Preparation and surface characterization of carboxymethylchitin-incorporated submicron bilayer-lipid membrane artificial cells (liposomes) encapsulating hemoglobin

Research of storable and ready-to-use artificial red blood cells (hemoglobin vesicles) for emergency medicine and other clinical applications

Hemoglobin (Hb) is the most abundant protein in blood, with concentration of about 12-15 g/dl. The highly concentrated Hb solution (35 g/dl) is compartmentalized in red blood cells (RBCs). Once Hb is released from RBCs by hemolysis during blood circulation, it induces renal and cardiovascular toxicities. To date, hemoglobin-based oxygen carriers of various types have been developed as blood substitutes to mitigate the Hb toxicities. One method is Hb encapsulation in phospholipid vesicles (liposomes). Although the Hb toxicity can be shielded, it is equally important to ensure the biocompatibility of the liposomal membrane. We have developed Hb-vesicles (HbV). A new encapsulation method using a rotation-revolution mixer which enabled efficient production of HbV with a high yield has considerably facilitated R&D of HbV. Along with our academic consortium, we have studied the preclinical safety and efficacy of HbV extensively as a transfusion alternative, and finally conducted a phase I clinical trial. Moreover, carbonyl-HbV and met-HbV are developed respectively for an anti-inflammatory and anti-oxidative agent and an antidote for poisons. This review paper specifically presents past trials of liposome encapsulated Hb, biocompatible lipid bilayer membranes, and efficient HbV preparation methods, in addition to potential clinical applications of HbV based on results of our in vivo studies.

Adsorption of chitin derivatives onto liposomes: optimization of adsorption conditions

A 2(4) factorial design is used to optimize the adsorption conditions of the hydrophilic anionic polyelectrolytes. Carboxymethylchitin (CMC) and Carboxymethyl/Glycolchitin (CO) onto liposomes at physiological ionic strength (I) and pH using phosphate buffered saline (PBS, I = 154 mM, pH = 7.4). Positive ([+]) or high surface affinity liposomes (DSPC:CHOL:DMTAP, 5:4:1), and Neutral ([N]) or low surface affinity liposomes (DSPC:CHOL, 1:1) were used as adsorption surfaces. Results of the calculations of the main effects indicate that polymer molecular weight (mwt), Surface Affinity (S), Number of Adsorption Shots (Sh), Temperature (T), and the combinations mwt x S, mwt x Sh are the most important process parameters. Results of a study conducted at T = 37 degrees C show that no loss occurs from the positive surface at the highest particle concentration, Np = 4.043 x 10(11). Finally, the extent of polymer-induced particle aggregation is decreased when the diameter of the uncoated liposomes is doubled from 0.22 to 0.45 micron. These results are as expected, given the stiffness and the dimensions of the macromolecules.

Kinetic aspects of polyelectrolyte adsorption: adsorption of chitin derivatives onto liposomes as a model system

Carboxymethylchitin (CMC) and Carboxymethyl/Glycolchitin (CO) have been adsorbed onto liposomes at physiological ionic strength (I) and pH using phosphate buffer saline (PBS, I = 154 mM, pH = 7.4). Adsorption isotherms at different polymer weight average molecular weights (Mw), for Positive ([+]) or high surface affinity liposomes (DSPC:CHOL:DMTAP, 5:4:1), and Neutral ([N]) or low surface affinity liposomes (DSPC:CHOL, 1:1), have been obtained at T = 25 degrees C. For all CMCs, the adsorbed amount increases with polymer concentration ([P]zero) and no true plateau is observed. The CMC Mw = 4.19 x 10(5) adsorbed on a positive surface fits Langmuir kinetics with maximal coverage gamma max = 325.4 micrograms/mg (polymer/lipid), and inverse of equilibrium constant K* = 4.743 x 10(-4) mg/ml. For all isotherms the predicted amount of polymer needed to coat the entire surface based on the Radius of Gyration (Rg) is inferior to the amount adsorbed. This fact in conjunction with the dependence of gamma max on the number of adsorption shots, suggests that the adsorption is not thermodynamically but kinetically controlled.

The importance of standardization of carboxymethylchitin concentration by the dye-binding capacity of alcian blue before adsorption on liposomes

A new method based on the measurement of the relative dye-binding capacity of Alcian Blue to carboxymethylchitin (CMC) at various molecular weights (MW) has been developed to facilitate the standardization of the initial polyelectrolyte concentration. In the absence of standardization, non-reproducible adsorption patterns are encountered during the adsorption of the MW CMC on neutral and positively charged liposomes. This method is sensitive down to a concentration of 5 mu g/ml of polymer in water. Static Light Scattering (SLS) measurements are used to obtain the weight average molecular weight (Mw) and the size of the polyelectrolyte (Rg) and overlap concentrations (c*). The Mws are then used to determine the constants K and a of the Mark-Houwink equation which are 1.65 x 10(-2) dl/g and 0.4701, respectively, evaluated at kappa = 0.154 M, pH = 7.4 and T = 25 degrees C. The critical electrolyte concentration decreases with molecular weight for Mws ranging from 5.0 x 10(4)-1.2 x 10(6). The dye-binding capacity changes with the molecular weight distribution of the polyelectrolyte demonstrating the sensitivity of this technique to polydispersity.

Purification and quantitative determination of carboxymethylchitin incorporation into submicron bilayer-lipid membrane artificial cells (liposomes) encapsulating hemoglobin

The separation of carboxymethylchitin-coated hemoglobin-loaded liposomes (CMC-LEHb)s from the non-adsorbed CMC has been achieved by gel chromatography. This purification takes place at the physiological pH of 7.4 favoring HbO2 preservation. A comparative study between experimental techniques for the quantitative determination of the absorption of carboxymethylchitin (CMC) onto liposomes encapsulating hemoglobin (LEHb)s has been conducted. Results suggest that FT-IR spectroscopy gives a more accurate quantitative absorption index while the chitinase-based enzymatic assay should be used as a qualitative detection tool. Quantitative bilayer and surface characterization show that the RBC membrane composition has been closely simulated by that of CMC-LEHbs in terms of total lipids and carbohydrates at 87.8% (phospholipids and cholesterol) and 12.2% CMC respectively.

Blood substitutes based on modified hemoglobin prepared by encapsulation or crosslinking: an overview

Modified hemoglobin consists of (1) encapsulated hemoglobin and (2) crosslinked hemoglobin (polyhemoglobin, intramolecularly cross-linked hemoglobin and conjugated hemoglobin). There have been new advances in all types of modified hemoglobins. Modified hemoglobins are effective in hemorrhagic shock. However, it is important to define hemorrhagic shock models and experimental designs. Important progress has been made in research on vasoactivities, organ perfusion, organ preservation, biodistribution, hematology, complement activation immunology and other areas. A preclinical screening test may bridge the gap between animal safety studies and injection into human. Potential new sources of hemoglobin included bovine hemoglobin, recombinant human hemoglobin and synthetic heme.