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Glucose Uptake Measurement and Response to Insulin Stimulation in In Vitro Cultured Human Primary Myotubes

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Oxidative modifications in glycated insulin.

Sofia Guedes¹, Rui Vitorino, Maria R M Domingues

¹Department of Chemistry, University of Aveiro, 3810-193, Aveiro, Portugal.

Analytical and Bioanalytical Chemistry

|May 25, 2010

Summary

Glycoxidation, the combined effect of glycation and oxidation, damages proteins like insulin. This study shows glycated insulin undergoes more severe and earlier oxidative damage, particularly with increased glycation, impacting protein structure and function.

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Area of Science:

Biochemistry
Oxidative Stress
Protein Chemistry

Background:

Glycoxidation involves synergistic glycation and oxidation, producing harmful tissue modifications.
This process contributes to non-functional damaged proteins and cellular oxidative damage.
Insulin's central role in diabetes necessitates understanding its glycoxidation susceptibility.

Purpose of the Study:

To investigate the site-specific oxidation of native and glycated insulin.
To analyze the impact of varying glycation levels (mono, di, tri) on insulin oxidation.
To identify oxidized residues and peptide fragments resulting from metal-catalyzed oxidation.

Main Methods:

Metal-catalyzed oxidation of native and glycated insulin.
Liquid chromatography-mass spectrometry for identifying oxidized residues and fragments.
Time-course analysis (0-48 hours) to track oxidative damage progression.

Main Results:

Tyrosine, phenylalanine, and cysteine were primary oxidized residues.
Glycated insulin showed more pronounced and earlier oxidative modifications than native insulin.
Oxidative damage severity increased with higher glycation levels, leading to carbonylation of proline, histidine, valine, leucine, and glycine.
New peptide cleavage sites were identified, particularly in chain B, with fragmentation near cysteine bridges in both chains for diglycated and triglycated forms.

Conclusions:

Glycoxidation significantly impacts insulin structure and function.
Increased glycation exacerbates oxidative damage and fragmentation in insulin.
Understanding these modifications is crucial for diabetes research and therapeutic strategies.