Lecithin: cholesterol acyltransferase activity and fatty acid composition of erythrocyte phospholipids in Friedreich's ataxia

Abnormal activity of membrane phospholipid synthetic enzymes in the brain of patients with Friedreich's ataxia and spinocerebellar atrophy type-1

Much evidence, derived from biochemical studies of both blood and autopsied brain, has suggested that phospholipid metabolism is abnormal in patients with Friedreich's ataxia (FA), a disorder characterized by severe neuronal loss in the spinal cord and lower brain stem with no, or only modest, damage in other brain regions. To establish the cause of our recent finding of reduced brain levels of phospholipids in FA, we assayed activities of 10 phospholipid-metabolizing enzymes in the autopsied cerebellar cortex of patients with the disorder and, for comparison, in a group of patients with spinocerebellar ataxia type 1 (SCA-1), a disease characterized, unlike FA, by marked neuronal loss in the cerebellar cortex. Enzyme activities were also measured in four brain areas which are relatively unaffected morphologically in both FA and SCA-1. We found that ethanolamine kinase activity was increased in multiple brain regions of patients with FA (increased 31%-137%) and, more modestly, in SCA-1 (increased 39%-60%), suggesting a nonspecific enhancement of phosphoethanolamine production in both disorders. In contrast, the activity of phosphoethanolamine cytidylyltransferase (PECT), the rate-limiting enzyme of phosphatidylethanolamine synthesis, was significantly and markedly decreased by 35%-78% in the cerebellar, frontal, and occipital cortices of patients with FA but was normal in SCA-1. Reduced PECT activity in FA may explain the lower brain levels of phosphatidylethanolamine in the disorder. Moreover, because decreased PECT activity in FA occurs in brain regions having no, or only modest, morphologic damage, this may represent a systemic change consequent to the frataxin gene defect. Our data also suggest that therapeutic intervention in FA designed to increase synthesis of membrane phospholipids may warrant further investigation.

Brain phospholipids and fatty acids in Friedreich's ataxia and spinocerebellar atrophy type-1

Previous studies of patients with spinocerebellar atrophy type 1 (SCA-1) and Friedreich's ataxia (FA) have suggested the occurrence of membrane disturbances in both disorders. We measured concentrations of phosphatidylcholine (PC), diacyl and plasmalogen phosphatidylethanolamine (PE), and phosphatidylserine (PS), along with their fatty acid profiles, in the brains of eight patients with Friedreich's ataxia (FA) and nine patients with dominantly inherited spinocerebellar atrophy type 1 (SCA-1). Compared with the controls, levels of all phospholipid types (PE, PS, and PC) were reduced in the cerebellar but not occipital cortex of SCA-1 patients. In contrast, in the FA group, levels of PS and PE, but not PC, were reduced in both cerebellar and occipital cortices. The fatty acid composition of individual brain phospholipids was altered in both FA and SCA-1 patients, most markedly in the plasmalogen PE and PS classes of cerebellar phospholipids. Given the neuropathologic characteristics of each disorder, it is likely that altered fatty acid composition and phospholipid levels in SCA-1 cerebellar cortex occur as a consequence of pronounced cerebellar degeneration. In contrast, reduced phospholipid levels in FA cerebellar and occipital cortex, areas characterized by, at most, minimal neuronal loss in FA, may represent a widespread alteration in cellular phospholipid metabolism occurring in response to the specific gene defect in the disorder.

Friedreich's ataxia: electrophysiologic and histologic findings in patients and relatives

Peripheral nerve conduction velocity and cortical evoked potentials were investigated in 48 patients with Friedreich's disease and in 35 relatives. There were 14 patients and 2 relatives who underwent sural nerve biopsy. In the patients sensory conduction velocity was moderately slowed, whereas sensory responses were markedly reduced. Nerve biopsy showed a severe loss of large myelinated fibers and no demyelination. On teased nerve fiber preparations, most fibers presented uniformly short internodes. No correlation was seen between sensory conduction findings or histologic abnormalities and clinical disability. In patients SSEP changes, which were constant, and VEPs, which were frequently involved, were unrelated to the severity or duration of clinical disability. There were 14 relatives who showed clinical signs of Friedreich's disease. Slightly decreased distal conduction velocity along sensory fibers was observed in more than half of the relatives. Nerve biopsy was noncontributory. In conclusion, we could not determine whether the abnormalities observed in the siblings were an expression of a heterozygotic condition, or whether they were early signs of the disease.

Glucose intolerance in Friedreich's ataxia: association with insulin resistance and decreased insulin binding

Friedreich's Ataxia (FA) is a neurologic disorder associated with a high prevalence of diabetes mellitus. To assess insulin secretion and insulin resistance, glucose and insulin responses to oral glucose and insulin binding to circulating monocytes and dextran gradient fractionated and unfractionated red blood cells (RBCs) were compared in 11 subjects with FA to 11 age-matched controls. Glucose and insulin responses were elevated from one to three hours after oral glucose in FA. The mean corrected insulin responses were not different while peripheral insulin activity (A) was significantly decreased (1.38 +/- 0.22 v 0.77 +/- 0.16, control v FA, P less than 0.025) indicating the presence of insulin resistance. A significant correlation between the degree of insulin resistance (A) and duration of neurologic symptoms was found (r = .65. P less than 0.025). Resistance to exogenous insulin was confirmed in ten subjects with FA by intravenous insulin tolerance tests (KITT, %/min, 6.25 +/- 0.90 v 3.93 +/- 0.61, P less than .05). Both FA and control groups showed highest insulin binding to fraction A (youngest) RBCs, but no difference was observed between the two groups. However, insulin binding to monocytes was significantly decreased in subjects with FA (% specific binding/10(7) cells/mL, 6.37 +/- 0.71 v 4.51 +/- 0.39, P less than 0.05, control v FA). This was associated with a decrease in apparent receptor affinity. We conclude that FA is associated with insulin resistance, which increases with the duration of neurologic impairment. The insulin binding to monocytes suggests that the insulin resistance may be partially explained by a receptor defect.

The inherited ataxias

Clinical, biochemical, and genetic studies have brought clarity to many issues concerning the inherited ataxias. The classification, diagnosis, and therapy of hereditary ataxias are now better understood although many questions remain. Basic defects are identified in some disorders.

Plasma cholesteryl sulfate in Friedreich's ataxia

Alteration of membrane fluidity and anomalies of membrane structural proteins have been suspected in Friedreich's ataxia. Plasma lecithin:cholesterol acyltransferase (LCAT) activity is also lowered in this disease, presumably because of a substrate effect. The membrane-stabilizing effect of cholesteryl sulfate (CS) and its inhibitory effect on LCAT activity prompted us to measure this substance in the plasma of Friedreich's ataxia patients as well as in normal subjects and in patients with Charlevoix-Saguenay disease. Plasma cholesteryl sulfate concentrations were significantly higher in Friedreich's ataxia, with levels above the upper limit of normal in nearly half of the cases. This increase was unrelated to age, sex or plasma cholesterol levels, but closely associated with the severity of the disease and thus considered to be secondary. A similar phenomenon (except the association with severity) was observed in Charlevoix-Saguenay ataxia. Levels also tended to be higher in first-degree relatives of Friedreich cases. The significance of these findings is discussed in the light of recent knowledge and experimental data obtained in this laboratory on rats made deficient in essential fatty acids. The highest concentrations of CS observed in Friedreich's ataxia (1097 micrograms/dL, 6 times the normal mean) was only 25% as high as the concentrations reported to inhibit LCAT activity.

Distribution of apolipoprotein E phenotypes in Friedreich's ataxia

Allelic polymorphism at the apolipoprotein E (apo E) gene locus (alleles epsilon 2, epsilon 3, and epsilon 4) is responsible for the existence of 6 discrete electrophoretic phenotypes of plasma apo E. Since the presence of the epsilon 2 allele in the genotype tends to be associated with higher triglyceride levels, a study was undertaken to determine if a higher frequency of this allele could account for the presence of higher plasma triglycerides in subsets of patients with Friedreich's Ataxia. The frequency of the apo E phenotypes was determined in 37 subjects with Friedreich's Ataxia and compared with that of 102 normolipidemic and 102 hyperlipidemic individuals. There was no increased prevalence of the E3/2 phenotype and the epsilon 2 allele in the Friedreich's sample as is found in a hyperlipidemic sample. Furthermore, the epsilon 2 subset did not have significantly higher plasma triglycerides than the non-epsilon 2 subset and the hypothesis was rejected. On the other hand, there was a trend for a decreased frequency of the E4/3 phenotype in the Friedreich's sample relative to the hyperlipidemic group but the difference did not reach statistical significance. The apo E phenotype distribution was also measured in a smaller sample of Charlevoix-Saguenay disease; this led to the discovery of two siblings with the relatively rare E2/2 phenotype and unexpectedly low levels of plasma lipid and lipoprotein concentrations. Plasma apolipoprotein E concentrations in both diseases were within the normal range except for subjects bearing the E2/2 phenotype.

Zinc and taurine in Friedreich's ataxia

Zinc and taurine were measured in urine in the fasting state and following a 4mg/kg load of taurine in subjects with Friedreich's Ataxia (FA), and healthy controls (C), and subjects with Duchenne type muscular dystrophy (MD). Of the FA, 25% had increased fasting excretion of zinc, and 50% had increased excretion of zinc following the taurine load. The MD subjects all had increased zinc excretion at all times. The increased zinc excretion did not correlate with increased excretion of taurine. As an index of zinc deficiency, uptake of zinc by erythrocytes was measured in all subjects and in heterozygotes for FA. The pattern of uptake was abnormal for FA and heterozygotes. Hair analysis for zinc showed that 10 of the 12 FA subjects had low values. We conclude that significant abnormalities in zinc metabolism exist in some, but not all cases of FA. The evidence available does not permit definition of the cause of these abnormalities, whether zinc deficiency or abnormal zinc transport is the primary factor.

Platelet taurine content in Friedreich's disease

We have studied the concentrations of taurine and of 6 other amino acids in platelets from 12 patients with Friedreich's disease and 12 age sex-matched normal control subjects. No significant differences could be demonstrated between the two groups. The glycine/serine ratio was lower in all the patients but this change did not reach statistical significance. From these and other data, we conclude that the taurine retention deficit observed previously in Friedreich's disease cannot be the primary causal defect.

Fatty acid composition of tissue phospholipids and prostaglandin excretion in hyperlipidemia induced in rats by implantation of the mammotropic pituitary tumor MtT-F4

A mammotropic pituitary tumor, MtT-F4, was implanted into male Fisher 344 rats for a period of 4 weeks. This tumor induced growth retardation, hyperlipidemia, hepatic hypertrophy and adrenal hyperplasia. Lipids were extracted from various tissues. In tumor-bearing rats, phospholipid concentration was found to be increased in plasma, spleen and testis. Distribution among the various phospholipid classes was similar to that of controls except in liver and heart, where phosphatidylcholine was increased at the expense of phosphatidylinositol and phosphatidylserine. The main difference was in the fatty acid composition of major phospholipids. The proportion of omega 6 fatty acids was lower and that of docosahexaenoic acid of the omega 3 series (22:6 omega 3) was higher in most tissues, especially in plasma, liver, heart and kidney. Concurrently, the urinary excretion of two endogenous metabolites of PGI2 (2,3-dinor-6-keto-PGF1 alpha and 6,15-diketo-13,14-dihydro-2,3-dinor-PGF1 alpha) was found to be increased significantly in tumor-bearing rats. The results raise the hypothesis that hormonal changes induced by the MtT-F4 tumor accelerate the conversion of arachidonic acid (20:4 omega 6) to prostaglandins. This effect, perhaps coupled with a diversion of linoleic acid (18:2 omega 6) towards other metabolic processes, would account for a partial depletion of membrane phospholipids in 18:2 omega 6 and for the reduced production of longer chain omega 6 unsaturated acids from 20:4 omega 6, creating a state of "relative essential fatty acid deficiency." As a result, the metabolism of omega 3 fatty acids is altered towards an enhanced production of 22:6 omega 3 which accumulates in the lipids of cell membranes to compensate for the depletion of unsaturated acids of the omega 6 series.

Pyruvate dehydrogenase activity in the liver, brain and adipose-tissue of lipid-deprived developing rats. Effect of minute amounts of polyunsaturated fatty acids

The present experiment was carried out using the following diets: FF, fat-free, and LP in same diet with 0.7% sunflower oil - given to the progeny of females kept on the FF diet since the mating. after 10 mM Mg2+ activation of the PDH phosphatase, and rate of [1-14C[ pyruvate decarboxylation into acetyl-CoA ester units was determined in the liver, brain and adipose-tissue of the pair-fed developing rats.

RESULTS

In the male progeny, pyruvate dehydrogenase (PDH) activity was higher (61%) in the LP group livers than in the FF group livers, at the end of the 13 week experiment. Such a difference was not observed in the two group brains up to the 91 days postweaning, but was even larger (94%) between adipose-tissues of the LP and FF groups. In the female progeny kept 12 weeks on the diets, PDH activity in the LP group tissues was also higher than in the FF group tissues: 63% in the liver, 43% in adipose-tissues, and less than 10% in the brain. Therefore, a minute amount of lipids high in linoleic acid appeared to increase PDH activity, and especially in the liver and adipose-tissues of animals kept on a strictly fat-free diet. This stimulation of the PDH activity seems closely related to the phospholipid rehabilitation in the tissues (decrease in the trienoic, tetraenoic acid ratio values).

Friedreich's disease 1982: etiologic hypotheses a personal analysis

The author reviews the arguments for and against the four etiologic hypotheses in Friedreich's disease that have been proposed since 1974: the "pyruvate hypothesis", the "lipid-membrane hypothesis", the "energy-defect hypothesis" and finally the "taurine hypothesis". While none of these hypotheses are mutually exclusive, the author shows that all of these mechanisms play some role in the pathophysiology of the symptoms, but that only the "taurine hypothesis" appears to be compatible with all the known facts and the biochemical abnormalities reported. The author proposed that the taurine retention defect (possibly due to a block in the high affinity-low capacity transport of taurine - The TH System) is a primary event in Friedreich's disease. Whether it is the primary genetic event still has to be determined.

Plasma catecholamines in Friedreich's ataxia assayed using high performance liquid chromatography with electrochemical detection

Resting levels of plasma norepinephrine, epinephrine and dopamine were determined in 9 patients diagnosed as having Friedreich's Ataxia using a relatively new assay method, HPLC with electrochemical detection. Levels of norepinephrine and dopamine were found to be significantly elevated in patients as compared to controls while epinephrine, though increased, was not significantly higher. These results confirm in most parts previous findings of Pasternak et al. of increased plasma catecholamines and demonstrate the sensitivity and utility of the present method for the routine assay of plasma catecholamines.