Physiochemical properties plasma

Carotenoids are a class of lipophilic compounds with a polyisoprenoid structure. Most carotenoids contain a series of conjugated double bonds, which are sensitive to oxidative modification and cis-trans isomerization. There are six major carotenoids (ji-carotenc, a-carotene, lycopene, P-cryptoxanthin, lutein, and zeaxanthin) that can be routinely found in human plasma and tissues. Among them, p-carotene has been the most extensively studied. More recently, lycopene has attracted considerable attention due to its association with a decreased risk of certain chronic diseases, including cancers. Considerable efforts have been expended in order to identify its biological and physiochemical properties. Relative to P-carotene, lycopene has the same molecular mass and chemical formula, yet lycopene is an open-polyene chain lacking the P-ionone ring structure. While the metabolism of P-carotene has been extensively studied, the metabolism of lycopene remains poorly understood. 

As well as an effect on the activity, different stereoisomers will also exhibit differences in other physiochemical properties, such as absorption, metabolism and elimination. For example, (—)norgestrel is absorbed at twice the rate of (+)norgestrel through buccal and vaginal membranes. The plasma half life of S-indacrinone is 2-5 hours whilst the value for the R isomer is 10-12 hours. 

Platelets adhere to and become activated by nearly all artificial sur ces surfeces (McManna, 1986 Steen, 1987 Mason, 1974), and this is a problem in the development of new particulate medicaments or artificial organs. Plasma proteins adsorb to the surface before the platelets adhere, i.e. the platelets adhere to the coat of plasma proteins. The physiochemical properties of the surface determine the composition of the surface/liquid interlace ofplasmaproteins and therefore its platelet activating potential. (McManama et al, 1986). Artificial surfaces therefore induce adhesion signaling in platelets via the receptors described above. 

E2. Ecobichon, D. J., and Gomeau, A. M., Pseudocholinesterase of mammalian plasma. Physiochemical properties and organophosphate inhibition in eleven species. Toxicol. Appl. Pharmacol. 24, 92-100 (1973). 

Yet, physicochemical studies using differential scanning calorimetry, infrared spectroscopy and small-angle X-ray diffraction have shown that B[a]P incorporates into phospholipid bilayers and localizes in the most apolar region of the phospholipid matrix. This phenomenon may account for the observation of an expanded and swollen membrane [11]. We have therefore, proposed that distortion of the physiochemical properties of the adipocyte plasma membrane by B[a]P decreases the signalling capacity of G-coupled receptors intimately linked to the phospholipid bilayer, via their seven transmembrane domains. 

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