Figure 7.

Visualizing the anti-mitochondrial effects of Metformin in human breast cancer tumor tissue. Frozen sections from human breast cancers were subjected to mitochondrial Complex I (NADH) activity staining. NADH-positive cells are positively stained blue (see red arrows). In breast cancers, note that the tumor stroma is glycolytic and is NADH-negative, while epithelial tumor cell nests are oxidative and are NADH-positive. Note that treatment with Metformin, a known complex I inhibitor, prevented the NADH-staining of epithelial cancer cell nests. Positive controls with skeletal muscle were performed in parallel to ensure the specificity of the staining procedure and allowed us to detect complex I-positive muscle fibers (blue), which represent oxidative slow-twitch fibers. Reproduced and modified with permission from reference ¹⁴.