Effects of philanthotoxin-343 on CA1 pyramidal neurons of rat hippocampus in vitro

Neuroprotection Against NMDA-Induced Retinal Damage by Philanthotoxin-343 Involves Reduced Nitrosative Stress

N-methyl-D-aspartate receptor (NMDAR) overstimulation is known to mediate neurodegeneration, and hence represents a relevant therapeutic target for neurodegenerative disorders including glaucoma. This study examined the neuroprotective effects of philanthotoxin (PhTX)-343 against NMDA-induced retinal injury in rats. Male Sprague Dawley rats were divided into three groups; group 1 received phosphate buffer saline as the negative control, group 2 was injected with NMDA (160 nM) to induce retinal excitotoxic injury, and group 3 was pre-treated with PhTX-343 (160 nM) 24 h before NMDA exposure. All treatments were given intravitreally and bilaterally. Seven days post-treatment, rats were subjected to visual behaviour assessments using open field and colour recognition tests. Rats were then euthanized, and the retinas were harvested and subjected to haematoxylin and eosin (H&E) staining for morphometric analysis and 3-nitrotyrosine (3-NT) ELISA protocol as the nitrosative stress biomarker. PhTX-343 treatment prior to NMDA exposure improved the ability of rats to recognize visual cues and preserved visual functions (i.e., recognition of objects with different colours). Morphological examination of retinal tissues showed that the fractional ganglion cell layer thickness within the inner retina (IR) in the PhTX-343 treated group was greater by 1.28-fold as compared to NMDA-treated rats (p < 0.05) and was comparable to control rats (p > 0.05). Additionally, the number of retinal cell nuclei/100 μm² in IR for the PhTX-343-treated group was greater by 1.82-fold compared to NMDA-treated rats (p < 0.05) and was comparable to control group (p > 0.05). PhTX-343 also reduced the retinal 3-NT levels by 1.74-fold compared to NMDA-treated rats (p < 0.05). In conclusion, PhTX-343 pretreatment protects against NMDA-induced retinal morphological changes and visual impairment by suppressing nitrosative stress as reflected by the reduced retinal 3-NT level.

Synthesis and Biological Activities of Naturally Functionalized Polyamines: An Overview

Recently, extensive researches have emphasized the fact that polyamine conjugates are becoming important in all biological and medicinal fields. In this review, we will focus our attention on natural polyamines and highlight recent progress in both fundamental mechanism studies and interests in the development and application for the therapeutic use of polyamine derivatives.

Long-term potentiation in the presence of NMDA receptor antagonist arylalkylamine spider toxins

The role of the NMDA receptor (NMDAR) in long-term potentiation (LTP) is now well established. All potent NMDAR antagonists known to date inhibit the induction of LTP at the Schaffer collateral-CA1 pyramidal cell synapse in rat hippocampus, regardless of their site and mechanism of action. Arylalkylamine toxins are noncompetitive NMDAR antagonists in the mammalian central nervous system (CNS). The synthetic toxins argiotoxin-636 (Arg-636), Joro spider toxin (JSTX-3), alpha-agatoxin-489 and -505 (Agel-489 and Agel-505) and philanthotoxin-433 (delta-PhTX) were found in the present study to have no effect on the induction of LTP in the Schaffer collateral-CA1 pyramidal cell pathway in rat hippocampal slices maintained in vitro. Arylalkylamine toxins represent a class of potent NMDAR antagonists that fail to affect hippocampal LTP, and thus provide novel structural leads for the development of NMDAR antagonists that do not impair cognition.

Multiple actions of arylalkylamine arthropod toxins on the N-methyl-D-aspartate receptor

The effects of the arylalkyamine arthropod toxins argiotoxin 636 and philanthotoxin 343 were studied on N-methyl-D-aspartate receptor currents in cultured rat hippocampal neurons using whole-cell recording techniques. Argiotoxin 636 and philanthotoxin 343 blocked 10 microM N-methyl-D-aspartate (+10 microM glycine) currents in a concentration-dependent fashion (steady-state IC50 values, 0.9 and 56 microM, respectively). The onset and recovery from argiotoxin 636 block occurred slowly (forward and reverse rate constants, 7.5 x 10(3) s-1 M-1 and 6.9 x 10(-3) s-1, respectively) whereas the philanthotoxin 343 block was more rapid (forward and reverse rate constants, 1.1 x 10(5) s-1 M-1 and 0.1 s-1). A portion, but not all, of the block by the two toxins could be reversed by depolarization to positive holding potentials, indicating that there are voltage-dependent and non-voltage-dependent components of the block. The long-lasting argiotoxin 636 block at -60 mV occurred in a use-dependent fashion and could be substantially reduced by co-application with 10 mM Mg2+, providing evidence that the toxin has a channel blocking action. In contrast to the use dependence of the voltage-dependent argiotoxin 636 block, the non-voltage-dependent component of block (at +60 mV) did not require agonist gating of the channel. The non-voltage-dependent block by argiotoxin 636 was unaffected by increasing the glycine concentration, but was reversed by increasing the N-methyl-D-aspartate concentration, suggesting that the toxin may act as a competitive antagonist at the N-methyl-D-aspartate recognition site. This mechanism was further supported by the near identity of the time constant for argiotoxin 636 block with the time constant for agonist dissociation, irrespective of whether the rapidly dissociating agonist N-methyl-D-aspartate or the more slowly dissociating agonist glutamate was used. With high concentrations of N-methyl-D-aspartate (> or = 100 microM), argiotoxin 636 produced a potentiation of the peak N-methyl-D-aspartate response (at +60 mV) that was accompanied by a slowing in the rate of current desensitization and an increase in the affinity for glycine. We conclude that the arylalkylamine toxins antagonize N-methyl-D-aspartate receptor currents by two distinct mechanisms: use-dependent and voltage-dependent open channel block and competitive antagonism at the N-methyl-D-aspartate recognition site. In addition, argiotoxin 636 exerts a polyamine-like facilitation of N-methyl-D-aspartate receptor currents. This facilitation occurs via both the glycine-dependent and glycine-independent mechanisms, whereby spermine is known to potentiate N-methyl-D-aspartate receptor responses.