51V NMR investigation of cell-associated vanadate species in Phycomyces blakesleeanus mycelium

Uptake of vanadium and its intracellular metabolism by Coprinellus truncorum mycelial biomass

BACKGROUND

Fungi absorb and solubilize a broad spectrum of heavy metals such as vanadium (V), which makes them a main route of its entry into the biosphere. V as vanadate (V5+) is a potential medical agent due to its many metabolic actions such as interaction with phosphates in the cell, and especially its insulin-mimetic activity. Antidiabetic activity of V-enriched fungi has been studied in recent years, but the biological and chemical bases of vanadium action and status in fungi in general are poorly understood, with almost no information on edible fungi.

METHODS

This manuscript gives a deeper insight into the interaction of V5+ with Coprinellus truncorum, an edible autochthonous species widely distributed in Europe and North America. Vanadium uptake and accumulation as V5+ was studied by 51V NMR, while the reducing abilities of the mycelium were determined by EPR. 31P NMR was used to determine its effects on the metabolism of phosphate compounds, with particular focus on phosphate sugars identified using HPLC.

RESULTS

Vanadate enters the mycelium in monomeric form and shows no immediate detrimental effects on intracellular pH or polyphosphate (PPc) levels, even when applied at physiologically high concentrations (20 mM Na3VO4). Once absorbed, it is partially reduced to less toxic vanadyl (V4+) with notable unreduced portion, which leads to a large increase in phosphorylated sugar levels, especially glucose-1-phosphate (G1P) and fructose-6-phosphate (F6P).

CONCLUSIONS

Preservation of pH and especially PPc reflects maintenance of the energy status of the mycelium, i.e., its tolerance to high V5+ concentrations. Rise in G1P and F6P levels implies that the main targets of V5+ are most likely phosphoglucomutase and phosphoglucokinase(s), enzymes involved in early stages of G6P transformation in glycolysis and glycogen metabolism. This study recommends C. truncorum for further investigation as a potential antidiabetic agent.

Kinetic Studies of Sodium and Metforminium Decavanadates Decomposition and In Vitro Cytotoxicity and Insulin- Like Activity

The kinetics of the decomposition of 0.5 and 1.0 mM sodium decavanadate (NaDeca) and metforminium decavanadate (MetfDeca) solutions were studied by 51V NMR in Dulbecco’s modified Eagle’s medium (DMEM) medium (pH 7.4) at 25 °C. The results showed that decomposition products are orthovanadate [H2VO4]− (V1) and metavanadate species like [H2V2O7]2− (V2), [V4O12]4− (V4) and [V5O15]5− (V5) for both compounds. The calculated half-life times of the decomposition reaction were 9 and 11 h for NaDeca and MetfDeca, respectively, at 1 mM concentration. The hydrolysis products that presented the highest rate constants were V1 and V4 for both compounds. Cytotoxic activity studies using non-tumorigenic HEK293 cell line and human liver cancer HEPG2 cells showed that decavanadates compounds exhibit selectivity action toward HEPG2 cells after 24 h. The effect of vanadium compounds (8–30 μM concentration) on the protein expression of AKT and AMPK were investigated in HEPG2 cell lines, showing that NaDeca and MetfDeca compounds exhibit a dose-dependence increase in phosphorylated AKT. Additionally, NaDeca at 30 µM concentration stimulated the glucose cell uptake moderately (62%) in 3T3-L1 adipocytes. Finally, an insulin release assay in βTC-6 cells (30 µM concentration) showed that sodium orthovanadate (MetV) and MetfDeca enhanced insulin release by 0.7 and 1-fold, respectively.

Hydrophobicity may enhance membrane affinity and anti-cancer effects of Schiff base vanadium(v) catecholate complexes

Anti-cancer activities of vanadium compounds have generated recent interest because of a combination of desirable properties for chemotherapy, i.e., strong cytotoxicities, anti-metastatic activities and relatively low systemic toxicities. Certain hydrophobic vanadium(v) Schiff base/catecholate compounds, which as shown herein, have increased stability in aqueous media and affinity for membrane interfaces. Depending on their hydrophobicity, they may be able to enter cells intact. In this manuscript, two hydrophobic V(v) catecholate substituted analogues, [VO(Hshed)(cat)] and [VO(Hshed)(dtb)], (Hshed = N-(salicylideneaminato)-N'-(2-hydroxyethyl)-1,2-ethanediamine, cat = pyrocatechol, and dtb = 3,5-di(tert-butyl)catechol and the vanadium(v) precursor [V(O)2(Hshed)]) were synthesized for their ability to interact with membranes and their anti-cancer effects. Using 51V and 1H NMR spectroscopy, the presence and location of the free ligand, H2shed, and the three V(v) complexes were examined in a model membrane microemulsion system. The stability of the three complexes was measured in aqueous solution, cell media and an inhomogeneous microemulsion system. Our results demonstrated that free ligand H2shed and the intact V(v) complexes associated with the interface but that the V-complexes hydrolyzed to some extent because oxovanadates were observed by 51V NMR spectroscopy and decreasing complex by absorption spectroscopy in cell media. When determining the effects of V(v) catecholate complexes on bone cancer cells, the strongest effects were observed with the more stable hydrophobic complex [VO(Hshed)(dtb)] that was able to best associate and penetrate the model membrane system intact. These studies are consistent with the membrane permeability studies being a good predictor for in vitro cytotoxicity assays because [VO(Hshed)(dtb)] can pass through the cellular membrane intact, which may enhance its anti-cancer activities.

Effects of vanadate on the mycelium of edible fungus Coprinus comatus

Vanadate is proposed to play a pivotal role in application of edible fungus Coprinus comatus for medical purposes. In this study the concentration of extracellular vanadate acceptable for the submerged cultivation of C. comatus mycelium was established. The mycelium could grow, and overcome vanadate toxic effects, up to the concentration of 3.3 mM. Moreover, in this condition, at the end of the exponential phase of growth, biomass yield was almost identical to that in the control. ³¹P NMR spectroscopy showed that addition of 10 mM vanadate to the mycelium in the exponential phase of growth provoked instantaneous increase of a sugar phosphates level which could be related to changes in activities of glycolytic enzymes. Exposure to higher vanadate concentration was toxic for the cell. ⁵¹V NMR measurements revealed that monomer of vanadate is present in the cytoplasm causing the metabolic changes. C. comatus has also capacity for vanadate reduction, as shown by EPR measurements, but vanadyl uptake is significantly less comparing to vanadate.

Decavanadate Inhibits Mycobacterial Growth More Potently Than Other Oxovanadates

51V NMR spectroscopy is used to document, using speciation analysis, that one oxometalate is a more potent growth inhibitor of two Mycobacterial strains than other oxovanadates, thus demonstrating selectivity in its interaction with cells. Historically, oxometalates have had many applications in biological and medical studies, including study of the phase-problem in X-ray crystallography of the ribosome. The effect of different vanadate salts on the growth of Mycobacterium smegmatis (M. smeg) and Mycobacterium tuberculosis (M. tb) was investigated, and speciation was found to be critical for the observed growth inhibition. Specifically, the large orange-colored sodium decavanadate (V10O 28 6 - ) anion was found to be a stronger inhibitor of growth of two mycobacterial species than the colorless oxovanadate prepared from sodium metavanadate. The vanadium(V) speciation in the growth media and conversion among species under growth conditions was monitored using 51V NMR spectroscopy and speciation calculations. The findings presented in this work is particularly important in considering the many applications of polyoxometalates in biological and medical studies, such as the investigation of the phase-problem in X-ray crystallography for the ribosome. The findings presented in this work investigate the interactions of oxometalates with other biological systems.

The interactions of vanadate monomer with the mycelium of fungus Phycomyces blakesleeanus: reduction or uptake?

The possibility of reduction of vanadate monomer in the mycelium of fungus Phycomyces blakesleeanus was investigated in this study by means of polarography. Control experiments were performed with vanadyl [V(IV)] and vanadate [V(V)] in 10 mM Hepes, pH 7.2. Addition of P. blakesleeanus mycelium resulted in disappearance of all V(IV) polarographic waves recorded in the control. This points to the uptake of all available V(IV) by the mycelium, up to 185 µmol/g_FW, and suggests P. blakesleeanus as a potential agent in V(IV) bioremediation. Polarographic measurements of mycelium with low concentrations (0.1-1 mM) of V(V), that only allows the presence of monomer, showed that fungal mycelia removes around 27% of V(V) from the extracellular solution. Uptake was saturated at 104 ± 2 µmol/g_FW which indicates excellent bioaccumulation capability of P. blakesleeanus. EPR, ⁵¹V NMR and polarographic experiments showed no indications of any measurable extracellular complexation of V(V) monomer with fungal exudates, reduction by the mycelium or adsorption to the cell wall. Therefore, in contrast to vanadium oligomers, vanadate monomer interactions with the mycelium are restricted to its transport into the fungal cell, probably by a phosphate transporter.