Two galactomannan preparations from seeds from Mimosa scabrella (bracatinga): Complexation with oxovanadium(IV/V) and cytotoxicity on HeLa cells

Two galactomannans, GALMAN-A and GALMAN-B, were isolated from seeds of Mimosa scabrella (bracatinga), with deactivation and exposure to native enzymes, respectively. They were treated with oxovanadium(IV) and oxovanadium(V), designated (VO2+/VO3+) to form GALMAN-A:VO2+/VO3+ and GALMAN-B:VO2+/VO3+ complexes, respectively. The potentiometric studies provided the binding constants for the complexes and the resulting complexed species were a function of pH. 51V NMR spectra of GALMAN-A:VO2+/VO3+ and GALMAN-B:VO2+/VO3+ at pH 7.8 and at 30 °C indicated the occurrence of two types of complexes formed by oxovanadium ions and galactomannans. GALMAN-A:VO2+/VO3+ and GALMAN-B:VO2+/VO3+ caused loss of HeLa cells viability at concentrations of 50–200 μg/mL. GALMAN-A:VO2+/VO3+ exhibited low toxicity for 24 h, although GALMAN-B:VO2+/VO3+ was extremely toxic, since 50 μg/mL was sufficient to decrease HeLa cell viability after 48 h by 60%. GALMAN-A gave rise to a slight increase in cell proliferation after 48 h at 100 μg/mL, whereas GALMAN-B promoted a slight decrease at concentrations of 50–100 μg/mL. GALMAN-A:VO2+/VO3+ and GALMAN-B:VO2+/VO3+ exhibited a significant decrease in cell proliferation after 48 h, each reaching 60% inhibition at 5–10 μg/mL. The complexes which caused this effect were at concentrations 10 times lower than the uncomplexed polymers.