Salivary markers of kidney function - Potentials and limitations

Liquid Chromatography-Mass Spectrometry Analytical Methods for the Quantitation of p-Cresol Sulfate and Indoxyl Sulfate in Human Matrices: Biological Applications and Diagnostic Potentials

Indoxyl sulfate (IxS) and p-cresyl sulfate (pCS) are toxic uremic compounds with documented pathological outcomes. This review critically and comprehensively analyzes the available liquid chromatography-mass spectrometry methods quantifying IxS and pCS in human matrices and the biological applications of these validated assays. Embase, Medline, PubMed, Scopus, and Web of Science were searched until December 2023 to identify assays with complete analytical and validation data (N = 23). Subsequently, citation analysis with PubMed and Scopus was utilized to identify the biological applications for these assays (N = 45). The extraction methods, mobile phase compositions, chromatography, and ionization methods were evaluated with respect to overall assay performance (e.g., sensitivity, separation, interference). Most of the assays focused on human serum/plasma, utilizing acetonitrile or methanol (with ammonium acetate/formate or formic/acetic acid), liquid-liquid extraction, reverse phase (e.g., C18) chromatography, and gradient elution for analyte separation. Mass spectrometry conditions were also consistent in the identified papers, with negative electrospray ionization, select multiple reaction monitoring transitions and deuterated internal standards being the most common approaches. The validated biological applications indicated IxS and/or pCS were correlated with renal disease progression and cardiovascular outcomes, with limited data on central nervous system disorders. Methods for reducing IxS and/or pCS concentrations were also identified (e.g., drugs, natural products, diet, dialysis, transplantation) where inconsistent findings have been reported. The clinical monitoring of IxS and pCS is gaining significant interest, and this review will serve as a useful compendium for scientists and clinicians.

Noninvasive and Multiplex Self-Test of Kidney Disease Biomarkers with Graphene-Based Lab-on-a-Chip (G-LOC): Toward Digital Diagnostics in the Hands of Patients

Chronic kidney disease is one of the major health issues worldwide. However, diagnosis is now highly centralized in large laboratories, resulting in low access to patient monitoring and poor personalized treatments. This work reports the development of a graphene-based lab-on-a-chip (G-LOC) for the digital testing of renal function biomarkers in serum and saliva samples. G-LOC integrates multiple bioelectronic sensors with a microfluidic system that enables multiplex self-testing of urea, potassium, sodium, and chloride. The linearity, limit of detection (LOD), accuracy, and coefficient of variability (CV) were studied. Accuracy values higher than 95.5% and CV lower than 9% were obtained for all of the biomarkers. The analytical performance was compared against three reference lab benchtop analyzers by measuring healthy- and renal-failure-level samples of serum. From receiver operating characteristic (ROC) plots, sensitivities (%) of 99.7, 97.6, 99.1, and 89.0 were obtained for urea, potassium, sodium, and chloride, respectively. Then, the test was evaluated in noninvasive saliva samples and compared against reference methods. Correlation and Bland-Altman plots showed good correlation and agreement of the G-LOC with the reference methods. It is noteworthy that the precision of G-LOC was similar to better than benchtop lab analyzers, with the advantage of being highly portable. Finally, a user testing study was conducted. The analytical performance obtained with untrained volunteers was similar to that obtained with trained chemists. Additionally, based on a user experience survey, G-LOC was found to have very simple usability and would be suitable for at-home diagnostics.

Exploring the Relationship Between Serum Creatinine and Salivary Creatinine Levels in Patients With Chronic Kidney Disease in South India: A Cross-Sectional Study

Background In this study, researchers investigated non-invasive methods for analyzing creatinine levels by using saliva to address the need for frequent phlebotomy in chronic kidney disease (CKD) patients, which can damage their veins due to repeated blood withdrawals for creatinine level assessments. Methods This is a cross-sectional study in a tertiary healthcare setting conducted on 50 patients diagnosed with CKD. After collecting serum and salivary creatinine, we used Pearson correlation to assess the correlation between the two factors. Results The mean age of the patients was 50 years with a standard deviation of ± 15.32 years. 33 (66%) patients were males and 17 (34%) were females. Most patients were in the age group of 51 - 70 years, comprising 26 (52%) of the sample. The serum creatinine and salivary creatinine values ranged between 7.26-12.00 and 0.45-0.98, respectively. The median values were 9.72 and 0.75, respectively. There was a very weak positive linear relationship between serum and salivary creatinine levels; however, there was no significant association between them (p = 0.52). Nonetheless, a statistically significant, moderately negative linear correlation exists between serum urea and serum albumin (r = -0.36; p = 0.01). Additionally, there is a statistically significant weak negative linear correlation between serum chloride and serum urea (r = -0.3; p = 0.03). Comparing serum chloride and serum sodium reveals a statistically significant, moderately positive linear relationship (r = 0.4; p = 0.004). Serum phosphorus and serum creatinine display a statistically significant moderate positive linear relationship (r = 0.44; p = 0.001). Moreover, estimated glomerular filtration rate (eGFR) and serum creatinine exhibit a statistically significant strong negative linear correlation (r = -0.79; p < 0.001), while eGFR and serum phosphorus demonstrate a statistically significant weak negative linear correlation (r = -0.30; p = 0.03). Conclusion The study found no significant association between salivary and serum creatinine levels. Further multicentric studies on a larger population must be conducted to find the potential correlation between serum and salivary markers.

Development of a novel method for the simultaneous detection of trimethylamine N-oxide and creatinine in the saliva of patients with chronic kidney disease - Its utility in saliva as an alternative to blood

Chronic kidney disease (CKD) is associated with increased levels of creatinine and other uremic toxins (UTs), which impaired kidneys cannot filtrate. Typically, CKD is diagnosed by calculating the estimated glomerular filtration rate using serum creatinine or cystatin C levels. In pursuit of more sensitive and reliable biomarkers of kidney dysfunction, scientific attention has turned towards other UTs, such as trimethylamine N-oxide (TMAO), successfully quantified in standard matrices, blood and urine. However, less invasive monitoring of kidney function can be performed using an alternative diagnostic biofluid, saliva, which has been shown to contain clinically relevant concentrations of renal function markers. Accurate quantitative estimation of serum biomarkers using saliva measurements can only be achieved provided that there is a tight saliva-serum correlation for the analyte of interest. Therefore, we aimed to verify the correlation between saliva and serum levels of TMAO in CKD patients using newly developed and validated quantitative liquid chromatography coupled to mass spectrometry (LC-MS) method for simultaneous detection of TMAO, and creatinine - the conventional marker of renal impairment. Secondly, we applied this method to quantify TMAO and creatinine levels in the resting saliva of CKD patients collected with a standardised method involving swab-based collectors. A good linear correlation was obtained between the concentration of creatinine in serum and resting saliva of CKD patients (r = 0.72, p = 0.029) and even better in the case of TMAO (r = 0.81, p = 0.008). The analysed validation criteria were fulfilled. No significant influence of the type of swab in the Salivette® device on creatinine and TMAO concentrations in saliva was detected. Our study indicates that saliva can be successfully used in the non-invasive monitoring of renal failure in CKD by measuring salivary TMAO concentrations.

The relationship between immune fitness and saliva biomarkers of systemic inflammation

Purpose

It is vital that Immune fitness, i.e., how well the immune system functions and reacts to challenges, can be reliably be examined. The current study aimed to compare immune fitness with assessments of saliva biomarkers of systemic inflammation.

Methods

N = 108 healthy young adults (18-30-year-old students of Utrecht University, the Netherlands) participated in the study. A saliva sample was collected for biomarker assessment (Interleukin (IL)-1β, IL-6, IL-8, IL-10, immunoglobulin A (IgA), and tumor necrosis factor-alpha (TNF-α), and c-reactive protein (CRP). Additionally, a survey was completed to assess immune fitness, mood, mental resilience, and quality of life. The correlations between the biomarker assessments, immune fitness and mood were determined.

Results

No significant correlations between immune fitness and biomarkers of systemic inflammation were found. Significant sex differences in correlations with immune fitness were demonstrated for loneliness (significant only in men) and fatigue (significant only in women). For both sexes, immune fitness correlated significantly with anxiety, mental resilience, and quality of life.

Conclusion

No significant correlations were found between immune fitness and saliva biomarkers of systemic inflammation. Immune fitness correlated significantly with anxiety, mental resilience, and quality of life. Sex differences were demonstrated in the relation of immune fitness with loneliness and fatigue. Future research should further investigate factors that may influence the relationship between immune fitness, mood, and biomarkers of systemic inflammation, including underlying psychological mechanisms of possible sex differences.

A Novel Salivary Sensor with Integrated Au Electrodes and Conductivity Meters for Screening of Diabetes

The rise in diabetes cases is a growing concern due to the aging of populations. This not only places a strain on healthcare systems but also creates serious public health problems. Traditional blood tests are currently used to check blood sugar levels, but they are invasive and can discourage patients from regularly monitoring their levels. We recently developed nano-sensing probes that integrate Au microelectrodes and conductivity meters, requiring only 50 μL of saliva for measurement. The usage of the co-planar design of coating-free Au electrodes makes the measurement more stable, precise, and easier. This study found a positive correlation between the participant's fasting blood sugar levels and salivary conductivity. We observed a diabetes prevalence of 11.6% among 395 adults under 65 years in this study, using the glycated hemoglobin > 6.5% definition. This study found significantly higher salivary conductivity in the diabetes group, and also a clear trend of increasing diabetes as conductivity levels rose. The prediction model, using salivary conductivity, age, and body mass index, performed well in diagnosing diabetes, with a ROC curve area of 0.75. The study participants were further divided into low and high groups based on salivary conductivity using the Youden index with a cutoff value of 5.987 ms/cm. Individuals with higher salivary conductivity had a 3.82 times greater risk of diabetes than those with lower levels, as determined by the odds ratio calculation. In conclusion, this portable sensing device for salivary conductivity has the potential to be a screening tool for detecting diabetes.

Association between serum biomarkers and oral health status in children with chronic kidney disease: A cross-sectional study

OBJECTIVES

The aim of this study was to investigate the association between serum biomarkers and oral health parameters in children with chronic kidney disease (CKD).

MATERIALS AND METHODS

Serum hemoglobin, blood urea nitrogen, serum creatinine, calcium, parathormone, magnesium, and phosphorus levels were measured in 62 children with CKD aged between 4 and 17 years. Intraoral examinations of the patients were performed by two different pediatric dentists. Dental caries was assessed using the decayed-missing-filled-teeth (DMFT/dmft) indexes, and oral hygiene was assessed using the debris (DI), calculus (CI), and simplified oral hygiene (OHI-S) indexes. Spearman's rho coefficient and generalized linear modeling were used to examine the association between serum biomarkers and oral health parameters.

RESULTS

The results of the study showed that there were negative and statistically significant correlations between serum hemoglobin and creatinine levels and dmft scores in pediatric patients with CKD (p = 0.021 and p = 0.019, respectively). Furthermore, blood urea nitrogen levels and DI and OHI-S scores (p = 0.047 and p = 0.050, respectively); serum creatinine levels and DI, CI, and OHI-S scores (p = 0.005, p = 0.047, p = 0.043, respectively); and parathormone levels and CI and OHI-S scores (p = 0.001 and p = 0.017, respectively) were found to be positively and statistically significantly related.

CONCLUSIONS

There are associations between various serum biomarker levels and dental caries and oral hygiene parameters in pediatric patients with CKD.

CLINICAL RELEVANCE

The impact of changes in serum biomarkers on oral and dental health is important for dentists' and medical professionals' approaches to patients' oral and systemic health.

Saliva based diagnostic methodologies for a fast track detection of autism spectrum disorder: A mini-review

Autism spectrum disorder (ASD) is considered a complicated neurodevelopment disorder with rising prevalence globally. ASD is characterized by a series of events including varying degrees of defects in communication, learning, and social interaction which is accompanied by stereotypical behavioral patterns. Despite extensive research, the current diagnosis for ASD is complex and almost solely based on the behavioral assessments of the suspected individuals. The multifactorial etiopathology of this disease along with the diversity of symptoms among different individuals adds to the current intricacies for accurate prognosis of ASD. Hence, there exists a dire need for biologically relevant biomarkers for an early diagnosis and for tracking the efficacy of therapeutic interventions. Until recently, among various biofluids, saliva has gained increasing interest for biomarker identification, the advantages include the non-invasive nature and ease of sample handling. This mini-review aims to provide a succinct summary of recent literature on saliva-based diagnostic modalities for ASD, examine various studies that highlight the potential use of proteomic and/or RNA-based biomarkers. Finally, some conclusive perspectives of using the salivary system for ASD mechanistic details and diagnosis are also discussed.

Association Between Salivary Cytokines, Chemokines and Growth Factors and Salivary Gland Function in Children with Chronic Kidney Disease

Introduction

Chronic kidney disease (CKD) is a systemic inflammatory disease that leads to multiple organ complications not only in the kidneys and the cardiovascular system, but also in the oral cavity. CKD children experience reduced saliva secretion (hyposalivation), which leads to increased incidence of dental caries and significant impairment of patients' quality of life. However, the causes of salivary gland dysfunction in children with CKD are unknown. The present study is the first to evaluate the inflammatory and anti-inflammatory profile in the saliva of children with CKD at different stages of renal failure with normal and reduced salivary gland function.

Methods

Thirty children with CKD (age 9-16) and thirty age- and gender-matched healthy children were classified for the study. Salivary inflammatory and anti-inflammatory profile were assayed using the multiplex ELISA assay.

Results

We demonstrated statistically significant changes in salivary pro-inflammatory (↑TNF-α, ↓IL-7), anti-inflammatory (↑IL-10), Th1 (↑INF-γ, ↑IL-15), Th2 (↑IL-4, ↑IL-5, ↑IL-6, ↑IL-9) and Th17 (IL-17) cytokines as well as chemokines (↑MCP-1/CCL-2, ↑MIP-1α/CCL3, ↓MIP-1β/CCL4, ↓EOTAXIN/CCL11) and growth factors (↑G-CSF, ↑FGF) in unstimulated saliva of children with CKD compared to the controls. Although the evaluation of the salivary inflammatory profile does not indicate a particular dominance of any of the branches of the immune system, we observed a statistically significant increase in the concentration of all Th2 cytokines assayed. The multivariate regression analysis showed that the content of salivary cytokines, chemokines and growth factors depends on the secretory function of the salivary glands, ie, salivary flow, total protein concentration and amylase activity in the saliva. Salivary MIP-1α/CCL3 was the most effective to differentiate children with CKD and hyposalivation from patients with normal saliva secretion.

Discussion

Inflammation is involved in salivary gland dysfunction in children with CKD, although further studies on in vitro and in vivo models are necessary to confirm this hypothesis.

Hyperreactivity of Salivary Alpha-Amylase to Acute Psychosocial Stress and Norepinephrine Infusion in Essential Hypertension

It is unknown whether the observed general physiological hyperreactivity to acute psychosocial stress in essential hypertension also extends to salivary alpha-amylase (sAA), a surrogate sympathetic nervous system marker. Here, we investigated sAA reactivity to acute psychosocial stress in essential hypertensive males (HT) as compared to normotensive controls (NT). To shed light on underlying mechanisms, we moreover tested for sAA reactivity following a standardized norepinephrine (NE) infusion. We hypothesized that both acute psychosocial stress and an NE infusion of similar duration would lead to greater sAA reactivity in HT than in NT. In the stress study, we examined sAA reactivity to 15 min of acute psychosocial stress induced by the Trier Social Stress Test (TSST) in 19 HT and 23 NT up to 40 min after stress. In the infusion study, 20 HT and 22 NT received a standardized NE infusion (5 μg/mL/min) over 15 min mimicking NE release in reaction to acute psychosocial stress. HT exhibited greater sAA reactivity to the TSST as compared to NT (p = 0.049, η_p² = 0.08, f = 0.29). In reaction to the standardized NE infusion, HT showed higher sAA reactivity as compared to NT (p = 0.033, η_p² = 1.00, f = 0.33). Our findings suggest stress-induced sAA hyperreactivity in essential hypertension that seems to be at least in part mediated by a higher reactivity to a standardized amount of NE in HT. With respect to clinical implications, sAA stress reactivity may serve as a noninvasive marker indicative of early cardiovascular risk.

A colorimetric electronic tongue for point-of-care detection of COVID-19 using salivary metabolites

The monitoring of profile concentrations of chemical markers in saliva samples can be used to diagnose COVID-19 patients, and differentiate them from healthy individuals. Here, this purpose is achieved by designing a paper-based colorimetric sensor with an origami structure, containing general receptors such as pH-sensitive organic dyes, Lewis donors or acceptors, functionalized nanoparticles, and ion metal complexes. The color changes taking place in the receptors in the presence of chemical markers are visually observed and recorded with a digital instrument. Different types and amounts of the chemical markers provide the sensor with a unique response for patients (60 samples) or healthy (55 samples) individuals. These two categories can be discriminated with 84.3% accuracy. This study evidences that the saliva composition of cured and healthy participants is different from each other with accuracy of 85.7%. Moreover, viral load values obtained from the rRT-PCR method can be estimated by the designed sensor. Besides COVID-19, it may possible to simultaneously identify smokers and people with kidney disease and diabetes using the specified electronic tongue. Due to its high efficiency, the prepared paper device can be employed as a rapid detection kit to detect COVID-19.

Application of a Novel Biosensor for Salivary Conductivity in Detecting Chronic Kidney Disease

The prevalence of chronic kidney disease (CKD) is increasing, and it brings an enormous healthcare burden. The traditional measurement of kidney function needs invasive blood tests, which hinders the early detection and causes low awareness of CKD. We recently designed a device with miniaturized coplanar biosensing probes for measuring salivary conductivity at an extremely low volume (50 μL). Our preliminary data discovered that the salivary conductivity was significantly higher in the CKD patients. This cross-sectional study aims to validate the relationship between salivary conductivity and kidney function, represented by the estimated glomerular filtration rate (eGFR). We enrolled 214 adult participants with a mean age of 63.96 ± 13.53 years, of whom 33.2% were male. The prevalence rate of CKD, defined as eGFR < 60 mL/min/1.73 m2, is 11.2% in our study. By multivariate linear regression analyses, we found that salivary conductivity was positively related to age and fasting glucose but negatively associated with eGFR. We further divided subjects into low, medium, and high groups according to the tertials of salivary conductivity levels. There was a significant trend for an increment of CKD patients from low to high salivary conductivity groups (4.2% vs. 12.5% vs. 16.9%, p for trend: 0.016). The receiver operating characteristic (ROC) curves disclosed an excellent performance by using salivary conductivity combined with age, gender, and body weight to diagnose CKD (AUC equal to 0.8). The adjusted odds ratio of CKD is 2.66 (95% CI, 1.10−6.46) in subjects with high salivary conductivity levels. Overall, salivary conductivity can serve as a good surrogate marker of kidney function; this real-time, non-invasive, and easy-to-use portable biosensing device may be a reliable tool for screening CKD.

Blood and Salivary Inflammatory Biomarkers Profile in Patients with Chronic Kidney Disease and Periodontal Disease: A Systematic Review

Introduction: Periodontitis is the most prevalent inflammatory disease worldwide. Its inflammatory levels spread systemically, which can be associated with chronic kidney disease. Biomarkers have the potential to diagnose and correlate periodontitis and chronic kidney disease, helping to monitor systemic inflammation. Thereby, this study aimed to analyze the association between chronic kidney disease and periodontitis by conducting a biomarker analysis on blood and saliva. Material and methods: An electronic search through PubMed/MEDLINE, EMBASE, and Web of Science databases was conducted to identify clinical studies published in the last ten years, with no language restrictions. Twelve articles met all the inclusion criteria, two randomized controlled trials, one cohort study, and nine observational studies. Results: The studies included a total of 117 patients for saliva biomarkers, with a mean age of approximately 57 years old, and 56.68% of the subjects were female. After analyzing all the included studies, it was possible to verify the following biomarkers assessed: CRP, WBC, fibrinogen, IL-4 and -6, cardiac troponin T, NOx, ADMA, albumin, osteocalcin, cystatin C, PGLYRP1, cholesterol, HDL, LDL, triglycerides, and hemoglobin. Conclusion: A direct cause–effect association between periodontitis and CKD could not be established. However, it was possible to conclude that there was a correlating effect present, through the analyzed biomarkers.

Salivary cytokine profile in patients with ischemic stroke

Inflammation plays a crucial role in stroke pathogenesis. Thus, it is not surprising that cytokines, chemokines, and growth factors have been advocated in stroke diagnostics. Our study is the first to evaluate the salivary cytokine profile in patients with ischemic stroke. Twenty-five patients with subacute ischemic stroke and an age-, sex-, and oral hygiene status-matched control group were enrolled in the study. The number of patients was set a priori based on our previous experiment (α = 0.05, test power = 0.9). Salivary concentrations of tumor necrosis factor α (TNF-α), interleukin 6 (IL-6), and interleukin 10 (IL-10) were assessed using an ELISA method. We showed that salivary TNF-α and IL-6 were significantly higher, whereas IL-10 content was statistically lower in both non-stimulated (NWS) and stimulated (SWS) whole saliva of ischemic stroke patients. However, evaluation of cytokines in NWS rather than in SWS may be of greater diagnostic value. Of particular note is salivary TNF-α, which may indicate cognitive/physical impairment in post-stroke individuals. This parameter distinguishes stroke patients from healthy controls and correlates with cognitive decline and severity of functional impairment. It also differentiates (with high sensitivity and specificity) stroke patients with normal cognition from mild to moderate cognitive impairment. Saliva may be an alternative to blood for assessing cytokines in stroke patients, although further studies on a larger patient population are needed.

Oxidative status in plasma, urine and saliva of girls with anorexia nervosa and healthy controls: a cross-sectional study

BACKGROUND

Anorexia nervosa (AN) is a serious psychosomatic disorder with unclear pathomechanisms. Metabolic dysregulation is associated with disruption of redox homeostasis that might play a pivotal role in the development of AN. The aim of our study was to assess oxidative status and carbonyl stress in plasma, urine and saliva of patients with AN and healthy controls.

METHODS

Plasma, spot urine, and saliva were collected from 111 girls with AN (aged from 10 to 18 years) and from 29 age-matched controls. Markers of oxidative stress and antioxidant status were measured using spectrophotometric and fluorometric methods.

RESULTS

Plasma advanced oxidation protein products (AOPP) and advanced glycation end products (AGEs) were significantly higher in patients with AN than in healthy controls (by 96, and 82%, respectively). Accordingly, urinary concentrations of AOPP and fructosamines and salivary concentrations of AGEs were higher in girls with AN compared with controls (by 250, and 41% in urine; by 92% in saliva, respectively). Concentrations of thiobarbituric acid reactive substances (TBARS) in saliva were 3-times higher in the patients with AN than in the controls. Overall antioxidants were lower in plasma of girls with AN compared to the controls, as shown by total antioxidant capacity and ratio of reduced and oxidized glutathione (by 43, and 31%, respectively).

CONCLUSIONS

This is the first study assessing wide range of markers of oxidative status in plasma, urine and saliva of the patients with AN. We showed that both, higher levels of markers of oxidative stress and lower antioxidants play a role in redox disruption. Restoration of redox homeostasis might be of the clinical relevance.

Salivary Biomarkers of Oxidative Stress and Inflammation in Stroke Patients: From Basic Research to Clinical Practice

Cerebral stroke is a serious worldwide health problem, as can be seen by the global epidemic of the disease. In this disorder, when the blood flow is compromised by ruptures or blocked arteries, sudden death of neurons is observed as a result of a lack of oxygen and nutrients. Numerous severe problems and frequent complications also exist in stroke patients; therefore, there is an urgent need to develop new therapeutic, diagnostic, and prognostic methods for the disease. At present, the diagnosis of stroke is based on a neurological examination, medical history, and neuroimaging, due to the fact that rapid and noninvasive diagnostic tests are unavailable. Nevertheless, oxidative stress and inflammation are considered key factors in stroke pathogenesis. Oxygen free radicals are responsible for oxidation of lipids, proteins, and DNA/RNA, which in turn contributes to oxidative damage of the brain. Toxic products of the oxidation reactions act cytostatically on the cell by damaging cell membranes and leading to neuronal death by apoptosis or necrosis. Thus, it seems that redox/inflammatory biomarkers might be used in the diagnosis of the disease. Nowadays, saliva is of increasing interest in clinical laboratory medicine. Redox biomarkers could be obtained easily, noninvasively, cheaply, and stress-free from saliva. This minireview is aimed at presenting the current knowledge concerning the use of salivary biomarkers of oxidative stress and inflammation in the diagnosis and prognosis of stroke.

Saliva as a tool for monitoring hemodialysis: a systematic review and meta-analysis

This study aimed to assess whether the reductions in serum urea and creatinine levels are different from the reductions in salivary urea and creatinine levels that occur after hemodialysis in chronic renal patients. The systematic review protocol was registered in the PROSPERO database. Eight databases were searched to identify pretest-posttest studies of chronic kidney disease patients undergoing hemodialysis, with no language or year restrictions. The JBI Critical Appraisal Tool was used to assess the risk of bias. Meta-analyses using random-effect models were conducted to compare salivary and serum correlations and to pooled mean and proportion differences from pre- to posthemodialysis urea and creatinine levels by subgroup analysis. The I2 test was used to assess heterogeneity, and a meta-regression was performed to statistically assess correlations and differences in the pooled effects pre- and postdialysis. The Grading of Recommendation, Assessment, Development, and Evaluation (GRADE) was used to assess the certainty of evidence. The search resulted in 1404 records, and only six studies (n = 252 participants) fulfilled the eligibility criteria and were included. The studies were published between 2013 and 2018. All studies showed a significant reduction in both salivary and serum urea/creatinine levels. All eligible studies presented a low risk of bias. The meta-analysis shows a moderate to high correlation between salivary and blood levels of urea (r: 0.79; 95% CI: 0.56-1.00) and creatinine (r: 0.64; 95%CI: 0.16-1.00), with a very low level of certainty. The reductions in salivary urea and creatinine levels are similar to and correlated with the reductions in blood urea and creatine levels after hemodialysis among chronic kidney disease patients.

Dynamics of salivary markers of kidney functions in acute and chronic kidney diseases

Saliva can be used as an alternative diagnostic fluid enabling easy and non-invasive disease monitoring. Urea and creatinine can be measured in saliva and both were shown to be increased in renal failure. However, the dynamics of these markers during the development of kidney diseases is unknown. We aimed to describe the dynamics of salivary urea and creatinine in various animal models of acute kidney injury (AKI) and chronic kidney disease (CKD) and in patients with different stages AKI or CKD. Ninety Wistar rats underwent bilateral nephrectomy (BNX), ischemia–reperfusion injury (IRI) or glycerol-induced kidney injury to model AKI. CKD was modelled using 5/6 nephrectomy. In the clinical part 57 children aged 12.6 ± 4.9 years with AKI (n = 11) or CKD (n = 46) and 29 healthy controls (aged 10.2 ± 3.7 years) were enrolled. Saliva and blood samples were collected in both, animal experiments and the human study. In animal models of AKI, plasma urea and creatinine were higher than in controls. An increase of salivary urea and creatinine (twofold) was observed in BNX and IRI, but only after 12 h and 24 h, respectively. In glycerol nephropathy and 5/6 nephrectomy, salivary urea increased (by 100% and by 50%), while salivary creatinine did not change during the observation period. Salivary urea and creatinine were significantly higher in all patients compared to controls (threefold) and in both, AKI and CKD they were associated with the severity of renal failure. Plasma and salivary concentrations correlated only in children with renal failure (R = 0.72 for urea; R = 0.93 for creatinine), but not in controls (R = -0.007 for urea; R = 0.02 for creatinine). Our study indicates that during the development of renal impairment saliva could be used for non-invasive monitoring in higher stages of AKI or CKD, rather than for screening of early stages of kidney diseases.

Saliva as an alternative to blood in the determination of uremic state in adult patients with chronic kidney disease: a systematic review and meta-analysis

OBJECTIVES

To assess whether salivary urea and creatinine levels accurately reflect their serum levels in blood samples of adults to detect chronic kidney disease.

MATERIALS AND METHODS

A systematic review was conducted in eight electronic databases. The protocol was registered in PROSPERO. Only diagnostic test studies were included. The JBI critical appraisal tools assessed the risk of bias. A meta-analysis of proportions was performed. The GRADE tool assessed the quality of evidence and strength of recommendation across the studies included.

RESULTS

Eight studies met the eligibility criteria and were included. Six studies assessed salivary urea, and six studies assessed salivary creatinine. All studies presented moderate risk of bias. The meta-analysis depicted an overall sensitivity of 93.3% (95% CI = 88.6; 97.9) for salivary creatinine levels and 87.5% (95% CI = 83.2; 91.8) for salivary urea levels, while the overall specificity was 87.1% (95% CI = 82.8; 91.3) and 83.2% (95% CI = 65.0; 101.4) for salivary creatinine and urea levels, respectively. The overall accuracy of salivary creatinine was 5.2 percentage points higher compared with salivary urea levels (90.8% vs. 85.6%). According to the GRADE tool, the analysed outcomes were classified as having low to moderate level of certainty.

CONCLUSION

Compared with blood samples, salivary urea and creatinine levels presented high diagnostic values for chronic kidney disease screening, but should not be considered equivalent to levels obtained from blood at stages three, four, or five of the disease.

CLINICAL SIGNIFICANCE

Chronic kidney disease patients could receive a clinically significant benefit from replacing blood with saliva for potentially monitoring renal function. Saliva collection presents greater simplicity, comfort, safety, and lower collection cost.

Saliva for assessing creatinine, uric acid, and potassium in nephropathic patients

Background

Lab tests on saliva could be useful because of low invasivity. Previous reports indicated that creatinine, uric acid, and potassium are measurable in saliva. For these analytes the study investigated methodology of saliva tests and correlations between plasma and saliva levels.

Methods

The study enrolled 15 healthy volunteers for methodological analyses and 42 nephropathic patients for plasma-saliva correlations (35 non-dialysis and 7 dialysis). Saliva was collected by synthetic swap right after venipuncture for blood withdrawal. Blood and saliva, unless otherwise indicated, were collected early in the morning after overnight fast and lab tests were performed in fresh samples by automated biochemistry (standard). Methodological analyses included blind duplicates, different collection mouth sites, day-to-day variability, different collection times, and freezing-thawing effects. Analyses on plasma-saliva correlations included post-dialysis changes.

Results

For saliva lab tests of all analytes, blind duplicates, samples from different mouth sites or of different days were not significantly different but were significantly correlated (differences ≤14.4%; R ≥ 0.620, P ≤ 0.01). For all analytes, mid-morning saliva had lower levels than but correlated with standard saliva (differences ≥15.8%; R ≥ 0.728, P ≤ 0.01). Frozen-thawed saliva had lower levels than fresh saliva for uric acid only (− 17.2%, P < 0.001). Frozen-thawed saliva correlated with fresh saliva for all analytes (R ≥ 0.818, P ≤ 0.001). Saliva and plasma levels differed but correlated with plasma for creatinine (R = 0.874, P < 0.001), uric acid (R = 0.821, P < 0.001) and potassium (R = 0.767, P < 0.001). Post-dialysis changes in saliva paralleled post-dialysis changes in plasma.

Conclusion

Saliva levels of creatinine, uric acid, and potassium are measurable and correlated with their plasma levels. Early morning fasting fresh saliva samples are advisable because later collection times or freezing lower the saliva levels of these analytes.

Urea and creatinine levels in saliva of patients with and without periodontitis

Despite the fact that saliva contains measurable concentrations of urea and creatinine, it is not widely used in clinical nephrology. One of the reasons is the high inter- and intra-individual variability in the salivary markers of kidney function. We hypothesized that gingival bleeding in patients with periodontitis could contribute to this variability by increasing the concentration of salivary urea or creatinine. Samples were collected from 25 patients with periodontitis and 29 healthy controls. In addition, saliva samples from five healthy volunteers were artificially contaminated with blood. The concentration of urea, but not that of creatinine, was more than twice as high in patients with periodontitis than in controls. Artificial contamination of saliva with blood did not affect the salivary concentration of creatinine. Salivary urea increased only with very high levels of contamination (≥2.5% blood in saliva), but that did not occur in patients. In conclusion, periodontitis increases the concentration of salivary urea, but this is not likely to be a result of contamination with blood. Future studies should investigate the composition of the oral microbiome, specifically regarding how it affects the concentration of salivary urea. Salivary creatinine seems to be a more robust non-invasive marker of renal functions than salivary urea.

PSO optimized 1-D CNN-SVM architecture for real-time detection and classification applications

In this paper, we propose a novel Particle Swarm Optimized (PSO) One-Dimensional Convolutional Neural Network with Support Vector Machine (1-D CNN-SVM) architecture for real-time detection and classification of diseases. The performance of the proposed architecture is validated with a novel hardware model for detecting Chronic Kidney Disease (CKD) from saliva samples. For detecting CKD, the urea concentration in the saliva sample is monitored by converting it into ammonia. The urea on hydrolysis in the presence of urease enzyme produces ammonia. This ammonia is then measured using a semiconductor gas sensor. The sensor response is given to the proposed architecture for feature extraction and classification. The performance of the architecture is optimized by regulating the parameter values using a PSO algorithm. The proposed architecture outperforms current conventional methods, as this approach is a combination of strong feature extraction and classification techniques. Optimal features are extracted directly from the raw signal, aiming to reduce the computational time and complexity. The proposed architecture has achieved an accuracy of 98.25%.

Dental condition and salivary characteristics in Vietnamese patients with chronic kidney disease

OBJECTIVES

To determine the dental status and salivary characteristics and to analyse the correlation between creatinine clearance with DMFT index and salivary flow rate in Vietnamese patients with chronic kidney disease (CKD).

METHODS

This study was conducted on 111 CKD and 109 non-CKD patients. The socio-demographic characteristics associated with dental habits and xerostomia status were recorded from a self-administered questionnaire. Dental status (DT, MT, FT) and salivary characteristics (flow rate; pH; buffering capacity; urea and creatinine concentrations) were examined. The multivariate regression models were used to assess the correlation of creatinine clearance with DMFT index and salivary flow rate with adjustment for confounders.

RESULTS

Patients with CKD made MT and DMFT indices significantly higher than non-CKD subjects. Chronic kidney disease patients had reduced salivary flow rate; but higher xerostomia level, salivary pH and buffering capacity than those in non-CKD subjects. Results of multivariate regression models showed that with lower creatinine clearance 1 mL/min, DMF index was higher 0.02 teeth, and salivary flow rate lower 0.003 mL/min.

CONCLUSIONS

There were no differences in dental status between patients with CKD and those without CKD, except that poor renal function is directly related with a higher DMFT index and lower salivary flow rate. Dental professionals should pay greater attention to oral problems during the progression of CKD to prevent deterioration of oral health.

Salivary creatinine and urea are higher in an experimental model of acute but not chronic renal disease

Plasma creatinine and urea are commonly used markers of kidney function in both acute and chronic renal failure. The needed repeated blood collection is associated with pain, stress and might lead to infections. Saliva has the potential to be a non-invasive alternative diagnostic fluid. The use of saliva in clinical practice is limited, since many factors affect the concentration of salivary biomarkers. The aim of our study was to analyze salivary creatinine and urea in the animal models of acute and chronic renal disease. Bilateral nephrectomy and adenine nephropathy were induced in adult male mice. Both, plasma creatinine and urea were higher in animals with renal failure compared to controls. Salivary creatinine was higher by 81% and salivary urea by 43% in comparison to the control group, but only in animals with bilateral nephrectomy and not in adenine nephropathy. Our results indicate that the increase of salivary creatinine and urea depends on the experimental model of renal failure and its severity. Further studies are needed to monitor the dynamics of salivary markers of renal function and to reveal determinants of their variability.

Salivary levels of phosphorus and urea as indices of their plasma levels in nephropathic patients

BACKGROUND

Phosphorus and urea are measurable in saliva. Measurements of saliva phosphorus (S-Pho) and saliva urea (S-Urea) could be useful because of low invasivity. Data are limited to saliva tests methodology and to correlations between plasma and saliva compositions. S-Pho and S-Urea were investigated focusing on blind duplicates, differences between collection sites, differences between collection times, freezing-thawing effects, and plasma-saliva correlations.

METHODS

Tests were performed using fresh saliva collected by synthetic swap early morning after overnight fast (standard). Methodology was investigated in fifteen healthy volunteers. Plasma-saliva correlations were investigated in thirty nephropathic outpatients.

RESULTS

S-Pho and S-Urea in all measurements ranged above detection limits (0.3 mmol/L). In healthy volunteers, S-Pho and S-Urea were similar in duplicates (results for S-Pho and S-Urea: % difference between samples ≤ 4.85%; R between samples ≥ .976, P < .001), in samples from different mouth sites (≤4.24%; R ≥ .887, P < .001), and in samples of different days (≤5.61%; R ≥ .606, P < .01) but, compared to standard, were substantially lower in after-breakfast samples (-28.0% and -21.3%; R ≥ .786, P < .001) and slightly lower in frozen-thawed samples (-12.4% and -5.92%; R ≥ .742, P < .001). In nephropathic patients, S-Pho was higher than but correlated with plasma phosphorus (saliva/plasma ratio 4.80; R = .686, P < .001), whereas S-Urea and plasma urea were similar and correlated with each other (saliva/plasma ratio 0.96; R = .944, P < .001). Post-dialysis changes in S-Pho and S-Urea paralleled post-dialysis changes in plasma phosphorus and urea.

CONCLUSION

S-Pho and S-Urea reflect plasma phosphorus and plasma urea. Early morning fasting fresh samples are advisable because collection time and freezing-thawing affect saliva tests.

Validation of the salivary urea and creatinine tests as screening methods of chronic kidney disease in Vietnamese patients

OBJECTIVES

The aims of this case control study were to correlate the serum and salivary urea as well as creatinine levels; and to evaluate salivary urea and creatinine as noninvasive alternatives to serum for creatinine estimation in chronic kidney disease (CKD) patients.

METHODS

Blood and saliva samples were collected from 112 CKD patients and 108 subjects without CKD for quantitative analysis of urea and creatinine. Spearman's correlation coefficients between salivary and serum urea as well as creatinine were obtained. Receiver operating characteristic analysis was done to assess the diagnostic tests of salivary urea and creatinine. Cut-off values were determined based on the best trade-off between the sensitivity and specificity for both salivary urea and creatinine.

RESULTS

Salivary urea and creatinine concentrations were significantly higher in CKD patients than those in control subjects; and increased by the stages of the severity of the disease. The positive correlation was significantly found between salivary and serum creatinine (r  =  0.90) and between salivary and serum urea (r  =  0.73). Area under the curve for salivary urea was 0.76 and a cut-off value of 14.25 mmol/L gave a sensitivity of 82.9% and specificity of 57.8%. Area under the curve for salivary creatinine was 0.92 and a cut-off value of 0.24 mg/dL gave a sensitivity of 86.5% and specificity of 87.2%.

CONCLUSIONS

Both salivary urea and creatinine have a high capacity for serum creatinine estimation. Salivary urea and creatinine tests can be used as low-cost, easily accessible and noninvasive tools for screening, diagnosing, monitoring treatment outcomes and ascertaining prognosis of chronic kidney disease.

Production of encapsulated creatinase using yeast spores

Yeast spores can be used as a carrier to produce enzyme capsules. In the present study, this technique was applied to a diagnostic enzyme named creatinase. We found that a secretory form of Pseudomonas putida creatinase could be entrapped in the spore wall, and such spores were used as creatinase capsules. The activity of the encapsulated creatinase was largely improved by mild spore wall defective mutations, such as DIT1 or OSW2 deletions. The advantages of this method include the following: encapsulated and freeze-dried creatinase is produced without preparing the purified enzyme, and it exhibits resistance to environmental stresses, such as high temperature and SDS treatments. Thus, yeast spores could be applied to establish quick and easy clinical diagnostic methods.