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The COVID-19 pandemic has taken the entire globe by storm. The pathogenesis of this virus has shown a cytokine storm release, which contributes to critical or severe multi-organ failure. Currently the ultimate treatment is palliative; however, many modalities have been introduced with effective or minimal outcomes. Meanwhile, enormous efforts are ongoing to produce safe vaccines and therapies. Phototherapy has a wide range of clinical applications against various maladies. This necessitates the exploration of the role of phototherapy, if any, for COVID-19. This critical review was conducted to understand COVID-19 disease and highlights the prevailing facts that link phototherapy utilisation as a potential treatment modality for SARS-CoV-2 viral infection. The results demonstrated phototherapy’s efficacy in regulating cytokines and inflammatory mediators, increasing angiogenesis and enhancing healing in chronic pulmonary inflammatory diseases. In conclusion, this review answered the following research question. Which molecular and cellular mechanisms of action of phototherapy have demonstrated great potential in enhancing the immune response and reducing host–viral interaction in COVID-19 patients? Therefore, phototherapy is a promising treatment modality, which needs to be validated further for COVID-19 by robust and rigorous randomised, double blind, placebo-controlled, clinical trials to evaluate its impartial outcomes and safety.
Phototherapy as a Rational Antioxidant Treatment
Modality in COVID-19 Management; New Concept
and Strategic Approach: Critical Review
Reem Hanna 1, 2, * , Snehal Dalvi 1,3 , Tudor Sălăgean 4 ,*, Ioana Roxana Bordea 5 ,
and Stefano Benedicenti 1,
1Department of Surgical Sciences and Integrated Diagnostics, Laser Therapy Centre, University of Genoa,
Viale Benedetto XV,6, 16132 Genoa, Italy; (S.D.); (S.B.)
2Department of Oral Surgery, Dental Institute, King’s College Hospital NHS Foundation Trust,
London SE5 9RS, UK
3Department of Periodontology, Swargiya Dadasaheb Kalmegh Smruti Dental College and Hospital,
Nagpur 441110, India
4Department of Land Measurements and Exact Sciences, University of Agricultural Sciences and Veterinary
Medicine Cluj-Napoca, 400372 Cluj-Napoca, Romania
5Department of Oral Rehabilitation, “Iuliu Hat
,ieganu” University of Medicine and Pharmacy Cluj-Napoca,
400012 Cluj-Napoca, Romania;
*Correspondence: (R.H.); (T.S.);
Tel.: +39-010-353-7446 (R.H.); +40-744-707-371 (T.S.)
Joined last authorship.
Received: 7 August 2020; Accepted: 13 September 2020; Published: 16 September 2020
The COVID-19 pandemic has taken the entire globe by storm. The pathogenesis of this
virus has shown a cytokine storm release, which contributes to critical or severe multi-organ failure.
Currently the ultimate treatment is palliative; however, many modalities have been introduced with
eective or minimal outcomes. Meanwhile, enormous eorts are ongoing to produce safe vaccines
and therapies. Phototherapy has a wide range of clinical applications against various maladies. This
necessitates the exploration of the role of phototherapy, if any, for COVID-19. This critical review was
conducted to understand COVID-19 disease and highlights the prevailing facts that link phototherapy
utilisation as a potential treatment modality for SARS-CoV-2 viral infection. The results demonstrated
phototherapy’s ecacy in regulating cytokines and inflammatory mediators, increasing angiogenesis
and enhancing healing in chronic pulmonary inflammatory diseases. In conclusion, this review
answered the following research question. Which molecular and cellular mechanisms of action of
phototherapy have demonstrated great potential in enhancing the immune response and reducing
host–viral interaction in COVID-19 patients? Therefore, phototherapy is a promising treatment
modality, which needs to be validated further for COVID-19 by robust and rigorous randomised,
double blind, placebo-controlled, clinical trials to evaluate its impartial outcomes and safety.
SARS-CoV-2; COVID-19; phototherapy; photobiomodulation; photodynamic therapy;
low-level laser therapy; nitric oxide; antioxidant; cytokines; vaccines
1. Highlights
The etiopathogenesis of coronavirus disease 2019 (COVID-19), cytokine release syndrome and
how they contribute in multi-organ dysfunction represent prospective therapeutic targets.
The molecular and cellular activities of phototherapy and how they can regulate COVID-19
induced a cytokine storm.
Antioxidants 2020,9, 875; doi:10.3390/antiox9090875
Antioxidants 2020,9, 875 2 of 23
Applications of photobiomodulation and photodynamic therapies are promising treatment
modalities in COVID-19 management.
Exploring the role of lasers in whole inactivated virus vaccine production and as vaccine adjuvants,
which requires further investigation.
2. Introduction
In December 2019, the World Health Organization (WHO) was alerted of a rapid and
wide-spreading pneumonia of an unknown origin, which was first detected in Wuhan, the capital city
of China’s Hubei province [
]. With the sudden exponential rise in the number of cases and thorough
sample detection, WHO announced that this infection was associated with a novel coronavirus, which
was named “severe acute respiratory syndrome coronavirus 2” (SARS-CoV-2) [
]. Later, the disease
was denoted as “coronavirus disease 2019” (COVID-19)’ [3].
Over the past seven months, this viral infection has emerged as a pandemic, encroaching lives of
the global population. As of 15 September 2020, there have been 29,309,546 reported confirmed cases,
including 928,890 deaths [
]. As we are suering from this fatal catastrophe at present, worldwide
research is being conducted to find ways to prevent or slow the transmission of COVID-19. At this
time, there are no specific vaccines or treatments for COVID-19, but there are many ongoing clinical
trials assessing prospective remedies. Until a vaccine or a treatment is found, it is necessary to provide
symptomatic relief to the infected patients in order to minimise their suering.
Laser photonic energy possesses a wide range of local as well as systemic benefits, which
have been experimented and evaluated extensively over the past few decades. Phototherapy by
means of photobiomodulation therapy (PBMT) and photodynamic therapy (PDT) has shown to be an
eective treatment modality, which has a significant role in tissue repair and regeneration [
], wound
healing [6,7], pain alleviation [8,9] and oxidant reduction [10,11].
PBMT is a noninvasive, available, cost-saving physical therapy modality with no side eects,
which also delivers antioxidant and anti-inflammatory eects [
]. Its anti-inflammatory eects
have been studied by many authors who examined the cellular signalling responsible for these eects
and concluded that reduction in calcium (Ca
) sensitivity may be responsible for its anti-inflammatory
eect [
]. PBM has fundamental advantages in terms of cell proliferation and dierentiation,
modulating the immune responses and improving oxygenation [
]. Therefore, it can play a crucial
role in regulating the cytokines storm syndrome (CSS) in COVID-19 and improve lung function, while
restoring multi-organ dysfunction. It can reduce inflammatory mediators, increasing angiogenesis
and enhancing healing in chronic pulmonary inflammatory diseases. Ultrashort pulsed laser is an
innovation treatment modality of PBM, which selectively inactivates the virus by utilising a femtosecond
pulsed laser, which has been well documented in the literature [
]. While PDT has a crucial role in
reducing or totally eliminating the potential risks of transmission of coronaviruses via blood products
or its derivatives, which were observed during the outbreak of SARS and MERS [
], it is important
to note that adding a laser therapy as an adjunctive agent to the vaccine could be the future to enhance
the potency of the vaccine [24].
This is why, the role of phototherapy, if any, for COVID-19 needs to be explored. In lieu of
the prevailing literature, the aim of the present critical review was to evaluate the eectiveness of
phototherapy in the management of COVID-19. The following objectives were determined with an
intention to fulfil the aim of this review.
To understand the etiopathogenesis of COVID-19.
To address the mechanism of action of PBM in relation to COVID-19 treatment.
To recognise the mechanism of action of PDT as a possible strategy for the management
of COVID-19.
This review was conducted to address the following focused research question. “Does the
molecular and cellular mechanism of action of phototherapy have the potential in reducing host–viral
interaction, by regulating the immune responses, in patients infected with SARS-CoV-2?” Electronic
Antioxidants 2020,9, 875 3 of 23
search strategies of MEDLINE (NCBI PubMed and PMC), Cochrane Central Register of Controlled
Trials (CCRCT), Scopus, Science Direct, Google Scholar, EMBASE, EBSCO, and Google Scholar
databases applied from August 2000 to August 2020, with an objective to identify all the relevant
data, demonstrating the role and mechanism of action of phototherapy for COVID-19 patients.
Additionally, a manual search of the following journals was performed; Lancet, Viruses, Virus Research,
Journal of Virology, Antiviral Research, Lasers in Medical Science, Journal of Photochemistry and
Photobiology B: Biology, Photodiagnosis and Photodynamic Therapy, Biophotonics, Laser Therapy
and Photobiomodulation, Photomedicine and Laser Surgery. The search strategy comprised of only
terms, which were related to or described the study domain and interventions. The keywords utilised
for the search strategy were “COVID-19”, “SARS-CoV-2”, “phototherapy”, “photobiomodulation
therapy (PBMT)”, “low-level laser therapy (LLLT)”, photodynamic therapy (PDT), nitric oxide,
antioxidant, cytokines and vaccines. In order to obtain maximum information restrictions, language or
publication date was not applied. All relevant evidence on this topic existing until 10th September
2020 was gathered.
3. Pathophysiology and Etiopathogenesis
3.1. The Behaviour of the Virus
It is important to capture the current understanding of SARS-CoV-2 behaviour, given the biological
complexity and diversity in its pathophysiology, mechanism and interaction with the host.
3.1.1. Type I Interferon (IFN-1) Signalling Pathway
Type I interferon alpha and beta (IFN-
, IFN-
) is a cytokine that is produced against viral
infection. It acts as an eective innate immune response (IIR), and its downstream cascade results in
regulating viral replication and induction of an eective adaptive immune response [
]. INF type I
) is recognised by the interferon-alpha beta-receptor 1 and 2 (IFNAR 1 and 2), which are present
in the plasma membrane of most cells. Upon binding of Type I INF, the IFNAR receptors activate the
Janus kinases-signal transducer and activator of transcription proteins (JAK-STAT) signalling pathway,
thereby stimulating the interferon-stimulating genes, which are involved in inflammation signalling
and immunomodulation [
]. They interfere with viral replication and spread via several mechanisms
such as a delay in the cell metabolism or cytokine secretion, which ultimately promote the activation of
adaptive immunity as well as preventing viral entry or membrane infusion [
]. It was noted that
cytokine induction and signalling occurs during the SARS-CoV-2 infection [
]. The Orf6 protein
produced by SARS-CoV-2 inhibits the transcriptional factor such as signal transducer and activator of
transcription 1 (STAT1) inside the nucleolus resulting in reduction of interferon response. Similarly,
another protein “Orf3b” reduces the expression of interferon; however, in COVID-19 these two proteins
are truncated and may have lost their anti-interferon function [25].
is the most relevant interferon subtype [
]. COVID-19 may diminish
antiviral responses of Type I INF resulting in uncontrolled viral replication [
]. Therefore, Type I
INF should be administered as soon as the virus is detected to optimise antiviral therapy and prevent
adverse events. Chinese guidelines have recommended an administration of five million units of
inhalation via nebulisation in combination with ribavirin for COVID-19 therapy [
]. Active
viral replication causes Type I IFN upregulation and influx of macrophages and neutrophils, which are
the major sources of proinflammatory cytokines. COVID-19 induces delay Type I IFN and loss of viral
load control in an early phase of the infection.
3.1.2. Role of Mitochondrial Antiviral-Signalling Protein (MAVS) and IIR
Recent research has identified the mitochondrial protein MAVS, located on the outer membrane
of the mitochondria, as a key component of an intracellular pathway, which ultimately links
mitochondria to the mammalian antiviral defence system (innate immunity) [
]. This protein
Antioxidants 2020,9, 875 4 of 23
can activate nuclear factor kappa-light-chain-enhancer of activated B cells (NF Kappa) and interferon
regulatory transcription factor (IRF3) [
], which are the major players in the antiviral response
and inflammation as well as acting as two major eectors of IIR. [
]. Activation of this protein
releases a stream of cytokines from the infected cells; this induces an immune reaction which assists
in eradicating the virus-host cell [
]. In this context, MAVS is also known as “an interferon-beta
promoter stimulator I (INF-
IPS-1)” [
]. It is important to highlight that the reactive oxygen species
(ROS) generated during the antiviral response acts as a negative regulator at the transcriptional level
where the expression of MAVS is regulated [
]. This eukaryotic organelle “mitochondria” could
be considered a crucial player in future COVID-19 therapy.
3.1.3. Host–Viral Interaction
The mechanisms underlying COVID-19 docking to the host cells are still not fully understood,
especially in patients with co-morbidities [
]. SARS-CoV-2 enters target cells through an endosomal
pathway [
]. Firstly, the receptor-binding domain of COVID-19 spike (S) protein binds to the host
receptor, which is an angiotensin-converting enzyme receptor 2 (ACE2) [
], expressed in the lungs,
hearts, kidneys and intestines as well as by endothelial cells [
] (Figure 1). Second, the ACE2–virus
complex is then translocated to endosomes, where S protein is cleaved by the endosomal acid proteases
(cathepsin L.), to activate its fusion anity [
]. The major viral host interaction is as follows; delayed or
suppressed Type I IFN response during initial infection, viral replication triggers hyper-inflammatory
conditions, influx of activated neutrophils and inflammatory monocytes/macrophages, and induction
of Th1/Th17 and production of specific antibodies [28].
Antioxidants 2020, 9, x FOR PEER REVIEW 4 of 24
3.1.2. Role of Mitochondrial Antiviral-Signalling Protein (MAVS) and IIR
Recent research has identified the mitochondrial protein MAVS, located on the outer membrane
of the mitochondria, as a key component of an intracellular pathway, which ultimately links
mitochondria to the mammalian antiviral defence system (innate immunity) [31]. This protein can
activate nuclear factor kappa-light-chain-enhancer of activated B cells (NF Kappa) and interferon
regulatory transcription factor (IRF3) [32,33], which are the major players in the antiviral response
and inflammation as well as acting as two major effectors of IIR. [34]. Activation of this protein
releases a stream of cytokines from the infected cells; this induces an immune reaction which assists
in eradicating the virus-host cell [35]. In this context, MAVS is also known as an interferon-beta
promoter stimulator I (INF-β IPS-1) [31]. It is important to highlight that the reactive oxygen species
(ROS) generated during the antiviral response acts as a negative regulator at the transcriptional level
where the expression of MAVS is regulated [31,36,37]. This eukaryotic organelle mitochondria
could be considered a crucial player in future COVID-19 therapy.
3.1.3. HostViral Interaction
The mechanisms underlying COVID-19 docking to the host cells are still not fully understood,
especially in patients with co-morbidities [2,38]. SARS-CoV-2 enters target cells through an
endosomal pathway [39]. Firstly, the receptor-binding domain of COVID-19 spike (S) protein binds
to the host receptor, which is an angiotensin-converting enzyme receptor 2 (ACE2) [40], expressed in
the lungs, hearts, kidneys and intestines as well as by endothelial cells [41] (Figure 1). Second, the
ACE2virus complex is then translocated to endosomes, where S protein is cleaved by the
endosomal acid proteases (cathepsin L.), to activate its fusion affinity [42]. The major viral host
interaction is as follows; delayed or suppressed Type I IFN response during initial infection, viral
replication triggers hyper-inflammatory conditions, influx of activated neutrophils and
inflammatory monocytes/macrophages, and induction of Th1/Th17 and production of specific
antibodies [28].
Figure 1. The host sites where COVID-19 spike protein binds to the ACE2.
Figure 1. The host sites where COVID-19 spike protein binds to the ACE2.
The endothelium is a principle target of ACE2 activation and assists in minimising inflammation
and ANG II-mediated vascular diseases [
]. Varga et al. (2020) demonstrated that COVID-19 is
a blood vessel disease rather than what was understood initially as disease-induced pneumonia.
Antioxidants 2020,9, 875 5 of 23
COVID-19 attacks the ACE2 receptor of the endothelial membrane of the blood vessels leading to
inflammation [
]. The ACE2 modulates angiotensin II-induced ROS production in endothelial cells.
COVID-19 downregulates the ACE2 function in modulating the ANGII-induced ROS generation
causing production of super oxides, ROS, which ultimately lead to build-up of the oxidative stress that
initiates the disease [45].
3.2. Cytokines Outburst in COVID-19
Regardless of the debate in the precise concept of inflammatory outburst, the immune-mediated
inflammatory responses play a crucial role in the pathogenesis of COVID-19 [
]. One of the mechanisms
associated with COVID-19 progression is a significant rise in the neutrophil count and a decrease in the
level of the lymphocyte count. Meanwhile, there is an increase in the levels of inflammatory markers
such as ferritin, interleukin (IL) 6, Interferon-inducible protein 10 (IP-10), MCP1, tumour necrosis factor
alpha (TNF-
) and D-dimer, all of which have been associated in mortality of COVID-19 and reported
in various studies [
]. The main mechanism of lymphopenia in critical COVID-19 patients is still
not fully understood. Nevertheless, it has been reported that a decrease in the level of B and T cells
prevails in critical cases [
]. Additionally, it has shown that T lymphocytes trigger the spike protein
of SARS-CoV-2, possibly via an endocytosis pathway, with a prominent susceptibility to the latter than
SARS-CoV [52].
It is important to note that cytokine storm (CRS) is one of the main mechanisms of acute
respiratory dysfunction syndrome (ARDS). A systemic inflammatory response occurs as result of
release of proinflammatory cytokines storm (IFN-
, IFN-
, IL-1
, IL-6, IL-12, IL-18, IL-33, TNF-
) and chemokines (CCL2, CCL3, CCL5, CXCL8, CXCL9 and CXCL10) [
]. This CRS will trigger
the immune system, leading to ARDS and multiple organ failure, and subsequently death in critical
cases [54].
3.3. The Severity of COVID-19 in Co-Relation to Biochemistry Analysis
Increased procalcitonin values are associated with a nearly fivefold higher risk of severe
SARS-CoV-2 infection. As the synthesis of this biomarker is inhibited by INF-
, whose concentration is
expected to increase during viral infections, the authors of this study speculated that increased
pro-calcitonin could reflect bacterial super-infection in severe disease cases. However, more
investigations are needed to identify the origin of the biomarker [
]. The angiotensin II level
in the plasma sample from COVID-19 patients was markedly elevated and linearly associated with
viral load and lung injury [
]. Alanine aminotransferase, LDH levels, high-sensitivity CRP and ferritin
were significantly higher in severe cases than moderate cases. IL-2R, TNF-
and IL-10 concentrations
on admission were significantly higher in severe cases than moderate cases [
]. It is important to
note that in SARS-CoV-2, many contributing factors play a role in the coagulation cascade turbulences,
which are as follows, persistent inflammatory status, fibrinolytic activity suppression by IL-6 and
induction of coagulation cascade dysfunction (hypercoagulation), due to pulmonary and peripheral
endothelial injuries [47].
4. The Rational in Utilising Phototherapy in COVID-19 Management
Current studies and clinical trials are focused on antiviral, anti-inflammatory, cytokine syndrome
suppression and increasing tissue oxygenation in the management of COVID-19 [
]. On this note,
phototherapy can be instrumental in modulating the immune system and acting as an antiviral and
anti-inflammatory agent.
4.1. Photobiomodulation (PBM) Therapy (PBMT)
PBMT is a noninvasive eective tool without any adverse eects which modulates the molecular
and cellular activities for therapeutic purposes [
] such as lymphoedema [
], stroke, Alzheimer’s
disease, lung inflammation, diabetic wound healing [60], tissue regeneration and chronic obstructive
Antioxidants 2020,9, 875 6 of 23
pulmonary disorder (COPD) [
]. Well-documented publications have shown that red and near-infrared
(NIR) lights prompt tissue healing by downregulation of inflammatory cytokines and increased
angiogenesis [
]. PBMT has been utilised in the management of viral infections by suppressing the
virus replication and modulating the inflammatory cytokines [
]. Moreover, blue wavelength (
nm) PBM irradiation has positive eects in reducing the viral load of HSV-1 [
]. The photonic energy
of the red and NIR lights is absorbed by the cytochrome C oxidase (CCO) on the outer membrane of
the mitochondria, which results in various molecular and cellular signalling cascades which are as
follows, adenosine triphosphate (ATP) induction (cell proliferation and dierentiation), synthesis of
DNA and RNA, NO release and modification of intracellular organelle membrane activity, resulting in
Ca+2flux and expression of stress proteins [15,6669].
4.1.1. Mechanisms of Action and Its Relation to COVID-19
ATP Versus COVID-19
ATP as an intercellular signalling molecule allows modulation of molecular and cellular
cascades [
], which is first observed as a result of an increase in the mitochondrial membrane
potential and oxygen consumption; this results in a rapid production of NO and ROS. Subsequently,
antiapoptotic proteins, antioxidant defence pathways, heat shock proteins and anti-inflammatory
cytokines are increased. Cell migration and adhesion and DNA synthesis are stimulated as long-term
healing parameters [
]. The biological response of vital infections to PBMT and ATP synthesis
are involved in a purinergic signalling, which plays an important role in regulating the immune
system [72].
Some mechanisms can explain the improvement in the muscle performance, which is due
to the eects of PBMT on musculoskeletal tissues. This has already been addressed in previous
studies [
]. The mechanisms that are worth highlighting are as follows, improvement in the
oxidative and nitrosative stresses; an increase in the mitochondrial metabolism (CCO activity); increased
haemoglobin and oxyhaemoglobin, regardless of any possible tissue heating [
]; synthesis of ATP [
as well as an increase in muscle glycogen synthesis and muscle cell proliferation [
]. Additionally, a
recent literature demonstrated an increase in the oxygen availability in muscle cells [
], activation
of the transcription factors, cytoprotection and protein syntheses [15].
NO Versus COVID-19
NO is a key part of the immune defence system. It is an endogenously produced molecule, which
has a crucial defensive role against infection. NO is present in the endothelium lining of the blood
vessels [
]. The white blood cells can use NO to create unstable molecules that damage the infectious
pathogen. NO acts a signalling molecule and loss of its function is one of earliest indicators of a
disease [80].
The proposed mechanism of action of NO is as follows. First, NO or its derivatives play a role in
palmitoylation reduction expressed by S protein, which aects the ACE 2 and S protein fusion. Second,
NO or its derivatives can cause a reduction in the viral RNA production at the early stage of viral
replication. This is possibly due to an eect on either one or both of the cysteine proteases encoded in
Orf1a (protein expression and amino acid substitutions) of SARS-CoV [
]. This was supported by Li
et al. (2006), who stated that NO is eective in reducing the cell–cell fusion activity of the S protein
of SARS-CoV S protein [
]. Additionally, NO inhibits the replication cycle of SARS-CoV [
]. The
evidence showed that COVID-19 patients have a low level of NO (less natural production). Therefore,
PBMT, which enhances the production of NO, can be utilised as an adjunctive therapy [12].
in vivo
animal study by Keyaerts et al. (2004) has shown that the virus replication reduced and
cytopathic eects inhibited in SARS-CoV infected cells when treated with donor NO [
]. Currently,
based on this, an ongoing clinical trial entitled “Nitric Oxide Gas Inhalation for Severe Acute Respiratory
Syndrome in COVID-19”, aiming to evaluate the use of NO inhalation to improve oxygenation in
Antioxidants 2020,9, 875 7 of 23
moderate to high risks patients and prevent them from developing the severe outcomes of COVID-19
which require intensive care management (mechanical ventilation) [
]. However, the dose delivery is
the key in optimising the clinical outcome, as a higher dose of NO can lead to toxicity.
Perhaps PBMT can be considered as a safe modality as it stimulates NO, which is a potent
vasodilator by increasing the blood flow, facilitating more oxygenation to the stressed tissue as well
as increasing the lymphatic flow by raising the neutrophil levels. Therefore, PBMT optimises the
inflammatory processes as an anti-inflammatory and an antioxidant, which drastically improves
immunity and tissue repair [
]. The release of NO into the cytoplasm and vasculature after being
stimulated with PBM photonic energy prevents smooth muscle cells proliferation in the artery walls,
adhesion of leukocytes and platelet aggregation, as well as reduces the oxidation of low-density
lipoprotein cholesterol (LDL) (major component of plaque). This therapy can be considered to protect
against atherogenesis, which is predominant in severe and high-risk cases of COVID-19 patients.
Supplementary to this concept, Shi et al. (2020) highlighted that 20% of 416 patients hospitalised in
Wuhan with the coronavirus had heart damage [58].
A single-blind, placebo-controlled randomised clinical trial by Mitchell at al. (2013) was conducted
to measure and evaluate the eects of NIR LEDs PBM (
880 nm and
890 nm at power output of 636
mW per four pads) on venous NO, by its nitrite and nitrate metabolites, in venous blood draining from
the tissue of 15 healthy young recruited subjects (21–27 years old). Positive results have shown a peak
increase in the venous NO level only for five minutes into the treatment, and then slowly dropped [
NIR light proves to stimulate and upregulate the local production of NO through various methods of
administration to act as an antiviral agent in inhibiting RNA replication of the virus, enhancing the
immune system and minimising atherosclerosis in healthy young individuals. Whether this response
can be achieved with patients with co-morbidities remains to be investigated.
ROS is a major contributor in the immune responses as signalling messengers, which are produced
via nicotinamide the adenine dinucleotide phosphate hydrogen (NADPH) oxidases (NOX) pathway.
They are produced in the endothelial cells. Reperfusion injury (reoxygenation injury) is directly related
to the formation of ROS, endothelial cell restoration and increase in vascular permeability [
]. In
acute lung injury, especially in severe COVID-19 cases, the virus downregulates ACE2 function, thus
enhancing inflammation and causing vascular permeability [1].
in vitro
study by Amaroli et al. (2019) demonstrated that the photonic energy of NIR PBM can
stimulate mitochondrial oxygen consumption and ATP synthesis in human endothelial cells (HEC). It
is important to note that short exposure of NIR irradiation had no eect on the viability of HEC, but
rather led to an increase in the rate of wound healing stimulation, which is most likely sustained via
ROS-mediated stimulation of mitochondrial activity [
]. This study was supported by G
et al. (2015)
in vitro
study [
]. This promising therapeutic light can be useful to protect against
inflammation-induced endothelial dysfunction in COVID-19 patients. A study by Fujimaki et al., 2003
showed that utilisation of
830 nm PBMT at a fluence of 150 mW/cm
induces the production of ROS
by the neutrophils, which play a crucial role in inflammatory tissue repair and promote healing [90].
4.1.2. PBM Eects on Modulating the Immune Response
PBMT acts as an immunomodulator, inducing antioxidant and anti-inflammatory eects [
Many studies have examined PBM cellular signalling and proved that a reduction in Ca
sensitivity is
accountable for its anti-inflammatory eects [
]. As our findings in this critical review showed
that COVID-19 dysregulates the immune response which is a feature of severe disease, the immune
profile of SARS-CoV-2 associated with intensive care unit (ICU) admission is related to IL-1
and IFN
gamma, which correlate with Th1 response, whereas IL-4 and IL-10 correlate with Th-2 response and
IL-6 and TNF-
correlate with innate response. Several studies showed the eectiveness of utilising
PBMT in modulating the pulmonary immune responses in COPD [14,21,92,93].
Antioxidants 2020,9, 875 8 of 23
A study by Alves et al. (2017) showed radical molecular changes in lung tissue injury: an increase in
the anti-inflammatory cytokine IL-10; an augmentation in the production of proinflammatory cytokines
, TNF-
, IL-6 and IL-17) and chemokine (CXCL1/KC); and a decrease in the peri-bronchial
density, collagen production, alveolar enlargement, P2X7 purinergic receptor expression and cell
death 7AAD [
]. This study demonstrated that PBMT reduced the number of cells (Th2/Th17) in
bronchoalveolar lavage (BAL). Therefore, it is worth considering PBMT in COVID-19 as a useful tool
in regulating IL-4 and IL-10 which correlate with Th-2 response.
in vivo
animal study by Sergio et al. (2018) recruited Wistar rats aected by acute lung injury
(ALI). The animals in the laser group were irradiated with
808 nm PBM at a low power output setting
(100 mW; 3.571 W/cm
; four points per lung), while the control group received sham irradiation. The
results revealed an increase in the level of Bcl-2 mRNA and decrease in the caspase-3 mRNA level
in the irradiated group, in comparison to the control group. This indicates that PBMT can modify
the mRNA levels in the gene expression, which is associated with DNA fragmentation in alveolar
inflammatory cells after lipopolysaccharide-induced ALI [94].
in vivo
animal study by Moraes et al. (2018) utilised
660 nm PBM at a power output of 30
mW with a fluence of 3 J/cm
, aiming to reduce the lung inflammation [
]. The results showed a
reduction in protein deposition, alveolar enlargement, proinflammatory cytokine secretion (such as;
, IL-6 and TNF-
in BAL fluid) as well the expression of P2X7 receptor [
]. Studies have shown
that PBMT can improve the injured musculature, by reducing the oxidative stress and inflammatory
cytokines such as IL-6 and TNF-
, and increasing the IL-10 [
]. This was supported by an
in vivo
animal study conducted by de Lima et al. (2014) [
]. In the latter study, mice subjected to a mesenteric
occlusion (45 minutes) were recruited, then euthanised after the clam was released, and subsequently
intestinal reperfusion was carried out for 2 hours (h). The upper bronchus of the animal model was
irradiated with
660 nm PBM for five minutes after starting reperfusion, at various fluences (1, 3, 5
and 7 J/cm
). The authors concluded that PBMT significantly induced an increase in the IL-10 levels in
animals subjected to intestinal ischemia/reperfusion (i-I/R), highlighting the anti-inflammatory role of
this therapy. Thus, it mitigates the i-I/R-induced ALI by modulating the anti-inflammatory responses,
as well the proinflammatory cytokines release. Additionally, this study was the first, to prove that
various laser fluences may well be eective in reducing the i-I/R-induced ALI [98].
Another study showed that PBMT reduced the neutrophils influx, myeloperoxidase (MPO) activity,
cellular adhesion molecule-1 (CAM-1) mRNA expression as well as the oedema. It is important to
note that PBMT reduced the ROS formation and increased the glutathione (GSH) concentration in
lung from i-I/R group. This study demonstrated the eectiveness of PBMT in regulating the oxidative
stress, which is notably raised in COVID-19 patients [
]. Additionally, PBMT can reduce mucus
overproduction, collagen deposition and cytokine release [
]. Furthermore, PBMT can be
utilised as an adjunctive therapy to reduce lung inflammation and enhance the immune system. A
randomised controlled clinical study by Mehani et al. (2017) aimed to evaluate the eectiveness of
PBMT acupuncture stimulation in comparison to the inspiration muscle training (IMT), on modulating
the immune disturbances in patients with stable COPD [
]. The acupuncture points (large intestine
11, kidney meridian 27, large intestine 4, lung meridian 1 and lung meridian 7) were irradiated with
904 nm at a peak power of 5W and with pulse width of 200 nanoseconds. Each point was irradiated
for 90 seconds, twice per day, three times per week for two months. The specification of the laser
pointer utilised in this study was LLL3A, GALAS, He-Ne Laser acupuncture. The results revealed a
reduction in plasma IL-6 concentration associated with an increase in CD4+/CD8+ratio in both groups,
nevertheless, laser therapy’s eectiveness was superior to inspiratory muscle training. Interestingly,
the levels of IL-6 and CD4+/ CD8+were negatively correlated. In this context, studies conducted
by Silva et al. (2014) and Peron et al. (2015) showed that PBMT might induce a reduction in mucus
overproduction, cytokines release and collagen deposition [101,102].
Antioxidants 2020,9, 875 9 of 23
4.1.3. Eects of PBMT on Angiogenesis Versus COVID-19
The endothelium plays many important functions in the human body in terms of maintaining
vascular homeostasis. Vascular endothelial growth factor (VEGF) is one of the key regulators of
angiogenesis vascular permeability and the survival of endothelial cells. The early release of VEGF can
increase pulmonary permeability, whereas a decrease in the VEGF and VEGF-receptor-1 (VEGFR-1)
expressions in the lung which ultimately contributes into alveolar epithelial death [103].
PBMT, most importantly, influences the endothelial cells proliferation and secretion of angiogenic
factors, which contribute into modulation of angiogenesis to improve in the management of diseases,
which require blood vessels formation and repair [
]. PBMT can assist to restore the endothelium
membrane of the aected site by COVID-19, as this viral infection contributes in inducing coagulation
cascades dysfunction which ultimately leads to hypercoagulation [
]. An
in vivo
study by Cury et al.
(2014) showed the eectiveness of
660 nm and
780 nm laser PBM in modulating VEGF secretion,
MMP-2 activity and HIF-1
expression in a dose-dependent manner [
]. This was supported by
another study, which confirmed that PBMT causes an increase in proliferation of vascular endothelial
cells and decrease in VEGF and TGF-
secretion [
]. In terms of hypoxia and damage tissue, PBMT
reduces the overexpression of hypoxia-inducible factor-1
), TNF-
and IL-1
, and increases
in the levels of VEGF, nerve growth factor (NGF) and S100 proteins in rats with chronic constriction
injury [
]. Thus, utilising PBMT to enhance the angiogenesis in COVID-19 patients in Phase I and II
of the disease, as a therapeutic approach, is the way forward.
A novel innovation, worthy of consideration, is the utilisation of PBMT as an intravascular laser
irradiation of the body blood flow that can enhance immune responses [
]. Transdermal PBM
(t-PBM) is another therapy that has beneficial eects on the endothelium and blood flow [
]. Studies
have shown that PBMT improves the immune system [
]. A study conducted by Szmcyszyn
et al. (2016) to evaluate the eects of t-PBM therapy on endothelial function [
]. Forty healthy
young individuals (20–40 years old) were recruited and divided into two groups: laser group (n=
30) and control group (n=10). Transdermal illumination of radial artery with
808 nm (LED) was
performed once a day for three consecutive days according to the following protocol; power output 50
mW, irradiance 1.6 W/cm
, energy 20 J/day and total energy 20 J. The result showed a beneficial eect
of t-PBM therapy on endothelium and blood flow due to a significant increase in glutathione (GSH)
levels and an extensive decrease in angiostatin concentration. However, no significant dierence in the
levels of the following biochemistry parameters observed; VEGF, FGF, symmetric dimethylarginine
(SDMA), asymmetric dimethylarginine (ADMA) and NO pathway metabolites within 24 h after the
laser irradiation. Based on this, it appeared that the latter protocol required further testing prior to
utilising it in clinical human studies. Dominguez et al. (2020) suggested that an increase in super
peroxide dismutase (SOD) synthesis as a result of red light PBM irradiation requires more attention
from researchers [
]. SOD is an important enzyme to protect cells against mutation and replication
when ROS are declined [
]. Furthermore, the same author suggested utilisation of t-PBM
approach in COVID-19 management to control the CRS by irradiating the wrist level as a point of
application with either visible or invisible diode lasers for 30 minutes per day for 3–5 days.
Interestingly, a study by Zhang et al. (2010) showed that after preconditioning the infarcted
myocardium with
635 nm PBM irradiation, prior to cell translation an increase in the activity of SOD
activity and a decrease in the malondialdehyde (MDA) of an infarcted myocardium [
]. Additionally,
preconditioning with PBMT increased the survival rate and angiogenesis and decreased the apoptotic
percentage of implanted cells. This study established that PBM preconditioning therapy is a unique
noninvasive approach, which might be worth considering in severe cases of COVID-19 [113].
4.1.4. Light Emitted Diodes (LEDs)
Light-emitting diode (LED) is a PBM feature when the light emission is non-coherent and
non-collimated. The biostimulatory eects of LEDs exert an anti-inflammatory as well as anti-fibrotic
Antioxidants 2020,9, 875 10 of 23
eects resulting in the release of inflammatory mediators [
] and fibroblast proliferation
inhibition [117].
in vivo
animal study conducted by Brochetti et al. (2017) utilised mice induced with lung
fibrosis (LF), as an animal model to evaluate the biostimulatory eects of
660 nm LED on the
development of the LF [
]. Positive results showed that LED treatment reduced the following factors:
cell influx in the BAL, presence of dynamic and static elastases, collagen production and interstitial
tissue thickening, increased levels of TNF-
, IL-17A, IL-6 and CXCL1/KC released by pneumocytes
and fibroblasts fibrotic mice culture. The findings of this study revealed that LED can be a promising
treatment modality for COVID-19 patients [118].
A randomised, double-blind crossover clinical trial conducted by de Souza et al. (2019) utilised a
light-emitting device of a low-intensity LEDs PBM applied on the main respiratory muscles (Figure 2)
by means of a cluster with 69 LEDs, containing 35 red (
10 nm; 10 mW; 0.2 cm
) and 34 NIR
20 nm; 10 mW; 0.2 cm
) LEDs, while the control group received sham irradiation [
]. The
twelve recruited patients with COPD received two sessions of PBMT with one week apart. The primary
outcomes and methods of assessment were as follows. The functional capacity assessed by the 6-min
walk test (6 MWT) at baseline and 24 h after intervention, while the pulmonary function (spirometric
indexes), thoracoabdominal mobility (cirtometry) and respiratory muscle strength (maximal respiratory
pressures) tests were assessed at baseline, 1 h and 24 h after intervention. No significant interactions
were noted for spirometric variables, maximal respiratory pressures and cirtometry. However, an
increase in the functional capacity after PBMT was statistically significant (p<0.01) in the 6 MWT
after 24 h of innervation, compared with the baseline. The authors of this study concluded that LEDs
PBMT was an eective tool for improving acute functional capacity in COPD patients observed in the
6 MWT after 24 h of intervention. Equally, this treatment can be useful to treat COVID-19 patients and
is of worthy consideration, as it irradiates larger surface areas (Figure 2), as the cluster spot size is
approximately 40cm
, which delivers two wavelengths,
630 nm and
830nm, with various penetration
depths. Ultimately, this therapy can provide optimal therapeutic eects in COVID-19 patients [119].
A series of medical papers published over the last months, suggests that the contagion can spread
deep into the vascular system and even the brain. Many studies have shown that transracial NIR PBM
is a very ecient approach in reducing the cerebral ischemia both
in vivo
and clinical setups. The
NIR PBM irradiation produces vasodilatory eects via NO-mediated pathway [
]. Interestingly,
in vivo
animal study by Kimizuka et al. (2017) showed the eects of NIR in a mouse model of
influenza vaccination using an LED device of various wavelengths:
1258 nm or
1301 nm,
which replicates the adjuvant eect of a diode pump solid-state laser (DPSSL) system [
]. The results
indicated that a broad range of NIR laser wavelengths has the ability to enhance vaccine immune
responses. This could be the future in utilising PBM laser therapy to enhance the vaccine properties
against COVID-19.
After highlighting the mechanisms of action of PBMT in regulating and restoring the immune
responses in injured tissue (oxidative stress), which are supported by
in vitro
in vivo
studies and clinically; therefore, it is important to appreciate the eectiveness of PBMT in modulating
the immune responses. Ultimately, this therapy could be useful in regulating the CRS in COVID-19
patients in ICU admissions, as it enhances respiratory function and angiogenesis, therefore PBMT can
be utilised in clinical studies to manage COVID-19 patients as an eective therapeutic modality at early
and late phases of the infection, as well as preventive approach.
Antioxidants 2020,9, 875 11 of 23
Antioxidants 2020, 9, x FOR PEER REVIEW 11 of 24
Figure 2. Modified schematic description of the respiratory musculature application points (red dots)
for light-emitting diodes (LEDs) photobiomodulation (PBM) irradiation with 69 clustered head
probe: 35 red ( 630 ± 10 nm) and 34 of near-infrared ( 830 ± 20 nm) in the management of COPD-19
A series of medical papers published over the last months, suggests that the contagion can
spread deep into the vascular system and even the brain. Many studies have shown that transracial
NIR PBM is a very efficient approach in reducing the cerebral ischemia both in vivo and clinical
setups. The NIR PBM irradiation produces vasodilatory effects via NO-mediated pathway
[120,121]. Interestingly, an in vivo animal study by Kimizuka et al. (2017) showed the effects of NIR
in a mouse model of influenza vaccination using an LED device of various wavelengths: 1061nm,
1258 nm or 1301 nm, which replicates the adjuvant effect of a diode pump solid-state laser
(DPSSL) system [122]. The results indicated that a broad range of NIR laser wavelengths has the
ability to enhance vaccine immune responses. This could be the future in utilising PBM laser therapy
to enhance the vaccine properties against COVID-19.
After highlighting the mechanisms of action of PBMT in regulating and restoring the immune
responses in injured tissue (oxidative stress), which are supported by in vitro and in vivo animal
studies and clinically; therefore, it is important to appreciate the effectiveness of PBMT in
modulating the immune responses. Ultimately, this therapy could be useful in regulating the CRS in
COVID-19 patients in ICU admissions, as it enhances respiratory function and angiogenesis,
therefore PBMT can be utilised in clinical studies to manage COVID-19 patients as an effective
therapeutic modality at early and late phases of the infection, as well as preventive approach.
Figure 2.
Modified schematic description of the respiratory musculature application points (red dots)
for light-emitting diodes (LEDs) photobiomodulation (PBM) irradiation with 69 clustered head probe:
35 red (λ630 ±10 nm) and 34 of near-infrared (λ830 ±20 nm) in the management of COPD-19 [119].
4.2. Photodynamic Therapy (PDT)
4.2.1. Mechanism of Action of PDT
PDT is a treatment in which a photosensitiser (PS) dye is utilised in conjunction with suitable
wavelength, corresponding to the absorption spectrum of the PS resulting in generation of ROS and
death of the pathogen or tumour by the oxidative damage [
]. PDT induces a strong oxidative stress
response in addition to triggering a vascular-mediated response, and modulating the cytokines such as
IL-6 and IL-10 [123]. All these processes are sensitive to NO [124].
4.2.2. Biological Response of Viral Infections to PDT
A review by Pal et al. (2020) stated that CoVs are enveloped single-stranded RNA viruses, which
resemble the SARS-CoV-2 genome [
]. These viruses are generally susceptible to acid, alkaline and
heat [
]. After the outbreak of SARS and MERS, many researchers investigated the potential of
utilising photochemical therapy, which can reduce or totally eliminate the potential risks of transmission
of coronaviruses via blood products or its derivatives [22,127,128].
The current research focuses on plasma inactivation treatments based on heat and photochemical
treatment modalities. The heat method uses various temperatures and exposure times to reduce
the virus concentration in the plasma. A temperature of 60
C for 30 min exposure was found to
be sucient to reduce SARS-CoV from cell-free plasma [
], while 56
C for 25 min exposure has
reduced MERS virus by more than 4 log10 tissue culture infectious dose 50%/mL (TCID50/mL) [
The eectiveness of this method was due to the heat, which denatures the proteins in blood products
Antioxidants 2020,9, 875 12 of 23
(only manufactured plasma-derived products). On the other hand, photochemical treatment methods
are based on utilising dierent wavelengths of light, which aect the viability of SARS and MERS
viruses in the blood. Ultraviolet (UV) light, Amotosalen or riboflavin can inactivate pathogenic nucleic
acids. Because the penetrating power of UV light is low the inactivation eciency is not high enough
especially when blood bags are used. Methylene blue also has a great potential in this field [131,132].
4.2.3. Impact of Various PS on Viruses
Methylene Blue (MB)
The use of MB with visible light can inactivate coronavirus in plasma have been reported [
Eichmann et al. (2020) investigated the inactivation of three viruses, which emerged from the
SARS-CoV. The results showed both THERAFLEX UV-Platelets (short-wave ultraviolet C (UVC) light)
and THERAFLEX MB-Plasma (MB +visible light of
630 nm) eectively reduce the contagion of
SARS-CoV, Crimean–Congo Haemorrhagic fever virus (CCHFV) and Nipah virus (NiV) in platelet
concentrates and plasma, respectively [
]. Presently, an interventional controlled clinical trial on
adult COVID-19 patients is being conducted to evaluate eciency of exchange transfusion versus
plasma from convalescent patients with MB [
]. Hopefully, the results of this trial will bring some
clarity to the potential role of MB in COVID-19 management. In this context, a recent
in vitro
by Jin et al. (2020) concluded that BX-1 (an AIDS treatment instrument based on MB photochemistry
technology) can eectively eliminate SARS-CoV-2 within 2 min and its titre decline can reach 4.5 log10
TCID50/mL [134].
Indocyanine Green (ICG)
ICG-based PS is a marker used to assess the perfusion of tissues and organs in many areas of
medicine, especially in blood for diagnostic purposes. ICG can be activated with
810 nm wavelength,
which has a deep penetration depth. Owing to this fact, if the ICG can reach the alveolar tissue via a
specific tool, it could be useful to treat COVID-19 patients [135].
Aminolevulinic acid (ALA) and its derivatives are predominant PS in clinical PDT and have been
utilised in few studies related to PDT of viruses, using haematoporphyrin derivatives [
]. Yin
et al. (2012) investigated the eect of PDT using haematoporphyrin monomethyl ether (HMME) on
bovine and HIV. The results showed positive responses in inhibiting the HIV
in vitro
experiments [
In terms of the nanoparticle-based approach and its eects in PDT, a study by Banerjee et al. (2012)
targeted to develop ex vivo reusable antiviral agents based on protoporphyrin IX (PpIX) connected to
multiwalled carbon nanotubes. The results showed a reduction in the contagion of influenza A virus
in mammalian cells [140].
The above-mentioned data opens a new door for exploration of the potential of PDT in the
treatment of COVID-19. Indeed, further research in this field is a necessity to claim its ecacy.
4.3. Ultrashort Pulsed (USP) Laser as an Antiviral Agent
The ultrashort pulsed (USP) laser is an innovative approach, as it selectively inactivates viruses
by utilising femtosecond laser pulses. It has been observed that a range of fluences between 1 and 10
allows killing of viral particles without causing cytotoxicity to the mammalian cells [
This process targets the intrinsic mechanical or vibrational properties of the viral capsids, which
therefore become insensitive to genetic mutation of the virus, thus projecting the superiority of this
technique over the current antiviral drugs. This method can be the future of an antiviral drug in
treating COVID-19 patients.
The visible light shows insignificant intrinsic absorption by nucleic acids and proteins without
presence of chromophores. Unlike UV or gamma radiation, the visible light of electromagnetic spectrum
Antioxidants 2020,9, 875 13 of 23
does not initiate molecular ionisation. These properties could enable the use of USP lasers to selectively
inactivate pathogens without harming desired biological constituents such as mammalian proteins in
blood products. [
]. Therefore, the structure of a mammalian protein is well preserved [
]. Visible
USP lasers have shown a broad-spectrum ecacy against both DNA and RNA viruses [
including nonenveloped viruses that are conventionally dicult to inactivate.
4.4. Ultraviolet (UV) Therapy
The use of UV light as an antiviral agent has been the subject of much controversy. It is important
to note that prolonged exposure to UVA or UVB or any use of UVC can be detrimental to health.
The ultraviolet blood irradiation (UBI) was widely used to treat many diseases such as septicaemia,
pneumonia and asthma. Its eects to treat infection are related to its immune-modulating therapy
as well as its ability to normalise blood parameters. Low doses of UV can kill microorganisms by
damaging the DNA, while any DNA repair enzymes can rapidly repair damage in the host cells [
However, its eectiveness still remains controversial due to the shallow penetration depth of the phonic
energy. A study by Hashem et al., 2019 investigated the eect of Amotosalen/UVA light in reducing
the risk of MERS-CoV transmission, via human platelet concentrates, which minimises the risk of
transfusion-related MERS-CoV transmission [
]. It was concluded that Amotosalen and UVA light
was eective in reducing the contagion of MERS-CoV-spiked platelet concentrates and completely
inactivated MERS-CoV by >4 logs.
5. Potential Future Scope of Phototherapy in Augmenting the COVID-19 Vaccine Production
Undoubtedly, vaccination is going to be the supreme cure for the currently circulating deadly
SARS-CoV-2 strain. Global eorts in the field of research and diagnosis to fight this situation are
unparalleled in terms of the rate and magnitude of vaccine production. As of today, there are more
than a hundred potential candidate vaccines either; in the pre-clinical or developmental stage or under
dierent phases of animal or human trials [
]. In spite of the escalation in speed for production
and mass distribution, the vaccine must be strategically designed for safe and eective use. Imposing
quality control measures on the methods of production and administration can greatly help in assuring
high standards of public health safety [153].
5.1. Utilisation of USP Laser Irradiation for Inactivation of SARS-CoV-2 to Optimise Vaccine Production
Whole inactivated virus (WIV) vaccines are a rapid method to obtain vaccines of emerging viral
strains [
]. This is because in comparison to other types of vaccines, WIV vaccines can be manufactured
quickly by chemical or physical inactivation of a purified virus strain regardless of the need to identify
antigens [
]. At the same time, they can produce an eective immune response. The traditional
methods of pathogen inactivation methods are formalin, Beta-propiolactone (
- propiolactone), heat,
ultraviolet light and gamma rays [
]. Recent report on the rapid development of an inactivated
vaccine for SARS-CoV-2 infection indicated utilisation of
- propiolactone for virus inactivation [
However, the use of
-propiolactone or any other methods, as mentioned above, has been associated
with several structural alterations in the virus proteins as well as the vaccine antigens leading to a
suppressed immune response generation from the vaccine and an overall diminished potency [
Therefore, it is necessary to search for comprehensive techniques for safe and immunogenic WIV
vaccine production.
During the last decade, the use of USP laser irradiation for preparation of WIV vaccines has been
tried and tested to combat the influenza A virus subtype H1N1 [
]. Unlike its counterparts,
USP irradiation utilises laser pulses with a pulse duration of several femtoseconds, which helps
in the physical inactivation of the virus [
]. This occurs through the process of impulsive
stimulated Raman scattering (ISRS), which causes rapid molecular vibrations within viral capsids
through spontaneous and excited Raman scattering [
]. The resultant clumping of viral
capsid proteins, which is a universal feature of viruses, leads to their inactivation. The use of visible
Antioxidants 2020,9, 875 14 of 23
light in the range of
400 to
700 nm, enables several characteristic features to this technique, such
as (1) prevention of disintegration in the structure of the virus, thus reducing the risk of an adverse
helper T cell, type 2 response caused by the vaccine; (2) prevention of a heat-initiated structural
denaturation of B-cell epitopes; and (3) preserving the toll like receptor (TLR)-stimulating capacity
of viral nucleic acids, thus upholding the potency of the virus which is sucient to generate an
eective immune response [
]. It has been proven that WIV vaccines can be inactivated by the
chemical-free; therefore, the USP laser irradiation process could do so at a dose which is 10 times lower
than that of the conventionally used formalin inactivation method required for the production of the
HINI influenza vaccine [
]. In lieu of the beneficial eects of USP laser irradiation-mediated virus
inactivation protocol, the use of the same could be a prospective method of choice for the production
of the COVID-19 vaccine, provided all essential laboratory and clinical requirements and regulations
are foreseen and met.
5.2. Potential Role of Lasers as COVID-19 Vaccine Adjuvants
Traditionally utilised vaccines possess poor immunogenic potential on their own and optimisation
of their ecacy to treat infection holds a key role in the future of vaccine development [
Immunological or vaccine adjuvants are chemical compounds or macromolecules, which provide
enhanced synergistic benefits to the vaccine antigen, resulting in improved and long-lasting
immunological memory to combat a viral infection [
]. However, in spite of a higher rate
of seroconversion in adjuvant vaccines, the latter are often supplanted by an increased likelihood
of adverse local or systemic reactions, resulting in very few being commercially available while
having Food and Drug administration (FDA) approval [
]. Some of the most commonly used
vaccine adjuvants comprise particulate aluminium salts, alum with mono-phosphoryl lipid A (AS04) or
squalene-based oil-in-water emulsion (AS03) [
]. The most common adverse eects noted with
the use of the above-mentioned adjuvants are as follows; injection site reactions, reduced immunogenic
potential with subsequent doses and inability to mediate a broad-spectrum immune response [
In a clinical study based in France, an intramuscular alum-adjuvanted vaccine injection was linked with
the development of macrophagic myofascitis in some patients [
]. Additionally,
in vitro
have shown that the use of an alum-complex vaccine adjuvant has several structural limitations, which
degrade the potency of the vaccine [
]. A recently conducted pilot trial to test a vaccine
for SARS-CoV-2, reports the utilisation of an alum vaccine adjuvant [
]. The precise demerits of
the conventionally used adjuvants explained through the above-mentioned facts have instilled the
urgency to discover novel, ecient and non-toxic vaccine adjuncts.
It is important to highlight that use of laser, as an adjunctive therapy to antiviral vaccines
[laser vaccine adjuvants (LVA)] has captured the attention of many researchers. LVA are novel and
ecient vaccine adjuvants, which are upcoming in the field of research and diagnosis for vaccine
production [
]. When applied intra-muscularly LVA has demonstrated a boost in the Th1-mediated
immune responses that are crucial to combat viral infections [
]. The ability of LVA to enhance the
cell-mediated, in particular, the CD8+T cell-mediated immune response, which is almost negligible
by means of an alum vaccine adjuvant, has also been demonstrated [
]. LVA requires a transient
photo-illumination with specific dosimetry at the intramuscular or intradermal sites [
]. This
procedure avoids the formation of any kind of adjuvant-related complex unlike other vaccine adjuvants
and therefore it is able to provoke the antigen presenting cells (APCs), without inducing any significant
localised inflammatory response or foreign body tissue reactions [
]. LVA application shortens the
pharmaceutical time-frame since they do not require any prior chemical preparation unlike other
chemical compounds currently being utilised, as vaccines adjuvants [
]. LVA most certainly
appears to be an ecient, simple, convenient and profitable treatment modality, without long-term
adverse eects. Although, there exists ample evidence on the use of the LVA technique, in the past for
viral infectious diseases, it is possible application in the management of COVID-19 is unexplored and
needs to be established through laboratory and clinical analyses.
Antioxidants 2020,9, 875 15 of 23
6. Conclusions
This review highlighted that PBMT can deactivate viruses and reduce viral load. This potential
therapy could be a way forward via trans-tracheal or trans-dermal PBMT approach in the management
COVID-19 patients. Equally, new innovative laser technologies have emerged such as LVAs and USP
laser. The latter modality is well documented in the literature for its ability to selectively inactivate
viruses by utilising femtosecond laser pulses. On the other hand, LEDs PBM of single or multiple
wavelengths, delivered via clustered probe, can enhance immune responses and improve functionality
of inflamed lungs. Nevertheless, utilisation of precise laser dosimetry and necessity to follow laser
safety guidelines remains irrefutable. PDT is a well-documented modality in the literature for its
eective photochemical reaction on eliminating the viability of SARS and MERS viruses in the blood,
which ultimately eliminates the potential risk of CoVs transmission via blood products or its derivatives.
We answered our research question that the molecular and cellular mechanisms of action of
phototherapy as a potential antioxidant treatment in enhancing immune response and reducing the
host–viral interaction in patients infected with SARS-CoV-2. Therefore, it is a promising treatment
modality which needs to be further validated for COVID-19 management by robust and rigorous
randomised, double blind, placebo-controlled clinical trials to evaluate its impartial outcomes and safety.
Author Contributions:
Conceptualization, R.H.; Methodology, R.H.; Software, I.R.B.; Validation, R.H., S.B., I.R.B.,
and T.S.; Formal Analysis, I.R.B; Investigation, R.H. and S.D.; Resources, T.S. and I.R.B.; Data Curation, R.H.;
Writing—Original Draft Preparation, R.H. and S.D.; Writing-Review and Editing, R.H. and S.D.; Visualization,
I.R.B.; Supervision, S.B.; Project Administration, R.H.; Funding Acquisition, T.S. and I.R.B. All authors have read
and agreed to the published version of the manuscript.
This work was funded by National Research Development Projects to finance excellence
(PFE)-37/2018-2020 granted by the Romanian Ministry of Research and Innovation.
Conflicts of Interest: The authors declare no conflict of interest.
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... A fundamental aspect of COVID-19 disease is the tissue and organ damage caused by a hyper-inflammatory state [3] often referred to as a cytokine storm. Oral and inhaled steroids have been widely used to address this issue but using broad immunosuppressive agents in the context of severe infection may have potential drawbacks. ...
... Oral and inhaled steroids have been widely used to address this issue but using broad immunosuppressive agents in the context of severe infection may have potential drawbacks. Methylene blue (MB) and photobiomodulation both offer anti-inflammatory and immune modulating effects which appear to be additive and of significant benefit in COVID-19 disease [3,4]. In fact, MB appears to ameliorate COVID-19 disease at virtually every stage of the pathophysiological process as documented by Dabholkar et al., 2021 [5] and outlined in Table 1. ...
... A recent evidence-based review conducted by highlighted the molecular mechanisms of COVID-19 and potential therapeutic strategies of which phototherapy can be considered, as a potential treatment modality in COVID-19 management [3,31]. ...
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Coronavirus disease 2019 (COVID-19) caused by SARS-CoV-2 virus was first recognized in late 2019 and remains a significant threat. We therefore assessed the use of local methylene blue photodynamic viral inactivation (MB-PDI) in the oral and nasal cavities, in combination with the systemic anti-viral, anti-inflammatory and antioxidant actions of orally ingested methylene blue (MB) and photobiomodulation (PBM) for COVID-19 disease. The proposed protocol leverages the separate and combined effects of MB and 660nm red light emitted diode (LED) to comprehensively address the pathophysiological sequelae of COVID-19. A total of eight pilot subjects with COVID-19 disease were treated in the Bahamas over the period June 2021–August 2021, using a remote care program that was developed for this purpose. Although not a pre-requisite for inclusion, none of the subjects had received any COVID-19 vaccination prior to commencing the study. Clinical outcome assessment tools included serial cycle threshold measurements as a surrogate estimate of viral load; serial online questionnaires to document symptom response and adverse effects; and a one-year follow-up survey to assess long-term outcomes. All subjects received MB-PDI to target the main sites of viral entry in the nose and mouth. This was the central component of the treatment protocol with the addition of orally ingested MB and/or PBM based on clinical requirements. The mucosal surfaces were irradiated with 660 nm LED in a continuous emission mode at energy density of 49 J/cm2 for PDI and 4.9 J/cm2 for PBM. Although our pilot subjects had significant co-morbidities, extremely high viral loads and moderately severe symptoms during the Delta phase of the pandemic, the response to treatment was highly encouraging. Rapid reductions in viral loads were observed and negative PCR tests were documented within a median of 4 days. These laboratory findings occurred in parallel with significant clinical improvement, mostly within 12–24 h of commencing the treatment protocol. There were no significant adverse effects and none of the subjects who completed the protocol required in-patient hospitalization. The outcomes were similarly encouraging at one-year follow-up with virtual absence of “long COVID” symptoms or of COVID-19 re-infection. Our results indicate that the protocols may be a safe and promising approach to challenging COVID-19 disease. Moreover, due its broad spectrum of activity, this approach has the potential to address the prevailing and future COVID-19 variants and other infections transmitted via the upper respiratory tract. Extensive studies with a large cohort are warranted to validate our results.
... In the same way that there a diversity in the processes that stimulate inflammation, there exists also a breadth of inflammatory diseases in virtually every system of the human body. For instance, defects of the immune system in Crohn's disease cause dysregulation of interferon-alpha (IFN-α) and interleukin-17 (IL- 17), which culminates in a form of inflammatory bowel disease [10]. The cascade of viral myocarditis begins by pattern recognition receptors of self-antigens by toll like receptors that lead to production of pro-inflammatory cytokines [11]. ...
... The history of Laser Research and clinical application in medicine can be traced back to the late 1960s [17]. In the late nineteenth century, the Danish physician Niles Finsen demonstrated the beneficial effect of the red and blue spectrum of sunlight on mycobacterial skin infections. ...
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Non-invasive laser irradiation can induce photobiomodulation (PBM) effects in cells and tissues, which can help reduce inflammation and pain in several clinical scenarios. The purpose of this study is to review the current literature to verify whether PBM can produce dose effects in anti-inflammatory experiments by summarizing the clinical and experimental effects of different laser parameters of several diseases. The so-called Arndt-Schulz curve is often used to describe two-phase dose reactions, assuming small doses of therapeutic stimulation, medium doses of inhibition, and large doses of killing. In the past decade, more and more attention has been paid to the clinical application of PBM, especially in the field of anti-inflammation, because it represents a non-invasive strategy with few contraindications. Although there are different types of lasers available, their use is adjusted by different parameters. In general, the parameters involved are wavelength, energy density, power output, and radiation time. However, due to the biphasic effect, the scientific and medical communities remain puzzled by the ways in which the application of PBM must be modified depending on its clinical application. This article will discuss these parameter adjustments and will then also briefly introduce two controversial theories of the molecular and cellular mechanisms of PBM. A better understanding of the extent of dualistic dose response in low-intensity laser therapy is necessary to optimize clinical treatment. It also allows us to explore the most dependable mechanism for PBM use and, ultimately, standardize treatment for patients with various diseases.
... In simple terms, physics controls chemistry, not the converse. Furthermore, PBM may be used for COVID-19 disease as a primary therapeutic modality 80 or adjunctively in concert with pharmacology 81 . Transcranial PBM, extensively studied in the treatment of neurological disease 82 (such as Alzheimer's-dementia (AD) and stroke) also holds promise in ameliorating the effects of long COVID on neurological conditions 83 (brain fog) and mental health. ...
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Background. Infectivity, genomic variability, and symptomatic diversity of the SARS-CoV-2 virus represents a persistent challenge in the treatment of acute and long COVID-19 diseases. A direct consequence of pervasive ACE-2 receptors susceptible to the virion’s spike protein, disease trajectories commence as upper respiratory infection migrating into bronchia (presenting coughing, dyspnea, and fever), followed by viremic infection and circulatory distress from inflammation of visceral epithelium and vascular endothelia, decreased blood perfusion, and hypoxia. Severe cases include hyperinflammation, cytokine storms, and multisystem inflammatory syndrome with lung and nerve damage, and chronic cognitive deficits. Method. This paper (Part I) considers the requirements for treating acute and chronic COVID-19 with deep-tissue photobiomodulation (PBM) of sinuses, lungs and other ACE-2 populated organs using transdermal and transcranial light as a primary therapeutic modality. Analysis. A detailed analysis of optics, biophysics, numerical simulations, and quantum photochemistry for non-invasive deep tissue PBM of SARS-CoV-2 infected organs was performed including optical design, photonic control, irradiance, fluence, modulation, and protocols. Results. Analysis concludes large-area 3D bendable LED pads are best suited for deep-tissue PBM to transdermally treat whole-organ infection of the lungs, sinuses, abdominal cavity (and to transcranially treat long-COVID). Robotic laser scanning represents another viable option for deep-tissue PBM provided the optical angle of incidence is minimal. Penetration depth depends on wavelength (not optical power) with red (635nm) and NIR (850nm) shown to adequately penetrate through cutaneious tissue and parietal fascia into viscera. Conclusions. Red and NIR LEDs with average pulsed irradiances of 8.5 and 13.5 mW/cm2 respectively deliver hands-free whole-organ deep-tissue doses of between 0.5 to 4.0 J/cm2 in 60 min sessions from a surface dose of Pl/A = 40 J/cm2 depending on tissue transmission coefficients Yx at depth x>6mm. The designed photonic PBM system performs algorithmic variable frequency pulsed protocols covering up to 1,200 cm2. Duty factor control limits skin temperatures below 43°C irrespective of pulse modulating frequency. A mechanistic model for deep-tissue PBM, phenomenologically consistent with biophysics, photon penetration studies, COVID disease trajectories, and patient recovery profiles is presented. Part II details various acute and chronic case studies and positive outcomes thereof confirming PBM as a efficacious modality for COVID-19.
... PBM therapy is a non-invasive treatment modality, whereby its mechanism of action is evolving. The light photonic energy is absorbed by the cytochrome C oxidase (photoacceptor) of the mitochondria, generating a cascade of cellular and molecular activities, leading to an upregulation of anti-inflammatory cytokines while modulating ROS and nitric oxide (NO) [28][29][30], promoting analgesic effects [31,32] and regenerating biological tissues [33,34]. Hence, PBM showed to be an effective therapy in the management of autoimmune diseases such as rheumatoid arthritis [35,36]. ...
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Hashimoto thyroiditis (HT) is a thyroid-specific autoimmune disorder, triggering hypothyroidism in a population with an adequate dietary intake. Despite the current conventional treatment focuses on the permanent replacement of levothyroxine (LT4) deficiency, it appears that thyroid autoimmunity remains the cause of persistent symptoms in patients with HT, even when they achieve to be euthyroid from a biochemical standpoint. Photobiomodulation (PBM) showed to be an effective therapy in the management of autoimmune diseases, but with limited evidence. Hence, our study was conducted to appraise the efficacy of PBM therapy with supplements in restoring thyroid gland homeostasis in patients with HT compared with supplements alone. Seventy-four female subjects aged between 20 and 50 years old were recruited and divided equally into two groups: PBM and supplements group (group 1); and supplements alone group (group 2). The PBM dosimetry and treatment protocols were as follows: wavelength, 820 nm; power output, 200 mW; continuous emission mode; irradiating time, 20 s per point; fluence, 32 J/cm2 per point; treatment frequency, twice a week (excluding weekends); and treatment duration, three consecutive weeks. Whereas, the supplements protocol for both groups was the same, as follows: subjects with a serum level of vitamin D3
... Photobiomodulation (PBM) therapy appears to have a wide range of applications [71][72][73][74][75] and has been shown to be effective in reducing the severity of the side effects induced by chemotherapy and radiotherapy such as; oral mucositis, dermatitis. 2,76,77 Thereby, we believe that a combined approach of PBM-PDT deserves investigating to improve PDT outcomes in OPMLs management, as this treatment strategy showed to have positive effects on PDT in the management of head and neck squamous cell carcinoma. ...
... 57 Additional to the influencing immune system, PBMT has directly contribute in pathogen clearance. 57,58 Despite the availability of many anti-inflammatory drugs, there is still the problem of the inability to successfully treat inflammation, especially the type of inflammation associated with COVID-19 disease. Due to the clinical problems caused by inflammation, researchers are still trying to find new, better, more effective treatments with more limited side effects. ...
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Background Different expression of cytokine genes in the body determines the type of immune response (Th1 or Th2), which can play an important role in the pathogenesis of the COVID-19 disease. Aims This meta-analysis was conducted to evaluate the probable effect of photobiomodulation (PBMT) therapy on the cytokine’s mRNA expression in the lung. Methods We systematically searched indexing databases, including PubMed/Medline, ISI web of science, Scopus, EMBASE, and Cochrane central, using standard terms without language, study region or type restrictions. Studies on using PBM in lung injury modeling with samples collected from lung tissue to observe IL-1β, TNF-α, IL-10, and IL-6 mRNA expression were included. RevMan 5.3 software was used for data analysis and standardized mean difference as effect size. Results Of the 438 studies found through initial searches, 17 met the inclusion criteria. The main properties of 13 articles on 384 animals included in this meta-analysis with a wide range of species include rats (n = 10) and rabbits (n = 3). The analysis revealed that PBMT reduced the mRNA expression of TNFα (SMD: −3.70, 95% CI: −6.29, −1.11, P = .005, I ² = 71%) and IL-1β (SMD: −5.85, 95% CI: −8.01, −3.69, P < .00001, I ² = 37%) significantly, but no statistically significant reduction in IL-6 (SMD: −2.89, 95% CI: −5.79, 0.01, P = .05, I ² = 88%) was observed compared with the model controls. Also, PBMT increased IL-10 mRNA expression significantly compared with the model controls (SMD: 1.04, 95% CI: 0.43, 1.64, P = .0008, I ² = 17%). Conclusion This meta-analysis revealed that the PBMT utilizes beneficial anti-inflammatory effects and modulation of the immune system on lung damage in animal models and clinical studies. However, animal models and clinical studies appear limited considering the evidence’s quality; therefore, large clinical trials are still required.
... Assuming strict adherence to revised procedures for the effective and safe use of phototherapy along with new approaches that improve patient compliance in this historical era, probably the most interesting aspect investigated concerns its antiviral activity [54]. One of the earliest reviews on the subject by Hanna et al. pointed out that, although the antiviral efficacy of ultraviolet blood irradiation (UBI) remained controversial due to the reduced penetrating ability of radiation, indirect confirmation of its potential comes from the effectiveness of Amotosalen/UVA light in minimizing the risk of transfusion-related MERS-CoV transmission through its ability to completely inactivate MERS-CoV in human platelet concentrates [55]. In subsequent work, the same research group confirmed the effectiveness of UV light in reducing MERS-CoV titer below the detection limit in human platelets [56]. ...
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Atopic dermatitis is a chronic inflammatory skin disease in which the overproduction of reactive oxygen species plays a pivotal role in the pathogenesis and persistence of inflammatory lesions. Phototherapy represents one of the most used therapeutic options, with benefits in the clinical picture. Studies have demonstrated the immunomodulatory effect of phototherapy and its role in reducing molecule hallmarks of oxidative stress. In this review, we report the data present in literature dealing with the main signaling molecular pathways involved in oxidative stress after phototherapy to target atopic dermatitis-affected cells. Since oxidative stress plays a pivotal role in the pathogenesis of atopic dermatitis and its flare-up, new research lines could be opened to study new drugs that act on this mechanism, perhaps in concert with phototherapy.
Full-text available
Phototherapy incorporating; photobiomodulation therapy and antimicrobial photodynamic therapy has been utilised as antioxidants in symptomatic oral lichen planus (OLP) management; however, its role of intervention remains controversial. The aim of this systematic review of CRD42021227788 PROSPERO (an international prospective register of systematic reviews in health and social care) registration numberwas to oversee and determine phototherapy efficacy in patients with symptomatic OLP, identifying and bridging the literature gaps by proposing recommendations for future studies. A search strategy was developed in consistent with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Various electronic databases were exercised to search for randomised controlled clinical trials (RCTs).. Several search engines were employed to analyse a total of 177 studies of which nine included. A wide range of utilised laser and light-emitted diode wavelengths between 630-808 nm and irradiance ranged between 10-13 mW/cm2 were noted. 67% of studies reported a high risk of bias and a high heterogeneity obtained from numerical data for quantitative analysis, therefore meta-analysis was impossible to conduct. Despite inconsistency and diversity in phototherapy parameters, treatment protocols treatment protocols, photosensitiser (type, concentration and method of application) and outcomes assessment tools, the majority of the studies showed positive results compared with standard care treatments. Hence, a necessity to perform well-designed RCTs with robust methodology is warranted, after acknowledging the current drawbacks and addressing the suggested recommendations highlighted in our review. Moreover, advanced knowledge in understanding further phototherapy-antioxidants molecular mechanistic in symptomatic OLP is required.
Along with other COVID-19 clinical manifestations, management of both olfactory and gustatory dysfunction have drawn a considerable attention. Photobiomodulation (PBM) has emerged to be a possible effective therapy in restoring taste and smell functionality, but the evidence is scarce. Hence, the present pilot study is aimed to evaluate the effectiveness of intranasal and intraoral PBM administrations in management of anosmia and ageusia respectively. Twenty Caucasian subjects who diagnosed with anosmia and ageusia were recruited. Visual Analogue Scale was utilised to evaluate patients' self-reported for both olfactory and gustatory functionality. The laser-PBM parameters and treatment protocols for anosmia and ageusia were as follows respectively: 660nm, 100mW, two points intranasally, 60 J/session, 12 sessions; dual wavelengths (660nm and 808nm), 100mW, three points intraorally, 216 J/session, 12 sessions. Our results showed a significant functionality improvement of both olfactory and gustatory functionality. Extensive studies with large data and long-term follow-up period are warranted.
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It is postulated that the inflammatory process resulting from SARS‐CoV‐2 infection is the main cause of smell and taste dysfunctions in patients. In view of this, photobiomodulation, due to its anti‐inflammatory and antioxidant effects, may be a promising therapeutic modality to treat these disorders. In the present case report, we observed clinical improvement in the symptoms of anosmia and ageusia related to COVID‐19 after treatment with photobiomodulation. Due to the inflammatory nature of COVID‐19 and the anti‐inflammatory effects, photobiomodulation antioxidants already proven in the literature make it a promising therapeutic modality, especially sequela COVID‐related, including olfactory (anosmia) and taste (ageusia) dysfunction. In the present case report, the patient's olfactory and gustatory functions were re‐established after 10 treatment sessions with photobiomodulation. This article is protected by copyright. All rights reserved.
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Vaccine candidate tested in monkeys Global spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has led to an urgent race to develop a vaccine. Gao et al. report preclinical results of an early vaccine candidate called PiCoVacc, which protected rhesus macaque monkeys against SARS-CoV-2 infection when analyzed in short-term studies. The researchers obtained multiple SARS-CoV-2 strains from 11 hospitalized patients across the world and then chemically inactivated the harmful properties of the virus. Animals were immunized with one of two vaccine doses and then inoculated with SARS-CoV-2. Those that received the lowest dose showed signs of controlling the infection, and those receiving the highest dose appeared more protected and did not have detectable viral loads in the pharynx or lungs at 7 days after infection. The next steps will be testing for safety and efficacy in humans. Science , this issue p. 77
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The number of COVID-19 patients is increasing dramatically worldwide and treatment in intensive care units (ICU) has become a major challenge, the early recognition of severe forms of is absolutely essential for timely triaging of patients. While the clinical status, in particular Peripheral oxygen saturation (SpO2) levels and concurrent comorbidities of COVID-19 patients largely determines the need of their admittance to ICUs, several laboratory parameters may facilitate the assessment of disease severity. In hospitalized patients, clinicians should consider low lymphocyte count as well as the serum levels of CRP, D-dimers, ferritin and IL-6 which may be used in risk stratification to predict severe and fatal COVID-19. The more several or all of these parameters are altered, the more likely it is that the course of the disease will be unfavourable.
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
The elevated circulating levels of cytokines associated with a variety of infectious and immune-mediated conditions are frequently termed a cytokine storm. Here, we explain the protective functions of cytokines in “ideal” responses; the multi-factorial origins that can drive these responses to become pathological; and how this ultimately leads to vascular damage, immunopathology, and worsening clinical outcomes.
We have previously provided the first genetic evi- dence that angiotensin converting enzyme 2 (ACE2) is the critical receptor for severe acute respiratory syndrome coronavirus (SARS-CoV), and ACE2 pro- tects the lung from injury, providing a molecular explanation for the severe lung failure and death due to SARS-CoV infections. ACE2 has now also been identified as a key receptor for SARS-CoV-2 in- fections, and it has been proposed that inhibiting this interaction might be used in treating patients with COVID-19. However, it is not known whether human recombinant soluble ACE2 (hrsACE2) blocks growth of SARS-CoV-2. Here, we show that clinical grade hrsACE2 reduced SARS-CoV-2 recovery from Vero cells by a factor of 1,000–5,000. An equivalent mouse rsACE2 had no effect. We also show that SARS- CoV-2 can directly infect engineered human blood vessel organoids and human kidney organoids, which can be inhibited by hrsACE2. These data demonstrate that hrsACE2 can significantly block early stages of SARS-CoV-2 infections.
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