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1.  Pattern of Functional TTX-Resistant Sodium Channels Reveals a Developmental Stage of Human iPSC- and ESC-Derived Nociceptors 
Stem Cell Reports  2015;5(3):305-313.
Human pluripotent stem cells (hPSCs) offer the opportunity to generate neuronal cells, including nociceptors. Using a chemical-based approach, we generated nociceptive sensory neurons from HUES6 embryonic stem cells and retrovirally reprogrammed induced hPSCs derived from fibroblasts. The nociceptive neurons expressed respective markers and showed tetrodotoxin-sensitive (TTXs) and -resistant (TTXr) voltage-gated sodium currents in patch-clamp experiments. In contrast to their counterparts from rodent dorsal root ganglia, TTXr currents of hPSC-derived nociceptors unexpectedly displayed a significantly more hyperpolarized voltage dependence of activation and fast inactivation. This apparent discrepancy is most likely due to a substantial expression of the developmentally important sodium channel NAV1.5. In view of the obstacles to recapitulate neuropathic pain in animal models, our data advance hPSC-derived nociceptors as a better model to study developmental and pathogenetic processes in human nociceptive neurons and to develop more specific small molecules to attenuate pain.
•hPSC-derived nociceptors express TTX-resistant sodium channels NAV1.8 and NAV1.9•SCN5A mRNA, coding for NAV1.5, is present in hPSC-derived nociceptors•The biophysical Nav characteristics support strong functional expression of NAV1.5•Human hPSC-derived nociceptors offer a suitable model of developing sensory neurons
This study investigates detailed electrophysiological characteristics of hPSC-derived peripheral nociceptive neurons with focus on voltage-gated sodium channels. Besides the pain-relevant subtypes NAV1.8 and NAV1.9, Lampert, Winner, and colleagues find that significant amounts of the developmentally important NAV1.5 are expressed and functionally active. Thus, human hPSC-derived nociceptors offer a suitable model of developing sensory neurons.
PMCID: PMC4618592  PMID: 26321143
2.  Evaluating predictive modeling algorithms to assess patient eligibility for clinical trials from routine data 
The necessity to translate eligibility criteria from free text into decision rules that are compatible with data from the electronic health record (EHR) constitutes the main challenge when developing and deploying clinical trial recruitment support systems. Recruitment decisions based on case-based reasoning, i.e. using past cases rather than explicit rules, could dispense with the need for translating eligibility criteria and could also be implemented largely independently from the terminology of the EHR’s database. We evaluated the feasibility of predictive modeling to assess the eligibility of patients for clinical trials and report on a prototype’s performance for different system configurations.
The prototype worked by using existing basic patient data of manually assessed eligible and ineligible patients to induce prediction models. Performance was measured retrospectively for three clinical trials by plotting receiver operating characteristic curves and comparing the area under the curve (ROC-AUC) for different prediction algorithms, different sizes of the learning set and different numbers and aggregation levels of the patient attributes.
Random forests were generally among the best performing models with a maximum ROC-AUC of 0.81 (CI: 0.72-0.88) for trial A, 0.96 (CI: 0.95-0.97) for trial B and 0.99 (CI: 0.98-0.99) for trial C. The full potential of this algorithm was reached after learning from approximately 200 manually screened patients (eligible and ineligible). Neither block- nor category-level aggregation of diagnosis and procedure codes influenced the algorithms’ performance substantially.
Our results indicate that predictive modeling is a feasible approach to support patient recruitment into clinical trials. Its major advantages over the commonly applied rule-based systems are its independency from the concrete representation of eligibility criteria and EHR data and its potential for automation.
PMCID: PMC4029400  PMID: 24321610
3.  Activation of TRPA1 by membrane permeable local anesthetics 
Molecular Pain  2011;7:62.
Low concentrations of local anesthetics (LAs) suppress cellular excitability by inhibiting voltage-gated Na+ channels. In contrast, LAs at high concentrations can be excitatory and neurotoxic. We recently demonstrated that LA-evoked activation of sensory neurons is mediated by the capsaicin receptor TRPV1, and, to a lesser extent by the irritant receptor TRPA1. LA-induced activation and sensitization of TRPV1 involves a domain that is similar, but not identical to the vanilloid-binding domain. Additionally, activation of TRPV1 by LAs involves PLC and PI(4,5)P2-signalling. In the present study we aimed to characterize essential structural determinants for LA-evoked activation of TRPA1.
Recombinant rodent and human TRPA1 were expressed in HEK293t cells and investigated by means of whole-cell patch clamp recordings. The LA lidocaine activates TRPA1 in a concentration-dependent manner. The membrane impermeable lidocaine-derivative QX-314 is inactive when applied extracellularly. Lidocaine-activated TRPA1-currents are blocked by the TRPA1-antagonist HC-030031. Lidocaine is also an inhibitor of TRPA1, an effect that is more obvious in rodent than in human TRPA1. This species-specific difference is linked to the pore region (transmembrane domain 5 and 6) as described for activation of TRPA1 by menthol. Unlike menthol-sensitivity however, lidocaine-sensitivity is not similarly determined by serine- and threonine-residues within TM5. Instead, intracellular cysteine residues known to be covalently bound by reactive TRPA1-agonists seem to mediate activation of TRPA1 by LAs.
The structural determinants involved in activation of TRPA1 by LAs are disparate from those involved in activation by menthol or those involved in activation of TRPV1 by LAs.
PMCID: PMC3179737  PMID: 21861907
4.  Isoflurane Inhibits the Tetrodotoxin-resistant Voltagegated Sodium Channel Nav1.8 
Anesthesiology  2009;111(3):591-599.
Voltage-gated sodium channels (Nav) mediate neuronal action potentials. Tetrodotoxin inhibits all Nav isoforms, but Nav1.8 and Nav1.9 are relatively tetrodotoxin-resistant (TTX-r) compared to other isoforms. Nav1.8 is highly expressed in dorsal root ganglion neurons and is functionally linked to nociception, but the sensitivity of TTX-r isoforms to inhaled anesthetics is unclear.
The sensitivities of heterologously expressed rat TTX-r Nav1.8 and endogenous tetrodotoxin-sensitive (TTX-s) Nav to the prototypic inhaled anesthetic isoflurane were tested in mammalian ND7/23 cells using patch-clamp electrophysiology.
From a holding potential of −70 mV, isoflurane (0.53±0.06 mM, ~1.8 MAC at 24°C) reduced normalized peak Na+ current (INa) of Nav1.8 to 0.55±0.03 and of endogenous TTX-s Nav to 0.56±0.06. Isoflurane minimally inhibited INa from a holding potential of −140 mV. Isoflurane did not affect voltage-dependence of activation, but significantly shifted voltage-dependence of steady-state inactivation by −6 mV for Nav1.8 and by −7 mV for TTX-s Nav. IC50 values for inhibition of peak INa were 0.67±0.06 mM for Nav1.8 and 0.66±0.09 mM for TTX-s Nav; significant inhibition occurred at clinically relevant concentrations as low as 0.58 MAC. Isoflurane produced use-dependent block of Nav1.8; at a stimulation frequency of 10 Hz, 0.56±0.08 mM isoflurane reduced INa to 0.64±0.01 vs. 0.78±0.01 for control.
Isoflurane inhibited the tetrodotoxin-resistant isoform Nav1.8 with potency comparable to that for endogenous tetrodotoxin-sensitive Nav isoforms, indicating that sensitivity to inhaled anesthetics is conserved across diverse Nav family members. Block of Nav1.8 in dorsal root ganglion neurons could contribute to the effects of inhaled anesthetics on peripheral nociceptive mechanisms.
PMCID: PMC2756082  PMID: 19672182
5.  Use of Bulleyaconitine A as an Adjuvant for Prolonged Cutaneous Analgesia in the Rat 
Anesthesia and analgesia  2008;107(4):1397-1405.
Bulleyaconitine A (BLA) is an analgesic and antiinflammatory drug isolated from Aconitum plants. BLA has several potential targets, including voltage-gated Na+ channels. We tested whether BLA elicited long-lasting cutaneous analgesia, when co-injected with lidocaine and epinephrine, as a model for prolonged infiltration anesthesia.
The local anesthetic properties of BLA were assessed by the patch-clamp technique in HEK293t cells expressing Nav1.7 and Nav1.8 neuronal Na+ channels, both crucial for nociception. Drug solutions (0.6 mL) were injected subcutaneously via rat shaved dorsal skin. Inhibition of the cutaneous trunci muscle reflex was evaluated by pinpricks. Skin cross-sections were stained with hematoxylin and eosin or with antibodies against PGP9.5.
BLA at 10 µM interacted minimally with resting or inactivated Nav1.7 and Nav1.8 Na+ channels when infrequently stimulated to +50 mV for 3 ms. However, when stimulated at 2 Hz for 1000 pulses, their peak Na+ currents were >90% reduced by BLA. This use-dependent inhibition was not significantly reversed after 15-min washing. Complete nociceptive blockade after injection of lidocaine (0.5%)/epinephrine (1:200,000) lasted for approximately 1 h in rats; full recovery occurred after approximately 6 h. Co-injection of 0.125 mM BLA with lidocaine/epinephrine increased the duration of complete nociceptive blockade to 24 h. Full recovery occurred after approximately 6 days. Skin histology including peripheral nerve fibers appeared unaffected by BLA.
BLA inhibits Nav1.7 and Nav1.8 Na+ currents in a use-dependent manner. Co-injection of BLA at ≤0.125 mM with lidocaine and epinephrine elicits complete cutaneous analgesia that lasts for up to 24 h without adverse effects.
PMCID: PMC2712758  PMID: 18806059
6.  The vanilloid receptor TRPV1 is activated and sensitized by local anesthetics in rodent sensory neurons 
Local anesthetics (LAs) block the generation and propagation of action potentials by interacting with specific sites of voltage-gated Na+ channels. LAs can also excite sensory neurons and be neurotoxic through mechanisms that are as yet undefined. Nonspecific cation channels of the transient receptor potential (TRP) channel family that are predominantly expressed by nociceptive sensory neurons render these neurons sensitive to a variety of insults. Here we demonstrated that the LA lidocaine activated TRP channel family receptors TRPV1 and, to a lesser extent, TRPA1 in rodent dorsal root ganglion sensory neurons as well as in HEK293t cells expressing TRPV1 or TRPA1. Lidocaine also induced a TRPV1-dependent release of calcitonin gene–related peptide (CGRP) from isolated skin and peripheral nerve. Lidocaine sensitivity of TRPV1 required segments of the putative vanilloid-binding domain within and adjacent to transmembrane domain 3, was diminished under phosphatidylinositol 4,5-bisphosphate depletion, and was abrogated by a point mutation at residue R701 in the proximal C-terminal TRP domain. These data identify TRPV1 and TRPA1 as putative key elements of LA-induced nociceptor excitation. This effect is sufficient to release CGRP, a key component of neurogenic inflammation, and warrants investigation into the role of TRPV1 and TRPA1 in LA-induced neurotoxicity.
PMCID: PMC2157564  PMID: 18172555

Results 1-6 (6)