Beta cell compensation for insulin resistance in Zucker fatty rats: increased lipolysis and fatty acid signalling.

AIMS/HYPOTHESIS: The aim of this study was to determine the role of fatty acid signalling in islet beta cell compensation for insulin resistance in the Zucker fatty fa/fa (ZF) rat, a genetic model of severe obesity, hyperlipidaemia and insulin resistance that does not develop diabetes. MATERIALS AND METHODS: NEFA augmentation of insulin secretion and fatty acid metabolism were studied in isolated islets from ZF and Zucker lean (ZL) control rats. RESULTS: Exogenous palmitate markedly potentiated glucose-stimulated insulin secretion (GSIS) in ZF islets, allowing robust secretion at physiological glucose levels (5-8 mmol/l). Exogenous palmitate also synergised with glucagon-like peptide-1 and the cyclic AMP-raising agent forskolin to enhance GSIS in ZF islets only. In assessing islet fatty acid metabolism, we found increased glucose-responsive palmitate esterification and lipolysis processes in ZF islets, suggestive of enhanced triglyceride-fatty acid cycling. Interruption of glucose-stimulated lipolysis by the lipase inhibitor Orlistat (tetrahydrolipstatin) blunted palmitate-augmented GSIS in ZF islets. Fatty acid oxidation was also higher at intermediate glucose levels in ZF islets and steatotic triglyceride accumulation was absent. CONCLUSIONS/INTERPRETATION: The results highlight the potential importance of NEFA and glucoincretin enhancement of insulin secretion in beta cell compensation for insulin resistance. We propose that coordinated glucose-responsive fatty acid esterification and lipolysis processes, suggestive of triglyceride-fatty acid cycling, play a role in the coupling mechanisms of glucose-induced insulin secretion as well as in beta cell compensation and the hypersecretion of insulin in obesity.

[Reactions of social workers in a mental health day center and the avoidance of institutionalization of individual defense mechanisms]. / Des réactions des intervenants dans un centre de jour en santé mentale et de l'évitement de l'institutionnalisation des défenses individuelles.

The author attempts to describe the different strengths that emerge from the role of the supervisor (clinic) in a community organization in relation to two aspects: the maintaining of the defining characteristics of the notion of "alternative" and the dynamic understanding of the social worker-user relationship. After a review of how a day centre operates, the author describes the individual and collective "defense mechanisms" that are used by social workers to alleviate the impact of the user's baffling behaviour on their personality. The author follows by showing that failure to use these defense mechanisms can lead to burnout for the social worker, while certain forms of collective defense mechanisms can prompt this alternative care system to institutionalize itself from within.

Dominantly inherited ataxias in Portugal.

We analysed the clinical features of 82 patients with dominantly inherited ataxia in a cohort survey. All patients fulfilled the diagnostic criteria for Machado-Joseph disease. The mean age of onset of symptoms was 39.8 (+/- 12.5) years and the duration of the disease was 9.2 (+/- 6.7) years. Ataxia, peripheral neuropathy, and fasciculation scores correlated with age of onset and duration of disease. Upper motor neuron scores failed to correlate with age of onset. In a follow-up study we analysed the clinical data of 46 patients two years after the first examination. A paired t-test was used to compare differences between observations. The results are in agreement with those of the cross-section in time, suggesting a deterioration of the symptoms with the evolution of the disease. We conclude that dynamic definition of the disease according to age of onset and duration of symptoms is preferable to subdivision into classical types.

Linkage studies of Friedreich ataxia by means of blood-group and protein markers.

Friedreich ataxia (FA) is an autosomal recessive, neuro-degenerative disorder in which the pathogenetic mechanism remains unidentified despite extensive biochemical studies. Genetic-linkage studies provide an alternative approach to determining the basic defect. Linkage analysis between FA and 36 polymorphic-blood-group and protein markers has been carried out on three separate patient populations--16 families from the inbred Acadian population of Louisiana, 21 French-Canadian families from Quebec, and nine apparently unrelated British families--in an attempt to determine the chromosomal location of the disease mutation. Neither evidence of linkage to any of the markers investigated nor heterogeneity among the populations was found for any of the comparisons. The negative lod scores exclude the locus for FA from greater than 20% of the genome.

MPTP potentiates iron-induced lipid peroxidation without the involvement of free radicals derived from oxygen.

We demonstrate here that MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) potentiates iron-catalyzed lipid peroxidation in intact erythrocytes, whereas it does not mediate hydrogen peroxide catalysed lipid peroxidation. The malonaldehyde formation which results from this lipid peroxidation is generated in the absence of superoxides, hydroxyl radicals, hydrogen peroxide or singlet oxygen. The MPTP reaction is blocked by addition of iron +2 chelator but not by iron +3 chelator. These results suggest that an iron-MPTP complex promotes the formation of lipid peroxidation by interacting directly with membrane polyunsaturated lipids.

Erythrocyte antioxidant activity in human patients with Parkinson's disease.

Three groups have reported defective antioxidant mechanisms in substantia nigra of patients with Parkinson's disease, namely a decreased catalase and peroxidase activity, a reduction of glutathione and, more recently, a diminished nigral glutathione peroxidase activity. We decided to investigate these mechanisms in erythrocytes to determine whether these brain defects represent generalized or genetic aberrations, in which case they should also be present in blood cells. The glutathione cycle has been investigated (reduced and oxidized glutathione, glutathione reductase and peroxidase) plus the activities of catalase and superoxide dismutase. The basal malonaldehyde content of erythrocytes was used as an index of endogenous lipid peroxidation. None of the above-mentioned parameters were found altered in erythrocytes of parkinsonians, suggesting that no genetic or generalized biochemical abnormalities underly the deficiencies detected in substantia nigra.

Ecogenetics of Parkinson's disease: prevalence and environmental aspects in rural areas.

We make use of the unique combination of a homogeneous genetic and racial origin in the rural population of Quebec and the facilities of free and universal access to medical care, to study the distribution of the prevalence of Parkinson's disease in the 9 rural hydrographic regions of the Province. Through 3 different methods of ascertainment, confirmed by two control probes, we demonstrate that the prevalence of Parkinson's disease is of uneven distribution within rural areas. We further investigated the characteristics of the regions of high prevalence. These regions which are predominantly agricultural and areas of intensive market gardening were also the areas with the highest use of pesticides.

Ecogenetics of Parkinson's disease: 4-hydroxylation of debrisoquine.

It is postulated that Parkinson's disease is the result of environmental factors acting on genetically susceptible individuals against a background of normal ageing. Many potentially neurotoxic xenobiotics are detoxified by hepatic cytochrome P450. The function of one such system was studied in forty patients with Parkinson's disease and forty normal control subjects. Significantly more parkinsonian than control subjects had partially or totally defective 4-hydroxylation of debrisoquine. Poor metabolisers of debrisoquine tended to have had earlier onset of disease.

1-Methyl-4-phenyl-pyridinium-induced inhibition of nicotinamide adenosine dinucleotide cytochrome c reductase.

The effect of 1-methyl-4-phenyl-pyridinium (MPP+), the main toxic metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a parkinsonism-causing neurotoxin, upon the activity of nicotinamide adenine dinucleotide (NADH) cytochrome c reductase (EC 1.6.99.3) and upon that of glutathione reductase (EC 1.6.4.2) was monitored spectrophotometrically. For the cytochrome c reductase, the increase in absorbance of reduced cytochrome c was measured at 550 nm; for evaluating glutathione reductase, the absorbance of nicotinamide adenine dinucleotide phosphate (NADPH) was followed at 340 nm. MPP+ but not MPTP reversibly inhibited NADH cytochrome c reductase, but not glutathione reductase. This may be a direct mechanism of cell toxicity by this neurotoxin.

A method to quantitate Coomassie blue-stained proteins in cylindrical polyacrylamide gels.

A method for the quantitation of Coomassie blue-stained proteins in cylindrical polyacrylamide gels is described. It involves an elution of the dye with an 80% methanol solution in a sealed Pyrex tube at 100 degrees C for 3 h and a measurement of its concentration at 585 nm. Using a 6.5% polyacrylamide gel and bovine serum albumin as a protein standard, the curve of absorbance of the dye solution as a function of the amount of protein was observed to be linear up to 30-40 micrograms of protein and as little as 0.8-1.0 micrograms of protein could be measured. The validity of the method was indicated by the values obtained for the relative proportions of the human erythrocyte membrane proteins. Using this method, the color yields of several proteins varying widely with respect to their size, amino acid composition, and carbohydrate content were determined in a 6.5% polyacrylamide gel. The results showed that they were generally the same except for proteins having a high carbohydrate content which were significantly lower.

Comparative behavioral, biochemical and pigmentary effects of MPTP, MPP+ and paraquat in Rana pipiens.

We demonstrate that injections of 1-methyl-4-phenyl-1,2,3,6-tetra-hydropyridine (MPTP), 1-methyl-4-phenyl-pyridinium ion (MPP+) and Paraquat (PQ+) produce in Rana Pipiens different behavioral, biochemical and skin pigmentation changes. MPTP causes in frogs the main symptoms of Parkinsonism (rigidity, akinesia and tremor) and it darkens the skin of animals. It also decreases brain and, less so, adrenal medulla dopamine. These effects are blocked by Pargyline. MPP+ causes the same symptoms but more rapidly. In contrast, skin pigmentation is clearly lightened. Brain and particularly adrenal dopamine reserves are nearly abolished. Pargyline increases these effects. Paraquat, in a cumulative fashion, eventually causes the same behavioral changes and a slight increase in pigmentation. It initially produces an increase in brain and adrenal dopamine concentrations, but later a significant dopamine concentration decrease. Pargyline potentiates these long term effects, blocks the dopamine increase, but reverses the PQ+ effect upon melanin, producing the same depigmentation as MPP+ alone.

A catalyst function for MPTP in superoxide formation.

We demonstrate that 1-methyl-4-phenyl-1,2-dihydropyridine (MPDP) can be generated, in an alternate pathway, from the catalyst action of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) upon the iron redox equilibrium reaction. Superoxide and ferric iron are instantaneously produced after addition of MPTP to a solution of ferrous iron. This reaction is oxygen and pH dependent. Superoxide, through a iron dependent Haber-Weiss reaction with peroxide, can generate the cytotoxic hydroxyl radical. A small portion of the superoxide reacts with MPTP to produce the reactive species X. which, in the presence of Fe+3 can also generate MPDP.

The specific vulnerability of the substantia nigra to MPTP is related to the presence of transition metals.

We demonstrate that the high concentration of transition metals in the substantia nigra could be a major factor responsible for the specificity of cell damage by the Parkinsonism-causing neurotoxin MPTP. It will be shown that these metals in vitro, and MPTP, each potentiate the autoxidation of dopamine and the production of aminochrome through the generation of superoxide, hydroxyl radicals, hydrogen peroxide and reactive semiquinones. Moreover, the same metals contribute to the oxidation of MPTP itself, further enhancing dopamine autoxidation.

Gel chromatography on a Sepharose 4B column: earlier elution of protein-sodium dodecyl sulfate complexes of low Stokes radii.

A procedure is described for the determination of the Stokes radius of a detergent micelle by gel chromatography. It was observed that different lots of Sepharose 4B can exhibit a wide variation in the permeation of their gel pores. It is shown that this variation is due to differences in their pore size distribution. It has been observed that protein-sodium dodecyl sulfate (SDS) complexes of high Stokes radii eluted on a Sepharose 4B column with Stokes radii lower than the theoretical, as it has been previously reported but that protein-SDS complexes of low Stokes radii (less than 70 A), contrary to what might have been expected, eluted with Stokes radii higher than the theoretical. Evidence was obtained that their anomalous elution is due to an interaction of the detergent SDS with the gel pores of small diameter.