Synthesis, Characterization, and In vitro Studies of PLGA–PEG Nanoparticles for Oral Insulin Delivery Sara Hosseininasab 1 , Roghiyeh Pashaei-Asl 2 , Amir Ahmad Khandaghi 3 , Hamid Tayefi Nasrabadi 2 , Kazem Nejati-Koshki 2 , Abolfazl Akbarzadeh 2,4, *, Sang Woo Joo 5, *, Younes Hanifehpour 2,5 and Soodabeh Davaran 4, * 1 Department of Medicinal Chemistry and Drug Applied Research Center, Faculty of Pharmacy, Tabriz University of Medical Sciences, Tabriz 51368, Iran 2 Department of Medical Nanotechnology, Faculty of Advanced Medical Science, Tabriz University of Medical Sciences, Tabriz, Iran 3 Department of Medicine, Tabriz University of Medical Sciences, Tabriz, Iran 4 Drug Applied Research Center, Tabriz University of Medical Sciences, Tabriz, Iran 5 WCU Nanoresearch Center, School of Mechanical Engineering, Yeungnam University, Gyeongsan 712-749, South Korea *Corresponding authors: Abolfazl Akbarzadeh, akbarzadehab@tbzmed.ac.ir; Sang Woo Joo, swjoo@yu.ac.kr; Soodabeh Davaran, davaran@tbzmed.ac.ir Therapeutic proteins and peptides are corresponding to a major area of research in biotechnology compa- nies and current pharmaceutical. Because of their nat- ural instability, the enormous majority of these drugs require parent eral administration. Oral insulin delivery would be a highly attractive alternative process of administration, though it continues to be a mysterious target due to the enzymatic digestion of insulin and low levels of absorption from the gastrointestinal region. Hydrogel polymers can be considered as potential carriers for oral insulin delivery. In particular, a pH responsive hydrogel composed of PLGA–PEG has shown the ability to protect insulin from enzymes in the gastric environment and release in small intes- tines. However, this material has not shown similar potential for oral protein delivery of further model drugs. To date, the unique interaction between PLGA– PEG and insulin, as a potential drug for oral delivery, is not completely understood. The focus of this research is synthetization and characterization of hydrogels PLGA–PEG insulin nanoparticles and also pH sensitiv- ity of insulin nanoparticles was investigated. Key words: oral delivery, pH sensitivity, PLGA–PEG insulin Received 13 August 2013, revised 14 January 2014 and accepted for publication 3 March 2014 Diabetes is a chronic progressive disease, which can direct to complications such as kidney collapse blindness and foot amputation, and it is also a main risk factor for coro- nary heart disease and stroke. There are two main types of diabetes, type 1 and type 2. About 20% of diabetic people in UK have type 1 which is more widespread among chil- dren, young people, and young adults. Type 2 accounts for the rest and is most normally diagnosed in adults over the age of 45, although it is increasingly being diagnosed in younger people. On average, life expectancy is reduced by more than 20 years in people with type 1 diabetes and by up to 10 years in people with type 2 diabetes (1). Insulin is usually administered to diabetic patients through subcutaneous injection. One major problem encountered when treating diabetic patients with insulin is the very large inter- and intra-individual variability in subcutaneous insulin absorption. Other problems encountered with subcutane- ous insulin injections are pain, allergic reactions, hyperin- sulinemia, and insulin lipodystrophy around the injection sitea. Oral insulin delivery has received increasing attention in insulin formulations due to its high patient compliance and its potential to mimic the physiologic insulin secretion seen in nondiabetic individuals. However, oral insulin delivery has major limitations due to rapid enzymatic degradation in the stomach, digestion by proteolytic enzymes, and poor permeability across intestinal epithelium (2–5). Hence, vari- ous studies for oral insulin delivery have been investigated (6,7). Alternative methods for insulin delivery that have been investigated include intrapulmonary (6) intrauterine (7) ocu- lar, nasal (8) buccal (9), and transdermal (10) systems. In the recent years, the majority of research and develop- ment has been conducted involving a wide range of protein therapeutics for various conditions (11,12). Most of the pro- teins have been successfully applied in therapy, mainly as parenterals (15). An oral dosage form is the favorite form of delivery because of ease of administration, patient confor- mity, and cost. Major hurdles must be overcome before the oral delivery of a protein becomes a reality. Among the proteins, oral delivery of insulin has been the main focus of the scientists (13); however, no administered ª 2014 John Wiley & Sons A/S. doi: 10.1111/cbdd.12318 307 Chem Biol Drug Des 2014; 84: 307–315 Research Article