Biomedical subjects

D Marchington

Publications and source records attributed to D Marchington.

8 recordsLinked to original sources

PubMed2000

Decrease of 3243 A-->G mtDNA mutation from blood in MELAS syndrome: a longitudinal study.

It is widely held that changes in the distribution of mutant mtDNAs underlie the progressive nature of mtDNA diseases, but there are few data documenting such changes. We compared the levels of 3243 A-->G mutant mtDNA in blood at birth from Guthrie cards and at the time of diagnosis in a blood DNA sample from patients with mitochondrial encephalopathy, lactic acidosis, and strokelike episodes (MELAS) syndrome. Paired blood DNA samples separated by 9-19 years were obtained from six patients with MELAS. Quantification of mutant load, by means of a solid-phase minisequencing technique, demonstrated a decline (range 12%-29%) in the proportion of mutant mtDNA in all cases (P=.0015, paired t-test). These results suggest that mutant mtDNA is slowly selected from rapidly dividing blood cells in MELAS.

Adolescent↗

PubMed1995

Duplications of mitochondrial DNA in Kearns-Sayre syndrome.

mtDNA duplications were detectable in 10 of 10 patients with mtDNA deletions and Kearns-Sayre syndrome (KSS) and in none of 8 patients with chronic progressive external ophthalmoplegia (CPEO). Thus, duplications of mtDNA seem to be a distinctive feature of KSS, including patients where Pearson's syndrome is the first manifestation. Diabetes mellitus was identified in 4 of 7 patients with high or moderate levels of mtDNA duplications. The balance of mtDNA rearrangements may be central to the pathogenesis of this unique group of disorders.

Adult↗

PubMed1995

Intracellular heteroplasmy for disease-associated point mutations in mtDNA: implications for disease expression and evidence for mitotic segregation of heteroplasmic units of mtDNA.

Studies in vitro have shown that a respiratory-deficient phenotype is expressed by cells when the proportion of mtDNA with a disease-associated mutation exceeds a threshold level, but analysis of tissues from patients with mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes (MELAS) have failed to show a consistent relationship between the degree of heteroplasmy and biochemical expression of the defect. One possible explanation for this phenomenon is that there is variation of heteroplasmy between individual cells that is not adequately reflected by the mean heteroplasmy for a tissue. We have confirmed this by study of fibroblast clones from subjects heteroplasmic for the MELAS 3243 (A-->G) mtDNA mutation. Similar observations were made with fibroblast clones derived from two subjects heteroplasmic for the 11778 (G-->A) mtDNA mutation of Leber's hereditary optic neuropathy. For the MELAS 3243 mutation, the distribution of mutant mtDNA between different cells was not randomly distributed about the mean, suggesting that selection against cells with high proportions of mutant mtDNA had occurred. To explore the way in which heteroplasmic mtDNA segregates in mitosis we followed the distribution of heteroplasmy between clones over approximately 15 generations. There was either no change or a decrease in the variance of intercellular heteroplasmy for the MELAS 3243 mutation, which is most consistent with segregation of heteroplasmic units of multiple mtDNA molecules in mitosis. After mitochondria from one of the MELAS 3243 fibroblast cultures were transferred to a mitochondrial DNA-free (rho0) cell line derived from osteosarcoma cells by cytoplast fusion, the mean level and intercellular distribution of heteroplasmy was unchanged. We interpret this as evidence that somatic segregation (rather than nuclear background or cell differentiation state) is the primary determinant of the level of heteroplasmy.

Adolescent↗

PubMed1993

Neurodevelopmental abnormalities and lactic acidosis in a girl with a 20-bp deletion in the X-linked pyruvate dehydrogenase E1 alpha subunit gene.

We describe a girl with developmental abnormalities of the CNS and a lactic acidosis whose cultured fibroblasts showed a profound deficiency of pyruvate dehydrogenase complex (PDHC) activity (patient = 0.14 nmol/mg protein per minute, controls = 0.7 to 1.1 nmol/mg protein per minute). Immunocytochemistry demonstrated the fibroblast culture to be mosaic, with 14% of cells expressing the PDHC E1 alpha subunit protein in normal amounts and the remaining 86% having no detectable immunoreactive activity. Direct sequencing of cDNA for the X-linked PDHC E1 alpha subunit established that the patient was heterozygous for a 20-bp deletion beginning in the codon for Ser300 of the derived amino acid sequence. The pattern of methylation at the DXS255 locus suggested predominant expression of the X chromosome carrying the mutant allele in the fibroblast culture. There was a good correlation between the residual PDHC activity, the proportion of cells with immunoreactive E1 alpha protein, and the X chromosome inactivation ratio, demonstrating the importance of X-inactivation for expression of this X-linked neurometabolic disease in females.

Acidosis, Lactic↗

PubMed1986

Thermogenesis and sympathetic activity in BAT of overfed rats after adrenalectomy.

Resting oxygen consumption was elevated by 30% in young rats fed a cafeteria diet compared with their chow-fed controls and by 22% in cafeteria-fed, adrenalectomized (ADX) rats compared with the ADX chow-fed group, but injection of propranolol reduced oxygen consumption in the cafeteria-fed animals and abolished these differences. Brown adipose tissue (BAT) mass was increased by cafeteria feeding, and the activity of the mitochondrial proton conductance pathway (assessed from purine nucleotide binding) was enhanced by adrenalectomy and by cafeteria feeding. Norepinephrine turnover in BAT (determined from the time-dependent loss of tissue [3H]norepinephrine specific activity) was increased by 105% in sham-operated, cafeteria-fed rats, by 142% in chow-fed ADX rats, and by 400% in cafeteria-fed ADX rats, compared with chow-fed controls. Cardiac norepinephrine turnover was elevated by 80% in sham-operated, cafeteria-fed rats, but unaffected by adrenalectomy. These data indicate that the enhanced thermogenesis and BAT activity induced by adrenalectomy in chow- or cafeteria-fed rats is due to increased sympathetic activity in the tissue.

Adipose Tissue, Brown↗

PubMed1985

Regulation of sympathetic activity in lean and obese Zucker (fa/fa) rats.

Norepinephrine concentration and turnover (measured by the time-dependent loss of tissue [3H]norepinephrine specific activity) were reduced in the brown adipose tissue (BAT) of obese Zucker rats but were normal in the heart. After acclimation to a 4 degrees C environment for 7 days, BAT norepinephrine turnover was increased to similar levels in lean and obese rats. After overfeeding with sucrose BAT norepinephrine turnover increased in lean rats but was unaffected in obese rats. Propranolol prevented the normalization of BAT mitochondrial GDP binding that followed adrenalectomy of obese rats. Adrenalectomy of obese rats restored BAT norepinephrine turnover to levels observed in lean rats. However, the increase in BAT GDP binding associated with sucrose overfeeding of adrenalectomized lean and obese rats was neither prevented by propranolol nor associated with a stimulation of norepinephrine turnover. The results suggest that the pituitary-adrenal endocrine axis may influence diet-related BAT thermogenesis and that this influence is only partially mediated by the sympathetic nervous system.

Acclimatization↗

PubMed1985

Regulation of brown adipose tissue thermogenesis by corticosterone in obese fa/fa rats.

The defective BAT function of obese Zucker rats has been related primarily to a loss of diet-induced thermogenesis. The normalisation of BAT function by adrenalectomy has been related to the removal of corticosterone. Experiments with propranolol-blockade and on tissue norepinephrine turnover suggest that corticosterone impairs diet-related sympathetic activity but does not alter BAT response to exogenous norepinephrine. The reduction in serum T3 in obese rats is related to the loss of sympathetic activity.

Adipose Tissue, Brown↗

PubMed1983

Energy balance, diet-induced thermogenesis and brown adipose tissue in lean and obese (fa/fa) Zucker rats after adrenalectomy.

Five-week-old male, lean (+/?) and genetically obese (fa/fa) Zucker rats received either bilateral adrenalectomy or sham operations, and energy balance was measured over the subsequent 21 days. Body weight and energy intake were similar for intact lean and obese rats, but the latter group showed a marked increased in body energy gain and energetic efficiency, and reduced energy expenditure. Adrenalectomy did not significantly influence energy balance in lean rats but caused decreases in food intake and body weight gain in obese rats, and restored their energetic efficiency and body energy gain to the level of lean animals. The lower thermic response to a single meal (40 kJ) in intact obese rats was restored to normal by adrenalectomy. Brown adipose tissue (BAT) mass was larger in sham-operated obese rats, but tissue protein concentration, mitochondrial yield and mitochondrial GDP binding were all markedly reduced in obese rats. BAT mass, composition and GDP binding were almost identical in adrenalectomized obese and all lean rats. These findings demonstrate that the reduced fat deposition in Zucker rats after adrenalectomy is mainly due to the large decrease in the efficiency of energy utilization associated with a restoration of brown fat activity.

Adipose Tissue, Brown↗