PubMed Health⌕ Search

Biomedical subjects

L Key

Publications and source records attributed to L Key.

12 recordsLinked to original sources
PubMed2000

A new superoxide-generating oxidase in murine osteoclasts.

Superoxide production contributes to osteoclastic bone resorption. Evidence strongly indicates that NADPH oxidase is an enzyme system responsible for superoxide generation in osteoclasts. A membrane-bound subunit, p91, is the catalytic domain of NADPH oxidase. However, osteoclasts from p91 knockout mice still produce superoxide at a rate similar to that observed in wild type mice. This unexpected phenomenon prompted us to examine the osteoclasts for an alternative to the p91-containing oxidase. In this study, the cloning of a NADPH oxidase subunit (Nox 4) with 578 amino acids is reported. Nox 4 has 58% similarity in amino acids with the known p91 subunit of NADPH oxidase. Nox 4 is present and active in osteoclasts. Antisense oligonucleotides of Nox 4 reduced osteoclastic superoxide generation as well as resorption pit formation by osteoclasts. This new oxidase complex was present and functional in osteoclasts from p91 knockout mice, explaining the normal resorptive activity seen in the osteoclasts where no p91 is present.

Amino Acid Sequence↗
PubMed1988

Increased in vitro bone resorption by monocytes in the hyper-immunoglobulin E syndrome.

Children with the hyper-immunoglobulinemia E syndrome are prone to bone fractures. We determined bone density in six patients with hyper-IgE syndrome using photon absorptiometry. All six patients had significantly reduced bone density compared with age- and sex-matched controls. The capacity of peripheral blood monocytes to degrade 45Ca-labeled bone in vitro was studied. The mean percent 45Ca release in four hyper-IgE patients (40.8 +/- 8.6) was significantly higher (p less than 0.01) than in ten age-matched healthy control subjects (7.1 +/- 2.6), seven age-matched patients with recurrent infections (7.9 +/- 1.6), or nine patients with severe atopic dermatitis and elevated serum IgE levels (5.8 +/- 1.3). Monocytes from four of four patients studied spontaneously released abnormally high levels of prostaglandin E2. Bone degradation by these monocytes was significantly reduced in the presence of 10(-6) M indomethacin in vitro. Administration of aspirin in vivo to two hyper-IgE patients reduced boned degradation by their monocytes to normal levels. These results suggest that monocytes from patients with hyper-IgE syndrome are activated to resorb bone via products of the prostaglandin synthase (cyclooxygenase) pathway. The activation of cells in the monocyte/macrophage family to resorb bone may contribute to the osteopenia observed in hyper-IgE syndrome.

Aspirin↗
PubMed1986

Neutrophil defect associated with malignant infantile osteopetrosis.

We studied the phagocytes from three infants with malignant osteopetrosis and from their families in an attempt to define further the phagocyte abnormalities associated with this disorder. The rapid membrane potential depolarization in response to the soluble stimuli formylmethionylleucylphenylalanine (FMLP) and phorbol myristate acetate (PMA) served as a measure of neutrophil activation, with 3,3-dipentyloxacarbocyanine (diOC5 [3]) used as the probe. A fluorescence-activated cell sorter (FACS) allowed us to use small volumes of blood in a new quantitative evaluation of neutrophil response. The neutrophils from the infants with malignant osteopetrosis were very minimally activated with either stimulus, as demonstrated by incomplete membrane potential depolarization (10% to 15% of normal controls). This finding indicates that malignant osteopetrosis is accompanied by a significantly reduced neutrophil response to stimulation. The abnormal activation process was also reflected in the respiratory burst response of the patients' neutrophils and monocytes. Fifty percent to 60% of the infants' neutrophils totally failed to reduce nitro blue tetrazolium dye (NBT), 30% to 40% of the cells showed only slight reduction after PMA or FMLP stimulation, and only 5% to 10% demonstrated normal reduction. Peripheral blood monocytes failed to reduce NBT in 35% to 70% of the cells tested. Similar testing of granulocyte-macrophage colonies grown in vitro from circulating progenitor cells also showed an abnormal distribution of response to PMA, with a majority of colonies showing a decrease or absence of NBT reduction. Thus control of expression of the osteopetrotic defect occurs at or before the progenitor cell level.

Flow Cytometry↗
PubMed1984

Treatment of congenital osteopetrosis with high-dose calcitriol.

We administered high doses of calcitriol (up to 32 micrograms per day) to an infant with malignant osteopetrosis, in an attempt to stimulate bone resorption. The patient was placed on a low-calcium diet to prevent hypercalcemia. Measures of bone turnover increased during calcitriol therapy; hydroxyproline excretion rose from 140 to 1358 micrograms per milligram of creatinine per 24 hours, with parallel increases in the ratio of calcium to creatinine in the urine, urinary gamma-carboxyglutamic acid, serum osteocalcin, and serum alkaline phosphatase. A pretreatment bone-biopsy specimen contained no osteoclasts with ruffled borders, a feature of active osteoclasts. After 11 days of calcitriol, ruffled borders were noted. After three months, numerous osteoclasts with ruffled borders and associated bony disruption were evident. Before therapy, the patient's monocytes were incapable of in vitro bone resorption, but after calcitriol, their resorptive capacity was increased to 3.3 times control levels. These data demonstrate that calcitriol increased bone mineral and matrix turnover in our patient. However, during the three months of calcitriol therapy there was only slight clinical improvement in her severe disease. Early and sustained treatment with calcitriol may be useful in osteopetrosis.

1-Carboxyglutamic Acid↗