Testing P450 Enzyme Activity in Blood May Allow for Early Diagnosis
A blood test that assesses how the activity of a group of enzymes, called P450s, changes when they are blocked could be useful for diagnosing Parkinson’s disease in early stages, according to a new study.
“Effective diagnostic systems and biomarkers for patients without subjective motor symptoms have not yet been established. Consequently, the poor diagnostic options for [Parkinson’s] delay the development of therapeutic approaches and medication,” the researchers wrote.
Cytochrome P450s (abbreviated CYPs or P450s) are a group of enzymes that help to coordinate numerous metabolic processes — collectively, the various P450s are known to act on at least 3,000 different molecules. The activity of these enzymes may be altered under inflammatory or disease conditions.
Scientists in Japan previously devised a test, or assay, to assess levels of various P450-related molecules in serum, the non-cell part of blood.
Simply put, this assay involved P450 enzymes expressed by bacteria, which were treated with a sample of serum alongside a fluorescent molecule that the enzyme can break down. The researchers could then track changes in fluorescence levels as a proxy for measuring enzyme activity, and observe how the activity changes in different samples.
The scientists had used the assay to differentiate between various inflammatory conditions in mice. Now, they evaluated whether it might be a useful blood test for a Parkinson’s diagnosis.
“We hypothesized that the P450 inhibition assay can discriminate [serum samples] between patients with PD and healthy individuals,” the team wrote.
A first test used serum from healthy rats and rats in a Parkinson’s model. Compared with their healthy counterparts, the Parkinson’s rats showed significant alterations in inhibition dynamics for four of the P450s: specifically, CYP2A13, CYP2C18, CYP3A4, and CYP3A5.
To determine whether these differences could distinguish between rats with or without Parkinson’s, the researchers applied a statistical test called the area under the receiver operator characteristic curve (AUC). This test measures how well a metric — in this case, results from the inhibition, or blocking, assay — can tell the difference between two groups (i.e., those with Parkinson’s or not). AUC values can range from 0.5 to 1, with higher values reflecting a better ability to distinguish between the groups.
AUC values for each of the four P450s altered in Parkinson’s rats ranged from 0.814 to 0.914. Further statistical tests showed that rates of inhibition for two of the enzymes — CYP2A13 and CYP2A18 — correlated with levels of motor dysfunction.
Next, the researchers used the assay to analyze 20 serum samples from Parkinson’s patients, as well as 20 samples from healthy volunteers. Here, inhibition rates for three P450s — CYP1A1, CYP2C8, and CYP3A5 — were significantly altered in the Parkinson’s patients.
AUC values for each of these three enzymes individually ranged from 0.740 to 0.775. A further analysis that used both CYP1A1 and CYP2C8 yielded an AUC of 0.910, which suggests “that the P450 inhibition assay may be applicable for PD diagnosis in humans,” the researchers wrote.
Additional analyses showed that inhibition rates for all three of these P450s correlated with Parkinson’s severity as measured by stage on the Hoehn and Yahr scale.
These findings in patients largely parallel the initial results in rats, though the researchers noted that “the inhibition rates determined using rat and human sera were completely different,” which likely reflects species-to-species differences in P450 activities.
In further analyses, the researchers also used the assay to evaluate 19 samples from people with Alzheimer’s disease and 10 from people with type 2 diabetes. Inhibition rates for several P450s differed in people with Parkinson’s or diabetes, and inhibition rates for one of the enzymes — CYP3A4 — was significantly different between Parkinson’s and Alzheimer’s patients.
“These results indicate that the P450 inhibition assay can detect PD-specific changes that differentiate it from other neurodegenerative [Alzheimer’s] and inflammatory [type 2 diabetes] diseases,” the researchers wrote.
They also noted that all disease samples showed marked differences from those of healthy people, suggesting the P450 inhibition assay could be useful in diagnosing Alzheimer’s and type 2 diabetes as well.
The scientists stressed that this was a preliminary study with small sample sizes, so further work is needed to validate its results.
“This study preliminarily demonstrated the possibility of a novel diagnosis system, P450 inhibition assay, which can be used for [Parkinson’s] diagnosis,” they concluded.