Endocrine Abstracts

Introduction: Diabetes mellitus (DM) is a disease characterized by increased glucose levels, mostly either due to insulin deficiency (type 1 DM) or a decreasing ability of insulin receptor binding (type 2 DM) or both. Biomarker measurements such as fasting glucose and haemoglobin A1c are vital to detect and monitor DM. In addition to these parameters and antibody testing, insulin determination has been used for classifying different types of DM. However, the disadvantage of insulin measurement is a rapid degradation in the blood through hepatic metabolism. Moreover, interferences may arise from exogeneous insulin injection. In contrast, C-peptide is co-secreted along with insulin in equimolar quantity, consisting of 31 amino acids and a longer half-life of 30 minutes compared to 3-5 minutes with insulin. Therefore, it can be detected in urine samples, reflecting insulin metabolism by non-invasive samples, as this is also not subjected to exogeneous insulin interference.

Objective: We aim to validate urinary C-peptide as a reliable and sensitive biomarker for determination of the beta cell function using a point-of-care approach.

Method: The proof-of-concept for electrochemical detection of C-peptide is based on competition format. We utilize a self-assembled monolayer for covalent attachment of the coating C-peptide onto the screen-printed electrodes. Various concentrations of C-peptide were measured using an antibody against C-peptide, labelled with an enzyme to generate the signal, and a laptop/mobile phone used as the output reader.

Result: We are able to show that our proof-of-concept works for C-peptide determination. The developed sensor obtained a limit of detection of 3.5 μg/ml in spiked urine samples. In addition, the assay showed a high specificity to C-peptide with no known cross-reactivity to other related structures such as insulin.

Conclusion: Further evaluation of the assay is ongoing in our laboratory to further improve the sensitivity of the assay. Overall, our proof-of-concept for the determination of urinary C-peptide is a reliable and it can be miniaturized for easy-to-use portable assay which can be used to support diagnosis and monitoring of DM to prevent the progression of the disease and further complications.