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Abstract

Background

The cAMP and cGMP pathways are implicated in the initiation of migraine attacks, but their interactions remain unclear. Calcitonin gene-related peptide (CGRP) triggers migraine attacks via cAMP, whereas the phosphodiesterase-5 inhibitor sildenafil induces migraine attacks via cGMP. Our objective was to investigate whether sildenafil could induce migraine attacks in individuals with migraine pre-treated with the CGRP-receptor antibody erenumab.

Methods

In this randomized, double-blind, placebo-controlled, cross-over study, adults with migraine without aura received a single subcutaneous injection of 140 mg erenumab on day 1. They were then randomized to receive sildenafil 100 mg or placebo on two experimental days, each separated by at least one week, between days 8 and 21. The primary endpoint was the difference in the incidence of migraine attacks between sildenafil and placebo during the 12-h observation period after administration.

Results

In total, 16 participants completed the study. Ten participants (63%) experienced a migraine attack within 12 h after sildenafil administration compared to three (19%) after placebo (p = 0.016). The median headache intensity was higher after sildenafil than after placebo (area under the curve (AUC) for the 12-h observation period, p = 0.026). Furthermore, sildenafil induced a significant decrease in mean arterial blood pressure (AUC, p = 0.026) and a simultaneous increase in heart rate (AUC, p < 0.001) during the first hour after administration compared to placebo.

Conclusion

These findings provide evidence that migraine induction via the cGMP pathway can occur even under CGRP receptor blockade.

Trial registration

ClinicalTrials.gov: Identifier NCT05889455.

Keywords

CGRP cGMP PDE-5 human models migraine trigeminovascular system

Introduction

Migraine is a disabling neurological disorder that affects more than one billion people worldwide, considerably diminishing their quality of life (1). The quest to decipher the pathogenesis of migraine is an ongoing and challenging pursuit (2). Although numerous molecular and cellular signaling pathways have been implicated in the initiation of migraine attacks (2), a complete understanding of their interplay and specific contributions remains elusive.

Central to our current understanding of migraine pathogenesis are two primary intracellular signaling pathways: one mediated by cAMP and the other by cGMP (2). The downstream action of both pathways, according to a recent hypothesis (2), converges on the opening of specific potassium channels, suggesting a common mechanism in migraine pathogenesis (3). Ample evidence from human experimental studies lend support to this hypothesis, demonstrating that activation of either pathway can initiate migraine attacks. The signaling molecules calcitonin gene-related peptide (CGRP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are known to induce migraine attacks, and both of them activate the cAMP-dependent pathway (4,5). Furthermore, administration of glyceryl trinitrate (a nitric oxide (NO) donor) and phosphodiesterase-5 (PDE-5) inhibitors, including sildenafil, can elicit migraine attacks and activate the cGMP-dependent pathway (6,7). However, the exact relationship between the cAMP- and cGMP-dependent signaling pathways is not fully understood. Some reports suggest independent functioning, whereas others indicate potential cross-talk and mutual modulation (8 –10). This subject warrants further investigation to ascertain whether these pathways operate independently or interact, possibly through feedback loops, in the initiation of migraine attacks.

Here, we aimed to further elucidate the relationship between the cAMP- and cGMP-dependent signaling pathways in migraine pathogenesis. To this end, we investigated whether the administration of sildenafil, an indirect activator of the cGMP-dependent pathway, can induce migraine attacks in people with migraine who were pre-treated with erenumab, an anti-CGRP receptor monoclonal antibody.

Methods

Study oversight

The study protocol was approved by the Regional Health Research Ethics Committee of the Capital Region of Denmark (H-22031717). Additional approval was obtained from the Danish Data Protection Agency. All participants provided their written informed consent before engaging in any study-related procedures. The study was registered with ClinicalTrials.gov (NCT05889455) and conducted in accordance with the principles outlined in the Declaration of Helsinki.

Study population

The study population were adults with a diagnosis of migraine without aura, as defined in the International Classification of Headache Disorders, 3rd edition (ICHD-3) (11). Advertisement was posted on a website (https://forskningnu.dk) to direct potential participants to contact the site investigators conducting the trial.

Eligible participants were aged between 18 and 65 years, with a documented history of migraine without aura for ≥12 months prior to enrollment. Furthermore, the participants had to report experiencing one to five monthly migraine days before screening. Exclusion criteria were a history of other primary or secondary headache disorders, with the exception of tension-type headache occurring on ≤5 days per month. Additional exclusion criteria were history of any significant somatic or psychiatric conditions and use of preventive migraine medication within 30 days or five plasma half-lives (whichever period was longer) prior to enrollment. Those who reported previous use of CGRP-targeted therapies were also excluded. Furthermore, female participants were excluded if they were pregnant, breastfeeding, or planned to become pregnant during the study period.

Study design

This study used a randomized, double-blind, placebo-controlled, two-way cross-over design. The participant recruitment process commenced with a pre-screening conducted via telephone. Subsequent on-site visits included a screening visit, a pre-experimental visit and two experimental visits (Figure 1).

Figure 1.

Study design. ECG = electrocardiogram. s.c. = subcutaneous.

During the screening visit, participants underwent a comprehensive evaluation to confirm their eligibility. A semi-structured interview was also performed to record the participants’ clinical data. Furthermore, site investigators conducted a neurological examination, measured vital signs, performed a 12-lead electrocardiogram (ECG), and administered a urine pregnancy test for females of childbearing potential.

Following confirmation of their eligibility, participants attended a pre-experimental visit (i.e. day 1), where they received a single subcutaneous injection of 140-mg erenumab, administered in the thigh, abdomen or upper arm. For the experimental visits, participants were randomly allocated to one of two intervention sequences: receiving sildenafil on the first experimental day and placebo on the second, or the reverse order. These experimental visits were scheduled between days 8–14 and days 15–21 post-injection of erenumab, ensuring a minimum interval of seven days between visits.

The randomization was performed in permuted blocks of 4 by the Capital Region Hospital Pharmacy. Within each block, two participants received sildenafil during the first visit and placebo during the second, whereas the other two received placebo during the first visit and sildenafil during the second. Both sildenafil and placebo were enclosed in capsules that were opaque and identical in appearance, taste and smell. Participants swallowed the capsules whole with water under supervision and could not open them to see the contents, ensuring complete blinding. The randomization list was disclosed to the investigators only upon completion of the study.

Participants were informed about the potential of sildenafil to induce headache or migraine attacks without specific details on the expected headache characteristics. They were also made aware that erenumab might weaken the effects of sildenafil.

All experimental visits took place in a non-fasting and interictal state, defined as free of any headache or acute pain medication for at least 48 hours. In case of headache within this timeframe, visits were rescheduled. After establishing baseline values, participants received either sildenafil 100 mg or placebo. They remained under in-hospital observation for 60 minutes, during which study staff recorded headache characteristics and vital signs every 10 minutes.

After one hour, participants left the hospital and were instructed to complete the headache diary hourly for the subsequent 11 hours, comprising a 12-hour observation period in total.

Endpoints

The primary endpoint was the incidence of migraine attacks after the administration of sildenafil, as compared with placebo during a 12-hour observation period. An event was classified as a migraine attack if it met the ICHD-3 criteria C and D for migraine without aura (11) or closely resembled the participant's usual spontaneous migraine attack and was treated with the participant's usual acute medication (see Supplemental material, Table S1). The secondary endpoints were the difference in the incidence of headache, the area under the curve (AUC) values for headache intensity scores on an 11-point numeric rating scale (NRS) from 0 to 10, and the incidence of adverse events during the 12-hour observational period after the administration of sildenafil, as compared with placebo. The AUCs values were computed using the trapezium rule.

Statistical analysis

The determination of the sample size relied on paired proportions at a 5% significance level with ≥80% power through a one-sided McNemar's test. We made assumptions about off-diagonal probabilities, with P01 (the proportion of participants experiencing migraine exclusively on the placebo day) set at 0.1 and P10 (the proportion of participants experiencing migraine exclusively on the sildenafil) set at 0.7. Through this computation, assuming 10% and 70% of pairs to be discordant, a balanced distribution necessitated a sample size of 16 participants completing both experimental days.

Demographic and clinical features were summarized using descriptive statistics. Categorical variables are expressed as absolute frequencies and percentages, numerical variables as mean or median values (range or SD), contingent upon the data distribution. We used McNemar's test for the comparisons of migraine attack and headache incidence between study arms, treating them as categorical paired data. For the AUC values of headache intensity scores, we used the Wilcoxon signed-rank test. p ≤ 0.05 was considered statistically significant. Statistical analyses were performed with SPSS, version 27.0 (IBM Corp., Armonk, NY, USA).

Results

Between April and October 2023, we pre-screened 70 participants, of which 16 were randomized and completed the study protocol (Figure 2).

Figure 2.

Flowchart of study progress.

Participants had a mean age of 30.8 (range 19–44) years and a mean body mass index of 23.8 kg/m² (range 19.6–31.0 kg/m²). The majority of them were female (n = 12, 75%) and white (n = 14, 88%). The mean number of migraine days in the month prior to screening was 3.3 (range 2–5) and the mean total number of monthly headache days was 4.9 (range 2–8). Nine participants (56%) reported current use of triptans as acute treatment, whereas the remaining seven relied solely on non-specific acute treatment. Additionally, three participants (19%) had previously used antihypertensive medication as preventive treatment, whereas the rest were treatment-naïve in terms of preventive medication.

Migraine attacks

Ten participants (63%) developed a migraine attack during the 12 hours after sildenafil administration compared to three (19%) after placebo (p = 0.016) (Table 1). These three participants reported migraine both on the sildenafil and the placebo day. Migraine attacks were reported by five participants who received sildenafil between days 8 and 14 after erenumab administration and five who received sildenafil between days 15 and 21. The onset of migraine attacks occurred after a median time of 196 (range 40–420) minutes after sildenafil and 200 (range 120–300) minutes after placebo.

Table 1.

Characteristics of spontaneous and provoked headache (0–12-hour observation period).

Participant		Peak headache (duration of headache)	Headache characteristics^a	Associated symptoms^b	Mimics usual migraine	Migraine-like attack (onset)	Treatment (time)
1	Spontaneous		Unilat/7/pres/+	+/−/−
	Sildenafil	50 minutes (6 hours)	Unilat/2/pres/+	+/−/−	Yes	Yes (1 hour)	Rizatriptan 10 mg (1 hour)
	Placebo	None
2	Spontaneous		Unilat/7/pres/+	+/+/+
	Sildenafil	7 hours (1 hour)	Unilat/1/pres/−	−/−/−	No	No	None
	Placebo	None
3	Spontaneous		Unilat/7/throb/+	+/+/+
	Sildenafil	5 hours (9 hours)	Unilat/5/pres/+	+/−/−	Yes	Yes (3 hours)	Paracetamol 1000 mg/Ibuprofen 800 mg (3 hours and 7 hours)
	Placebo	None
4	Spontaneous		Unilat/6/throb/+	−/+/+
	Sildenafil	4 hours (1 hour)	Unilat/1/pres/−	−/−/−	No	No	None
	Placebo	5 hours (3 hours)	Unilat/2/pres/−	−/−/−	No	No	None
5	Spontaneous		Unilat/6/throb/+	+/+/+
	Sildenafil	3 hours (8 hours)	Unilat/2/throb/−	+/−/−	No	Yes (1 hour)	None
	Placebo	None
6	Spontaneous		Unilat/5/throb/+	+/+/+
	Sildenafil	6 hours (4 hours)	Bilat/2/pres/+	−/+/+	Yes	Yes (6 hours)	Sumatriptan 50 mg (6 hours)
	Placebo	11 hours (11 hours)	Bilat/6/throb/+	+/+/+	Yes	Yes (2 hours)	Sumatriptan 50 mg (2 hours and 4 hours)
7	Spontaneous		Unilat/6/throb/+	+/+/+
	Sildenafil	None^c
	Placebo	None
8	Spontaneous		Unilat/4/throb/+	+/+/+
	Sildenafil	4 hours (8 hours)	Bilat/4/throb/+	+/+/+	Yes	Yes (3 hours)	Sumatriptan 50 mg (3 hours and 9 hours)/ ASA 500 mg+Coffein 50 mg (5 hours)
	Placebo	1 hour (2 hours)	Unilat/1/pres/−	−/−/−	Yes	Yes (3 hours)	Sumatriptan 50 mg
9	Spontaneous		Unilat/10/throb/+	+/+/+
	Sildenafil	9 hours (7 hours)	Unilat/4/throb/+	+/+/+	Yes	Yes (6 hours)	Paracetamol 1000 mg/ibuprofen 400 mg (9 hours)
	Placebo	None
10	Spontaneous		Unilat/7/throb/+	+/+/+
	Sildenafil	2 hours (11 hours)	Unilat/4/throb/+	+/−/+	Yes	Yes (7 hours)	Codein 9,6 mg + ASA 500 mg + magnesium 150 mg (7 hours)
	Placebo	7 hours (10 hours)	Unilat/4/throb/+	−/+/−	Yes	Yes (5 hours)	Codein 9,6 mg + ASA 500 mg + magnesium 150 mg (5 hours)
11	Spontaneous		Unilat/6/throb/+	+/+/+
	Sildenafil	20 minutes (6 hours)	Bilat/1/throb/−	−/−/−	No	No	None
	Placebo	None
12	Spontaneous		Bilat/7/pres/+	+/+/+
	Sildenafil	4 hours (7 hours)	Bilat/3/throb/+	+/+/+	Yes	Yes (3 hours)	Rizatriptan 10 mg (3 hours)
	Placebo	3 hours (20 minutes)	Bilat/1/pres/−	+/−/−	No	No	None
13	Spontaneous		Unilat/8/pres/+	+/+/−
	Sildenafil	3 hours (4 hours)	Bilat/2/throb/+	−/+/−	No	No	None
	Placebo	None
14	Spontaneous		Unilat/7/throb/+	+/+/+
	Sildenafil	6 hours (8 hours)	Unilat/7/throb/+	+/+/−	Yes	Yes (2 hours)	Ibuprofen 800 mg (1 hour)/sumatriptan 10 mg nasal (3 hours)
	Placebo	None
15	Spontaneous		Unilat/7/throb/+	−/+/+
	Sildenafil	None
	Placebo	None
16	Spontaneous		Unilat/6/pres/+	+/+/+
	Sildenafil	2 hours (5 hours)	Unilat/5/pres/+	+/+/+	Yes	Yes (40 minutes)	Sumatriptan 100 mg (1 hour)
	Placebo	None

Localization (bilat = bilateral; unilat = unilateral)/intensity/quality (throb = throbbing; pres = pressing)/aggravation by cough or physical activity.

Nausea/photophobia/phonophobia.

Neck pain (intensity 4/10), beginning two hours after infusion start, for one hour. No headache, no other symptoms.

Headache responses

Headache of any kind was experienced by 14 participants (88%) after sildenafil and by five participants (31%) after placebo (p < 0.004). The five participants who experienced headache on the placebo day also reported headache on the sildenafil day. None of the participants exclusively reported headache on the placebo day. Onset of headache was reported after a median time of 123 (range 20–420) minutes after sildenafil and 96 (range 40–180) minutes after placebo. The AUC of headache intensity in the 12-hour observation period was higher after sildenafil than after placebo (AUC_{0–12 hours}, p = 0.026) (Figure 3). Peak headache after sildenafil occurred in median after 240 (range 20–540) minutes.

Figure 3.

Headache intensity scores on a numerical rating scale (NRS) during the 12-hour observation period after intake of sildenafil (A) or placebo (B). The thin black lines represent individual headache scores, and the thick red line represents the median value.

Among the 14 participants who experienced headache after sildenafil administration, the median peak headache intensity was 2.5 NRS (range 1–7). At the time of peak headache, eight of 14 participants (57%) reported a unilateral headache localization and 10 of 14 participants (71%) reported a throbbing character. The most frequent accompanying symptoms at the time of peak headache were photophobia (8/14; 57%) and nausea (6/14; 43%), followed by phonophobia (3/14; 21%) and vomiting (1/14; 7%).

Nine participants (56%) took rescue medication on the sildenafil day after a median time of 180 (range 60–540) minutes. On the placebo day, three participants (19%) reported the intake of rescue medication after a median time of 180 (range 120–300) minutes.

Hemodynamic variables

During the first hour after sildenafil administration, we observed a significant decrease in the mean arterial blood pressure compared to placebo (AUC_{0–60 minutes,} p = 0.026), in parallel with a significant increase in heart rate (AUC_{0–60 minutes,} p < 0.001) (Figure 4).

Figure 4.

Mean arterial blood pressure (bpm) (A) and heart rate (mmHg) (B) in the first hour after intake of sildenafil or placebo.

Adverse events

In total, 14 participants (88%) reported adverse events after taking sildenafil compared to four participants (25%) after taking placebo. The most frequently reported adverse events after sildenafil intake were flushing, warm sensation, nasal congestion and fatigue (Table 2).

Table 2.

Summary of adverse events occurring after infusion of sildenafil or placebo (12-hour observation time).

	Sildenafil			Placebo
	n	Onset (minutes)	Duration (minutes)	n	Onset (minutes)	Duration (minutes)
Total	14			4
Flushing	9	40 (20–120)	80 (20–210)	1	40	20
Warm sensation	9	40 (10–120)	150 (10–440)	2	105 (30–180)	40 (20–60)
Nasal congestion	8	35 (30–60)	75 (20–500)	1	120	240
Fatigue	8	40 (20–300)	20 (10–60)	–
Palpitations	4	120 (20–240)	60 (10–60)	–
Bilateral lacrimation	3	40 (30–50)	10 (10–10)	–
Neck pain/neck stiffness	2	90 (60–120)	60 (60–60)	–
Dizziness	2	210 (120–300)	90 (60–120)	–
Dry mouth	2	80 (40–120)	125 (10–240)	–
Conjunctival injection	1	60	60	–
Sweating	1	20	10	–

Values are the median (range).

Discussion

Our findings demonstrate that PDE-5 inhibition can induce migraine attacks in people with migraine who were pre-treated with an anti-CGRP receptor monoclonal antibody. These results indicate that the initiation of migraine attacks via the cGMP-dependent signaling pathways may occur independently of CGRP receptor activation. This observation aligns well with a previous report showing that CGRP receptor antagonism was unable to prevent migraine attacks induced by a NO donor (12). Therefore, it seems plausible that migraine attacks are mediated via two distinct intracellular signaling pathways, namely the cAMP-dependent pathway and cGMP-dependent pathway, each initiating attacks seemingly independent of the other.

Intracellular signaling in migraine: the cAMP-dependent and cGMP-dependent pathways

A recent hypothesis posits that the cAMP-dependent and cGMP-dependent signaling pathways converge, culminating in a shared downstream mechanism (2). This line of reasoning assumes that a person with migraine can experience migraine attacks via activation of either signaling pathway. In support, a previous experimental study reported that 63% of participants with migraine experienced migraine attacks after administration of CGRP and sildenafil on two separate days, with a considerable overlap in the attack features (13). However, it should be noted that this previous study did not include a placebo group, which might introduce some expectation bias. In addition, it is important to note that the exact signaling pathways involved in migraine pathophysiology are still a subject of investigation, and it is possible that additional pathways may be implicated.

The induction rate of migraine attacks was 63% in our study population, which aligns well with previous placebo-controlled experimental studies involving sildenafil (7,14). However, our participants seemingly reported lower headache intensity scores, which might be attributed to the pre-treatment with erenumab, along with the information regarding its potential effectiveness in treating migraine attacks. In line with previous study results with a comparable design (15,16), this might have introduced a placebo effect, impacting the reported headache intensity scores after intake of sildenafil. However, it is important to recognize that comparing trends in headache intensity scores requires tailored investigations, which are adequately powered for that purpose.

Preclinical studies have indicated a bidirectional relationship between the cAMP-dependent and cGMP-dependent pathway (8 –10). In animal models, sildenafil has been shown to inhibit the degradation of cGMP (9), whereas cAMP itself has been observed to cross-activate the cGMP-dependent pathway (8,10). Although our study does not explore the intricacies of these interactions in depth, it does confirm that a functional CGRP receptor is not a prerequisite for the initiation of cGMP-mediated migraine attacks. Indeed, administering erenumab at a subcutaneous dose of 140 mg is expected to achieve full saturation of CGRP receptors, effectively blocking CGRP binding and the subsequent activation of the CGRP pathway (17). This does not exclude a potential residual activity of CGRP by binding to other receptors such as the amylin receptor 1 (AMY1), which was not the focus of this study (15).

Our findings might hold some therapeutic implications. Medications directed against the CGRP receptor have proven effective for the majority of patients in both acute and preventive management of migraine (18 –21). However, an absolute therapeutic response is rarely, if ever, observed (22), leaving a continued unmet treatment need (23,24). Therefore, investigating other drug targets, such as the cGMP-dependent signaling pathway, might represent a promising direction for future migraine research. In particular, PDE-5 activators might hold therapeutic promise for migraine. To date, there are no available drugs designed to activate PDE-5, but research is ongoing in this field (25). In addition, it is worth noting that sildenafil inhibits another subform of PDE, namely PDE-6, also known to inhibit cGMP degradation (26). Further data, however, are needed to clarify the potential role of PDE-6 in migraine. As a further step, exploring combination treatments targeting both the cAMP- and cGMP-dependent signaling pathways could be an intriguing approach. The efficacy and tolerability of such combination strategies need to be carefully assessed in future migraine research endeavors.

Proposed site(s) and mechanisms of action

The exact site of action of PDE-5 inhibition using sildenafil within the trigeminovascular system remains a subject of ongoing debate, with evidence suggesting involvement at both vascular and neuronal sites.

Critical insights into the site and mechanism of action of the cGMP-dependent signaling pathway in migraine pathogenesis have been gleaned from experimental studies using NO, the primary activator of this pathway (27). The role of NO as a mediator of vasodilation has been established for several decades (28). Upon its release from the vascular endothelium, NO diffuses into vascular smooth muscle cells (VSMC), where it stimulates the production of cGMP (29). The intracellular cGMP-dependent signaling pathway in VSMC culminates in the opening of K_ATP and BKCa channels, inducing potassium efflux and promoting vasodilation. A recently proposed model of migraine suggests that these processes lead to the sensitization of perivascular trigeminal afferent nerve fibers (2). This sensitization occurs both chemically, through potassium efflux, and, at least partially, mechanically, through the induced vasodilation. Consequently, nociceptive impulses are transmitted to the central nervous system, culminating in the manifestation of migraine pain (2).

The hemodynamic changes observed in our study provide support for a vascular site of action. However, the data regarding the effects of sildenafil as vasodilator are mixed. Some earlier investigations using ultrasonography in both healthy individuals and patients with migraine failed to reveal any effect of sildenafil on intracerebral or extracranial arterial dilatation (7,30,31). Therefore, the migraine induction ability of sildenafil was predominantly attributed to non-vascular mechanisms (7,30,31). By contrast, later investigations using advanced 3 Tesla magnetic resonance angiography demonstrated dilation of meningeal and cerebral arteries after sildenafil administration in both healthy individuals and patients with migraine (32,33). These newer imaging techniques provide enhanced sensitivity and ability to capture subtle vascular changes that might have been overlooked by earlier methods. Therefore, the current evidence suggests that sildenafil may indeed exert a vasodilatory effect on cranial arteries, as demonstrated by the more sophisticated imaging modalities employed in recent research.

Apart from the vasculature, the cGMP pathway also exerts its influence within the nervous system. Indeed, this pathway is involved in neuronal nociceptive processes, exerting varied effects on neuronal background activity and excitability depending on the specific site of action (34). This suggests that sildenafil's site of action in inducing migraine could extend to sensory nerve terminals or even the central nervous system (35,36). Older investigations showed that activation of the cGMP pathway in the trigeminal ganglion might exert pro-nociceptive effects through modulation of ion channel activity (37). Within the central nervous system, NO and the cGMP pathway mediate neurotransmission, influencing nociceptive perception, central sensitization and hyperalgesia (38). Evidence from animal research suggests that NO may contribute to neuronal hyperexcitability in the spinal trigeminal nucleus, pointing to a modulation of central trigeminal activity by the cGMP pathway (39).

Sildenafil, being a lipophilic drug, can cross the blood–brain barrier, allowing for potential central effects (40). In healthy human subjects, PDE-5 inhibition and the resulting stimulation of the cGMP pathway through sildenafil administration resulted in a transient increase in glutamate concentrations in the brainstem (41). This observation reflects increased extracellular glutamate levels and suggests an activation of excitatory neuronal pathways at the level of second-order neurons that may contribute to migraine attack initiation (41). However, it remains uncertain whether a central site of action is responsible for these effects because it may be also secondary to activation of peripheral nociceptive pathways.

The multifaceted effects of the cGMP pathway within the peripheral and central trigeminovascular system underscore its intricate role in migraine pathophysiology. Future research endeavors should aim to unravel the precise molecular and cellular mechanisms through which sildenafil modulates nociception in migraine.

Considering the limited permeability of the blood–brain barrier for monoclonal antibodies under physiological conditions (42), it is likely that the CGRP receptor blockade in the present study primarily affected peripheral structures. Therefore, although our study establishes that sildenafil induces migraine attacks in individuals pre-treated with erenumab, definitive conclusions regarding the exact sites of action or the potential contribution of a central CGRP receptor blockade on the cGMP pathway remain elusive. Our study primarily provides observations about the peripheral site of action, and exploring the specific interaction between sildenafil and the central CGRP signaling pathways falls beyond the scope of our study design.

Strengths and limitations

The key strengths of the present study lie in its placebo-controlled, randomized and double-blind design, along with stringent inclusion and exclusion criteria. The adoption of a cross-over design not only minimizes clinical variability, but also heightens control over confounding factors. A potential limitation pertains to side effects induced by sildenafil, such as flushing or nasal congestions, which could have compromised blinding and increased the likelihood of a nocebo effect. Moreover, the disclosure to participants regarding the potential weakening effects of erenumab on the sildenafil provocation may have influenced placebo and nocebo effects. It should also be considered that pharmacologically induced migraine attacks via sildenafil may deviate from the physiological processes underlying migraine initiation. Therefore, the conclusions drawn from our study may not fully reflect the intricate physiological signaling cascades involved in spontaneous migraine attacks. Moreover, uncontrollable external factors such as stress or hormonal fluctuations may have influenced migraine induction. We cannot rule out variations in how erenumab is absorbed by different individuals may affect the results. However, an estimated time to reach maximum concentration (T_max) of 6 days in healthy volunteers aligns with an anticipated early onset of effect during the first week of treatment in patients (43). The experimental study days were conducted between days 7 and 21 after randomization, allowing for both onset and maintenance of efficacy (44). Finally, the in-hospital observation period was confined to just one hour, shorter than in prior investigations. Although longer observation periods might offer further insights, given the significant changes in vital parameters within the initial hour, it is improbable that extended observations would unveil substantial new findings.

Conclusions

Migraine provocation via the PDE-5 inhibitor sildenafil can occur even under CGRP receptor blockade via erenumab. These results of this hypothesis generating study support that cGMP-mediated migraine attacks may be independent of the CGRP-cAMP signaling axis and underscore the significant involvement of the cGMP pathway in migraine pathogenesis, emphasizing its potential as a target for future treatment avenues.

Clinical implications

Sildenafil, an activator of the cGMP-dependent pathway, induces migraine attacks in individuals with migraine pre-treated with the CGRP-receptor antibody erenumab.

Migraine provocation via the cGMP pathway is independent of CGRP receptor activation, underscoring the central role of the cGMP pathway in migraine pathophysiology.

Supplemental Material

sj-docx-1-cep-10.1177_03331024241259489 - Supplemental material for Induction of cGMP-mediated migraine attacks is independent of CGRP receptor activation

Supplemental material, sj-docx-1-cep-10.1177_03331024241259489 for Induction of cGMP-mediated migraine attacks is independent of CGRP receptor activation by Bianca Raffaelli, Thien Phu Do, Håkan Ashina, Josefin Snellman, Tina Maio-Twofoot and Messoud Ashina in Cephalalgia

Footnotes

Acknowledgments

We thank the unblinded staff members (Anne Mette Autzen, Rune Häckert Christensen, Marianne Hestad and Susanne Leed) for their help in preparing the infusions.

Data availability

The data that support the findings of this study are available from the corresponding author, upon reasonable request.

Declaration of conflicting interests

We declare the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: BR reports personal fees from AbbVie/Allergan, Eli Lilly, Lundbeck, Novartis and Teva, as well as research grants from Novartis and Lundbeck, all outside of the submitted work. BR reports serving as junior associate editor of The Journal of Headache and Pain, and associate editor of Frontiers In Neurology. TPD has nothing to disclose. HA reports personal fees from Lundbeck and Teva, outside of the submitted work. JS and TMT are full-time employees and shareholders of Novartis Pharma AG, Basel, Switzerland. MA reports receiving personal fees from AbbVie, Amgen, Eli Lilly, GlaxoSmithKline, Lundbeck, Novartis, Pfizer and Teva Pharmaceuticals, all outside of the submitted work. MA reports serving as associate editor of The Journal of Headache and Pain, and associate editor of Brain.

Funding

We disclose receipt of the following financial support for the research, authorship and/or publication of this article: the research was funded by and conducted in collaboration with Novartis Pharma AG, Basel, Switzerland. BR was supported by a research grant of the German Research Foundation (GZ: RA 3907/1-1). MA was supported by a Lundbeck Foundation professor grant (R310-2018–3711).

ORCID iDs

Bianca Raffaelli

Thien Phu Do

Håkan Ashina

Supplemental material

Supplemental material for this article is available online.

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