Biomedical subjects
Publications and source records attributed to M J Bennett.
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Overproduction of very low-density lipoprotein apolipoprotein B by the liver is a metabolic marker for familial combined hyperlipidaemia, a common inherited disorder of lipoprotein metabolism. Four subjects with familial combined hyperlipidaemia had rates of apolipoprotein B production which were 2-7 times normal, using a protocol in which [15N]glycine was used to label newly synthesized hepatic proteins. Following 4-6 months of therapy with lovastatin, very low-density lipoprotein apolipoprotein B production in all four subjects had returned to the normal range. This demonstrates that lovastatin, an inhibitor of cholesterol biosynthesis, acts also to reduce the apparent production rate of apolipoprotein B by the liver.
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Prenatal diagnosis has been undertaken in 17 pregnancies in 15 families at risk for aspartoacylase deficiency. Amniocentesis was at 14-18 weeks gestation followed by measurement of amniotic fluid N-acetyl-L-aspartate (NAA) levels in all pregnancies and amniocyte aspartoacylase activity in most pregnancies. In one case amniocentesis was performed at 11 weeks gestation in conjunction with chorionic villus sampling. At 14-18 weeks of gestation, control levels of NAA were 0.30-2.55 mumol/L. The fetus was predicted to be affected in 8 of the pregnancies, 4 of which were confirmed by enzyme analysis on fetal tissue and 2 by the clinical and metabolic expression of Canavan disease in a newborn. In two cases there was no fetal tissue available for enzyme confirmation. One of these had the highest amniotic fluid NAA level (8.68 mumol/L) and in the other pregnancy there were two amniocenteses, both with markedly elevated levels. Of 9 fetuses predicted to be normal, 8 newborns were clinically and biochemically normal. A single case with amniotic fluid NAA in the normal range (1.56 mumol/L, measured in one laboratory only) resulted in an aborted fetus in whom aspartoacylase was deficient in cultured skin fibroblasts. We propose that amniotic fluid NAA levels remain the best predictor of an affected fetus and recommend that the assay be performed in multiple laboratories.
An infant with glycogen storage disease and prolonged malnourishment showed a urinary organic acid profile during an episode of fasting hypoglycaemia with inappropriate hypoketotic dicarboxylic aciduria that was indistinguishable from that reported in long-chain L-3-hydroxyacyl-CoA dehydrogenase deficiency. Although there was a striking elevation of urinary 3-hydroxydecanedioic acid, the ratios between hydroxydicarboxylic acids were consistent with values reported to be indicate of medium-chain acyl-CoA dehydrogenase deficiency. We suspect that the fasting 3-hydroxydicarboxylic aciduria was attributable to secondarily impaired enzyme activities, the consequence of malnutrition, early infancy, and/or glycogen storage disease. Caution is advised in the interpretation of urinary organic acid patterns that indicate a 3-hydroxydicarboxylic aciduria, as well as an inappropriate hypoketotic dicarboxylic aciduria, as they may represent non-specific findings.
The phenomenon of managed care is misperceived by its critics as a movement. Atheoretical in nature, and driven by spiralling health care costs, it represents the introduction of an executive function into the free-for-all (a supremely ironic term) of American medicine. Part one of this article traces the origin and development of the mental health carve-out, relating it to its antecedents, and describing its 3 overlapping phases: utilization review, discounted fees, and network development and management. Part two describes the key concept of the continuum of care and the role of the case manager in monitoring a care episode. The article concludes by anticipating seven future trends and calling for mental health leadership to recognize and ally with the need to manage resources in a more rational and efficient manner.
Screening for medium-chain acyl-coenzyme A dehydrogenase (MCAD) deficiency by urinary 3-phenylpropionylglycine may not be reliable in early infancy because young infants are not colonized with adult-type colonic flora. In this study we delineated the microbes that produce 3-phenylpropionic acid, the precursor of 3-phenylpropionylglycine. We found that the use of some antibiotics may alter gut flora, thereby confounding this method of screening for MCAD deficiency.
Sixty-one plasma samples from patients with inborn errors of fatty acid oxidation and from control subjects were analyzed in a blinded fashion for acylcarnitines by the radioisotopic exchange-high-performance liquid chromatographic method. All samples from patients with medium-chain acyl-coenzyme A dehydrogenase (MCAD) deficiency (n = 30), some of which had been stored in a frozen state for several years, showed a prominent octanoylcarnitine peak. In all blood spots from 11 patients with MCAD deficiency, octanoylcarnitine was also detected. Control plasma specimens and blood spots contained small amounts of octanoylcarnitine; however, the octanoylcarnitine/acetylcarnitine ratio differentiated patients with MCAD deficiency. Longer-chain acylcarnitines were found in plasma of all three patients with defects in long-chain fatty acid oxidation. Plasma and blood spots from a patient with multiple acyl-coenzyme A dehydrogenase deficiency contained C4-acylcarnitine, hexanoylcarnitine, octanoylcarnitine, and decanoylcarnitine. The results suggest that the method may be highly sensitive in detecting MCAD deficiency and other defects in fatty acid oxidation from plasma or blood spots.
PROBLEM: It remains unclear whether maternal immunization with paternal lymphocytes prior to conception improves the reproductive outcome in women with recurrent abortion in whom all secondary causes have been excluded. METHOD: A double-blind placebo controlled trial was instituted in women with unexplained recurrent spontaneous abortion, comparing immunization with 400 million paternal to 400 million maternal (autologous) lymphocytes. The groups were compared in a paired sequential trials chart, by logistic regression, and, in addition, a meta-analysis of this and other published trials was carried out. RESULTS: The live birth rate among pregnancies in paired couples with paternal lymphocyte immunization was 68% compared to 47% in the women who received their own cells. The results bordered on, but did not achieve, statistical significance. The women in each group were thoroughly investigated to exclude known causes of recurrent pregnancy loss and appeared to have been well matched in all variables. Women with lymphocytotoxic antibodies against paternal lymphocytes were excluded. Unlike our previous study there was not association between the time to conception and the chance of a successful outcome. Indeed, the time to conception was relatively short, 12 wk in all groups. The meta-analysis supported an overall modest favorable experience with paternal cells. CONCLUSION: The study is consistent with a general trend favoring paternal over maternal lymphocyte immunization but reinforces the need for larger multicenter controlled trials as well as more detailed biological study in humans to understand the nature of the maternal-fetal interface and its breakdown.
Reduced plasma and tissue concentrations of carnitine, a cofactor required for fatty acid oxidation, are present in patients with inherited disorders of mitochondrial acyl-CoA oxidation that are associated with accumulations of acylcarnitines. To determine whether the secondary carnitine deficiency in these patients is due to excessive urinary loss of acylcarnitines, the development of carnitine deficiency was examined in patients with four different acyl-CoA oxidation disorders, including medium-chain and long-chain fatty acyl-CoA dehydrogenase deficiencies, isovaleric acidemia, and propionic acidemia. After a 3-mo period of treatment with oral carnitine to raise plasma total carnitine concentrations to or above normal, patients were started on a carnitine-free diet and the changes in plasma total and free carnitine levels and urinary total and free carnitine excretion were followed for 5 d. Patients with all four disorders showed a return of plasma carnitine levels and urinary carnitine excretion to baseline within 2 to 4 d. The rapidity of these changes could not be explained solely by excessive acylcarnitine wasting. Continued excretion of free carnitine in all patients indicated the additional presence of an impairment in renal transport of free carnitine. Consistent with this interpretation, estimates of renal thresholds for free carnitine gave values that were less than that for a control child in all four disorders and ranged as low as one half those reported in normal individuals. These results suggest that secondary carnitine deficiency in the acyl-CoA oxidation disorders is due to indirect as well as direct effects of accumulated acylcarnitines.(ABSTRACT TRUNCATED AT 250 WORDS)
Three patients presented with evidence of a fatty acid oxidation disorder. Analysis of urinary organic acids by gas chromatography/mass spectrometry demonstrated the presence of medium-chain (C6-C12) dicarboxylic, 3-hydroxydicarboxylic, and 3-ketodicarboxylic acids in all three urines. 3-Ketodicarboxylic aciduria is reported for the first time here, as are the mass spectra for 3-ketosuberic, 3-ketosebacic, and 3-ketododecanedioic acids and the oximated spectrum for 3-ketoadipic acid. The presence of 3-ketodicarboxylic acids suggests a defect at the level of a long-chain 3-ketoacyl-CoA thiolase, an enzyme for which a deficiency state has not previously been described. Our patients may represent the first cases of a long-chain thiolase defect.
Ibuprofen [(+/-)-2-(p-isobutylphenyl)propionic acid] has recently been introduced as a pediatric anti-inflammatory agent. To determine how this agent interferes with urine organic acid analysis, an important pediatric investigation, we have analyzed urine from two subjects pre- and post-Ibuprofen dosage and two subjects on chronic Ibuprofen therapy. A distinctive pattern of drug interference on the organic acid profile was detected. There were three major components, corresponding to unmetabolized Ibuprofen and to the oxidation products hydroxy Ibuprofen and carboxy Ibuprofen. Therefore, the major mechanism of Ibuprofen metabolism appears to be microsomal, although mitochondrial and peroxisomal routes cannot be excluded. Laboratories carrying out routine organic acid analysis should be aware of the nature and magnitude of the organic aciduria caused by Ibuprofen.
A series of modifications of the CCK7 analogue (des-NH2)Tyr(SO3-)-Nle-Gly-Trp-Nle-Asp-Phe-NH2 was prepared and tested for binding to guinea pig CCK-A and CCK-B receptors and in CCK-A-mediated functional assays. Selected analogues also were tested for appetite suppressant activity in rats. Several conformationally restricted residues in the C-terminal tetrapeptide region, including delta Z-Phe33, (N-Me)Phe33, (N-Me)Asp32, (N-Me)Leu31, and 3PP31 (3PP = trans-3-n-propyl-L- proline) were found to be acceptable modifications at one or both receptor subtypes. The (N-Me)Asp32 and (N-Me)Leu31 modifications afforded potent and selective CCK-A and CCK-B ligands, respectively. SAR studies in the N-terminal acyldipeptide region examined structural requirements for the side chain at position 28, where Gly and Pro replacements were found to possess high affinity at both receptor subtypes. Other conformationally restrictive modifications were less active. All of the analogues that showed high affinity (less than 10 nM) for the CCK-A receptor also were full agonists in amylase release and most were full or nearly full agonists in the phosphoinositide (PI) turnover assay, the most notable exception being the delta Z-Phe33 analogue, which showed 69% of the maximal response in the PI assay. Potent activity in suppression of food intake in rats was found for selected analogues.
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The crystal structure of the diphtheria toxin dimer at 2.5 A resolution reveals a Y-shaped molecule of three domains. The catalytic domain, called fragment A, is of the alpha + beta type. Fragment B actually consists of two domains. The transmembrane domain consists of nine alpha-helices, two pairs of which are unusually apolar and may participate in pH-triggered membrane insertion and translocation. The receptor-binding domain is a flattened beta-barrel with a jelly-roll-like topology. Three distinct functions of the toxin, each carried out by a separate structural domain, can be useful in designing chimaeric proteins, such as immunotoxins, in which the receptor-binding domain is substituted with antibodies to target other cell types.
In Phaseolus vulgaris L. (French bean) glutamine synthetase (GS) is encoded by four closely-related genes termed gln-alpha, gln-beta, gln-gamma and gln-delta. We have constructed and characterised in vitro a number of hammerhead ribozymes designed to cleave individual RNAs encoded by these genes. The three ribozymes, termed J1, J2 and J3, were targeted to cleave RNA at the start of the gamma and beta, and the middle of the gamma, GS open reading frames respectively. All three ribozymes successfully discriminated between the four (alpha, beta, gamma and delta) highly homologous sequences, even though the targeted sites of cleavage shared up to 18 out of 22 identical bases with other gene family members. The ribozyme-mediated cleavage reactions were Mg2+ dependent and enhanced at higher temperatures, although the J1 ribozyme retained considerable activity at physiological temperatures. Both J1 and J2 demonstrated a time-dependent cleavage of their targeted GS RNAs, although these two ribozymes differed markedly in their ability to cleave multiple substrate molecules. The rate of cleavage by J1 was found to be reduced in the presence of related GS RNAs and by total leaf poly(A) RNAs. The implications of these results for ribozyme activity in vivo are discussed.
Azelaic and pimelic acids are excreted in elevated amounts in urine in disorders of mitochondrial beta-oxidation and disorders of peroxisomal beta-oxidation, for which they are of significant diagnostic value. We have detected the presence of azelaic, pimelic and even-chain-length dicarboxylic acids (adipic, suberic and sebacic acids) arising artefactually as a result of storage of small sample volumes in plastic containers. Storage of samples for organic acid analysis in glass containers is recommended.