L’omocistinuria classica in età pediatrica

Classical homocystinuria is an inborn error of methionin metabolism. It is characterized by an accumulation of homocysteine, due to a deficiency of the enzyme involved in its metabolism, namely cystathionine beta synthase. If not treated, the increase in homocysteine leads to a multisystem syndrome that involves connective tissue, nervous and vascular systems with a predisposition to thromboembolism and developmental delay in childhood. An early diagnosis allows the specific therapy to be promptly started and prevents the classical manifestations of the disease. Since 2016 in Italy homocystinuria detection has been included in the expanded newborn screening. However, it is important not to forget this disease, because of its severe consequences of an untreated condition on the quality and expectancy of life.

MYCN mediates cysteine addiction and sensitizes to ferroptosis

Aberrant expression of MYC family members predicts poor clinical outcome in many human cancers. Oncogenic MYC profoundly alters metabolism and mediates an antioxidant response to maintain redox balance. Here we show that MYC induces massive lipid peroxidation upon depletion of cysteine, the rate-limiting amino acid for glutathione biosynthesis and sensitizes cells to ferroptosis, an oxidative, non-apoptotic and iron-dependent type of cell death. In MYCN-amplified childhood neuroblastoma, MYCN mediates resistance to ferroptosis by activating transsulfuration of methionine to cysteine. MYCN may contribute to spontaneous tumor regression in low-risk neuroblastomas by promoting ferroptosis in cells with epigenetically silenced cystathionine-beta-synthase, the rate-limiting enzyme for transsulfuration. We identified enzymes and antiporter proteins crucial to ferroptotic escape, providing multiple previously unknown sites that may be acted on therapeutically.

Severe homocysteinemia in two givosiran-treated porphyria patients: is free heme deficiency the culprit?

Givosiran is a novel approach to treat patients with acute intermittent porphyrias (AIP) by silencing of ∂-ALA-synthase 1, the first enzyme of heme biosynthesis in the liver. We included two patients in the Envision study who responded clinically well to this treatment. However, in both patients, therapy had to be discontinued because of severe adverse effects: One patient (A) developed local injection reactions which continued to spread all over her body with increasing number of injections and eventually caused a severe systemic allergic reaction. Patient B was hospitalized because of a fulminant pancreatitis. Searching for possible causes, we also measured the patients plasma homocysteine (Hcy) levels in fluoride-containing collection tubes: by LC–MS/MS unexpectedly, plasma Hcy levels were 100 and 200 in patient A and between 100 and 400 μmol/l in patient B. Searching for germline mutations in 10 genes that are relevant for homocysteine metabolism only revealed hetero- and homozygous polymorphisms in the MTHFR gene. Alternatively, an acquired inhibition of cystathionine-beta-synthase which is important for homocysteine metabolism could explain the plasma homocysteine increase. This enzyme is heme-dependent: when we gave heme arginate to our patients, Hcy levels rapidly dropped. Hence, we conclude that inhibition of ∂-ALA-synthase 1 by givosiran causes a drop of free heme in the hepatocyte and therefore the excessive increase of plasma homocysteine. Hyperhomocysteinemia may contribute to the adverse effects seen in givosiran-treated patients which may be due to protein-N-homocysteinylation.

Involvement of HAND1 and CBS in maintenance of cardiac micro-architecture following obesity-induced heart failure

Purpose: To study the role of heart and neural crest derivatives expressed 1 (HAND1) and cystathionine-beta-synthase (CBS) in the maintenance of cardiac architecture following high fat dietinduced obesity. Methods: Mouse models of initial and critical heart disease were established by continuous feeding of high fat diet for 7 and 12 months, respectively. The expression of HAND1 and CBS were assayed using immunohistochemistry and Western blotting. Results: Obesity led to mild and severe forms of heart disease which were confirmed through histological imaging. Initial obesity resulted in cardiac tissue remodeling along with initial degeneration, while critical obesity resulted in tissue hardening. The expression of HAND1 was upregulated 4.3 folds in the mild form of cardiac failure, relative to marginal expression pattern of HAND1 in control tissue. However, as the disease progressed, the expression of HAND1 was limited in serve form of cardiac failure. Moreover, the expression of cystathionine beta-synthase (CBS) was upregulated 3.7-fold in the initial form of heart failure, but was subsequently reduced in serve form of heart disease. Conclusion: These results reveal that in high fat diet-induced cardiac stress, the over-expressions of HAND1 and CBS at the initial stages induce extensive alterations in cardiac architecture.

Recurrent dislocation of binocular crystal lenses in a patient with cystathionine beta-synthase deficiency

Background Ectopia lentis is the common ocular manifestation of homocystinuria resulting from cystathionine beta-synthase (CBS) deficiency which has a high risk of thromboembolic complications. Case presentation The present study reports the case of a teenager with recurrent lens dislocation and glaucoma. He was diagnosed with CBS deficiency according to a high level of serum homocysteine and compound heterozygous mutations at two different positions on the CBS gene. Antiglaucoma eyedrops and a mydriatic successfully controlled the intraocular pressure, while oral pyridoxine and betaine uptake lowered the serum homocysteine level effectively. Conclusions Children with CBS deficiency may suffer from ectopia lentis, glaucoma and/or amblyopia. We firstly discovered a new mutation of CBS c. 697 T > G which had not been reported before. The patient was pyridoxine responsive and well controlled by medicine.

A meet-up of two second messengers: the c-di-AMP receptor DarB controls (p)ppGpp synthesis in Bacillus subtilis

Many bacteria use cyclic di-AMP as a second messenger to control potassium and osmotic homeostasis. In Bacillus subtilis, several c-di-AMP binding proteins and RNA molecules have been identified. Most of these targets play a role in controlling potassium uptake and export. In addition, c-di-AMP binds to two conserved target proteins of unknown function, DarA and DarB, that exclusively consist of the c-di-AMP binding domain. Here, we investigate the function of the c-di-AMP-binding protein DarB in B. subtilis, which consists of two cystathionine-beta synthase (CBS) domains. We use an unbiased search for DarB interaction partners and identify the (p)ppGpp synthetase/hydrolase Rel as a major interaction partner of DarB. (p)ppGpp is another second messenger that is formed upon amino acid starvation and under other stress conditions to stop translation and active metabolism. The interaction between DarB and Rel only takes place if the bacteria grow at very low potassium concentrations and intracellular levels of c-di-AMP are low. We show that c-di-AMP inhibits the binding of DarB to Rel and the DarB–Rel interaction results in the Rel-dependent accumulation of pppGpp. These results link potassium and c-di-AMP signaling to the stringent response and thus to the global control of cellular physiology.