The pentapeptide QYNAD does not inhibit neuronal network activity

Introduction: Controversial data was published about the endogenous pentapeptide QYNAD, which is elevated in serum and cerebrospinal fluid of patients with demyelinating diseases like multiple sclerosis. QYNAD was made responsible for the rapid clinical fluctuations in these patients by blocking voltage-gated sodium channels of single cells with a maximum effect at a concentration of 10 micromol/l.

Methods: To determine the impact of QYNAD on neuronal network activity, we used the micro-electrode array (MEA) technique. This new technique allows convenient monitoring of spontaneous electrical activity of excitable cells and can be used as a cell-based biosensor for neuroactive substances. Cryopreserved rat cortical neurons were plated onto MEAs and developed a spontaneously active network within a few days. Extracellular potentials were recorded on MEAs with a square grid of 60 planar microelectrodes. Analysis of the network parameters spike rate, burst rate, burst duration, number of spikes per burst, duration of inter-burst interval and of inter-spike interval were performed offline by a custom-built software (Result, Tönisvorst, Germany).

Results: In concentrations between 100 nanomol/l and 800 micromol/l QYNAD did not alter network activity whereas the sodium channel blockers lidocaine (IC50 14.9 micromol/l) and tetrodotoxine [TTX] (IC50 1.1 nanomol/l) reversibly decreased network activity by prolonging the inter-burst intervals. After application of 10 micromol/l QYNAD the mean network activity was 88.8%±17.1% of control value. Comparison of network parameters in eight measurements after application of 100µM QYNAD showed no change in number of spikes per minute (ratio 1.1±0.2), number of bursts per minute (ratio 1.2±0.2), number of spikes per burst (ratio 1.1±0.2), burst duration (ratio 1.0±0.2), duration of inter-burst intervals (ratio 1.1±0.2) and of inter-spike intervals (ratio 1.0±0.1).

Conclusion: TTX and lidocaine remarkably reduced network activity in similar concentrations as in patch-clamp experiments, pointing to the high sensitivity of this biosensor. In contrast, QYNAD did not exhibit any acute inhibitory effect on rat cortical networks. Thus, QYNAD may not have a relevant impact on functional disability in patients with demyelinating diseases. The controversial data on QYNAD indicates a further challenge to identify neuroactive components in inflammatory mediated diseases like multiple sclerosis.