Detection of asymptomatic nigrostriatal dopaminergic lesion in rats by exhaled air analysis using carbon nanotube sensors

Abstract

The ante-mortem diagnosis of Parkinson's disease (PD) still relies on clinical symptoms. Biomarkers could in principle be used for the early detection of PD-related neuronal damage, but no validated, inexpensive, and simple biomarkers are available yet. Here we report on the breath-print of presymptomatic PD in rats, using a model with 50% lesion of dopaminergic neurons in substantia nigra. Exhaled breath was collected from 19 rats (10 lesioned and 9 sham operated) and analyzed using organically functionalized carbon nanotube sensors. Discriminant factor analysis detected statistically significant differences between the study groups and a classification accuracy of 90% was achieved using leave-one-out cross-validation. The sensors' breath-print was supported by determining statistically significant differences of several volatile organic compounds in the breath of the lesioned rats and the sham operated rats, using gas chromatography combined with mass spectrometry. The observed breath-print shows potential for cost-effective, fast, and reliable early PD detection.

Keywords: Parkinsonism; breath analysis; early diagnosis; nanomaterial; sensor; volatile organic compound.

Figure 1

Amount of dopamine in striatal tissue. Rats treated with the toxin 6-hydroxydopamine (6OHDA 250 μg, by intracerebroventricular injection) showed a 55 ± 5% lower level of dopamine in the striatal tissue homogenate compared to control animals (standard error of the mean, SEM, for 9–10 rats per treatment, ***p < 0.001).

Figure 2

DFA plot of the first canonical variable that was calculated from the responses of two RN-CNT sensors to the 6-OHDA treated rats and the sham operated control animals. Each rat is represented by 1 point in the plot. The standard distribution (SD) of the CV1 values is represented by the error bars. The boxes represent the 95% confidence intervals of the CV1 values, corresponding to 1.96 × SEM.

Figure 3

Abundance of volatile organic compounds (VOCs) that were found in the breath of >80% of both the 6-OHDA treated and sham operated rats. The columns represent the average abundance and the error bars mark the borders of the 90% CIs. The VOCs were tentatively identified.