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To the Editor I have read the article about the changes in ghrelin and obestatin levels authored by Dr. Gutierrez-Grobe, et al., and published in Annals of Hepatology with great interest. Ghrelin and obestatin are peptide hormones which are easily broken down by proteases. These structures which contain less than 50 amino acids are called peptide hormones, while those with more than 50 amino acids are referred to as proteins. Hormones with protein structure are more resistant against proteases. In 2004 Hosada, et al. reported the pre-analytical rules that should be followed when studying ghrelin.2 In accordance with the suggestion of Hosada, et al., a protease inhibitor should be used to protect the ghrelin peptide against proteases. In another study about the optimal stabilization of ghrelin by Blatnik and Soderstrom, the authors stated that protease inhibitors should be used to protect ghrelin against proteases. Furthermore, companies manufacturing kits (Phoenix, bioquote, etc.) all recommend the use of protease inhibitors while studying hormones in peptide structure to protect peptides against proteases. Gutierrez-Grobe, et al. studied ghrelin and obestatin changes in patients with non-alcoholic fatty liver disease (NAFLD) and compared those with the levels in control subjects. Total ghrelin levels in NAFLD patients were reported to drop significantly, while obestatin levels also fell, but without a statistically significant difference. Since the authors did not use protease inhibitors while collecting the samples in their study, the decrease in ghrelin and obestatin levels in the patients with NAFLD may be due to the fact that the increased proteases associated with NAFLD has led to the breakdown of these peptides, which were found lower relative to the controls. In NAFLD, the amounts of gamma glutamyl transpeptidase and caspase enzymes increase and these are proteases. These elevated proteases may have broken down the peptides studied and lowered their amounts. A closer examination of the obestatin values that are reported in the study confirms our arguments, as the standard deviation of the obestatin values reported are higher than mean obestatin values. This demonstrates that the amount of protease produced by the patients varies depending on the severity of NAFLD. The protease amounts that vary depending on the severity of the disease affect the rate by which peptides are broken down and lead to higher standard deviations. If the authors had used protease inhibitors in their study, the standard deviations would not have been so high.

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2011-11-29   |   681 visitas   |   Evalua este artículo 0 valoraciones

Vol. 11 Núm.1. Enero-Febrero 2012 Pags. 145-146 Ann Hepatol 2012; 11(1)