LSA Fellows 2

Morphine has long since been valued for its sedating and pain reducing effect but it also causes addiction in patients and must be given in elevated doses over time to preserve effectiveness due to a tolerance effect that sets in. The team of scientist surrounding Dr. Thomas Koch at the Institute for pharmacology and toxicology is studying how and why a tolerance to opiates including morphine is obtained when chronically induced and if there are possible ways of preventing this effect. They have found that different types of opiate substances can affect the same type of receptor in various ways: some opiates such as morphine cause the receptors to shut off in long term treatment and they continue to rest in this state, causing elevated levels of tolerance. Other substances cause an internalization of the receptors, where they are replaced in the membrane and are then available again to perform their task. This mechanism called receptor-endocytosis counteracts tolerance development.

The scientists were able to prove in cell cultures that apart from the commonly used endorphins, other clinically used opiates such as Fentanyl, Piritramid, and Sufentanil can also cause receptor-endocytosis. They found that opiates with elevated endocytoical potential lead to slower tolerance development in cell models. "Due to this negative correlation between endocytoical potential and the resulting level of tolerance observed, the conclusion could be obtained that these substances are better suited for long term therapy" states Dr. Koch. "However, the human body initiates an array of countermeasures on the cellular level as a result of the missing shutdown of the receptors, which can lead to a higher level of substance addiction." Therefore, further in vivo testing is needed to conclude whether endocytoical agonists are really better suited for long term therapy.