Acetyl-L-carnitine in the treatment of peripheral neuropathic pain: a systematic review and meta-analysis of randomized controlled trials

Neuropsychiatric Manifestations of COVID-19 Disease and Post COVID Syndrome: The Role of N-acetylcysteine and Acetyl-L-carnitine

COVID-19 is associated with neuropsychiatric symptoms, such as anosmia, anxiety, depression, stress-related reactions, and psychoses. The illness can cause persistent cognitive impairment and "brain fog", suggesting chronic brain involvement. Clinical entities of ongoing symptomatic COVID-19 and Post COVID Syndrome (PCS) mainly present neuropsychiatric symptoms such as dysgeusia, headache, fatigue, anxiety, depression, sleep disturbances, and post-traumatic stress disorder. The pathophysiology of COVID-19-related brain damage is unclear, but it is linked to various mechanisms such as inflammation, oxidative stress, immune dysregulation, impaired glutamate homeostasis, glial and glymphatic damage, and hippocampal degeneration. Noteworthy is that the metabotropic receptor mGluR2 was discovered as a mechanism of internalisation of SARS-CoV-2 in Central Nervous System (CNS) cells. N-acetylcysteine (NAC) and acetyl-L-carnitine (ALC) are two supplements that have already been found effective in treating psychiatric conditions. Furthermore, NAC showed evidence in relieving cognitive symptomatology in PCS, and ALC was found effective in treating depressive symptomatology of PCS. The overlapping effects on the glutamatergic system of ALC and NAC could help treat COVID-19 psychiatric symptoms and PCS, acting through different mechanisms on the xc-mGluR2 network, with potentially synergistic effects on chronic pain and neuro-astrocyte protection. This paper aims to summarise the current evidence on the potential therapeutic role of NAC and ALC, providing an overview of the underlying molecular mechanisms and pathophysiology. It proposes a pathophysiological model explaining the effectiveness of NAC and ALC in treating COVID-19-related neuropsychiatric symptoms.

A Comprehensive Review of Safety, Efficacy, and Indications for the Use of Alpha-Lipoic Acid and Acetyl-L-Carnitine in Neuropathic Pain

The debilitating, chronic symptoms of neuropathic pain result in decreased quality of life, depressed mood, and anxiety in patients suffering from neuropathic pain. Despite hundreds of dollars in monthly treatment-related costs, more than half of the patients report inadequate pain relief. Traditional first-line agents are expensive and may have disruptive side effects. Given the disease burden of neuropathic pain, many patients turn to over-the-counter supplements. Here we review two supplements, alpha-lipoic acid (ALA), also known as thioctic acid, and acetyl-L-carnitine (ALC), and data of treatment outcomes from the available literature suggest comparable efficacy to currently available pharmaceuticals for the treatment of neuropathic pain. Meta-analysis of randomized controlled trials demonstrates that ALA can significantly improve neuropathic pain and nerve conduction velocity. ALA has been evaluated in the treatment of multiple sources of neuropathic pain, including chemotherapy-induced peripheral neuropathy, entrapment neuropathies, radicular nerve pain, and burning mouth syndrome. Common dose-dependent side effects include nausea, vomiting, and vertigo. Cost analysis from June 2022 indicates that a clinically effective dose (600 mg/day) of ALA costs patients $14.40 monthly. Two randomized control trials demonstrate that ALC exhibits neuroprotective effects, can regenerate nerves, and improve vibratory perception in the early stages of DPN. In terms of adverse reactions, no significant differences were observed between treatment and placebo groups, implying that ALC is generally well-tolerated. Cost analysis from June 2022 indicates that a clinically effective dose of ALC (2000 mg/day) costs patients $27.60 monthly. Comparable efficacy in clinical trials, minimal side effects, and lower monthly costs suggest that ALA and ALC should be considered among the accepted first-line treatment options for neuropathic pain.

Pharmacotherapeutic advances in fibromyalgia: what's new on the horizon?

INTRODUCTION

This review delves into Fibromyalgia Syndrome (FMS), a chronic pain condition demanding thorough understanding for precise diagnosis and treatment. Yet, a definitive pharmacological solution for FMS remains elusive.

AREAS COVERED

In this article, we systematically analyze various pharmacotherapeutic prospects for FMS treatment, organized into sections based on the stage of drug development and approval. We begin with an overview of FDA-approved drugs, discussing their efficacy in FMS treatment. Next, we delve into other medications currently used for FMS but still undergoing further study, including opioids and muscle relaxants. Further, we evaluate the evidence behind medications that are currently under study, such as cannabinoids and naltrexone. Lastly, we explore new drugs that are in phase II trials. Our research involved a thorough search on PUBMED, Google Scholar, and clinicaltrials.gov. We also discuss the action mechanisms of these drugs and their potential use in specific patient groups.

EXPERT OPINION

A focus on symptom-driven, combination therapy is crucial in managing FMS. There is also a need for ongoing research into drugs that target neuroinflammation, immunomodulation, and the endocannabinoid system. Bridging the gap between benchside research and clinical application is challenging, but it holds potential for more targeted and effective treatment strategies.

The role of diet and non-pharmacologic supplements in the treatment of chronic neuropathic pain: A systematic review

BACKGROUND/IMPORTANCE

Dietary interventions, vitamins, and nutritional supplementation are playing an increasingly important role in the management of neuropathic pain. Current pharmacological treatments are poorly tolerated and ineffective in many cases.

OBJECTIVE

This systematic review aims to study the efficacy of dietary interventions, vitamins, and nutritional supplementation in the management of chronic neuropathic pain in adults.

EVIDENCE REVIEW

The review followed PRISMA guidelines and was registered with PROSPERO (#CRD42022300312). Ten databases and gray literature, including Embase.com, MEDLINE and Web of Science, were systematically searched using a combination of keywords and controlled vocabulary related to chronic neuropathic pain and oral non-pharmacological supplements. Studies on adult humans published between 2000 and 2021 were considered for inclusion. The Cochrane Handbook was used to assess risk of bias, and Grading of Recommendations Assessment, Development, and Evaluation was used to determine overall quality of evidence.

FINDINGS

Forty studies were included in the final review, and results were categorized according to pain type including pain related to chemotherapy-induced peripheral neuropathy (CIPN, 22 studies, including 3 prospective cohorts), diabetic peripheral neuropathy (DPN, 13 studies, including 2 prospective), complex regional pain syndrome (CRPS-I, 3 studies, including 1 prospective), and other (2 studies, both RCT). The CIPN studies used various interventions including goshajinkigan (4 studies), vitamin E (5), vitamin B12 (3), glutamine (3), N-acetyl-cysteine (2), acetyl-l-carnitine (2), guilongtonluofang (1), ninjin'yoeito (1), alpha-lipoic acid (1), l-carnosine (1), magnesium and calcium (1), crocin (1), and antioxidants (1), with some studies involving multiple interventions. All CIPN studies involved varying cancers and/or chemotherapies, advising caution for generalizability of results. Interventions for DPN included alpha-lipoic acid (5 studies), vitamin B12 (3), acetyl-l-carnitine (3), vitamin E (1), vitamin D (2), and a low-fat plant-based diet (1). Vitamin C was studied to treat CRPS-I (3 studies, including 1 prospective). Magnesium (1) and St. John's wort (1) were studied for other or mixed neuropathologies.

CONCLUSIONS

Based on the review, we cannot recommend any supplement use for the management of CIPN, although further research into N-acetyl-cysteine, l-carnosine, crocin, and magnesium is warranted. Acetyl-l-carnitine was found to be likely ineffective or harmful. Alpha-lipoic acid was not found effective. Studies with goshajinkigan, vitamin B12, vitamin E, and glutamine had conflicting results regarding efficacy, with one goshajinkigan study finding it harmful. Guilongtonluofang, ninjin'yoeito, and antioxidants showed various degrees of potential effectiveness. Regarding DPN, our review supports the use of alpha-lipoic acid, acetyl-l-carnitine, and vitamin D. The early use of vitamin C prophylaxis for the development of CRPS-I also seems promising. Further research is warranted to confirm these findings.

Interventions for treating pain and disability in adults with complex regional pain syndrome- an overview of systematic reviews

BACKGROUND

Complex regional pain syndrome (CRPS) is a chronic pain condition that usually occurs in a limb following trauma or surgery. It is characterised by persisting pain that is disproportionate in magnitude or duration to the typical course of pain after similar injury. There is currently no consensus regarding the optimal management of CRPS, although a broad range of interventions have been described and are commonly used. This is the first update of the original Cochrane review published in Issue 4, 2013.

OBJECTIVES

To summarise the evidence from Cochrane and non-Cochrane systematic reviews of the efficacy, effectiveness, and safety of any intervention used to reduce pain, disability, or both, in adults with CRPS.

METHODS

We identified Cochrane reviews and non-Cochrane reviews through a systematic search of Ovid MEDLINE, Ovid Embase, Cochrane Database of Systematic Reviews, CINAHL, PEDro, LILACS and Epistemonikos from inception to October 2022, with no language restrictions. We included systematic reviews of randomised controlled trials that included adults (≥18 years) diagnosed with CRPS, using any diagnostic criteria.  Two overview authors independently assessed eligibility, extracted data, and assessed the quality of the reviews and certainty of the evidence using the AMSTAR 2 and GRADE tools respectively. We extracted data for the primary outcomes pain, disability and adverse events, and the secondary outcomes quality of life, emotional well-being, and participants' ratings of satisfaction or improvement with treatment.  MAIN RESULTS: We included six Cochrane and 13 non-Cochrane systematic reviews in the previous version of this overview and five Cochrane and 12 non-Cochrane reviews in the current version. Using the AMSTAR 2 tool, we judged Cochrane reviews to have higher methodological quality than non-Cochrane reviews. The studies in the included reviews were typically small and mostly at high risk of bias or of low methodological quality. We found no high-certainty evidence for any comparison.  There was low-certainty evidence that bisphosphonates may reduce pain intensity post-intervention (standardised mean difference (SMD) -2.6, 95% confidence interval (CI) -1.8 to -3.4, P = 0.001; I2 = 81%; 4 trials, n = 181) and moderate-certainty evidence that they are probably associated with increased adverse events of any nature (risk ratio (RR) 2.10, 95% CI 1.27 to 3.47; number needed to treat for an additional harmful outcome (NNTH) 4.6, 95% CI 2.4 to 168.0; 4 trials, n = 181).  There was moderate-certainty evidence that lidocaine local anaesthetic sympathetic blockade probably does not reduce pain intensity compared with placebo, and low-certainty evidence that it may not reduce pain intensity compared with ultrasound of the stellate ganglion. No effect size was reported for either comparison. There was low-certainty evidence that topical dimethyl sulfoxide may not reduce pain intensity compared with oral N-acetylcysteine, but no effect size was reported. There was low-certainty evidence that continuous bupivacaine brachial plexus block may reduce pain intensity compared with continuous bupivacaine stellate ganglion block, but no effect size was reported. For a wide range of other commonly used interventions, the certainty in the evidence was very low and provides insufficient evidence to either support or refute their use. Comparisons with low- and very low-certainty evidence should be treated with substantial caution. We did not identify any RCT evidence for routinely used pharmacological interventions for CRPS such as tricyclic antidepressants or opioids.

AUTHORS' CONCLUSIONS

Despite a considerable increase in included evidence compared with the previous version of this overview, we identified no high-certainty evidence for the effectiveness of any therapy for CRPS. Until larger, high-quality trials are undertaken, formulating an evidence-based approach to managing CRPS will remain difficult. Current non-Cochrane systematic reviews of interventions for CRPS are of low methodological quality and should not be relied upon to provide an accurate and comprehensive summary of the evidence.

Between guidelines and clinical trials: evidence-based advice on the pharmacological management of non-specific chronic low back pain

The pharmacological management of nonspecific chronic low back pain (NCLBP) aims to restore patients' daily activities and improve their quality of life. The management of NCLBP is not well codified and extremely heterogeneous, and residual symptoms are common. Pharmacological management should be considered as co-adjuvant to non-pharmacological therapy, and should be guided by the symptoms reported by the patients. Depending on the individual severity of NCLPB, pharmacological management may range from nonopioid to opioid analgesics. It is important to identify patients with generalized sensory hypersensitivity, who may benefit from dedicated therapy. This article provides an evidence-based overview of the principles of pharmacological management of NCLPB.

NICEdrug.ch, a workflow for rational drug design and systems-level analysis of drug metabolism

The discovery of a drug requires over a decade of intensive research and financial investments - and still has a high risk of failure. To reduce this burden, we developed the NICEdrug.ch resource, which incorporates 250,000 bioactive molecules, and studied their enzymatic metabolic targets, fate, and toxicity. NICEdrug.ch includes a unique fingerprint that identifies reactive similarities between drug-drug and drug-metabolite pairs. We validated the application, scope, and performance of NICEdrug.ch over similar methods in the field on golden standard datasets describing drugs and metabolites sharing reactivity, drug toxicities, and drug targets. We use NICEdrug.ch to evaluate inhibition and toxicity by the anticancer drug 5-fluorouracil, and suggest avenues to alleviate its side effects. We propose shikimate 3-phosphate for targeting liver-stage malaria with minimal impact on the human host cell. Finally, NICEdrug.ch suggests over 1300 candidate drugs and food molecules to target COVID-19 and explains their inhibitory mechanism for further experimental screening. The NICEdrug.ch database is accessible online to systematically identify the reactivity of small molecules and druggable enzymes with practical applications in lead discovery and drug repurposing.

Analgesic and Antidepressant Effects of the Clinical Glutamate Modulators Acetyl-L-Carnitine and Ketamine

Pain and depression are leading causes of disability and of profound social and economic burden. Their impact is aggravated by their chronicity and comorbidity and the insufficient efficacy of current treatments. Morphological and functional metabolism studies link chronic pain and depressive disorders to dysfunctional neuroplastic changes in fronto-limbic brain regions that control emotional responses to painful injuries and stressful events. Glutamate modulators are emerging new therapies targeting dysfunctional brain areas implicated in the generation and maintenance of chronic pain and depression. Here, we report the effects of two clinically approved glutamate modulators: acetyl-L-carnitine (ALCAR) and S, R(±)ketamine (KET). ALCAR is a natural neurotrophic compound currently marketed for the treatment of neuropathies. KET is the prototypical non-competitive antagonist at N-methyl-D-aspartate glutamate receptors and a clinically approved anesthetic. Although they differ in pharmacological profiles, ALCAR and KET both modulate aminergic and glutamatergic neurotransmissions and pain and mood. We assessed in rats the effects of ALCAR and KET on cerebral metabolic rates for glucose (rCMRglc) and assessed clinically the effects of ALCAR in chronic pain and of KET in post-operative pain. ALCAR and KET increased rCMRglc at similar degrees in prefrontal, somatosensory, and cingulate cortices, and KET increased rCMRglc at a different, much larger, degree in limbic and dopaminergic areas. While rCMRglc increases in prefrontal cortical areas have been associated with analgesic and antidepressant effects of ALCAR and KET, the marked metabolic increases KET induces in limbic and dopaminergic areas have been related to its psychotomimetic and abuse properties. In patients with chronic neuropathic pain, ALCAR (1,000 mg/day) yielded to a fast (2 weeks) improvement of mood and then of pain and quality of life. In day-surgery patients, KET improved dischargeability and satisfaction. In obese patients undergoing bariatric surgery, a single, low dose of KET (0.5 mg/kg) at induction of anesthesia determined a very fast (hours) amelioration of post-operative depression and pain and an opioid-sparing effect. These findings indicate that ALCAR and KET, two non-selective glutamate modulators, still offer viable therapeutic options in comorbid pain and depression.

Vitamin B12 Supplementation in Diabetic Neuropathy: A 1-Year, Randomized, Double-Blind, Placebo-Controlled Trial

AIM

To investigate the effect of normalizing vitamin B12 (B12) levels with oral B12 (methylcobalamin) 1000 μg/day for one year in patients with diabetic neuropathy (DN).

PATIENTS AND METHODS

In this prospective, double-blind, placebo-controlled trial, 90 patients with type 2 diabetes on metformin for at least four years and both peripheral and autonomic DN were randomized to an active treatment group (n = 44) receiving B12 and a control group (n = 46) receiving a placebo. All patients had B12 levels less than 400 pmol/L. Subjects underwent measurements of sural nerve conduction velocity (SNCV), sural nerve action potential (amplitude) (SNAP), and vibration perception threshold (VPT), and they performed cardiovascular autonomic reflex tests (CARTs: mean circular resultant (MCR), Valsalva test, postural index, and orthostatic hypotension). Sudomotor function was assessed with the SUDOSCAN that measures electrochemical skin conductance in hands and feet (ESCH and ESCF, respectively). We also used the Michigan Neuropathy Screening Instrument Questionnaire and Examination (MNSIQ and MNSIE, respectively) and questionnaires to evaluate quality of life (QoL) and level of pain (pain score).

RESULTS

B12 levels increased from 232.0 ± 71.8 at baseline to 776.7 ± 242.3 pmol/L at follow-up, p < 0.0001, in the active group but not in the control group. VPT, MNSIQ, QoL, pain score, SNCV, SNAP, and ESCF significantly improved in the active group (p < 0.001, p = 0.002, p < 0.0001, p < 0.000, p < 0.0001, p < 0.0001, and p = 0.014, respectively), whereas CARTS and MNSIE improved but not significantly. MCR, MNSIQ, SNCV, SNAP, and pain score significantly deteriorated in the control group (p = 0.025, p = 0.017, p = 0.045, p < 0.0001, and p < 0.0001, respectively).

CONCLUSIONS

The treatment of patients with DN with 1 mg of oral methylcobalamin for twelve months increased plasma B12 levels and improved all neurophysiological parameters, sudomotor function, pain score, and QoL, but it did not improve CARTS and MNSIE.

Efficacy and Safety of the Combination of Superoxide Dismutase, Alpha Lipoic Acid, Vitamin B12, and Carnitine for 12 Months in Patients with Diabetic Neuropathy

Aim: To investigate the efficacy of Superoxide Dismutase, Alpha Lipoic Acid, Acetyl L-Carnitine, and Vitamin B12 (B12) in one tablet in Diabetic Neuropathy (DN). Patients–methods: In this prospective, double-blind, placebo-controlled study, 85 patients with Diabetes Mellitus Type 2 (DMT2) were randomly assigned, either to receive the combination of four elements (active group, n = 43), or placebo (n = 42) for 12 months. We used the Michigan Neuropathy Screening Instrument Questionnaire and Examination (MNSIQ and MNSIE), measured the vibration perception threshold (BIO), and Cardiovascular Autonomic Reflex Tests (CARTs). Nerve function was assessed by DPN Check [sural nerve conduction velocity (SNCV) and amplitude (SNAP)]. Pain (PS) and quality of life (QL) questionnaires were administered. Results: At follow-up, BIO, MNSIQ, QL, PAIN, and SNCV, SNAP, and B12 levels had significantly improved inactive group (p < 0.001, p < 0.001, p < 0.001, p < 0.001, p = 0.027, p = 0.031, and p < 0.001 respectively), whereas the inplacebo group MCR (mean circular resultant) and PAIN deteriorated (p < 0.001, p < 0.001). The changes in MNSIQ, QL, SNCV, BIO, and PAIN differed significantly between groups (p < 0.001, p < 0.001, p = 0.031, p < 0.001, and p < 0.001 respectively). Conclusions: The combination of the four elements in one tablet for 12 months in patients with DMT2 improved all indices of peripheral neuropathy, including SNAP and SNCV, pain, and Quality of Life perception, except CARTs and MNSIE.

Acetyl-L-carnitine for the treatment of diabetic peripheral neuropathy

BACKGROUND

Diabetic peripheral neuropathy (DPN) is a common and severe complication that affects 50% of people with diabetes. Painful DPN is reported to occur in 16% to 24% of people with diabetes. A complete and comprehensive management strategy for the prevention and treatment of DPN, whether painful or not, has not yet been defined.Research into treatment for DPN has been characterised by a series of failed clinical trials, with few noteworthy advances. Strategies that support peripheral nerve regeneration and restore neurological function in people with painful or painless DPN are needed. The amino acid acetyl-L-carnitine (ALC) plays a role in the transfer of long-chain fatty acids into mitochondria for β-oxidation. ALC supplementation also induces neuroprotective and neurotrophic effects in the peripheral nervous system. Therefore, ALC supplementation targets several mechanisms relevant to potential nerve repair and regeneration, and could have clinical therapeutic potential. There is a need for a systematic review of the evidence from clinical trials.

OBJECTIVES

To assess the effects of ALC for the treatment of DPN.

SEARCH METHODS

On 2 July 2018, we searched the Cochrane Neuromuscular Specialised Register, CENTRAL, MEDLINE, Embase, LILACS, ClinicalTrials.gov, and the World Health Organization International Clinical Trials Registry Platform. We checked references, searched citations, and contacted study authors to identify additional studies.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) and quasi-RCTs of ALC compared with placebo, other therapy, or no intervention in the treatment of DPN. Participants could be of any sex and age, and have type 1 or type 2 diabetes mellitus, of any severity, with painful or painless DPN. We accepted any definition of minimum criteria for DPN, in accordance with the Toronto Consensus. We imposed no language restriction.Pain was the primary outcome, measured as the proportion of participants with at least 30% (moderate) or 50% (substantial) decrease in pain over baseline, or as the score on a visual analogue scale (VAS) or Likert scale for pain.

DATA COLLECTION AND ANALYSIS

We followed standard Cochrane methods.

MAIN RESULTS

We included four studies with 907 participants, which were reported in three publications. Three trials studied ALC versus placebo (675 participants); in one trial the dose of ALC was 2000 mg/day, and in the other two trials, it was 1500 mg/day or 3000 mg/day. The fourth trial studied ALC 1500 mg/day versus methylcobalamin 1.5 mg/day (232 participants). The risk of bias was high in both trials of different ALC doses and low in the other two trials.No included trial measured the proportion of participants with at least moderate (30%) or substantial (50%) pain relief. ALC reduced pain more than placebo, measured on a 0- to 100-mm VAS (MD -9.16, 95% CI -16.76 to -1.57; three studies; 540 participants; P = 0.02; I² = 56%; random-effects; very low-certainty evidence; a higher score indicating more pain). At doses of 1500 mg/day or less, the VAS score after ALC treatment was little different from placebo (MD -0.05, 95% CI -10.00 to 9.89; two studies; 159 participants; P = 0.99; I² = 0%), but at doses greater than 1500 mg/day, ALC reduced pain more than placebo (MD -14.93, 95% CI -19.16 to -10.70; three studies; 381 participants; P < 0.00001; I² = 0%). This subgroup analysis should be viewed with caution as the evidence was even less certain than the overall analysis, which was already of very low certainty.Two placebo-controlled studies reported that vibration perception improved after 12 months. We graded this evidence as very low certainty, due to inconsistency and a high risk of bias, as the trial authors did not provide any numerical data. The placebo-controlled studies did not measure functional impairment and disability scores. No study used validated symptom scales. One study performed sensory testing, but the evidence was very uncertain.The fourth included study compared ALC with methylcobalamin, but did not report effects on pain. There was a reduction from baseline to 24 weeks in functional impairment and disability, based on the change in mean Neuropathy Disability Score (NDS; scale from zero to 10), but there was no important difference between the ALC group (mean score 1.66 ± 1.90) and the methylcobalamin group (mean score 1.35 ± 1.65) groups (P = 0.23; low-certainty evidence).One placebo-controlled study reported that six of 147 participants in the ALC > 1500 mg/day group (4.1%) and two of 147 participants in the placebo group (1.4%) discontinued treatment because of adverse events (headache, facial paraesthesia, and gastrointestinal disorders) (P = 0.17). The other two placebo-controlled studies reported no dropouts due to adverse events, and more pain, paraesthesia, and hyperaesthesias in the placebo group than the 3000 mg/day ALC group, but provided no numerical data. The overall certainty of adverse event evidence for the comparison of ALC versus placebo was low.The study comparing ALC with methylcobalamin reported that 34/117 participants (29.1%) experienced adverse events in the ALC group versus 33/115 (28.7%) in the methylcobalamin group (P = 0.95). Nine participants discontinued treatment due to adverse events (ALC: 4 participants, methylcobalamin: 5 participants), which were most commonly gastrointestinal symptoms. The certainty of the adverse event evidence for ALC versus methylcobalamin was low.Two studies were funded by the manufacturer of ALC and the other two studies had at least one co-author who was a consultant for an ALC manufacturer.

AUTHORS' CONCLUSIONS

We are very uncertain whether ALC causes a reduction in pain after 6 to 12 months' treatment in people with DPN, when compared with placebo, as the evidence is sparse and of low certainty. Data on functional and sensory impairment and symptoms are lacking, or of very low certainty. The evidence on adverse events is too uncertain to make any judgements on safety.

Acetyl-L-carnitine in painful peripheral neuropathy: a systematic review

Acetyl-L-carnitine (ALC) has shown a neuroprotective effect in patients with peripheral neuropathies of different etiologies. Preclinical studies demonstrated a central anti-nociceptive action, both in neuropathic and nociceptive pain models. The present review aims to provide the knowledge on the efficacy of ALC in patients with painful peripheral neuropathy, based on the evidence. Consistent with the PRISMA statement, authors searched PubMed, Embase and the Cochrane Database of Systematic Reviews for relevant papers, including those issued before April 2018. Two authors independently selected studies for inclusion and data extraction: only trials including patients with a diagnosis of peripheral neuropathy and involving at least 10 patients were considered for the purposes of this review. Fourteen clinical trials were revised, to provide the level of evidence for neuropathy. To assess the global efficacy of ALC in painful peripheral neuropathy, a meta-analysis of four randomized controlled trials was performed. Mean difference in pain reduction as measured on a 10-cm VAS, and 95% CIs were used for pooling continuous data from each trial. Four randomized controlled trials tested ALC in patients with neuropathy secondary to diabetes and to antiretroviral therapy for HIV. Compared to placebo, ALC produced a significant pain reduction equal to 20.2% (95% CI: 8.3%-32.1%, P<0.0001) with respect to baseline. Clinical trials also showed beneficial effects on nerve conduction parameters and nerve fiber regeneration, with a good safety profile. These data indicate that ALC provides an effective and safe treatment in patients with painful peripheral neuropathy. We recommend further studies to assess the optimal dose and duration of the therapeutic effect (also after treatment withdrawal).

Acetyl-L-Carnitine Supplementation and the Treatment of Depressive Symptoms: A Systematic Review and Meta-Analysis

OBJECTIVE

Deficiency of acetyl-L-carnitine (ALC) seems to play a role in the risk of developing depression, indicating a dysregulation of fatty acid transport across the inner membrane of mitochondria. However, data about ALC supplementation in humans are limited. We thus conducted a systematic review and meta-analysis investigating the effect of ALC on depressive symptoms across randomized controlled trials (RCTs).

METHODS

A literature search in major databases, without language restriction, was undertaken from inception until 30 December 2016. Eligible studies were RCTs of ALC alone or in combination with antidepressant medications, with a control group taking placebo/no intervention or antidepressants. Standardized mean differences (SMDs) and 95% confidence intervals (CIs) were used for summarizing outcomes with a random-effect model.

RESULTS

Twelve RCTs (11 of which were ALC monotherapy) with a total of 791 participants (mean age = 54 years, % female = 65%) were included. Pooled data across nine RCTs (231 treated with ALC versus 216 treated with placebo and 20 no intervention) showed that ALC significantly reduced depressive symptoms (SMD = -1.10, 95% CI = -1.65 to -0.56, I = 86%). In three RCTs comparing ALC versus antidepressants (162 for each group), ALC demonstrated similar effectiveness compared with established antidepressants in reducing depressive symptoms (SMD = 0.06, 95% CI = -0.22 to 0.34, I = 31%). In these latter RCTs, the incidence of adverse effects was significantly lower in the ALC group than in the antidepressant group. Subgroup analyses suggested that ALC was most efficacious in older adults.

CONCLUSIONS

ALC supplementation significantly decreases depressive symptoms compared with placebo/no intervention, while offering a comparable effect with that of established antidepressant agents with fewer adverse effects. Future large scale trials are required to confirm/refute these findings.

Micronized Palmitoylethanolamide: A Post Hoc Analysis of a Controlled Study in Patients with Low Back Pain - Sciatica

BACKGROUND

Despite being widely prescribed, relatively few controlled trials have been conducted on the class of neurotrophic/antinociceptive nutraceuticals. While performing a search in the literature, we came across an old registration study on micronized palmitoylethanolamide in patients with low back pain - sciatica by Guida and colleagues.

METHODS

We contacted the authors of the article and obtained all the original material, which allowed us to reanalyze the study. We assessed its clinical relevance by calculating the numbers needed to treat for pain (visual analog scale) and function (Roland-Morris Questionnaire). After excluding patients for whom the information available was insufficient, we assigned each patient to one of the five categories of increasing probability of neuropathic pain: pure lumbago, lumbago with projecting pain to surrounding regions (e.g. gluteus or groin), lumbago with projecting pain to the thigh or leg, pure sciatica and radiculopathy, and investigated any correlations (Spearman) between the improvement in pain and function with these five classes.

RESULTS

Compared with placebo, palmitoylethanolamide 600 mg/die yielded a number needed to treat of 1.7 (95% confidence interval: 1.4-2) for pain, and 1.5 (95% confidence interval: 1.4-1.7) for function. The correlation between the five categories was highly significant for pain relief (P <0.0001), though not significant for reduced dysfunction.

CONCLUSION

Palmitoylethanolamide was extremely effective on pain and function in a large cohort of patients with low back pain - sciatica. Although, the multiple mechanisms of action of palmitoylethanolamide are ideal for mixed pain conditions such as low back pain - sciatica, the correlation between pain relief and the likelihood of neuropathic pain suggests that this drug exerts a predominant action on the neuropathic pain component.

Effects of L-carnitine supplementation on the quality of life in diabetic patients with muscle cramps

Diabetic patients often suffer from muscle cramps. This study aimed to compare the quality of life (QOL) of diabetic patients with and without muscle cramps and to investigate the effect of L-carnitine supplementation in diabetic patients with muscle cramps. A total of 91 patients with diabetes were enrolled in this study: 69 patients with muscle cramps and 22 patients without muscle cramps. Muscle cramps and QOL were evaluated using the muscle cramp questionnaire and the Short Form 36 health survey version 2 (SF-36), respectively. Clinical characteristics were compared between diabetic patients with and without muscle cramps. In the prospective portion of the study, 25 diabetic patients with muscle cramps received L-carnitine supplementation (600 mg/day orally) for 4 months. The questionnaires were administered before and after supplementation. The SF-36 scores in diabetic patients with muscle cramps were lower than those in patients without muscle cramps on the subscales of physical function, role physical, bodily pain, vitality, general health, and social function. In the 25 patients with muscle cramps who received L-carnitine supplementation, the monthly frequency of muscle cramps and Wong-Baker FACES^® Pain Rating Scale scores were significantly decreased. Scores on the following SF-36 subscales improved after L-carnitine supplementation: body pain, vitality, social function, and role emotional. This study demonstrated that muscle cramps decrease the QOL in patients with diabetes, and L-carnitine supplementation may improve the QOL by reducing the frequency and severity of muscle cramps in these patients.

Effects of acetyl-L-carnitine in diabetic neuropathy and other geriatric disorders

A long history of diabetes mellitus and increasing age are associated with the onset of diabetic neuropathy, a painful and highly disabling complication with a prevalence peaking at 50% among elderly diabetic patients. Acetyl-L-carnitine (ALC) is a molecule derived from the acetylation of carnitine in the mitochondria that has an essential role in energy production. It has recently been proposed as a therapy to improve the symptoms of diabetic neuropathy. ALC is widely distributed in mammalian tissues, including the brain, blood-brain barrier, brain neurons, and astrocytes. Aside from its metabolic activity, ALC has demonstrated cytoprotective, antioxidant, and antiapoptotic effects in the nervous system. It exerts an analgesic action by reducing the concentration of glutamate in the synapses. It facilitates nerve regeneration and damage repair after primary trauma: its positive effects on metabolism promote the synthesis, fluidity, and functionality of neuronal membranes, increase protein synthesis, and improve the axonal transport of neurofilament proteins and tubulin. It also amplifies nerve growth factor responsiveness, an effect that is believed to enhance overall neurite growth. ALC has been proposed for the treatment of various neurological and psychiatric diseases, such as mood disorders and depression, dementias, Alzheimer's disease, and Parkinson's disease, because synaptic energy states and mitochondrial dysfunction are core factors in their pathogenesis.

l-Acetylcarnitine: A Mechanistically Distinctive and Potentially Rapid-Acting Antidepressant Drug

Current therapy of mood disorders has several limitations. Although a high number of drugs are clinically available, as of today, nearly two-thirds of individuals do not achieve full symptomatic remission after treatment with conventional antidepressants. Moreover, several weeks of drug treatment are usually required to obtain clinical effects, a limitation that has considerable clinical implications, ranging from high suicide risk to reduced compliance. The characteristic lag time in classical antidepressant effectiveness has given great impulse to the search for novel therapeutics with more rapid effects. l-acetylcarnitine (LAC), a small molecule of growing interest for its pharmacological properties, is currently marketed for treatment of neuropathic pain. Recent preclinical and clinical data suggested that LAC may exert antidepressant effects with a more rapid onset than conventional drugs. Herein, we review data supporting LAC antidepressant activity and its distinctive mechanisms of action compared with monoaminergic antidepressants. Furthermore, we discuss the unique pharmacological properties of LAC that allow us to look at this molecule as representative of next generation antidepressants with a safe profile.

Analgesia induced by the epigenetic drug, L-acetylcarnitine, outlasts the end of treatment in mouse models of chronic inflammatory and neuropathic pain

Background L-acetylcarnitine, a drug marketed for the treatment of chronic pain, causes analgesia by epigenetically up-regulating type-2 metabotropic glutamate (mGlu2) receptors in the spinal cord. Because the epigenetic mechanisms are typically long-lasting, we hypothesized that analgesia could outlast the duration of L-acetylcarnitine treatment in models of inflammatory and neuropathic pain. Results A seven-day treatment with L-acetylcarnitine (100 mg/kg, once a day, i.p.) produced an antiallodynic effect in the complete Freund adjuvant mouse model of chronic inflammatory pain. L-Acetylcarnitine-induced analgesia persisted for at least 14 days after drug withdrawal. In contrast, the analgesic effect of pregabalin, amitryptiline, ceftriaxone, and N-acetylcysteine disappeared seven days after drug withdrawal. L-acetylcarnitine treatment enhanced mGlu2/3 receptor protein levels in the dorsal region of the spinal cord. This effect also persisted for two weeks after drug withdrawal and was associated with increased levels of acetylated histone H3 bound to the Grm2 gene promoter in the dorsal root ganglia. A long-lasting analgesic effect of L-acetylcarnitine was also observed in mice subjected to chronic constriction injury of the sciatic nerve. In these animals, a 14-day treatment with pregabalin, amitryptiline, tramadol, or L-acetylcarnitine produced a significant antiallodynic effect, with pregabalin displaying the greatest efficacy. In mice treated with pregabalin, tramadol or L-acetylcarnitine the analgesic effect was still visible 15 days after the end of drug treatment. However, only in mice treated with L-acetylcarnitine analgesia persisted 37 days after drug withdrawal. This effect was associated with an increase in mGlu2/3 receptor protein levels in the dorsal horns of the spinal cord. Conclusions Our findings suggest that L-acetylcarnitine has the unique property to cause a long-lasting analgesic effect that might reduce relapses in patients suffering from chronic pain.

Global histone modification fingerprinting in human cells using epigenetic reverse phase protein array

The balance between acetylation and deacetylation of histone proteins plays a critical role in the regulation of genomic functions. Aberrations in global levels of histone modifications are linked to carcinogenesis and are currently the focus of intense scrutiny and translational research investments to develop new therapies, which can modify complex disease pathophysiology through epigenetic control. However, despite significant progress in our understanding of the molecular mechanisms of epigenetic machinery in various genomic contexts and cell types, the links between epigenetic modifications and cellular phenotypes are far from being clear. For example, enzymes controlling histone modifications utilize key cellular metabolites associated with intra- and extracellular feedback loops, adding a further layer of complexity to this process. Meanwhile, it has become increasingly evident that new assay technologies which provide robust and precise measurement of global histone modifications are required, for at least two pressing reasons: firstly, many approved drugs are known to influence histone modifications and new cancer therapies are increasingly being developed towards targeting histone deacetylases (HDACs) and other epigenetic readers and writers. Therefore, robust assays for fingerprinting the global effects of such drugs on preclinical cell, organoid and in vivo models is required; and secondly, robust histone-fingerprinting assays applicable to patient samples may afford the development of next-generation diagnostic and prognostic tools. In our study, we have used a panel of monoclonal antibodies to determine the relative changes in the global abundance of post-translational modifications on histones purified from cancer cell lines treated with HDAC inhibitors using a novel technique, called epigenetic reverse phase protein array. We observed a robust increase in acetylation levels within 2–24 h after inhibition of HDACs in different cancer cell lines. Moreover, when these cells were treated with N-acetylated amino acids in addition to HDACs, we detected a further increase in histone acetylation, demonstrating that these molecules could be utilized as donors of the acetyl moiety for protein acetylation. Consequently, this study not only offers a novel assay for diagnostics and drug screening but also warrants further research of the novel class of inexpensive, non-toxic natural compounds that could potentiate the effects of HDAC inhibitors and is therefore of interest for cancer therapeutics.

Effects of acetyl-L-carnitine and methylcobalamin for diabetic peripheral neuropathy: A multicenter, randomized, double-blind, controlled trial

AIMS/INTRODUCTION

To assess the efficacy and safety of acetyl-L-carnitine (ALC) on diabetic peripheral neuropathy compared with methylcobalamin (MC).

MATERIALS AND METHODS

This was a multicenter, randomized, parallel-group, double-blind, double-dummy, positive-controlled, non-inferior phase II clinical trial. Diabetic patients with abnormal nerve conduction test results were randomized in a 1:1 ratio to receive oral ALC 500 mg t.i.d. or MC 0.5 mg t.i.d. for 24 weeks. The neuropathy symptom score, neuropathy disability score and neurophysiological parameters were measured during follow up.

RESULTS

A total of 232 patients were randomized (ALC n = 117, MC n = 115), 88% of which completed the trial. At week 24, patients from both groups had significant reductions in both neuropathy symptom score and neuropathy disability score with no significant difference between two groups (neuropathy symptom score reduction: ALC vs MC 2.35 ± 2.23, P < 0.0001 vs 2.11 ± 2.48, P < 0.0001, intergroup P = 0.38; neuropathy disability score reduction ALC vs MC 1.66 ± 1.90, P < 0.0001 vs 1.35 ± 1.65, P < 0.0001, intergroup P = 0.23). Neurophysiological parameters were also improved in both groups. No significant difference was found between groups in the development of adverse events.

CONCLUSIONS

ALC is as effective as MC in improving clinical symptoms and neurophysiological parameters for patients with diabetic peripheral neuropathy over a 24-week period with good tolerance.

Group II mGluRs suppress hyperexcitability in mouse and human nociceptors

We introduce a strategy for preclinical research wherein promising targets for analgesia are tested in rodent and subsequently validated in human sensory neurons. We evaluate group II metabotropic glutamate receptors, the activation of which is efficacious in rodent models of pain. Immunohistochemical analysis showed positive immunoreactivity for mGlu2 in rodent dorsal root ganglia (DRG), peripheral fibers in skin, and central labeling in the spinal dorsal horn. We also found mGlu2-positive immunoreactivity in human neonatal and adult DRG. RNA-seq analysis of mouse and human DRG revealed a comparative expression profile between species for group II mGluRs and for opioid receptors. In rodent sensory neurons under basal conditions, activation of group II mGluRs with a selective group II agonist produced no changes to membrane excitability. However, membrane hyperexcitability in sensory neurons exposed to the inflammatory mediator prostaglandin E2 (PGE2) was prevented by (2R,4R)-4-aminopyrrolidine-2,4-dicarboxylate (APDC). In human sensory neurons from donors without a history of chronic pain, we show that PGE2 produced hyperexcitability that was similarly blocked by group II mGluR activation. These results reveal a mechanism for peripheral analgesia likely shared by mice and humans and demonstrate a translational research strategy to improve preclinical validation of novel analgesics using cultured human sensory neurons.

Serum Levels of Acyl-Carnitines along the Continuum from Normal to Alzheimer's Dementia

This study aimed to determine the serum levels of free L-carnitine, acetyl-L-carnitine and 34 acyl-L-carnitine in healthy subjects and in patients with or at risk of Alzheimer's disease. Twenty-nine patients with probable Alzheimer's disease, 18 with mild cognitive impairment of the amnestic type, 24 with subjective memory complaint and 46 healthy subjects were enrolled in the study, and the levels of carnitine and acyl-carnitines were measured by tandem mass spectrometry. The concentrations of acetyl-L-carnitine progressively decreased passing from healthy subjects group (mean±SD, 5.6±1.3 μmol/L) to subjective memory complaint (4.3±0.9 μmol/L), mild cognitive impairment (4.0±0.53 μmol/L), up to Alzheimer's disease (3.5±0.6 μmol/L) group (p<0.001). The differences were significant for the comparisons: healthy subjects vs. subjective memory complaint, mild cognitive impairment or Alzheimer's disease group; and subjective memory complaint vs. Alzheimer's disease group. Other acyl-carnitines, such as malonyl-, 3-hydroxyisovaleryl-, hexenoyl-, decanoyl-, dodecanoyl-, dodecenoyl-, myristoyl-, tetradecenoyl-, hexadecenoyl-, stearoyl-, oleyl- and linoleyl-L-carnitine, showed a similar decreasing trend, passing from healthy subjects to patients at risk of or with Alzheimer's disease. These results suggest that serum acetyl-L-carnitine and other acyl-L-carnitine levels decrease along the continuum from healthy subjects to subjective memory complaint and mild cognitive impairment subjects, up to patients with Alzheimer's disease, and that the metabolism of some acyl-carnitines is finely connected among them. These findings also suggest that the serum levels of acetyl-L-carnitine and other acyl-L-carnitines could help to identify the patients before the phenotype conversion to Alzheimer's disease and the patients who would benefit from the treatment with acetyl-L-carnitine. However, further validation on a larger number of samples in a longitudinal study is needed before application to clinical practice.