Pure natural products isolated from marine sponges, algae, and cyanobacteria were examined for antioxidant activity using a 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) solution-based chemical assay and a 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA) cellular-based assay. The DCFH system detects only antioxidants that penetrate cellular membranes. Potent antioxidants were identified and the results from each system compared. The algal metabolites cymopol (1), avrainvilleol (3), and fragilamide (4), and the invertebrate constituent puupehenone (5) showed strong antioxidant activity in both systems. Several compounds were active in the DPPH assay but significantly less active in the DCFH system. The green algal metabolite 7-hydroxycymopol (2) was isolated from Cymopolia barbataand its structure determined. Compound 2 was significantly less active in the DCFH system than cymopol (1). The sponge metabolites (1S)-(+)-curcuphenol (6), aaptamine (7), isoaaptamine (8), and curcudiol (9) and the cyanobacterial pigment scytonemin (10) showed strong antioxidant activity in the DPPH assay, but were relatively inactive in the DCFH system. Thus, cellular uptake dramatically affects the potential significance of antioxidants discovered using only the DPPH assay. The apparent "proantioxidants" hormothamnione A diacetate (11) and Laurencia monomer diacetate (12) require metabolic activation for antioxidant activity. Significant advantages are achieved using both a solution- and cellular-based assay to discover new antioxidants.

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The sodium-bicarbonate cotransporter NBCn1 (SLC4A7) is an acid-base transporter that normally moves Na(+) and HCO(3)(-) into the cell. This membrane protein is sensitive to cellular and systemic pH changes. We examined NBCn1 expression and localization in the brain and its response to chronic metabolic acidosis. Two new NBCn1 antibodies were generated by immunizing a rabbit and a guinea pig. The antibodies stained neurons in a variety of rat brain regions, including hippocampal pyramidal neurons, dentate gyrus granular neurons, posterior cortical neurons, and cerebellar Purkinje neurons. Choroid plexus epithelia were also stained. Double immunofluorescence labeling showed that NBCn1 and the postsynaptic density protein PSD-95 were found in the same hippocampal CA3 neurons and partially colocalized in dendrites. PSD-95 was pulled down from rat brain lysates with the GST/NBCn1 fusion protein and was also coimmunoprecipitated with NBCn1. Chronic metabolic acidosis was induced by feeding rats with normal chow or 0.4 M HCl-containing chow for 7 days. Real-time PCR and immunoblot showed upregulation of NBCn1 mRNA and protein in the hippocampus of acidotic rats. NBCn1 immunostaining was enhanced in CA3 neurons, posterior cortical neurons, and cerebellar granular cells. Intraperitoneal administration of N-methyl-d-aspartate caused neuronal death determined by caspase-3 activity, and this effect was more severe in acidotic rats. Administering N-methyl-d-aspartate also inhibited NBCn1 upregulation in acidotic rats. We conclude that NBCn1 in neurons is upregulated by chronic acid loads, and this upregulation is associated with glutamate excitotoxicity.

A new indanone (1) has been isolated from the filamentous marine cyanobacterium Lyngbya majuscula, and its structure determined spectroscopically. Vascular endothelial growth factor (VEGF) is an important regulator of tumor angiogenesis. Compound 1 inhibits hypoxia-induced activation of the VEGF gene promoter in Hep3B human liver tumor cells, in vitro.