ISSUE FOCUS FEED & ADDITIVE MAGAZINE September 2023 47 may significantly differ by molecular masses (up to 10 kDa). Furthermore, Hsps can also be classified based on expression patterns, constitutive cognate (Hsc) or inducible (Hsp). Hscs share 50-80% homology with their Hsp counterparts but are either silent or play a housekeeping function. Hsps on the other hand, are synthesized at very low levels in the cell under normal conditions but on exposure to a stressor, induction of Hsp synthesis increases hundreds fold. HSP FUNCTION What are these highly conserved group of proteins and what do they do? Typically, when Hsps are mentioned in the same moment as livestock, it is often assumed that heat stress is the topic of discussion. This is unfortunate, as Hsps are involved with so much more than just heat stress; they are integral to cellular homeostasis. Hsps act as molecular chaperones with a role in protein secretion and maintenance of cellular protein structures, for example, refolding proteins that denature due to cellular stress, helping to prevent cell apoptosis and contributing to cell survival. Hsps are upregulated in response to numerous stressors including nutritional deficiency, toxins, UV radiation, pathogens, microbial damage or, indeed, any cellular stress. When the cell is stressed, there is up-regulation of the Hscs to produce newly formed HSPs, which can be detected in the cell at concentrations significantly greater than the constitutive chaperones. Hsps act as an interconnected network of cell signals, a cascade of Hscs and Hsps driving cellular responses. For example, numerous Hsps are involved in the innate and adaptive immune response (e.g., Hsp60, Hsp70 and Hsp90; a response which is also dependent upon Hsp regulation (e.g., Hsp70) of oxidative stress via the Nrf2-Keap1 pathway. Crucially, Hsps have also been observed to have a protective immune function e.g., restoring tolerance in autoimmune diseases, in part due to their upregulation during inflammatory stress (Van Eden et al., 2017). Malfunction of HSPs is related with many diseases, including cancers, neurodegeneration, and other diseases. HARNESSING THE POWER OF HSP USING PLANT EXTRACTS As discussed earlier, Hsps are not confined to higher organisms. In fact, Hsps are also found in plants, and a good example is nopal or the prickly cactus pear (Opuntia ficus indica) and its fruits (Figure 1). O. ficus tends to be found in arid and semi-arid regions and is rich in phytosterols, flavonoids and phytols and in many cultures was a source of food, drink and medicine for centuries. Importantly, the environment where O. ficus is found can be exposed to extremes of temperature. It was observed that O. ficus rapidly produces high levels of Hsps (including 71-75kDa and 62 kDa) on exposure to extreme temperature (Somers et al., 1991). Recently, the potential of O. ficus cactus extract (CE) to stimulate Hsps in cell lines and subsequently aquatic and terrestrial species was explored with interesting results. Using sustainable practices, the fruits of O. ficus are harvested, and the cactus juice extracted, concentrated and combined with a novel carrier to increase bioavailability for use in animal production (as the product Opuntech, Nutri Biotech Services, Malta). When (CE) was applied to Artemia, Hsp70 was expressed within 1 hour of application and provided protection against abiotic stressors as well as increasing resistance to disease infection (Baruah et al., 2012; 2014). In horses, exercise was shown to increase the production of Hsp72 after 120 minutes. However, when horses were fed CE prior to exercise, Hsp72 was significantly increased within 30 minutes Figure 1. Fruits of the prickly cactus pear (Opuntia ficus indica)
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