Cambios en el proceso de asignación de recursos

Molecular pharming refers to the generation transgenic plants which are genetically engineered to maximise production of pharmaceutical and industrial proteins

(Obembe et al., 2011). Hacker et al., (2009) reported that about 100 human therapeutic proteins are on the market and work is on-going to develop over 370 more. Molecular approaches which show prospect for high-yield production of L- DOPA or natural product pharmaceuticals both in situ or heterologously in vitro could include; enhancement of gene transcription and translation efficiency by using optimised constitutive or inducible promoters, engineering enhancers, activators or repressors. Xu et al., (2011) reported that a hybrid promoter comprised of CaM35S

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elements and a mannopine synthase promoter of Agrobacterium Ti plasmid increased GUS expression by 3 - 5 folds higher when compared to the double enhanced CaMV35S promoter. In another study to enhance promoter efficiency, Lee et al., (2006) demonstrated that foreign protein expression in plant cells increased by 30 folds when an oxidative stress-inducible peroxidase (SWAP2) promoter was used instead the constitutive CaMV35S. In addition, the use of 5’ leader sequences from tobacco etch virus or Alfalfa mosaic virus among others as translation elements could enable efficient translation at the 3’end sequence of the transgene (Xu et al., 2011). Other molecular approaches for enhancing yield of natural biopharmaceutical product both in vitro and in vivo, include strategies for reducing post-translation degradation by for instance co-expressing of protease inhibitors with recombinant proteins (Komarnytsky et al., 2006).

Besides molecular approaches, the yields of natural L-DOPA and other natural pharmaceutical products could be enhanced by using M. pruriens cell cultures approaches such as; optimisation of culture medium by supplementing with hormones, precursors or protein stabilising agents such as polyvinyl pyrrolidone (PVP). Other strategies include; immobilisation of exponential growth stage cells a on a porous matrix or alginate which protect the cells from hydrodynamic shear (Bodeutsh et al., 2001). On the other hand, cells cultures used for heterologous expression of foreign proteins could also potentially produce harmful effects to the cells (Joo et al., 2006). The a fore mentioned potential harmful effects could however be avoided by; using a two-phase aqueous culture system such as polyethylene glycol (PEG) and dextran in which cultured cells get immobilised in the PEG phase along with substrates and nutrients while the generated recombinant proteins collect in the dextrin culture phase (Cabral, 2007). Alternatively protein

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binding resins binds to the recombinant protein and protects it from proteolysis. James et al., (2002) reported an 8-fold increase in the production mouse HCmAb protein upon supplementing the culture medium of N. tabacum cells with protein G resin.

However, there is a limit to which biological systems could be manipulated to enhance production of natural products such L-DOPA or therapeutical proteins besides environmental and related policy matters. In light of the above, using non biological approaches such as improving the engineering designs of bioreactors to achieve commercial scale production of natural products or therapeutic proteins. Optimising bioreactors to enhance sterile culture environment, improved aeration and reduction of shear stress on cells could lead to more efficient natural product synthesis (Paul and Ma, 2011; Xu et al., 2011). A stirred tank bioreactor could for instance improve aeration required especially by rapidly growing bacterial cells during heterologous expression experiments (Sambrook et al., 1989). Disposable plastic or polyvinyl bioreactors could be used to further reduce risks of contamination especially when human pathogens are used in the experiments. On the other hand advanced bioreactors such as fed-batch cultures, perfusion culture, continuous and semi-continuous culture bioreactors allow either continuous nutrient enrichment or replacement with fresh media at intervals. As a consequence of constant nutrient supply and replacement of old cells with new, the cells production potential is maintained at the exponential stage production which could result in increased yield of the natural product (Paul and Ma, 2011; Xu et al., 2011). Besides enhancing production of natural products or recombinant proteins, equally important is devising an efficient method for recovery and purification of natural products such as L-DOPA or recombinant proteins from cultured cells (Sambrook et al., 1989). In both bacterial

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and plant cell systems, the target recombinant proteins are either secreted into the medium or are retained inside the cells (Sambrook et al., 1989; Xu, et al., 2011). Proteins secreted into the media are often get diluted, become unstable and tend to require quick purification whereas proteins retained in the cytosol of cells tend to be pure, stable and in high concentration (Ma and Paul, 2011; Xu et al., 2011).

Molecular pharming has consistently shown great potential to emerge as source for commercial production pure natural products such as L-DOPA and therapeutical proteins by using plant and bacterial cells as bio-factories. The fact there is a growing number of patients who are allergic to some synthetic medical drugs and while many drugs have been recalled from the market (Ma and Paul, 2011). The natural product industry on the other hand is increasingly being accepted world-wide as an alternative source for natural pharmaceutical products.

We still depend upon biological sources for a number of secondary metabolites including pharmaceuticals (Pezzuto, 1995), over 80% of the approximately 30,000 known natural products are of plant origin (Balandrin and Klocke, 1988; Fowler and Scragg, 1988; Phillipson, 1990). In 1985, of the 3,500 new chemical structures identified, 2,600 came from higher plants. In addition 75% of the World population rely on plants for traditional medicine and 25% of the pharmaceuticals are based on plant-derived chemicals (Farnsworth, 1985; Payne et al., 1991). The chemistry of

Mucuna pruriens and for most other plants needs to be characterised so as to

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