Glucagon-like peptide-1 secretion in people with versus without type 2 diabetes: a systematic review and meta-analysis of cross-sectional studies

AIMS/HYPOTHESIS

The aim of this systematic review was to synthesise the study findings on whether GLP-1 secretion in response to a meal tolerance test is affected by the presence of type 2 diabetes (T2D). The influence of putative moderators such as age, sex, meal type, meal form, and assay type were also explored.

METHODS

A literature search identified 32 relevant studies. The sample mean and SD for fasting GLP-1TOTAL and GLP-1TOTAL iAUC were extracted and used to calculate between-group standardised mean differences (SMD), which were meta-analysed using a random-effects model to derive pooled estimates of Hedges' g and 95 % prediction intervals (PI).

RESULTS

Pooled across 18 studies, the overall SMD in GLP-1TOTAL iAUC between individuals with T2D (n = 270, 1047 ± 930 pmol·L-1·min) and individuals without T2D (n = 402, 1204 ± 937 pmol·L-1·min) was very small, not statistically significant and heterogenous across studies (g = -0.15, p = 0.43, PI: -1.53, 1.23). Subgroup analyses demonstrated an effect of assay type whereby Hedges' g for GLP-1 iAUC was greater in individuals with, versus those without T2D when using ELISA or Mesoscale (g = 0.67 [moderate], p = 0.009), but not when using RIA (g = -0.30 [small], p = 0.10). Pooled across 30 studies, the SMD in fasting GLP-1TOTAL between individuals with T2D (n = 580, 16.2 ± 6.9 pmol·L-1) versus individuals without T2D (n = 1363, 12.4 ± 5.7 pmol·L-1) was small and heterogenous between studies (g = 0.24, p = 0.21, PI: -1.55, 2.02).

CONCLUSIONS

Differences in fasting GLP-1TOTAL and GLP-1TOTAL iAUC between individuals with, versus those without T2D were generally small and inconsistent between studies. Factors influencing study heterogeneity such as small sample sizes and poor matching of groups may help to explain the wide prediction intervals observed. Considerations to improve comparisons of GLP-1 secretion in T2D and potential mediating factors more important than T2D diagnosis per se are outlined.

PROSPERO ID

CRD42020195612.

Thermal resilience of ensilicated lysozyme via calorimetric and in vivo analysis

Ensilication is a novel method of protein thermal stabilisation using silica. It uses a modified sol–gel process which tailor fits a protective silica shell around the solvent accessible protein surface. This, electrostatically attached, shell has been found to protect the protein against thermal influences and retains its native structure and function after release. Here, we report the calorimetric analysis of an ensilicated model protein, hen egg-white lysozyme (HEWL) under several ensilication conditions. DSC, TGA-DTA-MS, CD, were used to determine unfolding temperatures of native, released and ensilicated lysozyme to verify the thermal resilience of the ensilicated material. Our findings indicate that ensilication protects against thermal fluctuations even at low concentrations of silica used for ensilication. Secondly, the thermal stabilisation is comparable to lyophilisation, and in some cases is even greater than lyophilisation. Additionally, we performed a mouse in vivo study using lysozyme to demonstrate the antigenic retention over long-term storage. The results suggest that protein is confined within the ensilicated material, and thus is unable to unfold and denature but is still functional after long-term storage.

Ensilication is a novel method of protein thermal stabilisation using silica. It uses a modified sol–gel process which tailor fits a protective silica shell around the protein to enable room temperature storage of biopharmaceuticals.

Physiological and molecular responses to an acute bout of reduced-exertion high-intensity interval training (REHIT)

PURPOSE

We have previously shown that 6 weeks of reduced-exertion high-intensity interval training (REHIT) improves VO2max in sedentary men and women and insulin sensitivity in men. Here, we present two studies examining the acute physiological and molecular responses to REHIT.

METHODS

In Study 1, five men and six women (age: 26 ± 7 year, BMI: 23 ± 3 kg m(-2), VO2max: 51 ± 11 ml kg(-1) min(-1)) performed a single 10-min REHIT cycling session (60 W and two 20-s 'all-out' sprints), with vastus lateralis biopsies taken before and 0, 30, and 180 min post-exercise for analysis of glycogen content, phosphorylation of AMPK, p38 MAPK and ACC, and gene expression of PGC1α and GLUT4. In Study 2, eight men (21 ± 2 year; 25 ± 4 kg·m(-2); 39 ± 10 ml kg(-1) min(-1)) performed three trials (REHIT, 30-min cycling at 50 % of VO2max, and a resting control condition) in a randomised cross-over design. Expired air, venous blood samples, and subjective measures of appetite and fatigue were collected before and 0, 15, 30, and 90 min post-exercise.

RESULTS

Acutely, REHIT was associated with a decrease in muscle glycogen, increased ACC phosphorylation, and activation of PGC1α. When compared to aerobic exercise, changes in VO2, RER, plasma volume, and plasma lactate and ghrelin were significantly more pronounced with REHIT, whereas plasma glucose, NEFAs, PYY, and measures of appetite were unaffected.

CONCLUSIONS

Collectively, these data demonstrate that REHIT is associated with a pronounced disturbance of physiological homeostasis and associated activation of signalling pathways, which together may help explain previously observed adaptations once considered exclusive to aerobic exercise.

Malignant gliomas display altered plasma membrane potential and pH regulation--interaction with Tc-99m-MIBI and Tc-99m-Tetrofosmin uptakes

Two radiopharmaceuticals, Tc-99m-MIBI (MIBI) and Tc-99m-Tetrofosmin (Tfos), are currently used for in vivo non-invasive monitoring of the MultiDrug Resistant (MDR) status of tumours. As gliomas are highly multidrug resistant, it is expected that the tracers would be poorly retained in those cells, but the in vivo and in vitro studies to date have shown that Tfos was highly retained in malignant gliomas. The high degree of malignancy of tumour cells is linked to alterations of physiological parameters as plasma membrane potential and intracellular pH. In order to elucidate the contribution of those parameters to Tfos and MIBI uptakes in malignant gliomas, we used several glioma cell lines--G111, G5, G152, and 42 MG-BA. These cells showed to be chemoresistant with a high level of expression and activity of the Multidrug Resistant associated Protein 1 (MRP1). They also had an alkaline intracellular pH (pHi) related to the Na+/H+ antiporter (NHE-1) expression and depolarised plasma membranes (-45 to -55 mV). In spite of their chemoresistance, we have found a high accumulation of both radiotracers in gliomas, more important for Tfos than MIBI, related to the presence and activity of NHE-1. In conjunction, the uptakes of the tracers were only partially dependent upon the plasma membrane potential of the glioma cell lines, again Tfos uptake being less dependent on this parameter than MIBI uptake. In conclusion, the evidence accumulated in this study suggests that Tfos could be a suitable glioma marker in vivo.

Involvement of the glutathione S-conjugate compounds and the MRP protein in Tc-99m-tetrofosmin and Tc-99m-sestamibi uptake in glioma cell lines

The objective of this study was to compare the accumulation of Tc-99m-tetrofosmin and Tc-99m-sestamibi in four grade IV glioma cell lines and to correlate their accumulation with the multidrug resistance of the cells. Tc-99m-tetrofosmin in all glioma cell lines showed slightly higher uptake and more efficient release beyond 150 min than Tc-99m-sestamibi and the retention of both tracers in the cells was to a certain extend inversely proportional to their degree of multidrug resistance. The results obtained showed that the efflux of both tracers was carried out only in part through the MRP/GS-X pump system. Tc-99m-tetrofosmin showed good potential as a marker of recurrent malignant glioma and in vivo studies are currently underway to confirm these observations.

Association of AP1 adaptor complexes with GLUT4 vesicles

Nycodenz gradients have been used to examine the in vitro effects of GTP-(gamma)-S on adaptor complex association with GLUT4 vesicles. On addition of GTP-(gamma)-S, GLUT4 fractionates as a heavier population of vesicles, which we suggest is due to a budding or coating reaction. Under these conditions there is an increase in co-sedimentation of GLUT4 with AP1, but not with AP3. Western blotting of proteins associated with isolated GLUT4 vesicles shows the presence of high levels of AP1 and some AP3 but very little AP2 adaptor complexes. Cell free, in vitro association of the AP1 complex with GLUT4 vesicles is increased approximately 4-fold by the addition of GTP-(gamma)-S and an ATP regenerating system. Following GTP-(gamma)-S treatment in vitro, ARF is also recruited to GLUT4 vesicles, and the temperature dependence of ARF recruitment closely parallels that of AP1. The recruitment of both AP1 and ARF are partially blocked by brefeldin A. These data demonstrate that the coating of GLUT4 vesicles can be studied in isolated cell-free fractions. Furthermore, at least two distinct adaptor complexes can associate with the GLUT4 vesicles and it is likely that these adaptors are involved in mediating distinct intracellular sorting events at the level of TGN and endosomes.

Cell-surface biotinylation of GLUT4 using bis-mannose photolabels

New cell-impermeant bis-mannose photolabels have been developed with biotinyl groups attached to 4-(1-azi-2,2,2-trifluoroethyl)-benzoyl-1, 3-bis(d-mannos-4-yloxy)-2-propylamine (ATB-BMPA) by either a polyethoxy spacer (Bio-ATB-BMPA) or an additional hexanoic acid spacer (Bio-LC-ATB-BMPA). The half-maximal inhibition constants, Ki values, for inhibition of glucose transport activity in insulin-stimulated rat adipocytes were determined to be 359+/-10 and 273+/-28 microM for Bio-ATB-BMPA and Bio-LC-ATB-BMPA, respectively. These values are similar to those previously reported for the non-biotinylated compound ATB-BMPA. Following UV-irradiation-induced cross-linking of the biotinylated photolabels to rat adipocytes, the biotinylated glucose transporter isoform 4 (GLUT4) could be detected by non-radioactive and radioactive methods that utilized the interaction with streptavidin. Biotinylated GLUT4 from 1-2 microg of adipose cell membranes, precipitated onto magnetic streptavidin beads, could be sensitively and quantitatively detected using an electrochemiluminescent assay method. This utilized a ruthenium-tagged anti-GLUT4 antibody that on excitation at an electrode generated an electrochemiluminescent signal in an ORIGEN analyser. Alternatively, surface-biotinylated GLUT4 could be easily, but less sensitively, detected in streptavidin agarose precipitates which were analysed by conventional GLUT4 Western blotting. Data obtained using the non-radioactive methods compared favourably with those using tritiated versions of the biotinylated probes. Insulin treatment of adipocytes increased the levels of signals from surface biotinylated GLUT4 by approximately 10-fold or approximately 20-fold, respectively, when the electrochemiluminescent or the Western blot detection methods were used and these signals were blocked by cytochalasin B.

[123I]-6-deoxy-6-iodo-D-glucose (6DIG): a potential tracer of glucose transport

A glucose analogue labelled with iodine-123 in position 6 has been synthesized: [123I]-6-deoxy-6-iodo-D-glucose (6DIG). The aim of this study was to examine its biological behaviour in order to assess whether it could be used to evaluate glucose transport with SPECT. To establish whether 6DIG enters the cells using the glucose transporter, four biological models have been used: human erythrocytes in suspension, neonatal rat cardiomyocytes in culture, isolated perfused rat hearts, and biodistribution in mice. 6DIG competed with D-glucose to enter the cells and its entry was increased by insulin and inhibited in the presence of cytochalasin B. The biological behaviour of 6DIG was similar to that of 3-O-methyl-D-glucose. 6DIG is a tracer of glucose transport which is very promising for clinical studies.

Biological evaluation of two anomeric glucose analogues iodinated in position 6

Two anomeric analogues of glucose labelled with 123 iodine in position 6, proposed as tracers of glucose transport in vivo, have been synthesized: alpha- and beta-methyl-6-deoxy-6-iodo-D-glucopyranoside (alpha MDIG and beta MDIG). The aim of this study was to determine whether these molecules interact with the glucose transporter and whether they could be used as tracers of glucose transport in vivo. The biodistribution of alpha MDIG and beta MDIG was studied in the mouse in vivo. To determine if these two anomers enter the cell via the glucose transporter, their uptake was measured in isolated perfused rat hearts, in human erythrocytes in suspension, and in cardiomyocytes of neonatal rat in culture. Both alpha MDIG and beta MDIG had similar repartitions in the mouse: myocardial uptake averaged 7% of the injected dose/g of organ at 2 min postinjection and alpha MDIG competed with D-glucose to enter the cells. Insulin produced a 123% increase of its uptake in isolated perfused rat hearts and a 100% increase in cardiomyocytes of neonatal rat in culture. alpha MDIG uptake was lowered in the presence of glucose transport inhibitors in each experimental model. An interaction between beta MDIG and glucose transporters was observed only in human erythrocytes in suspension. Only alpha MDIG interacts with the glucose transporter, and thus could be used to estimate glucose transport in vivo.

Biological studies of analogues of glucose iodinated in positions 1, 2, or 3

Analogues of glucose labeled with 123 iodine in positions 1, 2 or 3 have been synthesized. The aim of this study was to examine their biological behavior in four experimental models in order to assess whether they could be used to evaluate the uptake of glucose with single photon emission computed tomography (SPECT). The results obtained have shown that none of these molecules enters the cell using the glucose transporter. Therefore, they cannot be used as tracers of glucose uptake.

Experimental models, protocols, and reference values for evaluation of iodinated analogues of glucose

For an iodinated analogue of glucose to be useful for evaluating glucose uptake using single-photon emission computed tomography (SPECT), it must enter the cell via the same transporter as glucose and accumulate within the cell without being degraded. The biological behavior of the iodinated tracer must therefore be similar to that of 2-deoxy-D(-)[1-14C]-glucose (2-DG). In the present study, four experimental models (biodistribution in mouse, isolated rat heart, human erythrocytes in suspension and cultured neonatal rat cardiomyocytes) have been chosen and protocols have been set up which allow for the examination of small quantities of iodinated analogues of glucose. The uptakes of 2-DG and of L(-)[1-14C]-glucose have been measured in these models to establish reference values which will be compared with uptake values for iodinated analogues of glucose.