Experimental approaches to the study of beta-carotene metabolism: potential of a 13C tracer approach to modeling beta-carotene kinetics in humans.
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Carbon Isotopes↗
Biomedical subjects
K J Goodman
Publications and source records attributed to K J Goodman.
Evidence of cis-trans isomerization of 9-cis-beta-carotene during absorption in humans.
Absorption and metabolism of [13C]9-cis-beta-carotene ([13C]9c beta C) was studied in three subjects after a single oral dose. Subjects given 1.0 mg [13C]beta-carotene (mean: 99.4% 9-cis-beta-carotene, 0.6% all-trans-beta-carotene; dose A) had substantial concentrations of [13C]all-trans-beta-carotene ([13C]tr beta C) and [13C]all-trans retinol ([13C]retinol) but very low concentrations of [13C]cis-beta-carotene ([13C]cis beta C) in saponified plasma 5 h after dosing, as determined by HPLC and isotope-ratio mass spectrometry. There was no evidence of appreciable absorption of [13C]9-cis retinol. To determine the proportion of [13C]tr beta C and [13C]retinol derived from [13C]9c beta C, a second set of studies in the same subjects was performed with the same isomeric composition except with 13C labeling only in all-trans-beta-carotene (dose B). The results indicated that > 95% of plasma [13C]tr beta C and [13C]retinol observed after dose A was derived from [13C]9c beta C. The concentrations of [13C]tr beta C observed, in excess of that derived from the trace amounts of [13C]tr beta C in the dose, indicated that a significant proportion of the [13C]9c beta C dose was isomerized to [13C]tr beta C before entering the bloodstream. Although precise quantitative estimates of the extent of isomerization of 9-cis-beta-carotene could not be made, it is apparent that cis-trans isomerization of 9-cis-beta-carotene to all-trans-beta-carotene contributed to the near absence of postprandial plasma 9-cis-beta-carotene after its oral administration in humans. The observation of different ratios of beta-carotene to retinol between the two dosing protocols suggests that isomerization did not occur exclusively before uptake by the intestinal mucosa. These results indicate that isomerization of ingested 9-cis-beta-carotene before its secretion into the bloodstream limits the potential supply of 9-cis retinoids to tissues, and increases the vitamin A value of 9-cis-beta-carotene.
Absorption↗
Linoleate, alpha-linolenate, and docosahexaenoate recycling into saturated and monounsaturated fatty acids is a major pathway in pregnant or lactating adults and fetal or infant rhesus monkeys.
Carbon recycling and desaturation and elongation of linoleate, alpha-linolenate and docosahexaenoate in ten fetuses and two nursing infants of chow-fed rhesus monkey mothers were studied in vivo using uniformly labeled tracer molecules and high precision mass spectrometry. Doses of [U-13C]-18:2n-6, [U-13C]-18:3n-3 or [U-13C]-22:6n-3 free fatty acids were infused intravenously to the adults, and milk, maternal plasma, fetal plasma and tissues, and infant plasma were analyzed for enrichment in fatty acids of length C14 to C22. Conversion of tracer fatty acids to palmitic, stearic, oleic, and long chain polyunsaturated fatty acids was observed in fetal liver, brain, and retina ca. 5 days after dosing, and in milk and infant plasma 1 and 7 days after dosing. Animals dosed with [U-13C]-22:6n-3 accumulated more label in the fetal organs compared to the animals dosed with [U-13C]-18:3n-3 or [U-13C]-18:2n-6. The greatest fractions of doses were found in the fetal brains at levels of 0.21%, 0.24% and 1.7% for the [U-13C]-18:2n-6, [U-13C]-18:3n-3, and [U-13C]-22:6n-3, dosed mothers, respectively. Label was found in saturated and monounsaturated fatty acids in liver, brain and retina (0.05-1.5 ppm dose/mg lipid) for all doses. These results demonstrate that 1) recycling of carbon from 18:2n-6, 18:3n-3, and 22:6n-3 into saturates and monounsaturates is a major metabolic pathway in chow-fed primates in the perinatal period; 2) less than 2% of the n-3 doses are found in brain fatty acids of developing fetuses from chow-fed mothers; and 3) [13C]-22:6n-3 accumulates in retina and brain at an order of magnitude higher level when provided as preformed [13C]-22:6 n-3 compared to [13C]-18:3n-3.
Animals↗
High-precision D/H measurement from hydrogen gas and water by continuous-flow isotope ratio mass spectrometry.
Two instrumental approaches are described for continuous-flow high-precision determinations of D/H ratios from hydrogen gas or via on-line reduction of water. In the first system, Ar is used as a carrier gas, with a Ni reduction furnace and a water trap to remove minor levels of unreduced water that are a potential source of memory effects. Precisions of SD < 10/1000 (delta DSMOW) over a 600/1000 range from -55 to +532/1000 are obtained for liquid water (0.4 microL). Linearity is excellent over 4 orders of magnitude of D concentration in tap water (r2 > 0.9999), although precision degrades at enrichments delta DSMOW > 5000/1000. In the second system, a heated Pd metal foil functions as a filter to admit purified hydrogen into the mass spectrometer. Hydrogen gas injections are made into flowing Ar and are directed to the Pd filter (approximately 330 degrees C) which passes hydrogen isotopes only while diverting the carrier flow to waste. Precisions of these measurements are SD < 6/1000 over the D enrichment range -213 to 340/1000, with excellent linearity (r2 > 0.9999) and accuracy (< 2/1000). Similar precision is obtained using the on-line reduction apparatus and a water trap prior to the Pd filter with injections of 0.4 microL of liquid water, with acceptable linearity (r2 > 0.999) over 3 orders of magnitude of D concentration. Neither system shows any sign of memory effects when water is analyzed. The data indicate that either one of these systems is a useful means for continuous-flow IRMS of D/H isotope ratio determinations.
Deuterium↗
High-precision gas chromatography-combustion isotope ratio mass spectrometry at low signal levels.
Precision and accuracy of gas chromatography-combustion isotope ratio mass spectrometry are investigated for sample levels down to about 5 pmol C in fatty acid methyl ester mixtures spanning 1000-fold in concentration. Precision and accuracy of isotope ratios diverge rapidly for conventional summation methods, and become unusable below 30 pmol material on column. At lower levels, mean isotope ratios were statistically different from reference values indicating bias as well as poor precision. In contrast, curve fitting, using the exponentially modified Gaussian line shape, gives improved precision for most peaks and useful results down to 3 pmol. The curve-fitting algorithm was also less sensitive to signal integration time than the summation method. These data indicate that curve fitting may be the method of choice for integration of noisy data when high-precision isotope ratios are desired.
Carbon↗
Proportional melanoma incidence and occupation among white males in Los Angeles County (California, United States).
A case-control analysis of cancer registry data was used to examine the hypothesis that occupational exposure to sunlight influences the risk of melanoma. Occupation at diagnosis was available for 3,527 cutaneous melanomas and 53,129 other cancers identified by the Los Angeles County (California, United States) Cancer Surveillance Program among non-Spanish-surnamed White males aged 20 to 65 years between 1972 and 1990. Occupational exposure to sunlight was assessed by blinded expert coding of job titles as indoor, outdoor, and mixed indoor/outdoor. Relative to indoor occupations, proportionate odds ratios (OR) adjusted for age, level of education, and birthplace were 1.16 (95 percent confidence interval [CI] = 1.07-1.27) for indoor/outdoor occupations and 1.15 (CI = 0.94-1.40) for outdoor occupations. However, increasing levels of the education or training required for the occupation was associated more strongly with increased melanoma occurrence (ORs adjusted for age, occupational sun exposure, and birthplace, were 1.0, 1.63, 2.09, 2.23, and 2.99 for low-skill occupation, high school, college, postgraduate, and doctoral levels, respectively). Analysis of melanoma occurrence by job titles confirmed a clear variation by the required education or training level but not by the category of occupational sunlight exposure. The findings suggest that lifestyle factors associated with higher levels of education may be more important determinants of melanoma risk than characteristics of the work environment.
Adult↗
The transmission of Helicobacter pylori. A critical review of the evidence.
This paper critically reviews the reported data regarding the transmission of Helicobacter pylori. The mode of transmission remains poorly understood; no single transmission pathway has been clearly identified. Laboratory studies have experienced difficulty in isolating this organism from material other than gastric tissue. The problematic detection of this bacterium has presented obstacles to pinpointing portals of entry and exit and to implicating or ruling out environmental reservoirs. It is shown additionally that knowledge of H. pylori transmission is limited due to lack of solid epidemiological evidence from population-based analyses that adequately consider confounding. Reported observations in general support a person-to-person mode of transmission that occurs most frequently early in life; H. pylori is consistently linked to conditions associated with residential crowding in childhood. Laboratory studies have yielded evidence in favour of both faecal-oral and oral-oral pathways. However, a role for either waterborne or zoonotic transmission has not been ruled out. The failure of investigations to single out a mode of transmission for H. pylori signals the possibility of multiple transmission pathways.
Adult↗
Curve fitting for restoration of accuracy for overlapping peaks in gas chromatography/combustion isotope ratio mass spectrometry.
The effect of graded degrees of overlap on high-precision and -accuracy carbon isotope ratios determined by gas chromatography/combustion isotope ratio mass spectrometry (GCC/IRMS) is reported. Overlapping peaks of closely matched isotope ratio (difference delta 13CPDB < 1%) were analyzed by the conventional vertical drop summation algorithm and by curve fitting using the Levenberg-Marquardt algorithm. The conventional algorithm resulted in systematic bias related to degree of overlap even though precision was not noticeably affected. The exponentially modified Gaussian (EMG) and HaarhoffVanderLinde (HVL) functions were found to model GCC/IRMS peaks satisfactorily. Useful models over a wide range of overlap were obtained by applying consecutive HVL/HVL or HVL/EMG functions to overlapping peaks. Accuracy was improved in most cases and was never degraded. This study demonstrates the presence of subtle bias in isotope ratio determinations of overlapping peaks and the ability of automated curve fitting to compensate for these biases.
Algorithms↗
Study of beta-carotene metabolism in humans using 13C-beta-carotene and high precision isotope ratio mass spectrometry.
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Adult↗
High sensitivity tracer detection using high-precision gas chromatography-combustion isotope ratio mass spectrometry and highly enriched [U-13C]-labeled precursors.
The use of highly enriched, uniformly labeled fatty acid ([U-13C]) with analysis by high-precision gas chromatography-combustion isotope ratio mass spectrometry (GCC-IRMS) has been evaluated as a metabolic tracer technique. 13C/12C ratios are routinely determined to precisions (SD) of less than 0.00001 (delta PDB less than 1/1000) for greater than 10 ng of fatty acid, and less than 0.001 (delta PDB less than 100/1000) for samples of 30 pg of fatty acid, the latter corresponding to a 100-fmol sample. Baseline fatty acid 13C/12C in human plasma fractions is shown to fluctuate not more than 0.000 04 (delta PDB 4/1000) over 10 h. 13C/12C enrichments greater than 0.001 (delta PDB 100/1000) are obtained in a fatty acid plasma fraction subsequent to a 10-mg dose of 42% 13C-labeled stearic acid to a 78-kg adult. Biokinetics are discerned over an 13C/12C enrichment range of less than 0.0002 (approximately 13/1000 in delta PDB units) in plasma. A means for correction of isotope ratio contamination due to carbon-containing derivatives is presented. High-precision GCC-IRMS used in concert with highly enriched tracers is shown to possess advantages versus organic GC/MS for stable isotopic tracer detection and is superior to radiotracer methods in terms of dose sizes and analysis efficiency.
Adult↗
Screening for cervical cancer in emergency centers and sexually transmitted disease clinics.
Low-income women are at increased risk of developing cervical cancer compared with middle- and upper-income women. How can poor women be reached for screening and early diagnosis of cervical cancer and its precursor stages? One answer to this question is based on the observation that a high percentage of the unscreened population has received some form of medical care within the previous 5 years. Emergency centers and sexually transmitted disease (STD) clinics often provide such care to patients who lack a regular source of health care. Thus, they represent potential resources for cervical cancer screening. However, in a survey of 19 hospitals whose patient populations include a high proportion of low-income patients, only five reported a protocol for cervical cancer screening in their emergency centers. Similarly, all 11 STD clinics included in this survey reported that fewer than 5% of their female patients had a Papanicolaou smear taken even though virtually all of them received a pelvic examination. Based on these findings, it appears that health care administrators and policymakers could intensify their cancer prevention programs by mobilizing these resources for cancer control.
Community Health Centers↗
Second-trimester placental changes associated with elevated maternal serum alpha-fetoprotein.
Measuring maternal serum alpha-fetoprotein (AFP) levels in the second trimester is an effective screening test for identifying pregnancies at increased risk for neural tube defects. In the absence of a neural tube defect there are many nonpathologic and pathologic causes for elevated AFP including underestimated gestational age, twin gestation, impending fetal death, and rare fetal malformations. In this series, intraplacental sonolucent spaces were detected in a significant percentage of second trimester pregnancies with elevated serum AFP in the absence of any other cause for the elevation. It is postulated that these cystic spaces are a conduit for the transfer of fetal blood into the maternal circulation, thus accounting for the nonpathologic AFP elevation in the maternal serum.
Chorion↗
Radiologic findings in anorectal gonorrhea.
Gonorrhea is the most prevalent communicable disease in the United States and the incidence of anorectal involvement is high. Anorectal gonorrhea may be clinically elusive making the radiologic findings crucial in suggesting the diagnosis. Edematous rectal mucosa with limited distensibility and small ulcerations are the prominent radiologic findings.
Adult↗
Pathways of extrapelvic spread of disease: Anatomic-radiologic correlation.
Extrapelvic spread of disease, particularly from gastrointestinal tract perforations which may be clinically occult, may first present in the buttock, hip, thigh, and even lower leg, and the extraperitoneal space of the abdomen itself. Clinical manifestations at these remote sites may be very misleading. Anatomic and roentgenologic observations establish the preferential pathways of extrapelvic spread. These are related to the insertions and fascial investments of the iliopsoas, pyriformis, and obturator internus muscles and the ensheathed penetrations of the superior gluteal arteries. Superiorly, extension from the pelvic tissues seeks out the posterior pararenal compartment of the extraperitoneal region of the abdomen. Roentgenologic signs may first identify the presence, extent, and localization of the primary process.
Adult↗
A comprehensive review of the natural history of Helicobacter pylori infection in children.
Across populations of children, Helicobacter pylori prevalence ranges from under 10% to over 80%. Low prevalence occurs in the U.S., Canada, and northern and western Europe; high prevalence occurs in India, Africa, Latin America, and eastern Europe. Risk factors include socioeconomic status, household crowding, ethnicity, migration from high prevalence regions, and infection status of family members. H. pylori infection is not associated with specific symptoms in children; however, it is consistently associated with antral gastritis, although its clinical significance is unclear. Duodenal ulcers associated with H. pylori are seldom seen in children under 10 years of age. H. pylori-infected children demonstrate a chronic, macrophagic, and monocytic inflammatory cell infiltrate and a lack of neutrophils, as compared with the response observed in adults. The effect of H. pylori infection on acid secretion in children remains poorly defined. The events that occur during H. pylori colonization in children should be studied more thoroughly and should include urease activity, motility, chemotaxis, adherence, and downregulation of the host response. The importance of virulence determinants described as relevant for disease during H. pylori infection has not been extensively studied in children. Highly sensitive and specific methods for the detection of H. pylori in children are needed, especially in younger pediatric populations in which colonization is in its early phases. Criteria for the use of eradication treatment in H. pylori-infected children need to be established. Multicenter pediatric studies should focus on the identification of risk factors, which can be used as prognostic indicators for the development of gastroduodenal disease later in life.
Child↗