containing COCs (3 mg DRSP/20 µg EE and 3 µg DRSP/30 µg EE) on the viscoelasticity of whole blood clots along with the biophysical and biochemical characteristics of erythrocytes. Thromboelastography (TEG) analysis showed a tendency toward a hypercoagulable state in the COCs groups that was more pronounced with higher EE concentrations. Light microscopy and scanning electron microscopy (SEM) showed rouleaux formation of erythrocytes and alterations to the erythrocyte shape for both COC groups, which was attributed to membrane damage. SEM analysis showed spontaneous activation of fibrin and platelets in the COC groups, along with interactions between erythrocytes and platelets and/or fibrin. Confocal microscopy confirmed compromised membrane integrity in the COC groups compared to controls. Global thrombosis test analysis showed increased platelet activation and low thrombolysis in both COC groups when compared to controls. In conclusion, DRSP/EE formulations impact erythrocytes' biophysical and biochemical properties to cause a shift in hemostasis to a prothrombotic state. Although these effects are mostly subclinical the long-term effects and risks involved with the use of these hormones should be considered carefully for each individual.

Smallest lectin-like peptide identified from the skin secretion of an endemic frog, Hydrophylax bahuvistara.

Lectins are sugar-binding proteins and considered as attractive candidates for drug delivery and targeting. Here, we report the identification of the smallest lectin-like peptide (odorranalectin HYba) from the skin secretion of Hydrophylax bahuvistara which is being the shortest lectin-like peptide identified so far from the frog skin secretion, with 15 amino acid residues. The peptide is the first report from an Indian frog and lacks antimicrobial activity but strongly agglutinate intact human erythrocytes. The sequences at the L-fucose recognizing region is conserved as in other lectins reported from frog skin secretion and could be exploited for specificity and drug targeting properties.

Effect of Polylysine on Blood Clotting, and Red Blood Cell Morphology, Aggregation and Hemolysis.

Polylysine has broad biomedical applications, though little is known about its hemocompatibility. Here, we studied the influence of polylysine on human red blood cells (RBCs) and blood clotting. We observed the morphology and aggregation and determined the hemolysis of RBCs incubated with polylysine. Plasma coagulation in the presence of polylysine was evaluated by measuring the activated partial thromboplastin time (APTT) and prothrombin time (PT). Human whole blood coagulation in the presence of polylysine was evaluated with the thromboelastograph (TEG). We found that polylysine at 0.01 mg/mL did not result in RBC aggregation or morphological change, while polylysine at ≥ 0.1 mg/mL caused RBC aggregation. The RBCs did not lyze in the presence of 0.01­0.5 mg/mL of polylysine. Polylysine at 0.001 mg/mL did not cause a significantly different APTT from the control, while polylysine at ≥ 0.01 mg/mL caused a significantly higher APTT than the control. Polylysine at ≤ 0.1 mg/mL did not cause a significantly different PT from the control, while polylysine at 1 mg/mL caused a significantly higher PT than the control. TEG parameters for whole blood coagulation in the presence of 0.01 mg/mL polylysine were within the normal range; while polylysine ≥ 0.1 mg/mL caused one or more abnormal TEG parameters. From these results, the effect of polylysine on RBC aggregation and blood coagulation was concentration-dependent. The results provide important information for the biomedical applications of polylysine.

Effects of pentoxifylline on hemodynamic, hemorheological, and microcirculatory parameters in young SHRs during arterial hypertension development.

The most common form of hypertension in young adults is isolated diastolic hypertension. Diastolic arterial pressure is determined by the total peripheral resistance and depends on both vascular hindrance and blood viscosity. The aim of our work was to study the efficiency of pentoxifylline (PTX) in young spontaneously hypertensive rats (SHRs) during the development of arterial hypertension. The effects of a treatment course with PTX (100 mg/kg/day p.o. for 6 weeks, from 5 to 11 weeks old) on the mean, systolic, and diastolic blood pressure (BP); stroke volume; cardiac output; total peripheral resistance (TPR); whole blood viscosity (BV); plasma viscosity; hematocrit; RBC aggregation and deformability; local cerebral blood flow (lCBF); and microvascularization of the visual cortex were studied in SHRs in comparison with control SHRs and Wistar Kyoto rats. PTX-treated SHRs had significantly lower systolic, diastolic, and mean BP (by 24%, 26%, and 15%, respectively) and BV (by 5-9%) and a higher erythrocyte deformability index (by 1.5-2%), lCBF (by 42%), average diameter of capillaries (by 11%), density of the capillary network (by 23%), and percentage of capillaries with a diameter of 3-7 µm in comparison with control SHRs. In conclusion, PTX exerted positive effects on the hemodynamic, hemorheological, and microcirculatory parameters in SHRs during the development of arterial hypertension.

Modes of Hypotensive Action of Dihydroquercetin in Arterial Hypertension.

We studied the effect of dihydroquercetin (20 mg/kg/day intragastrically for 6 weeks) on mean BP and macro- and microrheological blood parameters in hypertensive SHR rats; in vitro effect of dihydroquercetin on the tone in thoracic aorta rings isolated from hypertensive SHR rats were also examined. At the end of the treatment course, the mean BP in the experimental rats decreased by 11%; the left ventricular mass index by 2%, and whole blood viscosity by 7-10% in comparison with control SHR rats; erythrocyte aggregation half-time increased by 15%; plasma viscosity, hematocrit, and erythrocyte deformability did not change. In in vitro experiments, dihydroquercetin (10-8-10-6M) induced relaxation of the isolated thoracic aorta rings in a dose-dependent manner. Hence, the antihypertensive effect of dihydroquercetin results from the decrease in blood viscosity and vasodilation.

Effects of Poloxamer 188 on red blood cell membrane properties in sickle cell anaemia.

Vaso-occlusive crisis (VOC) is the main acute complication in sickle cell anaemia (SS) and several clinical trials are investigating different drugs to improve the clinical severity of SS patients. A phase III study is currently exploring the profit of Velopoloxamer in SS during VOCs. We analysed, in-vitro, the effect of poloxamer (P188) on red blood cell (RBC) properties by investigating haemorheology, mechanical and adhesion functions using ektacytometry, microfluidics and dynamic adhesion approaches, respectively. We show that poloxamer significantly reduces blood viscosity, RBC aggregation and adhesion to endothelial cells, supporting the beneficial use of this molecule in SS therapy.

Blood vessel occlusion in peri-burn tissue is secondary to erythrocyte aggregation and mitigated by a fibronectin-derived peptide that limits burn injury progression.

Although vascular occlusion has long been noted in peri-burn tissue, the literature is inconsistent regarding the nature of the occlusion, with articles in the 1940s claiming that erythrocytes were the culprit and in the 1980s-1990s that microthrombi were responsible. To better define the nature of vessel occlusion, we studied two porcine burn models, a hot comb horizontal injury model and a vertical injury progression model. In both cases, tissue from the first two days after burn were stained with hemotoxylin and eosin, or probed for platelets or for fibrinogen/fibrin. Erythrocytes, identified as nonstained, clumped, anuclear, 5 µm cells, occluded most blood vessels (BVs) in both burn models. In contrast, platelet or fibrinogen/fibrin antibodies stained BV occlusions minimally at early time points, and only up to 16% of deep dermal BVs at 48 hours in the hot comb model and up to 7% at 24 hours in the vertical injury progression model. Treatment of animals with a fibronectin-derived peptide (P12), which limits burn injury progression and can dilate peripheral microvasculature, reduced erythrocyte occlusion by at least 50%, speeded healing and reduced scarring. Early erythrocyte aggregation, rather than thrombosis, explains the ineffectiveness of anticoagulants to prevent burn injury progression.

Crystallization of Galectin-8 Linker Reveals Intricate Relationship between the N-terminal Tail and the Linker.

Galectin-8 (Gal-8) plays a significant role in normal immunological function as well as in cancer. This lectin contains two carbohydrate recognition domains (CRD) connected by a peptide linker. The N-terminal CRD determines ligand binding specificity, whereas the linker has been proposed to regulate overall Gal-8 function, including multimerization and biological activity. Here, we crystallized the Gal-8 N-terminal CRD with the peptide linker using a crystallization condition that contains Ni2+. The Ni2+ ion was found to be complexed between two CRDs via crystal packing contacts. The coordination between Ni2+ and Asp25 plays an indirect role in determining the structure of ß-strand F0 and in influencing the linker conformation which could not be defined due to its dynamic nature. The linker was also shortened in situ and crystallized under a different condition, leading to a higher resolution structure refined to 1.08 Å. This crystal structure allowed definition of a short portion of the linker interacting with the Gal-8 N-terminal tail via ionic interactions and hydrogen bonds. Observation of two Gal-8 N-terminal CRD structures implies that the N-terminal tail and the linker may influence each other's conformation. In addition, under specific crystallization conditions, glycerol could replace lactose and was observed at the carbohydrate binding site. However, glycerol did not show inhibition activity in hemagglutination assay.

Monitoring of glucose, salt and pure water in human whole blood: An in vitro study.

Designing and implementation of non-invasive methods for glucose monitoring in blood is main focus of biomedical scientists to provide a relief from skin puncturing of diabete patient. The objective of this research work is to investigate the shape deformations and the aggregation of red blood cells (RBCs) in the human blood after addition of three different analytes i) (0mM-400mM: Range) of glucose (C(6)H(12)O(6)), ii) (0mM-400mM: range) of pure salt (NaCl) and iii) (0mM- 350mM: range) of pure water (H(2)O). We have observed that the changes in the shape of individual cells from biconcave discs to spherical shapes and eventually the lysis of the cells at optimum concentration of glucose, salts and pure water. This demonstration also provides a base line to facilitate diabetes during partial diagnosis and monitoring of the glucose levels qualitatively both in research laboratories and clinical environment.

Red blood cells mediate the onset of thrombosis in the ferric chloride murine model.

Application of ferric chloride (FeCl(3)) to exposed blood vessels is widely used to initiate thrombosis in laboratory mice. Because the mechanisms by which FeCl(3) induces endothelial injury and subsequent thrombus formation are little understood, we used scanning electron and brightfield intravital microscopy to visualize endothelial damage and thrombus formation occurring in situ. Contrary to generally accepted belief, FeCl(3) does not result in appreciable subendothelial exposure within the time frame of thrombosis. Furthermore, the first cells to adhere to FeCl(3)-treated endothelial surfaces are red blood cells (RBCs) rather than platelets. Energy dispersive x-ray spectroscopy demonstrated that ferric ions predominantly localize to endothelial-associated RBCs and RBC-derived structures rather than to the endothelium. With continuing time points, RBC-derived structures rapidly recruit platelets, resulting in large complexes that subsequently enlarge and coalesce, quickly covering the endothelial surface. Further studies demonstrated that neither von Willebrand factor nor platelet glycoprotein Ib-α receptor (GPIb-α) is required for RBCs to adhere to the endothelium, and that deficiency of GPIb-α greatly abrogated the recruitment of platelets to the endothelial-associated RBC material. These findings illuminate the mechanisms of FeCl(3)-mediated thrombosis and reveal a previously unrecognized ability of RBCs to participate in thrombosis by mediating platelet adhesion to the intact endothelial surface.

The investigation of interspecies diversity of erythrocyte aggregation properties by two different photometric methods in four animal species.

Among the haemorheological parameters, red blood cell (RBC) aggregation shows the largest interspecies diversity, and often controversial data can be found in the literature, besides the methodology-dependent issues. In this present investigation, we compared four experimental/laboratory animal species' RBC aggregation by two different photometric methods for better revealing the differences. Blood samples (K3-EDTA, 1.5 mg/ml) were taken from female animals: 16 inbred mice (Mus musculus, cardiac puncture), 15 outbred rats (Rattus norvegicus, caudal caval vein puncture), 15 beagle dogs (Canis canis, cephalic vein) and 23 juvenile pigs (Sus scrofa domesticus, medial saphenous vein). Haematological parameters (microcell counter) and RBC aggregation (light transmission and syllectometry-laser backscatter methods) were determined within 2 h after sampling. Describing the first 5-10 s of the aggregation process, additional parameters were calculated out of the syllectometric raw data. Standardized difference was calculated to determine the sensitivity of the two devices. Parameters describing the extent and magnitude of red blood cell aggregation showed the lowest values in the rat and the highest in the pig and canine blood. In turn, parameters describing the kinetics of aggregation showed the lowest values in the mouse and the highest in the rat. The standardized difference values for the laser backscattering method were 2-4 times larger vs. the light transmission one. The magnitude of the differences was not consequent in the aggregation parameters. These comparative results show that the laser backscattering method can detect the RBC aggregation differences between the investigated species more sensitively than the light transmission method.

Sex Differences in the Hemorheological Effect of Antidiuretic Hormone.

Experiments on rats showed that treatment with desmopressin in combination with water load contributes to the general nonspecific response of the blood. Increased blood viscosity, fibrinogen concentration, and erythrocyte aggregation were observed. Hemorheological changes in comparison with the control were less pronounced in females. Sex differences in erythrocyte aggregation were most significant.

Brattleboro Rats as the Model of Blood Hyperviscosity Syndrome for Testing Substances with Hemorheological Activity.

Hyperviscosity syndrome was described in Brattleboro rats. The aim of this study was to investigate the possibility of Brattleboro rats using, as a test system for the study of agents with hemorheological activity. Under conditions of this model of high blood viscosity syndrome in Brattleboro rats, Lychnis chalcedonica L. extract (150 mg/kg) administered intragastrically for 10 days exhibited hemorheological activity by modulating macro- (plasma viscosity, fibrinogen concentration) and microrheological (erythrocyte aggregation and deformability parameters. Hence, Brattleboro rats are an adequate model of hyperviscosity syndrome that can be used for search and testing of substances with hemorheological activity.