ABSTRACT
Colloidal encapsulations can be applied as protective matrices in aquaculture feeds. They promise an ideal approach to protect bioactive substances such as oral vaccines, pre- or probiotics against degradation due to acidic environments or untimely lixiviation. Alginate, chitosan and polyethylene glycol (PEG) are substances frequently applied in encapsulations as protective matrices. However, essential information on their direct and comparable characteristics and their effects on digestion speeds after oral application in aquaculture are lacking. The current study evaluated in vitro release and retention profiles of a model protein bovine serum albumin (BSA) after encapsulation with four experimental formulations of protective matrices: ALG - alginate; AC -alginate and chitosan, AP - alginate and PEG and APC - alginate, PEG and chitosan. The iron marked treatment diets were fed to juvenile rainbow trout and digestion speed was investigated using radiographic imaging. Digestion speeds did not differ significantly between treatments, with all test diets reaching the anterior fish intestine 10 h after feeding. The BSA retention under low pH was highest for the alginate-chitosan PM (84.7 ± 5.8 %). The inclusion of PEG reduced the retention rate in low pH but significantly increased the absolute BSA release. An oil coating significantly reduced the BSA release during the initial burst for the alginate, alginate-PEG and alginate-chitosan-PEG treatments and significantly reduced retention potential under neutral pH conditions. The feeding simulation trial showed that an oil-coated diet containing alginate-chitosan as a protective matrix can be used to protect the model protein during feeding (release to the water) and against the harmful milieu of the fish stomach. Different combinations of the investigated encapsulation substances can be used to achieve optimal encapsulation and protective characteristics depending on the application objective.
ABSTRACT
Phosphaalumenes are the heavier isoelectronic analogs of alkynes and have eluded facile synthesis until recently. We have reported that the combination of a phosphinidene transfer agent, Ar TerP(PMe3 ) (Ar Ter=2,6-Ar2 -C6 H3 ), with (Cp*Al)4 (Cp*=C5 (CH3 )5 ) afforded the phosphaalumenes Ar TerPAlCp* as isolable, violet, thermally stable compounds. In here we describe attempts to utilize Mes*P(PMe3 ) (Mes*=2,4,6-tBu3 -C6 H2 ) as a phosphinidene source in combination with different Al(I) precursors, namely Dip NacnacAl (Dip Nacnac=HC[C(Me)NDip]2 , Dip=2,6-iPr2 -C6 H3 ), (Cp*Al)4 and Cp3t Al (Cp3t =1,2,4-tBu3 -C5 H2 ). In all cases the formation of phosphaalumenes was not observed, however, their intermediate formation is indicated by formation of the dimer [Cp*Al(µ-PMes*)]2 (2) and C-H-bond activation products along the putative P=Al bond, giving unusual 1,2-P,Al-tetrahydronaphtalene derivatives 1 and 4, clearly underlining the role the sterically demanding group on phosphorus plays in these transformations. The reactivity studies are supported by theoretical studies, demonstrating a thermodynamic preference for the C-H activation products. Additionally, we show that there are potential pitfalls in the synthesis of Cp*2 AlH, the precursor to make (Cp*Al)4 and give recommendations how to circumvent these.
ABSTRACT
In poikilothermic vertebrates, seasonality influences different immunological parameters such as leukocyte numbers, phagocytic activity, and antibody titers. This phenomenon has been described in different teleost species, with immunological parameters peaking during warmer months and decreased levels during winter. In this study, the cellular immune responses of rainbow trout (Oncorhynchus mykiss) kept under constant photoperiod and water temperature against intraperitoneally injected Aeromonas salmonicida during the summer and winter were investigated. The kinetics of different leukocyte subpopulations from peritoneal cavity, spleen, and head kidney in response to the bacteria was measured by flow cytometry. Furthermore, the kinetics of induced A. salmonicida-specific antibodies was evaluated by ELISA. Despite maintaining the photoperiod and water temperature as constant, different cell baselines were detected in all organs analyzed. During the winter months, B- and T-cell responses were decreased, contrary to what was observed during summer months. However, the specific antibody titers were similar between the two seasons. Natural antibodies, however, were greatly increased 12 h post-injection only during the wintertime. Altogether, our results suggest a bias toward innate immune responses and potential lymphoid immunosuppression in the wintertime in trout. These seasonal differences, despite photoperiod and water temperature being kept constant, suggest an internal inter-seasonal or circannual clock controlling the immune system and physiology of this teleost fish.
