According to a 1999 paper about murder cases involving insulin overdose, an 83-y

Question

According to a 1999 paper about murder cases involving insulin overdose, an 83-year old lady in a nursing home showed signs of extremely low blood glucose level (0.1 mmol/L, healthy range= 4-8 mmol/L). At first, kidney failure was suspected as the cause of hypoglycemia, but blood analysis showed that insulin level was extremely high (83,360 pmol/L, healthy range= 60-120 pmol/L during fasting, Up to 2,000 pmol/L after glucose intake) while C-peptide level was low (170 pmol/L, healthy range= 260- 1,000 pmol/L). Elevated insulin level coupled with suppressed C-peptide level is virtually diagnostic of an exogenous insulin administration (insulin overdose). (Unfortunately, the lady died 11 months later and the perpetrator was not identified.)

1. What is C-peptide and how is it related to insulin production and secretion?

2. With your answer to question 1, explain how elevated insulin level and suppressed C-peptide level strongly supports exogenous insulin administration, as opposed to overproduction of insulin in such cases of endogenous insulin overproduction as insulinoma or treatment with sulphonylurea.

Explanation / Answer

The connecting peptide, or C-peptide, is a short 31-amino-acid polypeptide that connects insulin's A-chain to its B-chain in the proinsulin molecule. It is released from the pancreatic beta-cells during production of insulin from proinsulin. In cases of insulinoma or sulphonylurea treatment, there is excessive insulin production endoogenously, which in turn means excessive C-peptide production. But the patients still undergo hypoglycemia even after such high levels of both insulin and C-peptide. Hence, it is well discernible that exogenous insulin administraiton is the root cause as the commercially available innsulin does not have C-peptide present in it rather it is removed during purification process. Hence, radioimmunoassay can not detect the C-peptides. therefore we can easily confer that less C-peptide concentration and high levels of insulin mean exogenous administration of insulin.

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