Towards a new sensitive method for the early detection of amyloidosis.

Amyloidosis is a general term for several different types of disease. Aggregates of amyloid proteins form and deposit in different tissues which can affect the normal function. As the disease progresses and amyloid deposits grow, tissues become irreversibly damaged. Amyloid deposits can be found in many different organs leading to a wide range of possible symptoms and making diagnosis challenging.

According to the National Institute of Health (NIH), amyloidosis is a rare disease, affecting less than 200,000 people in the USA. However, it is suspected that the figures are underreported and that amyloidosis is not that rare, just rarely diagnosed. Therefore, a more sensitive diagnostic method would help to uncover the reality of the situation.  Now, researchers from Linkoping University have developed a molecular probe that can detect an array of different amyloid deposits in several human tissues. The team state that their new probe is extremely sensitive and was used at very low concentrations to correctly identify every positive amyloidosis sample when compared to the traditional clinical tests, and also picked up some amyloidosis signals that the traditional methods were unable to detect.  The opensource study is published in the journal Amyloid.

Previous studies show that the primary mode of diagnosis for amyloidosis has been the Congo red stain.  However, the use of Congo red also has several pitfalls and un-experienced examiners might reach primary false positive results. In addition, small amounts of amyloid, pre-fibrillar deposits or a sub-set of protein aggregates not formally classified as amyloid, may remain undetected.  In comparison luminescent conjugated polythiophenes (LCPs) and luminescent conjugated oligothiophenes (LCOs) have been shown to identify a broader sub-set of disease associated protein deposits and heterogenic populations of protein aggregates have also been distinguished due to distinct spectroscopic signatures from these dyes.  Hence, LCO and LCPs have proven to be hypersensitive amyloid ligands that can be utilized for detection and spectral assignment of a plethora of protein deposit.  The current study shows that a novel LCO h-FTAA probe is much more sensitive than the current gold-standard, being able to detect small amyloid deposits in samples that were previously determined to be amyloid-free.

The current study investigated two separate disease cohorts with amyloid depositions in over 25 different organs. Results show that histological staining with h-FTAA resulted in intense fluorescence light emitted from amyloid deposits that were positive for Congo red and immunohistochemistry on adjacent sections.  Data findings show that staining with h-FTAA also facilitated detection of amyloid and small amyloid-like protein deposits that were Congo red negative.

Results show that screening of 114 amyloid containing tissues derived from 107 verified amyloidosis patients revealed complete correlation between h-FTAA and Congo red fluorescence with 107/107, or 100% sensitivity. Data findings show that 27 of 32 of Congo red negative control cases, were negative when diagnosed with h-FTAA. The lab note that small Congo red negative amyloid-like protein aggregates in kidney, liver, pancreas and duodenum were found by h-FTAA fluorescence in five control patients aged 72–83 years.  They conclude that their results mean their new probe could be used to detect amyloidosis before symptoms present, leading to faster and hence more effective treatment.

The team surmise that their findings show their probe could also be used to identify new types of amyloids and presymptomatic patients who are at risk of developing the disease.  For the future, the researchers state that they hope to apply this to other diseases where amyloids are present and develop real-time, non-invasive diagnostic probes.

Source: Linköping University