Transdermal delivery of β-blockers

β-Adrenoceptor blocking drugs (β-blockers) are one of the most frequently used class of cardiovascular drugs that are mainly used in conventional dosage forms., which have their own limitations including hepatic first-pass metabolism, high incidence of adverse effects due to variable absorption profiles, higher frequency of administration and poor patient compliance. Essentially, attempts have been made to develop novel drug delivery systems for β-blockers, including transdermal delivery systems, to circumvent the drawbacks of conventional drug delivery. However, so far none of the β-blocker drugs have been marketed as transdermal delivery systems. Nevertheless, there have been noteworthy research endeavours worldwide at the laboratory level to investigate the skin permeation and to develop transdermal formulations of β-blockers including: propranolol, metoprolol, atenolol, timolol, levobunolol, bupranolol, bopindolol, mepindolol, sotalol, labetolol, pindolol, acebutolol and oxprenolol. Innovative research exploiting penetration-enhancing strategies, such as iontophoresis, electroporation, microneedles and sonophoresis, holds promise for the successful use of these drugs as consumer-friendly transdermal dosage forms in clinical practice. This paper presents an overview of the transdermal research on this important class of drugs.     

Pharmaceutical evaluation of hydroxyalkyl ethers of β-cyclodextrins

Hydroxyalkylated β-cyclodextrins (HA-β-CyDs), 2-hydroxypropyl-β-cyclodextrin (HP-β-CyD), and hydroxyethyl-β-cyclodextrin (HE-β-CyD), were prepared and their physicochemical and biological properties and solubilizing abilities were studied and compared with those of parent β-cyclodextrin (β-CyD). HA-β-CyDs had much higher aqueous solubility ( > 50 w/v%) and were less hygroscopic than the parent β-CyD. Their surface activities were between those of β CyD and alkylated-β-cyclodextrins and were increased proportionately to their average degrees of substitution. The hemolytic activity (human erythrocytes) and local irritancy (rabbit muscle) of these compounds, and particularly of HE-β-CyD, were considerably less than those of natural cyclodextrin or dimethyl-β-cyclodextrin (DM-β-CyD). In contrast to surface activity, the hemolytic activity of HA-β-CyD decreased with the degree of substitution; possibly the difference in their ability to dissolve membrane components may be the reason. HA-β-CyDs were found to be powerful solubilizers of several drugs and no crystalline complexes were precipitated at high concentrations of solubilizer, a phenomenon which is often observed when β-CyD is used. HP-β-CyDs were somewhat better solubilizers than HE-β-CyDs and the preparations with the lower degrees of substitution were again better than those with the higher ones. The above data suggest that HA-β-CyDs are safer and more effective solubilizers for poorly water-soluble drugs than the parent cyclodextrin.     

The Development of β-Lactam Antibiotics in Response to the Evolution of β-Lactamases

beta-Lactam antibiotics, viz., penicillin, penicillin derivatives, cephalosporins, cephamycins, carbapenems, monobactams. and monocarbams, are the most widely used of all antimicrobial classes by virtue of their high efficacy and specificity and the availability of several derivatives. The expression of one or several beta-lactamases (beta-lactam antibiotic-inactivating enzymes) represents the most widespread and the most clinically relevant resistance mechanism to these antibiotics. The development of beta-lactam antibiotics has thus been a continuous battle of the design of new compounds to withstand inactivation by the ever-increasing diversity of beta-lactamases. This article traces antibiotic development in response to the evolution of beta-lactamases.     

Disposition of β-methyldigoxin in man

Summary The time course of radioactivity in plasma and the excretion in urine and faeces over 7 days were determined in 12 healthy subjects after single oral and intravenous doses of a solution of³H--methyldigoxin. 62.2±2.1 and 29.0±5.2 per cent of the dose were excreted in urine and faeces, respectively, within 7 days of intravenous administration, compared with 55.2±2.8 and 28.6±5.7 per cent after oral administration. This indicates almost complete absorption of the glycoside when given in solution. 12 hours after its administration a pseudo-distribution equilibrium was reached and the average half life of tritiated compounds was 1.3 days. By 48 – 96 hours after treatment the average half life was 2.8 days. O-demethylation was revealed as the main metabolic degradation step in man. The rate of Demethylation was higher after oral than i.v. administration. Thus, only 31% of the radioactivity excreted in the urine consisted of unchanged -methyldigoxin after oral administration compared to 51% after i.v. dosing. Only traces of bis- and monoglycosides were excreted in urine, but there were considerable amounts in faeces, where they accounted for more than 35% of the total excretion. Up to 40% of the radioactivity in plasma and urine consisted of polar conjugates during the first 12 hours after administration of -methyldigoxin. The mono- and bisglycosides were identified as the main products of conjugation. During the 7 days approximately 15% of the administered dose was metabolized by splitting off glycosidic bonds and conjugation to polar compounds.Supported by the Deutsche Forschungsgemeinschaft and by Boehringer Mannheim, Germany     

Statine-derived tetrapeptide inhibitors of β-secretase

Alzheimer’s disease (AD) is characterised by the accumulation of amyloid β-peptide (Aβ) within senile plaques in the brain. β-secretase is one of the enzymes necessary for the production of amyloid β-peptide from the amyloid precursor protein (APP), the other being γ-secretase. β-Secretase was recently characterised as a novel aspartyl protease. Statine-derived tetrapeptide inhibitors of this enzyme, described in this patent, may have therapeutic applications in AD.     

Opioid activities of human β-casomorphins

Summary Opioid activities of human -casomorphin-4,-5,-7 and -8 and, for comparison, of the corresponding bovine -casomorphins were studied in the guinea-pig ileum preparation. Binding parameters, i.e. K _d -values and binding site concentrations, for the interaction of human and bovine -casomorphins with opioid receptors in rat brain homogenates were determined in inhibition experiments, using [³H]-(d-Ala², MePhe⁴, Gly-ol⁵)enkephalin, [³H]-(d-Ala², d-Leu⁵)enkephalin and [³H]ethylketazocin as -, - and -opioid receptor ligands. Analysis of binding data was performed using a non-linear curve fitting program. All -casomorphins examined displayed opioid activity. The affinity was highest for -receptors, less so for -receptors and lowest for -receptors. It is suggested that human -casomorphins might play a role as food hormones.     

Different steric characteristics of β1- and β2-adrenoceptors

Summary -Adrenoceptors of lung (75% ₂) and heart (95% ₁) of calf were labelled with ³H-(–)-propranolol. The stereoisomers of 10 ligands were used to inhibit the binding of ³H-(–)-propranolol to membrane particles. The affinity ratio of sereoisomers is consistently greater for ₁-adrenoceptors than for ₂-adrenoceptors, regardless of whether the ligands are agonists, partial agonists or antagonists. The ₁-adrenoceptor appears to possess stricter steric requirements than the ₂-adrenoceptor. This property may prove helpful in differentiating the -adrenoceptor subtypes during receptor solubilization and purification.     

Genotoxicity assessment of β-caryophyllene oxide

β-caryophyllene oxide is a biciclic sesquiterpene, occurring naturally in essential oils from various medicinal and edible plants and used as a flavouring agent. Due to its potential hazardous chemical structure, the European Food Safety Authority reported to be pending a safety assessment for this compound. Here, this flavouring agent was tested for its mutagenic effect in the Ames test and micronucleus assay. Furthermore, considering that the penetration of a substance through phospholipid bilayers is determinant for its activity, the ability of β-caryophyllene oxide to be absorbed into cells was evaluated by differential scanning calorimetry (DSC) using multilamellar vesicles of dimyristoylphosphatidylcholine as a biomembrane model. β-caryophyllene oxide was found to be devoid of mutagenic effect, both at gene level (frameshift or base-substitution mutations), and on chromosome (clastogenicity and aneuploidogenicity). Results of DSC analysis highlighted that the substance was strongly absorbed through the membrane bilayer. Present results show that β-caryophyllene oxide, although absorbed through cell membranes and in spite of its potentially reactive chemical structure, is devoid of genotoxic effects, inducing neither point mutations nor chromosomal damages. These negative genotoxic findings will be critical to the safety assessment of β-caryophyllene oxide as used as a flavouring/fragrance ingredient.     

Mechanism of phthalate-induced inhibition of hepatic mitochondrial β-oxidation

Studies show that peroxisome proliferators inhibit mitochondrial β-oxidation of fatty acids. However, mechanism(s) of this inhibitory effect has not been identified. This study was undertaken to delineate such mechanism(s). Ketogenesis was significantly diminished in perfused livers from rats pre-treated with diethylhexyl phthalate (DEHP) compared with livers from control rats. Monoethylhexyl phthalate (MEHP; 200 μM), a primary metabolite of DEHP and a known peroxisome proliferator, inhibited the oxidation of palmitic acid as well as its acyl-CoA and acylcarnitine derivatives in isolated mitochondria by about 50–60%. Similar concentrations of MEHP also inhibited mitochondrial respiration of succinate and malate plus glutamate. However, respiration of ascorbate was not influenced by MEHP. Considering the assembly of the mitochondrial respiratory chain, these data indicate that phthalates inhibit fatty acid metabolism as a result of inhibiting the respiratory chain at the level of cytochrome c reductase. This effect may represent an early step in the mechanism by which phthalates cause hepatic proxisome proliferation.     

Delivery of Nasal Powders of β-Cyclodextrin by Insufflation

Purpose. Delivery of nasal powders of granulated -cyclodextrin by insufflation was studied in order to find the relationship between powder properties and delivery behavior. Methods. Three nasal powder formulations, prepared by granulating -cyclodextrin with different binders, were delivered from a powder insufflation device, in which the dose to be emitted was loaded in a gelatin capsule. The delivery sequence of powder was recorded and characterized using an image analysis program. Results. Particle size was the main parameter affecting nasal powder delivery, both as to the amount of dose sprayed and the aspect of cloud produced. Between 50–150 µm of particle size a substantial change in delivery behavior of powders was observed. Powder of around 100 µm in size showed useful insufflation characteristics for nasal delivery. Bioavailability of nasal formulations of progesterone/-cyclodextrin powders was discussed in term of delivery behavior. Conclusions. The formulation approaches for improving nasal delivery of powders require the use of size optimized carriers. Insufflation of powders over 50 µm can favour the particle deposition by impaction, whereas for powders below 50 µm, deposition by sedimentation is moved. -cyclodextrin is a suitable carrier for achieving high systemic availability following nasal administration of powder formulations.     

Antiviral activity of ammonium salts of β-alkylthiopropionic acids

A number of ammonium salts of -alkylthiopropionic acids and their oxidized derivatives, as well as two oxygen analogs and phenyl hydroxide, were synthesized and their antiviral activity was studied. Derivatives with a smaller alkyl radical (C₂-C₃) were found to have a higher antiviral activity. The results suggest that -alkylthiopropionic acid derivatives may be promising in the search for antiviral preparations.     

Synthesis and β-Adrenergic Activities of R-Fluoronaphthyloxypropanolamine

Purpose. Many biogenic amines where an aromatic proton is substituted with fluorine have exhibited pharmacological properties that are dependent on the position of fluorine on the aromatic ring. For example, 6-fluoroepinephrine is selective for -adrenergic receptors whereas the 2-fluoroisomer is selective for -receptors. Aryloxypropanolamines are -receptor agonists or antagonists, depending on the aryl group and its substituents. We therefore hypothesized that fluorine substitution on the aromatic ring could lead to significant biological effects in this class. A target with fluorine on naphthyl group of a known -antagonist was chosen for investigation. Methods. Synthesis of the target compound began with fluoronaphthalene and involved introduction of 4-hydroxy group by Friedel-Crafts acylation followed by Baeyer Villiger oxidation. The side chain was introduced stereoselectively using the chiral synthon (2R)-glycidyl 3-nitrobenzenesulfonate, a Sharpless epoxidation technique. The epoxide was opened with t-butyl amine. HPLC methods were used to characterize %ee of the enantiomer. Results. The target compound was synthesized in several hundred milligram quantity, and in good yield and high enantiomeric excess, showing practicality of the synthetic scheme. It exhibited potent binding activities on -adrenergic receptors, and was found to be two times selective for ₂-receptors over ₁. Conclusions. The current report demonstrates that aromatic fluorine substitution on -adrenergic ligands can be achieved, and that such can be used to obtain binding selectivity between receptors.     

Quantum chemical treatment of β-sitosterol molecule

β-Sitosterol is used as a dietary supplement for lowering plasma cholesterol, and has atherosclerosis preventive, anti-inflammatory, antimicrobial, antipyretic, induced apoptosis, and anticancer effects. In order to understand the effect of the molecule we have investigated the molecule theoretically. The structural, vibrational, and electronic properties of the β-sitosterol molecule have been investigated theoretically by performing molecular mechanics (MM+ force field), semiempirical self-consistent-field molecular-orbital (PM3), and density functional theory (B3LYP) calculations. The geometry of the considered molecule has been optimized; the vibrational dynamics and the electronic properties have been calculated in its ground state in the gas phase. The optimized structure of the molecule is not planar, and its heat of formation is exothermic. The calculated infrared spectrum for β-sitosterol agrees well qualitatively with the experimentally determined FTIR spectrum. The interfrontier molecular orbitals are localized mainly on the double C-C bond, and the energy difference of the corresponding orbitals is relatively small, which makes the molecule kinetically stable. According to the calculated dipole moment, β-sitosterol is a polar molecule. The calculated results for the β-sitosterol molecule in the present study will aid in elucidation of the mechanism of action and may further be used in lipid metabolism drug design studies.     

Investigation of hallucinogenic and related β-carbolines

Certain β-carbolines are known to be hallucinogenic in humans, and several produce stimulus effects in animals similar to those of the classical hallucinogen 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM). Classical hallucinogens bind at 5-HT₂ serotonin receptors and these receptors are thought to play a role in their mechanism of action. In the present study, we examined the binding of 15 β-carbolines at rat 5-HT_2A and 5-HT_2C receptors. Affinities (K_i values) of the β-carbolines ranged from about 100 nM to greater than 10 000 nM depending upon the degree of saturation of the pyridyl ring, and upon the presence and location of methoxy substituents in the benzenoid ring. In a further study, six rats were trained to discriminate the hallucinogenic β-carboline harmaline (3.0 mg/kg, i.p.) from vehicle using a VI-15s schedule of reinforcement. This represents the first time a hallucinogenic β-carboline has been used as a training drug in a drug discrimination study. Administration of DOM to the harmaline-trained animals resulted in 76% harmaline-appropriate responding at 1.25 mg/kg DOM and disruption of behavior at a higher dose. Taken together, the results of the present investigation demonstrate that: (a) certain β-carbolines bind at 5-HT₂ receptors; (b) that harmaline serves as a training drug at 3.0 mg/kg in drug discrimination studies with rats as subjects; and that (c) there is some similarity between the stimulus effects produced by harmaline and DOM.     

Differential aversive stimulus properties of β-phenylethylamine and of d-amphetamine

In a conditioned taste-aversion experiment with male Wistar rats (two-bottle test, single pairing), the effects of -phenylethylamine (PEA 12.5, 25.0, 50.0, 100.0 mg/kg IP) and of d-amphetamine (2.5 mg/kg IP) were compared with the effect of the saline vehicle. The amphetamine-treated group exhibited a marked aversion to saccharin on each of four retention trials. A decrease in saccharin intake after PEA was limited to the highest dose group (100 mg/kg) and the first retention trial for that group. Doses of up to 50 mg/kg of PEA were also ineffective with a single-bottle conditioned taste-aversion procedure involving multiple conditioning trials, although doses of 25 and 50 mg/kg of PEA induced marked changes in spontaneous motor activity. These data demonstrate that behaviourally active doses of PEA are ineffective in inducing a conditioned taste aversion to saccharin. This result extends previous reports that structurally similar compounds may have different potencies in this paradigm. It is proposed that further studies of structureactivity relationships may help to reveal the features of drug action that are necessary for the induction of a conditioned taste aversion.     

A set of multiplex PCRs for genotypic detection of extended-spectrum β-lactamases, carbapenemases, plasmid-mediated AmpC β-lactamases and OXA β-lactamases

Worldwide, resistance of Gram-negative micro-organisms to third-generation cephalosporins and carbapenems owing to β-lactamases is an increasing problem. Although the CTX-M, TEM and SHV extended-spectrum β-lactamases (ESBLs) are most widely disseminated, other β-lactamase families have also recently emerged, such as plasmid-mediated AmpC β-lactamases and carbapenemases. Here we describe a new set of multiplex polymerase chain reactions (PCRs) with one amplification protocol enabling detection of 25 prevalent β-lactamase families, including ESBLs, carbapenemases, plasmid-mediated AmpC β-lactamases and OXA β-lactamases.     

Inhibition of the Formation of the Alzheimer's β-Amyloid Peptide

Anorexia and body weight loss are characteristic of many diseases, including cancer and AIDS. Neuropeptides play a pivotal role in the physiological mechanisms regulating food intake and body weight. Neuropeptide Y (NPY) is a key molecule of the orexigenic network for energy intake and for normal adaptive feeding response to energy deficits. Therefore, the NPY receptors (notably, Y1 and Y5) may be one of the most significant target classes for treatment of anorexia and body weight loss. In addition, several anorexigenic peptides including corticotropin-releasing factor (CRF), cholecystokinin (CCK), leptin and melanocortin (MC) are emerging as potential targets for anorexia. Antagonists for CRF 2 receptor, CCK A receptor, MC 4 receptor and leptin receptor may be useful in stimulating food intake. The development of highly specific and selective non-peptide antagonists for these receptors is awaited. Anorexia is a crucial and critical disease. Increasing knowledge of its pathophysiology could lead to innovative new medicines for anorexia-cachexia syndrome.     

Study of the Complexation Behaviour of Fexofenadine with β-Cyclodextrin

Fexofenadine is a selective histamine H(1) receptor antagonist, used for relief of the symptoms of allergy. However its aqueous solubility is very poor. Solid inclusion complexes of fexofenadine and β-cyclodextrin were prepared at the molar ratios of 1:1 and 1:2 by kneading, and coprecipitation methods to improve its solubility. Characterization of the complexes was performed using infrared spectroscopy, X-ray diffractometry, and in vitro dissolution studies. Fexofenadine was found to exhibit interaction with β-cyclodextrin both in solid and liquid state. Phase solubility studies indicated that fexofenadine forms a stable complex with β-cyclodextrin. Both IR spectroscopy and X-ray diffractometry studies indicated interaction of fexofenadine with β-cyclodextrin. Kneading method at 1:1 and co-precipitation method at 1:1 and 1:2 molar ratios showed significant interaction. In vitro dissolution studies confirmed the same results.