5-aminolevulinic acid combined with sodium ferrous citrate ameliorates H2O2-induced cardiomyocyte hypertrophy via activation of the MAPK/Nrf2/HO-1 pathway.

Hydrogen peroxide (H2O2) causes cell damage via oxidative stress. Heme oxygenase-1 (HO-1) is an antioxidant enzyme that can protect cardiomyocytes against oxidative stress. In this study, we investigated whether the heme precursor 5-aminolevulinic acid (5-ALA) with sodium ferrous citrate (SFC) could protect cardiomyocytes from H2O2-induced hypertrophy via modulation of HO-1 expression. HL-1 cells pretreated with/without 5-ALA and SFC were exposed to H2O2 to induce a cardiomyocyte hypertrophy model. Hypertrophy was evaluated by planar morphometry, (3)H-leucine incorporation, and RT-PCR analysis of hypertrophy-related gene expressions. Reactive oxygen species (ROS) production was assessed by 5/6-chloromethyl-2',7'-ichlorodihydrofluorescein diacetate acetylester. HO-1 and nuclear factor erythroid 2-related factor 2 (Nrf2) protein expressions were analyzed by Western blot. In our experiments, HL-1 cells were transfected with Nrf2 siRNA or treated with a signal pathway inhibitor. We found several results. 1) ROS production, cell surface area, protein synthesis, and expressions of hypertrophic marker genes, including atrial natriuretic peptide, brain natriuretic peptide, atrial natriuretic factor, and ß-myosin heavy chain, were decreased in HL-1 cells pretreated with 5-ALA and SFC. 2) 5-ALA and SFC increased HO-1 expression in a dose- and time-dependent manner, associated with upregulation of Nrf2. Notably, Nrf2 siRNA dramatically reduced HO-1 expression in HL-1 cells. 3) ERK1/2, p38, and SAPK/JNK signaling pathways were activated and modulate 5-ALA- and SFC-enhanced HO-1 expression. SB203580 (p38 kinase), PD98059 (ERK), or SP600125 (JNK) inhibitors significantly reduced this effect. In conclusion, our data suggest that 5-ALA and SFC protect HL-1 cells from H2O2-induced cardiac hypertrophy via activation of the MAPK/Nrf2/HO-1 signaling pathway.

Permanent acceptance of mouse cardiac allografts with CD40 siRNA to induce regulatory myeloid cells by use of a novel polysaccharide siRNA delivery system.

The CD40/CD154 co-stimulatory pathway is crucial in alloimmune response. We developed a novel small interfering RNA (siRNA) delivery system with a poly-dA extension at the 5'-end of the siRNA sense strand that was stably incorporated into 1,3-ß-glucan (schizophyllan, SPG). This was captured and incorporated into dendritic cells (DCs) through its receptor, Dectin-1, specifically silencing CD40 genes (siCD40) to exert immunoregulatory activity. siCD40/SPG-treated CBA mice permanently accepted B10 fully mismatched cardiac allografts. Consistent with graft survival, the infiltration of CD4(+), CD8(+) T cells into the graft was lower, and that the numbers of CD40(low)CD11c(+) DCs cells and CD4(+)Foxp3(+)cells were increased in both the graft and in the recipient spleen. In addition, naive CBA recipients given an adoptive transfer of splenocytes from the primary recipients with siCD40/SPG accepted a heart graft from donor-type B10, but not third-party Balb/c mice. In conclusion, the treatment with siCD40/SPG targeting DCs could generate antigen-specific Tregs, resulting in the permanent acceptance of mouse cardiac allografts. These findings have important implications for clarifying the mechanism underlying the induction of tolerance in DCs, and also highlight the potential of immunomodulation and the feasibility of siRNA-based clinical therapy in the transplantation field.

New neuropeptides containing carboxy-terminal RFamide and their receptor in mammals.

Only a few RFamide peptides have been identified in mammals, although they have been abundantly found in invertebrates. Here we report the identification of a human gene that encodes at least three RFamide-related peptides, hRFRP-1-3. Cells transfected with a seven-transmembrane-domain receptor, OT7T022, specifically respond to synthetic hRFRP-1 and hRFRP-3 but not to hRFRP-2. RFRP and OT7T022 mRNAs are expressed in particular regions of the rat hypothalamus, and intracerebroventricular administration of hRFRP-1 increases prolactin secretion in rats. Our results indicate that a variety of RFamide-related peptides may exist and function in mammals.

Development of a novel, nearly insoluble antiadhesive membrane.

BACKGROUND: Sodium hyaluronate/carboxymethylcellulose (HA/CMC) is difficult to use in a moist environment because of its susceptibility to moisture. METHODS: We developed the three-layered nDM-14R membrane. The surface layers are composed of 1-lactide, glycolide and e-caprolactone copolymers. HA/CMC and nDM-14R were used in all these studies. (1) The central region of 1 × 10 cm specimens (n = 5) was moistened for 0, 5, 10, 20, 30 or 60 s, after which the tensile strength was determined; (2) one side of specimens of 1 × 10 cm (n = 5) was moistened with agar gel for 5, 10, 15 or 30 s, after which the adhesion strength was determined, and (3) Rat cecum (n = 10) was scratched, 3 × 3 cm specimens were placed on the scratched area, and adhesions were evaluated on postoperative day 14. RESULTS AND CONCLUSION: (1) The tensile strength of nDM-14R after contact for 10-30 s was greater than that of HA/CMC. (2) The adhesive strength of HA/CMC after contact for 5-10 s was greater than that of nDM-14R. (3) Adhesion scores in treatment groups were significantly lower than in the control group. The results suggest that nDM-14R has the same antiadhesive effect and allows easier placement under moist conditions than HA/CMC.

PD-1/B7-H1 interaction contribute to the spontaneous acceptance of mouse liver allograft.

The programmed death-1 (PD-1)/B7-H1 pathway acts as an important negative regulator of immune responses. We herein investigated the role of the PD-1/B7-H1 pathway in establishing an immunological spontaneous tolerance status in mouse liver allografting. B7-H1 is highly expressed on the donor-derived tissue cells and it is also associated with the apoptosis of infiltrating T cells in the allografts. Strikingly, a blockade of the PD-1/B7-H1 pathway via anti-B7-H1mAb or using B7-H1 knockout mice as a donor led to severe cell infiltration as well as hemorrhaging and necrosis, thus resulting in mortality within 12 days. Furthermore, the expression of the FasL, perforin, granzyme B, iNOS and OPN mRNA in the liver allografts increased in the antibody-treated group in comparison to the controls. Taken together, these data revealed that the B7-H1 upregulation on the tissue cells of liver allografts thus plays an important role in the apoptosis of infiltrating cells, which might play a critical role of the induction of the spontaneous tolerance after hepatic transplantation in mice.

Isolation and structure of bacterial sex pheromone, cPD1.

The Streptococcus faecalis sex pheromone cPD1, which induces a mating response in cells harboring the conjugative plasmid pPD1, has been isolated and its structure determined. It was found to have a molecular weight of 912, and its amino acid sequence was H-Phe-Leu-Val-Met-Phe-Leu-Ser-Gly-OH. A synthetic octapeptide showed the same biological activity and chromatographic behavior as the isolated cPD1. Pheromone activity was detectable at a concentration of approximately 4 X 10(-11)M.

Intestinal thrombotic microangiopathy induced by FK506 in rats.

Thrombotic microangiopathy (TMA) is one of the severe complications after stem cell transplantation (SCT) and is associated with graft-versus-host disease (GVHD) prophylaxis including FK506. In this study, we experimented on rats using FK506 to demonstrate the occurrence of intestinal TMA. FK506 was administrated into Wistar/ST rats intraperitoneally for 7 days. Rats were examined histopathologically after FK506 injection using light and electron microscopy and immunohistochemistry. FK506 concentrations in whole blood were measured by enzyme immunoassay. In the acute phase, hemorrhagic lesions with multifocal erosions and crypt loss were found in the small intestines of all treated rats. Capillary vessels were dilated, and a few platelet thrombi were found. Electron microscopy demonstrated degenerative swelling of endothelial cells and platelet aggregates adhering to the vessel walls. In the later phase, epithelial regenerative failure, characterized by crypt ghosts, was found in the affected mucosa. Apoptotic epithelial cells were increased in number. The extent of intestinal injury was proportional to the whole blood levels of FK506. The intestinal lesions in rats were consistent with TMA and induced by the injection of FK506 alone. Apoptotic enteropathy was also observed and similar to intestinal GVHD. In this study, we established an intestinal TMA model induced by immunosuppressant (Tacrolimus) only without irradiation.

Antagonistic controls of autophagy and glycogen accumulation by Snf1p, the yeast homolog of AMP-activated protein kinase, and the cyclin-dependent kinase Pho85p.

In the yeast Saccharomyces cerevisiae, glycogen is accumulated as a carbohydrate reserve when cells are deprived of nutrients. Yeast mutated in SNF1, a gene encoding a protein kinase required for glucose derepression, has diminished glycogen accumulation and concomitant inactivation of glycogen synthase. Restoration of synthesis in an snf1 strain results only in transient glycogen accumulation, implying the existence of other SNF1-dependent controls of glycogen storage. A genetic screen revealed that two genes involved in autophagy, APG1 and APG13, may be regulated by SNF1. Increased autophagic activity was observed in wild-type cells entering the stationary phase, but this induction was impaired in an snf1 strain. Mutants defective for autophagy were able to synthesize glycogen upon approaching the stationary phase, but were unable to maintain their glycogen stores, because subsequent synthesis was impaired and degradation by phosphorylase, Gph1p, was enhanced. Thus, deletion of GPH1 partially reversed the loss of glycogen accumulation in autophagy mutants. Loss of the vacuolar glucosidase, SGA1, also protected glycogen stores, but only very late in the stationary phase. Gph1p and Sga1p may therefore degrade physically distinct pools of glycogen. Pho85p is a cyclin-dependent protein kinase that antagonizes SNF1 control of glycogen synthesis. Induction of autophagy in pho85 mutants entering the stationary phase was exaggerated compared to the level in wild-type cells, but was blocked in apg1 pho85 mutants. We propose that Snf1p and Pho85p are, respectively, positive and negative regulators of autophagy, probably via Apg1 and/or Apg13. Defective glycogen storage in snf1 cells can be attributed to both defective synthesis upon entry into stationary phase and impaired maintenance of glycogen levels caused by the lack of autophagy.

Phosphorylation of sic1, a cyclin-dependent kinase (Cdk) inhibitor, by Cdk including Pho85 kinase is required for its prompt degradation.

In the yeast Saccharomyces cerevisiae, Sic1, an inhibitor of Clb-Cdc28 kinases, must be phosphorylated and degraded in G1 for cells to initiate DNA replication, and Cln-Cdc28 kinase appears to be primarily responsible for phosphorylation of Sic1. The Pho85 kinase is a yeast cyclin-dependent kinase (Cdk), which is not essential for cell growth unless both CLN1 and CLN2 are absent. We demonstrate that Pho85, when complexed with Pcl1, a G1 cyclin homologue, can phosphorylate Sic1 in vitro, and that Sic1 appears to be more stable in pho85Delta cells. Three consensus Cdk phosphorylation sites present in Sic1 are phosphorylated in vivo, and two of them are required for prompt degradation of the inhibitor. Pho85 and other G1 Cdks appear to phosphorylate Sic1 at different sites in vivo. Thus at least two distinct Cdks can participate in phosphorylation of Sic1 and may therefore regulate progression through G1.

Differential-display analysis of gene expression in livers from normal and partially hepatectomized mice.

Partial hepatectomy, resulting in the removal of approximately 70% of the liver, is widely utilized for studies of liver growth in experimental animals. The regenerative response is proportional to the amount of liver removed. Knowing when and where genes are expressed provides a strong clue as to its biological role. The RNA differential-display (DD) technique facilitates monitoring the differential expression of a large number of activated or suppressed genes under various biological conditions. To reveal mechanisms of liver regeneration, we performed a comparative analysis of gene expression during liver regeneration using DD. We sacrificed male Balb/c mice, aged 10 to 12 weeks, at 0, 24, 48, and 72 hours, and 1 and 2 weeks after PHx. The livers were weighed, and the amount of glutamic-oxaloacetate transaminase in serum measured. We extracted the total RNA from frozen liver tissue and confirmed the RNA quality using a lab-chip system. DD analysis was performed essentially as described by Liang and Pardee. Semiquantitative reverse-transcription polymerase chain reaction was performed to confirm the results of DD analysis. Of the 56 fragments that exhibited changed expression levels during PHx, 39 were cloned and sequenced. There were 31 known genes, 13 unknown genes, and 9 expressed-sequence tags. These results indicated that DD is a powerful approach for monitoring molecular events in the regenerating liver.

The reduction of hypoxia-induced and reoxygenation-induced apoptosis in rat islets by epigallocatechin gallate.

The survival of transplanted tissue is affected by the detrimental consequences of hypoxia followed by reoxygenation. The majority of transplanted cells undergo apoptosis due to hypoxia and reoxygenation (H/R) injury, but protection from H/R has been less examined. In this study, we examined whether epigallocatechin gallate (EGCG) protected rat islets from H/R injury. Rat islets, freshly prepared from F344 rat strain by collagenase digestion and density centrifugation, were seeded in triplicate at concentrations of 100 per well in 24-well plates for culture under normoxia. The cells were then exposed to hypoxia for 14 hours with or without EGCG, after which they were reoxygenated for 72 hours in a humidified oxygenated CO(2) incubator at 37 degrees C. Apoptosis, lactate dehydrogenase (LDH), and 8-hydroxy-2'-deoxyguanosine (8-OHdG) were evaluated according to the manufacturer's instructions. The H/R induced apoptosis in the islets that was reduced in dose-dependent manner by EGCG treatment. The viability of islets exposed to H/R was assessed by LDH release. H/R reduced viability compared with the controls, while the viability of the islets improved upon EGCG treatment. The secretion of insulin was also decreased by H/R, as well as the dose dependent EGCG protective ability on insulin secretion. The content of 8-OHdG in islets from H/R was also reduced by EGCG. Our results indicated that apoptosis and the decline in insulin secretion by H/R were inhibited by EGCG treatment. EGCG may be considered useful for protection of islets from oxidative injury associated with the transplantation procedure.

Exogenous expression of Fas-ligand or CrmA prolongs the survival in rat liver transplantation.

Modulation of donor organs by transfection of a gene encoding immmunosuppresive molecules has been recognized as a less toxic approach to prevent allograft rejection. Fas-ligand (FasL) plays a critical role in activation-induced cell death of activated cytotoxic lymphocytes. This may provide a potential for induction of "immune privileged sites" to escape the host immune surveillance system. Cytokine response modifier A (CrmA), a gene product of cowpox virus, blocks caspase as well as perforin/granzyme-mediated apoptotic pathways. Therefore, it may suppress intragraft apoptosis. The aim of the present study was to investigate whether transfection of FasL or CrmA genes prolonged the survival of rat liver allografts. Using the high responder rat combination of DA (RT-1(a)) donor to LEW (RT-1(1)) recipient, we performed orthotopic liver transplantation with subsequent delivery of adenoviral vectors containing FasL, CrmA, or LacZ, at a dose of 1 x 10(9) pfu via a recipient tail vein using a Cre-mediated gene expression system. Recipient survival was assessed as well as immunohistochemical examination of the grafts for anti-CD2, TUNEL, and H&E staining. Statistical analysis was performed with the Mann-Whitney U test. The therapeutic groups showed significantly prolonged recipient survival compared with the LacZ-treated control group. Histologic analysis revealed reduced hepatocyte apoptosis in the CrmA-treated group and increased apoptosis of infiltrating mononuclear cells in the FasL-treated group. These data suggested that FasL and CrmA may be potent genes to prolong rat liver allograft survival.

Influence of the numbers of islets on the models of rat syngeneic-islet and allogeneic-islet transplantations.

One of the main barriers to widespread application of islet transplantation is the limited availability of human pancreatic islets. The reduction of graft islet mass for transplantation to a recipient is one of the strategies in islet transplantation. However, transplantation of only a small number of islets may result in primary nonfunction. To optimize the sites and numbers of islets for transplantation, we analyzed these factors using pancreatic islets from Lewis or F344 rats transplanted into rats rendered diabetic by streptozotocin (50 mg/kg IV) and confirmed as such prior to transplantation (>300 mg/dL blood glucose). Approximately 500 to 1500 islets were injected via the portal vein or under the renal capsule into the diabetic F344 rats. The blood glucose level of all animals bearing 1500 syngeneic or allogeneic islets transplanted to the liver or under the kidney capsule exhibited restored normoglycemia (<200 mg/dL) at 1 day after transplantation. Graft function deteriorated after only 3 days in three animals (5.8%). The loss of graft function after 3 days occurred in 10 of 28 rats transplanted with 1000 to 1200 syngeneic islets, 4 of 19 rats transplanted with 800 to 900 syngeneic islets, and 7 of 17 rats transplanted with 500 to 600 syngeneic islets. There was no significant difference in the loss of graft function between the sites of transplantation via portal vein or under the kidney capsule. In conclusion, higher frequencies of primary nonfunction occurred with less than 1500 islets transplanted. They were independent of the sites in the rat-islet transplantation model.

p53R2-dependent pathway for DNA synthesis in a p53-regulated cell cycle checkpoint.

A recently identified ribonucleotide reductase (RR), p53R2, is directly regulated by p53 for supplying nucleotides to repair damaged DNA. We examined the role of this p53R2-dependent pathway for DNA synthesis in a p53-regulated cell cycle checkpoint, comparing it to R2-dependent DNA synthesis. The elevation of DNA synthesis activity through RR in response to gamma-irradiation was closely correlated with the level of expression of p53R2 but not of R2. The p53R2 product accumulated in nuclei, whereas R2 levels in cytoplasm decreased. We found a point mutation of p53R2 in cancer cell line HCT116, which resulted in loss of RR activity. In those cells, DNA damage-inducible apoptotic cell death was enhanced through transcriptional activation of p53AIP1. The results suggest that p53R2-dependent DNA synthesis plays a pivotal role in cell survival by repairing damaged DNA in the nucleus and that dysfunction of this pathway might result in activation of p53-dependent apoptosis to eliminate dangerous cells.

Simultaneous racemization and isomerization at specific aspartic acid residues in alpha B-crystallin from the aged human lens.

We provide evidence that the racemization and isomerization of aspartyl(Asp) residues occur simultaneously in the alpha B-crystallin in the lens of aged (mean age: 80 years) and young (age: 11 months) humans. We purified alpha B-crystallin and subjected it to tryptic digestion. The resulting peptides were separated by reverse-phase high-performance chromatography (RP-HPLC) and were characterized by amino-acid composition, sequence analysis and mass spectrometry. Two specific sites, Asp-36 (D/L of Asp: 0.92) and Asp-62(D/L of Asp: 0.57), among 13 Asp/asparginyl (Asn) residues in aged alpha B-crystallin, were found to be highly racemized and isomerized to form beta-Asp residues. The beta-Asp-containing peptides were clearly distinguished from normal Asp-containing (alpha-Asp) peptides by RP-HPLC. The racemization and isomerization of Asp residues in aged alpha B-crystallin may occur via a succinimide intermediate. In young alpha B-crystallin, we observed neither racemization nor isomerization. We also found that Met-68 was oxidized to form Met sulfoxide to a greater extent in aged alpha B-crystallin than in young alpha B-crystallin. We concluded that racemization, isomerization, and oxidation of alpha B-crystallin occur spontaneously in the aging process.

Cloning and expression of a complementary DNA encoding the bovine receptor for pituitary adenylate cyclase-activating polypeptide (PACAP).

A cDNA encoding a pituitary adenylate cyclase-activating polypeptide (PACAP) receptor was cloned from a bovine brain cDNA library using a synthetic oligonucleotide probe corresponding to the partial N-terminal amino acid sequence of the PACAP receptor purified from the bovine brain. The cloned cDNA encoded a polypeptide of 513 amino acid residues with seven putative transmembrane domains. The deduced amino acid sequence exactly matched the N-terminal amino acid sequence of the purified PACAP receptor. It also shared an apparent similarity with the vasoactive intestinal peptide (VIP), secretin, growth hormone releasing hormone, calcitonin, and glucagon receptors, suggesting that the PACAP receptor is a member of the secretin receptor subfamily of the guanine nucleotide-binding regulatory protein-coupled receptor family. Northern blot analysis showed that the size of the major mRNA band which hybridized with the cDNA was about 7 kb in the bovine cerebral-cortex and hippocampus. An expression vector containing the cloned cDNA for the PACAP receptor was introduced into Chinese hamster ovary (CHO) cells. The affinity of PACAP receptors expressed on the transfected CHO cells was quite similar to that of natural PACAP receptors on the bovine brain membranes. Competitive binding experiments showed that PACAP38 displaced the binding of 125I-labeled PACAP27 to the receptors on the CHO cells more efficiently than PACAP27, while VIP was less effective. In addition, both of PACAP27 and PACAP38 elevated the levels of cAMP and inositol phosphates in the transformed CHO cells. These results indicate that the PACAP receptors encoded by the cloned cDNA are identical to the purified PACAP receptors, and that they can stimulate dual signaling cascades.

Molecular properties of apelin: tissue distribution and receptor binding.

We analyzed the tissue distribution of apelin mRNA in rats by a quantitative reverse transcription-polymerase chain reaction and that of immunoreactive apelin (ir-apelin) by an enzyme immunoassay (EIA) using a monoclonal antibody. The expression levels of apelin mRNA and ir-apelin seemed to be consistent among tissues: they were highly expressed in the lung and mammary gland. By the combination of gel filtration and EIA, we found that the molecular forms of apelin differ among respective tissues: apelin molecules with sizes close to apelin-36 (long forms) were major components in the lung, testis, and uterus, but both long and short (whose sizes were close to [

Apelin, the natural ligand of the orphan receptor APJ, is abundantly secreted in the colostrum.

By using a strategy that we have developed to search for the ligands of orphan seven-transmembrane-domain receptors [S. Hinuma et al., Nature 393 (1998) 272-276], we have recently identified a natural ligand, apelin, for the orphan 7TMR, APJ [K. Tatemoto et al., Biochem. Biophys. Res. Commun. 251 (1998) 471-476]. In this paper, we isolated rat and mouse apelin cDNAs, and analyzed the tissue distribution of apelin mRNA in rats. Although apelin mRNA was widely detected in a variety of tissues, the highest expression of apelin mRNA was detected in the mammary gland of pregnant rats. In the mammary gland, biologically active apelin and its mRNA considerably increased during pregnancy and lactation, and reached a maximal level around parturition. Moreover, a large amount of apelin (14-93 pmol/ml) was found to be secreted in the bovine colostrum, and it was still detectable even in commercial bovine milk. Since apelin partially suppressed cytokine production by mouse spleen cells in response to T cell receptor/CD3 cross-linking, the oral intake of apelin in the colostrum and milk might modulate immune responses in neonates.

Characteristics and distribution of endogenous RFamide-related peptide-1.

We have recently identified RFamide-related peptide (RFRP) gene that would encode three peptides (i.e., RFRP-1, -2, and -3) in human and bovine, and demonstrated that synthetic RFRP-1 and -3 act as specific agonists for a G protein-coupled receptor OT7T022. However, molecular characteristics and tissue distribution of endogenous RFRPs have not been determined yet. In this study, we prepared a monoclonal antibody for the C-terminal portion of rat RFRP-1. As this antibody could recognize a consensus sequence among the C-terminal portions of rat, human, and bovine RFRP-1, we purified endogenous RFRP-1 from bovine hypothalamus on the basis of immunoreactivity to the antibody. The purified bovine endogenous RFRP-1 was found to have 35-amino-acid length that corresponds to 37-amino-acid length in human and rat. We subsequently constructed a sandwich enzyme immunoassay using the monoclonal antibody and a polyclonal antibody for the N-terminal portion of rat RFRP-1, and analyzed the tissue distribution of endogenous RFRP-1 in rats. Significant levels of RFRP-1 were detected only in the central nervous system, and the highest concentration of RFRP-1 was detected in the hypothalamus. RFRP-1-positive nerve cells were detected in the rat hypothalamus by immunohistochemical analyses using the monoclonal antibody. In culture, RFRP-1 lowered cAMP production in Chinese hamster ovary cells expressing OT7T022 and it was abolished by pre-treatment with pertussis toxin, suggesting that OT7T022 couples G(i)/G(o) in the signal transduction pathway.

Significance of fetal hemoglobin-containing erythroblasts (F blasts) and the F blast/F cell ratio in myelodysplastic syndromes.

To investigate the relationship between the fetal hemoglobin-containing erythroblasts (F blasts) and apoptosis in myelodysplastic syndromes (MDS), we immunohistochemically assessed F blasts, F cells, and apoptosis in 137 patients with MDS. A marked increase in the number of F blasts in the bone marrow was identified in 116 of 137 patients (84.7%), and the number of F cells was elevated in 54 patients (39.4%). Among the erythroblasts stained by anti-glycophorin C antibody, the mean percentage of F blasts was 14.63 +/- 9.17% in MDS, which was significantly higher than that in non-MDS patients with stress erythropoiesis (4.82 +/- 3.35%, P < 0.01), although there were no significant differences in the number of F cells between these groups. In particular, 62 of the 137 MDS patients (45.3%) had an apparent increase in F blasts but no elevation of F cells. The apoptotic rate was significantly higher in the patients with a F blast/F cell (Fb/Fc) ratio >or=5.0 than in those with a Fb/Fc ratio <1.0 (P < 0.01). The results indicate that F cell precursors are incapable of maturing into functioning end-stage F cells, presumably owing to apoptotic cell death. The measurement of F blasts in the bone marrow is needed for the precise evaluation of fetal-type erythropoiesis in MDS.