Participation in this study will consist of a total of 5 visits to the UCSD Dermatology Clinic over approximately a one-month period. At the first visit, two psoriatic plaques between 2-cm and 5-cm in diameter to be studied in this trial will be agreed upon by the patient as well as the blinded and unblinded investigators. Preference will be given to plaques on the elbows since the elbow is a common place of psoriatic plaques, and since scarring on the elbows is usually more acceptable than scarring on other parts of the skin since the skin on the elbows is naturally hyperpigmented in most people. For the remainder of the study, all grading and measurements of the psoriatic plaques will be completed by a blinded investigator who is unaware of which plaque is receiving which treatment. An unblinded investigator will complete all other portions of the study visit, including digital photography, injecting the plaques, and completing the biopsies. The subject will also be blinded as to which plaque is being injected with which treatment.
During the first 4 visits, plaques will be injected with 1-mL of Hylenex® or 1-mL of sterile (pharmaceutical grade) normal saline (NS). 1-mL of Hylenex® contains 150 Units of recombinant hyaluronidase. This is the standard dose of the drug that has been approved by the FDA, and therefore this dose is considered to be safe for use in adults. If injected subcutaneously into the center of a psoriatic plaque that is between 2 and 5 centimeters in diameter, this 1-mL dose should be able to diffuse throughout the entire area beneath the plaque. The exact pharmacokinetics of Hylenex® are difficult to study due to its rapid inactivation after intravenous injection. According to the Hylenex® package insert, though, disruptions to the dermal barrier that occur in response to subcutaneous Hylenex® injection persist 24 hours after injection, but this barrier is completely restored after 48 hours. Cutaneous dendritic cells residing in the epidermis are thought to migrate away from the epidermis through either lymphatic or vascular channels after Hylenex® is injected. This process should take a few hours. Since cutaneous dendritic cells are thought to turnover only every several weeks, new dendritic cells should not populate the epidermis before patients receive the next injection of Hylenex®. Since dendritic cell activation initiates the inflammatory cascade thought to result in psoriasis, preventing dendritic cells from being harbored in the epidermis should essentially prevent the inflammatory cascade that results in psoriasis. Therefore, during the month-long period while patients are receiving Hylenex® injections, the inflammatory cascade triggering their psoriasis will potentially be turned off, allowing affected plaques to heal without propagation of further psoriasis. If this is true, there should be differences in the Hylenex®-treated versus the NS-treated plaques both morphologically and histologically upon completion of the final set of biopsies on the Visit 5.
