THE DISTRIBUTION OF GLUCOSE IN HUMAN BLOOD

Impact on result interpretation of correct and incorrect selection of veterinary glucometer canine and feline settings

Veterinary glucometers should be correctly coded for the patient species; however, coding errors occur in clinical settings and the impact of such errors has not been characterized. We compared glucose concentrations in 127 canine and 37 feline samples using both canine and feline settings on a veterinary glucometer (AlphaTrak; Zoetis). All samples were measured first on the canine setting and then measured using the feline setting. Glucose concentration was also measured using a central laboratory biochemical analyzer (Cobas c311; Roche). Three data comparisons for each species were investigated: incorrectly coded glucometer vs. correctly coded glucometer, correctly coded glucometer vs. Cobas c311, and incorrectly coded glucometer vs. Cobas c311. For each comparison, the following analyses were conducted: Spearman rank correlation coefficient, Bland-Altman difference plot analysis, mountain plot analysis, and Deming regression. For clinical context, Clarke error grids were constructed. There was high positive correlation for all comparisons with both species. For all comparisons, mean difference was low (-0.7 to 0.5 mmol/L for canine samples, 1.0-2.0 mmol/L for feline samples). Incorrect glucometer coding resulted in proportional bias for canine samples and positive constant bias for feline samples, and individual differences could be large (-4.44 mmol/L for one dog, 6.16 mmol/L for one cat). Although the glucometer should be used per the manufacturer's recommendation, coding errors are unlikely to have severe adverse clinical consequences for most patients based on error grid analysis.

Non-invasive blood glucose sensing by machine learning of optic fiber-based speckle pattern variation

SIGNIFICANCE

The ability to perform frequent non-invasive monitoring of glucose in the bloodstream is very applicable for diabetic patients.

AIM

We experimentally verified a non-invasive multimode fiber-based technique for sensing glucose concentration in the bloodstream by extracting and analyzing the collected speckle patterns.

APPROACH

The proposed sensor consists of a laser source, digital camera, computer, multimode fiber, and alternating current (AC) generated magnetic field source. The experiments were performed using a covered (with cladding and jacket) and uncovered (without cladding and jacket) multimode fiber touching the skin under a magnetic field and without it. The subject's finger was placed on a fiber to detect the glucose concentration. The method tracks variations in the speckle patterns due to light interaction with the bloodstream affected by blood glucose.

RESULTS

The uncovered fiber placed above the finger under the AC magnetic field (150 G) at 140 Hz was found to have a lock-in amplification role, improving the glucose detection precision. The application of the machine learning algorithms in preprocessed speckle pattern data increase glucose measurement accuracy. Classification of the speckle patterns for uncovered fiber under the AC magnetic field allowed for detection of the blood glucose with high accuracy for all tested subjects compared with other tested configurations.

CONCLUSIONS

The proposed technique was theoretically analyzed and experimentally validated in this work. The results were verified by the traditional finger-prick method, which was also used for classification as a conventional reference marker of blood glucose levels. The main goal of the proposed technique was to develop a non-invasive, low-cost blood glucose sensor for easy use by humans.

Revisiting glucose regulation in birds - A negative model of diabetes complications

Birds naturally have blood glucose concentrations that are nearly double levels measured for mammals of similar body size and studies have shown that birds are resistant to insulin-mediated glucose uptake into tissues. While a combination of high blood glucose and insulin resistance is associated with diabetes-related pathologies in mammals, birds do not develop such complications. Moreover, studies have shown that birds are resistant to oxidative stress and protein glycation and in fact, live longer than similar-sized mammals. This review seeks to explore how birds regulate blood glucose as well as various theories that might explain their apparent resistance to insulin-mediated glucose uptake and adaptations that enable them to thrive in a state of relative hyperglycemia.

Vitamin B6 deficiency disrupts serotonin signaling in pancreatic islets and induces gestational diabetes in mice

In pancreatic islets, catabolism of tryptophan into serotonin and serotonin receptor 2B (HTR2B) activation is crucial for β-cell proliferation and maternal glucose regulation during pregnancy. Factors that reduce serotonin synthesis and perturb HTR2B signaling are associated with decreased β-cell number, impaired insulin secretion, and gestational glucose intolerance in mice. Albeit the tryptophan-serotonin pathway is dependent on vitamin B6 bioavailability, how vitamin B6 deficiency impacts β-cell proliferation during pregnancy has not been investigated. In this study, we created a vitamin B6 deficient mouse model and investigated how gestational deficiency influences maternal glucose tolerance. Our studies show that gestational vitamin B6 deficiency decreases serotonin levels in maternal pancreatic islets and reduces β-cell proliferation in an HTR2B-dependent manner. These changes were associated with glucose intolerance and insulin resistance, however insulin secretion remained intact. Our findings suggest that vitamin B6 deficiency-induced gestational glucose intolerance involves additional mechanisms that are complex and insulin independent.

Fields et al. investigate the impact of vitamin B6 deficiency on islet β-cell proliferation during pregnancy, using vitamin B6-deficient mice. They find that gestational vitamin B6 deficiency decreases serotonin levels in pancreatic islets and reduces β-cell proliferation, showing that vitamin B6 deficiency regulates maternal glucose tolerance in a serotonin-dependent manner.

Development and evaluation of a formula to correct blood glucose concentration measurements in hemodiluted and hemoconcentrated feline blood samples tested by use of a veterinary point-of-care glucometer

OBJECTIVE

To determine the effect of PCV on blood glucose concentration measurements in feline blood samples tested with a point-of-care (POC) glucometer and to develop and evaluate a correction formula that adjusts POC glucometer-measured blood glucose concentration (POCgluc) for a given PCV.

DESIGN

Experimental and prospective study.

SAMPLE

Blood samples from 4 healthy and 16 hospitalized cats.

PROCEDURES

Heparinized blood samples from healthy cats were processed into packed RBCs and plasma. Packed RBCs were resuspended with plasma to achieve PCVs ranging from 0% to 87%. Duplicate PCV and POCgluc measurements were obtained for each suspension. Plasma glucose concentration as measured by a clinical laboratory biochemical analyzer (LABgluc) was assessed; results were compared with the POCgluc. A formula to correct POCgluc measurements for PCV was developed. Blood samples from hospitalized cats were used to evaluate the formula.

RESULTS

For each healthy cat, LABgluc values were similar for all PCVs; the mean difference between POCgluc and LABgluc at PCVs outside a range of 35% to 55% was significant. Mean differences between POCgluc and LABgluc were 24.3 and 41.5 mg/dL, whereas mean differences between corrected POCgluc and LABgluc were 3 and 25.9 mg/dL for samples from healthy and hospitalized cats, respectively. Correlation between corrected POCgluc and LABgluc was stronger than that between POCgluc and LABgluc for samples from healthy and hospitalized cats.

CONCLUSIONS AND CLINICAL RELEVANCE

The POCgluc did not reflect LABgluc in hemodiluted or hemoconcentrated feline blood samples. Use of a correction formula appeared to reduce this error. Additional studies are needed to evaluate the frequency with which this correction formula might prevent clinical errors. (J Am Vet Med Assoc 2019;254:1180-1185).

Neural stem/progenitor cells display a low requirement for oxidative metabolism independent of hypoxia inducible factor-1alpha expression

Neural stem/progenitor cells (NSPCs) are multipotent cells within the embryonic and adult brain that give rise to both neuronal and glial cell lineages. Maintenance of NSPC multipotency is promoted by low oxygen tension, although the metabolic underpinnings of this trait have not been described. In this study, we investigated the metabolic state of undifferentiated NSPCs in culture, and tested their relative reliance on oxidative versus glycolytic metabolism for survival, as well as their dependence on hypoxia inducible factor-1alpha (HIF-1α) expression for maintenance of metabolic phenotype. Unlike primary neurons, NSPCs from embryonic and adult mice survived prolonged hypoxia in culture. In addition, NSPCs displayed greater susceptibility to glycolytic inhibition compared with primary neurons, even in the presence of alternative mitochondrial TCA substrates. NSPCs were also more resistant than neurons to mitochondrial cyanide toxicity, less capable of utilizing galactose as an alternative substrate to glucose, and more susceptible to pharmacological inhibition of the pentose phosphate pathway by 6-aminonicotinamide. Inducible deletion of exon 1 of the Hif1a gene improved the ability of NSPCs to utilize pyruvate during glycolytic inhibition, but did not alter other parameters of metabolism, including their ability to withstand prolonged hypoxia. Taken together, these data indicate that NSPCs have a relatively low requirement for oxidative metabolism for their survival and that hypoxic resistance is not dependent upon HIF-1α signaling.

Whole body glucose metabolism

This review describes major factors that, singly or together, influence the concentration and distribution of D-glucose in mammals, particularly in humans, with emphasis on rest, physical activity, and alimentation. It identifies areas of uncertainty: distribution and concentrations of glucose in interstitial fluid, kinetics and mechanism of transcapillary glucose transport, kinetics and mechanism of glucose transport via its transporters into cells, detailed mechanisms by which hormones, exercise, and hypoxia affect glucose movement across cell membranes, whether translocation of glucose transporters to the cell membrane accounts completely, or even mainly, for insulin-stimulated glucose uptake, whether exercise stimulates release of a circulating insulinomimetic factor, and the relation between muscle glucose uptake and muscle blood flow. The review points out that there is no compartment of glucose in the body at which all glucose is at the same concentration, and that models of glucose metabolism, including effects of insulin on glucose metabolism based on assumptions of concentration homogeneity, cannot be entirely correct. A fresh approach to modeling is needed.