In this study, we found that chitosan significantly activated PPAR activity in brain and stomach. Microarray analysis of brain and stomach further showed that several pathways involved in glucose and lipid metabolism were affected by chitosan. PPARs are ligand-activated nuclear receptors and key regulators of fatty acid and glucose homeostasis [19], [20]. In vivo and ex vivo imaging showed that maximal luciferase activities were detected in brain and gastrointestinal tract. These data suggested that PPARs were highly expressed in these organs. Previous studies have shown that PPAR activities are activated in brain and gastrointestinal tract, and their activation play important roles in these organs. For examples, in the brain, PPARα plays a major role in acetylcholine biosynthesis and defense against oxidative stress, PPARγ regulates the action of dopamine on the gene transcription, and PPARβ/δ transcriptionally upregulates the acyl-CoA synthetase 2 and mediates the fatty acid utilization [32]. Additionally, the constitutive expression of PPARβ/δ in the gastrointestinal tract is very high compared with other tissues. It plays physiological roles in the homeostatic regulation of intestinal cell proliferation/differentiation and the modulation of
