Can SARS-CoV-2 Cause Direct Kidney And Renal Infection?

Contact: emily.li@wecistanche.com

Wei Ling Lau, Jonathan E. Zuckerman, Ajay Gupta, Kamyar Kalantar-Zadeh

Division of Nephrology, Hypertension and Kidney Transplantation, University of California Irvine School of  Medicine, Orange, CA, USA; bDepartment of Pathology and Laboratory Medicine, David Geffen School of Medicine  at University of California Los Angeles, Los Angeles, CA, USA

Keywords: COVID-19, SARS-CoV-2, Kidney pathology, Immunohistochemistry, Ribonucleic acid

Abstract 

Context: Determining whether SARS-CoV-2 causes direct infection of the kidneys is challenging due to limitations in imaging and molecular tools.

Subject of Review: A growing  number of conflicting kidney biopsy and autopsy reports  highlight this controversial issue.

Second Opinion: Based on  the collective evidence, therapies that improve hemodynamic stability and oxygenation, or dampen complement  activation, are likely to ameliorate acute kidney injury in COVID-19. At this time, whether inhibition of viral infection and  replication directly modulates kidney damage is inconclusive.

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Introduction 

The severe acute respiratory syndrome coronavirus 2  (SARS-CoV-2) virus outbreak in China at the end of 2019  led to the COVID-19 pandemic, which has claimed over  1 million lives as of October 1, 2020. SARS-CoV-2 demonstrates broad organotropism, that is, cells in many organ systems can be directly infected and may act as a reservoir for the virus. Angiotensin-converting enzyme 2  (ACE2) is the functional receptor of SARS-CoV-2 and is  expressed in most organs, with highest expression in the  kidneys (proximal tubular cells and podocytes) and ileum  [1]. Given what is known about ACE2 tissue distribution,  the association between acute kidney injury and increased  mortality risk in COVID-19, and the urgent need to identify therapeutic targets, it is no surprise that SARS-CoV- 2-associated kidney injury is an area of active research.

Several indirect pathways of SARS-CoV-2 acute kidney injury have been elucidated. Kidney pathology shows  varying degree of acute tubular injury which includes necrosis when severe, due to a combination of a virus-induced cytokine storm, hypoxemia, and polypharmacy.  Complement and coagulation cascades are triggered and  may activate each other [2]; however, kidney thrombotic  microangiopathy is present only in a subset of cases [3–6].  A few cases of glomerular disease have been reported,  with the most common being collapsing glomerulopathy  [6–10] which can be associated with high-risk APOL1  gene variants [7–9]. Minimal change disease, membranous glomerulopathy, anti-GBM disease, infection-associated glomerulonephritis, and ANCA-associated vasculitis have also been reported concurrently with SARS-CoV-2 infection [3, 6, 7, 11–13]. 

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Table 1. Summary of studies as of November 30, 2020, that have investigated direct kidney infection by SARS-CoV-2

Whether direct viral kidney infection occurs with  SARS-CoV-2 is a controversial topic. Detection methods  include histology, that is, immunohistochemistry (IHC)  and transmission electron microscopy (TEM), and ribonucleic acid (RNA) assays, that is, in situ hybridization  (RNA-ISH) and quantitative real-time reverse transcriptase-polymerase chain reaction (RT-PCR). These methods have inherent limitations. 

IHC is valid only if the antibody probe is specific; unfortunately, the commercially available antibodies targeting the SARS-CoV-2 nucleocapsid protein (NP) and  spike (S) antigens have not been well validated. In particular, there are concerns with the anti-SARS-NP antibody from clone ID: 019 (Sino Biological, Beijing, China)  which has been tested under numerous conditions and  has shown nonspecific positive staining in the kidney parenchyma [8]. Moreover, proximal tubules are prone to  nonspecific staining of many antibodies due to their intense absorptive capacity.  

TEM is challenging as numerous ultrastructures  (termed viral-like particles) can mimic viruses [14]. For  example, multivesicular bodies in podocyte cytoplasm  and clathrin-coated endocytosed vesicles in tubular epithelial cells can have the appearance of a viral corona [8,  15]. Several investigations of pre-COVID era biopsies  have demonstrated structures morphologically identical  to those reported as “SARS-CoV-2 viral particles” [16,  17]. To date, no studies utilizing immunoelectron microscopy for specific viral antigens have been reported. 

RNA assays are regarded as the most sensitive and specific, but may be limited if the virus is present below the  level of detection. RT-PCR requires homogenization of a  tissue sample and may report a false positive if blood is not  carefully washed out from the sample, such that the test is  actually detecting extracellular circulating virus. Moreover, if tissue samples are obtained at time of autopsy, extent of postmortem autolysis and cell degeneration can  complicate interpretation of viral detection assays.

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Conflicting studies published between April and November 2020 have provoked an ongoing debate about  whether SARS-CoV-2 causes direct kidney infection (Table 1). Several postmortem studies have reported detection  of SARS-CoV-2 by electron microscopy, IHC, and/or RNA  assays [18–23] (including one medRxiv preprint by Diao  et al.). Of note, 2 of these studies utilized the anti-SARS-NP  antibody that has raised concerns for a nonspecific signal  as discussed above [8]. Puelles et al. [22] provided compelling evidence of punctate staining of viral RNA in glomeruli and tubules by in situ hybridization, and their study  included multiple SARS-CoV-2 negative controls. The  study by Braun et al. [20] demonstrated successful infection of cultured primate kidney tubular epithelial cells, utilizing homogenized kidney specimens obtained at time of  autopsy from SARS-CoV-2 patients; however, the possibility of virus present within residual blood in the kidney tissue could also explain this observation.

Of note, difficulty interpreting RNA-ISH in autopsy  tissue has been reported [5] whereby there is rare tubular  positivity in both SARS-CoV-2-positive and -negative  patients. Thus, in autopsy tissue, RNA-ISH may show  false positives, and the threshold as well as characteristics  for true positive staining remains to be established.

In contrast, biopsy data from live patients and other  autopsy studies have not detected SARS-CoV-2 in the  kidney via IHC, RT-PCR, and RNA-ISH [3, 5–11, 15, 24,  25]. It is possible that the absence of virus detection may reflect viral clearing from the kidney as there is frequently delay between initial SARS-CoV-2 infection and either  renal biopsy or autopsy. Nonetheless, the negative reports  are more consistent with the fact that SARS-CoV-2 is  rarely detected in the urine, and urinary levels do not correlate with degree of kidney injury [26, 27]. Furthermore,  blood levels are also generally low or nondetectable [27].  These data support the notion that the majority of SARSCoV-2 renal complications likely result from indirect  mechanisms, even if a minority of cases may indeed show  direct kidney viral infection. 

Given this controversy, future studies should utilize  rigorous controls including both SARS-CoV-2-positive  and -negative tissue. Multimodel detection strategies including IHC, RNA-ISH, and immunoelectron microscopy are warranted. We believe without immunoelectron  detection, morphologic evaluation by electron microscopy alone is not sufficient to confirm the presence of viral  particles. Fortunately, published validation studies of  SARS-CoV-2 antibodies and RNA-ISH are emerging [28] which will help guide the use of appropriate commercially available antibodies and RNA-ISH probes.

Proof of viral replication in human kidney cells remains to be confirmed [29, 30]. Based on the collective  evidence, therapies that improve hemodynamic stability  and oxygenation, or dampen complement activation, are  likely to ameliorate acute kidney injury in COVID-19. At  this time, whether inhibition of viral infection and replication directly modulates kidney damage is inconclusive.

Conflict of Interest Statement 

W.L. Lau has received honoraria and/or support from Fresenius, Hub Therapeutics, Roche, Sanofi, and ZS Pharma. J.E. Zuckerman is a paid consultant for Leica Biosystems. A. Gupta has filed  3 provisional patent applications for use of PGD2 and thromboxane A2 antagonists, including ramatroban, as a treatment for COVID-19 (Application Nos. 63/003,286 filed on March 31, 2020;  63/005,205 filed on April 3, 2020; and 63/027,751 filed on May 2,  2020). K. Kalantar-Zadeh has received honoraria and/or support  from Abbott, Abbvie, ACI Clinical (Cara Therapeutics), Akebia,  Alexion, Amgen, Ardelyx, Astra-Zeneca, Aveo, BBraun, Chugai,  Cytokinetics, Daiichi, DaVita, Fresenius, Genentech, Haymarket  Media, Hospira, Kabi, Keryx, Kissei, Novartis, Pfizer, Regulus, Relypsa, Resverlogix, Sandoz, Sanofi, Shire, Vifor, UpToDate, and ZS  Pharma. 

Funding Sources 

The authors acknowledge funding from NIH NINDS R01- NS113337 (W.L.L.) and NIH NIDDK K24-DK091419 (K.K.Z.).

Author Contributions 

W.L.L. and J.E.Z. drafted the manuscript. W.L.L., J.E.Z., A.G.,  and K.K.Z. made revisions and approved the final manuscript version.

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