Fotodinamic

Fotodinamic refers to processes and therapies that rely on light-activated chemicals, known as photosensitizers, to generate reactive oxygen species in the presence of tissue oxygen. This combination of a light-absorbing agent, light exposure at a specific wavelength, and oxygen leads to cellular damage and can induce cell death in targeted tissues. The approach is used both for diagnostic purposes and for treatment, most notably in photodynamic therapy (PDT) and antimicrobial photodynamic therapy (aPDT).

The mechanism involves three components: a photosensitizer that selectively accumulates in abnormal or diseased cells, light of a wavelength that activates the photosensitizer, and molecular oxygen in the tissue. Upon activation, the photosensitizer transfers energy to oxygen, forming singlet oxygen and other reactive species. These reactive molecules cause damage to cellular membranes, proteins, and nucleic acids, triggering cell death pathways such as apoptosis or necrosis. PDT can also damage tumor vasculature and stimulate local immune responses, contributing to therapeutic effects.

Historically, photodynamic concepts emerged in the early 20th century, with clinical development progressing through the latter half of the century. Today, PDT is used in dermatology for conditions like actinic keratoses and certain skin cancers, in oncology for selected solid tumors, and in ophthalmology with agents such as verteporfin. Photosensitizers include porphyrin- and chlorin-based compounds, and more recently phthalocyanines, chosen for their light absorption properties and tissue selectivity. Light sources range from lasers to light-emitting diodes, tuned to the photosensitizer’s activation wavelength.

Limitations include variable tissue oxygenation, depth of light penetration, and prolonged skin photosensitivity after treatment. Ongoing research seeks to improve selectivity, reduce side effects, and expand indications through targeted photosensitizers and combination therapies.

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