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Biomedical subjects

R A Iles

Publications and source records attributed to R A Iles.

At least 19 recordsLinked to original sources
PubMed2006

Diagnosis and management of trimethylaminuria (FMO3 deficiency) in children.

Persistent trimethylaminuria in children is caused by autosomal recessively inherited impairment of hepatic trimethylamine (TMA) oxidation due to deficiency of flavin monooxygenase 3 (FMO3) secondary to mutations in the FMO3 gene. Trimethylaminuria or 'fish odour syndrome' is due to excessive excretion into body fluids and breath of TMA derived from the enterobacterial metabolism of dietary precursors. The disorder is present from birth but becomes apparent as foods containing high amounts of choline or of trimethylamine N-oxide (TMAO) from marine (sea or saltwater) fish are introduced into the diet. In our experience, trimethylaminuria (FMO3 deficiency) in children is rare. We have compared the dynamics and diagnostic efficacy of choline loading with marine fish meals in six children with trimethylaminuria. Loading with a marine fish meal provides a simple and acceptable method for confirmation of diagnosis of suspected trimethylaminuria in children, with the effects being cleared more quickly than with a choline load test. However, oral loading with choline bitartrate allows estimation of residual oxidative capacity in vivo and is a useful adjunct to molecular studies. Patients homozygous for the 'common' P153L mutation in the FMO3 gene showed virtual complete lack of residual TMA N-oxidative capacity, consistent with a nonfunctional or absent FMO3 enzyme, whereas a patient with the M82T mutation showed some residual oxidative capacity. A patient compound heterozygous for two novel mutations, G193E and R483T, showed considerable residual N-oxidative capacity. A further patient, heterozygous for two novel sequence variations in the FMO3 gene, consistently showed malodour and elevated urinary TMA/TMAO ratios under basal conditions but a negative response to both choline and marine fish meal loading. Comparison of the effects of administration of antibiotics (metronidazole, amoxicillin, neomycin) on gut bacterial production of trimethylamine from choline showed they all reduced TMA production to a limited extent, with neomycin being most effective. 'Best-practice' diagnostic and treatment guidelines are summarized.

Adult↗
PubMed2001

Lactate supply as a determinant of the distribution of intracellular pH within the hepatic lobule.

When isolated livers from starved rats are perfused with lactate at constant perfusate pH and P(co(2)), there is a marked gradient of cell pH (pH(i)) along the length of the lobular radius, with periportal cells being substantially more alkaline than perivenous cells. In the present studies, the perivenous 21% of the lobular volume was destroyed by retrograde digitonin perfusion, and antegrade perfusion restored. pH(i) was determined by (31)P-NMR. The remaining periportal cells, the site of gluconeogenesis from lactate, had a substantially higher mean pH(i) (7.42) than did the intact liver (7.23). When lactate was removed from the perfusate, mean pH(i) decreased to 7.25. The corresponding concentration of cell bicarbonate fell with a half-time of approximately 5 min. When lactate was re-introduced mean pH(i) rose to 7.34. We conclude that a major contributor to periportal alkalinity under these conditions is proton consumption during gluconeogenesis from lactate ions.

Animals↗
PubMed2000

Investigation of human low-density lipoprotein by (1)H nuclear magnetic resonance spectroscopy: mobility of phosphatidylcholine and sphingomyelin headgroups characterizes the surface layer.

The resolution of the trimethyl headgroup resonance of phosphatidylcholine (PC) and sphingomyelin (SM) in the intact human low-density lipoprotein (LDL) (1)H NMR spectrum at 600 MHz enabled the investigation of LDL surface structure and phospholipid-apoB interactions. We have previously shown that a higher proportion of PC headgroups (25-35% of total PC in LDL) compared to SM were tightly bound to apoB and therefore NMR-invisible [Murphy, H. C., et al. (1997) Biochem. Biophys. Res. Commun. 234 (3), 733-737]. In the present study, we have investigated the mobility of phospholipid (PL) headgroups, using (1)H NMR spin-spin (T(2)) relaxation measurements, in LDL isolated from nine volunteers. We show that both PC and SM exist in two additional and distinct environments indicated by the biexponential behavior of the relaxation decays in each case. The data showed that 36% of PC headgroups had a short T(2) component, mean T(2) of 31 ms, and 64% had a longer T(2) component of 54 ms. Approximately 15% of SM headgroups had a short T(2) component (mean T(2) of 27 ms) and 85% had a longer T(2) component of 78 ms. Therefore the majority of SM headgroups (85%) were more mobile than PC (P < 0.001) and since PC headgroups in organic media were more mobile than SM, we conclude that the characteristic high mobility of LDL SM is not an intrinsic property but arises from a high degree of order in molecular packing of the surface PL of human LDL. We suggest that because PC and SM interact differentially with cholesterol and possibly with neighboring phospholipids, this results in the formation of relatively long-lived microdomains of PL in vivo.

Humans↗
PubMed2000

Hepatic intralobular mapping of fructose metabolism in the rat liver.

Detailed mapping of glucose and lactate metabolism along the radius of the hepatic lobule was performed in situ in rat livers perfused with 1.5 mM lactate before and during the addition of 5 mM fructose. The majority of fructose uptake occurred in the periportal region; 45% of fructose taken up in the periportal half of the lobular volume being converted into glucose. Periportal lactate uptake was markedly decreased by addition of fructose. Basal perivenous lactate output, which was derived from glucose synthesized periportally, was increased in the presence of fructose. During fructose infusion there was a small decrease in cell pH periportally, but acidification of up to 0.5 pH units perivenously. The evidence suggests that in situ the apparent direct conversion of fructose into lactate represents, to a substantial extent, the result of periportal conversion of fructose into glucose and the subsequent uptake and glycolysis to lactate in the perivenous zone of some of that glucose. (31)P NMR spectroscopy showed that the cellular concentration of phosphomonoesters changes very little periportally during fructose infusion, but there was an approximate twofold increase perivenously, presumably due to the accumulation of fructose 1-phosphate. It may be inferred that fructokinase activity is expressed throughout the hepatic lobule.

Animals↗
PubMed2000

Changes in the choline content of human breast milk in the first 3 weeks after birth.

UNLABELLED: Choline is an essential constituent of membrane phospholipids in great demand in the developing brain and liver. We have previously demonstrated that human neonates excrete large amounts of betaine, a product of choline oxidation, in their urine. Estimates of perinatal choline intake using previously published data compared with our measurements of betaine excretion indicated that choline insufficiency might occur at certain periods after birth. In this study we measured the choline content of expressed human breast milk in colostrum (2-6 days after birth), mature milk (7-22 days after birth) and several infant formula foods, using proton nuclear magnetic resonance spectroscopy. In colostrum choline was present in both the aqueous (free choline, phosphocholine and glycerophosphocholine) and lipid fractions (phosphatidylcholine and sphingomyelin). After 6-7 days there was a mean increase of 114% in the total choline content; 82% of the rise was accounted for by increases in phosphocholine and glycerophosphocholine, and 14% by (free) choline. The choline content of most formula feeds was comparable with the level in colostrum but below that of mature milk. Both the total choline content and ester composition of mature milk were comparable with more recent measurements using high-performance liquid chromatography. CONCLUSION: The choline content of human breast milk doubles 6-7 days after birth and, unlike that of many formula feeds, appears to be sufficient to account for betaine excretion in healthy full-term neonates. However, for premature babies who usually receive much lower quantities of milk, yet have a higher demand for choline, the intake may be inadequate.

Adult↗
PubMed2000

A novel mutation in the flavin-containing monooxygenase 3 gene, FM03, that causes fish-odour syndrome: activity of the mutant enzyme assessed by proton NMR spectroscopy.

We have previously shown that primary trimethylaminuria, or fish-odour syndrome, is caused by an inherited defect in the flavin-containing monooxygenase 3 (FMO3) catalysed N-oxidation of the dietary-derived malodorous amine, trimethylamine (TMA). We now report a novel causative mutation for the disorder identified in a young girl diagnosed by proton nuclear magnetic resonance (NMR) spectroscopy of her urine. Sequence analysis of genomic DNA amplified from the patient revealed that she was homozygous for a T to C missense mutation in exon 3 of the FMO3 gene. The mutation changes an ATG triplet, encoding methionine, at codon 82 to an ACG triplet, encoding threonine. A polymerase chain reaction/restriction enzyme-based assay was devised to genotype individuals for the FMO3Thr82 allele. Wild-type and mutant FMO3, heterologously expressed in a baculovirus-insect cell system, were assayed by ultraviolet spectrophotometry and NMR spectroscopy for their ability to catalyse the N-oxidation of TMA. The latter technique has the advantage of enabling the simultaneous, direct and semi-continuous measurement of both of the products, TMA N-oxide and NADP, and of one of the reactants, NADPH. Results obtained from both techniques demonstrate that the Met82Thr mutation abolishes the catalytic activity of the enzyme and thus represents the genetic basis of the disorder in this individual. The combination of NMR spectroscopy with gene sequence and expression technology provides a powerful means of determining genotype-phenotype relationships in trimethylaminuria.

Adult↗
PubMed1999

Zonation of gluconeogenesis, ketogenesis and intracellular pH in livers from normal and diabetic ketoacidotic rats: evidence for intralobular redistribution of metabolic events in ketoacidosis.

The intralobular distribution of metabolism was examined in the livers from rats with severe diabetic ketoacidosis (DKA), perfused at pH 6.8, and compared with that in livers from normal starved animals perfused at either pH 7.4 or 6.8. With lactate and palmitate as substrates, the perivenous uptake of periportally synthesized glucose seen in normal livers at pH 7.4 was abolished during DKA; indeed, gluconeogenesis was most active in the perivenous region. Whereas in normal livers perfused at pH 7.4 the periportal region showed a markedly elevated intracellular pH (pH(i)) compared with the perivenous zone, this distribution of pH(i) was reversed in DKA, with an intermediate distribution in normal livers perfused at pH 6. 8. 3-Hydroxybutyrate was generated throughout the lobule. Some acetoacetate generated periportally was converted to 3-hydroxybutyrate more perivenously. A steep gradient of oxygen uptake along the radius of the lobule was apparent in all three groups; oxygen uptake was greatly decreased perivenously despite adequate oxygen supply. These findings are consistent with our previous observations of the lobular co-location of high pH(i) and gluconeogenesis, and might offer an explanation of how high gluconeogenic rates can continue in spite of severe systemic acidosis in DKA. The findings provide direct evidence for a marked redistribution of intralobular metabolism in DKA.

Animals↗
PubMed1998

Proton NMR spectroscopic analysis of multiple acyl-CoA dehydrogenase deficiency--capacity of the choline oxidation pathway for methylation in vivo.

Proton NMR spectra of urine from subjects with multiple acyl-CoA dehydrogenase deficiency, caused by defects in either the electron transport flavoprotein or electron transport flavoprotein ubiquinone oxidoreductase, provide a characteristic and possibly diagnostic metabolite profile. The detection of dimethylglycine and sarcosine, intermediates in the oxidative degradation of choline, should discriminate between multiple acyl-CoA dehydrogenase deficiency and related disorders involving fatty acid oxidation. The excretion rates of betaine, dimethylglycine (and sarcosine) in these subjects give an estimate of the minimum rates of both choline oxidation and methyl group release from betaine and reveal that the latter is comparable with the calculated total body methyl requirement in the human infant even when choline intake is very low. Our results provide a new insight into the rates of in vivo methylation in early human development.

Acyl-CoA Dehydrogenases↗
PubMed1998

13C-Glycogen deposition during pregnancy in the rat following routine meal feeding.

In vivo -NMR was employed to determine the hepatic fate of infused [1-]-d-glucose (200 mg/kg) following ad libitum or routine meal feeding (RMF) regimes imposed during pregnancy. Hepatic glycogen synthesis was measured immediately following the last meal in virgin, 10 and 20 day pregnant rats. No detectable incorporation of -glucose into glycogen was observed in 20 day pregnant and control fed virgin rats. In 20 day pregnant RMF rats, glycogen synthesis from -glucose occurred at a linear rate of 0.10/s (S.D. 0.018/s). By 50 min post-infusion, 13C-glycogen levels were 131% (p<0.01) higher than those seen for the 22 h starved and 2 h refed virgin group. Following 10 days of gestation, glucose incorporation into glycogen was maximal in both the ad libitum and RMF groups. Compared with the 20 day pregnant RMF group, the 10 day pregnant ad libitum and RMF rats produced 146% (p<0.001) and 315% (p<0.001) more incorporation of -glucose into the glycogen macromolecule, respectively. Hepatic glycogen values were similar for both 10 and 20 day pregnant ad libitum rats (65.7+/-4.7 and 58.8+/-4.5 mg/g weight) but lower in the RMF groups by 58% and 48%, respectively. In conclusion, meal feeding regimes in the pregnant rat alter carbohydrate control of the liver producing increased glycogen synthesis initially via direct incorporation of glucose into the macromolecule.

Animal Feed↗
PubMed1997

Gluconeogenesis, glucose handling, and structural changes in livers of the adult offspring of rats partially deprived of protein during pregnancy and lactation.

Maternal protein restriction is a model of fetal programming of adult glucose intolerance. Perfused livers of 48-h- starved adult offspring of rat dams fed 8% protein diets during pregnancy and lactation produced more glucose from 6 mM lactate than did control livers from rats whose dams were fed 20% protein. In control livers, a mean of 24% of the glucose formed from lactate in the periportal region of the lobule was taken up by the most distal perivenous cells; this distal perivenous uptake was greatly diminished in maternal low protein (MLP) livers, accounting for a major fraction of the increased glucose output of MLP livers. In control livers, the distal perivenous cells contained 40% of the total glucokinase of the liver; this perivenous concentration of glucokinase was greatly reduced in MLP livers. Intralobular distribution of phosphenolpyruvate carboxykinase was unaltered, though overall increased activity could have contributed to the elevated glucose output. Hepatic lobular volume in MLP livers was twice that in control livers, indicating that MLP livers had half the normal number of lobules. Fetal programming of adult glucose metabolism may operate partly through structural alterations and changes in glucokinase expression in the immediate perivenous region.

Animals↗
PubMed1997

In vivo assessment of metabolic perturbations following alanine and glucagon administration using 31P-MRS in the rat.

This study set out to validate the use of 31P-NMR spectroscopy together with alanine +/- glucagon infusions to assess hepatic gluconeogenic flux in vivo. Bolus infusions of alanine (2.8 or 5.6 mmol/kg) +/- glucagon (250 microg/kg) were used. Maximal changes in the phosphomonoesters (PME), inorganic phosphate (Pi) and beta-NTP occurred 40 mins post infusion. PME increased 13.1% (p < 0.02) and 20.8% (P < 0.01) at 2.8 mmol/kg + glucagon and 5.6 mmol/kg +/- glucagon, respectively. Pi was unaltered at 2.8 mmol/kg but increased by 28.8% (P < 0.01) at 5.6 mmol/kg alanine + glucagon. beta-NTP decreased by 14.4% (P < 0.02) and 16.1% (P < 0.02) at 5.6 mmol/kg -/+ glucagon, respectively. This latter infusion showed slower recovery rates of NTP which remained 12.3% (P < 0.05) lower 70 min post infusion compared with pre-infusion values. 31 P-NMR analysis of liver extracts revealed that PME increases were partly due to 3-phosphoglycerate and corroborated reductions in beta-NTP and gamma-NTP: beta-NDP ratio upon infusion of 5.6 mmol/kg alanine +/- glucagon. Hepatic glucose output from perfused liver experiments showed no difference between alanine concentrations indicating maximal glucose output at the lower concentration. This study has shown that in vivo 31P-NMR in combination with alanine infusion, can be used to determine metabolic changes associated with gluconeogenesis.

Alanine↗
PubMed1997

Evidence for distinct behaviour of phosphatidylcholine and sphingomyelin at the low density lipoprotein surface.

This study demonstrates that the use of high field 1H NMR spectroscopy permits individual detection of phosphatidylcholine and sphingomyelin molecules at the surface of native low density lipoprotein (LDL) particles. Distinct behaviour was observed for the choline head group -N(CH3)3 resonances of these different phospholipids revealing preferential immobilisation for phosphatidylcholine. This suggests the existence of reversible and irreversible phosphatidylcholine-apolipoprotein B interactions and is consistent with microdomain formation at the surface monolayer of LDL. The novel resonance assignment and results show that 1H NMR can provide efficient and practical means for future studies on the structure and dynamics at the LDL surface.

Adult↗
PubMed1997

Noninvasive characterization of neonatal adipose tissue by 13C magnetic resonance spectroscopy.

In vivo 13C magnetic resonance spectroscopy (MRS) was applied noninvasively to analyze the fatty acid composition of adipose tissue in 21 full-term newborn infants and 6 mothers. In order to assess the effects of gestational and postnatal age on adipose tissue composition, we studied preterm infants at birth, term infants at the ages of 6 wk and at 6 mon. We also investigated the influence of maternal diet on infant adipose tissue composition by studying the breast-fed infants of women who maintained either an omnivore or a vegan diet. Significant differences were observed in adipose tissue composition of neonates compared with their mothers. Neonates had more saturated and less unsaturated fatty acids than their mothers (P < 0.01). We also observed changes in adipose tissue composition with maturity. From birth to 6 wk of age 13C MR spectra showed a significant increase in the amount of unsaturated fatty acids, particularly polyunsaturated fatty acids (P < 0.01). Similarly, differences were seen as a result of gestational age. Preterm infants had relatively fewer unsaturated fatty acids than full-term infants. A greater proportion of these unsaturated fatty acids were polyunsaturated. Our results demonstrate that 13C MRS can be utilized to assess noninvasively neonatal adipose tissue lipid composition and to monitor the effects of developmental changes due to gestational age and oral feeding.

Adipose Tissue↗