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Biomedical subjects

J Caro

Publications and source records attributed to J Caro.

At least 73 records · Page 4Linked to original sources
PubMed1990

Erythropoietin fails to reverse the anemia in mice continuously exposed to tumor necrosis factor-alpha in vivo.

Tumor necrosis factor-alpha (TNF) is a monokine produced by activated macrophages that has cytotoxic and cytostatic effects on erythroid progenitor cells. We have recently shown that Chinese hamster ovary cells transfected with the human TNF gene and which constitutively express TNF induced a hypoproliferative anemia, mild thrombocytopenia, and mild leukocytosis when injected into nude mice. We have used this murine model to determine if treatment with recombinant human erythropoietin can prevent or ameliorate the anemia seen with long-term continuous exposure to high concentrations of TNF. Mice bearing TNF-producing tumors became anemic with hematocrits ranging from 30% to 32%. Treatment with recombinant human erythropoietin (100-1000 U/kg body weight three times per week) increased the reticulocyte counts initially in mice bearing TNF-producing tumors but failed to reverse the anemia seen in these animals. Erythropoietin did not significantly increase the number of marrow erythroid colony-forming units (CFU-E) or erythroid burst-forming units (BFU-E) in mice bearing TNF-producing tumors. The data suggest that erythropoietin could not sufficiently overcome the decreased number of erythroid progenitors in mice bearing tumors producing high levels of TNF to correct their anemia.

Anemia↗
PubMed1989

Quantitation of erythropoietin-producing cells in kidneys of mice by in situ hybridization: correlation with hematocrit, renal erythropoietin mRNA, and serum erythropoietin concentration.

In situ hybridization was used to quantitate the cells that produce erythropoietin (EP) in the renal cortices of mice with varying severities of acute anemia and of mice recovering from severe, acute anemia. The number of EP-producing cells in the renal cortex increased in an exponential manner as hematocrit was decreased. Individual EP-producing cells had very similar densities of silver grains in autoradiograms regardless of whether they were from normal mice or from slightly, moderately or severely anemic animals. With increasingly severe anemia, total renal EP mRNA levels and serum EP concentrations showed increases that correlated with the number of renal EP-producing cells. These results indicate that as mice become more anemic, additional cells are recruited to produce EP rather than the cells already producing EP being stimulated to increase their individual production. In mildly and moderately anemic animals, small clusters of EP-producing cells were found in the inner cortex with large areas of cortex containing no EP-producing cells. In severely anemic mice, EP-producing cells were found throughout the inner cortex with only a very few found scattered in the outer cortex and outer medulla. The data indicate that only a subset of total renal interstitial cells produce EP. During recovery from severe, acute anemia, the numbers of EP-producing cells decreased exponentially as hematocrits rose and correlated with decreases in total renal EP mRNA and serum EP concentrations. These results suggest that following an acute blood loss and during the recovery from a blood loss, the capacity to deliver oxygen, as represented by hematocrit, is the major regulator of EP production.

Acute Disease↗
PubMed1989

Inappropriate increase in erythropoietin titers during chemotherapy.

Serial erythropoietin measurements by RIA were performed in six patients with acute leukemia treated by intensive chemotherapy. In all cases erythropoietin titers increased after the onset of treatment, although the hemoglobin concentration remained at stable values. Subsequently the erythropoietin titers gradually returned to baseline levels. In same patients this reduction occurred at the end of chemotherapy, in others coincident with infections and antibiotic therapy. In four patients this decrease occurred at the time of bone marrow recovery. The explanation for this inappropriate increase in erythropoietin titers is not clear but may be related to a direct or indirect effect of a suppressed marrow on sites of erythropoietin production or catabolism.

Adult↗
PubMed1989

Erythropoiesis in cancer patients undergoing immunotherapy.

We studied ten patients with various types of cancer who were being treated with Interleukin-2 (IL-2) and lymphokine activated killer cells (LAK). All patients developed a reticulocytopenic, normochromic, normocytic anemia. We noted some variability but no significant suppression of circulating erythroid progenitors. The levels of erythropoietin were lower than expected for the hemoglobin/hematocrit values. We could not detect Interferon or Tumor Necrosis Factor (TNF) in the serum of these patients; however, the supernatant of LAK cells did contain Interferon and TNF which could be neutralized with appropriate antibodies. These results suggest that the etiology of this anemia is multi-factorial. Administration of recombinant erythropoietin (Ep) may be of benefit in some of these patients.

Anemia↗
PubMed1989

Circulating erythropoietin in patients with myelodysplastic syndromes.

Serum concentration of erythropoietin (Epo) has been measured by radioimmunoassay in 46 patients with myelodysplastic syndromes. There is an overall inverse relationship between the level of Epo and the degree of anaemia but a wide range of Epo response between patients with similar haemoglobin concentrations. No differences were found between the different FAB groups, but the highest Epo levels were found in those patients with erythroid hypoplasia in the bone marrow. It is suggested that the intensity of erythroid activity in the marrow, as well as the degree of anaemia, may be a factor determining serum Epo concentration.

Adult↗
PubMed1989

Chronic exposure to tumor necrosis factor in vivo preferentially inhibits erythropoiesis in nude mice.

The anemia of chronic disease (ACD) is associated with conditions in which macrophage activation occurs. Activated marrow macrophages suppress erythropoiesis in vitro and produce tumor necrosis factor (TNF). Therefore, we tested the effects of chronic in vivo exposure to TNF to determine if it was a candidate for a mediator of ACD. Nude mice were inoculated with Chinese hamster ovary (CHO) cells expressing the human TNF gene or with control cells containing the transfection vector alone. The TNF mice promptly became reticulocytopenic, and after 3 weeks their corrected reticulocytes were 2.6% +/- 0.7% as compared with 7.3% +/- 4% in control mice. The hematocrit at 3 weeks was 28.4% +/- 1.7% in TNF mice as compared with 46% +/- 0.8% in control mice. This anemia was also associated with low serum iron and normal iron stores and increased erythropoietin (Epo) levels. The TNF mice showed an absolute monocytosis with twice the number of circulating monocytes as control mice and had M-colony-stimulating factor (CSF) activity in their serum. The TNF mice also became mildly thrombocytopenic. Marrow CFU-E and BFU-E were profoundly decreased (1.2 +/- 0.2 x 10(3) v 8.6 +/- 0.2 x 10(4) CFU-E per femur, and 6.5 +/- 1 x 10(2) v 8.5 +/- 0.2 x 10(4) BFU-E per femur). Splenic CFU-E and BFU-E were similarly depressed. In contrast, marrow CFU-GM and CFU-GEMM were not affected. The residual BFU-E in TNF mice were relatively resistant to TNF as compared with control mice. These data demonstrate that TNF preferentially inhibits erythropoiesis in vivo and may be important in the pathogenesis of ACD.

Anemia↗
PubMed1989

Stimulation of erythropoietin gene transcription during hypoxia and cobalt exposure.

Erythropoietin, a plasma glycoprotein produced primarily by the kidney, is a growth and differentiation factor for erythroid progenitor cells. Production of renal erythropoietin is regulated by modulation of mRNA levels in response to changes in tissue oxygenation. Exposure to cobalt, a nonphysiologic stimulus for erythropoietin production, also acts by inducing mRNA accumulation. To determine whether variations in erythropoietin mRNA levels result from enhanced transcription of the erythropoietin gene, in vitro transcription reactions were performed using isolated rat kidney cell nuclei. Quantitation of specific nuclear RNAs labeled during in vitro transcription revealed active erythropoietin gene transcription in kidney nuclei from anemic-hypoxic and cobalt-treated animals while erythropoietin transcriptional activity was undetectable in normal kidney nuclei. Time course studies showed that stimulation of transcription begins between two and four hours following cobalt treatment and parallels the kinetics of mRNA and plasma erythropoietin accumulation. These results indicate that tissue hypoxia and cobalt exposure specifically enhance erythropoietin gene expression. This increase in erythropoietin production is regulated at least in part at the level of gene transcription.

Animals↗
PubMed1989

Correlation between erythropoietic activity and body growth rate in hypertransfused polycythemic growing rats as the result of an erythropoietin-dependent operating mechanism.

The established relationship between erythropoietic activity and body growth rate in the polycythemic growing rat could be the result of either an erythropoietin (EPO)-dependent or an EPO-independent operating mechanism. The present study was thus undertaken to elucidate the nature of the aforementioned mechanism by assessing the ratio between plasma immunoreactive EPO (iEPO) concentration and erythropoietic activity in young hypertransfused rats for different body growth rates. Red blood cell (RBC)-59Fe uptake was about 75% in 21-day-old rats; it rapidly decreased with time when the animals were placed on a protein-free diet, approaching a level of about 1% by the 10th day of protein starvation. Over the same period plasma iEPO decreased from 55 mU/ml to 7 mU/ml. Body growth rate was 0. Following this "protein depletion period" the rats received diets containing different amounts of casein ("protein repletion period") added isocalorically to the protein-free diet to elicit a rise in body growth rate. Statistically significant relationships (p less than 0.001) were found between dietary casein concentration and body growth rate (r = 0.991), dietary casein concentration and RBC-59Fe uptake (r = 0.991), dietary casein concentration and plasma iEPO level (r = 0.992), body growth rate and RBC-59Fe (r = 0.986), and body growth rate and plasma iEPO level (r = 0.994) in hypertransfused polycythemic rats during the protein repletion period. These findings suggest that the correlation between erythropoietic activity and growth rate in the growing rat is the result of an erythropoietin-dependent operating mechanism, which appears to be independent of the ratio tissue oxygen supply/tissue oxygen demand.

Aging↗
PubMed1988

Erythropoietin-beta-D-galactosidase. The generation, purification and use of a fusion protein.

A human erythropoietin (Epo) cDNA fragment encoding the complete erythropoietin peptide sequence was fused to the 3'-end of the lacZ gene in the polylinker region of the high expression vector, pUR 278. Escherichia coli bacteria were transformed with the recombinant plasmid harboring the hybrid Epo-beta-D-galactosidase gene. After induction with isopropyl-thiogalactoside large amounts of the fusion protein, Epo-beta-D-galactosidase were synthesized in the transformed bacteria. The fusion protein was partially purified and shown to exhibit intact galactosidase enzymatic activity. Although no biological activity of the Epo counterpart of the fusion protein was detected both in an in vivo and in an in vitro bioassay, the fusion protein served as an effective antigen for the production of anti-erythropoietin antibodies. Antifusion protein antibodies raised in rabbits were shown to react with the intact human Epo molecule from erythropoietin producing culture supernatants. The affinity of these anti-fusion protein antibodies was sufficiently high to permit the development of a sensitive radioimmunoassay for human Epo. This fusion protein approach is a relatively straightforward and rapid method of generating antibodies with specificity for any protein encoded by a cloned eukaryotic gene.

Animals↗
PubMed1987

Dynamics of erythropoiesis following renal transplantation.

We examined the temporal dynamics of the correction of anemia following renal transplantation in 65 recipients using a sensitive radioimmunoassay for erythropoietin to determine the effects of modern immunosuppressive agents, delayed graft function, and early acute rejection. Pretransplant mean erythropoietin (25.6 +/- 3.3 mU/ml) was only 25% of the expected value at the mean hematocrit of 27.2 +/- 0.7, and erythropoietin correlated positively with hematocrit (r = 0.37, P less than 0.05). Following onset of graft function, erythropoietin increased to 109 +/- 13 mU/ml and then decreased in a negative feedback fashion over the next several months. Delayed graft function was associated with delay in the assumption of this orderly process irrespective of the immunosuppressive regimen used. Cyclosporine A produced a biphasic response despite delayed graft function in recipients with underlying adult polycystic kidney disease. Correction of anemia required resumption of graft function. Onset of acute graft rejection within the first month posttransplantation (14 episodes in 11 patients) abrogated the hematopoietic response until the rejection was successfully reversed. We conclude that a major cause for the anemia of renal failure is subnormal production of erythropoietin. Following transplantation, anemia corrects in an orderly manner with restoration of the normal biofeedback process between erythropoietin and red cell mass. This process is delayed by failure of graft to function initially and interrupted by acute early rejection, re-commencing following successful reversal.

Adolescent↗