Academic literature on the topic 'Cellular antioxidant activity – red blood cells'

Plant polyphenols, with broadly known antioxidant properties, represent very effective agents against environmental oxidative stressors, including mercury. This heavy metal irreversibly binds thiol groups, sequestering endogenous antioxidants, such as glutathione. Increased incidence of food-derived mercury is cause for concern, given the many severe downstream effects, ranging from kidney to cardiovascular diseases. Therefore, the possible beneficial properties of Feijoa sellowiana against mercury toxicity were tested using intact human red blood cells (RBC) incubated in the presence of HgCl2. Here, we show that phenol-rich (10–200 µg/mL) extracts from the Feijoa sellowiana fruit potently protect against mercury-induced toxicity and oxidative stress. Peel and pulp extracts are both able to counteract the oxidative stress and thiol decrease induced in RBC by mercury treatment. Nonetheless, the peel extract had a greater protective effect compared to the pulp, although to a different extent for the different markers analyzed, which is at least partially due to the greater proportion and diversity of polyphenols in the peel. Furthermore, Fejioa sellowiana extracts also prevent mercury-induced morphological changes, which are known to enhance the pro-coagulant activity of these cells. These novel findings provide biochemical bases for the pharmacological use of Fejioa sellowiana-based functional foods in preventing and combating mercury-related illnesses.

Objective: to study the electrokinetic and aggregation properties, as well as the pro-oxidant and antioxidant processes in red blood cells following kidney transplantation in donors and in recipients in the postoperative period. Materials and methods. Blood from 12 recipients and 5 kidney donors over time – before transplantation, as well as at week 1, months 1, 2, 7, 10 and 12 after surgery, as well as from 8 healthy volunteers who formed the control group. We used microelectrophoresis to measure the electrophoretic mobility of red blood cells, characterizing the electrokinetic properties of cells. Aggregation was calculated microscopically by counting unaggregated red blood cells. Malondialdehyde concentration was measured spectrophotometrically at its absorbance maximum at 530 nm by reaction with thiobarbituric acid. Catalase activity was analyzed by reducing hydrogen peroxide in the sample spectrophotometrically at 240 nm wavelength. The obtained values were compared using the Mann–Whitney U test. Results. Decreased electrophoretic mobility of red blood cells within 2 months after transplantation was associated with increased malondialdehyde concentration and erythrocyte aggregation, decreased catalase activity in kidney recipients, followed by restoration of indicators to the control values. Electrophoretic mobility of red blood cells decreased, while malondialdehyde concentrations increased in donors after surgery. However, the increase was less pronounced than in recipients. The changes indicate that the postoperative period causes changes at the cellular level both in donors and in recipients. This is manifested by decreased stability of erythrocyte membrane structure, which is largely determined by lipid peroxidation processes. At the systemic level, a change in the electrophoretic mobility of red blood cells indicates a stress reaction before and after kidney transplantation in recipients within 2 months after surgery, and in donors in 1–2 months in the postoperative period with gradual increase in the body’s resistance. Conclusion. Kidney transplantation is manifested at the cellular and systemic levels. At the cellular level, there is decreased stability of the membrane structure, which is largely determined by lipid peroxidation processes. At the systemic level, a change in the electrophoretic mobility of red blood cells indicates a stress reaction with gradual increase in the body’s resistance. The data obtained demonstrate changes in the functional properties of red blood cells both in kidney transplant recipients and in donors. These changes need to be taken into account when carrying out therapeutic measures.

Abstract The capacity of mature red blood cells (RBCs) to respond to oxidative stress is limited due to lack of a full complement of organelles and as such, when faced with an oxidative environment, they rely on their endogenous antioxidant capacity (including superoxide dismutase, catalase, peroxiredoxin and glutathione) to protect against cellular damage. Low blood glutathione activity has been reported in several red cell disorders leading to increased oxidative stress. Targeting oxidative stress has thus been proposed as a secondary treatment in multiple anemia-causing diseases, such as sickle cell disease (SCD) and malaria, although its overall efficacy remains unclear. As glutathione itself is not permeable through the RBC membrane, treatment with cell-permeable amino acid precursors of glutathione (glutamine, cysteine and/or glycine) is a potential strategy to expand the RBC's antioxidant capacity and alleviate oxidative stress. Indeed, L-glutamine has recently been approved as a therapeutic for SCD, although the mechanistic basis for its effect is not clear. To fill this gap in our understanding, we performed detailed characterization of biophysical phenotype, morphology, and intracellular redox environment of oxidatively stressed RBCs in environments with varying amounts of available precursor amino acids. To assess the impact of exogenous amino acid precursors on the RBC's glutathione antioxidant capacity, we exposed mature RBCs from healthy adults to hydrogen peroxide (H 2O 2) and co-incubated with media that included glutamine, cysteine, and/or glycine. As catalase has the ability to scavenge high levels of exogenously fluxed H 2O 2, we performed these experiments using sodium azide to block catalase activity, enabling us to model oxidatively stressed RBCs. We performed osmotic gradient ektacytometry to quantify RBC deformability and hydration status, and assessed RBC morphology using osmotic-adjusted fixation techniques and scanning electron microscopy. As previously documented, H 2O 2 exposure in sodium azide-treated healthy RBCs was associated with decreased deformability, decreased hydration and increased numbers of echinocytes in a dose-dependent manner. We monitored red cell phenotypic changes following co-incubation with glutamine, cysteine, and/or glycine individually and in combination to test whether these amino acids extended the RBC's antioxidant abilities and contributed to improved function and morphology. We found that supplementation with all three amino acids in combination significantly improved both deformability and hydration of H 2O 2-stressed RBCs, as opposed to treatment with glutamine alone. To directly assess whether the exogenous amino acids were in fact contributing to less intracellular oxidative stress in RBCs, we quantified intracellular reactive oxygen species (ROS) using 2', 7' -dichlorofluorescein diacetate (DCFDA), a cell permeable dye used to measure ROS production. As expected, H 2O 2 exposure alone was associated with elevated intracellular ROS inside RBCs in both a time- and dose-dependent manner. Supplementation with the three amino acid cocktail during H 2O 2 stress resulted in a reduction in the level of intracellular ROS activity. In summary, we documented that exogenous added amino acids reduce oxidative damage in RBCs and we hypothesize that this protection occurs via the glutathione antioxidant pathways. In future studies, we plan to investigate the impact of exogenous amino acids on sickled and irreversibly sickled RBCs (ISCs) in the context of SCD, and on uninfected and infected RBCs in the context of malaria. Disclosures Kim-Shapiro: Beverage Operations LLC: Current holder of stock options in a privately-held company, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties: co-inventor on a patent related to the use of nitrite under cardiovascular conditions, and a co-author on patents related to treatment of hemolysis.

Objective. To study and compare indicators of systemic inlammation and red blood cells glutathione redox potential by chronic oxidative stress (OS) in patients with coronary heart disease (CHD), type 2 diabetes mellitus (T2DM) and the combination of both diseases.Design and methods. The study included 35 patients with CHD and newly diagnosed T2DM, 109 patients with CHD, 19 patients with T2DM, and 89 healthy individuals. Systemic inlammation indicators were measured including concentration of interleukin (IL) 6 and 8, myeloperoxidase (MPO) and OS in plasma, oxidized (GSSG) and reduced (GSH) glutathione, as well as their ratio and redox potential (E), the activity of glutathione reductase (GR) and glutathione peroxidase (GP) in red blood cells.Results. Signiicant growth of systemic inlammation (IL-6, IL-8, MPO) indicators on the weakening antioxidant defense enzyme has been registered in patients with a combination of CHD and T2DM, a 3,4-fold reduction of GSH level, 5,8-fold of 2GSH/GSSH in red blood cells and E values towards the oxidized state at 36,3 mV were noted. These changes were less pronounced in CHD group and were absent in T2DM group. All subjects showed a decreased activity of GP and increased level of glycosylated hemoglobin. The correlation of E and activity GR have been found in patients with carbohydrate metabolism disorder. High positive relationship between IL concentration and red blood cells GR, E indicators has been identiied in patients with CHD and T2DM. There is a need to control and correct cellular redox potential in patients with CHD and T2DM.Conclusion. The combination of CHD and T2DM contributes to the decrease of red blood cells redox status glutathione secondary to the increased systemic inlammatory response and chronic OS indicators.

Plant extracts are a rich source of natural compounds with antimicrobial properties, which are able to prevent, at some extent, the growth of foodborne pathogens. The aim of this study was to investigate the potential of polyphenolic extracts from cladodes of Opuntia ficus-indica (L.) Mill. to inhibit the growth of some enterobacteria and the biofilm formation by Staphylococcus aureus. Opuntia ficus-indica cladodes at two stages of development were analysed for total phenolic content and antioxidant activity by Oxygen Radical Absorbance Capacity (ORAC) and Trolox equivalent antioxidant capacity (TEAC) (in vitro assays) and by cellular antioxidant activity in red blood cells (CAA-RBC) (ex vivo assay). The Liquid Chromatography Time-of-Flight Mass Spectrometry (LC/MS–TOF) analysis of the polyphenolic extracts revealed high levels of piscidic acid, eucomic acid, isorhamnetin derivatives and rutin, particularly in the immature cladode extracts. Opuntia cladodes extracts showed a remarkable antioxidant activity (in vitro and ex vivo), a selective inhibition of the growth of Gram-positive bacteria, and an inhibition of Staphylococcus aureus biofilm formation. Our results suggest and confirm that Opuntia ficus-indica cladode extracts could be employed as functional food, due to the high polyphenolic content and antioxidant capacity, and used as natural additive for food process control and food safety.

The purpose of the current study was green synthesis of ZnO-nanoparticles (NPs) from different tissues of Silybum marianum (L.) Gaernt. (i.e., seeds, wild plant, in vitro derived plantlets and callus cultures) followed by extensive characterization and evaluation of their biological potency. ZnO-NPs thus synthesized were subjected to characterization using standard techniques such as XRD, FTIR and SEM. Thermal stability of synthesized NPs was also evaluated using thermo-gravimetric analysis. Highly stable crystalline NPs with size ranging between 30.8 and 46.0 nm were obtained from different tissues of S. marianum. These NPs have revealed a wide range of biological applications showing antioxidant, moderate α-amylase inhibitor, antibacterial and cytotoxic potencies. The highest antibacterial activity (20 ± 0.98 mm) was shown by seed extract-mediated ZnO NPs against Staphylococcus aureus (ATCC-6538). Seed extract-mediated ZnO NPs also showed the most potent antioxidant activity (27.7 ± 0.9 µgAAE/mg, 23.8 ± 0.7 µgAAE/mg and 12.7 ± 1.9% total antioxidant capacity (TAC), total reducing power (TRP) and DPPH-free radical scavenging assay (FRSA), respectively). All of the synthesized ZnO NPs also showed cytotoxic activity against the hepato-cellular carcinoma (HepG2) human cells. Interestingly, these ZnO NPs were also highly biocompatible, as evidenced by the brine shrimp lethality and human red blood cells hemolytic assays. Among all of the NPs synthesized and used, the effect of seed extract-mediated NPs was found to be most promising for future applications.

Abstract The excess of genetic information in patients with Down syndrome (DS) produces an increase in the catalytic activity of superoxide dismutase (SOD1), an antioxidant enzyme coded on chromosome 21. It has been suggested that an increase in oxidative stress in DS patients may cause adverse effects in the cell membranes through the oxidation of polyunsaturated fatty acids (PUFAs). The aim of this study was to evaluate the cellular antioxidant system by determining the catalytic activity of the SOD1, glutathione peroxidase (GPx), catalase (CAT), and glutathione reductase (GR) enzymes and the concentrations of α-tocopherol in red blood cells (RBCs) in a group of 72 DS patients. The profile of fatty acids in the phospholipids of RBC membranes was also evaluated. The activity of the erythrocyte antioxidant enzymes is significantly higher in the DS group than in the control group (SOD1, 635 ± 70 U/g Hb vs 476 ± 67 U/g Hb; CAT, 1843 ± 250 U/g Hb vs 1482 ± 250 U/g Hb; GPx, 23.2 ± 5.3 U/g Hb vs 21.5 ± 3.6 U/g Hb; and GR, 9.32 ± 1.4 U/g Hb vs 6.9 ± 1.3 U/g Hb, respectively). No differences were observed in RBC α-tocopherol concentrations between the two groups studied. Long-chain n6 PUFA (C20:3n6, C20:4n6) concentrations were increased in DS patients, suggesting enhanced Δ-6-desaturase activity. The long-chain n3 PUFA (docosahexenoic acid) does not appear to be affected by increased oxidative stress, probably because of the existence of compensatory antioxidant mechanisms.

Wound is known as disruption in the integrity of a tissue. The mechanisms of regeneration and tissue repair consist of a series of molecular and cellular events that occur after the onset of a tissue lesion to rebuild the damaged tissue. The remodelling phases of the exudative, proliferative, and extracellular matrix are concurrent events that occur through the interaction of complex processes involving soluble mediators, blood cells and parenchymal cells. Exudative phenomena that occur after injury, lead to tissue edema growth. The proliferative stage aims to minimize the area of tissue damage by myofibroblasts and fibroplasia contracting. Angiogenesis and reepithelialisation processes can still be observed at this point. Endothelial cells are capable of differentiating into mesenchymal components and this distinction seems to be finely coordinated by a series of signalling proteins. Many of the medicines available today is derived from natural sources. Flavonoids are essential components of the human diet apart from their physiological functions in plants, even though they are not considered as nutrients. In this review, naturally occurring flavonoid is discussed which occur in citrus fruits, vegetables, nuts, and beverages like coffee, tea, and red wine, and also in medical herbs. They exhibit different pharmacological actions, like antioxidant, anti-allergic, anti-bacterial, anti-inflammatory, anti-mutagenic and anti-cancer activity. One of the flavanones is Naringenin which is the ordinary dietary poly-phenolic constituent of the citrus fruits (grapefruit and oranges) and vegetables. It is beneficial in various neurological, cardiovascular, gastrointestinal, rheumatological, metabolic, malignant disorders, and functionally, this ameliorative effect of naringenin is primarily attributed to its anti-inflammatory (via inhibiting staffing of cytokines and inflammatory transcription factors) and anti-oxidant (via scavenging of free radicals, bolstering of endogenous antioxidant defence system and metal ion chelation) effects

Abstract Sickle cell disease (SCD) patients suffer from hemolysis in microcirculation. On the one hand, hemoglobin and heme released from sickled red blood cells catalyze reactive oxygen species (ROS) generation by Fenton chemistry. On the other hand, sickled red blood cells occlude capillaries, creating a hypoxic condition that exacerbates ROS production. As an essential antioxidant mechanism, superoxide dismutase 2 (SOD2) detoxifies superoxide by converting it to hydrogen peroxide (H 2O 2) in the mitochondria. In SCD patients, despite the elevated ROS production, we found that SOD2 expression is suppressed in the pulmonary endothelium (Figure 1A,B). Therefore, we hypothesize the depletion of endothelial SOD2 compromises endothelial function and exacerbates the progression of SCD. To examine the role of endothelial SOD2, we silenced SOD2 gene expression (SOD2 KD) with siRNA in primary human pulmonary microvascular endothelial cells (hPMVECs). Knocking down SOD2 in hPMVECs accelerated mitochondrial superoxide production and compromised mitochondrial potential. However, mitochondrial respiration, the activity of respiratory complexes, and the cellular ATP content were not affected by SOD2 KD. An important function of endothelial cells is to form a barrier and sequester cellular and molecular contents in the blood. SOD2 KD hPMVECs exhibited increased albumin leakage and decreased transendothelial resistance, indicating a disrupted endothelial barrier(Figure 1C). The defect in the endothelial barrier was rescued by adding 4 mM H 2O 2(Figure 1D), suggesting SOD2-derived H 2O 2 may serve as a critical signaling molecule. Moreover, cell migration or proliferation was inhibited in SOD2 KD hPMVECs, which was examined by a scratch assay. Since both cell migration and barrier maintenance require focal adhesion assembly, we next investigated the role of SOD2 in focal adhesion dynamics. In an attachment assay, SOD2 KD reduced cell attachment rate on uncoated plates, which was blunted by fibronectin precoating, indicating a fibronectin-dependent defect in cell adhesion(Figure 1E,F). Notably, although fibronectin protein expression in hPMVECs was not altered, SOD2 KD decreased the dimer/monomer ratio. Furthermore, confocal images showed that fibronectin was retained in SOD2 KD cells(Figure 1G), highlighting the importance of SOD2 in fibronectin assembly. In conclusion, we demonstrated for the first time that SOD2 expression is diminished in the pulmonary endothelium of SCD patients and that endothelial SOD2 is crucial for endothelial function by facilitating fibronectin assembly. The importance of SOD2 in endothelial function may prove therapeutic value in SCD patients, which requires further investigation. Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.

For well over 20 years the Oxygen Radical Absorbance Capacity (ORAC) assay has been an important research tool in identifying antioxidant candidates in food and serum samples. The ORAC value is derived from a series of fluorescence intensity measurements taken over a period of time, usually a few hours. The kinetics of this reaction is controlled by the sustained release of peroxyl radicals at 37°C by an azo compound (AAPH). The peroxyl radicals attack the fluorescent probe causing a gradual decrease in fluorescence intensity. Ultimately, the test yields fluorescence decay curves over time, with the presence of any antioxidants in a sample having a protective effect, delaying probe decay and resulting in a greater area under the decay curve. This forms the basis of the ORAC measurement. Concerns have been raised about the applicability of this assay, chemical interferences influencing the data, and the use of ORAC values to attribute health benefits of foods. In an effort to curb misrepresentation of health benefits from ORAC data, the USDA retracted its ORAC database in 2012 and published a statement by Dr Ronald Prior, a founding researcher for the ORAC assay. The explanatory statement by Dr Prior identified the misapplication of ORAC values and misleading perceived health benefits as major reasons for withdrawal of the database. Despite this, ORAC remains a popular assay, and the method is widely used as a product development and marketing tool. Some researchers have reported that ORAC values can be influenced by factors such as choice of solvent, chemical constituents in matrices, and pH conditions. However, little has been published on antioxidant synergies in food systems and their contribution to the ORAC value. Given the predisposition of the assay to interferences, a better understanding of antioxidant synergies is necessary to understand the contributing factors to measurement in real foods, and also to determine how these values may be manipulated. With the USDA caution in mind, this research was carried out to systematically investigate the factors influencing the ORAC measurement and its interpretation. Firstly, an alternative mode of reporting antioxidant activity to consumers on product labeling was proposed. Calculations needed to convert ORAC units from μM Trolox equivalents (μM T.E/kg or μM T.E/L) to mass units (g T.E/kg or g T.E/L) of Trolox equivalents per kg or per L of foodstuff are provided. We propose that mass units are less misleading to consumers, by not reporting very large and impressive-looking values when a simple conversion reveals most of them to be much more modest when viewed as a mass of vitamin E equivalent. For example, the antioxidant activity of blueberries when measured by the ORAC assay was equivalent to over 71,000 μM of Trolox equivalents. When converted, the blueberries can be said to have the same antioxidant activity as 17.9g of vitamin E per kg of fruit (17.9g T.E/kg). This new mode of reporting was successfully applied to a range of commodities including fruit, confection and beverages. Influencing factors, including environmental conditions, role of additives and nanoparticles and interactions between classes of chemical constituents were all investigated. Environmental conditions, specifically rainfall, were found to influence the levels of antioxidant compounds/bioactives in Australian wines. Six chemical constituents were identified as warranting further investigation; namely 6-methylcoumarin, protocatechuic acid, vanillic acid, p-coumaric acid, rutin and chlorogenic acid. Significant differences were also observed between the antioxidant capacity of wines by in vitro ORAC and ex vivo CAA-RBC assays, where wines with similar ORAC values had vastly different bioavailability and activity in the cellular system. Amino acids and CuNPs additives were found to greatly influence the antioxidant measurements of “superfoods”. Results indicated strong enhancements and synergies related to the properties of the amino acids and complexes formed with Cu(I) and essentially matrix independent.. The order of antioxidant enhancement in bilberry, coffee berry, and apple concentrates was Tryptophan > Tyrosine > Methionine ≥ Histidine ≥ 4-Hydroxyproline. This order was also consistent with the order of calculated bond dissociation energies (BDEs), reflecting the inherent antioxidant potentials of the amino acids studied. Density Functional Theory (DFT) was used to support a proposed “substrate zone” and “antioxidant zone” postulate for amino acids and related additives and this concept assists in demonstrating potential mechanisms involved in achieving such extraordinary enhancements and synergies. Histidine was used as a model system for DFT calculations, and allowable species had homolytic BDEs ranging from high (deactivated) to very low (activated), in the case of species (b) the BDE was at a level well below that of vitamin E, making it an excellent and potentially potent antioxidant. DFT calculations revealed that the histidine-Cu(I) complex had a comparable BDE to that of Trolox, again demonstrating how interactions between chemical constituents can influence, and in this case enhance antioxidant activity measurements. Synergies and antagonisms were also reported for eight classes of chemical constituents typically found in navel oranges. These mixtures were prepared based on the levels reported in nutritional data tables, and analyzed by ORAC and CAA-RBC assays. A correlation analysis revealed that the ORAC and CAA-RBC data did not correlate overall, however distinct clustering and several interesting outliers were noted. Cluster (a) had low ORAC and low CAA-RBC values, involving combinations of preservatives, sugars and CuNPs. Cluster (b) had low to moderate responses in both assays, and was made up primarily of vitamins in combination with CuNPs, preservatives, sugars and flavonoids. Cluster (c) was dominated by phenolics and their interactions with a number of groups, which gave high antioxidant activity in both ORAC and CAA-RBC assays, and amino acids are the main contributors in cluster (d). Organic acids featured in both outliers, firstly with a high antioxidant activity in both assays when combined with polyphenolics, and secondly as having an auto-oxidation effect in the CAA-RBC assay but a high ORAC value when analysed individually. Antioxidant activities of individual mixtures and combinations of classes of compounds showed antagonism/suppression of antioxidant activity between sugars and vitamins, and between polyphenolics and flavonoids in the ORAC assay. However, these same solutions resulted in antioxidant synergy in the CAA-RBC assay. In fact, the auto-oxidation effect of organic acids was reversed and synergies were noted in interaction with polyphenolics. A number of synergisms ex vivo involved polyphenolics in combination with other constituents such as vitamins, the amino acid Tryptophan, preservatives and CuNPs. These findings support the postulate that interactions at the “substrate zone” are influencing factors of antioxidant capacity at the molecular level. Computational chemistry was used to postulate mechanisms for antioxidant synergy, activation and deactivation of phenolic O-H groups, using quercetin and (-)-epicatechin-3-gallate as examples. It was concluded that factors including rainfall, amino acid and CuNPs addition, and interactions between common classes of food constituents influenced antioxidant activity in food systems. Computational chemical calculations were used to postulate mechanisms for antioxidant enhancement and synergy, a major influencing factor in antioxidant measurements. This research describes the potential for unlocking new and powerful antioxidant synergies in food systems, nutrition and health and the medical/pharmaceutical fields.

Plasminogen activators (PA) are thought to play a role in the invasive and metastatic properties of many types of cancer cells. Though, discrepancies in correlations between fibrinolytic activity and metastatic potential of malignant cells have been described.In this study, we evaluated both tissue type (tPA) and urokinase type (UK) cellular PA activities in different mononuclear cell types : normal T and B human peripheral lymphocytes, B cells from patients with chronic lymphocytic leukemia (CLL), human blood monocytes, alveolar macrophages, U 937, RAJI and JM cell 1ines.Mononuclear cells were isolated by Ficoll-hypaque gradients and monocytes by plastic adhesion. T and B cells were separated by a rosetting technique using sheep red blood cells. Cellular extracts were prepared by 0.5 % Triton X 100 buffer treatment followed by sonication and centrifugation 10 ' at 2000 g. PA assays were performed on the supernatants.UK-type PA was evaluated by a liquid-phase assay in presence of human plasminogen (Kabi) and chromogenic substrate S 2251 (Kabi).tPA was determinated using a solid-phase fibrin activity assay which involves an affinity separation step and thus allows selective detection of tPA.In both cases, results were reported in international units by reference to standard curves of UK (Choay) or tPA (Kabi).In all cell types tested, PA detected was essentially urokinase-type. Highest PA activity was found in U 937 cells (0.7 IU/5×l06 cells). In normal blood lymphocytes, mean PA activity was 0.08 IU/5×l06 cells. Examination of lymphocytes from patients with CLL revealed a marked decrease in UK activity as compared to normals (< 0.01 IU/5×106 cells in more than 50 % cases).The function of PA in normal lymphocyte physiology and the potential pathogenic role of diminished PA in CLL lymphocytes remains to be investigated.

Changes in the composition of the blood, venous stasis, and interaction of the blood with the vessel wall (Virchow's triad) all have rheological aspects which may promote venous thrombogenesis.Blood composition and rheology. Increasing levels of venous haematocrit and fibrinogen increase bulk blood viscosity, especially at low shear rates such as are encountered in veins, when red cell aggregation occurs. Static blood requires a minimum shear stress for flow (yield stress), which is also strongly dependent on haematocrit and fibrinogen levels. Increases in haematocrit and fibrinogen also promote platelet adhesion and aggregation. Polycythaemia carries an increased risk of venous thromboembolism, which can be reduced by lowering the haematocrit; conversely, anaemic patients (renal failure, pernicious anaemia) have a subnormal prevalence of pulmonary embolism at autopsy. Increased preoperative levels of haematocrit, fibrinogen and blood viscosity predicted postoperative deep vein thrombosis in some studies, but not in others: they have complex relationships to other risk factors and illnesses. Postoperative changes in haematocrit, fibrinogen and blood viscosity may also be relevant to thrombogenesis, as may haemoconcentration in leg veins.Venous flow disturbance and rheology. The flow behaviour of particles and cells in venous valve pockets has been studied by Karino: particles and cells were observed to leave mainstream flow and circulate in paired vortices in low-shear areas within the valve pockets. A cell-poor hypoxic area at the apex of the valve pocket may favour thrombogenesis. Valve pockets might therefore act as in vivo aggregometers, with optimal conditions for activated cells or coagulation products to promote platelet and red cell aggregation, which might be facilitated by increases in haematocrit or fibrinogen. Sevitt has observed cellular aggregates in valve pockets at autopsy, which might act as a nidus for thrombus initiation. Successive layers of thrombus will disturb flow steamlines, as well as generating procoagulant activity: hence a series of "aggregometers" might result in successive bursts of thrombosis and the layered structure of venous thrombi observed by Sevitt. Variations in haematocrit, fibrinogen and red cell aggregation may influence stasis of blood following venous occlusion by thrombus, and hence affect thrombotic extension; they may also influence residual lung perfusion following pulmonary embolism.Therapeutic aspects of rheology. Leg stockings and other physical methods of preventing deep vein thrombosis may improve flow disturbance in valve pockets, as well as in axial veins. The efficacy of perioperative dextran in prevention of venous thromboembolism may partly reflect haemodilution and its rheological consequences. Likewise, postoperative defibrination with ancrod reduced the incidence and extent of deep vein thrombosis after hip surgery, which may partly reflect reductions in plasma viscosity and red cell aggregation. Defibrination with ancrod reduced the haemodynamic disturbance, and the mortality, of experimental pulmonary embolism in dogs, possibly by increasing residual perfusion.. Similarly, improved perfusion after thrombolytic therapy of pulmonary embolism in man may reflect the rheological consequences of fibrinogen depletion, as well as thrombolysis.