True, you must measure c-peptide if your subject or patient is taking insulin , such as in the case of a pancreas transplant patient who is on insulin post-op or because the graft is not working well.

Another reason is that insulin levels drop significantly during the first pass through the liver. This is not the case with C-peptide, so you can get a better measure of actual secretion from C-Peptide.

Hi Ediz,

Insulin detection reflects the insulin from outside (exogenous) source, such as insulin injections and inside (endogenous) source that is pancreas, whereas C-peptide test reflects only endogenous insulin. Therefore, C-peptide is mostly used to detect functional beta cell mass.

True, you must measure c-peptide if your subject or patient is taking insulin , such as in the case of a pancreas transplant patient who is on insulin post-op or because the graft is not working well.

Another reason is that insulin levels drop significantly during the first pass through the liver. This is not the case with C-peptide, so you can get a better measure of actual secretion from C-Peptide.

You can assess beta cell function in patients under insulin treatment.

And postprandilal or post-glucagon stimulated C-peptide level is a good marker for treatment choices.

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While I was writing my questions I had forgotten something. I had wanted to cell culture situation. For instance, you have differentiated some cell type into beta cell. Namely, you think that. So you add glucose into medium of this new cell which you think differantiaton. And you would detect functionality of this new cell ( if there is beta cell ). But why investigations use the C-peptide? There is insulin in Serum as far as I know even if low level. İn that case, there is no C-peptide in serum ? But how can it be ? C-peptide is released into blood ?

If a cell line secretes insulin, it will also secrete c-peptide. You can check the level of insulin and/or c-peptide in your serum, but it is not really necessary for secretion studies unless you are performing the studies using serum supplemented media, as opposed to some buffer system such as Krebs-Ringer with BSA.

ChEers!

Please,  note that  sometimes we do  measure insulin. Generally  c-peptide are measure as these are mainly  endogenous to  the beta cells

Circumstance that in secretion or in cell, So what ? 

Birefly and briefly, I wonder and I ask that short question. C-peptide is generally used to detect beta cell in ''''' cell culture, so, in cell, in single beta cell  ''''. In immunoflorescence technique for example. Why, why, why ? Why the scientists mark the beta cell by using c-peptide instead of insulin generally. 

C-peptide must be more appropriate than insulin in detection as a construction etc ? And might be c-peptide detection is lower than insulin staining in terms of money.

I hope that I can explain myself this time. 

In humans there are physiological advantages to measuring C-peptide rather than insulin, as outlined above and summarised here as:

1-C-peptide is not present in insulin injections therefore it only represents the patient's own insulin production

2- C-peptide is renally cleared and insulin is predominantly metabolized in the liver leading to a longer half life of C-peptide (30 mins vs 6 mins)

3- A large and variable proportion of insulin is cleared on first pass through the liver.

However, in your situation where you are interested in measuring insulin secretion from a cell culture you should just measure insulin directly.

In in-vivo studies in humans, C-peptid has two main differences to insulin:

1. there is no hepatic extraction (or "clearance")

2. it has a longer half-life (appr.30 minutes, insulin has just 6 min) and is therefore less influenced by the pulsatile nature of its secretion

Finally, I satisfied. Thank you for all answer :) 

Best wishes...

Ediz

I did not publish my data on C peptide because the data were too similar to data on insulin. I considered C peptide data as a verification of insulin measurements.

In cell culture, C-peptide secretion is used rather than insulin secretion, as cell culture media may contain insulin, which the cells can then uptake and later excrete (as opposed to synthesising proinsulin themselves). Hence, insulin secretion may not indicate true insulin production by the cell. This has been previously shown to be the case with mouse ES cells which were differentiated towards a beta cell fate, where the insulin from the media was uptaken by differentiated ES cells and later excreted following glucose stimulation (see Hansson et.al Diabetes 2004; 53(10): 2603). 

Dear Jacqueline,

I understand what you meant. On the other hand, you mean negative regulation when the insulin is uptaken by beta cell. Ok if we postulate this completely correct process.

What about the C-peptide ? Namely, c-peptide exist in serum. For the c-peptide alike process as insulin might be valid? If there are, seems there is no advantage of using C-peptide to detect beta cell function. 

And the secondly, do you know about the immunofloresence statining, not secretion why we use c-peptide to detect beta cell as differ with insulin ?

I investigated clinically healthy adults by GTT. Complitely differeent from working in vitro!

Hi Ediz,

I was referring specifically to in vitro studies, for example where stem cells are differentiated to form beta cells. In this case, multiple previous studies have found that the cells are able to uptake insulin from the cell culture media (the cell culture media contains only insulin, not c-peptide). Therefore, using either insulin secretion or immunofluorescence may not demonstrate that the stem cell derived beta cells are synthesizing insulin de novo; and hence the use of C-peptide as an alternative. In an in vivo situation of course, this would not apply. I hope that this helps!

Dear Jacqueline,

You know serum doesn't contain C-peptide. How dou you know ? Can you show any proof ? I think, serum contains everything, thereby containing c-peptide.

Don't misunderstand me please. I just want to reach truth.

Hi Ediz,

What are you referring to by serum? Many cell culture medium is serum-free.. Those that so contain serum use either BSA or FBS - neither of which will contain human C-peptide, which is what you would assay for (antibodies are specific for the human form of C-peptide). In contrast, they often contain exogenous human insulin, which is why you would not commonly use a human insulin secretion assay. Hope that this helps!

Ediz Coşkun, I believe your may be overlooking the fact that C peptide sequence from various species has greater differences than insulin. It is much easier to accurately measure mouse C peptide in the presence of C peptide from bovine C peptide.

As for insulin added to the medium during derivation from ES cells, the concentration of insulin is very high and substantial amount of insulin is non-specifically retained by cells, as well as internalized (published information). To bring insulin levels at background level in a normal ELISA (

I want to point out that unless you get BSA preparations that are specifically listed as insulin free, you will have insulin, sometimes quite a bit of insulin. Presumably there is also c-peptide present, though as Tausif mentions, c-peptide assays are generally species specific, so if your assay does not cross react with bovine c peptide, you should be fine.

Even BSA listed as RIA grade is not often tested for insulin. Sigma (A-7888) is a good one, but if you do not wish to add exogenous insulin to your experiment, be careful of your albumin source. I have measured as much as 10 U/g, which would blow out my RIA at the concentrations used in my buffer system.

When my lab conducts secretion studies in vitro, we use Krebs-Ringer buffer that contains 0.1% Sigma A-7888 RIA grade BSA and the desired concentrations of glucose and whatever other secretagogue or inhibitor or other agent that you may be testing. This allows us to measure insulin secretion in cells from various species with a single assay, rather than buying multiple cpeptide assays to accomodate various species. We use species specific assays for human and rodent cpeptide and/or insulin as needed for samples from in vivo studies.

There is an (exogenous) insulin source, like insulin injections and (endogenous) source that is making by pancreas, whereas C-peptide indicate only endogenous insulin