CBS and Alzheimer disease: Thus, cerebral amyloid angiopathy-associated changes in eNOS expression and activity might be linked to dysregulated production of H2S. Indeed, in AD, CBS activity, and H2S production are reduced in the brain (Eto et al., 2002), and plasma H2S levels are negatively correlated with the severity of AD (Giuliani et al., 2013), thus, neuroprotective and angioprotective properties of H2S are reduced (Figure 2).