DHA and Angiogenesis: The Bottom Line

Posted by on May 4, 2011 72 comments

So I thought I’d finish up the series on DHA and angiogenesis by discussing 2 issues:

1.      First, an assertion: The pathway by which oxidized DHA drives angiogenesis may be really important for human health.

2.      Second, the $64,000 question: Is there evidence that high levels of dietary DHA promotes diseases of pathological angiogenesis? What about other dietary factors bearing on DHA oxidation?

Significance of the Oxidized DHA Link to Angiogenesis

The papers discussed in Friday’s post about a major angiogenesis pathway stimulated by oxidized DHA (Omega-3s, Angiogenesis and Cancer: Part II, April 29, 2011) may not seem important to many readers. But to cancer researchers and pharmaceutical companies, this is blockbuster work.

A tumor is, in the words of Hal Dvorak, “a wound that never heals.” [1] To support growth, cancers invoke the wound healing process – especially, creation of new blood vessels, or angiogenesis. But the tumor prevents the wound healing process from completing. If it ever did complete, then the tumor itself would be healed. It would cease to grow and become benign.

It’s been recognized for decades that an ability to block angiogenesis would effectively constitute a cure for cancer. The William Li video explains why: nearly everyone gets microscopic tumors that never develop the ability to induce angiogenesis. Life-threatening cancer is the result of tumors that can induce angiogenesis. No angiogenesis, and no one would die of cancer.

But existing anti-angiogenic cancer therapies have produced disappointing results. Avastin, an anti-angiogenic drug targeting VEGF (vascular endothelial growth factor), has been estimated to extend colon cancer patient lifespan by only 6 weeks.  (Nevertheless, Avastin generated $7.3 billion in revenue last year. Imagine how much money there would be in an anti-angiogenic therapy that worked!)

The work I discussed last Friday suggests a reason for that failure. Recall these pictures:

If only the VEGF pathway is blocked (upper right), there is almost as much angiogenesis and wound healing as in a normal wound (upper left). But when both the VEGF and TLR-2 angiogenic pathways are blocked (lower right), there is no wound healing.

If these are the operative pathways in cancer also, then blocking the TLR-2 angiogenesis pathway might be the key to cancer therapy.

But cancer is not the only disease of pathological angiogenesis. Others include:

  • Age-related macular degeneration, diabetic retinopathy, and retinopathy of prematurity – three common causes of blindness.
  • Atherosclerosis, which often features angiogenic vessels in thickened arterial walls.
  • Vascular malformations and tumors.
  • Obesity. Adipose tissue utilizes angiogenic pathways, and angiogenesis inhibition prevents the deposition of fat.
  • Rosacea, psoriasis, and some other skin conditions.
  • Endometriosis, uterine fibroids, and some other causes of female infertility.
  • Rheumatoid arthritis.
  • Crohn’s disease.
  • Preeclampsia.

It may be that the TLR-2 pathway is key to these diseases as well, and that a treatment that inhibits this pathway can cure or improve all of these diseases.

Add up the size of these markets and a pharmaceutical company executive would swoon.

Luckily, we’re not pharmaceutical company executives. But we can still get excited over possibilities to improve these diseases through diet and anti-microbial medicine.

Infections as Contributing Causes of These Diseases

TLR-2 is stimulated by other things besides oxidized DHA. In particular, TLR-2 is an immune molecule which is stimulated by pathogen proteins. As Wikipedia notes:

TLR-2 recognizes many bacterial, fungal, viral, and certain endogenous substances.

This tells us that many pathogens may stimulate angiogenesis through the TLR-2 pathway. As a result, anti-microbial medicines might help treat some diseases of pathological angiogenesis.

Some antibiotics, including doxycycline and minocycline, are known to exercise anti-angiogenic effects independent of the antibiotic effects. [2]

Diet-Induced Angiogenesis

Many foods affect angiogenesis. In fact, cancer studies have identified dozens of plant foods, from garlic to tomatoes to leeks, that possess anti-angiogenic properties.

However, foods can also promote angiogenesis. Let’s stick to the oxidized DHA pathway and see if there’s evidence that foods drive it.

You’ll recall the recipe was:

DHA + oxidative stress + retinyl protein = TLR-2 driven angiogenesis

If this pathway is important in human disease, then we should expect diseases of angiogenesis to be worsened by adding the ingredients on the left.

Specifically, cancer, AMD, rosacea, and so forth should be worsened by high doses of DHA, high doses of vitamin A, and low doses of antioxidant minerals like zinc or selenium.

Is there any evidence for that pattern?

Cancer Studies

First, let me give my bottom line on the Brasky study that kicked off this series. High tissue levels of DHA were associated with increased risk of high-grade prostate cancer, and the oxidized DHA angiogenesis pathway provides a mechanism for this association. What’s not clear is why tissue DHA levels were high. EPA levels were also elevated in the high-grade prostate cancers, but not by nearly as much as DHA levels. EPA and DHA appear together in fish and fish oil, so this suggests that fish consumption contributed to but was not the primary cause of the elevated tissue DHA. The drug finasteride greatly raised risk of high-grade prostate cancer, but the paper did not break down the DHA-cancer association between the finasteride and placebo arms. The most likely explanation, in my view, is that finasteride increases conversion of EPA to DHA and creates artificially high tissue DHA levels. The high DHA levels combined with oxidative stress drive cancer through the TLR-2 angiogenesis pathway.

A clever but unlikely alternative explanation was suggested by Peter at Hyperlipid: perhaps extra dietary fish oil raises testosterone levels. Prostate cancer is a hormone-dependent cancer and can be promoted by testosterone, just as breast cancer is promoted by estrogen. Possible supporting evidence comes from a paper showing an inverse association between metabolic syndrome / diabetes and prostate cancer. The trouble with this idea is that (a) this effect should have been strongest in the low-grade cancers, since diabetes reduced the incidence of low-grade cancers, but in the Brasky study DHA had no association with low-grade cancers, (b) fish oil lowers testosterone levels in rats, (c) in the Brasky study high-grade prostate cancers were strongly associated with obesity and the obese generally have low testosterone levels, and (d) surprisingly, high-grade prostate cancers are associated with low testosterone, not high. So one could argue that fish oil might promote high-grade prostate cancer by lowering testosterone!

A unified explanation along this line would be: Finasteride raises DHA levels, and DHA lowers testosterone. Low testosterone reduces incidence of low-grade prostate cancers but makes it much more likely they will progress to high-grade. Thus, finasteride reduces prostate cancer incidence but increases high-grade prostate cancer incidence and overall prostate cancer mortality. Fits all the facts. Could be.

My bottom line: the Brasky study is weak evidence for anything, but it does raise a whiff of evidence that high dietary fish oil intake might encourage a transition from low-grade to high-grade cancer.

What about other ingredients in the recipe? Does increasing retinyl levels raise cancer risk?

Retinyl palmitate (vitamin A) has been tested in clinical trials for its effect on cancer risk. The trials had to be cut short when it was found that vitamin A increased cancer mortality:

The Carotene and Retinol Efficacy Trial (CARET) was a multicenter randomized, double-blind placebo-controlled chemoprevention trial testing whether daily supplementation with 30 mg β-carotene + 25,000 IU retinyl palmitate would reduce lung cancer risk among 18,314 heavy smokers, former heavy smokers and asbestos-exposed workers. The intervention ended 21 months early in January, 1996 when interim analysis found evidence that the supplements increased the risk of lung cancer and total mortality in this high-risk population by 28% and 17%, respectively (10). [3]

After the study ended participants were tracked for years afterward. Those who had received vitamin A during the trial, but especially those in the vitamin A arm who took additional supplements (mainly multivitamins which are rich in A, but possibly also fish oil), had more high-grade prostate cancers:

As a proportion of the total prostate cancer cases, more men who were randomized to the active arm developed high-grade prostate cancer (Gleason 7-10) than in the placebo arm (44.6% vs. 40.1%, respectively)….

For aggressive prostate cancer, men in the CARET intervention arm who used additional supplements had a relative risk for aggressive prostate cancer (Gleason >or=7 or stage III/IV) of 1.52 (95% CI, 1.03-2.24; P < 0.05), relative to all others. [3]

Interestingly, in the placebo arm taking multivitamins and other supplements reduced cancer risk.

Other studies have found similar results.

Men with higher retinol concentrations at baseline were more likely to develop prostate cancer (quintile 5 vs. quintile 1 hazard ratio = 1.19, 95% confidence interval: 1.03, 1.36; P(trend) = 0.009). The results were similar for aggressive disease. Joint categorization based on baseline and 3-year retinol levels showed that men who were in the highest quintile at both time points had the greatest increased risk (baseline/3-year quintile 5/quintile 5 vs. quintile 1/quintile 1 hazard ratio = 1.31, 95% confidence interval: 1.08, 1.59). In this largest study to date of vitamin A status and subsequent risk of prostate cancer, higher serum retinol was associated with elevated risk, with sustained high exposure conferring the greatest risk. [4]

Carotenoids, which can generally be converted to vitamin A, are also associated with higher cancer risk. There is one exception – lycopene:

Lycopene was inversely associated with prostate cancer risk (comparing highest with lowest quartiles, odds ratio (OR) = 0.65, 95% confidence interval (CI): 0.36, 1.15; test for trend, p = 0.09), particularly for aggressive disease (comparing extreme quartiles, OR = 0.37, 95% CI: 0.15, 0.94; test for trend, p = 0.04). Other carotenoids were positively associated with risk. [5]

What’s special about lycopene? Wikipedia explains:

Lycopene may be the most powerful carotenoid quencher of singlet oxygen,[18] being 100 times more efficient in test tube studies of singlet-oxygen quenching action than vitamin E … The absence of the beta-ionone ring structure for lycopene increases its antioxidant action….

Lycopene is not modified to vitamin A in the body …

So lycopene does not increase retinyl levels, but does act as an extraordinarily powerful antioxidant, thus reducing oxidative stress! If you wanted a good food for stopping the DHA – angiogenesis pathway, you’ve found it: tomatoes.

Hmmm, tomatoes go well with salmon …

That gets us to the third part of the recipe, oxidative stress. If oxidized DHA drives angiogenesis, then antioxidants should be preventative for these diseases.

The evidence here is rather mixed, because with the exception of the negative effects of vitamin A, most antioxidants seem to have little effect on cancer. Nevertheless, I’ll give some studies. Selenium is a antioxidant mineral due to its role in glutathione peroxidase:

Serum selenium was inversely associated with risk of prostate cancer (comparing highest to lowest quartiles, OR = 0.71, 95% CI 0.39-1.28; p for trend = 0.11), with similar patterns seen in both blacks and whites. [6]

Zinc is an antioxidant due to its role in zinc-copper superoxide dismutase. Prostate cancer is associated with low tissue levels of zinc. [7, 8] High dietary intake of zinc is associated with lower rates of prostate cancer. [9]

N-acetylcysteine is an antioxidant supplement that is a precursor to glutathione. N-acetylcysteine has been shown to prevent angiogenesis and has been proposed as a likely cancer preventative, but this is as yet untested. [10]

Other Diseases of Angiogenesis

I’ll skip those for now, other than to note that fish oil is a well-known trigger of rosacea. Is it possible that the mechanism is via TLR-2 activation by oxidized DHA?

Conclusion

At the moment there’s some puffs of smoke but no fire. Observational studies weakly link high DHA, high vitamin A, and low antioxidant status to diseases of angiogenesis such as cancer.

This pattern would be consistent with the idea that the natural pathway used in wound healing to trigger angiogenesis – DHA oxidation and combination with retinyl protein to trigger TLR-2 pathways – is also important for cancer progression.

It suggests a strategy of reduced fish oil and vitamin A consumption and increased intake of certain antioxidants (such as lycopene, zinc, selenium, or NAC) may be helpful against cancer.

However, this idea needs testing. No study in animal cancer models has tested this dietary combination.

Given the many proven benefits of moderate amounts of fish oil, I don’t see a reason yet to alter our recommendation that healthy people should eat a pound of fish per week. That said, I do think very high intakes of fish or fish oil are ill advised. And I’m intrigued by the idea that dietary changes may have the potential to play a powerful role in recovery from diseases of angiogenesis such as cancer.

References

[1] Dvorak HF. Tumors: wounds that do not heal. Similarities between tumor stroma generation and wound healing. N Engl J Med. 1986 Dec 25;315(26):1650-9. http://pmid.us/3537791.

[2] Yao JS et al. Comparison of doxycycline and minocycline in the inhibition of VEGF-induced smooth muscle cell migration. Neurochem Int. 2007 Feb;50(3):524-30. http://pmid.us/17145119.

[3] Neuhouser ML et al. Dietary supplement use and prostate cancer risk in the Carotene and Retinol Efficacy Trial. Cancer Epidemiol Biomarkers Prev. 2009 Aug;18(8):2202-6. http://pmid.us/19661078.

[4] Mondul AM et al. Serum retinol and risk of prostate cancer. Am J Epidemiol. 2011 Apr 1;173(7):813-21. http://pmid.us/21389041.

[5] Vogt TM et al. Serum lycopene, other serum carotenoids, and risk of prostate cancer in US Blacks and Whites. Am J Epidemiol. 2002 Jun 1;155(11):1023-32. http://pmid.us/12034581.

[6] Vogt TM et al. Serum selenium and risk of prostate cancer in U.S. blacks and whites. Int J Cancer. 2003 Feb 20;103(5):664-70. http://pmid.us/12494476.

[7] Sarafanov AG et al. Prostate cancer outcome and tissue levels of metal ions. Prostate. 2011 Jan 26. doi: 10.1002/pros.21339. [Epub ahead of print] http://pmid.us/21271612.

[8] Costello LC, Franklin RB. Zinc is decreased in prostate cancer: an established relationship of prostate cancer! J Biol Inorg Chem. 2011 Jan;16(1):3-8. http://pmid.us/21140181.

[9] Epstein MM et al. Dietary zinc and prostate cancer survival in a Swedish cohort. Am J Clin Nutr. 2011 Mar;93(3):586-93. http://pmid.us/21228268.

[10] Noonan DM et al. Angiogenesis and cancer prevention: a vision. Recent Results Cancer Res. 2007;174:219-24. http://pmid.us/17302199.

Rack of Lamb

Posted by on May 1, 2011 11 comments

We made rack of lamb for Easter dinner.

We made two flavors of crust. Both were excellent.

Ingredients

The first crust flavor had macadamia nuts, parsley, regular mustard, and parmesan cheese:

The second crust flavor used macadamia nuts, pistachio nuts, butter, and Dijon mustard:

In addition to the ingredients shown, you’ll need a bit of olive oil.

Preparation

First, coat the lamb in salt and pepper and then pan-sear it in a little olive oil at high heat:

This takes less than 2 minutes per side; the goal is not to cook the lamb, which will be done in the oven, but to seal the surface to retain internal moisture during cooking and to prepare the surface for the crust.

With the back of a spoon, spread the mustard over the seared lamb:

Meanwhile, in a food processor combine the other crust ingredients with a bit of butter or olive oil for better cohesion. For the parsley crust, we ground the nuts first and added the parsley last with a bit of oil:

Spread the rest of the crust ingredients over the mustard-covered lamb:

Preheat the oven to 400ºF, and place the lamb on a foil-covered baking sheet:

Cook for 20-25 minutes. They’ll come out looking like this:

Slice between each rib and serve:

Some of the crust detaches, but it still goes great with the lamb. (Conventional recipes use bread crumbs, which we eschew.)

Conclusion

This is an easy entrée to prepare and it tastes fantastic! With a little wine, it’s excellent for your HDL.

Around the Web, Spring Arrives in Boston Edition

Posted by on April 30, 2011 17 comments

Here’s what caught my eye this week:

[1] Interesting posts this week: Do people biangulate? Chris Highcock gives us more reason to use a standing desk. A question I never would have seen before reading PaleoHacks:  “Do you brush your teeth with bacon?” Peter notes mice that become obese on a “high-fat diet” can lose weight rapidly if their diet gets even fattier.

Dr. John Briffa discusses the link between HbA1c and mortality (also discussed in our book) and the vast scale of publication bias in medical journals. The issue of publication bias has a counterpart among the public which we might call readership bias. Once people become convinced something is good, they are reluctant to credit evidence that it may be bad. So, for example, the genuinely good evidence in favor of omega-3s can retard acceptance of evidence for harmful effects in some contexts.

Emily has a great post on the links between diet and violence . Mark’s Daily Apple has a nice overview of some things I’ll be talking about in the months to come – traditional cooking herbs.

Via O Primitivo, a Mediterranean diet reduces risk of cancer by 4%. I think we can do better than that.

Last week, when Gary Taubes reported his cholesterol, he also reported his diet:

I do indeed eat three eggs with cheese, bacon and sausage for breakfast every morning, typically a couple of cheeseburgers (no bun) or a roast chicken for lunch, and more often than not, a ribeye or New York steak (grass fed) for dinner, usually in the neighborhood of a pound of meat. I cook with butter and, occasionally, olive oil (the sausages). My snacks run to cheese and almonds.

This week, Anthony Colpo disapproves — twice.

Via Craig Newmark, pro surfer Laird Hamilton has a health tip:

One of my favorite things to do in the morning is to stand on golf balls and roll them along my arches. You have seventy-four hundred nerve endings on your feet, so you stimulate your whole metabolism when you do that.

[2] Is the DHA-cancer connection drug-driven?: Via Dennis Mangan, I’m informed of a helpful comment on the Brasky study by commenter Karl at FuturePundit. Key points: Half of the subjects in the study were on the drug finasteride (Propecia, Proscar). The finasteride arm had 78% more high-grade cancers than the placebo arm.

While tissue DHA levels were strongly associated with high-grade cancer, EPA levels weren’t. On the one hand this is consistent with our idea that high tissue DHA drives cancer via the DHA-angiogenesis mechanism we’ve been discussing: only DHA, not EPA, produces high-grade cancer.

However, normally tissue DHA and EPA are obtained from food and levels go up or down together. Few people in the study supplemented DHA alone; so DHA and EPA levels should have been high or lower together and both should have shown the association.

A plausible explanation would be that the drug was raising DHA levels artificially, and triggering high-grade cancers.

Unfortunately the study doesn’t report the level-response relationship between DHA and high-grade cancers separately in the finasteride and placebo arms – only in the two groups combined. I see this as a failure of the reviewers and an embarrassment to the authors.

Taking Propecia for an enlarged prostate may be much more dangerous than eating salmon.

This plausible hypothesis makes me more comfortable maintaining our recommendation to eat a pound of cold-water marine fish per week.

[3] Vanishing symbol of love: Will the turtle dove disappear?

[4] At least we’ll still have kittens:

Via Yves Smith.

[5] Heh, heh: Denise Minger says we “make DHA seem a little fishy.”

[6] Stabby hearts Denise!: They’d make a cute couple. I can see them 20 years from now:

[7] Because the purpose of government is to harass the citizenry: Feds sting Amish farmer for selling raw milk locally. Via Liberation Wellness.

[8] Carbs for weight loss: Barbra is worried that adding carbs to her very low-carb diet to fix her dry eyes might prevent weight loss. The experience of NourishedEm at Mark’s Daily Apple forum may reassure her:

I find it really interesting that a lot of us who’ve been at this for 6 months or more are finding that we do better with more starch.

When I started PB, I was all about the sub 30g of carbs as my main aim was to lose weight. Well, 7 months of that saw me lose precisely nothing. In the last 6 weeks (after having read PHD), I have added potatoes, rice, taro and sweet potatoes to my diet; in addition I have started eating in a 6 hour eating window. I’ve been losing 2-3lbs a week ever since, it’s like a magic formula for me!

The best part is no longer having to think so hard about what to eat. A lot of ‘normal’ foods have made their way back into the roster with the addition of more starch. I use rice noodles as pasta and can have carbonara and bolognaise again, a baked potato stuffed with chilli and cheese is a great, quick meal, asian stir fries, sushi, risotto, etc….

(Related: Perfect Health Diet: Weight Loss Version, Feb 1, 2011.)

[9] Kate did the wrong diet!: She ate the Dukan Diet before her wedding.

As it happens, I had a correspondent who got very sick on the Dukan Diet; it seems to have re-activated a dormant infection. I rather agree with this nutritionist:

[10] McDonald’s diet produces big baby: What strikes me about this Daily Mail story is that their measure of a baby’s health is its size:

When Suzanne Franklin fell pregnant, she was at a loss as to how she would eat for two.

The 23-year-old had suffered from extreme food allergies for years from eggs to dairy and fruit and vegetables.

Burger baby: Suzanne Franklin and baby son Harry with a Big Mac, which helped sustain both of them during Suzanne’s pregnancy

Doctors warned her that pregnancy would make the symptoms worse but that antihistamines could harm her baby.

But Ms Franklin knew she wasn’t allergic to McDonald’s burgers – so she ate a Big Mac burger everyday throughout her pregnancy.

Any worries about her unusual diet affecting her baby’s growth were unfounded – as she has given birth to her own 10 lb 2 oz whopper.

Miss Franklin said: ‘All those burgers definitely didn’t do him any harm. It was the only thing I could eat safely during my pregnancy, so I just lived on them….

Baby Harry is now three months old – and he has shown signs of inheriting Miss Franklin’s allergies too. He is already allergic to seven different types of milk.

Via John J. Ray.

[11] Has science degenerated?: Bruce Charlton, former editor of Medical Hypotheses, reflects on the negative consequences of the professionalization of science:

There is a dark side to science … in the sense that science is done for reasons of power rather than love.

There was a time when science really was done – mostly – for love; by people who loved knowledge, and were not intending to *use* it….

[O]riginally even medical science was done for love, by doctors and other clinicians, as an overflow from their practice: they wanted to understand, not to control.

As a by-product, in practice, the old medical scientists actually made more frequent, more useful, more powerful discoveries than we do nowadays …

[12] He doesn’t even need 30 bananas: This guy hasn’t stopped bicycling all day:

Via Zero Hedge.

[13] Money does buy happiness!: According to a new review in the Lancet by Bill Easterly.

[14] Another reason not to eat at the Road Kill Café:  The New York Times reports that Armadillos Can Transmit Leprosy to Humans, Federal Researchers Confirm:

Armadillos have never been among the cuddly creatures routinely included in petting zoos, but on Wednesday federal researchers offered a compelling reason to avoid contact with the armored animals altogether: They are a source of leprosy infections in humans.

Using genetic sequencing machines, researchers were able to confirm that about a third of the leprosy cases that arise each year in the United States almost certainly result from contact with infected armadillos. The cases are concentrated in Louisiana and Texas, where some people hunt, skin and eat armadillos.

[15] Ella Fitzgerald: Born on April 25, she deserves a listen:

[16] Celiacs do react to oats: This came up long ago in a comment thread. It turns out that some varieties of oats do trigger gluten autoantibodies.

[17] Shou-Ching’s photo-aphorism project: Shou-Ching likes photography and her latest art project is to combine her photograph with an apposite aphorism. Here’s one – click to enlarge:

[18] Weekly video: The Aurora by Terje Sorgjerd.

The Aurora from Terje Sorgjerd on Vimeo.

Omega-3s, Angiogenesis and Cancer: Part II

Posted by on April 29, 2011 62 comments

On Tuesday (Omega-3 Fats, Angiogenesis, and Cancer: Part I, April 26, 2011) I introduced the issue of possible relationships between omega-3 fatty acids, their lipid peroxidation products, and diseases of angiogenesis such as cancer, and promised to discuss a possible mechanism today.

It may be well, however, to start by saying a little bit more about the Brasky paper [1] linking prostate cancer to DHA.

Denise Minger’s Commentary on the Brasky Paper

Denise Minger wrote a commentary on this paper for Mark’s Daily Apple, which is excellent. Her conclusion – “given the oxidation-prone nature of all polyunsaturated fats, a massive intake of omega-3’s – despite their brilliance in moderation – could potentially do more harm than good” – is the proper one.

A few of Denise’s observations, however, could stand elaboration.

The study measured the fraction of serum phospholipid fatty acids in various polyunsaturated and trans-fat species, not dietary intake. This is the right parameter to measure, as fatty acid profiles can be measured precisely while dietary intakes assessed through questionnaires are notoriously unreliable. Also, phospholipids are the fats in cell membranes, and these are the ones involved in the inflammatory signaling pathways long thought to drive cancer risk. So cell membrane lipid measurements have the best chance to demonstrate a link to cancer risk.

Denise makes the important point, however, that the connection between dietary fish oil intake and serum fatty acid profile is not simple. Higher DHA intake raises phospholipid DHA levels, but lower intake of non-omega-3 fats also raises the DHA fraction. She points to a study [2] comparing a low-fat diet (20% fat, 6.7% PUFA, n-6:n-3 ratio 11.1) to a high-fat diet (45% fat, 15% PUFA, n-6:n-3 ratio 12.3).  The low-fat diet had more of its fat in the form of long-chain omega-3s, but the specific DHA intake on the diets was not reported. Membrane DHA ended up 28% higher on the low-fat diet.

So if DHA is dangerous, low-fat dieters will be in the most trouble. Another reason to eat a high-fat diet!

Does this affect our interpretation of the Brasky study? I don’t think it affects it much, because study participants were healthy at the start of the study with no history of cancer and macronutrient intakes don’t vary a lot among the general public. Americans vary surprisingly little from the median of about 50% carbs, 15% protein, and 35% fat – so it’s likely that the quartile with high tissue DHA levels were also high fish oil consumers.

However, study participants were followed for 7 years, at which point their prostate cancer status was assessed. Incidence of low-grade prostate cancers had no association with start-of-the-study DHA intake, but incidence of high-grade prostate cancers was strongly associated.

Here are a couple of possible explanations for this pattern:

  1. DHA is bad: DHA doesn’t drive early cancer development but does drive late-stage cancer growth – i.e. the transition from low-grade to high-grade cancer. So the DHA consumers got the high-grade cancers. Angiogenesis does, in fact, drive the shift from low-grade to high-grade cancer, so a DHA-angiogenesis association would be consistent with this explanation.
  2. Hospital diet advice is bad: DHA was a marker at the start of the study for conscientious, educated, disciplined persons who followed health advice and ate fish oil. When these people were diagnosed with low-grade cancer, they followed the dietary advice of their cancer dietitian. The dietitian’s advice?  Eat lots of wheat, whole grains, legumes, and vegetable oils. It could be the conscientious folks who followed bad diet advice from the hospital dietitian who got the high-grade cancers.

So there is a possible confounding effect.

Another of Denise’s assertions is that there is an “otherwise consistent train of research showing that DHA seems protective at best (and neutral at worst).” Now it is true that there are more studies showing DHA to have benefits against cancer than harm. But this trend is hardly consistent, and the vast majority of studies have failed to detect a relationship.

In the comments to Tuesday’s post, eric linked to a 2005 meta-review of studies on omega-3 fats and cancer. [3] The reviewers looked at 1,210 journal articles and found a mixed bag of mostly insignificant evidence:

Significant associations between omega-3 consumption and cancer risk were reported for lung cancer in two studies; for breast cancer in one; for prostate cancer in one; and for skin cancer in one. However, for lung cancer, one of the significant associations was for increased cancer risk and the other was for decreased risk (four other risk ratios were not significant for lung cancer). For breast cancer, five other estimates did not show a significant association. Only one study assessed skin cancer risk. No effects were reported for cancers of the aerodigestive tract, bladder cancer, colorectal cancer, lymphoma, ovarian cancer, pancreatic cancer, or stomach cancer. Thus, omega-3 fatty acids do not appear to decrease overall cancer risk.

Data were insufficient to permit assessment of a temporal or dose-response relationship. [3]

So the score was 4 studies finding that DHA is associated with less cancer, 1 that it is associated with more, and a boatload that it had no association.

Now there are two ways of interpreting this general insignificance of DHA against cancer. One is to note that there are slightly more studies showing DHA to have benefits than harm, and therefore to judge that DHA might be helpful against cancer.

But another, equally plausible, interpretation is this. Most Americans eat far too much omega-6, and their omega-6 to omega-3 tissue ratio is too high, which is pro-inflammatory via the COX-2 pathway. Eating omega-3s including DHA reduces inflammation by downregulating the COX-2 pathway. This accounts for the well-attested benefits of DHA against cardiovascular disease. Now, cancer is promoted by COX-2 pathway inflammation, which is why COX-2 inhibitors such as aspirin and ibuprofen are protective against cancer. [4] DHA’s action to downregulate this pathway must generate an anti-cancer effect. But, unlike aspirin and ibuprofen, DHA has no observable effect on overall cancer risk. This suggests that DHA has other effects, unrelated to its anti-inflammatory activity, that are cancer promoting. These counterbalance the benefits from its anti-inflammatory effect. If DHA has pro-angiogenic effects that are independent of COX-2 mediated inflammation, then this could account for the observations.

One reason an association of DHA with high-grade cancer may have been missed is that it would be detected only in large studies able to segregate cancers by grade. Brasky et al note:

In the European Prospective Investigation into Cancer and Nutrition (EPIC) (12), the highest quintile of percent DHA was associated with elevated risks of both low-grade (relative risk (RR) = 1.53, 95% CI: 0.96, 2.44) and high-grade (RR = 1.41, 95% CI: 0.76, 2.62) prostate cancer. They also reported significant positive associations of the percent EPA with high-grade prostate cancer (RR = 2.00, 95% CI: 1.07, 3.76). Given that the Prostate Cancer Prevention Trial and the European Prospective Investigation into Cancer and Nutrition, the 2 largest studies of blood levels of phospholipid fatty acids, reported increased risks of high-grade prostate cancer with high levels of ω-3 fatty acids, it remains a possibility that these fatty acids promote tumorigenesis. [1]

If there were no other evidence linking DHA to angiogenesis, the Brasky and EPIC study associations would be interesting, but unlikely to change anyone’s mind. Denise points out the need for other evidence – especially, mechanistic evidence – to make the connection more plausible:

We haven’t sleuthed out any mechanism that could explain why DHA (but not other polyunsaturated fats) promotes rapid tumor growth.

And this is where today’s post comes in. In fact, there is a known mechanism by which DHA but not other polyunsaturated fats can promote rapid tumor growth. Shou-Ching told me about it a few months ago.

DHA and Angiogenesis in Macular Degeneration

Let’s start by going back to 2003 and a paper on the role of a compound called carboxyethylpyrrole (CEP) in age-related macular degeneration (AMD). [5] AMD is an eye disease caused by improper angiogenesis. Basically, malformed blood vessels overgrow the eye, causing retinal detachment and blindness. It afflicts 35% of those over age 75, and is the leading cause of blindness in developed countries. CEP? Well, the paper explains:

Free radical-induced oxidation of docosahexaenoate (DHA)-containing lipids generates ω-(2-carboxyethyl)pyrrole (CEP) protein adducts that are more abundant in ocular tissues from AMD than normal human donors…. The CEP adduct uniquely indicates oxidative modification from DHA derivatives because CEP protein modifications cannot arise from any other common polyunsaturated fatty acid. [5]

CEP is uniquely produced by oxidation of DHA, not other PUFAs. Its abundance depends on DHA abundance, availability of retinyl proteins, and the level of oxidative stress.

CEP is elevated in AMD. The correlation is strong: a person in whom the immune system is trying but failing to clear elevated CEP levels almost invariably has macular degeneration (AMD):

Of individuals (n = 13) exhibiting both antigen and autoantibody levels above the mean for non-AMD controls, 92% had AMD. [5]

So CEP is a great marker for AMD. Is it causal?

Well, first it’s worth noting that the retina is uniquely vulnerable to DHA oxidation:

Although rare in most human tissues, DHA is present in ~80 mol % of the polyunsaturated lipids in photoreceptor outer segments (13). The abundance of DHA in photoreceptors, the high photooxidative stress in retina, and the fact that DHA is the most oxidizable fatty acid in humans (13) suggests that DHA oxidation products may have possible utility as biomarkers for AMD susceptibility. [5]

Oxidation is linked to AMD, and antioxidants slow AMD progression:

Oxidative damage appears to contribute to the pathogenesis of AMD (4) based on epidemiological studies showing that smoking significantly increases the risk of AMD (1, 24). The molecular mechanism for how smoking enhances the risk for AMD is not known. We speculate that reactive oxygen and nitrogen species derived from tobacco smoke in the lungs leads to oxidative protein modifications in the blood that contribute to drusen formation and choroidal neovascularization. Results from a recent clinical trial (5) also demonstrate that the progression of AMD can be slowed in some individuals by high daily doses of antioxidant vitamins and zinc. Direct evidence of oxidative damage in AMD donor eye tissues include elevated levels of CEP adducts uniquely derived from the oxidative fragmentation of DHA (6). [5]

This is where things stood in 2003. By 2010 this group, led by Case Western Reserve University chemist Robert G. Salomon, had established that administering CEP to mice can cause AMD:

To test the hypothesis that this hapten is causally involved in initiating an inflammatory response in AMD, we immunized C57BL/6J mice with mouse serum albumin (MSA) adducted with CEP. Immunized mice develop antibodies to CEP, fix complement component-3 in Bruch’s membrane, accumulate drusen below the retinal pigment epithelium during aging, show decreased a- and b-wave amplitudes in response to light, and develop lesions in the retinal pigment epithelium mimicking geographic atrophy, the blinding end-stage condition characteristic of the dry form of AMD. Inflammatory cells are present in the region of lesions and may be actively involved in the pathology observed. [6]

This constitutes the first really good animal model for AMD. [6]

How does this relate to cancer? That leads us to a Nature paper from October 2010 [7], from the group of Tatiana Byzova at the Cleveland Clinic.

DHA, Immunity, and Angiogenesis

This is a rich paper. Briefly, CEP has a physiological function: it is transiently elevated in wounds and recruits immune cells from bone marrow to the site of the wound. These immune cells further increase oxidative stress and promote angiogenesis; CEP levels are highest at the time of peak angiogenesis. CEP is highly elevated in cancers. Unlike in wounds, where CEP is elevated for a few days, in cancers CEP elevation is chronic.

Here’s a staining comparing CEP in normal skin and in melanoma:

The CEP is co-localized with CD68, a glycoprotein which binds to LDL and is found on macrophages, and with CD31, a membrane marker of neutrophils, macrophages, and endothelial cells. CEP is marking endothelial cells and white blood cells in angiogenic vessels, and possibly LDL.

It turns out that CEP drives angiogenesis by attaching to an immune receptor, Toll-like receptor 2 (TLR2). There are two major pathways for angiogenesis: one driven by vascular endothelial growth factor (VEGF), which is dominant in conditions of hypoxia (oxygen starvation), and one by TLR2. Of these, the TLR2 pathway may in some contexts be more important. Here are pictures of wound healing in mice:

On the upper left is a normal mouse. On the upper right is a similar wound treated with the VEGF inhibitor AAL-993. This wound is rather like a cancer treated with the VEGF inhibitor Avastin. Wound healing is slightly impaired, but still works.

On the lower left is a similar wound with no VEGF inhibition, but the TLR2 pathway blocked by TLR2 knockout. The wound can’t scab and doesn’t heal successfully. If TLR2 is knocked out and VEGF inhibited, there is no wound healing at all (lower right).

You can accelerate angiogenesis and wound healing by adding CEP to the wound.

In the bottom row, CEP has been added. Left is without VEGF inhibition, right with.

If you administer CEP-neutralizing antibodies to a normal wound, wound healing takes more than twice as long. This confirms that angiogenesis driven specifically by CEP (and therefore by DHA oxidation) is part of healthy wound healing.

Tumors use these same pathways to generate vessels and feed their growth. As the paper notes:

[T]umors implanted in TLR2-/- mice exhibited dramatically decreased vascularization and increased areas of necrosis. [7]

Here’s the paper’s conclusion:

Altogether our results establish a novel mechanism of angiogenesis that is independent of hypoxia-triggered VEGF expression. The products of lipid oxidation are generated as a consequence of oxidative stress and are recognized by TLR2, possibly in a complex with TLR1 on ECs, and promote angiogenesis in vivo, thereby contributing to accelerated wound healing and tissue recovery. If high levels of CEP and its analogs accumulate in tissues, it may lead to excessive vascularization, e.g. in tumors. Contribution of the CEP/TLR2 axis to angiogenesis varies in different physiological settings possibly depending on the extent of oxidative stress. CEP-driven angiogenesis may be an attractive therapeutic target, especially in cancers resistant to anti-VEGF therapy. Inflammation and oxidation-driven angiogenesis may occur in other pathologies, for example atherosclerosis, where arterial thickening can depend on its microvasculature. In these settings, there is an extensive generation of oxidative products which might promote atherogenesis via TLR2. Indeed, it was shown that TLR2?/? mice are protected from atherosclerosis, and this effect could be mediated by cells other than bone marrow-derived29. Thus, along with pathogen- and danger-associated molecular patterns, TLR2 recognizes an oxidation-associated molecular pattern. This new function of TLR2 as a sensor of oxidative stress reveals the shortcut link between innate immunity, oxidation and angiogenesis. [7]

Connection to Vitamin A

DHA is oxidized to a compound called HOHA which then combines with a protein, generally a retinyl (vitamin A-derived) protein to form CEP.

Cancers generate lots of CEP from DHA, and perhaps one way they do that is by generating lots of retinyl proteins. Cancers are known to have disturbed vitamin A biology with lots of retinyl:

Disturbance in vitamin A metabolism seems to be an important attribute of cancer cells. Retinoids, particularly retinoic acid, have critical regulatory functions and appear to modulate tumor development and progression. The key step of vitamin A metabolism is the esterification of all-trans retinol, catalyzed by lecithin/retinol acyltransferase. In this work we show that malignant melanoma cells are able to esterify all-trans retinol and subsequently isomerise all-trans retinyl esters into 11-cis retinol, whereas their benign counterparts – melanocytes are not able to catalyze these reactions. Besides, melanoma cell lines express lecithin/retinol acyltranseferase both at the mRNA and protein levels. In contrast, melanocytes do not express this enzyme … [8]

I haven’t looked much into this literature but it may speak to higher cancer risk with excessive vitamin A intake. Thus high-vitamin A cod liver oil may be a double risk for cancer patients.

Conclusion

It looks like we have a recipe for angiogenesis:

DHA + retinyl + oxidative stress = angiogenesis

This recipe is invoked normally and properly during wound healing. But it is also invoked excessively in pathological contexts – notably in cancers and age-related macular degeneration, probably also in other angiogenesis-associated diseases such as arthritis, rosacea, obesity, psoriasis, endometriosis, dementia, and multiple sclerosis.

In the case of cancer, DHA oxidation to CEP might transform miniscule, harmless cancers to high-grade, life-threatening cancers.

Should this possibility affect our dietary omega-3 recommendations? Well, we need to know the relative importance of the three ingredients on the left side of the above equation in producing angiogenesis. Chris Kresser wondered in the comments Tuesday whether oxidation may be the key factor:

I question whether DHA supplementation would truly play a causative role in the absence of a *pro-oxidative environment*.

In other words, perhaps in someone eating a SAD, not exercising, under a lot of stress, etc. DHA is more easily oxidized and thus potentially carcinogenic.

But in someone that is keeping all other oxidative risk factors low (i.e. they’re avoiding n-6, exercising, managing stress, reducing exposure to chemical toxins, etc.) I tend to doubt that supplementing with DHA could cause significant harm.

That’s the last piece of the puzzle: how do we minimize the level of oxidized DHA?

As I replied to Chris in the comments, low-carb Paleo dieters are not out of the woods in regard to oxidative stress. Oxidative stress is generated normally during metabolism, immune function – and by cancers. If anti-oxidant minerals like zinc, copper, and selenium and vitamins like vitamin C are deficient, then oxidative stress can be very high on a low-carb Paleo diet.

At the moment, I think it’s prudent to eat no more than 1 pound of salmon or similar cold-water fish per week, to avoid further EPA/DHA supplements, and to avoid low-fat diets which tend to elevate membrane DHA levels. Moderate omega-3 consumption is especially important for those suffering from diseases of pathological angiogenesis – especially cancer. DHA is essential for good health – but in excess, it is probably dangerous.

References

[1] Brasky TM et al. Serum Phospholipid Fatty Acids and Prostate Cancer Risk: Results From the Prostate Cancer Prevention Trial. Am. J. Epidemiol. April 24, 2011 DOI: 10.1093/aje/kwr027 (Will be at http://pmid.us/21518693.)

[2] Raatz SK et al. Total fat intake modifies plasma fatty acid composition in humans. J Nutr. 2001 Feb;131(2):231-4. http://pmid.us/11160538.

[3] MacLean CH, Newberry SJ, Mojica WA, et al. Effects of Omega-3 Fatty Acids on Cancer. Summary, Evidence Report/Technology Assessment: Number 113. AHRQ Publication Number 05-E010-1, February 2005. Agency for Healthcare Research and Quality, Rockville, MD. http://www.ahrq.gov/clinic/epcsums/o3cansum.htm.

[4] Harris RE. Cyclooxygenase-2 (cox-2) and the inflammogenesis of cancer. Subcell Biochem. 2007;42:93-126. http://pmid.us/17612047.

[5] Gu X et al. Carboxyethylpyrrole protein adducts and autoantibodies, biomarkers for age-related macular degeneration. J Biol Chem. 2003 Oct 24;278(43):42027-35. http://pmid.us/12923198.

[6] Hollyfield JG et al. A hapten generated from an oxidation fragment of docosahexaenoic acid is sufficient to initiate age-related macular degeneration. Mol Neurobiol. 2010 Jun;41(2-3):290-8. http://pmid.us/20221855.

[7] West XZ et al. Oxidative stress induces angiogenesis by activating TLR2 with novel endogenous ligands. Nature. 2010 Oct 21;467(7318):972-6. http://pmid.us/20927103.

[8] Amann PM et al. Vitamin A metabolism in benign and malignant melanocytic skin cells: Importance of lecithin/retinol acyltransferase and RPE65. J Cell Physiol. 2011 Apr 4. doi: 10.1002/jcp.22779. [Epub ahead of print] http://pmid.us/21465477.