Pharmacokinetic/Pharmacodynamic Modeling of Spiramycin against Mycoplasma synoviae in Chickens

The Pharmacokinetics of tilmicosin in plasma and joint dialysate in an experimentally Mycoplasma synoviae infection model

Mycoplasma synoviae (MS) infection is a serious threat to poultry industry in China, thus it is essential to study the pharmacokinetics (PK) in the target site of MS-infected chickens, but there are no relevant reports at present. The aim of this study was to compare the PK of tilmicosin in plasma and joint dialysate in MS-infected chickens. The MS infection model was established by evaluating the influence factors of the susceptibility of chicken species, day age of chicken, infection routes, infection cycle, infection dose, and stress response. The clinical symptoms, pathogen isolation, PCR identification, and ELISA antibody were detected to determine whether the MS infection model has been successfully established. Eight-week-old Mahuang chickens were challenged with MS by joint combined with footpad, 2 mL each time, twice a day for 5 d, then the MS infection model was successfully established. The infection group was orally administrated a single dose of 15 mg/kgbody weight (b. w.) tilmicosin. The joint dialysate was collected by the microdialysis technique, then the concentration of tilmicosin in plasma samples and joint dialysate were determined by triple quadrupole high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). There was no significant difference in elimination half-life (t_1/2) and the mean residence time (MRT) of dialysate and plasma. In contrast, the time of the area under the concentration-time curve (AUC) and the (maximum concentration of tilmicosin in plasma) C_max of tilmicosin in plasma was 2.1 and 1.4 times higher than in dialysate. The distribution coefficient of tilmicosin in joint and plasma (AUC_dialysate/AUC_plasma) was 0.51. In conclusion, tilmicosin concentration in joints of MS-infected chicken was much lower than that of plasma, which may result in the poor clinical effect and drug resistance. The study could provide a reference for the clinical use of tilmicosin against MS.

Anti-Inflammatory Effects of Spiramycin in LPS-Activated RAW 264.7 Macrophages

Drug repurposing is a simple concept with a long history, and is a paradigm shift that can significantly reduce the costs and accelerate the process of bringing a new small-molecule drug into clinical practice. We attempted to uncover a new application of spiramycin, an old medication that was classically prescribed for toxoplasmosis and various other soft-tissue infections; specifically, we initiated a study on the anti-inflammatory capacity of spiramycin. For this purpose, we used murine macrophage RAW 264.7 as a model for this experiment and investigated the anti-inflammatory effects of spiramycin by inhibiting the production of pro-inflammatory mediators and cytokines. In the present study, we demonstrated that spiramycin significantly decreased nitric oxide (NO), interleukin (IL)-1β, and IL-6 levels in lipopolysaccharide (LPS)-stimulated RAW 264.7 cells. Spiramycin also inhibited the expression of NO synthase (iNOS), potentially explaining the spiramycin-induced decrease in NO production. In addition, spiramycin inhibited the phosphorylation of mitogen-activated protein kinases (MAPKs); extracellular signal-regulated kinase (ERK) and c-Jun N terminal kinase (JNK) as well as the inactivation and subsequent nuclear translocation of nuclear factor κB (NF-κB). This indicated that spiramycin attenuates macrophages’ secretion of IL-6, IL-1β, and NO, inducing iNOS expression via the inhibition of the NF-κB and MAPK signaling pathways. Finally, we tested the potential application of spiramycin as a topical material by human skin primary irritation tests. It was performed on the normal skin (upper back) of 31 volunteers to determine whether 100 μM and μM of spiramycin had irritation or sensitization potential. In these assays, spiramycin did not induce any adverse reactions. In conclusion, our results demonstrate that spiramycin can effectively attenuate the activation of macrophages, suggesting that spiramycin could be a potential candidate for drug repositioning as a topical anti-inflammatory agent.