A Bioactive Extract Rich in Triterpenic Acid and Polyphenols from Olea europaea Promotes Systemic Immunity and Protects Atlantic Salmon Smolts Against Furunculosis

Abstract

In the present study, the modulation of the transcriptional immune response (microarray analysis) in the head kidney (HK) of the anadromous fish Atlantic salmon (Salmo salar) fed a diet supplemented with an olive fruit extract (AQUOLIVE®) was evaluated. At the end of the trial (133 days), in order to investigate the immunomodulatory properties of the phytogenic tested against a bacterial infection, an in vivo challenge with Aeromonas salmonicida was performed. A total number of 1,027 differentially expressed genes (DEGs) (805 up- and 222 downregulated) were found when comparing the transcriptomic profiling of the HK from fish fed the control and AQUOLIVE® diets. The HK transcripteractome revealed an expression profile that mainly favored biological processes related to immunity. Particularly, the signaling of i-kappa B kinase/NF-kappa and the activation of leukocytes, such as granulocytes and neutrophils degranulation, were suggested to be the primary actors of the innate immune response promoted by the tested functional feed additive in the HK. Moreover, the bacterial challenge with A. salmonicida that lasted 12 days showed that the cumulative survival was higher in fish fed the AQUOLIVE® diet (96.9 ± 6.4%) than the control group (60.7 ± 13.5%). These results indicate that the dietary supplementation of AQUOLIVE® at the level of 0.15% enhanced the systemic immune response and reduced the A. salmonicida cumulative mortality in Atlantic salmon smolts.

Phytogenics From Sage and Lemon Verbena Promote Growth, Systemic Immunity and Disease Resistance in Atlantic Salmon (Salmo salar)

“…In our study, we observed a modulation of the biological process "Regulation of I-kappaB kinase/NF-kappaB signaling (GO:0043122)". This modulation is in line with a recent study from our group, in which we demonstrated that a phytogenic feed additive from the olive fruit (Olea europaea), with biochemical and functional properties similar to MPLE, was also able to modulate biological process such as "Regulation of I-kappaB kinase/NF-kappaB signaling" (Salomón et al, 2021b).…”

“…In this context, eight of the ten hub genes related to leukocyte activation (fn1, notch1, grb2, rac2, rdx, ezr, smad3, abl1) were upregulated. Similarly, a modulation of immunerelated GOs such as "Leukocyte activation involved in immune response" were enriched in Atlantic salmon smolts fed a feed additive AQUOLIVE R as we mentioned above from a phytogenic derived from olive (O. europaea) fruit with similar biochemical and functional properties to the MPLE phytogenic tested in the current study (Salomón et al, 2021b). For instance, notch1 a gene we have previously discussed highlighting its connection between NF-κB and IFN-γ as biological processes that have a key role in the differentiation of granulocytes, macrophages, and dendritic cells (Schroeder et al, 2003;Monsalve et al, 2009).…”

“…Fish (55.0 ± 0.1 g and 16.2 ± 0.2 mm in BW and SL, respectively) were distributed among twelve experimental tanks (n = 58 fish per tank; 6 replicate tanks per experimental diet). Both experimental diets were offered to parrs at a daily feeding rate of 3.0% of the stocked biomass as described in Salomón et al (2021b). In addition, feed utilization was evaluated by the following formula: feed conversion ratio (FCR) = feed intake (g)/increase of fish biomass (g).…”

“…A speciesspecific PCR (Beaz-Hidalgo et al, 2008) was performed from DNA of bacterial colonies recovered from head kidney smears of all moribund fish in order to confirm the cause of death. For this purpose, animals were aseptically dissected and a sample from the head kidney was taken and plated on TSA, incubated at 23 • C for 72 h. Confluent pure bacterial growth was found from all samples, from which A. salmonicida was confirmed by means of PCR as described in Salomón et al (2021b).…”

“…RNA handling and the microarray analysis of samples were conducted as described by Salomón et al (2021b). Total RNA (200 ng) was reverse transcribed (Agilent One-Color RNA spike-in kit; Agilent Technologies) and used as a template for Cyanine-3 (Cy3) labeled cRNA synthesis and amplification (Quick Amp Labeling kit, Agilent Technologies).…”