RNA based antagonist of NMDA receptors

Nucleic Acid Aptamers for Molecular Therapy of Epilepsy and Blood-Brain Barrier Damages

Epilepsy is the fourth most prevalent brain disorder affecting millions of people of all ages. Epilepsy is divided into six categories different in etiology and molecular mechanisms; however, their common denominator is the inability to maintain ionic homeostasis. Antiepileptic drugs have a broad spectrum of action and high toxicity to the whole organism. In many cases, they could not penetrate the blood-brain barrier (BBB) and reach corresponding targets. Nucleic acid aptamers are a new and promising class of antiepileptic drugs as they are non-toxic, specific, and able to regulate the permeability of ion channels or inhibit inflammatory proteins. In this review, we summarize the mechanisms of epileptogenesis and its interconnection with the BBB and show the potential of aptamers for antiepileptic treatment.

Chemical methods for the modification of RNA

RNA is often considered as being the vector for the transmission of genetic information from DNA to the protein synthesis machinery. However, besides translation RNA participates in a broad variety of fundamental biological roles such as gene expression and regulation, protein synthesis, and even catalysis of chemical reactions. This variety of function combined with intricate three-dimensional structures and the discovery of over 100 chemical modifications in natural RNAs require chemical methods for the modification of RNAs in order to investigate their mechanism, location, and exact biological roles. In addition, numerous RNA-based tools such as ribozymes, aptamers, or therapeutic oligonucleotides require the presence of additional chemical functionalities to strengthen the nucleosidic backbone against degradation or enhance the desired catalytic or binding properties. Herein, the two main methods for the chemical modification of RNA are presented: solid-phase synthesis using phosphoramidite precursors and the enzymatic polymerization of nucleoside triphosphates. The different synthetic and biochemical steps required for each method are carefully described and recent examples of practical applications based on these two methods are discussed.

Chemically Modified, α-Amino-3-hydroxy-5-methyl-4-isoxazole (AMPA) Receptor RNA Aptamers Designed for in Vivo Use

Glutamate ion channels have three subtypes, that is, α-amino-3-hydroxy-5-methyl-4-isoxazole (AMPA), kainate, and N-methyl-d-aspartate (NMDA) receptors. Excessive activity of these receptor subtypes either individually or collectively is involved in various neurological disorders. RNA aptamers as antagonists of these receptors are potential therapeutics. For developing aptamer therapeutics, the RNA aptamers must be chemically modified to become ribonuclease-resistant or stable in biological fluids. Using systematic evolution of ligands by exponential enrichment (SELEX) and a chemically modified library, prepared enzymatically (i.e., the library contains RNAs with 2'-fluoro modified nucleoside triphosphates or ATPs, CTPs and UTPs, but regular GTPs), we have isolated an aptamer. The short aptamer (69 nucleotides) FN1040s selectively inhibits the GluA1 and GluA2Q_flip AMPA receptor subunits, whereas the full-length aptamer (101 nucleotides) FN1040 additionally inhibits GluK1, but not GluK2, kainate receptor, and GluN1a/2A and GluN1a/2B, the two major native NMDA receptors. The two aptamers show similar potency (2-4 μM) and are stable with a half-life of at least 2 days in serum-containing medium or cerebrospinal fluid. Therefore, these two aptamers are amenable for in vivo use.

Conformationally selective RNA aptamers allosterically modulate the β2-adrenoceptor

G-protein-coupled receptor (GPCR) ligands function by stabilizing multiple, functionally distinct receptor conformations. This property underlies the ability of 'biased agonists' to activate specific subsets of a given receptor's signaling profile. However, stabilizing distinct active GPCR conformations to enable structural characterization of mechanisms underlying GPCR activation remains difficult. These challenges have accentuated the need for receptor tools that allosterically stabilize and regulate receptor function through unique, previously unappreciated mechanisms. Here, using a highly diverse RNA library combined with advanced selection strategies involving state-of-the-art next-generation sequencing and bioinformatics analyses, we identify RNA aptamers that bind a prototypical GPCR, the β2-adrenoceptor (β2AR). Using biochemical, pharmacological, and biophysical approaches, we demonstrate that these aptamers bind with nanomolar affinity at defined surfaces of the receptor, allosterically stabilizing active, inactive, and ligand-specific receptor conformations. The discovery of RNA aptamers as allosteric GPCR modulators significantly expands the diversity of ligands available to study the structural and functional regulation of GPCRs.

Neuroprotective Effects of Pregabalin on Cerebral Ischemia and Reperfusion

BACKGROUND

Stroke is one of the most common causes of death and the leading cause of disability in adults. Cerebral ischemia/reperfusion injury causes cerebral edema, hemorrhage, and neuronal death.

AIMS

In post-ischemic reperfusion, free radical production causes brain tissue damage by oxidative stress. Pregabalin, an antiepileptic agent was shown to have antioxidant effects. The aim of this study was to evaluate the neuroprotective and antioxidant effects of pregabalin on ischemia and reperfusion in rat brain injury.

STUDY DESIGN

Animal experimentation.

METHODS

Male Wistar rats weighing (250-300 g) were randomly divided into six groups, each consisting of 6 rats: control (C), pregabalin (P), ischemia (I), pregabalin + ischemia (PI), ischemia + reperfusion (IR) and ischemia + reperfusion + pregabalin (PIR). Rats were initially pre-treated with 50 mg/kg/d pregabalin orally for two days. Then, animals that applied ischemia in I, PI, IR and PIR groups were exposed to carotid clamping for 30 minutes and 20 minutes reperfusion was performed in the relevant reperfusion groups.

RESULTS

NR2B receptor levels were significantly lower in the PIR group in comparison to the IR group. In the PIR group, Thiobarbituric acid reactive substance (TBARS) level had statistically significant decrease compared with IR group. Glutathione peroxidase (GSH-PX) levels were also significantly increased in the PIR group compared with I, IR and control groups. In the PI and PIR groups, catalase (CAT) levels were also significantly increased compared with I and IR groups (p=0.03 and p=0.07, respectively).

CONCLUSION

Pregabalin may protect the damage of oxidative stress after ischemia + reperfusion. This result would illuminate clinical studies in the future.

Generation of Aptamers with an Expanded Chemical Repertoire

The enzymatic co-polymerization of modified nucleoside triphosphates (dN*TPs and N*TPs) is a versatile method for the expansion and exploration of expanded chemical space in SELEX and related combinatorial methods of in vitro selection. This strategy can be exploited to generate aptamers with improved or hitherto unknown properties. In this review, we discuss the nature of the functionalities appended to nucleoside triphosphates and their impact on selection experiments. The properties of the resulting modified aptamers will be described, particularly those integrated in the fields of biomolecular diagnostics, therapeutics, and in the expansion of genetic systems (XNAs).