Copper and amine oxidases in connective tissue metabolism

Inner-sphere mechanism for molecular oxygen reduction catalyzed by copper amine oxidases

Copper and topaquinone (TPQ) containing amine oxidases utilize O2 for the metabolism of biogenic amines while concomitantly generating H2O2 for use by the cell. The mechanism of O2 reduction has been the subject of long-standing debate due to the obscuring influence of a proton-coupled electron transfer between the tyrosine-derived TPQ and copper, a rapidly established equilibrium precluding assignment of the enzyme in its reactive form. Here, we show that substrate-reduced pea seedling amine oxidase (PSAO) exists predominantly in the Cu(I), TPQ semiquinone state. A new mechanistic proposal for O2 reduction is advanced on the basis of thermodynamic considerations together with kinetic studies (at varying pH, temperature, and viscosity), the identification of steady-state intermediates, and the analysis of competitive oxygen kinetic isotope effects, (18)O KIEs, [kcat/KM((16,16)O2)]/[kcat/KM((16,18)O2)]. The (18)O KIE = 1.0136 +/- 0.0013 at pH 7.2 is independent of temperature from 5 degrees C to 47 degrees C and insignificantly changed to 1.0122 +/- 0.0020 upon raising the pH to 9, thus indicating the absence of kinetic complexity. Using density functional methods, the effect is found to be precisely in the range expected for reversible O2 binding to Cu(I) to afford a superoxide, [Cu(II)(eta(1)-O2)(-I)](+), intermediate. Electron transfer from the TPQ semiquinone follows in the first irreversible step to form a peroxide, Cu(II)(eta(1)-O2)(-II), intermediate driving the reduction of O2. The similar (18)O KIEs reported for copper amine oxidases from other sources raise the possibility that all enzymes react by related inner-sphere mechanisms although additional experiments are needed to test this proposal.

Copper and the synthesis of elastin and collagen

Copper's role in connective tissue is linked to the enzyme lysyl oxidase. From a biochemical perspective, copper is a cofactor for the enzyme and a determinant of its activity in connective tissues. Lysyl oxidase catalyses a post-translational oxidation of certain lysine and hydroxylysine residues. The peptidyl aldehydes so formed become active centres for the formation of cross-links in collagen and elastin. Less well understood is how copper controls the steady-state activity of lysyl oxidase; the enzyme fails in copper deficiency. Giving copper to a deprived animal increases lysyl oxidase activity in aortic tissue. Such activation in vivo appears to require caeruloplasmin. Suspending aortic tissue in a copper-enriched growth medium also activates lysyl oxidase provided that tissue structure is kept intact. Activation in vitro occurs with the binding of copper to a large-molecular-weight component, presumably the enzyme. Binding will not occur if protein synthesis is blocked. These studies clearly show that the synthesis of mature elastin and collagen can be controlled by the availability of copper. They further suggest that transport of copper to aortic tissue and its engagement to lysyl oxidase are linked to the synthesis or lysyl oxidase, an extracellular carrier, or both.

Copper complexes stimulate hemopoiesis and lymphopoiesis

Copper(II)2(3,5-diisopropylsalicylate)4 [Cu(II)2(3,5-DIPS)4] is a synthetic copper complex with a variety of effects, including radiation recovery, anti-inflammatory, and accelerated wound healing activities. When C57BL/6 mice were injected subcutaneously with 80 mumol/kg Cu(II)2(3,5-DIPS)4 their spleens significantly enlarged. This splenomegally lasted for at least 3 weeks and was accompanied by increased myelopoiesis in the spleen. Bone marrow had no significant change in cellularity or myelopoiesis. The treatment with Cu(II)2(3,5-DIPS)4 had only minor effects on the ability of spleen cells to respond to mitogenic or antigenic stimulation. Cu(II)2(3,5-DIPS)4 did stimulate lymphopoiesis, since it accelerated the recovery of immune reactivity following exposure to 8 Gy whole body irradiation. Copper levels in the spleens and bone marrow of unirradiated mice treated with Cu(II)2(3,5-DIPS)4 were not significantly elevated 24 hr after treatment and copper levels were transiently reduced 7 days after treatment.

Copper(II)(3,5-diisopropylsalicylate)2 accelerates recovery of B and T cell reactivity following irradiation

Copper(II)(3,5-diisopropylsalicylate)2 (Cu-DIPS), administered subcutaneously to mice at 80 mg/kg body weight, had marked radioprotective activity. Given 3 h before exposure to 8.0 Gy (800 rad) irradiation, Cu-DIPS increased the 42-day survival from 40% to 86%. Seven days after exposure to 8.0 Gy, there were severe reductions in spleen weight (73%) and cellularity (98%) in both Cu-DIPS- and vehicle-treated mice. Viable spleen cells collected 7 days after irradiation were totally unresponsive to mitogenic or antigenic stimulation regardless of Cu-DIPS or vehicle treatment, suggesting that Cu-DIPS did not prevent radiation-induced damage to mature lymphocytes. At 14 days, when Cu-DIPS-treated mice started to show improved survival over vehicle-treated mice, spleen weights and cellularity were 2.5- and 3.5-fold higher, respectively, in Cu-DIPS-treated mice. Treatment with Cu-DIPS not only enhanced splenic repopulation, but also accelerated the reappearance of both B and T cell reactivities. Spleen cell responsiveness to the B cell mitogen, lipopolysaccharide (LPS), and the T cell mitogen, concanavalin A (Con A), regenerated significantly faster in Cu-DIPS-treated mice. Cu-DIPS also significantly accelerated the regeneration of T-dependent antibody induction. Based on these assays of immunocompetence, Cu-DIPS-treated mice had, on average, a seven-fold greater capacity to respond to immune stimulation than vehicle-treated mice 24 days after irradiation.

The inhibition of protein-lysine 6-oxidase by various lathyrogens. Evidence for two different mechanisms

Lathyrogens decrease collagen and elastin cross-linking by inhibiting lysine oxidase. The lathyrogens isoniazid and semicarbazide decrease liver pyridoxal phosphate and are teratogenic; all their effects are reversed by pyridoxal. beta-Aminopropionitrile, another lathyrogen, does not affect liver pyridoxal phosphate, and its lathyrogenic and teratogenic effects are not reversed by pyridoxal. Time courses of these effects differ greatly, suggesting enzyme inhibition by different mechanisms.

Antilupus activity of copper (II)

Collagen-like syndrome was induced in rats by oral hydralazine administration during 5 months. After 4 months, a subgroup of rats was shifted from the standard diet to the diet supplemented with copper (II) (60 micrograms of copper per g of pellet) as copper sulphate. A decreased serum copper concentration was noted, LE cells were observed in the blood of 75% of rats fed with standard diet. In the subgroup of copper supplemented rats, the LE cells were observed in 40% of rats only. The activity of superoxide dismutase, the antioxidative copper-dependent enzyme, was significantly lower in erythrocytes of rats fed with standard diet, than the activity in rats fed with copper supplemented diet. These results are briefly discussed.

Copper and ceruloplasmin (Cp) concentrations during the acute inflammatory process in the rat

We have measured the concentration of copper and ceruloplasmin in serum of rats with carrageenan foot-oedema and in serum and exudate of rats with carrageenan pleurisy. Both serum copper and ceruloplasmin were found to increase in both models of inflammation. In these experimental conditions we have shown a strong positive correlation between copper and ceruloplasmin, in the serum of both normal and inflamed rats.

Concerning the role of endogenous copper in the acute inflammatory process

The development of two models of acute inflammation (carrageenan-induced foot oedema and pleurisy) was studied in rats after 1 month of a 0.2 p.p.m. copper-deficient diet and after 5 months of a 0.6-0.8 p.p.m. copper-deficient diet. A 'pro-inflammatory' effect of copper deficiency was observed with the 0.2 p.p.m. diet, whilst no effect was evident following the 0.6-0.8 p.p.m. copper deficient diet. These results are briefly commented upon.

Contribution to the aetiology of synovitis in chickens, with special reference to non-infective factors. IV

Summary The comparative study reported in the present paper was undertaken to collect data on the collagen content and collagen quality of tendons showing high (low) tensile strength levels and a compact (loose) histological structure. It was shown that tendon tissues of these two groups do not differ in this regard. The effect of administering a number of nutrients (known to be essential in collagenesis) was tested during this study. Administration of these nutrients did not prevent synovitis and did not increase tensile strength.