Supplementary file 4_Dracaena trifasciata (Prain) Mabb leaf extract protects MIN6 pancreas-derived beta cells against the diabetic toxin streptozotocin: role of the NF-κB pathway.pdf

BackgroundDracaena trifasciata (Prain) Mabb. [Asparagaceae; also known as Sansevieria trifasciata Prain (ST)] may have health-promoting activities, including resolution of diabetes mellitus (DM). This in vitro study evaluated whether and how a leaf extract of ST could directly protect pancreas-derived MIN6 cells against the diabetogenic toxin streptozotocin (STZ).
MethodsComposition of the ST extract (by 100% methanol) was investigated using high resolution mass spectrometry, which revealed several compounds with beneficial bioactive efficacy. MIN6 cells were exposed to 50% lethal dose of STZ, with or without ST extract. Cell viability was assessed using the MTT method. Inflammatory activity of ST extract was assessed in MIN6 cells and macrophage-like RAW cells, and addition of TNF-α to combinations of ST and STZ were tested on MIN6 cell viability. The role of the NF-κB pathway in effects of STZ and ST were investigated using the proteosome inhibitor MG132.
ResultsExposure of MIN6 cells to the ST extract (in concentrations that did not notably affect MIN6 cells: 5-15 mg/mL) was indeed able to minimize STZ-induced toxicity in MIN6 cells. Exposing macrophage-like RAW cells to ST extract (at 10-15 mg/mL) increased TNF-α gene expression, and this response was highly augmented by co-exposure to lipopolysaccharide (LPS, 1.0 mg/mL), indicating that ST extract contained inflammatory compounds too. The implication of this finding was investigated by exposing MIN6 cells to a subthreshold dose (100 ng/mL) of TNF-α, which 1) prevented the protective effect of the ST extract (10-15 mg/mL) against STZ toxicity, and 2) caused ST to become toxic to MIN6 cells even without the presence of STZ. TNF-α is known to activate the NF-κB pathway leading to cell death, however, NF-κB is also known to stimulate cell proliferation and survival. To investigate the relevance of the NF-κB pathway in our findings, we treated MIN6 cells with the proteasome inhibitor MG132 (at doses ≥0.2 μM), and observed that ST extract was no longer able to block STZ toxicity in MIN6 cells (p < 0.05), and to block CIAP2 expression, an anti-apoptotic target downstream from NF-κB.
ConclusionThese data suggest that a leaf extract of ST has anti-diabetogenic efficacy, which may depend on the integrity of the NF-κB pathway. This protective effect appears to be impeded in a pro-inflammatory environment.