SUMMARY. The high variation often observed in the ex vivo fibroblastic-colony forming unit (CFU-f) assay is likely to be due to both biological and experimental variation. To determine whether we could improve experimental methods we developed an alternative method of bone marrow cell (BMC) isolation employing a centrifugation step. The osteogenic capacity of centrifugally isolated BMC was compared to that of BMC that were isolated using the standard "flushing" technique using the CFU-f assay. The centrifugation method was found to be both quick and simple to perform and allowed simultaneous preparation of all samples. Centrifugally isolated BMC gave rise to approximately 100% more cfu-ap and cfu-f in cultures from both tibiae and femurae. The proportion of alkaline phosphatase positive colonies remained the same and colony morphologies were similar for both isolation methods. Histological comparison of the flushed and spun bones showed that after the flushing procedure many cells remained in the marrow cavity especially in the trabecular area. In contrast, centrifugation completely emptied the marrow space of all cells except bone lining cells and osteoblasts. Thus the osteogenic capacity of the bone marrow can be expressed as the number of CFU-f per bone instead of the frequency as is the norm. Using these methods to isolate BMC for ex vivo investigations should lead to a reduction in CFU-f number variation due to the isolation method. http://link.springer-ny. com/link/service/journals/00223/bibs/65n5p411.html++ +hea
A great deal of the work characterizing stromal cell precursors in the bone marrow has been performed using the fibroblastic colony-forming unit (CFU-f) assay. However, the assay is limited in its usefulness by the necessity for manual colony counting which means that assay quantitation is highly subjective, time consuming, and much information regarding the colony size is lost. To rectify this, we have developed a computer-automated method for the analysis of CFU-f. Bone marrow cells were cultured at low density and treated with either prostaglandin E(2) (PGE(2)), basic fibroblast growth factor (bFGF), or dexamethasone, and colony formation was assessed by staining with methylene blue. After staining, the dishes were photographed over a light box using a digital camera and the image was then analyzed using Bioimage "Intelligent Quantifier" image analysis software which automatically locates and quantifies each individual colony. The data can then be imported to a spreadsheet program and processed. We have shown that this system can accurately identify, assign coordinates, and quantitate each individual colony. Colony numbers obtained with this method and manually counting showed a linear relationship with a correlation coefficient of 0.99. In addition, using the colony intensity and surface area data, the colony size can be calculated. With this methodology, we have shown that dexamethasone, PGE(2), and bFGF can all modulate total cell numbers in bone marrow stromal cells (BMSC) cultures but modulating both colony number and colony size.
Osteoblastic induction is commonly studied using the colony-forming unit-fibroblastic (CFU-f) assay, in which bone marrow stromal cells (BMC) are grown in a tissue culture environment permissive for osteoblastic differentiation (DMEM containing dexamethasone, ascorbic acid and beta-glycerophosphate). These cells form colonies, which express alkaline phosphatase, and form a collagenous matrix that becomes calcified. However, these same cells originate in the bone marrow where under normal circumstances they do not proliferate or differentiate despite being subjected to many of the same growth factors and hormones present within the tissue culture environment. We show here that phenol red, present within tissue culture medium as a pH indicator, may itself be a factor that permits osteoblastic recruitment. BMC cultured in the presence of the bone anabolic agents PGE2, PGA2, or bFGF, but in the absence of phenol red, failed to respond to these agents in terms of total or osteoblastic colony number. This effect was dose dependent, with low (2.5 mg/l) and high (15-20 mg/l) doses of phenol red being nonpermissive for the stimulatory effects of PGE2 whereas doses of 5-10 mg/l were permissive. Furthermore, the effects observed in the absence of phenol red could not be abrogated by the addition of 17beta-estradiol indicating that these effects cannot be attributed to estrogenic impurities within the phenol red preparation. This indicates that phenol red itself can affect the differentiation of BMC by a mechanism not previously described.
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