C. Agen

Macrolide antibiotics as antiinflammatory agents : roxithromycin in an unexpected role

The antiinflammatory activity of a new 14-membered macrolide antibiotic, roxithromycin, was evaluated in various rat models including carrageenan- and poly-l-arginine-induced hind-paw oedema, croton oil inflamed ear assay and polyester sponge granuloma. When administered orally to animals, roxithromycin displayed an atypical profile in the assays utilized, including: (1) marked antioedema activity similar to that of indomethacin in poly-l-arginine assay, (2) significant inhibition of λ-carrageenan hind-paw oedema and croton-oil-induced inflammation in the ear, although indomethacin was more effective, and (3) failure to reduce the development of granuloma induced by implanted polyester sponges, while indomethacin significantly reduced the chronic inflammatory reaction. Based on these results, it is concluded that roxithromycin is active in reducing the acute inflammatory reaction in rat models through mechanisms different from conventional nonsteroidal antiinflammatory agents such as indomethacin. Therefore, roxithromycin may have a favorable impact on skin inflammatory reactions accompanying microbial infections.

Reducing doxorubicin cardiotoxicity in the rat using deferred treatment with ADR-529

SummaryThe purpose of this study was to evaluate the optimal timing of ADR-529 administration to protect rats treated with doxorubicin (DXR) against drug-induced cardiotoxicity. Complete electrocardiographic monitoring (QRS complex, SαT segment and T wave) and the histopathological analysis of cardiac tissue were used to assess the degree of heart damage produced in female rats treated with ten i.v. doses of 1 mg/kg DXR over a period of 15 weeks; body-weight increase and survival were also analyzed to evaluate the toxicity of treatments. Cardiac alterations induced by DXR were compared with those occurring in animals receiving 20 mg/kg i.v. ADR-529 at 30 min prior to DXR administration, starting at the first, third, or sixth DXR dose and given until the end of the study (15th week). Rats treated with DXR were severely cardiomyopathic, showing progressive and irreversible ECG alterations (QRS-complex and SαT-segment widening and T-wave flattening) and marked degeneration of the myocardium (myocyte vacuolation, myofibrillar loss, and endomyocardial fibrosis). The most effective cardiac protection was provided by the administration of ADR-529 beginning with the first or third DXR dose. Delaying treatment with ADR-529 until the sixth DXR dose resulted in a significant reduction in its therapeutic action on heart damage. A significant difference in body-weight increase and survival was observed between the treatment groups: ADR-529 injected prior to the first DXR dose significantly protected animals from DXR toxicity, but this schedule was significantly more toxic than the administration of ADR-529 beginning with the third or sixth DXR dose. Taking into account the degree of cardiac protection and the toxicity of combination treatments, the results of the present study demonstrate the superiority of ADR-529 given prior to the third DXR dose over the other schedules tested. This finding suggests that significant protection against DXR-induced chronic cardiotoxicity in the rat can be obtained using deferred treatment with ADR-529.

Doxorubicin cardiotoxicity is associated with alterations of plasma levels of atrial natriuretic factor

In order to determine the involvement of the atrial natriuretic factor (ANF) in a model of drug-induced cardiomyopathy, the effects of a single or repeated doses of doxorubicin on plasma ANF levels were examined. Female Wistar rats were treated with doxorubicin at two different schedules: a single 10 mg/kg iv dose or multiple 3 mg/kg iv doses once a week for 3 weeks; control groups were given vehicle (isotonic saline, 0.9% NaCI) intravenously. ANF was assayed in plasma by a specific and sensitive radioimmunoassay method and cardiac function was evaluated by monitoring of ECG and hemodynamic parameters. In the doxorubicin single-dose study plasma ANF values were measured during a period of 6 hours after dosing and were found to be significantly decreased at the 180th (12.5 ± 2.9 pg/ml) and 360th minute (19.4 ± 1.2 pg/ml) after dosing, compared to vehicle-treated animals (35.1 ± 5.7 and 37.9 ± 4.1 pg/ml, 180 and 360th minute, respectively). Rats treated with multiple doses of doxorubicin showed a significant increase in plasma ANF levels at the 21st (88.3 ± 7.7 pg/ml) and 31st day (61.0 ± 14.3 pg/ml) of the study compared to vehicle-treated animals at the same time points (41.8 ± 8.0 and 26.5 ± 7.2 pg/ml, respectively). At the 42nd day plasma ANF concentration in doxorubicin-treated rats was not significantly different from vehicle-treated rats. In both studies ANF level changes occurred in the setting of acute or chronic doxorubicin-induced cardiac damage, as evidenced by alterations of hemodynamic and ECG parameters. These results suggest that the significant alterations in plasma ANF levels during doxorubicin treatment represent a new aspect of cardiac toxicity of the drug and might contribute to doxorubicin-induced heart damage.

Inhibitory effect of the somatostatin analogue SMS 201–995 and cytokines on the proliferation of human colon adenocarcinoma cell lines

The activity of the synthetic somatostatin analogue SMS 201-995 was investigated in vitro on the growth of SW480 and SW620 human colon adenocarcinoma cell lines. The inhibition of cell proliferation was significant in SW480 cells (-19.6 +/- 1.4% at SMS 201-995 10-9 M, P < 0.05), but not in SW620 cells (-5.5 +/- 0.8% at SMS 201-995 10-8 M) as compared to untreated cultures. Moreover, SMS 201-995 10-8 M decreased the mitogenic effect of epidermal growth factor (EGF) on the SW480 cell line (-26.6 +/- 3.4% vs. cells exposed to EGF 10 ng ml-1 alone, P < 0.05). The effect of combining SMS 201-995 plus the cytokines interleukin-2 (IL-2) or gamma-interferon (gamma-IFN) on SW480 and SW620 cancer cell growth was also evaluated. The treatment produced a synergistic antiproliferative effect against SW620 cells as compared to untreated cultures, with growth inhibition being -20.2 +/- 1.2 and -19.3 +/- 1.3%, at SMS 201-995 10-8 M plus IL-2 or gamma-IFN 100 IU ml-1, respectively, but did not increase the activity of SMS 201-995 against the SW480 cells. In conclusion, the effect of SMS 201-995 on colon cancer cell growth can be enhanced by its combination with cytokines in SW620 but not in SW480 colon adenocarcinoma cells.

Effects of quinolone carboxylic acid derivatives on GABAA receptor-mediated stimulation of gastric acid secretion and intestinal motility

The present study investigates the effects of some quinolone carboxylic acid derivatives on GABAA receptor-mediated excitatory responses in gastrointestinal preparations in vivo and in vitro. In stomach-perfused rats, norfloxacin, nalidixic and pipemidic acid dose dependently antagonized acid hypersecretion induced by muscimol. Under the same conditions, the quinolone derivatives failed to modify acid hypersecretion evoked by 2-deoxy-D-glucose. In the isolated guinea-pig ileum, norfloxacin, nalidixic and pipemidic acid antagonized muscimol-elicited contractions in a non-competitive manner. In contrast, these drugs did not influence ileal cholinergic contractions evoked by transmural electrical stimulation or by exogenous acetylcholine. Taken together, these results suggest that the quinolone derivatives tested act as antagonists at both central and peripheral GABAA receptors. In addition, GABAA-mediated gastrointestinal responses might represent a simple and reliable method to assay the GABAA receptor antagonist properties of new quinolone derivatives.

Atrial natriuretic peptide inhibits the spontaneous contractions of rabbit isolated ileum

Abstract— The present study investigates the effects of atriopeptin II on spontaneous phasic contractions of rabbit isolated ileum. Atriopeptin II caused a significant and concentration‐dependent decrease in ileum motor activity. This effect was mimicked by 8‐Br‐cGMP and it was not affected by pretreatment with tetrodotoxin. Verapamil significantly decreased ileum contractions; however, in the presence of this calcium blocker, atriopeptin II further reduced ileal motility. These findings demonstrate that atriopeptin II depresses the motility of rabbit ileum through a cGMP‐dependent mechanism and suggest that neither ileal neural networks nor extracellular calcium are involved in this effect.

Characterization of the toxicity of distamycin derivatives on cancer cell lines and rat heart

The cytotoxicity and cardiotoxicity of benzoyl mustard (FCE 24517) and epoxamido (FCE 24561) synthetic derivatives of distamycin A were reported in the present study. The 50% inhibiting concentration (IC50) of colony formation of FCE 24517 on human SNB-19 glioblastoma, A2780 ovarian cancer and DU 145 prostate cancer was at least three times lower than that of FCE 24561; on the same cell lines the IC50 of DXR was up to 14 and 240 times higher than that of FCE 24561 and FCE 24517, respectively. Isolated rat hearts perfused with concentrations of both derivatives equivalent to their respective IC50 values did not show any significant change in ECG parameters, contractility and coronary flow. Compared to control hearts, FCE 24517 10(-6) M induced a significant increase in PR interval, reduction in + dF/dtmax, heart rate and coronary flow, while FCE 24561 10(-6) M produced a modest but significant increase in S alpha T segment and decrease in + dF/dtmax. Rats treated with FCE 24561 3, 6 or 12 mg/kg, intravenously (i.v.), once weekly for 3 weeks had a modest increase in S alpha T segment and QRS complex duration, while a slight alteration of S alpha T segment and QRS complex duration were observed in rats given FCE 24517 1 or 2 mg/kg i.v. once weekly for 3 weeks. No cardiac histologic alterations were found in hearts from rats receiving FCE 24517 or FCE 24561. For comparison, the cardiotoxicity of doxorubicin (DXR) was evaluated in the same experimental models; perfusion of hearts with DXR 10(-6) M induced severe alterations in all parameters of the isolated hearts; the administration of DXR 3 mg/kg i.v. once a week for 3 weeks was associated with a widening of the S alpha T segment and QRS complex and cardiac histologic picture was markedly altered. In conclusion, distamycin A derivatives display elevated cytotoxicity while no substantial cardiotoxicity was observed.

Liver and spleen enhancement after intravenous injection of carboxydextran magnetite: effect of dose, delay of imaging, and field strength in an ex vivo model

It has been predicted that liver and spleen enhancement after administration of superparamagnetic contrast agents may be different, depending on the strength of the main magnetic field. With the use of anex vivo model, we investigated at 0.3, 0.5, and 1.5 T the effects on liver and spleen signal intensity of 5, 15, and 45 µmol/kg body weight of dextran magnetite (SHU 555A) in 54 rats. Nine rats served as controls. At different time delays since injection, the animals were killed, and after perfusion with saline, the liver, brain, and spleen were fixed in formalin. The specimens were embedded in an agar gel matrix and imaged with inversion recovery T1-weighted, proton density spin echo, and T2*-weighted gradient recalled echo (GRE) sequences. At each magnetic field strength, peak liver and spleen signal loss increased with increasing dose of the contrast medium. Signal loss was significantly more conspicuous after a dose of 15 than 5 µmol/kg body weight, but not after a dose of 45 compared with 15 µmol/kg. No signal change was observed in the brain. GRE images showed higher enhancement than proton density-weighted spin echo and inversion recovery images but were noisier. The enhancement showed a plateau between 30 min and 24 hours. Only the signal decrease of the liver after a low dose of contrast medium on GRE images was significantly higher (p<0.01) at 1.5 than at 0.5 and 0.3 T. Other differences in respect to the field strength were less significant (p<0.05) or nonsignificant. Differences in the spleen enhancement were nonsignificant. SHU 555A at a dose of 15 µmol/kg is an efficient intracellular contrast agent for liver and spleen at low, mid, and high field strength. Proton density spin echo images are probably the sequence of choice to exploit SHU 555A contrast effects and a wide time window for imaging after its intravenous injection does exist.

Reduced cardiotoxicity and increased cytotoxicity in a novel anthracycline analogue, 4′-amino-3′-hydroxy-doxorubicin

SummaryThe acute and chronic cardiotoxicity and cytotoxicity of the novel doxorubicin (DXR) derivative 4′-amino-3′-hydroxy-DXR were compared with those of 4′-deoxy-DXR and DXR. In the acute cardiotoxicity study, the ECG and hemodynamic changes recorded in anesthetized rats that had been treated i.v. with 10 mg/kg 4′-amino-3′-hydroxy-DXR or 8.6 mg/kg 4′-deoxy-DXR were significantly less severe than those caused by 13 mg/kg DXR. In the chronic cardiotoxicity study, rats received 3 weekly i.v. injections of 3 mg/kg DXR, 3 mg/kg 4′-amino-3′-hydroxy-DXR, or 2 mg/kg 4′-deoxy-DXR during the first 14 days of the study and were observed for an additional 35-day period. DXR induced severe cardiomyopathy that was characterized by ECG changes in vivo (SαT-segment widening and T-wave flattening) and by impairment of the contractile responses (Fmax,±dF/dtmax) to adrenaline of hearts isolated from treated animals. 4′-Deoxy-DXR caused a progressive enlargement of the SαT segment in vivo and a significant impairment of the-dF/dtmax value in vitro, which were less severe than those produced by DXR. The least cardiotoxic drug was 4′-amino-3′-hydroxy-DXR, which induced minor ECG changes without causing significant alterations in the contractile responses of isolated hearts to adrenaline. On the basis of the drug concentration required to inhibit 50% of the colony formation (IC50) of cell lines in vitro, 4′-amino-3′-hydroxy-DXR was less active than 4′-deoxy-DXR but at least twice as active as DXR against human cancer and murine transformed cell lines. These data indicate that 4′-amino-3′-hydroxy-DXR is significantly less cardiotoxic and more cytotoxic than DXR.

Ex-vivo MR imaging of liver intracellular contrast agents

The objective is to evaluate whether an ex-vivo model can be used to test intracellular contrast agents for MR imaging of the liver. T1 weighted inversion recovery, proton density spin echo and T2* weighted gradient echo images of the liver were acquired at 0.5 T in 10 rats before and 30 min after intravenous injection of 0.075 mmol/kg Gadolinium benzyloxypropionictetraacetate (Gd-BOPTA, n = 5) or 0.015 mmol/kg dextran magnetite (DM, n = 5), Four additional animals served as controls. After exsanguination and perfusion with saline and formalin, specimens of the liver and brain were embedded in an agar gel and examined with MR imaging one to three weeks later using the same protocol. In-vivo, the mean liver signal enhancement caused by Gd-BOPTA in T1, proton density and T2* weighted images was +23%, +28% and -70%, respectively. The mean liver signal enhancement caused by DM was -71%, -76% and -94%. In-vitro, no signal change was seen in the brain of animals injected with Gd-BOPTA and DM as compared to controls. Liver signal was increased by Gd-BOPTA and decreased by DM. Mean liver enhancement rate induced by Gd-BOPTA was +22%, +5% and +27% for T1, proton density and T2* weighted images, respectively. Mean liver enhancement rate induced by DM was -27%, -19% and -31%. MR imaging signal changes induced by liver intracellular contrast agents are still appreciable in an ex-vivo model. The latter might be useful for for preliminary investigation of intracellular contrast agents for MR imaging of the liver.