By H. Ayitos. University of New England.
Similarly buy 250 mg mefenamic amex, a depression of body temperature to approximately 31° C (88° F) — a level which is sometimes produced artificially during anesthesia or which may occur naturally in men after extreme exposure to cold — also impairs brain function (2 generic 500mg mefenamic with amex, 9, 37, 62, 123). The nature of the impairments of brain function that occur during these and similar disturbances of homeostasis are discussed shortly. These impairments show many points of similarity, regardless of the conditions causing them. The concentration of the fluid in the internal milieu is maintained remarkably close to 310 miliosmols per liter. An increase in its concentration (as may occur after hemorrhage or after injuries that create shock) may impair the function of the brain. A decrease in its concentration (which can take place if a man is forced to drink excessive amounts of water over a short period of time) also may impair brain funtion 1 (38, 134). The internal milieu contains a number of organic and inorganic substances in solution, and the concentration of each of these is also maintained at a remarkably steady level. Disturbances in the concentration of any of these substances, upward, downward, or in their relative proportions, may impair brain function. This impairment may be produced directly by the effect of these changes on the brain, or indirectly through the impairment of the function of other vital organs, which in turn produce a disturbance of the internal milieu. It would not be profitable to attempt to list the limits of the various elevations, depressions, or relative disproportions of these substances beyond which an impairment of brain function may occur. In practice no single change occurs, but rather a disturbance of the concentration of several. Among these are excessive sweating, deprivation of water, diets deficient in salt, ingestion of excessive amounts of water or other nonsalty beverages over a short period of time, ingestion of excessive amounts of salt in food when water is restricted, ingestion of sea water in the absence of other water, poison- 1 The awkward term “brain function” is used here because there is no other that denotes all of the complex activities that the higher centers of the brain make possible. Even very rapid breathing, which sometimes occurs in people who are anxious or afraid, may lead to chemical changes in the blood that cause disturbances of brain function (17, 36, 77, 96). Many of the crude procedures that interrogators have utilized from time to time to make informants "tractable" and to "make them talk" have an adverse effect upon the composition of body fluids: the "hot box" or "sweat box"; the deprivation of water; the salty diet; the "water treatment"; the use of emetics to produce vomiting; and the use of cathartics such as castor oil to produce diarrhea. These procedures have been used by both European and Oriental interrogators in the historical past. They were also in use quite recently in Communist countries, and perhaps still are. The brain, like other organs, maintains its functions by constant metabolic activity. The basis for this activity is energy obtained by the oxidation of the organic chemicals available from food. Thus, a constant supply of oxygen must be brought to the brain by the blood in the amount of approximately 50 cc per minute (40, 66, 102). The most common way by which the brain becomes deprived of oxygen is by failure of the circulation (65), which may be brought about by loss of blood from hemorrhage, by shock resulting from injury (which has an effect on the circulation quite similar to that of hemorrhage), or by illness. Such failure of the circulation may occur also when a man is forced to stand still in a fixed position for a long time. It is responsible for the common phenomenon of the soldier who faints while standing at attention (20, 22, 89, 90, 107). Transient circulatory failure is also involved in "emotional fainting," which occurs as a result of an acute fall in blood pressure produced by an "emotional" stimulus. Failure of the circulation has other adverse effects on cerebral metabolism in addition to the effects produced by relative anoxia. Unlike other organs, the brain cannot use proteins and fats as sources of energy, and thus must rely on carbohydrates (65). It is, therefore, peculiarly sensitive to deficiencies in its supply of sugar, a substance normally present in blood. Small increases in sugar concentration, which usually occur after meals, have no discernible effect on brain function, but relatively small decreases in concentration -22- may have a distinct effect on mood and behavior. Small decreases set in motion homeostatic processes that lead to feelings of nervousness, restlessness, sweating, and inability to concentrate (27, 36, 92). A fall in blood sugar occasionally occurs in people who are anxious or fearful, and seems to contribute to their symptoms. This is one of the terminal events of starvation, and it contributes to the final stupor of the starved man (54, 67). The brain is not dependent on the immediate level in the blood of any foodstuff other than sugar, but it does ultimately suffer if it is deprived of other foods over a long period of time. The prolonged deficiency of protein and fat, which is usual in general starvation, very probably contributes to changes in brain function occurring under these circumstances (1, 18, 54, 67, 82). More immediate and readily recognizable changes in brain function occur when the diet is relatively deficient in one of the accessory foodstuffs, or vitamins, which the body cannot produce itself, but which it requires in minute but definite amounts. Among these the "B" group of vitamins are the most immediately relevant to the brain, probably because they take part in various processes of carbohydrate metabolism. A relative deficiency of thiamin (vitamin B1) causes beriberi; a deficiency of niacin causes pellagra; a deficiency of vitamin B12 causes pernicious anemia; and a deficiency of pyridoxine (vitamin B6) causes nervousness, insomnia, weakness, abdominal pain, and difficulty in walking. All these diseases may be associated with pronounced changes in brain function (95, 99, 120). Beriberi and pellagra have been endemic among prisoners of war from time immemorial (54).
Protein Solubility The solubility of the protein in aqueous or organic solvent dictates the choice of the method and the nanoparticle characteristics order mefenamic 250mg free shipping. Protein nanoparticles are prepared by utilizing the differential solubility of the protein in aqueous and nonaqueous solvents buy 250mg mefenamic free shipping, as proteins can fold or unfold depending on the polarity of the solvent (1). The pH value of the aqueous solution was found to have a signiﬁcant inﬂuence on the size of the albumin nanoparticles (45). At a pH away from the pI, the hydrophobic interactions in the protein are reduced, result- ing in lesser aggregation (26). Type A gelatin has a pI of 7 to 9, whereas type B gelatin has a pI of 4 to 7 (Table 1). Hence, the source of gelatin can inﬂuence the size, zeta-potential, and drug loading in gelatin nanoparticles (46, 47). For type A gelatin and type B gelatin, pH 7 and pH 3, respectively, were found to be critical for the preparation of nanoparticles (48). At these pH values, the strengths of electrostatic interactions are maximized for obtaining stable particles with optimal drug loading. Furthermore, in the case of gelatin, due to its high viscosity, a preheating (40◦C) step was used to prepare smaller size nanoparticles (48). However, a higher temperature (50◦C) was found to increase the particle size, due to the excessive unfolding of the protein (48). In a comparative study between different strengths of gelatin (75, 175, and 300 bloom strength), it was found that 300 bloom strength was optimal in terms of particle size, polydispersity index, and drug encapsulation (48). Surface Properties One of the signiﬁcant advantages of protein polymers is the presence of numerous surface functional groups that can be used for modifying the surface of the pro- tein nanoparticles to alter their biodistribution or biocompatibility or drug loading and/or improve their enzymatic stability (Fig. Particle size and surface proper- ties of protein nanoparticles depend on the number of disulﬁde bonds, number of thiol groups, degree of unfolding, electrostatic repulsion among protein molecules, pH, and ionic strength. The surface amine groups can be cross-linked using cross-linkers such as glutaraldehyde (Fig. The protonation or deprotonation of the surface amine groups can inﬂuence the degree of cross-linking (46). An increase in cross-linker concentration generally decreases the particle size of protein nanoparticles due to the formation of denser particles (48). Cross-linking helps in controlling the drug release from protein nanoparticles, as well as stabilizing the particles against prote- olytic breakdown. The surface functional groups can also be used to load drugs by electrostatic interactions (47). Kommareddy and Amiji (50) thiolated the surface amine groups to form disulﬁde bonds in gelatin nanoparticles. These nanoparticles can release their cargo under the highly reduc- ing environment in the tumor cells (50). Similarly, ligands have been attached to the surface of protein nanoparticles for drug targeting to speciﬁc tissues in the body (51,52). The surface functional groups in the protein can also directly interact with the biological membrane. Gliadin nanoparticles have been reported to show bioad- hesive property in the intestinal membrane, where the surface amino acids adhered to the intestinal membrane through hydrogen bonding and hydrophobic interac- tions (39). Drug Properties The physicochemical properties of the drug, such as solubility, log P, and molec- ular weight, inﬂuence the drug loading in protein nanoparticles. The drugs can be loaded through encapsulation in the nanoparticle or by the interaction of drug with the protein through covalent or noncovalent interactions. Highly hydrophobic drugs have been found to interact with cysteine residues in the albumin through hydrophobic interactions (19). For example, paclitaxel a highly hydrophobic drug is loaded in albumin nanoparticles by mixing albumin and paclitaxel in a high pressure homogenizer (53). A large number of drugs are known to bind to serum albumin, and hence albumin appears to be a promising carrier (19). In the case of gelatin nanoparticles, higher encapsulation efﬁciency was reported for hydrophilic drugs than for hydrophobic drugs (46). Doxorubicin was adsorbed onto gelatin- coated iron oxide nanoparticles for targeting using magnetic ﬁeld (47). It was found that the adsorption of cationic doxorubicin onto gelatin nanoparticles increased with increasing pH due to the negative charge of gelatin at higher pH. On the other hand, the encapsulation of doxorubicin in gelatin-coated iron oxide nanopar- ticles showed a slower drug release than surface-adsorbed nanoparticles (47). The release of hydrophilic drugs from gelatin nanoparticles was found to occur by zero- order kinetics, whereas hydrophobic drugs were released by pseudo zero-order kinetics (46). It was found that hydrophobic drugs are slowly released because of their higher afﬁnity to hydrophobic gliadin. On the other hand, hydrophilic drugs showed a burst release followed by slower drug diffusion from the nanoparticle matrix. High encapsulation efﬁciency (90%) of bone mor- phogenetic protein was reported with albumin nanoparticles (55). Unlike synthetic polymers, macromolecular drugs can be loaded in protein nanoparticles under milder conditions.
Te demonstration of a decline in risk afer ity may provide evidence that reinforces biologi- cessation of or reduction in exposure in indi- cal plausibility mefenamic 500mg overnight delivery. It should be noted order mefenamic 500mg line, however, that viduals or in whole populations also supports a when data on genetic susceptibility originate causal interpretation of the fndings. On the one hand, an agent results and inconsistencies across studies, and may be specifc in causing tumours at one site or such data therefore require careful evaluation. On the other, carci- If the known phenotype of a genetic polymor- nogenicity may be evident through the causation phism can explain the carcinogenic mechanism of multiple tumour types. Temporality, precision of the agent being evaluated, data on this pheno- of estimates of efect, biological plausibility and type may be useful in making causal inferences. Such a judgement requires tal animals was established or highly suspected frst that the studies meet, to a sufcient degree, before epidemiological studies confrmed their the standards of design and analysis described carcinogenicity in humans (Vainio et al. Specifcally, the possibility that bias, con- Although this association cannot establish that founding or misclassifcation of exposure or out- all agents that cause cancer in experimental ani- come could explain the observed results should mals also cause cancer in humans, it is biologically be considered and excluded with reasonable cer- plausible that agents for which there is sufcient tainty. In addition, all studies that are judged to evidence of carcinogenicity in experimental ani- be methodologically sound should (a) be con- mals (see Part B, Section 6b) also present a car- sistent with an estimate of efect of unity for any cinogenic hazard to humans. Accordingly, in observed level of exposure, (b) when considered the absence of additional scientifc information, together, provide a pooled estimate of relative these agents are considered to pose a carcinogenic risk that is at or near to unity, and (c) have a nar- hazard to humans. Examples of additional scien- row confdence interval, due to sufcient popula- tifc information are data that demonstrate that tion size. Moreover, no individual study nor the a given agent causes cancer in animals through pooled results of all the studies should show any a species-specifc mechanism that does not oper- consistent tendency that the relative risk of can- ate in humans or data that demonstrate that the cer increases with increasing level of exposure. Experience with extent of impurities or contaminants present in human cancer indicates that the period from frst the agent being evaluated are given when avail- exposure to the development of clinical cancer is able. Animal species, strain (including genetic sometimes longer than 20 years; latent periods background where applicable), sex, numbers per substantially shorter than 30 years cannot pro- group, age at start of treatment, route of expo- vide evidence for lack of carcinogenicity. Tose studies in experimental animals that are judged to be irrel- evant to the evaluation or judged to be inadequate 18 Preamble (e. Guidelines An assessment of carcinogenicity involves for conducting long-term carcinogenicity exper- several considerations of qualitative impor- iments have been published (e. Another larly in inhalation experiments; (iii) whether the consideration is that chemical and toxicological doses, duration of treatment and route of expo- interactions of components in a mixture may sure were appropriate; (iv) whether the survival alter dose–response relationships. Te relevance of treated animals was similar to that of con- to human exposure of the test mixture adminis- trols; (v) whether there were adequate numbers tered in the animal experiment is also assessed. When benign tumours (a) occur together Te relevance of results obtained with an with and originate from the same cell type as agent that is analogous (e. Such results may provide stage in the progression to malignancy, they are biological and mechanistic information that is usually combined in the assessment of tumour relevant to the understanding of the process of incidence (Huf et al. Te occurrence of carcinogenesis in humans and may strengthen lesions presumed to be preneoplastic may in cer- the biological plausibility that the agent being tain instances aid in assessing the biological plau- evaluated is carcinogenic to humans (see Part B, sibility of any neoplastic response observed. When detailed informa- ground and age of the animal, and on the dose, tion on survival is not available, comparisons route, timing and duration of the exposure. Te lethal- Te form of the dose–response relation- ity of the tumour also requires consideration: for ship can vary widely, depending on the par- rapidly fatal tumours, the time of death provides ticular agent under study and the target organ. Since many chemicals require metabolic fcult to determine, methods such as the Poly-K activation before being converted to their reac- test that do not require such information can tive intermediates, both metabolic and toxicoki- also be used. When results are available on the netic aspects are important in determining the number and size of tumours seen in experimen- dose–response pattern. Te dose–response relationship Formal statistical methods have been devel- can also be afected by diferences in survival oped to incorporate historical control data into among the treatment groups. Tese methods assign an appropriate weight to (c) Statistical analyses historical and concurrent controls on the basis Factors considered include the adequacy of of the extent of between-study and within-study the information given for each treatment group: variability: less weight is given to historical con- (i) number of animals studied and number exam- trols when they show a high degree of variability, ined histologically, (ii) number of animals with a and greater weight when they show little varia- given tumour type and (iii) length of survival. It is generally not appropriate to discount Te statistical methods used should be clearly a tumour response that is signifcantly increased stated and should be the generally accepted tech- compared with concurrent controls by arguing niques refned for this purpose (Peto et al. For example, a mutation in a between-study variability and are, thus, of little gene that codes for an enzyme that metabolizes relevance to the current experiment. In analys- the agent under study could be discussed in the ing results for uncommon tumours, however, the subsections on toxicokinetics, mechanisms and analysis may be improved by considering histori- individual susceptibility if it also exists as an cal control data, particularly when between-study inherited polymorphism. Historical controls should be selected to resemble the concurrent controls as (a) Toxicokinetic data closely as possible with respect to species, gen- Toxicokinetics refers to the absorption, dis- der and strain, as well as other factors such as tribution, metabolism and elimination of agents basal diet and general laboratory environment, in humans, experimental animals and, where which may afect tumour-response rates in con- relevant, cellular systems. Studies experiments than for epidemiological studies that indicate the metabolic fate of the agent in due to diferences in animal strains, they can be humans and in experimental animals are sum- useful aids in interpreting animal data when the marized briefy, and comparisons of data from experimental protocols are sufciently similar. Mechanistic and other relevant between exposure and the dose that reaches the data target site may be important for the extrapola- tion of hazards between species and in clarifying Mechanistic and other relevant data may pro- the role of in-vitro fndings. Te nature of the mechanistic and other relevant data To provide focus, the Working Group depends on the biological activity of the agent attempts to identify the possible mechanisms by being considered. Relevant topics may include toxi- given to gaps in the data and to data that suggests cokinetics, mechanisms of carcinogenesis, sus- that more than one mechanism may be operat- ceptible individuals, populations and life-stages, ing. Te relevance of the mechanism to humans other relevant data and other adverse efects.