NT-702 (parogrelil hydrochloride, NM-702), a novel and potent phosphodiesterase inhibitor, improves reduced walking distance and lowered hindlimb plantar surface temperature in a rat experimental intermittent claudication model

Natural Molecules as Talented Inhibitors of Nucleotide Pyrophosphatases/Phosphodiesterases (PDEs)

BACKGROUND

Phosphodiesterases (PDEs) are a wide group of enzymes with multiple therapeutic actions, including vasorelaxation, cardiotonic, antidepressant, anti-inflammatory, antithrombotic, anti-spasmolytic, memory-enhancing, and anti-asthmatic. PDEs with eleven subtypes from PDE-1 to PDE-11 typically catalyze the cleavage of the phosphodiester bond and, hence, degrades either cyclic adenosine monophosphate (cAMP) or cyclic guanosine monophosphate (cGMP).

OBJECTIVE

Several selective or non-selective inhibitors of the PDE subtypes are used clinically, i.e. sildenafil, rolipram, cysteine, etc. Recently, interest in plant-based pharmacologically bioactive compounds having potent PDEs inhibitory potential has increased. Purposely, extensive research has been carried out on natural products to explore new inhibitors of various PDEs. Therefore, this review summarizes the published data on natural PDEs inhibitors and their potential therapeutic applications.

METHODS

For this purpose, natural compounds with PDE inhibitory potential have been surveyed through several databases, including PubMed, Web of Sciences (WoS), Scopus, and Google Scholar.

RESULTS

According to a detailed literature survey, the most promising class of herbal compounds with PDE-inhibiting property has been found to belong to phenolics, including flavonoids (luteolin, kaempferol, icariin, etc.). Many other encouraging inhibitors from plants have also been identified, such as coumarins (23, 24) (licoarylcoumarin and glycocoumarin,), saponins ( agapanthussaponins), lignans (31, 33) [(±)-schizandrin and kobusin], terpenes (28, 29, 31) (perianradulcin A, quinovic acid, and ursolic acid), anthraquinones (18, 19) (emodin and chrysophanol), and alkaloids (Sanjoinine-D) (36).

CONCLUSION

In this review, studies have revealed the PDE-inhibitory potential of natural plant extracts and their bioactive constituents in treating various diseases; however, further clinical studies comprising synergistic use of different therapies (synthetic & natural) to acquire multi-targeted results might also be a promising option.

Potential functional and pathological side effects related to off-target pharmacological activity

Most pharmaceutical companies test their discovery-stage proprietary molecules in a battery of in vitro pharmacology assays to try to determine off-target interactions. During all phases of drug discovery and development, various questions arise regarding potential side effects associated with such off-target pharmacological activity. Here we present a scientific literature curation effort undertaken to determine and summarize the most likely functional and pathological outcomes associated with interactions at 70 receptors, enzymes, ion channels and transporters with established links to adverse effects. To that end, the scientific literature was reviewed using an on-line database, and the most commonly reported effects were summarized in tabular format. The resultant table should serve as a practical guide for research scientists and clinical investigators for the prediction and interpretation of adverse side effects associated with molecules interacting with components of this screening battery.

Pyridazinone: an attractive lead for anti-inflammatory and analgesic drug discovery

In spite of the availability of a large number of anti-inflammatory and analgesic agents, fighting pain and inflammation remains a common problem. The current review article discusses the need of novel therapeutic targets for risk-free anti-inflammatory and analgesic therapy and summarizes some new agents in various stages of drug discovery pipeline. Pyridazin-3(2H)-ones are nitrogen-rich heterocyclic compounds of considerable medicinal interest due to their diverse biological activities. The current review article focuses on progressive development of this attractive scaffold for the design and synthesis of new pyridazinone-based anti-inflammatory and analgesic agents. Mechanistic insights into the anti-inflammatory and analgesic properties of pyridazinone derivatives and various synthetic techniques used for their synthesis are also described.

Prasugrel, a Platelet P2Y12 Receptor Antagonist, Improves Abnormal Gait in a Novel Murine Model of Thrombotic Hindlimb Ischemia

Background

The efficacy of P2Y₁₂ inhibition for the prevention of cardiovascular events in patients with peripheral arterial disease (PAD) has been established. However, the therapeutic effects on ischemic limb complications are less clear. Accordingly, we aimed to develop a novel murine model of thrombotic hindlimb ischemia to reflect that found in patients with PAD exhibiting ischemic limb symptoms. We further investigated the effects of P2Y₁₂ deficiency and P2Y₁₂ inhibition by prasugrel in this model.

Methods and Results

Thrombus formation induced by application of ferric chloride to the femoral artery resulted in a significant reduction in blood flow in the injured limb. In gait analysis using the CatWalk system, moderate difficulties in grounding and weight bearing of the ischemic limb, including reduction of maximum contact area and stance phase duration and increasing in swing phase duration in the ischemic limb, were observed in this model. Blood flow reduction and gait abnormalities gradually recovered over 21 days to levels present before arterial injury. Compared to wild‐type (WT) mice, significant increases in blood flow and improvement in gait were observed in P2Y₁₂‐deficient mice. In addition, daily oral administration of prasugrel (3 mg/kg per day) to WT mice resulted in significant inhibition of blood flow reduction and gait abnormalities to levels found in P2Y₁₂ deficient mice.

Conclusions

Acute femoral artery thrombosis resulted in hindlimb ischemia and moderate gait abnormalities in mice. In addition, the present study suggests a possible role of P2Y₁₂ in the complications with thrombotic limb ischemia.

Prostaglandin E1 -containing nanoparticles improve walking activity in an experimental rat model of intermittent claudication

OBJECTIVES

Due to the low stability of lipid emulsions, a lipid emulsion of prostaglandin E1 (Lipo-PGE1 ) necessitates daily intravenous drip infusions. To overcome this issue, we developed nanoparticles containing PGE1 (Nano-PGE1 ). Nano-PGE1 showed a good sustained-release profile of PGE1 from the nanoparticles in vitro, which may permit a longer-lasting therapeutic effect to be achieved. We here examined the pharmacological activity of Nano-PGE1 in a rat experimental model of intermittent claudication induced by femoral artery ligation.

METHODS

The walking activity of the rat was tested on a rodent treadmill. Tissue levels of PGE1 were determined by enzyme immunoassay, and skeletal muscle angiogenesis (capillary growth) was monitored by immunohistochemical analysis.

KEY FINDINGS

PGE1 could be detected in the lesion site one day after the intravenous administration of Nano-PGE1 but not of Lipo-PGE1 . An increased accumulation of Nano-PGE1 in the lesion site compared with control (unlesioned) site was also observed. The ligation procedure reduced the walking activity, which in turn was improved by a single administration of Nano-PGE1 but not of Lipo-PGE1 . The single administration of Nano-PGE1 also stimulated angiogenesis in the skeletal muscle around the ligated artery.

CONCLUSIONS

The findings of this study suggest that Nano-PGE1 improves the walking activity of femoral artery-ligated rats through the accumulation and sustained release of PGE1 .

A phosphodiesterase 3 inhibitor, K-134, improves hindlimb skeletal muscle circulation in rat models of peripheral arterial disease

OBJECTIVE

Cilostazol is a phosphodiesterase (PDE)3 inhibitor used to treat peripheral arterial disease with intermittent claudication, as there is clinical evidence that it improves treadmill exercise capacity. However, details of the mechanism underlying this enhanced walking capacity remain to be elucidated.

METHODS

Based on the hypothesis that PDE3 inhibitors improve peripheral microcirculation in the hindlimbs via vascular smooth muscle relaxation and antiplatelet effects, we examined the effects of a more potent and selective PDE3 inhibitor, K-134, in rat models of peripheral arterial disease (PAD).

RESULTS

In a hindlimb ischemia model established by bilateral femoral artery occlusion, oral administration of K-134 for 27 days significantly increased blood flow in hindlimb skeletal muscle after exercise induced by electrical stimulation of the sciatic nerve. Moreover, K-134 enlarged the luminal area of intramuscular arteries and prevented rarefaction of capillary density in the gastrocnemius muscle. These effects were observed without pre-administration on the day following the last administration, suggesting that vasodilatory, antiplatelet and angiogenic activities of K-134 were indirectly responsible for the long-term beneficial effects. In fact, K-134 dose-dependently induced relaxation of rat femoral arteries in vitro, and inhibited rat platelet aggregation ex vivo. Interestingly, in a laurate-induced peripheral vascular injury model, oral administration of K-134 for 6 days prevented progression of hindlimb necrosis.

CONCLUSION

These findings suggest that the beneficial effects of PDE3 inhibitors on walking capacity are due to increased hindlimb skeletal muscle blood flow via intramuscular artery enlargement, and that K-134 is a promising drug for PAD associated with platelet hyperaggregability.

Phosphodiesterases as targets for intermittent claudication

Intermittent claudication (IC) is one of the most frequent forms of lower extremity peripheral arterial disease (PAD) and is most commonly caused by arterial atherosclerosis. Its clinical manifestation includes fatigue, discomfort, or pain occurring in limb muscles due to exercise-induced ischemia, thus limiting the ability of IC patients to walk and exercise. In addition to lifestyle changes (diet, exercise, and smoking cessation), pharmacological treatments are needed. Pathologically, atherosclerotic lesions cause a mismatch in oxygen supply and metabolic demand in the leg muscles during walking/exercise. This subjects the muscles to repeated ischemia and reperfusion injury that can alter structure and oxidative metabolism, resulting in insufficient utilization of oxygen supply. Despite extensive research efforts, cilostazol and pentoxifylline are the only drugs indicated for relieving the symptoms of IC, with cilostazol demonstrating significant improvement in walking distance and quality of life in these patients. Originally developed as a PDE3 inhibitor, cilostazol was later found to have several other pharmacological actions, and its success has been attributed to its multifactorial actions on platelets, endothelium, smooth muscle, and lipid profiles. Using cilostazol as an example, we discuss the rationales and pitfalls of targeting PDEs in IC, and potential strategies for the development of new and more effective pharmacological treatments.

NT-702 (parogrelil hydrochloride, NM-702), a novel and potent phosphodiesterase 3 inhibitor, suppress the asthmatic response in guinea pigs, with both bronchodilating and anti-inflammatory effects

We evaluated the effects of NT-702 (parogrelil hydrochloride, NM-702, 4-bromo-6-[3-(4-chlorophenyl) propoxy]-5-[(pyridine-3-ylmethyl) amino] pyridazin-3(2H)-one hydrochloride), a selective phosphodiesterase 3 inhibitor, on the asthmatic response in guinea pigs. NT-702 at a concentration of 1 x 10(-7)M elevated the cyclic adenosine monophosphate content in prostaglandin E(2)-treated guinea pig tracheal smooth muscle cells. Leukotriene (LT) D(4)- and histamine-induced contraction of isolated guinea pig tracheal strips was inhibited by NT-702, with EC(50) values of 3.2 x 10(-7) and 2.5 x 10(-7)M, respectively. In an in vivo study, NT-702 suppressed LTD(4)-induced bronchoconstriction and the ovalbumin-induced immediate asthmatic response in guinea pigs through its bronchodilating effect. Furthermore, NT-702 also suppressed the ovalbumin-induced late asthmatic response, airway hyperresponsiveness, and the accumulation of inflammatory cells in the bronchoalveolar lavage fluid. These results suggest that NT-702 has an anti-inflammatory effect as well as a bronchodilating effect and might be useful as a novel potent therapeutic agent for the treatment of bronchial asthma, a new type of agent with both a bronchodilating and an anti-inflammatory effect.

NT-702, a selective phosphodiesterase 3 inhibitor, dilates rabbit spinal arterioles via endothelium-dependent and endothelium-independent mechanisms

We investigated the effects of NT-702, a selective phosphodiesterase (PDE) 3 inhibitor, on arterioles isolated from rabbit lumbar spinal cords. NT-702 caused a dose-dependent dilation of the isolated spinal arterioles. The disruption of endothelium produced a significant reduction of higher concentrations (10(-7) and 10(-6) M), but not lower concentrations (less than 10(-8) M), of NT-702-induced vasodilation. The NT-702-induced vasodilation of the arterioles with endothelium was not affected by pretreatment with an inhibitor of nitric oxide, cyclooxygenase, or cytochrome P-450 monooxygenase. In contrast, catalase reduced significantly the higher concentrations of NT-702-induced vasodilation only. Tetraethylammonium (TEA) completely reduced the lower concentrations of NT-702-induced vasodilation, but decreased only partially the higher concentrations of NT-702-induced vasodilation of the arterioles with endothelium. Hydrogen peroxide dilated significantly the isolated arterioles with endothelium, the response of which was reduced significantly by TEA. KT5720 (a selective protein kinase inhibitor) significantly decreased both the lower and higher concentrations of NT-702-induced vasodilation of the arterioles with endothelium. The findings suggest that NT-702 dose-dependently dilated the isolated spinal arterioles of rabbits via endothelium-dependent and endothelium-independent mechanisms. Protein kinase A (PKA)- and TEA-sensitive K(+) channels may be involved in the NT-702-induced vasodilation. Moreover, hydrogen peroxide may contribute in part to the endothelium-dependent higher concentrations of NT-702-induced vasodilation.