Prognostic Serum Calcitonin Gene-Related Peptide Level Value in Patients Following Traumatic Brain Injury

Abstract

Background Traumatic brain injury (TBI) is a significant cause of disability and death worldwide. It is important to have affordable and accessible biomarkers to assess the prognosis of patients. This study investigated the prognostic significance of calcitonin gene-related peptide (CGRP) serum levels in individuals with TBI.

Materials and Methods In this cross-sectional analytical study, CGRP levels were measured at admission, 24 hours, and 1 week after hospitalization. Patients were divided into two groups based on the Glasgow Coma Scale (GCS) score at admission: patients with mild/moderate TBI (GCS 9–15) and patients with severe TBI (GCS score 3–8), and CGRP levels were compared between the two groups.

Results A total of 102 patients with TBI were included. Higher levels of CGRP were observed in all three stages of measurement (at admission, 24 hours, and 1 week after hospitalization) in severe TBI patients. The occurrence of CGRP levels of 2 to 10 ng/L or higher than 10 ng/L in the mild/moderate and severe groups upon admission was 68.6 and 91%, respectively (p < 0.001). Within 24 hours of hospitalization, a more significant decrease in CGRP levels to lower ranges (> 0.5 and 0.5–2 ng/L) was observed in mild/moderate TBI patients (51.5%) compared with the severe group (19.4%). As indicated by logistic regression analysis, increased CGRP levels were directly associated with a higher risk of severe TBI.

Conclusion The increase in CGRP level is directly related to the risk of severe TBI. Investigating the ability of CGRP as an easy and accessible biomarker to predict the prognosis of TBI patients is recommended in future studies.

 

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Keywords

calcitonin gene-related peptide - traumatic brain injury - prognosis - Glasgow Coma Scale

Introduction

Brain damage is a leading cause of death following trauma. In less developed and developing countries, traffic accidents are the primary cause of brain damage, and most accident-related deaths are attributed to brain injuries.[1] Traumatic brain injury (TBI) is a significant contributor to disability and mortality worldwide.[2] It is estimated that there were 27.16 and 48.99 million new cases and prevalent cases of TBI in 2019, respectively.[3] The high-income North American region has the highest age-standardized incidence rate of TBI, followed by Australasia and tropical Latin America, with 23 (17–30), 14 (11–17), and 14 (11–19) patients per 100,000, respectively.[3]

The diagnosis of TBI relies on neurological examinations. In acute cases, the diagnosis is based on neurological examinations and neuroimaging tools such as computed tomography (CT) scans and magnetic resonance imaging. Several factors influence the prognosis of patients, including the patient's age, motor score of the Glasgow Coma Scale (GCS), pupillary response, and diagnostic indicators in CT scans, such as Marshall's classification and traumatic subarachnoid hemorrhage (SAH).[4]

In numerous studies, the GCS and the Glasgow Outcome Scale (GOS) have been utilized to assess the clinical outcomes of TBI patients, including mortality and functional status.[5] The GCS classifies TBIs as mild, moderate, or severe.[6] According to this classification, individuals with a GCS score of 13 to 15 fall into the mild, 9 to 12 into the moderate, and 3 to 8 into the severe category. However, variables such as hypoxia, hypotension, and alcohol intoxication can influence GCS scores, potentially leading to misclassification.[7] Predicting the outlook for TBI patients during the early stages can be challenging. While biochemical markers are valuable for diagnosing other bodily organs, there is currently no rapid and definitive blood test for TBI.[8]

Calcitonin gene-related peptide (CGRP) is a 37-amino acid regulatory neuropeptide with diverse functions in biological processes. This peptide, found in alpha and beta forms in humans, belongs to the calcitonin family and is produced in both peripheral and central nervous system (CNS) neurons.[9] [10] [11] CGRP has a bone-stimulating effect, promoting the mitosis of stem cells or the differentiation of osteoprogenitor cells.[12] While its role in nonneuronal tissues is not fully understood, two key indicators for further study include its presence as a free and active compound in cerebral circulation and its function as a potent vasodilator and cross-linker with the peripheral sympathetic nervous system.[13] Limited studies have explored the potential of CGRP as a new biomarker for predicting outcomes of patients with TBI. One study revealed that CGRP levels were notably lower in patients with severe damage compared with those with mild or moderate damage and the control group.[9] However, another study found no significant difference in serum CGRP levels between patients with severe TBI and the control group.[14]

Given the critical importance of promptly diagnosing and early treatment of patients with TBI, it is essential to utilize laboratory markers for early clinical assessment and decision-making. These markers should be cost-effective, easily accessible, and capable of comparing outcomes across different patients. Currently, there is no definitive blood marker that can reliably predict the outcome of TBI patients, and there is limited research on the predictive value of CGRP as a new biomarker. Therefore, this study aims to explore the prognostic value of serum CGRP levels in patients with TBI.

 

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Materials and Methods

Participants and Methods

This study was conducted within the approved ethical framework by the ethics committee of Urmia University of Medical Science, Urmia, Iran, and adhered to the Strengthening the Reporting of Observational Studies in Epidemiology guideline for epidemiological observational studies.[15]

 

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Inclusion and Exclusion Criteria

In this prospective study all patients with TBI who were referred to Imam Khomeini Educational Hospital, Urmia University of Medical Sciences whose guardians/accompanying person provided written informed consent were included. These patients were referred to the hospital between May 2022 and May 2023. Subsequently, participants were followed up for a period of 1 week.

Inclusion criteria comprised age 18 to 60 years and signing the informed consent. Exclusion criteria included multiple traumas including abdomen, pelvic, extremities, comorbidities and chronic diseases, pregnancy, and inability to comply with follow-up appointments.

 

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Data Collection

After 12 hours from the TBI, patients were divided into mild, moderate, and severe TBI groups based on their GCS scores. GOS scores were assessed 1 week after the patient's discharge. Demographic information, including age, sex, and clinical variables such as the injury mechanism, GCS, and GOS scores were recorded. Peripheral blood samples of 10 mL were collected upon admission, 24 hours later, and 1 week after hospitalization. The levels of CGRP in the serum were measured using radioimmunoassay kits following the manufacturer's guidelines. Patient progress during hospitalization was documented and analyzed along with all relevant data.

 

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Study Outcomes

The primary outcome of the study was to assess the morbidity and mortality rates associated with CGRP level following trauma. Secondary outcomes included evaluating short-term CGRP serum level in various GCS scores following TBI.

 

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Statistical Analyses

The data analysis employed descriptive statistics tests, presenting results as mean ± standard deviation for quantitative variables and frequency as a percentage for qualitative variables. Qualitative variables were assessed using the chi-square test, while the independent t-test was applied to compare quantitative variables. Analysis of variance was utilized to compare the mean GCS and GOS across different levels of CGRP. Logistic regression was performed to assess the association of CGRP with the likelihood of severe TBI and final outcome of patients. IBM SPSS Statistics for Windows, version 28 (IBM Corp., Armonk, New York, United States), was employed for data analysis, with statistical significance set at p ≤ 0.05.

 

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Results

Participants

A total of 102 TBI patients were enrolled in this study. The average age of the patients was 31.09 ± 15.78. Among them, 75% were male and 26.5% were female. The average GCS at admission was 8.04 ± 1.76, and the GOS at discharge was 4.83 ± 0.4. The majority of injuries (87.3%) were due to accidents. In this study, 35 patients (34.3%) were categorized as having mild to moderate TBI, while 67 patients (65.7%) were classified as having severe TBI. A higher percentage of men was observed among the mild/moderate and severe TBI groups (82.9% vs. 68.7%). However, the difference in gender distribution between the two groups was not statistically significant (p = 0.12). The average age of patients in the severe group (32.44 ± 17.37 years) was slightly higher than that of the mild/moderate group (28.51 ± 12.03 years). However, this disparity was not statistically significant between the two groups (p = 0.23). The mean GCS score upon admission for the mild/moderate group (9.97 ± 0.71) was significantly higher than that of the severe group (7.03 ± 1.21) (p < 0.001). Furthermore, the average GOS score at the time of discharge was notably higher in the mild/moderate group (5.00 ± 0.001) compared with the severe group (4.74 ± 0.47) (p = 0.002) ([Table 1]).

Table 1 Demographic data of patients enrolled in the study

Variable		Mild and moderate TBI (%)	Severe TBI (%)	p-Value
Age		28.51 ± 12.03	32.44 ± 17.37	0.23
Sex	Male	29 (82.9)	46 (68.7)	0.12
	Female	6 (17.1)	21 (31.3)
GCS upon admission (mean ± SD)		9.97 ± 0.71	7.03 ± 1.21	0.001
GOS upon discharge (mean ± SD)		5 ± 0.001	4.74 ± 0.47	0.002

Abbreviations: GCS, Glasgow Coma Scale; GOS, Glasgow Outcome Scale; SD, standard deviation; TBI, traumatic brain injury.

 

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CGRP Level among GCS Groups

The analysis of CGRP levels in patients with mild/moderate and severe TBI demonstrated that a higher proportion of patients in the severe group had elevated CGRP levels at all three measurement points (at admission, 24 hours posthospitalization, and 1 week posthospitalization) compared with the mild group. Initially, 68.6% of patients in the mild/moderate group exhibited CGRP levels of 2 to 10 or higher than 10 ng/L, whereas 91% of patients in the severe TBI group had similar CGRP levels, indicating a significant disparity between the groups (p < 0.001) ([Table 2]). Following 24 hours of hospitalization, CGRP levels substantially decreased in the mild/moderate group to lower levels (> 0.5 and 0.5–2 ng/L) compared with the severe group. After 24 hours, only 17.1% of patients in the mild/moderate group had CGRP levels of 2 to 10 or higher than 10 ng/L, while 71.6% of patients in the severe group maintained these higher levels, highlighting a significant difference between the two groups (p < 0.001). One week after hospitalization, none of the patients in either group displayed CGRP levels of 2 to 10 or higher than 10 ng/L. However, the percentage of patients with CGRP levels less than 0.5 in the mild/moderate group (3.94%) was significantly higher than that in the severe group (66.1%) (p = 0.002).

Table 2 CGRP level distribution following trauma in patients following trauma

Variable	CGRP level (ng/L)	Mild and moderate TBI (%)	Severe TBI (%)	p-Value
CGRP upon admission	≤ 0.5	5 (14.3)	3 (4.5)	0.001
	0.5–2	6 (17.1)	3 (4.5)
	2–10	21 (60)	13 (19.4)
	> 10	3 (8.6)	48 (71.6)
CGRP level 24 hours later	≤ 0.5	5 (14.3)	3 (4.5)	0.001
	0.5–2	24 (68.6)	16 (23.9)
	2–10	4 (11.4)	38 (56.7)
	> 10	2 (5.7)	10 14.9)
CGRP 1 week later	≤ 0.5	33 (94.3)	41 (66.1)	0.002
	0.5–2	2 (5.7)	21 (33.9)
	2–10	0	0
	> 10	0	0

Abbreviations: CGRP, calcitonin gene-related peptide; TBI, traumatic brain injury.

The analysis of the average GCS prior to hospitalization across various levels of CGRP revealed that patients with higher CGRP levels consistently had lower average GCS scores before hospitalization during all three measurement periods. This difference in GCS scores across different CGRP levels was statistically significant in all three measurement periods (p < 0.05).

 

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Relation between GCS and CGRP Level

The study findings indicate a direct correlation between elevated CGRP levels and the likelihood of severe TBI across all three time periods examined. Upon admission, patients with a CGRP level exceeding 10 ng/L face a significantly higher risk of severe TBI than those below 0.5 ng/L (odds ratio [OR] = 26.67, 95% confidence interval [CI] 4.21–168.99, p < 0.001). Additionally, 24 hours posthospitalization, patients with CGRP levels between 2 and 10 ng/L exhibit a greater likelihood of severe TBI compared with those with levels below 0.5 ng/L (OR = 15.83, 95% CI 2.71–92.36, p = 0.002). Similarly, 1 week after hospitalization, patients with CGRP levels ranging from 0.5 to 2 ng/L show an increased chance of severe TBI compared with those with levels below 0.5 ng/L (OR = 8.45, 95% CI 1.84–38.68, p = 0.006). [Table 3] shows the relationship between GCS and different levels of CGRP.

Table 3 The comparison between GCS and CGRP level in patients following trauma

Variable	CGRP level (ng/L)	GCS (mean ± SD)	p-Value
CGRP upon admission	< 0.5	8.75 ± 1.48	0.008
	0.5–2	8.64 ± 3.21
	2–10	8.44 ± 2.14
	> 10	7.45 ± 0.75
CGRP 24 hours later	< 0.5	8.75 ± 1.48	0.04
	0.5–2	8.47 ± 2.39
	2–10	7.64 ± 1.03
	> 10	7.5 ± 0.90
CGRP 1 week later	< 0.5	8.5 ± 1.56	0.005
	0.5–2	7.52 ± 0.73
	2–10	0
	> 10	0

Abbreviations: CGRP, calcitonin gene-related peptide; GCS, Glasgow Coma Scale; SD, standard deviation.

 

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Relation between GOS and CGRP Level

The analysis of the average GOS score at the time of discharge across different levels of CGRP at the onset of hospitalization, 24 hours posthospitalization, and 1 week posthospitalization revealed no statistically significant variance in the average based on varying levels of CGRP (p < 0.05).

Additionally, out of the total patients, five were dead, with two patients exhibiting CGRP levels between 0.5 and 2 ng/L and three patients with CGRP levels between 2 and 10 ng/L at the time of hospitalization. Notably, no significant distinction was evident between mortality and CGRP levels (p < 0.05) in the study. [Table 4] shows the relationship between GOS and different levels of CGRP.

Table 4 The comparison between GOS and CGRP level in patients following trauma

Variable	CGRP level (ng/L)	GOS (mean ± SD)	p-Value
CGRP upon admission	< 0.5	4.87 ± 0.35	0.98
	0.5–2	4.85 ± 0.37
	2–10	4.83 ± 0.45
	> 10	4.82 ± 0.40
CGRP 24 hours later	< 0.5	5 ± 0.001	0.43
	0.5–2	4.87 ± 0.35
	2–10	4.82 ± 0.45
	> 10	4.78 ± 0.41
CGRP 1 week later	< 0.5	5 ± 0.001	0.34
	0.5–2	4.87 ± 0.44
	2–10	0
	> 10	0

Abbreviations: CGRP, calcitonin gene-related peptide; GOS, Glasgow Outcome Scale; SD, standard deviation.

 

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Discussion

In this study, it was demonstrated that patients in the severe TBI group had significantly higher serum levels of CGRP as compared with patients in the mild/moderate TBI group at admission and 24-hour posthospitalization. Moreover, we showed that CGRP serum levels in patients with mild/moderate TBI significantly decreased after 24 hours compared with patients with severe TBI. CGRP, an endogenous neuropeptide with vasodilatory effects, was described in 1983 by Rosenfeld et al.[16] Since then, it has been an interesting subject for exploring different mechanisms in brain injury and neuronal loss. Consistently, a study investigating effects of TBI on CGRP levels in subjects with bone fractures, found that the group with TBI had higher levels of CGRP compared with controls.[12] Another animal study indicated that in subjects with simultaneous TBI and fracture CGRP levels were higher within 7 days after surgery compared with subjects with fracture alone.[17] The results of these study were in line with the present study.

Moreover, it has been shown that CGRP as an amino acid is expressed by neural cells in both the CNS and the peripheral nervous system and could potentially have a neuroprotective role during bleeding and ischemia through vasodilation and reperfusion.[18] [19] Following an injury, the CGRP level increases, leading to the dilation of the brain blood vessels. The dilation and increasing blood flow in the early stages following injury and ischemia could protect the brain tissue from further damage; however, as the injury gets severe, this mechanism becomes ineffective.[20] [21]

In a prospective study it was indicated that CGRP is increased broadly in CSF after SAH, which protects the brain against ischemia by regulating vascular tone and decreasing vasospasm.[19] It has also been demonstrated that leptin, which is a stress mediator after injury, may deploy its neuroprotective effects during ischemia/reperfusion brain injury by expression and release of CGRP.[22] One study found that intranasal CGRP could be a promising treatment option for focal ischemic brain injury.[23] They observed that intranasal CGRP can decrease the volume of infarction and improve neurologic functions, probably through limiting apoptosis. Additionally, following administration of CGRP the expression of vascular endothelial growth factor and basic fibroblast growth factor was elevated.[23]

In contrast to our findings, a study found that serum CGRP levels were lower in patients with severe TBI compared with patients with mild/moderate TBI and controls. However, they found that lower levels of CGRP in severe TBI were correlated with 6-month mortality.[9] It is important to note that there is limited data on the impact of prognostic serum CGRP levels in patients following TBI. Most of the available information is from preclinical studies, and the results of this study could encourage further investigation by scientists.

While our study provides valuable insights into early CGRP serum level and outcomes in patients with TBI, several limitations warrant consideration. The relatively small sample size and single-center design may limit the generalizability of our findings. Future research efforts should aim to validate these results in larger, multicenter studies to enhance their applicability and robustness. Additionally, longitudinal follow-up beyond 1 week is needed to assess long-term CGRP serum level, outcomes, and identify potential predictors of late complications in patients with TBI.

 

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Conclusion

In this prospective study, we concluded that patients with severe TBI had a higher serum level of CGRP compared with patients with mild to moderate TBI. In other words, an increased level of CGRP could be an important indicator of severity of TBI in patients with brain injury; however, it cannot be used to predict the outcome following TBI. More studies are needed to confirm this correlation and possible treatment options.

 

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Conflict of Interest

None declared.

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Publication History

Article published online:
10 January 2025