This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Vitamin B12 (B12) is an essential nutrient required for the normal functioning of mammalian cells, particularly in the hematological and neurological systems. All naturally occurring B12 is synthesized exclusively by bacteria since both plants and animals lack the necessary enzymes for the biosynthesis of B12. Intestinal bacteria synthesize B12, which is absorbed and incorporated into animal tissues, as well as milk and eggs, making these products primary dietary sources of B12 for humans. However, there is only limited information available on the bioavailability of B12 from these dietary sources. A major technological advance, accelerator mass spectrometry (AMS), available through collaborative arrangements with the Lawrence Livermore National Laboratory, provides the capacity to detect trace levels of carbon-14 (14C) in biological samples at attomolar (10-18) concentrations. The instrument is therefore uniquely suited for assessing the biological fates of 14C-labeled substances after oral ingestion. In ongoing NIH-sponsored human studies, we are assessing the absorption, metabolism, and turnover of a single oral dose of 14C-labeled B12 (14C-B12) dissolved in water. In a pilot feasibility study funded by the National Cattlemen's Beef Association (NCBA), we have successfully enriched beef muscle and liver in vivo with 14C-B12. The goal of this proposal is to enrich chicken eggs in vivo with 14C-B12 and feed the 14C-B12-enriched eggs to healthy human subjects to determine B12 bioavailability from eggs. Eggs and dairy products are the only non-meat sources of vitamin B12. Eggs Chicken eggs enriched in vivo with 14C-B12 were fed to human volunteers. Baseline and post-ingestion blood, urine and stool samples were collected over a one-week period and assessed for 14C-B12 content using accelerator mass spectrometry. Bioavailability is being determined by measurement of the fraction of the total oral dose appearing in the stool, as well as calculation of the area under the curve (AUC) reflecting the appearance and disappearance of 14C-B12 from plasma. The hypothesis to be tested is that an accurate value for the bioavailability of B12 from chicken eggs can be determined, which in turn can allow us to definitively determine the nutritional value of eggs as a source of B12. Data is currently being analyzed. Bread Cobalamin (vitamin B12) deficiency is highly prevalent in the US and worldwide. Deficiency is most common in the elderly, with an average prevalence H25% over age 60 y. The situation is similar in California;in a representative sample of 1545 Latinos aged e60 y in the Sacramento region, we observed 6.5% deficiency and an additional 16% marginal status. About 40% of older persons with low serum cobalamin have food cobalamin malabsorption (F-CM), in which gastric atrophy and/or dysfunction is implicated. The gastric atrophy is often the result of chronic infection with Helicobacter pylori, which over time causes hypochlorhydria and diminished production of gastric pepsin, followed by loss of mucosal integrity, and subsequent overgrowth of bacteria in the stomach and upper intestine. The hypochlorhydria and failure of pepsin production impairs release of cobalamin from proteins in food, and the bacterial overgrowth may compete for uptake of cobalamin. Most elderly with F-CM can still absorb synthetic, crystalline forms of the vitamin when added to fortified cereals or used as supplements. It is generally recommended that elderly consume a higher proportion of their cobalamin in fortified foods than younger people. However there is considerable debate about whether crystalline cobalamin is absorbed as well by elderly with F-CM, especially if added as a fortificant to food. Elderly in general seem to need substantially higher intakes than the RDA to restore or maintain their cobalamin status, even when the vitamin is given as a supplement. The question of whether the most at-risk elderly, those with gastric atrophy, can absorb vitamin cobalamin added as a fortificant to cereals is especially timely based on recent reports that those with deficiency but high serum folate have five times the risk of cognitive impairment and anemia compared to those with normal cobalamin and folate status. Another problem is that when low serum cobalamin is diagnosed in older people, it is often ignored by medical practitioners until depletion progresses further, or there are symptoms of deficiency (such as nerve damage). Alternatively high oral doses, or injections, are prescribed for the rest of life. Diagnosis of F-CM is rarely attempted. It has not yet been investigated whether treating the Helicobacter pylori and bacterial overgrowth, achievable with the same medications, will improve ability to absorb cobalamin from food or in the crystalline form. Our hypothesis is: Older adults with markers of gastric atrophy will absorb less 14C-cobalamin added as a fortificant to bread than will older adults with no sign of gastric atrophy. The research will employ a novel method to assess absorption using 14C-cobalamin that has very low levels of radioactivity which will be quantified by accelerator mass spectrometry. The 14C-cobalamin will be added to bread as a fortificant, at a level similar to that which might be added in flour fortification. Persons aged e60 y will be screened to identify those with low cobalamin, who will then be assessed for serum markers of gastric atrophy. Ten with evidence of gastric atrophy, and ten without, will consume the labeled bread, and absorption of cobalamin compared by quantifying radioactivity in plasma and urine during the next 24 h. The main limitation of the study is that assessment of absorption of cobalamin from endogenously labeled food is not possible with the limited resources available, but this will be basis of future research proposals. However, we will be able to determine whether cobalamin added as a fortificant to bread is equally well absorbed by older persons with gastric atrophy and those without, and whether absorption of fortificant cobalamin can be improved by treatment for Helicobacter pylori and bacterial overgrowth.

National Institute of Health (NIH)
National Center for Research Resources (NCRR)
Biotechnology Resource Grants (P41)
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