desmosine and 3-hydroxypyridine

Photocarcinogenesis and photoaging are established consequences of chronic exposure of human skin to solar irradiation. Accumulating evidence supports a causative involvement of UVA irradiation in skin photo-damage. UVA photodamage has been attributed to photosensitization by endogenous skin chromophores leading to the formation of reactive oxygen species and organic free radicals as key mediators of cellular photooxidative stress. In this study, 3-hydroxypyridine derivatives contained in human skin have been identified as a novel class of potential endogenous photosensitizers. A structure-activity relationship study of skin cell photosensitization by endogenous pyridinium derivatives (pyridinoline, desmosine, pyridoxine, pyridoxamine, pyridoxal, pyridoxal-5'-phosphate) and various synthetic hydroxypyridine isomers identified 3-hydroxypyridine and N-alkyl-3-hydroxypyridinium cation as minimum phototoxic chromophores sufficient to effect skin cell sensitization toward UVB and UVA, respectively. Photosensitization of cultured human skin keratinocytes (HaCaT) and fibroblasts (CF3) by endogenous and synthetic 3-hydroxypyridine derivatives led to a dose-dependent inhibition of proliferation, cell cycle arrest in G2/M, and induction of apoptosis, all of which were reversible by thiol antioxidant intervention. Enhancement of UVA-induced intracellular peroxide formation and p38 mitogen-activated protein kinase-dependent stress signaling suggest a photooxidative mechanism of skin cell photosensitization by 3-hydroxypyridine derivatives. 3-hydroxypyridine derivatives were potent photosensitizers of macromolecular damage, effecting protein (RNase A) photocross-linking and peptide (melittin) photooxidation with incorporation of molecular oxygen. Based on these results, we conclude that 3-hydroxypyridine derivatives comprising a wide range of skin biomolecules, such as enzymatic collagen cross-links, B6 vitamers, and probably advanced glycation end products in chronologically aged skin constitute a novel class of UVA photosensitizers, capable of skin photooxidative damage.

Topics: Antioxidants; Apoptosis; Cations; Cell Cycle; Cell Division; Cell Line; Cells, Cultured; Desmosine; Dose-Response Relationship, Drug; Fibroblasts; Flow Cytometry; Humans; Hydrogen Peroxide; Light; Mitogen-Activated Protein Kinases; Models, Chemical; Oxidative Stress; p38 Mitogen-Activated Protein Kinases; Peptides; Photosensitizing Agents; Pyridines; Pyridinium Compounds; Reactive Oxygen Species; Ribonuclease, Pancreatic; Skin; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; Structure-Activity Relationship; Ultraviolet Rays; Vitamin B 6

Sprague-Dawley rats were exposed for 6 h daily to 0.8 ppm of ozone and 14.4 ppm of nitrogen dioxide. Approximately 7 to 10 wk after the initiation of exposure, animals began to demonstrate respiratory insufficiency and severe weight loss. About half of the rats died between Days 55 and 78 of exposure; no overt ill effects were observed in animals exposed to filtered air, to ozone alone, or to nitrogen dioxide. Biochemical findings in animals exposed to ozone and nitrogen dioxide included increased lung content of DNA, protein, collagen, and elastin, which was about 300% higher than the control values. The collagen-specific crosslink hydroxy-pyridinium, a biomarker for mature collagen in the lung, was decreased by about 40%. These results are consistent with extensive breakdown and remodeling of the lung parenchyma and its associated vasculature. Histopathologic evaluation showed severe fibrosis, alveolar collapse, honeycombing, macrophage and mast cell accumulation, vascular smooth muscle hypertrophy, and other indications of severe progressive interstitial pulmonary fibrosis and end-stage lung disease. This unique animal model of progressive pulmonary fibrosis resembles the final stages of human idiopathic pulmonary fibrosis and should facilitate studying underlying mechanisms and potential therapy of progressive pulmonary fibrosis.

Topics: Administration, Inhalation; Animals; Collagen; Desmosine; Disease Models, Animal; DNA; Elastin; Environmental Exposure; Hydroxyproline; Lung; Male; Nitrogen Dioxide; Ozone; Proteins; Pulmonary Fibrosis; Pyridines; Rats; Rats, Sprague-Dawley; Survival Rate

The effects of chronic exposure to ozone on lung collagen crosslinking were investigated in two groups of juvenile cynomolgus monkeys exposed to 0.61 ppm of ozone 8 hrs per day for 1 year. One group was killed immediately after the exposure period; the second exposed group breathed filtered air for 6 months after the ozone exposure before being killed. Previous studies of these monkeys had revealed that lung collagen content was increased in both exposed groups (J.A. Last et al., (1984). Toxicol. Appl. Pharmacol. 72, 111-118). In the present study specific collagen crosslinks were quantified in order to determine whether the excess collagen in the lungs of these animals was structurally normal or abnormal. In the group killed immediately after exposure, the difunctional crosslink dehydrodihydroxylysinonorleucine (DHLNL) was elevated, as was the ratio of DHLNL to dehydrohydroxylysinonorleucine (HLNL). Lung content of the mature nonreducible crosslink hydroxypyridinium was also increased in this group. In the group killed after a 6-month postexposure period, lung content of the difunctional crosslinks DHLNL and HLNL was indistinguishable from control values. However, lung hydroxypyridinium content was significantly increased. The changes in collagen crosslinking observed in the group killed at the termination of exposure are characteristic of those seen in lung tissue in the acute stage of experimental pulmonary fibrosis. The changes seen in the postexposure group suggest that while the lung collagen being synthesized at the time the animals were killed was apparently normal, "abnormal" collagen synthesized during the period of ozone exposure was irreversibly deposited in the lungs. This study suggests that long-term exposure to relatively low levels of ozone may cause irreversible changes in lung collagen structure.

Topics: Animals; Chromatography, High Pressure Liquid; Collagen; Desmosine; Dipeptides; Female; Lung; Macaca fascicularis; Male; Pyridines; Sulfuric Acids

During pregnancy the collagen content of the human uterus increases sevenfold and the elastin content increases fourfold to fivefold. The stable pyridinoline cross-link is found in uterine collagen at a level of 0.11 mol per mole of collagen. The same ratio, or a higher one, is found at the end of pregnancy, indicating that pyridinoline synthesis keeps pace with the rapid synthesis of collagen. This cross-link would participate in the maintenance of high mechanical strength of the uterus needed during parturition. Uterine elastin contains 2.4 residues of desmosine plus isodesmosine in 1000 residues of amino acids. This value falls to 0.95 at term, indicating that synthesis of desmosines does not keep pace with the synthesis of elastin. Therefore, desmosine measurements do not provide an accurate index of elastin changes in pregnancy. Collagen and elastin contents in nongravid uteri increase with successive pregnancies; the cross-links remain constant during this change.

Topics: Amino Acids; Collagen; Connective Tissue; Desmosine; Elastin; Female; Humans; In Vitro Techniques; Isodesmosine; Postpartum Period; Pregnancy; Pyridines; Reproduction; Uterus