Nicholas A. Peppas

Bio: Nicholas A. Peppas is an academic researcher from University of Texas at Austin. The author has contributed to research in topics: Self-healing hydrogels & Drug delivery. The author has an hindex of 141, co-authored 825 publications receiving 90533 citations. Previous affiliations of Nicholas A. Peppas include National Technical University & University of Texas System.

Complexation hydrogels as oral delivery vehicles for insulin-transferrin conjugates

Abstract: Protein bioconjugation is being currently investigated as a strategy to improve oral absorption of proteins. By conjugating proteins of therapeutic interest, such as insulin, to macromolecular PEG chains or other proteins, such as transferrin (Tf), the enzymatic stability of the protein drug and its transport characteristics across the intestinal epithelium may be improved. Complexation graft copolymers of poly(methacrylic acid-g-ethylene glycol), have also shown to be excellent carriers for oral protein delivery. In this work we demonstrated the use of complexation hydrogels as delivery vehicles for insulin-transferrin bioconjugates. Introduction: Complexation graft copolymers of poly(methacrylic acid-g-ethylene glycol), designated as P(MAA-g-EG), have been shown to be effective in oral delivery of insulin. Their hydrogen bonding complexation/decomplexation characteristics render these responsive hydrogels able to protect the insulin in the harsh, acidic environment of the stomach before releasing the bioactive agent in the small intestine. Further, these network structures can inhibit the activity of Ca dependent proteolytic enzymes [1], and increase the residence time of the drug in the small intestine by mucoadhesion. Oral administration of insulin entrapped in polymer microparticles resulted in high bioavailability of the drug in diabetic rats [2]. One of the other effective strategies for enhancing bioavailability of proteins exploits the receptor-mediated endocytotic pathway used by the cells for selective and efficient uptake of specific macromolecules required for various cell processes. By coupling proteins and peptides to ligands that can recognize specific receptors on the epithelial cells, transcellular delivery of these macromolecular biopharmaceuticals may be achieved [3]. Since only those molecules that are conjugated to the ligands are transcytosed, this process eliminates the potential side effects associated with the unspecific transport via the paracellular pathway. Researchers have used insulin-transferrin conjugates for enhancing the oral bioavailability of insulin [4]. Transferrin is a naturally occurring protein involved in the uptake of iron by the cells that binds specific receptors on the epithelial cells and is endocytosed. We are investigating the use of the complexation hydrogel as a delivery vehicle for the insulin conjugates. Since the insulin conjugates thus released from the polymer microparticles will have better enzymatic resistance and enhanced permeability across the epithelium, high bioavailability of the drug could be achieved. In this work we investigated the loading and release profiles of transferrin and insulin-transferrin conjugates from P(MAA-g-EG) microparticles. Experimental: Polymer Synthesis: Polymer microparticles of 150-210 μm size rage were prepared by free radical UV polymerization as described elsewhere [5]. The initial monomer feed ratio of MAA:EG was 1:1. Tetraethylene glycol dimethacrylate (TEGDMA) was added as a crosslinker at 0.75 mol% of the total monomer. 1-Hydroxylcyclohexyl phenyl ketone (Irgacure-184) was used as the free-radical initiator and added in the amount of 0.1 wt% of the monomer mixture. Conjugate Synthesis and Analysis: The conjugates were synthesized by coupling the proteins via succinimidyl 3-(2-pyridyldithio)propionate (SPDP), an amine reactive heterobifunctional crosslinker [4, 6]. Briefly, The N-terminal amino groups of bovine insulin (2 mg/ml) were protected by reaction with dimethylmaleic anhydride (DMMA) at a controlled pH of 6.8-7.0. Following this, the reaction products were dialyzed overnight (MWCO 3500) to remove the unreacted DMMA. The dialyzed protein was then reacted with 1 mg SPDP dissolved in minimum quantity of dimethylformamide for 2 hr. Insulin-PDP thus prepared was then dialyzed overnight and reacted with human holo transferrin-PDP complex (Tf-PDP) prepared by a similar procedure. The PDP:protein ratio was measured spectrophotometrically by measuring absorbance at 343 nm after reaction with 25 mM dithiothreitol (DTT) solution [6]. The conjugate was purified by size exclusion chromatography by elution on a Sephacryl-S200 column and protein modifications were confirmed by mass spectroscopy. The insulin: transferrin ratio in the conjugates was also measured to determine the number of insulin molecules coupled to a single transferrin molecule. Protein Loading and Release Studies: The proteins were loaded into the polymer microparticles by equilibrium partitioning from a concentrated protein solution at pH 6.8 [7, 8]. Briefly 140 mg of polymer particles were soaked in protein solution for 6 hr. The microparticles were then collapsed by addition of 20 ml of 0.1 M HCl, filtered through 0.45 μm pore size membrane, and freeze dried for 24 hrs. The release studies were performed in a USP II dissolution apparatus. 10 mg of the protein loaded particles were placed in 50 ml pH 2.0 buffer solution. 50 μl samples were withdrawn at different time points and analyzed by reversed phase HPLC. After 1 hr, the pH was increased to 7.4 by addition of NaOH solution. The samples were withdrawn and analyzed for 2 hrs. The fractional release of the protein from the formulations, defined here as the ratio of the amount released at any time (Mt) to the total amount released at the end of release experiment (M∞) was calculated. Results: Mass spectroscopy analysis of the prepared conjugates confirmed both the Nterminal primary amine blocking and PDP attachment to the lysine primary amine at β-29 position of insulin. Insulin conjugation to Tf was also confirmed by mass spectroscopy. The loading and release were performed initially for Tf as a preliminary step towards the development of conjugate loaded formulation since the Tf molecule is significantly larger (hydrodynamic radius, Rh, of 40Ǻ) as compared to insulin (Rh=20Ǻ). Hence the diffusion of Tf in and out of the polymer network may be significantly hindered. The release profile of Tf from P(MAA-g-EG) microparticles is shown in Fig. 1. The loading efficiency in these studies, based on the initial protein present in the loading solution was 54.6± 4.7% and the release efficiency based on the loaded amount was 64.4± 6.7%. The loading and release profiles of the conjugates from the polymer formulation was also studied in this work. 0 0.2 0.4 0.6 0.8 1 1.2 0 30 60 90 120 150 180 210 240 270 Time (min) Fr ac tio n of tr an sf er rin re le as ed

Quantum Dots in Biomedical Applications

Abstract: Semiconducting nanocrystals, more commonly known as quantum dots, possess unique size and shape dependent optoelectronic properties. In recent years, these unique properties have attracted much attention in the biomedical field to enable real-time tissue imaging (bioimaging), diagnostics, single molecule sensors, and drug delivery, among many other areas. The optical properties of quantum dots can be tuned by size and composition, and their small size and high surface area make them excellent candidates for intracellular tracking, diagnostics, in vivo imaging, and therapeutic delivery. We discuss recent advances and challenges in the molecular design of quantum dots are discussed, along with applications of quantum dots as drug delivery vehicles, theranostic agents, single molecule sensors, and real-time in vivo deep tissue imaging agents. We present a detailed discussion of the biodistribution and toxicity of quantum dots, and highlight recent advances to improve long-term stability in biological buffers, increase quantum yield following bioconjugation, and improve clearance from the body. Last, we present an outlook on future challenges and strategies to further advance translation to clinical application.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

The Design and Analysis of Experiments

Abstract: THE DESIGN AND ANALYSIS OF EXPERIMENTS. By Oscar Kempthorne. New York, John Wiley and Sons, Inc., 1952. 631 pp. $8.50. This book by a teacher of statistics (as well as a consultant for \"experimenters\") is a comprehensive study of the philosophical background for the statistical design of experiment. It is necessary to have some facility with algebraic notation and manipulation to be able to use the volume intelligently. The problems are presented from the theoretical point of view, without such practical examples as would be helpful for those not acquainted with mathematics. The mathematical justification for the techniques is given. As a somewhat advanced treatment of the design and analysis of experiments, this volume will be interesting and helpful for many who approach statistics theoretically as well as practically. With emphasis on the \"why,\" and with description given broadly, the author relates the subject matter to the general theory of statistics and to the general problem of experimental inference. MARGARET J. ROBERTSON

Harrison's Principles of Internal Medicine

Abstract: The 11th edition of Harrison's Principles of Internal Medicine welcomes Anthony Fauci to its editorial staff, in addition to more than 85 new contributors. While the organization of the book is similar to previous editions, major emphasis has been placed on disorders that affect multiple organ systems. Important advances in genetics, immunology, and oncology are emphasized. Many chapters of the book have been rewritten and describe major advances in internal medicine. Subjects that received only a paragraph or two of attention in previous editions are now covered in entire chapters. Among the chapters that have been extensively revised are the chapters on infections in the compromised host, on skin rashes in infections, on many of the viral infections, including cytomegalovirus and Epstein-Barr virus, on sexually transmitted diseases, on diabetes mellitus, on disorders of bone and mineral metabolism, and on lymphadenopathy and splenomegaly. The major revisions in these chapters and many

Understanding biophysicochemical interactions at the nano–bio interface

Abstract: Rapid growth in nanotechnology is increasing the likelihood of engineered nanomaterials coming into contact with humans and the environment. Nanoparticles interacting with proteins, membranes, cells, DNA and organelles establish a series of nanoparticle/biological interfaces that depend on colloidal forces as well as dynamic biophysicochemical interactions. These interactions lead to the formation of protein coronas, particle wrapping, intracellular uptake and biocatalytic processes that could have biocompatible or bioadverse outcomes. For their part, the biomolecules may induce phase transformations, free energy releases, restructuring and dissolution at the nanomaterial surface. Probing these various interfaces allows the development of predictive relationships between structure and activity that are determined by nanomaterial properties such as size, shape, surface chemistry, roughness and surface coatings. This knowledge is important from the perspective of safe use of nanomaterials.