Chondroprotective effect of zinc oxide nanoparticles in conjunction with hypoxia on bovine cartilage-matrix synthesis Eraj Humayun Mirza, 1,2 Chong Pan-Pan, 3 Wan Mohd Azhar Bin Wan Ibrahim, 1 Ivan Djordjevic, 1 Belinda Pingguan-Murphy 1 1 Faculty of Engineering, Department of Biomedical Engineering, University of Malaya, Kuala Lumpur 50603, Kuala Lumpur, Malaysia 2 Department of Biomedical Technology, College of Applied Medical Sciences, King Saud University, Riyadh, Kingdom of Saudi Arabia 3 Faculty of Medicine, Department of Orthopaedic Surgery, Tissue Engineering Group (TEG), National Orthopaedic Centre of Excellence for Research and Learning (NOCERAL), University of Malaya, 50603 Kuala Lumpur, Malaysia Received 8 January 2015; revised 1 April 2015; accepted 30 April 2015 Published online 27 May 2015 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/jbm.a.35495 Abstract: Articular cartilage is a tissue specifically adapted to a specific niche with a low oxygen tension (hypoxia), and the presence of such conditions is a key factor in regulating growth and survival of chondrocytes. Zinc deficiency has been linked to cartilage-related disease, and presence of Zinc is known to provide antibacterial benefits, which makes its inclusion attractive in an in vitro system to reduce infection. Inclusion of 1% zinc oxide nanoparticles (ZnONP) in poly octanediol citrate (POC) polymer cultured in hypoxia has not been well determined. In this study we investigated the effects of ZnONP on chondrocyte proliferation and matrix synthesis cultured under normoxia (21% O 2 ) and hypoxia (5% O 2 ). We report an upregulation of chondrocyte proliferation and sulfated glycosaminoglycan (S-GAG) in hypoxic culture. Results demonstrate a synergistic effect of oxygen concen- tration and 1% ZnONP in up-regulation of anabolic gene expression (Type II collagen and aggrecan), and a down reg- ulation of catabolic (MMP-13) gene expression. Furthermore, production of transcription factor hypoxia-inducible factor 1A (HIF-1A) in response to hypoxic condition to regulate chondrocyte survival under hypoxia is not affected by the presence of 1% ZnONP. Presence of 1% ZnONP appears to act to preserve homeostasis of cartilage in its hypoxic envi- ronment. VC 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 103A: 3554–3563, 2015. Key Words: articular cartilage, elastomeric scaffolds, hypoxia, nanocomposite, zinc oxide, nanoparticles How to cite this article: Humayun Mirza E, Pan-Pan C, Mohd Azhar Bin Wan Ibrahim W, Djordjevic I, Pingguan-Murphy B. 2015. Chondroprotective effect of zinc oxide nanoparticles in conjunction with hypoxia on bovine cartilage-matrix synthesis. J Biomed Mater Res Part A 2015:103A:3554–3563. INTRODUCTION The physiological environment of articular cartilage is typi- cally avascular and aneural. 1 Moreover, it is well established that the microenvironment of cartilage is hypoxic, with oxy- gen (O 2 ) tension ranging from <10% at the surface to <1% in the deepest layer. 2 However, although cartilage naturally resides in this spe- cific low oxygen tension microenvironment, articular chon- drocytes are customarily cultured at normal atmospheric oxygen tension (19–21%). 3,4 Nevertheless, many studies have reported that hypoxia is a key factor in the growth and survival of chondrocytes, 5–7 a factor which enhances the production of cartilage-like extracellular matrix (ECM), and maintains cell phenotype. 8,9 How chondrocytes make use of oxygen is not clear; however, researchers have recognized that 5% oxygen tension up-regulates matrix synthesis. 8–11 Because of the avascular nature of cartilage, its complex biological characteristics and low cell concentra- tion, articular cartilage has a limited capacity for self- repair. 12 Tissue engineering (TE) offers an alternative option for cartilage treatment. 13,14 Many studies have focused on tissue-engineering methods to create cartilaginous tissue in vitro, to enable cartilage transplantation. 15,16 Zinc (Zn) is an essential trace element for human and animal growth 17 has a critical role in cell proliferation, dif- ferentiation, and survival. 18 A Zn deficient diet has been shown to result in inhibited chondrocyte proliferation and increased apoptosis. 19 Zn deficiency has also been related to rheumatoid arthritis (RA) 20 defects in epiphyseal cartilage 21 and growth retardation. 22 Further, Zn is also known to possess antibacterial, anti- inflammatory, and antioxidant properties, 23–30 and hence Correspondence to: B. Pingguan-Murphy; e-mail: bpingguan@um.edu.my Contract grant sponsor: University of Malaya IPPP; contract grant numbers: PV012–2012A Contract grant sponsors: Ministry of Higher Education (MOHE), Government of Malaysia; contract grant number: UM.C/HIR/MOHE/ENG/44 3554 VC 2015 WILEY PERIODICALS, INC.