Faculty Bibliography

Over the past three decades, there has been a significant growth in the use of natural products, with approximately 80% of individuals using them for some aspect of primary healthcare. Our laboratories have identified and studied natural compounds with analgesic effects from dry land plants or their associated fungus during the past ten years. Here, we isolated and characterized thirteen betulin analogs and fifteen betulinic acid analogs for their capacity to prevent calcium influx brought on by depolarization in sensory neurons. The in vitro inhibition of voltage-gated calcium channels by the top drugs was then assessed using whole cell patch clamp electrophysiology. In vivo experiments, conducted at two sites, evaluated the best compound in acute and tonic, neuropathic, inflammatory, post-operative and visceral models of pain. We found that the betulinic acid analog 8 inhibited calcium influx in rat dorsal root ganglion neurons by inhibiting N- (CaV2.2) and T- (CaV3) type voltage-gated calcium channels. Moreover, intrathecal delivery of analog 8 had analgesic activity in both spared nerve injury model of neuropathic pain and acute and tonic pain induced by formalin. The results presented herein highlight the potential antinociceptive properties of betulinic acid analog 8 and set the stage for the development of novel non-opioid pain therapeutics based on the triterpenoid scaffold of betulinic acid.

BACKGROUND:Rheumatoid arthritis patients usually suffer from arthritic chronic pain. However, due to an incomplete understanding of the mechanisms underlying autoimmune disorders, the management of arthritic pain is unsatisfactory. Here, we investigated the analgesic effect and underlying mechanism of the natural flavonoid naringenin (NAR) in collagen-induced arthritis (CIA) pain. METHODS:NAR was injected (i.p.) once per day for 42 days after initial immunization, and rats were sacrificed on the 28th (the 21st day after final immunization, PID 21) and 42nd days (PID 35). The inflammatory factors, central sensitization indicators, and CRMP2 phosphorylation, as well as the anti-rheumatoid activity and analgesic effect of NAR, were further investigated. RESULTS:We found that NAR decreased the arthritis score and paw swelling, as well as the mechanical and thermal pain. The immunofluorescence results also showed a dose dependent effect of NAR on reducing the expressions of spinal cFos, IBA-1, and GFAP on the 28th (PID 21) and 42nd day (PID 35). NAR decreased the phosphorylation of CRMP2 S522 and the expression of the kinase CDK5 in the spinal dorsal horn, but pCRMP2 Y479 was unchanged. In addition, CRMP2 was co-localized with NEUN, but not IBA-1 or GFAP, indicating the involvement of neural CRMP2 phosphorylation in CIA-related pain. Finally, CRMP2 S522 phosphorylation selective inhibitor (S)-lacosamide also alleviated arthritic pain. CONCLUSIONS:Taken together, our results demonstrate that NAR alleviates inflammation and chronic pain in CIA model, which might be related to its inhibition of neuronal CRMP2 S522 phosphorylation, potentially mitigating the central sensitization. Our study provide evidence for the potential use of NAR as non-opioid-dependent analgesia in arthritic pain.

Vascular endothelial growth factor A (VEGF-A) is a pronociceptive factor that causes neuronal sensitization and pain. We reported that blocking the interaction between the membrane receptor neuropilin 1 (NRP1) and VEGF-A-blocked VEGF-A-mediated sensory neuron hyperexcitability and reduced mechanical hypersensitivity in a rodent chronic neuropathic pain model. These findings identified the NRP1-VEGF-A signaling axis for therapeutic targeting of chronic pain. In an in-silico screening of approximately 480 K small molecules binding to the extracellular b1b2 pocket of NRP1, we identified 9 chemical series, with 6 compounds disrupting VEGF-A binding to NRP1. The small molecule with greatest efficacy, 4'-methyl-2'-morpholino-2-(phenylamino)-[4,5'-bipyrimidin]-6(1H)-one, designated NRP1-4, was selected for further evaluation. In cultured primary sensory neurons, VEGF-A enhanced excitability and decreased firing threshold, which was blocked by NRP1-4. In addition, NaV1.7 and CaV2.2 currents and membrane expression were potentiated by treatment with VEGF-A, and this potentiation was blocked by NRP1-4 cotreatment. Neuropilin 1-4 reduced VEGF-A-mediated increases in the frequency and amplitude of spontaneous excitatory postsynaptic currents in dorsal horn of the spinal cord. Neuropilin 1-4 did not bind to more than 300 G-protein-coupled receptors and receptors including human opioids receptors, indicating a favorable safety profile. In rats with spared nerve injury-induced neuropathic pain, intrathecal administration of NRP1-4 significantly attenuated mechanical allodynia. Intravenous treatment with NRP1-4 reversed both mechanical allodynia and thermal hyperalgesia in rats with L5/L6 spinal nerve ligation-induced neuropathic pain. Collectively, our findings show that NRP1-4 is a first-in-class compound targeting the NRP1-VEGF-A signaling axis to control voltage-gated ion channel function, neuronal excitability, and synaptic activity that curb chronic pain.

The voltage-gated sodium channel isoform NaV1.7 is a critical player in the transmission of nociceptive information. This channel has been heavily implicated in human genetic pain disorders and is a validated pain target. However, targeting this channel directly has failed, and an indirect approach - disruption of interactions with accessory protein partners - has emerged as a viable alternative strategy. We recently reported that a small-molecule inhibitor of CRMP2 SUMOylation, compound 194, selectively reduces NaV1.7 currents in DRG neurons across species from mouse to human. This compound also reversed mechanical allodynia in a spared nerve injury and chemotherapy-induced model of neuropathic pain. Here, we show that oral administration of 194 reverses mechanical allodynia in a chronic constriction injury (CCI) model of neuropathic pain. Furthermore, we show that orally administered 194 reverses the increased latency to cross an aversive barrier in a mechanical conflict-avoidance task following CCI. These two findings, in the context of our previous report, support the conclusion that 194 is a robust inhibitor of NaV1.7 function with the ultimate effect of profoundly ameliorating mechanical allodynia associated with nerve injury. The fact that this was observed using both traditional, evoked measures of pain behavior as well as the more recently developed operator-independent mechanical conflict-avoidance assay increases confidence in the efficacy of 194-induced anti-nociception.

Voltage-gated sodium and calcium channels (VGSCs and VGCCs) play an important role in the modulation of physiologically relevant processes in excitable cells that range from action potential generation to neurotransmission. Once their expression and/or function is altered in disease, specific pharmacological approaches become necessary to mitigate the negative consequences of such dysregulation. Several classes of small molecules have been developed with demonstrated effectiveness on VGSCs and VGCCs; however, off-target effects have also been described, limiting their use and spurring efforts to find more specific and safer molecules to target these channels. There are a great number of plants and herbal preparations that have been empirically used for the treatment of diseases in which VGSCs and VGCCs are involved. Some of these natural products have progressed to clinical trials, while others are under investigation for their action mechanisms on signaling pathways, including channels. In this review, we synthesize information from ~30 compounds derived from natural sources like plants and fungi and delineate their effects on VGSCs and VGCCs in human disease, particularly pain. [Figure: see text].

BACKGROUND AND PURPOSE/OBJECTIVE:Postoperative pain occurs in as many as 70% of the over 230 million surgeries performed annually worldwide. Postoperative pain management still relies on opioids despite their negative consequences, resulting in a public health crisis. Therefore, it is of utmost importance to develop alternative therapies to treat chronic pain. Natural products derived from medicinal plants are potential sources of novel and biologically active compounds for development of safe analgesics. Hence, in this study, we screened a library of natural products to identify small molecules that target the activity of voltage-gated sodium and calcium channels which have important roles in nociceptive sensory processing. EXPERIMENTAL APPROACH/METHODS:Fractions derived from the Native American medicinal plant, Parthenium incanum, were assessed using depolarization-evoked calcium influx in rat dorsal root ganglion (DRG) neurons. Further separation of these fractions yielded a cycloartane-type triterpene identified as argentatin C, which was additionally evaluated using whole-cell voltage and current clamp electrophysiology, and behavioral analysis in a mouse model of postsurgical pain. KEY RESULTS/RESULTS:currents as well as excitability in rat and macaque DRG neurons. Consistent with these observations, argentatin C treatment reversed mechanical allodynia in a mouse model of postsurgical pain. CONCLUSIONS & IMPLICATIONS/CONCLUSIONS:These results suggest that the dual effect of argentatin C on voltage-gated sodium and calcium channels supports its potential as a novel treatment for painful conditions.

ABSTRACT/UNASSIGNED:Intrathecal application of contulakin-G (CGX), a conotoxin peptide and a neurotensin analogue, has been demonstrated to be safe and potentially analgesic in humans. However, the mechanism of action for CGX analgesia is unknown. We hypothesized that spinal application of CGX produces antinociception through activation of the presynaptic neurotensin receptor (NTSR)2. In this study, we assessed the mechanisms of CGX antinociception in rodent models of inflammatory and neuropathic pain. Intrathecal administration of CGX, dose dependently, inhibited thermal and mechanical hypersensitivities in rodents of both sexes. Pharmacological and clustered regularly interspaced short palindromic repeats/Cas9 editing of NTSR2 reversed CGX-induced antinociception without affecting morphine analgesia. Electrophysiological and gene editing approaches demonstrated that CGX inhibition was dependent on the R-type voltage-gated calcium channel (Cav2.3) in sensory neurons. Anatomical studies demonstrated coexpression of NTSR2 and Cav2.3 in dorsal root ganglion neurons. Finally, synaptic fractionation and slice electrophysiology recordings confirmed a predominantly presynaptic effect. Together, these data reveal a nonopioid pathway engaged by a human-tested drug to produce antinociception.

OBJECTIVE:To establish a tonic chemical model of pain in quail and evaluate the efficacy of opioid and non-steroidal anti-inflammatory drugs. STUDY DESIGN/METHODS:A randomized, blinded, experimental study design. ANIMALS/METHODS:A total of 120 male Japanese quail, aged 7 weeks. METHODS:). The treatment effect was analyzed by one-way anova and the time course effect analyzed using repeated measures anova, both followed by Dunnett's post hoc test (p < 0.05). RESULTS:) significantly reduced foot lift responses. Preening activity was significantly decreased following injection of 0.6% and 0.9% formalin. Preening was normalized with ibuprofen, but not with morphine. Morphine, but not ibuprofen, reduced quail activity. CONCLUSION AND CLINICAL RELEVANCE/CONCLUSIONS:These results suggest that the formalin test was a reliable method for assessing tonic pain behavior in quail. The acute phase of the formalin test was not affected by morphine or ibuprofen. Although ibuprofen reduced the pain response in phase 2, the analgesic effects of morphine were not conclusive because morphine appeared to induce sedation.