Delayed increase of Ca2+ influx elicited by glutamate: role in neuronal death

The mechanism of delayed neurotoxicity, triggered by glutamate, was studied in 7-8-day-old primary cultures of rat cerebellar granule cells. Treatment of cultures for 15 min with 50 microM glutamate in Mg2+ -free medium, followed by removal of the excitoxin, resulted in neuronal death, which started to appear 2-3 hr after the termination of glutamate treatment. The number of dead neurons increased gradually in the next few hours and 80-85% of neurons were found dead 24 hr later. Antagonists of N-methyl-D-aspartate-sensitive glutamate receptors (phencyclidine) or 1.2 mM MgCl2, but not the antagonist of N-methyl-D-asparatate-insensitive glutamate receptors (6-cyano-7-nitroquinoxaline-2,3-dione), abolished the neurotoxic effect of kainate. Development of glutamate-induced neuronal death depends strongly on Ca2+. Removal of extracellular Ca2+ (with 1mM ethyleneglycol-bis-(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid) immediately after the termination of glutamate exposure and before the appearance of the early signs of neuronal death (post-glutamate period) dramatically reduced neuronal degeneration. Neurotoxic concentrations of glutamate induced sustained increase of 45Ca2+ uptake in the post-glutamate period. The delayed increase of 45Ca2+ uptake, as well as the delayed neurotoxicity, were not affected by post-glutamate treatment with phencyclidine, dibenzocyclohepteneimine; DL-2-amino-5-phosphonovalerate, or MgCl2 or with voltage-dependent Ca2+ channel blockers (nitrendipine, verapamil, diltiazem). Neurotoxic concentrations of glutamate also induced a delayed sustained increase of [3H]phorbol-12,13-dibutyrate binding, reflecting an increased translocation of protein kinase C (PKC) from cytosol to the cell membrane during the post-glutamate period. Pretreatment of neurons with the ganglioside GT1b (trisialosylgangliotetraglycosylceramide), followed by removal of free GT1b from the incubation medium, prevented PKC translocation, the sustained increase of 45Ca2+ uptake in the post-glutamate period, and the delayed neuronal death. We suggest that the sustained activation and translocation of PKC primed by glutamate receptor stimulation may be the triggering event causing the protracted increase of neuronal Ca2+ influx. This influx is insensitive to voltage-dependent Ca2+ channel blockers and glutamate receptor antagonists. It appears that this delayed increase of Ca2+ influx may be important in causing neuronal death.     

Effect of dihydroergosine (DHESN) on the serotoninergic system and behaviour: Is DHESN a new antidepressive agent?

Acute (50.0 mg/kg) and repeated (0.1–10.0 mg/kg) administration of dihydroergosine (DHESN) to rats over 5 days lowered the concentration of 5-HIAA in the brain. DHESN given acutely increased the brain 5-HT in p-CPA-treated animals and diminished the probenecid-induced increase in brain 5-HIAA. In pargyline-treated rats DHESN enhanced the 5-HT/5-HIAA ratio. DHESN administered to rats repeatedly over 5 days decreased the level of 5-HT in blood platelets, and in vitro at concentrations of 10^-4 M and 10^-3 M inhibited the uptake of [¹⁴C]-5-HT in platelets. DHESN (10.0–100.0 mg/kg) potentiated the 5-HT syndrome produced in rats by pargyline and 5-HTP. This potentiation was blocked with cyproheptadine but not with haloperidol. DHESN (1.0 and 10.0 mg/kg) lowered the locomotor activity of rats and 10.0 mg/kg DHESN also reduced the duration of immobility in rats forced to swim in a restricted space. The results indicate that DHESN, like antidepressants, decreases the turnover of serotonin in the brain and potentiates the 5-HT-mediated behaviour. This might suggest that the drug should be further investigated for its potential antidepressive properties.     

Immune response of stressed rats treated with drugs affecting serotoninergic and adrenergic transmission.

Stressful conditions interfere with immune response. One of the principal mechanisms is activation of hypothalamo-pituitary-suprarenal axis by central serotoninergic and adrenergic pathways. Alternative mechanisms bypassing the axis also take part in stress-induced immunomodulation. Immunosuppression caused by repeated restraints or over-crowding was usually accompanied by increased metabolism of serotonin in the brain (as indicated by increased level of its metabolite, 5-HIAA) and by increased levels of corticosterone in plasma. Changes in lymphatic tissues of stressed animals that result in suppression of immune response apparently "outlive" fluctuating changes in neurotransmitter and corticosterone levels. Drugs that alter serotoninergic or adrenergic transmission interfere with immunosuppressive effect of stress either synergistically (augmenting suppression) or antagonistically (preventing it). Since immunocompetent cells possess serotoninergic and adrenergic receptors, such drugs may exert their effect either via central neuroendocrine mechanisms, or by direct effects on immunocompetent cells.     

Interactions between Tacrolimus and Metronidazole in a renal transplant patient

We present a case which reports the occurrence of a potential elevation of Tacrolimus (Tac) plasma levels to toxic values in a renal transplant recipient after adding Metronidazole (Met) to the medication regimen. A 30-year old female, status post living-related renal transplant, who was stabilized on Tac 4.5 mg, twice daily, for 4 months, presented to the clinic with diarrhea. We used Microparticle Enzyme Immunoassay (MEIA) to determine Tac trough concentration (trough concentrations 5–10 ng/ml). After 6 days of Met therapy on 1.5 g/d, Tac trough concentration and serum creatinine (sCr) increased to 20.2 ng/ml and 7.8 mg/dl respectively. Met therapy was discontinued, also one dose of Tac was withheld, while daily dose was decreased to 2 mg/d. Four days after Met discontinuation, Tac concentration dropped to 8.7 ng/ml, sCr to 2.1 mg/dl, warranting Tac dose increase to 3 mg/d. Co-administration of Tac with Met may result in elevated Tac concentrations, possibly leading to tacrolimus nephrotoxicity. Clinicians should be aware of this potential interaction and closely monitor Tac concentration and renal function.     

Abnormal calcium signaling and sudden cardiac death associated with mutation of calsequestrin

Mutations in human cardiac calsequestrin (CASQ2), a high-capacity calcium-binding protein located in the sarcoplasmic reticulum (SR), have recently been linked to effort-induced ventricular arrhythmia and sudden death (catecholaminergic polymorphic ventricular tachycardia). However, the precise mechanisms through which these mutations affect SR function and lead to arrhythmia are presently unknown. In this study, we explored the effect of adenoviral-directed expression of a canine CASQ2 protein carrying the catecholaminergic polymorphic ventricular tachycardia-linked mutation D307H (CASQ2(D307H)) on Ca2+ signaling in adult rat myocytes. Total CASQ2 protein levels were consistently elevated approximately 4-fold in cells infected with adenoviruses expressing either wild-type CASQ2 (CASQ2(WT)) or CASQ2(D307H). Expression of CASQ2(D307H) reduced the Ca2+ storing capacity of the SR. In addition, the amplitude, duration, and rise time of macroscopic I(Ca)-induced Ca2+ transients and of spontaneous Ca2+ sparks were reduced significantly in myocytes expressing CASQ2(D307H). Myocytes expressing CASQ2(D307H) also displayed drastic disturbances of rhythmic oscillations in [Ca2+]i and membrane potential, with signs of delayed afterdepolarizations when undergoing periodic pacing and exposed to isoproterenol. Importantly, normal rhythmic activity was restored by loading the SR with the low-affinity Ca2+ buffer, citrate. Our data suggest that the arrhythmogenic CASQ2(D307H) mutation impairs SR Ca2+ storing and release functions and destabilizes the Ca2+-induced Ca2+ release mechanism by reducing the effective Ca2+ buffering inside the SR and/or by altering the responsiveness of the Ca2+ release channel complex to luminal Ca2+. These results establish at the cellular level the pathological link between CASQ2 mutations and the predisposition to adrenergically mediated arrhythmias observed in patients carrying CASQ2 defects.     

Neuroactive pregnanolone isomers during pregnancy

The pregnanolone isomers (PI) allopregnanolone (3alpha-hydroxy-5alpha-pregnan-20-one), pregnanolone (3alpha-hydroxy-5beta-pregnan-20-one), isopregnanolone (3beta-hydroxy-5alpha-pregnan-20-one), epipregnanolone (3beta-hydroxy-5beta-pregnan-20-one), progesterone, and estradiol were measured in 138 pregnant women. The sampling was carried out from the first through the 10th month of pregnancy. Gas chromatography-mass spectrometry analysis and RIA were used for the measurement of steroid levels. The ratios of individual PI were similar to those found previously around parturition: about 25:10:7:1 for allopregnanolone, pregnanolone, isopregnanolone, and epipregnanolone, respectively. All the PI showed a significant increase during pregnancy, which was more pronounced in the 3alpha-steroids. The results indicated changing ratios between 3alpha- and 3beta-PI and between 5alpha- and 5beta-PI throughout pregnancy. The constant allopregnanolone/isopregnanolone ratio found through pregnancy weakened the hypothesis of the role of isopregnanolone in the onset of parturition. The ratio of estradiol (stimulating uterine activity) to 5alpha-PI and epipregnanolone exhibited significant changes during pregnancy in favor of estradiol up to the sixth or seventh month, in contrast to the constant estradiol/pregnanolone ratio. A pregnancy-stabilizing role of pregnanolone, counterbalancing the stimulating effect of estradiol on the onset of parturition, was suggested.     

Utility of B-type natriuretic peptide in predicting postoperative complications and outcomes in patients undergoing heart surgery

OBJECTIVES: The purpose of the present study was to assess whether preoperative and postoperative B-type natriuretic peptide (BNP) levels could be used as predictors of postoperative complications and outcomes in patients after open-heart surgery. BACKGROUND: A variety of multifactor indexes have been proposed for preoperative risk assessment of patients undergoing cardiac surgery, but they have shown limited ability and utility in accurately predicting postoperative complications, hospital stay, and mortality. METHODS: Subjects consisted of 98 male patients (63 +/- 9.1 years) undergoing open-heart surgery at the San Diego Veterans Administration Health System during a 19-month period. B-type natriuretic peptide levels were analyzed, and postoperative data recorded. RESULTS: There was a higher preoperative BNP level in patients requiring the use of intra-aortic balloon pumps (IABPs) (mean BNP = 387 +/- 112 pg/ml vs. 181 +/- 25 pg/ml), in patients who died within one year (357 +/- 93 pg/ml vs. 184 +/- 26 pg/ml), and in patients with postoperative hospital stays of 10 days or more (307 +/- 68 pg/ml vs. 179 +/- 27 pg/ml). Receiver operating characteristic curves demonstrated preoperative BNP levels as predictors of postoperative IABP use, hospital stay 385 pg/ml predict the postoperative complications and one-year mortality after heart surgery. Postoperatively, elevated peak BNP levels and elevated change to peak BNP levels were associated with prolonged hospital stay and mortality within one year.     

Detection of DNA mutations based on analysis of multiple wavelength excitation/emission fluorescence kinetics curves in real-time PCR

The key method for therapies of various cancer types could be the molecular-targeted therapy, based on individual gene profile for each patient. One of the main procedures used for genetic testing is the real-time polymerase chain reaction (real-time PCR).