Perspective on statistical power and equivalences tests

The use of both sexes or genders should be considered in experimental design, analysis, and reporting. Since there is no requirement to double the sample size or to have sufficient power to study sex differences, challenges for the statistical analysis can arise. In this article we focus on the topics of statistical power and ways to increase this power. We also discuss the choice of an appropriate design and statistical method, and include a separate section on equivalence tests needed to show the absence of a relevant difference.

Developmental changes in lung function of mice are independent of sex as a biological variable

Pulmonary function testing (PFT) in mice includes biomechanical assessment of lung function relevant to physiology in health and its alteration in disease, hence, it is frequently used in preclinical modeling of human lung pathologies. Despite numerous reports of PFT in mice of various ages, there is a lack of reference data for developing mice collected using consistent methods. Therefore, we profiled PFTs in male and female C57BL/6J mice from 2 to 23 wk of age, providing reference values for age- and sex-dependent changes in mouse lung biomechanics during development and young adulthood. Although males and females have similar weights at birth, females weigh significantly less than males after 5 wk of age (P < 0.001) with largest weight gain observed between 3 and 8 wk in females and 3 and 13 wk in males, after which weight continued to increase more slowly up to 23 wk of age. Lung function parameters including static compliance and inspiratory capacity also increased rapidly between 3 and 8 wk in female and male mice, with male mice having significantly greater static compliance and inspiratory capacity than female mice (P < 0.001). Although these parameters appear higher in males at a given age, allometric scaling showed that static compliance and inspiratory compliance were comparable between the two sexes. This suggests that differences in measurements of lung function are likely body weight-based rather than sex-based. We expect these data to facilitate future lung disease research by filling a critical knowledge gap in our field.NEW & NOTEWORTHY This study provides reference values for changes in mouse lung biomechanics from 2 to 23 wk of age. There are rapid developmental changes in lung structure and function of male and female mice between the ages of 3 and 8 wk. Male mice become noticeably heavier than female mice at or about 5 wk of age. We identified that differences in normal lung function measurements are likely weight-based, not sex-based.

Sex contextualism in laboratory research: Enhancing rigor and precision in the study of sex-related variables

Understanding sex-related variation in health and illness requires rigorous and precise approaches to revealing underlying mechanisms. A first step is to recognize that sex is not in and of itself a causal mechanism; rather, it is a classification system comprising a set of categories, usually assigned according to a range of varying traits. Moving beyond sex as a system of classification to working with concrete and measurable sex-related variables is necessary for precision. Whether and how these sex-related variables matter-and what patterns of difference they contribute to-will vary in context-specific ways. Second, when researchers incorporate these sex-related variables into research designs, rigorous analytical methods are needed to allow strongly supported conclusions. Third, the interpretation and reporting of sex-related variation require care to ensure that basic and preclinical research advance health equity for all.

Pharmacogenetics of sodium-glucose co-transporter-2 inhibitors: Validation of a sex-agnostic pharmacodynamic biomarker

AIM

To validate pharmacodynamic responses to sodium-glucose co-transporter-2 (SGLT2) inhibitors and test for association with genetic variants in SLC5A4, SLC5A9, and SLC2A9.

METHODS

Canagliflozin (300 mg), a SGLT2 inhibitor, was administered to 30 healthy volunteers. Several endpoints were measured to assess clinically relevant responses, including drug-induced increases in urinary excretion of glucose, sodium and uric acid.

RESULTS

This pilot study confirmed that canagliflozin (300 mg) triggered acute changes in mean levels of several biomarkers: fasting plasma glucose (-4.1 mg/dL; P = 6 × 10-5 ), serum creatinine (+0.05 mg/dL; P = 8 × 10-4 ) and serum uric acid (-0.90 mg/dL; P = 5 × 10-10 ). The effects of sex on glucosuria depended upon how data were normalized. Whereas males' responses were ~60% greater when data were normalized to body surface area, males and females exhibited similar responses when glucosuria was expressed as grams of urinary glucose per gram-creatinine. The magnitude of glucosuria was not significantly correlated with fasting plasma glucose, estimated glomerular filtration rate or age in those healthy individuals without diabetes with an estimated glomerular filtration rate of more than 60 mL/min/1.73m2 .

CONCLUSIONS

Normalizing data relative to creatinine excretion will facilitate including data from males and females in a single analysis. Furthermore, because our ongoing pharmacogenomic study (NCT02891954) is conducted in healthy individuals, this will facilitate detection of genetic associations with limited confounding by other factors such as HbA1c and renal function.

Best practices to promote rigor and reproducibility in the era of sex-inclusive research

To enhance inclusivity and rigor, many funding agencies and journals now mandate the inclusion of females as well as males in biomedical studies. These mandates have enhanced generalizability and created unprecedented opportunities to discover sex differences. However, education in sound methods to consider sex as a subgroup category has lagged behind, resulting in a problematic literature in which study designs, analyses, and interpretations of results are often flawed. Here, we outline best practices for complying with sex-inclusive mandates, both for studies in which sex differences are a primary focus and for those in which they are not. Our recommendations are organized within the "4 Cs of Studying Sex to Strengthen Science: Consideration, Collection, Characterization and Communication," a framework developed by the Office of Research on Women's Health at the National Institutes of Health in the United States. Following these guidelines should help researchers include females and males in their studies while at the same time upholding high standards of rigor.

Comparative Outcomes of Groin Hernia Repair by Sex Among Medicare Beneficiaries

OBJECTIVE

To compare the rates of operative recurrence between male and female patients undergoing groin hernia repair.

BACKGROUND DATA

Groin hernia repair is common but understudied in females. Limited prior work demonstrates worse outcomes among females.

METHODS

Using Medicare claims, we performed a retrospective cohort study of adult patients who underwent elective groin hernia repair between January 1, 2010 and December 31, 2017. We used a Cox proportional hazards model to evaluate the risk of operative recurrence up to 5 years following the index operation. Secondary outcomes included 30-day complications following surgery.

RESULTS

Among 118,119 patients, females comprised the minority of patients (n=16,056, 13.6%). Compared with males, female patients were older (74.8 vs. 71.9 y, P <0.01), more often white (89.5% vs. 86.7%, P <0.01), and had a higher prevalence of nearly all measured comorbidities. In the multivariable Cox proportional hazards model, we found that female patients had a significantly lower risk of operative recurrence at 5-year follow-up compared with males (aHR 0.70, 95% CI 0.60-0.82). The estimated cumulative incidence of recurrence was lower among females at all time points: 1 year [0.68% (0.67-0.68) vs. 0.88% (0.88-0.89)], 3 years [1.91% (1.89-1.92) vs. 2.49% (2.47-2.5)], and 5 years [2.85% (2.82-2.88) vs. 3.7% (3.68-3.75)]. We found no significant difference in the 30-day risk of complications.

CONCLUSIONS

We found that female patients experienced a lower risk of operative hernia recurrence following elective groin hernia repair, which is contrary to what is often reported in the literature. However, the risk of operative recurrence was low overall, indicating excellent surgical outcomes among older adults for this common surgical condition.

Lower female survival from an opportunistic infection reveals progesterone-driven sex bias in trained immunity

Immune responses differ between females and males, although such sex-based variance is incompletely understood. Observing that bacteremia of the opportunistic pathogen Burkholderia gladioli caused many more deaths of female than male mice bearing genetic deficiencies in adaptive immunity, we determined that this was associated with sex bias in the innate immune memory response called trained immunity. Female attenuation of trained immunity varies with estrous cycle stage and correlates with serum progesterone, a hormone that decreases glycolytic capacity and recall cytokine secretion induced by antigen non-specific stimuli. Progesterone receptor antagonism rescues female trained immune responses and survival from controlled B. gladioli infection to magnitudes similar to those of males. These data demonstrate progesterone-dependent sex bias in trained immunity where attenuation of female responses is associated with survival outcomes from opportunistic infection.

Inclusion of Sex as a Biological Variable in Biomedical Sciences at the Undergraduate Level and Beyond

To improve research on women's health, and to achieve better understanding of the factors controlling disease across diverse populations of humans, it is imperative to study sex differences in physiology and disease. After the introduction of the "SABV policy" at NIH, which requires investigators using animals or humans to consider sex as a biological factor, it became clear that many investigators were unaware of concepts of sexual differentiation or methods that can be used to study sex as a biological variable (SABV). To remedy this situation, efforts have increased to teach concepts and methods of SABV at all educational levels. The UCLA Scientific Center of Research Excellence (SCORE) grant "Sex differences in the metabolic syndrome" promotes education about SABV through three primary mechanisms: (1) through didactic course content for students at the undergraduate level, (2) by providing pilot funding for early career investigators to study the role of sex in metabolism-related areas, and (3) through curation of a video library, which may be useful for investigators performing research at the graduate, postgraduate, and faculty levels.

Developing Researchers with Expertise in Sex as a Biological Variable through SCORE Career Enhancement Core Center Programs

There is a critical need for interdisciplinary and translational scientists to apply sex as a biological variable (SABV) research to address knowledge gaps in the health of women. In 2018, the Office of Research on Women's Health (ORWH) partnered with several National Institute of Health (NIH) Institutes and Centers to expand the Specialized Centers of Research (SCOR) Excellence (SCORE) Programs (together referred to as SCOR/E) with an important feature-the Career Enhancement Core (CEC). The SCORE CEC mentors early career investigators to become the next generation of biomedical and behavioral researchers focused on SABV and women's health. In this article, we outline our approach at the Yale University SCORE to support early career trajectories through the provision of salary support, educational curricula, translational mentorship, pilot project funding, and professional development. Using the Yale-SCOR/E CEC Programs as instructional models, we highlight critical measures of academic success, namely grant funding and publications, among early career investigators. At Yale University, 12 pilot projects funded by the SCOR/E Programs resulted in 14 extramural grants, amounting to an $80 return on every $1 invested in "seed" funding. So far, our SCOR/E Programs have resulted in 129 publications, 83% of which were first-authored by trainees, and 100% of trainees continued research careers with an emphasis on SABV. Finally, we provide recommendations on how biomedical scientists can apply SABV in their studies of major medical conditions in an interdisciplinary and integrative way.

Establishment of a Private Foundation-Academic Partnership to Promote Careers of Early-Stage Investigators Examining the Influence of Sex and Gender on Health and Health Care

Biological sex and gender-based constructs contribute significantly to the diversity of disease outcomes and treatment responses across the life course. To promote research considering sex and gender, the National Institutes of Health (NIH) Office of Research on Women's Health (ORWH) launched the Specialized Centers of Research Excellence (SCORE) on sex differences program. The Career Enhancement Core (CEC) of the Johns Hopkins SCORE on Sex and Age Differences in Immunity to Influenza (SADII) partnered with the Foundation for Gender-Specific Medicine, which matched NIH funding to support seed grants. Over 3 years we awarded 12 (10 were women faculty) seed grants to early-stage investigators. One year after the award, the seed grant awardees highlighted their progress, including publications, grant applications, and abstracts. All awardees noted challenges with their progress related to the COVID-19 pandemic and supply chain delays and shared suggestions for improving the programming of the CEC. They also highlighted the multiple ways the awards had helped them gain pilot data toward larger grants, build collaborative relationships, and present at the annual SCORE symposium. We describe a model and evidence supporting a private-academic collaboration to support the careers of early-stage investigators conducting research related to sex and gender.

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.

Reasons for the Sex Bias in Osteoarthritis Research: A Review of Preclinical Studies

Osteoarthritis (OA) is one of the most common degenerative diseases of articular cartilage. During OA, all the elements that contribute to the joint undergo physiological and structural changes that impair the joint function and cause joint pain and stiffness. OA can arise naturally, with the aging population witnessing an increase in diagnoses of this pathology, but the root causes of OA have yet to be identified, and increasing interest is arising towards investigating biological sex as a risk factor. Clinical studies show increased prevalence and worse clinical outcomes for female patients, yet most clinical and preclinical studies have disproportionately focused on male subjects. This review provides a critical overview of preclinical practices in the context of OA, highlighting the underlying need for taking biological sex as both a risk factor and an important component affecting treatment outcome. A unique insight into the possible reasons for female underrepresentation in preclinical studies is offered, including factors such as lack of specific guidelines requiring the analysis of sex as a biological variable (SABV), research-associated costs and animal handling, and wrongful application of the reduction principle. Additionally, a thorough investigation of sex-related variables is provided, stressing how each of them could add valuable information for the understanding of OA pathophysiology, as well as sex-dependent treatment strategies.

Pharmacogenetics of SGLT2 Inhibitors: Validation of a sex-agnostic pharmacodynamic biomarker

Aim

SGLT2 inhibitors provide multiple benefits to patients with type 2 diabetes - including improved glycemic control and decreased risks of cardiorenal disease. Because drug responses vary among individuals, we initiated investigations to identify genetic variants associated with the magnitude of drug responses.

Methods

Canagliflozin (300 mg) was administered to 30 healthy volunteers. Several endpoints were measured to assess clinically relevant responses - including drug-induced increases in urinary excretion of glucose, sodium, and uric acid.

Results

This pilot study confirmed that canagliflozin (300 mg) triggered acute changes in mean levels of several biomarkers: fasting plasma glucose (-4.1 mg/dL; p=6x10), serum creatinine (+0.05 mg/dL; p=8×10 -4 ), and serum uric acid (-0.90 mg/dL; p=5×10 -10 ). The effects of sex on glucosuria depended upon how data were normalized. Whereas males' responses were ∼60% greater when data were normalized to body surface area, males and females exhibited similar responses when glucosuria was expressed as grams of urinary glucose per gram-creatinine. The magnitude of glucosuria was not significantly correlated with fasting plasma glucose, estimated GFR, or age in these healthy non-diabetic individuals with estimated GFR>60 mL/min/1.73m 2 .

Conclusions

Normalizing data relative to creatinine excretion will facilitate including data from males and females in a single analysis. Furthermore, because our ongoing pharmacogenomic study ( NCT02891954 ) is conducted in healthy individuals, this will facilitate detection of genetic associations with limited confounding by other factors such as age and renal function.

Registration

NCT02462421 ( clinicaltrials.gov ).

Funding

Research grants from the National Institute of Diabetes and Digestive and Kidney Diseases: R21DK105401, R01DK108942, T32DK098107, and P30DK072488.

Quality control and analytic best practices for testing genetic models of sex differences in large populations

Phenotypic sex-based differences exist for many complex traits. In other cases, phenotypes may be similar, but underlying biology may vary. Thus, sex-aware genetic analyses are becoming increasingly important for understanding the mechanisms driving these differences. To this end, we provide a guide outlining the current best practices for testing various models of sex-dependent genetic effects in complex traits and disease conditions, noting that this is an evolving field. Insights from sex-aware analyses will not only teach us about the biology of complex traits but also aid in achieving the goals of precision medicine and health equity for all.

CORP: Sources and degrees of variability in whole animal intermittent hypoxia experiments

Chamber exposures are commonly used to evaluate the physiological and pathophysiological consequences of intermittent hypoxia in animal models. Researchers in this field use both commercial and custom-built chambers in their experiments. The purpose of this Cores of Reproducibility in Physiology paper is to demonstrate potential sources of variability in these systems that researchers should consider. Evaluating the relationship between arterial oxygen saturation and inspired oxygen concentration, we found that there are important sex-dependent differences in the commonly used C57BL6/J mouse model. The time delay of the oxygen sensor that provides feedback to the system during the ramp-down and ramp-up phases was different, limiting the number of cycles per hour that can be conducted and the overall stability of the oxygen concentration. The time to reach the hypoxic and normoxic hold stages, and the overall oxygen concentration, were impacted by the cycle number. These variables were further impacted by whether there are animals present in the chamber, highlighting the importance of verifying the cycling frequency with animals in the chamber. At ≤14 cycles/h, instability in the chamber oxygen concentration did not impact arterial oxygen saturation but may be important at higher cycle numbers. Taken together, these data demonstrate the important sources of variability that justify reporting and verifying the target oxygen concentration, cycling frequency, and arterial oxygen concentration, particularly when comparing different animal models and chamber configurations.NEW & NOTEWORTHY Intermittent hypoxia exposures are commonly used in physiology and many investigators use chamber systems to perform these studies. Because of the variety of chamber systems and protocols used, it is important to understand the sources of variability in intermittent hypoxia experiments that can impact reproducibility. We demonstrate sources of variability that come from the animal model, the intermittent hypoxia protocol, and the chamber system that can impact reproducibility.

Sex Differences in Pain: Spinal Cord Injury in Female and Male Mice Elicits Behaviors Related to Neuropathic Pain

Spinal cord injury (SCI) in humans frequently causes intractable chronic pain. Females are susceptible to worse pain than males, and females may show higher pain prevalence after SCI. Despite this difference in the clinical prevalence of SCI pain, few pre-clinical studies have systematically studied sex differences in SCI-elicited pain-related behaviors in rodents. Here, we leverage data from a large cohort of mice to test whether contusion SCI consistently causes pain symptoms in mice, and to establish whether female (vs. male) mice display heightened hypersensitivity after SCI. Mechanical and heat sensory thresholds were assessed using the von Frey and Hargreaves tests, respectively. In an initial experiment, female mice receiving moderate 60 kDyn SCI or moderate-to-severe 75 kDyn SCI at T9 both exhibited mechanical and heat pain symptoms compared with sham controls. A 75 kDyn SCI caused excess motor deficits that confounded defining pain sensitivity at acute times; therefore, the moderate SCI force was used for subsequent experiments. Next, adult female and male C57BL6/J mice received sham surgery or T9 moderate contusion SCI. Comparing female to male mice after SCI, we reveal that mice of both sexes displayed mechanical and heat hypersensitivity compared with sham controls, from acute-to-chronic post-injury times. Females had amplified SCI-elicited hypersensitivity compared with males. Our data suggest that thoracic contusion SCI elicits consistent and persistent pain-associated symptoms, which are more intense in female than in male mice. These results have important implications for uncovering sex-specific mechanisms and therapeutic targets to ameliorate neuropathic pain after SCI.

Improving translatability of spinal cord injury research by including age as a demographic variable

Pre-clinical and clinical spinal cord injury (SCI) studies differ in study design, particularly in the demographic characteristics of the chosen population. In clinical study design, criteria such as such as motor scores, neurological level, and severity of injury are often key determinants for participant inclusion. Further, demographic variables in clinical trials often include individuals from a wide age range and typically include both sexes, albeit historically most cases of SCI occur in males. In contrast, pre-clinical SCI models predominately utilize young adult rodents and typically use only females. While it is often not feasible to power SCI clinical trials to test multi-variable designs such as contrasting different ages, recent pre-clinical findings in SCI animal models have emphasized the importance of considering age as a biological variable prior to human experiments. Emerging pre-clinical data have identified case examples of treatments that diverge in efficacy across different demographic variables and have elucidated several age-dependent effects in SCI. The extent to which these differing or diverging treatment responses manifest clinically can not only complicate statistical findings and trial interpretations but also may be predictive of worse outcomes in select clinical populations. This review highlights recent literature including age as a biological variable in pre-clinical studies and articulates the results with respect to implications for clinical trials. Based on emerging unpredictable treatment outcomes in older rodents, we argue for the importance of including age as a biological variable in pre-clinical animal models prior to clinical testing. We believe that careful analyses of how age interacts with SCI treatments and pathophysiology will help guide clinical trial design and may improve both the safety and outcomes of such important efforts.

Methods for detecting probable COVID-19 cases from large-scale survey data also reveal probable sex differences in symptom profiles

BACKGROUND

Daily symptom reporting collected via web-based symptom survey tools holds the potential to improve disease monitoring. Such screening tools might be able to not only discriminate between states of acute illness and non-illness, but also make use of additional demographic information so as to identify how illnesses may differ across groups, such as biological sex. These capabilities may play an important role in the context of future disease outbreaks.

OBJECTIVE

Use data collected via a daily web-based symptom survey tool to develop a Bayesian model that could differentiate between COVID-19 and other illnesses and refine this model to identify illness profiles that differ by biological sex.

METHODS

We used daily symptom profiles to plot symptom progressions for COVID-19, influenza (flu), and the common cold. We then built a Bayesian network to discriminate between these three illnesses based on daily symptom reports. We further separated out the COVID-19 cohort into self-reported female and male subgroups to observe any differences in symptoms relating to sex. We identified key symptoms that contributed to a COVID-19 prediction in both males and females using a logistic regression model.

RESULTS

Although the Bayesian model performed only moderately well in identifying a COVID-19 diagnosis (71.6% true positive rate), the model showed promise in being able to differentiate between COVID-19, flu, and the common cold, as well as periods of acute illness vs. non-illness. Additionally, COVID-19 symptoms differed between the biological sexes; specifically, fever was a more important symptom in identifying subsequent COVID-19 infection among males than among females.

CONCLUSION

Web-based symptom survey tools hold promise as tools to identify illness and may help with coordinated disease outbreak responses. Incorporating demographic factors such as biological sex into predictive models may elucidate important differences in symptom profiles that hold implications for disease detection.

Investigation of murine host sex as a biological variable in epithelial barrier function and muscle contractility in human intestinal organoids

Intestinal failure (IF) occurs when intestinal surface area or function is not sufficient to support digestion and nutrient absorption. Human intestinal organoid (HIO)-derived tissue-engineered intestine is a potential cure for IF. Research to date has demonstrated successful HIO transplantation (tHIO) into mice with significant in vivo maturation. An area lacking in the literature is exploration of murine host sex as a biological variable (SABV) in tHIO function. In this study, we investigate murine host SABV in tHIO epithelial barrier function and muscle contractility. HIOs were generated in vitro and transplanted into nonobese diabetic, severe combined immunodeficiency gamma chain deficient male and female mice. tHIOs were harvested after 8-12 weeks in vivo. Reverse transcriptase polymerase chain reaction and immunohistochemistry were conducted to compare tight junctions and contractility-related markers in tHIOs. An Ussing chamber and contractility apparatus were used to evaluate tHIO epithelial barrier and muscle contractile function, respectively. The expression and morphology of tight junction and contractility-related markers from tHIOs in male and female murine hosts is not significantly different. Epithelial barrier function as measured by transepithelial resistance, short circuit current, and fluorescein isothiocyanate-dextran permeability is no different in tHIOs from male and female hosts, although these results may be limited by HIO epithelial immaturity and a short flux time. Muscle contractility as measured by total contractile activity, amplitude, frequency, and tension is not significantly different in tHIOs from male and female hosts. The data suggest that murine host sex may not be a significant biological variable influencing tHIO function, specifically epithelial barrier maintenance and muscle contractility, though limitations exist in our model.

Sex-specific effects of maternal weight loss on offspring cardiometabolic outcomes in the obese preeclamptic-like mouse model, BPH/5

AbstractPreeclampsia (PE) is a hypertensive disorder that impacts 2-8% of pregnant women worldwide. It is characterized by new onset hypertension during the second half of gestation and is a leading cause of maternal and fetal morbidity/mortality. Maternal obesity increases the risk of PE and is a key predictor of childhood obesity and potentially offspring cardiometabolic complications in a sex-dependent manner. The influence of the maternal obesogenic environment, with superimposed PE, on offspring development into adulthood is unknown. Obese BPH/5 mice spontaneously exhibit late-gestational hypertension, fetal demise and growth restriction, and excessive gestational weight gain. BPH/5 females have improved pregnancy outcomes when maternal weight loss via pair-feeding is imposed beginning at conception. We hypothesized that phenotypic differences between female and male BPH/5 offspring can be influenced by pair feeding BPH/5 dams during pregnancy. BPH/5 pair-fed dams have improved litter sizes and increased fetal body weights. BPH/5 offspring born to ad libitum dams have similar sex ratios, body weights, and fecal microbiome as well as increased blood pressure that is reduced in the dam pair-fed offspring. Both BPH/5 male and female offspring born to pair-fed dams have a reduction in adiposity and an altered gut microbiome, while only female offspring born to pair-fed dams have decreased circulating leptin and white adipose tissue inflammatory cytokines. These sexually dimorphic results suggest that reduction in the maternal obesogenic environment in early pregnancy may play a greater role in female BPH/5 sex-dependent cardiometabolic outcomes than males. Reprograming females may mitigate the transgenerational progression of cardiometabolic disease.

Copper-Binding Domain Variation in a Novel Murine Lysyl Oxidase Model Produces Structurally Inferior Aortic Elastic Fibers Whose Failure Is Modified by Age, Sex, and Blood Pressure

Lysyl oxidase (LOX) is a copper-binding enzyme that cross-links elastin and collagen. The dominant LOX variation contributes to familial thoracic aortic aneurysm. Previously reported murine Lox mutants had a mild phenotype and did not dilate without drug-induced provocation. Here, we present a new, more severe mutant, Loxb2b370.2Clo (c.G854T; p.Cys285Phe), whose mutation falls just N-terminal to the copper-binding domain. Unlike the other mutants, the C285F Lox protein was stably produced/secreted, and male C57Bl/6J Lox+/C285F mice exhibit increased systolic blood pressure (BP; p < 0.05) and reduced caliber aortas (p < 0.01 at 100mmHg) at 3 months that independently dilate by 6 months (p < 0.0001). Multimodal imaging reveals markedly irregular elastic sheets in the mutant (p = 2.8 × 10−8 for breaks by histology) that become increasingly disrupted with age (p < 0.05) and breeding into a high BP background (p = 6.8 × 10−4). Aortic dilation was amplified in males vs. females (p < 0.0001 at 100mmHg) and ameliorated by castration. The transcriptome of young Lox mutants showed alteration in dexamethasone (p = 9.83 × 10−30) and TGFβ-responsive genes (p = 7.42 × 10−29), and aortas from older C57Bl/6J Lox+/C285F mice showed both enhanced susceptibility to elastase (p < 0.01 by ANOVA) and increased deposition of aggrecan (p < 0.05). These findings suggest that the secreted Lox+/C285F mutants produce dysfunctional elastic fibers that show increased susceptibility to proteolytic damage. Over time, the progressive weakening of the connective tissue, modified by sex and blood pressure, leads to worsening aortic disease.

DFP-Induced Status Epilepticus Severity in Mixed-Sex Cohorts of Adult Rats Housed in the Same Room: Behavioral and EEG Comparisons

Sex is a biological variable in experimental models. In our previous diisopropylfluorophosphate (DFP) studies, female rats required a higher dose of DFP to achieve a somewhat similar severity of status epilepticus (SE) as males. In those studies, male and female rats were bought separately from the same vendor, housed in different rooms, and the DFP used was from different batches. We had also shown that surgery for epidural electrodes implantation reduces the threshold for SE. Our recent study in the soman (GD) model using a mixed-sex cohort of rats housed individually but in the same room showed that females achieved significantly higher SE severity than males for the same dose of GD. In this study, we demonstrate that housing the mixed-sex cohorts in the same room and treating them with DFP (4 mg/kg, s.c.) from the same pool, though from different batches, yielded reproducible SE severity in both sexes and both telemetry (surgery) and non-telemetry (non-surgery) groups. We conducted experiments in four mixed-sex cohorts of adult Sprague-Dawley rats. In females, the surgery for implanting the telemetry devices reduced the latency to convulsive seizure (CS) and increased SE severity compared to non-telemetry females. However, there were no sex differences in latency or SE severity within telemetry or non-telemetry groups. Once animals reached CS stage ≥3, they remained in CS stage in both sexes until midazolam was administered. Midazolam (3 mg/kg, i.m.) treatment 1-one-hour post-DFP significantly reduced epileptiform spikes in both sexes. The mortality was only 2% in 24 h. Irrespective of sex or stage of estrous cycle or surgery, the animals had continuous convulsive SE for ∼40 min. In telemetry rats, electrographic changes correlated with behavioral seizures. However, there was a significant difference in SE severity and the latency between directly-observed behavioral CS and EEG-based CS quantification in both sexes. Overall, these results suggest that housing both sexes in the same room and treating with DFP in a mixed-sex cohort from the same pool of reagents will minimize variability in SE severity. Such rigorous experiments will yield better outcomes while testing disease-modifying agents in epilepsy models.

Sex as a Biological Variable in Cardiovascular Diseases: JACC Focus Seminar 1/7

Sex and gender influence all aspects of cardiovascular health and disease-including epidemiology, pathophysiology, diagnosis, clinical manifestation, disease progression, and response to treatment-in complex and interrelated ways. Sex-based and gender-based differences have been identified in risk and presentation of cardiovascular diseases (CVDs); however, failure to address sex and gender as key variables in CVD research and reporting and limited understanding of differences have contributed to disparities in risk assessment, prevention, diagnosis, treatment, and outcomes. Improved consideration of both sex and gender in all phases of the biomedical research continuum, along with educational and training curricula focused on the role of sex and gender in CVD, are needed to provide targeted therapies and improve cardiovascular health outcomes for all.

Soman (GD) Rat Model to Mimic Civilian Exposure to Nerve Agent: Mortality, Video-EEG Based Status Epilepticus Severity, Sex Differences, Spontaneously Recurring Seizures, and Brain Pathology

Modeling a real-world scenario of organophosphate nerve agent (OPNA) exposure is challenging. Military personnel are premedicated with pyridostigmine, which led to the development of OPNA models with pyridostigmine/oxime pretreatment to investigate novel therapeutics for acute and chronic effects. However, civilians are not premedicated with pyridostigmine/oxime. Therefore, experimental models without pyridostigmine were developed by other laboratories though often only in males. Following OPNA exposure, prolonged convulsive seizures (CS) or status epilepticus (SE) are concerning. The duration and severity of CS/SE determine the extent of brain injury in survivors even after treating with medical countermeasures (MCM)/antidotes such as atropine, an oxime, and an anticonvulsant such as diazepam/midazolam. In this study, using a large mixed sex cohort of adult male and female rats, without pretreatment, we demonstrate severe SE lasting for >20 min in 82% of the animals in response to soman (GD,132 μg/kg, s.c.). Atropine sulfate (2 mg/kg, i.m.) and HI-6 (125 mg/kg, i.m.) were administered immediately following soman, and midazolam (3 mg/kg, i.m.) 1 h post-exposure. Immediate MCM treatment is impractical in civilian exposure to civilians, but this approach reduces mortality in experimental models. Interestingly, female rats, irrespective of estrous stages, had an average of 44 min CS (stage ≥ 3), while males had an average of 32 min CS during SE, starting from soman exposure to midazolam treatment. However, in telemetry device implanted groups, there were no significant sex differences in SE severity; males had 40 min and females 43 min of continuous CS until midazolam was administered. No animals died prior to midazolam administration and less than 5% died in the first week after soman intoxication. In telemetered animals, there was a direct correlation between EEG changes and behavioral seizures in real-time. In the long-term, convulsive spontaneously recurring seizures (SRS) were observed in 85% of randomly chosen animals. At 4-months post-soman, the brain histology confirmed reactive gliosis and neurodegeneration. The novel findings of this study are that, in non-telemetered animals, the SE severity following soman intoxication was significantly greater in females compared to males and that the estrous cycle did not influence the response.

Research on Women's Health: Ready for the Future

The National Institutes of Health (NIH) Office of Research on Women's Health (ORWH) was established in 1990. With the completion of the office's 30th anniversary year, we look back and recount some of the key events and overall zeitgeist that led to ORWH's formation, and how it became the focal point at the nation's primary biomedical research agency for coordinating research on science to improve the health of women. We discuss ORWH's mission and signature programs and the bold vision that drives the NIH-wide strategic, interdisciplinary, and collaborative approach to research on women's health and efforts to promote women in biomedical careers. Also discussed are several of the many scientific advances in research on the health of women, policy innovations and their effects, and career advancements made by women in medicine and related scientific fields. We also highlight key challenges for the health of women, the need to continue pushing for equity in biomedical research careers, and NIH's approach to addressing these problems to ensure progress for the next 30 years and beyond.

Sex Differences in Magnetoencephalography-Identified Functional Connectivity in the Human Connectome Project Connectomics of Brain Aging and Dementia Cohort

Introduction: The human brain shows modest traits of sexual dimorphism, with the female brain, on average, 10% smaller than the male brain. These differences do not imply a lowered cognitive performance, but suggest a more optimal brain organization in women. Here we evaluate the patterns of functional connectivity (FC) in women and men from the Connectomics of Brain Aging and Dementia sample. Methods: We used phase locking values to calculate FC from the magnetoencephalography time series in a sample of 138 old adults (87 females and 51 males). We compared the FC patterns between sexes, with the intention of detecting regions with different levels of connectivity. Results: We found a frontal cluster, involving anterior cingulate and the medial frontal lobe, where women showed higher FC values than men. Involved connections included the following: (1) medial parietal areas, such as posterior cingulate cortices and precunei; (2) right insula; and (3) medium cingulate and paracingulate cortices. Moreover, these differences persisted when considering only cognitively intact individuals, but not when considering only cognitively impaired individuals. Discussion: Increased anteroposterior FC has been identified as a biomarker for increased risk of developing cognitive impairment or dementia. In our study, cognitively intact women showed higher levels of FC than their male counterparts. This result suggests that neurodegenerative processes could be taking place in these women, but the changes are undetected by current diagnosis tools. FC, as measured here, might be valuable for early identification of this neurodegeneration.

Males and Females Have Distinct Molecular Events in the Articular Cartilage during Knee Osteoarthritis

Osteoarthritis (OA) is a major public health challenge that imposes a remarkable burden on the affected individuals and the healthcare system. Based on the clinical observation, males and females have different prevalence rates and severity levels of OA. Thus, sex-based differences may play essential roles in OA’s prognosis and treatment outcomes. To date, the comprehensive understanding of the relationship between sex and OA is still largely lacking. In the current study, we analyzed a published transcriptome dataset of knee articular cartilage (GSE114007) from 18 healthy (five females, 13 males) and 20 OA (11 females, nine males) donors to provide a slight insight into this important but complex issue. First, comparing female healthy cartilage samples with those of males revealed 36 differential expression genes (DEGs), indicating the fundamental sex-related differences at the molecular level. Meanwhile, 923 DEGs were distinguished between OA and healthy female cartilage, which can be enriched to 15 Reactome pathways. On the other hand, when comparing OA and healthy male cartilage, there are only 419 DEGs were identified, and only six pathways were enriched against the Reactome database. The different signaling response to OA in the male and female cartilage was further enforced by recognizing 50 genes with significantly different OA-responsive expression fold changes in males and females. Particularly, 14 Reactome pathways, such as “Extracellular matrix organization”, “Collagen biosynthesis and modifying enzymes”, “Dissolution of fibrin clot”, and “Platelet Aggregation (Plug formation)”, can be noted from these 50 sex-dependent OA-responsive genes. Overall, the current study explores the Sex as a Biological Variable (SABV) at the transcriptomic level in the knee articular cartilage in both healthy status and OA event, which could help predict the differential OA prognosis and treatment outcome of males and female patients.

Sex Differences Are Here to Stay: Relevance to Prenatal Care

Sex differences exist in the incidence and presentation of many pregnancy complications, including but not limited to pregnancy loss, spontaneous preterm birth, and fetal growth restriction. Sex differences arise very early in development due to differential gene expression from the X and Y chromosomes, and later may also be influenced by the action of gonadal steroid hormones. Though offspring sex is not considered in most prenatal diagnostic or therapeutic strategies currently in use, it may be beneficial to consider sex differences and the associated mechanisms underlying pregnancy complications. This review will cover (i) the prevalence and presentation of sex differences that occur in perinatal complications, particularly with a focus on the placenta; (ii) possible mechanisms underlying the development of sex differences in placental function and pregnancy phenotypes; and (iii) knowledge gaps that should be addressed in the development of diagnostic or risk prediction tools for such complications, with an emphasis on those for which it would be important to consider sex.

National Survey

Background: In 2015, the National Institutes of Health (NIH) established a policy on sex as a biological variable (SABV) in an effort to address the overrepresentation of men and male animals in biomedical research and the lack of attention to sex-based responses to medical treatments. However, questions remain regarding how U.S. biomedical researchers perceive the impact of the SABV policy on their own research and on translational science more broadly. Materials and Methods: A national survey of U.S. scientists who use vertebrate animals in their research was conducted. Respondents were asked how they select and use animal species as model organisms as well as how they perceive the impact of the SABV policy on their research practices. Results: Almost all respondents reported that they had previously heard of the NIH SABV policy, and over one-third had altered their study designs to comply with the policy. There were robust differences in perceptions of the SABV policy based on researchers' primary species of model organism. However, there was no significant difference in the likelihood of researchers analyzing their results by sex based on whether they had received recent NIH funding. Conclusions: While many researchers report adhering to the SABV policy requirements, more work needs to be done to ensure that the policy is being evenly applied to researchers using all types of animal models and that researchers adhere to the policy after receiving NIH funding, particularly in terms of reporting on and analyzing SABV in their study findings for publication.

Biological sex differences in Alzheimer's preclinical research: A call to action

INTRODUCTION

For decades, researchers have largely ignored sex as a biological variable (SABV) within preclinical studies. Recent literature indicates scientists are increasingly including male and female subjects in studies, but fewer studies assess for sex differences in study outcome. This is particularly concerning within the field of Alzheimer's disease (AD), as disease burden is higher among women and evidence suggests sex differences exist in etiology and disease course.

METHODS

We conducted an informal review of preclinical AD research studies.

RESULTS

Results confirmed that only about one-third of ≈150 recent studies included both male and female mice, and <15 of nearly 150 studies examined SABV as an outcome of interest.

DISCUSSION

Previous research supports the idea that better integration of SABV could open new doors in treatment research. We provide examples of best practices and discuss the need for Alzheimer's researchers to account for SABV within preclinical studies.

Understanding the Impact of Sex and Gender in Osteoarthritis: Assessing Research Gaps and Unmet Needs

Osteoarthritis (OA) affects more than 300 million individuals globally, with higher prevalence in women than in men. In addition, OA affects women and men differently, with women demonstrating both increased disease severity and disability. The Society for Women's Health Research (SWHR) convened an interdisciplinary group of expert researchers and clinicians for a roundtable meeting to review the current state of the science on OA and to identify knowledge gaps in the scientific literature, especially as they relate to the topics of sex and gender. The current review summarizes discussions from the roundtable and prioritizes areas of need that warrant further attention in OA research, diagnosis, care, and education. Improvements in basic and clinical research, clinical practice, patient education, and policy are needed to allow for better understanding as to the pathogenesis of sex- and gender-related disparities in OA.

Evaluating the National Institutes of Health's Sex as a Biological Variable Policy: Conflicting Accounts from the Front Lines of Animal Research

Background: Since the National Institutes of Health (NIH) Revitalization Act of 1993, focus on the equitable inclusion of women in clinical research has been ongoing. NIH's 2015 sex as a biological variable (SABV) policy aims to transform research design, analysis, and reporting in the preclinical sphere by including male and female organisms in vertebrate animal research as well as human studies. However, questions remain regarding how researchers and members of research oversight committees perceive the value and need of the SABV policy. Materials and Methods: Based on 62 interviews with animal researchers and oversight personnel, we analyze what the animal research community knows about the policy and sees as the benefits and challenges of implementation. Results: We found that the 62 interviewees disagreed about the need for the policy, with some being supportive and others questioning whether the policy is based on science or is politically motivated. There were also tensions in how interviewees conceptualized the challenges to and resources needed for implementing the SABV policy. For instance, while some thought implementation would require a significant increase in numbers of animals used for each study, others explicitly rejected this claim. Conclusions: We conclude by discussing the practical and social implications of our findings about the views of members of the animal research community regarding the SABV policy.

Prefrontal Cortex Representation of Learning of Punishment Probability During Reward-Motivated Actions

Actions executed toward obtaining a reward are frequently associated with the probability of harm occurring during action execution. Learning this probability allows for appropriate computation of future harm to guide action selection. Impaired learning of this probability may be critical for the pathogenesis of anxiety or reckless and impulsive behavior. Here we designed a task for punishment probability learning during reward-guided actions to begin to understand the neuronal basis of this form of learning, and the biological or environmental variables that influence action selection after learning. Male and female Long-Evans rats were trained in a seek-take behavioral paradigm where the seek action was associated with varying probability of punishment. The take action remained safe and was followed by reward delivery. Learning was evident as subjects selectively adapted seek action behavior as a function of punishment probability. Recording of neural activity in the mPFC during learning revealed changes in phasic mPFC neuronal activity during risky-seek actions but not during the safe take actions or reward delivery, revealing that this region is involved in learning of probabilistic punishment. After learning, the variables that influenced behavior included reinforcer and punisher value, pretreatment with the anxiolytic diazepam, and biological sex. In particular, females were more sensitive to probabilistic punishment than males. These data demonstrate that flexible encoding of risky actions by mPFC is involved in probabilistic punishment learning and provide a novel behavioral approach for studying the pathogenesis of anxiety and impulsivity with inclusion of sex as a biological variable.SIGNIFICANCE STATEMENT Actions we choose to execute toward obtaining a reward are often associated with the probability of harm occurring. Impaired learning of this probability may be critical for the pathogenesis of anxiety or reckless behavior and impulsivity. We developed a behavioral model to assess this mode of learning. This procedure allowed us to determine biological and environmental factors that influence the resistance of reward seeking to probabilistic punishment and to identify the mPFC as a region that flexibly adapts its response to risky actions as contingencies are learned.

Filling the Regulatory Gap: Potential Role of Institutional Review Boards in Promoting Consideration of Sex as a Biological Variable

Consideration of sex differences in biomedical research is crucial to ensure the safety and effectiveness of drugs and devices for both sexes and to improve the rigor and reproducibility of scientific discoveries. Historically, women were underrepresented in clinical research and sex differences typically were not considered. The U.S. Food and Drug Administration (FDA) and the National Institutes of Health (NIH) have played a role in improving the representation of women in clinical trials and in encouraging the consideration of sex differences. As it is not appropriate for all studies to be reviewed by the FDA nor do all studies have NIH funding, this results in a regulatory gap. We propose that local institutional review boards (IRBs) and institutional animal care and use committees (IACUCs) provide greater oversight by encouraging researchers to consider sex as a biological variable (SABV) during protocol review. In this perspective article, we review how FDA and NIH policies have fostered change and highlight how IRBs and IACUCs could encourage investigators to consider SABV.

Incorporating Sex as a Biological Variable into Clinical and Translational Research Training

Incorporating sex as a biological variable (SABV) into basic and medical research requires a deliberate plan that weaves concepts of basic genetics, cellular and molecular physiology, and pharmacology into translational medicine. An R4 approach (Right content to the Right learner at the Right time with the Right modality) allows for content to be available in a variety of formats that reinforces the concepts at staged levels of integration. Weaving SABV throughout the varied formats of the R4 approach within the Clinical and Translational Research Training Programs, into the mentoring and training of scholars in NIH Building Interdisciplinary Careers in Women's Health (BIRCWH), and into the Career Enhancement Core of the Specialized Centers of Research Excellence (SCORE) on sex differences through curriculum, case-based approach and journal clubs, and workshops ensures that learners grasp its fundamental relevancy to their own research and beyond. In addition, the collaborative work among the BIRCWH and SCORE programs brings collective expertise from centers around the United States to individual programs through development of best practices and materials. These collective efforts assure that the next generation of basic, clinical, and translational scientists will bring the dimension of SABV into their research and clinical practice.

Synthesizing Views to Understand Sex Differences in Response to Early Life Adversity

Sex as a biological variable (SABV) is critical for understanding the broad range of physiological, neurobiological, and behavioral consequences of early life adversity(ELA). The study of the interaction of SABV and ELA ties into several current debates, including the importance of taking into account SABV in research, differing strategies employed by males and females in response to adversity, and the possible evolutionary and developmental mechanisms of altered development in response to adversity. This review highlights the importance of studying both sexes, of understanding sex differences (and similarities) in response to ELA, and provides a context for the debate surrounding whether the response to ELA may be an adaptive process.

Sex as a Biological Variable: A 5-Year Progress Report and Call to Action

A little over 5 years ago, the U.S. National Institutes of Health (NIH) announced the intention to develop policies to require applicants to report plans to balance male and female cells and animals in preclinical investigations. Soon thereafter, the NIH issued a request for information from the scientific community and consulted with various stakeholders. The feedback received was considered during development of policy requiring the consideration of sex as a biological variable (SABV) in NIH-funded research on vertebrate animals and humans, which went into effect for applications due on or after January 25, 2016. We identified NIH programs related to SABV and reviewed SABV-relevant scientific literature. We find that the application of SABV throughout the research process can serve as a guiding principle to improve the value of biomedical science. The NIH is engaged in ongoing efforts to develop resources to help investigators consider SABV in their research. We also provide an update on lessons learned, highlight ways that different disciplines consider SABV, and describe the opportunities for scientific discovery that applying SABV offers. We call on NIH's various stakeholders to redouble their efforts to integrate SABV throughout the biomedical research enterprise. Sex- and gender-aware investigations are critical to the conduct of rigorous and transparent science and the advancement of personalized medicine. This kind of research achieves its greatest potential when sex and gender considerations are integrated into the biomedical research enterprise in an end-to-end manner, from basic and preclinical investigations, through translational and clinical research, to improved health care delivery.

Preclinical stress research: where are we headed? An early career investigator's perspective

Stress is a major risk factor in the development of various psychiatric disorders such as depression, anxiety and post-traumatic stress disorder. The use of stress paradigms in preclinical contexts is essential to advance our understanding of the pathophysiology of these disorders. However, they are not without their limitations and in this commentary, we have examined some of the practical issues associated with their use. We also highlight some of the latest techniques to identify their neuromolecular correlates as well as the potentially important and integrative role of computational neuroscience. Finally, we share our perspective on future directions in the field of preclinical stress research.

Differential Susceptibility of Male Versus Female Laboratory Mice to Anaplasma phagocytophilum Infection

Human granulocytic anaplasmosis (HGA) is a debilitating, non-specific febrile illness caused by the granulocytotropic obligate intracellular bacterium called Anaplasma phagocytophilum. Surveillance studies indicate a higher prevalence of HGA in male versus female patients. Whether this discrepancy correlates with differential susceptibility of males and females to A. phagocytophilum infection is unknown. Laboratory mice have long been used to study granulocytic anaplasmosis. Yet, sex as a biological variable (SABV) in this model has not been evaluated. In this paper, groups of male and female C57Bl/6 mice that had been infected with A. phagocytophilum were assessed for the bacterial DNA load in the peripheral blood, the percentage of neutrophils harboring bacterial inclusions called morulae, and splenomegaly. Infected male mice exhibited as much as a 1.85-fold increase in the number of infected neutrophils, which is up to a 1.88-fold increase in the A. phagocytophilum DNA load, and a significant increase in spleen size when compared to infected female mice. The propensity of male mice to develop a higher level of A. phagocytophilum infection is relevant for studies utilizing the mouse model. This stresses the importance of including SABV and aligns with the observed higher incidence of infection in male versus female patients.