Frutalin reduces acute and neuropathic nociceptive behaviours in rodent models of orofacial pain

Development of a Nanoformulation for Oral Protein Administration: Characterization and Preclinical Orofacial Antinociceptive Effect

Nanoencapsulation is a valid alternative for the oral administration of peptide drugs and proteins, as nanoparticles protect them from proteolytic degradation in the gastrointestinal tract and promote the absorption of these macromolecules. The orofacial antinociceptive effect of frutalin (FTL), through the intraperitoneal route, has already been proven. This study aimed to develop, characterize, and evaluate the orofacial antinociceptive activity of an oral formulation containing FTL in acute and neuropathic preclinical tests. Nanoencapsulated FTL was administered by oral route. The acute nociceptive behavior was induced by administering capsaicin to the upper lip and NaCl to the right cornea. The nociceptive behavior was also induced by formalin injected into the temporomandibular joint. The neuropathic pain model involved infraorbital nerve transection (IONX), which induced mechanical hypersensitivity and was assessed by von Frey stimulation. Trpv1 gene expression was analyzed in the trigeminal ganglion. The analyzed sample did not show any cytotoxicity; 52.2% of the FTL was encapsulated, and the size of the nanocapsule was less than 200 nm, the polydispersion was 0.361, and the zeta potential was - 5.87 and - 12.8 mV, with and without FTL, respectively. Nanoencapsulated FTL administered by oral route had an orofacial antinociceptive effect in acute and neuropathic rodent models. The antinociceptive effect of FTL was prevented by ruthenium red, but not by camphor. FTL reduced Trpv1 gene expression. FTL promotes orofacial antinociception, probably due to the antagonism of TRPV1 channels, and the nanoformulation represents an effective method for the oral administration of this protein. HIGHLIGHTS: • Nanoformulation for oral protein administration. • Nanocapsule containing FTL prevents orofacial nociceptive acute and neuropathic pain. • Frutalin promotes orofacial antinociception behavior antagonism of TRPV1 channels.

Therapeutic Agents for the Treatment of Temporomandibular Joint Disorders: Progress and Perspective

Temporomandibular joint disorders (TMD) are a common health condition caused by the structural or functional disorders of masticatory muscles and the temporomandibular joint (TMJ). Abnormal mandibular movement in TMD patients may cause pain, chronic inflammation, and other discomfort, which could be relieved by a variety of drugs through various delivery systems. In this study, we summarized commonly used therapeutic agents in the management of TMD as well as novel bioactive molecules in preclinical stage and clinical trials. The emerging therapy strategies such as novel intra-TMJ delivery systems and implants based on tissue engineering are also discussed. This comprehensive review will strengthen our understanding of pharmacological approaches for TMD therapy.

Is the orofacial antinociceptive effect of lectins intrinsically related to their specificity to monosaccharides?

Lectins are proteins of non-immunological origin that may play several biological applications, of which we can highlight the anti-inflammatory and antinociceptive activities. In this work, we evaluated the possible effect of orofacial antinociceptive activity of three plant lectins, Dioclea violacea (DVL - Man/Glc-binding), Vatairea macrocarpa (VML - Gal-binding) and PPL (Parkia platycephala - Man/Glc-binding) in adult zebrafish. Acute nociception was induced by menthol (1.2 μM), or capsaicin (4.93 μM) applied into in the upper lip (5.0 μL) of adult wild zebrafish. Zebrafish were pretreated by intraperitoneal injection (20 μL) with vehicle (Control) or lectins (0.025; 0.05 or 0.1 mg/mL) 30 min before induction. The effect of lectins on zebrafish locomotor behavior was evaluated with the open field test. Naive groups (n = 8) were included in all tests. Our results indicate that only PPL presented antinociceptive induced by capsaicin, suggesting the potential clinical application of PPL as inhibitor of orofacial nociception and that this effect may be due to the modulation of TRPV1 channel. In conclusion, lectins that exhibit affinity to the same or different carbohydrates do not necessarily have an antinociceptive effect on the orofacial nociception model, indicating that the glycan carbohydrate binding pattern may be related to the effect on nociception inhibition.

The effect of natural products in animal models of temporomandibular disorders

Treatment of temporomandibular disorders (TMD) is a challenge for health care professionals. Therefore, new approaches have been investigated, such as the use of natural products.

Natural products for orofacial nociception in pre-clinical studies: A systematic review

OBJECTIVE

The aim of this systematic review was to summarize the use of natural products (NP) in the treatment of orofacial nociception in animal models.

METHODS

Pre-clinical studies that have evaluated the efficacy of NPs in experimental orofacial nociception were sought in the Medline, Web of Science, Scopus, Embase, SciELO, LILACS and Scholar databases in January 2020, covering the period since the inception of each one. Two reviewers independently selected the studies, extracted the data and evaluated the risk of bias of the included studies.

RESULTS

We included 41 records in qualitative synthesis. Fifty different NPs were investigated. All studies presented positive results for at least one orofacial nociception test. Regarding the risk of bias, most studies presented poor experimental design, mainly lack of randomization and blinding. The main class of isolated compounds tested was terpenes, of which monoterpenes were investigated in the majority of the studies.

CONCLUSION

These results indicate that NPs are effective in treating experimental orofacial nociception and highlight some of these NPs, mainly terpenes, suggesting their potential for translational research.

Neuropharmacological Characterization of Dioclea altissima Seed Lectin (DAL) in Mice: Evidence of Anxiolytic-like Effect Mediated by Serotonergic, GABAergic Receptors and NO Pathway

BACKGROUND

Plant lectins have shown promising biological activities in the central nervous system (CNS).

OBJECTIVE

This study evaluated the effect of DAL, a lectin isolated from the seeds of the Dioclea altissima species, having binding affinity to D-glucose or D-mannose residues, on mice behavior.

METHODS

Mice (n=6/group) were treated (i.p.) with DAL (0.25, 0.5 or 1 mg/kg) or vehicle and subjected to several tests (open field/OFT, marble-burying/MBT, hole-board/HBT, elevated plus maze/PMT, tail suspension/ TST, forced swimming/FST or rotarod/RRT). Pizotifen, cyproheptadine, flumazenil, L-NAME, 7-NI, Larginine or yohimbine were administered 15 min before DAL (0.5 mg/kg) and the animals were evaluated on PMT. It was also verified whether the DAL effect depended on its structural integrity and ability to interact with carbohydrates.

RESULTS

The results showed there were no neurobehavioral changes in the mice at the RRT, FST and locomotion in the OFT. DAL (0.25, 0.5 or 1 mg/kg) increased the behavior of grooming and rearing in the OFT, head dips in the HBT, pedalling in the TST and decreased the number of marbles hidden in the MBT. In the PMT, DAL (0.25, 0.5 and 1 mg/kg) and Diazepam increased the frequency of entries in the open arms and the time of permanence in the open arms without affecting the locomotor activity. The effect of DAL was dependent on carbohydrate interaction and protein structure integrity and it prevented by pizotifen, cyproheptadine, flumazenil, L-NAME and 7-NI, but not by L-arginine or yohimbine.

CONCLUSION

DAL was found to have an anxiolytic-like effect mediated by the 5-HT and GABAergic receptors and NO pathway.

Animal Galectins and Plant Lectins as Tools for Studies in Neurosciences

Lectins are proteins or glycoproteins of non-immunological origin capable of reversibly and specifically binding to glycoconjugates. They exist in free form or associated with cells and are widely distributed in nature, being found in plants, microorganisms, and animals. Due to their characteristics and mainly due to the possibility of reversible binding to glycoconjugates, lectins have stood out as important tools in research involving Neurobiology. These proteins have the ability to modulate molecular targets in the central nervous system (CNS) which may be involved with neuroplasticity, neurobehavioral effects, and neuroprotection. The present report integrates existing information on the activity of animal and plant lectins in different areas of Neuroscience, presenting perspectives to direct new research on lectin function in the CNS, providing alternatives for understanding neurological diseases such as mental disorders, neurodegenerative, and neuro-oncological diseases, and for the development of new drugs, diagnoses and therapies in the field of Neuroscience.

Is TRPA1 Burning Down TRPV1 as Druggable Target for the Treatment of Chronic Pain?

Over the last decades, a great array of molecular mediators have been identified as potential targets for the treatment of chronic pain. Among these mediators, transient receptor potential (TRP) channel superfamily members have been thoroughly studied. Namely, the nonselective cationic channel, transient receptor potential ankyrin subtype 1 (TRPA1), has been described as a chemical nocisensor involved in noxious cold and mechanical sensation and as rivalling TRPV1, which traditionally has been considered as the most important TRP channel involved in nociceptive transduction. However, few TRPA1-related drugs have succeeded in clinical trials. In the present review, we attempt to discuss the latest data on the topic and future directions for pharmacological intervention.

Molecular mechanism underlying orofacial antinociceptive activity of Vanillosmopsis arborea Baker (Asteraceae) essential oil complexed with β-cyclodextrin

BACKGROUND

Vanillosmopsis arborea Baker has recognized economic value owing to the high content of (-)-α-bisabolol (BISA) in the essential oil of its stem (EOVA). The antinociceptive effect of EVOA has already been demonstrated, and β-cyclodextrin (βCD) is known to improve the analgesic effect of various substances.

PURPOSE

Thus, we aimed to evaluate the orofacial antinociceptive effect of a complex containing EOVA-βCD in rodents.

METHODS

EOVA was obtained by simple hydrodistillation, and the essential oil was complexed with βCD. The animals (n = 6/group) were treated orally with EOVA-βCD (10 or 50 mg/kg), or vehicle (control), and subjected to cutaneous orofacial nociception (formalin, capsaicin, acidic saline or glutamate), corneal (hypertonic saline) or temporomandibular (formalin) tests. The expression of FOS protein was analyzed in the spinal cord. Molecular docking was performed using the 5-HT₃ and M₂ receptors and BISA.

RESULTS

The oral administration of EOVA-βCD reduced nociceptive behaviour. Moreover, EOVA-βCD decreased FOS expression. The molecular docking study indicates that BISA interacts with 5-HT3 and M2 receptors, indicating the potential mechanism of action of the tested compound.

CONCLUSIONS

Our results indicate that EOVA-βCD possesses orofacial antinociceptive effect, indicating that this complex can be used in analgesic drug development.

New structural insights into anomeric carbohydrate recognition by frutalin: an α-d-galactose-binding lectin from breadfruit seeds

Frutalin (FTL) is a multiple-binding lectin belonging to the jacalin-related lectin (JRL) family and derived from Artocarpus incisa (breadfruit) seeds. This lectin specifically recognizes and binds α-d-galactose. FTL has been successfully used in immunobiological research for the recognition of cancer-associated oligosaccharides. However, the molecular bases by which FTL promotes these specific activities remain poorly understood. Here, we report the whole 3D structure of FTL for the first time, as determined by X-ray crystallography. The obtained crystals diffracted to 1.81 Å (Apo-frutalin) and 1.65 Å (frutalin-d-Gal complex) of resolution. The lectin exhibits post-translational cleavage yielding an α- (133 amino acids) and β-chain (20 amino acids), presenting a homotetramer when in solution, with a typical JRL β-prism. The β-prism was composed of three 4-stranded β-sheets forming three antiparallel Greek key motifs. The carbohydrate-binding site (CBS) involved the N-terminus of the α-chain and was formed by four key residues: Gly25, Tyr146, Trp147 and Asp149. Together, these results were used in molecular dynamics simulations in aqueous solutions to shed light on the molecular basis of FTL-ligand binding. The simulations suggest that Thr-Ser-Ser-Asn (TSSN) peptide excision reduces the rigidity of the FTL CBS, increasing the number of interactions with ligands and resulting in multiple-binding sites and anomeric recognition of α-d-galactose sugar moieties. Our findings provide a new perspective to further elucidate the versatility of FTL in many biological activities.

Hydrogel and membrane scaffold formulations of Frutalin (breadfruit lectin) within a polysaccharide galactomannan matrix have potential for wound healing

Plant lectins are carbohydrate-binding proteins, which can interact with cell surfaces to initiate anti-inflammatory pathways, as well as immunomodulatory functions. Here, we have extracted, purified and part-characterized the bioactivity of Jacalin, Frutalin, DAL and PNA, before evaluating their potential for wound healing in cultured human skin fibroblasts. Only Frutalin stimulated fibroblast migration in vitro, prompting further studies which established its low cytotoxicity and interaction with TLR4 receptors. Frutalin also increased p-ERK expression and stimulated IL-6 secretion. The in vivo potential of Frutalin for wound healing was then assessed in hybrid combination with the polysaccharide galactomannan, purified from Caesalpinia pulcherrima seeds, using both hydrogel and membrane scaffolds formulations. Physical-chemical characterization of the hybrid showed that lectin-galactomannan interactions increased the pseudoplastic behaviour of solutions, reducing viscosity and increasing Frutalin's concentration. Furthermore, infrared spectroscopy revealed -OH band displacement, likely caused by interaction of Frutalin with galactose residues present on galactomannan chains, while average membrane porosity was 100 μm, sufficient to ensure water vapor permeability. Accelerated angiogenesis and increased fibroblast and keratinocyte proliferation were observed with the optimal hybrid recovering the lesioned area after 11 days. Our findings indicate Frutalin as a biomolecule with potential for tissue repair, regeneration and chronic wound healing.

Chronic orofacial pain animal models - progress and challenges

INTRODUCTION

Chronic orofacial pain is one of the most common pain conditions experienced by adults. Animal models are often selected as the most useful scientific methodology to explore the pathophysiology of the disorders that cause this disabling pain to facilitate the development of new treatments. The creation of new models or the improvement of existing ones is essential for finding new ways to approach the complex neurobiology of this type of pain. Areas covered: The authors describe and discuss a variety of animal models used in chronic orofacial pain (COFP). Furthermore, they examine in detail the mechanisms of action involved in orofacial neuropathic pain and orofacial inflammatory pain. Expert opinion: The use of animal models has several advantages in chronic orofacial pain drug discovery. Choosing an animal model that most closely represents the human disease helps to increase the chances of finding effective new therapies and is key to the successful translation of preclinical research to clinical practice. Models using genetically modified animals seem promising but have not yet been fully developed for use in chronic orofacial pain research. Although animal models have provided significant advances in the pharmacological treatment of orofacial pain, several barriers still need to be overcome for better treatment options.

Orofacial antinociceptive effect of Mimosa tenuiflora (Willd.) Poiret

Mimosa tenuiflora (Willd.) Poiret, popularly known in Brazil as "jurema-preta" is widely used against bronchitis, fever, headache and inflammation. Its antioxidant, anti-inflammatory and antinociceptive potential has already been reported. To assess the orofacial antinociceptive effect of M. tenuiflora, ethanolic extracts of M. tenuiflora (leaves, twigs, barks and roots) were submitted to in vitro tests of antioxidant activity. The extract with the highest antioxidant potential was partitioned and subjected to preliminary chemical prospecting, GC-MS, measurement of phenolic content and cytotoxicity tests of the fraction with the highest antioxidant activity. The nontoxic fraction with the highest antioxidant activity (FATEM) was subjected to tests of acute and chronic orofacial nociception and locomotor activity. The possible mechanisms of neuromodulation were also assessed. The EtOAc fraction, obtained from the ethanolic extract of M. tenuiflora barks, was the one with the highest antioxidant potential and nontoxic (FATEM), and Benzyloxyamine was the major constituent (34.27%). FATEM did not alter the locomotor system of mice and reduced significantly the orofacial nociceptive behavior induced by formalin, glutamate, capsaicin, cinnamaldehyde or acidic saline compared to the control group. FATEM also inhibited formalin- or mustard oil-induced temporomandibular nociception. In addition, it also reduced mustard oil-induced orofacial muscle nociception. However, FATEM did not alter hypertonic saline-induced corneal nociception. Neuropathic nociception was reversed by treatment with FATEM. The antinociceptive effect of FATEM was inhibited by naloxone, L-NAME and glibenclamide. FATEM has pharmacological potential for the treatment of acute and neuropathic orofacial pain and this effect is modulated by the opioid system, nitric oxide and ATP-sensitive potassium channels. These results lead us to studies of isolation and characterization of bioactive principles.