trans-3-Methylglutaconyl CoA isomerization-dependent protein acylation.

3-methylglutaconic (3MGC) aciduria is associated with a growing number of discrete inborn errors of metabolism. Herein, an antibody-based approach to detection/quantitation of 3MGC acid has been pursued. When trans-3MGC acid conjugated keyhole limpet hemocyanin (KLH) was inoculated into rabbits a strong immune response was elicited. Western blot analysis provided evidence that immune serum, but not pre-immune serum, recognized 3MGC-conjugated bovine serum albumin (BSA). In competition ELISAs using isolated immune IgG, the limit of detection for free trans-3MGC acid was compared to that for cis-3MGC acid and four structurally related short-chain dicarboxylic acids. Surprisingly, cis-3MGC acid yielded a much lower limit of detection (∼0.1 mg/ml) than trans-3MGC acid (∼1.0 mg/ml) while all other dicarboxylic acids tested were poor competitors. The data suggest trans-3MGC- isomerized during, or after, conjugation to KLH such that the immunogen was actually comprised of KLH harboring a mixture of cis- and trans-3MGC haptens. To investigate this unexpected isomerization reaction, trans-3MGC CoA was prepared and incubated at 37 °C in the presence of BSA. Evidence was obtained that non-enzymatic isomerization of trans-3MGC CoA to cis-3MGC CoA precedes intramolecular catalysis to form cis-3MGC anhydride plus CoASH. Anhydride-dependent acylation of BSA generated 3MGCylated BSA, as detected by anti-3MGC immunoblot. The results presented provide an explanation for the unanticipated detection of 3MGCylated proteins in a murine model of primary 3MGC aciduria. Furthermore, non-enzymatic hydrolysis of cis-3MGC anhydride represents a potential source of cis-3MGC acid found in urine of subjects with 3MGC aciduria.

The Burgeoning World of Immunometabolites: Th17 Cells Take Center Stage.

Dysregulation of the Th17/Treg balance is a key driver of autoimmunity. A new study by Xu et al. (2017) has revealed that small-molecule inhibition of 2-hydroxyglutarate synthesis skews Th17 differentiation to the Treg lineage, which is protective against autoimmune inflammation.

Resisting fatal attraction: a glioma oncometabolite prevents CD8+ T cell recruitment.

Immunotherapy has emerged as a potent approach for treating aggressive cancers, such as non-small-cell lung tumors and metastatic melanoma. Clinical trials are now in progress for patients with malignant gliomas; however, a better understanding of how these tumors escape immune surveillance is required to enhance antitumor immune responses. With gliomas, the recruitment of CD8+ T cells to the tumor is impaired, in part preventing containment or elimination of the tumor. In this issue of the JCI, Kohanbash and colleagues present an elegant dissection of how gliomas exploit an enzymatic activity acquired through a common mutation to abrogate the migration of CD8+ T cells to the tumor. They show that the oncometabolite 2-hydroxyglutarate (2HG), generated by mutated forms of isocitrate dehydrogenase (IDH1 and IDH2), reduces the expression of STAT1, thereby limiting the production of the chemokines CXCL9 and CXCL10. As a result, IDH1-mutated tumors are less effectively infiltrated by CD8+ T cells, contributing to tumor escape. Finally, in mice harboring syngeneic gliomas, an inhibitor of 2HG synthesis complemented vaccination to ameliorate tumor control. Understanding how to increase immune infiltration of gliomas represents a key first step in achieving tumor destruction through immunotherapy.

S-2-hydroxyglutarate regulates CD8+ T-lymphocyte fate.

R-2-hydroxyglutarate accumulates to millimolar levels in cancer cells with gain-of-function isocitrate dehydrogenase 1/2 mutations. These levels of R-2-hydroxyglutarate affect 2-oxoglutarate-dependent dioxygenases. Both metabolite enantiomers, R- and S-2-hydroxyglutarate, are detectible in healthy individuals, yet their physiological function remains elusive. Here we show that 2-hydroxyglutarate accumulates in mouse CD8+ T cells in response to T-cell receptor triggering, and accumulates to millimolar levels in physiological oxygen conditions through a hypoxia-inducible factor 1-alpha (HIF-1α)-dependent mechanism. S-2-hydroxyglutarate predominates over R-2-hydroxyglutarate in activated T cells, and we demonstrate alterations in markers of CD8+ T-cell differentiation in response to this metabolite. Modulation of histone and DNA demethylation, as well as HIF-1α stability, mediate these effects. S-2-hydroxyglutarate treatment greatly enhances the in vivo proliferation, persistence and anti-tumour capacity of adoptively transferred CD8+ T cells. Thus, S-2-hydroxyglutarate acts as an immunometabolite that links environmental context, through a metabolic-epigenetic axis, to immune fate and function.

A selective immunoaffinity chromatography for determination of plasma 1 alpha, 25-dihydroxyvitamin D3: application of specific antibodies raised against a 1 alpha, 25-dihydroxyvitamin D3-bovine serum albumin conjugate linked through the 11 alpha-position.

A selective and simple immunoaffinity chromatography of 1 alpha, 25-dihydroxyvitamin D3 has been developed and found to be a useful pretreatment tool for determining the metabolite in human plasma. A reasonably designed, haptenic derivative, 11 alpha-hemiglutaryloxy-1 alpha, 25-dihydroxyvitamin D3, was linked to bovine serum albumin, and rabbits were immunized repeatedly with the conjugate. The resulting polyclonal antibodies were specific to 1 alpha, 25-dihydroxyvitamin D3, recognizing both the A-ring and the side-chain structures. The antibodies were then immobilized on agarose gel to produce an immunosorbent which was stable and repeatedly usable. A plasma extract prepared with a Chem Elut column was applied to an affinity column containing the immunosorbent. After adequate washing, the adsorbed 1 alpha, 25-dihydroxyvitamin D3 was eluted selectively with a satisfactory recovery rate. This immunoaffinity chromatography enabled a simple radioreceptor assay for human plasma 1 alpha, 25-dihydroxyvitamin D3 which does not require any preparative high-performance liquid chromatography. The mean (+/-SD) values for 30 normal subjects and 8 patients with chronic renal failure were 36.0 (10.2) and 13.1 (2.1) pg/ml, respectively. The present method also gave reliable assay values for the plasma specimens from 1 alpha-hydroxyvitamin D3-administered volunteers, which have conventionally been difficult to measure unless complicated pretreatment is used.