Inhibitory effects of tetradecanoylphorbol acetate and diacylglycerol on erythropoietin production in human renal carcinoma cell cultures

A human renal carcinoma from a patient with an erythrocytosis, serially transplanted into athymic nude mice, was grown in primary monolayer cell cultures. After reaching confluency the cultured cells formed multicellular hemicysts (domes) which became more abundant as the cultures approached saturation density. Erythropoietin (Ep) production by this renal carcinoma in culture was only slightly increased at the time of semiconfluency but showed a marked increase in Ep levels in the culture medium after the cultures reached confluency, in parallel with an increase in dome formation. The phorbol ester tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) showed a significant dose-related inhibitory effect on Ep production and dome formation in the renal carcinoma cell cultures, suggesting an important role of protein kinase C, the only known receptor for TPA, in inhibiting the expression of differentiated phenotypes in the renal carcinoma cells. TPA also suppressed Ep secretion over a period of 96 h, indicating a time course of suppression of this differentiated function of the renal carcinoma cells in culture. This hypothesis was further supported by the observation that diacylglycerol, the endogenous activator of protein kinase C, likewise inhibited Ep production and dome formation in the renal carcinoma cell cultures. These studies suggest a role of the inositol-lipid second messenger path and protein kinase C in the regulation of Ep production.

The action of erythropoietin is mediated by lipoxygenase metabolites in murine fetal liver cells

Erythroid progenitor cells synthesize 12-hydroxyeicosatetraenoic acid (12-HETE) and 15-hydroxyeicosatetraenoic acid (15-HETE) when stimulated by erythropoietin (Ep). Maximal stimulation of 12-HETE production occurred at one hour, whereas 15-HETE activity remained constant in response to Ep for 24 hours. Lipoxygenase-selective inhibitors of arachidonic acid metabolism blocked HETE production and Ep-stimulated growth and differentiation of erythroid progenitor cell-derived colonies (CFU-E). On the other hand, specific inhibitors of cyclooxygenase (aspirin and meclofenamate) did not significantly inhibit Ep-induced erythroid colony formation. It is hypothesized that the stimulation of HETE production from arachidonic acid (AA) is an essential step in the mechanism of action of Ep.

Enhanced erythropoietin production by calcium entry blockers in rats exposed to hypoxia

In order to determine the influence of calcium on erythropoietin release in response to hypoxia, the effects of the calcium entry blocker verapamil on erythropoietin production were investigated. Hypoxia was induced in male Sprague-Dawley rats by placing them in a hypobaric chamber at 0.42 atmospheres for 6 and 12 hr. Serum levels of erythropoietin were measured by the exhypoxic polycythemic mouse bioassay and a sensitive radioimmunoassay for erythropoietin. Verapamil (5, 10 and 20 mg/kg i.p.) produced significant increases in mean serum erythropoietin levels after 6 and 12 hr of hypoxia, which was significantly higher than those of saline-injected hypoxic control rats. Mean arterial blood pressure values in rats injected with 5 and 10 mg/kg of verapamil were not significantly different from the preinjection controls when measured at ambient pressure over a 12-hr period. A dosage of 20 mg/kg of verapamil i.p. in rats produced a significant decrease in mean arterial pressure between 5 and 30 min after injection but was not significantly different from the vehicle controls between 30 min and 12 hr postinjection. In conclusion, the calcium entry blocker verapamil enhanced erythropoietin production in response to hypoxia. Thus, it is postulated that calcium plays a significant role in erythropoietin production and/or release.

Serum erythropoietin concentrations in patients with hepatocellular carcinoma

Erythrocytosis (polycythemia) is a well-described paraneoplastic phenomenon in patients with hepatocellular carcinoma, but its pathogenesis remains uncertain. Using a radioimmunoassay, we have measured serum erythropoietin concentrations in 65 southern African blacks with this tumor and 61 matched controls. Four patients had an increased hemoglobin concentration and packed cell volume, and the remainder had normal values. Twenty-three percent of the patients with hepatocellular carcinoma (15/65) were found to have raised serum erythropoietin concentrations, the values ranging up to 344 mu/ml. Only one of these patients had an increased hemoglobin concentration and packed cell volume. This apparent anomaly could be explained if the erythrocytosis that would normally result from high serum erythropoietin values had been counteracted by the inhibition of erythropoiesis which occurs in advanced malignant disease. Alternatively, the erythropoietin produced by the tumor might not always be biologically active. Three patients had increased hemoglobin values and packed cell volumes in the presence of normal serum erythropoietin concentrations. One of these patients was hypoxic as a result of multiple pulmonary metastases, and the others may also have been. There was no correlation between serum erythropoietin and alpha-fetoprotein concentrations in individual patients.

Serum erythropoietin concentrations in patients with hepatocellular carcinoma

Erythrocytosis (polycythemia) is a well-described paraneoplastic phenomenon in patients with hepatocellular carcinoma, but its pathogenesis remains uncertain. Using a radioimmunoassay, we have measured serum erythropoietin concentrations in 65 southern African blacks with this tumor and 61 matched controls. Four patients had an increased hemoglobin concentration and packed cell volume, and the remainder had normal values. Twenty-three percent of the patients with hepatocellular carcinoma (15/65) were found to have raised serum erythropoietin concentrations, the values ranging up to 344 mu/ml. Only one of these patients had an increased hemoglobin concentration and packed cell volume. This apparent anomaly could be explained if the erythrocytosis that would normally result from high serum erythropoietin values had been counteracted by the inhibition of erythropoiesis which occurs in advanced malignant disease. Alternatively, the erythropoietin produced by the tumor might not always be biologically active. Three patients had increased hemoglobin values and packed cell volumes in the presence of normal serum erythropoietin concentrations. One of these patients was hypoxic as a result of multiple pulmonary metastases, and the others may also have been. There was no correlation between serum erythropoietin and alpha-fetoprotein concentrations in individual patients.

Intramolecular nucleophilic amino attack in a monobactam: synthesis and stability of (2S,3S)- 3-[(2R)-2-amino-2-phenylacetamido]-2-methyl-4-oxo-1- azetidinesulfo nic acid

The potentially orally bioavailable arylglycine-substituted monobactam, (2S,3S)- 3-[(2R)-2-amino-2-phenylacetamido]-2-methyl-4-oxo-1- azetidinesulfonic acid, was prepared as a crystalline solid. No significant antibacterial activity [i.e., MICs were greater than 128 (micrograms/mL)] was found when the monobactam was tested against Gram positive and Gram negative bacteria. Solution instability (greater than 2,000 times less stable than aztreonam) due to intramolecular nucleophilic amine attack on the beta-lactam is believed to be a contributing factor to the poor microbiological activity.

Isolation and characterization of an anti-peptide monoclonal antibody to human erythropoietin

A site-specific monoclonal antibody to human erythropoietin has been developed. It is secreted by a hybridoma cell line derived from the fusion of murine myeloma cells with the splenocytes of a mouse that had been immunized with a 26-residue synthetic peptide antigen homologous to the amino-terminal sequence of the hormone. The antibody binds specifically to peptide, 125I-erythropoietin, and biologically active erythropoietin. The equilibrium dissociation constants of the antibody-erythropoietin and the antibody-peptide interactions are identical, Kd = 6.7 X 10(-9) M, suggesting strong conformational similarity or identity of the epitope as expressed on the peptide and the hormone. Immune complexes formed between the antibody and either human or rat erythropoietin exhibit full biologic activity. However, the antibody does not recognize the baboon, sheep, or canine hormones, indicating antigenic differences or structural variation among these erythropoietins. These results indicate that the amino-terminal region of erythropoietin is not involved in receptor binding. Furthermore, they form a basis for the study of the structure and function of the hormone using anti-peptide antibodies.

Effects of dibutyryl adenosine 3',5'-cyclic monophosphate on erythropoietin production in human renal carcinoma cell cultures

A human renal carcinoma from a patient with erythrocytosis, serially transplanted into athymic nude mice, was grown in primary monolayer cell cultures. After reaching confluency, the cultured cells formed multicellular hemicysts (domes), which became more abundant as the cultures approached saturation density. Erythropoietin (Ep) production by this renal carcinoma in culture was only slightly increased at the time of semiconfluency but showed a marked increase after the cultures reached confluency, in parallel with dome formation. Dibutyryl adenosine 3',5'-cyclic monophosphate significantly (P less than .01) stimulated Ep production and dome formation in the semiconfluent and confluent cultures of the renal carcinoma.

Erythropoietin and inhibitors of in vitro erythropoiesis in the development of anemia in children with renal disease

The relative roles of erythropoietin and potential inhibitors of erythropoiesis in the development of anemia in children with renal disease have been studied. Thirty-five children with renal disease of varied origins and severity were compared with 30 children with anemia of similar severity and with normal renal function. Serum erythropoietin was measured by radioimmunoassay; erythroid (CFU-E) and granulocytic (CFU-GM) progenitor cell growth were assessed in fetal mouse liver cell and normal human bone marrow cell cultures, respectively. The degree of serum inhibition of in vitro CFU-E growth in children with renal disease correlated with both creatinine clearance (r = 0.59, P less than 0.001) and hematocrit level (r = 0.55, P less than 0.005). Serum from children with renal disease inhibited in vitro CFU-E growth in a dose-related manner. Normal serum did not inhibit CFU-E growth in culture. The mean serum erythropoietin concentration was significantly (P less than 0.025) higher in children with anemia of renal disease (32.4 +/- 2.4 mU/ml) in comparison with serum values in normal children (19.6 +/- 1.5 mU/ml), but serum erythropoietin levels did not correlate with hematocrit level, creatinine clearance, or serum inhibition of in vitro erythropoiesis. In contrast, children with anemia and normal renal function showed a significant (P less than 0.001) linear increase in serum erythropoietin concentration (range 28.7 to 327 mU/ml), increased reticulocyte count, and stimulation of CFU-E formation with decreasing hematocrit levels. Coincubation of human urinary erythropoietin in the presence of serum from patients with uremia revealed markedly less immunoreactivity in the radioimmunoassay and less biologic activity in the fetal mouse liver CFU-E assay for erythropoietin than when erythropoietin was incubated with normal human serum, suggesting some alteration of erythropoietin in the presence of uremic serum, which reduced both the immunologic and biologic activity of erythropoietin. Normal and uremic sera inhibited CFU-GM growth to the same degree in comparison with controls. In conclusion, relative erythropoietin deficiency, direct alteration in the biologic activity of erythropoietin by uremic toxins, and serum inhibition of erythroid progenitor cells in the bone marrow are probably important factors in the pathogenesis of anemia in children with renal disease.

Erythropoietin response to anaemia in children with sickle cell disease and Fanconi's hypoproliferative anaemia

The erythropoietin response to anaemia was compared in 30 children with haemolytic anaemia and in 5 children with Fanconi's hypoproliferative anaemia. Serum erythropoietin was measured by radioimmunoassay. In children with haemolytic anaemia the serum erythropoietin concentration increased exponentially with decreasing haematocrit values (r = 0.74; p less than 0.001). Serum erythropoietin levels also correlated with reticulocyte counts (r = 0.62; p less than 0.001). Children with Fanconi's hypoproliferative anaemia had considerably higher serum erythropoietin levels than children with haemolysis for the same degree of anaemia. These data indicate that erythropoietin production in Fanconi's anaemia may be dependent on other factors in addition to the degree of anaemia and relative hypoxaemia.

Potential role of parathyroid hormone as an inhibitor of erythropoiesis in the anemia of renal failure

Patients with varying degrees of renal insufficiency and patients with end-stage renal disease receiving continuous ambulatory peritoneal dialysis or regular hemodialysis therapy were studied to assess the independent relationship between serum parathyroid hormone concentration, and both severity of anemia and degree of serum inhibition of erythropoiesis. In patients with renal insufficiency not receiving dialysis, a significant curvilinear relationship between serum parathyroid hormone and creatinine concentrations was present (r = 65, p less than 0.001). Serum parathyroid hormone (by radioimmunoassay) also correlated with hematocrit level (r = -0.54, p less than 0.001) and degree of serum inhibition of in vitro erythroid progenitor cell growth in fetal mouse liver cultures (r = -0.45, p less than 0.001). However, multiple linear regression analysis revealed that after controlling for the effect of creatinine, m-parathyroid hormone is no longer a significant predictor of hematocrit level or erythroid progenitor cell growth. On the other hand, when a restricted population of patients with creatinine values between 1 and 4 mg/dl was analyzed separately, controlling for the effect of creatinine, there was still a significant correlation between hematocrit level and m-parathyroid hormone, but no such relationship was seen when participants with parathyroid hormone levels of less than or equal to 1000 pg/ml were analyzed. No significant correlation was seen between hematocrit level or inhibition of erythroid colony growth and serum parathyroid hormone concentrations in patients receiving either regular hemodialysis or continuous ambulatory peritoneal dialysis. In 13 patients given regular hemodialysis studied before and after parathyroidectomy, there was no significant change in serum erythropoietin (by radioimmunoassay) or serum inhibition of erythropoiesis, although hematocrit levels increased in six of the 13 patients. The 1-34 human parathyroid hormone, 1-84 bovine parathyroid hormone, and 1,25-dihydroxycholecalciferol had no effect on in vitro erythroid burst-forming unit growth. Parathyroid hormone (8 mu/ml) inhibited and 1,25-dihydroxycholecalciferol (4.0 ng/ml) stimulated erythroid colony-forming unit growth only in the absence of exogenous erythropoietin in culture. In summary, it was not possible to demonstrate a significant relationship between serum parathyroid hormone levels and anemia or inhibition of erythropoiesis in patients with uremia either before starting dialysis or after receiving long-term dialysis treatment.(ABSTRACT TRUNCATED AT 400 WORDS)

Erythropoietin production in long-term cultures of human renal carcinoma cells. The role of cell population density

The present studies report the maintenance of erythropoietin (Ep) production in long-term cultures of a human renal carcinoma from a patient with erythrocytosis. The renal carcinoma cells were grown and maintained in monolayer cultures for 7 months. They were serially passaged every 2-3 weeks when the cultured cells reached confluency. Ep levels measured with a sensitive radioimmunoassay in the spent culture media of the cells in the stage of semiconfluent or confluent density were less than 20 and 30 mU/ml, respectively, throughout the period of 15 successive passages. However, when the renal carcinoma cells were maintained in culture without passage after reaching confluency, Ep levels in the spent media of these cells reproducibly showed an exponential increase to more than 300 mU/ml at the time of saturation density. The importance of cell population density in Ep production by the renal carcinoma cell cultures was further confirmed by the observation that the cultures with higher seeding density reached confluency earlier and began an exponential increase in Ep production sooner than those cultures with lower seeding density.

Role of endogenous prostaglandin E2 in erythropoietin production and dome formation by human renal carcinoma cells in culture

Studies were carried out on the role of endogenous prostaglandin E2 (PGE2) in erythropoietin (Ep) production and dome formation in primary monolayer cultures of a human renal carcinoma from a patient with erythrocytosis that has been serially transplanted into BALB/c athymic nude mice. The metabolism of [14C]arachidonic acid (14C-AA) by cultured renal carcinoma cells, which were plated in 25-cm2 flasks at a density of 2 X 10(4) cells/cm2 and grown for 6, 12 (confluence, 13 X 10(4) cells/cm2), 16, 24, and 30 d in Eagle's minimum essential medium (MEM) supplemented with 10% fetal bovine serum, was examined by using radiometric thin-layer chromatography (TLC). TLC revealed PGE2 to be the major metabolite of 14C-AA produced by the cultured cells throughout the 30 d of cultivation. In addition, the cultured cells at each time period were incubated for 24 h in 5 ml of serum-free Eagle's MEM and the levels of PGE2 and Ep in the incubated media were measured via radioimmunoassay. PGE2 levels in the serum-free media incubated with the cultured cells grown for 6 d were significantly (P less than 0.001) elevated (174 +/- 2.5 pg/ml, n = 5), compared with the unincubated control media (1.5 +/- 0.19 pg/ml, n = 5) and gradually decreased at each time period to 97.6 +/- 4.4 pg/ml (n = 5) at 30 d. On the other hand, the levels of Ep in the incubated media of the cells grown for 6 d were 11.5 +/- 0.52 mU/ml (n = 5) compared with 7.6 +/- 0.62 mU/ml (n = 5) in the control media. However, after the cultured cells became confluent, the levels of Ep in the incubated media showed a marked increase to 222.9 +/- 5.26 mU/ml (n = 5) at 30 d of cultivation. Multicellular hemicysts (domes) developed after the cultured cells reached confluence and their numbers increased with increasing time in confluence in parallel with the increase in Ep. Meclofenamate (MF) (3 X 10(-6)-3 X 10(-5) M), a prostaglandin synthesis inhibitor, produced a significant dose-related decrease in PGE2, Ep, and dome formation without producing a significant effect on cell viability in the 30-d cells. This inhibitory effect of MF on Ep production and dome formation was completely abolished by the addition of 10(-8) M PGE2 to the incubation medium. In conclusion, endogenous PGE2 plays an important role in supporting and/or stimulating Ep production and dome formation in cultured renal carcinoma cells.

Erythropoietin production in a primary culture of human renal carcinoma cells maintained in nude mice

The present studies report erythropoietin (Ep) production in primary cultures of a human renal carcinoma from a patient with erythrocytosis that has been serially transplanted to BALB/c nude mice. The levels of erythropoietin in the culture media were estimated using the exhypoxic polycythemic mouse assay (EHPCMA), fetal mouse liver erythroid colony-forming technique (FMLC), and a radioimmunoassay (RIA). The spent culture media of the exponentially growing cells contained less than 10 mU/ml of Ep measured by RIA. However, after the cells became confluent, Ep levels (RIA) in the spent media showed a marked increase to approximately 300 mU/ml. Ep levels estimated using the FMLC and EHPCMA were approximately 2/3 and 1/10, respectively, of those measured by RIA. Rabbit antiserum to highly purified human urinary Ep (70,400 U/mg protein) was utilized for immunocytochemical (peroxidase-antiperoxidase method) localization of Ep in the cultured cells. Very few of the cells in exponential growth exhibited Ep-like immunoreactivity, whereas intense Ep-like immunoreactivity was observed in the cytoplasm of the cells maintained in culture for a prolonged period after reaching confluency. The most intense staining was observed in some of the cells forming domes. The domes developed after the cells reached confluency, and their numbers increased with increasing time in confluent culture, in parallel with the increase in Ep levels in the spent media. This primary cell culture system of a renal cell carcinoma maintained in nude mice, which produces immunologically and biologically active Ep, may provide a useful model for studies of the mechanism of Ep production.

Hemodialysis and continuous ambulatory peritoneal dialysis effects on erythropoiesis in renal failure

Parameters of erythropoiesis were studied in patients with endstage renal disease established on continuous ambulatory peritoneal dialysis (CAPD) and regular hemodialysis treatment (RDT). Serum erythropoietin was measured by radioimmunoassay, and erythroid progenitor cell (CFU-E) formation was assayed in fetal mouse liver cultures. Serum erythropoietin concentrations in both CAPD (35.3 +/- 4.0 mU/ml) and RDT (31.9 +/- 1.9 mU/ml) patients were significantly higher (P less than 0.01) than normal values (23.1 +/- 1.0 mU/ml). The serum erythropoietin concentration did not correlate with either hematocrit or inhibition of CFU-E formation in either group of dialysis patients. In both CAPD and RDT patients the hematocrit correlated significantly (P less than 0.001) with the degree of serum inhibition of CFU-E formation. CFU-E formation decreased from 74.5 +/- 2.5 to 62.5 +/- 3.5% of control with increasing concentrations of uremic serum in cell cultures from 5 to 20%. In RDT patients a single hemodialysis produced a decrease in the mean serum erythropoietin concentration from 31.8 +/- 2.1 to 27.4 +/- 1.8 mU/ml (P less than 0.01) but no significant change in CFU-E formation. In conclusion, although serum immunoreactive erythropoietin levels are elevated above the normal range in dialysis patients, the response remains inadequate for the severity of the anemia, and it is the degree of serum inhibition of erythropoiesis in both CAPD and RDT patients which correlates with and possibly determines the degree of anemia.

Erythropoietin deficiency and inhibition of erythropoiesis in renal insufficiency

The relative importance of erythropoietin (Ep) and inhibition of erythropoiesis in the anemia of chronic renal insufficiency has been investigated. Sixty patients with varying degrees of renal insufficiency, 40 normal subjects and 40 patients with anemia and normal renal function, were studied. Erythroid (CFU-E) and granulocytic (CFU-GM) progenitor cell colony formation were assayed in fetal mouse liver and human bone marrow cultures, respectively. Erythropoietin was measured by radioimmunoassay. Hematocrit and plasma creatinine concentration correlated with the degree of serum inhibition of CFU-E formation (r = 0.69, P less than 0.001, and r = 0.62, P less than 0.001, respectively). Serum erythropoietin levels in patients with renal insufficiency (34.4 +/- 6.7 mU/ml) were slightly higher than normal values (23.1 +/- 0.98 mU/ml), but showed no relationship to plasma creatinine, hematocrit, or inhibition of CFU-E formation. In contrast, serum erythropoietin concentrations increased exponentially as the hematocrit decreased below 32% (r = 0.61, P less than 0.001), and CFU-E formation was stimulated by serum in anemia patients with normal renal function. Studies of granulopoiesis showed uremic sera supported in vitro CFU-GM growth more efficiently than sera from normal subjects. These results suggest that inhibition of erythroid, but not granulocytic, progenitor cell formation, in addition to a relative erythropoietin deficiency, are the primary factors responsible for the anemia of chronic renal failure.

Effects of prostaglandins on erythropoiesis

A model has been presented for the role of the kidney in the physiologic and pathophysiologic control of erythropoiesis. It is postulated that an oxygen deficit created by anemia or hypobaric hypoxia results in the release of prostacyclin and its metabolite 6-keto PGE1, and the release of PGE2 with ischemic hypoxia. Prostacyclin, 6-keto-PGE1, or PGE2 activation of adenylate cyclase, an increase in cyclic AMP, activation of a protein kinase and the phosphorylation of hydrolases, which have been released from lysosomes by hypoxia, lead to increased biosynthesis of erythropoietin (Ep). The mechanism of labilization of lysosomes and the release of hydrolases from these cell organelles is postulated to be related to increases in cyclic GMP levels in a renal cell. An Ep-producing human renal carcinoma cell line grown in tissue culture has been demonstrated to produce significant amounts of PGE2. Meclofenamate, an inhibitor of prostaglandins synthesis, was found to inhibit in vitro production of PGE2, Ep, and dome formation in these renal carcinoma cells, giving support to our hypothesis that pathophysiologic production of Ep tumor cells depends upon prostaglandins production. An Ep-producing clone from this renal carcinoma cell line has been developed that contains low electron density (LED) cells after the cells reach confluency, which show a cytoplasm, with abundant and widely dilated endoplasmic reticulum, an oval nucleus, dispersed chromatin, and prominent nucleoli. These are the cells responsible for dome formation and Ep production. Non-EP-producing clones have also been produced from this renal carcinoma cell line, which did not produce domes even at high cell density and had a distinctly different cell type than the Ep-producing clone. Thus, it is postulated that prostacyclin (PGI2) and its metabolite 6-keto PGE1 play a significant role in hypoxic hypoxia stimulation of Ep production and PGE2 is involved in ischemic hypoxia and renal carcinoma cell production of Ep. A modulating effect of PGE2 and PGD2, the two primary bone marrow prostaglandins, has been proposed in Ep stimulation of the erythroid progenitor cell compartment (CFU-E and BFU-E).

Prostanoid activation of erythropoiesis

A model is proposed for the role of the kidney in the control of erythropoietin production in which the initial trigger is an oxygen deficit created by anemia, hypobaria or ischemia. It is postulated that hypoxia creates a decrease in the oxygen level in a critical renal sensor cell, perhaps in the glomerular tuft, which eventually leads to the production of prostacyclin. It is possible that the endothelial cell in the glomerular tuft responds to this oxygen deficit to produce prostacyclin to trigger erythropoietin production. Recent studies on prostaglandin synthesis by human isolated glomeruli indicate that the most abundant prostanoid synthesized by the glomerular tuft cells was 6-keto PGF1 alpha, a metabolite of prostacyclin (PGI2). PGI2 has also been reported to be produced by isolated vascular endothelial cells. The mechanism by which hypoxia may initiate the synthesis and/or release of prostaglandins and prostacyclin in the renal cell has not been elucidated. Significant to erythropoietin production is the production by hypoxia of prostacyclin which eventually leads to the production of the metabolite 6-keto PGE1. We further propose that 6-keto PGE1 is the prostanoid which activates a specific cell membrane adenylate cyclase, causing the conversion of ATP to cyclic AMP. This is a very critical step in that there must be a sufficient amount of ATP remaining to generate cyclic AMP in order for erythropoietin biosynthesis to occur with the reduced level of ATP which may have caused a perturbation of the cell membrane. The elevated cyclic AMP leads to the activation of protein kinases which are essential in phosphorylating the lysosomal hydrolases released by hypoxia into the cytosol of the cell and may be the precursors of erythropoietin. Neutral proteases and lysosomal hydrolases, documented triggers of erythropoietin production, have been demonstrated to be elevated in the kidney after hypoxia. The mechanism of labilization and release of these enzymes from the renal lysosomes has been postulated to be related to increases in cyclic GMP levels in a renal cell. Hypoxia causes the release of renal lysosomal hydrolases which then undergo phosphorylation through activation by protein kinases following prostanoid stimulation of renal adenylate cyclase to generate cyclic AMP, resulting in increased biosynthesis of erythropoietin.

beta-Adrenergic blockade of prostaglandin E2- and D2-induced erythroid colony formation

beta-Adrenergic receptors have been linked to the actions of beta-adrenergic agonists as well as that of other hormones on erythroid cells. In the present studies, arachidonic acid, the precursor for the endoperoxide intermediates for prostaglandins, was demonstrated to produce a significant increase in erythroid colony (CFU-E) formation in normal mouse bone marrow cultures. Meclofenamate, a cyclooxygenase inhibitor drug that inhibits prostaglandins synthesis, significantly inhibited the increase in CFU-E colony-forming cells produced by arachidonic acid, thus establishing that arachidonic acid was probably converted to some prostaglandin or prostaglandin metabolite in the bone marrow to trigger CFU-E. Prostaglandins E2 (PGE2) and D2 (PGD2), both of which have been demonstrated to be produced in the bone marrow, were found in the present studies to increase the number of CFU-E colonies in normal mouse bone marrow cultures. DL-Propranolol, a beta 1, beta 2-adrenergic blocking agent, and D-propranolol, a non-beta-blocking isomer with nonspecific membrane stabilizing effects, both produced a significant (P less than 0.01) inhibition of the effects of PGE2 or PGD2 on CFU-E in murine bone marrow cultures. Butoxamine, a somewhat selective beta 2-adrenergic antagonist drug, also produced a significant inhibition of the effects of PGE2 on CFU-E in murine marrow cultures. These results indicate that the effects of beta-adrenergic blocking agents on prostaglandin-stimulated CFU-E are due to their membrane-stabilizing action rather than specific beta-adrenergic blockade.

Erythropoietin production in human renal carcinoma cells passaged in nude mice and in tissue culture

Renal cell carcinoma tissues from two patients, one with and one without erythrocytosis, were successfully transplanted into athymic nude mice. Transplantations of the erythrocytic tumor through six successive generations of nude mice produced a significant (P less than 0.001) elevation in mean hematocrit from 36.5 +/- 2.1% (range 32-42%) to 53.7 +/- 5.1% (range 40-63%), in comparison with a non-erythrocytic tumor which showed a progressive fall in hematocrit from 46.5 +/- 2.0% (range 41-50%) to 36.8 +/- 1.6% (range 33-40%). Non-grafted control nude mice maintained stable hematocrit levels from an initial level of 45 +/- 0.5% to 46.5 +/- 1.2% when studied over the same time interval. Similarly red cell mass values in the mice transplanted with the erythrocytic tumor (5.04 +/- 1.85 ml/100 g) were considerably higher than in both the non-grafted nude mice (3.39 +/- 0.81 ml/100 g) and the non-erythrocytic tumor-grafted mice (3.8 +/- 0.3 ml/100 g) after 6 generations of transplants. Plasma erythropoietin levels in the erythrocytic tumor-grafted mice (169.4 +/- 83.1 mU/ml) were significantly (P less than 0.02) higher than in the non-grafted controls (22.2 +/- 9.5 mU/ml), and furthermore the erythropoietin levels in the tumor extracts were significantly (P less than 0.02) higher in the tumors from erythrocytic mice (range 54.7 to 234.6 mU/g tumor) than in the tumors from non-erythrocytic mice (range 0.3 to 1.9 mU/g tumor). In vitro monolayer cultures of these tumors confirmed the higher erythropoietin levels in the erythrocytic renal carcinoma (138 mU/ml) as compared with culture media of non-erythrocytic tumors (15-91 mU/ml) using the fetal mouse liver assay (59Fe incorp. into heme). The present studies indicate autonomous erythropoietin production by human renal cell carcinomas both in vivo in nude mice and in vitro in tissue cultures.