The effects of anti-insulin antibodies and cross-reactivity with human recombinant insulin analogues in the E170 insulin immunometric assay

Is insulin intoxication still the perfect crime? Analysis and interpretation of postmortem insulin: review and perspectives in forensic toxicology

Insulin is an anabolic hormone essential to glucose homeostasis. Insulin therapy, comprising human insulin (HI) or biosynthetic analogs, is critical for the management of type-1 diabetes and many of type-2 diabetes. However, medication error including non-adapted dose and confusion of insulin type, and misuse, such as massive self-administration or with criminal intent, can have lethal consequences. The aim of this paper is to review the state of knowledge of insulin analysis in biological samples and of the interpretation of insulin concentrations in the situation of insulin-related death investigations. Analytic aspects are considered, as quantification can be strongly impacted by methodology. Immunoanalysis, the historical technique, has a prominent role due to its sensitivity and ease of implementation. Recently, liquid chromatography coupled to mass spectrometry has provided indispensable selectivity in forensic contexts, distinguishing HI, analogs, and degradation products. We review the numerous antemortem (dose, associated pathology, injection-to-death interval, etc.) and postmortem parameters (in corpore degradation, in vitro degradation related to hemolysis, etc.) involved in the interpretation of insulin concentration. The interest and limitations of various alternative matrices providing a valuable complement to blood analysis are discussed. Vitreous humor is one of the most interesting, but the low diffusion of insulin in this matrix entails very low concentrations. Injection site analysis is relevant for identifying which type of insulin was administered. Muscle and renal cortex are matrices of particular interest, although additional studies are required. A table containing most case reports of fatal insulin poisoning published, with analytical data, completes this review. A logic diagram is proposed to highlight analytical issues and the main parameters to be considered for the interpretation of blood concentrations. Finally, it remains a challenge to provide reliable biological data and solid interpretation in the context of death related to insulin overdose. However, the progress of analytical tools is making the "perfect crime" ever more difficult to commit.

Insulin: a review of analytical methods

Insulin is an important polypeptide hormone that regulates carbohydrate metabolism.

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.

Euglycaemic glucose clamp: what it can and cannot do, and how to do it

The hyperinsulinaemic-euglycaemic glucose clamp has always been regarded as the "gold standard" for the assessment of pharmacodynamic (PD) properties of insulin preparations; however, there has been controversy over a variety of methodogical details, such as study population, dosing time and the initial stabilization of blood glucose (BG) concentrations at the clamp target level, among clamp groups. As the impact of these details on PD results is unclear, the present review provides an overview of different methodological approaches for both the manual and the automated hyperinsulinaemic-euglycaemic glucose clamp. The advantages and limitations of several methodological details are discussed as well as the relevance of clamp results for the prediction of clinical outcomes. Overall, the best method strongly depends on the exact objective of the trial. If, for instance, duration of action is the primary objective, studies should be carried out in patients with type 1 diabetes to avoid any interference of endogenous insulin. This is less important for variables such as onset of action or early metabolic activity. The hyperinsulinaemic-euglycaemic glucose clamp has a high sensitivity to detect even minor differences between different insulin preparations. The practical relevance of potential differences, however, needs to be investigated in clinical studies. A major prerequisite for obtaining reliable glucose clamp results is the attainment of high clamp quality (i.e. keeping BG concentrations close to the clamp target throughout the experiments). Unfortunately, measures of clamp quality are often under-reported, as is the variability in PD profiles, although these might explain some unconfirmed extreme results obtained in a few clamp studies.

Direct comparison of radioimmunoassay and LC–MS/MS for PK assessment of insulin glargine in clinical development

Background: A direct comparison of radioimmunoassay (RIA) and LC–MS/MS for insulin glargine quantification in human plasma is provided. Results: Compared with the RIA, the LC–MS/MS assay exhibited comparable/improved sensitivity (LLOQ at 0.1 ng/ml [˜16.7 pM or 2.8 μU/ml] for glargine and its metabolites M1 and M2, respectively) and ruggedness. Most importantly, it demonstrated a superior specificity advantage against the interference from endogenous insulin, exogenous insulin analogs (e.g., Novolog®, Humalog® or Levemir®, routine treatment for diabetes mellitus) and potentially pre-existing anti-insulin antibodies in patient samples. The data obtained from diabetic patients suggested the LC–MS/MS assay substantially improved pharmacokinetic characterization of glargine. Conclusion: LC–MS/MS overcame common limitations of RIA, and provided critically needed specificity to support glargine clinical development, without sacrificing assay sensitivity and ruggedness.

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.