L-EGCG-Mn nanoparticles as a pH-sensitive MRI contrast agent

This study aimed to synthesize and characterize L-epigallocatechin gallate (EGCG) complexed Mn²⁺ nanoparticle (L-EGCG-Mn), a proof-of-concept pH-sensitive manganese core nanoparticle (NP), and compare its magnetic resonance (MR) properties with those of Gd-DTPA, both in vitro and in vivo. Reverse microemulsion was used to obtain the L-EGCG-Mn NPs. The physicochemical properties of L-EGCG-Mn were characterized using dynamic light scattering, transmission electron microscopy, and near-infrared fluorescence small animal live imaging. The in vitro relaxivity of L-EGCG-Mn incubated with different pH buffer solutions (pH = 7.4, 6.8, 5.5) was evaluated. The T1-weighted MR imaging (MRI) properties were evaluated in vitro using hypoxic H22 cells as well as in H22 tumor-bearing mice. Cytotoxicity tests and histological analysis were performed to evaluate the safety of L-EGCG-Mn. L-EGCG-Mn showed good biocompatibility, stability, pH sensitivity, and tumor-targeting ability. Moreover, when the pH was decreased from 7.4 to 5.5, the r₁ relaxivity of L-EGCG-Mn was shown to gradually increase from 1.79 to 6.43 mM⁻¹·s⁻¹. Furthermore, after incubation with L-EGCG-Mn for 4 h, the T1 relaxation time of hypoxic H22 cells was significantly lower than that of normoxic H22 cells (1788 ± 89 vs. 1982 ± 68 ms, p=.041). The in vivo analysis showed that after injection, L-EGCG-Mn exhibited a higher MRI signal compared to Gd-DTPA in H22 tumor-bearing mice (p < .05). Furthermore, L-EGCG-Mn was found to have a good safety profile via cytotoxicity tests and histological analysis. L-EGCG-Mn has a good safety profile and pH sensitivity and may thus serve as a potential MRI contrast agent.     

Biodegradable hollow mesoporous organosilica nanotheranostics (HMONs) as a versatile platform for multimodal imaging and phototherapeutic-triggered endolysosomal disruption in ovarian cancer

A major impediment in the development of nanoplatform-based ovarian cancer therapy is endo/lysosome entrapment. To solve this dilemma, a hollow mesoporous organosilica-based nanoplatform (HMON@CuS/Gd₂O₃) with a mild-temperature photothermal therapeutic effect and multimodal imaging abilities was successfully synthesized. HMON@CuS/Gd₂O₃ exhibited an appropriate size distribution, L-glutathione (GSH)-responsive degradable properties, and high singlet oxygen generation characteristics. In this study, the nanoplatform specifically entered SKOV-3 cells and was entrapped in endo/lysosomes. With a mild near infrared (NIR) power density (.5 W/cm²), the HMON@CuS/Gd₂O₃ nanoplatform caused lysosome vacuolation, disrupted the lysosomal membrane integrity, and exerted antitumour effects in ovarian cancer. Additionally, our in vivo experiments indicated that HMON@CuS/Gd₂O₃ has enhanced T1 MR imaging, fluorescence (FL) imaging (wrapping fluorescent agent), and infrared thermal (IRT) imaging capacities. Using FL/MRI/IRT imaging, HMON@CuS/Gd₂O₃ selectively caused mild phototherapy in the cancer region, efficiently inhibiting the growth of ovarian cancer without systemic toxicity in vivo. Taken together, the results showed that these well-synthesized nanoplatforms are likely promising anticancer agents to treat ovarian cancer and show great potential for biomedical applications.     

Stimulation of angiotensin AT2 receptors by the non-peptide agonist,Compound 21, evokes vasodepressor effects in conscious spontaneously hypertensive rats

Background and purpose:

Angiotensin type 2 receptor (AT₂ receptor) stimulation evokes vasodilator effects in vitro and in vivo that oppose the vasoconstrictor effects of angiotensin type 1 receptors (AT₁ receptors). Recently, a novel non-peptide AT₂ receptor agonist, Compound 21, was described, which exhibited high AT₂ receptor selectivity.

Experimental approach:

Functional cardiovascular effects of the drug candidate Compound 21 were assessed, using mouse isolated aorta and rat mesenteric arteries in vitro and in conscious spontaneously hypertensive rats (SHR).

Key results:

Compound 21 evoked dose-dependent vasorelaxations in aortic and mesenteric vessels, abolished by the AT₂ receptor antagonist, PD123319. In vivo, Compound 21 administered alone, at doses ranging from 50 to 1000 ng·kg⁻¹·min⁻¹ over 4 h did not decrease blood pressure in conscious normotensive Wistar-Kyoto rats or SHR. However, when given in combination with the AT₁ receptor antagonist, candesartan, Compound 21 (300 ng·kg⁻¹·min⁻¹) lowered blood pressure in SHR only. Further analysis in separate groups of conscious SHR revealed that, at a sixfold lower dose, Compound 21 (50 ng·kg⁻¹·min⁻¹) still evoked a significant depressor response in adult SHR (∼30 mmHg) when combined with different doses of candesartan (0.01 or 0.1 mg·kg⁻¹). Moreover, the Compound 21-evoked depressor effect was abolished when co-infused (50 µg·kg⁻¹·min⁻¹ for 2 h) with the AT₂ receptor antagonist PD123319.

Conclusion and implications:

Collectively, our results indicate that acute administration of Compound 21 evoked blood pressure reductions via AT₂ receptor stimulation. Thus Compound 21 can be considered an excellent drug candidate for further study of AT₂ receptor function in cardiovascular disease.     

Human microdose evaluation of the novel EP1 receptor antagonist GSK269984A

AIM

The primary objective was to evaluate the pharmacokinetics (PK) of the novel EP₁ antagonist GSK269984A in human volunteers after a single oral and intravenous (i.v.) microdose (100 µg).

METHOD

GSK269984A was administered to two groups of healthy human volunteers as a single oral (n= 5) or i.v. (n= 5) microdose (100 µg). Blood samples were collected for up to 24 h and the parent drug concentrations were measured in separated plasma using a validated high pressure liquid chromatography-tandem mass spectrometry method following solid phase extraction.

RESULTS

Following the i.v. microdose, the geometric mean values for clearance (CL), steady-state volume of distribution (V_ss) and terminal elimination half-life (t_1/2) of GSK269984A were 9.8 l h⁻¹, 62.8 l and 8.2 h. C_max and AUC(0,∞) were 3.2 ng ml⁻¹ and 10.2 ng ml⁻¹ h, respectively; the corresponding oral parameters were 1.8 ng ml⁻¹ and 9.8 ng ml⁻¹ h, respectively. Absolute oral bioavailability was estimated to be 95%. These data were inconsistent with predictions of human PK based on allometric scaling of in vivo PK data from three pre-clinical species (rat, dog and monkey).

CONCLUSION

For drug development programmes characterized by inconsistencies between pre-clinical in vitro metabolic and in vivo PK data, and where uncertainty exists with respect to allometric predictions of the human PK profile, these data support the early application of a human microdose study to facilitate the selection of compounds for further clinical development.     

The plasma–occupancy relationship of the novel GABAA receptor benzodiazepine site ligand, α5IA,is similar in rats and primates

Background and purpose:

α5IA (3-(5-methylisoxazol-3-yl)-6-[(1-methyl-1,2,3-triazol-4-yl)methyloxy]-1,2,4-triazolo[3,4-a]phthalazine) is a triazolophthalazine with subnanomolar affinity for α1-, α2-, α3- and α5-containing GABA_A receptors. Here we have evaluated the relationship between plasma α5IA concentrations and benzodiazepine binding site occupancy in rodents and primates (rhesus monkey).

Experimental approach:

In awake rats, occupancy was measured at various times after oral dosing with α5IA (0.03–30 mg·kg⁻¹) using an in vivo {[³H]flumazenil (8-fluoro 5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5-a][1,4]benzodiazepine-3-carboxylic acid ethyl ester)} binding assay. In anaesthetized rhesus monkeys, occupancy was measured using {[¹²³I]iomazenil (ethyl 5,6-dihydro-7-iodo-5-methyl-6-oxo-4H-imidazo[1,5-a][1,4]benzodiazepine-3-carboxylic acid ethyl ester)} γ-scintigraphy and a bolus/infusion paradigm. In both rat and rhesus monkey, the plasma drug concentration corresponding to 50% occupancy (EC₅₀) was calculated.

Key results:

In rats, α5IA occupancy was dose- and time-dependent with maximum occupancy occurring within the first 2 h. However, rat plasma EC₅₀ was time-independent, ranging from 42 to 67 ng·mL⁻¹ over a 24 h time course with the average being 52 ng·mL⁻¹ (i.e. occupancy decreased as plasma drug concentrations fell). In rhesus monkeys, the EC₅₀ for α5IA displacing steady-state [¹²³I]iomazenil binding was 57 ng·mL⁻¹.

Conclusions and implications:

Rat plasma EC₅₀ values did not vary as a function of time indicating that α5IA dissociates readily for the GABA_A receptor in vivo. These data also suggest that despite the different assays used (terminal assays of [³H]flumazenil in vivo binding in rats and [¹²³I]iomazenil γ-scintigraphy in anaesthetized rhesus monkeys), these techniques produced similar plasma α5IA EC₅₀ values (52 and 57 ng·mL⁻¹ respectively) and that the plasma–occupancy relationship for α5IA translates across these two species.     

Simultaneous Effect of Temperature and Irradiance on Growth and Okadaic Acid Production from the Marine Dinoflagellate Prorocentrum belizeanum

Benthic marine dioflagellate microalgae belonging to the genus Prorocentrum are a major source of okadaic acid (OA), OA analogues and polyketides. However, dinoflagellates produce these valuable toxins and bioactives in tiny quantities, and they grow slowly compared to other commercially used microalgae. This hinders evaluation in possible large-scale applications. The careful selection of producer species is therefore crucial for success in a hypothetical scale-up of culture, as are appropriate environmental conditions for optimal growth. A clone of the marine toxic dinoflagellate P. belizeanum was studied in vitro to evaluate its capacities to grow and produce OA as an indicator of general polyketide toxin production under the simultaneous influence of temperature (T) and irradiance (I₀). Three temperatures and four irradiance levels were tested (18, 25 and 28 °C; 20, 40, 80 and 120 µE·m⁻²·s⁻¹), and the response variables measured were concentration of cells, maximum photochemical yield of photosystem II (PSII), pigments and OA. Experiments were conducted in T-flasks, since their parallelepipedal geometry proved ideal to ensure optically thin cultures, which are essential for reliable modeling of growth-irradiance curves. The net maximum specific growth rate (µ_m) was 0.204 day⁻¹ at 25 °C and 40 µE·m⁻²·s⁻¹. Photo-inhibition was observed at I₀ > 40 μEm⁻²s⁻¹, leading to culture death at 120 µE·m⁻²·s⁻¹ and 28 °C. Cells at I₀ ≥ 80 µE·m⁻²·s⁻¹ were photoinhibited irrespective of the temperature assayed. A mechanistic model for µ_m-I₀ curves and another empirical model for relating µ_m-T satisfactorily interpreted the growth kinetics obtained. ANOVA for responses of PSII maximum photochemical yield and pigment profile has demonstrated that P. belizeanum is extremely light sensitive. The pool of photoprotective pigments (diadinoxanthin and dinoxanthin) and peridinin was not able to regulate the excessive light-absorption at high I₀-T. OA synthesis in cells was decoupled from optimal growth conditions, as OA overproduction was observed at high temperatures and when both temperature and irradiance were low. T-flask culture observations were consistent with preliminary assays outdoors.     

Local neurogenic regulation of rat hindlimb circulation: CO2-induced release of calcitonin gene-related peptide from sensory nerves

1. The mechanism of release of calcitonin gene-related peptide (CGRP) from sensory nerves in response to skeletal muscle contraction was investigated in the rat hindlimb in vivo and in vitro.
2. In the anaesthetized rat, sciatic nerve stimulation at 10 Hz for 1 min caused a hyperaemic response in the hindlimb. During the response, partial pressure of CO₂ in the venous blood effluent from the hindlimb significantly increased from 43±3 to 73±8 mmHg, whereas a small decrease in pH and no appreciable change in partial pressure of O₂ were observed.
3. An intra-arterial bolus injection of NaHCO₃ (titrated to pH 7.2 with HCl), which elevated PCO₂ of the venous blood, caused a sustained increase in regional blood flow of the iliac artery. Capsaicin (0.33 μmol kg⁻¹, i.a.) and a specific calcitonin gene-related peptide (CGRP) receptor antagonist, CGRP(8–37), (100 nmol kg⁻¹ min⁻¹, i.v.) significantly suppressed the hyperaemic response to NaHCO₃. Neither ND_Ω-nitro-L-arginine methyl ester (1 μmol kg⁻¹ min⁻¹, i.v.) nor indomethacin (5 mg kg⁻¹, i.v.) affected the response.
4. The serum level of CGRP-like immunoreactivity in the venous blood was significantly increased by a bolus injection of NaHCO₃ (pH=7.2) from 50±4 to 196±16 fmol ml⁻¹.
5. In the isolated hindlimb perfused with Krebs-Ringer solution, a bolus injection of NaHCO₃ (pH=7.2) caused a decrease in perfusion pressure which was composed of two responses, i.e., an initial transient response and a slowly-developing long-lasting one. CGRP(8–37) significantly inhibited the latter response by 73%.
6. These results suggest that CO₂ liberated from exercising skeletal muscle activates capsaicin-sensitive perivascular sensory nerves locally, which results in the release of CGRP from their peripheral endings, and then the released peptide causes local vasodilatation.

     

Reduction of urinary 8-epi-prostaglandin F2α during cyclo-oxygenase inhibition in rats but not in man

1. 8-epi-prostaglandin (PG) F_2α, a major F₂ isoprostane, is produced in vivo by free radical-dependent peroxidation of lipid-esterified arachidonic acid. Both cyclo-oxygenase isoforms (COX-1 and COX-2) may also form free 8-epi-PGF_2α as a minor product. It has been recently seen in human volunteers that the overall basal formation of 8-epi-PGF_2α in vivo is mostly COX-independent and urinary 8-epi-PGF_2α is therefore an accurate marker of ‘basal'' oxidative stress in vivo.
2. To test the validity of this marker in the rat, we evaluated in vivo the effect of COX inhibition on the formation of 8-epi-PGF_2α vs prostanoids. Two structurally unrelated COX inhibitors (naproxen: 30 mg kg⁻¹ day⁻¹; indomethacin: 4 mg kg⁻¹ day⁻¹) were given i.p. to rats kept in metabolic cages. In vivo formation of 8-epi-PGF_2α was assessed by measuring its urinary excretion. Prostanoid biosynthesis was assessed by measuring urinary excretion of major metabolites of thromboxane (TX) and prostacyclin (2,3-dinor-TXB₁ and 2,3-dinor-6-keto-PGF_1α). All compounds were selectively measured by immunopurification/gas chromatography-mass spectrometry.
3. Naproxen reduced urinary excretion of 2,3-dinor-TXB₁ and 2,3-dinor-6-keto-PGF_1α but, unexpectedly, also that of 8-epi-PGF_2α (82, 49 and 52% inhibition, respectively). Indomethacin had a similar effect (77, 69 and 55% inhibition). Esterified 8-epi-PGF_2α in liver and plasma remained unchanged after indomethacin.
4. These findings prompted us to re-assess the contribution of COX activity to the systemic production of 8-epi-PGF_2α in man. We gave naproxen (1 g day⁻¹) to healthy subjects (four nonsmokers and four smokers). Urinary 8-epi-PGF_2α remained unchanged in the two groups (9.63±0.99 before vs 10.24±1.01 after and 20.14±3.00 vs 19.03±2.45 ng h⁻¹ 1.73 m⁻²), whereas there was a marked reduction of major urinary metabolites of thromboxane and prostacyclin (about 90% for both 11-dehydro-TXB₂ and 2,3-dinor-TXB₂; >50% for 2,3-dinor-6-keto-PGF_1α).
5. To investigate whether rat COX-1 produces 8-epi-PGF_2α more efficiently than human COX-1, we measured the ex vivo formation of 8-epi-PGF_2α and TXB₂ simultaneously in whole clotting blood. Serum levels of 8-epi-PGF_2α and TXB₂ were similar in rats and man.
6. We conclude that a significant amount of COX-dependent 8-epi-PGF_2α is present in rat but not in human urine under normal conditions. This implies that urinary 8-epi-PGF_2α cannot be used as an index of near-basal oxidant stress in rats. On the other hand, our data further confirm the validity of this marker in man.

     

A validated HPTLC method for determination of terbutaline sulfate in biological samples: Application to pharmacokinetic study

Terbutaline sulfate (TBS) was assayed in biological samples by validated HPTLC method. Densitometric analysis of TBS was carried out at 366 nm on precoated TLC aluminum plates with silica gel 60F₂₅₄ as a stationary phase and chloroform–methanol (9.0:1.0, v/v) as a mobile phase. TBS was well resolved at R_F 0.34 ± 0.02. In all matrices, the calibration curve appeared linear (r² ⩾ 0.9943) in the tested range of 100–1000 ng spot⁻¹ with a limit of quantification of 18.35 ng spot⁻¹. Drug recovery from biological fluids averaged ⩾95.92%. In both matrices, rapid degradation of drug favored and the T_0.5 of drug ranged from 9.92 to 12.41 h at 4 °C and from 6.31 to 9.13 h at 20 °C. Frozen at −20 °C, this drug was stable for at least 2 months (without losses >10%). The maximum plasma concentration (Cp_max) was found to be 5875.03 ± 114 ng mL⁻¹, which is significantly higher than the maximum saliva concentration (Cs_max, 1501.69 ± 96 ng mL⁻¹). Therefore, the validated method could be used to carry out pharmacokinetic studies of the TBS from novel drug delivery systems.     

Antioxidant and anti-inflammatory effects of Marrubium alysson extracts in high cholesterol-fed rabbits

The antioxidant and anti-inflammatory effects of hexane (HEXA), chloroform (CHLORO), ethyl acetate (EA) and total alcoholic (T. ALCOH) extracts of Marrubium alysson in hypercholesterolemic-fed rabbits were evaluated. Hypercholesterolemia was induced in male rabbits by high cholesterol diet (HCD) (350 mg/kg) for 8 weeks. Hypercholesterolemic rabbits were allocated into groups, treated with simvastatin (SIM 5 mg/kg), different extracts of M. alysson at two doses of 250, 500 mg/kg. A normal control group and an HCD control one were used for comparison. Lipid profile, as well as oxidized low density lipoprotein-cholesterol (ox-LDL-C), myeloperoxidase activity (MPO) and superoxide anion production (O₂•⁻), C-reactive protein (CRP) and monocyte chemoattractant protein-1 (MCP-1) were also evaluated. In addition, histological examination of ascending aorta was performed. We found dyslipidemia associated with significant increases in ox-LDL-C 123.5 ± 9.8 nmol MDA/mg non-HDL, MPO activity 0.08 ± 0.05 U/100 mg tissue and O₂•⁻ production 3.5 ± 0.3 nmol cytochrome C reduced/min/g tissue × 10⁻⁴ in hypercholerterolemic rabbits. In addition, there was a significant increase in CRP 6.6 ± 0.49 μmol/L and MCP-1 190.9 ± 6.4 pg/ml and its mRNA expression in HCD. Intima appeared thick with thick plaques surrounding the intima and luminal narrowing. SIM, EA and HEXA extracts of M. alysson had lipid lowering effect, decrease in ox-LDL-C, MPO, O₂•⁻, CRP and MCP-1 mRNA expression with improvement of the pathological picture. M. alysson enhanced the stability of plaque, had lipid lowering, anti-inflammatory and antioxidant activities.     

Selectivity of action of 8-alkylamino analogues of N6-cyclopentyladenosine in vivo: haemodynamic versus anti-lipolytic responses in rats

1. A₁ adenosine receptor agonists with reduced intrinsic activity may be therapeutically useful as result of an increased selectivity of action. In this study the tissue selectivity of three 8-alkylamino substituted analogues of N⁶-cyclopentyladenosine (CPA) was investigated for haemodynamic and anti-lipolytic effects using an integrated pharmacokinetic-pharmacodynamic approach.
2. Chronically instrumented male Wistar rats received intravenous infusions of 4.0 mg kg⁻¹ 8-methylaminoCPA (8MCPA), 12.0 mg kg⁻¹ 8-ethylaminoCPA (8ECPA), 20.0 mg kg⁻¹ 8-butylaminoCPA (8BCPA) or vehicle during 15 min. During experimentation, serial arterial blood samples were drawn for the determination of agonist concentrations and plasma non-esterified fatty acid (NEFA) levels. Blood pressure and heart rate were monitored continuously. In addition to the CPA analogues, each rat received a rapid bolus infusion of CPA to determine the maximal effects of the full agonist.
3. The concentration-time profiles of the CPA analogues could be described by a bi-exponential function. Values for clearance, volume of distribution at steady state and elimination half-life were 44±5, 48±6 and 39±2 ml min⁻¹ kg⁻¹, 0.97±0.09, 0.84±0.10 and 1.05±0.07 1 kg⁻¹ and 25±2, 28±2 and 40±2 min for 8MCPA, 8ECPA and 8BCPA, respectively (mean±s.e.mean, n=6–8).
4. Different models were used to derive the concentration-effect relationships for heart rate and NEFA, yielding estimates of potency (EC₅₀) and instrinsic activity (E_max) for both effects of the compounds in vivo. On heart rate the compounds acted as partial agonists, with E_max values of −173±14, −131±11 and −71±6 beats min⁻¹ for 8MCPA, 8ECPA and 8BCPA, respectively. These E_max values were significantly lower than the maximal effect of CPA (−208±8 beats min⁻¹). With regard to the anti-lipolytic effect all three compounds were full agonists and lowered NEFA levels to the same extent as CPA (69%). The estimated E_max values were 63±5, 63±4 and 68±2%, respectively.
5. Furthermore, the compounds were more potent in causing anti-lipolytic than cardiovascular effects. The EC₅₀ values for the NEFA and heart rate lowering effects were 37±15, 68±22 and 659±108 ng ml⁻¹ and 164±22, 341±76 and 975±190 ng ml⁻¹ for 8MCPA, 8ECPA and 8BCPA, respectively (mean±s.e.mean, n=6–8).
6. This study demonstrates that partial agonists for the A₁ adenosine receptor have increased selectivity of action in vivo. The 8-alkylamino analogues of CPA may be useful anti-lipolytics with less pronounced haemodynamic side effects.

     

Regulation of the inducible cyclo-oxygenase pathway in human cultured airway epithelial (A549) cells by nitric oxide

1. In airway epithelium, nitric oxide (NO) is synthesized in the setting of inflammation by inducible nitric oxide synthase (iNOS). Although the role of epithelial derived NO in the regulation of human airways is unknown, prostaglandin E₂ (PGE₂) is recognised as an important inhibitory mediator in human airways. Cyclo-oxygenase (COX) is the rate limiting enzyme in the production of prostanoids and since inflammatory pathways enhance the expression of an inducible COX (COX-2), both COX-2 and iNOS may be co-expressed in response to an inflammatory stimulus. Although regulation of the COX-2 pathway by NO has been demonstrated in animal models, its potential importance in human airway epithelium has not been investigated.
2. The effect of endogenous and exogenous NO on the COX-2 pathway was investigated in the A549 human airway epithelial cell culture model. Activity of the COX-2 pathway was assessed by PGE₂ EIA, and iNOS pathway activity by nitrite assay. A combination cytokine stimulus of interferon gamma (IFNγ) 100 u ml⁻¹, interleukin-1β (IL-1β) 1 u ml⁻¹ and lipopolysaccharide (LPS) 10 μg ml⁻¹ induced nitrite formation which could be inhibited by the competitive NOS inhibitor N^G-nitro-L-arginine-methyl-ester (L-NAME). IL-1β alone (1–50 u ml⁻¹) induced PGE₂ formation without significant nitrite formation, a response which was inhibited by the COX-2 specific inhibitor nimesulide. Submaximal stimuli used for further experiments were IFNγ 100 u ml⁻¹, IL-1β 1 u ml⁻¹ and LPS 10 μg ml⁻¹ to induce both the iNOS and COX-2 pathways, and IL-1β 3 u ml⁻¹ to induce COX-2 without iNOS activity.
3. Cells treated with IFNγ 100 u ml⁻¹, IL-1β 1 u ml⁻¹ and LPS 10 μg ml⁻¹ for 48 h either alone, or with the addition of L-NAME (0 to 10⁻² M), demonstrated inhibition by L-NAME of PGE₂ (3.61±0.55 to 0.51±0.04 pg/10⁴ cells; P<0.001) and nitrite (34.33±8.07 to 0 pmol/10⁴ cells; P<0.001) production. Restoration of the PGE₂ response (0.187±0.053 to 15.46±2.59 pg/10⁴ cells; P<0.001) was observed after treating cells with the same cytokine stimulus and L-NAME 10⁻⁶ M, but with the addition of the NOS substrate L-arginine (0 to 10⁻⁵ M).
4. Cells incubated with IL-1β 3 u ml⁻¹ for 6 h, either alone or with addition of the NO donor S-nitroso-acetyl-penicillamine (SNAP) (0 to 10⁻⁴ M), demonstrated increased PGE₂ formation (1.23±0.03 to 2.92±0.19 pg/10⁴ cells; P< 0.05). No increase in PGE₂ formation was seen when the experiment was repeated in the presence of the guanylate cyclase inhibitor methylene blue (50 μM). Cells treated with SNAP alone did not demonstrate an increased PGE₂ formation. Cells incubated with IL-1β 3 u ml⁻¹ for 6 h in the presence of dibutyryl cyclic guanylate monophosphate (0 to 10⁻³ M) also demonstrated an increased PGE₂ response (2.56±0.21 to 4.53±0.64 pg/10⁴ cells; P<0.05).
5. These data demonstrate that in a human airway epithelial cell culture system, both exogenous and endogenous NO increase the activity of the COX-2 pathway in the setting of inflammatory cytokine stimulation, and that this effect is likely to be mediated by guanylate cyclase. This suggests a role for NO in the regulation of human airway inflammation.

     

Renal effects of intrathecally injected tachykinins in the conscious saline-loaded rat: receptor and mechanism of action

1. The effects of intrathecally (i.t.) injected substance P (SP), neurokinin A (NKA), [β-Ala⁸]NKA (4–10) and [MePhe⁷]neurokinin B (NKB) at T₁₃ thoracic spinal cord level were investigated on renal excretion of water, sodium and potassium in the conscious saline-loaded rat. Antagonists selective for NK₁ (RP 67580), NK₂ (SR 48968) and NK₃ (R 820; 3-indolylcarbonyl-Hyp-Phg-N(Me)-Bzl) receptors were used to characterize the spinal effect of SP on renal function.
2. Saline gavage (4.5% of the body weight) enhanced renal excretion of water, sodium and potassium over the subsequent hour of measurement. Whereas these renal responses were not affected by 0.65 nmol SP, the dose of 6.5 nmol SP blocked the natriuretic response (aCSF value 3.9±0.8; SP value 0.7±0.3 μmol min⁻¹, P<0.01) as well as the renal excretion of water (aCSF value 48.9±5.8; SP value 14.5±4.0 μl min⁻¹, P<0.01) and potassium (aCSF value 4.8±0.6; SP value 1.5±0.6 μmol min⁻¹, P<0.01) at 30 min post-injection. SP had no significant effect on urinary osmolality. The SP-induced renal inhibitory effects during the first 30 min were abolished in rats subjected to bilateral renal denervation 1 week earlier or in rats injected i.t. 5 min earlier with 6.5 nmol RP 67580. In contrast, the co-injection of SR 48968 and R 820 (6.5 nmol each) did not affect the inhibitory responses to SP. On their own, these antagonists had no direct effect on renal excretion function. Since SP induced only transient changes in mean arterial blood pressure (−18.8±3.8 mmHg at 1 min and +6.3±2.4 mmHg at 5 min post-injection), it is unlikely that the renal effects of SP are due to systemic haemodynamic changes.
3. NKA (6.5 nmol but not 0.65 nmol) produced a transient drop in renal excretion of water (aCSF value 31.2±5.1; NKA value 11.3±4.2 μl min⁻¹, P<0.05), sodium (aCSF value 1.7±0.8; NKA value 0.4±0.2 μmol min⁻¹, P<0.05) and potassium (aCSF value 4.1±0.7; NKA value 1.5±0.4 μmol min⁻¹, P<0.05) at 15 min post-injection. However, the same doses (6.5 nmol) of selective agonists for tachykinin NK₂ ([β-Ala⁸]NKA(4-10)) and NK₃ ([MePhe⁷]NKB) receptors were devoid of renal effects.
4. This study provided functional evidence that tachykinins may be involved in the renal control of water and electrolyte excretion at the level of the rat spinal cord through the activation of NK₁ receptors and the sympathetic renal nerve.

     

Bone-targeted nanoplatform enables efficient modulation of bone tumor microenvironment for prostate cancer bone metastasis treatment

As there is currently no effective therapy for patients with prostate cancer (PCa) bone metastasis, it was stringent to explore the relevant treatment strategies. Actually, the interaction between cancer cells and bone microenvironment plays important role in prostate cancer bone metastasis, especially the Sonic hedgehog protein (SHH) signaling in the bone microenvironment. The SHH promotes osteoblast maturation and osteoblast then secretes RANKL to induce osteoclastogenesis. Herein, this study develops bone-targeting calcium phosphate lipid hybrid nanoparticles (NPs) loaded with docetaxel (DTXL) and SHH siRNA for PCa bone metastasis treatment. For bone targeting purposes, the nanoplatform was modified with alendronate (ALN). (DTXL + siRNA)@NPs-ALN NPs effectively change the bone microenvironment by inhibiting the SHH paracrine and autocrine signaling, enhancing the anti-tumor effects of DTXL. Besides showing good in vitro cellular uptake, the NPs-ALN also inhibited tumor growth both in vitro and in vivo by inducing apoptosis, cell cycle arrest, and autophagy. This DDS comprised of (DTXL + siRNA)-loaded NPs provides an excellent strategy to treat PCa bone metastasis.     

Catecholamine synthesis and metabolism in the central nervous system of mice lacking α2-adrenoceptor subtypes

Background and purpose:

This study investigates the role of α₂-adrenoceptor subtypes, α_2A, α_2B and α_2C, on catecholamine synthesis and catabolism in the central nervous system of mice.

Experimental approach:

Activities of the main catecholamine synthetic and catabolic enzymes were determined in whole brains obtained from α_2A-, α_2B- and α_2C-adrenoceptor knockout (KO) and C56Bl\7 wild-type (WT) mice.

Key results:

Although no significant differences were found in tyrosine hydroxylase activity and expression, brain tissue levels of 3,4-dihydroxyphenylalanine were threefold higher in α_2A- and α_2C-adrenoceptor KO mice. Brain tissue levels of dopamine and noradrenaline were significantly higher in α_2A and α_2CKOs compared with WT [WT: 2.8 ± 0.5, 1.1 ± 0.1; α_2AKO: 6.9 ± 0.7, 1.9 ± 0.1; α_2BKO: 2.3 ± 0.2, 1.0 ± 0.1; α_2CKO: 4.6 ± 0.8, 1.5 ± 0.2 nmol·(g tissue)⁻¹, for dopamine and noradrenaline respectively]. Aromatic L-amino acid decarboxylase activity was significantly higher in α_2A and α_2CKO [WT: 40 ± 1; α_2A: 77 ± 2; α_2B: 40 ± 1; α_2C: 50 ± 1, maximum velocity (V_max) in nmol·(mg protein)⁻¹·h⁻¹], but no significant differences were found in dopamine β-hydroxylase. Of the catabolic enzymes, catechol-O-methyltransferase enzyme activity was significantly higher in all three α₂KO mice [WT: 2.0 ± 0.0; α_2A: 2.4 ± 0.1; α_2B: 2.2 ± 0.0; α_2C: 2.2 ± 0.0 nmol·(mg protein)⁻¹·h⁻¹], but no significant differences were found in monoamine oxidase activity between all α₂KOs and WT mice.

Conclusions and implications:

In mouse brain, deletion of α_2A- or α_2C-adrenoceptors increased cerebral aromatic L-amino acid decarboxylase activity and catecholamine tissue levels. Deletion of any α₂-adrenoceptor subtypes resulted in increased activity of catechol-O-methyltransferase. Higher 3,4-dihydroxyphenylalanine tissue levels in α_2A and α_2CKO mice could be explained by increased 3,4-dihydroxyphenylalanine transport.     

Pharmacological characterization of CGRP receptors mediating relaxation of the rat pulmonary artery and inhibition of twitch responses of the rat vas deferens

1. CGRP receptors mediating vasorelaxation of the rat isolated pulmonary artery and inhibition of contractions of the rat isolated prostatic vas deferens were investigated using CGRP agonists, homologues and the antagonist CGRP_8-37.
2. In the pulmonary artery, human (h)α-CGRP-induced relaxation of phenylephrine-evoked tone was abolished either by removal of the endothelium or by N^G-nitro-L-arginine (10⁻⁵ M). The inhibitory effect of N^G-nitro-L-arginine was stereoselectively reversed by L- but not by D-arginine (10⁻⁴ M). Thus, CGRP acts via nitric oxide released from the endothelium.
3. In the endothelium-intact artery, hα-CGRP, hβ-CGRP and human adrenomedullin (10⁻¹⁰–3×10⁻⁷ M), dose-dependently relaxed the phenylephrine-induced tone with similar potency. Compared with hα-CGRP, rat amylin was around 50 fold less potent, while [Cys(ACM^2,7)] hα-CGRP (10⁻⁷–10⁻⁴ M) was at least 3000 fold less potent. Salmon calcitonin was inactive (up to 10⁻⁴ M).
4. Human α-CGRP_8-37 (3×10⁻⁷–3×10⁻⁶ M) antagonized hα-CGRP (pA₂ 6.9, Schild plot slope 1.2±0.1) and hβ-CGRP (apparent pK_B of 7.1±0.1 for hα-CGRP_8-37 10⁻⁶ M) in the pulmonary artery. Human β-CGRP_8-37 (10⁻⁶ M) antagonized hα-CGRP responses with a similar affinity (apparent pK_B 7.1±0.1). Human adrenomedullin responses were not inhibited by hα-CGRP_8-37 (10⁻⁶ M).
5. In the prostatic vas deferens, hα-CGRP, hβ-CGRP and rat β-CGRP (10⁻¹⁰–3×10⁻⁷ M) concentration-dependently inhibited twitch responses with about equal potency, while rat amylin (10⁻⁸–10⁻⁵ M) was around 10 fold less potent and the linear analogue [Cys(ACM^2,7)] hα-CGRP was at least 3000 fold weaker. Salmon calcitonin was inactive (up to 10⁻⁴ M).
6. The antagonist effect of hα-CGRP_8-37 (10⁻⁵–3×10⁻⁵) in the vas deferens was independent of the agonist, with pA₂ values against hα-CGRP of 6.0 (slope 0.9±0.1), against hβ-CGRP of 5.8 (slope 1.1±0.1), and an apparent pK_B value of 5.8±0.1 against both rat β-CGRP and rat amylin. Human β-CGRP_8-37 (3×10⁻⁵–10⁻⁴ M) competitively antagonized hα-CGRP responses (pA₂ 5.6, slope 1.1±0.2). The inhibitory effect of hα-CGRP on noradrenaline-induced contractions in both the prostatic and epididymal vas deferens was antagonized by hα-CGRP_8-37 (pA₂ 5.8 and 5.8, slope 1.0±0.2 and 1.0±0.3, respectively).
7. The effects of hα-CGRP and hα-CGRP_8-37 in both rat pulmonary artery and vas deferens were not significantly altered by pretreatment with peptidase inhibitors (amastatin, bestatin, captopril, phosphoramidon and thiorphan, all at 10⁻⁶ M). The weak agonist activity of [Cys(ACM^2,7)] hα-CGRP in the vas deferens was not increased by peptidase inhibitors.
8. These data demonstrate that two different CGRP receptors may exist in the rat pulmonary artery and vas deferens, a CGRP₁ receptor subtype in the rat pulmonary artery (CGRP_8-37 pA₂ 6.9), while the lower affinity for CGRP_8-37 (pA₂ 6.0) in the vas deferens is consistent with a CGRP₂ receptor.

     

Validity of (−)-[3H]-CGP 12177A as a radioligand for the ‘putative β4-adrenoceptor' in rat atrium

1. We have recently suggested the existence in the heart of a ‘putative β₄-adrenoceptor'' based on the cardiostimulant effects of non-conventional partial agonists, compounds that cause cardiostimulant effects at greater concentrations than those required to block β₁- and β₂-adrenoceptors. We sought to obtain further evidence by establishing and validating a radioligand binding assay for this receptor with (−)-[³H]-CGP 12177A ((−)-4-(3-tertiarybutylamino-2-hydroxypropoxy) benzimidazol-2-one) in rat atrium. We investigated (−)-[³H]-CGP 12177A for this purpose for two reasons, because it is a non-conventional partial agonist and also because it is a hydrophilic radioligand.
2. Increasing concentrations of (−)-[³H]-CGP 12177A, in the absence or presence of 20 μM (−)-CGP 12177A to define non-specific binding, resulted in a biphasic saturation isotherm. Low concentrations bound to β₁- and β₂-adrenoceptors (pK_D 9.4±0.1, B_max 26.9±3.1 fmol mg^-1 protein) and higher concentrations bound to the ‘putative β₄-adrenoceptor'' (pK_D 7.5±0.1, B_max 47.7±4.9 fmol mg⁻¹ protein). In other experiments designed to exclude β₁- and β₂-adrenoceptors, (−)-[³H]-CGP 12177A (1–200 nM) binding in the presence of 500 nM (−)-propranolol was also saturable (pK_D 7.6±0.1, B_max 50.8±7.4 fmol mg⁻¹ protein).
3. The non-conventional partial agonists (−)-CGP 12177A (pK_i 7.3±0.2), (±)-cyanopindolol (pK_i 7.6±0.2), (−)-pindolol (pK_i 6.6±0.1) and (±)-carazolol (pK_i 7.2±0.2) and the antagonist (−)-bupranolol (pK_i 6.6±0.2), all competed for (−)-[³H]-CGP 12177A binding in the presence of 500 nM (−)-propranolol at the ‘putative β₄-adrenoceptor'', with affinities closely similar to potencies and affinities determined in organ bath studies.
4. The catecholamines competed with (−)-[³H]-CGP 12177A at the ‘putative β₄-adrenoceptor'' in a stereoselective manner, (−)-noradrenaline (pK_iH 6.3±0.3, pK_iL 3.5±0.1), (−)-adrenaline (pK_iH 6.5±0.2, pK_iL 2.9±0.1), (−)-isoprenaline (pK_iH 6.2±0.5, pK_iL 3.4±0.1), (+)-isoprenaline (pK_i<1.7), (−)-RO363 ((−)-(1-(3,4-dimethoxyphenethylamino)-3-(3,4-dihydroxyphenoxy)-2-propranol)oxalate, pK_i 5.5±0.1).
5. The inclusion of guanosine 5-triphosphate (GTP 0.1 mM) had no effect on binding of (−)-CGP 12177A or (−)-isoprenaline to the ‘putative β₄-adrenoceptor''. In competition binding studies, (−)-CGP 12177A competed with (−)-[³H]-CGP 12177A for one receptor state in the absence (pK_i 7.3±0.2) or presence of GTP (pK_i 7.3±0.2). (−)-Isoprenaline competed with (−)-[³H]-CGP 12177A for two states in the absence (pK_iH 6.6±0.3, pK_iL 3.5±0.1; % H 25±7) or presence of GTP (pK_iH 6.2±0.5, pK_iL 3.4±0.1; % H 37±6). In contrast, at β₁-adrenoceptors, GTP stabilized the low affinity state of the receptor for (−)-isoprenaline.
6. The specificity of binding to the ‘putative β₄-adrenoceptor'' was tested with compounds active at other receptors. High concentrations of the β₃-adrenoceptor agonists, BRL 37344 ((RR+SS)[4-[2-[[2-(3-chlorophenyl)-2-hydroxy - ethyl]amino]propyl]phenoxy]acetic acid, 6 μM), SR 58611A (ethyl{(7S)-7-[(2R)-2 - (3 - chlorophenyl) - 2 - hydroxyethylamino] - 5,6,7,8 - tetrahydronaphtyl2 - yloxy} acetate hydrochloride, 6 μM), ZD 2079 ((±)-1-phenyl-2-(2-4-carboxymethylphenoxy)-ethylamino)-ethan-1-ol, 60 μM), CL 316243 (disodium (R,R)-5-[2-[2-(3-chlorophenyl)-2-hydroxyethyl-amino]propyl]- 1,3-benzodioxole-2,2-dicarboxylate, 60 μM) and antagonist SR 59230A (3-(2-ethylphenoxy)-1-[(1S)-1,2,3,4-tetrahydronaphth-1-ylamino]-2S-2-propanol oxalate, 6 μM) caused less than 22% inhibition of (−)-[³H]-CGP 12177A binding in the presence of 500 nM (−)-propranolol. Histamine (1 mM), atropine (1 μM), phentolamine (10 μM), 5-HT (100 μM) and the 5-HT₄ receptor antagonist SB 207710 ((1-butyl-4-piperidinyl)-methyl 8-amino-7-iodo-1,4-benzodioxan-5-carboxylate, 10 nM) caused less than 26% inhibition of binding.
7. Non-conventional partial agonists, the antagonist (−)-bupranolol and catecholamines all competed for (−)-[³H]-CGP 12177A binding in the absence of (−)-propranolol at β₁-adrenoceptors, with affinities (pK_i) ranging from 1.6–3.6 log orders greater than at the ‘putative β₄-adrenoceptor''.
8. We have established and validated a radioligand binding assay in rat atrium for the ‘putative β₄-adrenoceptor'' which is distinct from β₁-, β₂- and β₃-adrenoceptors. The stereoselective interaction with the catecholamines provides further support for the classification of the receptor as ‘putative β₄-adrenoceptor''.

     

Inhibition of colonic motility and defecation by RS-127445 suggests an involvement of the 5-HT2B receptor in rodent large bowel physiology

Background:

5-HT_2B receptors are localized within the myenteric nervous system, but their functions on motor/sensory neurons are unclear. To explore the role of these receptors, we further characterized the 5-HT_2B receptor antagonist RS-127445 and studied its effects on peristalsis and defecation.

Experimental approach:

Although reported as a selective 5-HT_2B receptor antagonist, any interactions of RS-127445 with 5-HT₄ receptors are unknown; this was examined using the recombinant receptor and Biomolecular Interaction Detection technology. Mouse isolated colon was mounted in tissue baths for isometric recording of neuronal contractions evoked by electrical field stimulation (EFS), or under an intraluminal pressure gradient to induce peristalsis; the effects of RS-127445 on EFS-induced and on peristaltic contractions were measured. Faecal output of rats in grid-bottom cages was measured over 3 h following i.p. RS-127445 and separately, validation of the effective doses was achieved by determining the free, unbound fraction of RS-127445 in blood and brain.

Key results:

RS-127445 (up to 1 µmol·L⁻¹) did not interact with the 5-HT₄ receptor. RS-127445 (0.001–1 µmol·L⁻¹) did not affect EFS-induced contractions of the colon, although at 10 µmol·L⁻¹ the contractions were reduced (to 36 ± 8% of control, n= 4). RS-127445 (0.1–10 µmol·L⁻¹) concentration-dependently reduced peristaltic frequency (n= 4). RS-127445 (1–30 mg·kg⁻¹), dose-dependently reduced faecal output, reaching significance at 10 and 30 mg·kg⁻¹ (n= 6–11). In blood and brain, >98% of RS-127445 was protein-bound.

Conclusions and implications:

High-protein binding of RS-127445 indicates that relatively high doses are required for efficacy. The results suggest that 5-HT_2B receptors tonically regulate colonic motility.     

Pharmacological analysis of the haemodynamic effects of 5-HT1B/D receptor agonists in the normotensive rat

1. The receptors involved in mediating the haemodynamic effects of three 5-HT_1B/D receptor agonists were investigated in pentobarbitone anaesthetized rats (n=6–17 per group).
2. Cumulative intravenous (i.v.) infusions of rizatriptan and sumatriptan (from 0.63 to 2500 μg kg⁻¹; each dose over 5 min) induced dose-dependent and marked hypotension (−42±6 and −34±4 mmHg at the highest dose, respectively; both P<0.05 vs vehicle: +5±3 mmHg) and bradycardia (−85±16 and −44±12 beats min⁻¹ at the highest dose, respectively; both P<0.05 vs vehicle: +16±6 beats min⁻¹). Zolmitriptan evoked only moderate hypotension at the highest dose (−19±9 mmHg; P<0.05 vs vehicle).
3. A high dose of the 5-HT_1B/D receptor antagonist, GR 127935 (0.63 mg kg⁻¹, i.v.), failed to antagonize the hypotension and bradycardia evoked by sumatriptan (−35±6 mmHg and −52±19 beats min⁻¹, respectively; both not significant vs sumatriptan in untreated rats), but moderately reduced the hypotension and bradycardia evoked by rizatriptan (−20±5 mmHg and −30±17 beats min⁻¹, respectively; both P<0.05 vs vehicle and vs rizatriptan in untreated rats).
4. The selective 5-HT_1A receptor antagonist, WAY 100635 (0.16 and 0.63 mg kg⁻¹, i.v.), dose-dependently attenuated the haemodynamic responses evoked by rizatriptan and sumatriptan, which were almost abolished by the higher dose of WAY 100635 (−4±3 mmHg and −15±8 beats min⁻¹; both not significant vs vehicle and P<0.05 vs rizatriptan in untreated rats). A slight but statistically significant reduction in mean arterial pressure (MAP) persisted at the highest dose of sumatriptan (−13±4 mmHg following the higher dose of WAY 100635; P<0.05 vs vehicle).
5. In pithed rats with MAP normalized by angiotensin II, rizatriptan failed to induce hypotension or bradycardia (+5±4 mmHg and −6±16 beats min⁻¹, respectively; both NS vs vehicle and P<0.05 vs rizatriptan in untreated rats). Similarly, sumatriptan failed to induce bradycardia in pithed rats (+5±6 beats min⁻¹; not significant vs vehicle and P<0.05 vs sumatriptan in untreated rats), whereas a slight but statistically significant reduction in MAP, compared to controls, occurred at the highest dose (−9±9 mmHg; P<0.05 vs both vehicle and sumatriptan in untreated rats).
6. In bilaterally vagotomized and atropine-treated (1 mg kg⁻¹, i.v.) rats, the reductions in MAP and heart rate evoked by rizatriptan (−31±4 mmHg and −64 ±9 beats min⁻¹, respectively; both P<0.05 vs vehicle and not significant vs rizatriptan in controls) and sumatriptan (−47±8 mmHg and −56±10 beats min⁻¹, respectively; both P<0.05 vs vehicle and not significant vs sumatriptan in controls) were not statistically significantly different from those observed in controls.
7. In conclusion, the 5-HT_1B/D receptor agonists, rizatriptan and sumatriptan, elicit hypotension and bradycardia in the normotensive anaesthetized rat predominantly via activation of central 5-HT_1A receptors, and a consequent reduction in sympathetic outflow.