An anti-inflammatory ent-kaurane from the stems of Annona squamosa that inhibits various human neutrophil functions

We have previously shown that 11 ent-kauranes isolated from the stems of Annona squamosa exhibited immunomodulating effects in leukocytes. In this study, a cellular model using isolated human neutrophils, which are important in the pathogenesis of rheumatoid arthritis, ischemia-reperfusion injury, chronic obstructive pulmonary disease, asthma and other inflammatory diseases, was established in order to elucidate the anti-inflammatory functions of 16beta,17-dihydroxy-ent-kauran-19-oic acid (1). Reactive oxygen species (ROS) and granule proteases produced by neutrophils contribute to the pathogenesis of inflammatory diseases. Compound 1 inhibited the generation of superoxide anion, the formation of ROS, and the release of elastase in formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP)-activated human neutrophils in a concentration-dependent manner with IC (50) values of 3.95 +/- 0.68, 12.20 +/- 2.16, and 12.52 +/- 2.26 microM, respectively. The anti-inflammatory actions were not attributable to cytotoxicity because incubation of the neutrophils with 1 did not result in lactate dehydrogenase release. Compound 1 did not display antioxidant or superoxide anion-scavenging activity. Furthermore, neither subcellular NADPH oxidase activity nor cAMP-dependent pathways were altered by 1. Compound 1 significantly inhibited rapid calcium release from internal calcium stores induced by FMLP but not by thapsigargin. In summary, the presented results indicate that the inhibitory effects of 1 on respiratory burst and degranulation of human neutrophils are through the inhibition of cytosolic calcium mobilization, but not via the cAMP-dependent pathways.

Increase of insulin sensitivity by stevioside in fructose-rich chow-fed rats

The intake of dietary fructose has undergone a marked increase around the world, especially the developed countries, in recent times. Stevioside, a glycoside contained in the leaves of Stevia rebaudiana Bertoni (Compositae), was used to screen the effect induced by a diet containing 60% fructose on insulin resistance in rats. Single oral administration of stevioside for 90 min decreased plasma glucose concentrations in a dose-dependent manner in rats receiving fructose-rich chow for four weeks. In addition, insulin action on glucose disposal rate was measured using the glucose-insulin index, the product of the areas under the curve of glucose, and insulin during the intraperitoneal glucose tolerance test. Oral administration of stevioside (5.0 mg/kg) in rats given four weeks of fructose-rich chow for 90 min reversed the value of glucose-insulin index, indicating that stevioside has the ability to improve insulin sensitivity in this insulin-resistant animal model. Time for the loss of plasma glucose lowering response to tolbutamide (10.0 mg/kg, i. p.) in fructose-rich chow fed rats was also markedly delayed by repeated stevioside treatment three times daily compared to the vehicle-treated group. The plasma glucose-lowering activity of tolbutamide was introduced to account for varying levels of endogenous insulin secretion, and is widely used as the indicator of insulin resistance development. Thus, it provided the supportive data that repeated oral administration of stevioside delayed the development of insulin resistance in rats on a high-fructose diet. Increased insulin sensitivity by stevioside administration was further identified using the plasma glucose-lowering action of exogenous insulin in streptozotocin-induced diabetic rats (STZ-diabetic rats). Oral administration of stevioside at 0.2 mg/kg three times daily into STZ-diabetic rats for ten days increased the response to exogenous insulin. Taken together, this demonstrated that oral administration of stevioside improves insulin sensitivity, and seems suitable as an adjuvant for diabetic patients and/or those that consume large amounts of fructose.

Two novel ent-kauranoid diterpenoids from Isodon japonica leaves

Two novel ent-kaurane diterpenoids, taihangjaponicain A (1), and taihangjaponicain B ( 2), and nine known diterpenoids, epinodosin (3), oridonin (4), epinodosinol (5), lasiokaurin ( 6), 1alpha- O-beta- D-glucopyranosylenmenol (7), lasiodonin (8), rabdosichuanin D ( 9), shikokianin (10) and rabdoternin A (11) were isolated from I. japonica leaves. The structures of the two new compounds were elucidated using 1-D and 2-D NMR spectroscopy. Compounds 1 and 3 - 11 were tested against HL-60, HO-8910 and A-549 human tumor cells. Compounds 4, 6 and 10 showed significant cytotoxicity against HL-60 cells with IC (50) values of 4.6, 2.0 and 3.4 microM, respectively, and against A-549 cells with IC (50) values of 17.5, 11.4 and 18.8 microM, respectively. Compound 6 exhibited moderate cytotoxicity against HO-8910 cells with an IC (50) value of 17.9 microM.

Activation of p38 mitogen-activated protein kinase during ent-11alpha-hydroxy-16-kauren-15-one-induced apoptosis in human leukemia HL-60 cells

Kaurene-type diterpenes possess various biological activities including antitumor and anti-inflammatory effects. Indeed, we have found that an ent-kaurene diterpene, ent-11alpha-hydroxy-16-kauren-15-one (KD), induced apoptosis via caspase-8 activation in human promyelocytic leukemia HL-60 cells. However, the mechanism of caspase-8 activation by KD is not clear. In this study, we investigated the involvement of p38 mitogen-activated protein kinase (p38 (MAPK)) in KD-induced apoptosis. p38 (MAPK) was activated by treatment with KD parallel to DNA ladder formation. Pretreatment with SB203580, a specific inhibitor of p38 (MAPK), attenuated induction of apoptosis by KD and inhibited activation of caspase-8. Cleavage of Bid, a typical substrate of caspase-8, was also inhibited by treatment with SB203580, suggesting that activation of p38 (MAPK) occurs upstream of caspase-8 during KD-induced apoptosis.

Glucose concentration in the blood of intact and alloxan-treated mice after pretreatment with commercial preparations of Stevia rebaudiana (Bertoni)

The study was concerned with the effect of mice pretreatment with two commercial products of Stevia rebaudiana Bertoni on the blood glucose concentration. One group of mice was pretreated four days with 200 mg/kg of Stevita (Stevita Co, INC, Arlington Texas) (stevia) and the other with 20 mg/kg of Clear Steviosides liquid (Stevita Co, INC, Herbal supplement, Brazil) (stevioside), whereas the animals of control group received at the same time physiological solution. Blood glucose concentration was measured before pretreatment and four days after that. The changes in glucose level were provoked by glucose-tolerance test (500 mg/kg, p.o.) and subcutaneous injection of adrenaline (0.2 mg/kg). The same procedure of measuring blood glucose was applied on the mice with alloxan-induced diabetes mellitus (two doses of 100 mg/kg with a 24-hour interval). Blood glucose levels in mice pretreated with stevia and stevioside were lower compared with control (7.82:6.82:8.01). Also, a smaller increase in this parameter compared to control was registered with pretreated mice in the glucose-tolerance test, pretreatment with stevioside being again more effective (8.68:6.36:5.82). Pretreatment with stevioside caused no significant increase in blood glucose concentration after administering adrenaline, which was not the case with the animals pretreated with stevia and control. Pretreatment with stevia, and to a greater extent with stevioside, protected test animals from the toxic action of alloxan compared with controls.

An ent-kaurene diterpene enhances apoptosis induced by tumor necrosis factor in human leukemia cells

Some antitumor agents, including tumor necrosis factor-alpha (TNF-alpha) and camptothecin (CPT), often cause resistance of tumor cells to antitumor agents through activation of the nuclear factor-kappa B (NF-kappa B) pathway that leads to up-regulation of anti-apoptotic proteins. Therefore, co-treatment of an inhibitor of the NF-kappa B pathway with antitumor agents is a useful strategy for chemotherapy. Here we report that ent-11 alpha-hydroxy-16-kauren-15-one (KD) selectively inhibits NF-kappa B-dependent gene expression due to treatment with TNF-alpha. KD in combination with TNF-alpha caused a dramatic increase in apoptosis in human leukemia cells accompanied by activation of caspases. A broad-spectrum inhibitor of caspases decreased the apoptosis induced by treatment with KD and TNF-alpha. KD in combination with CPT also caused an increase in apoptosis. These results suggest that the apoptotic potency of co-treatment of KD with TNF-alpha or CPT is elicited through selective inhibition of NF-kappa B-dependent anti-apoptotic proteins and thus may provide a basis for the development of useful approaches to the treatment of leukemia.

A novel cytotoxic oxetane ent-kauranoid from Isodon japonicus

A novel ll,20: 1,20-diepoxy-ent-kaurane diterpenoid, maoyecrystal 1 (1), was isolated from Isodan japonicus, and its structure was elucidated by spectroscopic methods and comparison with another new ent-kauranoid, rubescensin W (2) from Isodon rubescens var. taihangensis. The structure of 2 was determined by single crystal X-ray diffraction analysis. A bioassay of their cytotoxity against K562 cells showed that the oxetane group of 1 might be a bioactive moiety.

Structure of kaurane-type diterpenes from Parinari sprucei and their potential anticancer activity

Twenty-three kaurane-type diterpenes 1 - 23, including twenty new natural products 1 - 20, have been isolated from the leaves of Parinari sprucei and their structures elucidated by spectroscopic and chemical analysis. The isolated compounds were tested for their cytotoxic activity towards a panel of cancer cell lines. Compounds 9 and 10 showed activity against all cell lines with ED (50) values in the range of 10 - 20 microg/mL. The previously known 13-hydroxy-15-oxozoapatlin 21 was evaluated in an in vivo hollow fiber test, and found to be active with KB and LNCaP cells at the concentrations used.

A comparison of apoptosis and necrosis induced by ent-kaurene-type diterpenoids in HL-60 cells

We previously reported that ent-11alpha-hydroxy-16-kauren-15-one (KD) induces apoptosis through a caspase-dependent pathway and the induction of apoptosis is dependent on its enone group in human leukemia cells. Here we investigated the abilities of some KD-related compounds with enone group (Fig. 1) to induce apoptosis and to activate some caspases. The IC50 values of ent-kaurene-related compounds possessing the enone group, ent-1beta-hydroxy-9(11),16-kauradien-15-one (1), ent-9(11),16-kauradiene-12,15-dione (2) and the rearranged ent-kaurane-type diterpene (3), against HL-60 cells after 12 h of treatment were 40 microM, 1.8 microM and 5.5 microM, respectively. Although treatment with 3 induced apoptosis, DNA ladder formation was not observed after treatment with 1 or 2. Induction of necrosis, as assayed by trypan blue staining, was observed after treatment with 1 or 2. Treatment with compound 1, 2 or 3 induced proteolysis of poly(ADP-ribose) polymerase (PARP), a substrate of caspase-3, and processing of caspase-3. Activation of caspase-8 and processing of Bid, a typical substrate of caspase-8, were also observed on treatment with these compounds. Pretreatment with a broad-spectrum inhibitor of caspases attenuated apoptosis induced by 3 but not necrosis induced by 1 and 2. In summary, KD-related compounds are a unique family of diterpenes that cause either caspase-dependent apoptotic or necrotic cell death.

Antibacterial activity of ent -kaurene diterpenoids from Rabdosia rosthornii

Biological activities of ent-kaurene diterpenoids, rosthornins A-D, isolated from the ether extract of the dried leaves of Rabdosia rosthornii (Diels) Hara (Labiatae) were tested. They exhibited antibacterial activity specifically against Gram-positive bacteria, among which Propionibacterium acnes was noted to be the most susceptible.

Cytotoxic ent-kaurane diterpenoids from Isodon rubescens var. rubescens

Five new ent-kauranoids, xindongnins C - G ( 1 - 5), together with five known ones, xindongnins A and B ( 6 and 7), melissoidesin G ( 8), dawoensin A ( 9), and glabcensin V ( 10), were isolated from the leaves of Isodon rubescens var. rubescens, and structurally elucidated. Compounds 1, 4, and 6 - 10 showed inhibitory effects against human tumor K562 cells with IC (50) values ranging from 0.3 to 7.3 microg/mL. The structure of 6 was revised on the basis of its 2D-NMR spectral data.

Inhibitory effects of ent-kauranes from the stems of Annona squamosa on superoxide anion generation by human neutrophils

Eleven ent-kauranes, isolated from the fresh stems of Annona squamosa L. (Annonaceae), were subjected to assays on the generation of superoxide anion (O2.--) by human neutrophils. Except for ent-kaur-16-en-19-oic acid, 16beta,17-dihydroxy- ent-kauran-19-al, and 16alpha,17-dihydroxy -ent-kauran-19-al, all ent-kauranes showed significant inhibitory effect on O2.-- generation in response to formyl- L-methionyl- L-leucyl- L-phenylalanine (fMLP/CB). In contrast, phorbol myristate acetate (PMA)-induced O2.-- generation was not suppressed by any ent-kauranes. Especially, ent-kaur-16-en-19-oic acid could significantly increase O2.-- production. The structure-activity relationship of these compounds is also discussed herein. Furthermore, the effect of ent-kauranes on nitric oxide generation by NR8383 macrophages in response to lipopolysaccharide (LPS) was examined. None of the compounds showed an inhibitory effect on nitric oxide generation.

Kaurane-type diterpene glycoside from the stem bark of Acanthopanax trifoliatus

A new diterpene glycoside, acantrifoside D ( 1), as well as three known diterpenes (2 - 4) were isolated from the stem bark of Acanthopanax trifoliatus from Vietnam. Based on 1D and 2D NMR spectroscopic data, their chemical structures were determined to be 16alpha,17-dihydroxy- ent-kauran-19-oic acid 16- O-beta- D-glucopyranoside 19- O-beta- D-glucopyranosyl ester (1), 16alpha H,17-isovalerate- ent-kauran-19-oic acid (2), ent-kaur-16-en-19-oic acid ( 3), and ent-pimara-8(14),15-dien-19-oic acid (4). Compounds 2 - 4 had strong inhibitory effects against COX-1 in an in vitro assay, with IC50 values of 0.21, 0.15 and 0.19 mM, respectively.

A double-blind placebo-controlled study of the effectiveness and tolerability of oral stevioside in human hypertension

AIMS

Stevioside is a natural plant glycoside isolated from the plant Stevia rebaudiana which has been commercialized as a sweetener in Japan for more than 20 years. Previous animal studies have shown that stevioside has an antihypertensive effect. This study was to designed to evaluate the effect of stevioside in human hypertension.

METHODS

A multicentre, randomized, double-blind, placebo-controlled study was undertaken. This study group consisted of 106 Chinese hypertensive subjects with diastolic blood pressure between 95 and 110 mmHg and ages ranging from 28 to 75 years with 60 subjects (men 34, women 26; mean +/- s.d., 54.1+/-3.8 years) allocated to active treatment and 46 (men 19, women 27; mean +/- s.d., 53.7+/-4.1 years) to placebo treatment. Each subject was given capsules containing stevioside (250 mg) or placebo thrice daily and followed-up at monthly intervals for 1 year.

RESULTS

After 3 months, the systolic and diastolic blood pressure of the stevioside group decreased significantly (systolic: 166.0+/-9.4-152.6+/-6.8 mmHg; diastolic: 104.7 +/- 5.2-90.3+/-3.6 mmHg, P<0.05), and the effect persisted during the whole year. Blood biochemistry parameters including lipid and glucose showed no significant changes. No significant adverse effect was observed and quality of life assessment showed no deterioration.

CONCLUSIONS

This study shows that oral stevioside is a well tolerated and effective modality that may be considered as an alternative or supplementary therapy for patients with hypertension.