Subtherapeutic erythropoietin and insulin-like growth factor-1 correct the anemia of chronic renal failure in the mouse

The Role of the Multiple Hormonal Dysregulation in the Onset of "Anemia of Aging": Focus on Testosterone, IGF-1, and Thyroid Hormones

Anemia is a multifactorial condition whose prevalence increases in both sexes after the fifth decade of life. It is a highly represented phenomenon in older adults and in one-third of cases is "unexplained." Ageing process is also characterized by a "multiple hormonal dysregulation" with disruption in gonadal, adrenal, and somatotropic axes. Experimental studies suggest that anabolic hormones such as testosterone, IGF-1, and thyroid hormones are able to increase erythroid mass, erythropoietin synthesis, and iron bioavailability, underlining a potential role of multiple hormonal changes in the anemia of aging. Epidemiological data more consistently support an association between lower testosterone and anemia in adult-older individuals. Low IGF-1 has been especially associated with anemia in the pediatric population and in a wide range of disorders. There is also evidence of an association between thyroid hormones and abnormalities in hematological parameters under overt thyroid and euthyroid conditions, with limited data on subclinical statuses. Although RCTs have shown beneficial effects, stronger for testosterone and the GH-IGF-1 axis and less evident for thyroid hormones, in improving different hematological parameters, there is no clear evidence for the usefulness of hormonal treatment in improving anemia in older subjects. Thus, more clinical and research efforts are needed to investigate the hormonal contribution to anemia in the older individuals.

An acetate switch regulates stress erythropoiesis

Endocrine erythropoietin (Epo), which is synthesized in the kidney or liver of adult mammals, controls erythrocyte production and is regulated by the stress-responsive transcription factor Hypoxia Inducible Factor 2 (HIF-2). We previously reported that the lysine acetyltransferase Cbp is required for HIF-2α acetylation and efficient HIF-2 dependent Epo induction during hypoxia. We now show these processes require acetate-dependent acetyl CoA synthetase 2 (Acss2). In Hep3B hepatoma cells and in Epo-generating organs of hypoxic or acutely anemic mice, acetate levels increase and Acss2 is required for HIF-2α acetylation, Cbp/HIF-2α complex formation and recruitment to the Epo enhancer, and efficient Epo induction. In acutely anemic mice, acetate supplementation augments stress erythropoiesis in an Acss2-dependent manner. In acquired and genetic chronic anemia mouse models, acetate supplementation also increases Epo expression and resting hematocrits. Thus, a mammalian stress-responsive acetate switch controls HIF-2 signaling and Epo induction during pathophysiological states marked by tissue hypoxia.

Subcutaneous administration of rhIGF-I post irradiation exposure enhances hematopoietic recovery and survival in BALB/c mice

It is unclear how to effectively mitigate against irradiation injury. In this study, we studied the capacity of recombinant human insulin-like growth factor-I (rhIGF-I) on hematologic recovery in irradiated BALB/c mice and its possible mechanism. BALB/c mice were injected with rhIGF-I subcutaneously at a dose of 100 μg/kg twice daily for 7 days after total body irradiation. Compared with a saline control group, treatment with rhIGF-I significantly improved the survival of mice after lethal irradiation (7.5 Gy). It was found that treatment with rhIGF-I not only could increase the frequency of Sca-1(+) cells in bone marrow harvested at Day 14 after irradiation, but also it could decrease the apoptosis of mononuclear cells induced by irradiation as measured by flow cytometry, suggesting that rhIGF-I may mediate its effects primarily through promoting hematopoietic stem cell/progenitor survival and protecting mononuclear cells from apoptosis after irradiation exposure. Moreover, we have found that rhIGF-I might facilitate thrombopoiesis in an indirect way. Our data demonstrated that rhIGF-I could promote overall hematopoietic recovery after ionizing radiation and reduce the mortality when administered immediately post lethal irradiation exposure.

Mesenchymal stromal cells genetically engineered to overexpress IGF-I enhance cell-based gene therapy of renal failure-induced anemia

We previously demonstrated that erythropoietin (EPO)-secreting mesenchymal stromal cells (MSC) can be used for the long-term correction of renal failure-induced anemia. The present study provides evidence that coimplantation of insulin-like growth factor I (IGF-I)-overexpressing MSC (MSC-IGF) improves MSC-based gene therapy of anemia by providing paracrine support to EPO-secreting MSC (MSC-EPO) within a subcutaneous implant. IGF-I receptor RNA expression in murine MSC was demonstrated by RT-PCR. Functional protein expression was confirmed by immunoblots and MSC responsiveness to IGF-I stimulation in vitro. IGF-I was also shown to improve MSC survival following staurosporin-induced apoptosis in vitro. A cohort of C57Bl/6 mice was rendered anemic by right kidney electrocoagulation and left nephrectomy. MSC-EPO were subsequently admixed in a bovine collagen matrix and implanted, in combination with MSC-IGF or MSC null, by subcutaneous injection in renal failure mice. In mice receiving MSC-EPO coimplanted with MSC-IGF, hematocrit elevation was greater and enhanced compared with control mice; heart function was also improved. MSC-IGF coimplantation, therefore, represents a promising new strategy for enhancing MSC survival within implanted matrices and for improving cell-based gene therapy of renal anemia.

IGF-1 is an independent risk factor for anemia in diabetic pre-dialysis patients

BACKGROUND

We investigated whether the presence of diabetes mellitus (DM) was related to the degree of the anemia in predialytic patients with renal failure and what was the most relevant factor for anemia in patients with chronic kidney disease (CKD) from DM (DM-CKD).

METHODS

Seventy seven patients (47 predialytic patients with long-term type 2 DM (DM-CKD) and 30 predialytic patients whose disease was due to other causes (non DM-CKD)) were enrolled in this study. The blood hemoglobin (Hb) and hematocrit, and the creatinine, ferritin, vitamin B12, folate, iron, LDH, albumin, hs-CRP, intact-PTH, erythropoietin, leptin and Insulin-like growth factor I (IGF-1) levels were measured using standard methods. The estimated GFR was calculated using the abbreviated MDRD equation.

RESULTS

The two groups did not significantly differ as to age, gender, the serum creatinine level and the inflammatory status. The Hb level was significantly lower in the DM-CKD patients than that in the non DM-CKD patients (8.5+/-1.7 g/dL vs 9.6+/-1.6 g/dL, respectively, p=0.01). The Hb level was significantly lower in the DM-CKD patients who were being treated with ACE inhibitors (the DM-ACE patients) than that in the non DM-CKD patients who were being treated with ACE inhibitors (the non DM-ACE patients) (8.5+/-1.5 g/dL vs 10.8+/-1.6 g/dL, respectively, p=0.001). Multiple regression analysis indicated that serum IGF-1 concentration was independently associated with the Hb level (beta=0.425, p=0.02) in the DM-CKD patients.

CONCLUSIONS

The Hb concentration was significantly lower in the DM-CKD patients than that in the non DM-CKD patients. It was independently associated with the serum IGF-1 concentration in the DM-CKD patients.

Erythropoietin delivery by genetically engineered bone marrow stromal cells for correction of anemia in mice with chronic renal failure

The goal of this research was to develop a strategy to couple stem cell and gene therapy for in vivo delivery of erythropoietin (Epo) for treatment of anemia of ESRD. It was shown previously that autologous bone marrow stromal cells (MSCs) can be genetically engineered to secrete pharmacologic amounts of Epo in normal mice. Therefore, whether anemia in mice with mild to moderate chronic renal failure (CRF) can be improved with Epo gene-modified MSCs (Epo+MSCs) within a subcutaneous implant was examined. A cohort of C57BL/6 mice were rendered anemic by right kidney electrocoagulation and left nephrectomy. In these CRF mice, the hematocrit (Hct) dropped from a prenephrectomy baseline of approximately 55% to 40% after induction of renal failure. MSCs from C57BL/6 donor mice were genetically engineered to secrete murine Epo at a rate of 3 to 4 units of Epo/10(6) cells per 24 h, embedded in a collagen-based matrix, and implanted subcutaneously in anemic CRF mice. It was observed that Hct increased after administration of Epo+MSCs, according to cell dose. Implants of 3 million Epo+MSCs per mouse had no effect on Hct, whereas 10 million led to a supraphysiologic effect. The Hct of CRF mice that received 4.5 or 7.5 million Epo+MSCs rose to a peak 54+/-4.0 or 63+/-5.5%, respectively, at 3 wk after implantation and remained above 48 or 54% for >19 wk. Moreover, mice that had CRF and received Epo+MSCs showed significantly greater swimming exercise capacity. In conclusion, these results demonstrate that subcutaneous implantation of Epo-secreting genetically engineered MSCs can correct anemia that occurs in a murine model of CRF.

Hormonal adjuvants for the treatment of renal anaemia

Hormonal adjuvants, besides being erythropoietic agents, broaden the spectrum of therapeutic options for the treatment of the anaemia of chronic kidney disease (CKD). Lowering elevated parathyroid hormone levels by oral calcium supplementation and phosphate restriction, by varying dialysate calcium concentrations, by administration of vitamin D3 derivatives and, in the near future, by treatment with calcimimetics may prove efficient in some patients to fight extensive requirements of erythropoietic agents. Clinical evidence for a principal role of secondary hyperparathyroidism in resistance to erythropoietin, however, is lacking. Active vitamin D3 derivatives, in addition to their beneficial effects on secondary hyperparathyroidism, appear to exert a direct, stimulatory action on erythroid precursor cells and possibly also an inhibitory action on collagen synthesis by bone marrow stromal cells. Growth hormone (GH) induces insulin-like growth factor (IGF)-1, which in turn counteracts apoptosis similarly to erythropoietin, and fosters proliferation of burst- and colony-forming units-erythroid (BFU-E, CFU-E). If erythropoietic agents improve survival of CKD patients, a similar benefit should apply for strategies that increase synthesis and bioavailabilty of IGF-1. The latter appears to be reduced in CKD patients, and zinc supplementation potentially enhances it via an increase in free IGF-1. Finally, androgens also exert anti-anaemic effects. Nandrolone decanoate constitutes the only androgen currently applicable for selected male dialysis patients over the age of 50 years. It should not be given to women, however, because of serious side effects. Collectively, hormonal interventions offer the potential to reduce requirements of erythropoietic agents, and some may also improve physical performance.

Quotidian nocturnal hemodialysis improves cytokine profile and enhances erythropoietin responsiveness

Inflammation is implicated in the pathogenesis of erythropoietin (EPO) resistance in patients with end-stage renal disease. Interleukin (IL)-6 and tumor necrosis factor (TNF)-alpha are suggested to suppress erythropoiesis in uremia. Insulin like growth factor (IGF)-1 has been proposed to stimulate erythropoiesis. Nocturnal hemodialysis (NHD) has been demonstrated to improve anemia management with enhanced EPO responsiveness without altering survival of red blood cells. We tested the hypothesis that augmentation of uremia clearance by NHD results in a reduction of proinflammatory cytokine levels, thereby enhancing EPO responsiveness. Using a cross-sectional study design, 14 prevalent patients on NHD and 14 patients on conventional hemodialysis (CHD) matched for age and comorbidities and controlled for hemoglobin concentrations and iron status were studied. Outcome variables included EPO requirement and plasma levels of EPO, parathyroid hormone, C reactive protein, IL-6, TNF-alpha, and IGF-1. The primary outcome was to determine the between group differences in (1) cytokine profile and (2) EPO requirement. The secondary outcome was to examine the potential correlation between cytokine levels and EPO requirement. There were no significant differences in patient characteristics, comorbidities, hemoglobin, iron indices, and parathyroid hormone levels between the two cohorts. EPO requirement was significantly lower in the NHD cohort [90.5 +/- 22.1 U/kg/ week (NHD) vs. 167.2 +/- 25.4 U/kg/week (CHD), p = 0.04]. Plasma IL-6 levels were lower in the NHD cohort [3.9 +/- 0.7 pg/ml (NHD) vs. 6.5 +/- 0.8 pg/ml (CHD), p = 0.04]. C reactive protein tended to decrease [4.59 +/- 1.34 (NHD) vs. 8.43 +/- 1.83 mg/L (CHD), p = 0.14]. TNF-alpha, and IGF-1 levels did not differ between the two groups. Direct associations were found between EPO requirement and C reactive protein levels (R = 0.62, p = 0.001), and IL-6 levels (R = 0.57, p = 0.002). Augmentation of uremic clearance by NHD improves EPO responsiveness in end-stage renal disease. A possible mechanism for this improvement is through better control of inflammation, as manifested by lowering of plasma IL-6 levels. Further studies are required to clarify the mechanisms by which NHD decreases inflammation.

Enhanced recovery from thrombocytopenia and neutropenia in mice constitutively expressing a placental hematopoietic cytokine

Expression of the placental hormone, prolactin-like protein E (PLP-E), a potent cytokine that acts on multiple myeloid lineages, is normally restricted to pregnancy and certain hematopoietic disease states. We hypothesized that the restricted pattern of PLP-E expression is necessary to avoid hyperstimulation of myelopoiesis. To test this idea, we have produced PLP-E transgenic mice and analyzed their steady-state blood cell levels. We find that blood cell levels remain in the normal range, and thus the constitutive expression of a cytokine of pregnancy fails to overcome the tight control of hematopoietic set points for blood cell levels. In contrast, an effect of constitutive PLP-E expression is detected during the recovery from low blood platelet levels (acute thrombocytopenia) and from low granulocyte levels (acute neutropenia) but not from anemia. Mice producing high circulating concentrations of PLP-E recover more rapidly from both thrombocytopenia and neutropenia, as seen both by an earlier increase of progenitor numbers in the bone marrow and the earlier return to normal circulating blood cell levels.

Attenuation of the alcohol preference of C57BL/6 mice during chronic renal failure

The C57BL/6 inbred mouse strain is known for its strong, genetically determined preference for alcohol over water. In this study we examined the voluntary alcohol consumption (VAC) of C57BL/6 mice during chronic renal failure (CRF). Two weeks after the surgical induction of renal failure, CRF mice, together with normal and sham-operated control mice, were submitted to a standard 24-day VAC protocol. The mice were offered water for the first 6 days (period of acclimatization), alcohol (10% ethanol solution) for the next 4 days (period of forced alcohol exposure), and a choice between water and alcohol for the last 14 days (VAC period). The results (mean +/- SEM) obtained from the last 8 days of the VAC period were significantly different (P <.05) between CRF mice and the 2 control groups. As expected, CRF mice had a higher total fluid intake than did normal and sham-operated controls (9.5 +/- 0.2 vs 5.4 +/- 0.2 and 5.4 +/- 0.2 g/d). Surprisingly, despite their increased total fluid consumption, CRF mice nearly abolished their absolute alcohol intake compared with that of both control groups (3.2 +/- 0.5 vs 13.1 +/- 0.8 and 14.2 +/- 1.1 g alcohol/kg body wt/d). The resulting alcohol preference ratio (g alcohol/g total fluid) was markedly decreased in the CRF mice compared with that in both control groups (0.09 +/- 0.01 vs 0.62 +/- 0.03 and 0.64 +/- 0.05). We conclude that the innate alcohol preference of C57BL/6 mice is nearly abolished during CRF. Additional studies to clarify the mechanism of this striking change in drinking pattern are required, with special emphasis on the possible role of angiotensin II, which is involved in thirst regulation and known to reduce the alcohol consumption of normal alcohol-preferring rats.

Malnutrition-inflammation complex syndrome in dialysis patients: causes and consequences

Protein-energy malnutrition (PEM) and inflammation are common and usually concurrent in maintenance dialysis patients. Many factors that appear to lead to these 2 conditions overlap, as do assessment tools and such criteria for detecting them as hypoalbuminemia. Both these conditions are related to poor dialysis outcome. Low appetite and a hypercatabolic state are among common features. PEM in dialysis patients has been suggested to be secondary to inflammation; however, the evidence is not conclusive, and an equicausal status or even opposite causal direction is possible. Hence, malnutrition-inflammation complex syndrome (MICS) is an appropriate term. Possible causes of MICS include comorbid illnesses, oxidative and carbonyl stress, nutrient loss through dialysis, anorexia and low nutrient intake, uremic toxins, decreased clearance of inflammatory cytokines, volume overload, and dialysis-related factors. MICS is believed to be the main cause of erythropoietin hyporesponsiveness, high rate of cardiovascular atherosclerotic disease, decreased quality of life, and increased mortality and hospitalization in dialysis patients. Because MICS leads to a low body mass index, hypocholesterolemia, hypocreatininemia, and hypohomocysteinemia, a "reverse epidemiology" of cardiovascular risks can occur in dialysis patients. Therefore, obesity, hypercholesterolemia, and increased blood levels of creatinine and homocysteine appear to be protective and paradoxically associated with a better outcome. There is no consensus about how to determine the degree of severity of MICS or how to manage it. Several diagnostic tools and treatment modalities are discussed. Successful management of MICS may ameliorate the cardiovascular epidemic and poor outcome in dialysis patients. Clinical trials focusing on MICS and its possible causes and consequences are urgently required to improve poor clinical outcome in dialysis patients.

Effect of malnutrition-inflammation complex syndrome on EPO hyporesponsiveness in maintenance hemodialysis patients

BACKGROUND

Elements of malnutrition-inflammation complex syndrome (MICS) may blunt the responsiveness of anemia of end-stage renal disease (ESRD) to recombinant human erythropoietin (EPO).

METHODS

The authors examined cross-sectional associations between the required dose of EPO within a 13-week interval as prescribed by practicing nephrologists who were blind to the study and several laboratory values known to be related to nutrition and/or inflammation, as well as the malnutrition-inflammation score (MIS), which is a fully quantitative assessment tool based on the subjective global assessment of nutrition.

RESULTS

A total of 339 maintenance hemodialysis (MHD) outpatients, including 181 men, who were aged 54.7 +/- 14.5 years (mean +/- SD), who had undergone dialysis for 36.3 +/- 33.2 months, were selected randomly from 7 DaVita dialysis units in Los Angeles South/East Bay area. The average weekly dose of administered recombinant human EPO within a 13-week interval was 217 +/- 187 U/kg. Patients were receiving intravenous iron supplementation (iron gluconate or dextran) averaging 39.5 +/- 47.5 mg/wk. The MIS and serum concentrations of high-sensitivity C-reactive protein, interleukin 6 (IL-6), tumor necrosis factor-alpha, and lactate dehydrogenase had positive correlation with required EPO dose and EPO responsiveness index (EPO divided by hemoglobin), whereas serum total iron binding capacity (TIBC), prealbumin and total cholesterol, as well as blood lymphocyte count had statistically significant but negative correlations with indices of refractory anemia. Most correlations remained significant even after multivariate adjustment for case-mix and anemia factors and other relevant covariates. Similar associations were noticed across EPO per body weight tertiles via analysis of variance and after estimating odds ratio for higher versus lower tertile via logistic regression after same case-mix adjustment.

CONCLUSION

The existence of elements of MICS as indicated by a high MIS and increased levels of proinflammatory cytokines such as IL-6 as well as decreased nutritional values such as low serum concentrations of total cholesterol, prealbumin, and TIBC correlates with EPO hyporesponsiveness in MHD patients.

Contribution of quinolinic acid in the development of anemia in renal insufficiency

Quinolinic acid (QA) is a potent endogenous excitotoxin; elevation of its concentration in an organism has been implicated in the pathogenesis of various disorders. The purpose of this study was the assessment of QA impact on the process of erythropoiesis. Marked increase of QA concentration was observed in plasma and peripheral tissues of uremic rats. These changes were proportional to the amount of the removed renal tissue and positively correlated with the concentration of creatinine but negatively correlated with hematological parameters, i.e., hematocrit and Hb red blood cells count. The changes were accompanied by a slight decrease in the concentration of endogenic erythropoietin (EPO) in the plasma of animals with uremia. Chronic treatment with QA diminished the increase in EPO concentration after introduction of cobalt in rats. These changes were associated with the decrease in all hematological parameters after QA administration. The in vitro study in the conditions of hypoxia showed that QA inhibited the EPO release from HepG2 cells to the culture base. Additionally, in HepG2 cells QA had a dose-dependent inhibitory effect on hypoxia- and cobalt-induced EPO gene expression without any cell toxicity. In conclusion, the erythropoiesis in chronic renal failure could be attributed to the influence of QA on EPO synthesis. Thus we propose that QA can be a uremic toxin responsible for anemia in animals or patients with renal failure.

Physiology of erythropoietin during mammalian development

Growth is a fundamental process of mammalian development. Several observations regarding regulation of erythropoiesis during growth are not easily explained by the hypoxia-erythropoietin (Epo) concept. This review focuses primarily on this aspect of the physiology of Epo. The question is raised of whether this regulation during growth is based on the hypoxia-Epo mechanism alone, or whether Epo acts in concert with general growth-promoting factors, particularly growth hormone (GH) and the insulin-like growth factors (IGF-I and -II). Supporting the latter hypothesis is the observation that the Epo and GH/IGF systems are activated by hypoxia and share similar receptors and pathways. Recent studies indicate that human fetal and infant growth is stimulated by GH, IGF-I and IGF-II. Epo, GH and IGFs are expressed early in fetal life. Although the rate of erythropoiesis in the fetus is high, serum Epo levels are low. The Epo response to hypoxia in the fetus and neonate is reduced compared with adults. Following delivery the Epo levels vary between species, probably related to the oxygen transport capacity of the hemoglobin (Hb) mass. IGF-I levels are low in the fetus and increase slowly following birth, except in preterm infants in whom the levels decline. In all mammals Hb declines following birth, giving rise to "early anemia". Except in the human, Epo levels increase proportionally with the fall in Hb, but there is a discrepancy between the curves for serum immunoreactive Epo (siEpo) and for erythropoiesis stimulating factors (ESF): the latter include other stimulatory factors in addition to Epo. Hypertransfusion of mice in the period of "early anemia" suppresses siEpo, but not ESF and erythropoiesis, as it does in adult mice. GH and IGF-I have direct effects on erythropoiesis in vitro and act particularly at the later stages of red cell differentiation. IGF-I acts synergistically with Epo, and its effects are most marked when Epo levels are low. Human recombinant (rhu) IGF-I stimulates erythropoiesis in neonatal rats, but not in newborn mice and lambs. In adult mice, in hypophysectomized rats and in mice with end-stage renal failure, however, a stimulatory effect of this growth factor was found on red cell production. RhuGH stimulates erythropoiesis in GH-deficient short children.

CONCLUSION

Fetal and early postnatal erythropoiesis are dependent on factors in addition to Epo. The likely candidates are GH and IGF-I. The in vitro stimulating effects of these factors on erythropoiesis are convincing, but more data are needed on the in vivo effects.

Mechanism of Inhibitory Effect of 3- Hydroxykynurenine on Erythropoiesis in Patients with Renal Insufficiency

Increase of 3-hydroxykynurenine (3-HKYN) concentration was observed in plasma patients with chronic renal insufficiency (CRI). These changes positively correlated with the concentration of creatinine, but negatively correlated with haematological parameters: haematocrit, haemoglobin and red blood cells count. The changes were accompanied by a slight decrease of the concentration of erythropoietin (EPO) in plasma of patients with CRI. The "in vitro" study in the conditions of hypoxia showed that 3-HKYN inhibited the release of EPO from HepG2 cells to the culture base. In conclusion, the erythropoiesis in CRI could be attributed to the influence of 3-HKYN on EPO synthesis. Thus, we propose that 3-HKYN can be an uraemic of toxin partially responsible for anaemia patients with CRI.

Effects of losartan or enalapril on hemoglobin, circulating erythropoietin, and insulin-like growth factor-1 in patients with and without posttransplant erythrocytosis

Both angiotensin-converting enzyme inhibitors and angiotensin II receptor antagonists reduce hemoglobin (Hb) levels in patients with posttransplantation erythrocytosis (PTE). However, their effects in transplant recipients without PTE are not certain, and the mechanism by which they reduce Hb levels in patients with PTE remains unclear. This study evaluated the effects of losartan and enalapril on Hb levels in relation to serum erythropoietin (EPO) and insulin-like growth factor-1 (IGF-1) levels in 8 patients with PTE and 10 patients without PTE. All 18 patients were treated sequentially with 24 weeks of losartan therapy, followed by 24 weeks of enalapril therapy; the two treatment phases were separated by a washout period. Patients with PTE showed significantly greater baseline Hb and IGF-1 concentrations compared with patients without PTE before both losartan and enalapril treatments. Baseline serum EPO levels were similar for patients with and without PTE. Baseline Hb level correlated significantly with IGF-1 level (r = 0.517; P = 0.002), but not with EPO level. Treatment with enalapril, 5 mg, reduced Hb levels more markedly than treatment with losartan, 50 mg, in patients with PTE. In patients without PTE, enalapril, 5 mg, mildly reduced Hb levels, whereas losartan, 50 mg, had no significant Hb-lowering effect. The reduction in Hb levels with enalapril therapy in patients with PTE was associated with a significant reduction in circulating IGF-1 levels, but not EPO levels, whereas losartan reduced Hb levels with no significant change in circulating IGF-1 and EPO levels. In patients without PTE, no significant change was noted in serum EPO and IGF-1 levels with either treatment. The differential Hb-lowering effect with losartan and enalapril treatment in patients with and without PTE suggests that the pathogenesis for PTE is complex and heterogeneous. Different erythropoietic mechanisms may be involved in patients with and without PTE. Further large-scale study is needed to determine the exact interaction between the renin-angiotensin system and regulation of IGF-1 and EPO synthesis and define the exact mechanism by which losartan and enalapril reduce Hb levels.

Angiotensin-converting enzyme inhibition induces apoptosis in erythroid precursors and affects insulin-like growth factor-1 in posttransplantation erythrocytosis

A number of studies suggest that erythropoietin (Ep), angiotensin II, and insulin-like growth factor (IGF-1) are involved in the pathogenesis of posttransplantation erythrocytosis (PTE). Angiotensin-converting enzyme inhibitors (ACEI) are the treatment of choice in PTE, but their mechanism of action is unclear. It was shown previously that ACEI added directly to cultures of erythroid precursors from patients with PTE inhibit colony growth. In this report, the effect of ACEI on CD34+ erythroid precursor apoptosis was studied, as were hematocrit (Hct), Ep, IGF-1, and IGF-binding protein 3 (IGF-BP3) levels. Ten patients with PTE, 10 transplant control patients, and 7 normal control subjects were studied. Peripheral blood CD34+ cells were isolated, and apoptosis was assessed by annexin assay and DNA laddering before and during ACEI therapy. At the same time, Hct, Ep, IGF-1, and IGF-BP3 levels were measured. Baseline CD34+ cell number, CD34+ apoptosis, Ep, IGF-1, and IGF-BP3 levels were the same between PTE and transplant control subjects. ACEI therapy was associated with a striking increase in CD34+ cell apoptosis and a decrease in Hct in both groups. In contrast to control subjects, patients with PTE on ACEI showed a significant decrease in IGF-1 levels and a greater percentage decrease in Hct. In normal control subjects, ACEI therapy was associated with a fall in Hct but no change in CD34+ cell apoptosis. In PTE, ACEI-related increase in erythroid progenitor apoptosis may partially explain the ACEI-associated decrease in Hct. However, it is not clear that erythroid precursor apoptosis is related to changes in IGF-1 or IGF-BP3.

Role of uremic toxins in exacerbating anemia in renal failure

The anemia associated with renal failure is largely due to inappropriate erythropoietin production. There is also good evidence, however, that substances present in uremic serum can inhibit erythropoiesis, although the exact identity of these substances and the mechanism(s) by which they exert this effect remain obscure. Candidates that have been suggested to play a role in uremic inhibition of erythropoiesis include the polyamines (such as spermine, spermidine, putrescine, and cadaverine), parathyroid hormone, and some of the inflammatory cytokines. The potential role of each of these inhibitory substances is discussed in this article.

Erythropoietin stimulates proliferation of human renal carcinoma cells

BACKGROUND

We reported recently that normal human, rat, and mouse tubular cells express authentic erythropoietin-receptors (EPO-R) through which EPO stimulates mitogenesis. The present study examines whether EPO could elicit such a proliferative and thereby potentially detrimental response in cells of human renal-cell carcinoma (RCC).

METHODS

Nephrectomy samples were screened from patients with RCC (one chromophilic, two clear cell) as well as cell lines of human (Caki-2, 786-0) and mouse (RAG) renal adenocarcinomas for expression of EPO-R transcripts and protein. Cells were further tested for specific 125I-EPO binding and mitogenic response to EPO.

RESULTS

Authentic EPO-R transcripts and protein (approximately 72 kD) were detected in renal tumors and cell lines. Tumors showed low-level EPO expression, while cell lines did not. In cells, specific 125I-EPO binding to a single class of EPO-R (apparent Kd 1. 3 to 1.4 nmol/L, Bmax 2.2 to 2.6 fmol/mg protein) was observed. EPO stimulated cell proliferation dose dependently, and the individual mitogenic effects of either EPO or 10% newborn calf serum were markedly amplified when both were coadministered.

CONCLUSION

These data are the first to demonstrate, to our knowledge, that human RCCs express EPO-R message and protein and that receptor activation stimulates their proliferation in vitro. If these mitogenic effects of EPO are also operative in patients with RCC, endogenous EPO or its administration for the treatment of anemia could potentially hasten proliferation of renocellular malignancies.

ACE inhibitors do not induce recombinant human erythropoietin resistance in hemodialysis patients

Angiotensin-converting enzyme (ACE) inhibitors may exacerbate anemia in patients with chronic renal failure, as well as in dialysis patients. To better answer this question, a prospective, crossover study was conducted to evaluate the effect of ACE inhibitors on recombinant human erythropoietin (rHuEPO) requirements in hemodialysis patients. Patients administered an ACE inhibitor when entering the study remained on this drug for the initial 4 months and were then switched to another antihypertensive agent for 4 more months. Patients not initially administered an ACE inhibitor were switched to lisinopril at 4 months. rHuEPO doses were adjusted using a sliding scale based on weekly laboratory hematocrit values. The inclusion criteria were met by 51 patients undergoing dialysis. Demographics were as follows: 61% were women, 64% were black, 46% had diabetes, average age was 53.2 +/- 13.3 years, and time on hemodialysis was 38.0 +/- 44.5 months. Thirty-three patients completed the study. Hematocrit averaged 32.7% +/- 1.9% while on ACE inhibitor therapy and 33.1% +/- 2.1% off ACE inhibitor therapy (P = 0.217). There was no difference in rHuEPO dose per treatment during each period (3,500 +/- 1,549 U on ACE inhibitor therapy versus 3,312 +/- 1,492 U off ACE inhibitor therapy; P = 0.300). No significant differences were found in degree of blood pressure control or various clinical and laboratory parameters that might be associated with rHuEPO resistance between the two periods. Similarly, no differences were found in hospitalization days, duration of infections, or transfusion requirements. These findings suggest that ACE inhibitors do not contribute to rHuEPO resistance in hemodialysis patients.

Advanced glycosylation end products (AGEs), insulin-like growth factor-1 (IGF-1) and IGF-binding protein-3 (IGFBP-3) in patients with type 2 diabetes mellitus

BACKGROUND

Advanced glycosylation end product (AGE) formation is a major mechanism for the development of complications in diabetes, and the possible roles of insulin-like growth factor 1 (IGF-1) and IGF binding protein 3 (IGFBP-3) are not clearly established.

METHODS

We examined the associations of AGEs, free IGF-I and IGFBP-3 in Type 2 diabetes mellitus (DM) patients under diverse conditions. In a cross-sectional design we studied 110 subjects (67 women and 43 men): non-diabetic controls in group 1, (n = 15) and diabetes patients as follows: group 2, without complications (n = 25); group 3, with chronic complications (n = 25); group 4, with acute or chronic infections (n = 24); group 5, hospitalized for reasons unrelated to diabetes (n = 9); group 6, with end-stage renal disease (ESRD) (n = 12). AGEs were determined by a spectrofluorometric method (HPLC). Insulin and IGFBP-3 were measured by RIA and free IGF-1 with an IRMA method.

RESULTS

AGEs were 13-fold higher in patients with ESRD (p<0.001), and lower in healthy individuals. Free IGF-1 was lower in the patients with complications (p = 0.017), with infections (p = 0.006) and hospitalized (p = 0.04). IGFBP-3 was higher in hospitalized patients (p=0.017). AGEs were associated with free IGF-1 (r = 0.41, p = 0.04) in the group with complications, and with HbA(1c) (r = -0.90, p = 0.002) in hospitalized patients. In the total group, free IGF-1 (r = -0.25, p = 0.008), and IGFBP-3 (r = -0.22, p = 0.021) were associated with HbA(1c).

CONCLUSION

We concluded that AGEs were markedly increased in diabetic patients with ESRD, IGF-1 was decreased in patients with infections and hospitalized, and was negatively associated with HbA(1c). IGFBP-3 was increased in hospitalized patients, with higher levels in patients with long bone fractures. A complex interaction of humoral factors may participate in the acceleration of complications of diabetes.

Mimicry of erythropoietin by a nonpeptide molecule

Erythropoietin (EPO) controls the proliferation and differentiation of erythroid progenitor cells into red blood cells. EPO induces these effects by dimerization of the EPO receptors (EPOR) present on these cells. To discover nonpeptide molecules capable of mimicking the effects of EPO, we identified a small molecule capable of binding to one chain of EPOR and used it to synthesize molecules capable of inducing dimerization of the EPOR. We first identified compound 1 (N-3-[2-(4-biphenyl)-6-chloro-5-methyl]indolyl-acetyl-L-lysine methyl ester) by screening the in-house chemical collection for inhibitors of EPO binding to human EPOR and then prepared compound 5, which contains eight copies of compound 1 held together by a central core. Although both compounds inhibited EPO binding of EPOR, only compound 5 induced dimerization of soluble EPOR. Binding of EPO to its receptor in cells results in activation of many intracellular signaling molecules, including transcription factors like signal transducer and activator of transcription (STAT) proteins, leading to growth and differentiation of these cells. Consistent with its ability to induce dimerization of EPOR in solution, compound 5 exhibited much of the same biological activities as EPO, such as (i) the activation of a STAT-dependent luciferase reporter gene in BAF3 cells expressing human EPOR, (ii) supporting the proliferation of several tumor cell lines expressing the human or mouse EPOR, and (iii) the in vitro differentiation of human progenitor cells into colonies of erythrocytic lineage. These data demonstrate that a nonpeptide molecule is capable of inducing EPOR dimerization and mimicking the biological activities of EPO.

Optimizing erythropoietin therapy

Much attention has been focused in recent years on ways of optimizing the use and cost-effectiveness of erythropoietin therapy. The balance of evidence suggests that the subcutaneous route allows lower doses to be used compared with the intravenous route, and dosing should be two to three times weekly. Concomitant use of intravenous iron potently enhances the response to erythropoietin, and more recently other adjuvant therapies such as ascorbic acid, L-carnitine, folic acid, vitamin D, androgens, and other cytokines and growth factors have been investigated. Many factors can affect the response to erythropoietin, and underdialysis and co-administration of angiotensin converting enzyme inhibitors have attracted much recent interest. Controversy regarding the optimum target hemoglobin concentration in patients with renal failure remains, but three multicenter studies are providing useful data on this issue.

Serum erythropoietin and interleukin-6 levels in hemodialysis patients with hepatitis virus infection

The influence of hepatitis B (HBV) and hepatitis C virus (HCV) infection on blood hemoglobin (Hb) and serum erythropoietin (Epo) and interleukin-6 (IL-6) concentrations was studied in 48 anemic patients on regular hemodialysis. They were grouped as follows: (I) 19 patients whose Hb values improved after infection (Hb > 85 g/L), (II) 10 patients with persisting anemia after infection (Hb < 75 g/L), and, without hepatitis virus markers (III) 8 patients with Hb > 85 g/L and (IV) 11 patients with Hb < 75 g/L. Serum immunoreactive Epo levels were significantly higher in group I (34.4+/-47.1 U/L) than in the other groups (II, 10.8+/-6.0; III, 7.9+/-3.2; IV, 8.4+/-4.3). Serum IL-6 was higher in group I than group III (7.7+/-7.8 pg/ml vs. 3.6+/-2.4; p = 0.05) but similar to the other groups. Hb levels in group I were maximal at the time of serum alanine aminotransferase normalization. Red cell production increases as a result of elevated circulating Epo during hepatic regeneration after HBV or HCV infection.

Erythrocytosis after renal transplantation represents an abnormality of insulin-like growth factor-I and its binding proteins

BACKGROUND

Secondary erythrocytosis is classically defined by an increase in erythropoietin (EPO) production. Despite increased levels of EPO often seen in secondary erythrocytosis, some of these forms such as that seen after renal transplantation remain undefined. Our group has recently investigated the in vivo function of insulin-like growth factor-I (IGF-I) in erythropoiesis both in humans and in a murine model of chronic renal failure. These data, and the recently recognized role of IGF-I in polycythemia vera, suggested that IGF-I might be involved in secondary erythrocytosis.

METHODS

Renal transplant recipients who developed erythrocytosis after transplantation were compared to normal individuals and to renal transplant recipients without erythrocytosis. We measured fasting serum EPO and IGF-I in all three groups. Because binding proteins may modify IGF-I function, IGF-I-binding proteins (IGFBP) 1 and 3, major binding proteins of IGF-I, were also measured.

RESULTS

Renal transplant recipients have significantly elevated serum of IGF-I and IGFBP3 compared to normal individuals. When transplant recipients with and without posttransplant erythrocytosis were compared, similar levels of IGF-I were found; however, the group with erythrocytosis had significantly elevated IGFBP1 and IGFBP3. No other significant differences including EPO levels were found between the groups.

CONCLUSIONS

Erythrocytosis after renal transplantation represents an anomaly of both IGF-I and its major binding proteins. Further studies are under way to better define this dysregulation and determine whether IGF-I can play a more generalized role in secondary forms of erythropoiesis.

Interference of angiotensin-converting enzyme inhibitors on erythropoiesis in kidney transplant recipients: role of growth factors and cytokines

BACKGROUND

Recent data indicate that factors other than erythropoietin (EPO), such as insulin-like growth factor 1 (IGF-1), can promote erythropoiesis in vitro and correct the anemia of chronic renal failure in vivo. IGF-1 is produced by the liver under growth hormone control, as well as by other sources, including the kidney. The erythropoietic role of growth factors and cytokines and their possible modulation by angiotensin-converting enzyme inhibitors (ACEI) has never been explored.

METHODS

This study evaluated the serum levels of EPO, IGF-1, interleukin (IL)-2, IL-3, and granulocyte macrophage-colony-stimulating factor in 40 kidney transplanted patients with or without posttransplant erythrocytosis (PTE) and in 10 living kidney donors. Then, the effect of ACEI therapy on the above pattern was examined in patients with PTE.

RESULTS

EPO and IGF-1 serum levels were significantly higher in patients with PTE than in patients without PTE and in living kidney donor subjects. ACEI therapy significantly reduced hematocrit (Hct) as well as circulating IGF-1 and EPO levels. Of note, the decrease in IGF-1 was prominent mainly in those patients whose EPO levels were not significantly modified by ACEI therapy. In all of the patients Hct levels displayed a direct relationship with circulating IGF-1 levels, but not with EPO concentration. Growth hormone did not significantly differ among the groups examined, whereas it steeply increased under ACEI. Finally, no significant difference in IL-2, IL-3, and granulocyte macrophage-colony-stimulating factor serum levels was detected.

CONCLUSIONS

IGF-1 seems to play a role in the ACEI-related decrease of Hct in patients with PTE, chiefly in patients without any modification of EPO serum levels.