Nonsynaptic communication in the central nervous system

Classical synaptic functions are important and suitable to relatively fast and discretely localized processes, but the nonclassical receptorial functions may be providing revolutionary possibilities for dealing at the cellular level with many of the more interesting and seemingly intractable features of neural and cerebral activities. Although different forms of nonsynaptic communication (volume transmission) often appear in different studies, their importance to modulate and mediate various functions is still not completely recognized. To establish the existence and the importance of nonsynaptic communication in the nervous system, here we cite pieces of evidence for each step of the interneuronal communication in the nonsynaptic context including the release into the extracellular space (ECS) and the extrasynaptic receptors and transporters that mediate nonsynaptic functions. We are now faced with a multiplicity of chemical communication. The fact that transmitters can even be released from nonsynaptic varicosities without being coupled to frequency-coded neuronal activity and they are able to diffuse over large distances indicates that there is a complementary mechanism of interneuronal communication to classical synaptic transmission. Nonconventional mediators that are also important part of the nonsynaptic world will also be overviewed.     

The major role of human AP-endonuclease homolog Apn2 in repair of abasic sites in Schizosaccharomyces pombe

The abasic (AP) sites, the major mutagenic and cytotoxic genomic lesions, induced directly by oxidative stress and indirectly after excision of damaged bases by DNA glycosylases, are repaired by AP-endonucleases (APEs). Among two APEs in Saccharomyces cerevisiae, Apn1 provides the major APE activity, and Apn2, the ortholog of the mammalian APE, provides back-up activity. We have cloned apn1 and apn2 genes of Schizosaccharomyces pombe, and have shown that inactivation of Apn2 and not Apn1 sensitizes this fission yeast to alkylation and oxidative damage-inducing agents, which is further enhanced by Apn1 inactivation. We also show that Uve1, present in S.pombe but not in S.cerevisiae, provides the back-up APE activity together with Apn1. We confirmed the presence of APE activity in recombinant Apn2 and in crude cell extracts. Thus S.pombe is distinct from S.cerevisiae, and is similar to mammalian cells in having Apn2 as the major APE.     

Ubc6p and ubc7p are required for normal and substrate-induced endoplasmic reticulum-associated degradation of the human selenoprotein type 2 iodothyronine monodeiodinase

The type 2 monodeiodinase (D2) is an endoplasmic reticulum-resident membrane selenoprotein responsible for catalyzing the first step in thyroid hormone action, T(4) deiodination to T(3). Its short half-life is due to ubiquitination and proteolysis by proteasomes, a mechanism that is accelerated by D2 interaction with T(4). To identify proteins involved in D2 ubiquitination, a FLAG-tagged selenocystine133-to-Cys mutation of the human D2 (CysD2) was created and expressed in Saccharomyces cerevisiae using the GAL1 gene promoter. CysD2 activity was detected in the microsomes, indistinguishable from transiently expressed CysD2 in vertebrate cells. Treatment with 100 mg/ml cycloheximide or 30 micro M T(4) caused rapid loss of CysD2 (t(1/2) = approximately 30 min). Clasto-lactacystin beta-lactone not only increased galactose-inducible CysD2 but also stabilized CysD2 in the presence of cycloheximide or T(4). Immunoprecipitation with anti-FLAG antibody combined with Western analysis with antiubiquitin revealed that CysD2 is heavily ubiquitinated. Expression of CysD2 in yeast strains that lack the ubiquitin conjugases Ubc6p or Ubc7p stabilized CysD2 half-life by markedly reducing CysD2 ubiquitination, whereas no difference was detected in Ubc1p-deficient mutants. Similarly, expression of CysD2 in UBC6 and UBC7 mutants also impaired the substrate-induced loss of CysD2 activity and protein. In conclusion, Ubc6p and Ubc7p are required for normal and substrate-induced ubiquitination and proteolysis of D2.     

Immune status of free-ranging green turtles with fibropapillomatosis from Hawaii

Cell-mediated and humoral immune status of free-ranging green turtles (Chelonia mydas) in Hawaii (USA) with and without fibropapillornatosis (FP) were assessed. Tumored and non-tumored turtles from Kaneohe Bay (KB) on the island of Oahu and from FP-free areas on the west (Kona/Kohala) coast of the island of Hawaii were sampled from April 1998 through February 1999. Turtles on Oahu were grouped (0-3) for severity of tumors with 0 for absence of tumors, 1 for light, 2 for moderate, and 3 for most severe. Turtles were weighed, straight carapace length measured and the regression slope of weight to straight carapace length compared between groups (KB0, KB1, KB2, KB3, Kona). Blood was assayed for differential white blood cell count, hematocrit, in vitro peripheral blood mononuclear cell (PBMC) proliferation in the presence of concanavalin A (ConA) and phytohaemagglutinin (PHA), and protein electrophoresis. On Oahu, heterophil/lymphocyte ratio increased while eosinophil/monocyte ratio decreased with increasing tumors score. Peripheral blood mononuclear cell proliferation indices for ConA and PHA were significantly lower for turtles with tumor scores 2 and 3. Tumor score 3 turtles (KB3) had significantly lower hematocrit, total protein, alpha 1, alpha 2, and gamma globulins than the other four groups. No significant differences in immune status were seen between non-tumored (or KB1) turtles from Oahu and Hawaii. There was no significant difference between groups in regression slopes of body condition to carapace length. We conclude that turtles with severe FP are imunosuppressed. Furthermore, the lack of significant difference in immune status between non-tumored (and KB1) turtles from Oahu and Kona/Kohala indicates that immunosuppression may not be a prerequisite for development of FP.     

Evidence of an oxidative challenge in the Alzheimer's brain

Alzheimer's disease may arise from or produce oxidative damage in the brain. To assess the responses of the Alzheimer's brain to possible oxidative challenges, we assayed for glutathione, glucose-6-phosphate dehydrogenase, catalase and superoxide dismutase in twelve regions of Alzheimer's disease and aged control brains. In addition, we determined levels of malondialdehyde to evaluate lipid peroxidation in these brain regions. Most brain regions showed evidence of a response to an oxidative challenge, but the cellular response to this challenge differed among brain regions. These data suggest that the entire Alzheimer's brain may be subject to an oxidative challenge, but that some brain areas may be more vulnerable than others to the consequent neural damage that characterizes the disease.     

METABOLIC COMPARTMENTATION IN THE BRAIN: EFFECTS OF A CENTRAL NERVOUS SYSTEM DEPRESSANT, 1-HYDROXY-3-AMINO-PYRROLIDONE-2

—The effect of 1-hydroxy-3-aminopyrrolidone-2(HA-966), a CNS depressant, was studied on the metabolism of [¹⁴C]glucose and [³H]acetate in the brain in mice. HA-966 had a marked effect on glucose metabolism. The conversion of glucose carbon into amino acids associated with the tricarboxylic acid cycle (‘cycle’) was severely reduced, while the concentration of brain glucose was approximately doubled. Relative to the specific radioactivity of glucose in the brain, the specific radioactivity of alanine was 60–70 per cent of the control, indicating a reduction in the rate of glycolysis, and those of the‘cycle’amino acids were also lowered. A reduction in‘cycle’flux of 30–35 per cent was estimated. It was established that the depressed glucose utilization flux was not due to either impaired uptake of glucose from blood to brain or to hypothermia. In contrast to [¹⁴C]glucose, there was no change in the labelling of the amino acid fraction from [³H]acetate, which is preferentially metabolized in the 'small’compartment believed to be associated with glia. Thus it seems that CNS depression caused by HA-966 resulted in a selective decrease in energy production in the‘large’metabolic compartment where glucose is oxidized preferentially and which is believed to be associated with neuronal structures. The results also suggested that communication between the metabolic compartments mediated via glutamine and GABA was reduced, since the labelling from [³H]acetate of glutamine was increased and that of GABA decreased by HA-966.     

Drug-induced antinuclear antibodies in the guinea pig

Antinuclear antibodies (ANA) development was studied in male guinea pigs in response to chronic treatment with procainamide, hydralazine, acetanilide or caffeine. Acetanilide and caffeine have not previously been associated with ANA induction. Fifty-one weanling Hartley guinea pigs were divided into five groups which received either procainamide, hydralazine, acetanilide, caffeine or saline sc for 55 weeks; drug dosage was 10 mg/kg initially and was increased incrementally to 40 mg/kg by 10 months except for hydralazine, which was increased to 20 mg/kg. Two weeks before initiation of treatment, 1 mg of the appropriate drug in 0.4 ml of buffered Freund's complete adjuvant (FCA-PBS) was administered intradermally. Controls received FCA-PBS only. Sera ANA were assayed at 6, 10 and 13 months. After 13 months of treatment, those sera which were ANA positive were assayed for anti-deoxyribunucleoprotein antibodies and were titered for ANA. Chi-square analyses were performed on results of the 10- and 13-month ANA screening results. ANA induction was significant at P = 0.05 only for the group receiving procainamide at both 10 and 13 months of treatment. When the cumulative results of all ANA screens were analyzed, ANA induction was significant for procainamide, acetanilide and caffeine. The test system did not prove to be promising for unambiguous identification of drugs with ANA-inducing potential, but may be useful for studies of mechanisms of ANA induction by chemicals.     

Postischemic cardiac recovery in heme oxygenase‐1 transgenic ischemic/reperfused mouse myocardium

Heme oxygenase-1 (HO-1) transgenic mice (Tg) were created using a rat HO-1 genomic transgene. Transgene expression was detected by RT-PCR and Western blots in the left ventricle (LV), right ventricle (RV) and septum (S) in mouse hearts, and its function was demonstrated by the elevated HO enzyme activity. Tg and non-transgenic (NTg) mouse hearts were isolated and subjected to ischemia/reperfusion. Significant post-ischemic recovery in coronary flow (CF), aortic flow (AF), aortic pressure (AOP) and first derivative of AOP (AOPdp/dt) were detected in the HO-1 Tg group compared to the NTg values. In HO-1 Tg hearts treated with 50 μmol/kg of tin protoporphyrin IX (SnPPIX), an HO enzyme inhibitor, abolished the post-ischemic cardiac recovery. HO-1 related carbon monoxide (CO) production was detected in NTg, HO-1 Tg and HO-1 Tg + SnPPIX treated groups, and a substantial increase in CO production was observed in the HO-1 Tg hearts subjected to ischemia/reperfusion. Moreover, in ischemia/reperfusion-induced tissue Na⁺ and Ca²⁺ gains were reduced in HO-1 Tg group in comparison with the NTg and HO-1 Tg + SnPPIX treated groups; furthermore K⁺ loss was reduced in the HO-1 Tg group. The infarct size was markedly reduced from its NTg control value of 37 ± 4% to 20 ± 6% (P < 0.05) in the HO-1 Tg group, and was increased to 47 ± 5% (P < 0.05) in the HO-1 knockout (KO) hearts. Parallel to the infarct size reduction, the incidence of total and sustained ventricular fibrillation were also reduced from their NTg control values of 92% and 83% to 25% (P < 0.05) and 8% (P < 0.05) in the HO-1 Tg group, and were increased to 100% and 100% in HO-1 KO^−/− hearts. Immunohistochemical staining of HO-1 was intensified in HO-1 Tg compared to the NTg myocardium. Thus, the HO-1 Tg mouse model suggests a valuable therapeutic approach in the treatment of ischemic myocardium.     

Direct semi-synthesis of the anticancer lead-drug protoapigenone from apigenin, and synthesis of further new cytotoxic protoflavone derivatives

Protoapigenone, a natural flavonoid possessing an unusual p-quinol moiety on its B-ring, is a novel prospective anticancer agent with low toxicity that is currently in development. The first economical, one-step synthesis of protoapigenone from apigenin is described on up to gram scale. 13 new 1'-O-alkylflavone analogs were also synthesized, either from apigenin or β-naphthoflavone. The in vitro cytotoxic activity of each compound was tested on six human cancer cell lines (HepG2, Hep3B, Ca9-22, A549, MCF-7 and MDA-MB-231). In the case of 1'-O-alkyl-protoapigenone derivatives, structure-activity relationships were found depending on the side-chain, and protoapigenone 1'-O-butyl ether was found to exert significantly stronger activity against three of the cell lines (Hep3B, MCF-7 and MDA-MB-231) than its non-substituted analog, protoapigenone itself. In contrast to this, all β-naphthoflavone derivatives bearing the same pharmacophore on their B-ring showed decreased cytotoxic activities when substituted with an O-alkyl side-chain at position 1', comparing to that of the non-substituted compound.