The impact of topical treatment for chalazia on the odds of procedural management

Chalazia in pediatric patients are often treated with topical antibiotics or steroids, although no strong evidence supports their use. This retrospective review of pediatric patients with chalazia did not find a decreased odds of undergoing procedural treatment (incision and curettage and/or intralesional steroid injection) with initial topical antibiotics and/or steroids compared to conservative measures. Inflamed chalazia may benefit from topical treatment, but small sample size limits this subgroup analysis. Shorter pre-topical treatment chalazion duration correlated with a lower risk of procedural intervention. Regimens that included steroids were not found to be more effective than topical antibiotics alone.

Stem cell-derived sensory neurons modelling inherited erythromelalgia: normalization of excitability

Effective treatment of pain remains an unmet healthcare need that requires new and effective therapeutic approaches. NaV1.7 has been genetically and functionally validated as a mediator of pain. Preclinical studies of NaV1.7-selective blockers have shown limited success and translation to clinical studies has been limited. The degree of NaV1.7 channel blockade necessary to attenuate neuronal excitability and ameliorate pain is an unanswered question important for drug discovery. Here, we utilize dynamic clamp electrophysiology and induced pluripotent stem cell-derived sensory neurons (iPSC-SNs) to answer this question for inherited erythromelalgia, a pain disorder caused by gain-of-function mutations in Nav1.7. We show that dynamic clamp can produce hyperexcitability in iPSC-SNs associated with two different inherited erythromelalgia mutations, NaV1.7-S241T and NaV1.7-I848T. We further show that blockade of approximately 50% of NaV1.7 currents can reverse neuronal hyperexcitability to baseline levels.

Depolarizing NaV and Hyperpolarizing KV Channels Are Co-Trafficked in Sensory Neurons

Neuronal excitability relies on coordinated action of functionally distinction channels. Voltage-gated sodium (NaV) and potassium (KV) channels have distinct but complementary roles in firing action potentials: NaV channels provide depolarizing current while KV channels provide hyperpolarizing current. Mutations and dysfunction of multiple NaV and KV channels underlie disorders of excitability, including pain and epilepsy. Modulating ion channel trafficking may offer a potential therapeutic strategy for these diseases. A fundamental question, however, is whether these channels with distinct functional roles are transported independently or packaged together in the same vesicles in sensory axons. We have used Optical Pulse-Chase Axonal Long-distance imaging to investigate trafficking of NaV and KV channels and other axonal proteins from distinct functional classes in live rodent sensory neurons (from male and female rats). We show that, similar to NaV1.7 channels, NaV1.8 and KV7.2 channels are transported in Rab6a-positive vesicles, and that each of the NaV channel isoforms expressed in healthy, mature sensory neurons (NaV1.6, NaV1.7, NaV1.8, and NaV1.9) is cotransported in the same vesicles. Further, we show that multiple axonal membrane proteins with different physiological functions (NaV1.7, KV7.2, and TNFR1) are cotransported in the same vesicles. However, vesicular packaging of axonal membrane proteins is not indiscriminate, since another axonal membrane protein (NCX2) is transported in separate vesicles. These results shed new light on the development and organization of sensory neuron membranes, revealing complex sorting of axonal proteins with diverse physiological functions into specific transport vesicles.SIGNIFICANCE STATEMENT Normal neuronal excitability is dependent on precise regulation of membrane proteins, including NaV and KV channels, and imbalance in the level of these channels at the plasma membrane could lead to excitability disorders. Ion channel trafficking could potentially be targeted therapeutically, which would require better understanding of the mechanisms underlying trafficking of functionally diverse channels. Optical Pulse-chase Axonal Long-distance imaging in live neurons permitted examination of the specificity of ion channel trafficking, revealing co-packaging of axonal proteins with opposing physiological functions into the same transport vesicles. This suggests that additional trafficking mechanisms are necessary to regulate levels of surface channels, and reveals an important consideration for therapeutic strategies that target ion channel trafficking for the treatment of excitability disorders.

Evaluation of the Content of Ophthalmology Fellowship Program Web sites

Purpose To assess the availability and content of fellowship program Web sites (FPWs) among ophthalmology subspecialties.

Design This is a cross-sectional study.

Subjects Web sites of all Association of University Professors of Ophthalmology-accredited fellowship programs in five subspecialties (i.e., surgical retina and vitreous; cornea, external disease, and refractive surgery; glaucoma; neuro-ophthalmology; and pediatric ophthalmology).

Methods FPWs were assessed for the presence of 26 key content criteria encompassing program demographics (n = 13), features (n = 10), and social life (n = 3). The presence of each content criterion as well as the content criteria groups were compared across subspecialties.

Main Outcome Measures The main outcome measured is the average percentage of key content criteria present among ophthalmology fellowship Web sites.

Results Among 266 accredited fellowship programs, 240 (90.2%) had Web sites. On average, Web sites reported 14.9 of 26 key content criteria (57.2%), 8.29 of 13 demographic criteria (63.8%), 5.84 of the 10 program features criteria (58.4%), and 0.705 of the 3 social life criteria (23.5%). Significant differences were identified among subspecialties in the presence of program description (p = 0.046), hospital affiliation (p < 0.001), names of current fellows (p = 0.004), case diversity (p = 0.001), and surgical statistics (p = 0.015). The average number of key criteria differed between subspecialties (p < 0.001).

Conclusion There is significant heterogeneity in program fellowship Web site content among ophthalmology subspecialties. Information regarding social life, such as wellness programs and community information, was largely absent across all disciplines. Addressing missing information on ophthalmology FPWs may help optimize program-applicant fit.

iPSCs and DRGs: stepping stones to new pain therapies

There is a pressing need for more effective nonaddictive treatment options for pain. Pain signals are transmitted from the periphery into the spinal cord via dorsal root ganglion (DRG) neurons, whose excitability is driven by voltage-gated sodium (NaV) channels. Three NaV channels (NaV1.7, NaV1.8, and NaV1.9), preferentially expressed in DRG neurons, play important roles in pain signaling in humans. Blockade of these channels may provide a novel approach to the treatment of pain, but clinical translation of preclinical results has been challenging, in part due to differences between rodent and human DRG neurons. Human DRG neurons and iPSC-derived sensory neurons (iPSC-SNs) provide new preclinical platforms that may facilitate the development of novel pain therapeutics.

Lacosamide Inhibition of NaV1.7 Channels Depends on its Interaction With the Voltage Sensor Domain and the Channel Pore

Lacosamide, developed as an anti-epileptic drug, has been used for the treatment of pain. Unlike typical anticonvulsants and local anesthetics which enhance fast-inactivation and bind within the pore of sodium channels, lacosamide enhances slow-inactivation of these channels, suggesting different binding mechanisms and mode of action. It has been reported that lacosamide's effect on Na_V1.5 is sensitive to a mutation in the local anesthetic binding site, and that it binds with slow kinetics to the fast-inactivated state of Na_V1.7. We recently showed that the Na_V1.7-W1538R mutation in the voltage-sensing domain 4 completely abolishes Na_V1.7 inhibition by clinically-achievable concentration of lacosamide. Our molecular docking analysis suggests a role for W1538 and pore residues as high affinity binding sites for lacosamide. Aryl sulfonamide sodium channel blockers are also sensitive to substitutions of the W1538 residue but not of pore residues. To elucidate the mechanism by which lacosamide exerts its effects, we used voltage-clamp recordings and show that lacosamide requires an intact local anesthetic binding site to inhibit Na_V1.7 channels. Additionally, the W1538R mutation does not abrogate local anesthetic lidocaine-induced blockade. We also show that the naturally occurring arginine in Na_V1.3 (Na_V1.3-R1560), which corresponds to Na_V1.7-W1538R, is not sufficient to explain the resistance of Na_V1.3 to clinically-relevant concentrations of lacosamide. However, the Na_V1.7-W1538R mutation conferred sensitivity to the Na_V1.3-selective aryl-sulfonamide blocker ICA-121431. Together, the W1538 residue and an intact local anesthetic site are required for lacosamide's block of Na_V1.7 at a clinically-achievable concentration. Moreover, the contribution of W1538 to lacosamide inhibitory effects appears to be isoform-specific.

A novel gain-of-function sodium channel β2 subunit mutation in idiopathic small fiber neuropathy

Small fiber neuropathy (SFN) is a common condition affecting thinly myelinated Aδ and unmyelinated C fibers, often resulting in excruciating pain and dysautonomia. SFN has been associated with several conditions, but a significant number of cases have no discernible cause. Recent genetic studies have identified potentially pathogenic gain-of-function mutations in several the pore-forming voltage-gated sodium channel α subunits (Na_Vs) in a subset of patients with SFN, but the auxiliary sodium channel β subunits have been less implicated in the development of the disease. β subunits modulate Na_V trafficking and gating, and several mutations have been linked to epilepsy and cardiac dysfunction. Recently, we provided the first evidence for the contribution of a mutation in the β2-subunit to pain in human painful diabetic neuropathy. Here, we provide the first evidence for the involvement of a sodium channel β subunit mutation in the pathogenesis of SFN with no other known causes. We show, through current-clamp analysis, that the newly-identified Y69H variant of the β2 subunit induces neuronal hyperexcitability in dorsal root ganglion neurons, lowering the threshold for action potential firing and allowing for increased repetitive action potential spiking. Underlying the hyperexcitability induced by the β2-Y69H variant, we demonstrate an upregulation in tetrodotoxin-sensitive, but not tetrodotoxin-resistant sodium currents. This provides the first evidence for the involvement of β2 subunits in SFN and strengthens the link between sodium channel β subunits and the development of neuropathic pain in humans.

Paclitaxel increases axonal localization and vesicular trafficking of Nav1.7

The microtubule-stabilizing chemotherapy drug paclitaxel (PTX) causes dose-limiting chemotherapy-induced peripheral neuropathy (CIPN), which is often accompanied by pain. Among the multifaceted effects of PTX is an increased expression of sodium channel Na_v1.7 in rat and human sensory neurons, enhancing their excitability. However, the mechanisms underlying this increased Na_v1.7 expression have not been explored, and the effects of PTX treatment on the dynamics of trafficking and localization of Na_v1.7 channels in sensory axons have not been possible to investigate to date. In this study we used a recently developed live imaging approach that allows visualization of Na_v1.7 surface channels and long-distance axonal vesicular transport in sensory neurons to fill this basic knowledge gap. We demonstrate concentration and time-dependent effects of PTX on vesicular trafficking and membrane localization of Na_v1.7 in real-time in sensory axons. Low concentrations of PTX increase surface channel expression and vesicular flux (number of vesicles per axon). By contrast, treatment with a higher concentration of PTX decreases vesicular flux. Interestingly, vesicular velocity is increased for both concentrations of PTX. Treatment with PTX increased levels of endogenous Na_v1.7 mRNA and current density in dorsal root ganglion neurons. However, the current produced by transfection of dorsal root ganglion neurons with Halo-tag Na_v1.7 was not increased after exposure to PTX. Taken together, this suggests that the increased trafficking and surface localization of Halo-Na_v1.7 that we observed by live imaging in transfected dorsal root ganglion neurons after treatment with PTX might be independent of an increased pool of Na_v1.7 channels. After exposure to inflammatory mediators to mimic the inflammatory condition seen during chemotherapy, both Na_v1.7 surface levels and vesicular transport are increased for both low and high concentrations of PTX. Overall, our results show that PTX treatment increases levels of functional endogenous Na_v1.7 channels in dorsal root ganglion neurons and enhances trafficking and surface distribution of Na_v1.7 in sensory axons, with outcomes that depend on the presence of an inflammatory milieu, providing a mechanistic explanation for increased excitability of primary afferents and pain in CIPN.

Status of peripheral sodium channel blockers for non-addictive pain treatment

The effective and safe treatment of pain is an unmet health-care need. Current medications used for pain management are often only partially effective, carry dose-limiting adverse effects and are potentially addictive, highlighting the need for improved therapeutic agents. Most common pain conditions originate in the periphery, where dorsal root ganglion and trigeminal ganglion neurons feed pain information into the CNS. Voltage-gated sodium (Na_V) channels drive neuronal excitability and three subtypes - Na_V1.7, Na_V1.8 and Na_V1.9 - are preferentially expressed in the peripheral nervous system, suggesting that their inhibition might treat pain while avoiding central and cardiac adverse effects. Genetic and functional studies of human pain disorders have identified Na_V1.7, Na_V1.8 and Na_V1.9 as mediators of pain and validated them as targets for pain treatment. Consequently, multiple Na_V1.7-specific and Na_V1.8-specific blockers have undergone clinical trials, with others in preclinical development, and the targeting of Na_V1.9, although hampered by technical constraints, might also be moving ahead. In this Review, we summarize the clinical and preclinical literature describing compounds that target peripheral Na_V channels and discuss the challenges and future prospects for the field. Although the potential of peripheral Na_V channel inhibition for the treatment of pain has yet to be realized, this remains a promising strategy to achieve non-addictive analgesia for multiple pain conditions.

Rat NaV1.7 loss-of-function genetic model: Deficient nociceptive and neuropathic pain behavior with retained olfactory function and intra-epidermal nerve fibers

Recapitulating human disease pathophysiology using genetic animal models is a powerful approach to enable mechanistic understanding of genotype–phenotype relationships for drug development. Na_V1.7 is a sodium channel expressed in the peripheral nervous system with strong human genetic validation as a pain target. Efforts to identify novel analgesics that are nonaddictive resulted in industry exploration of a class of sulfonamide compounds that bind to the fourth voltage-sensor domain of Na_V1.7. Due to sequence differences in this region, sulfonamide blockers generally are potent on human but not rat Na_V1.7 channels. To test sulfonamide-based chemical matter in rat models of pain, we generated a humanized Na_V1.7 rat expressing a chimeric Na_V1.7 protein containing the sulfonamide-binding site of the human gene sequence as a replacement for the equivalent rat sequence. Unexpectedly, upon transcription, the human insert was spliced out, resulting in a premature stop codon. Using a validated antibody, Na_V1.7 protein was confirmed to be lost in the brainstem, dorsal root ganglia, sciatic nerve, and gastrointestinal tissue but not in nasal turbinates or olfactory bulb in rats homozygous for the knock-in allele (HOM-KI). HOM-KI rats exhibited normal intraepidermal nerve fiber density with reduced tetrodotoxin-sensitive current density and action potential firing in small diameter dorsal root ganglia neurons. HOM-KI rats did not exhibit nociceptive pain responses in hot plate or capsaicin-induced flinching assays and did not exhibit neuropathic pain responses following spinal nerve ligation. Consistent with expression of chimeric Na_V1.7 in olfactory tissue, HOM-KI rats retained olfactory function. This new genetic model highlights the necessity of Na_V1.7 for pain behavior in rats and indicates that sufficient inhibition of Na_V1.7 in humans may reduce pain in neuropathic conditions. Due to preserved olfactory function, this rat model represents an alternative to global Na_V1.7 knockout mice that require time-intensive hand feeding during early postnatal development.

A gain-of-function sodium channel β2-subunit mutation in painful diabetic neuropathy

Diabetes mellitus is a global challenge with many diverse health sequelae, of which diabetic peripheral neuropathy is one of the most common. A substantial number of patients with diabetic peripheral neuropathy develop chronic pain, but the genetic and epigenetic factors that predispose diabetic peripheral neuropathy patients to develop neuropathic pain are poorly understood. Recent targeted genetic studies have identified mutations in α-subunits of voltage-gated sodium channels (Na_vs) in patients with painful diabetic peripheral neuropathy. Mutations in proteins that regulate trafficking or functional properties of Na_vs could expand the spectrum of patients with Na_v-related peripheral neuropathies. The auxiliary sodium channel β-subunits (β1–4) have been reported to increase current density, alter inactivation kinetics, and modulate subcellular localization of Na_v. Mutations in β-subunits have been associated with several diseases, including epilepsy, cancer, and diseases of the cardiac conducting system. However, mutations in β-subunits have never been shown previously to contribute to neuropathic pain. We report here a patient with painful diabetic peripheral neuropathy and negative genetic screening for mutations in SCN9A, SCN10A, and SCN11A—genes encoding sodium channel α-subunit that have been previously linked to the development of neuropathic pain. Genetic analysis revealed an aspartic acid to asparagine mutation, D109N, in the β2-subunit. Functional analysis using current-clamp revealed that the β2-D109N rendered dorsal root ganglion neurons hyperexcitable, especially in response to repetitive stimulation. Underlying the hyperexcitability induced by the β2-subunit mutation, as evidenced by voltage-clamp analysis, we found a depolarizing shift in the voltage dependence of Na_v1.7 fast inactivation and reduced use-dependent inhibition of the Na_v1.7 channel.