A case report: retigabine induced oral mucosal dyspigmentation of the hard palate

Drug-Induced Pigmentation: A Review

Drug-induced pigmentation (DIP) is estimated to account for 20% of all cases of acquired hyperpigmentation. Over 50 agents have been implicated, including antibiotics, antimalarials, antiretrovirals, antipsychotics, prostaglandin analogs, heavy metals, and chemotherapeutic agents. The skin, mucosal surfaces, nails, and hair can all be affected, with the color, distribution, onset, and duration of pigmentation varying between offending agents. Both a thorough physical examination and medication history are necessary to determine the offending agent. In terms of mechanism, DIP occurs most frequently through the accumulation of melanin within the dermis but also by drug accumulation, pigment synthesis, and iron deposition. Photoprotection, including applying a broad-spectrum sunscreen, wearing photoprotective clothing, and seeking shade, plays an important role in the prevention of exacerbation of DIP. Multiple lasers, including the picosecond alexandrite, Q-switched Nd:YAG, Q-switched alexandrite, and Q-switched ruby lasers, have been successful in obtaining clearance of DIP. In this review, we examine the unique characteristics of each of the inciting agents in terms of incidence, clinical presentation, time to onset and resolution, and pathogenesis.

Acute Treatment with the M-Channel (Kv7, KCNQ) Opener Retigabine Reduces the Long-Term Effects of Repetitive Blast Traumatic Brain Injuries

We investigated whether pharmacological increase of "M-type" (KCNQ, Kv7) K + channel currents by the M-channel opener, retigabine (RTG), acutely after repetitive traumatic brain injuries (rTBIs), prevents or reduces their long-term detrimental effects. rTBIs were studied using a blast shock air wave mouse model. Animals were monitored by video and electroencephalogram (EEG) records for nine months after the last injury to assess the occurrence of post-traumatic seizures (PTS), post-traumatic epilepsy (PTE), sleep-wake cycle architecture alterations, and the power of the EEG signals. We evaluated the development of long-term changes in the brain associated with various neurodegenerative diseases in mice by examining transactive response DNA-binding protein 43 (TDP-43) expression and nerve fiber damage ~ 2 years after the rTBIs. We observed acute RTG treatment to reduce the duration of PTS and impair the development of PTE. Acute RTG treatment also prevented post-injury hypersomnia, nerve fiber damage, and cortical TDP-43 accumulation and translocation from the nucleus to the cytoplasm. Mice that developed PTE displayed impaired rapid eye movement (REM) sleep, and there were significant correlations between seizure duration and time spent in the different stages of the sleep-wake cycle. We observed acute RTG treatment to impair injury-induced reduction of age-related increase in gamma frequency power of the EGG, which has been suggested to be necessary for a healthy aged brain. The data show that RTG, administered acutely post-TBI, is a promising, novel therapeutic option to blunt/prevent several long-term effects of rTBIs. Furthermore, our results show a direct relationship between sleep architecture and PTE.

Blue Nail Discoloration: Literature Review and Diagnostic Algorithms

Blue nail discoloration is a distinctive clinical presentation, and diagnosis is challenging given the broad differential diagnosis. A comprehensive review of the literature describing blue discoloration of one or multiple nails was performed using the PubMed, Embase, Scopus, and Web of Science databases. A total of 245 publications were included and grouped based on involvement of a single nail (monodactylic) or multiple nails (polydactylic). Monodactylic blue discoloration was associated with tumors or benign nevi, most commonly glomus tumors, followed by blue nevi and less commonly melanomas. Polydactylic blue discoloration was frequently associated with medications (such as minocycline, zidovudine, and hydroxyurea), toxic and exogenous exposures (such as silver), and other medical conditions (such as HIV/AIDS and systemic lupus erythematous). Patients presenting with blue nail discoloration warrant a thorough history, physical examination, and workup to rule out malignancy, systemic disease, or toxic exposure. We present diagnostic algorithms for monodactylic and polydactylic blue nail discoloration to guide workup and treatment plans.

Discovery of HN37 as a Potent and Chemically Stable Antiepileptic Drug Candidate

We previously reported that P-retigabine (P-RTG), a retigabine (RTG) analogue bearing a propargyl group at the nitrogen atom in the linker of RTG, displayed moderate anticonvulsant efficacy. Recently, our further efforts led to the discovery of HN37 (pynegabine), which demonstrated satisfactory chemical stability upon deleting the ortho liable -NH₂ group and installing two adjacent methyl groups to the carbamate motif. HN37 exhibited enhanced activation potency toward neuronal Kv7 channels and high in vivo efficacy in a range of pre-clinical seizure models, including the maximal electroshock test and a 6 Hz model of pharmacoresistant limbic seizures. With its improved chemical stability, strong efficacy, and better safety margin, HN37 has progressed to clinical trial in China for epilepsy treatment.

Chemical modulation of Kv7 potassium channels

The rising interest in Kv7 modulators originates from their ability to evoke fundamental electrophysiological perturbations in a tissue-specific manner. A large number of therapeutic applications are, in part, based on the clinical experience with two broad-spectrum Kv7 agonists, flupirtine and retigabine. Since precise molecular structures of human Kv7 channel subtypes in closed and open states have only very recently started to emerge, computational studies have traditionally been used to analyze binding modes and direct the development of more potent and selective Kv7 modulators with improved safety profiles. Herein, the synthetic and medicinal chemistry of small molecule modulators and the representative biological properties are summarized. Furthermore, new therapeutic applications supported by in vitro and in vivo assay data are suggested.

Medication-Induced Oral Hyperpigmentation: A Systematic Review

BACKGROUND

Medication-induced oral hyperpigmentation is an oral condition that impacts patients' quality of life and has been linked to many systemic therapeutic agents. The exact pathogenesis of tissue pigmentation varies greatly and is not completely known. This systematic review aimed to present data on the causal association between medications and the development of oral/mucosal pigmentation as an adverse drug reaction.

METHODS

A systematic review and analysis of literature were conducted using the following databases: PubMed, Science Direct, ProQuest, Web of Science, and Scopus. The systematic review included original articles written in English and published between January 1982 and June 2020. Following the PRISMA statement, eligible articles were systematically reviewed, and data were extracted from eligible studies and analyzed.

RESULTS

A total of 235 articles were identified, of which 57 met the inclusion criteria and were included in this review. The mean age of included patients was 46.2±16.38 years (range: 10-90 years) with a male to female ratio of 1:1.45. Oral mucosal hyperpigmentation was reported following the use of several classes of medications such as antiviral (eg, zidovudine), antibiotic (eg, minocycline), antimalarial (eg, chloroquine), anti-fungal (eg, ketoconazole), antileprotic (eg, clofazimine), antihypertensive (eg, amlodipine), chemotherapeutic, and antineoplastic drugs. The risk of developing oral pigmentation was significantly higher with antimalarial medications, antibiotics, antineoplastic and chemotherapeutic agents. Medication-induced oral hyperpigmentation was most frequent among women and in the hard palate.

CONCLUSION

Future research is warranted to better understand the pathogenesis and risk factors for medication-induced oral hyperpigmentation in order to reassure patients during prescription and management.

Pharmacological Manipulation of K v 7 Channels as a New Therapeutic Tool for Multiple Brain Disorders

K _v 7 ("M-type," KCNQ) K⁺ currents, play dominant roles in controlling neuronal excitability. They act as a "brake" against hyperexcitable states in the central and peripheral nervous systems. Pharmacological augmentation of M current has been developed for controlling epileptic seizures, although current pharmacological tools are uneven in practical usefulness. Lately, however, M-current "opener" compounds have been suggested to be efficacious in preventing brain damage after multiple types of insults/diseases, such as stroke, traumatic brain injury, drug addiction and mood disorders. In this review, we will discuss what is known to date on these efforts and identify gaps in our knowledge regarding the link between M current and therapeutic potential for these disorders. We will outline the preclinical experiments that are yet to be performed to demonstrate the likelihood of success of this approach in human trials. Finally, we also address multiple pharmacological tools available to manipulate different K _v 7 subunits and the relevant evidence for translational application in the clinical use for disorders of the central nervous system and multiple types of brain insults. We feel there to be great potential for manipulation of K _v 7 channels as a novel therapeutic mode of intervention in the clinic, and that the paucity of existing therapies obligates us to perform further research, so that patients can soon benefit from such therapeutic approaches.

Prevention of brain damage after traumatic brain injury by pharmacological enhancement of KCNQ (Kv7, "M-type") K+ currents in neurons

Nearly three million people in the USA suffer traumatic brain injury (TBI) yearly; however, there are no pre- or post-TBI treatment options available. KCNQ2-5 voltage-gated K⁺ channels underlie the neuronal "M current", which plays a dominant role in the regulation of neuronal excitability. Our strategy towards prevention of TBI-induced brain damage is predicated on the suggested hyper-excitability of neurons induced by TBIs, and the decrease in neuronal excitation upon pharmacological augmentation of M/KCNQ K⁺ currents. Seizures are very common after a TBI, making further seizures and development of epilepsy disease more likely. Our hypothesis is that TBI-induced hyperexcitability and ischemia/hypoxia lead to metabolic stress, cell death and a maladaptive inflammatory response that causes further downstream morbidity. Using the mouse controlled closed-cortical impact blunt TBI model, we found that systemic administration of the prototype M-channel "opener", retigabine (RTG), 30 min after TBI, reduces the post-TBI cascade of events, including spontaneous seizures, enhanced susceptibility to chemo-convulsants, metabolic stress, inflammatory responses, blood-brain barrier breakdown, and cell death. This work suggests that acutely reducing neuronal excitability and energy demand via M-current enhancement may be a novel model of therapeutic intervention against post-TBI brain damage and dysfunction.

The color of skin: blue diseases of the skin, nails, and mucosa

Diseases of the skin, hair, nails and mucosa can appear as flesh-colored lesions or may present as any of the colors of the visual spectrum. Diseases associated with blue (or shades of blue) discoloration represent a unique group of conditions that occur de novo or as a reaction to either a topical or a systemic agent to which the individual has been exposed. Blue diseases can affect the skin, the nails or the mucosal membranes of the mouth (buccal mucosa, gingiva, lips, palate or tongue) or eyes (sclera). In addition to appearing blue, they can also appear as blue-black, blue-brown, blue-gray, blue-green, blue-purple, blue-red, and blue-silver. The conditions range from those secondary to exogenous agents (systemic or tattoo or topical) to syndromes to systemic diseases to tumors (adnexal, melanocytic, vascular, or miscellaneous). A comprehensive attempt to include all conditions that have been described as blue (or a shade of blue) has been performed by evaluating the following terms using the medical search engine PubMed: blue and either gingiva, lips, lunula, mucosa, nails, oral, palate, sclera, skin, or tongue. Subsequently, the conditions were organized by color (blue and shades of blue) and within each color by location (skin, nails, oral mucosa and sclera). The results are presented in organized tables; in addition, there is discussion of some of the conditions that are unique to one or more specific locations. In conclusion, 'preserve and cherish the pale blue dot' and remember that a big red rock eater with chrysiasis is the answer to the riddle, "What is big and blue and eats rocks?"

In silico re-engineering of a neurotransmitter to activate KCNQ potassium channels in an isoform-specific manner

Voltage-gated potassium (Kv) channel dysfunction causes a variety of inherited disorders, but developing small molecules that activate Kv channels has proven challenging. We recently discovered that the inhibitory neurotransmitter γ-aminobutyric acid (GABA) directly activates Kv channels KCNQ3 and KCNQ5. Here, finding that inhibitory neurotransmitter glycine does not activate KCNQs, we re-engineered it in silico to introduce predicted KCNQ-opening properties, screened by in silico docking, then validated the hits in vitro. Attaching a fluorophenyl ring to glycine optimized its electrostatic potential, converting it to a low-nM affinity KCNQ channel activator. Repositioning the phenyl ring fluorine and/or adding a methylsulfonyl group increased the efficacy of the re-engineered glycines and switched their target KCNQs. Combining KCNQ2- and KCNQ3-specific glycine derivatives synergistically potentiated KCNQ2/3 activation by exploiting heteromeric channel composition. Thus, in silico optimization and docking, combined with functional screening of only three compounds, facilitated re-engineering of glycine to develop several potent KCNQ activators.

How to replace the lost keys? Strategies toward safer KV7 channel openers

The highly structurally similar drugs flupirtine and retigabine have been regarded as safe and effective for many years but lately they turned out to exert intolerable side effects. While the twin molecules share the mode of action, both stabilize the open state of voltage-gated potassium channels, the form and severity of adverse effects is different. The analgesic flupirtine caused drug-induced liver injury in rare but fatal cases, whereas prolonged use of the antiepileptic retigabine led to blue tissue discoloration. Because the adverse effects seem unrelated to the mode of action, it is likely, that both drugs that occupied important therapeutic niches, could be replaced. Reasons for the clinically relevant toxicity will be clarified and future substitutes for these drugs presented in this review.

An Update on Drug-Induced Pigmentation

Drug-induced pigmentation accounts for up to 20% of all cases of acquired pigmentation. A thorough review of medical history and previous and ongoing medications as well as a complete skin examination can guide diagnosis. Implicated agents include alkylating/cytotoxic agents, analgesics, antiarrhythmics, anticoagulants, antiepileptics, antimalarials, antimicrobials, antiretrovirals, metals, prostaglandin analogs, and psychotropic agents, among others. Confirming true drug associations can be challenging, especially in the setting of delayed onset of pigmentation and coexisting polypharmacy.

An Investigation into Retigabine (Ezogabine) Associated Dyspigmentation in Rat Eyes by MALDI Imaging Mass Spectrometry

Retigabine (RTG) is an antiepileptic drug approved as an adjunctive treatment for refractory partial-onset seizures in adults. In April 2013, the Food and Drug Administration issued a warning that RTG could cause changes in retinal pigmentation and discoloration of skin, resulting in a blue appearance. As part of a larger preclinical effort to gain a mechanistic understanding as to the origins of retinal pigment changes associated with RTG, we conducted a long-term repeat dosing study in rats. Matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI IMS) was used to determine the distribution of RTG and its metabolites in the rat eye following 13 and 39 weeks of dosing. IMS revealed the presence of RTG, a previously characterized N-acetyl metabolite of RTG (NAMR), and several species structurally related through the dimerization of RTG and NAMR. These species were highly localized to the melanin-containing layers of the uveal tract of the rat eye including the choroid, ciliary body, and iris, suggesting that the formation of these dimers occurs from melanin bound RTG and NAMR. Furthermore, several of the RTG-related dimers have UV absorbance which give them a purple color in solution. We propose that the melanin binding of RTG and NAMR effectively concentrates the two compounds to enable mixed condensation reactions to occur when the binding provides the proper geometry in the redox environment of the uveal tissues. High lateral resolution images illustrate that the blood-retinal barrier effectively restricts retinal access to RTG-related compounds. The spatial information provided by MALDI IMS was critical in contextualizing the homogenate concentrations of key RTG-related compounds and helped provide a basis for the mechanism of dimer formation.

Ezogabine skin discoloration is reversible after discontinuation

There is concern that bluish skin discoloration associated with ezogabine treatment could be permanent. We present a case of ezogabine-induced skin discoloration that resolved completely after discontinuation. A 55-year-old woman started ezogabine 400 mg three times a day at age 41. Bluish pigmentation over the toe nails, finger nails, around eyes and over and around lips was first noted after 5 years of treatment. Ezogabine was discontinued eight years after initiation. Skin discoloration improved within 6 months and completely resolved within 6 years of discontinuation. This case suggests that ezogabine-induced discoloration is reversible after discontinuation of treatment.

Adolescent Clinical Development of Ezogabine/Retigabine as Adjunctive Therapy for Partial-Onset Seizures: Pharmacokinetics and Tolerability

OBJECTIVES: To explore the pharmacokinetic (PK) profile and safety of ezogabine (EZG)/retigabine (RTG) as adjunctive therapy for uncontrolled partial-onset seizures (POS) in adolescents. METHODS: In this multiple-dose study (NCT01494584), adolescents with POS received EZG/RTG immediate-release tablets three times daily (TID) as adjunctive therapy to 1 to 3 concurrent antiepileptic drugs. The study comprised a screening phase, and a 5- to 8-week treatment phase starting with 100 mg TID up-titrated once weekly by ≤50 mg TID to a maximum dosage of 300 mg TID. There were 8 venous blood samples and 2 finger-prick blood samples collected for PK analysis during 8-hour time periods at the target dosages of 100, 200, and 300 mg TID. RESULTS: This study was terminated prematurely on US Food and Drug Administration advice due to pigmentation/discoloration findings in long-term, open-label extension studies in adults. Five participants (ages 13-16 years) had enrolled in the study. For the EZG/RTG 100-, 200-, and 300-mg doses, the area under the concentration-time curve during the dosage intervals was 1680, 2559, and 3784 ng/hr/mL; maximum plasma concentrations were 370, 536, and 751 ng/mL, and minimum plasma concentrations were 105, 200, and 287 ng/mL, respectively. Venous and finger-prick concentrations of EZG/RTG were similar. No significant adverse events were observed during treatment (133-213 days). CONCLUSIONS: EZG/RTG PK appeared linear across the dosage range of 100 to 300 mg TID in adolescents with POS, and were consistent with adult observations. The small sample size and short study duration preclude conclusions regarding the safety and efficacy of EZG/RTG.

Practical Use of Newer Antiepileptic Drugs as Adjunctive Therapy in Focal Epilepsy

This article lays the background for, and discusses the practical issues surrounding, the adjunctive use of the last four antiepileptic drugs (AEDs) to be licensed for the treatment of pharmacoresistant focal seizures in the UK and elsewhere. More than 30% of adolescent and adult patients will not be fully controlled on the currently available therapeutic armamentarium. After not responding to their first three AED schedules, only a handful of patients attained seizure freedom on subsequent regimens. To optimise the response to any new AED in this setting, it is often necessary to reduce the existing drug burden. The pharmacology, tolerability and safety, and everyday use of lacosamide, eslicarbazepine acetate, retigabine (ezogabine) and perampanel will be reviewed and discussed. This will be accompanied by data from prospective audits with each drug undertaken at the Western Infirmary in Glasgow, Scotland, and a report of their successful introduction in an illustrative case. Overall, there is a large variation in the course of refractory epilepsy and the effect of AED therapy on this process seems minimal. Nevertheless, a number of patients will benefit from the introduction of each new AED, with some becoming seizure-free.