Quantitative analysis of sanshool compounds in Japanese pepper (Xanthoxylum piperitum DC.) and their pungent characteristics

Degradation and transformation mechanisms of pungent substances in huajiao (Zanthoxylum bungeanum) oil during storage: Induced by ultraviolet irradiation

The pungency of huajiao (scientifically known as Zanthoxylum bungeanum) oil (ZBO), a crucial seasoning oil, is notably influenced by storage conditions, an aspect insufficiently explored in current research. Through the use of high-performance liquid chromatography and liquid chromatography-mass spectrometry, this study systematically investigated the stability of pungent compounds in ZBO under various storage conditions. It also elucidated the degradation and transformation mechanisms of these substances when exposed to ultraviolet (UV) irradiation. The results underscore elevated temperature, light exposure, oxygen, and storage duration as pivotal factors influencing compound degradation, with UV light emerging as the primary driving force. After 48 h of UV exposure, the primary pungent compound, hydroxy-α-sanshool, experienced a significant loss of 85.49%, indicating a pronounced inclination towards isomerization and oxidation. Notably, this study reveals, for the first time, the possible degradation-transformation pattern of hydroxy-γ-sanshool: a mutual conversion with hydroxy-γ-isosanshool and isomerization to (2E,4E,8Z,10E,12Z)-N-(2-hydroxy-2-methylpropyl) tetradeca-2,4,8,10,12-pentaenamide.

Rapid purification of alkylamides from Zanthoxylum bungeanum by medium-pressure liquid chromatography and the establishment of a numbness prediction model using an electronic tongue

In the present study, an efficient and rapid method for the preparation of high-purity typical alkylamides from Zanthoxylum bungeanum (Z. bungeanum) pericarps using medium-pressure liquid chromatography (MPLC) was developed. Under the optimized conditions using a mobile phase of methanol : water (70 : 30, v/v) at a flow rate of 25 mL min-1 and one run for 30 min, hydroxy-α-sanshool with a purity of 97.85% could be obtained. Sensory evaluation and electronic tongue analysis of the hydroxyl-α-sanshool were performed, and the aftertastes of bitterness and astringency were found to be more representative of the compounds in Chinese prickly ash that causes numbness, which has not been reported in the literature before. An electronic tongue prediction model for the evaluation of numbing intensity was established: Y = 20.452X1 - 7.594X2 - 2.876, R2 = 0.973, where Y is a sensory evaluation value based on the 15 cm linear scale method and X1 and X2 are the aftertastes from astringency and bitterness, respectively. The evaluation model can be used for the evaluation of the numbing intensity of amides of Zanthoxylum bungeanum.

Mechanistic elucidation of the degradation and transformation of hydroxy-α-sanshool and its conformers as the pungent dietary components in Sichuan pepper: A DFT study

To better understand the structural changes of sanshool pungent dietary components during the process and preservation of Sichuan pepper and pungent foods, the mechanistic insights into the intrinsic degradation and transformation of 16 hydroxy-α-sanshool conformers have been explored computationally. Our results have revealed that increasing the cis-CC bond numbers in the most stable all-trans hydroxy-β-sanshool structure causes the maximum 34.21 kJ/mol conformational energetic difference, and the existent probability of C2nnn would be lower than that of C1nnn (n = 1,2). The isomerization between the conformers could be much easier when they are excited by light radiation, as the strength of the CC bonds and their connected CC bonds becomes significantly close, and the relative energies among conformers are largely reduced. Besides, the different combination of cis/trans-CC bonds changes the delocalization degree of molecular Frontier orbitals, which consequently causes the different photochemical stability. Finally, the possible molecular oxidation degradation mechanism is proposed.

Stability of Hydroxy-α-Sanshool in Medium-Chain Triglyceride Oil and Corresponding Oil/Water Emulsions

The pungent component of sansho (Japanese pepper, Zanthoxylum pipritum) is sanshool, which is easily oxidized and decomposed. We have previously reported several sanshool stabilizers, such as α-tocopherol (α-Toc). Sansho pericarp powder treated with middle-chain triglycerides (MCTs) can be used to obtain extracts containing hydroxy-α-sanshool (HαS). Although HαS is stabilized when α-Toc is added to the MCT extracts, the loss of HαS is accelerated when it is mixed with a powder such as lactose. The separation of α-Toc from sanshools was thought to inevitably lead to their oxidation. Therefore, using sansho pericarp MCT extracts with or without α-Toc, oil/water (o/w) emulsions were prepared by adding a surfactant, glycerin, and water to these extracts. In both emulsions, HαS was stable in accelerated tests at 50 °C. However, when lactose powder was added to the emulsions and an accelerated test was performed, HαS in the emulsion containing α-Toc was stable, but HαS in the emulsion without α-Toc was unstable. These results highlight the importance of maintaining the close proximity of HαS and α-Toc in the emulsion. The stabilization of sanshools using emulsion technology can facilitate the production of various processed beverages, foods, cosmetics, and pharmaceuticals containing Japanese pepper.

Stabilization of Hydroxy-α-Sanshool by Antioxidants Present in the Genus Zanthoxylum

Japanese pepper (sansho, Zanthoxylum piperitum) contains several types of sanshools belonging to N-alkylamides. Because of the long-chain unsaturated fatty acids present in their structure, sanshools are prone to oxidative deterioration, which poses problems in processing. In this paper, we evaluated the effects of antioxidants from the genus Zanthoxylum in preventing sanshool degradation using accelerated tests. An ethanolic extract of segment membranes of the sansho fruit pericarp was incubated at 70 °C for 7 days with different antioxidants to determine the residual amount of hydroxy-α-sanshool (HαS) in the extract. α-Tocopherol (α-Toc) showed excellent HαS-stabilizing activity at low concentrations. Among phenolic acids, we noted that the HαS-stabilizing activity increased with the number of hydroxy groups per molecule. For example, gallic acid and its derivatives exhibited excellent sanshool-stabilizing activity. Quercetin was found to be a superior HαS stabilizer compared with hesperetin and naringenin. However, the effective concentration was much higher for phenolic compounds than for α-Toc. These substances are believed to play a role in preventing the decomposition of sanshools in the pericarp of sansho. These sanshool stabilizers should be useful in the development of new beverages, foods, cosmetics, and pharmaceuticals that take advantage of the taste and flavor of sansho.

Separation and Purification of Hydroxyl-α-Sanshool from Zanthoxylum armatum DC. by Silica Gel Column Chromatography

Hydroxyl-α-sanshool is the main alkylamide produced by Zanthoxylum armatum DC., and it is responsible for numbness after consuming Z. armatum-flavored dishes or food products. The present study deals with the isolation, enrichment, and purification of hydroxyl-α-sanshool. The results indicated that the powder of Z. armatum was extracted with 70% ethanol and then filtrated; the supernatant was concentrated to get pasty residue. Petroleum ether (60-90 °C) and ethyl acetate at a 3:2 ratio, with an Rf value of 0.23, were chosen as the eluent. Petroleum ether extract (PEE) and ethyl acetate-petroleum ether extract (E-PEE) were used as the suitable enriched method. Afterward, the PEE and E-PEE were loaded onto silica gel for silica gel column chromatography. Preliminary identification was carried out by TLC and UV. The fractions containing mainly hydroxyl-α-sanshool were pooled and dried by rotary evaporation. Lastly, all of the samples were determined by HPLC. The yield and recovery rates of hydroxyl-α-sanshool in the p-E-PEE were 12.42% and 121.65%, respectively, and the purity was 98.34%. Additionally, compared with E-PEE, the purity of hydroxyl-α-sanshool in the purification of E-PEE (p-E-PEE) increased by 88.30%. In summary, this study provides a simple, rapid, economical, and effective approach to the separation of high-purity hydroxyl-α-sanshool.

Classification of Japanese Pepper (Zanthoxylum piperitum DC.) from Different Growing Regions Based on Analysis of Volatile Compounds and Sensory Evaluation

The Japanese pepper (Zanthoxylum piperitum DC.) is an attractive plant that is highly palatable and benefits human health. There are several lineages of pepper plants in Japan. However, the classification of each lineage by analyzing its volatile compounds and studies on the effects of differences in volatile compounds on human flavor perception have not been performed in detail. Herein, we conducted gas chromatography (GC) and GC/mass spectrometry (GC/MS) analysis of volatile compounds and sensory evaluation of flavor by an analytical panel using 10 commercially available dry powdered Japanese pepper products from different regions. GC and GC/MS analysis detected limonene, β-phellandrene, citronellal, and geranyl acetate as the major volatile compounds of Japanese peppers. The composition of volatile compounds showed different characteristics depending on the growing regions, and cluster analysis of composition classified the products into five groups. The sensory evaluation classified the products into four groups, and the results of both classifications were in good agreement. Our results provide an important basis for proposing cooking and utilization methods that take advantage of the unique characteristics of each lineage based on scientific evidence.

Analisis Senyawa Aktif Trigeminal Andaliman dengan Variasi Metode Pengeringan dengan Pendekatan GC-MS

Sanshool compounds are the trigeminal active compounds in andaliman (Zanthoxylum acantho-podium DC) with a numbing and tingling sensation. The analysis of such compounds is usually done through HPLC approach; however, limited studies have reported that the analysis of such compounds could be conducted with Gas Chromatography-Mass Spectrometry (GC-MS). This method could save research time and funding by analyzing both sanshools and volatiles simultaneously, which would describe the complete profile of andaliman flavor compounds. This study aimed to confirm the potency of GC-MS in analyzing sanshool compounds and to utilize this method in studying the impact of different drying methods towards andaliman trigeminal active compounds. Andaliman was dried with five drying methods (sun, sunshade, air, oven, and freeze-drying) and was macerated with chloroform, concentrated, and analyzed with GC-MS. The results of this study showed that GC-MS was able to analyze sanshool compounds efficiently. Drying had no statistically significant impact on sanshool quantities extracted from andaliman. Fresh andaliman contained 0.69 % (dry weight basis) of α-sanshool, the main sanshool in andaliman. On the other hand, dried andaliman contained 0.80-1.08% of α-sanshool (dry weight basis). As oven drying managed to produce andaliman with a similar concentration of α-sanshool at a faster time and more affordable cost than other drying methods, oven drying was suggested as the ideal drying method to extend the shelf life of andaliman.

Composition, structure and flavor mechanism of numbing substances in Chinese prickly ash in the genus Zanthoxylum: A review

Chinese prickly ash is known for producing a typical pungent sensation in Sichuan Cuisine. Accumulating evidence suggest a series of health benefits and pharmacological effects associated with prickly ash. Therefore, a systematic analysis of the composition, structural properties, detection, and flavor mechanism of numbing substances is highly necessitated to address their future application. Sanshool-based unsaturated amides are the primary cause of tingling. The numbing substances have poor stability and are prone to oxidation and decomposition reactions due to their highly unsaturated conjugated diene structures. Pungent sensations evoked by different sanshools are distinct, which is attributed to different mechanisms of interaction with membrane ion channels (TRPV1, TRPA1, and KCNK). In this paper, the composition, structural properties (such as isomerization, oxidation), detection, and flavor mechanism of numbing substances of prickly ash were summarized. The prospective application and future research direction of numbing substances in the prickly ash industry were also proposed.

Zanthoxylum-specific whole genome duplication and recent activity of transposable elements in the highly repetitive paleotetraploid Z. bungeanum genome

Zanthoxylum bungeanum is an important spice and medicinal plant that is unique for its accumulation of abundant secondary metabolites, which create a characteristic aroma and tingling sensation in the mouth. Owing to the high proportion of repetitive sequences, high heterozygosity, and increased chromosome number of Z. bungeanum, the assembly of its chromosomal pseudomolecules is extremely challenging. Here, we present a genome sequence for Z. bungeanum, with a dramatically expanded size of 4.23 Gb, assembled into 68 chromosomes. This genome is approximately tenfold larger than that of its close relative Citrus sinensis. After the divergence of Zanthoxylum and Citrus, the lineage-specific whole-genome duplication event η-WGD approximately 26.8 million years ago (MYA) and the recent transposable element (TE) burst ~6.41 MYA account for the substantial genome expansion in Z. bungeanum. The independent Zanthoxylum-specific WGD event was followed by numerous fusion/fission events that shaped the genomic architecture. Integrative genomic and transcriptomic analyses suggested that prominent species-specific gene family expansions and changes in gene expression have shaped the biosynthesis of sanshools, terpenoids, and anthocyanins, which contribute to the special flavor and appearance of Z. bungeanum. In summary, the reference genome provides a valuable model for studying the impact of WGDs with recent TE activity on gene gain and loss and genome reconstruction and provides resources to accelerate Zanthoxylum improvement.

Changes in volatiles and aroma profile of andaliman (Zanthoxylum acanthopodium DC.) upon various drying techniques

Andaliman is a highly perishable Indonesian spice that could be preserved by drying. As the drying influence on andaliman volatiles and aroma profile has not been reported, this study aimed to determine the impact of five drying processes on them and the critical volatiles correlated with favorable aroma attributes. Limonene, geranial, α-pinene, sabinene, β-myrcene, (E)-2-hexenal tended to decrease while geranyl acetate, citronellal, neral tended to increase upon drying. Limonene, andaliman major volatiles, was lost considerably from 28093 µg/g solids (fresh) to 19299-21857 µg/g solids (dried). Drying significantly altered citrus, orange peel, green, warm, and lime leaf aroma. Citronellal, limonene, (Z)-β-ocimene, (E)-β-ocimene, β-citronellol, sabinene, and geranial, played substantial roles in andaliman sensory acceptability due to significant correlation to the favorable aroma attributes (citrus, orange peel, acidic). Oven drying was proposed as the ideal drying method because of its short duration, low water activity, superior overall liking, and high volatile content.

Two Japanese pepper (Zanthoxylum piperitum) fruit-derived compounds attenuate IgE-mediated allergic response in vitro and in vivo via inhibition of mast cell degranulation

Zanthoxylum piperitum (ZP, 'Japanese pepper') is a traditional medicine and pepper used in Asian countries such as Japan. Hydroxy-α-sanshool, a pungent-tasting substance contained within ZP, has been reported to slightly suppress immunoglobulin E (IgE)-mediated mast cell degranulation. The current study aims to newly identify anti-allergic compounds derived from ZP. We examine the inhibitory mechanisms behind IgE-mediated mast cell degranulation. By inhibitory effect-guided isolation, we identified degranulation inhibitory compounds derived from ZP fruit: 1-acetoxy-7-hydroxy-3, 7-dimethylocta-2E, 5E-diene (ZP1) and 8-hydroxygeranyl acetate (ZP2). ZP1 and ZP2 inhibited IgE-mediated degranulation and A23187-mediated degranulation in RBL-2H3 mast cells. Our findings suggest the inhibition of degranulation by ZP1 and ZP2 was by inhibition of Lyn phosphorylation, followed by inhibition of intracellular Ca²⁺ mobilization, protein kinase C alpha phosphorylation, membrane ruffling, and granule-to-plasma membrane fusion. Oral administration of ZP1 or ZP2 attenuated an IgE-mediated passive cutaneous anaphylactic reaction in mice. Histological observation suggests that this effect occurred via inhibition of mast cell degranulation. These findings indicate that ZP1 and ZP2 attenuate allergic reaction via inhibition of IgE-mediated mast cell degranulation.

The relationship between alkylamide compound content and pungency intensity of Zanthoxylum bungeanum based on sensory evaluation and ultra-performance liquid chromatography-mass spectrometry/ mass spectrometry (UPLC-MS/MS) analysis

BACKGROUND

Zanthoxylum bungeanum originating in different places varies in alkylamide content and pungency intensity.

RESULTS

The pungency intensity of 19 Zanthoxylum bungeanum samples was first determined with Scoville pungency units (SPUs). The SPUs were found to range from 3.80E + 04 to 5.40E + 05. The chemical compositions and contents were measured next, using the ultra-performance liquid chromatography-mass spectrometry/ mass spectrometry (UPLC-MS/MS) method. The total alkylamide content ranged from 9.83 ± 0.15 to 89.98 ± 1.35 g kg^-1 . Hydroxy-ϵ-sanshool, hydroxy-α-sanshool, hydroxy-β-sanshool, hydroxy-γ-sanshool, bungeanool, and isobungeanool were found to be the key pungent compounds, ranging in proportion from 92.65% to 97.69%. The relationship between alkymide compound content and pungency intensity was also analyzed by ridge regression, and it was found that the β values of independent variables were stable when k was more than 0.6. The regression coefficients of hydroxy-ϵ-sanshool, hydroxy-α-sanshool, hydroxy-β-sanshool, hydroxy-γ-sanshool, bungeanool, isobungeanool, and other alkylamides were 0.105, 0.177, 0.386, -0.166, -0.006, 0.005, and -0.018, respectively.

CONCLUSION

Hydroxy- sanshool compounds were important in determinant the pungency intensity of Z. bungeanum. Knowledge of the relationship between alkymide compound content and pungency intensity will assist in the creation of new methods to determine pungency intensity and provide a scientific basis for flavor design, development of pungent food products, and consumer choice evaluations. © 2018 Society of Chemical Industry.

Spilanthol Enhances Sensitivity to Sodium in Mouse Taste Bud Cells

Overconsumption of NaCl has been linked to increased hypertension-related morbidity. Compounds that can enhance NaCl responses in taste cells could help reduce human NaCl consumption without sacrificing perceived saltiness. Spilanthol is an unsaturated alkylamide isolated from the Jambu plant (Acmella oleracea) that can induce tingling, pungency, and numbing in the mouth. Structurally similar fatty acid amides, such as sanshool, elicit numbing and tingling sensations by inhibiting 2-pore-domain potassium leak channels on trigeminal sensory neurons. Even when insufficient to induce action potential firing, leak current inhibition causes depolarization and increased membrane resistance, which combine to make cells more sensitive to subsequent depolarizing stimuli, such as NaCl. Using calcium imaging, we tested whether spilanthol alters sensitivity to NaCl in isolated circumvallate taste bud cells and trigeminal sensory neurons of mice (Mus musculus). Micromolar spilanthol elicited little to no response in taste bud cells or trigeminal neurons. These same perithreshold concentrations of spilanthol significantly enhanced responses to NaCl (140 and 200 mM) in taste bud cells. Trigeminal neurons, however, exhibited response enhancement only at the highest concentrations of NaCl and spilanthol tested. Using a combination of potassium depolarization, immunohistochemistry, and Trpm5-GFP and Tas1r3-GFP mice to characterize taste bud cells by type, we found spilanthol enhancement of NaCl responses most prevalent in NaCl-responsive type III cells, and commonly observed in NaCl-responsive type II cells. Our results indicate that spilanthol enhances NaCl responses in taste bud cells and point to a family of compounds that may have utility as salty taste enhancers.

Sanshool on The Fingertip Interferes with Vibration Detection in a Rapidly-Adapting (RA) Tactile Channel

An Asian spice, Szechuan pepper (sanshool), is well known for the tingling sensation it induces on the mouth and on the lips. Electrophysiological studies have revealed that its active ingredient can induce firing of mechanoreceptor fibres that typically respond to mechanical vibration. Moreover, a human behavioral study has reported that the perceived frequency of sanshool-induced tingling matches with the preferred frequency range of the tactile rapidly adapting (RA) channel, suggesting the contribution of sanshool-induced RA channel firing to its unique perceptual experience. However, since the RA channel may not be the only channel activated by sanshool, there could be a possibility that the sanshool tingling percept may be caused in whole or in part by other sensory channels. Here, by using a perceptual interference paradigm, we show that the sanshool-induced RA input indeed contributes to the human tactile processing. The absolute detection thresholds for vibrotactile input were measured with and without sanshool application on the fingertip. Sanshool significantly impaired detection of vibrations at 30 Hz (RA channel dominant frequency), but did not impair detection of higher frequency vibrations at 240 Hz (Pacinian-corpuscle (PC) channel dominant frequency) or lower frequency vibrations at 1 Hz (slowly adapting 1 (SA1) channel dominant frequency). These results show that the sanshool induces a peripheral RA channel activation that is relevant for tactile perception. This anomalous activation of RA channels may contribute to the unique tingling experience of sanshool.

Hypoglycemic effects of Zanthoxylum alkylamides by enhancing glucose metabolism and ameliorating pancreatic dysfunction in streptozotocin-induced diabetic rats

Alkylamides extracted from Zanthoxylum, a seasoning spice and folk medicine, exhibited hypoglycemic properties by enhancing glucose metabolism and ameliorating pancreatic dysfunction.

Antiviral effect of flavonol glycosides isolated from the leaf of Zanthoxylum piperitum on influenza virus

The ethanol extract of Zanthoxylum piperitum (L.) DC. showed in vitro antiviral activity against influenza A virus. Three flavonol glycosides were isolated from the EtOAc fraction of Z. piperitum leaf by means of activity-guided chromatographic separation. Structures of isolated compounds were identified as quercetin 3-O-β-D-galactopyranoside (1), quercetin 3-O-α-L-rhamnopyranoside (2), kaempferol 3-O-α-L-rhamnopyranoside (3) by comparing their spectral data with literature values. The anti-influenza viral activity of isolates was evaluated using a plaque reduction assay against influenza A/NWS/33 (H1N1) virus. The compounds also were subjected to neuraminidase inhibition assay in influenza A/NWS/33 virus. Compounds 1-3 exhibited antiviral activity against an influenza A virus in vitro, and inhibited the neuraminidase activity at relatively high concentrations.

TRP modulation by natural compounds

The use of medicinal plants or other naturally derived products to relieve illness can be traced back over several millennia, and these natural products are still extensively used nowadays. Studies on natural products have, over the years, enormously contributed to the development of therapeutic drugs used in modern medicine. By means of the use of these substances as selective agonists, antagonists, enzyme inhibitors or activators, it has been possible to understand the complex function of many relevant targets. For instance, in an attempt to understand how pepper species evoke hot and painful actions, the pungent and active constituent capsaicin (from Capsicum sp.) was isolated in 1846 and the receptor for the biological actions of capsaicin was cloned in 1997, which is now known as TRPV1 (transient receptor potential vanilloid 1). Thus, TRPV1 agonists and antagonists have currently been tested in order to find new drug classes to treat different disorders. Indeed, the transient receptor potential (TRP) proteins are targets for several natural compounds, and antagonists of TRPs have been synthesised based on the knowledge of naturally derived products. In this context, this chapter focuses on naturally derived compounds (from plants and animals) that are reported to be able to modulate TRP channels. To clarify and make the understanding of the modulatory effects of natural compounds on TRPs easier, this chapter is divided into groups according to TRP subfamilies: TRPV (TRP vanilloid), TRPA (TRP ankyrin), TRPM (TRP melastatin), TRPC (TRP canonical) and TRPP (TRP polycystin). A general overview on the naturally derived compounds that modulate TRPs is depicted in Table 1.

Food vibrations: Asian spice sets lips trembling

Szechuan pepper, a widely used ingredient in the cuisine of many Asian countries, is known for the tingling sensation it induces on the tongue and lips. While the molecular mechanism by which Szechuan pepper activates tactile afferent fibres has been clarified, the tingling sensation itself has been less studied, and it remains unclear which fibres are responsible. We investigated the somatosensory perception of tingling in humans to identify the characteristic temporal frequency and compare this to the established selectivity of tactile afferents. Szechuan pepper was applied to the lower lip of participants. Participants judged the frequency of the tingling sensation on the lips by comparing this with the frequencies of mechanical vibrations applied to their right index finger. The perceived frequency of the tingling was consistently at around 50 Hz, corresponding to the range of tactile RA1 afferent fibres. Furthermore, adaptation of the RA1 channel by prolonged mechanical vibration reliably reduced the tingling frequency induced by Szechuan pepper, confirming that the frequency-specific tactile channel is shared between Szechuan pepper and mechanical vibration. Combining information about molecular reactions at peripheral receptors with quantitative psychophysical measurement may provide a unique method for characterizing unusual experiences by decomposing them into identifiable minimal units of sensation.

A 'toothache tree' alkylamide inhibits Aδ mechanonociceptors to alleviate mechanical pain

In traditional medicine, the 'toothache tree' and other plants of the Zanthoxylum genus have been used to treat inflammatory pain conditions, such as toothache and rheumatoid arthritis. Here we examined the cellular and molecular mechanisms underlying the analgesic properties of hydroxy-α-sanshool, the active alkylamide produced by Zanthoxylum plants. Consistent with its analgesic effects in humans, sanshool treatment in mice caused a selective attenuation of mechanical sensitivity under naïve and inflammatory conditions, with no effect on thermal sensitivity. To elucidate the molecular mechanisms by which sanshool attenuates mechanical pain, we performed single fibre recordings, calcium imaging and whole-cell electrophysiology of cultured sensory neurons. We found that: (1) sanshool potently inhibits Aδ mechanonociceptors that mediate both sharp acute pain and inflammatory pain; (2) sanshool inhibits action potential firing by blocking voltage-gated sodium currents in a subset of somatosensory neurons, which express a unique combination of voltage-gated sodium channels; and (3) heterologously expressed Nav1.7 is most strongly inhibited by sanshool as compared to other sodium channels expressed in sensory neurons. These results suggest that sanshool targets voltage-gated sodium channels on Aδ mechanosensory nociceptors to dampen excitability and thus induce 'fast pain' analgesia.

Physiological basis of tingling paresthesia evoked by hydroxy-alpha-sanshool

Hydroxy-alpha-sanshool, the active ingredient in plants of the prickly ash plant family, induces robust tingling paresthesia by activating a subset of somatosensory neurons. However, the subtypes and physiological function of sanshool-sensitive neurons remain unknown. Here we use the ex vivo skin-nerve preparation to examine the pattern and intensity with which the sensory terminals of cutaneous neurons respond to hydroxy-alpha-sanshool. We found that sanshool excites virtually all D-hair afferents, a distinct subset of ultrasensitive light-touch receptors in the skin and targets novel populations of Abeta and C fiber nerve afferents. Thus, sanshool provides a novel pharmacological tool for discriminating functional subtypes of cutaneous mechanoreceptors. The identification of sanshool-sensitive fibers represents an essential first step in identifying the cellular and molecular mechanisms underlying tingling paresthesia that accompanies peripheral neuropathy and injury.

Compounds from Sichuan and Melegueta peppers activate, covalently and non-covalently, TRPA1 and TRPV1 channels

BACKGROUND AND PURPOSE

Oily extracts of Sichuan and Melegueta peppers evoke pungent sensations mediated by different alkylamides [mainly hydroxy-alpha-sanshool (alpha-SOH)] and hydroxyarylalkanones (6-shogaol and 6-paradol). We assessed how transient receptor potential ankyrin 1 (TRPA1) and TRP vanilloid 1 (TRPV1), two chemosensory ion channels, participate in these pungent sensations.

EXPERIMENTAL APPROACH

The structure-activity relationships of these molecules on TRPA1 and TRPV1 was measured by testing natural and synthetic analogues using calcium and voltage imaging on dissociated dorsal root ganglia neurons and human embryonic kidney 293 cells expressing the wild-type channels or specific cysteine mutants using glutathione trapping as a model to probe TRPA1 activation. In addition, using Trpv1 knockout mice, the compounds' aversive responses were measured in a taste brief-access test.

KEY RESULTS

For TRPA1 activation, the cis C6 double bond in the polyenic chain of alpha-SOH was critical, whereas no structural specificity was required for activation of TRPV1. Both 6-shogaol and 6-paradol were found to activate TRPV1 and TRPA1 channels, whereas linalool, an abundant terpene in Sichuan pepper, activated TRPA1 but not TRPV1 channels. Alkylamides and 6-shogaol act on TRPA1 by covalent bonding whereas none of these compounds activated TRPV1 through such interactions. Finally, TRPV1 mutant mice retained sensitivity to 6-shogaol but were not responsive to alpha-SOH.

CONCLUSIONS AND IMPLICATIONS

The pungent nature of components of Sichuan and Melegueta peppers was mediated via interactions with TRPA1 and TRPV1 channels and may explain the aversive properties of these compounds.

Activation of lumbar spinal wide-dynamic range neurons by a sanshool derivative

The enigmatic sensation of tingle involves the activation of primary sensory neurons by hydroxy-alpha-sanshool, a tingly agent in Szechuan peppers, by inhibiting two-pore potassium channels. Central mechanisms mediating tingle sensation are unknown. We investigated whether a stable derivative of sanshool-isobutylalkenyl amide (IBA)-excites wide-dynamic range (WDR) spinal neurons that participate in transmission of chemesthetic information from the skin. In anesthetized rats, the majority of WDR and low-threshold units responded to intradermal injection of IBA in a dose-related manner over a >5-min time course and exhibited tachyphylaxis at higher concentrations (1 and 10%). Almost all WDR and low-threshold units additionally responded to the pungent agents mustard oil (allyl isothiocyanate) and/or capsaicin, prompting reclassification of the low-threshold cells as WDR. The results are discussed in terms of the functional role of WDR neurons in mediating tingle sensation.

Influence of composition upon the variety of tastes in Cinnamomi cortex

Cinnamomi cortex, which is normally referred to as cinnamon, is a very popular spice as well as an important natural medicine. High-quality cinnamon is traditionally believed to taste sweet and be strongly pungent without astringency. Cinnamomi cortex with larger amounts of cinnamaldehyde was sweeter in taste comparisons. The contents of tannins and sugars in cinnamon powder had little effect on the taste. Evaluations of the sweetness and pungency of cinnamaldehyde solutions (0.1, 0.25, 0.50, 0.75, 1.0, and 5.0 mg/ml) were performed using volunteers. The scores for sweetness increased significantly from 0.10 to 0.50 mg/ml (P < 0.05, Mann-Whitney U-test), but there was no significant difference above 0.75 mg/ml. The concentration threshold for the sweet taste of cinnamaldehyde appeared to be less than 0.75 mg/ml, and the more concentrated solutions gave excessive pungency. Therefore, two contrastive tastes of Cinnamomi cortex, sweet and pungent, were both attributed to cinnamaldehyde. Consequently, its taste, one of its indices of quality, seems to vary mainly according to the content of cinnamaldehyde.

Pungent agents from Szechuan peppers excite sensory neurons by inhibiting two-pore potassium channels

In traditional folk medicine, Xanthoxylum plants are referred to as 'toothache trees' because their anesthetic or counter-irritant properties render them useful in the treatment of pain. Psychophysical studies have identified hydroxy-alpha-sanshool as the compound most responsible for the unique tingling and buzzing sensations produced by Szechuan peppercorns or other Xanthoxylum preparations. Although it is generally agreed that sanshool elicits its effects by activating somatosensory neurons, the underlying cellular and molecular mechanisms remain a matter of debate. Here we show that hydroxy-alpha-sanshool excites two types of sensory neurons, including small-diameter unmyelinated cells that respond to capsaicin (but not mustard oil) as well as large-diameter myelinated neurons that express the neurotrophin receptor TrkC. We found that hydroxy-alpha-sanshool excites neurons through a unique mechanism involving inhibition of pH- and anesthetic-sensitive two-pore potassium channels (KCNK3, KCNK9 and KCNK18), providing a framework for understanding the unique and complex psychophysical sensations associated with the Szechuan pepper experience.

New polyunsaturated fatty acid amides isolated from the seeds of Zanthoxylum piperitum

Five linear fatty acid amides (1-5) of the sandshool class, including two new compounds, were isolated from Zanthoxylum piperitum seeds. Based on combined spectral analyses, the structures of new compounds 4 and 5 were determined to be 2',3'-dihydroxy-alpha-sanshool and 2',3'-dihydroxy-beta-sanshool, respectively. These compounds exhibited weak cytotoxicity in the A-549 (human lung cancer) cell line.