Current Medicinal Chemistry - Volume 17, Issue 5, 2010

St. John's Wort (SJW) has been used medicinally for over 5,000 years. Relatively recently, one of its phloroglucinol derivatives, hyperforin, has emerged as a compound of interest. Hyperforin first gained attention as the constituent of SJW responsible for its antidepressant effects. Since then, several of its neurobiological effects have been described, including neurotransmitter re-uptake inhibition, the ability to increase intracellular sodium and calcium levels, canonical transient receptor potential 6 (TRPC6) activation, N-methyl-D-aspartic acid (NMDA) receptor antagonism as well as antioxidant and anti-inflammatory properties. Until recently, its pharmacological actions outside of depression had not been investigated. However, hyperforin has been shown to have cognitive enhancing and memory facilitating properties. Importantly, it has been shown to have neuroprotective effects against Alzheimer's disease (AD) neuropathology, including the ability to disassemble amyloid-β (Aβ) aggregates in vitro, decrease astrogliosis and microglia activation, as well as improve spatial memory in vivo. This review will examine some of the early studies involving hyperforin and its effects in the central nervous system (CNS), with an emphasis on its potential use in AD therapy. With further investigation, hyperforin could emerge to be a likely therapeutical candidate in the treatment of this disease.

MicroRNAs (miRNAs) are non-coding single-stranded RNAs with about 21˜ 23 nucleotides in length, which originate from encoding genes in nucleus. In most cases miRNAs play an inhibitory role in gene expression in a posttranscriptional level by partially complementary binding to the 3' unstranlated region (UTR) of target mRNAs. Large bodies of evidence have shown that miRNAs were involved in various diseases, such as cancer, infectious diseases, diabetes etc, and rising as critical modulators of pathological processes. Lately, some highlight articles revealed that the altered expression of miRNAs such as miR-1, miR-133, miR-21, miR-208 etc in hearts also contributed to cardiovascular diseases, such as heart ischemia, cardiac hypertrophy, and arrhythmias. Moreover, miRNAs are also identified to regulate heart development. These exciting findings not only improve our understanding of the molecular mechanisms of heart diseases, but also provide a new class of potential molecular targets— miRNAs, for the development of novel agents to treat heart diseases. Here, we summarized the recent discoveries about the role of miRNAs in cardiac physiological and pathological functions, and then discussed about their therapeutic potentials for heart diseases.

Glucocorticoids (GC) play a fundamental role in controlling physiologic homeostasis and, when present in excess, can have a detrimental impact on glucose control, blood pressure and lipid levels. The oxidoreductase 11β- hydroxysteroid dehydrogenase type 1 (11β-HSD1) mainly catalyzes the intracellular regeneration of active GCs (cortisol, corticosterone) from inert inactive 11-keto forms (cortisone) in liver, adipose tissue and brain, amplifying local GC action. Multiple lines of evidence have indicated that 11β-HSD1-mediated intracellular cortisol production may have a pathogenic role in type 2 diabetes and its co-morbidities. The 11β-HSD1 becomes a novel target for anti-type 2 diabetes drug developments, and inhibition of 11β-HSD1 offers a potential therapy to attenuate the type 2 diabetes. In the past several years, a lot of 11β-HSD1 inhibitors have been designed, synthesized, screened and discovered. Lowering intracellular glucocorticoid concentrations through administration of small molecule 11β-HSD1 selective inhibitors, significantly attenuates the signs and symptoms of disease in preclinical animal models and clinical trials of diabetes and metabolic syndrome. Among published inhibitors, DIO-902 from DiObex Inc. and INCB13739 from Incyte Inc. are now being investigated under Phase 2B clinical trials. However, the selectivity of current selective 11β-HSD1 inhibitors has been just focused on the difference between 11β-HSD1 and 11β-HSD2. They inhibit the bi-directional activities of 11β-HSD1, both 11β-HSD1 reductase (major) and oxidase (minor). In our lab, we have recently found novel chemicals that not only inhibit 11β-HSD1 reductase activity but also increase its oxidase activity without inhibition against 11β-HSD2. We propose that this dual modulation on 11β-HSD1 may provide a better therapeutic strategy for type 2 diabetes.

Chagas disease, also known as American trypanosomiasis, is caused by infection with the protozoan parasite Trypanosoma cruzi. The Pan American Health Organization (PAHO) estimates that currently 7.7 million of people have Trypanosoma cruzi infection in the 21 endemic countries from the southern and southwestern United States to central Argentina and Chile. The only approved therapeutics for the treatment of Chagas disease are two nitroheterocyclic compounds as a nitrofuran (nifurtimox; Lampit) and a nitroimidazole (benznidazole; Rochagan). However, the anti-Trypanosoma cruzi activities of these compounds were discovered empirically over three decades ago. The treatment of Chagas disease with nifurtimox or benznidazole is unsatisfactory because of their limited efficacy in the prevalent chronic stage of the disease and their toxic side effects. In this context, this article will review the current knowledge of the different aspects involved in this illness, such as Trypanosoma cruzi transmission, physiology and biochemistry of the etiological agent, epidemiological aspects and current treatments for American trypanosomiasis. An important section of this review will focus on the different strategies in drug discovery for Chagas disease, including methodology, in vitro screening studies against whole parasites, novel rationally developed approaches on the basis of the increasing knowledge of the biochemistry of Trypanosoma cruzi and the recent progress in the understanding and validation of several targets for the therapy of Chagas disease. A summary of the most relevant drug targets such as sterol biosynthesis pathway, cysteine protease pathway, pyrophosphate metabolism and purine salvage pathway will be reviewed. Moreover, recent studies regarding other strategies currently under development including thiol-dependent redox metabolism, lysophospholipid analogues and DNA binders will also be discussed.

Primary prevention of osteoporosis must aim at increasing bone mass acquisition before late adolescence. During pubertal years both genders reach peak bone acquisition, though males develop a greater skeletal mass. This dimorphism is largely regulated by endocrine factors, with critical roles played by gonadal steroids, growth hormone and insulin growth factor-1, amongst the most important. Menstrual history is a surrogate for the adequacy of hormonal functioning, nutrition and physical activity that may be a marker of bone status and development in young women. Adequate levels of adrenal, reproductive and pituitary hormones, growth factors and leptin are needed for the initiation and maintenance of regular menstrual cycles as well as for the achievement of peak bone mass. Adequate regular exercise and body composition are also pivotal elements in maintaining normal mechanical bone stimulus during bone growth. Avoidance of carbonated soft drink consumption, or excessive alcohol and any tobacco should be considered as these may interfere reaching adequate bone mass.

Since its discovery in the early 1960's, abscisic acid (ABA) has received considerable attention as an important phytohormone, and more recently, as a candidate medicinal in humans. In plants it has been shown to regulate important physiological processes such as response to drought stress, and dormancy. The discovery of ABA synthesis in animal cells has generated interest in the possible parallels between its role in plant and animal systems. The importance of this molecule has prompted the development of several methods for the chemical synthesis of ABA, which differ significantly from the biosynthesis of ABA in plants through the mevalonic acid pathway. ABA recognition in plants has been shown to occur at both the intra- and extracellularly but little is known about the perception of ABA by animal cells. A few ABA molecular targets have been identified in vitro (e.g., calcium signaling, G protein-coupled receptors) in both plant and animal systems. A unique finding in mammalian systems, however, is that the peroxisome proliferator-activated receptor, PPAR γ, is upregulated by ABA in both in vitro and in vivo studies. Comparison of the human PPAR γ gene network with Arabidopsis ABA-related genes reveal important orthologs between these groups. Also, ABA can ameliorate the symptoms of type II diabetes, targeting PPAR γ in a similar manner as the thiazolidinediones class of anti-diabetic drugs. The use of ABA in the treatment of type II diabetes, offers encouragement for further studies concerning the biomedical applications of ABA.

Thioredoxin (Trx) is the major cellular protein disulfide reductase in a broad range of organisms, including humans. Trx, together with glutaredoxin (Grx), plays critical roles in the regulation of cellular protein redox homeostasis. Reduced thioredoxin transfers reducing equivalents to disulphides in target proteins, leading to reversible oxidation of its active centre dithiol to a disulphide. The resulting disulphide bridge is, in turn, reduced to a dithiol by thioredoxin reductase (TrxR). Increasing attention has been paid to the role of Trx, as it has been shown to be a signalling intermediate beyond its intrinsic antioxidant activity. Indeed, this protein acts as a growth factor, activates a number of transcription factors regulating cell growth and survival, acts as cofactor for ribonucleotide reductase, and promotes angiogenesis. In addition, Trx has been demonstrated to cooperatively inhibit programmed cell death. Because of the multiple roles of Trx system in tumorigenesis, this protein represents an emerging target for anti-cancer drugs. Several Trx system modulators have been identified: a semi-synthetic Trx inhibitor, PX-12 (1-methylpropyl 2-imidazolyl disulfide), has been placed in a clinical trial. However, there is a growing interest in finding new selective ones. Natural products continue to provide structurally complex, but highly original lead structures for drug discovery programs: polyphenols, quinones, and terpenoids showed to affect the Trx/TrxR system at different levels. The purpose of this review is to provide an overview of the plant and fungal secondary metabolites interfering with Trx and TrxR activities, paying particularly attention to their mechanism of action. Among polyphenols, curcumin and some flavonoids such as myricetin and quercetin, have been identified as potential anticancer agents with a mechanism of action that may be mediated by the Trx system.