Topical capsaicin. The fire of a 'hot' medicine is reignited

Embryonic Zebrafish Irritant-evoked Hyperlocomotion (EZIH) as a high-throughput behavioral model for nociception

Behavioral models have served a key role in understanding nociception, the sensory system by which animals detect noxious stimuli in their environment. Developing zebrafish (Danio rerio) are a powerful study organism for examining nociceptive pathways, given the vast array of genetic, developmental, and neuroscience tools available for these animals. However, at present there are few widely-adopted behavioral models for nociception in developing zebrafish. This study examines the locomotor response of hatching-stage zebrafish embryos to dilute solutions of the noxious chemical and TRPA1 agonist allyl isothiocyanate (AITC). At this developmental stage, AITC exposure induces a robust uniphasic hyperlocomotion response. This behavior was thoroughly characterized by determining the effects of pre-treatment with an array of pharmacological agents, including anesthetics, TRPA1 agonists/antagonists, opioids, NSAIDs, benzodiazepines, SSRIs, and SNRIs. Anesthetics suppressed the response to AITC, pre-treatment with TRPA1 agonists induced hyperlocomotion and blunted the response to subsequent AITC exposures, and TRPA1 antagonists and the opioid buprenorphine tended to reduce the response to AITC. The behavioral responses of zebrafish embryos to a noxious chemical were minimally affected by the other pharmacological agents examined. The feasibility of using this behavioral model as a screening platform for drug discovery efforts was then evaluated by assaying a library of natural product mixtures from microbial extracts and fractions. Overall, our results indicate that irritant-evoked locomotion in embryonic zebrafish is a robust behavioral model for nociception with substantial potential for examining the molecular and cellular pathways associated with nociception and for drug discovery efforts.

Topical Medications for Chronic Itch in Older Patients: Navigating a Pressing Need

Chronic itch in older patients is a common problem, with a significant impact on quality of life. Chronic itch in the older population may be attributable to several causes, such as age-related changes, skin conditions, systemic conditions, medications, and psychological conditions. Given the complexity of itch in this population, comorbidities, and polypharmacy in most geriatric patients, treating chronic itch can be challenging for healthcare providers. Therefore, optimized topical treatment regimens are paramount to help these patients and prevent side effects.

Capsaicin nanocrystals burdened topical polymeric gel: An encouraging tactic for alleviation of paclitaxel-induced peripheral neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is triggered by clinically recommended chemotherapeutics. Topical capsaicin (CAP) is a US-FDA-approved therapeutic entity for the mitigation of CIPN. Besides good skin permeation efficiency, CAP concentration in a topical dermal dosage form must be controlled due to its dose-dependent therapeutic and adverse effects. Therefore, in the present investigation, capsaicin nanocrystals (CAP-NCs) were scaled up using the nanoprecipitation technique. CAP-NCs exhibited 145.4 ± 0.90 nm particle size, 0.254 ± 0.005 polydispersity index (PDI), -17.2 ± 0.80 mV surface charge (ζ), and markedly higher cumulative percentage drug release (85.68 ± 0.89 %) compared to pure CAP (12.56 ± 0.57 %) in 12 h. Later, capsaicin nanocrystals burdened polymeric gel (CAP-NCs-Gel) was characterized using analytical and spectral techniques. Furthermore, CAP-NCs-Gel depicted remarkable textural properties, and desirable viscosity along with ∼2.23-fold enhancement in permeability, ∼1.61-fold augmentation of CAP steady-state flux, and permeability coefficient. Additionally, the in vivo therapeutic efficacy assessment of CAP-NCs-Gel in the paclitaxel-induced peripheral neuropathy (PIPN) demonstrated remarkable improvements in mechanical hyperalgesia, heat hyperalgesia, cold allodynia, and locomotor behavior. Capsaicin nanocrystals burdened polymeric gel once-a-day (CAP-NCs-Gel-OD) and twice-a-day (CAP-NCs-Gel-TD) applications outstandingly diminished the levels of TNF-α (P < 0.0001) and IL-6 (P < 0.01) in the sciatic nerve homogenate in contrast to the positive control group and insignificant difference (P > 0.05) was noticed compared to the normal control group. Correspondingly, significant modulation of oxidative stress biomarkers, and noticeable regeneration of nerve fibers, a typical arrangement of the axon, with preserved intact myelin sheath integrity were professed in sciatic nerve; aimed at diminishing neuroinflammation, oxidative stress, and mitigating nerve damage in PIPN. In conclusion, CAP-NCs-Gel is a top-notch nanotherapeutic for translating into a clinically viable dosage form for treating CIPN.

Cough and itch: Common mechanisms of irritation in the throat and skin

Cough and itch are protective mechanisms in the body. Cough occurs as a reflex motor response to foreign body inhalation, while itch is a sensation that similarly evokes a scratch response to remove irritants from the skin. Both cough and itch can last for sustained periods, leading to debilitating chronic disorders that negatively impact quality of life. Understanding the parallels and differences between chronic cough and chronic itch may be paramount to developing novel therapeutic approaches. In this article, we identify connections in the mechanisms contributing to the complex cough and scratch reflexes and summarize potential shared therapeutic targets. An online search was performed using various search engines, including PubMed, Web of Science, Google Scholar, and ClinicalTrials.gov from 1983 to 2024. Articles were assessed for quality, and those relevant to the objective were analyzed and summarized. The literature demonstrated similarities in the triggers, peripheral and central nervous system processing, feedback mechanisms, immunologic mediators, and receptors involved in the cough and itch responses, with the neuronal sensitization processes exhibiting the greatest parallels between cough and itch. Given the substantial impact on quality of life, novel therapies targeting similar neuroimmune pathways may apply to both itch and cough and provide new avenues for enhancing their management.

From Compression to Itch: Exploring the Link Between Nerve Compression and Neuropathic Pruritus

Neuropathic itch is a type of chronic pruritus resulting from neural dysfunction along the afferent pathway. It is often accompanied by abnormal sensations such as paresthesia, hyperesthesia, or hypoesthesia. This condition, which may involve motor or autonomic neural damage, significantly impacts patients' quality of life, causing severe itch and associated comorbidities such as depression, disrupted sleep, and social strain. Neuropathic itch accounts for 8% of chronic pruritus cases, though this may be underestimated. This comprehensive review focuses on nerve impingement as the primary pathophysiological mechanism for various forms of neuropathic itch including brachioradial pruritus (BRP), notalgia paresthetica (NP), and anogenital itch. BRP, often seen in middle-aged white women, manifests as pruritus in the dorsolateral forearms typically exacerbated by ultraviolet (UV) exposure and related to cervical spine pathology. NP, prevalent in middle-aged women, presents as pruritus in the upper back due to thoracic spine nerve compression. Anogenital pruritus, affecting 1-5% of adults, is often linked to lumbosacral spine issues after ruling out dermatologic conditions such as lichen sclerosus or lichen simplex chronicus. The pathophysiology of neuropathic itch involves both peripheral and central mechanisms, with nerve damage being a key factor. Diagnosis requires a thorough history, physical examination, and potentially imaging studies. Topical agents such as menthol, capsaicin, and lidocaine are used for mild cases, while systemic medications such as gabapentin, pregabalin, and antidepressants are prescribed for moderate to severe cases; however, no US Food and Drug Administration (FDA)-approved therapies currently exist specifically for neuropathic itch. Understanding the underlying neural dysfunction and appropriate therapeutic strategies is crucial for managing neuropathic itch effectively.

Targeting the TRPV1 pain pathway in osteoarthritis of the knee

INTRODUCTION

The growing prevalence and lack of effective pain therapies for knee osteoarthritis (KOA) results in a substantial unmet need for novel analgesic therapies. The transient receptor potential vanilloid 1 (TRPV1) receptor is expressed in subsets of nociceptive sensory neurons and has major roles in pain transmission and regulation. In the structures of the knee joint, nociceptors are present in abundance.

AREAS COVERED

TRPV1-expressing nociceptors in the knee represent a rational target to modulate activity at the origin of the pain pathway in KOA and may avoid systemic side effects seen with currently available analgesics. TRPV1 antagonists can induce analgesia, but hyperthermia and thermal hypesthesia side effects have limited their utility. Clinical development of TRPV1 agonists for pain management has progressed further than that of TRPV1 antagonists. Capsaicin and resiniferatoxin have provided proof-of-concept for the modulation of TRPV1 activity in KOA.

EXPERT OPINION

Intra-articular administration of TRPV1 agonists enables direct delivery to target nerve terminals in the knee, offering a potentially transformative approach for the management of pain associated with KOA. Here, we explore the advances in understanding innervation of the knee joint in KOA, the role of TRPV1-expressing neurons and progress in developing TRPV1 modulators for KOA.

Sweet Bell Pepper: A Focus on Its Nutritional Qualities and Illness-Alleviated Properties

Sweet bell pepper (SBP, Capsicum annuum L.) can be employed as a spice in many dishes and may also be eaten as a delicious fruit. These two nutritional attributes are owing to the strong, deep taste of many SBP phytochemicals. This fruit has many additional beneficial properties because it contains high concentrations of minerals and vitamins that distinguish it from other kinds of fruits. Almost every part of the SBP is thought to be an excellent source of bioactive substances that are health supporters, such as flavonoids, polyphenols, and various aromatic substances. The ability of SBP-phytochemicals to work as antioxidants, reducing the harmful effects of oxidative stress and consequently preventing many chronic illnesses, is one of their main biomedical characteristics. These phytochemicals have good antibacterial properties, mostly against gram-positive pathogenic microbes, in addition to their anti-carcinogenic and cardio-preventive effects. So, this review aims to highlight the nutritional qualities of SBP-derived phytochemicals and their illness-alleviated characteristics. Antioxidant, anti-inflammatory, antitumor, antidiabetic, and analgesic properties are some of the ones discussed.

8-shogaol derived from dietary ginger alleviated acute and inflammatory pain by targeting TRPV1

Ginger, a well-known spice plant, has been used widely in medicinal preparations for pain relief. However, little is known about its analgesic components and the underlying mechanism. Here, we ascertained, the efficacy of ginger ingredient 8-Shogaol (8S), on inflammatory pain and tolerance induced by morphine, and probed the role of TRPV1 in its analgesic action using genetic and electrophysiology approaches. Results showed that 8S effectively reduced nociceptive behaviors of mice elicited by chemical stimuli, noxious heat as well as inflammation, and antagonized morphine analgesic tolerance independent on opioid receptor function. Genetic deletion of TRPV1 significantly abolished 8S' analgesia action. Further calcium imaging and patch-clamp recording showed that 8S could specifically activate TRPV1 in TRPV1-expressing HEK293T cells and dorsal root ganglion (DRG) neurons. The increase of [Ca2+]i in DRG was primarily mediated through TRPV1. Mutational and computation studies revealed the key binding sites for the interactions between 8S and TRPV1 included Leu515, Leu670, Ile573, Phe587, Tyr511, and Phe591. Further studies showed that TRPV1 activation evoked by 8S resulted in channel desensitization both in vitro and in vivo, as may be attributed to TRPV1 degradation or TRPV1 withdrawal from the cell surface. Collectively, this work provides the first evidence for the attractive analgesia of 8S in inflammatory pain and morphine analgesic tolerance mediated by targeting pain-sensing TRPV1 channel. 8S from dietary ginger has potential as a candidate drug for the treatment of inflammatory pain.

Current and emerging drugs for the treatment of pruritus: an update of the literature

INTRODUCTION

Pruritus, particularly in its chronic form, often imposes significant suffering and reductions in patients' quality of life. The pathophysiology of itch is varied depending on disease context, creating opportunities for unique drug development and multimodal therapy.

AREAS COVERED

The purpose of this article is to provide an update of the literature regarding current and emerging therapeutics in itch. We review the multitudes of drug targets available and corresponding drugs that have shown efficacy in clinical trials, with a particular emphasis on phase 2 and 3 trials and beyond. Broadly, these targets include therapies directed against type 2 inflammation (i.e. Th2 cytokines, JAK/STAT, lipid mediators, T-cell mediators, and other enzymes and receptors) and neural receptors and targets (i.e. PARs, TRP channels, opioid receptors, MRGPRs, GABA receptors, and cannabinoid receptors).

EXPERT OPINION

Therapeutics for itch are emerging at a remarkable pace, and we are entering an era with more and more specialized therapies. Increasingly, these treatments are able to relieve itch beyond their effect on inflammation by directly targeting the neurosensory system.

Hepatoprotection of capsaicin in alcoholic and non-alcoholic fatty liver diseases

Alcoholic liver disease (ALD) and non-alcoholic fatty liver disease (NAFLD) are common causes of chronic liver disease that share the range of steatosis, steatohepatitis, fibrosis, cirrhosis, and finally, hepatocellular carcinoma. They are identified by the dysregulation of disease-specific signalling pathways and unique microRNAs. Capsaicin is an active ingredient of chilli pepper that acts as an agonist of transient receptor potential vanilloid subfamily 1. It seems that the protective role of capsaicin against NAFLD and ALD is linked to its anti-steatotic, antioxidant, anti-inflammatory, and anti-fibrotic effects. Capsaicin-induced inhibiting metabolic syndrome and gut dysbiosis and increasing bile acids production are also involved in its anti-NAFLD role. This review summarises the different molecular mechanisms underlying the protective role of capsaicin against NAFLD and ALD. More experimental studies are needed to clarify the effects of capsaicin on the expression of genes involved in hepatic lipid metabolism and hepatocytes apoptosis in NAFLD and ALD.

Uncovering Novel Capsaicin Inhibitory Activity towards Human Carbonic Anhydrase Isoforms IX and XII by Combining In Silico and In Vitro Studies

Hot pepper (Capsicum annuum) represents one of the most widespread functional foods of the Mediterranean diet, and is associated with a reduced risk of developing cardiovascular disease, cancer, and mental disorders. In particular, its bioactive spicy molecules, named Capsaicinoids, exhibit polypharmacological properties. Among them, Capsaicin (trans-8-methyl-N-vanillyl-6-nonenamide) is the most studied and reported in variegated scientific contributions for its beneficial effects, often linked to mechanisms of action unrelated to the activation of Transient Receptor Potential Vanilloid 1 (TRPV1). In this study, we present the application of in silico methods to Capsaicin for evaluating its inhibitory activity against the tumor-associated human (h) expressed CA IX and XII. In vitro assays confirmed Capsaicin inhibitory activity towards the most relevant tumor-related hCA isoforms. In particular, the hCAs IX and XII showed an experimental K_I value of 0.28 μM and 0.064 μM, respectively. Then, an A549 model of non-small cell lung cancer, typically characterized by an elevated expression of hCA IX and XII, was employed to test the inhibitory effects of Capsaicin in vitro under both normoxic and hypoxic conditions. Finally, the migration assay revealed that Capsaicin [10 µM] inhibits cells from moving in the A549 cells model.

Uremic pruritus: pathophysiology, clinical presentation, and treatments

Uremic pruritus is one of the most common and bothersome symptoms in patients with end-stage renal disease. Most patients with uremic pruritus experience a prolonged and relapsing course and significant impairments of quality of life. The pathophysiology of uremic pruritus is not completely understood. A complex interplay among cutaneous biology and the nervous and immune systems has been implicated, with the involvement of various inflammatory mediators, neurotransmitters, and opioids. Uremic pruritus treatment outcomes are often unsatisfactory. Clinical trials have mostly been small in scale and have reported inconsistent results. Recent evidence shows that gabapentinoids, nalfurafine, and difelikefalin are effective for relieving uremic pruritus in hemodialysis patients. This review provides an overview of the epidemiology and proposed mechanisms of uremic pruritus, then highlights the manifestations of and clinical approach to uremic pruritus. Current evidence regarding treatment options, including topical treatments, treatment of underlying disease, phototherapy, and systemic treatments, is also outlined. With a better understanding of uremic pruritus, more therapeutic options can be expected in the near future.

Transient Receptor Potential Channels and Itch

Transient Receptor Potential (TRP) channels are multifunctional sensory molecules that are abundant in the skin and are involved in the sensory pathways of itch, pain, and inflammation. In this review article, we explore the complex physiology of different TRP channels, their role in modulating itch sensation, and their contributions to the pathophysiology of acute and chronic itch conditions. We also cover small molecule and topical TRP channel agents that are emerging as potential anti-pruritic treatments; some of which have shown great promise, with a few treatments advancing into clinical trials-namely, TRPV1, TRPV3, TRPA1, and TRPM8 targets. Lastly, we touch on possible ethnic differences in TRP channel genetic polymorphisms and how this may affect treatment response to TRP channel targets. Further controlled studies on the safety and efficacy of these emerging treatments is needed before clinical use.

Druggable Targets and Compounds with Both Antinociceptive and Antipruritic Effects

Pain and itch are both important manifestations of various disorders, such as herpes zoster, atopic dermatitis, and psoriasis. Growing evidence suggests that both sensations have shared mediators, overlapping neural circuitry, and similarities in sensitization processes. In fact, pain and itch coexist in some disorders. Determining pharmaceutical agents and targets for treating pain and itch concurrently is of scientific and clinical relevance. Here we review the neurobiology of pain and itch and discuss the pharmaceutical targets as well as novel compounds effective for the concurrent treatment of these sensations.

Monograph of wild and cultivated chili peppers (Capsicum L., Solanaceae)

Capsicum L. (tribe Capsiceae, Solanaceae) is an American genus distributed ranging from the southern United States of America to central Argentina and Brazil. The genus includes chili peppers, bell peppers, ajíes, habaneros, jalapeños, ulupicas and pimientos, well known for their economic importance around the globe. Within the Solanaceae, the genus can be recognised by its shrubby habit, actinomorphic flowers, distinctive truncate calyx with or without appendages, anthers opening by longitudinal slits, nectaries at the base of the ovary and the variously coloured and usually pungent fruits. The highest diversity of this genus is located along the northern and central Andes. Although Capsicum has been extensively studied and great advances have been made in the understanding of its taxonomy and the relationships amongst species, there is no monographic treatment of the genus as a whole. Based on morphological and molecular evidence studied from field and herbarium specimens, we present here a comprehensive taxonomic treatment for the genus, including updated information about morphology, anatomy, karyology, phylogeny and distribution. We recognise 43 species and five varieties, including C.mirum Barboza, sp. nov. from São Paulo State, Brazil and a new combination C.muticum (Sendtn.) Barboza, comb. nov.; five of these taxa are cultivated worldwide (C.annuumL.var.annuum, C.baccatumL.var.pendulum (Willd.) Eshbaugh, C.baccatumL.var.umbilicatum (Vell.) Hunz. & Barboza, C.chinense Jacq. and C.frutescens L.). Nomenclatural revision of the 265 names attributed to chili peppers resulted in 89 new lectotypifications and five new neotypifications. Identification keys and detailed descriptions, maps and illustrations for all taxa are provided.

Capsaicin Potently Blocks Salmonella typhimurium Invasion of Vero Cells

Salmonella typhimurium (S. typhimurium) is one of the major food and waterborne bacteria that causes several health outbreaks in the world. Although there are few antibiotics against this bacterium, some of these drugs are challenged with resistance and toxicity. To mitigate this challenge, our group explored the ethnomedicinal/herbalism knowledge about a certain spice used in Northern Ghana in West Africa against bacterial and viral infection. This plant is Capsicum chinense (C. chinense). The plant is one of the commonest food spices consumed across the world. The seed of the plant contains both capsaicin and dihydrocapsaicin. Apart from capsaicin and dihydrocapsaicin, other major capsaicinoids in C. chinense include nordihydrocapsaicin, homodihydrocapsaicin, and homocapsaicin. In this pilot work, we investigated the antibacterial activity of pure capsaicin and capsaicin extract obtained from C. chinense against S. typhimurium in vitro. Capsaicin extract showed potent inhibition of S. typhimurium growth at concentrations as low as 100 ng/mL, whereas pure capsaicin comparatively showed poorer inhibition of bacteria growth at such a concentration. Interestingly, both capsaicin extract and pure capsaicin were found to potently block a S. typhimurium invasion of the Vero cell in vitro. Taken together, we believed that capsaicin might work synergistically with dihydrocapsaicin or the other capsaicinoids to inhibit S. typhimurium growth, whereas individually, capsaicin or dihydrocapsaicin could potently block the bacteria entry and invasion of Vero cells.

Effect of Topical Analgesia on Desensitization Following 8% Topical Capsaicin Application

To prevent pain associated with 8% capsaicin application, pretreatment with local anesthetics, such as EMLA (eutectic mixture of lidocaine 2.5% and prilocaine 2.5%), is considered an option. However, there is contradicting evidence regarding the effects of local analgesia on capsaicin-induced desensitization. In session 1, 2 skin areas in each forearm of 24 healthy volunteers were randomized to 2-hour pretreatment with EMLA/placebo cream. After pretreatment, 8% capsaicin patches were applied for 3 hours in 1 placebo and 1 EMLA pretreated area, obtaining the following four areas: Capsaicin + EMLA, Capsaicin + Placebo, EMLA alone, and Placebo. Pain intensity scores were assessed during the 3-hour application of capsaicin. Warmth detection, heat pain sensitivity, and microvascular reactivity were measured after the removal of capsaicin. After 24 hours, in session 2, all tests were repeated followed by histamine application in each area to examine itch intensity and neurogenic flare. Overall, EMLA caused significant reductions in capsaicin-induced pain compared with placebo (P= .007) and enhanced the capsaicin-induced increase in superficial blood perfusion immediately after the 3-hour capsaicin application (P< .01). Regardless of pretreatment, capsaicin induced heat hyperalgesia immediately after the application (P< .001). Twenty-four hours post application, heat pain sensitivity was normalized. However, WDT increased significantly (P< .001). Capsaicin tended to reduce the itch intensity and significantly reduced the neurogenic flare (P< .05) induced by histamine compared with EMLA alone. The findings suggest that pretreatment with topical analgesic cream reduces application site pain without interfering with the 8% topical capsaicin-induced desensitization. PERSPECTIVE: Pretreatment with local anesthetic EMLA cream might be considered a good therapeutic option to reduce the pain associated with 8% capsaicin application currently used for treatment of neuropathic pain syndromes. This study also suggests the existence of a synergistic effect of capsaicin and EMLA on the process of neurogenic inflammation.

Approach to the Patient with Chronic Pruritus

Chronic pruritus (itch lasting ≥6 weeks) is a bothersome chief complaint that may present in a broad variety of diseases. Most itch-causing diagnoses fit into 1 of 5 categories (inflammatory, secondary to systemic disease, neuropathic, chronic pruritus of undetermined origin, and psychogenic itch) and this broad differential can be narrowed using key findings in the history and physical. In this article, we discuss which key findings are most pertinent for narrowing this differential and guiding further workup and treatment, as well as how to treat many itchy conditions.

A capsaicinoid-based soft drug, AG1529, for attenuating TRPV1-mediated histaminergic and inflammatory sensory neuron excitability

TRPV1, a member of the transient receptor potential (TRP) family, is a nonselective calcium permeable ion channel gated by physical and chemical stimuli. In the skin, TRPV1 plays an important role in neurogenic inflammation, pain and pruritus associated to many dermatological diseases. Consequently, TRPV1 modulators could represent pharmacological tools to respond to important patient needs that still represent an unmet medical demand. Previously, we reported the design of capsaicinoid-based molecules that undergo dermal deactivation (soft drugs), thus preventing their long-term dermal accumulation. Here, we investigated the pharmacological properties of the lead antagonist, 2-((4-hydroxy-2-iodo-5-methoxybenzyl) amino)-2-oxoethyl dodecanoate (AG1529), on heterologously expressed human TRPV1 (hTRPV1), on nociceptor excitability and on an in vivo model of acute pruritus. We report that AG1529 competitively blocked capsaicin-evoked activation of hTRPV1 with micromolar potency, moderately affected pH-induced gating, and did not alter voltage- and heat-mediated responses. AG1529 displays modest receptor selectivity as it mildly blocked recombinant hTRPA1 and hTRPM8 channels. In primary cultures of rat dorsal root ganglion (DRG) neurons, AG1529 potently reduced capsaicin-evoked neuronal firing. AG1529 exhibited lower potency on pH-evoked TRPV1 firing, and TRPA1-elicited nociceptor excitability. Furthermore, AG1529 abolished histaminergic and inflammation mediated TRPV1 sensitization in primary cultures of DRG neurons. Noteworthy, dermal wiping of AG1529, either in an acetone-based formulation or in an anhydrous ointment, dose-dependently attenuated acute histaminergic itch in a rodent model. This cutaneous anti-pruritic effect was devoid of the normal nocifensive action evoked by the burning sensation of capsaicin. Taken together, these preclinical results unveil the mode of action of AG1529 on TRPV1 channels and substantiate the tenet that this capsaicinoid-based soft drug is a promising candidate for drug development as a topical anti-pruritic and anti-inflammatory medication.

Investigational drugs in early phase clinical trials targeting thermotransient receptor potential (thermoTRP) channels

INTRODUCTION

Thermo transient receptor potential (thermoTRP) channels are some of the most intensely pursued therapeutic targets of the past decade. They are considered promising targets of numerous diseases including chronic pain and cancer. Modulators of these proteins, in particular TRPV1-4, TRPM8 and TRPA1, have reached clinical development, but none has been approved for clinical practice yet.

AREAS COVERED

The therapeutic potential of targeting thermoTRP channels is discussed. The discussion is centered on our experience and on available data found in SciFinder, PubMed, and ClinicalTrials.gov database from the past decade. This review focuses on the therapeutic progress concerning this family of channels, including strategies to improve their therapeutic index for overcoming adverse effects.

EXPERT OPINION

Although thermoTRPs are pivotal drug targets, translation to the clinic has faced two key problems, (i) unforeseen side effects in Phase I trials and, (ii) poor clinical efficacy in Phase II trials. Thus, there is a need for (i) an enhanced understanding of the physiological role of these channels in tissues and organs and (ii) the development of human-based pre-clinical models with higher clinical translation. Furthermore, progress in nanotechnology-based delivery strategies will positively impact thermoTRP human pharmacology.

Evaluation of the Single-Dose Toxicity of Capsaicin Pharmacopuncture in Rats

Background: This study aimed to assess the toxicity of capsaicin (CP) pharmacopunture in an animal model.<br/>Methods: The toxicity of a single-muscular dose of CP (45.45 mg/mL) was evaluated in 6-week-old male and female Sprague-Dawley rats. A total of 20 rats were assigned to 2 groups which were sex and weight matched. All rats acclimatized for 1 week before receiving 1.0 mL of CP (45.45 mg/mL) or normal saline solution(control) intramuscularly. The general condition and mortality of the animals were observed. The rats were sacrificed 2 weeks after CP was administered and histopathology was performed.<br/>Results: No abnormal symptoms or deaths were observed, and there was no difference in body weights between the CP and control groups throughout the study. No significant differences in histopathology were observed between the groups.<br/>Conclusion: No toxicological changes related to the administration of CP were observed. This study indicated that the safe dose of CP in Sprague-Dawley rats was 1.0 mL of CP (45.45 mg/mL) or less. Further studies are needed to confirm the safety of CP in the human body.

Capsicum carassense (Solanaceae), a new species from the Brazilian Atlantic Forest

Capsicum carassense Barboza & Bianchetti sp. nov., a species from mid-elevation of the Atlantic Forest (Minas Gerais, Brazil) is described and illustrated. This endemic new species is distinguished from the most similar C. mirabile Mart. by its moderate to dense general pubescence, narrowly elliptic leaves and larger calyx appendages and corollas. A key for the native Brazilian species of Capsicum growing in the state of Minas Gerais is also provided.

Safety considerations when using drugs to treat pruritus

Introduction: Treatment for chronic pruritus ranges from use of topical formulations to newer biologic agents. Targeting treatment to the underlying etiology is key in reducing the burden of disease while avoiding systemic or adverse effects.Areas covered: This review details the effective medical treatments used in various etiologies of chronic itch with a focus on the potential adverse effects and safety data available for each.Expert opinion: New drug developments in the areas of neural signaling and immune targeting show great promise for the future of chronic itch treatment. These new therapies broaden the available treatment options but also pose new considerations for safety and adverse effects.

Mediterranean products as promising source of multi-target agents in the treatment of metabolic syndrome

Alteration of nutritional habits play an essential role on the risk of developing Metabolic Syndrome (MetS). Several epidemiological studies have shown that assuming diets rich of foods included in the Mediterranean diet (MetDiet) pattern like, such as olive oil, nuts, fruit, fiber, vegetables, wine and grain cereals has protective effects on the different risk factors characterizing the MetS. The beneficial effects of the MetDiet in the MetS are mainly due to the antioxidant and anti-inflammatory properties of the most abundant phytochemical components of such foods as polyphenols like resveratrol and oleuropein, allyl sulfides, ellagic acid, mono- and poly-unsaturated fatty acids (MUFA and PUFA), tocopherols and flavonoids like quercetin, which have shown positive results in the prevention of cardiovascular diseases (CVDs), with related risk factors, like hypertension, hypercholesterolemia and obesity. In this review, we highlighted the multi-target activities of the bioactive components contained in some foods typical of the Mediterranean area like olive oil, onion, liquorice, rosemary, oregano, hazelnut, pistachio, "Melannurca" apple, red wine, hot pepper, Citrus sp. fruits, saffron and garlic, with particular focus on their impact on health outcomes in relation to MetS main key factors, such as insulin resistance (IR) and type 2 diabetes mellitus (T2DM), endothelial dysfunctions, inflammatory response, oxidative stress and dyslipidaemic and hypercholesterolemic effects.

Itch: From mechanism to (novel) therapeutic approaches

Itch is a common sensory experience that is prevalent in patients with inflammatory skin diseases, as well as in those with systemic and neuropathic conditions. In patients with these conditions, itch is often severe and significantly affects quality of life. Itch is encoded by 2 major neuronal pathways: histaminergic (in acute itch) and nonhistaminergic (in chronic itch). In the majority of cases, crosstalk existing between keratinocytes, the immune system, and nonhistaminergic sensory nerves is responsible for the pathophysiology of chronic itch. This review provides an overview of the current understanding of the molecular, neural, and immune mechanisms of itch: beginning in the skin, proceeding to the spinal cord, and eventually ascending to the brain, where itch is processed. A growing understanding of the mechanisms of chronic itch is expanding, as is our pipeline of more targeted topical and systemic therapies. Our therapeutic armamentarium for treating chronic itch has expanded in the last 5 years, with developments of topical and systemic treatments targeting the neural and immune systems.

Capsaicin, an inhibitor of Ochratoxin A production by Aspergillus section Nigri strains in grapes (Vitis vinifera L.)

Food decay by spoilage fungi leads to significant economic losses and hazards to consumers' health due to the potential of mycotoxin occurrence. Ochratoxin A (OTA) is a mycotoxin known as nephrotoxic and carcinogenic to humans. Natural capsaicin was evaluated for its effectiveness against the growth of five Aspergillus section Nigri strains and accumulation of OTA in inoculated black grapes. Results showed that capsaicin was effective in inhibiting fungal growth and OTA production by new four Aspergillus section Nigri strains (ATHUM 6997, 6998, 6999, 7000) and by Aspergillus carbonarius as well. Moreover, capsaicin addition exhibited maximum inhibition of OTA produced by ATHUM 6997, 6998, 6999, and 7000 in black grapes at 28.9%, 8.6%, 68.4%, and 78.1%, respectively. Inhibition percentage of OTA production by A. carbonarius in grapes treated with capsaicin was estimated at 61.5%. These results suggest that capsaicin influences the OTA biosynthesis pathway of all Aspergillus section Nigri strains and therefore could be used as an effective natural preservative against OTA contamination of vineyards. Risk assessment revealed that when grapes are treated with capsaicin, consumers are less exposed to OTA.

Chronic itch management: therapies beyond those targeting the immune system

OBJECTIVE

Chronic itch can be a debilitating, unrelenting symptom. Over the years, we have advanced our knowledge about immune-mediated itch (eg, atopic dermatitis) and have developed several treatments targeting these immune pathways. Chronic itch that is noninflammatory in nature is more elusive. However, we have gained some understanding of the neural component mediating itch and have made progress in treating this challenging symptom.

DATA SOURCES

A comprehensive literature search was conducted, and data and literature were reviewed on the topics of chronic itch, its pathophysiology, and nonimmunological treatments for chronic itch that work on the nerves.

STUDY SELECTIONS

Basic science papers, review articles, case reports, and clinical trial data were considered.

RESULTS

A variety of topical and systemic therapies targeting the nerves have shown effectiveness in treating patients with chronic itch of different types.

CONCLUSION

Treating chronic itch may be challenging, but an arsenal of treatments are available and many are on the horizon as we expand our knowledge of mechanisms of itch and the neural receptors involved.

Four new species of Capsicum (Solanaceae) from the tropical Andes and an update on the phylogeny of the genus

Four new species of Capsicum (Capsiceae, Solanaceae) from Andean tropical forests in South America are described. Capsicum benoistii Hunz. ex Barboza sp. nov. (incertae sedis) is endemic to a restricted area in south-central Ecuador and is most similar to the more widespread C. geminifolium (Dammer) Hunz. (Colombia, Ecuador, and Peru). Capsicum piuranum Barboza & S. Leiva sp. nov. (Andean clade) is found in northern Peru (Department Piura) and is morphologically most similar to C. caballeroi M. Nee of the Bolivian yungas (Departments Santa Cruz and Cochabamba) but closely related to C. geminifolium and C. lycianthoides Bitter. Capsicum longifolium Barboza & S. Leiva sp. nov. (Andean clade) occurs from northern Peru (Departments Amazonas, Cajamarca, and Piura) to southern Ecuador (Province Zamora-Chinchipe), and is morphologically most similar to C. dimorphum (Miers) Kuntze (Colombia, Ecuador, and Peru). Capsicum neei Barboza & X. Reyes sp. nov. (Bolivian clade) is endemic to southeastern Bolivia (Departments Chuquisaca and Santa Cruz) in the Boliviano-Tucumano Forest, is morphologically most similar to another Bolivian endemic species C. minutiflorum Rusby (Hunz.), and is closely related to C. caballeroi. Complete descriptions, illustrations, distributions and conservation assessments of all new species are given. Chromosome numbers for C. piuranum and C. longifolium are also provided. Three of the new species were included in a new phylogenetic analysis for Capsicum; their positions were strongly resolved within clades previously recognized in the genus.

Utility of in vitro and in vivo systems for studying the permeability of capsaicin and nonivamide through different intestinal regions

1. The present study determined and compared the permeability of capsaicin and nonivamide along the length of the intestine in rats. Accordingly, the purpose was to evaluate this synthetic analog as a clinical substitute for capsaicin.. 2. Permeabilities of capsaicin and nonivamide were measured in experiments utilizing Ussing chambers and in vivo methods. Capsaicin concentrations were examined by liquid chromatography-tandem mass spectrometry (LC-MS/MS). 3. Both capsaicin (0.80 × 10^-6cm/s) and nonivamide (0.22 × 10^-6cm/s, p > 0.05) had poor permeabilities across the jejunal membrane. The permeability of nonivamide (10.12 × 10^-6cm/s) was significantly greater than that of capsaicin (5.34 × 10^-6cm/s, p < 0.05) across the iliac membrane. In contrast, the permeability of nonivamide (8.42 × 10^-6cm/s) across the colonic membrane was markedly lower than that of capsaicin (14.48 × 10^-6cm/s, p < 0.05). In accordance with the in vitro study, the drug concentration-time curve of nonivamide was significantly higher in the ileum (F = 14.18, p < 0.05) but lower in the colon (F = 11.86, p < 0.05) compared with capsaicin. 4. The results demonstrate that capsaicin and nonivamide exhibit varying permeabilities across several different intestinal tissues. The relevance of such extended investigations to healthcare is underscored by the lower cost of nonivamide versus capsaicin, along with potential application in prevention and management of the disease.

Management of Itch in Atopic Dermatitis

Atopic dermatitis (AD) is the most common itchy dermatosis that affects millions of children and adults worldwide. Chronic itch in this condition has significant impact on measures of quality of life, such as sleep. Treating itch in AD has been challenging for decades, but new drugs have emerged in the last year with significant anti-pruritic effect. The optimal treatment regimen for atopic itch addresses barrier dysfunction, inflammation, neural hypersensitivity, and the itch-scratch cycle. Topical moisturizers remain the foundation of treatment and should be used by all patients with AD-associated pruritus. Step-wise therapy, from topical anti-inflammatory creams to systemic monoclonal antibodies and immunosuppressants, is recommended. There are multiple adjuvant therapies that can be used, especially to target itch in the setting of minimal skin inflammation. Finally, patient education, sleep management, and stress relief are important components to optimize outcomes. This review assesses the latest advances and treatment recommendations for pruritus in AD. Finally, suggested therapeutic ladders and emerging treatments are discussed.

Chronic Pruritus in the Geriatric Population

Chronic pruritus (>6 week's duration) in the geriatric population (≥65 years old), is an increasing health care problem. The pathophysiologic predisposing factors are abnormalities of the epidermal barrier, immune system, and nervous system. Causes can be dichotomized into histaminergic and nonhistaminergic pruritus. Topical treatments are generally safe. Systemic treatments are chosen depending on the condition, comorbid diseases, and drug interactions. Treatment options are limited. Progress has been made in identifying itch-selective mediators over the last decade. Numerous new medications are currently undergoing clinical trials and they are anticipated to enter the clinics in the near future.

Transdermal immunomodulation: Principles, advances and perspectives

Immunomodulation, manipulation of the immune responses towards an antigen, is a promising strategy to treat cancer, infectious diseases, allergies, and autoimmune diseases, among others. Unique features of the skin including the presence of tissue-resident immune cells, ease of access and connectivity to other organs makes it a unique target organ for immunomodulation. In this review, we summarize advances in transdermal delivery of agents for modulating the immune responses for vaccination as well as tolerization. The biological foundation of skin-based immunomodulation and challenges in its implementation are described. Technological approaches aimed at enhancing the delivery of immunomodulatory therapeutics into skin are also discussed in this review. Progress made in the treatment of several specific diseases including cancer, infections and allergy are discussed. Finally, this review discusses some practical considerations and offers some recommendations for future studies in the field of transdermal immunomodulation.

Effect of lipopolysaccharide on the responsiveness of equine bronchial tissue

Recurrent airway obstruction (RAO) is a main characteristic of horses with severe equine asthma syndrome. The presence of bacterial lipopolysaccharide (LPS) in the airways of horses is thought to play a crucial role in the clinical expression of this disorder. This study pharmacologically characterized the effect of LPS on the responsiveness of equine bronchial tissue. Equine isolated bronchi were incubated overnight with LPS (0.1-100 ng/ml) and then stimulated by electrical field stimulation (EFS). The role of capsaicin sensitive-sensory nerves (capsaicin desensitization treatment), neurokinin-2 (NK₂) receptors (blocked by GR159897), transient receptor potential vanilloid type 1 receptors (TRPV1; blocked by SB366791), and neurokinin A (NKA) were investigated. Untreated bronchi were used as control tissues. LPS (1 ng/ml) significantly increased the EFS-evoked contractility of equine bronchi compared with control tissues (+742 ± 123 mg; P < 0.001). At higher concentrations LPS induced desensitization to airways hyperresponsiveness (AHR; EC₅₀: 5.9 ± 2.6 ng/ml). Capsaicin desensitization and GR159897 significantly prevented AHR induced by LPS at EFS_1-50Hz (-197 ± 25%; P < 0.01). SB366791 inhibited AHR at very low EFS frequency (EFS_1Hz -193 ± 29%; P < 0.01 vs. LPS-treated bronchi). LPS (1 ng/ml) significantly (P < 0.01) increased 3.7 ± 0.7 fold the release of NKA compared with control bronchi. LPS induces biphasic dysfunctional bronchial contractility due to the stimulation of capsaicin sensitive-sensory nerves, increased release of NKA, and activation of NK₂ receptors, whereas TRPV1 receptors appear to play a marginal role in this response. The overnight challenge with low concentrations of LPS represents a suitable model to investigate pharmacological options that may be of value in the treatment of equine RAO.

Capsaicin: Friend or Foe in Skin Cancer and Other Related Malignancies?

Capsaicin is the main pungent in chili peppers, one of the most commonly used spices in the world; its analgesic and anti-inflammatory properties have been proven in various cultures for centuries. It is a lipophilic substance belonging to the class of vanilloids and an agonist of the transient receptor potential vanilloid 1 receptor. Taking into consideration the complex neuro-immune impact of capsaicin and the potential link between inflammation and carcinogenesis, the effect of capsaicin on muco-cutaneous cancer has aroused a growing interest. The aim of this review is to look over the most recent data regarding the connection between capsaicin and muco-cutaneous cancers, with emphasis on melanoma and muco-cutaneous squamous cell carcinoma.

Psychocutaneous disease: Pharmacotherapy and psychotherapy

Building a strong therapeutic alliance with the patient is of utmost importance in the management of psychocutaneous disease. Optimal management of psychocutaneous disease includes both pharmacotherapy and psychotherapy. This article reviews psychotropic medications currently used for psychocutaneous disease, including antidepressants, antipsychotics, mood stabilizers, and anxiolytics, with a discussion of relevant dosing regimens and adverse effects. Pruritus management is addressed. In addition, basic and complex forms of psychotherapy, such as cognitive-behavioral therapy and habit-reversal training, are described.

Antinociceptive effect of natural and synthetic alkamides involves TRPV1 receptors

Objective

To establish the role of TRPV1 receptor in the antinociceptive effect of natural alkamides (i.e. affinin, longipinamide A, longipenamide A and longipenamide B) isolated from Heliopsis longipes (A. Gray) S.F. Blake and some related synthetic alkamides (i.e. N-isobutyl-feruloylamide and N-isobutyl-dihydroferuloylamide).

Methods

The orofacial formalin test was used to assess the antinociceptive activity of natural (1–30 μg, orofacial region) and synthetic alkamides (0.1–100 μg, orofacial region). The alkamide capsaicin was used as positive control, while capsazepine was used to evaluate the possible participation of TRPV1 receptor in alkamide-induced antinociception.

Key findings

Natural (1–30 μg) and synthetic (0.1–100 μg) alkamides administered to the orofacial region produced antinociception in mice. The antinociceptive effect induced by affinin, N-isobutyl-feruloylamide and N-isobutyl-dihydroferuloylamide was antagonized by capsazepine but not by vehicle.

Conclusions

These results suggest that alkamide affinin, longipinamide A, longipenamide A and longipenamide B isolated from Heliopsis longipes as well as the synthesized analogue compounds N-isobutyl-feruloylamide and N-isobutyl-dihydroferuloylamide produce their effects by activating TRPV1 receptor and they may have potential for the development of new analgesic drugs for the treatment of orofacial pain.

Current and Emerging Therapies for Itch Management in Psoriasis

Pruritus is a common and significant symptom among patients with psoriasis. Pruritus is often present beyond the borders of psoriatic plaques, and frequently affects the scalp and genital regions. Psoriatic itch may be severe and can profoundly affect quality of life and sleep, even in the context of mild-to-moderate disease. These features often make the treatment of psoriatic pruritus challenging. However, there are a variety of effective topical and systemic treatment modalities available to address this symptom. While there remains a need for treatments that specifically target psoriatic itch, newly licensed therapies including secukinumab, ixekizumab and apremilast have been shown to rapidly and effectively mediate itch reduction.

Harnessing the Therapeutic Potential of Capsaicin and Its Analogues in Pain and Other Diseases

Capsaicin is the most predominant and naturally occurring alkamide found in Capsicum fruits. Since its discovery in the 19th century, the therapeutic roles of capsaicin have been well characterized. The potential applications of capsaicin range from food flavorings to therapeutics. Indeed, capsaicin and few of its analogues have featured in clinical research covered by more than a thousand patents. Previous records suggest pleiotropic pharmacological activities of capsaicin such as an analgesic, anti-obesity, anti-pruritic, anti-inflammatory, anti-apoptotic, anti-cancer, anti-oxidant, and neuro-protective functions. Moreover, emerging data indicate its clinical significance in treating vascular-related diseases, metabolic syndrome, and gastro-protective effects. The dearth of potent drugs for management of such disorders necessitates the urge for further research into the pharmacological aspects of capsaicin. This review summarizes the historical background, source, structure and analogues of capsaicin, and capsaicin-triggered TRPV1 signaling and desensitization processes. In particular, we will focus on the therapeutic roles of capsaicin and its analogues in both normal and pathophysiological conditions.

(1) H and (13) C NMR data on natural and synthetic capsaicinoids

Capsaicinoids are the compounds responsible for the pungency of chili peppers. These substances have attracted the attention of many research groups in recent decades because of their antinociceptive, analgesic, anti-inflammatory, and anti-obesity properties, among others. There are nearly 160 capsaicinoids reported in the literature. Approximately 25 of them are natural products, while the rest are synthetic or semi-synthetic products. A large amount of NMR data for the capsaicinoids is dispersed throughout literature. Therefore, there is a need to organize all this NMR data in a systematic and orderly way. This review summarizes the (1) H and (13) C NMR data on 159 natural and synthetic capsaicinoids, with a brief discussion of some typical and relevant aspects of these NMR data. Copyright © 2015 John Wiley & Sons, Ltd.

Topical Citrullus colocynthis (bitter apple) extract oil in painful diabetic neuropathy: A double-blind randomized placebo-controlled clinical trial

BACKGROUND

The aim of the present study was to examine the safety and efficacy of a topical formulation of Citrullus colocynthis in patients with painful diabetic polyneuropathy (PDPN).

METHODS

The study was designed as a two-arm double-blind randomized placebo-controlled clinical trial using a parallel design. Sixty patients with PDPN were randomly allocated to receive either a topical formulation of C. colocynthis or placebo (1:1 allocation ratio) for 3 months. Patients were evaluated before and after the intervention using the neuropathic pain scale, electrodiagnostic findings, World Health Organization Biomedical Research and Education Foundation (BREF) quality of life (WHOQOL-BREF) scores, and reported adverse events.

RESULTS

There was a significantly greater decrease in mean pain score after 3 months in the C. colocynthis (-3.89; 95% confidence interval [CI] -3.19, -4.60) than placebo (-2.28; 95% CI -1.66, -2.90) group (P < 0.001). Mean changes in nerve conduction velocity of the tibial nerve, distal latency of the superficial peroneal nerve and sural nerve, and sensory amplitude of the sural nerve were significantly higher in the intervention than placebo group (P < 0.001) in favour of the intervention. In the different domains of WHOQOL-BREF, there was a significant improvement only for the mean score in the physical domain.

CONCLUSIONS

Application of a topical formulation of C. colocynthis fruit extract can decrease pain in patients with PDPN. It also may have some uncertain effects on nerve function and the physical domain of quality of life, which require further investigation in studies with larger sample sizes and of longer duration.

Current topical and systemic therapies for itch

Itch is a common distressing symptom which may be caused by multifactorial aetiologies including inflammatory skin diseases, systemic diseases, neuropathic conditions and psychogenic disorders. Itch is a term used synonymously with pruritus and is defined as acute if it lasts less than 6 weeks or chronic if it persists for more than 6 weeks. It can have the same impact on the quality of life as chronic pain and shares many of the same pathophysiological pathways. Depending on the aetiology of the itch, different pathogenic mechanisms have been postulated with a number of mediators identified. These include histamine, leukotrienes, proteases, neuropeptides, cytokines and opioids, which may activate peripheral itch-mediating C-fibres via receptors on the nerve terminals and central neuronal pathways. Therefore, there is no single universally effective anti-itch treatment available. First-line treatments for itch include topical therapies, such as emollients, mild cleansers (low pH), topical anaesthetics, steroids, calcineurin inhibitors and coolants (menthol). Treatment with systemic therapies can vary according to the aetiology of the chronic itch. Non-sedating antihistamines are helpful in conditions such as urticaria where the itch is primarily histamine mediated. Although the itch of eczema is not mediated by histamine, sedating antihistamines at night are helpful to break the itch-scratch cycle. Chronic itch may also be treated with other systemic therapies, such as anticonvulsants, antidepressants as well as mu-opioid antagonists, kappa-opioid agonists and phototherapy, depending on the cause of the itch. This article summarises the topical and systemic therapies available with our current understanding of the pathophysiology of itch.