Vanadium in blood

A number of biophysical techniques have been used to probe the valence state of vanadium in blood cells and their intracellular pH. Most data suggest a predominance... 

Cornells R, VersieckJ. 1981. Vanadium in blood plasma and serum. Lancet 2 1179. 

Kelm, W. and Schaller, K.H. (1978). The quantitative determination of vanadium in blood samples of ecologically and occupationally exposed persons with a specific and sensitive method, Wissenschaft u. Umwelt, 1, 34. 

The present record could resemble that of the spedes Ascidia gemmata, for which the concentration factor of vanadium is 10 (350 mM vanadium in blood cells, of which 97.6% is in oxidation state III) (Michibata et al, 1991a). 

Certain vertebrates have an astonishing ability to accumulate vanadium in their blood. For example, the ascidian seaworm Phallusia mammilata has a blood concentration of V up to 1900 ppm, which represents more than a millionfold concentration with respect to the sea-water in which it lives. The related organism Ascidia nigra has an even more spectacular accumulation with concentrations up to 1.45% V (i.e. 14 500 ppm) in its blood cells, which also contain considerable concentrations of sulfuric acid (pH 0). One possibility that has been mooted is that the ascidia accumulates vanadate and polyvanadate ions in mistake for phosphate and polyphosphates (p. 528). 

Tunicates (ascidians or sea-squirts) are invertebrate marine organisms, which can accumulate vanadium at concentrations approaching 350 mM (the concentration of vanadium in seawater is 10 8 M). This vanadium is taken up as V(V) from seawater (Figure 17.16), reduced to oxidation state III or IV and stored in a soluble form in the blood cells within acidic vacuoles at concentrations a million fold higher than in their external surroundings. 

High concentration of vanadium in the blood of some tunicates has been a long-standing problem of biochemistry. That vanadium(III) ions are part of the respiratory pigment has been ruled out recently. The efficient mechanism used to concentrate vanadium from sea water is now understood but the utility of vanadium for these living organisms is still an intriguing question. 

The sea squirts or tunicates are fascinating marine creatures, their name being derived from the tunic made of cellulosic material that surrounds the body of the animal. In 1911, Henze discovered vanadium in the blood of Phallusia mammillata C.343 He later found the same with other ascidians (a class of tunicates). In vanadium-accumulating species, most vanadium is located in the vacuoles—vanadophores—of certain types of blood cells—the vanadocytes. The concentration in the vanadophore can be as high as 1M and this value must be compared with concentrations of the order of 2 x 10-8 M for vanadium in sea water.344 Kustin et al. have reviewed the work done to understand the efficient accumulation and the possible biological roles of the metal.345... 

The phylum Chordata, to which we ourselves belong, includes not only the vertebrates but also more primitive marine animals that have a spinal cord. Among these primitive species, which may be related to early ancestral forms, are the tunicates or sea squirts. They have a very high concentration of vanadium in their blood. 

Vanadium and nickel are present in parts-per-million quantities in most crude oils, usually in large, oil-soluble organometallic compounds termed porphyrins. The chemical structure of porphyrins is closely akin to the coloring matter in blood and to chlorophyll in plants. 

The ascidians or tunicates (sea squirts) accumulate vanadium from seawater (about 5x 10-8 mol dm-3) to a level of about 1 mol dm-3 and store it in a dilute solution of sulfuric acid (pH<2) in blood cells called vanadocytes. The tunicates thus concentrate vanadium several million-fold. 079 NMR, ESR and EXAFS determinations on whole vanadocyte cells of Ascidia ceratodes and Ascidia nigra indicate that the vanadium is present mainly as aquated V111 probably complexed with sulfate. Some vanadyl ion (5-10%) is also present.1080 1081... 

It has been demonstrated that the distribution of vanadium species inside the cell can depend on the form in which the vanadium is administered, as was seen in fish where a different distribution of vanadium in red blood cells (RBCs) was found depending upon whether metavanadate or decavanadate was given. In contrast to this, a similar accumulation was found in plasma and cardiac cytosol. However, the ratio of vanadium in plasma to vanadium in RBCs increased over time with metavanadate administration and remained constant for decavanadate administration. When either of the vanadium compounds was used, most of the vanadium was first found in plasma before moving into the mitochondrial fraction [9,10], Although one can know with some certainty what vanadium compound is given to an animal or put into a tissue culture growth medium, it is difficult to always know the identity of the active form inside the cell. 

To date, there is limited published material concerning the pharmacokinetics of vanadium compounds in humans. The concentration of vanadium in humans not dosed with the metal is extremely low and at the limits of detection of many of the analytical techniques used. It is not possible to ascertain if the large differences observed in different populations are the result of environmental exposure or experimental variability. Studies using blood have shown vanadium levels of 0.4 to 2.8 pg/L in normal people. The serum contains the largest amount of vanadium with concentration values ranging from 2 to 4 pg/L using atomic absorption spectroscopy [90], The upper limit of vanadium in the urine of normal people was reported to be 22 pg/L, with excretion values averaging below 8 pg/24 h. Vanadium is widely available in nutrition stores for athletes, who believe it to be a nonsteroidal compound that increases muscle mass at a dose of approximately 7 to 10 mg day, without any reports of toxicity [91]. 

Extended X-ray absorption fine structure (EXAFS) and K edge absorption spectroscopy have been used to study vanadium in coaI7). In contrast to the common belief that vanadyl porphyrins are the major compounds present, these studies demonstrate that in the high vanadium content samples examined, the metal is tetravalent and coordinated to oxygen ligands. Similar investigations have been carried out on the vanadocytes of aci-dians to identify the form of vanadium in tunicate blood cells22 (vide infra). 

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