Competitive HIF Prolyl Hydroxylase Inhibitors Show Protection against Oxidative Stress by a Mechanism Partially Dependent on Glycolysis.

The hypoxia inducible factor 1 (HIF-1) is a central transcription factor involved in the cellular and molecular adaptation to hypoxia and low glucose supply. The level of HIF-1 is to a large degree regulated by the HIF prolyl hydroxylase enzymes (HPHs) belonging to the Fe(II) and 2-oxoglutarate-dependent dioxygenase superfamily. In the present study, we compared competitive and noncompetitive HPH-inhibitor compounds in two different cell types (SH-SY5Y and PC12). Although the competitive HPH-inhibitor compounds were found to be pharmacologically more potent than the non-competitive compounds at inhibiting HPH2 and HPH1, this was not translated into the cellular effects of the compounds, where the non-competitive inhibitors were actually more potent than the competitive in stabilizing and translocatingHIF1 α to the nucleus (quantified with Cellomics ArrayScan technology). This could be explained by the high cellular concentrations of the cofactor 2-oxoglutarate (2-OG) as the competitive inhibitors act by binding to the 2-OG site of the HPH enzymes. Both competitive and non-competitive HPH inhibitors protected the cells against 6-OHDA induced oxidative stress. In addition, the protective effect of a specific HPH inhibitor was partially preserved when the cells were serum starved and exposed to 2-deoxyglucose, an inhibitor of glycolysis, indicating that other processes than restoring energy supply could be important for the HIF-mediated cytoprotection.

Endogenous 2-oxoglutarate levels impact potencies of competitive HIF prolyl hydroxylase inhibitors.

The stability and transcriptional activity of the hypoxia-inducible factors (HIFs) are regulated by oxygen-dependent hydroxylation that is catalyzed by three HIF prolyl 4-hydroxylases (HPHs). Use of HPH inhibition as a mean for HIF-upregulation has recently gained interest as a potential treatment paradigm against neurodegenerative diseases like ischemia and Parkinson's disease. In the present investigation we report the development of a new and robust assay to measure HPH activity. The assay is based on capture of hydroxylated peptide product by the von Hippel-Lindau protein which is directly measured in a scintillation proximity assay. In addition we describe the determination of HPH subtype potencies of HPH inhibitors which either directly or indirectly inhibit the HPH enzyme. The potencies of the HPH inhibitors displayed almost identical IC(50) values toward the HPH1 and HPH2 subtype while the potency against the HPH3 subtype was increased for several of the compounds. For the most potent compound, a hydroxyl thiazole derivative, the potency against HPH2 and HPH3 was 7nM and 0.49nM, respectively corresponding to a 14-fold difference. These results suggest that HPH subtype-selective compounds may be developed. In addition we determined the 2-oxoglutarate concentration in brain tissue and neuronal cell lines as 2-oxoglutarate is an important co-factor used by the HPH enzyme during the hydroxylation reaction. The high intracellular 2-oxoglutarate concentration provides an explanation for the diminished cellular HIF activating potency of a competitive HPH inhibitor compared to its orders of magnitude higher HPH inhibiting potency. The present reported data suggest that in the development of specific Hif prolyl hydroxylase inhibitors the high 2-oxoglutarate tissue level should be taken into account as this might affect the cellular potency. Thus to specifically inhibit the intracellular HPH enzymatic reaction a competitive inhibitor with a low Ki should be developed.

HIF prolyl hydroxylase inhibition increases cell viability and potentiates dopamine release in dopaminergic cells.

Hypoxia-inducible factor (HIF) controls the expression of genes that adapts the cellular condition to accommodate oxidative stress. The potential beneficial effect of HIF up-regulation in ischemia has recently gained interest substantiated by the known HIF-regulation of erythropoietin and other hypoxia accommodating genes. So far the perspectives for HIF up-regulation has been focused on anemia and ischemia related diseases but little information is available about the relevance of HIF biology for neurodegenerative disease like Parkinson's disease. We therefore sought out to characterize the effect of HIF-up-regulation on survival and dopamine homeostasis in dopaminergic cells. We used a low molecular weight HIF prolyl hydroxylase (HPH) inhibitor and lentiviral based shRNA knockdown of HPH subtypes as molecular tools to increase HIF protein level and downstream HIF-regulated genes. We show that HIF induction results in protection against oxidative stress in cellular models based on PC12 cells and LUHMES cells. In addition, HPH inhibition elevates tyrosine hydroxylase expression and activity, which causes increased dopamine synthesis and release in both PC12 cells and a primary rat ventral mesencephalic cell culture. All together these findings suggest that prolyl hydroxylases may represent novel targets for therapeutic intervention in disorders characterized by dopamine homeostasis dysregulation like Parkinson's disease.

Nest building performance following MPTP toxicity in mice.

Systemic injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in mice is one of the primary models used to evaluate neuroprotective and symptomatic treatment strategies for Parkinson's disease. Many behavioral methods for evaluation of MPTP toxicity have been described, but they often involve challenging scenarios that require handling and transfer of animals to novel environments and in some cases prior animal training. These factors can profoundly influence animal behavior and potentially influence experimental outcome. Presented here is a new nest building scoring paradigm based on the animals' normal home cage behavior that is a simple, non-invasive, and reproducible measure for estimating neurological dysfunction in MPTP intoxicated mice. Nest building behavior requires orofacial and forelimb movement and has been shown to be dopamine-dependent making it a possible method for assessing parkinsonian-like symptoms. Significant deficits in nest building scores after 2x20 and 2x25 mg/kg MPTP coincided with a 90% reduction in striatal dopamine. Nest building deficits could be detected for more than a week after intoxication. However, after 28 days the change in behavior was no longer detected, which may reflect the plasticity of the tyrosine hydroxylase positive neurons in the dorsolateral part of striatum.

Synthesis and preliminary biological evaluation of 2'-substituted 2-(3'-carboxybicyclo[1.1.1]pentyl)glycine derivatives as group I selective metabotropic glutamate receptor ligands.

The first series of 2'-substituted 2-(3'-carboxybicyclo[1.1.1]pentyl)glycine derivatives, (2R)- and (2S)-(2',2'-dichloro-3'-carboxybicyclo[1.1.1]pentyl)glycine (10) and (11), and 2-(2'-chloro-3'-carboxybicyclo[1.1.1]pentyl)glycine (12) were synthesized and evaluated as mGluR ligands. Compounds 11 and 12 were shown to be competitive group I mGluR antagonists. These results are also discussed in light of docking studies with both the active (closed) and inactive (open) conformations of mGluR1.