The acid and alkaline phosphatases, inorganic pyrophosphatases and phosphoprotein phosphatase of bone. II. Distribution in subcellular fractions of bone tissue homogenates and structure-linked latency

Retention of insulin-like growth factor I bioactivity during the fabrication of sintered polymeric scaffolds

The use of growth factors in tissue engineering offers an added benefit to cartilage regeneration. Growth factors, such as insulin-like growth factor I (IGF-I), increase cell proliferation and can therefore decrease the time it takes for cartilage tissue to regrow. In this study, IGF-I was released from poly(lactic-co-glycolic acid) (PLGA) scaffolds that were designed to have a decreased burst release often associated with tissue engineering scaffolds. The scaffolds were fabricated from IGF-I-loaded PLGA microspheres prepared by a double emulsion (W1/O/W2) technique. The microspheres were then compressed, sintered at 49 °C and salt leached. The bioactivity of soluble IGF-I was verified after being heat treated at 37, 43, 45, 49 and 60 °C. Additionally, the bioactivity of IGF-I was confirmed after being released from the sintered scaffolds. The triphasic release lasted 120 days resulting in 20%, 55% and 25% of the IGF-I being released during days 1-3, 4-58 and 59-120, respectively. Seeding bone marrow cells directly onto the IGF-I-loaded scaffolds showed an increase in cell proliferation, based on DNA content, leading to increased glycosaminoglycan production. The present results demonstrated that IGF-I remains active after being incorporated into heat-treated scaffolds, further enhancing tissue regeneration possibilities.

Activity and localisation of the lysosomal marker enzymes acid phosphatase, N-acetyl-beta-D-glucosaminidase, and beta-galactosidase in the earthworms Eisenia fetida and E. veneta

The present study describes the activity and localisation of three putative lysosomal marker enzymes, acid phosphatase (AP), N-acetyl-beta-D-glucosaminidase (beta-NAG), and beta-galactosidase (beta-Gal), in whole individuals and in distinct parts of the earthworms, Eisenia veneta and Eisenia fetida. Activities of AP and beta-NAG were high in the two species with most of the activity located to the anterior and mid-parts of the worms. The activity of beta-Gal was low in all body regions. We found interspecies difference in the AP activity as E. veneta had significantly higher activity of AP than E. fetida in posterior and mid-parts, as well as in whole individuals. Of the three enzymes tested, AP was the only enzyme located to lysosomes, yielding high latency all over the worms with especially high latency in the coelomic fluids and posterior regions. The lysosomal APs in E. veneta and E. fetida may be utilised as a new biomarker for xenobiotic-induced lysosomal membrane damage in earthworms.

A comparative study of osteoblasts: in situ versus isolated specimens

Osteoblasts and osteoclasts are known to adhere tenaciously to bone surfaces even when the fibrous periosteal covering is removed. Brush-smear isolates and in situ, whole bone mounts of the osteogenic periosteum on the inner and outer calvarial tables of young adult rats were examined at the light microscopic level after exposing the cells by removing the fibrous periosteum. Based on staining, enzymatic activity, and overall morphology, most of the cells could be classified as osteogenic in nature. However, detailed analysis revealed that some cells exhibited certain unique morphologic appearances that suggested the existence of subpopulations or variant forms of the conventional or prototypic osteoblast. Three variant forms were the large nucleate, small nucleate, and multinucleate osteoblast-like cells, the latter with nuclear numbers ranging from 2-10. The finding of all such forms in smears, short-term cell cultures, and in situ specimens greatly lessened the probability that the unusual forms were artifactual. Phase contrast microscopic studies and sectioning of cellular isolates for study at both the light and electron microscopic levels provided additional support for the existence of the multinucleate osteoblast-like cell. The small size of these osteoblast-like subpopulations and the orientation of the cells to the commonly used plane of section of most histologic bone specimens, particularly with the multinucleate type, could explain why they had escaped earlier detection.

Subcellular localisation and properties of histone phosphate phosphatase in human polymorphonuclear leukocytes: alterations in pregnancy and chronic granulocytic leukaemia and relationship to alkaline phosphatase

Using [32P]histone as substrate, an assay for histone phosphate phosphatase was optimised for human polymorphonuclear leukocytes. Kinetic studies showed that the activity was optimal at pH 6.8, was stimulated by Mn2+ and Co2+, and inhibited by sodium sulphite and zinc chloride. The apparent Km of the enzyme for histone phosphate was 0.89 mumol/l. Neutrophils were homogenized in isotonic sucrose and, after low speed centrifugation, the supernatant was subjected to analytical subcellular fractionation. Gradient fractions were assayed for principal marker enzymes and for histone phosphate phosphatase. Histone phosphate phosphatase activity was shown to be solely located to the cytosol. No activity was detected in the alkaline phosphatase-containing granules. Neutrophils were isolated from the blood of control subjects, patients with chronic granulocytic leukaemia and women in the third trimester of pregnancy. The specific activity (milliunits/mg protein) of histone phosphate phosphatase was significantly reduced in patients with chronic granulocytic leukaemia compared to control values but this decrease was considerably less than that found for alkaline phosphatase. The possible implication of the reduced histone phosphatase activity in leukaemia neutrophils is discussed. There was no significant change in histone phosphate phosphatase in leucocytes from pregnant women. These results, together with the subcellular fractionation experiments and inhibitor studies, strongly indicate that histone phosphate phosphatase is not attributable to neutrophil alkaline phosphatase.

Interaction of 24,25-dihydroxyvitamin D3 and parathyroid hormone on bone enzymes in vitro

The in vitro effects of vitamin D3 metabolites, parathyroid extract (PTE), purified parathyroid hormone (bPTH), vitamin A, and heparin on acid and alkaline phosphatases in rat or mouse calvaria in culture were investigated. Results show that: (a) when compared to values found in half calvaria incubated for 24 h in control medium, the bone acid and alkaline phosphatase content is significantly higher in paired halves incubated with PTE (L USP/ml), bPTH (4 x 10(-8)M), heparin (5 USP/ml), vitamin A (23 USP/ml), 25-(OH)D3 (2.5 x 10(-11) to 2.5 x 10(-8)M), 24,25-(OH)2D3, and 1,25-(OH)2D3 (2.5 x 10(-12) to 2.5 x 10(-7M); (b) the presence of 24,25-(OH)2D3 at low concentrations in the incubation medium decreases significantly the PTE, bPTH, vitamin A, or heparin induced stimulation of the phosphatase activities. This interaction is also observed when measuring beta glucuronidase and glucose-6-phosphatase activities and 45Ca release from previously labeled mouse calvaria; (c) a similar activity could not be found with 1,25-(OH)2D3 suggesting that 24,25-(OH)2D3 may have a specific role in bone metabolism.

Phosphatase content of rat calvaria after in vivo administration of vitamin D3 metabolites

The effects of acute or chronic administration of small doses (130 pmol) of 25-hydroxycholecalciferol, 24,25-dihydroxycholecalciferol, and 1,25-dihydroxycholecalciferol on rat calvaria acid and alkaline phosphatase activities were investigated in weanling male albino Wistar rats raised on a vitamin D-deficient, low-calcium diet. The results indicate that each of these active metabolites has a different effect on calvarial phosphatase activities. 25-hydroxycholecalciferol causes a significant increase, and 24,25-dihydroxycholecalciferol a decrease in the enzymatic activity. In animals treated with 1,25-dihydroxycholecalciferol these activities are lower after one injection, but after seven daily doses they are not different from those of ethanol-injected control rats. The observed changes do not seem to be related to changes in serum calcium and/or phosphorus concentrations.

Alkaline phosphatase activity, characterization, and subcellular distribution during initial skeletogenesis in the prenatal rat limb

The specific activity, tissue specificity, and subcellular distribution of alkaline phosphatase were studied in the fetal rat limb during initial cartilage calcification and bone formation. The pH optimum, Km, activation, and inhibition characteristics of the enzyme assayed for in 900 X g supernates of whole limb homogenates indicated that the activity represented a fetal bone alkaline phosphatase. Studies examining temporal changes of the enzyme in these preparations demonstrated a substantial increase in activity over each of the days during which they were studied (days 15-18). Fractions derived from the discontinuous density gradient centrifugation of the limb preparations were used to study the chronological subcellular distribution of the enzyme. Enzyme activity was found in all of the fractions with the greatest activity occurring in fractions consisting of ribosomes and small vesicles. The vesicular component was similar to the matrix vesicles dexcribed by others in calcifying tissues. The daily increase in activity measured in the curde supernate was further reflected in the distribution studies. The association of alkaline phosphatase with the vesicular structure is compatible with the theorized functions of matrix vesicles, and the substantial increase in activity between days 15 and 18 further demonstrates an intimate association of alkaline phosphatase with skeletal development.

Enzyme histochemistry of bone and cartilage cells

Initial studies indicated that bone and cartilage, when treated with a hypertonic glutaraldehyde fixative for a short period, retained significant enzyme activity for histochemistry and also maintained excellent fine structure. We used 6% glutaraldehyde in 0.1 M cacodylate buffer, pH = 7.2, 4 degrees C to fix small pieces of bone or cartilage for three hours while the tissues were being constantly agitated. These samples were demineralized in 10% ethylene diamine tetraacetic acid, buffered to pH = 7.2 with 0.1 M Tris HC1, at 4 degrees C. The demineralized tissue was frozen and cryostat sections 32 microns thick were taken for incubation at 37 degrees C in various media for histochemistry. For electron microscopic localization of enzymes a heavy metal capturing method had to be used. For light microscopy, the azo dye methods were frequently used, but these were not usable for electron microscopy. Alkaline phosphatase was found on the outer surface of osteoblast and hypertrophic cartilage cell membranes. The only intracellular enzyme activity was found on the mitochondrial membranes of the osteoclast and only when the pH of the media was lowered from the optimum 9.5 to 8.5. Alkaline phosphatase was not found along the osteocyte or young cartilage cell membranes...