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Biomedical subjects

D K Burns

Publications and source records attributed to D K Burns.

At least 37 records · Page 2Linked to original sources
PubMed1999

Measurement of intracellular triglyceride stores by H spectroscopy: validation in vivo.

We validate the use of 1H magnetic resonance spectroscopy (MRS) to quantitatively differentiate between adipocyte and intracellular triglyceride (TG) stores by monitoring the TG methylene proton signals at 1.6 and 1.4 ppm, respectively. In two animal models of intracellular TG accumulation, intrahepatic and intramyocellular TG accumulation was confirmed histologically. Consistent with the histological changes, the methylene signal intensity at 1.4 ppm increased in both liver and muscle, whereas the signal at 1.6 ppm was unchanged. In response to induced fat accumulation, the TG concentration in liver derived from 1H MRS increased from 0 to 44.9 +/- 13.2 micromol/g, and this was matched by increases measured biochemically (2.1 +/- 1.1 to 46.1 +/- 10.9 micromol/g). Supportive evidence that the methylene signal at 1.6 ppm in muscle is derived from investing interfascial adipose tissue was the finding that, in four subjects with generalized lipodystrophy, a disease characterized by absence of interfacial fat, no signal was detected at 1.6 ppm; however, a strong signal was seen at 1.4 ppm. An identical methylene chemical shift at 1.4 ppm was obtained in human subjects with fatty liver where the fat is located exclusively within hepatocytes. In experimental animals, there was a close correlation between hepatic TG content measured in vivo by 1H MRS and chemically by liver biopsy [R = 0.934; P <.0001; slope 0.98, confidence interval (CI) 0.70-1.17; y-intercept 0.26, CI -0.28 to 0. 70]. When applied to human calf muscle, the coefficient of variation of the technique in measuring intramyocellular TG content was 11.8% in nonobese subjects and 7.9% in obese subjects and of extramyocellular (adipocyte) fat was 22.6 and 52.5%, respectively. This study demonstrates for the first time that noninvasive in vivo 1H MRS measurement of intracellular TG, including that within myocytes, is feasible at 1.5-T field strengths and is comparable in accuracy to biochemical measurement. In addition, in mixed tissue such as muscle, the method is clearly advantageous in differentiating between TG from contaminating adipose tissue compared with intramyocellular lipids.

Adipose Tissue↗
PubMed1999

A limited interval of delayed modest hypothermia for ischemic brain resuscitation is not beneficial in neonatal swine.

This investigation determined if a short interval of modest hypothermia (1 h) initiated 30 min after brain ischemia provided neuroprotection. The rationale for the time and duration of brain cooling reflects the likelihood that the implementation of neuroprotective strategies will occur at an interval shortly after ischemia, and that long-term maintenance of normothermia is a cornerstone of neonatal stabilization. Studies were performed in 22 ventilated neonatal mini-swine in a superconducting magnet to obtain 31P magnetic resonance spectra. After a control period all animals underwent 15 min of global brain ischemia and were maintained normothermic for the first 30 min post-ischemia. In one group of 11 swine normothermia was continued. In the other group of 11 swine, modest hypothermia was initiated at 30 min post-ischemia, continued for 1 h and followed by resumption of normothermia. Animals were subsequently weaned from ventiltor support, removed from the magnet, and underwent neurobehavioral and histologic assessment at 72 h post-ischemia. Both groups had similar severity of ischemia, as indicated by identical changes in arterial blood pressure and pH, alterations in brain beta-nucleotide triphosphate (% of control where control = 100%, 32 +/- 28 vs 27 +/- 26% for normothermic and hypothermic groups, respectively), and the extent of intraischemic brain acidosis (6.13 +/- 0.19 vs 6.14 +/- 0.14 for normothermic and hypothermic groups, respectively). In both groups the distribution of stages of encephalopathy were the same: 1 normal and 10 abnormal (4 mild, 2 moderate, and 4 severe) normothermic, and, 3 normal and 8 abnormal (4 mild, 2 moderate, and 2 severe) hypothermic animals. There was no difference in the extent of neuronal injury between groups. We conclude that a 1-h interval of modest hypothermia initiated at 30 min post-ischemia does not confer neuroprotection.

Animals↗
PubMed1998

Genomic characterization of the coding region of the human type II 5'-deiodinase gene.

Type II 5'-Deiodinase (5'DII) is a key element in the maintenance of peripheral thyroid hormone homeostasis through the regulation of local T4 to T3 conversion in pituitary, brain, brown adipose tissue and placenta. The cDNA containing the coding region of the human 5'DII (HDII) has been recently cloned from infant brain. In the present paper we report the genomic structure, chromosomal localization and restriction map of the coding region of HDII. The presence of a single intron located at codon 75 was demonstrated using a PCR-based strategy; the exon-intron junctions were then cloned and partially sequenced. Chromosomal localization was performed by radiation hybrid mapping. This study demonstrated that the entire coding region of the HDII gene is contained in two exons spliced at codon 75 by a 7.4 Kb intron and that the HDII chromosomal location is 14q24.3. These data will allow further studies of the role of HDII in the pathophysiology of thyroid homeostasis.

Base Sequence↗
PubMed1998

An autosomal genomic scan for loci linked to prediabetic phenotypes in Pima Indians.

Type 2 diabetes mellitus is a common chronic disease that is thought to have a substantial genetic basis. Identification of the genes responsible has been hampered by the complex nature of the syndrome. Abnormalities in insulin secretion and insulin action predict the development of type 2 diabetes and are, themselves, highly heritable traits. Since fewer genes may contribute to these precursors of type 2 diabetes than to the overall syndrome, such genes may be easier to identify. We, therefore, undertook an autosomal genomic scan to identify loci linked to prediabetic traits in Pima Indians, a population with a high prevalence of type 2 diabetes. 363 nondiabetic Pima Indians were genotyped at 516 polymorphic microsatellite markers on all 22 autosomes. Linkage analyses were performed using three methods (single-marker, nonparametric multipoint [MAPMAKER/SIBS], and variance components multipoint). These analyses provided evidence for linkage at several chromosomal regions, including 3q21-24 linked to fasting plasma insulin concentration and in vivo insulin action, 4p15-q12 linked to fasting plasma insulin concentration, 9q21 linked to 2-h insulin concentration during oral glucose tolerance testing, and 22q12-13 linked to fasting plasma glucose concentration. These results suggest loci that may harbor genes contributing to type 2 diabetes in Pima Indians. None of the linkages exceeded a LOD score of 3.6 (a 5% probability of occurring in a genome-wide scan). These findings must, therefore, be considered tentative until extended in this population or replicated in others.

Adult↗
PubMed1998

An autosomal genomic scan for loci linked to type II diabetes mellitus and body-mass index in Pima Indians.

Genetic factors influence the development of type II diabetes mellitus, but genetic loci for the most common forms of diabetes have not been identified. A genomic scan was conducted to identify loci linked to diabetes and body-mass index (BMI) in Pima Indians, a Native American population with a high prevalence of type II diabetes. Among 264 nuclear families containing 966 siblings, 516 autosomal markers with a median distance between adjacent markers of 6.4 cM were genotyped. Variance-components methods were used to test for linkage with an age-adjusted diabetes score and with BMI. In multipoint analyses, the strongest evidence for linkage with age-adjusted diabetes (LOD = 1.7) was on chromosome 11q, in the region that was also linked most strongly with BMI (LOD = 3.6). Bivariate linkage analyses strongly rejected both the null hypothesis of no linkage with either trait and the null hypothesis of no contribution of the locus to the covariation among the two traits. Sib-pair analyses suggest additional potential diabetes-susceptibility loci on chromosomes 1q and 7q.

Analysis of Variance↗
PubMed1998

Neuropathy associated with hyperoxaluria: improvement after combined renal and liver transplantations.

Little is known about oxaluria-associated neuropathy, and no effective treatments have been described. We report two patients with clinically severe and progressive sensorimotor polyneuropathy associated with oxaluria. Electrodiagnostic testing and sural nerve histopathology revealed evidence of severe axon loss and demyelination. In addition, birefringent crystalline deposits were identified within endoneurial and perineurial blood vessel walls, axon cylinders, and perimysial blood vessel walls. Electron probe microscopy confirmed that calcium (consistent with calcium oxalate) was a major constituent of the crystals. Both patients had substantial improvement in neuropathic signs and symptoms after kidney and liver transplantations despite no prior improvement with hemodialysis. Our results confirm previous reports of a mixed axonal and demyelinating neuropathy with calcium oxalate deposition in association with oxaluria. In addition, our findings suggest that renal and liver transplantation may be potential treatments for the associated neuropathy.

Adult↗
PubMed1998

Preferential utilization of newly synthesized cholesterol for brain growth in neonatal lambs.

These studies used the suckling lamb as a model to determine the sources of cholesterol that are utilized for development of the central nervous system in the neonate. Lambs were studied at 1.3 and 16.4 days after birth. Over this 15-day interval, 14 g of new brain tissue were formed. About 9-10 mg of cholesterol were utilized daily for this new tissue growth. To determine the source of this cholesterol, the absolute rates of low-density lipoprotein clearance and cholesterol synthesis were measured in vivo in nine separate regions of the central nervous system. Low-density lipoprotein clearance throughout the brain was very low and at most could have contributed only 0.3-0.4 mg cholesterol daily for new brain growth. In contrast, the brain synthesized 7-8 mg of cholesterol/day. There were pronounced regional differences in the concentration of cholesterol throughout the brain, and these correlated closely with the rate of sterol synthesis (r = 0.95) in these same regions. We conclude that the principal source of sterol for brain growth in suckling lambs is de novo synthesis.

Aging↗
PubMed1998

Systemic calciphylaxis associated with massive gastrointestinal hemorrhage.

A 38-year-old woman with insulin-dependent diabetes mellitus, hypertension, and end-stage renal disease developed digital ischemia, widespread cutaneous necrosis and eschar formation of both lower extremities, and extensive ulceration of the large intestine and cecum resulting in gastrointestinal hemorrhage. A mesenteric arteriogram revealed multiple stenotic areas and filling defects of the superior mesenteric artery and its tributaries, suggestive of vasculitis. A diagnosis of calciphylaxis was suspected, on antemortem skin biopsy, and was later confirmed by postmortem examination. This case further documents the relationship between calciphylaxis and significant visceral injury, and it represents, to our knowledge, the first case of calciphylaxis associated with massive gastrointestinal hemorrhage.

Adult↗
PubMed1997

Molecular scanning of the human peroxisome proliferator activated receptor gamma (hPPAR gamma) gene in diabetic Caucasians: identification of a Pro12Ala PPAR gamma 2 missense mutation.

Peroxisome proliferator activated receptor-gamma (PPAR gamma) is a nuclear receptor that regulates adipocyte differentiation, and possibly lipid metabolism and insulin sensitivity. As such, PPAR gamma is a promising candidate gene for several human disorders including obesity and type 2 diabetes mellitus. Screening for mutations in the entire coding region of the PPAR gamma gene (both gamma 1 and gamma 2 isoforms) was performed with DNA of 26 diabetic Caucasians with or without obesity. Two base substitutions were identified: a silent mutation at nucleotide 1431 (CACHis-->CATHis) and a missense mutation (CCGPro-->GCGAla) at codon 12 of PPAR gamma 2. The allele frequency of the Pro12Ala PPAR gamma 2 variant was 0.12 in Caucasian Americans, 0.10 in Mexican Americans, 0.08 in Samoans, 0.03 in African Americans, 0.02 in Nauruans, and 0.01 in Chinese. We conclude that the Pro12Ala PPAR gamma 2 gene variant is present in diverse populations. Further studies of the Pro12Ala variant will determine its relevance to obesity, insulin resistance, and type 2 diabetes.

Adult↗
PubMed1997

Identification of Rad's effector-binding domain, intracellular localization, and analysis of expression in Pima Indians.

In order to characterize the endogenous gene product for rad (ras-related protein associated with diabetes), we prepared antibodies to synthetic peptides that correspond to amino acids (109-121, 178-195, 254-271) within the protein. These antibodies were used to analyze the expression, structure, and function of rad. Western analysis with these antibodies revealed that rad was a 46 kDa protein which was expressed during myotube formation. Further, immunolocalization studies showed that rad localized to thin filamentous regions in skeletal muscle. Interestingly, when muscle biopsies from diabetic and control Pima Indians were compared, no differences in rad protein or mRNA expression were observed. Similarly, no differences were observed in protein expression in diabetic and control Zucker diabetic fatty (ZDF) rats. Functional analysis of muscle rad revealed that its GTP-binding activity was inhibited by the addition of N-ethylmaliemide, GTP, GTP gamma S, and GDP beta S but not ATP or dithiothreitol. Moreover, cytosol-dependent rad-GTPase activity was stimulated by the peptide corresponding to amino acids 109-121. Antibodies corresponding to this epitope inhibited cytosol-dependent rad-GTPase activity. Taken together, the results indicate that 1) rad is a 46 kDa GTP-binding protein localized to thin filaments in muscle and its expression increases during myoblast fusion, 2) expression of rad in Pima Indians and ZDF rats does not correlate with diabetes, and 3) the amino acids (109-121) may be involved in regulating rad-GTPase activity, perhaps by interacting with a cytosolic factor(s) regulating nucleotide exchange and/or hydrolysis.

Actin Cytoskeleton↗
PubMed1997

Chromosomal localization and partial genomic structure of the human peroxisome proliferator activated receptor-gamma (hPPAR gamma) gene.

We determined the chromosomal localization and partial genomic structure of the coding region of the human PPAR gamma gene (hPPAR gamma), a nuclear receptor important for adipocyte differentiation and function. Sequence analysis and long PCR of human genomic DNA with primers that span putative introns revealed that intron positions and sizes of hPPAR gamma are similar to those previously determined for the mouse PPAR gamma gene[13]. Fluorescent in situ hybridization localized hPPAR gamma to chromosome 3, band 3p25. Radiation hybrid mapping with two independent primer pairs was consistent with hPPAR gamma being within 1.5 Mb of marker D3S1263 on 3p25-p24.2. These sequences of the intron/exon junctions of the 6 coding exons shared by hPPAR gamma 1 and hPPAR gamma 2 will facilitate screening for possible mutations. Furthermore, D3S1263 is a suitable polymorphic marker for linkage analysis to evaluate PPAR gamma's potential contribution to genetic susceptibility to obesity, lipoatrophy, insulin resistance, and diabetes.

Adipose Tissue↗
PubMed1997

Characterization of defective nucleotide excision repair in XPC mutant mice.

Nucleotide excision repair (NER) is a fundamental process required for maintaining the integrity of the genome in cells exposed to environmental DNA damage. Humans defective in NER suffer from the hereditary cancer-prone disease xeroderma pigmentosum. In order to model this disease in mice a mutation in the mouse XPC gene was generated and used to replace a wild-type XPC allele in mouse embryonic stem cells by homologous recombination. These cells were used to derive XPC mutant mice. Fibroblasts from mutant embryos were more sensitive to the cytotoxic effects of ultraviolet light than wild-type and heterozygous cells. Repair synthesis of DNA following irradiation with ultraviolet light was reduced in these cells, indicating a defect in NER. Additionally, XPC mutant embryo fibroblasts were specifically defective in the removal of pyrimidine (6-4) pyrimidone photoproducts from the non-transcribed strand of the transcriptionally active p53 gene. Mice defective in the XPC gene appear to be an excellent model for studying the role of NER and its interaction with other proteins in the molecular pathogenesis of cancer in mammals following exposure to environmental carcinogens.

Alleles↗
PubMed1997

Cylindrical spirals of myofilamentous origin associated with exertional cramps and rhabdomyolysis.

We describe the presence of cylindrical spirals on muscle biopsy from a 31-year-old man who developed rhabodomyolysis following a long run. He had a prior history of exertional cramps and myoglobinuria. His maternal grandfather had similar symptoms. Transmission electron micrographs demonstrated continuity between the lamellae of the cylindrical spirals and native myofilaments. Whether these unusual structures confer a derangement in myofilament function is uncertain.

Actin Cytoskeleton↗
PubMed1997

Modest hypothermia provides partial neuroprotection when used for immediate resuscitation after brain ischemia.

Intraischemic reduction in temperature of 2-3 degrees C (modest hypothermia) has been demonstrated to provide partial neuroprotection in neonatal animals. This investigation determined if modest hypothermia initiated immediately after brain ischemia provides neuroprotection. Piglets were studied with rectal temperature maintained during the 1st h after 15 min of brain ischemia at either 38.3 +/- 0.3 degrees C (normothermia, n = 11) or at 35.8 +/- 0.5 degrees C (modest hypothermia, n = 11). The severity of brain ischemia was similar between groups as indicated by equivalent reduction in mean blood pressure (90 +/- 15 to 24 +/- 3 versus 92 +/- 13 to 26 +/- 3 mm Hg), and changes in cerebral metabolites and intracellular pH (pH(i)) measured by magnetic resonance spectroscopy (beta-nucleoside triphosphate = 44 +/- 9 versus 42 +/- 18% of control, control = 100%, pH(i): 6.25+/- .15 versus 6.24 +/- 0.22 for normothermic and modestly hypothermic groups, respectively). In the first 90 min after ischemia, there were no differences between groups in the duration and extent of brain acidosis, and relative concentrations of phosphorylated metabolites. Categorical assessment of neurobehavior was evaluated at 72 h postischemia (n = 16), or earlier if an animal's condition deteriorated (n = 6). Postischemic hypothermia was associated with less severe stages of encephalopathy compared with normothermia (p = 0.05). Histologic neuronal injury was assessed categorically in 16 brain regions, and postischemic hypothermia resulted in less neuronal injury in temporal (p = 0.024) and occipital (p = 0.044) cortex at 10 mm beneath the cortical surface, and in the basal ganglia (p = 0.038) compared with that in normothermia. Modest hypothermia for 1 h immediately after brain ischemia provides partial neuroprotection and may represent an adjunct to resuscitative strategies.

Animals↗
PubMed1997

Muscle Rad expression and human metabolism: potential role of the novel Ras-related GTPase in energy expenditure and body composition.

Ras associated with diabetes (Rad), a new ras-related GTPase, was recently identified by subtractive cloning as an mRNA in skeletal muscle that is overexpressed in NIDDM. To better understand its metabolic significance, we measured skeletal muscle Rad expression in well-characterized insulin sensitive (IS) and insulin resistant (IR) subjects with normal glucose tolerance and in untreated NIDDM patients. We found no differences in expression of Rad mRNA levels among IS, IR, and NIDDM groups using a ribonuclease protection assay (0.22 +/- 0.06, 0.13 +/- 0.01, and 0.16 +/- 0.02 relative units, respectively; NS) and no differences in Rad protein expression using a specific anti-peptide Rad antibody (1.05 +/- 0.18, 1.14 +/- 0.08, and 1.08 +/- 0.21 units/mg protein, respectively; NS). However, Rad protein levels were positively correlated with BMI (r = 0.43, P = 0.03) and percentage body fat (r = 0.55, P < 0.005), two independent measures of obesity, and negatively correlated with resting metabolic rate (r = 0.49, P = 0.01). In multiple regression analyses, percentage body fat and resting metabolic rate independently accounted for 30 and 10% of individual variability in muscle Rad protein expression. In conclusion, Rad expression in skeletal muscle is not altered as a function of insulin resistance or NIDDM in humans. However, these data, for the first time, implicate a role for Rad in regulating body composition and energy expenditure and provide a framework for studies designed to elucidate Rad's cellular functions.

Absorptiometry, Photon↗