Intracellular chromophore

Intracellular chromophores are endogenous or exogenous molecules that possess specific chemical groups capable of absorbing light at particular wavelengths, thereby initiating photochemical or photophysical processes within the cell (Hamblin, 2017, Frontiers in Physiology). In the context of photobiomodulation (PBM), the primary intracellular chromophore is cytochrome c oxidase (CCO), a terminal enzyme in the mitochondrial respiratory chain that absorbs red and near-infrared light, leading to increased ATP synthesis and the activation of transcription factors (Karu, 1999, Journal of Photochemistry and Photobiology B). Another critical class includes porphyrins, such as protoporphyrin IX, which accumulate in malignant cells and act as targets for photodynamic therapy (PDT); upon light activation, these chromophores transfer energy to molecular oxygen, generating cytotoxic reactive oxygen species (ROS) that induce apoptosis (Agostinis et al., 2011, CA: A Cancer Journal for Clinicians). Melanin and hemoglobin also function as significant intracellular chromophores, particularly in dermatological applications where they are targeted for selective photothermolysis to treat pigmented lesions or vascular malformations (Anderson & Parrish, 1983, Science). While "intracellular chromophores" represents a broad category rather than a single receptor, targeting these molecules allows for non-invasive therapeutic interventions in oncology, wound healing, and various inflammatory conditions. The clinical efficacy of such treatments is highly dependent on the optical properties of the tissue and the specific absorption spectra of the targeted chromophores.

Other names

Endogenous chromophorePhotoacceptorCellular chromophoreLight-absorbing molecule

Absorption of photons by endogenous molecules (e.g., Cytochrome c oxidase) or exogenous precursors (e.g., Protoporphyrin IX) leading to electronic excitation, which subsequently modulates mitochondrial ATP production or generates reactive oxygen species (ROS) to induce therapeutic biological responses or selective cell death.