Current Pharmaceutical Biotechnology - Volume 13, Issue 7, 2012

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The recent developement of platelet concentrate for surgical use is an evolution of the fibrin glue technologies used since many years. The initial concept of these autologous preparations was to concentrate platelets and their growth factors in a plasma solution, and to activate it into a fibrin gel on a surgical site, in order to improve local healing. These platelet suspensions were often called Platelet-Rich Plasma (PRP) like the platelet concentrate used in transfusion medicine, but many different technologies have in fact been developed; some of them are even no more platelet suspensions, but solid fibrin-based biomaterials called Platelet-Rich Fibrin (PRF). These various technologies were tested in many different clinical fields, particularly oral and maxillofacial surgery, Ear-Nose-Throat surgery, plastic surgery, orthopaedic surgery, sports medicine, gynecologic and cardiovascular surgery and ophthalmology. This field of research unfortunately suffers from the lack of a proper accurate terminology and the associated misunderstandings, and the literature on the topic is quite contradictory. Indeed, the effects of these preparations cannot be limited to their growth factor content: these products associate many actors of healing in synergy, such as leukocytes, fibrin matrix, and circulating progenitor cells, and are in fact as complex as blood itself. If platelet concentrates were first used as surgical adjuvants for the stimulation of healing (as fibrin glues enriched with growth factors), many applications for in situ regenerative medicine and tissue engineering were developed and offer a great potential. However, the future of this field is first dependent on his coherence and scientific clarity. The objectives of this article is to introduce the main definitions, problematics and perspectives that are described in this special issue of Current Pharmaceutical Biotechnology about platelet concentrates.

In the field of platelet concentrates for surgical use, most products are termed Platelet-Rich Plasma (PRP). Unfortunately, this term is very general and incomplete, leading to many confusions in the scientific database. In this article, a panel of experts discusses this issue and proposes an accurate and simple terminology system for platelet concentrates for surgical use. Four main categories of products can be easily defined, depending on their leukocyte content and fibrin architecture: Pure Platelet-Rich Plasma (P-PRP), such as cell separator PRP, Vivostat PRF or Anitua's PRGF; Leukocyteand Platelet-Rich Plasma (L-PRP), such as Curasan, Regen, Plateltex, SmartPReP, PCCS, Magellan, Angel or GPS PRP; Pure Plaletet-Rich Fibrin (P-PRF), such as Fibrinet; and Leukocyte- and Platelet-Rich Fibrin (L-PRF), such as Choukroun's PRF. P-PRP and L-PRP refer to the unactivated liquid form of these products, their activated versions being respectively named P-PRP gels and L-PRP gels. The purpose of this search for a terminology consensus is to plead for a more serious characterization of these products. Researchers have to be aware of the complex nature of these living biomaterials, in order to avoid misunderstandings and erroneous conclusions. Understanding the biomaterials or believing in the magic of growth factors ? From this choice depends the future of the field.

More or less after a decade of experimental and pioneering manual procedures to prepare platelet-rich plasma (PRP) for topical use, several portable and bedside devices were made available to prepare the PRP at the point-of-care. This technical opportunity increased the number of patients who got access to the treatment with autologous PRP and PRP-gel. Since topical treatment of tissue with PRP and PRP-gel was restricted to autologous preparation, blood transfusion centers that professionally prepare donor-derived platelet concentrates were not able to cover the overwhelming request for autologous PRP supply. Principally for logistic and organization reasons blood transfusion centers usually fail the challenge of prompt delivery of PRP to the physician over large territory. Nevertheless the blood bank production of platelet concentrates is associated with high standardization and quality controls not achievable from bedside and portable devices. Furthermore it easy to demonstrate that high-volume blood bank-produced platelet concentrates are less expensive than low-volume PRP produced by portable and bedside devices. Taking also in consideration the ever-increasing safety of the blood components, the relationship between bedside device-produced and blood-bank-produced PRP might be reconsidered. Here we discuss this topic concluding that the variety of sources of PRP production is an opportunity for versatility and that, ultimately, versatility is an opportunity for the patient's care.

Platelet concentrates for surgical use are tools of regenerative medicine designed for the local release of platelet growth factors into a surgical or wounded site, in order to stimulate tissue healing or regeneration. Leukocyte content and fibrin architecture are 2 key characteristics of all platelet concentrates and allow to classify these technologies in 4 families, but very little is known about the impact of these 2 parameters on the intrinsic biology of these products. In this demonstration, we highlight some outstanding differences in the growth factor and matrix protein release between 2 families of platelet concentrate: Pure Platelet-Rich Plasma (P-PRP, here the Anitua's PRGF - Preparation Rich in Growth Factors - technique) and Leukocyte- and Platelet-Rich Fibrin (L-PRF, here the Choukroun's method). These 2 families are the extreme opposites in terms of fibrin architecture and leukocyte content. The slow release of 3 key growth factors (Transforming Growth Factor β1 (TGFβ1), Platelet-Derived Growth Factor AB (PDGF-AB) and Vascular Endothelial Growth Factor (VEGF)) and matrix proteins (fibronectin, vitronectin and thrombospondin-1) from the L-PRF and P-PRP gel membranes in culture medium is described and discussed. During 7 days, the L-PRF membranes slowly release significantly larger amounts of all these molecules than the P-PRP gel membranes, and the 2 products display different release patterns. In both platelet concentrates, vitronectin is the sole molecule to be released almost completely after only 4 hours, suggesting that this molecule is not trapped in the fibrin matrix and not produced by the leukocytes. Moreover the P-PRP gel membranes completely dissolve in the culture medium after less than 5 days only, while the L-PRF membranes are still intact after 7 days. This simple demonstration shows that the polymerization and final architecture of the fibrin matrix considerably influence the strength and the growth factor trapping/release potential of the membrane. It also suggests that the leukocyte populations have a strong influence on the release of some growth factors, particularly TGFβ1. Finally, the various platelet concentrates present very different biological characteristics, and an accurate definition and characterization of the different families of product is a key issue for a better understanding and comparison of the reported clinical effects of these surgical adjuvants.

Platelet concentrates for topical use are innovative tools of regenerative medicine and their effects in various therapeutical situations are hotly debated. Unfortunately, this field of research mainly focused on the platelet growth factors, and the fibrin architecture and the leukocyte content of these products are too often neglected. In the four families of platelet concentrates, 2 families contain significant concentrations of leukocytes: L-PRP (Leukocyte- and Platelet-Rich Plasma) and L-PRF (Leukocyte- and Platelet-Rich Fibrin). The presence of leukocytes has a great impact on the biology of these products, not only because of their immune and antibacterial properties, but also because they are turntables of the wound healing process and the local factor regulation. In this article, the various kinds of leukocytes present in a platelet concentrate are described (particularly the various populations of granulocytes and lymphocytes), and we insist on the large diversity of factors and pathways that these cells can use to defend the wound site against infections and to regulate the healing process. Finally, the impact of these cells in the healing properties of the L-PRP and L-PRF is also discussed: if antimicrobial properties were already pointed out, effects in the regulation of cell proliferation and differentiation were also hypothesized. Leukocytes are key actors of many platelet concentrates, and a better understanding of their effects is an important issue for the development of these technologies.

Tissue repair at wound sites begins with clot formation, and subsequently platelet degranulation with the release of platelet growth factors, which are necessary and well-regulated processes to achieve wound healing. Plateletderived growth factors are biologically active substances that enhance tissue repair mechanisms, such as chemotaxis, cell proliferation, angiogenesis, extracellular matrix deposition, and remodeling. This review describes the biological background and results on the topical use of autologous platelet-rich plasma and platelet gel in gynecologic, cardiac, and general surgical procedures, including chronic wound management and soft-tissue injuries.

Leukocyte- and platelet-rich plasma (L-PRP) contains high concentrations of platelet, leukocytes and other bioactivities, which play an prominent role in both bone and soft tissue healing processes. Large numbers of studies provide evidence for application of L-PRP in experiments and clinical practice. It has been identified to improve cellular chemotaxis, proliferation and differentiation, angiogenesis, and production of extracellular matrix, but also responsible for stimulating defense mechanisms against infections. L-PRP is now playing an increasing role in the management of patients with traumatic injuries. However, most studies are only anecdotal or case reports, and then larger controlled studies are needed. This article introduces the reader to L-PRP properties and L-PRP applications in trauma surgery, including applications of L-PRP in bone healing, acute soft tissue wound healing, and repairing of acute muscle, tendon, ligament, nerve and cartilage injury caused by trauma.

Platelet rich plasma (PRP) is a powerful new biologic tool in sports medicine. PRP is a fraction of autologous whole blood containing and increased number of platelets and a wide variety of cytokines such as platelet derived growth factor (PDGF), vascular endothelial growth factor (VEGF) and transforming growth factor beta-1 (TGF-B1), fibroblast growth factor (FGF), Insulin-like growth factor-1 (IGF-1) among many others. Worldwide interest in this biologic technology has recently risen sharply. Basic science and preclinical data support the use of PRP for a variety of sports related injuries and disorders. The published, peer reviewed, human data on PRP is limited. Although the scientific evaluation of clinical efficacy is in the early stages, elite and recreational athletes already use PRP in the treatment of sports related injuries. Many questions remain to be answered regarding the use of PRP including optimal formulation, including of leukocytes, dosage and rehabilitation protocols. In this review, a classification for platelet rich plasma is proposed and the invitro, preclinical and human investigations of PRP applications in sports medicine will be reviewed as well as a discussion of rehabilitation after a PRP procedure. The regulation of PRP by the World Anti-Doping Agency will also be discussed. PRP is a promising technology in sports medicine; however, it will require more vigorous study in order to better understand how to apply it most effectively.

Surgical repair of the rotator cuff repair is one of the most common procedures in orthopedic surgery. Despite it being the focus of much research, the physiological tendon-bone insertion is not recreated following repair and there is an anatomic non-healing rate of up to 94%. During the healing phase, several growth factors are upregulated that induce cellular proliferation and matrix deposition. Subsequently, this provisional matrix is replaced by the definitive matrix. Leukocyte- and platelet-rich fibrin (L-PRF) contain growth factors and has a stable dense fibrin matrix. Therefore, use of LPRF in rotator cuff repair is theoretically attractive. The aim of the present study was to determine 1) the optimal protocol to achieve the highest leukocyte content; 2) whether L-PRF releases growth factors in a sustained manner over 28 days; 3) whether standard/gelatinous or dry/compressed matrix preparation methods result in higher growth factor concentrations. 1) The standard L-PRF centrifugation protocol with 400 x g showed the highest concentration of platelets and leukocytes. 2) The L-PRF clots cultured in medium showed a continuous slow release with an increase in the absolute release of growth factors TGF-β1, VEGF and MPO in the first 7 days, and for IGF1, PDGF-AB and platelet activity (PF4=CXCL4) in the first 8 hours, followed by a decrease to close to zero at 28 days. Significantly higher levels of growth factor were expressed relative to the control values of normal blood at each culture time point. 3) Except for MPO and the TGFβ-1, there was always a tendency towards higher release of growth factors (i.e., CXCL4, IGF-1, PDGF-AB, and VEGF) in the standard/gelatinous- compared to the dry/compressed group. L-PRF in its optimal standard/gelatinous-type matrix can store and deliver locally specific healing growth factors for up to 28 days and may be a useful adjunct in rotator cuff repair.

Platelet concentrates for surgical use are innovative tools of regenerative medicine, and were widely tested in oral and maxillofacial surgery. Unfortunately, the literature on the topic is contradictory and the published data are difficult to sort and interpret. In periodontology and dentoalveolar surgery, the literature is particularly dense about the use of the various forms of Platelet-Rich Plasma (PRP) - Pure Platelet-Rich Plasma (P-PRP) or Leukocyte- and Platelet-Rich Plasma (L-PRP) - but still limited about Platelet-Rich Fibrin (PRF) subfamilies. In this first article, we describe and discuss the current published knowledge about the use of PRP and PRF during tooth avulsion or extraction, mucogingival surgery, Guided Tissue Regeneration (GTR) or bone filling of periodontal intrabony defects, and regeneration of alveolar ridges using Guided Bone Regeneration (GBR), in a comprehensive way and in order to avoid the traps of a confusing literature and to highlight the underlying universal mechanisms of these products. Finally, we particularly insist on the perspectives in this field, through the description and illustration of the systematic use of L-PRF (Leukocyte- and Platelet- Rich Fibrin) clots and membranes during tooth avulsion, cyst exeresis or the treatment of gingival recessions by root coverage. The use of L-PRF also allowed to define new therapeutic principles: NTR (Natural Tissue Regeneration) for the treatment of periodontal intrabony lesions and Natural Bone Regeneration (NBR) for the reconstruction of the alveolar ridges. In periodontology, this field of research will soon find his golden age by the development of user-friendly platelet concentrate procedures, and the definition of new efficient concepts and clinical protocols.

Platelet concentrates for surgical use are innovative tools of regenerative medicine, and were widely tested in oral and maxillofacial surgery. Unfortunately, the literature on the topic is contradictory and the published data are difficult to sort and interpret. In bone graft, implant and reconstructive surgery, the literature is particularly dense about the use of the various forms of Platelet-Rich Plasma (PRP) - Pure Platelet-Rich Plasma (P-PRP) or Leukocyte- and Platelet-Rich Plasma (L-PRP) - but still limited about Platelet-Rich Fibrin (PRF) subfamilies. In this second article, we describe and discuss the current published knowledge about the use of PRP and PRF during implant placement (particularly as surface treatment for the stimulation of osseointegration), the treatment of peri-implant bone defects (after peri-implantitis, during implantation in an insufficient bone volume or during immediate post-extraction or post-avulsion implantation), the sinuslift procedures and various complex implant-supported treatments. Other potential applications of the platelet concentrates are also highlighted in maxillofacial reconstructive surgery, for the treatment of patients using bisphosphonates, anticoagulants or with post-tumoral irradiated maxilla. Finally, we particularly insist on the perspectives in this field, through the description and illustration of the use of L-PRF (Leukocyte- and Platelet-Rich Fibrin) clots and membranes during the regeneration of peri-implant bone defects, during the sinus-lift procedure and during complex implant-supported rehabilitations. The use of L-PRF allowed to define a new therapeutic concept called the Natural Bone Regeneration (NBR) for the reconstruction of the alveolar ridges at the gingival and bone levels. As it is illustrated in this article, the NBR principles allow to push away some technical limits of global implant-supported rehabilitations, particularly when combined with other powerful biotechnological tools: metronidazole solution, adequate bone substitutes and improved implant designs and surfaces (for example here AstraTech Osseospeed or Intra-Lock Ossean implants). As a general conclusion, we are currently living a transition period in the use of PRP and PRF in oral and maxillofacial surgery. PRPs failed to prove strong strategic advantages that could justify their use in daily practice, and the use of most PRP techniques will probably be limited to some very specific applications where satisfactory results have been reached. Only a few simple, inexpensive and efficient techniques such as the L-PRF will continue to develop in oral and maxillofacial surgery in the next years. This natural evolution illustrates that clinical sciences need concrete and practical solutions, and not hypothetical benefits. The history of platelet concentrates in oral and maxillofacial surgery finally demonstrates also how the techniques evolve and sometimes promote the definition of new therapeutical concepts and clinical protocols in the today's era of regenerative medicine.

Blood derived products have demonstrated their capacity to enhance healing and stimulate the regeneration of different tissues and this enhancing effect is attributed to the growth factors and bioactive proteins that are synthesized and present in blood. Eye platelet rich plasma (E-PRP) provides higher concentration of essential growth factors and cell adhesion molecules by concentrating platelets in a small volume of plasma as compared with autologous serum, the latter being used widely in ophthalmology for epithelial wound healing of the cornea for the last two decades. These growth factors and cell adhesion molecules have a major role in wound healing and enhance the physiological process at the site of the injury/surgery via eye drops or clot. E-PRP has been used more recently, and has achieved successful outcomes in peer-review articles in the treatment of dormant ulcers (epithelial defects of the cornea that fail to heal), moderate to severe dry eye syndrome, ocular surface syndrome post Laser In Situ Keratomileusis (LASIK), and for surface reconstruction after corneal perforation associated with amniotic membrane transplantation. Preparation of E-PRP in the two available formulations, eyedrops and clot, is inexpensive and easy although it requires following strict sterility conditions using sterile and disposable materials and operating inside a laminar flow hood. No serious adverse effects have been described with the use of these products, and it is generally well tolerated. In summary, Platelet enriched plasma in the form obtained in ophthalmology, E-PRP, is a reliable and effective therapeutic tool to enhance epithelial wound healing in ocular surface disease.

The use of platelet concentrates for topical use is of particular interest for the promotion of skin wound healing. Fibrin-based surgical adjuvants are indeed widely used in plastic surgery since many years in order to improve scar healing and wound closure. However, the addition of platelets and their associated growth factors opened a new range of possibilities, particularly for the treatment of chronic skin ulcers and other applications of regenerative medicine on the covering tissues. In the 4 families of platelet concentrates available, 2 families were particularly used and tested in this clinical field: L-PRP (Leukocyte- and Platelet-rich Plasma) and L-PRF (Leukocyte- and Platelet-Rich Fibrin). These 2 families have in common the presence of significant concentrations of leukocytes, and these cells are important in the local cleaning and immune regulation of the wound healing process. The main difference between them is the fibrin architecture, and this parameter considerably influences the healing potential and the therapeutical protocol associated to each platelet concentrate technology. In this article, we describe the historical evolutions of these techniques from the fibrin glues to the current L-PRP and L-PRF, and discuss the important functions of the platelet growth factors, the leukocyte content and the fibrin architecture in order to optimize the numerous potential applications of these products in regenerative medicine of the skin. Many outstanding perspectives are appearing in this field and require further research.

For non-invasive or systemic delivery of therapeutic agents or drug carriers, it is very important that these cargos can successfully cross the microvessel wall, arrive the target cells through interstitial transport, and/or penetrate the cell membrane, diffuse in the cytoplasm, and cross the nuclear envelope. Meanwhile they should be non-toxic to the healthy tissues and can survive the plasma clearance, degradation and consumption during the journey to the target cells and/or cell nuclei. In this issue of non-invasive delivery of iRNAs, proteins, peptides, cytokines and nanoparticles, recent technologies and transport models related to the drug carrier design and delivery are presented. First, Rivera and Yuan discuss “critical issues in delivery of RNAi therapeutics in vivo”. Interfering RNAs (iRNAs) are a new class of drugs for treatment of various diseases through gene regulation. To achieve their therapeutic effects, novel strategies have to be developed to enhance their stability, overcome transport barriers, and reduce immunogenicity and cytotoxicity. This review describes recent approaches and concerns in iRNA delivery in vivo. Following iRNA delivery, Wu et al., have reviewed “challenges and strategies in developing microneedle patches for transdermal delivery of protein and peptide therapeutics”. This review updates the advantages and disadvantages of a variety of newly designed microneedles including insoluble solid, soluble/degradable solid, phase-transition and hollow microneedles, which are specifically designed for non-invasive delivery of proteins and peptides across the skin. Controlled releases of growth factors and cytokines have been widely used in wound repair and tissue engineering. Peattie has thus contributed a review about “release of growth factors, cytokines and therapeutic molecules by hyaluronan-based hydrogels”. “Simple” and “Regulated” releases of these molecules by modified forms of hyaluronan have been presented for the therapeutic, clinical, veterinary and laboratory applications. This decade has been marked the rapid development of nanoparticles for therapeutic and diagnostic purposes. Many progresses have been achieved in drug delivery using nanoparticles, especially in solid tumor treatment. Bhagat et al., have reviewed “nanocarriers to solid tumors: considerations on tumor penetration and exposure of tumor cells to therapeutic agents”. Their review describes a variety of rational designs of self-assembling nanocarriers, e.g., liposomes and micelles, for achieving adequate tumor penetration and lethal doses to all cancer cells of a solid tumor but minimizing normal organ toxicities. To increase the treatment efficacy and reduce side effects, multiple drugs can be co-delivered to the tumor. Choudhury and He have thus contributed a review for “nanocarriers for the simultaneous co-delivery of therapeutic genes and anticancer drugs”, which summarizes novel strategies that can simultaneously load genes and chemical drugs on the same nanoparticles but release these cargos at specific times. More and more men and women suffer from Alzheimer's and Parkinson's diseases and other brain disorders when they are aging. Many therapeutic drugs for these central nervous diseases have been developed but their applications are limited by their delivery to the brain, particularly by the blood-brain barrier (BBB) if they are delivered through systemic administration. In the review by Konofagou et al., they have demonstrated a novel brain drug delivery through “ultrasound-induced blood-brain barrier opening”. A controllable focused ultrasound, in conjunction with microbubbles, is the effective technique that can induce localized BBB opening non-invasively and regionally. In addition to ultrasound-induced BBB opening, in “experimental methods and transport models for drug delivery across the blood-brain barrier”, Fu has suggested other delivery strategies across the BBB based on the quantitative experimental approaches and transport models for the BBB permeability to water, ions, and solutes including nutrients, therapeutic agents and drug carriers. Finally, in “pharmacokinetics/pharmacodynamics model-supported early drug development”, Chen et al., have discussed how pharmacokinetic pharmacodynamic (PK/PD) modeling and simulation (M&S), which offer quantitative assessment of exposure- response relationships, contribute to the drug development and regulatory decisions in pharmaceutical industry.

RNA interference (RNAi) is a fundamental mechanism of gene regulation and has been harnessed to produce a new class of drugs for treatment of various diseases. A key issue in these applications is how to effectively deliver RNAi therapeutics into target cells. This review is focused on advances in RNA delivery in vivo. To achieve it, novel strategies have been developed to enhance stability of RNA in cells and tissues, overcome barriers to transport of RNA or its carriers in the body, and reduce immunogenicity and cytotoxicity of treatment. Approaches to RNA delivery are divided into three categories in this review: biological, chemical, and physical. Advantages and disadvantages of each method are discussed. At present, effective delivery of RNAi therapeutics in vivo is still a challenge although significant advances have been made in this field.

The birth of microneedles, an array of needles sufficiently long to penetrate epidermis but small enough to do not cause skin injury and pain feeling, has offered a highly promising solution for non-invasive delivery of protein and peptide drugs, a long-cherished desire over eighty years. However, the attempts to develop clinically feasible microneedle transdermal delivery methods encountered series of difficulties, for which a decade research efforts have yet to result in a single product. Microneedles may be incorporated into devices as skin pre-treatment tools, skin microinjectors as well as transdermal patches by their functions in drug delivery. They may also be categorized to insoluble solid microneedles, hollow microneedles, soluble/degradable solid microneedles and phase-transition microneedles by their structure and forming materials. This review article is aimed to update the progress and discuss the technical challenges raised in developing protein/peptide loaded microneedle patches.

Hyaluronan (HA) is a highly biocompatible biopolymer that is widely used for a variety of therapeutic purposes including surgical preparations, adhesion prevention, viscosupplementation and drug and cytokine delivery. Delivery can be accomplished effectively when HA-based carriers are synthesized in the form of hydrogels, though doing so normally requires chemical modification of the native HA structure. Solute delivery from HA-based gels can be either “simple”, that is from a gel not including separate components intended to control release, or “regulated” when specific components are included for that purpose. A variety of modified forms of HA have been developed and used for delivery of desired molecules in therapeutic, clinical, veterinary and laboratory research environments, and the number of such applications is likely to grow in future years.

Solid tumors constitute the majority of diagnosed cancers. For effective killing, therapeutic agents should ideally be delivered uniformly and at lethal doses to all cancer cells comprising the tumors, while keeping normal organ toxicities to a minimum. This requirement sets two of the major challenges in drug delivery to solid cancers: uniformity in delivery, and delivery of at least a minimum amount of therapeutics per cancer cell. Herein we review various approaches that aim to improve the penetration and content release of delivered therapeutic agents from nanocarriers of selfassembling nature. Biophysical characteristics of solid tumors are briefly discussed to motivate and rationalize the design of reported nanoparticle structures. This review does not aim to be exhaustive of the various designs and strategies, but to mostly give a flavor of the general current directions aiming to address these challenges.

Due to the molecular complexity of cancer, combination therapy is becoming increasingly important for better long-term prognosis with fewer side effects. To further increase the therapeutic effects, advanced drug delivery systems (DDSs), capable of simultaneously delivering multiple drugs to the site of action with specific time-programmed release profiles, are important requirements. Nanocarriers for the simultaneous co-delivery of multiple chemical drugs in combination therapy have been extensively reviewed. Here we focus on the nanotechnology enabled DDSs for the simultaneous co-delivery of therapeutic genes and chemical drugs for cancer treatment. The opportunities for this combination strategy and their challenges will be discussed.

Over 4 million U.S. men and women suffer from Alzheimer's disease; 1 million from Parkinson's disease; 350,000 from multiple sclerosis (MS); and 20,000 from amyotrophic lateral sclerosis (ALS). Worldwide, these four diseases account for more than 20 million patients. In addition, aging greatly increases the risk of neurodegenerative disease. Although great progress has been made in recent years toward understanding of these diseases, few effective treatments and no cures are currently available. This is mainly due to the impermeability of the blood-brain barrier (BBB) that allows only 5% of the 7000 small-molecule drugs available to treat only a tiny fraction of these diseases. On the other hand, safe and localized opening of the BBB has been proven to present a significant challenge. Of the methods used for BBB disruption shown to be effective, Focused Ultrasound (FUS), in conjunction with microbubbles, is the only technique that can induce localized BBB opening noninvasively and regionally. FUS may thus have a huge impact in trans-BBB brain drug delivery. The primary objective in this paper is to elucidate the interactions between ultrasound, microbubbles and the local microenvironment during BBB opening with FUS, which are responsible for inducing the BBB disruption. The mechanism of the BBB opening in vivo is monitored through the MRI and passive cavitation detection (PCD), and the safety of BBB disruption is assessed using H&E histology at distinct pressures, pulse lengths and microbubble diameters. It is hereby shown that the BBB can be disrupted safely and transiently under specific acoustic pressures (under 0.45 MPa) and microbubble (diameter under 8 μm) conditions.

The blood-brain barrier (BBB) is a dynamic barrier essential for maintaining the micro-environment of the brain. Although the special anatomical features of the BBB determine its protective role for the central nervous system (CNS) from blood-born neurotoxins, however, the BBB extremely limits the therapeutic efficacy of drugs into the CNS, which greatly hinders the treatment of major brain diseases. This review summarized the unique structures of the BBB, described a variety of in vivo and in vitro experimental methods for determining the transport properties of the BBB, e.g., the permeability of the BBB to water, ions, and solutes including nutrients, therapeutic agents and drug carriers, and presented newly developed mathematical models which quantitatively correlate the anatomical structures of the BBB with its barrier functions. Finally, on the basis of the experimental observations and the quantitative models, several strategies for drug delivery through the BBB were proposed.

Pharmacokinetic/pharmacodynamic (PK/PD) modeling & simulation (M&S) provides quantitative assessment of dose/exposure-response relationships with extensive applications at the late stage drug development as well as during regulatory decision making. However, at preclinical and early phase clinical drug development, the importance of PK/PD M&S has not been as widely recognized. We reviewed selected PK/PD M&S literatures in order to convey importance of M&S in these early development phases. We focused on the application of M&S to select and optimize lead candidates, the use of preclinical PK/PD data to project the range of clinical doses, and the development of comprehensive dose/exposure-response models that can be used to forecast the probability of achieving a target response based on Phase 1 safety, PK and biomarker information. We also reviewed several other M&S approaches that are often used in early drug development such as physiologically-based pharmacokinetic (PBPK) modeling, meta-analysis, PK-pharmacogenomics modeling, and etc. Our aims were to provide expert opinions on the practical utility of PK/PD model-based approaches that have positive impact on early decision-making with the goal of improving the success rate of early to late stage drug development.