Characteristics Defined for Therapeutic Nanoparticles

Nanoparticles have great potential for patient treatment, but researchers remain unsure of the optimal size and charge of these particles so nanoscale devices can efficiently exit the body once their therapeutic work is done.

Courtesy John Frangioni

Go with the flow. In vivo fluorescence images track quantum dots flowing through mice ureters. In the two hours after mice received an intravenous injection of nanosized quantum dots with a cystine coating, the particles leave the bladder (Bl), travel down the ureter (Ur), and reach the kidneys (Ki) to be expelled from the body. (Scale bar, 1 cm.)

If nanoparticles are unable to either biodegrade into safe, biological components or fully leave the body, patients could experience amplified toxicity as they collect in the liver, spleen, and bone marrow. The side effects of in vivo nanoparticle accumulation are unknown. Residual particles could also interfere with medical imaging devices, including CT and ultrasound scans.

Reporting in the October Nature Biotechnology, John Frangioni, an HMS associate professor of radiology and of medicine at Beth Israel Deaconess Medical Center, and his colleagues determined the size requirements and charge characteristics for renal filtration and urinary excretion of inorganic, metal-containing nanoparticles.

Frangioni and his colleagues used quantum dots, metallic semiconducting particles that fluoresce when exposed to blue light, as models for metal-containing nanoparticles due to their similarity in size and composition. The quantum dots can be detected in tissue up to one centimeter thick. By monitoring the quantum dots in mice and rats, the researchers were able to define the optimal size and charge requirements for in vivo particles.

“Semiconductor formulations that exist today all have elements of either known or suspected toxicity,” said Frangioni. “In order for them to be viable, we need to be able to remove them from the body relatively quickly.”

The researchers synthesized several different quantum dots with similar cores and shells, but with varied coatings. Positively or negatively charged quantum dots were trapped in the body because serum proteins bound to them, thereby increasing their overall size to above 15 nm. To prevent proteins from being adsorbed, the researchers chose a zwitterionic coating, cysteine, for the nanoparticles.

“We tried different surface charges and different-sized particles to define what combination would be cleared rapidly from the body after intravenous injection,” said Frangioni, adding that “the blood half-lives are such that there is still adequate time for the dots to find targets.”

Ultimately, the researchers proposed three criteria—dubbed Choi criteria after the lead author, HMS research fellow Hak Soo Choi—that distinguish metal-containing nanoparticles with potential medical application. Nanoparticles should have a hydrodynamic diameter equal to or less than 5.5 nm, contain nontoxic components, and be composed of biodegradable or clearable components. According to Frangioni, “Unless we satisfy these criteria, we don’t consider the nanoparticle as having much medical utility because you run into the problem of extended exposure to the body.”

—Laura Geggel

Energy-boosting Protein Found to Tone Skeletal Muscle

The potent driver of gene expression, PGC-1 alpha, known for its role in energy balance and metabolism, appears critical to the stability of skeletal muscle, a new study in mice reports. The findings, from the lab of Bruce Spiegelman, where PGC-1 alpha’s role in mitochondrial function was first identified, offer insight into the mechanisms of skeletal muscle dysfunction. The study appears in the Oct. 12 Journal of Biological Chemistry.

Because a whole-body knockout of PGC-1 alpha (short for peroxisome proliferator–activated receptor gamma coactivator 1 alpha) results in an indistinct mix of disorders in mice, the researchers ablated the transcriptional coactivator only in skeletal muscle. PGC-1 alpha emerged as pivotal for maintenance of muscle fiber composition. The researchers found that the knockouts had a reduced number of oxidative type I and IIa muscle fibers and an increase in glycolytic IIx and IIb, fast-twitch fibers that quickly lose energy.

“Type I and IIa fibers, which are the most oxidative fibers, give muscles exercise tolerance and reduce fatigue ability,” said Spiegelman, HMS professor of cell biology at Dana–Farber Cancer Institute.

The mice lacking PGC-1 alpha in their skeletal muscle exhibited reduced endurance compared with control mice and increased muscle fiber injury (along with signs of regeneration). Expression levels in the skeletal muscle declined for mitochondrial genes, necessary for energy production, and for genes that support detoxification of reactive oxygen species, which can damage muscle fibers. Muscle injury in the knockouts rose markedly after physical activity. One demonstration of the decline in physical capacity for the knockouts was a test of muscle grip strength that showed a 60 percent drop in performance compared with control mice.

Since PGC-1 alpha also regulates genes involved in plasticity of the postsynaptic neurosmuscular junction, the knockouts had a lower number of acetylcholine clusters on muscle fiber membranes, suggesting the fibers might be insufficiently innervated.

Spiegelman and his colleagues observed increased levels of the cytokines IL-6 and TNF-alpha in the blood; the rise of TNF-alpha accompanied the increase in muscle fiber damage after exercise. TNF-alpha is known to cause inflammatory myopathies in rodent models and human patients. So the experimental mice may have harbored increased systemic inflammation, a strong promoter of skeletal muscle wasting.
“PGC-1 alpha appears to mediate almost every known effect of exercise on muscle,” Spiegelman said. “We hope we can use it in a way that will be therapeutically beneficial.”

Schizophrenia Care in Developing Countries May Not Be Superior

One of the surprising discoveries of international psychiatric research is that people with schizophrenia in developing countries seem to have better outcomes than those living in industrialized countries. “This has been one of the central findings of cultural psychiatry for 30 years,” said Alex Cohen, HMS assistant professor of social medicine. But a review by Cohen and researchers in England, India, and Nigeria casts doubt on this conception. The paper, published online Sept. 29 in Schizophrenia Bulletin, evaluates nearly two dozen studies on schizophrenia in the developing world and concludes that outcomes are not always so rosy.

Cohen said that the notion that schizophrenia is more benign in poorer countries came from a series of studies, including two large investigations from the World Health Organization, that compared outcomes among a small group of developed and developing countries. Both studies found that patients in developing countries fared better over time. The studies led to theories that less developed societies had close-knit family structures and social support that helped to lessen the severity and impact of the disease and that people with schizophrenia are better integrated into these societies through work and marriage.

But after reviewing data from 23 longitudinal studies in 11 low- and middle-income countries, Cohen and his colleagues found a picture that is much more complex. Outcomes, for example, varied widely across and even within countries. Measures of how well people with the disease functioned socially were also highly varied.

Furthermore, the review revealed important gaps in knowledge about schizophrenia in the developing world. For instance, mortality rates for people with schizophrenia are high, but deaths are often not incorporated into study results. And although relatively high marriage rates have been cited in support of the theory, the researchers found that marriages are still less frequent than in the general population, and divorce and separation rates are much higher.

There is also limited knowledge about how medical intervention or lack of it affects the outcomes of patients in developing countries. “The real revelation to me was that treatment is never mentioned in any of these studies,” Cohen said. He pointed out that in some cases, patients enrolled in studies were receiving care from clinics that provide the best possible care in the country, which may have just as much to do with their success as their family support.

Though the authors agree that the social environment might affect the course of disease, they call into question the idea that a country’s wealth alone is a useful distinction. “I don’t mean to totally deny that some societies have better outcomes than other societies, but to lump the entire developing world together does not stand up to the evidence. Even within India, there is tremendous variation,” Cohen said. Further research, he added, should compare sites with good outcomes and poor outcomes, and look for social, biological, or medical factors to explain the differences.

—Courtney Humphries

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