Collagenolytic activity during active bone resorption in tissue culture

Ventral sacroiliac ligament. Anatomic and pathologic considerations

RATIONALE AND OBJECTIVES

The ventral sacroiliac ligament (VSL), which bridges the sacroiliac (SI) joint anteriorly, has been described as an important stabilizing structure of the joint, but no data exist regarding its assessment with routine and advanced imaging methods. The authors determine the imaging appearance of the normal and abnormal VSL using close anatomic-histologic-imaging correlation.

METHODS

Eight and 10 cadaveric SI joints were examined with magnetic resonance imaging in axial and coronal planes, respectively; and in four computed tomography scanning in both planes was obtained. Anatomic sectioning with histologic correlation at levels corresponding to those of imaging planes was performed. Representative examples of diseases that produce abnormalities of the VSL and connective tissue about the SI joint were reviewed.

RESULTS

Magnetic resonance images showed the VSL-anterior capsular complex as a hypointense, linear, or minimally curved structure of approximately 2 mm thickness traversing the SI joint anteriorly. The VSL could not be separated from the anterior joint capsule by imaging studies, but such differentiation by histology could be determined based upon the orientation of its collagen fibers. Any disease process that affects the ligament or the site of ligamentous attachment to bone produces characteristic imaging alterations.

Effects of calcium and (inorganic) phosphate on bone resorption produced by vitamin D3 metabolites in vitro

The effects of changing the concentrations of calcium (Ca2+) and inorganic phosphate (Pi) on 45Ca release from prelabeled fetal rat bones caused by parathyroid hormone (PTH), 25-hydroxyvitamin D3 (25-OH-D3) and 1, 25-dihydroxyvitamin D3 (1,25-(OH)2-D3) were tested, in vitro. Increasing total (Ca2+) from 1.25 mM to 2.5 mM caused a significant increase in bone resorption caused by submaximal concentrations of these materials. Further increase in total (Ca2+) to 3.5 mM abolished this potentiating effect of bone resorption. Increasing the (Pi) from 1 mM to 2-3 mM caused significant inhibition of bone resorption caused by these resorbing materials. In addition, a (Pi) of 3 mM caused significant inhibition of higher concentrations of PTH and 25-OH-D3. (Pi) of 2 and 3 mM also caused significant inhibition of 45Ca release from control bones. It is concluded that a moderate increase in medium (Ca2+) mimics the effect of these bone resorbing materials on bone. Phosphate appears to be a direct inhibitor of bone resorption. Therefore, changing the (Ca2+) and (Pi) in the medium can affect the bone resorbing effect of vitamin D3 metabolites, similar to their effect on PTH.

Tetracyclines inhibit parathyroid hormone-induced bone resorption in organ culture

Several tetracyclines (minocycline, doxycycline, tetracycline), in levels approximating physiologic concentrations, were found to inhibit parathyroid hormone-induced bone resorption in organ culture; the specificity of this effect was demonstrated by comparison with other (non-tetracycline) types of antibiotics. The ability of tetracyclines to inhibit bone resorption is consistent with the recent proposal by Golub et al. that these antibiotics can inhibit mammalian collagenolytic enzymes by a mechanism unrelated to the drug's antibacterial efficacy, a property which could be therapeutically useful in diseases characterized by excessive collagen breakdown.

Enhanced collagenase activity in diabetic rat gingiva: in vitro and in vivo evidence

Gingiva from alloxan and streptozotocin-diabetic rats exhibited markedly enhanced collagenolytic activity in tissue culture. This effect was eliminated by puromycin or by repeated freeze-thawing of the tissue prior to incubation. Soluble extracts of the diabetic gingiva in situ were found to contain breakdown products of collagen similar in size to the reaction products generated by tissue collagenase. These fragments were not detected in the control tissue. This study indicates that experimental diabetes stimulates the synthesis of gingival collagenase in culture and that a similar effect occurs in vivo.

Tumor cell collagenase and its inhibition by a cartilage-derived protease inhibitor

Human osteosarcoma and mammary carcinoma cells were cultured separately in a medium supplemented with fetal calf serum, until they were confluent. The medium was then replaced by serum-free medium supplemented with heparin. Both cell cultures secreted collagenase, and this activity was inhibited by a cartilage-derived protein of low molecular weight. Since cartilage is rarely invaded by neoplasms, the presence of this inhibitor may play an important role in the regulation of tumor invasion.

Therapeutic effects of heparin on Pseudomonas-induced corneal ulceration

Fifty organisms of Pseudomonas aeruginosa were injected intralamellarly in both eyes of 60 albino rabbits. Twenty-four hours later, all eyes were graded and stratified into six groups of ten rabbits with equivalent infections. Treatment was begun with gentamicin alone or 0.3% polymyxin B alone, and in combination with acetylcysteine, 0.3M edetate disodium, and 2.500 units/ml of heparin sodium, four times daily. We also compared topical colistin and colistin and topical heparin. After two weeks, those corneas treated with polymyxin B and topical heparin showed a reduction in ulceration, corneal thinning, and descemetocele formation compared to those treated with polymyxin B alone. Based on these studies, heparin was administered topically, four times daily, to three patients with Pseudomonas-induced corneal ulcers in addition to antibiotics. Before treatment all corneas showed evidence of corneal liquefaction and two of the corneas were in imminent danger of perforation. After therapy, no corneas perforated; one patient recovered visual acuity of 6/9 (20/30), one patient recovered visual acuity of 6/6 (20/20) after keratoplasty, and the third has a vascularized leukoma.

Effect of estrogen on the collagenolytic activity of rat bone

Rats were injected with 17 beta-estradiol benzoate intramuscularly and the collagenolytic activity of the rat bones was assayed by measuring the degradation of purified reconstituted 3H-proline- and 3H-hydroxyproline-labeled collagen. A diminution of the collagenolytic activity which could be recovered from the culture medium of estrogen-treated rat bone was observed. However, the addition of estrogen to the enzyme using the same assay revealed no diminution of collagenolytic activity. These results suggest that the diminution of collagenolytic activity in the culture medium of estrogen-treated rat bone is due to an alteration in the production or activation of collagenolytic activity.

Collagenase studies in bones of guinea pigs

A specific collagenase has been demonstrated in culture fluids of guinea pig bones. Based on the acrylamide gel electrophoretic pattern, the mechanism of action of guinea pig bone collagenase appears similar to other known vertebrate collagenases. 2 peaks of enzymatic activity were found upon assay of fractions from gel chromatography, corresponding to molecular weights in the range of 137,000 daltons and 29,000 daltons. The enzyme is inhibited by cysteine and EDTA. Alpha1-macroglobulin is a much stronger inhibitor of the collagenase than alpha-antitrypsin. Activation studies suggested the presence of a proenzyme to guinea pig bone collagenase that was converted to an active enzyme by proteases present in the culture fluid.

Changes in the fine structure of bone cells after the administration of parathyroid extract

This paper describes the effect of parathyroid extract on the fine structure of bone cells in the proximal metaphysis of the tibia. The extract was given to rats intraperitoneally, in single or repeated doses of 1-14 units (USP) per gram body weight, over short or extended periods, and the tissue was examined between 6 and 26 hr after the commencement of injection. During this period, osteoblasts showed the greatest changes. Their mitochondria became swollen and contained dense granules; both rough- and smooth-surfaced vesicles were distended; ribosomes were separated from the membranes; and various dense bodies appeared in the cytoplasm. Osteocytes were similarly but less affected, and osteoclasts differed little from those in normal animals. Eventually after repeated injections, the fine structure of many of the cells was disrupted. These changes were accompanied by erosion of the bony trabeculae without any great increase in numbers of osteoclasts. It is possible that the alterations in fine structure were the result of damage to the cells by the parathyroid extract. However, since the extract did not seem to stimulate classical osteoclastic activity, the mitochondrial swelling and dense bodies could have been related to the removal of mineral and matrix, respectively.

Collagen degradation and the response to parathyroid extract in the intact rhesus monkey

Proline-(14)C was administered to five adult rhesus monkeys, and the degradation of collagen was followed by the excretion of hydroxyproline-(14)C. The results suggested the presence of at least three separate pools of collagen with half-lives of 1 to 2, 2 to 3, and 50 to 70 days. The monkeys were killed after 44 days; at that time the specific activity of the hydroxyproline-(14)C in urine was found to be four to five times that of the hydroxyproline in soluble collagen and 81 to 93% that of hydroxyproline in insoluble collagen. The relationships between urinary hydroxyproline and the degradation of collagen were similar to those previously demonstrated in rats. Parathyroid hormone was administered daily to two of the monkeys from the 27th to the 44th day of the study. The parathyroid hormone increased the amount of hydroxyproline-(14)C excreted, but there was no significant change in the specific activity of the urinary hydroxyproline-(14)C. Since under the conditions of the experiment insoluble collagen was the only possible source of hydroxyproline-(14)C of relatively high specific activity, the results indicated that parathyroid hormone directly or indirectly increased the degradation of insoluble collagen. The results also suggested that parathyroid hormone increased the degradation of soluble collagen, but the relative magnitude of this effect was not clearly established.