Environmentally induced oxidative stress in aquatic animals

ACE inhibitors have achieved widespread usage in the treatment of cardiovascular and renal disease. ACE inhibitors alter the balance between the vasoconstrictive, salt-retentive, and hypertrophic properties of angiotensin II (Ang II) and the vasodilatory and natriuretic properties of bradykinin and alter the metabolism of a number of other vasoactive substances. ACE inhibitors differ in the chemical structure of their active moieties, in potency, in bioavailability, in plasma half-life, in route of elimination, in their distribution and affinity for tissue-bound ACE, and in whether they are administered as prodrugs. Thus, the side effects of ACE inhibitors can be divided into those that are class specific and those that relate to specific agents. ACE inhibitors decrease systemic vascular resistance without increasing heart rate and promote natriuresis. They have proved effective in the treatment of hypertension, they decrease mortality in congestive heart failure and left ventricular dysfunction after myocardial infarction, and they delay the progression of diabetic nephropathy. Ongoing studies will elucidate the effect of ACE inhibitors on cardiovascular mortality in essential hypertension, the role of ACE inhibitors in patients without ventricular dysfunction after myocardial infarction, and the role of ACE inhibitors compared with newly available angiotensin AT1 receptor antagonists.

Angiotensin-Converting Enzyme Inhibitors

The metal chelating properties of flavonoids suggest that they may play a role in metal-overload diseases and in all oxidative stress conditions involving a transition metal ion. A detailed study has been made of the ability of flavonoids to chelate iron (including Fe3+) and copper ions and its dependence of structure and pH. The acid medium may be important in some pathological conditions. In addition, the ability of flavonoids to reduce iron and copper ions and their activity-structure relationships were also investigated. To fulfill these objectives, flavones (apigenin, luteolin, kaempferol, quercetin, myricetin and rutin), isoflavones (daidzein and genistein), flavanones (taxifolin, naringenin and naringin) and a flavanol (catechin) were investigated. All flavonoids studied show higher reducing capacity for copper ions than for iron ions. The flavonoids with better Fe3+ reducing activity are those with a 2,3-double bond and possessing both the catechol group in the B-ring and the 3-hydroxyl group. The copper reducing activity seems to depend largely on the number of hydroxyl groups. The chelation studies were carried out by means of ultraviolet spectroscopy and electrospray ionisation mass spectrometry. Only flavones and the flavanol catechin interact with metal ions. At pH 7.4 and pH 5.5 all flavones studied appear to chelate Cu2+ at the same site, probably between the 5-hydroxyl and the 4-oxo groups. Myricetin and quercetin, however, at pH 7.4, appear to chelate Cu2+ additionally at the ortho-catechol group, the chelating site for catechin with Cu2+ at pH 7.4. Chelation studies of Fe3+ to flavonoids were investigated only at pH 5.5. Only myricetin and quercetin interact strongly with Fe3+, complexation probably occurring again between the 5-hydroxyl and the 4-oxo groups. Their behaviour can be explained by their ability to reduce Fe3+ at pH 5.5, suggesting that flavonoids reduce Fe3+ to Fe2+ before association.

Interactions of Flavonoids with Iron and Copper Ions: A Mechanism for their Antioxidant Activity

Milk Thistle ( Silybum marianum ) for the Therapy of Liver Disease

The high prevalence of liver diseases such as chronic hepatitis and cirrhosis underscores the need for efficient and cost-effective treatments. The potential benefit of silymarin (extracted from the seeds of Silybum marianum or milk thistle) in the treatment of liver diseases remains a controversial issue. Therefore, the objective of this review is to assess the clinical efficacy and safety of silymarin by application of systematic approach. 525 references were found in the databases, of which 84 papers were retained for closer examination and 36 were deemed suitable for detailed analysis. Silymarin has metabolic and cell-regulating effects at concentrations found in clinical conditions, namely carrier-mediated regulation of cell membrane permeability, inhibition of the 5-lipoxygenase pathway, scavenging of reactive oxygen species (ROS) of the R-OH type and action on DNA-expression, for example, via suppression of nuclear factor (NF)-κB. Pooled data from case record studies involving 452 patients with Amanita phalloides poisoning show a highly significant difference in mortality in favour of silibinin [the main isomer contained in silymarin] (mortality 9.8% vs 18.3% with standard treatment; p < 0.01). The available trials in patients with toxic (e.g. solvents) or iatrogenic (e.g. antispychotic or tacrine) liver diseases, which are mostly outdated and underpowered, do not enable any valid conclusions to be drawn on the value of silymarin. The exception is an improved clinical tolerance of tacrine. In spite of some positive results in patients with acute viral hepatitis, no formally valid conclusion can be drawn regarding the value of silymarin in the treatment of these infections. Although there were no clinical end-points in the four trials considered in patients with alcoholic liver disease, histological findings were reported as improved in two out of two trials, improvement of prothrombin time was significant (two trials pooled) and liver transaminase levels were consistently lower in the silymarin-treated groups. Therefore, silymarin may be of use as an adjuvant in the therapy of alcoholic liver disease. Analysis was performed on five trials with a total of 602 patients with liver cirrhosis. The evidence shows that, compared with placebo, silymarin produces a nonsignificant reduction of total mortality by −4.2% [odds ratio (OR) 0.75 (0.5–1.1)]; but that, on the other hand, the use of silymarin leads to a significant reduction in liver-related mortality of −7% [OR: 0.54 (0.3–0.9); p < 0.01]. An individual trial reported a reduction in the numberof patients with encephalopathy of −8.7% (p = 0.06). In one study of patients with cirrhosis-related diabetes mellitus, the insulin requirement was reduced by −25% (p < 0.01). We conclude that available evidence suggests that silymarin may play a role in the therapy of (alcoholic) liver cirrhosis. Silymarin is has a good safety record and only rare case reports of gastrointestinal disturbances and allergic skin rashes have been published. This review does not aim to replace future prospective trials aiming to provide the ‘final’ evidence of the efficacy of silymarin.

The Use of Silymarin in the Treatment of Liver Diseases

Scavenging of reactive oxygen species by silibinin dihemisuccinate

The authors have compared the ability of two non-SH-containing angiotensin converting enzyme (ACE) inhibitors (enalaprilat and lisinopril) with an -SH containing ACE inhibitor (captopril) to scavenge the hydroxyl radical (OH). All three compounds were able to scavenge -OH radicals generated in free solution at approximately diffusion-controled rates (1010 M-1s-1) as established by the deoxyribose assay in the presence of EDTA. The compounds also inhibited deoxyribose degradation in reaction mixtures which did not contain EDTA but not so effectively. This later finding also suggests that they have some degree of metal-binding capability. Chemiluminescence assays of oxidation of hypoxanthine by xanthine oxidase in the presence of luminol, confirm that the three ACE inhibitors are oxygen free radical scavengers. Our results indicate that the presence of a sulphydryl group in the chemical structure of ACE inhibitors is not relevant for their oxygen free radical scavenging ability.

Angiotensin Converting Enzyme Inhibitors as Oxygen Free Radical Scavengers

The relative activities of some hydrogen-donating antioxidants were assessed by comparing their activities with that of Trolox (Trolox equivalent antioxidant capacity, TEAC) for scavenging the ABTS radical cation (ABTS.+) generated in the aqueous phase. We have verified, however, that TEAC values may change with the concentration of compounds and with the measuring times used. Not withstanding, TEAC values do not differ significantly if the compounds have kinetic curves of ABTS.+ formation similar to that of Trolox. This is the case with ascorbic acid, whose TEAC values, determined by using five concentrations at three different measuring times, are very close. For the flavonoids studied (catechin, rutin, naringenin and silibinin) which have kinetic curves of ABTS.+ formation different from that of Trolox, the TEAC values decrease with increasing concentrations of the compounds for each measuring time, and increase with increasing measuring times for each concentration. In the present study, we conclude that, in order to evaluate relative antioxidant activities of compounds by the ABTS assay, it is essential to perform kinetic studies to assess scavenging of ABTS.+ by these compounds. Therefore, when the TEAC values of compounds are determined for more than one measuring time, we may be sure that all the antioxidant potential of compounds is being considered and whether or not it is possible to establish a hierarchy for their antioxidant activities.

Measurement of relative antioxidant activity of compounds: a methodological note.

Iron and copper complexation by angiotensin-converting enzyme inhibitors. A study by ultraviolet spectroscopy and electrospray mass spectrometry

It has been proposed that some angiotensin-converting enzyme (ACE) inhibitors possessing a sulfhydryl (SH) group in their chemical structures have additional cardioprotective effects due to the scavenging of oxygen free radicals. I In this study we compare, using the deoxyribose assay,* the capacity to scavenge hydroxyl radicals (.OH) by an ACE inhibitor that possesses an -SH group (captopril) with other inhibitors not containing -SH groups (enalaprilat and lisinopril). We have also examined the ability of ACE inhibitors to inhibit the luminol-enhanced luminescence, produced during the oxidation of hypoxanthine by xanthine oxidase.3 There is growing evidence that the production of oxygen radicals, by xanthine oxidase system, is one of the important mechanisms involved in reoxygenation injury of hypoxic tissues. All three drugs tested are powerfbl scavengers of .OH generated with rate constants around 1010 M-Isec-l and they also have some degree of iron-binding capability, as established by the deoxyribose method. When assaying the three ACE inhibitors, as .OH radicals scavengers, we also wanted to evaluate the importance of the -SH group present in the chemical structure of captopril. Experiments of deoxyribose assay in which the -SH group of captopril is blocked by N-ethylmaleimide suggest that the -SH group of captopril contributes to its antioxidant capacity. However, in relation to .OH scavenging, it shows much the same reactivity as enalaprilat and lisinopril. This is to be expected from their chemical structure since enalaprilat and lisinopril, although they have no -SH group, possess an aromatic ring. The effects of enalaprilat, lisinopril, and captopril on the luminol-enhanced chemiluminescence produced during the oxidation of hypoxanthine by xanthine oxidase are represented in FIGURE 1. The chemiluminescence assays confirm that the three ACE inhibitors are oxygen free radical scavengers. The assay was highly sensitive to SOD and the ACE inhibitors

The Scavenging of Oxygen Free Radicals by Angiotensin Converting Enzyme Inhibitors: The Importance of the Sulfhydryl Group in the Chemical Structure of the Compounds

Manuela Silva

Papers

Scavenging of reactive oxygen species by silibinin dihemisuccinate

Angiotensin Converting Enzyme Inhibitors as Oxygen Free Radical Scavengers

Measurement of relative antioxidant activity of compounds: a methodological note.

Iron and copper complexation by angiotensin-converting enzyme inhibitors. A study by ultraviolet spectroscopy and electrospray mass spectrometry

The Scavenging of Oxygen Free Radicals by Angiotensin Converting Enzyme Inhibitors: The Importance of the Sulfhydryl Group in the Chemical Structure of the Compounds