Oxidation products of amino acids and collagen

Influence of residual composition on the structure and properties of extracellular matrix derived hydrogels

In this work, hydrolysates of extracellular matrix (hECM) were obtained from rat tail tendon (TR), bovine Achilles tendon (TAB), porcine small intestinal submucosa (SIS) and bovine pericardium (PB), and they were polymerized to generate ECM hydrogels. The composition of hECM was evaluated by quantifying the content of sulphated glycosaminoglycans (sGAG), fibronectin and laminin. The polymerization process, structure, physicochemical properties, in vitro degradation and biocompatibility were studied and related to their composition. The results indicated that the hECM derived from SIS and PB were significantly richer in sGAG, fibronectin and laminin, than those derived from TAB and TR. These differences in hECM composition influenced the polymerization and the structural characteristics of the fibrillar gel network. Consequently, the swelling, mechanics and degradation of the hydrogels showed a direct relationship with the remaining composition. Moreover, the cytocompatibility and the secretion of transforming growth factor beta-1 (TGF-β1) by macrophages were enhanced in hydrogels with the highest residual content of ECM biomolecules. The results of this work evidenced the role of the ECM molecules remaining after both decellularization and hydrolysis steps to produce tissue derived hydrogels with structure and properties tailored to enhance their performance in tissue engineering and regenerative medicine applications.

[Interaction of lipids and meat proteins. 2. Digestibility of proteins in vitro, thermohydrolysis of collagen, changes in the content of essential amino acids and coefficients of the relative nutritive value of proteins]

Changes in the nutritive value of meat under the influence of an interaction between oxidized fats and proteins were studied in model experiments. Parameters were the digestibility of protein, sensitivity of tissue against thermohydrolysis, changes in the content of essential amino acids and in the RNV coefficient of the protein. Muscle gel and tissue served as meat substrates, methyl ester of linoleic acid and its oxidation products were used as fat substrates. It has been found that reactions of the oxidation products of methyl linoleate with meat proteins lead to a crosslinking of proteins. Hexanal and hydroperoxide of the oxidized methyl linoleate influence the decrease in digestibility of muscle protein and the thermohydrolysis of the collagen. Proteins of pasteurized gels showed losses in essential amino acids, which corresponded to a lower nutritive value (determined in the RNV coefficient).

Degradation of articular cartilage by copper and hydrogen peroxide

When porcine articular cartilage particles were incubated in the presence of Cu2+ and H2O2 at pH 7.4, solubilization of collagen and proteoglycan was observed. Both agents were necessary and the rate of solubilization was concentration dependent. Other transition metal ions showed much lower catalytic activity. The solubilized polypeptides were polydispersed in size and the hydroxyproline content of the larger fragments was 13% by weight. Further incubation of the released material with Cu2+ and H2O2 resulted in further degradation and partial destruction of hydroxyproline residues. Competitive studies with scavengers of OH X and 1O2 as well as the effect of D2O excluded these two species as major mediators in this system.

Nonenzymatic hydroxylations of proline and lysine by reduced oxygen derivatives

The biosynthesis of trans-3- and trans-4-hydroxyprolines and 5-hydroxylysine in animal cells requires polypeptide proline or lysine, enzymes and cofactors including iron, and possibly involves peroxidatic intermediates. Several laboratories have reported the presence of low-molecular-weight hydroxyproline and hydroxylysine peptides in cell and organ cultures. We found that these small peptides contained the trans-3 and cis-4 isomers of hydroxyproline as well as trans-4 ones and that their production was not completely inhibited by alpha, alpha-dipyridyl, and iron chelator and effective inhibitor of enzyme-mediated hydroxylations. It is known that oxygen or hydrogen peroxide in the presence of metal can hydroxylate proline and other aromatic compounds. We show here that reduced oxygen derivatives can hydroxylate both free and polypeptide-bound proline and lysine, and that scavengers of hydroxyl radicals suppress, but do not completely inhibit, this reaction. Reduced oxygen derivatives can be generated in normal and pathological circumstances, and some of the low-molecular-weight hydroxyproline and hydroxylysine peptides found in cell and organ cultures might be derived from these derivatives and therefore do not reflect collagen turnover, but rather some other cellular activity.

Copper (II) complex-catalyzed oxidation of NADH by hydrogen peroxide

Among various metal ions of physiological interest, Cu(2+) is uniquely capable of catalyzing the oxidation of NADH by H2O2. This oxidation is stimulated about fivefold in the presence of imidazole. A similar activating effect is found for some imidazole derivatives (1-methyl imidazole, 2-methyl imidazole, andN-acetyl-L-histidine). Some other imidazole-containing compounds (L-histidine,L-histidine methyl ester, andL-carnosine), however, inhibit the Cu(2+)-catalyzed peroxidation of NADH. Other chelating agents such as EDTA andL-alanine are also inhibitory. Stoichiometry for NADH oxidation per mole of H2O2 utilized is 1, which excludes the possibility of a two-step oxidation mechanism with a nucleotide free-radical intermediate. About 92% of the NADH oxidation product can be identified as enzymatically active NAD(+). D2O, 2,5-dimethylfuran, and 1,4-diazabicyclo [2.2.2]-octane have no significant effect on the oxidation, thus excluding(1)O2 as a mediator. Similarly, OH· is also not a likely intermediate, since the system is not affected by various scavengers of this radical. The results suggest that a copper-hydrogen peroxide intermediate, when complexed with suitable ligands, can generate still another oxygen species much more reactive than its parent compound, H2O2.