4-Thiaproline reduces heart lipid peroxidation and collagen accumulation in the diabetic db/db mouse

Consequences of incorporating thiaproline and its oxidized derivatives into collagen triple helices

(2R)-4-thiaproline (Thp) is an analog of proline, replacing Cγ in the pyrrolidine ring with sulfur. Its thiazolidine ring easily interconverts between endo and exo puckers due to a small energy barrier, which leads to destabilize polyproline helices. Collagen, composed of three polyproline II helices, mainly consists of X-Y-Gly triplets, where X is often proline and Y is frequently (2S,4R)-hydroxyproline. In this study, we incorporated Thp into either position-X or position-Y to investigate the consequences of such a replacement on the triple helix. Circular dichroism and differential scanning calorimetry analyses showed that the Thp-containing collagen-mimetic peptides (CMPs) can fold into stable triple helices, in which the substitution at position-Y exhibits a larger destabilization effect. Additionally, we also prepared the derivative peptides by oxidizing Thp in the peptide to N-formyl-cysteine or S,S-dioxide Thp. The results showed that the oxidized derivatives at position-X only slightly affect collagen stability, but those at position-Y induce a large destabilization effect. The consequences of incorporating Thp and its oxidized derivatives into CMPs are position dependent. Computational results suggested that the ease of interconversion between exo and endo puckers for Thp and the twist conformation of S,S-dioxide Thp may cause the destabilization effect at position-Y. We have revealed new insights into the impacts of Thp and its oxidized derivatives on collagen and demonstrated that Thp can be used to design collagen-related biomaterials.

Inhibition of collagen production delays malignant mesothelioma tumor growth in a murine model

Malignant mesothelioma is an aggressive fibrous tumor, predominantly of the pleura, with a very poor prognosis. Cell-matrix interactions are recognized important determinants of tumor growth and invasiveness but the role of the extracellular matrix in mesothelioma is unknown. Mesothelioma cells synthesize collagen as well as transforming growth factor-beta (TGF-β), a key regulator of collagen production. This study examined the effect of inhibiting collagen production on mesothelioma cell proliferation in vitro and tumor growth in vivo. Collagen production by mesothelioma cells was inhibited by incubating cells in vitro with the proline analogue thiaproline (thiazolidine-4-carboxylic acid) or by oral administration of thiaproline in a murine tumor model. Cell cytotoxicity was measured using neutral red uptake and lactate dehydrogenase assays. Proliferation was measured by tritiated thymidine incorporation, and inflammatory cell influx, proliferation, apoptosis and angiogenesis in tumors examined by immunohistochemical labelling. Tumor size was determined by tumor weight and collagen production was measured by HPLC. Thiaproline at non-toxic doses significantly reduced basal and TGF-β-induced collagen production by over 50% and cell proliferation by over 65%. In vivo thiaproline administration inhibited tumor growth at 10 days, decreasing the median tumor weight by 80%. The mean concentration of collagen was 50% lower in the thiaproline-treated tumors compared with the controls. There were no significant differences in vasculature or inflammatory cell infiltration but apoptosis was increased in thiaproline treated tumors at day 10. In conclusion, these observations strongly support a role for collagen in mesothelioma growth and establish the potential for inhibitors of collagen synthesis in mesothelioma treatment.