Improvement of therapeutic index of phosphodiesterase type IV inhibitors as anti-Asthmatics

Instantaneous Hydrolysis of Methyl Paraoxon Nerve Agent Simulant Is Catalyzed by Nontoxic Aminoguanidine Imines

Exposure to organophosphate-based nerve agents and pesticides poses health and security threats to civilians, soldiers, and first responders. Thus, there is a need to develop effective decontamination agents that are nonhazardous to human health. To address this, we demonstrate that instantaneous hydrolysis of methyl paraoxon (Me-POX), a nerve agent simulant, can be achieved in the presence of aminoguanidine imines at pH 10: ● the pyridine-4-aldehyde aminoguanidine-imine (1) and ● the 2,3-butanedione aminoguanidine-imine (2). The hydrolysis of Me-POX under these conditions is substantially faster than that of the state-of-the-art decontaminating agent, Dekon-139 (2,3-butanedione oxime, potassium salt). Furthermore, Dekon-139 shows adverse effects when applied on skin surfaces, making it of great interest to develop safer but effective decontaminating agents for neutralizing nerve agents and pesticides exposed to skin-surface areas. Our pharmaceutically relevant aminoguanidine derivatives serve as rather nontoxic and safe decontaminating agents for organophosphate-based nerve agents and pesticides. The hydrolytic degradation products of Me-POX by our aminoguanidine-based imines and Dekon-139 are pH dependent. At pH > 10, Me-POX is hydrolyzed to give dimethyl phosphate as the exclusive product, whereas at pH < 9, the major product of hydrolysis is methyl 4-nitrophenyl phosphate (M4NP). We applied Quantum Mechanics calculations to investigate the mechanism of this dramatically accelerated decontamination process. We predict that in the rate-determining transition state, both 1 and 2 stabilize the reaction center through hydrogen bonding. Compared to Dekon-139, the rate constants of the rate-determine steps (RDS) are predicted to be over 9,000 times larger for 1 and over 600 times larger for 2, explaining the improvement. Quantum Mechanics calculations rationalize the pH-dependent hydrolysis products of the Me-POX in the gas phase, and gauge-including atomic orbital (GIAO)-31P NMR chemical shift calculations confirm the experimental values.

Exploring the Role of Water Molecules in the Ligand Binding Domain of PDE4B and PDE4D: Virtual Screening Based Molecular Docking of Some Active Scaffolds

BACKGROUND

The phosphodiesterase (PDE) is a superfamily represented by four genes: PDE4A, B,C, and D which cause the hydrolysis of phosphodiester bond of cAMP to yield inactive AMP. c-AMP catalyzing enzyme is predominant in inflammatory and immunomodulatory cells. Therapy to treat Chronic Obstructive Pulmonary Disease (COPD) with the use of PDE4 inhibitors is highly envisaged.

OBJECTIVE

A molecular docking experiment with large dataset of diverse scaffolds has been performed on PDE4 inhibitors to analyze the role of amino acid responsible for binding and activation of the secondary transmitters. Apart from the general docking experiment, the main focus was to discover the role of water molecules present in the ligand-binding domain.

METHODS

All the compounds were docked in the PDE4B and PDE4D active cavity to produce the free binding energy scores and spatial disposition/orientation of chemical groups of inhibitors around the cavity. Under uniform condition, the experiments were carried out with and without water molecules in the LBD. The exhaustive study was carried out on the Autodock 4.2 software and explored the role of water molecules present in the binding domain.

RESULTS

In presence of water molecule, Roflumilast has more binding affinity (-8.48 Kcal/mol with PDE4B enzyme and -8.91 Kcal/mol with PDE4D enzyme) and forms two hydrogen bonds with Gln443 and Glu369 and amino acid with PDE4B and PDE4D enzymes respectively. While in absence of water molecule its binding affinity has decreased (-7.3 Kcal/mol with PDE4B enzyme and -5.17 Kcal/mol with PDE4D enzyme) as well as no H-bond interactions were observed. Similar observation was made with clinically tested molecules.

CONCLUSION

In protein-ligand binding interactions, appropriate selection of water molecules facilitated the ligand binding, which eventually enhances the efficiency as well as the efficacy of ligand binding.

Hesperetin-5,7,3'-O-triacetate suppresses airway hyperresponsiveness in ovalbumin-sensitized and challenged mice without reversing xylazine/ketamine-induced anesthesia in normal mice

Background

We recently reported that hesperetin-5,7,3’-O-triacetate (HTA) dually inhibited phosphodiesterase (PDE)3/4 with a therapeutic ratio of 20.8. The application and development of PDE4 inhibitors for treating asthma or COPD are limited by their side effects, such as nausea, vomiting and gastric hypersecretion. PDE4 inhibitors were reported to reverse xylazine/ketamine-induced anesthesia in rats and triggered vomiting in ferrets. Thus the reversing effect of HTA on xylazine/ketamine-induced anesthesia in mice was studied to assess emetic effect of HTA. The aim of this study was to prove the therapeutic effect of HTA without vomiting effect at an effective dose for treating COPD.

Methods

Ten female BALB/c mice in each group were sensitized by ovalbumin (OVA) on days 0 and 14. On day 21, these mice were emphasized the sensitization by Freund’s complete adjuvant. Mice were challenged by 1% OVA nebulization on days 28, 29, and 30. Airway hyperresponsiveness (AHR) was assessed on day 32 in each group, using the FlexiVent system to determine airway resistance (R_L) and lung dynamic compliance (C_dyn) in anesthetized ovalbumin (OVA)-sensitized and challenged mice. Each group was orally administered HTA (10 ~ 100 μmol/kg), roflumilast (1 and 5 mg/kg) or vehicles (controls) 2 h before and 6 and 24 h after OVA provocation. For comparison, sham-treated mice were challenged with saline instead of 1% OVA. The ability to reverse xylazine/ketamine-induced anesthesia by HTA or roflumilast for 3 h was determined in normal mice. We used roflumilast, a selective PDE4 inhibitor and bronchodilator for severe COPD approved by the US Food and Drug Administration, as a reference drug.

Results

In the results, HTA (100 μmol/kg, p.o.) or roflumilast (5 mg/kg, p.o.) significantly suppressed all R_L values of MCh at 0.78 ~ 25 mg/mL and enhanced C_dyn values of MCh at 3.125 ~ 25 mg/mL compared to OVA-sensitized and -challenged control mice. Orally administered 1, 3 or 10 mg/kg roflumilast, but not 30 or 100 μmol/kg HTA, significantly reversed xylazine/ketamine-induced anesthesia.

Conclusions

In contrast to roflumilast, HTA may ameliorate COPD but induce few side effects of nausea, vomiting and gastric hypersecretion at an effective dose for treating COPD, because HTA did not reverse xylazine/ketamine-induced anesthesia in mice.

Hesperidin-3'-o-methylether is more potent than hesperidin in phosphodiesterase inhibition and suppression of ovalbumin-induced airway hyperresponsiveness

Hesperidin is present in the traditional Chinese medicine, "Chen Pi," and recently was reported to have anti-inflammatory effects. Therefore, we were interested in comparing the effects of hesperidin and hesperidin-3'-O-methylether on phosphodiesterase inhibition and airway hyperresponsiveness (AHR) in a murine model of asthma. In the present results, hesperidin-3'-O-methylether, but not hesperidin, at 30 μmol/kg (p.o.) significantly attenuated the enhanced pause (P(enh)) value, suppressed the increases in numbers of total inflammatory cells, macrophages, lymphocytes, neutrophils, and eosinophils, suppressed total and OVA-specific immunoglobulin (Ig)E levels in the serum and BALF, and enhanced the level of total IgG(2a) in the serum of sensitized and challenged mice, suggesting that hesperidin-3'-O-methylether is more potent than hesperidin in suppression of AHR and immunoregulation. The different potency between them may be due to their aglycons, because these two flavanone glycosides should be hydrolyzed by β-glucosidase after oral administration. Neither influenced xylazine/ketamine-induced anesthesia, suggesting that they may have few or no adverse effects, such as nausea, vomiting, and gastric hypersecretion. In conclusion, hesperidin-3'-O-methylether is more potent in phosphodiesterase inhibition and suppression of AHR and has higher therapeutic (PDE4(H)/PDE4(L)) ratio than hesperidin. Thus, hesperidin-3'-O-methylether may have more potential for use in treating allergic asthma and chronic obstructive pulmonary disease.

Hesperetin, a Selective Phosphodiesterase 4 Inhibitor, Effectively Suppresses Ovalbumin-Induced Airway Hyperresponsiveness without Influencing Xylazine/Ketamine-Induced Anesthesia

Hesperetin, a selective phosphodiesterase (PDE)4 inhibitor, is present in the traditional Chinese medicine, “Chen Pi.” Therefore, we were interested in investigating its effects on ovalbumin- (OVA-) induced airway hyperresponsiveness, and clarifying its rationale for ameliorating asthma and chronic obstructive pulmonary disease (COPD). Hesperetin was revealed to have a therapeutic (PDE4_H/PDE4_L) ratio of >11. Hesperetin (10 ~ 30 μmol/kg, intraperitoneally (i.p.)) dose-dependently and significantly attenuated the airway hyperresponsiveness induced by methacholine. It also significantly suppressed the increases in total inflammatory cells, macrophages, lymphocytes, neutrophils, and eosinophils, and levels of cytokines, including interleukin (IL)-2, IL-4, IL-5, interferon-γ, and tumor necrosis factor-α in bronchoalveolar lavage fluid (BALF). It dose-dependently and significantly suppressed total and OVA-specific immunoglobulin E levels in the BALF and serum. However, hesperetin did not influence xylazine/ketamine-induced anesthesia, suggesting that hesperetin has few or no emetic effects. In conclusion, the rationales for ameliorating allergic asthma and COPD by hesperetin are anti-inflammation, immunoregulation, and bronchodilation.

Hesperetin-7,3'-O-dimethylether selectively inhibits phosphodiesterase 4 and effectively suppresses ovalbumin-induced airway hyperresponsiveness with a high therapeutic ratio

Background

Hesperetin was reported to selectively inhibit phosphodiesterase 4 (PDE4). While hesperetin-7,3'-O-dimethylether (HDME) is a synthetic liposoluble hesperetin. Therefore, we were interested in investigating its selectivity on PDE4 and binding ability on high-affinity rolipram-binding sites (HARBs) in vitro, and its effects on ovalbumin-induced airway hyperresponsiveness in vivo, and clarifying its potential for treating asthma and chronic obstructive pulmonary disease (COPD).

Methods

PDE1~5 activities were measured using a two-step procedure. The binding of HDME on high-affinity rolipram-binding sites was determined by replacing 2 nM [³H]-rolipram. AHR was assessed using the FlexiVent system and barometric plethysmography. Inflammatory cells were counted using a hemocytometer. Cytokines were determined using mouse T helper (Th)1/Th2 cytokine CBA kits, and total immunoglobulin (Ig)E or IgG_2a levels were done using ELISA method. Xylazine (10 mg/kg)/ketamine (70 mg/kg)-induced anesthesia was performed.

Results

HDME revealed selective phosphodiesterase 4 (PDE4) inhibition with a therapeutic (PDE4_H/PDE4_L) ratio of 35.5 in vitro. In vivo, HDME (3~30 μmol/kg, orally (p.o.)) dose-dependently and significantly attenuated the airway resistance (R_L) and increased lung dynamic compliance (C_dyn), and decreased enhanced pause (P_enh) values induced by methacholine in sensitized and challenged mice. It also significantly suppressed the increases in the numbers of total inflammatory cells, macrophages, lymphocytes, neutrophils, and eosinophils, and levels of cytokines, including interleukin (IL)-2, IL-4, IL-5, interferon-γ, and tumor necrosis factor-α in bronchoalveolar lavage fluid (BALF) of these mice. In addition, HDME (3~30 μmol/kg, p.o.) dose-dependently and significantly suppressed total and ovalbumin-specific immunoglobulin (Ig)E levels in the BALF and serum, and enhanced IgG_2a level in the serum of these mice.

Conclusions

HDME exerted anti-inflammatory effects, including suppression of AHR, and reduced expressions of inflammatory cells and cytokines in this murine model, which appears to be suitable for studying the effects of drugs on atypical asthma and COPD, and for screening those on typical asthma. However, HDME did not influnce xylazine/ketamine-induced anesthesia. Thus HDME may have the potential for use in treating typical and atypical asthma, and COPD.

Biochanin a, a phytoestrogenic isoflavone with selective inhibition of phosphodiesterase 4, suppresses ovalbumin-induced airway hyperresponsiveness

The present study investigated the potential of biochanin A, a phytoestrogenic isoflavone of red clover (Triflolium pratense), for use in treating asthma or chronic obstructive pulmonary disease (COPD). Biochanin A (100 μmol/kg, orally (p.o.)) significantly attenuated airway resistance (R_L), enhanced pause (P_enh), and increased lung dynamic compliance (C_dyn) values induced by methacholine (MCh) in sensitized and challenged mice. It also significantly suppressed an increase in the number of total inflammatory cells, neutrophils, and eosinophils, and levels of cytokines, including interleukin (IL)-2, IL-4, IL-5, and tumor necrosis factor (TNF)-α in bronchoalveolar lavage fluid (BALF) of the mice. However, it did not influence interferon (IFN)-γ levels. Biochanin A (100 μmol/kg, p.o.) also significantly suppressed the total and ovalbumin (OVA)-specific immunoglobulin E (IgE) levels in the serum and BALF, and enhanced the total IgG_2a level in the serum of these mice. The PDE4_H/PDE4_L value of biochanin A was calculated as >35. Biochanin A did not influence xylazine/ketamine-induced anesthesia. Biochanin A (10~30 μM) significantly reduced cumulative OVA (10~100 μg/mL)-induced contractions in the isolated guinea pig trachealis, suggesting that it inhibits degranulation of mast cells. In conclusion, red clover containing biochanin A has the potential for treating allergic asthma and COPD.

S-Petasin, the Main Sesquiterpene of Petasites formosanus, Inhibits Phosphodiesterase Activity and Suppresses Ovalbumin-Induced Airway Hyperresponsiveness

S-Petasin is the main sesquiterpene of Petasites formosanus, a traditional folk medicine used to treat hypertension, tumors and asthma in Taiwan. The aim of the present study was to investigate its inhibitory effects on phosphodiesterase (PDE) 1–5, and on ovalbumin (OVA)-induced airway hyperresponsiveness (AHR) in a murine model of allergic asthma. S-Petasin concentration-dependently inhibited PDE3 and PDE4 activities with 50% inhibitory concentrations (IC₅₀) of 25.5, and 17.5 μM, respectively. According to the Lineweaver-Burk analysis, S-petasin competitively inhibited PDE3 and PDE4 activities with respective dissociation constants for inhibitor binding (K_i) of 25.3 and 18.1 μM, respectively. Both IC₅₀ and K_i values for PDE3 were significantly greater than those for PDE4. S-Petasin (10–30 μmol/kg, administered subcutaneously (s.c.)) dose-dependently and significantly attenuated the enhanced pause (P_enh) value induced by methacholine (MCh) in sensitized and challenged mice. It also significantly suppressed the increases in total inflammatory cells, lymphocytes, neutrophils, eosinophils and levels of cytokines, including interleukin (IL)-2, IL-4 and IL-5, tumor necrosis factor (TNF)-α and interferon (IFN)-γ in bronchoalveolar lavage fluid (BALF) of these mice. In addition, S-petasin (10–30 μmol/kg, s.c.) dose-dependently and significantly attenuated total and OVA-specific immunoglobulin E (IgE) levels in the serum and BALF, and enhanced the IgG_2a level in serum of these mice. The PDE4_H value of S-petasin was >300 μM; therefore, its PDE4_H/PDE4_L value was calculated to be >17. In conclusion, the present results for S-petasin at least partially explain why Petasites formosanus is used as a folk medicine to treat asthma in Taiwan.

Genistein, a competitive PDE1-4 inhibitor, may bind on high-affinity rolipram binding sites of brain cell membranes and then induce gastrointestinal adverse effects

The affinities of genistein on phosphodiesterase (PDE)1-4 and cause of gastrointestinal adverse effects of genistein remain unclear. Female BALB/c mice were actively sensitized by intraperitoneal injections of ovalbumin and challenged by aerosolized ovalbumin (1%). After secondary challenge, aerosolized methacholine (6.25-50mg/ml) induced increases of enhanced pause (P(enh)) values in conscious mice in a concentration-dependent manner. Genistein (30-100 micromol/kg, i.p.) markedly inhibited methacholine (12.5-50mg/ml)-induced increase of P(enh) value in the sensitized and challenged mice. In addition, genistein significantly reduced total inflammatory cells, macrophages, lymphocytes, neutrophils, and eosinophils in bronchoalveolar lavage fluid, with the exception that lymphocytes and neutrophils were not significantly inhibited by genistein at the lowest dose (10 micromol/kg). Genistein also markedly attenuated the release of cytokines, including interleukin (IL)-2, IL-4, IL-5, interferon (IFN)-gamma and tumor necrosis factor (TNF)-alpha. Genistein competitively inhibited PDE1-4, with a K(i) value ranging from 4.3 to 13.7 microM. Genistein (3-300 microM) concentration-dependently displaced 2nM [(3)H]-rolipram bound on high-affinity rolipram binding sites of brain cell membranes. The therapeutic ratio of genistein was calculated to be 7.9. Genistein (100 micromol/kg, s.c.) significantly shortened xylazine/ketamine-induced anesthesia, suggesting that genistein administered at a higher dose may have gastrointestinal adverse effects. In conclusion, owing to the low therapeutic ratio of genistein, the gastrointestinal adverse effects may be induced via the binding of genistein on high-affinity rolipram binding sites of brain cell membranes, when it is used for a long term or at higher doses for treating allergies, asthma or chronic obstructive pulmonary disease.

Ayanin, a non-selective phosphodiesterase 1-4 inhibitor, effectively suppresses ovalbumin-induced airway hyperresponsiveness without affecting xylazine/ketamine-induced anesthesia

In recent in vitro reports, the IC(50) value of ayanin (quercetin-3,7,4'-O-trimethylether) was 2.2microM for inhibiting interleukin (IL)-4 production from purified basophils, and its therapeutic ratio was >19. Therefore, we were interested in investigating the effects on ovalbumin induced airway hyperresponsiveness in vivo, and to clarify its potential for treating asthma. Ayanin (30-100micromol/kg, orally (p.o.)) dose-dependently and significantly attenuated the enhanced pause (P(enh)) value induced by methacholine in sensitized and challenged mice. It also significantly suppressed the increases in total inflammatory cells, macrophages, lymphocytes, neutrophils, and eosinophils, and levels of cytokines, including IL-2, IL-4, IL-5, and tumor necrosis factor (TNF)-alpha in bronchoalveolar lavage fluid of these mice. However, at 100micromol/kg, it significantly enhanced the level of interferon (IFN)-gamma. In addition, ayanin (30-100micromol/kg, p.o.) dose-dependently and significantly suppressed total and OVA-specific immunoglobulin (Ig)E levels in the serum and bronchoalveolar lavage fluid, and enhanced the IgG(2a) level in serum of these mice. In the present results, ayanin did not affect xylazine/ketamine-induced anesthesia, suggesting that ayanin has few or no adverse effects, such as nausea, vomiting, and gastric hypersecretion. In conclusion, the above results suggest that ayanin may have the potential for use in treating allergic asthma.