Antibacterial graphene-based hydroxyapatite/chitosan coating with gentamicin for potential applications in bone tissue engineering.

Electrophoretic deposition process (EPD) was successfully used for obtaining graphene (Gr)-reinforced composite coating based on hydroxyapatite (HAP), chitosan (CS), and antibiotic gentamicin (Gent), from aqueous suspension. The deposition process was performed as a single step process at a constant voltage (5 V, deposition time 12 min) on pure titanium foils. The influence of graphene was examined through detailed physicochemical and biological characterization. Fourier transform infrared spectroscopy, field emission scanning electron microscopy, thermogravimetric analysis, X-ray diffraction, Raman, and X-ray photoelectron analyses confirmed the formation of composite HAP/CS/Gr and HAP/CS/Gr/Gent coatings on Ti. Obtained coatings had porous, uniform, fracture-free surfaces, suggesting strong interfacial interaction between HAP, CS, and Gr. Large specific area of graphene enabled strong bonding with chitosan, acting as nanofiller throughout the polymer matrix. Gentamicin addition strongly improved the antibacterial activity of HAP/CS/Gr/Gent coating that was confirmed by antibacterial activity kinetics in suspension and agar diffusion testing, while results indicated more pronounced antibacterial effect against Staphylococcus aureus (bactericidal, viable cells number reduction >3 logarithmic units) compared to Escherichia coli (bacteriostatic, <3 logarithmic units). MTT assay indicated low cytotoxicity (75% cell viability) against MRC-5 and L929 (70% cell viability) tested cell lines, indicating good biocompatibility of HAP/CS/Gr/Gent coating. Therefore, electrodeposited HAP/CS/Gr/Gent coating on Ti can be considered as a prospective material for bone tissue engineering as a hard tissue implant.

Gentamicin-Loaded Bioactive Hydroxyapatite/Chitosan Composite Coating Electrodeposited on Titanium.

Composite coating of antibiotic gentamicin (Gent), natural polymer chitosan (CS), and hydroxyapatite (HAP) was successfully assessed by applying the electrophoretic deposition (EPD) technique. EPD was performed under optimized deposition conditions (5 V, 12 min) on pure titanium plates, to obtain HAP/CS and HAP/CS/Gent composite coatings in a single step from three-component aqueous suspension, with favorable antibacterial properties. Composite coatings were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray photoelectron analysis, confirming the formation of composite HAP/CS and HAP/CS/Gent coatings on the titanium surface, which is due to intermolecular hydrogen bonds. Employing the XRD technique, HAP was detected by obtaining the characteristic diffraction maximums. Good antibacterial activity of the composite coating loaded with antibiotic (HAP/CS/Gent) was confirmed against Staphylococcus aureus and Escherichia coli, pointing to the high potential for bioapplication. Introduction of gentamicin in HAP/CS/Gent coating caused very mild cytotoxicity in the tested cell lines MRC-5 and L929. MTT testing was used to evaluate cell viability, and HAP/CS was classified as noncytotoxic.

Evaluation of angiotensin-converting enzyme inhibitor's absorption with retention data of micellar thin-layer chromatography and suitable molecular descriptor.

Twelve angiotensin-converting enzyme (ACE) inhibitors were studied to evaluate correlation between their absorption (ABS) data available in the literature (22-96%) and hydrophobicity parameters (km and Pm/w) obtained in micellar thin-layer chromatography (MTLC) using Brij 35. The theoretical considerations showed that the geometric molecular descriptor-volume value (Vol) should be considered as an independent variable simultaneously with calculated hydrophobicity parameters in multiple linear regression analysis to obtain reliable correlation between ACE inhibitor's absorption and lipophilicity (calculated KOWWINlog P) and that captopril should be excluded from further correlations. The results of MTLC confirmed that between the two hydrophobicity parameters km and Pm/w, for absorption prediction of 11 ACE inhibitors, the micelle-water partition coefficient Pm/w provided higher correlation (R(2) = 0.756), while for the km parameter R(2) = 0.612 was obtained. The micelle-water partition coefficient Pm/w could be considered as analogous to hydrophobicity parameter C0 from reversed-phase thin-layer chromatography. Dissimilar retention behavior of lisinopril indicated its lowest non-polar interaction with micelle, because of its di-acid form. The proposed model which included ACE inhibitors on the opposite site of lipophilicity-lisinopril and fosinopril (KOWWINlog P = -0.96 and KOWWINlog P = 6.61, respectively), both with similar absorption values (25 and 36%, respectively), could indicate that absorption of investigated compounds occurs via two different mechanisms: active and passive transport.

Estimation of angiotensin-converting enzyme inhibitors protein binding degree using chromatographic hydrophobicity data.

INTRODUCTION: Angiotensin-converting enzyme (ACE) inhibitors represent a significant group of drugs primarily used in the treatment of hypertension and congestive heart failure. OBJECTIVE: Selected ACE inhibitors (enalapril, quinapril, fosinopril, lisinopril, cilazapril) were studied in order to establish a fast and easy estimation method of their plasma protein binding degree based on their lipophilicity data. METHODS: Chromatographic hydrophobicity data (parameter C0) were obtained on cellulose layers under conditions of normal-phase thin-layer chromatography (NPTLC), using different binary solvent systems. The ACE inhibitors lipophilicity descriptors (logP) values were calculated using the software package Virtual Computational Chemistry Laboratory.The ACE inhibitors plasma protein binding data were collected from relevant literature. RESULTS: ACE inhibitors protein binding data varied from negligible (lisinopril) to 99% (fosinopril). The calculated lipophilicity descriptors, logP(KOWWIN) values ranged from -0.94 (lisinopril) to 6.61 (fosinopril). Good correlations were established between plasma protein binding values and calculated logP(KOWWIN) values (R2 = 0.8026) as well as chromatographic hydrophobicity data, C0 parameters (R2 = 0.7662). Even though good correlation coefficients (R2) were obtained in both relations, unacceptable probability value with p > 0.05 was found in relation between protein binding data and calculated logP(KOWWIN) values. Subsequently, taking into consideration the request for probability value lower than 0.05, a better relationship was observed between protein binding data and chromatographically obtained hydrophobicity parameters C0 values. CONCLUSION: Cellulose layers are easily available and cost effective sorbent to assess hydrophobicity. Experimentally obtained data on ACE inhibitors hydrophobicity and plasma protein binding estimation are important parameters in evaluating bioavailability of these drugs.

In vitro modeling of angiotensin-converting enzyme inhibitor's absorption with chromatographic retention data and selected molecular descriptors.

Set of nine angiotensin-converting enzyme inhibitors (enalapril, quinapril, fosinopril, lisinopril, cilazapril, ramipril, benazepril, perindopril and moexipril) were studied to evaluate the correlation between their intestinal absorption and salting-out thin-layer chromatography hydrophobicity parameters (RM(0) or C0) obtained by ascending technique applying four different salts, (NH4)2SO4, NH4NO3, NH4Cl and NaCl as mobile phases. The best correlations between KOWWIN logP and both hydrophobicity parameters, RM(0) and C0, (R(2)>0.850) were observed for NaCl (1.0-3.0M) while the lowest R(2) was obtained for (NH4)2SO4 (0.649 and 0.427, respectively) due to highest salting-out effect of (NH4)2SO4. The effect of selected inorganic salts in the salting-out mobile phases, on the solutes solubility and retention was evaluated. The topological polar surface area should be selected as independent variable (only this molecular descriptor showed low correlation with chromatographic hydrophobicity parameters) for multiple linear regression analysis, to obtain reliable correlation between angiotensin-converting enzyme inhibitor's intestinal absorption data and salting-out thin-layer chromatograpic hydrophobicity parameters. These correlations provide R(2)=0.823 for RM(0) or R(2)=0.799 for C0 indicating good relationship between predicted and literature available intestinal absorption (ranged from 22% to 70%) of investigated angiotensin-converting enzyme inhibitors. The proposed in vitro model was checked with three in addition experimentally analyzed drugs, zofenopril, trandolapril and captoril. The satisfactory absorption prediction was obtained for zofenopril and trandolapril, while divergence established for captopril resulted from considerably different structure.

Correlation between ultra-high performance liquid chromatography-tandem mass spectrometry and reversed-phase thin-layer chromatography hydrophobicity data for evaluation of angiotensin-converting enzyme inhibitors absorption.

In this research seven ACE inhibitors (enalapril, quinapril, fosinopril, lisinopril, cilazapril, ramipril, benazepril) were studied to evaluate the correlation between their absorption and ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS) and reversed-phase thin-layer chromatography (RP-TLC) hydrophobicity data (φ(0) or C(0) parameters, respectively). Their absorption values were in the range of 25-60%, while calculated KOWWIN logP values were from -0.94 to 6.61. Additionally, perindopril (absorption 70%, KOWWIN logP 2.59) and moexipril (absorption 22%, KOWWIN logP 3.36) were introduced for the theoretical considerations due to their high/low absorption values which were on the opposite sites in comparison with the majority of ACE inhibitors (25-60%). In the theoretical considerations it was shown that the solubility data (logS) must be considered, as independent variable, simultaneously with KOWWIN logP to obtain reliable correlation (r(2)=0.7208) between absorption and ACE inhibitors lipophilicity. As the main topic of this study, the relationships between literature available and absorption data predicted by multiple linear regression (MLR) using logS values besides chromatographically obtained hydrophobicity parameters C(0) (r(2)=0.6424) or φ(0) (r(2)=0.6762) were studied proving that these parameters could be used in ACE inhibitors absorption evaluation. The UHPLC-MS method provides the direct application of experimentally obtained φ(0) values that is the advantage of this method. For better MLR correlation of ACE inhibitors absorption with C(0) parameters (RP-TLC) and logS, mathematical conversion of C(0) parameters to logC(0) values was necessary based on requisite for probability value of regression analysis (P<0.05). The accordance and differences between hydrophobicity parameters obtained by UHPLC-MS and RP-TLC were defined.

A PAMPA assay as fast predictive model of passive human skin permeability of new synthesized corticosteroid C-21 esters.

The permeation properties of twenty newly synthesized α-alkoxyalkanoyl and α-aryloxyalkanoyl C-21 esters of standard corticosteroids: Fluocinolone acetonide, dexamethasone, triamcinolone acetonide and hydrocortisone were established using a PAMPA assay (70% silicone oil and 30% isopropyl myristate). The data were compared with parent corticosteroids with addition of mometasone furoate and hydrocortisone acetate. All newly synthesized corticosteroid C-21 esters have effective permeability coefficients higher then -6, mostly followed with high values of retention factors and low permeation. The examined compounds were grouped through relationship between obtained retention factors and permeation parameters (groups I-III). The classification confirmed group I (membrane retentions as well as permeation lower then 30%) for all corticosteroid standards except mometasone furoate, a potent topical corticosteroid which, with high membrane retention (81%) and low permeation (7.7%) fits into group III. The largest number of new synthesized corticosteroids C-21 esters, among them all fluocinolone acetonide C-21 esters, have high membrane retentions (32.4%-86.5%) and low permeations (1.3%-27.1%), fitting in group III. The classification was related to previously obtained anti-inflammatory activity data for the fluocinolone acetonide C-21 esters series. According to the PAMPA results the new synthesized esters could be considered as potential new prodrugs with useful benefit/risk ratio.

Lipophilicity Examination of Some ACE inhibitors andHydrochlorothiazide on Cellulose in RP Thin-Layer Chromatography.

In this assay, the evaluation of lipophilicity of four ACE-inhibitors and hydrochlorothiazide (HCTZ) with RP-TLC on cellulose layers was described using three binary solvent systems. The selected ACE inhibitors had sufficiently different structures which can indicate the method suitability for their lipophilicity evaluation as the model substances in comparison with HCTZ. In addition, the linear relationship between the RM-values and composition of mobile phases was established in the current study. From the regression data of the plots, the hydrophobicity parameters, R(0) M and m, were determined and C0 parameter was calculated. The correlations between the experimentally obtained hydrophobicity parameters and calculated log p values were studied. Furthermore, the obtained results were compared with those previously obtained on RP-18 modified silica gel. Very good correlation (r = 0.91; water-ethanol solvent system) between the chromatographically obtained hydrophobicity parameters and calculated log p values confirmed the selection of ACE inhibitors since lisinopril and quinapril were on the opposite sites of linear relationship. The results indicate that cellulose as an easily available sorbent can be successfully used for the lipophilicity investigation of examined substances with RP-TLC.