Dietary alpha-linolenic acid suppresses the formation of lysophosphatidic acid, a lipid mediator, in rat platelets compared with linoleic acid

5-oxoETE triggers nociception in constipation-predominant irritable bowel syndrome through MAS-related G protein-coupled receptor D

Irritable bowel syndrome (IBS) is a common gastrointestinal disorder that is characterized by chronic abdominal pain concurrent with altered bowel habit. Polyunsaturated fatty acid (PUFA) metabolites are increased in abundance in IBS and are implicated in the alteration of sensation to mechanical stimuli, which is defined as visceral hypersensitivity. We sought to quantify PUFA metabolites in patients with IBS and evaluate their role in pain. Quantification of PUFA metabolites by mass spectrometry in colonic biopsies showed an increased abundance of 5-oxoeicosatetraenoic acid (5-oxoETE) only in biopsies taken from patients with IBS with predominant constipation (IBS-C). Local administration of 5-oxoETE to mice induced somatic and visceral hypersensitivity to mechanical stimuli without causing tissue inflammation. We found that 5-oxoETE directly acted on both human and mouse sensory neurons as shown by lumbar splanchnic nerve recordings and Ca2+ imaging of dorsal root ganglion (DRG) neurons. We showed that 5-oxoETE selectively stimulated nonpeptidergic, isolectin B4 (IB4)-positive DRG neurons through a phospholipase C (PLC)- and pertussis toxin-dependent mechanism, suggesting that the effect was mediated by a G protein-coupled receptor (GPCR). The MAS-related GPCR D (Mrgprd) was found in mouse colonic DRG afferents and was identified as being implicated in the noxious effects of 5-oxoETE. Together, these data suggest that 5-oxoETE, a potential biomarker of IBS-C, induces somatic and visceral hyperalgesia without inflammation in an Mrgprd-dependent manner. Thus, 5-oxoETE may play a pivotal role in the abdominal pain associated with IBS-C.

[Antinociceptive effect of docosahexaenoic acid (DHA) through long fatty acid receptor G protein-coupled receptor 40 (GPR40)]

Fatty acids, one class of essential nutrients for humans, are an important source of energy and an essential component of cell membranes. They also function as signal transduction molecules in a variety of biological phenomena. The important functional role of fatty acids in both onset and suppression of pain has become increasingly apparent in recent years. Recently, we have also demonstrated that the release of an endogenous opioid peptide, β-endorphin, plays an important role in the induction of docosahexaenoic acid (DHA)-induced antinociception. It is well known that fatty acids affect intracellular and intercellular signaling as well as the membrane fluidity of neurons. In addition to intracellular actions, unbound free fatty acids (FFAs) can also carry out extracellular signaling by stimulating the G protein-coupled receptor (GPCR). Among these receptors, G protein-coupled receptor 40 (GPR40) has been reported to be activated by long-chain fatty acids such as DHA, eicosapentaenoic acid (EPA) and arachidonic acid. In the peripheral area, GPR40 is preferentially expressed in pancreatic β-cells and is known to relate to the secretion of hormone and peptides. On the other hand, even though this receptor is widely distributed in the central nervous system, reports studying the role and functions of GPR40 in the brain have not been found. In this review, we summarize the findings of our recent study about the long-chain fatty acid receptor GPR40 as a novel pain regulatory system.

Three dissimilar high fat diets differentially regulate lipid and glucose metabolism in obesity-resistant Slc:Wistar/ST rats

Epidemiologic and ecologic studies suggest that dietary fat plays an important role in the development of obesity. Certain Wistar rat strains do not become obese when fed high-fat diets unlike others. In a preliminary study, we confirmed that Slc:Wistar/ST rats did not become obese when fed high-fat diets. The mechanisms governing the response of hepatic lipid-metabolizing enzymes to large quantities of dietary lipids consumed by obesity-resistant animals are unknown. The aim of the present study is to examine how obesity-resistant animals metabolize various types of high-fat diets and why they do not become obese. For this purpose, male Slc:Wistar/ST rats were fed a control low-fat diet (LS) or a high-fat diet containing fish oil (HF), soybean oil (HS), or lard (HL) for 4 weeks. We observed their phenotypes and determined lipid profiles in plasma and liver as well as mRNA expression levels in liver of genes related to lipid and glucose metabolism using DNA microarray and quantitative reverse transcriptase polymerase chain analyses. The body weights of all dietary groups were similar due to isocaloric intakes, whereas the weight of white adipose tissues in the LS group was significantly lower. The HF diet lowered plasma lipid levels by accelerated lipolysis in the peroxisomes and suppressed levels of very-low-density lipoprotein (VLDL) secretion. The HS diet promoted hepatic lipid accumulation by suppressed lipolysis in the peroxisomes and normal levels of VLDL secretion. The lipid profiles of rats fed the LS or HL diet were similar. The HL diet accelerated lipid and glucose metabolism.

Mechanisms of lysophosphatidic acid (LPA) mediated stimulation of intestinal apical Cl-/OH- exchange

Lysophosphatidic acid (LPA), a potent bioactive phospholipid, is a natural component of food products like soy and egg yolk. LPA modulates a number of epithelial functions and has been shown to inhibit cholera toxin-induced diarrhea. Antidiarrheal effects of LPA are known to be mediated by inhibiting chloride secretion. However, the effects of LPA on chloride absorption in the mammalian intestine are not known. The present studies examined the effects of LPA on apical Cl(-)/OH(-) exchangers known to be involved in chloride absorption in intestinal epithelial cells. Caco-2 cells were treated with LPA, and Cl(-)/OH(-) exchange activity was measured as DIDS-sensitive (36)Cl(-) uptake. Cell surface biotinylation studies were performed to evaluate the effect of LPA on cell surface levels of apical Cl(-)/OH(-) exchangers, downregulated in adenoma (DRA) (SLC26A3), and putative anion transporter-1 (SLC26A6). Treatment of Caco-2 cells with LPA (100 muM) significantly stimulated Cl(-)/OH(-) exchange activity. Specific agonist for LPA2 receptor mimicked the effects of LPA. LPA-mediated stimulation of Cl(-)/OH(-) exchange activity was dependent on activation of phosphatidylinositol 3-kinase/Akt signaling pathway. Consistent with the functional activity, LPA treatment resulted in increased levels of DRA on the apical membrane. Our results demonstrate that LPA stimulates apical Cl(-)/OH(-) exchange activity and surface levels of DRA in intestinal epithelial cells. This increase in Cl(-)/OH(-) exchange may contribute to the antidiarrheal effects of LPA.

Lysophosphatidic acid stimulates the intestinal brush border Na(+)/H(+) exchanger 3 and fluid absorption via LPA(5) and NHERF2

BACKGROUND & AIMS

Diarrhea results from reduced net fluid and salt absorption caused by an imbalance in intestinal absorption and secretion. The bulk of sodium and water absorption in the intestine is mediated by Na(+)/H(+) exchanger 3 (NHE3), located in the luminal membrane of enterocytes. We investigated the effect of lysophosphatidic acid (LPA) on Na(+)/H(+) exchanger activity and Na(+)-dependent fluid absorption in the intestine.

METHODS

We analyzed the effects of LPA on fluid absorption in intestines of wild-type mice and mice deficient in Na(+)/H(+) exchanger regulatory factor 2 (NHERF2; Nherf2(-/-)) or LPA(2) (Lpa(2)(-/-)). Roles of LPA(5) and NHERF2 were determined by analysis of heterologous expression.

RESULTS

Under basal conditions, LPA increased fluid absorption in an NHE3-dependent manner and restored the net fluid loss in a mouse model of acute diarrhea. Expression of the LPA receptor LPA(5) was necessary for LPA-induced stimulation of NHE3 activity in colonic epithelial cells. Stimulation of NHE3 by the LPA-LPA(5) signaling required coexpression of NHERF2, which interacted with LPA(5). LPA-mediated intestinal fluid absorption was impaired in Nherf2(-/-) mice, demonstrating the requirement for NHERF2 in LPA(5) activity. However, fluid absorption was unaltered in Lpa(2)(-/-) mice. LPA stimulated NHE3 and fluid absorption in part by increasing NHE3 protein abundance at the brush border membrane of intestinal epithelial cells.

CONCLUSIONS

LPA is a potent stimulant of NHE3 and fluid absorption in the intestine, signaling through LPA(5). Regulation by LPA(5) depends on its interaction with NHERF2. LPA might be useful in the treatment of certain diarrheal diseases.

Effects of removal of dietary polyunsaturated fatty acids on plasma extravasation and mechanical allodynia in a trigeminal neuropathic pain model

Background

Neuropathic pain (NP) is partially mediated by neuroinflammatory mechanisms, and also modulates local neurogenic inflammation. Dietary lipids, in particular the total amount and relative proportions of polyunsaturated fatty acids (PUFAs) of the ω-3 and ω-6 families, have been reported to modify the threshold for thermal and mechanical allodynia in the partial sciatic nerve ligation model of NP in rats. The effects of dietary lipids on other popular NP models, such as the chronic constriction injury (CCI), have not yet been examined. It is also unknown whether dietary PUFAs exert any effect on the capsaicin (CAP)-induced neurogenic inflammation under control or NP conditions. In this study we investigated these interrelated phenomena in the trigeminal territory, which has been much less explored, and for which not all data derived from limb nerves can be directly applied.

Results

We studied the effects of a CCI of the infraorbital nerve (IoN) on the development of mechanical allodynia and CAP-induced plasma extravasation in rats fed either a regular diet (RD), or a modified diet (MD) with much lower total content and ω-3:ω-6 ratio of PUFAs. In rats kept on MD, mechanical allodynia following CCI-IoN was more pronounced and developed earlier. Extravasation was substantially increased in naive rats fed MD, and displayed differential diet-depending changes one and four weeks after CCI-IoN. When compared with basal levels (in naive and/or sham cases), the net effect of CCI-IoN on ipsilateral extravasation was a reduction in the MD group, but an increase in the RD group, effectively neutralizing the original intergroup differences.

Conclusion

In summary, PUFA intake reduces CAP-induced neurogenic plasma extravasation in the trigeminal territory, and their removal significantly alters the mechanical allodynia and the plasma extravasation that result from a unilateral CCI-IoN. It is likely that this "protective" effect of dietary lipids is temporary. Also, the presence of contralateral effects of CCI-IoN precludes using the contralateral side as control.