Experimental Studies of Molybdenum Physiology and Toxicity

Pathological Effects Observed in Experimental Animals

Symptoms of acute molybdenum poisoning and pathological (abnormal)changes in body tissue arising from massive doses by oral and intraperitoneal administration of molybdenum trioxide and ammonium molybdate in lethal or near lethal doses are summarised in Table 7.7 [Browning, 1969].

Browning, E.,Toxicity of Industrial Metals, Butterworths, London, 2nd edn., 1969.

Effects of molybdenum on rats ^a

Substance and concentration	Effect	Ref.
Sodium molybdate/ppm
80-140	achromotrichia (loss of hair pigment)	[1]
75 - 300	femuro-tibial joint enlargement	[2]
75- 400	Reduced erythrocyte counts and hemoglobin conc.	[2,3]
400	mandibular and maxillary exostoses	[3,4]
800-1400	diarrhoea	[3]
400 - 1200	Feed consumption and body weight gain reduced	[5]
400 -1200	increased liver xanthine oxidase	[6]
400-1200	increased alkaline phosphatase activities	[4,7]
400 -1200	decreased liver sulfide oxidase, decreased phosphatase and decreased cytochrome oxidase activities	[8]
400- 1200.	caused fatty degeneration of the liver and kidney	[4]
4000-5000	death	[5]
Sodium molybdate 0.1- 0. 4 % in feed (rabbits ) for 5 weeks
(weanlings)	anorexia, weight loss, decreased erythrocyte counts and hemoglobin concentrations, alopecia, dermatosis, death
abnormality of the front legs, bending of the humerus	[9]
Ammonium heptamolybdate oral, in water at 80 mg/kg daily for 8 weeks	mild chronic renal failure	[10]
Ammonium molybdate 5 mg/kg per day for 4 to 6 months	increase in spleen weight, reduction in liver weight	[11, 12, 13]
Ammonium tetrathiomolybdate (6 mg Mo)and 3 mg copper per kg body weight for 2 to 21 days in feed (weanling male rats )	changes at long bone growth plates, at muscle insertions, and beneath the periosteum .	[14]
molybdenum trioxide dust 1 h ( mice)	mild irritation of mucous membrane	[15]
2730 mg/ml molybdenum trioxide (total)dust at 4 h/day for 5.5 months.(rabbits) inhalation	Reductions in serum alkaline and acid phosphatase activities, decreased inorganic phosphorus levels in tibia, and increased ascorbic acid levels in serum and urine	[11, 12, 13]

^a rats unless otherwise state

[1] Jeter, M. A. and Davis, G. K., J. Nutr., 1954, 54, 215.

[2] Miller, R. F., Price, N. O. and Engel, R. W., J. Nutr., 1956, 60, 539.

[3] Ostrom, C. A., Van Reen, R. and Miller, C. W., J. Dent. Res., 1961,40, 520.

[4] Van Reen, R., J. Nutr., 1959, 68, 243.

[5] Neilands, J. B., Strong, F. m. and Elvehjem, C. A., J. Biol. Chem., 1948, 172, 431.

[6] Luo, X. -M., Wei, H. -J. and Yang, S. P., JNCI, 1983, 71, 75.

[7] Mills, C. F., Monty, K. J., Ichihara, A. and Pearson, P. B., J. Nutr., 1958, 65, 129.

[8] Mills, C. F. and Davis, G.K., in "Trace Elements in Human and Animal Nutrition", Metrz, W., ed., 5th Ed. 1987, 1, 429. Academic Press. Inc., San Diego.

[9] Arrington, L.R. and Davis, G. K., J. Nutr., 1953, 51, 295.

[10] Bompart, G., Pecher, C., Prevot, D. and Girolami, J. -P., Toxicol. Lett., 1990, 52, 293.

[11] Lukashev, A. A. and Shishkova, Tr. Nauch.-Issled. Inst. Kraev. Patol. Alma Ata, 1971, 22, 152.

[12] Lukashev, A. A. and Shishkova, Tr. Nauch.-Issled. Inst. Kraev. Patol. Alma Ata, 1971, 22, 175.

[13] Lukashev, A. A. and Shishkova, Tr. Nauch.-Issled. Inst. Kraev. Patol. Alma Ata, 1971, 22, 191.

[14] Spence, J. A., Shuttle, N. F., Wenham, G., El-Gaim, T. and Bremner, I., J. Comp. Pathol., 1980, 90, 139.

[15] ACGIH: American Conference of Governmental Industrial Hygienists, 1992.

Symptoms of acute molybdenum poisoning

High doses of soluble molybdates caused experimental animals to become listless and to lose their appetites. Their physical condition deteriorated; their hair became harsh and rough and was easily removed; they lost weight. Loss of weight or a decreased rate of weight increase compared with controls is general with animals fed large doses of molybdenum compounds [Johnson et al., 1969]. In high doses molybdenum has a deleterious effect on bones and skin. The breaking strength of femurs, skin, and tail ring was decreased in molybdenum fed rats [Johnson et al., 1969]and rabbits developed a deformity of the forelegs. Bodily functions were impaired leading to diuresis and hypersalivation.

Johnson, R. H., Little, J. W. and Bickley, H. C., J. Dent. Res., 1969, 48, 1290.

Sodium molybdate, 2000 mg/kg in aqueous solution, was given intragastrically to rats. There were no deaths. Mo caused a high urinary excretion of N-acetyl-beta-glucosaminidase, a reduction in serum proteins and an increase in lactate dehydrogenase. There were no histopatholgical changes to organs. Since the LD50 of molybdate is greater than 2000 mg/kg it should be described as 'not toxic' according to Directive 83/467/EC [Rodriguez-Consuegra et al., 1994].

Rodriguez-Consuegra, M.A., Rodriguez-Vicente, M.C., Martinez, M.C., Repetto, M., Acute oral toxicity study of molybdenum in Wistar and Brown Norway rats, Rev. Toxicol.,1994, 11, 122 - 126.

Histopathological changes in acute molybdenum poisoning

The liver and kidneys were most affected. Cells became swollen and fat globules were deposited. The extent of damage increased with increasing exposure to molybdenum compounds [Table 7.7].

General effects of Acute Molybdenum Toxicity in Test Animals

Substance and concentration	Effect	Ref.
Sodium molybdate/ppm
80-140	achromotrichia (loss of hair pigment)	[1]
75 - 300	femuro-tibial joint enlargement	[2]
75- 400	Reduced erythrocyte counts and hemoglobin conc.	[2,3]
400	mandibular and maxillary exostoses	[3,4]
800-1400	diarrhoea	[3]
400 - 1200	Feed consumption and body weight gain reduced	[5]
400 -1200	increased liver xanthine oxidase	[6]
400-1200	increased alkaline phosphatase activities	[4,7]
400 -1200	decreased liver sulfide oxidase, decreased phosphatase and decreased cytochrome oxidase activities	[8]
400- 1200.	caused fatty degeneration of the liver and kidney	[4]
4000-5000	death	[5]
Sodium molybdate 0.1- 0. 4 % in feed (rabbits ) for 5 weeks
(weanlings)	anorexia, weight loss, decreased erythrocyte counts and hemoglobin concentrations, alopecia, dermatosis, death
abnormality of the front legs, bending of the humerus	[9]
Ammonium heptamolybdate oral, in water at 80 mg/kg daily for 8 weeks	mild chronic renal failure	[10]
Ammonium molybdate 5 mg/kg per day for 4 to 6 months	increase in spleen weight, reduction in liver weight	[11, 12, 13]
Ammonium tetrathiomolybdate (6 mg Mo)and 3 mg copper per kg body weight for 2 to 21 days in feed (weanling male rats )	changes at long bone growth plates, at muscle insertions, and beneath the periosteum .	[14]
molybdenum trioxide dust 1 h ( mice)	mild irritation of mucous membrane	[15]
2730 mg/ml molybdenum trioxide (total)dust at 4 h/day for 5.5 months.(rabbits) inhalation	Reductions in serum alkaline and acid phosphatase activities, decreased inorganic phosphorus levels in tibia, and increased ascorbic acid levels in serum and urine	[11, 12, 13]

^a In lethal or near-lethal dose. Abbreviations: ingest., ingestion in food; inhal., inhalation of dust; i.p., intraperitoneal injection; or., oral administration. See also note d of Table 2.a(i).

[1] Test carried out for Climax Molybdenum Co. by Scientific Associates and New Drug Institute.

[2] Browning, E., Toxicity of Industrial Metals, Butterworths, London, 2nd edn., 1969.

[3] Fairhall, L. T., Dunn, R. C., Sharpless, N. E.and Pritchard, E. A., The toxicity of molybdenum ,US Public Health Service, Public Health Bulletin, 1945, 294.

[4] (a) Underwood, E. J., Trace Elements in Human and Animal Nutrition, Academic Press, London, 2nd Ed., 1962, 100. (b) Kolomiitseva, M. G., Polonskaya, M. N.and Osipov, G. K., Mikroelem. Sel. Khoz. Med., 1968, 4, 183.(c) Schroeder, H. A.,. Balassa, J. J.and Tipton, I. H., J. Chronic Diseases, 1970, 23, 481.

Histopathological Changes in Acute Molybdenum Poisoning in Test Animals ^a

Histopathological Changes in Acute Molybdenum Poisoning in Test Animals ^a

Organ	Animal	Changes observed
Adrenals	guinea pig, rat	congested and swollen
Gastrointestinal tract	rat	stained deep blue
Heart	guinea pig	no change
Kidneysb	guinea pig	some cells swollen, fat globules deposited
Liverb	guinea pig	cells swollen, fat globules deposited
Lungs	guinea pig	slight to moderate congestion, cellular exudate

^a MoO₃ and ammonium molybdate administered orally, intraperitoneally, and by inhalation.

^b Organs most affected.

[1] (a) Underwood, E. J., Trace Elements in Human and Animal Nutrition, 2nd Ed. 1962, 100, Academic Press, London. (b) Kolomiitseva, M. G., Polonskaya, M. N. and Osipov, G. K., Mikroelem. Sel. Khoz. Med., 1968, 4, 183. (c) Schroeder, H. A., Balassa, J. J. and Tipton, I. H., J. Chronic Diseases, 1970, 23, 481.

[2] Test carried out for Climax Molybdenum Co. by Scientific Associates and New Drug Institute.

[3] Browning, E., Toxicity of Industrial Metals, 2nd Ed., 1969, Butterworths, London.

[4] Fairhall, L.T., Dunn, R. C., Sharpless N. E. and Pritchard, E. A., The toxicity of molybdenum, US Public Health Service, Public Health Bulletin, 294, 1945.

Molybdenum Fe-S flavin hydroxylases in hepatic injury

The role of molybdenum iron-sulfur flavin hydroxylases in the pathogenesis of

liver injuries in rats induced

(a) by carbon tetrachloride (CCl4), thioacetamide (TAA) and chloroform (CHCl3), which produce free radicals were associated with elevated activity levels of hepatic Mo-Fe-S flavin hydroxylases. Inhibition of these hydroxylases by sodium tungstate suppressed biochemical and oxidative stress markers of hepatic tissue damage.

(b) by acetaminophen (AAP) and bromobenzene (BB), which cause severe glutathione depletion. Mo-Fe-S flavin hydroxylases did not with these toxicants show any change. Mo-Fe-S hydroxylases contribute to the hepatic injury inflicted by free radical generating agents. and does not play any role in hepatic injury produced by glutathione depleting agents. The study has implication for understanding human liver diseases caused by liver toxicants and for inhibitors of Mo-Fe-S flavin hydroxylases as potential therapeutic agents.

Ali, S., Pawa, S., Naime, M., Prasad, R., Ahmad, T., Farooqui, H., and Zafar, H., Role of mammalian cytosolic molybdenum Fe-S flavin hydroxylases in hepatic injury, Life Sciences, 2008, 82, 780-788.

Cytosol = the non-particulate components of the cytoplasm

Cytoplasm = that part of the cell outside the nucleus but inside the cell wall if it exists

IMOA Testing Programme Skin and Eye Irritation ^a

Skin and Eye Irritation rat

Substance	Test
	skin irritation b	eye irritation c	skin sensitisation d
Molybdenum trioxide (pure)	none	mild inflammation	0% positive
Molybdenum trioxide (tech)	none	mild inflammation	0% positive
Ammonium dimolybdate	none	mild inflammation	20% positive
Sodium molybdate	none	mild inflammation	4% positive
Risk phrases required if:	significant irritation	significant inflammation	>30%

Notes

^a Combination of 4 tests. Results may be affected by pH and/or alkali content of the sodium molybdate.

^b Skin irritation: Material applied to skin of rabbits (6) for 4 hours. Animals observed for erythema and oedema daily for 4 days. No irritation was noted in any animals.

^c Eye irritation: Material applied to eyes of rabbits (6) (100 mg). Animals observed for 7 days. Only mild transient irritation was observed in test animals.

^d Skin sensitization: Guinea pigs exposed to material intradermally and topically twice (induction and challenge). Sodium molybdate with low alkali content gave positive reactions at frequencies of less than 30%. Higher frequencies were obtained in high alkali samples. It is uncertain if these were sensitization or irritation reactions.