On-a-chip tryptic digestion of transthyretin: a step toward an integrated microfluidic system for the follow-up of familial transthyretin amyloidosis.

A microfluidic microreactor for trypsin mediated transthyretin (TTR) digestion has been developed as a step towards the elaboration of a fully integrated microdevice for the detection of a rare and disabling disease, the familial transthyretin amyloidosis (ATTR) which is related to specific TTR mutations. Therefore, an enzymatic microreactor coupled to an analytical step able to monitor the mutation of TTR on specific peptide fragments would allow an accurate monitoring of the treatment efficiency of ATTR. In this study, two types of immobilized trypsin microreactors have been investigated: a new miniaturized, microfluidic fluidized bed packed with trypsin functionalized magnetic particles (MPs), and a thiol-ene (TE) monolith-based chip. Their performances were first demonstrated with N-benzoyl-dl-arginine-4-nitroanilide hydrochloride BApNA, a low molecular weight substrate. High reaction yields (75.2%) have been reached within 0.6 min for the TE-based trypsin microreactor, while a lower yield (12.4%) was obtained for the micro-fluidized bed within a similar residence time. Transposition of the optimized conditions, developed with BApNA, to TTR digestion in the TE-based trypsin microreactor was successfully performed. We demonstrated that the TE-chip can achieve an efficient and reproducible digestion of TTR. This has been assessed by MS detection. In addition, TTR hydrolysis led to the production of a fragment of interest allowing the therapeutic follow-up of more than twenty possible ATTR mutations. High sequence coverage (90%), similar to those obtained with free trypsin, was achieved in a short time (2.4 min). Repeated experiments showed good reproducibility (RSD = 6.8%). These promising results open up the route for an innovative treatment follow-up dedicated to ATTR.