HIGH SALT PREVENTS WEIGHT GAIN IN MICE ON A HIGH FAT DIET

In a study that seems to defy conventional dietary wisdom, University of Iowa scientists have found that adding high salt to a high-fat diet actually prevents weight gain in mice.

As exciting as this may sound to fast food lovers, the researchers caution that very high levels of dietary salt are associated with increased risk for cardiovascular disease in humans. Rather than suggest that a high salt diet is suddenly a good thing, the researchers say these findings really point to the profound effect non-caloric dietary nutrients can have on energy balance and weight gain.

"People focus on how much fat or sugar is in the food they eat, but [in our experiments] something that has nothing to do with caloric content -- sodium -- has an even bigger effect on weight gain," say Justin Grobe, PhD, assistant professor of pharmacology at the UI Carver College of Medicine and co-senior author of the study, which was published in the journalScientific Reports on June 11.

The UI team started the study with the hypothesis that fat and salt, both being tasty to humans, would act together to increase food consumption and promote weight gain. They tested the idea by feeding groups of mice different diets: normal chow or high-fat chow with varying levels of salt (0.25 to 4 percent). To their surprise, the mice on the high-fat diet with the lowest salt gained the most weight, about 15 grams over 16 weeks, while animals on the high-fat, highest salt diet had low weight gain that was similar to the chow-fed mice, about 5 grams.

"We found out that our 'french fry' hypothesis was perfectly wrong," says Grobe, who also is a member of the Fraternal Order of Eagles Diabetes Research Center at the UI and a Fellow of the American Heart Association. "The findings also suggest that public health efforts to continue lowering sodium intake may have unexpected and unintended consequences."

To investigate why the high salt prevented weight gain, the researchers examined four key factors that influence energy balance in animals. On the energy input side, they ruled out changes in feeding behavior -- all the mice ate the same amount of calories regardless of the salt content in their diet. On the energy output side, there was no difference in resting metabolism or physical activity between the mice on different diets. In contrast, varying levels of salt had a significant effect on digestive efficiency -- the amount of fat from the diet that is absorbed by the body.

"Our study shows that not all calories are created equal," says Michael Lutter, MD, PhD, co-senior study author and UI assistant professor of psychiatry. "Our findings, in conjunction with other studies, are showing that there is a wide range of dietary efficiency, or absorption of calories, in the populations, and that may contribute to resistance or sensitivity to weight gain."

"This suppression of weight gain with increased sodium was due entirely to a reduced efficiency of the digestive tract to extract calories from the food that was consumed," explains Grobe.

It's possible that this finding explains the well-known digestive ill effects of certain fast foods that are high in both fat and salt, he adds.

Through his research on hypertension, Grobe knew that salt levels affect the activity of an enzyme called renin, which is a component in the renin- angiotensin system, a hormone system commonly targeted clinically to treat various cardiovascular diseases. The new study shows that angiotensin mediates the control of digestive efficiency by dietary sodium.

The clinical usefulness of reducing digestive efficiency for treating obesity has been proven by the drug orlistat, which is sold over-the-counter as Alli. The discovery that modulating the renin-angiotensin system also reduces digestive efficiency may lead to the developments of new anti-obesity treatments.

Lutter, who also is an eating disorders specialist with UI Health Care, notes that another big implication of the findings is that we are just starting to understand complex interactions between nutrients and how they affect calorie absorption, and it is important for scientists investigating the health effects of diet to analyze diets that are more complex than those currently used in animal experiments and more accurately reflect normal eating behavior.

"Most importantly, these findings support continued and nuanced discussions of public policies regarding dietary nutrient recommendations," Grobe adds.

In addition to Grobe and Lutter, the UI research team included Benjamin Weidemann; Susan Voong; Fabiola Morales-Santiago; Michael Kahn; Jonathan Ni; Nicole Littlejohn; Kristin Claflin; Colin Burnett; and Nicole Pearson. The study was funded in part by grants from the National Heart, Lung and Blood Institute, the American Diabetes Association, and American Heart Association.

HIGHLY EFFECTIVE NEW ANTI CANCER DRUG SHOWS FEW SIDE EFFECTS IN MICE

A new drug, known as OTS964, can eradicate aggressive human lung cancers transplanted into mice, according to a report in Science Translational Medicine. The drug, given as a pill or by injection, inhibits the action of a protein that is overproduced by several tumor types, including lung and breast, but is rarely expressed in healthy adult tissues. Without this protein, cancer cells fail to complete the cell-division process and die.

When taken by mouth, the drug was well tolerated with limited toxicity. An intravenous form, delivered within a liposome, was just as effective with fewer side effects. Both approaches -- described in the October 22, 2014 issue of Science Translational Medicine -- led to complete regression of transplanted tumors.

"We identified the molecular target for this drug ten years ago, but it took us nearly a decade to find an effective way to inhibit it," said study author Yusuke Nakamura, MD, PhD, professor of medicine at the University of Chicago and deputy director of the University's Center for Personalized Therapeutics. "We initially screened 300,000 compounds and then synthesized more than 1,000 of them, and found a few that were likely to work in humans. We focused on the most effective. We think we now have something very promising."

OTS964 targets TOPK (T -- lymphokine-activated killer cell -- originated protein kinase), a protein that is produced by a wide range of human cancers and is believed to promote tumor growth. High TOPK expression correlates with poor prognosis in patients with breast and lung cancer.

Initial studies of the drug, and a precursor called OTS514, found they were effective in killing cancer cells. But they could disrupt the production of new red and white blood cells, causing hematopoietic toxicity such as mild anemia and increasing the risk of infection. At the same time, the drugs increased the production of platelets, which help in blood clotting.

When the researchers encapsulated the drugs in liposomes -- microscopic bubbles similar to a cell membrane, commonly used to transport drugs within the body -- the drug no longer caused this decrease in red and white blood cells. This approach "completely eliminated the hematopoietic toxicity," the researchers wrote.

They tested OTS964 alone and in liposomes in mice with a highly aggressive human lung tumor known as LU-99. They allowed the tumors to grow to 150 cubic millimeters -- about the size of a raisin -- and then administered the drug intravenously to six mice, twice a week for three weeks. The tumors shrank rapidly and continued to shrink even after treatment stopped. In five of the six mice, the tumors completely disappeared -- three within 25 days of the first treatment and two within 29 days. Mice that received the liposome-coated drug had no detectable toxicity.

The drug also proved effective when taken in larger doses by mouth. Six mice with LU-99 lung tumors were fed 100 milligrams per kilogram of OTS964 every day for two weeks. Again, continuous tumor shrinkage was observed after the final dose of the drug. In all six mice the tumors completely regressed. All of the mice had low white-blood-cell counts after treatment, but they recovered within two weeks.

Although this was a small study, the outcome was dramatic. Seeing these results was a "quite exciting moment," said Nakamura, who stepped down from his role as Director in the Japanese Government's Office of Medical Innovation to join the faculty at the University of Chicago in April 2012. "It is rare to see complete regression of tumors in a mouse model," he said. "Many drugs can repress the growth, but it is uncommon to see them eradicated. This has rarely been reported."

Similar studies of the drug's effects on tumor cells growing outside the body enabled the researchers to videotape the process as the cancer cells died. TOPK appears to play a central role late in cytokinesis, the final stage in cell division. Dividing cancer cells would begin to separate into two new cells, but were unable to fully disconnect, retaining an intercellular bridge.

"Without TOPK the cells can't seem to divide; they can't make the break," Nakamura said. "They can't complete the process. Instead they remain tethered by a tiny bridge. When that finally breaks apart, they can't close the membrane. Everything within the cells spills out, they suffer and then die."

TOPK may provide a good drug target for several types of cancer. This study involved primarily lung cancers, but the gene is frequently upregulated in breast, brain, liver, bladder and other solid tumors as well as certain types of leukemia. The researchers are working with oncologists at the University to begin a phase-1 clinical trial as soon as the fall of 2015.

EARLY ANTIBIOTIC EXPOSURE LEADS TO LIFE LONG METABOLIC DISTURBANCE IN MICE

A new study published in Cell suggests that antibiotic exposure during a critical window of early development disrupts the bacterial landscape of the gut, home to trillions of diverse microbes, and permanently reprograms the body's metabolism, setting up a predisposition to obesity. Moreover, the study shows that it is altered gut bacteria, rather than the antibiotics, driving the metabolic effects.

The new study by NYU Langone Medical Center researchers reveals that mice given lifelong low doses of penicillin starting in the last week of pregnancy or during nursing were more susceptible to obesity and metabolic abnormalities than mice exposed to the antibiotic later in life.

Most intriguing, in a complementary group of experiments, mice given low doses of penicillin only during late pregnancy through nursing gained just as much weight as mice exposed to the antibiotic throughout their lives.

"We found that when you perturb gut microbes early in life among mice and then stop the antibiotics, the microbes normalize but the effects on host metabolism are permanent," says senior author Martin Blaser, MD, the Muriel G. and George W. Singer Professor of Translational Medicine, director of the NYU Human Microbiome Program, and professor of microbiology at NYU School of Medicine. "This supports the idea of a developmental window in which microbes participate. It's a novel concept, and we're providing direct evidence for it."

The researchers stress that more evidence is needed before it can be determined whether antibiotics lead to obesity in humans, and the present study should not deter doctors from prescribing antibiotics to children when they are necessary. "The antibiotic doses used in this study don't mirror what children get," says Laura M. Cox, PhD, a postdoctoral fellow in Dr. Blaser's laboratory and the lead author of the study. "But it has identified an early window in which microbes can influence metabolism, and so further studies are clearly warranted."

In one experiment in the study, Dr. Cox administered water with low doses of penicillin to three groups of mice. One group received antibiotics in the womb during the last week of pregnancy and continued the medication throughout life. The second group received the same dose of penicillin after weaning and, like the first group, continued it throughout life. The third received no antibiotics. "We saw increased fat mass in both penicillin groups, but it was higher in the mice who received penicillin starting in the womb," Dr. Cox says. "This showed that mice are more metabolically vulnerable if they get antibiotics earlier in life."

The treated mice also grew fatter than the untreated mice when both were fed a high-fat diet. "When we put mice on a high-calorie diet, they got fat. When we put mice on antibiotics, they got fat," explains Dr. Blaser. "But when we put them on both antibiotics and a high-fat diet, they got very, very fat." Normally, adult female mice carry three grams of fat. The animals in the study fed the high-fat diet had five grams of fat. By comparison, the mice who received antibiotics plus the high-fat chow packed on 10 grams of fat, accounting for a third of their body weight. The treated rodents were not only fatter but also suffered elevated levels of fasting insulin, and alterations in genes related to liver regeneration and detoxification -- effects consistent with metabolic disorders in obese patients.

This work confirms and extends landmark research published by Dr. Blaser's lab in 2012 in Nature. That research showed that mice on a normal diet who were exposed to low doses of antibiotics throughout life, similar to what occurs in commercial livestock, packed on 10 to 15 percent more fat than untreated mice and had a markedly altered metabolism in their liver.

Among the unanswered questions in that study was whether the metabolic changes were the result of altered bacteria or antibiotic exposure. This latest study addresses the question by transferring bacterial populations from penicillin-exposed mice to specially bred germ-free, antibiotic-free mice, starting at three weeks of age, which corresponds to infancy just after weaning. The researchers discovered that mice inoculated with bacteria from the antibiotic-treated donors were indeed fatter than the germ-free mice inoculated with bacteria from untreated donors. "This shows us that the altered microbes are driving the obesity effects, not the antibiotics," says Dr. Cox.

Contrary to a longstanding hypothesis within the agricultural world that holds that antibiotics reduce total microbial numbers in the gut, therefore reducing competition for food and allowing the host organism to grow fatter, the team found that the penicillin did not, in fact, diminish bacterial abundance. It did, however, temporarily suppress four distinct organisms early in life during the critical window of microbial colonization:Lactobacillus, Allobaculum, Candidatus Arthromitus, and an unnamed member of theRikenellaceae family, which may have important metabolic and immunological interactions. "We're excited about this because not only do we want to understand why obesity is occurring, but we also want to develop solutions," says Dr. Cox. "This gives us four potential new candidates that might be promising probiotic organisms. We might be able to give back these organisms after antibiotic treatments."

The researchers worked with six different mouse models over five years to obtain their results. To identify bacteria, they used a powerful molecular method that involves extracting DNA and sequencing a subunit of genetic material called 16S ribosomal DNA. Altogether, the scientists evaluated 1,007 intestinal samples, which yielded more than 6 million sequences of bacterial ribosomal genes, the order of the nucleotides that spell out DNA. Studies like these are possible because of technological advances in high-throughput sequencing, which allows scientists to survey microbes in the gut and other parts of the body. The Genome Technology Center at NYU Langone Medical Center played a key role in identifying the genetic sequences in the study.