Using screening tools to identify neuropathic pain.
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Health Status Indicators↗
Biomedical subjects
Joachim Scholz
Publications and source records attributed to Joachim Scholz.
GTP cyclohydrolase and tetrahydrobiopterin regulate pain sensitivity and persistence.
We report that GTP cyclohydrolase (GCH1), the rate-limiting enzyme for tetrahydrobiopterin (BH4) synthesis, is a key modulator of peripheral neuropathic and inflammatory pain. BH4 is an essential cofactor for catecholamine, serotonin and nitric oxide production. After axonal injury, concentrations of BH4 rose in primary sensory neurons, owing to upregulation of GCH1. After peripheral inflammation, BH4 also increased in dorsal root ganglia (DRGs), owing to enhanced GCH1 enzyme activity. Inhibiting this de novo BH4 synthesis in rats attenuated neuropathic and inflammatory pain and prevented nerve injury-evoked excess nitric oxide production in the DRG, whereas administering BH4 intrathecally exacerbated pain. In humans, a haplotype of the GCH1 gene (population frequency 15.4%) was significantly associated with less pain following diskectomy for persistent radicular low back pain. Healthy individuals homozygous for this haplotype exhibited reduced experimental pain sensitivity, and forskolin-stimulated immortalized leukocytes from haplotype carriers upregulated GCH1 less than did controls. BH4 is therefore an intrinsic regulator of pain sensitivity and chronicity, and the GTP cyclohydrolase haplotype is a marker for these traits.
Adult↗
Blocking caspase activity prevents transsynaptic neuronal apoptosis and the loss of inhibition in lamina II of the dorsal horn after peripheral nerve injury.
We show that transsynaptic apoptosis is induced in the superficial dorsal horn (laminas I-III) of the spinal cord by three distinct partial peripheral nerve lesions: spared nerve injury, chronic constriction, and spinal nerve ligation. Ongoing activity in primary afferents of the injured nerve and glutamatergic transmission cause a caspase-dependent degeneration of dorsal horn neurons that is slow in onset and persists for several weeks. Four weeks after spared nerve injury, the cumulative loss of dorsal horn neurons, determined by stereological analysis, is >20%. GABAergic inhibitory interneurons are among the neurons lost, and a marked decrease in inhibitory postsynaptic currents of lamina II neurons coincides with the induction of apoptosis. Blocking apoptosis with the caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp(OMe)-fluoromethylketone (zVAD) prevents the loss of GABAergic interneurons and the reduction of inhibitory currents. Partial peripheral nerve injury results in pain-like behavioral changes characterized by hypersensitivity to tactile or cold stimuli. Treatment with zVAD, which has no intrinsic analgesic properties, attenuates this neuropathic pain-like syndrome. Preventing nerve injury-induced apoptosis of dorsal horn neurons by blocking caspase activity maintains inhibitory transmission in lamina II and reduces pain hypersensitivity.
Afferent Pathways↗
Reduction of a 1-aza-1,3-diene to a 1-azabut-2-ene-1,4-diyl dianion: an unusual reaction course.
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Journal Article↗
Modeled ligand-protein complexes elucidate the origin of substrate specificity and provide insight into catalytic mechanisms of phenylalanine hydroxylase and tyrosine hydroxylase.
NMR spectroscopy and X-ray crystallography have provided important insight into structural features of phenylalanine hydroxylase (PAH) and tyrosine hydroxylase (TH). Nevertheless, significant problems such as the substrate specificity of PAH and the different susceptibility of TH to feedback inhibition by l-3,4-dihydroxyphenylalanine (l-DOPA) compared with dopamine (DA) remain unresolved. Based on the crystal structures 5pah for PAH and 2toh for TH (Protein Data Bank), we have used molecular docking to model the binding of 6(R)-l-erythro-5,6,7,8-tetrahydrobiopterin (BH4) and the substrates phenylalanine and tyrosine to the catalytic domains of PAH and TH. The amino acid substrates were placed in positions common to both enzymes. The productive position of tyrosine in TH.BH4 was stabilized by a hydrogen bond with BH4. Despite favorable energy scores, tyrosine in a position trans to PAH residue His290 or TH residue His336 interferes with the access of the essential cofactor dioxygen to the catalytic center, thereby blocking the enzymatic reaction. DA and l-DOPA were directly coordinated to the active site iron via the hydroxyl residues of their catechol groups. Two alternative conformations, rotated 180 degrees around an imaginary iron-catecholamine axis, were found for DA and l-DOPA in PAH and for DA in TH. Electrostatic forces play a key role in hindering the bidentate binding of the immediate reaction product l-DOPA to TH, thereby saving the enzyme from direct feedback inhibition.
Amino Acid Sequence↗
Hsp27 upregulation and phosphorylation is required for injured sensory and motor neuron survival.
Peripheral nerve transection results in the rapid death by apoptosis of neonatal but not adult sensory and motor neurons. We show that this is due to induction and phosphorylation in all adult axotomized neurons of the small heat shock protein Hsp27 and the failure of such induction in most neonatal neurons. In vivo delivery of human Hsp27 but not a nonphosphorylatable mutant prevents neonatal rat motor neurons from nerve injury-induced death, while knockdown in vitro and in vivo of Hsp27 in adult injured sensory neurons results in apoptosis. Hsp27's neuroprotective action is downstream of cytochrome c release from mitochondria and upstream of caspase-3 activation. Transcriptional and posttranslational regulation of Hsp27 is necessary for sensory and motor neuron survival following peripheral nerve injury.
Aging↗
Partial peripheral nerve injury promotes a selective loss of GABAergic inhibition in the superficial dorsal horn of the spinal cord.
To clarify whether inhibitory transmission in the superficial dorsal horn of the spinal cord is reduced after peripheral nerve injury, we have studied synaptic transmission in lamina II neurons of an isolated adult rat spinal cord slice preparation after complete sciatic nerve transection (SNT), chronic constriction injury (CCI), or spared nerve injury (SNI). Fast excitatory transmission remains intact after all three types of nerve injury. In contrast, primary afferent-evoked IPSCs are substantially reduced in incidence, magnitude, and duration after the two partial nerve injuries, CCI and SNI, but not SNT. Pharmacologically isolated GABA(A) receptor-mediated IPSCs are decreased in the two partial nerve injury models compared with naive animals. An analysis of unitary IPSCs suggests that presynaptic GABA release is reduced after CCI and SNI. Partial nerve injury also decreases dorsal horn levels of the GABA synthesizing enzyme glutamic acid decarboxylase (GAD) 65 kDa ipsilateral to the injury and induces neuronal apoptosis, detected by terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling staining in identified neurons. Both of these mechanisms could reduce presynaptic GABA levels and promote a functional loss of GABAergic transmission in the superficial dorsal horn.
Animals↗
1-Trichloromethyl-1,2,3,4-tetrahydro-beta-carboline (TaClo) and related derivatives: chemistry and biochemical effects on catecholamine biosynthesis.
1-Trichloromethyl-1,2,3,4-tetrahydro-beta-carboline (TaClo, 2) is a mammalian alkaloid that readily originates in the human organism, by Pictet-Spengler condensation of endogenously present tryptamine (Ta) and the non-natural hypnotic agent trichloroacetaldehyde (chloral, Clo). Due to its structural analogy to the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP, 1), TaClo is discussed to possibly contribute to the pathogenesis of Parkinson's disease acting as an environmental toxin. Previous investigations on rats and neuronal cell cultures revealed 2 to be capable of inducing severe disturbances on the dopamine metabolism. In this paper, we report on the effects of 2 on the activity of tyrosine hydroxylase [L-tyrosine, tetrayhydropteridine/oxygen oxidoreductase (3-hydroxylating), EC 1.14,16.2; TH] in vitro using rat brain homogenates prepared from the TH-rich nucleus accumbens. TaClo (2) dose-dependently inhibited basal TH activity (IC(50)=3 microM), and after enzyme activation by pituitary adenylate cyclase-activating polypeptide (PACAP-27), it also reduced L-DOPA formation (IC(50)=15 microM). Moreover, two presumable TaClo metabolites, 2-methyl-TaClo (N-Me-TaClo, 3) and 1-dichloromethylene-1,2,3,4-tetrahydro-beta-carboline (1-CCl(2)-TH beta C, 4), which were synthesized in good yields, also proved to be potent inhibitors of TH, with the strongest effect on basal activity (similar to TaClo) being observed for 3 (IC(50)=3 microM). In contrast to TaClo, however, 3 and 4 showed biphasic effects after TH activation with PACAP-27, inducing a marked increase of enzyme activity in the nanomolar range (<0.1 microM), while TH activity was nearly completely blocked at high concentrations (IC(100)=0.1mM). An X-ray diffraction investigation on the 3-dimensional structure of the 1-CCl(2)-TH beta C-derived trifluoroacetamide 7 revealed the voluminous and quite rigid dichloromethylene substituent to be only moderately twisted out of the beta-carboline ring 'plane', thus resulting in an increased ring strain of the partially hydrogenated pyrido moiety accompanied by a strong steric hindrance of Cl(1), Cl(2), C(13), and N(2), which pushes the N-trifluoroacetyl group upwards to an even higher extent than for the TaClo-related trifluoroacetamide 8.
Animals↗
Can we conquer pain?
Pain can be an adaptive sensation, an early warning to protect the body from tissue injury. By the introduction of hypersensitivity to normally innocuous stimuli, pain may also aid in repair after tissue damage. Pain can also be maladaptive, reflecting pathological function of the nervous system. Multiple molecular and cellular mechanisms operate alone and in combination within the peripheral and central nervous systems to produce the different forms of pain. Elucidation of these mechanisms is key to the development of treatments that specifically target underlying causes rather than just symptoms. This new approach promises to revolutionize pain diagnosis and management.
Afferent Pathways↗
Modification of tyrosine hydroxylase activity by chloral derived beta-carbolines in vitro.
Beta-carbolines have been suggested to be involved in the pathogenesis of Parkinson's disease as a result of their structural similarity to the neurotoxin N -methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). The chloral-derived beta-carboline derivative 1-trichloromethyl-1,2,3,4-tetrahydro-beta-carboline (TaClo) causes cell loss in neuronal and glial cell cultures and induces a slowly developing neurodegenerative process in rats. In our experiments, effects of TaClo and its derivatives 2-methyl-TaClo (2-Me-TaClo), and 1-dichloromethylene-1,2,3,4-tetrahydro-beta-carboline (1-CCl(2) -THbetaC) on tyrosine hydroxylase (TH) activity were investigated in TH assays using homogenate preparations of the rat nucleus accumbens and recombinant human TH (hTH1). TH activity was determined in vitro by measuring l-DOPA production with HPLC-ECD. Using homogenate preparations, TaClo, 2-Me-TaClo, and 1-CCl(2) -THbetaC inhibited TH in concentrations of 0.1 mm, while 1-CCl(2) -THbetaC in low concentrations enhanced TH activity. When TH was activated by PACAP-27, TaClo, 2-Me-TaClo, or 1-CCl(2) -THbetaC also inhibited activated enzyme activity in high concentrations. However, in the case of 2-Me-TaClo and 1-CCl(2) -THbetaC a biphasic effect was observed with a marked increase of TH activity in the nanomolar range. In our experiments using recombinant hTH1, TaClo, 2-Me-TaClo, or 1-CCl(2) -THbetaC did not modify enzyme activity. After activation of hTH1 by PKA all the tetrahydro-beta-carbolines investigated in this study decreased l-DOPA formation. We suggest that these beta-carbolines modulate dopamine synthesis by interacting with a protein kinase TH-activating system.
Animals↗
Reaction of Ketones with 1,4-Diaza-1,3-diene Zirconium and Hafnium Complexes: First Example of a 1,3-Dipolar Cycloaddition Reaction of 1,4-Diaza-1,3-diene Complexes of Early Transition Metals.
The novel complexes M[O(R)PhCH{CH=N(tBu)}N(tBu)](2) [M = Zr, R = Me (4a), R = Ph (4b) and M = Hf, R = Me (5a), R = Ph (5b)] have been prepared in almost quantitative yield by reaction of (tBu-DAD)(2)Zr (1) and (tBu-DAD)(2)Hf (2) [tBu-DAD = (tBu)N=CHCH=N(tBu)] with 2 equiv of the ketones MeCOPh (3a) or PhCOPh (3b). The reaction proceeds via a 1,3-dipolar cycloaddition of the C=O bond across the M-N-C unit of the DAD complexes. The molecular structures of the complexes 4a and 5b have been determined by a single-crystal X-ray diffraction study (4a, triclinic, space group P&onemacr;; a = 10.395(2) Å, b = 10.865(2) Å, c = 16.842(3) Å, alpha = 93.80(3) degrees, beta = 99.84(3) degrees, gamma = 106.12(3) degrees, V = 1787.4(6) Å(3), Z = 2, R1 = 0.035 (wR2 = 0.101) for 6963 reflections with I > 2sigma(I); 5b, monoclinic, space group P2(1)/c, a = 19.961(4) Å, b = 10.482(2) Å, c = 20.150(4) Å, beta = 91.30(1) degrees, V = 4215(1) Å(3), Z = 4, R1 = 0.036 (wR2 = 0.097) for 4650 reflections with I > 2sigma(I)). The metal atoms in 4a and 5b adopt a pseudooctahedral coordination sphere consisting of four nitrogen and two oxygen atoms. The distortion is a consequence of the [2.2.1] bicyclic structure of the newly formed tridentate ligands which are not able to span three regular octahedral positions.
Journal Article↗