Still, recommended clotting time varies greatly between different BDNF assays. During the coagulation process activation of platelets causes a release of BDNF from platelets into serum 12, suggesting that the length of the clotting time constitutes a critical methodological issue, when measuring the concentration of BDNF in serum 14, 15, 16. In order to obtain serum, blood samples must coagulate prior to centrifugation. It is well-established that much higher concentrations of BDNF are observed in serum than in plasma 12, 13. Also, it is uncertain how precisely BDNF levels measured in venous blood samples reflects circulating BDNF levels in vivo, and how various methodological approaches affect the result of the analysis.
#Serum vs plasma free#
Since platelets cannot pass the blood-brain barrier, the BDNF level in the brain may not be reflected by the amount of BDNF associated with platelets, but rather by the amount of free BDNF in plasma 13. Peripheral BDNF is mainly stored in platelets (~99%), and only a small amount of free BDNF is present in plasma 12, 13. biological medium, centrifugation strategy, temperature, and choice of bioassay) may introduce bias and complicate comparisons between studies.
Although research in animals suggests that changes in circulating BDNF may be used as a proxy for changes occurring in the brain, application of different methodologies (e.g. The relevance of this measure is supported by animal studies showing that BDNF is able to cross the blood-brain barrier in both directions 9 and that peripheral and central BDNF levels are associated 10, 11. In humans, BDNF levels in the brain (central BDNF) are difficult to measure, and therefore measurement of BDNF in the periphery is often used as a proxy. In resting adult rats high levels of BDNF have been identified in structures of the basal forebrain, the amygdala and the hippocampus 3, and it is well accepted that BDNF plays an important role in the formation of memory and learning 7, 8. BDNF is widely distributed in the central nervous system (CNS) 2, 3, where it binds to the non-selective low-affinity necrosis factor receptor, p75 NTR and the high-affinity receptor tropomyosin-related kinase B (TrkB), and induces cell survival, -growth, and -differentiation as well as synaptic plasticity 1, 4, 5, 6. The biological relevance of the velocity of BDNF release during clotting and its dependence upon fitness must be investigated further.īrain-derived neurotrophic factor (BDNF) is a growth factor protein and member of the neurotrophin family, which also includes, neurotrophin 3 and neurotrophin 4/5 1. Importantly, BDNF in serum and plasma appears to reflect two different pools of BDNF.
In conclusion, BDNF levels in serum were affected by clotting time, whereas BDNF levels in plasma were influenced by centrifugation strategy. to negative when clotting time was ≥60 min. Though not statistical significant, correlations between fitness and BDNF in serum changed from positive at 30 min. BDNF in NP correlated with PPP, whereas no correlations were found between BDNF in serum and plasma. A large increase was observed in serum BDNF levels during the first hour of clotting. Also, waist circumference and cardiorespiratory fitness were measured.
BDNF was analyzed in serum, normal plasma (NP) and platelet-poor plasma (PPP).
Blood samples were drawn after an overnight fast and treated to different protocols, varying in time before centrifugation and centrifugation strategy. Seventeen healthy males (25.2 (4.1) years) were included in the study. In addition, we analyzed associations between BDNF levels, cardiorespiratory fitness and waist circumference. The aims of the study were to clarify the impact of storage time and centrifugation strategy on brain-derived neurotrophic factor (BDNF) levels in human serum and plasma samples.