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Biomedical subjects

V Robert

Publications and source records attributed to V Robert.

At least 91 records · Page 5Linked to original sources
PubMed1997

Differential regulation of matrix metalloproteinases associated with aging and hypertension in the rat heart.

We compared two models of cardiac fibrosis in which collagen synthesis is controlled at different levels. Regulation is pretranslational in aldosterone-salt-induced hypertension in young rats and posttranslational in 24-month-old rats. However, little is known about the role of matrix metalloproteinases (MMP) in fibrosis development. Ventricular MMP activities were studied by zymography, and MMP-2 and MMP-1 mRNA levels were determined using slot-blot and ribonuclease protection assay, respectively. After 1 month of aldosterone-salt treatment, proMMP-2, MMP-2, and proMMP-1 collagenolytic activities and their gene expression were unchanged compared with sham-operated rats. After 2 months, total MMP-2 activity was increased by 40% with parallel stimulation of its gene expression. These changes were localized by in situ zymography within the media of coronary vessels. These results suggest that MMP play a prominent role in vascular remodeling during the first steps of hypertension. During aging, however, there were 40% and 45% decreases in MMP-2 and proMMP-1 activity, respectively, with a corresponding down-regulation of MMP-2 mRNA. These observations suggest that depression of the degradative pathway is partly responsible for age-associated fibrosis. Thus, MMP have differing involvements in the cardiac remodeling associated with hypertension or aging.

Aging↗
PubMed1996

Sodium nitroprusside inhibits proliferation and putrescine synthesis in human colon carcinoma cells.

In human colon carcinoma HT-29 Glc(-/+) cells, L-arginine is the common precursor of polyamines which are absolutely necessary for cellular proliferation and nitric oxide (NO) with reported anti-proliferative activity. The aim of the present work was to test the effect of the NO donor sodium nitroprusside (SNP) on polyamine synthesis and cellular growth in HT-29 cells. SNP in the micromolar range inhibits cellular putrescine synthesis and this effect is greatly reversed by haemoglobin, supporting the view that the effect of SNP is related to the generation of NO. This corresponds to the inhibition by SNP of ornithine decarboxylase activity. Furthermore, SNP inhibits cellular proliferation. The effect of SNP is reversed by haemoglobin after 2 days of treatment but not after 4 days. Although no acute toxic effect of SNP was detected after 90 min incubation, it greatly enhanced the cellular death rate after several days in culture as estimated by the LDH leakage test. In conclusion, our data raise the possibility of an inhibitory interrelationship between NO and polyamine metabolic pathways. NO induced inhibition of putrescine synthesis and growth in HT-29 cells is discussed from a causal perspective.

Cell Death↗
PubMed1996

Effect of the sickle cell trait status of gametocyte carriers of Plasmodium falciparum on infectivity to anophelines.

Insect-reared Anopheles gambiae were experimentally fed with the blood of naturally infected human volunteers carrying gametocytes of Plasmodium falciparum. Infection of at least one mosquito was successful in 86 experiments. For these gametocyte carriers, the hemoglobin types studied were AA (normal, n = 77), AS (heterozygous sickle cell, n = 8), and SS (homozygous sickle cell, n = 1). The mean of the percentages of infected mosquitoes by gametocyte carriers of AS hemoglobin was almost double that of carriers of AA: 30.4% versus 17.5%. The genetic protection in humans conferred by the beta(s) gene in its heterozygous form seems to be associated with an increasing effect on P. falciparum transmission from humans to mosquitoes. The epidemiologic and evolutionary aspects of this finding are discussed.

Adult↗
PubMed1996

Short report: gametocytes, chloroquine pressure, and the relative parasite survival advantage of resistant strains of falciparum malaria in west Africa.

Patients with Plasmodium falciparum infections were selected with an in vivo chloroquine sensitivity assay. Fourteen days after treatment, the gametocytes were studied in relation to asexual parasite responses classified as drug-sensitive or showing RI or RII resistance. Gametocyte prevalence and density appeared significantly higher in RII than RI strains and higher in RI than in sensitive strains. This finding on gametocyte variation in vivo may explain why the RII type of chloroquine resistance has became more prevalent than RI everywhere in tropical Africa in the short time since its emergence. The biological and epidemiologic advantage of chloroquine-resistant malaria mediated through gametocytes is discussed in the context of the present drug pressure in Africa.

Adolescent↗
PubMed1995

Metabolism of L-arginine through polyamine and nitric oxide synthase pathways in proliferative or differentiated human colon carcinoma cells.

HT-29 Glc-/+ cells originate from a human colon adenocarcinoma. These cells have been selected in a glucose-free culture medium and switched back in a glucose-containing medium. In this condition, they can spontaneously differentiate after confluency in enterocyte-like cells according to the activity of the brush-border associated hydrolase dipeptidyl peptidase IV. Since L-arginine can generate polyamines which are necessary for cellular proliferation and also differentiation, and nitric oxide with reported anti-proliferative property, the metabolism of this amino acid was examined in proliferative and differentiated isolated HT-29 cells. Proliferative HT-29 cells were characterized by micromolar intracellular concentration of putrescine and millimolar concentration of spermidine and spermine. In these cells, L-arginine is converted to L-ornithine and putrescine and to a minor part to nitric oxide and L-citrulline. Putrescine was taken up by HT-29 cells, leading to the production of a modest amount of spermidine. The diamine was slightly incorporated into cellular proteins and largely released in the incubation medium. The proliferative HT-29 cells take up spermidine and spermine but do not catabolize these polyamines and slightly released spermidine. Differentiation of HT-29 cells is not associated with change in intracellular polyamine content but is paralleled by an almost complete extinction of de novo synthesis of putrescine (due to a dramatic decrease of ornithine decarboxylase activity) and by a reduced release capacity of putrescine. In contrast, putrescine net uptake and incorporation into cellular proteins remained unchanged after differentiation. Furthermore, spermidine and spermine metabolism as well as the circulation of L-arginine in the nitric oxide synthase pathway were also not modified after differentiation. In conclusion, putrescine is the L-arginine-derived molecule, the metabolism of which is specifically and markedly modified when HT-29 cells move from proliferative to differentiated state.

Adenocarcinoma↗
PubMed1995

Accumulation of fetal fibronectin mRNAs after balloon denudation of rabbit arteries.

BACKGROUND: Fibronectin (FN), a component of the extracellular matrix, influences cellular migration and differentiation. It is a prominent component of the extracellular matrix of normal arteries and is thought to play an important role in the pathogenesis of restenosis after angioplasty. FN exists in multiple forms that arise from a single RNA transcript that can be alternatively spliced. EIIIA- and EIIIB-containing FN mRNAs predominate in the embryo, whereas in the adult, most of the normal tissue FN lacks these domains. Since few data were available concerning pattern of expression of the different alternatively spliced forms of FN mRNA in arteries after endoluminal injury, we analyzed the expression of EIIIA and EIIIB FN isoforms at different times after experimental angioplasty. METHODS AND RESULTS: The spatial and temporal alterations in FN expression were studied in an in vivo model of endothelial denudation in the rabbit aorta and iliac artery by a combination of immunochemistry and in situ hybridization methods. Alternatively spliced forms of FN EIIIA and EIIIB were detected in the media and the adventitia of both types of vessels 24 to 48 hours after injury. Two weeks after injury, EIIIA and EIIIB mRNAs were found to accumulate within the luminal layers of the neointima. The cellular form of FN protein was not found until 2 weeks after the injury and accumulated in the inner part of the neointima. CONCLUSIONS: These data demonstrate that FN upregulation is an early and long-lasting process after arterial injury. These results suggest that the induction of the embryonic FN isoforms may be involved in the restenotic process that follows balloon denudation of arteries.

Animals↗
PubMed1995

Transglutaminase activity in enterocytes isolated from pig jejunum.

Polyamines appear to be involved in the turnover, growth and maintenance of intestinal mucosa integrity. Since polyamines could act -in part at least- through their incorporation into cellular proteins as catalyzed by transglutaminase, we have measured this enzyme activity in villus enterocytes isolated from pig jejunum and in homogenate derived from isolated cells. A part of putrescine, spermidine and spermine taken up by enterocytes is incorporated in TCA precipitable material derived from cells and this corresponds to the presence of transglutaminase activity in cellular homogenates. This activity which is time and substrate concentration dependent is strongly inhibited by the transglutaminase inhibitor glycine methyl ester. The capacity for de novo production of polyamines from L-arginine or L-glutamine is very limited in isolated enterocytes, and this coincided with a very low ornithine decarboxylase activity when compared with polyamine cell content. It is concluded that the main source of polyamines for pig enterocytes is extracellular and that exogenous polyamines are substrates for enterocyte transglutaminase.

Animals↗
PubMed1995

Biological determinants of aldosterone-induced cardiac fibrosis in rats.

To determine the events leading to cardiac fibrosis in aldosterone-salt hypertensive rats, we studied protein and mRNA accumulation of procollagens I and III for 60 days. After 3 and 7 days of treatment systolic pressure was normal, and no histological or biochemical changes were seen in rat hearts. At day 15 arterial pressure was raised (+40%) and left ventricular hypertrophy was +15%. Cardiac examination after hemalun-eosin staining and immunolabeling with anticollagen I and III antibodies showed no structural alterations, but an 83% increase in right ventricular type III procollagen mRNA levels was found. At 30 and 60 days we found progressive cardiac fibrosis, with inflammatory cells, myocyte necrosis, and elevation of both types I and III procollagen mRNA levels in both ventricles. To determine whether aldosterone had effects on Na,K-ATPase that might lead to ionic disturbances and induce myocyte necrosis, we studied the major cardiac Na,K-ATPase isoform genes. Although Na,K-ATPase alpha 1- and beta 1-subunit mRNA levels were elevated in kidney at day 1, neither of these cardiac transcripts nor the specific alpha 2 isoform was altered between 1 and 15 days. These results show that accumulation of procollagen mRNAs occurs before collagen deposition. Cardiac alterations are late and not preceded by changes in Na,K-ATPase cardiac gene expression, precluding a direct modulation of cardiac collagen synthesis and Na,K-ATPase by aldosterone.

Aldosterone↗
PubMed1995

Detection of falciparum malarial forms in naturally infected anophelines in Cameroon using a fluorescent anti-25-kD monoclonal antibody.

Anopheles gambiae s.s. and An. funestus were sampled in houses located in a Plasmodium falciparum-holoendemic site in southern Cameroon. The midguts of female mosquitoes in half-gravid or gravid stages of blood digestion were incubated with a fluorescent monoclonal antibody directed against the P. falciparum zygote/ookinete surface protein Pfs25 and examined using a fluorescent light microscope. Malarial forms were detected in 11.6% of the half-gravid mosquitoes and in 0.0% of the gravid ones (P = 0.012). No difference in infections or the occurrence of malarial forms between An. gambiae and An. funestus was observed. Overall, 127 malarial forms were counted and distributed among round forms, retorts, and ookinetes in 77.2%, 9.5%, and 13.4%, respectively. Round forms include macrogametes, activating microgametocytes, and zygotes. The mean number of malarial forms per infected midgut was 2.16 and the maximum number observed was 13. In four anophelines, round forms, retorts, and ookinetes were simultaneously observed. Sporozoite rates were 5.7% for An. gambiae and 3.8% for An. funestus. In the human population, the gametocyte index for P. falciparum was 38% with a mean density of 1.11 gametocytes per microliter of blood. Differences concerning malarial forms in mosquito midguts were observed between houses (range percentage = 4.7--21.3%; mean range of forms per positive anopheline = 1.1--3.1). In each house, relationships existed between infected vectors and the gametocyte reservoir of their inhabitants. The role in transmission of people with very low gametocytemia, approximately one per microliter, as a reservoir of falciparum malaria in highly endemic areas, is emphasized.

Adolescent↗
PubMed1994

Expression of fibronectin during rat fetal and postnatal development: an in situ hybridisation and immunohistochemical study.

OBJECTIVE: Fibronectin is a protein of the extracellular matrix with numerous binding sites to the other elements of the matrix and to the cells. The aim of this study was to determine the relative importance of fibronectin isoform expression (FN-EIIIA, FN-EIIIB) during fetal and postnatal development of the rat heart. METHODS: In situ hybridisation and immunolabelling approaches were used to describe the cellular synthesis of fibronectin and its distribution throughout the rat heart from 11 d postconception until adulthood. The distribution of fibronectin was compared to that of laminin and of alpha type III procollagen. RESULTS: The accumulation and pattern of distribution of the major fibronectin mRNA isoforms were identical, that is, there was a progressive decrease in their accumulation as a function of time after 11 d postconception, resulting in a complete absence in the adult. The distribution of fibronectin and procollagen type III mRNAs were, however, quite distinct. At the protein level the time course of synthesis and secretion of the locally synthesised fibronectin (c-FN) did not follow fibronectin mRNA expression, the accumulation of the protein being rather poor, except just before birth, where it was found mainly in the coronary vessels. CONCLUSIONS: During the development of the fetal rat heart fibronectin gene transcription is active and progressively decreases with age, whereas the translation of the mRNAs into their corresponding proteins is always relatively poor. If fibronectin is involved in fetal and postnatal morphogenesis of the rat myocardium, it is the plasma form (p-FN) that is most probably involved in the process of growth and differentiation of the rat heart.

Animals↗
PubMed1994

Nonsynchronous changes in myocardial collagen mRNA and protein during aging: effect of DOCA-salt hypertension.

Myocardial fibrosis has been investigated in 3-, 16-, and 24-mo-old normal rats and also in 24-mo-old rats subjected to deoxycorticosterone acetate (DOCA)-salt treatment-induced-hypertension. Collagen content was assessed both histologically and by hydroxyproline assay. Type I and III procollagen mRNA levels were quantitated by Slot Blot analyses. Aging is associated with fibrosis as shown both biochemically (hydroxyproline concentration in 3-, 16-, and 24-mo-old rats was 0.70 +/- 0.05, 0.92 +/- 0.07, and 1.57 +/- 0.13 mg/g of left ventricle, respectively, P < 0.05 and P < 0.0001 vs. 3 mo) and histologically. By contrast, type I procollagen mRNA levels decreased during aging (from -63%, P < 0.001 in 16-mo-old rats and -51%, P < 0.01 in 24-mo-old rats vs. 3-mo-old rats) as well as type III procollagen mRNA levels. DOCA-salt treatment in 24-mo-old rats had no effect on either the degree of fibrosis or the mRNA levels. We conclude that nonsynchronous changes in myocardial collagen mRNA and protein occur during aging, indicating translational and/or posttranslational mechanisms in collagen regulation. Hypertension during senescence did not modify collagen deposition at either the protein or mRNA levels.

Aging↗
PubMed1994

Increased cardiac types I and III collagen mRNAs in aldosterone-salt hypertension.

Cardiac fibrosis is one of the deleterious events accompanying hypertension that may be implicated in the progression toward heart failure. To determine the mechanisms involved in fibrosis and the role of hemodynamic versus humoral factors, we studied the expression of genes involved in hypertrophy and fibrosis in the heart of rats treated with aldosterone for 2 months with addition of 1% NaCl and 0.3% KCl in water. This treatment induced arterial hypertension, a moderate left ventricular hypertrophy, and a decrease in plasma thyroxine. Equatorial sections of hearts from treated rats showed numerous foci of proliferating nonmuscular cells and a biventricular fibrosis. Computerized videodensitometry demonstrated an increase of collagen volume fraction by 152% and 146% and of the ratio of the perivascular collagen area and vascular area by 86% and 167% in left and right ventricles, respectively. As measured by slot blot, this cardiac fibrosis was accompanied by an increase in alpha 1-I procollagen mRNA by 75% and 160% (P < .01) and in alpha 1-III mRNA by 76% and 319% (P < .01) in left and right ventricles, respectively. Atrial natriuretic peptide mRNA was induced only in the hypertrophied left ventricle. We conclude that fibrosis is occurring and involves pretranslational regulation of collagen synthesis. Whereas hypertrophy and atrial natriuretic peptide mRNA increase are restricted to the left ventricle, fibrosis is initiated in both ventricles, supporting the hypothesis that this cardiac response is independent of hemodynamic factors.

Aldosterone↗
PubMed1994

Early sporogonic development in local vectors of Plasmodium falciparum in rural Cameroon.

In ongoing studies on experimental transmission of Plasmodium falciparum in the city of Yaounde gametocyte carriers are daily being identified among dispensary patients with malaria-like complaints. This species comprises 93% of all parasitemias and because of the selection criteria most patients have it as a recent infection. 17% of all P. falciparum-positives carry detectable gametocytes with little difference between youngsters and adults. Blood of adult carriers is taken and infection of Anopheles gambiae mosquitoes is attempted by membrane feeding; the establishment of infection is judged by the presence of oocysts.

Animals↗
PubMed1993

Role of mechanical and hormonal factors in cardiac remodeling and the biologic limits of myocardial adaptation.

Patients with chronic congestive heart failure manifest > or = 1 of the following abnormalities: diastolic dysfunction, systolic dysfunction, and arrhythmias. Diastolic dysfunction, one of the first symptoms to occur during hypertensive cardiopathy, depends on both active relaxation of the cardiac muscle and passive ventricular compliance. The ability of the ventricles to relax depends on normal calcium metabolism and adenosine triphosphate concentration. Ability to extrude intracellular calcium is depressed in the hypertrophied, overloaded heart as compared with the normal myocardium. Myocardial fibrosis is the major cause of increased diastolic ventricular stiffness. Left ventricular (LV) hypertrophy and myocardial fibrosis also greatly increase the likelihood of ventricular arrhythmias, in particular by prolonging the QRS interval and facilitating the occurrence of reentry arrhythmias. Findings in animal studies have indicated that such fibrosis, which involves excessive collagen deposition, is independent of LV hypertrophy and that LV hypertrophy does not necessarily result in myocardial fibrosis. Instead, the development of myocardial fibrosis is sensitive to circulating levels of both angiotensin II and aldosterone, and the fibrotic response to each of these substances is independent. The aldosterone antagonist spironolactone prevents myocardial fibrosis in several animal models, thus confirming the importance of aldosterone in the genesis of excessive collagen deposition.

Adaptation, Physiological↗