Hydroxyproline is a non-essential amino acid found in collagen and few other extracellular animal proteins. It’s two isomeric forms trans-4-hydroxy-L-proline and trans-3-hydroxy-L-proline play a crucial role in collagen synthesis and thermodynamic stability of the triple-helical conformation of collagen and associated tissues. Various abnormalities in hydroxyproline metabolism have been shown to play key roles in the pathophysiology and pathogenesis of different diseases. The elevated level of hydroxyproline is observed in several disorders, e.g., graft versus host disease, keloids, and vitiligo while its decreased level is a marker of poor wound-healing. This review explores the potential of using hydroxyproline as a biochemical marker to understand the pathogenesis, molecular pathophysiology and treatment of these diseases. The review concludes with an outlook on the scope and challenges in the clinical implementation of hydroxyproline as a biomarker.

Objectives. The present study was aimed at investigating the wound healing effect of ethanolic extract of Cestrum nocturnum (L.) leaves (EECN) using excision and incision wound model. Methods. Wistar albino rats were divided into five groups each consisting of six animals; group I (left untreated) considered as control, group II (ointment base treated) considered as negative control, group III treated with 5% (w/w) povidone iodine ointment (Intadine USP), which served as standard, group IV treated with EECN 2% (w/w) ointment, and group V treated with EECN 5% (w/w) ointment were considered as test groups. All the treatments were given once daily. The wound healing effect was assessed by percentage wound contraction, epithelialization period, and histoarchitecture studies in excision wound model while breaking strength and hydroxyproline content in the incision wound model. Result. Different concentration of EECN (2% and 5% w/w) ointment promoted the wound healing activity significantly in both the models studied. The high rate of wound contraction (P<0.001), decrease in the period for epithelialization (P<0.01), high skin breaking strength (P<0.001), and elevated hydroxyproline content were observed in animal treated with EECN ointments when compared to the control and negative control group of animals. Histopathological studies of the EECN ointments treated groups also revealed the effectiveness in improved wound healing. Conclusions. Ethanolic extract of Cestrum nocturnum (EECN) leaves possesses a concentration dependent wound healing effect.