Figure 2. Piperine increases AMPK phosphorylation by mitochondrial oxygen consumption.

(A) ¹H-NMR-based metabolic profiling analysis shows the intensity of adenosine phosphates ATP, ADP, and AMP in piperine-treated or untreated cell metabolite extracts. (B) AMP:ATP ratio from ¹H-NMR spectral intensities. (C) C2C12 cells were treated with 30 μM piperine or 10 mM metformin for 24 h. The cells were lysed with ATP assay buffer, and the amount of ATP was evaluated by colorimetric absorbance assay. Metformin was used as a positive control. (D) C2C12 cells were treated with 30 μM piperine or 10 mM metformin for 24 h. Mitochondrial oxygen consumption rate (OCR) was measured using an XF24 analyzer. Metformin was used as a positive control. (E) C2C12 cells were treated with indicated doses of piperine for 24 h. Mitochondrial oxygen consumption rate (OCR) was measured using an XF24 analyzer. *P < 0.05 compared with the untreated cells. Results from three independently replicated experiments. (F) C2C12 cells were treated with indicated doses of piperine for 24 h. Cell viability was analyzed with MTT assay. Results from three independently replicated experiments. *P < 0.05, **P < 0.01 compared with the untreated cells. Results from three independently replicated experiments. Cropped images of full-length blots are shown.