Certain diets cause a marked reduction in milk fat production in ruminants. Commonly referred to as milk fat depression (MFD), the mechanism involves an interrelationship between rumen microbial processes and tissue metabolism. Numerous theories to explain this interrelationship have been proposed and investigations offer little support for theories that are based on a limitation in the supply of lipogenic precursors. Rather, the basis involves alterations in rumen biohydrogenation of dietary polyunsaturated fatty acids and a specific inhibition of mammary synthesis of milk fat. The biohydrogenation theory proposes that under certain dietary conditions, typical pathways of rumen biohydrogenation are altered to produce unique fatty acid intermediates that inhibit milk fat synthesis. Trans-10, cis-12 conjugated linoleic acid (CLA) has been identified as one example that is correlated with the reduction in milk fat. Investigations with pure isomers have shown that trans-10, cis-12 CLA is a potent inhibitor of milk fat synthesis, and similar to diet-induced MFD, the mechanism involves a coordinated reduction in mRNA abundance for key enzymes involved in the biochemical pathways of fat synthesis. A more complete identification of these naturally produced inhibitors of fat synthesis and delineation of cellular mechanisms may offer broader opportunities for application and understanding of the regulation of lipid metabolism.

/pdf/nutritional-regulation-of-milk-fat-synthesis-2ltygj39ak.pdf

Nutritional regulation of milk fat synthesis.

The Composition of Bovine Milk Lipids: January 1995 to December 2000

▪ Abstract Conjugated linoleic acid (CLA) is a group of polyunsaturated fatty acids found in beef, lamb, and dairy products that exist as positional and stereo-isomers of octadecadienoate (18:2). Over the past two decades numerous health benefits have been attributed to CLA in experimental animal models including actions to reduce carcinogenesis, atherosclerosis, onset of diabetes, and body fat mass. The accumulation of CLA isomers and several elongated/desaturated and β-oxidation metabolites have been found in tissues of animals fed diets with CLA. Molecular mechanisms of action appear to include modulation of eicosanoid formation as well as regulation of the expression of genes coding for enzymes known to modulate macronutrient metabolism. This review focuses on health benefits, metabolism, and potential mechanisms of action of CLA and postulates the implications regarding dietary CLA for human health.

Dietary conjugated linoleic acid in health: physiological effects and mechanisms of action.

http://www2.kobe-u.ac.jp/~toyoda/beef/BEEF/Ref/beef%20production_fat.pdf

Innovations in beef production systems that enhance the nutritional and health value of beef lipids and their relationship with meat quality.

The potential to modify the milk fatty acid (FA) composition by changing the cow or goat diets is reviewed. Ruminal biohydrogenation (RBH), combined with mammary lipogenic and A-9 desaturation pathways, considerably modifies the profile of dietary FA and thus milk composition. The pasture has major effects by decreasing saturated FA and increasing FA considered as favorable for human health (c9-18:1, 18:3n-3 and c9t11-CLA), compared to winter diets, especially those based on maize silage and concentrates. Plant lipid supplements have effects similar to pasture, especially linseed, but they increase to a larger extent, simultaneously several trans isomers of 18:1 and, conjugated or non-conjugated 18:2, especially when added to maize silage or concentrate-rich diets. The goat responds better for milk 18:3n-3 and c9t11-CLA, and sometimes less for c9-18:1, and is less prone to the RBH trans-11 to trans-10 shift, which has been shown to be time dependent in the cow. The respective physiological roles of most milk trans FA have not been studied to date, and more studies in rodents and humans fed dairy products modified by changing ruminant diet are required before recommending a larger use of lipid sources and how to combine them with the different feeding systems used by dairy farmers.

Diet, rumen biohydrogenation and nutritional quality of cow and goat milk fat

Conjugated linoleic acid (CLA) is a naturally occurring anticarcinogen found in milk fat and body fat of ruminants. Although CLA is an intermediate in ruminal biohydrogenation of linoleic acid, we hypothesized that its primary source was from endogenous synthesis. This would involve Delta(9)-desaturase and synthesis from trans-11 18:1, another intermediate in ruminal biohydrogenation. Our first experiment supplied lactating cows (n = 3) with trans-11 18:1 by abomasal infusion and examined the potential for endogenous synthesis by measuring changes in milk fat CLA. By d 3, infusion of trans-11 18:1 resulted in a 31% increase in concentration of cis-9, trans-11 CLA in milk fat, demonstrating that an active pathway for endogenous synthesis of CLA exists. Our second experiment examined the quantitative importance of endogenous synthesis of CLA in lactating cows (n = 3) by abomasally infusing a putative stimulator (retinol palmitate) or an inhibitor (sterculic oil) of Delta(9)-desaturase. Infusion of retinol palmitate had no influence on milk fatty acid desaturation, and yield of CLA in milk fat was not altered. However, sterculic oil infusion decreased the concentration of CLA in milk fat by 45%. Consistent with Delta(9)-desaturase inhibition, the sterculic oil treatment also altered the milk fat concentration of other Delta(9)-desaturase products as indicated by the two- to threefold increase in the ratios of 14:0 to 14:1(,) 16:0 to 16:1 and 18:0 to cis-18:1. Using changes in the ratio of 14:0 to 14:1 as an indication of the extent of Delta(9)-desaturase inhibition with the sterculic oil treatment, an estimated 64% of the CLA in milk fat was of endogenous origin. Overall, results demonstrate that endogenous synthesis of CLA from trans-11 18:1 represented the primary source of CLA in milk fat of lactating cows.

Conjugated linoleic acid is synthesized endogenously in lactating dairy cows by Delta(9)-desaturase.

The resolution of inflammation is an active and dynamic process, mediated in large part by the innate immune system. Resolution represents not only an increase in anti-inflammatory actions, but also a paradigm shift in immune cell function to restore homeostasis. PPARγ, a ligand activated transcription factor, has long been studied for its anti-inflammatory actions, but an emerging body of literature is investigating the role of PPARγ and its ligands (including thiazolidinediones, prostaglandins, and oleanolic acids) in all phases of resolution. PPARγ can shift production from pro- to anti-inflammatory mediators by neutrophils, platelets, and macrophages. PPARγ and its ligands further modulate platelet and neutrophil function, decreasing trafficking, promoting neutrophil apoptosis, and preventing platelet-leukocyte interactions. PPARγ alters macrophage trafficking, increases efferocytosis and phagocytosis, and promotes alternative M2 macrophage activation. There are also roles for this receptor in the adaptive immune response, particularly regarding B cells. These effects contribute towards the attenuation of multiple disease states, including COPD, colitis, Alzheimer's disease, and obesity in animal models. Finally, novel specialized proresolving mediators-eicosanoids with critical roles in resolution-may act through PPARγ modulation to promote resolution, providing another exciting area of therapeutic potential for this receptor.

/pdf/pparg-and-the-innate-immune-system-mediate-the-resolution-of-23ddtecchk.pdf

PPARγ and the Innate Immune System Mediate the Resolution of Inflammation.

The differentiation of interstitial lung fibroblasts into contractile myofibroblasts that proliferate and secrete excessive extracellular matrix is critical for the pathogenesis of pulmonary fibrosis. Certain lipid signaling molecules, such as prostaglandins (PGs), can inhibit myofibroblast differentiation. However, the sources and delivery mechanisms of endogenous PGs are undefined. Activated primary human lung fibroblasts (HLFs) produce PGs such as PGE2. We report that activation of primary HLFs with IL-1β inhibited transforming growth factor β-induced myofibroblast differentiation in both the IL-1β-treated cells themselves (autocrine signal) and adjacent naive HLFs in cocultures (paracrine signal). Additionally, we demonstrate for the first time that at least some of the antifibrotic effect of activated fibroblasts on nearby naive fibroblasts is carried by exosomes and other extracellular vesicles that contain several PGs, including high levels of the antifibrotic PGE2. Thus, activated fibroblasts communicate with surrounding cells to limit myofibroblast differentiation and maintain homeostasis. This work opens the way for future research into extracellular vesicle-mediated intercellular signaling in the lung and may inform the development of novel therapies for fibrotic lung diseases.

/pdf/activated-human-lung-fibroblasts-produce-extracellular-m4chc8iqcp.pdf

Activated Human Lung Fibroblasts Produce Extracellular Vesicles with Antifibrotic Prostaglandins.

The aryl hydrocarbon receptor (AhR) is a transcription factor that has been extensively studied as a regulator of toxicant metabolism. However, recent evidence indicates that the AhR also plays an important role in immunity. We hypothesized that the AhR is a novel, immune regulator of T helper type 2 (Th2) -mediated allergic airway disease. Here, we report that AhR-deficient mice develop increased allergic responses to the model allergen ovalbumin (OVA), which are driven in part by increased dendritic cell (DC) functional activation. AhR knockout (AhR(-/-) ) mice sensitized and challenged with OVA develop an increased inflammatory response in the lung compared with wild-type controls, with greater numbers of inflammatory eosinophils and neutrophils, greater T-cell proliferation, greater production of Th2 cytokines, and higher levels of OVA-specific IgE and IgG1. Lung DCs from AhR(-/-) mice stimulated antigen-specific proliferation and Th2 cytokine production by naive T cells in vitro. Additionally, AhR(-/-) DCs produced higher levels of tumour necrosis factor-α and interleukin-6, which promote Th2 differentiation, and expressed higher cell surface levels of stimulatory MHC Class II and CD86 molecules. Overall, loss of the AhR was associated with enhanced T-cell activation by pulmonary DCs and heightened pro-inflammatory allergic responses. This suggests that endogenous AhR ligands are involved in the normal regulation of Th2-mediated immunity in the lung via a DC-dependent mechanism. Therefore, the AhR may represent an important target for therapeutic intervention in allergic airways inflammation.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/imm.12540

Endogenous ligands of the aryl hydrocarbon receptor regulate lung dendritic cell function.

Nontypeable Haemophilus influenzae (NTHi) is a Gram-negative, opportunistic pathogen that frequently causes ear infections, bronchitis, pneumonia, and exacerbations in patients with underlying inflammatory diseases, such as chronic obstructive pulmonary disease. In mice, NTHi is rapidly cleared, but a strong inflammatory response persists, underscoring the concept that NTHi induces dysregulation of normal inflammatory responses and causes a failure to resolve. Lipid-derived specialized proresolving mediators (SPMs) play a critical role in the active resolution of inflammation by both suppressing proinflammatory actions and promoting resolution pathways. Importantly, SPMs lack the immunosuppressive properties of classical anti-inflammatory therapies. On the basis of these characteristics, we hypothesized that aspirin-triggered resolvin D1 (AT-RvD1) would dampen NTHi-induced inflammation while still enhancing bacterial clearance. C57BL/6 mice were treated with AT-RvD1 and infected with live NTHi. AT-RvD1-treated mice had lower total cell counts and neutrophils in bronchoalveolar lavage fluid, and had earlier influx of macrophages. In addition, AT-RvD1-treated mice showed changes in temporal regulation of inflammatory cytokines and enzymes, with decreased KC at 6 h and decreased IL-6, TNF-α, and cyclooxygenase-2 expression at 24 h post infection. Despite reduced inflammation, AT-RvD1-treated mice had reduced NTHi bacterial load, mediated by enhanced clearance by macrophages and a skewing toward an M2 phenotype. Finally, AT-RvD1 protected NTHi-infected mice from weight loss, hypothermia, hypoxemia, and respiratory compromise. This research highlights the beneficial role of SPMs in pulmonary bacterial infections and provides the groundwork for further investigation into SPMs as alternatives to immunosuppressive therapies like steroids.

/pdf/resolvin-d1-dampens-pulmonary-inflammation-and-promotes-4c7wc72c56.pdf

Shannon H. Lacy

Papers

Conjugated linoleic acid is synthesized endogenously in lactating dairy cows by Delta(9)-desaturase.

PPARγ and the Innate Immune System Mediate the Resolution of Inflammation.

Activated Human Lung Fibroblasts Produce Extracellular Vesicles with Antifibrotic Prostaglandins.

Endogenous ligands of the aryl hydrocarbon receptor regulate lung dendritic cell function.

Resolvin D1 Dampens Pulmonary Inflammation and Promotes Clearance of Nontypeable Haemophilus influenzae