A new cycloartane-type triterpenoid saponin xanthine oxidase inhibitor from Homonoia riparia Lour

Natural Products and Extracts as Xantine Oxidase Inhibitors - A Hope for Gout Disease?

Xanthine oxidase (EC 1.17.3.2) (XO) is one of the main enzymatic sources that create reactive oxygen species (ROS) in the living system. It is a dehydrogenase enzyme that performs electron transfer to nicotinamide adenine dinucleotide (NAD+), while oxidizing hypoxanthin, which is an intermediate compound in purine catabolism, first to xanthine and then to uric acid. XO turns into an oxidant enzyme that oxidizes thiol groups under certain stress conditions in the tissue. The last metabolic step, in which hypoxanthin turns into uric acid, is catalyzed by XO. Uric acid, considered a waste product, can cause kidney stones and gouty-type arthritis as it is crystallized, when present in high concentrations. Thus, XO inhibitors are one of the drug classes used against gout, a purine metabolism disease that causes urate crystal storage in the joint and its surroundings caused by hyperuricemia. Urate-lowering therapy includes XO inhibitors that reduce uric acid production as well as uricosuric drugs that increase urea excretion. Current drugs that obstruct uric acid synthesis through XO inhibition are allopurinol, febuxostat, and uricase. However, since the side effects, safety and tolerability problems of some current gout medications still exist, intensive research is ongoing to look for new, effective, and safer XO inhibitors of natural or synthetic origins for the treatment of the disease. In the present review, we aimed to assess in detail XO inhibitory capacities of pure natural compounds along with the extracts from plants and other natural sources via screening Pubmed, Web of Science (WoS), Scopus, and Google Academic. The data pointed out to the fact that natural products, particularly phenolics such as flavonoids (quercetin, apigenin, and scutellarein), tannins (agrimoniin and ellagitannin), chalcones (melanoxethin), triterpenes (ginsenoside Rd and ursolic acid), stilbenes (resveratrol and piceatannol), alkaloids (berberin and palmatin) have a great potential for new XO inhibitors capable of use against gout disease. In addition, not only plants but other biological sources such as microfungi, macrofungi, lichens, insects (silk worms, ants, etc) seem to be the promising sources of novel XO inhibitors.

Targeting Xanthine Oxidase by Natural Products as a Therapeutic Approach for Mental Disorders

Mental disorders comprise diverse human pathologies, including depression, bipolar affective disorder, schizophrenia, and dementia that affect millions of people around the world. The causes of mental disorders are unclear, but growing evidence suggests that oxidative stress and the purine/adenosine system play a key role in their development and progression. Xanthine oxidase (XO) is a flavoprotein enzyme essential for the catalysis of the oxidative hydroxylation of purines -hypoxanthine and xanthine- to generate uric acid. As a consequence of the oxidative reaction of XO, reactive oxygen species (ROS) such as superoxide and hydrogen peroxide are produced and, further, contribute to the pathogenesis of mental disorders. Altered XO activity has been associated with free radical-mediated neurotoxicity inducing cell damage and inflammation. Diverse studies reported a direct association between an increased activity of XO and diverse mental diseases including depression or schizophrenia. Small-molecule inhibitors, such as the well-known allopurinol, and dietary flavonoids, can modulate the XO activity and subsequent ROS production. In the present work, we review the available literature on XO inhibition by small molecules and their potential therapeutic application in mental disorders. In addition, we discuss the chemistry and molecular mechanism of XO inhibitors, as well as the use of structure-based and computational methods to design specific inhibitors with the capability of modulating XO activity.

Effect of Muntingia calabura L. Stem Bark Extracts on Uric Acid Concentration and Renal Histopathology in Diabetic Rats

Background and objectives: This study was designed to determine uric acid concentration and renal histopathology of Muntingia calabura L. stem bark extract in diabetic rats and to compare the natural product of M. calabura L. stem bark extract with allopurinol. Materials and Methods: A completely randomized design was used for the experiment, which consisted of six treatment groups, each consisting of four rats, as follows: 1) NR, normal rat; 2) KN, diabetic rat (negative control); 3) KP, diabetic rats given allopurinol 10 mg/kg body weight; 4) EM150, diabetic rats given the test extract 150 mg/kg body weight/day; 5) EM300, diabetic rats given the test extract 300 mg/kg body weight/day; and 6) EM450, diabetic rats given for extract 450 mg/kg body weight/ day. Results: The results showed that M. calabura L. stem bark extract decreased (p < 0.05) uric acid concentrations in diabetic rats and no specific damage to renal proximal tubular cells was seen. Conclusions: It was concluded that M. calabura L. stem bark extract has a potential as an antihyperuricemic in diabetic rats. The recommended dose was 300 mg/kg body weight to provide a significant effect on reducing the uric acid level in diabetic rats. Our results support the use of this plant for the treatment of degenerative and inflammatory diseases.

Optimization of Microwave-Assisted Extraction Saponins from Sapindus mukorossi Pericarps and an Evaluation of Their Inhibitory Activity on Xanthine Oxidase

A microwave-assisted extraction (MAE) method was applied to separate saponins from Sapindus mukorossi pericarps. The most important factors of the six extraction parameters were selected using Plackett–Burman designs; therefore, the further extraction procedure was optimized using the Box–Behnken designs; meanwhile, the optimum processing parameters and well-pleasing saponins extraction rate were inferred. The final operation conditions were the ethanol concentration of 40%, soaking time of 3 h, particle size of 80–100 meshes, extraction time of 13 min, solvent-solid ratio of 19 mL/g, and microwave power of 425 W. Based on the optimal extraction parameters, the extraction rate of the saponins by means of MAE technique reached 280.55 ± 6.81 mg/g, which exceeds yields acquired using conventional manners. Saponins from S. mukorossi have obvious xanthine oxidase inhibitory properties in vitro compared with allopurinol. The saponins displayed a type of competitive inhibition of xanthine oxidase. In conclusion, a MAE technique in association with a response surface design provides an efficient extraction tactics, which could sufficiently isolate saponins from S. mukorossi pericarps; further, this technique could be applied to the dissociation of other bioactive substances from plant sources. In addition, the saponins may be a promising alternative to conventional medicine to treat gout and other inflammation-associated disorders to mitigate the side effects of traditional drugs.

Triterpenoids

Covering 2014. Previous review: Nat. Prod. Rep., 2017, 34, 90-122 This review covers the isolation and structure determination of triterpenoids reported during 2014 including squalene derivatives, lanostanes, holostanes, cycloartanes, cucurbitanes, dammaranes, euphanes, tirucallanes, tetranortriterpenoids, quassinoids, lupanes, oleananes, friedelanes, ursanes, hopanes, serratanes, isomalabaricanes and saponins; 374 references are cited.

Riparsaponin isolated from Homonoia riparia Lour induces apoptosis of oral cancer cells

Homonoia riparia Lour (Euphorbiaceae) is a known source of herbal medicine in China, and riparsaponin (RSP) is an active constituent isolated from H. riparia. The aim of the present study was to investigate the antitumor effect of RSP on human oral carcinoma cells and its potential underlying molecular mechanism. RSP was isolated from roots of H. riparia and identified using nuclear magnetic resonance. An MTT assay was used to evaluate the cytotoxicity of RSP on human oral carcinoma cells. Subsequently, DAPI staining was performed to investigate the apoptotic effect of RSP. To investigate the potential underlying molecular mechanism of action of RSP, western blotting was performed to determine the expression of cleaved caspase 3/9, B-cell lymphoma 2 (Bcl-2), Bcl-2-associated X protein (Bax), Bcl-2-associated death promoter (Bad), epithelial cadherin (E-CAD), c-MET, matrix metalloproteinase (MMP)-2 and MMP-9. RSP exhibited a significant anti-proliferative effect on oral carcinoma cells at concentrations between 10 and 200 µg/ml via apoptosis. Following treatment with RSP (20, 40 and 80 µg/ml), expression of cleaved caspase-3 (P<0.05, P<0.01 and P<0.01, respectively), cleaved caspase-9 (P<0.01), Bad (P<0.01), Bax (P<0.01), c-MET (P<0.01), MMP-2 (P<0.01) and MMP-9 (P<0.01) in oral carcinoma cells was increased significantly compared with the control group, whereas expression of Bcl-2 (P<0.01) and E-CAD (P<0.01) was decreased. These results suggest that RSP possessed notable antitumor activity against oral squamous cell carcinoma by inducing mitochondria-mediated apoptosis.

Homonoia riparia and its major component, myricitrin, inhibit high glucose-induced apoptosis of human retinal pericytes

Background

The loss of retinal pericytes is one of the earliest changes associated with diabetic retinopathy (DR). Chronic hyperglycemia induces apoptosis of these cells, leading to the onset and progression of DR. In this study, we investigated the effects of Homonoia riparia (H. riparia) and its major component, myricitrin, on high glucose (HG)-induced apoptosis of primary human retinal pericytes (HRPs).

Methods

The effects of an ethanol extract of H. riparia leaves and of myricitrin on HRP viability and apoptosis were investigated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and flow cytometry. Reactive oxygen species (ROS) levels were measured using 2′,7′-dichlorofluorescein diacetate. The activity of specificity protein 1 (Sp1), a transcription factor, was measured using a luciferase reporter assay and western blot analyses were performed to measure the expression of proteins involved in signaling and apoptosis.

Results

HG produced cytotoxic effects on HRPs, which showed increased Sp1 expression and ROS levels. H. riparia extract and myricitrin significantly inhibited HG-induced apoptosis and ROS generation, and also inhibited Sp1 activity. This was evidenced by an attenuation of the HG-mediated increase in extracellular signal-regulated kinase phosphorylation.

Conclusion

These data indicate that HG-mediated induction of Sp1 is one of a number of key signaling pathways involved in HRP apoptosis, and that H. riparia extracts or myricitrin may provide useful approaches to preventing and treating DR.

Antioxidant and Nephroprotective Activities of the Extract and Fractions of Homonoia riparia Lour

BACKGROUND

Homonoia riparia is a plant, which is widely used in the indigenous system of medicine for the treatment of urolithiasis, renal disorders and inflammatory conditions. This is the first report on the antioxidant and nephroprotective activities of whole plant of H. riparia.

OBJECTIVE

The present study aims at investigating the in vitro antioxidant and nephroprotective activity of the methanol extract and its different fractions of H. riparia.

METHODS

Petroleum ether (HRPE), Ethyl acetate (HREA), Butanol (HRBU), aqueous fractions (HRAQ) were prepared from the crude methanol extract of H. riparia (HRM) using liquid partitioning. Total phenolic content, flavonoid content and antioxidant activity assay were performed according to suitable methods. Nephroprotective activities were evaluated by MTT assay using Human Embryonic Kidney cells against cisplatin induced toxicity. Quantification of gallic acid was performed using validated HPTLC method.

RESULTS

The studies showed that extract and fractions possess significant nephroprotective activity against cisplatin induced renal toxicity. All the extracts/fractions of whole plant of Homonoia riparia was found to be significantly reducing cisplatin induced toxicity (< 0.05). The highest activity was observed with HRBU and HRAQ with a percentage viability of 293.09 ± 4.3 and 345.07 ± 3.2 at a concentration of 200 µg/ml. Gallic acid was detected in the HRM/fractions using HPTLC.

SUMMARY

Cisplatin (8 μg/ml) exhibited 50 % inhibition in cell viability in HEK 293 cellsButanol and aqueous fractions of Homonoia riparia showed significant nephroprotective activity against cisplatin induced cell damage in HEK cells.Gallic acid was detected and quantified in the extract and fractions of whole plant of Homonoia ripariaAbbreviations used: HPTLC: High Performance Thin Layer Chromatography, DPPH: 1,1-diphenyl-2-picrylhydrazyl, ABTS: 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt, MTT: 3-(4,5-dimethylthiazolyl-2-yl)-2,5- diphenyl tetrazolium bromide, GAE: Gallic acid equivalents, QE: Quercetin equivalents, HEK: Human Embryonic Kidney, HRM: Methanol extract of H. riparia, HRPE: Petroleum ether fraction of H. riparia, HREA: ethyl acetate fraction of H. riparia, HRBU: Butanol fraction of H. riparia, HRAQ: Aqueous fraction of H. riparia, DMEM: Dulbecco's minimum essential medium, FBS: Foetal bovine serum, DMSO: Dimethyl sulfoxide, ANOVA: One way analysis of variance.

Hyperuricemia-Related Diseases and Xanthine Oxidoreductase (XOR) Inhibitors: An Overview

Uric acid is the final oxidation product of purine metabolism in humans. Xanthine oxidoreductase (XOR) catalyzes oxidative hydroxylation of hypoxanthine to xanthine to uric acid, accompanying the production of reactive oxygen species (ROS). Uric acid usually forms ions and salts known as urates and acid urates in serum. Clinically, overproduction or under-excretion of uric acid results in the elevated level of serum uric acid (SUA), termed hyperuricemia, which has long been established as the major etiologic factor in gout. Accordingly, urate-lowering drugs such as allopurinol, an XOR-inhibitor, are extensively used for the treatment of gout. In recent years, the prevalence of hyperuricemia has significantly increased and more clinical investigations have confirmed that hyperuricemia is an independent risk factor for cardiovascular disease, hypertension, diabetes, and many other diseases. Urate-lowering therapy may also play a critical role in the management of these diseases. However, current XOR-inhibitor drugs such as allopurinol and febuxostat may have significant adverse effects. Therefore, there has been great effort to develop new XOR-inhibitor drugs with less or no toxicity for the long-term treatment or prevention of these hyperuricemia-related diseases. In this review, we discuss the mechanism of uric acid homeostasis and alterations, updated prevalence, therapeutic outcomes, and molecular pathophysiology of hyperuricemia-related diseases. We also summarize current discoveries in the development of new XOR inhibitors.

Synthesis and Biological Evaluation of Novel Aryl-2H-pyrazole Derivatives as Potent Non-purine Xanthine Oxidase Inhibitors

A series of aryl-2H-pyrazole derivatives were synthesized and evaluated for inhibitory activity against xanthine oxidase in vitro as potent xanthine oxidase inhibitors. Among them, 2 aryl-2H-pyrazole derivatives showed significant inhibitory activities against xanthine oxidase. Compound 19 emerged as the most potent xanthine oxidase inhibitor (IC50=9.8 µM) in comparison with allopurinol (IC50=9.5 µM). The docking study revealed that compound 19 might have strong interactions with the active site of xanthine oxidase. This compound is thus a new candidate for further development for the treatment of gout.