The Health Benefits of Saliva

Abstract

Unbeknownst to many, saliva has many purposes, both inside and outside of our mouths.  Aside from it allowing for the mastication and swallowing of food, saliva from humans and other organisms have health benefits behind them that, although not as common in practicing medicine. It can provide insight and access to possible solutions, in emergency settings and for future clinical use.  In this paper, we take a look at the underlying science and the hidden properties of saliva, and how they can be applied in medicine for a variety of health concerns and problems, minor and possibly major. 

Introduction

Saliva is an extracellular oral fluid that is taken for granted. It serves many roles for different species, ranging from reptilian venomous drops to acting as a glue in construction of birds’ nests, thus demonstrating to have a diverse variety of functions [1]. 

Saliva production is stimulated by the sympathetic and the parasympathetic nervous system, and produced in the salivary glands, which are formed of clusters of acini cells. Secretion is controlled by the salivary centre composed of nuclei in the medulla [1].  In the human body, its main function is the preparation of food, from beginning the process of chemical digestion, to acting as a lubricant to make it easier to swallow, and even acting as a chemical carrier to taste cells.

However, it plays many more roles such as encouraging healing of wounds and tissue repair, protection and lubrication of our mouth, contributing to the upkeep of oral health and water balance [2].  Despite coming into contact with an abundance of microorganisms and flora found in or on the body, saliva protects our body from most of it, thus acting as one of the body’s strongest defence systems [3].  In addition to this, saliva holds a lot of power in diagnostics of many health issues and conditions including but not limited to: acne, allergies, heart conditions, cancer, and more [4]. 

Saliva is composed of 99.5% water, a variety of electrolytes, including sodium, potassium, calcium, magnesium, bicarbonate, and phosphates, as well as immunoglobulins, proteins, enzymes, mucins, and nitrogenous products, such as urea and ammonia [5,6]. 

Analysis of several studies have confirmed the importance of saliva in maintaining a healthy oral environment but it can also be used for purposes outside of the oral cavity in addition [7]. 

Oral Health

The oral cavity, in an average human, is estimated to have possibly as many as 8 million cells, with over 500 million bacterial cells per mL. Thus it is important to upkeep oral health in order to prevent different dental and oral diseases, and avoid foul odours from breath [6]. 

Saliva as a fluid constantly flushes the oral cavity of food debris, and keeps the mouth relatively clean [4].  However, from the moment teeth start to erupt in the oral cavity, saliva provides protection to the teeth on a more molecular basis. While the crown of the tooth is fully formed structurally, as it erupts, it is crystallographically incomplete.  So an interaction with saliva provides a post-eruptive maturation through diffusion of ions including calcium, magnesium, phosphorus, and fluoride, in addition to other molecules into the surface enamel. This maturation decreases permeability and absorption, increasing the hardness of the surface enamel, which has been shown to increase defence against cavities [5, 8].  Proline-rich proteins, statherin, and cysteine-containing phosphoproteins provide protection by effectively binding calcium and helping to maintain saliva with a high saturation calcium phosphate salts. They bind to the surfaces of early crystal nuclei and delay crystal growth [5]. 

Cystatins, a family of cysteine-containing proteins, have a minor role in regulating calcium levels in saliva. It is supposed that the main action of cystatins might be to inhibit the pathogenesis of periodontal disease [6]. 

Xerostomia, also known as dry mouth, is when an individual doesn’t produce enough saliva.  This can cause several problems to the individual such as difficulty ingesting food, foul breath, and the damage and weakening of the teeth [9].  As the flow of saliva is halted as one sleeps, in order to not choke, masses of bacteria can accumulate in the mouth, causing morning breath.[4] Lysozyme, an antibacterial enzyme present in saliva, which lyzes bacteria, preventing the overgrowth of microbial populations in the mouth [4]. The lack of saliva makes chewing and swallowing also difficult which often begins to affect an individual’s health. In order to treat xerostomia, doctors may prescribe saliva substitutes, which although can provide some temporary relief for the lack of moisture within the oral cavity. Saliva stimulants, parasympathomimetic drugs, organic acid and even lozenges are often used to stimulate the production of saliva.

Dental cavities/caries begins with acid dissolution of tooth minerals, initiated by acidogenic microorganisms in dental plaque which has been exposed to fermentable carbohydrate.  Macromolecule proteins and mucins serve to cleanse, aggregate, and/or attach oral microorganisms and contribute to dental plaque metabolism [6].  Individuals with xerostomia are more susceptible to dental caries because of the loss of the many protective factors in saliva [10]. 

Proline-rich proteins are also present, that contribute to the formation of the enamel, the outermost layer of teeth, as well as a substance capable of killing microbes in the oral cavity [6]. 

One major role of saliva is its participation in the formation of the acquired enamel pellicle (AEP) which is a protective layer that forms over teeth. The composition of the AEP selectively determines the types of microorganisms which can attach to the oral mucosa, thus protecting the enamel from any harmful molecules and damage. Because of the fairly rapid turnover of the cells in the oral mucosa, it is not possible for thick layers of biofilm to accumulate on them. The AEP is primarily a protein layer which covers all surfaces of the enamel and the underlying dentine or cementum when these have become exposed by loss of enamel, although the presence of certain lipids has also been reported [11]. 

Wound Healing

Wound healing involves four overlapping phases: hemostasis, inflammation, proliferation, and tissue remodelling.  The mouth is susceptible to wounds of various types, ranging from cheek biting to tooth extraction, and saliva plays an important role in the healing of all wounds [12]. Notably, oral wounds heal much faster than skin wounds and with relatively much less scar formation as proven by studies on pigs, and some studies suggest it is due to the properties of saliva[13]. 

Saliva contains nerve growth factor and epidermal growth factor, which have been found to accelerate the rate of wound healing [5, 10, 14, 15].  

Levels of stress have been proven to alter saliva composition and are in correlation to reduce wound healing.  Saliva contains catecholamines (hormones produced by the adrenal glands) and keratinocytes (outermost skin layer). These keratinocytes contain receptors which when activated, impair oral keratinocyte migration.  As levels of stress increase, the higher levels of catecholamines, which may cause delayed healing by their inhibitory action on oral keratinocytes [10].

Tadokoro et al.  showed that leptin, an anti-obesity hormone present in saliva, promotes wound healing by stimulating angiogenesis, the production of new blood vessels [15].  Likewise in 1942 Volker demonstrated that saliva speeds up blood flow, coagulation which leads to scabbing, in the specific areas, ultimately providing protection [5, 16]. 

Histatins are histidine-rich proteins which have also been found to be contributors to wound healing as it promotes cell migration observed in the oral cavity [17,18].  They hold antibacterial and antifungal properties.  Histatine-1, histatine-2, and histatine-3 promote the migration of oral keratinocytes within in vitro wound closure, improving the re-epithelialization phase [19-21]. 

Antimicrobial Aspects

As well as a diagnosis tool, many salivary components have anti-fungal, antibacterial and antiviral properties [22]. 

ANTIVIRAL:

Saliva has been found to eliminate or reduce the presence of influenza A as well as HIV [22]. The protein, salivary agglutinin(gp340) is encoded by the dmbt1 gene and has been found to be anti-HIV.  In 1997 gp340 was proven to inhibit the virus by binding to gp120 on the surface of the virus [22].  HIV is deemed not transmittable via the oral route due to the antiviral properties being able to inhibit and kill the virus [23]. 

Mucins are complex antiviral proteins which act by aggregation and encapsulation. Similarly to cell membranes and as a big component of mucus, they act by selectively modulating the adhesion of the virus to the surface of oral tissue by trapping the virus, controlling how they can enter the tissue and the colonization of viruses.

Von Ebner glands protein (VEGh) is a cysteine proteinase inhibitor protein. VEGh belongs to the lipocalin superfamily, the members of which possess very similar structural features.  Lipocalin, which is identical to VEGh possess endonuclease activity which may act as an antiviral and inhibit of RNA and DNA viruses [24] 

ANTIBACTERIAL: 

Saliva contains lysozyme, lactoferrin, salivary lactoperoxidase, and immunoglobulin A (IgA), all of which are antibacterial enzymes. It also contains thiocyanate, hydrogen peroxide and secretory immunoglobulin, which are also antibacterial compounds [6, 25].  

Lactoferrin, produced in intercalated ductal cells, binds ferric iron in saliva. This process makes ferric iron unavailable as a food source for microbes including cariogenic streptococci, that need iron to live [6].  This process of restricting and starving bacteria of vital nutrients is called nutritional immunity [6]. Lactoferrin is also capable of a bactericidal effect that is distinct from simple iron deprivation [5]. 

Peroxidase, also known as sialoperoxidase or lactoperoxidase, catalyzes bacterial metabolic by-products with thiocyanate, which is highly toxic to bacterial systems [6, 26].  Secreted by acinar cells, peroxidase also protects mucosa from the strong oxidizing effects of hydrogen peroxide produced by oral bacteria [6]. Salivary peroxidase is part of an antibacterial system.  This system involves oxidising salivary thiocyanate with hydrogen peroxide which is generated by oral bacteria to hypothiocyanite and hypothiocyanous acid. These products, in turn, affect bacterial metabolism, particularly acid production, by oxidizing the sulfhydryl groups of the enzymes involved in glycolysis and sugar transport. The antimicrobial effect of salivary peroxidase against the bacteria S. mutans is increased by interacting with secretory IgA [5]. 

Immunologic contents of saliva include secretory IgA, IgG, and IgM. Nonimmunologic salivary contents are selected proteins, mucins, peptides, and enzymes [27].  Nonimmunologic antibacterial salivary contents such as proteins, mucins, peptides, lactoferrin, lysozyme, and peroxidase, protect teeth against physical, chemical, and microbes and threats [6]. 

Secretory IgA, the largest immunologic component of saliva, is an immunoglobulin produced by plasma cells in connective tissues and translocated through the duct cells of major and minor salivary glands. IgA, while active on mucosal surfaces, also acts to neutralize viruses, serves as an antibody to bacterial antigens, and works to aggregate or clump bacteria, thus inhibiting bacterial attachment to host tissues [6]. 

Proteins such as glycoproteins, statherins, agglutinins, histatins, and proline-rich proteins act by aggregating bacteria. Clumping the microorganisms reduces the ability of bacteria to stick to hard or soft tissue oral surfaces, spreading throughout the oral cavity and thereby controls bacterial, fungal, and viral colonization [6, 28].

 Although saliva has numerous antibacterial functions, it supports and contributes to the selective growth of bacteria and non-cariogenic microflora [6].  For example some probiotics including lactobacilli can fight harmful bacteria in the oral cavity and can help to heal gum disease, plaque buildup and inflammation [30].

Conclusion

From creating protective layers on the teeth, to increase scabbing for wound healing for preventative measures, and encapsulating and lysing bacteria and viruses in the mouth, saliva has far more health benefits and qualities that more than often go unnoticed.    In contrast to the common connotations of saliva within society being disgusting and offensive, saliva holds so much power within medicine, being a diagnostic tool, a protector and a healer. 

References

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Can Humans Use Smell to Detect Cancer?

OLFACTORY RECEPTORS: 

Olfactory receptors (ORs) are specialised proteins that detect volatile chemicals that are common odorants in the environment.  Discovered in 1991 by Buck and Axel, these chemicals constitute for the largest gene family in humans with approximately four hundred genes [10].  Most ORs are not exclusively expressed or located in the olfactory sensory neurons, however. They have been found in all other human tissues tested to date, yet they’re poorly understood [11].  ORs are highly expressed in different cancer tissues and thus, has been found to possibly be conceivable when it comes to treating specific types of cancer [11]. 

ORs being nerve cells are most often directly connected to the brain.  The olfactory system simply works by scent molecules being detected and recognized by ORs embedded in the ciliary membrane.   

Odour recognition firstly involves the binding of odorant molecules to ORs, where once bound, a biochemical chain reaction occurs in the OR cell, which results in a shift of the cell’s electrical charge [12].  This shift causes the cell to set off electrical impulses that are sent to the brain along axons from the olfactory epithelium, the primary region in which signals are successfully processed at neurological level [13].  When this process reaches a critical level, the receptor cells send more signals to the olfactory bulb (OB), which is the part of the brain that processes odour information [14,15].  The OB is situated in the forebrain and relays the olfactory stimuli to transmit them to the olfactory cortex, where the conscious awareness of a smell takes place, and to the limbic system, which is the part of the brain heavily involved with memory and emotion [11,16-19].  

COLORECTAL CANCER: 

Colorectal is one of the most pertinent types of cancer amongst humanity.  With approximately 1.8 million cases in 2018 alone, according to the WHO, this cancer causes much burden and pain for patients.  The symptoms can range from rectal bleeding, to change in bowel habits and anaemia [20].  Colorectal cancer affects the digestive system, and depending on where the primary tumour originated, it can be referred to as bowel cancer, colon cancer, or rectal cancer.  This form of cancer typically spreads via the bloodstream and the lymph nodes to other parts of the body, particularly the liver, lungs and the peritoneum, and sometimes even bones, as metastatic or stage IV colorectal cancer.  Generally, colorectal cancers have been found to be relatively slow growing however they are still very aggressive. 

Colorectal cancer develops through multistage processes, involving accumulation of genetic, epigenetic and environmental factors and alterations [21].  In many cases, colorectal cancer is linked with physical inactivity, excess body weight, and the overconsumption of energy, which is especially prominent in Western countries [22]. 

In recent years, the investigation on how olfactory receptors are linked to the pathogenesis of colorectal cancer has increased, but it is still very scarce and not in depth.  Due to the very diverse nature of many ORs, it appears that many have different and versatile functions. Sailem et al. most recently used AI to find that specific ORs being “turned on” can cause worse colon cancer outcomes [23]. Li et al. found that OR1D2, OR4F15 and OR1A1 also disrupted colorectal cancer cases [24]. Xu et. Al also found that OR8D2 acts as a predictor of recurrence risk and prognosis for colon cancer patients [25].  Some ORs seem to have been slightly more researched than others with their involvement in colorectal cancer, one of them being 0R51B4. 

OR51B4 is found to be highly expressed primarily in the colon cancer cell line HCT116, and in native human colon cancer tissues.  Weber et al. Found that by stimulating the OR with its ligand, Troenan, cell proliferation and growth were inhibited as well as inducing apoptosis, cell death [26].  Lee et al. seems to further agree and find that the regulation of OR51B4 via Troenan can inhibit cancer in the cells thus may be able to be a possible novel target for colon cancer [27]. As colon cancer is accessible from the lumen, the rectal or oral ingestion of Troenan could be plausible to use for a potential treatment. 

OR7C1 is another example of a more commonly studied OR in the involvement of colorectal cancer.  It has been found to play a crucial role in the physiology of cancer, initiating cells in the colon as an increased expression of OR7C1 correlates to a higher tumorigenicity [28]. In addition, immunohistochemical staining revealed that OR7C1 high expression was correlated with poorer prognosis in CRC patients, thus could also be a viable target for treating colon cancer [29]. 

CONCLUSION: 

Olfactory receptors, their involvement, and their potential to act as targets for treating colon/colorectal cancer, more so than many other types of cancer, seems to be promising as being efficacious.  Nevertheless, whether humans would be able to find a way to consciously recognise the scent of specific cancer directly is heavily questionable.  ORs have very little research to back up any statements and prospects, particularly to administer clinically as of yet, thus it would need much heavier investigation. 

BIBLIOGRAPHY: 

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MicroRNA-146a: A Potential Target for Treating Neurological Disease

ABSTRACT: 

Neurological diseases, though having significant impact on individuals, thoroughly lack in knowledge and insight of epidemiology due to their complex nature. As of current research, neurological diseases are classified as the gradual functional deterioration and loss of neurons.  Various neurological diseases have been recognised to have mutual aspects such as pathological nature, nervous mechanisms but also inflammatory responses in the nervous system.  MicroRNAs (MiRNAs) are small non-coding RNAs that regulate the expression of most of the genes in humans.  MiRNAs have been discovered to hold significant roles, many known and yet to find, in the pathogenesis of many diseases and conditions.  This review depicts the potential for MicroRNAs, more specifically, MiRNA-146a as a potential target and biomarker for the treatment of neurological diseases, focusing on its involvement within Alzheimer’s disease (AD) in particular.

INTRODUCTION: 

Initially identified in 1993 under the lab of Victor Ambrose, the discovery of MicroRNAs (MiRNAs) has paved the way for many possibilities and prospective insights to combating diseases and conditions; some having been looked into, and others completely unexplored [1].  MiRNAs are 21- to 23-oligonucleotide non-coding RNAs processed from longer transcripts, which regulate gene expression in most human genes.  Conserved in many species alike, MiRNAs have widespread, conserved targets, and at some point, in development most genes have been regulated by these MiRNAs, providing a possibility of efficacy for treating diseases [2]. 

MiRNAs act through inhibition of protein expression of messenger RNA (mRNA) at post-transcription level within Argonaute proteins in order to regulate gene expression [3].  It is critical for many biological processes and animal development for MiRNAs to be expressed at a normal rate as dysregulated MiRNAs have been associated with multiple diseases [4].  A number of MiRNAs have been found to function for biologically diverse processes including that of cell death, neuronal patterning, immunity, and cell proliferation, just to state a few [5,6].  They can be secreted by living neurons and other cells within the CNS into extracellular vesicles (EVs) packaged in microvesicles, lipoprotein complexes and exosomes, thus carves the way for many neurological diseases to be linked to aberrant MiRNA expression and distribution [4, 7]. 

Amongst recent literature on potential targets for the treatment of diseases, MiRNAs are one of the most extensively characterized, yet heavily require more experimental confirmation [6].  As MiRNAs are a potential novel class of therapeutic targets, advances in research, particularly in its involvement within central nervous system (CNS) disease, would be beneficial, due to the CNS being the least accessible of all tissues [4]. 

A plethora of MiRNAs have been identified as having significant roles within processes in neurological diseases, and with the growing collection of literature on MicroRNAs, MiRNA-146a is often highlighted in its involvement with neurological diseases [8]. 

THE SIGNIFICANCE OF MICRORNA-146a: 

MiRNA-146a is a small, non-coding, regulatory RNA that pertains to crucial roles in physiological and pathophysiological processes such as negatively regulating antiviral pathways, immune, and neuroinflammatory responses [5].  It is one of the most abundant MiRNAs that can be expressed in the CNS, and its polymorphisms are found to be closely associated to a majority of major neurological disorders not limited to but including: neuro autoimmune diseases, neurodegenerative diseases, neurological tumours, CNS trauma and cerebrovascular diseases [8].  These neurological diseases share nerve cellular mechanisms within pathogenesis, and are complicated processes from the limited knowledge that is currently available, thus cannot be treated or cured as of yet.  MiRNA-146a is important in the development of these diseases as it has been shown, at post transcriptional level, to act via the inhibition of target genes such as: IRAK1, IRAK2, IRF-5, PTC1, RIG-I, STAT-1, TRAF6, and Numb [9, 10]. 

MiRNA-146a and its polymorphisms are not distributed by random; its particular sequences are carefully arranged to occupy very specific cellular microenvironments.  Some of the miRNAs are expressed at higher levels in the exosomes than in the cells [7].  Two of the most important single-nucleotide polymorphisms (SNPs) in MiR-146a: rs2910164, and rs57095329, have been shown to influence the level of mature MiR-146a and are associated with the onset of several major neurological diseases, such as Alzheimer’s disease (AD), ischemic stroke (IS), epilepsy, and multiple sclerosis (MS) [8].  In animal models, it has been demonstrated that it is possible to improve and, in some cases, reverse neurological diseases and even tumours present on the brain and the central nervous system by restoring a normal level of MiRNAs and its polymorphisms [5].  For example, Giraldez et al. Discovered that zebrafish without MiRNA had problems with development of the brain, Chen et al. found that MiRNA-146a can protect the brain against cognitive decline in mice, Liu et al. Showed that treatment by restoring MiRNA-146a levels improves neurological and nerve function [11-13]. 

Polymorphisms of MiRNA-146a have possible clinical relevance and implication in pharmacogenetics [9]. As it is an upcoming, potential therapeutic target, its genetic polymorphisms would be critical in diagnosis and interindividual variation in drug response, as detecting underlying molecular responses and genetic environment can be detected earlier on, thus can prevent the onset of neurological diseases [14].  This epigenetic regulation of MiRNA-146 could justify why different patients respond differently to the same treatments, and as the brain and central nervous system are all so delicate and sensitive, further understanding how this gene works could be the answer to tailoring therapeutics and targets for treating neurological diseases [15]. 

INVOLVEMENT IN ALZHEIMER’S DISEASE: 

Originally described by Alois Alzheimer in 1906 as “a peculiar severe disease process of the cerebral cortex”, Alzheimer’s disease (AD) is currently the most common cause of dementia in the elderly [16-18].  This neurodegenerative disorder is clinically defined as a progressive cognitive impairment including impaired cognition and judgement and in severe cases, psycho behavioural disturbances such as psychosis [19].  Disorders like AD are considered multifactorial, as they are currently recognised to emerge due to genetic programming and environmental influences but primary causes are still unknown.  Neurodegeneration in AD most often goes unknown until severe and is estimated to start 20-30 years before clinical diagnosis, and the time from diagnosis to death is typically ~8 years [19,20].  This underlines why it would be crucial to find prospective targets and genes that could be used for early diagnosis or the treatment for AD. 

AD is characterised by neuronal loss, the accumulation of senile plaques composed of β-amyloid proteins, neurofibrillary tangles (NFTs) and the activation of microglia and glia [21, 22].  These damaged and lost neurons, senile plaques and NFTs can ultimately pave way for the appearance of activated microglia [21].  These microglia, both in animal models and human brains, generate β-Amyloid, a pro-inflammatory agent, providing stimuli for neuroinflammation, inducing the activation of glia and many inflammatory components [22].  Though this just represents the very ‘tip of the iceberg’ of how AD can affect the brain, an understanding of this disease is critical in coming up with prevention and ways to combat AD before the damage to the nervous system becomes irreversible [23]. 

Inflammation clearly plays a critical role in the pathology of Alzheimer’s and is therefore recognised as a potential aspect to target, when it comes to treating AD.  As stated before, microglia are the major producers of inflammatory factors, clustering in the brain during the early stage of pathogenesis of AD [24].  Inflammation in the CNS can in some circumstances be beneficial however, most often it can worsen pathology and cause secondary damage [22, 25].  In a healthy adult CNS, microglia are dormant but remain a vigilant state, and only respond to infection or CNS damage in order to restore CNS homeostasis [25].   

Wenk and colleagues have studied the effects of nitric oxide flurbiprofen in reducing inflammation in the brain in rats, and although not a MiRNA, the study suggests that anti-inflammatory therapies may be effective in slowing onset of AD, which is where MiRNA-146a steps in [21]. 

MiRNA-146a is known to be an anti-inflammatory regulator that uses a negative feedback response.  In conditions that are attended by cellular stress, such as Alzheimer’s, it is expected that MiRNAs have altered expression patterns and this is the case for MiRNA-146a [26].  It is known that MiRNA-146a is heavily upregulated in the brain of AD patients and in mice [27, 28].  In AD, MiRNA-146a levels are found to increase with disease severity and be local to brain regions most affected by neuroinflammation [29].  This is probably due to the anti-inflammatory nature of MiRNA-146a trying to decrease the inflammatory response from being too harsh and initiating more damage than good to the brain. 

Cui et al. found MiRNA-146a to be increased to an average of 2.6-fold over age-matched controls in the temporal lobe of AD brains, and with increased expression correlating to increased senile plaque density, it may be assumed that this upregulation of MiRNA-146a may contribute to the progression of Alzheimer’s [30-32].  In a study by Shaik et al. this increase in MiRNA-146a can be partially eliminated by inhibiting the gene through NFκB, a protein complex that is the cause of this upregulation of MiRNA-146a [33].  The significance of this study is that it shows that there’s potential to not completely eradicate the expression of MiRNA-146a, which would be crucial as this can further lead to neurodegeneration as shown in animal models [34].  This sparks prospects into the clinical utilisation of an inhibitor targeting MiRNA-146a to slow down the progression of AD.  As shown in a study by Mai et al., targeting and restoring normal levels of MiRNA-146a can alleviate the pathological process and the neurodegeneration of AD, thus further proving it possible to use MiRNA as a target in treating Alzheimer’s [35]. 

The ideal diagnostic technique and treatment for AD would be non-invasive and that can tackle the condition before onset of severe symptoms.  As of present day, there is also no cure for AD, only drugs that relieve some AD symptoms and the diagnosis techniques include cognitive testing, neuroimaging and biomarker detection, and others, most of which only detect AD at a moderate to severe progress [15, 36].  With the further exploration of MiRNA-146a, it may be possible to use as a target for the diagnosis and treatment of Alzheimer’s as it is most commonly reported to be found abundant in cerebrospinal fluid and has demonstrated the potential pharmacological value when overexpressed [36-39]. 

CONCLUSION: 

The research, literature, and execution of using MicroRNAs in the pharmaceutical industry and medicine is rapidly growing, ongoing and relatively promising.  Whilst the technological and biological discoveries are encouraging, there are still many risks and obstacles to overcome before scaling up the use of MiRNAs in the real world [6].  The CNS being one of the most delicate and difficult to reach aspects in the human body, in order to treat and prevent neurological disorders, it is crucial to have a reliable resource in order to achieve this.  MiRNAs being a natural agent, may have prospects in being able to assist clinically to the treatment of these diseases like Alzheimer’s but much more study is required.  The road for the use of MiRNAs might be a long and hard road for therapeutics but MiRNA-146a could potentially be an answer to unlocking many doors for medicine, more so neurology and research in this area. 

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Combination Ab/Ag Paper-Based Lateral Flow Assay for COVID-19

Problem Investigated:

As of the beginning of June, there have been over 3.5 million cases of infection and roughly 250,000 deaths due to COVID-19.  It is crucial to pinpoint the whereabouts of the virus in terms of rates and progression in individuals.  The only way to do this is via testing.  Yet this is an aspect that has failed, time and time again.  Developed countries despite having some of the strongest healthcare systems have the highest numbers of cases due to lack of effective and efficient testing and developing countries too face this very uncertainty due to the scarcity of cheap point of care testing kits.  With this lack of resources, even those working on the frontline, such as healthcare workers, have very little access to tests, let alone the general public. Hence, in order to reduce the high levels of uncertainty, to plan how to eventually lift lockdowns, and ultimately overcome this pandemic, developing effective and affordable testing kits is quintessential.

Our aims and hypothesis:

Through our test, we aim to significantly increase testing capacity globally and make testing more inclusive so that people, especially those in developing nations, are not deprived of the resources necessary to combat COVID-19.  Our hypothesis states that with our combination of antibody-antigen tests, we can provide researchers, labs, and hospitals a ‘truer’ value and indication of the severity and extent of the virus outbreak so that the strain on the healthcare system can be reduced.

Our solution:

We have designed a combination antibody/antigen (Ab/Ag) paper-based lateral flow assay that is sustainable, easily manufactured, and easy to utilize as a point-of-care (POC) device.  Integrating QR codes onto our tests, which would be connected to an app, we can connect researchers to non-personal data to track the virus and provide users a platform to assess their own progress.

Our prototype:

Diagnosis is the primary strategy towards the overarching goal of virus control and elimination, which would be effective ultimately everywhere to detect active cases, but mainly in developing countries and those with currently low numbers of cases as it may give those countries a chance to thoroughly control and prevent the outbreak from growing.  Testing for antibodies would be more effective in countries and regions where the virus has spread to a much wider vicinity.  Such tests can give an indication of historical infection and as many have debated, a possible sign of immunity, which can be used to slowly lift lockdown restrictions, however that is to be further explored.

Ultimately to get the fullest and the most accurate picture, both tests are needed simultaneously.

Our test is a double-sided combination Ab/Ag paper-based lateral flow assay, which on one side, can detect the presence of the COVID-19 virus itself, and on the other, both IgM and IgG antibodies from blood, urine, serum, plasma, saliva, and sputum samples [1].

FIGURE 1: A schematic representation of the appearance of our test.  Both sides of the paper will have this structure and appearance.

The standard method of diagnosis so far throughout this current pandemic has been through polymerase chain reaction(PCR) and serological tests.  PCR tests detect viral RNA, thus can only determine who has an active case of COVID-19.  Serological tests, on the other hand, can only reveal if an individual has previously been exposed to the virus and developed antibodies as a natural immune response.  Though these two forms of diagnostics respectively have their benefits such as high sensitivity and accuracy, they are constantly challenged by many quality assurance issues.  This includes but is not limited to: cross-reactivity of used antibodies in ELISA specifically, virus stability, reagent storage, equipment performance, and staff competency just to name a few [2].  Furthermore, with PCR and serology, there are high risks of false-positives from contamination and transcription errors, or false-negative results from malfunctioning equipment and degraded samples and reagents [2, 3].  Currently, these tests are administered separately, should an individual have the rare privilege to have access to both forms.

Dr James Gill, Locum GP & Honorary Clinical Lecturer at Warwick Medical school has stated, “The best test for early detection is combining the antibody test AND  the PCR swab taken from the patient.  Then we have a 98.6% detection rate within the first 5.5 days of infection.”

The timing of diagnosis has proven to be crucial in outbreak response in order to mitigate and track the virus not just for an entire country but for an individual’s health too.  Currently, PCR takes a few hours to run and prospective serology tests claim to show results in 15-30 minutes, however, on their own they do not normally benefit patients as immune responses can only be detected for a period of time after initial viral infection [1].  Studies have shown that within the first week of infection, PCR tests can detect covid-19 from nasal swabs with ~95% accuracy, in which gradually after that, the percentage decreases [4].  However at the moment of writing there seems to be a range of PCR detection rates according to many factors such as where the sample was taken from, lab and clinical settings and different protocols for different countries [5].

As stated before, both tests are clearly needed simultaneously therefore we believe our combination Ab/Ag test can possibly override the separate tests.  This has been proven possible in diagnosing HIV through 4^th generation combination tests, which have overtaken the market.  This combination test is one of the most preferred and recommended methods of diagnosis for HIV, approved by authorities [6].

Unlike the traditional diagnostic methods like PCR, a paper-based platform provides a basis for point-of-care (POC) diagnosis in resource-limited settings, and removes the necessity for any heavy machinery or professional to administer the tests, whilst maintaining the high sensitivity and accuracy as diagnostic tests should.  In addition, they have numerous advantages including: affordability, sustainability, portability, disposability, and the ability to handle small volumes of unprocessed samples of biofluids such as blood, urine, saliva, sputum or plasma [1].  Paper is an inexpensive, lightweight, easy to functionalize and versatile material.  The most common kinds of paper used for POC devices are filter paper and chromatography paper [7].  Due to its 3D, porous, heterogeneous morphology, paper most often have the ability to store reagents and samples without the use of refrigeration, which would be especially useful in developing countries where there is often a lack of accessibility to electricity, and given the contagious nature of the samples, our paper-based assay should be able to protect users from even more exposure to other biohazards [1, 8].

FIGURE 2: A more in-depth representation as to how each side of the paper functions, and how the detection is carried out via bioconjugated AuNPs.  Top: Covid-19 detection.  Bottom: IgM and IgG detection.

How our test works:

Our test is a lateral flow assay thus functions quite similarly to pregnancy tests.  The user will put a sample of blood, urine, saliva, sputum, serum or plasma on to the sample pad.  Due to capillary force, the cellulose fibers of the paper allows for the biofluids to penetrate the hydrophilic matrix and flow up the test without external power [9].  As the sample rehydrates the conjugated pad, the target will bind to the bioconjugated gold nanoparticles on either side(AuNPs).  As studies have found that covid-19 enters host cells by using their spike glycoprotein (S-protein), on the top layer of the assay we have placed AuNP’s that are functionalised with a complementary antibody to that of the s-protein in order for only the virus to attach to it and aggregate the nanoparticles.  In addition, on the bottom layer, in order to only attach to the desired IgM and IgG antibodies, we functionalised the AuNP’s with dead or inactive covid-19 antigens.  The sample will continue to flow up the paper by capillary action.  As the sample reaches the detection zone and the control line,  there are capture reagents allocated in certain regions, overall forming a QR code image.  Should the test turn out to be positive, the conjugated AuNPs will bind to the capture reagents, causing a visible color change on the QR code to the naked eye, indicating positive for the biomarker detected.  Should the test be negative, no binding will be initiated, causing no color change.  We would expect our test to be able to show results within 5-10 minutes.  Once results have been processed, the user should scan the QR code, connected to our app, which would be able to recognize the different colored QR codes.  The app has an option by which the users would be able to report any symptoms should they have any, indicating their progress, and non-personal data such as how many are positive for COVID-19 can be sent easily to researchers, hospitals, and authorities.  Should the user report severe symptoms we will allow them to contact nearby hospitals, which will allow for hospitals to capacity plan a lot better, without further risk of being overwhelmed and will allow for those who really require intensive care, the opportunity to receive the help they need.

FIGURE 3: A depiction of the color changes of the QR code detection zone upon aggregation with different biomarkers. Top left: Red QR code contains unaggregated AuNPs indicating Negative results for both COVID-19 and IgM and IgG antibodies.  Top right: Deep blue QR code as a result of positive detection for COVID-19.  Bottom left: Light blue QR code as a result of positive for ONLY IgG antibodies.  Bottom centre: Light pink QR code as a result of positive for ONLY IgM antibodies.  Bottom right: Purple QR code as a result of positive for BOTH IgM and IgG antibodies.

In order to detect the presence of COVID-19 and IgG and IgM antibodies at the detection zone, we have decided to use gold nanoparticles (AuNPs) in order to efficiently provide results in a short time period.

Coronaviruses are enveloped positive single-stranded RNA (+ssRNA) viruses which are round, elliptical and often pleomorphic in their form [10].  They have a crown-like appearance under electron microscopes due to the spike glycoproteins (S-proteins) on the envelope, hence the name of coronavirus.  There are two main biorecognition strategies: directly detecting the pathogen, in this case, it would be through the viral RNA or detecting biomarkers, such as antigens like the S-proteins.  Traditionally, PCR directly detects nucleic acids, however, recent innovations in detecting biomarkers for many diseases and conditions have been proven to be faster and more robust [11].  In order to detect the virus, we wanted to use a particle or similar sized material which could detect the S-proteins.  In the case of COVID-19, the virus is 60-140nm in diameter, thus we found it most suitable to integrate nanotechnology and nanomaterials to be able to track the virus from the same scale, hence using APS.

AuNPs are a leading class of metal nanostructures that are widely known for their versatile traits such as chemical inertness, water-solubility, high electron density, and strong optical absorption [12, 13].  They have such broad size and shape controllability, ranging from 1 to 800nm in size and have different morphological shapes from spheres, cubes, rods, dog bones, shells, crystals and even hollow structures[12].  Abundant in characteristics, AuNPs have in recent decades been applied in genomics, clinical chemistry, vaccine development, microorganisms control, cancer-cell imaging, and drug delivery, but have also been recognized to constitute ideal tools in virus detection [13, 14].  AuNPs as labeling agents and bioconjugates are easily visualized to the naked eye due to their intense colors, thus would contribute to the simplicity and portability of our prototype, making it an ideal POC platform, whilst maintaining high levels of sensitivity and accuracy.

To be able to visually and easily present test results, the QR code detection zone relies on the colorimetric changes of AuNP solutions upon aggregation, which can be mediated upon the recognition of COVID-19 antigens and IgM and IgG antibodies which are complementary to the bioconjugated AuNPs [15].

When aiming to use AuNPs in biomedicine as a diagnostic or therapeutic tool, it is necessary to rightly choose the targeting component such as a monoclonal antibody (mAb), and attach it on to the surface of the nanoparticle [16].  Sole AuNPs are ‘blind’ with respect to sensing COVID-19 or antibodies, so the bioconjugation of specific biomolecules to their surfaces is a crucial process.  There have been many successful examples of various AuNP bioconjugates being employed in colorimetric systems to detect well-known human viruses such as Dengue virus; Ebola virus; Hepatitis; HIV; Human Papillomavirus; Herpes; West Nile Virus and even SARS [3, 17].

As stated before, we believe our test would be able to present results within 5 minutes without compensating the accuracy and quality.  This contrasts previous attempts to employ efficiency to detect COVID-19 but with inaccuracy, as shown by the UK government using £3.5million to purchase faulty tests from China.  The technique of using bioconjugated AuNPs has exhibited very promising statistics when detecting SARS in the 2003 pandemic, with a sensitivity limit of 100fM, thus with SARS-CoV-2, we would expect it to show similar prospects [18].

Due to the need for easy and rapid access to data, for researchers, hospitals and authorities, and a platform to report symptoms and progress, we decided to integrate the use of smartphones and diagnosis through the detection zone for our test forming a QR code.  Upon aggregation of the AuNPs, the QR code on each side will change colors according to the sample contents [19].  As shown in figure 3, should the test be negative on each side, the QR codes will remain red.  Should the test show positive for COVID-19, the QR code on the antigen detection side will change into a deep blue color.  If positive for IgM antibodies the QR code will turn light pink, if only positive for IgG antibodies the QR will turn light blue, and if both are present the QR code will be purple.

According to Statista, the current number of smartphone users in the world today is 3.5 billion (45.04% of the current population) and these numbers are growing ever so fast in this day and age.  Aligning this to our aim of inclusivity in terms of availability to testing, we wanted to connect smartphone devices to the tests in a simple manner.  The first smartphone approaches for POC diagnostics have usually involved additional attachment parts, or very specific post-treatment of the used tests: Zangheri et al. described a lateral flow assay which required the use of an accessory lens [20], Mudanyali et Al. reported a smartphone-based platform with a 3D printed accessory with LED [21], You et Al. and Lee et Al. both used smartphone readers [22, 23].  These approaches all use customized add-ons and excessive resources, bringing down the people reached drastically.  In more recent attempts to make it easier to analyse or record data from lateral flow assays, Yang et Al. have innovated a way to integrate barcode on to the assay in order to be read by inexpensive barcode scanners similar to those used in supermarkets [9].  But yet again that lacks inclusivity as we don’t all have barcode scanners lying around hence QR codes seems to be the most effective.

Utilizing paper as the main material for our assay, functionalizing AuNPs for detection, and integrating QR codes as a mean of recording and analyzing data, we have considered the manufacturing process, how the tests will be utilized and the sustainability of our test, all in order to maximize the potential for our test to not be harmful to any party involved.  The materials for our test for COVID-19 can be easily synthesized, made, found, and disposed of, and show little to no toxicity in the case of AuNPs [13, 17].

Accessibility was a big motivation for us whilst designing the test.   Upon our research, we noticed that at the time of writing, out of the 50 countries with the lowest GDP per capita at nominal value in US dollars in 2019 according to the International Monetary Fund, 15 are in the lowest 50 nations in terms of numbers of cases and 13 are in the lowest 50 in terms of death from COVID-19.   But most of all, out of the 50 countries with the lowest recorded numbers of testing, there are 22 of those countries with the lowest GDP per capita.  With even more uncertainty as to how far and wide the disease has spread in these countries, it was our concern that we should not neglect them in our idea of how we should combat COVID-19.  Which raises the question: do these developing countries genuinely not have as many cases, or is it just due to a lack of testing, resources, and knowledge that has caused their data to appear the way that it does?  The only way to find out is through testing.  Testing as many people worldwide as possible.  And through our tests, we may find an answer.

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