Serum C-peptide

Measurements of urine C-peptide are useful when a continuous assessment of (3-ceU function is desired or frequent blood sampling is not practical. The 24-hour urine C-peptide content (in the absence of renal failure, which produces increased levels) correlates well with fasting serum C-peptide concentration or with the sum of C-peptide concentrations in sequential specimens after a glucose load. However, the fraction of secreted C-peptide that is excreted ill the urine exhibits high intersubject and intrasubject variability, limiting the value of urine C-peptide as a measure of insulin secretion. ... 

Horwitz DL, Kuzuya H, Rubenstein AH. Circulating serum C-peptide. A brief review of diagnostic implications. N Engl J Med 1976 295 207-9. 

An oral mixed micellar formulation containing 50 units of insulin was administered to normal human subjects, resulting in a serum C-peptide lowering effect similar to that of subcutaneous injection of insulin (10 U) over a 3 2-hour period postdose. The onset of action of the oral formulation was faster than that of insulin delivered by the subcutaneous route. The oral insulin formulation and subcutaneous insulin injection produced a similar blood glucose-lowering effect in 10 type I diabetic patients. The oral insulin formulation with 30 and 50 U of insulin provided areas under the curve (AUCs) of 77 and 82 pU/mL, respectively, representing 55 and 66% of the AUC obtained from injected insulin. 

Sosenko, J. M., Kitzmiller, J. L., Fliickiger, R., Loo, S. W. H., Younger, D. M., and Gabbay, K. H., Umbilical cord glycosylated hemoglobin in infants of diabetic mothers Relationships to neonatal hypoglycemia, macrosomia, and cord serum C-peptide. Diabetes Care 5, 566-570 (1982). 

Clegg (1980) reported that bovine serum and high-density lipoprotein (HDL) caused an increase in free fatty acid levels in unpasteurized bulk milk. Lipoprotein free serum, apo HDL, all individual HDL tested, and the unfractionated C-peptide fractions had no lipolytic effect. HDL-lipid in the presence of 2 C-peptides and the combination of HDL-lipid with unfractionated C-peptide caused a considerable stimulation of lipolysis. 

A 33-year-old nurse with unexplained hypoglycemia had only small increases in insulin and C-peptide, and glibenclamide was found in her serum (47). However, she denied using it and did not want psychiatric therapy. 

Indirect Two-Site Immunoradiometric Assay of Human Proinsulin. The method used is that described by Rainbow et al. Plastic tubes coated with purified guinea pig anti-insulin antibodies are prepared as described above 200-jul samples containing human proinsulin are added to these coated tubes and incubated at 4° for 24 hr. After removal of the sample, tubes are washed twice with 400 /tl of NIGP buffer. Rabbit antibody to human C-peptide is diluted to 1/1000 in 50 mM sodium phosphate buffer, pH 7.4, containing 150 mM sodium chloride, 10 g of bovine serum albumin per liter, and 100 mg of guinea pig IgG per liter 200 /til are added to each tube. After a further 24 hr of incubation at 4 the tubes are washed twice as previously and 200 /u,l of I-labeled sheep anti-rabbit IgG (10,000 cpm) are added in the same buffer as that used for diluting the C-peptide antiserum. After a final 24 hr of incubation and two further washes as above, the tubes are counted. 

Suicide by insulin has been reported in a 68-year-old, non-diabetic physician who had also taken metoprolol and alcohol. The blood metoprolol concentration was 0.4 microgram/ml (usual target range 0.035-0.5 microgram/ml) and alcohol 122 mg/dl (27 mmol/1). C-peptide conld not be detected, serum insulin was 1849 pU/ml (normal fasting concentration below 16 pU/ml) (214). 

A stable isotope dilution assay using mass spectrometry to measure insulin, proinsulin, and C-peptide has been developed. The difference in mass among the three analytes allows specific measurement of each protein. Comparison of patient samples revealed that most, but not all, results were higher by immunoassay than mass spectrometry. Thus immunoassays may overestimate insulin, particularly at low concentrations. The high protein concentration in the serum requires extraction of proteins (e.g., by immunoaffinity) and purification by high-performance liquid chromatography (HPLC) before quantification by mass spectrometry. This method is not suitable for routine laboratory analysis. 

HIGHLY SENSITIVE CLEIA FOR C-PEPTIDE IN SERUM WITH CHEMILUMINESCENT SUBSTRATE USING A NEW CLEIA SYSTEM... 

The measurement of C-peptide provides a fully validated means of quantifying endogenous insulin secretion, preventing influence of exogenous insulin or insulin antibody. However, most C-peptide assay kits cannot differentiate C-peptide from proinsulin and proinsulin conversion products. The influence of proinsulin may be significant in cases where serum proinsulin is elevated, as in Type 2 diabetes, familial hyperproinsulinemia and in patients with proinsulin antibody. 

To solve the problem, we have developed a highly specific and sensitive assay for C-peptide in serum and plasma using specific monoclonal antibody (MoAb) to the N-terminal of the C-peptide molecule. In this report, we describe the assay performance of C-peptide on the LUMIPULSE system. The system is a fully automated chemiluminescent enzyme immunoassay (CLEIA) system that uses AMPPD as a substrate for alkaline phosphatase and ferrite micro-particles as a solid phase. ... 

All evaluations of this C-peptide assay performance were performed by LUMIPULSE FORTE. The method used on LUMIPULSE FORTE was as follows 20 pL of serum or standard was mixed with 250 pL of antibody-coated ferrite particle suspension and the mixture was incubated for 37 °C, 10 min. After B/F separation, 250 pL of Enzyme-labeled antibody was added to the ferrite particle suspension and the mixture was incubated for 37 °C, 10 min. After the second B/F separation, 200 pL of AMPPD solution was added. During the washing steps, the ferrite particles were magnetically separated from the bulk solution on the wall of the cartridge. After the enzyme reaction had proceeded for 5 min, the chemiluminescent light emission was measured for 2 s. 

Melani F, Rubenstein AH, Oyer PE, Steiner DF. Identification of proinsulin and C-peptide in human serum by a specific immunoassay. Proc Nat Acad Sci USA 1970 67 148-55. 

Bruno A, Carucci P, Cassader M, Cavallo-Perin P, Gruden G, Olivetti C, Pagano G. Serum glucose, insulin and C-peptide response to oral glucose after intravenous adninistration of hydrocortisone and methylprednisolone in man. EurJ Clin Pharmacol ( 994) 46, 411-15. 

Insulin in the body is derived from its precursor molecule proinsulin. During the conversion of proinsulin to insulin, a small peptide (C-peptide) is released by enzymic action. Measurement of this peptide in serum provides a measure of pancreatic -cell function, even in patients on insulin. C-pep-tide determination can be used in the evaluation of a number of metabolic conditions, e.g. brittle diabetes, insulinoma. 

High-GI diets have been shown to slightly increase hemoglobin Ale, total serum cholesterol and triacylglycerols, and decrease HDL cholesterol and urinary C-peptide in diabetic and hyperlipi-demic individuals. In addition, low-GI diets have been shown to decrease cholesterol and triacylglycerol levels in dyslipidemic individuals. There are insufficient studies performed on healthy individuals and further research on the role of GI in lipid profile and CVD risk factors is warranted. 

Ferric ion was immobilized on a Chelating Sepharose Fast Flow column preparatory to the separation of seven enkephalin-related phosphopep-tides.17 Non-phosphorylated peptides flowed through the column, and the bound fraction contained the product. The capacity of the column was found to be 23 pmol/mL by frontal elution analysis. Cupric ion was immobilized on Chelating Superose for the isolation of bovine serum albumin.18 Cupric ion was immobilized on a Pharmacia HiTrap column for the separation of Protein C from prothrombin, a separation that was used to model the subsequent apparently successful separation of Factor IX from prothrombin Factor IX activity of the eluate was, however, not checked.19 Imidazole was used as the displacement agent to recover p-galactosidase from unclarified homogenates injected onto a nickel-loaded IMAC column.20 Pretreatment with nucleases and cleaning in place between injections were required procedures. A sixfold purification factor was observed. 

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