Histamine metabolism in the visual system of the horseshoe crab Limulus polyphemus

A Novel Oral Glutarimide Derivative XC8 Suppresses Sephadex-Induced Lung Inflammation in Rats and Ovalbumin-induced Acute and Chronic Asthma in Guinea Pigs

BACKGROUND

Corticosteroids are the preferred option to treat asthma, however, they possess serious side effects and are inefficient in 10% of patients. Thus, new therapeutic approaches for asthma treatment are required.

OBJECTIVE

To study the efficacy of a novel glutarimide derivative XC8 in a Sephadex-induced lung inflammation in rats as well as in acute and chronic ovalbumin-induced allergic asthma in guinea pigs.

METHOD

Rats were treated with 0.18-18 mg/kg of XC8 intragastrically 4 times (24 h and 1 h prior to and 24 h and 45 h after endotracheal administration of Sephadex). The number of inflammatory cells in bronchoalveaolar lavages (BAL) was determined. Guinea pigs were treated with 0.045 -1.4 mg/kg (acute asthma) or with 1.4 and 7.0 mg/kg of XC8 (chronic asthma) intragastrically following the sensitization with ovalbumin and during aerosol challenge. Lung inflammation, numbers of eosinophils (BAL and lung tissue), goblet cells, degranulating mast cells and specific airway resistance (sRAW) were determined. The comparator steroid drug budesonide (0.5 mg/kg for rats and 0.16 mg/kg for guinea pigs) was administered by inhalation.

RESULTS

XC8 reduced influx of eosinophils into BAL in Sephadex-induced lung inflammation model in rats (by 2.6-6.4 times). Treatment of acute asthma in guinea pigs significantly reduced eosinophils in guinea pigs in BAL (from 55% to 30%-39% of the total cell count) and goblet cells in lung tissue. In a model of acute and chronic asthma, XC8 reduced significantly the number of eosinophils and degranulating mast cells in the lung tissue. Treatment with XC8 but not with budesonide decreased the specific airway resistance in acute and chronic asthma model up to the level of naive animals.

CONCLUSION

XC8 induced a profound anti-inflammatory effect by reducing eosinophils in BAL and eosinophils and degranulating mast cell numbers in the airway tissue. The anti-asthmatic effect of XC8 is comparable to that of budesonide. Moreover, in contrast to budesonide, XC8 was capable to reduce goblet cells and airway resistance.

Evolution of insect arylalkylamine N-acetyltransferases: structural evidence from the yellow fever mosquito, Aedes aegypti

Arylalkylamine N-acetyltransferase (aaNAT) catalyzes the transacetylation from acetyl-CoA to arylalkylamines. aaNATs are involved in sclerotization and neurotransmitter inactivation in insects. Phyletic distribution analysis confirms three clusters of aaNAT-like sequences in insects: typical insect aaNAT, polyamine NAT-like aaNAT, and mosquito unique putative aaNAT (paaNAT). Here we studied three proteins: aaNAT2, aaNAT5b, and paaNAT7, each from a different cluster. aaNAT2, a protein from the typical insect aaNAT cluster, uses histamine as a substrate as well as the previously identified arylalkylamines. aaNAT5b, a protein from polyamine NAT -like aaNAT cluster, uses hydrazine and histamine as substrates. The crystal structure of aaNAT2 was determined using single-wavelength anomalous dispersion methods, and that of native aaNAT2, aaNAT5b and paaNAT7 was detected using molecular replacement techniques. All three aaNAT structures have a common fold core of GCN5-related N-acetyltransferase superfamily proteins, along with a unique structural feature: helix/helices between β3 and β4 strands. Our data provide a start toward a more comprehensive understanding of the structure-function relationship and physiology of aaNATs from the mosquito Aedes aegypti and serve as a reference for studying the aaNAT family of proteins from other insect species. The structures of three different types of aaNATs may provide targets for designing insecticides for use in mosquito control.

Elicitation studies in cell suspension cultures of Cannabis sativa L

Cannabis sativa L. plants produce a diverse array of secondary metabolites. Cannabis cell cultures were treated with biotic and abiotic elicitors to evaluate their effect on secondary metabolism. Metabolic profiles analysed by (1)H NMR spectroscopy and principal component analysis (PCA) showed variations in some of the metabolite pools. However, no cannabinoids were found in either control or elicited cannabis cell cultures. Tetrahydrocannabinolic acid (THCA) synthase gene expression was monitored during a time course. Results suggest that other components in the signaling pathway can be controlling the cannabinoid pathway.

The dynamics of signaling at the histaminergic photoreceptor synapse of arthropods

Histamine, a ubiquitous aminergic messenger throughout the body, also serves as a neurotransmitter in both vertebrates and invertebrates. In particular, the photoreceptors of adult arthropods use histamine, modulating its release to signal increases and decreases in light intensity. Strong evidence from various arthropod species indicates that histamine is synthesized and stored in photoreceptors, undergoes Ca-dependent release, inhibits postsynaptic interneurons by gating Cl channels, and is then recycled. In Drosophila, the synthetic enzyme, histidine decarboxylase, and the subunits of the histamine-gated chloride channel have been cloned. Possible histamine transporters at synaptic vesicles and for reuptake remain elusive. Indeed, the mechanisms that remove histamine from the synaptic cleft, and that help terminate histamine's action, are unexpectedly complex, their details remaining unresolved. A major pathway in Drosophila, and possibly other arthropod species, is by conjugation of histamine to beta-alanine to form carcinine in adjacent glia. This conjugate then returns to the photoreceptors where it is hydrolysed to liberate histamine, which is then loaded into synaptic vesicles. Evidence from other species suggests that direct reuptake of histamine into the photoreceptors may also occur. Light depolarizes the photoreceptors, causing histamine release and postsynaptic inhibition; dimming hyperpolarizes the photoreceptors, causing a decrease in histamine release and an "off" response in the postsynaptic cell. Further pursuit of histamine's action at these highly specialized synapses should lead to an understanding of how they signal minute changes in presynaptic membrane potential, how they reliably extract signals from noise, and how they adapt to a wide range of presynaptic membrane potentials.

The eyes of Limulus polyphemus (Xiphosura, Chelicerata) and their afferent and efferent projections

The visual system of the American horseshoe crab Limulus polyphemus (L. polyphemus) is an important preparation for studying the photoresponse, the circadian modulation of the photoresponse and visual information processing. Given its unique position in phylogeny the structure of its visual system also informs studies of the relationships among arthropods and the characteristics of eurarthropods. Much has been learned about the organization of the relatively simple L. polyphemus visual system, but much remains to be discovered. This review summarizes current knowledge of the structure of L. polyphemus eyes and the organization of their afferent and efferent projections and points to important unanswered questions.

tan and ebony genes regulate a novel pathway for transmitter metabolism at fly photoreceptor terminals

In Drosophila melanogaster, ebony and tan, two cuticle melanizing mutants, regulate the conjugation (ebony) of beta-alanine to dopamine or hydrolysis (tan) of the beta-alanyl conjugate to liberate dopamine. beta-alanine biosynthesis is regulated by black. ebony and tan also exert unexplained reciprocal defects in the electroretinogram, at ON and OFF transients attributable to impaired transmission at photoreceptor synapses, which liberate histamine. Compatible with this impairment, we show that both mutants have reduced histamine contents in the head, as measured by HPLC, and have correspondingly reduced numbers of synaptic vesicles in their photoreceptor terminals. Thus, the histamine phenotype is associated with sites of synaptic transmission at photoreceptors. We demonstrate that when they receive microinjections into the head, wild-type Sarcophaga bullata (in whose larger head such injections are routinely possible) rapidly (<5 sec) convert exogenous [3H]histamine into its beta-alanine conjugate, carcinine, a novel metabolite. Drosophila tan has an increased quantity of [3H]carcinine, the hydrolysis of which is blocked; ebony lacks [3H]carcinine, which it cannot synthesize. Confirming these actions, carcinine rescues the histamine phenotype of ebony, whereas beta-alanine rescues the carcinine phenotype of black;tan double mutants. The equilibrium ratio between [3H]carcinine and [3H]histamine after microinjecting wild-type Sarcophaga favors carcinine hydrolysis, increasing to only 0.5 after 30 min. Our findings help resolve a longstanding conundrum of the involvement of tan and ebony in photoreceptor function. We suggest that reversible synthesis of carcinine occurs in surrounding glia, serving to trap histamine after its release at photoreceptor synapses; subsequent hydrolysis liberates histamine for reuptake.