Microrheology and light transmission of blood. IV. The kinetics of artificial red cell aggregation induced by Dextran

Sialylated Glycan Bindings from SARS-CoV-2 Spike Protein to Blood and Endothelial Cells Govern the Severe Morbidities of COVID-19

Consistent with well-established biochemical properties of coronaviruses, sialylated glycan attachments between SARS-CoV-2 spike protein (SP) and host cells are key to the virus's pathology. SARS-CoV-2 SP attaches to and aggregates red blood cells (RBCs), as shown in many pre-clinical and clinical studies, causing pulmonary and extrapulmonary microthrombi and hypoxia in severe COVID-19 patients. SARS-CoV-2 SP attachments to the heavily sialylated surfaces of platelets (which, like RBCs, have no ACE2) and endothelial cells (having minimal ACE2) compound this vascular damage. Notably, experimentally induced RBC aggregation in vivo causes the same key morbidities as for severe COVID-19, including microvascular occlusion, blood clots, hypoxia and myocarditis. Key risk factors for COVID-19 morbidity, including older age, diabetes and obesity, are all characterized by markedly increased propensity to RBC clumping. For mammalian species, the degree of clinical susceptibility to COVID-19 correlates to RBC aggregability with p = 0.033. Notably, of the five human betacoronaviruses, the two common cold strains express an enzyme that releases glycan attachments, while the deadly SARS, SARS-CoV-2 and MERS do not, although viral loads for COVID-19 and the two common cold infections are similar. These biochemical insights also explain the previously puzzling clinical efficacy of certain generics against COVID-19 and may support the development of future therapeutic strategies for COVID-19 and long COVID patients.

Chronic-intermittent urokinase therapy in patients with end-stage coronary artery disease and refractory angina pectoris--a pilot study

Patients with coronary artery disease and severe angina pectoris refractory to conventional medical treatment (beta blockers, nitrates, calcium antagonists) and without the option for invasive revascularization procedures represent an increasing clinical problem. For these patients, chronic-intermittent urokinase therapy has been developed. Twenty patients received 500,000 IU urokinase as intravenous bolus injection 3 times a week over a period of 12 weeks. The average reduction in anginal symptoms in 19 patients was 74%, from 23.5 +/- 10.8 to 5.2 +/- 4.8 events/week (p < 0.001); 1 patient was excluded from further treatment because of an increase of > 66% in anginal events. Fibrinogen decreased by 34% from 370 +/- 57 to 244 +/- 44 mg/dl (p < 0.001), the rheological parameters plasma viscosity by 6.1% from 1.39 +/- 0.04 to 1.31 +/- 0.03 mPas (< 0.001), and red blood cell aggregation by 18% from 13.9 +/- 2.4 to 11.2 +/- 2.2 (p < 0.001). Exercise tolerance increased by 51%. Average ST-segment depression decreased from 0.16 +/- 0.10 to 0.12 +/- 0.09 (p < 0.01). After 12 weeks of follow-up, angina pectoris and fibrinogen levels were still significantly reduced compared with baseline values. Chronic-intermittent urokinase therapy represents an effective anti-ischemic and antianginal approach in patients with refractory angina pectoris and end-stage coronary artery disease. Improvement of rheological blood properties and thrombolytic effects are likely therapeutic mechanisms.

Simultaneous influence of erythrocyte deformability and macromolecules in the medium on erythrocyte aggregation: a kinetic study by a laser scattering technique

The aggregation and sedimentation kinetics of human erythrocytes was studied by modifying the cellular properties and medium compositions simultaneously. Dextrans of average molecular weight 70400 and 494000 were used to provide suspending medium modifications, while diamide (diazene dicarboxylic acid bis(N,N-dimethylamide)) was used to alter the membrane structural properties. Laser scattering method was employed for this study, and it was compared with a kinetic method combined with a low-shear rheoscope and an image analyzer. From scattered light intensity profiles continuously obtained during aggregation of erythrocytes and sedimentation of the aggregates, characteristic kinetic parameters were computed. Kinetic parameters obtained from a phase of the one-dimensional aggregate formation and sedimentation corresponded well to the velocity of rouleaux formation obtained by the low-shear rheoscope technique. Dextrans accelerated the erythrocyte aggregation and the sedimentation, and diamide treatment suppressed the process by decreasing the erythrocyte deformability. The aggregating force by dextrans overcame the disaggregating force by the decreased deformability. However, the arrangement of erythrocytes as expressed in specific units for aggregates (i.e., rouleaux) became irregular by decreasing the erythrocyte deformability. In conclusion, the progression of erythrocyte aggregation and the structure of the aggregates were dependent on both erythrocyte properties and macromolecules in the medium.

Regular physical exercise and low-fat diet. Effects on progression of coronary artery disease

BACKGROUND

Significant regression of coronary and femoral atherosclerotic lesions has been documented by angiographic studies using aggressive lipid-lowering treatment. This study tested the applicability and effects of intensive physical exercise and low-fat diet on coronary morphology and myocardial perfusion in nonselected patients with stable angina pectoris.

METHODS AND RESULTS

Patients were recruited after routine coronary angiography for stable angina pectoris; they were randomized to an intervention group (n = 56) and a control group on "usual care" (n = 57). Treatment comprised intensive physical exercise in group training sessions (minimum, 2 hr/wk), daily home exercise periods (20 min/d), and low-fat, low-cholesterol diet (American Heart Association recommendation, phase 3). No lipid-lowering agents were prescribed. After 12 months of participation, repeat coronary angiography was performed; relative and minimal diameter reductions of coronary lesions were measured by digital image processing. Change in myocardial perfusion was assessed by 201Tl scintigraphy. In patients participating in the intervention group, body weight decreased by 5% (p less than 0.001), total cholesterol by 10% (p less than 0.001), and triglycerides by 24% (p less than 0.001); high density lipoproteins increased by 3% (p = NS). Physical work capacity improved by 23% (p less than 0.0001), and myocardial oxygen consumption, as estimated from maximal rate-pressure product, by 10% (p less than 0.05). Stress-induced myocardial ischemia decreased concurrently, indicating improvement of myocardial perfusion. Based on minimal lesion diameter, progression of coronary lesions was noted in nine patients (23%), no change in 18 patients (45%), and regression in 13 patients (32%). In the control group, metabolic and hemodynamic variables remained essentially unchanged, whereas progression of coronary lesions was noted in 25 patients (48%), no change in 18 patients (35%), and regression in nine patients (17%). These changes were significantly different from the intervention group (p less than 0.05).

CONCLUSIONS

In patients participating in regular physical exercise and low-fat diet, coronary artery disease progresses at a slower pace compared with a control group on usual care.

Increased plasma viscosity and erythrocyte aggregation: indicators of an unfavourable clinical outcome in patients with unstable angina pectoris

OBJECTIVE

To determine the prognostic significance of altered plasma viscosity and erythrocyte aggregation in unstable angina.

DESIGN

A prospective study of 96 consecutive patients with unstable angina allocated to one of two groups according to predefined threshold values for plasma viscosity and erythrocyte aggregation at study entry. The patients received a standardised treatment and were followed up for six months or until angioplasty or bypass surgery.

MAIN OUTCOME MEASURE

Frequency of myocardial infarction.

RESULTS

Myocardial infarctions occurred in 7/26 patients with a plasma viscosity greater than or equal to 1.38 mPa s and in 8/35 with a rate constant of erythrocyte aggregate formation greater than or equal to 0.5 mPa (corrected for plasma viscosity) but in only 4/70 with a plasma viscosity less than 1.38 mPa s and in 3/61 with an erythrocyte aggregation less than 0.5 mPa (odds ratios: 6.1 (95% confidence interval 1.3 to 31), p = 0.008, and 5.7 (95% CI 1.2 to 35), p = 0.016). Plasma viscosity and erythrocyte aggregation were more predictive of myocardial infarction than age, male gender, fibrinogen concentration, ST segment abnormalities, or coronary score. Furthermore, Holter monitoring with ST segment analysis showed that ischaemic episodes were more common in patients in whom the rate constant of erythrocyte aggregate formation was greater than 0.5 mPa (15/27 v 17/50, p = 0.029). Cardiac troponin T release was increased in patients with a plasma viscosity of greater than 1.38 mPa s (10/26 v 9/70, p = 0.010).

CONCLUSIONS

In patients with unstable angina a considerable increase in plasma viscosity and erythrocyte aggregation identified a subgroup of patients at a high risk of acute myocardial infarction in whom medical treatment was likely to be unsuccessful.

Blood rheology and ischaemia

Ischaemia is essentially the failure of tissue to obtain a sufficient oxygen supply for its function. In the context of rheology, which is the study of the deformation and flow of materials, this implies failure to deliver the blood, rather than failure to oxygenate the blood or extract oxygen from it. Resistance to the delivery of blood is generally considered to have vascular and rheological components. Vascular effects on resistance may often be dominant, and there is wide appreciation of the ischaemic consequences of vascular obstruction and narrowing, for example in atherosclerotic disease. However, rheological factors can vary widely between individuals and in disease, and such variations have the potential to influence oxygen supply. Here, the rheological factors which affect blood flow are reviewed and their role in the development of ischaemia is discussed, with particular reference to the eye where possible.

Haemorrheological abnormalities in unstable angina pectoris: a relation independent of risk factor profile and angiographic severity

Plasma viscosity, photometric erythrocyte aggregation index, and erythrocyte filterability were measured in 194 patients with coronary artery disease. Patients with unstable angina (n = 64) had a higher plasma viscosity and photometric erythrocyte aggregation index than patients with stable angina (95% confidence intervals for the mean difference: 0.052-0.100 mPa.s for plasma viscosity, and 43%-72% for the photometric erythrocyte aggregation index). Multiple regression with fibrinogen, cholesterol, high density lipoprotein cholesterol, triglycerides, blood pressure, smoking habits, coronary artery score, and left ventricular ejection fraction as independent variables showed a significant partial correlation between fibrinogen and the photometric erythrocyte aggregation index (r2 = 0.20) and plasma viscosity (r2 = 0.09), between triglycerides and plasma viscosity (r2 = 0.05), and between aortic pressure and erythrocyte filterability (r2 = 0.03). Logistic regression for unstable/stable angina with the haemorrheological variables as independent variables correctly identified 72% of the patients with stable angina and 78% of those with unstable angina. Inclusion of all the variables investigated did not substantially improve the discriminative potential of the logistic regression model. Unstable angina is associated with an impairment of blood fluidity that is essentially independent of risk factor profile and angiographic data.

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.

Temperature-dependence of red cell aggregation

To investigate the temperature-dependence of red cell aggregation 20 blood samples of normal donors and 20 blood samples of patients with venous ulcers of the leg were examined by photometric aggregometry at 3 degrees C, 10 degrees C, 20 degrees C, 30 degrees C and 37 degrees C. With decreasing temperature red cell aggregates become more resistant to hydrodynamic dispersion and they become more prone to growing under low shear stress. It is concluded that a decrease in temperature causes an increase in adsorptive energy of red cell aggregation, which is most likely due to an increase in molecular adsorption stress. Red cell aggregate formation as an overall process is retarded by a decrease in temperature, which is primarily due to an increase in plasma viscosity causing increased damping of aggregate formation. Accordingly the rate constant of aggregate formation corrected for plasma viscosity increases with decreasing temperature. The temperature-dependence of the kinetic parameters can be explained by a theoretical model that suggests the increase in contact area between aggregating red blood cells as the rate-limiting step of red cell aggregation. As a whole red cell aggregation is favoured by lowering of temperature.

Red blood cell aggregation in nephrotic syndrome

Red blood cell (RBC) aggregation induced by fibrinogen is a major determinant of the non-Newtonian flow behavior of human blood and has been suggested as a possible contributing factor for thrombogenesis. Given the elevated fibrinogen levels and the high incidence of thrombotic accidents in nephrotic syndrome (NS), a study was designed to assess RBC aggregation in this disease. Three different aggregation assays were used: (1) changes in light transmission through static cell suspensions, aggregation half time (AHT); (2) low gravity centrifugation of blood in nearly vertical tubes, zeta sedimentation ratio (ZSR); (3) direct observation of dilute RBC suspensions, microscopic aggregation index (MAI). The results indicate that RBC aggregation, as measured by AHT and ZSR, is increased significantly in NS patients versus healthy controls (P less than 0.001 for both methods); this increase was not a function of renal insufficiency. The AHT and ZSR data were well correlated with plasma fibrinogen levels (r = 0.75 and 0.84, respectively). No differences were observed with the MAI method, since with this technique the aggregation process reaches an asymptotic plateau for the range of fibrinogen found in NS. Implications of increased RBC aggregation and thus increased blood viscosity and flow disturbances on thrombogenesis are discussed.

[Quantification of the effects of fibrinolytic therapy upon the flow behavior of blood (author's transl)]

The effect of Streptokinase-infusion upon the flow properties of blood was investigated by viscometric and aggregometric methods. Under fibrinolytic therapy, we found in all cases a significant fall in fibrinogen content, as well as a strong reduction in plasma viscosity, velocity of red cell aggregate formation and shear resistance of red cell aggregates. In addition, a drop in apparent blood viscosity at all shear rates was found. In no case, a total desaggregation of red cell was noted. The hematocrit value remained practically constant; consequently, the drop in apparent blood viscosity at high (160 s-1) shear rates and intermediate (8 s-1) shear rates can be solely accounted for by the observed drop in plasma viscosity. At low shear rates (2.3 s-1) the observed drop in apparent viscosity is partly caused by aggregation desaggregation, but mainly by a drop in plasma viscosity. The presented results again confirm that the method of rotational viscometry only incompletely records the improvement in the flow properties of blood that are caused by a therapy aimed at a reduction of the plasma fibrinogen content.

Red cell aggregation in blood flow. II. Effect on apparent viscosity of blood

The apparent viscosity of blood strongly increases at low shear in rotational viscometers, this phenomenon is based on the reversible formation of red cell aggregates. The magnitude of this increase strongly depends on the hematocrit value, on plasma viscosity and lastly on the microrheological properties of the aggregates. The independent measurement of the microrheological behavior and the effects on viscosity allows a detailed analysis of the hemodynamic effects of red cell aggregates under defined flow conditions in vivo. The comparative analysis shows that the conventional viscometry strongly underestimates the rheological differences between normal and pathologically intensified aggregation. Based on detailed analysis under defined flow conditions in vitro, the biological significance of viscometric results and the hemodynamic relevance of red cell aggregates are discussed.

Red cell aggregation in blood flow. I. New methods of quantification

The rheological behavior of normal and pathological red cell aggregates in viscometric flow (artificial flow in cone plate chamber) is studied by direct microscopy, (rheoscopy) viscometry and photometry. Marked differences between normal and pathological blood are measured in the microrheological properties of red cell aggregates; only discreet differences are measured by blood viscometry (macrorheology). Both in normal and abnormal blood, red cell aggregation is a reversible process in the presence of adequate shear forces; their respective influences on apparent blood viscosity at low rates of shear are complex functions of shear rate, shear time, hematocrit and plasma viscosities. Pathological red cell aggregation (RCA) forms more rapidly and extensively than normal RCA. The pathological aggregates frequently have a tendency to grow at low rates of shear and they are highly shear resistant.

Microrheology and light transmission of blood. III. The velocity of red cell aggregate formation

The formation of primary (rouleaux) and secondary (rouleaux networks) RCA was studied by microcinematography (12 frames/sec) and photometry in a counterrotating "rheoscope" chamber. The blood was first subjected to rapid viscometric flow (460 sec-1, all RBC dispersed and aligned in flow) and then brought abruptly to full stop. In normal human blood, primary and secondary RCA occurred simultaneously, and were completed within 8 to 10 sec after stop. Blood from pregnant women at term, known for its pronounced red cell aggregation, shows a dissociation between the formation of short primary rouleaux (initiated even before full stop and completed 1-2 see thereafter) and secondary RCA completed 3-5 see after stop. RCA increases the light transmission of blood (measured by an increase in photovoltage V), the process and its first derivative (dV/dt equals I) can be recorded. After flow stop, there is an exponential decay of I(I equals t-I-o with e-lambda-t). The half time of this decay is recorded and correlated to the kinetics of red cell aggregate formation In human blood the half time of this process varies between 1.0 and 6.0 sec. In suspensions of human RBC in artificial plasmas, t-1/2 decreases with increasing concentration of fibrinogen and/or Dextran 250000, the second component appearing at concentrations above 500 mg-%. The method lend sitself for the quantification of RCA in small blood samples (20 mul).