Reduction of Neuropathic and Inflammatory Pain through Inhibition of the Tetrahydrobiopterin Pathway

Abstract

SUMMARY Human genetic studies have revealed an association between GTP cyclohydrolase 1 polymorphisms, which decrease tetrahydrobiopterin (BH4) levels, and reduced pain in patients. We now show that excessive BH4 is produced in mice by both axotomized sensory neurons and macrophages infiltrating damaged nerves and inflamed tissue. Constitutive BH4 overproduction in sensory neurons increases pain sensitivity, whereas blocking BH4 production only in these cells reduces nerve injury-induced hypersensitivity without affecting nociceptive pain. To minimize risk of side effects, we targeted sepiapterin reductase (SPR), whose blockade allows minimal BH4 production through the BH4 salvage pathways. Using a structure-based design, we developed a potent SPR inhibitor and show that it reduces pain hypersensitivity effectively with a concomitant decrease in BH4 levels in target tissues, acting both on sensory neurons and macrophages, with no development of tolerance or adverse effects. Finally, we demonstrate that sepiapterin accumulation is a sensitive biomarker for SPR inhibition in vivo.

Tetrahydrobiopterin Biosynthesis as a Potential Target of the Kynurenine Pathway Metabolite Xanthurenic Acid

“…The structure was solved by molecular replacement using 4HWK (8) as a search model and refined as described in Ref. 5. For isothermal titration calorimetry experiments, an N-terminal hexahistidine-tagged human SPR was expressed in BL21(DE3) Escherichia coli, purified to homogeneity by Ni 2ϩ -nitrilotriacetic acid chromatography (7), and subjected to chromatography on a HiTrap Blue HP resin (GE Healthcare) to obtain SPR devoid of any cofactor, as verified by the absence of absorbance bands at 260 and 340 nm.…”

“…The latter observation suggests that BH 4 plays a role in inflammatory processes. Furthermore, accumulating evidence shows that increased levels of BH 4 intensify pain sensitivity, whereas reduction of BH 4 biosynthesis is an efficient strategy to diminish neuropathic and inflammatory pain (3)(4)(5).…”

Progranulin overexpression in sensory neurons attenuates neuropathic pain in mice: Role of autophagy

“…Advillin-Cre mice express Cre-recombinase in all peripheral sensory neurons (Zurborg et al, 2011). The functionality of the specific Advillin-Cre line has been confirmed (Latremoliere et al, 2015). Phenotypes of transgenic mice generated with AdvillinCre or SNS-Cre are similar in terms of nociception in nerve injury models (Latremoliere et al, 2015).…”

Toward a Mechanism-Based Approach to Pain Diagnosis

“…the serotonin transporter gene ( SLC6A4 ) and serotonin and epinephrine receptors 161 ), in the enzymatic breakdown of the neurotransmitters dopamine, epinephrine, and norepinephrine by variations in catecholamine- O -methyltransferase (COMT) 10 and in guanosine triphosphate cyclohydrolase (GCH1), the rate-limiting enzyme for tetrahydrobiopterin (BH4) synthesis, an essential cofactor for phenylalanine, tyrosine and tryptophan hydroxylases 142 . Increased levels of GCH1 and BH4 are implicated in inflammatory and neuropathic pain, whereas blockade of this pathway results in analgesia 94, 141 . Variants in the human GCH1 haplotype reduce radicular leg pain after discectomy, experimental pain, and improve outcomes after surgically treated degenerative disc disease 141 .…”

“…Variants in the human GCH1 haplotype reduce radicular leg pain after discectomy, experimental pain, and improve outcomes after surgically treated degenerative disc disease 141 . While the anti-inflammatory drug sulfasalazine, which decreases BH4 levels, has not shown benefit in patients with lumbar spondylarthritis 18 , pharmacological blockade of sepiapterin reductase 35 , which decreases neuronal and macrophage BH4 production, is effective in rodent chronic inflammatory and neuropathic pain and constitutes a possible pharmacological target for humans 94 .…”