Identification of 9- cis -retinoic acid as a pancreas-specific autacoid that attenuates glucose-stimulated insulin secretion

Abstract

The all-trans-retinoic acid (atRA) isomer, 9-cis-retinoic acid (9cRA), activates retinoic acid receptors (RARs) and retinoid X receptors (RXRs) in vitro. RARs control multiple genes, whereas RXRs serve as partners for RARs and other nuclear receptors that regulate metabolism. Physiological function has not been determined for 9cRA, because it has not been detected in serum or multiple tissues with analytically validated assays. Here, we identify 9cRA in mouse pancreas by liquid chromatography/tandem mass spectrometry (LC/MS/MS), and show that 9cRA decreases with feeding and after glucose dosing and varies inversely with serum insulin. 9cRA reduces glucose-stimulated insulin secretion (GSIS) in mouse islets and in the rat β-cell line 832/13 within 15 min by reducing glucose transporter type 2 (Glut2) and glucokinase (GK) activities. 9cRA also reduces Pdx-1 and HNF4α mRNA expression, ∼8-and 80-fold, respectively: defects in Pdx-1 or HNF4α cause maturity onset diabetes of the young (MODY4 and 1, respectively), as does a defective GK gene (MODY2). Pancreas β-cells generate 9cRA, and mouse models of reduced β-cell number, heterozygous Akita mice, and streptozotocin-treated mice have reduced 9cRA. 9cRA is abnormally high in glucose-intolerant mice, which have β-cell hypertropy, including mice with diet-induced obesity (DIO) and ob/ob and db/db mice. These data establish 9cRA as a pancreas-specific autacoid with multiple mechanisms of action and provide unique insight into GSIS.retinol | vitamin A | rexinoids I mpaired glucose-stimulated insulin secretion (GSIS) develops through multiple mechanisms, including actions of metabolic hormones and inflammatory cytokines, products of metabolic overload, and endoplasmic reticulum stress; however, mechanisms of GSIS and impaired glucose tolerance remain incompletely understood (1-4). Also uncertain is the contribution of impaired glucose tolerance to diminished pancreatic β-cell function and mass associated with type 2 diabetes (5). GSIS relies on the pancreas, and pancreas development, islet formation, and function require normal vitamin A nutriture (6-8). Vitamin A restriction during development impairs islet development and promotes glucose intolerance in adult rodents. On the other hand, restricting vitamin A in mature diabetes-prone rats reduces diabetes and insulitis, possibly through enhancing glucose sensing and metabolism. Alltrans-retinoic acid (atRA), an activated metabolite of vitamin A, regulates pancreas development, and atRA does not enhance the incidence of diabetes in diabetes-prone rats fed a vitamin Adeficient diet (7, 9, 10). Although the contribution of vitamin A to pancreas development through atRA seems clear, mechanisms whereby vitamin A affects mature pancreas function have not been determined in depth, nor have the specific vitamin A metabolites been identified that contribute to GSIS control.atRA induces differentiation and regulates cell processes by activating the nuclear receptors RAR α, -β, and -γ, which regulate transcription and translation (11...

Cyanobacteria blooms produce teratogenic retinoic acids

“…Although the physiological function for the normal existence and role of 9cRA is of great interest in vertebrates (25), 9cRA was only identified in Xenopus embryos (38), in humans, or in mice after excessive amounts of retinol or atRA (39,40). A recent study determined 9cRA to be a naturally occurring RA with concentrations of 3-12 ng/g (10-40 pmol/g) in mouse pancreas, which confirms that 9cRA contributes to the biological activity of vitamin A in vivo (41). Our findings of relatively frequent detections and relatively great concentrations of 9cRA (up to 5.2 × 10 2 ng/g DW) and 9c-4-oxo-RA (up to 4.0 × 10 ng/g DW) in cultured cyanobacteria and algae suggested that more studies about RAs should focus on cyanobacteria and algae in the future.…”

Vitamin A and retinoid signaling: genomic and nongenomic effects

“…Indeed defi ciency of considered as a bona fi de RXR ligand ( 10,11 ), it is now controversial due to the inability to detect this compound in vivo (12)(13)(14). Note, however, that 9cRA has been detected recently in pancreatic cells and found to have a function in regulating glucose-stimulated insulin secretion ( 15 ). Thus endogenous 9cRA exists and is physiological relevant.…”

A sensitive and specific method for measurement of multiple retinoids in human serum with UHPLC-MS/MS

“…In brief, 100 mg of 9-cis -retinal was dissolved in 20 ml of methanol. Eight milliliters of Tollens Reagent (equal volumes of 10% AgNO 3 and 10% NaOH mixed and titrated with ammonium hydroxide until precipitate dissolved) was added to the solution, and the mixture was stirred at 37°C for 6 h. The reaction was quenched with 4 N HCl on ice and fi ltered, and the products were extracted with hexane and evaporated to dryness. The mixture of 9-cis RA and 9,13-dicis RA was purifi ed using silica gel chromatography and ethyl acetate:hexane mobile phase.…”