In Situ Single-Crystal Diffraction Studies of the Structural Transition of Metal-Organic Framework Copper 5-Sulfoisophthalate, Cu-SIP-3

The flexibility of the metal-organic framework Cu-2(OH)(C8H3O7S)(H2O)center dot 2H(2)O (Cu-SIP-3) toward reversible single-crystal to single-crystal transformations is demonstrated using in situ diffraction methods at variable temperature. At temperatures below a dehydration-induced phase transition (T < 370 K) the structure is confirmed as being hydrated. In the temperature range where the transition takes place (370 K < T < 405 K) no discrete, sharp Bragg peaks can be seen in the single-crystal X-ray diffraction pattern, indicating significant loss of long-range order. At temperatures higher than 405 K, the Bragg peaks return and the structure can be refined as dehydrated Cu-SIP-3. The loss of guest water molecules can be followed at temperatures below the phase transition giving insight into the mechanism of the dehydration. Addition of nitric oxide gas to the material above the gating opening pressure of 275 mbar also leads to loss of Bragg scattering in the diffraction pattern.

Chemically blockable transformation and ultraselective low-pressure gas adsorption in a non-porous metal organic framework

Metal organic frameworks (MOFs) are among the most exciting materials discovered recently, attracting particular attention for their gas-adsorption and -storage properties. Certain MOFs show considerable structural flexibility in response to various stimuli. Although there are several examples of 'breathing' MOFs, in which structural changes occur without any bond breaking, examples of transformations in which several bonds are broken and made are much rarer. In this paper we demonstrate how a flexible MOF, Cu-2(OH)(C8H3O7S)(H2O)center dot 2H(2)O, can be synthesized by careful choice of the organic linker ligand. The flexibility can be controlled by addition of a supplementary coordinating molecule, which increases the thermal stability of the solid sufficiently for direct imaging with electron microscopy to be possible. We also demonstrate that the MOF shows unprecedented low-pressure selectivity towards nitric oxide through a coordination-driven gating mechanism. The chemical control over these behaviours offers new possibilities for the synthesis of MOFs with unusual and potentially exploitable properties.

Exceptional Behavior over the Whole Adsorption-Storage-Delivery Cycle for NO in Porous Metal Organic Frameworks

Two porous metal organic frameworks (MOFs), [M-2(C8H2O6)(H2O)(2)] center dot 8H(2)O (M = Co, Ni), perform exceptionally well for the adsorption, storage, and water-triggered delivery of the biologically important gas nitric oxide. Adsorption and powder X-ray diffraction studies indicate that each coordinatively unsaturated metal atom in the structure coordinates to one NO molecule. All of the stored gas is available for delivery even after the material has been stored for several months. The combination of extremely high adsorption capacity (similar to 7 mmol of NO/g of MOF) and good storage stability is ideal for the preparation of NO storage solids. However, most important is that the entire reservoir of stored gas is recoverable on contact with a simple trigger (moisture). The activity of the NO storage materials is proved in myography experiments showing that the NO-releasing MOFs cause relaxation of porcine arterial tissue.

NO-releasing zeolites and their antithrombotic properties

Transition metal-exchanged zeolite-A adsorbs and stores nitric oxide in relatively high capacity (up to 1 mmol of NO/g of zeolite). The stored NO is released on contact with an aqueous environment under biologically relevant conditions of temperature and pH. The release of the NO can be tuned by altering the chemical composition of the zeolite, by controlling the amount of water contacting the zeolite, and by blending the zeolite with different polymers. The high capacity of zeolite for NO makes it extremely attractive for use in biological and medical applications, and our experiments indicate that the NO released from Co-exchanged zeolite-A inhibits platelet aggregation and adhesion of human platelets in vitro.

Metal organic frameworks as NO delivery materials for biological applications

Metal organic frameworks (MOFs) are highly porous materials that can store significant amounts of gas, including nitric oxide. The chemical composition and toxicology of many (but not all) of these materials makes them potentially suitable for medical applications. In this paper, we will describe how triggered release methods can be used to deliver biologically relevant amounts of NO and then show how Ni, Co and Cu-containing MOFs are biologically active materials with potential applications in several different areas (anti-thrombosis, dermatology and wound healing, anti-bacterial, vasodilation etc.). We will also discuss the pros and cons of MOFs, including their chemical and biological stability and the toxicology of MOFs in general. (C) 2009 Elsevier Inc. All rights reserved.

Simultaneous Gas Storage and Catalytic Gas Production Using Zeolites-A New Concept for Extending Lifetime Gas Delivery

Copper containing MCM-41 materials can be used to both store gaseous nitric oxide and to catalytically produce nitric oxide from nitrite. The active species for the reaction is copper (I). Addition of cysteine to the solution in contact with the material has different effects depending on how much Cu(I) is present. This is a new method of extending the lifetime of gas delivery from a gas storage material.

Simultaneous and cooperative gas storage and gas production using bifunctional zeolites

Nitric oxide can be stored in and produced from zeolites in a simultaneous and cooperative process

Activation of the ACE2/Angiotensin-(1-7)/Mas Receptor Axis Enhances the Reparative Function of Dysfunctional Diabetic Endothelial Progenitors

We tested the hypothesis that activation of the protective arm of the renin angiotensin system, the angiotensin-converting enzyme 2 (ACE2)/angiotensin-(1-7) [Ang-(1-7)]/Mas receptor axis, corrects the vasoreparative dysfunction typically seen in the CD34(+) cells isolated from diabetic individuals. Peripheral blood CD34(+) cells from patients with diabetes were compared with those of nondiabetic controls. Ang-(1-7) restored impaired migration and nitric oxide bioavailability/cGMP in response to stromal cell-derived factor and resulted in a decrease in NADPH oxidase activity. The survival and proliferation of CD34(+) cells from diabetic individuals were enhanced by Ang-(1-7) in a Mas/phosphatidylinositol 3-kinase (PI3K)/Akt-dependent manner. ACE2 expression was lower, and ACE2 activators xanthenone and diminazine aceturate were less effective in inducing the migration in cells from patients with diabetes compared with controls. Ang-(1-7) overexpression by lentiviral gene modification restored both the in vitro vasoreparative functions of diabetic cells and the in vivo homing efficiency to areas of ischemia. A cohort of patients who remained free of microvascular complications despite having a history of longstanding inadequate glycemic control had higher expression of ACE2/Mas mRNA than patients with diabetes with microvascular complications matched for age, sex, and glycemic control. Thus, ACE2/Ang-(1-7)\Mas pathway activation corrects existing diabetes-induced CD34(+) cell dysfunction and also confers protection from development of this dysfunction.

The complex effects of the slow-releasing hydrogen sulfide donor GYY4137 in a model of acute joint inflammation and in human cartilage cells

The role of hydrogen sulfide (H2 S) in inflammation remains unclear with both pro- and anti-inflammatory actions of this gas described. We have now assessed the effect of GYY4137 (a slow-releasing H2 S donor) on lipopolysaccharide (LPS)-evoked release of inflammatory mediators from human synoviocytes (HFLS) and articular chondrocytes (HAC) in vitro. We have also examined the effect of GYY4137 in a complete Freund's adjuvant (CFA) model of acute joint inflammation in the mouse. GYY4137 (0.1-0.5 mM) decreased LPS-induced production of nitrite (NO2 (-) ), PGE2 , TNF-a and IL-6 from HFLS and HAC, reduced the levels and catalytic activity of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) and reduced LPS-induced NF-?B activation in vitro. Using recombinant human enzymes, GYY4137 inhibited the activity of COX-2, iNOS and TNF-a converting enzyme (TACE). In the CFA-treated mouse, GYY4137 (50 mg/kg, i.p.) injected 1 hr prior to CFA increased knee joint swelling while an anti-inflammatory effect, as demonstrated by reduced synovial fluid myeloperoxidase (MPO) and N-acetyl-ß-D-glucosaminidase (NAG) activity and decreased TNF-a, IL-1ß, IL-6 and IL-8 concentration, was apparent when GYY4137 was injected 6 hrs after CFA. GYY4137 was also anti-inflammatory when given 18 hrs after CFA. Thus, although GYY4137 consistently reduced the generation of pro-inflammatory mediators from human joint cells in vitro, its effect on acute joint inflammation in vivo depended on the timing of administration.

Strawberries, Blueberries, and Cranberries in the Metabolic Syndrome:Clinical Perspectives

Emerging science supports therapeutic roles of strawberries, blueberries, and cranberries in metabolic syndrome, a prediabetic state characterized by several cardiovascular risk factors. Interventional studies reported by our group and others have demonstrated the following effects: strawberries lowering total and LDL-cholesterol, but not triglycerides, and decreasing surrogate biomarkers of atherosclerosis (malondialdehyde and adhesion molecules); blueberries lowering systolic and diastolic blood pressure and lipid oxidation and improving insulin resistance; and low-calorie cranberry juice selectively decreasing biomarkers of lipid oxidation (oxidized LDL) and inflammation (adhesion molecules) in metabolic syndrome. Mechanistic studies further explain these observations as up-regulation of endothelial nitric oxide synthase activity, reduction in renal oxidative damage, and inhibition of the activity of carbohydrate digestive enzymes or angiotensin-converting enzyme by these berries. These findings need confirmation in future studies with a focus on the effects of strawberry, blueberry, or cranberry intervention in clinical biomarkers and molecular mechanisms underlying the metabolic syndrome.

Tyrosine nitration of prostacyclin synthase is associated with enhanced retinal cell apoptosis in diabetes

The risk of diabetic retinopathy is associated with the presence of both oxidative stress and toxic eicosanoids. Whether oxidative stress actually causes diabetic retinopathy via the generation of toxic eicosanoids, however, remains unknown. The aim of the present study was to determine whether tyrosine nitration of prostacyclin synthase (PGIS) contributes to retinal cell death in vitro and in vivo. Exposure of human retinal pericytes to heavily oxidized and glycated LDL (HOG-LDL), but not native forms of LDL (N-LDL), for 24 hours significantly increased pericyte apoptosis, accompanied by increased tyrosine nitration of PGIS and decreased PGIS activity. Inhibition of the thromboxane receptor or cyclooxygenase-2 dramatically attenuated HOG-LDL-induced apoptosis without restoring PGIS activity. Administration of superoxide dismutase (to scavenge superoxide anions) or L-N(G)-nitroarginine methyl ester (L-NAME, a nonselective nitric oxide synthase inhibitor) restored PGIS activity and attenuated pericyte apoptosis. In Akita mouse retinas, diabetes increased intraretinal levels of oxidized LDL and glycated LDL, induced PGIS nitration, enhanced apoptotic cell death, and impaired blood-retinal barrier function. Chronic administration of tempol, a superoxide scavenger, reduced intraretinal oxidized LDL and glycated LDL levels, PGIS nitration, and retina cell apoptosis, thereby preserving the integrity of blood-retinal barriers. In conclusion, oxidized LDL-mediated PGIS nitration and associated thromboxane receptor stimulation might be important in the initiation and progression of diabetic retinopathy.

Berries:emerging impact on cardiovascular health

Berries are a good source of polyphenols, especially anthocyanins, micronutrients, and fiber. In epidemiological and clinical studies, these constituents have been associated with improved cardiovascular risk profiles. Human intervention studies using chokeberries, cranberries, blueberries, and strawberries (either fresh, or as juice, or freeze-dried), or purified anthocyanin extracts have demonstrated significant improvements in LDL oxidation, lipid peroxidation, total plasma antioxidant capacity, dyslipidemia, and glucose metabolism. Benefits were seen in healthy subjects and in those with existing metabolic risk factors. Underlying mechanisms for these beneficial effects are believed to include upregulation of endothelial nitric oxide synthase, decreased activities of carbohydrate digestive enzymes, decreased oxidative stress, and inhibition of inflammatory gene expression and foam cell formation. Though limited, these data support the recommendation of berries as an essential fruit group in a heart-healthy diet.

Pigment epithelium-derived factor mitigates inflammation and oxidative stress in retinal pericytes exposed to oxidized low-density lipoprotein

Oxidized and/or glycated low-density lipoprotein (LDL) may mediate capillary injury in diabetic retinopathy. The mechanisms may involve pro-inflammatory and pro-oxidant effects on retinal capillary pericytes. In this study, these effects, and the protective effects of pigment epithelium-derived factor (PEDF), were defined in a primary human pericyte model. Human retinal pericytes were exposed to 100 microg/ml native LDL (N-LDL) or heavily oxidized glycated LDL (HOG-LDL) with or without PEDF at 10-160 nM for 24 h. To assess pro-inflammatory effects, monocyte chemoattractant protein-1 (MCP-1) secretion was measured by ELISA, and nuclear factor-kappaB (NF-kappaB) activation was detected by immunocytochemistry. Oxidative stress was determined by measuring intracellular reactive oxygen species (ROS), peroxynitrite (ONOO(-)) formation, inducible nitric oxide synthase (iNOS) expression, and nitric oxide (NO) production. The results showed that MCP-1 was significantly increased by HOG-LDL, and the effect was attenuated by PEDF in a dose-dependent manner. PEDF also attenuated the HOG-LDL-induced NF-kappaB activation, suggesting that the inhibitory effect of PEDF on MCP-1 was at least partially through the blockade of NF-kappaB activation. Further studies demonstrated that HOG-LDL, but not N-LDL, significantly increased ONOO(-) formation, NO production, and iNOS expression. These changes were also alleviated by PEDF. Moreover, PEDF significantly ameliorated HOG-LDL-induced ROS generation through up-regulation of superoxide dismutase 1 expression. Taken together, these results demonstrate pro-inflammatory and pro-oxidant effects of HOG-LDL on retinal pericytes, which were effectively ameliorated by PEDF. Suppressing MCP-1 production and thus inhibiting macrophage recruitment may represent a new mechanism for the salutary effect of PEDF in diabetic retinopathy and warrants more studies in future.

Susceptibility of streptozotocin-induced diabetic rat retinal function and ocular blood flow to acute intraocular pressure challenge.

PURPOSE: To consider whether STZ-induced hyperglycemia renders rat retinal function and ocular blood flow more susceptible to acute intraocular pressure (IOP) challenge.

METHODS: Retinal function (electroretinogram, ERG) was measured during acute IOP challenge (10-100 mmHg, 5 mmHg increments, 3 min/step, vitreal cannulation) in adult Long-Evans rats (6-week old, citrate: n=6, STZ: n=10) 4 weeks after citrate buffer or streptozotocin (STZ, 65 mg/kg, blood glucose > 15 mmol/l) injection. At each IOP, dim and bright flash (-4.56, -1.72 log cd.s.m^-2) ERG responses were recorded to measure inner retinal and ON-bipolar cell function, respectively. Ocular blood flow (laser Doppler flowmetry, citrate; n=6, STZ; n=10) was also measured during acute IOP challenge. Retinae were isolated for qPCR analysis of nitric oxide synthase mRNA expression endothelial, eNos; inducible, iNos; neuronal, nNos).

RESULTS: STZ-induced diabetes increased the susceptibility of inner retinal (IOP at 50% response, 60.1, CI: 57.0-62.0 mmHg vs. citrate: 67.5, CI: 62.1-72.4 mmHg) and ON-bipolar cell function (STZ: 60.3, CI: 58.0-62.8 mmHg vs. citrate: 65.1, CI: 58.0-62.78 mmHg) and ocular blood flow (43.9, CI: 40.8-46.8 vs. citrate: 53.4, CI: 50.7-56.1 mmHg) to IOP challenge. Citrate eyes showed elevated eNos mRNA (+49.7%) after IOP stress, an effect not found in STZ-diabetic eyes (-5.7%, P<0.03). No difference was observed for iNos or nNos (P>0.05) following IOP elevation.

CONCLUSIONS: STZ-induced diabetes increased functional susceptibility during acute IOP challenge. This functional vulnerability is associated with a reduced capacity for diabetic eyes to upregulate eNOS expression and to autoregulate blood flow in response to stress.