When barriers ignore the "rule-of-five"

Why are a few drugs with properties beyond the rule of 5 (bRo5) absorbed across the intestinal mucosa while most other bRo5 compounds are not? Are such exceptional bRo5 compounds exclusively taken up by carrier-mediated transport or are they able to permeate the lipid bilayer (passive lipoidal diffusion)? Our experimental data with liposomes indicate that tetracycline, which violates one rule of the Ro5, and rifampicin, violating three of the rules, significantly permeate a phospholipid bilayer with kinetics similar to labetalol and metoprolol, respectively. Published data from experimental work and molecular dynamics simulations suggest that the formation of intramolecular H-bonds and the possibility to adopt an elongated shape besides the presence of a significant fraction of net neutral species facilitate lipid bilayer permeation. As an alternative to lipid bilayer permeation, carrier proteins can be targeted to improve absorption, with the potential drawbacks of drug-drug interactions and non-linear pharmacokinetics.

Noradrenaline increases intracellular glutathione in human astrocytoma U-251 MG cells by inducing glutamate-cysteine ligase protein via β3-adrenoceptor stimulation

Glutathione (GSH) plays a critical role in protecting cells from oxidative damage. Since neurons rely on the supply of GSH from astrocytes to maintain optimal intracellular GSH concentrations, the GSH concentration of astrocytes is important for the survival of neighboring neurons against oxidative stress. The neurotransmitter noradrenaline is known to modulate the functions of astrocytes and has been suggested to have neuroprotective properties in neurodegenerative diseases. To elucidate the mechanisms underlying the neuroprotective properties of noradrenaline, in this study, we investigated the effect of noradrenaline on the concentrations of intracellular GSH in human U-251 malignant glioma (MG; astrocytoma) cells. Treatment of the cells with noradrenaline for 24h concentration-dependently increased their intracellular GSH concentration. This increase was inhibited by a non-selective β-adrenoceptor antagonist propranolol and by a selective β3-adrenoceptor antagonist SR59230A, but not by a non-selective α-adrenoceptor antagonist phenoxybenzamine, or by a selective β1-adrenoceptor antagonist atenolol or by a selective β2-adrenoceptor antagonist butoxamine. In addition, the selective β3-adrenoceptor agonist CL316243 increased the intracellular GSH in U-251 MG cells. Treatment of the cells with noradrenaline (10μM) for 24h increased the protein level of the catalytic subunit of glutamate-cysteine ligase (GCLc), the rate-limiting enzyme of GSH synthesis; and this increase was inhibited by SR59230A. These results thus suggest that noradrenaline increased the GSH concentration in astrocytes by inducing GCLc protein in them via β3-adrenoceptor stimulation.

3D printing of five-in-one dose combination polypill with defined immediate and sustained release profiles

We have used three dimensional (3D) extrusion printing to manufacture a multi-active solid dosage form or so called polypill. This contains five compartmentalised drugs with two independently controlled and well-defined release profiles. This polypill demonstrates that complex medication regimes can be combined in a single personalised tablet. This could potentially improve adherence for those patients currently taking many separate tablets and also allow ready tailoring of a particular drug combination/drug release for the needs of an individual. The polypill here represents a cardiovascular treatment regime with the incorporation of an immediate release compartment with aspirin and hydrochlorothiazide and three sustained release compartments containing pravastatin, atenolol, and ramipril. X-ray powder diffraction (XRPD) and Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR) were used to assess drug-excipient interaction. The printed polypills were evaluated for drug release using USP dissolution testing. We found that the polypill showed the intended immediate and sustained release profiles based upon the active/excipient ratio used.

Norepinephrine responses in rat renal and femoral veins are reinforced by vasoconstrictor prostanoids

Norepinephrine (NE) responses are larger in renal and femoral veins compared to phenylephrine (PE). These differences may be due to the subtypes of adrenoceptor involved in these responses or to the involvement of local modulatory mechanisms. Therefore, the present study investigated in organ bath the adrenoceptor subtypes involved in the NE and PE responses in both renal and femoral veins as well as the influence of local mechanisms related to NO and to prostanoids upon these responses. The obtained data showed that the NE responses in these veins were not significantly modified by the selective inhibition of β1 or β2-adrenoceptors as well as AT1 or AT2 receptors. However, yohimbine reduced the NE Rmax in renal veins and, in parallel, right shifted the NE concentration-response curves in femoral veins. In both veins, prazosin reduced the NE Rmax and the clonidine induced a measurable contraction. The endothelium removal attenuated the NE responses in femoral veins, thereby abolishing the differences of NE and PE responses. Furthermore, the NE responses in renal and femoral veins were attenuated by indomethacin, which suppressed the statistical difference in relation to the PE response. In conclusion, a synergism between α1- and α2-adrenoceptors is essential to assure full NE contractile responses in both renal and femoral veins. Thus, by acting simultaneously in these adrenoceptors, NE induces more pronounced contractile responses, in comparison to PE, not only in renal but also in femoral veins. Moreover, this pronounced NE response in both renal and femoral veins appears to involve endothelium-derived vasoconstrictor prostanoids.

Setup and validation of shake-flask procedures for the determination of partition coefficients (logD) from low drug amounts

Several procedures based on the shake-flask method and designed to require a minimum amount of drug for octanol-water partition coefficient determination have been established and developed. The procedures have been validated by a 28 substance set with a lipophilicity range from -2.0 to 4.5 (logD7.4). The experimental partition is carried out using aqueous phases buffered with phosphate (pH 7.4) and n-octanol saturated with buffered water and the analysis is performed by liquid chromatography. In order to have accurate results, four procedures and eight different ratios between phase volumes are proposed. Each procedure has been designed and optimized (for partition ratios) for a specific range of drug lipophilicity (low, regular and high lipophilicity) and solubility (high and low aqueous solubility). The procedures have been developed to minimize the measurement in the octanolic phase. Experimental logD7.4 values obtained from different procedures and partition ratios show a standard deviation lower than 0.3 and there is a nice agreement when these values are compared with the reference literature ones.

Effects of hippadine on the blood pressure and heart rate in male spontaneously hypertensive Wistar rats

ETHNOPHARMACOLOGICAL RELEVANCE

Hippadine is an alkaloid isolated from Crinum macowanii. Crinum macowanii is used in South Africa to treat oedema, 'heart disease', rheumatic fever, cancer and skin diseases, and belongs to the plant family Amaryllidaceae, assumed to have originated in the South African region. The aim of this study was to evaluate the effect of hippadine, an alkaloid extracted from Crinum macowanii, on the blood pressure (BP) and heart rate (HR) in anaesthetized male spontaneously hypertensive Wistar rats (SHR); and to find out if α1 and⧸or β1 adrenoceptors contribute to its effects.

MATERIALS AND METHODS

Hippadine (2.5-12.5mg/kg), adrenaline (0.05-0.20mg/kg), atenolol (0.5-40mg/kg) and prazosin hydrochloride (100-500µg/kg) were infused intravenously, and the BP and HR measured via a pressure transducer connecting the femoral artery and the PowerLab. Adrenaline increased the systolic, diastolic and mean arterial BP, while hippadine, atenolol and prazosin respectively decreased the systolic, diastolic and mean arterial BP. Increases in HR were observed with both adrenaline and prazosin, while reductions in HR were observed with atenolol and hippadine. Infusion of adrenaline in rats pre-treated with atenolol (30mg/kg), prazosin (400µg/kg), and hippadine (10mg/kg) led to similar increases in BP and HR in all groups. All changes in HR or BP were significant (p<0.05) and dose dependent.

CONCLUSION

Hippadine decreases the BP and HR in SHR, and these effects may be due to α1 and β1 adrenoceptor inhibition.

Nanocarriers and the delivered drug: effect interference due to intravenous administration

Intravenously administered nanocarriers are widely studied to improve the delivery of various therapeutic agents. However, recent in vivo studies have demonstrated that intravenously administered nanocarriers that do not contain any drug may affect cardiovascular function. Here we provide an example where the drug and the nanocarrier both affect the same cardiovascular parameters following intravenous administration. The peptide ghrelin antagonist (GhA) increases arterial pressure, while thermally hydrocarbonized porous silicon nanoparticles (THCPSi) transiently decrease it, as assessed with radiotelemetry in conscious rats. As a result, intravenous administration of GhA-loaded THCPSi nanoparticles partially antagonized GhA activity: arterial pressure was not increased. When the cardiovascular effects of GhA were blocked with atenolol pretreatment, GhA-loaded nanoparticles reduced arterial pressure to similar extent as drug-free nanoparticles. These data indicate that the biological activity of a drug delivered within a nanocarrier may be obscured by the biological responses induced by the nanocarrier itself.