Photosensitization: Definition, Agents, Signs & Symptoms

Photosensitization can be defined as the method of initiating a reaction by using a material capable of absorbing light and transferring the energy to the appropriate reactants. The method is extensively used in photochemical research, especially for processes that require light sources of specific wavelengths that aren't readily available.
 

Key Terms: Photosensitization, Phototoxicity, Vivo Phototoxicity, Sheep Photosensitivity, Phylloerythrin

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What is Photosensitization?

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The method of initiating a reaction by using a material capable of absorbing light and transferring the energy to the appropriate reactants is known as photosensitization. Skin (particularly parts exposed to light and without extensive protective hair, fur, or pigmentation) becomes more vulnerable to UV radiation when photodynamic agents are present. Sunburn, photodermatitis, and photosensitization are not the same thing because they all cause pathologic skin changes without the application of a photodynamic substance.

Photosensitization produces unstable, high-energy molecules when photons interact with a photodynamic agent. These high-energy molecules react with skin substrate molecules, creating free radicals that increase permeability in outer cells and lysosomes' membranes. Cellular potassium leaks out and cytoplasmic extrusion occurs when the outer cell membranes are damaged. 

The lytic enzymes might enter the cell if the lysosomal membrane is damaged. Ulceration, necrosis, and edema are all possible side effects. The type of photodynamic agent, its dosage, and the amount of sunlight exposure all influence how long it takes for clinical symptoms to appear after exposure to it.
 

Also Read: Difference Between Apoptosis and Necrosis

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Photosensitizing Agents

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Photosensitization is usually classified according to the source of the photodynamic agent. Main (type I) photosensitivity, aberrant endogenous pigment synthesis (type II) photosensitivity, and hepatogenous (secondary, type III) photosensitivity are the three types of photosensitivity. A fourth group has been identified: idiopathic (type IV) photosensitivity.

Photosensitizing agents can take many different forms, including those that are fungi or bacteria. The most common sources of photosensitivity in animals, on the other hand, are plant-derived chemicals. Photosensitization can affect any animal, but it is most common in cattle, sheep, goats and horses.

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Primary Photosensitization and Secondary Photosensitization

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Primary photosensitization happens when plants containing photodynamic chemicals are consumed. These substances are absorbed through the digestive tract and further reach the skin. Secondary photosensitization is a side effect of liver injury. The accumulation of phylloerythrin, a photodynamic breakdown product of chlorophyll, can be caused by liver failure.

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Working Mechanism of Tetracycline Phototoxicity

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Seven commonly used tetracyclines were investigated to see what parameters were important in the phototoxicity process (TC). Clinical phototoxicity, photochemical degradation rates, and in vitro phototoxicity were all associated qualitatively, but not quantitatively, in the TCs. 

Phototoxicity was partially oxygen-dependent in vitro, and singlet oxygen may have played a role. The observed disparities between the in vivo action spectrum and the absorption spectrum of demethylchlortetracycline could be attributed to the phototoxic process' involvement of photoproducts. According to a mechanistic model for in vivo phototoxicity, the absorption of UVA radiation by TC plays a role in at least two important processes.

Also read: Types of Radiation

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Photosensitization Signs and Symptoms

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Photosensitivity can occur in as little as a few days after sheep are moved to biserrula pastures, although it can take weeks. The initial indicators of photosensitization in animals include but are not limited to,

1. Restlessness
2. Head trembling
3. e
4. Rubbing
5. Finding shelter in the shade

Early indicators of photosensitization include swelling of the head, eyelids, muzzles, mulesed region (tail), backline, and muzzles. These are the most noticeable parts of the body. These spots can become reddish and inflammatory if not treated, with the surrounding skin withering and peeling away, revealing raw tissue beneath. In severe situations, lambs may lose the tips or both of their ears, there may be a widespread split in the hair, and sheep may appear lame due to coronet inflammation.

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Things to Remember

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• Photosensitization is the process of initiating a reaction by absorbing light and transmitting it to the right reactants.
• When a photodynamic substance is ingested, injected, or absorbed through the skin, this results in primary photosensitization. 
• After the animal is exposed to ultraviolet radiation, the agent enters the systemic circulation in its natural state, causing skin cell membrane destruction.
• When there is liver damage, secondary photosensitization occurs.
• As dye-sensitized solar cells (DSSCs) resemble the photosynthesis process in green plants, chlorophyll has been tested as a photosensitizer.
• When photons react with a photodynamic agent in photosensitization, unstable, high-energy molecules are created.

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