Identification of cytochrome P450 1A2 as enzyme involved in the microsomal metabolism of Huperzine A

Natural product-derived therapies for treating drug-resistant epilepsies: From ethnopharmacology to evidence-based medicine

ETHNOPHARMACOLOGICAL RELEVANCE

Epilepsy is one of the most prevalent neurological human diseases, affecting 1% of the population in all age groups. Despite the availability of over 25 anti-seizure medications (ASMs), which are approved in most industrialized countries, approximately 30% of epilepsy patients still experience seizures that are resistant to these drugs. Since ASMs target only limited number of neurochemical mechanisms, drug-resistant epilepsy (DRE) is not only an unmet medical need, but also a formidable challenge in drug discovery.

AIM

In this review, we examine recently approved epilepsy drugs based on natural product (NP) such as cannabidiol (CBD) and rapamycin, as well as NP-based epilepsy drug candidates still in clinical development, such as huperzine A. We also critically evaluate the therapeutic potential of botanical drugs as polytherapy or adjunct therapy specifically for DRE.

METHODS

Articles related to ethnopharmacological anti-epileptic medicines and NPs in treating all forms of epilepsy were collected from PubMed and Scopus using keywords related to epilepsy, DRE, herbal medicines, and NPs. The database clinicaltrials.gov was used to find ongoing, terminated and planned clinical trials using herbal medicines or NPs in epilepsy treatment.

RESULTS

A comprehensive review on anti-epileptic herbal drugs and natural products from the ethnomedical literature is provided. We discuss the ethnomedical context of recently approved drugs and drug candidates derived from NPs, including CBD, rapamycin, and huperzine A. Recently published studies on natural products with preclinical efficacy in animal models of DRE are summarized. Moreover, we highlight that natural products capable of pharmacologically activating the vagus nerve (VN), such as CBD, may be therapeutically useful to treat DRE.

CONCLUSIONS

The review highlights that herbal drugs utilized in traditional medicine offer a valuable source of potential anti-epileptic drug candidates with novel mechanisms of action, and with clinical promise for the treatment of drug-resistant epilepsy (DRE). Moreover, recently developed NP-based anti-seizure medications (ASMs) indicate the translational potential of metabolites of plant, microbial, fungal and animal origin.

Potential Herb-Drug Interactions in the Management of Age-Related Cognitive Dysfunction

Late-life mild cognitive impairment and dementia represent a significant burden on healthcare systems and a unique challenge to medicine due to the currently limited treatment options. Plant phytochemicals have been considered in alternative, or complementary, prevention and treatment strategies. Herbals are consumed as such, or as food supplements, whose consumption has recently increased. However, these products are not exempt from adverse effects and pharmacological interactions, presenting a special risk in aged, polymedicated individuals. Understanding pharmacokinetic and pharmacodynamic interactions is warranted to avoid undesirable adverse drug reactions, which may result in unwanted side-effects or therapeutic failure. The present study reviews the potential interactions between selected bioactive compounds (170) used by seniors for cognitive enhancement and representative drugs of 10 pharmacotherapeutic classes commonly prescribed to the middle-aged adults, often multimorbid and polymedicated, to anticipate and prevent risks arising from their co-administration. A literature review was conducted to identify mutual targets affected (inhibition/induction/substrate), the frequency of which was taken as a measure of potential interaction. Although a limited number of drugs were studied, from this work, interaction with other drugs affecting the same targets may be anticipated and prevented, constituting a valuable tool for healthcare professionals in clinical practice.

Pharmacogenetic considerations when prescribing cholinesterase inhibitors for the treatment of Alzheimer's disease

INTRODUCTION

Cholinergic dysfunction, demonstrated in the late 1970s and early 1980s, led to the introduction of acetylcholinesterase inhibitors (AChEIs) in 1993 (Tacrine) to enhance cholinergic neurotransmission as the first line of treatment against Alzheimer's disease (AD). The new generation of AChEIs, represented by Donepezil (1996), Galantamine (2001) and Rivastigmine (2002), is the only treatment for AD to date, together with Memantine (2003). AChEIs are not devoid of side-effects and their cost-effectiveness is limited. An option to optimize the correct use of AChEIs is the implementation of pharmacogenetics (PGx) in the clinical practice.

AREAS COVERED

(i) The cholinergic system in AD, (ii) principles of AD PGx, (iii) PGx of Donepezil, Galantamine, Rivastigmine, Huperzine and other treatments, and (iv) practical recommendations.

EXPERT OPINION

The most relevant genes influencing AChEI efficacy and safety are APOE and CYPs. APOE-4 carriers are the worst responders to AChEIs. With the exception of Rivastigmine (UGT2B7, BCHE-K), the other AChEIs are primarily metabolized via CYP2D6, CYP3A4, and UGT enzymes, with involvement of ABC transporters and cholinergic genes (CHAT, ACHE, BCHE, SLC5A7, SLC18A3, CHRNA7) in most ethnic groups. Defective variants may affect the clinical response to AChEIs. PGx geno-phenotyping is highly recommended prior to treatment.

Huperzine A as a neuroprotective and antiepileptic drug: a review of preclinical research

Huperzine A (HupA) is an acetylcholinesterase (AChE) inhibitor extracted from Huperzia Serrata, a firmoss, which has been used for various diseases in traditional Chinese medicine for fever and inflammation. More recently, it has been used in Alzheimer's disease and other forms of dementia with a presumed mechanism of action via central nicotinic and muscarinic receptors. HupA is marketed as a dietary supplement in the U.S. This article reviews newly proposed neuroprotective and anticonvulsant HupA properties based on animal studies. HupA exerts its effects mainly via α7nAChRs and α4β2nAChRs, thereby producing a potent anti-inflammatory response by decreasing IL-1β, TNF-α protein expression, and suppressing transcriptional activation of NF-κB signaling. Thus, it provides protection from excitotoxicity and neuronal death as well as increase in GABAergic transmission associated with anticonvulsant activity.

Analysis of acetylcholinesterase inhibitors: bioanalysis, degradation and metabolism

Alzheimer's is a neurodegenerative disease. Its symptoms are attributed to a deficiency of cholinergic neurotransmission. The drugs of choice for the treatment of Alzheimer's disease are acetylcholinesterase (AChE) inhibitors. Starting in the 1980's from non-specific AChE inhibitors, the first-generation drugs such as physostigmine, a second generation of more selective and better tolerated products has been developed. Methods to detect and quantify these drugs and their metabolites in biological samples have been developed for analysis in plasma, blood, urine and cerebrospinal fluid. Diverse detection techniques have been used, such as ultraviolet, fluorescence, electrochemical and mass spectrometry. In this review, the methods applied to the analysis of these drugs and their metabolites in different biological matrices are reviewed and discussed. The stability of these drugs in biological matrices and under stress-conditions is also included in the discussion.

Photohuperzine A-A new photoisomer of huperzine A: structure elucidation, formation kinetics and activity assessment

A new photoisomer of the promising "anti-Alzheimer" drug candidate (+/-) huperzine A is described. The new substance was formed via a photoisomerization reaction and was found to be 1-amino-13-ethylidene-11-methyl-6-aza-tetracyclo-[7.3.1.0(2.7).0(4.7)]-trideca-2,10-diene-5-one using NMR analysis. The kinetics of its formation was studied and proven to be of first-order. The described photoisomer showed a significant loss in activity, being more than 100 times less active than (-) huperzine A itself. The new substance was named photohuperzine A, referring to its photopyridone substructure.

Progress in studies of huperzine A, a natural cholinesterase inhibitor from Chinese herbal medicine

Huperzine A (HupA), a novel alkaloid isolated from the Chinese herb Huperzia serrata, is a potent, highly specific and reversible inhibitor of acetylcholinesterase(AChE). Compared with tacrine, donepezil, and rivastigmine, HupA has better penetration through the blood-brain barrier, higher oral bioavailability, and longer duration of AChE inhibitory action. HupA has been found to improve cognitive deficits in a broad range of animal models. HupA possesses the ability to protect cells against hydrogen peroxide, beta-amyloid protein (or peptide), glutamate, ischemia and staurosporine-induced cytotoxicity and apoptosis. These protective effects are related to its ability to attenuate oxidative stress, regulate the expression of apoptotic proteins Bcl-2, Bax, P53, and caspase-3, protect mitochondria, upregulate nerve growth factor and its receptors, and interfere with amyloid precursor protein metabolism. Antagonizing effects of HupA on N-methyl-D-aspartate receptors and potassium currents may also contribute to its neuroprotection as well. Pharmacokinetic studies in rodents, canines, and healthy human volunteers indicated that HupA was absorbed rapidly, distributed widely in the body, and eliminated at a moderate rate with the property of slow and prolonged release after oral administration. Animal and clinical safety tests showed that HupA had no unexpected toxicity, particularly the dose-limiting hepatotoxicity induced by tacrine. The phase IV clinical trials in China have demonstrated that HupA significantly improved memory deficits in elderly people with benign senescent forgetfulness, and patients with Alzheimer disease and vascular dementia, with minimal peripheral cholinergic side effects and no unexpected toxicity. HupA can also be used as a protective agent against organophosphate intoxication.

Recent pharmacological studies on natural products in China

Natural products have been used as medicinal agents for many years. In addition, these compounds have also served as the starting points for semisynthetic analogs with improved properties. This review focuses on recent advances in the pharmacological studies on natural products mainly performed and published in China. Emphasis will be placed on those compounds that show the greatest promise clinically such as huperzine A (9-amino-13-ethylidene-11-methyl-4-azatricyclo[7.3.1.0(3.8)]trideca-3(8),6,11-trien-5-one), s-(-)-3-n-butylphthalide (s-(-)-3-butyl-1(3H)-isobenzofuranone), (-)-clausenamide (3-hydroxy-4-phenyl-5a-hydroxybenzyl-N-methyl-gamma-lactam) and Ginkgo biloba extract and its active components.