Photodynamic therapy (PDT) incorporates the use of photosensitive drugs that are activated using a light source. Already used to successfully treat some eye and skin conditions as well as certain types of cancer, scientists are now exploring its potential for treating bacterial infections.
Previously, PDT was limited to treating local or superficial applications – meaning that it was unsuitable for systemic bacterial infections, such as sepsis of the blood. But recently, researchers have demonstrated its potential effectiveness for treating such illnesses – although this currently involves disinfection of the patient’s blood whilst outside of the body.
As the vast majority of clinically-approved photosensitive agents are delivered intravenously, there is a need to develop new methods that can work within the patient’s bloodstream.
Most PDT experimental testing systems currently available for researchers involve static conditions, which are not physiologically-relevant for bloodstream infections.
In a first-of-its-kind approach, a team of scientists in Germany have now made use of a unique dynamic circulation model to facilitate antibacterial PDT under flow conditions created to mimic the bloodstream.1 Designed with the human circulatory system in mind, the researchers simulated the heart with a pump, the blood vessels using silicone tubing corresponding to a mid-sized vein – and achieved a constant body temperature by submerging most of the tubing within a water bath.
To test their model, the researchers prepared PLGA2 nanoparticles loaded with the naturally-occurring photosensitiser, curcumin – which, once activated with light of a specific wavelength, generates reactive oxygen species that can kill bacteria.
For the steps involved in the preparation and characterisation of the curcumin-loaded nanoparticles, the researchers used ultrapure water obtained from a ELGA PURELAB® Flex 4 laboratory water purification system – minimising the risk of introducing any contaminants that could affect the outcome of their experiments.
The researchers added a suspension of bacteria and nanoparticles into their experimental circulation system, using the pump to achieve an even distribution. After a short incubation period, they administered different doses of irradiation using a laser light that they incorporated into the silicone tubing. Their results showed that the local administration of PDT using nanoparticles loaded with curcumin led to a significant reduction in bacterial viability.
This new circulation model will now enable researchers to simulate the physiological environment of the venous circulatory system for testing new photosensitizers under flow conditions – paving the way for the development of new PDT strategies for treating bloodstream infections that could help to decrease our reliance on antibiotics.
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Dr Alison Halliday
After completing an undergraduate degree in Biochemistry & Genetics at Sheffield University, Alison was awarded a PhD in Human Molecular Genetics at the University of Newcastle. She carried out five years as a Senior Postdoctoral Research Fellow at UCL, investigating the genes involved in childhood obesity syndrome. Moving into science communications, she spent ten years at Cancer Research UK engaging the public about the charity’s work. She now specialises in writing about research across the life sciences, medicine and health.