Autocrine role for the endothelin-B receptor in the secretion of adrenomedullin

Adrenomedullin, originally discovered in human pheochromocytoma, is a vasodilating and natriuretic peptide of vascular endothelial and smooth muscle cell origin. Although endothelin-1 (ET-1) has been implicated as a vasoconstricting and growth-promoting peptide of endothelial origin, it may more importantly function as an autocrine factor and release vasodilatory substances such as nitric oxide by mechanisms linked to the endothelin-B (ETB) receptor subtype. The present study was designed to establish that the ETB receptor stimulates the secretion of adrenomedullin from cultured canine aortic endothelial cells. We first sought to determine the presence and production of adrenomedullin in canine aortic endothelial cells using immunohistochemistry and Northern blot analysis, which revealed that adrenomedullin immunoreactivity and adrenomedullin mRNA were present in canine aortic endothelial cells. Second, adrenomedullin was time-dependently secreted from canine aortic endothelial cells, with a secretion rate of 15.7+/-1.5 pg/10(5) cells per 24 hours. Furthermore, immunohistochemistry revealed the presence of the ETB receptor in canine aortic endothelial cells, and ETB receptor stimulation by sarafotoxin S6c increased adrenomedullin production and secretion from canine aortic endothelial cells. Such actions were blocked with the ETB receptor antagonist IRL-2500 but not with ETA receptor antagonist FR-139317. These studies are the first to report an additional autocrine role of the ETB receptor in the release of vasodilating and natriuretic peptide adrenomedullin, and they suggest another important vasoactive system regulated by the ET receptor subtype.     

Stimulation of cyclic adenosine monophosphate formation by the novel vasorelaxant peptide adrenomedullin in cultured rat mesangial cells

This study was conducted to compare the tensile bond strength at the two interfaces of the "sandwich technique". 48 hours after the specimens were tested, using Hounsfield tensometer. Load was gradually applied on to the specimen till the bond at the interface failed. The load at which the bond failed was recorded and analysed for statistical significance. From the present study it can be concluded that the bond between glass ionomer and dentine is better than the bond between glass ionomer and composite resin.     

Autocrine regulation of endothelial exocytosis: von Willebrand factor release is induced by prostacyclin in cultured endothelial cells

OBJECTIVE: To find out whether recombinant human erythropoietin (r-HuEPO) given perioperatively has any effect on haemostatic activity in patients undergoing elective colorectal resection. DESIGN: A placebo-controlled double-blind study. SETTING: Odense university hospital, Denmark. SUBJECTS: 24 patients undergoing elective colorectal resection, 13 of whom were given r-HuEPO (Eprex) and 11 placebo. MAIN OUTCOME MEASURES: Concentrations of haemoglobin, tissue-type plasminogen activator and plasminogen activator inhibitor-1; activated partial thromboplastin time; prothrombin time; platelet and reticulocyte counts; blood loss; and transfusions. RESULTS: There was no significant change in fibrinolytic activity, prothrombin time, or activated prothrombin time in the treatment group. Platelet counts differed slightly but not significantly, being higher in the r-HuEPO group. There was a significant increase in reticulocyte counts in the r-HuEPO group. CONCLUSION: R-HuEPO given perioperatively significantly increased erythropoiesis in patients undergoing elective colorectal operations but had no influence on haemostatic activity.     

Autocrine and paracrine functions of cytokines in malignant lymphomas

Cytokines play important roles in the pathogenesis of lymphomas via an autocrine or a paracrine mechanism, or both. The characteristic clinical and histopathological features of malignant lymphomas may be due in part to elevated serum or tissue levels of cytokines. Determination of the effects of cytokines on the growth or differentiation of lymphoma cells is often complicated by the fact that more than one cytokine is responsible, and by the failure of anti-cytokine antibodies or antisense oligonucleotides to block the proliferation in vitro of lymphoma cells. However, it appears that IL-6 and/or IL-9 may play a prominent role in the tumor cell proliferation of Hodgkin's disease (HD), anaplastic large-cell lymphoma, or immunoblastic lymphoma. IL-6 may also be responsible for the plasmacytoid differentiation of lymphoma cells in polymorphic immunocytoma. The histopathological changes as a result of paracrine effects are most noticeable in HD. The malignant (H-RS) cells of HD have been shown to express IL-1, IL-5, IL-6, IL-9, TNF-alpha, M-CSF, TGF-beta, and CD80, and, less frequently, IL-4 and G-CSF. These cytokines may be responsible for the increased cellular reaction and fibrosis observed in tissues involved by HD and for the immunosuppression found in patients with HD. In contrast to H-RS cells, most non-HD lymphoma cells do not produce cytokines in excess amounts and reveal only a minimal cellular reaction. Exceptions include T-cell-rich B-cell lymphoma, angiocentric T-cell lymphoma, and angio-immunoblastic lymphadenopathy (AILD-like T-cell lymphoma. IL-4 is responsible for the T-cell reaction in T-cell-rich B-cell lymphoma, whereas IL-6 accounts for the plasma cell reaction in AILD-type T-cell lymphoma. The authors extensively review the role of cytokines in lymphomas because this may lead to major advances in the understanding of the molecular processes involved in the histopathogenesis of lymphomas.     

Expression of adrenomedullin mRNA in adrenocortical tumors and secretion of adrenomedullin by cultured adrenocortical carcinoma cells

Immunoreactive-adrenomedullin concentrations and the expression of adrenomedullin mRNA were studied in the tumor tissues of adrenocortical tumors. Northern blot analysis showed the expression of adrenomedullin mRNA in tumor tissues of adrenocortical tumors, including aldosterone-producing adenomas, cortisol-producing adenomas, a non-functioning adenoma and adrenocortical carcinomas, as well as normal parts of adrenal glands and pheochromocytomas. On the other hand, immunoreactive-adrenomedullin was not detected in about 90% cases of adrenocortical tumors (<0.12 pmol/g wet weight (ww)). Immunoreactive-adrenomedullin concentrations ranged from 0.44 to 198.2 pmol/g ww in tumor tissues of pheochromocytomas and were 9.2 +/- 1.2 pmol/g ww (mean +/- SD, n = 4) in normal parts of adrenal glands. Adrenomedullin mRNA was expressed in an adrenocortical adenocarcinoma cell line, SW-13 and immunoreactive-adrenomedullin was detected in the culture medium of SW-13 (48.9 +/- 1.8 fmol/10(5) cells/24h, mean +/- SEM, n = 4). On the other hand, immunoreactive-adrenomedullin was not detectable in the extract of SW-13 cells (<0.09 fmol/10(5) cells), suggesting that adrenomedullin was actively secreted from SW-13 cells without long-term storage. These findings indicate that adrenomedullin is produced and secreted, not only by pheochromocytomas, but also by adrenocortical tumors. Undetectable or low levels of immunoreactive-adrenomedullin in the tumor tissues of adrenocortical tumors may be due to very rapid secretion of this peptide soon after the translation from these tumors.     

Anti-mitogenic effects of sarpogrelate in cultured rat mesangial cells

We investigated the effects of the new 5-HT2A receptor antagonist, sarpogrelate, on DNA synthesis in renal mesangial cells stimulated with 5-HT in the presence and absence of platelet-derived growth factor (PDGF)-BB. Both 5-HT and PDGF-BB demonstrated a mitogenic effect on these cells. When mesangial cells were incubated in the absence of PDGF-BB, sarpogrelate inhibited DNA synthesis in these cells in a dose-dependent manner. In the presence of PDGF-BB, sarpogrelate had a weaker anti-mitogenic effect in mesangial cells stimulated with 5-HT. Sarpogrelate was cytotoxic at concentrations over 10(-5) M according to the results of LDH release assays, and it reduced the S1 phase in mesangial cells stimulated with 5-HT by a flow cytometry. These findings suggest that sarpogrelate may be effective in the treatment of some glomerulonephritis associated with mesangial cell proliferation.     

Effect of lipoproteins on cultured human mesangial cells

It was recently reported that low-density lipoprotein (LDL) promotes mesangial cell proliferation, and oxidized LDL is cytotoxic for mesangial cells. However, there have been few studies about the effects of other lipoproteins on mesangial cells. Accordingly, we investigated the effect of various lipoproteins on cultured human mesangial cells using 3H-thymidine (3H-TdR) incorporation and cell counting assays. We also investigated the levels of several cytokines in mesangial cell culture supernatants after stimulation by the lipoproteins. Addition of very-low-density lipoprotein (VLDL) at concentrations up to 100 micrograms/mL, intermediate-density lipoprotein (IDL) at up to 50 micrograms/mL, and LDL at up to 50 micrograms/mL induced the proliferation of cultured human mesangial cells, whereas cell growth was inhibited at higher concentrations. Oxidized LDL caused a concentration-dependent decrease of 3H-TdR incorporation. High-density lipoprotein (HDL) had no proliferative effective effect at any concentration. Exposure to VLDL, IDL, LDL, or a high concentration of HDL enhanced the secretion of interleukin-6, platelet-derived growth factor, and transforming growth factor-beta by mesangial cells, whereas tumor necrosis factor-alpha secretion was stimulated by oxidized LDL. These finding indicate that triglyceride (TG)-rich lipoproteins (VLDL and IDL) promote mesangial cell proliferation as well as LDL, whereas oxidized LDL has the reverse effect. These effects of lipoproteins may be related to modulation of various cytokines. Accordingly, TG-rich lipoproteins, LDL, and oxidized LDL may be involved in mesangial cell proliferation and injury in patients with mesangial proliferative glomerulonephritis.     

Direct interactions between platelets and cultured rat mesangial cells

Platelets seem to be involved in the pathogenesis of some kidney diseases, but the exact relationships between platelets and the changes in renal function are incompletely known. Mesangial cells (MC) were incubated with platelet-supernatants (PS) and cellular surface area (CSA) and myosin light-chain phosphorylation (MLCP) were measured. CSA of PS-incubated MC (PS-MC) significantly diminished, as compared to control MC (70 +/- 6% vs. 100 +/- 5%). PS induced a significant increase in MLCP with respect to control cells (150 +/- 23% vs. 100 +/- 18%). When platelets were pretreated with indomethacin, the PS-dependent contraction was abolished. Pretreatment with sulotroban (SU) or BN-52021 (BN), a thromboxane A2 (TXA2) and a platelet-activating factor (PAF) receptor blocker respectively, also completely blocked the PS effects. In other experiments, platelets were activated with thrombin (T), adding the so obtained PS to MC. Moreover, cells were also preincubated with T and then added PS. No changes in CSA were observed in either case. It may be concluded that PS contracted cultured MC, and these changes could be related to the decreased glomerular filtration rate (GFR) observed in some diseases in which platelets seem to be involved. TXA2 and PAF may be responsible for this effect. In contrast, T incubation inhibited the effect of PS, perhaps through a direct relaxing effect of T in MC.     

Effect of serum from patients with mesangial proliferative glomerulonephritis on cultured rat mesangial cells

Adenosine, an important neuromodulatory compound in the brain and retina, is a potent vasodilator in most vascular beds throughout the body. Its actions are potentiated by inhibitors of nucleoside transport into cells. Knowledge of the existence of specific adenosine uptake systems in mammalian retina and the inhibition of the uptake by nitrobenzylthioinosine (NBMPR), a potent inhibitor of nucleoside transport, raises the possibility that the associated nucleoside transport system may be of pharmacological importance in retinal function. We have characterized the binding of the nucleoside transporter probe, [3H]NBMPR, to a cultured human retinal cell line established by transfection of SV-40 T antigen plasmid-DNA. The binding was specific, saturable and reversible. Scatchard analysis of the saturation data revealed that NBMPR binds to a homogeneous population of high affinity binding sites (KD = 0.65 +/- 0.22 nM; Bmax = 466 +/- 157 fmol/mg protein) characteristically similar to the binding sites in human retinal tissue (KD = 0.32 +/- 0.01 nM; Bmax = 292 +/- 41 fmol/mg protein). Selected compounds inhibited the binding in the cell line and retinal tissue with the same rank order of potency, suggesting that the transporters in the cell line and retinal tissue are similar. The data showed that the cell line is a useful model for the study of nucleoside transporter function in human retina.     

Regulation of smooth muscle alpha-actin expression and hypertrophy in cultured mesangial cells

BACKGROUND: Mesangial cells during embryonic development and glomerular disease express smooth muscle alpha-actin (alpha-SMA). We were therefore surprised when cultured mesangial cells deprived of serum markedly increased expression of alpha-SMA. Serum-deprived mesangial cells appeared larger than serum-fed mesangial cells. We hypothesized that alpha-SMA expression may be more reflective of mesangial cell hypertrophy than hyperplasia. METHODS: Human mesangial cells were cultured in medium alone or with fetal bovine serum, thrombin, platelet-derived growth factor-BB (PDGF-BB) and/or transforming growth factor-beta1 (TGF-beta1). Alpha-SMA expression was examined by immunofluorescence, Western blot, and Northern blot analysis. Cell size was analyzed by forward light scatter flow cytometry. RESULTS: Alpha-SMA mRNA was at least tenfold more abundant after three to five days in human mesangial cells plated without serum, but beta-actin mRNA was unchanged. Serum-deprived cells contained 5.3-fold more alpha-SMA after three days and 56-fold more after five days by Western blot. Serum deprivation also increased alpha-SMA in rat and mouse mesangial cells. The effects of serum deprivation on alpha-SMA expression were reversible. Mesangial cell mitogens, thrombin or PDGF-BB, decreased alpha-SMA, but TGF-beta1 increased alpha-SMA expression and slowed mesangial cell proliferation in serum-plus medium. Flow cytometry showed that serum deprivation or TGF-beta1 treatment caused mesangial cell hypertrophy. PDGF-BB, thrombin, or thrombin receptor-activating peptide blocked hypertrophy in response to serum deprivation. CONCLUSIONS: We conclude that increased alpha-SMA expression in mesangial cells reflects cellular hypertrophy rather than hyperplasia.     

High glucose inhibits cytosolic calcium signaling in cultured rat mesangial cells

Glomerular vasodilatation in the early stages of type I diabetes mellitus apparently results from arteriolar insensitivity to vasoconstrictors. Since cytosolic free calcium ([Ca2+]i) is a major signaling mechanism for smooth muscle contraction, we studied whether growth of smooth muscle-like rat glomerular mesangial cells in media with high glucose concentration affects [Ca2+]i responses to vasoconstrictors. In cells grown for five days in 22 mM glucose, we observed blunted responsiveness to three structurally unrelated vasoconstrictors that elevate [Ca2+]i via a phospholipase C-dependent mechanism, angiotensin II, prostaglandin F2 alpha, and arginine vasopressin. Inhibition of [Ca2+]i responses was not due to an osmotic effect of high glucose, since it was not mimicked by hypertonic mannitol. While the size of intracellular Ca2+ pools was unaffected by elevated glucose, Na+/Ca2+ exchange was markedly inhibited, thus ruling out both impaired filling of Ca2+ stores and enhanced counter-regulatory mechanisms. Impaired myoinositol transport or intracellular sorbitol accumulation were not responsible for the effects of high glucose, since supplementation of media with myo-inositol or with the aldose reductase inhibitor. Alcon 1576, failed to reverse insensitivity to vasoconstrictors. On the other hand, down-regulation or pharmacological inhibition of protein kinase C completely reversed the effects of high glucose, thus indicating involvement of this signal transduction pathway. These data suggest a possible intracellular mechanism for the impaired vascular sensitivity underlying early renal hemodynamic changes in diabetes mellitus.     

High glucose inhibits nitric oxide production in cultured rat mesangial cells

Hyperglycemia directly contributes to the development of diabetic nephropathy. A high-serum glucose concentration alters intraglomerular hemodynamics and promotes deposition of extracellular matrix in the kidney. Nitric oxide (NO) is a short-lived messenger molecule that participates in the regulation of renal blood flow, GFR, and mesangial matrix accumulation. Therefore, in this study it was tested whether high glucose directly modulates NO synthesis by rat mesangial cells in vitro by measuring the accumulation of nitrite, the stable metabolite of NO, in the incubation media. Raising the external glucose concentration to 33.3 mM for 24 to 72 h reduced nitrite levels in cell supernatants in a time-dependent manner to a nadir of 14 +/- 3% of the amount in normal glucose media (5.6 mM) (P < 0.01). The decline in NO synthesis in high glucose media was paralleled by decreased cyclic guanosine monophosphate generation; however, there was no alteration in rat mesangial cell expression of inducible NO synthase protein. The suppressive effect of high glucose on NO production by mesangial cells was not modified by inhibition of protein kinase C (H-7), the addition of antioxidants (vitamin E or superoxide dismutase), or a pan-specific anti-transforming growth factor-beta antibody. An elevated ambient glucose caused a time-dependent reduction in mesangial cell L-arginine content. Addition of L-arginine (10 to 20 mM) to external media partially reversed the inhibitory effect of high glucose on mesangial cell NO production in a dose-dependent manner. The highest dose of L-arginine (20 mM) increased mesangial cell L-arginine content to comparable levels in normal and high glucose media. These results indicate that high glucose causes depletion of L-arginine in mesangial cells and compromises NO synthesis. Limitation in the metabolic precursor and other, as yet unidentified, factors act to reduce NO production by mesangial cells in the presence of an elevated ambient glucose level, a change that may play a role in the development of diabetic glomerulosclerosis.     

Effect of emodin on c-myc proto-oncongen expression in cultured rat mesangial cells

We report a patient with chronic asymptomatic Chagas' disease that presented Trypanosoma cruzi reactivation after kidney transplantation and immune depression. The only clinical manifestation of the disease was ulcerative skin lesions, which is unusual in Chagas' disease.     

Regulation of tissue plasminogen activator production in cultured human fetal mesangial cells

This study was designed to determine the persistence of culturable bacteria versus DNA in the presence of a middle ear effusion in a chinchilla model of otitis media. Cohorts of animals were either infected with an ampicillin-resistant Haemophilus influenzae strain or injected with a tripartite inoculum consisting of freeze-thawed Streptococcus pneumoniae; pasteurized Moraxella catarrhalis; and DNA from H influenzae. The H influenzae-infected animals displayed culture positivity and polymerase chain reaction positivity through day 35. In the chinchillas infected with the low-copy number inocula of S pneumoniae, DNA was not detectable after day 1 from the co-inoculated pasteurized M catarrhalis bacteria or the purified H influenzae DNA; however, amplifiable DNA from the live low-copy number bacteria persisted through day 21 even though they were not culture-positive past day 3. These results demonstrate that DNA, and DNA from intact but nonviable bacteria, does not persist in an amplifiable form for more than a day in the presence of an effusion; however, live bacteria, while not culturable, persist in a viable state for weeks.     

Endothelin-1 mediates erythropoietin-stimulated glomerular endothelial cell-dependent proliferation of mesangial cells

These experiments were performed in an attempt to determine whether chronic stimulation of glomerular endothelial cells with recombinant human erythropoietin would alter mesangial cell proliferation. Glomerular endothelial cells in culture incubated with various concentrations of erythropoietin for up to 4 days exhibited dose-dependent endothelin-1 production. Moreover, the conditioned medium from erythropoietin-stimulated glomerular endothelial cells enhanced [3H]thymidine incorporation into mesangial cells. This enhancement was significantly attenuated in the presence of a endothelin A receptor antagonist, BQ-123. These results suggest that endothelin-1 mediates erythropoietin-stimulated glomerular endothelial cell-dependent mesangial cell proliferation, resulting in the progression of glomerulonephritis.