IGF1 project

Before reading

There are a few terms that I would like to explain to you before you start reading the text below:
–biomarkers: biomarkers are measurable parameters that, for instance, can be used to tell whether you are healthy, sick, or whether a treatment is effective (or not). Think about tests that measure glucose in urine to diagnose diabetes or the well-known pregnancy test that measures the hormone ‘HCG’ in urine. For these examples, glucose in urine represents a biomarker for diabetes and HCG in urine represents a biomarker for pregnancy.
–mass spectrometry (MS): mass spectrometry is an analytical technique that can be used to detect various compounds such as drugs, lipids, and proteins. MS instruments, so-called mass spectrometers, separate these compounds on the basis of their mass (weight) and thereby can detect multiple compounds at the same time. Basically, mass spectrometers are very sensitive balances which you can use to simultaneously measure several compounds at a molecular level.

My Insulin-like Growth Factor 1 (IGF1) project is carried out under the umbrella of the Dutch Biomarker Development Center (BDC) which is a multi-center research consortium that aims at translating promising biomarkers to actual clinical tests. Unlike the BDC’s other targets of interest, IGF1 is not a promising biomarker but instead is already measured in hospitals for several decades now as a marker for specific growth-related disorders. However, several reports were published around 2012 mentioning reliability issues of commonly-used IGF1 tests. These issues triggered us to develop a novel test for this compound which needed to be simple, fast, and reliable of course.

An important characteristic of our method is that it is based on mass spectrometry. More specifically, we used a ‘MALDI-TOF’ mass spectrometer which is a specific type of MS instrument that is unique for its simplicity and speed. To illustrate this, a measurement can be started at a simple push of a button, and results are reported in a matter of seconds. Moreover, MALDI-TOF instruments are already available in thousands of hospitals around the world where they are used for the diagnosis of infectious diseases. It has thus already been shown that these instruments can be implemented in the complex environment of a hospital, so there is no need to doubt their usefulness in clinical practice.

Well, you can feel it coming, there is a ‘but’, as MALDI-TOF otherwise would already have been used for biomarker analysis in every hospital by now. For this particular technique, speed and simplicity come at the price of low sensitivity. Patient samples need to undergo all kinds of preparatory procedures in consequence, and these procedures can be time-consuming, labor-intensive, and are potential sources of variability. We managed to resolve these issues for IGF1 by developing a sample preparation protocol that can be performed entirely by lab robots. Furthermore, we applied a so-called ‘internal standard’ which corrects for any source of variability, either from the sample preparation or the MALDI-TOF detection procedures. After method development, we thoroughly tested our method based on regulatory guidelines and thereby proved that this method meets the quality requirements relevant for analytical techniques to be used for clinical purposes.

It is obviously nice to develop a method and to show that its quality is good, but we did not stop at that point. We wanted to apply the method to a large number of patient samples to answer important clinical questions and also to assess the performance of our method in a true clinical setting. So in a matter of days I analyzed over 1,000 patient samples which were from a clinical study on patients who previously underwent kidney transplantation. Well, to be honest, the robot and the mass spectrometer did most of the work, but I was around to keep a close eye and to interpret the results afterwards. Anyway, these analyses were revealing for two reasons:

• First of all, we found that our method performed very well in this clinical setting but also that the mass spectrometer’s performance decreased over time. This decreased performance was caused by dirtying of the instrument, which can actually be resolved easily although corresponding cleaning procedures do take time. The instrument thus needs to be cleaned often enough to ensure good quality results, but not too often as the instrument would then be out of order longer than it needs to be. Fortunately, we discovered specific readouts by which we, and others, can follow the dirtying of MALDI-TOF mass spectrometers in time and thereby establish appropriate intervals for cleaning these instruments.
• Second of all, we found that low IGF1 levels in people who underwent kidney transplantation were associated with poor health outcomes. To be more specific, we only found this association in female subjects and not in males, which is a very important outcome of our work. Some researchers have been claiming for years that IGF1 should be considered as the female version of testosterone, the well-known male hormone involved in growth. It is thus maybe not surprising that we also found that the association between IGF1 and poor health outcomes in female kidney transplant recipients is linked to muscle mass in these subjects. Anyway, as you may understand, there is still so much we do not know yet, and these uncertainties set the stage for interesting followup projects.