Increased Levels of Renal Lysophosphatidic Acid in Rodent Models with Renal Disease

Lysophosphatidic acid (LPA) is a bioactive lipid mediator that has been implicated in the pathophysiology of kidney disease. However, few studies have attempted to measure changes in the levels of various LPA species in the kidney after the development of renal disease. The present study measured the renal LPA levels during the development of kidney disease in rat models of hypertension, diabetes, and obstructive nephropathy using liquid chromatography/mass spectrometry/mass spectrometry. LPA levels (sum of 16:0, 18:0, 18:1, 18:2, and 20:4 LPA) were higher in the renal cortex of hypertensive Dahl salt-sensitive (Dahl S) rats fed a high-salt diet than those in normotensive rats fed a low-salt diet (296.6 ± 22.9 vs. 196.3 ± 8.5 nmol/g protein). LPA levels were elevated in the outer medulla of the kidney of streptozotocin-induced type 1 diabetic Dahl S rats compared with control rats (624.6 ± 129.5 vs. 318.8 ± 17.1 nmol/g protein). LPA levels were also higher in the renal cortex of 18-month-old, type 2 diabetic nephropathy (T2DN) rats with more severe renal injury than in 6-month-old T2DN rats (184.9 ± 20.9 vs. 116.9 ± 6.0 nmol/g protein). LPA levels also paralleled the progression of renal fibrosis in the renal cortex of Sprague-Dawley rats after unilateral ureteral obstruction (UUO). Administration of an LPA receptor antagonist, Ki16425, reduced the degree of renal fibrosis in UUO rats. These results suggest that the production of renal LPA increases during the development of renal injury and contributes to renal fibrosis. SIGNIFICANCE STATEMENT: The present study reveals that the lysophosphatidic acid (LPA) levels increase in the kidney in rat models of hypertension, diabetes, and obstructive nephropathy, and administration of an LPA receptor antagonist attenuates renal fibrosis. Therapeutic approaches that target the formation or actions of renal LPA might be renoprotective and have therapeutic potential.

A low level of lysophosphatidic acid in human gingival crevicular fluid from patients with periodontitis due to high soluble lysophospholipase activity: Its potential protective role on alveolar bone loss by periodontitis

We previously detected a submicromolar concentration of lysophosphatidic acid (LPA) in human saliva. Here, we compare LPA concentrations in human gingival crevicular fluid (GCF) from patients with periodontitis and healthy controls, and examine how the local LPA levels are regulated enzymatically. The concentrations of LPA and its precursor lysophospholipids in GCF was measured by liquid chromatography-tandem mass spectrometry. The LPA-producing and LPA-degrading enzymatic activities were measured by quantifying the liberated choline and free fatty acid, respectively. The concentration of LPA in GCF of periodontitis patients was lower than that of healthy controls, due to higher soluble lysophospholipase activity toward LPA. LPA was found to prevent survival of Sa3, a human gingival epithelium-derived tumor cell line, activate Sa3 through Ca²⁺ mobilization, and release interleukin 6 from Sa3 in vitro. Furthermore, local injection of LPA into the gingiva attenuated ligature-induced experimental alveolar bone loss induced by oral bacteria inoculation in a rat model of periodontitis in vivo. A high concentration of LPA in human GCF is necessary to maintain normal gingival epithelial integrity and function, protecting the progression of periodontitis.

Relative expression and regulation by short-term fasting of lysophosphatidic acid receptors and autotaxin in white and brown adipose tissue depots

Lysophosphatidic acid (lysoPtdOH) levels have previously been reported to decrease in rodents with short-term fasting. We investigated whether a 16 h fast would change expression of autotaxin, the predominant phospholipase D responsible for adipose-derived lysoPtdOH synthesis, or any of the lysophosphatidic acid receptors (1-6) in four white adipose tissue (WAT) depots and interscapular brown adipose tissue (BAT) in male C57Bl/6J mice fed ad libitum, or fasted for 16 h. Aside from small inductions of Lpar1 in epididymal WAT and Lpar2 in epididymal and inguinal WAT, no significant changes were observed in expression of the Lpar family members, or autotaxin in perirenal, retroperitoneal, epididymal, or inguinal WAT or BAT with fasting. Comparison of the relative expression of Lpar1-6 in various depots showed that Lpar6 was the predominant Lpar in both WAT and BAT, and suggests that further work on the adipose-specific role of Lpar6 is warranted.

Lysophosphatidic Acid Signaling in Obesity and Insulin Resistance

Although simple in structure, lysophosphatidic acid (LPA) is a potent bioactive lipid that profoundly influences cellular signaling and function upon binding to G protein-coupled receptors (LPA1-6). The majority of circulating LPA is produced by the secreted enzyme autotaxin (ATX). Alterations in LPA signaling, in conjunction with changes in autotaxin (ATX) expression and activity, have been implicated in metabolic and inflammatory disorders including obesity, insulin resistance, and cardiovascular disease. This review summarizes our current understanding of the sources and metabolism of LPA with focus on the influence of diet on circulating LPA. Furthermore, we explore how the ATX-LPA pathway impacts obesity and obesity-associated disorders, including impaired glucose homeostasis, insulin resistance, and cardiovascular disease.

Comprehensive and quantitative analysis of lysophospholipid molecular species present in obese mouse liver by shotgun lipidomics

Shotgun lipidomics exploits the unique chemical and physical properties of lipid classes and individual molecular species to facilitate the high-throughput analysis of a cellular lipidome on a large scale directly from the extracts of biological samples. A platform for comprehensive analysis of lysophospholipid (LPL) species based on shotgun lipidomics has not been established. Herein, after extensive characterization of the fragmentation pattern of individual LPL class and optimization of all experimental conditions including developing new methods for optimization of collision energy, and recovery and enrichment of LPL classes from the aqueous phase after solvent extraction, a new method for comprehensive and quantitative analysis of LPL species was developed. This newly developed method was applied for comprehensive analysis of LPL species present in mouse liver samples. Remarkably, the study revealed significant accumulation of LPL species in the liver of ob/ob mice. Taken together, by exploiting the principles of shotgun lipidomics in combination with a novel strategy of sample preparation, LPL species present in biological samples can be determined by the established method. We believe that this development is significant and useful for understanding the pathways of phospholipid metabolism and for elucidating the role of LPL species in signal transduction and other biological functions.

The potential protective role of lysophospholipid mediators in nephrotoxicity induced by chronically exposed cadmium

Cadmium is a hazardous metal whose chronic exposure induces renal failure due to fibrosis, but the mechanisms are not well known. In this study we analyzed the molecular species of lysophosphatidic acid (LPA) and related phospholipids, together with their metabolic enzyme activity, in plasma from Wistar rats exposed up to 300ppm Cd(2+) in drinking water for 114days. Exposure of 300ppm Cd(2+) for 114days enhanced autotoxin (ATX)/lysophospholipase D activity, but significantly lowered the total levels of LPA and lysophosphatidylethanolamine. Interestingly, the total level of sphingosine-1-phosphate (S1P) was elevated dose-dependently by Cd(2+). Cultured rat kidney-derived interstitial fibroblast cells, NRK49F cells and proximal epithelial cells, NRK52E cells, were both responsive to the protective action of LPA or S1P against Cd(2+) toxicity. The former cell expresses ATX RNA. In conclusion, the elevation of LPA-producing enzyme activity and S1P concentrations in plasma after exposure of rats to Cd(2+) would protect from the renal toxicity of Cd(2+).