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.