Delivery of loperamide across the blood-brain barrier with polysorbate 80-coated polybutylcyanoacrylate nanoparticles

Delivery of peptide and protein drugs over the blood-brain barrier

Peptide and protein (P/P) drugs have been identified as showing great promises for the treatment of various neurodegenerative diseases. A major challenge in this regard, however, is the delivery of P/P drugs over the blood-brain barrier (BBB). Intense research over the last 25 years has enabled a better understanding of the cellular and molecular transport mechanisms at the BBB, and several strategies for enhanced P/P drug delivery over the BBB have been developed and tested in preclinical and clinical-experimental research. Among them, technology-based approaches (comprising functionalized nanocarriers and liposomes) and pharmacological strategies (such as the use of carrier systems and chimeric peptide technology) appear to be the most promising ones. This review combines a comprehensive overview on the current understanding of the transport mechanisms at the BBB with promising selected strategies published so far that can be applied to facilitate enhanced P/P drug delivery over the BBB.

Nanotechnology approaches to crossing the blood-brain barrier and drug delivery to the CNS

Nanotechnologies are materials and devices that have a functional organization in at least one dimension on the nanometer (one billionth of a meter) scale, ranging from a few to about 100 nanometers. Nanoengineered materials and devices aimed at biologic applications and medicine in general, and neuroscience in particular, are designed fundamentally to interface and interact with cells and their tissues at the molecular level. One particularly important area of nanotechnology application to the central nervous system (CNS) is the development of technologies and approaches for delivering drugs and other small molecules such as genes, oligonucleotides, and contrast agents across the blood brain barrier (BBB). The BBB protects and isolates CNS structures (i.e. the brain and spinal cord) from the rest of the body, and creates a unique biochemical and immunological environment. Clinically, there are a number of scenarios where drugs or other small molecules need to gain access to the CNS following systemic administration, which necessitates being able to cross the BBB. Nanotechnologies can potentially be designed to carry out multiple specific functions at once or in a predefined sequence, an important requirement for the clinically successful delivery and use of drugs and other molecules to the CNS, and as such have a unique advantage over other complimentary technologies and methods. This brief review introduces emerging work in this area and summarizes a number of example applications to CNS cancers, gene therapy, and analgesia.

Biomaterials for the central nervous system

Biomaterials are widely used to help treat neurological disorders and/or improve functional recovery in the central nervous system (CNS). This article reviews the application of biomaterials in (i) shunting systems for hydrocephalus, (ii) cortical neural prosthetics, (iii) drug delivery in the CNS, (iv) hydrogel scaffolds for CNS repair, and (v) neural stem cell encapsulation for neurotrauma. The biological and material requirements for the biomaterials in these applications are discussed. The difficulties that the biomaterials might face in each application and the possible solutions are also reviewed in this article.

Body distribution of polysorbate‐80 and doxorubicin-loaded [14C]poly(butyl cyanoacrylate) nanoparticles after i.v. administration in rats

Previously it was shown that poly(butyl cyanoacrylate) (PBCA) nanoparticles coated with polysorbate 80 are able to cross the blood-brain barrier (BBB) after i.v. administration. The objective of the present study was to investigate the influence of polysorbate 80 and doxorubicin-loading on the body distribution in rats. The biodistribution profile and brain concentration of (14)C-radiolabeled PBCA nanoparticles, polysorbate 80 coated (14)C-PBCA nanoparticles, and doxorubicin-loaded (14)C-PBCA nanoparticles were determined by radioactivity counting after i.v. administration in rats. The (14)C-PBCA nanoparticles showed a significant accumulation in the organs of the reticuloendothelial system (RES). Polysorbate 80 coating of the (14)C-PBCA nanoparticles decreased this accumulation to about 40% after 1 h post injection. The brain concentration was increased about 2-fold after polysorbate 80-coating at this time point. The presence of doxorubicin in this preparation, however, decreased the brain concentration to levels similar to uncoated particles, probably caused by the positive charge of this compound. After longer time periods after injection the differences between the three preparations decreased.

Endocytosis at the blood–brain barrier: From basic understanding to drug delivery strategies

The blood-brain barrier (BBB) protects the central nervous system (CNS) from potentially harmful xenobiotics and endogenous molecules. Anatomically, it comprises the brain microvasculature whose functionality is nevertheless influenced by associated astrocyte, pericyte and neuronal cells. The highly restrictive paracellular pathway within brain microvasculature restricts significant CNS penetration to only those drugs whose physicochemical properties afford ready penetration into hydrophobic cell membranes or are capable of exploiting endogenous active transport processes such as solute carriers or endocytosis pathways. Endocytosis at the BBB is an essential pathway by which the brain obtains its nutrients and affords communication with the periphery. The development of strategies to exploit these endocytic pathways for the purposes of drug delivery to the CNS is still an immature field although some impressive results have been documented with the targeting of particular receptors. This current article initially provides an overview of general endocytosis processes and pathways showing evidence of their functional existence within the BBB. Subsequent sections provide, in an entity-specific manner, comprehensive reviews on BBB transport investigations of endocytosis involving: transferrin and the targeting of the transferrin receptor; hormones; cytokines; cell penetrating peptides; microorganisms and toxins, and nanoparticles aimed at more effectively delivering drugs to the CNS.

Drug delivery and nanoparticles:applications and hazards

The use of nanotechnology in medicine and more specifically drug delivery is set to spread rapidly. Currently many substances are under investigation for drug delivery and more specifically for cancer therapy. Interestingly pharmaceutical sciences are using nanoparticles to reduce toxicity and side effects of drugs and up to recently did not realize that carrier systems themselves may impose risks to the patient. The kind of hazards that are introduced by using nanoparticles for drug delivery are beyond that posed by conventional hazards imposed by chemicals in classical delivery matrices. For nanoparticles the knowledge on particle toxicity as obtained in inhalation toxicity shows the way how to investigate the potential hazards of nanoparticles. The toxicology of particulate matter differs from toxicology of substances as the composing chemical(s) may or may not be soluble in biological matrices, thus influencing greatly the potential exposure of various internal organs. This may vary from a rather high local exposure in the lungs and a low or neglectable exposure for other organ systems after inhalation. However, absorbed species may also influence the potential toxicity of the inhaled particles. For nanoparticles the situation is different as their size opens the potential for crossing the various biological barriers within the body. From a positive viewpoint, especially the potential to cross the blood brain barrier may open new ways for drug delivery into the brain. In addition, the nanosize also allows for access into the cell and various cellular compartments including the nucleus. A multitude of substances are currently under investigation for the preparation of nanoparticles for drug delivery, varying from biological substances like albumin, gelatine and phospholipids for liposomes, and more substances of a chemical nature like various polymers and solid metal containing nanoparticles. It is obvious that the potential interaction with tissues and cells, and the potential toxicity, greatly depends on the actual composition of the nanoparticle formulation. This paper provides an overview on some of the currently used systems for drug delivery. Besides the potential beneficial use also attention is drawn to the questions how we should proceed with the safety evaluation of the nanoparticle formulations for drug delivery. For such testing the lessons learned from particle toxicity as applied in inhalation toxicology may be of use. Although for pharmaceutical use the current requirements seem to be adequate to detect most of the adverse effects of nanoparticle formulations, it can not be expected that all aspects of nanoparticle toxicology will be detected. So, probably additional more specific testing would be needed.

Development of a smart nano-vehicle to target cerebrovascular amyloid deposits and brain parenchymal plaques observed in Alzheimer's disease and cerebral amyloid angiopathy

PURPOSE

To design a smart nano-vehicle (SNV) capable of permeating the blood-brain barrier (BBB) to target cerebrovascular amyloid formed in both Alzheimer's disease (AD) and cerebrovascular amyloid angiopathy (CAA).

METHODS

SNV consists of a chitosan polymeric core prepared through ionic gelation with tripolyphosphate. A polyamine modified F(ab') portion of IgG4.1, an anti-amyloid antibody, was coated as a biosensor on the SNV surface. A similar polymeric core coated with bovine serum albumin (BSA) served as a control nano-vehicle (CNV). The BBB uptake of (125)I-SNVs and (125)I-CNVs was evaluated in mice. The uptake and transcytosis of SNVs and CNVs across bovine brain microvascular endothelial cells (BBMECs) was evaluated using flow cytometry and confocal microscopy.

RESULTS

Plasma clearance of (125)I-SNVs was nine times higher than that of the (125)I-CNVs. However, the uptake of (125)I-SNVs in various brain regions was about 8 to 11 times higher than that of (125)I-CNVs. The uptake of FITC-BSA loaded SNVs in BBMECs was twice the uptake of FITC-BSA loaded CNVs. Confocal micrographs demonstrated the uptake and transcytosis of Alexa Fluor 647 labeled SNVs, but not CNVs, across the BBMEC monolayer.

CONCLUSIONS

SNVs are capable of carrying a payload of model protein across the BBB to target cerebral amyloid.

An ion pairing approach to increase the loading of hydrophilic and lipophilic drugs into PEGylated PLGA nanoparticles

The aim of this study was to enhance the loading of dalargin (enkephalin derivatives) a hydrophilic drug and loperamide HCl (non-opiate antidiarrheal agent) a lipophilic drug candidates within PEGylated nanoparticles. A novel nanoencapsulation method based on the concept of s/o/w and ion pairing followed by solvent diffusion was adopted. The copolymers with three different mPEG densities (5%, 12% and 17%) were employed separately in combination with two different grades of dextran sulphate (DS) 5000 and 500,000 MW in the preparations. Nanoparticles prepared from copolymers with increasing mPEG densities, showed an insignificant (p>0.05) increasing trend of drug loading, this was however significantly increased when DS5000 was included in the preparations. The particle size remains unchanged after dalargin loading, with no significant (p>0.05) alteration in the neutral zeta potential compared to that of the preparations without DS5000. Considering that a dalargin ion pair could also have a neutral charge, it was not advisable to conclude its incorporation, as the size remain unchanged, which would otherwise increase if an ion pair was incorporated within the core of nanoparticles. Therefore, it was expected that a dalargin ion pair might be located outside the core as a separate particulate entity or reside in the hydrophilic shell of the nanoparticles. A loperamide HCl ion pair showed significant (p<0.05) increase in size when incorporated; at the same time it provided a neutral zeta potential despite adding negatively charged DS5000 in the preparation, hence it seemed encapsulated. Inclusion of DS500,000 in the preparation further increased the drug loading of dalargin and loperamide HCl. However, a significant (p<0.05) negative zeta potential was noted in both cases which suggested that excess charge was still available on the surface of nanoparticles which could trap further amounts of drug on the surface rather than inside the core of nanoparticles. During in vitro evaluation of drug loaded nanoparticles, dalargin released as quickly as free drug, when loperamide HCl showed almost burst free sustained release profile with respect to the release of their free drug solutions, suggested that ion pairing approach was more pronounced for loperamide HCl formulation.

Drug delivery to the spinal cord tagged with nanowire enhances neuroprotective efficacy and functional recovery following trauma to the rat spinal cord

The possibility that drugs attached to innocuous nanowires enhance their delivery within the central nervous system (CNS) and thereby increase their therapeutic efficacy was examined in a rat model of spinal cord injury (SCI). Three compounds--AP173 (SCI-1), AP713 (SCI-2), and AP364 (SCI-5) (Acure Pharma, Uppsala, Sweden)--were tagged with TiO(2)-based nanowires using standard procedure. Normal compounds were used for comparison. SCI was produced by making a longitudinal incision into the right dorsal horn of the T10-T11 segments under Equithesin anesthesia. The compounds, either alone or tagged with nanowires, were applied topically within 5 to 10 min after SCI. In these rats, behavioral outcome, blood-spinal cord barrier (BSCB) permeability, edema formation, and cell injury were examined at 5 h after injury. Topical application of normal compounds in high quantity (10 microg in 20 microL) attenuated behavioral dysfunction (3 h after trauma), edema formation, and cell injury, as well as reducing BSCB permeability to Evans blue albumin and (131)I. These beneficial effects are most pronounced with AP713 (SCI-2) treatment. Interestingly, when these compounds were administered in identical conditions after tagging with nanowires, their beneficial effects on functional recovery and spinal cord pathology were further enhanced. However, topical administration of nanowires alone did not influence trauma-induced spinal cord pathology or motor functions. Taken together, our results, probably for the first time, indicate that drug delivery and therapeutic efficacy are enhanced when the compounds are administered with nanowires.

Neurosurgery in the realm of 10(-9), part 1: stardust and nanotechnology in neuroscience

Nanotechnology as a science has evolved from notions and speculation to emerge as a prominent combination of science and engineering that stands to impact innumerable aspects of technology. Medicine in general and neurosurgery in particular will benefit greatly in terms of improved diagnostic and therapeutic capabilities. The recent explosion in nanotechnology products, including diverse applications such as beauty products and medical contrast agents, has been accompanied by an ever increasing volume of literature. Recent articles from our institution provided an historical and scientific background of nanotechnology, with a purposeful focus on nanomedicine. Future applications of nanotechnology to neuroscience and neurosurgery were briefly addressed. The present article is the first of two that will further this discussion by providing specific details of current nanotechnology applications and research related to neuroscience and clinical neurosurgery. This article also provides relevant perspective in scale, history, economics, and toxicology. Topics of specific importance to developments or advances of technologies used by neuroscientists and neurosurgeons are presented. In addition, advances in the field of microelectromechanical systems technology are discussed. Although larger than nanoscale, microelectromechanical systems technologies will play an important role in the future of medicine and neurosurgery. The second article will discuss current nanotechnologies that are being, or will be in the near future, incorporated into the armamentarium of the neurosurgeon. The goal of these articles is to keep the neuroscience community abreast of current developments in nanotechnology, nanomedicine, and, in particular, nanoneurosurgery, and to present possibilities for future applications of nanotechnology. As applications of nanotechnology permeate all forms of scientific and medical research, clinical applications will continue to emerge. Physicians of the present and future must take an active role in shaping the design and research of nanotechnologies to ensure maximal clinical relevance and patient benefit.

Targeting the central nervous system: In vivo experiments with peptide-derivatized nanoparticles loaded with Loperamide and Rhodamine-123

Polymeric nanoparticles (Np) represent one of the most innovative non-invasive approaches for the drug delivery to the central nervous system (CNS). It is known that the ability of the Np to cross the Blood Brain Barrier (BBB), thus allowing the drugs to exert their pharmacological activity in the central nervous district, is linked to their surface characteristics. Recently it was shown that the biocompatible polyester poly(d,l-lactide-co-glycolide) (PLGA) derivatized with the peptide H(2)N-Gly-l-Phe-d-Thr-Gly-l-Phe-l-Leu-l-Ser(O-beta-d-Glucose)-CONH(2) [g7] was a useful starting material for the preparation of Np (g7-Np); moreover, fluorescent studies showed that these Np were able to cross the BBB. In this research, g-7 Np were loaded with Loperamide in order to assess their ability as drug carriers for CNS, and with Rhodamine-123, in order to qualitatively determine their biodistribution in different brain macro-areas. A pharmacological evidence is given that g7-Np are able to cross the BBB, ensuring, for the first time, a sustained release of the embedded drug, and that these Np are able to reach all the brain areas here examined. The ability to enter the CNS appears to be linked to the sequence of the peptidic moiety present on their surface.

Active targeting of brain tumors using nanocarriers

The delivery of drugs to brain tumors is limited by the presence of the blood-brain barrier (BBB) separating the blood from the cerebral parenchyma. An understanding of the specific mechanisms of the brain capillary endothelium has led to the development of various strategies to enhance the penetration of drugs into the brain tissue. Active targeting is a non-invasive approach, which consists in transporting drugs to target organs using site-specific ligands. Drug-loaded nanocarriers capable of recognizing brain capillary endothelial cells and cerebral tumoral cells have shown promising potential in oncology. Endogenous and chimeric ligands binding to carriers or receptors of the BBB have been directly or indirectly conjugated to nanocarriers. This review indexes the main targeted colloidal systems used for drug delivery to the brain. Their pharmacological behavior and their therapeutic effect are discussed.

Targeted nanoparticle-based drug delivery and diagnosis

Nanotechnology, or systems/device manufacture at sizes generally ranging between 1 and 100 nm, is a multidisciplinary scientific field undergoing explosive development. The genesis of nanotechnology can be traced to advances in medicine, communications, genomics and robotics. One of the greatest values of nanotechnology will be in the development of new and effective medical treatments (i.e. nanomedicine). This review focuses on the potential of nanomedicine as it relates to the development of nanoparticles for enabling and improving the targeted delivery of therapeutic and diagnostic agents. We highlight the use of nanoparticles for specific intra-compartmental analysis using the examples of delivery to malignant cancers, to the central nervous system, and across the gastrointestinal barriers.

Blood-brain barrier transport of therapeutics via receptor-mediation

Drug delivery to the brain is hindered by the presence of the blood-brain barrier (BBB). Although the BBB restricts the passage of many substances, it is actually selectively permeable to nutrients necessary for healthy brain function. To accomplish the task of nutrient transport, the brain endothelium is endowed with a diverse collection of molecular transport systems. One such class of transport system, known as a receptor-mediated transcytosis (RMT), employs the vesicular trafficking machinery of the endothelium to transport substrates between blood and brain. If appropriately targeted, RMT systems can also be used to shuttle a wide range of therapeutics into the brain in a noninvasive manner. Over the last decade, there have been significant developments in the arena of RMT-based brain drug transport, and this review will focus on those approaches that have been validated in an in vivo setting.

Translocation of Poly(ethylene glycol-co-hexadecyl)cyanoacrylate Nanoparticles into Rat Brain Endothelial Cells: Role of Apolipoproteins in Receptor-Mediated Endocytosis

Previous in vivo observations in rats have shown that poly(ethylene glycol) polyhexadecylcyanoacrylate (PEG-PHDCA) nanoparticles could translocate into the brain after intravenous injection, which polyhexadecylcyanoacrylate (PHDCA) nanoparticles did not. Through the detailed analysis of the plasma protein adsorption onto the surface of PEG-PHDCA nanoparticles, the present study aimed at clarifying the mechanism by which nanoparticles could penetrate into rat brain endothelial cells (RBEC). Two-dimensional polyacrylamide gel electrophoresis and Western blotting revealed that, after incubation with rat serum, apolipoprotein E (ApoE) adsorbed more onto PEG-PHDCA than on PHDCA nanoparticles. Adsorption of apolipoprotein B-100 (ApoB-100) onto PEG-PHDCA nanoparticles was demonstrated by capillary electrophoresis experiments. Moreover, only when ApoE or ApoB-100 were preadsorbed onto PEG-PHDCA nanoparticles, nanoparticles were found to be more efficient than control nanoparticles for penetrating into RBEC, suggesting the involvement of a low density lipoprotein receptor in this process. Thus, these data clearly demonstrate the involvement of apolipoproteins in the brain transport of PEG-PHDCA nanoparticles, which may open interesting prospects for brain drug delivery.

Covalent attachment of apolipoprotein A-I and apolipoprotein B-100 to albumin nanoparticles enables drug transport into the brain

Apolipoprotein E3, A-I as well as B-100 were covalently attached to human serum albumin nanoparticles via the NHS-PEG-Mal 3400 linker. Loperamide as a model drug was bound to these nanoparticles, and the antinociceptive reaction of these preparations was recorded after intravenous injection in mice by the tail-flick test. After 15 min, all three nanoparticle preparations with the coupled apolipoproteins E3, A-I, and B-100 yielded considerable antinociceptive effects, which lasted over 1 h. The maximally possible effects [MPE] of these preparations amounted to 95%, 65%, and 50%, respectively, and were statistically different from the controls (p<0.02), whereas the loperamide solution achieved no effect. This result demonstrates that more than one mechanism is involved in the interaction of nanoparticles with the brain endothelial cells and the resulting delivery of drugs to the central nervous system.

Nanotechnology approaches for drug and small molecule delivery across the blood brain barrier

Nanotechnology involves the design, synthesis, and characterization of materials and devices that have a functional organization in at least one dimension on the nanometer (ie, one billionth of a meter) scale. One area in which nanotechnology may have a significant clinical impact in neuroscience is the selective transport and delivery of drugs and other small molecules across the blood brain barrier that cannot cross otherwise. Using a variety of nanoparticles composed of different chemical compositions, different groups are exploring proof-of-concept approaches for the delivery of different antineoplastic drugs, oligonucleotides, genes, and magnetic resonance imaging contrast agents. This review discusses some of the main technical challenges associated with the development of nanotechnologies for delivery across the blood brain barrier and summarizes ongoing work.

Nanoparticles aggravate heat stress induced cognitive deficits, blood-brain barrier disruption, edema formation and brain pathology

Our knowledge regarding the influence of nanoparticles on brain function in vivo during normal or hyperthermic conditions is still lacking. Few reports indicate that when nanoparticles enter into the central nervous system (CNS) they may induce neurotoxicity. On the other hand, nanoparticle-induced drug delivery to the brain enhances neurorepair processes. Thus, it is likely that the inclusion of nanoparticles in body fluid compartments alters the normal brain function and/or its response to additional stress, e.g., hyperthermia. New data from our laboratory show that nanoparticles derived from metals (e.g., Cu, Ag or Al, approximately 50-60nm) are capable of inducing brain dysfunction in normal animals and aggravating the brain pathology caused by whole-body hyperthermia (WBH). Thus, normal animals treated with nanoparticles (for 1 week) exhibited mild cognitive impairment and cellular alterations in the brain. Subjection of these nanoparticle-treated rats to WBH resulted in profound cognitive and motor deficits, exacerbation of blood-brain barrier (BBB) disruption, edema formation and brain pathology compared with naive animals. These novel observations suggest that nanoparticles enhance brain pathology and cognitive dysfunction in hyperthermia. The possible mechanisms of nanoparticle-induced exacerbation of brain damage in WBH and its functional significance in relation to our current knowledge are discussed in this review.

Effects of apolipoproteins on dalargin transport across the blood-brain barrier

Antinociceptive activity of dalargin (7.5 mg/kg) adsorbed on poly(butyl)cyanoacrylate nanoparticles with different coating was studied on outbred albino mice by the tail-flick test. poly(butyl)cyanoacrylate nanoparticles without coating did not increase the antinociceptive activity of dalargin and hence, did not increase its transport across the blood-brain barrier. poly(butyl)cyanoacrylate nanoparticles coated with apolipoprotein B, apolipoprotein E, and polysorbate 80 increased the transport of dalargin across the blood-brain barrier. Delivery of dalargin to the brain was most effective in case of using poly(butyl)cyanoacrylate nanoparticles with polysorbate 80 coating and subsequent supercoating with apolipoprotein E.

Biodistribution of polysorbate 80-coated doxorubicin-loaded [14C]-poly(butyl cyanoacrylate) nanoparticles after intravenous administration to glioblastoma-bearing rats

It was recently shown that doxorubicin (DOX) bound to polysorbate-coated nanoparticles (NP) crossed the intact blood-brain barrier (BBB), and thus reached therapeutic concentrations in the brain. Here, we investigated the biodistribution in the brain and in the body of poly(butyl-2-cyano[3-(14)C]acrylate) NP ([(14)C]-PBCA NP), polysorbate 80 (PS 80)-coated [(14)C]-PBCA NP, DOX-loaded [(14)C]-PBCA NP in glioblastoma 101/8-bearing rats after i.v. injection. The biodistribution profiles and brain concentrations of radiolabeled NP were determined by radioactivity counting after i.v. administration in rats. Changes in BBB permeability after tumour inoculation were assessed by i.v. injection of Evans Blue solution. The accumulation of NP in the tumour site and in the contralateral hemisphere in glioblastoma bearing-rats probably was augmented by the enhanced permeability and retention effect (EPR effect) that may have been becoming instrumental due to the impaired BBB on the NP delivery into the brain. The uptake of the NP by the organs of the reticuloendothelial system (RES) was reduced after PS 80-coating, but the addition of DOX increased again the concentration of NP in the RES.

Covalent linkage of apolipoprotein e to albumin nanoparticles strongly enhances drug transport into the brain

Drug delivery to the brain is becoming more and more important but is severely restricted by the blood-brain barrier. Nanoparticles coated with polysorbates have previously been shown to enable the transport of several drugs across the blood-brain barrier, which under normal circumstances is impermeable to these compounds. Apolipoprotein E was suggested to mediate this drug transport across the blood-brain barrier. In the present study, apolipoprotein E was coupled by chemical methods to nanoparticles made of human serum albumin (HSA-NP). Loperamide, which does not cross the blood-brain barrier but exerts antinociceptive effects after direct injection into the brain, was used as model drug. Apolipoprotein E was chemically bound via linkers to loperamide-loaded HSA-NP. This preparation induced antinociceptive effects in the tail-flick test in ICR mice after i.v. injection. In contrast, nanoparticles linked to apolipoprotein E variants that do not recognize lipoprotein receptors failed to induce these effects. These results indicate that apolipoprotein E attached to the surface of nanoparticles facilitates transport of drugs across the blood-brain barrier, probably after interaction with lipoprotein receptors on the brain capillary endothelial cell membranes.

Influence of particle size on transport of methotrexate across blood brain barrier by polysorbate 80-coated polybutylcyanoacrylate nanoparticles

Transports of methotrexate-loaded polybutylcyanoacrylate nanoparticles with different sizes across blood brain barrier were investigated in this experiment. The drug-loaded nanoparticles were prepared by emulsion polymerization method. After coating with polysorbate 80, nanoparticles with the size 70, 170, 220, 345 nm were, respectively, i.v. injected into rats at the dose of 3.2 mg/kg. Uncoated nanoparticles and methotrexate solution were also i.v. injected at the same dosage as controls. 0.5, 1, 1.5, 2, 3, 4 h after injection, cerebrospinal fluids and brain tissues were collected for tests. Drug level in all biological samples was determined by HPLC. It was found out that nanoparticles overcoated by polysorbate 80 could significantly improve the drug level in both brain tissues and cerebrospinal fluids compared with uncoated ones and simple solution. Seventy-nanometer nanoparticles could deliver more drugs into brain while no significant difference was observed among the other three size ranges. In conclusion, polysorbate 80-coated polybutylcyanoacrylate nanoparticles could be used to overcome blood brain barrier especially those whose diameter was below 100 nm.

Barriers to carrier mediated drug and gene delivery to brain tumors

Brain tumor patients face a poor prognosis despite significant advances in tumor imaging, neurosurgery and radiation therapy. Potent chemotherapeutic drugs fail when used to treat brain tumors because biochemical and physiological barriers limit drug delivery into the brain. In the past decade a number of strategies have been introduced to increase drug delivery into the brain parenchyma. In particular, direct drug administration into the brain tumor has shown promising results in both animal models and clinical trials. This technique is well suited for the delivery of liposome and polymer drug carriers, which have the potential to provide a sustained level of drug and to reach cellular targets with improved specificity. We will discuss the current approaches that have been used to increase drug delivery into the brain parenchyma in the context of fluid and solute transport into, through and from the brain, with a focus on liposome and polymer drug carriers.

Novel advances in drug delivery to brain cancer

The therapy of brain tumors has been limited by a lack of effective methods of drug delivery to the brain. Systemic administration is often associated with toxic side effects and ultimately fails to achieve therapeutic concentrations within a tumor. An attractive strategy that has gained importance in brain tumor therapy has relied on local and controlled delivery of chemotherapeutic agents by biodegradable polymers. This technique allows direct exposure of tumor cells to a therapeutic agent for a prolonged period of time and has been shown to prolong the survival of patients with malignant brain tumors. The use of polymers for local drug delivery greatly expands the spectrum of drugs available for the treatment of malignant brain tumors. This review discusses the rationale for local drug delivery, describes the development of currently available polymer-based therapeutic agents, and highlights examples of promising non-polymer based drug delivery methods for use in the treatment of malignant brain tumors.

Using different structure types of microemulsions for the preparation of poly(alkylcyanoacrylate) nanoparticles by interfacial polymerization

A phase diagram of the pseudoternary system ethyloleate, polyoxyethylene 20 sorbitan mono-oleate/sorbitan monolaurate and water with butanol as a cosurfactant was prepared. Areas containing optically isotropic, low viscosity one-phase systems were identified and systems therein designated as w/o droplet-, bicontinuous- or solution-type microemulsions using conductivity, viscosity, cryo-field emission scanning electron microscopy and self-diffusion NMR. Nanoparticles were prepared by interfacial polymerization of selected w/o droplet, bicontinuous- or solution-type microemulsions with ethyl-2-cyanoacrylate. Morphology of the particles and entrapment of the water-soluble model protein ovalbumin were investigated. Addition of monomer to the different types of microemulsions (w/o droplet, bicontinuous, solution) led to the formation of nanoparticles, which were similar in size ( approximately 250 nm), polydispersity index ( approximately 0.13), zeta-potential ( approximately -17 mV) and morphology. The entrapment of the protein within these particles was up to 95%, depending on the amount of monomer used for polymerization and the type of microemulsion used as a polymerization template. The formation of particles with similar characteristics from templates having different microstructure is surprising, particularly considering that polymerization is expected to occur at the water-oil interface by base-catalysed polymerization. Dynamics within the template (stirring, viscosity) or indeed interfacial phenomena relating to the solid-liquid interface appear to be more important for the determination of nanoparticle morphology and characteristics than the microstructure of the template system.

A relevant in vitro rat model for the evaluation of blood-brain barrier translocation of nanoparticles

Poly(MePEG2000cyanoacrylate-co-hexadecylcyanoacrylate) (PEG-PHDCA) nanoparticles have demonstrated their capacity to reach the rat central nervous system after intravenous injection. For insight into the transport of colloidal systems across the blood-brain barrier (BBB), we developed a relevant in vitro rat BBB model consisting of a coculture of rat brain endothelial cells (RBECs) and rat astrocytes. The RBECs used in our model displayed and retained structural characteristics of brain endothelial cells, such as expression of P-glycoprotein, occludin and ZO-1, and immunofluorescence studies showed the specific localization of occludin and ZO1. The high values of transendothelial electrical resistance and low permeability coefficients of marker molecules demonstrated the functionality of this model. The comparative passage of polyhexadecylcyanoacrylate and PEG-PHDCA nanoparticles through this model was investigated, showing a higher passage of PEGylated nanoparticles, presumably by endocytosis. This result was confirmed by confocal microscopy. Thanks to a good in vitro/in vivo correlation, this rat BBB model will help in understanding the mechanisms of nanoparticle translocation and in designing new types of colloidal carriers as brain delivery systems.

Colloidal carriers and blood–brain barrier (BBB) translocation: A way to deliver drugs to the brain?

The major problem in drug delivery to the brain is the presence of the blood-brain barrier (BBB) which limits drug penetration even if in certain pathological situations the BBB is partly disrupted. Therefore, various strategies have been proposed to improve the delivery of drugs to this tissue. This review presents the status of the BBB in healthy patients and in pathologies like neurodegenerative, cerebrovascular and inflammatory diseases. The second part of this article aims to review the invasive and non-invasive strategies developed to circumvent the BBB and deliver drugs into the brain. The use of nanotechnologies (liposomes, nanoparticles) is especially discussed in the ultimate part of the review evidencing their potentiality as non-invasive technique in the brain delivery of drugs with the possibility to target specific brain tissue thanks to ligand linked to carrier surface.

Role of drug efflux transporters in the brain for drug disposition and treatment of brain diseases

The blood-brain barrier (BBB) serves as a protective mechanism for the brain by preventing entry of potentially harmful substances from free access to the central nervous system (CNS). Tight junctions present between the brain microvessel endothelial cells form a diffusion barrier, which selectively excludes most blood-borne substances from entering the brain. Astrocytic end-feet tightly ensheath the vessel wall and appear to be critical for the induction and maintenance of the barrier properties of the brain capillary endothelial cells. Because of these properties, the BBB only allows entry of lipophilic compounds with low molecular weights by passive diffusion. However, many lipophilic drugs show negligible brain uptake. They are substrates for drug efflux transporters such as P-glycoprotein (Pgp), multidrug resistance proteins (MRPs) or organic anion transporting polypeptides (OATPs) that are expressed at brain capillary endothelial cells and/or astrocytic end-feet and are key elements of the molecular machinery that confers the special permeability properties to the BBB. The combined action of these carrier systems results in rapid efflux of xenobiotics from the CNS. The objective of this review is to summarize transporter characteristics (cellular localization, specificity, regulation, and potential inhibition) for drug efflux transport systems identified in the BBB and blood-cerebrospinal fluid (CSF) barrier. A variety of experimental approaches available to ascertain or predict the impact of efflux transport on brain access of therapeutic drugs also are described and critically discussed. The potential impact of efflux transport on the pharmacodynamics of agents acting in the CNS is illustrated. Furthermore, the current knowledge about drug efflux transporters as a major determinant of multidrug resistance of brain diseases such as epilepsy is reviewed. Finally, we summarize strategies for modulating or by-passing drug efflux transporters at the BBB as novel therapeutic approaches to drug-resistant brain diseases.

Drug transport to brain with targeted nanoparticles

Nanoparticle drug carriers consist of solid biodegradable particles in size ranging from 10 to 1000 nm (50-300 nm generally). They cannot freely diffuse through the blood-brain barrier (BBB) and require receptor-mediated transport through brain capillary endothelium to deliver their content into the brain parenchyma. Polysorbate 80-coated polybutylcyanoacrylate nanoparticles can deliver drugs to the brain by a still debated mechanism. Despite interesting results these nanoparticles have limitations, discussed in this review, that may preclude, or at least limit, their potential clinical applications. Long-circulating nanoparticles made of methoxypoly(ethylene glycol)- polylactide or poly(lactide-co-glycolide) (mPEG-PLA/PLGA) have a good safety profiles and provide drug-sustained release. The availability of functionalized PEG-PLA permits to prepare target-specific nanoparticles by conjugation of cell surface ligand. Using peptidomimetic antibodies to BBB transcytosis receptor, brain-targeted pegylated immunonanoparticles can now be synthesized that should make possible the delivery of entrapped actives into the brain parenchyma without inducing BBB permeability alteration. This review presents their general properties (structure, loading capacity, pharmacokinetics) and currently available methods for immunonanoparticle preparation.

Delivery of therapeutic agents to the central nervous system: the problems and the possibilities

The presence of a blood-brain barrier (BBB) and a blood-cerebrospinal fluid barrier presents a huge challenge for effective delivery of therapeutics to the central nervous system (CNS). Many potential drugs, which are effective at their site of action, have failed and have been discarded during their development for clinical use due to a failure to deliver them in sufficient quantity to the CNS. In consequence, many diseases of the CNS are undertreated. In recent years, it has become clear that the blood-CNS barriers are not only anatomical barriers to the free movement of solutes between blood and brain but also transport and metabolic barriers. The cell association, sometimes called the neurovascular unit, constitutes the BBB and is now appreciated to be a complex group of interacting cells, which in combination induce the formation of a BBB. The various strategies available and under development for enhancing drug delivery to the CNS are reviewed.

Challenges and solutions for the delivery of biotech drugs – a review of drug nanocrystal technology and lipid nanoparticles

Biotechnology allows tailor-made production of biopharmaceuticals and biotechnological drugs; however, many of them require special formulation technologies to overcome drug-associated problems. Such potential challenges to solve are: poor solubility, limited chemical stability in vitro and in vivo after administration (i.e. short half-life), poor bioavailability and potentially strong side effects requiring drug enrichment at the site of action (targeting). This review describes the use of nanoparticulate carriers, developed in our research group, as one solution to overcome such delivery problems, i.e. drug nanocrystals, solid lipid nanoparticles (SLN), nanostructured lipid carriers (NLC) and lipid-drug conjugate (LDC) nanoparticles, examples of drugs are given. As a recently developed targeting principle, the concept of differential protein adsorption is described (PathFinder Technology) using as example delivery to the brain.

In vitro evaluation of PLA nanoparticles containing a lipophilic drug in water-soluble or insoluble form

Cloricromene (AD6), an anti-ischemic drug, is rapidly metabolised into a stable and active metabolite (cloricromene acid, AD6-acid) poorly soluble in water and less lipophilic than cloricromene. The aim of this study was to evaluate which of the two forms has more possibility to be efficiently encapsulated in nanoparticles based on poly(D,L-lactide) and prepared using the nanoprecipitation method. Increasing the theoretical loading of AD6, an increase in drug actual loading and in the mean particle size occurred, while no formation of nanoparticles was observed when the highest theoretical loading (50 mg) was employed. Changing the pH of the aqueous phase the drug content dramatically increased. However, at a pH value of 11 a more rapid hydrolysis of AD6 occurred. When AD6-acid was embedded in the nanoparticles, suitable results concerning both drug content and encapsulation efficiency were achieved. A good control in the release of AD6 from the AD6-loaded nanoparticles was observed while the liberation of AD6-acid from the AD6-acid-loaded nanoparticles was faster than the dissolution of the AD6-acid free. These results confirm that the most easy encapsulable form in nanoparticles is AD6-acid probably owing to its poor water solubility. Further studies will be carried out in order to evaluate if the increase in the liberation of AD6-acid by nanoencapsulation may have outcomes in its bioavaibility in vivo.

Lipid–drug conjugate nanoparticles of the hydrophilic drug diminazene—cytotoxicity testing and mouse serum adsorption

Sleeping sickness is a widely distributed disease in great parts of Africa. It is caused by Trypanosoma brucei gambiense and rhodiense, transmitted by the Tse-Tse fly. After a hemolymphatic stage, the parasites enter the central nervous system where they cannot be reached by hydrophilic drugs. To potentially deliver the hydrophilic antitrypanosomal drug diminazene diaceturate to the brain of infected mice, the drug was formulated as lipid-drug conjugate (LDC) nanoparticles (NP) by combination with stearic- (SA) and oleic acid (OA). To estimate the in vivo compatibility, the particles were incubated with human granulocytes. Because as potential delivery mechanism the absorption of specific serum proteins (ApoE, Apo AI and Apo AIV) was found to be responsible for the delivery of nanoparticles to the brain, demonstrated using PBCA nanoparticles coated with polysorbate 80 (LDL uptake mechanism) the nanoparticles were incubated with mouse serum and the adsorption pattern was determined using the 2-D PAGE technique. As a result of this study, the cytotoxic potential was shown to decrease when diminazene is part of the particle matrix compared to pure fatty acid nanoparticles and the mouse serum protein adsorption pattern differs from the samples studied earlier in human serum. Especially, the fact concerning Apo-E that could be detected when the particles were incubated in human serum is absent after the mouse serum incubation, potentially, is a critical point for the delivery via the LDL-uptake mechanism but the data demonstrate that LDC nanoparticles, with 33% (wt/wt) drug loading capacity possess the potential to act as a delivery system for hydrophilic drugs like diminazene diaceturate and that further studies have to demonstrate the usability as a brain delivery system.

Chemotherapy of glioblastoma in rats using doxorubicin-loaded nanoparticles

Glioblastomas belong to the most aggressive human cancers with short survival times. Due to the blood-brain barrier, they are mostly inaccessible to traditional chemotherapy. We have recently shown that doxorubicin bound to polysorbate-coated nanoparticles crossed the intact blood-brain barrier, thus reaching therapeutic concentrations in the brain. Here, we investigated the therapeutic potential of this formulation of doxorubicin in vivo using an animal model created by implantation of 101/8 glioblastoma tumor in rat brains. Groups of 5-8 glioblastoma-bearing rats (total n = 151) were subjected to 3 cycles of 1.5-2.5 mg/kg body weight of doxorubicin in different formulations, including doxorubicin bound to polysorbate-coated nanoparticles. The animals were analyzed for survival (% median increase of survival time, Kaplan-Meier). Preliminary histology including immunocytochemistry (glial fibrillary acidic protein, ezrin, proliferation and apoptosis) was also performed. Rats treated with doxorubicin bound to polysorbate-coated nanoparticles had significantly higher survival times compared with all other groups. Over 20% of the animals in this group showed a long-term remission. Preliminary histology confirmed lower tumor sizes and lower values for proliferation and apoptosis in this group. All groups of animals treated with polysorbate-containing formulations also had a slight inflammatory reaction to the tumor. There was no indication of neurotoxicity. Additionally, binding to nanoparticles may reduce the systemic toxicity of doxorubicin. This study showed that therapy with doxorubicin bound to nanoparticles offers a therapeutic potential for the treatment of human glioblastoma.