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Biomedical subjects

A P Mee

Publications and source records attributed to A P Mee.

At least 19 recordsLinked to original sources
PubMed2006

Cyclic hydrostatic pressure and particles increase synthesis of 1,25-dihydroxyvitamin D3 by human macrophages in vitro.

1,25-Dihydroxyvitamin D(3) has a pivotal role in bone resorption and osteoclast activity. As activated macrophages are known to synthesise 1,25-dihydroxyvitamin D(3), this study examined whether pressure modulated its synthesis. Pressure and particles have been shown to increase synthesis of pro-resorptive cytokines and other factors by cultured macrophages. Human peripheral blood macrophages were isolated, cultured and exposed to pressure (similar to that found in the human joint) and/or particles. Synthesis of 1,25-dihydroxyvitamin D(3) by macrophages was assayed using high pressure liquid chromatography and in situ hybridization. Synthesis of 1,25-dihydroxyvitamin D(3) but not 24,25-dihydroxyvitamin D(3) was increased in macrophages under pressure. In situ hybridization demonstrated an increase in 1alpha-hydroxylase expression in response to pressure or particles and simultaneous exposure to both stimuli generated higher expression of 1alpha-hydroxylase. In conclusion, this is the first study to demonstrate that mechanical loading, in the form of pressure, stimulates 1,25-dihydroxyvitamin D(3) synthesis in human macrophages. These findings have implications for the in vivo situation, as they suggest that 1,25-dihydroxyvitamin D(3) could be one factor stimulating osteoclastic bone resorption in pathologies, such as arthritis or implant loosening, where intra-articular or intra-osseous pressure is raised or where wear particles interact with macrophages.

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗
PubMed2006

Hypercalcaemia associated with granulomatous lymphadenitis and elevated 1,25 dihydroxyvitamin D concentration in a dog.

A seven-year-old Labrador was presented with weight loss and mild generalised lymphadenopathy. Histopathology of an excised lymph node by the referring veterinarian demonstrated granulomatous lymphadenitis. At the time of referral, fine-needle aspirates of the lymph nodes confirmed the presence of ongoing granulomatous inflammation. Further investigations revealed marked hypercalcaemia, a low parathyroid hormone concentration, a parathyroid hormone related protein concentration within the reference range, and an elevated serum concentration of 1,25 dihydroxyvitamin D. An underlying cause of the granulomatous lymphadenitis could not be identified. The clinical signs, hypercalcaemia and elevated serum concentrations of 1,25 dihydroxyvitamin D resolved following prednisolone treatment. In contrast to dogs, hypercalcaemia occurred secondarily to granulomatous disease and elevated 1,25 dihydroxyvitamin D concentrations is a well-recognised condition in human beings. To the authors' knowledge, this is the first case report to describe elevated serum calcium and 1,25 dihydroxyvitamin D concentrations in a dog with histologically confirmed granulomatous disease.

Animals↗
PubMed2005

Hypercalcaemia in two dogs caused by excessive dietary supplementation of vitamin D.

A three-year-old Border collie was presented with a two-week history of lethargy, stiff gait, polydipsia and polyuria. Biochemical analysis revealed hypercalcaemia. Serum concentrations of 25-hydroxyvitamin D (25[OH]D) and 1,25-dihydroxyvitamin D (1,25[OH]2D) were markedly elevated and parathyroid hormone was undetectable. Subsequent analysis of the dog's diet revealed that the food contained excessive amounts of vitamin D. The hypercalcaemia resolved following treatment with bisphosphonates and dietary change. Hypervitaminosis D was diagnosed in a second unrelated dog, which had been fed the same brand of dog food as case 1. The dog was also hypercalcaemic and had markedly elevated serum concentrations of 25(OH)D and 1,25(OH)2D. Hypervitaminosis D in dogs has been reported to occur secondarily to ingestion of either rodenticides containing cholecalciferol or antipsoriatic ointments that contain vitamin D analogues. Hypervitaminosis D has also been reported following the treatment of hypoparathyroidism. To the authors' knowledge, this is the first report of hypervitaminosis D in dogs following the accidental over supplementation of a commercial diet with vitamin D. While the benefits of adequate dietary vitamin D are well established in dogs, the potential deleterious effects of over supplementation of vitamin D should also be acknowledged.

Animals↗
PubMed2005

Hypocalcaemia associated with low serum vitamin D metabolite concentrations in two dogs with protein-losing enteropathies.

Protein-losing enteropathies were diagnosed in two dogs that were initially presented with diarrhoea and weight loss. Plasma biochemistry in both cases revealed low concentrations of albumin, calcium and ionised calcium. Both dogs had an elevated plasma parathyroid hormone concentration and low serum 25-hydroxyvitamin D (25[OH]D) concentration. The first dog was diagnosed with lymphangiectasia on postmortem examination, and the second dog was diagnosed with chronic lymphocytic/ plasmacytic enteritis and severe cystic mucoid changes based on endoscopic duodenal biopsies. While a causal effect was not demonstrated, the protein-losing enteropathies may have caused reduced intestinal absorption of vitamin D leading to low plasma concentrations of ionised calcium and secondary hyperparathyroidism. To the authors' knowledge, this is the first report of low ionised calcium concentrations, low 25(OH)D and 1,25-dihydroxyvitamin D concentrations, and high parathyroid hormone concentrations in dogs with protein-losing enteropathies.

Animals↗
PubMed1999

Paramyxoviruses and Paget's disease: the affirmative view.

Evidence has accumulated over the past 20 years to implicate paramyxoviruses in the etiopathology of Paget's disease. In the USA, the predominant virus detected is MV, whereas in northwestern England, CDV is most prevalent. The viruses are known to be easily spread by aerosol transmission to the respiratory tissues, from which they gain entry to the skeletal tissues via the hematopoietic system. Another characteristic of these viruses is their ability to persist at very low levels, thus evading the host immune response. Further studies have shown that IL-6, c-fos, and Bcl-2 are all elevated in Paget's disease--all of these factors can be activated by virally induced ROS. The genetic predisposition to Paget's disease and the perplexing focal nature of the disorder can also be explained by viral infection. Finally, the bisphosphonates, the class of drugs used so successfully to treat Paget's disease, have been shown to act, at least in part, by counteracting two of the major effects of the viruses in Paget's disease. The weight of evidence in support of a viral etiology for Paget's disease is overwhelming.

Animals↗
PubMed1999

Novel mutations in the 1alpha-hydroxylase (P450c1) gene in three families with pseudovitamin D-deficiency rickets resulting in loss of functional enzyme activity in blood-derived macrophages.

Pseudovitamin D-defiency rickets (PDDR) is an autosomal recessive disorder characterized by hypocalcemia, rickets (which are resistant to treatment with vitamin D), and low or undetectable serum levels of 1,25-dihydroxyvitamin D (1,25(OH)2D). The symptoms are corrected with 1,25(OH)2D treatment, and the disease is now believed to result from a defect in the cytochrome P450 component (P450c1; CYP27B1) of the renal 25-hydroxyvitamin D-1alpha-hydroxylase (1-OHase). We have studied genomic DNA from three families with PDDR and have identified the same homozygous mutation in the P450c1 gene in two of the index cases, causing a frameshift in exon 8, resulting in a premature stop codon in the heme-binding domain. The two cases in the third kindred were compound heterozygotes with missense mutations in exons 6 and 9. We have also identified a C/T polymorphism in intron 6 of the P450c1 genomic DNA. Interferon gamma-inducible 1-OHase activity in blood-derived macrophages was shown by 1,25(OH)2D synthesis in all control cells tested (37-184 fmol/h/106 cells) and those from the PDDR family parents (34-116 fmol/h/106 cells) but was totally absent from the patients' cells, indicating a defect in their macrophage 1-OHase, similar to the presumed renal defect. The assumption of similarity between the renal and macrophage P450c1 was supported by our ability to clone a 514 bp sequence, including the heme-binding region of the macrophage P450c1 cDNA from controls, which was identical to that published for both the renal and keratinocyte P450c1 cDNAs.

24,25-Dihydroxyvitamin D 3↗
PubMed1998

Detection of canine distemper virus in 100% of Paget's disease samples by in situ-reverse transcriptase-polymerase chain reaction.

Previous evidence implicating paramyxoviruses in the aetiopathology of Paget's disease of bone has been controversial. While several groups have demonstrated the presence of paramyxoviruses using electron microscopy, immunohistochemistry, and molecular biological techniques, others have found no evidence of viruses using reverse transcriptase-polymerase chain reaction (RT-PCR). We have previously provided evidence that canine distemper virus (CDV) is present in approximately 65% of samples of pagetic bone, using in situ hybridization and RT-PCR; however, these results have been criticized. To further investigate the possible Role of CDV, we have now developed the technique of in situ-RT-PCR (IS-RT-PCR) to examine for the presence of CDV-nucleocapsid (CDV-N) ribonucleic acid (RNA) in pagetic bone. Control samples consisted of uninvolved sites from patients with the disease, normal bone, and several active remodeling states. IS-RT-PCR was optimized to detect CDV-N using distemper-infected vero cells. The specificity of the technique was confirmed using vero cells infected with CDV, which showed amplified signal following IS-RT-PCR, and cells infected with measles virus (MV), in which no positive signal for CDV was detected by IS-RT-PCR. Following conventional in situ hybridization, CDV-N was detectable in 10 of 15 pagetic bone samples. However, after five, and particularly 10, cycles of IS-RT-PCR, CDV-N was found in all 15 samples. There was no evidence of CDV in four samples from uninvolved sites from pagetic patients, or in any of the other control samples. In this study, using the novel technique of IS-RT-PCR, CDV was found to be present in 100% of pagetic samples examined. There was no evidence of the virus in any of the control samples, including samples of bone from uninvolved sites from patients with Paget's disease. These results provide additional proof that CDV is present within pagetic bone and further support the hypothesis that paramyxoviruses are involved in the etiopathology of Paget's disease.

Animals↗
PubMed1997

Quantification of vitamin D receptor mRNA in tissue sections demonstrates the relative limitations of in situ-reverse transcriptase-polymerase chain reaction.

In situ-reverse transcriptase-polymerase chain reaction (IS-RT-PCR) is a recently described technique that is used to localize low levels of mRNA within cells and tissue sections. One of the major criticisms levelled at this technique is that positive results may be meaningless, as amplification is required to demonstrate the transcripts of interest. The use of IS-RT-PCR to demonstrate mRNA for receptors for 1,25-dihydroxyvitamin D3 (VDR) in sections of human kidney and bone has previously been described. To ascertain whether the levels of VDR mRNA detected following IS-RT-PCR were transcriptionally significant, computerized image analysis was used to determine the mean silver grain density in human kidney and bone cells following conventional in situ hybridization and after various cycles of IS-RT-PCR. Only a few cycles of PCR were needed to produce an optimum signal, but amplification of signal following IS-RT-PCR was found to be relatively inefficient. Following the optimum number of cycles of IS-RT-PCR in kidney sections, there was a less than four-fold increase in signal. Similarly, in bone, the optimum signal detected was only approximately five times greater than that found with conventional in situ hybridization. These results clearly demonstrate that the increase in signal following IS-RT-PCR follows a more linear pattern and is relatively inefficient, compared with the usual exponential increase with conventional solution phase RT-PCR.

Bone and Bones↗
PubMed1997

Demonstration of estrogen receptor mRNA in bone using in situ reverse-transcriptase polymerase chain reaction.

Falling estrogen levels affect the female skeleton profoundly. Following menopause, estrogen lack is a major cause of osteoporosis. The site of estrogen action in human bone, however, is unclear, but responsive cells must express the estrogen receptor (ER). One obstacle to localizing these cells is that mRNA for ER is expressed in low copy number. Hence, conventional molecular techniques are either too insensitive to detect receptor transcripts (in situ hybridization) or necessitate amplification of RNA extracted from tissue [Northern analysis and polymerase chain reaction (PCR)], thus failing to identify the specific target cells within the mixed-cell population of bone. In situ PCR (IS-PCR) is a technique that combines the sensitivity of PCR with the localization of conventional in situ hybridization. The technique has previously been used primarily to detect single-copy genes and viral DNA within cells. More recently, incorporation of a reverse-transcriptase reaction (IS-RT-PCR) has allowed the technique to be used to identify rare mRNAs within tissues. We have therefore applied the technique of IS-RT-PCR to localize ER mRNA first in human breast tumors, a known positive tissue, and then in bone. Using conventional riboprobe in situ hybridization, ER transcripts were not detectable in any bone cells within sections taken from normal bone and several actively remodeling bone tissues, namely, Paget's disease, renal hyperparathyroidism, and healing fracture callus. The technique of IS-RT-PCR, however, allowed amplification of transcripts to a detectable level. Following two cycles of amplification, hybridization signal was observed in osteoblasts and to a lower level in osteoclasts and occasional osteocytes. This positive signal was more obvious after five cycles, particularly in osteoclasts and osteocytes. After ten cycles, although signal was increased in osteoclasts and osteocytes, it appeared to be decreased in osteoblasts, suggesting that overamplification leads to loss of target complex from these cells. We conclude that several cell types in human bone express ER mRNA in vivo.

Bone Marrow↗
PubMed1996

Demonstration of vitamin D receptor transcripts in actively resorbing osteoclasts in bone sections.

The effects of the active metabolite of vitamin D, 1,25 dihydroxyvitamin D3 (1,25D), are mediated via the vitamin D receptor (VDR). 1,25D is known to have profound effects on bone resorption, but proof that the human osteoclast expresses VDR in vivo is absent. Receptors have been demonstrated in osteoblasts, and it has been generally accepted that the effects of 1,25D on formed osteoclasts are mediated via osteoblasts. Using conventional riboprobe in situ hybridization, VDR transcripts were readily detectable in osteoblasts within sections taken from normal bone and several actively remodelling bone tissues, namely, Paget's disease, renal hyperparathyroidism, and healing fracture callus. However, VDR transcripts also appeared to be present at low levels within osteoclasts from two pagetic samples and two hyperparathyroid samples. To examine this latter finding further, we have used the novel technique of in situ-reverse transcriptase-polymerase chain reaction (IS-RT-PCR) for specific amplification and detection of VDR mRNA within sections taken from the same conditions described above, and also from osteoclastoma samples. As expected, VDR transcripts were amplified and detected in osteoblasts and marrow cells, but were also prominently found in osteoclasts at approximately 50% of the level detected in osteoblasts in normal bone and at 60% in the active bone tissues. This suggests that in addition to effects on osteoclast precursors and those mediated via osteoblasts, 1,25D could exert direct effects on the active bone resorbing cells in vivo.

Bone Remodeling↗
PubMed1996

Novel and sensitive detection systems for the vitamin D receptor--in situ-reverse transcriptase-polymerase chain reaction and immunogold cytochemistry.

The receptor for the active metabolite of vitamin D, 1,25(OH)(2)D(3), known as the vitamin D receptor (VDR), belongs to the steroid hormone nuclear receptor superfamily. We have developed novel methods for detection of VDR mRNA and protein within a human promyelomonocytic cell line, HL-60. Using the newly developed technique of in situ-reverse transcriptase-polymerase chain reaction (IS-RT-PCR), low levels of VDR mRNA could be amplified and demonstrated unequivocally within these cells, and also within a human kidney proximal tubule cell line, CL-8. Use of a novel immunogold cytochemical technique has allowed clear and sensitive detection of VDR protein expression within the HL-60 cells. Further development of IS-RT-PCR has allowed us to apply this technique to tissue sections. We have shown clear amplification of VDR transcripts within sections of formalin-fixed paraffin-embedded human kidney and liver. These techniques will be useful to localise specifically the VDR within cell types that contain low levels of mRNA and protein, and will permit further investigation of the role played by 1,25(OH)(2)D(3) in cellular regulatory mechanisms.

Base Sequence↗
PubMed1995

Generation of multinucleated osteoclast-like cells from canine bone marrow: effects of canine distemper virus.

Recent evidence has implicated canine distemper virus (CDV) as a possible aetiologic agent in Paget's disease of bone and the canine bone disorder, metaphyseal osteopathy. We have therefore examined the effects of CDV on the formation of multinucleated osteoclast-like cells in cultures of canine bone marrow mononuclear cells. Marrow cells from a distemper-infected dog and from five uninfected dogs were cultured in the presence of 1 alpha, 25-(OH)2 vitamin D3 and the number of tartrate resistant acid phosphatase positive multinucleated cells (MNCs) was determined. The presence of calcitonin (CT) receptors was confirmed by autoradiography with 125I-labeled human CT. Cultures from the distemper-infected dog contained a higher level of MNCs than those from the normal dogs. The in vitro addition of CDV to the cultures from all the dogs produced a dose-dependent increase in the number of MNCs, and an increase in size of these cells in the cultures from the infected dog. Cells infected with CDV were hyperresponsive to 1 alpha,25-(OH)2 vitamin D3. The presence of the virus in the relevant samples was confirmed using molecular techniques. In situ hybridization studies also revealed a significant increase in the level of infection following in vitro addition of the virus to the culture from the distemper-infected dog, suggesting that further infection had taken place. Resorption pits were formed on bone slices, although the number of pits was not significantly altered by viral infection.(ABSTRACT TRUNCATED AT 250 WORDS)

Acid Phosphatase↗
PubMed1995

Canine bone marrow cell cultures infected with canine distemper virus: an in vitro model of Paget's disease.

We have previously shown that the canine paramyxovirus, canine distemper virus (CDV), is a possible aetiologic agent in Paget's disease of bone and in the canine bone disorder, metaphyseal osteopathy. More recently, we have examined the effects of CDV on the formation of multinucleated, tartrate resistant acid phosphatase positive, calcitonin receptor positive, osteoclast-like cells in cultures of canine bone marrow mononuclear cells, and shown that both in vitro and in vivo infection with CDV produced a dose dependent increase in the number and size of osteoclast-like cells. We have now extended these results to show that CDV infection induces interleukin-6 and c-Fos mRNA in these cells, similar to our recent findings in pagetic bone cells. These results further support the hypothesis that CDV might be involved in the aetiopathogenesis of Paget's disease and metaphyseal osteopathy and suggest that canine marrow culture systems will prove useful as an in vitro model to examine the disease processes in more detail.

Animals↗
PubMed1993

Dogs, distemper and Paget's disease.

The cause of Paget's disease is still unknown, despite many years of intensive study. During this time, evidence has sporadically emerged to suggest that the disease may result from a slow viral infection by one or more of the Paramyxoviruses. More recently, epidemiologic and molecular studies have suggested that the canine paramyxovirus, canine distemper virus, is the virus responsible for the disease. If true, then along with rabies, this would be a further example of a canine virus causing human disease. Studies in the natural host have now supported these findings. Further investigations have proposed that the bony abnormalities seen in Paget's disease are due to the effects of the virus on osteoclastic interleukin-6 and c-FOS production, possibly via the transcription factor NF-kappa B.

Animals↗
PubMed1993

Prevalence of canine distemper antibodies in the pagetic population.

Recent molecular evidence has implicated canine distemper virus (CDV) as a possible aetiologic agent in Paget's disease. However, previous serological studies have shown no differences in levels of anti-CDV antibodies between Paget's patients and controls. In this study, the technique of enzyme linked immunosorbent assay was used to measure anti-CDV antibodies in a group of Paget's patients from the North West of England. Some patients were undergoing treatment with 3-amino-hydroxypropylidene (APD), and the pre-treatment levels of antibody were compared with those following treatment. With several patients, it was also possible to compare the antibody levels with results from in situ hybridisation studies. No significant difference was found between the levels of anti-CDV antibodies in patients and controls. However, several patients and some of the controls did have markedly elevated levels of anti-CDV antibody. Antibody levels remained fairly constant following treatment with APD, except for two patients who showed marked changes. The patients positive for CDV by in situ hybridisation had significantly lower levels of anti-CDV antibodies when compared with those that were negative by in situ hybridisation. These results suggest that if CDV does cause Paget's disease, anti-CDV antibodies play little or no part in the disease pathogenesis. High levels of anti-CDV antibodies in both Paget's patients and controls suggest that a canine virus can infect humans. The fact that those patients that had CDV transcripts detectable in their bone cells had low levels of anti-CDV antibodies might suggest failure to clear the virus during an initial infection.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Canine distemper virus transcripts detected in the bone cells of dogs with metaphyseal osteopathy.

Using the technique of in situ hybridisation, we have recently extended our observations that canine distemper virus (CDV) is present in the bone cells of patients with Paget's disease, and have shown that CDV is also detectable in the bone cells of dogs that are naturally infected with the virus. Since hybridisation was localised to bone cells within the metaphyses of the affected dogs, we investigated the possibility that CDV might be involved in the canine metaphyseal bone disorder, metaphyseal osteopathy. Bone samples from three cases of metaphyseal osteopathy were examined for the presence of the CDV nucleocapsid (CDV-N) gene and the measles virus nucleocapsid (MV-N) gene, using 35S-labelled sense and antisense riboprobes. As with our previous findings in Paget's disease of bone, only the antisense probe was found to hybridize to the osteoblasts and osteoclasts within the affected metaphyses. No hybridisation was seen with the CDV-N sense and MV-N probes in any of the samples tested. Bone samples were also taken from one of the cases to check for the presence of the CDV-N gene using the polymerase chain reaction (PCR). Our findings with in situ hybridisation were confirmed by PCR and subsequent Southern blotting and probing with a 32P-labelled cDNA probe. The detection of CDV RNA within the bone cells of dogs with metaphyseal osteopathy suggests that this virus may be a cause of the disease and provides further, indirect evidence that CDV might be responsible for the bony abnormalities seen in Paget's disease of bone.

Animals↗