Cytotoxic 1-deoxysphingolipids are metabolized by a cytochrome P450-dependent pathway

Abstract

This article is available online at http://www.jlr.org Sphingolipid (SL) de novo synthesis typically starts with the condensation of serine and palmitoyl-CoA, a reaction catalyzed by serine palmitoyltransferase (SPT) (1-3). SPT can also use alanine in certain conditions (4), which results in the formation of the atypical cytotoxic 1-deoxysphingolipids (1-deoxySLs). These lack the C1-hydroxyl group of regular SLs, which is essential for further metabolic steps and degradation (4, 5). As such, 1-deoxySLs are commonly believed to be "dead-end" metabolites that accumulate within cells, tissues, and body fluids.Pathologically elevated 1-deoxySLs have been found in a number of neurological and metabolic disorders. They are a hallmark of hereditary sensory autonomic neuropathy type 1 (HSAN1), a rare autosomal dominant inherited peripheral neuropathy that is caused by various mutations in SPT. Plasma 1-deoxySLs are also elevated in patients with nondiabetic metabolic syndrome (MetS) and T2D (6) and may contribute to the development of diabetic sensory polyneuropathy (DSN), which is clinically very similar to HSAN1 (7,8). Both conditions start in the lower extremities with a loss of sensation often accompanied by positive sensory symptoms such as hyperpathia and neuropathic pain, as well as the development of painless wounds leading to ulcers (9, 10). L-serine supplementation was shown to effectively lower 1-deoxySL levels while improving Abstract The 1-deoxysphingolipids (1-deoxySLs) are atypical sphingolipids (SLs) that are formed when serine palmitoyltransferase condenses palmitoyl-CoA with alanine instead of serine during SL synthesis. The 1-deoxySLs are toxic to neurons and pancreatic -cells. Pathologically elevated 1-deoxySLs cause the inherited neuropathy, hereditary sensory autonomic neuropathy type 1 (HSAN1), and are also found in T2D. Diabetic sensory polyneuropathy (DSN) and HSAN1 are clinically very similar, suggesting that 1-deoxySLs may be implicated in both pathologies. The 1-deoxySLs are considered to be dead-end metabolites, as they lack the C1-hydroxyl group, which is essential for the canonical degradation of SLs. Here, we report a previously unknown metabolic pathway, which is capable of degrading 1-deoxySLs. Using a variety of metabolic labeling approaches and high-resolution high-accuracy MS, we identified eight 1-deoxySL downstream metabolites, which appear to be formed by cytochrome P450 (CYP)4F enzymes. Comprehensive inhibition and induction of CYP4F enzymes blocked and stimulated, respectively, the formation of the downstream metabolites. Consequently, CYP4F enzymes might be novel therapeutic targets for the treatment of HSAN1 and DSN, as well as for the prevention of T2D. (I.A., A.O., T.H., and A.v.E.) Abbreviations: ATRA, all-trans retinoic acid; CYP, cytochrome P450; DB, double bond; 1-deoxySA, 1-deoxysphinganine; 1-deoxySAdiene, deoxysphingadiene; 1-deoxySA-OH, hydroxyl-deoxysphinganine; 1-deoxySA-2OH, dihydroxyl-deoxysphinganine; 1-deoxySL, 1-deoxysphingolipid; 1-deoxySO, 1-deoxysphingosi...

Farnesoid X receptor activation induces the degradation of hepatotoxic 1‐deoxysphingolipids in non‐alcoholic fatty liver disease

“…Moreover, hepatic mRNA levels of genes related to sphingolipid de novo synthesis, such as serine palmitoyltransferase, long chain base subunit 1, 2 and 3 ( Sptlc1 , Sptlc2 and Sptlc3 ), or ceramide synthase 2, 4, 5 and 6 ( Cers2 , 4 , 5 and 6 , the main CerS isoforms expressed in mouse liver), were not significantly different between all groups (Figure F). It has been shown recently that Cyp4f enzymes are involved in the degradation of 1‐deoxysphingolipids . Among the Cyp4f members, Cyp4f13, Cyp4f14, Cyp4f15, Cyp4f16 and Cyp4f18, which have by far the highest expression in mouse liver, were selected for analysis.…”

“…Similar induction of CYP4F2 gene expression was also observed in human primary hepatocytes treated with OCA (Figure J). Treatment with HET0016 (HET), a potent pan‐inhibitor of Cyp4f enzymes which blocks downstream of 1‐deoxySO metabolism, results in a higher 1‐deoxySO accumulation than PA alone. HET also abolished the 1‐deoxySO‐lowering effect of OCA (Figure H), suggesting that OCA may reduce 1‐deoxysphingolipid levels by enhancing their degradation.…”

“…Because of the absence of the C1 hydroxyl group, 1‐deoxysphingolipids cannot be converted to sphingosine‐1‐P, and therefore not degraded by the canonical sphingolipid catabolic pathway. In contrast, we showed recently that 1‐deoxysphingolipids are further metabolized by a cytochrome P450 (CYP) 4F‐dependent pathway . The CYP4F family hydroxylates a variety of long chain fatty acids, and is physiologically important for leukotriene and prostaglandin synthesis .…”

“…FXR is involved in bile acid synthesis, and interestingly, bile acids and retinoic acid play similar roles in the regulation of insulin sensitivity and lipid homoeostasis . The induction of CYP4F by FXR activation could be attributable to two possible mechanisms: (1) Aside from the retinoid X receptor (RXR), retinoic acid, which activates FXR‐mediated pathways, can also induce the downstream metabolism of 1‐deoxysphingolipids . Furthermore, all‐trans retinoic acids have been shown to induce CYP4F expression in hepatocytes .…”

“…Lipids were extracted from cell pellets or tissue samples, and then were acid/base hydrolysed as described earlier . Acid/base hydrolysis was performed to remove the N ‐acyl fatty acid chains, enabling analysis of sphingoid and 1‐deoxyshingoid bases.…”