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T R Brown

Publications and source records attributed to T R Brown.

At least 55 records · Page 3Linked to original sources
PubMed1996

Molar quantitation of hepatic metabolites in vivo in proton-decoupled, nuclear Overhauser effect enhanced 31P NMR spectra localized by three-dimensional chemical shift imaging.

Proton decoupling and nuclear Overhauser effect (NOE) enhancement significantly improve the signal-to-noise ratio and enhance resolution of metabolites in in vivo 31P MRS. We obtained proton-decoupled, NOE-enhanced, phospholipid-saturated 31P spectra localized to defined regions within the normal liver using three-dimensional chemical shift imaging. Proton-decoupling resulted in the resolution of two major peaks in the phosphomonoester (PME) region, three peaks in the phosphodiester (PDE) region and a diphosphodiester peak. In order to obtain molar quantitation, we measured the NOE of all hepatic phosphorus resonances, and we corrected for saturation effects by measuring hepatic metabolite T1 using the variable nutation angle method with phase-cycled, B1-independent rotation, adiabatic pulses. After corrections for saturation effects, NOE enhancement, B1 variations and point spread effects, the following mean concentrations (mmol/l of liver) (+/-SD) were obtained: [PME1] = 1.2 +/- 0.4, [PME2 + 2,3-DPG] = 1.1 +/- 0.1, [Pi + 2,3-DPG] = 2.8 +/- 0.5, [GPEth] = 2.8 +/- 0.7, [GPChol] = 3.5 +/- 0.6 and [beta-NTP] = 3.8 +/- 0.3. T1 and NOE enhancement were strongly correlated (r = 90), and indicated that the fractional contribution of 1H-31P dipolar relaxation to total 31P relaxation is minimal for NTPs, moderate for PMEs and high for PDEs in liver. Proton-decoupling and NOE enhancement permit one to obtain more information about in vivo metabolism of liver than previously available and should enhance the utility of 31P MRS for the study of hepatic disorders.

Adult↗
PubMed1996

NMR spectral quantitation by principal-component analysis. II. Determination of frequency and phase shifts.

This paper extends the use of principal-component analysis in spectral quantification to the estimation of frequency and phase shifts in a single resonant peak across a series of spectra. The estimated parameters can be used to correct the spectra accordingly, resulting in more accurate peak-area estimation. Further, the removal of the variations in phase and frequency cause by instrumental and experimental fluctuations makes it possible to determine more accurately the remaining variations, which bear biological significance. The procedure is demonstrated on simulated data, a 3D chemical-shift-imaging dataset acquired from a cylinder of inorganic phosphate (Pi), and a set of 736 31P NMR in vivo spectra taken from a kinetic study of rate muscle energetics. In all cases, the procedure rapidly and automatically identifies the frequency and phase shifts present in the individual spectra. In the kinetic study, the procedure is used twice, first to adjust the phase and frequency of a reference peak (phosphocreatine) and then to determine the individual frequencies of the Pi peak in each of the spectra which further can be used for estimation of pH changes during the experiment.

Computer Simulation↗
PubMed1996

Abnormal gonadal differentiation in two subjects with ambiguous genitalia, Mullerian structures, and normally developed testes: evidence for a defect in gonadal ridge development.

Among a group of patients with abnormal sexual differentiation, we have identified two subjects who had a 46,XY karyotype, ambiguous genitalia, and well-developed Müllerian structures, but normal appearing testes. The presence of ambiguous genitalia and persistent Müllerian structures implied both Leydig cell and Sertoli cell dysfunction, hence, gonadal dysgenesis. However, the normal testicular histology suggested that the underlying abnormality was not a defect in testis determination itself but an abnormality in timing of gonadal ridge and testis development. In one of the two subjects genomic DNA was available. The sequence of the SRY gene was normal. Because rare patients with partial androgen insensitivity may have a similar phenotype, the AR gene was evaluated by denaturing gradient gel electrophoresis (DGGE) and was normal. Some subjects with mutation of the WT1 gene or with deletion of the distal short arm of chromosome 9 may have similar phenotypes. The WT1 gene was studied by single-strand conformation polymorphism (SSCP) analysis and was normal. In addition, there was no loss of heterozygosity of polymorphic markers in distal 9p. The gene for Müllerian inhibiting substance (MIS) was also studied by SSCP and was normal. Although the exact mechanism for the defect in the two subjects is unknown, it may be due to an abnormality in a gene or genes involved in the timing of gonadal ridge development.

Cell Differentiation↗
PubMed1996

A clinician looks at androgen resistance.

Androgen resistance in genetic males occurs when gonadotropins and testosterone are normal, but the physiological androgen response in androgen target organs is absent or decreased. In androgen-dependent target tissues two main defects may be found: 1) defective testosterone metabolism (5 alpha-reductase type 2 deficiency) and 2) anomalies in androgen receptors (androgen insensitivity syndrome (AIS)). The clinical manifestations of these defects vary from subjects with female external genitalia to subjects with mild forms of impaired masculinization. In particular, in the complete form of AIS (CAIS) the phenotype is feminine, and in the partial form (PAIS) the external genitalia are ambiguous with an extremely variable phenotype. The diagnosis requires clinical, hormonal, genetic, and molecular investigation for appropriate gender assignation and treatment. In AIS, cloning of androgen receptor cDNA using the polymerase chain reaction, denaturing gradient gel electrophoresis, and nucleotide sequencing have enabled a variety of molecular defects in the androgen receptor to be identified. The complexity of phenotypic presentation of AIS probably reflects the heterogeneity of androgen receptor gene mutations, but to date a relationship between genotype/phenotype has been difficult to establish, with the same point mutation reported to be associated with different phenotypic expressions. Other factors must therefore also contribute to the clinical presentation of AIS, although none have yet been identified. Establishing the functional consequences of androgen receptor mutations in vitro systems and correlating them with clinical presentation may ultimately provide an explanation for the variable clinical presentation of AIS and perhaps enable prediction of the response to androgen therapy in infants with PAIS.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗
PubMed1996

The obese strain chicken as a model for human Hashimoto's thyroiditis.

The OS and the related Cornell C strain are interesting animal models for the study of the etiology of autoimmune thyroiditis. They are especially valuable for studying the etiologic role of thyroid abnormalities and abnormalities in the processing of iodine. Limitations of the model are the scarcity of immunological reagents for chickens, the absence of avian cloned thyroid-specific genes, minimal amounts of microsomal antibody and some differences between OS chickens and Hashimoto's patients in the types of thyroid abnormalities observed.

Animals↗
PubMed1996

Distinct regions of thyroglobulin control the proliferation and suppression of thyroid-specific lymphocytes in obese strain chickens.

The effect of thyroglobulin (Tg)iodination on the proliferation and suppression of thyroid-specific lymphocytes was examined in vivo in the obese strain (OS) and Cornell strain chicken models of autoimmune thyroiditis. Spleen cells from OS chickens were able to transfer disease to Cornell strain recipients. The ability to transfer disease was markedly reduced if the donors were raised on an iodine-depleting regimen. This deficiency was corrected by immunization of donor chickens with iodinated Tg. Immunization with low iodine Tg was ineffective. Neonatal tolerance induction with either iodinated or low iodine Tg reduced thyroiditis in 2-week-old OS chickens. Spleen cells from these tolerized chickens transferred to 4-day-old OS chickens were less thyroiditogenic. These results indicate that thyroid autoreactive cells are responsive to iodinated Tg, but not to low iodine Tg. Both of the Tg preparations, however, can induce tolerance to the disease. We conclude that distinct regions of the Tg molecule regulate the proliferation and suppression of thyroid-reactive lymphocytes, respectively. Only the former is dependent on the iodination of Tg. These results emphasize the importance of Tg as a self-antigen and provide one mechanism by which iodine may induce autoimmune thyroiditis.

Animals↗
PubMed1996

Proton magnetic resonance spectroscopy in patients with glial tumors: a multicenter study.

The authors represent a cooperative group of 15 institutions that examined the feasibility of using metabolic features observed in vivo with 1H-magnetic resonance (MR) spectroscopy to characterize brain tumors of the glial type. The institutions provided blinded, centralized MR spectroscopy data processing long with independent central review of MR spectroscopy voxel placement, composition and contamination by brain, histopathological typing using current World Health Organization criteria, and clinical data. Proton 1H-MR spectroscopy was performed using a spin-echo technique to obtain spectra from 8-cc voxels in the tumor and when feasible in the contralateral brain. Eighty-six cases were assessable, 41 of which had contralateral brain spectra. Glial tumors had significantly elevated intensities of choline signals, decreased intensities of creatine signals, and decreased intensities of N-acetylaspartate compared to brain. Choline signal intensities were highest in astrocytomas and anaplastic astrocytomas, and creatine signal intensities were lowest in glioblastomas. However, whether expressed relative to brain or as intratumoral ratios, these metabolic characteristics exhibited large variations within each subtype of glial tumor. The resulting overlaps precluded diagnostic accuracy in the distinction of low-and high-grade tumors. Although the extent of contamination of the 1H-MR spectroscopy voxel by brain had a marked effect on metabolite concentrations and ratios, selection of cases with minimal contamination did not reduce these overlaps. Thus, each type and grade of tumor is a metabolically hetero-geneous group. Lactate occurred infrequently and in all grades. Mobile lipids, on the other hand, occurred in 41% of high-grade tumors with higher mean amounts found in glioblastomas. This result, coupled with the recent demonstration that intratumoral mobile lipids correlate with microscopic tumor cell necrosis, leads to the hypothesis that mobile lipids observed in vivo in 1H-MR spectroscopy may correlate independently with prognosis of individual patients.

Adolescent↗
PubMed1996

Provocative aspects of androgen genetics.

Androgens play a key role in prostate structure and function, leading to the hypothesis that effects of the hormone are an important component in the development of prostatic disease. Differences in serum testosterone levels and 5alpha-reductase activities between ethnic and racial groups have been implicated in the variable incidence of prostate cancer among certain populations. Androgen receptors transduce the steroid signal within cells, but attempts to correlate differences in receptor levels with prostatic disease have been unsuccessful. However, molecular studies of androgen receptor gene structure have recently provided new insights toward defining a genetic basis for the pathology associated with three diseases--spinal bulbar muscular atrophy, breast carcinoma, and prostate cancer--affecting middle-aged and older men. In summary, epidemiologic data on androgen biosynthesis, metabolism, and action of androgens and molecular genetic analysis of gene structure have led to a new understanding of the interrelationships between environmental and genetic factors that may impact on the incidence of certain pathologic conditions in men.

Animals↗
PubMed1996

Quantitation of 5-fluorouracil catabolism in human liver in vivo by three-dimensional localized 19F magnetic resonance spectroscopy.

The development of clinical applications of 19F magnetic resonance (MR) spectroscopy of 5-fluorouracil (5-FU) has been limited by the inability to localize 19F spectra to specific regions of interest, making it difficult to quantitate drug and metabolite concentrations accurately. To develop methodology for quantitation, we studied the liver of patients receiving rapid bolus i.v. injections of 5-FU. In serial studies, 5-FU disappeared from the liver within 17-26 min, and its catabolite, alpha-fluoro-beta-alanine (FBAL), rose to reach a plateau after 40 min. A high peak level of fluoro-ureido-propionic acid preceded that of FBAL in only one patient, and dihydrofluorouracil was never observed. During the plateau, we obtained MR imaging-directed 19F MR spectra localized using three-dimensional chemical shift imaging. The spin-lattice relaxation time of FBAL in liver, measured using a variable nutation angle method, was 1.6 +/- 0.2 s (mean +/- SD; n = 5). The concentration of FBAL at 60 +/- 10 min after injection was 1.0 +/- 0.2 mm in liver (mean +/- SD; n = 7). This amount represents approximately 20% of the injected dose and 1.4 times the initial hepatic 5-FU concentration. Our approach may permit one to obtain molar concentrations of fluoropyrimidine metabolites simultaneously in hepatic cancers and surrounding liver, and it helps expand pharmacokinetic modeling of fluoropyrimidine catabolism.

Antimetabolites, Antineoplastic↗
PubMed1995

Metabolic characterization of human non-Hodgkin's lymphomas in vivo with the use of proton-decoupled phosphorus magnetic resonance spectroscopy.

Development of biological and clinical uses of in vivo 31P magnetic resonance spectroscopy has been hampered by poor anatomic localization of spectra and poor resolution of overlapping signals within phosphomonoester and phosphodiester regions of the spectrum. We applied 1H-decoupling and nuclear Overhauser enhancement to improve resolution of 31P magnetic resonance spectra accurately localized to 21 non-Hodgkin's lymphomas (NHL) by using three-dimensional chemical shift imaging. All 21 spectra had large phosphomonoester signals (26% of total phosphorus) that contained high amounts of phosphoethanolamine relative to phosphocholine. There were no signals from glycerophosphoethanolamine or glycerophosphocholine but only a broad signal from membrane phospholipids in the phosphodiester region (20% of phosphorus). Prominent nucleoside triphosphates (47% of phosphorus) and low inorganic phosphate (7% of phosphorus) indicate well-perfused tissue with viable cells. Mean intracellular pH was 7.23. These characteristics were similar in all grades and stages of NHL. By analogy with recently reported studies in cell lines in vitro, we hypothesize that the pattern of phospholipid metabolites observed in NHL in vivo is partly a manifestation of sustained activation of phospholipase C or D. The techniques we implemented permitted us to obtain more information about in vivo metabolism of NHL than has heretofore been available. This information is important for the establishment of appropriate experimental models and provides a basis from which to examine potential clinical uses of 31P magnetic resonance spectroscopy.

2,3-Diphosphoglycerate↗
PubMed1995

Identification of a phorbol ester responsive region in the myeloid-specific promoter of the c-fgr proto-oncogene.

Expression of the c-fgr proto-oncogene is activated during differentiation of myeloid cells. We used a luciferase reporter assay to identify sequences that regulate c-fgr gene transcription during differentiation of human U937 promonocytic cells, induced by phorbol 12-myristate 13-acetate (PMA) or by tumour necrosis factor-alpha (TNF-alpha) and 1,25-dihydroxycholecalciferol (1,25-DHCC). We found that the region from nucleotides -344 to -116, with respect to the transcriptional start site, is required for basal activity of the c-fgr promoter in U937 cells, and that the region from nucleotides -1211 to -752 is responsive to PMA. No sequence elements responsive to TNF-alpha and 1,25-DHCC were found, suggesting that these agents induce c-fgr mRNA accumulation by a mechanism differing from that mediating the effects of PMA.

Bone Marrow↗
PubMed1995

Metabolism of fructose-3-phosphate in the diabetic rat lens.

Fructose-3-phosphate and sorbitol-3-phosphate are produced in diabetic rat lenses by a 3-phosphokinase. While sorbitol-3-phosphate appears to be an inert polyol phosphate, fructose-3-phosphate is a potent cross-linking agent and a potential in vivo source of 3-deoxyglucosone. The objective of this study was to investigate the production and decomposition of fructose-3-phosphate in the diabetic rat lens. The results indicate that this metabolite achieves a steady-state concentration of almost 1 mumol/g wet weight within 2 weeks after the onset of diabetes. These steady-state levels appear to be a consequence of a balance between its production from fructose and its further decomposition to 3-deoxyglucosone. This conclusion is supported by results from disappearance of fructose-3-phosphate in insulin-treated diabetic rats and in vitro incubations of fructose-3-phosphate with amines where production of 3-deoxyglucosone was detected using a number of different methods including mass spectrometry. In agreement with these results, elevated concentrations of 3-deoxyglucosone along with its detoxification product, 3-deoxyfructose, were detected in the diabetic rat lenses. Other sugars and sugar phosphates which were detectable in the diabetic rat lenses were glucose, fructose, glucose-6-phosphate, fructose-6-phosphate, and sedoheptulose-7-phosphate. In conclusion, results from this study suggest that fructose-3-phosphate and 3-deoxyglucosone are likely to be important contributors to the process of nonenzymatic glycation in diabetic rat lenses.

Animals↗
PubMed1995

Properties of fructose-1,6-bisphosphate aldolase from Escherichia coli: an NMR analysis.

A class II Zn(2+)-dependent fructose-1,6-bisphosphate (FBP)- aldolase was purified from an overproducer strain of Escherichia coli and characterized by standard biochemical techniques and 13C NMR spectroscopy. The principal finding of these studies was identification, by 13C NMR spectroscopy, of an enzyme-bound reaction intermediate, the enediol(ate) form of dihydroxyacetone phosphate (DHAP). Formation of this intermediate requires the presence of Zn2+ and is pH dependent, with increasing amounts of this tautomer appearing at alkaline pH's. This pH dependence closely parallels the pH activity profile of the enzyme, suggesting an involvement of the enediol-DHAP form in the reaction pathway. In addition to these results the following observations were made on this enzyme: (a) E. coli FBP aldolase binds and utilizes only the carbonyl forms of FBP and DHAP; (b) the function of Zn2+ in this metalloaldolase appears to be polarization of the C = O bond of DHAP; (c) activity of this enzyme is unaffected by glycolytic intermediates or nucleotide phosphates such as ATP. Although these studies provide some information about the catalytic mechanism of E. coli FBP aldolase, they do not provide an explanation for the apparent regulation of this enzyme reported in previous in vivo NMR studies. While the possibility that the enzyme is allosterically regulated cannot be excluded at this time, an interesting possibility suggested by this and other studies is that in E. coli glycolytic substrates may be channeled through a multienzyme complex.

Binding Sites↗
PubMed1995

Human androgen insensitivity due to point mutations encoding amino acid substitutions in the androgen receptor steroid-binding domain.

Mutations of the human androgen receptor gene were identified in five subjects from four families with androgen insensitivity syndrome. Individual exons of the androgen receptor gene were amplified by the polymerase chain reaction from genomic DNA and screened for sequence-dependent differences in their melting characteristics by denaturing gradient gel electrophoresis. DNA fragments from exons with altered mobility were sequenced. Four different single nucleotide base substitutions were found within exons 5, 6, and 7 encoding the steroid-binding domain of the androgen receptor. In one subject with ambiguous genitalia, amino acid residue 763 was changed from tyrosine to cysteine (TAC-->TGC; Y763C). Four subjects, including two siblings, had complete androgen insensitivity. In one subject, residue 779 was changed from arginine to tryptophan (CGC-->TGG; R779W), another subject (M807V) had a substitution of valine (GTG) for methionine (ATG) residue at position 807, and the two siblings (R855C) had a mutation in residue 855 changing arginine (CGC) to cysteine (TGC). Binding of the synthetic androgen ligand, methyltrienolone (R1881), by the mutant receptor Y763C was decreased by 54% compared to the normal receptor. Transcriptional activation of a mouse mammary tumor virus-chloramphenicol acetyltransferase (MMTV-CAT) reporter gene by AR mutant Y763C was negligible at 0.1 nM R1881 and only 55% at 10 nM R1881 when compared to the maximal response with the normal AR, as assessed by CAT activity. Mutant M807V retained only 22% of normal R1881 binding and mutant R855C was unable to bind the steroid. In accordance with the steroid binding, transcriptional activation of MMTV-CAT by M807V rose to only 26% of control in the presence of 10 nM R1881, a concentration at which R855C remained functionally inactive. In summary, missense mutations within the exons of the androgen receptor gene encoding the steroid-binding domain of the receptor are common causes of both partial and complete forms of androgen insensitivity syndrome.

Adolescent↗
PubMed1995

Hybrid three dimensional (1D-Hadamard, 2D-chemical shift imaging) phosphorus localized spectroscopy of phantom and human brain.

A hybrid of two localized spectroscopy techniques, chemical shift imaging (CSI) and Hadamard spectroscopic imaging (HSI), is used to obtain an array of 16 x 16 x 4 (3 x 3 x 3 cm3 voxels) proton-decoupled phosphorus (31P) spectra of human brain. For equal spatial resolution, this organ's oblate shape requires fewer axial than coronal or sagittal slices. These different spatial requirements are well suited to 1D, 4th order, transverse HSI in the axial direction, combined with 2D 16 x 16 CSI in the other two orientations. The reduced localization matrix (16 x 16 x 4 over just the brain versus a cubic-16 x 16 x 16 matrix of equal resolution, over the entire head) may proportionally shorten data acquisition if the voxel size is not signal-to-noise limited. In addition, the use of Hadamard encoding can improve the intervoxel spectral isolation.

Aged↗
PubMed1995

NOE enhancements and T1 relaxation times of phosphorylated metabolites in human calf muscle at 1.5 Tesla.

Nuclear Overhauser effect (NOE) enhancements and relaxation times of 31P metabolites in human calf were measured in 12 volunteers (4 men and 8 women) at 1.5 T using a dual tuned four-ring birdcage. The NOE enhancements of inorganic phosphate (Pi), phosphocreatine (PCr), gamma-, alpha-, and beta-nucleoside triphosphate (NTP) from 19 measurements were 0.51 +/- 0.10, 0.64 +/- 0.03, 0.53 +/- 0.03, 0.56 +/- 0.08, and 0.47 +/- 0.05, respectively. The relaxation times were independent of proton irradiation and from 23 measurements were 3.49 +/- 0.35, 4.97 +/- 0.58, 4.07 +/- 0.36, 2.90 +/- 0.25, and 3.61 +/- 0.25 s for Pi, PCr, gamma-, alpha-, and beta-NTP, respectively. No significant differences between gender and age were observed for either NOE enhancements or relaxation times. Also, among nine volunteers, we observed no significant differences in T1 between the coupled and decoupled cases.

Adolescent↗
PubMed1995

A fast, reliable, automatic shimming procedure using 1H chemical-shift-imaging spectroscopy.

The importance and the difficulty of achieving good B0 homogeneity over the volume of interest in in vivo NMR spectroscopy are well known. A fast, reliable, versatile, and fully automatic shimming procedure has been developed, using 3D chemical-shift imaging to measure the field distribution using only the water peak in the sample of interest. The procedure minimizes the mean-square error in the field distribution with respect to a constant field where the signal exists (e.g., the head). This produces a set of linear equations that can be solved by standard matrix methods. The procedure has been applied on a commercial imager producing water linewidths from the entire head as low as 8 Hz at 1.5 T. The mean linewidth and standard deviation from 94 head studies were 11.7 +/- 1.9 Hz.

Algorithms↗