Luminescent Cu4I4-Cu3(Pyrazolate)3 Coordination Frameworks: Postsynthetic Ligand Substitution Leads to Network Displacement and Entanglement.

Six daughter complexes based on two-dimensional (2-D) luminescent Cu4I4-Cu3Pz3 (Pz = pyrazolate) coordination networks, which exhibit an uncommon Cu4I4L3L' (L = pyridine; L' = acetonitrile, pyridine, pyrazine, 1,4-diazabicyclo[2.2.2]octane, triphenylphosphine, none) local configuration, were prepared through a postsynthetic modification method starting from a parent complex (L' = NH3). This work has successfully implemented the single-site substitution of Cu4I4-based coordination frameworks, which have rarely been reported for isolated Cu4I4-type compounds, by taking advantage of the solvent-assisted ligand substitution strategy recently developed in metal-organic framework (MOF) chemistry. Such a procedure not only resulted in the variation of local geometry in the Cu4I4 units but also led to interlayer network displacement and entanglement. Particularly, an interesting topological transformation (from 2-D to 2-D → 3-D interpenetration) occurred when linear bidentate linkers (e.g., pyrazine and 1,4-diazabicyclo[2.2.2]octane) are inserted between the 2-D layers. Moreover, the variation in the L' sites can effectively tune the emission colors, ranging from green to orange (λemmax 540-605 nm at room temperature). The photoluminescence origins are tentatively assigned to be a mixture of 3MLCT and 3XLCT, different from that of the well-studied isolated Cu4I4-type complexes.

[Study on directional separation of picroside II from extract of traditional Chinese medicine by molecularly imprinted technology].

Picroside II, separated from Chinese herbal medicine, is an active compound with neroprotective activity. Molecularly imprinted polymers (MIPs) have high affinity toward template molecules synthesized by molecularly imprinted technology for its specific combined sites, which can overcome the shortcomings of traditional separation methods, such as complex operation and low efficiency. In this paper, MIPs were prepared by precipitation polymerization with picroside II as the template molecule, 1-vinylimidazole (1-Vinyl) as functional monomer, ethylene glycol dimethacrylate (EDMA) as cross-linker. The morphology of MIPs was characterized by scanning electronmicroscope (SEM) and its static adsorption capacity was measured by the scatchard equation. The results showed that picroside II MIPs have spherical shape, and most of them are uniform in size. Furthermore, the maximum binding capacity (Q(max)) of MIPs is 3.02 mg x g(-1), higher than that of non-imprinted polymers (NIPs). This result indicated that picroside II MIPs with good morphology and high targeted affinity toward the template molecules can be prepared by precipitation polymerization, which can be used to separate picroside II and its analogies from extract of Chinese herbal medicine. In addition, this method has the advantages of good environment and simple operation, which might offer a novel method for the efficient separation of picroside II in the traditional herbal medicines.

Activation of AMP-activated protein kinase by temozolomide contributes to apoptosis in glioblastoma cells via p53 activation and mTORC1 inhibition.

Methylating drugs such as temozolomide (TMZ) are widely used in the treatment of brain tumors including malignant glioblastoma. The mechanism of TMZ-induced glioblastoma cell death and apoptosis, however, is not fully understood. Here, we tested the potential involvement of AMP-activated protein kinase (AMPK) in this process. We found that methylating agents TMZ and N-methyl-N'-nitro-N-nitrosoguanidine induce AMPK activation in primary cultured human glioblastoma and glioblastoma cell lines. TMZ-induced O(6)-methylguanine production is involved in AMPK activation. O(6)-benzylguanine, an O(6)-methylguanine-DNA methyltransferase inhibitor, enhances TMZ-induced O(6)-methylguanine production, leading to enhanced reactive oxygen species production, which serves as an upstream signal for AMPK activation. Activation of AMPK is involved in TMZ-induced glioblastoma cell death and apoptosis. AMPK inhibitor (Compound C) or AMPKα siRNA knockdown inhibits TMZ-induced glioblastoma cell death and apoptosis, whereas AMPK activator 5-aminoimidazole-4-carboxamide-1-ß-d-ribofuranoside enhances it. In further studies, we found that activation of AMPK is involved in TMZ-induced p53 activation and subsequent p21, Noxa, and Bax up-regulation. Activation of AMPK by TMZ also inhibits mTOR complex 1 (mTORC1) signaling and promotes anti-apoptosis protein Bcl-2 down-regulation, which together mediate TMZ-induced pro-cell apoptosis effects. Our study suggests that activation of AMPK by TMZ contributes to glioblastoma cell apoptosis, probably by promoting p53 activation and inhibiting mTORC1 signaling.

High-frequency genetic contents variations in clinical Candida albicans isolates.

Genome plasticity is a hallmark of Candida albicans and is believed to be an adaptation strategy. But the extent of such genomic variability is not well investigated. In this study, genetic contents of clinical C. albicans isolates were investigated at whole-genome level with array-based comparative genomic hybridization (array CGH) technology. It was revealed that C. albicans possessed variations of genetic contents, as well as aneuploidy. The variable genes were scattered across the chromosomes, as well clustered in particular regions, including sub-telomeric regions, retrotransposon-insertion sites and a variable region on chromosome 6.

Design, synthesis, and biological evaluation of 1,5-diaryl-1,2,4-triazole derivatives as selective cyclooxygenase-2 inhibitors.

A series of 1,5-diaryl-1,2,4-triazole derivatives were synthesized and evaluated as cyclooxygenase-2 (COX-2) inhibitors. The results of the preliminary biological assays in vivo showed that eight compounds 5b, 6b, 6c, 7c, 8b, 8d, 9c, and 9d have potent anti-inflammatory activity (P < 0.01), while compounds 6b, 6c, and 9c exhibit marked potency. Compound 6c was then selected for further investigation. In the COX inhibition assay in vitro, compound 6c was identified as a potent and selective inhibitor of COX-2 (COX-2 IC(50) = 0.37 µM; SI = 0.018), being equipotent to celecoxib (COX-2 IC(50) = 0.26 µM; SI = 0.015). In a rat carrageenan-induced paw edema assay, 6c exhibited moderate anti-inflammatory activity (35% inhibition of inflammation) at 2 h after administration of 15 mg/kg as an oral dose. A docking study also revealed that compound 6c binds in the active site of COX-2 in a similar mode to that of the known selective COX-2 inhibitor SC-558.

Design, synthesis and biological evaluation of novel substituted benzoylguanidine derivatives as potent Na+/H+ exchanger inhibitors.

A novel series of substituted benzoylguanidine derivatives were designed and synthesized as potent NHE1 inhibitors. Most compounds can significantly inhibit NHE1-mediated platelet swelling in a concentration-dependent manner, among which compound 5f (IC(50)=3.60 nM) and 5l (IC(50)=4.48 nM) are 18 and 14 times respectively more potent than cariporide (IC(50)=65.0 nM). Furthermore, when tested in vivo and in vitro, compound 5f showed superior cardioprotective effects against SD rat myocardial ischemic-reperfusion injury over cariporide, representing a promising lead compound for further exploration.

Synthesis and biological activities of 2,4-diaminopteridine derivatives.

Substituted 2,4-diaminopteridine derivatives 10a-10l were prepared in moderate to good yield. Their structures were confirmed by 1H-NMR and MS spectroscopy, as well as by elemental analysis. Their inhibitory properties against inducible nitric oxide synthase (iNOS) were evaluated in vitro. Biological tests indicated that compound 10a, 10d, 10e, 10h, 10i, and 10l showed potent inhibitory activities similar to that of methotrexate (MTX), while the activities of compound 10b, 10c, 10f, 10g, 10j, and 10k are stronger than MTX. Two compounds, i. e., 10b (IC(50 )= 18.85 microM) and 10i (IC(50) = 24.08 microM) were further studied for their effect on septic shock in rats and immunologically liver injured mice (in vivo). The results demonstrated that 10b and 10i had the capacity to increase the blood pressure in septic shock and showed notable protective activities on immunological hepatic injury.

Chiral separation of racemate CPU86017, an anti-arrhythmic agent, produces stereoisomers possessing favourable ion channel blockade and less alpha-adrenoceptor antagonism.

1. CPU86017 is an effective anti-arrhythmic agent of the Class III complex that has two chiral centres, 7N and 13aC. As a promising anti-arrhythmic agent, the blockade on I(Kr), I(Ks) and calcium influx may be modulated to be mild, moderate and potent, with less a-adrenoceptor blockade. In order to improve activity at ion channels, four stereoisomers, namely SS ((+)-7S,13aS-CPU86017), SR ((-)-7S,13aR-CPU86017), RR ((-)-7R,13aR-CPU86017) and RS ((+)-7R,13aS-CPU86017), have been separated. In the present study, the effects of these four isomers on I(Kr) and I(Ks), calcium channels and a-adrenoceptors were compared with the effects of the racemate CPU86017. 2. In the present study, I(Kr) and I(Ks) were measured as tail currents (I(Kr.tail) and I(Ks.tail), respectively) using the whole-cell patch-clamp technique. Antagonism of receptor-operated calcium channels and voltage-dependent calcium channels (VDC) in vascular smooth muscle by CPU86017 and the four isomers were tested as suppression of phenylephrine- or KCl-induced contractions of aortic rings, respectively. 3. For I(Kr.tail) inhibition, the IC(50) of SS, SR, RR, RS and CPU86017 was 2.86 +/- 1.20, 39.4 +/- 8.5, 3.48 +/- 0.80, 7.65 +/- 1.50 and 12.5 +/- 7.8 x 10(-9) mol/L, respectively; for I(Ks.tail) inhibition IC(50) values were 16.9 +/- 4.0, 20.0 +/- 2.1, 99.1 +/- 5.9, 160 +/- 81 and 65.0 +/- 4.7 x 10(-9) mol/L, respectively. The SR isomer showed balanced blockade of I(Kr) and I(Ks) that was associated with a loss of a-adrenoceptor antagonism but enhanced VDC blockade. 4. Configuration of 13aC critically determines I(Kr) blockade and the Ca(2+) antagonism of the isomers of CPU86017. The SR isomer exhibits mild blockade of I(Kr), moderately enhanced blockade of I(Ks) and Ca(2+) influx and less a-adrenoceptor antagonism compared with the racemate and may be promising as an anti-arrhythmic.

Effects of strontium fructose 1,6-diphosphate on expression of apoptosis-related genes and oxidative stress in testes of diabetic rats.

OBJECTIVE: To investigate the effects of strontium fructose 1,6-diphosphate (FDP-Sr) on testicular dysfunction induced by diabetes. METHODS: Diabetes was induced by a single injection of streptozotocin (65 mg/kg, i.p.). After 28 days, therapy with three doses (50, 100, and 200 mg/kg per day, p.o.) of FDP-Sr was carried out for another 4 weeks. RESULTS: The rats exhibited morphological lesions of testes and significant decreases in serum testosterone levels after 2 months of diabetes. Testicular tissues of diabetic rats showed significantly increased malondialdehyde levels and declined glutathione peroxidase activity. Meanwhile, augmented DNA fragmentation was observed, along with downregulated Bcl-2 and upregulated Bax expressions at both mRNA and protein levels. FDP-Sr showed significant antioxidant effects in both in vitro and in vivo experiments, and significantly relieved apoptosis and the decline of serum testosterone caused by diabetes. CONCLUSIONS: Testicular injury and apoptosis induced by diabetes are partially attributed to the augmented oxidative stress in testicular tissue. FDP-Sr indirectly alleviates these pathologic alterations by suppressing the generation of reactive oxygen species.

Alleviating effects of active fraction of Euonymus alatus abundant in flavonoids on diabetic mice.

Euonymus alatus (E. alatus) has been used as a folk medicine for diabetes in China for more than one thousand years. In order to identify major active components, effects of different fractions of E. alatus on the plasma glucose levels were investigated in normal mice and alloxan-induced diabetic mice. Our results show that ethyl acetate fraction (EtOAc Fr.) displayed significant effects on reducing plasma glucose. In oral glucose tolerance, EtOAc Fr. at 17.2 mg/kg could significantly decrease the blood glucose of both normal mice and diabetic mice. After 4 weeks administration of the EtOAc Fr, when compared with the diabetic control, there were significant difference in biochemical parameters, such as glycosylated serum protein, superoxide dismutase and malondial dehyde, triglyceride, and total cholesterol, between alloxan-induced diabetic mice and the control group. Additional histopathological studies of pancreatic islets also showed EtOAc Fr. has beneficial effects on diabetic mice. Chemical analysis with three-dimensional HPLC demonstrated that the major components from EtOAc Fr were flavonoids and phenolic acids, which had anti-oxidative effects on scavenging DPPH-radical in vitro. All these experimental results suggest that EtOAc Fr. is an active fraction of E. alatus and can prevent the progress of diabetes. The mechanism of E. alatus for glucose control may be by stimulating insulin release, improving glucose uptake and improving oxidative-stress.

Survival Comparisons Between Early Male and Female Breast Cancer Patients.

We aimed to compare the overall survival (OS) and standardized mortality rate (SMR) of the male breast cancer (MBC) with female breast cancer (FBC) after propensity score matching. Based on the Surveillance, Epidemiology, and End Results (SEER), the early breast cancer patients (T1-2N0-2M0) were extracted from 1998-2007. This study included 1,111 and 2,151 patients with early MBC and FBC, respectively, whose clinicopathological characteristics were well balanced. At a mean follow-up time of 97 months, 10-year OS rate was 58.3% in the MBC group and 68.7% in the FBC (log-rank test, P < 0.001; hazard ratio (HR) = 1.45, 95% confidence interval (CI) = 1.29 to 1.64). Adjusted HR for OS between MBC and FBC were revealed from propensity score matched-multivariable Cox proportional hazards models (HR = 1.53, 95% CI = 1.35 to 1.73). Similar adjusted SMRs between MBC and FBC ((SMR = 1.98, 95% CI = 1.83,2.14) for FBC and (SMR = 2.07, 95% CI = 1.88-2.28) for MBC) were observed. The nomogram was constructed for FBC, and predicted probabilities were generally good (C-index = 0.71), whose area under curve is higher than TNM stage classification (0.74 vs 0.62). OS was significantly decreased among early MBC patients compared with FBC, but similar SMRs and its trends by age groups were observed between MBC and FBC except for young patients.

Recombinant human ciliary neurotrophic factor reduces weight partly by regulating nuclear respiratory factor 1 and mitochondrial transcription factor A.

Ciliary neurotrophic factor (CNTF) can lead to weight loss by up-regulating energy metabolism and the expression of UCP-1 in mitochondria. To investigate the up-stream regulators of the expression of UCP-1, recombinant human CNTF (rhCNTF) (0.1, 0.3, 0.9 mg/kg/day s.c.) administered to KK-Ay mice for 30 days resulting in reductions in body weight and perirenal fat mass. In brown adipose tissues, the gene expressions of nuclear respiratory factor (NRF)-1, mitochondrial transcription factor A (TFam) and uncoupling protein (UCP)-1 were found up-regulated by rhCNTF. To the best of our knowledge, these effects represent new insights on the mechanisms of action of weight loss by rhCNTF. In addition, we also found that rhCNTF increased the activity of mitochondrial complex IV. The stimulation of NRF-1, TFam, UCP-1 and the enhanced activity of mitochondrial complex IV may be associated with remedying obesity. The result indicates that rhCNTF can enhance the expressions of NRF-1 and TFam, both of which can up-regulate the expression of UCP-1.

The novel mechanism of recombinant human ciliary neurotrophic factor on the anti-diabetes activity.

In a previous study, the ciliary neurotrophic factor (CNTF) were demonstrated to lead to weight-loss partly by up-regulating the energy metabolism and the expression of uncoupling protein-1, mitochondrial transcription factor A and nuclear respiratory factor-1 in adipose tissues or muscle. To investigate the up-stream regulators of the expression, recombinant human CNTF (rhCNTF) (0.1, 0.3 and 0.9 mg/kg/day subcutaneously) were administered to KK-Ay mice for 30 days, resulting in reduction of perirenal fat mass, serum free fatty acids and islet triacylglycerol; furthermore, the values of oral glucose tolerance test were found improved. In brown adipose tissues, the gene expressions of peroxisome proliferator-activated receptor alpha (PPARalpha) and peroxisome proliferator-activated receptor coactivator-1 alpha (PGC-1alpha) were found to be up-regulated by rhCNTF. To the best of our knowledge, the changes of gene expression of PPARalpha and PGC-1alpha represent new insights into the mechanisms of anti-diabetes by rhCNTF. In addition, the activity of mitochondrial complexII was found to be increased by rhCNTF. Stimulation of PPARalpha, PGC-1alpha, uncoupling protein-1 and enhanced activity of mitochondrial complex II may be associated with the effects of anti-diabetes. The present study indicates new mechanisms of the activity and mechanisms on anti-diabetes of rhCNTF, which may be a novel anti-diabetes reagent partly acting by enhancing energy metabolism.

Effect of solanine on the membrane potential of mitochondria in HepG2 cells and [Ca2+]i in the cells.

AIM: To observe the effect of solanine on the membrane potential of mitochondria in HepG(2) cells and [Ca(2+)](i) in the cells, and to uncover the mechanism by which solanine induces apoptosis. METHODS: HepG(2) cells were double stained with AO/EB, and morphological changes of the cells were observed using laser confocal scanning microscopy (LCSM). HepG(2) cells were stained with TMRE, and change in the membrane potential of mitochondria in the cells were observed using LCSM. HepG(2) cells were double stained with Fluo-3/AM, and change of [Ca(2+)](i) in the cells were observed using LCSM. HepG(2) cells were double stained with TMRE and Fluo-3/AM, and both the change in membrane potential of mitochondria and that of [Ca(2+)](i) in the cells were observed using LCSM. RESULTS: Cells in treated groups showed typical signs of apoptosis. Staining with TMRE showed that solanine could lower membrane potential; staining with Fluo-3/AM showed that solanine could increase the concentration of Ca(2+) in tumor cells; and those of double staining with TMRE and Fluo-3/AM showed that solanine could increase the concentration of Ca(2+) in the cells at the same time as it lowered the membrane potential of mitochondria. CONCLUSION: Solanine opens up the PT channels in the membrane by lowering the membrane po-tential, leading to Ca(2+) being transported down its concentration gradient, which in turn leads to the rise of the concentration of Ca(2+) in the cell, turning on the mechanism for apoptosis.

Anti-asthma effects of synthetic salidroside through regulation of Th1/Th2 balance.

AIM: The aim of the study was to investigate the effect and mechanism of action of synthetic salidroside in an ovalbumin (OVA)-induced asthma model in mice. METHOD: BALB/c mice were sensitized with an intraperitoneal injection of ovalbumin (OVA) to induce a mouse model of asthma in paracmasis. The mice were treated with dexamethasone as the positive control. At the end of the study, respiratory reactivity was detected, the numbers of various kinds of white blood cells in the bronchoalveolar lavage fluid (BALF) were counted, and the levels of IL-4 and INF-γ in BALF were determined. Quantitative PCR was used to detect the mRNA contents of IL-4 and INF-γ in lung tissue. Histologic examination was performed to observe inflammatory cellular infiltration. RESULTS: Salidroside treatment virtually eliminated airway hyper-reactivity, markedly reduced the eosinophil percent, obviously reduced the levels of IL-4 and raised INF-γ in the bronchoalveolar lavage fluid (BALF) compared with the sham-treated group. Quantitative PCR on the mRNA content of IL-4 and INF-γ provided confirmation. Lung histologic observations showed that salidroside reduced inflammation and edema. These effects were equivalent to the effects of dexamethasone. CONCLUSION: Synthetic salidroside exhibits an anti-asthma effect which is related to the regulation of Th1/Th2 balance. This provides a new possibility for treatment of allergic asthma.

Synthesis and Na+/H+ exchanger inhibitory activity of benzoylguanidine derivatives.

Twenty-two compounds of substituted benzoylguanidine derivatives were designed and synthesized as potent NHE1 inhibitors. Twelve compounds showed more potent NHE1 inhibitory activity than cariporide. The activities of compounds 7e, 7h and 7j (IC(50) = 0.073 ± 0.021, 0.084 ± 0.012 and 0.068 ± 0.021 nmol/L, respectively) were two orders of magnitude higher than that of cariporide (30.7 ± 2.5 nmol/L). Myocardial cells in vitro screening showed 7j had highlighted protective effect on cardiomyocytes subjected to hypoxia/reoxygenation. Thus it is valuable for further investigation.

[Characteristic analysis of the adsorption/desorption of nitrogen and phosphorus in the sediments of Taihu Lake].

The adsorption isotherms curves of 90 simples were studied in Taihu Lake through the experiment of adsorption/desorption. And the relation between the equilibrium concentrations, NAP, adsorption efficiency and corresponding parameter in interstitial water and sediment has been analyzed, in order to analyze the "source" and "collection" of Taihu. The results showed that the isotherms curves of nitrogen and phosphorus in the sediment had significant correlations in the range of the concentrations of experiment. The average equilibrium concentrations of nitrogen and phosphorus are 1.10 mg/L and 0.11 mg/L respectively. The average of NAP of nitrogen and phosphorus are 23.55 mg/kg and 11.72 mg/kg respectively. The NAP of nitrogen and phosphorus are higher in the area of serious pollution. The average adsorption efficiency of nitrogen and phosphorus are 23.14 L/kg and 102.09 L/kg respectively. Significant correlations were found between the equilibrium concentrations of adsorption/desorption of nitrogen and phosphous and corresponding parameter in interstitial water or sediment. Overall the sediment is the "source" of the nitrogen and phosphorus.

Apoptosis induction of ZBB-006, a novel synthetic diterpenoid, in the human hepatocellular carcinoma cell line HepG2 in vitro and in vivo.

Diterpenes, present in many medicinal plants, have been the focus of continuous studies for the development of new anticancer agents. ZBB-006 is a new synthetic diterpenoid derivative which exhibited significant anti-proliferation activity against various cancer cell lines in our previous study. Here, we investigated the antitumor effect of ZBB-006 and its potential mechanisms in the human hepatocellular carcinoma cell line HepG2, both in vitro and in vivo. We found that oral administration of ZBB-006 effectively suppressed the growth of HepG2 xenograft tumor in nude mice without body weight decline as compared with the control group. Meanwhile, the growth inhibitory effect of ZBB-006 on HepG2 cells was observed with MTT assay. Apoptosis induced by ZBB-006 in HepG2 cells was evidenced by DAPI staining and Annexin V/PI double staining assay. ZBB-006 also dissipated the mitochondrial membrane potential (ΔΨm) apparently as revealed by JC-1 staining. Furthermore, the cleavage of PARP, activation of caspase-3 and caspase-9 but not caspase-8 was demonstrated by western blot assay both in vitro and in vivo. Additionally, the proapoptotic protein Bax was markedly elevated, while the antiapoptotic protein Bcl-2 was downregulated. Collectively, our data indicated that ZBB-006 exerted a strong antitumor effect on HepG2 cells by initiating the mitochondrial-dependent apoptosis, and it has potential to be explored as a new promising therapeutic agent against human hepatoma.

Reinioside C, a triterpene saponin of Polygala aureocauda Dunn, exerts hypolipidemic effect on hyperlipidemic mice.

Reinioside C is a triterpene saponin from the the root of Polygala aureocauda Dunn (PAD). This study examined the effects of reinioside C on hyperlipidemic mice in vivo and endothelium cells, macrophages and smooth muscle cells in vitro. Mice were given a hyperlipidemic diet for 30 days, then administered reinioside C (4, 8, 16 mg/kg/day, p.o.) for 30 days. Then the serum lipid, superoxide dismutase (SOD), malonaldehyde (MDA), the total cholesterol (TC) and triglyceride (TG) in the liver extract were measured. Human umbilical vein endothelial (HUVECs), peritoneal macrophages and smooth muscle cells (SMCs) pre-treated with reinioside C were treated with oxidized low-density lipoprotein (OxLDL). The results showed that reinioside C decreased serum and liver tissue lipid profiles in hyperlipidemic mice. Moreover, reinioside C protected the HUVECs against the Ox-LDL induced LDH leakage and exerted a protective effect on oxidative lesions induced by OxLDL, inhibited cholesteryl ester accumulation in macrophages, and decreased [Ca2+](i) and SMC proliferation in vitro. Based on these results, it is suggested that reinioside C is a promising hypolipidemic candidate.

Synthesis and biological activity of 2-alkylbenzimidazoles bearing a N-phenylpyrrole moiety as novel angiotensin II AT1 receptor antagonists.

A series of 2-alkylbenzimidazoles bearing a N-phenylpyrrole moiety were synthesized and evaluated as a novel class of AT(1) receptor antagonists. Among them, compounds 10a and 10g inhibited [(125)I] AngII-binding affinity to AT(1) receptor at nanomolar level and potently inhibited the Ang II-induced pressor response by oral administration. Moreover, evaluation in spontaneously hypertensive rats showed that 10a is an orally active AT(1) receptor antagonist.