POLYOL DEHYDROGENASE: PURIFICATION. EVIDENCE FOR MULTIPLE FORMS AND SOME PROPERTIES OF THE DOMINANT VARIANT OF THE HORSE LIVER ENZYME

Purification of horse-liver polyoi dehydrogenase (PDH) on DE52 anion-exchange cellulose reveals the presence of three fractions with enzyme activity. These appear in the breakthrough volume (PDH-3) and the salt gradient (PDH-1, -2) respectively. The major band of activity (< 90%) is found in the PDH-2 fraction. A reexamination of sheep-liver polyol dehydrogenase also reveals the presence of three bands of activity, with the dominant fraction (PDH-3) corresponding to the preparation described by Smith (Biochem. J., 83, 135–144, (1962))³. The interaction between horse-liver (and sheep-liver) PDH and Blue Sepharose CL-6B is found to be endothermic. This property is utilized in the final purification step. Horse-liver PDH-2 has a molecular/subunit weight of 85, 000/28, 000, a Stokes' radius of 3.8 nm, and an isoelectric point of 7.4.     

A systematic review of the literature examining the diagnostic efficacy of measurement of fractionated plasma free metanephrines in the biochemical diagnosis of pheochromocytoma

BACKGROUND: Fractionated plasma metanephrine measurements are commonly used in biochemical testing in search of pheochromocytoma. METHODS: We aimed to critically appraise the diagnostic efficacy of fractionated plasma free metanephrine measurements in detecting pheochromocytoma. Nine electronic databases, meeting abstracts, and the Science Citation Index were searched and supplemented with previously unpublished data. Methodologic and reporting quality was independently assessed by two endocrinologists using a checklist developed by the Standards for Reporting of Diagnostic Studies Accuracy Group and data were independently abstracted. RESULTS: Limitations in methodologic quality were noted in all studies. In all subjects (including those with genetic predisposition): the sensitivities for detection of pheochromocytoma were 96%-100% (95% CI ranged from 82% to 100%), whereas the specificities were 85%-100% (95% CI ranged from 78% to 100%). Statistical heterogeneity was noted upon pooling positive likelihood ratios when those with predisposition to disease were included (p < 0.001). However, upon pooling the positive or negative likelihood ratios for patients with sporadic pheochromocytoma (n = 191) or those at risk for sporadic pheochromocytoma (n = 718), no statistical heterogeneity was noted (p = 0.4). For sporadic subjects, the pooled positive likelihood ratio was 5.77 (95% CI = 4.90, 6.81) and the pooled negative likelihood ratio was 0.02 (95% CI = 0.01, 0.07). CONCLUSION: Negative plasma fractionated free metanephrine measurements are effective in ruling out pheochromocytoma. However, a positive test result only moderately increases suspicion of disease, particularly when screening for sporadic pheochromocytoma.     

Impact of chronic fructose infusion on hepatic metabolism during TPN administration

During chronic total parenteral nutrition (TPN), net hepatic glucose uptake (NHGU) is markedly elevated. However, NHGU is reduced by the presence of an infection. We recently demonstrated that a small, acute (3-h) intraportal fructose infusion can correct the infection-induced impairment in NHGU. The aim of this study was to determine whether the addition of fructose to the TPN persistently enhances NHGU in the presence of an infection. TPN was infused continuously into the inferior vena cava of chronically catheterized dogs for 5 days. On day 3, a bacterial clot was implanted in the peritoneal cavity, and either saline (CON, n = 5) or fructose (+FRUC, 1.0 mg. kg(-1). min(-1), n = 6) infusion was included with the TPN. Forty-two hours after the infection was induced, hepatic glucose metabolism was assessed in conscious dogs with arteriovenous and tracer methods. Arterial plasma glucose concentration was lower with chronic fructose infusion (120 +/- 4 vs. 131 +/- 3 mg/dl, +FRUC vs. CON, P < 0.05); however, NHGU was not enhanced (2.2 +/- 0.5 vs. 2.8 +/- 0.4 mg. kg(-1). min(-1)). Acute removal of the fructose infusion dramatically decreased NHGU (2.2 +/- 0.5 to -0.2 +/- 0.5 mg. kg(-1). min(-1)), and net hepatic lactate release also fell (1.6 +/- 0.3 to 0.5 +/- 0.3 mg. kg(-1). min(-1)). This led to an increase in the arterial plasma glucose (Delta13 +/- 3 mg/dl, P < 0.05) and insulin (Delta5 +/- 2 micro U/ml) concentrations and to a decrease in glucagon (Delta-11 +/- 3 pg/ml) concentration. In conclusion, the addition of chronic fructose infusion to TPN during infection does not lead to a persistent augmentation of NHGU.     

Role of ALDP (ABCD1) and mitochondria in X-linked adrenoleukodystrophy

Peroxisomal disorders have been associated with malfunction of peroxisomal metabolic pathways, but the pathogenesis of these disorders is largely unknown. X-linked adrenoleukodystrophy (X-ALD) is associated with elevated levels of very-long-chain fatty acids (VLCFA; C(>22:0)) that have been attributed to reduced peroxisomal VLCFA beta-oxidation activity. Previously, our laboratory and others have reported elevated VLCFA levels and reduced peroxisomal VLCFA beta-oxidation in human and mouse X-ALD fibroblasts. In this study, we found normal levels of peroxisomal VLCFA beta-oxidation in tissues from ALD mice with elevated VLCFA levels. Treatment of ALD mice with pharmacological agents resulted in decreased VLCFA levels without a change in VLCFA beta-oxidation activity. These data indicate that ALDP does not determine the rate of VLCFA beta-oxidation and that VLCFA levels are not determined by the rate of VLCFA beta-oxidation. The rate of peroxisomal VLCFA beta-oxidation in human and mouse fibroblasts in vitro is affected by the rate of mitochondrial long-chain fatty acid beta-oxidation. We hypothesize that ALDP facilitates the interaction between peroxisomes and mitochondria, resulting, when ALDP is deficient in X-ALD, in increased VLCFA accumulation despite normal peroxisomal VLCFA beta-oxidation in ALD mouse tissues. In support of this hypothesis, mitochondrial structural abnormalities were observed in adrenal cortical cells of ALD mice.