Optimization of Self-Double Emulsifying Drug Delivery System Using Design of Experiments for Enhanced Oral Bioavailability of Gentamicin: In-vitro, Ex-vivo and In-vivo Studies.

Water-in-oil-in-water (w/o/w) double emulsions have shown excellent capability in augmenting the enteral bioavailability of BCS class III drugs, besides being effective controlled-release formulations. However, the problem of thermodynamic instability has restrained their industrial applicability. The self-double emulsifying drug delivery system (SDEDDS) is one of several approaches used to improve the stability of double emulsions. SDEDDS is a mixture of primary emulsion and secondary surfactant that can spontaneously emulsify into double emulsions in an external aqueous environment with mild agitation. Here, we prepared SDEDDS of gentamicin sulfate by response surface methodology. Selected optimized formulations (ODS1 and ODS2) were evaluated for zeta potential (Y1), optical clarity (Y2), release at 420 min (Y3), emulsion stability index (Y4) and self-emulsification time (Y5). For ODS1, Y1=-35.45 (±1.06)mV, Y2=53.19 (±0.35)%, Y3=75.79 (±0.60)%, Y4=93.97(±0.15)% and Y5=0.631 (±0.014)min, whereas for ODS2, Y1=-35.70 (±0.56)mV, Y2=48.09 (±0.64)%, Y3=76.61 (±0.99)%, Y4=93.00(±0.94)% and Y5=0.687(±0.02)min. Furthermore, ex-vivo studies on intestinal permeability revealed that SDEDDS improved membrane permeability compared to drug solution. Histopathology investigations revealed that SDEDDS promoted permeation without causing significant local membrane distortion. In addition, in-vivo studies revealed a 2.84 -fold increase in AUC0-∞ of optimized SDEDD compared to pure drug oral solution.

Reaction of a {Co(NO)}8 complex with superoxide: Formation of a six coordinated [CoII(NO)(O2-)] species followed by peroxynitrite intermediate.

A nitrosyl complex of cobalt(II) porphyrinate, [Co(F20TPP2-)(NO)], (F20TPPH2 = 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin) having {Co(NO)}8 configuration was synthesized and characterized by means of spectroscopic and structural analyses. Single crystal X-ray structure of the complex revealed the square pyramidal geometry around the cobalt center with a bent nitrosyl group. It reacts with superoxide (O2-) ion in CH2Cl2 at -40 °C to result in the corresponding nitrite (NO2-) complex. Involvement of a cobalt(II)-peroxynitrite intermediate is proposed in the course of the reaction. Moreover, spectroscopic studies suggested the formation of a transient six-coordinated [CoII(NO)(O2-)] species.

Nitric Oxide Dioxygenase Activity of a Nitrosyl Complex of Mn(II)-Porphyrinate in the Presence of Superoxide: Formation of a Mn(IV)-oxo Species through a Putative Peroxynitrite Intermediate.

A nitrosyl complex of MnII-porphyrinate, [(F20TPP)MnII(NO)], 1 (F20TPPH2 = 5,10,15,20 tetrakis(pentafluorophenyl)porphyrin), was synthesized and characterized. Spectroscopic and structural characterization revealed complex 1 as a penta-coordinated MnII-nitrosyl with a linear Mn-N-O (180.0°) moiety. Complex 1 does not react with O2. However, it reacts with superoxide (O2-) in THF at -80 °C to result in the corresponding nitrate (NO3-) complex, 2, via the formation of a presumed MnIII-peroxynitrite intermediate. ESI-mass spectrometry and UV-visible and X-band EPR spectroscopic studies suggest the generation of MnIV-oxo species in the reaction through homolytic cleavage of the O-O bond of the peroxynitrite ligand as proposed in NOD activity. The intermediate formation of the MnIII-peroxynitrite was further supported by the well accepted phenol ring nitration which resembles the biologically well-established tyrosine nitration.

Nitric Oxide Dioxygenase Activity of a Nitrosyl Complex of Cobalt(II) Porphyrinate in the Presence of Hydrogen Peroxide via Putative Peroxynitrite Intermediate.

The reaction of a cobalt porphyrin complex, [(F8TPP)Co], 1 {F8TPP = 5,10,15,20- tetrakis(2,6-difluorophenyl)porphyrinate dianion} in dichloromethane with nitric oxide (NO) led to the nitrosyl complex, [(F8TPP)Co(NO)], 2. Spectroscopic studies and structural characterization revealed it as a bent nitrosyl of {CoNO}8 description. It was stable in the presence of dioxygen. However, it reacts with H2O2 in acetonitrile (or THF) solution at -40 °C (or -80 °C) to result in the corresponding Co(III)-nitrate complex, [(F8TPP)Co(NO3)], 3. The reaction presumably proceeds via the formation of a Co-peroxynitrite intermediate. X-Band electron paramagnetic resonance and electrospray ionization-mass spectroscopic studies suggest the intermediate formation of the [(porphyrin)Co(III)-O•] radical, which in turn supports the generation of the corresponding Co(IV)-oxo species during the reaction. This is in accord with the homolytic cleavage of the O-O bond in heme-peroxynitrite proposed in the nitric oxide dioxygenases activity. In addition, the characteristic peroxynitrite-induced phenol ring reaction was also observed.

Dioxygenation Reaction of a Cobalt-Nitrosyl: Putative Formation of a Cobalt-Peroxynitrite via a {CoIII(NO)(O2-)} Intermediate.

A cobalt-nitrosyl complex, [(BPI)Co(NO)(OAc)], 1 {BPI = 1,3-bis(2'-pyridylimino)isoindol} was prepared and characterized. Structural characterization revealed that the cobalt center has a distorted square pyramidal geometry with the NO group coordinated from the apical position in a bent fashion. The addition of dioxygen (O2) to the dichloromethane solution of complex 1 resulted in the formation of nitro complex, [(BPI)Co(NO2)(OAc)], 2. It was characterized structurally. Kinetic studies suggested the involvement of an associative mechanism. FT-IR spectroscopic studies suggested the formation of the intermediate 1a [(BPI)CoIII(NO)(O2-)(OAc)] in the reaction. The intermediate 1a decomposed to complex 2 via a presumed peroxynitrite intermediate which was implicated by its characteristic phenol ring nitration reaction.

Reaction of a Co(III)-Peroxo Complex and NO: Formation of a Putative Peroxynitrite Intermediate.

A Co(II) complex, [Co(L)2]Cl2, 1 of the ligand L (L = bis(2-ethyl-4-methylimidazol-5-yl)methane) upon reaction with H2O2 in methanol solution at -40 °C resulted in the formation of the corresponding Co(III)-peroxo complex [Co(L)2(O2)]+ (2). The addition of NO gas to the freshly generated solution of the complex 2 led to the formation of the Co(II)-nitrato complex 3 through the putative formation of a Co(II)-peroxynitrite intermediate, 2a. The intermediate 2a was found to mediate the nitration of the externally added phenol resembling the nitration of tyrosine in biological systems.

Reaction of a Nitrosyl Complex of Cobalt Porphyrin with Hydrogen Peroxide: Putative Formation of Peroxynitrite Intermediate.

The cobalt porphyrin complex [(Cl4TPP)Co], 1, {Cl4TPP = 5,10,15,20-tetrakis(4'-chlorophenyl)porphyrinate dianion} in dichloromethane solution was subjected to react with nitric oxide (NO) gas and resulted in the formation of the corresponding nitrosyl complex [(Cl4TPP)Co(NO)], 2, having {CoNO}8 description. It was characterized by spectroscopic studies and single-crystal X-ray structure determination. It did not react with dioxygen. However, in CH2Cl2/CH3CN solution, it reacted with H2O2 to result in the Co-nitrito complex [(Cl4TPP)Co(NO2)], 3, with the simultaneous release of O2. It induced ring nitration to the added phenol in an appreciable yield. The reaction presumably proceeds through the formation of corresponding Co-peroxynitrite intermediate.