A total of n = 274 SARS-CoV-2 PCR-positive patients were admitted to the Department of Intensive Care Medicine, at the University Medical Center Hamburg-Eppendorf within the period 9th March to 18th April 2021. Of these, n = 144 (53%) were patients secondarily admitted from referring intensive care units from all over Northern Germany. In summary, n = 181 (66%) of all COVID-19 patients were male and n = 93 (34%) of all COVID-19 patients were female. A total of n = 95 (35%) patients died, of which n = 65 (68%) were male and n = 30 (32%) were female. These data are in line with large epidemiological data analysis identifying being male as a high-risk factor for COVID-19 related death [3].
Critically ill COVID-19 patients were compared to the respective control group of critically ill non-COVID-19 patients with negative SARS-CoV-2 PCR (Table 1). In the COVID-19 group, 78% of the patients were male, in the control group 64.3%. The median age was 63 (IQR: 58–73) years for COVID-19 males and 67 (IQR: 59–71) years for COVID-19 females. The ICU non-COVID-19 group was older with a median age of 67 (IQR: 58–75) years for the men and 71 (IQR: 69–82) years for the women. All COVID-19 patients admitted to the ICU presented at least one comorbidity with obesity, arterial hypertension, coronary heart diseases and diabetes mellitus type II being among the most frequent (Table 1). The body mass index was higher in the COVID-19 cohort (median, male 27.4, female 25) than in the non-COVID-19 group (median, male 25.2, female 23.5). Accordingly, the diagnosis of obesity was more frequent among COVID-19 sufferers. There were no significant differences between the two groups (COVID-19 cohort vs. male AND female non-COVID-19 group) with regard to the admission diagnoses of arterial hypertension, bronchial asthma, chronic obstructive pulmonary disease (COPD), coronary heart disease (CHD) and diabetes mellitus type II. Of the patients in the COVID-19 group, 39 (78%) were hospitalized due to COVID-19 disease, while the remaining 11 (22%) patients were hospitalized for their underlying oncological disease prior to ICU admission. The ICU non-COVID-19 group contains critically ill patients from all medical specializations. 26 (61.9%) of these patients were admitted after major surgical interventions. 32 (64%) patients meets the ARDS criteria [6] in the COVID-19 group, in the ICU non-COVID-19 group 11 (26.2%) of the patients. There were no statistical relevant differences in the need of mechanical ventilation (invasive and non-invasive) in both groups (p = 1.0). In the ICU non-COVID-19 group, 14 (33.3%) patients had a suspected bacterial infection on admission to the ICU. CRP was significantly higher in COVID-19 patients (p < 0.001). 15 (30%) of the COVID-19 patients deceased, in the non-COVID-19 control group 5 (11.9%) patients.
First, we wanted to assess whether sex hormone levels are altered within the critically ill male and female COVID-19 patients potentially providing a link to sex-dependent disease severity. However, diabetes type II (p = 1.0) and obesity (p = 1.0) showed same frequencies in male and female COVID-19 patients (supplementary Table 1). Albeit statistically not significant (p = 0.6), more coronary heart diseases patients were present in the male compared to the female COVID-19 cohort, which might reflect extended frequency of CHD in men [7]. Since obesity and type II diabetes were evenly distributed between male and female COVID-19 patients, sex hormone analysis might be shifted due to this unbalance of CHD presence. Therefore, we recruited age- and sex-matched male and female SARS-CoV-2 negative CHD patients (n = 39) as an internal control. As an additional healthy control, we recruited age-and sex-matched SARS-CoV-2 negative male and female blood donors (HC) (n = 50). Furthermore, we recruited SARS-CoV-2 PCR-negative ICU patients (n = 42) as an additional control for critical illness independently of COVID-19 (herein referred as ICU non-COVID-19).
Male, critically ill COVID-19 patients presented the highest estradiol levels detected when compared to critically ill male non-COVID-19 patients (p = 0.0123) or male patients with CHD (p = 0.0002) or healthy males (p = 0.0007) (Fig. 1a). This finding is further confirmed that estradiol levels of male critically ill COVID-19 patients were far above clinical reference values [8, 9]. No significant differences in estradiol levels were detected within the control cohorts, all being within clinical reference values. Conversely, testosterone levels were lowest in critically ill male COVID-19 patients compared to critically ill male non-COVID-19 patients (p = 0.0094) or male patients with CHD (p = 0.0068) or healthy males (p < 0.0001) (Fig. 1b). In line, testosterone levels of male critically ill COVID-19 patients were below clinical reference values, albeit not significant, some critically ill COVID-19 patients also presented testosterone levels below clinical references [8, 9]. No significant differences in testosterone levels were detected within the HC and CHD control cohorts. Female, critically ill COVID-19 patients presented a trend towards elevated estradiol levels, albeit statistically not significant (Fig. 1c). Testosterone levels were not significantly altered within the female critically ill COVID-10 patients, albeit a trend towards elevated levels was observed comparable to CHD female controls above clinical references [8, 9] (Fig. 1d).
Collectively, these findings show that male COVID-19 patients present significantly increased estradiol and reduced testosterone levels compared to non-COVID-19 males.
Sex hormone levels in COVID-19 patients, non-COVID-19 patients, patients with coronary heart diseases and healthy individuals. Estradiol (a,c) and testosterone (b,d) levels were measured in plasma obtained from critically ill COVID-19 patients (ICUCOVID−19), critically ill non-COVID-19 patients (ICUnon−COVID−19), patients with coronary heart diseases (CHD) and healthy individuals (HC). Male data sets are shown in blue color-toned columns and female data sets are shown in red color-toned columns. The laboratory assessed hormone reference ranges are indicated in grey. Percentile boxplots represent 25–75% of values, with the median value indicated by a crossline, and mean values by a plus icon. Statistical significance was assessed via One-Way-ANOVA.
To shed light on the origin of severe testosterone deficiency in male COVID-19 patients, we further analyzed related hormones (Table 2). Free testosterone levels were reduced in 66.7% of male COVID-19 patients compared to reference values. Conversely, 54.5% of female COVID-19 patients presented elevated levels of free testosterone. Thus, changes in total testosterone levels reported above correlate with levels of free bioavailable testosterone levels in the respective sex. We then measured levels of the sex hormone-binding globulin (SHBG) since the majority (98%) of total testosterone is bound to SHBG and only 2% is in its free, bioavailable form. Thus, in some cases, testosterone deficiencies might be masked by elevated SHBG levels. In 28.2% of male COVID-19 patients, SHBG levels were elevated, which might suggest masked testosterone deficiencies in some patients. Luteinizing hormone (LH) levels were elevated in 30.8% of male COVID-19 patients, while being within the normal range in all female patients. Interestingly, 7 out of the 28 male patients with low total testosterone levels presented elevated LH levels at the same time (data not shown), suggesting impairment of Leydig cell steroidogenesis in 25% of the male patients. Follicle stimulating hormone (FSH) levels were elevated in 12.8% of male patients. Elevated FSH levels in these male patients were combined with elevated LH levels. In 45.5% of female patients, FSH levels were reduced, which may indicate loss of ovarian function. This would be in line with the postmenopausal status of the 10 out of 11 COVID-19 females in our cohort. Other hormones, such as thyroid stimulating hormone (TSH) and T4 were within normal ranges in the majority of male and female patients. Cortisol levels were elevated in 56.4% of male and 81.8% of female COVID-19 patients.
These findings suggest that in 25% of the male COVID-19 patients with low total testosterone levels, testosterone deficiency is likely of testicular origin. Thus, in 75% of male patients, the origin of testosterone deficiency is likely of hypothalamic-hypopituitary origin.
Testosterone is further metabolized to dihydrotestosterone by 5-α reductase. Dihydrotestosterone also acts as an androgen and plays a key role in activating the transcription of various genes and activation of various immune cells similar to testosterone [10]. Thus, we wanted to assess whether alterations in testosterone levels detected in male COVID-19 patients are also reflected in its most potent metabolite. In male COVID-19 patients, dihydrotestosterone levels were reduced compared to HC males (p < 0.0001) (supplementary Figure s2a). In line, a substantial proportion of plasma dihydrotestosterone levels in COVID-19 males was even below the lowest reference range, confirming dihydrotestosterone deficiency in men. In contrast, dihydrotestosterone levels were comparable between female COVID-19 and HC cohorts within clinical references (p = 0.9568) (supplementary Figure s2c). To assess whether the increase in estradiol levels is attributed to a general increase in estrogens, we next measured estrone concentrations. Estrone levels in the plasma of COVID-19 males were higher compared to HC males (p < 0.0001) (supplementary Figure s2b). Similarly, estrone levels were elevated in the plasma of female COVID-19 patients unlike HC females (p = 0.0009) (supplementary Figure s2d).
Thus, male critically ill COVID-19 patients present additionally elevated estrone levels accompanied by severely reduced dihydrotestosterone levels. Female critically ill COVID-19 patients present elevated estrone levels, while dihydrotestosterone levels remain unchanged.
Next, we analyzed whether sex hormone levels correlate with an increased risk for severe disease outcome as assessed by the Sequential Organ Failure Assessment Score (SOFA) scores or the requirement for extracorporeal membrane oxygenation (ECMO) later during their ICU stay. In male critically ill COVID-19 patients, estradiol levels increased with disease severity (Fig. 2a) unlike in non-COVID-19 males (Fig. 2b) (p = 0.0245 and p = 0.0273). In female COVID-19 patients, a trend towards higher estradiol levels with increasing SOFA scores was also observed (Fig. 2c). Male COVID-19 patients with elevated estradiol levels were more likely to be require ECMO treatment than those having estradiol levels within normal clinical references (p = 0.0307) (Fig. 2d). Within the female COVID-19 cohort only 1 patient required ECMO treatment; thus, not allowing statistical analysis (data not shown). Testosterone levels did not show statistical significant changes comparing groups with different disease severity or those requiring ECMO treatment (supplementary Figure s3a-d). This might be due to the fact that most male patients presented low testosterone levels below clinical references [8, 9].
These data show that critically ill male COVID-19 patients with elevated estradiol levels are more likely to require ECMO treatment.
Estradiol levels in dependency of disease severity. Estradiol levels were measured in plasma obtained from critically ill male (blue columns) and female (red columns) COVID-19 or non-COVID-19 patients are displayed in dependency of disease severity as assessed by SOFA scores (a-c). Male COVID-19 patients were subdivided into patients requiring ECMO therapy (+ ECMO) and patients not requiring ECMO therapy (-ECMO) (d). Percentile boxplots represent 25–75% of values, with the median value indicated by a crossline, and mean values by a plus icon. The laboratory assessed hormone reference ranges are indicated in grey. Values are shown as median and interquartile range. Statistical significance in males was assessed by NON-parametric tests (Kruskal-Wallis test and Dunn’s test for multiple comparisons). Statistical significance in females was evaluated by unpaired, two-tailed NON-parametric Student’s t-test (Mann-Whitney test).
We then compared cytokine and chemokine patterns in male and female COVID-19 patients. Therefore, we analyzed a panel of 27 different cytokines and chemokines in the plasma of COVID-19 patients and correlated to disease severity as assessed by the Sequential Organ Failure Assessment Score (SOFA) (Fig. 3, supplementary Figure s3e-m). In male COVID-19 patients, particularly IFN-γ (p = 0.0301), IL-1RA (p = 0.0160), IL-6 (p = 0.0145), MCP-1 (p = 0.0052) and MIP-1α (p = 0.0134) levels were elevated in those with higher SOFA scores (8–11) compared to those with lower SOFA scores (2–3) (Fig. 3a-e). In female COVID-19 patients, TNF-α levels were higher in those with high SOFA scores compared to those with low SOFA scores (p = 0.0476) (Fig. 3f). Albeit statistically not significant, IFN-γ showed a trend towards elevation with increasing SOFA scores (Fig. 3g).
These findings show that cytokine and chemokine responses, particularly IFN-γ, IL-1RA, IL-6, MCP-1 and MIP-1α are generally elevated in dependency of disease severity in critically ill male and female COVID-19 patients.
Chemokine and cytokine responses in COVID-19 patients. Cytokine and chemokines were measured in plasma obtained from critically ill male (a-e) and female (f and g) COVID-19 patients by using a 27-plex immunoassay. Here, those with significant differences are shown. Cytokine and chemokine levels of male and female COVID-19 patients are displayed in dependency of disease severity as assessed by SOFA scores (2–3; 4–7; 8–11).
We next addressed the question whether changes in cytokine and chemokine responses in critically ill COVID-19 patients might correlate with their respective sex hormone levels given that most immune cells possess androgen and estrogen receptors [10–12]. Performing linear regression analysis between all 27 cytokine and chemokines assessed, only IFN-γ presented a significant correlation to estradiol in male and female COVID-19 patients (R2 = 0.216, p = 0.0009; Fig. 4). Testosterone levels did not significantly correlate with changes in IFN-γ levels (R2 = 0.133, p = 0.3111; supplementary Fig. 4).
These findings show a direct association of estradiol levels and IFN-γ induction in line with previous studies reporting on the estradiol-controlled transcription of IFN-γ due to the presence of an estrogen responsive element (ERE) in its promoter region [13–15].
Correlation of IFN-γ levels in male and female COVID-19 patients to estradiol levels.
Estradiol levels were measured in plasma of critically ill male and female COVID-19 patients and were plotted over the expression levels of all assessed cytokines and chemokines. Here, only IFN-γ is displayed, which showed significant correlations in regression analysis with estradiol among 27 different cytokines and chemokines assessed. Statistical significance was assessed by generalized linear regression.