An Insight into the Role of Marine Biopolymer Alginate in Endodontics: A Review.

Alginate is a natural marine biopolymer that has been widely used in biomedical applications, but research on its use as an endodontic material is still sparse in the literature. This pioneer review aims to summarize the emerging roles of alginate and to outline its prospective applications as a core biomaterial in endodontics. Ten electronic databases and five textbooks were used to perform a search of English-language literature on the use of alginate in endodontics published between January 1980 and June 2022. The risk of bias (RoB) of each included study was assessed using the Office of Health Assessment and Translation (OHAT) tool. Subsequently, studies were categorized into three tiers to represent the overall risk. Qualitative analysis was performed, and the articles were sorted into different thematic categories. An initial search yielded a total of 1491 articles, but only 13 articles were chosen. For most domains, all the studies were rated with 'probably low' or 'definitely low' RoB, except for domains 2 and 6. All included studies fall in the Tier 1 category and were either in vitro, in vivo, or ex vivo. Four thematic categories were identified: endodontic regeneration, intracanal medicament, filing material, and chelating agent. Based on the available evidence, alginate has emerged as a cell carrier and scaffold in regenerative endodontics, a microcapsule delivery system for intracanal medicaments, a chelating agent reinforcing material, and a root canal sealer. More well-designed experiments and clinical trials are needed to warrant the promising advent of this hydrogel-based biomaterial.

Enkephalin analogues with N-phenyl-N-(piperidin-2-ylmethyl)propionamide derivatives: Synthesis and biological evaluations.

N-Phenyl-N-(piperidin-2-ylmethyl)propionamide based bivalent ligands are unexplored for the design of opioid based ligands. Two series of hybrid molecules bearing N-phenyl-N-(piperidin-2-ylmethyl)propionamide derived small molecules conjugated with an enkephalin analogues with and without a linker (ß-alanine) were designed and synthesized. Both bivalent ligand series exhibited remarkable binding affinities from nanomolar to subnanomolar range at both µ and δ opioid receptors and displayed potent agonist activities as well. The replacement of Tyr with Dmt and introduction of a linker between the small molecule and enkephalin analogue resulted in highly potent ligands. Both series of ligands showed excellent binding affinities at both µ (0.6-0.9nM) and δ (0.2-1.2nM) opioid receptors respectively. Similarly, these bivalent ligands exhibited potent agonist activities in both MVD and GPI assays. Ligand 17 was evaluated for in vivo antinociceptive activity in non-injured rats following spinal administration. Ligand 17 was not significantly effective in alleviating acute pain. The most likely explanations for this low intrinsic efficacy in vivo despite high in vitro binding affinity, moderate in vitro activity are (i) low potency suggesting that higher doses are needed; (ii) differences in experimental design (i.e. non-neuronal, high receptor density for in vitro preparations versus CNS site of action in vitro); (iii) pharmacodynamics (i.e. engaging signalling pathways); (iv) pharmacokinetics (i.e. metabolic stability). In summary, our data suggest that further optimisation of this compound 17 is required to enhance intrinsic antinociceptive efficacy.

Cyclic non-opioid dynorphin A analogues for the bradykinin receptors.

Nerve injury and inflammation cause up-regulation of an endogenous opioid ligand, dynorphin A (Dyn A), in the spinal cord resulting in hyperalgesia via the interaction with bradykinin receptors (BRs). This is a non-opioid neuroexcitatory effect that cannot be blocked by opioid antagonists. Our systematic structure-activity relationships study on Dyn A identified lead ligands 1 and 4, along with the key structural feature (i.e. amphipathicity) for the BRs. However, the ligands showed very low metabolic stability in plasma (t1/2 <1h) and therefore, in order to improve their metabolic stabilities with retained biological activities, various modifications were performed. Cyclization of ligand 4 afforded a cyclic Dyn A analogue 5 that retained the same range of binding affinity as the linear ligand with improved metabolic stability (t1/2 >5h) and therefore possesses the potential as a pharmacophoric scaffold to be utilized for drug development.

Design synthesis and structure-activity relationship of 5-substituted (tetrahydronaphthalen-2yl)methyl with N-phenyl-N-(piperidin-2-yl)propionamide derivatives as opioid ligands.

Here, we report the design, synthesis and structure activity relationship of novel small molecule opioid ligands based on 5-amino substituted (tetrahydronaphthalen-2-yl)methyl moiety with N-phenyl-N-(piperidin-2-yl)propionamide derivatives. We synthesized various molecules including amino, amide and hydroxy substitution on the 5th position of the (tetrahydronaphthalen-2-yl)methyl moiety. In our further designs we replaced the (tetrahydronaphthalen-2-yl)methyl moiety with benzyl and phenethyl moiety. These N-phenyl-N-(piperidin-2-yl)propionamide analogues showed moderate to good binding affinities (850-4 nM) and were selective towards the µ opioid receptor over the δ opioid receptors. From the structure activity relationship studies, we found that a hydroxyl substitution at the 5th position of (tetrahydronapthalen-2yl)methyl group, ligands 19 and 20, showed excellent binding affinities 4 and 5 nM, respectively, and 1000 fold selectivity towards the µ opioid relative to the delta opioid receptor. The ligand 19 showed potent agonist activities 75±21 nM, and 190±42 nM in the GPI and MVD assays. Surprisingly the fluoro analogue 20 showed good agonist activities in MVD assays 170±42 nM, in contrast to its binding affinity results.

Design, synthesis and biological evaluation of multifunctional ligands targeting opioid and bradykinin 2 receptors.

We report here the design and synthesis of novel multifunctional ligands that act as (µ/δ) opioid agonists and bradykinin 2 receptor antagonists. These multifunctional ligands were designed to interact with the multiple receptors to show an enhanced analgesic effect, with no opioid-induced tolerance. We designed our multifunctional ligands based on the well-known second generation bradykinin 2 receptor antagonist Hoe 140 (DArg-Arg-Pro-Hyp-Gly-Thi-Ser-DTic-Oic-Arg-OH) and the opioid enkephalin analogues Tyr-DAla-Phe, Tyr-DAla-Gly-Phe and Tyr-Pro-Phe. We explored the conjugation of opioid pharmacophore to the Hoe 140 (DArg-Arg-Pro-Hyp-Gly-Thi-Ser-DTic-Oic-Arg-OH) in various positions with and without a linker. These bifunctional ligands showed very good binding affinity towards the both µ and δ opioid receptors. Among these bifunctional ligands 8, 11 and 12 showed excellent and balanced binding affinity at both µ and δ opioid receptors (0.5 nM, 2.0 nM; 0.3 nM, 2 nM; 2 nM and 3 nM), respectively. On the other hand these bifunctional ligands showed very weak and no binding affinity for rat brain bradykinin 2 receptors. Similarly, the Hoe 140 showed very low affinity (>10,000 nM and 9,000 nM) against [(3)H] BK binding in rat brain membranes and in HEK293 cells, respectively. In contrast, the Hoe 140 showed very good binding affinity in guinea pig ileum (0.43 nM) similar to that of previously reported. The bradykinin 2 receptors are known to be present in rat brain membrane, guinea pig ileum (GPI) and rabbit jugular vein. Previously the binding affinity of Hoe 140 for bradykinin 2 receptor was reported using guinea pig ileum. The above results suggest that the bradykinin 2 receptors present in rat brain membrane are a different sub type than the bradykinin 2 receptor present in guinea pig ileum (GPI).

Modification of amphipathic non-opioid dynorphin A analogues for rat brain bradykinin receptors.

It has been shown that under chronic pain or nerve injury conditions, up-regulated dynorphin A (Dyn A) interacts with bradykinin receptors (BRs) to cause hyperalgesia in the spinal cord. Thus BRs antagonist can modulate hyperalgesia by blocking Dyn A's interaction with the BRs in the central nervous system. In our earlier structure-activity relationship (SAR) study, [des-Arg(7)]-Dyn A-(4-11) 13 was discovered as a minimum pharmacophore for rat brain BRs with its antagonist activity (anti-hyperalgesic effect) in in vivo tests using naïve or injured animals. We have pursued further modification on the [des-Arg(7)]-Dyn A analogues and identified a key insight into the pharmacophore of the rat brain BRs: amphipathicity.

Design and synthesis of novel bivalent ligands (MOR and DOR) by conjugation of enkephalin analogues with 4-anilidopiperidine derivatives.

We describe the design and synthesis of novel bivalent ligands based on the conjugation of 4-anilidopiperidine derivatives with enkephalin analogues. The design of non-peptide analogues is explored with 5-amino substituted (tetrahydronaphthalen-2yl) methyl containing 4-anilidopiperidine derivatives, while non-peptide-peptide ligands are explored by conjugating the C-terminus of enkephalin analogues (H-Xxx-DAla-Gly-Phe-OH) to the amino group of 4-anilidopiperidine small molecule derivatives with and without a linker. These novel bivalent ligands are evaluated for biological activities at µ and δ opioid receptors. They exhibit very good affinities at µ and δ opioid receptors, and potent agonist activities in MVD and GPI assays. Among these the lead bivalent ligand 17 showed excellent binding affinities (0.1 nM and 0.5 nM) at µ and δ opioid receptors respectively, and was found to have very potent agonist activities in MVD (56 ± 5.9 nM) and GPI (4.6 ± 1.9 nM) assays. In vivo the lead bivalent ligand 17 exhibited a short duration of action (<15 min) comparable to 4-anilidopiperidine derivatives, and moderate analgesic activity. The ligand 17 has limited application against acute pain but may have utility in settings where a highly reversible analgesic is required.

Discovery of tripeptide-derived multifunctional ligands possessing delta/mu opioid receptor agonist and neurokinin 1 receptor antagonist activities.

Several bifunctional peptides were synthesized and characterized based on the pentapeptide-derived ligand NP30 (1: Tyr-DAla-Gly-Phe-Gly-Trp-O-[3',5'-Bzl(CF3)2]). Modification and truncation of amino acid residues were performed, and the tripeptide-derived ligand NP66 (11: Dmt-DAla-Trp-NH-[3',5'-(CF3)2-Bzl]) was obtained based on the overlapping pharmacophore concept. The Trp(3) residue of ligand 11 works as a message residue for both opioid and NK1 activities. The significance lies in the observation that the approach of appropriate truncation of peptide sequence could lead to a tripeptide-derived chimeric ligand with effective binding and functional activities for both mu and delta opioid and NK1 receptors with agonist activities at mu and delta opioid and antagonist activity at NK1 receptors, respectively.

Design, synthesis, and biological evaluation of a series of bifunctional ligands of opioids/SSRIs.

A series of opioid and serotonin re-uptake inhibitors (SSRIs) bifunctional ligands have been designed, synthesized, and tested for their activities and efficacies at µ-, δ- and κ opioid receptors and SSRIs receptors. Most of the compounds showed high affinities for µ- and δ-opioid receptors and lower affinities for SSRIs and κ opioid receptors. A docking study on the µ-opioid receptor binding pocket has been carried out for ligands 3-11. The ligands 7 and 11 have displayed the highest binding profiles for the µ-opioid receptor binding site with ΔGbind (-12.14kcal/mol) and Ki value (1.0nM), and ΔGbind (-12.41kcal/mol) and Ki value (0.4nM), respectively. Ligand 3 was shown to have the potential of dual acting serotonin/norepinephrine re-uptake inhibitor (SNRI) antidepressant activity in addition to opioid activities, and thus could be used for the design of multifunctional ligands in the area of a novel approach for the treatment of pain and depression.

Discovery of 5-substituted tetrahydronaphthalen-2yl-methyl with N-phenyl-N-(piperidin-4-yl)propionamide derivatives as potent opioid receptor ligands.

A new series of novel opioid ligands have been designed and synthesized based on the 4-anilidopiperidine scaffold containing a 5-substituted tetrahydronaphthalen-2yl)methyl group with different N-phenyl-N-(piperidin-4-yl)propionamide derivatives to study the biological effects of these substituents on µ and δ opioid receptor interactions. Recently our group reported novel 4-anilidopiperidine analogues, in which several aromatic ring-contained amino acids were conjugated with N-phenyl-N-(piperidin-4-yl)propionamide and examined their biological activities at the µ and δ opioid receptors. In continuation of our efforts in these novel 4-anilidopiperidine analogues, we took a peptidomimetic approach in the present design, in which we substituted aromatic amino acids with tetrahydronaphthalen-2yl methyl moiety with amino, amide and hydroxyl substitutions at the 5th position. In in vitro assays these ligands, showed very good binding affinity and highly selective toward the µ opioid receptor. Among these, the lead ligand 20 showed excellent binding affinity (2 nM) and 5000 fold selectivity toward the µ opioid receptor, as well as functional selectivity in GPI assays (55.20 ± 4.30 nM) and weak or no agonist activities in MVD assays. Based on the in vitro bioassay results the lead compound 20 was chosen for in vivo assessment for efficacy in naïve rats after intrathecal administration. Compound 20 was not significantly effective in alleviating acute pain. This discrepancy between high in vitro binding affinity, moderate in vitro activity, and low in vivo activity may reflect differences in pharmacodynamics (i.e., engaging signaling pathways) or pharmacokinetics (i.e., metabolic stability). In sum, our data suggest that further optimization of this compound 20 is required to enhance in vivo activity.

Discovery of amphipathic dynorphin A analogues to inhibit the neuroexcitatory effects of dynorphin A through bradykinin receptors in the spinal cord.

We hypothesized that under chronic pain conditions, up-regulated dynorphin A (Dyn A) interacts with bradykinin receptors (BRs) in the spinal cord to promote hyperalgesia through an excitatory effect, which is opposite to the well-known inhibitory effect of opioid receptors. Considering the structural dissimilarity between Dyn A and endogenous BR ligands, bradykinin (BK) and kallidin (KD), this interaction could not be predicted, but it allowed us to discover a potential neuroexcitatory target. Well-known BR ligands, BK, [des-Arg(10), Leu(9)]-kallidin (DALKD), and HOE140 showed different binding profiles at rat brain BRs than that previously reported. These results suggest that neuronal BRs in the rat central nervous system (CNS) may be pharmacologically distinct from those previously defined in non-neuronal tissues. Systematic structure-activity relationship (SAR) study at the rat brain BRs was performed, and as a result, a new key structural feature of Dyn A for BR recognition was identified: amphipathicity. NMR studies of two lead ligands, Dyn A-(4-11) 7 and [des-Arg(7)]-Dyn A-(4-11) 14, which showed the same high binding affinity, confirmed that the Arg residue in position 7, which is known to be crucial for Dyn A's biological activity, is not necessary, and that a type I ß-turn structure at the C-terminal part of both ligands plays an important role in retaining good binding affinities at the BRs. Our lead ligand 14 blocked Dyn A-(2-13) 10-induced hyperalgesic effects and motor impairment in in vivo assays using naïve rats. In a model of peripheral neuropathy, intrathecal (i.th.) administration of ligand 14 reversed thermal hyperalgesia and mechanical hypersensitivity in a dose-dependent manner in nerve-injured rats. Thus, ligand 14 may inhibit abnormal pain states by blocking the neuroexcitatory effects of enhanced levels of Dyn A, which are likely to be mediated by BRs in the spinal cord.

Structure-activity relationships of non-opioid [des-Arg(7)]-dynorphin A analogues for bradykinin receptors.

In our earlier studies, bradykinin receptors (BRs) were identified as a potential target for the neuroexcitatory effects of dynorphin A (Dyn A) in the central nervous system (CNS), and [des-Arg(7)]-Dyn A-(4-11) (6) was discovered as a lead ligand to modulate Dyn A-(2-13) induced neuroexcitatory effects in the CNS as an antagonist. In an effort to gain insights into key structural features of the Dyn A for the BRs, we pursued further structure-activity relationships (SAR) study on the [des-Arg(7)]-Dyn A analogs and confirmed that all of the [des-Arg(7)]-Dyn A analogues showed good binding affinities at the BRs.

Effect of anchoring 4-anilidopiperidines to opioid peptides.

We report here the design, synthesis, and in vitro characterization of new opioid peptides featuring a 4-anilidopiperidine moiety. Despite the fact that the chemical structures of fentanyl surrogates have been found suboptimal per se for the opioid activity, the corresponding conjugates with opioid peptides displayed potent opioid activity. These studies shed an instructive light on the strategies and potential therapeutic values of anchoring the 4-anilidopiperidine scaffold to different classes of opioid peptides.

Truncation of the peptide sequence in bifunctional ligands with mu and delta opioid receptor agonist and neurokinin 1 receptor antagonist activities.

The optimization and truncation of our lead peptide-derived ligand TY005 possessing eight amino-acid residues was performed. Among the synthesized derivatives, NP30 (Tyr(1)-DAla(2)-Gly(3)-Phe(4)-Gly(5)-Trp(6)-O-[3',5'-Bzl(CF3)2]) showed balanced and potent opioid agonist as well as substance P antagonist activities in isolated tissue-based assays, together with significant antinociceptive and antiallodynic activities in vivo.

Dislodgment Resistance, Adhesive Pattern, and Dentinal Tubule Penetration of a Novel Experimental Algin Biopolymer-Incorporated Bioceramic-Based Root Canal Sealer.

The currently available bioceramic-based sealers still demonstrate low bond strength with a poor seal in root canal despite desirable biological properties. Hence, the present study aimed to determine the dislodgment resistance, adhesive pattern, and dentinal tubule penetration of a novel experimental algin-incorporated bioactive glass 58S calcium silicate-based (Bio-G) sealer and compared it with commercialised bioceramic-based sealers. A total of 112 lower premolars were instrumented to size 30. Four groups (n = 16) were assigned for the dislodgment resistance test: control, gutta-percha + Bio-G, gutta-percha + BioRoot RCS, and gutta-percha + iRoot SP, with exclusion of the control group in adhesive pattern and dentinal tubule penetration tests. Obturation was done, and teeth were placed in an incubator to allow sealer setting. For the dentinal tubule penetration test, sealers were mixed with 0.1% of rhodamine B dye. Subsequently, teeth were cut into a 1 mm-thick cross section at 5 mm and 10 mm levels from the root apex, respectively. Push-out bond strength, adhesive pattern, and dentinal tubule penetration tests were performed. Bio-G showed the highest mean push-out bond strength (p < 0.05), while iRoot SP showed the greatest sealer penetration (p < 0.05). Bio-G demonstrated more favourable adhesive patterns. No significant association was noted between dislodgment resistance and dentinal tubule penetration (p > 0.05).

Fabrication and characterisation of novel algin incorporated bioactive-glass 58S calcium-silicate-based root canal sealer.

Background/purpose: The usage of bioceramic-based root canal sealers has escalated over the years due to their excellent properties. The present study aimed to fabricate a novel algin incorporated bioactive glass 58S calcium-silicate (Bio-G) sealer and characterise its surface microstructure and chemical compositions in comparison to commercially available bioceramic sealers (BioRoot RCS and iRoot SP). Materials and methods: The powder form of experimental Bio-G sealer consisted of synthesised BG 58S particle, calcium silicate, zirconia dioxide, calcium carbonate and alginic acid powder as binder. The liquid composed of 5% calcium chloride solution. Five standardised disc specimens were prepared for each sealer group according to the manufacturer's instructions. Subsequently, sealer disc-specimens were placed in an incubator at 37 °C, 95% relative humidity for 72 h to allow setting prior to testing under scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Fourier transformed infrared spectroscopy (FTIR) and X-ray diffraction (XRD). Results: Experimental Bio-G sealer revealed irregular micro-sized particles ranging from 0.5 µm to 105 µm aggregated in clusters comparable to those of BioRoot RCS and iRoot SP. EDS microanalysis showed that Bio-G had high content of oxygen, silicon, and calcium, with the presence of aluminium and chloride similar to BioRoot RCS. Meanwhile, the FTIR and XRD findings suggested that all sealers predominantly contained calcium silicate hydrate, calcium carbonate, and zirconium dioxide, while calcium aluminium silicate oxide was detected in Bio-G. Conclusion: The present novel Bio-G sealer demonstrated desirable particle size distribution and acceptable degree of purity. Future studies are warranted to explore its properties and clinical application.

Triptan-induced latent sensitization: a possible basis for medication overuse headache.

OBJECTIVE: Identification of the neural mechanisms underlying medication overuse headache resulting from triptans. METHODS: Triptans were administered systemically to rats by repeated intermittent injections or by continuous infusion over 6 days. Periorbital and hind paw sensory thresholds were measured to detect cutaneous allodynia. Immunofluorescent histochemistry was employed to detect changes in peptidic neurotransmitter expression in identified dural afferents. Enzyme-linked immunoabsorbent assay was used to measure calcitonin gene-related peptide (CGRP) levels in blood. RESULTS: Sustained or repeated administration of triptans to rats elicited time-dependent and reversible cutaneous tactile allodynia that was maintained throughout and transiently after drug delivery. Triptan administration increased labeling for CGRP in identified trigeminal dural afferents that persisted long after discontinuation of triptan exposure. Two weeks after triptan exposure, when sensory thresholds returned to baseline levels, rats showed enhanced cutaneous allodynia and increased CGRP in the blood following challenge with a nitric oxide donor. Triptan treatment thus induces a state of latent sensitization characterized by persistent pronociceptive neural adaptations in dural afferents and enhanced responses to an established trigger of migraine headache in humans. INTERPRETATION: Triptans represent the treatment of choice for moderate and severe migraine headaches. However, triptan overuse can lead to an increased frequency of migraine headache. Overuse of these medications could induce neural adaptations that result in a state of latent sensitization, which might increase sensitivity to migraine triggers. The latent sensitization could provide a mechanistic basis for the transformation of migraine to medication overuse headache.

New potent biphalin analogues containing p-fluoro-L-phenylalanine at the 4,4' positions and non-hydrazine linkers.

We report the synthesis and the biological evaluation of two new analogues of the potent dimeric opioid peptide biphalin. The performed modification is based on the replacement of two key structural elements of the native biphalin, namely: the hydrazine bridge which joins the two palindromic moieties and the phenylalanine residues at the 4,4' positions of the backbone. The new analogues 9 and 10 contain 1,2-phenylenediamine and piperazine, respectively, in place of the hydrazidic linker and p-fluoro-L-phenylalanine residues at 4 and 4' positions. Binding values are: Kµ(i)=0.51 nM and Kδ(i)=12.8 nM for compound 9, Kµ(i)=0.09 nM and Kδ(i)=0.11 nM for analogue 10.

Synthesis and biological evaluation of new opioid agonist and neurokinin-1 antagonist bivalent ligands.

Newly designed bivalent ligands-opioid agonist/NK1-antagonists have been synthesized. The synthesis of new starting materials-carboxy-derivatives of Fentanyl (1a-1c) was developed. These products have been transformed to 'isoimidium perchlorates' (2a-c). The new isoimidium perchlorates have been successfully implemented in nucleophilic addition reactions, with l-tryptophan 3,5-bis(trifluoromethyl)benzyl ester to give the target compounds-amides (3a-c). Perchlorates (2a-c) successfully undergo reactions with other nucleophiles such as alcohols, amines or hydrazines. The obtained compound 3b exhibited µ-opioid agonist activity and NK1-antagonist activity and may serve as a useful lead compound for the further design of a new series of opioid agonist/NK1-antagonist compounds.

Multiple actions of systemic artemin in experimental neuropathy.

The clinical management of neuropathic pain is particularly challenging. Current therapies for neuropathic pain modulate nerve impulse propagation or synaptic transmission; these therapies are of limited benefit and have undesirable side effects. Injuries to peripheral nerves result in a host of pathophysiological changes associated with the sustained expression of abnormal pain. Here we show that systemic, intermittent administration of artemin produces dose- and time-related reversal of nerve injury-induced pain behavior, together with partial to complete normalization of multiple morphological and neurochemical features of the injury state. These effects of artemin were sustained for at least 28 days. Higher doses of artemin than those completely reversing experimental neuropathic pain did not elicit sensory or motor abnormalities. Our results indicate that the behavioral symptoms of neuropathic pain states can be treated successfully, and that partial to complete reversal of associated morphological and neurochemical changes is achievable with artemin.