M. F. Beal

Evidence for irnnairment of energy metabofism in vivo in Huntington's disease using localized 1H NMR spectroscopy

The Huntingtons disease (HD) gene mutation has recently been found; however, the biochemical defect that leads to neurodegeneration is still unknown. A progressive impairment of neuronal energy metabolism is a possible etiologic factor. We tested this possibility using localized proton nuclear magnetic resonance (NMR) spectroscopy in 18 patients at high risk for, or suffering from, HD as compared with normal controls. Lactate concentrations were increased in the occipital cortex of symptomatic HD patients when compared with normal controls, and the lactate level correlated with duration of illness. In addition, several patients showed highly elevated lactate levels in the basal ganglia. Basal ganglia levels of N-acetylaspartate were lowered and choline dramatically elevated, relative to creatine, reflecting neuronal loss and gliosis in this brain region. These findings are consistent with a possible defect in energy metabolism in HD, which could contribute to the pathogenesis of the disease. The presence of elevated lactate in HD brains may provide a simple marker that can be followed over time noninvasively and repeatedly to aid in devising and monitoring possible therapies for HD patients.

Creatine in Huntington disease is safe, tolerable, bioavailable in brain and reduces serum 8OH2′dG

In a randomized, double-blind, placebo-controlled study in 64 subjects with Huntington disease (HD), 8 g/day of creatine administered for 16 weeks was well tolerated and safe. Serum and brain creatine concentrations increased in the creatine-treated group and returned to baseline after washout. Serum 8-hydroxy-2′-deoxyguanosine (8OH2′dG) levels, an indicator of oxidative injury to DNA, were markedly elevated in HD and reduced by creatine treatment.

In vivo neurotoxicity of beta-amyloid [β(1–40)] and the β(25–35) fragment

Abstract We examined the histological changes produced by injections of beta-amyloid [β(1–40)], and control peptides in rat and monkey cerebral cortex. β(25–35) injections were also studied in rat cortex. Standard immunoperoxidase procedures were used to detect the distribution of tau, MAP2, β(1–40) and ALZ 50 immunoreactivity. All injections produced localized necrosis at the injection site surrounded by a zone of neuronal loss and gliosis. In rat cortex, lesions produced by solubilized β(1–40) and β(25–35) in water were generally larger than those produced by control peptides. Tau and ALZ 50 antibodies labeled neurites and diffusely positive perikarya around β(1–40) injections, whereas MAP2 staining wasreduced, paralleling the distribution of neuronal loss and gliosis. In aged primate cortex, β(1–40) lesion size was dose dependent. Hyalinized, ALZ 50 positive neurons, and abnormal neurites were prominent around the injection site. Although β-amyloid is acutely neurotoxic in both rat and monkey cerebral cortex, neuronal degeneration in the primate more closely resembles that found in AD.

1H NMR spectroscopy studies of Huntington's disease Correlations with CAG repeat numbers

Huntingtons disease (HD) is the result of an expanded (CAG) repeat in a gene on chromosome 4. A consequence of the gene defect may be progressive impairment of energy metabolism. We previously showed increased occipital cortex lactate in HD using localized 1H spectroscopy. We have now extended these studies to show an almost threefold elevation in occipital cortex lactate in 31 HD patients as compared with 17 normal control subjects(p < 10-11). The spectra in three presymptomatic gene-positive patients were identical to normal control subjects in cortical regions, but three in eight showed elevated lactate in the striatum. Similar to recently reported increases in task-related activation of the striatum in the dominant hemisphere, we found that striatal lactate levels in HD patients were markedly asymmetric (higher on the left side). Markers of neuronal degeneration, decreased N-acetylaspartate (NAA)/creatine and increased choline/creatine levels, were symmetric. Both decreased NAA and increased lactate in the striatum significantly correlated with duration of symptoms. When divided by his or her age, an individuals striatal NAA loss and lactate increase were found to directly correlate with the subjects CAG repeat number, with correlation coefficients of 0.8 and 0.7, respectively. Similar correlations were noted between postmortem cell loss and age versus CAG repeat length. Together, these data provide further evidence for an interaction between neuronal activation and a defect in energy metabolism in HD that may extend to presymptomatic subjects.

MPTP induces alpha-synuclein aggregation in the substantia nigra of baboons.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxicity reproduces many of the features of Parkinsons disease (PD). α-Synuclein has been identified as a prominent component of the Lewy body (LB), the pathological hallmark of PD. MPTP-treated primates have been reported to develop intraneuronal inclusions but not true Lewy bodies. We administered MPTP to baboons and used a monoclonal α-synuclein antibody to define the relationship between neuronal degeneration and α-synuclein immunoreactivity in the substantia nigra. MPTP-induced neuronal degeneration was associated with the redistribution of α-synuclein from its normal synaptic location to aggregates in degenerating neuronal cell bodies. α-Synuclein aggregation induced by MPTP models the early stages of Lewy body formation and may be a fundamental step in the evolution of neuronal degeneration in PD.

Kynurenine pathway abnormalities in Parkinson's disease

We measured metabolites of tyrosine and tryptophan (TRP) in the frontal cortex, putamen (PT), and pars compacta of the substantia nigra (SN) of control and Parkinsons disease (PD) brain tissues. Dopamine concentrations were significantly decreased in the PT and SN of PD tissue, regardless of L-dopa therapy. However, 3-O-methyldopa (3OMD) concentration showed a significant increase in each region of the PD group treated with L-dopa (PD[+]) as compared with both the control group and the PD group without L-dopa therapy (PD[-]). Therefore, 3OMD concentration appears to be a reliable marker of L-dopa therapy. Serotonin concentration was lower in each region of the PD groups than in the control group. Although the magnitude of decrease was greater in the PD(+) group, there was no statistical significance between the two PD groups. The same patterns of decrease were present in kynurenine (KYN) and kynurenic acid (KYA) concentrations, but the molar ratios of TRP to KYN and KYN to KYA were unchanged among three groups. In contrast, 3-hydroxykynurenine (3OHKY) concentration was increased in the PT and SN of both PD(-) and PD(+) groups, and the ratio of KYN to 3OHKY was significantly reduced in the PT of the PD(-) group and in three regions of the PD(+) group. Since the KYN pathway leads to formation of nicotinamide-adenine dinucleotide (NADH), the present results may be a further indication of a defect in NADH:ubiquinone oxidoreductase (complex I) in mitochondria in PD.

The role of mitochondrial dysfunction and neuronal nitric oxide in animal models of neurodegenerative diseases

Excitotoxicity, mitochondrial dysfunction and free radical induced oxidative damage have been implicated in the pathogenesis of several different neurodegenerative diseases, such as amyotrophic lateral sclerosis, Parkinson’s disease (PD), Alzheimer’s disease (AD), and Huntington’s disease. Much of the interest in the association of neurodegeneration with mitochondrial dysfunction and oxidative damage emerged from animal studies using mitochondrial toxins. Within mitochondria l-methyl-4-phenylpyridinium (MPP+), the active metabolite of l-methyl-4-phenyl-l,2,3,6-tetrahydropyridine (MPTP), acts to inhibit NADH-coenzyme Q reductase (complex I) of the electron transport chain. MPTP produces Parkinsonism in humans, primates, and mice. Similarly, lesions produced by the reversible inhibitor of succinate dehydrogenase (complex II), malonate, and the irreversible inhibitor, 3-nitropropionic acid (3-NP), closely resemble the histologic, neurochemical and clinical features of HD in both rats and non-human primates. The interruption of oxidative phosphorylation results in decreased levels of ATP. A consequence is partial neuronal depolarization and secondary activation of voltage-dependent NMD A receptors, which may result in excitotoxic neuronal cell death (secondary excitotoxicity). The increase in intracellular Ca2+ concentration leads to an actiation of Ca2+ dependent enzymes, including the constitutive neuronal nitric oxide synthase (cnNOS) which produces NO-. NO- may react with the Superoxide anion to form peroxynitrite. We show that systemic administration of 7-nitroindazole (7-NI), a relatively specific inhibitor of cnNOS in vivo, attenuates lesions produced by striatal malonate injections or systemic treatment with 3-NP or MPTP. Furthermore 7-NI attenuated increases in lactate production and hydroxyl radical and 3-nitrotyrosine generation in vivo, which may be a consequence of peroxynitrite formation. Our results suggest that neuronal nitric oxide synthase inhibitors may be useful in the treatment of neurologic diseases in which excitotoxic mechanisms play a role. (Mol Cell Biochem 174: 193–197, 1997)

Neuroprotective strategies for treatment of lesions produced by mitochondrial toxins : Implications for neurodegenerative diseases

Neuronal death in neurodegenerative diseases may involve energy impairment leading to secondary excitotoxicity, and free radical generation. Potential therapies for the treatment of neurodegenerative diseases therefore include glutamate release blockers, excitatory amino acid receptor antagonists, agents that improve mitochondrial function, and free radical scavengers. In the present study we examined whether these strategies either alone or in combination had neuroprotective effects against striatal lesions produced by mitochondrial toxins. The glutamate release blockers lamotrigine and BW1003C87 significantly attenuated lesions produced by intrastriatal administration of 1-methyl-4-phenylpyridinium. Lamotrigine significantly attenuated lesions produced by systemic administration of 3-nitropropionic acid. Memantine, an N-methyl-D-aspartate antagonist, protected against malonate induced striatal lesions. We previously found that coenzyme Q10 and nicotinamide, and the free radical spin trap n-tert-butyl-alpha-(2-sulfophenyl)-nitrone (S-PBN) dose-dependently protect against lesions produced by intrastriatal injection of malonate. In the present study we found that the combination of MK-801 (dizocipiline) with coenzyme Q10 exerted additive neuroprotective effects against malonate. Lamotrigine with coenzyme Q10 was more effective than coenzyme Q10 alone. The combination of nicotinamide with S-PBN was more effective than nicotinamide alone. These results provide further evidence that glutamate release inhibitors and N-acetyl-D-aspartate antagonists can protect against secondary excitotoxic lesions in vivo. Furthermore, they show that combinations of agents which act at sequential steps in the neurodegenerative process can produce additive neuroprotective effects. These findings suggest that combinations of therapies to improve mitochondrial function, to block excitotoxicity and to scavenge free radicals may be useful in treating neurodegenerative diseases.

Heterogeneous Topographic and Cellular Distribution of Huntingtin Expression in the Normal Human Neostriatum

A striking heterogeneous distribution of topographic and cellular huntingtin immunoreactivity was observed within the human neostriatum using three distinct huntingtin antibodies. Patchy areas of low huntingtin immunoreactivity were present in both the caudate nucleus and putamen, surrounded by an intervening area of greater immunoreactivity. Comparison of huntingtin immunoreactivity with contiguous serial sections stained for enkephalin and calbindin D28k immunoreactivities showed that the topographic heterogeneity of huntingtin immunostaining corresponded to the patch (striosome) and matrix compartments within the striatum. Huntingtin immunoreactivity was confined primarily to neurons and neuropil within the matrix compartment, whereas little or no neuronal or neuropil huntingtin immunostaining was observed within the patch compartment. There was marked variability in the intensity of huntingtin immunolabel among medium-sized striatal neurons, whereas a majority of large striatal neurons were only faintly positive or without any immunoreactivity. Combined techniques for NADPH-diaphorase enzyme histochemistry and huntingtin immunocytochemistry, as well as double immunofluorescence for either nitric oxide synthase or calbindin D28k in comparison with huntingtin expression, revealed a striking correspondence between calbindin D28k and huntingtin immunoreactivities, with little or no colocalization between NADPH-diaphorase or nitric oxide synthase neurons and huntingtin expression. These observations suggest that the selective vulnerability of spiny striatal neurons and the matrix compartment observed in Huntington’s disease is associated with higher levels of huntingtin expression, whereas the relative resistance of large and medium-sized aspiny neurons and the patch compartments to degeneration is associated with low levels of huntingtin expression.

Inhibition of the leucine-rich repeat protein LINGO-1 enhances survival, structure, and function of dopaminergic neurons in Parkinson's disease models.

The nervous system-specific leucine-rich repeat Ig-containing protein LINGO-1 is associated with the Nogo-66 receptor complex and is endowed with a canonical EGF receptor (EGFR)-like tyrosine phosphorylation site. Our studies indicate that LINGO-1 expression is elevated in the substantia nigra of Parkinsons disease (PD) patients compared with age-matched controls and in animal models of PD after neurotoxic lesions. LINGO-1 expression is present in midbrain dopaminergic (DA) neurons in the human and rodent brain. Therefore, the role of LINGO-1 in cell damage responses of DA neurons was examined in vitro and in experimental models of PD induced by either oxidative (6-hydroxydopamine) or mitochondrial (N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) toxicity. In LINGO-1 knockout mice, DA neuron survival was increased and behavioral abnormalities were reduced compared with WT. This neuroprotection was accompanied by increased Akt phosphorylation (p-Akt). Similar neuroprotective in vivo effects on midbrain DA neurons were obtained in WT mice by blocking LINGO-1 activity using LINGO-1-Fc protein. Neuroprotection and enhanced neurite growth were also demonstrated for midbrain DA neurons in vitro. LINGO-1 antagonists (LINGO-1-Fc, dominant negative LINGO-1, and anti-LINGO-1 antibody) improved DA neuron survival in response to MPP+ in part by mechanisms that involve activation of the EGFR/Akt signaling pathway through a direct inhibition of LINGO-1s binding to EGFR. These results show that inhibitory agents of LINGO-1 activity can protect DA neurons against degeneration and indicate a role for the leucine-rich repeat protein LINGO-1 and related classes of proteins in the pathophysiological responses of midbrain DA neurons in PD.