Endogenous Conjugation of Biomimetic Dinitrosyl Iron Complex with Protein Vehicles for Oral Delivery of Nitric Oxide to Brain and Activation of Hippocampal Neurogenesis

Abstract

Nitric oxide (NO), a pro-neurogenic and antineuroinflammatory gasotransmitter, features the potential to develop a translational medicine against neuropathological conditions. Despite the extensive efforts made on the controlled delivery of therapeutic NO, however, an orally active NO prodrug for a treatment of chronic neuropathy was not reported yet. Inspired by the natural dinitrosyl iron unit (DNIU) [Fe(NO) 2 ], in this study, a reversible and dynamic interaction between the biomimetic [(NO) 2 Fe(μ-SCH 2 CH 2 OH) 2 Fe(NO) 2 ] ( DNIC-1 ) and serum albumin (or gastrointestinal mucin) was explored to discover endogenous proteins as a vehicle for an oral delivery of NO to the brain after an oral administration of DNIC-1 . On the basis of the in vitro and in vivo study, a rapid binding of DNIC-1 toward gastrointestinal mucin yielding the mucin-bound dinitrosyl iron complex (DNIC) discovers the mucoadhesive nature of DNIC-1 . A reversible interconversion between mucin-bound DNIC and DNIC-1 facilitates the mucus-penetrating migration of DNIC-1 shielded in the gastrointestinal tract of the stomach and small intestine. Moreover, the NO-release reactivity of DNIC-1 induces the transient opening of the cellular tight junction and enhances its paracellular permeability across the intestinal epithelial barrier. During circulation in the bloodstream, a stoichiometric binding of DNIC-1 to the serum albumin, as another endogenous protein vehicle, stabilizes the DNIU [Fe(NO) 2 ] for a subsequent transfer into the brain. With aging mice under a Western diet as a disease model for metabolic syndrome and cognitive impairment, an oral administration of DNIC-1 in a daily manner for 16 weeks activates the hippocampal neurogenesis and ameliorates the impaired cognitive ability. Taken together, these findings disclose the synergy between biomimetic DNIC-1 and endogenous protein vehicles for an oral delivery of therapeutic NO to the brain against chronic neuropathy.

Cell-Penetrating Delivery of Nitric Oxide by Biocompatible Dinitrosyl Iron Complex and Its Dermato-Physiological Implications

“…As a potential biological equivalent of NO, bioinorganic engineering of [Fe(NO) 2 ] unit has emerged to develop biomimetic DNICs as a chemical biology tool for controlled delivery of NO and translation of NO-related functions into biomedical applications [23,24]. In particular, biomimetic DNICs and their conjugates with drug delivery systems were explored for antiaging/anti-inflammatory/anti-viral effect, anti-cancer/anti-hypertensive therapy, diabetic angiogenesis/wound healing, penile erection, and treatment of mild cognitive impairment and neurodegenerative diseases [25][26][27][28][29][30][31][32][33][34][35]. In particular, phase I and phase II clinical trials of glutathione-bound DNICs [Fe 2 (µ-glutathione) 2 (NO) 4 ], a commercial medical product with the pharmacological name Oxacom ® , was reported for application as a clinical medicine against hypertension [30,31].…”

“…Inspired by the potential of biomimetic DNICs for biomedical applications, synthetic advances in the development of structure-characterized and water-soluble DNICs enabled the study of trafficking and NO-delivery reactivity of DNICs under simulated physiological conditions, in vitro, and in vivo [26,28,[36][37][38][39]. Water-soluble DNIC [Fe 2 (µ-SCH 2 CH 2 OH) 2 (NO) 4 ] (DNIC-1) displays an O 2 -triggered degradation mechanism for the release of nitric oxide, ferric ion, and disulfide with a half-life of 27.4 h and 15.5 h in an aqueous buffer solution (pH = 7.0 or 7.4) at 25 • C and 37 • C, respectively [25,32,34]. In simulated gastric fluid (SGFsp, pH 1.2), a shortened half-life of 0.4 h indicates the acid-sensitive nature of DNIC-1.…”

“…In simulated gastric fluid (SGFsp, pH 1.2), a shortened half-life of 0.4 h indicates the acid-sensitive nature of DNIC-1. To mimic the systemic circulation system, the addition of serum albumin initiated the coordination of Cys-34 toward DNIC-1 leading to the partial formation of albumin-bound DNIC, which features an accelerated release of NO with a half-life of 3.5 h in phosphate-buffered saline (PBS) [34,[39][40][41][42]. Regarding the NO-release reactivity of synthetic DNICs, their capability for the elevation of intracellular NO levels, activation of the NO-soluble guanylyl cyclase (sGC)-cyclic guanosine monophosphate (cGMP) pathway (NO-sGC-cGMP pathway), and regulation of cGMP-dependent cell proliferation was also reported [32,34,39,43].…”

“…To mimic the systemic circulation system, the addition of serum albumin initiated the coordination of Cys-34 toward DNIC-1 leading to the partial formation of albumin-bound DNIC, which features an accelerated release of NO with a half-life of 3.5 h in phosphate-buffered saline (PBS) [34,[39][40][41][42]. Regarding the NO-release reactivity of synthetic DNICs, their capability for the elevation of intracellular NO levels, activation of the NO-soluble guanylyl cyclase (sGC)-cyclic guanosine monophosphate (cGMP) pathway (NO-sGC-cGMP pathway), and regulation of cGMP-dependent cell proliferation was also reported [32,34,39,43]. Moreover, the discovery of multidrug-resistance-associated protein 1 as a transporter for the efflux of glutathione-bound DNICs from the cells may establish a mechanism for transcellular trafficking of DNIC after its uptake by cells [44][45][46].…”

“…Moreover, the discovery of multidrug-resistance-associated protein 1 as a transporter for the efflux of glutathione-bound DNICs from the cells may establish a mechanism for transcellular trafficking of DNIC after its uptake by cells [44][45][46]. Of importance, the endogenous conjugation of DNIC-1 with gastrointestinal mucin and serum albumin in a reversible manner was reported to facilitate oral delivery of the [Fe(NO) 2 ] unit to the brain across the intestinal epithelial and blood-brain barriers, respectively [34]. Despite the investigations put forward, kinetics for in vitro NO-release reactivity, the mechanism for cellular uptake and intracellular release of NO, and the biocompatibility of synthetic DNICs remain elusive.…”