Delayed administration of the nucleic acid analog 2Cl-C.OXT-A attenuates brain damage and enhances functional recovery after ischemic stroke

Raman Spectroscopic and DFT Study of COA-Cl and Its Analogues

COA-Cl is a newly synthesized adenosine analogue that exhibits various physiological activities. Its angiogenic, neurotropic, and neuroprotective potencies make it promising for the development of medicines. In this study, we show Raman spectroscopic study of COA-Cl to elucidate molecular vibrations and related chemical properties. Density functional theory calculations were combined with the Raman spectroscopic data to understand the details of each vibrational mode. Comparative analysis with adenine, adenosine, and other nucleic acid analogues enabled identification of unique Raman peaks originating from the cyclobutane moiety and chloro group of COA-Cl. This study provides fundamental knowledge and crucial insights for further development of COA-Cl and related chemical species.

COA-Cl Evokes Protective Responses Against H2O2-and 6-OHDA-Induced Toxic Injury in PC12 Cells

COA-Cl, a novel adenosine-like nucleic acid analog, has recently been shown to exert neuroprotective effects and to increase dopamine levels both in vivo and in vitro. Therefore, we hypothesized that COA-Cl could protect dopaminergic neurons against toxic insults. Thus, the present study aimed to investigate the protective effects of COA-Cl against hydrogen peroxide (H₂O₂)- and 6-hydroxydopamine (6-OHDA)-induced toxicity in PC12 cells and to elucidate the possible mechanisms. PC12 cells were incubated with COA-Cl (100 μM) with or without H₂O₂ or 6-OHDA (200 μM) for 24 h. Treatment with COA-Cl attenuated the decrease in cell viability, SOD activity and the Bcl-2/Bax ratio caused by H₂O₂. In addition, COA-Cl attenuated the increase in LDH release, ROS production, caspase-3 activity, and apoptosis induced by H₂O₂. Further, COA-Cl enhanced the protection of PC12 cells against the toxicity caused by 6-OHDA, as evidenced by an increase in cell viability and the Bcl-2/Bax ratio, and a decrease in LDH release. Our results are the first to demonstrate that COA-Cl potentially protects PC12 cells against toxicity induced by H₂O₂ and 6-OHDA, implying that COA-Cl could be a promising neuroprotective agent for the treatment of Parkinson's disease.

The protective effect and mechanism of COA-Cl in acute phase after spinal cord injury

Spinal cord injury (SCI) induces severe motor and sensory dysfunction. We previously showed the neuroprotective effects of COA-Cl, a novel synthesized adenosine analog, in a rat stroke model. In this study, we evaluated the neuroprotective effects of COA-Cl in acute phase of SCI. SCI was induced in rats at the T9 vertebra by using a drop device. Rats were divided into acute and subacute groups. A 5-day dose of 6 mg/kg COA-Cl in saline was given to the acute group immediately after SCI and the subacute group 4 days after SCI. Motor function assessed by Basso-Beattie-Bresnahan scoring and inclined plane test improved significantly in the acute group while the subacute group did not. Histological evaluation and TUNEL staining revealed that both the cavity volume and apoptosis were significantly decreased in the acute group compared with the subacute group. In addition, pERK/ERK was increased in the acute group 7 days after SCI. These results suggest that COA-Cl exerts neuroprotective effects via the ERK pathway when administered in the acute phase after SCI, resulting in the recovery of motor function. COA-Cl could be a novel therapeutic agent for the acute phase of SCI.

Delayed administration of suramin attenuates peritoneal fibrosis in rats

BACKGROUND

Peritoneal fibrosis is the most common complication of peritoneal dialysis, but there is currently no effective treatment. We previously reported that suramin pretreatment prevents the development of peritoneal fibrosis in a rat model of peritoneal fibrosis induced by chlorhexidine gluconate (CG). Here, we further examined the effectiveness of delayed administration of suramin on peritoneal fibrosis and the mechanism (s) involved in this process.

METHODS

In the rat model of peritoneal fibrosis induced by CG, suramin or saline was administered at day 21 and 28. All rats were then sacrificed to collect peritoneal tissues for Western blot analysis and histological staining at day 35.

RESULTS

Our results demonstrated that delayed administration of suramin starting at 21 days following CG injection can ameliorate peritoneal damage, with greater efficacy after two injections. Suramin also reduced the expression of α-smooth muscle actin, Collagen 1, and Fibronectin and suppressed phosphorylation of Smad-3, epidermal growth factor receptor (EGFR), signal transducers, activator of transcription 3 (STAT3) as well as extracellular signal-regulated kinases 1/2 (ERK 1/2) in the peritoneum injured with CG. Moreover, delayed administration of suramin inhibited overproduction of transforming growth factor-β1(TGF-β1) and expression of several pro-inflammatory cytokines, including monocyte chemoattractant protein-1, tumor necrosis factor-α, interleukin-1, and interleukin-6.

CONCLUSIONS

Our results indicated that suramin can attenuate progression of peritoneal fibrosis by a mechanism involving inhibition of the TGF-β1/Smad3 and EGFR signaling pathways as well as suppression of multiple proinflammatory cytokines. Thus, suramin may have the potential to offer an effective treatment for peritoneal fibrosis.

COA-Cl induces dopamine release and tyrosine hydroxylase phosphorylation: In vivo reverse microdialysis and in vitro analysis

We found that local perfusion of COA-Cl (0.1, 0.4, or 1.0 mM) into the dorsal striatum of living mice produced a significant and dose-dependent increase in extracellular DA levels, with the highest dose of 1.0 mM COA-Cl producing an approximately 5-fold increase in DA. Consistent with in vivo findings, 0.1 and 0.2 mM COA-Cl significantly and dose-dependently enhanced DA release 3.0 to 5.0-fold in PC12 cells, an in vitro model of DA-responsive neurons. Interestingly, the increase in striatal DA levels by COA-Cl in vivo was similar in magnitude to that observed in PC12 cells. Treatment with 0.1 mM COA-Cl significantly increased both Ser31 and Ser40 phosphorylation of tyrosine hydroxylase (TH) in PC12 cells, and Ser40 phosphorylation in iCell neurons, without altering total TH protein levels. Further, we examined whether COA-Cl could stimulate neurite outgrowth in PC12 cells and iCell neurons and found that COA-Cl significantly induced neurite outgrowth in both cell lines. Our results provide the first evidence that COA-Cl can stimulate dose-dependent DA release and activation of TH phosphorylation, suggesting that COA-Cl may be a promising therapeutic candidate for the treatment of neurological dysfunction associated with low DA.

COA-Cl (2-Cl-C.OXT-A) can promote coronary collateral development following acute myocardial infarction in mice

2-Cl-C.OXT-A (COA-Cl) is a novel nucleic acid analogue that promotes tube-forming activity of human umbilical vein endothelial cells (HUVEC) through vascular endothelial growth factor (VEGF). The development of coronary collateral circulation is critical to rescue the ischemic myocardium and to prevent subsequent irreversible ischemic injury. We evaluated whether COA-Cl can promote angiogenesis in ischemic tissue, reduce infarct size and preserve cardiac contractility in vivo. Mice received COA-Cl or placebo daily for three days after myocardial infarction (MI) by coronary ligation. The degree of angiogenesis in ischemic myocardium was assessed by staining endothelial cells and vascular smooth muscle cells, and measuring infarct size/area-at-risk. In mice treated with COA-Cl, enhanced angiogenesis and smaller infarct size were recognized, even given a similar area at risk. We observed increases in the protein expression levels of VEGF and in the protein phosphorylation level of eNOS. In addition, the heart weight to body weight ratio and myocardial fibrosis in COA-Cl mice were decreased on Day 7. Administration of COA-Cl after MI promotes angiogenesis, which is associated with reduced infarct size and attenuated cardiac remodeling. This may help to prevent heart failure due to cardiac dysfunction after MI.

The Role of Endogenous Neurogenesis in Functional Recovery and Motor Map Reorganization Induced by Rehabilitative Therapy after Stroke in Rats

BACKGROUND AND OBJECTIVE

Endogenous neurogenesis is associated with functional recovery after stroke, but the roles it plays in such recovery processes are unknown. This study aims to clarify the roles of endogenous neurogenesis in functional recovery and motor map reorganization induced by rehabilitative therapy after stroke by using a rat model of cerebral ischemia (CI).

METHODS

Ischemia was induced via photothrombosis in the caudal forelimb area of the rat cortex. First, we examined the effect of rehabilitative therapy on functional recovery and motor map reorganization, using the skilled forelimb reaching test and intracortical microstimulation. Next, using the same approaches, we examined how motor map reorganization changed when endogenous neurogenesis after stroke was inhibited by cytosine-β-d-arabinofuranoside (Ara-C).

RESULTS

Rehabilitative therapy for 4 weeks after the induction of stroke significantly improved functional recovery and expanded the rostral forelimb area (RFA). Intraventricular Ara-C administration for 4-10 days after stroke significantly suppressed endogenous neurogenesis compared to vehicle, but did not appear to influence non-neural cells (e.g., microglia, astrocytes, and vascular endothelial cells). Suppressing endogenous neurogenesis via Ara-C administration significantly inhibited (~50% less than vehicle) functional recovery and RFA expansion (~33% of vehicle) induced by rehabilitative therapy after CI.

CONCLUSIONS

After CI, inhibition of endogenous neurogenesis suppressed both the functional and anatomical markers of rehabilitative therapy. These results suggest that endogenous neurogenesis contributes to functional recovery after CI related to rehabilitative therapy, possibly through its promotion of motor map reorganization, although other additional roles cannot be ruled out.

Neural network remodeling underlying motor map reorganization induced by rehabilitative training after ischemic stroke

Motor map reorganization is believed to be one mechanism underlying rehabilitation-induced functional recovery. Although the ipsilesional secondary motor area has been known to reorganize motor maps and contribute to rehabilitation-induced functional recovery, it is unknown how the secondary motor area is reorganized by rehabilitative training. In the present study, using skilled forelimb reaching tasks, we investigated neural network remodeling in the rat rostral forelimb area (RFA) of the secondary motor area during 4weeks of rehabilitative training. Following photothrombotic stroke in the caudal forelimb area (CFA), rehabilitative training led to task-specific recovery and motor map reorganization in the RFA. A second injury to the RFA resulted in reappearance of motor deficits. Further, when both the CFA and RFA were destroyed simultaneously, rehabilitative training no longer improved task-specific recovery. In neural tracer studies, although rehabilitative training did not alter neural projection to the RFA from other brain areas, rehabilitative training increased neural projection from the RFA to the lower spinal cord, which innervates the muscles in the forelimb. Double retrograde tracer studies revealed that rehabilitative training increased the neurons projecting from the RFA to both the upper cervical cord, which innervates the muscles in the neck, trunk, and part of the proximal forelimb, and the lower cervical cord. These results suggest that neurons projecting to the upper cervical cord provide new connections to the denervated forelimb area of the spinal cord, and these new connections may contribute to rehabilitation-induced task-specific recovery and motor map reorganization in the secondary motor area.

Synthesis and Evaluation of Novel Carbocyclic Oxetanocin A (COA-Cl) Derivatives as Potential Tube Formation Agents

Six novel carbocyclic oxetanocin A analogs (2-chloro-C.OXT-A; COA-Cl) with various hydroxymethylated or spiro-conjugated cyclobutane rings at the N(9)-position of the 2-chloropurine moiety were synthesized and evaluated using human umbilical vein endothelial cells. All prepared compounds (2a-f) showed good to moderate activity with angiogenic potency. Among these compounds, 100 µM cis-trans-2',3'-bis(hydroxymethyl)cyclobutyl derivative (2b), trans-3'-hydroxymethylcyclobutyl analog (2d), and 3',3'-bis(hydroxymethyl)cyclobutyl derivative (2e) had greater angiogenic activity, with relative tube areas of 3.43±0.44, 3.32±0.53, and 3.59±0.83 (mean±standard deviation (S.D.)), respectively, which was comparable to COA-Cl (3.91±0.78). These data may be important for further development of this class of compounds as potential tube formation agents.

Evaluation of biomolecular distributions in rat brain tissues by means of ToF-SIMS using a continuous beam of Ar clusters

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) provides detailed chemical structure information and high spatial resolution images. Therefore, ToF-SIMS is useful for studying biological phenomena such as ischemia. In this study, in order to evaluate cerebral microinfarction, the distribution of biomolecules generated by ischemia was measured with ToF-SIMS. ToF-SIMS data sets were analyzed by means of multivariate analysis for interpreting complex samples containing unknown information and to obtain biomolecular mapping indicated by fragment ions from the target biomolecules. Using conventional ToF-SIMS (primary ion source: Bi cluster ion), it is difficult to detect secondary ions beyond approximately 1000 u. Moreover, the intensity of secondary ions related to biomolecules is not always high enough for imaging because of low concentration even if the masses are lower than 1000 u. However, for the observation of biomolecular distributions in tissues, it is important to detect low amounts of biological molecules from a particular area of tissue. Rat brain tissue samples were measured with ToF-SIMS (J105, Ionoptika, Ltd., Chandlers Ford, UK), using a continuous beam of Ar clusters as a primary ion source. ToF-SIMS with Ar clusters efficiently detects secondary ions related to biomolecules and larger molecules. Molecules detected by ToF-SIMS were examined by analyzing ToF-SIMS data using multivariate analysis. Microspheres (45 μm diameter) were injected into the rat unilateral internal carotid artery (MS rat) to cause cerebral microinfarction. The rat brain was sliced and then measured with ToF-SIMS. The brain samples of a normal rat and the MS rat were examined to find specific secondary ions related to important biomolecules, and then the difference between them was investigated. Finally, specific secondary ions were found around vessels incorporating microspheres in the MS rat. The results suggest that important biomolecules related to cerebral microinfarction can be detected by ToF-SIMS.

[Synthesis and evaluation of novel nucleic acid derivatives as bioactive substances]

This review describes the synthesis and evaluation of novel nucleic acid derivatives performed by our research group to date. We developed a new method for the synthesis of 2-alkoxyadenosine analogs via nonaqueous diazotization-dediazoniation reactions. By applying these reactions, we effectively synthesized four types of carbocyclic oxetanocin analogs (2-alkoxy-C.OXT-A). The angiogenic activities of these compounds were evaluated using human umbilical vein endothelial cells. This resulted in increased activities of the analogs, especially of 2-methoxy-C.OXT-A and 2-isopropoxy-C.OXT-A, at a concentration of 100 μM; they showed angiogenic potency similar to or greater than that of vascular endothelial growth factor. We also synthesized and evaluated a novel series of uracil derivatives carrying a 3,5-dimethylbenzyl group at the N(3)-position and acting as non-nucleoside HIV-1 reverse transcriptase inhibitors. Some of these compounds showed good-to-moderate inhibitory activity, with EC₅₀ values in the submicromolar range. Among them, the analog 6-amino-1-(4-picolyl)-uracil showed significant HIV-1 reverse transcriptase inhibition, with an EC₅₀ value of 0.03 μM and a high selectivity index of 2863.

Involvement of S1P1 receptor pathway in angiogenic effects of a novel adenosine-like nucleic acid analog COA-Cl in cultured human vascular endothelial cells

COA-Cl (2Cl-C.OXT-A) is a recently developed adenosine-like nucleic acid analog that promotes angiogenesis via the mitogen-activated protein (MAP) kinases ERK1/2. Endothelial S1P₁ receptor plays indispensable roles in developmental angiogenesis. In this study, we examined the functions of S1P₁ in COA-Cl-induced angiogenic responses. Antagonists for S1P₁, W146, and VPC23019, substantially but still partly inhibited the effects of COA-Cl with regard to ERK1/2 activation and tube formation in cultured human umbilical vein endothelial cells (HUVEC). Antagonists for adenosine A₁ receptor and purinergic P2Y₁ receptor were without effect. Genetic knockdown of S1P₁ with siRNA, but not that of S1P₃, attenuated COA-Cl-elicited ERK1/2 responses. The signaling properties of COA-Cl showed significant similarities to those of sphingosine 1-phosphate, an endogenous S1P₁ ligand, in that both induced responses sensitive to pertussis toxin (Gα i/o inhibitor), 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis (acetoxymethyl ester) (BAPTA-AM), (calcium chelator), and PP2 (c-Src tyrosine kinase inhibitor). COA-Cl elevated intracellular Ca²⁺ concentration and induced tyrosine phosphorylation of p130Cas, a substrate of c-Src, in HUVEC. COA-Cl displaced [³H]S1P in a radioligand-binding competition assay in chem-1 cells overexpressing S1P₁. However, COA-Cl activated ERK1/2 in CHO-K1 cells that lack functional S1P₁ receptor, suggesting the presence of additional yet-to-be-defined COA-Cl target in these cells. The results thus suggest the major contribution of S1P₁ in the angiogenic effects of COA-Cl. However, other mechanism such as that seen in CHO-K1 cells may also be partly involved. Collectively, these findings may lead to refinement of the design of this nucleic acid analog and ultimately to development of small molecule-based therapeutic angiogenesis.