Skin autofluorescence is high in patients with cirrhosis – Further arguing for the implication of Advanced Glycation End Products
Authors: Elisa Maury, Julien Vergniol, Victor de Ledinghen, Vincent Rigalleau
Journal: Journal of Hepatology (2010)

Advanced glycation end products induce production of reactive oxygen species via the activation of NADPH oxidase in murine hepatic stellate cellsJournal of HepatologyVol. 52Issue 3PreviewAdvanced glycation end products are known to play an important role in the metabolic syndrome and were recently suggested to contribute to liver fibrosis development. However, little is known about the effect of advanced glycation end products on hepatic stellate cells, the major contributors to liver fibrosis development. We therefore studied the effect of advanced glycation end products on reactive oxygen species generation, a main feature for the activation hepatic stellate cells. Full-Text PDF To the Editor: Guimaraes et al. recently reported that the Advanced Glycation End products (AGE) induces the production of reactive oxygen species in hepatic stellate cells, providing an attractive mechanism for the development of liver fibrosis in the metabolic syndrome [[1]Guimarães E. Empsen C. Geerts A. van Grunsven L. Advanced glycation end products induce production of reactive oxygen species via the activation of NADPH oxidase in murine hepatic stellate cells.J Hepatol. 2010; 52: 389-397Abstract Full Text Full Text PDF PubMed Scopus (159) Google Scholar]. As mentioned by the authors, the deleterious consequences of the accumulation of AGEs are well documented in the context of diabetes [[2]Singh R. Barden A. Mori T. Beilin L. Advanced glycation end-products: a review.Diabetologia. 2001; 44: 129-146Crossref PubMed Scopus (1996) Google Scholar] or chronic renal failure [[3]Meerwaldt R. Hartog J.W. Graaff R. Huisman R.J. Links T.P. den Hollander N.C. et al.Skin autofluorescence, a measure of cumulative metabolic stress and advanced glycation endproducts, predicts mortality in hemodialysis patients.J. Am. Soc. Nephrol. 2005; 16: 3687-3693Crossref PubMed Scopus (313) Google Scholar], whereas they have been less reported in cirrhotic patients. High levels of Nε-(carboxymethyl)lysine "CML" [[4]Yagmur E. Tacke F. Weiss C. Lahme B. Manns M.P. Kiefer P. et al.Elevation of Nε-(carboxymethyl)lysine-modified advanced glycation end products in chronic liver disease is an indicator of liver cirrhosis.Clin Biochem. 2006; : 39-45Crossref PubMed Scopus (67) Google Scholar] or other fluorescent AGEs [[5]Sebeková K. Kupcová V. Schinzel R. Heidland A. Markedly elevated levels of plasma advanced glycation end products in patients with liver cirrhosis–amelioration by liver transplantation.J Hepatol. 2002; 36: 123-125Abstract Full Text Full Text PDF PubMed Scopus (123) Google Scholar] have been detected in the serum of these patients using ELISA or liquid chromatography–mass spectrometry assays [[6]Ahmed N. Thornalley P. Lu-then R. Häussinger D. Sebekova S. Schinzel R. et al.Increased protein glycation in cirrhosis and therapeutic strategies to prevent it.Ann NY Acad Sci. 2005; 1043: 718-724Crossref PubMed Scopus (25) Google Scholar], but these analytical methods are not routinely available, and the accumulation in other tissues, requiring biopsies, has not been reported. The optic properties of most AGEs may in fact help to provide further evidence for this accumulation. The fluorescence of AGEs, as used by Guimaraes et al. to confirm the glycation of AGE-BSA that they applied to hepatic cells [[1]Guimarães E. Empsen C. Geerts A. van Grunsven L. Advanced glycation end products induce production of reactive oxygen species via the activation of NADPH oxidase in murine hepatic stellate cells.J Hepatol. 2010; 52: 389-397Abstract Full Text Full Text PDF PubMed Scopus (159) Google Scholar], allows for assessment of the accumulation of AGEs in the skin, in a simple and non-invasive manner, by measuring skin autofluorescence (AF) with the AGE-Reader (DiagnOptics BV, Groningen, The Netherlands). Briefly, the AGE-Reader illuminates approximately 1 cm2 of skin (which is guarded against surrounding light) with an excitation light source of 300–420 nm (peak excitation ∼350 nm). AF is calculated by dividing the average light intensity emitted per nm over the 420- to 600-nm range by the average light intensity emitted per nm over the 300- to 420-nm range. The value of this technique is supported by correlations between skin autofluorescence and collagen-linked fluorescence (CLF; excitation at 370 nm, emission at 440 nm) following pepsin digestion, and the pentosidine (by HPLC), Nε-(carboxyethyl)lysine (CEL) and Nε-(carboxymethyl)lysine (CML) (by gas chromatography and mass spectrometry) concentrations in skin biopsies, (r = 0.47–0.62, p <0.002) [[7]Meerwaldt R. Graaff R. Oomen P.H.N. Links T.P. Jager J.J. Alderson N.L. Smit A.J. et al.Simple non-invasive assessment of advanced glycation endproduct accumulation.Diabetologia. 2004; 47: 1324-1330Crossref PubMed Scopus (564) Google Scholar], and it is a strong predictor of cardiac mortality in patients with type 2 diabetes [[8]Meerwaldt R. Lutgers H. Links T. Graaff R. Baynes J. Gans R. et al.Skin autofluorescence is a strong predictor of cardiac mortality in diabetes.Diabetes Care. 2007; 30: 107-112Crossref PubMed Scopus (232) Google Scholar]. We are not aware of any report about skin AF in patients with cirrhosis. The potential influence of an icterus, that may modify the optic properties of the skin, is also unknown. Using the AGE-Reader, we have measured the forearm skin AF of 32 patients with cirrhosis (diagnosis on liver biopsy; alcoholic, viral, and metabolic origins), 16 patients with type 2 diabetes and at least one previous cardiovascular event, and seven healthy control subjects who were members of our staff (physicians, nurses). All participants signed an informed consent. Among the cirrhotic patients, 13 had jaundice icterus which was confirmed by the dosage of bilirubinemia. The results are presented as mean ± SD, compared by ANOVA with a Bonferroni correction. As expected, the 16 patients with diabetes had higher skin AF results than control subjects (3.4 ± 0.7; p <0.001), but the skin AF were also higher in the patients with cirrhosis as compared with the control subjects (2.4 ± 0.6 vs 1.9 ± 0.2; p <0.05). As shown in Table 1, the icteric patients had lower results than those without icterus (p = 0.08 vs cirrhosis without icterus). We, therefore, measured the AF of six normal subjects before and after painting their forearm with bilirubin (Calbiochem, La Jolla, CA 92037): this immediately reduced the AF (before: 1.7 ± 0.2, after painting with bilirubin: 1.4 ± 0.2; p <0.05).Table 1AutoFluorescence results in patients with cirrhosis, type 2 diabetes and control subjects. Open table in a new tab Although these results are preliminary, the higher AF, as we found, further argues for the implication of AGEs in liver fibrosis. Of course, such clinical data do not replace mechanistic studies: as mentioned by Guimaraes et al., the liver is critical for the clearance of AGEs [[9]Smedsrød B. Melkko J. Araki N. Sano H. Horiuchi S. Advanced glycation end products are eliminated by scavenger-receptor-mediated endocytosis in hepatic sinusoidal Kupffer and endothelial cells.Biochem J. 1997; 322: 567-573Crossref PubMed Scopus (173) Google Scholar], so their accumulation in the tissues of patients with cirrhosis may in fact be a consequence, rather than a cause, of liver damage. Even in this case, deleterious effects of this accumulation may occur outside the liver: further vascular complications have been reported in patients with type 2 diabetes and Non alcoholic Fatty Liver Disease (NAFLD) [[10]Targher G. Bertolini L. Padovani R. Rodella S. Zoppini G. Zenari L. et al.Diabetes Care. 2006; 29: 1325-1330Crossref PubMed Scopus (346) Google Scholar]. In any case, we feel that the hepatologists should be informed that the accumulation of AGEs in tissues can be evaluated by non-invasive techniques, as we did, and that cirrhosis and icterus influence the results. The authors who have taken part in this study declared that they do not have anything to disclose regarding funding or conflict of interest with respect to this manuscript. We would like to thank Dr. S. Jarman, retired member of the University Victor Segalen-Bordeaux 2, for revision of the English manuscript, and Dr. MC Beauvieux, who provided bilirubin.