The Main (Glyco) Phospholipid (MPL) of Thermoplasma acidophilum

Recent progress of microneedles in transdermal immunotherapy: A review

Since human skin is an immune organ, a large number of immune cells are distributed in the epidermis and the dermis of the skin. Transdermal immunotherapy shows great therapeutic advantages in innate immunotherapy and adaptive immunotherapy. To solve the problem that macromolecules are difficult to penetrate into the skin, the microneedle technology can directly break through the skin barrier using micron-sized needles in a non-invasive and painless way for transdermal drug delivery. Therefore, it is considered to be an effective technology to increase drug transdermal absorption. In this review, the types of preparation, the combinations with different techniques and the mechanisms of microneedles in transdermal immunotherapy were summarized. Compared with traditional immunotherapy like intramuscular injection and subcutaneous injection, the microneedle has many advantages in transdermal immunotherapy, such as reducing patient pain, enhancing vaccine stability, and inducing stronger immune responses. Although there are still some limitations to be solved, the application of microneedle technology in transdermal immunotherapy is undoubtedly a promising means of drug delivery.

Self-assembly and biophysical properties of archaeal lipids

Archaea constitute one of the three fundamental domains of life. Archaea possess unique lipids in their cell membranes which distinguish them from bacteria and eukaryotes. This difference in lipid composition is referred to as 'Lipid Divide' and its origins remain elusive. Chemical inertness and the highly branched nature of the archaeal lipids afford the membranes stability against extremes of temperature, pH, and salinity. Based on the molecular architecture, archaeal polar lipids are of two types - monopolar and bipolar. Both monopolar and bipolar lipids have been shown to form vesicles and other well-defined membrane architectures. Bipolar archaeal lipids are among the most unique lipids found in nature because of their membrane-spanning nature and mechanical stability. The majority of the self-assembly studies on archaeal lipids have been carried out using crude polar lipid extracts or molecular mimics. The complexity of the archaeal lipids makes them challenging to synthesize chemically, and as a result, studies on pure lipids are few. There is an ongoing effort to develop simplified routes to synthesize complex archaeal lipids to facilitate diverse biophysical studies and pharmaceutical applications. Investigation on archaeal lipids may help us understand how life survives in extreme conditions and therefore unlock some of the mysteries surrounding the origins of cellular life.

Vesicular and Planar Membranes of Archaea Lipids: Unusual Physical Properties and Biomedical Applications

Liposomes and planar membranes made of archaea or archaea-like lipids exhibit many unusual physical properties compared to model membranes composed of conventional diester lipids. Here, we review several recent findings in this research area, which include (1) thermosensitive archaeosomes with the capability to drastically change the membrane surface charge, (2) MthK channel's capability to insert into tightly packed tetraether black lipid membranes and exhibit channel activity with surprisingly high calcium sensitivity, and (3) the intercalation of apolar squalane into the midplane space of diether bilayers to impede proton permeation. We also review the usage of tetraether archaeosomes as nanocarriers of therapeutics and vaccine adjuvants, as well as the biomedical applications of planar archaea lipid membranes. The discussion on archaeosomal therapeutics is focused on partially purified tetraether lipid fractions such as the polar lipid fraction E (PLFE) and glyceryl caldityl tetraether (GCTE), which are the main components of PLFE with the sugar and phosphate removed.

Certain, but Not All, Tetraether Lipids from the Thermoacidophilic Archaeon Sulfolobus acidocaldarius Can Form Black Lipid Membranes with Remarkable Stability and Exhibiting Mthk Channel Activity with Unusually High Ca2+ Sensitivity

Bipolar tetraether lipids (BTL) have been long thought to play a critical role in allowing thermoacidophiles to thrive under extreme conditions. In the present study, we demonstrated that not all BTLs from the thermoacidophilic archaeon Sulfolobus acidocaldarius exhibit the same membrane behaviors. We found that free-standing planar membranes (i.e., black lipid membranes, BLM) made of the polar lipid fraction E (PLFE) isolated from S. acidocaldarius formed over a pinhole on a cellulose acetate partition in a dual-chamber Teflon device exhibited remarkable stability showing a virtually constant capacitance (~28 pF) for at least 11 days. PLFE contains exclusively tetraethers. The dominating hydrophobic core of PLFE lipids is glycerol dialky calditol tetraether (GDNT, ~90%), whereas glycerol dialkyl glycerol tetraether (GDGT) is a minor component (~10%). In sharp contrast, BLM made of BTL extracted from microvesicles (Sa-MVs) released from the same cells exhibited a capacitance between 36 and 39 pF lasting for only 8 h before membrane dielectric breakdown. Lipids in Sa-MVs are also exclusively tetraethers; however, the dominating lipid species in Sa-MVs is GDGT (>99%), not GDNT. The remarkable stability of BLM_PLFE can be attributed to strong PLFE–PLFE and PLFE–substrate interactions. In addition, we compare voltage-dependent channel activity of calcium-gated potassium channels (MthK) in BLM_PLFE to values recorded in BLM_Sa-MV. MthK is an ion channel isolated from a methanogenic that has been extensively characterized in diester lipid membranes and has been used as a model for calcium-gated potassium channels. We found that MthK can insert into BLM_PLFE and exhibit channel activity, but not in BLM_Sa-MV. Additionally, the opening/closing of the MthK in BLM_PLFE is detectable at calcium concentrations as low as 0.1 mM; conversely, in diester lipid membranes at such a low calcium concentration, no MthK channel activity is detectable. The differential effect of membrane stability and MthK channel activity between BLM_PLFE and BLM_Sa-MV may be attributed to their lipid structural differences and thus their abilities to interact with the substrate and membrane protein. Since Sa-MVs that bud off from the plasma membrane are exclusively tetraether lipids but do not contain the main tetraether lipid component GDNT of the plasma membrane, domain segregation must occur in S. acidocaldarius. The implication of this study is that lipid domain formation is existent and functionally essential in all kinds of cells, but domain formation may be even more prevalent and pronounced in hyperthermophiles, as strong domain formation with distinct membrane behaviors is necessary to counteract randomization due to high growth temperatures while BTL in general make archaea cell membranes stable in high temperature and low pH environments whereas different BTL domains play different functional roles.

Improvement of Pulmonary Photodynamic Therapy: Nebulisation of Curcumin-Loaded Tetraether Liposomes

Lung cancer is one of the most common causes for a high number of cancer related mortalities worldwide. Therefore, it is important to improve the therapy by finding new targets and developing convenient therapies. One of these novel non-invasive strategies is the combination of pulmonary delivered tetraether liposomes and photodynamic therapy. In this study, liposomal model formulations containing the photosensitiser curcumin were nebulised via two different technologies, vibrating-mesh nebulisation and air-jet nebulisation, and compared with each other. Particle size and ζ-potential of the liposomes were investigated using dynamic light scattering and laser Doppler anemometry, respectively. Furthermore, atomic force microscopy and transmission electron microscopy were used to determine the morphological characteristics. Using a twin glass impinger, suitable aerodynamic properties were observed, with the fine particle fraction of the aerosols being ≤62.7 ± 1.6%. In vitro irradiation experiments on lung carcinoma cells (A549) revealed an excellent cytotoxic response of the nebulised liposomes in which the stabilisation of the lipid bilayer was the determining factor. Internalisation of nebulised curcumin-loaded liposomes was visualised utilising confocal laser scanning microscopy. Based on these results, the pulmonary application of curcumin-loaded tetraether liposomes can be considered as a promising approach for the photodynamic therapy against lung cancer.