Nitroprusside─Expanding the Potential Use of an Old Drug Using Nanoparticles

For more than 70 years, sodium nitroprusside (SNP) has been used to treat severe hypertension in hospital emergency settings. During this time, a few other clinical uses have also emerged such as in the treatment of acute heart failure as well as improving mitral incompetence and in the intra- and perioperative management during heart surgery. This drug functions by releasing nitric oxide (NO), which modulates several biological processes with many potential therapeutic applications. However, this small molecule has a short lifetime, and it has been administered through the use of NO donor molecules such as SNP. On the other hand, SNP also has some setbacks such as the release of cyanide ions, high water solubility, and very fast NO release kinetics. Currently, there are many drug delivery strategies that can be applied to overcome many of these limitations, providing novel opportunities for the use of old drugs, including SNP. This Perspective describes some nitroprusside properties and highlights new potential therapeutic uses arising from the use of drug delivery systems, mainly silica-based nanoparticles. There is a series of great opportunities to further explore SNP in many medical issues as reviewed, which deserves a closer look by the scientific community.

Wheat Germ Agglutinin-Conjugated Disulfide Cross-Linked Alginate Nanoparticles as a Docetaxel Carrier for Colon Cancer Therapy

PURPOSE

In chemotherapy, oral administration of drug is limited due to lack of drug specificity for localized colon cancer cells. The inability of drugs to differentiate cancer cells from normal cells induces side effects. Colonic targeting with polymeric nanoparticulate drug delivery offers high potential strategies for delivering hydrophobic drugs and fewer side effects to the target site. Disulfide cross-linked polymers have recently acquired high significance due to their potential to degrade in reducing colon conditions while resisting the upper gastrointestinal tract's hostile environment. The goal of this project is, therefore, to develop pH-sensitive and redox-responsive fluorescein-labeled wheat germ agglutinin (fWGA)-mounted disulfide cross-linked alginate nanoparticles (fDTP2) directly targeting docetaxel (DTX) in colon cancer cells.

METHODS

fDTP2 was prepared by mounting fWGA on DTX-loaded nanoparticles (DTP2) using the two-step carbodiimide method. Morphology of fDTP2 was examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Dynamic light scattering (DLS) study was carried out to determine the mean diameter, polydispersity index (PDI) and zeta potential of fDTP2. Cellular uptake efficiency was examined using fluorescence microplate reader. Biocompatibility and active internalization of fDTP2 were conducted on HT-29.

RESULTS

fDTP2 was found to exhibit a DTX loading efficiency of 19.3%. SEM and TEM tests revealed spherical nanoparticles. The in vitro DTX release test showed a cumulative release of 54.7%. From the DLS study, fDTP2 reported a 277.7 nm mean diameter with PDI below 0.35 and -1.0 mV zeta potential. HT-29 which was fDTP2-treated demonstrated lower viability than L929 with a half maximal inhibitory concentration (IC50) of 34.7 µg/mL. HT-29 (33.4%) internalized fDTP2 efficiently at 2 h incubation. The study on HT-29 active internalization of nanoparticles through fluorescence and confocal imaging indicated such.

CONCLUSION

In short, fDTP2 demonstrated promise as a colonic drug delivery DTX transporter.

Saying NO to H2S: A Story of HNO, HSNO, and SSNO. Inorg Chem 2019;58:4039-4051. [PMID: 30883105 DOI: 10.1021/acs.inorgchem.8b02592]

Interactions between small inorganic molecules are fundamental to the understanding of basic reaction mechanisms and some of the initial processes of chemical evolution that preceded organic molecules and led to the origin of life. The kinetics of these processes are suitable for the fast generation of a variety of new chemical entities and the propagation of a cascade of chemical reactions, a property that is ideal for signaling purposes even in biological systems. NO and H₂S are such molecules that are nowadays recognized as biological gasotransmitters involved in the regulation of physiological functions through protein modifications such as S-nitrosothiol, disulfide, and persulfide formations. In this Viewpoint, we review the current understanding of interactions of NO (and organic and metal nitrosyl species) with H₂S, in both chemical and biochemical contexts. Through the formation of HNO, (H)SNO (and its isomers), (H)SSNO, and polysulfides, these two gasotransmitters initiate reaction networks with significant roles in cell signaling. The chemical reactivities and biological effects of these nitrogen and sulfur species are still unresolved, and, thus, a cross-talk between all of them represents a challenging interdisciplinary field that awaits exciting new findings. We tackle some of the intriguing and open questions and provide perspectives for future research directions.

Nitrosodisulfide [S2NO]- (perthionitrite) is a true intermediate during the "cross-talk" of nitrosyl and sulfide

Nitrosodisulfide S₂NO^- is a controversial intermediate in the reactions of S-nitrosothiols with HS^- that produce NO and HNO. QM-MM molecular dynamics simulations combined with TD-DFT analysis contribute to a clear identification of S₂NO^- in water, acetone and acetonitrile, accounting for the UV-Vis signatures and broadening the mechanistic picture of N/S signaling in biochemistry.

Direct NMR detection of the unstable “red product” from the reaction between nitroprusside and 2-mercaptosuccinic acid

First NMR characterization of the unstable “red product” produced from the reaction between nitroprusside and organic thiolates.

A unique family of stable and water-soluble S-nitrosothiol complexes

In this work, we present a complete and detailed experimental characterization and theoretical study of a variety of coordinated S-nitrosothiols (RSNOs), such as cysteine derivatives, mercaptosuccinic acid, benzyl thiol, and phenyl thiol. Some of them are extremely unstable and sensitive in free form. Strikingly, in contrast with free S-nitrosothiols, we found that, upon coordination to iridium, they become very stable even in aqueous solutions. The study of these coordinated complexes provides further insight on the elucidation of structural aspects dealing with the nature of the S-N bond in RSNOs, a fact which still remains a matter of controversy.

In-gel detection of urease activity by nitroprusside-thiol reaction

A new staining method for urease activity in non-denaturing polyacrylamide gels is described. The increase in local pH of the gel, resulting from ureolytic activity of urease, causes a purple red coloured band after incubation of the polyacrylamide gel with urea. Staining of urease activity using this method is very specific for catalytically active urease even in crude preparations. Detection of urease activity by this method is rapid, simple and economical. The described method is also more sensitive than existing methods of urease staining. A minimum of 0.25 mU of urease activity can be detected after 5 min of incubation with the substrate. The method has been used to demonstrate the presence of different charge isoforms of urease in a member of the plant family Cucurbitaceae.

Biomedical implications of information processing in chemical systems: Non-classical approach to photochemistry of coordination compounds

Analogies between photoactive nitric oxide generators and various electronic devices: logic gates and operational amplifiers are presented. These analogies have important biological consequences: application of control parameters allows for better targeting and control of nitric oxide drugs. The same methodology may be applied in the future for other therapeutic strategies and at the same time helps to understand natural regulatory and signaling processes in biological systems.

Performing organic chemistry with inorganic compounds: electrophilic reactivity of selected nitrosyl complexes

The inorganic nitrosyl (NO(+)) complexes [Fe(CN) 5NO](2-), [Ru(bpy)2(NO)Cl](2+), and [IrCl 5(NO)](-) are useful reagents for the nitrosation of a variety of organic compounds, ranging from amines to the relatively inert alkenes. Regarding [IrCl 5(NO)](-), its high electrophilicity and inertness define it as a unique reagent and provide a powerful synthetic route for the isolation and stabilization of coordinated nitroso compounds that are unstable in free form, such as S-nitrosothiols and primary nitrosamines. Related to the high electrophilicity of [IrCl 5(NO)](-), an unusual behavior is described for its PPh 4(+) salt in the solid state, showing an electronic distribution represented by Ir(IV)-NO(*) instead of Ir (III)-NO(+) (as for the K(+) and Na(+) salts).

Electrospray Ionization Mass Spectrometry of a Novel Family of Complexes in which Various Nitroso Compounds are Stabilized via Coordination to [IrCl5]2-

Electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (ESI-MS/MS) data of a unique family of complexes of nitroso compounds coordinated to pentachloroiridate(III), [Cl5IrN(O)XR]2- (X=NH, S, CH and R=alkyl, aryl) are presented. These novel complexes are obtained by nucleophilic attack of primary amines, thiols. and alkenes to the coordinated nitrosyl. Despite their lability and low volatility, MS analysis of complexes of the type MN(O)X was done for the first time, complementing other spectroscopic techniques. The intrinsic dissociation chemistry of the gaseous diagnostic ions was studied via ESI-MS/MS and found to be very useful to confirm the proposed connectivities of the parent complexes. In particular, ESI-MS of their solutions allows the detection of series of diagnostic ions, mainly, [M-Cl]-, [M+K]-, [M-NO]-*, and [M-Cl+AcN]- (AcN=acetonitrile), which confirmed the identity of the analyzed complexes to be M=[Cl5IrN(O)XR]2-. Major fragments were formed by losses of NO or N(O)XR. ESI-MS and ESI-MS/MS measurements are therefore shown to be the proper techniques to complement the spectroscopic characterization of this important class of nitroso complexes. An interesting rearrangement that does not take place in solution was observed in the gaseous phase, and a plausible mechanism is discussed.

Reactivity of aquacobalamin and reduced cobalamin toward S-nitrosoglutathione and S-nitroso-N-acetylpenicillamine

The reactions of aquacobalamin (Cbl(III)H2O, vitamin B12a) and reduced cobalamin (Cbl(II), vitamin B12r) with the nitrosothiols S-nitrosoglutathione (GSNO) and S-nitroso-N-acetylpenicillamine (SNAP) were studied in aqueous solution at pH 7.4. UV-vis and NMR spectroscopic studies and semiquantitative kinetic investigations indicated complex reactivity patterns for the studied reactions. The detailed reaction routes depend on the oxidation state of the cobalt center in cobalamin, as well as on the structure of the nitrosothiol. Reactions of aquacobalamin with GSNO and SNAP involve initial formation of Cbl(III)-RSNO adducts followed by nitrosothiol decomposition via heterolytic S-NO bond cleavage. Formation of Cbl(III)(NO-) as the main cobalamin product indicates that the latter step leads to efficient transfer of the NO- group to the Co(III) center with concomitant oxidation of the nitrosothiol. Considerably faster reactions with Cbl(II) proceed through initial Cbl(II)-RSNO intermediates, which undergo subsequent electron-transfer processes leading to oxidation of the cobalt center and reduction of the nitrosothiol. In the case of GSNO, the overall reaction is fast (k approximately 1.2 x 10(6) M(-1) s(-1)) and leads to formation of glutathionylcobalamin (Cbl(III)SG) and nitrosylcobalamin (Cbl(III)(NO-)) as the final cobalamin products. A mechanism involving the reversible equilibrium Cbl(II) + RSNO <==> Cbl(III)SR + NO is suggested for the reaction on the basis of the obtained kinetic and mechanistic information. The corresponding reaction with SNAP is considerably slower and occurs in two distinct reaction steps, which result in the formation of Cbl(III)(NO-) as the ultimate cobalamin product. The significantly different kinetic and mechanistic features observed for the reaction of GSNO and SNAP illustrate the important influence of the nitrosothiol structure on its reactivity toward metal centers of biomolecules. The potential biological implications of the results are briefly discussed.

Evidence for the formation of a novel nitrosothiol from the gaseous mediators nitric oxide and hydrogen sulphide

The gaseous mediators hydrogen sulphide (H2S) and nitric oxide (*NO) are synthesised in the body from L-cysteine and L-arginine, respectively. In the cardiovascular system, *NO is an important regulator of vascular tone and its over- or under-production has been linked to a variety of diseases. The physiological significance of H2S is not yet clear but, like *NO, it exhibits vasodilator activity and may play a part in septic and haemorrhagic shock, hypertension, regulation of cardiac contractility, and in inflammation. To date, there have been no reports of a chemical interaction between H2S and *NO. Here we show that incubation of the H2S donor, sodium hydrosulphide, with a range of *NO donors and *NO gas in vitro leads to the formation of a nitrosothiol molecule as determined by a combination of techniques; electron paramagnetic resonance, amperometry, and measurement of nitrite. We further show that this nitrosothiol did not induce cGMP accumulation in cultured RAW264.7 cells unless *NO was released with Cu2+. Finally, using liver homogenates from LPS treated rats we present evidence for the endogenous formation of this nitrosothiol. These findings provide the first evidence for the formation of a novel nitrosothiol generated by reaction between H2S and *NO. We propose that generation of this nitrosothiol in the body may regulate the physiological effects of both *NO and H2S.

A Surprisingly Stable S-Nitrosothiol Complex

In this work we present for the first time an X-ray structure of a coordinated S-nitrosothiol obtained by reaction of the extremely reactive K[IrCl5NO] with benzylmercaptan in acetonitrile. This surprisingly stable compound, trans-K[IrCl4(CH3CN)N(O)SCH2Ph], was isolated in high yield (80%) and fully characterized by FTIR, 1H NMR, and ESI-MS. To our knowledge this is the first example of a coordinated S-nitrosothiol that has been isolated.

Sodium nitroprusside potentiates hydrogen-sulfide-induced contractions in body wall muscle from a marine worm

Hydrogen sulfide (H2S) at concentrations of about 0.05 to 1 mmol.l(-1) appears to function as a gasotransmitter in vertebrates, analogous to nitric oxide (NO) and carbon monoxide, but the actions of H2S in invertebrate tissue have not been well studied. In this study, we investigated the role of H2S in modulating body wall muscle tone in the marine echiuran worm Urechis caupo (Echiuridae). We first determined that U. caupo body wall homogenates produce H2S upon addition of L-cysteine and pyridoxal-5'-phosphate (PLP), and that the rate is increased by addition of 2-mercaptoethanol, suggesting the presence of an activated L-serine sulfhydrase pathway. We then measured the contractile response of U. caupo body wall circular muscle strips to sodium hydrosulfide (NaHS)--which produces H2S in solution--and the NO donor sodium nitroprusside (SNP), both with and without subsequent application of acetylcholine (ACh). We found that NaHS alone stimulated contraction in muscle strips equivalent to about one-third the force of ACh alone, whereas SNP alone had no effect on muscle tone. However, simultaneous addition of NaHS with SNP elicited a much stronger contraction, reaching more than twice that of ACh alone, which could be increased further by subsequent application of ACh.

The Reactions of Nitrosyl Complexes with Cysteine

The reaction kinetics of a set of ruthenium nitrosyl complexes, {(X)5MNO}n, containing different coligands X (polypyridines, NH3, EDTA, pz, and py) with cysteine (excess conditions), were studied by UV-vis spectrophotometry, using stopped-flow techniques, at an appropriate pH, in the range 3-10, and T = 25 degrees C. The selection of coligands afforded a redox-potential range from -0.3 to +0.5 V (vs Ag/AgCl) for the NO+/NO bound couples. Two intermediates were detected. The first one, I1, appears in the range 410-470 nm for the different complexes and is proposed to be a 1:1 adduct, with the S atom of the cysteinate nucleophile bound to the N atom of nitrosyl. The adduct formation step of I1 is an equilibrium, and the kinetic rate constants for the formation and dissociation of the corresponding adducts were determined by studying the cysteine-concentration dependence of the formation rates. The second intermediate, I2, was detected through the decay of I1, with a maximum absorbance at ca. 380 nm. From similar kinetic results and analyses, we propose that a second cysteinate adds to I1 to form I2. By plotting ln k1(RS-) and ln k2(RS-) for the first and second adduct formation steps, respectively, against the redox potentials of the NO+/NO couples, linear free energy plots are obtained, as previously observed with OH- as a nucleophile. The addition rates for both processes increase with the nitrosyl redox potentials, and this reflects a more positive charge at the electrophilic N atom. In a third step, the I2 adducts decay to form the corresponding Ru-aqua complexes, with the release of N2O and formation of cystine, implying a two-electron process for the overall nitrosyl reduction. This is in contrast with the behavior of nitroprusside ([Fe(CN)5NO]2-; NP), which always yields the one-electron reduction product, [Fe(CN)5NO]3-, either under substoichiometric or in excess-cysteine conditions.

Sodium nitroprusside: mechanism of NO release mediated by sulfhydryl-containing molecules

Sodium nitroprusside (SNP) is among the most widely studied nitric oxide donors, and its capability of producing NO seems to depend on its interaction with sulfhydryl-containing molecules present in vivo. The aim of this research has been the study of the mechanism of interaction between SNP and sulfhydryl-containing compounds, such as cysteine and glutathione, through detection by EPR, UV-vis, and IR spectroscopy of both the radical and nonradical species involved. An electron-transfer process can be invoked as the key step, which leads to the formation of the reduced SNP radical, the main detectable radical intermediate, and the corresponding S-nitrosothiol, the ending product of NO that can be considered the real storage and transporters of NO. When cysteine was used, a second radical species (A) is detectable: it can be accounted for by the interaction of a byproduct with unreacted cysteine.