China
Africa
Explore chapters and articles related to this topic
Archaeosomes for Skin Injuries
Published in Andreia Ascenso, Sandra Simões, Helena Ribeiro, Carrier-Mediated Dermal Delivery, 2017
Monica Vazzana, Joana F. Fangueiro, Caterina Faggio, Antonello Santini, Eliana B. Souto
Besides archaeosome size, size distribution, shape and structure characterizations, studies to evaluate vesicle stabilities under various conditions have to be performed. Choquet et al. tested the stability of archaeosomes prepared from TPL of various archaea under different conditions (presence of phospholipases, temperature, pH) by fluorescence measurements (CF release), by radioactivity leakage ([14C]-sucrose leakage) and by vesicle size measurements. The results demonstrated that archaeobacterial ether lipids formed archaeosomes able to resist enzymatic attack. Studies on CF release as a function of temperature and on [14C]-sucrose leakage as a function of pH suggested that: (1) the presence of tetraether lipids is a stabilizing factor of vesicles at high temperature; (2) the ether bonds are partly responsible for the enhanced stability of archaeosomes at high temperature and extreme pH. Moreover, oxidation degradation is limited because of high stability of fully saturated phytanyl chains [33]. Similar studies were also carried out by Benvegnu et al. with vesicles based on synthetic archaeal lipid analogues. They showed that increasing amounts of synthetic archaeal lipids in archaeosome formulations exhibited a better stability in the presence of surfactants reproducing the behavior of bile salts, calf serum mimicking the blood medium and in acid pH conditions as found in the stomach [7].
Origins of Life
Published in Jim Lynch, What Is Life and How Might It Be Sustained?, 2023
So, with man at the summit of the evolutionary tree, when and where did the first living systems originate? The Phanerozoic timescale which was the first 600 million years has been well-documented and is divided into eras, periods, and epochs from stratigraphical dating and from the fossils themselves. Evidence for the Pre-Cambrian (the oldest) period came later. Most of the dating is done using isotopic measurements. The fossils are the results of living organisms, and much attention has been on the prokaryotic blue-green algae (cyanobacteria) leaving calcareous residues of their mats as they settled. Other bacteria also existed, and these can be seen in cherts (sedimentary rocks composed almost entirely of silica with the general properties of quartz). The structures seen in the rocks often resemble those of organisms in soils today. For example, at Harlech Castle in Wales, an organism that requires ammonia has been found bearing a resemblance to those in older rocks, thought to be enriched from a continuous input of urea from human action! The oldest such rock is the Fig Tree Chert from South Africa at 3100 million years (Figure 3.1). Much younger are the shales (about 60 million years old) which are sedimentary rocks formed from mud with clay and silt. The challenge has been to evaluate if there are chemical markers in the ancient rocks which have analogues in modern organisms. As I investigated such processes during my postgraduate studies referred to in Chapter 1, I was stimulated by the treatise produced at that time by Nobel Laureate Melvin Calvin on Chemical Evolution in 1969. To assemble a cell, critical building molecules are amino acids, polypeptides, purines, pyrimidines, and nucleotides, which would have to come from the primordial atmosphere of methane, ammonia, and water. Of greatest interest in determining markers has been the lipid fraction and especially those with distinctive branched carbon chain structures contained in the lipid (fat) fraction, notably phytane (17 carbon atoms) and pristane (18 carbon atoms). Both are thought to be derived from chlorophyll, the green photosynthetic pigment. Importantly pristane is formed in sediments on oxidising conditions and phytane is formed under reducing conditions. The ratio is therefore an indicator of the oxidative status of sediments. The cellular equivalent of these markers is isoprenoid, which can then be polymerised to squalene (30 carbon atoms), and then can potentially be cyclised into steroids and triterpenoids. We saw in the Introduction that these have been found in a methane-utilising bacterium and the fully saturated steranes and triterpanes found in ancient sediments. Much attention in the field of study has been the photosynthetic bacteria or blue-green algae, and green algae, but the important factor seems be whether the cells have internal membrane networks which are important sources of lipids.
Relevance of animal studies in the toxicological assessment of oil and wax hydrocarbons. Solving the puzzle for a new outlook in risk assessment
Published in Critical Reviews in Toxicology, 2021
Juan-Carlos Carrillo, Dirk Danneels, Jan Woldhuis
To round up and confirming the observations of Boitnott and Margolis on the type of hydrocarbons retained in human livers (Boitnott and Margolis 1970), the hydrocarbon composition of the tissues collected by Barp et al. 2014 was characterized using comprehensive two-dimensional chromatography (GCxGC-FID), presently the best technique for characterizing the composition of saturated hydrocarbons (Biedermann et al. 2015). The absence of n-alkanes (both those from vegetable origin and mineral oil derived products) was noted in the liver. Furthermore, all hydrocarbon components forming distinct signals are essentially removed including lightly branched, pristane and phytane, which are clearly present in the fat. What is left behind in the liver is an unresolved “gray cloud” of hydrocarbons mainly represented by highly isomerized and polycyclic compounds, as shown in Figure 9.
In vitro evaluation of archaeosome vehicles for transdermal vaccine delivery
Published in Journal of Liposome Research, 2018
Yimei Jia, Michael J. McCluskie, Dongling Zhang, Robert Monette, Umar Iqbal, Maria Moreno, Janelle Sauvageau, Dean Williams, Lise Deschatelets, Zygmunt J. Jakubek, Lakshmi Krishnan
Archaeal lipid core structures have characteristic branched phytanyl chains, which are fully saturated in many species and are attached via ether bonds to the glycerol backbone carbons at the sn-2, 3 positions (Krishnan et al.2000). The core structure of the archaeobacterial ether lipids consists of either the standard diether lipid (archaeol; 2,3-di-O-phytanyl-sn-glycerol), which is the major portion of the total polar lipids (TPL) of extreme halophiles such as Halobacterium salinarum, or the standard tetraether lipid (caldarchaeol; 2,2′,3,3′-tetra-O-dibiphytanyl-sn-diglycerol), which comprise about 90% of Thermoplasma acidophilum (Langworthy 1977). The polar head groups, attached to the sn-1 glycerol carbon in the diethers and to the sn-1 and sn-1′ glycerol carbons in the tetraethers, can vary depending on the archaeal genus (Sprott et al.1997). For example, extreme halophilic Archaea, such as Halobacterium salinarum and Haloferax volcanii, contain large amounts of phospholipids, whereas Methanobrevibacter smithii which is composed of both caldarchaeol (40% mass fraction) and archaeol (60% mass fraction) core lipids, contains a relatively high amount of phosphoserine as head group (Sprott et al.1999). The chemical structures of archaeol and caldarchaeol core lipids are illustrated in Figure 1.
In vitro anti-melanoma activity of imiquimod in ultradeformable nanovesicles
Published in Drug Development and Industrial Pharmacy, 2022
Ayelen Tatiana Caimi, Cecilia Ramirez, Ana Paula Perez, Eder Lilia Romero, Maria Jose Morilla
IMQ is a small, moderately lipophilic water insoluble molecule at neutral pH with poor skin permeability [47], difficult to formulate. Previously, our group have reported the properties of IMQ loaded into UDA made of TPA extracted from the archaea Halorubrum tebenquichense plus soybean phosphatidylcholine and sodium cholate as topical adjuvant [34]. Polar archaeolipids extracted from archaea have unique structural properties that distinguish them from lipids extracted from Eukarya and Bacteria. TPA from Halorubrum tebenquichense are a mixture of the sn 2,3 ether-linked phytanyl saturated archaeolipids: phosphatidylglycerol phosphate methyl ester (PGP-Me), sulfated diglycosyl diphytanylglycerol diether (SDGD5), phosphatidylglycerol (PG), bisphosphatidyl glycerol (BPG) and the glycocardiolipin (SDGD5PA) [38]. On one hand, TPA are resistant to hydrolysis, oxidation, and stereospecific phospholipases [48]; on the other hand, PGP-Me (main component of TPA) is ligand for cells expressing SRA1 [49], such as macrophages and endothelial cells. Nanovesicles containing TPA, such as UDA, are resistant to gastrointestinal digestion [50], lyophilization [51] and nebulization [49] and are targeted to different cells, not only macrophages expressing SRA1, such as epithelial lung cells (A549) [49], endothelial cells (HUVECS) [52], and Caco-2 cells [53]. Sugars such as SDGD and SDGD-5PA in TPA may also be recognized by receptors for advanced glycation end products (RAGE), present for example in melanoma cells [54]. Besides, we have showed that the total IMQ accumulation in human skin was 3 times higher when applied as UDA than as UDL and 1.5 times higher than as free IMQ; being the most IMQ in the stratum corneum [34].