PRODUCTION OF HUMAN RECOMBINANT DIFFERENTIATION FACTORS IN TRANSGENIC TOBACCO PLANTS

Research on bone regeneration began decades ago as a result of intensive studies on bone growth and healing. Bone has been recognised, among the many tissues in human body, as having the highest potential for regeneration, and it is the second most transplanted tissue following blood. Due to both internal mediators and external mechanical demands, it possesses the intrinsic ability for regeneration and is constantly engaged in a cycle of resorption and renewal undergoing continual chemical exchange and structural remodelling throughout adult life as well as during repair process in response to injury. Despite these abilities, beyond a critical point clinical intervention measures are needed; there are different clinical conditions requiring a large quantity of bone regeneration, such as for skeletal reconstruction of large bone defects created by trauma, infection, or cases in which the regenerative process is compromised, including necrosis, atrophic non-unions and osteoporosis. To describe the extent of this situation, it is estimated that annually more than 2.2 million patients receive bone defect repairs worldwide, with a cost greater than $2.5 billion just in the United States; this figure is expected to globally double by 2020 due to a variety of factors, including increased life expectancy. The board of the Bone and Joint Decade in 2009 has assessed that half of the people aged over 65, affected by chronic conditions, suffers of joint diseases and that the number of osteoporotic fractures has doubled in the previous 15 years. It should be also pointed out that the worldwide incidence of bone disorders and conditions is increasing in those societies where population ageing is combined with increased obesity and poor physical activity. Shortcomings, limitations, and complications of current clinical treatments for bone repair and regeneration have been reported in different studies. A variety of graft materials are currently used to enhance bone healing, and the relative success of these materials depends on many factors, not only on the specific properties of the graft itself. In addition to its physical properties, to be effective, a grafting material is required to even provide osteoconductive and/or osteoinductive activities. Osteoconduction, the ability of promoting bone growth by allowing bone formation on material’s surface, may suffice in clinical condition of less severe defects, where sufficient quantities and margins of bone exist. Osteoinduction instead, is the capability of promoting de novo bone formation at soft or hard tissue sites, and offers needful advantages for biologic reconstruction of severe situations. Among most commonly used materials there are allografts, cadaveric bone usually obtained from a bone bank, autologous grafts, bone harvested from the patient’s own body, or synthetic ones, often made of hydroxyapatite or other naturally and biocompatible substances. Allografts, mineralized or demineralized, are histocompatible, available in various forms including demineralized bone matrix and cortical grafts and whole-bone segments, depending on the host-site requirements, and provide an osteoconductive environment; however, their osteoinductive capacity is highly variable depending on the processing method and sourcing, and may be present in inadequate amounts for any bone-inductive effect. To date, autografts serve as the gold standard for bone grafts because they are histocompatible, non-immunogenic, and they offer all of the properties required. Specifically, this material provides an osteoconductive environment (i.e., three-dimensional scaffolds and porous matrix) coupled with cells (i.e., osteoprogenitor cells) as well as growth and differentiation factors(i.e., growth factors) that can result in osteoinduction Nevertheless, autogenous grafting is sometimes an expensive procedure that has a number of shortcomings, including the need for secondary surgery to harvest the graft, donor site morbidity, irregular resorption of transplanted tissue, and limited availability of donor bone. Furthermore autograft may be a useless or inadequate treatment option in cases where the defect site requires larger amounts of bone than is available. Other commonly used bone repair techniques involve synthetic materials and fillers, and growth and differentiation factors, but, although all these clinical interventions have been shown to improve bone repair, none of them possess all of the necessary characteristics: high osteoinductive and angiogenic potentials, biological safety, low patient morbidity, ready access to surgeons, no size restrictions, long shelf life and reasonable cost; all these limitations have led to an extensive research for alternatives. The discovery and subsequent production of the osteoinductive agents in bone, the Bone Morphogenetic Proteins (BMPs), have provided the possibility of reducing or avoiding the need for autograft, through a tissue-engineering product. Clinically, BMPs have demonstrated the potential to replace the use of autogenous bone in many applications so that costs and complications related to harvesting autograft can be prevented; in addition, the ability to control quality, activity and dose of the osteoinductive agent may provide greater assurance of bone induction and repair. Despite this, a widespread therapeutic use of BMPs has been hindered by difficulties in obtaining large amounts of pure, biologically active protein at a cost-effective price. Thus, the aim of this study was to develop a plant based system for cost-effective production of active recombinant BMPs. This introduction provides a review of the relevant literature pertaining to BMPs (especially to BMP-2) synthesis, processing and recombinant production process.