Hippocampal cholinergic receptors and the mTOR participation in fear-motivated inhibitory avoidance extinction memory

Evidence has demonstrated the hippocampal cholinergic system and the mammalian target of rapamycin (mTOR) participation during the memory formation of aversive events. This study assessed the role of these systems in the hippocampus for the extinction memory process by submitting male Wistar rats to fear-motivated step-down inhibitory avoidance (IA). The post-extinction session administration of the nicotinic and muscarinic cholinergic receptor antagonists, mecamylamine and scopolamine, respectively, both at doses of 2 µg/µl/side, and rapamycin, an mTOR inhibitor (0.02 µg/µl/side), into the CA1 region of the dorsal hippocampus, impaired the IA extinction memory. Furthermore, the nicotinic and muscarinic cholinergic receptor agonists, nicotine and muscarine, respectively, had a dose-dependent effect on the IA extinction memory when administered intra-CA1, immediately after the extinction session. Nicotine (0.6 µg/µl/side) and muscarine (0.02 µg/µl/side), respectively, had no effect, while the higher doses (6 and 2 µg/µl/side, respectively) impaired the IA extinction memory. Interestingly, the co-administration of muscarine at the lower dose blocked the impairment that was induced by rapamycin. This effect was not observed when nicotine at the lower dose was co-administered. These results have demonstrated the participation of the cholinergic receptors and mTOR in the hippocampus for IA extinction, and that the cholinergic agonists had a dose-dependent effect on the IA extinction memory. This study provides insights related to the behavioural aspects and the neurobiological properties underlying the early stage of fear-motivated IA extinction memory consolidation and suggests that there is hippocampal muscarinic receptor participation independent of mTOR in this memory process.

Functional interplay between adenosine A2A receptor and NMDA preconditioning in fear memory and glutamate uptake in the mice hippocampus

N-methyl D-aspartate (NMDA) administered at subtoxic dose plays a protective role against neuronal excitotoxicity, a mechanism described as preconditioning. Since the activation of adenosinergic receptors influences the achievement of NMDA preconditioning in the hippocampus, we evaluated the potential functional interplay between adenosine A₁ and A_2A receptors (A₁R and A_2AR) activities and NMDA preconditioning. Adult male Swiss mice received saline (NaCl 0.9 g%, i.p.) or a nonconvulsant dose of NMDA (75 mg/kg, i.p.) and 24 h later they were treated with the one of the ligands: A₁R agonist (CCPA, 0.2 mg/kg, i.p.) or antagonist (DPCPX, 3 mg/kg, i.p.), A_2AR agonist (CGS21680, 0.05 mg/kg, i.p.) or antagonist (ZM241385, 0.1 mg/kg, i.p.) and subjected to contextual fear conditioning task. Binding properties and content of A_2AR and glutamate uptake were assessed in the hippocampus of mice subjected to NMDA preconditioning. Treatment with CGS21680 increased the time of freezing during the exposure of animals to the new environment. NMDA preconditioning did not affect the freezing time of mice per se, but it prevented the response observed after the activation of A_2AR. Furthermore, the activation of A_2AR by CGS21680 after the preconditioning blocked the increase of glutamate uptake induced by NMDA preconditioning. The immunodetection of A_2AR in total hippocampal homogenates showed no significant differences evoked by NMDA preconditioning and did not alter A_2AR maximum binding for the selective ligand [³H]CGS21680. These results demonstrate changes in A_2AR functionality in mice following NMDA preconditioning.

Polyphenol nanoformulations for cancer therapy: experimental evidence and clinical perspective

Cancer is defined as the abnormal cell growth that can cause life-threatening malignancies with high financial costs for patients as well as the health care system. Natural polyphenols have long been used for the prevention and treatment of several disorders due to their antioxidant, anti-inflammatory, cytotoxic, antineoplastic, and immunomodulatory effects discussed in the literature; thus, these phytochemicals are potentially able to act as chemopreventive and chemotherapeutic agents in different types of cancer. One of the problems regarding the use of polyphenolic compounds is their low bioavailability. Different types of formulations have been designed for the improvement of bioavailability of these compounds, nanonization being one of the most notable approaches among them. This study aimed to review current data on the nanoformulations of natural polyphenols as chemopreventive and chemotherapeutic agents and to discuss their molecular anticancer mechanisms of action. Nanoformulations of natural polyphenols as bioactive agents, including resveratrol, curcumin, quercetin, epigallocatechin-3-gallate, chrysin, baicalein, luteolin, honokiol, silibinin, and coumarin derivatives, in a dose-dependent manner, result in better efficacy for the prevention and treatment of cancer. The impact of nanoformulation methods for these natural agents on tumor cells has gained wider attention due to improvement in targeted therapy and bioavailability, as well as enhancement of stability. Today, several nanoformulations are designed for delivery of polyphenolic compounds, including nanosuspensions, solid lipid nanoparticles, liposomes, gold nanoparticles, and polymeric nanoparticles, which have resulted in better antineoplastic activity, higher intracellular concentration of polyphenols, slow and sustained release of the drugs, and improvement of proapoptotic activity against tumor cells. To conclude, natural polyphenols demonstrate remarkable anticancer potential in pharmacotherapy; however, the obstacles in terms of their bioavailability in and toxicity to normal cells, as well as targeted drug delivery to malignant cells, can be overcome using nanoformulation-based technologies, which optimize the bioefficacy of these natural drugs.

Antiproliferative effect of extracts and pyranonaphthoquinones obtained from Cipura paludosa bulbs

CONTEXT

Cipura paludosa Aubl. (Iridaceae) is widely used in folk medicine to treat several ailments. Experimental studies have confirmed its anti-inflammatory, antinociceptive, and neuroprotective effects.

OBJECTIVE

This study evaluates the possible antiproliferative potential of the crude methanol extract and three isolated compounds from the bulbs of C. paludosa.

MATERIALS AND METHODS

Phytochemical analysis was carried out by conventional chromatographic techniques, and the resulting compounds were identified by NMR (1)H and (13)C. The antiproliferative activity was analysed using the sulforhodamine B assay.

RESULTS

Crude methanol extract of C. paludosa bulbs showed GI50 values of between 1.6 and 30.8 μg/mL. The naphthoquinone derivatives (eleutherine, isoeleutherine, and eleutherol) isolated from the bulbs of C. paludosa exhibited promising cytotoxicity against several human tumour cell lines, especially the two main compounds, eleutherine and isoeleutherine, against glioma and breast cancer cell lines, with TGI values of between 2.6 and 13.8 μg/mL.

CONCLUSION

Cipura paludosa bulbs produce active principles with relevant antiproliferative potential, such as naphthoquinone derivatives, identified as eleutherine, isoeleutherine, and eleutherol. This is the first report indicating C. paludosa with antiproliferative potential.

Antifungal Activity of Pyranonaphthoquinones Obtained from Cipura paludosa Bulbs

Previous studies with the bulbs of Cipura paludosa (Iridaceae) showed the presence of pyranonaphthoquinones, including eleutherine, isoeleutherine and eleutherol. The aim of this study was to evaluate the antifungal properties of these compounds. The activity was tested against the clinically relevant yeasts Candida albicans, C. tropicalis, Saccharomyces cerevisiae and Cryptococcus neoformans with the microbroth dilution method, following the guidelines of CLSI. Eleutherine, isoeleutherine and eleutherol all presented significant antifungal activity, especially the first two, the major components, with MIC values between 7.8 and 250 μg/mL. In conclusion, these results demonstrate that C. paludosa bulbs produce active principles with relevant antifungal potential, contributing, at least in part, to the antimicrobial effect evidenced for this plant and justifying its popular use against infections.