fumarates and Paraganglioma

Pheochromocytomas and paragangliomas (PPGLs) are rare neuroendocrine tumors originating from chromaffin cells, holding significant clinical importance due to their capacity for excessive catecholamine secretion and associated cardiovascular complications. Roughly 80% of cases are associated with genetic mutations. Based on the functionality of these mutated genes, PPGLs can be categorized into distinct molecular clusters: the pseudohypoxia signaling cluster (Cluster-1), the kinase signaling cluster (Cluster-2), and the WNT signaling cluster (Cluster-3). A pivotal factor in the pathogenesis of PPGLs is hypoxia-inducible factor-2α (HIF2α), which becomes upregulated even under normoxic conditions, activating downstream transcriptional processes associated with pseudohypoxia. This adaptation provides tumor cells with a growth advantage and enhances their ability to thrive in adverse microenvironments. Moreover, pseudohypoxia disrupts immune cell communication, leading to the development of an immunosuppressive tumor microenvironment. Within Cluster-1a, metabolic perturbations are particularly pronounced. Mutations in enzymes associated with the tricarboxylic acid (TCA) cycle, such as succinate dehydrogenase (SDHx), fumarate hydratase (FH), isocitrate dehydrogenase (IDH), and malate dehydrogenase type 2 (MDH2), result in the accumulation of critical oncogenic metabolic intermediates. Notable among these intermediates are succinate, fumarate, and 2-hydroxyglutarate (2-HG), which promote activation of the HIFs signaling pathway through various mechanisms, thus inducing pseudohypoxia and facilitating tumorigenesis. SDHx mutations are prevalent in PPGLs, disrupting mitochondrial function and causing succinate accumulation, which competitively inhibits α-ketoglutarate-dependent dioxygenases. Consequently, this leads to global hypermethylation, epigenetic changes, and activation of HIFs. In FH-deficient cells, fumarate accumulation leads to protein succination, impacting cell function. FH mutations also trigger metabolic reprogramming towards glycolysis and lactate synthesis. IDH1/2 mutations generate D-2HG, inhibiting α-ketoglutarate-dependent dioxygenases and stabilizing HIFs. Similarly, MDH2 mutations are associated with HIF stability and pseudohypoxic response. Understanding the intricate relationship between metabolic enzyme mutations in the TCA cycle and pseudohypoxic signaling is crucial for unraveling the pathogenesis of PPGLs and developing targeted therapi

Topics: Adrenal Gland Neoplasms; Citric Acid Cycle; Dioxygenases; Fumarates; Humans; Ketoglutaric Acids; Mutation; Paraganglioma; Pheochromocytoma; Signal Transduction; Succinates; Succinic Acid; Tumor Microenvironment

Pheochromocytomas and paragangliomas (PPGLs) with SDHx pathogenic variants (PVs) are characterized by a higher intratissular succinate/fumarate ratio (RS/F) than non-SDHx-mutated ones. Also, an increase in serum succinate levels has been reported in patients with germline SDHB or SDHD PV.. To assess whether measurement of serum succinate, fumarate levels, and RS/F might aid identification of an SDHx germline PV/likely pathogenic variant (LPV) in patients with PPGL or in asymptomatic relatives; and to guide identification of a PV/LPV among the variants of unknown significance (VUS) identified in SDHx by next-generation sequencing.. This prospective monocentric study included 93 patients attending an endocrine oncogenetic unit for genetic testing. Succinate and fumarate were measured in serum by gas chromatography coupled to mass spectrometry. The RS/F was calculated to assess SDH enzymatic function. Diagnostic performance was assessed by receiver operating characteristic analysis.. RS/F had a higher discriminant power than succinate alone to identify an SDHx PV/LPV in patients with PPGL. However, SDHD PVs/LPVs are frequently missed. Only RS/F differed between asymptomatic SDHB/SDHD PV/LPV carriers and SDHB/SDHD-linked patients with PPGL. Finally RS/F could be helpful to easily evaluate the functional impact of VUS in SDHx.. Measurement of serum RS/F in patients with PPGL and in asymptomatic relatives is a valuable initial workup tool to detect those carrying a germline PV/LPV in SDHx. Its discriminative power is equal or superior to those of succinate measured alone. SDHD PVs/LPVs are less frequently identified by these biochemical tools. Use of RS/F for SDHx VUS reclassification needs to be evaluated further.

Topics: Adrenal Gland Neoplasms; Carcinogenesis; Cell Transformation, Neoplastic; Fumarates; Germ-Line Mutation; Humans; Paraganglioma; Pheochromocytoma; Prospective Studies; Succinate Dehydrogenase; Succinic Acid

Disruption of the Krebs cycle is a hallmark of cancer. IDH1 and IDH2 mutations are found in many neoplasms, and germline alterations in SDH genes and FH predispose to pheochromocytoma/paraganglioma and other cancers. We describe a paraganglioma family carrying a germline mutation in MDH2, which encodes a Krebs cycle enzyme. Whole-exome sequencing was applied to tumor DNA obtained from a man age 55 years diagnosed with multiple malignant paragangliomas. Data were analyzed with the two-sided Student's t and Mann-Whitney U tests with Bonferroni correction for multiple comparisons. Between six- and 14-fold lower levels of MDH2 expression were observed in MDH2-mutated tumors compared with control patients. Knockdown (KD) of MDH2 in HeLa cells by shRNA triggered the accumulation of both malate (mean ± SD: wild-type [WT] = 1±0.18; KD = 2.24±0.17, P = .043) and fumarate (WT = 1±0.06; KD = 2.6±0.25, P = .033), which was reversed by transient introduction of WT MDH2 cDNA. Segregation of the mutation with disease and absence of MDH2 in mutated tumors revealed MDH2 as a novel pheochromocytoma/paraganglioma susceptibility gene.

Topics: Citric Acid Cycle; DNA, Neoplasm; Down-Regulation; Exome; Fumarates; Gene Expression Regulation, Enzymologic; Gene Expression Regulation, Neoplastic; Genetic Predisposition to Disease; Germ-Line Mutation; HeLa Cells; Humans; Malate Dehydrogenase; Malates; Male; Middle Aged; Paraganglioma; Pheochromocytoma; Sequence Analysis, DNA

Pheochromocytomas (PHEOs) and paragangliomas (PGLs; extra-adrenal tumors) are rare neuroendocrine chromaffin cell tumors with a hereditary background in about 30%-35%. Those caused by succinate dehydrogenase subunit B (SDHB) germline mutations are associated with a high metastatic potential and ultimately higher patient mortality. Succinate dehydrogenase converts succinate to fumarate, uniquely linking the Krebs cycle and oxidative phosphorylation. SDH mutations result in the accumulation of succinate associated with various metabolic disturbances and the shift to aerobic glycolysis in tumor tissue. In the present study, we measured succinate and fumarate levels in mouse pheochromocytoma (MPC) and mouse tumor tissue (MTT) cells and in 10 apparently sporadic, 10 SDHB-, 5 SDHD-, and 2 neurofibromatosis 1-related PHEOs/PGLs and plasma samples using mass spectrometry. We found that the succinate-to-fumarate ratio was significantly higher in the SDHB- and SDHD-related PGLs than in apparently sporadic and neurofibromatosis 1-related PHEOs/PGLs (P = .0376). To further support our data, we silenced SDHB expression in MPC and MTT cells and evaluated the succinate and fumarate levels. Compared with control samples, SDHB-silenced MTT cells also showed an increase in the succinate-to-fumarate ratio (MTT cells: 2.45 vs 7.53), similar to the findings in SDHB-related PGLs. The present findings for the first time demonstrate a significantly increased succinate-to-fumarate ratio in SDHB/D-related PGLs and thus suggest this ratio may be used as a new metabolic marker for the detection of SDHB/D-related PHEOs/PGLs.

Topics: Adrenal Gland Neoplasms; Animals; Biomarkers, Tumor; Citric Acid Cycle; Female; Fumarates; Gene Expression Regulation, Enzymologic; Gene Expression Regulation, Neoplastic; Gene Silencing; Humans; Male; Mice; Mutation; Oxidative Phosphorylation; Paraganglioma; Phosphorylation; Succinate Dehydrogenase; Succinic Acid

Mutations of succinate dehydrogenase A/B/C/D genes (SDHx) increase susceptibility to development of pheochromocytomas and paragangliomas (PPGLs), with particularly high rates of malignancy associated with SDHB mutations.. We assessed whether altered succinate dehydrogenase product-precursor relationships, manifested by differences in tumor ratios of succinate to fumarate or other metabolites, might aid in identifying and stratifying patients with SDHx mutations.. PPGL tumor specimens from 233 patients, including 45 with SDHx mutations, were provided from eight tertiary referral centers for mass spectrometric analyses of Krebs cycle metabolites.. Diagnostic performance of the succinate:fumarate ratio for identification of pathogenic SDHx mutations.. SDH-deficient PPGLs were characterized by 25-fold higher succinate and 80% lower fumarate, cis-aconitate, and isocitrate tissue levels than PPGLs without SDHx mutations. Receiver-operating characteristic curves for use of ratios of succinate to fumarate or to cis-aconitate and isocitrate to identify SDHx mutations indicated areas under curves of 0.94 to 0.96; an optimal cut-off of 97.7 for the succinate:fumarate ratio provided a diagnostic sensitivity of 93% at a specificity of 97% to identify SDHX-mutated PPGLs. Succinate:fumarate ratios were higher in both SDHB-mutated and metastatic tumors than in those due to SDHD/C mutations or without metastases.. Mass spectrometric-based measurements of ratios of succinate:fumarate and other metabolites in PPGLs offer a useful method to identify patients for testing of SDHx mutations, with additional utility to quantitatively assess functionality of mutations and metabolic factors responsible for malignant risk.

Topics: Adolescent; Adrenal Gland Neoplasms; Adult; Aged; Citric Acid Cycle; Female; Follow-Up Studies; Fumarates; Germ-Line Mutation; Humans; Male; Metabolic Diseases; Middle Aged; Paraganglioma; Pheochromocytoma; Sensitivity and Specificity; Succinate Dehydrogenase; Succinic Acid; Young Adult