Enzymatic analysis of individual anterior horn cells in amyotrophic lateral sclerosis and duchenne muscular dystrophy

Oxidative stress: free radical production in neural degeneration

It is not yet established whether oxidative stress is a major cause of cell death or simply a consequence of an unknown pathogenetic factor. Concerning chronic diseases, as Parkinson's and Alzheimer's disease are assumed to be, it is possible that a gradual impairment of cellular defense mechanisms leads to cell damage because of toxic substances being increasingly formed during normal cellular metabolism. This point of view brings into consideration the possibility that, besides exogenous factors, the pathogenetic process of neurodegeration is triggered by endogenous mechanisms, either by an endogenous toxin or by inherited metabolic disorders, which become progressively more evident with aging. In the following review, we focus on the oxidative stress theory of neurodegeneration, on excitotoxin-induced cell damage and on impairment of mitochondrial function as three major noxae being the most likely causes of cell death either independently or in connection with each other. First, having discussed clinical, pathophysiological, pathological and biochemical features of movement and cognitive disorders, we discuss the common features of these biochemical theories of neurodegeneration separately. Second, we attempt to evaluate possible biochemical links between them and third, we discuss experimental findings that confirm or rule out the involvement of any of these theories in neurodegeneration. Finally, we report some therapeutic strategies evolved from each of these theories.

Motor neuron disease (amyotrophic lateral sclerosis)

Amyotrophic lateral sclerosis is an insidiously developing, adult-onset, progressive anterior horn cell degeneration with associated degeneration of descending motor pathways. It has been recognized as an important clinical syndrome since the middle of the 19th century. Despite increasing clinical and research interest in this condition, its cause remains obscure, even in the broadest terms. Epidemiologic characteristics of the disease have been interpreted as evidence of both genetic and environmental causes. A major change in the view of this disease is the widely developing perception that it is a disease of elderly persons more than of middle-aged adults as was previously taught. Etiologic hypotheses encompass a broad range of postulated pathophysiologic mechanisms, and we review these in detail. The clinical limits of the disease can now be better defined by using modern diagnostic techniques. Although interest in supportive symptomatic therapy is growing, no intervention has yet been shown to modify the biologically determined motor system degeneration.

Choline acetyltransferase activities in single spinal motor neurons from patients with amyotrophic lateral sclerosis

Activities of choline acetyltransferase (ChAT) were microassayed in individual cell bodies of motor neurons, isolated from freeze-dried sections after autopsy of lumbar spinal cords from four patients with sporadic amyotrophic lateral sclerosis (ALS) and four control patients with nonneurological diseases. Numerous large neurons were found in the anterior horn at the early degeneration stage of ALS, but the cell bodies atrophied and decreased in number at the late advanced stage. The small, atrophied neurons were very fragile and were easily destroyed during the isolation procedure with a microknife. The average activity, expressed on a dry weight basis, of 58 ALS neurons was lower than that of 67 control neurons. The large, well-preserved neurons at the early nonadvanced stage had markedly lower ChAT activities than control neurons. The specific activity gradually increased with the progress of atrophy but did not return to the control level.

Lactic dehydrogenase activities in single motoneurons in relation to amyotrophic lateral sclerosis

Histograms of LDH activity in anterior horn cells (AHCs) of rabbit, cat, monkey and man cannot be as clearly divided into 2 groups as can muscle fibers. However, on the basis of the difference in LDH activities between oculomotoneurons and AHCs, and between immature and mature feline AHCs, motoneurons can be divided functionally into 2 groups. From LDH activities of single motoneurons and muscle fibers and those of the remaining AHCs in amyotrophic lateral sclerosis (ALS) determined in this study, it may be assumed that the motoneurons in the high LDH activity group--a high activity being an immature quality--may be resistant to ALS.

Amyotrophic lateral sclerosis: Part 2. Etiopathogenesis

The pathogenesis of the motor neuronal degeneration in amyotrophic lateral sclerosis (ALS) is unclear, though several possible etiological factors are currently being investigated. A unifying hypothesis will have to explain the diverse geographical occurrence, clinical features, and selective vulnerability and relative resistance of different neuronal populations in the disease. It is possible that different biochemical defects underlie this diversity, or alternatively that the many factors incriminated in the etiology may act upon an underlying genetic-biochemical abnormality to trigger premature neuronal death. Viruses, metals, endogenous toxins, immune dysfunction, endocrine abnormalities, impaired DNA repair, altered axonal transport, and trauma have all been etiologically linked with ALS, but convincing research evidence of a causative role for any of these factors is yet to be demonstrated.

Enzymatic analysis of individual posterior root ganglion cells in olivopontocerebellar atrophy, amyotrophic lateral sclerosis and Duchenne muscular dystrophy

Four enzyme activities related to glucose metabolism, i.e. those of glucose-6-phosphate dehydrogenase (G6PDH; EC 1.1.1.49), lactic dehydrogenase (LDH; EC 1.1.1.27), pyruvate dehydrogenase complex (PDC) and citrate synthase (CS; EC 4.1.3.7) were estimated in posterior root ganglion cells (PRGCs) of the spinal cord in patients suffering from olivopontocerebellar atrophy (OPCA), amyotrophic lateral sclerosis (ALS), and Duchenne muscular dystrophy (DMD) by means of the NAD, NADP and CoA cycling methods. In ALS and DMD, the enzyme activities examined were within normal ranges. In OPCA, PDC activity was significantly reduced and LDH activity tended to be lower than that in controls.

Glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase and glyceraldehyde-3-phosphate dehydrogenase activities in early stages of development in dystrophic chickens

Glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconate dehydrogenase (6PGDH) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) activities were assayed in superficial pectoral muscles of hereditary dystrophic chickens, 1 week, 2 weeks, 4 weeks and 4 months after hatching. In control chickens, activities of G6PDH and 6PGDH were very low at 4 months of age; however, at 1 week of age, they were much higher than those at 4 months of age. Activities of G6PDH and 6PGDH were significantly higher in dystrophic chickens compared with those in the controls at all the stages of development studied. These findings suggest that considerable activities of G6PDH and 6PGDH are present within the pectoral muscle cells at early stages of development, at least in dystrophic chickens. GAPDH activity was significantly lower in dystrophic chickens at 2 weeks, 4 weeks and 4 months of age compared with those in control chicken. These findings together with our previous studies (Mizuno 1984a,b) in which increased activities of superoxide dismutases, catalase, glutathione peroxidase and glutathione reductase were reported in dystrophic chickens, indicate the presence of an increased capacity for the turnover of oxygen-free radicals within muscle cells in dystrophic chickens, and that oxygen-free radicals and the related activated oxygen species may be playing a role in inducing cellular damage.