Protective role of ascorbic acid against lipid peroxidation and myocardial injury

An update on drugs with therapeutic potential for SARS-CoV-2 (COVID-19) treatment

The COVID-19 pandemic is one of the greatest threats to human health in the 21st century with more than 257 million cases and over 5.17 million deaths reported worldwide (as of November 23, 2021. Various agents were initially proclaimed to be effective against SARS-CoV-2, the etiological agent of COVID-19. Hydroxychloroquine, lopinavir/ritonavir, and ribavirin are all examples of therapeutic agents, whose efficacy against COVID-19 was later disproved. Meanwhile, concentrated efforts of researchers and clinicians worldwide have led to the identification of novel therapeutic options to control the disease including PAXLOVID™ (PF-07321332). Although COVID-19 cases are currently treated using a comprehensive approach of anticoagulants, oxygen, and antibiotics, the novel Pfizer agent PAXLOVID™ (PF-07321332), an investigational COVID-19 oral antiviral candidate, significantly reduced hospitalization time and death rates, based on an interim analysis of the phase 2/3 EPIC-HR (Evaluation of Protease Inhibition for COVID-19 in High-Risk Patients) randomized, double-blind study of non-hospitalized adult patients with COVID-19, who are at high risk of progressing to severe illness. The scheduled interim analysis demonstrated an 89 % reduction in risk of COVID-19-related hospitalization or death from any cause compared to placebo in patients treated within three days of symptom onset (primary endpoint). However, there still exists a great need for the development of additional treatments, as the recommended therapeutic options are insufficient in many cases. Thus far, mRNA and vector vaccines appear to be the most effective modalities to control the pandemic. In the current review, we provide an update on the progress that has been made since April 2020 in clinical trials concerning the effectiveness of therapies available to combat COVID-19. We focus on currently recommended therapeutic agents, including steroids, various monoclonal antibodies, remdesivir, baricitinib, anticoagulants and PAXLOVID™ summarizing the latest original studies and meta-analyses. Moreover, we aim to discuss other currently and previously studied agents targeting COVID-19 that either show no or only limited therapeutic activity. The results of recent studies report that hydroxychloroquine and convalescent plasma demonstrate no efficacy against SARS-CoV-2 infection. Lastly, we summarize the studies on various drugs with incoherent or insufficient data concerning their effectiveness, such as amantadine, ivermectin, or niclosamide.

Variations in oxidative stress and antioxidant defense level during different phases of hibernation in common Asian toad, Duttaphrynus melanostictus

To assess redox status during hibernation with metabolic depression, oxidative stress parameters and antioxidant defense were assessed during different phases of hibernation including active period, hibernation, arousal, and post-arousal period, in the liver and brain tissues of Duttaphrynus melanostictus. We hypothesized low levels of oxidative stress and antioxidant defense during the hibernation period in comparison to the summer active period, due to hypometabolism and their subsequent increase during the arousal period following an increase in body temperature and metabolism. Contrary to our hypothesis, increased oxidative stress with significantly higher lipid peroxidation, protein carbonylation, oxidized glutathione (GSSG): glutathione (GSH) ratio, and elevated antioxidants defense consisting of higher catalase activity and high ascorbic acid content to control oxidative stress were found during hibernation. However, GSH and uric acid levels were found low with super oxide dismutase (SOD) activities at a steady level during hibernation. Supporting our hypothesis, increased oxidative stress with high lipid peroxidation and GSSG:GSH ratio were found during arousal from hibernation owing to increased oxygen consumption and rewarming. Augmented catalase and SOD activities and nonenzymatic antioxidants (GSH, ascorbic acid, and uric acid) level were found to counteract oxidative stress during arousal periods as it was expected. A steady level of protein carbonylation, indicating no oxidative damage during arousal from hibernation due to elevated antioxidant defense, shows the significance of hibernation to overcome food and water scarcity and cold climatic condition. Decrease in antioxidants levels accompanying coming down of lipid peroxidation, protein carbonylation, and GSSG:GSH ratio to their lower levels during the post-arousal period showing normalcy in redox status as it was during active period indicates controllability of oxidative stress in hibernating toads.

The efficiency and safety of high-dose vitamin C in patients with COVID-19: a retrospective cohort study

BACKGROUND

The inflammatory reaction is the main cause of acute respiratory distress syndrome and multiple organ failure in patients with Coronavirus disease 2019, especially those with severe and critical illness. Several studies suggested that high-dose vitamin C reduced inflammatory reaction associated with sepsis and acute respiratory distress syndrome. This study aimed to determine the efficacy and safety of high-dose vitamin C in Coronavirus disease 2019.

METHODS

We included 76 patients with Coronavirus disease 2019, classified into the high-dose vitamin C group (loading dose of 6g intravenous infusion per 12 hr on the first day, and 6g once for the following 4 days, n=46) and the standard therapy group (standard therapy alone, n=30).

RESULTS

The risk of 28-day mortality was reduced for the high-dose vitamin C versus the standard therapy group (HR=0.14, 95% CI, 0.03-0.72). Oxygen support status was improved more with high-dose vitamin C than standard therapy (63.9% vs 36.1%). No safety events were associated with high-dose vitamin C therapy.

CONCLUSION

High-dose vitamin C may reduce the mortality and improve oxygen support status in patients with Coronavirus disease 2019 without adverse events.

Ankle-brachial pressure index and mini nutritional assessment in community-dwelling elderly people

BACKGROUND

A low ankle-brachial pressure index (an ABPI value <0.90) is considered predictive of cardiovascular disease, and is widely thought to increase morbidity and mortality in the elderly. However, good nutrition is beneficial both for the health and the ability to resist and recover from the disease.

OBJECTIVE

The aim of the present study was to evaluate the relationship between the ankle-brachial pressure index and the nutritional status of the elderly in a city of Kochi prefecture, Japan.

METHODS

This was a cross-sectional study in which a total of 100 elderly people, both males and females, were screened for ankle-brachial pressure index (ABPI), nutritional status (through the use of the short form of the mini nutritional assessment), activities of daily living, lifestyle, gait speed (10MWT), postural stability (OLST), and functional mobility (TUG).

RESULTS

About 67% of the participants were found to have a normal nutritional status, 27% were at risk of malnutrition, and six percent were classified as malnourished. The mean ABPI of the participants was 1.08±0.10, and three participants had an ABPI lower than 0.90. The ABPI was statistically higher in well nourished participants compared with those at risk of malnutrition or the malnourished. The mean ABPI was significantly higher in non-smokers compared with former smokers. The ABPI was found to correlate negatively with gait speed and with TUG score.

CONCLUSION

Well-nourished elderly had a higher normal ankle-brachial pressure index as compared with the malnourished elderly. This study provides supportive evidence for the necessity of adequate nutrition for elderly people.

Molecular and cellular mechanisms of cigarette smoke-induced myocardial injury: prevention by vitamin C

BACKGROUND

Cardiovascular disease (CVD) remains one of the major killers in modern society. One strong risk factor of CVD is cigarette smoking that causes myocardial injury and leads to the genesis of pathological cardiovascular events. However, the exact toxic component(s) of cigarette smoke (CS) and its molecular and cellular mechanisms for causing myocardial injury leading to heart damage and its prevention are largely unknown.

METHODOLOGY/PRINCIPAL FINDINGS

Using a guinea pig model, here we show that chronic exposure to CS produces myocardial injury that is prevented by vitamin C. Male guinea pigs were fed either vitamin C-deficient (0.5 mg/day) or vitamin C-sufficient (15 mg/day) diet and subjected to CS exposure from 5 Kentucky Research cigarettes (3R4F)/day (6 days/week) in a smoke chamber up to 8 weeks. Pair-fed sham controls were subjected to air exposure instead of CS exposure under similar conditions. Myocardial injury was produced in CS-exposed marginal vitamin C-deficient guinea pigs as evidenced by release of cardiac Troponin-T and I in the serum, oxidative stress, inflammation, apoptosis, thrombosis and collagen deposition in the myocardium. Treatment of rat cardiomyocyte cells (H9c2) in vitro and guinea pigs in vivo with p-benzoquinone (p-BQ) in amounts derived from CS revealed that p-BQ was a major factor responsible for CS-induced myocardial damage. A moderately large dose of vitamin C (15 mg/day) prevented CS/p-BQ-induced myocardial injury. Population based studies indicated that plasma vitamin C levels of smokers without disease were significantly lower (p = 0,0000) than that of non-smokers. Vitamin C levels of CS-related cardiovascular patients were further lower (p = 0.0000) than that of smokers without disease.

CONCLUSIONS/SIGNIFICANCE

The results indicate that dietary supplementation of vitamin C may be a novel and simple therapy for the prevention of pathological cardiovascular events in habitual smokers.

Enhanced heme oxygenase activity increases the antioxidant defense capacity of guinea pig liver upon acute cobalt chloride loading: comparison with rat liver

Changes in the activity of so-called oxidative stress defensive enzymes, superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase and heme oxygenase, as well as changes in lipid peroxidation and reduced glutathione levels, were measured in guinea pig and rat liver after acute cobalt loading. Cobalt chloride administration produced a much higher degree of lipid peroxidation in guinea pig than in rat liver compared with the control animals. The intrahepatic reduced glutathione content in control guinea pig was higher than that in rat, but was equally decreased in both species after cobalt administration. The enzymatic scavengers of free radicals, superoxide dismutase, catalase and glutathione peroxidase, were significantly decreased in rat liver after acute cobalt loading, and as a compensatory reaction, the heme oxygenase activity was increased (seven-fold). In guinea pig liver, only superoxide dismutase activity was depleted in response to cobalt-induced oxidative stress, while catalase and glutathione peroxidase were highly activated and the heme oxygenase activity was dramatically increased (13-fold). It is assumed that enhanced heme oxygenase activity may have important antioxidant significance by increasing the liver oxidative-stress defense capacity.

Dietary effects of conjugated octadecatrienoic fatty acid (9 cis, 11 trans, 13 trans) levels on blood lipids and nonenzymatic in vitro lipid peroxidation in rats

The present study examined the antioxidant activity of conjugated octadecatrienoic fatty acid (9 cis,11 trans,13 trans-18:3), alpha-eleostearic acid, of karela seed (Momordica charantia), fed to rats for 4 wk. The growth pattern of rats and the effect on plasma cholesterol and high density lipoprotein (HDL) cholesterol and peroxidation of plasma lipid, lipoprotein, eryhrocyte membrane, and liver lipid were measured. Rats were raised on diets containing sunflower oil mixed with three different levels of conjugated trienoic fatty acid (9c,11t,3t-18:3) 0.5, 2, and 10% by weight; the control group was raised with sunflower oil as dietary oil as the source of linoleic acid (9c,12c-18:2). The growth pattern of the three experimental groups of rats showed no significant difference compared to the control group of rats, but the group with 10% 9c,11t,13t-18:3 had slightly higher body weight than the control group of rats. Concentrations of total cholesterol, HDL-cholesterol, and non-HDL-cholesterol in plasma were similar in all four groups. Plasma lipid peroxidation was significantly lower in the case of 0.5% 9c,11t,13t-18:3 group than the control group and the 2 and 10% 9c,11t,13t-18:3 dietary groups as well. Lipoprotein oxidation susceptibility test with 0.5, 2, and 10% 9c,11t,13t-18:3 dietary groups was significantly less susceptible to lipoprotein peroxidation when compared with sunflower oil dietary group, and the dietary group with 0.5% 9c,11t,13t-18:3 showed least susceptibility. There was significant lowering in erythrocyte ghost membrane lipid peroxidation in the 0.5, 2, and 10% 9c,11t,13t-18:3 dietary groups compared to the sunflower oil groups. Nonenzymatic liver tissue lipid peroxidation was significantly lower in the group of rats raised on 0.5% 9c,11t,13t-18:3, but the groups on 2 and 10% 9c,11t,13t-18:3 acid did not show any significant difference compared with the control group of rats.

NADPH-initiated cytochrome P450-dependent free iron-independent microsomal lipid peroxidation: specific prevention by ascorbic acid

In this paper we demonstrate that ascorbic acid specifically prevents NADPH-initiated cytochrome P450 (P450)-mediated microsomal lipid peroxidation in the absence of free iron. Lipid peroxidation has been evidenced by the formations of conjugated dienes, lipid hydroperoxide and malondialdehyde. Other scavengers of reactive oxygen species including superoxide dismutase, catalase, glutathione, alpha-tocopherol, uric acid, thiourea, mannitol, histidine, beta-carotene and probucol are ineffective to prevent the NADPH-initiated P450-mediated free iron-independent microsomal lipid peroxidation. Using a reconstituted system comprised of purified NADPH-P450 reductase, P450 and isolated microsomal lipid or pure L-alpha-phosphatidylcholine diarachidoyl, a mechanism has been proposed for the iron-independent microsomal lipid peroxidation and its prevention by ascorbic acid. It is proposed that the perferryl moiety P450 Fe3+.O2.- initiates lipid peroxidation by abstracting methylene hydrogen from polyunsaturated lipid to form lipid radical, which then combines with oxygen to produce the chain propagating peroxyl radical for subsequent formation of lipid peroxides. Apparently, ascorbic acid prevents initiation of lipid peroxidation by interacting with P450 Fe3+.O2.-.

Proteins but not nucleic acids are molecular targets for the free radical attack during reoxygenation of rat hepatocytes

Isolated rat hepatocytes generate large amounts of reactive oxygen species and suffer a significant cell injury during postanoxic reoxygenation. The aim of this study was to determine whether oxidation of proteins and nucleic acids occurs during reoxygenation and whether their damage is related to the development of hepatocyte injury. Isolated perfused rat hepatocytes were exposed sequentially to 1 h of aerobic control, 2.5 h of anoxia, and 2 h of reoxygenation. Protein oxidation was determined by measuring the hepatocyte protein carbonyl content. DNA and RNA oxidation was assessed by measuring the 8-hydroxydeoxyguanosine and 8-hydroxyguanosine adducts, respectively. The control preanoxic carbonyl content was 6.48 +/- 1.03 nmol/mg protein. The preanoxic 8-8 hydroxydeoxyguanosine and 8-hydroxyguanosine levels were 4.76 +/- 1.22 pmol/ml and 14.19 +/- 2.17 pmol/ml, respectively. During anoxia, protein and nucleic acid oxidation did not change significantly. With reoxygenation, the protein carbonyl content increased significantly within 30 min, reaching a value of 10.25 +/- 1.58 nmol/mg. The nucleic acid oxidation level remained stable. Perfusion with 100 muM of during reoxygenation abolished protein oxidation. These results indicate that in rat hepatocytes during the early phase of reoxygenation: (1) the protein oxidation level increased significantly above the preanoxic aerobic values; (2) DNA and RNA oxidation does not appear to occur; and (3) free metal-mediated free radical reactions are involved in the oxidative protein damage.

Ascorbic acid prevents lipid peroxidation and oxidative damage of proteins in guinea pig extrahepatic tissue microsomes

It has recently been indicated that in the absence of free iron, NADPH initiates oxidative damage of proteins in guinea pig liver microsomes and also lipid peroxidation and protein damage in cardiac microsomes and that ascorbic acid specifically inhibits both the lipid peroxidation and protein damage [Mukhopadhyay CK, Chatterjee IB: J Biol Chem 269: 13390-13397, 1994; Mukhopadhyay M et al.: Mol Cell Biochem 126: 69-75, 1993]. In this paper we demonstrate that Fe(III)-independent NADPH-initiated lipid peroxidation and oxidative damage of proteins occur in the microsomes of all the extrahepatic tissues including lung, kidney, adrenal gland and brain and that both the lipid peroxidation and protein damage are specifically prevented by ascorbic acid. We further demonstrate that when NADPH is replaced by O2 as the electron donor, the O2-initiated lipid peroxidation and protein damage are also inhibited by ascorbic acid.

Ascorbate protects guinea pig tissues against lipid peroxidation

In recent years we and others have shown that ascorbic acid (AH2) is a potential scavenger of superoxide (O2.-) and peroxyl (LOO.) radicals, the species involved in lipid peroxidation (LPO) in animal tissues. In this paper we have demonstrated that AH2 protects guinea pig tissues from LPO both in vivo and in vitro. The extent of LPO has been determined by estimating malonaldehyde using the thiobarbituric acid test and HPLC and also by measuring the accumulation of fluorescent pigment and occurrence of protein changes in the microsomal membranes. In AH2-deficiency, LPO occurs progressively in guinea pig tissues, despite the presence of adequate levels of antioxidants like alpha-tocopherol, GSH, protein thiols, and scavenging enzymes, namely, superoxide dismutase, catalase, and glutathione peroxidase. In a model in vitro system, microsomal LPO initiated by O2.- is completely prevented by AH2 but not by alpha-tocopherol, GSH, uric acid, and catalase. AH2 is also the most effective antioxidant in preventing microsomal LPO mediated by tert-butylhydroperoxide or the chain propagating species LOO., generated from 2,2'-azobis (2-amidinopropane) hydrochloride. The results obtained with guinea pigs may be applicable to humans, because humans are also dependent on dietary AH2. Our data suggest that an adequate vitamin C nutrition may prevent common cellular degenerative diseases associated with LPO.

Protective effect of ascorbic acid against lipid peroxidation and oxidative damage in cardiac microsomes

One of the current theories of cardiovascular disease is that it may begin with oxygen radical-induced damages. Extensive studies have been made in different laboratories to elucidate the mechanism of oxidative damages in the presence of added iron salts. However, those in vitro studies are unlikely to be relevant to the in vivo situation, where in the normal physiological condition most of the iron remains bound with proteins. In the present study we have demonstrated that an in vitro system containing desferrioxamine, a strong iron chelator, superoxide generated by the action of xanthine oxidase on acetaldehyde initiates lipid peroxidation and protein changes in the guinea pig cardiac microsomes. We have further demonstrated that superoxide-initiated lipid peroxidation and protein changes are completely prevented by ascorbic acid. SOD also prevents but catalase, alpha-tocopherol, glutathione, uric acid, thiourea, mannitol and histidine are without effect. When NADPH is used instead of generated superoxide, the lipid peroxidation and protein changes are exclusively inhibited by ascorbic acid. SOD, catalase and other antioxidants are ineffective. The results obtained with guinea pigs may be extrapolated to humans, because like guinea pigs humans are also incapable of synthesizing ascorbic acid.