Biomedical subjects
Publications and source records attributed to S Chirico.
Explore the source record for details and available documents.
Low density lipoprotein (LDL) plays an important role in atherogenesis. Focal accumulation within the arterial intima of excess amounts of cholesterol-rich LDL leads to the migration and recruitment of monocytes, which then differentiate into macrophages after taking up large amounts of oxidatively modified LDL via their scavenger receptors and become lipid-laden 'foam cells' within the subendothelial space. It is generally accepted that oxidized LDL and hyperlipidaemia impair endothelial-dependent vascular relaxation, yet the existing literature on the effects of oxidatively modified LDL on endothelium-derived nitric oxide (NO) and prostacyclin (PGI2) release is inconclusive, since oxidized LDL has been reported to enhance or reduce NO and PGI2 production. Our studies using cultured human endothelial and smooth muscle cells have established that basal rates of L-arginine (NO precursor) transport, NO and PGI2 production and soluble guanylyl cyclase activity are unaffected by pretreatment (for 1 or 24 h) with native LDL, or with mildly or highly oxidized LDL. In contrast, highly oxidized LDL inhibited histamine-stimulated release of NO and PGI2 from human endothelial cells and induced an adaptive increase in the level of intracellular glutathione in human smooth muscle cells, a response which was prevented by the chain-breaking antioxidant alpha-tocopherol. Although initial rates of L-arginine transport and basal NO and PGI2 release from human endothelium are unaffected by oxidized LDL, agonist-stimulated release of these vasodilators is markedly attenuated. Elucidation of the mechanisms regulating these responses and their sensitivity to dietary antioxidants could lead to alternative strategies for reducing atherogenesis.
BACKGROUND: Fresh fruit consumption and vitamin C intake have been associated with improved lung function in adults. Whether this is due to enhancement of lung growth, to a reduction in lung function decline, or to protection against bronchospasm is unclear. METHODS: In a cross-sectional school based survey of 2650 children aged 8-11 from 10 towns in England and Wales the main outcome measure was forced expiratory volume in one second (FEV1) standardised for body size and sex. Exposure was assessed by a food frequency questionnaire to parents and by measurement of plasma levels of vitamin C in a subsample of 278 children. RESULTS: FEV1 was positively associated with frequency of fresh fruit consumption. After adjustment for possible confounding variables including social class and passive smoking, those who never ate any fresh fruit had an estimated FEV1 some 79 ml (4.3%) lower than those who ate these items more than once a day (95% CI 22 to 136 ml). The association between FEV1 and fruit consumption was stronger in subjects with wheeze than in non-wheezers (p = 0.020 for difference in trend), though wheeze itself was not related to fresh fruit consumption. Frequency of consumption of salads and of green vegetables were both associated with FEV1 but the relationships were weaker than for fresh fruit. Plasma vitamin C levels were unrelated to FEV1 (r = -0.01, p = 0.92) or to wheeze and were only weakly related to fresh fruit consumption (r = 0.13, p = 0.055). CONCLUSIONS: Fresh fruit consumption appears to have a beneficial effect on lung function in children. Further work is needed to confirm whether the effect is restricted to subjects who wheeze and to identify the specific nutrient involved.
Earlier studies have shown that inhibition of aggregation of washed platelets (WP) by NO was enhanced almost 100-fold by H2O2. In the present study, the interactions of H2O2 with nitrosothiols, the influence of the presence of plasma and the mechanism of the synergism were investigated. H2O2 strongly enhanced the inhibitory effects of S-nitrosoglutathione (GSNO) on thrombin-induced aggregation of WP. S-Nitrosoalbumin also inhibited platelets, and this was similarly enhanced by H2O2. The synergism with H2O2 was demonstrable for both exogenous GSNO and NO in the presence of plasma when platelets were stimulated with collagen. The inhibition of platelets by GSNO and H2O2 was completely inhibited by guanylate cyclase inhibitors. Synergism was also observed whether the H2O2 was added simultaneously or 1 min before or after the GSNO (or NO). This suggests that the action of H2O2 follows the occupation by NO of haem sites in guanylate cyclase and that a prior reaction between NO and H2O2 was not required. In the absence of exogenous GSNO or NO, H2O2 inhibited activation of platelets in plasma, an effect abolished by guanylate cyclase inhibitors. This suggested that endogenous NO donors in plasma or NO synthesized in platelets may interact with H2O2. Addition of NG-nitro-L-arginine methyl ester (hydrochloride) (L-NAME) decreased the effects of the H2O2 by 25%, indicating that the major endogenous source of NO in platelet-rich plasma was not derived from platelet synthesis of NO but from NO donors in plasma, such as nitrosothiols. Inhibition by H2O2 was also enhanced by beta-mercaptosuccinate, a glutathione peroxidase inhibitor that protects the H2O2. These results suggest a potent synergism of H2O2 with endogenous plasma nitrosothiols that inhibit platelet function through an intracellular mechanism involving guanylate cyclase.
A wide variety of oxygen free radicals and other reactive oxygen species can be formed in the human body and in food systems. Transition metal ions accelerate free-radical damage. Antioxidant defenses, both enzymic and nonenzymic, protect the body against oxidative damage, but they are not 100% efficient, and so free-radical damage must be constantly repaired. Nonenzymatic antioxidants are frequently added to foods to prevent lipid peroxidation. Several lipid antioxidants can exert prooxidant effects toward other molecules under certain circumstances, and so antioxidants for food and therapeutic use must be characterized carefully. Methods of measuring oxidative damage and trapping free radicals in vivo are briefly discussed. Such methods are essential in checking proposals that increased intake of food-derived antioxidants (such as antioxidant vitamins) would be beneficial to humans.
Explore the source record for details and available documents.
An increased concentration of end products of lipid peroxidation is the evidence most frequently quoted for the involvement of free radicals in human disease. However, it is likely that increased oxidative damage occurs in most, if not all, human diseases and plays a significant pathological role in only some of them. For example, peroxidation appears to be important in atherosclerosis and in worsening the initial tissue injury caused by ischemic or traumatic brain damage. Oxidative stress can damage many biological molecules; indeed, proteins and DNA are often more significant targets of injury than are lipids, and lipid peroxidation often occurs late in the injury process. Many assays are available to measure lipid peroxidation, but no single assay is an accurate measure of the whole process. Application of simple diene-conjugate and thiobarbituric acid (TBA) assays to human tissues and body fluids can produce artifacts. An HPLC-based TBA test can eliminate some of these artifacts.
The question of "increased lipid peroxidation" in plasma from hyperlipidaemic patients was investigated using an improved HPLC-based assay for thiobarbituric acid-reactive material. Levels of TBARS in healthy human controls were at or close to zero, provided that butylated hydroxytoluene was added to the sample with the TBA reagents. Levels of plasma TBARS in hyperlipidaemic patients were elevated, although the absolute levels were much lower than those reported previously in the literature.
Explore the source record for details and available documents.
The ability of fresh sera to resist attack by peroxyl radicals (TRAP) was found to be significantly lower in 20 patients with rheumatoid arthritis (RA) than in 20 healthy controls, consistent with the existence of a redox stress in RA imposed by inflammation. TRAP values in RA varied inversely with a combination of visual analogue pain scale, duration of early morning stiffness, grip strength, and articular index (reflecting inflammatory activity) using multiple linear regression analysis. The concentration of the antioxidant vitamin ascorbic acid was lower in RA plasma and the oxidation-reduction equilibrium of ascorbic acid was disturbed, giving further support to the existence of a redox stress. The major determinant of TRAP in vitro was found to be serum uric acid in RA and serum vitamin E in controls. Serum urate concentration in RA correlated inversely with oxidative changes in serum albumin and IgG. It is suggested that serum urate might have an antioxidant role under certain conditions by limiting free radical induced oxidative changes to protein during inflammation.
The mechanism by which a synovial flare occurred in a patient with rheumatoid arthritis after intravenous infusion of iron-dextran was investigated. After the infusion, serum and synovial-fluid iron-binding capacity became saturated, giving rise to low-molecular-mass iron chelates with the capacity to cause oxidative damage ("bleomycin-iron"). At the same time lipid peroxidation and the concentration of oxidised ascorbic acid (dehydroascorbate) increased in both serum and synovial fluid, and red-cell glutathione fell. These changes corresponded closely to an exacerbation of rheumatoid synovitis. Hepatic function was transiently disturbed 7 days after the infusion, reflecting hepatic oxidant stress within the iron-loaded liver. Such changes provide clear evidence that iron-catalysed oxidative reactions influence the inflammatory process in human beings.
Explore the source record for details and available documents.
Recent evidence has suggested that diabetic microangiopathy is associated with increased free radical induced oxidative damage. Ascorbic acid (AA) is a free radical scavenger and using a specific HPLC method we have investigated its concentration and that of its oxidized metabolite dehydroascorbic acid (DHAA) in diabetic patients and matched normal controls. The findings have been related to the presence of microangiopathy and to glycaemic control. Ascorbic acid levels were significantly lower in diabetics (mean +/- SD 42.5 +/- 26.2 mumol/l) compared with controls (58 +/- 21 mumol/l p less than 0.02). Although there was no differences in DHAA levels between the groups the ratio DHAA/AA was increased in diabetics (0.72 +/- 0.8) compared with controls (0.4 +/- 0.2 p less than 0.05). There were no significant differences between insulin and non-insulin dependent patients in these measurements and there was no association with the presence of microangiopathy or poor glycaemic control. The plasma ratio DHAA/AA may be a reflection of increased oxidative stress and our results suggest that diabetics may be less able to prevent oxidative damage occurring due to their lower AA concentrations.
Oxidative damage in three inflammatory neurological disorders; Guillain Barré syndrome (GBS), multiple sclerosis and aseptic meningitis, were assessed by measuring the peroxidation of lipids in body fluids. The results were compared to a control group consisting of patients with either migraine, chronic/tension headaches, benign intracranial hypertension or psychological disorders. Antioxidant status was assessed by the measurement of the extracellular proteins, haptoglobin, albumin, caeruloplasmin and transferrin. The results of the study suggested that firstly, haptoglobin levels might be a useful, easily obtainable marker to aid the diagnosis of GBS. Secondly, free radical damage may be implicated in the pathology of GBS and therefore appropriate free radical scavenging might have beneficial effects.