In vitro and in vivo evaluation of O-alkyl derivatives of tramadol

Tramadol is a centrally acting opioid analgesic structurally related to codeine and morphine. O-Alkyl, N-desmethyl, and non-phenol containing derivatives of tramadol were synthesized to probe their effect on metabolic stability and both in vitro and in vivo potency.     

New fluorescent cytidine 5''-phosphate derivatives.

Interaction of cytidine 5'-phosphate with chloroacetone or p-tosyloxyacetone leads to 2-methyl-5,6-dihydro-5-oxo-6-(5-0-phospho-beta-D-ribofuranosyl)-imidazo/1,2-c/pyrimidine (2-methylethenocytidine 5'-phosphate) whereas analogous reaction with phenacyl bromide produces similar 2-phenyl-derivative. The bicyclic nucleotides obtained showed significant UV absorption at long wavelength where common nucleotides and proteins exhibited no absorption. These derivatives are highly fluorescent when heterocyclic ring is protonated. The absorption and fluorescent properties of the substituted ethenocytidine 5'-phosphoate derivatives seem to be suitable for their use as fluorescent probes or labels in biochemical studies.     

Catabolism of the methyl derivatives of adenosine and cytidine in staphylococci.

Products of 1-methyladenosine, 2'-O-methyladenosine, 2'-O-methylcytidine, and 5-methylcytidine catabolism by resting cells of Staphylococcus aureus and Staphylococcus intermedius were chromatographically separated. The methyl group in 1-methyladenosine protected the adenosine derivative from deamination by S. intermedius but it did not protect N-glycosidic bond from cleavage by S. intermedius and S. aureus. The methyl group in 2'-O-methyladenosine and 2'-O-methylcytidine protected the N-glycosidic bond from cleavage by S. aureus and S. intermedius but it did not protect the adenosine and cytidine derivatives from deamination by S. intermedius. 5-Methylcytidine was converted by the common route in which 5-methylcytidine was first deaminated to ribothymidine which was cleaved to yield thymine. S. intermedius deaminated the purine and pyrimidine ribonucleosides adenosine, 2'-O-methyladenosine, cytidine, and 5-methylcytidine. Pyrimidine ribonucleosides (cytidine, 5-methyl-cytidine) were deaminated only slowly and purine ribonucleosides (adenosine, 2'-O-methyladenosine) not at all by S. aureus.     

Archaeal phospholipids: Structural properties and biosynthesis

Phospholipids are major components of the cellular membranes present in all living organisms. They typically form a lipid bilayer that embroiders the cell or cellular organelles, constitute a barrier for ions and small solutes and form a matrix that supports the function of membrane proteins. The chemical composition of the membrane phospholipids present in the two prokaryotic domains Archaea and Bacteria are vastly different. Archaeal lipids are composed of highly-methylated isoprenoid chains that are ether-linked to a glycerol-1-phosphate backbone while bacterial phospholipids consist of straight fatty acids bound by ester bonds to the enantiomeric glycerol-3-phosphate backbone. The chemical structure of the archaeal lipids and their compositional diversity ensures the required stability at extreme environmental conditions as many archaea thrive at such conditions including high or low temperature, high salinity and extreme acidic or alkaline pH values. However, not all archaea are extremophiles, and the presence of ether-linked phospholipids is a phylogenetic marker that distinguishes Archaea from other life forms. During the past decade, our understanding of the biosynthesis of archaeal lipids has progressed resulting in the characterization of the main biosynthetic steps of the pathway including the reconstitution of lipid biosynthesis in vitro. Here we describe the chemical and physical properties of archaeal lipids and membranes derived thereof, summarize the existing knowledge about the enzymology of the archaeal lipid biosynthetic pathway and discuss evolutionary theories associated with the “Lipid Divide” that resulted in the differentiation of bacterial and archaeal organisms. This article is part of a Special Issue entitled: Bacterial Lipids edited by Russell E. Bishop.     

Involvement of phospholipids in triglyceride biosynthesis by developing soybean cotyledons

The incorporation of phospholipids specifically labeled with glycerol-2³H and acyl-¹⁴C by whole cell tissues of developing soybean cotyledons (Glycine max L.) reveals that phosphatidylinositol, phosphatidylcholine, phosphatidylethanolamine, N-acylphosphatidylethanolamine, and phosphatidic acid can be metabolized to diglyceride. The diglyceride formed may be recylced into phospholipid or acylated to triglyceride. Diglyceride from phosphatidic acid and phosphatidylethanolamine is used readily in triglyceride biosynthesis compared to the other phospholipids. Incorporation of N-acylphosphatidylethanolamine having [9-10-³H(N)]oleic acid esterified at sn-3 in cotyledons shows rapid acyltransfer of ³H into triglyceride and therefore N-acylphosphatidylethanolamine appears to participate in triglyceride biosynthesis as an acyl donor. These studies emphasize phospholipid metabolism in developing soybean cotyledons is a dynamic process which plays a key role in triglyceride formation.     

Peroxisome-driven ether-linked phospholipids biosynthesis is essential for ferroptosis

It is well established that ferroptosis is primarily induced by peroxidation of long-chain poly-unsaturated fatty acid (PUFA) through nonenzymatic oxidation by free radicals or enzymatic stimulation of lipoxygenase. Although there is emerging evidence that long-chain saturated fatty acid (SFA) might be implicated in ferroptosis, it remains unclear whether and how SFA participates in the process of ferroptosis. Using endogenous metabolites and genome-wide CRISPR screening, we have identified FAR1 as a critical factor for SFA-mediated ferroptosis. FAR1 catalyzes the reduction of C16 or C18 saturated fatty acid to fatty alcohol, which is required for the synthesis of alkyl-ether lipids and plasmalogens. Inactivation of FAR1 diminishes SFA-dependent ferroptosis. Furthermore, FAR1-mediated ferroptosis is dependent on peroxisome-driven ether phospholipid biosynthesis. Strikingly, TMEM189, a newly identified gene which introduces vinyl-ether double bond into alkyl-ether lipids to generate plasmalogens abrogates FAR1-alkyl-ether lipids axis induced ferroptosis. Our study reveals a new FAR1-ether lipids-TMEM189 axis dependent ferroptosis pathway and suggests TMEM189 as a promising druggable target for anticancer therapy.Subject terms: Phospholipids, Cancer metabolism

Ether phospholipids represent an important group of phospholipids containing a glycerol backbone with an alkyl or a vinyl bond connecting a fatty alcohol at sn-1 position, usually polyunsaturated fatty acid (PUFA) including docosahexaenoic acid and arachidonic acid at sn-2. Ether phospholipids are initially synthesized in peroxisomes and processed in the endoplasmic reticulum (ER) [1–3]. Plasmalogens are the most abundant form of ether phospholipids which have a vinyl ether bond, enriched in the brain and heart tissues [1–3]. The plasmalogens have been found as endogenous antioxidants with vinyl ether bond susceptible to cleavage by reactive oxygen species (ROS). The deficiency of plasmalogens correlates with various human disorders, including Alzheimer’s disease and cancer [1, 2, 4].Ferroptosis is an iron-dependent form of non-apoptotic cell death induced by excess accumulation of peroxidized phopholipids, generated through oxidation of the PUFA moieties at sn-2 position of membrane phospholipids [5–9]. Ferroptosis is morphologically, biochemically and genetically distinct from other forms of cells death [5], which is tightly regulated by glutathione peroxidase 4 (GPX4) via converting lipid hydroperoxides (PUFA-OOH) into non-toxic lipid alcohols (PUFA-OH) [10, 11]. Emerging evidence indicates that ferroptosis is implicated in ischemia–reperfusion injury (IRI), neurodegeneration, antiviral immunity, cancer immunotherapy and tumor suppression [11–19].Accumulating evidence reveals a robust link between lipid metabolism and ferroptosis [14, 20–24]. However, little is known about the role of ether phospholipids in ferroptosis. In the present study, we revealed the FAR1-TMEM189 axis as a central pathway to drive the susceptibility of ferroptosis. FAR1-TMEM189 axis specifically synthesizes alkyl and vinyl ether phospholipid, where the two isoforms of ether phospholipid play distinct role in ferroptosis. Our findings provide an insight into the mechanism of ether phospholipid-mediated ferroptosis, with implications for novel treatment options for cancer therapy.     

Microsomal inducers of drug-metabolizing enzymes suppress cytidine nucleotide biosynthesis in rat liver.

The biosynthesis of cytidine nucleotides of liver rRNA was studied following single administration of seventeen different compounds. Only the substances recognized as inducers of the mixed-function oxidases of liver microsomes decrease the utilization of [2-¹⁴C]orotic acid for the synthesis of rRNA cytidine nucleotides.