Yusaku Iwasaki

A nonpungent component of steamed ginger--[10]-shogaol--increases adrenaline secretion via the activation of TRPV1.

Abstract We investigated the components of ginger that are involved in increasing body temperature. Gingerols ([6,8,10]-gingerols) and shogaols ([6,8,10]-shogaols) having different alkyl carbon chain lengths were targeted. All the gingerols and shogaols increased intracellular calcium concentration in rat transient receptor potential vanilloid subtype 1 (TRPV1)-expressing HEK293 cells via TRPV1. In this regard, the shogaols were more potent than the gingerols. Aversive responses were induced by [6]-, [10]-gingerol, and [6]-shogaol (5 mmol/l) in rats when these compounds were applied to the eye; however, no response was observed in response to [10]-shogaol (5 and 10 mmol/l). [10]-Shogaol induced nociceptive responses via TRPV1 in rats following its subcutaneous injection into the hindpaw; the pungent compound capsaicin (CAP) and [6]-shogaol were observed to have similar effects. Moreover, adrenal catecholamine secretion, which influences energy consumption, was promoted in rats in response to [6]- and [10]-gingerols and [6]- and [10]-shogaols (1.6 μmol/kg, i.v.). [10]-Shogaol-induced adrenaline secretion was inhibited by administration of capsazepine, a TRPV1 antagonist. In conclusion, gingerols and shogaols activated TRPV1 and increased adrenaline secretion. Interestingly, [10]-shogaol is the only nonpungent compound among the gingerols and shogaols, suggesting its usefulness as a functional ingredient in food.

Activation of TRPV1 and TRPA1 by Black Pepper Components

We searched in this study for novel agonists of transient receptor potential cation channel, subfamily V, member 1 (TRPV1) and transient receptor potential cation channel, subfamily A, member 1 (TRPA1) in pepper, focusing attention on 19 compounds contained in black pepper. Almost all the compounds in HEK cells heterogeneously expressed TRPV1 or TRPA1, increased the intracellular Ca2+ concentration ([Ca2+]i) in a concentration-dependent manner. Among these, piperine, isopiperine, isochavicine, piperanine, pipernonaline, dehydropipernonaline, retrofractamide C, piperolein A, and piperolein B relatively strongly activated TRPV1. The EC50 values of these compounds for TRPV1 were 0.6–128 μM. Piperine, isopiperine, isochavicine, piperanine, piperolein A, piperolein B, and N-isobutyl-(2E,4E)-tetradeca-2,4-diamide also relatively strongly activated TRPA1, the EC50 values of these compounds for TRPA1 were 7.8–148 μM. The Ca2+ responses of these compounds for TRPV1 and TRPA1 were significantly suppressed by co-applying each antagonist. We identified in this study new transient receptor potential (TRP) agonists present in black pepper and found that piperine, isopiperine, isochavicine, piperanine, piperolein A, and piperolein B activated both TRPV1 and TRPA1.

Pungent Qualities of Sanshool-Related Compounds Evaluated by a Sensory Test and Activation of Rat TRPV1

The detection threshold and taste characteristics of sanshools were examined by sensory evaluation, after isolating four sanshools (α-, β-, γ-, and δ-), and two hydroxy sanshools (α- and β-) from the pericarp of Japanese pepper. The Scoville unit (SU) values of the four sanshools were in the range of 80,000–110,000, while those of hydroxy sanshools were 3–5 fold lower than corresponding sanshools. The pungent qualities of each sanshool were different. Burning and tingling were predominantly perceived and lasted for the longest time with α-sanshool. Burning and fresh for γ-sanshool, and tingling and numbing for hydroxy α-sanshool were perceived. Tests on the activation of rat TRPV1 were also performed. All of them were weak agonists. Among them, γ-sanshool was the most potent agonist, although its EC50 value of 5.3 μM was 230 fold higher than that of capsaicin. These results indicate that it would be difficult to explain the pungent quality of each sanshool simply in terms of TRPV1 activation.

TRPA1 Agonists—Allyl Isothiocyanate and Cinnamaldehyde—Induce Adrenaline Secretion

Thermosensitive transient receptor potential (TRP) channels, especially TRPV1 and TRPA1, are activated by the pungent compounds present in spices. TRPV1 activation by the intake of capsaicin, the irritant in hot pepper, induces adrenaline secretion and increases energy consumption. TRPV1 is mainly expressed in the sensory neurons and coexpressed with TRPA1 at a high frequency. However, the mechanism underlying adrenaline secretion by TRPA1 agonists such as allyl isothiocyanate (AITC) and cinnamaldehyde (CNA), the pungent ingredients in mustard and cinnamon, is not known. We examined whether AITC and CNA could induce adrenaline secretion in anesthetized rats. An intravenous injection of AITC or CNA (10 mg/kg) increased adrenaline secretion. These responses disappeared completely in capsaicin-treated rats with an impaired sensory nerve function. Moreover, pretreatment with cholinergic blockers (hexamethonium and atropine) attenuated the AITC- or CNA-induced adrenaline secretion. These results suggest that TRPA1 agonists activate the sensory nerves and induce adrenaline secretion via the central nervous system.

Diallyl sulfides in garlic activate both TRPA1 and TRPV1

We searched for novel agonists of TRP receptors especially for TRPA1 and TRPV1 in foods. We focused attention on garlic compounds, diallyl sulfide (DAS), diallyl disulfide (DADS), and diallyl trisulfide (DATS). In TRPA1 or TRPV1 heterogeneously expressed CHO cells, all of those compounds increased [Ca(2+)](i) in concentration-dependent manner. The EC(50) values of DADS and DATS were similar to that of allyl isothiocyanate (AITC) and that of DAS was 170-fold larger than that of AITC. Maximum responses of these sulfides were equal to that of AITC. The EC(50) values of these compounds for TRPV1 were around 100 microM against that of capsaicin (CAP), 25.6 nM and maximum responses of garlic compounds were half to that of CAP. The Ca(2+) responses were significantly suppressed by co-application of antagonist. We conclude that DAS, DADS, and DATS are agonist of both TRPA1 and TRPV1 but with high affinity for TRPA1.

Assessment of the Biological Similarity of Three Capsaicin Analogs (Capsinoids) Found in Non-Pungent Chili Pepper (CH-19 Sweet) Fruits

CH-19 Sweet is a newly found chili pepper breed bearing much less pungent fruits. Because CH-19 Sweet fruits were found to contain three analogs (capsinoids) of capsaicin, a major component of pungency of hot peppers (the analogs are capsiate or CST, dihydrocapsiate or DCT, and nordihydrocapsiate or NDCT), we assessed in this study the bio-potencies of these three capsinoids by comparing them with capsaicin. The three capsinoids bound to transient potential vanilloid 1 (TRPV1) receptors expressed in cultured cells and activated Ca2+ influx in a concentration-dependent manner with similar magnitudes. In contrast to capsaicin, capsinoids at the same concentration induced virtually no nociceptive responses when applied to the eyes or the oral cavities of mice. Intravenous administration of capsaicin or 20-fold increased doses of each capsinoid to rats induced significant increases in plasma catecholamine levels. Orally administered, each capsinoid enhanced oxygen consumption in mice. Based on the present results, capsaicin and these three capsinoids should have similar bio-potency, though capsinoids do not generate pungency or sensory irritation.

Miogadial and miogatrial with α,β-unsaturated 1,4-dialdehyde moieties - novel and potent TRPA1 agonists.

AIMS Most of the terpenoids with an alpha,beta-unsaturated 1,4-dialdehyde moiety, which are found in plants, fungi, and insects, have a pungent taste. However, the neural receptors responsible for the pungency of these terpenoids have not been identified yet. The transient receptor potential ankyrin 1 (TRPA1) and transient receptor potential vanilloid 1 (TRPV1), which are expressed in the nociceptive neurons, induce a sensation of heat on activation by some pungent ingredients in food. In this study, we selected miogadial (MD), miogatrial (MT), and polygodial (PG) from the terpenoids with an alpha,beta-unsaturated 1,4-dialdehyde moiety and examined the effects of these 3 terpenoids on TRPA1 or TRPV1. MAIN METHODS TRPV1 and TRPA1 activity by 3 terpenoids were evaluated using Ca(2+) imaging and patch-clamp methods in mammalian cells that express TRP heterologously and mouse sensory neurons. KEY FINDINGS The 3 terpenoids activated TRPA1 that was heterologously expressed in HEK293 or CHO cells. The potencies of activation by the 3 terpenoids were equal and almost 10 times stronger than that of allyl isothiocyanate (AITC), which is known as the most potent TRPA1 agonist among all natural products. Moreover, these 3 terpenoids exhibited increased intracellular Ca(2+) concentration in mouse sensory neuron cells compared to AITC. High concentrations of the 3 terpenoids also activated TRPV1 that was heterologously expressed in HEK293 cells. SIGNIFICANCE These results indicated that MD, MT, and PG were more potent in activating TRPA1 than TRPV1, and suggested that they primarily activate TRPA1 to induce pungency.

TRPV1 Agonist Monoacylglycerol Increases UCP1 Content in Brown Adipose Tissue and Suppresses Accumulation of Visceral Fat in Mice Fed a High-Fat and High-Sucrose Diet

The administration of such a transient receptor potential vanilloid 1 (TRPV1) agonist as capsaicin, which is a pungent ingredient of red pepper, promotes energy metabolism and suppresses visceral fat accumulation. We have recently identified monoacylglycerols (MGs) having an unsaturated long-chain fatty acid as the novel TRPV1 agonist in foods. We investigated in this present study the effects of dietary MGs on uncoupling protein 1 (UCP1) expression in interscapular brown adipose tissue (IBAT) and on fat accumulation in mice fed with a high-fat, high-sucrose diet. The MG30 diet that substituted 30% of all lipids for MGs (a mixture of 1-oleoylglycerol, 1-linoleoylglycerol and 1-linolenoylglycerol) significantly increased the UCP1 content of IBAT and decreased the weight of epididymal white adipose tissue, and the serum glucose, total cholesterol and free fatty acid levels. The diet containing only 1-oleoylglycerol as MG also increased UCP1 expression in IBAT. MGs that activated TRPV1 also therefore induced the expression of UCP 1 and prevented visceral fat accumulation as well as capsaicin.

TRPA1 and TRPV1 activation is a novel adjuvant effect mechanism in contact hypersensitivity

We have revealed that local stimulation of sensory neurons is involved in the adjuvant effect of dibutyl phthalate (DBP) in a fluorescein isothiocyanate-induced mouse contact hypersensitivity model. Transient receptor potential (TRP) A1 and TRPV1 seemed to be candidate DBP targets. Here we directly demonstrated that DBP activates a subset of neurons in mouse dorsal root ganglia responsive to TRPA1 and TRPV1 agonists. TRPA1 and TRPV1 activation was further demonstrated using cultured cells expressing TRP channels. Among structurally different phthalate esters, there is a positive relationship between the activation of TRPA1- or TRPV1-expressing cells and the adjuvant effect.

Galangal Pungent Component, 1′-Acetoxychavicol Acetate, Activates TRPA1

We investigated the activation of transient receptor potential cation channel (TRP) subfamily V, member 1 (TRPV1) and TRP subfamily A, member 1 (TRPA1) by 1′-acetoxychavicol acetate (ACA), the main pungent component in galangal. ACA did not activate TRPV1-expressing human embryonic kidney (HEK) cells, but strongly activated TRPA1-expressing HEK cells. ACA was more potent than allyl isothiocyanate, the typical TRPA1 agonist.