Influence of oxygen at atmospheric and high pressure on the developing tooth germ in rat embryos

Hypoxia increases the expression of enamel genes and cytokines in an ameloblast-derived cell line

The aim of this study was to investigate the effect of hypoxic conditions on the expression of enamel genes and on the secretion of alkaline phosphatase (ALP), lactate dehydrogenase (LDH), cytokines, and interleukins by an ameloblast-derived cell line. Murine ameloblast-derived cells (LS-8 cells) were exposed to 1% oxygen for 24 and 48 h and harvested after 1, 2, 3, and 7 d. The effect of culture in hypoxic conditions on the expression of structural enamel matrix genes and on the secretion of cytokines and interleukins, as well as ALP and LDH, into the cell-culture medium was calculated relative to the expression and secretion of these factors by untreated cells (controls) at each time point. Hypoxia increased expression of the structural enamel matrix genes amelogenin (Amelx), ameloblastin (Ambn), and enamelin (Enam), and the enamel protease matrix metalloproteinase-20 (Mmp20). Expression of hypoxia-inducible factor 1-alpha (Hif1α), and secretion of several vascularization factors and pro-inflammatory factors, were increased after 24 and 48 h of hypoxia. The ALP activity was reduced after 24 and 48 h of hypoxia, whereas the LDH level in the cell-culture medium was higher after 24 h of hypoxic conditions compared with 48 h. In conclusion, hypoxic exposure may disrupt the controlled fine-tuned expression and processing of enamel genes, and promote the secretion of pro-inflammatory factors.

Osteogenesis and leukopoiesis within diffusion-chamber implants of isolated bone marrow subpopulations

The developmental potential of isolated rabbit bone marrow cell populations was examined following autogeneous implantation into diffusion chambers. After 4 weeks, the implants were harvested and processed for light and electron microscopy. More total tissue was formed in abdominally implanted chambers than in corresponding femoral chambers. Two of the separated marrow cell populations produced significantly greater amounts of fibrous connective tissue, cartilage, and bone than did whole-marrow controls. These two populations, which were defined by density gradients of 1.050-1.055 gm/cm3 and 1.064-1.067 gm/cm3, consistently produced a fibrous connective tissue nodule in which were found dispersed foci of hyaline cartilage and woven bone. The denser population was distinguished further by the presence of leukopoietic foci in several of the implant chambers. Cartilage foci were found predominantly towards the center of the tissue nodules, whereas bone was dominant towards the periphery. Blood vessels, osteoclasts, bone remodeling, and mature lamellar bone were found only in those chambers which had been penetrated by the host's vascular system. The results indicate that 1) normal marrow tissue contains two separate osteoprogenitor cell populations; 2) these two progenitor populations represent separate osteogenic and chondrogenic capabilities; 3) one of these populations possesses a leukopoietic as well as an osteogenic potential; and 4) a competent vascular system is essential for the remodelling of bone into mature bone organs.

Growth of the tooth germ in new born rats exposed to oxygen at atmospheric and high pressure

Newborn rats were exposed intermittently to oxygen at high pressure (93 psig) 15 times for a period of eight days. Growth of the tooth germs was the same as that of the control rats in air at atmospheric pressure, with the exception of the enamel and dentin layers, which grew less. The width of the tooth germ of rats exposed to oxygen at atmospheric pressure increased.