engleski

The clinical value of AGE-hemoglobin assay

Glycation process in vivo results in two different products: early (EGP) and advanced glycation endproducts (AGEs). The mechanism of EGP formation has been well described, with HbA1c as the best- studied example. However, much less is known amout AGEs. Once synthesized, early glycation products may form heterogenous polymers due to a chain of chemical rearrangements. Therefore, some of the early compounds are precursors for the cascade of events forming AGEs. The finding that AGEs are also formed on hemoglobin suggests that HbA1c is a precursor for Hb-AGE formation. HbA1c has been well estabnlished as an important indicator for glycemia monitoring, but the diagnostic role of Hb-AGE is still not clarified. Are HbA1c and Hb- AGE competitive or complementary parameters? Hb- AGE was quantified by the competitive ELISA technique using polyclonal anti-AGe-RNase- antibodies to detect AGE immunoreactivities of proteins precipitated in red cell hemolysate. Results are expreses as AGE units/mg Hb. HbA1c was measured by means of high performamnce liquid chromatography (HPLC). Hb-AGE was analysed in three group of patients divided accordingly to HbA1c values as follows:group I (n=25) HbA1c<7% Hb-AGE=6.7+-0.22 U/mg ; group II (n=25) HbA1c 7- 10% Hb-AGE=9.1+-0.34 U/mg ; and group III (n=25) HbA1c>10%, Hb-AGE=12.7+-0.43 U/mg (mean+-SE). Linear correlation coefficient for total analyzed samples (n=75) was r=0.82 p<0.001. Patientsd with HbA1c level > 8% were considered to be in poor glycemia control and those with HbA1c<85 in good control. In the well controlled subgroup (n=33) HbA1c=6.15+-0.16%, Hb-AGE=7.13+-0.24 U/mg, the correlation was not significant (r=0.45). However, in those with HbA1c=11.4+-0.35, (n=42), Hb-AGE ranged from 6.56 to 18.68 U/mg yielding a significant correlation (r=0.64, p<0.001). The observed difference may reflect a different kinetic rate of HbA1c production and subsequently the rate of Hb-AGE formation. The discrepancy in the correlation between HbA1c and Hb-AGE suggested them to be complementary rather than opposed parameters, as only their combined use provided in vivo screening of the processes of glycation.

advanced glycation endproducts ; hemoglobin A1c ; antibodies to AGEs

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