Non-invasive monitoring of gingival crevicular fluid for estimation of blood glucose level

The Need to Pair Molecular Monitoring Devices with Molecular Imaging to Personalize Health

By enabling the non-invasive monitoring and quantification of biomolecular processes, molecular imaging has dramatically improved our understanding of disease. In recent years, non-invasive access to the molecular drivers of health versus disease has emboldened the goal of precision health, which draws on concepts borrowed from process monitoring in engineering, wherein hundreds of sensors can be employed to develop a model which can be used to preventatively detect and diagnose problems. In translating this monitoring regime from inanimate machines to human beings, precision health posits that continual and on-the-spot monitoring are the next frontiers in molecular medicine. Early biomarker detection and clinical intervention improves individual outcomes and reduces the societal cost of treating chronic and late-stage diseases. However, in current clinical settings, methods of disease diagnoses and monitoring are typically intermittent, based on imprecise risk factors, or self-administered, making optimization of individual patient outcomes an ongoing challenge. Low-cost molecular monitoring devices capable of on-the-spot biomarker analysis at high frequencies, and even continuously, could alter this paradigm of therapy and disease prevention. When these devices are coupled with molecular imaging, they could work together to enable a complete picture of pathogenesis. To meet this need, an active area of research is the development of sensors capable of point-of-care diagnostic monitoring with an emphasis on clinical utility. However, a myriad of challenges must be met, foremost, an integration of the highly specialized molecular tools developed to understand and monitor the molecular causes of disease with clinically accessible techniques. Functioning on the principle of probe-analyte interactions yielding a transducible signal, probes enabling sensing and imaging significantly overlap in design considerations and targeting moieties, however differing in signal interpretation and readout. Integrating molecular sensors with molecular imaging can provide improved data on the personal biomarkers governing disease progression, furthering our understanding of pathogenesis, and providing a positive feedback loop toward identifying additional biomarkers and therapeutics. Coupling molecular imaging with molecular monitoring devices into the clinical paradigm is a key step toward achieving precision health.

Gingival Crevicular Blood as a Potential Screening Tool: A Cross Sectional Comparative Study

Background: Diabetes is known to be one of the major global epidemic diseases, significantly associated with mortality and morbidity worldwide, conferring a substantial burden to the health care system. The epidemiological transition of this chronic disease tends to worsen unless preventive health strategies are implemented. Appropriate screening devices and standardized methods are crucial to prevent this potentially inauspicious life condition. Currently, the glucometer is the conventional device employed for blood glucose level determination that outputs the blood glucose reading. Glucometer performed in the dental office may be an important device in screening diabetes, so it can be addressed during a periodontal examination. Because gingival blood is a useful source to detect the glucose level, the focus is placed on the opportunity that might provide valuable diagnostic information. This study aimed to compare gingival crevicular blood with finger-stick blood glucose measurements using a self-monitoring glucometer, to evaluate whether gingival crevicular blood could be an alternative to allow accurate chairside glucose testing. Methods: A cross-sectional comparative study was performed among a 31–67-year-old population. Seventy participants with diagnosed type 2 diabetes and seventy healthy subjects, all with positive bleeding on probing, were enrolled. The gingival crevicular blood was collected using a glucometer to estimate the blood glucose level and compared with finger-stick blood glucose level. Results: The mean capillary blood glucose and gingival crevicular blood levels from all samples were, respectively, 160.42 ± 31.31 mg/dL and 161.64 ± 31.56 mg/dL for diabetic participants and 93.51 ± 10.35 mg/dL and 94.47 ± 9.91 mg/dL for healthy patients. In both groups, the difference between gingival crevicular blood and capillary blood glucose levels was non-significant (P < 0.05). The highly significant correlation between capillary blood glucose and gingival crevicular blood (r = 0.9834 for diabetic patients and r = 0.8153 for healthy participants) in both the groups was found. Conclusions: Gingival crevicular blood test was demonstrated as a feasible and useful primary screening tool test for detecting diabetes and for glucose estimation in non-diabetic patients. Use of gingival crevicular blood for screening is an attractive way of identifying a reasonable option of finger-stick blood glucose measurement under the appropriate circumstances. Rapid assessment may precede diagnostic evaluation in diabetic as well as healthy patients with acute severe bleeding. In addition, gingival crevicular blood levels may be needed to monitor the diabetic output.

Feasibility study of portable microwave microstrip open-loop resonator for non-invasive blood glucose level sensing: proof of concept

Self-management of blood glucose level is part and parcel of diabetes treatment, which involves invasive, painful, and uncomfortable methods. A proper non-invasive blood glucose monitor (NIBGM) is therefore desirable to deal better with it. Microwave resonators can potentially be used for such a purpose. Following the positive results from an in vitro previous work, a portable device based upon a microwave resonator was developed and assessed in a multicenter proof of concept. Its electrical response was analyzed when an individual's tongue was placed onto it. The study was performed with 352 individuals during their oral glucose tolerance tests, having four measurements per individual. The findings revealed that the accuracy must be improved before the diabetes community can make real use of the device. However, the relationship between the measuring parameter and the individual's blood glucose level is coherent with that from previous works, although with higher data dispersion. This is reflected in correlation coefficients between glycemia and the measuring magnitude consistently negative, although small, for the different datasets analyzed. Further research is proposed, focused on system improvements, individual calibration, and multitechnology approach. The study of the influence of other blood components different to glucose is also advised. Graphical abstract.

Glucose Concentration Measurement in Human Blood Plasma Solutions with Microwave Sensors

Three microwave sensors are used to track the glucose level of different human blood plasma solutions. In this paper, the sensors are evaluated as glucose trackers in a context close to real human blood. Different plasma solutions sets were prepared from a human blood sample at several added glucose concentrations up to 10 wt%, adding also ascorbic acid and lactic acid at different concentrations. The experimental results for the different sensors/solutions combinations are presented in this work. The sensors show good performance and linearity as glucose level retrievers, although the sensitivities change as the rest of components vary. Different sensor behaviors depending upon the concentrations of glucose and other components are identified and characterized. The results obtained in terms of sensitivity are coherent with previous works, highlighting the contribution of glucose to the dielectric losses of the solution. The results are also consistent with the frequency evolution of the electromagnetic signature of glucose found in the literature, and are helpful for selecting frequency bands for sensing purposes and envisioning future approaches to the challenging measurement in real biological contexts. Discussion of the implications of the results and guidelines for further research and development of more accurate sensors is offered.

Saliva-based biosensors: noninvasive monitoring tool for clinical diagnostics

Saliva is increasingly recognised as an attractive diagnostic fluid. The presence of various disease signalling salivary biomarkers that accurately reflect normal and disease states in humans and the sampling benefits compared to blood sampling are some of the reasons for this recognition. This explains the burgeoning research field in assay developments and technological advancements for the detection of various salivary biomarkers to improve clinical diagnosis, management, and treatment. This paper reviews the significance of salivary biomarkers for clinical diagnosis and therapeutic applications, with focus on the technologies and biosensing platforms that have been reported for screening these biomarkers.

Metabolite cross-feeding enhances virulence in a model polymicrobial infection

Microbes within polymicrobial infections often display synergistic interactions resulting in enhanced pathogenesis; however, the molecular mechanisms governing these interactions are not well understood. Development of model systems that allow detailed mechanistic studies of polymicrobial synergy is a critical step towards a comprehensive understanding of these infections in vivo. In this study, we used a model polymicrobial infection including the opportunistic pathogen Aggregatibacter actinomycetemcomitans and the commensal Streptococcus gordonii to examine the importance of metabolite cross-feeding for establishing co-culture infections. Our results reveal that co-culture with S. gordonii enhances the pathogenesis of A. actinomycetemcomitans in a murine abscess model of infection. Interestingly, the ability of A. actinomycetemcomitans to utilize L-lactate as an energy source is essential for these co-culture benefits. Surprisingly, inactivation of L-lactate catabolism had no impact on mono-culture growth in vitro and in vivo suggesting that A. actinomycetemcomitans L-lactate catabolism is only critical for establishing co-culture infections. These results demonstrate that metabolite cross-feeding is critical for A. actinomycetemcomitans to persist in a polymicrobial infection with S. gordonii supporting the idea that the metabolic properties of commensal bacteria alter the course of pathogenesis in polymicrobial communities.

Many bacterial infections are not the result of colonization and persistence of a single pathogenic microbe in an infection site but instead the result of colonization by several. Although the importance of polymicrobial interactions and pathogenesis has been noted by many prominent microbiologists including Louis Pasteur, most studies of pathogenic microbes have focused on single organism infections. One of the primary reasons for this oversight is the lack of robust model systems for studying bacterial interactions in an infection site. Here, we use a model co-culture system composed of the opportunistic oral pathogen Aggregatibacter actinomycetemcomitans and the common oral commensal Streptococcus gordonii to assess the impact of polymicrobial growth on pathogenesis. We found that the abilities of A. actinomycetemcomitans to persist and cause disease are enhanced during co-culture with S. gordonii. Remarkably, this enhanced persistence requires A. actinomycetemcomitans catabolism of L-lactate, the primary metabolite produced by S. gordonii. These data demonstrate that during co-culture growth, S. gordonii provides a carbon source for A. actinomycetemcomitans that is necessary for establishing a robust polymicrobial infection. This study also demonstrates that virulence of an opportunistic pathogen is impacted by members of the commensal flora.

Characteristics of inflammation common to both diabetes and periodontitis: are predictive diagnosis and targeted preventive measures possible?

Diabetes and periodontitis are chronic inflammatory disorders that contribute to each others' severity and worsen each others' prognosis. Studies have shown that patients with diabetes are at increased risk of developing periodontitis, and that diabetics with untreated periodontitis have more difficulty controlling serum glucose. Periodontal treatment that reduces gingival inflammation aids in the control of hyperglycemia. Periodontitis is accompanied by gingival bleeding and the production of an inflammatory exudate termed gingival crevicular fluid (GCF) that arises from the inflamed gingival tissues surrounding the teeth. GCF contains byproducts of connective tissue degradation, enzymes from host and bacterial cells, cytokines and other inflammatory mediators, and has been studied for screening blood glucose and for biomarkers of both diabetes and periodontitis. This review focuses on the inter-relationship between diabetes and periodontitis and the biomarkers common to both these diseases that may enable earlier detection, targeted preventive measures and individualized therapeutic intervention of these chronic conditions.

The potential use of gingival crevicular blood for measuring glucose to screen for diabetes: an examination based on characteristics of the blood collection site

BACKGROUND

This study examined conditions under which gingival crevicular blood (GCB) could be used to obtain a useful glucose reading to screen for undiagnosed diabetes during routine dental visits.

METHODS

GCB and capillary finger-stick blood (CFB) glucose readings obtained with a glucometer were compared for 46 patients recruited from an urban university dental clinic. Study participants were divided into two groups based on probing depth or bleeding on probing (BOP) at the site of collection of the GCB sample. Group 1 participants had blood collected from sites with adequate BOP to obtain a sample without touching the tooth or gingival margin, whereas group 2 participants had blood collected from sites with little or no bleeding. For each group, Pearson correlations were calculated for glucose readings obtained using GCB and CFB samples, and the limits of agreement between the two samples were examined.

RESULTS

For group 1 participants, correlations between CFB and GCB glucose readings were high (0.89), and the limits of agreement were acceptable (-27.1 to 29.7). By contrast, for participants in group 2, correlations between the glucose readings were lower (0.78), and limits of agreement were much broader (-25.1 to 80.5).

CONCLUSION

GCB samples were suitable to screen for diabetes in persons with sufficient BOP to obtain a sample without touching the tooth or gingival margin (i.e., in patients having the basic clinical signs of gingivitis or periodontal disease).

Polymicrobial interactions stimulate resistance to host innate immunity through metabolite perception

Bacteria in the human oral cavity often grow in an attached multispecies biofilm community. Members of this community display defined interactions that have an impact on the physiology of the individual and the group. Here, we show that during coculture growth with streptococci, the oral pathogen Aggregatibacter actinomycetemcomitans displays enhanced resistance to killing by host innate immunity. The mechanism of resistance involves sensing of the streptococcal metabolite hydrogen peroxide by A. actinomycetemcomitans, which stimulates a genetic program resulting in enhanced expression of the complement resistance protein ApiA. The oxidative stress response regulator OxyR mediates induction of apiA transcription, and this induction is required for coculture resistance to killing by human serum. These findings provide evidence that interaction between community members mediates prokaryotic resistance to host innate immunity and reinforce the need to understand how polymicrobial growth affects interaction with the host immune system.

A novel exclusion mechanism for carbon resource partitioning in Aggregatibacter actinomycetemcomitans

The bacterium Aggregatibacter actinomycetemcomitans is a common commensal of the human oral cavity and the putative causative agent of the disease localized aggressive periodontitis. A. actinomycetemcomitans is a slow-growing bacterium that possesses limited metabolic machinery for carbon utilization. This likely impacts its ability to colonize the oral cavity, where growth and community composition is mediated by carbon availability. We present evidence that in the presence of the in vivo relevant carbon substrates glucose, fructose, and lactate A. actinomycetemcomitans preferentially metabolizes lactate. This preference for lactate exists despite the fact that A. actinomycetemcomitans grows faster and obtains higher cell yields during growth with carbohydrates. The preference for lactate is mediated by a novel exclusion mechanism in which metabolism of lactate inhibits carbohydrate uptake. Coculture studies reveal that A. actinomycetemcomitans utilizes lactate produced by the oral bacterium Streptococcus gordonii, suggesting the potential for cross-feeding in the oral cavity.

Control oriented model of insulin and glucose dynamics in type 1 diabetics

The aim of the study was to realize a mathematical model of insulin-glucose relationship in type I diabetes and test its effectiveness for the design of control algorithms in external artificial pancreas. A new mathematical model, divided into glucose and insulin sub-models, was developed from the so-called "minimal model". The key feature is the representation of insulin sensitivity so as to permit the personalisation of the parameters. Real-time applications are based on an insulin standardised model. Clinical data were used to estimate model parameters. Root mean square error between simulated and real blood glucose profiles (G(rms)) was used to evaluate system efficacy. Results from parameter estimation and insulin standardisation showed a good capability of the model to identify individual characteristics. Simulation results with a G(rms) 1.30 mmol/l in the worst case testified the capacity of the model to accurately represent glucose-insulin relationship in type 1 diabetes allowing self tuning in real time.

Error Grid Analysis of Noninvasive Glucose Monitoring Via Gingival Crevicular Fluid

In order to realize a noninvasive blood glucose monitor, we monitored the gingival crevicular fluid (GCF). In this paper, the clinical evaluations were performed on not only normal subjects but also diabetic subjects using a GCF-glucose monitor to determine blood glucose levels. Meal load tests were carried out and the time-course changes in blood glucose level and GCF glucose level were measured continuously. A positive correlation of more than 0.9 was found between blood glucose level and GCF glucose level, necessitating the calibration of individual correlations for every subject. Finally, the performance of the GCF-glucose monitor was evaluated using Error Grid Analysis. As the results, significant information for the glucose level decision was obtained not only for normal subjects, but also for diabetic subjects.

Evaluation of Time-Course Changes of Gingival Crevicular Fluid Glucose Levels in Diabetics

A minute volume such as a few hundred nano-litres of gingival crevicular fluid (GCF) will evaporate within one minute at room temperature after collection. In order to investigate the feasibility of a method for noninvasive blood glucose measurement using this fluid, a fabricated GCF-collecting device, and the time-course changes of blood and GCF glucose levels in diabetics were evaluated. As a result of improvement in the GCF-collecting device such that the color of a filter paper changed from white to black upon collection of the sample, the completion of the collecting procedure could be visually confirmed. Using this device, we succeeded in collecting 200 nl of GCF within 30 s, despite the fact that GCF is usually secreted at a rate between 2 and 3 microl per tooth per hour. This method could be applicable for collecting small volume of other biological fluids. The time-course changes of blood and GCF glucose levels in ten type 2 diabetic subjects were examined, the correlation coefficient, R, between both glucose levels was 0.878. The result proved to be similar to that for normal healthy subjects in a previous study. A significant time difference between the two glucose levels was not observed. In diabetes period of 4.8 +/- 1.7 years, the influence of the disease on the GCF glucose level was minimal. Furthermore, from the ROC curve analysis, both sensitivity and specificity showed favorable results. It was suggested that the measurement of GCF glucose levels was a promising screening method for diabetics.

Point of care testing system via enzymatic method for the rapid, efficient assay of glycated albumin

The ratio of glycated albumin to albumin concentration in serum is termed the glycated albumin (GA) value. The GA value provides a time-averaged index of the state of glycemic control for the previous 2 weeks. In this study, a dry chemistry system (GA monitor) via an enzymatic method was proposed in order to provide a GA value measurement for point of care testing (POCT). The GA monitor was made from three devices a set of test-tapes, a test-strip and an optical analyzer. A GA test-tape, a ketoamine test-tape and an albumin test-tape were enclosed in the fabricated test-strip. Time-course changes of the optical characteristics were evaluated using the test-strip. It was found that the three test tapes must be enclosed in the test-strip to create a dry chemistry system for small sample volumes (20 microl). A temperature control unit, which could hold the temperature of the GA test-tape at 45 degrees C and at 25 degrees C for the other two types of test-tape was incorporated into the optical analyzer. With the GA test-tape held separately and controlled at 45 degrees C, the analytical time decreased to one-third of the time taken for the three tapes at 25 degrees C. The analytical accuracy of the three types of test-tape showed favorable results, with R2 values of 0.96-0.98 and coefficients of variation (CV) of 2.4-6.8%. Compared with a commercially available liquid chemistry system, the analytical accuracy of the GA monitor exhibited a relatively favorable linearity of R=0.82. According to these results, a new GA value analytical system was realized, in which the GA value could be assayed within five minutes using only 20 microl of blood sample with a disposable test-strip. This system could potentially be used for clinical purposes as test equipment for rapid and efficient POCT.