25 July 2009

Hypoglycemia in Hereditary Fructose Intolerance

What are the specific reasons for hypoglycemia seen in hereditary fructose intolerance?

Hereditary fructose intolerance (HFI) an autosomal recessive disorder in which there is subnormal activity of the enzyme fructose 1-phosphate aldolase B (1;2). Largely found in the liver, the enzyme is needed for normal fructose metabolism for splitting fructose 1-phosphate to form dihydroacetone and glyceraldehyde (1).

Hypoglycemia after consumption of fructose (also sucrose or sorbitol) results because of the lack of maintenance of proper blood glucose levels by the liver (2). The fructose ingestion and the lack of aldolase B results in the accummulation of fructose 1-phosphate in cells, particularly in the liver (1). The accumulation leads to depletion of Pi, which in turn keeps mitochondria in hepatocytes from producing ATP causing cell damage, and inhibition of glycogenolysis and, thus, guconeogenesis (1;2).

HFI often goes unrecognized and is life-threatening due to hypoglycemia along with possible liver and renal failure (3;4). Many of patients afflicted with the disorder have a noted distaste for sweet foods due to having suffered symptoms early in life such as vomiting and abdominal pain (2-4). The cure for HFI is exclusion of sources of fructose from the diet (1-4).

Reference List

1. Devlin TM. Textbook of Biochemistry with Clinical Correlations. Philadelphia: Wiley-Liss, 2002, pp 597 & 643.
2. Shils ME, Shike M, Ross AC, Caballero B, Cousins RJ. Modern Nutrition in Health and Disease. Baltimore, MD: Lippincott Williams & Wilkins, 2009.
3. Yasawy MI, Folsch UR, Schmidt WE, Schwend M. Adult hereditary fructose intolerance. World J Gastroenterol 2009;15:2412-3.
4. Cox TM. Hereditary fructose intolerance. Baillieres Clin Gastroenterol 1990;4:61-78.

22 July 2009

Niacin and Hyperlipidemia

The recommended daily intake for niacin, or vitamin B3, is only 14 mg for women and 16 mg for men with a tolerable upper intake level of 35mg (1). Nutrition professionals should also be aware that niacin, as nicotinic acid (not nicotinamide), has also been used in much larger doses—up to 6 g per day—for decades as a treatment for hyperlipidemia (1). Note that nicotinic acid is available as a dietary supplement.

Use as a Drug
High-dose niacin, in fact, was the first-ever lipid-modifying drug treatment. It helps increase HDL cholesterol while lowering total serum cholesterol, triglycerides and LDL cholesterol (2). After initial discovery in the 1950s and research in the ‘70s, it was found that niacin helped prevent myocardial infarction and reduced risk of death from myocardial infarction when used in doses of 3 g daily (2;3).

The mechanism of high-dose nicotinic acid is broad and unique. It inhibits lipolysis in adipose tissue decreasing free fatty plasma levels within minutes (1;2). Within a few hours it inhibits the liver’s synthesis of triglycerides reducing overall triglycerides in plasma (1;2). And, although it’s unclear just how, after only a few days it lowers LDL and increases HDL cholesterol (1;2).

Unpleasant Side Effects
Although an effective treatment and cost effective, the unpleasant side effects of high-dose niacin have kept many patients from adopting niacin as a regular drug treatment (2). By the 1980s, statins were on the market and greater in popularity (2). Still, niacin continues to present potential.

The main side effect is vasodilation, which includes flushing and redness like a temporary sunburn-like sensation (1;2). This is harmless, but bothersome (2). It is mediated partly by release of histamine; thus, an aspirin or COX inhibitors can reduce the response (1;2).

Other side effects can include gastrointestinal problems like heartburn, elevated plasma glucose concentration, and hyperuricemia that can lead to gout since niacin competes with uric acid for excretion (1). Most worrisome is possible hepatotoxicity, which can go as far as obstructing bile flow, hepatitis or liver failure (1).

Newer forms of extended-release niacin, such as Niaspan from Abbot, are reported to have fewer side effects and no hepatotoxicity (2). This is significant for re-establishing niacin as the preferred, cost-effective treatment in comparison to other drugs. Newer studies are now researching niacin’s effectiveness in comparison to or in combination with other lipid- and cholesterol-lowering drugs (3). See "Research Summary and Critique" below.

Niacin is available in immediate-release (IR), sustained-release (SR), and extended-release (ER) (Niaspan) (4). They all differ in effectiveness, side effects and safety. Flushing is seen most with IR, hepatotoxicity is mostly noted with SR (4). The hepatotoxicity has to do with absorption rate (4). ER apparently allows absorption to be "intermediate" in comparison to IR and SR (4). In conclusion, avoid SR niacin!

Reference List

1. Gropper SS, Smith JL, Groff JL. Advanced Nutrition and Human Metabolism. Belmont, CA: Thomson Wadsworth, 2009.

2. E T Bodor and S Offermanns. Nicotinic acid: an old drug with a promising future. Br J Pharmacol. 2008 March; 153(S1): S68–S75. Published online 2007 November 26. doi: 10.1038/sj.bjp.0707528. Available at: http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=18037924.

3. Guyton JR, Blazing MA, Hagar J, Kashyap ML, Knopp RH, McKenney JM, Nash DT, Nash SD. Extended-release niacin vs gemfibrozil for the treatment of low levels of high-density lipoprotein cholesterol. Arch Intern Med. 2000 Apr 24;160(8):1177-84. Available at: http://archinte.ama-assn.org/cgi/content/full/160/8/1177#TABLEIOI90276T3

4. Pieper JA. Understanding niacin formulations. Am J Manag Care 2002;8:S308-S314.

One randomized, double-blind human clinical study in 2000 made a direct comparison using Niaspan and gemfibrozil.

Full reference: Guyton JR, Blazing MA, Hagar J, Kashyap ML, Knopp RH, McKenney JM, Nash DT, Nash SD. Extended-release niacin vs gemfibrozil for the treatment of low levels of high-density lipoprotein cholesterol. Arch Intern Med. 2000 Apr 24;160(8):1177-84. Available at: http://archinte.ama-assn.org/cgi/content/full/160/8/1177#TABLEIOI90276T3

Purpose of Study: To compare effects of Niaspan with gemfibrozil, a lipid-lowering drug from a class called fibrates. Commercially, gemfibrozil goes by names of Lopid, Jezil and Gen-Fibro.

Type of study: Randomized, double-blind human clinical study.

Methods: Patients exhibiting factors for hypercholesterolemia and atherosclerosis were given Niaspan at doses increased sequentially from 1g to 2 g before bedtime and 80 or gemfibrozil at 600 mg given twice daily. Of 173 patients, 72 of 88 given Niaspan and 68 of 85 given gemfibrozil completed the study.

Percentage change from baseline was provided through analysis of blood samples collected after 12-hour fasts. They provided measurements for total cholesterol, HDL cholesterol, LDL cholesterol, lipoprotein levels, total triglycerides and fibrinogen levels.

Exclusions included most diabetics (not with normal-range fasting glucose), patients on blood thinners, patients with active gout as well as those with other serious illnesses and/or abnormalities.

The patients were men and women between ages 21 and 75 years. All were counseled by a National Cholesterol Education Program.

Results Summary: Niaspan increased HDL cholesterol twice as much as gemfibrozil and had better results in improving LDL cholesterol while lowering levels of fibrinogen (protein involved in clotting). The gemfibrozil had greater effects at lowering triglycerides, but increased LDL cholesterol.

Much more Niaspan flushing responses (78% compared to 10%) were observed in comparison to gemfibrozil; however, dyspepsia was observed more often in patients taking gemfibrozil.

Critique of Research Design: The study was well-designed and included appropriate measurements to determine biological response to treatment. The exclusions were appropriate in nature. The support of a pharmaceutical company for the study hinted at a natural bias that could be noted since there was no discussion given by the authors of this study regarding possible confounding variables. The flushing responses clearly indicate that the patients would have known what they were taking, which may have affected results. Also, dietary factors were not noted in the study. There was conversation seeming out of place about the possible use of both drugs for complementary treatment, which would need further research.

Nutritional Implications and Implications for Future Study: Nutrition professionals should have a thorough understanding of its uses and possible side effects when used as a drug for hypercholesterolemia. Because niacin is a vitamin found in many foods, further research should also review the potential role of diet along with niacin treatment.

18 July 2009

Bs for Stress and Energy

B-complex supplement products are popular commodities, often marketed for "stress" or "energy." Is there scientific justification for these claims? Why should anyone choose a B-complex supplement as opposed to either broader multivitamin-mineral supplements or narrower single B-vitamin supplements?

You might remember in the early ‘90s when a neuropathy epidemic broke out in Cuba among unsuspecting tobacco growers. They complained of burning sensations in their feet, pain in their arms and legs, frequent urination, blurred vision, weight loss, sensitivity to sunlight, and, well, lots of stress and fatigue (1). After assessing their diets it was discovered they were deficient in B complex vitamins and the amount of alcohol they drank daily contributed to loss of the little Bs they had (1).

The tobacco growers may have not known that B vitamins play essential roles in the health of their bodies relating to energy metabolism and stress, but let’s be sure we do.


For generating ATP energy in the body, B vitamins act mainly in synergy. Specifically, the vitamins thiamin, riboflavin, niacin and pantothenic acid are all needed to act as co enzymes in the formation of a multi-enzyme complex known as pyruvate dehydrogenase complex (2). Pyruvate dehydrogenase complex is essential for the oxidative decarboxylation of pyruvate to form acetyl CoA, which feeds into the citric acid cycle (2). Take any of the B vitamins away and cellular respiration is no more.

Further, niacin either as nicotinic acid and nicotinamide is necessary for use in the forms of NAD, nicotinamide adenine dinucleotide, and, with a phosphate at the end, NADP. NAD and NADP act as coenzymes for about 200 enzymes (oxidation-reduction reactions). But a major role of NAD in its reduced form as NADH is to shuttle electrons through the electron transport chain creating ATP energy (2). Apart from joining the other Bs in oxidative decarboxylation of pyruvate, NAD and NADH also act as coenzymes in glycolysis, oxidation of acetyl CoA, beta-oxidation of fatty acids and oxidation of ethanol for energy (2).

Riboflavin is needed for its coenzyme derivatives flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). Like NAD and NADP, FMN and FAD act as coenzymes in oxidative-reduciton reactions for many reactions (2). Apart from use in pyruvate dehydrogenase complex in which FAD acts as an electron carrier, FAD also is needed for the flavoprotein succinate dehydrogenase to remove electrons from succinate to form fumarate (2). Then electrons are passed into electron transport chain by coenzyme Q (2).

Biotin’s role in energy has to do with its coenzyme role in enzymes. Two regulatory enzymes are dependent on biotin: pyruvate carboxylase, regulator of carboxylation of pyruvate, acetyl CoA carboxylase, regulator of fatty acid synthesis (2). Two enzymes need biotin for catabolism of amino acids need biotin, propionyl CoA carboxylase and beta-methylcrotnonyl CoA carboxylase (2). Lack of biotin will produce lethargy, depression, hallucinations and muscle pain (2).

Cobalamin once converted to adenosylcobalamin can act along with biotin in a energy metabolism in which it acts to help convert methylmalonyl CoA mutase convert L-methylmalonyl CoA to succinyl CoA (2). L-methylmalonyl CoA is produced from D-methylmalonyl CoA, which was produced from propionyl CoA that arose from from oxidation of amino acids and odd-chain fatty acids from the biotin-dependent reaction (2).

Pantothenic acid, aside its role in pyruvate dehydrogenase complex as a component of CoA, also acts as a component of CoA in lipid metabolism such as synthesis of ketone bodies and fatty acids (2). Although deficiency is unlikely—it’s ubiquitous in food—among the symptoms would be fatigue and weakness (2). Its deficiency is characterized by numbness in the toes called “burning feet syndrome” of which was no doubt suffered by the Cuban tobacco farmers who lacked it (1;2).


Some examples of stress were given above, but stress help from B vitamins is largely the work of thiamin. Thiamin, in this case not as a coenzyme, may activate ion transport in nerve membranes as well as regulating sodium channels and acetylcholine receptors in nerve impulse transmissions (2). A thiamin deficiency produces beriberi (beri meaning “weakness”) and one of its first signs is anorexia and weight loss, then neurological symptoms of confusion and apathy in what can only end up as irritability (2).

Riboflavin has its role in stress too—and I’m using the word “stress” as a very wide-reaching general term. FAD-dependent monomaine oxidase is required by neurotransmitters such as dopamine (2). Regeneration of the antioxidant glutathione—which supports against oxidative stress—is dependent also on FAD-dependent glutathione reductase (2).

Without niacin life could be especially stressful due to pellagra, which comes with its four Ds: dermatitis, dementia, diarrhea and death (2). But the B vitamin’s more direct role is in reducing oxidative stress via regeneration of glutathione, vitamin C and thioredoxin (2).

Finally, the pernicious anemia from a deficiency or poor absorption of cobalamin would lead to neuropathy of which is characterized by demyelination of the nerves—painfully stressful indeed (2).


OK, so we know the roles of B vitamins as related to energy and stress. We definitely need them. The question remains, however, whether or not a normally healthy person should supplement? Plus, will taking more of B-complex act as an ergogenic aid such as for athletes?

The studies aren’t showing much promise. There is indication that exercise causes greater need for B-complex supplements (5). Athletes should continue to take them. But, despite widespread use of B-complex supplements among athletes even in massive doses, they should not be expected to increase actual performance unless a deficiency was in existence beforehand (3;4).

Those of us who aren’t athletes would benefit from B-complex vitamins simply to help us avoid deficiency and because of their lack of toxicity. But don’t expect huge increases in “energy” or reductions of “stress” unless you are deficient. Deficiency can happen if you're malnourished, abuse alcohol, are a strict vegetarian (B12 or riboflavin) or if you have a disorder such as pernicious anemia (B12 deficiency) (2).

Reference List

1. Arnaud J, Fleites-Mestre P, Chassagne M et al. Vitamin B intake and status in healthy Havanan men, 2 years after the Cuban neuropathy epidemic. Br J Nutr 2001;85:741-8.
2. Gropper SS, Smith JL, Groff JL. Advanced Nutrition and Human Metabolism. Belmont, CA: Thomson Wadsworth, 2009.
3. Williams MH. Vitamin supplementation and athletic performance. Int J Vitam Nutr Res Suppl 1989;30:163-91.
4. Williams MH. Vitamin and mineral supplements to athletes: do they help? Clin Sports Med 1984;3:623-37.
5. Woolf K, Manore MM. B-vitamins and exercise: does exercise alter requirements? Int J Sport Nutr Exerc Metab 2006;16:453-84.

12 July 2009

Vitamin E

Vitamin E refers to eight compounds (vitamers: tocopherols and tocotrienols) and is found in both plants and animal foods (1). The most studied natural source of vitamin E is alpha-tocopherol because of its prevention of lipoprotein oxidation and inhibition of platelet aggregation, which suggests prevention of cardiovascular disease (1).

Alpha-tocopherol is the only one with biological activity and offers the most protection against oxidative stress through its oxygen-quenching capacity (2). The natural and most active form is designated by its steroisomer RRR alpha-tocopherol and continues to be found on supplement labels as d-alpha tocopherol (2).

Beta-tocopherol also exhibits oxygen-quenching capacity albeit not as much as alpha-tocopherol and its abilities are followed by gamma- and delta-tocopherol (2). The tocotrienols may not exhibit significant antioxidant role, but have another role in which they reduce plasma cholesterol concentration (2).

A recently discovered natural form of vitamin E is alpha-tocopheryl phosphate found to be ubiquitous in tissues of animals and plants (3). Its role is not yet clear.
Supplementation with vitamin E is widely popular for taking guesswork out of how to get enough of this seemingly non-toxic vitamin for cardiovascular health (1;4). Newer research on vitamin E, however, is showing that it may be possible that people are taking too much (1;5).

Clinical trials on alpha-tocopherol have mostly found negative results including possible increased adverse effects on those with high blood pressure and increased risk of death in those with cardiovascular disease (1).

Until further is known about the most appropriate amount to take for reduced risk of disease, the Recommended Dietary Allowance for vitamin E continues to be 15 mg daily, based on the natural form of alpha-tocopherol, and is still considered one of the least toxic vitamins (2).

Reference List

1. Clarke MW, Burnett JR, Croft KD. Vitamin E in human health and disease. Crit Rev Clin Lab Sci 2008;45:417-50.
2. Gropper SS, Smith JL, Groff JL. Advanced Nutrition and Human Metabolism. Belmont, CA: Thomson Wadsworth, 2009.
3. Gianello R, Libinaki R, Azzi A et al. Alpha-tocopheryl phosphate: a novel, natural form of vitamin E. Free Radic Biol Med 2005;39:970-6.
4. Gutierrez AD, de Serna DG, Robinson I, Schade DS. The response of gamma vitamin E to varying dosages of alpha vitamin E plus vitamin C. Metabolism 2009;58:469-78.
5. Bell SJ, Grochoski GT. How safe is vitamin E supplementation? Crit Rev Food Sci Nutr 2008;48:760-74.

Bugs Bunny diet

Could it be that when Bugs Bunny chose his special diet of carrots because he knew that the discovery of vitamin A in 1915 found it was an essential growth factor in animals (1)? Maybe he knew that vitamin A kept his skin healthy under all that fur (1). Or, more likely, that vitamin A kept his eyes healthy for seeing underground (1).

Bugs can also celebrate that his enjoyment of carrots might keep him from later having to say, “What’s up doc?” This is because clinical evidence has led the U.S. Food and Drug Administration to approve a cancer health claim for a low-fat diet rich in fruits and vegetables when it includes vitamin A (1).

Vitamin A’s benefits are all appealing to humans too. But while vitamin A deficiency is not common in developed countries, a few are deficient not being regular eaters of foods high in vitamin A like carrots, sardines or liver (1).

How much should you get? What kind of vitamin A should you be getting? And, how do you know when you should supplement? Clinicians should be familiar with the differences of the various kinds of vitamin A because it would affect recommendations.

Vitamin A references any compound that can produce biological activity of all-trans retinol (1). These include preformed vitamin A retinoids (retinol, retinal, retinoic acid, retinyl esters and others) and provitamin A carotenoids (alpha-carotene, beta-carotene, beta-cryptoxanthin) (1).

Absorption of vitamin A first requires digestion in which enzymes help free up vitamin A from proteins and fats (1). The vitamin A compounds then become solubilized into bile micelles to be transported and absorbed across the brush border membrane of the duodenum and jejunum (1).

The preformed vitamin A retinoids are absorbed easily (about 70-90 percent) as long as a meal includes sufficient fat (1). Provitamin A carotenoids are less absorbed ranging from less than 5 percent in raw foods and juices and up to 60 percent when cooked or taken purely in oil (1).

Retinoids, being lipid-soluble, are not as stable as carotenoids and can oxidize when exposed to light, oxygen, heat or some metals (2). But, again being lipid soluble, about 70-90 percent of the preformed vitamin A retinoids are absorbed (1).

In developing countries, vitamin A deficiency is not common (1). It generally occurs among children leading to increased mortality and infectious morbidity (1). The symptoms of vitamin A deficiency can include xerophthalmia (night blindness, Bitot’s spots, conjunctival abnormalities, corneal scarring and ulcerations), anorexia, retarded growth, karatinization of mucous cells (1).

The best measure of vitamin A from which to make recommendations is retinol activity equivalents (RAE) (1). For example, retinol 1 mcg is equal to RAE 1 mcg, beta-carotene 12 mcg is equal to RAE 1 mcg, and alpha-carotene or beta-cryptoxanthin 24mcg is equal to RAE 1 mcg (1). The requirements of vitamin A intake published by the Institute of Medicine’s Food and Nutrition Board published in 2001 that adult men should consume 625mcg RAE and women 500mcg RAE (1).The Recommended Dietary Allowance (RDA) is 900 and 700 mcg RAE for men and women (1).

Pregnant women have a higher RDA ranging from 770 and 1,300 mcg RAE (1)Smokers, however, should watch any increase because newer research shows vitamin A may increase risk for lung cancer rather than decrease it (1). The biochemical reasons for increasing lung cancer risk are not clear yet, but may have to do with break down products and mitochondriotoxicity (3).

Because main food labels still list vitamin A in the older International Units (IU), it’s important to point out that 1 IU vitamin A is equal to 0.3 mcg regtinal, 3.6 mcg beta-carotene and 7.2 mcg of alpha-carotene and beta-cryptoxanthin (1).

It is possible to get too much vitamin A. Hypervitaminosis A is a disorder that can lead to nausea, vomiting, double vision, headache, dizziness and skin problems (1).

The tolerable upper intake level for preformed vitamin A in adults is 3,000 mcg (1). Beta-carotene and the other provitamin A carotenoids do not have any known tolerable upper intake level (1). A tolerable upper intake level of beta-carotene levels in smokers has yet to be established (1).

Reference List

1. Gropper SS, Smith JL, Groff JL. Advanced Nutrition and Human Metabolism. Belmont, CA: Thomson Wadsworth, 2009.
2. Carlotti ME, Rossatto V, Gallarate M, Trotta M, Debernardi F. Vitamin A palmitate photostability and stability over time. J Cosmet Sci 2004;55:233-52.
3. Siems W, Salerno C, Crifo C, Sommerburg O, Wiswedel I. Beta-carotene degradation products - formation, toxicity and prevention of toxicity. Forum Nutr 2009;61:75-86.

11 July 2009

Antioxidants - Comparing Apples to Oranges

Which will keep the doctor way? The orange contains about 10 times more vitamin C, which is an essential antioxidant for many complex roles in the human body (1). On the other hand, the apple contains quercetin, which has been shown to have a higher antioxidant capacity than vitamin C, thus, potentially offering better protect against free radicals (2;3). Clearly these antioxidants are not equal.

Free radicals are atoms or molecules that have one or more unpaired electrons. These are mainly result of the mitochondria leaking electrons that bind to oxygen; however, there are a variety of other free radicals from exposure to smog, ozone, drugs, and drugs (1).

Because “oxidative stress” is thought to be associated with many diseases including cancer, antioxidant nutrients are frequently evaluated for ability to neutralize free radicals, particularly the oxygen-centered radicals: superoxide, hydroxyl and peroxyl radicals (1).

While antioxidants help decrease neutralize free radicals, they themselves become free radicals although—in some cases such as vitamin E, C, ubiquinol and glutathione—regeneration pathways in the body often help them function over again (1). The regeneration process is key for optimal defense against oxidative stress and so is receiving enough of different kind of antioxidants (1).

As science continues to discover more and more, high-antioxidant foods continue to grown in the marketplace. Walk down the isle of any health food store and you’re sure to spot the latest and greatest—pomegranate, blueberry, acai berry, green tea. What makes one food greater than another?

These compete by antioxidant capacity including measures of oxygen radical absorption Capacity (ORAC) (4;5). Each ORAC unit indicates greater antioxidant protection—the higher the score, the more “super” the food (5). Another test more relevant biologically is cellular antioxidant activity (CAA), performed on cell cultures, which has found quercetin, pomegranate and berries clear favorites for decreasing oxidative stress (6). Antioxidant capacity can also be helpful to determine one fruit with another of the same fruit. For example, organically grown fruit and vegetables often have a higher ORAC score indicating greater content of fruit (7).

Should consumers rely strictly on ORAC or CAA tests for making food choices? The answer is, no. While single antioxidants may have unique functions that may link them to reduced risk of disease, such as vitamin C and heart disease (1), quercetin and liver cancer (8), no single antioxidant or antioxidant complex has appeared yet to decreases oxidative stress enough overall to reduce risk of all diseases (1).

As discussed above, however, antioxidants often work with each other synergistically in the body. Thus, for superior nutrition, adopt the “color code”: five to nine servings daily of fruits and vegetables of different colors provides the reds, red-purples, oranges, yellows, and greens for your body daily and is in line the National Cancer Institute and American Institute (9). Until more is known about antioxidants, the color code offers the the best guideline for health and prevention of disease (1).

Reference List

1. Gropper SS, Smith JL, Groff JL. Advanced Nutrition and Human Metabolism. Belmont, CA: Thomson Wadsworth, 2009.
2. Wolfe KL, Liu RH. Cellular antioxidant activity (CAA) assay for assessing antioxidants, foods, and dietary supplements. J Agric Food Chem 2007;55:8896-907.
3. Kim DO, Lee KW, Lee HJ, Lee CY. Vitamin C equivalent antioxidant capacity (VCEAC) of phenolic phytochemicals. J Agric Food Chem 2002;50:3713-7.
4. Kohri S, Fujii H, Oowada S et al. An oxygen radical absorbance capacity-like assay that directly quantifies the antioxidant's scavenging capacity against AAPH-derived free radicals. Anal Biochem 2009;386:167-71.
5. Cao G, Alessio HM, Cutler RG. Oxygen-radical absorbance capacity assay for antioxidants. Free Radic Biol Med 1993;14:303-11.
6. Wolfe KL, Kang X, He X, Dong M, Zhang Q, Liu RH. Cellular antioxidant activity of common fruits. J Agric Food Chem 2008;56:8418-26.
7. Di RL, Di PD, Bigioni M et al. Is antioxidant plasma status in humans a consequence of the antioxidant food content influence? Eur Rev Med Pharmacol Sci 2007;11:185-92.
8. Seufi AM, Ibrahim SS, Elmaghraby TK, Hafez EE. Preventive effect of the flavonoid, quercetin, on hepatic cancer in rats via oxidant/antioxidant activity: molecular and histological evidences. J Exp Clin Cancer Res 2009;28:80.
9. Heber D, Bowerman S. Applying science to changing dietary patterns. J Nutr 2001;131:3078S-81S.

05 July 2009

What is the biochemical reason why bile secretion is important for health?

Micelles are made up of amphipathic compounds such as bile acids, fatty acids and monoacylglycerols that interact leaving a relatively stable hydrophilic surface and hydrophobic interior (1). They form at certain temperature ranges when a mixture of lipids is present in concentrated amounts (1). Fatty acid and phospholipid micelles are spherical, but pure bile acid micelles are sandwich-shaped rectangles (1p1062).

During lipid digestion after hydrolysis of triacylglycerols by lipases, it’s up to the bile acid sandwiches to solubilize the spheres, thereby forming “mixed” micelles that appear not unlike rods (1p1062). These rods become longer as more lipids (including limited cholesterol) are solubilized (1p1062). The bile acid micelles form at concentrations of 2-5 mM and at pH values above pK, meaning in equilibrium with other micelles in solution (1p1061-2).

From the lumen, the micelles then transfer the lipids to the mucosal surface for absorption by diffusion (1p1063). Lipid-soluble vitamins A, D, E, and K are also transported within the micelles (1p1065). The delivery is dependent on bile acid micelles increasing effective concentration to create solute flux across the unstirred fluid layer (1p1063). Without bile acids, the absorption of triacylglycerols and the lipid-soluble vitamins would be reduced drastically (1p1063).

Reference List

1. Devlin TM. Textbook of Biochemistry with Clinical Correlations. Philadelphia: Wiley-Liss, 2002.

04 July 2009

Why so many proteolytic enzymes?

When studying the evolution timeline that led to modern biochemistry, one can always turn to studying protein architecture. Proteins have been called “molecular fossils” that serve to mark milestones in the “history of life” (1). There is a wide diversity of proteolytic enzymes in humans and the network of enzymes have a grand complexity that calls for investigation of how they were shaped over time (2).

In digestion there is a variety of proteolytic enzymes—pepsins, enteropeptidases, carboxypeptidases, and aminopeptidases (3). Each work to hydrolyse proteins by cleaving off amino acids from differing peptide bonds, in different stages and conditions (gastric, pancreatic and intestinal phases) and at varied pH ranges (3). The system is indeed complex, not exactly perfect (a better system may have used only a one or two enzymes), but it works and that's evolution.

Each highly structured enzyme would have evolved accordingly at some time, and some, which may have had major roles in the past, have only minor ones now. An example of biochemical “fossils” studied currently in Germany are particular aspartic proteases (4). They are structurally similar to other proteases suggesting a common "major role" ancestor", but have evolved now only to act in “chaperone-like” fashion for substrate binding in digestion (4).

More than 2 percent of human genes are proteases or protease inhibitors (5). New genomic data is expected reveal more about how proteases, their substrates, proteolytic complexes, inhibitors, and interactions all co-evolved (5;6). The complete human degradome—set of protease genes—is also being compared with degradomes of other mammals such as chimpanzees and mice and serving to provide further understanding of ancestral relationship of species (5;7).

Reference List

1. Caetano-Anolles G, Wang M, Caetano-Anolles D, Mittenthal JE. The origin, evolution and structure of the protein world. Biochem J 2009;417:621-37.
2. Page MJ, Di CE. Evolution of peptidase diversity. J Biol Chem 2008;283:30010-4.
3. Devlin TM. Textbook of Biochemistry with Clinical Correlations. Philadelphia: Wiley-Liss, 2002.
4. Hulko M, Lupas AN, Martin J. Inherent chaperone-like activity of aspartic proteases reveals a distant evolutionary relation to double-psi barrel domains of AAA-ATPases. Protein Sci 2007;16:644-53.
5. Puente XS, Sanchez LM, Gutierrez-Fernandez A, Velasco G, Lopez-Otin C. A genomic view of the complexity of mammalian proteolytic systems. Biochem Soc Trans 2005;33:331-4.
6. Southan C. Exploiting new genome data and Internet resources for the phylogenetic analysis of proteases, substrates and inhibitors. Biochem Soc Trans 2007;35:599-603.
7. Ordonez GR, Puente XS, Quesada V, Lopez-Otin C. Proteolytic systems: constructing degradomes. Methods Mol Biol 2009;539:33-47.

03 July 2009

Whether or Not to Take Vitamin C

Unlike most other mammals, humans and other primates don't synthesize vitamin C because we lack the enzyme glunolactone oxidase (1). The enzyme was lost long ago without affecting our survival due to frequent intake of high-vitamin C fruits and vegetables.

Thus, we must continue to get vitamin C from our diet by the same manner (fruits or veggies) or otherwise, lest we succumb to scurvy as British sailors did in the early 1800s before they adopted rationing limes on naval vessels (1).

Vitamin C deficiency leading to scurvy is now rare (1) and in the developed world, but studies on North American and European populations have found that many people who do not eat enough fruits and high-vitamin C vegetables continue to have inadequate levels of vitamin C (2;3).

Supplementation or dietary change would serve the majority of these patients because—when taken along with other vitamins—vitamin C may lead to reduced risk of chronic diseases such as cancer, cardiovascular disease and cataracts (1). The antioxidant vitamin is thought to possibly have a role in counteracting and detoxifying carcinogens, preventing myocardial lipid peroxidation and LDL oxidation, and prevent oxidative damage to lens in the eye (1).

Note that the vitamin has not been found to have any effect on reducing risk of colds (1). This is in contrast to what's marketed on many dietary supplements.

Large intakes of vitamin C (above 2g daily) can cause diarrhea (1). The vitamin C competes with uric acid inhibiting renal absorption of uric acid that can lead to increases of uric acid excretion, urine acidification and precipitation of uric acid crystals (1). This may increase risk of urate kidney stones if high doses are taken chronically (1). Chronic high doses may not be appropriate also for those with iron metabolism disorders since vitamin C increases iron absorption (1).

Recommended dietary intake levels are 75mg for women and 90 mg for men (1). If pregnant, elderly, smoking or afflicted with chronic disease, a little more may be needed (4-6). Supplementation with a multivitamin may be sufficient for oxidative stress protection, however, findings on reducing risk of chronic disease are mostly related to antioxidant vitamin intake from fruit and vegetables (6-10).

Based on the above rationale, I would recommend patients first attempt to increase fruit and vegetable consumption to meet desired plasma levels and with optimal synergistic effects of other vitamins. If there’s any doubt of the patient’s ability or motivation to eat fruits and vegetables, then vitamin C in form of a multivitamin would be the next step.

Reference List

1. Gropper SS, Smith JL, Groff JL. Advanced Nutrition and Human Metabolism. Belmont, CA: Thomson Wadsworth, 2009.
2. Hampl JS, Taylor CA, Johnston CS. Vitamin C deficiency and depletion in the United States: the Third National Health and Nutrition Examination Survey, 1988 to 1994. Am J Public Health 2004;94:870-5.
3. Taylor CA, Hampl JS, Johnston CS. Low intakes of vegetables and fruits, especially citrus fruits, lead to inadequate vitamin C intakes among adults. Eur J Clin Nutr 2000;54:573-8.
4. Valdes F. [Vitamin C]. Actas Dermosifiliogr 2006;97:557-68.
5. Brubacher D, Moser U, Jordan P. Vitamin C concentrations in plasma as a function of intake: a meta-analysis. Int J Vitam Nutr Res 2000;70:226-37.
6. Goodwin JS, Brodwick M. Diet, aging, and cancer. Clin Geriatr Med 1995;11:577-89.
7. Genkinger JM, Platz EA, Hoffman SC, Comstock GW, Helzlsouer KJ. Fruit, vegetable, and antioxidant intake and all-cause, cancer, and cardiovascular disease mortality in a community-dwelling population in Washington County, Maryland. Am J Epidemiol 2004;160:1223-33.
8. Nagyova A, Krajcovicova-Kudlackova M, Horska A et al. Lipid peroxidation in men after dietary supplementation with a mixture of antioxidant nutrients. Bratisl Lek Listy 2004;105:277-80.
9. Broekmans WM, Klopping-Ketelaars IA, Schuurman CR et al. Fruits and vegetables increase plasma carotenoids and vitamins and decrease homocysteine in humans. J Nutr 2000;130:1578-83.
10. Zino S, Skeaff M, Williams S, Mann J. Randomised controlled trial of effect of fruit and vegetable consumption on plasma concentrations of lipids and antioxidants. BMJ 1997;314:1787-91.

Carrageenans - Good or Bad for You?

Carrageenans are food additives derived from red seaweed such as Chondrus crispus (Irish moss) and other species and are used as a thickening, stabilizing, and texturizing agents in foods and also for reduced-fat meat products (1;2).

They nicely replace animal-based gelatin found in many foods such as soymilk, chocolate milk, yogurts, beers and wines. Lamda-carrageenan, for example, is used to provide a creamy texture to dairy products.

The polymers are high-molecular-weight polysaccharides made up of repeating disaccharide units have a charged nature and their structure gives them their highly reactive properties (2). Concentration and greater molecular weight increases viscosity further (2).

Safety of use of carrageenans in foods has been a matter of controversy and confusion. Leading manufacturers of carrageenan such as FMC corporation have maintained that the use of carrageenan has a centuries-old history of safety in humans that has been confirmed by studies on animals such as dogs and rodents (3). Food-grade carrageenans are not thought to be degraded or absorbed from the gastrointestinal tract of humans (1).
It is known that, when administered systemically, carrageenans are linked to acute liver toxicity (4), are carcinogenic (5) and affect the immune system (6). Also, a substance formed of degraded carrageenan, now known as poligeenan, has long been banned from use in food because of links to fetal toxicity, birth defects, liver toxicity, ulcerative disease, pulmonary lesions and colon cancer in animals (5).

Toxicity concerns of undegraded carrageenans arose when studies in a few experimental animals found that carrageenans were degraded leading to absorption and toxicity (5;6). Another study on rats found that given small quantities of for 90 days, undegraded carrageenans had “penetrated the intestinal barrier degree” in adult rats (7). Low concentrations were also tested on tissue cultures where it was found that lamda-carrageenans entered cells by what appeared to be endocytosis (8).

Despite these data, however, the World Health Organization Expert committee on Food Additives and Joint Food and Agriculture Organization have kept recommendations of allowable daily intake as “not specified” (6).

The groups cited that there was “no credible evidence” to support that food-grade carrageenans were degraded or absorbed in “rodents, dogs, and non-human primates” or that they presented any toxic or carcinogenic effect in these species or in humans long term (6). High doses of carrageenans had been found to lead to cecal enlargement, but the studied amounts were in excess of which humans would consume normally (6).

Reference List

1. Trius A, Sebranek JG. Carrageenans and their use in meat products. Crit Rev Food Sci Nutr 1996;36:69-85.
2. Food and Agriculture Organization. FAO Corporate Document Repository. Training Manual on Gracilaria Culture and Seaweed Processing in China. Available: http://www.fao.org/docrep/field/003/AB730E/AB730E03.htm.
3. Weiner ML. Toxicological properties of carrageenan. Agents Actions 1991;32:46-51.
4. Abe T, Kawamura H, Kawabe S, Watanabe H, Gejyo F, Abo T. Liver injury due to sequential activation of natural killer cells and natural killer T cells by carrageenan. J Hepatol 2002;36:614-23.
5. Watt J, Marcus R. Harmful effects of carrageenan fed to animals. Cancer Detect Prev 1981;4:129-34.
6. Cohen SM, Ito N. A critical review of the toxicological effects of carrageenan and processed eucheuma seaweed on the gastrointestinal tract. Crit Rev Toxicol 2002;32:413-44.
7. Nicklin S, Miller K. Effect of orally administered food-grade carrageenans on antibody-mediated and cell-mediated immunity in the inbred rat. Food Chem Toxicol 1984;22:615-21.
8. Tobacman JK, Walters KS. Carrageenan-induced inclusions in mammary myoepithelial cells. Cancer Detect Prev 2001;25:520-6.

Tidbit: GLUT6 - the "pseudogene"

GLUT6 is expressed in various tissues in the body, but doesn't encode any functional glucose transport protein (1). Why does it occur at all? It's thought that GLUT6’s nucleotide sequence may have simply occurred from an insertion of GLUT3 reverse transcribed in a region of an untranslated gene (1).

Reference List

1. Kayano T, Burant CF, Fukumoto H et al. Human facilitative glucose transporters. Isolation, functional characterization, and gene localization of cDNAs encoding an isoform (GLUT5) expressed in small intestine, kidney, muscle, and adipose tissue and an unusual glucose transporter pseudogene-like sequence (GLUT6). J Biol Chem 1990;265:13276-82.

Review of study on using antioxidant response as predictor for radiation pneumonitis

A currently unpredictable outcome of radiotherapy on lung cancer patients is radiation pneumonitis (lung inflammation). This study was the first performed on humans to determine how antioxidant response may be used to predict this “potentially lethal treatment-related complication”. The oxidative stress link had been established through studies on irradiated mice.

Type of study: Observational study on humans; physicians grading for pneumonitis were blinded to antioxidant data

Method used to conduct study: Fifteen total lung cancer patients were found eligible for the study after signing informed consents, having stage III disease, receiving concurrent definitive radiotherapy and paclitaxel-based chemotherapy, and having good performance status. Excluded were patients who had received radiotherapy or chemotherapy previously and those with unfavorable Eastern Cooperative Oncology Group performance status or chronic obstructive pulmonary disease.

Blood samples were collected at baseline and weekly during the 6-week treatment. Radiation pneumonitis was diagnosed three months after the treatment according to different grades ranging from mild, moderate, and severe. Cross-validation was used to analyze test sensitivity to variables. Detection of proteins was performed through gel electrophoresis, secondary antibody and enhanced chemiluminescence in the blot analysis.

Summary: Researchers found that the patients who developed pneumonitis had higher levels of superoxide dismutase (SOD) and lower levels of glutathione peroxidase (GPX) overall. The data suggest that higher SOD activity increased the conversion of superoxide anion to hydrogen peroxide. In conjunction with low GPX, an increase of hydrogen peroxide and hydroxyl radicals would occur creating oxidative stress that would predispose patients to radiation pneumonitis.

Critique of research design quality and relevance: Blinding methods and appropriate exclusions make this a well-designed study with few confounding variables. Although strong data from animals confirm its findings, the study’s great weakness is that of being a small one. Its relevance, however, may be large since using GPX/SOD as predictive markers may save lives in the future.

Nutritional implications and implications of future study: High SOD/low GPX activity may serve as a marker for prediction of radiation pneumonits and that increasing the ratio of GPX/SOD would reduce risk of radiation pneumonitis. Clinical trials on use of antioxidant supplements is warranted; however, the researchers warn, antioxidant therapies must take into account other treatments (e.g. chemotherapy) and how it would affect the patient as "a whole".


Park EM, Ramnath N, Yang GY et al. High superoxide dismutase and low glutathione peroxidase activities in red blood cells predict susceptibility of lung cancer patients to radiation pneumonitis. Free Radic Biol Med 2007;42:280-7. Available at: http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1892164