Neuropeptide Y and measures of stress in a longitudinal study of women with the fibromyalgia syndrome

Introduction

Neuropeptide Y (NPY), a 36-amino acids peptide, first described in 1981 by Victor Mutt and co-workers [1], is one of the most abundant peptides in the brain and strongly associated with the fear/alarm system [2, 3] but also with neurodegenerative diseases [4]. Outside the brain, in the peripheral autonomic nervous system, NPY co-exists with nor-epinephrine [5]. NPY is localized and released from many noradrenergic cell neurons in the peripheral nervous system [6, 7].

There is evidence that NPY is crucial for stress adaptation processes, in addition to its role in maintaining vascular tone and the regulation of appetite [8], [9], [10], [11]. NPY is believed to act as an endogenous anxiolytic agent with behavior effects similar to benzodiazepines [7, 12], and has an inhibitory regulator effect on the hypothalamus-pituitary-adrenal (HPA) axis and the sympathetic nervous system [13].

Fibromyalgia syndrome (FMS), a chronic disorder attributed to stress [10, 14, 15], is clinically characterized by widespread pain, soft tissue tenderness, stiffness, general fatigue, and cognitive dysfunctions [11, 14, 15]. Moreover, the cerebrospinal fluid NPY and plasma NPY levels are significantly elevated as compared to healthy controls [16, 17]. This suggests that NPY is of importance in the complex patho-physiologic mechanism behind the development of FMS and the response to this syndrome.

In a previous report based on data from the same study as in this report, the effects of cognitive behavior therapy (CBT) on FMS were investigated. The intervention focused on stress management in women with FMS [18]. The primary outcomes were: psychometric measurements with the West Haven-Yale Multiple Pain Inventory dimensions for pain and coping with pain (MPI) [19], the Maastricht Scale for Vital Exhaustion (fatigue) [20], the Everyday Life Stress for stress behavior (ELS) [21, 22], and the self-reported Montgomery-Åsberg Depression rating scale for depression (MADRS-S) [23]. After the CBT intervention, the women reported higher subjective ratings of pain but improved coping behavior with chronic pain and improved well-being and less self-reported stress behavior [18].

The current study is part of a study examining various biomarkers of pain, depression, and stress as possible mechanisms mediating the effects on primary outcomes for the participating women in the CBT intervention study. We reported an association with reduced levels of the neuropeptide substance P in the plasma after the CBT intervention, and an association with some of the MPI dimensions [24].

So far, no study has investigated changes in the NPY levels in relation to changes in stress measures. The aims of the present explorative study were to assess changes of plasma NPY and of various measures of pain, depression, and stress at baseline before the CBT intervention, after six months of CBT intervention, and after another six months of follow-up. According to the hypothesis, NPY levels decrease when measures of pain, depression, and stress improve.

Methods

Results

Change across time

As seen in Table 2, the mean pre-intervention plasma NPY level was 93.2 ± 38.8 fmol/mL, the post-intervention level was 68.0 ± 35.5 fmol/mL, and the follow-up level was 75.6 ± 42.9. The difference for change throughout the study was statistically significant (p=0.001).

Table 2:

Change of neuropeptide Y and various pain, depression, and stress measures.

Variable	Before intervention	After intervention	6 months follow-up	p for change during intervention	p for change throughout study
P-neuropeptide Y, fmol/mL	93.2 ± 38.8	68.0 ± 35.5	75.6 ± 42.9	0.002	0.001
MPI part 1a	15.7 ± 2.8	15.1 ± 3.8	14.6 ± 3.4	0.33	0.17
Life controla	3.0 ± 0.9	3.4 ± 1.1	3.6 ± 1.0	0.07	0.02
Pain severitya	3.8 ± 0.8	3.8 ± 1.1	3.6 ± 1.1	0.72	0.45
Vital exhaustionb	23.2 ± 7.0	21.1 ± 6.4	20.1 ± 7.4	0.13	0.053
MADRS-S sumc	16.3 ± 7.1	13.9 ± 7.1	12.4 ± 6.3	0.17	0.03
Everyday life stressd	20.5 ± 8.6	18.0 ± 8.8	17.1 ± 8.0	0.17	0.09
Hostilityd	4.3 ± 2.5	3.7 ± 2.5	3.7 ± 2.5	0.27	0.26
Time urgencyd	11.4 ± 5.1	9.6 ± 4.9	8.6 ± 3.9	0.08	0.001
Competitivenessd	4.8 ± 2.8	4.7 ± 2.7	4.8 ± 3.1	0.83	0.86

1. ^aThe West Haven-Yale Multiple Pain Inventory, score. ^bThe Maastricht scale for Vital Exhaustion (fatigue), score. MADRS –S = ^cMontgomery-Åsberg Depression Rating Scale – self-rated, score. ^dEveryday Life Stress questionnaire, score.

Among the pain, depression, and stress variables, the MPI subscale life control improved significantly (p=0.02), and so did the depression score (MADRS-S) (p=0.03), and the ELS subscale time urgency (p<0.001), while the improvement of vital exhaustion was borderline (p=0.053). The MPI subscale pain severity improved but not significantly, and so did the ELS subscale hostility, while the ELS subscale competitiveness was unchanged.

Table 3 shows a multivariable analysis of the significant variables in Table 2. The trend of the MADRS-S levels was significantly related to the corresponding trend of the NPY levels (p<0.0001), while the trends for time urgency and life control were not.

Table 3:

Multivariable analysis of P-neuropeptide Y trends during the study period versus life control, MADRS-S and time urgency trend.

Parameter	Estimatea	Standard error	t-value	p-Value
Intercept	−0.0513	0.0156	−3.29	0.0022
MADRS-S trendb	−0.2180	0.0366	−5.95	<0.0001
Time urgency trendc	−0.0155	0.0252	−0.61	0.54
Life control trendd	0.0000	0.0000	0.60	0.55

1. ^aRegression coefficients. ^bMontgomery-Åsberg Depression Rating Scale, self-rated score. ^cEveryday Life Stress questionnaire, time urgency score. ^dThe West Haven-Yale Multiple Pain Inventory, life control score.

Since the levels of NPY and the pain, depression, and stress measures in Table 2 were rather different and therefore hard to compare, all levels were standardized so that the before intervention level was set at 100 and the other two measurements were set at proportionate levels. Figure 1 shows a plot of standardized levels. There was a uniform change across time with lower levels of NPY and improved levels in most other variables, where life control (coping) increased and all others except competitiveness decreased.

Figure 1:

Change of variable level across time. All data are standardized so that the start value is 100.

Discussion

This is the first prospective clinical study on the association between change of stress-related variables after psychological intervention, in this case by means of a CBT program with a protocol designed to reduce stress and pain, and plasma NPY. Stress-related variables improved across the study period, while plasma NPY levels subsided.

Fibromyalgia is a complex disorder where stress of various origins has been proposed as an important component in the etiology. Stressors are defined by their ability to disturb homeostasis in the body [12, 33], which entails a number of psycho-neuro-immunological reactions [33]. The present study indicates a comparatively broad distribution of the NPY values detected in the plasma samples of the examined subjects. This is in line with a previous study on fibromyalgia patients, where elevated levels of NPY in their plasma were linked to an increase in their response to prolonged and repeated stress, including distress, anxiety, and pain [17].

The CBT in this study was delivered according to a protocol developed to reduce stress and Type A behavior after myocardial infarction [18]. The present study design was explorative and observational and the associations between the plasma NPY and CBT as well as the substance P and CBT in our previous study [24] are interesting and might be a clue to a biochemical understanding of the unique effect of CBT according to this protocol.

In animal models, evidence of NPY associations with stress-related activities and diseases have been gathered over the past 30 years [2, 10, 11, 34, 35] and a protective effect on stress has been proposed. Animals with low levels of plasma or cerebrospinal fluid NPY exhibit a disrupted behavior after stress exposure as compared to animals with higher NPY levels. Nasal infusion of NPY given to rats reverses anxiety and depression behavior after exposition to prolonged stress [36], and attenuates the effect of stress when given before exposure to stressful events [36, 37] In rat models, central NPY, via the Y1 receptor, appears to play an important role in mediating the adaptation mechanism against chronic stress [37].

In studies on humans, plasma NPY levels in U.S. soldiers subjected to military survival training, a standardized stress exposure, showed that soldiers who responded with a higher increase of plasma NPY had a better ability to adapt to stress. Correspondingly, soldiers with a low plasma NPY release had signs of maladaptive stress response [38]. Soldiers in the U S. Special Forces showed a more rapid and higher increase of plasma NPY and less symptoms of stress during survival training as compared to non-Special Forces soldiers [9]. These data support that NPY is involved in the enhanced stress resilience in humans, which supports the finding in the present study.

Available data have suggested a potential of the NPY system as a target for pharmacological treatments of stress-related disorders, including anxiety and depression. As mentioned above, in experimental animals NPY has been suggested to be protective against stress, and intranasal NPY was found to reverse several behavioral impairments triggered by exposure to prolonged stress [36]. Nasal administration of NPY has also been proposed as a route for relieving mood and anxiety disorders also in humans [39, 40]. The authors of these studies suggest that stress is connected with low levels of NPY in various body fluids [39]. According to a recent review and meta-analysis, it has been noted that NPY is low in plasma of depressive patients [41] and in CSF in patients subjected to treatment for refractory depression [41]. However, studies also reveal that chronic stress patients had significantly higher plasma NPY levels as compared to controls [42]. The altered NPY activity may be indicative of an endogenous mechanism to modulate stress.

The strengths of this study include that the participation rate was high, the statistical power was sufficient, and the study monitoring was excellent, resulting in minor data loss. The latter might also be regarded as a limitation, since the study subjects may have been influenced by the study monitoring, however balanced by the possibility to fill in data that were overlooked by the study participant. A further limitation of the study might be that blood samples were taken only once daily, perhaps not catching physiologic diurnal variations or patterns of release variation. NPY has a half-life in plasma of up to 39 min [43], which is considerably longer than that of catecholamines, other mediators of the stress response, but still a short half-life regarding possible diurnal variation. However, to standardize the testing procedure, all samples were taken at approximately the same time between 8 and 10 a.m. and in the same phase of the menstrual cycle (day 9–14 after the end of the last menstrual period). The study population was large enough for the hypothesis to be tested, as shown by a post hoc power analysis.

Another limitation may be the use of the ACR 1990 criteria rather than the revised versions from 2010 [44] and 2016 [45]. However, although we did not have all the necessary data, a retrospective analysis showed that the study population in this report most likely also fulfilled the new ACR criteria. The ACR 1990 criteria are still recommended for scientific purposes.

In conclusion, in this longitudinal study, women with FMS subjected to a CBT program intervention had an improvement in a number of pain, depression, and stress markers as well as a decrease in the plasma NPY levels in a before-and-after-intervention design. This is in line with evidence that central NPY may have an important role in mediating the adaptation mechanism against chronic pain, depression, and stress. Based on our and others’ findings, we suggest that high plasma NPY levels do not cause a stress response. On the contrary, the stress level causes the NPY response, which increases the ability to handle the stress level. As soon as the stress level diminishes, the high NPY level is no longer needed and also diminishes. Individuals who have an insufficient NPY response to stress have been shown to get a maladaptive stress response. Similar findings have been obtained in laboratory mammals. Therefore, NPY may be regarded as a mean, developed during the evolution to facilitate coping with stressful situations.