Caffeine and its main targets of colorectal cancer

Figure 3 The effect of accumulated cAMP and cGMP caused by the inhibition of phosphodiesterase by caffeine. cAMP and cGMP levels are regulated by the balance between the activities of two types of enzymes, the generating enzymes (adenylate cyclase/guanylyl cyclase) and the degrading enzymes (phosphodiesterase). Caffeine can inhibit the degrading enzymes, which causes the accumulation of cAMP and cGMP. The accumulated cAMP and cGMP can interact with many factors and finally may result in a series of events of colorectal cancer cells. cAMP: Cyclic adenosine 3′,5′-monophosphate; cGMP: Cyclic guanosine 3′-5′ monophosphate; AC: Adenylate cyclases; GC: Guanylyl cyclase; PDEs: Phosphodiesterase; PKA: Protein kinase A; VEGF: Vascular endothelial growth factor; TCF: T cell factor.