Mass spectrometry of the subcutaneous interstitial fluid obtained by microdialysis in situ in lean man: A novel in vivo application of proteomics

<I>Background:</I> Obesity and the metabolic syndrome is a global problem, and it is known that the adipose tissue plays a crucial role in its development. Many methods exist to study this problem, but there is a need of a minimally invisive in vivo technique. The combination of microdialysis with Mass spectrometry could present a further insight into what mechanisms in the adipose tissue that promote development of the metabolic syndrome.<p></p><I>Aim:</I> To develop and evaluate a method for studies of the adipose tissue secretome in vivo.<p></p><I>Method:</I> Basic protocols for microdialysis and Mass spectrometry were adapted to one another before subcutaneous dialysates of 8 healthy subjects were run through the protocol. The proteins detected in all subjects were checked through a database for information regarding origin, function, size and if they were secreted or not. A general overview of the results was also made investigating the relation to protein concentration in the dialysate and the number of different proteins detected for each additional subject.<p<</p> <I>Results:</I> 531 proteins were detected, of which 63 were found in all subjects. Out of these 63 proteins, 87% were identified as secreted proteins, about half of them having an inflammatory or cell damage response function whereas the other proteins were transporters, metabolic proteins or had other functions. About 50% of the proteins were described as plasma proteins, a third had an unknown origin and all the remaining but one protein had an origin from a cell type within the adipose tissue. The correlation between the protein concentration in the collected dialysate and the amount of detected proteins was low. For each subject added to the study additional proteins unique for that sample were detected. There was a low variation between subjects regarding protein concentration of individual proteins.<p></p><I>Conclusions:</I> The method provides a unique insight to the adipose tissue secretome which previously did not exist. However, there is a large amount of cell damage and inflammation which to some extent may be caused by the inserted catheters. Therefore, when applying this method to a comparative study between two groups, inflammatory components will have to be interpreted with caution. Nevertheless, there are indications that the protocol could be further refined by simple means