Increased collagen synthesis in psoriasis in vivo

Psoriasis is an inflammatory skin disease of unknown a etiology which also involves changes in dermal elements. Previous in vitro studies have shown an increased collagen synthesis rate in cultured fibroblasts. In this study collagen synthesis was studied in vivo in the uninvolved skin of psoriatic patients using a newly developed method in which collagen propeptides were measured in suction blister fluid. Both type I and type III collagen synthesis rates, as measured in terms of the carboxyterminal propeptide of type I procollagen (PICP) and the aminoterminal propeptide of type III procollagen (PIIINP), were increased about two-fold in uninvolved psoriatic skin as compared with controls, the mean level of PICP being 870 and 457 micrograms, respectively (P < 0.001), and of PIIINP being 294 and 124 micrograms, respectively (P < 0.01). The increased collagen synthesis rate was also confirmed by in situ hybridization using specific probes. Collagen mRNAs were found to be particularly abundant in psoriatic patients, who also demonstrated a high collagen synthesis rate when assayed by measuring collagen propeptides. The increased rate of collagen synthesis in the uninvolved psoriatic skin seemed not to be related to the severity of the disease or to various treatments such as UVB, PUVA, retinoids or cytostatic drugs, but seemed more likely to be due to the psoriasis itself. Interestingly, skin thickness was not increased in the patients with psoriasis, even though collagen synthesis was markedly elevated, perhaps suggesting that in psoriasis the turnover rate of collagen is enhanced.