Cell Replacement Therapy: The Rationale for Encapsulated Porcine Islet Transplantation

Among the problems posed by chronic diseases today, one of the most daunting is that posed by diabetes mellitus, which is a very significant public health problem resulting in substantial morbidity and mortality (American Diabetes Association, 2011). With the increasing life-expectancy of the world's population, increasing exposure to environmental trigger factors, the rising incidence of obesity, and lifestyle changes such as unhealthy diets and decreased physical activity, the prevalence of diabetes has risen dramatically over recent years and is now reaching epidemic proportions globally. This rapid increase is a significant cause for concern, with an additional 7 million diagnosed each year (International Diabetes Federation, 2011). Diabetes is now the fourth or fifth leading cause of death in most developed countries (International Diabetes Federation 2000). Globally, it is estimated that more than 200 million adults now have diabetes and this number is expected to increase alarmingly in the coming decades. By the year 2025, it is estimated that almost 333 million people will have the disease (International Diabetes Federation 2006). Type 1 (insulin-dependent) diabetes accounts for 5% to 10% of all diagnosed cases. In 2003, approximately 4.9 million people (0.09% of the world’s population) were estimated to have type 1 disease, with Europe having the highest number of sufferers (1.27 million) followed by North America (1.04 million) and Southeast Asia (0.91 million). The highest prevalence of type 1 diabetes was in North America (0.25%) followed by Europe (0.19%) (International Diabetes Federation 2006). In 2002, there were an estimated 0.9 to 1.2 million people with type 1 diabetes in the USA (American Diabetes Association 2006). The incidence in recent years may have accelerated alarmingly as shown in a recent study from Finland where the rate increased from 31.4 per 100,000 per year in 1980 to 64.2 per 100,000 per year in 2005 (Harjutsalo et al, 2008). In New Zealand, the incidence of type 1 diabetes has doubled in the last 15 years, reflecting international trends. In 2003, the estimated prevalence of type 1 disease among the population aged <25 years was 0.18%, with the total number of sufferers in this age range numbering 2540. The majority, 85% (2158 people), were of European descent, while 9% were Maori, 2.9% were Pacific peoples, and 3.0% were Asian (Wu et al. 2005). Although the life-expectancy of patients with type 1 (insulin-dependent) diabetes mellitus has vastly improved since the introduction of insulin, the ability of insulin injections to