Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.24.64 (MPP)
 1,876 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1-Methyl-4-phenylpyridinium (MPP+), the cytotoxic metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), has been shown to be toxic to a variety of cell types in culture. The addition of media containing 1 mM MPP+ to cultures of Chinese hamster ovary (CHO) fibroblasts led to the gradual depletion of cellular ATP stores and subsequent cell death. A 12-min heat shock of the cells at 45 degrees C, 3 h prior to the addition of MPP(+)-containing media, significantly attenuated cell death. Heat shock pretreatment led to an increased synthesis of all the major heat shock proteins (HSPs) in CHO cells. Further, the addition of the protein synthesis inhibitor, cycloheximide, prevented the protective effect of heat shock pretreatment, indicating that this protection was dependent upon new protein synthesis. In additional experiments, a rat fibroblast cell line which has been stably transfected with, and constitutively expresses a cloned human HSP-70 gene, was found to be more resistant to the cytotoxic effects of MPP+ than the parental fibroblast cell line. These results indicate that HSPs are protective toward the deleterious effects of MPP+ and that their synthesis represents an important parameter in the neurotoxicity of MPTP.
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PMID:Heat shock proteins protect cultured fibroblasts from the cytotoxic effects of MPP+. 890 68

The neurotoxicity of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, which produces Parkinsonism, is mediated by its metabolite 1-methyl-4-phenylpyridinium ion (MPP+). When injected into the striatum MPP+ is accumulated by dopaminergic nerve terminals and is then retrogradely transported to the substantia nigra compacta. The mechanism by which it mediates cell death involves both inhibition of complex I of the electron transport chain and free radical generation. In the present experiments we found that administration of the free radical spin trap N-tert-butyl-alpha-(2-sulfophenyl) nitrone (S-PBN) significantly attenuated substantia nigra cell loss produced by MPP+ administration into rat striatum. We also found that coadministration of coenzyme Q10 with nicotinamide, which attenuates energy depletion, significantly blocked MPP(+)-induced substantia nigra damage. Last, we found that a single administration of MPP+ into rat striatum can produce progressive cell loss in the substantia nigra and that administration of S-PBN starting 7 days after administration of MPP+ can block the ensuing neuronal damage. These observations suggest that a one-time exposure to a neurotoxic agent may result in progressive neuronal degeneration mediated by oxidative stress.
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PMID:MPP+ produces progressive neuronal degeneration which is mediated by oxidative stress. 912 70

Selective loss of central dopaminergic neurons in vitro and in vivo can be initiated by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) through its metabolite phenylpyridium ion (MPP+). Such MPTP-mediated cytotoxicity can be blocked by (-)-Deprenyl, a monoamine oxidase (MAO)-B inhibitor, but the exact mechanisms of MPP(+)-induced cytotoxicity and (-)-Deprenyl's protection against such neurotoxicity are not fully understood. Using a hybrid clone MES 23.5, a dopaminergic cell line that does not contain MAO-B, we document that MPP+ induces apoptotic cell death. Application of (-)-Deprenyl at concentrations of 0.1-10 microM significantly reduces MPP(+)-induced apoptosis in MES 23.5 cells; (-)-Deprenyl at higher concentrations (> 100 microM) that completely inhibit MAO-B activity, however, induces apoptosis. Pretreatment with N-(2-aminoethyl)-p-chlorobenzamide (Ro 16-6491), a selective MAO-B inhibitor, does not protect MES 23.5 cells against MPP(+)-induced cell death. These results suggest that the protective action of (-)-Deprenyl against MPP+ neuro-toxicity in dopaminergic cell line may be independent of the inhibition of MAO-B.
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PMID:(-)-Deprenyl protection of 1-methyl-4 phenylpyridium ion (MPP+)-induced apoptosis independent of MAO-B inhibition. 913 70

In vivo administration of either 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or methamphetamine (MA) produces damage to the dopaminergic nervous system which may be due in part to the generation of reactive oxygen species (ROS). The resistance of superoxide dismutase (SOD) over-expressing transgenic mice to the effects of both MPTP and MA suggests the involvement of superoxide in the resulting neurotoxicity of both compounds. Superoxide can be converted by SOD to hydrogen peroxide, which itself can cause cellular degeneration by reacting with free iron to produce highly reactive hydroxyl radicals resulting in damage to proteins, nucleic acids and membrane phospholipids. Hydrogen peroxide has also been reported to be produced via inhibition of NADH dehydrogenase by MPP + formed during oxidation of MPTP by MAO-B and by dopamine auto-oxidation following MA-induced dopamine release from synaptic vesicles within nerve terminals. To test whether hydrogen peroxide is an important factor in the toxicity of either of these two neurotoxins, we created clonal PC12 lines expressing elevated levels of the hydrogen peroxide-reducing enzyme glutathione peroxidase (GSHPx). Elevation of GSHPx levels in PC12 was found to diminish the rise in ROS levels and lipid peroxidation resulting from MA but not MPTP treatment. Elevated levels of GSHPx also appeared to prevent decreases in transport-mediated dopamine uptake produced via MA administration as well as to attenuate toxin-induced cell loss as measured by either MTT reduction or LDH release. Our data, therefore, suggest that hydrogen peroxide production likely contributes to MA toxicity in dopaminergic neurons.
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PMID:Elevated expression of glutathione peroxidase in PC12 cells results in protection against methamphetamine but not MPTP toxicity. 919 Oct 89

Three steps in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxicity were compared with the neurodegenerative effects of the toxin in mice and rats. Firstly, we compared the neurotoxicity of MPTP, mediated by monoamine oxidase (MAO)-B, to that of 1-methyl-4-(2'-methylphenyl)-1,2,3,6-tetrahydropyridine (2'-CH3-MPTP), an analogue oxidized by MAO-A and MAO-B. Both toxins caused degeneration of dopamine terminals in mice but not in rats. In NMRI mice noradrenaline terminals were also affected by both toxins. Pretreatment with deprenyl to prevent MAO-B-mediated oxidation in the capillary endothelium enhanced dopamine toxicity to 2'-CH3-MPTP in nucleus accumbens but no potentiation was seen in striatum and the olfactory tubercle. Secondly, synaptosomal uptake of the 1-methyl-4-phenylpyridinium ion (MPP+) was studied. Uptake in rats was not significantly different from that in the two mice strains. Thirdly, no significant differences were found in MPP(+)-induced lactate production in striatal slices or synaptosomes. We conclude that the lack of effect of MPTP in rats is not due to mechanisms specific for MPTP but probably to the ability of rat catecholamine neurons to cope with, and survive, impaired energy metabolism.
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PMID:Comparison of key steps in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxicity in rodents. 939 88

The neurotoxicity of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is dependent upon the MAO-B (monoamine oxidase type B)-catalyzed production of 1-methyl-4-phenylpyridinium ion (MPP(+)) and is likely to involve a perturbation of energy metabolism. Protection against MPTP neurotoxicity has been shown by treating mice with 7-nitroindazole (7-NI), a reversible inhibitor of both MAO-B and neuronal nitric oxide synthase (nNOS) activity. The objective of the present study was to evaluate (i) the relationship between the neuroprotective effect of 7-NI and MPTP-induced energy deficiency, and (ii) the role of nitric oxide production as a potential mechanism for energy perturbation after MPTP exposure. Maximum protection against striatal dopamine depletion and nigral neuronal loss was achieved when 7-NI (50 mg/kg, i.p.) was administered to C57BL/6 mice immediately before and after MPTP (50 mg/kg, s.c.). This short-term regimen of 7-NI administration parallels the time when MPTP exposure causes energy failure. 7-NI also completely prevented the loss of striatal ATP that occurs in mice during the initial hours after MPTP administration. In contrast, N(G)-nitro-L-arginine (two injections of 50 mg/kg each, given i.p. 20 and 4 h prior to MPTP), another NOS inhibitor, failed to affect MPTP-induced ATP depletion. Taken together, data indicate that (i) a temporal and causal relationship exists between the neuroprotective effect of 7-NI and its ability to counteract ATP reduction, and (ii) MAO-B rather than NOS inhibition is the mechanism by which 7-NI counteracts MPTP-induced ATP depletion.
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PMID:7-Nitroindazole prevents 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine-induced ATP loss in the mouse striatum. 1048 97

We have studied the interaction of coenzyme Q with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and its metabolites, 1-methyl-4-phenyl-2,3-dihydropyridinium (MPDP(+)) and 1-methyl-4-phenylpyridinium (MPP(+)), the real neurotoxin to cause Parkinson's disease. Incubation of MPTP or MPDP(+) with rat brain synaptosomes induced complete reduction of endogenous ubiquinone-9 and ubiquinone-10 to corresponding ubiquinols. The reduction occurred in a time- and MPTP/MPDP(+) concentration-dependent manner. The reduction of ubiquinone induced by MPDP(+) went much faster than that by MPTP. MPTP did not reduce liposome-trapped ubiquinone-10, but MPDP(+) did. The real toxin MPP(+) did not reduce ubiquinone in either of the systems. The reduction by MPTP but not MPDP(+) was completely prevented by pargyline, a type B monoamine oxidase (MAO-B) inhibitor, in the synaptosomes. The results indicate that involvement of MAO-B is critical for the reduction of ubiquinone by MPTP but that MPDP(+) is a reductant of ubiquinone per se. It is suggested that ubiquinone could be an electron acceptor from MPDP(+) and promote the conversion from MPDP(+) to MPP(+) in vivo, thus accelerating the neurotoxicity of MPTP.
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PMID:1-Methyl-4-phenyl-2,3-dihydropyridinium is transformed by ubiquinone to the selective nigrostriatal toxin 1-methyl-4-phenylpyridinium. 1056 96

The endogenous neurotoxin 1-methyl-6,7-dihydroxy-1,2,3, 4-tetrahydroisoquinoline (salsolinol), which is structurally similar to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), has been reported to inhibit mitochondrial complex I (NADH-Q reductase) activity as does the MPTP metabolite 1-methyl-4-phenylpyridinium ion (MPP(+)). However, the mechanism of salsolinol leading to neuronal cell death is still unknown. Thus, we correlated indices of cellular energy production and cell viability in human dopaminergic neuroblastoma SH-SY5Y cells after exposure to salsolinol and compared these results with data obtained with MPP(+). Both toxins induce time and dose-dependent decrease in cell survival with IC(50) values of 34 microM and 94 microM after 72 h for salsolinol and MPP(+), respectively. Furthermore, salsolinol and MPP(+) produce a decrease of intracellular net ATP content with IC(50) values of 62 microM and 66 microM after 48 h, respectively. In contrast to MPP(+), salsolinol does not induce an increase of intracellular net NADH content. In addition, enhancing glycolysis by adding D-glucose to the culture medium protects the cells against MPP(+) but not salsolinol induced cellular ATP depletion and cytotoxicity. These results suggest that cell death induced by salsolinol is due to impairment of cellular energy supply, caused in particular by inhibition of mitochondrial complex II (succinate-Q reductase), but not complex I.
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PMID:1-Methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (salsolinol) is toxic to dopaminergic neuroblastoma SH-SY5Y cells via impairment of cellular energy metabolism. 1065 Jan 31

To elucidate the toxicological relevance of hepatic aldehyde oxidase (AO) as a detoxification enzyme of 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine (MPTP), we studied the metabolism and the hepatotoxicity of MPTP in intact rat livers exhibiting different AO activities by using a recirculating perfusion method. In the perfusate during a 90-min recirculation of 1 mM MPTP, the perfused liver from Jcl:Wistar rat, a strain showing high AO activity, generated almost equal amounts of 1-methyl-4-phenylpyridinium species (MPP(+)) and 1-methyl-4-phenyl-5,6-dihydro-2-pyridone (MPTP lactam) as major metabolites, together with 4-phenyl-1,2,3, 6-tetrahydropyridine, 1-methyl-4-phenyl-2-pyridone (MP 2-pyridone) and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine N-oxide. However, a marked decrease of MPTP lactam as well as MP 2-pyridone and a concomitant increase of MPP(+) were caused by coinfusion of 2-hydroxypyrimidine (2-OH PM), a competitive inhibitor of AO, into Jcl:Wistar rat liver. A quite similar metabolic profile was obtained on perfusion of AO-deficient WKA/Sea rat liver. Rather large amounts of MPP(+) were retained in the liver in all cases, but especially in Jcl:Wistar rat in the presence of 2-OH PM. Lactate dehydrogenase leakage into the perfusate from rat liver perfused with 1 mM MPTP was greater in the strain with lower AO activity, WKA/Sea, than in that with higher AO activity, Jcl:Wistar. Furthermore, inhibition of AO in Jcl:Wistar rat in the presence of 2-OH PM caused an enhancement of lactate dehydrogenase leakage. These results suggest that hepatic AO is a key detoxification enzyme for MPTP.
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PMID:Metabolism of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in perfused rat liver: involvement of hepatic aldehyde oxidase as a detoxification enzyme. 1077 32

Significant differences exist in the sensitivity of mice and rats to the neurotoxicity of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) that cannot be explained by differences in exposure to or uptake of 1-methyl-4-phenylpyridinium (MPP(+)) into dopamine (DA) neurons. MPP(+) is also a substrate for the brain vesicular monoamine transporter (VMAT2), and sequestration into synaptic vesicles may be one mechanism of protection against MPP(+) toxicity. A greater sequestration of MPP(+) into vesicles of DA neurons in rats versus mice could explain the lower vulnerability of DA neurons in the rat to MPP(+) toxicity. To test this hypothesis, the kinetics of uptake for [(3)H]MPP(+) and [(3)H]DA as well as [(3)H]dihydrotetrabenazine binding to VMAT2 were compared in vesicles isolated from the striata of rats and mice. The K(m) value of [(3)H]MPP(+) transport was similar in the two species. In contrast, the maximal transport rate (V(max)) was 2-fold greater in vesicles from rats than in those from mice. Likewise, the K(m) value for [(3)H]DA transport was similar in both preparations, but the V(max) value was 2-fold greater in rat than in mouse vesicles. The B(max) value for [(3)H]dihydrotetrabenazine binding was also 2-fold greater in striatal vesicles from rats than in those from mice. Electron micrographs demonstrated that vesicles isolated from rats and mice were approximately the same size. Based on these observations, we propose that striatal vesicles from rats have more VMAT2 than vesicles from mice and that this species difference in VMAT2 density may help explain the reduced vulnerability of rat DA neurons to MPP(+) neurotoxicity.
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PMID:In vitro studies of striatal vesicles containing the vesicular monoamine transporter (VMAT2): rat versus mouse differences in sequestration of 1-methyl-4-phenylpyridinium. 1077 99


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