Role of L-carnitine in Cardiovascular Health: Literature Review

Cardiovascular diseases (CVDs) remain the leading cause of morbidity and mortality worldwide. Secondary preventive measures, like anti-platelet medications, B-blockers, and angiotensin-converting enzyme (ACE) inhibitors, have been found to dramatically lower the risk of cardiovascular disease. However, prolonged usage of these drugs has been linked to multiple adverse impacts. Hence, finding more efficient treatments, especially dietary strategies for long-term use in daily life, is advantageous for primary prevention and treatment. L-carnitine, a naturally occurring amino acid derivative normally synthesized in the liver and kidney, is believed to have a considerable influence on cardiovascular health. L-carnitine can enhance both contractile performance and structural integrity of the cardiac muscle by maintaining efficient energy production and reducing oxidative stress. This literature review aims to address several pressing questions regarding the role of L-carnitine in cardiovascular health: what are the physiological functions of L-carnitine, particularly in relation to cardiovascular health; how effective and safe is L-carnitine supplementation in the management of various cardiovascular diseases, primarily ischemic heart disease, heart failure, and peripheral vascular disease; what are the underlying mechanisms through which L-carnitine exerts its cardioprotective effects; what controversies exist in the current research; and finally, what should be the future directions? Through this comprehensive analysis, the review aims to enrich our understanding of L-carnitine's role in cardiovascular health, providing a robust foundation for future academic and clinical endeavors. PubMed, Embase, and Google Scholar have been used to search the following keywords: L-carnitine, cardiovascular health, mitochondrial function, and L-carnitine side effects. Then, using the existing search engine formats, some keyword combinations were used to find the related articles included and every possibility, including using every first keyword combination with another keyword, using every keyword in every place at each given box, etc. Around 308 articles were reviewed using this process, including systemic reviews, meta-analysis studies, randomized controlled trials, and literature review articles. In the end, after leaving the pure articles related to the topic as 35 articles, which are attached below with direct citation, the majority of them were very fresh articles, as recent as 2010, and back words, except just one paper related to the impact of L-carnitine post-myocardial infarction, as its data provided us with a positive and promising impact of L-carnitine in this field. L‑carnitine seems to have a pivotal role in cardiovascular health due to its energy metabolism, anti-oxidative stress, and endothelial role. The safety and effectiveness of L-carnitine administration remain an issue for scientific investigation. One of the major concerns is that the intestinal metabolism of L-carnitine generates trimethylamine-N-oxide (TMAO), a compound that has been linked with faster atherosclerosis progression.

Multifunctional nanoparticle-mediated combining therapy for human diseases

Combining existing drug therapy is essential in developing new therapeutic agents in disease prevention and treatment. In preclinical investigations, combined effect of certain known drugs has been well established in treating extensive human diseases. Attributed to synergistic effects by targeting various disease pathways and advantages, such as reduced administration dose, decreased toxicity, and alleviated drug resistance, combinatorial treatment is now being pursued by delivering therapeutic agents to combat major clinical illnesses, such as cancer, atherosclerosis, pulmonary hypertension, myocarditis, rheumatoid arthritis, inflammatory bowel disease, metabolic disorders and neurodegenerative diseases. Combinatorial therapy involves combining or co-delivering two or more drugs for treating a specific disease. Nanoparticle (NP)-mediated drug delivery systems, i.e., liposomal NPs, polymeric NPs and nanocrystals, are of great interest in combinatorial therapy for a wide range of disorders due to targeted drug delivery, extended drug release, and higher drug stability to avoid rapid clearance at infected areas. This review summarizes various targets of diseases, preclinical or clinically approved drug combinations and the development of multifunctional NPs for combining therapy and emphasizes combinatorial therapeutic strategies based on drug delivery for treating severe clinical diseases. Ultimately, we discuss the challenging of developing NP-codelivery and translation and provide potential approaches to address the limitations. This review offers a comprehensive overview for recent cutting-edge and challenging in developing NP-mediated combination therapy for human diseases.

Effect of Dietary Supplements Which Upregulate Nitric Oxide on Walking and Quality of Life in Patients with Peripheral Artery Disease: A Meta-Analysis

This systematic review pooled evidence from randomised controlled trials (RCTs) on the effectiveness of dietary upregulators of nitric oxide (NO) in improving the walking and quality of life of patients with peripheral artery disease (PAD). RCTs examining the effect of dietary upregulators of NO in patients with PAD were included. The primary outcome was the maximum walking distance. Secondary outcomes were the initial claudication distance, the six-minute walking distance, quality of life, the ankle-brachial pressure index (ABI), adverse events and risk of mortality, revascularisation or amputation. Meta-analyses were performed using random effects models. The risk of bias was assessed using Cochrane's ROB-2 tool. Leave-one-out and subgroup analyses were conducted to assess the effect of individual studies, the risk of bias and intervention type on pooled estimates. Thirty-four RCTs involving 3472 participants were included. Seven trials tested NO donors, nineteen tested antioxidants, three tested NO synthase inducers and five tested enhancers of NO availability. Overall, the dietary supplements significantly improved the initial claudication (SMD 0.34; 95%CI 0.04, 0.64; p = 0.03) but not maximum walking (SMD 0.13; 95%CI -0.17, 0.43; p = 0.39) distances. Antioxidant supplements significantly increased both the maximum walking (SMD 0.36; 95%CI 0.14, 0.59; p = 0.001) and initial claudication (SMD 0.58; 95%CI 0.26, 0.90; p < 0.001) distances. The dietary interventions did not improve the physical function domain of the Short Form-36 (SMD -0.16; 95%CI -0.32, 0.00; p = 0.38), ABI or risk of adverse events, mortality, revascularisation or amputation. Dietary NO upregulators, especially antioxidants, appear to improve the initial claudication distance in patients with PAD. Larger high-quality RCTs are needed to fully examine the benefits and risks of these treatments. PROSPERO Registration: CRD42022256653.

Propionyl-L-carnitine for intermittent claudication

BACKGROUND

Peripheral arterial disease (PAD) is a manifestation of systemic atherosclerosis. Intermittent claudication is a symptomatic form of PAD that is characterized by pain in the lower limbs caused by chronic occlusive arterial disease. This pain develops in a limb during exercise and is relieved with rest. Propionyl-L-carnitine (PLC) is a drug that may alleviate the symptoms of PAD through a metabolic pathway, thereby improving exercise performance.

OBJECTIVES

The objective of this review is to determine whether propionyl-L-carnitine is efficacious compared with placebo, other drugs, or other interventions used for treatment of intermittent claudication (e.g. exercise, endovascular intervention, surgery) in increasing pain-free and maximum walking distance for people with stable intermittent claudication, Fontaine stage II.

SEARCH METHODS

The Cochrane Vascular Information Specialist searched the Cochrane Vascular Specialised Register, CENTRAL, MEDLINE, Embase, and CINAHL databases and the World Health Organization International Clinical Trials Registry Platform and the ClinicalTrials.gov trials register to July 7, 2021. We undertook reference checking and contact with study authors and pharmaceutical companies to identify additional unpublished and ongoing studies.

SELECTION CRITERIA

Double-blind randomized controlled trials (RCTs) in people with intermittent claudication (Fontaine stage II) receiving PLC compared with placebo or another intervention. Outcomes included pain-free walking performance (initial claudication distance - ICD) and maximal walking performance (absolute claudication distance - ACD), analyzed by standardized treadmill exercise test, as well as ankle brachial index (ABI), quality of life, progression of disease, and adverse events.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected trials, extracted data, and evaluated trials for risk of bias. We contacted study authors for additional information. We resolved any disagreements by consensus. We performed fixed-effect model meta-analyses with mean differences (MDs) and 95% confidence intervals (CIs). We graded the certainty of evidence according to GRADE.

MAIN RESULTS

We included 12 studies in this review with a total number of 1423 randomized participants. A majority of the included studies assessed PLC versus placebo (11 studies, 1395 participants), and one study assessed PLC versus L-carnitine (1 study, 26 participants). We identified no RCTs that assessed PLC versus any other medication, exercise, endovascular intervention, or surgery. Participants received PLC 1 grams to 2 grams orally (9 studies) or intravenously (3 studies) per day or placebo. For the comparison PLC versus placebo, there was a high level of both clinical and statistical heterogeneity due to study size, participants coming from different countries and centres, the combination of participants with and without diabetes, and use of different treadmill protocols. We found a high proportion of drug company-backed studies. The overall certainty of the evidence was moderate. For PLC compared with placebo, improvement in maximal walking performance (ACD) was greater for PLC than for placebo, with a mean difference in absolute improvement of 50.86 meters (95% CI 50.34 to 51.38; 9 studies, 1121 participants), or a 26% relative improvement (95% CI 23% to 28%). Improvement in pain-free walking distance (ICD) was also greater for PLC than for placebo, with a mean difference in absolute improvement of 32.98 meters (95% CI 32.60 to 33.37; 9 studies, 1151 participants), or a 31% relative improvement (95% CI 28% to 34%). Improvement in ABI was greater for PLC than for placebo, with a mean difference in improvement of 0.09 (95% CI 0.08 to 0.09; 4 studies, 369 participants). Quality of life improvement was greater with PLC (MD 0.06, 95% CI 0.05 to 0.07; 1 study, 126 participants). Progression of disease and adverse events including nausea, gastric intolerance, and flu-like symptoms did not differ greatly between PLC and placebo. For the comparison of PLC with L-carnitine, the certainty of evidence was low because this included a single, very small, cross-over study. Mean improvement in ACD was slightly greater for PLC compared to L-carnitine, with a mean difference in absolute improvement of 20.00 meters (95% CI 0.47 to 39.53; 1 study, 14 participants) or a 16% relative improvement (95% CI 0.4% to 31.6%). We found no evidence of a clear difference in the ICD (absolute improvement 4.00 meters, 95% CI -9.86 to 17.86; 1 study, 14 participants); or a 3% relative improvement (95% CI -7.4% to 13.4%). None of the other outcomes of this review were reported in this study.

AUTHORS' CONCLUSIONS

When PLC was compared with placebo, improvement in walking distance was mild to moderate and safety profiles were similar, with moderate overall certainty of evidence. Although In clinical practice, PLC might be considered as an alternative or an adjuvant to standard treatment when such therapies are found to be contraindicated or ineffective, we found no RCT evidence comparing PLC with standard treatment to directly support such use.

Mitigating the pro-oxidant state and melanogenesis of Retinitis pigmentosa: by counteracting mitochondrial dysfunction

Retinitis pigmentosa (RP) is a group of mitochondrial diseases characterized by progressive degeneration of rods and cones leading to retinal loss of light sensitivity and, consequently, to blindness. To date, no cure is available according to the clinical literature. As a disease associated with pigmentation-related, pro-oxidant state, and mitochondrial dysfunction, RP may be viewed at the crossroads of different pathogenetic pathways involved in adverse health outcomes, where mitochondria play a preeminent role. RP has been investigated in a number of experimental and clinical studies aimed at delaying retinal hyperpigmentation by means of a number of natural and synthetic antioxidants, as well as mitochondrial cofactors, also termed mitochondrial nutrients (MNs), such as alpha-lipoic acid, coenzyme Q10 and carnitine. One should consider that each MN plays distinct-and indispensable-roles in mitochondrial function. Thus, a logical choice would imply the administration of MN combinations, instead of individual MNs, as performed in previous studies, and with limited, if any, positive outcomes. A rational study design aimed at comparing the protective effects of MNs, separately or in combinations, and in association with other antioxidants, might foresee the utilization of animal RP models. The results should verify a comparative optimization in preventing or effectively contrasting retinal oxidative stress in mouse RP models and, in prospect, in human RP cases.

Principal predictors of major adverse limb events in diabetic peripheral artery disease: A narrative review

Background and aims

The increasing prevalence of diabetes mellitus is causing a massive growth of peripheral artery disease incidences, a disabling complication of diabetic atherosclerosis, which leads often to the amputation of the affected limb. Critical limb ischemia is the terminal disease stage, which requires a prompt intervention to relieve pain and save limbs. However, patients undergoing revascularization often suffer from cardiovascular, cerebrovascular and major adverse limb events with poor outcomes. Furthermore, the same procedure performed in apparently similar patients has various outcomes and lack of an outcome predictive support causes a high lower limb arterial revascularization rate with disastrous effects for patients. We collected the main risk factors of major adverse limb events in a more readable and immediate format of the topic, to propose an overview of parameters to manage effectively peripheral artery disease patients and to propose basics of a new predictive tool to prevent from disabling vascular complications of the disease.

Methods

Most recent and updated literature about the prevalence of major adverse limb events in peripheral artery disease was reviewed to identify possible main predictors.

Results

In this article, we summarized major risk factors of limb revascularization failure and disabling vascular complications collecting those parameters principally responsible for major adverse limb events, which provides physio-pathological explanation of their role in peripheral artery disease.

Conclusion

We evaluated and listed a panel of possible predictors of MALE (Major Adverse Limb Event) in order to contribute to the development of a predictive score, based on a summary of the main risk factors reported in scientific articles, which could improve the management of peripheral artery disease by preventing vascular accidents.

Effectiveness of Propionyl-L-Carnitine Supplementation on Exercise Performance in Intermittent Claudication: A Systematic Review

Lower extremity peripheral artery disease (PAD) affects 8.5 million people in the United States and more than 200 million worldwide. The most significant risk factors for PAD are hyperlipidemia, hypertension, diabetes mellitus, chronic kidney disease, and smoking. Intermittent claudication (IC) is the predominant symptom of PAD, but only about 10% of patients with PAD experience IC and are associated with reduced exercise capacity. The pathophysiology of IC is characterized by different degrees of stenosis and obstruction, with a progressive reduction in distal perfusion pressure and blood flow. Supervised exercise therapy is recommended as the initial therapy for IC, but the recommendations for medical treatment of IC vary significantly. Propionyl L-carnitine is an acyl derivative of levocarnitine (L-carnitine) and is indicated for patients with the peripheral arterial occlusive disease. It corrects secondary muscle carnitine deficiency in patients with PAD, significantly improving the walking capacity; its levels increase in serum and muscle. Thus, it is suggested to enhance blood flow and oxygen supply to the muscle tissue via improved endothelial function, thereby reducing hypoxia-induced cellular and biochemical disruptions.

Cilostazol for intermittent claudication

BACKGROUND

Peripheral arterial disease (PAD) affects between 4% and 12% of people aged 55 to 70 years, and 20% of people over 70 years. A common complaint is intermittent claudication (exercise-induced lower limb pain relieved by rest). These patients have a three- to six-fold increase in cardiovascular mortality.  Cilostazol is a drug licensed for the use of improving claudication distance and, if shown to reduce cardiovascular risk, could offer additional clinical benefits. This is an update of the review first published in 2007.

OBJECTIVES

To determine the effect of cilostazol on initial and absolute claudication distances, mortality and vascular events in patients with stable intermittent claudication.

SEARCH METHODS

The Cochrane Vascular Information Specialist searched the Cochrane Vascular Specialised Register, CENTRAL, MEDLINE, Embase, CINAHL, and AMED databases, and the World Health Organization International Clinical Trials Registry Platform and ClinicalTrials.gov trials registries, on 9 November 2020.

SELECTION CRITERIA

We considered double-blind, randomised controlled trials (RCTs) of cilostazol versus placebo, or versus other drugs used to improve claudication distance in patients with stable intermittent claudication.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed trials for selection and independently extracted data. Disagreements were resolved by discussion. We assessed the risk of bias with the Cochrane risk of bias tool. Certainty of the evidence was evaluated using GRADE. For dichotomous outcomes, we used odds ratios (ORs) with corresponding 95% confidence intervals (CIs) and for continuous outcomes we used mean differences (MDs) and 95% CIs. We pooled data using a fixed-effect model, or a random-effects model when heterogeneity was identified. Primary outcomes were initial claudication distance (ICD) and quality of life (QoL). Secondary outcomes were absolute claudication distance (ACD), revascularisation, amputation, adverse events and cardiovascular events.

MAIN RESULTS

We included 16 double-blind, RCTs (3972 participants) comparing cilostazol with placebo, of which five studies also compared cilostazol with pentoxifylline. Treatment duration ranged from six to 26 weeks. All participants had intermittent claudication secondary to PAD. Cilostazol dose ranged from 100 mg to 300 mg; pentoxifylline dose ranged from 800 mg to 1200 mg. The certainty of the evidence was downgraded by one level for all studies because publication bias was strongly suspected. Other reasons for downgrading were imprecision, inconsistency and selective reporting. Cilostazol versus placebo Participants taking cilostazol had a higher ICD compared with those taking placebo (MD 26.49 metres; 95% CI 18.93 to 34.05; 1722 participants; six studies; low-certainty evidence). We reported QoL measures descriptively due to insufficient statistical detail within the studies to combine the results; there was a possible indication in improvement of QoL in the cilostazol treatment groups (low-certainty evidence). Participants taking cilostazol had a higher ACD compared with those taking placebo (39.57 metres; 95% CI 21.80 to 57.33; 2360 participants; eight studies; very-low certainty evidence). The most commonly reported adverse events were headache, diarrhoea, abnormal stools, dizziness, pain and palpitations. Participants taking cilostazol had an increased odds of experiencing headache compared to participants taking placebo (OR 2.83; 95% CI 2.26 to 3.55; 2584 participants; eight studies; moderate-certainty evidence).Very few studies reported on other outcomes so conclusions on revascularisation, amputation, or cardiovascular events could not be made. Cilostazol versus pentoxifylline There was no difference detected between cilostazol and pentoxifylline for improving walking distance, both in terms of ICD (MD 20.0 metres, 95% CI -2.57 to 42.57; 417 participants; one study; low-certainty evidence); and ACD (MD 13.4 metres, 95% CI -43.50 to 70.36; 866 participants; two studies; very low-certainty evidence). One study reported on QoL; the study authors reported no difference in QoL between the treatment groups (very low-certainty evidence). No study reported on revascularisation, amputation or cardiovascular events. Cilostazol participants had an increased odds of experiencing headache compared with participants taking pentoxifylline at 24 weeks (OR 2.20, 95% CI 1.16 to 4.17; 982 participants; two studies; low-certainty evidence).

AUTHORS' CONCLUSIONS

Cilostazol has been shown to improve walking distance in people with intermittent claudication. However, participants taking cilostazol had higher odds of experiencing headache. There is insufficient evidence about the effectiveness of cilostazol for serious events such as amputation, revascularisation, and cardiovascular events. Despite the importance of QoL to patients, meta-analysis could not be undertaken because of differences in measures used and reporting. Very limited data indicated no difference between cilostazol and pentoxifylline for improving walking distance and data were too limited for any conclusions on other outcomes.

Current experience in testing mitochondrial nutrients in disorders featuring oxidative stress and mitochondrial dysfunction: rational design of chemoprevention trials

An extensive number of pathologies are associated with mitochondrial dysfunction (MDF) and oxidative stress (OS). Thus, mitochondrial cofactors termed "mitochondrial nutrients" (MN), such as α-lipoic acid (ALA), Coenzyme Q10 (CoQ10), and l-carnitine (CARN) (or its derivatives) have been tested in a number of clinical trials, and this review is focused on the use of MN-based clinical trials. The papers reporting on MN-based clinical trials were retrieved in MedLine up to July 2014, and evaluated for the following endpoints: (a) treated diseases; (b) dosages, number of enrolled patients and duration of treatment; (c) trial success for each MN or MN combinations as reported by authors. The reports satisfying the above endpoints included total numbers of trials and frequencies of randomized, controlled studies, i.e., 81 trials testing ALA, 107 reports testing CoQ10, and 74 reports testing CARN, while only 7 reports were retrieved testing double MN associations, while no report was found testing a triple MN combination. A total of 28 reports tested MN associations with "classical" antioxidants, such as antioxidant nutrients or drugs. Combinations of MN showed better outcomes than individual MN, suggesting forthcoming clinical studies. The criteria in study design and monitoring MN-based clinical trials are discussed.