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The decrease in bone volume associated with osteoporosis and age-related osteopenia is accompanied by increased marrow adipose tissue formation. Reversal of this process may provide a novel therapeutic approach for osteopenic disorders. We have shown that cells cultured from human trabecular bone are not only osteogenic, but are able also to undergo adipocyte differentiation under defined culture conditions. Osteoblast differentiation was induced by 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) and adipocyte differentiation by dexamethasone (dex) plus 3-isobutyl-1-methylxanthine (IBMX) treatment. Adipogenesis was characterized by lineage-specific enzyme and gene activities, alpha-glycerophosphate-3-dehydrogenase activity, fatty acid binding protein, aP2 and lipoprotein lipase expression. Osteoblastogenesis was assessed by osteoblast characteristic 1,25(OH)2D3 induction of alkaline phosphatase activity and osteoblast-specific 1,25(OH)2D3-induced osteocalcin synthesis and release. We provide evidence for a common pluripotent mesenchymal stem cell that is able either to undergo adipogenesis or osteoblastogenesis, using clonal cell lines derived from human trabecular bone cell cultures. Adipogenesis can be induced also by long chain fatty acids and the thiazolidinedione troglitazone. Dex plus IBMX-induced adipogenesis can be inhibited by interleukin-1beta, tumor necrosis factor-alpha, and transforming growth factor-beta. Interestingly, and in contrast to extramedullary adipocyte differentiation as shown by mouse 3T3L-1 and a human liposarcoma SW872 cell line, trabecular bone adipogenesis was unaffected by insulin. Also, the formation of fully differentiated adipocytes from trabecular bone cells after troglitazone treatment and long chain fatty acids was dependent on increased expression of the nuclear hormone receptor peroxisome proliferator-activated receptor gamma2 caused by dex plus IBMX. Specific inhibition of marrow adipogenesis and promotion of osteoblastogenesis of a common precursor cell may provide a novel therapeutic approach to the treatment of osteopenic disorders.

It has been suggested that the stromal element of human osteoclastomas contains osteoblastic cells. In this study, we demonstrate that osteoclast-depleted, passaged stromal cells express alkaline phosphatase and osteocalcin in vitro and form mineralized nodules under appropriate culture conditions. In addition, we describe a model in which severe combined immunodeficient (SCID) mice were used to support the differentiation of these putative human osteoblast progenitors in vivo. Lesions formed from human stromal cells were identified using the OKa blood group antigen and human procollagen type I antibodies. By 21 days, the lesion was a complete bone unit: a fully mineralized cortex, remodeling trabeculae, and a highly cellular marrow space. Stromal cells derived from six out of seven osteoclastomas produced identical lesions. Further studies have demonstrated that the capacity of the osteoclastoma-derived stromal cells to form bone in vivo and in vitro is passage dependent; early passages were osteogenic in both model systems, while later passages were not. In conclusion, we have developed a model in which the osteogenic nature of cells can be confirmed in vivo. Furthermore, human osteoclastoma-derived stromal cells provide a source of these osteogenic cells to study human osteoblast differentiation, both in vivo and in vitro.

Three inhibitors of calcium-dependent cyclic adenosine 3'5'-monophosphate (cAMP) dependent phosphodiesterase IV (PDE IV) were evaluated for their effects on lipopolysaccharide (LPS)-induced tumor necrosis factor (TNF) production in vitro and in vivo and for their ability to protect mice from LPS-induced lethality in D-galactosamine (D-gal) sensitized mice. In vitro, on LPS-stimulated murine peritoneal macrophages (PEM), BRL 61063 (1,3-di(cyclopropylmethyl)-8-aminoxanthine) and rolipram (4-(3-cyclopentyloxy-4-methoxyphenyl)-2-pyrrolidone) had similar TNF inhibitory activity with an IC50 ranging from 0.1 to 0.5 microM. Pentoxifylline (PTX), (3,7-dimethyl-1-(5-oxohexyl)xanthine) was less potent with an IC50 = 100 microM. In vivo, there was a rank order potency on serum TNF levels in LPS challenged D-gal sensitized mice. BRL 61063 inhibited TNF production with an ID50 of 0.1 mg/kg, rolipram at 1 mg/kg, and PTX at 200 mg/kg. Thus, BRL 61063 is 2,000 times more potent than PTX in reducing TNF serum levels in this model. Interestingly, TNF is implicated as having a central pathogenic role in the LPS/D-gal model, since survival of animals correlated directly with reduction of serum TNF levels for all three compounds tested. It is proposed that potent inhibitors of TNF may have therapeutic activity in disease states where TNF appears to play a role in the pathogenesis of the disease.

The immunosuppressive effects of cyclosporin A, FK506, and rapamycin were compared in mouse and rat systems of in vitro cellular stimulation. The inhibitory profile of rapamycin was distinctly different in the two species. In mouse systems, rapamycin caused a dose-dependent inhibition of both Ca(2+)-dependent (concanavalin A (Con A), phytohemagglutinin (PHA), and phorbol 12-myristate 13-acetate + ionomycin) and Ca(2+)-independent (lipopolysaccharide and PMA + interleukin-2) activation, whereas in the rat only Ca(2+)-independent responses were inhibited. Rapamycin's lack of activity in Ca(2+)-dependent responses in the rat does not appear to reside in a general insensitivity of this pathway to inhibition as cyclosporin A and FK506 demonstrated potent inhibitory activity. Additionally, rapamycin was able to block the inhibitory effect of FK506 on rat cells stimulated with the Ca(2+)-dependent stimulus, Con A. These results indicate a further dissociation in the biological activity of rapamycin compared to cyclosporin A and FK506 and may point to intriguing species differences in the immunosuppressive effects of these compounds in vitro.

The effects of SK&F 86002 and other pyridinyl imidazole compounds on murine cytokine production were investigated. In vitro, SK&F 86002 inhibited LPS stimulated TNF-alpha production by the RAW 264.7 cell line and by oil elicited peritoneal macrophages with an IC50 of 5 microM. In general, the activity was reflective of previous results obtained with human monocytes as SK&F 86002 and its analogs demonstrated identical rank order potency for TNF-alpha inhibition in both species. These compounds also inhibited TNF-alpha in vivo in a murine model of endotoxin shock. Following oral administration, SK&F 86002 and its analogs reduced serum TNF-alpha levels by > 80% and afforded 100% protection from lethality. In contrast, tenidap, a novel anti-inflammatory drug, had minimal to no effect on murine TNF-alpha production in the same assays. These data further extend the pharmacological profile of the pyridinyl imidazoles by demonstrating that these compounds potently inhibit murine TNF-alpha production both in vitro and in vivo.

SK&F 105809 is a structurally novel dual inhibitor of lipoxygenase and cyclooxygenase-mediated arachidonic acid (AA) metabolism, which has demonstrated antiinflammatory activity in rodent models of inflammation. In addition, the active metabolite of this compound, SK&F 105561, has been shown in vitro to inhibit the production of the inflammatory cytokine interleukin-1 (IL-1) in human monocytes stimulated with lipopolysaccharide (LPS). We report here that in vitro SK&F 105561 also blocks the production of tumor necrosis factor (TNF) from human monocytes (IC50 0.8-3 microM). Furthermore, in a murine model of endotoxin shock in which animals are injected with LPS in combination with D-galactosamine (D-gal), SK&F 105809 (10, 30, and 100 mg/kg p.o.), delivered 30 min prior to LPS/D-gal, caused a dramatic reduction in serum TNF (40-90%) and protected the animals from the lethal effects of this treatment. Similar results were obtained in a second model of endotoxin shock in which mice were sensitized with Propionibacterium acnes 10 days prior to LPS injection. In this system 100-fold higher levels of serum TNF are elicited than with the LPS/D-gal model. Treatment with SK&F 105809 (30 and 100 mg/kg p.o.) delivered 30 min prior to LPS resulted in 90-100% inhibition of serum TNF. Protection from the lethal effects of LPS was observed at these doses in the P. acnes/LPS model.

SK&F 105685 (N,N-Dimethyl-8,8-dipropyl-2-azaspiro[4.5]decane-2-propanamine+ ++ dihydrochloride) is a novel azaspirane with beneficial activity in animal models of autoimmune diseases such as adjuvant-induced arthritis and experimental autoimmune encephalomyelitis in the Lewis rat and lupus-like disease in the MRL mouse. The effect of SK&F 105685 on the proliferation of rat lymphoid cells was examined in vitro. The compound inhibited the proliferative response of spleen, thymus and lymph node cells to the mitogen concanavalin A (Con A) in a dose-dependent manner but had little or no effect on the mitogenic response of peripheral blood lymphocytes. Although less potent than cyclosporin A, SK&F 105685 was able to inhibit the proliferation of spleen cells stimulated with PMA and ionomycin or the mitogens phytohemagglutinin (PHA), Con A and pokeweed mitogen (PWM). Relatively early event(s) in cell proliferation were affected by SK&F 105685 since delaying addition of the drug by 24 to 48 hours after Con A stimulation of rat spleen cells resulted in reduced levels of suppression. The mode of action of SK&F 105685 appeared to differ from that of cyclosporin A or rapamycin. Unlike cyclosporin A, SK&F 105685 did not affect IL-2 production by Con A-stimulated spleen cells or the IL-2-producing Jurkat cell line, but, like rapamycin, the compound significantly reduced the IL-2-induced proliferation of rat ConA blasts. These results suggest that inhibition of lymphocyte proliferation by SK&F 105685 may require the activity of an intermediate effector cell(s) present in susceptible populations such as cells from the spleen, thymus, lymph nodes and Con A blast preparations but absent or present in low numbers in resistant populations such as peripheral blood cells. Indomethacin and NG-monomethyl-L-arginine (NGMMA), a competitive inhibitor of nitric oxide synthase, were both unable to relieve SK&F 105685-induced suppression of splenic Con A responses thereby ruling out a role for the production of prostaglandins or nitric oxide by macrophages as an intermediate in drug-mediated suppression. In summary, SK&F 105685 was unable to inhibit lymphoproliferative responses by a mechanism distinct from that of cyclosporin A or rapamycin and which appears to involve regulation of cellular interactions rather than a direct effect on responding lymphocytes.