Urinary Neurotransmitter Patterns Are Altered in Canine Epilepsy

Abstract

Epilepsy is the most common chronic neurological disease in humans and dogs. Epilepsy is thought to be caused by an imbalance of excitatory and inhibitory neurotransmission. Intact neurotransmitters are transported from the central nervous system to the periphery, from where they are subsequently excreted through the urine. In human medicine, non-invasive urinary neurotransmitter analysis is used to manage psychological diseases, but not as yet for epilepsy. The current study aimed to investigate if urinary neurotransmitter profiles differ between dogs with epilepsy and healthy controls. A total of 223 urine samples were analysed from 63 dogs diagnosed with idiopathic epilepsy and 127 control dogs without epilepsy. The quantification of nine urinary neurotransmitters was performed utilising mass spectrometry technology. A significant difference between urinary neurotransmitter levels (glycine, serotonin, norepinephrine/epinephrine ratio, ɤ-aminobutyric acid/glutamate ratio) of dogs diagnosed with idiopathic epilepsy and the control group was found, when sex and neutering status were accounted for. Furthermore, an influence of antiseizure drug treatment upon the urinary neurotransmitter profile of serotonin and ɤ-aminobutyric acid concentration was revealed. This study demonstrated that the imbalances in the neurotransmitter system that causes epileptic seizures also leads to altered neurotransmitter elimination in the urine of affected dogs. Urinary neurotransmitters have the potential to serve as valuable biomarkers for diagnostics and treatment monitoring in canine epilepsy. However, more research on this topic needs to be undertaken to understand better the association between neurotransmitter deviations in the brain and urine neurotransmitter concentrations in dogs with idiopathic epilepsy.

Keywords: biomarker; canine; epilepsy; neurotransmitter; urinary.

Figure 1

Differences in the urinary neurotransmitter profile between dogs with idiopathic epilepsy (IE) (n = 63 dogs/96 samples) and the healthy control group (CTRL) (n = 127 dogs/127 samples). Figure shows an increase of urinary (A) glycine (p ≤ 0.05) and (B) serotonin (p ≤ 0.001) concentrations and a decrease of the (C) norepinephrine/epinephrine ratio (p ≤ 0.05) and the (D) ɤ-aminobutyric acid (GABA)/glutamate ratio (p ≤ 0.01) in dogs affected by idiopathic epilepsy. Data are presented as box-and-whisker plots (the median is represented by the central line, the 25th and the 75th percentile represent the lower and upper limit, and the length of the whiskers represent the 1.5 multiple of the interquartile range). Unpaired two-sided two-sample t-test and Wilcoxon–Mann–Whitney test were used to compare the urinary neurotransmitter excretion between dogs with epilepsy and the healthy control group. *p ≤ 0.05, **p ≤ 0.01 and ***p ≤ 0.001.

Figure 2

Effects of the sex and neutering status on the urinary neurotransmitter profile of dogs with idiopathic epilepsy (IE) compared to the healthy control group (CTRL). (A) Glycine levels differ significantly in neutered females (nf) (p ≤ 0.05) (IE: n = 22 dogs/31 samples vs. CTRL: n = 39 dogs/39 samples). (B) Serotonin levels differ significantly in intact males (m) (p ≤ 0.01) (IE: n = 11 dogs/18 samples vs. CTRL n = 21 dogs/21 samples), neutered males (nm) (p ≤ 0.001) (IE: n = 24 dogs/37 samples vs. CTRL n = 33 dogs/33 samples) and neutered females (p ≤ 0.001) (IE: n = 22 dogs/31 samples vs. CTRL n = 39 dogs/39 samples). (C) The norepinephrine/epinephrine ratio differs significantly in neutered females (p ≤ 0.05) (IE: n = 22 dogs/31 samples vs. CTRL n = 39 dogs/39 samples). (D) The ɤ-aminobutyric acid (GABA)/glutamate ratio differs significantly in intact males (p ≤ 0.05) (IE: n = 11 dogs/18 samples vs. CTRL n = 21 dogs/21 samples) and neutered females (p ≤ 0.05) (IE: n = 22 dogs/31 samples vs. CTRL n = 39 dogs/39 samples). In intact females (f) no significant difference (NS.) of all analysed neurotransmitter between the groups was found (IE: n = 5 dogs/9 samples vs. CTRL n = 21 dogs/21 samples). Data are presented as box-and-whisker plots (the median is represented by the central line, the 25th and the 75th percentile represent the lower and upper limit, and the length of the whiskers represent the 1.5 multiple of the interquartile range). Unpaired two-sided two-sample t-test and Wilcoxon–Mann–Whitney test were used to compare the urinary neurotransmitter excretion between dogs with epilepsy and the healthy control group. *p ≤ 0.05, **p ≤ 0.01 and ***p ≤ 0.001.

Figure 3

Influence of the antiseizure drug treatment on the urinary neurotransmitter profile. (A) Urinary serotonin concentration compared between treated (n = 56 dogs/89 samples) and untreated dogs (n = 7 dogs/7 samples) affected by idiopathic epilepsy (p ≤ 0.05). (B) Multiple group comparison of the urinary serotonin excretion between treated (n = 56 dogs/89 samples) and untreated dogs (n = 7 dogs/7 samples) with idiopathic epilepsy and the healthy control group (ctrl) (n = 127 dogs/127 samples). (C) Urinary ɤ-aminobutyric acid (GABA) concentration compared between treated (n = 56 dogs/89 samples) and untreated dogs (n = 7 dogs/7 samples) with idiopathic epilepsy (p ≤ 0.05). (D) Multiple comparisons of the urinary ɤ-aminobutyric acid excretion between treated (n = 56 dogs/89 samples) and untreated dogs (n = 7 dogs/7 samples) with idiopathic epilepsy and the healthy control group (n = 127 dogs/127 samples). Data are presented as box-and-whisker plots (the median is represented by the central line, the 25th and the 75th percentile represent the lower and upper limit, and the length of the whiskers represent the 1.5 multiple of the interquartile range). Unpaired two-sided two-sample t-test and Wilcoxon–Mann–Whitney test were used for group comparison. For multiple group comparisons a one-way analysis of variance (ANOVA) and a Games-Howell post-hoc test with the Holm correction was utilised. *p ≤ 0.05.