Performance Evaluation and Cross-Reactivity from Insulin Analogs with the ARCHITECT Insulin Assay,

Insights into insulin analog cross-reactivity: a comparative study of Siemens Atellica and LC-MS/MS

BACKGROUND

To address the challenges posed by inconsistent detection of analog insulin in commercially available insulin immunoassays, resulting in potential discrepancies in clinical findings and misdiagnosis during the investigation of factitious hypoglycemia., we aimed to evaluate the ability of the Siemens Atellica automated immunoassay to detect insulin analogs compared with LC-MS/MS.

METHODS

Five insulin analogs were analyzed at 10 ng/mL spiked into serum samples, with recombinant human insulin as positive controls. Insulin and C-peptide assays were performed using Siemens Atellica and LC-MS/MS. Recovery rates were calculated.

RESULTS

Siemens Atellica immunoassay demonstrated robust cross-reactivity (92-121%) of insulin analogs. In contrast, glargine was detected by LC-MS/MS but other analogs were not observed (<10% recovery).

CONCLUSION

Our results indicate that the insulin assay conducted on the Siemens Atellica platform could be used to diagnose factitious hypoglycemia by detecting the specific insulin analogs involved. The findings from our studies indicate the suitability of this method for clinical laboratory use in cases where factitious hypoglycemia is under consideration as a potential diagnosis. Clinicians should take these results into account when interpreting insulin measurements, particularly in instances where insulin analog overdose is suspected.

When discordant insulin and C-peptide levels lead to a medical diagnosis in a patient with transient hypoglycemia: Varying degrees of interference of insulin-antibody complexes on three insulin immunoassays

Background

Determining the cause of hypoglycemia partly relies on blood insulin and C-peptide assays. Although the pancreatic secretion of these peptides is equimolar, discrepancies in their concentrations may occur.

Case presentation

We report the case of a 73-year-old woman with type 2 diabetes mellitus (T2DM) and a history of gastric bypass. The T2DM was initially treated with insulin analogs, which were interrupted due to transient hypoglycemia episodes three years before hospitalization in our endocrinology department. During this hospitalization, the most common etiologies of hypoglycemia were excluded. Fasting insulin level was high (190 mIU/L, reference values (RV): 5-25) on Architect i2000 (an assay recognizing insulin analogs) despite normal blood C-peptide (4.5 μg/L, RV: 0.8-5.2) and slight hypoglycemia (4.5 mmol/L, RV: 4.6-6.1). Insulin level using the Elecsys assay (an assay with low sensitivity to insulin analogs) was very high (>1000 mIU/L, RV: 2.6-24.9). This pattern was observed on several samples, including some taken during a fasting test. Insulin level was only slightly increased using the Mercodia iso-insulin ELISA kit (an assay recognizing insulin analogs). These results excluded an exogenous insulin intake and were suggestive of an interference on insulin assays. To explore the latter possibility, free anti-insulin antibodies were measured and found strongly positive. The presence of interfering insulin-antibody complexes was further investigated using gel filtration chromatography, polyethylene glycol precipitation, and dilution test. Based on these findings, an insulin autoimmune syndrome (IAS) was suspected to cause the hypoglycemic episodes observed.

Conclusion

Although a discrepancy between blood insulin and C-peptide levels points to insulin analog intake, IAS should also be considered, particularly in a patient with transient hypoglycemia. IAS is characterized by the presence of insulin-antibody complexes, which can induce varying degrees of interference on insulin immunoassays and may lead to discordant insulin and C-peptide levels according to the insulin immunoassay used.

Insulin: Know what your immunoassay detects. Evaluation of two new immunoassays

BACKGROUND

Insulin is essential for glycemic regulation but diseases can cause a default or an excess of insulin secretion leading to dysregulated glycemia. Hence, measurement of insulinemia is useful to investigate hypoglycemia, determine the pathogenesis of diabetes and evaluate β-cell function. Thus, diabetic patients need supplementation with recombinant human insulin and/or insulin analogues. Analogues have primary sequences different from native human insulin and may not be detected by some immunoassays. The objective of our study was to evaluate new insulin immunoassays by determining their ability to detect different types of human insulin or analogues.

METHODS

This study compared the reactivity of two new insulin immunoassays with five well-established immunoassays on ten commercial insulins. We also measured insulin in blood samples from diabetic or pancreas transplant patients with known treatment.

RESULTS

Contrary to recombinant human insulin, there were differences in the specificity to insulin analogues. We distinguished three immunoassay categories: those recognizing all types of insulin such as the non-specific BI-INS-IRMA®, Architect® and Access® immunoassays; those recognizing human insulin only (Cobas®); and those recognizing human insulin and analogues in variable proportions (Liaison XL®, iFlash® and Maglumi®).

CONCLUSION

An accurate biological interpretation of insulinemia relies on knowledge of the specificity of the immunoassay used.

Assessment of circulating insulin using liquid chromatography-mass spectrometry during insulin glargine treatment in type 2 diabetes: Implications for estimating insulin sensitivity and β-cell function

AIM

To determine the potential impact of the cross-reactivity of insulin glargine U-100 and its metabolites on insulin sensitivity and β-cell measures in people with type 2 diabetes.

MATERIALS AND METHODS

Using liquid chromatography-mass spectrometry (LC-MS), we measured concentrations of endogenous insulin, glargine and its two metabolites (M1 and M2) in fasting and oral glucose tolerance test-stimulated plasma from 19 participants and fasting specimens from another 97 participants 12 months after randomization to receive the insulin glargine. The last dose of glargine was administered before 10:00 PM the night before testing. Insulin was also measured on these specimens using an immunoassay. We used fasting specimens to calculate insulin sensitivity (Homeostatic Model Assessment 2 [HOMA2]-S%; QUICKI index; PREDIM index) and β-cell function (HOMA2-B%). Using specimens following glucose ingestion, we calculated insulin sensitivity (Matsuda ISI[comp] index) and β-cell response (insulinogenic index [IGI], and total incremental insulin response [iAUC] insulin/glucose).

RESULTS

In plasma, glargine was metabolized to form the M1 and M2 metabolites that were quantifiable by LC-MS; however, the analogue and its metabolites cross-reacted by less than 100% in the insulin immunoassay. This incomplete cross-reactivity resulted in a systematic bias of fasting-based measures. By contrast, because M1 and M2 did not change following glucose ingestion, a bias was not observed for IGI and iAUC insulin/glucose.

CONCLUSIONS

Despite glargine metabolites being detected in the insulin immunoassay, dynamic insulin responses can be used to assess β-cell responsiveness. However, given the cross-reactivity of the glargine metabolites in the insulin immunoassay, fasting-based measures of insulin sensitivity and β-cell function are biased.

The Effect of Starting Blood Glucose Levels on Serum Electrolyte Concentrations during and after Exercise in Type 1 Diabetes

Fear of hypoglycemia is a major exercise barrier for people with type 1 diabetes (PWT1D). Consequently, although guidelines recommend starting exercise with blood glucose (BG) concentration at 7-10 mmol/L, PWT1D often start higher, potentially affecting hydration and serum electrolyte concentrations. To test this, we examined serum and urine electrolyte concentrations during aerobic exercise (cycling 45 min at 60%VO₂peak) in 12 PWT1D (10F/2M, mean ± SEM: age 29 ± 2.3 years, VO₂peak 37.9 ± 2.2 mL·kg^-1·min^-1) with starting BG levels: 8-10 (MOD), and 12-14 (HI) mmol/L. Age, sex, and fitness-matched controls without diabetes (CON) completed one exercise session with BG in the normal physiological range. Serum glucose was significantly higher during exercise and recovery in HI versus MOD (p = 0.0002 and p < 0.0001, respectively) and in MOD versus CON (p < 0.0001). During exercise and recovery, MOD and HI were not significantly different in serum insulin (p = 0.59 and p = 0.63), sodium (p = 0.058 and p = 0.08), potassium (p = 0.17 and p = 0.16), calcium (p = 0.75 and 0.19), and magnesium p = 0.24 and p = 0.09). Our findings suggest that exercise of moderate intensity and duration with higher BG levels may not pose an immediate risk to hydration or serum electrolyte concentrations for PWT1D.

Factitious Hypoglycemia in an Infant With Undetectable Exogenous Insulin by a Commercial Insulin Immunoassay: A Diagnostic Pitfall

Factitious hypoglycemia in infancy is a rare, life-threatening manifestation of Munchausen syndrome by proxy (MSBP). The hallmark of such presentation is the detection of low c-peptide combined with high insulin at the time of hypoglycemia. We report the case of a male infant who presented with recurrent severe unexplained hypoglycemic episodes since the age of six months. Two of his siblings had similar unexplained hypoglycemia episodes at a young age. He was extensively investigated, and all were normal, for endocrine and metabolic etiologies. He underwent fundoplication and insertion of a gastrostomy tube with multiple lengthy hospital admissions. His mother had diabetes and was on insulin treatment; she also had mental health issues with family-related social stressors. His hypoglycemic attacks resolved once separated briefly from his mother on the ward, raising our suspicion of MSBP. The exogenous administration of insulin was only confirmed following a scheduled change of our local Insulin assay in our laboratory when his insulin was detectable with low C-peptide on one of his typical attacks. Apparently, our previous insulin immunoassay lacked sensitivity for his mother's long-acting insulin. We are reporting this case to raise awareness about this potential diagnostic pitfall.

Quantification of Insulin Analogs by Liquid Chromatography-High-Resolution Mass Spectrometry

Administration of exogenous insulin or insulin analogs is a common cause of hypoglycemia. The etiology of hypoglycemic episodes can be investigated by the measurement of insulin. However, frequently used synthetic insulin analogs show variable reactivity with immunoassays designed for the quantification of human insulin and may produce misleading results. To overcome this challenge, mass spectrometric methods can be applied to differentiate and accurately quantify insulin and its analogs. Here we describe a liquid chromatography-tandem high-resolution accurate mass (LC-HRAM) for the highly specific and independent quantification of insulin and its synthetic analogs including aspart, detemir, glargine, glulisine, and lispro. This method utilizes antibody affinity extraction followed by analysis on a high-resolution accurate mass spectrometer.

Human Milk Metabolic Hormones: Analytical Methods and Current Understanding

Human milk (HM) contains a wide array of peptide hormones including leptin and adiponectin, which are involved in the regulation of infant growth and development. These essential hormones might play an important role in the regulation of metabolic reprogramming of the new-born infant. However, HM hormone studies are sparse and heterogeneous in regard to the study design, sample collection, preparation and analysis methods. This review discussed the limitations of HM hormone analysis highlighting the gaps in pre-analytical and analytical stages. The methods used to quantify HM metabolic hormones (leptin, adiponectin, ghrelin, insulin, obestatin, resistin and apelin) can be classified as immunoassay, immunosensor and chromatography. Immunoassay methods (ELISA and RIA) have been predominantly used in the measurement of these HM hormones. The relative validity parameters of HM hormones analysis are often overlooked in publications, despite the complexity and differences of HM matrix when compared to that of plasma and urine. Therefore, appropriate reports of validation parameters of methodology and instrumentation are crucial for accurate measurements and therefore better understanding of the HM metabolic hormones and their influences on infant outcomes.

Clinical Case of Surreptitious Hypoglycemia Due to Deliberate Insulin Analog Administration

Hypoglycemic syndrome is a life-threatening condition that can lead to hypoglycemic coma and death. Surreptitious hypoglycemic syndrome is the deliberate use of insulin preparations or oral hypoglycemic drugs aimed to reduce blood glucose level. If human insulin is injected, high level of immunoreactive insulin (IRI) and low level of C-peptide at the moment of hypoglycemia are always detected. However, the fact of deliberate administration of insulin analogs is difficult to prove. In these cases if insulin kit test with low cross-reactivity with insulin analogs is used, the low levels of IRI and C-peptide will be suspected. Some experts suggest the presence of cross reactivity with analogs of insulin in a number of commercial kits, which makes it possible to detect cases of surreptitious hypoglycemia. We present a clinical case of a patient with surreptitious hypoglycemia due to the administration of insulin analogs and discuss the problems of its laboratory diagnosis.

Recent advances in the determination of insulins from biological fluids

The qualitative and quantitative determination of insulin and its related substances (e. g., C-peptide) is of great importance in many different areas of analytical chemistry. In particular, due to the steadily increasing prevalence of metabolic disorders such as diabetes mellitus, an adequate control of the circulating amount of insulin is desirable. In addition, also in forensics and doping control analysis, the determination of insulin in blood, urine or other biological matrices plays a major role. However, in order to establish general reference values for insulin and C-peptide for diabetology, the comparability of measured concentrations is indispensable. This has not yet been fully implemented, although enormous progress has been made in recent years, and the search for a "gold standard" method is still ongoing. In addition to established ligand-binding assays, an increasing number of mass-spectrometric methods have been developed and employed as the to-date available systems (for example, high-resolution/high accuracy mass spectrometers) provide the sensitivity required to determine analyte concentrations in the sub-ng/mL (sub-100pmol/L) level. Meanwhile, also high-throughput measurements have been realized to meet the requirement of testing a high number of samples in a short period of time. Further developments aim at enabling the online measurement of insulin in the blood with the help of an insulin sensor and, in the following, in addition to a brief review, today's state of the art testing developments are summarized.

A Case of Surreptitious Glargine Overdose Confirmed by Insulin Pharmacokinetic Time Curves

CASE

A 49-year-old man presented with recurrent altered conscious state suggestive of encephalitis. This was followed by an episode of severe hypoglycemia requiring protracted intravenous glucose administration. Comparing the pharmacokinetic time curves of serum insulin levels on two insulin immunoassays with different insulin analog cross-reactivity allowed the likely diagnosis of surreptitious glargine overdose to be made rapidly.

DISCUSSION

The differing insulin analog cross-reactivity of serum insulin immunoassays, in this case the Abbott ARCHITECT and Roche Elecsys, allows the presence of insulin analog to be detected. Through comparison of time curves the characteristic signature of the specific causative insulin analog can be identified. This information confirms surreptitious insulin overdose in a timely manner, therefore avoiding the expensive and time-consuming investigations required to exclude alternate causes of severe hypoglycemia.

Enhancement of postprandial endogenous insulin secretion rather than exogenous insulin injection ameliorated insulin antibody-induced unstable diabetes: a case report

BACKGROUND

Insulin injection, especially with insulin analogs, occasionally induces the production of insulin antibodies with high binding capacity and low affinity, similar to the insulin autoantibodies characteristic of insulin autoimmune syndrome (IAS). Production of these "IAS-like" insulin antibodies causes marked glycemic fluctuations with postprandial hyperglycemia and fasting hypoglycemia.

CASE PRESENTATION

A 66-year-old man with a 27-year history of diabetes was admitted because of marked glycemic fluctuations. Human insulin treatment had been initiated at age 56, followed by multiple daily injections of insulin analogs 5 years later. After the initial year of insulin analog treatment, the patient began to experience frequent morning hypoglycemic attacks and day-time hyperglycemia. Marked hyperinsulinemia (4500 μU/mL) and high titers of insulin antibodies (80.4%) with high binding capacity and low affinity indicated that IAS-like insulin antibodies were causing severe glucose fluctuations. Altering insulin formulations (insulin aspart → regular human insulin→ insulin lispro) proved to be ineffective. After several therapeutic trials, cessation of exogenous insulin and addition of mitiglinide to liraglutide with voglibose finally attenuated glycemic fluctuations with increased postprandial insulin secretion. Continuous glucose monitoring revealed improvement of morning hypoglycemia and postprandial hyperglycemia with smaller mean amplitude of glycemic excursion. Therefore, compared to exogenously injected insulin, endogenously secreted insulin directly and rapidly acts on hepatocytes and suppresses postprandial glucose output.

CONCLUSIONS

Proper enhancement of postprandial endogenous insulin aimed at suppressing postprandial glucose output without stimulating excessive glucose uptake in the periphery is potentially useful for treating diabetes with insulin antibody-induced glycemic instability.

Pharmacokinetics of insulin disappearance after massive overdosing

Long-term glucose supplementation is required to prevent hypoglycemia after massive insulin overdosing. We fitted the blood insulin concentration-time profile to the model: I = A·exp^(-a·t) + B·exp^(-b·t), where I (μU/mL) is the serum/plasma insulin concentration, A (μU/mL) and B (μU/mL) are the peak insulin concentrations of each component, a (time^-1) and b (time^-1) are the time constants of each component, and t (h) is the time elapsed from the peak of blood insulin level. Additional components were considered as needed. Patient 1 had auto-injected 600 U NovoRapid^® 30Mix, and Patient 2 had auto-injected 300 U Novolet^®R (regular) and 1,800 U NovoLet^®N (NPH). We used the disappearance of therapeutic doses of the respective insulin in healthy individuals as controls, and we obtained parameters by Excel solver. In Patient 1, the parameter values were A = 1490.04 and a = 0.15 for insulin aspart and B = 60.66 and b = 0.04 for protaminated aspart. In Patient 2, the values were A = 784.45 and a = 0.38 for regular insulin and B = 395.84 and b = 0.03 for NPH. Compared with controls, the half-lives (t_1/2) for insulin aspart and protaminated aspart were 4 and 2 times longer, respectively, in Patient 1. In Patient 2, the t_1/2 for regular and NPH insulin were 2 and 7 times longer than those in the controls, respectively. In conclusion, the t_1/2 for insulin was elongated 2 to 7 times after massive overdosing, explaining why glucose supplementation is needed for long periods in these cases.

Clinical Utility and Cross-Reactivity of Insulin and C-Peptide Assays by the Lumipulse G1200 System

BACKGROUND

Measurement of insulin and C-peptide concentrations is important for deciding whether insulin treatment is required in diabetic patients. We aimed to investigate the analytical performance of insulin and C-peptide assays using the Lumipulse G1200 system (Fujirebio Inc., Tokyo, Japan).

METHODS

We examined the precision, linearity, and cross-reactivity of insulin and C-peptide using five insulin analogues and purified proinsulin. A method comparison was conducted between the Lumipulse G1200 and Roche E170 (Roche Diagnostics, Mannheim, Germany) systems in 200 diabetic patients on insulin treatment. Reference intervals for insulin and C-peptide concentrations were determined in 279 healthy individuals.

RESULTS

For insulin and C-peptide assays, within-laboratory precision (% CV) was 3.78-4.14 and 2.89-3.35%, respectively. The linearity of the insulin assay in the range of 0-2,778 pmol/L was R²=0.9997, and that of the C-peptide assay in the range of 0-10 nmol/L was R²=0.9996. The correlation coefficient (r) between the Roche E170 and Lumipulse G1200 results was 0.943 (P<0.001) for insulin and 0.996 (P<0.001) for C-peptide. The mean differences in insulin and C-peptide between Lumipulse G1200 and the Roche E170 were 19.4 pmol/L and 0.2 nmol/L, respectively. None of the insulin analogues or proinsulin showed significant cross-reactivity with the Lumipulse G1200. Reference intervals of insulin and C-peptide were 7.64-70.14 pmol/L and 0.17-0.85 nmol/L, respectively.

CONCLUSIONS

Insulin and C-peptide tests on the Lumipulse G1200 show adequate analytical performance and are expected to be acceptable for use in clinical areas.

Use of growth hormone, IGF-I, and insulin for anabolic purpose: Pharmacological basis, methods of detection, and adverse effects

Hormones with anabolic properties such as growth hormone (GH), insulin-like growth factor-1 (IGF-I), and insulin are commonly abused among professional and recreational athletes to enhance physical ability. Performance enhancing drugs (PEDs) such as these are also commonly used by recreational athletes to improve body aesthetics. The perception of increased muscle mass due to supraphysiologic hormone supplementation, or doping, is widespread among PED users despite a paucity of evidence-based data in humans. Even still, athletes will continue to abuse PEDs in hopes of replicating anecdotal results. It is important to educate the general public and potential treating physicians of the risks of PED use, including the dangers of polypharmacy and substance dependence. It will also be important for the research community to address the common challenges associated with studying PED use such as the ethical considerations of PED administration, the general reticence of the PED-using community to volunteer information, and the constant need to improve or create new detection methods as athletes continually attempt to circumvent current methods. This review highlights the anabolic mechanisms and suggestive data implicating GH, IGF-I, and insulin for use as PEDs, the specific detection methods with cutoff ranges that may be utilized to diagnose abuse of each substance, and their respective side effects.

Interpreting insulin immunoassays during investigation of apparent spontaneous hypoglycaemia and insulin overdose

We report two cases of hypoglycaemia; one with apparently spontaneous hypoglycaemia and one with presumed insulin overdose. In both cases insulin concentration was normal when measured with the Roche immunoassay, but elevated when remeasured with the Advia Centaur immunoassay and a diagnosis of hypoglycaemia secondary to insulin analogue administration was made. These cases highlight that physicians need to understand the binding characteristics of the insulin immunoassay they use.

Alterations in the levels of plasma amino acids in polycystic ovary syndrome--A pilot study

Background & objectives:

Plasma amino acid levels are known to be altered in conditions like sepsis and burns which are situations of metabolic stress. Polycystic ovary syndrome (PCOS), a condition which affects a woman throughout her life, is said to be associated with metabolic stress. This study was undertaken to assess if there were significant alterations in the levels of plasma amino acids in women with PCOS.

Methods:

Sixty five women with PCOS along with the similar number of age matched normal controls were included in this study. Levels of 14 amino acids were determined using reverse phase high performance liquid chromatography.

Results:

The levels of methionine, cystine, isoleucine, phenylalanine, valine, tyrosine, proline, glycine, lysine and histidine were found to be significantly (P<0.001) lower in cases than in controls. Arginine and alanine levels were found to be significantly (P<0.001) higher in cases compared with controls.

Interpretation & conclusions:

Our findings showed significant derangement in the levels of plasma amino acids in women with PCOS which might be due to the oxidative and metabolic stress associated with it. Further studies need to be done to confirm the findings.

Development of a Microsphere-Based System to Facilitate Real-Time Insulin Monitoring

BACKGROUND

The speed of insulin absorption after subcutaneous delivery is highly variable. Incorrect assumptions about insulin pharmacokinetics compromise effective glycemic regulation. Our ultimate goal is to develop a system to monitor insulin levels in vivo continuously, allowing pharmacokinetic parameters to be calculated in real time. We hypothesize that a bead-based detection system can be run on a flow-through microfluidic platform to measure insulin in subcutaneous fluid sampled via microdialysis. As a first step in development, we focused on microsphere-based measurement of insulin.

METHODS

Polystyrene microspheres coated with an anti-insulin monoclonal antibody were exposed to insulin-containing solutions, and after addition of a fluorescently labeled anti-insulin monoclonal antibody with a distinct epitope, bead-associated fluorescence was detected by fluorescence microscopy in 96-well plates or in a flow-through, microfluidic platform.

RESULTS

The bead detection system in plates had a linear range in buffer for regular human insulin (RHI), insulin lispro, and insulin aspart of 15-1115 µIU/ml, 14-976 µIU/ml, and 25-836 µIU/ml, respectively. Measurement on plasma samples demonstrated proportionality between basal and peak insulin levels similar to the laboratory reference method. Preliminary results in a polydimethylsiloxane-based, flow-through, microfluidic platform showed a strong signal at peak insulin levels.

CONCLUSIONS

We have developed a microsphere-based system to rapidly measure levels of insulin and insulin analogs. We have further demonstrated proof of concept that this bead detection system can be implemented in a lab-on-a-chip format, which will be further developed and combined with microdialysis for real-time monitoring of insulin in vivo.

Association of Insulin Resistance, Arterial Stiffness and Telomere Length in Adults Free of Cardiovascular Diseases

Background

Chronic inflammation and oxidative stress might be considered the key mechanisms of aging. Insulin resistance (IR) is a phenomenon related to inflammatory and oxidative stress. We tested the hypothesis that IR may be associated with cellular senescence, as measured by leukocyte telomere length (LTL), and arterial stiffness (core feature of arterial aging), as measured by carotid-femoral pulse wave velocity (c-f PWV).

Methods

The study group included 303 subjects, mean age 51.8 ±13.3 years, free of known cardiovascular diseases and regular drug consumption. For each patient, blood pressure was measured, blood samples were available for biochemical parameters, and LTL was analyzed by real time q PCR. C-f PWV was measured with the help of SphygmoCor. SAS 9.1 was used for statistical analysis.

Results

Through multiple linear regression analysis, c-f PWV is independently and positively associated with age (p = 0.0001) and the homeostasis model assessment of insulin resistance (HOMA-IR; p = 0.0001) and independently negatively associated with LTL (p = 0.0378). HOMA-IR seems to have a stronger influence than SBP on arterial stiffness. In all subjects, age, HOMA-IR, LTL, and SBP predicted 32% of the variance in c-f PWV. LTL was inversely associated with HOMA-IR (p = 0.0001) and age (p = 0.0001). In all subjects, HOMA-IR, age, sex, and SBP predicted 16% of the variance in LTL.

Conclusions

These data suggest that IR is associated with cell senescence and arterial aging and could, therefore, become the main target in preventing accelerated arterial aging, besides blood pressure control. Research in telomere biology may reveal new ways of estimating cardiovascular aging and risk.

Commercial insulin immunoassays fail to detect commonly prescribed insulin analogues

OBJECTIVES

Blood insulin and C-peptide are key investigations in the differential diagnosis of hypoglycaemia. Analogues of insulin have modified primary-sequences compared to native human insulin, as such may not cross react with insulin assays. This has important implications in detecting surreptitious or malicious insulin administration. The aim of this study is to assess the cross-reactivity of all insulins currently listed in the British National Formulary (BNF65, 2013) in clinical insulin assays currently used in UK clinical laboratories.

DESIGN AND METHODS

Sample sets were prepared for all 15 exogenous insulin classes listed in the BNF, at concentrations of 1000 pmol/L and 300 pmol/L, using pooled human serum. Samples were sent blinded to 5 participating analytical laboratories to cover analysis on the 10 major clinical insulin assays used in the UK.

RESULTS

The ability of insulin assays to detect exogenous insulin preparations was highly variable and ranged from 0% to >140% for a single exogenous insulin. Four assays were highly specific for the human insulin sequence and had no cross-reactivity with any synthetic analogue insulin. Two detected all insulin types (human sequence, animal and synthetic analogue), with the remaining having variable cross-reactivity.

CONCLUSION

The cross-reactivity of the 15 exogenous insulin preparations is highly variable in the assays used in clinical laboratories around the UK. It is important that laboratories and clinicians are aware of the limitations of their local assays to avoid missing the important diagnosis of hypoglycaemia secondary to excessive exogenous insulin. Where necessary, samples should be referred to specialist centres for insulin analysis and ideally by a validated and fully-quantitative mass spectrometry-based method.

Importance of insulin immunoassays in the diagnosis of factitious hypoglycemia

We report two cases emphasizing the importance of insulin assays for evaluation of hypoglycemia in diabetic patients. Case 1 was a 96/12-year-old female patient with type 1 diabetes mellitus and case 2 was a 1010/12-year-old male patient with DIDMOAD. Both patients were on a basal-bolus insulin regimen. Both were admitted because of persistent hypoglycemia. Analyses of serum samples obtained at the time of hypoglycemia initially showed low insulin and C-peptide levels. Recurrent episodes of unexplained hypoglycemia necessitated measurement of insulin levels by using different insulin assays, which revealed hyperinsulinemic hypoglycemia with low C-peptide levels, findings which confirmed a diagnosis of factitious hypoglycemia. Surreptitious administration of insulin should not be excluded in diabetic patients with hypoglycemia without taking into account the rate of cross-reactivity of insulin analogues with the insulin assay used.

Cross-reactivity of insulin analogues with three insulin assays

Background

Immunometric assays have recently shown higher specificity in the detection of human insulin than radioimmunoassays with almost no cross-reaction with proinsulin or C peptide. The introduction of the new insulin analogues on the market, however, has raised the need to define their cross-reactivity in these assays. Several studies have been published in this regard with different results.

Methods

The analogues studied were insulins lispro, aspart, glargine, detemir, and glulisine. Insulin concentrations were measured in Immulite® 2000 and Advia Centaur® XP (Siemens Healthcare Diagnostics), and Elecsys® Modular Analytics E170 (Roche). All samples were processed 15 times in the same analytical run following a random sequence. Those samples which showed statistically and clinically significant changes in insulin concentration were reprocessed using increasing concentrations of analogue, and this was done twice, using two different serum pools, one with a low concentration of insulin and one with a high concentration of insulin.

Results

In the Elecsys® E170 analyser, glargine showed statistical changes (comparison of mean concentrations with p < 0.05) and clinically significant changes in measured insulin (percentage difference 986.2% > reference change value: 59.8%), and the interference increased with increasing concentrations of analogue; the differences were not significant in the case of the other analogues. In the Advia Centaur® and Immulite® 2000 only the results for glulisine did not present significance (percentage difference 44.7% < reference change value 103.5%). Increasing concentrations of aspart, glargine, and lispro showed increased interference in Immulite® 2000.

Conclusions

In the Elecsys® E170 assay, relevant cross-reactivity was only detected with insulin glargine, whereas in the other analysers all analogues except glulisine showed significant interference.

Extensive study of human insulin immunoassays: promises and pitfalls for insulin analogue detection and quantification

Background: Over the last few decades, new synthetic insulin analogues have been developed. Their measurement is of prime importance in the investigation of hypoglycaemia, but their quantification is hampered by variable cross-reactivity with many insulin assays. For clinical analysis, it has now become essential to know the potential cross-reactivity of analogues of interest.

Methods: In this work, we performed an extensive study of insulin analogue cross-reactivity using numerous human insulin immunoassays. We investigated the cross-reactivity of five analogues (lispro, aspart, glulisine, glargine, detemir) and two glargine metabolites (M1 and M2) with 16 commercial human insulin immunoassays as a function of concentration.

Results: The cross-reactivity values for insulin analogues or glargine metabolites ranged from 0% to 264%. Four assays were more specific to human insulin, resulting in negligible cross-reactivity with the analogues. However, none of the 16 assays was completely free of cross-reactivity with analogues or metabolites. The results show that analogue cross-reactivity, which varies to a large degree, is far from negligible, and should not be overlooked in clinical investigations.

Conclusions: This study has established the cross-reactivity of five insulin analogues and two glargine metabolites using 16 immunoassays to facilitate the choice of the immunoassay(s) and to provide sensitive and specific analyses in clinical routine or investigation.

Development of a fast method for direct analysis of intact synthetic insulins in human plasma: the large peptide challenge

Background: Intact insulins are difficult to analyze by LC–MS/MS due to nonspecific binding and poor sensitivity, solubility and fragmentation. This work aims to provide a simpler, faster LC–MS method and focuses on solving the above issues. Results: A novel charged-surface chromatographic column produced peak widths for insulin that were significantly narrower than traditional C18 columns when using formic acid as mobile phase. Mass spectral fragments m/z >700 provided greater specificity, significantly reducing endogenous background. Detection limits in human plasma were 0.2 ng/ml for insulin glargine, glulisine and detemir, and 0.5 ng/ml for insulin aspart. Average accuracy for standard curve and QC samples was 93.4%. Conclusion: A simple SPE LC–MS analysis was developed for direct, simultaneous quantification of insulin glargine, detemir, aspart and glulisine.

Impact of early growth on postprandial responses in later life

Background

Low birth weight and slow growth during infancy are associated with increased rates of chronic diseases in adulthood. Associations with risk factors such as fasting glucose and lipids concentrations are weaker than expected based on associations with disease. This could be explained by differences in postprandial responses, which, however, have been little studied. Our aim was to examine the impact of growth during infancy on postprandial responses to a fast-food meal (FF-meal) and a meal, which followed the macro-nutrient composition of the dietary guidelines (REC-meal).

Methodology/Principal Findings

We recruited 24 overweight 65–75 year-old subjects, 12 with slow growth during infancy (SGI-group) and 12 with normal early growth. All the subjects were born at term. The study meals were isocaloric and both meals were consumed once. Plasma glucose, insulin, triglycerides (TG) and free fatty acids (FFA) were measured in fasting state and over a 4-h period after both meals. Subjects who grew slowly during infancy were also smaller at birth. Fasting glucose, insulin or lipid concentrations did not differ significantly between the groups. The TG responses were higher for the SGI-group both during the FF-meal (P = 0.047) and the REC-meal (P = 0.058). The insulin responses were significantly higher for the SGI-group after the FF-meal (P = 0.036). Glucose and FFA responses did not differ significantly between the groups.

Conclusions

Small birth size and slow early growth predict postprandial TG and insulin responses. Elevated responses might be one explanation why subjects who were small at birth and experiencing slow growth in infancy are at an increased risk of developing cardiovascular diseases in later life.

Insights in regulated bioanalysis of human insulin and insulin analogs by immunoanalytical methods

Despite the long and illustrious history of insulin and insulin analogs as important biotherapeutics, the regulated bioanalysis (in this article, regulated bioanalysis refers to the formalized process for generating bioanalytical data to support pharmacokinetic and toxicokinetic assessments intended for development of insulin and insulin analogs as biotherapeutics, as opposed to the analytical process used for measuring insulin as a biomarker) of these peptides remains a challenging endeavor for a number of reasons. Paramount is the fact that the therapeutic concentrations are often low in serum/plasma and not too dissimilar from the endogenous level, particularly in patients with insulin resistance, such as Type 2 diabetes mellitus. Accordingly, this perspective was written to provide helpful background information for the design and conduct of immunoassays to support regulated bioanalysis of insulin and insulin analogs. Specifically, it highlights the technical challenges for determination of insulin and insulin analogs by immunoanalytical methods that are intended to support evaluations of pharmacokinetics and toxicokinetics. In a broader sense, this perspective describes the general bioanalytical issues that are common to regulated bioanalysis of peptides and articulates some of the bioanalytical differences between conventional monoclonal antibodies and peptide therapeutics.

An innovative method for determining lipemia interference in blood specimens

BACKGROUND

Lipemia interference in blood samples is usually determined by adding exogenous substances that cause turbidity or by using ultracentrifugation to clarify the sample. However, there are a number of problems associated with these methods, which make it difficult to ascertain with certainty that lipemia is the cause of interference. We assessed a novel method for evaluating lipemia interference.

METHODS

Lipemic and non-lipemic serum samples, with similar HDL cholesterol concentrations, were mixed in various proportions (5 concentrations) and assayed for HDL and triglycerides. Thus, matched HDL samples with increasing triglycerides concentrations were tested. We then calculated the percent recovery for HDL for each mixture.

RESULTS

Six matched sets of samples had HDL recoveries ranging from 95.9% to 101.1% (n=6 sets, 5 concentrations per set, total of 30 concentrations), with HDL concentrations ranging from 0.78 to 2.16 mmol/l. Triglycerides concentrations in these samples ranged from 1.06 to 9.78 mmol/l for the 30 concentrations.

CONCLUSIONS

We determined that there was no triglycerides interference on the HDL method performed on the Hitachi S40 Clinical Analyzer up to a triglycerides concentration of 9.78 mmol/l. This matching method is simple to perform and proved useful in evaluating interference due to lipemia.

Cross-reactivity of 12 recombinant insulin preparations in the Beckman Unicel DxI 800 insulin assay

Background

Insulin analogues used in the treatment of insulin-dependent diabetes may result in hypoglycaemia; however, these preparations show variable cross-reactivity in many insulin assays. In order to investigate a suspected insulin overdose, it is therefore essential to characterize the cross-reactivity of these preparations in insulin assays.

Methods

The cross-reactivity of 12 commercial insulin preparations was assessed on the Beckman DxI analyser, by comparison with the insulin calibration curve corresponding to the midpoint of the dose–response curve. This was achieved by manually plotting the relative light units generated by the analyser for each preparation.

Results

All 12 insulin preparations examined showed significant cross-reactivity with the Beckman DxI insulin assay, with 11 of the insulin preparations demonstrating cross-reactivity of 83% or greater. The lowest cross-reactivity was observed with detemir with a value of 47.6%.

Conclusion

When investigating hypoglycaemia it is important to be aware of the cross-reactivity of the recombinant insulin analogues in insulin assays. This study has established the cross-reactivity of 12 preparations in the Beckman DxI insulin assay.

Insulin glargine safety in pregnancy: a transplacental transfer study

OBJECTIVE

Insulin glargine (Lantus) is an extended-action insulin analog with greater stability and duration of action than regular human insulin. The long duration of action and decreased incidence of hypoglycemia provide potential advantages for its use in pregnancy. However, the placental pharmacokinetics of insulin glargine have not been studied. Therefore, the objective of this study was to determine whether insulin glargine crosses the human placenta using the human perfused placental lobule technique.

RESEARCH DESIGN AND METHODS

Placentae were obtained with informed consent after elective cesarean section delivery of noncomplicated term pregnancies. Insulin glargine, at a therapeutic concentration of 150 pmol/l (20 microU/ml) was added to the maternal circulation. Additional experiments were carried out at insulin glargine concentrations 1,000-fold higher than therapeutic levels (150, 225, and 300 nmol/l). A subsequent perfusion for which the maternal circuit remained open and insulin glargine was continuously infused at 150 pmol/l was completed for further confirmation of findings. The appearance of insulin glargine in the fetal circulation was analyzed by a chemiluminescence immunoassay.

RESULTS

Results from perfusions carried out at therapeutic concentrations (150 pmol/l) of insulin glargine showed no detectable insulin glargine in the fetal circuit. After perfusion with very high insulin glargine concentrations of 150, 225, and 300 nmol/l, the rate of transfer remained low at 0.079 +/- 0.01, 0.14, and 0.064 pmol . min(-1) . g tissue(-1), respectively.

CONCLUSIONS

Insulin glargine, when used at therapeutic concentrations, is not likely to cross the placenta.

Nocturnal glucose metabolism after bedtime injection of insulin glargine or neutral protamine hagedorn insulin in patients with type 2 diabetes

AIMS/HYPOTHESIS

Insulin glargine is a long-acting human insulin analog often administered at bedtime to patients with type 2 diabetes. It reduces fasting blood glucose levels more efficiently and with less nocturnal hypoglycemic events compared with human neutral protamine Hagedorn (NPH) insulin. Therefore, bedtime injections of insulin glargine and NPH insulin were compared overnight and in the morning.

METHODS

In 10 type 2 diabetic patients, euglycemic clamps were performed, including [6,6'](2)H(2) glucose, to study the rate of disappearance (Rd) and endogenous production (EGP) of glucose during the night. On separate days at bedtime (2200 h), patients received a sc injection of insulin glargine, NPH insulin, or saline in a randomized, double-blind fashion.

RESULTS

Similar doses of both insulins had different metabolic profiles. NPH insulin had a greater effect on both Rd and EGP in the night compared with insulin glargine. By contrast, in the morning, insulin glargine was more effective, increasing Rd by 5.8 micromol/kg(-1).min(-1) (95% confidence interval 4.7-6.9) and reducing EGP -5.7 (-5.0 to -6.4) compared with NPH insulin. Nearly 80% of the glucose lowering effect in the morning was due to insulin glargine's reduction of EGP. Its injection was associated with one-third lower morning glucagon levels compared with NPH insulin (P = 0.021).

CONCLUSION/INTERPRETATION

Nocturnal variations of EGP and Rd explain the reduced incidence of hypoglycemia and lower fasting glucose levels reported for insulin glargine compared with human NPH insulin.

Comparison of 11 human insulin assays: implications for clinical investigation and research

BACKGROUND

The American Diabetes Association task force on standardization of insulin assays in 1996 showed wide variation in assay bias. Newer assays are specific for insulin, with several now available on automated immunoassay analyzers.

METHODS

In 2004, we compared 11 commercially available insulin assays by analyzing 150 serum samples (99 fasting/51 postprandial) from study participants with various degrees of glucose intolerance (exclusions being type 1 diabetes, insulin treatment, or presence of insulin antibodies). All assays were calibrated against International Reference Preparation 66/304. One assay was not specific for insulin and another was an RIA; 10 assays used enzyme/chemiluminescent labels. Bland-Altman difference plots were modified to use the mean insulin from all assays on the x-axis as a common comparator.

RESULTS

As in the 1996 study, insulin values from the different assays varied by a factor of 2, with the nonspecific assay ranking in the middle of the distribution. Spearman rank correlation coefficients, for ranking samples vs the mean, were 0.983-0.997. Both offsets and concentration-dependent differences were seen in the modified difference plots. Imprecision (mean CV) for automated assays (3%) was not significantly different from manual assays (5%). Similar values were obtained when one automated assay was run in laboratories in both the UK and the US. Results of 1 assay showed lower insulin concentrations in heparinized plasma than in serum.

CONCLUSIONS

Assay performance must be considered before comparing insulin results. The 2-fold variation in insulin results may be related to specificity, manufacturers' calibration procedures or conversion factors.

Glargine blood biotransformation: in vitro appraisal with human insulin immunoassay

AIM

Glargine, a long-acting insulin analogue, is metabolized in the bloodstream and in subcutaneous tissue. Glargine metabolism and its implications for diabetes therapy remain poorly understood. The aim of our study was to assess in vitro the glargine blood biotransformation and its inter-individual variability.

METHODS

Formation of M1 glargine metabolite in vitro was studied with Elecsys Insulin immunoassay in pools of sera and sera from patients spiked with glargine. Elecsys Insulin assay is specific of human insulin, does not recognize glargine and its M2 metabolite but does recognize its M1 metabolite.

RESULTS

Glargine incubation with serum resulted in M1 metabolite formation which was detected and characterized as an enzymatic process: metabolite kinetics were dependant on temperature, substrate concentration and serum proportion. Carboxypeptidase inhibitors and chelating agents partially inhibited the activity of the enzyme(s). Glargine biotransformation was decreased when blood was collected on EDTA tubes. After 30 min incubation of glargine (100 mU/l) in 69 sera at 37 degrees C, percentage of glargine converted into M1 ranged from 46% to 98% (mean 72%; S.D. 11%).

CONCLUSION

Glargine blood biotransformation is an enzymatic process probably involving serum carboxypeptidase(s). Metabolite formation is rapid and non negligible. Inter-individual variability of glargine biotransformation is noteworthy and should be confronted to M1 metabolite bioactivity which has not been fully documented yet.

Use of insulin immunoassays in clinical studies involving rapid-acting insulin analogues: Bi-insulin IRMA preliminary assessment

BACKGROUND

In clinical studies involving rapid-acting analogues (RAAs), insulin immunoreactivity is frequently measured, including endogenous, regular insulin (RI) and RAA immunoreactivities. Such a procedure implies equivalent cross-reactivities of all insulins present in serum. Commercially available human insulin immunoassays have been widely used, but their limitations (including hemolysis and anti-insulin antibodies) were not fully investigated. The aims of our study were to compare cross-reactivities of RI and RAAs in buffer and in serum and to investigate insulin immunoassay pitfalls.

METHODS

Cross-reactivities were assessed using Bi-insulin IRMA (Schering Cis-Bio International) in phosphate-buffered saline (PBS)-1% bovine serum albumin (BSA) and in pools of sera spiked with RI and RAAs (lispro and aspart). To investigate the influence of hemolysis, a pool of sera spiked with RAA was mixed with a concentrated hemolysate (final hemoglobin concentration 10 g/L) and incubated for 3 h at room temperature. To determine interference by anti-insulin antibodies, insulin was removed using charcoal from 18 sera with anti-insulin antibodies and from 17 sera without detectable anti-insulin antibodies. These insulin-free samples were then spiked with RI and RAAs and the immunoreactivity was determined.

RESULTS

Compared with buffer, cross-reactivity in serum for RI, lispro and aspart was lower (35%, 29% and 26% lower, respectively). Hemolysis degraded almost all RI and RAAs contained in the serum (>or=95%). Anti-insulin antibody interference was significant for RI and RAAs (p<or=0.004) and correlated with anti-insulin antibody level in the serum (p<or=0.001).

CONCLUSIONS

In serum, RI and RAA cross-reactivities are slightly lower than in buffer. For RAA assessment, hemolysed samples should be discarded and anti-insulin antibodies should be removed from samples before immunoreactivity measurements.