By C. Domenik. Peace College.
The modest yet highly significant clastogenic effect observed in both sexes was below the limit of detection of conventional micronucleus assays which rely on microscopic inspection to score the rare micronucleated cell population purchase depakote 500mg with mastercard symptoms of anxiety. This study strongly suggested that low depakote 500mg discount treatment of lyme disease, clinically relevant concentrations of zidovudine are clastogenic. This effect was not observed in offspring of Erythrocebus patas monkeys given 20% of the human equivalent dose of zidovudine during the last half of gestation. Thus, techniques have been devised to determine the amount of zido- vudine incorporated, to elucidate the conditions under which such incorporation occurs and to define the generalized toxic and specific mutagenic consequences of such incorporation. As mentioned earlier, zidovudine is preferentially incorporated into the telomeric regions of some cell types (Olivero & Poirier, 1993; Gomez et al. Exposure of human cells in culture to zidovudine can be correlated directly with a significant mutagenic response, and the exposure of mice led to increased incidences of transplacentally induced cancers and inactivation of Ha-ras oncogene in skin tumours. These results indicate that the dose and plasma concen- trations of zidovudine do not account by themselves for its mutagenic and carcino- genic effects. Didanosine was more cytotoxic than zidovudine, and didanosine alone was less muta- genic than zidovudine alone at both genes. Further investigations are needed to determine if other clinically relevant combinations of antiretroviral agents have synergistic genotoxic effects in cell culture, in animal models and in human populations. Incorporation values of about 7−500 molecules/106 nucleotides (approxi- mately 10 000−100 000 zidovudine molecules/cell) have been obtained in adults and transplacentally exposed mice, monkeys (E. The presence of distinct activating point mutations in Ha-ras of zidovudine-induced mouse skin tumours suggests that multiple mechanisms, which include point mutations and clastogenic events, with concomitant loss of heterozygosity, are all likely to be involved in the process of zido- vudine-induced tumour formation. Zidovudine is in widespread use in combination regimens with other antiretroviral agents. A number of other cohort studies were available which also involved limited length of follow-up and few subjects. No data were available on the risks for types of cancers other than non-Hodgkin lymphoma. None of the studies provided information on the risk for cancer associated with use of zidovudine for more than three years. Administration of zidovudine by gavage induced vaginal squamous-cell carcinomas in two studies in mice. A low incidence of vaginal tumours was observed in rats treated with the highest dose. Administration of zidovudine to mice by the intravaginal route resulted in an increased incidence of vaginal squamous-cell carcinomas. Combined administration of zidovudine with α-interferon also induced vaginal tumours in mice. Transplacental administration to mice resulted in an increased incidence and multi- plicity of lung and liver tumours and in an increased incidence of female reproductive tract tumours in one study, whereas no increased tumour incidence was associated with treatment in another study at a lower dose. After transplacental and postnatal adminis- tration of zidovudine to mice, an increased incidence of vaginal squamous-cell carci- nomas was seen. The achievement of maximum plasma concentrations and removal from plasma of the parent compound are rapid except in patients with compromised renal function. The pharmacokinetics in nonhuman primates is virtually identical to that in humans. The absorption, distribution and elimination of zidovudine in rodents are more rapid than in humans, and its bioavailability is higher in rats and mice than in primates. Zidovudine is metabolized by three pathways: glucuronidation, which accounts for up to three-quarters of the human urinary product; mixed-function oxidase- mediated reactions, giving 3′-amino-3′-deoxythymidine, a minor urinary metabolite; and phosphorylation, which is fundamental to the antiviral activity of zidovudine but accounts for only about 1% of its total disposition. In rats and mice, unchanged drug accounts for up to 90% of the urinary recovery, which represents about 80% of the dose; the remaining urinary products consist of five metabolites, which have been identified.
The observed numbers of cases in hospitals with universal and selective policies were compared with the numbers expected on the basis of national rates cheap depakote 500 mg fast delivery medicine to induce labor. Separate analyses were carried out for births in hospitals that followed one policy throughout the period of study and births in hospitals in which the policy changed during the period of study cheap depakote 500 mg on-line treatment 31st october. The ratio tended to be smaller in hospitals with a selective policy than in those offering universal prophylaxis. Studies of Cancer in Experimental Animals No reports of studies specifically designed to investigate the carcinogenicity of vitamin K substances were available to the Working Group. One study on the initiating effects of menadione in an assay of liver foci in rats was available (Denda et al. Other Data Relevant to an Evaluation of Carcinogenicity and its Mechanisms The studies summarized in this section should be considered in the light of the differences between naturally occurring forms of vitamin K that have a lipophilic side- chain at the 3-position of the 2-methyl-1,4-naphthoquinone (menadione) ring structure (phylloquinone and menaquinones) and the synthetic forms which lack this side-chain (menadione and its water-soluble derivatives). Lack of this side-chain results in profound differences in the absorption, tissue distribution and metabolism of natural K vitamins. In the strict sense, menadione is a provitamin K, because it is biologically active for the synthesis of vitamin K-dependent proteins only after conversion to the naturally occurring menaquinone-4 (four prenyl units) in vivo. It is absorbed chemically unchanged from the proximal intestine after solubilization into mixed micelles composed of bile salts and the products of pancreatic lipolysis. In healthy adults, the efficiency of absorption of phylloquinone in its free form is about 80% (Shearer et al. Within the intestinal mucosa, phylloquinone is incorporated into chylomicrons, is secreted into the lymph and enters the blood via the lacteals (Shearer et al. After a phylloquinone-containing meal, the plasma concentration peaks between 3 and 6 h (Shearer et al. Once in the circulation, phylloquinone is rapidly cleared at a rate consistent with its continuing association with chylomicrons and the chylomicron remnants that are produced by lipoprotein lipase hydrolysis at the surface of capillary endothelial cells. During the postprandial phase and after an overnight fast, more than half of the circulating phylloquinone is asso- ciated with triglyceride-rich lipoproteins, and the remainder is carried by low-density and high-density lipoproteins (Kohlmeier et al. Although phylloquinone is the major circulating form of vitamin K, menaquinone-7 is present in plasma at lower concentrations and has a similar lipoprotein distribution to phylloquinone. While phylloquinone in blood is derived exclusively from the diet, it is not known what proportion of circulating menaquinones such as menaquinone-7 derives from the diet or the intestinal flora (Shearer et al. A gradual slowing of the clearance rate was seen after the first 6 h (Shearer et al. This slowing of the clearance rate may be explained by the complexity of the plasma transport of phylloquinone, in which the proportion of phylloquinone associated with low-density and high-density lipo- proteins increases progressively (Lamon-Fava et al. The plasma disposition of oral doses of 5–60 mg phylloquinone (Konakion or AquaMephyton) is similar to that found after a more physiological dose (≤ 1 mg), with peak plasma concentrations at 4–6 h followed by a rapid clearance phase (Shearer et al. After an oral dose of 10 or 50 mg Konakion, the plasma concentration declined from the peak absorptive level at a similar log-linear rate as that seen after intravenous adminis- tration, with a terminal half-time of about 2 h for measurements up to 9–12 h (Park et al. The absorption of oral preparations of phylloquinone shows inter- and intra-individual variation and, for doses of Konakion ranging from 10 to 60 mg, the bioavailability was 10–63% (Park et al. The pharmacokinetics of phylloquinone after an intramuscular dose is completely different, showing sustained, slow release from the muscle site over many hours and marked inter-individual variation (Hagstrom et al. After intramuscular injection of phylloquinone (AquaMephyton R), most of the substance was carried by low-density and high- density lipoproteins instead of by triglyceride-rich (very-low-density) lipoproteins as found after oral administration (Hagstrom et al. An early study of the plasma disposition of 1 mg Konakion given orally or intra- muscularly at birth showed wide inter-individual differences during the first 24 h, especially after oral administration (McNinch et al. The peak plasma concen- tration after an oral dose occurred after 4 h; the median concentration was 73 ng/mL, which fell to 23 ng/mL after 24 h. The plasma concentration after administration of 1 mg of Konakion intramuscularly exceeded those after oral administration at all times, and after 24 h the median was 444 ng/mL.
Photody- namic therapy is a type of cancer treatment that uses a drug called a photosensitizer or photosensitizing agent (12) 250 mg depakote amex treatment kawasaki disease. When photosensitizers are exposed to this speciﬁc wavelength discount 250mg depakote medications hypertension, they produce singlet oxygen, which destroys cancer cells. Targeted cancer therapy uses target-speciﬁc drugs that invade cancer cells and block the growth and metasta- sis of cancer cells by interfering with speciﬁc molecules involved in carcinogenesis and tumor growth (13). To overcome the disadvantages of current cancer treatment techniques, the scientiﬁc community has turned toward nanotechnology to develop newer and more effective drug carrier systems to safely shepherd the anticancer drugs to the cancer cells. Examples of drugs in this class include methotrexate, ﬂuorouracil, hydroxyurea, and mercaptopurine. A few examples of drugs in this class include cisplatin and antibiotics such as daunorubicin, doxorubicin, and etoposide. Disruption of Synthesis or Breakdown of Mitotic Spindles Mitotic spindles serve as molecular railroads with “north and south poles” in the cell when it starts to divide. These drugs disrupt the formation of these spindles and therefore interrupt cell division. Classic examples of drugs in this class of mitotic disrupters include vinblastine, vincristine, and paclitaxel. The applications of nanoparticles as carriers for these anticancer drugs are discussed in the following sections. Results of numerous scientiﬁc research studies done in nanotech- nology and nanomedicine are inspiring the scientiﬁc community to discover new, innovative, noninvasive tools at the nanoscale level for such purposes. Nanoscale cantilevers (15) and quantum dots (16,17) are being studied as cancer detection tools at the cellular level. If the tumor has not been detected in its early stage, treatment methods should be devised to eradicate the fully developed cancer cells without harming the normal, healthy cells of human body. The various types of nanoparticles that are currently studied for their use as drug delivery systems are polymeric micelles, magnetic nanoparticles, colloidal gold nanoparticles, and ceramic nanoparticles (18–20). These nanoparticulate-based drug delivery systems can be characterized for their localization in tumor cells by coating them with tumor-speciﬁc antibodies, peptides, sugars, hormones, and anticarcinogenic drugs. These nanoparticles have been effectively coupled with the abovementioned anti- carcinogenic chemotherapeutic agents and have been tested for their target speci- ﬁcity. These nanoparticles are superior over conventionally available drug delivery systems, as the chemotherapeutic agents can be targeted to a speciﬁed area of the human body by adding nanoscale surface receptors. These receptors speciﬁcally recognize the target tissue and bind to it and release the drug molecules (21). Drugs can also be pro- tected from degradation by encapsulating them with nanoparticle coatings (22). As nanoparticles are extremely small, they can penetrate through smaller capillaries and are easily taken up by cancer cells. The use of biodegradable nanoparticles allows sustained drug release over a period of time (23). Thus, nanoparticles as drug delivery systems, with enhanced target speciﬁcity, can overcome the limitations of conventional cancer treatment techniques. There are numerous other nanobiotechnology-based approaches being developed to formulate nanoparticles as carriers of anticar- cinogenic agents. These include dendrimers, chitosan nanoparticles, low-density lipoproteins, nanoemulsions, nanolipospheres, nanoparticle composites, polymeric nanocapsules, nanospheres, and nanovesicles.
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