RESUMEN

Knee osteoarthritis (OA) poses a significant health care burden globally, necessitating innovative therapeutic approaches. CCoat, a novel poly(2-[methacryloyloxy]ethyl phosphorylcholine) (pMPC)ylated liposome device, protects the cartilage surface of the joint from mechanical wear through an entropy-favored process. Two preclinical studies were performed to explore the safety of CCoat following repeated intra-articular (IA) injections into the knee joint (i.e., femorotibial joint) in Sprague-Dawley rats. The studies involved 2 or 3 IA injections, at an interval of 2 or 3 weeks, and an observation period of 1 or 13 weeks after the last injection. Assessments included clinical, histopathological, and immunofluorescent evaluations. In study 1, no mortality or abnormal clinical signs occurred. At 1 week post last injection, histopathology revealed minimal vacuolated macrophages beneath the synovial membrane, predominantly M2-like, indicating a nonadverse response. Immunofluorescent staining supported M2-like macrophage predominance. Study 2 confirmed these findings with no systemic effects over 13 weeks. Statistical analyses indicated no significant differences in body weight, clinical pathology, or organ weights compared with controls. Results affirming the safety of pMPCylated liposomes following repeated IA injections in rat. This novel lubricant coating approach shows promise in OA therapy, with this safety assessment supporting its potential clinical application.

Asunto(s)

RESUMEN

Drug delivery via nanovehicles is successfully employed in several clinical settings, yet bacterial infections, forming microbial communities in the form of biofilms, present a strong challenge to therapeutic treatment due to resistance to conventional antimicrobial therapies. Liposomes can provide a versatile drug-vector strategy for biofilm treatment, but are limited by the need to balance colloidal stability with biofilm penetration. We have discovered a liposomic functionalization strategy, using membrane-embedded moieties of poly[2-(methacryloyloxy)ethyl phosphorylcholine], pMPC, that overcomes this limitation. Such pMPCylation results in liposomic stability equivalent to current functionalization strategies (mostly PEGylation, the present gold-standard), but with strikingly improved cellular uptake and cargo conveyance. Fluorimetry, cryo-electron, and fluorescence microscopies reveal a far-enhanced antibiotic delivery to model Pseudomonas aeruginosa biofilms by pMPC-liposomes, followed by faster cytosolic cargo release, resulting in significantly greater biofilm eradication than either PEGylation or free drug. Moreover, this combination of techniques uncovers the molecular mechanism underlying the enhanced interaction with bacteria, indicating it arises from bridging by divalent ions of the zwitterionic groups on the pMPC moieties to the negatively charged lipopolysaccharide chains emanating from the bacterial membranes. Our results point to pMPCylation as a transformative strategy for liposomal functionalization, leading to next-generation delivery systems for biofilm treatment.

Asunto(s)

RESUMEN

Osteoarthritis (OA) can lead to a significant functional disability. Poly[2-(methacryloyloxy)ethyl phosphorylcholine] (pMPC) liposomes are a novel treatment modality for OA, intended to restore the natural lubrication properties of articular cartilage. Here, we report on two studies aimed to assess the local and systemic safety and toxicity of pMPCylated liposomes in comparison with physiological saline, in Sprague-Dawley (SD) rats and in sheep after a single intra-articular (IA) injection. The animals were sacrificed after 1 and 6 weeks (rats) and 3 and 6 weeks (sheep). No signs of toxicity or abnormal clinical findings were observed. Histopathological evaluation revealed no signs of reactivity or abnormal findings in the injected joints or in any other organs. In conclusion, a single IA injection of the pMPCylated liposomes demonstrated an excellent safety profile and did not result in local reactivity or systemic toxicity, thus supporting its further development for use in humans.

Asunto(s)

RESUMEN

Surface-attached layers of phosphatidylcholine (PC) lipid vesicles (liposomes) may reduce the friction coefficient µ (= force-to-slide/load) between the sliding surfaces down to µ ≈ 10-3-10-4 up to tens of atm contact pressures, as high as those in the major joints (hips or knees). Such friction reduction is attributed to hydration lubrication by the highly-hydrated phosphocholine head-groups exposed at the outer vesicle surfaces. It has been suggested therefore that intra-articular (IA) administration of liposomes as potential boundary lubricants may alleviate degenerative, friction-associated joint conditions such as osteoarthritis (OA), which is associated with insufficient lubrication at the articular cartilage surface. To overcome the problem, common to all nanoparticles, of rapid removal by the mononuclear phagocyte system, as well as to ensure long-term colloidal stability during storage, functionalizing liposomes with poly(ethylene glycol) moieties, PEGylation, is often used. Here we describe a different liposome functionalization approach, using poly(2-methacryloyloxyethyl phosphorylcholine), PMPC, moieties (strictly, lipid-PMPC conjugates), and compare the retention time in mice joints of such PMPCylated liposomes with otherwise-identical but PEGylated vesicles following IA administration. We find, using fluorescence labeling and in vivo optical imaging, that when PMPC-stabilized liposomes are injected into mice knee joints, there is a massive increase of the vesicles' retention half-life in the joints of about (4-5)-fold (ca. 300-400% increase in retention time) compared with the PEGylated liposomes (and some 100-fold longer than the retention time of intra-articularly injected hyaluronan or HA). Such PMPCylated liposomes are therefore promising candidates as potential long-lived boundary lubricants at the articular cartilage surface, with implication for friction-associated pathologies. Moreover, as lipid vesicles are well known to be efficient drug carriers, such long retention in the joints may enable analgesic or anti-inflammatory agents for joint pathologies to be more efficiently delivered via IA administration using PMPCylated liposomal vehicles relative to PEGylated ones.

Asunto(s)

RESUMEN

The lubrication of hydrogels arises from fluid or solvated surface phases. By contrast, the lubricity of articular cartilage, a complex biohydrogel, has been at least partially attributed to nonfluid, lipid-exposing boundary layers. We emulated this behavior in synthetic hydrogels by incorporating trace lipid concentrations to create a molecularly thin, lipid-based boundary layer that renews continuously. We observed a 80% to 99.3% reduction in friction and wear relative to the lipid-free gel, over a wide range of conditions. This effect persists when the gels are dried and then rehydrated. Our approach may provide a method for sustained, extreme lubrication of hydrogels in applications from tissue engineering to clinical diagnostics.

Asunto(s)

RESUMEN

We have prepared phosphatidylcholine (PC) vesicles (liposomes) incorporating a novel lipid/poly-phosphocholine conjugate. This both stabilizes the liposomes against aggregation (for example, during storage or when being delivered) and allows them to act as very efficient lubricating elements readily attaining superlubric performance (defined as coefficient of friction µ < 10-2) via hydration lubrication at physiological salt concentrations and pressures. In contrast, vesicles sterically protected by poly(ethylene glycol) chains (PEGylation), which is the general method of choice, while being equally stable to aggregation are much poorer lubricants under these conditions, which is attributed to the relatively poor hydration of the PEG. Our approach enables the use of PC liposomes as stable superlubrication vectors in potential biomedical applications.

Asunto(s)

RESUMEN

Hyaluronan (HA)-lipid layers on model (mica) surfaces massively reduce friction as the surfaces slide past each other, and have been proposed, together with lubricin, as the boundary layers accounting for the extreme lubrication of articular cartilage. The ability of such HA-lipid complexes to lubricate sliding biological tissues has not however been demonstrated. Here we show that HA-lipid layers on the surface of an intrasynovial tendon can strongly reduce the friction as the tendon slides within its sheath. We find a marked lubrication synergy when combining both HA and lipids at the tendon surface, relative to each component alone, further enhanced when the polysaccharide is functionalized to attach specifically to the tissue. Our results shed light on the lubricity of sliding biological tissues, and indicate a novel approach for lubricating surfaces such as tendons and, possibly, articular cartilage, important, respectively, for alleviating function impairment following tendon injury and repair, or in the context of osteoarthritis. STATEMENT OF SIGNIFICANCE: Lubrication breakdown between sliding biological tissues is responsible for pathologies ranging from dry eye syndrome to tendon-injury repair impairment and osteoarthritis. These are increasing with human longevity and impose a huge economic and societal burden. Here we show that synergy of hyaluronan and lipids, molecules which are central components of synovial joints and of the tendon/sheath system, can strongly reduce friction between sliding biological tissues (the extrasynovial tendon sliding in its sheath), relative to untreated tissue or to either component on its own. Our results point to the molecular origins of the very low friction in healthy tendons and synovial joints, as well as to novel treatments of lubrication breakdown in these organs.

Asunto(s)

RESUMEN

Hyaluronan, lubricin and phospholipids, molecules ubiquitous in synovial joints, such as hips and knees, have separately been invoked as the lubricants responsible for the remarkable lubrication of articular cartilage; but alone, these molecules cannot explain the extremely low friction at the high pressures of such joints. We find that surface-anchored hyaluronan molecules complex synergistically with phosphatidylcholine lipids present in joints to form a boundary lubricating layer, which, with coefficient of friction µ≈0.001 at pressures to over 100 atm, has a frictional behaviour resembling that of articular cartilage in the major joints. Our findings point to a scenario where each of the molecules has a different role but must act together with the others: hyaluronan, anchored at the outer surface of articular cartilage by lubricin molecules, complexes with joint phosphatidylcholines to provide the extreme lubrication of synovial joints via the hydration-lubrication mechanism.

Asunto(s)

RESUMEN

Glucosamine sulfate (GAS) is a charged monosaccharide molecule that is widely used as a treatment for osteoarthritis, a joint disease related to friction and lubrication of articular cartilage. Using a surface force balance, we examine the effect of GAS on normal and, particularly, on shear (frictional) interactions between surfaces in an aqueous environment coated with small unilamellar vesicles (SUVs), or liposomes, of hydrogenated soy phosphatidylcholine (HSPC). We examine the effect of GAS solution, pure water, and salt solution (0.15 M NaNO3) both inside and outside the vesicles. Cryoscanning electron microscopy shows a closely packed layer of liposomes whose morphology is affected only slightly by GAS. HSPC-SUVs with encapsulated GAS are stable upon shear at high compressions (>100 atm) and provide very good lubrication when immersed both in pure water and physiological-level salt solutions (in the latter case, the liposomes are exceptionally stable and lubricious up to >400 atm). The low friction is attributed to several parameters based on the hydration lubrication mechanism.

Asunto(s)

RESUMEN

In this paper we review recent work (Goldberg et al., 2011a,b) on a new use for phosphatidylcholine liposomes: as ultra-efficient boundary lubricants at up to the highest physiological pressures. Using a surface force balance, we have measured the normal and shear interactions as a function of surface separation between layers of hydrogenated soy phophatidylcholine (HSPC) small unilamellar vesicles (SUVs) adsorbed from dispersion, at both pure water and physiologically high salt concentrations of 0.15 M NaNO(3). Cryo-Scanning Electron Microscopy shows each surface to be coated by a close-packed HSPC-SUV layer with an over-layer of liposomes on top. The shear forces reveal strikingly low friction coefficients down to 2×10(-5) in pure water system or 6×10(-4) in the 150 mM salt system, up to contact pressures of at least 12 MPa (pure water) or 6 MPa (high salt), comparable with those in the major joints. This low friction is attributed to the hydration lubrication mechanism arising from rubbing of the highly hydrated phosphocholine-headgroup layers exposed at the outer surface of each liposome, and provides support for the conjecture that phospholipids may play a significant role in biological lubrication.

Asunto(s)

RESUMEN

Lubrication by hydration shells that surround, and are firmly attached to, charges in water, and yet are highly fluid, provide a new mode for the extreme reduction of friction in aqueous media. We report new measurements, using a mica surface-force balance, on several different systems which exhibit hydration lubrication, extending earlier studies significantly to shed new light on the nature and limits of this mechanism. These include lubrication by hydrated ions trapped between charged surfaces, and boundary lubrication by surfactants, by polyzwitterionic brushes and by close-packed layers of phosphatidylcholine vesicles. Sliding friction coefficients as low as 10(-4) or even lower, and mean contact pressures of up to 17 MPa or higher are indicated. This suggests that the hydration lubrication mechanism may underlie low-friction sliding in biological systems, in which such pressures are rarely exceeded.

Asunto(s)

RESUMEN

Using a surface force balance, we measured normal and shear interactions as a function of surface separation between layers of hydrogenated soy phosphatidylcholine (HSPC) small unilamellar vesicles (SUVs) adsorbed from dispersion at physiologically high salt concentrations (0.15 M NaNO3). Cryo-scanning electron microscopy shows that each surface is coated by a close-packed HSPC-SUV layer with an overlayer of liposomes on top. A clear attractive interaction between the liposome layers is seen upon approach and separation, followed by a steric repulsion upon further compression. The shear forces reveal low friction coefficients (µ = 0.008-0.0006) up to contact pressures of at least 6 MPa, comparable to those observed in the major joints. The spread in µ-values may be qualitatively accounted for by different local liposome structure at different contact points, suggesting that the intrinsic friction of the HSPC-SUV layers at this salt concentration is closer to the lower limit (µ = ~0.0006). This low friction is attributed to the hydration lubrication mechanism arising from rubbing of the hydrated phosphocholine-headgroup layers exposed at the outer surface of each liposome, and provides support for the conjecture that phospholipids may play a significant role in biological lubrication.

Asunto(s)

RESUMEN

Prompted by the recent discovery that water and aqueous monovalent Na+ solutions remain fluid-like when confined to films of a few molecular layers between mica surfaces,[Raviv et al., Nature, 2001, 413, 51-54; and Raviv and Klein, Science, 2002, 297, 1540-1543] we now extend the previous study by comparing the shear- and normal-force properties of 0.1 M Na+, Cs+ and Ni2+ salt solutions which demonstrate a diverse range of behaviours under confinement. In the case of hydrated Na+ we extend the previous study to higher pressures, up to approximately 10 atmospheres, and record similar fluidity of the hydration layers at these elevated pressures. Aqueous Cs+ films under confinement between mica sheets have been found to be unable to support an applied load--that is to say they do not demonstrate any hydration repulsion regime--as a result of their lower hydration energy [see Goldberg et al., Phys. Chem. Chem. Phys., 2008, 10, 4939-4945] which contrasts with the properties of Na+. We show that 0.1 M Ni2+ solution remains close to its bulk viscosity down to nanometre thin films, but does not demonstrate a hydration repulsion. By comparing the properties of this range of cations, with differing valency and hydration, we aim to examine the conditions under which ions serve as effective lubricants and what we call the 'hydration lubrication' mechanism.

Asunto(s)

RESUMEN

Using a surface force balance, we have measured the normal and shear forces between mica surfaces across aqueous caesium salt solutions (CsNO(3) and CsCl) up to 100 mM concentrations. In contrast to all other alkali metal ions at these concentrations, we find no evidence of hydration repulsion between the mica surfaces on close approach: the surfaces appear to be largely neutralized by condensation of the Cs ions onto the charged lattice sites, and are attracted on approach into adhesive contact. The contact separation at adhesion indicates that the condensed Cs ions protrude by 0.3 +/- 0.2 nm from each surface, an observation supported both by the relatively weak adhesion energies between the surfaces, and the relatively weak frictional yield stress when they are made to slide past each other. These observations show directly that the hydration shells about the Cs(+) ions are removed as the ions condense into the charged surface lattice. This effect is attributed to the low energies-resulting from their large ionic radius-required for dehydration of these ions.

RESUMEN

Using a surface force balance, we have measured normal and shear interactions between mica surfaces across pure water and across 0.1 M aqueous solutions of LiNO3, NaNO3, KNO3, and CsNO3, both prior to adding polymer and following addition of 1.5 x 10(-4) w/w poly(ethylene oxide) (PEO, Mw = 170 kD) and overnight incubation. Our results reveal that while the PEO adsorbs strongly from the KNO3 and CsNO3 solutions, unexpectedly it does not adsorb at all from the LiNO3 and NaNO3 salt solutions. We attribute this to the different nature of the hydration layers about the alkali metal ions: these favor liganding to the negatively charged mica surface of the etheric -O- group on the ethylene oxide monomer for the case of the more weakly hydrated K+ and Cs+, but not for the case of Na+ or Li+ with their more strongly bound water. A simple model relating the electrostatic energy changes occurring upon such liganding to the experimentally measured hydration energies of the different alkali metal ions supports this attribution.

Asunto(s)