Pigmentation Chemistry and Radical-Based Collagen Degradation in Alkaptonuria and Osteoarthritic Cartilage.

Wing Ying Chow, Brendan P Norman, Norman B Roberts, Lakshminarayan R Ranganath, Christian Teutloff, Robert Bittl, Melinda J Duer, James A Gallagher, Hartmut Oschkinat

Angewandte Chemie (International ed. in English) 2020 Jul 13

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Alkaptonuria (AKU) is a rare disease characterized by high levels of homogentisic acid (HGA); patients suffer from tissue ochronosis: dark brown pigmentation, especially of joint cartilage, leading to severe early osteoarthropathy. No molecular mechanism links elevated HGA to ochronosis; the pigment's chemical identity is still not known, nor how it induces joint cartilage degradation. Here we give key insight on HGA-derived pigment composition and collagen disruption in AKU cartilage. Synthetic pigment and pigmented human cartilage tissue both showed hydroquinone-resembling NMR signals. EPR spectroscopy showed that the synthetic pigment contains radicals. Moreover, we observed intrastrand disruption of collagen triple helix in pigmented AKU human cartilage, and in cartilage from patients with osteoarthritis. We propose that collagen degradation can occur via transient glycyl radicals, the formation of which is enhanced in AKU due to the redox environment generated by pigmentation. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Citation

Wing Ying Chow, Brendan P Norman, Norman B Roberts, Lakshminarayan R Ranganath, Christian Teutloff, Robert Bittl, Melinda J Duer, James A Gallagher, Hartmut Oschkinat. Pigmentation Chemistry and Radical-Based Collagen Degradation in Alkaptonuria and Osteoarthritic Cartilage. Angewandte Chemie (International ed. in English). 2020 Jul 13;59(29):11937-11942