Experimental validation of blood flow derived from pulse oximeter wave signals in beagles

Purpose Pulse oximeter wave reflects blood volume changes in tissue, suggesting the possibility of monitoring changes in tissue blood flow. Thus, our aim was to examine the correlation between tissue blood flow derived from pulse oximeter wave signals (Q_pulse) at a toe and the arterial flow measured by a Doppler probe at the femoral artery (Q_Doppler).Methods Six beagles under general anesthesia were studied. A 24-G catheter was placed in the proximal femoral artery for drug infusion and an ultrasonic transit-time flow probe applied to the artery to measure Q_Doppler. The pulse oximeter signals from the right toe were processed with in-house-developed software to obtain Q_pulse. Three saline solutions containing respectively the vasodilators isosorbide dinitrate (20μg/mL), adenosine (20μg/mL), and nicardipine (10μg/mL) were infused at increasing rates of 0, 2.5, 5.0, 10, or 20 mL/h for 8 minutes into the femoral artery with a syringe pump. Results Both Q_Doppler and Q_pulse increased fourfold with increasing rates of infusion of the three vasodilators. Plotting of Q_Doppler and Q_pulse across the three vasodilators in each animal revealed linear correlations (R^2 = 0.17-0.76). Overall regression analysis showed a less strong but still statistically significant linear relation (y=3.68x + 18.5, R^2 = 0.25, P < 0.01). Conclusions We found a linear correlation between Q_Doppler and Q_pulse in a wide range of femoral arterial blood flow measures induced by different vasodilators in each animal. Arterial flow wave derived from pulse oximetry was quantitatively validated

Novel analgesics targeting brain-derived neurotrophic factor for neuropathic pain

　Brain-derived neurotrophic factor (BDNF) is necessary for the development, growth, and maintenance of nerve cells. BDNF is expressed in the dorsal root ganglion (DRG); binds to the Tropomyosin receptor kinasa B (TrkB) receptor, which has a tyrosine kinase domain, in the spinal cord; and plays an important role as a pain modulator. BDNF expression is increased in various types of pain, including acute pain, neuropathic pain, and cancer pain. Activation of the BDNF–TrkB pathway transmits pain information. In order to inhibit the BDNF–TrkB pathway, by sequestering BDNF, we constructed a cDNA expression plasmid encoding the extracellular region of rat TrkB fused to enhanced green fluorescent protein (EGFP). When the expression plasmid vector was administered to rat models of neuropathic pain, induced by spinal nerve ligation, statistically significant relief of pain was observed in terms of a 50% paw-withdrawal threshold using the von Frey test. The expression of TrkB-EGFP mRNA was detected in L5 lumbar vertebral nerves by quantitative reverse transcriptase polymerase chain reaction. To verify the pain-suppressive effect of the expression vector, truncated TrkB protein, without EGFP, was purified, and administered to pain model rats. A statistically significant suppressive effect of the truncated TrkB protein on neuropathic pain was observed 2 days after administration. The pain-suppressive effect of the truncated TrkB protein was more effective than that of the TrkB-Fc chimera protein and lasted longer than that of the TrkB antagonist ANA-12. Our results suggested that the truncated TrkB cDNA expression vector and truncated TrkB protein could be used as molecular targeted drugs in patients with neuropathic pain

Development of a novel analgesic for cancer pain targeting brain-derived neurotrophic factor

Brain-derived neurotrophic factor (BDNF) is necessary for nerve growth. BDNF is expressed in the dorsal root ganglion (DRG) and modulates pain transduction from peripheral nociceptors. TrkB, which is a BDNF receptor with a tyrosine kinase domain, acts as a pain modulator on the cell membrane of second neuron. If an exogenous truncated TrkB lacking a tyrosine kinase domain can competitively block the binding of BDNF to endogenous TrkB, inhibitory effects on pain are expected. We constructed two expression vectors coding truncated TrkB-GFP fusion proteins, lacking intracellular tyrosine kinase domain, with and without the transmembrane domain. By transfection of the vectors to HEK293 cells, the expression and localization of the modified receptor proteins were confirmed. The truncated TrkB with the transmembrane domain, TM (+), was localized on cell membrane surface of the transfected cells, and capable of BDNF binding on cell surface. TM (-) without the transmembrane domain was secreted from the transfected cells, and the secreted TrkB protein was confirmed the capability for binding with BDNF by pull-down assay. Furthermore, we developed a rat model of cancerous osteocopic pain for evaluating an analgesic effect of the modified TrkB vectors on cancer pain. Pain-related behavior, as assessed by von Frey tests, indicated hyperalgesia after cancer cell administration. BDNF expression was higher on the affected side of the DRG at the third lumbar vertebra L3 than on the unaffected side. When the modified TrkB vectors were administrated to the cancer pain model rats, both the TM (+) and TM (-) vector administration groups exhibited an analgesic effect. These results suggest that the modified TrkB receptors and their vectors are applicable as molecular targeted drugs for pain control in cancer patients