10 June 2005. The recent emphasis on caloric restriction (CR) as a means to extend lifespan didn’t stop the American Aging Association from serving up plenty of exciting presentations at their 34th annual meeting held last weekend in Oakland, California. Check back over the next few days when we’ll be posting summaries of the most appetizing fare, starting today with a summary of the 1-day pre-meeting symposium on nutrition and successful aging.
Eat, Drink, and Age Successfully
The 1-day symposium, hosted by Jim Joseph of Tufts University, Medford, Massachusetts, addressed the impact of nutrition and lifestyle on aging and neurodegenerative disease. Stephane Bastianetto, Douglas Hospital Research Centre, Verdun, Canada, got the morning off to a brisk start when he reported on experiments to identify how polyphenols derived from wine and green or black tea can act as neuroprotective agents.
The polyphenol resveratrol, found in grapes and red wine, has, of course, been linked to increased lifespan in yeast and worms (see ARF related news story), and more recently has been shown to protect against polyglutamine toxicity in roundworms (see ARF related news story). Bastianetto found that only some compounds in teas, those gallate esters of polyphenols, such as epicatechin gallate and epigallocatechin gallate (EGCG), can compete for resveratrol binding in rat brain homogenates. Non-gallate esters, such as epicatechin and epigallocatechin, did not compete with resveratrol, suggesting that polyphenols have multiple sites of action. In addition, only those compounds that did compete for resveratrol binding seem to protect against the toxic effects of amyloid-β. Bastianetto reported that EGCG protected hippocampal neurons treated with the fibrillogenic Aβ25-35 (see ARF related news story), as did epicatechin gallate, though this polyphenol was slightly less effective. Epigallocatechin or catechin itself failed to spare neurons.
How these polyphenols protect against Aβ is unclear. Resveratrol has been shown to stimulate deacetylases and may prevent apoptosis (see ARF related news story). While other polyphenols that compete for resveratrol binding might have similar modes of action, it is generally believed that these compounds are beneficial to cells and organisms because they are very good quenchers of reactive oxygen species (ROS). But when Bastianetto compared the antioxidant activity of these polyphenols, he found that EGCG and epigallocatechin are equally effective in cultured neurons, indicating that the reduction of ROS species cannot explain why EGCG alone protects against Aβ. Instead, Bastianetto suggested that this particular polyphenol might well inhibit formation of Aβ oligomers.
But the antioxidant activity of polyphenols should be not be dismissed. Polyphenolics from nuts can help reduce the risk of cardiovascular disease by up to 25 percent, Jeffrey Blumberg, Tufts University, reminded us. In fact, so good are the epidemiological data on the inverse relationship between nut consumption and coronary heart disease that the FDA came up with a “B level health claim for nuts which states: ‘scientific evidence suggests, but does not prove, that consuming 1.5 ounces per day of most nuts as part of a diet low in saturated fat and cholesterol can reduce the risk of heart disease,’” said Blumberg. Those partial to Brazil, macadamia, and cashew nuts will be disappointed to hear that those particular varieties are not included in the dietary claim, mostly because of their high saturated fat content, but walnuts, almonds, pistachios, hazelnuts, and pecans are.
So how do nuts protect against cardiovascular disease. Earlier studies showed that eating one to two ounces of almonds per day over about a month can lower total cholesterol by 6 percent, LDL cholesterol by 10 percent, and oxidized cholesterol by up to 14 percent (see Jenkins et al., 2002). It was the oxidized cholesterol finding that particularly intrigued Blumberg and colleagues.
Blumberg showed that almond skin phenolics (ASP) can increase the resistance of human LDL cholesterol to oxidation, and works in synergy with vitamin E in this regard. He also showed how a single dose of ASPs in vivo can increase the lag time to LDL oxidation, and that the polyphenols catechin, naringenin, and quercetin all increased in plasma in a time-dependent manner. Their appearance correlated with an increase in the ratio of reduced:oxidized glutathione, indicative of the antioxidant properties of the phenols.
Navindra Seeram of the UCLA Center for Human Nutrition also addressed the issue of bioavailability of polyphenols. Yes, these high-molecular-weight compounds may have a variety of effects in vitro and in vivo, but in what state do these compounds actually reach the blood or target tissues?
Seeram reported some data on absorption of polyphenols from pomegranate juice. This juice is a rich source of polyphenols and has potent anti-atherosclerosis activity in ApoE-deficient mice and in in vitro models.
In mice, punicalagin, one of the major pomegranate polyphenols, has been found to cross the gut into the blood even though it is a relatively large molecule (mol wt 1,084). But what about in humans? Are we getting equivalent doses when we imbibe? Seeram found that, in fact, we are not. Instead, elagic acid, a product of punicalagin hydrolysis, turns up in the plasma and urine of human volunteers given the juice after being starved of polyphenols for four days. The finding suggests that we should take care not to rely too heavily on mouse bioavailability data when considering human nutrition. In fact, bioavailability turns out to be a very complex affair, something you might want to consider next time you peruse or plan a menu. Steven Schwartz from Ohio State University showed how carotene uptake can be profoundly influenced by the other food on your plate.
Carotenes come in two flavors, hydrocarbon carotenes like lycopene, and their oxygenated analogs, the xanthophylls. There are over 700 natural carotenes identified to date and they include vitamin A and provitamin A, and other essential compounds such as lutein and zeaxanthin, which prevent the photo-oxidation that causes macular degeneration. Epidemiological studies show that carotene may help fight against a wide variety of cancers including prostate cancer.
But carotenes are hydrophobic and their absorption may depend on emulsification or other processing in the intestine. Lycopene, for example, found in tomatoes as predominantly the all trans variety, turns up in mammalian tissues as 65-80 percent cis lycopene (cis and trans refer to the relative positions of carbon chains about a carbon-carbon double bond, which is rotationally constrained). Even in cooked tomatoes, lycopene is all trans, so clearly there are some chemical rearrangements going on in vivo, either during or after absorption from the gut. And yet, cooking your tomatoes might turn out to be not such a bad idea. Schwartz found that lycopene is more readily absorbed from tomato sauce or tomato soup than from V8 tomato juice, indicating that cooking or food processing helps to make the carotene more biologically available.
And for those who like tomatoes raw, consider using full fat dressing on your next salad. Schwartz showed how different dietary components, particularly the presence of lipids, can dramatically impact lycopene uptake. He showed how full fat dressing gave maximal uptake of lycopene from raw tomatoes. Low fat dressing did help, but with non-fat dressing, the amount of lycopene absorbed was virtually nil. The findings may help explain why the Mediterranean diet, though drizzled as it is with olive oil, is still good for you. And for those of you who insist on that non-fat dressing, try spicing up your salad with avocado. Schwartz found that the pear-shaped veggie, weighing in at 17 percent lipid, is not so green when it comes to helping the absorption of lycopene from tomatoes, working almost as well as the full fat dressing. Guacamole and salsa, anyone?
Dietary balance also served as the theme for Rui Hai Liu, from Cornell University, New York. Liu emphasized how important it is to consider the whole package of micronutrients rather than focusing on one or two flavors of the month. “Why has the single antioxidant approach to therapy never proven to be effective?” he asked. In a recent study that tested the potential of β-carotene to prevent cancer, for example, those taking the supplement actually did worse than did those on placebo. Is this because the dose wasn’t optimal, or is it because we are better sticking to whole fruits and vegetables? he asked (see also recent ARF related news story on vitamin E and Alzheimer disease and ARF related news story on the potential benefit of vitamin E in reducing the risk of Parkinson disease).
Here’s some evidence for the whole food approach. Liu reported how there are about 5.7 mg of vitamin C in 100 g of your average apple. But the same amount of apple contains the equivalent of 1,500 mg of vitamin C when the total antioxidant power of the fruit is measured. In fact, Liu presented data showing how, in a dose-dependent manner, apple extract can prevent the growth of breast cancer cells in mice. Apple extract also reduces the total number of tumors and the average tumor size.
Other fruit extract has similar properties. Grape extract, he showed, can prevent expression of proliferating cell nuclear antigen (PCNA), a tumor cell marker, in mice, while cranberry or apple extract can induce arrest of mitosis in the G1 phase of cell division in MCF7 breast cancer cells. There are over 8,000 known phytochemicals that we can access in our diet, and Liu suggested that some, if not many, of these may act synergistically. The EC50s for the two polyphenols catechin and chlorogenic acid, for example, are halved if the compounds are given together.
Fight Fire with Antioxidants
So how might dietary nutrients be of help to the aged and aging? Simin Meydani from Tufts University reported on the effects of antioxidants in aged macrophages. These cells are involved in inflammatory responses, which of course have been linked to a variety of diseases including cardiovascular, autoimmune, and neurodegenerative diseases. Meydani showed how macrophages from older animals produced more prostaglandin E2 (PGE2) when exposed to the inflammatory toxin bacterial lipopolysaccharide (LPS) than do those cells isolated from younger animals. As PGE2 stimulates the release of proinflammatory cytokines, this may explain, in part, why inflammatory responses are more pronounced in the aged.
What leads to the increase in PGE2? Meydani’s work has shown that the increased production of the prostaglandin in the LPS-treated older macrophages is due to increased activity of cyclooxygenase (COX). This enzyme comes in two isoforms, COX-1 and COX-2. Inhibitors of the latter have been studied for their potential to slow the progression of AD, but those trials have been stopped due to safety concerns (see ARF related news story). COX-2, rather than COX-1, also appears to be the culprit in the increased PGE2 in older macrophages as Meydani showed that the activity of this enzyme is significantly and dramatically increased when these cells are treated with LPS.
There are several modulators that can influence production of COX-2, including glutathione and glucocorticoids, which decrease its expression, and cytokines such as interleukin-1 (IL-1), IL-6, and the sphingolipid ceramide, which all increase expression of the oxygenase. It was ceramide and glutathione that Meydani and colleagues found to modulate COX-2 in older macrophages. Ceramide and glutathione are, in fact, related, because glutathione inhibits the activity of sphingomyelinase, which is necessary for ceramide synthesis.
Meydani and colleagues found that old animals produce much higher levels of ceramide than do young during the initial response to LPS. Work in her lab has also shown that ceramide can lead to an increase in NF-κB, and that the NF-κB inhibitor I-κB is less abundant in older macrophages.
So how might dietary nutrients affect these signaling mechanisms? At first, Meydani looked at the influence of antioxidants because oxidizers such as peroxides have been implicated in the mechanism of action of the COX enzymes. She found that macrophages isolated from old mice that had been fed a diet high in vitamin E for 30 days had significantly lowered production of PGE2 in response to LPS than did cells isolated from mice fed normal lab chow. In contrast, vitamin E made no difference to production of PGE2 in macrophages from young mice.
But surprisingly, Meydani found that the COX-2 activity in the older, vitamin-supplemented macrophages was unchanged from controls. But she did find that vitamin E quenched the activity of peroxynitrite, a nitric oxide derivative that drives cyclooxygenase catalysis. This theory fits with another observation from the Meydani lab, namely, that levels of nitric oxide synthase are elevated in old macrophages (see Wu and Meydani, 2004).
The effect of vitamin E on macrophages might be clinically relevant as it has been shown to improve T cell-mediated function. Meydani also reported that when supplemented in the diet, it can reduce the incidence of upper respiratory infection in elderly nursing home residents.
Other interventions, including green tea and oat extracts, can also reduce PGE2 levels, reported Meydani. In fact, caloric restriction in humans has been shown to reduce PGE2 in blood mononuclear cells. PGE2 may be a very useful marker of aging, Meydani suggested.
Brain Food or Pie in the Sky?
Does brain food really exist? There are plenty of models of cognitive function that can be used to address this issue, not to mention studies on human volunteers. Michael Forster, North Texas Health Science Center, Forth Worth, reported on water maze experiments designed to test the effect of dietary supplements on cognition in the mouse.
Forster and colleagues tested vitamin E and coenzyme Q10 (CoQ) to determine if their antioxidant prowess could lead to smarter laboratory mice. When given as lifelong supplements, neither compound had much effect on survival (mice on the highest does of Q10, 370 mg/Kg body weight/day, actually tended to have a lower lifespan), and had no effect on performance in the classic Morris water maze test, where the animals must search for and climb to safety on a hidden platform in a water tank.
Similarly, vitamin E given late in life (18 months) failed to halt the normal cognitive decline in the laboratory mice, but while CoQ had no effect in the standard water maze test, when Forster and colleagues tried a slight variation on the theme, that is, moving the platform to a different location, they found that, compared to mice on normal chow, the CoQ-treated mice spent a significantly longer time searching the section of the tank where the platform used to be. This suggests that CoQ, when given late in life, does help to improve learning and working memory.
William Milgram, University of Toronto, Scarborough, Canada, reported similarly encouraging data from studies on cognitive performance in beagle dogs.
Dogs develop natural amyloid plaques with very similar pathology to that seen in humans. Magnetic resonance imaging of dog brain shows increased ventricular volume as the animals age, much like in humans, and the changes seem to correlate with cognitive decline.
Milgram and colleagues reported results from two trials of dietary antioxidant therapy, one in young and one in old dogs. The antioxidants included vitamin E and C, lipoic acid, L-carnitine and other controlled ingredients. Measurement of cognitive function consisted of testing the animal’s ability to discern one odd object out of a set of three. Correct choices were rewarded with food.
The results showed that two years on the antioxidant diet had little effect on the young animals. The older animals, however, had much better performance in the discrimination task. Those dogs that had also been treated with a special behavioral enrichment program also did better, while dogs that received both the antioxidant and the special program did best of all. Postmortem analysis showed that dogs that did better in the cognitive tests also had reduced plaque load in the entorhinal, parietal, and occipital cortices, but not in the prefrontal cortex.
Finishing up the day’s symposium, Greg Cole, VA Medical Center, UCLA, reported on a theme much covered on Alzforum, the turmeric spice curcumin (see ARF related news story). Cole has previously shown that the spice works at multiple levels. In transgenic mice expressing human Aβ precursor protein (AβPP), curcumin reduces the number of plaques. In vitro it appears to activate microglia surrounding plaques, and it can also disassemble Aβ fibrils, and reduce oxidative damage. Because the spice is widely used, has been through many toxicological studies, and is readily available, it could be of enormous benefit in slowing the progression of AD. So logically, the next step is a pilot clinical trial, which Cole reported is now ongoing at UCLA. The plan is to test 40 or so volunteers for a variety of parameters including bioavailability, oxidative damage, cognitive function, brain imaging, and cerebrospinal fluid markers.
In the pre-conference symposium, Donald Ingram, National Institute on Aging, and Larry Reagan, University of South Carolina, gave presentations on caloric restriction in primates and insulin resistance in aging, respectively, which we shall report in our coverage of the main conference.—Tom Fagan.