Mihalj Poša

Solubilization of fullerene C60 in micellar solutions of different solubilizers

Fullerene (C(60)), the third carbon allotrope, is a classical engineered material with the potential application in biomedicine. However, extremely high hydrophobicity of fullerene hampers its direct biomedical evaluation and application. In this work, we investigated the solubilization of fullerene using 9 different solubility enhancers: Tween 20, Tween 60, Tween 80, Triton X-100, PVP, polyoxyethylene (10) lauryl ether, n-dodecyl trimethylammonium chloride, myristyl trimethylammonium bromide and sodium dodecyl sulphate and evaluated its antioxidant activity in biorelevant media. The presence of C(60) entrapped in surfactant micelles was confirmed by UV/VIS spectrometry. The efficacy of each modifier was evaluated by chemometric analysis using experimental data for investigating the relationship between solubilization and particle size distribution. Hierarchical clustering and principal component analysis was applied and showed that non-ionic surfactants provide better solubilization efficacy (>85%). A correlation was established (r=0.975) between the degree of solubilization and the surfactant structure. This correlation may be used for prediction of C(60) solubilization with non-tested solubility modifiers. Since the main potential biomedical applications of fullerene are based on its free radical quenching ability, we tested the antioxidant potential of fullerene micellar solutions. Lipid peroxidation tests showed that the micellar solutions of fullerene with Triton and polyoxyethylene lauryl ether kept high radical scavenging activity, comparable to that of aqueous suspension of fullerene and BHT. The results of this work provide a platform for further solubilization and testing of pristine fullerene and its hydrophobic derivatives in a biological benign environment.

Hydrophobicity and haemolytic potential of oxo derivatives of cholic, deoxycholic and chenodeoxycholic acids.

The objective of this work was to study the effect of structure of bile acids on their membranolytic potential and extent of overlapping of the information about the membranolytic potential of bile acids and their physico-chemical parameters, namely: retention index R(M0) (as a measure of bile acid hydrophobicity, reversed-phase thin-layer chromatography (RPTLC)), lecithin solubilisation (measure of the interaction of bile acids with phospholipids) and critical micellar concentration (CMC). It was found that bile acid concentrations at 100% lysis of erythrocyte membranes is described best by their CMC values, whereas at 50% lysis the parameter used is lecithin solubilisation. This indicates that different mixed micelles are formed in the membrane lysis at lower and higher concentrations of bile acids. Replacement of the hydroxyl (OH) group in the bile acid molecule with an oxo group yields derivatives with lowered hydrophobicity, power of lecithin solubilisation, tendency for self-aggregation as well as the membranolytic activity.

Modeling and prediction (correction) of partition coefficients of bile acids and their derivatives by multivariate regression methods.

Different multiple regression methods including forward stepwise multiple linear regression (MLR), principal component regression (PCR) and partial least squares (PLS) have been applied to the modeling of partition coefficient (lipophilicity) of bile acids and their derivatives by means of 16 different descriptors obtained by using Alchemy package software and retention index R(Mo) as an experimental estimation of lipophilicity. Retention indices for bile acids and their derivatives were determined by reversed phase high-performance thin layer chromatography on RP-18 W bounded stationary phase with methanol-water in different volume proportions as mobile phase. The results achieved concerning the prediction of Log P are highly significant and consistent with the molecular structure of the compounds investigated. The sum of absolute values of the charges on each atom of the molecule, in electrons (SQ), the sum of absolute values of the charges on the nitrogens and oxygens in the molecule, in electrons (SQ(NO)), specific polarizability of a molecule (SP), the third-order connectivity index ((3)chi) and molecular lipophilicity, seem to be dominant in the partition mechanism. In addition, regression models developed have allowed a correct estimation of the partition coefficients of cholic acid (Log P(HA)=2.93; Log P(A)(-)=2.02) as compared with reported experimental values (Log P(HA)=2.02; Log P(A)(-)=1.1).

Formation of hydrogen-bonded complexes between bile acids and lidocaine in the lidocaine transfer from an aqueous phase to chloroform.

Bile acids are amphiphilic molecules, which, in addition to their physiological role, have also acquired increasingly more important pharmacological applications. It has been shown that these compounds have a promoting effect on the transport of many drugs through the cell membrane. Pharmacodynamic studies showed that they exerted a significant effect on the analgesic action of lidocaine. This study is concerned with the determination of the constants of hydrogen-bonded complexes formed between the investigated bile acids and lidocaine. It was found that a prerequisite for forming such a complex is the existence of at least two OH groups or one OH group and one keto group in the bile acid molecule at an appropriate mutual distance. If a keto group is involved in lidocaine binding, the resulting complex has a larger equilibrium constant. A model--multiple linear regression equation--was constructed, relating the molecular descriptors to the equilibrium constant of hydrogen-bonded complex. It was also shown how the complex formed between lidocaine and bile acid influences the rate constant of the decrease of lidocaine concentration in the aqueous phase during its transfer to the chloroform solution of a bile acid. It was found that the complex formed between lidocaine and bile acids plays an important role in the appearance of the depot effect of lidocaine.

Effect of cholic acid and its keto derivatives on the analgesic action of lidocaine and associated biochemical parameters in rats.

SummaryThis study examined the effect of the structure and concentration of cholic acid and its keto derivatives on the local analgesic action of lidocaine in rats, measured by an analgesimetric method. The increase in bile acid concentrations in the administered lidocaine solution increased the duration of local anesthesia. It was found that the introduction of keto groups into the cholic acid molecule yielded derivatives with lower promotory action, i.e. decreased the duration of local anesthesia. The biochemical parameters investigated indicated that the keto derivatives of cholic acid exhibited no toxicity compared to that of cholic acid itself.

Conductometric study of sodium dodecyl sulfate - nonionic surfactant (Triton X-100, Tween 20, Tween 60, Tween 80 or Tween 85) mixed micelles in aqueous solution

The present study is concerned with the determination of the critical micelle concentration (cmc) of mixed micelles of sodium dodecyl sulfate with one of five nonionic surfactants (Triton X-100, Tween 20, Tween 60, Tween 80 or Tween 85) from conductance measurements. Based on the calculated values of the β parameter we have noticed that SDS-nonionic surfactants mostly showed strong synergistic effects. It was found that nonionic surfactants with mainly longer and more hydrophobic tails show stronger interactions with hydrophobic parts of SDS, thus expressing stronger synergism. The strongest synergistic effect was noticed in an SDS-Tween 80 binary system. The SDS-Tween 85 micellar system showed antagonistic effect, most probably because the presence of the double bond in its three hydrophobic tails (three C18 tails) makes it sterically rigid.

Determination of number-average aggregation numbers of bile salts micelles with a special emphasis on their oxo derivatives—The effect of the steroid skeleton

BACKGROUND The special geometry of the steroid skeleton causes that bile acid anions, in contrast to aliphatic amphiphiles, form micelles with a small aggregation number. METHODS The number-average aggregation numbers (n¯) are determined using Moroi-Matsuoka-Sugioka thermodynamic method. Also, for analysed bile acid sodium salts functions between spin-lattice relaxation time (T1) and concentration of monomers ( [Formula: see text] ) are determined. RESULTS For 7-oxodeoxicholic (7-ODC) acid and hyodeoxicholic acid (HD) monomers, curve [Formula: see text] contains two inflexion points. Mentioned monomers and cholic acid anion (C) are influential observations in relation to a line of linear regression between n¯ and para\meter of monomer hydrophobicity (lnk, retention capacity from RPHPLC). This suggests that, in micelles of bile acid anions: 7-ODC, HD and C, beside main, hydrophobic interactions, hydrogen bonds are also possible between building units. CONCLUSION The increase in the number of oxo groups in the molecule is accompanied with a decrease in the hydrophobicity of the convex side of the steroid skeleton of the bile acid anion, resulting in a lower aggregation number. Obtained results indicate that C12 and C7 α-axial OH and oxo groups on the same C atoms of the investigated bile acid molecules have different spatial environment, which is confirmed by conformational analysis. GENERAL SIGNIFICANCE Deviation from the linear model: number-average aggregation numbers with hydrophobicity of monomers, suggests the existence of additional, intermolecular interactions beside hydrophobic in micelles.

Effect of stevioside and sodium salt of monoketocholic acid on glycemia in normoglycemic and diabetic rats

SummaryThis study investigated the effect of a commercial preparation of stevioside and a synthetic compound, sodium salt of monketocholic acid (MKC), administered per os (p.o.) and also adminstered via an osmotic pump, on glycemia in normoglycemic and diabetic Wistar rats. Diabetes was induced with alloxan, 100 mg/kg, i.p. Normoglycemic and diabetic rats were treated p.o. for five days either with physiological solution (1 ml/kg, controls), stevioside (20 mg/kg), MKC (4 mg/kg) and a combination of stevioside (20 mg/kg) and MKC (4 mg/kg). Apart from p.o. adminstration, stevioside and MKC were also administered via a subcutaneously (s.c.) implanted osmotic pump. During treatment and upon termination of the latter, glycemia was measured and the rats that were treated p.o. were subjected to the oral glucose tolerance test (OGTT) at a dose of 1 g/kg. Following this animals were anesthetized with urethane (0.75 g/kg, i.p.) and killed by cardiopunction to determine C-peptide levels in the serum. In all three groups of normoglycemic rats highest decrease in glucose levels was observed on the fourth day of the experiment. The stevioside + MKC combination showed a stronger hypoglycemic effect compared to individual treatments with stevioside and MKC (3.73:4.80:4.73 mmol/L). In the group of diabetic rats that received both substances via the osmotic pump, the hypoglycemic action was also stronger compared to the individual treatments with stevioside and MKC (16.15:18.89:18.75 mmol/L). The treatment of healthy rats with both substances p.o. caused no statistically significant difference in glycemia, whereas in diabetic rats the combination of stevioside + MKC showed a statistically significant decrease in glycemia compared to control values. In both groups of rats, treatment with stevioside and MKC and their combination prevented an increase in glucose concentrations in the OGTT. Only the administration of stevioside by osmotic pump yielded a statistically significant increase in the concentrations of C-peptide in the serum of healthy rats. Compared to controls, the concentrations of C-peptide in diabetic rats were significantly higher after treatment with either stevioside or its combination with MKC, irrespective of the mode of administration.

QSPR study of the effect of steroidal hydroxy and oxo substituents on the critical micellar concentration of bile acids.

Measurements of the fluorescence intensity of 1,6-diphenylhexatriene (DPH) as a probe molecule allowed the determination of critical micellar concentrations (CMCs) for 30 bile acid (BA) molecules belonging to three linear congeneric groups, with three (Group I) and two (Group II) oxygen atoms from OH or oxo groups bound to the steroid skeleton, and glyco conjugated cholic acid and glyco conjugated cholic acid derivatives (Group III). The CMC values are related to the structure of the steroid nucleus by constructing novel molecular descriptors with 2D and 3D characteristics of topological descriptors. Namely, with conventional topological descriptors (first-order connectivity index, third-order connectivity index, Wiener-index, Balaban-index, molecular topological index, cluster count, etc.) BA molecules from the same congeneric group have identical values, so that these descriptors cannot be used to form a new model for the given congeneric group. The linear regressions (models) obtained in this work for each congeneric group relate the CMCs to this new descriptor. Statistical parameters of these models, as well as their predictivity, indicate the significance of the obtained equations, that is that the micelle formation is influenced not only by the number of OH and oxo groups in the steroid nucleus but also by their steric environment.

Interactions between selected bile salts and Triton X-100 or sodium lauryl ether sulfate

BackgroundIn order to develop colloidal drug carriers with desired properties, it is important to determine physico-chemical characteristics of these systems. Bile salt mixed micelles are extensively studied as novel drug delivery systems. The objective of the present investigation is to develop and characterize mixed micelles of nonionic (Triton X-100) or anionic (sodium lauryl ether sulfate) surfactant having oxyethylene groups in the polar head and following bile salts: cholate, deoxycholate and 7-oxodeoxycholate.ResultsThe micellization behaviour of binary anionic-nonionic and anionic-anionic surfactant mixtures was investigated by conductivity and surface tension measurements. The results of the study have been analyzed using Clints, Rubinghs, and Motomuras theories for mixed binary systems. The negative values of the interaction parameter indicate synergism between micelle building units. It was noticed that Triton X-100 and sodium lauryl ether sulfate generate the weakest synergistic interactions with sodium deoxycholate, while 7-oxodeoxycholate creates the strongest attractive interaction with investigated co-surfactants.ConclusionIt was concluded that increased synergistic interactions can be attributed to the larger number of hydrophilic groups at α side of the bile salts. Additionally, 7-oxo group of 7-oxodeoxycholate enhance attractive interactions with selected co-surfactants more than 7-hydroxyl group of sodium cholate.