Lever, J., and Bibr., Effects of Molybdenum on the Organism (A Review) , 1986.
A compartmental model of molybdenum metabolism based on stable isotope excretion patterns was developed. Molybdenum is an essential trace element in humans, with an estimated safe and adequate daily dietary intake (ESADDI) of 75-250 microg Mo/d. Four adult men were fed low molybdenum diets, 22 microg Mo/d, for a period of 102 d. The stable isotopes 97Mo and 100Mo were administered in intravenous and oral doses respectively at selected intervals. The resulting 6 d cumulative urinary and faecal isotope excretion data were used to model molybdenum metabolism using SAAM/CONSAM software. A kinetic model, including gastrointestinal (GI),plasma, slow-turnover tissue and fast-turnover tissue compartments, accurately simulated the observed pattern of urinary and faecal excretion for both stable isotopes in all four subjects. Residence time for molybdenum in the GI tract was estimated at 1.7 0.4 d. Predicted residence time for plasma molybdenum was 224 min, whereas slow-turnover tissue (possibly hepatic) retention averaged 58 16 d. The model thus permitted estimation of kinetic parameters for molybdenum metabolism in tissues not readily accessible or measurable in humans.
Thompson, K.H., Turnlund, J.R., Kinetic-Model Of Molybdenum Metabolism Developed From Dual Stable-Isotope Excretion In Men Consuming A Low Molybdenum Diet, Journal Of Nutrition, 1996, 126, 963-972.
The gastrointestinal tract readily absorbs soluble, but not insoluble, molybdenum compounds [Wester et al., 1971]. Absorption rate of molybdenum from the diet of both patients and healthy volunteers averaged about 50% in one study and 88-93% in another study in which the patients received 22-1490 microg Mo/d for 24 days.
Wester, P.O., Trace element balances in two cases of pancreatic insufficiency. Acta Med. Scand., 1971;190,155-161.
The Mo intake of adults in Germany and Mexico was determined in food duplicate samples by inductively coupled plasma atomic emission spectrometry [Holzinger et al. 1998]. Each test population consisted of seven men and seven women and also 10 female and 10 male vegetarians and two Mexican test groups. Molybdenum intake of adults with mixed diets increased from 1988 to 1996. German women with a mixed diet consumed 89 mu g/ din 1996 and men 100 mu g/ d, In comparison, female and male vegetarians consumed 179 mu g /d and 170 mu g/ d. Mexican women consumed 162 mu g /d and Mexican men 208 mu g /d. The Mo requirement of adults, 25 mu g /d, is met by normal intake, An intake of 150 mu g /kg body weight may be toxic for humans, Therefore, people in Germany and Mexico are not endangered by Mo exposure.
Holzinger, S., Anke, M., Rohrig, B., Gonzalez, D., Molybdenum intake of adults in Germany and Mexico, Analyst, 1998,3, 447-450.
When Mo in aqueous solution (0.5 - 5 mg Mo in ca 0.005M HCl) was administered to 3 healthy human volunteers on a total of 15 occasions, at doses up to 1 mg almost complete uptake (by intestinal absorption) of Mo was observed and only a slight decrease (< 30%) for higher doses [Werner et al., 1998]. Addition of black tea reduced the absorbed fraction by about a factor of ten. Mo uptake (intestinal absorption) from intrinsically labelled cress (60%)was less than the Mo uptake from extrinsically labelled cress (75%) and aqueous solutions (100%). Even less Mo (below 45%) was absorbed from an extrinsically labelled composite meal comprising chicken, vegetables and noodles).
Werner, E., Giussani, A., Heinrichs, U., Roth, P., Greim, H., Biokinetic studies in humans with stable isotopes as tracers. Part 2: Uptake of molybdenum from aqueous solutions and labelled foodstuffs, Isotopes In Environmental And Health Studies, 1998,.34, 297-301.
Molybdenum biokinetics in humans is of interest in connexion with the fate in the body of the radionuclide 99Mo [Giussani et al., 1998] which is used as a 99 mTc generator in nuclear medicine and may be released after accidents in nuclear power plants. (In Chernobyl ca 6% of the total radioactivity released within the first 10 d was due to 99Mo.). The aim in developing a biokinetic model is to provide an estimate of the number of radioactive transformations taking place in a given period in the organs where the radionuclides are distributed. Such studies, undertaken in humans with the stable isotopes 95Mo and 96Mo provide also data on the absorption, excretion of molybdenum and its distribution in the body. Values of the fractional transfer coefficients, e.g. from the stomach, to the intestines, the kidney and the bladder are given for Mo supplied in aqueous solution (chloride) (orally, 5.2 to 55 microg kg-1 body weight), in a foodstuff (cress), and intravenously.
The conclusions of these and related and earlier experiments are:
Intestinal absorption of Mo supplied as an aqueous solution is almost complete (>90%, Mo < 5 mg).
Intestinal absorption of Mo supplied with a solid meal is less than 50% of the administered amount.
Plasma clearance is fast:: mean sojourn time in the transfer compartment is ca 100 min.
Urinary excretion regulates rapidly the body content of Mo and its pattern is independent of the administered form (injection or ingestion, extrinsic or intrinsic tracer). The excreted amount rises strongly with increasing Mo dietary level. Thus when 33 microgMo were injected into human volunteers the excreted amounts (microg) in the urine within 18 d at increasing daily diet Mo values (microg) were: 13 at 22 in diet, 28 at 120 and 31 at 1500.
Gastric emptying is much slower with solid meals than with aqueous solutions of Mo: residence half-times for solids 30 min, for liquids 10 min.
Mean residence time for Mo in the kidney was 14 d.
Giussani, A., Cantone, M.C., deBartolo, D., Roth, P., Werner, E., A revised model of molybdenum biokinetics in humans for application in radiation protection, Health Physics, 1998, 75, 479-486.
In a study of molybdenum uptake by men and women absorption and excretion of molybdenum in foodstuffs and molybdenum added to the diet were compared. Molybdenum (100 mu g Mo per meal) in soy was less available than molybdenum added to the diet, but the molybdenum in kale was as available as molybdenum added to the diet. Once absorbed, urinary excretion was not significantly different for soy, kale, and extrinsic molybdenum [Turnlund et al., 1999].
Turnlund, J.R., Weaver, C.M., Kim, S.K., Keyes, W.R., Gizaw, Y., Thompson, K.H., Peiffer, G.L., Molybdenum absorption and utilization in humans from soy and kale intrinsically labeled with stable isotopes of molybdenum, American Journal Of Clinical Nutrition, 1999, 69, 1217-1223.
Dose coefficients for ingestion of radionuclides of molybdenum from members of the public have been calculated according to the guidelines using a revised biokinetic model. A constant daily intake of 200 microg/day is assumed. The results obtained for the effective dose do not differ remarkably from the estimates. However, considerable deviations are observed for the equivalent dose to some individual organs; for example, the dose coefficient for colon after ingestion of Mo-99 in solid form is about 7 times higher than the International Commission on Radiological Protection value, whereas for other organs the new estimates are about one tenth. In agreement with earlier work liver and kidney are the organs where molybdenum is more easily found with concentrations (microg/g wet weight): for liver, 0.5 to 1.0; kidney, average 0.3, range 0.2 – 0.4.
Giussani, A., Cantone, M.C., deBartolo, D., Roth, P., Werner, E., Internal dose for ingestion of molybdenum radionuclides based on a revised biokinetic model, Health Physics, 2000, 78, 1, 46-52.