Research Article Metformin-Loaded Hyaluronic Acid Nanostructure for Oral Delivery Sonal Bhujbal 1 and Alekha K. Dash 1,2 Received 11 April 2018; accepted 24 May 2018 Abstract. The objective of this study was to develop a nanodelivery system containing a mucoadhesive polymer hyaluronic acid (HA) for oral delivery. Metformin was used as a model drug. Blank and drug-loaded HA nanostructures were prepared by precipitation method and characterized for particle size (PS), zeta potential (ZP), physical stability (over 65 days), surface morphology, moisture content, and physical state of the drug in the nanostructures. The cytotoxicity and hemolysis potential of the delivery system was assessed in Caco-2 cells and whole human blood, respectively. The in vitro release of metformin and its uptake in Caco-2 cells was evaluated using high-performance liquid chromatography. Ex vivo permeability of metformin was measured through goat intestinal membrane. The nanoparticles were physically stable and neutrally charged with an average PS of 114.53 ± 12.01 nm. This nanodelivery system existed as nanofibers containing metformin in a crystalline state. This delivery system released the drug rapidly with > 50% of metformin released within 1 h. Cellular uptake studies on Caco-2 cells indicated higher uptake of metformin from nanoparticle as compared to metformin in solution, up to first 45 min. Ex vivo permeability studies on the other hand showed a higher metformin permeability from solution relative to that from nanoparticles through the goat intestinal membrane. Metformin nanoparticles were non-toxic at therapeutic concentrations in Caco-2 cells and showed no hemolytic effect to RBCs. This study indicates the preparation, characterization, as well as the potential use of HA nanostructures for oral delivery. KEY WORDS: hyaluronic acid; nanostructure; oral delivery; metformin; permeability. INTRODUCTION Globally, an increasing prevalence of people stricken with diabetes occurred with an estimated 422 million adults, living with diabetes in 2014, as compared to 180 million in 1980. The global prevalence of diabetes nearly doubled since 1980, rising from 4.7 to 8.5% in the adult population. In addition, diabetes caused 1.5 million deaths in 2012 (1). In 2014, 29.1 million people in the USA (9.3% of the popula- tion) had diabetes and 8.1 million people were undiagnosed (2). Type 2 diabetes is the most common type of diabetes which accounts for 90–95% of those with diabetes around the world (3). It is a chronic condition that results from the body’s ineffective use of insulin and affects the way the body processes blood sugar (glucose) because of beta cell defi- ciency coupled with peripheral insulin resistance (4). Type 2 diabetes used to occur nearly entirely among adults, but now can be seen in children as well (1). It is usually controlled by oral drug therapy and may require insulin therapy when oral drug therapy alone fails to control the blood glucose level (5). Metformin is generally recommended as a first-line treatment for type 2 diabetes. The glucose-lowering effect of metformin is the result of the drug action on liver, muscle, and adipose tissues. Effect of metformin on hepatic glucose production is considered to be dominant. Explanations offered for its hypoglycemic action are suppressing of hepatic gluconeogenesis and glucose output from liver and enhance- ment of insulin-mediated glucose disposal in muscle and adipose tissues (6). It seems to alter the location of GLUT4 transport from the intracellular site to plasma membrane (7). In addition, metformin lowers the blood sugar level by increasing glucose uptake in peripheral tissues. Also, it inhibits intestinal glucose absorption by increasing anaerobic glucose metabolism, i.e., by stimulating glycolysis. It is important to note that it does not stimulate insulin secretion (8). Hence, metformin requires insulin for its action and acts as an anti-hyperglycemic agent and does not cause hypoglycemia. Metformin has a low oral bioavailability (50–60%). Despite its high solubility (50 mg/mL in water), metformin’s oral bioavailability is limited due to its saturable and poor intestinal absorption (9). Active transport is the primary mechanism of transport for metformin (10). Passive diffusion 1 Department of Pharmacy Sciences, School of Pharmacy and Health Professions, Creighton University, 2500 California Plaza, Omaha, Nebraska 68178, USA. 2 To whom correspondence should be addressed. (e–mail: adash@creighton.edu) AAPS PharmSciTech ( # 2018) DOI: 10.1208/s12249-018-1085-1 1530-9932/18/0000-0001/0 # 2018 American Association of Pharmaceutical Scientists