MPA increases idarubicin-induced apoptosis in chronic lymphatic leukaemia cells via caspase-3

The caspase family of protease is speculated to have a crucial role in apoptosis. The effect of treatment with Idarubicin (IDA) and Medroxyprogesterone acetate (MPA), used alone or in combination, on the activation of Caspase-3 in canine Chronic Lymphatic Leukaemia (CLL) cells was investigated, in order to clarify the mechanism of chemo- and hormone-therapy mediated apoptosis. Caspase activity was determined by a quantitative fluorimetric assay. Apoptosis was monitored by propidium iodide (PI) and nucleosomes assay. Treatment of CLL cells for 24 h with MPA 5 microM did not significantly activate caspase-3 but its activity was increased almost 5-fold more with IDA 1 microM (P < 0.05) than control. Treatment of CLL cells with IDA 1 microM in equimolecular association with MPA was able to increase the activation of caspase-3 induced by IDA of the 61.2% (P < 0.05) in comparison with IDA alone. The activation of caspase-3 was confirmed evaluating apoptosis by PI and nucleosomes assay. Furthermore, both caspase-3 activation and apoptosis triggered by IDA alone or in combination with MPA were significantly inhibited by specific caspase-3 inhibitor AC-DEVD-CMK. These findings provide an explanation for IDA and MPA induced-apoptosis mechanism.

Interference of bovine herpesvirus 1 (BHV-1) in sorbitol-Induced apoptosis

In order to determine the ability of bovine herpesvirus type 1 (BHV-1) to suppress apoptosis, we examined the effects of BHV-1 infection on sorbitol-induced apoptosis on Madin-Darby bovine kidney (MDBK) cells. BHV-1 suppresses sorbitol-induced apoptosis in a manner similar to that of herpes simplex virus type 1 (HSV-1), indicating that BHV-1 has one or more anti-apoptotic genes. To elucidate the molecular mechanisms of apoptosis, expression of some genes encoding apoptosis-inhibiting and -promoting factors were analyzed on BHV-1 infected cells during the process of sorbitol-induced apoptosis. Our results revealed that the expression of bcl-2 and bcl-x(L) decreased after 5 and 3 h p.i., respectively; while bax and procaspase-3 expression increased with respect to control as a function of p.i. times and at 7 h p.i. they were not observed. We further show that the expression of p53 gene was also enhanced, suggesting that this apoptotic mechanism is p53 dependent. From these results, we propose that BHV-1 has one or more genes encoding apoptosis-inhibiting factors which interfere with the involvement of bcl-2 gene family members and apoptotic pathway, depending upon caspase-3, triggered by sorbitol.

Hydrocortisone has a protective effect on CyclosporinA-induced cardiotoxicity

CyclosporinA (CsA) is an immunosuppressive drug which induces severe adverse effects such as cardiotoxicity and nephrotoxicity. In several therapeutic protocols CsA is used in association with corticosteroids to obtain better therapeutic results. Recently, our studies showed that CsA increases blood pressure while inhibit Nitric Oxide (NO) production in vivo. In this study we evaluated in rat cardiomyocytes the effects of CsA, used alone or in association with Hydrocortisone (HY), on intracellular calcium concentration, NO production and lipid peroxidation (MDA level). Our results demonstrated that CsA increased intracellular calcium and such effect was dose-dependent. HY used alone, slightly decreased intracellular calcium, while dramatically reduced CsA-induced calcium fluxes. CsA (3.2 microM) increased lipid peroxidation and this effect was blunted by HY. Both CsA and HY inhibited NO production in rat cardiomyocytes acting on this pathway synergically. Our results demonstrated that in rat cardiomyocytes, CsA toxicity is due to a calcium overload, which in turn induce lipid peroxidation and determines oxidative stress-induced cell injury. Treatment with HY effectively inhibits CsA-induced toxicity, decreasing lipid peroxidation as well as calcium intracellular concentration. Our findings seem to suggest that glucocorticoids may be effective in reducing CsA-induced cardiotoxicity at concentrations which are consistent with current therapeutic doses.

Direct effect of a gonadotropin-releasing hormone agonist on the growth of canine mammary tumour cells

Gonadotropin-releasing hormone (GnRH) agonist exert "in vivo" an inhibitory action on the growth of hormone-dependent canine mammary tumours (Lombardi et al. [1999] J. Vet. Pharmacol Ther. 22(1):56-61). The present experiments have been performed "in vitro" in order to investigate the mechanisms involved in this direct antiproliferative action of GnRH agonists. In particular, the aim was to study whether these compounds might exert their antiproliferative effect by interfering with the stimulatory action of epidermal growth factor (EGF). To this purpose, the effects of GnRH agonist, Goserelin (GnRH-A), on the mitogenic action of EGF, on EGF-activated intracellular signaling mechanisms (intracellular calcium and nitric oxide production) as well as on ATP induced cell proliferation and signalling, and on the binding of EGF receptors have been evaluated in primary culture of canine mammary tumour cells. The results of these "in vitro" studies show that GnRH-A counteracts the mitogenic action of EGF and ATP, decreases the EGF/ATP-induced calcium signalling and reduces EGF binding, probably by means of NO-induced [Ca2+]i downregulation. These data suggest that GnRH agonists may inhibit the proliferation of the tumour cells by interfering with the stimulatory action of EGF.

GnRH and steroids in cancer

Gonadotropin-releasing-hormone (GnRH) analogues are synthetic compounds derived from decapeptide neurohormones (LHRH; LH/FSH-RH). They have a key role in hormone dependent cancer, particularly breast and prostate cancer. GnRH analogues produce an efficient inhibition of gonadotropins and sex steroid hormones. Their use in cancer therapy result in a, pharmacological castration (i.e. ovariectomy and orchiectomy), providing an androgen and estrogen ablation. GnRH exert an inhibitory action on the growth of hormone-dependent human and canine mammary tumor. Mammary tumors can produce growth factor that potentially could modulate their own proliferation in an autocrine fashion (i.e. TGF-alpha and TGF-beta or with a paracrine mechanism (i.e. EGF, IGF, FGF). The expression of EGF receptors is related in mammary tissues to the action of oestrogen and progesteron and to the presence of functional receptors for oestrogen (ER) and progesteron (PR). The present review elucidate the role of GnRH receptors in cancer and their connection with steroid hormones. Besides we showed the link between GnRH and signal transductions pathways: Estrogen-receptors, GnRH-receptors, EGF-receptors signal transduction pathways. A very tight link exists between steroid hormones and GnRH analogues both on central pituitary gonadal axis and on tumor receptors peripherically. This last mechanism could be explained either locally activating GnRH receptors or locally interacting with EGF receptor-Intracellular NitricOxide system.

Cerebellum mediates modality-specific modulation of sensory responses of midbrain and forebrain in rat

Evidence of a sensory role of the cerebellum, mediating a modulation of effectiveness of afferent input at other parts of the brain, has been reported previously for certain sense modalities but has not been evaluated across several in a mammal. After a conditioning train of stimuli applied to the cerebellar surface in unanesthetized rats, diffuse flashes, acoustic clicks, and shocks to the sciatic nerve evoked multiunit and field potential responses that were recorded at three levels: midbrain, thalamus, and cerebral cortex. At a best interval between end of conditioning train (cerebellar) and test (sensory) stimuli, all three levels show modulation of the evoked responses, each in a specific direction (enhancement or depression), with a characteristic time course. Visual responses in the tectum are enhanced; those in the cortex are depressed. Tectal responses that have been nearly abolished by increasing background illumination are partially restored by the conditioning cerebellar train. Auditory brainstem responses (short latency, less than 10 ms, far-field waves I to III, attributed to medullary levels) are depressed; wave IV from the inferior colliculus is relatively enhanced at short intervals and is depressed at longer intervals. Somatosensory responses in thalamus and cortex are depressed. Lobulae V, VI, and VII of the vermis are more effective sites of stimulation than other areas tested. Most of the modulations are ascribed to central sites; a few are ascribed to peripheral sites.

Dynamic analysis of cockroach giant interneuron activity evoked by forced displacement of cercal thread-hair sensilla

This investigation involved extracellular recordings of cockroach abdominal giant interneuron (GI) action potentials evoked by cercal "threadlike" hair sensilla (THS) stimulation with a galvanometric device, by controlled displacements of about seven THS. Small and large GIs, distinguished by their amplitudes, were studied simultaneously. Only the small GIs were spontaneously active. Responses to sine, pulse, and ramp stimulation of sensilla produced phasic responses in both GI types. Some GIs were directionally sensitive and had shorter response latencies in the direction of best sensitivity while others were omnidirectional. Contralateral stimulation decreased responses to homolateral stimuli. In experiments using paired pulses (less than 50-ms intervals) there is a period of hyperexcitability, in large GIs, in which the response to the second stimulus is greater. Repeated stimulation caused an exponential decline in the response which was steeper in GIs at higher stimulating frequencies and had a faster time course in large GIs. Because of this last property GIs function as low-pass filters limiting the flow of information, with large GIs having a lower frequency "cutoff" than smaller GIs.

Dynamic properties of cockroach cercal "bristlelike" hair sensilla

Responses of cercal "bristlelike" hair sensilla (BHS) on Periplaneta americana L. to movement were investigated by recording generator (GP) and spike potentials with an extracellular pipette electrode which held the bristle by its tip. BHSs had no resting discharge, were purely phasic, with sensitivity only to stimulus transitions. They were directionally sensitive. Sinusoidal analysis suggested, to a first approximation because of the important nonlinearities, the behavior of a first-order lead system with corner frequencies distributed between 8 and 20 Hz. Responses elicited by step- and ramplike displacements were roughly in accord with the above behavior. Nonlinearities occurred both at GP level and at the level of spike generation. The phasic and the nonlinear behaviors at GP level may have a mechanical origin. The lack of spontaneous activity and the threshold nature of the spike generator account for other linearities. The operation of BHS could be separated conceptually into a linear element followed by nonlinear elements. A computer simulation based on these concepts showed a close fit to the biological responses.

Cerebellar actions on cochlear microphonics and on auditory nerve action potential

The influence exerted by cerebellar stimulation upon cochlear microphonics (CM) and auditory nerve action potential (AP) has been analyzed in curarized guinea pigs. Round window recordings demonstrated that conditioning electrical stimulus trains delivered to the cerebellar cortex diminished the CM and AP amplitude at the same time and in a parallel fashion. On the other hand, cooling of the cerebellar cortex showed the opposite results of increased amplitudes. All pre-receptorial mechanisms were avoided. A PDP-12 computer performed parametric and non-parametric statistical analysis showing the differences to be significant for the shifts. Evidence of simultaneous inhibitory cerebellar action on both potentials has been demonstrated and a cerebello-olivo-cochlear pathway is proposed for such action upon the receptor cells and/or incoming fibers.