Development of biotin-retinoid conjugates as chemical probes for analysis of retinoid function

Synthesis and Identification of a Novel Peptide, Ac-SDK (Biotin) Proline, That Can Elicit Anti-Fibrosis Effects in Rats Suffering from Silicosis

Background

N-Acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) is a short peptide with an anti-silicosis effect. However, the short biological half-life and low plasma concentration of Ac-SDKP hamper discovery of specific targets in organisms and reduce the anti-silicosis effect. A novel peptide, Ac-SDK (biotin) proline, termed “Ac-B”, with anti-fibrotic properties was synthesized.

Methods

Ac-B was detected quantitatively by high-performance liquid chromatography. Phagocytosis of Ac-B by the alveolar epithelial cell line A549 was investigated by confocal laser scanning microscopy and flow cytometry. To further elucidate the cellular-uptake mechanism of Ac-B, chemical inhibitors of specific uptake pathways were used. After stimulation with transforming growth factor-β1, the effects of Ac-B on expression of the myofibroblast marker vimentin and accumulation of collagen type I in A549 cells were analyzed by Western blotting. Sirius Red staining and immunohistochemical analyses of the effect of Ac-B on expression of α-smooth muscle actin (SMA) in a rat model of silicosis were undertaken.

Results

Ac-B had good traceability during the uptake, entry, and distribution in cells. Ac-B treatment prevented an increase in α-SMA expression in vivo and in vitro and was superior to that of Ac-SDKP. Caveolae-mediated uptake of Ac-B by A549 cells led to achieving anti-epithelial–mesenchymal transformation (EMT) effects.

Conclusion

Ac-B had an anti-fibrotic effect and could be a promising agent for the fibrosis observed in silicosis in the future.

Design of synthetic retinoids

This chapter has been conceived as an introductory text to aid in the understanding of the key design strategies for the development of synthetic analogs of endogenous retinoids as ligands for the retinoic acid receptors (RARs) and retinoid X receptors (RXRs). The structure and binding characteristics of the endogenous retinoids are first explained to put the main chemical design challenges in context. Existing biochemical and structural data is then used to describe the guiding principles used to develop agonists and antagonists of the RARs and RXRs. In light of the increasing proliferation of biophysical methods that employ fluorescence measurements or molecular tags, we also examine the application of retinoids as probes and the chemical principles required to develop these tools.