• Conflict of interest: Nothing to report.


For both studies published in HEPATOLOGY,1, 2 we used biliverdin IX dihydrochloride (Formula C33H34N4O6 × 2HCl) from ICN Biomedicals Inc., not, as it was indicated, from Sigma Chemicals. We apologize for this mistake, which we overlooked in Materials and Methods, and thank HEPATOLOGY for giving us the opportunity to correct this. ICN Biomedicals Inc. now sells this product under the name of MP Biomedicals, LLC (Ohio, USA; available under Cat. no. 194886). This substance from ICN was commonly used when investigating effects of HO-1 products in vivo and exerted biological and protective effects not only in our hands.3, 4 According to its data sheet, it passed the identity test and was about 95% pure. We actually did not perform thin-layer chromatography of any batch of the biliverdin IX dihydrochloride used in our experiments but instead relied on the description of ICN regarding identity and purity. Biliverdin IX dihydrochloride was dissolved in saline, kept in the dark at anytime, and applied to mice at 25 mg/kg in a volume of 200 μL intraperitoneally. As controls for the activity of biliverdin IX dihydrochloride we used heat- and light-inactivated aliquots in parallel groups of mice to rule out, for example, lipopolysaccharide effects or effects of other unknown contaminants. We did not add any ingredients, which were not indicated in the manuscripts, to increase solubility. In our hands, solubility was good enough to inject mice using a 0.4-mm diameter needle. The experiments described in our manuscripts were repeated several times and gave consistent results.

Regarding the controls used, we feel that the readers of HEPATOLOGY do not have to fear that we or others presented a Gigo effect by using biliverdin IX dihydrochloride. Furthermore, as suggested by McDonagh, effects of biliverdin in vivo might be even stronger than observed so far.

Gisa Tiegs*, Gabriele Sass*, * University of Erlangen, Department of Pharmacology and Toxicology, Erlangen, Germany.