A Novel Prediction Tool for Endoscopic Intervention in Patients with Acute Upper Gastro-Intestinal Bleeding.

(1) Background: Predicting which patients with upper gastro-intestinal bleeding (UGIB) will receive intervention during urgent endoscopy can allow for better triaging and resource utilization but remains sub-optimal. Using machine learning modelling we aimed to devise an improved endoscopic intervention predicting tool. (2) Methods: A retrospective cohort study of adult patients diagnosed with UGIB between 2012−2018 who underwent esophagogastroduodenoscopy (EGD) during hospitalization. We assessed the correlation between various parameters with endoscopic intervention and examined the prediction performance of the Glasgow-Blatchford score (GBS) and the pre-endoscopic Rockall score for endoscopic intervention. We also trained and tested a new machine learning-based model for the prediction of endoscopic intervention. (3) Results: A total of 883 patients were included. Risk factors for endoscopic intervention included cirrhosis (9.0% vs. 3.8%, p = 0.01), syncope at presentation (19.3% vs. 5.4%, p < 0.01), early EGD (6.8 h vs. 17.0 h, p < 0.01), pre-endoscopic administration of tranexamic acid (TXA) (43.4% vs. 31.0%, p < 0.01) and erythromycin (17.2% vs. 5.6%, p < 0.01). Higher GBS (11 vs. 9, p < 0.01) and pre-endoscopy Rockall score (4.7 vs. 4.1, p < 0.01) were significantly associated with endoscopic intervention; however, the predictive performance of the scores was low (AUC of 0.54, and 0.56, respectively). A combined machine learning-developed model demonstrated improved predictive ability (AUC 0.68) using parameters not included in standard GBS. (4) Conclusions: The GBS and pre-endoscopic Rockall score performed poorly in endoscopic intervention prediction. An improved predictive tool has been proposed here. Further studies are needed to examine if predicting this important triaging decision can be further optimized.

Overexpression and Purification of Human Cis-prenyltransferase in Escherichia coli.

Prenyltransferases (PT) are a group of enzymes that catalyze chain elongation of allylic diphosphate using isopentenyl diphosphate (IPP) via multiple condensation reactions. DHDDS (dehydrodolichyl diphosphate synthase) is a eukaryotic long-chain cis-PT (forming cis double bonds from the condensation reaction) that catalyzes chain elongation of farnesyl diphosphate (FPP, an allylic diphosphate) via multiple condensations with isopentenyl diphosphate (IPP). DHDDS is of biomedical importance, as a non-conservative mutation (K42E) in the enzyme results in retinitis pigmentosa, ultimately leading to blindness. Therefore, the present protocol was developed in order to acquire large quantities of purified DHDDS, suitable for mechanistic studies. Here, the usage of protein fusion, optimized culture conditions and codon-optimization were used to allow the overexpression and purification of functionally active human DHDDS in E. coli. The described protocol is simple, cost-effective and time sparing. The homology of cis-PT among different species suggests that this protocol may be applied for other eukaryotic cis-PT as well, such as those involved in natural rubber synthesis.

Purification and characterization of human dehydrodolychil diphosphate synthase (DHDDS) overexpressed in E. coli.

Protein asparagine (N)-linked glycosylation is a post-translational modification that occurs in the endoplasmic reticulum; it plays an important role in protein folding, oligomerization, quality control, sorting, and transport. Accordingly, disorders of glycosylation may affect practically every organ system. Dehydrodolichyl diphosphate synthase (DHDDS) is an eukaryotic cis prenyltransferase (cis-PT) that catalyzes chain elongation of farnesyl diphosphate via multiple condensations with isopentenyl diphosphate to form dehydrodolichyl diphosphate, a precursor for the glycosyl carrier dolichylpyrophophate involved in N-linked glycosylation. Mutations in DHDDS were shown to result in retinitis pigmentosa, ultimately leading to blindness, but the exact molecular mechanism by which the mutations affect DHDDS function remains elusive. In addition, bacterial cis-PT homologs are involved in bacterial wall synthesis and are therefore potential targets for new antibacterial agents. However, as eukaryotic cis-PT were not thoroughly characterized structurally and functionally, rational design of prokaryotic cis-PT specific drugs is currently impossible. Here, we present a simple protocol for purification of functionally active human DHDDS under non-denaturating conditions using a codon-optimized construct. The purified protein forms a stable homodimer, similar to its bacterial homologs, and shows time- and substrate-dependent activity. Purification of this protein requires the presence of a detergent for protein solubility. The protocol described here may be utilized for the overexpression of other eukaryotic cis-PT. Future structural and functional studies of the recombinant DHDDS may shed light on the mechanisms underlying DHDDS-related retinitis pigmentosa and lead to novel therapeutic approaches.