Surgical Neurology
Volume 65, Issue 1 , Pages 7-10, January 2006

Lack of association between the IL1A gene (-889) polymorphism and outcome after head injury

  • Taner Tanriverdi, MD

      Affiliations

    • Department of Neurosurgery, Cerrahpasa Medical Faculty, Istanbul University, Istanbul, Turkey
    • ,
  • Mustafa Uzan, MD

      Affiliations

    • Department of Neurosurgery, Cerrahpasa Medical Faculty, Istanbul University, Istanbul, Turkey
    • Corresponding Author InformationCorresponding author. PO Box 5, Cerrahpasa, 34301 Istanbul, Turkey. Tel.: +90 212 414 34 27; fax: +90 212 414 34 27.
    • ,
  • Galip Zihni Sanus, MD

      Affiliations

    • Department of Neurosurgery, Cerrahpasa Medical Faculty, Istanbul University, Istanbul, Turkey
    • ,
  • Onur Baykara, MSc

      Affiliations

    • Department of Medical Biology, Cerrahpasa Medical Faculty, Istanbul University, Istanbul, Turkey
    • ,
  • Merih Is, MD

      Affiliations

    • Department of Neurology, Cerrahpasa Medical Faculty, Istanbul University, Istanbul, Turkey
    • ,
  • Cigdem Ozkara, MD

      Affiliations

    • Department of Neurosurgery, Medical Faculty, Duzce Izzet Baysal University, Duzce, Turkey
    • ,
  • Nur Buyra, PhD

      Affiliations

    • Department of Medical Biology, Cerrahpasa Medical Faculty, Istanbul University, Istanbul, Turkey

Received 1 November 2004; accepted 16 May 2005.

Article Outline

Abstract 

Background

Interleukin (IL) 1 is a proinflammatory cytokine that has been identified as an important mediator of neurodegeneration induced by ischemia or traumatic brain injury. Accumulating evidence to date has suggested that the major cytokine contributing to neurodegeneration after head injury is IL-1β rather than IL-1α; however, there is no sufficient data regarding IL-1α in literature, and there may be an association between IL1A gene polymorphism and outcome after head injury.

Methods

We performed a prospective clinical study and included a recruited series of 71 patients who had head injury and were admitted to our neurosurgical unit. Severity of initial injury was assessed by the Glasgow Coma Scale. Outcome at 6 months after injury was assessed by means of the Glasgow Outcome Score. Interleukin 1α genotypes were determined from blood samples by standard methods.

Results

Of 40 patients with IL1A*2, 18 (45%) had an unfavorable outcome (dead, vegetative state, or severe disability) compared with 7 (22.5%) of 31 without IL1A*2 (P = .08).

Conclusion

Our findings show that there is no genetic association between IL1A gene polymorphism and outcome after head injury. Further clinical studies should be designed to confirm and further evaluate these findings.

Abbreviations: AD, Alzheimer disease, CT, Computed tomography, FML, Focal mass lesion, GCS, Glasgow Coma Scale, GOS, Glasgow Outcome Score, HI, Head injury, IL-1α, Interleukin 1α, IL-1β, Interleukin 1β, PD, Parkinson disease

Keywords: Cytokine, Head injury, Interleukin 1α, Outcome

 

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1. Introduction 

The contribution of cytokines, particularly interleukin (IL) 1β, to acute or chronic neurodegenerative central nervous system diseases, including stroke, brain trauma, epilepsy, AD, PD, motor neuron diseases, and encephalopathies, has only recently been recognized. The literature underlines that the cytokines play key roles in these inflammatory processes within and outside the brain [2], [5], [14], [21], [23], [24]. However, little information is available in literature concerning the role of IL-1α in traumatic brain injury. Outcome variability after an acute HI is only partly explained by known prognostic factors such as the age of the patient and severity of damage. Furthermore, little attention has been given to the possibility that there may be genetic association between outcome after HI and certain gene polymorphism of IL-1.

Interleukins 1α and 1β are 2 isoforms of IL-1 and are encoded by separate genes, IL1A and IL1B, respectively, located on the long arm of chromosome 2 [15]. The IL1A has a common polymorphism in the 5′ regulatory region (a C to T transition at position -889 relative to the start site of transcription), which gives rise to 2 alleles, allele 1 and allele 2 [15]. Evidence from the studies indicates that IL1A*2 has been associated with juvenile rheumatoid arthritis and periodontitis [10], [11], suggesting a functional effect of this polymorphism on inflammatory processes. Further evidence suggested that the patients with AD, a remarkable degenerative state in which HI is among the known risk factors, have greater risk if the patients have composite of IL1A*2/*2 and IL1B*2/*2 genotype [6], [16], [20].

We have previously demonstrated that there is an association between IL-1β polymorphism and outcome after HI in 69 patients [30]. We now report the results of a prospective clinical study, which tested whether there is an association between outcome after HI and IL-1α polymorphism.

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2. Patients and methods 

Ethical approval for this study was obtained from the Human Investigations Committee at Istanbul University, and all patients or the next of kin, if the patient was unconscious, provided informed consent. Seventy-one patients with acute HI were evaluated prospectively without any selection criteria between January to March 2002. The following clinical data influencing the outcome were collected: age, sex, injury type (CT of the head), and postresuscitation GCS at emergency department. Six months after the injury, the patients were evaluated by means of the GOS during follow-up visits or by contacting either the patients or their relatives. The outcome of every patient was evaluated by the senior author (MU) without knowing the patient's IL-1α genotype, and the results of the tests were submitted independently for statistical analysis.

Patients with severe HI (GCS, ≤8) were transferred to the intensive care unit after initial stabilization or surgical evacuation of a traumatic intracerebral lesion and were treated according to the Brain Trauma Foundation's guidelines for the Management of Severe Head Injury [3]. The patients whose postresuscitation GCS score were greater than 8 and did not require admission to the intensive care unit were transferred to our neurosurgical clinic, where laboratory and/or radiological workup were performed.

Interleukin 1α C(-889)T genotyping genomic DNA was determined with polymerase chain reaction–restriction fragments length polymorphism technique on blood samples obtained for routine clinical workup according to standard procedures [8]. Polymerase chain reaction fragment of the IL-1α promoter region (-889) was amplified using the following primers: 5′-GCATGCCATCACACCTAGTT-3′ and 5′-TTACATATGAGCCTTCAATG-3′ as upstream and downstream primers, respectively. The polymerase chain reaction products were digested with NcoI (New England Biolabs, Inc, Beverly, MA) overnight at 37°C and were run on an ethidium bromide–stained 2% agarose gel for 45 minutes at 200 V and were directly detected under UV light.

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3. Data analysis 

The patients with and without IL1A*2 were compared by use of the χ2 test. A logistic regression analysis was performed to control age, sex, GCS, and initial CT findings. Age was included in the regression model as a continuous variable. GCS was grouped into 3 (3-8, 9-12, and 13-15), and outcome at 6 months was grouped into 2 categories (favorable [mild disability or good recovery] and unfavorable [dead, vegetative state, or severe disability] outcome). Computed tomographic findings were allocated to 1 of 3 categories (diffuse injury with no swelling, diffuse injury with swelling or midline shift, and FML). These were included as a categorical variable.

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4. Results 

The patients in this preliminary study consisted of 56 males (78.8%) and 15 females, with a mean age of 25.8 years. Of the patients, 23 had a severe (GCS, 3-8); 40, a moderate (GCS, 9-12); and 8, a mild/minor injury (GCS, 13-15). Twenty-two patients had an FML, and 49 had a diffuse brain edema. Of 22 patients with FML, 12 underwent surgical operation because of intracerebral (6 patients), epidural (4 patients), and subdural (2 patients) hematoma. The remaining 10 patients were managed conservatively. Six months after the injury, GOS disclosed that 9 patients were dead, 6 continued in vegetative state, 7 were severely disabled, 20 were moderately disabled, and 29 had a good recovery.

Table 1 demonstrates the proportion of 71 patients with each IL-1α-889 genotype. There were 31 (43.6%) IL1A*1/*1, 31 (43.6%) IL1A*1/*2, and 9 (12.6%) IL1A*2/*2 genotypes. We found no significant association between the presence of IL1A*2 and the occurrence of an unfavorable outcome. Of 31 patients without IL1A*2, 7 (22.5%) had an unfavorable outcome compared with 18 (43.5%) of 40 with IL1A*2 (P = .08) (Table 2). Logistic regression analysis demonstrated no significant difference when age, sex, GCS, and CT findings (P > .05) were compared.

Table 1. Proportion of each IL-1α genotype in 71 patients with HI
IL-1α genotypeNo. of patient
IL1A-889*1/*131 (43.6)
IL1A-889*1/*231 (43.6)
IL1A-889*2/*29 (12.6)

Values are presented as n (%).

Table 2. Comparison of patients with HI with (+) and without (−) IL1A*2
Position -889
IL1A*2−IL1A*2+
Initial findings
Mean age (y)2624
Sex (M/F)23:833:7
GCS on admission
3-812 (38.7)11 (27.5)
9-1216 (51.6)24 (60)
13-153 (9.6)5 (12.5)
CT findings
FML9 (29)13 (32.5)
Diffuse edema22 (70.9)27 (67.5)
With swelling13 (59)16 (59.2)
Without swelling9 (39.1)11 (39.2)
Outcome (at 6 mo)
Dead2 (6.45)7 (17.5)
PVS3 (9.67)3 (7.5)
SD3 (9.67)5 (12.5)
MD8 (25.8)12 (30)
GR15 (48.3)13 (32.5)
FO24 (77.4)22 (53.6)
UFO7 (22.5)18 (43.5)

Values are presented as n (%) unless otherwise indicated. M indicates male; F, female; PVS, persistent vegetative state; SD, severe disability; MD, moderate disability; GR, good recovery; FO, favorable outcome; UFO, unfavorable outcome.

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5. Discussion 

Contribution of the genetic polymorphisms to outcome after acute HI has not been studied extensively, and it is likely that multiple genes may influence the outcome. Up to date, only 1 study concerning genetic association with outcome after acute HI has been reported, which showed significant genetic association between apolipoprotein E polymorphism and occurrence of bad outcome after HI [26]. Based on the results of the study mentioned previously, we have shown that there is a significant association between outcome after HI and IL1B*2 polymorphism [30]. It seems that other genetic factors may exist to explain variations in outcome among patients with HI with similar age, neurologic status, and almost the same type of injury. For this reason, we present a clinical study that tries to show contribution of IL1A gene polymorphism to outcome after HI.

The amount of cytokine produced may be related to the cytokine gene polymorphism, especially in the regulatory region. Because they segregate independently, each person has an individual profile of high and low responses, which may account for individual susceptibility to inflammatory conditions, including cerebral injury.

Potent proinflammatory cytokine, IL-1, has 3 structurally related variants (IL-1α, IL-1β, and IL-1 receptor antagonist), each of which is encoded by a separate gene located in a cluster on the long arm of chromosome 2 [25]. In a healthy adult brain, it is expressed at low levels; however, it is rapidly up-regulated in pathological conditions [14], [21]. Therefore, it seems reasonable to suggest that, because inflammatory processes may be a part of the pathogenic cascade after HI in the brain, IL-1 may play important role in the pathogenesis of HI and may influence outcome.

Confirmation of the role of IL-1 in a variety of inflammatory-based diseases, including PD and AD, has been ruled out by exposing the genetic association between disease progression and cytokines, particularly IL-1β. Although genetic studies demonstrated overrepresentation of an IL-1α-889T allele of polymorphism in the promoter region of the gene in patients with AD [6], [7], [16], [20], there is still some controversy regarding the relationship between IL-1α-889T polymorphism and AD [4], [9], [12], [19]. Some recent articles published in the literature demonstrated lack of genetic association between IL1A gene polymorphisms and AD [13], [17], [29] and/or PD [23]. These results led us to investigate possible association between IL1A gene polymorphism and outcome in patients with HI, and this is the first study to investigate the association of IL1A gene polymorphism and outcome in patients with HI. In this study, we found a lack of association between the IL1A gene polymorphism and outcome in 71 patients with HI. Nonetheless, we must insist that our results therefore need to be confirmed by future clinical studies with a large cohort of patients with acute HI.

Accumulating evidence from animal and clinical studies implicates the contribution of IL-1 to neuronal injury. Expression of IL-1α, particularly IL-1β, is induced rapidly as a response to acute brain insults [1], [18], [22]. Clinical studies also reported elevated IL-1 levels in postmortem brain tissue of patients with stroke [21]. Microglia and perivascular macrophages are the main sources of IL-1, but it has been also found that astrocytes, endothelial cells, invading immune cells, and neurons can express IL-1 [21]. Interleukin 1 receptor antagonist is believed to block all actions of IL-1 and reproducibly reduces neuronal loss caused by cerebral trauma and ischemia [27], [28]. Intracerebrovascular injection of neutralizing anti–IL-1β antibody in rats reduces ischemic neurons, implicating IL-1β as the major mediator of inflammatory processes after injury [27]. Such findings are important for therapeutic implications. Deletion of either IL1A or IL1B gene has no effect on the damage in mice caused by cerebral ischemia [2]. In contrast, deletion of both IL1A and IL1B gene caused almost 80% reductions in ischemic brain region [2]. These encouraging results suggest that IL-1 might have a key role, which may regulate the inflammatory process in neuronal injury.

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6. Conclusions 

As we understand the role of cytokines and their gene polymorphisms in the setting of traumatic brain injury, potentially useful neuroprotective agents will be developed and further genetic studies with large number of patients are necessary to investigate the genetic basis and factors involved in the development of neurodegenerative process after HI.

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PII: S0090-3019(05)00400-3

doi:10.1016/j.surneu.2005.05.024

Surgical Neurology
Volume 65, Issue 1 , Pages 7-10, January 2006

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