It's Pomegranate Season

by Margaret Hill

For pomegranate lovers, pomegranate season is too short. The California orchards that supply U.S. markets begin harvesting in October and wrap up by January. Right now, you can find plump, tasty samples in your local grocery store, but get them while you can, for their availability is short-lived. Fortunately, pomegranate juice is sold year-round, so if you miss the fruit harvest, you can still enjoy the juice whenever you like.

Your body will love you for it, too—plenty of research suggests that pomegranate juice has strong health benefits. As elaborated in two articles published this year in the Proceedings of the National Academy of Sciences, pomegranate juice has positive effects on cardiovascular health and can slow tumor growth.

Improving Cardiovascular Health

A study led by Claudio Napoli, professor of medicine and clinical pathology at the University of Naples in Italy (Proc. Natl. Acad. Sci. USA 102: 4896–4901, 2005), demonstrated that pomegranate juice reduces atherosclerotic lesions in mice bred to develop the disease. The juice, which the mice drank diluted in their water supply, significantly slowed the onset of atherosclerosis in mice that had not yet developed it and reversed it in mice with existing lesions.

In exploring the mechanisms behind these effects, Napoli’s group showed that the juice did two things: It enhanced production of the enzyme nitric oxide synthase, and it reduced production of two transcription factors involved in stimulating oxidative metabolism. The researchers demonstrated both of these activities in living mice, and in human cardiovascular cells grown in culture.

The effect on nitric oxide synthase is significant because this is the enzyme responsible for generating nitric oxide, a small signaling molecule necessary for relaxation and dilation of blood vessels. Atherosclerosis is accompanied by a loss of production of this important metabolic messenger. Atherosclerosis is also accompanied by increases in oxidative degradation of cellular components at lesion sites. Reversal of these processes can reestablish good cardiovascular health, as the researchers showed.

Slowing Cancer

Another group at the University of Wisconsin investigated pomegranate juice and its effects on human cancer cells in culture and on mice with actively growing tumors (Proc. Natl. Acad. Sci. USA 102: 14813–14818, 2005). Led by Hasan Mukhtar, director and vice chair for research in the department of dermatology, this team found that pomegranate extracts inhibited cell proliferation in culture and slowed tumor growth in living mice.

Test animals received pomegranate extract in their water supply: one group received an amount that corresponds to the human equivalent of a daily 8-oz glass of juice, and a second group received a 16-oz equivalent. A third group received water only. After receiving injections of cancer cells, the mice consuming the highest dose took 50 days to develop tumors of a size that water-fed mice developed in about 30 days. It took about 40 days for the mice receiving the low pomegranate dose to grow tumors of similar size.

A probable mechanism underlying this effect became apparent during experiments with human prostate carcinoma cells grown in culture. When pomegranate extract was added to these cultures, cell growth dropped off. A further look at changes in cellular protein profiles revealed that the pomegranate-treated cells were producing proteins characteristic of apoptosis, or programmed cell death. Nontreated cells did not share this characteristic.

Researchers from both studies have yet to determine the identities of the specific compounds responsible for the observed effects. Many lines of research from these and other labs point to polyphenols as likely contenders. Pomegranate juice is rich in compounds of this class, which are known to have potent antioxidant properties. Future work is expected to identify the active agents as well as to provide more detail about their molecular mechanisms of action.