Biochemical and Biophysical Research Communications 377 (2008) 729–733 0006-291X/$ - see front matter © 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.bbrc.2008.10.059 Contents lists available at ScienceDirect Biochemical and Biophysical Research Communications journal homepage: www.elsevier.com/locate/ybbrc Transplantation of islets of Langerhans has recently proven to provide a good alternative to insulin treatment for some type 1 diabetes patients [1,2]. However, due to the limited supply of islets and the risks associated with immunosuppression, this procedure is mostly limited to patients suffering from severe hypoglycaemia unawareness. One problem that has become evident with islet transplantation is a blunted glucagon response or loss of alpha cells from the grafted islets, which has been demonstrated in patients [3,4] as well as in several animal models [5–9]. It has recently been suggested that alpha cell loss is associated with close contact of the alpha cells with the implantation organ, which seems to be particularly problematic in the liver [10], which is the implan- tation site of choice in humans. It is also evident from studies in both humans and animals that islet beta cell mass is lost after islet transplantation [1,11–14]. However it is not evident from these studies whether whole islets die or whether a proportion of beta cells within islets die. In the present study, we make use of the technique of microen- capsulation. Encapsulating individual islets of Langerhans in algi- nate beads is a simple technique that enables islet transplantation without the need for immunosuppression. It is based on physical separation of the islets from the host and thus large immune cells are excluded whereas small molecules such as oxygen, glucose and insulin easily can pass through the alginate gel barrier [15–18]. This system allows us to study transplanted islets that are not in direct contact with the host implantation site, which has, as men- tioned above, previously been reported to be detrimental for alpha cells. In addition, this model also provides an opportunity to study individual islets after implantation. The aim of the current investigation was to study the efficacy of encapsulated islets in reversing hyperglycaemia in chemically induced as well as spontaneous models of diabetes. In addition, we aimed to investigate the effect long term implantation had on the morphology and composition of transplanted islets which are not in direct contact with host tissues. Methods Animals. Inbred male C57BL/6J and BALB/c mice were used as islet donors, whereas male C57BL/6J and spontaneously diabetic female NOD mice, weighing 25–30 g (M&B; Shensved; Denmark), served as recipients. Recipient C57BL/6J mice were made diabetic by an intravenous alloxan injection (75 mg/kg body weight, Sigma, Irvine, UK). Mice with a non-fasting blood glucose concentration greater than 16.7 mmol/l were considered diabetic and used as islet transplant recipients. During the experiments, the animals had free access to tap water and pelleted food. The animal exper- iments were approved by the local animal ethics committee for Uppsala University. Islet isolation. Pancreatic islets were isolated using collagenase digestion and density gradient purification. Briefly, the animals were anesthetized with an intraperitoneal injection of 100 mg/kg pentobarbital sodium. Thereafter 2–3 ml cold collagenase solu- tion (from Clostridium histolyticum; Roche Diagnostics, Mann- heim, Germany; 2.5 mg/ml Hanks´ balanced salt solution; Statens Islet alpha cell number is maintained in microencapsulated islet transplantation Sara Bohman a , Aileen J.F. King b, * a Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden b Beta Cell Development and Function Group, Division of Reproduction and Endocrinology, Hodgkin Building 2.4N, Guy’s Campus, King’s College, London SE1 1UL, UK article info abstract Article history: Received 30 September 2008 Available online 23 October 2008 Islet transplantation can reverse hyperglycaemia in Type 1 diabetes patients. One problem in islet trans- plantation is a loss of beta cell mass as well as blunted glucagon responses from the grafted islets. It has been suggested that alpha cell loss is associated with close contact of the alpha cells with the implanta- tion organ. In the present study we made use of microencapsulation, where transplanted islets are not in direct contact with the host implantation site. After transplantation, the number of glucagon cells stained per microencapsulated islet section was increased whereas the number of insulin cells stained was decreased. DNA content of the islets was reduced, as was insulin content, whereas glucagon content was unchanged. This indicates that cell number in transplanted microencapsulated islets diminishes, which can be accounted for by loss of beta cells. However, in contrast to previous studies using non- encapsulated islets, alpha cell number seems to be maintained. © 2008 Elsevier Inc. All rights reserved. Keywords: Islet transplantation Microencapsulation Alginate Glucagon Alpha cells * Corresponding author. Fax: +44 207 848 6290. E-mail address: aileen.king@kcl.ac.uk (A.J. King).