Inhibition of membrane bone formation by vitamin A in the embryonic chick mandible

Retinoic acid-induced cell death in the wound epidermis of regenerating zebrafish fins

Previous work has shown that treatment with retinoic acid (RA) can induce malformations in regenerating pectoral and caudal fins. RA-treated regenerates are narrower than unamputated and regenerated control fins because of a decrease in the distance between rays, and either partial or total fusion of some of them. In order to tackle the issue of how RA induces its teratogenic effects on regenerating fins, and which cell types may be specifically affected by RA, we have examined the cellular changes occurring in early regenerates following treatment with retinoids. The work presented here shows for the first time that RA induces significant apoptosis in the wound epidermis, but not in the mesenchyme, of a regenerating appendage, besides inhibiting blastema development as reported in other species. We also show that RA does not retard regeneration by inhibiting accumulation of blastemal cells, but probably by impairing their ability to migrate distal to the amputation plane. This effect is rapidly reversed by discontinuing the treatment, and within 24 hr of removing the drug, blastema development is well advanced. By this time the teratogenic effects induced by RA are already apparent. A correlation between the length of the apical ectodermal ridge (AER) and the number of digits formed has been demonstrated in developing limb buds. We therefore suggest that RA-induced patterning abnormalities in regenerating fins are the consequence of a reduction in the size of the wound epidermis, due to increased cell death, which would affect patterning of the underlying mesenchyme.

Comparative assessment of the toxicology of vitamin A and retinoids in man

As the title implies, any assessment of the toxic effects of vitamin A derivatives must distinguish between vitamin A in the truest sense, i.e. retinol, and retinoic acid and its synthetic derivatives. Just as no single description is universally applicable to the mode of action of vitamin A derivatives, so too do their toxic effects defy generalization. The recommendation made in 1982 by IUPAC [Eur. J. Biochem., 129 (1989) 1] to designate all derivatives with the typical structure of the vitamin as being retinoids may be chemically logical and correct but, when it comes to describing the effects and side-effects of vitamin A derivatives, it leads to misunderstandings. Retinol, which is frequently used as synonym for vitamin A, can eliminate all symptoms of vitamin A deficiency if it is taken in sufficient quantity with the diet. The term retinol will therefore be used here as a synonym for vitamin A whereas retinoic acid and its derivatives--including the synthetic ones--will be referred to as retinoids because they do not cover the whole spectrum of effects exerted by retinol and because they also vary markedly in their side-effects. In contrast to the nomenclature proposed by IUPAC, this system provides a clear and logical distinction for describing biological processes. Other authors have favoured it in recent times [Chytil, F., J. Am. Acad. Dermatol., 15 (1986) 741; Olson, J.A., Semin. Oncol., x (3) (1983) 290; Olson, J.A., Am. J. Clin. Nutr., 45 (1987) 704; Zbinden, G., Acta Dermatovener., 74 (1975) 36]. By vitamin A, therefore, is meant all derivatives that can possibly originate from retinol in the organism. This also covers the small quantities of retinoic acid formed from retinol. On the other hand, by retinoids is meant the natural retinoic acid derivatives and their synthetic forms in their special modes of action. Since retinoic acid cannot be reduced to retinol in the organism, this nomenclature provides a clear demarcation within the biological system. Vitamin A is essential to the growth and development of higher life forms and functions in many different ways within the organism. Although vitamin A was one of the first vitamins to be described, even today there is still some uncertainty as to its mode of action, with the exception of that of retinal (vitamin A aldehyde) in vision.(ABSTRACT TRUNCATED AT 400 WORDS)

Retinyl acetate-induced arthritis in C3H-A(vy) mice

Severely impaired musculoskeletal mobility in C3H-A(vy) mice was noted during a pharmacologic trial evaluating the antitumorigenic properties of retinyl acetate (RAc). To determine the etiology of this impairment, we studied 103 female C3H-A(vy) mice that were fed RAc in daily doses of 75-300 micrograms or placebo and were killed after 3-16 months. Whole-body radiographs and histologic sections of the hindlimbs were scored for presence and severity of arthritis. C3H-A(vy) mice treated with RAc in any dose had a significantly higher incidence of arthritis than placebo-treated mice. Histologic evidence of enthesopathic disease closely paralleled the radiographic changes and ranged from small enthesophytes at tendinous and capsular insertions to complete periarticular bony bridging. Articular cartilage was not grossly affected. The incidence and severity of arthritis were significantly correlated with the total dose of RAc administered. The bony metaplasia induced by RAc was similar to the pathologic changes caused by other retinoids. This model may be useful for studying the pathogenesis of periarticular bone formation in diffuse idiopathic skeletal hyperostosis and related syndromes.

Development of osteogenic and chondrogenic potentials along the mediolateral axis of the embryonic chick mandible

Various regions of the mandibular process were tested for these potentials to determine whether regional differences exist and vary with embryonic age. Mandibular processes from HH stages 17-21.5 were cultured and grafted intact, or were subdivided into medial, mediolateral and lateral fragments and the separate regions cultured or grafted. The intact mandible from all these stages can form cartilage and membrane bone, but the 3 regions are not equally osteogenic and chondrogenic. The lateral region from all stages could form cartilage and membrane bone; the mediolateral region could form cartilage and membrane bone but, in mediolateral fragments from HH stage 17, membrane bone was formed only in scant amounts. The medial region from HH stages 17 and 18 formed cartilage in only 50 per cent of cases and never formed membrane bone. By HH stage 20, the medial region could form membrane bone, but only in scant amounts. Medial fragments from HH stage 21.5 formed extensive membrane bone and cartilage. The acquisition of these potentials, therefore, proceeds in a lateral-to-medial sequence, and the acquisition of an osteogenic potential lags slightly behind that of a chondrogenic potential. These findings do not indicate the mechanisms by which the two subpopulations of chondrogenic and osteogenic cells are distinguished from one another, but they give the temporal and spatial sequence in which this determination must occur.