Science Concentrates

Nanotubes cross cell membranes

A carbon-nanotube-based carrier system that could have applications in drug and vaccine delivery has been discovered by scientists in Europe. Organic chemistry professor Maurizio Prato at the University of Trieste, in Italy; Alberto Bianco, an organic chemist at the Institute of Molecular & Cellular Biology, Strasbourg, France; and their colleagues show that single-walled carbon nanotubes (SWNTs) functionalized with a fluorescent probe--fluorescein isothiocyanate (FITC)--or with an FITC-peptide conjugate are able to penetrate the membranes of human and mouse fibroblasts [Chem. Comm., 2004, 16]. Functionalized SWNTs could be used to deliver peptides or small organic molecules into cells, the authors suggest. Both types of SWNTs are water soluble and nontoxic to the cells at low concentrations. The SWNT-FITC derivative (shown) accumulates mainly in the cytoplasm of the cells, whereas the SWNT-peptide-FITC derivative enters the nuclei. How the nanotubes get across the membranes remains to be elucidated. "The absence of immunogenicity of the nanotubes, in comparison to common protein carriers, will increase the efficacy of the therapeutics delivered in this manner," the group notes.

Plants pick up gaseous nitrate

Researchers have gathered the first proof that plants take up a reactive organic nitrogen gas from the atmosphere [Geophys. Res. Lett., 30, 2189 (2003)]. By directly measuring the entry of peroxyacetyl nitrate (PAN) through the leaf pores, or stomata, of eight plant species ranging from mango to lodgepole pine, Jed P. Sparks, a professor of ecology and evolutionary biology at Cornell University, and his colleagues at the University of Colorado, Boulder, and the National Oceanic & Atmospheric Administration watched plants breathe in reactive nitrogen. Sparks calls PAN a transport compound for reactive nitrogen. The two main nitrogen gases emitted by cars and factories, NO and NO₂, don't travel far alone. Instead, they are incorporated into larger organic molecules--most commonly PAN. "In effect, PAN is the form that can transport 'pollution' nitrogen to pristine or rural sites," Sparks says. When plants take up PAN, the pollution is distributed less widely. Sparks and coworkers estimate that plants remove about 3% of the total reactive nitrogen in air. This affects not only global nitrogen cycling, Sparks says, but carbon cycling as well; plants with more nitrogen available to them can do more photosynthesis and take up more CO₂.

Borates stabilize ribose

For the "RNA world" hypothesis of the origins of life to be true, RNA must have been synthesized prebiotically. Ribose--the sugar in RNA--and other pentoses can be made from the precursors formaldehyde and glycolaldehyde, which are known to exist in interstellar space and presumably would have been available on early Earth. Using these precursors, pentoses can be formed under alkaline conditions. However, the pentoses under those conditions rapidly decompose to polymeric mixtures of brown tar. A team led by University of Florida chemistry professor Steven A. Benner shows that borate minerals help stabilize ribose synthesized under alkaline conditions [Science, 303, 196 (2004)]. In the absence of borate, a mixture of pentoses, including ribose, turns brown and degrades after an hour of incubation. When the mixture is incubated in the presence of borate minerals, the solution doesn't degrade over an extended period. Borate minerals were probably also available on early Earth. The authors argue that their results help support--or at least don't exclude--prebiotic formation of ribose.

Helping drugs go more than just skin deep

Despite the advantages of transdermal drug delivery, such as increased patient compliance, only a few drugs are delivered via patches, and those are generally small molecules. Chemical engineers at the University of California, Santa Barbara, have developed a method that could make it easier to find effective transdermal formulations. In a method that they call INSIGHT screening (for in vitro skin-impedance-guided high-throughput screening), assistant professor Samir Mitragotri, grad student Pankaj Karande, and postdoc Amit Jain use impedance measurements of skin to identify combinations of penetration enhancers that improve transdermal delivery [Nat. Biotechnol., published online Jan. 4, http://dx.doi.org/10.1038/nbt928]. Their screening method is 100 times more efficient than the current method of discovering penetration enhancers, in which the penetration of radiolabeled solutes into or across the skin is measured. Using the INSIGHT method with a library of more than 5,000 formulations, they found potent penetration enhancers that cause minimal skin irritation. Two promising formulations increased the flux of macromolecular drugs across skin during in vitro experiments. And one formulation was used to deliver leuprolide acetate across the skin of hairless rats in vivo.

Contaminants in farmed salmon

Farm-raised salmon hold more persistent chlorinated contaminants, including polychlorinated biphenyls and dioxins, than those caught in the wild, according to a research collaboration led by environmental chemistry professor Ronald A. Hites at Indiana University [Science, 303, 226 (2004)]. In addition, farmed salmon bought in European cities hold more contaminants than equivalent fillets picked up in North American cities. (Much of the farmed salmon sold in the U.S. comes from Canada and Chile; salmon sold in Europe are usually raised in European waters.) The researchers suspect that farm-raised salmon accumulate more contaminants because of what they eat. Feed used on salmon farms consists of fish oil and meal made from small oceanic fish. The oil concentrates the contaminants. And perhaps European feed holds a higher load of contaminants, the researchers say, because it comes from the more industrial waters of Europe's North Atlantic compared with the waters off North and South America.