Fenugreek lactone attenuates palmitate-induced apoptosis and dysfunction in pancreatic β-cells

Figure 1 Viability of pancreatic NIT-1 β-cells exposed to various concentrations of palmitic acid (A) and fenugreek lactone (B). To select the appropriate concentration of palmitate (PA), dose-response experiments were conducted (A). When NIT-1 cells were cultured in medium with 0.25 mmol/L PA for 24 h, the survival rate was between 60%-70%. (B) NIT-1 cells were treated with various concentrations of fenugreek lactone (FL) (0.01-10 μmol/L) for 24 h. The maximum non-toxic concentration of FL is 1 μmol/L. Data represent the mean ± SD. ^bP < 0.01 vs PA group.

Figure 2 Effects of fenugreek lactone on palmitate-induced lipid accumulation in NIT-1 pancreatic β-cells. A-C: Oil Red O staining of lipid droplets showed that palmitate (PA) induced a palpable increase in lipid accumulation, which was inhibited by the fenugreek lactone (FL) treatment (A: Control group; B: PA group; and C: FL-treated group); D: Intracellular triglyceride (TG) content extracted from NIT-1 cells. FL decreased intracellular TG content in NIT-1 pancreatic β-cells compared with PA group. CON refers to control group, PA refers to palmitic acid intervention group and FL refers to FL-treated group. Data are reported as the mean ± SD (n = 4). ^bP < 0.01 vs control group; ^dP < 0.01 vs PA group.

Figure 3 Effects of fenugreek lactone on glucose stimulated insulin secretion in NIT-1 pancreatic β-cells exposed to palmitate. Insulin content in the supernatant was measured using a radio-immunoassay kit after the treatment. Insulin concentration was corrected with cell numbers. Data represent the mean ± SD from six wells. ^bP < 0.01 vs control group; ^dP < 0.01 vs PA alone. PA: Palmitate; FL: Fenugreek lactone.

Figure 4 Effects of fenugreek lactone on caspase-3 viability in NIT-1 islet β-cells exposed to palmitate. Each bar represents mean ± SD; ^bP < 0.01 vs control group; ^dP < 0.01 vs PA group. PA: Palmitate; FL: Fenugreek lactone.

Figure 5 Comparison of apoptosis rates of NIT-1 cells by flow cytometry in different groups. A: Control group; B: PA intervention group; C: FL-treated group; D: Data are reported as the mean ± SD of percentages from four wells. ^bP < 0.01 vs control group; ^dP < 0.01 vs PA group. PA: Palmitate; FL: Fenugreek lactone.

Figure 6 Effects of fenugreek lactone on protein expression of protein kinase C-α, P-protein kinase C-α and p47phox in NIT-1 β-cells exposed to palmitate. Each bar is described as corresponding proteins/β-actin. FL supplementation inhibited the expression of above mentioned proteins. Representative gels and protein levels for (A) p47phox and PKC-α or P-PKC-α (B) were measured by Western blot in NIT-1 pancreatic β-cells. Data are shown as the mean ± SD. ^aP < 0.01 vs control group; ^bP < 0.01 vs PA group; ^dP< 0.01 vs PA group. PA: Palmitate; FL: Fenugreek lactone.

Figure 7 Effects of fenugreek lactone on mRNA levels of protein kinase C (A) and p47phox (B) in NIT-1 β-cells. Each bar represents mean 2^-ΔΔCT± SD (n = 3). ^bP < 0.01 vs control group; ^dP < 0.01 vs PA group; ^aP < 0.05 vs PA group. PA: Palmitate; FL: Fenugreek lactone.