Antony Kam

The Pentacyclic Triterpenoids in Herbal Medicines and Their Pharmacological Activities in Diabetes and Diabetic Complications

Pentacyclic triterpenoids including the oleanane, ursane and lupane groups are widely distributed in many medicinal plants, such as Glycyrrhiza species, Gymnema species, Centella asiatica, Camellia sinensis, Crataegus species and Olea europaea, which are commonly used in traditional medicine for the treatment of diabetes and diabetic complications. A large number of bioactive pentacyclic triterpenoids, such as oleanolic acid, glycyrrhizin, glycyrrhetinic acid, ursolic acid, betulin, betulinic acid and lupeol have shown multiple biological activities with apparent effects on glucose absorption, glucose uptake, insulin secretion, diabetic vascular dysfunction, retinopathy and nephropathy. The versatility of the pentacyclic triterpenes provides a promising approach for diabetes management.

Herbal Medicines and Nutraceuticals for Diabetic Vascular Complications: Mechanisms of Action and Bioactive Phytochemicals

Diabetes is one of the most prevalent chronic diseases throughout the world. The majority of its complications arise from vascular-related inflammation apparently initiated by endothelial cell injury. One cause of this injury has been attributed to hyperglycaemia-induced reactive oxygen species. Consequently, current drug developmental strategy has targeted specific inflammatory and oxidative stress pathways for the prevention of diabetic vascular complications. Herbal medicines have traditionally been used for the treatment of diabetes and its complications. In fact, current pre-clinical and clinical studies have demonstrated that many of them exhibit potent anti-inflammatory and anti-oxidative properties, and have also identified the active phytochemicals responsible for their activities. The present review summarises the latest research on the molecular mechanisms of diabetic vascular complications, and evaluates the level of scientific evidence for common herbal medicines and their bioactive phytochemicals. These agents have been shown to be effective through various mechanisms, particularly the NF-κB signalling pathways. Overall, herbal medicines and nutraceuticals, as well as their bioactive components, which exhibit anti-inflammatory and anti-oxidative properties, provide a promising approach for the prevention and treatment of diabetic complications.

Butelase 1: A Versatile Ligase for Peptide and Protein Macrocyclization.

Macrocyclization is a valuable tool for drug design and protein engineering. Although various methods have been developed to prepare macrocycles, a general and efficient strategy is needed. Here we report a highly efficient method using butelase 1 to macrocyclize peptides and proteins ranging in sizes from 26 to >200 residues. We achieved cyclizations that are 20,000 times faster than sortase A, the most widely used ligase for protein cyclization. The reactions completed within minutes with up to 95% yields.

Herbal medicines for the management of diabetes.

Herbal medicines have been used in the management of diabetes in traditional medicine. This chapter reviews recent findings of the most popular herbs reported to treat diabetes through their relevant mechanistic pathways. These include increased insulin secretion, improvement in insulin sensitivity, enhanced glucose uptake by adipose and muscle tissues, inhibition of glucose absorption from intestine, inhibition of glucose production from hepatocytes and anti-inflammatory activities. The pharmacological activities have highlighted the potential efficacy of these herbal medicines in the management of diabetes.

The Protective Effects of Natural Products on Blood-Brain Barrier Breakdown

The blood-brain barrier (BBB) is a protective fence between the central nervous system and the systemic circulation, and is essential for maintaining the normal homeostasis of the central nervous system. BBB breakdown is instigated in many neurological disorders such as Alzheimers disease and multiple sclerosis. Recent literature has advanced the knowledge on the physiology and pathophysiology of BBB breakdown, including the attribution of detrimental inducers and signalling transduction cascades. Natural products, such as flavonoids, phenolic compounds, terpenes, alkaloids, lipids and phthalides have been reported to attenuate many neurological diseases by modulating the signalling transduction cascades associated with BBB breakdown. Understanding the activities of these natural products through the molecular mechanisms associated with BBB breakdown will offer considerable scope in the discovery and development of novel agents for preventing BBB breakdown and thus, the progression of neurological disorders.

Gallic acid protects against endothelial injury by restoring the depletion of DNA methyltransferase 1 and inhibiting proteasome activities

BACKGROUND The aim of this study was to investigate the protective effects of gallic acid, a common phenolic compound naturally present in food and nutraceuticals, on endothelial cell death and the mechanisms involved. METHODS Endothelial cell death was induced by the combination of homocysteine, adenosine and tumour necrosis factor (TNF) in human vascular endothelial cells (EAhy926 and HBEC-5i cells). The protective effects of gallic acid were evaluated against cytotoxicity, apoptosis and microparticle release. Underlying mechanisms were further investigated focusing on the involvement of DNA methyltransferase 1 (DNMT1) and proteasome activities. RESULTS Our results showed that gallic acid dose-dependently arrested cytotoxicity in EAhy926 and HBEC-5i cells induced by the combination. Gallic acid showed anti-apoptotic effects and reduced the formation of microparticles. Notably, gallic acid reversed DNMT1 depletions at the protein level. The cytoprotective and anti-apoptotic effects of gallic acid were counteracted by the pre-treatment with DNMT1 inhibitor, 5-aza-2-deoxycytidine (5-aza-dC). Treatment with gallic acid led to the accumulation of ubiquitinated protein aggregates and the reduction in chymotrypsin-like proteasome activities indicating proteasome inhibition. CONCLUSION Our results demonstrate for the first time that gallic acid is capable of protecting endothelial cells from injury induced by the combination of homocysteine, adenosine and TNF, at least in part, by restoring the depletion of DNMT1 and inhibiting proteasome activities.

Combination of TNF-α, homocysteine and adenosine exacerbated cytotoxicity in human cardiovascular and cerebrovascular endothelial cells.

Disruption to the vascular homoeostasis is detrimental in vascular diseases. This study examined how the combination of homocysteine, adenosine and tumor necrosis factor-alpha (TNF-α) influenced endothelial cell survival. In cultured human-derived cardiovascular (EA.hy926) and cerebrovascular (HBEC-5i) endothelial cells, cell death events were initiated by TNF-α (0.1-10 ng/mL) only when both homocysteine (0.5 mM) and adenosine (0.5 mM) were present. The accelerated cell death events induced by the combination were triggered through excessive apoptosis. This was evident by membrane phospholipid phosphatidylserine externalisation, cell shrinkage and DNA fragmentation, as well as an increase in the expressions and occurrence of active caspase-3 and cleaved poly(ADP-ribose) polymerase (PARP) positive cells. Collectively, homocysteine, adenosine and TNF-α are interrelated in the survival of endothelial cells, and this co-existence should be considered in future drug development for cardiovascular and cerebrovascular diseases.

Synergistic effects of Danshen (Salvia Miltiorrhiza Radix et Rhizoma) and Sanqi (Notoginseng Radix et Rhizoma) combination in inhibiting inflammation mediators in RAW264.7 cells

Aims. This study aims to investigate the possible synergistic interactions of the Danshen-Sanqi combination on vascular disease via their anti-inflammatory activities. Methods. Nine combination ratios of Danshen-Sanqi extracts were screened in the RAW264.7 cell line and their anti-inflammatory effects were examined in lipopolysaccharide- (LPS-) induced nitric oxide (NO), tumor necrosis factor (TNF), and monocyte chemoattractant protein-1 (MCP-1) generation pathways. The interaction between Danshen and Sanqi on each target was analysed using combination index (CI) and isobologram models. Additionally, the anti-inflammatory activities of key bioactive compounds from Danshen and Sanqi were tested using the same models. The compounds from each herb that exerted the most potent activity were combined to evaluate their possible synergistic/antagonistic interactions. Results. Danshen-Sanqi 8 : 2 was found to be the optimal ratio and exerted a synergistic effect in inhibiting NO, TNF, and MCP-1 when the concentrations were higher than 1.24, 1.89, and 2.17 mg/mL, respectively. Although dihydrotanshinone I (DT) and ginsenoside Rd (Rd) from Danshen and Sanqi, respectively, exhibited the greatest individual bioactivity in the assays, antagonistic effects were observed for the DT-Rd combination 7 : 3. Conclusion. This study provided scientific evidence to support the traditional use of the Danshen-Sanqi combination for vascular disease through their synergistic interactions on anti-inflammatory pathways.

Identification and Characterization of Roseltide, a Knottin-type Neutrophil Elastase Inhibitor Derived from Hibiscus sabdariffa

Plant knottins are of therapeutic interest due to their high metabolic stability and inhibitory activity against proteinases involved in human diseases. The only knottin-type proteinase inhibitor against porcine pancreatic elastase was first identified from the squash family in 1989. Here, we report the identification and characterization of a knottin-type human neutrophil elastase inhibitor from Hibiscus sabdariffa of the Malvaceae family. Combining proteomic and transcriptomic methods, we identified a panel of novel cysteine-rich peptides, roseltides (rT1-rT8), which range from 27 to 39 residues with six conserved cysteine residues. The 27-residue roseltide rT1 contains a cysteine spacing and amino acid sequence that is different from the squash knottin-type elastase inhibitor. NMR analysis demonstrated that roseltide rT1 adopts a cystine-knot fold. Transcriptome analyses suggested that roseltides are bioprocessed by asparagine endopeptidases from a three-domain precursor. The cystine-knot structure of roseltide rT1 confers its high resistance against degradation by endopeptidases, 0.2 N HCl, and human serum. Roseltide rT1 was shown to inhibit human neutrophil elastase using enzymatic and pull-down assays. Additionally, roseltide rT1 ameliorates neutrophil elastase-stimulated cAMP accumulation in vitro. Taken together, our findings demonstrate that roseltide rT1 is a novel knottin-type neutrophil elastase inhibitor with therapeutic potential for neutrophil elastase associated diseases.

Nucleoside Transport Inhibition by Dipyridamole Prevents Angiogenesis Impairment by Homocysteine and Adenosine

PURPOSE Adenosine plays an important role in the pathogenesis of homocysteine-associated vascular complications. METHODS This study examined the effects of dipyridamole, an inhibitor for nucleoside transport, on impaired angiogenic processes caused by homocysteine and adenosine in human cardiovascular endothelial cell line (EAhy926). RESULTS The results showed that dipyridamole restored the extracellular adenosine and intracellular S-adenosylhomocysteine concentrations disrupted by the combination of homocysteine and adenosine. Dipyridamole also ameliorated the impaired proliferation, migration and formation of capillary-like tubes of EAhy926 cells caused by the combination of homocysteine and adenosine. Mechanism analysis revealed that dipyridamole induced the phosphorylation of mitogen-activated protein kinase kinase (MEK) and extracellular signal-regulated kinases (ERK) and its effect on cell growth was attenuated by the MEK inhibitor, U0126. CONCLUSION Dipyridamole protected against impaired angiogenesis caused by homocysteine and adenosine, at least in part, by activating the MEK/ERK signalling pathway, and this could be associated with its effects in suppressing intracellular S-adenosylhomocysteine accumulation. NOVELTY OF THE WORK This is the first paper showing that nucleoside transport inhibition by dipyridamole reduced impaired angiogenic process caused by homocysteine and adenosine.