Vitamin B3 Counters MS-like Symptoms in Mice

Multiple sclerosis is characterized by inflammatory episodes that trigger axonal demyelination, followed eventually by irreversible axon degeneration. Although there are several anti-inflammatory therapeutic agents in use for MS, none prevents axon loss. New research from the laboratory of Zhigang He, HMS associate professor of neurology at Children’s Hospital Boston, has found that injections of nicotinamide, a form of vitamin B3, may offer some protection against axonal degeneration in the murine model of MS, offering hope for a new therapy. The study was led by research fellow Shinjiro Kaneko and published in the Sept. 20 Journal of Neuroscience.

Image courtesy of Shinjiro Kaneko, reprinted
from the Journal of Neuroscience, ©2006
by the Society for Neuroscience

Vitamin B3 treats mouse MS. Injections of nicotinamide, a form of vitamin B3, appear to delay the onset of symptoms and to reduce their severity in a mouse model of multiple sclerosis, called experimental allergic encephalomyelitis (EAE). When EAE was induced in wild-type mice, those that received either low-dose (orange line) or high-dose (pink line) injections of nicotinamide had improved (lower) behavioral scores over time when compared with mice that received placebo injections (dark blue line). This effect was particularly noticeable in the Wld^s mutant mice (aqua line), which have abnormally high levels of the enzyme that converts nicotinamide to its neurologically protective form.

When an axon is severed from its cell body, it degenerates quickly. The entry point for Kaneko and He’s study was a spontaneous mutation in certain mice, called Wld^s, that results in slower axonal degeneration. Studies in other laboratories had found that these mice have high levels of an enzyme that helps convert nicotinamide into nicotinamide adenine dinucleotide (NAD). “This was exciting, because it suggested to us that axonal degeneration may be an active process, something that could be changed,” said He. The He laboratory then showed that supplying NAD to degenerating axons in vitro significantly slows degeneration. “We immediately thought this might have in vivo relevance in the mouse model of MS,” said He.

Kaneko set out to test the idea that increasing the levels of NAD in the nervous system of MS-model mice would prevent axon loss. He induced experimental autoimmune encephalomyelitis (EAE) in both wild-type mice and in Wld^s mutant mice and treated part of each group with subcutaneous injections of nicotinamide each day. The treated mice showed a delayed onset of neurological deficits, with attenuated severity. Histologically, the number of demyelinated but still surviving axons was increased in the treated animals. The behavioral and histological effects were seen in both wild-type and Wld^s mutant mice, but were most pronounced in the mutants. Most strikingly, Kaneko also found that injected nicotinamide was therapeutically active even when treatment was delayed by 10 days, mimicking the chronic phase of MS.

“Nicotinamide and other components of the NAD pathway show very good promise for treating MS, since they easily cross the blood–brain barrier,” said He. Because the protective benefit of nicotinamide began to wear off after four weeks, Kaneko and He are now focusing on other components of the NAD synthetic pathway that appear to have even stronger therapeutic effects.

—Jillian Lokere

Prostate Cancer Therapy May Raise Diabetes and Heart Risks

Most prostate cancers are indolent. For men with nonaggressive local or regional prostate cancer, the five-year survival rate approaches 100 percent—regardless of treatment given, or not given. Nonetheless, over the last decade, androgen-deprivation therapy with gonadotropin-releasing hormone (GnRH) agonists has soared, and up to one third of men with local and regional prostate cancer now receive androgen blockers. Surprisingly, men with prostate cancer are actually more likely than others to die of causes other than cancer. Now, HMS researchers led by Nancy Keating, assistant professor of health care policy, report that anti-androgenic therapy may contribute to noncancer mortality.

The study shows an association between GnRH agonists and incident diabetes (adjusted hazard ratio (HR), 1.44; P < .001), coronary heart disease (adjusted HR, 1.16; P < .001), acute myocardial infarction (adjusted HR, 1.11; P = .03), and sudden cardiac death (adjusted HR, 1.16; P = .004). Orchiectomy also raised the risk of diabetes (HR, 1.34; P < .001) but not that of heart disease, heart attack, or sudden cardiac death. The research appears in the Sept. 20 Journal of Clinical Oncology.

“The association of GnRH agonists with increased risk of diabetes and cardiovascular disease appears biologically plausible,” write Keating and her colleagues, alluding to earlier research by co-author Matthew Smith, HMS associate professor of medicine at Massachusetts General Hospital. Smith showed that men on hormone antagonists developed central obesity, loss of muscle mass, increased fasting insulin, and insulin resistance. Other research suggests androgen blockers may contribute to sudden cardiac death, arterial stiffness, and a rise in serum lipoproteins.

In this study, 73,196 fee-for-service Medicare enrollees age 66 or older and diagnosed with locoregional prostate cancer from 1992 to 1999 were observed through 2001. Of this group, 36.3 percent received a GnRH agonist and 6.9 percent received orchiectomy. The researchers used Cox proportional hazards models to analyze the data.

Keating offers some caveats. Treatment was not randomized and perhaps other factors predisposing the subjects to diabetes or heart disease, such as other recently diagnosed diseases, might also be associated with receipt of androgen blockers. Nonetheless, she says, measures were taken to address the limitations.

The putative risks identified in the study rise quickly and remain elevated during treatment. Do they subside after stopping treatment? “We don’t know yet,” said Keating. “It may depend on how long it takes a man to regain gonadal function.”

Regarding treatment implications, “men who have metastatic disease or locally advanced, aggressive tumors should still get androgen blockers, although doctors should be alert for signs of diabetes and heart disease,” said Keating. As for those with nonaggressive locoregional disease, she urges “caution until the risks [of GnRH agonists] are better understood.”

—David Holzman

Cross-species Approach Finds Functional Transcription Factor Targets

Finding targets of your favorite transcription factor has just gotten easier, thanks to an interspecies bioinformatic approach designed by Erik Nelson, research fellow in the laboratory of David Frank, HMS assistant professor of medicine at the Dana–Farber Cancer Institute. The scientists used the novel method to identify new targets of the oncogenic transcription factor STAT5; however, they believe the technique will be broadly applicable to any transcription factor with a known consensus binding sequence.

A main goal of the Frank laboratory is to design small-molecule therapeutics that are active against cancer cells. To accomplish this, they have sought to identify the genetic targets of oncogenic transcription factors like STAT5, which play a major role in mediating the neoplastic transformation of mutated cells. Although using bioinformatics to search for transcription factor targets is not new, the difference in Nelson’s method is its reliance on interspecies homology. “Over the years, we’ve put a lot of thought and effort into identifying the targets of transcription factors,” said Frank. “As more and more genomes have been sequenced, we’ve tried to leverage the data to better address that goal.”

Work from the Frank laboratory and others has shown that control regions of DNA are often conserved across species. Nelson therefore reasoned that he would be able to locate new, functional targets of STAT5 by searching for its binding site only in non–protein-coding areas of the human genome that have extensive interspecies homology. He focused on human chromosomes 21 and 22, which are small and well-characterized, and located the STAT5 binding site in noncoding regions of 200 bases or fewer with greater than 70 percent homology between human and mouse or rat. Lead author Nelson further narrowed his results to only those in which the STAT5 binding sites had 100 percent homology among the human, chimp, mouse, and rat genomes.

Of the four regions identified using this method, one was located in a known STAT5 target, providing a proof of principle. A second site was found within a natural killer cell gene called NCAM2. Further in vivo experiments confirmed that NCAM2 is a functional target of STAT5. The research appears in the Sept. 8 Journal of Biological Chemistry.

“Traditionally people have studied one gene at a time,” said Frank, “but we now know that key transcription factors regulate multiple genes at once to produce biological effects. This type of approach can be very powerful for identifying groups of targets, and the beauty of it is that all you need is a known consensus binding sequence and a computer.”

—Jillian Lokere

top