The effect of different mineral frames on ectopic bone formation in mouse hind leg muscles induced by native reindeer bone morphogenetic protein.

INTRODUCTION: Bone morphogenetic proteins (BMPs) require carrier material for slow release and framing material for osteoconduction. MATERIALS AND METHODS: The effect of a frame on early bone formation induced by partially purified native reindeer BMP in composite implants containing 3 mg of BMP, type IV collagen and tricalcium phosphate (TCP/Col/BMP) or hydroxyapatite (HA/Col/BMP) or biphasic tricalcium phosphate-hydroxyapatite (TCP/HA/Col/BMP) or biocoral (NC/Col/BMP) was evaluated using a mouse hind leg muscle pouch model. Collagen with native reindeer BMP (Col/BMP) and corresponding implants without native reindeer BMP served as controls. Evaluation was done by incorporation of 45Ca, radiographically and histologically 3 weeks after the implantation. RESULTS: None of the implants without native reindeer BMP were able to induce new bone visible on radiographs. The area of new bone formation in the Col/BMP (p=0.026) and TCP/HA/Col/BMP (p=0.012) groups was significantly greater than in the TCP/Col/BMP group. The optical density of the new bone area was significantly greater in the TCP/HA/Col/BMP group than in the TCP/Col/BMP (p=0.036) or Col/BMP (p=0.02) groups. 45Ca incorporation was many times greater in all the groups containing native reindeer BMP than in the corresponding groups without BMP. In the Col/BMP (p=0.046) and TCP/HA/Col/BMP (p=0.046) groups, 45Ca incorporation was significantly greater than in the TCP/Col/BMP group. No significant differences were found in any parameters between HA/Col/BMP and NC/Col/BMP groups and the other BMP-containing groups. CONCLUSIONS: Hydroxyapatite, biocoral and biphasic tricalciumphosphate-hydroxyapatite are equally good as framing material for native reindeer BMP, while tricalciumphosphate is somewhat worse. Osteoinduction of native reindeer BMP works well with collagen alone.

Influence of ethylene oxide sterilization on the activity of native reindeer bone morphogenetic protein.

We studied the effects of ethylene oxide sterilization (Steri-Vac 4XL, temperature 29 degrees C, exposure time 4 h 10 min, ethylene oxide concentration 860 mg/l) on the osteoinductivity of partially purified native reindeer bone morphogenetic protein (BMP) in a hind leg muscle pouch model of male NMRI mice. BMP was administered in implants containing 3 mg in a collagen carrier. Implants without sterilization and without BMP served as controls. New bone formation was evaluated based on the calcium yield, radiographic and histological examination 3 weeks after implantation. The implants without BMP were not able to induce new bone visible in radiographs. In the sterilized BMP group, the mean area of new bone was 35% ( p=0.004) and density 32% ( p=0.000) smaller than in the nonsterilized group. Calcium yield was 20% lower in the sterilized group than in the nonsterilized group, but this difference was not significant ( p=0.22). It was many times lower in the group without BMP than in the above-mentioned groups ( p=0,001). We conclude that ethylene oxide gas sterilization reduces the bone-forming activity of native reindeer BMP by one third.

New bone formation induced by injection of native reindeer bone morphogenetic protein extract.

BACKGROUND AND AIMS: Bone morphogenetic proteins (BMPs) are usually administered with a solid framing material during open surgery. In some instances, percutaneous administration of injectable BMP would be preferable. We tested the new bone-forming activity of injectable native reindeer BMP extract in the Balb/C mouse thigh muscle pouch model. MATERIALS AND METHODS: The injectable implants contained 6 mg of native reindeer BMP extract and either physiological saline (NaCl/BMP) or collagen (Gel/BMP). Corresponding implants without BMP served as controls. New bone formation was evaluated based on incorporation of Ca45 and radiographically three weeks after the injection into the mouse thigh muscles. RESULTS: None of the injections without BMP were able to induce new bone visible in radiographs, whereas the injections with BMP induced new bone effectively. There were no significant differences in the area of new bone (p = 0.247) and its density (p = 0.739) between the NaCl/BMP and Gel/BMP groups. Ca-45 incorporation was multifold in the NaCl/BMP and Gel/BMP groups compared to the controls (p = 0.000). No significant differences in Ca-45 incorporation (p = 0.739) between the NaCl/BMP and Gel/BMP groups were observed. CONCLUSION: Our results suggest that BMP can be administered percutaneously, and that collagen and physiological saline are equally good carriers of injectable implants of native reindeer BMP.

Abnormal ornithine decarboxylase activity in transgenic mice increases tumor formation and infertility.

A transgenic mouse line carrying ornithine decarboxylase cDNA as the transgene under the control of a mouse mammary tumor virus long terminal repeat (MMTV LTR) promoter was generated in order to study whether ornithine decarboxylase transgene expression will have any physiological or pathological effect during the entire life of a transgenic mouse. The high frequency of infertile animals and the loss of pups made the breeding of homozygous mice unsuccessful. However, a colony of heterozygous transgenic mice was followed for 2 years. In adult heterozygous transgenic mice, ornithine decarboxylase activity was significantly increased in the testis, seminal vesicle and preputial gland when compared to non-transgenic controls. In contrast, ornithine decarboxylase activity was decreased in the kidney and prostate of transgenic mice. No significant changes in ornithine decarboxylase activity were found in the ovary and mammary gland and only moderate changes in ornithine decarboxylase activity were detected in the heart, brain, pancreas and lung. The most common abnormalities found in adult animals (12 males and 20 females) of the transgenic line were inflammatory processes, including pancreatitis, hepatitis, sialoadenitis and pyelonephritis. Spontaneous tumors were observed in eight animals, including two benign tumors (one dermatofibroma, one liver hemangioma) and six malignant tumors (one lymphoma, one intestinal and three mammary adenocarcinomas and one adenocarcinoma in the lung). No significant pathological changes were found in 17 nontransgenic controls.

Expression of ODC and its regulatory protein antizyme in the adult rat brain.

Ornithine decarboxylase and its inhibitor protein, antizyme are key regulators of polyamine biosynthesis. We examined their expression in the adult rat brain using in situ hybridization and immunocytochemistry. Both genes were widely expressed and their expression patterns were mostly overlapping and relatively similar. The levels of antizyme mRNA were always higher than those of ornithine decarboxylase mRNA. The highest expression for both genes was detected in the cerebellar cortex, hippocampus, hypothalamic paraventricular and supraoptic nuclei, locus coeruleus, olfactory bulb, piriform cortex and pontine nuclei. Ornithine decarboxylase and antizyme mRNAs appeared to be localized in the nerve cells. ODC antibody displayed mainly cytoplasmic staining in all brain areas. Antizyme antibody staining was mainly cytoplasmic in the most brain areas, although predominantly nuclear staining was detected in some areas, most notably in the cerebellar cortex, anterior olfactory nucleus and frontal cortex. Our study is the first detailed and comparative analysis of ornithine decarboxylase and antizyme expression in the adult mammalian brain.

Mutation of aspartate-233 to valine in mouse ornithine decarboxylase reduces enzyme activity.

Ornithine decarboxylase is the first and key enzyme in mammalian polyamine biosynthesis. All eukaryotic ornithine decarboxylases contain several highly conserved regions and the amino acid residues 232-238 form one of the most highly conserved sequences. This region contains a glycine-rich sequence typically found in a number of pyridoxal 5'-phosphate-dependent or nucleotide-binding proteins. We mutated aspartate-233 which is the only acidic residue within this region to valine. This mutation causes striking sequence similarity with the guanine nucleotide binding domain of c-H-ras. Mutated ornithine decarboxylase cDNA with a mouse mammary tumor virus long terminal repeat promoter has been transfected for stable expression into ornithine decarboxylase-deficient C55.7 cells. Ornithine decarboxylase activity of the mutated enzyme was about 20% of wild-type ornithine decarboxylase activity and it was not activated by guanosine triphosphate like the ornithine decarboxylase isoform found in some tumors and rat brain. The mutation caused an increase in K(m) value of about 20-fold both for the substrate L-ornithine and for the cofactor pyridoxal 5'-phosphate. The Ki value for the irreversible inhibitor alpha-difluoromethylornithine was also increased, whereas the half-life of the enzyme was shortened. These results suggest that the region containing aspartate-233 is essential for binding of the cofactor and thus forms part of enzymatic active site, and the mutation of aspartate-233 to valine cannot, at least alone, cause the activation of ornithine decarboxylase by guanosine triphosphate (230).

The expression of ornithine decarboxylase antizyme mRNA and protein in rat motoneurons.

The distribution of ornithine decarboxylase antizyme messenger ribonucleic acid (AZ mRNA) and AZ-like immunoreactivity (LI) was studied in the brainstem and spinal cord motoneurons and in the extraocular and triceps surae muscles of rat. In situ hybridization showed AZ mRNA in the gray matter of the spinal cord at different levels of spinal cord with highest AZ mRNA levels in the ventral horn of the spinal cord. No apparent changes in AZ mRNA contents were seen after unilateral transection of the sciatic nerve in lumbar motoneurons. AZ-immunoreactive (IR) motoneurons were observed in the nucleus of the VI cranial nerve and in the ventral horn of the spinal cord. These motoneurons also showed ornithine decarboxylase (ODC)-LI. Subcellularly, AZ-LI was observed both in the nuclei and cytoplasm of labeled motoneurons. Heavily stained AZ-IR nerve fibers and myoneural junctions were observed among muscle fibers in different muscles. In addition, the nuclei of muscle fibers showed AZ-LI.

Association between high levels of ornithine decarboxylase activity and favorable prognosis in human colorectal carcinoma.

Several studies have documented increased expression of ornithine decarboxylase (ODC) in neoplastic colorectal tissue versus normal-appearing colonic mucosa. The present study was undertaken to determine whether there is an association between the degree of overexpression of ODC in colorectal carcinomas and survival in a series of 74 patients. A high level of tumor ODC expression was found to be significantly associated with greater survival in our patient series. Patients with tumor ODC activities greater than the median and especially in the highest quartile experienced a more favorable outcome than those patients with ODC values below the median or in the lowest quartile (P = 0.03 and 0.02, respectively). The presence of a GTP-activatable isoform of ODC was also significantly associated with a favorable prognosis but only in tumors of the right colon (P = 0.01). There was no association found between ODC activity and tumor grade, tumor size, or patient age, sex, or race. Our results demonstrate that high levels of ODC expression (and presence of a GTP-activatable isoform for right-sided colon tumors) predict a favorable prognosis in human colorectal carcinoma. Knowledge of a patient's ODC status at the time of surgery may be useful in decisions regarding adjuvant therapy. Understanding the mechanism(s) involved should lead to new therapeutic approaches for advanced colorectal carcinoma.

Activation of rat brain ornithine decarboxylase by GTP.

The activity of ornithine decarboxylase (ODC) measured in different regions of rat brain was highest in the hippocampus and lowest in the cerebellum. The ODC activity of a crude extract of the cerebellum was increased by the addition of GTP to the enzyme assay. Following dissociation of the ODC-antizyme complex by Sephadex G-75 chromatography in buffer containing 0.25 M NaCl, the GTP-activatable ODC was found in every brain region analysed. This GTP-activatable brain ODC has greater affinity for antizyme than the non-GTP-activatable brain ODC or the kidney ODC. The irreversible inhibitor of ODC, alpha-difluoromethylornithine (DFMO), inhibited approx. 60% of the ODC activity of all brain regions, whereas kidney ODC was inhibited totally by DFMO. When extracts of brain and kidney were incubated at 55 degrees C, kidney ODC was rapidly inactivated, but brain ODC was more heat-stable. Brain ODC, but not kidney ODC, was activated by GTP and ATP, and also by their deoxy forms. The K1/2 for activation of the enzyme was 2 microM for GTP and 40 microM for ATP. Using partially purified brain ODC, the activation by GTP was irreversible. These results demonstrate for the first time that the GTP-activatable ODC exists in the brain and is associated with the antizyme. The possible mechanisms of activation by GTP, the significance of this finding for the regulation of brain ODC, and the similarities to and differences from the GTP-activatable ODC found in certain rodent and human tumours are all discussed.

Developmental expression of ornithine and S-adenosylmethionine decarboxylases in mouse brain.

The activities of the two key enzymes in mammalian polyamine synthesis, ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (AdoMetDC) in mouse brain show distinct, but inverse, changes during ontogeny. The level of ODC activity is about 70 fold higher at the time of birth than in the adult mouse, whereas AdoMetDC activity is very low after birth and increases as the brain matures. The correlation between the changes in enzyme activities and in the levels of the corresponding mRNAs diminishes dramatically during development. The increase in AdoMetDC mRNA level exceeds the increase in enzyme activity by 100%. Whereas ODC mRNA level falls initially, in concert with decreasing enzyme activity, but then shows an abrupt rise to a very high level during the late period of brain maturation while the enzyme activity continues to decrease to an almost undetectable level. These data suggest the development-dependent appearance of post-transcriptional regulation mechanisms.

Identification of epidermal cell subpopulations with increased ornithine decarboxylase activity following treatment of murine epidermis with 12-O-tetradecanoylphorbol-13-acetate.

Ornithine decarboxylase (ODC), the initial enzyme in the polyamine biosynthetic pathway, has been used as a marker for the hyperplasia that occurs following exposure of mouse epidermis to the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). Using flow cytometry in combination with polyclonal antibodies to ODC, we examined the levels of ODC-associated immunoreactive protein present within mouse epidermal cells at 4 and 24 h after a single topical application of TPA, as well as following chronic exposure to TPA and in papillomas. Basal levels of ODC-specific antibody binding were detectable in acetone-treated CD-1 mouse epidermis and were increased 3-fold at 4 h after TPA treatment. The amount of ODC antibody binding detected after exposure to 17 nmol TPA twice weekly for 3 weeks was similar to that detected within cells isolated from papillomas and was 2.5-fold higher than in cells isolated at 4 h after a single topical treatment of mice with TPA. These observations support the hypothesis that specific subpopulations of keratinocytes constitutively express high levels of ODC following chronic exposure to TPA. The novel method for ODC detection described in these studies provides a means to identify, isolate, and further characterize epidermal cells that may give rise to papillomas and carcinomas.

Properties of ornithine decarboxylase in human colorectal adenocarcinomas.

Ornithine decarboxylase (ODC) activity was measured in colon adenocarcinomas and adjacent normal-appearing colon mucosa from a total of 40 patients undergoing surgical resections. The enzyme activity was measured in the presence and absence of GTP, since recent work has demonstrated a GTP-activatable form of ODC in some murine and human tumors. In general, ODC specific activity was higher in adenocarcinomas than in adjacent normal-appearing mucosa. Of greater interest, however, was the finding that 13 of 40 tumors and 3 of 40 mucosae contained a GTP-activatable form of ODC. These are minimal estimates of the proportion of tissues positive for this enzyme form, since a multiple sampling protocol indicated that expression of a GTP-activatable ODC was not uniform throughout a given tumor. Chromatographic analyses of tumor extracts revealed the presence in some tumors of multiple size forms of ODC, only some of which were activated by GTP. Enzyme kinetic data indicated that the multiple forms of ODC can have different affinities for L-ornithine and that GTP can "normalize" the aberrant kinetic properties of these forms. While there was no statistically significant correlation of the presence of a GTP-activatable ODC with stage of disease, analysis of our data revealed a positive association of a GTP-activatable ODC with tumor site; a much higher percentage of tumors of the cecum contained this ODC isoform than tumors of other colonic segments (64% versus less than or equal to 25% for other sites). These results demonstrate (a) the presence of a functionally distinct form of ODC in some human colon adenocarcinomas and (b) a distinct regional distribution of this ODC form within the colon. We suggest this alteration in a key enzyme in the growth-associated pathway of polyamine biosynthesis may play a role in colon tumor progression.

Flow cytometric detection of ornithine decarboxylase activity in epidermal cell subpopulations.

Using flow cytometry in combination with membrane permeabilization techniques to enhance binding of antibodies with immunoreactive protein within the cytoplasm, we have developed a method to examine the ornithine decarboxylase (ODC) activity present within subpopulations of epidermal cells following acute and chronic exposure to the phorbol ester tumor promoter 12-0-tetradecanoylphorbol-13-acetate (TPA). The method described has the sensitivity to detect basal levels of ODC as well as increases in ODC at early time points following treatment with TPA and has the additional advantage of allowing subpopulation identification and characterization.

Activation of human squamous cell carcinoma ornithine decarboxylase activity by guanosine triphosphate.

Previous studies have demonstrated the presence in mouse epidermal tumors of a structurally and functionally altered ornithine decarboxylase (ODC). In this report, the enzymatic properties of ODC from normal human skin and squamous cell carcinomas are examined. Some tumors contained a more heat stable ODC than the enzyme found in normal skin. GTP stimulated enzyme activity in four of seven tumor extracts tested but had no effect on normal skin ODC. Kinetic analyses indicated that GTP either lowered the apparent Km of tumor ODC for L-ornithine, increased the Vmax, or had both effects, depending on the tumor examined. Gel filtration chromatography of crude tumor extracts indicated the existence of multiple molecular weight forms of ODC, some of which can be activated by GTP and some of which are unaffected by GTP. Some tumors contain both a GTP-activatable and -nonactivatable form of the enzyme. Immunolocalization studies demonstrated the presence within squamous cell carcinomas of cells with a constitutively high level of immunoreactive ODC, a situation never observed in normal skin tissue. These results suggest that some human squamous cell carcinomas contain a functionally altered ODC that may be aberrantly regulated.

Activation of mouse epidermal tumor ornithine decarboxylase by GTP: evidence for different catalytic forms of the enzyme.

In crude extracts of epidermal papillomas induced by an initiation-promotion protocol, ornithine decarboxylase (OrnDCase) activity was increased by the addition of GTP to the enzyme assay. No effect of GTP on the phorbol ester-induced enzyme isolated from normal epidermis was observed. Kinetic analyses indicated that the major effect of the nucleotide on the tumor-derived enzyme was to lower the apparent Km for L-ornithine. When papilloma OrnDCase was partially purified by gel-filtration chromatography, two forms of the enzyme were resolved, only one of which was found in an epidermal extract from phorbol 12-myristate 13-acetate-treated mice. The enzymatic properties of the two forms of papilloma enzyme were compared. The higher molecular weight form (peak I) was activated by GTP, while the lower molecular weight form (peak II) was not. As expected from the kinetic analyses of the crude papilloma extracts, the apparent Km of peak I enzyme for L-ornithine was very high (1.25 mM) but was much lower in the presence of GTP (0.02 mM). The two forms of papilloma OrnDCase differed in their sensitivities to heat inactivation and the ability of GTP to protect against heat inactivation. The K1/2 for activation of peak I OrnDCase by GTP was 0.1 microM. The activation process was irreversible and did not require Mg2+. When several nucleotides were tested for their ability to activate peak I OrnDCase, only GTP, dGTP, and the nonhydrolyzable derivative GTP[gamma-S] were effective, while GDP, GMP, ATP, and CTP were relatively ineffective. Our results demonstrated the existence of two forms of OrnDCase in epidermal tumor extracts, of which one can be activated by GTP and one cannot. The significance of these findings for the regulation of this enzyme in normal and tumor cells is discussed.

Purification of mouse brain ornithine decarboxylase reveals its presence as an inactive complex with antizyme.

Mouse brain ornithine decarboxylase (ODC) was purified to near-homogeneity by using (NH4)2SO4 precipitation and chromatography on heparin-Sepharose, pyridoxamine phosphate-agarose and DEAE-cellulose. On SDS/polyacrylamide-gel electrophoresis, the final preparation gave one protein band similar to that obtained for purified mouse kidney enzyme, corresponding to an Mr of 53.000. The overall yield of the purification exceeded about 50-fold the total activity of the enzyme in the starting material. By affinity chromatography on ODC-bound Sepharose, the extra enzyme activity was shown to originate, at least partly, from the enzyme-antizyme complex. These results demonstrate that ODC in mouse brain occurs mainly in an inactive form and is activated during purification.

Ornithine decarboxylase activity in brain regulated by a specific macromolecule, the antizyme.

Mouse brain ornithine decarboxylase activity is about 70-fold higher at the time of birth compared with that of adult mice. Enzyme activity declines rapidly after birth and reaches the adult level by 3 weeks. Immunoreactive enzyme concentration parallels very closely the decrease of enzyme activity during the first postnatal week, remaining constant thereafter. The content of brain antizyme, the macromolecular inhibitor to ornithine decarboxylase, in turn is very low during the first 7 days and starts then to increase and at the age of 3 weeks it is about six times the level of that in newborn mice. This may explain the decrease in enzyme activity during brain maturation, and suggests the regulation of polyamine biosynthesis by an antizyme-mediated mechanism in adult brain.

Phenothiazines and structurally related compounds as inhibitors of adenosylmethionine decarboxylase: effects on the purified enzyme.

The effects of chlorpromazine, imipramine, thioridazine, chlorprothixene, amitriptyline, desipramine and triflupromazine on adenosylmethionine decarboxylase purified from rat liver have been studied. The compounds caused competitive inhibition of the enzyme at 10(-5) - 10(-3) M concentrations. For chlorprothixene and triflupromazine the inhibition was linear, while the other drugs showed increasing, nonlinear inhibition at higher concentrations. Apparent Ki's for the compounds were between 6.8 X 10(-5) M (for chlorprothixene) and 6.4 X 10(-4) M (for desipramine). Inhibition of 50% under optimal assay conditions was achieved between drug concentrations of 1.3 X 10(-4) M (thioridazine) and 1.3 X 10(-3) M (imipramine).