Polyunsaturated fatty acids

• Cis configuration in nature• Generally unsaturated fatty acids are confined to the sn-2 position of

phospholipids and are 18-20 carbons long• MUFA tend to be in the sn-1 position, like saturated fats.• Hydrocarbon portion is saturated or partially unsaturated

3,6-PUFA

9-MUFA

PUFA, MUFA• Monounsaturated fatty acids (MUFA)- only one

double bond present• Polyunsaturated fatty acids (PUFA)- at least 2

double bonds are present• Acetylenic – one or more triple bonds• Polyunsaturated/Monounsaturated

– Ex. Docosahexaenoic Acid, Oleic Acid• Double bonds have a planar conformation

MUFA• Most of the 100 MUFAs identified are rare• Oleic acid is very abundant in nature

-most prevalent unsaturated fat in human diet -highest content in extra virgin olive oil

(70g/100g)

3 categories of PUFA

• Conjugated – if double bonds alternate with single bonds (– C = C – C = C –)

• Unconjugated – of the double bonds are separated by carbon atoms bonded with

single bonds (– C = C – C – C = C –)

• A third category exist in which double bonds are not all entirely in the methylene interrupted arrangement (present in certain microorganisms, marine lipids and some seed oils.

Methylene

interrupted

Unconjugated most common• Subdivided into

families, depending on the position of the double bond closest to the methyl side (), numbered 1 on the fatty acid chain.

• 12 omega families• -3,6,9 are what’s

found in normal diet

-3 and -6 are Essential Fatty Acids

• Mammals lack the enzymes to introduce double bonds at carbon atoms beyond C9.

• Hence, all fatty acids containing a double bond at positions beyond C9 have to be supplied in the diet.

• Linoleate (18:2 Δ 9,12) and Linolenate (18:3 Δ 9,12,15) are the two essential fatty acids in mammals.

• Interconversion between PUFAs occur only within the same family

Oleic Acid (OA): C18:1, n-9 or -9

Good source: Olive oil, Peanut oil, Soy oil

Linoleic Acid (LA): C18:2, n-6 or -6. Essential Fatty Acid

Alpha Linolenic Acid (ALA): C18-3, n-3 or -3. Essential Fatty Acid

Good source: Flaxseed

Eicosapentaenoic Acid (EPA): C20:5, n-3 or -3. Essential Fatty Acid. Good source: Fish oil

Docosahexaenoic Acid (DHA): C22:6, n-3 or -3. Essential Fatty Acid. Good Source: Fish oil

Arachidonic Acid (AA): C20:4, n-6 or -6. Good source: Liver, Beef.

Omega-6 fatty acids• Linoleic (C18:2) is

essential• Found in:

-vegetable oil-nuts and seeds

• Only need about a tbsp/day

Omega-3 Fatty Acids

• primarily in fish and marine mammals

• Also found in soybean, canola, walnut, flaxseed oils

Recommended omega6:omega-3 ratio is 2.3:1

Most Common Natural Products

• Anthropological research suggest that our hunter gatherer ancestors consumed roughly 1:1 ratio of omega-6:omega 3.

• Vegetable oil consumption rose dramatically between the beginning and end of the 20th century.

-Between 1935 and 1939, the ratio of n-6 to n-3 fatty acids was reported to be 8.4:1

-Ratio increased to 10.3:1 by 1985-Todays estimates range between 10:1 to 20:1

• Americans now get almost 20% of their calories from a single food source – soybean oil – with almost 9% of all calories from the omega-6 fat linoleic acid (LA) alone!

• recommended 30% of diet-10%

monounsaturated-10% saturated-10% unsaturated

How Can Fatty Acids Modulate the Immune System?

• Membrane fluidity• Lipid peroxidation• inflammatory cytokines (IL-6, IL-12, IL-23)

production• Eicosanoid production• Membrane fusion and phagocytic activity• Lymphocytic proliferation• Immune cell migration

Fatty acids impact:

• Depending on diet, fatty acids end up in plasma membrane

• Consumption of hydrogenated oils results in reduction of PUFAs in plasma membrane

• Most tissues contain mainly omega-6 fatty acids (75% as LA and AA), with small amounts of omega-3 fatty acids

-the exception is retina, brain and testes

18

Eicosanoids: paracrine hormones

• Derived from the 20 carbon polyunsaturated fatty acid (arachidonic acid)

• Involved in reproduction, inflammation, fever and pain• 3 classes: Prostaglandins, thromboxanes, leukotrienes

Regulate synthesis of cAMP production fever, pain, blood flow, and uterine contraction

Produced by platelets, important in clotting and blood flow

Inflammation, asthma, allergy

Arachidonic Acid (AA): C20:4, n-6 or -6. Good source: Liver, Beef.

Arachidonic Acid Metabolism

Eiscosanoids mainly formed from AA sincse it is dominant in cell membrane and plasma lipidsCleaved by phospholipasesThree pathways of eicosanoid production from AA:

1) COX: AA PG, TXs2) LOX: AA HPETE and HETE LTs and

lipoxins3) Cytochrome P450: AA EET and DHET

NSAIDs inhibit the COX pathway

Eicosanoid action

• Released into extracellular fluid• Bind to membrane receptors on target cell• Binding causes signal transduction• Main function is cell-cell communication

(paracrine)• Can also act on itself (autocrine)

Phospholipid membrane

Phospholipase A2

Cyclooxygenases (COX)

Prostaglandins (PG) &Thromboxanes (TX)

Lipoxygenases (LOX)

Leukotrienes

O

HO

O

HOArachidonic acid Eicosapentaenoic acid

• EPA ompetes with AA for incorporation into the cell membrane

• poor substrate for cyclooxygenases• gives rise to series 5 leukotrienes

DHA and Phosphatidylserine• PS is a recognition marker for apoptotic cells

– It is highly prevalent in Brain tissue– Made up of predominantly Stearic Acid (C18:0) and DHA (C22:6)

• PS predominantly resides on the interior (cytoplasmic side of plasma membrane)– Flippase is responsible for the assymetry

• Upon apoptosis, more of PS translocates to the exterior facilitating uptake by scavenger cells such as macrophages and neutrophils.

• Reduced levels of PS with DHA, may decrease efficiency uptake by scavenger cells.

• Anecdotal evidence for preventing dementia

• NF-B/IkB dimer resides in cytosol

• Upon stimulation, IkB is phosphorylated/degraded

• NF-B translocates to nucleus facilitating transcription of cytokines

• There is a reduction in IkB degradation when DHA is present

• DHA reduces translocation of NF-B to nucleus

Effect of DHA on IB & NF-B

Kong W. et al, 2010

Kong W. et al, 2010

ELISA Assays show: • Reduction in IL-12• Reduction in IL-23• Reduction in IL-27• Effect diminishes below 1 M

Effect of DHA on Cytokine Production

Lipid Peroxidation

• PUFAs are highly susceptible!• Free radical attacks the methylene C between

the double bonds in the FA chain• Increased by presence of O2 and transition

metal ions. • Autocatalytic• Considered as one of the few examples of

carbon-centered radical production in cells

Membrane lipid peroxidation involves 3 steps

1) Initiation-by hydrogen extraction by a

radical species

2) Propagation-O2 rapidly adds on to carbon-centered radical L, yielding peroxy radical, LOO

-LOO can then attack nearby PUFA, creating a chain reaction

3) Termination- Arrangement into stable products

The Good,• Reactive lipid species may

benefit cell• Fast & easy way for

membrane to initiated a nonspecific response to external stress

The Bad• Reactive Lipid Species (RLS)

are electrophilic in nature and capable of reacting with nucleophilic amino acids

• Thiol groups can act as a redox-switch controlling cell signaling, metabolism or gene expression

& the Gooder

RLS-mediated signaling is involved in various physiological pathways: apoptosis, induction of antioxidative defense, membrane repair, proteosomal pathways

MUFAs have many of the benefits of

PUFAs but are less susceptible

to oxidation

PUFA & membrane fission?

• PUFAs make lipid bilayers more flexible

• Up to 80% of phospholipids in exocytotic synaptic vesicles are polyunsaturated

• Treatment of neurons with PUFAs stimulate SNARE assembly and the recycling of synaptic vesicles

• In GUVs, PUFAs facilitates the enzyme, dynamin that self-assembly, involved in membrane fission