Photodynamic Therapy– Is Selective Damage Really that Selective?

Why doesn’t photodynamic therapy (PDT) cause any noticeable damage to human tissue? After all, the reaction causes damage to the bacterial membrane, and human cells have membranes as well.

This was a topic that really grabbed my attention when I first learned about photodynamic therapy.   How is it possible that with the creation of highly reactive molecules are we only limiting cellular destruction to bacterial cells? Although there may be a few different answers to this question, the primary solution is that we are not. Don’t be afraid and swear off photodynamic therapy right away, here me out first. Photodynamic therapy is primarily used as a treatment option for cancers. This treatment is used on cancerous tumours formed in esophageal cancer, lung cancer, skin cancer, as well as many different types. The photosensitizer is accumulated in the tumour either by direct injection or utilizing mutations of the cancerous cells that concentrate the photosensitizer inside the cell. After light is applied, the tumour cells are damaged, but the healthy cells are not greatly harmed. Why? One trait of a cancerous growth is the mutation of certain DNA repair enzymes. (Have a look at this Wikipedia article to give you a small background on DNA repair enzymes) These repair enzymes are responsible for fixing oxidative damage problems caused by free radicals. Scientific researchers, knowing this small fact about most cancerous tumour cells, use PDT and reactive oxygen species to their advantage. A healthy human cell can take some free radical “abuse”, but a tumour cell can only take so much until the cell dies. This fact, coupled with selective photosensitizer accumulation within tumour cells, makes PDT an excellent treatment option in some forms of cancer.

But what about antimicrobial PDT, commonly known as Photodisinfection? Firstly, an interesting finding is how terrible cancer photosensitizers work on bacteria. (Photodynamic therapy: a new antimicrobial approach to infectious disease? by Micheal R. Hamblin and Tayyaba Hasan is a great paper on antimicrobial photosensitizers) This means that we are not using photosensitizers that are known to cause the most oxidative damage against eukaryotic cells. Secondly, we are using a cell that is more attracted to bacterial cells. By this I mean that the photosensitizer molecule itself is positively charged, whereas the bacterial outer membrane is negatively charged, on average more so than a human cell membrane. It doesn’t take a photochemist to tell you that a big negative and positive attract more than a little negative and a positive.

The third, but not necessarily the final reason, is in the application strategy of photosensitizer. Periowave and MRSAid, two of Ondine’s main products, utilize local application of a photosensitizing solution to areas known to posses bacterial infection/colonization. This cuts down on any toxic effects that could occur by means of global injection of the photosensitizing solution in the body. Another application strategy utilized is the small amount of solution that is applied to the treatment site. Ondine uses small amounts of 0.6-2 ml of solution per treatment. Ten times that amount by ingestion would have very little effect on you with or without your body being illuminated!!

To wrap it up, antimicrobial PDT (or Photodisinfection) employs targeting to bacterial cells, application strategies, and your body’s general “super enzymatic” abilities to reduce, repair, and eliminate the negative side effects of PDT on human cells. To learn more about Photodisinfection, click here.

Related Posts Plugin for WordPress, Blogger...

Leave a Reply

Staypressed theme by Themocracy