Urinary abnormality in mixed connective tissue disease predicts development of other connective tissue diseases and decrease in renal function

OBJECTIVE

To clarify the clinical significance of development of urinary abnormality in mixed connective tissue disease (MCTD).

METHODS

Forty-one patients with an initial diagnosis of MCTD, followed at five hospitals between April 1, 2000 and December 31, 2013, were included. The relationship between urinary abnormality and various clinical parameters were retrospectively analyzed. Urinary abnormality was defined as proteinuria and/or hematuria detected by urinalysis. Development of other connective tissue diseases (CTDs) was defined as satisfaction of the criteria of each respective disease.

RESULTS

Of 41 patients (34 females, 7 males, mean age at diagnosis 42.2 ± 15.2 years), 16 developed urinary abnormality (UrA(+) patients). The total incidences of development of other CTDs were higher in the UrA(+) patients than UrA(-) (62.5% versus 16.0%, p = .01). In the comparison between UrA(+) and UrA(-) patients, there were no significant differences in follow-up duration or last determined estimated glomerular filtration rate (eGFR), although eGFR decreased more significantly in the UrA(+) patients than UrA(-). (-20.2 ± 17.2 vs -6.1 ± 13.8 ml/min/1.73m2, p = .01; -21.0 ± 18.9 vs -6.7 ± 14.1%, p = .03).

CONCLUSION

Urinary abnormality during the clinical course in MCTD is predictive of a higher incidence of developing other CTDs. Furthermore, it might also predict long-term renal prognosis in patients with an initial diagnosis of MCTD.

Upregulation of PTH receptor mRNA expression by dexamethasone in UMR-106 osteoblast-like cells

OBJECTIVES

Glucocorticoids influence receptor interactions of the parathyroid hormone (PTH) that are crucial for osteoblast function. As mechanisms linking receptor mRNA with glucocorticoids are incompletely understood, we investigated regulation of PTH receptor (PTH1R) mRNA expression in rat osteoblast-like UMR-106 cells by using dexamethasone (Dex), a synthetic glucocorticoid.

MATERIALS AND METHODS

UMR-106 cells were exposed to 10(-8) to 10(-5) M Dex, while some cells were also exposed to a transcriptional inhibitor (DRB) for 24 h with or without Dex. PTH-stimulated cyclicAMP activities were measured by an enzyme-linked immunosorbent assay. PTH1R mRNA was determined by Northern analysis. Transcriptional activities were measured as heretogeneous nuclear PTH1R RNA and also as luciferase activity in constructs, including the PTH1R gene promoter.

RESULTS

Dexamethasone dose-dependently increased PTH-stimulated adenylyl cyclase activity at 72 h. Dex markedly increased PTH1R mRNA accumulation, but did not change transcriptional activity. PTH1R mRNA stability was significantly increased by Dex in transcriptionally arrested cells.

CONCLUSION

In osteoblast-like cells, Dex induced upregulation of PTH1R mRNA followed by increased functional PTH receptor expression. This was caused by posttranscriptional mechanisms increasing mRNA stability.

Treatment of Congenital Nephrogenic Diabetes insipidus with Hydrochlorothiazide and Amiloride in an Adult Patient

AIM

The effects of treatment with hydrochlorothiazide (HCTZ) combined with amiloride were elucidated and compared to HCTZ treatment alone and combined with acemetacin or triamterene in a Japanese adult patient with congenital nephrogenic diabetes insipidus.

METHODS

The study was divided into seven periods: (1) HCTZ and acemetacin; (2) control period; (3) HCTZ; (4) a second control period; (5) HCTZ and amiloride; (6) a third control period, and (7) HCTZ and triamterene. Fluid intake, urine volume, urinary Na, K, creatinine, and osmolality and serum Na, K, Cl, CO2, and osmolality were measured, and free water clearance and proximal and distal tubular Na reabsorption rates were calculated.

RESULTS

Without drug administration, the urine volume was about 8,000 ml/day. The urine volume was reduced to about 6,000 ml/day with HCTZ. A further urine volume reduction to about 5,000 ml/day was obtained with the second drug administration, and the effects were similar among the three regimens. Serum and urinary osmolality and free water clearance were also similar among the three combinations, whereas the urinary potassium excretion was the least, and the serum potassium concentration was the highest with HCTZ plus amiloride. Besides, no alkalosis was observed only with this combination.

CONCLUSION

HCTZ plus amiloride may be superior to HCTZ plus acemetacin and HCTZ plus triamterene in preventing hyperkaliuria, hypokalemia, and metabolic alkalosis.

Parathyroid hormone (PTH) down-regulates PTH/PTH-related protein receptor gene expression in UMR-106 osteoblast-like cells via a 3',5'-cyclic adenosine monophosphate-dependent, protein kinase A-independent pathway

Parathyroid hormone (PTH) regulates osteoblast function via a G protein-linked PTH/PTH-related protein (PTHrP) receptor. We have studied the mechanisms of PTH/PTHrP receptor gene repression by PTH in UMR-106 osteoblast-like cells. Inhibition of PTH/PTHrP receptor mRNA expression by rat (r) PTH(1-34) and Insulin-like growth factor-I (IGF-I) at 10(-7)M was significant at 1 h and 3 h, and maximal at 2 h and 6 h. A maximal decrease in receptor mRNA abundance by rPTH(1-34) and IGF-I was maintained for 24 h. Inhibition of receptor gene expression by rPTH(1-34) was mimicked in UMR-106 cells by the addition of forskolin (an adenylyl cyclase activator), or 8-(4-chlorophenylthio)-adenine 3',5'-cyclic monophosphate (8-pCPTcAMP; a cAMP analogue). Although H89, a selective protein kinase A (PKA) inhibitor, completely inhibited PKA activity stimulated by rPTH(1-34), forskolin or 8-pCPTcAMP, suppression of PTH/PTHrP receptor mRNA synthesis induced by these substances in UMR-106 cells was not affected by H89. In primary osteoblast cultures, rPTH(1-34) inhibited synthesis of PTH/PTHrP receptor mRNA irrespective of H89. The down-regulation effect of rPTH(1-34) was also unaltered by PD98059 (an extracellularly regulated kinase 1/2 mitogen-activated protein kinase pathway inhibitor). Pretreatment with cycloheximide, a protein synthesis inhibitor, did not alter the inhibition of PTH/PTHrP receptor mRNA expression by rPTH(1-34), indicating that receptor mRNA suppression does not require new protein synthesis. Transcriptional activation of PTH/PTHrP receptor gene promoter (U3P or U4P)-luciferase constructs was decreased by rPTH(1-34), forskolin and 8-pCPTcAMP irrespective of H89. Thus, PTH transcriptionally down-regulates PTH/PTHrP receptor gene expression in osteoblast-like cells via a cAMP-dependent, PKA-independent pathway.

Anabolic effects of recombinant human parathyroid hormone (1 - 84) and synthetic human parathyroid hormone (1 - 34) on the mandibles of osteopenic ovariectomized rats with maxillary molar extraction

In rodent osteoporosis models such as ovariectomized (OVX) rats, intermittently administered human parathyroid hormone (hPTH) has an anabolic effect in vertebrae and long bones. In the present experiments, subcutaneously injected hPTH(1 - 34) or hPTH(1 - 84) dose- and time-dependently increased bone mineral density (BMD) as measured by dual energy X-ray absorptiometry in mandibles, L2 to L4 vertebrae and femurs of such rats. The highest dose (15.9 nmol/kg, s. c.) of either peptide given four times weekly for 10 weeks completely reversed the effects of overiectomy on BMD. Significant elevation in lumbar BMD after 10 weeks was observed with hPTH(1 - 34) or hPTH(1 - 84) at 1.1 nmol/kg, whereas hPTH(1 - 34) at 1.1 and 4.2 nmol/kg significantly increased BMD of the whole bone and the metaphysis of the femur and the diaphysis of the bone, respectively. In contrast, significant effects of hPTH(1 - 84) administration on BMD increase in the femur were observed at 4.2 and 15.9 nmol/kg in the whole bone and the metaphysis, and in the diaphysis, respectively. Maxillary molar extraction left mandibular BMD in rats with intact ovaries unchanged, but significantly decreased mandibular BMD in OVX rats. Administration of hPTH(1 - 84) for 10 weeks in OVX rats without or with extraction significantly increased BMD in the mandibular molar region at doses of 15.9 and 4.2 nmol/kg, respectively, indicating that efficacy was increased by extraction. A significant BMD increase in the molar region in OVX rats with extraction occurred at only 1.1 nmol/kg of hPTH(1 - 34) and 4.2 nmol/kg of hPTH(1 - 84). Also, BMD of the ramus region was increased by administration of both peptides to a lesser extent than that of the molar region in these rats. Thus, intermittent administration of hPTH, especially hPTH(1 - 34), has an anabolic effect on bone, particularly alveolar bone. Such treatment may increase alveolar bone mass in postmenopausal women with osteoporosis.

Parathyroid hormone (PTH) suppresses rat PTH/PTH-related protein receptor gene promoter

Parathyroid hormone (PTH) regulates osteoblasts via a G protein-linked PTH/PTH-related protein (PTHrP) receptor. PTH effects on PTH/PTHrP receptor gene expression were studied in UMR 106 osteoblast-like cells. In heterogeneous nuclear RNA and Northern analysis, PTH suppressed PTH/PTHrP receptor transcription. We cloned the 7-kb promoter region of the rat PTH/PTHrP receptor gene and transiently transfected chimeric deletion constructs containing the 5'-flanking region and the luciferase gene into UMR 106 cells. In transfected cells the minimal region for basal promoter activity was between positions -128 and +103. The 5'-flanking region of exon U1 contained several putative-binding sites for Sp1 and the myc-associated zinc finger protein (MAZ). The minimal PTH-suppressive region (PTHSR) was between +1 and +25 in exon U1, but the 5'-flanking region or Sp1 and MAZ-binding sites also were required for PTH-mediated repression. By gel mobility shift assay PTH markedly decreased binding of PTHSR-protein complex in UMR 106 cells. The mutation experiments showed that the most critical sequence for the repression of PTH was 5'-GGGGGAGGGGAG-3' (+1 to +12) of PTHSR. This represents the first characterization of a PTH-suppressive region of the PTH/PTHrP receptor gene in rat.

Simvastatin promotes osteoblast differentiation and mineralization in MC3T3-E1 cells

The cholesterol-lowering drug, simvastatin, is a pro-drug of a potent 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor and inhibits cholesterol synthesis in humans and animals. In addition, the bone effects of statins including simvastatin are being studied. We assessed the effects of simvastatin on osteoblastic differentiation in nontransformed osteoblastic cells (MC3T3-E1) and rat bone marrow cells. Simvastatin enhanced alkaline phosphatase (ALP) activity and mineralization in a dose- and time-dependent fashion. This stimulatory effect of the statin was observed at relatively low doses (significant at 10(-8) M and maximal at 10(-7) M). Northern blot analysis showed that the statin (10(-7) M) increased in bone morphogenetic protein-2 as well as ALP mRNA concentrations in MC3T3-E1 cells. Simvastatin (10(-7) M) slightly increased in type I collagen mRNA abundance throughout the culture period, whereas it markedly inhibited the gene expression of collagenase-1 between days 14 and 22 of culture. These results indicate that simvastatin has anabolic effects on bone through the promotion of osteoblastic differentiation, suggesting that it could be used for the treatment of common metabolic bone diseases such as osteoporosis.

Regulation of vitamin D-1alpha-hydroxylase and -24-hydroxylase expression by dexamethasone in mouse kidney

We investigated the effects of dexamethasone on vitamin D-1alpha-hydroxylase and -24-hydroxylase expression and on vitamin D receptor (VDR) content in the kidneys of mice fed either a normal (NCD) diet or a calcium- and vitamin D-deficient (LCD) diet for 2 weeks. For the last 5 days mice received either vehicle or dexamethasone (2 mg/kg per day s.c.). Dexamethasone significantly increased plasma calcium concentrations without changing plasma concentrations of 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) in both NCD and LCD groups. Northern blot and enzyme activity analyses in NCD mice revealed that dexamethasone increased renal VDR mRNA expression modestly and greatly increased 24-hydroxylase mRNA abundance and enzyme activity, but did not affect 1alpha-hydroxylase mRNA abundance and enzyme activity. In mice fed an LCD diet, dexamethasone increased renal VDR mRNA expression 1.5-fold, decreased 1alpha-hydroxylase mRNA abundance (52%) and activity (34%), and markedly increased 24-hydroxylase mRNA abundance (16-fold) and enzyme activity (9-fold). Dexamethasone treatment did not alter functional VDR number (B(max) 125-141 fmol/mg protein) or ligand affinity (K(d) 0.13-0.10 nM) in LCD mice. Subcutaneous injections of 1,25(OH)(2)D(3) (0.24 nmol/kg per day for 5 days) into NCD mice strongly increased renal 24-hydroxylase mRNA abundance and enzyme activity, while there was no effect of dexamethasone on renal 24-hydroxylase expression in these mice. This may be due to overwhelming induction of 24-hydroxylase by 1,25(OH)(2)D(3). These findings suggest that glucocorticoid-induced osteoporosis is caused by direct action of the steroids on bone, and the regulatory effect of glucocorticoids on renal 25-hydroxyvitamin D(3) metabolism may be less implicated in the initiation and progression of the disease.

Regulation of small intestinal transit by central nervous calcitonin receptor

Salmon calcitonin (sCT) suppresses small intestinal transit (SIT) or motility, but the mechanism is not well understood. Bolus s. c. administration of a pharmacologic dose of sCT (140 IU/kg) to mice significantly decreased plasma calcium and phosphorus, and suppressed SIT from 1 to 8 h for plasma calcium and phosphorus or 20 h for SIT (respective maximal effects were seen at 5 h, between 2 and 8 h, and between 1 and 5 h). Significant SIT inhibition did not occur at doses smaller than 140 IU/kg. Reverse transcription-polymerase chain reactions and Southern analysis demonstrated high levels of calcitonin receptor mRNA in diencephalon and lung, moderate levels of mRNA in cerebellum, kidney, and muscle, and barely detectable amounts in cerebral cortex and thymus. No message was detectable in duodenum, jejunum, liver, testis, or heart. Specific binding of [125I] sCT was demonstrated in the diencephalon. Intracerebroventricular (i.c.v.) administration of sCT inhibited SIT time- and dose-dependently. Maximal inhibition was obtained at a dose of 4 IU/kg, 20 min after injection. Pretreatment with sCT (140 IU/kg s.c.) completely abolished inhibition of SIT by i.c.v. sCT (4 IU/kg). These results suggest that sCT binds to receptors in the central nervous system and inhibits small bowel transit.

Induction of metalloelastase mRNA in murine peritoneal macrophages by diethylmaleate

Macrophage-specific metalloelastase (MME) hydrolyzes elastin and other matrix proteins and plays an important physiological role in tissue remodeling and pathological tissue destruction. We have examined the effects of diethylmaleate (DEM), an electrophilic agent that reacts with sulfhydryls, on the expression of MME mRNA in mouse peritoneal macrophages. Quantification of MME mRNA by Northern blot analysis revealed that basal mRNA levels were quite low in freshly isolated cells, although mRNA levels increased markedly and reached a steady level within 12 h when cells were cultured in a serum-supplemented RPMI 1640 medium. When macrophages were challenged with DEM at 0.05-1.0 mM for 8 h the expression of the MME gene was enhanced further. In the presence of 0.1 mM DEM, the level of the MME mRNA increased 2-fold compared to the control levels after 6-9 h and decreased to control levels in 24 h. Other electrophilic agents, catechol and 1-chloro-2,4-dinitrobenzene, also enhanced MME gene expression. However, oxidative stress agents such as hydrogen peroxide, menadione, paraquat (an O-2 generator), sodium arsenite and cadmium chloride had no effect on MME gene expression. These results indicate that the electrophilic agents selectively enhance the expression of MME mRNA during primary culture of the macrophages.

Insulin-like growth factor I suppresses parathyroid hormone (PTH)/PTH-related protein receptor expression via a mitogen-activated protein kinase pathway in UMR-106 osteoblast-like cells

Insulin-like growth factor I (IGF-I) is important in skeletal growth and has been implicated in the maintenance of bone integrity. PTH stimulates bone resorption through the G protein-linked PTH/PTH-related protein (PTHrP) receptor in osteoblasts. Using a heterogeneous nuclear RNA assay and Northern blot analysis, we showed that IGF-I inhibited expression of the gene for PTH/PTHrP receptor in a dose- and time-dependent fashion, but did not alter the stability of the receptor messenger RNA (mRNA) in UMR-106 osteoblast-like cells. IGF-I treatment for 48 h also caused a decrease in the receptor number to 45% of that in controls without affecting receptor affinity and in functional receptor expression to 50-60% of that in controls as measured by PTH-stimulated cAMP production. In MC3T3-E1 murine nontransformed osteoblasts, IGF suppressed receptor mRNA expression dose dependently. In UMR-106 cells, IGF-I induced the mitogen-activated protein (MAP) kinase pathway. The effect of IGF-I was blocked by PD98059, a specific inhibitor of the MAP kinase-activating kinase, but not by wortmannin, a specific inhibitor of phosphatidylinositol 3-kinase. IGF-I inhibition of PTH/PTHrP receptor mRNA expression in UMR-106 cells was abrogated completely by pretreatment with cycloheximide, an inhibitor of protein synthesis. These findings indicate that IGF-I suppresses gene expression for PTH/PTHrP receptor via the MAP kinase pathway, and this inhibition is required for new protein synthesis in UMR-106 osteoblast-like cells.

Starvation-induced increase in the parathyroid hormone/PTH-related protein receptor mRNA of bone and kidney in sham-operated and thyroparathyroidectomized rats

Parathyroid hormone (PTH) acts on bone and kidneys by binding to PTH/PTH-related protein (PTHrP) receptors and regulating calcium (Ca) and phosphorus (P) homeostasis. PTH/PTHrP receptor mRNA was expressed at high levels in PTH target tissues such as the kidneys and bone including the calvaria, femur, and tibia. Because short-term starvation influences Ca and P ion homeostasis, we measured changes in PTH/PTHrP receptor mRNA expression in the bone and kidneys. Food deprivation for 3 days decreased the serum Ca and P concentrations, and reinstitution of feeding for 2 days normalized the serum Ca level and significantly increased the serum P level. Concomitantly, rat immunoreactive PTH (riPTH) was increased during starvation and returned to the control level after 2 days of subsequent feeding. Serum 1 alpha, 25-dihydroxyvitamin D3 (1,25(OH)2D3) concentrations did not significantly change during starvation and subsequent feeding. Starvation up-regulated PTH/PTHrP receptor mRNA expression in both bone and kidney. The effects of food deprivation on the receptor transcript abundance were greater in bone (threefold increase compared with control) than in the kidney (1.8-fold increase), whereas the mRNA level increase by food deprivation was more rapid in the kidneys than in bone. The PTH-induced adenylyl cyclase activity of renal membranes increased in starvation. Feeding after starvation normalized the mRNA levels in both tissues. Serum PTH depression, initiated by thyroparathyroidectomy, did not affect PTH/PTHrP receptor mRNA levels in bone and kidney in rats that were fed or starved for 3 days. The abundance of receptor mRNA in bone and kidney was significantly lower in fed rats given either corticosterone or vehicle than in starved rats. These data indicate that starvation induces PTH/PTHrP receptor mRNA expression in bone and kidney, independently of serum PTH and corticosterone concentrations. The factors leading to up-regulated receptor mRNA induced by starvation remain unknown.

Mouse vitamin D-24-hydroxylase: molecular cloning, tissue distribution, and transcriptional regulation by 1alpha,25-dihydroxyvitamin D3

Vitamin D-24-hydroxylase (24-OHase) is a cytochrome P-450 enzyme that catalyzes the conversion of 25-hydroxyvitamin D3 (25OHD3) and 1alpha,25-dihydroxyvitamin D3 [1,25-(OH)2D3] to 24,25-dihydroxyvitamin D3 and 1,24,25-trihydroxyvitamin D3, respectively. A full-length complementary DNA for mouse 24-OHase has now been characterized. The complementary DNA consists of 3309 bp and encodes a protein of 514 amino acids that shows 82% and 95% sequence identity with the human and rat enzymes, respectively. Northern blot analysis of tissues from mice injected with 1,25-(OH)2D3 (24 pmol/g) revealed that the 3.4-kb 24-OHase messenger RNA (mRNA) is most abundant in kidney and intestine, with smaller amounts present in skin, thymus, and bone. RT-PCR and Southern blot analysis detected 24-OHase mRNA in several other tissues including lung, testis, spleen, pancreas, and heart. Intraperitoneal injection of 1,25-(OH)2D3 induced dose- and time-dependent increases in both 24-OHase mRNA abundance and enzyme activity in mouse kidney. Similarly, 1,25-(OH)2D3-induced increases in both 24-OHase mRNA and activity were apparent in the duodenum. Although 1,25-(OH)2D3 increased the amount of 24-OHase mRNA in skin, enzyme activity was not detected in this tissue. Pretreatment of mice with cycloheximide (400 microg/g), an inhibitor of protein synthesis, potentiated the increase in 24-OHase mRNA abundance, but blocked the increase in 24-OHase activity, induced by 1,25-(OH)2D3 in kidney and duodenum, suggesting that 24-OHase gene expression may be regulated not only by the vitamin D receptor but also by a short-lived repressor protein.

Low micromolar levels of hydrogen peroxide and proteasome inhibitors induce the 60-kDa A170 stress protein in murine peritoneal macrophages

We previously reported cDNA cloning of a novel oxidative stress protein termed A170 from murine macrophages. Further experiments have demonstrated that exposure of the cells to low levels of H2O2 produced by glucose/glucose oxidase markedly induced the 60-kDa A170 protein. This result suggests that the level of A170 protein can also be controlled at posttranscriptional levels, because we showed previously that H2O2 hardly increased the level of A170 mRNA. We have found that proteasome inhibitors markedly induced the A170 protein after 2 to 8 h similarly to glucose/glucose oxidase, suggesting rapid degradation of the A170 protein by proteasome under normal conditions. Activation of cellular signaling pathways either by epidermal growth factor, lipopolysaccharide or tumor necrosis factor-alpha did not enhance the level of the A170 protein. The levels of glucose oxidase-induced A170 protein did not decrease after the addition of cycloheximide. These results suggest that low levels of H2O2 may stabilize the A170 protein, allowing it to accumulate within cells.

Matrix metalloproteinases-1 and -8 and TIMP-1 mRNA levels in normal and diseased human gingivae

Interstitial collagenases, including matrix metalloproteinase-1 (MMP-1) and -8 (MMP-8), serve as initiators of extracellular matrix destruction in periodontal disease. Collagenase activities are mainly regulated by tissue inhibitors of metalloproteinases (TIMPs). We tested the effects of inflammation on MMP-1 and MMP-8 gene expression in periodontal disease. To determine the relative abundance of these mRNAs in gingiva, we used a reverse transcription-polymerase chain reaction (RT-PCR) assay. Gingival biopsies were divided into 2 groups; a control group and an inflamed group with severe gingivitis or periodontitis. The MMP-1 mRNA levels were significantly elevated in inflamed gingiva, while the levels of the MMP-8 transcript were not different in the 2 groups and barely detectable by RT-PCR assay. The expression of the TIMP-1 gene was not altered, and remained higher than any of these other genes in both control and diseased gingivae. These results suggest that MMP-1 rather than MMP-8 may play an important role in the initiation of collagen degradation in periodontal disease. However, the possibility remains that MMP-8 plays an important role in periodontal tissue destruction, since the mRNA abundance and not the enzyme activity was assessed.

Murine peritoneal macrophages induce a novel 60-kDa protein with structural similarity to a tyrosine kinase p56lck-associated protein in response to oxidative stress

Using differential screening we have cloned a cDNA encoding a novel oxidative stress protein designated A170 from murine peritoneal macrophages. It has a Zn-finger domain, a PEST domain and several potential phosphorylation sites for kinases. Treatments with oxidative stress agents such as diethyl maleate and paraquat increased a 2.0-kilobase A170 mRNA about twofold in the macrophages after 12 hours in culture. However, H2O2 or glucose/glucose oxidase did not increase the level of the A170 mRNA. Using an A170-specific antibody we have detected in the macrophages a 60-kDa protein that was induced 5 to 10 hours after the addition of the oxidative stress agents. A search of sequence databases revealed that the A170 protein is roughly 90% identical to a human protein that binds to the Src homology 2 domain of the T-cell-specific tyrosine kinase p56lck. These features suggest that the A170 protein plays a significant role in oxidative stress-responsive signal transduction in macrophages.

Inhibition of the thiol-specific antioxidant activity of rat liver MSP23 protein by hemin

Mouse stress-inducible 23-kDa protein (MSP23) belongs to a new type of antioxidative protein family and is highly expressed in livers. To examine its physiological role in the tissue, we have purified native MSP23 protein from the cytosolic fraction of rat liver. The purified protein showed the thiol-specific antioxidant activity and protected glutamine synthetase from inactivation by a mixed metal-thiol oxidation. We examined the effect of hemin on that activity since it was recently shown by others that the rat liver MSP23 protein had a high binding affinity to heme. We have found that hemin at low concentrations inhibits the antioxidative activity of MSP23. This result suggests that one type of oxidant damage caused by hemin to cells is due to inactivation of the antioxidative protein, MSP23.