Adiponectin complexes in human cerebrospinal fluid: Distinct complex distribution from serum

Aims/hypothesis: Adiponectin is an adipocyte-derived secretory factor that is specifically produced in adipocytes. It exerts effects on energy homeostasis via peripheral and central mechanisms. However, it is not clear whether adiponectin crosses 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 with peripheral serum samples. We also wanted to establish whether there is a sex-related difference with regard to the distribution of adiponectin oligomers in CSF. Materials and methods: We studied 22 subjects (11 men, 11 women) in this study. Their average BMI was 28.0 ± 4.7 kg/m²; average age was 70 ± 7 years. Results: Analysis of total adiponectin revealed that adiponectin protein is present in human CSF at approximately 0.1% of serum concentration. The distribution of adiponectin oligomers differs considerably in CSF from that of serum within matched samples from the same patients. Only the adiponectin trimeric and low-molecular-mass hexameric complexes are found in CSF, with a bias towards the trimeric form in most patients. Male subjects have a higher CSF:serum ratio of total adiponectin (p < 0.05; n = 20) and have slightly higher trimer levels in serum and CSF than female subjects. Conclusions/interpretation: We conclude that the adiponectin trimer is the predominant oligomer in human CSF.