In This Issue

doi:10.1073/iti1110107

New Research In

Leptin may provide improved treatment for diabetes

Mouse pancreatic islet of Langerhans typical for a type 1 diabetes model.

Since its discovery in 1922, insulin injection has remained the primary treatment for Type 1 diabetes patients. However, insulin levels are difficult to regulate and too much of the hormone may enhance a person’s risk of elevated cholesterol, fat levels, and coronary artery disease. May-Yun Wang et al. (pp 4813–4819) report that treating diabetic mice with leptin provided equivalent or improved disease management compared to insulin. Leptin treatment also reduced the animal’s body fat, cholesterol, and risk factors for heart disease. The authors found that nonobese, diabetic mice treated with leptin alone or with low-dose insulin demonstrated similar or superior blood sugar normalization and disease recovery compared to mice treated with only insulin, but that mice treated with leptin also exhibited significantly reduced cholesterol-producing enzyme levels. The authors suggest that leptin’s down-regulation of fat and cholesterol formation relative to insulin may be due to leptin’s ability to stimulate lipid oxidation. Although their initial study used high doses of leptin, later experiments demonstrated that doses small enough to be practically administered to humans may be equally as effective, according to the authors. — J.M.

Single DNA mutation increases pain

As little as a single nucleotide polymorphism may contribute to increased pain sensations associated with several common diseases, a finding that may lend insight into analgesics and that could help researchers better understand pain perceptions. Frank Reimann et al. (pp. 5148–5153) identified the SNP SCN9A in a sample of 578 Caucasians with osteoarthritis and found the same mutation in patients with sciatica, phantom pain, back problems, and pancreatitis. A subsequent analysis of 186 healthy women revealed that those with the mutation—an exon of the gene for the sodium channel protein Nav1.7, which has been previously identified as a cause of rare pain disorders—felt enhanced pain sensations. Patch clamp recordings showed that the mutated protein channel stayed open longer than the normal channel. The longer time open likely causes more activation of C-fibers, which produces sensations of diffuse, dull, aching pain, according to the authors. The authors suggest that drugs designed to modify the protein’s activity could make effective painkillers. The study could help explain how genetic differences in patients can affect the varying responses they have to different classes of painkillers. — P.D.

Simulations shed light on solar cells

Iodide near the dye interface of dye sensitive solar cells.

Dye sensitized solar cells (DSSCs) convert sunlight into electricity with less bulk, greater mechanical robustness, and less expensive materials than traditional solid state solar cells. DSSCs are proposed to provide energy to small needs consumers such as home owners. The cells work by replacing a solar cell’s silicon inversion layer, which is used in traditional solar cell designs as a source of photoelectrons and charge separator with photosensitive dye-coated semiconductor particles and a liquid electrolyte. The dye sensitized cells, however, suffer from lagging performance compared with traditional solar cells. Florian Schiffmann et al. (pp. 4830–4833) explored the key reaction mechanisms of DSSCs and uncovered the electron regeneration process and oxide–electrolyte interaction in a representative type of high-efficiency DSSCs. The authors demonstrated that dye regeneration likely occurs in the system via a barrier-free pathway from the oxidized dye and iodide ions to the reduced dye and triiodide ions, which completes the electrical circuit and replenishes electrons in the cell. The study may help researchers optimize the design of DSSCs and increase the conversion efficiency of the cells, according to the authors. — J.M.

Smokers’ brains yield insights into nicotine addiction

Brain nicotine distribution for dependent smokers after inhalation.

Breaking a person’s smoking habits and ending their nicotine addiction has proven difficult, in part because researchers do not have a full understanding of why smokers are addicted. Jed Rose et al. (pp. 5190–5195) challenged one popular theory called Russell’s “high nicotine boli” hypothesis, which suggests that brain nicotine concentrations spike with each cigarette puff, and that those spikes are associated with addiction. The authors used positron emission tomography and 11C-nicotine loaded into cigarettes to compare nicotine accumulation in the lungs and brains of dependent smokers with nicotine accumulation in non-dependent smokers. The study found no such spikes as predicted by Russell’s theory. Rather, the authors found that nicotine levels rose steadily after each puff so that each successive puff was superimposed on a brain nicotine concentration that was still rising. In addition, nicotine accumulated slower in the brains of dependent smokers, in part because nicotine washed out of their lungs and into their blood less efficiently. Dependent smokers then compensated for slower nicotine accumulation by inhaling a larger volume of smoke. The research suggests that nicotine dependence cannot be explained solely by faster accumulation of nicotine in the brain, according to the authors. — B.A.

Homophily and high school friendships

Previous research has shown that people tend to associate with others who are similar to themselves. Two factors thought to drive this tendency, referred to as homophily, are biases in individual preference and the rate of meeting people outside one’s peer group. Using an economics technique that estimates consumers’ preferences, Sergio Currarini et al. (pp. 4857–4861) analyzed homophily patterns in friendship networks in a sample from the National Longitudinal Study of Adolescent Health conducted among more than 90,000 students in grades 7–12 during the 1994–1995 school year in the United States. The authors discerned that both preference and meeting rates differ according to race, and may provide insights into the racial mix of high school students’ friends. The analysis showed that although Asian and Black students in the sample interacted significantly more often with members of their own race than did Whites and Hispanics, Asians placed the highest value on interracial friendships and Blacks the lowest. The authors speculate that this result may indicate that homophily among Black students stems from the combination of choice and chance, but the association tendency among White students depends primarily on preference. The study could help researchers and policymakers shape policies designed to produce high schools that are more fully integrated than present. — T.J.

Targeting a receptor for multiple myeloma

Control (right) and treated (left) mid-sections of bone fields.

Multiple myeloma is a cancer that affects a subset of plasma cells that reside in bone marrow. Despite improved survival with the use of pharmaceutical treatments and stem cell transplantation, myeloma remains incurable in humans. Myeloma is characterized by an imbalance between osteoblasts, which make bone, and osteoclasts, which remove and remodel bone, which creates a niche promoting tumor growth. Through cytokine profiling of bone marrow samples from multiple myeloma patients with and without bone disease, Sonia Vallet et al. (pp. 5124–5129) discovered that activin A, a member of the TGF-β family, is found at higher levels in patients with the bone disease. The authors show that activin A inhibits osteoblast differentiation in addition to promoting osteoclastogenesis in a mouse model of the human disease. The researchers show that RAP-011, a soluble activin A receptor, can restore bone homeostasis by reversing the effects of activin A and can inhibit tumor growth. Targeting the micro-environment that promotes tumor growth within plasma cells may represent a strategy for cancer therapeutics, according to the authors. — B.P.T.