CAT and Parkinson disease: For exosomal small molecular substances, most studies have focused on the loading of chemotherapeutic drugs in exosome, such as incubation of paclitaxel with mesenchymal stem cell (MSC)-derived exosomes to inhibit tumor growth (Pascucci et al., 2014), catalase loading into exosomes to treat Parkinson’s disease (PD) (Haney et al., 2015).