Cerebrospinal Fluid Levels of Angiotensin-converting Enzyme, Acetylcholinesterase, and Dopamine Metabolites in Dementia Associated with Alzheimer's Disease and Parkinson's Disease: a Correlative Study

Mean levels of the two hydrolases angiotensin-converting enzyme (ACE) and acetylcholinesterase (AChE), the dopamine metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), and total protein concentration were examined in cerebrospinal fluid (CSF) samples from a group of patients with dementia of the Alzheimer's type, a group of comparably demented patients with Parkinson's disease, and a neurologically healthy elderly control group. Both pathological groups exhibited a significant decrease in the mean levels of ACE activity and DOPAC per milliliter and were distinguishable from one another based on mean CSH HVA levels. Unlike the Parkinson's disease group, whose mean concentration of HVA was lower than, but not significantly different from that of the control group, the mean HVA concentration of the Alzheimer's disease group was significantly elevated. In contrast, comparisons of the mean CSF AChE activity (expressed per milliliter or per milligram of protein) and CSF total protein concentration did not reveal significant differences for any of the groups. Independent of CSF protein concentration, ACE activity per milliliter exhibited a positive correlation with AChE activity per milliliter within the control and Parkinson's disease groups, whereas a statistically significant correlation for these CSF hydrolases was not observed within the Alzheimer's disease group. Thus, the CSF profiles for patients with mild dementias associated with Alzheimer's or Parkinson's disease differed by at least two neurochemical criteria. Based on the levels of ACE activity, DOPAC, and HVA per milliliter of CSF, two discriminant functions were derived and resulted in the correct classification of 71% of all subjects (n = 38) into Alzheimer's disease, Parkinson's disease, and neurologically healthy control groups.