The effect of a vitamin B-6 antagonist, 4-deoxypyridoxine, on the cross-linking of collagen in the developing chick embryo

Combined osteolathyric effects of beta-aminopropionitrile and penicillamine on Xenopus embryos: statistical comparison with dose-addition and independence

The combined osteolathyric effects of beta-aminopropionitrile (beta APN) and penicillamine (PNC) on developing Xenopus embryos were determined and compared with theoretical effects for the dose-addition and independence models. The testing protocol utilized a 1.2-factor matrix design that generated two single chemical and seven mixture concentration-response curves within 36 treatments. Testing was for 96-h with daily solution removal and replacement. The chi 2 goodness-of-fit test was used to compare experimental responses with theoretical responses. Response curve analyses indicated, in general, a combined effect between that expected for dose-addition and that for independence, which is a combined effect typical of chemicals acting dissimilarly.

Pyridoxine deficiency affects biomechanical properties of chick tibial bone

The mechanical integrity of bone is dependent on the bone matrix, which is believed to account for the plastic deformation of the tissue, and the mineral, which is believed to account for the elastic deformation. The validity of this model is shown in this study based on analysis of the bones of vitamin B6-deficient and vitamin B6-replete chick bones. In this model, when B6-deficient and control animals are compared, vitamin B6 deficiency has no effect on the mineral content or composition of cortical bone as measured by ash weight (63 +/- 6 vs. 58 +/- 3); mineral to matrix ratio of the FTIR spectra (4.2 +/- 0.6 vs. 4.5 +/- 0.2), line-broadening analyses of the X-ray diffraction 002 peak (beta 002 = 0.50 +/- 0.1 vs. 0.49 +/- 0.01), or other features of the infrared spectra. In contrast, collagen was significantly more extractable from vitamin B6-deficient chick bones (20 +/- 2% of total hydroxyproline extracted vs. 10 +/- 3% p < or = 0.001). The B6-deficient bones also contained an increased amount of the reducible cross-links DHLNL, dehydro-dihydroxylysinonorleucine, (1.03 +/- 0.07 vs. 0.84 +/- 0.13 p < or = 0.001); and a nonsignificant increase in HLNL, dehydro-hydroxylysinonorleucine, (0.51 +/- 0.03 vs. 0.43 +/- 0.03, p < or = 0.10). There were no significant changes in bone length, bone diameter, or area moment of inertia. In four-point bending, no significant changes in elastic modulus, stiffness, offset yield deflection, or fracture deflection were detected. However, fracture load in the B6-deficient animals was decreased from 203 +/- 35 MPa to 151 +/- 23 MPa, p < or = 0.01, and offset yield load was decreased from 165 +/- 9 MPa to 125 +/- 14 MPa, p < or = 0.05. Since earlier histomorphometric studies had demonstrated that the B6-deficient bones were osteopenic, these data suggest that although proper cortical bone mineralization occurred, the alterations of the collagen resulted in changes to bone mechanical performance.

Developmental changes in skin collagen biosynthesis pathway in posthatch male and female chickens

The developmental changes in skin collagen biosynthesis pathway in male and female chickens were evaluated. Concentration of collagen, levels of mRNA for collagen type I subunits and for lysyl hydroxylase, and the level of three lysyl oxidase-derived cross-links: dehydro-dihydroxylysinonorleucine (DHLNL), dehydro-hydroxylysinonorleucine (HLNL), and dehydro-histidinohydroxymerodesmosine (HHMD) were determined during 4 wk posthatching. Skin collagen content increased with age and was higher in males than in females. In both sexes, the expression of the genes coding for alpha 1 and alpha 2 of collagen type I decreased with age: alpha 1(I) gene expression decreased from Day 3 onwards, whereas the reduction in alpha 2(I) gene expression started 1 wk later. At all ages examined, the expression of both genes was higher in male than in female skin. Males and females lysyl hydroxylase gene expression remained low until Day 16, after which an increase in the enzyme gene expression was observed. An increase in skin HLNL content was observed from Day 3 in both sexes reaching a peak in males at Day 9 and in females 1 wk later. The DHLNL content, which was higher in males than in females at all ages tested, dramatically decreased in both male and female skin from 3 d of age, reaching its lowest level at Day 16, and remained at that low level thereafter. The skin content of HHMD in males and females followed an oscillatory behavior with higher peaks in the male skin. The results suggest that the higher tensile strength of male skin than female skin may be due to the elevated skin collagen content that resulted from increased expression in collagen type I genes on the one hand, and from the higher amounts of various collagen cross-links on the other.

Comparative joint actions of semicarbazide and thiosemicarbazide on induction of malformations and osteolathyrism in mixtures with benzoic hydrazide

A developed mixture testing protocol, evaluating malformation of Xenopus embryos, was used to examine the joint actions of semicarbazide (SC) and thiosemicarbazide (TSC) with benzoic hydrazide (BZH). These compounds were selected to evaluate the effect of a substitution of sulfur for oxygen on osteolathyrism induced in Xenopus embryos. Binary combinations of SC with BZH and TSC with BZH were tested using three mixture ratios for each combination. Each compound was simultaneously tested alone in 96 h static-renewal tests, starting with late-blastula stage embryos. Toxic unit analysis, evaluating induction of malformations in general and osteolathyrism specifically, indicated the joint action for each combination was concentration addition. The results indicate that the three chemicals are similar and non-interactive and are likely to induce osteolathyrism by the same primary mechanism of action.

Joint toxic action of binary mixtures of osteolathyrogens at malformation-inducing concentrations for Xenopus embryos

The joint action of binary mixtures of the osteolathyrogens semicarbazide (SC), beta-aminopropionitrile (beta APN) and penicillamine (PNC) were determined at malformation-inducing concentrations for Xenopus embryos. Tests were static with renewal every 24 h for the 96-h test period. Simultaneous tests on each individual component of the binary mixtures alone gave baseline malformation data (EC50) for joint action analyses. Toxic unit analysis and isobole diagrams were used to determine the type of joint action for 3:1, 1:1 and 1:3 mixtures of each combination. The joint action was concentration additive (strictly additive) for SC with beta APN and response additive (less-than-additive) for SC with PNC and beta APN with PNC. The joint actions were not changed when only osteolathyrogenic lesions, rather than all types of malformations, were considered. The different specific location and character of PNC lesions, as opposed to those for SC and beta APN, may signify a different type of osteolathyrogenic effect for PNC. The mixture testing approach has potential value in determining compounds that act similarly.

Nature of the organic cofactor of pig plasma benzylamine oxidase

The identification of the organic cofactor of pig plasma benzylamine oxidase is described. Acid hydrolysis of the enzyme in argon in the presence of phenylhydrazine (6 h at 115 degrees C in 0.027 M sulphuric acid) allowed the isolation of an adduct which was purified by HPLC and identified as phenylhydrazone of pyridoxal by spectrophotometry, spectrofluorimetry and mass spectrometry.

Protein lysine 6-oxidase (lysyl oxidase) cofactor: methoxatin (PQQ) or pyridoxal?

1. Treatment of chick embryos with two lathyrogens lowered lysyl oxidase and increased collagen extractability. 2. Subsequent treatment with pyridoxal restored both parameters towards normal, whereas PQQ treatment was less effective. 3. These results suggest the requirement of a pyridoxal derivative for the formation of the enzyme, acting either as cofactor or because its formation requires some pyridoxal-dependent enzyme. The cochromatography of the enzyme with [3H]pyridoxine-derived radioactivity supports the cofactor role. 4. The conclusions of other authors that lysyl oxidase contains PQQ relates to enzymes from other species or to amine oxidases not characterised as lysyl oxidase.

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.

Effect of vitamin B-6 (pyridoxine) deficiency on lung elastin cross-linking in perinatal and weanling rat pups

Weanling and perinatal rats were rendered vitamin B-6 (pyridoxine)-deficient. The rat pups were nursed from vitamin B-6-deficient or -sufficient dams and were killed at day 15 after parturition. The weanling rats were fed vitamin B-6-deficient or -sufficient diets and were killed after 5 weeks of treatment. Lung elastin from the groups of rats was then studied with respect to its content of lysine-derived cross-linking amino acids. Lung lysyl oxidase activity was also measured. B-6 deficiency decreased the number of lysine residues in elastin that were converted into the cross-linking amino acid precursor allysine. However, a more significant defect in cross-link formation was an apparent block in the condensation steps leading to the formation of desmosine. Desmosine was decreased, with an increase in the amounts of aldol condensation products (aldol CP) in elastin. It is proposed that the elevation in aldol CP results from the formation of thiazines, which are produced from the reaction between aldehyde and homocysteine. The concentration of homocysteine is significantly elevated in vitamin B-6-deficient rats.