Pellagra: a review with emphasis on photosensitivity.

Niacin has recently been demonstrated to lower blood pressure in hypertensive patients and to reduce cardiovascular events when combined with a statin. As a consequence, niacin has been elevated from being of historical interest as the treatment for pellagra, to being a compound with possible relevance to contemporary therapeutics. In spite of this, niacin deficiency leading to pellagra continues to be a health problem in some countries. Characterized by an exposed-site hyperpigmented dermatitis, pellagra is generally accepted to have been the first photosensitivity syndrome described. At its worst, pellagra manifests as one of the most striking examples of systemic photosensitivity. This is the only photosensitivity syndrome where death is included as a cardinal clinical feature (the often quoted four 'Ds': dermatitis, diarrhoea, dementia and death). However, the pathogenetic mechanism for the photosensitivity caused by niacin deficiency has yet to be determined. This review seeks to update the classification and phenotypic characterization of the various forms of niacin-deficient photosensitivity. Previous speculation about possible mechanisms for the pathogenesis of photosensitivity due to niacin deficiency is reviewed in the context of advances in the understanding of the photochemical basis of photosensitivity reactions. The review concludes by highlighting research required to advance the understanding of this photosensitivity syndrome.

High- but not low-dose folic acid improves endothelial function in coronary artery disease.

BACKGROUND: While folic acid (FA) reduces plasma homocysteine (Hcy), whether the simultaneous improvement in endothelial function is dependent on Hcy lowering per se is questionable. In the present study the relationship between FA dose, Hcy lowering and endothelial function in patients with coronary artery disease (CAD) was investigated. MATERIALS AND METHODS: Eighty-four patients with CAD received either 400 microg FA or 5 mg placebo daily for a 6-week treatment period. A further 44 patients with CAD received either 100 mg kg(-1) day(-1) of betaine or placebo for a 6-week treatment period. Flow-mediated dilatation (FMD), a measure of endothelial function, was assessed before and after the 6-week periods. Isometric tension and Western blotting were used to investigate the effect of FA on endothelial function and endothelial nitric oxide synthase (eNOS) dimerization in isolated rabbit aortic rings and cultured porcine aortic endothelial cells (PAEC), respectively. RESULTS: Both 400 micro g day(-1) and 5 mg day(-1) FA significantly increased plasma folate and decreased plasma Hcy. The FMD improved significantly after 6 weeks' treatment of 5 mg day(-1) FA but did not correlate with the reduction in Hcy. There was no change in FMD in either the 400 micro g FA or placebo group. In a subgroup analysis of 11 patients in the betaine group, despite a reduced Hcy, a significant impairment in FMD was observed. In the in vitro studies FA, but not betaine, reversed methionine-induced endothelial dysfunction. Moreover, the FA promoted eNOS dimerization in cultured PAEC. CONCLUSIONS: These data suggest that FA dose-dependently improves endothelial function in CAD via a mechanism independently of Hcy lowering. It may involve promotion of eNOS dimerization.

Accumulation of Krebs cycle intermediates and over-expression of HIF1alpha in tumours which result from germline FH and SDH mutations.

The nuclear-encoded Krebs cycle enzymes, fumarate hydratase (FH) and succinate dehydrogenase (SDHB, -C and -D), act as tumour suppressors. Germline mutations in FH predispose individuals to leiomyomas and renal cell cancer (HLRCC), whereas mutations in SDH cause paragangliomas and phaeochromocytomas (HPGL). In this study, we have shown that FH-deficient cells and tumours accumulate fumarate and, to a lesser extent, succinate. SDH-deficient tumours principally accumulate succinate. In situ analyses showed that these tumours also have over-expression of hypoxia-inducible factor 1alpha (HIF1alpha), activation of HIF1alphatargets (such as vascular endothelial growth factor) and high microvessel density. We found no evidence of increased reactive oxygen species in our cells. Our data provide in vivo evidence to support the hypothesis that increased succinate and/or fumarate causes stabilization of HIF1alpha a plausible mechanism, inhibition of HIF prolyl hydroxylases, has previously been suggested by in vitro studies. The basic mechanism of tumorigenesis in HPGL and HLRCC is likely to be pseudo-hypoxic drive, just as it is in von Hippel-Lindau syndrome.

Downstream effects on human low density lipoprotein of homocysteine exported from endothelial cells in an in vitro system.

A model system is presented using human umbilical vein endothelial cells (HUVECs) to investigate the role of homocysteine (Hcy) in atherosclerosis. HUVECs are shown to export Hcy at a rate determined by the flux through the methionine/Hcy pathway. Additional methionine increases intracellular methionine, decreases intracellular folate, and increases Hcy export, whereas additional folate inhibits export. An inverse relationship exists between intracellular folate and Hcy export. Hcy export may be regulated by intracellular S-adenosyl methionine rather than by Hcy. Human LDLs exposed to HUVECs exporting Hcy undergo time-related lipid oxidation, a process inhibited by the thiol trap dithionitrobenzoate. This is likely to be related to the generation of hydroxyl radicals, which we show are associated with Hcy export. Although Hcy is the major oxidant, cysteine also contributes, as shown by the effect of glutamate. Finally, the LDL oxidized in this system showed a time-dependent increase in uptake by human macrophages, implying an upregulation of the scavenger receptor. These results suggest that continuous export of Hcy from endothelial cells contributes to the generation of extracellular hydroxyl radicals, with associated oxidative modification of LDL and incorporation into macrophages, a key step in atherosclerosis. Factors that regulate intracellular Hcy metabolism modulate these effects.

Reduction in plasma total homocysteine through increasing folate intake in healthy individuals is not associated with changes in measures of antioxidant activity or oxidant damage.

BACKGROUND: Various mechanisms have been proposed to explain the association between plasma total homocysteine (tHcy) and risk of cardiovascular disease, including oxidative activity of homocysteine. OBJECTIVE: To explore the putative role of reactive oxygen species in the association between plasma tHcy and risk of cardiovascular disease in healthy individuals. DESIGN: A double-blind, placebo-controlled crossover intervention to increase folate intake through diet (increased consumption of folate-rich foods) and supplement (400 micro g folic acid) was carried out in 126 healthy men and women. Measurements were made of antioxidant activity in red blood cells and plasma, and products of oxidant damage in plasma. RESULTS: Diet and supplement-based interventions led to an increase in measures of folate status and a reduction in plasma tHcy. This was not associated with any significant change in measures of antioxidant activity (plasma and red blood cell glutathione peroxidase activity and red blood cell superoxide dismutase activity) or oxidant damage (plasma malondialdehyde), although an improvement in plasma total antioxidant capacity just failed to reach significance. CONCLUSIONS: In healthy individuals lowering plasma tHcy does not have any functional implications regarding oxidative damage.

A comparison of the effect of advice to eat either '5-a-day' fruit and vegetables or folic acid-fortified foods on plasma folate and homocysteine.

OBJECTIVE: To assess and compare the effects of natural folate (100 micro g) with those of folic acid from fortified sources (100 micro g/day) on plasma folate and homocysteine. DESIGN: Randomized controlled trial (parallel groups). SETTING: Men and women living in South Wales, UK. SUBJECTS: A total of 135 healthy individuals recruited from the local workforce and blood donor sessions. All subjects possessed the 'wild-type' CC genotype for C677T polymorphism in methylenetetrahydrofolate reductase (MTHFR). INTERVENTIONS: Subjects underwent one of the following dietary interventions for 4 months: (1) fortified diet-usual diet plus 100 microg/day folic acid from fortified foods; (2) natural folate diet-usual diet plus 100 microg/day folate from natural sources; (3) control-usual diet. RESULTS: The fortified group increased reported intake of folic acid from fortified foods compared to other groups (P<0.001) achieving an extra 98 microg/day (95% CI 88-108). The natural folate group increased reported intake of natural source folates compared with the other two groups (P<0.001), but achieved a mean increase of only 50 microg/day (95% CI 34-66). Plasma folate increased (P<0.01) by a similar amount in both intervention groups compared to controls (fortified group 2.97, 95% CI 0.8-5.1; natural group 2.76, 95% CI 0.6-4.9. Plasma homocysteine, vitamins B(6) and B(12) were not significantly changed. CONCLUSIONS: Subjects achieved increases in folate intake using fortified foods more easily than by folate-rich foods, however both sources increased plasma folate by a similar amount. These levels of intake were insufficient to reduce homocysteine concentrations in MTHFR CC homozygotes, but may be more effective in other genotypes.

Vitamin C therapy ameliorates vascular endothelial dysfunction in treated patients with homocystinuria.

OBJECTIVES: We sought to investigate the effects of short- and long-term vitamin C therapy on endothelial dysfunction in patients with homocystinuria. BACKGROUND: Untreated homocystinuria due to cystathionine beta-synthase deficiency is associated with premature atherothrombotic disease; 25% of untreated patients suffer a vascular event by the age of 16 years and 50% by 29 years. Treatment directed at reducing homocysteine accumulation significantly reduces this risk. However, despite 'optimal' treatment and compliance, hyperhomocysteinaemia usually persists and individuals exhibit endothelial dysfunction indicative of an adverse cardiovascular prognosis. Additional intervention is therefore required to further reduce cardiovascular risk. METHODS: We investigated the endothelial effects of acute (2 g single dose) and chronic (1 g/day for 6 months) administration of oral vitamin C in 5 patients with homocystinuria (mean age 26 years, 1 male) and 5 age- and sex-matched controls. Brachial artery endothelium-dependent flow-mediated dilatation (FMD) and endothelium-independent responses to nitroglycerin (NTG) were measured using high-resolution ultrasonic vessel wall-tracking. RESULTS: Baseline: Plasma total homocysteine was 100.8 +/- 61.6 and 9.2 +/- 1.9 micromol/L in the patient and control groups, respectively (p < 0.001). FMD responses were impaired in the patient group (20 +/- 40 microm) compared with the controls (116 +/- 30 microm) (p < 0.001). Vitamin C administration: FMD responses in the patient group improved both acutely, 160 +/- 65 microm at 4 h (p < 0.001), and chronically, 170 +/- 70 microm at 2 weeks (p < 0.001) and 170 +/- 40 microm at 6 months (p < 0.001). FMD responses in the control group were unaltered (p = 0.526). Within both groups, neither the vascular response to NTG nor plasma homocysteine was altered (p > 0.4). CONCLUSIONS: Vitamin C ameliorates endothelial dysfunction in patients with homocystinuria, independent of changes in homocysteine concentration and should therefore be considered as an additional adjunct to therapy to reduce the potential long-term risk of atherothrombotic disease.

Optimization of dietary folate or low-dose folic acid supplements lower homocysteine but do not enhance endothelial function in healthy adults, irrespective of the methylenetetrahydrofolate reductase (C677T) genotype.

OBJECTIVES: We sought to study the effect of low-dose folic acid supplementation or optimization of dietary folate intake on plasma homocysteine and endothelial function in healthy adults. BACKGROUND: Elevated homocysteine is associated with cardiovascular disease, but it is not known whether this relationship is causal. Individuals homozygous (TT) for the C677T mutation in the methylenetetrahydrofolate reductase (MTHFR) gene ( approximately 12% of the population) have increased homocysteine levels, particularly in association with suboptimal folate intake. METHODS: Healthy subjects (n = 126; 42 of each MTHFR genotype) were included in this cross-over study of three interventions of four months each: 1) placebo plus natural diet; 2) daily 400-microg folic acid supplement plus natural diet; and 3) increased dietary folate intake to 400 microg/day. RESULTS: At baseline, homocysteine was inversely related to plasma folate and was higher in TT homozygotes. For the whole group, plasma folate increased by 46% after dietary folate and by 79% after supplementation, with reductions of homocysteine of 14% and 16%, respectively. Within the genotype, TT homozygotes exhibited the most marked changes in these variables. Brachial artery endothelial function, as determined by a change in end-diastolic diameter in response to increased flow, was not changed by increased folate intake (98 +/- 73 microm at baseline, 110 +/- 69 microm after a high-folate diet, 114 +/- 59 microm after supplementation and 118 +/- 68 microm after placebo). Plasma von Willebrand factor antigen was unaltered. CONCLUSIONS: Optimization of dietary folate or low-dose folic acid supplementation reduces plasma homocysteine but does not enhance endothelial function, irrespective of the MTHFR (C667T) genotype.

Folate, homocysteine, endothelial function and cardiovascular disease. What is the link?

Elevated plasma homocysteine concentrations are associated with an increased risk of cardiovascular disease, but the relationship has not been proven to be causal. Folate is the strongest nutritional and pharmacological determinant of plasma homocysteine concentrations, which also interact with the genetic variation in methylenetetrahydrofolate reductase (MTHFR). Endothelial dysfunction due to reduced nitric oxide bioavailability is an early feature of vascular pathology. This can be assessed noninvasively by measurement of flow-mediated dilatation. Human studies on folic acid, homocysteine and endothelial function are reported. It is proposed that folic acid in high doses may have beneficial effects on endothelial function, which are independent of homocysteine lowering.

Acute hyperhomocysteinaemia affects pulse pressure but not microvascular vasodilator function.

AIMS: Raised homocysteine (hcy) levels are associated with premature coronary artery disease, but the underlying vascular mechanism and the extent to which hcy affects small vessel vasodilator responses (especially non-nitric oxide mediated pathways) are unclear. METHODS: This double-blind, placebo-controlled crossover study in 14 healthy male subjects evaluated the effects of single-dose oral methionine 15 g (to induce acute hyperhomocysteinaemia) on cutaneous microvascular vasodilator responses to incremental-dose iontophoretic administration of acetylcholine (Ach) and sodium nitroprusside (SNP) using laser Doppler fluximetry (LDF), and the effects on von Willibrand factor (vWF) levels and systemic haemodynamics. RESULTS: Methionine administration produced a three fold rise in plasma hcy levels at 8 h, which was accompanied by a significant increase in pulse pressure (53 vs 49 mmHg, P < 0.05) but no change in heart rate. Acute hyperhomocysteinaemia had no significant effect on incremental microvascular vasodilator dose-response curves to Ach and SNP, or circulating levels of vWF. CONCLUSIONS: The present study shows that acute hyperhomocysteinaemia increases pulse pressure (a marker of large vessel stiffness) but has no effect on endothelial-dependent (non-NO-mediated) microvascular vasodilation.

Folate improves endothelial function in coronary artery disease: an effect mediated by reduction of intracellular superoxide?

Homocysteine is a risk factor for coronary artery disease (CAD). Folic acid lowers homocysteine and may improve endothelial function in CAD, although the mechanism is unclear. We investigated the effect of folic acid on endothelial function, homocysteine, and oxidative stress in patients with CAD. We also examined the acute effect of 5-methyltetrahydrofolate (5-MTHF), the principal circulating folate, on endothelial function in vivo and on intracellular superoxide in cultured endothelial cells. A randomized crossover study of folic acid (5 mg daily) for 6 weeks was undertaken in 52 patients with CAD. Ten further patients were given intra-arterial 5-MTHF. Endothelial function was assessed by flow-mediated dilatation (FMD). Folic acid increased plasma folate (P<0.001), lowered homocysteine by 19% (P<0.001), and improved FMD (P<0.001). FMD improvement did not correlate with homocysteine reduction. Malondialdehyde and total plasma antioxidant capacity, markers of oxidative stress, were unchanged. 5-MTHF acutely improved FMD (P<0.001) without altering homocysteine (P=0.47). In vitro, 5-MTHF abolished homocysteine-induced intracellular superoxide increase (P<0.001); this effect was also observed with folic acid and tetrahydrobiopterin. Our data support the beneficial effect of folic acid on endothelial function in CAD but suggest that the mechanism is independent of homocysteine. Reduction of intracellular endothelial superoxide may have contributed to the effect.

Renal function, plasma homocysteine and carotid atherosclerosis in elderly people.

Although epidemiological studies suggest that people with minor impairment of renal function are at higher risk of stroke and coronary heart disease, the mechanisms underlying this relation are unclear. One explanation may lie with observations that deterioration in renal function is accompanied by elevations in plasma homocysteine concentrations. There is evidence that moderate hyperhomocysteinemia may play a causal role in atherosclerotic disease. We investigated the relations between renal function, plasma homocysteine and atherosclerosis of the carotid arteries in 128 men and women aged 69-74 years. Renal function was assessed by creatinine clearance and serum creatinine. Duplex ultrasonography was used to quantify the degree of stenosis in the extracranial carotid arteries. Severity of carotid atherosclerosis was greatest in men and women with the poorest renal function, whether measured by creatinine clearance or serum creatinine. After adjustment for plasma homocysteine, pulse pressure and other cardiovascular risk factors, the odds ratio for having carotid stenosis >30% was 4.3 (95% CI 1.4-12.9) in those whose creatinine clearance rate was 55 ml/min or less compared with those whose creatinine clearance rate was >73 ml/min. Even small decrements in renal function were associated with increased risk; people whose creatinine clearance rate was between 56 and 73 ml/min had an odds ratio of 3.8 (95% CI 1.2-11.9). Plasma homocysteine concentrations were significantly higher in people with poorer renal function, but they did not explain the associations we found between carotid atherosclerosis and creatinine clearance or serum creatinine.

Role of aminothiols as a component of the plasma antioxidant system and relevance to homocysteine-mediated vascular disease.

Hyperhomocysteinaemia is considered to be an independent risk factor for vascular disease. Elevated plasma homocysteine may pose an oxidative stress, leading to the development of vascular damage. A component of this effect may be a disturbance of the extracellular aminothiol redox state. The relative contributions of plasma total homocysteine (tHcy) and plasma total cysteine (tCys) to the total antioxidant capacity (TAOC) of plasma was established in subjects with normal and elevated plasma tHcy. A total of 10 subjects with severe hyperhomocysteinaemia (due to inherited metabolic defects), 13 of their heterozygous parents and 72 normal healthy subjects were recruited to the study. The mean plasma tHcy in the patients was 91.8 micromol/l, compared with 13.2 micromol/l in the parents and 14.7 micromol/l in healthy control subjects. Plasma tCys and plasma TAOC were significantly lower in the subjects with severe hyperhomocysteinaemia compared with the parents and healthy control subjects (P<0.05). In blood samples from subjects with a normal tHcy, a positive correlation was observed between tCys and tHcy (P=0.0001). In contrast, in blood samples with tHcy >or=20 micromol/l, plasma tCys was negatively correlated with tHcy (P=0.0001). In samples with tHcy >or=20 micromol/l, tHcy was inversely correlated with TAOC (P=0.0001), whereas tCys was positively associated with TAOC (P=0.0001). Multiple regression analysis revealed that tCys was the most important independent determinant of TAOC in the patient and control groups when the effects of tHcy and several factors known to influence TAOC, such as urate, were taken into account. Thus hyperhomocysteinaemia may pose an oxidative stress not only through the direct cytotoxicity of homocysteine, but also from an associated fall in plasma cysteine.

Elevated plasma homocysteine elicits an increase in antioxidant enzyme activity.

Elevated plasma homocysteine is considered to be a risk factor for cardiovascular disease. The mechanisms for this effect are not fully understood but there is some evidence for a role for reactive oxygen species (ROS). This study was conducted to explore the effects of elevated plasma total homocysteine (tHcy) concentration on activity of antioxidant enzymes in the circulation. The study group consisted of 10 patients with inherited defects of homocysteine metabolism, from whom 41 blood samples were collected over a period of six months. Blood samples were also collected from 13 of their obligate heterozygous parents. For data analysis samples were classified as those with plasma tHcy < 20 microM or > 20 microM. The activity of erythrocyte superoxide dismutase (SOD) and plasma glutathione peroxidase (GSHPx) was elevated in samples with plasma tHcy > 20 microM. Moreover, a significant correlation was demonstrated between plasma GSHPx activity, plasma glutathione peroxidase protein and plasma tHcy. III vitro studies confirmed that this observation was not due to a simple chemical enhancement of enzyme activity. Homocysteine protected GSHPx from loss of activity following incubation at 37 degrees C. A similar effect was seen with another thiol-containing amino acid, cysteine. Results suggest that elevated plasma tHcy represents an oxidative stress, resulting in an adaptive increase in activity of antioxidant enzymes in the circulation.

Homocysteine-induced inhibition of endothelium-dependent relaxation in rabbit aorta: role for superoxide anions.

Hyperhomocysteinemia is associated with endothelial dysfunction, although its mechanism is unknown. Isometric tension recordings and lucigenin chemiluminescence were used to assess the effects of homocysteine exposure on endothelium-dependent and -independent relaxation in isolated rabbit aortic rings and superoxide anion (O(2)(-)) production by cultured porcine aortic endothelial cells, respectively. Homocysteine (0.1 to 10 mmol/L) produced a significant (P<0.001) concentration- and time-dependent inhibition of endothelium-dependent relaxation in response to both acetylcholine and the calcium ionophore A23187. Only the intracellular O(2)(-) scavenger 4,5-dihydroxy-1,3-benzene disulfonic acid (Tiron, 10 mmol/L) significantly (P<0.001) inhibited the effect of homocysteine on acetylcholine- and A23187-induced relaxation. Incubation of porcine aortic endothelial cells with homocysteine (0.03 to 1 mmol/L for up to 72 hours) caused a significant (P<0.001) time-dependent increase in the O(2)(-) released by these cells on the addition of Triton X-100 (1% [vol/vol]), with levels returning to values comparable to those of control cells at the 72-hour time point. These changes in O(2)(-) levels were associated with a time-dependent increase in endothelial cell superoxide dismutase activity, becoming significant (P<0.001) after 72 hours. Furthermore, the homocysteine-induced increase in endothelial cell O(2)(-) levels was completely inhibited (P<0.001) by the concomitant incubation with either Tiron (10 mmol/L), vitamin C (10 micromol/L), or vitamin E (10 micromol/L). These data suggest that the inhibitory effect of homocysteine on endothelium-dependent relaxation is due to an increase in the endothelial cell intracellular levels of O(2)(-) and provide a possible mechanism for the endothelial dysfunction associated with hyperhomocysteinemia.

Developments in the measurement of plasma total homocysteine.

Elevated plasma homocysteine is considered to be a graded risk factor for cardiovascular disease, and for this reason there is great interest in high-performance analytical techniques. Methods have evolved from ion-exchange chromatography to embrace high-performance liquid chromatography with fluorescence or electrochemical detection, immunoassays, gas chromatography-mass spectroscopy and liquid chromatography with tandem mass spectrometry. Immunoassays and high-performance liquid chromatography methods are currently available in kit form, fluorescence polarization immunoassay showing the best performance.

Recommended approaches for the laboratory measurement of homocysteine in the diagnosis and monitoring of patients with hyperhomocysteinaemia.

Several recent studies have indicated that an increased concentration of plasma homocysteine is an independent risk factor for the premature development of vascular disease. These important findings emphasize the need for careful selection of an appropriate analytical approach to diagnose and treat individuals who may be at risk. We compared the results obtained from the measurement of plasma total homocysteine (free + protein-bound fractions) by high-performance liquid chromatography (HPLC) with the measurement of plasma free homocystine (free fraction) by conventional ion-exchange chromatography in 10 patients with inherited defects of homocysteine metabolism and 13 obligate heterozygote individuals. This study can be used to formulate recommendations on the appropriate use of these assays in different clinical circumstances. Our results show that the concentration of total plasma homocysteine must exceed 60 mumol/L before plasma free homocystine becomes detectable by conventional ion-exchange chromatography. Similarly, assessment of the urinary excretion of homocysteine in these patients indicates that it may not become consistently detectable by conventional ion-exchange chromatography or HPLC until plasma total homocysteine exceeds 150 mumol/L. On this basis, while most patients with classical homocystinuria would be detected by analysis of plasma using conventional ion-exchange chromatography or by measurement of of the urinary homocysteine excretion, occasional patients would be missed. When monitoring patients receiving treatment for classical homocystinuria, in whom metabolic control is good, and when investigating individuals with a suspected inherited defect of cobalamin or folate metabolism, a method which measures plasma total homocysteine should be used. The identification of moderate hyperhomocysteinaemia of undefined cause investigated in relation to a history of early vacsular disease can only be identified by this approach.