Bio-detoxification of ricin in castor bean (Ricinus communis L.) seeds

Abstract

Ricin is a highly toxic ribosome-inactivating lectin occurring in the seeds of castor bean (Ricinus communis L.). Castor bean grows throughout tropical and sub-tropical regions and is a very important crop due to its high seed content of ricinoleic acid, an unusual fatty acid, which has several industrial applications. However, due to the presence of the toxin, castor bean can cause death after the exposure of animals to low doses of ricin through skin contact, injection, inhalation or oral routes. Aiming to generate a detoxified genotype, we explored the RNAi concept in order to silence the ricin coding genes in the endosperm of castor bean seeds. Results indicated that ricin genes were effectively silenced in genetically modified (GM) plants, and ricin proteins were not detected by ELISA. Hemagglutination activity was not observed with proteins isolated from GM seeds. In addition, we demonstrated that seed proteins from GM plants were not toxic to rat intestine epithelial cells or to Swiss Webster mice. After oil extraction, bio-detoxified castor bean cake, which is very rich in valuable proteins, can be used for animal feeding. Gene silencing would make castor bean cultivation safer for farmers, industrial workers and society.Castor bean (Ricinus communis L.) is commercially cultivated due to the high quality and content (mainly ricinoleic acid) of its seed oil. Major producers are India, Mozambique, China and Brazil, responsible for 1.7 million, 68.9, 40.0 and 37.5 thousand tons, respectively (http://www.fao.org/faostat). India is the main oil exporter, and the United States, the European Union, and China import about 84% of the castor oil available on the international market 1,2 . Ricinoleic acid (12-hydroxy-cis-9-octadecenoic acid) confers higher stability and viscosity on castor bean oil when compared to other vegetable oils and makes it a highly valued material in the composition of lubricants, plastics, cosmetics, paints, varnishes, ethanol and biodiesel 2,3 . However, castor bean seeds contain ricin, which is a highly toxic storage 7 S lectin. Ricin is a dimeric glycoprotein constituted of A-and B-polypeptide chains covalently linked by a disulfide bond 4 . The A-chain is a ribosome-inactivating enzyme that specifically depurinates the first adenosine in the GAGA nucleotide sequence from the conserved loop on the 28 S rRNA subunit 5,6 . This modification impairs the formation of a critical rRNA stem-loop configuration, to which elongation factor 2 binds during the translocation step of translation. The B-chain binds specifically to cell surface glycoproteins or glycolipids and facilitates the movement of the A-chain into animal cells. One A-chain molecule of ricin is able to irreversibly inactivate one thousand ribosomes per minute, impairing protein synthesis and causing cell death 7 . Castor bean seeds also contain the ricin homologue R. communis agglutinin (RCA 120 ), which is a tetrameric protein composed of two A-chains (90% similar to the ricin A-chain) and two B-chains (84% similar to the ricin...

Ricin and Ricinus communis in pharmacology and toxicology-from ancient use and “Papyrus Ebers” to modern perspectives and “poisonous plant of the year 2018”

“…In this context, the development of low-ricin or ricin-free castor cultivars (as well as low-ricin, low-ricinine, lowallergen cultivars) is of special interest for commercial castor oil production (Severino et al 2012). Sousa and co-workers explored the concept of gene knockdown by RNA interference (RNAi) in order to silence the ricinencoding genes in the endosperm of castor beans, aiming at increased safety of castor bean cultivation for farmers, industrial workers, and society (Sousa et al 2017). Furthermore, after oil extraction, bio-detoxified castor bean cake is attractive for animal feeding due to its rich content in valuable proteins (Sousa et al 2017).…”

“…Sousa and co-workers explored the concept of gene knockdown by RNA interference (RNAi) in order to silence the ricinencoding genes in the endosperm of castor beans, aiming at increased safety of castor bean cultivation for farmers, industrial workers, and society (Sousa et al 2017). Furthermore, after oil extraction, bio-detoxified castor bean cake is attractive for animal feeding due to its rich content in valuable proteins (Sousa et al 2017). In contrast, however, since lectins such as ricin play an important role in plant protection against insect pests, the development of ricin-free castor genotypes may increase the risk of pest incidence rates (for review, see Vandenborre et al 2011).…”

Spermatogenesis in sheep supplemented with detoxified castor bean (Ricinus communis L.) as a replacement for soybean meal

“…Silva et al (2015) proposed castor beans to be one of the most suitable oilseeds for the production of biofuel in northeastern Brazil, because of their ability to produce in water shortage, can be used in consortium with other crops, and in family farming production systems, besides being popular with consumers and therefore having high market value. Sub-products of castor bean obtained after oil extraction can potentially be used in the preparation of animal feed, because of their considerable protein content, low cost, and ease of use (Sousa et al, 2017). Besides, the exploitation of waste products generated by industries prevents them from being released directly into the environment (Santos et al, 2016).…”

Nutritional value and safety of castor bean (Ricinus communis) seeds detoxified in solid-state fermentation by Pleurotus ostreatus

“…Castor oil plant (Ricinus communis) belongs to the family of Euphorbiaceae and grows throughout tropical and sub-tropical regions of the world (Ojinnaka et al 2013;Sousa et al 2017). Castor seed is a poisonous seed of the castor oil plant (R. communis).…”