Juan Sánchez-Avila

Folate metabolism is intricately linked to purine de novo synthesis through the incorporation of folate-derived one-carbon units into the purine scaffold. By investigating chemical and genetic dependencies caused by mutations in methylenetetrahydrofolate dehydrogenase, cyclohydrolase, and formyltetrahydrofolate synthetase 1 (MTHFD1), we discovered a key role for Nudix hydrolase 5 (NUDT5) in regulating purine de novo synthesis. Genetic depletion and selective chemical degradation showed that a scaffolding role, rather than NUDT5 enzymatic activity, was causing this phenotype. NUDT5 interacted with phosphoribosyl pyrophosphate amidotransferase (PPAT), the rate-limiting enzyme of purine de novo synthesis, to repress the pathway in response to increased purine abundance. Through this mechanism, loss of NUDT5 mediates resistance to purine analogs in cancer treatment and prevents adenosine toxicity in MTHFD1 deficiency.

Many analytical methods for thyroid hormone (TH) determination lack sensitivity and/or specificity. The thyroid hormone metabolites (THMs) are usually not measured at all. This study describes the development of sensitive high-throughput analytical methods for determining the total concentration and free fraction of TH and THM in the human serum. For the analysis of the TOTAL fraction, we employed protein precipitation and anionic exchanger solid-phase extraction. For the FREE fraction, ultrafiltration and salt-out liquid partitioning were used. Derivatization using dansyl chloride was employed to enhance the sensitivity of HPLC-ESI-MS/MS analysis. Both protocols were validated according to the European Analytical Guidelines (2002/657/EC). We obtained very good recoveries (73-115%) and precision. Interday coefficients of variation (CVs) for most of the analytes ranged from 1.2 to 16.4%. The sensitivity was excellent with detection limits in the sub ppt range for the majority of TH and THM. A significant enhancement in sensitivity (>10 fold) was achieved through derivatization. The applicability was proved on a set of samples from pregnant women enrolled in the CELSPAC cohort (n = 120). Our TH reference ranges are in good agreement with those reported in the literature. The methods also allowed us to quantify the levels of 11 THM, including some previously undetected THM in total and free fractions, and proved to be suitable for high-throughput routine TH and THM analyses. Our approach offers an important advancement in thyroid hormone analysis. To the best of our knowledge, it is for the first time that data for T1A and T2A as well as for free THM levels in the human serum are published in the literature. Moreover, our study also brings the first information about the levels of most of the THM in pregnant women.

Targeted protein degradation (TPD) relies on small molecules to recruit proteins to E3 ligases to induce their ubiquitylation and degradation by the proteasome. Only a few of the approximately 600 human E3 ligases are currently amenable to this strategy. This limits the actionable target space and clinical opportunities and thus establishes the necessity to expand to additional ligases. Here we identify and characterize SP3N, a specific degrader of the prolyl isomerase FKBP12. SP3N features a minimal design, where a known FKBP12 ligand is appended with a flexible alkylamine tail that conveys degradation properties. We found that SP3N is a precursor and that the alkylamine is metabolized to an active aldehyde species that recruits the SCF^FBXO22 ligase for FKBP12 degradation. Target engagement occurs via covalent adduction of Cys326 in the FBXO22 C-terminal domain, which is critical for ternary complex formation, ubiquitylation and degradation. This mechanism is conserved for two recently reported alkylamine-based degraders of NSD2 and XIAP, thus establishing alkylamine tethering and covalent hijacking of FBXO22 as a generalizable TPD strategy.

It is important to develop a regional hydrogeological model to identify possible recharge and discharge areas for a sustainable use of a geothermal reservoir. The Los Humeros geothermal area is situated within five surficial watersheds and coveres an area of more than 15.000 km². A total of 208 well and spring samples were collected between June 2017 and November 2018. The stable isotope data for this region define a regression line of δD_H2O = 8.032·δ¹⁸O + 12 and indicate that groundwater is recharged by regional precipitation. At least 39 groundwater wells, with a maximum temperature of 35 °C, show temperatures above the reported mean average surface temperature of 15 °C. Characteristic elements for geothermal reservoir fluids (B, Li, As) are also present in these groundwaters, indicating a possible connection between the reservoir fluid and the local groundwater through local fracture systems. Concentration of B in these hot wells is between 150 and 35000 ppb.

Because agriculture and offshore oil extraction are significant economic activities in the southern Gulf of Mexico, high concentrations of nutrients and hydrocarbons are expected. As parasite communities are sensitive to environmental impacts, these contaminants should have an effect on metrics such as species richness, relative abundance and similarity. Consequently, these community metrics can be used as indicators of aquatic environmental health. Our objectives were to describe the parasite communities of the shoal flounder Syacium gunteri and to determine potential thresholds above which environmental contaminants become major controlling factors of parasite community metrics. The study area included 33 sampling sites in the southern Gulf of Mexico, where benthic sediments, water and shoal flounder individuals were collected. Data on ecto- and endo-parasites from flounder and nutrients, contaminants and physicochemical variables from the water and sediments were obtained. The statistical associations of the parasite community metrics at the component and infracommunity levels and the environmental data were analysed using redundancy analysis (RDA). Overall, 203 shoal flounder were examined for parasites, recovering 13 metazoan parasite species, and 48 physicochemical (e.g. temperature, nutrients) and contaminant (e.g. hydrocarbons, heavy metals) variables were obtained. The larval stages of the cestode Oncomegas wageneri and the nematodes Pseudoterranova decipiens and Hysterothylacium sp. were numerically dominant at the component and infracommunity levels. The parasite community metrics had significant negative statistical associations with both nitrate and total PAHs. With the exception of these two chemicals, which exceeded the threshold effect levels (TELs), no other environmental variable exceeded the range considered safe for marine organisms. The community metrics chosen generally had robust statistically significant associations with both physicochemical and contaminant variables, which supports the ecological relevance of these parameters as indicators of aquatic environmental health. Within the study area, the shoal flounder and their parasites live in a polluted environment with relatively high levels of hydrocarbons and nitrate. Regarding nitrate, we emphasise that if uncontrolled sewage discharge continues in the southern Gulf of Mexico, hypoxic conditions similar to those caused by the Mississippi river can be expected in the near future.

Pesticide chemical residues in water samples and biomarker responses in transplanted fish were used to monitor environmental hazards of pesticides in Palo Verde National Park (Costa Rica). The Costarican fish, Parachromis dovii (Ciclhidae) and Poecilia gillii (Poecillidae), were selected as sentinel species. Contaminant analyses detected up to 15 different pesticide residues in water with hexachlobenzene (2261 ng l(-1)), phorate (473 ng l(-1)), epoxiconazole (314) and bromacil (117 ng l(-1)) being the compounds found in higher concentrations. Biomarker responses evidenced impacts on cholinesterase activities in transplanted fish at Barbudal site probably due to the presence of organophosphate insecticides such as phorate. High enzyme activities of glutathione S-transferase and catalase and elevated levels of lipid peroxides were also observed at a site impacted by rice fields (Cabuyo); those effects could be associated with the presence of hexachloro benzene and triazole fungicides. In general, P. dovii biomarkers were affected to a greater extent than those of P. gillii in fish transplanted to sites associated with agriculture, which suggests the former species is a good candidate for future surveys.