The toxicity of repeated exposures to rolipram, a type IV phosphodiesterase inhibitor, in rats

Genes Differentially Expressed Across Major Arteries Are Enriched in Endothelial Dysfunction-Related Gene Sets: Implications for Relative Inter-artery Atherosclerosis Risk

Atherosclerosis differs across major arteries. Although the biological basis is not fully understood, limited evidence of genetic differences has been documented. This study, therefore, was aimed to identify differentially expressed genes between clinically relevant major arteries and investigate their enrichment in endothelial dysfunction-related gene sets. A bioinformatic analysis of publicly available gene-level read counts for coronary, aortic, and tibial arteries was performed. Differential gene expression was conducted with DeSeq2 at a false discovery rate of 0.05. Differentially expressed genes were then subjected to over-representation analysis and active-subnetwork-oriented enrichment analysis, both at a false discovery rate of 0.005. Enriched terms common to both analyses were categorized for each contrast into immunity/inflammation-, membrane biology-, lipid metabolism-, and coagulation-related terms, and the top differentially expressed genes validated against Swiss Institute of Bioinformatics' Bgee database. There was mostly upregulation of differentially expressed genes for the coronary/tibial and aorta/tibial contrasts, but milder changes for the coronary/aorta contrast. Transcriptomic differences between coronary or aortic versus tibial samples largely involved immunity/inflammation-, membrane biology-, lipid metabolism-, and coagulation-related genes, suggesting potential to modulate endothelial dysfunction and atherosclerosis. These results imply atheroprone coronary and aortic environments compared with tibial artery tissue, which may explain observed relative inter-artery atherosclerosis risk.

The cAMP-phosphodiesterase 4 (PDE4) controls β-adrenoceptor- and CFTR-dependent saliva secretion in mice

Saliva, while often taken for granted, is indispensable for oral health and overall well-being, as inferred from the significant impairments suffered by patients with salivary gland dysfunction. Here, we show that treatment with several structurally distinct PAN-PDE4 inhibitors, but not a PDE3 inhibitor, induces saliva secretion in mice, indicating it is a class-effect of PDE4 inhibitors. In anesthetized mice, while neuronal regulations are suppressed, PDE4 inhibition potentiates a β-adrenoceptor-induced salivation, that is ablated by the β-blocker Propranolol and is absent from homozygous ΔF508-CFTR mice lacking functional CFTR. These data suggest that PDE4 acts within salivary glands to gate saliva secretion that is contingent upon the cAMP/PKA-dependent activation of CFTR. Indeed, PDE4 contributes the majority of total cAMP-hydrolytic capacity in submandibular-, sublingual-, and parotid glands, the three major salivary glands of the mouse. In awake mice, PDE4 inhibitor-induced salivation is reduced by CFTR deficiency or β-blockers, but also by the muscarinic blocker Atropine, suggesting an additional, central/neuronal mechanism of PDE4 inhibitor action. The PDE4 family comprises four subtypes, PDE4A-D. Ablation of PDE4D, but not PDE4A-C, produced a minor effect on saliva secretion, implying that while PDE4D may play a predominant role, PDE4 inhibitor-induced salivation results from the concurrent inactivation of multiple (at least two) PDE4 subtypes. Taken together, our data reveal a critical role for PDE4/PDE4D in controlling CFTR function in an in vivo model and in inducing salivation, hinting at a therapeutic potential of PDE4 inhibition for cystic fibrosis and conditions associated with xerostomia.

Pharmacologic manipulation of skin pigmentation

Skin complexion is among the most recognizable phenotypes between individuals and is mainly determined by the amount and type of melanin pigment deposited in the epidermis. Persons with dark skin complexion have more of a brown/black pigment known as eumelanin in their epidermis whereas those with fair skin complexions have less. Epidermal eumelanin acts as a natural sunblock by preventing incoming UV photons from penetrating into the skin and therefore protects against UV mutagenesis. By understanding the signaling pathways and regulation of pigmentation, strategies can be developed to manipulate skin pigmentation to improve UV resistance and to diminish skin cancer risk.

Temporal Reduction in Size of Salivary Acinus in Rats Induced by Theophylline

Repeated administration of theophylline, a phosphodiesterase inhibitor, induces the enlargement of the salivary glands in rats. Time-course changes after a single administration of theophylline were examined in the salivary glands, including phosphodiesterase enzyme activity, and the expression of aquaporin 5 (AQP5), a water channel. We also examined the contribution of β-adrenergic receptors to theophylline-induced salivary changes. Male F344 rats were given 50 mg/kg of theophylline intraperitoneally either alone or concurrently with a 10 mg/kg subcutaneous injection of propranolol. After treatment with theophylline alone, the weight and histology of the submaxillary and parotid glands were examined. Phosphodiesterase activity and AQP5 were detected by enzyme- and immuno-histochemistry, respectively. At 4 hours, 8 hours, or both, organ weights were decreased with depletion of secretory vesicles in the acinar cells. In the submaxillary glands, reduced activity of phosphodiesterase and increased expression of AQP5 in the intercalated ducts were observed at 4 hours. When co-administered, propranolol partially abolished theophylline-induced glandular reduction. These results suggest that the theophylline-induced transient reduction in size of the salivary glands is attributable not only to phosphodiesterase inhibition but also to β-adrenergic receptor activation and that the intercalated ducts in submaxillary glands play a role in the production of saliva.

Detrimental Effects of an Inhaled Phosphodiesterase-4 Inhibitor on Lung Inflammation in Ventilated Preterm Lambs Exposed to Chorioamnionitis Are Dose Dependent

Background: Treatment of bronchopulmonary dysplasia in preterm infants is challenging due to its multifactorial origin. In rodent models of neonatal lung injury, selective inhibition of phosphodiesterase 4 (PDE4) has been shown to exert anti-inflammatory properties in the lung. We hypothesized that GSK256066, a highly selective, inhalable PDE4 inhibitor, would have beneficial effects on lung injury and inflammation in a triple hit lamb model of Ureaplasma parvum (UP)-induced chorioamnionitis, prematurity, and mechanical ventilation. Methods: Twenty-one preterm lambs were surgically delivered preterm at 129 days after 7 days intrauterine exposure to UP. Sixteen animals were subsequently ventilated for 24 hours and received endotracheal surfactant and intravenous caffeine citrate. Ten animals were randomized to receive twice a high (10 μg/kg) or low dose (1 μg/kg) of nebulized PDE4 inhibitor. Results: Nebulization of high, but not low, doses of PDE4 inhibitor led to a significant decrease in pulmonary PDE activity, and was associated with lung injury and vasculitis, influx of neutrophils, and increased proinflammatory cytokine messenger RNA levels. Conclusion: Contrary to our hypothesis, we found in our model a dose-dependent proinflammatory effect of an inhaled highly selective PDE4 inhibitor in the lung. Our findings indicate the narrow therapeutic range of inhaled PDE4 inhibitors in the preterm population.

Use of Rat Primary Mesenteric Cells for the Prediction of PDE4 Inhibitor Drug-Induced Vascular Injury

Drug-induced vascular injury (DIVI) in preclinical studies can delay, if not terminate, a drug development program. Clinical detection of DIVI can be very difficult as there are no definitive biomarkers known to reliably detect this disorder in all instances. The preclinical identification of DIVI requires detailed microscopic examination of a wide range of tissues although one of the most commonly affected areas in rats is the mesenteric vasculature. The reason for this predisposition of mesenteric arteries in rats as well as the exact mechanism and cell types involved in the initial development of these lesions have not been fully elucidated. We hypothesized that by using a mixed culture of cells from rat mesenteric tissue, we would be able to identify an RNA expression signature that could predict the invivo development of DIVI. Five compounds designed to inhibit Phosphodiesterase 4 activity (PDE4i) were chosen as positive controls. PDE4i's are well known to induce DIVI in the mesenteric vasculature of rats and there is microscopic evidence that this is associated, at least in part, with a proinflammatory mechanism. We surveyed, by qRT-PCR, the expression of 96 genes known to be involved in inflammation and using a Random-Forest model, identified 12 genes predictive of invivo DIVI outcomes in rats. Using these genes, we were able to cross-validate the ability of the Random-Forest modeling to predict the concentration at which PDE4i caused DIVI invivo.

Apoptosis and Nitrative Stress Associated with Phosphodiesterase Inhibitor-Induced Mesenteric Vasculitis in Rats

Nitric oxide may play a role in phosphodiesterase (PDE) inhibitor-induced rat mesenteric vasculitis. The present study was conducted to identify cellular sources of iNOS, determine the distribution of nitrotyrosine (NT) residues as a footprint of peroxynitrite (ONOO-) production, and evaluate their association with vascular apoptosis. To dissociate primary events from secondary changes associated with the inflammatory response, rats were given the PDE IV inhibitor CI-1018 orally at 750 mg/kg alone or concurrently with dexamethasone (DEX) intraperitoneally at 1 mg/kg for 4—5 days. Neutrophil (PMN) involvement in apoptosis was investigated in CI-1018 treated rats dosed with rabbit anti-rat PMN serum (APS). iNOS expression, NT residues, and caspase-3 were detected by immuno-histochemistry. Apoptosis was evaluated by TUNEL assay. CI-1018 induced vascular lesions were associated with iNOS expression in endothelial cells and inflammatory infiltrates; NT was evident only in the latter. Caspase-3 and TUNEL-positive staining were prominent only in medial smooth muscle cells (SMC) from CI-1018-treated rats and only when associated with active inflammation. iNOS- and NT-positive inflammatory cells were present in close proximity to SMC with caspase-3 staining. Inflammatory infiltrates were absent in rats given DEX with minimal SMC necrosis and hemorrhage remained. DEX eliminated apoptosis and immunoreactivity associated with caspase-3, iNOS, and NT. APS depletion of PMNs decreased the incidence and severity of vasculitis but failed to abolish completely caspase-3 immunoreactivity. Expression patterns for caspase-3, iNOS, and NT demonstrated that nitrative stress is a prominent feature of PDE inhibitor-induced vasculitis, with a possible role in medial SMC apoptosis. Further, medial SMC apoptosis may not be a primary event, but instead may be secondary to the inflammatory response.

Physiological, pharmacological and toxicological considerations of drug-induced structural cardiac injury

The incidence of drug-induced structural cardiotoxicity, which may lead to heart failure, has been recognized in association with the use of anthracycline anti-cancer drugs for many years, but has also been shown to occur following treatment with the new generation of targeted anti-cancer agents that inhibit one or more receptor or non-receptor tyrosine kinases, serine/threonine kinases as well as several classes of non-oncology agents. A workshop organized by the Medical Research Council Centre for Drug Safety Science (University of Liverpool) on 5 September 2013 and attended by industry, academia and regulatory representatives, was designed to gain a better understanding of the gaps in the field of structural cardiotoxicity that can be addressed through collaborative efforts. Specific recommendations from the workshop for future collaborative activities included: greater efforts to identify predictive (i) preclinical; and (ii) clinical biomarkers of early cardiovascular injury; (iii) improved understanding of comparative physiology/pathophysiology and the clinical predictivity of current preclinical in vivo models; (iv) the identification and use of a set of cardiotoxic reference compounds for comparative profiling in improved animal and human cellular models; (v) more sharing of data (through publication/consortia arrangements) on target-related toxicities; (vi) strategies to develop cardio-protective agents; and (vii) closer interactions between preclinical scientists and clinicians to help ensure best translational efforts.

Roflumilast-induced Local Vascular Injury Is Associated with a Coordinated Proteome and Microparticle Change in the Systemic Circulation in Pigs

Drug-induced vascular injury (DIVI) is commonly associated with phosphodiesterase (PDE) inhibitors. Despite histological characterization, qualified biomarkers for DIVI detection are lacking. We investigated whether a single administration of roflumilast (PDE-IV inhibitor) induces vascular damage and identified novel surrogate biomarkers of acute vascular injury. Pigs received postoperative 250, 375, or 500 μg of roflumilast or placebo/control. After 1.5 hr, coronary reactivity was determined by catheter-based administration of acetylcholine and sodium nitroprusside (SNP) in the coronary sinus. Immunohistochemical analysis of vessel integrity (von Willebrand factor [vWF]) and fibrin(ogen) deposition was performed in the coronary artery and aorta. Peripheral blood was collected for differential proteomics and microparticles analysis. Circulating interleukin (IL)-6 was analyzed. Roflumilast-treated animals displayed higher vasodilation to acetylcholine and SNP versus controls (p < .05). Roflumilast-treated animals showed a dose-dependent (p < .05) decrease in vessel integrity and dose-dependent increase in fibrin deposition forming a continuous layer at roflumilast-500 μg. Peripheral blood of roflumilast-500-μg-treated animals showed increased levels of total and endothelial-derived microparticles and exhibited a coordinated change in proteins kininogen-1, endothelin-1, gelsolin, apolipoprotein A-I, and apolipoprotein-J associated with vascular injury (p < .05 vs. controls). IL-6 remained unaltered. Roflumilast-induced vascular injury can be detected by novel markers in peripheral blood. Validation of these surrogate markers in human samples seems required.

Characterization of chemically induced liver injuries using gene co-expression modules

Liver injuries due to ingestion or exposure to chemicals and industrial toxicants pose a serious health risk that may be hard to assess due to a lack of non-invasive diagnostic tests. Mapping chemical injuries to organ-specific damage and clinical outcomes via biomarkers or biomarker panels will provide the foundation for highly specific and robust diagnostic tests. Here, we have used DrugMatrix, a toxicogenomics database containing organ-specific gene expression data matched to dose-dependent chemical exposures and adverse clinical pathology assessments in Sprague Dawley rats, to identify groups of co-expressed genes (modules) specific to injury endpoints in the liver. We identified 78 such gene co-expression modules associated with 25 diverse injury endpoints categorized from clinical pathology, organ weight changes, and histopathology. Using gene expression data associated with an injury condition, we showed that these modules exhibited different patterns of activation characteristic of each injury. We further showed that specific module genes mapped to 1) known biochemical pathways associated with liver injuries and 2) clinically used diagnostic tests for liver fibrosis. As such, the gene modules have characteristics of both generalized and specific toxic response pathways. Using these results, we proposed three gene signature sets characteristic of liver fibrosis, steatosis, and general liver injury based on genes from the co-expression modules. Out of all 92 identified genes, 18 (20%) genes have well-documented relationships with liver disease, whereas the rest are novel and have not previously been associated with liver disease. In conclusion, identifying gene co-expression modules associated with chemically induced liver injuries aids in generating testable hypotheses and has the potential to identify putative biomarkers of adverse health effects.

Nonclinical Safety Biomarkers of Drug-induced Vascular Injury

Better biomarkers are needed to identify, characterize, and/or monitor drug-induced vascular injury (DIVI) in nonclinical species and patients. The Predictive Safety Testing Consortium (PSTC), a precompetitive collaboration of pharmaceutical companies and the U.S. Food and Drug Administration (FDA), formed the Vascular Injury Working Group (VIWG) to develop and qualify translatable biomarkers of DIVI. The VIWG focused its research on acute DIVI because early detection for clinical and nonclinical safety monitoring is desirable. The VIWG developed a strategy based on the premise that biomarkers of DIVI in rat would be translatable to humans due to the morphologic similarity of vascular injury between species regardless of mechanism. The histomorphologic lexicon for DIVI in rat defines degenerative and adaptive findings of the vascular endothelium and smooth muscles, and characterizes inflammatory components. We describe the mechanisms of these changes and their associations with candidate biomarkers for which advanced analytical method validation was completed. Further development is recommended for circulating microRNAs, endothelial microparticles, and imaging techniques. Recommendations for sample collection and processing, analytical methods, and confirmation of target localization using immunohistochemistry and in situ hybridization are described. The methods described are anticipated to aid in the identification and qualification of translational biomarkers for DIVI.

Selective inhibition of PDE4 in Wistar rats can lead to dilatation in testis, efferent ducts, and epididymis and subsequent formation of sperm granulomas

Testicular tubular dilatation and degeneration and epididymal sperm granulomas were frequently seen in 4-week toxicity studies using different phosphodiesterase-4 (PDE4) inhibitors in Wistar rats, including the prototypic PDE4 inhibitor BYK169171. To investigate the pathogenesis of testicular and epididymal lesions, a time course study with BYK169171 was conducted with sequential necropsies after 7, 14, 21, and 28 days of treatment. After 7 days, a dilatation of efferent ducts and of the initial segment of the epididymis and a subacute interstitial inflammation were seen followed by a diffuse dilatation of seminiferous tubules in the testis. Dilatation and inflammation were most pronounced after 14 days. Single animals also exhibited vascular necrosis in the inflamed interstitium. Although dilatation decreased later in the study, the incidence and severity of tubular degeneration increased from 14 days onward. Sperm granulomas developed in efferent ducts and in the caput and cauda of the epididymis after 14 days. Our results demonstrate a clear time course of PDE4 inhibition-induced lesions, with dilatation preceding sperm granuloma formation. We conclude that the most likely mechanism of toxicity is a disturbance of fluid homeostasis in efferent and epididymal ducts resulting in abnormal luminal fluid and sperm contents, epithelial damage at specific sites of the excurrent duct system, sperm leakage, and granuloma formation.

The therapeutic profile of rolipram, PDE target and mechanism of action as a neuroprotectant following spinal cord injury

The extent of damage following spinal cord injury (SCI) can be reduced by various neuroprotective regimens that include maintaining levels of cyclic adenosine monophosphate (cyclic AMP), via administration of the phosphodiesterase 4 (PDE4) inhibitor Rolipram. The current study sought to determine the optimal neuroprotective dose, route and therapeutic window for Rolipram following contusive SCI in rat as well as its prominent PDE target and putative mechanism of protection. Rolipram or vehicle control (10% ethanol) was given subcutaneously (s.c.) daily for 2 wk post-injury (PI) after which the preservation of oligodendrocytes, neurons and central myelinated axons was stereologically assessed. Doses of 0.1 mg/kg to 1.0 mg/kg (given at 1 h PI) increased neuronal survival; 0.5 mg to 1.0 mg/kg protected oligodendrocytes and 1.0 mg/kg produced optimal preservation of central myelinated axons. Ethanol also demonstrated significant neuronal and oligo-protection; though the preservation provided was significantly less than Rolipram. Subsequent use of this optimal Rolipram dose, 1.0 mg/kg, via different routes (i.v., s.c. or oral, 1 h PI), demonstrated that i.v. administration produced the most significant and consistent cyto- and axo- protection, although all routes were effective. Examination of the therapeutic window for i.v. Rolipram (1.0 mg/kg), when initiated between 1 and 48 h after SCI, revealed maximal neuroprotection at 2 h post-SCI, although the protective efficacy of Rolipram could still be observed when administration was delayed for up to 48 h PI. Importantly, use of the optimal Rolipram regimen significantly improved locomotor function after SCI as measured by the BBB score. Lastly we show SCI-induced changes in PDE4A, B and D expression and phosphorylation as well as cytokine expression and immune cell infiltration. We demonstrate that Rolipram abrogates SCI-induced PDE4B1 and PDE4A5 production, PDE4A5 phosphorylation, MCP-1 expression and immune cell infiltration, while preventing post-injury reductions in IL-10. This work supports the use of Rolipram as an acute neuroprotectant following SCI and defines an optimal administration protocol and target for its therapeutic application.

Therapeutic potential of ASP3258, a selective phosphodiesterase 4 inhibitor, on chronic eosinophilic airway inflammation

We investigated and compared the pharmacological effects of a PDE4 inhibitor ASP3258 (3-[4-(3-chlorophenyl)-1-ethyl-7-methyl-2-oxo-1,2-dihydro-1,8-naphthyridin-3-yl] propanoic acid), with those of roflumilast, the most clinically advanced PDE4 inhibitor known. ASP3258 inhibited human PDE4A, 4B, 4C, and 4D with respective IC(50) values of 0.036, 0.050, 0.45, and 0.035 nmol/l, all approximately 3-6 times more potent than roflumilast. ASP3258 inhibited LPS-induced TNF-α production and PHA-induced IL-5 production in human whole blood cells with respective IC(50) values of 110 and 100 nmol/l, both approximately 10 times less potent than roflumilast. Repeatedly administered ASP3258 and roflumilast both suppressed chronic airway eosinophilia induced by repeated exposure to ovalbumin in Brown Norway rats with respective ED(50) values of 0.092 and 0.17 mg/kg. We also evaluated the toxicological profiles of ASP3258. Although PDE4 inhibitors induce emesis by mimicking the pharmacological action of an α(2)-adrenoceptor antagonist, repeated administration of ASP3258 (3 mg/kg) had no such inhibitory effect on rats anesthetized with α(2) - adrenoceptor agonist. PDE4 inhibitors are also known to induce vascular injury in rats. Although repeatedly administered ASP3258 (3 and 10 mg/kg) significantly increased plasma fibrinogen, a biomarker for toxicity, 1 mg/kg of ASP3258 did not. These results suggest that ASP3258 is an attractive PDE4 inhibitor for treating chronic eosinophilic airway inflammation due to asthma.

Evidence for the nitric oxide pathway as a potential mode of action in fenoldopam-induced vascular injury

Fenoldopam, a dopaminergic DA1 agonist, induces vasodilatation via nitric oxide (NO), and this may be associated with mesenteric arterial injury. NO is produced from the enzymatic action of nitric oxide synthase (NOS), which is regulated by the shear-stress mediating protein caveolin-1. Profound vasodilatation and accompanied decreased shear are early events that could initiate vascular injury. Therefore, it is of interest to determine the role of caveolin-1 and the NO pathway in fenoldopam-induced vascular injury. At sites of fenoldopam-induced mesenteric arterial injury, decreased caveolin-1 expression and apoptosis were prominent immunohistochemical findings. An additional finding at these sites of injury were loss and/or reduced expression of caveolin-1 regulated structural proteins, connexin-43, (gap junction) ZO-1, and claudin (tight junctions). Because functional loss of caveolin-1 is associated with increased NOS activity and vasodilatation via NO, studies were conducted to show a NO donor produced vascular lesions in the mesenteric arteries morphologically similar to those induced by fenoldopam. Moreover, the incidence and severity of fenoldopam-induced vascular injury were reduced when an NOS inhibitor or a scavenger of NO-generated free radicals were coadministered with fenoldopam. Collectively, these data suggest that caveolin-1 and its regulated NO pathway may play an important role in vasodilatory drug-induced vascular injury.

Antenatal phosphodiesterase 4 inhibition restores postnatal growth and pulmonary development in a model of chorioamnionitis in rabbits

Chorioamnionitis is implicated in the pathophysiology of bronchopulmonary disease, and the associated inflammatory response is responsible for adverse effects on alveolar development. The aim of this work was to analyze the effects of a phosphodiesterase 4 (PDE4)-selective inhibitor, rolipram (a modulator of the inflammatory response), in an experimental model of chorioamnionitis on pulmonary development and on the processes of infection and inflammation. Rabbit mothers were assigned to four groups: 1) saline serum inoculation (controls); 2) Escherichia coli intrauterine inoculation (C+); 3) rolipram infusion (R+); and 4) E. coli inoculation + rolipram infusion (C+R+). High rates of morbility and mortality were noticed in mothers and pups (5 of 13 pregnant rabbits in groups with rolipram). Alveolar development, inflammation, and infection were analyzed in pups at day 0 and day 5. At day 0, in the context of chorioamnionitis, rolipram significantly decreased birth weight (p < 0.01) relative to that of controls (p < 0.05). At day 5, weight normalized in group C+R+ but not in group C+ relative to controls (p < 0.001); moreover, alveolar airspace volume was preserved in group C+R+ but not in group C+ (p < 0.05). Interstitial volume decreased in group C+ versus controls (p < 0.05) but was preserved in group C+R+. Specific alveolar area was not significantly modified by rolipram. No significant difference was found concerning bronchoalveolar lavage cellularity, and all blood cultures remained sterile. In this model of impaired alveologenesis, rolipram significantly preserved specific alveolar density. However, PDE4 inhibition induced antenatal fetal demise and growth retardation.

Inhibition of cyclooxygenase-2 prevents adverse effects induced by phosphodiesterase type 4 inhibitors in rats

BACKGROUND AND PURPOSE

Phosphodiesterase type 4 (PDE4) inhibitors such as roflumilast are currently being developed as anti-inflammatory treatments for chronic airway disorders. However, high doses of PDE4 inhibitors have also been linked to several side effects in different animal species, including pro-inflammatory effects in the rat. Here, we analysed PDE4-related toxicological findings in a rat model and how these side effects might be therapeutically prevented.

EXPERIMENTAL APPROACH

Wistar rats were treated orally once daily with 10 mg·kg⁻¹ roflumilast for 4 days. Macroscopic changes were monitored throughout the study and further parameters were analysed at the end of the experiment on day 5. In addition, the effects of concomitant treatment with cyclooxygenase (COX) inhibitors were assessed.

KEY RESULTS

Supratherapeutical treatment with roflumilast induced marked body and spleen weight loss, diarrhea, increased secretory activity of the harderian glands, leukocytosis, increased serum cytokine-induced neutrophil chemoattractant-1 (CINC-1) levels, and histopathological changes in thymus, spleen, mesentery and mesenteric lymph nodes. All these toxicological findings could be prevented by the non-steroidal anti-inflammatory drug (NSAID) and non-selective COX inhibitor, diclofenac, given orally. Similar protective effects could be achieved by the COX-2 selective inhibitor lumiracoxib, whereas the COX-1 selective inhibitor SC-560 was generally not effective.

CONCLUSIONS AND IMPLICATIONS

Treatment with an NSAID inhibiting COX-2 prevents the major effects found after subchronic overdosing with the PDE4-specific inhibitor roflumilast. If this effect translates into humans, such combined treatment may increase the therapeutic window of PDE4 inhibitors, currently under clinical development.

Update on roflumilast, a phosphodiesterase 4 inhibitor for the treatment of chronic obstructive pulmonary disease

Phosphodiesterase 4 (PDE4) is a member of the PDE enzyme superfamily that inactivates cyclic adenosine monophosphate and cyclic guanosine monophosphate, and is the main PDE isoenzyme occurring in cells involved in inflammatory airway disease such as chronic obstructive pulmonary disease (COPD). COPD is a preventable and treatable disease and is characterized by airflow obstruction that is not fully reversible. Chronic progressive symptoms, particularly dyspnoea, chronic bronchitis and impaired overall health are worse in those who have frequent, acute episodes of symptom exacerbation. Although several experimental PDE4 inhibitors are in clinical development, roflumilast, a highly selective PDE4 inhibitor, is the first in its class to be licensed, and has recently been approved in several countries for oral, once-daily treatment of severe COPD. Clinical trials have demonstrated that roflumilast improves lung function and reduces exacerbation frequency in COPD. Furthermore, its unique mode of action may offer the potential to target the inflammatory processes underlying COPD. Roflumilast is effective when used concomitantly with all forms of bronchodilator and even in patients treated with inhaled corticosteroids. Roflumilast thus represents an important addition to current therapeutic options for COPD patients with chronic bronchitis, including those who remain symptomatic despite treatment. This article reviews the current status of PDE4 inhibitors, focusing on the pharmacokinetics, efficacy and safety of roflumilast. In particular, it provides an overview of the effects of roflumilast on lung function and exacerbations, glucose homoeostasis and weight loss, and the concomitant use of long-acting beta(2)-adrenergic receptor agonists and short-acting muscarinic receptor antagonists.

Early events in vascular injury in the rat induced by the phosphodiesterase IV inhibitor SCH 351591

Treatment with drugs from multiple classes induces vascular injury with medial necrosis, hemorrhage, endothelial damage, and inflammation. Previous research has suggested early events might be occurring well in advance of the full lesions that appear forty-eight to seventy-two hours after dosing with SCH 351591, a PDE IV inhibitor. This study was performed to study early events in detail. Rats were dosed with 20 mg/kg of drug by gavage and sacrificed at times between fifteen and 240 minutes after dosing. Tissues were collected for histopathological analysis and gene expression studies. Serum was collected for biomarker analysis. The data from biomarker analysis showed a three-part response with an early phase that was maximal at fifteen to thirty minutes, a second phase from forty-five to 180 minutes, and the third phase that was starting to rise at four hours. The first phase included increases in lymphocytes, serum histamine, and serum nitrite. The second phase shows continued elevation of serum nitrite. The third phase was marked by an increase in serum GRO/CINC-1. At fifteen minutes, histopathology showed activation of mast cells, but not degranulation. Increases in endothelial activation and perivascular inflammatory cells were first apparent at thirty minutes and increased through 240 minutes.

Myocardial and Reproductive System Toxicity of SCH 351591, a Selective Phosphodiesterase-4 Inhibitor, in CD-1 Mice

This report describes the findings of preclinical testing of SCH 351591, a selective phosphodiesterase 4 inhibitor, in CD-1 mice over a wide range of doses, in which the heart and reproductive organs of both sexes demonstrated toxic effects. Repeat-dose toxicity studies assessed 5, 15, 50, 100, 200, 400, and 800 mg/kg/day, orally by gavage, for one or three months. Findings included higher testes and ovary weights and lower uterus weights (≥200 mg/kg), small ovaries/uterus (≥400 mg/kg), and histopathologic changes of large corpora lutea and ovarian atrophy at 200 and 800 mg/kg, respectively. In addition, chronic myocardial inflammation of the heart base occurred at 100 mg/kg. Vaginal staging of the estrous cycle revealed persistent diestrus. There was no histopathologic correlate or morphometric change to explain higher testes weights. A pilot fertility and early embryonic developmental toxicity study assessing doses of 100, 200, 400, and 800 mg/kg/day produced complementary results. Females had prolonged or abnormal estrous cycles, fewer successful pregnancies, increased ovarian corpora lutea, and decreased size of live litters owing to fetal resorptions. Male fertility was not affected. However, males had a 25% increase in testes weights at all doses. The pharmacology of specific PDE4 isoenzymes may explain both the reproductive and cardiac findings.

Effects of phosphodiesterase 4 inhibition on alveolarization and hyperoxia toxicity in newborn rats

BACKGROUND

Prolonged neonatal exposure to hyperoxia is associated with high mortality, leukocyte influx in airspaces, and impaired alveolarization. Inhibitors of type 4 phosphodiesterases are potent anti-inflammatory drugs now proposed for lung disorders. The current study was undertaken to determine the effects of the prototypal phosphodiesterase-4 inhibitor rolipram on alveolar development and on hyperoxia-induced lung injury.

METHODOLOGY/FINDINGS

Rat pups were placed under hyperoxia (FiO2>95%) or room air from birth, and received rolipram or its diluent daily until sacrifice. Mortality rate, weight gain and parameters of lung morphometry were recorded on day 10. Differential cell count and cytokine levels in bronchoalveolar lavage and cytokine mRNA levels in whole lung were recorded on day 6. Rolipram diminished weight gain either under air or hyperoxia. Hyperoxia induced huge mortality rate reaching 70% at day 10, which was prevented by rolipram. Leukocyte influx in bronchoalveolar lavage under hyperoxia was significantly diminished by rolipram. Hyperoxia increased transcript and protein levels of IL-6, MCP1, and osteopontin; rolipram inhibited the increase of these proteins. Alveolarization was impaired by hyperoxia and was not restored by rolipram. Under room air, rolipram-treated pups had significant decrease of Radial Alveolar Count.

CONCLUSIONS

Although inhibition of phosphodiesterases 4 prevented mortality and lung inflammation induced by hyperoxia, it had no effect on alveolarization impairment, which might be accounted for by the aggressiveness of the model. The less complex structure of immature lungs of rolipram-treated pups as compared with diluent-treated pups under room air may be explained by the profound effect of PDE4 inhibition on weight gain that interfered with normal alveolarization.

Histopathology of vascular injury in Sprague-Dawley rats treated with phosphodiesterase IV inhibitor SCH 351591 or SCH 534385

Histopathological and immunohistochemical studies were conducted to characterize vascular injuries in rats treated with phosphodiesterase (PDE) IV inhibitors SCH 351591 or SCH 534385. Sprague-Dawley rats were administered PDE IV inhibitors by gavage at a range of doses and times. The two PDE IV inhibitors induced comparable levels of vascular injury, primarily in the mesentery and to a lesser extent in the pancreas, kidney, liver, small intestine, and stomach. Mesenteric vascular changes occurred as early as one hour, progressively developed over twenty-four to forty-eight hours, peaked at seventy-two hours, and gradually subsided from seven to nine days. The typical morphology of the vascular toxicity consisted of hemorrhage and necrosis of arterioles and arteries, microvascular injury, fibrin deposition, and perivascular inflammation of a variety of blood vessels. The incidence and severity of mesenteric vascular injury increased in a time- and dose-dependent manner in SCH 351591- or SCH 534385-treated rats. Mesenteric vascular injury was frequently associated with activation of mast cells (MC), endothelial cells (EC), and macrophages (MØ). Immunohistochemical studies showed increases in CD63 immunoreactivity of mesenteric MC and in nitrotyrosine immunoreactivity of mesenteric EC and MØ. The present study also provides a morphological and cellular basis for evaluating candidate biomarkers of drug-induced vascular injury.

Synthesis of pyrrolo[2,3-d]pyridazinones as potent, subtype selective PDE4 inhibitors

A series of pyrrolo [2,3-d]pyridazinones was synthesized and tested for their inhibitory activity on PDE4 subtypes A, B and D and selectivity toward Rolipram high affinity binding site (HARBS). New agents with interesting profile were reported; in particular compound 9e showed a good PDE4 subtype selectivity, being 8 times more potent (IC50 = 0.32 microM) for PDE4B (anti-inflammatory) than for PDE4D (IC50 = 2.5 microM), generally considered the subtype responsible for emesis. Moreover the ratio HARBS/PDE4B was particularly favourable for 9e (147), suggesting that the best arranged groups around the pyrrolopyridazinone core are an isopropyl at position-1, an ethoxycarbonyl at position-2, together with an ethyl group at position-6. For compounds 8 and 15a the ability to inhibit TNFalpha production in PBMC was evaluated and the results are consistent with their PDE4 inhibitory activity.

Effect of inhaled roflumilast on the prevention and resolution of allergen-induced late phase airflow obstruction in Brown Norway rats

Orally active phosphodiesterase 4 (PDE4) inhibitors have been developed for the treatment of asthma and chronic obstructive pulmonary disorders (COPD) although their full development has been limited by adverse side effects. Administration of PDE4 inhibitors by inhalation may improve their therapeutic index, but limited information exists on the efficacy of inhaled PDE4 inhibitors to improve lung function. In this study in ovalbumin-sensitized Brown Norway rats, roflumilast was given either intratracheally or by nose-only inhalation and changes in lung function (forced vital capacity, FVC; peak expiratory flow, PEF) and inflammatory cell influx (total cells, eosinophils and neutrophils) into the bronchoalveolar lavage (BAL) fluid were evaluated 24 h after allergen challenge. Intratracheal roflumilast, given 5 h before antigen challenge, inhibited the antigen-induced reductions in FVC (ED50 = 140 microg/kg, i.t.) and total cells appearing in the bronchoalveolar lavage fluid (ED50 = 50 microg/kg, i.t.). By the nose-only inhalation route, roflumilast reduced the bronchoalveolar lavage fluid total cells (ED50 = 10 microg/kg, estimated pulmonary deposition). Intratracheal roflumilast (600 microg/kg, i.t.) was also given to rats 24 h after the antigen challenge and reversed the antigen-induced reductions of FVC by 38% at 1 h, 54% at 5 h and 71% by 16 h. Intratracheal roflumilast also reduced the number of inflammatory cells in the bronchoalveolar lavage fluid and reduced the interstitial airway edema caused by the antigen challenge. These results support the development of inhaled PDE4 inhibitors for the treatment of asthma and COPD, particularly for the improvement of lung function.

Investigation of the molecular mechanisms preceding PDE4 inhibitor-induced vasculopathy in rats: tissue inhibitor of metalloproteinase 1, a potential predictive biomarker

Phosphodiesterase (PDE) 4 inhibitors are a class of drugs that can provide novel therapies for asthma and chronic obstructive pulmonary disease. Their development is frequently hampered by the induction of vascular toxicity in rat mesenteric tissue during preclinical studies. Whereas these vascular lesions in rats have been well characterized histologically, little is known about their pathogenesis and in turn, sensitive and specific biomarkers for preclinical and clinical monitoring do not exist. In order to investigate the early molecular mechanisms underlying vascular injury, time-course studies were performed by treating rats for 2-24 h with high doses of the PDE4 inhibitor CI-1044. Transcriptomics analyses in mesenteric tissue were performed using oligonucleotide microarray and real-time RT-PCR technologies and compared to histopathological observations. In addition, protein measurements were performed in serum samples to identify soluble biomarkers of vascular injury. Our results indicate that molecular alterations preceded the histological observations of inflammatory and necrotic lesions in mesenteric arteries. Some gene expression changes suggest that the development of the lesions could follow a primary modulation of the vascular tone in response to the pharmacological effect of the compound. Activation of genes coding for pro- and antioxidant enzymes, cytokines, adhesion molecules, and tissue inhibitor of metalloproteinase 1 (TIMP-1) indicates that biomechanical stimuli may contribute to vascular oxidant stress, inflammation, and tissue remodeling. TIMP-1 appeared to be an early and sensitive predictive biomarker of the inflammatory and the tissue remodeling components of PDE4 inhibitor-induced vascular injury.

New histologic findings in idiopathic mesenteric phlebosclerosis: clues to its pathogenesis and etiology--probably ingested toxic agent-related

BACKGROUND

Idiopathic mesenteric phlebosclerosis (IMP) is a recently known and rare disease entity, which is a member of non-thrombotic, non-inflammatory stenosis or occlusion of the mesenteric veins. In spite of the unique histopathology and particular location, the cause and pathogenesis of IMP remain unknown. The aim of this brief study was to propose a pathogenesis and possible etiology based on the reviewed clinical data and some newly discovered pathologic findings in several recent cases in our and other hospitals.

METHODS

The clinical data of 5 patients were collected, with detailed tracing of past history, drug use and dietary habit. The histologic sections were reviewed in detail, with additional histochemical stains and immunohistochemical stains in 4 available cases.

RESULTS

The most important of our findings other than the previously described typical features was a unique type of coagulative necrosis, which we call mummification, involving not only the muscular coat of veins in early and late phases but also the subsequent hyperplastic myointima in veins, portion of the media of arteries closely neighboring the sclerotic vein, a zone of muscular wall of the colon around the passing sclerotic veins and the inner zone of muscular wall of the colon, and accompanied by fibrosis/sclerosis and then calcification in the damaged tissues. Two of our patients were a couple who had been taking Chinese herbs regularly.

CONCLUSION

A pathogenesis is suggested for at least a subgroup of cases of IMP: the disease is initiated by a slow but longstanding direct hypoxic injury to the venous muscular layer, which leads to gradual mummification and then sclerosis and calcification of the venous muscle. This is followed by the repeated same damage of the subsequent reactively hyperplastic myointima in the veins, and these changes finally result in gradual venous occlusion. Certain toxins or biochemicals, probably existing in the frequently ingested contents and absorbed to the venous return, may play the most important role in this damage. However, analysis of more cases is required to support the proposal, and if such support is found, the toxic agents remain to be clarified via further laboratory investigations.

An update and appraisal of the cilomilast Phase III clinical development programme for chronic obstructive pulmonary disease

Cilomilast (Ariflo, SB 207499) is an orally active, second-generation phosphodiesterase (PDE) 4 inhibitor that is being developed by GlaxoSmithkline for the treatment of chronic obstructive pulmonary disease (COPD). The results of Phase I and Phase II studies have demonstrated that cilomilast significantly improves lung function and quality of life to a clinically meaningful extent, which has led to a comprehensive Phase III programme of research evaluating efficacy, safety and mechanism of action. However, the results of those Phase III studies are unremarkable and disappointing, raising doubt over the future of cilomilast as a novel therapy for COPD. This review summarizes data obtained from the Phase III clinical development programme, highlights some of the potential concerns both specific to cilomilast and to PDE4 inhibitors in general and assesses the likelihood that cilomilast will reach the market.

Phosphodiesterase Type 4 Inhibitors Cause Proinflammatory Effects in Vivo

Phosphodiesterase type 4 (PDE(4)) inhibitors are currently being evaluated as potential therapies for inflammatory airway diseases. However, this class of compounds has been shown to cause an arteritis/vasculitis of unknown etiology in rats and cynomolgus monkeys. Studies in rodents have demonstrated the anti-inflammatory effects of PDE(4) inhibitors on lipopolysaccharide (LPS)-induced airway inflammation. The aim of this work was to assess the direct effects of PDE(4) inhibitors on inflammatory cells and cytokine levels in the lung in relation to therapeutic effects. The effects of the PDE(4) inhibitors 3-cyclo-propylmethoxy-4-difluoromethoxy-N-[3,5-di-chloropyrid-4-yl]-benzamide (roflumilast) and 3-(cyclopentyloxy)-N-(3,5-dichloro-4-pyridyl)-4-methoxybenzamide (piclamilast) were assessed in vivo, using BALB/c mice, and in vitro, in unstimulated human endothelial and epithelial cell lines. In BALB/c mice, LPS challenge caused an increase in neutrophils in bronchoalveolar lavage (BAL) and lung tissue and BAL tumor necrosis factor-alpha levels, which were inhibited by treatment with either roflumilast or piclamilast (30-100 mg/kg subcutaneously). However, roflumilast and piclamilast alone (100 mg/kg) caused a significant increase in plasma and lung tissue keratinocyte-derived chemokine (KC) levels, and lung tissue neutrophils. In vitro, both piclamilast and roflumilast caused an increase in interleukin (IL)-8 release from human umbilical vein endothelial cells but not BEAS-2B cells, suggesting that one source of the increased KC may be endothelial cells. At doses that antagonized an LPS-induced inflammatory response, the PDE(4) inhibitors possessed proinflammatory activities in the lung that may limit their therapeutic potential. The proinflammatory cytokines KC and IL-8 therefore may provide surrogate biomarkers, both in preclinical animal models and in the clinic, to assess potential proinflammatory effects of this class of compounds.

Changes in submaxillary gland gene expression in F344 rats by multiple dosing of theophylline

Multiple exposure to theophylline, a phosphodiesterase (PDE) inhibitor, induces acinar hypertrophy in the salivary gland. This study examined the effect of theophylline on the gene expression of secretory proteins and phosphodiesterases in the submaxillary gland. Male F344 rats received saline or theophylline (50 mg/kg) intraperitoneally for 4 days. The gene expressions for the secretory protein, cystatin S (CysS), and PDE subfamilies 3A and 4D in the submaxillary gland were quantified using RT-PCR. Theophylline exposure resulted in a sustained increase in mRNA expression for CysS and PDE3A, but PDE4D gene expression was unchanged. Our results suggest that submaxillary hypertrophy is primarily caused by the enhanced transcription of CysS, and that the transcription of each PDE subfamily gene is regulated differently.

Mesenteritis precedes vasculitis in the rat mesentery after subacute administration of a phosphodiesterase type 4 inhibitor

Inhibitors of phosphodiesterase type 4 (PDE4) are currently exploited as potent drugs for pulmonary diseases. Some PDE4 inhibitors induce necrotizing panarteritis in the mesentery of rats, comparable to spontaneous polyarteritis nodosa in rats and vascular alterations that are induced by various vasoactive compounds, such as fenoldopam and inhibitors of PDE3. The mechanism of toxicity is unknown. In order to investigate the development of arteritis in the splanchnic vasculature of rats, a time-course study was performed with high doses of a compound (BYK169171), specifically inhibiting PDE4. Rats were treated orally for 1-28 days, and alterations in the mesentery were evaluated by histology, morphometry, and immunohistology. As early as 3 days after the onset of treatment, a mesenteritis was found, characterized by macrophage infiltration, fibroblast proliferation, neovascularization, and loss of adipocytes. Incidence and severity of the mesenteritis were low during the first 2 weeks of treatment, but increased with duration of treatment, finally affecting 2/3 of all animals. A segmental necrotizing panarteritis was detected in some rats treated for 21 or 28 days, but always followed a mesenteritis, whereas many animals with mesenteric inflammation did not have vascular lesions. We postulate that PDE4 inhibitors do not cause a primary vasculitis/arteritis in rats, but induce a non-purulent inflammation as the predominant initial toxic effect in the mesentery. This renders their toxic effect distinct from that of PDE3 inhibitors.

Characterization of the inflammatory response to a highly selective PDE4 inhibitor in the rat and the identification of biomarkers that correlate with toxicity

The primary toxicity associated with repeated oral administration of the PDE4 inhibitor IC542 to the rat is an inflammatory response leading to tissue damage primarily in the gastrointestinal tract and mesentery. Although necrotizing vasculitis is frequently seen with other PDE4 inhibitors, blood vessel injury was rare following IC542 administration and was always associated with inflammation in the surrounding tissue. The incidence and severity of the histologic changes in these studies correlated with elevated peripheral blood leukocytes, serum IL-6, haptoglobin, and fibrinogen, and with decreased serum albumin. By monitoring haptoglobin, fibrinogen and serum albumin changes in IC542-treated rats, it was possible to identify rats with early histologic changes that were reversible. Since PDE4 inhibition is generally associated with anti-inflammatory activity, extensive inflammation in multiple tissues was unexpected with IC542. Co-administration of dexamethasone completely blocked IC542-induced clinical and histologic changes in the rat, confirming the toxicity resulted from inflammatory response. In addition, IC542 augmented release of the proinflammatory cytokine IL-6 in LPS-activated whole blood from rats but not monkeys or humans. The effect of IC542 on IL-6 release from rat leukocytes in vitro is consistent with the proinflammatory response observed in vivo and demonstrates species differences to PDE4 inhibition.

Phosphodiesterase-4 as a potential drug target

Phosphodiesterase-4 (PDE4) is the predominant enzyme in some specific cell types that is responsible for the degradation of the second messenger, cAMP. Consequently, PDE4 plays a crucial role in cell signalling and, as such, it has been the target of clinical drug development of various indications, ranging from anti-inflammation to memory enhancement. In this review, the fundamental biological role of PDE4 in intracellular signalling, its tissue distribution and regulation are described. The historical development of various chemical classes of PDE4 inhibitors and the challenges that face these inhibitors as therapeutics are also discussed. Finally, recent advances in the structural biology of PDE4 and their complexes with various inhibitors, as well as its potential impact on the rational design of potent and selective PDE4 inhibitors, are presented.

Rolipram, a specific type IV phosphodiesterase inhibitor, ameliorates aspirin-induced gastric mucosal injury in rats

Inhibition of type IV phosphodiesterase (PDE IV) activity reduces the production of various proinflammatory cytokine and suppresses neutrophil activation. Nonsteroidal anti-inflammatory drugs such as aspirin induce gastric mucosal lesions. In the pathogenesis of aspirin-induced gastric mucosal lesion, the contributions, of activated inflammatory cells and proinflammatory cytokine production are critical. The specific PDE IV inhibitor rolipram is known to be a potent inhibitor of inflammation by increasing intracellular cyclic AMP in leukocytes. The aim of the present study was to determine whether rolipram can ameliorate aspirin-induced gastric mucosal lesions in rats and whether the agent can inhibit the inrease in neutrophil accumulation and the production of proinflammatory cytokines. Gastric lesions were produced by administration of aspirin (200 mg/kg) and HCI (0.15 N; 8.0 ml/kg). Rolipram was injected 30 min before aspirin administration. The tissue myeloperoxidase concentration in gastric mucosa was measured as an indicat or of neutrophil infiltration. The gastric mucosal concentrations of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) were determined by ELISA. The intragastric administration of aspirin induced multiple hemorrhagic erosions in rat gastric mucosa. Gastric mucosal lesions induced by aspirin were significantly inhibited by treatment with rolipram. The mucosal myeloperoxidase concentration was also suppressed by rolipram. Increases in the gastric content of TNF-alpha and IL-1beta after aspirin administration were inhibited by pretreatment with rolipram. We demonstrated that the specific type IV PDE inhibitor, rolipram, could have a potent antiulcer effect, presumably mediated by its anti-inflammatory properties.

The toxicity of SCH 351591, a novel phosphodiesterase-4 inhibitor, in Cynomolgus monkeys

SCH351591, a novel phosphodiesterase-4 inhibitor under investigation as a potential therapeutic for asthma and chronic obstructive pulmonary disease (COPD), was evaluated in a 3-month rising-dose study in Cynomolgus monkeys. Four groups, containing four monkeys/sex, received vehicle control or rising doses up to 12, 24, or 48 mg/kg of SCH351591 daily. Although initial exposure produced clinical signs of emesis, reduced food intake, and reduced body weight, tachyphylaxis to the emesis allowed dose escalation up to 48 mg/kg/day. Two monkeys died and 3 were sacrificed in moribund condition over the course of the study. Early mortality, involving monkeys dosed with 12 or 24 mg/kg, was attributed to sepsis (2 monkeys) or colon inflammation (3 monkeys). Leukocyte function assays on low- and mid-dose group survivors revealed an inhibition of T lymphocyte proliferation for 12 mg/kg group males and 24 mg/kg group monkeys of both sexes. Necropsy findings, unassociated with early mortality, included reduced size and weight of the thymus, depletion of body fat, red discoloration of the gastric mucosa, and perivascular hemorrhage of the stomach and heart. Stomach and heart gross findings were present in the high-dose group only. Histopathologic lesions, in addition to those attributed to concurrent bacterial infection, included thymic atrophy, serous atrophy of fat, myocardial degeneration and acute to chronic inflammation of small to medium-sized arteries in various organs and tissues including the heart, kidneys, stomach, salivary glands, pancreas, esophagus, gallbladder, and mesentery. The findings of this study demonstrate the potential of a PDE4 inhibitor to alter immunologic response as well as to produce arteriopathy in nonhuman primates.

Specific type IV phosphodiesterase inhibitor ameliorates thioacetamide-induced liver injury in rats

BACKGROUND AND AIMS

Rolipram is a specific type IV phosphodiesterase inhibitor that suppresses the activity of immune cells and the production of pro-inflammatory cytokines. In this study, we assessed the effect of rolipram on acute liver injury using thioacetamide (TAA)-induced liver injury in rats as a model.

METHODS

Rats were treated with rolipram (0.5-5 mg/kg, intraperitoneally) or vehicle and injected 30 min later with TAA (100 mg/kg, subcutaneously). Serum transaminase concentrations and tumor necrosis factor-alpha (TNF-alpha), interleukin 1beta (IL-1beta) and growth related oncogene/cytokine-induced neutrophil chemoattractant-1 (GRO/CINC-1) levels were measured and livers were examined for microscopic changes. Dose-dependent protection against TAA liver injury was based on transaminase levels and inflammatory cytokine production, and was measured 9 h after TAA when the peak release of cytokines occurred.

RESULT

Rolipram suppressed liver injury based on serum aspartate transaminase (AST), alanine transaminase (ALT) and histology and reduced TNF-alpha, IL-1beta and GRO/CINC-1 levels. Rolipram, at doses of 0.5-5 mg/kg, suppressed serum transaminase and TNF-alpha production in a dose-dependent manner, and these effects were significant at doses of 2.5 and 5 mg/kg.

CONCLUSION

In our rodent model of acute liver injury, rolipram clearly reduced liver damage and inhibited pro-inflammatory cytokine production. These results suggest that specific type IV phosphodiesterase inhibitors, such as rolipram, have potent hepatoprotective effects that are associated with suppressing inflammatory cytokine production.

Differential type 4 cAMP-specific phosphodiesterase (PDE4) expression and functional sensitivity to PDE4 inhibitors among rats, monkeys and humans

It has been suggested that the rat is relatively more susceptible to toxicity induced by inhibitors for type 4 cAMP-specific phosphodiesterase (PDE4). In this study designed to elucidate possible biochemical basis for the higher susceptibility, we compared PDE4 expression levels and their functional relevance among rats, monkeys and humans. In several toxicologically relevant tissues and blood leukocytes, the mRNA expression levels of PDEs 4A, 4B, 4C and 4D were significantly higher in rats than in humans. We confirmed that higher PDE4 expression levels were correlated with a higher enzyme activity level in rat leukocytes. The PDE4 enzyme activity level of leukocytes in monkeys fell between that of rats and humans. Functionally, the potencies of the PDE4 inhibitors rolipram, SB 207499 and SCH 351591 in inhibiting tumor necrosis factor production from leukocytes were in the following order: rat > monkey > human. In addition, rolipram was about 10-fold more potent in rats than in humans in inhibiting phenylephrine-induced contraction of renal artery. These inhibitors were confirmed to be highly selective for PDE4 in comparison to all other PDE families, and to inhibit rat and human PDE4s with identical potencies. Taken together, these results suggest that the higher susceptibility of rats to PDE4 inhibitor-induced toxicity might be due to their higher expression levels of PDE4, and that PDE4 inhibitors may be safer in humans than in monkeys and, particularly, rats.

Subacute toxicity and toxicokinetics of CJ-10882, a type IV phosphodiesterase inhibitor, after 4-week repeated oral administration in dogs

The subacute toxicity and toxicokinetics of a type IV phosphodiesterase inhibitor, CJ-10882, were evaluated after single (on the 1st day) and 4-week (on the 27th day) oral administration of the drug, in doses of 0 (to serve as a control), 2, 10 and 50 mg/kg/day, to male and female dogs (n=3 for male and female dogs for each dose). During the test period, clinical signs, mortality, body weight, food consumption, ophthalmoscopy, urinalysis, hematology, serum biochemistry, gross findings, organ weight and histopathology were examined. The 4-week repeated oral doses of CJ-10882 resulted in salivation, vomiting, and atrophy of the thymus. The absolute toxic dose was 50 mg/kg/day and the level at which no adverse effects were observed was 2 mg/kg/day for male and female dogs. There were no significant gender differences in the pharmacokinetic parameters of CJ-10882 for each dose after both single and 4-week oral administration. The pharmacokinetic parameters of CJ-10882 were dose independent after a single oral administration; the time to reach a peak plasma concentration (T(max)) and the dose-normalized area under the plasma concentration-time curve from time zero to 8 h in plasma (AUC(0-8 h)) were not significantly different among three doses. The accumulation of CJ-10882 after 4-week oral administration was not notable at the toxic dose of 50 mg/kg/day. For example, after 4-week administration, the dose-normalized AUC(0-8 h) value at 50 mg/kg/day (0.132 microg h/ml) was not significantly greater than that at 10 mg/kg/day (0.131 microg h/ml). After 4-week oral administration, the dose-normalized C(max) and AUC(0-8 h) at 50 mg/kg/day were not significantly higher and greater, respectively, than those after the single oral administration.

Rolipram, a specific type IV phosphodiesterase inhibitor, ameliorates indomethacin-induced gastric mucosal injury in rats

Inhibition of type IV phosphodiesterase activity is beneficial in various inflammation mediated by its function to suppress the production of inflammatory cytokines in inflammatory cells. Nonsteroidal anti-inflammatory drugs (NSAIDs) such as indomethacin are well known to develop gastric mucosal lesion. As pathogenesis of indomethacin induced gastric mucosal lesion, activation of neutrophils and inflammatory cytokine production play critical roles. However, the effect of phosphodiesterase inhibitors on development of gastric mucosal lesion has not been reported. In the present study, we examined the effect of specific type IV phosphodiesterase inhibitor (rolipram) on NSAIDs-induced gastric mucosal lesion. Also, we examined the effect of rolipram on tissue prostaglandin E2 (PGE2) production. Indomethacin-induced gastric mucosal injury was produced by the intragastric administration of indomethacin (30 mg/kg). Rolipram was injected to the rats intraperitoneally 30 min before the indomethacin administration. Ulcer index and tissue myeloperoxidase (MPO) activity of the gastric mucosa was evaluated. The gastric concentration of PGE2 was determined by RIA. Gastric mucosal lesion induced by indomethacin was significantly inhibited with treatment of rolipram. Mucosal MPO activity was also suppressed by administration of rolipram. Gastric mucosal PGE2 concentration was not affected by intraperitoneal injection of rolipram. Based on these data, the beneficial effects of rolipram on indomethacin-induced gastric mucosal injury may be attributed to its anti-inflammatory properties.

The antidepressant and antiinflammatory effects of rolipram in the central nervous system

Rolipram is a selective inhibitor of phosphodiesterases (PDE) IV, especially of the subtype PDE IVB. These phosphodiesterases are responsible for hydrolysis of the cyclic nucleotides cAMP and cGMP, particularly in nerve and immune cells. Consequences of rolipram-induced elevation of intracellular cAMP are increased synthesis and release of norepinephrine, which enhance central noradrenergic transmission, and suppress expression of proinflammatory cytokines and other mediators of inflammation. In humans and animals rolipram produces thereby a variety of biological effects. These effects include attenuation of endogenous depression and inflammation in the central nervous system (CNS), both effects are of potential clinical relevance. There are some discrepancies between in vitro and in vivo effects of rolipram, as well as between results obtained in animal models and clinical studies. The clinical use of rolipram is limited because of its behavioral and other side effects. Newly developed selective PDE IV inhibitors with presumably higher potency and lower toxicity are currently under investigation.