Lipid-soluble compounds

Water solubility (polarity) is essential for excretion. Even though lipid-soluble compounds may also be excreted to primary urine, they are usually at least partially reabsorbed. The metabolites formed in the liver and extrahe-patic tissues remain free (i.e., not bound to proteins) and are, therefore, readily excreted. 

Lungs also secrete nonvolatile compounds. Lipid-soluble compounds may thus be transported with the alveobronchotracheal mucus to the pharynx, where they are swallowed. They may then be excreted or reabsorbed. Particles are also removed by this mucociliary escalator. 

Larvae of the tunicate Trididemnum solidum are most likely protected by didemnins like 44-46, cyclic depsipeptides that were initially identified from adults of this species [92]. The larvae are highly unpalatable to the wrasse Thalassoma bifasciatum, which rejected the larvae while readily consuming krill eyes that served as larval mimics. Coating one krill eye with the lipid soluble compounds from a single T. solidum larva rendered it as unpalatable as the larvae themselves. Reduced feeding was also observed when didemnin B (45) and nor-didemnin B (46) were administered to reef fishes in the field (Scheme 12) [92]. 

Figure 7 shows an example of the measurements of the antioxidant capacity of lipid-soluble compounds (ACL). In this figure, recording 1 corresponds to blank, while recordings 2-5 demonstrate the effect of adding lipid extracts from equivalently 20,40, 60, and 80 pL of blood plasma from a healthy volunteer... 

ACL—Integral Antiradical Capacity of Lipid-Soluble Compounds... 

The significant benefits of the PCL method include speed, precision, and the possibility to investigate water- and lipid-soluble compounds in a single system and to alter the type of radicals originated by selection of the respective photosensitizer. In contrast to other methods currently in use, the method discussed here is not restricted to a limited pH or temperature range. 

Ubiquinones (coenzymes Q) Q9 and Qi0 are essential cofactors (electron carriers) in the mitochondrial electron transport chain. They play a key role shuttling electrons from NADH and succinate dehydrogenases to the cytochrome b-c1 complex in the inner mitochondrial membrane. Ubiquinones are lipid-soluble compounds containing a redox active quinoid ring and a tail of 50 (Qio) or 45 (Q9) carbon atoms (Figure 29.10). The predominant ubiquinone in humans is Qio while in rodents it is Q9. Ubiquinones are especially abundant in the mitochondrial respiratory chain where their concentration is about 100 times higher than that of other electron carriers. Ubihydroquinone Q10 is also found in LDL where it supposedly exhibits the antioxidant activity (see Chapter 23). 

Formation of. glucuronide conjugates is a major metabolic conversion for many lipid-soluble compounds. The product glucuronides are more water soluble and usually more readily excreted. The glucuronic acid donor in this reaction is... 

Lipid-soluble compounds (nonionized) are more readily absorbed than water-soluble compounds (ionized). 

The thesis that all lipid-soluble compounds basically penetrate faster than water-soluble ones cannot be supported in this absolute form. A lipophilic agent can penetrate faster or slower or at the same rate as a hydrophilic agent, depending on the vehicle used. 

Vitamin (a-tocopherol) is an antioxidant. As a lipid-soluble compound, it is especially important for protecting other lipids from oxidative damage. 

In cytochrome bci, ubiquinone, also known as coenzymeQ, coQ, or Qio, is a lipid-soluble compound that can move within the membrane. It is involved... 

Currently, there are a number of organophosphorous compounds used in everyday life and agriculture as insecticides. Many of them are lipid-soluble compounds that are quickly and completely absorbed in practically every way, including skin as well as respiratory and... 

Thus, the system comprising membrane, solution 2 of constant composition (internal filling solution), and electrode 2 (internal reference electrode) constitutes an ion selective electrode. The electrically neutral carrier antibiotics of the valinomycin group and related lipid-soluble compounds can serve as the active components of highly selective liquid... 

The organophosphorus cholinesterase inhibitors like diisopropyl fluorophosphate, phospholine, parathion, malathion etc. are highly toxic compound and cause irreversible inhibition of both true and pseudocholinesterases. They are highly lipid soluble compound and can easily cross the blood-brain barrier. 

The influence of physicochemical properties of liposomes, such as charge density, membrane fluidity, and epitope density, on the immune response elicited by antigens has been extensively studied [37]. In addition to antigens, other immune stimulators that are amphoteric muramyl peptides or lipid-soluble compounds, such as monophosphoryl lipid A or muramyl tripeptidyl-phosphatidylethanolamine, can also be incorporated into liposomes to increase their adjuvant effect in eliciting immune responses [34]. 

Most psychotropic medications are highly lipophilic. The percentage of total body fat, which is a reservoir for these lipid-soluble compounds, increases during the first year of life and then decreases until the prepubertal increase ( 30). Thus, children at different ages have different volumes of deep storage, which can affect the overall residual time a drug remains in the body after its discontinuation. 

These conditions are embodied in the pH-partition theory only nonionized lipid-soluble compounds will be absorbed by passive diffusion down a concentration gradient. Let us examine the three conditions in turn. 

There are a number of factors that affect the absorption of foreign compounds from the gut or their disposition one factor, which is of particular importance, is the aqueous solubility of the compound in the nonionized form. With very lipid-soluble compounds, water solubility may be so low that the compound is not well absorbed (Table 2), because it is not dispersed in the aqueous environment of the gastrointestinal tract. In relation to this, a factor of particular importance in absorption of chemicals from the gut is the presence of bile, which is produced in the liver and secreted into the small intestine. This contains detergent-like substances, which will facilitate the dispersal of lipid-soluble chemicals in the aqueous medium of the intestine. 

Passive diffusion into the lumen of the gut may occur for compounds, such as weak bases, which are nonionized in the plasma but ionized in the stomach. This route may be of particular significance for highly lipid-soluble compounds. 

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