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Biomedical subjects

C Caramelo

Publications and source records attributed to C Caramelo.

At least 37 records · Page 2Linked to original sources
PubMed2000

Molecular analysis of hepatitis B virus DNA in serum and peripheral blood mononuclear cells from hepatitis B surface antigen-negative cases.

We have analyzed the molecular bases of the persistence of hepatitis B virus (HBV) DNA in serum and peripheral blood mononuclear cells (PBMC) in the absence of detectable hepatitis B surface antigen (HBsAg) in hemodialysis patients and dialysis-unit staff members who had suffered acute hepatitis B that resolved previously. HBV DNA was found in both compartments by polymerase chain reaction (PCR) using primers of the pre-S/S region. Viral DNA was transcriptionally active in PBMC, because the covalently closed circular (ccc) HBV DNA, the template for the viral RNA transcription, was detected in 47% of the samples. Furthermore, all PBMC had HBV RNA. HBsAg-negative cases had statistically lower levels of HBV DNA in serum and PBMC than a control group of chronic HBsAg carriers. We have also studied the presence of immune complexes and the existence of mutations in the pre-S/S gene to explain the lack of detection of HBsAg in these cases. No serum HBsAg/hepatitis B surface antigen antibody (anti-HBs) immune complexes or mutations in the "a determinant of the S gene were found. However, we have observed that all HBsAg-negative cases were infected by a mixture of the wild-type virus and a deletion mutant in the pre-S1 region. This deletion (amino acids 58-118) affects the S gene promoter, and previous in vitro studies have shown that it produces a reduction of the HBsAg synthesis. In conclusion, this work shows that the lack of detection of HBsAg in the presence of low viral levels of replication may be caused by the existence of viral genomes harboring deletions in the pre-S1 region that affect the S promoter.

Antigen-Antibody Complex↗
PubMed2000

Role of renal medullary inducible nitric oxide synthase in the regulation of arterial pressure.

In the present work, we have examined the effects of selective inhibition of the inducible isoform of nitric oxide synthase (iNOS) in rat medulla by aminoguanidine (AG) on the arterial pressure of Dahl salt sensitive (DS), Dahl salt-resistant (DR) and Sprague Dawley (SD) rats by chronic in vivo hemodynamic experiment, the effect of sodium chloride (NaCl) or NaCl plus AG infusion on urinary nitrate/nitrite (urinary NO3/NO2 UNO(x)), the end product of nitric oxide (NO), excretion, glomerular filtration rate (GFR), effective renal plasma flow (ERPF) and plasma renin activity (PRA). Furthermore, an iNOS activity assay was also made. The results showed that AG infusion significantly augmented the pressor response of DS and SD rats to high NaCl (8%) intake, and decreased GFR, ERPF and PRA of DS rats. In addition, in DS rats, renal medullary interstitial administration of high NaCl significantly elevated the iNOS activity of renal tissue, especially inner medulla and outer medulla, and greatly increased UNO(x) excretion. Therefore, it is concluded that inducible NOS is an important modulator of blood pressure in case of NaCl-induced hypertension.

Animals↗
PubMed1999

Induction of microalbuminuria by l-arginine infusion in healthy individuals: an insight into the mechanisms of proteinuria.

Despite evidence from individuals with diabetes mellitus or reduced renal mass, the actual relationship between protein- or amino acid-induced changes in renal function and urinary albumin excretion (UAE) is largely unknown in subjects without renal disease. In humans, infusions of l-arginine have been used recently in vascular and renal pathophysiological studies. The present study was undertaken to analyze the mechanisms involved in a particular effect; namely, the behavior of UAE during amino acid loading. A prospective interventional protocol was performed on 10 healthy adults by means of an intravenous infusion of l-arginine. The main results show that l-arginine induced a significant increase in UAE from 13.1 +/- 3.8 before to 53.3 +/- 11.1 microgram/min after the infusion (P < 0.005). This increment was simultaneous to an increase in glomerular filtration rate (GFR) and renal plasma flow (RPF). Furthermore, l-arginine markedly increased the urinary excretion of beta2-microglobulin. UAE correlated significantly with GFR (r = 0. 738; P = 0.014) and RPF (r = 0.942; P < 0.0001), but not with urinary beta2-microglobulin (r = 0.05; P = not significant). Furthermore, marked differences (P = 0.001) were found between the percentage of increase in UAE (306.8% +/- 163.2%) with respect to either albumin filtered load (FLAlb; 57.9% +/- 16.3%) and beta2-microglobulin excretion (1,088.5% +/- 424.6%). No changes were found in vehicle-infused individuals. In conclusion, the present study shows, in controlled conditions, that l-arginine infusion induces a relevant increase in UAE in healthy individuals that significantly exceeds that expected from the increase in GFR alone. The intense and simultaneous increment in beta2-microglobulin excretion strongly suggests that the effect of l-arginine on UAE is, in a relevant part, mediated through a blockade in the tubular protein reabsorption pathways. However, the profound differences observed in the changes induced by l-arginine on UAE and beta2-microglobulin excretion and the differences in the correlation of UAE and beta2-microglobulin with respect to GFR suggest that substantial diversity exists in the mechanisms by which l-arginine affects the renal management of albumin and beta2-microglobulin. These findings are relevant for understanding the renal response to l-arginine and protein/amino acid loads.

Adult↗
PubMed1999

Hyperkalemia in patients infected with the human immunodeficiency virus: involvement of a systemic mechanism.

BACKGROUND: The appearance of hyperkalemia has been described in human immunodeficiency virus (HIV)-positive patients treated with drugs with amiloride-like properties. Recent in vitro data suggest that individuals infected with HIV have alterations in transcellular K+ transport. METHODS: With the objective of examining the presence of alterations in transmembrane K+ equilibrium in HIV-positive patients, we designed a prospective, interventional study involving 10 HIV-positive individuals and 10 healthy controls, all with normal renal function. An infusion of L-arginine (6%, intravenously, in four 30-min periods at 50, 100, 200, and 300 ml/hr) was administered, and plasma and urine electrolytes, creatinine, pH and osmolality, total and fractional sodium and potassium excretion, transtubular potassium gradient, plasma insulin, renin, aldosterone, and cortisol were measured. RESULTS: A primary disturbance consisting of a significant rise in plasma [K+] induced by L-arginine was detected in only the HIV patients but not in the controls (P < 0.001 between groups). A K+ redistribution origin of the hyperkalemia was supported by its rapid development (within 60 min) and the lack of significant differences between HIV-positive individuals and controls in the amount of K+ excreted in the urine. The fact that the HIV-positive individuals had an inhibited aldosterone response to the increase in plasma K+ suggested a putative mechanism for the deranged K+ response. CONCLUSIONS: These results reveal that HIV-infected individuals have a significant abnormality in systemic K+ equilibrium. This abnormality, which leads to the development of hyperkalemia after the L-arginine challenge, may be related, in part, to a failure in the aldosterone response to hyperkalemia. These results provide a new basis for understanding the pathogenesis of hyperkalemia in HIV individuals, and demonstrate that the risk of HIV-associated hyperkalemia exists even in the absence of amiloride-mimicking drugs or overt hyporeninemic hypoaldosteronism.

Adult↗
PubMed1999

GBV-C/HGV-RNA in serum and peripheral blood mononuclear cells in hemodialysis patients.

BACKGROUND: Hemodialysis patients are at high risk of hepatitis B, C, and G virus infection. The prevalence of GBV-C/HGV-RNA was analyzed in serum and peripheral blood mononuclear cells (PBMCs) from 52 hemodialysis patients. METHODS: GBV-C/HGV-RNA detection was performed by reverse transcription-polymerase chain reaction (RT-PCR) with primers of 5'-noncoding (5'-NC) and NS3 regions of the GBV-C/HGV genome. To increase sensitivity, serum samples were ultracentrifuged prior to the RT-PCR to concentrate the viral particles. The amplified products from 20 serum and 5 peripheral blood mononuclear cells (PBMC) samples were sequenced. RESULTS: GBV-C/HGV-RNA was detected in sera of 9 (17%) and in PBMCs of 30 (58%) patients. After serum ultracentrifugation, GBV-C/HGV-RNA was positive in 20 (95%) of the patients, with GBV-C/HGV-RNA only in PBMCs. Thus, GBV-C/HGV-RNA was detected in serum and PBMCs from 29 (56%) patients, four of whom had antibodies against GBV-C/HGV E2 protein (anti-HGE2); one patient (2%) had GBV-C/HGV-RNA only in PBMCs, but was anti-HGE2 positive. Seven (32%) patients who did not have GBV-C/HGV-RNA were anti-HGE2 positive. The nucleotide sequence homology between serum samples from the patients who were GBV-C/HGV-RNA positive after ultracentrifugation, and paired serum and PBMCs from five of them, ranged from 90 to 96% and from 92 to 98%, respectively. CONCLUSIONS: We found a high prevalence of GBV-C/HGV-RNA in serum and PBMC samples from hemodialysis patients. Whether or not this finding can be extended to other populations requires further study.

Aged↗
PubMed1999

Increased expression of vascular endothelial growth factor in pyogenic granulomas.

The expression of vascular endothelial growth factor (VEGF) was analysed in biopsy samples from patients with pyogenic granuloma. The results disclosed the presence of a strong VEGF signal in pyogenic granulomas, which are constituted by a vast majority of cells of endothelial lineage. A marked positivity was evident in areas of proliferating endothelial cells without vessel lumen formation. In the same respect, staining for VEGF was less marked in the vessels with a well-developed lumen. The fact that VEGF production appears to be limited to endothelial cell precursors or immature endothelial cells prior to the complete development of the vessels, leads to the possibility that VEGF may act as an autocrine factor in circumstances of endothelial cell stimulation.

Adolescent↗
PubMed1998

Expression of constitutive and inducible nitric oxide synthases in the vascular wall of young and aging rats.

Two NO synthase (NOS) isoforms have been described in vessels, an endothelial constitutive NOS (eNOS) and an inducible NOS (iNOS). The purpose of the present study was to examine the endothelium-dependent and endothelium-independent hypotensive response in aging rats, analyzing the ability of their vessels to produce NO. The studies were performed in 2 groups of euvolemic, conscious, male Wistar rats: aging rats (n=20, 18 months old) and young rats (n=20, 5 months old). The hypotensive responses to acetylcholine, bradykinin, and sodium nitroprusside were determined. Furthermore, the expression of the NOS isoforms by Western blot and the eNOS and iNOS activities, defined as Ca2+-dependent and Ca2+-independent conversion of [14C]L-arginine into [14C]L-citrulline, respectively, were also determined. In the aging rats, we found an impaired hypotensive response to acetylcholine and bradykinin (2 NO- and endothelium-dependent hypotensive agents) that was accompanied by a preserved hypotensive response to sodium nitroprusside. Aging rats also demonstrated an enhanced sensitivity response to the pressor effect of the L-arginine antagonist L-Nomega-nitro-L-arginine and a reduced vasoconstrictor response to angiotensin II. The inhibition of NO synthesis normalized the pressor effect of angiotensin II in the aging animals. Nitrite plus nitrate plasma levels were increased in aging rats. Furthermore, cGMP content was also higher in the aging vessels. In the aging aortas, the expression of both eNOS and iNOS isoforms was enhanced. However, in aging rats, the activity of the eNOS isoform was markedly reduced, a finding that was accompanied by the presence of iNOS activity. The vessel wall of aging rats showed an enhanced expression of eNOS and iNOS isoforms. However, eNOS activity was reduced in the aging animals. These findings could explain the impaired endothelium-dependent hypotensive response associated with aging.

Acetylcholine↗
PubMed1998

Role of cytokines in the response to erythropoietin in hemodialysis patients.

BACKGROUND: Cytokines are regulatory factors of erythropoiesis, especially in pathologic conditions. Even though a relevant role for a deranged cytokine production in the pathogenesis of dialysis anemia has been suggested, no data are available that analyze the role of cytokines in the key therapeutic issue of the needs of erythropoietin. The aim of the present study in hemodialysis patients was, therefore, to examine the relationship between the dose of recombinant human erythropoietin (EPO) and the production of cytokines by peripheral blood mononuclear cells (PBMC). METHODS: After the exclusion of subjects with major active causes of EPO resistance, data from 34 hemodialysis patients were available for analysis. Cytokine levels were measured in the supernatants of stimulated [with bacterial lipopolysaccharide and interferon gamma (IFN-gamma)] and unstimulated PBMC. Mean yearly values of hematocrit, hemoglobin, transferrin saturation, ferritin, parathormone (PTH) and aluminum levels and EPO doses (U/kg/week) were calculated. For analysis, the 34 patients were divided according to their cutoff requirements for EPO: patients with requirements of EPO > or = 60 U/kg/week (group A1, 26 subjects) versus EPO < 60 U/kg/week (group B1, 8 subjects) and patients with requirements of EPO > or = 100 U/kg/week (group A2, 18 subjects) versus <100 U/kg/week (group B2, 16 subjects). RESULTS: A significant direct correlation between interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-a) production values and EPO doses was found (P = 0.039 and P = 0.02 respectively). On the other hand, there was a significantly negative correlation between interleukin-12 (IL-12) production values and EPO doses (P = 0.029). Patients of groups A1 and A2 had spontaneously higher tumor necrosis factor-alpha (TNF-alpha) and lower IL-12 and IFNgamma production compared to patients from groups B1 and B2. CONCLUSIONS: Our data disclose a previously undescribed pattern of cytokine alteration that is relevant to determine increased needs of EPO in hemodialysis patients. The present results have potential applicability in designing strategies to improve EPO resistance.

Aged↗
PubMed1998

Role of vascular endothelial growth factor in the response to vessel injury.

In the post-embryonic life, physiological angiogenesis is tightly controlled. Angiogenesis also occurs in pathological circumstances such as tumor vessel proliferation, retinal neovascularization and ischemia. The development of collateral circulation is not only not deleterious, but life saving. Other cases such as neoplastic neovascularization are the basis of the continuous growth of tumors and metastases, and therefore constitute a target of therapeutical efforts. Among a list of molecules able to control angiogenesis, we emphasize the pivotal role of vascular endothelial growth factor (VEGF). VEGF is a potent mitogen for endothelial cells, but is devoid of mitogenic activity for other cell types. VEGF is a polypeptide with four main different isoforms that are remarkably different in terms of solubility and affinity for matrix proteins. VEGF interacts with two endothelial cell-specific tyrosine kinase receptors. The main interest of its study lies in VEGF's role in pathological angiogenic processes, where an increase in the VEGF mRNA expression has been consistently observed. An interesting example is the up-regulation of VEGF's and VEGF receptors' mRNA in a considerable number of human tumors and retina, where they have a critical role in the development of neovascularization. In recent work in our laboratory, we have found further potential interactions of VEGF with pathophysiological mechanisms, namely, the increase in VEGF gene expression under exposure to reactive oxygen species and the positive interaction between VEGF and erythropoietin. VEGF has outstanding possibilities for therapeutic applications aimed at inhibiting or favoring the development of new vessels.

Endothelial Growth Factors↗
PubMed1998

Role of nitric oxide-related mechanisms in renal function in ageing rats.

BACKGROUND: The impaired renal function and vasodilatation that accompany age need to be re-addressed based upon the new knowledge concerning vascular nitric oxide (NO)-dependent systems. The present study examined the effects of age on the NO-related renal response. METHODS: The study was performed in euvolaemic, conscious Wistar rats, aged 5 and 18 months. Renal function and haemodynamic measurements with fluorescent microspheres were employed to assess differences between groups. RESULTS: A first set of experiments showed that ageing rats had a reduced natriuretic and diuretic response to acetylcholine, whereas the response to sodium nitroprusside was preserved. In the same regard, a reduction of the renal functional effects of L-arginine (L-Arg) and L-glycine (L-Gly) was found in the older rats. In the ageing rats, these responses were accompanied by an enhanced effect of the L-Arg competitive analogue, NwNLA, which provoked a marked reduction of renal function. This effect of NwNLA was blocked by the simultaneous administration of a small dose of L-Arg in the ageing but not in the young rats. Systemic haemodynamic studies revealed that in ageing rats, NwNLA reduced renal blood flow and increased renal vascular resistances in a significantly higher proportion than in younger animals. However, flow to other organs, namely, brain, spleen or liver, was affected in a similar manner in both young and old rats. Ultrastructural alterations were found in endothelial cells, which might constitute the anatomical basis for the observed functional derangements. CONCLUSIONS: The present experiments reveal that ageing is accompanied by significant differences in NO-related responses in the kidney which do not appear to affect blood flow to other organs. The response to L-Arg and L-Arg competitive analogues supports the existence of a marked dependency on NO-related mechanisms in the ageing rats, but not of a decreased baseline activity of the NO-dependent pathways.

Acetylcholine↗
PubMed1998

Role of vascular endothelial growth factor on erythropoietin-related endothelial cell proliferation.

The vascular actions of recombinant human erythropoietin (rhEPO) are of particular relevance for fully understanding rhEPO effects. This study examines the mechanisms of action of rhEPO on endothelial cells from bovine aorta (BAEC). First, the studies demonstrated that rhEPO acts on BAEC proliferation as a comitogenic growth factor in the presence of fetal calf serum (FCS). The main experimental findings disclosed that an interaction between rhEPO and vascular endothelial growth factor (VEGF) is instrumental for the growth-promoting action of rhEPO, as shown by the blockade (92.8+/-2.2% inhibition, P < 0.01) of the rhEPO-induced BAEC proliferation by a specific anti-VEGF antibody and by the capability of VEGF for substituting FCS in the induction of rhEPO-related BAEC proliferation (increase in BAEC number in the absence of FCS: 20 U/ml rhEPO alone, 0.3+/-2.8%; 5 x 10(-11) M VEGF alone, 52.9+/-3.1%; 20 U/ml rhEPO + 5 X 10(-11) M VEGF, 117.8+/-6.9%, P < 0.01 between the two agents combined with respect to each agent alone). The existence of a positive interaction between rhEPO and VEGF was further demonstrated by observing an increased cytosolic Ca2+ ([Ca2+]i) mobilization response to VEGF (10(-11)M) in BAEC pretreated or not with 20 U/ml rhEPO (delta[Ca2+]i = 704+/-111 versus 246+/-36 nM, respectively, P < 0.01). To further examine the mechanism of the potentiation of VEGF effect by rhEPO, we analyzed the mRNA expression of the VEGF receptors KDR/flk-1 and flt-1. The results disclosed that BAEC pretreatment with rhEPO upregulated the expression of both KDR/flk-1 and flt-1, therefore providing a structural basis for the aforementioned positive interactions between VEGF and rhEPO. Furthermore, inhibition by genistein suggests that tyrosine phosphorylation was involved in the VEGF receptor upregulation. The mechanisms identified in the present study disclose an interaction at the level of mRNA expression and functional effects between a hormone with predominantly hemopoietic effects, namely, erythropoietin, and an angiogenic factor, namely, VEGF. This relationship between rhEPO and VEGF might be of particular importance in neovascularization processes and in patients receiving rhEPO as a treatment.

Animals↗
PubMed1998

Effects of angiotensin II on endothelial cell growth: role of AT-1 and AT-2 receptors.

Angiotensin II (AngII) is a main mediator in the regulation of vascular tone. Although its effects on vascular smooth muscle cells are well known, data on its role on endothelial biology are still insufficient. The present study examined the effect of endogenous and exogenous AngII on bovine aortic endothelial cells possessing both AT-1 and AT-2 receptors. A DNA synthesis-promoting effect of AT-2 blockade by PD123319 (10(-9) to 10(-7) M) was demonstrated. This effect was transduced through an AT-1-mediated pathway, as shown by using the AT-1 antagonist, losartan. In addition, an AT-1-mediated effect of AngII was demonstrated on bovine aortic endothelial cell proliferation, which occurred despite the absence of AngII-induced Ca2+ transients. In summary, the present study disclosed relevant characteristics of the effect of AngII on endothelial cell growth that have potential pathophysiologic projections, particularly for the use of selective AngII blocking agents.

Angiotensin II↗