Aims/hypothesis: Adiponectin is an adipocyte-derived secretory factor that is highly specifically expressed in adipocytes. It exerts effects on energy homeostasis via peripheral and central mechanisms. However, it is not clear whether adiponectin is crossing the blood brain barrier in humans. In serum, adiponectin circulates in several different complexes, each of which has distinct functions. Here, we wanted to test whether adiponectin can be found in human cerebrospinal fluid (CSF), and whether specific adiponectin complexes are enriched in CSF compared to peripheral serum samples. Furthermore, we also wanted to establish whether there is a gender difference with respect to the distribution of adiponectin oligomers in CSF.
Methods: A total of 22 subjects (11 male subjects and 11 female subjects) were analyzed in the study (BMI, 28.0±4.7 kg/m2; age, 70±7 years).
Results: Analysis of total adiponectin expression revealed that adiponectin protein is expressed in human CSF at levels approximately 0.1% of serum concentrations. Moreover, the distribution of adiponectin oligomers differs considerably in CSF to that of serum within matched samples from the same patients. Only the adiponectin trimeric and LMW hexameric complexes are found in CSF, with a bias towards the trimeric form in most patients. In terms of gender, male subjects have a higher CSF-to-serum ratio of total adiponectin expression than female subjects (P<0.05; n=20), and display slightly higher trimer expression in serum and CSF compared to female subjects.
Conclusions/interpretation: We conclude that the adiponectin trimer is the predominant oligomer expressed in human CSF.