The future of ACEI production

ACEI are a major first line treatment in managing hypertension, but synthetic ACEI carry side-effects.
Food-derived ACEIp have been effective in BP reduction without adverse effects and can be used as an alternative to synthetic ACEI. Potent ACEIp have been isolated from whole-food protein hydrolysates of both animal and plant origin. However, protein hydrolysis-based methods generate complex peptidic mixtures from which ACEIp must be purified, increasing production costs. Besides, the resulting recovery yields and ACEIp bioavailability are low, rendering the process economically unviable.
The use of recombinant technology for the production of ACEIp can extend its application for functional foods and pharmaceutical purposes as it allows the large-scale and low-cost production. E. coli has been the preferred host for recombinant ACEIp production, but lactic acid bacteria (LAB), plants (predominantly cereals and legumes) and the microalgae C. reinhardtii have also emerged as ACEIp production hosts.
Bacteria, such as E. coli have the advantage of growing fast and not requiring complex culture systems. A diverse set of molecular tools available for ACEIp production in E. coli including, a wide range of vectors, promotors and inducers, provide also an important competitive advantage. Furthermore, LAB species with its GRAS status and extensive use in the dairy industry are important ACEIp production hosts for the functional foods industry.
Nevertheless, in recent years, the potential use of plant biotechnology for the large-scale production of pharmaceutically relevant proteins and peptides has significantly increased. Given their low-price and safety, plants offer many advantages for producing valuable recombinant proteins and peptides, as ACEIp, when compared to mammalian cell cultures (Gomes et al., 2019). Further, plants are very versatile, encompassing a wide range of production platforms, from transgenic plants to cell suspension cultures. The use of rice and soybean, for example, allows ACEIp accumulation in edible seeds, a direct delivery vehicle with improved protein stability and storage (Twyman et al., 2003), with soybeans seeds accumulating up to 40% protein (dry weight). Legumes as soybeans produce more proteins than other plants, being promising host systems for molecular farming. Alternatively, tomato fruits are palatable as raw tissue and can be lyophilized and stored for a long time (Lico et al., 2012). The possibility of using plant tissues as direct oral delivery means, is a major differentiating factor of bioactive peptide production in plant platforms, compared to mainstream production platforms, such asE. coli . In bacteria, the produced peptides must undergo complex purification procedures, and processed into a consumable product. Plant cell suspension cultures are alternatives to transgenic plants; tobaccocalli cultures proliferate rapidly, and technologies for gene transfer and expression are well-established for this species (Pires et al., 2012; Schillberg et al., 2013). Further, plant cell suspension cultures grown in sterilized contained environments provide a cGMP-compatible production environment, advantageous to the pharmaceutical industry and regulatory authorities (Paul et al., 2013; Spök et al., 2008). Chloroplast-based expression platforms also attract great interest in mass scale production of ACEIp, given its high recombinant protein expression levels (Fletcher et al., 2007). The algae model C. reinhardtii has fast growth rates, GRAS designation, and can be grown in contained environments (González-Ortega et al., 2015). Direct oral delivery of ACEIp in this host is also an option, as green algae are edible and do not contain endotoxins, human viral or prion contaminants (Mayfield et al., 2007). All these expression platforms are compatible with the above described genetic engineering strategies to improve ACEIp expression, including the multimerization of small peptides in tandem repeats, their fusion with (or insertion in) highly expressed proteins - with the plus of targeting/ accumulating the ACEIp-carrying chimeric proteins in seeds - and the use of similar chimeras, assembling different ACEI and other peptides into multifunctional bioactive polypeptides/proteins. Together with the use of gastrointestinal proteases cleavage sites to flank the peptides, these approaches are perfect for the adequate release of pharmacologically relevant peptides in edible platforms, for preventive or therapeutic purposes.