Regarding diarrhea in liver transplant recipients: etiology and management.
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Adult↗
Biomedical subjects
I Graziadei
Publications and source records attributed to I Graziadei.
Safety and efficacy of lamivudine in patients with severe acute or fulminant hepatitis B, a multicenter experience.
Acute hepatitis B progresses to liver failure with the need of liver transplantation in about 1% of cases. We treated patients with severe acute or fulminant hepatitis B with lamivudine in an attempt to prevent hepatitis B virus (HBV) reinfection after potential liver transplantation. Since September 2000, 17 patients with severe acute or fulminant HBV infection were treated with 100 or 150 mg lamivudine daily once we had evidence for a severe course as indicated by an INR >2.0. These were compared to a historic control from our unit and to external patients. Fourteen of the 17 patients (82.4%) survived with full recovery without liver transplantation. All these 14 individuals cleared HBsAg on lamivudine within less than 6 months. Twelve patients recovered quickly as indicated by a normalized prothrombin time within 1 week while two patients had a more prolonged course. None of the patients showed an adverse event. Three patients requiring transplantation despite lamivudine therapy had more advanced disease on admission, of whom one had additionally ingested paracetamol (acetaminophen) while the second was already HBV-DNA negative by polymerase chain reaction on admission. The lamivudine treated patients had significant higher frequency of survival without liver transplantation 82.4 vs 20% (4/20) in the historic control (P < 0.001). Similar data were derived from external centres using lamivudine (15/20, 75%). Lamivudine is safe in patients with severe acute or fulminant hepatitis B, leading to fast recovery with the potential to prevent liver failure and liver transplantation when administered early enough.
Adult↗
Infectious complications limit the outcome of liver transplantation in medical urgency code 2 patients.
The Organ shortage has caused an accumulation of acutely decompensated patients listed as medical urgency code 2 (MUC 2) (United network for Organ Sharing 2) while awaiting liver transplantation. Between June 1997 and June 2003, 22 of 360 liver transplantation patients (6%) were listed as MUC 2. Prophylactic immunosuppression consisted of calcineurin inhibitor-based drug therapy, using antithymocyte globulin or interleukin-2 receptor antagonist induction in 64%. The overall perioperative infection rate was 50%, and the rejection rate was 23%. We observed 7 episodes of oral or genital herpes simplex virus lesions; 2 patients (both with cytomegalovirus-mismatched transplants) developed cytomegalovirus disease, and another 5 patients received ganciclovir for preemptive therapy or prophylaxis. Two patients developed pneumonia: 5, sepsis that originated in 4 cases from a contaminated central venous line; and 1 methicillin-resistant endocarditis, which resulted in Staphylococcus aureus lethal outcome. After a median follow up of 3 years, 1 patient underwent a repeat transplantation procedure and 6 patients had died, 4 of them from infectious complications. Liver transplantation of MUC 2-listed patients may result in acceptable results similar to those of MUC 3 and MUC 4 categories.
Adult↗
Kaposi sarcoma in solid organ transplant recipients: a single center report.
BACKGROUND: Human herpes virus (HHV8) is associated with Castleman's disease, primary effusion lymphoma, and the Kaposi's sarcoma (KS). PATIENTS AND METHODS: Among 3815 solid organ transplants performed at our center between 1977 and 2003, five patients (0.1%) were identified with KS. RESULTS: There were one cardiac, one liver, and three renal allograft recipients of median age of 52 (range 38 to 60) years, three of whom were females. Three patients were of Italian and one of Turkish descent; only one patient was a native Austrian. The onset of the disease was 2.0, 7.5, 7.8, 9.4 months, and 22 years posttransplant. Diagnosis of KS was based in all cases on histology. The heart recipient developed a tumor on the planta pedis; one renal recipient, on both legs. The liver and the two remaining renal recipients presented with disseminated disease. Treatment in all cases consisted of reduction in immunosuppression, together with surgery (n = 1), chemotherapy (n = 1), or irradiation (n = 2). Furthermore, immunosuppression was switched in two cases from Tacrolimus to Sirolimus. In the liver recipient a complete response was achieved; he died, however, due to noncompliance followed by graft failure. One renal recipient died without evidence of recurrent disease from myocardial infarction. The cardiac and two renal recipients are alive between 4 months and 17 years with well-functioning grafts and no evidence of recurrent disease. DISCUSSION: HHV8-associated lesions seem to be extremely rare in the Central European transplant population. Nevertheless, awareness of KS is important for early diagnosis and optimal treatment.
Adult↗
Our experience with combined liver-kidney transplantation: an update.
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Adult↗
Successful use of continuous intravenous prostacyclin in a patient with severe portopulmonary hypertension.
INTRODUCTION: Portopulmonary hypertension, defined by a mean pulmonary artery pressure > 25 mm Hg in the presence of normal pulmonary capillary wedge pressure and portal hypertension, is a known complication of end-stage liver disease that has been associated with high morbidity and mortality at the time of liver transplantation. DESIGN: Descriptive case report. PATIENT: A 32 year old male patient suffering from end-stage hepatitis C liver cirrhosis presented with severe portopulmonary hypertension. At presentation the following pulmonary hemodynamics were measured: systolic pulmonary artery pressure (PAP) 76 mm Hg, mean PAP 42 mm Hg, pulmonary vascular resistance index (PVRI) 931, pulmonary capillary wedge pressure (PCWP) 9 mm Hg, and cardiac output (CO) 4.03 l/min. INTERVENTION: After acute hemodynamic testing the patient received 8 ng/kg/min epoprostenol (prostacyclin) by continuous intravenous infusion with an infusion pump. Hemodynamic evaluation was performed monthly by transthoracic echocardiography and right heart catheterisation after 5 months. RESULTS: After 5 months of continuous therapy right heart catheterisation revealed the following hemodynamics: systolic pulmonary artery pressure (PAP) 59 mm Hg, mean PAP 32 mm Hg, pulmonary vascular resistance index (PVRI) 561, pulmonary capillary wedge pressure (PCWP) 7 mm Hg, and cardiac output (CO) 6.95 l/min. This presents a decrease in systolic pulmonary artery pressure of approximately 22%, a decrease in mean pulmonary artery pressure of approximately 30%, a decrease in pulmonary vascular resistance of approximately 40% and an increase in cardiac output of approximately 73%. Echocardiography demonstrated a decrease in estimated systolic pulmonary artery pressure of about 37% after 8 months of therapy. No complications were observed during epoprostenol therapy. CONCLUSION: In this adult patient suffering from end-stage liver disease and portopulmonary hypertension, administration of continuous intravenous epoprostenol resulted in significant reduction of pulmonary hypertension and therefore in acceptance for orthotopic liver transplantation. Utilisation of this new therapeutic strategy might be a helpful pharmacological tool for patients with portopulmonary hypertension to make them acceptable for orthotopic liver transplantation.
Adult↗
A novel binding site for the native hepatic acute-phase protein alpha1-antitrypsin expressed on the human hepatoma cell line HepG 2 and intestinal cell line Caco 2.
AIMS/BACKGROUND: alpha1-antitrypsin (alpha1-AT) is a hepatic acute phase protein which predominantly inhibits neutrophil elastase. Besides this major function, we have also previously shown that alpha1-AT markedly increased H-ferritin mRNA expression and ferritin synthesis in the human hepatoma cell line HepG 2. These actions suggest that alpha1-AT might interact with HepG 2 cells via a specific cell surface binding site. METHODS AND RESULTS: Using radio-labelled native alpha1-AT, we observed saturable binding to HepG 2 cells with a dissociation constant (Kd) of 63.3+/-6.9 nM and a maximal density of binding sites (Bmax) of 0.34+/-0.05 pmol/10(6) cells equivalent to 195,800+/-29,200 sites/cell. The binding of [125I]alpha1-AT was time dependent with a calculated association rate constant of 9.22+/-1.84x10(4)xM(-1)xmin(-1). Binding was highly specific since other acute phase proteins or protease inhibitors failed to block binding. Although alpha1-AT-trypsin, alpha1-AT-elastase and the pentapeptide FVYLI, the minimal binding sequence for the SEC receptor, increased [125I]alpha1-AT binding, in long term experiments these complexes failed to influence the number of alpha1-AT binding sites. Specific, saturable binding of [125I]alpha1-AT was also found on the human intestinal epithelial Caco 2 cells, but not on fibroblast or leukaemic cell lines. CONCLUSION: These experiments demonstrate a specific, high affinity binding site for native alpha1-AT on HepG 2 and Caco 2 cells, cell lines derived from tissues involved in the acute phase response.
Binding Sites↗
Combined liver-kidney transplantation: a single-center report.
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Adult↗
The acute-phase protein alpha 1-antitrypsin inhibits transferrin-receptor binding and proliferation of human skin fibroblasts.
Transferrin (Tf) is required for proliferation of most cells, because cellular iron uptake is mainly mediated by binding of Tf to its specific cell surface receptors (TfR). The acute-phase protein alpha 1-antitrypsin (alpha 1-AT) completely inhibits binding of diferric Tf to TfRs on human skin fibroblasts in a dose-dependent fashion. The inhibition is competitive as proved in equilibrium saturation binding and kinetic studies. In saturation binding experiments alpha 1-AT apparently increased the dissociation constant (KD), but did not change the maximal density of binding sites (Bmax). As shown in kinetic studies, this reduction of the affinity of Tf to its receptor caused by alpha 1-AT was due to a decrease of the association rate constant (k + 1), whereas the dissociation rate constant (k - 1) remained unchanged. Furthermore, alpha 1-AT almost completely prevented internalization of the Tf-TfR complex. These interactions demonstrated biological implication, as alpha 1-AT reduced the proliferation of human fibroblasts up to maximal 30% of control. The inhibitory potency of alpha 1-AT was already seen in physiologic concentrations; the maximal effect, however, was achieved at concentrations above the normal range, which are attained in the course of inflammation and infection. Therefore, we suppose that alpha 1-AT as an endogenous factor modulates the complex mechanism of fibrogenesis not only by its known antiproteolytic function but also by inhibiting the proliferation of fibroblasts.
Acute-Phase Proteins↗
Antitumor effect of the nucleoside analogs 2-chlorodeoxyadenosine and 2',2'-difluorodeoxycytidine on human hepatoma HepG2 cells.
BACKGROUND/AIMS: Hepatocellular carcinoma is one of the most malignant tumors in the world. Although a wide range of therapeutic options is available, the efficacy of these methods and the prognosis of hepatocellular carcinoma are still very poor. The nucleoside analogs 2-chlorodeoxyadenosine (Cladribine, 2-CdA) and 2',2'-difluorodeoxycytidine (Gemcitabine, dFdC) have shown potent cytotoxic effects on various human tumor cell lines in vitro and marked therapeutic efficacy in the treatment of lymphoproliferative disorders and several solid tumors in vivo. In the present study we evaluated the antitumor effect of 2-CdA and dFdC on human hepatoma HepG2 cells. METHODS: HepG2 cells were grown in the absence and presence of increasing concentrations of 2-CdA and dFdC. Antitumor activity was assessed by inhibition of cell growth, evaluated by counting cell numbers in a hemocytometer and by 3H-thymidine uptake, and by reduction of cell viability as determined by exclusion of 0.1% trypan blue. For rescue experiments, the natural pyrimidine deoxycytidine (dCyd) was added simultaneously or delayed. RESULTS: A strong antitumor activity was observed for both compounds. dFdC showed a more pronounced effect with an inhibition constant (IC50) of 3.98+/-0.03 nM in comparison to 2-CdA with an IC50 of 16.66+/-0.40 nM. Both drugs achieved their half-maximal antitumor activity after 31 h. With respect to dFdC, fractionated daily administrations showed a distinctly greater antitumor activity than a single transient administration. The cytotoxic effects of 2-CdA and dFdC were completely reversed by simultaneous addition of dCyd. CONCLUSION: In this paper we show strong antitumor effects of the nucleoside analogs 2-CdA and dFdC on the human hepatoma cell line HepG2. These findings suggest that both compounds, but in particular dFdC, are promising substances for further evaluations in the treatment of hepatocellular carcinoma.
Antimetabolites, Antineoplastic↗
The acute phase protein alpha-1-antitrypsin inhibits transferrin uptake in PLC/PRF/5 cells and increases release of hepatitis B virus surface antigen and alpha-fetoprotein.
BACKGROUND/AIMS: The present study was designed to investigate whether the acute phase protein alpha-1-antitrypsin (alpha1-AT), which has an inhibitory effect on transferrin (tf) receptor-mediated iron uptake in K562 and THP1 cells, has a similar effect in PLC/PRF/5 cells. This hepatic cell line is of specific interest because it is infected with hepatitis B virus (HBV). Therefore, we addressed the additional question whether alpha1-AT has any effect on cellular protein synthesis and replication of HBV in PLC/PRF/5 cells. METHODS: Cells were incubated with various concentrations of alpha1-AT, dexamethasone, IL-6 and desferrioxamine. HBs-AG, alpha-fetoprotein and albumin concentrations in culture media were measured using commercially available methods. For equilibrium inhibition binding experiments, cells were incubated with 85-182 pmol/l [125I]tf. To study the potential effect of alpha1-AT on DNA synthesis we measured the incorporation of [3H]thymidine into DNA. RESULTS: In equilibrium saturation binding experiments, [125I]tf bound to PLC/PRF/5 cells with K(D) 17.45 +/- 4.57 nM and a maximum density of binding sites of 267,285 +/- 39,915 sites/cell. In inhibition studies alpha1-AT demonstrated an apparently monophasic inhibition of [125I]tf to its receptor. At concentrations > 30 micromol/l alpha1-AT inhibited the growth of PLC/PRF/5 cells up to approximately 50%. The inhibitory effect of alpha1-AT on DNA synthesis was not as potent as that on growth. At the highest concentration of 100 micromol/l, alpha1-AT produced a 35% maximum inhibition of [3H]thymidine incorporation. Incubating PLC/PRF/5 cells with corticosteroids enhanced HBs-AG release significantly. Interestingly, alpha1-AT showed the same pattern of effects on cell metabolism and HBs-AG release as the corticosteroids. When we incubated the cells with 50 micromol/l alpha1-AT, alpha-fetoprotein production increased significantly and HBs-AG release almost doubled. CONCLUSION: We have to assume that there is a specific mechanism inducing HBs-AG release by alpha1-AT, as has been shown to be the case with steroids.
Cell Line↗
Modulation of iron metabolism in monocytic THP-1 cells and cultured human monocytes by the acute-phase protein alpha1-antitrypsin.
The reticuloendothelial (RE) system plays an important role in the changes in iron metabolism associated with the anemia of chronic disease (ACD). We previously reported that the acute-phase protein alpha1-antitrypsin (alpha1-AT) reduced growth and proliferation in cells of the erythroid cell system by interfering with transferrin (Tf)-mediated iron uptake. The regulation of iron metabolism in cells of the RE system is distinctly different from that in other cell systems; moreover, monocytes and macrophages play an essential part in the regulation of the production and clearance of alpha1-AT. In the present study we examined the effect of alpha1-AT on cells of the monocyte-macrophage lineage. Alpha1-AT completely inhibited the binding of Tf to its receptor (TfR) on THP-1 human myelomonocytic cells and cultured human monocytes. Results of equilibrium saturation and kinetic studies indicated that this inhibition was competitive. No other acute-phase protein demonstrated the same inhibitory potency. Furthermore, alpha1-AT almost completely prevented internalization of the Tf-TfR complex in a dose-dependent manner. Interestingly, and in sharp contrast to the results of our studies with erythroid cells, this inhibition did not reduce the growth and proliferation of THP-1 cells. Furthermore, alpha1-AT significantly increased the concentration of intracellular ferritin in THP-1 cells and monocytes, whereas the number of TfR remained unchanged. Because alpha1-AT showed no enhancing effect on ferritin transcription and translation, we believe that an as-yet unidentified posttranslational mechanism may be responsible for this phenomenon. In addition, our results indicate that the increase in ferritin concentration caused by alpha1-AT is mediated independently of iron supply, as has previously been shown for several proinflammatory cytokines. These data provide further evidence that alpha1-AT is a mediator of the alterations in iron metabolism characteristic of ACD.
Cell Division↗
Papillitis and vasculitis of the arteria spinalis anterior as complications of hepatitis C reinfection after liver transplantation.
It is well known that hepatitis C virus (HCV)-related chronic liver disease may be associated with various immunological disorders including mixed cryoglobulinemia, which is accompanied by cutaneous vasculitis, arthralgias, membrano-proliferative glomerulonephritis, and neuropathy in association with cryoprecipitable immune complexes in serum. We describe here the first case of central nervous system HCV infection with evidence of the virus in the cerebrospinal fluid in association with cryoglobulinemia in a patient who developed recurrent episodes of papillitis and vasculitis of the arteria spinalis anterior after liver transplantation.
Adult↗
Unidirectional upregulation of the synthesis of the major iron proteins, transferrin-receptor and ferritin, in HepG2 cells by the acute-phase protein alpha1-antitrypsin.
BACKGROUND/AIMS: We have previously shown that the hepatic acute-phase protein alpha1-antitrypsin (alpha1-AT) is an important mediator of changes in iron metabolism in the course of anaemia of chronic disease. Alpha1-AT profoundly reduces growth of erythroid cells by interfering with transferrin-mediated iron uptake. In the present work we investigate the effects of alpha1-AT on hepatic iron metabolism, as the liver plays a central role in body iron metabolism and in metabolic changes during acute-phase response. METHODS: The human hepatoma cell line Hep G2 was cultured in RPMI 1640+10% FCS. The effect of alpha1-AT on transferrin-receptor binding was investigated in equilibrium binding assays with 125I-transferrin. Expression of transferrin receptor was determined by saturation experiments and intracellular ferritin was measured in cell lysates after incubating cells either alone or with alpha1-AT. To determine iron regulatory protein binding activity to iron responsive elements we used gel retardation assays and Northern blot analysis was carried out to investigate transferrin receptor and ferritin mRNA expression. RESULTS: Alpha1-AT completely prevented transferrin from binding to its receptor and internalization of the transferrin-transferrin receptor complex on HepG2. In addition, alpha1-AT caused a distinct increase in iron regulatory protein binding activity to iron responsive elements, which is characteristic of iron deprivation. Normally, the synthesis of transferrin receptor and ferritin is regulated bidirectionally, but alpha1-AT promoted a unidirectional regulation. Alpha1-AT increased the synthesis of both transferrin receptor and ferritin and, moreover, increased cellular amounts of transferrin receptor mRNA and ferritin H-chain mRNA. CONCLUSIONS: The effect of alpha1-AT on transferrin receptor synthesis appears to be mediated via activation of iron responsive element binding affinity of iron regulatory protein leading to an increased stability of transferrin receptor mRNA. Changes in ferritin, however, may be related to a transcriptionally mediated, iron-independent pathway which overrides the influence of activated iron regulatory protein. These specific changes in iron metabolism are the very ones seen in the course of anaemia of chronic disease. Our results emphasize the central role of alpha1-AT as a mediator of altered iron metabolism, characteristic of anaemia of chronic disease, not only with respect to erythroid cells but also with respect to liver cells.
Cell Division↗
Predominance of the HLA-H Cys282Tyr mutation in Austrian patients with genetic haemochromatosis.
BACKGROUND/AIMS: Genetic haemochromatosis is the most common autosomal recessive disorder in Northern European populations. A major histocompatibility complex class I-like gene, HLA-H, has been proposed to be responsible for genetic haemochromatosis. The prevalence of HLA-H gene mutations 282(TGC; Cys/TAC; Tyr) and 63(CAT; His/GAT; Asp) was determined in patients of Austrian origin. METHODS: DNA extracted from the blood of 40 Austrian patients and 271 controls was used to amplify HLA-H gene fragments by the polymerase chain reaction method. The base changes responsible for mutations Cys282Tyr and His63Asp alter recognition sites for restriction enzymes SnaB I and Bcl I, respectively. Digestion products were separated by agarose gel electrophoresis and visualised by ethidium bromide staining. RESULTS: Thirty-one (77.5%) genetic haemochromatosis patients were homozygous for mutation Cys282Tyr and three compound heterozygous for mutations Cys282Tyr and His63Asp. One patient was homozygous for mutation His63Asp but normal for mutation Cys282Tyr. Four patients were normal at both genetic loci and one patient was heterozygous for mutation His63Asp. One control subject homozygous for mutation Cys282Tyr was found on investigation to fulfill diagnostic criteria for haemochromatosis. Eight control subjects homozygous for mutation His63Asp showed no biochemical or clinical evidence of haemochromatosis indicating that this variant is not directly responsible for haemochromatosis. Absence of the Cys282Tyr mutation in six genetic haemochromatosis patients with distinct haplotypes indicates mutations within the HLA-H gene or at alternative genetic loci are the cause of genetic haemochromatosis in these patients. CONCLUSIONS: The HLA-H Cys282Tyr defect is likely to play a key role in the pathogenesis of haemochromatosis in most patients. Predominance of a single HLA-H gene mutation in haemochromatosis allows presymptomatic screening by genotypic analysis.
Adult↗
High-dose interferon-alpha2b treatment prevents chronicity in acute hepatitis C: a pilot study.
Acute hepatitis C takes a chronic course in 50-80% of cases. Results with interferon treatment are conflicting. To evaluate the efficacy of high-dose interferon treatment, we initiated a pilot study in 1992 using 10 MU interferon-alpha2b administered subcutaneously daily until normalization of serum transaminase concentrations. Treatment was begun when a diagnosis of acute hepatitis C was established. HCV-RNA was tested using PCR prior to treatment, three times weekly during the first two weeks of treatment, and then once weekly until the end of therapy. During the 15-month follow-up, HCV-RNA tests were performed monthly up to month 6 and every two to three months thereafter. Twenty-four patients were enrolled at the time of writing; age ranged from 18 to 76 years (mean = 32), and nine patients were men. All patients presented with cholestatic hepatitis; 19 were actively abusing intravenous drugs, four had no known parenteral exposure, and one was a medical laboratory technician. All patients were anti-HCV positive, HCV-RNA positive, and HIV negative. Five patients were infected with genotype 3, five with genotype 1a, five with genotype 1b, three with genotypes 3 and 2, and one with genotypes 1 and 2. All patients exhibited normalized serum transaminase concentrations within 18-43 days; HCV-RNA became negative in all patients within 4-12 days. Toxicity did not exceed grade 1 and disappeared within three days of treatment. In the follow-up period, which ranged from six to 29 months (mean = 19.5 +/- 10.4), serum ALT concentrations remained normal and HCV-RNA remained negative in all patients except two dropouts and two patients who developed relapsing disease after having been HCV-RNA negative for three and eight months, respectively. In both patients, the same HCV genotype 3 reemerged. Serum ALT concentrations ranged from 531 to 1940 IU/liter (mean = 1055; normal < 22). Concentrations of HCV-RNA (Quantiplex; Chiron, Emeryville, California) were < 3.5 x 10(5) eq/ml in nine of 14 PCR-positive patients. In the other five patients, concentrations ranged from 10.4 x 10(5) eq/ml to 131.6 x 10(5) eq/ml (mean = 69.6 x 10(5)). No correlation was observed between HCV-RNA concentrations and serum ALT concentrations at presentation (r = 0.331; P = 0.67) and total dose of interferon-alpha2b administered until normalization of ALT (r = -0.088; P = 0.74). Twenty-two of 24 patients completed treatment (two were noncompliant). Of these, 20 achieved a complete response (HCV-RNA negative for at least six months). Two of these patients relapsed, and 18 (90%) remained HCV-RNA negative for 18.65 (+/-9.7) months. These findings suggest that high-dose interferon-alpha2b is well tolerated and effective in preventing a chronic course of hepatitis C infection.
Acute Disease↗
The acute-phase protein alpha 1-antitrypsin inhibits growth and proliferation of human early erythroid progenitor cells (burst-forming units-erythroid) and of human erythroleukemic cells (K562) in vitro by interfering with transferrin iron uptake.
We have previously shown that the hepatic acute-phase protein alpha 1-antitrypsin (alpha 1-AT) inhibits transferrin (tf) binding to its receptor (tfR) of human placental membranes. To evaluate the possibility that this interaction can explain the pathophysiology of the changes in iron metabolism in the course of chronic disease, subsequently leading to anemia in chronic disease (ACD), we examined the effect of alpha 1-AT on cells of the erythroid cell line. alpha 1-AT completely prevented tf binding to tfR on K562 human erythroleukemic cells and on reticulocytes. This inhibitory potency was dose-dependent and competitive, as proved in equilibrium saturation and kinetic studies. The cytokines interleukin-1 (IL-1), IL-6, and tumor necrosis factor alpha showed no such effect. Internalization of the tf-tfR complex was inhibited with alpha 1-AT in a dose-dependent manner. Furthermore, alpha 1-AT profoundly reduced the growth of K562 cells as well as their proliferation, albeit to a lesser degree. Growth of early erythroid progenitor cells (burst-forming units-erythroid) was significantly suppressed by alpha 1-AT, but no effect on the growth of late erythroid progenitor cells (colony-forming units-erythroid) was detected. These inhibitions of alpha 1-AT were seen in high physiologic concentrations attained in the course of acute-phase situations. These data show that alpha 1-AT might be a mediator of the changes in iron metabolism that are characteristic of clinical findings in the course of ACD.
Acute-Phase Proteins↗
The hepatic acute-phase proteins alpha 1-antitrypsin and alpha 2-macroglobulin inhibit binding of transferrin to its receptor.
Transferrin binding to human placental sites was inhibited by the acute-phase proteins alpha 1-antitrypsin (alpha 1-AT) and alpha 2-macroglobulin (alpha 2-MG), whereas haptoglobin, C-reactive protein and ferritin displayed no such effect. In equilibrium saturation binding assays, the effective acute-phase proteins decreased the apparent affinity of the binding sites for transferrin, but the transferrin binding-site density Bmax. was not significantly changed. For instance, the addition of 30 microM alpha 1-AT increased the KD of transferrin from 8.46 +/- 1.51 nM to 21.6 +/- 3.04 nM; the Bmax. values were 1.17 +/- 0.18 pmol/mg of protein and 1.04 +/- 0.25 pmol/mg of protein respectively. In kinetic studies, alpha 1-AT decreased the association rate constant k+1 of the 125I-transferrin-binding-site complex from 2.18(+/- 0.21) x 10(7) M-1.min-1 to 3.99(+/- 0.18) x 10(6) M-1.min-1. In contrast, the dissociation rate constant k-1 was not changed (0.0948 +/- 0.002 min-1, 0.089 +/- 0.0017 min-1). On isoelectric focusing, no alteration in transferrin protein pattern or shift in isoelectric point was detected in the presence of alpha 1-AT. Inhibition of transferrin binding by the acute-phase proteins alpha 1-AT and alpha 2-MG is competitive. Interestingly, inhibition is already present at physiological concentrations. However, full inhibition is only achieved at concentrations above the normal range, which are attained in acute-phase reactions.
Binding Sites↗