key: cord-1037261-mxho3jgz
authors: Favre, Guillaume; Legueult, Kevin; Pradier, Christian; Raffaelli, Charles; Ichai, Carole; Iannelli, Antonio; Redheuil, Alban; Lucidarme, Olivier; Esnault, Vincent
title: visceral fat is associated to the severity of COVID-19
date: 2020-11-25
journal: Metabolism
DOI: 10.1016/j.metabol.2020.154440
sha: 3478f6206ff8ad8f847b762d1620cd39edc9e6b9
doc_id: 1037261
cord_uid: mxho3jgz

BACKGROUND: Excess visceral fat (VF) or high body mass index (BMI) are risk factors for severe COVID-19. The receptor for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is expressed at higher levels in the VF than in the subcutaneous fat (SCF) of obese patients. AIM: To show that visceral fat accumulation better predicts severity of COVID-19 outcome compared to either SCF amounts or BMI. METHODS: We selected patients with symptomatic COVID-19 and a computed tomography (CT) scan. Severe COVID-19 was defined as requirement for mechanical ventilation or death. Fat depots were quantified on abdominal CT scan slices and the measurements were correlated with the clinical outcomes. ACE 2 mRNA levels were quantified in fat depots of a separate group of non-COVID-19 subjects using RT-qPCR. RESULTS: Among 165 patients with a mean BMI of 26.1 ± 5.4 kg/m(2), VF was associated with severe COVID-19 (p = 0.022) and SCF was not (p = 0.640). Subcutaneous fat was not different in patients with mild or severe COVID-19 and the SCF/VF ratio was lower in patients with severe COVID-19 (p = 0.010). The best predictive value for severe COVID-19 was found for a VF area ≥ 128.5 cm(2) (ROC curve), which was independently associated with COVID-19 severity (p < 0.001). In an exploratory analysis, ACE 2 mRNA positively correlated with BMI in VF but not in SCF of non-COVID-19 patients (r(2) = 0.27 vs 0.0008). CONCLUSION: Severe forms of COVID-19 are associated with high visceral adiposity in European adults. On the basis of an exploratory analysis ACE 2 in the visceral fat may be a trigger for the cytokine storm, and this needs to be clarified by future studies.

Obesity is a risk factor for hospitalisation during COVID-19 [1] and requirement for invasive mechanical ventilation [2] as recently confimed in a large metanalysis [3] .

More precisely, depots of visceral fat (VF) and ectopic fat are linked to the severity of COVID-19 in non-obese Asian people [4] [5] [6] [7] and metabolic syndrome is frequent among patients with severe COVID-19 [8] . The angiotensin-converting enzyme (ACE) 2 is the receptor for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) [9] and belongs to the renin-angiotensin-aldosterone system (RAAS). It is expressed in many tissues, including white adipose tissue (WAT). Since VF show a higher expression of ACE 2 than SCF in patients with severe or morbid obesity [10] , we looked for its expression in non-COVID-19 adults, and hypothesised that the amount of VF may predict the COVID-19 outcome better than SCF or than BMI in French patients.

We first selected 46 consecutive patients in Nice and we confirmed our results in 119 consecutive patients in Paris (Table 1) with symptomatic COVID-19 and a computed tomography (CT) scan. We then combined the two cohorts (Table 2) for multivariate analyses. Since our patients were not obese, we compared mRNA expression for ACE 2 both in VF and in SCF. To that aim, we measured ACE 2 with real-time quantitative polymerase chain reactions (RTq-PCR) in a historical cohort without COVID-19 and plotted the results against BMI (Table 3 and Figures 3) . Severe COVID-19 was defined as requirement for mechanical ventilation or death. All out-clinic COVID-19 patients were paucisymptomatic. Visceral and subcutaneous fat depots were quantified on a CT scan slice located between the 3 rd and the 4 th lumbar vertebrae by a radiologist blinded to the severity of the disease [11] . We correlated anthropometric measurements with clinical outcome. Our study followed the principles outlined in the Declaration of J o u r n a l P r e -p r o o f

Helsinki. Data were analysed using R version 4.0.1 and RStudio version 1.3.959. For inference statistics, the linear model ANOVA was used for continuous data and the chisquare test was used for categorical data. Univariate and multivariate regression analyses were performed. Logistic regression was used to determine the odds ratio for several explanatory variables in five different models. A receiver operating characteristics (ROC) curve was used to look for the best predictive cutoff value of VF for severe COVID-19. The level of statistical significance was set at 0.05.

In the combined cohort (patients from Paris and Nice), the mean age was 64 ± 17 years, the mean SCF was 152.8 ± 103.4 cm 2 , the mean VF was 131.7 ± 101.3 cm 2 and the mean BMI was 26.1 ± 5.4 kg/m 2 . Subcutaneous fat was not different in patients with mild or severe COVID-19 and the SCF/VF ratio was lower in patients with severe COVID-19 (p=0.010). The best predictive value for severe COVID-19 was found for a VF area 128.5 cm 2 according to the ROC curve.

In each cohort of patients, high VF amount 128.5 cm 2 was significantly associated with the severity of COVID-19. In the combined cohort, VF considered as a continuous variable or as a binary variable was associated to the severity of COVID-19 (Table 1) .

In multivariate analysis, VF considered as a continuous variable was not linked to the severity of COVID-19 (models 1 to 4), whereas VF considered as a binary variable (models 5 and 6) was strongly associated with the severity of COVID-19 (p=0.001).

The relationship between high VF amount and the severity of COVID-19 was stronger than the relationship between the severity of COVID-19 and BMI (p=0.022) or sex (p=0.010) ( Table 2) .

In a small exploratory analysis, we found a positive correlation between the expression of the mRNA of ACE 2 and the BMI in VF, but not in SCF; the patients from the J o u r n a l P r e -p r o o f Journal Pre-proof historical non-COVID-19 cohort were not statistically different from the COVID-19 patients in Nice (Table 3 and Figures 3) .

High VF amount was a stronger predictor of severe forms of COVID-19 in non-obese Caucasian patients than BMI. Low VF was not protective, and therefore there was not a linear correlation over the full spectrum of VF amounts. Subcutaneous fat was not related to COVID-19 severity, and consequently, the visceral over subcutaneous fat ratio is not relevant either. In multivariate analysis, only high VF was related to COVID-19 severity but not age and sex. Given that adults and men have more visceral fat than children and women [12] , is it likely that the relationship between severity of disease, age and sex is accounted for by the amount of VF. Indeed, men or elderly patients die more frequently from COVID-19 than women or young patients.

Visceral fat and the severity of COVID-19 are related in three other cohorts of patients [4, 5, 7] . We here show that a certain amount of VF is necessary to observe severe forms of COVID-19 (Table 2 ). White adipose tissue has a limited expansion capability following excess dietary intake [13] . Beyond a threshold, WAT accommodates excess calories by the production of pro-inflammatory adipocytokines in the VF and by ectopic fat storage leading to insulin resistance [14] . Accordingly, fatty liver, high epicardial adipose tissue [6] or increased intramuscular fat [4] are associated with severe COVID-19. Hypertension, type 2 diabetes and ischaemic cardiomyopathy are the most common comorbidities found in patients with severe COVID-19 [15] . The lack of relationship between VF as a continuous variable and COVID-19 severity might also partly depends on the uneven distribution of VF in our combined cohort. Indeed, the patients from Nice have twice as much VF than the patients from Paris (Table 1) . Of note, the VF from Chinese patients tend to be smaller than those from our French patients (90.5 versus J o u r n a l P r e -p r o o f Journal Pre-proof 119.7 cm 2 for good outcomes and 131.9 versus 158.0 cm 2 for bad outcomes, respectively). This is in accordance with the lower threshold for being overweight in Asian people, compared with European people [16] . Consistent with its harmless role regarding metabolic health, SCF was not linked to the severity of COVID-19 (Table 1) .

RAAS intrinsic to WAT modulates inflammation, oxidative stress and immune status of both visceral and ectopic fat depots [17] . For example, angiotensin-II (Ang-II) produced by the WAT contributes to the recruitment of macrophages [18, 19] and to their polarisation into a pro-inflammatory M1-phenotype [20] . We, and others, propose that RAAS imbalance could trigger the cytokine storm of severe COVID-19 [21, 22] . The virus would enter VF through the digestive tract because the intestinal cells highly express ACE 2 [23, 24] and are more often infected by SARS-CoV-2 in patients with severe COVID-19 [25, 26] . The engagement of SARS-CoV-2 on ACE 2 in the VF would impair the enzymatic activity of ACE 2 and increase the production of Ang-II, thereby enhancing the production of inflammatory cytokines and their release into the systemic circulation. In support of this hypothesis, in a small exploratory analysis in non-COVID-19 patients, ACE 2 mRNA expression in VF positively correlated with BMI (Table 3 and Figures 3) . Such a relationship was not observed for SCF. In addition, ACE 2 protein is higher in VF as compared to SCF of patients with severe or morbid obesity [10] . It is rather unlikely that VF would serve as a reservoir for SARS-CoV-2 in non-severe COVID-19 because the viral genome is not present in the VF depots of four patients with mild COVID-19 undergoing emergent abdominal surgery [27] . Mechanisms other than RAAS imbalance intrinsic to the WAT may play a role in the severity of COVID-19 because the use of ACE inhibitor or angiotensin receptor blockers for the purpose of treating hypertension in patients with COVID-19 does not lower the likelihood of severe COVID-19 [28] . As an alternate mechanism, the J o u r n a l P r e -p r o o f Journal Pre-proof translocation of microbial-associated molecular patterns into the VF following intestinal infection with SARS-CoV-2 might activate the TLR-receptors from M1-macrophages intrinsic to the WAT and trigger the cytokine storm [29] .

The strengths of our study are the presence of two independent cohorts of Caucasian patients showing the same association between VF and COVID-19 severity, and the finding that ACE 2 parallels BMI in the VF of overweight patients. However, our work is limited by the fact that ACE 2 measurements were taken in fat from non-COVID-19

individuals in a small exploratory analysis, by the lack of data regarding traits of metabolic syndrome in our combined cohort and by the small number of patients.

Larger studies are needed to confirm our observations. We conclude that severe forms of COVID-19 are more frequent in patients with high visceral adiposity, among European and Asian adults. Given that VF is central to metabolic syndrome, metabolic parameters should be carefully evaluated in every patient infected with SARS-CoV-2 [30] , keeping in mind their diverse thresholds among Asian and Caucasian people. We also propose that the constitutive overexpression of ACE 2the receptor of SARS-CoV-2in VF may contribute to the cytokine storm, and we await further work regarding the underlying mechanisms. J o u r n a l P r e -p r o o f Legend: Values are Odds Ratios with their related confidence-intervals and p-values using multivariable binomial logistic regression models. Data are collected from 2 centers "Nice", and "Paris" which is used as reference in the models. Subcutaneous fat J o u r n a l P r e -p r o o f and visceral fat are expressed in dm 2 and age in decade to increase the OR and to improve the reading. This does not change the p-values.

J o u r n a l P r e -p r o o f 

Presenting Characteristics, Comorbidities, and Outcomes Among 5700 Patients Hospitalized With COVID-19 in the New York City Area

High prevalence of obesity in severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) requiring invasive mechanical ventilation

Individuals with obesity and COVID-19: A global perspective on the epidemiology and biological relationships

Visceral Adiposity and High Intramuscular Fat Deposition Independently Predict Critical Illness in Patients with Sars-COV

Visceral fat shows the strongest association with the need of intensive Care in Patients with COVID-19

Obesity as a Potential Predictor of Disease Severity in Young COVID-19 Patients: A Retrospective Study

The role of visceral adiposity in the severity of COVID-19: Highlights from a unicenter cross-sectional pilot study in Germany

Covid-19 and Disparities in Nutrition and Obesity

Renin-Angiotensin-Aldosterone System Inhibitors in Patients with Covid-19

Comparative Expression of Renin-Angiotensin Pathway Proteins in Visceral Versus Subcutaneous Fat

Quantification of body fat distribution in the abdomen using computed tomography

The regulation of adipose tissue distribution in humans

Abdominal obesity: a marker of ectopic fat accumulation

Obesity is associated with macrophage accumulation in adipose tissue

Clinical Features of 85 Fatal Cases of COVID-19 from Wuhan. A Retrospective Observational Study

Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies

Modulation of glucose metabolism by the reninangiotensin-aldosterone system

Angiotensin receptor blockers improve insulin resistance in type 2 diabetic rats by modulating adipose tissue

JNK1 in hematopoietically derived cells contributes to diet-induced inflammation and insulin resistance without affecting obesity

Angiotensin type 1 receptor modulates macrophage polarization and renal injury in obesity

Obesity and COVID-19: ACE 2, the Missing Tile

Covid-19: the renin-angiotensin system imbalance hypothesis

SARS-CoV-2 Receptor and Regulator of the Renin-Angiotensin System: Celebrating the 20th Anniversary of the Discovery of ACE2

ACE2 links amino acid malnutrition to microbial ecology and intestinal inflammation

Enteric involvement of coronaviruses: is faecal-oral transmission of SARS-CoV-2 possible?

Detection of SARS-CoV-2 RNA in fecal specimens of patients with confirmed COVID-19: A meta-analysis

Abdominal Surgery in Patients with COVID-19: Detection of SARS-CoV-2 in Abdominal and Adipose Tissues

Renin-Angiotensin-Aldosterone System Inhibitors and Risk of Covid-19

Why is SARS-CoV-2 infection more severe in obese men? The gut lymphatics -Lung axis hypothesis

Obesity and impaired metabolic health in patients with COVID-19

Concept and design: Esnault, Favre, Pradier. Acquisition, analysis, or interpretation of data: All authors. Drafting of the manuscript: Favre, Esnault. Critical revision of the manuscript for important intellectual content: All authors

We are indebted to Veli Yildirim for measurements of fat depots on CT-scans

Drs Favre, Esnault and Pradier had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.