Psoralen

• Psoralen is a photosensitizing compound used in combination with UVA light for therapeutic purposes.
• It is primarily employed in photochemotherapy, specifically PUVA therapy, for conditions like psoriasis and vitiligo.
• The compound works by intercalating into DNA and forming cross-links upon UVA exposure, inhibiting cell proliferation.
• Common side effects include nausea, itching, and increased photosensitivity.
• Long-term use carries risks such as accelerated skin aging and an increased likelihood of skin cancer.

What is Psoralen?

Psoralen is a furocoumarin, a class of organic chemical compounds that are naturally present in a variety of plants, including celery, parsley, and limes. Its most significant characteristic is its ability to enhance the skin’s sensitivity to ultraviolet A (UVA) radiation. This photosensitizing effect is harnessed in medical treatments, where psoralen is administered before controlled exposure to UVA light. The compound itself is inactive until it absorbs UVA photons, after which it becomes reactive and can interact with biological molecules, primarily DNA.

What is Psoralen Used For?

Psoralen is predominantly used in a form of photochemotherapy known as PUVA therapy, which combines Psoralen with UVA light. This treatment is highly effective for various skin disorders characterized by rapid cell proliferation or pigmentary changes. The most common application is psoralen treatment for psoriasis, a chronic autoimmune condition causing rapid skin cell turnover. By slowing down the excessive growth of skin cells, PUVA therapy helps to clear psoriatic plaques.

Beyond psoriasis, psoralen is also utilized for treating other dermatological conditions, including vitiligo, where it stimulates melanocytes (pigment-producing cells) to repigment affected skin. It is also used in some cases of mycosis fungoides, a type of cutaneous T-cell lymphoma. The psoralen mechanism of action involves its ability to intercalate into the DNA of skin cells. When subsequently exposed to UVA light, psoralen forms covalent bonds with pyrimidine bases in the DNA, creating monoadducts and interstrand cross-links. These DNA adducts inhibit DNA synthesis and cell division, thereby reducing the rapid proliferation of skin cells seen in conditions like psoriasis and inducing apoptosis (programmed cell death) in abnormal cells.

Psoralen Side Effects and Risks

While effective, psoralen therapy carries several potential psoralen side effects and risks that require careful monitoring. Short-term side effects are often related to the photosensitizing nature of the compound and the UVA exposure. Patients commonly experience increased sensitivity to sunlight, which necessitates strict sun protection measures after treatment. Other acute reactions can include:

• Nausea and vomiting, particularly with oral administration.
• Itching or pruritus.
• Erythema (redness) or sunburn-like reactions if UVA exposure is excessive.
• Headache and dizziness.

Long-term risks are a significant concern, especially with prolonged or repeated courses of PUVA therapy. These include accelerated skin aging, characterized by dryness, wrinkling, and freckling. More seriously, long-term use of psoralen in combination with UVA therapy has been associated with an increased risk of certain skin cancers, particularly squamous cell carcinoma. Regular dermatological screenings are crucial for patients undergoing this treatment to detect any precancerous or cancerous lesions early. It is essential for patients to discuss all potential risks and benefits with their healthcare provider before initiating psoralen therapy.