Is vitamin C superior to diltiazem for radial artery vasodilation in patients awaiting coronary artery bypass grafting?

Role of ascorbic acid in cardiac allograft vasculopathy

PURPOSE OF THE REVIEW

Cardiac allograft vasculopathy (CAV) is a progressive fibroproliferative disease which occurs after heart transplantation and is associated with significant long-term morbidity and mortality. Currently available strategies including statins, mammalian target of rapamycin (mTOR) inhibitors, and revascularization, have limited overall effectiveness in treating this pathology once the disease process is established. mTOR inhibitors, while effective when used early in the disease process, are not well tolerated, and hence not routinely used in post-transplant care.

RECENT DATA

Recent work on rodent models have given us a novel mechanistic understanding of effects of ascorbic acid in preventing CAV. TET methyl cytosine dioxygenase2 (TET2) reduces vascular smooth muscle cell (VSMC) apoptosis and intimal thickening. TET2 is repressed by interferon γ (IFNγ) in the setting of CAV. Ascorbic acid has been shown to promote TET2 activity and attenuate allograft vasculopathy in animal models and CAV progression in a small clinical trial.

SUMMARY

CAV remains a challenging disease process and needs better preventative strategies. Ascorbic acid improves endothelial dysfunction, reduces reactive oxygen species, and prevents development of intimal hyperplasia by preventing smooth muscle cell apoptosis and hyperproliferation. Further large-scale randomized control studies of ascorbic acid are needed to establish the role in routine post-transplant management.

Association of Smoking and Other Factors With the Outcome of Mohs Reconstruction Using Flaps or Grafts

Importance

Smoking, a common lifestyle trait, is considered by many surgeons to be a major risk factor for postoperative complications. However, in the literature on local reconstruction, the association between smoking and the rate of postoperative complications after cutaneous tissue transfer is not well characterized.

Objective

To study the outcomes of flaps and grafts used in Mohs micrographic surgery reconstruction with respect to smoking status and patient-specific and surgery-specific variables.

Design, Setting, and Participants

This retrospective case-control study was conducted at a single tertiary referral center among 1008 patients who underwent Mohs reconstruction repaired by flap or graft between July 1, 2012, and June 30, 2016, and were selected via consecutive sampling. Cases with incomplete records or those in which a single flap or graft was used to repair multiple defects were excluded. Data analysis was performed from September 2017 to January 2018.

Main Outcomes and Measures

Postoperative acute and long-term complications. Acute complications included postsurgical infection, dehiscence, hematoma, uncontrolled bleeding, and tissue necrosis that required medical counseling or intervention. Long-term complications included functional or cosmetic outcomes that prompted the patient to request or the surgeon to offer additional intervention.

Results

Of the 1008 patients included in the study (396 women and 612 men), the median (SD) age was 70 (12) years (range, 21-90 years). A total of 128 patients (12.7%) were current smokers, 385 (38.2%) were former smokers, and 495 (49.1%) were never smokers. On multivariate logistic regression, current smoking (odds ratio [OR], 9.58; 95% CI, 3.63-25.3), former smoking (OR, 3.64; 95% CI, 1.41-9.38), larger defect size (OR, 2.25; 95% CI, 1.58-3.20), and the use of free cartilage graft (OR, 8.19; 95% CI, 2.02-33.1) were associated with increased risks of acute complications. For long-term complications, central face location (OR, 25.4; 95% CI, 6.16-106.5), use of interpolation flap or flap-graft combination (OR, 3.49; 95% CI, 1.81-6.74), larger flap size (OR, 1.42; 95% CI, 1.09-1.87), and basal cell carcinomas or other basaloid tumors (OR, 3.43; 95% CI, 1.03-11.5) were associated with an increased risk, whereas increased age (OR, 0.66 per 10-year interval; 95% CI, 0.54-0.80) was associated with decreased risk.

Conclusions and Relevance

This study suggests that both current and former smokers are at increased risk for acute postsurgical complications but that smoking status is not associated with long-term complications. These findings may allow the surgeon to better quantify the magnitude of risk and provide helpful information for patient counseling.

Level of Evidence

3.

Levels of l-ascorbic acid and cadmium in the saphenous vein of patients with coronary artery disease are negatively correlated

BACKGROUND

The aim of this study was the simultaneous determination of levels of cadmium and l-ascorbic Acid (AA) in human saphenous vein (SV) used in coronary artery bypass grafting (CABG) and check whether there is a relationship between these levels.

METHODS

Human SV were collected from 40 patients (20 men and 20 women; age, 40-75 years) at the time of routine coronary artery surgical revascularization. The concentration of cadmium in the tissue was determined according to the GF AAS-atomic absorption method. The concentration of AA was assayed in supernatant by FIA method with spectrophotometric detection.

RESULTS

AA concentration (mean±SD); men: 98,7±13,18μg/g tissue, women: 96,06±11,98μg/g tissue. Cadmium concentration(mean±SD); men: 309±103,71ng/g tissue, women: 348,5±255,71ng/g tissue. Correlations among concentrations of AA and cadmium were insignificant negative in the group of men (Pearson r=-0,1504, p=0,5269) and in the group women (Pearson r=-0339, p=0144).

CONCLUSIONS

Negative correlations among concentrations of AA and cadmium in human SV obtained in our study may indicate a protective effect of this vitamin in relation to toxic cadmium.

Does vitamin C or its combination with vitamin E improve radial artery endothelium-dependent vasodilatation in patients awaiting coronary artery bypass surgery?

Background

We evaluated the vasodilatory effects of two antioxidants, vitamins C (ascorbic acid) and E (α-tocopherol), on radial artery and endothelium-dependent responses in patients awaiting coronary artery bypass surgery.

Methods

The study was performed in three groups. The first group took 2 g of vitamin C orally (n = 31, vitamin C group), the second group took 2 g of vitamin C with 600 mg of vitamin E orally (n = 31, vitamins C + E group), and the third group took no medication (n = 31, control group). After baseline measurements were taken of the radial artery lumen diameter, flow volume and lumen area in the non-dominant radial artery, occlusion was maintained for five minutes with a pressure cuff placed around the arm. The measurements were taken again at the time of deflating the cuff, and 60 seconds later. The measurements were repeated after medication in two of the groups and after placebo in the third group.

Results

We compared values of the vitamin C group with those of the vitamins C + E group, and found that the latter were higher than those of the vitamin C group but not statistically significant. In the control group, there was no statistical difference.

Conclusion

Vitamin C or its combination with vitamin E significantly enhanced endothelium-dependent vasodilatation in the radial circulation of patients with coronary artery disease. Its combination with vitamin E was superior to vitamin C administration alone for endothelial enhancement but this difference was not statistically significant. We hypothesised that vitamin C or its combination with vitamin E may be used as antioxidants for arterial graft patency in patients undergoing coronary artery surgery.

Vitamin C activation of the biosynthesis of epoxyeicosatrienoic acids

The cardiovascular effects of vitamin C (VitC) could be mediated by epoxyeicosatrienoic acids (EETs). We aimed to study the mechanism of VitC-dependent microsomal formation of cis- and trans-EETs and the regulation of EET levels in rat isolated perfused kidneys and in vivo. VitC biphasically stimulated rat kidney microsomal cis- and trans-EET formation in a ratio of 1:2, involving the participation of lipid hydroperoxides (LOOHs), Fe²⁺, and cytochrome P450 (CYP). Levels of LOOHs correlated with microsomal EET production. LOOH stimulation of CYP isoforms resulted in preferred trans-over cis-EET formation from arachidonic acid and was associated with the cleavage of LOOHs, which indicated a CYP peroxygenase activity. EETs contributed to VitC-induced vasodilator responses in rat isolated perfused kidneys. VitC (1 mg/ml) given in the drinking water for 9 days doubled rat urinary EET excretion, increased plasma levels of EETs, mostly trans-EETs, by 40%, and reduced plasma levels of 20-hydroxyeicosatetraenoic acid. Depletion of VitC in brain cortex and kidney tissues by more than 20- and 50-fold, respectively, in gulonolactone oxidase-knockout mice was associated with mild increases in tissue EETs. These data suggest that LOOHs are a determinant factor for EET formation in vivo in which VitC exerts a key regulatory effect. VitC-activated CYP peroxygenase activity may represent a CYP interaction with lipoxygenases and cyclooxygenases to mediate the cardiovascular effects of VitC via formation of EETs.

Role of marginal vitamin C deficiency in atherogenesis: in vivo models and clinical studies

Vitamin C is a pivotal redox modulater in many biological reactions of which several remain poorly understood. Naturally, vitamin C has been the subject of many investigations over the past decades in relation to its possible beneficial effects on cardiovascular disease primarily based on its powerful yet general antioxidant properties. However, growing epidemiological, clinical and experimental evidence now suggests a more specific role of ascorbate in vasomotion and in the prevention of atherosclerosis. For example, in contrast to most other biological antioxidants, administration of vitamin C can apparently induce vasodilation. Millions of people worldwide can be diagnosed with vitamin C deficiency according to accepted definitions. In this perspective, the present review examines the evidence for a specific link between vitamin C deficiency and increased risk of atherosclerosis as well as the possible mechanisms by which vitamin C may exert its protective function.

C-Type Natriuretic Peptide Relaxes Human Coronary Artery Bypass Grafts Preconstricted by Endothelin-1

BACKGROUND

Endothelin is implicated in graft spasm after coronary artery bypass grafting. We assessed reversal by the endothelium-derived vasodilator C-type natriuretic peptide of prior contraction of radial artery and other vessels commonly used for coronary artery bypass surgery.

METHODS

Segments of human radial artery, saphenous vein, and internal mammary artery were mounted in organ baths after removal from patients undergoing cardiac surgery (n = 34; 64 +/- 2 years). Effects of increasing concentrations of C-type natriuretic peptide (with or without aprotinin, 1,000 U/mL) on endothelin-induced contraction were compared with acetylcholine, sodium nitroprusside, and papaverine.

RESULTS

C-type natriuretic peptide relaxed endothelin precontraction in all vessels (F = 17.8, 36.3, and 48.4, respectively; p < 0.001), with maximum relaxations of 44%, 54%, and 66% in saphenous vein, internal mammary artery, and radial artery, respectively. Aprotinin did not affect relaxation to C-type natriuretic peptide. Acetylcholine relaxed the saphenous vein weakly, with maximal relaxation of 9% at 10(-6) M. However, the radial artery and internal mammary artery relaxed strongly to acetylcholine. The highest concentration of papaverine completely relaxed all vessels, but responses were less sensitive than to sodium nitroprusside or acetylcholine.

CONCLUSIONS

C-type natriuretic peptide reverses endothelin-induced constriction in arterial and venous conduits used for coronary artery bypass, particularly the radial artery. Proteolytic breakdown of C-type natriuretic peptide by local vascular enzymes appears of little importance in vitro. This signals the therapeutic potential of using C-type natriuretic peptide as an antagonist of graft vasospasm after coronary artery bypass surgery.

Histamine H1 and H2 receptor–mediated vasoreactivity of human internal thoracic and radial arteries

BACKGROUND

Although internal thoracic arteries (ITAs) and radial arteries (RAs) have been shown to have similar patency, RAs tend to be more vasospastic postoperatively compared with ITAs. Therefore, the purpose of this study was to examine the effect of histamine subclass 1 (H1) receptors and histamine subclass 2 (H2) receptors on vasoreactivity in human ITAs and RAs.

METHODS

Vessels were obtained from coronary artery bypass grafting patients. Human arterial rings (2 mm) were mounted in tissue baths, and baseline contractility was determined. Histamine concentration response curves (10(-9)-10(-3) mol/L) were performed in the absence or presence of diphenhydramine (H1 antagonist, 10(-4) mol/L) or famotidine (H2 antagonist, 10(-4) mol/L). Comparison of curves was performed by 2-way analysis of variance with repeated measures and a Bonferroni post-t test.

RESULTS

Maximal contraction to histamine was significantly greater in RA (8.3 +/- 0.8 g, n = 6) than in ITA (2.9 +/- 0.3, n = 6), (P < .05). However, there was no difference in sensitivity. Histamine-mediated responses of both RA and ITA were blocked by pre-exposure to H1 antagonist, whereas an H2 antagonist only partially inhibited RA responses while blocking most of the ITA response to histamine.

CONCLUSION

These studies suggest that H1 receptors alone cause contraction in RA but not in ITA, which may have potential linkage to patency and vasospasm. Further studies are necessary to identify the exact role of H2 receptors in ITA.