C-peptide

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Not to be confused with C-reactive protein or Protein C.
C-peptide[1]
275px
Identifiers
59112-80-0 YesY
ChemSpider 17288968 N
Jmol 3D model Interactive image
MeSH C-Peptide
PubChem 16132309
  • InChI=1S/C112H179N35O46/c1-51(2)32-66(144-104(184)63(21-29-92(170)171)137-85(161)46-127-99(179)59(16-23-72(114)148)134-87(163)49-131-111(191)95(55(9)10)146-106(186)62(18-25-74(116)150)135-86(162)47-129-103(183)70(36-94(174)175)145-105(185)64(22-30-93(172)173)136-84(160)45-124-98(178)58(113)15-27-90(166)167)102(182)126-41-80(156)119-38-77(153)122-50-89(165)147-31-13-14-71(147)110(190)130-44-81(157)132-56(11)96(176)123-39-78(154)121-43-83(159)140-68(34-53(5)6)108(188)141-60(17-24-73(115)149)100(180)128-48-88(164)139-67(33-52(3)4)107(187)133-57(12)97(177)143-69(35-54(7)8)109(189)142-61(20-28-91(168)169)101(181)125-40-79(155)118-37-76(152)120-42-82(158)138-65(112(192)193)19-26-75(117)151/h51-71,95H,13-50,113H2,1-12H3,(H2,114,148)(H2,115,149)(H2,116,150)(H2,117,151)(H,118,155)(H,119,156)(H,120,152)(H,121,154)(H,122,153)(H,123,176)(H,124,178)(H,125,181)(H,126,182)(H,127,179)(H,128,180)(H,129,183)(H,130,190)(H,131,191)(H,132,157)(H,133,187)(H,134,163)(H,135,162)(H,136,160)(H,137,161)(H,138,158)(H,139,164)(H,140,159)(H,141,188)(H,142,189)(H,143,177)(H,144,184)(H,145,185)(H,146,186)(H,166,167)(H,168,169)(H,170,171)(H,172,173)(H,174,175)(H,192,193)/t56-,57-,58-,59-,60-,61-,62-,63-,64-,65-,66-,67-,68-,69-,70-,71-,95-/m0/s1 N
    Key: XTUNIGNWBZZIPT-NTMYLOQBSA-N N
  • InChI=1/C112H179N35O46/c1-51(2)32-66(144-104(184)63(21-29-92(170)171)137-85(161)46-127-99(179)59(16-23-72(114)148)134-87(163)49-131-111(191)95(55(9)10)146-106(186)62(18-25-74(116)150)135-86(162)47-129-103(183)70(36-94(174)175)145-105(185)64(22-30-93(172)173)136-84(160)45-124-98(178)58(113)15-27-90(166)167)102(182)126-41-80(156)119-38-77(153)122-50-89(165)147-31-13-14-71(147)110(190)130-44-81(157)132-56(11)96(176)123-39-78(154)121-43-83(159)140-68(34-53(5)6)108(188)141-60(17-24-73(115)149)100(180)128-48-88(164)139-67(33-52(3)4)107(187)133-57(12)97(177)143-69(35-54(7)8)109(189)142-61(20-28-91(168)169)101(181)125-40-79(155)118-37-76(152)120-42-82(158)138-65(112(192)193)19-26-75(117)151/h51-71,95H,13-50,113H2,1-12H3,(H2,114,148)(H2,115,149)(H2,116,150)(H2,117,151)(H,118,155)(H,119,156)(H,120,152)(H,121,154)(H,122,153)(H,123,176)(H,124,178)(H,125,181)(H,126,182)(H,127,179)(H,128,180)(H,129,183)(H,130,190)(H,131,191)(H,132,157)(H,133,187)(H,134,163)(H,135,162)(H,136,160)(H,137,161)(H,138,158)(H,139,164)(H,140,159)(H,141,188)(H,142,189)(H,143,177)(H,144,184)(H,145,185)(H,146,186)(H,166,167)(H,168,169)(H,170,171)(H,172,173)(H,174,175)(H,192,193)/t56-,57-,58-,59-,60-,61-,62-,63-,64-,65-,66-,67-,68-,69-,70-,71-,95-/m0/s1
    Key: XTUNIGNWBZZIPT-NTMYLOQBBL
  • CC(C)CC(C(=O)NC(C)C(=O)NC(CC(C)C)C(=O)NC(CCC(=O)O)C(=O)NCC(=O)NCC(=O)NCC(=O)NC(CCC(=O)N)C(=O)O)NC(=O)CNC(=O)C(CCC(=O)N)NC(=O)C(CC(C)C)NC(=O)CNC(=O)CNC(=O)C(C)NC(=O)CNC(=O)C1CCCN1C(=O)CNC(=O)CNC(=O)CNC(=O)C(CC(C)C)NC(=O)C(CCC(=O)O)NC(=O)CNC(=O)C(CCC(=O)N)NC(=O)CNC(=O)C(C(C)C)NC(=O)C(CCC(=O)N)NC(=O)CNC(=O)C(CC(=O)O)NC(=O)C(CCC(=O)O)NC(=O)CNC(=O)C(CCC(=O)O)N
Properties
C129H211N35O48
Molar mass 3020.29 g/mol
Vapor pressure {{{value}}}
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YesYN ?)
Infobox references

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.

In the insulin synthesis pathway, first preproinsulin is translocated into the endoplasmic reticulum of beta cells of the pancreas with an A-chain, a C-peptide, a B-chain, and a signal sequence. The signal sequence is cleaved from the N-terminus of the peptide by a signal peptidase, leaving proinsulin. After proinsulin is packaged into vesicles in the Golgi apparatus, the C-peptide is removed, leaving the A-chain and B-chain, bound together by disulfide bonds, that constitute the insulin molecule.

History

Proinsulin C-peptide was first described in 1967 in connection with the discovery of the insulin biosynthesis pathway.[2] It serves as a linker between the A- and the B- chains of insulin and facilitates the efficient assembly, folding, and processing of insulin in the endoplasmic reticulum. Equimolar amounts of C-peptide and insulin are then stored in secretory granules of the pancreatic beta cells and both are eventually released to the portal circulation. Initially, the sole interest in C-peptide was as a marker of insulin secretion and has, as such, been of great value in furthering the understanding of the pathophysiology of type 1 and type 2 diabetes. The first documented use of the C-peptide test was in 1972. During the past decade, however, C-peptide has been found to be a bioactive peptide in its own right, with effects on microvascular blood flow and tissue health.

Function

Cellular effects of C-peptide

C-peptide has been shown to bind to the surface of a number of cell types such as neuronal, endothelial, fibroblast and renal tubular, at nanomolar concentrations to a receptor that is likely G-protein-coupled. The signal activates Ca2+-dependent intracellular signaling pathways such as MAPK, PLCγ, and PKC, leading to upregulation of a range of transcription factors as well as eNOS and Na+K+ATPase activities.[3] The latter two enzymes are known to have reduced activities in patients with type I diabetes and have been implicated in the development of long-term complications of type I diabetes such as peripheral and autonomic neuropathy.

In vivo studies in animal models of type 1 diabetes have established that C-peptide administration results in significant improvements in nerve and kidney function. Thus, in animals with early signs of diabetes-induced neuropathy, C peptide treatment in replacement dosage results in improved peripheral nerve function, as evidenced by increased nerve conduction velocity, increased nerve Na+,K+ ATPase activity, and significant amelioration of nerve structural changes.[4] Likewise, C-peptide administration in animals that had C-peptide deficiency (type 1 model) with nephropathy improves renal function and structure; it decreases urinary albumin excretion and prevents or decreases diabetes-induced glomerular changes secondary to mesangial matrix expansion.[5][6][7][8] C-peptide also has been reported to have anti-inflammatory effects as well as aid repair of smooth muscle cells.[9][10]

Clinical uses of C-peptide testing

  • Patients with diabetes may have their C-peptide levels measured as a means of distinguishing type 1 diabetes from type 2 diabetes or Maturity onset diabetes of the young (MODY).[11] Measuring C-peptide can help to determine how much of their own natural insulin a person is producing as C-peptide is secreted in equimolar amounts to insulin. C-peptide levels are measured instead of insulin levels because C-peptide can assess a person's own insulin secretion even if they receive insulin injections, and because the liver metabolizes a large and variable amount of insulin secreted into the portal vein but does not metabolise C-peptide, meaning blood C-peptide may be a better measure of portal insulin secretion than insulin itself.[12][13] A very low C-peptide confirms Type 1 diabetes and insulin dependence and is associated with high glucose variability, hypoglycaemia and increased complications. The test may be less helpful close to diagnosis, particularly where a patient is overweight and insulin resistant, as levels close to diagnosis in Type 1 diabetes may be high and overlap with those seen in type 2 diabetes.[14]
  • Differential diagnosis of hypoglycemia. The test may be used to help determine the cause of hypoglycaemia (low glucose), values will be low if a person has taken an overdose of insulin but not suppressed if hypoglycaemia is due to an insulinoma or sulphonylureas.
  • Factitious (or factitial) hypoglycemia may occur secondary to the surreptitious use of insulin. Measuring C-peptide levels will help differentiate a healthy patient from a diabetic one.
  • C-peptide may be used for determining the possibility of gastrinomas associated with Multiple Endocrine Neoplasm syndromes (MEN 1). Since a significant number of gastrinomas are associated with MEN involving other hormone producing organs (pancreas, parathyroids, and pituitary), higher levels of C-peptide together with the presence of a gastrinoma suggest that organs besides the stomach may harbor neoplasms.

Therapeutics

Several physiological effects have been observed in several Phase 1 and exploratory Phase 2 studies in almost 300 type 1 diabetes patients, who lacked endogenous C-peptide. Improvements were seen on diabetic peripheral neuropathy, nephropathy and other decrements associated with long-term complications of type I diabetes.[15][16][17][18][19][20][21][22][23] So far, dosing with C-peptide has shown to be safe and there were no effects of C-peptide demonstrated in healthy subjects (who make their own C-peptide).

References

  1. ↑ C-Peptide - Compound Summary, PubChem.
  2. ↑ Lua error in package.lua at line 80: module 'strict' not found.
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  10. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  11. ↑ Jones AG, Hattersley AT. The clinical utility of C-peptide measurement in the care of patients with diabetes. Diabetic Medicine 2013 Jul;30(7):803-17.
  12. ↑ Clark PM. Assays for insulin, proinsulin and C-peptide. Ann Clin Biochem 1999;36:541-564
  13. ↑ Shapiro ET, Tillil H, Rubenstein AH, Polonsky KS. Peripheral insulin parallels changes in insulin secretion more closely than C-peptide after bolus intravenous glucose administration. J Clin Endocrinol Metab. 1988 Nov;67(5):1094-9
  14. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  15. ↑ Lua error in package.lua at line 80: module 'strict' not found.
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  23. ↑ Lua error in package.lua at line 80: module 'strict' not found.


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