Effect of replacement of dietary fish oil with four vegetable oils on prostaglandin E2 synthetic pathway and expression of inflammatory genes in marine fish Larimichthys crocea.

As a lipid mediator with important immune function, prostaglandin E2 (PGE2) has been widely studied in mammals, whereas its synthetic pathway and immune function in fish have yet to be fully studied. To investigate the regulation of PGE2 synthetic pathway and inflammatory genes expression by dietary different oils and the underlying relationship, a 10-week feeding experiment and an immune challenge were carried out in marine fish Larimichthys crocea. Replacement of dietary fish oil (FO) with four vegetable oils (VO), including soybean oil, linseed oil, palm oil, and olive oil, all reduced PGE2 levels, and the decrease of arachidonic acid (ARA, substrate for PGE2) could account for this decline. Meanwhile, the expression of PGE2 synthesis related genes was basically upregulated, which seemed to be a feedback regulation, but it cannot compensate the deficiency of ARA. In addition, mRNA expression of inflammatory genes, including interleukin (IL)-1ß, IL-6, tumor necrosis factor (TNF)α and interferon (IFN)γ was all upregulated in four VO groups compared with FO group, which was the opposite of PGE2 levels. To verify the inflammatory regulation of PGE2, an immune challenge was conducted, and PGE2 alleviated LPS-induced expression of inflammatory genes, including IL-6, TNFα and IFNγ, and the similar downregulation of toll-like receptor (TLR) genes expression revealed that TLR signaling pathway participated in the anti-inflammatory regulation of PGE2. In conclusion, replacement of dietary FO with four VO (lack of ARA) reduced the levels of PGE2 that could alleviate LPS-induced inflammatory genes expression via TLR signaling pathway, which could be one of the reasons that VO induced inflammation in marine fish.

[Occurrence of Denitrifying Dephosphatation in a Hybrid Constructed Wetland System and Its Stability].

This study was conducted to explore the startup characteristics and stability of a hybrid constructed wetland (HCW) system with a denitrifying dephosphatation process, which was composed of two tidal flow-constructed wetlands (termed T-A and T-B). As the system was operated according to the two-time feeding tidal flow operation mode, denitrifying dephosphatation and nitrification could be respectively enhanced in T-A and T-B, and the HCW achieved ideal simultaneous denitrification and phosphorus removal effects when treating domestic sewage. The introduction of periodical carbon source supplements for phosphorus harvesting alleviated excessive phosphorus accumulation in T-A and increased the storage of PHB within denitrifying phosphate-accumulating organisms (DPAOs). Subsequently, a stable and efficient denitrifying phosphorus removal effect could be guaranteed to some extent as the HCW system was operated during the test. As the phosphorus harvesting cycle length was 30 d, the mean phosphorus recovery efficiency of the HCW system was 63.97% throughout the experiment. Regarding the typical cycle, the mean TP and NOx--N removal efficiencies of T-A could respectively achieve (97.86±0.70)% and (98.29±2.62)% during the denitrifying dephosphatation process, and the amounts of phosphorus release and PHB synthesis in T-A could also reach up to (1486.29±123.25) mg and (4.43±0.57) mmol·g-1, respectively, during the phosphorus harvesting process. Meanwhile, the utilization rate of the supplementary carbon in the system was (94.65±2.66)%. To summarize, this study offers a new method for simultaneous denitrification and phosphorus removal in constructed wetlands, and expands the development and application range of phosphorus recovery processes.

A comparative study: In vitro effects of EPA and DHA on immune functions of head-kidney macrophages isolated from large yellow croaker (Larmichthys crocea).

Comparative effects of different concentrations of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on immune responses of head-kidney macrophages isolated from large yellow croaker were studied in vitro. After exposing to serum-free medium for 1 day, cultured cells were incubated in medium supplemented with graded levels of EPA or DHA (0, 5, 25, 100, 200 and 1000 µM, respectively) in the form of fatty acid bovine serum albumin (FA-BSA) complex for 12 h, 24 h and 36 h, respectively. Control samples were incubated in the absence of EPA or DHA (2% bovine serum albumin, BSA). Following stimulation, cell viability, lipid peroxidation, secretary phopholipase A2 (sPLA2) and prostaglandin E2 (PGE2) production as well as some immune parameters including phagocytosis, respiratory burst activity and interleukin 1ß (IL-1ß) production were determined. Results showed that EPA and DHA affected cell viability in dose-dependent and time-dependent manners. In particular, cell viability was significantly decreased after 24 h and 36 h incubation with 1000 µM EPA or DHA (P < 0.05). Higher levels of EPA (200 and 1000 µM) caused a significant increase in the production of malondialdehyde (MDA) (P < 0.05), while DHA did not significantly affect the MDA production. EPA significantly increased the intracellular superoxide anion synthesis which, on the contrary, was significantly reduced by DHA. Phagocytosis percentage (PP) values were significantly higher in treatments with 5 µM DHA (P < 0.05), but significantly decreased by 200 and 1000 µM EPA and DHA compared to the control group (P < 0.05). Decreased PGE2 production was produced by cells treated with relatively low doses of EPA or DHA. When high levels of stimulants (1000 µM EPA or DHA) were used, PGE2 levels were elevated and reached a significant level (P < 0.05). Both EPA and DHA significantly inhibited the production of sPLA2, where DHA exerted the more potent inhibitory effects than EPA. No pronounced effect was observed on IL-1ß production among all the treatments, and IL-1ß level in cell culture supernatant was fairly low (only approximately 6 pg/ml). Those findings suggested that EPA and DHA could influence the immunity and physiological conditions of macrophages from head kidney of large yellow croaker in vitro.