Albert E. Sobel

Local factors in the mechanism of calcification.

The fact that normal mineralization takes place at specific sites in the body indicates that a “local factor(s)” present in the calcifying matrix favors the process which gives mineralized tissues their characteristic hardness. The nature and operation of the “local factor(s)” may be regarded as the key problem in studies involving the understanding of the mineralizing process. The present approach to understanding the “local factor(s)” stemmed from physicochemical concepts of phase rule and solubility product. An attempt was made to determine from the composition and degree of mineralization whether the “local factor(s)” operates within these principles or in some way modifies the conditions so that the simple physicochemical principles do not apply. From both the agreements and the discrepancies between these concepts and the experimental results, further studies were designed to obtain insight into the minimal system required for the process of mineralization.

Calcification XIV. Investigation of the Role of Chondroitin Sulfate in the Calcifying Mechanism.

Summary 1. Toluidine blue and protamine, like inorganic cations, produce a reversible inactivation of the mechanism of calcification. This inactivation is a function of the inhibitor to calcium ratio. 2. Up to a concentration of about 15 meq/L, calcium ion in the dye solution increases the intensity of metachromatic staining. Above this concentration there is a gradual decrease of metachromasia. 3. Under certain conditions, the calcifiability of bone sections parallels metachromasia. But it is possible, by raising the calcium ion concentration, to destroy metachromasia while increasing calcifiability, or by treatment with certain protein denaturants, to destroy calcifiability while enhancing metachromasia. 4. Synthetic chondroitin sulfate-collagen complexes have been found to exhibit behavior similar to that of rachitic bone cartilage with regard to metachromasia and calcifiability.

A Rapid Method for the Determination of Ultramicro Quantities of Calcium and Magnesium.

Summary A method is presented for the ultramicro estimation of serum calcium and magnesium with ethylene-diamine-tetraacetate in the presence of eriochrome black T, at a pH of 10.0 to 10.5. The serum (0.02 to 0.05 ml) is titrated directly and the titration is completed in less than one minute; thus the speed of this determination compares favorably with that of the flame photometer. For rapid and approximate calcium value, the mean magnesium concentration of human serum (1.64 mE/L) is subtracted from the total calcium plus magnesium thus determined. For precise calcium values, magnesium is determined on an aliquot of serum and the value subtracted from the calcium plus magnesium values. For precise magnesium values, calcium is determined on an aliquot of serum and the value subtracted from the calcium plus magnesium values.

Calcification XXV. Mineralization of reconstituted collagen

Abstract Acid-soluble collagen, when reconstituted with chondroitin sulfate, heparin, lauryl sulfate, NaCl, by dialysis with sodium acetate, or by calcifying solution, mineralized when placed in a solution employed for calcification in vitro . No decisive difference was observed between collagen obtained from rat tail tendon and that from skin, except when calcifying solution was used as the precipitant. Improved calcifiability was obtained when the fibers were reconstituted with sulfate ester, from an acetic acid extract of NaCl-precipitated collagen. It is concluded that reconstituted fibers of acid-soluble collagen have calcifiability as an intrinsic property. Reasons for the likelihood that in vivo calcification involves factors in addition to collagen are discussed.

Influence of Vitamin D in Experimental Lead Poisoning

Conclusions Vitamin D causes a rise in the concentration of lead in the blood stream and in the bones of rats suffering from lead poisoning.

INTERRELATIONSHIP OF TOOTH COMPOSITION, BODY FLUIDS, DIET, AND CARIES SUSCEPTIBILITY*

For many years this laboratory has been concerned with the composition of mineralized tissues and the relationships that exist between the composition of the mineral fraction of the tissue, the composition of the body fluids, and the composition of the diet. This paper will emphasize those portions of the investigations that have bearing on the caries problem. As will be developed later, some of the relationships have been investigated extensively, while others require further study.

The Problem of the Absorption and Transportation of Fat-Soluble Vitamins

Publisher Summary The absorption and transportation of the fat-soluble vitamins is related to the absorption and transportation of vitamins that are insoluble in water, which is the basic solvent of the body. Thus, for both absorption and transportation, the fat-soluble vitamins are converted to water-soluble forms by means of derivatives or dispersing agents. This problem is not encountered for water-soluble vitamins. It is not surprising, therefore, that deficiencies of the fat-soluble vitamins on adequate intake manifest themselves frequently because of poor absorption or transportation in the body. Some evidence indicates that vitamin A serves as a good model for the absorption and transportation of the other fat-soluble vitamins. From the lack of solubility of the fat-soluble vitamins in water, a breakdown of the system responsible for absorption and transportation can often occur and frank or subacute symptoms of vitamin deficiencies manifest themselves.

The reversible inactivation of calcification in vitro.

Summary It was possible to demonstrate the reversible inactivation of calcification in vitro of the hypertrophic epiphyseal cartilage. When rachitic bone sections are shaken with strontium chloride, sodium chloride, calcification in vitro is inhibited. On subsequent shaking with calcium chloride calcification in vitro takes place. In addition, inactivation takes place with 1/2 mE of cupric chloride in the presence of 150 mE of calcium chloride. On subsequent shaking with 150 mE of calcium chloride (in the absence of cupric chloride) reactivation takes place.

Crystal growth in mineralizing tissues.

Abstract The growth of nuclei into crystals requires a metastable solution phase with respect to the growing particles (supersaturation), and the presence of impurities. The rate of growth is proportional to the diameter of the particles, and is related to the surface to volume ratio of the crystal. Trace components can modify cyrstal habit and may be factors in determining the characteristics of bone mineral. Orientation of bone cystals parallel to the collagen fibers implies that the organic matrix acts as a habit modifier. The small size of bone hydroxyapatite crystals (640 A or less), in contrast to the synthetic hydroxyapatite crystals prepared in the laboratory (2 · 10 7 A or 2.0 mm), suggests that factors in vivo operate to limit their size. Cessation of crystal growth in a supersaturated solution is likely to be caused by surface adsorption of inhibiting ions or compounds. A mechanical barrier imposed by the collagen fibrils, and decreased renewal of the fluids surrounding the crystal may also be involved. The inorganic portion of mineralized tissues in two phases: a crystalline core of hydroxyapatite of [Ca 10 (PO 4 ) 6 (OH 2 )] and an adsorbed outer shell which is of an amorphous or gel-like nature, containing anions such as carbonate, citrate, fluorides, and cations such as Na, Mg, Pb, and Sr. This does not preclude entry of a few such ions into the lattice. The inorganic composition of bones and teeth depends on the composition of the surrounding fluids (which can be regulated by dietar constituents). For example, the CO 3 /PO 4 ratio of minerals in bone and teeth is related to the CO 3 /PO 4 ratio of blood serum.

Calcification. XXII. A method of studying crystal growth.

STUDIES of in vitro calcification indicate that once nuclei of crystallization are formed in preosseous cartilage, further crystal growth is independent of the nucleus-forming mechanism. Thus, the degree of calcification detected by the silver nitrate stain represents the gross effect of two discrete processes which are not always distinguishable. For example, complete inhibition of in vitro calcification after an experimental treatment may be due not only to an injury of the nucleus-forming mechanism but also interference with the growth of nuclei which are below the threshold of visibility as determined by the silver stain. The purpose of this paper is to describe a method for the study of crystal growth independent of the nuclei-forming mechanism. This method depends upon the seeding of rachitic or demineralized tibia sections by a 2-stage calcium and phosphate treatment. The tibia sections then act as a collector of further mineralization and may be readily isolated for qualitative examination by the silver stain, or quantitative estimation by chemical analysis. It is also possible that nuclei produced by this method possess properties such as particle size and orientation similar to nuclei produced in vivo. This method is derived from the early experiments of Freudenberg and Gybrgy,1 who found that calcium uptake in cartilage is a prerequisite for the uptake of phosphate in cartilage. Boyd and Neuman2 and Belanger3 have corroborated this work and related the calcium uptake to the mucopolysaceharide content of cartilage.