1. Introduction
Migraine is the fifth (second in young women) cause of disability worldwide, but despite its high prevalence, it is undiagnosed and untreated [
1]. This may result from poor knowledge of the mechanisms of migraine pathogenesis, which, in turn, may be a consequence of the restricted availability of the disease target tissue and limited value of animal models of human migraine as they reflect some aspects of the migraine syndrome and not the entire spectrum of symptoms [
2]. Therefore, there is still a need for studies to expand current knowledge on the molecular mechanisms of migraine pathogenesis.
Migraine is a complex disease with many symptoms and many factors playing a role in its pathogenesis and these issues have been addressed in several excellent reviews, e.g., [
3]. In general, the activation and sensitization of the trigeminal system may be crucial for migraine headache induction (reviewed in [
4]).
Tryptophan (TRP) metabolism can be implicated in the pathogenesis of neurological and psychiatric disorders (reviewed in [
5]). Tryptophan was reported to be associated with migraine in several studies, but their results are inconsistent as they were performed in different types and phases of migraine (reviewed in [
6]). A negative correlation between dietary intake of TRP and migraine risk was observed [
7]. However, TRP is a precursor of several biologically active substances that may be responsible for the observed associations of migraine with TRP.
After intake, the majority of TRP is metabolized in the digestive tract in the kynurenine (KYN), serotonin (5-HT), and indole pathways that are competitively initiated by indoleamine 2,3-dioxygenase (IDO-1), TRP hydroxylase and bacterial TRPase (TNA), respectively [
8]. 5-Hydroxyindoleacetic acid (5-HIAA) is the main metabolite of serotonin produced by the action of monoamine oxidase and aldehyde dehydrogenase and excreted in the urine [
9]. Consequently, 5-HIAA is employed to determine serotonin levels in the body.
The KYN pathway of TRP metabolism gains an emerging role in migraine pathogenesis which is supported by its involvement in the pathogenesis of functional gastrointestinal diseases and the functioning of the gut-brain-microbiota axis [
6,
10,
11,
12].
Although most of the ingested TRP is metabolized in the KYN pathway, 5-HT has an established role as a neurotransmitter and consequently is a natural candidate to play a role in migraine pathogenesis. This is supported by the identification of 5-HT as a blood vasoconstrictor, fitting the role of neurovascular incidence in the causative role of the trigeminal system in migraine pathogenesis [
13]. Moreover, 5-HT receptors are widely distributed in the brain, including areas that are important in migraine [
14]. The agonists of the 5-HT1 serotonin receptor have a long history of anti-migraine drugs [
15]. Furthermore, serotonin is the precursor for the synthesis of melatonin in the pineal gland and melatonin may exert beneficial effects in migraine preventive and abortive treatment [
16].
In this work, we investigated the urinary levels of TRP and its main metabolites: 5-HIAA, KYN, kynurenic acid (KYNA), and quinolinic acid (QA) in the 5-HT and KYN pathways in migraine patients and controls. Our working hypothesis was that the serotonin pathway of TRP metabolism evaluated by the urinary level of 5-HIAA might play a role in migraine pathogenesis. To verify this hypothesis, we associated some migraine characteristics related to the severity of the disease and its timing with the urinary concentration of 5-HIAA in migraine patients.
Migraine is frequently reported to be associated with mood disorders, symptoms of anxiety, and depression [
17,
18]. On the other hand, tryptophan metabolism may be implicated in mental health [
19]. It was postulated that migraine patients with 3 or more headache days per month should be screened for anxiety symptoms [
20]. Therefore, we looked for a correlation between the concentration of TRP metabolites and some indicators of anxiety and depression.
3. Discussion
In the present work, we showed that patients with episodic migraine displayed different urinary levels of the TRP metabolites 5-HIAA, KYN, KYNA, and QA as compared with the controls. Consequently, the patients were characterized by different values of the KYN/TRP, KYNA/KYN, and KYNA/QA ratios. No differences were observed for the urinary levels of TRP and the 5-HIAA/TRP ratio. On the other hand, urinary concentration of 5-HIAA was negatively correlated with MIDAS score, MMD, MHD, and MIDAS score and MMD were also negatively correlated with the 5-HIAA/TRP ratio. Furthermore, a negative correlation of PHQ-9 with urinary 5-HIAA was observed.
The routine diagnosis of migraine is based on the reporting of symptoms by patients asked by a physician and the allocation of their answers on the scale(s) used by the physician. Therefore, such a diagnosis is subjective and so it is difficult to standardize the criteria for migraine diagnosis. Several indicators are postulated to be associated with migraine and so they can support the disease diagnosis. In general, migraine is considered a complex disease with its pathogenesis underlined by the interaction of genetic and environmental factors. Genetic markers are proposed in monogenic migraines, including familial hemiplegic migraine and migraine with aura associated with hereditary small-vessel disorders [
28]. Despite significant progress in genome analysis, the association of genetic factors with common migraine is still a big challenge [
29]. Moreover, these markers are more useful in migraine therapy than diagnosis. At present, neuroimaging cannot be considered a routine method in common migraine diagnosis and is recommended in migraine with specific, rare symptoms (reviewed in [
30]). Therefore, there is a need to establish migraine markers that could support the routine diagnosis of the disease.
In our work, we pointed out a non-invasive, easy-to-determine parameter, 5-HIAA, which correlated with certain characteristics of migraine. Surely, it cannot be considered an independent marker of migraine, but its informative potential may be high as this TRP metabolite is excreted with urine. Our results suggest that 5-HIAA is strongly associated with migraine as it was correlated, either singly or in combination with TRP with several migraine attributes, including MIDAS score MMD, MHD, and additionally with PHQ-9 scores.
Other studies associating migraine with 5-HIAA produced various results. However, we have not found any recent study on this subject. 5-HIAA is a representative of 5-hydroxyindoles (5-HIs), which were reported to fall during headache attacks in the blood of 17 out of 20 migraine patients [
31]. However, another study performed on 14 migraine patients showed that urine concentrations of 5-HT and 5-HIAA fluctuated during and after migraine attacks [
32]. The results of 5-HIAA variation were confirmed in a subsequent study performed in cerebrospinal fluid [
33]. However, a 1976 study showed a significant increase in urine excretion of 5-HIAA during the early headache stage and the lack of correlation between some migraine characteristics and the levels of 5-HIAA in cerebrospinal fluids of migraine patients and a positive correlation with others [
27]. A study with 9 migraine patients and 4 controls did not show any significant changes in the urine 5-HIAA in migraine patients relative to control individuals [
34]. It was shown that migraine patients displayed lower plasma 5-HT and higher 5-HIAA levels than controls and patients with tension headaches [
35]. However, during migraine attacks, plasma 5-HIAA concentrations were lower than in controls. A study performed on 8 migraine patients and 10 tension-type headache sufferers showed significantly decreased levels of 5-HIAA in the urine of both groups as compared with controls [
36]. Another study showed increased concentrations of serum 5-HIAA between attacks of migraine with aura and at the beginning of attacks of both migraine with and without aura [
37]. Urinary level of 5-HIAA was observed not to change in young men but it decreased in female migraine patients when compared with their sex-matched controls [
38]. No association was observed between 5-HIAA excretion and the characteristics of migraine. In summary, there are few studies investigating the urine level of 5-HIAA in migraine patients and the results of these studies are inconsistent and the most likely reasons for this inconsistency may be fluctuations of 5-HIAA levels during the disease course of different types of migraine and weak statistical power of those studies.
We observed a high interindividual variability among migraine patients in their responses to questions of questionnaires and no functional dependence was observed between scores following the answers and the levels of 5-HIAA, i.e., a single 5-HIAA concentration was measured in a few patients, but they differently responded to the questionnaire questions. This was especially striking when a regression line was drawn along with individual results. This underlines a need for more objective criteria for migraine characteristics.
Migraine is frequently associated with symptoms of anxiety and/or depression (reviewed in [
39,
40]). This association is reported as bidirectional, i.e., migraine headaches may increase the risk of anxiety/depression and vice versa [
41,
42]. Therefore, there is a need to identify these migraine patients who require special psychiatric care. Our study showed that PHQ-9 scores were correlated with urinary 5-HIAA levels and therefore its determination may help to identify such patients. However, our results based on a single self-reported questionnaire cannot determine any role of 5-HIAA in migraine-associated mental disorders as it would require performing special psychological examinations by specialized personnel. However, several studies showed fluctuations in 5-HIAA levels in neurological and psychiatric disorders (reviewed in [
43]). Therefore, the result we obtained may be considered a small contribution to the link between migraine and mental disorders suggesting that TRP metabolism in general, and 5-HIAA in particular, may contribute to the mechanism underlying that association. However, it is not justified to widely discuss our results in a comparison with other studies performed with specialized methods.
In our previous works, we considered tryptophan metabolism in the context of the gut-brain-microbiota axis [
44,
45,
46,
47]. However, those studies were performed on hospital patients, but this study enrolled patients of an outpatient clinic and most of them were not willing to donate blood or undergo the examination of the gut and the microbiota.
The two most important limitations of our study are the small number of enrolled individuals and the lack of standardization of TRP intake. The small number of individuals in our study resulted in a moderate statistical power of the tests we employed to analyze our data. However, we employed the resampling bootstrap technique to lower the chance of accepting a false hypothesis. We want to underline that many studies we cited in our discussion, published in highly impacted journals, enrolled even fewer patients than we did. Moreover, it could be considered that the determination of the sample size before research may not be the best solution, as it depends on the test that is to be used, which, in turn, depends on the distribution of data. We could not increase the number of patients due to limited financial and human resources, but the number of individuals in our cohort was in the typical range for 5’-HIAA/headache/migraine studies published so far.We did not interfere with the diet of enrolled individuals, but we did not observe any difference between the urine concentration of TRP in the patients and the control groups and also the 5’-HIAA/TRP ratio was the same in both groups. Another limitation of our study is not to measure the level of 3-hydroxykynurenine, a product of the KYN pathway of TRP metabolism, especially since this molecule is reported to exert a dual, pro- or anti-oxidative action in the central nervous system [
48]. Moreover, increased conversion of TRP to KYN with a decrease of KYNA/QA ratio suggests that the level of 3-hydroxykynurenine might change [
49].
Although we did not observe changes in the KYN, KYNA, and QA levels, we cannot exclude alterations in the kynurenine pathway of TRP metabolism in our patients, as we did not measure the level of all metabolites of that pathway. In particular, 3-hydroxykynurenine levels were not measured. More evidence on the role of the KYN pathway of TRP metabolism in migraine and headaches can be found in other works, e.g., [
50,
51,
52,
53].
Although our study was conducted in the interictal phase of migraine, there is emerging evidence that symptoms associated with the headache phase may persist between migraine attacks [
54]. These symptoms include allodynia, hypersensitivity, photophobia, phonophobia, osmophobia, visual/vestibular disturbances, and motion sickness. Therefore, the interictal phase of migraine should be further investigated to identify all migraine-related factors that may lower the quality of patients life.
In summary, the urinary concentration of 5-HIAA may be considered a marker of episodic migraine in the interictal period and may serve to identify these migraine patients who are at increased risk of migraine-associated mental disorders.
Figure 1.
Tryptophan (TRP) and its main metabolites in migraine patients and controls. Urinary levels of tryptophan (TRP), 5-hydroxyaminoacetic acid (5-HIAA), kynurenine (KYN), kynurenic acid (KYNA), and quinolinic acid (QA) were expressed in milligrams per gram of creatinine (mg/gCr). The results are presented as median with boxes representing I and III quartiles and whiskers representing Min to Max values. Differences between migraine patients and controls were analyzed by U Mann–Whitney test; n = 21 in migraine patients group and n = 32 in controls; *—p < 0.05; **—p < 0.01; ***—p < 0.001 as compared with controls.
Figure 1.
Tryptophan (TRP) and its main metabolites in migraine patients and controls. Urinary levels of tryptophan (TRP), 5-hydroxyaminoacetic acid (5-HIAA), kynurenine (KYN), kynurenic acid (KYNA), and quinolinic acid (QA) were expressed in milligrams per gram of creatinine (mg/gCr). The results are presented as median with boxes representing I and III quartiles and whiskers representing Min to Max values. Differences between migraine patients and controls were analyzed by U Mann–Whitney test; n = 21 in migraine patients group and n = 32 in controls; *—p < 0.05; **—p < 0.01; ***—p < 0.001 as compared with controls.
Figure 2.
Ratios of urinary levels of 5-hydroxyaminoacetic acid (5-HIAA) and kynurenine (KYN) to tryptophan (TRP), KYN to kynurenic acid (KYNA), and KYNA to quinolinic acid (QA) in migraine patients and controls. Results are presented as the median with boxes representing I and III quartiles and whiskers representing Min to Max values. Differences between migraine patients and controls were analyzed by U Mann–Whitney test; n = 21 in migraine patients group and n = 32 in controls; ***—p < 0.001 as compared with controls.
Figure 2.
Ratios of urinary levels of 5-hydroxyaminoacetic acid (5-HIAA) and kynurenine (KYN) to tryptophan (TRP), KYN to kynurenic acid (KYNA), and KYNA to quinolinic acid (QA) in migraine patients and controls. Results are presented as the median with boxes representing I and III quartiles and whiskers representing Min to Max values. Differences between migraine patients and controls were analyzed by U Mann–Whitney test; n = 21 in migraine patients group and n = 32 in controls; ***—p < 0.001 as compared with controls.
Figure 3.
Correlation between the severity of migraine evaluated by Migraine Disability Assessment Scale (MIDAS) score and urine concentration of 5- hydroxyaminoacetic acid (5-HIAA) measured in mg per g of creatinine (gCr) (upper panel) or the ratio of 5-HIAA to tryptophan (TRP) (lower panel) in migraine patients. The correlation was assessed by the Spearman rank test with the rho rank coefficient (r). A linear regression line was drawn by the least square method with the equations Y = –0.126X + 4.150 (R2 = 0.312, upper panel) and Y = –0.012X + 0.390 (R2 = 0.226, lower panel). .
Figure 3.
Correlation between the severity of migraine evaluated by Migraine Disability Assessment Scale (MIDAS) score and urine concentration of 5- hydroxyaminoacetic acid (5-HIAA) measured in mg per g of creatinine (gCr) (upper panel) or the ratio of 5-HIAA to tryptophan (TRP) (lower panel) in migraine patients. The correlation was assessed by the Spearman rank test with the rho rank coefficient (r). A linear regression line was drawn by the least square method with the equations Y = –0.126X + 4.150 (R2 = 0.312, upper panel) and Y = –0.012X + 0.390 (R2 = 0.226, lower panel). .
Figure 4.
Correlation between monthly migraine days (MMD) and urine concentration of 5- hydroxyaminoacetic acid (5-HIAA) measured in mg per g of creatinine (gCr) (upper panel) or the ratio of 5-HIAA to tryptophan (TRP) (lower panel) in migraine patients. The correlation was assessed by the Spearman rank test with the rho rank coefficient (r). The linear regression line was drawn by the least square method with the equations Y = –0.283X + 3.780 (R2 = 0.234, upper panel) and Y = –0.032X + 0.365 (R2 = 0.219, lower panel).
Figure 4.
Correlation between monthly migraine days (MMD) and urine concentration of 5- hydroxyaminoacetic acid (5-HIAA) measured in mg per g of creatinine (gCr) (upper panel) or the ratio of 5-HIAA to tryptophan (TRP) (lower panel) in migraine patients. The correlation was assessed by the Spearman rank test with the rho rank coefficient (r). The linear regression line was drawn by the least square method with the equations Y = –0.283X + 3.780 (R2 = 0.234, upper panel) and Y = –0.032X + 0.365 (R2 = 0.219, lower panel).
Figure 5.
Correlation between monthly headache days (MHD) and the urine concentration of 5- hydroxyaminoacetic acid (5-HIAA) measured in mg per g of creatinine (gCr) in migraine patients. The correlation was assessed by the Spearman rank test with the rho rank coefficient (r). The linear regression line was drawn by the least square method with the equation Y = –0.222X + 3.976 (R2 = 0.251).
Figure 5.
Correlation between monthly headache days (MHD) and the urine concentration of 5- hydroxyaminoacetic acid (5-HIAA) measured in mg per g of creatinine (gCr) in migraine patients. The correlation was assessed by the Spearman rank test with the rho rank coefficient (r). The linear regression line was drawn by the least square method with the equation Y = –0.222X + 3.976 (R2 = 0.251).
Figure 6.
Correlation between monthly headache days (MHD) and urine concentration of 5- hydroxyaminoacetic acid (5-HIAA) measured in mg per g of creatinine (gCr) in migraine patients. The correlation was assessed by the Spearman rank test with the rho rank coefficient (r). The linear regression line was drawn by the least square method with the equation Y = –0.122X + 3.601 (R2 = 0.080). .
Figure 6.
Correlation between monthly headache days (MHD) and urine concentration of 5- hydroxyaminoacetic acid (5-HIAA) measured in mg per g of creatinine (gCr) in migraine patients. The correlation was assessed by the Spearman rank test with the rho rank coefficient (r). The linear regression line was drawn by the least square method with the equation Y = –0.122X + 3.601 (R2 = 0.080). .
Table 1.
Characteristics of migraine patients enrolled in this study (n = 21).
Table 1.
Characteristics of migraine patients enrolled in this study (n = 21).
Characteristic |
Specification (Mean ± SD (range) or type and number) |
Age |
39 ± 13 (26-65) |
Sex |
14 F, 7 M |
Migraine type |
Episodic, 21 |
Aura |
8 |
Frequency of attacks (per month) |
1.2 ± 1.1 (0.3-4.0) |
Frequency of attacks (per quarter) |
3.5 ± 2.9 (1-12) |
Time since diagnosis (years) |
18 ± 12 (3-40) |
Treatment |
Abortive 16, prophylactic 5, both 3 |
Pain intensity (NRS 1) |
7.0 ± 1.5 (5-10) |
MIDAS |
10.0 ± 5.9 (3-26) |
Monthly migraine days Monthly headache days |
3.2 ± 2.4 (1-10) 5.0 ± 3.1 (1-14) |
Mood disorders |
8 |
Anxiety (GAD-7 score) |
4.4 ± 3.1 (0-12) |
Depression (PHQ-9 score) |
6.0 ± 3.2 (1-14) |
Table 2.
Correlation between the intensity of migraine headache evaluated by the MIDAS 1) questionnaire scores and the urinary levels of tryptophan (TRP), 5-hydroxyaminoacetic acid (5-HIAA), kynurenine (KYN), KYNA, and quinolinic acid QA as well as their ratios in migraine patients. The correlations were analyzed with the Spearman rank test with the rho rank correlation coefficient.
Table 2.
Correlation between the intensity of migraine headache evaluated by the MIDAS 1) questionnaire scores and the urinary levels of tryptophan (TRP), 5-hydroxyaminoacetic acid (5-HIAA), kynurenine (KYN), KYNA, and quinolinic acid QA as well as their ratios in migraine patients. The correlations were analyzed with the Spearman rank test with the rho rank correlation coefficient.
MIDAS score and |
rho-Spearman |
p |
TRP |
0.163 |
0.309 |
5-HIAA |
– 0.676 |
0.001 |
KYN |
0.242 |
0.304 |
KYNA |
– 0.050 |
0.835 |
QA |
0.145 |
0.543 |
5-HIAA/TRP |
– 0.679 |
0.001 |
KYN/TRP |
– 0.184 |
0.437 |
KYNA/KYN |
0.077 |
0.748 |
KYNA/QA |
– 0.158 |
0.506 |
Table 3.
Correlation between monthly migraine days (MMD) and the urinary levels of tryptophan (TRP), 5-hydroxyaminoacetic acid (5-HIAA), kynurenine (KYN), KYNA, and quinolinic acid QA as well as their ratios in migraine patients. The correlations were analyzed with the Spearman rank test with the rho rank correlation coefficient.
Table 3.
Correlation between monthly migraine days (MMD) and the urinary levels of tryptophan (TRP), 5-hydroxyaminoacetic acid (5-HIAA), kynurenine (KYN), KYNA, and quinolinic acid QA as well as their ratios in migraine patients. The correlations were analyzed with the Spearman rank test with the rho rank correlation coefficient.
MMD and |
rho-Spearman |
p |
TRP |
0.195 |
0.410 |
5-HIAA |
-0.646 |
0.002 |
KYN |
-0.188 |
0.427 |
KYNA |
0.002 |
0.995 |
QA |
0.143 |
0.548 |
5-HIAA/TRP |
-0.615 |
0.003 |
KYN/TRP |
-0.116 |
0.627 |
KYNA/KYN |
0.042 |
0.862 |
KYNA/QA |
-0.108 |
0.651 |
Table 4.
Correlation between monthly headache days (MHD) and the urinary levels of tryptophan (TRP), 5-hydroxyaminoacetic acid (5-HIAA), kynurenine (KYN), KYNA, and quinolinic acid (QA) as well as their ratios in migraine patients. The correlations were analyzed with the Spearman rank test with the rho rank correlation coefficient.
Table 4.
Correlation between monthly headache days (MHD) and the urinary levels of tryptophan (TRP), 5-hydroxyaminoacetic acid (5-HIAA), kynurenine (KYN), KYNA, and quinolinic acid (QA) as well as their ratios in migraine patients. The correlations were analyzed with the Spearman rank test with the rho rank correlation coefficient.
MHD and |
rho-Spearman |
p |
TRP |
0.149 |
0.518 |
5-HIAA |
-0.657 |
0.001 |
KYN |
-0.206 |
0.369 |
KYNA |
-0.051 |
0.826 |
QA |
0.159 |
0.491 |
5-HIAA/TRP |
-0.418 |
0.060 |
KYN/TRP |
-0.152 |
0.510 |
KYNA/KYN |
0.032 |
0.890 |
KYNA/QA |
-0.136 |
0.556 |
Table 5.
Correlation between the intensity of migraine headache evaluated by the PHQ-9 1) questionnaire and the urinary levels of tryptophan (TRP), 5-hydroxyaminoacetic acid (5-HIAA), kynurenine (KYN), KYNA, and quinolinic acid (QA) as well as their ratios in migraine patients. The correlations were analyzed with the Spearman rank test with the rho rank correlation coefficient.
Table 5.
Correlation between the intensity of migraine headache evaluated by the PHQ-9 1) questionnaire and the urinary levels of tryptophan (TRP), 5-hydroxyaminoacetic acid (5-HIAA), kynurenine (KYN), KYNA, and quinolinic acid (QA) as well as their ratios in migraine patients. The correlations were analyzed with the Spearman rank test with the rho rank correlation coefficient.
PHQ-9 score and |
rho-Spearman |
p |
TRP |
0.004 |
0.987 |
5-HIAA |
-0.427 |
0.048 |
KYN |
-0.334 |
0.139 |
KYNA |
-0.160 |
0.489 |
QA |
0.216 |
0.347 |
5-HIAA/TRP |
-0.307 |
0.176 |
KYN/TRP |
0.042 |
0.862 |
KYNA/KYN |
0.238 |
0.299 |
KYNA/QA |
-0.198 |
0.390 |