July 2008 Blog with Durk and Sandy

D&S Comment: Sure enough, Germany has recently released commemorative stamps of Albert Einstein.

The Saturated Fat Palmitate Induces Insulin Resistance, Which Is Reversed by the Monounsaturated Fat Oleate

A new study¹ reports a protective effect of oleic acid, a monounsaturated fatty acid, against negative effects of palmitic acid, the most common dietary saturated fatty acid, in mouse skeletal muscle cells. Exposure of cells to palmitate caused insulin resistance and inflammation, increasing levels of the inflammatory cytokine IL-6 and downregulating the expression of genes that control the oxidative capacity of skeletal muscles. Exposure to oleate did not cause any of these effects.

In fact, when cells were exposed to both palmitate and oleate, it reversed both inflammation and insulin signaling impairments by causing palmitate to be used in the production of triglycerides (rather than in an inflammation-producing pathway) and upregulating genes that regulate mitochondrial beta-oxidation (metabolism of fats for energy). This evidence is consistent with human studies that have shown, for example, that elevated IL-6 levels correlate most strongly with insulin resistance and human type 2 diabetes.¹ It is also known that saturated fatty acids decrease insulin sensitivity in diabetic patients and healthy subjects, whereas monounsaturated fatty acids increase it.¹

A good source of oleic acid is olive oil (with about 65% oleate), but a much better source is our high-oleic sunflower oil (with about 95% oleate). Not only does the high-oleic sunflower oil contain far more oleate than olive oil, but it also contains much less saturated fat (such as palmitate). It is an excellent cooking or salad oil and can withstand the high temperatures of frying. In our opinion, the high oleic acid content of the Mediterranean diet may be its single most distinctive feature.

Reference

1. Coll et al. Oleate reverses palmitate-induced insulin resistance and inflammation in skeletal muscle cells. J Biol Chem 283(17):11107-16 (2008).

Natural Metabolites of Dietary Quercetin Target and Protect Macrophages from Becoming Foam Cells

A very interesting new paper provides experimental evidence to support a novel mechanism whereby dietary flavonoids protect against cardiovascular disease.¹ The researchers used quercetin as a prime flavonoid as it is widely distributed in the human diet (onions are particularly rich in it, but it is also found in broccoli, apples, and other foods).

In the standard model of atherosclerosis (well supported by the evidence), macrophages enter the subendothelial linings of arteries, where they ingest modified LDL (especially oxidized LDL), becoming converted into foam cells, a major constituent of atherosclerotic lesions and a source of proinflammatory molecules that promote the development of these lesions. The authors found that pretreatment of RAW macrophages with quercetin-3-glucuronide (Q3GA), a major antioxidative quercetin metabolite, dose-dependently inhibited the accumulation of oxidized LDL in the cells.

Incredibly, the authors showed that Q3GA actually targeted and accumulated in the injured aorta of atherosclerotic plaques, primarily colocalizing with macrophage-derived foam cells—this was determined with an ingenious technique utilizing a monoclonal antibody that specifically bound to Q3GA. They showed that Q3GA dose-dependently downregulated the expression of two major scavenger molecules (SR-A and CD36) which are produced to remove excess cholesterol from foam cells, thus suggesting that the quercetin metabolite might prevent the development of foam cells and, hence, this might be a major source of quercetin’s (and other flavonoids’) protective effects against atherosclerosis. If you take our daily multinutrient supplement, Personal Radical Shield™, at its recommended dosage (3 capsules 4 times a day), you get a daily total of 130 mg of quercetin, which is about three times as much as would be found in a natural vegetarian diet rich in quercetin.

Reference

1. Kawai et al. Macrophage as a target of quercetin glucuronides in human atherosclerotic arteries. J Biol Chem 283(14):9424-34 (2008).
   
   

Astaxanthin Promotes Fat Metabolism, Rather Than Glucose Metabolism, During Exercise Improving Endurance

Astaxanthin is a carotenoid (not used to create vitamin A in the human body) found in algae, fish, and birds.¹ A new paper¹ reports on the beneficial effects of astaxanthin on exercise performance.

As the authors explain, when exercise depends upon glucose as its fuel, the intramuscular pH decreases due to the production of lactic acid, which may impair muscular contractions. On the other hand, utilizing fats as fuel for exercise works well, because it can be continuously and efficiently obtained via aerobic metabolism. The authors propose that fat burning during exercise not only reduces muscle fat content but also improves endurance. The authors had shown, in an earlier work, that astaxanthin “accumulates in muscle tissue, as well as liver and kidney, after oral administration, and dietary astaxanthin attenuates muscle damage and inhibits peroxidation of DNA and lipids due to prolonged exercise.”

In their new study, the researchers examined the effects of astaxanthin on lipid metabolism in exercising mice. They also looked at the protective effect of astaxanthin on oxidative damage to carnitine palmitoyl transferase 1 (CPT 1), an enzyme located in the mitochondrial membrane that plays an important role in the importation of fatty acids for metabolism in the mitochondria.

The mice were divided into four groups: a resting control group, a resting control group receiving astaxanthin (0.02% by weight), a running training group, and a running training group treated with astaxanthin. After 4 weeks, they were tested. The authors found that fat utilization was significantly higher in the astaxanthin-supplemented group compared with the normal-diet group. At the same time, carbohydrate utilization was significantly lower. The increase in lactic acid by exercise and the use of glycogen were reduced by astaxanthin. Oxidative modification of CPT 1 by one of the lipid peroxides was increased by exercise, but the increase was reduced by astaxanthin. Moreover, the running time to exhaustion for the running trained mice was increased with astaxanthin.

The authors propose that the specific lipolytic effect caused by astaxanthin—facilitating utilization of lipids in muscle rather than promoting release from fat stores—“may be unique in astaxanthin not obtained in other antioxidants. In fact, vitamins C and E failed to increase aerobic performance.” They suggest that astaxanthin’s high antioxidant activity and its intracellular location may be responsible, at least in part, for this.

Reference

1. Aoi et al. Astaxanthin improves muscle lipid metabolism in exercise via inhibitory effective of oxidative CPT 1 modification. Biochem Biophys Res Commun 366:892-7 (2008).

Seasonal Flu Shots May Protect Against Bird Flu

Good news for anyone concerned about bird flu: a recent paper¹ reports finding cross-reactivity between human and avian influenza strains in some healthy donors recently vaccinated against seasonal influenza. What this means is that there may be increased immune response to bird flu in people who received seasonal flu shots recently.

The researchers evaluated cell-mediated immunity in 42 healthcare workers at the Spallanzani Institute (Rome, Italy) who wished to receive seasonal flu shots. Peripheral blood mononuclear cells (PBMC) were isolated from each subject’s blood and were stimulated with the influenza vaccine preparation, UV-inactivated bird influenza, or synthetic influenza (of the bird flu variety) peptides for 3 days and then expanded for 6 more days in the presence of IL-2 (a cell-mediated immunity factor). What they found was that six donors had a “noteworthy” increase of IFN-gamma-producing CD4 T cells specific for avian influenza as compared to baseline levels. Three other donors had “an increased frequency of H5NI [bird flu strain] peptides-specific CD4 T cell even if they were unable to respond to whole virus.”

Seasonal vaccination also affected humoral (B-cell) immunity. “A 4-fold rise of HA [hemagglutinin] antibody titer is considered noteworthy, and after vaccination most donors (28/38, 73.7%) showed a noteworthy rise of HI [a subtype strain of influenza] titers against vaccine preparation . . .” The authors concluded that “Our findings indicate that seasonal vaccination can raise neutralizing immunity against influenza (H5N1) . . .” thereby “showing the existence of an antibody-dependent cross-type immunity.”

Reference

1. Gioia et al. Cross-subtype immunity against avian influenza in persons recently vaccinated for influenza. Emerging Infect Dis 14(1):121-8 (2008).

EMERGING SCIENCE

Ghrelin: A Mere Hormonal Appetite Stimulant or a 
Possible Anti-Aging Molecule

There are efforts being made by pharmaceutical companies to develop inhibitors or blockers of ghrelin because of its role in appetite stimulation. Indeed, studies have shown a good correlation between plasma ghrelin and corresponding food intakes or hunger.¹ Moreover, an experimental ghrelin receptor blocker was shown to attenuate food intake and weight gain in mice.¹ However, whether such suppression is a good idea might depend on whether it suppressed the beneficial effects of ghrelin, as we discuss below, including the possibility that ghrelin has anti-aging effects. Following the section on “The Ghrelin Receptor as a Possible Site for Anti-Aging Effects,” we also discuss the possibility that octanoic acid, the principal fatty acid found in MCTs (medium-chain triglycerides), might play a role in regulating the activity of ghrelin.

The ghrelin response to a meal is attenuated in obese individuals compared to young persons,¹ suggesting that, like leptin, another hormone that regulates food intake, obese individuals may be “ghrelin-resistant.”

Interestingly, although ghrelin is an appetite-stimulating hormone, and eating a carbohydrate-rich meal reduces ghrelin levels following the meal, eating a protein-rich, low-carbohydrate meal actually increases ghrelin levels.¹ Although the data are inconsistent, it appears that protein and carbohydrates are satiating to a similar degree. It is thought that insulin release may be what causes ghrelin levels to fall after a carbohydrate-rich meal.² Similarly to normal-weight subjects, ghrelin levels increase after a protein-rich meal in obese subjects, but to a lesser extent than in normals.¹

It appears too that a carbohydrate-rich meal enriched with fiber (arabinoxylan, a soluble fiber) that caused only a tendency (P=0.065; significance would require P≤0.05) toward lower insulin levels (though not glucose levels) can cause an increase in postprandial ghrelin levels³ in subjects with normal glucose regulation. (The authors doubt that the effect was mediated by insulin, however. We are not so sure, as P=0.065 is not far from 0.05, which would show significance.) Whether this is a real effect and whether it applies to other types of fiber remain to be determined.

Whether it is a good idea to suppress ghrelin in the obese to decrease appetite is, in our judgment, questionable, as there are data indicating that ghrelin has potentially important beneficial effects, including anti-inflammatory activity and thymus-protective (hence, improved immune activity) effects. Another paper⁶ proposes that ghrelin receptor agonists may be effective for anti-aging intervention. The ghrelin receptor is a powerful growth hormone secretagogue, that is, it causes growth hormone release when stimulated by ghrelin. The evidence indicates that ghrelin is important in regulating the growth hormone/insulinlike growth factor axis.

Ghrelin Effects on Immunity

A recent paper reports that ghrelin is expressed in the thymus gland, and in immune cells it regulates T-cell activation and inflammation.⁴ The authors of this paper found that ghrelin and ghrelin receptor expression within the thymus decline with age in mice. Infusion of ghrelin into 14-month old-mice resulted in significantly improving the age-associated decline in thymus architecture and thymocyte numbers. Conversely, they report, ghrelin and ghrelin receptor-deficient mice had enhanced age-associated thymic involution.

Ghrelin as an Anti-Inflammatory Molecule Could Protect Against Atherosclerosis

Another recent paper⁵ reports, in a cell culture study of human umbilical vein endothelial cells (HUVECs), that ghrelin inhibited both basal and tumor necrosis factor-alpha-induced proinflammatory cytokine release. They also found that intravenous administration of ghrelin to rats inhibited endotoxin-induced proinflammatory cytokine production. Moreover, ghrelin inhibited the cytokine release in the HUVECs in response to hydrogen peroxide. The authors suggest that “These novel anti-inflammatory actions of ghrelin suggest that the peptide could play a modulatory role in atherosclerosis, especially in obese patients, in whom ghrelin levels are reduced.”

The Ghrelin Receptor as a Possible Site for Anti-Aging Effects

A recent paper⁶ suggests that agonists of the ghrelin receptor show potential for anti-aging intervention. First, the authors report that “the weight of the evidence suggests that, in humans, aging is associated with reduced ghrelin production as well as ghrelin resistance.” This decline may be a cause of the decrease in pulsatile release of growth hormone, as ghrelin regulates the latter.

The authors further report that, although ghrelin is involved in appetite stimulation, it is also “localized to areas of the central nervous system that regulate mood, memory, and learning.” They report that an earlier experiment by a different group had found that “Chronic administration of the ghrelin mimetic MK-0677 to elderly humans produced a sustained rejuvenation of the GH/IGF-1 axis, suggesting that MK-0677 compensates for a deficit in endogenous ghrelin signaling.” They also reported that “in postmenopausal women, treatment [with MK-0677] for up to 18 months, produced increases in bone mineral density.” They also note that “. . . hyperstimulation of the GH/IGF-1 axis [by the ghrelin mimetic] was prevented by endogenous regulatory feedback loop.”

With respect to health span (length of the healthy active part of life), the authors report that in elderly women, “the 5-year mortality can be predicted according to the IGF-1/IL-6 ratio” and propose that, since ghrelin can decrease IL-6 and increase IGF-1, it may extend health span. They also report that in a study done by others, administration of ghrelin to rats caused increased expression of the mitochondrial UCP2 (uncoupling protein 2); UCP2 has been proposed to reduce the production of reactive oxygen species in the mitochondria as well as promoting the burning of fats.^6b

Also very interesting, the authors found that ghrelin could amplify dopamine signaling, which ordinarily declines during aging, in a cell culture study.

Ghrelin Activation by Octanoate, the Major Fatty Acid in Medium-Chain Triglycerides (MCTs)

Finally, there have been a number of recent reports^5,6 that suggest that octanoylation (chemical combination with octanoate) is critical for ghrelin’s anti-inflammatory effects in endothelial cells and is required for its growth hormone-releasing action via the growth hormone secretagogue receptor. We speculate that the consumption or supplementation of medium-chain triglycerides, which supplies octanoate (the most plentiful fatty acid in MCTs), might increase the activity of ghrelin. This exciting possibility will remain unclear, however, until appropriate studies are done. In the meantime, we use Durk & Sandy’s medium-chain triglycerides on our salads and in baked and other cooked food (but not fried, as MCTs cannot tolerate such high temperatures), because MCTs are mostly metabolized for energy rather than stored as body fat.

References

1. Erdmann et al. Ghrelin response to protein and carbohydrate meals in relation to food intake and glycerol levels in obese subjects. Regulatory Peptides 135:23-9 (2006).
2. Blom et al. Ghrelin responses to carbohydrate-enriched breakfast is related to insulin. Am J Clin Nutr 81:367-75 (2005).
3. Mohlig et al. Arabinoxylan-enriched meal increases serum ghrelin levels in healthy humans. Horm Metab Res 37:303-8 (2005).
4. Dixit et al. Ghrelin promotes thymopoiesis during aging. J Clin Invest117(10):2778-90 (2007).
5. Li et al. Ghrelin inhibits proinflammatory responses and nuclear factor-kappaB activation in human endothelial cells. Circulation 109:2221-6 (2004).
6. Smith et al. Ghrelin receptor (GHS-R1A) agonists show potential as interventive agents during aging. Ann NY Acad Sci 1119:147-64 (2007). 
   6b. Pecqueur et al. Uncoupling protein-2 controls proliferation by promoting fatty acid oxidation and limiting glycolysis-derived pyruvate utilization. FASEB J 22:9-18 (2008).
7. Zhu et al. On the processing of proghrelin to ghrelin. J Biol Chem 281(50):38867-70 (2006).