The involvement of TRPA1 channel activation in the inflammatory response evoked by topical application of cinnamaldehyde to mice

Discovery of non-electrophilic TRPA1 channel agonists with anti-nociceptive effects via rapid current desensitization

Desensitizing transient receptor potential ankyrin 1 (TRPA1) cation channel through agonists emerges as an effective strategy for developing analgesics. Many TRPA1 agonists are electrophilic irritants, including BITC and iodoacetamide (IA), which covalently bind to cysteine residues in the cytoplasmic region of the channel. The electrophile JT010 is also recognized as a potent TRPA1 agonist via covalent modification of Cys621, whose irritant effects have been confirmed in humans, highlighting a commonly undesirable property of these electrophilic agonists. Cryo-electron microscopy (cryo-EM) structures have shown that these electrophiles induce a strong driving force for conformational change through electrophilic modification of TRPA1. However, the stable activated conformation induced by electrophiles might delay subsequent desensitization, leading to prolonged TRPA1-mediated nociception responses in vivo. Therefore, developing non-electrophilic TRPA1 agonists may mitigate the irritation associated with electrophilic agonists by accelerating the desensitizing process. To test this hypothesis, we designed and synthesized a series of novel TRPA1 agonists by removing the electrophilic functional group of JT010. Among these synthetic compounds, whole-cell patch clamp recording assays identified compound 21 as a selective TRPA1 agonist with an EC50 of 25.47 ± 1.56 μM for hTRPA1, exhibiting faster desensitization (τ = 20.02 ± 1.66 s) of mTRPA1 compared to electrophiles JT010 (41.71 ± 4.10 s) and BITC (68.05 ± 5.57 s). Importantly, compound 21 demonstrated effective analgesic properties without irritation in mice. Our findings support the hypothesis that facilitating rapid desensitization of TRPA1 by non-electrophilic channel agonists enhances anti-nociceptive effects. Compound 21 may serve as a promising lead for further optimization.

Investigation of the participation of the TRPV1 receptor in the irritant effect of dithranol in mice

Dithranol is one of the most effective topical medications for treating plaque psoriasis. However, its clinical use is limited by irritative adverse reactions to the skin, such as oedema, erythema, and pruritus, caused by poorly understood mechanisms. Because TRPV1 activation mediates skin irritation caused by several drugs, we conducted blind and randomised experiments in male and female C57BL/6 mice to elucidate the role of TRPV1 in dithranol-induced irritation. Dithranol (0.01%-0.5%) or vehicle was applied topically to the right ear of the animals. Oedema, erythema, and pruritus were monitored from 2 h to 6 days after application. Treatment with 0.5% dithranol caused oedema and erythema, but not pruritus, starting at 6 h, reaching its highest point at 1 day, and persisting up to 6 days after treatment, mainly in male mice. The 0.1% dose induced erythema but not oedema. Interestingly, topical application of 1% capsaicin was shown to defunctionalise TRPV1-positive fibres and did not influence early irritation caused by dithranol (2 h-2 days). However, it increased the late phase of irritation (5-6 days). Similarly, salicylate did not reduce the early irritation caused by dithranol but also increased the late phase. Antagonism by SB366791 and 4-tert-butylcyclohexanol did not alter skin irritation. Our results suggest that, contrary to our initial hypothesis, TRPV1 appears to act protectively against skin irritation caused by dithranol, particularly in the late stage.

Role of TRPA1 in the pharmacological effect triggered by the topical application of trans-anethole in mice

PURPOSE

This study investigated the pharmacological effects of topical trans-anethole, a natural compound found in anise, star anise, and fennel essential oils, and its relationship with the transient receptor potential of ankyrin 1 (TRPA1).

METHODS

The effects of topical anethole were assessed by eye wiping, nociceptive behaviour, and ear oedema in mice. Histological evaluations were performed on the ears of the animals topically treated with anethole.

RESULTS

Anethole caused less eye irritation than capsaicin (a TRPV1 agonist) and allyl isothiocyanate (a TRPA1 agonist). Anethole (250 and 500 nmol/20 µL/paw) promoted neurogenic nociception in the paw (20.89 ± 3.53 s and 47.56 ± 8.46 s, respectively) compared with the vehicle (0.88 ± 0.38 s). HC030031 (56.1 nmol/20 µL/paw), a TRPA1 antagonist, abolished this nociceptive response. Anethole (4, 10, and 20 µmol/20 µL/ear) induced ear oedema (30.25 ± 4.78 μm, 78.00 ± 3.74 μm, and 127.50 ± 27.19 μm, respectively) compared with the vehicle (5.00 ± 0.5 μm). HC030031 (56.1 nmol/20 µL/ear) inhibited the oedema induced by anethole (10 µmol/20 µL/ear). Ears pre-treated with anethole or allyl isothiocyanate on the first day and re-exposed to these compounds on the third day showed a reduction in oedema (68.16 ± 6.04% and 38.81 ± 8.98.9%, respectively). Cross-desensitisation between anethole and allyl isothiocyanate was observed. Histological analysis confirmed the beneficial effects of anethol.

CONCLUSION

As repeated topical applications of anethole induce the desensitisation of TRPA1, we suggest its clinical application as a topical formulation for treating skin diseases or managing pain associated with this receptor. Anethole may also have advantages over capsaicin and allyl isothiocyanate because of its low pungency and pleasant aroma.

Critical Pronociceptive Role of Family 2 Voltage-Gated Calcium Channels in a Novel Mouse Model of HIV-Associated Sensory Neuropathy

Some people living with HIV present painful sensory neuropathy (HIV-SN) that is pharmacoresistant, sex-associated, and a major source of morbidity. Since the specific mechanisms underlying HIV-SN are not well understood, the aim of our study was to characterize a novel model of painful HIV-SN by combining the HIV-1 gp120 protein and the antiretroviral stavudine (d4T) in mice and to investigate the pronociceptive role of the family 2 voltage-gated calcium channel (VGCC) α1 subunit (Cav2.X channels) in such a model. HIV-SN was induced in male and female C57BL/6 mice by administration of gp120 and/or d4T and detected by a battery of behavior tests and by immunohistochemistry. The role of Cav2.X channels was assessed by the treatment with selective blockers and agonists as well as by mRNA detection. Repeated administration with gp120 and/or d4T produced long-lasting touch-evoked painful-like behaviors (starting at 6 days, reaching a maximum on day 13, and lasting up to 28 days after treatment started), with a greater intensity in female mice treated with the combination of gp120 + d4T. Moreover, gp120 + d4T treatment reduced the intraepidermal nerve fibers and well-being of female mice, without altering other behaviors. Mechanistically, gp120 + d4T treatment induced Cav2.1, 2.2, and 2.3 transcriptional increases in the dorsal root ganglion and the Cav2.X agonist-induced nociception. Accordingly, intrathecal selective Cav2.2 blockade presented longer and better efficacy in reversing the hyperalgesia induced by gp120 + d4T treatment compared with Cav2.1 or Cav2.3, but also presented the worst safety (inducing side effects at effective doses). We conclude that the family 2 calcium channels (Cav2.X) exert a critical pronociceptive role in a novel mouse model of HIV-SN.

Cinnamaldehyde modulates host immunoinflammatory responses in rat ligature-induced periodontitis and peripheral blood mononuclear cell models

Cinnamaldehyde is a natural product with anti-inflammatory and immune-modulatory properties, known to regulate host responses to bacterial stimuli. This study aimed to investigate the effects of cinnamaldehyde on ligature-induced periodontitis in rats, and its impact on the modulation of human peripheral blood mononuclear cells (PBMC). Male Wistar rats were assigned into three groups:i) control: no ligature + vehicle; ii) ligature: ligature + vehicle; and iii) ligature + cinnamaldehyde (50 mg/kg); all treatments by daily oral gavage. After 14 days of induced periodontitis, the hemimandibles were collected for bone loss evaluation. The gingival levels of IL-1β, MMP-9 and iNOS mRNA were evaluated. Nitric oxide (NO) was measured in both rat saliva and plasma. PBMC were stimulated with Aggregatibacter actinomycetemcomitans (Aa) in the presence or absence of cinnamaldehyde (5, 20 e 40 µM), and cytokine production was quantified in cell supernatant. Proliferating lymphocytes were taken for flow cytometer reading, while culture supernatants were used for IFN-γ and IL-10 assessment. The ligature group had both increased alveolar bone loss and gingival expression of IL-1β, MMP-9 and iNOS compared to the control group. All parameters were attenuated by cinnamaldehyde treatment. Lower salivary but not plasma NO was detected in the cinnamaldehyde compared to the ligature group. Aa-stimulated PBMCs treated with cinnamaldehyde produced less IL-1β; the compound also attenuated lymphocyte proliferation in a dose-dependent manner, as well as cell IL-10 production. Cinnamaldehyde treatment reduced periodontal bone loss, and downregulated key inflammatory mediators and human PBMC responses, pointing to novel potential therapeutic effects of this compound.

Inflammation-the role of TRPA1 channel

Recently, increasing numbers of studies have demonstrated that transient receptor potential ankyrin 1 (TRPA1) can be used as a potential target for the treatment of inflammatory diseases. TRPA1 is expressed in both neuronal and non-neuronal cells and is involved in diverse physiological activities, such as stabilizing of cell membrane potential, maintaining cellular humoral balance, and regulating intercellular signal transduction. TRPA1 is a multi-modal cell membrane receptor that can sense different stimuli, and generate action potential signals after activation via osmotic pressure, temperature, and inflammatory factors. In this study, we introduced the latest research progress on TRPA1 in inflammatory diseases from three different aspects. First, the inflammatory factors released after inflammation interacts with TRPA1 to promote inflammatory response; second, TRPA1 regulates the function of immune cells such as macrophages and T cells, In addition, it has anti-inflammatory and antioxidant effects in some inflammatory diseases. Third, we have summarized the application of antagonists and agonists targeting TRPA1 in the treatment of some inflammatory diseases.

Are TRPA1 and TRPV1 channel-mediated signalling cascades involved in UVB radiation-induced sunburn?

Burn injuries are underappreciated injuries associated with substantial morbidity and mortality. Overexposure to ultraviolet (UV) radiation has dramatic clinical effects in humans and is a significant public health concern. Although the mechanisms underlying UVB exposure are not fully understood, many studies have made substantial progress in the pathophysiology of sunburn in terms of its molecular aspects in the last few years. It is well established that the transient receptor potential ankyrin 1 (TRPA1), and vanilloid 1 (TRPV1) channels modulate the inflammatory, oxidative, and proliferative processes underlying UVB radiation exposure. However, it is still unknown which mechanisms underlying TRPV1/A1 channel activation are elicited in sunburn induced by UVB radiation. Therefore, in this review, we give an overview of the TRPV1/A1 channel-mediated signalling cascades that may be involved in the pathophysiology of sunburn induced by UVB radiation. These data will undoubtedly help to explain the various features of sunburn and contribute to the development of novel therapeutic approaches to better treat it.

Common and discrete mechanisms underlying chronic pain and itch: peripheral and central sensitization

Normally, an obvious antagonism exists between pain and itch. In normal conditions, painful stimuli suppress itch sensation, whereas pain killers often generate itch. Although pain and itch are mediated by separate pathways under normal conditions, most chemicals are not highly specific to one sensation in chronic pathologic conditions. Notably, in patients with neuropathic pain, histamine primarily induces pain rather than itch, while in patients with atopic dermatitis, bradykinin triggers itch rather than pain. Accordingly, repetitive scratching even enhances itch sensation in chronic itch conditions. Physicians often prescribe pain relievers to patients with chronic itch, suggesting common mechanisms underlying chronic pain and itch, especially peripheral and central sensitization. Rather than separating itch and pain, studies should investigate chronic itch and pain including neuropathic and inflammatory conditions. Here, we reviewed chronic sensitization leading to chronic pain and itch at both peripheral and central levels. Studies investigating the connection between pain and itch facilitate the development of new therapeutics against both chronic dysesthesias based on the underlying pathophysiology.

Oleic acid exhibits an expressive anti-inflammatory effect in croton oil-induced irritant contact dermatitis without the occurrence of toxicological effects in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Cutaneous inflammatory diseases, such as irritant contact dermatitis, are usually treated with topical corticosteroids, which cause systemic and local adverse effects limiting their use. Thus, the discovery of new therapeutic alternatives able to effectively treat skin inflammatory disorders, without causing adverse effects, is urgently needed.

AIM OF THE STUDY

To investigate the topical anti-inflammatory effect of oleic acid (OA), a monounsaturated fatty acid, into Pemulen® TR2-based semisolid dosage forms, employing a croton oil-induced irritant contact dermatitis model in mice.

MATERIALS AND METHODS

Male Swiss mice were submitted to skin inflammation protocols by acute and repeated applications of croton oil. The anti-inflammatory activity of Pemulen® TR2 hydrogels containing OA was evaluated by assessing oedema, inflammatory cell infiltration, and pro-inflammatory cytokine IL-1β levels. The mechanisms of action of OA were evaluated using cytokine IL-1β application or pretreatment with the glucocorticoid antagonist mifepristone. Possible toxic effects of OA were also assessed.

RESULTS

Pemulen® TR2 3% OA inhibited the acute ear oedema [maximal inhibition (I_max) = 76.41 ± 5.69%], similarly to dexamethasone (I_max = 84.94 ± 2.16%), and also inhibited ear oedema after repeated croton oil application with I_max = 85.75 ± 3.08%, similar to dexamethasone (I_max = 81.03 ± 4.66%) on the day 7 of the experiment. Croton oil increased myeloperoxidase activity, which was inhibited by Pemulen® TR2 3% OA (I_max = 71.37 ± 10.97%) and by 0.5% dexamethasone (I_max = 96.31 ± 3.73%). Pemulen® TR2 3% OA also prevented the increase in pro-inflammatory cytokine IL-1β levels induced by croton oil (I_max = 94.18 ± 12.03%), similar to 0.5% dexamethasone (I_max = 87.21 ± 10.58%). Besides, both Pemulen® TR2 3% OA and 0.5% dexamethasone inhibited IL-1β-induced ear oedema with an I_max of 80.58 ± 2.45% and 77.46 ± 1.92%, respectively. OA and dexamethasone anti-inflammatory effects were prevented by 100% and 91.43 ± 5.43%, respectively, after pretreatment with mifepristone. No adverse effects were related to Pemulen® TR2 3% OA administration.

CONCLUSIONS

OA demonstrated anti-inflammatory efficacy similar to dexamethasone, clinically used to treat skin inflammatory conditions, without presenting adverse effects.

Involvement of Neural Transient Receptor Potential Channels in Peripheral Inflammation

Transient receptor potential (TRP) channels are a superfamily of non-selective cation channels that act as polymodal sensors in many tissues throughout mammalian organisms. In the context of ion channels, they are unique for their broad diversity of activation mechanisms and their cation selectivity. TRP channels are involved in a diverse range of physiological processes including chemical sensing, nociception, and mediating cytokine release. They also play an important role in the regulation of inflammation through sensory function and the release of neuropeptides. In this review, we discuss the functional contribution of a subset of TRP channels (TRPV1, TRPV4, TRPM3, TRPM8, and TRPA1) that are involved in the body’s immune responses, particularly in relation to inflammation. We focus on these five TRP channels because, in addition to being expressed in many somatic cell types, these channels are also expressed on peripheral ganglia and nerves that innervate visceral organs and tissues throughout the body. Activation of these neural TRP channels enables crosstalk between neurons, immune cells, and epithelial cells to regulate a wide range of inflammatory actions. TRP channels act either through direct effects on cation levels or through indirect modulation of intracellular pathways to trigger pro- or anti-inflammatory mechanisms, depending on the inflammatory disease context. The expression of TRP channels on both neural and immune cells has made them an attractive drug target in diseases involving inflammation. Future work in this domain will likely yield important new pathways and therapies for the treatment of a broad range of disorders including colitis, dermatitis, sepsis, asthma, and pain.

Neuronal and non-neuronal transient receptor potential ankyrin 1 mediates UVB radiation-induced skin inflammation in mice

AIMS

Neuronal and non-neuronal TRPA1 channel plays an active role in the pathogenesis of several skin inflammatory diseases. Although a recent study identified the TRPA1 channel activation upon UVB exposure, its role in inflammatory, oxidative, and proliferative processes underlying UVB radiation-induced sunburn was not yet fully understood. We evaluated the TRPA1 channel contribution in inflammatory, oxidative, and proliferative states on skin inflammation induced by UVB radiation in mice.

MAIN METHODS

TRPA1 role was evaluated from inflammatory (ear edema, myeloperoxidase, and N-acetyl-β-D-glycosaminidase activities, histological changes, and cytokines levels), proliferative (epidermal hyperplasia, PCNA, and TRPA1 levels), and oxidative (reactive oxygen intermediates measure, H₂O₂ quantification, and NADPH oxidase activity) parameters caused by UVB radiation single (0.5 J/cm²) or repeated (0.1 J/cm²) exposure. We verified the contribution of non-neuronal and neuronal TRPA1 on UVB radiation-induced inflammatory parameters using RTX-denervation (50 μg/kg s.c.).

KEY FINDINGS

TRPA1 blockade by the selective antagonist Lanette® N HC-030031 reduced all parameters induced by UVB radiation single (at concentration of 1%) or repeated (at concentration of 0.1%) exposure. We evidenced an up-regulation of the TRPA1 protein after UVB radiation repeated exposure, which was blocked by topical Lanette® N HC-030031 (0.1%). By RTX-denervation, we verified that non-neuronal TRPA1 also interferes in some inflammatory parameters induction. However, cutaneous nerve fibers seem to be most needed in the development of UVB radiation-induced inflammatory processes.

SIGNIFICANCE

We propose the TRPA1 channel participates in the UVB radiation-induced sunburn in mice, and it could be a promising therapeutic target to treat skin inflammatory disorders.

Mammalian Transient Receptor Potential TRPA1 Channels: From Structure to Disease

The transient receptor potential ankyrin (TRPA) channels are Ca²⁺-permeable nonselective cation channels remarkably conserved through the animal kingdom. Mammals have only one member, TRPA1, which is widely expressed in sensory neurons and in non-neuronal cells (such as epithelial cells and hair cells). TRPA1 owes its name to the presence of 14 ankyrin repeats located in the NH₂ terminus of the channel, an unusual structural feature that may be relevant to its interactions with intracellular components. TRPA1 is primarily involved in the detection of an extremely wide variety of exogenous stimuli that may produce cellular damage. This includes a plethora of electrophilic compounds that interact with nucleophilic amino acid residues in the channel and many other chemically unrelated compounds whose only common feature seems to be their ability to partition in the plasma membrane. TRPA1 has been reported to be activated by cold, heat, and mechanical stimuli, and its function is modulated by multiple factors, including Ca²⁺, trace metals, pH, and reactive oxygen, nitrogen, and carbonyl species. TRPA1 is involved in acute and chronic pain as well as inflammation, plays key roles in the pathophysiology of nearly all organ systems, and is an attractive target for the treatment of related diseases. Here we review the current knowledge about the mammalian TRPA1 channel, linking its unique structure, widely tuned sensory properties, and complex regulation to its roles in multiple pathophysiological conditions.

Role of TRPA1 receptors in skin inflammation induced by volatile chemical irritants in mice

Contact dermatitis is a very common inflammatory reaction in the skin, causing not only aesthetic problems but also loss functionality at work. The molecular mechanisms of contact dermatitis induced by chemical irritants are still unclear. Considering that transient receptor potential channels (TRP) may induce neurogenic inflammation and the exacerbation of inflammatory responses, here we investigated the role of transient receptor potential channel ankyrin type-1 (TRPA1) in skin inflammation evoked by chemical irritants. Ear oedema and nociceptive responses elicited by the topical application of xylene and toluene were measured in Swiss mice, wild type and TRPA1 knockout (Trpa1^-/-) C57BL/6 mice. Histological analyses were performed in mice subjected to the ear oedema assay. Topical application of xylene and toluene in the mouse ear induced an edematogenic response (0.113 ± 0.008 mm and 0.067 ± 0.011 mm), compared to vehicle (0.008 ± 0.008 mm), assessed by ear thickness measurements and histological analyses. These responses were prevented by topical pretreatment with a selective TRPA1 antagonist, HC-030031 (% inhibition: xylene 36.8 ± 9.4% and toluene 50.7 ± 11.0%), and by the genetic deletion of TRPA1 ((% inhibition: xylene 66.6 ± 16.7% and toluene 75 ± 0%). In addition, the topical application of xylene and toluene to the mouse paw elicited nociceptive responses, which were significantly reduced by oral treatment with HC-030031 ((% of inhibition: 84.9 ± 1.3% and 27.1 ± 8.0%, respectively); nociceptive responses were almost completely abolished in Trpa1^-/-mice. Our data suggest that the activation of TRPA1 could be involved in some of the symptoms of irritant-mediated contact dermatitis, such as oedema, pain and neurogenic inflammation.

Tabernaemontana catharinensis leaves exhibit topical anti-inflammatory activity without causing toxicity

BACKGROUND

Tabernaemontana catharinensis, popularly known as snake skin, has been empirically used as an anti-inflammatory to treat cutaneous skin disorders. However, no study proves its effectiveness as a topical anti-inflammatory.

STUDY DESIGN

We investigated the topical anti-inflammatory effect of T.catharinensis leaves crude extract (TcE) in irritant contact dermatitis models in mice and its preliminary toxicity profile.

METHODS

The topical anti-inflammatory effect was evaluated by ear thickness measurement, inflammatory cell infiltration (MPO activity measurement and histological procedure) and cytokines levels. TcE qualitative phytochemical analysis was performed by UHPLC-ESI-HRMS and the TcE effect (therapeutic dose; 10 µg/ear) on preliminary toxicological parameters was also evaluated (on the 14° day of experiment).

RESULTS

TcE (10 μg/ear) prevented the development of ear edema induced by cinnamaldehyde, capsaicin, arachidonic acid, phenol, and croton oil with maximum inhibition of 100% to cinnamaldehyde, arachidonic acid, phenol, and croton oil and 75 ± 6% to capsaicin. Besides, the TcE (10 μg/ear) also prevented the increase of MPO activity by 96 ± 2%, 48 ± 7%, 100%, 87 ± 8%, and 93 ± 4%, respectively, to the same irritant agents. The positive controls also prevented both ear edema and the increased of MPO activity by 100% and 42 ± 8% (HC-030031), 54 ± 6% and 80 ± 4% (SB-366791), 100% and 54 ± 5% (indomethacin), 100% and 80 ± 4% (dexamethasone in skin inflammation model induced by phenol) and 100% and 97 ± 3% (dexamethasone in inflammation model induced by croton oil), respectively. TcE also prevented the inflammatory cells infiltration and the increase of MIP-2, IL-1β and TNF-α levels irritant agents-induced. TcE topical anti-inflammatory effect may be attributed to the combined effect of indole alkaloids, terpenes, and phenolic compounds found in the extract and identified by dereplication method. The TcE' therapeutic dose proved to be safe in preliminary toxicological tests.

CONCLUSION

Our results suggest that TcE could be an interesting strategy for the treatment of inflammatory diseases.

Buddleja thyrsoides Lam. crude extract presents antinociceptive effect on an arthritic pain model in mice

Arthritis is a chronic inflammatory disease which reduces the life quality of affected individuals. Therapeutic tools used for treating inflammatory pain are associated with several undesirable effects. Buddleja thyrsoides Lam., known as ‘Barbasco’ or ‘Cambara’, is mostly used in several disorders and possesses antirheumatic, anti-inflammatory, and analgesic properties. Here, we investigated the antinociceptive and anti-inflammatory effects of the B. thyrsoides crude extract applied orally and topically in acute pain models and an arthritic pain model induced by complete Freund's adjuvant (CFA) paw injection in male mice (25–30 g). The high-performance liquid chromatography (HPLC) of the B. thyrsoides extract crude revealed the presence of the lupeol, stigmasterol, and β-sitosterol. The stability study of the B. thyrsoides gel did not show relevant changes at low temperatures. The oral treatment with the B. thrysoides extract prevented the capsaicin-induced spontaneous nociception and the acetic acid-induced abdominal writhing, but did not alter the thermal threshold in the tail immersion test. The B. thyrsoides antinociceptive effect was not reversed by naloxone in the capsaicin test. The B. thyrsoides oral or topical treatment reversed the CFA-induced mechanical allodynia and thermal hyperalgesia with maximum inhibition (Imax) of 69 ± 6 and 68 ± 5% as well as 78 ± 15 and 87 ± 12%, respectively. Moreover, the topical but not oral treatment inhibited the CFA-induced cell infiltration, but did not reduce the paw edema significantly. The oral treatment with B. thyrsoides did not cause adverse effects. These findings suggest that the oral or topical treatment with B. thyrsoides presents antinociceptive actions in an arthritic pain model without causing adverse effects.

Solanum paranense Extracts and Solanine Present Anti-Inflammatory Activity in an Acute Skin Inflammation Model in Mice

The aim of the study was to evaluate the anti-inflammatory activity of the S. paranense crude extract, S. paranense alkaloid fraction, and solanine alkaloid. These samples reduce the croton oil-induced ear edema in a dose-dependent manner and a maximum inhibition of 81%, 98%, and 80% in the doses of 1.0, 0.73, and 0.37 mg/ear, respectively. Moreover, the samples inhibit the MPO activity with an inhibition maximum of 51%, 40%, and 46% in the doses of 1.0, 0.73, and 0.37 mg/ear, respectively. Similar results were found for dexamethasone 0.10 mg/ear (positive control), which showed inhibitions of ear edema and MPO activity of 100% and 65%, respectively. These results found probably are related to the presence of solanine which is present in significant quantity in the alkaloid fraction and others as rutin and rosmarinic, chlorogenic, and gallic acids. These results support the use of S. paranense for the treatment of inflammatory skin disorders.

TRPV1 and TRPA1 in cutaneous neurogenic and chronic inflammation: pro-inflammatory response induced by their activation and their sensitization

Cutaneous neurogenic inflammation (CNI) is inflammation that is induced (or enhanced) in the skin by the release of neuropeptides from sensory nerve endings. Clinical manifestations are mainly sensory and vascular disorders such as pruritus and erythema. Transient receptor potential vanilloid 1 and ankyrin 1 (TRPV1 and TRPA1, respectively) are non-selective cation channels known to specifically participate in pain and CNI. Both TRPV1 and TRPA1 are co-expressed in a large subset of sensory nerves, where they integrate numerous noxious stimuli. It is now clear that the expression of both channels also extends far beyond the sensory nerves in the skin, occuring also in keratinocytes, mast cells, dendritic cells, and endothelial cells. In these non-neuronal cells, TRPV1 and TRPA1 also act as nociceptive sensors and potentiate the inflammatory process. This review discusses the role of TRPV1 and TRPA1 in the modulation of inflammatory genes that leads to or maintains CNI in sensory neurons and non-neuronal skin cells. In addition, this review provides a summary of current research on the intracellular sensitization pathways of both TRP channels by other endogenous inflammatory mediators that promote the self-maintenance of CNI.

Topical antiedematogenic and anti-inflammatory effect of Scutia buxifolia Reissek gel and stability study

Scutia buxifolia Reissek (Rhamnaceae), popularly known in Brazil as "coronilha", is a plant species used in folk medicine for several disorders, including inflammation. However, no studies have been done with this species to confirm its topical anti-inflammatory action. In this study we evaluate the topical antiedematogenic and anti-inflammatory effects of the gel containing crude extract (CE) and the gel containing ethyl acetate (EtOAc) fraction of S. buxifolia on croton oil or UVB radiation-induced ear edema in mice, and perform gel stability study. Antiedematogenic and anti-inflammatory effects were evaluated through ear edema induced by irritant agent croton oil, UVB irradiation-induced skin injury model and neutrophil infiltration. The gel stability study was performed by analyzing organoleptical aspects, pH, viscosity, and quantification of quercetin and rutin by HPLC. The topical treatment with S. buxifolia gel reduced the ear edema and myeloperoxidase activity. Antiedematogenic and anti-inflammatory effects of S. buxifolia were obtained with concentrations of 0.3, 1 and 3%, with maximal inhibition in the concentration of 1% for gel containing CE (inhibitions of 100, 73±0.05 and 97±0.08% for croton oil- or UVB irradiation-induced ear edema and myeloperoxidase activity, respectively) and EtOAc fraction (inhibitions of 79±0.05, 73±0.05 and 89±0.04% for croton oil- or UVB irradiation-induced ear edema and myeloperoxidase activity, respectively). Such effects may be attributed, at least in part, to rutin and quercetin, as well as other compounds found in this species. No important changes were detected in the stability study, in all aspects analyzed in temperature below 25°C. Our results demonstrate that topically applied S. buxifolia gel presented anti-inflammatory effects, provided that it was maintained at a temperature below 25°C.

Ethnopharmacological study and topical anti-inflammatory activity of crude extract from Poikilacanthus glandulosus (Nees) Ariza leaves

ETHNOPHARMACOLOGICAL RELEVANCE

Ethnopharmacological studies are important tools as records and documentation of the empirical uses of medicinal plants in traditional communities with the purpose of generating useful knowledge to lead to the development of new medicines, biodiversity conservation and enhancement of knowledge and local culture. Poikilacanthus glandulosus is widely used by the population of City of Santiago, in Brazil, nevertheless, it does not have any validation regarding its use and its medicinal effects.

AIM

The objective of this study was to perform one ethnopharmacological survey about P. glandulosus in the City of Santiago and determine the anti-inflammatory activity in order to prove its uses in popular medicine.

METHODS

Personal and ethnopharmacological data were collected through a prepared questionnaire. The phytochemical analysis was performed observing the individual methodology for each reaction and by HPLC-UV. The antiedematogenic and anti-inflammatory (cell infiltration and histological procedure) activities of the P. glandulosus (0.01-1000μg/ear) were evaluated in the ear edema model induced by topical application of croton oil.

RESULTS

P. glandulosus is known in City of Santiago as "Gaiana" and its macerated leaves and branches are prepared with alcohol or sugarcane liquor especially for insect bites, cicatrization and inflammation. HPLC analysis revealed the presence of maslinic acid (2.024±0.10mg/g), uvaol (0.124±0.02mg/g) and sitosterol (0.502±0.05mg/g). The topical application of crude extract of P. glandulosus reduced in a dose-dependent manner the croton oil-induced ear edema and myeloperoxidase activity (neutrophils infiltration marker) with maximum inhibition of 87±2% and 64±12%, respectively at 1000µg/ear. Dexamethasone (100µg/ear), used as a positive control, inhibited croton oil-induced ear edema in 89±3% and decreased myeloperoxidase activity in 50±3%. Both P. glandulosus as dexamethasone reduced cell infiltration when evaluated by histological procedure CONCLUSION: This work allowed us to understand the specie P. glandulosus through ethnopharmacological study and it showed that the crude extract presented antiedematogenic and anti-inflammatory actions, proving their traditional use as anti-inflammatory.

Development of an in vivo target-engagement biomarker for TRPA1 antagonists in humans

AIM

To develop a non-invasive, safe and reproducible target-engagement biomarker for future TRPA1 antagonists in healthy volunteers.

METHODS

Dose finding (n = 11): 3%, 10%, and 30% cinnamaldehyde (CA) and placebo (= vehicle) was topically applied on the right forearm. One-way ANOVA with post-hoc Bonferroni was used to compare between doses. Reproducibility: 10% CA doses were topically applied during one visit on both arms (n = 10) or during two visits (n = 23) separated by a washout period of 7 days. CA-induced dermal blood flow (DBF) was assessed by laser Doppler imaging (LDI) at baseline and at 10, 20, 30, 40 and 50 min post-CA. Paired t-test was used to compare between arms or visits. Concordance correlation coefficient (CCC) was calculated to assess reproducibility. Data are expressed as percent change from baseline (mean ± 95% CI).

RESULTS

All three doses increased DBF compared to vehicle at all time-points, with the maximum response at 10-20 min post-CA. Dose response was found when comparing AUC_0-50min of 30% CA (51 364 ± 8475%*min) with 10% CA (32 239 ± 8034%*min, P = 0.03) and 3% CA (30 226 ± 11 958%*min, P = 0.015). 10% CA was chosen as an effective and safe dose. DBF response to 10% CA was found to be reproducible between arms (AUC_0-50min , CCC = 0.91) and visits (AUC_0-50min , CCC = 0.83). Based on sample size calculations, this model allows a change in CA-induced DBF of 30-50% to be detected between two independent groups of maximum 10-15 subjects with 80% power.

CONCLUSIONS

Evaluation of CA-induced changes in DBF offers a safe, non-invasive and reproducible target-engagement biomarker in vivo in humans to evaluate TRPA1 antagonists.

High-Concentration L-Menthol Exhibits Counter-Irritancy to Neurogenic Inflammation, Thermal and Mechanical Hyperalgesia Caused by Trans-cinnamaldehyde

The transient receptor potential cation channel subfamily M 8 (TRPM8) agonist L-menthol has been used traditionally for its topical counterirritant properties. Although the use of topical L-menthol for pain is casuistically established, evidence regarding its efficacy is negligible. This study aimed to characterize the effect of L-menthol as a counterirritant on cutaneous pain and hyperalgesia provoked by topical application of the transient receptor potential cation channel, subfamily A, member 1 (TRPA1) agonist trans-cinnamaldehyde (CA). In a randomized, double-blinded study CA was applied to a 3 × 3-cm area of the volar forearm evoking neurogenic inflammation, pain, mechanical, and thermal hyperalgesia in 14 healthy volunteers. In different sessions, 10% CA alone or 40% L-menthol applied simultaneously with 10% CA were administered for 20 minutes, throughout which the subjects rated the pain intensity on a visual analogue scale of 0 to 10. Extensive quantitative sensory testing was conducted and superficial blood flow (neurogenic inflammation) was recorded. Administration of CA evoked spontaneous pain, neurogenic inflammation, thermal hyperalgesia, and primary and secondary mechanical hyperalgesia. Coadministration of topical L-menthol reduced spontaneous pain intensity (P < .01), neurogenic inflammation (P < .01), primary mechanical hyperalgesia (P < .05), secondary mechanical hyperalgesia (P < .05), and heat hyperalgesia (P < .05), but not cold hyperalgesia. L-menthol exhibited inhibitory effects on simultaneously established pain, hypersensitivity, and neurogenic inflammation in a human TRPA1-induced pain model. Potent TRPM8 agonists could be useful as topical antihyperalgesics. The study and the trial protocol is registered and approved by the local research ethics committee under the jurisdiction of the Danish Medicines Agency number N-20130005. The protocol also is registered at Clinicaltrials.gov under NCT02653703.

PERSPECTIVE

Drugs interacting with transient receptor potential channels are of great therapeutic potential. In the present study we established cutaneous pain and hyperalgesia using the TRPA1 agonist CA. Subsequently, we showed that the frequently used topical counterirritant and TRPM8 agonist, L-menthol, decreased evoked pain, hyperalgesia, and inflammation, indicating direct and indirect antinociceptive mechanisms.

Topical anti-inflammatory activity of Solanum corymbiflorum leaves

Solanum corymbiflorum is popularly known as "baga-de-veado" and its leaves are applied on inflamed legs, scabies, tick bite, boils, mastitis, low back pain and otitis. The aim of this study was evaluate anti-inflammatory in vivo activity and relate this activity with antioxidant compounds present in the extract of S. corymbiflorum leaves. The extract from S. corymbiflorum leaves topically applied was able to reduce the croton oil-induced ear edema and myeloperoxidase (MPO) activity with maximum inhibition of 87±3% and 45±7%, rescpectively in the dose of 1mg/ear. Similar results were found for positive control dexamethasone, which presented inhibitions of ear edema and MPO activity of 89±3% and 50±3%, respectively in a dose of 0.1mg/ear. These findings are due, at least in part, the presence of polyphenols (195.28mg GAE/g) and flavonoids, as chlorogenic acid (59.27mg/g), rutin (12.72mg/g), rosmarinic acid, caffeic acid and gallic acid found by high performance liquid chromatography (HPLC) analysis. This species showed potencial antioxidant by 1,1-diphenyl-2-picrylhydrazyl (DPPH), and carbonyl groups in proteins methods which may be related with the presence of this compounds. This species possess anti-inflammatory activity confirming their popular use for the local treatment of skin inflammatory disorders.

Involvement of TRPA1 in the cinnamaldehyde-induced pulpal blood flow change in the feline dental pulp

Objectives

The purpose of this study was to investigate the involvement of TRPA1 in the cinnamaldehyde-induced pulpal blood flow (PBF) change in the feline dental pulp.

Materials and Methods

Mandibles of eight cats were immobilized and PBF was monitored with a laser Doppler flowmetry at the mandibular canine tooth. To evaluate the effect of cinnamaldehyde on PBF, cinnamaldehyde was injected into the pulp through the lingual artery at a constant rate for 60 seconds. As a control, a mixture of 70% ethanol and 30% dimethyl sulfoxide (DMSO, vehicle) was used. To evaluate the involvement of transient receptor potential ankyrin 1 (TRPA1) in PBF change, AP18, a specific TRPA1 antagonist, was applied into the pulp through the Class V dentinal cavity followed by cinnamaldehyde-administration 3 minutes later. The paired variables of experimental data were statistically analyzed using paired t-test. A p value of less than 0.05 was considered as statistically significant.

Results

Administration of cinnamaldehyde (0.5 mg/kg, intra-arterial [i.a.]) induced significant increases in PBF (p < 0.05). While administration of a TRPA1 antagonist, AP18 (2.5 - 3.0 mM, into the dentinal cavity [i.c.]) caused insignificant change of PBF (p > 0.05), administration of cinnamaldehyde (0.5 mg/kg, i.a.) following the application of AP18 (2.5 - 3.0 mM, i.c.) resulted in an attenuation of PBF increase from the control level (p < 0.05). As a result, a TRPA1 antagonist, AP18 effectively inhibited the vasodilative effect of cinnamaldehyde (p < 0.05).

Conclusions

The result of the present study provided a functional evidence that TRPA1 is involved in the mechanism of cinnamaldehyde-induced vasodilation in the feline dental pulp.

Nanoencapsulation of rice bran oil increases its protective effects against UVB radiation-induced skin injury in mice

Excessive UV-B radiation by sunlight produces inflammatory and oxidative damage of skin, which can lead to sunburn, photoaging, and cancer. This study evaluated whether nanoencapsulation improves the protective effects of rice bran oil against UVB radiation-induced skin damage in mice. Lipid-core nanocapsules containing rice bran oil were prepared, and had mean size around 200 nm, negative zeta potential (∼-9 mV), and low polydispersity index (<0.20). In order to allow application on the skin, a hydrogel containing the nanoencapsulated rice bran oil was prepared. This formulation was able to prevent ear edema induced by UVB irradiation by 60 ± 9%, when compared with a hydrogel containing LNC prepared with a mixture of medium chain triglycerides instead of rice bran oil. Protein carbonylation levels (biomarker of oxidative stress) and NF-κB nuclear translocation (biomarker of pro-inflammatory and carcinogenesis response) were reduced (81% and 87%, respectively) in animals treated with the hydrogel containing the nanoencapsulated rice bran oil. These in vivo results demonstrate the beneficial effects of nanoencapsulation to improve the protective properties of rice bran oil on skin damage caused by UVB exposure.

Transient receptor potential channels and itch: how deep should we scratch?

Over the past 30 years, transient receptor potential (TRP) channels have evolved from a somewhat obscure observation on how fruit flies detect light to become the center of drug discovery efforts, triggering a heated debate about their potential as targets for therapeutic applications in humans. In this review, we describe our current understanding of the diverse mechanism of action of TRP channels in the itch pathway from the skin to the brain with focus on the peripheral detection of stimuli that elicit the desire to scratch and spinal itch processing and sensitization. We predict that the compelling basic research findings on TRP channels and pruritus will be translated into the development of novel, clinically useful itch medications.

TRP channels in the skin

Emerging evidence suggests that transient receptor potential (TRP) ion channels not only act as 'polymodal cellular sensors' on sensory neurons but are also functionally expressed by a multitude of non-neuronal cell types. This is especially true in the skin, one of the largest organs of the body, where they appear to be critically involved in regulating various cutaneous functions both under physiological and pathophysiological conditions. In this review, we focus on introducing the roles of several cutaneous TRP channels in the regulation of the skin barrier, skin cell proliferation and differentiation, and immune functions. Moreover, we also describe the putative involvement of several TRP channels in the development of certain skin diseases and identify future TRP channel-targeted therapeutic opportunities.

Perineural pretreatment of bee venom attenuated the development of allodynia in the spinal nerve ligation injured neuropathic pain model; an experimental study

Background

Diluted bee venom (BV) is known to have anti-nociceptive and anti-inflammatory effects. We therefore assessed whether perineural bee venom pretreatment could attenuate the development of neuropathic pain in the spinal nerve ligation injured animal model.

Methods

Neuropathic pain was surgically induced in 30 male Sprague Dawley rats by ligation of the L5 and L6 spinal nerves, with 10 rats each treated with saline and 0.05 and 0.1 mg BV. Behavioral testing for mechanical, cold, and thermal allodynia was conducted on postoperative days 3 to 29. Three rats in each group and 9 sham operated rats were sacrificed on day 9, and the expression of transient receptor potential vanilloid type 1 (TRPV1), ankyrin type 1 (TRPA1), and melastatin type 8 (TRPM8) receptors in the ipsilateral L5 dorsal root ganglion was analyzed.

Results

The perineural administration of BV to the spinal nerves attenuated the development of mechanical, thermal, and cold allodynia, and the BV pretreatment reduced the expression of TRPV1, TRPA1, TRPM8 and c − Fos in the ipsilateral dorsal root ganglion.

Conclusion

The current study demonstrates that the perineural pretreatment with diluted bee venom before the induction of spinal nerve ligation significantly suppresses the development of neuropathic pain. Furthermore, this bee venom induced suppression was strongly related with the involvement of transient receptor potential family members.

Antinociceptive and anti-inflammatory activities of extract and two isolated flavonoids of Carthamus tinctorius L

ETHNOPHARMACOLOGICAL RELEVANCE

Safflower (Carthamus tinctorius L.) has been long used both in the traditional system and folk medicine as an analgesic anti-inflammatory agent in China. The aim of the study was to evaluate the antinociceptive and anti-inflammatory activities of hydroalcoholic extract (HE) and two isolated kaempferol glycosides of Carthamus tinctorius L. to provide experimental evidence for its traditional use.

MATERIALS AND METHODS

Antinociceptive effects of HE, kaempferol 3-O-rutinoside (K-3-R) and kaempferol 3-O-glucoside (K-3-G) were assessed in mice using the acetic acid-induced writhing test, formalin test and cinnamaldehyde test. The anti-inflammatory effects of HE, K-3-R and K-3-G were determined in two animal models: carrageenan-induced paw edema and xylene-induced ear edema.

RESULTS

The HPLC analysis showed the presence of K-3-R and K-3-G in Carthamus tinctorius L. HE (500 and 1000mg/kg) as well as K-3-R and K-3-G (150, 300 and 600mg/kg) produced significant inhibition on nociception induced by acetic acid and formalin. Oral treatment of HE, K-3-R and K-3-G at all doses significantly reduced both the nociceptive response and cinnamaldehyde-induced paw edema, effect that was superior to aspirin. In anti-inflammatory tests, HE and K-3-G significantly inhibited the paw edema during the both phases of carrageenan-induced inflammation while K-3-G suppressed the late phase inflammation only. HE (400 and 800mg/kg) and K-3-G (200, 400, 800mg/kg) produced significant dose-dependent inhibition of xylene-induced ear edema development. K-3-R only suppressed ear edema formation at a high dose (800mg/kg).

CONCLUSIONS

These results demonstrate that Carthamus tinctorius L. extract possess remarkable antinociceptive and anti-inflammatory activities which may be due to K-3-R and K-3-G at least in part, supporting the folkloric usage of the plant to treat various inflammatory and pain diseases.

Achillea millefolium L. essential oil inhibits LPS-induced oxidative stress and nitric oxide production in RAW 264.7 Macrophages

Achillea millefolium L. is a member of the Asteraceae family and has been used in folk medicine in many countries. In this study, 19 compounds in A. millefolium essential oil (AM-EO) have been identified; the major components are artemisia ketone (14.92%), camphor (11.64%), linalyl acetate (11.51%) and 1,8-cineole (10.15%). AM-EO can suppress the inflammatory responses of lipopolysaccharides (LPS)-stimulated RAW 264.7 macrophages, including decreased levels of cellular nitric oxide (NO) and superoxide anion production, lipid peroxidation and glutathione (GSH) concentration. This antioxidant activity is not a result of increased superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) activities, but rather occurs as a result of the down-regulation of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and heme oxygenase-1 (HO-1) expression, thus reducing the inflammatory response. Therefore, AM-EO can be utilized in many applications, including the treatment of inflammatory diseases in the future.

The role of transient receptor potential ankyrin 1 (TRPA1) receptor activation in hydrogen-sulphide-induced CGRP-release and vasodilation

Activation of transient receptor potential ankyrin 1 (TRPA1) and vanilloid 1 (TRPV1) channels on capsaicin-sensitive sensory neurons causes release of inflammatory neuropeptides, including calcitonin gene-related peptide (CGRP). We investigated whether the hydrogen sulphide (H(2)S)-evoked CGRP release from sensory neurons of isolated rat tracheae and H(2)S-induced increases in the microcirculation of the mouse ear were mediated by TRPA1 receptor activation. Allylisothiocyanate (AITC) or the H(2)S donor sodium hydrogen sulphide (NaHS) were used as stimuli and CGRP release of the rat tracheae was measured by radioimmunoassay. AITC or NaHS were applied to the ears of Balb/c, C57BL/6, TRPA1 and TRPV1 receptor gene knockout mice and blood flow was detected by laser Doppler imaging. Both AITC and NaHS increased CGRP release from isolated rat tracheae, and both responses were inhibited by the TRPA1 antagonist, HC-030031, but was not affected by the TRPV1 receptor blocker, BCTC. Application of AITC or NaHS increased the cutaneous blood flow in the mouse ears. Similarly to the effect of AITC, the vasodilatory response to NaHS was reduced by HC-030031 or in TRPA1 deleted mice. In contrast, genetic deletion of TRPV1 did not affect the increase in the ear blood flow evoked by AITC or NaHS. We conclude that H(2)S activates TRPA1 receptors causing CGRP release from sensory nerves of rat tracheae, as well as inducing cutaneous vasodilatation in the mouse ear. TRPV1 receptors were not involved in these processes. Our results highlight that TRPA1 receptor activation should be considered as a potential mechanism of vasoactive effects of H(2)S.

Blockade of TRPA1 with HC-030031 attenuates visceral nociception by a mechanism independent of inflammatory resident cells, nitric oxide and the opioid system

BACKGROUND

Some studies have shown a somatic nociceptive response due to the activation of transient receptor potential A1 channels (TRPA1), which is modulated by the TRPA1 antagonist HC-030031. However, a few studies report the role of TRPA1 in visceral pain. Therefore, we investigated the participation of TRPA1 in visceral nociception and the involvement of nitric oxide, the opioid system and resident cells in the modulation of these channels.

METHODS

Mice were treated with vehicle or HC-030031 (18.75-300 mg/kg) before ifosfamide (400 mg/kg), 0.75% mustard oil (50 μL/colon), acetic acid 0.6% (10 mL/kg), zymosan (1 mg/cavity) or misoprostol (1 μg/cavity) injection. Visceral nociception was assessed through the electronic von Frey test or the writhing response. Ifosfamide-administered mice were euthanized for bladder analysis. The involvement of nitric oxide and the opioid system were investigated in mice injected with ifosfamide and mustard oil, respectively. The participation of resident peritoneal cells in acetic acid-, zymosan- or misoprostol-induced nociception was also evaluated.

RESULTS

HC-030031 failed to protect animals against ifosfamide-induced bladder injury (p > 0.05). However, a marked antinociceptive effect against ifosfamide, mustard oil, acetic acid, zymosan and misoprostol was observed (p < 0.05). Neither L-arginine (600 mg/kg) nor naloxone (2 mg/kg) could reverse the antinociceptive effect of HC-030031. The reduction of the peritoneal cell population inhibited the acetic acid and zymosan-related writhes without interfering with the misoprostol effect.

CONCLUSIONS

Our findings suggest that the blockade of TRPA1 attenuates visceral nociception by a mechanism independent of the modulation of resident cells, nitric oxide and opioid pathways.

The channel physiology of the skin

During embryonic development, the skin, the largest organ of the human body, and nervous system are both derived from the neuroectoderm. Consequently, several key factors and mechanisms that influence and control central or peripheral nervous system activities are also present and hence involved in various regulatory mechanisms of the skin. Apparently, this is the case for the ion and non-ion selective channels as well. Therefore, in this review, we shall focus on delineating the regulatory roles of the channels in skin physiology and pathophysiology. First, we introduce key cutaneous functions and major characteristics of the channels in question. Then, we systematically detail the involvement of a multitude of channels in such skin processes (e.g. skin barrier formation, maintenance, and repair, immune mechanisms, exocrine secretion) which are mostly defined by cutaneous non-neuronal cell populations. Finally, we close by summarizing data suggesting that selected channels are also involved in skin diseases such as e.g. atopic dermatitis, psoriasis, non-melanoma cancers and malignant melanoma, genetic and autoimmune diseases, etc., as well as in skin ageing.