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

The immunomodulatory activity of degradation products of Sesbania cannabina galactomannan with different molecular weights

Galactomannan (GM) is widely recognized as an immune enhancer; however, the underlying molecular mechanism is still unknown. Herein, four products with molecular weights in descending order, namely GM40, GM50, GM65, and GMOS, were separated from incomplete degradation products of Sesbania cannabina GM by ethanol precipitation, followed by their immunomodulatory activity. Through FTIR and XPS spectra, the amount of free hydroxyl groups was shown to decrease in the following order: GM > GM50 > GMOS > GM40 > GM65. Moreover, the immunomodulatory activity of different products decreased in abovementioned order. The TNF-α, IL-6 and TLR4 content in RAW 264.7 cells treated with different GM products in the presence or absence of TAK-242 (TLR4 inhibitor) suggested that the immunomodulatory activity of GM and its degradation products is TLR4-dependent. Overall, the preliminary relationship indicated here between the hydroxyl groups or the possible deeper structural changes of GM and the immunomodulatory activity need to be further investigated.

Cytotoxic effect of xyloglucan and oxovanadium (IV/V) xyloglucan complex in HepG2 cells

It is well known that the chemical structure of polysaccharides is important to their final biological effect. In this study we investigated the cytotoxic effect of xyloglucan from Copaifera langsdorffii seeds (XGC) and its complex with oxovanadium (XGC:VO) on hepatocellular carcinoma cells (HepG2). After 72 h of incubation, XGC and XGC:VO (200 μg/mL) reduced cell viability in ~20% and ~40%, respectively. At same conditions, only XGC:VO increased in ~20% the LDH enzyme release. In permeabilized cells, incubated with XGC and XGC:VO (200 μg/mL) for 72 h, NADH oxidase activity was reduced by ~45% with XGC and XGC:VO. The succinate oxidase activity was reduced by ~35% with XGC and ~65% with XGC:VO, evidencing that polysaccharide complexation with vanadium could intensify its effects on the respiratory chain. According to this result, the mitochondrial membrane potential was also reduced by ~9% for XGC and ~30% for XGC:VO, when compared to the control group. Interestingly, ATP levels were more elevated for XGC:VO in respect to XGC, probably due the enhance in glycolytic flux evidenced by increased levels of lactate. These results show that the xyloglucan complexation with oxovanadium (IV/V) potentiates the cytotoxic effect of the native polysaccharide, possibly by impairment of oxidative phosphorylation.

Are Structurally Modified Galactomannan Derivatives Biologically Active?

Galactomannans are versatile macromolecules with broad industrial potential. The influence of changes in the chemical structures and respective bioactivities of these polysaccharides have been extensively studied. The derivatives obtained by sulfation, complexation, and phosphorylation are the most studied biological properties in galactomannans. The derivatives obtained have shown several pharmacological activities such as antiviral, antimicrobial, anticoagulant, fibrinolytic, chemopreventive, anticancer, antioxidant, chondroprotective, analgesic, immunomodulatory, and antileishmanial. Considering the relevance of these studies, we aim to provide an overview of studies that apply galactomannan modification or derivatization strategies to improve their properties for applications in the biomedical area. We identified the success of most modified galactomannans for pharmacological purposes. However, some studies found loss of bioactivity of the original polysaccharide after chemical changes to its original structures.

Hypoxia protects against the cell death triggered by oxovanadium-galactomannan complexes in HepG2 cells

BACKGROUND

Polysaccharides from various sources have been used in traditional medicine for centuries. The beneficial pharmacological effects of plant-derived polysaccharides include anti-tumor activity.

METHODS

Here, we evaluated the anti-cancer effect of the MSAGM:VO complex under hypoxic conditions (1% oxygen). MSAGM:VO is a complex of the hydrolysate of galactomannan (MSAGM) from Schizolobium amazonicum with oxovanadium (IV/V). The hepatocellular carcinoma (HCC) cell line HepG2 was selected as HCC are one of the most hypoxic solid tumors.

RESULTS

Our results showed that the strong apoptotic activity of MSAGM:VO observed in HepG2 cells under normoxic conditions was completely lost under hypoxic conditions. We found a dynamic balance between the pro- and anti-apoptotic members of the Bcl-2 protein family. The expressions of anti-apoptotic Mcl-1 and Bcl-XL increased in hypoxia, whereas the expression of pro-apoptotic Bax decreased. MSAGM:VO strongly induced autophagy, which was previously characterized as a pro-survival mechanism in hypoxia. These results demonstrate total elimination of the anti-cancer activity of MSAGM:VO with activation of autophagy under conditions of hypoxia.

CONCLUSION

Although this study is a proof-of-concept of the impact of hypoxia on the potential of polysaccharides, further study is encouraged. The anti-tumor activity of polysaccharides could be achieved in normoxia or through raising the activity of the immune system. In addition, combination strategies for therapy with anti-autophagic drugs could be proposed.

Leishmanicidal activity of polysaccharides and their oxovanadium(IV/V) complexes

The parasites of the genus Leishmania cause a range of leishmaniasis diseases, whose treatment is impaired due to intramacrophage parasites living in the mammalian host. Immunostimulation has been considered an important strategy to leishmaniasis treatment. The immunomodulatory effects of the polysaccharides arabinogalactan (ARAGAL), galactomannan (GMPOLY), and xyloglucan (XGJ), as well as their oxovanadium (IV/V) complexes (ARAGAL:VO, GMPOLY:VO, and XGJ:VO) were evaluated on peritoneal macrophages. At 25 μg/mL of GMPOLY:VO and of XGJ:VO, and 10 μg/mL of ARAGAL:VO, nitric oxide (NO) production by the macrophages was not altered compared with the control group. All polymers increased the production of interleukins 1 beta and 6 (IL-1β and IL-6), but the oxovanadium complexes were more potent activators of these mediators. ARAGAL:VO 10 μg/mL, GMPOLY:VO and XGJ:VO 25 μg/mL led to an increase of 562%, 1054%, and 523% for IL-1β, respectively. For IL-6 at the same concentration, the levels increased by 539% and 794% for ARAGAL:VO and GMPOLY:VO, respectively. Polysaccharides and their oxovanadium complexes exhibited important leishmanicidal effects on amastigotes of Leishmania (L.) amazonensis. The native and complexed polymers reduced the growth of promastigote-form Leishmania by ∼60%. This effect was reached at concentrations 12 times lower than that observed for Glucantime (300 μg/mL promoted an inhibition of ∼60%). The 50% inhibitory concentration (IC50) values for the complexes were determined. XGJ:VO showed the lowest IC50 value (6.2 μg/mL; 0.07 μg/mL of vanadium), which for ARAGAL:VO was 6.5 μg/mL (0.21 μg/mL of vanadium) and 7.3 μg/mL (0.06 μg/mL of vanadium) for GMPOLY:VO. The upregulation of IL-1β and IL-6 release and downregulation of NO production by macrophages and the important leishmanicidal effect are essential to stablish their potential use against this pathology.