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J Kovár

Publications and source records attributed to J Kovár.

At least 19 recordsLinked to original sources
PubMed2006

Sensitivity of cells to apoptosis induced by iron deprivation can be reversibly changed by iron availability.

We tested the effect of iron deprivation on cell death induction in human Raji cells pre-adapted to differing availability of extracellular iron. Iron deprivation was achieved by incubation in a defined iron-free medium. Original Raji cells have previously been adapted to long-term culture in a defined medium with 5 microg/ml of iron-saturated human transferrin as a source of iron. Raji/lowFe cells were derived from original Raji cells by subsequent adaptation to culture in the medium with 50 microm ferric citrate as a source of iron. Raji/lowFe-re cells were derived from Raji/lowFe cells by re-adaptation to the transferrin-containing (5 microg/ml) medium. Iron deprivation induced cell death in both Raji cells and Raji/lowFe-re cells; that is, cells pre-adapted to a near optimum source of extracellular iron (5 microg/ml of transferrin). However, Raji/lowFe cells preadapted to a limited source of extracellular iron (50 microm ferric citrate) became resistant to the induction of cell death by iron deprivation. We demonstrated that cell death induction by iron deprivation in Raji cells correlates with the activation of executioner caspase-3 and the cleavage of caspase-3 substrate, poly-ADP ribose polymerase. Two other executioner caspases, caspase-7 and caspase-6, were not activated. Taken together, we suggest that in human Raji cells, iron deprivation induces apoptotic cell death related to caspase-3 activation. However, the sensitivity of the cells to death induction by iron deprivation can be reversibly changed by extracellular iron availability. The cells pre-adapted to a limited source of extracellular iron became resistant.

Apoptosis↗
PubMed2005

Iron deprivation induces apoptosis via mitochondrial changes related to Bax translocation.

In order to elucidate the mechanisms involved in apoptosis induction by iron deprivation, we compared cells sensitive (38C13) and resistant (EL4) to apoptosis induced by iron deprivation. Iron deprivation was achieved by incubation in a defined iron-free medium. We detected the activation of caspase-3 as well as the activation of caspase-9 in sensitive cells but not in resistant cells under iron deprivation. Iron deprivation led to the release of cytochrome c from mitochondria into the cytosol only in sensitive cells but it did not affect the cytosolic localization of Apaf-1 in both sensitive and resistant cells. The mitochondrial membrane potential (Deltapsi(m)) was dissipated within 24 h in sensitive cells due to iron deprivation. The antiapoptotic Bcl-2 protein was found to be associated with mitochondria in both sensitive and resistant cells and the association did not change under iron deprivation. On the other hand, under iron deprivation we detected translocation of the proapoptotic Bax protein from the cytosol to mitochondria in sensitive cells but not in resistant cells. Taken together, we suggest that iron deprivation induces apoptosis via mitochondrial changes concerning proapoptotic Bax translocation to mitochondria, collapse of the mitochondrial membrane potential, release of cytochrome c from mitochondria, and activation of caspase-9 and caspase-3.

Animals↗
PubMed2005

[Tumorous diseases in patients with the testicular feminization syndrome ("androgen insensitivity" syndrome)--description of two cases].

OBJECTIVE: To describe tumors occurring in two cases of testicular feminization syndrome. SUBJECT: Case report. SETTING: Dpt. of Special Diagnostics SPAU, University Hospital Plzen. SUBJECT AND METHOD: Two cases of testicular feminization syndrome were selected from four cases in our registry. Patients were 45 and 84-year-old Caucasian "females". Resected material was fixed in formaldehyde, routinely processed and stained with hematoxiline-eosin, inhibin, cytokeratines 20, placentar alkaline phosphatase, CD 99, Melan A, hCG. Sertoli cell adenoma was diagnosed in both patients. Older patient had in addition unclassified sex cord tumor of Leydig cell type. The number of sex chromosomes was examined using FISH analysis in both patients. CONCLUSION: Patients with testicular feminization syndrome are frequently affected by benign or malignant tumors in the cryptorchid testes. We documented two benign Sertoli cell adenomas and one sex cord tumor of uncertain biological behavior in our patients. The testes should be removed after puberty with subsequent estrogen therapy in patients with testicular feminization syndrome.

Aged↗
PubMed2004

Hyperglycemia downregulates total lipoprotein lipase activity in humans.

To address the question whether an increase in insulinemia and/or glycemia affects the total activity of lipoprotein lipase (LPL) in circulation, the enzyme activity was measured after periods of hyperinsulinemia (HI), hyperglycemia (HG), and combined hyperinsulinemia and hyperglycemia (HIHG) induced by euglycemic hyperglycemic clamp, hyperglycemic clamp with the infusion of somatostatin to inhibit endogenous insulin secretion, and hyperglycemic clamp, respectively. The results obtained were compared to those after saline infusion (C). Twelve healthy normolipidemic and non-obese men with normal glucose tolerance were included in the study. At the end of each clamp study, LPL activity was determined first in vivo using an intravenous fat tolerance test and then in vitro in postheparin plasma. Whereas isolated HI had no effect on LPL activity in postheparin plasma, both HG and HIHG reduced LPL activity to 60 % and 56 % of that observed after saline infusion. Similarly, the k2 rate constant determined in intravenous fat tolerance test was reduced to 95 %, 84 %, and 54 % after periods of HI, HG, and HIHG, respectively. The activity of hepatic lipase, another lipase involved in lipoprotein metabolism, was not affected by hyperinsulinemia and/or hyperglycemia. In conclusion, our data suggest that hyperglycemia per se can downregulate the total LPL activity in circulation.

Adult↗
PubMed2004

The A-204C polymorphism in the cholesterol 7alpha-hydroxylase (CYP7A1) gene determines the cholesterolemia responsiveness to a high-fat diet.

The aim of the study was to ascertain whether the A-204C polymorphism in the cholesterol 7 -hydroxylase (CYP7A1) gene plays any role in determining LDL-cholesterol (LDL-C) concentration responsiveness to a high-fat diet. The concentrations of total cholesterol and LDL-cholesterol were measured in eleven healthy men (age: 30.9+/-3.2 years; BMI: 24.9+/-2.7 kg/m(2);;) who were homozygous for either the -204A or -204C allele, after 3 weeks on a low-fat (LF) diet and 3 weeks on a high-fat (HF) diet. During both dietary regimens, the isocaloric amount of food was provided to volunteers; LF diet contained 22 % of energy as a fat and 2.2 mg of cholesterol/kg of body weight a day, HF diet 40 % of fat and 9.7 mg of cholesterol/kg of body weight a day. In six subjects homozygous for the -204C allele, the concentrations of cholesterol and LDL-cholesterol were significantly higher on HF than on LF diet (cholesterol: 4.62 vs. 4.00 mmol/l, p<0.05; LDL-C: 2.15 vs. 1.63 mmol/l, p<0.01, respectively); no significant change was observed in five subjects homozygous for the -204A allele. There were no other differences in lipid and lipoprotein-lipid concentrations. Therefore, the polymorphism in the cholesterol 7alpha-hydroxylase promotor region seems to be involved in the determination of cholesterol and LDL-C responsiveness to a dietary fat challenge.

Adult↗
PubMed2004

Effect of diets on lipoprotein concentrations in heterozygous apolipoprotein E-deficient mice.

Loss of apolipoprotein E synthesis causes increased serum cholesterol concentrations and the sensitivity to high-fat diet in mice. We analyzed the changes in lipoprotein and hepatic structures in apolipoprotein E-deficient mice kept on control diet and cholesterol diets. Basal cholesterolemia of heterozygous (+/-) mice (2.2+/-0.28 mmol/l) was the same compared to wild-type (+/+) mice (2.3+/-0.15 mmol/l), but was lower compared to homozygous (-/-) mice (10.3+/-1.40 mmol/l). In +/- mice, cholesterolemia rose to 3.2 mmol/l on cholesterol diet and to 9 mmol/l on cholate diet, to 3 mmol/l and 3.6 mmol/l in +/+ mice, and to 23.4 mmol/l and 70.5 mmol/l in -/- mice, respectively. While the ratio of cholesterol/triglyceride concentrations in VLDL, IDL and LDL fractions was not increased in +/- mice and +/+ mice, it was increased in -/- mice on control diet. On the cholesterol diet, this ratio rose and was dramatically increased by cholate diet in all groups of mice. Even though cholate supplementation increased cholesterol concentration, it led to substantial toxic changes in hepatic morphology of all animals. In conclusion, one functional apo E allele in +/- mice is effective in keeping serum cholesterol concentrations in normal range on a control diet, but not on the cholesterol and cholate diets.

Administration, Oral↗
PubMed2003

Iron deprivation induces apoptosis independently of p53 in human and murine tumour cells.

Iron deprivation induces apoptosis in some sensitive cultured tumour cells, while other cells are resistant. In order to elucidate the mechanisms involved in apoptosis induction by iron deprivation, we studied the expression of p53 and the expression of selected p53-regulated genes. To discriminate between changes coupled only with iron deprivation and changes involved in apoptosis induction by iron deprivation, we compared the expression of the genes in sensitive (human Raji, mouse 38C13) versus resistant (human HeLa, mouse EL4) cells under iron deprivation. Iron deprivation was achieved by incubation in a defined iron-free medium. The level of p53 mRNA decreased significantly under iron deprivation in sensitive cells, but it did not change in resistant cells. On the contrary, the level of the p53 protein under iron deprivation was slightly increased in sensitive cells while it was not changed in resistant cells. The activity of p53 was assessed by the expression of selected p53-regulated targets, i.e. p21(WAF1/CIP1) gene, mdm2, bcl-2 and bax. We did not detect any relevant change in mRNA levels as well as in protein levels of these genes under iron deprivation with the exception of p21(WAF1/CIP1). We detected a significant increase in the level of p21 mRNA in both (sensitive and resistant) mouse cell lines tested, however, we did not find any change in both (sensitive and resistant) human cell lines. Moreover, the p21(WAF1/CIP1) protein was accumulated in mouse-sensitive 38C13 cells under iron deprivation while all other cell lines tested, including human-sensitive cell line Raji, did not show any accumulation of p21(WAF1/CIP1) protein. It seems that the p21(WAF1/CIP1) mRNA, as well as protein accumulation, is not specifically coupled with apoptosis induction by iron deprivation and that it is rather cell-line specific. Taken together, we suggest that iron deprivation induces apoptosis at least in some cell types independently of the p53 pathway.

Animals↗
PubMed2002

Apoptosis induction in lymphoma cells: thiol deprivation versus thiol excess.

We studied the effects of thiol availability on apoptosis induction in B-cell lymphoma 38C13, T-cell lymphoma EL4, and also other cells. Compounds with a free SH group are required for survival and growth of 38C13 cells but not of EL4 cells. Thiol deprivation (2-mercaptoethanol concentrations about 0.3 microM and lower) induced apoptosis in 38C13 cells. On the other hand, thiol excess (2-mercaptoethanol concentrations higher than 300 microM) induced apoptosis in 38C13 cells and EL4 cells as well as in other cells (e.g. Raji, HeLa). L-cystine and non-thiol antioxidant ascorbic acid were unable to support survival of 38C13 cells. Ascorbic acid induced cell death at concentrations higher than 600 microM. Thiol cross-linking compound diamide (100 microM and higher) abrogated the survival-supporting effect of 2-mercaptoethanol (50 microM). Apoptosis induction by thiol deprivation and by thiol excess was not directly related to a specific significant change in the p53 level or p53 activation. Apoptosis induction by thiol excess was associated with a certain decrease in the Bcl-2 level while the Bax level did not change. We conclude that both thiol deprivation and thiol excess can induce apoptosis in lymphoma cells. Apoptosis induction by thiol deprivation is specifically related to the presence of a free SH group. However, apoptosis induction by thiol excess does not seem to be specifically related to the presence of a free SH group. It probably results from the excess of a reductant. Apoptotic control protein p53 does not seem to play a significant role in apoptosis induction either by thiol deprivation or by thiol excess.

Animals↗
PubMed2002

The effect of an acute fat load on endothelial function after different dietary regimens in young healthy volunteers.

Attention has recently been focused on endothelial function after a single high-fat meal, i.e. on the anticipated direct atherogenic effect of triglyceride-rich lipoproteins. Our study was designed to investigate the effect of a low-fat diet given for four weeks followed by a high-fat diet for another four weeks. At the end of each dietary period, a noninvasive ultrasound investigation of endothelial function of the brachial artery was performed along with laboratory tests. Endothelial function was measured immediately before the dietary load and after three and six hours in 11 healthy volunteers. The results were expressed as percentage of the changes in artery diameter at rest and during hyperemia; the data were processed using computer technology. When compared to the low-fat regimen, the total cholesterol content rose after the high-fat diet from 4.28 mmol/l to 5.15 mmol/l (p<0.05) in the whole group of volunteers. There was no difference between both dietary regimens in baseline triglycerides. The brachial artery dilatation under basal conditions was 5.26+/-2.88 mm after the high-fat diet compared with the value of 3.13+/-3.01 mm (p<0.05) after the low-fat diet. When measured individually endothelial function in the whole group of volunteers in the course of the day, the degree of arterial dilatation after one month on low-fat diet was 3.13+/-3.0%, 3.88+/-2.5% and 5.23+/-3.3% at single measurement. When comparing arterial dilatation at two closest measurements, a non-significant trend, p>0.05 was seen in either case. The following values were obtained after one month on the high-fat diet: 5.26+/-2.9%, 4.47+/-1.7%, and 6.2+/-3.6%; again showing a non-significant trend of p>0.05. In this study, a single high-fat meal at the different dietary regimen did not significantly influence the vasoreactivity of the brachial artery in young volunteers.

Adult↗
PubMed2001

Additive stimulatory effect of extracellular calcium and potassium on non-transferrin ferric iron uptake by HeLa and K562 cells.

We studied the effects of Ca(2+) and K(+) on non-transferrin iron uptake from ferric citrate complex by HeLa and K562 cells. Uptake experiments in Na-HEPES buffer (137 mM NaCl, 4 mM KCl) showed that extracellular Ca(2+) stimulated the iron uptake. The rate of iron uptake in 4 mM Ca(2+) was about 3-5 times higher than without Ca(2+). The iron uptake in K-HEPES buffer (68 mM NaCl, 75 mM KCl) with a high K(+) level was transiently stimulated during the first 10 min. The rate of iron uptake for 0.4 mM Ca(2+) was approximately 3 times higher in K-HEPES buffer than in Na-HEPES buffer. The calcium channel blockers verapamil (50 microM) and nifedipine (5 microM) had no effect on the uptake either in control Na-HEPES buffer or after K(+) stimulation in K-HEPES buffer. The sodium channel blocker lidocaine (50 microM) also had no effect on the uptake of iron in Na-HEPES buffer as well as after K(+) stimulation. Furthermore, the iron uptake was not significantly affected when Na(+) in the Na-HEPES and K-HEPES buffers was replaced by isotonic saccharose. We conclude that extracellular calcium per se, and not intracellular calcium or Ca(2+) transport, stimulates ferric iron uptake by both HeLa and K562 cells. A high level of extracellular K(+) also stimulates the uptake, probably via cell membrane depolarization. Na(+) is not involved in these stimulations of iron uptake. The transient K(+) effect and continuous Ca(2+) effect seem to be additive.

Biological Transport↗
PubMed2000

Role of melanotransferrin (p97) in non-transferrin iron uptake by HeLa and K562 cells.

We tested whether melanotransferrin (p97), an iron-binding protein of the plasma membrane, is involved in the transport of non-transferrin iron into human HeLa and K562 cells. The expression of melanotransferrin was detected in HeLa but not in K562 cells. PI-PLC treatment dramatically decreased (to 20% of the original value) p97 expression by HeLa cells. However, the rate of iron uptake from 55Fe-ferric citrate by PI-PLC-treated HeLa cells was comparable or only slightly lower (80-100%) than the rate of iron uptake by untreated cells. PI-PLC treatment had no effect on iron uptake by K562 cells. These findings strongly support the suggestion that melanotransferrin does not play a substantial role in non-transferrin iron uptake by either HeLa or K562 cells.

Antigens, Neoplasm↗
PubMed2000

Sex differences in the response of postprandial lipemia to a change from a low-fat low-cholesterol diet to a high-fat high-cholesterol diet.

To determine whether a short-term change in dietary habits affects postprandial lipemia in men and women in the same way, postprandial triglyceridemia was measured in age- and BMI-matched young healthy men and women after two weeks on the self-selected low-fat low-cholesterol (LF) diet and after another two weeks on the self-selected high-fat high-cholesterol (HF) diet. After a standardized challenge meal (1.4 g fat/kg of body weight), men had higher postprandial triglyceridemia than women on the HF diet but no such difference was observed on the LF diet. The results of this preliminary study suggest that there may be important sex differences in the mechanisms regulating the postprandial lipemia response to different diets, women being able to adapt better to the HF diet with respect to postprandial lipemia.

Adult↗
PubMed1998

Specific binding to plasma membrane is the first step in the uptake of non-transferrin iron by cultured cells.

We studied transport of non-transferrin iron into HeLa cells adapted for growth in defined medium, containing either 5 micrograms/ml of iron-saturated transferrin (HeLa/Tf cells) or 5 microM ferric citrate (HeLa/Fe5 cells) as a source of iron. Employing 55Fe-ferric citrate, iron uptake by intact cells was compared with iron binding to isolated membranes. Uptake characteristics of both HeLa/Tf and HeLa/Fe5 cells seemed to be similar: Km = 14 microM and Vmax = 135 pmol Fe/min/10(5) cells for HeLa/Tf, Km = 22 microM and Vmax = 165 pmol Fe/min/10(5) cells for HeLa/Fe5. Increasing concentrations (0.3-1.2 microM) of 55Fe-ferric citrate, producing levels of free 55Fe which were independent of total Fe under the experimental conditions used, led to increased binding of 55Fe for both HeLa/Tf and HeLa/Fe5 cells (1.08-8.03 nmol Fe/h/10(5) cells). This corresponds with the suggestion that iron was bound in the form of ferric citrate rather than in the form of free iron. Dissociation constants of Fe binding, KD = 0.61 microM for HeLa/Tf and KD = 1.53 microM for HeLa/Fe5, were obtained from competition experiments. We conclude that specific binding sites for ferric citrate are constitutively expressed in plasma membrane and that their expression does not require the induction by the presence of ferric citrate. The uptake of non-transferrin iron is realized in at least two steps. The first step is iron binding to the specific binding sites in plasma membrane. The binding does not represent a limiting step of the uptake.

Binding Sites↗
PubMed1998

Transferrin receptor expression is controlled differently by transferrin-bound and non-transferrin iron in human cells.

We studied the effects of iron supplied as transferrin-bound iron and iron supplied as non-transferrin iron on transferrin receptor expression by human cell lines. Defined conditions of iron supply were represented by (i) 5 microg/ml of iron-saturated transferrin (transferrin medium) and by (ii) 500 microM ferric citrate (ferric citrate medium). Transferrin receptor expression of studied cell lines (HeLa, K562, Jiyoye) grown as long-term cultures in transferrin medium was somewhat higher (up to 137% of the mean fluorescence intensity) than in ferric citrate medium. The receptor expression corresponded with cellular iron regulatory protein (IRP) activity (ratio activated/total), which was also higher in transferrin medium (0.69-0.84) than in ferric citrate medium (0.33-0.60). However, unexpectedly much higher (about 65-135-fold) cellular iron levels were found in ferric citrate medium (13.9-14.9 nmol/10(6) cells) than in transferrin medium (0.11-0.21 nmol/10(6) cells). In contrast to the iron levels, cellular ferritin levels of the cells in ferric citrate medium (38.3-130 ng/10(6) cells) were only about 2-7-fold higher than in transferrin medium (6.8-61.5 ng/10(6) cells). We suggest that iron supplied as non-transferrin iron (ferric citrate) is apparently less available for the control of transferrin receptor expression via IRP activity than iron supplied as transferrin.

Cell Line↗
PubMed1997

The inability of cells to grow in low iron correlates with increasing activity of their iron regulatory protein (IRP).

We studied the factors that determine the differing growth requirements of low-iron-tolerant (LIT) versus high-iron-dependent (HID) cells for extracellular nontransferrin iron. The growth of LIT cells HeLa and THP-1, when transferred from transferrin (5 micrograms/ml) medium into low-iron (5 microM ferric citrate) medium, was not significantly affected while HID cells Jiyoye and K562 showed nearly no growth. HeLa and THP-1 cells, as well as Jiyoye and K562 cells, do not produce transferrin in sufficient amounts to support their growth in low-iron medium. Surprisingly, similar rates of iron uptake in low-iron medium (0.033 and 0.032 nmol Fe/min and 10(6) cells) were found for LIT cells HeLa and HID cells K562. Furthermore, the intracellular iron level (4.64 nmol/10(6) cells) of HeLa cells grown in low-iron medium was much higher than iron levels (0.15 or 0.20 nmol/10(6) cells) of HeLa or K562 cells grown in transferrin medium. We demonstrated that the activity (ratio activated/total) of the iron regulatory protein (IRP) in HID cells Jiyoye and K562 increased more than twofold (from 0.32 to 0.79 and from 0.47 to 1.12, respectively) within 48 h after their transfer into low-iron medium. In the case of LIT cells HeLa and THP-1, IRP activity stayed at similar or slightly decreased levels (0.86-0.73 and 0.58-0.55, respectively). Addition of iron chelator deferoxamine (50 microM, i.e., about half-maximal growth-inhibitory dose) resulted in significantly increased activity of IRP also in HeLa and THP-1 cells. We hypothesize that the relatively higher bioavailability of nontransferrin iron in LIT cells, over that in HID cells, determines the differing responses observed under low-iron conditions.

Biological Transport↗
PubMed1995

Non-transferrin iron uptake by HeLa cells cultured in serum-free media with different iron sources.

HeLa cells cultured in defined serum-free media supplied with iron wither in the form of diferric transferrin (transferrin-dependent cells), ferric citrate at 500 micromol/l (high-iron dependent cells) or ferric citrate at 5 micromol/l (low-iron dependent cells) accumulate iron from ferric citrate in different ways. The uptake rate in transferrin-dependent cells is always much lower in the other two lines. In all three, the uptake rate rises almost linearly with the concentration of iron up to 10 micromol/l. In high-iron dependent cells, the uptake of radiolabelled iron is suppressed by a 100-fold excess of the iron complex, whereas this same excess stimulates iron uptake in the other two lines. The same concentrations of pure citrate completely inhibit iron uptake by all three types of cell. Only high-iron dependent cells take up citrate at measurable and reproducible rates. These rates are independent on the presence of iron, and the uptake is inhibited by an unlabelled surplus. The pH-dependence of iron uptake in high-iron dependent cells is also different from that of the other cells. Low-iron dependent cells transferred to medium containing 500 micromol/l iron show increased uptake rates within 3 to 7 h, and after overnight maintenance in this medium they acquire the uptake characteristics of high-iron dependent cells. The special characteristics of iron uptake by high-iron dependent cells are paralleled by low binding activity of iron-regulatory protein to iron-responsive elements of RNA. We conclude that low-iron dependent cells maintain their iron supply from the culture medium by unspecific uptake of oligomeric complexes, while cells in media with a high content of low-molecular weight iron induce a specific uptake system which might have a protective function.

Biological Transport↗
PubMed1994

Lymphocyte lines under iron-depriving conditions: transferrin receptor expression related to various growth responses.

The relation of expression of cell surface transferrin receptors to growth responses under defined iron-depriving conditions was studied in mouse B-cell line PLV-01, human T-cell line Jurkat, and human B-cell line Raji. Iron chelator deferoxamine at a concentration of 150 microM, which inhibited completely growth of the cell lines cultured in a serum-free transferrin-containing (5 micrograms/ml) medium, stimulated the surface transferrin receptor number to increase to 150-250% within a 24-h incubation period. The increased number (300%) of transferrin receptors on PLV-01 cells was associated with complete growth inhibition of these cells in counterpart serum-free transferrin-free medium. Only a slight increase in transferrin receptor number on Raji cells corresponded with unaffected growth of these cells in the transferrin-free medium. Jurkat cells increased the number of transferrin receptors to 150-200% and decreased the number of cells grown in the transferrin-free medium to about 60%. The data show that, under limited availability of iron, a significant increase of transferrin receptor expression on lymphoid cells was found only when the growth of the cells was inhibited. However, complete inhibition of growth achieved under different iron-depriving conditions is accompanied by different degrees of increase in transferrin receptor number.

Animals↗