Vitamin C protects low-density lipoprotein from homocysteine-mediated oxidation

Association between homocysteine and blood pressure in the NHANES 2003-2006: the mediating role of Vitamin C

Background

The yearly escalation in hypertension prevalence signifies a noteworthy public health challenge. Adhering to a nutritious diet is crucial for enhancing the quality of life among individuals managing hypertension. However, the relationship between vitamin C and hypertension, as well as homocysteine, remains unclear.

Objective

The primary aim of this investigation was to scrutinize the potential mediating role of Vitamin C in the association between homocysteine levels and blood pressure, utilizing data extracted from the National Health and Nutrition Examination Survey (NHANES) database.

Methods

A total of 7,327 participants from the NHANES 2003-2006 were enrolled in this cross-sectional survey. The main information was obtained using homocysteine, Vitamin C, systolic blood pressure (SBP) and diastolic blood pressure (DBP). Correlation analysis was used to assess the correlation between homocysteine, SBP, DBP and vitamin C. Linear regression analysis was utilized to determine the β value (β) along with its 95% confidence intervals (CIs). Mediation analysis was performed to investigate whether the relationship between homocysteine and blood pressure was mediated by Vitamin C, and to quantify the extent to which Vitamin C contributed to this association.

Results

The results manifested that the homocysteine was positively associated with SBP (r = 0.24, p < 0.001) and DBP (r = 0.03, p < 0.05), while negatively correlated with Vitamin C (r = -0.008, p < 0.001). Vitamin C was found to be negatively associated with SBP (r = -0.03, p < 0.05) and DBP (r = 0.11, p < 0.001). Mediation effect analysis revealed that a partial mediation (indirect effect: 0.0247[0.0108-0.0455], p < 0.001) role accounting for 11.5% of total effect, among homocysteine and SBP. However, the mediating effect of Vitamin C between homocysteine and DBP was not statistically significant.

Conclusion

Hypertension patients should pay attention to homocysteine and Vitamin C level. What is more, hypertension patients ought to formulate interventions for Vitamin C supplementation as well as homocysteine reduce strategies to lower blood pressure.

SARS-CoV-2 Infection: What Is Currently Known about Homocysteine Involvement?

Since December 2019, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has spread rapidly throughout the world causing health, social and economic instability. The severity and prognosis of patients with SARS-CoV-2 infection are associated with the presence of comorbidities such as cardiovascular disease, hypertension, chronic lung disease, cerebrovascular disease, diabetes, chronic kidney disease, and malignancy. Thrombosis is one of the most serious complications that can occur in patients with COVID-19. Homocysteine is a non-proteinogenic α-amino acid considered a potential marker of thrombotic diseases. Our review aims to provide an updated analysis of the data on the involvement of homocysteine in COVID-19 to highlight the correlation of this amino acid with disease severity and the possible mechanisms by which it intervenes.

Prevalence and Predictors of Insufficient Plasma Vitamin C in a Subtropical Region and Its Associations with Risk Factors of Cardiovascular Diseases: A Retrospective Cross-Sectional Study

Background: to evaluate the prevalence and predictors of insufficient plasma vitamin C among adults in a subtropical region and its associations with cardiovascular disease risk factors including dyslipidemia and lipid-independent markers, namely homocysteine, high-sensitivity C-reactive protein (hs-CRP) and lipoprotein(a). Methods: Data of this retrospective cross-sectional study were extracted from electronic medical database of a Medical Center. Based on plasma vitamin C status, subjects were split into two groups—subjects with sufficient and insufficient plasma vitamin C levels (<50 µmol/L, ≤8.8 mg/L). Results: Prevalence of insufficient plasma vitamin C in 3899 adults was 39%. Multivariate logistic regression identified male gender, high body mass index, age 20−39, and winter/spring as independent predictors of insufficient vitamin C among all subjects. Greater proportions of subjects with insufficient plasma vitamin C had lower high-density lipoprotein cholesterol levels and elevated levels of triglyceride, homocysteine and hs-CRP (all p < 0.001). There were no differences in total cholesterol, low-density lipoprotein cholesterol and lipoprotein(a) between groups. Conclusions: There was a high prevalence of insufficient plasma vitamin C in the subtropical region, which indicates that insufficient plasma vitamin C remains a public health issue. Further study is needed to confirm these findings and to determine the underlying mechanisms.

Vitamins E and C do not effectively inhibit low density lipoprotein oxidation by ferritin at lysosomal pH

Low density lipoprotein (LDL) might be oxidized by iron in the lysosomes of macrophages in atherosclerotic lesions. We have shown previously that the iron-storage proteinferritin can oxidize LDL at lysosomal pH. We have now investigated the roles of the most important antioxidant contained in LDL, α-tocopherol (the main form of vitamin E) and of ascorbate (vitamin C), a major water-soluble antioxidant, on LDL oxidation by ferritin at lysosomal pH (pH 4.5). We incubated LDL with ferritin at pH 4.5 and 37 °C and measured its oxidation by monitoring the formation of conjugated dienes at 234 n min a spectrophotometer. α-Tocopherol is well known to inhibit LDL oxidation at pH 7.4, but enrichment of LDL with α-tocopherol was unable to inhibit LDL oxidation by ferritin at pH 4.5. Ascorbate had a complex effect on LDL oxidation by ferritin at lysosomal pH and exhibited both antioxidant and pro-oxidant effects. It had no antioxidant effect on partially oxidized LDL, only a pro-oxidant effect. Ascorbate completely inhibited LDL oxidation by copper at pH 7.4 for a long period, but in marked contrast did not inhibit LDL oxidation by copper at lysosomal pH. Dehydroascorbate, the oxidation product of ascorbate, had a pronounced pro-oxidant effect on LDL incubated with ferritin at pH 4.5. The inability of α-tocopherol and ascorbate to effectively inhibit LDL oxidation by ferritin at lysosomal pH might help to explain why the large clinical trials with these vitamins failed to show protection against cardiovascular diseases.

Aqueous Extract of Adansonia digitata reversed Cotton Seed Extract-Induced Testicular Damage in Wistar rats

Objective:

Infertility is the inability of sexually active couples without using birth control to get pregnant after one year of uninterrupted sexual intercourse. Cotton Seed Extract (CSE) has been linked to male infertility by causing oxidative damage to the testes due to the action of its active component, Gossypol. Adansonia digitata has been known to have many medically useful properties, including antioxidant effects. This study aimed at evaluating the effects of Adansonia digitata on Cottonseed extract-induced testicular damage.

Methods:

Forty (40) Adult male Wistar rats were divided into 8 groups of five rats per group (n=5). Group 1 served as the control and received 0.5 ml of phosphate buffer orally; Group 2 received 800 mg/kg b.wt A. digitata orally; Group 3 received 300 mg/kg b.wt Vitamin E only orally; Group 4 received 60 mg/kg b.wt CSE intraperitoneally; Group 5 received 20 mg/kg b.wt CSE intraperitoneally; Group 6 received 60 mg/kg b.wt CSE intraperitoneally and 800 mg/kg b.wt A. digitata orally; Group 7 received 20 mg/kg b.wt CSE intraperitoneally and 800 mg/kg b.wt A. digitata orally; Group 8 received 60 mg/kg b.wt CSE intraperitoneally and 300 mg/kg Vit. E orally. It was administered for 21 days. The testes and epididymis were dissected following abdominal incision. The epididymis was used for semen analysis while the testes was processed for histological analysis and biochemical assay. All the data was analyzed by ANOVA, using the SPSS version 17.0 software. A p<0.05 was considered significant.

Results:

CSE administration caused significant (p<0.05) decrease in sperm count, found in the group treated with CSE only. However, the Administration of A. digitata caused significant increase (p<0.05) in sperm count, G6PDH, LDH, GPx and SOD; however, MDA levels were decreased. Histological observations showed a decrease in the number of Spermatogonia and differentiating cells in the testes of rats treated with CSE.

Conclusions:

The results obtained revealed the antioxidant ability of A. digitata in counter-acting the testicular damage caused by CSE administration.

Phenylethyl isothiocyanate induces oxidative damage of porcine kidney cells mediated by reactive oxygen species

The aim of this study is to confirm the toxic effect of phenylethyl isothiocyanate (PEITC) on porcine kidney cells (PK-15) and explore the effect of oxidative damage mediated by reactive oxygen species (ROS) induced by PEITC in PK-15 cells. Porcine kidney cell line (PK-15) was treated with PEITC (2, 5, and 10  µM) for 24 hours, and the oxidative damage mediated by PEITC through ROS was investigated. The survival rate of PK-15 cells decreased in a dose-dependent manner after the treatment of PEITC in a dose-dependent manner. A high concentration of PEITC (10 µM) can change cell morphology, increase the content of malondialdehyde, ROS, and lactate dehydrogenase, and decrease the activity of SOD, CAT, GSH-PX, and GSH. PEITC has a toxic effect on PK-15 cells by inducing oxidative stress in PK-15 cells through the generation of ROS.

The Role of Oxidative Stress and Membrane Transport Systems during Endometriosis: A Fresh Look at a Busy Corner

Endometriosis is a condition characterized by the presence of endometrial tissue outside the uterine cavity, leading to a chronic inflammatory reaction. It is one of the most widespread gynecological diseases with a 10-15% prevalence in the general female population, rising up to 30-45% in patients with infertility. Although it was first described in 1860, its etiology and pathogenesis are still unclear. It is now accepted that inflammation plays a central role in the development and progression of endometriosis. In particular, it is marked by an inflammatory process associated with the overproduction of an array of inflammatory mediators such as prostaglandins, metalloproteinases, cytokines, and chemokines. In addition, the growth and adhesion of endometrial cells in the peritoneal cavity due to reactive oxygen species (ROS) and free radicals lead to disease onset, its ensuing symptoms-among which pain and infertility. The aim of our review is to evaluate the role of oxidative stress and ROS in the pathogenesis of endometriosis and the efficacy of antioxidant therapy in the treatment and mitigation of its symptoms.

T-2 toxin-induced cytotoxicity and damage on TM3 Leydig cells

T-2 toxin is a highly toxic mycotoxin produced by various Fusarium species, mainly, Fusarium sporotrichoides, and has been reported to have toxic effects on reproductive system of adult male animals. This study investigated the dose-dependent cytotoxicity of T-2 toxin on reproductive cells using TM3 Leydig cells. Specifically, the cytotoxic effect of T-2 toxin was assessed by measuring cell viability; lactate dehydrogenase (LDH); malondialdehyde (MDA); antioxidant activity by measuring superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-PX), and DNA damage; and cell apoptosis. Results showed that T-2 toxin is highly cytotoxic on TM3 Leydig cells. However, Trolox-treated TM3 Leydig cells showed significantly reduced oxidative damage, DNA damage, and apoptosis induced by T-2 toxin. This study proves that T-2 toxin can damage the testes and thus affects the reproductive capacity of animals and humans. Furthermore, oxidative stress plays an important role in the cytotoxic effect of T-2 toxin.

Honey and cardiovascular risk factors, in normal individuals and in patients with diabetes mellitus or dyslipidemia

Diabetes mellitus, hypercholesteremia, hypertension (HTN), and obesity are well-known risk factors for cardiovascular diseases (CVD). Various medications are currently in use for management of these comorbidities. Undesirable side effects are unavoidable and the ultimate and ideal goal is hardly achieved. Honey and other bee products are widely used in traditional medicine for management of many diseases. Others and the authors have found potent biological activities of these products. Honey is now reintroduced in modern medicine as part of wound and burn management. Honey has antioxidant, anti-inflammatory, and antimicrobial activities. More studies are exploring other aspects of honey activity such as its effect on blood sugar, body weight, lipid profile, C-reactive protein, nitric oxide, proinflammatory prostaglandins, and homocysteine. Growing evidence and scientific data support the use of honey in patients with diabetes, HTN, dyslipidemia, obesity, and CVD. This review discusses clinical and preclinical studies on potential influence of honey on diabetes mellitus and cardiovascular risk factors, and emphasizes the importance of conducting more clinical and controlled studies.

Red orange: experimental models and epidemiological evidence of its benefits on human health

In recent years, there has been increasing public interest in plant antioxidants, thanks to the potential anticarcinogenic and cardioprotective actions mediated by their biochemical properties. The red (or blood) orange (Citrus sinensis (L.) Osbeck) is a pigmented sweet orange variety typical of eastern Sicily (southern Italy), California, and Spain. In this paper, we discuss the main health-related properties of the red orange that include anticancer, anti-inflammatory, and cardiovascular protection activities. Moreover, the effects on health of its main constituents (namely, flavonoids, carotenoids, ascorbic acid, hydroxycinnamic acids, and anthocyanins) are described. The red orange juice demonstrates an important antioxidant activity by modulating many antioxidant enzyme systems that efficiently counteract the oxidative damage which may play an important role in the etiology of numerous diseases, such as atherosclerosis, diabetes, and cancer. The beneficial effects of this fruit may be mediated by the synergic effects of its compounds. Thus, the supply of natural antioxidant compounds through a balanced diet rich in red oranges might provide protection against oxidative damage under differing conditions and could be more effective than, the supplementation of an individual antioxidant.

Association between oxidized LDL and folate during pregnancy

High levels of oxidized low-density lipoprotein (ox-LDL) during pregnancy are a risk factor for preeclampsia. Ox-LDL levels might be affected by folate and total homocysteine (tHcy) levels because of their effects on oxygen free radicals. The relationships between ox-LDL and folate and tHcy during pregnancy, however, remain unclear. The present study investigated whether serum folate levels and plasma tHcy levels were associated with plasma ox-LDL levels in pregnant women. A sample of 137 healthy subjects with singleton pregnancies (age 30.3 ± 4.5 years) was recruited from a prenatal clinic in metropolitan Tokyo between June and October 2008. Their levels of plasma ox-LDL, plasma tHcy, and serum folate were measured, and lifestyle variables were obtained using a questionnaire. Dietary intake was assessed by means of a validated self-administered diet history questionnaire. A negative correlation between plasma ox-LDL levels and serum folate levels was found (r(s) = -.218, p =.011). However, there was no association between plasma ox-LDL levels and plasma tHcy levels (r(s) = .055, p = .525). The mean of the logarithmic ox-LDL levels was significantly lower among the participants taking folic acid-containing supplements regularly than among those who were not, after adjusting for confounding factors (p = .024). Serum folate levels and folic acid supplementation might be associated with plasma ox-LDL levels, independent of tHcy levels. The association observed between ox-LDL and folate can be used as evidence for dietary instruction by prenatal care providers.

The Role of Antioxidant Vitamins in Cardiovascular Disease

Objective:

To review the current data on the role of antioxidant vitamins in cardiovascular disease.

Data Sources:

Articles were obtained from a MEDLINE search covering all years. Terms used in the search included combinations of antioxidant, vitamin, vitamin E, vitamin C, beta-carotene, and cardiovascular disease. Reference lists from articles were examined for additional references.

Study Selection and Data Extraction:

Randomized clinical trials were selected and evaluated for study design and data obtained. Observational studies, meta-analyses, and basic science articles were also reviewed for background.

Data Synthesis:

The use of dietary supplements, including vitamins, minerals, and herbal products, is common among patients in the US. Vitamin E, vitamin C, and beta-carotene are all supplements with reported antioxidant activity. Because oxidative stress has been implicated in the development of cardiovascular disease, there has been significant research at the basic science level as well as observational studies and randomized placebo-controlled trials examining the potential impact of vitamin E, vitamin C, and beta-carotene in the prevention and treatment of cardiovascular disease. While basic science data and data from observational studies have identified benefit from antioxidant vitamin supplementation, randomized clinical trials have failed to support a role for antioxidant vitamin supplementation in the prevention or treatment of cardiovascular disease.

Conclusions:

Data from randomized clinical trials do not support the use of antioxidant vitamins in cardiovascular disease. Therefore, antioxidant vitamins should not be recommended to patients for prevention or treatment of cardiovascular disease.

Cadmium suppresses the proliferation of piglet Sertoli cells and causes their DNA damage, cell apoptosis and aberrant ultrastructure

OBJECTIVE

Very little information is known about the toxic effects of cadmium on somatic cells in mammalian testis. The objective of this study is to explore the toxicity of cadmium on piglet Sertoli cells.

METHODS

Sertoli cells were isolated from piglet testes using a two-step enzyme digestion and followed by differential plating. Piglet Sertoli cells were identified by oil red O staining and Fas ligand (FasL) expression as assayed by immunocytochemistry and expression of transferrin and androgen binding protein by RT-PCR. Sertoli cells were cultured in DMEM/F12 supplemented with 10% fetal calf serum in the absence or presence of various concentrations of cadmium chloride, or treatment with p38 MAPK inhibitor SB202190 and with cadmium chloride exposure. Apoptotic cells in seminiferous tubules of piglets were also performed using TUNEL assay in vivo.

RESULTS

Cadmium chloride inhibited the proliferation of Piglet Sertoli cells as shown by MTT assay, and it increased malondialdehyde (MDA) but reduced superoxide dismutase (SOD) and Glutathione peroxidase (GSH-Px) activity. Inhibitor SB202190 alleviated the proliferation inhibition of cadmium on piglet Sertoli cells. Comet assay revealed that cadmium chloride caused DNA damage of Piglet Sertoli cells and resulted in cell apoptosis as assayed by flow cytometry. The in vivo study confirmed that cadmium induced cell apoptosis in seminiferous tubules of piglets. Transmission electronic microscopy showed abnormal and apoptotic ultrastructure in Piglet Sertoli cells treated with cadmium chloride compared to the control.

CONCLUSION

cadmium has obvious adverse effects on the proliferation of piglet Sertoli cells and causes their DNA damage, cell apoptosis, and aberrant morphology. This study thus offers novel insights into the toxicology of cadmium on male reproduction.

Evaluation of the antioxidant properties of N-acetylcysteine in human platelets: prerequisite for bioconversion to glutathione for antioxidant and antiplatelet activity

N-Acetylcysteine (NAC) is a frequently used "antioxidant" in vitro, but the concentrations applied rarely correlate with those encountered with oral dosing in vivo. Here, we investigated the in vitro antioxidant and antiplatelet properties of NAC at concentrations (10-100 microM) that are achievable in plasma with tolerable oral dosing. The impact of NAC pretreatment (2 hours) on aggregation of platelets from healthy volunteers in response to thrombin and adenosine diphosphate and on platelet-derived nitric oxide (NO) was examined. NAC was found to be a weak reducing agent and a poor antioxidant compared with glutathione (reduced form) (GSH). However, platelets treated with NAC showed enhanced antioxidant activity and depression of reactive oxygen species generation associated with increases in intraplatelet GSH levels. An approximately 2-fold increase in NO synthase-derived nitrite was observed with 10 microM NAC treatment, but the effect was not concentration dependent. Finally, NAC significantly reduced both thrombin-induced and adenosine diphosphate-induced platelet aggregation. NAC should be considered a weak antioxidant that requires prior conversion to GSH to convey antioxidant and antithrombotic benefit at therapeutically relevant concentrations. Our results suggest that NAC might be an effective antiplatelet agent in conditions where increased oxidative stress contributes to heightened risk of thrombosis but only if the intraplatelet machinery to convert it to GSH is functional.

Effect of daily fruit ingestion on angiotensin converting enzyme activity, blood pressure, and oxidative stress in chronic smokers

OBJECTIVE

This study examined whether, daily fruit (blueberries) consumption (250 g) for three weeks or acute fruit ingestion (250 g) would attenuate angiotensin converting enzyme (ACE) activity and reduce oxidative stress in chronic cigarette smokers.

METHODS

Twenty subjects were recruited and randomized into fruit or control groups. Blood samples and blood pressure were obtained at baseline and then pre and one hour post when subjects returned to the lab three weeks later. To examine acute effects, the fruit group immediately ingested 250 g of blueberries after returning and at least one hour prior to the post blood draw. Plasma samples were analyzed for ACE activity, F(2)- isoprostanes and lipid hydroperoxides (LH) as measures of oxidative stress, and ferric reducing ability of plasma (FRAP) as a measure of antioxidant potential. A 2 (treatment) x 3 (time) repeated measures ANOVA was used for statistical analysis. If interaction was significant, then Student's t-tests were used to further examine this relationship. For these comparisons, a Bonferroni adjustment was made with statistical significance set at P < 0.025.

RESULTS

The pattern of change between treatments was not significant for any variable except LH (P < 0.001).

CONCLUSION

This study indicates that LH are significantly reduced by daily fruit consumption, but not affected by acute ingestion. This finding could be one way in which fruit consumption contributes to prevention of cardiovascular disease.

Modification with homocysteine does not increase susceptibility of human low-density lipoprotein to iron-mediated oxidation

Oxidation of human low-density lipoprotein (LDL) is centrally involved in the development of cardiovascular diseases. This study investigated whether homocysteine-mediated thiolation of LDL rendered it more susceptible to oxidation by iron. After in vitro exposure to homocysteine thiolactone for 60 minutes, LDL's thiol content increased from 26 +/- 5 (control) to 224 +/- 20 nmol/mg of protein (thiolated; P < .0001). Control and thiolated LDL (0.2 mg of protein per milliliter) were incubated with either redox active iron (Fe(3+); 10 micromol/L) or, as a positive control, copper (Cu(2+); 10 micromol/L). Consistent with the observation of others, thiolation decreased Cu(2+)-dependent formation of lipid oxidation products in LDL (17 +/- 16 nmol/mg of protein formed in thiolated LDL, compared with 81 +/- 21 nmol/mg of protein in control, during 6 hours of incubation; P < .01). Thiolation had no effect, however, on Fe(3+)-mediated oxidation of LDL with lipid oxidation products remaining essentially nondetectable during prolonged incubation (up to 48 hours). Thiolation similarly had no effect on oxidation of LDL (0.2 mg of protein per milliliter) by heme-complexed iron (hemin; 10 micromol/L), with lipid oxidation products increasing to 24 +/- 1 and 27 +/- 4 nmol/mg of protein for control and thiolated LDL, respectively, during 6 hours of incubation (P > .05). Similar results were observed using LDL with varying degrees of thiolation (29 +/- 5, 85 +/- 14, 130 +/- 15, and 213 +/- 19 nmol of thiol per milligram of protein). In conclusion, these results demonstrate that thiolation has no effect on LDL's susceptibility to iron-mediated oxidation.

New developments and novel therapeutic perspectives for vitamin C

Vitamin C is required for collagen synthesis and biosynthesis of certain hormones and recommended dietary intake levels are largely based these requirements. However, to function effectively as an antioxidant (or a pro-oxidant), relatively high levels of this vitamin must be maintained in the body. The instability of vitamin C combined with its relatively poor intestinal absorption and ready excretion from the body reduce physiological availability of this vitamin. This inability to maintain high serum levels of vitamin C may have serious health implications and is particularly relevant in the onset and progression of degenerative disease, such as cancer and cardiovascular disease (CVD), which have a strong contributing oxidative damage factor. In this review, we examine recent studies on the regulation of transport mechanisms for vitamin C, related clinical ramifications, and potential implications in high-dose vitamin C therapy. We also evaluate recent clinical and scientific evidence on the effects of this vitamin on cancer and CVD, with focus on the key mechanisms of action that may contribute to the therapeutic potential of this vitamin in these diseases. Several animal models that could be utilized to address unresolved questions regarding the feasibility of vitamin C therapy are also discussed.

Nutrient intake during peritoneal dialysis at the Prince of Wales Hospital in Hong Kong

BACKGROUND

Individuals undergoing peritoneal dialysis are at increased risk of developing cardiac disease and malnutrition.

STUDY DESIGN

A cross-sectional survey.

SETTINGS AND PARTICIPANTS

249 Chinese continuous ambulatory peritoneal dialysis (CAPD) patients were recruited from the Prince of Wales Hospital in Hong Kong. Another 249 age- and sex-matched controls were recruited from an archive of 1,010 individuals with known food frequency questionnaire (FFQ) data.

OBJECTIVE

To compare the dietary intake pattern of CAPD patients with controls and evaluate its association with background cardiac disease.

OUTCOMES AND MEASUREMENTS

Intake of different nutrients was estimated by using a 7-day FFQ.

RESULTS

Intake of all nutrients was lower in CAPD patients than controls, with resulting lower overall energy intake. Nutrient intake was decreased further in CAPD patients with background cardiac disease, which corresponded to worse nutritional status. Controlling for age, male sex, body weight, diabetes mellitus, dialysis therapy duration, residual renal function, peritoneal dialysis urea clearance, and Charlson Comorbidity Index score, background cardiac disease was associated independently with less intake of energy and most macronutrients and micronutrients. However, the association between background cardiac disease and energy and most nutrient intake was decreased or even lost when additional adjustment was made for C-reactive protein and serum albumin levels.

LIMITATIONS

An FFQ is limited in that nutrient quantitation is not exact and may be underestimated as a result of underreporting by patients. CAPD patients were compared with a control group without cardiovascular disease ascertainment that did not include subjects with diabetes.

CONCLUSIONS

Chinese CAPD patients had significantly lower nutrient intake than age- and sex-matched controls. The association between cardiac disease and lower dietary macronutrient and micronutrient intake in CAPD patients was mediated in part through systemic inflammation, which also was associated with more malnutrition. More attention should be focused on improving the intake pattern of Chinese CAPD patients.

Vitamin C preserves the cardio-protective paraoxonase activity of high-density lipoprotein during oxidant stress

HDL-associated paraoxonase (PON) antioxidant enzyme activity is cardio-protective. We investigated whether vitamin C prevented loss of PON activity from HDL during oxidant stress. HDL was incubated with either hydrophilic or lipophilic peroxyl radical initiators in the absence (control) or presence of vitamin C (50 and 100 micromol/L). Regardless of the type of radical, accumulation of lipid oxidation products in HDL was similar in incubations lacking vitamin C. Loss of PON activity was greater in HDL exposed to hydrophilic, in contrast to lipophilic, radicals, but addition of vitamin C maintained enzyme activity. Vitamin C's capacity to attenuate loss of the HDL ability to prevent atherogenic modification of LDL (assessed as electrophoretic mobility) was, however, modest, and appeared limited only to those incubations in which HDL was exposed to lipophilic radicals. Our results indicate that vitamin C may, under some conditions, prevent loss of cardio-protective function from HDL during oxidant stress.

LDL oxidized with iron in the presence of homocysteine/cystine at acidic pH has low cytotoxicity despite high lipid peroxidation

Fe(III) can have a strong oxidizing effect in the presence of reductants at acidic pH, which may occur under anaerobic conditions or in regions of inflammation. Low density lipoprotein (LDL) oxidation with Fe(III) and homocysteine/cystine at acidic pH provoked mainly formation of lipid hydroperoxides and thiobarbituric acid reactive substances (TBARS) in the absence of significant protein modification. Even when oxidized to a high TBARS content, LDL oxidized at acidic pH was not cytotoxic when added to THP-1 monocytes in a concentration causing cell death when LDL was oxidized to a similar TBARS content at plasma pH with Fe(III) or Cu(II) in the presence or absence of homocysteine/cystine. Inducible nitric oxide production by RAW264.7 mouse macrophages was only weakly inhibited by LDL oxidized at acidic pH, even if acetylated before oxidation to increase uptake, as compared to LDL oxidized with Cu(II) at plasma pH to a similar TBARS content or anodic electrophoretic mobility. LDL oxidized at acidic pH may mainly induce protective mechanisms against oxidative stress while causing little acute damage of cells.

Oxidative Susceptibility of Unfractionated Serum or Plasma: Response to Antioxidants in Vitro and to Antioxidant Supplementation

Background: The susceptibility of plasma lipids to oxidation is thought to be a factor contributing to atherogenic risk. Various groups have studied the in vitro oxidizability of isolated LDL and examined the effects of conventional antioxidants. The drawbacks associated with the isolation of LDL for evaluation of in vitro oxidizability, however, have limited the application of this measurement in large-scale studies.

Methods: We developed and evaluated an assay that can be used to directly assess the oxidative susceptibility of unfractionated serum or plasma lipids, obviating the need for isolation of lipoprotein fractions. Oxidative conditions were initiated in vitro with cuprous chloride and 2,2′-azobis(2-amidinopropane) hydrochloride. The effects of antioxidants added in vitro, and as an oral supplement, were monitored by conjugated diene formation.

Results: The addition of ascorbic acid (0–50 μmol/L) in vitro elicited a dose-dependent protective effect, increasing the lag time to oxidation (P &lt;0.001). In contrast, α-tocopherol demonstrated prooxidant behavior at increasing concentrations (0–50 μmol/L), although we observed a decrease in the maximum rate of oxidation. Our findings are supported by the results from plasma samples of participants in a randomized antioxidant (vitamins C and E) intervention study after acute ischemic stroke. The group receiving vitamins C and E for 14 days showed an increased lag time to plasma lipid oxidation in vitro compared with the nonsupplemented group (P &lt;0.05).

Conclusion: The susceptibility of unfractionated plasma or serum lipids to oxidation in vitro offers an alternative to LDL for evaluating the efficacy of antioxidant regimens.

Ascorbate is particularly effective against LDL oxidation in the presence of iron(III) and homocysteine/cystine at acidic pH

Metal-catalyzed LDL oxidation is enhanced by the presence of homocysteine. In this study, the effectiveness of ascorbic acid against low-density lipoprotein (LDL) oxidation by iron(III) and copper(II) in the presence of homocysteine and the main plasma disulfide cystine was investigated. Relative to the degree of LDL oxidation reached in the absence of antioxidants, ascorbic acid was particularly effective against iron-catalyzed LDL oxidation at pH 6.0. This can be explained from its stability under acidic conditions and is likely to be important in ischemia, in inflammation and exhausting exercise. At pH 7.4, an ascorbic acid concentration at least as high as the concentration of homocysteine might be necessary to efficiently inhibit LDL oxidation by iron(III) and copper(II) in the presence of homocysteine and cystine. Histidine increased the efficiency of ascorbic acid as an antioxidant against copper-mediated oxidation in this system. The capacity of homocysteine to regenerate ascorbic acid from dehydroascorbic acid appeared to play a minor role in inhibition of ascorbic acid oxidation by copper as compared to copper chelation by homocysteine.

Ascorbate uptake in pig coronary artery endothelial cells

Although smooth muscle and endothelial cells in pig coronary artery are morphologically and functionally distinct, ascorbate uptake has been characterized only in smooth muscle cells. Ascorbate transporters in kidney and intestinal epithelial cells differ from those in smooth muscle. We examined ascorbate transport and mRNA expression of sodium-dependent vitamin C transporters (SVCT) by RT-PCR in the pig coronary artery endothelial cell cultures. When 14C-ascorbate uptake in endothelial cells was examined as 14C or by HPLC, the two values did not differ from each other. 14C-ascorbate uptake was Na(+)-dependent, stereoselective for L-ascorbate and inhibited by sulfinpyrazone. The kinetic characteristics of the uptake were: Km = 27 +/- 3 microM (Hill coefficient = 1) for ascorbate and Km = 73 +/- 14 mM (Hill coefficient = 2) for Na+. Surprisingly, endothelial cells had similar kinetic parameters as smooth muscle cells, except for a slightly lower uptake velocity in endothelial cells. Comparison with the smooth muscle showed that both tissue types expressed mRNA for SVCT2. Endothelial cells differ from epithelial cells which express mainly SVCT1 but resemble smooth muscle cells in this respect.

Optimization of ascorbic and uric acid separation in human plasma by free zone capillary electrophoresis ultraviolet detection

In this paper we propose a new fast free zone capillary electrophoresis method for the simultaneous determination of ascorbic acid (AA) and uric acid (UA) in human plasma. We investigated the effect of analytical parameters, such as concentration and pH of borate running buffer, cartridge temperature, and sample treatment, on resolution, migration times, corrected peak areas, and efficiency. A good separation was achieved using a 60.2-cmx75-microm uncoated silica capillary and 100 mmol/L sodium borate buffer, pH 8, when metaphosphoric acid was employed as protein precipitant, in less than 4 min. These conditions gave a good reproducibility of migration times (CV 0.35 and 0.34%) and peak areas (CV 3.2 and 3.1%) for ascorbate and urate, respectively. The limit of detection was 0.5mg/L for both analytes when the detection was performed at 254 nm for AA and at 292 nm for UA. We compared the present method with a validated capillary electrophoresis assay by measuring plasma urate and ascorbate in 32 normal subjects and the obtained data were analyzed by the Passing and Bablok regression.

Natural Honey Lowers Plasma Glucose, C-Reactive Protein, Homocysteine, and Blood Lipids in Healthy, Diabetic, and Hyperlipidemic Subjects: Comparison with Dextrose and Sucrose

This study included the following experiments: (1) effects of dextrose solution (250 mL of water containing 75 g of dextrose) or honey solution (250 mL of water containing 75 g of natural honey) on plasma glucose level (PGL), plasma insulin, and plasma C-peptide (eight subjects); (2) effects of dextrose, honey, or artificial honey (250 mL of water containing 35 g of dextrose and 40 g of fructose) on cholesterol and triglycerides (TG) (nine subjects); (3) effects of honey solution, administered for 15 days, on PGL, blood lipids, C-reactive protein (CRP), and homocysteine (eight subjects); (4) effects of honey or artificial honey on cholesterol and TG in six patients with hypercholesterolemia and five patients with hypertriglyceridemia; (5) effects of honey for 15 days on blood lipid and CRP in five patients with elevated cholesterol and CRP; (6) effects of 70 g of dextrose or 90 g of honey on PGL in seven patients with type 2 diabetes mellitus; and (7) effects of 30 g of sucrose or 30 g of honey on PGL, plasma insulin, and plasma C-peptide in five diabetic patients. In healthy subjects, dextrose elevated PGL at 1 (53%) and 2 (3%) hours, and decreased PGL after 3 hours (20%). Honey elevated PGL after 1 hour (14%) and decreased it after 3 hours (10%). Elevation of insulin and C-peptide was significantly higher after dextrose than after honey. Dextrose slightly reduced cholesterol and low-density lipoprotein-cholesterol (LDL-C) after 1 hour and significantly after 2 hours, and increased TG after 1, 2, and 3 hours. Artificial honey slightly decreased cholesterol and LDL-C and elevated TG. Honey reduced cholesterol, LDL-C, and TG and slightly elevated high-density lipoprotein-cholesterol (HDL-C). Honey consumed for 15 days decreased cholesterol (7%), LDL-C (1%), TG (2%), CRP (7%), homocysteine (6%), and PGL (6%), and increased HDL-C (2%). In patients with hypertriglyceridemia, artificial honey increased TG, while honey decreased TG. In patients with hyperlipidemia, artificial honey increased LDL-C, while honey decreased LDL-C. Honey decreased cholesterol (8%), LDL-C (11%), and CRP (75%) after 15 days. In diabetic patients, honey compared with dextrose caused a significantly lower rise of PGL. Elevation of PGL was greater after honey than after sucrose at 30 minutes, and was lower after honey than it was after sucrose at 60, 120, and 180 minutes. Honey caused greater elevation of insulin than sucrose did after 30, 120, and 180 minutes. Honey reduces blood lipids, homocysteine, and CRP in normal and hyperlipidemic subjects. Honey compared with dextrose and sucrose caused lower elevation of PGL in diabetics.

Vitamin C Inhibits Lipid Oxidation in Human HDL

HDL are susceptible to oxidation, which affects their cardioprotective properties. Although several studies have reported inhibition of HDL oxidation by vitamin E, none has determined the potential protective effect of vitamin C, another important blood antioxidant. We investigated whether vitamin C protects HDL from oxidation by incubating HDL (0.2 g of protein/L) at 37 degrees C with cupric (Cu2+) ions (10 micromol/L) in the absence (control) or presence of vitamin C (20-200 micromol/L). In the absence of vitamin C, lipid oxidation in HDL began immediately and proceeded rapidly. Cholesteryl linoleate declined to a minimum, whereas lipid oxidation products (lipid dienes and TBARS) increased to near-maximal levels within 1 h. Vitamin C (50-200 micromol/L) retarded initiation of lipid oxidation for at least 4 h under the same conditions. The ability of vitamin C to preserve the cardioprotective antioxidant function of HDL was also assessed. HDL (0.5 g of protein/L) preincubated with Cu2+ (10 micromol/L) for 2 h in the absence of vitamin C lost antioxidant activity (45.4 +/- 6.2% inhibition of LDL oxidation compared with 93.2 +/- 3.6% for native HDL, P < 0.05). The addition of vitamin C (50-200 micromol/L) during preincubation of HDL with Cu2+, however, resulted in no significant loss of HDL antioxidant activity (77.3 +/- 0.3 to 89.8 +/- 5.4% inhibition of LDL oxidation, P > 0.05 compared with native HDL). Our results demonstrate that vitamin C inhibits lipid oxidation in HDL and preserves the antioxidant activity associated with this lipoprotein fraction.