COVID-19 Disease and Vitamin D: A Mini-Review

Novel coronavirus disease (COVID-19) pandemic caused by SARS-CoV-2, for which there is no effective treatment except employing prevention strategies, has already instituted significant number of deaths. In this review, we provide a scientific view on the potential role of vitamin D in SARS-CoV-2 virus/COVID-19 disease. Vitamin D is well-known to play a significant role in maintaining the immune health of an individual. Moreover, it induces antimicrobial peptide expression that can decrease viral replication and regulate the levels of pro-inflammatory/anti-inflammatory cytokines. Therefore, supplementation of vitamin D has the potential to reduce the incidence, severity and the risk of death from pneumonia resulting from the cytokine storm of many viral infections including COVID-19. We suggest that supplementation of subjects at high risk of COVID-19 with vitamin D (1.000 to 3.000 IU) to maintain its optimum serum concentrations may be of significant benefit for both in the prevention and treatment of the COVID-19.


INTRODUCTION
The occurrence of respiratory tract infections (RTI) is more common in winter, especially in the northern regions, than in the summer months (Hope-Simpson, 1981). This also applies to the rapidly spreading in the winter period around the world of the infectious Coronavirus disease 2019  which became a pandemic, since the virus is more easily transmitted at low temperatures (Qu et al., 2020;Sajadi et al., 2020). This rises the possibility that insufficient intake of vitamin D 3 may have a role in the development and severity of COVID-19. Thus, in order to curb the current pandemic of COVID-19, it is opined that the administration of an adequate amounts of vitamin D 3 may stem the current situation till an effective therapy, chemoprophylaxis, and vaccination is developed.
Deficiency of vitamin D 3 in all age groups is a public health problem (Palacios and Gonzalez, 2014) that is well recognized. It is estimated that more than one billion people suffer from vitamin D 3 deficiency (Van Schoor and Lips, 2011). Several previous studies suggested that there is an independent association between low plasma concentrations of 25-hydroxyvitamin D 3 and susceptibility to acute respiratory infections (Cannell et al., 2006). Vitamin D 3 deficiency has been associated with many diseases including but not limited to type 2 diabetes mellitus, heart disease, stroke, autoimmune diseases, asthma and RTIs (Hollick, 2007;Hollick, 2017). The relation between low levels of vitamin D 3 and infection with bovine diarrhea virus in calves has been well established (Nonnecke et al., 2014). It is evident that in winter due to the shorter time spent in the sun, the plasma levels of vitamin D 3 is likely to be low (Berardi and Newton, 2009;https://www.medlineplus.gov/ vitamind.html). This is especially evident in countries such as the United States of America (USA), United Kingdom (UK), Switzerland, Italy, Spain, Iran, France, Turkey, etc. It is rather interesting that COVID-19 pandemic and its high mortality (Pharmacy Times, 2020; https://www.pharmacytimes.com/ publications/issue/2010/february2010/otcfocusvitamind-0210) has been reported in these countries. According to the US National Center for Health Statistics, approximately 70% of the population may be deficient in vitamin D 3 and surprisingly while the United States is presently the most affected by COVID-19 (Kmiec et al., 2014). This is in line with the current proposal that severe acute respiratory syndrome due to SARS-CoV-2 and its associated high mortality rate may be as a result of vitamin D 3 deficiency. Furthermore, vitamin D 3 deficiency is known to elevate with increasing age and comorbidities that are associated with lower vitamin D 3 levels.
In the current review, we present a scientific rationale on the potential relationship between vitamin D 3 content and higher incidence of Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) virus infection. Moreover, our review also summarizes the current understanding of the link among vitamin D 3 , the immune system, and respiratory infections.

VITAMIN D AND IMMUNE SYSTEM
Vitamin D is a pluripotent hormone that modulates the innate and adaptive immune responses (Rezaei, 2018). Vitamin D could play a decisive role in the proliferation and immunomodulation of cells, affecting several immune pathways enhancing the protective properties of the mucous membranes of the body and inhibiting excessive inflammation (D'Ambrosio et al., 1998;Khare et al., 2013;Parlak et al., 2015). Immunocytes such as macrophages, B and T lymphocytes, neutrophils and dendritic cells express Vitamin D 3 receptors (VDRs) that is enable to the actions of vitamin D (Di Rosa et al., 2011). The active metabolite of vitamin D lead to the activation of VDRs that can form Retinoid X Receptor (RXR) heterodimer that, in turn, influences the proteins of the innate and adaptive immune system (the regulatory T cells, defensins, cytokines, pattern recognition receptors, etc.) (Chun et al., 2014).
The immune system is influenced in various ways by both vitamin D 3 and its metabolite 1,25-hydroxy-vitamin D 3 . 1,25hydroxy-vitamin D 3 rigorously regulates antimicrobial peptides such as defensin and cathelicidin (Adams et al., 2009). Cathelicidin possesses an antimicrobial function against mycobacteria, Gram-positive and Gram-negative bacteria due to its ability to destroy cell membranes. 1,25-hydroxy-vitamin D 3 has antiviral effect against adenovirus, herpes simplex virus, enveloped and non-enveloped retroviruses, and fungi (Herr et al., 2007). By damaging cell membranes, these peptides penetrate infected cells and neutralize the action of endotoxins (Agier et al., 2015). For instance, the LL-37, antimicrobe peptide, has antibacterial and antifungal properties by virtue of its ability to disrupt the integrity of the cell membrane and proton gradient (Bals and Wilson, 2003) by vitamin D 3 (Howell et al., 2004;Leikina et al., 2005;Steinstraesser et al., 2005;Bergman et al., 2007). In addition, vitamin D 3 inhibits the production of proinflammatory cytokines and augments that of anti-inflammatory cytokines (Gombart et al., 2020). Thus, vitamin D 3 influences the incidence and severity of viral infections by altering the production of pro-inflammatory cytokines. There is reasonable evidence to suggest that vitamin D 3 can inhibit the transcription induced by tumor-necrosis-factor-α (TNF-α) in latently infected cells by human immunodeficiency viruses (HIV) (Nunnari et al., 2016). These and other results suggest that vitamin D 3 can inhibit the production of inflammatory cytokines and chemokines such as TNF-α, interferon-β (IFN-β), interleukine (IL)-8, IL-6 and Regulated upon Activation, Normal T Cell Expressed and Presumably Secreted (RANTES) (Hansdottir et al., 2010;Khare et al., 2013). Increase in mortality in those with COVID-19 is due to acute respiratory distress syndrome (ARDS) due to unantagonized production of proinflammatory cytokines IL-6 and TNF-α. Vitamin D 3 has a decisive role in the regulation of the innate and adaptive immune responses implying that adequate intake of vitamin D 3 may protect patients with COVID-19 at least, in part by inhibiting the excess production of IL-6 and TNF-α (Daneshkhah et al., 2020). Vitamin D 3 can also contribute to the modification of the antiviral response by enhancing the secretion of pro-inflammatory chemokines (C-X-C Motif Chemokine Ligand 8, CXCL8 and C-X-C Motif Chemokine Ligand 10, CXCL10) (Brockman-Schneider et al., 2014). Lytic phase of cytomegalovirus (CMV) replication can be induced by vitamin D 3 in vitro (Wu and Miller, 2015).
Vitamin D 3 promotes immunoglobulin and complementmediated phagocytosis by stimulating the maturation of monocytes to macrophages. In addition, vitamin D 3 maintains self-tolerance by reducing a hyperactive adaptive immune system (Bowie and Unterholzner, 2008). Vitamin D 3 reduces the replication of influenza A (Barlow et al., 2011), rotavirus (Zhao et al., 2019) and dengue microbes (Martínez-Moreno et al., 2019). These results imply that excess innate immune response induced by viral and other microbial infections seen in patients with SARS-CoV-2 and associated cytokine storm can be effectively reduced by vitamin D 3 (Huang et al., 2020). The immunomodulatory effect of vitamin D 3 on viral infections appears to be temporary and at least, this in part could be attributed to its immunomodulatory role in viral infections is rather complex and depends on the nature of the pathogen and the type of immune function that is needed to resolve the disease process (Sacco et al.,2012;Gotlieb et al., 2018).
There is reasonable evidence to suggest that vitamin D 3 modulates adaptive immune responses by inhibiting the Th1 cell function that leads to a reduction in the production of TNF-α, IL-2, granulocyte macrophage colony-stimulating factor and IFN-β. 1,25-(OH) 2 -Vitamin D 3 enhances the action of Th2 cells and production of their anti-inflammatory cytokines, IL-Frontiers in Pharmacology | www.frontiersin.org December 2020 | Volume 11 | Article 604579 2 4, IL-5, and IL-10 (Hughes and Norton, 2009). In addition, supplementation of vitamin D 3 increases the number of regulatory T cells (Treg cells), suppresses IgG production and differentiation of dendritic cells (Kamen and Tangpricha, 2010;Aranow, 2011;Rondanelli et al., 2018). 1,25-(OH) 2 -Vitamin D 3 inhibits the proliferation and activation of T cells and T and B lymphocytes (Martineau et al., 2017). Thus, vitamin D 3 suppresses T-cell-mediated inflammation and promote the proliferation of Treg cells that results in an increase in the production of IL-10 that leads to suppression of inappropriate inflammation (Adorini and Penna, 2009;Chun et al., 2014). Vitamin D 3 can also increase the expression of glutathione reductase and glutamate-cysteine ligase modifier subunit (Lei et al., 2017) that may lead to a decrease in oxidative stress. These results led to the proposal that (Biancatelli et al., 2019;Mousavi et al., 2019;Wimalawansa, 2020) vitamin D 3 may be of benefit to combat SARS-CoV-2 infection (Grant et al., 2020a).
Vitamin D deficiency is common in patients with HIV (Herr et al., 2007). The antiviral action of vitamin D 3 can also be attributed to its ability to increase the production of cathelicidin and defensins (Herr et al., 2007;Hughes and Norton, 2009;Beard et al., 2011). Furthermore, 1,25-dihydroxy-cholecalciferol is known to regulate more than 200 genes including those responsible for cell proliferation, differentiation, and apoptosis (Umar and Sastry, 2018) including those involved in immune homeostasis (Van Herwegen et al., 2017). Recent meta-analysis of randomized controlled trials (RCTs) showed that vitamin D deficiency increases the overall mortality (Bjelakovic et al., 2014;Keum et al., 2019;Manson et al., 2019;Scragg, 2020). All above-mentioned effects of Vitamin D 3 are presented in Table 1.

RELEVANCE OF VITAMIN D REGARDING TO RESPIRATORY TRACT INFECTIONS AND INFLUENZA
There is a provided evidence given by many reviewed studies to support the hypothesis that higher serum level of vitamin D 3 is associated with a low risk of microbial infections and deaths from RTIs caused by pneumonia and influenza. In addition, SARS-CoV-2 infection and decrease the severity and mortality may be avoided by a normal serum vitamin D 3 levels (Wimalawansa, 2020). Unfortunately, there are no standard recommendations regarding the dose and the desired optimal concentration of vitamin D 3 required to protect people from RTI during the winter season.
Epidemiological studies revealed that vitamin D 3 plays a critical role in viral RTIs and associated acute lung injury (Hansdottir and Monick, 2011). In a recent meta-analysis, it has been shown that a daily or weekly vitamin D 3 dose between 20 and 50 μg resulted in a significant reduction of RTIs (Martineau et al., 2017). A high-dose, isolated, or added bolus of (2.5 mg once or monthly) did not reduce the risk. One study supplemented for one-year high risk individual for ARDS with a 100 μg/daily (Bergman et al., 2012). The overall infection score was significantly reduced in the treated groups, and those with vitamin D 3 deficiency showed the greatest benefit of the supplementation.
In addition, it is observed that the degree of protection generally increases when the concentration of vitamin D 3 reaches its optimal range of 40 to 60 ng/ml. To reach this level, an individual must take between 2,000 and 5,000 IU/day of vitamin D 3 (Heaney et al., 2003). Calcitriol protects against acute lung injury by modulating the expression of the renin-angiotensin system including angiotensin-converting enzyme 2 (ACE2) in lung tissue (Xu et al., 2017). There seems to be a direct relationship between plasma 25-(OH)-Vitamin D 3 concentrations and severity of COVID-19 (Huang et al., 2020;Wang et al., 2020;Zhou et al., 2020). It is noteworthy that the expression of the DPP-4/CD26 receptor is significantly reduced as a result of vitamin D 3 deficiency (Komolmit et al., 2017). Furthermore, adequate provision of vitamin D 3 seems to attenuate immunological events that may lead to prolonged interferon-gamma response (Zdrenghea et al., 2017), and persistent interleukin six elevation that are negative prognostic value indicators in those with severe COVID-19 (Miroliaee et al., 2018).
VDRs are very widely distributed in respiratory epithelial cells and immune cells (B cells, T cells, macrophages and monocytes). VDRs are in the epithelium of the bronchi and immune cells (Pfeffer and Hawrylowicz, 2012). The enzyme, 1a-hydroxylase (CYP27B1), required for vitamin D activation, is induced by diverse stimuli, including cytokines and toll-like receptor ligands in the respiratory tract. Nevertheless, adequate serum levels of 25-(OH)-vitamin D 3 is required to increase levels of 1,25-(OH) 2vitamin D 3 and to improve the immune response to respiratory virus infections (Greiller and Martineau, 2015). The development  (2000) of ARDS shows typical changes in membrane permeability of the alveolar capillary, progressive edema, severe arterial hypoxemia and pulmonary hypertension (Matthay et al., 2012). In animal studies, vitamin D 3 significantly attenuated lung damage caused by lipopolysaccharides (LPS) (Xu et al., 2017). This is noteworthy since LPS increase the pulmonary expression of renin and angiotensin 2 (Ang 2) that promotes inflammation. Vitamin D 3 reduces the increased renin and Ang 2 expression and thus significantly lowers lung injury. It has been suggested that vitamin D 3 promotes ACE2/Ang 1-7 activity. This is supported by the observation that calcitriol treatment significantly increased the expression of VDR mRNA and ACE2 mRNA that leads to a reduction in angiotensin II, ACE2 expression resulting in suppression of inflammation (Yang et al., 2016). VDRs are not only a negative regulator of renin, but also of NF-kB (Li et al., 2004), leading to an increase in Ang 2 formation, which promotes pro-inflammation (Jurewicz et al., 2007). Down-regulation of ACE2 expression by SARS-CoV infection is associated with acute lung damage (edema, increased vascular permeability, reduced lung function) and associated RAS dysregulation leads to increased inflammation and vascular permeability as seen in COVID-19 (Imai et al., 2005). It was reported that COVID-19 is associated with release of pro-vitamin D 3 enhances the cellular immunity and reduces the cytokine storm induced by the innate immune system. Vitamin D 3 can reduce the production of pro-inflammatory cytokines such as TNF-α and IF-γ (Tjabringa et al., 2005;Baeke et al., 2010;Laaki, 2012). Several studies showed that adequate intake and plasma levels of vitamin D 3 reduces the risk of viral infections through their action on immunocytes (Carnell et al., 2006;Baeke et al., 2010;Schwalfenberg, 2011;Lang and Samaras, 2012). Hence, it is suggested that vitamin D 3 may have a significant role in COVID-19 due to its action on T cells (Zhang et al., 2015).
Type-II pneumocytes which are the primary target of coronaviruses, express high levels of ACE2 receptor (Bombardini and Picano, 2020). Metabolites of 25-(OH)vitamin D 3 have been reported to stimulate surfactant synthesis in alveolar type-II cells (Rehan et al., 2002). Human fetal and adult alveolar type-II cells supplemented with 1,25dihydroxy-vitamin D 3 show increased levels of VDRs and expression of surfactant associated protein B, a lipid-associated protein of the pulmonary surfactant, indicating the potential of vitamin D 3 to reduce surface tension in COVID-19 (Phokela et al., 2005).Comorbid conditions such as diabetes mellitus, hypertension and chronic obstructive pulmonary disease are commonly associated with low plasma vitamin D 3 levels (Malinovschi et al., 2014;Kim et al., 2015;Grant et al., 2020a). Hence, it is reasonable to propose that COVID-19 may be associated with low plasma vitamin D 3 levels. Hence, it is suggested that vitamin D 3 supplementation may be of significant benefit in COVID-19. Grant, in the latest report, suggest that vitamin D level checking will be conducted only in as elected category of patients that involves pregnant mothers, obese and elderly people and others suffering from certain comorbid conditions (Grant et al., 2020b). Multiple factors such as an ability of the assimilation by the gastrointestinal tract, body weight, genetic factors and the baseline 25-(OH)-vitamin D 3 concentration, control the increase in vitamin D concentrations with respect to oral vitamin D 3 supplementation. Given the degree of vitamin D 3 deficiency, taking 5,000 IU of vitamin per day, it could be essential to elevate 25-(OH)-vitamin D 3 levels to 40 ng/ml by (Veugelers et al., 2015).
A recent article indicates that vitamin D 3 value >20 ng/ml is required and this advice is adopted by several countries (Amrein et al., 2020). Another research suggests a higher dose for RTIs, indicating rates >30 ng/ml of vitamin D 3 as effective in decreasing cancer incidence, unfavorable pregnancy and birth outcomes and type 2 diabetes mellitus (Grant et al., 2020b). From another analysis it is suggested that optimal vitamin D 3 standard should be 40-60 ng/ml for prevention of breast and colorectal cancer (Garland et al., 2009).
The U.S. Institute of Medicine noted that no research observed negative consequences of supplementation of vitamin D 3 of less than 10,000 IU/daily, but set the upper consumption limit at 4,000 IU/daily, partially owing to retrospective tests that found U-shaped 25-(OH)-vitamin D 3 concentration/health outcome relationships. However, further findings indicate that most observations of J-or U-shaps relationships came from observational studies that did not test serum 25-(OH)-vitamin D 3 concentrations, and that the likely explanation for these relationships was the presence of some participants who started taking vitamin D 3 complementation shortly before registration (Grant et al., 2016). Particularly in winter, supplementation with vitamin D 3 is required for many individuals to reach concentrations of 25-(OH)-vitamin D 3 above 30 ng/ml (Pludowski et al., 2018). However, vitamin D 3 fortification of basic foods such as dairy and flour products may increase serum 25(OH)D concentrations by a few ng/ml among those members of different populations with the lowest concentrations (Pilz et al., 2018;Grant and Boucher 2019). This will contribute to a decreased risk of ARTIs for persons with a severe vitamin D 3 deficiency (Camargo et al., 2012;Martineau et al., 2017). However, regular or weekly treatment of vitamin D 3 is advised for greater benefits (Martineau et al., 2017), as is the annual evaluation of serum 25-(OH)-vitamin D 3 levels for health risks individuals (Grant et al., 2020b). Table 2 describes the findings from meta-analyses that vitamin D 3 is protective against acute RTI, particularly in patients with vitamin D 3 deficiency.

HYPOTHESIS OF THE CORRELATION ON VITAMIN D 3 LEVELS AND CORONAVIRUS DISEASE-19 CASES/SEVERITY
Still there is a lack of a cohort studies and clinical trials in determining the role of vitamin D 3 in the prevention of COVID-19 infections and/or severity. Some retrospective studies have demonstrated the relationships between vitamin D 3 levels and COVID-19 cases and severity (Table 3).
For example, a preliminary information study from Philippines on 212 reported COVID-19 patients, found that the severity of the infection is a highly correlated to the Frontiers in Pharmacology | www.frontiersin.org December 2020 | Volume 11 | Article 604579 vitamin D 3 levels (Alipio, 2020). Authors have found that 85.5% of patients with an adequate status of vitamin D 3 (>30 ng/ml) showed a moderate disease, while a 72.8% of patients with vitamin D 3 deficiency (<20 ng/ml) had the serious disease symptoms (Alipio, 2020). The correlation between vitamin D 3 and COVID-19 have extensively investigated in a group of 178 Indonesians (Raharusun et al., 2020). According to this study, the patients with vitamin D 3 levels in the categories, 20-30 and <20 ng/ml, were 12.55 times and 19.12 times more likely to die from COVID-19, respectively, as compared with COVID-19 patients with sufficient levels of vitamin D 3 . The main conclusion is that, even after controlling for age, sex and comorbidities, deaths were 10.12 times more likely in patients with vitamin D 3 deficiency than in patients with normal vitamin D 3 levels (Raharusun et al., 2020). A limited cohort observational study with 43 cases in Singapore have found that a treatment of COVID-19 patients with an oral doses of vitamin D 3 (1.000 IU), Mg (150 mg), and vitamin B 12 (500 μg) significantly reduced the application of the subsequent oxygen therapy compared to controls (3/17 vs. 16/26, p 0.006) (Tan et al., 2020). Furthermore, such drugs combination have protected against the clinical deterioration (p 0.041) even after adjustment of confounders (age, sex and comorbidity) (Tan et al., 2020). Severe COVID-19 patients and patients with pre-existing medical conditions were reported to have low levels of vitamin D 3 (Glicio et al., 2020;Lau et al., 2020). A retrospective observational study with 186 positive cases and 2717 negative controls in Belgium have demonstrated a low median for vitamin D 3 in the COVID-19 patients compared to the control subjects (p 0.0016) (De Smet et al., 2020). A retrospective cohort study with 780 cases in Indonesia showed that below-normal vitamin D 3 levels and the pre-existing medical conditions in the older and male cases have higher odds of death. Moreover, the vitamin D 3 status has a strong relationship with COVID-19 mortality if it adjusted for age, sex and comorbidities (Raharusun et al., 2020). The similar retrospective study in the USA with many cases have showed that the reduced risks for both COVID-19 cases and the mortality are possibly associated with the sunlight and vitamin D 3 , as well with the latitude as an indicator .
In a new systematic review and meta-analysis with an ecological approach, they found a high percentage of COVID-19 patients who suffer from vitamin D 3 deficiency or insufficiency. Much more important its ecological investigation resulted in the substantial direct and reverse correlations between the recovery and mortality rates in COVID-19 patients with vitamin D 3 deficiency at the different countries. A small reverse correlation between vitamin D 3 status and the mortality rate have found globally. The populations with a lower levels of vitamin D 3 might be more susceptible to the novel coronavirus infection (Ghasemian et al., 2020). Recently, a cohort study of 489 patients who had a vitamin D 3 levels detected in the year before COVID-19 testing was 1.77 times greater for patients with vitamin D 3 deficiency compared to the patients with a normal vitamin D 3 status. These findings appear to support a role of vitamin D 3 status for the COVID-19 risk (Meltzer et al., 2020).
The hypothesis that supplementation with vitamin D 3 may reduce the risk of influenza and COVID-19 disease, as well the death should be examined in the trials to evaluate the correct doses, the serum 25-(OH)-vitamin D 3 concentrations and the existence of any health concerns. There are a good model from Atlanta and Georgia in which have done the RCT on vitamin D 3 supplementation for the ventilated ICU patients (Han et al., 2016).
There is a recommendation to take a vitamin D 3 at 10,000 IU/ day as an acceptable dose to raise circulatory concentration of vitamin D 3 to the optimum range of 40-60 ng/ml; after 1 month this dose should be lowered to 5,000 IU/day to the sustain serum rate (Ekwaru et al., 2014;Shirvani et al., 2019). A recent study have suggested a loading doses of 200,000-300,000 IU of vitamin D 3 to reach the optimum serum range, thereby the reducing of the risk/severity for COVID-19 (Wimalawansa, 2020).
The observation that normal vitamin D 3 status is important for the immune system as well as for the regulation of SAR should lead to a correction of vitamin D 3 status if a deficiency has been detected. There is no experience with the use of vitamin D 3 in COVID-19. In addition, it should be noted that a very high doses of the upper limit of 4,000 IU (100 μg) per day of vitamin D 3 still have the risks and may be dangerous. Since such doses might result in to the improvements in the VDR competency and could have an inhibitory impact on the immune function (Mangin et al., 2014).

CONCLUSION
It is evident from the preceding discussion that vitamin D 3 may be of benefit in COVID-19. Since the higher plasma concentrations of vitamin D 3 is better for the protection from   various viral and respiratory infections, it is reasonable to suggest that regular supplementation of vitamin D 3 to those who are at high risk of developing various viral respiratory infections including COVID-19 need to considered seriously. To verify this proposal, double-blind placebo-controlled trials and largescale intervention and prevention studies using vitamin D 3 are needed. If this proposal is true it leads to the development of a simple, easily implementable method of preventing the incidence of COVID-19 and reducing its serious complications by simple oral supplementation of vitamin D 3 . Furthermore, vitamin D 3 has several other benefits in the form of preventing rickets, improving general health, and reducing mortality due to its deficiency (though the exact cause for this association is not clear) add strength to the concept that its supplementation is warranted.

AUTHOR CONTRIBUTIONS
MB, VI, RM, DB interpreted the data from the literature. MB, VI, RM, JF, DB wrote the original draft. MB, VI, RM, JF, FD, LG, UD, AE-A reviewed, edited and drafted the manuscript, and approved the final version.