Bioavailability of capsaicin and its implications for drug delivery

Enhanced Transdermal Delivery of Concentrated Capsaicin from Chili Extract-Loaded Lipid Nanoparticles with Reduced Skin Irritation

The aim of this study was to develop lipid-based nanoparticles that entrapped a high concentration of capsaicin (0.25%) from a capsicum oleoresin extract. The solid lipid nanoparticles (SLNs) and nanostructured lipid carriers (NLCs) were strategically fabricated to entrap capsaicin without a hazardous solvent. Optimized nanosize lipid particles with high capsaicin entrapment and loading capacity were achieved from pair-wise comparison of the solid lipid mixtures consisting of fatty esters and fatty alcohols, representing small and large crystal-structure molecules combined with a compatible liquid lipid and surfactants (crystallinity index = 3%). This report was focused on selectively captured capsaicin from oleoresin in amorphous chili extract-loaded NLCs with 85.27% ± 0.12% entrapment efficiency (EE) and 8.53% ± 0.01% loading capacity (LC). The particle size, polydispersity index, and zeta potential of chili extract-loaded NLCs were 148.50 ± 2.94 nm, 0.12 ± 0.03, and -29.58 ± 1.37 mV, respectively. The favorable zero-order kinetics that prolonged capsaicin release and the significantly faster transdermal penetration of the NLC attributed to the reduction in skin irritation of the concentrated capsaicin NLCs, as illustrated by the in vitro EpiDerm^TM three-dimensional human skin irritation test and hen's egg test chorioallantoic membrane assay (HET-CAM).

A transport system based on a quantum dot-modified nanotracer is genetically and developmentally stable in pregnant mice

The use of nanoscale materials (NMs) could cause problems such as cytotoxicity, genomic aberration, and effects on human health, but the impacts of NM exposure during pregnancy remain uncharacterized in the context of clinical applications. It was sought to determine whether nanomaterials pass through the maternal-fetal junction at any stage of pregnancy. Quantum dots (QDs) coated with heparinized Pluronic 127 nanogels and polyethyleneimine (PEI) were administered to pregnant mice. The biodistribution of QDs, as well as their biological impacts on maternal and fetal health, was evaluated. Encapsulation of QDs with a nanogel coating produces a petal-like nanotracer (PNt), which could serve as a nano-carrier of genes or drugs. PNts were injected through the tail vein and accumulated in the liver, kidneys, and lungs. QD accumulation in reproductive organs (uterus, placenta, and fetus) differed among phases of pregnancy. In phase I (7 days of pregnancy), the QDs did not accumulate in the placenta or fetus, but by phase III (19 days) they had accumulated at high levels in both tissues. Karyotype analysis revealed that the PNt-treated pups did not have genetic abnormalities when dams were treated at any phase of pregnancy. PNts have the potential to serve as carriers of therapeutic agents for the treatment of the mother or fetus and these results have a significant impact on the development and application of QD-based NPs in pregnancy.

Feeding brown fat: dietary phytochemicals targeting non-shivering thermogenesis to control body weight

Excessive adipose accumulation, which is the main driver for the development of secondary metabolic complications, has reached epidemic proportions and combined pharmaceutical, educational and nutritional approaches are required to reverse the current rise in global obesity prevalence rates. Brown adipose tissue (BAT) is a unique organ able to dissipate energy and thus a promising target to enhance BMR to counteract a positive energy balance. In addition, active BAT might support body weight maintenance after weight loss to prevent/reduce relapse. Natural products deliver valuable bioactive compounds that have historically helped to alleviate disease symptoms. Interest in recent years has focused on identifying nutritional constituents that are able to induce BAT activity and thereby enhance energy expenditure. This review provides a summary of selected dietary phytochemicals, including isoflavones, catechins, stilbenes, the flavonoids quercetin, luteolin and resveratrol as well as the alkaloids berberine and capsaicin. Most of the discussed phytochemicals act through distinct molecular pathways e.g. sympathetic nerve activation, AMP-kinase signalling, SIRT1 activity or stimulation of oestrogen receptors. Thus, it might be possible to utilise this multitude of pathways to co-activate BAT using a fine-tuned combination of foods or combined nutritional supplements.

Acute Capsaicin Supplementation Improved Resistance Exercise Performance Performed After a High-Intensity Intermittent Running in Resistance-Trained Men

de Freitas, MC, Cholewa, JM, Panissa, VLG, Toloi, GG, Netto, HC, Zanini de Freitas, C, Freire, RV, Lira, FS, and Rossi, FE. Acute capsaicin supplementation improved resistance exercise performance performed after a high-intensity intermittent running in resistance-trained men. J Strength Cond Res XX(X): 000-000, 2019-We sought to investigate the acute effects of capsaicin supplementation on the rate of perceived exertion (RPE) and heart rate during high-intensity intermittent exercise (HIIE) and resistance exercise performance executed after HIIE in resistance-trained men. Eleven resistance-trained men completed 2 randomized, double-blind trials: capsaicin condition or a placebo condition. The concurrent exercise session was composed of a 5-km intermittent run (1:1 effort and passive recovery ratio) and subsequent resistance exercise (4 × 70% of 1RM until muscle failure in the half-squat exercise). Heart rate was recorded during HIIE and after the protocol RPE (0-10 scale) was accessed. The resistance exercise performance was analyzed by the maximum number of repetitions performed for each set and the total volume (repetitions × weight lifted). During HIIE, the RPE (capsaicin = 7 ± 1 vs. placebo = 8 ± 1 points, t = -3.674, p = 0.005) and mean heart rate (capsaicin = 153 ± 13 vs. placebo = 158 ± 12 bpm, t = -2.292, p = 0.048) were significantly lower in the capsaicin compared with placebo condition. For subsequent resistance exercise, there was a significant decrease in volume across time (F = 19.889, p < 0.001, η = 0.69) with maximal number of repetitions performed in capsaicin than placebo condition (2,077.6 ± 465.2 kg vs. 1,838.9 ± 624.1 kg, p = 0.028, d = 0.43), but the condition vs. set was not significant (F = 0.582, p = 0.632, η = 0.06). Acute capsaicin supplementation induced a lower mean heart rate and RPE during HIIE and improved subsequent resistance exercise performance in resistance-trained men.

Capsaicin topical cream (8%) for the treatment of myofascial pain syndrome

Background

Myofascial pain syndrome is a common cause of musculoskeletal pain. The objective of this study was to evaluate the potential analgesic action of 8% capsaicin cream for topical use in patients with myofascial pain syndrome.

Methods

Initially, cream formulations of PLA (Placebo) and CPS (Capsaicin 8%) were developed and approved according to the current requirements of the health authority agency. The 40 participating patients were randomly assigned to the PLA and CPS groups in a double-blind fashion. Before the creams were topically administered, according to the allocation group, the local anesthetic was used for a period of 50 minutes directly in the area of interest. The cream was applied to the area of the skin over the trigger point, represented by the area with pain at palpation, in an amount of 10 g for 30 minutes in a circular area of 24 mm diameter. Subsequently, the cream was removed and the skin tolerability parameters were evaluated. The pain was measured before and during the formulation application, as well as at 1 hour, 7 days, 30 days, and 60 days after the procedure, evaluated using a verbal numerical scale (from 0 to 10: with 0 = no pain and 10 = worst pain imaginable).

Results

No patient in PLA Group had hyperemia or burning sensation at the site of application, while 85% of patients in CPS Group had hyperemia or burning sensation at 15 minutes. These complaints disappeared 24 hours after the cream was removed. The pain score in CPS Group decreased steadily up to the 60^th day of evaluation (p < 0.0001).

Conclusion

Application of the formulations did not cause macroscopic acute or chronic skin lesions in patients, and the 8% capsaicin formulation was beneficial and well tolerated.

Toxicokinetic Study of a Gastroprotective Dose of Capsaicin by HPLC-FLD Method

BACKGROUND

A low dose of capsaicin and its natural homologs and analogs (capsaicinoids) have shown to prevent development of gastric mucosal damage of alcohol and non-steroid anti-inflammatory drugs. Based on this experimental observation, a drug development program has been initiated to develop per os applicable capsaicin containing drugs to eliminate gastrointestinal damage caused by non-steroid anti-inflammatory drugs.

METHODS

As a part of this program, a sensitive and selective reverse-phase high-performance liquid chromatography-based method with fluorescence detection has been developed for quantification of capsaicin and dihydrocapsaicin in experimental dog's plasma.

RESULTS

The method was evaluated for a number of validation characteristics (selectivity, repeatability, and intermediate precision, LOD, LOQ, and calibration range). The limit of detection (LOD) was 2 ng/mL and the limit of quantification (LOQ) was 10 ng/mL for both capsaicin and dihydrocapsaicin. The method was used for analysis of capsaicin and dihydrocapsaicin in the plasma samples obtained after per os administration of low doses (0.1, 0.3, and 0.9 mg/kg bw) of Capsaicin Natural (USP 29) to the experimental animals.

CONCLUSIONS

The obtained results indicated that the administered capsaicinoids did not reach the general circulation.

Capsaicin: Physicochemical properties, cutaneous reactions and potential applications in painful and inflammatory conditions

Capsaicin is a natural protoalkaloid recognized as the main pungent component in hot peppers (Capsicum annuum L.). The capsaicin receptor is highly expressed in the unmyelinated type C nerve fibers originating from small diameter sensory neurons in dorsal root ganglia and cranial nerve ganglia correspondents. Capsaicin and related vanilloids have a variety of effects on primary sensory neurons function, from sensory neuron excitation characterized by local burning sensation and neurogenic inflammation, followed by conduction blockage accompanied by reversible ultrastructural changes of peripheral nociceptive endings (desensitization), going as far as irreversible degenerative changes (neurotoxicity). The main role in capsaicin-induced neurogenic inflammation relies on the capsaicin sensitive, small diameter primary sensory neurons, therefore its evaluation could be used as a diagnostic instrument in functional alterations of cutaneous sensory nerve fibers. Moreover, capsaicin-induced desensitization and neurotoxicity explain the analgesic/anti-nociceptive and anti-inflammatory effects of topical capsaicin and its potential use in the management of painful and inflammatory conditions. In this study, we describe the effects of capsaicin on neurogenic inflammation and nociception, as well as its potential diagnostic value and therapeutic impact in various conditions involving impairment of sensory nerve fibers.

Capsaicin inhibits the function of α7-nicotinic acetylcholine receptors expressed in Xenopus oocytes and rat hippocampal neurons

Capsaicin is a naturally occurring alkaloid derived from Chili peppers fruits. Using the two-electrode voltage-clamp technique in Xenopus oocyte expression system, actions of capsaicin on the functional properties of α₇ subunit of the human nicotinic acetylcholine (α₇ nACh) receptor were investigated. Ion currents activated by ACh (100 μM) were reversibly inhibited with an IC₅₀ value of 8.6 μM. Inhibitory actions of capsaicin was independent of membrane potential. Furthermore, Ca²⁺-dependent Cl^- channels expressed endogenously in oocytes were not involved in inhibitory actions of capsaicin. In addition, increasing the ACh concentrations could not reverse the inhibitory effects of capsaicin. Importantly, specific binding of [¹²⁵I] α-bungarotoxin remained unaltered by capsaicin suggesting that its effect is noncompetitive. Whole cell patch-clamp technique was performed in CA1 stratum radiatum interneurons of rat hippocampal slices. Ion currents induced by choline, a selective-agonist of α₇-receptor, were reversibly inhibited by 10 min bath application of capsaicin (10 μM). Collectively, results of our investigation indicate that the function of the α7-nACh receptor expressed in Xenopus oocytes and in hippocampal interneurons are inhibited by capsaicin.

Pleiotropic Pharmacological Actions of Capsazepine, a Synthetic Analogue of Capsaicin, against Various Cancers and Inflammatory Diseases

Capsazepine is a synthetic analogue of capsaicin that can function as an antagonist of TRPV1. Capsazepine can exhibit diverse effects on cancer (prostate cancer, breast cancer, colorectal cancer, oral cancer, and osteosarcoma) growth and survival, and can be therapeutically used against other major disorders such as colitis, pancreatitis, malaria, and epilepsy. Capsazepine has been reported to exhibit pleiotropic anti-cancer effects against numerous tumor cell lines. Capsazepine can modulate Janus activated kinase (JAK)/signal transducer and activator of the transcription (STAT) pathway, intracellular Ca²⁺ concentration, and reactive oxygen species (ROS)-JNK-CCAAT/enhancer-binding protein homologous protein (CHOP) pathways. It can inhibit cell proliferation, metastasis, and induce apoptosis. Moreover, capsazepine can exert anti-inflammatory effects through the downregulation of lipopolysaccharide (LPS)-induced nuclear transcription factor-kappa B (NF-κB), as well as the blockage of activation of both transient receptor potential cation channel subfamily V member 1 (TRPV1) and transient receptor potential cation channel, subfamily A, and member 1 (TRPA1). This review briefly summarizes the diverse pharmacological actions of capsazepine against various cancers and inflammatory conditions.

Combination of the natural product capsaicin and docetaxel synergistically kills human prostate cancer cells through the metabolic regulator AMP-activated kinase

Background

Current chemotherapy for castration-resistant prostate cancer is established on taxane-based compounds like docetaxel. However, eventually, the development of toxic side effects and resistance limits the therapeutic benefit being the major concern in the treatment of prostate cancer. Combination therapies in many cases, enhance drug efficacy and delay the appearance of undesired effects, representing an important option for the treatment of castration-resistant prostate cancer. In this study, we tested the efficacy of the combination of docetaxel and capsaicin, the pungent ingredient of hot chili peppers, on prostate cancer cells proliferation.

Methods

Prostate cancer LNCaP and PC3 cell lines were used in this study. Levels of total and phosphorylated forms of Akt, mTOR, S6, LKB1, AMPK and ACC were determined by Western blot. AMPK, LKB1 and Akt knock down was performed by siRNA. PTEN was overexpressed by transient transfection with plasmids. Xenograft prostate tumors were induced in nude mice and treatments (docetaxel and capsaicin) were administered intraperitoneally. Statistical analyses were performed with GraphPad software. Combination index was calculated with Compusyn software.

Results

Docetaxel and capsaicin synergistically inhibited the growth of LNCaP and PC3 cells, with a combination index lower than 1 for most of the combinations tested. Co-treatment with docetaxel and capsaicin notably decreased Akt and its downstream targets mTOR and S6 phosphorylation. Overexpression of PTEN phosphatase abrogated the synergistic antiproliferative effect of docetaxel and capsaicin. The combined treatment also increased the phosphorylation of AMP-activated kinase (AMPK) and the phosphorylation of its substrate ACC. In addition, pharmacological inhibition of AMPK with dorsomorphin (compound C) as well as knock down by siRNA of AMPK or its upstream kinase LKB1, abolished the synergy of docetaxel and capsaicin. Mechanistically, we showed that the synergistic anti-proliferative effect may be attributed to two independent effects: Inhibition of the PI3K/Akt/mTOR signaling pathway by one side, and AMPK activation by the other. In vivo experiments confirmed the synergistic effects of docetaxel and capsaicin in reducing the tumor growth of PC3 cells.

Conclusion

Combination of docetaxel and capsaicin represents a therapeutically relevant approach for the treatment of Prostate Cancer.

Chemoprevention of Colorectal Cancer by Dietary Compounds

Colorectal cancer is one of the leading causes of death, and the third most diagnosed type of cancer, worldwide. It is most common amongst men and women over 50 years old. Risk factors include smoking, alcohol, diet, physical inactivity, genetics, alterations in gut microbiota, and associated pathologies (diabetes, obesity, chronic inflammatory bowel diseases). This review will discuss, in detail, the chemopreventive properties of some dietary compounds (phenolic compounds, carotenoids, iridoids, nitrogen compounds, organosulfur compounds, phytosterols, essential oil compounds, polyunsaturated fatty acids and dietary fiber) against colorectal cancer. We present recent data, focusing on in vitro, laboratory animals and clinical trials with the previously mentioned compounds. The chemopreventive properties of the dietary compounds involve multiple molecular and biochemical mechanisms of action, such as inhibition of cell growth, inhibition of tumor initiation, inhibition of adhesion, migration and angiogenesis, apoptosis, interaction with gut microbiota, regulation of cellular signal transduction pathways and xenobiotic metabolizing enzymes, etc. Moreover, this review will also focus on the natural dietary compounds' bioavailability, their synergistic protective effect, as well as the association with conventional therapy. Dietary natural compounds play a major role in colorectal chemoprevention and continuous research in this field is needed.

Synthesis and characterization of a polyurethane carrier used for a prolonged transmembrane transfer of a chili pepper extract

Purpose

Red chili peppers have been highly valued in gastronomy and traditional medicine since ancient times; it seems that it is not just an ingredient for food but also a good remedy for various medical conditions such as increased blood pressure and high levels of serum triglycerides and cholesterol, myocardial infarction, arthritis, and migraines. The objective of this study is the characterization of a new carrier used for encapsulated extract.

Methods

Chili pepper extract was obtained and was physically entrapped inside polyurethane microparticles in order to diminish the irritative potential of this extract. The particles were evaluated by Zetasizer measurements, small-angle neutron scattering and thermal analysis, scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy; the encapsulation efficacy and the drug release profile were assessed by UV-Vis spectroscopy. Bioevaluations on mice skin were performed to predict the irritative potential of the samples.

Results

Two different types of samples were compared: hollow polyurethane microparticles vs polyurethane particles containing the natural extract. The sizes of the particles were very similar, but the sample containing the extract presents three particle populations (the polydispersity index increases from 0.3 to 0.6 from one sample to another). The zeta-potential measurements and SEM images indicate a medium tendency to form clusters, while the UV-Vis study revealed an almost 70% encapsulation efficacy.

Conclusion

The results suggest that encapsulation of a chili pepper extract inside polyurethane microparticles leads to a non-irritative product with a prolonged release: ~30% of encapsulated extract is released within the first 8 days and a maximum 45% is reached in 2 weeks.

Acute Capsaicin Supplementation Improves Resistance Training Performance in Trained Men

Conrado de Freitas, M, Cholewa, JM, Freire, RV, Carmo, BA, Bottan, J, Bratfich, M, Della Bandeira, MP, Gonçalves, DC, Caperuto, EC, Lira, FS, and Rossi, FE. Acute capsaicin supplementation improves resistance training performance in trained men. J Strength Cond Res 32(8): 2227-2232, 2018-The purpose of this study was to investigate the acute effect of capsaicin supplementation on performance, rate of perceived exertion (RPE), and blood lactate concentrations during resistance exercise in healthy trained young men. Ten resistance-trained men (age = 22.7 ± 4.0 years, mass = 82.3 ± 9.6 kg, and height = 175 ± 0.1 cm) completed 2 randomized, double-blind trials: capsaicin condition (12 mg) or a placebo condition. Forty-five minutes after supplement consumption, subjects performed 4 sets until movement failure in the squat exercise at 70% of 1 repetition maximum with 90 seconds of rest interval between sets. The total mass lifted (total repetitions × mass lifted) was calculated. The RPE was recorded after the last set. Blood lactate was analyzed after each set of exercise, immediately postexercise, and after 3, 5, and at 30 minutes during recovery. The number of repetitions in each set decreased significantly after all sets compared with set-1 and after set-3 and set-4 in relation to set-2 (p < 0.001); however, total mass lifted was higher in capsaicin compared with placebo (3,919.4 ± 1,227.4 kg vs. 3,179.6 ± 942.4 kg, p = 0.002). Blood lactate increased significantly after each set (p < 0.001); however, there were no differences between conditions. Rate of perceived exertion was significantly less for the capsaicin condition than placebo (17.2 ± 1.0 vs. 18.3 ± 1.7, p = 0.048). In summary, acute capsaicin supplementation improves lower-body resistance training performance in trained young men.

Activation of TRPV1 channels leads to stimulation of NKCC1 cotransport in the lens

Lens ion homeostasis is crucial in maintaining water content and, in turn, refractive index and transparency of the multicellular syncytium-like structure. New information is emerging on the regulation of ion transport in the lens by mechanisms that rely on transient receptor potential vanilloid (TRPV) ion channels. We found recently that TRPV1 activation leads to Ca²⁺/PKC-dependent ERK1/2 signaling. Here, we show that the TRPV1 agonist capsaicin (100 nM) and hyperosmotic solution (350 vs. 300 mosM) each caused an increase of bumetanide-inhibitable Rb uptake by intact porcine lenses and Na-K-2Cl cotransporter 1 (NKCC1) phosphorylation in the lens epithelium. The TRPV1 antagonist A889425 (1 µM) abolished the increases of Rb uptake and NKCC1 phosphorylation in response to hyperosmotic solution. Exposing lenses to hyperosmotic solution in the presence of MEK/ERK inhibitor U0126 (10 µM) or the with-no-lysine kinase (WNK) inhibitor WNK463 (1 µM) also prevented NKCC1 phosphorylation and the Rb uptake responses to hyperosmotic solution. WNK463 did not prevent the increase in ERK1/2 phosphorylation that occurs in response to capsaicin or hyperosmotic solution, suggesting that ERK1/2 activation occurs before WNK activation in the sequence of signaling events. Taken together, the evidence indicates that activation of TRPV1 is a critical early step in a signaling mechanism that responds to a hyperosmotic stimulus, possibly lens shrinkage. By activating ERK1/2 and WNK, TRPV1 activation leads to NKCC1 phosphorylation and stimulation of NKCC1-mediated ion transport.

Isolation and Structural Characterization of Bioactive Molecules on Prostate Cancer from Mayan Traditional Medicinal Plants

Prostate cancer is the most common cancer in men around the world. It is a complex and heterogeneous disease in which androgens and their receptors play a crucial role in the progression and development. The current treatment for prostate cancer is a combination of surgery, hormone therapy, radiation and chemotherapy. Therapeutic agents commonly used in the clinic include steroidal and non-steroidal anti-androgens, such as cyproterone acetate, bicalutamide and enzalutamide. These few agents have multiple adverse effects and are not 100% effective. Several plant compounds and mixtures, including grape seed polyphenol extracts, lycopene and tomato preparations, soy isoflavones, and green tea extracts, have been shown to be effective against prostate cancer cell growth. In vivo activity of some isolated compounds like capsaicin and curcumin was reported in prostate cancer murine models. We prepared a library of plant extracts from traditional Mayan medicine. These plants were selected for their use in the contemporaneous Mayan communities for the treatment of different diseases. The extracts were assessed in a phenotypic screening using LNCaP prostate cancer androgen sensitive cell line, with a fixed dose of 25 μg/mL. MTT assay identified seven out of ten plants with interesting anti-neoplastic activity. Extracts from these plants were subjected to a bioguided fractionation to study their major components. We identified three compounds with anti-neoplastic effects against LNCaP cells, one of which shows selectivity for neoplastic compared to benign cells.

Capsaicin in Metabolic Syndrome

Capsaicin, the major active constituent of chilli, is an agonist on transient receptor potential vanilloid channel 1 (TRPV1). TRPV1 is present on many metabolically active tissues, making it a potentially relevant target for metabolic interventions. Insulin resistance and obesity, being the major components of metabolic syndrome, increase the risk for the development of cardiovascular disease, type 2 diabetes, and non-alcoholic fatty liver disease. In vitro and pre-clinical studies have established the effectiveness of low-dose dietary capsaicin in attenuating metabolic disorders. These responses of capsaicin are mediated through activation of TRPV1, which can then modulate processes such as browning of adipocytes, and activation of metabolic modulators including AMP-activated protein kinase (AMPK), peroxisome proliferator-activated receptor α (PPARα), uncoupling protein 1 (UCP1), and glucagon-like peptide 1 (GLP-1). Modulation of these pathways by capsaicin can increase fat oxidation, improve insulin sensitivity, decrease body fat, and improve heart and liver function. Identifying suitable ways of administering capsaicin at an effective dose would warrant its clinical use through the activation of TRPV1. This review highlights the mechanistic options to improve metabolic syndrome with capsaicin.

Capsaicin-enriched diet ameliorates autoimmune neuritis in rats

BACKGROUND

Autoimmune neuropathies are common PNS disorders and effective treatment is challenging. Environmental influence and dietary components are known to affect the course of autoimmune diseases. Capsaicin as pungent component of chili-peppers is common in human nutrition. An influence of capsaicin on autoimmune diseases has been postulated.

METHODS

We tested capsaicin in the animal model of experimental autoimmune neuritis (EAN) in Lewis rat. Rats were immunized with P2-peptide and were treated with capsaicin in different preventive settings. Electrophysiological, histological, and molecular biological analyses of the sciatic nerve were performed to analyze T-cell and macrophage cell count, TRPV1, and cytokine expression. Moreover, FACS analyses including the intestinal immune system were executed.

RESULTS

We observed an immunomodulatory effect of an early preventive diet-concept, where a physiological dosage of oral capsaicin was given 10 days before immunization in EAN. A reduced inflammation of the sciatic nerve was significant detectable clinically, electrophysiologically (CMAPs reduced in control group p < 0.01; increase of nerve conduction blocks in control group p < 0.05), histologically (significant reduction of T-cells, macrophages and demyelination), and at cytokine level. In contrast, this therapeutic effect was missing with capsaicin given from the day of immunization onwards. As possible underlying mechanism, we were able to show changes in the expression of the capsaicin receptor in the sciatic nerve and the small intestine, as well as altered immune cell populations in the small intestine.

CONCLUSION

This is the first report about the immunomodulatory effect of the common nutrient, capsaicin, in an experimental model for autoimmune neuropathies.

Is heterotopic ossification getting nervous?: The role of the peripheral nervous system in heterotopic ossification

Heterotopic ossification (HO), or de novo bone formation in soft tissue, is often observed following traumatic injury. Recent studies suggest that peripheral nerves may play a key functional role in this process. The results supporting a neurological basis for HO are examined in this article. Evidence supports the fact that BMPs released from bone matrix possess the capacity to induce HO. However, the process cannot be recapitulated using recombinant proteins without extremely high doses suggesting other components are required for this process. Study of injuries that increase risk for HO, i.e. amputation, hip replacement, elbow fracture, burn, and CNS injury suggests that a likely candidate is traumatic injury of adjacent peripheral nerves. Recent studies suggest neuroinflammation may play a key functional role, by its ability to open the blood-nerve barrier (BNB). Barrier opening is characterized by a change in permeability and is experimentally assessed by the ability of Evans blue dye to enter the endoneurium of peripheral nerves. A combination of BMP and barrier opening is required to activate bone progenitors in the endoneurial compartment. This process is referred to as "neurogenic HO".

Capsaicin enhances the antitumor activity of sorafenib in hepatocellular carcinoma cells and mouse xenograft tumors through increased ERK signaling

Sorafenib, a small inhibitor of tyrosine protein kinases, is currently the standard chemotherapy drug for the treatment of advanced hepatocellular carcinoma (HCC). Although sorafenib improves the survival of HCC patients, its efficacy is not optimal and requires further improvement. Capsaicin, the major active component of chili peppers from the genus Capsicum, is not only the agonist of TRPV1 channel, but also displays antitumor activity and enhances the sensitivity of cancer cells to cytotoxic drugs. In this study, we investigated the antitumor effects of combined sorafenib and capsaicin on HCC cells in vitro and xenograft tumors. Treatment with capsaicin alone dose-dependently inhibited the proliferation of the HCC cell lines PLC/PRF/7, HuH7 and HepG2 with IC₅₀ values of 137, 108 and 140.7 μmol/L, respectively. No obvious expression of TRPV1 channel was detected in the 3 HCC cell lines and TRPV1 channel blockers did not alleviate the cytotoxicity of capsaicin. By contrast, combining capsaicin and sorafenib significantly enhanced the suppression on cell proliferation, achieving a high-level synergistic effect (inhibition rates over 50%) and promoting HCC cell apoptosis. In nude mice with PLC/PRF/5 xenografts, combined administration of capsaicin and sorafenib significantly enhanced the suppression on tumor growth without apparent gross toxicity compared to either agent alone. Mechanistically, capsaicin (10-200 μmol/L) dose-dependently increased the levels of phosphorylated ERK (p-ERK) in PLC/PRF/5 cells, thus leading to enhanced sorafenib sensitivity and a synergistic suppression on the tumor cells. Taken together, our results suggest that capsaicin-increased phosphorylation of ERK contributes to the enhanced antitumor activity of sorafenib, and capsaicin may be useful in improving the efficacy of sorafenib for the treatment of HCC.

The genusCapsicum: a phytochemical review of bioactive secondary metabolites

The Capsicum genus is one of the most popular plants consumed and cultivated worldwide, containing approximately 50 000 varieties of pepper. Due to its wide biodiversity, the chemical composition within the genus also presents a great variability. Its major applications are in food and pharmacological industry, as pepper presents a chemical composition rich in capsaicinoids, carotenoids, flavonoids and volatile compounds which is attributed to the ability of the fruit to remove insipidity, produce aromas and act against oxidative diseases. Due the existence of several cultivars there is a huge intraspecific chemical variability within each species, which can be considered as an obstacle when selecting and cultivating a species to be applied as a natural product source for a specific objective. The usage of pepper-based products in different industrial areas requires pre-established ranges of chemical compounds, such as capsaicinoids, which in high concentration are toxic when consumed by humans. Applying a pepper with a chemical profile closely related to the concentration that is required after industrial processing can improve efficacy and effectiveness of the process. An insight into the chemical characteristics of major secondary bioactive compounds within Capsicum, the factors that affect their concentration and their chemosystematic implication are reported and discussed.

The Capsicum genus is economically important due to its chemical profile which is rich in capsaicinoids, carotenoids and flavonoids. Its unique chemical composition allows this genus to be applied from food additives to medicinal application.

Research progress of capsaicin responses to various pharmacological challenges

Capsaicin, a well known vanilloid, has shown evidence of an ample variety of biological effects which make it the target of extensive research ever since its identification. In spite of the fact that capsaicin causes health hazards in quite a few ways, yet, the verity cannot be ignored that capsaicin has several therapeutic implications. In patients with hypersensitive bladders, vesical instillation of 1 mM capsaicin markedly improved urinary frequency and urge incontinence. Again, administration of capsaicin favors an augmentation in lipid mobilization and a decrease in adipose tissue mass. Topical capsaicin cream as well decreases postsurgical neuropathic pain and is preferred by patients over a placebo among other therapies. Several in vitro studies have revealed that capsaicin results in growth arrest in some transformed cell lines. Furthermore, capsaicin has been proven to be an undeniably exciting molecule and remains a valuable drug for alleviating pain and itch. It has been recognized that capsaicinoids are the most potential agonists of capsaicin receptor (TRPV1). However, vanilloids could exert the beneficial effects not only through the receptor-dependent pathway but also through the receptor-independent one. The involvement of serotonin, neuropeptide Substance P and somatostatin in the pharmacological actions of capsaicin has been expansively investigated. Better understanding of the established TRPV1 receptor mechanism as well as exploring other possible receptor mechanism may publicize other new clinical efficacies of capsaicin. Further, clinical studies are required in several of these conditions to establish the efficacy of capsaicin.

Impact of capsaicin, an active component of chili pepper, on pathogenic chlamydial growth (Chlamydia trachomatis and Chlamydia pneumoniae) in immortal human epithelial HeLa cells

Chlamydia trachomatis is the leading cause of sexually transmitted infections worldwide. Capsaicin, a component of chili pepper, which can stimulate actin remodeling via capsaicin receptor TRPV1 (transient receptor potential vanilloid 1) and anti-inflammatory effects via PPARγ (peroxisome proliferator-activated receptor-γ) and LXRα (liver X receptor α), is a potential candidate to control chlamydial growth in host cells. We examined whether capsaicin could inhibit C. trachomatis growth in immortal human epithelial HeLa cells. Inclusion forming unit and quantitative PCR assays showed that capsaicin significantly inhibited bacterial growth in cells in a dose-dependent manner, even in the presence of cycloheximide, a eukaryotic protein synthesis inhibitor. Confocal microscopic and transmission electron microscopic observations revealed an obvious decrease in bacterial numbers to inclusions bodies formed in the cells. Although capsaicin can stimulate the apoptosis of cells, no increase in cleaved PARP (poly (ADP-ribose) polymerase), an apoptotic indicator, was observed at a working concentration. All of the drugs tested (capsazepine, a TRPV1 antagonist; 5CPPSS-50, an LXRα inhibitor; and T0070907, a PPARγ inhibitor) had no effect on chlamydial inhibition in the presence of capsaicin. In addition, we also confirmed that capsaicin inhibited Chlamydia pneumoniae growth, indicating a phenomena not specific to C. trachomatis. Thus, we conclude that capsaicin can block chlamydial growth without the requirement of host cell protein synthesis, but by another, yet to be defined, mechanism.

Regulation of microRNA using promising dietary phytochemicals: Possible preventive and treatment option of malignant mesothelioma

Malignant mesothelioma (MM) is a very aggressive, lethal cancer, and its incidence is increasing worldwide. Development of multi-drug resistance, therapy related side-effects, and disease recurrence after therapy are the major problems for the successful treatment of MM. Emerging evidence indicates that dietary phytochemicals can exert anti-cancer activities by regulating microRNA expression. Until now, only one dietary phytochemical (ursolic acid) has been reported to have MM microRNA regulatory ability. A large number of dietary phytochemicals still remain to be tested. In this paper, we have introduced some dietary phytochemicals (curcumin, epigallocatechin gallate, quercetin, genistein, pterostilbene, resveratrol, capsaicin, ellagic acid, benzyl isothiocyanate, phenethyl isothiocyanate, sulforaphane, indole-3-carbinol, 3,3'-diindolylmethane, diallyl disulphide, betulinic acid, and oleanolic acid) which have shown microRNA regulatory activities in various cancers and could regulate MM microRNAs. In addition to microRNA regulatory activities, curcumin, epigallocatechin gallate, quercetin, genistein, resveratrol, phenethyl isothiocyanate, and sulforaphane have anti-mesothelioma potentials, and pterostilbene, capsaicin, ellagic acid, benzyl isothiocyanate, indole-3-carbinol, 3,3'-diindolylmethane, diallyl disulphide, betulinic acid, and oleanolic acid have potentials to inhibit cancer by regulating the expression of various genes which are also known to be aberrant in MM.

Development of 68Ga-SCN-DOTA-Capsaicin as an Imaging Agent Targeting Apoptosis and Cell Cycle Arrest in Breast Cancer

⁶⁸Ga-labeled capsaicin using a DOTA (1,4,7,10-tetraazocyclododecane-N,N',N″,N'″-tetraacetic acid) derivative [⁶⁸Ga-SCN-Benzyl(Bn)-DOTA-capsaicin] was studied for the diagnosis of breast cancers, such as MCF-7 and SK-BR-3. The standard compound, ⁶⁹Ga-SCN-Bn-DOTA-capsaicin, was also prepared and characterized by spectroscopic analysis. The binding affinity of ⁶⁸Ga-SCN-Bn-DOTA-capsaicin was evaluated by using breast cancer cell lines (MCF-7, SK-BR-3) and colon cancer cell (CT-26); the biodistribution was carried out by using MCF-7-bearing nude mice, after which the positron emission tomography (PET) images were obtained at different time intervals (15-120 minutes). ⁶⁸Ga-SCN-Bn-DOTA-capsaicin showed a cellular uptake of 0.93% Injected Dose (ID) after 30 minutes of incubation, whereas ⁶⁸Ga-SCN-Bn-DOTA showed a lower uptake of 0.25% ID. The tumor-to-blood ID/g% ratios increased and were found to be 0.49, 0.22, and 0.77 for 15, 30, and 60 minutes, respectively. The small-animal PET study showed that the uptake of ⁶⁸Ga-SCN-Bn-DOTA-capsaicin was higher in the tumor regions even at 30 minutes after injection. These results suggest that ⁶⁸Ga-SCN-Bn-DOTA-capsaicin is a potential targeting agent for PET imaging of MCF-7.

Alleviation of Microglial Activation Induced by p38 MAPK/MK2/PGE2 Axis by Capsaicin: Potential Involvement of other than TRPV1 Mechanism/s

Exaggerated inflammatory responses in microglia represent one of the major risk factors for various central nervous system’s (CNS) associated pathologies. Release of excessive inflammatory mediators such as prostaglandins and cytokines are the hallmark of hyper-activated microglia. Here we have investigated the hitherto unknown effects of capsaicin (cap) - a transient receptor potential vanilloid 1 (TRPV1) agonist- in murine primary microglia, organotypic hippocampal slice cultures (OHSCs) and human primary monocytes. Results demonstrate that cap (0.1–25 µM) significantly (p < 0.05) inhibited the release of prostaglandin E₂ (PGE₂)_, 8-iso-PGF_2α, and differentially regulated the levels of cytokines (TNF-α, IL-6 & IL-1β). Pharmacological blockade (via capsazepine & SB366791) and genetic deficiency of TRPV1 (TRPV1^−/−) did not prevent cap-mediated suppression of PGE₂ in activated microglia and OHSCs. Inhibition of PGE₂ was partially dependent on the reduced levels of PGE₂ synthesising enzymes, COX-2 and mPGES-1. To evaluate potential molecular targets, we discovered that cap significantly suppressed the activation of p38 MAPK and MAPKAPK2 (MK2). Altogether, we demonstrate that cap alleviates excessive inflammatory events by targeting the PGE₂ pathway in in vitro and ex vivo immune cell models. These findings have broad relevance in understanding and paving new avenues for ongoing TRPV1 based drug therapies in neuroinflammatory-associated diseases.

Capsaicin synergizes with camptothecin to induce increased apoptosis in human small cell lung cancers via the calpain pathway

Small cell lung cancer (SCLC) is characterized by excellent initial response to chemotherapy and radiation therapy with a majority of the patients showing tumor shrinkage and even remission. However, the challenge with SCLC therapy is that patients inevitably relapse and subsequently do not respond to the first line treatment. Recent clinical studies have investigated the possibility of camptothecin-based combination therapy as first line treatment for SCLC patients. Conventionally, camptothecin is used for recurrent SCLC and has poor survival outcomes. Therefore, drugs which can improve the therapeutic index of camptothecin should be valuable for SCLC therapy. Extensive evidence shows that nutritional compounds like capsaicin (the spicy compound of chili peppers) can improve the anti-cancer activity of chemotherapeutic drugs in both cell lines and animal models. Statistical analysis shows that capsaicin synergizes with camptothecin to enhance apoptosis of human SCLC cells. The synergistic activity of camptothecin and capsaicin is observed in both classical and variant SCLC cell lines and, in vivo, in human SCLC tumors xenotransplanted on chicken chorioallantoic membrane (CAM) models. The synergistic activity of capsaicin and camptothecin are mediated by elevation of intracellular calcium and the calpain pathway. Our data foster hope for novel nutrition based combination therapies in SCLC.

Extraction, bioavailability, and bioefficacy of capsaicinoids

Capsaicinoids are active constituents responsible for the pungent and spicy flavor in chili peppers. During the past few decades, various extraction methods of capsaicinoids from peppers have been developed with high yields. Through biological studies, pharmacological benefits have been reported such as pain relief, antiinflammation, anticancer, cardioprotection, as well as weight loss. In this paper, the extraction methods and bioavailability of capsaicinoids are reviewed and discussed. In addition, the pharmacological effects and their underlying mechanisms are also studied.

Medicinal Chemistry, Pharmacology, and Clinical Implications of TRPV1 Receptor Antagonists

Transient receptor potential vanilloid 1 (TRPV1) is an ion channel expressed on sensory neurons triggering an influx of cations. TRPV1 receptors function as homotetramers responsive to heat, proinflammatory substances, lipoxygenase products, resiniferatoxin, endocannabinoids, protons, and peptide toxins. Its phosphorylation increases sensitivity to both chemical and thermal stimuli, while desensitization involves a calcium-dependent mechanism resulting in receptor dephosphorylation. TRPV1 functions as a sensor of noxious stimuli and may represent a target to avoid pain and injury. TRPV1 activation has been associated to chronic inflammatory pain and peripheral neuropathy. Its expression is also detected in nonneuronal areas such as bladder, lungs, and cochlea where TRPV1 activation is responsible for pathology development of cystitis, asthma, and hearing loss. This review offers a comprehensive overview about TRPV1 receptor in the pathophysiology of chronic pain, epilepsy, cough, bladder disorders, diabetes, obesity, and hearing loss, highlighting how drug development targeting this channel could have a clinical therapeutic potential. Furthermore, it summarizes the advances of medicinal chemistry research leading to the identification of highly selective TRPV1 antagonists and their analysis of structure-activity relationships (SARs) focusing on new strategies to target this channel.

Dissolving microneedles for enhanced local delivery of capsaicin to rat skin tissue

Capsaicin-loaded dissolving microneedles (DMNs) were prepared to investigate the analgesic effect of capsaicin on the skin. The dimensions of each microneedle (MN) were as follows: diameter of the basement, 17 mm; length, 500 μm; and width, 300 μm. The average capsaicin content in the DMNs loaded with a low and high dose of capsaicin was 8.8 ± 0.5 mg and 12.5 ± 0.4 mg. Almost all the capsaicin, 99.3 ± 4.1% and 99.7 ± 2.2% for low-dose and high-dose DMNs were released within 20 min. High amounts of capsaicin were recovered with 102.8 ± 0.1% of capsaicin after storage at 23 °C for 90 days. The pharmacological activity of capsaicin DMNs was compared to that of capsaicin cream as a positive control, by measuring the idiospasm of depilated rat skin. The time required to achieve 50% idiospasm suppression was 26.3 ± 1.9 min and 53.0 ± 2.3 min for low-dose and high-dose DMNs. A pharmacokinetic study showed high tissue capsaicin levels of 660.2 ± 120.6 and 1805.3 ± 218.1 μg/g wet weight for low-dose and high-dose DMNs at 5 min after administration. The results suggest that DMNs could exert a rapid local analgesic action on the skin.

Decreased inflammatory response in rat bladder after intravesical administration of capsaicin-loaded liposomes

The objective of this work was to study the reduction in the capsaicin toxicity by encapsulation in liposomes. Capsaicin was extracted from peppers and characterized with high performance liquid chromatography (HPLC). We determined the zeta potential, polydispersivity index (PdI) and vesicle size of liposomes. Wistar rats were submitted to intravesical instillation of liposomes (LIP), capsaicin (CAP) or liposomes with capsaicin (CAPLIP). After 24 hours, bladders were removed for histological analysis. Vesicle size ranged from 68 to 105 nm with PdI smaller than 0.2 and zeta potential around -30 mV. The vesicles maintained stability over the 14-day study. The histological analysis of the CAP group showed intense inflammation in almost all bladder layers, as well as ulcer formation. Conversely, the CAPLIP group showed a smooth inflammatory reaction and hyperemia. In conclusion, the liposomes effectively protected the bladder against the irritative action of capsaicin.

TRPV1 and TRPM8 in Treatment of Chronic Cough

Chronic cough is common in the population, and among some there is no evident medical explanation for the symptoms. Such a refractory or idiopathic cough is now often regarded as a neuropathic disease due to dysfunctional airway ion channels, though the knowledge in this field is still limited. Persistent coughing and a cough reflex easily triggered by irritating stimuli, often in combination with perceived dyspnea, are characteristics of this disease. The patients have impaired quality of life and often reduced work capacity, followed by social and economic consequences. Despite the large number of individuals suffering from such a persisting cough, there is an unmet clinical need for effective cough medicines. The cough treatment available today often has little or no effect. Adverse effects mostly follow centrally acting cough drugs comprised of morphine and codeine, which demands the physician's awareness. The possibilities of modulating airway transient receptor potential (TRP) ion channels may indicate new ways to treat the persistent cough "without a reason". The TRP ion channel vanilloid 1 (TRPV1) and the TRP melastin 8 (TRPM8) appear as two candidates in the search for cough therapy, both as single targets and in reciprocal interaction.

Pre-Bötzinger complex: Generation and modulation of respiratory rhythm

INTRODUCTION

In mammals, the preBötzinger complex (preBötC) is a bilateral and symmetrical neural network located in the brainstem which is essential for the generation and modulation of respiratory rhythm. There are few human studies about the preBötC and, its relationship with neurological diseases has not been described. However, the importance of the preBötC in neural control of breathing and its potential participation in neurological diseases in humans, has been suggested based on pharmacological manipulation and lesion of the preBötC in animal models, both in vivo and in vitro.

METHOD

In this review, we describe the effects of some drugs on the inspiratory activity in vitro in a transverse slice that contains the preBötC, as well as some in vivo experiments. Drugs were classified according to their effects on the main neurotransmitter systems and their importance as stimulators or inhibitors of preBötC activity and therefore for the generation of the respiratory rhythm.

CONCLUSION

Clinical neurologists will find this information relevant to understanding how the central nervous system generates the respiratory rhythm and may also relate this information to the findings made in daily practice.

Development of Organogel-Derived Capsaicin Nanoemulsion with Improved Bioaccessibility and Reduced Gastric Mucosa Irritation

Capsaicin (CAP) is the major active component in chili peppers with health-promoting benefits. However, the low bioavailability and irritating quality of CAP greatly limit its applications in functional foods. The objective of this study was to develop a food-grade nanoemulsion to increase the dissolution and bioaccessibility of CAP and to alleviate its irritating effects. To achieve this goal, CAP was first dissolved in medium-chain triacylglycerol (MCT), followed by the addition of sucrose stearate S-370 as organogelator to develop CAP-loaded organogel. The oil-in-water (O/W) emulsion was formed using organogel as the oil phase and Tween 80 as the emulsifier. After ultrasonication treatment, droplet sizes of emulsion were decreased to 168 nm with enhanced dissolution rate and bioaccessibility. In vivo study further confirmed the reduced rat gastric mucosa irritation caused by CAP. The organogel-derived nanoemulsion was proved to be an effective delivery system for CAP-based functional food products.