Andrea E. DeBarber

Soluble Epoxide Hydrolase Gene Deletion Is Protective Against Experimental Cerebral Ischemia

Background and Purpose— Cytochrome P450 epoxygenase metabolizes arachidonic acid to epoxyeicosatrienoic acids (EETs). EETs are produced in the brain and perform important biological functions, including vasodilation and neuroprotection. However, EETs are rapidly metabolized via soluble epoxide hydrolase (sEH) to dihydroxyeicosatrienoic acids (DHETs). We tested the hypothesis that sEH gene deletion is protective against focal cerebral ischemia through enhanced collateral blood flow. Methods— sEH knockout (sEHKO) mice with and without EETs antagonist 14, 15 epoxyeicosa-5(Z)-enoic acid (EEZE) were subjected to 2-hour middle cerebral artery occlusion (MCAO), and infarct size was measured at 24 hours of reperfusion and compared to wild-type (WT) mice. Local CBF rates were measured at the end of MCAO using iodoantipyrine (IAP) autoradiography, sEH protein was analyzed by Western blot and immunohistochemistry, and hydrolase activity and levels of EETs/DHETs were measured in brain and plasma using LC-MS/MS and ELISA, respectively. Results— sEH immunoreactivity was detected in WT, but not sEHKO mouse brain, and was localized to vascular and nonvascular cells. 14,15-DHET was abundantly present in WT, but virtually absent in sEHKO mouse plasma. However, hydrolase activity and free 14,15-EET in brain tissue were not different between WT and sEHKO mice. Infarct size was significantly smaller, whereas regional cerebral blood flow rates were significantly higher in sEHKO compared to WT mice. Infarct size reduction was recapitulated by 14,15-EET infusion. However, 14,15-EEZE did not alter infarct size in sEHKO mice. Conclusions— sEH gene deletion is protective against ischemic stroke by a vascular mechanism linked to reduced hydration of circulating EETs.

Cardiac effects of 3-iodothyronamine: a new aminergic system modulating cardiac function

3‐iodothyronamine T1AM is a novel endogenous thyroid hormone derivative that activates the G protein‐coupled receptor known as trace anime‐associated receptor 1 (TAAR1). In the isolated working rat heart and in rat cardiomyocytes, T1AM produced a reversible, dose‐dependent negative inotropic effect (e.g.,27±5, 51 ±3, and 65±2% decrease in cardiac output at 19, 25, and 38 μM concentration, respectively). An independent negative chronotropic effect was also observed. The hemodynamic effects of T1AM were remarkably increased in the presence of the tyrosine kinase inhibitor genistein, whereas they were attenuated in the presence of the tyrosine phosphatase inhibitor vanadate. No effect was produced by inhibitors of protein kinase A, protein kinase C, calcium‐calmodulin kinase II, phosphatidylinositol‐3‐kinase, or MAP kinases. Tissue cAMP levels were unchanged. In rat ventricular tissue, Western blot experiments with antiphosphotyrosine antibodies showed reduced phosphorylation of microsomal and cytosolic proteins after perfusion with synthetic T1AM;reverse transcriptase‐polymerase chain reaction experiments revealed the presence of transcripts for at least 5 TAAR subtypes; specific and saturable binding of [125I]T1AM was observed, with a dissociation constant in the low micromolar range (5 μM); and endogenous T1AM was detectable by tandem mass spectrometry. In conclusion, our findings provide evidence for the existence of a novel aminergic system modulating cardiac function.—Chiellini G., Frascarelli, S., Ghelardoni, S., Carnicelli, V., Tobias, S. C., DeBarber, A., Brogioni, S., Ronca‐Testoni, S., Cerbai, E., Grandy, D. K., Scanlan, T. S., Zucchi R. Cardiac effects of 3‐iodothyronamine: a new aminergic system modulating cardiac function. FASEB J. 21, 1597–1608 (2007)

Polymorphisms in the Human Soluble Epoxide Hydrolase Gene EPHX2 Linked to Neuronal Survival after Ischemic Injury

Single nucleotide polymorphisms (SNPs) in the human EPHX2 gene have recently been implicated in susceptibility to cardiovascular disease, including stroke. EPHX2 encodes for soluble epoxide hydrolase (sEH), an important enzyme in the metabolic breakdown of arachidonic acid-derived eicosanoids referred to as epoxyeicosatrienoic acids (EETs). We previously demonstrated that EETs are protective against ischemic cell death in culture. Therefore, we tested the hypothesis that polymorphisms in the human EPHX2 gene alter sEH enzyme activity and affect neuronal survival after ischemic injury in vitro. Human EPHX2 mutants were recreated by site-directed mutagenesis and fused downstream of TAT protein transduction domain. Western blot analysis and immunocytochemistry staining revealed high-transduction efficiency of human TAT-sEH variants in rat primary cultured cortical neurons, associated with increased metabolism of 14,15-EET to corresponding 14,15-dihydroxyeicosatrienoic acid. A human variant of sEH with Arg103Cys amino acid substitution, previously demonstrated to increase sEH enzymatic activity, was associated with increased cell death induced in cortical neurons by oxygen-glucose deprivation (OGD) and reoxygenation. In contrast, the Arg287Gln mutation was associated with reduced sEH activity and protection from OGD-induced neuronal cell death. We conclude that sequence variations in the human EPHX2 gene alter susceptibility to ischemic injury and neuronal survival in a manner linked to changes in the hydrolase activity of the enzyme. The findings suggest that human EPHX2 mutations may in part explain the genetic variability in sensitivity to ischemic brain injury and stroke outcome.

Smith-Lemli-Opitz syndrome.

Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive, multiple congenital malformation and intellectual disability syndrome, with clinical characteristics that encompass a wide spectrum and great variability. Elucidation of the biochemical and genetic basis for SLOS, specifically understanding SLOS as a cholesterol deficiency syndrome caused by mutation in DHCR7, opened up enormous possibilities for therapeutic intervention. When cholesterol was discovered to be the activator of sonic hedgehog, cholesterol deficiency with inactivation of this developmental patterning gene was thought to be the cause of SLOS malformations, yet this explanation is overly simplistic. Despite these important research breakthroughs, there is no proven treatment for SLOS. Better animal models are needed to allow potential treatment testing and the study of disease pathophysiology, which is incompletely understood. Creation of human cellular models, especially models of brain cells, would be useful, and in vivo human studies are also essential. Biomarker development will be crucial in facilitating clinical trials in this rare condition, because the clinical phenotype can change over many years. Additional research in these and other areas is critical if we are to make headway towards ameliorating the effects of this devastating condition.

Liquid chromatography-tandem mass spectrometry determination of plasma 24S-hydroxycholesterol with chromatographic separation of 25-hydroxycholesterol

Concentrations of circulating 24S-hydroxycholesterol (24SOHChol) are of interest as a practical measure of cholesterol efflux from the human brain. The current method of choice for 24SOHChol quantification is with gas chromatography-mass spectrometry (GC-MS). Liquid chromatography-mass spectrometry (LC-MS) methods to detect 24SOHChol have been described, but they lack rigorous high-performance liquid chromatography (HPLC) separation of a closely eluting isomeric oxysterol, 25-hydroxycholesterol. This is important because 25-hydroxycholesterol can be present in significant amounts and tandem mass spectrometry (MS/MS) cannot completely differentiate 24SOHChol. We describe an LC-MS method with rapid chromatographic separation of the oxysterols to permit accurate determination of plasma 24SOHChol. The availability of an LC-MS method offers advantages such as simplified sample work-up and analysis.

Iodothyronamines are Oxidatively Deaminated to Iodothyroacetic Acids in vivo

3‐Iodothyronamine (T1AM) and 3,3′,5‐triiodothyroacetic acid (Triac) are bioactive metabolites of the hormone thyroxine (T4). In the present study, the ability of T1AM and 3,3′,5‐triiodothyronamine (T3AM) to be metabolized to 3‐iodothyroacetic acid (TA1) and Triac, respectively, was investigated. Both T1AM and T3AM were converted to their respective iodinated thyroacetic acid analogues in both cell and tissue extracts. This conversion could be significantly inhibited with the monamine oxidase (MAO) and semicarbazide‐sensitive amine oxidase (SSAO) inhibitor iproniazid. TA1 was found to be present in trace quantities in human serum and in substantial levels in serum from T1AM‐treated rats. These results demonstrate that iodothyronamines are substrates for amine oxidases and that this metabolism may be the source of the corresponding endogenous arylacetic acid products Triac and TA1.

Hypomorphic Temperature-Sensitive Alleles of NSDHL Cause CK Syndrome

CK syndrome (CKS) is an X-linked recessive intellectual disability syndrome characterized by dysmorphism, cortical brain malformations, and an asthenic build. Through an X chromosome single-nucleotide variant scan in the first reported family, we identified linkage to a 5 Mb region on Xq28. Sequencing of this region detected a segregating 3 bp deletion (c.696_698del [p.Lys232del]) in exon 7 of NAD(P) dependent steroid dehydrogenase-like (NSDHL), a gene that encodes an enzyme in the cholesterol biosynthesis pathway. We also found that males with intellectual disability in another reported family with an NSDHL mutation (c.1098 dup [p.Arg367SerfsX33]) have CKS. These two mutations, which alter protein folding, show temperature-sensitive protein stability and complementation in Erg26-deficient yeast. As described for the allelic disorder CHILD syndrome, cells and cerebrospinal fluid from CKS patients have increased methyl sterol levels. We hypothesize that methyl sterol accumulation, not only cholesterol deficiency, causes CKS, given that cerebrospinal fluid cholesterol, plasma cholesterol, and plasma 24S-hydroxycholesterol levels are normal in males with CKS. In summary, CKS expands the spectrum of cholesterol-related disorders and insight into the role of cholesterol in human development.

Profiling sterols in cerebrotendinous xanthomatosis: Utility of Girard derivatization and high resolution exact mass LC―ESI-MSn analysis

In this study we profile free 3-oxo sterols present in plasma from patients affected with the neurodegenerative disorder of sterol and bile acid metabolism cerebrotendinous xanthomatosis (CTX), utilizing a combination of charge-tagging and LC-ESI-MS(n) performed with an LTQ-Orbitrap Discovery instrument. In addition, we profile sterols in plasma from 24-month-old cyp27A1 gene knockout mice lacking the enzyme defective in CTX. Charge-tagging was accomplished by reaction with cationic Girards P (GP) reagent 1-(carboxymethyl) pyridinium chloride hydrazide, an approach uniquely suited to studying the 3-oxo sterols that accumulate in CTX, as Girards reagent reacts with the sterol oxo moiety to form charged hydrazone derivatives. The ability to selectively generate GP-tagged 3-oxo-4-ene and 3-oxo-5(H) saturated plasma sterols enabled ESI-MS(n) analysis of these sterols in the presence of a large excess (3 orders of magnitude) of cholesterol. Often cholesterol detected in biological samples makes it challenging to quantify minor sterols, with cholesterol frequently removed prior to analysis. We derivatized plasma (10 μl) without SPE removal of cholesterol to ensure detection of all sterols present in plasma. We were able to measure 4-cholesten-3-one in plasma from untreated CTX patients (1207±302 ng/ml, mean±SD, n=4), as well as other intermediates in a proposed pathway to 5α-cholestanol. In addition, a number of bile acid precursors were identified in plasma using this technique. GP-tagged sterols were identified utilizing high resolution exact mass spectra (±5 ppm), as well as MS(2) ([M](+)→) spectra that possessed characteristic neutral loss of 79Da (pyridine) fragment ions, and MS(3) ([M](+)→[M-79](+)→) spectra that provided additional structurally informative fragment ions.

ESI-MS/MS quantification of 7α-hydroxy-4-cholesten-3-one facilitates rapid, convenient diagnostic testing for cerebrotendinous xanthomatosis

BACKGROUND The genetic disorder cerebrotendinous xanthomatosis (CTX) frequently remains undiagnosed for many years. Left untreated CTX is associated with the development of cataracts, xanthomas and severe neurological dysfunction. The method routinely used to screen for CTX is GC-based measurement of elevated 5alpha-cholestanol from hydrolyzed plasma. A plasma test for CTX utilizing ESI-MS/MS methodology would be beneficial. METHODS Development of rapid, simple LC-ESI-MS/MS methodology to test plasma for CTX is described. Two hour Girard derivatization allowed for 7alpha-hydroxy-4-cholesten-3-one quantification by isotope dilution LC-ESI-MS/MS within 12 min from un-hydrolyzed affected patient plasma (5 microl). RESULTS Adequate sensitivity and reproducibility were achieved for quantification of 7alpha-hydroxy-4-cholesten-3-one, which demonstrated improved utility as a diagnostic marker of disease and to monitor treatment compared to 5alpha-cholestanol. The mean plasma concentration of 7alpha-hydroxy-4-cholesten-3-one in untreated CTX-affected patients (n=6) was 107-fold that in unaffected subjects (n=9), with the lowest concentration in affected patients >10-fold the highest concentration in unaffected subjects. CONCLUSION Quantification of the bile acid precursor 7alpha-hydroxy-4-cholesten-3-one with LC-ESI-MS/MS is a novel approach to improved diagnostic testing of plasma for CTX, amenable to high-throughput analysis and automated sample handling. Development of ESI-MS/MS methodology should make CTX testing more widely available and facilitate easier diagnosis of CTX.

Apparent underdiagnosis of Cerebrotendinous Xanthomatosis revealed by analysis of ~60,000 human exomes

Cerebrotendinous Xanthomatosis (CTX) is a treatable inborn error of metabolism caused by recessive variants in CYP27A1. Clinical presentation varies, but typically includes infant-onset chronic diarrhea, juvenile-onset bilateral cataracts, and later-onset tendinous xanthomas and progressive neurological dysfunction. CYP27A1 plays an essential role in side-chain oxidation of cholesterol necessary for the synthesis of the bile acid, chenodeoxycholic acid, and perturbations in this gene that reduce enzyme activity result in elevations of cholestanol. It is commonly held that CTX is exceedingly rare, but epidemiological studies are lacking. In order to provide an accurate incidence estimate of CTX, we studied the ExAC cohort of ~60,000 unrelated adults from global populations to determine the allele frequency of the 57 variants in CYP27A1 reported pathogenic for CTX. In addition, we conducted bioinformatics analyses on these CTX-causing variants and determined a bioinformatics profile to predict variants that may be pathogenic but have not yet been reported in the CTX patient literature. An additional 29 variants were identified that met bioinformatics criteria for being potentially pathogenic. Incidence was estimated based allele frequencies of pathogenic CTX variants plus those determined to be potentially pathogenic. One variant, p.P384L, previously reported in three unrelated CTX families had an allele frequency ≥ 1% in European, Latino and Asian populations. Three additional mutations had a frequency of ≥ 0.1% in Asian populations. CTX disease incidence was calculated excluding the high frequency p.P384L and separately using a genetic paradigm where this high frequency variant only causes classic CTX when paired in trans with a null variant. These calculations place CTX incidence ranging from 1:134,970 to 1:461,358 in Europeans, 1:263,222 to 1:468,624 in Africans, 1:71,677 to 1:148,914 in Americans, 1:64,267 to 1:64,712 in East Asians and 1:36,072 to 1:75,601 in South Asians. This work indicates CTX is under-diagnosed and improved patient screening is needed as early intervention prevents disease progression.