Sex, Genes, and Traumatic Brain Injury (TBI): A Call for a Gender Inclusive Approach to the Study of TBI in the Lab

Mechanisms of vascular injury in neurotrauma: A critical review of the literature

One in every two individuals will experience a traumatic brain injury in their lifetime with significant impacts on the global economy and healthcare system each year. Neurovascular injury is a key aspect of neurotrauma to both the brain and the spinal cord and an important avenue of current and future research seeking innovative therapies. In this paper, we discuss primary and secondary neurotrauma, mechanisms of injury, the glymphatic system, repair and recovery. Each of these topics are directly connected to the vasculature of the central nervous system, affecting severity of injury and recovery. Consequently, neurovascular injury in trauma represents a promising target for future therapeutics and innovation.

Neuroprotection or Sex Bias: A Protective Response to Traumatic Brain Injury in the Females

Traumatic brain injury (TBI) is a major healthcare problem and a common cause of mortality and morbidity. Clinical and preclinical research suggests sex-related differences in short- and longterm outcomes following TBI; however, males have been the main focus of TBI research. Females show a protective response against TBI. Female animals in preclinical studies and women in clinical trials have shown comparatively better outcomes against mild, moderate, or severe TBI. This reflects a favorable protective nature of the females compared to the males, primarily attributed to various protective mechanisms that provide better prognosis and recovery in the females after TBI. Understanding the sex difference in the TBI pathophysiology and the underlying mechanisms remains an elusive goal. In this review, we provide insights into various mechanisms related to the anatomical, physiological, hormonal, enzymatic, inflammatory, oxidative, genetic, or mitochondrial basis that support the protective nature of females compared to males. Furthermore, we sought to outline the evidence of multiple biomarkers that are highly potential in the investigation of TBI's prognosis, pathophysiology, and treatment and which can serve as objective measures and novel targets for individualized therapeutic interventions in TBI treatment. Implementations from this review are important for the understanding of the effect of sex on TBI outcomes and possible mechanisms behind the favorable response in females. It also emphasizes the critical need to include females as a biological variable and in sufficient numbers in future TBI studies.

Considering Sex as a Variable at a Research University: Knowledge, Attitudes, and Practices

Biomedical research has a history of excluding females as research subjects, which threatens rigor, reproducibility, and inclusivity. In 2016, to redress this bias, the U.S. National Institutes of Health (NIH) implemented a policy requiring the consideration of sex as a biological variable (SABV) in all studies involving vertebrate animals, including humans. Unless strongly justified, females and males must be included in all studies and results reported disaggregated by sex. Recent evidence indicates, however, that misunderstandings of the policy and other significant barriers impede its implementation. To shed light on those barriers at our home institution, we conducted a study funded by the Emory University Specialized Center of Research Excellence on Sex Differences (SCORE). In semistructured interviews of Emory principal investigators in the biological sciences, we noted their knowledge of what the policy entails and why it was implemented, their attitudes toward it, and the extent to which it has or has not changed their research practices. Although attitudes toward SABV were generally positive, most researchers face challenges with respect to its implementation. We suggest interventions that can be mounted at the level of home institutions, such as raising awareness of locally available core facilities, to help address these challenges. More training is needed on what the policy asks of researchers, how sex is defined, the nonhormonal ways that sex differences can manifest, and best practices for statistical analysis of sex-based data. Home institutions may also want to explore ways to lessen the stress associated with rollout of SABV policy.

The role of social determinants of health in the receipt of school services after\\ traumatic brain injury: A focus review on underserved pediatric populations

BACKGROUND

Return to school is key for community re-integration after a traumatic brain injury (TBI). School support facilitates and ensure a successful transition back to school. However, access to school services is not uniform among U.S. children.

OBJECTIVE

To describe school services for children with TBI from minoritized backgrounds and highlight population-specific risk factors and facilitators for accessing services.

METHODS

Narrative review of the literature including studies on return to school after a mild-complicated, moderate, or severe TBI, among children enrolled in the U.S. school system. We describe receipt of services, enabling and risk factors, and outcomes, for minority children.

RESULTS

There is a gap in knowledge regarding return to school among minoritized children with TBIs. Studies have few participants from racial and ethnic minority backgrounds, or low income or rural communities. Transgender and non-binary youth are not represented in present research efforts. Studies highlight larger barriers to receipt of school services among minority children and additional barriers associated with their minority status.

CONCLUSION

Diversity in the U.S pediatric population is increasing. Minoritized populations are at increased risk for TBI and poor outcomes. Research focused on the needs of these populations is required to optimize school return after TBI hospitalization and overall post-discharge care.

A Systematic Review and Meta-Analysis on the Therapeutic Efficacy of Heparin and Low Molecular Weight Heparins in Animal Studies of Traumatic Brain Injury

The identification of effective pharmacotherapies for traumatic brain injury (TBI) remains a major challenge. Treatment with heparin and its derivatives is associated with neuroprotective effects after experimental TBI; however, the optimal dosage and method of administration, modes of action, and effects on hemorrhage remain unclear. Therefore, this review aimed to systematically evaluate, analyze, and summarize the available literature on the use of heparin and low molecular weight heparins (LMWHs) as treatment options for experimental TBI. We searched two online databases (PubMed and ISI Web of Science) to identify relevant studies. Data pertaining to TBI paradigm, animal subjects, drug administration, and all pathological and behavior outcomes were extracted. Eleven studies met our pre-specified inclusion criteria, and for outcomes with sufficient numbers, data from seven publications were analyzed in a weighted mean difference meta-analysis using a random-effects model. Study quality and risk of bias were also determined. Meta-analysis revealed that heparin and its derivatives decreased brain edema, leukocyte rolling, and vascular permeability, and improved neurological function. Further, treatment did not aggravate hemorrhage. These findings must be interpreted with caution, however, because they were determined from a limited number of studies with substantial heterogeneity. Also, overall study quality was low based on absences of data reporting, and potential publication bias was identified. Importantly, we found that there are insufficient data to evaluate the variables we had hoped to investigate. The beneficial effects of heparin and LMWHs, however, suggest that further pre-clinical studies are warranted.

The outcome of severely injured patients following traumatic brain injury is affected by gender-A retrospective, multicenter, matched-pair analysis utilizing data of the TraumaRegister DGU®

INTRODUCTION

Traumatic brain injury (TBI) causes a major health-concern globally. Gender-dependent differences in mortality outcome after TBI have been controversially discussed.

MATERIALS AND METHODS

We conducted a retrospective, multicenter, matched-pair analysis using data collected by the TraumaRegister DGU® of the German Trauma Society between 2009 and 2020. All patients after severe trauma with the leading injury of TBI (AIS ≥ 3), above 18 years of age were included. Thereby, 42,034 cases were identified. We used 12 different matching criteria to ensure highly accurate matching and were able to match 11,738 pairs of one female and one male patient.

RESULTS

Average age at injury was 67.5 ± 19.6 years in women and 66.7 ± 19.1 years in men. Mean Injury Severity Score (ISS) was 21.3 ± 8.1 in women and 21.6 ± 8.2 in men. While women were more likely to die within the first week after trauma, the mortality was significantly higher in men overall (30.8 vs. 29.2%, p < 0.002). Women were less likely to suffer from multi organ failure (MOF) (27.5 vs. 33.0%) or sepsis (4.5 vs. 7.1%). When comparing younger (≤ 45-years) and older (> 45 years) patients, overall mortality was lower in men (13.1% men vs. 13.4% women) in the younger age group, but in the older group mortality was lower in women (33.8% men vs. 31.8% women).

DISCUSSION

Gender-specific differences in the clinical outcome of severely injured patients with leading TBI could be detected. While women are overall characterized by an advantage in survival, this feature is not equally reproducible in premenopausal women. Therefore, the exact pathophysiological reasons for the described survival advantages of women will have to be explored in further prospective clinical studies.

Traumatic brain injury augurs ill for prolonged deficits in the brain's structural and functional integrity following controlled cortical impact injury

Previous neuroimaging studies in rodents investigated effects of the controlled cortical impact (CCI) model of traumatic brain injury (TBI) within one-month post-TBI. This study extends this temporal window to monitor the structural–functional alterations from two hours to six months post-injury. Thirty-seven male Sprague–Dawley rats were randomly assigned to TBI and sham groups, which were scanned at two hours, 1, 3, 7, 14, 30, 60 days, and six months following CCI or sham surgery. Structural MRI, diffusion tensor imaging, and resting-state functional magnetic resonance imaging were acquired to assess the dynamic structural, microstructural, and functional connectivity alterations post-TBI. There was a progressive increase in lesion size associated with brain volume loss post-TBI. Furthermore, we observed reduced fractional anisotropy within 24 h and persisted to six months post-TBI, associated with acutely reduced axial diffusivity, and chronic increases in radial diffusivity post-TBI. Moreover, a time-dependent pattern of altered functional connectivity evolved over the six months’ follow-up post-TBI. This study extends the current understanding of the CCI model by confirming the long-term persistence of the altered microstructure and functional connectivity, which may hold a strong translational potential for understanding the long-term sequelae of TBI in humans.

Systematic Review of Sex and Gender Effects in Traumatic Brain Injury: Equity in Clinical and Functional Outcomes

Background: Although traumatic brain injury (TBI) is a leading cause of death and disability in male and female patients worldwide, little is known about the effect of sex and gender on TBI outcomes.

Objectives: This systematic review summarizes the evidence on the effect of sex and gender on core TBI outcomes.

Methods: All English-language studies from six literature databases that addressed core outcomes in adults with TBI and included sex or gender, TBI severity, and age in their analyses were considered eligible. Two reviewers extracted data, and two reviewers assessed study quality using tools recommended by the National Institutes of Health. The results were sorted according to time post-injury, injury severity, gender equity ranking of the study's country of origin, and outcomes studied. The results from the included studies were grouped based on the approach taken in reporting their respective findings.

Results and Limitations: Of 172 articles assessed, 58 studies were selected, comprising 1, 265, 955 participants with TBI (67% male across all studies) of all injury severities. All studies were conducted in countries with a very high or high human development index, while the Gender Inequality Index (GII) varied. While the heterogeneity across studies limited any meaningful conclusions with respect to the role of sex and gender, we did observe that as gender equality ranking improved, differences between male and female participants in outcomes would diminish. Inclusion of social equity parameters in the studies was limited.

Conclusions and Implications: The non-uniform findings observed bring forth the need to develop and use a comprehensive and consistent methodology in the study of sex and gender post-TBI, incorporating social equity parameters to uncover the potential social underpinnings of gender effects on health and functional outcomes.

Systematic Review Registration: CRD42018098697.