DPP-4 inhibitors sitagliptin and PF-00734,200 mitigate dopaminergic neurodegeneration, neuroinflammation and behavioral impairment in the rat 6-OHDA model of Parkinson's disease.

Epidemiological studies report an elevated risk of Parkinson's disease (PD) in patients with type 2 diabetes mellitus (T2DM) that is mitigated in those prescribed dipeptidyl peptidase 4 (DPP-4) inhibitors. With an objective to characterize clinically translatable doses of DPP-4 inhibitors (gliptins) in a well-characterized PD rodent model, sitagliptin, PF-00734,200 or vehicle were orally administered to rats initiated either 7-days before or 7-days after unilateral medial forebrain bundle 6-hydroxydopamine (6-OHDA) lesioning. Measures of dopaminergic cell viability, dopamine content, neuroinflammation and neurogenesis were evaluated thereafter in ipsi- and contralateral brain. Plasma and brain incretin and DPP-4 activity levels were quantified. Furthermore, brain incretin receptor levels were age-dependently evaluated in rodents, in 6-OHDA challenged animals and human subjects with/without PD. Cellular studies evaluated neurotrophic/neuroprotective actions of combined incretin administration. Pre-treatment with oral sitagliptin or PF-00734,200 reduced methamphetamine (meth)-induced rotation post-lesioning and dopaminergic degeneration in lesioned substantia nigra pars compacta (SNc) and striatum. Direct intracerebroventricular gliptin administration lacked neuroprotective actions, indicating that systemic incretin-mediated mechanisms underpin gliptin-induced favorable brain effects. Post-treatment with a threefold higher oral gliptin dose, likewise, mitigated meth-induced rotation, dopaminergic neurodegeneration and neuroinflammation, and augmented neurogenesis. These gliptin-induced actions associated with 70-80% plasma and 20-30% brain DPP-4 inhibition, and elevated plasma and brain incretin levels. Brain incretin receptor protein levels were age-dependently maintained in rodents, preserved in rats challenged with 6-OHDA, and in humans with PD. Combined GLP-1 and GIP receptor activation in neuronal cultures resulted in neurotrophic/neuroprotective actions superior to single agonists alone. In conclusion, these studies support further evaluation of the repurposing of clinically approved gliptins as a treatment strategy for PD.

Sitagliptin elevates plasma and CSF incretin levels following oral administration to nonhuman primates: relevance for neurodegenerative disorders.

The endogenous incretins glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) possess neurotrophic, neuroprotective, and anti-neuroinflammatory actions. The dipeptidyl peptidase 4 (DPP-4) inhibitor sitagliptin reduces degradation of endogenous GLP-1 and GIP, and, thereby, extends the circulation of these protective peptides. The current nonhuman primate (NHP) study evaluates whether human translational sitagliptin doses can elevate systemic and central nervous system (CNS) levels of GLP-1/GIP in naive, non-lesioned NHPs, in line with our prior rodent studies that demonstrated sitagliptin efficacy in preclinical models of Parkinson's disease (PD). PD is an age-associated neurodegenerative disorder whose current treatment is inadequate. Repositioning of the well-tolerated and efficacious diabetes drug sitagliptin provides a rapid approach to add to the therapeutic armamentarium for PD. The pharmacokinetics and pharmacodynamics of 3 oral sitagliptin doses (5, 20, and 100 mg/kg), equivalent to the routine clinical dose, a tolerated higher clinical dose and a maximal dose in monkey, were evaluated. Peak plasma sitagliptin levels were aligned both with prior reports in humans administered equivalent doses and with those in rodents demonstrating reduction of PD associated neurodegeneration. Although CNS uptake of sitagliptin was low (cerebrospinal fluid (CSF)/plasma ratio 0.01), both plasma and CSF concentrations of GLP-1/GIP were elevated in line with efficacy in prior rodent PD studies. Additional cellular studies evaluating human SH-SY5Y and primary rat ventral mesencephalic cultures challenged with 6-hydroxydopamine, established cellular models of PD, demonstrated that joint treatment with GLP-1 + GIP mitigated cell death, particularly when combined with DPP-4 inhibition to maintain incretin levels. In conclusion, this study provides a supportive translational step towards the clinical evaluation of sitagliptin in PD and other neurodegenerative disorders for which aging, similarly, is the greatest risk factor.

Phosphodiesterase 2 inhibition preferentially promotes NO/guanylyl cyclase/cGMP signaling to reverse the development of heart failure.

Heart failure (HF) is a shared manifestation of several cardiovascular pathologies, including hypertension and myocardial infarction, and a limited repertoire of treatment modalities entails that the associated morbidity and mortality remain high. Impaired nitric oxide (NO)/guanylyl cyclase (GC)/cyclic guanosine-3',5'-monophosphate (cGMP) signaling, underpinned, in part, by up-regulation of cyclic nucleotide-hydrolyzing phosphodiesterase (PDE) isozymes, contributes to the pathogenesis of HF, and interventions targeted to enhancing cGMP have proven effective in preclinical models and patients. Numerous PDE isozymes coordinate the regulation of cardiac cGMP in the context of HF; PDE2 expression and activity are up-regulated in experimental and human HF, but a well-defined role for this isoform in pathogenesis has yet to be established, certainly in terms of cGMP signaling. Herein, using a selective pharmacological inhibitor of PDE2, BAY 60-7550, and transgenic mice lacking either NO-sensitive GC-1α (GC-1α-/-) or natriuretic peptide-responsive GC-A (GC-A-/-), we demonstrate that the blockade of PDE2 promotes cGMP signaling to offset the pathogenesis of experimental HF (induced by pressure overload or sympathetic hyperactivation), reversing the development of left ventricular hypertrophy, compromised contractility, and cardiac fibrosis. Moreover, we show that this beneficial pharmacodynamic profile is maintained in GC-A-/- mice but is absent in animals null for GC-1α or treated with a NO synthase inhibitor, revealing that PDE2 inhibition preferentially enhances NO/GC/cGMP signaling in the setting of HF to exert wide-ranging protection to preserve cardiac structure and function. These data substantiate the targeting of PDE2 in HF as a tangible approach to maximize myocardial cGMP signaling and enhancing therapy.

In vitro and in vivo effects of 2,4 diaminoquinazoline inhibitors of the decapping scavenger enzyme DcpS: Context-specific modulation of SMN transcript levels.

C5-substituted 2,4-diaminoquinazoline inhibitors of the decapping scavenger enzyme DcpS (DAQ-DcpSi) have been developed for the treatment of spinal muscular atrophy (SMA), which is caused by genetic deficiency in the Survival Motor Neuron (SMN) protein. These compounds are claimed to act as SMN2 transcriptional activators but data underlying that claim are equivocal. In addition it is unclear whether the claimed effects on SMN2 are a direct consequence of DcpS inhibitor or might be a consequence of lysosomotropism, which is known to be neuroprotective. DAQ-DcpSi effects were characterized in cells in vitro utilizing DcpS knockdown and 7-methyl analogues as probes for DcpS vs non-DcpS-mediated effects. We also performed analysis of Smn transcript levels, RNA-Seq analysis of the transcriptome and SMN protein in order to identify affected pathways underlying the therapeutic effect, and studied lysosomotropic and non-lysosomotropic DAQ-DCpSi effects in 2B/- SMA mice. Treatment of cells caused modest and transient SMN2 mRNA increases with either no change or a decrease in SMNΔ7 and no change in SMN1 transcripts or SMN protein. RNA-Seq analysis of DAQ-DcpSi-treated N2a cells revealed significant changes in expression (both up and down) of approximately 2,000 genes across a broad range of pathways. Treatment of 2B/- SMA mice with both lysomotropic and non-lysosomotropic DAQ-DcpSi compounds had similar effects on disease phenotype indicating that the therapeutic mechanism of action is not a consequence of lysosomotropism. In striking contrast to the findings in vitro, Smn transcripts were robustly changed in tissues but there was no increase in SMN protein levels in spinal cord. We conclude that DAQ-DcpSi have reproducible benefit in SMA mice and a broad spectrum of biological effects in vitro and in vivo, but these are complex, context specific, and not the result of simple SMN2 transcriptional activation.

Design of Potent mRNA Decapping Scavenger Enzyme (DcpS) Inhibitors with Improved Physicochemical Properties To Investigate the Mechanism of Therapeutic Benefit in Spinal Muscular Atrophy (SMA).

The C-5 substituted 2,4-diaminoquinazoline RG3039 (compound 1), a member of a chemical series that was identified and optimized using an SMN2 promoter screen, prolongs survival and improves motor function in a mouse model of spinal muscular atrophy (SMA). It is a potent inhibitor of the mRNA decapping scavenger enzyme (DcpS), but the mechanism whereby DcpS inhibition leads to therapeutic benefit is unclear. Compound 1 is a dibasic lipophilic molecule that is predicted to accumulate in lysosomes. To understand if the in vivo efficacy is due to DcpS inhibition or other effects resulting from the physicochemical properties of the chemotype, we undertook structure based molecular design to identify DcpS inhibitors with improved physicochemical properties. Herein we describe the design, synthesis, and in vitro pharmacological characterization of these DcpS inhibitors along with the in vivo mouse CNS PK profile of PF-DcpSi (compound 24), one of the analogs found to be efficacious in SMA mouse model.

Selectivity Determination of a Small Molecule Chemical Probe Using Protein Microarray and Affinity Capture Techniques.

Small molecule selectivity is an essential component of candidate drug selection and target validation. New technologies are required to better understand off-target effects, with particular emphasis needed on broad protein profiling. Here, we describe the use of a tritiated chemical probe and a 9000 human protein microarray to discern the binding selectivity of an inhibitor of the mRNA decapping scavenger enzyme DcpS. An immobilized m7GTP resin was also used to assess the selectivity of a DcpS inhibitor against mRNA cap-associated proteins in whole cell extracts. These studies confirm the exquisite selectivity of diaminoquinazoline DcpS inhibitors, and highlight the utility of relatively simple protein microarray and affinity enrichment technologies in drug discovery and chemical biology.

The human decapping scavenger enzyme DcpS modulates microRNA turnover.

The decapping scavenger enzyme DcpS is known for its role in hydrolyzing the cap structure following mRNA degradation. Recently, we discovered a new function in miRNA degradation activation for the ortholog of DcpS in C. elegans. Here we show that human DcpS conserves its role in miRNA turnover. In human cells, DcpS is a nucleocytoplasmic shuttling protein that activates miRNA degradation independently of its scavenger decapping activity in the cytoplasmic compartment. We also demonstrate that this new function for DcpS requires the contribution of the 5'-3' exonuclease Xrn2. Our findings support a conserved role of DcpS as a modulator of miRNA turnover in animals.

A library approach to rapidly discover photoaffinity probes of the mRNA decapping scavenger enzyme DcpS.

Despite its diverse applications, such as identification of the protein binding partners of small molecules and investigation of intracellular drug-target engagement, photoaffinity labelling (PAL) is intrinsically challenging, primarily due to the difficulty in discovering functionally active photoaffinity probes. Here we describe the creation of a chemoproteomic library to discover a novel photoaffinity probe for DcpS, an mRNA decapping enzyme that is a putative target for Spinal Muscular Atrophy. This library approach expedites the discovery of photoaffinity probes and expands the chemical biology toolbox to include RNA cap-binding proteins.

Rational targeting of active-site tyrosine residues using sulfonyl fluoride probes.

This work describes the first rational targeting of tyrosine residues in a protein binding site by small-molecule covalent probes. Specific tyrosine residues in the active site of the mRNA-decapping scavenger enzyme DcpS were modified using reactive sulfonyl fluoride covalent inhibitors. Structure-based molecular design was used to create an alkyne-tagged probe bearing the sulfonyl fluoride warhead, thus enabling the efficient capture of the protein from a complex proteome. Use of the probe in competition experiments with a diaminoquinazoline DcpS inhibitor permitted the quantification of intracellular target occupancy. As a result, diaminoquinazoline upregulators of survival motor neuron protein that are used for the treatment of spinal muscular atrophy were confirmed as inhibitors of DcpS in human primary cells. This work illustrates the utility of sulfonyl fluoride probes designed to react with specific tyrosine residues of a protein and augments the chemical biology toolkit by these probes uses in target validation and molecular pharmacology.

Oral administration of soluble guanylate cyclase agonists to rats results in osteoclastic bone resorption and remodeling with new bone formation in the appendicular and axial skeleton.

Orally administered small molecule agonists of soluble guanylate cyclase (sGC) induced increased numbers of osteoclasts, multifocal bone resorption, increased porosity, and new bone formation in the appendicular and axial skeleton of Sprague-Dawley rats. Similar histopathological bone changes were observed in both young (7- to 9-week-old) and aged (42- to 46-week-old) rats when dosed by oral gavage with 3 different heme-dependent sGC agonist (sGCa) compounds or 1 structurally distinct heme-independent sGCa compound. In a 7-day time course study in 7- to 9-week-old rats, bone changes were observed as early as 2 to 3 days following once daily compound administration. Bone changes were mostly reversed following a 14-day recovery period, with complete reversal after 35 days. The mechanism responsible for the bone changes was investigated in the thyroparathyroidectomized rat model that creates a low state of bone modeling and remodeling due to deprivation of thyroid hormone, calcitonin (CT), and parathyroid hormone (PTH). The sGCa compounds tested increased both bone resorption and formation, thereby increasing bone remodeling independent of calciotropic hormones PTH and CT. Based on these studies, we conclude that the bone changes in rats were likely caused by increased sGC activity.

Acidic triazoles as soluble guanylate cyclase stimulators.

A series of acidic triazoles with activity as soluble guanylate cyclase stimulators is described. Incorporation of the CF(3) triazole improved the overall physicochemical and drug-like properties of the molecule and is exemplified by compound 25.

Palmitate attenuates myocardial contractility through augmentation of repolarizing Kv currents.

There is considerable evidence to support a role for lipotoxicity in the development of diabetic cardiomyopathy, although the molecular links between enhanced saturated fatty acid uptake/metabolism and impaired cardiac function are poorly understood. In the present study, the effects of acute exposure to the saturated fatty acid, palmitate, on myocardial contractility and excitability were examined directly. Exposure of isolated (adult mouse) ventricular myocytes to palmitate, complexed to bovine serum albumin (palmitate:BSA) as in blood, rapidly reduced (by 54+/-4%) mean (+/-SEM) unloaded fractional cell shortening. The amplitudes of intracellular Ca(2+) transients decreased in parallel. Current-clamp recordings revealed that exposure to palmitate:BSA markedly shortened action potential durations at 20%, 50%, and 90% repolarization. These effects were reversible and were occluded when the K(+) in the recording pipettes was replaced with Cs(+), suggesting a direct effect on repolarizing K(+) currents. Indeed, voltage-clamp recordings revealed that palmitate:BSA reversibly and selectively increased peak outward voltage-gated K(+) (Kv) current amplitudes by 20+/-2%, whereas inwardly rectifying K(+) (Kir) currents and voltage-gated Ca(2+) currents were unaffected. Further analyses revealed that the individual Kv current components I(to,f), I(K,slow) and I(ss), were all increased (by 12+/-2%, 37+/-4%, and 34+/-4%, respectively) in cells exposed to palmitate:BSA. Consistent with effects on both components of I(K,slow) (I(K,slow1) and I(K,slow)(2)) the magnitude of the palmitate-induced increase was attenuated in ventricular myocytes isolated from animals in which the Kv1.5 (I(K,slow)(1)) or the Kv2.1 (I(K,slow)(2)) locus was disrupted and I(K,slow)(1) or I(K,slow2) is eliminated. Both the enhancement of I(K,slow) and the negative inotropic effect of palmitate:BSA were reduced in the presence of the Kv1.5 selective channel blocker, diphenyl phosphine oxide-1 (DPO-1).Taken together, these results suggest that elevations in circulating saturated free fatty acids, as occurs in diabetes, can directly augment repolarizing myocardial Kv currents and impair excitation-contraction coupling.

Ca2+-independent alterations in diastolic sarcomere length and relaxation kinetics in a mouse model of lipotoxic diabetic cardiomyopathy.

Previous studies demonstrated increased fatty acid uptake and metabolism in MHC-FATP transgenic mice that overexpress fatty acid transport protein (FATP)1 in the heart under the control of the alpha-myosin heavy chain (alpha-MHC) promoter. Doppler tissue imaging and hemodynamic measurements revealed diastolic dysfunction, in the absence of changes in systolic function. The experiments here directly test the hypothesis that the diastolic dysfunction in MHC-FATP mice reflects impaired ventricular myocyte contractile function. In vitro imaging of isolated adult MHC-FATP ventricular myocytes revealed that mean diastolic sarcomere length is significantly (P<0.01) shorter than in wild-type (WT) cells (1.79+/-0.01 versus 1.84+/-0.01 microm). In addition, the relaxation rate (dL/dt) is significantly (P<0.05) slower in MHC-FATP than WT myocytes (1.58+/-0.09 versus 1.92+/-0.13 microm/s), whereas both fractional shortening and contraction rates are not different. Application of 40 mmol/L 2,3-butadionemonoxime (a nonspecific ATPase inhibitor that relaxes actin-myosin interactions) increased diastolic sarcomere length in both WT and MHC-FATP myocytes to the same length, suggesting that MHC-FATP myocytes are partially activated at rest. Direct measurements of intracellular Ca(2+) revealed that diastolic [Ca(2+)](i) is unchanged in MHC-FATP myocytes and the rate of calcium removal is unexpectedly faster in MHC-FATP than WT myocytes. Moreover, diastolic sarcomere length in MHC-FATP and WT myocytes was unaffected by removal of extracellular Ca(2+) or by buffering of intracellular Ca(2+) with the Ca(2+) chelator BAPTA (100 micromol/L), indicating that elevated intracellular Ca(2+) does not underlie impaired diastolic function in MHC-FATP ventricular myocytes. Functional assessment of skinned myocytes, however, revealed that myofilament Ca(2+) sensitivity is markedly increased in MHC-FATP, compared with WT, ventricular cells. In addition, biochemical experiments demonstrated increased expression of the beta-MHC isoform in MHC-FATP, compared with WT ventricles, which likely contributes to the slower relaxation rate observed in MHC-FATP myocytes. Collectively, these data demonstrate that derangements in lipid metabolism in MHC-FATP ventricles, which are similar to those observed in the diabetic heart, result in impaired diastolic function that primarily reflects changes in myofilament function, rather than altered Ca(2+) cycling.

Circulating succinate is elevated in rodent models of hypertension and metabolic disease.

BACKGROUND: Recent evidence suggests that succinate, long known as an intermediate in the citric acid cycle, may also have a role as a signaling molecule through GPR91 and that activation of this receptor results in blood pressure (BP) elevation via the renin-angiotensin system. We sought to test the hypothesis that GPR91 contributes to BP elevation in hypertension. In addition we investigated whether elevated succinate in diabetes could contribute to the increased rate of gluconeogenesis in that condition. METHODS: Circulating succinate concentration was measured using liquid chromatography tandem mass spectrometry in rodent models of hypertension and metabolic disease as well as in human hypertensives and type 2 diabetics in comparison to control subjects. RESULTS: Elevated succinate was detected in spontaneously hypertensive rats (SHR), ob/ob mice, db/db mice, and fa/fa rats in comparison to their non-diseased controls. The changes in concentration are consistent with activation of GPR91. In contrast, neither human hypertensives nor diabetic patients had elevated succinate in comparison to controls. CONCLUSIONS: These findings are consistent with a role of GPR91 signaling in rodent hypertension and diabetes models but not in the analogous human diseases.

Transcript profiling of functionally related groups of genes during conditional differentiation of a mammalian cochlear hair cell line.

We have used Affymetrix high-density gene arrays to generate a temporal profile of gene expression during differentiation of UB/OC-1, a conditionally immortal cell line derived from the mouse cochlea. Gene expression was assessed daily for 14 days under differentiating conditions. The experiment was replicated in two separate populations of cells. Profiles for selected genes were correlated with those obtained by RT-PCR, TaqMan analysis, immunoblotting, and immunofluorescence. The results suggest that UB/OC-1 is derived from a population of nonsensory epithelial cells in the greater epithelial ridge that have the potential to differentiate into a hair-cell-like phenotype, without the intervention of Math1. Elements of the Notch signaling cascade were identified, including the receptor Notch3, with a transient up-regulation that suggests a role in hair cell differentiation. Several genes showed a profile similar to Notch3, including the transcriptional co-repressor Groucho1. UB/OC-1 also expressed Me1, a putative partner of Math1 that may confer competence to differentiate into hair cells. Cluster analysis revealed expression profiles for neural guidance genes associated with Gata3. The temporal dimension of this analysis provides a powerful tool to study genetic mechanisms that underlie the conversion of nonsensory epithelial cells into hair cells.