Mutations resulting in replacement of one obligate Gly residue within the repeating (Gly-Xaa-Yaa) n triplet pattern of the collagen type I triple helix are the major cause of osteogenesis imperfecta (OI). Phenotypes of OI involve fragile bones and range from mild to perinatal lethal. In this study, host-guest triple-helical peptides of the form acetyl-(Gly-Pro-Hyp) 3-Zaa-Pro-Hyp-(Gly-Pro-Hyp)4-GlyGly-amide are used to isolate the influence of the residue replacing Gly on triple-helix stability, with Zaa ‫؍‬ Gly, Ala, Arg, Asp, Glu, Cys, Ser, or Val. Any substitution for Zaa ‫؍‬ Gly (melting temperature, Tm ‫؍‬ 45°C) results in a dramatic destabilization of the triple helix. For Ala and Ser, T m decreases to Ϸ10°C, and for the Arg-, Val-, Glu-, and Asp-containing peptides, Tm < 0°C. A Gly 3 Cys replacement results in T m < 0°C under reducing conditions but shows a broad transition (T m Ϸ 19°C) in an oxidizing environment. Addition of trimethylamine N-oxide increases T m by Ϸ5°C per 1 M trimethylamine N-oxide, resulting in stable triple-helix formation for all peptides and allowing comparison of relative stabilities. The order of disruption of different Gly replacements in these peptides can be represented as Ala < Ser < CPOred < Arg < Val < Glu < Asp. The rank of destabilization of substitutions for Gly in these Gly-ProHyp-rich homotrimeric peptides shows a significant correlation with the severity of natural OI mutations in the ␣1 chain of type I collagen.

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Collagens contain a high amount of charged residues involved in triple-helix stability, fibril formation, and ligand binding. The contribution of charged residues to stability was analyzed utilizing a host-guest peptide system with a single Gly-X-Y triplet embedded within Ac(Gly-Pro-Hyp) 3 -Gly-X-Y-(Gly-Pro-Hyp) 4 -Gly-Gly-NH 2 . The ionizable residues Arg, Lys, Glu, and Asp were incorporated into the X position of Gly-X-Hyp; in the Y position of Gly-Pro-Y; or as pairs of oppositely charged residues occupying X and Y positions. The Gly-X-Hyp peptides had similar thermal stabilities, only marginally less stable than Gly-Pro-Hyp, whereas Gly-Pro-Y peptides showed a wide thermal stability range (T m ‫؍‬ 30 -45°C). The stability of peptides with oppositely charged residues in the X and Y positions appears to reflect simple additivity of the individual residues, except when X is occupied by a basic residue and Y ‫؍‬ Asp. The side chains of Glu, Lys, and Arg have the potential to form hydrogen bonds with available peptide backbone carbonyl groups within the triple-helix, whereas the shorter Asp side chain does not. This may relate to the unique involvement of Asp residues in energetically favorable ion pair formation. These studies clarify the dependence of triple-helix stability on the identity, position, and ionization state of charged residues.

An understanding of the cytokine cascade in a rheumatoid joint has led to the development of new therapeutic options, including drugs targeting tumor necrosis factor-alpha (TNF-alpha). The safety profile of these agents in patients with hepatitis-induced liver disease, however, remains a concern because of risks associated with immune suppression. To examine the effect of three different TNF-alpha antagonists, infliximab, etanercept, and adalimumab, on serum transaminases and hepatitis viral load in patients with rheumatoid arthritis (RA) and concurrent hepatitis B (HBV) or hepatitis C (HCV). Medical records of 11 patients with diagnosis of RA and documented seropositivity for hepatitis B or hepatitis C were retrospectively reviewed for worsening of hepatic inflammation and viral proliferation as measured by a rise in aspartate aminotransferase (AST) or alanine aminotransferase (ALT) and viral load while using these agents. Three patients had RA with concurrent chronic HBV and eight patients had RA with concurrent chronic HCV. Seven patients remained on a single anti-TNF-alpha agent and four patients switched to a second anti-TNF-alpha agent due to treatment failure. Two patients showed a transient elevation in AST and/or ALT from normal, but in all 11 patients, AST and ALT levels were within one time the upper range of normal at the conclusion of the study. No significant increase in viral load was seen except one patient who showed a fourfold increase from baseline. Our case series supports results obtained from previous studies examining the safety of anti-TNF-alpha agents in patients with underlying hepatic disease. Use of these agents in patients with HBV or HCV may be associated with a transient transaminitis but appears to be safe overall. In both groups, frequent monitoring of serum transaminase levels and viral load is essential.

Tumor necrosis factor (TNF)-alpha antagonists successfully modulate the pathogenesis of rheumatoid arthritis (RA). However, little is known about the effect of TNF-alpha blockade on the histology of chronic viral hepatitis. We describe the cases of two patients with RA, one with concurrent chronic hepatitis B virus and the other with hepatitis C virus infection who, as part of their evaluation, underwent liver biopsies while undergoing treatment with a TNF-alpha antagonist.