Structure-activity relationships of the ultrapotent vanilloid resiniferatoxin (RTX): The side chain benzylic methylene

Use of ISSR markers to assess the genetic diversity of an endemic plant of Morocco (Euphorbia resinifera O. Berg)

BACKGROUND

Euphorbia resinifera is a melliferous, medicinal, and endemic plant to Morocco. Nevertheless, its ecological and genetic diversity still unknown. The objective of this study is to analyze the diversity and genetic structure of Moroccan wild populations of E. resinifera using ISSR markers. Twelve natural populations collected from its geographical range in Morocco were analyzed using 14 ISSR primers.

RESULTS

A total of 125 bands were obtained, with polymorphism of 74.81%. The polymorphic information content (PIC), resolving power (Rp), Shannon's information index (I), and total genetic diversity (Ht) were 0.33, 2.8, 0.35, and 0.21, respectively. The analysis of molecular variance showed that 75.56% of the total variability is present within populations and that 24.44% exists among populations. Also, the analysis showed a very low genetic differentiation between groups of mountain range type (FCT = 0.066), mountain versant type groups (FCT =  -0.024), and altitude groups (FCT =  -0.022). Moreover, the geographical distances between populations are correlated with their corresponding genetic distances according to the Mantel test (r = 0.507; P < 0.0001).

CONCLUSION

These results suggest that the population structuring follows a model of isolation by geographical distance. Indeed, the genetic structuring of populations into two groups obtained from PCoA and structure analysis revealed a dependence on the geographical origin of the populations. By contrast, the genetic distances are not correlated with the altitude.

Phenotypic diversity of natural populations of an endemic Moroccan plant (Euphorbia resinifera O. Berg)

The Euphorbia resinifera is melliferous and medicinal plant and one of the endemic species of Moroccan Atlas Mountains. It is very well known for its honey of high nutritional and therapeutic quality. The objective of our study is to characterize and evaluate the phenotypic variation of this spontaneous species. Seventeen qualitative and quantitative morphological characters related to the bush, stem, spine, flower, and fruit of the plant were used to assess the morphological variability of twelve natural populations collected from its geographical range in Morocco. The results of the analysis of variance showed significant differences between the studied populations for the most examined traits reflecting the existence of a high phenotypic variability within this species. The principal component analysis showed that E. resinifera populations were clustered in three distinct groups not related to mountain range type. The results highlight a high phenotypic diversity within studied populations of this species in Morocco. This work aims to study the phenotypic variability of E. resinifera to delineate conservation strategies and also to establish forms of rational economic exploitation.

Expression of functional TRPV1 receptor in primary culture of canine keratinocytes

The interest for the endovanilloid system and for transient receptor potential vanilloid 1 (TRPV1) is continuously increasing, due to their involvement in inflammation, nociception and pruritus. Even if TRPV1 enrolment was highlighted in both physiological and pathological conditions, some aspects remain unclear, mostly in veterinary medicine. This study aimed to verify the expression and functionality of TRPV1 in canine keratinocytes to investigate in vitro the role of TRPV1 in these cells that are involved in different cutaneous pathologies. Keratinocytes primary cultures were isolated from bioptical samples and cultivated. Binding assay (using ³ [H]-resiniferatoxin), displacement assay (in the presence of 1.2 nM ³ [H]-resiniferatoxin) and functional assays (in the presence of 1 μCi/⁴⁵ Ca²⁺ ) with vanilloid agonists and antagonists, specifically addressed to TRPV1 receptor, were performed. Binding assay demonstrated the presence of measurable concentrations of TRPV1 (B_max  = 1,240 ± 120 fmol/mg protein; K_d  = 0.01 ± 0.004 nM). Displacement assay highlighted the highest affinity for resiniferatoxin (RTX) and 5-iodo-resiniferatoxin (5-I-RTX), among agonists and antagonists, respectively. The same compounds results as the most potent in the functional assays. This study demonstrated the identification and the characterization of TRPV1 receptor in primary canine keratinocytes cultures. The results are promising for a clinical use, but further in vivo investigations are required.

Molecular Surgery Concept from Bench to Bedside: A Focus on TRPV1+ Pain-Sensing Neurons

"Molecular neurosurgery" is emerging as a new medical concept, and is the combination of two partners: (i) a molecular neurosurgery agent, and (ii) the cognate receptor whose activation results in the selective elimination of a specific subset of neurons in which this receptor is endogenously expressed. In general, a molecular surgery agent is a selective and potent ligand, and the target is a specific cell type whose elimination is desired through the molecular surgery procedure. These target cells have the highest innate sensitivity to the molecular surgery agent usually due to the highest receptor density being in their plasma membrane. The interaction between the ligand and its receptor evokes an overactivity of the receptor. If the receptor is a ligand-activated non-selective cation channel, the overactivity of receptor leads to excess Ca²⁺ and Na⁺ influx into the cell and finally cell death. One of the best known examples of such an interaction is the effect of ultrapotent vanilloids on TRPV1-expressing pain-sensing neurons. One intrathecal resiniferatoxin (RTX) dose allows for the receptor-mediated removal of TRPV1+ neurons from the peripheral nervous system. The TRPV1 receptor-mediated ion influx induces necrotic processes, but only in pain-sensing neurons, and usually within an hour. Besides that, target-specific apoptotic processes are also induced. Thus, as a nano-surgery scalpel, RTX removes the neurons responsible for generating pain and inflammation from the peripheral nervous system providing an option in clinical management for the treatment of morphine-insensitive pain conditions. In the future, the molecular surgery concept can also be exploited in cancer research for selectively targeting the specific tumor cell.

The carbonate analogues of 5'-halogenated resiniferatoxin as TRPV1 ligands

A series of carbonate analogues of 5'-halogenated RTX have been investigated in order to examine the effect of the carbonate group as a linker and the role of halogens in the reversal of activity from agonism to antagonism for rat and human TRPV1 heterologously expressed in Chinese hamster ovary cells. The carbonate analogues showed similar activities to the corresponding RTX derivatives in rat TRPV1 but lower potency in human TRPV1. 5-Halogenation converted the agonists to partial agonists or full antagonists and the extent of antagonism reflected the order of I>Br>Cl>F, with a somewhat greater extent of antagonism for the derivatives of the 4-amino RTX surrogates compared to the corresponding derivatives of RTX itself. The carbonate analogues of I-RTX (60) and 5-bromo-4-amino-RTX (66) were potent and full antagonists with Ki(ant)=2.23 and 2.46 nM, respectively, for rat TRPV1, which were ca. 5-fold more potent than I-RTX (2) under our conditions. The conformational analysis of the I-RTX-carbonate (60) indicated that its bent conformation was similar to that of I-RTX, consistent with compound 60 and I-RTX showing comparable potent antagonism.

Zorrimidazolone, a bioactive alkaloid from the non-indigenous mediterranean stolidobranch Polyandrocarpa zorritensis

Chemical analysis of the Mediterranean ascidian Polyandrocarpa zorritensis (Van Name 1931) resulted in the isolation of a series of molecules including two monoindole alkaloids, 3-indolylglyoxylic acid (3) and its methyl ester (4), 4-hydroxy-3-methoxyphenylglyoxylic acid methyl ester (1) and a new alkaloid we named zorrimidazolone (2). The structure of the novel compound 2 has been elucidated by spectroscopic analysis and bioactivity of all compounds has been investigated. Zorrimidazolone (2) showed a modest cytotoxic activity against C6 rat glioma cell line.

Receptor activity and conformational analysis of 5'-halogenated resiniferatoxin analogs as TRPV1 ligands

A series of 5'-halogenated resiniferatoxin analogs have been investigated in order to examine the effect of halogenation in the A-region on their binding and the functional pattern of agonism/antagonism for rat TRPV1 heterologously expressed in Chinese hamster ovary cells. Halogenation at the 5-position in the A-region of RTX and of 4-amino RTX shifted the agonism of parent compounds toward antagonism. The extent of antagonism was greater as the size of the halogen increased (I > Br > Cl > F) while the binding affinities were similar, as previously observed for our potent agonists. In this series, 5-bromo-4-amino RTX (39) showed very potent antagonism with K(i) (ant) = 2.81 nM, which was thus 4.5-fold more potent than 5'-iodo RTX, previously reported as a potent TRPV1 antagonist. Molecular modeling analyses with selected agonists and the corresponding halogenated antagonists revealed a striking conformational difference. The 3-methoxy of the A-region in the agonists remained free to interact with the receptor whereas in the case of the antagonists, the compounds assumed a bent conformation, permitting the 3-methoxy to instead form an internal hydrogen bond with the C4-hydroxyl of the diterpene.