Metabolic approaches to studies on diabetic microangiopathy

Recent Advances in Computational Modeling of Biomechanics and Biorheology of Red Blood Cells in Diabetes

Diabetes mellitus, a metabolic disease characterized by chronically elevated blood glucose levels, affects about 29 million Americans and more than 422 million adults all over the world. Particularly, type 2 diabetes mellitus (T2DM) accounts for 90-95% of the cases of vascular disease and its prevalence is increasing due to the rising obesity rates in modern societies. Although multiple factors associated with diabetes, such as reduced red blood cell (RBC) deformability, enhanced RBC aggregation and adhesion to the endothelium, as well as elevated blood viscosity are thought to contribute to the hemodynamic impairment and vascular occlusion, clinical or experimental studies cannot directly quantify the contributions of these factors to the abnormal hematology in T2DM. Recently, computational modeling has been employed to dissect the impacts of the aberrant biomechanics of diabetic RBCs and their adverse effects on microcirculation. In this review, we summarize the recent advances in the developments and applications of computational models in investigating the abnormal properties of diabetic blood from the cellular level to the vascular level. We expect that this review will motivate and steer the development of new models in this area and shift the attention of the community from conventional laboratory studies to combined experimental and computational investigations, aiming to provide new inspirations for the development of advanced tools to improve our understanding of the pathogenesis and pathology of T2DM.

Quantifying Fibrinogen-Dependent Aggregation of Red Blood Cells in Type 2 Diabetes Mellitus

Fibrinogen is regarded as the main glycoprotein in the aggregation of red blood cells (RBCs), a normally occurring phenomenon that has a major impact on blood rheology and hemodynamics, especially under pathological conditions, including type 2 diabetes mellitus (T2DM). In this study, we investigate the fibrinogen-dependent aggregation dynamics of T2DM RBCs through patient-specific predictive computational simulations that invoke key parameters derived from microfluidic experiments. We first calibrate our model parameters at the doublet (a rouleau consisting of two aggregated RBCs) level for healthy blood samples by matching the detaching force required to fully separate RBC doublets with measurements using atomic force microscopy and optical tweezers. Using results from companion microfluidic experiments that also provide in vitro quantitative information on cell-cell adhesive dynamics, we then quantify the rouleau dissociation dynamics at the doublet and multiplet (a rouleau consisting of three or more aggregated RBCs) levels for obese patients with or without T2DM. Specifically, we examine the rouleau breakup rate when it passes through microgates at doublet level and investigate the effect of rouleau alignment in altering its breakup pattern at multiplet level. This study seamlessly integrates in vitro experiments and simulations and consequently enhances our understanding of the complex cell-cell interaction, highlighting the importance of the aggregation and disaggregation dynamics of RBCs in patients at increased risk of microvascular complications.

Structural and functional consequences of increased tubulin glycosylation in diabetes mellitus

The extent of in vitro nonenzymatic glycosylation of purified rat brain tubulin was dependent on time and glucose concentration. Tubulin glycosylation profoundly inhibited GTP-dependent tubulin polymerization. Electron microscopy and NaDodSO4/polyacrylamide gel electrophoresis showed that glycosylated tubulin forms high molecular weight amorphous aggregates that are not disrupted by detergents or reducing agents. The amount of covalently bound NaB3H4-reducible sugars in tubulin recovered from brain of streptozotocin-induced diabetic rats was dramatically increased as compared with tubulin recovered from normal rat brain. Moreover, tubulin recovered from diabetic rat brain exhibited less GTP-induced polymerization than tubulin from nondiabetic controls. The possible implications of these data for diabetic neuropathy are discussed.

Studies of retinopathy and the plasma co-factor of platelet hyperaggregation in type 1 (insulin-dependent) diabetic children

Only one out of 73 children with young-onset Type 1 (insulin-dependent) diabetes for less than 10 years had retinopathy detectable with fluorescein retinal angiography. Although these fluorescent studies were normal, retinal abnormalities were detected in 19 out of 53 patients by electro-retinography and in four out of 28 patients by the 100-hue colour test. We were unable to confirm recent reports indicating that most Type 1 diabetic patients have retinopathy detectable by fluorescein angiography. The diabetic plasma co-factor induces normal platelets to hyperaggregate in vitro. Plasma co-factor activities in adult diabetic patients have previously been shown to correlate with the degree of hyperaggregation, although in general, only those patients with severe retinopathy or nephropathy have high plasma activities. The plasma activities of 192 Type 1 diabetic patients were significantly higher than those of normal subjects (p less than 0.01). Of ten children with markedly elevated activities, nine did not have retinopathy.

Plasma beta-thromboglobulin in diabetes mellitus

Plasma beta-thromboglobulin was measured, using the Edinburgh radioimmunoassay technique and anticoagulant mixture (containing prostaglandin E1) in 61 normal subjects, 67 diabetics with and 54 diabetics without microangiopathic complications. Plasma beta-thromboglobulin was significantly higher in the diabetic patients (p < 0.01) but there was no significant difference between the two diabetic groups. Twenty-six normal subjects, 27 diabetics with and 39 diabetics without complications were studied further by measuring beta-thromboglobulin in four different ways using two different radioimmunoassay techniques and two anticoagulant mixtures (with and without prostaglandin E1). The Edinburgh assay gave a value 1.97 times that obtained with the Amersham assay, and the Edinburgh anticoagulant a value 0.78 times that with the Amersham anticoagulant. Beta-thromboglobulin concentration in the meniscus layer was approximately twice that in the middle layer. The lower beta-thromboglobulin values obtained with the Edinburgh anticoagulant may result from a different sampling technique or from prevention of in vitro beta-thromboglobulin release, after venepuncture, by prostaglandin E1. Abnormal platelet behaviour in diabetes was confirmed although its role in the pathogenesis of microangiopathic complications remains unclear.

Prostaglandins in blood of diabetic versus non-diabetic humans

We have found a higher concentration of prostaglandins in blood from the diabetic patient under long-term indomethacin therapy as compared with blood from non-diabetics. These findings are generally (qualitatively) similar to previous reports with studies of blood serum from diabetic patients, not on indomethacin treatment, compared with non-diabetics. Certain rationale are presented in an effort to explain the reason why blood prostaglandins in the diabetic are not lowered when the patients are treated with a drug which is clearly established as a blocker of prostaglandin synthesis.