Gossypol stimulates opening of a Ca2+ - and Na+ -permeable but Ni2+ - and Co2+ -impermeable pore in bEND.3 endothelial cells

Cytotoxicity of Thioalkaloid-Enriched Nuphar lutea Extract and Purified 6,6′-Dihydroxythiobinupharidine in Acute Myeloid Leukemia Cells: The Role of Oxidative Stress and Intracellular Calcium

Acute myeloid leukemia (AML) is an aggressive hematological malignancy characterized by uncontrolled proliferation of immature myeloid progenitors. Here, we report the in vitro antileukemic effects of the sesquiterpene thioalkaloid-enriched fraction of the Nuphar lutea leaf extract (NUP) and a purified thioalkaloid 6,6′-dihydroxythiobinupharidine (DTBN). Treatment with 0.3–10 µg/mL NUP caused a dose- and time-dependent reduction in proliferation and viability of human AML cells (KG-1a, HL60 and U937). This was associated with apoptosis induction manifested by annexin-V/propidium iodide binding as well as cleavage of caspases 8, 9, and 3 as well as poly (ADP-ribose) polymerase. Caspase-dependence of the apoptotic effect was confirmed using the pan-caspase inhibitor Q-VD-OPH. NUP induced significant biphasic changes in the cytosolic levels of reactive oxygen species (ROS) compared to untreated cells—a decrease at early time points (2–4 h) and an increase after a longer incubation (24 h). ROS accumulation was accompanied by lowering the cellular glutathione (GSH) levels. In addition, NUP treatment resulted in elevation of the cytosolic Ca²⁺ (Ca²⁺_cyt) levels. The thiol antioxidant and glutathione precursor N-acetyl cysteine prevented NUP-induced ROS accumulation and markedly inhibited apoptosis. A similar antiapoptotic effect was obtained by Ca²⁺_cyt chelating using BAPTA. These data indicate that NUP-induced cell death is mediated, at least in part, by the induction of oxidative stress and Ca²⁺_cyt accumulation. However, a substantial apoptotic activity of pure DTBN (0.05–0.25 µg/mL), was found to be independent of cytosolic ROS or Ca²⁺, suggesting that alternative mechanisms are involved in DTBN-induced cytotoxicity. Notably, neither NUP nor DTBN treatment significantly induced cell death of normal human peripheral blood mononuclear cells. Our results provide the basis for further investigation of the antileukemic potential of NUP and its active constituents.

Lytic and sublytic effects of gossypol on red blood cells and thymocytes

Gossypol is a natural polyphenol presently considered as a promising biological phytochemical with a range of activities including anticancer. We examined volume regulation-dependent effects of gossypol using erythrocytes and thymic lymphocytes. Gossypol effectively lysed human red blood cells (RBC) with a half-maximal concentration of 67.4 ± 1.6 μmol/L and in a non-colloid osmotic manner. Sublytic gossypol doses of 1-10 μmol/L significantly protected RBC from osmotic hemolysis, but potentiated their sensitivity to the colloid-osmotic lysis induced by a pore-former nystatin. When added to the thymocytes suspension, gossypol caused a strong depression of the ability of cells to restore their volume under hypoosmotic stress with a half-maximal activity at 2.1 ± 0.3 μmol/L. Gossypol suppressed regulatory volume decrease under experimental conditions, when cationic permeability was controlled by gramicidin D, and volume recovery depended mainly on anionic conductance, suggesting that the polyphenol inhibits the swelling-induced anion permeability. In direct patch-clamp experiments, gossypol inhibited the volume-sensitive outwardly rectifying (VSOR) chloride channel in thymocytes and in human HCT116 and HeLa cells, possibly by a mechanism when gossypol molecule with a radius close to the size of channel pore plugs into the narrowest portion of the native VSOR chloride channel. Micromolar gossypol suppressed proliferation of thymocytes, HCT116 and HeLa cells. VSOR blockage may represent new mechanism of anticancer activity of gossypol in addition to its action as a BH3-mimetic.

Gossypol Promotes Bone Formation in Ovariectomy-Induced Osteoporosis through Regulating Cell Apoptosis

Osteoporosis is among the most common forms of age-related diseases, especially for females, which has been a grave public health problem. Drug therapies have shown promising outcomes to promote bone formation and bone density. This study identified a novel potential drug, gossypol, for the treatment of osteoporosis. Treatments of ovariectomy-induced osteoporosis mice with gossypol significantly increased serum osteocalcin and osteoprotegerin (OPG) levels; meanwhile they decreased serum RANKL levels. Microcomputed tomography (microCT) analysis showed that treatment of gossypol improved bone density and strength and decreased bone postyield displacement for both medullar and cortical bones. In vitro experiments also showed that gossypol increased cell viability in a time- and dose-dependent manner. Furthermore, incubation of the osteoblast MC3T3-E1 cells with gossypol inhibited cell apoptosis through intrinsic apoptotic pathway as evidenced by the Annexin V/PI assay, TUNEL assay, biochemical analysis, and western blot assays. Moreover, the classical Wnt/β-catenin signaling pathway was found to be regulated by gossypol treatments. Inhibition of Wnt/β-catenin signaling reversed the prevention effects of gossypol in osteoporosis. Our findings provided novel clues for the treatment of osteoporosis in clinic.