Serum-insulin or plasma-insulin?

Progress in nanoparticle-based electrochemical biosensors for hormone detection

Hormones are chemical messengers that regulate a wide range of physiological processes including metabolism, development, growth, reproduction and mood. The concentration of hormones that orchestrate the numerous bodily functions is very low (1 nM or less). Efforts have been made to develop highly sensitive tools to detect them. This review represents a critical comparison between different types of nanoparticle-based electrochemical biosensors for the detection of various hormones, namely cortisol, sex hormones (estradiol, progesterone, testosterone), insulin, thyroid-stimulating hormone (TSH) and growth hormone (GH). The electrochemical biosensors investigated for each hormone are first divided on the basis of the biological fluid tested for their detection, and successively on the basis of the electrochemical transducer utilized in the device (voltammetric or impedimetric). Focus is placed on the nanoparticles employed and the successive electrode modification developed in order to improve detection sensitivity and specificity and biosensor stability. Limit of detection (LOD), linear range, reproducibility and possibility of regeneration for continuous reuse are also investigated and compared. The review also addresses the recent trends in the development of wearable biosensors and point-of-care testing for hormone detection in clinical diagnostics useful for endocrinology research, and the future perspectives regarding the integration of nanomaterials, microfluidics, near field communication (NFC) technology and portable devices.

Metabolic and Cardiovascular Benefits of Apple and Apple-Derived Products: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Background

Quantitative evidence of the metabolic and cardiovascular effects of apples (Malus domestica) is lacking in interventional studies. This study aimed to summarize the available evidence of the beneficial effects of apples and apple-derived products (ADPs) on metabolic and cardiovascular markers.

Methods

Peer-reviewed randomized controlled trials (RCTs) were identified from four databases on May 3, 2021 and regularly updated until the end of May 2021. Demographic characteristics, intervention types, and evaluation parameters were extracted. A meta-analysis on the mean difference of change scores was conducted on commonly presented outcomes in the RCTs.

Results

The metabolic and cardiovascular effects of diverse regimens, including whole apple, apple extract, and apple juice, were examined in 18 eligible RCTs. Nine common evaluation outcomes were eventually introduced to the meta-analysis, including total cholesterol (TC), low-density lipoprotein (LDL), high-density lipoprotein (HDL), triglyceride, glucose, insulin, C-reactive protein, and systolic/diastolic blood pressures. The levels of TC (-2.69 mg/dL; 95% CI: -5.43, 0.04 mg/dL) and LDL (-2.80 mg/dL; 95% CI: -5.78, 0.17 mg/dL) showed a non-significant decreasing tendency after at least a week of apple consumption. Further subgroup analysis, particularly, a comparison with placebo as a control, showed a significant reduction in TC and LDL levels. When stratified by the baseline level, subjects with high TC and LDL level were shown to have more benefits from the apple intake. Intriguingly, apple and ADPs significantly reduced HDL levels to a small extent (-1.04 mg/dL; 95% CI: -1.79, -0.29 mg/dL). The other markers were mostly unaffected by the intervention.

Conclusion

Our investigation revealed that apples could improve blood cholesterol levels.

Systematic Review Registration

[https://www.crd.york.ac.uk/prospero/], identifier [CRD42020215977].

Assessing the test–retest repeatability of insulin resistance measures: Homeostasis model assessment 2 and oral glucose insulin sensitivity

Background: Insulin resistance is commonly assessed using the homeostasis model assessment (HOMA) variants. HOMA is potentially insensitive to change because of its high coefficient of variation. The repeatability coefficient is an alternative means of assessing test repeatability. To be confident of clinical change, rather than biological variation, a subsequent test needs to differ from the former by more than the repeatability coefficient using the equation.Test 1 = Test 2 ± repeatability coefficient.The repeatability coefficients for measures of insulin resistance are unknown.Aim: To compare the repeatability coefficient of HOMA2 variants (Beta-cell function [%B], insulin sensitivity [%S], insulin resistance [IR]) to a dynamic measure of insulin resistance, and the oral glucose insulin sensitivity (OGIS) test.Setting: The raw data from a previously used data set were reanalysed.Methods: Glycaemic and insulinaemic tests were performed on 32 men and women both with (n = 10) and without type 2 diabetes (n = 22). From these data, eight fasting tests and three 50-g oral glucose tolerance tests were used to calculate HOMA2 and OGIS. The methods of Bland and Altman assessed repeatability.Results: Repeatability coefficients for all participants for the HOMA2 %B, %S and IR variants were 72.91, 189.75 and 0.9, which equates to 89%, 135% and 89% of their respective grand means. By contrast, OGIS had a repeatability coefficient of 87.13, which equates to 21% of the grand mean.Conclusion: Because of the high repeatability coefficient relative to the grand mean, use of HOMA2 measures for assessing insulin resistance in small population studies should be reconsidered.

Murder by insulin: suspected, purported and proven-a review

Murder by insulin-whether attempted, suspected or proven-is rare. Only 66 cases worldwide could be found for this review. A conviction was secured in 31 cases and additional weapon was employed in 11. Differentiation of attempted homicide from Munchausen syndrome by proxy in the young and from 'mercy killing' in the elderly was not attempted. Most perpetrators were close relatives and most victims were alive when discovered and responded to treatment. Hypoglycaemia is the first clue to homicidal insulin use in living subjects and requires the demonstration of a plasma insulin concentration of generally more than 1000 pmol/L and undetectable plasma C-peptide concentration to establish the diagnosis. Serum glucose measurements are valueless in victims found dead. The presence near the body of insulin vials, syringes or needles, loose talk by the suspected perpetrator or their ready access to insulin may be the only clue. The demonstration of insulin in tissue around an injection site by immunohistopathology or by measuring it in an extract clinches the diagnosis. Immunoassays suitable for clinical use to detect and measure insulin and C-peptide are subject to random errors and cannot be relied upon unless special precautions including separation by gel filtration or HPLC are undertaken prior to analysis. They do not detect or measure accurately a new generation of synthetic insulin analogues. Mass spectrometry will be required to do this and to validate clinical immunoassays, upon which convictions have always had to rely in the past.

Comparison of the effects of different anticoagulants and sample handling procedures on rat insulin radioimmunoassay

1. The effects of several potential inducers of artifacts on insulin RIA: use of anticoagulant (heparin, EDTA) versus clotting , repeated freezing/thawing and the presence of added ions (Ca2+, Zn2+) has been studied on a large uniform pooled sample of rat blood. 2. Repeated freezing and thawing resulted in a very significant loss of RIA insulin. 3. The use of heparin or added lipid (Intralipid) to serum samples resulted in lower insulin measurements, whereas low protein or EDTA addition resulted in higher values. The effect of EDTA was not a consequence of its sequestering of calcium or zinc, as their combined addition did not change the EDTA effect. 4. The use of individualized non-specific binding for actual insulin estimations did not correct most of the artifacts induced by the different treatments studied. 5. As a general conclusion, utmost care must be taken to prevent the incidence of these sources of error by referring the data to controls, avoiding the use of EDTA as well as taking into account the actual composition and handling of the samples when measuring their insulin levels.

C-peptide measurement: methods and clinical utility

Proinsulin is the single chain precursor of insulin. It consists of insulin, plus a peptide which connects the A and B chains of insulin. This peptide is termed C-peptide. C-peptide an insulin are secreted in equimolar amounts from pancreatic beta-cells, Hence, circulating C-peptide levels provide a measure of beta-cell secretory activity. C-peptide measurements are preferable to insulin measurements because of lack of hepatic extraction, slower metabolic clearance rate, and lack of cross reactivity with antibodies to insulin. This article reviews the methods for determination of C-peptide levels in body fluids, and discusses the applications of C-peptide measurement. These include the investigation of hypoglycemia and the assessment of insulin secretory function in insulin-treated and non-insulin-dependent diabetics. The contribution of C-peptide measurement to the understanding of the interrelationships between insulin secretory function and age, sex, obesity, blood lipids, and blood glucose concentrations will also be evaluated.

Insulin radioimmunoassay: inappropriately high results obtained using a preprecipitated antibody technique

A brief comparison of the results of three insulin radioimmunoassay methods indicated that insulin levels measured in heparinised plasma by a pre-precipitated antibody technique were inappropriately high. The error was greatest when low but clinically important levels of the hormone were studied. This effect was due to non-insulin components of the plasma and could be eliminated by the addition of insulin-free plasma to the standard tubes.

Effect of essential oil of onion (allyl propyl disulphide) on blood glucose, free fatty acid and insulin levels of normal subjects

The administration of allyl propyl disulphide (APDS), a volatile substance contained in onion, to six normal volunteers after a 12 hour fast caused a significant fall in the blood glucose levels and a significant rise in the serum insulin levels during the subsequent 4 hours. It is argued that this effect is due to an insulin sparing action. The expected rise of serum free fatty acid levels after fasting did not occur after APDS administration and this effect is probably related to the simultaneous rise in the insulin levels.

Observations on blood glucose and insulin determinations

The relation of capillary to venous blood glucose concentration, whole blood to plasma values, and, where possible, the effect of pregnancy on the variables have been studied. We have not been able to show constant relations between capillary and venous blood glucose concentrations as have been implied by a W.H.O. expert committee on diabetes mellitus and the British Diabetic Association.The choice of anticoagulant was shown to have a negligible effect on the results of a single antibody-charcoal separation insulin assay method.