In SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) infected patients,
hemostasis shows an uncontrolled activation, with a high D-dimer concentration.
1
2
It has been also shown that the SARS-CoV-2 can promote endotheliitis,
3
and in turn, pulmonary endothelial damage fostering thrombogenesis.
4
Thrombotic microangiopathy (TMA) is defined by microangiopathic hemolytic anemia,
thrombocytopenia, and organ failure
5
and can be observed in several disorders.
6
Infectious diseases could be one of these disorders.
7
A disintegrin and metalloproteinase with thrombospondin motifs 13 (ADAMTS13) plays
a pathophysiological role in the TMA, including that arousing on sepsis.
8
Moreover, a key role of the ADAMTS13 in the coagulopathy of sepsis is also acknowledged.
9
In the same scenario, ADAMTS13 was shown to be one of the endothelium-related markers
showing changes, with a trend toward a reduction.
10
Furthermore, in response to the endothelial activation-induced vascular inflammation,
reciprocal changes of the ADAMTS13 and its substrate, the von Willebrand factor (vWF),
are observed.
11
In septic patients, reduced synthesis of protein C (PC) and its cofactor protein S
(PS) in addition to impaired expression of thrombomodulin and endothelial PC receptor
on endothelium determines reduced PC levels with an imbalance of thrombin regulation.
12
Furthermore, antithrombin (AT)— the most important inhibitor of thrombin and activated
factor X—is reduced as a consequence of its consumption and impaired synthesis and
degradation.
13
We aimed at assessing whether ADAMTS13 levels predict mortality in patients with a
diagnosis of SARS-CoV-2 infection. The secondary aim was to investigate a possible
relationship between ADAMTS13, D-dimer, vWF, and natural anticoagulants levels to
have easy-to-handle markers of clinical outcomes. Seventy-seven patients admitted
between March 1 and April 30, 2020 at the “Casa Sollievo della Sofferenza” Research
Hospital with a laboratory-confirmed diagnosis (i.e., RT-PCR according to the protocol
established by the WHO)
14
of the SARS-CoV-2 infection were investigated. Demographic and clinical information
and routine laboratory data at the hospital admission were extracted from hospital
electronic medical records. In all patients, ADAMTS13, vWF antigen (vWF:Ag)/functional,
and natural anticoagulants (AT, PC, and PS) levels were measured on a blood sample
obtained within seven hospitalization days. The ADAMTS13 activity levels were measured
using a chromogenic enzyme-linked immunosorbent assay (ELISA) method (TECHNOZYM ADAMTS13
Activity ELISA Kit, Technoclone, Austria). Continuous variables are presented as a
median and interquartile range, whereas discrete variables as numbers and percentage.
After testing for data normality distribution, Mann–Whitney test was used to analyze
differences in continuous variables. Fisher's exact test was also performed to estimate
the association between D-dimer positive test (> 500 ng/mL) and ADAMTS13 activity
levels below median value. Spearman's
r
was used to explore the reciprocal relationship between ADAMTS13 and D-dimer, vWF,
and natural anticoagulants: results are given as
r
- and
p
-values. Multiple linear regression analysis, which controlled for D-dimer concentration,
age, and sex was performed to evaluate a predictive model for ADAMTS13 activity levels.
Kaplan–Meier analysis was performed to assess whether ADAMTS13 can predict mortality.
Statistical significance was set at
p
-values < 0.05. All the analyses were performed using GraphPad Prism version 8.00
for Windows, GraphPad Software (La Jolla, California, United States,
www.graphpad.com
). The study was approved by the local ethics committee and was performed according
to the Declaration of Helsinki on Ethical Principles for medical research involving
human subjects. All patients gave written informed consent.
Descriptive analysis is shown in
Table 1
. Most patients (73%) were older than 60 years, with a slightly higher percentage
(56 vs. 46%) of women. Almost all the patients (97.5%) showed comorbidities. Fourteen
patients (18%) were admitted to the intensive care unit. Median value of ADAMTS13
in the entire sample was 70 U/dL. Kaplan–Meier analysis showed a significantly lower
survival in those individuals with ADAMTS13 activity below the median value (
p
= 0.025) (
Fig. 1
). Overall, we recorded four deaths (5.2%), all in patients with hypertension, two
of them with associated ischemic cardiomyopathy (one diabetic). We cannot exclude
that comorbidities could have contributed to mortality in these patients. Seventy-three
patients were discharged (
n
= 51) or are still alive (
n
= 22) at the end of the study. Since vWF might be directly involved in the pathophysiology
of TMA, we performed also the Kaplan–Meier analysis according to vWF ristocetin cofactor
(vWF:RCo) levels: no statistically significant difference was found, in terms of mortality
prevalence (
p
= 0.80). Multiple linear regression showed that D-dimer concentration at admission
(
p
= 0.0145) and age (
p
= 0.0036) were independently associated with ADAMTS13 activity levels. D-dimer concentration
above 500 ng/mL at admission was associated with a 2.8-fold higher likelihood of ADAMTS13
activity below the median value (odds ratio: 4.8 [95% confidence interval: 1.3–16.9],
p
= 0.02). Lastly, D-dimer concentration, vWF:Ag, and natural anticoagulants (AT, PC,
and PS) levels were inversely (D-dimer and vWF) or directly (AT, PC, PS) associated
with ADAMTS13 levels (
Supplementary Table S1
). ADAMTS13 activity negatively correlated with D-dimer concentration (Spearman's
r
: –0.41,
p
= 0.002
)
and vWF:Ag (Spearman's
r
: –0.34,
p
= 0.005) levels, whereas a positive correlation was found with AT (Spearman's
r
: 0.45,
p
<
0.001), PC (Spearman's
r
: 0.33,
p
= 0.004), and PS (Spearman's
r
: 0.23,
p
= 0.04). The main finding of this study is that patients with ADAMTS13 activity below
70 U/dL have a higher risk of in-hospital death. Present findings are consistent with
those observed in patients with sepsis, in whom low ADAMTS13 levels are inversely
correlated with vWF
15
and a poor prognosis, as well as with sepsis severity.
16
17
Elevated levels of vWF and reduced ADAMTS13 could correlate with endothelial damage
and a progressive worsening of the organ function. In our setting, the ratio of vWF:RCo/vWF:Ag
is 0.65. This value does not reflect a predominance of ultra-large vWF multimers,
which could represent the culprit of microangiopathic thrombosis. We hypothesize that,
at variance with other TMA, the underlying pathogenetic mechanism is the endothelial
inflammation and damage resulting in a slight reduction of ADAMTS13 levels. Consistent
with this possible pathogenetic mechanism is the lack of thrombocytopenia. Indeed,
in TMA other than thrombotic thrombocytopenic purpura, the relationship between reduced
ADAMTS13 activity and thrombocytopenia is not clearly demonstrated.
18
As reported in other septic patients, the endothelial damage triggers the coagulation
cascade, as suggested by elevated D-dimer and decreased natural anticoagulants plasma
levels.
19
20
Notably, we observed that D-dimer, a blood parameter routinely investigated in SARS-CoV-2
patients for the possible clinical impact on mortality in these settings,
21
22
strongly predicts ADAMTS13 levels. Thus, it is conceivable that endothelial dysfunction
could be reflected in any of the hemostasis phases and variables, including the natural
anticoagulants. Endothelial dysfunction is a key finding and major determinant of
poor prognosis in SARS-CoV-2 patients.
23
Indeed, direct or indirect activation by SARS-CoV-2 on endothelium would cause intensive
vWF secretion from Weibel–Palade bodies, as expected upon perturbations on these vascular
cells.
13
Our data are consistent with previous findings suggesting that SARS-CoV-2 patients
present a low-grade disseminated coagulopathy and localized pulmonary microangiopathy,
resulting in organ dysfunction.
24
Notwithstanding the retrospective nature and limited size of this study, overall,
present findings may speculatively suggest that ADAMTS13 would represent a clinic-diagnostic
marker predicting SARS-CoV-2-related prognosis.
Table 1
Demographic/clinical information and laboratory data collected in the study population
Variables
Values
Demographic and clinical information
Age, median (IQR)
61.5 (80–62)
Female/Male
43/34
Coexisting morbidities,
n
(%)
Any
22 (28.5)
Hypertensive disorder
17 (22)
Chronic renal disease
8 (10.4)
Diabetes
8 (10.3)
Dilated cardiomyopathy
7 (9)
Chronic obstructive chronic disease
7 (9)
Atrial fibrillation
6 (7.8)
None
2 (3)
Deaths,
n
(%)
4 (5.2)
Laboratory data
ADAMTS13 activity (U/dL), median (IQR)
70 (80–60)
vWF:Ag (%), median (IQR)
231.2 (415.3–205.7)
vWF:RCo (%), median (IQR)
150.0 (334.3–116.9)
ADAMTS13/vWF:RCo, median (IQR)
0.40 (0.50–0.23)
vWF:RCo/vWF:Ag, median (IQR)
0.65 (0.87–0.6)
Factor VIII (%), median (IQR)
95.20 (133.0–69.40)
D-dimer (ng/mL)
882.0 (2250–460.0)
Hemoglobin (g/dL), median (IQR)
11.9 (13.3–9.8)
Platelet count (×10
9
/L), median (IQR)
234 (283–149)
White cell count (×10
9
/L), median (IQR)
6.1 (9.4–4.5)
Lactate dehydrogenase (U/L), median (IQR)
236.0 (314.5–197.0)
Creatinine (mg/dL), median (IQR)
0.9 (1.5–0.6)
C-reactive protein (mg/L), median (IQR)
1.7 (9.3–0.4)
Erythrocyte sedimentation rate (mm/h)
34 (79.5–23.5)
Prothrombin time (International Normalized Ratio), median (IQR)
1.09 (1.18–1.06)
Activated partial thromboplastin time (s), median (IQR)
25.0 (26.5–23.0)
Abbreviations: ADAMTS13, a disintegrin and metalloproteinase with thrombospondin motifs
13; IQR, interquartile range; vWF:Ag, von Willebrand factor antigen; vWF:RCo, von
Willebrand factor ristocetin cofactor.
Fig. 1
Kaplan–Meier survival analysis according to a disintegrin and metalloproteinase with
thrombospondin motifs 13 (ADAMTS13) activity levels: four deaths were observed in
the group with values < 70 U/dL.