Prostaglandins antagonize fibroblast proliferation stimulated by tumor necrosis factor

Bioactive Lipids in Age-Related Disorders

Our own studies and those of others have shown that defects in essential fatty acid (EFA) metabolism occurs in age-related disorders such as obesity, type 2 diabetes mellitus, hypertension, atherosclerosis, coronary heart disease, immune dysfunction and cancer. It has been noted that in all these disorders there could occur a defect in the activities of desaturases, cyclo-oxygenase (COX), and lipoxygenase (LOX) enzymes leading to a decrease in the formation of their long-chain products gamma-linolenic acid (GLA), arachidonic acid, eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA). This leads to an increase in the production of pro-inflammatory prostaglandin E2 (PGE2), thromboxanes (TXs), and leukotrienes (LTs) and a decrease in anti-inflammatory lipoxin A4, resolvins, protectins and maresins. All these bioactive molecules are termed as bioactive lipids (BALs). This imbalance in the metabolites of EFAs leads to low-grade systemic inflammation and at times acute inflammatory events at specific local sites that trigger the development of various age-related disorders such as obesity, type 2 diabetes mellitus, hypertension, coronary heart disease, atherosclerosis, and immune dysfunction as seen in rheumatoid arthritis, lupus, nephritis and other localized inflammatory conditions. This evidence implies that methods designed to restore BALs to normal can prevent age-related disorders and enhance longevity and health.

Human lung fibroblasts inhibit macrophage inflammatory protein-1α production by lipopolysaccharide-stimulated macrophages

We investigated the effect of interaction between lung fibroblasts and macrophages on macrophage inflammatory protein 1alpha (MIP-1alpha) production by macrophages. In a co-culture system consisting of WI-38 lung fibroblasts layered over THP-1 macrophages stimulated with lipopolysaccharide (LPS), MIP-1alpha production by THP-1 was significantly lower in co-culture with WI-38 than in THP-1 alone. Treatment with conditioned medium generated from WI-38 (CM-WI-38) suppressed MIP-1alpha production and mRNA expression in THP-1 cells. Such inhibitory effect of CM-WI-38 on MIP-1alpha production was abrogated by treatment with indomethacin, NS-398 (a specific COX-2 inhibitor), or anti-prostaglandin E(2) antibody. Furthermore, even in a transwell filter system separating both types of cells, co-culture-induced reduction of MIP-1alpha production was observed. Therefore, soluble factors such as prostaglandin E(2) released from lung fibroblasts are responsible for the co-culture-induced inhibition of macrophage-derived MIP-1alpha production, suggesting that immune and inflammatory cell interactions can contribute to the modulatory mechanisms involved in the regulation of the inflammatory or fibrotic process.

Bone marrow fibroblasts in patients with advanced lung cancer

In a previous study we demonstrated that the incidence of fibroblast colony-forming units (CFU-F) was very low in bone marrow primary cultures from the majority of untreated advanced non-small lung cancer patients (LCP) compared to normal controls (NC). For this reason, we studied the ability of bone marrow stromal cells to achieve confluence in primary cultures and their proliferative capacity following four continuous subcultures in consecutive untreated LCP and NC. We also evaluated the production of interleukin-1beta (IL-1beta) and prostaglandin E2 (PGE2) by pure fibroblasts. Bone marrow was obtained from 20 LCP and 20 NC. A CFU-F assay was used to investigate the proliferative and confluence capacity. Levels of IL-1beta and PGE2 in conditioned medium (CM) of pure fibroblast cultures were measured with an ELISA kit and RIA kit, respectively. Only fibroblasts from 6/13 (46%) LCP confluent primary cultures had the capacity to proliferate following four subcultures (NC = 100%). Levels of spontaneously released IL-1beta were below 10 pg/ml in the CM of LCP, while NC had a mean value of 1,217 +/- 74 pg/ml. In contrast, levels of PGE2 in these CM of LCP were higher (77.5 +/- 23.6 pg/ml) compared to NC (18.5 +/- 0.9 pg/ml). In conclusion, bone marrow fibroblasts from LCP presented a defective proliferative and confluence capacity, and this deficiency may be associated with the alteration of IL-1beta and PGE2 production.

Is increased arachidonic acid release a cause or a consequence of replicative senescence?

Arachidonic acid (AA) has been related to both stimulation and inhibition of cellular proliferation. During replicative senescence of human fibroblasts, increased levels of AA have been thought to play a causal role in the limited proliferative capacity of the cells. To clarify the role of AA in the proliferation of normal fibroblasts and in cellular senescence, we examined uptake from and release of AA into the culture media and its effects on DNA synthesis. Our results indicate that some aspects of AA metabolism in normal human fibroblasts aged in culture are significantly different in comparison to early passage cells. Particularly, AA release following different mitogenic stimulation is higher in senescent than in young cells. Notwithstanding this significant difference, AA, at the concentration used, has no inhibitory effect on fibroblast DNA synthesis. Moreover AA and prostaglandins are responsible for the proliferative block in neither senescent cells nor mediate ceramide inhibition of DNA synthesis. So our results suggest that the increasing AA release is not causal, but rather the result of in vitro aging.

Different expression of TNF-alpha receptors and prostaglandin E(2 )Production in normal and fibrotic lung fibroblasts: potential implications for the evolution of the inflammatory process

Normal human lung fibroblasts downregulate the production of tumor necrosis factor (TNF)-alpha by activated monocytes through the production of prostaglandin E(2) (PGE(2)), contributing to the local control of the inflammatory process. In this study, we provide evidence that fibroblasts derived from diseased tissue, such as fibrotic lung fibroblasts, exhibit different functional features compared with normal cells, with particular regard to their modulatory role. Indeed, fibrotic fibroblasts (FF) spontaneously produced less PGE(2) (3,300 +/- 410 pg/ml) compared with normal fibroblasts (NF) (7,500 +/- 270 pg/ml) and, as a consequence, they showed a reduced ability to downregulate the production of TNF-alpha by lipopolysaccharide (LPS)- activated monocytes. The percentage of inhibition induced by normal cells on the production of TNF-alpha by LPS-activated monocytes was 61 +/- 5.9%, whereas the inhibitory effect exerted by fibrotic cells was reduced to 32 +/- 4% (P < 0.01). We have also observed that the ability of TNF-alpha to induce PGE(2) was impaired in FF and was related to a reduced expression of cyclooxygenase 2. This was possibly due to the reduction of the expression of TNF receptors (TNFRs) in fibrotic cell lines compared with normal cell lines. Flow cytometry revealed that the mean fluorescence intensity (MFI) of both isoforms of TNFR was significantly lower in FF compared with NF. The MFI of TNFR1 was 3. 55 +/- 0.12 for NF and 1.78 +/- 0.35 for FF (P < 0.001). The MFI of TNFR2 was 1.95 +/- 0.27 for NF and 0.99 +/- 0.16 for FF (P < 0.01). The analysis of the effect of TNF-alpha on some functions associated with collagen metabolism in NF and FF showed an increase of the expression of the receptor for collagen type I (alpha(2)beta(1) integrin) in NF (42 +/- 10%) and an even larger increase in FF (102 +/- 23%) (P < 0.05). Interestingly, unlike NF, TNF-alpha failed to increase matrix metalloproteinase 1 levels in FF and did not cause any growth inhibition in these cells. The reduced capability of fibrotic cells to produce PGE(2) either spontaneously or after TNF-alpha treatment may lead to an unrestrained release of TNF-alpha from activated monocytes and, as a result of the reduced expression of TNFRs, to a different response of these cells to TNF-alpha. These changes may be important in the evolution of the inflammatory process, potentially contributing to its transformation into a chronic and self-perpetuating process.

Bacterial products primarily mediate fibroblast inhibition in biomaterial infection

PURPOSE

The stimulation of fibroblast growth is essential for the normal healing and tissue integration of biomaterials. The local elevation of proinflammatory mediators in infected perigraft fluid (PGF) may inhibit this growth. We sought to determine whether infected PGF inhibited fibroblast growth, and, if so, whether this was primarily dependent on the biomaterial, bacteria, or host.

METHODS

In vivo Dacron or expandable polytetra-fluoroethylene (ePTFE) grafts, sterile or colonized with slime-producing (RP-62A, viable or formalin-killed) or nonslime-producing (RP-62NA) Staphylococcus epidermidis (1 x 10(7) CFU/cm2), were implanted in Swiss Webster mice, and the PGF was harvested at 7 and 28 days. Antibodies to tumor necrosis factor alpha, interleukin 1 alpha, interferon gamma (7 micrograms/day), and indomethacin (50 micrograms/day) were administered by microinfusion pumps for 7 days and the PGF was harvested. Inhibition of the proinflammatory mediators was confirmed by enzyme-linked immunosorbant assay. The nontreated, heat-treated, or trypsin-digested in vivo PGF was incubated with an in vitro [3H]thymidine murine fibroblast (ATCC CCL-12) proliferation assay.

RESULTS

Fibroblast inhibition was significant at 7 and 28 days with infected PGF incubation compared with sterile and was not dependent on bacterial slime production or viability. Dacron sterile PGF did not significantly inhibit fibroblasts compared with control, whereas sterile ePTFE stimulated (P < 0.05) fibroblasts. Treatment of the PGF with proinflammatory cytokines, heat, and trypsin failed to reverse fibroblast inhibition in the infected state.

CONCLUSION

Biomaterial infection is associated with fibroblast inhibition that is dependent primarily on bacterial products and not the host or biomaterial. Conservative intervention strategies for graft infection need to address the problem of poor healing as well as bacterial clearance.

Interaction of substance P with epidermal growth factor and fibroblast growth factor in cyclooxygenase-dependent proliferation of human skin fibroblasts

Substance P (SP), fibroblast growth factor (FGF), and epidermal growth factor (EGF) are mitogens for fibroblasts. EGF acts as a progression factor, whereas FGF and SP have competence factor activity. The ability of eicosanoids to regulate proliferation of fibroblasts and the increased production of prostaglandins by fibroblasts in response to the growth factors, led us to investigate the involvement of cyclooxygenase-dependent arachidonic acid metabolites in the mitogenic response of serum-starved human skin fibroblasts to SP, FGF, and EGF. We tested the interaction of a submaximal concentration of SP(10(-9)M) with baFGF(40 micrograms/ml) and EGF(0.01 microgram/ml) both on fibroblast proliferation and release of arachidonic acid metabolites. A combination of SP and EGF synergistically stimulated fibroblast proliferation and prostaglandin E2 release, whereas addition of SP to FGF-containing cultures did not affect cell growth. Inhibition of cyclooxygenase by acetylsalicylic acid augmented the growth response of fibroblasts to all: SP, FGF, and EGF. In the presence of acetylsalicylic acid, SP combined with FGF enhanced fibroblasts proliferation, whereas a combination with EGF inhibited cellular growth with respect to growth induced by EGF alone. Thus, interactions of SP with FGF and EGF differently affected the mitogenic response depending on the formation of arachidonic acid metabolites. The findings indicate that eicosanoids may be important mediators of competence and progression factor activities that may determine the effects of substance P on fibroblast proliferation in a cytokine network.

Distribution of cyclooxygenase isoforms in murine chronic granulomatous inflammation. Implications for future anti-inflammatory therapy

Inhibition of the enzyme cyclooxygenase (COX) is the basis for the mechanism of action of non-steroidal anti-inflammatory drugs (NSAIDs). COX exists as a constitutive (COX-1) and a mitogen-inducible (COX-2) isoform. The relative contribution of COX-1 and COX-2 to inflammation is unknown. This study investigated COX activity and the distribution of COX-1 and COX-2 during the development of a murine air pouch model of chronic granulomatous inflammation. COX activity progressively rose and was maximal at day 14. Of the COX metabolites measured, PGE2 was the greatest > 6-keto PGF1a > TXB2 > PGF2a. By day 7, COX-2-labelled fibroblast- and macrophage-like cells were observed and their number and distribution increased with time. At all time points, endothelial cells of venules in the loose connective tissue of the dermis showed immunoreactivity for COX-2. After day 14, labelling of capillaries in the granuloma was also observed. This study is the first to show that COX-2 is the predominant COX isoform in all stages of the inflammatory response. These results suggest that selective inhibition of COX-2 may prove more beneficial, with fewer gastric and renal side-effects, than existing NSAID therapy for the treatment of chronic inflammatory diseases.

Fibroblast growth-promoting activity in proliferative vitreoretinopathy: antagonism by acetylsalicylic acid

Proliferative vitreoretinopathy is a severe reactive process which leads to the formation of cellular membranes on the surface of the retina and in the vitreous. We determined the fibroblast growth-promoting activity of intraocular fluid from patients suffering from proliferative vitreoretinopathy, retinal detachment or cataract and further evaluated the effect of acetylsalicylic acid on growth-stimulated fibroblasts. The results demonstrated a significant enhancement of growth-promoting activity of intraocular fluid in proliferative vitreoretinopathy as compared to that of control samples. We showed that the augmented growth-promoting activity of intraocular fluid in proliferative vitreoretinopathy was significantly antagonized by inhibition of cyclooxygenase with acetylsalicylic acid (ID50 approximately 5 microM). In contrast, no significant effect was seen in corresponding control experiments. The findings suggest that metabolites of the cyclooxygenase pathway are involved in the regulation of enhanced intraocular fluid-induced fibroblast proliferation in proliferative vitreoretinopathy and that acetylsalicylic acid might be useful as an antiproliferative agent in intraocular fibrogenesis.

The role of cyclic-3',5'-adenosine monophosphate in prostaglandin-mediated inhibition of basic calcium phosphate crystal-induced mitogenesis and collagenase induction in cultured human fibroblasts

Synovial fluid basic calcium phosphate (BCP) crystals are associated with severe destructive arthropathies characterised by synovial proliferation and non-inflammatory degradation of intra-articular collagenous structures. BCP crystals stimulate fibroblast and chondrocyte mitogenesis, metalloprotease secretion and prostaglandin production. As a tissue protective effect of prostaglandins has been suggested, we recently studied the effect of PGE1 on BCP crystal-induced mitogenesis and collagenase mRNA accumulation in human fibroblasts (HF). We demonstrated a dose-dependent inhibition of BCP crystal-induced mitogenesis and collagenase mRNA accumulation. The mechanism of PGE1 inhibition of BCP crystal-induced mitogenesis and collagenase mRNA accumulation was therefore explored. PGE1 (100 ng/ml) increased HF intracellular cAMP 40-fold over control. BCP alone caused no such change but inhibited the PGE1-induced increase in intracellular cAMP by at least 60%. The PGE1-induced increase in intracellular cAMP was also blocked by the adenyl cyclase inhibitor, 2',5'-dideoxyadenosine (ddA) (10 microM) and ddA reversed the PGE1-mediated inhibition of BCP crystal-induced mitogenesis. Dibutyryl cAMP also inhibited BCP crystal-induced mitogenesis in a concentration-dependent manner. Agents which increase intracellular cAMP levels such as the adenyl cyclase activator forskolin and the phosphodiesterase, inhibitor 3-isobutyl-1-methylxanthine (IBMX) mimicked the effect of PGE1 on HF collagenase mRNA levels. PGE1 inhibits the biologic effects of BCP crystals through the cAMP signal transduction pathway and such inhibition may have significant therapeutic implications.

Inducible isoforms of cyclooxygenase and nitric-oxide synthase in inflammation

Cyclooxygenase (COX) converts arachidonic acid to prostaglandin H2, which is further metabolized to prostanoids. Two isoforms of COX exist: a constitutive (COX-1) and an inducible (COX-2) enzyme. Nitric oxide is derived from L-arginine by isoforms of nitric-oxide synthase (NOS; EC 1.14.13.39): constitutive (cNOS; calcium-dependent) and inducible (iNOS; calcium-independent). Here we have investigated inducible isoforms of COX and NOS in the acute, chronic, and resolving stages of a murine air pouch model of granulomatous inflammation. COX and NOS activities were measured in skin samples in the acute phase, up to 24 h. Activities in granulomatous tissue were measured at 3, 5, 7, 14, and 21 days for the chronic and resolving stages of inflammation. COX-1 and COX-2 proteins were assessed by Western blot. COX activity in the skin increased over the first 24 h and continued to rise up to day 14. COX-2 protein rose progressively, also peaking at day 14. COX-1 protein remained unaltered throughout. The iNOS activity increased over the first 24 h in the skin, with a further major increase in the granulomatous tissue between days 3 and 7, followed by a decrease at day 14 and a further increase at day 21. The rise in COX and NOS activities in the skin during the acute phase reinforces the proinflammatory role for prostanoids and suggests one also for nitric oxide. However, in the chronic and resolving stages, a dissociation of COX and NOS activity occurred. Thus, there may be differential regulation of these enzymes, perhaps due to the changing pattern of cytokines during the inflammatory response.

Stimulation of prostaglandin production by hepatocyte growth factor in human gastric carcinoma cells

Hepatocyte growth factor (HGF), a protein with pleiotropic biological activity affecting cell growth and motility, was found to markedly activate prostaglandin production in human gastric carcinoma TMK-1 cells. HPLC analysis revealed that HGF stimulated the production of prostaglandin E2 (PGE2), which is the major prostaglandin produced in these cells. HGF maximally stimulated PGE2 production at a concentration of 10 ng/ml, and it was a more potent stimulator of PGE2 production than epidermal growth factor (EGF), which is known to stimulate prostaglandin production in various cell lines. The simultaneous addition of HGF and EGF caused no further stimulation of the PGE2 production observed in HGF-treated cells. We showed also that HGF increased the arachidonate release from TMK-1 cells, which release was completely suppressed by the addition of phospholipase A2 (PLA2) inhibitors. Further studies in vitro showed that HGF enhanced cellular activities of cytosolic PLA2 and cyclooxygenase 1.5-fold each. These results indicate that HGF stimulates prostaglandin production through increases in both cytosolic PLA2 and cyclooxygenase activities.

Prostaglandin E2 antagonizes gingival fibroblast proliferation stimulated by interleukin-1 beta

Treatment of human gingival fibroblasts with prostaglandin E2 (PGE2) resulted in significant concentration-dependent inhibition in deoxyribonucleic acid (DNA) synthesis (8.40-37.89%), while indomethacin (INDO) (PG inhibitor), interleukin-1 beta (IL-1 beta) or IL-1 beta+INDO caused a significant and dose-dependent increase in DNA synthesis. Addition of PGE2 to culture media containing IL-1 beta and INDO caused a significant concentration-dependent reduction in IL-1 beta- and INDO-induced stimulation of DNA synthesis. The findings suggest that IL-1 beta and PGE2, which are also produced by fibroblasts, could play an important role in regulation of gingival tissue development and wound healing, and their modulation may have therapeutic potential.

Substance P: a competence factor for human fibroblast proliferation that induces the release of growth-regulatory arachidonic acid metabolites

Substance P (SP) was recognized to stimulate cell growth. The mechanisms of growth control by SP are unknown. We, therefore, investigated mechanisms of the effect of SP on proliferation of human skin fibroblasts. SP did not stimulate proliferation of fibroblasts growth arrested by serum starvation over 48 hours. However, in the presence of acetylsalicylic acid SP potently stimulated fibroblast growth. A bell-shaped dose-response curve with maximal stimulation at picomolar concentrations was found. Specificity of the mitogenic effect was analyzed by use of synthetic SP analogs. Only neurokinin-1 receptor agonists were active, whereas a specific neurokinin-2 receptor analog did not exhibit mitogenicity. Analyzing the supernatants of growth-arrested fibroblasts treated with SP indicated that SP provokes release of the arachidonic acid metabolites, prostaglandin E2, and prostacyclin but not thromboxane B2 or leukotriene B4. Since similar response patterns in proliferation and arachidonic acid metabolite release have been described for several proinflammatory cytokines, some of which are known to act as competence factors in proliferation, we characterized the mitogenic effect of SP. Results established that SP stimulates fibroblast growth in a manner typical of competence factors. We conclude that arachidonic acid metabolites are involved in the cell cycle-dependent mitogenic action of SP on human skin fibroblasts.

Misoprostol, a prostaglandin E1 analogue, inhibits basic calcium phosphate crystal-induced mitogenesis and collagenase accumulation in human fibroblasts

Synovial fluid basic calcium phosphate (BCP) crystals are associated with severe destructive arthropathy. BCP crystals induce the secretion of matrix-degrading enzymes such as collagenase. No prophylactic or therapeutic agents are recognized to ameliorate the cartilage damage associated with BCP deposits in joints. As a chondroprotective effect of prostaglandins (PG) has been suggested, we studied the effect of misoprostol, a PGE1 analogue, on BCP crystal-induced mitogenesis and collagenase messenger RNA (mRNA) accumulation in human fibroblasts (HF). Mitogenesis was determined by 3H-thymidine incorporation assays and collagenase mRNA accumulation by Northern blot analysis, in HF stimulated with BCP crystals in the presence or absence of misoprostol. Misoprostol caused concentration-dependent inhibition of BCP crystal-induced mitogenesis. The inhibition of BCP-stimulated mitogenesis was not specific as misoprostol also inhibited the mitogenic response to 10% serum. There was only 50 (+/-5)% inhibition of serum-induced mitogenesis by misoprostol at 500 ng/ml, the concentration that completely inhibited BCP crystal-induced mitogenesis. Misoprostol also inhibited the accumulation of collagenase mRNA in BCP-stimulated HF by 63%. These data suggest that misoprostol may inhibit the synovial proliferation and cartilage degradation that accompany BCP crystal deposition.