Biochemical medicine and metabolic biology最新文献

The purpose of this review is to describe the relationship between the dopamine and amino acid neurotransmitter systems and cortical oxygen pressure during different levels of cerebral hypoxia using newborn piglets as an animal model, adding new data from our laboratory. The extracellular dopamine increases as the oxygen pressure in the cortex decreases. The relationship between oxygen pressure and dopamine levels is the same whether the hypoxia is induced by reduced F_iO₂ (high-flow hypoxia) or by hypocapnia-induced cerebral vasoconstriction (low-flow hypoxia). Thus it appears that, particularly in mild hypoxia, the extracellular level of dopamine depends primarily on the oxygen concentration in the tissue with minimal influence of parameters such as blood flow and pH. There is no "oxygen reserve" in the brain of newborn piglets and the extracellular levels of dopamine in the striatum increase almost linearly with decrease in oxygen pressure, with even small decreases in oxygen pressure resulting in increased dopamine levels. In contrast, the changes in extracellular concentrations of the excitatory amino acids glutamate and aspartate are variable and transient. In a majority of 2- to 5 day-old piglets even very low oxygen pressures in the brain did not result in significant alterations in the extracellular levels of glutamate and aspartate. These changes in the dopaminergic system may contribute directly and indirectly to the neuronal damage that occurs during hypoxic/ischemic insult and reoxygenation in newborn brain, particularly in the striatum. A variety of mechanisms are discussed by which dopamine, in particular extracellular dopamine, can increase cellular toxicity.

Studies from our laboratory demonstrated that the free radical scavenger, nitro blue tetrazolium, and iron chelators, such as dypyrydil, are potent inhibitors of arachidonic acid oxidation and platelet function. In the present study, we have evaluated the effects of known antioxidants, such as butylated hydroxyanisol (BHA), butylated hydroxytoluene (BHT), and diphenylamine, on arachidonic acid metabolism and platelet function. Diphenylamine, a common dye intermediate used in hair color formulations, was the most potent inhibitor of arachidonic acid metabolism by platelet cyclooxygenases. Diphenyl and BHA were also potent inhibitors of arachidonic acid oxidation. Other diphenyl analogues and BHT were relatively poor inhibitors of arachidonic-mediated platelet activation. Results of this study, as well as those of our earlier studies, suggest that antioxidants and iron chelators prevent arachidonic acid metabolism and alter platelet function by interfering with the heme/arachidonic acid interaction and blocking cyclooxygenase metabolites essential for the formation of thromboxane A₂, a potent platelet agonist.

Previous studies of the molecular basis of 21-hydroxylase deficiency have shown four common gene conversion mutations in exons 7 and 8. Current molecular diagnostic protocols use allele-specific oligonucleotide hybridization (ASOH) to individually detect each of these mutations and the corresponding normal alleles. This method is costly, labor intensive, and may not provide quantitative results. To expedite molecular diagnosis in families with 21-hydroxylase deficiency, we have designed and implemented single-strand conformational polymorphism (SSCP) analysis. We applied SSCP analysis to 12 families in whom mutations in exons 7 or 8 had been previously identified by ASOH. Using a single polymerase chain reaction (PCR) amplification, unique conformers can be assigned to three mutations: V281L, Q318X, and R356W. The fourth mutation, T insertion at nucleotide 1761, was detected by heteroduplex analysis of the same PCR product. Thus, we were able to identify all four mutations using a single PCR product on a single gel.

To determine the nature of the molecule(s) that is responsible for the melatonin like immunoreactivity (MLI), we measured the effect of pretreatment of plasma samples with detergents, reducing agent, and proteinase K. Nonidet P-40 Triton X-100, and ethylacetate extraction had no effect, while sodium deoxycholate, sodium dodecyl sulfate, β-mercaptoethanol, ether extraction, proteinase K, and temperature increased the MLI. Since the radioimmunoassay (RIA) was sensitive to proteinase K, ionic detergents, and a reducing compound, we hypothesize that a proteinaceous molecule might be responsible for this MLI. We compared our column procedure for RIA of plasma melatonin (1) with procedures involving extraction with either ethylacetate or ether. In our hands preextraction of samples with organic solvents caused a loss of immunoreactivity. We also found that passing samples through the column is more efficient in eliminating interference in the melatonin assay than extracting samples either with ethylacetate or ether.

The most common α-thalassemia in Southeast Asian or Southern Chinese populations is the (- -^SEA) double α-globin deletion. Couples heterozygous for (- - ^SEA) have 25% risk for hydrops fetalis from loss of all four α-globin genes. The (- -^SEA) deletion spares the embryonic ζ-globin genes and causes traces of ζ-peptide to persist throughout life. A colorimetric monoclonal anti-ζ antibody test for raised ζ-peptide has detected the (- -^SEA) deletion in liquid blood samples, but not deletions of the entire α-globin region with loss of the ζ-globin genes. Eluates from dried blood spots had the same anti-ζ antibody color reaction as whole blood, even after storage at 4°C for up to 77 days. The anti-ζ antibody test was positive in 24 of 91 microcytic samples (mean corpuscular hemoglobin <24 pg), including four with iron deficiency; it was negative in 26 provisionally diagnosed α-thalassemia-1 heterozygotes and all 32 nonmicrocytic samples. Southern blot analysis and a specific SEA-polymerase chain reaction test confirmed that 18 anti-ζ antibody-positive samples and 1 anti-ζ antibody-negative sample had the (- -^SEA) deletion. Two anti-ζ antibody-negative microcytic samples had the (- -^Fil) total α-globin region deletion, 2 had single α-gene deletions, 22 others may also have had a total α-region deletion. Hence specificity was very high and sensitivity was 95%. The anti-ζ antibody test can detect the (- -^SEA) deletion in dried blood samples, even after prolonged storage. This simple inexpensive test can conveniently screen samples collected at a distance from a central laboratory.

The measurement of individual respiratory chain complexes is an important component of the investigation of diseases due to mitochondrial dysfunction. We have evaluated assays which measure complexes I to IV in human skeletal muscle mitochondria and in addition optimized these assays to provide sensitive and reliable diagnostic techniques, particularly in situations where a partial interruption at a single complex needs to identified. Using several established methods of membrane disruption we have found that optimal activities of complexes I and II are obtained by freeze-thawing the mitochondria in hypotonic potassium phosphate buffer, whereas complex III and IV activities are markedly increased by the addition of the detergent n-dodecyl-β-D-maltoside. Complex I activity is measured in the presence of 2.5 mg · ml⁻¹ bovine serum albumin, which increases rotenone sensitivity, and we have shown that NADH-cytochrome b₅ reductase makes an important contribution to the rotenone-insensitive NADH-ubiquinone oxidoreductase activity. Complex II activity is measured after preincubation of the mitochondrial fraction with succinate to fully activate the complex. Complex I and III activities are dependent upon the length of the isoprenoid chain of the ubiquinone and ubiquinol, respectively. These assays have been used to establish a control range.

The effects of allopurinol (AP) on functional and metabolic recovery of the isolated rat heart after global ischemia were studied. Hearts were subjected to aerobic perfusion (30 min), cardioplegic infusion (5 min), normothermic ischemia (37 min), and reperfusion (50 min) which was started with secondary cardioplegic infusion (10 min). AP was injected into rats (44 mg/kg body wt ip 2 h before heart excision) and added to cardioplegic solution (2 mM) prior and after ischemia. AP treatment significantly improved postischemic recovery of the function and reduced the leakage of lactate dehydrogenase from reperfused hearts. These beneficial effects were accompanied by a better preservation of tissue content of ATP, the total adenine nucleotides, phosphocreatine, and the total creatine at the end of reperfusion. Inhibition of xanthine oxidase by AP substantially decreased pre- and postischemic release of xanthine and uric acid and increased postischemic release of hypoxanthine into the coronary effluent. Despite this, AP treated hearts did not exhibit a reduction in hydroxyl radical adduct formation in the effluents at reperfusion assessed by the spin-trap measurements. The results suggest that AP may protect the heart from ischemia/reperfusion injury due to enhanced energy provision rather than by prevention of oxygen-derived free radical formation.

The present study examined the in vitro and in vivo metabolism of 18:2n-6 and 18:3n 6 by kidney and liver in the male adult spontaneously hypertensive (SHR) and normotensive (WKY) rats. In liver and kidney slices incubated for 1 h with either [1-¹⁴C]18:2n-6 or [1-¹⁴C]18:3n-6 (60 μM), substantial amounts of radioactivity were incorporated into triacylglycerol and phospholipid fractions. Approximately 15% of the radiolabeled 18:2n-6 was converted into 18:3n-6 in liver slices but no conversion was found in kidney slices. When incubated with radiolabeled 18:3n-6, over 40% of the radioactivity was metabolized mainly to 20:4n-6 in liver slices, but evenly to 20:3n-6 and 20:4n-6 in kidney slices. There were no differences between the results from SHR and those from WKY. In WKY rats given an oral bolus of radiolabeled 18:3n-6, most of the radioactivity was recovered in the liver and significantly less in the kidney. In both tissues, the radioactivity was associated initially only with 18:3n-6 and later with its elongation product, 20:3n-6. These findings indicated that the kidney, although unable to metabolize 18:2n-6, could metabolize 18:3n-6 taken up from the circulation. The effectiveness of 18:3n-6, compared to 18:2n-6, as an anti hypertensive agent may result from the provision of a post-Δ6-desaturation metabolite which can be directly converted to blood pressure-regulating eicosanoids in the kidney.

Bone marrow transplantation (BMT) in mice was utilized to determine the relative importance of carbonic anhydrase II (CA II) deficiency in blood compared to kidney in the pathogenesis of the ammonium chloride intolerance observed in CA II-deficient mice. "Normal" BMT experiments utilized normal donors and CA II-deficient recipients (NL→DEF), "reverse" BMT experiments utilized CA II-deficient donors and normal recipients, and control BMT experiments utilized normal mice with a hemoglobin polymorphism (Hbb d/s). Unstressed urinary pH was not significantly altered by normal or reverse BMT, nor was any change induced by control BMT. However, DEF→NL mice showed markedly altered weight changes when placed on oral ammonium chloride, an effect apparently secondary to dehydration due to decreased water intake. In addition, some CA II deficient mice have a urinary concentrating defect. Red blood cell and kidney CA II deficiency contribute additively to these effects.

The involvement of protein kinase C in differentiation of rat adipocyte precursor cells in serum-free culture was evaluated by using various protein kinase inhibitors. Induction of adipose conversion, which was maximal after 10 days of culture in the presence of 5 μg/ml insulin, 10 μg/ml transferrin, and 200 pM triiodothyronine, was inhibited by the addition of protein kinase C inhibitors, H-7 and staurosporine, in a dose dependent fashion with the maximal effect at 10 μM and 10 nM, respectively. Inhibition of adipocyte differentiation by 12-O-tetradecanoylphorbol 13-acetate (10⁻⁸M), an activator of protein kinase C, was reversed by a concomitant addition of either 10 μM H-7 or 10 nM staurosporine. HA1004, a potent inhibitor of cAMP- and cGMP-dependent protein kinases, with minimal inhibitory activity on protein kinase C, did not affect adipose conversion. Furthermore, H-89, another isoquinoline derivative with a selective inhibitory action on cAMP-dependent protein kinase, was without effect on cellular differentiation. These results indicate that the potentiation of adipogenesis by H-7 and staurosporine is mediated by suppression of protein kinase C and that protein kinase C is involved in adipocyte differentiation in an inhibitory fashion.