Afonso Fernandes

Anti‐ and pro‐oxidant effects of urate in copper‐induced low‐density lipoprotein oxidation

We recently reported that, depending on its concentration, urate is either a pro- or an antioxidant in Cu(2+)-induced low-density lipoprotein (LDL) oxidation. We also previously demonstrated an antioxidant synergy between urate and some flavonoids in the Cu(2+)-induced oxidation of diluted serum. As a result, the effect of the flavonoid quercetin on the Cu(2+)-induced oxidation of isolated LDL has been studied either in the presence or absence of urate. We demonstrate that, like urate, quercetin alone, at low concentration, exhibits a pro-oxidant activity. The pro-oxidant behavior depends on the Cu(2+) concentration but it is not observed at high Cu(2+) concentration. When compared with urate, the switch between the pro- and the antioxidant activities occurs at much lower quercetin concentrations. As for urate, the pro-oxidant character of quercetin is related to its ability to reduce Cu(2+) with the formation of semioxidized quercetin and Cu(+) with an expected yield larger than that obtained with urate owing to a more favorable redox potential. It is also shown that the pro-oxidant activity of urate can be inhibited by quercetin. An electron transfer between quercetin and semioxidized urate leading to the repair of urate could account for this observation as suggested by recently published pulse radiolysis data. It is anticipated that the interactions between quercetin-Cu(2+)-LDL and urate, which are tightly controlled by their respective concentration, determine the balance between the pro- and antioxidant behaviors. Moreover, as already observed with other antioxidants, it is demonstrated that quercetin alone behaves as a pro-oxidant towards preoxidized LDL.

Flavonoids and urate antioxidant interplay in plasma oxidative stress

Flavonoids are naturally occurring plant compounds with antioxidant properties. Their consumption has been associated with the protective effects of certain diets against some of the complications of atherosclerosis. Low‐density lipoprotein (LDL) oxidative modification is currently thought to be a significant event in the atherogenic process. Most of the experiments concerning the inhibition of LDL oxidation used isolated LDL. We used diluted human whole plasma to study the influence of flavonoids on lipid peroxidation (LPO) promoted by copper, and their interaction with uric acid, one of the most important plasma antioxidants. Lipid peroxidation was evaluated by the formation of thiobarbituric acid reactive substances (TBARS) and of free malondialdehyde (MDA). The comparative capability of the assayed flavonoids on copper (II) reduction was tested using the neocuproine colorimetric test. In our assay system, urate disappears and free MDA and TBARS formation increase during the incubation of plasma with copper. Most of the tested flavonoids inhibited copper‐induced LPO. The inhibition of LPO by flavonoids correlated positively with their capability to reduce copper (II). The urate consumption during the incubation of plasma with copper was inhibited by myricetin, quercetin and kaempferol. The inhibition of urate degradation by flavonoids correlated positively with the inhibition of LPO. Urate inhibited the copper‐induced LPO in a concentration‐dependent mode. Luteolin, rutin, catechin, quercetin had an antioxidant synergy with urate. Our results show that some flavonoids could protect endogenous urate from oxidative degradation, and demonstrate an antioxidant synergy between urate and some of the flavonoids.

Analysis of a bone metastasis gene expression signature in patients with bone metastasis from solid tumors

Bone is a major target for metastases in the most frequent solid tumors, which result in severe complications and are a major cause of pain. A bone metastasis gene expression signature was identified using human breast cancer cells in a mouse model. The bone metastasis-related genes encode secretory and cell surface proteins implicated in bone-homing (CXCR4), angiogenesis (CTGF and FGF5), invasion (MMP-1 and ADAMTS1), and osteoclast recruitment (IL11). This signature superimposes on the 70-gene poor prognosis gene expression signature for breast cancer, and only ADAMTS1, CTGF and IL11 were found to be overexpressed in human primary breast cancers with bone relapse. We analyzed the expression of the six bone metastasis-related genes in bone metastases from patients with different types of solid tumors, to assess its relevance in human clinical samples. MMP-1, CXCR4, FGF5 and CTGF were found to be overexpressed in tumor cells of human bone metastases when compared to a human normal epithelial cell line. All the analyzed genes were overexpressed in the tumor cells of breast cancer bone metastases when compared to normal breast tissue. We did not detect any differences between the expression of these genes in bone metastases from breast cancer or from other types of solid tumors. Importantly, there was a significant correlation between the expressions of IL11/CTGF, IL11/ADAMTS1, CTGF/CXCR4, CTGF/ADAMTS1, and MMP-1/ADAMTS1, supporting the cooperative function of these proteins in the bone microenvironment, and the potential functional role of these genes in the establishment of bone metastases in vivo.

Oxidative Stress in Chronic Hepatitis C: The Effect of Interferon Therapy and Correlation with Pathological Features

AIMS To evaluate the oxidative stress parameters before, during and after interferon treatment. PATIENTS/METHODS Twenty patients were treated with interferon a2b 5 MU, three times a week, subcutaneously, for 12 months. Liver biopsy was performed six months before treatment and at the six month follow-up. Chromosomal breakage studies were evaluated by the adjusted clastogenic score (ACS, normal value [nv] 1.1 +/- 2.4%). Plasma malondialdehyde (MDA) was measured according to the Yagi method (nv 6.6 +/- 1.4 nmol/mL) and total thiols using the Ellmans reagent (DTNB) (nv 9.8 +/- 1.3 micromol/g protein). A serum marker of fibrogenesis, the amino-terminal propeptide of Procollagen type III (PIIIP), was quantified by radioimmunoassay (nv 0.37 +/- 0.18 U/L). RESULTS Compared with reference samples, the plasma of patients before treatment showed an increase of ACS (9.2 +/- 3.2%, P<0.001); higher MDA values (12.6 +/- 2.7 nmol/mL, P<0.001) and total plasma sulfhydryl groups (t-SH) were decreased (6.3 +/- 1.1 micromol/g protein, P<0.001). During treatment and at the follow-up, a decrease in ACS was noticed in all patients (P<0.001), but without normalization; a decrease in MDA was seen, with progressive normalization until the end of the follow up only in sustained responders (P<0.003), while an increase of t-SH was seen, with progressive normalization until the end of follow up in all patients (P<0.005). A positive correlation of ACS with grading of inflammation was found (r=0.52, P<0.03) but not with fibrosis staging. In contrast, plasma MDA correlates with fibrosis staging (r=0.51, P<0.03) and with PIIIP (r=0.57, P<0.03) but without grading of inflammation. CONCLUSIONS The present study confirmed the presence of oxidative stress in chronic hepatitis C patients. Interferon promotes a long term inhibition of oxidative stress with concomitant improvement of activity and fibrosis. In the management of chronic hepatitis C, adjuvant therapy with antioxidants could be useful.

CLASTOGENIC FACTORS AS BIOMARKERS OF OXIDATIVE STRESS IN CHRONIC HEPATITIS C.

Background/Aims: Clastogenic factors (CFs) are composed of lipid peroxidation products, cytokines and other oxidants with chromosome-damaging properties. They are regularly observed after radiation exposure and in chronic inflammatory diseases, where they are supposed to be risk factors for carcinogenesis. It appeared of interest to investigate their presence in the plasma of patients with chronic hepatitis C. Methods: CFs are detected by chromosomal breakage studies. They were compared to malondialdehyde (MDA), total plasma thiols (t-SH), alanine aminotransferase (ALT), viral load and histological data. Results: CFs were increased in 19 of 20 patients, 16 had increased MDA levels and 15 had decreased t-SH levels. Mean values were significantly different from the 20 controls (p < 0.001). After the first 3 months of interferon treatment, all three markers showed significant improvement, but were not completely normalized. There was a positive correlation between CFs and necroinflammatory activity (p < 0.03), while MDA was correlated with fibrosis (p < 0.03). Viral load was correlated with necrosis and inflammation (p < 0.05). Conclusion: The presence of CFs in chronic hepatitis C confirms the occurrence of oxidative stress in this disease and could be useful in clinical trials for testing antioxidants. The CF test is a sensitive assay for the detection of oxidative stress and correlates with necroinflammatory activity.

Prognostic significance of AKT/mTOR signaling in advanced neuroendocrine tumors treated with somatostatin analogs

Introduction: Somatostatin analogs (SSAs) are used as part of standard treatment for advanced neuroendocrine tumors (NETs). The mechanisms behind the antiproliferative action of SSAs remain largely unknown, but a connection with the mammalian target of rapamycin (mTOR) signaling pathway has been suggested. Our purpose was to evaluate the activation status of the AKT/mTOR pathway in advanced metastatic NETs and identify biomarkers of response to SSA therapy. Patients and methods: Expression of phosphatase and tensin homolog (PTEN), phosphorylated (p)-AKT(Ser473), and p-S6(Ser240/244) was evaluated using immunohistochemistry in archival paraffin samples from 23 patients. Expression levels were correlated with clinicopathological parameters and progression-free survival under treatment with SSAs. Results: A positive association between p-AKT and p-S6 expression was identified (P = 0.01) and higher expression of both markers was observed in pancreatic NETs. AKT/mTOR activation was observed without the loss of PTEN expression. Tumors showing AKT/mTOR signaling activation progressed faster when treated with SSAs: higher expression of p-AKT or p-S6 predicted a median progression-free survival of 1 month vs 26.5 months for lower expression (P = 0.02). Conclusion: Constitutive activation of the AKT/mTOR pathway was associated with shorter time-to-progression in patients undergoing treatment with SSAs. Larger case series are needed to validate whether p-AKT(Ser473) and p-S6(Ser240/244) can be used as prognostic markers of response to therapy with SSAs.

Oxygen-Copper (II) Interplay in the Repair of Semi-Oxidized Urate by Quercetin Bound to Human Serum Albumin

The 1:1 complex of copper (II) and human serum albumin (HSA) slowly reacts with radiolytically generated •O2- radical-anion at a rate constant of 6.1×106 M-1 s-1. Absorbance and fluorescence spectroscopies demonstrate that addition of an equimolar portion of quercetin (QH2) to the solution of the copper (II)-HSA complex induces a relocalization of the copper resulting in a ternary copper (II)-QH2-HSA complex. This form of quercetin slowly oxidizes in air-saturated solutions. A 10-fold excess urate, a plasma antioxidant, cannot displace copper (II) bound to HSA. In N2O-saturated solutions the ternary complex form of QH2 can repair the urate radical with a rate constant of 2.7×106 M-1 s-1 by an electron transfer reaction similar to that observed in the absence of copper (II). In O2-saturated solutions and in the absence of copper, HSA-bound QH2 fails to repair the urate radical because of the fast competitive reaction of •O2- with urate radicals. However, addition of equimolar copper (II) restores the electron transfer from QH2 to the urate radical. These contrasting results are tentatively explained either by an enhanced reactivity of copper (II) with •O- in the ternary complex or by direct production of quercetin radicals via a copper-catalyzed reduction of the •O- radicals by QH2.