Omolola Eniola-Adefeso

Potential role of size and hemodynamics in the efficacy of vascular-targeted spherical drug carriers

Targeting of drug carriers to the vascular wall is of interest for localized delivery of therapeutics in many human diseases. Nanometer-sized spherical particles are widely proposed for use as carriers for vascular targeting, yet very little evidence has been presented as to their ability to interact with the vascular wall. Thus, this work focuses on elucidating the effect of particle size along with hemodynamics, blood rheology, and vessel size on the adhesion efficiency of targeted polymeric spheres to inflamed endothelium in vitro via parallel plate flow chamber assays. We find that the binding efficiency of spheres to the endothelium from blood flow generally increased with increasing particle size, wall shear rate and channel height for particle sizes from 100 nm up to 10 microm. However, nano-sized particles showed minimal adhesion to the endothelium from blood flow in horizontal (gravity or anti-gravity direction) and vertical channels on the order of small to medium-sized venules and arteries when compared to micron-sized spheres. Furthermore, adhesion of nanospheres was not enhanced with pulsatility in flow. Overall, the presented data suggests that spheres 2-5 microm in size are optimal for targeting the wall in medium to large vessels relevant in several cardiovascular diseases.

Targeting therapeutics to the vascular wall in atherosclerosis–Carrier size matters

OBJECTIVE Vascular-targeted imaging and drug delivery systems are promising for the treatment of atherosclerosis due to the vast involvement of endothelium in the initiation and growth of plaque. Herein, we investigated the role of particle size in dictating the ability of vascular-targeted spherical particles to interact with the vascular wall (VW) from pulsatile and recirculating human blood flow relevant in atherosclerosis. METHODS In vitro parallel plate flow chambers (PPFC) with straight or vertical step channel were used to examine the localization and binding efficiency of inflammation-targeted polymeric spheres sized from 0.2 to 5 μm to inflamed endothelium from disturbed reconstituted and whole blood flow. Apolipoprotein deficient mice were used to study particle localization and binding to plaque in vivo. RESULTS The efficiency of particle binding in disturbed reconstituted blood flow increases as spherical diameter increases from 500 nm to 5 μm. No significant difference was observed between adhesion of 200 nm and 500 nm spheres. Binding efficiency for all particle size was enhanced in disturbed whole blood flow except adhesion of 5 μm in pulsatile whole blood. The adhesion trend in the in vivo model confirmed the binding pattern observed in in vitro assays. CONCLUSIONS The presented data shows that the binding efficiency of vascular-targeted drug carriers in blood flow is a function of particle size, wall shear rate, flow type, blood composition and ligand characteristics. Overall, the presented results suggest that micron-sized spherical particles (2 μm), not nanospheres, are optimal for vascular-targeted drug delivery applications in medium to large vessel relevant in atherosclerosis.

Particle-cell dynamics in human blood flow: Implications for vascular-targeted drug delivery

The outcome of vascular-targeted therapies is generally determined by how efficiently vascular-targeted carriers localize and adhere to the endothelial wall at the targeted site. This study investigates the impact of leukocytes, platelets and red blood cells on the margination of vascular-targeted polymeric nanospheres and microspheres under various physiological blood flow conditions. We report that red blood cells either promote or hinder particle adhesion to an endothelial wall in a parallel plate flow chamber depending on the blood flow pattern, hematocrit, and particle size. Leukocytes prevent microspheres - but not nanospheres - from adhering in laminar and pulsatile flows via (1) competition for the available binding space and (2) physical removal of previously bound spheres. In recirculating blood flow, the negative effect of leukocytes on particle adhesion is minimal for large microspheres in the disturbed flow region beyond the flow reattachment. Resting platelets were found to have no effect on particle binding likely due to their dimensions and minimal interaction with the endothelial wall. Overall, the findings of the present work would be critical for designing effective vascular-targeted carriers for imaging and drug delivery applications in several human diseases.

Fabrication of biodegradable spheroidal microparticles for drug delivery applications.

Particle shape, in addition to size, is becoming increasingly recognized as important in the design of drug carriers for in vivo use. However, few methods exist for fabricating non-spherical particles from biodegradable polymers. This work describes for the first time the fabrication of biodegradable spheroidal microparticles using the simple oil-in-water emulsion solvent evaporation technique (O/W ESE). Unloaded and paclitaxel-loaded spheroids were fabricated from poly(lactic-co-glycolic acid) (PLGA), and the shape and size of fabricated spheroids were manipulated by controlling fabrication process parameters including stir speed, aqueous and oil phase viscosity, aqueous phase pH, and the polymer molecular weight and end group. The presented data show that high aqueous phase viscosity, basic aqueous phase pH and hydrophilic polymer side chains and end groups are all conditions that favor the formation of spheroidal particles. The described technique is advantageous over methods currently described in the literature in its simplicity in setup, high particle yield and adaptability to a wide range of biodegradable polymers and therapeutics.

Shear Stress Modulation of IL-1β-Induced E-Selectin Expression in Human Endothelial Cells

Background Endothelial cells (ECs) are continuously exposed to hemodynamic forces imparted by blood flow. While it is known that endothelial behavior can be influenced by cytokine activation or fluid shear, the combined effects of these two independent agonists have yet to be fully elucidated. Methodology We investigated EC response to long-term inflammatory cues under physiologically relevant shear conditions via E-selectin expression where monolayers of human umbilical vein ECs were simultaneously exposed to laminar fluid shear and interleukin-1ß (shear-cytokine activation) in a parallel plate flow chamber. Results and Conclusion Naïve ECs exposed to shear-cytokine activation display significantly higher E-selectin expression for up to 24 hr relative to ECs activated in static (static-cytokine). Peak E-selectin expression occurred after 8–12 hr of continuous shear-cytokine activation contrary to the commonly observed 4–6 hr peak expression in ECs exposed to static-cytokine activation. Cells with some history of high shear conditioning exhibited either high or muted E-selectin expression depending on the durations of the shear pre-conditioning and the ensuing shear-cytokine activation. Overall, the presented data suggest that a high laminar shear enhances acute EC response to interleukin-1ß in naïve or shear-conditioned ECs as may be found in the pathological setting of ischemia/reperfusion injury while conferring rapid E-selectin downregulation to protect against chronic inflammation.

Plasma Protein Corona Modulates the Vascular Wall Interaction of Drug Carriers in a Material and Donor Specific Manner

The nanoscale plasma protein interaction with intravenously injected particulate carrier systems is known to modulate their organ distribution and clearance from the bloodstream. However, the role of this plasma protein interaction in prescribing the adhesion of carriers to the vascular wall remains relatively unknown. Here, we show that the adhesion of vascular-targeted poly(lactide-co-glycolic-acid) (PLGA) spheres to endothelial cells is significantly inhibited in human blood flow, with up to 90% reduction in adhesion observed relative to adhesion in simple buffer flow, depending on the particle size and the magnitude and pattern of blood flow. This reduced PLGA adhesion in blood flow is linked to the adsorption of certain high molecular weight plasma proteins on PLGA and is donor specific, where large reductions in particle adhesion in blood flow (>80% relative to buffer) is seen with ∼60% of unique donor bloods while others exhibit moderate to no reductions. The depletion of high molecular weight immunoglobulins from plasma is shown to successfully restore PLGA vascular wall adhesion. The observed plasma protein effect on PLGA is likely due to material characteristics since the effect is not replicated with polystyrene or silica spheres. These particles effectively adhere to the endothelium at a higher level in blood over buffer flow. Overall, understanding how distinct plasma proteins modulate the vascular wall interaction of vascular-targeted carriers of different material characteristics would allow for the design of highly functional delivery vehicles for the treatment of many serious human diseases.

Effect of PEGylation on ligand-based targeting of drug carriers to the vascular wall in blood flow.

The blood vessel wall plays a prominent role in the development of many life-threatening diseases and as such is an attractive target for treatment. To target diseased tissue, particulate drug carriers often have their surfaces modified with antibodies or epitopes specific to vascular wall-expressed molecules, along with poly(ethylene glycol) (PEG) to improve carrier blood circulation time. However, little is known about the effect of poly(ethylene glycol) on carrier adhesion dynamics-specifically in blood flow. Here we examine the influence of different molecular weight PEG spacers on particle adhesion in blood flow. Anti-ICAM-1 or Sialyl Lewis(a) were grafted onto polystyrene 2 μm and 500 nm spheres via PEG spacers and perfused in blood over activated endothelial cells at physiological shear conditions. PEG spacers were shown to improve, reduce, or have no effect on the binding density of targeted-carriers depending on the PEG surface conformation, shear rate, and targeting moiety.

Dense nanoparticles exhibit enhanced vascular wall targeting over neutrally buoyant nanoparticles in human blood flow.

For vascular-targeting carrier (VTC) systems to be effective, carriers must be able to localize and adhere to the vascular wall at the target site. Research suggests that neutrally buoyant nanoparticles are limited by their inability to localize to the endothelium, making them sub-optimal as carriers. This study examines whether particle density can be exploited to improve the targeting (localization and adhesion) efficiency of nanospheres to the vasculature. Silica spheres with 500 nm diameter, which have a density roughly twice that of blood, exhibit improved adhesion to inflamed endothelium in an in vitro model of human vasculature compared to neutrally buoyant polystyrene spheres of the same size. Silica spheres also display better near-wall localization in the presence of red blood cells than they do in pure buffer, likely resulting in the observed improvement in adhesion. Titania spheres (4 times more dense than blood) adhere at levels higher than polystyrene, but only in conditions when gravity or centrifugal force acts in the direction of adhesion. In light of the wide array of materials proposed for use as carrier systems for drug delivery and diagnostics, particle density may be a useful tool for improving the targeting of diseased tissues.

Effect of Variation in hemorheology between human and animal blood on the binding efficacy of vascular-targeted carriers

Animal models are extensively used to evaluate the in vivo functionality of novel drug delivery systems (DDS). However, many variations likely exist in vivo between the animals and human physiological environment that significantly alter results obtained with animal models relative to human system. To date, it is not clear if the variation in hemorheology and hemodynamics between common animal and human models affect the functionality of DDS. This study investigates the role of hemorheology of humans and various animal models in dictating the binding efficiency of model vascular-targeted carriers (VTCs) to the wall in physiological blood flows. Specifically, the adhesion of sLeA-coated nano- and micro-spheres to inflamed endothelial cells monolayers were conducted via a parallel plate flow chamber assay with steady and disturbed red blood cells (RBCs)-in-buffer and whole blood flows of common animal models. Our results suggest that the ratio of carrier size to RBC size dictate particle binding in blood flow. Additionally, the presence of white blood cells affects the trend of particle adhesion depending on the animal species. Overall, this work sheds light on some deviation in VTC vascular wall interaction results obtained with in vivo animal experimentation from expected outcome and efficiency in vivo in human.

Differential Impact of Plasma Proteins on the Adhesion Efficiency of Vascular-Targeted Carriers (VTCs) in Blood of Common Laboratory Animals.

Vascular-targeted carrier (VTC) interaction with human plasma is known to reduce targeted adhesion efficiency in vitro. However, the role of plasma proteins on the adhesion efficiency of VTCs in laboratory animals remains unknown. Here, in vitro blood flow assays are used to explore the effects of plasma from mouse, rabbit, and porcine on VTC adhesion. Porcine blood exhibited a strong negative plasma effect on VTC adhesion while no significant plasma effect was found with rabbit and mouse blood. A brush density poly(ethylene glycol) (PEG) on VTCs was effective at improving adhesion of microsized, but not nanosized, VTCs in porcine blood. Overall, the results suggest that porcine models, as opposed to mouse, can serve as better models in preclinical research for predicting the in vivo functionality of VTCs for use in humans. These considerations hold great importance for the design of various pharmaceutical products and development of reliable drug delivery systems.