Nutrition, HIV, and drug abuse: the molecular basis of a unique role for selenium.

HIV-infected injection drug users (IDUs) often suffer from serious nutritional deficiencies. This is a concern because plasma levels of micronutrients such as vitamin B12, zinc, and selenium have been correlated with mortality risk in HIV-positive populations. Injection drug use also increases lipid peroxidation and other indicators of oxidative stress, which, combined with antioxidant deficiencies, can stimulate HIV-1 replication through activation of NF-kappaB transcription factors, while weakening immune defenses. As detailed herein, these prooxidant stimuli can also increase the pathogenic effects of HIV-1 by another mechanism, involving viral selenoproteins. Overlapping the envelope coding region, HIV-1 encodes a truncated glutathione peroxidase (GPx) gene (see #6 in reference list). Sequence analysis and molecular modeling show that this viral GPx (vGPx) module has highly significant structural similarity to known mammalian GPx, with conservation of the catalytic triad of selenocysteine (Sec), glutamine, and tryptophan. In addition to other functions, HIV-1 vGPx may serve as a negative regulator of proviral transcription, by acting as an NF-kappaB inhibitor (a known property of cellular GPx). Another potential selenoprotein coding function of HIV-1 is associated with the 3' end of the nef gene, which terminates in a conserved UGA (potential Sec) codon in the context of a sequence (Cys-Sec) identical to the C-terminal redox center of thioredoxin reductase, another cellular regulator of NF-kappaB. Thus, in combination with known cellular mechanisms involving Se, viral selenoproteins may represent a unique mechanism by which HIV-1 monitors and exploits an essential micronutrient to optimize its replication relative to the host.

Molecular modeling and in vitro activity of an HIV-1-encoded glutathione peroxidase.

Based on theoretical evidence, it has been proposed that HIV-1 may encode several selenoprotein modules, one of which (overlapping the env gp41-coding region) has highly significant sequence similarity to the mammalian selenoprotein glutathione peroxidase (GPx; EC ). The similarity score of the putative HIV-1 viral GPx homolog relative to an aligned set of known GPx is 6.3 SD higher than expected for random sequences of similar composition. Based on that alignment, a molecular model of the HIV-1 GPx was constructed by homology modeling from the bovine GPx crystal structure. Despite extensive truncation relative to the cellular GPx gene, the structural core and the geometry of the catalytic triad of selenocysteine, glutamine, and tryptophan are well conserved in the viral GPx. All of the insertions and deletions predicted by the alignment proved to be structurally feasible. The model is energetically favorable, with a computed molecular mechanics strain energy close to that of the bovine GPx structure, when normalized on a per-residue basis. However, considering the remote homology, this model is intended only to provide a working hypothesis allowing for a similar active site and structural core. To validate the theoretical predictions, we cloned the hypothetical HIV-1 gene and found it to encode functional GPx activity when expressed as a selenoprotein in mammalian cells. In transfected canine kidney cells, the increase in GPx activity ranged from 21% to 43% relative to controls (average 30%, n = 9, P < 0.0001), whereas, in transfected MCF7 cells, which have low endogenous GPx activity, a near 100% increase was observed (average 99%, n = 3, P < 0.05).

Inhibition of volatile sevoflurane degradation product formation in an anesthesia circuit by a reduction in soda lime temperature.

BACKGROUND: Sevoflurane reacts with carbon dioxide absorbents, such as soda lime, to release the volatile products compounds A and B. These two products, which have been detected in anesthesia circuits, are among five formed when sevoflurane is degraded by soda lime at increased temperature; the others, compounds C, D, and E, have been detected only in heated sealed systems. The current study attempted to determine the influence of soda lime temperature on compounds A and B generation in an anesthesia circuit and whether a decrease in soda lime temperature could eliminate product formation in the circulating gases. METHODS: Sevoflurane (1.5% in oxygen) was circulated (6 l/min) in a partially closed, low-flow (215 ml/min fresh gas) anesthesia circuit that included a canister containing 1.2 kg fresh soda lime. Carbon dioxide was introduced into the circuit at 200 ml/min, and gas samples for analysis of sevoflurane, compounds A, B, C, and D, and carbon dioxide were taken at the opening of an attached artificial lung. The circuit was operated for 8 h under conditions whereby the soda lime temperature could increase freely or the soda lime was chilled with ice. RESULTS: A maximum core soda lime temperature of about 46 degrees C was measured when the experiment was run under conditions whereby the soda lime temperature was allowed to increase. Compounds A and B increased with time to a maximum of 23 and 9 ppm, respectively. At 4.5 h of circuit operation, compound C/D was found. Chilling of the soda lime canister, which produced a maximum core soda lime temperature of 25 degrees C, resulted in neither compound B nor C/D being detected during the 8-h period. Compound A was present in the circuit at all times at approximately 10 ppm; however, its concentration did not increase as occurred when the experiment was conducted under nonchilled conditions. Carbon dioxide levels at the opening of the lung remained at a constant 5% for 8 h with or without soda lime chilling. CONCLUSIONS: This study demonstrates that the release of volatile sevoflurane degradation products in an anesthesia circuit is highly dependent on soda lime temperatures. A reduction of the temperature of soda lime may be a feasible method of preventing the release of significant levels of sevoflurane degradation products without interfering with carbon dioxide absorption or altering the sevoflurane concentration.

Estrogen receptor affinity and effects on MCF-7 cell growth of triarylethylene carboxylic acids related to tamoxifen.

The estrogen receptor binding, and growth suppressant and stimulating effects in MCF-7 human breast cancer cells, of four structural variants of the triarylethylene antiestrogen tamoxifen (1) were studied. In these analogs, the dialkylaminoethoxy side chain of 1 was replaced by carboxylic acid or oxyacetic acid substituents. The presence of a p-hydroxy group in the ring geminal to the one bearing the side chain resulted in ligands with estrogen receptor affinities greater than that of 1 but less than that of estradiol. Compared to 1, none of the test compounds were effective suppressants of cell growth. To the contrary, the phenolic oxyacetic acid analog effectively reversed the growth suppressive effect of 1. Also, it was as effective as estradiol, though less potent, in stimulating growth of cells grown in estrogen depleted medium, suggestive of full estrogen agonist activity. Its carboxylic acid counterpart had little or no effect on proliferation. Because the phenolic oxyacetic acid is a metabolite of 1 in animals, its estrogenicity may have therapeutic implications of concern, depending on the extent to which it is formed and distributed in tissues of patients receiving 1.

Determination of fluorine in bones and teeth with xylenol orange.

Fluorine is determined in the ash of bone or tooth tissue after the sample has been dissolved in dilute perchloric acid. Interfering phosphate is precipitated by the addition of silver perchlorate and sodium carbonate and then filtered off. The fluoride contained in the filtrate is determined spectrophotometrically, by the bleaching of the coloured complex of zirconium with Xylenol Orange. The reaction is carried out in dilute perchloric acid and allowed to proceed for 1 hr. The absorbance is measured at 540 mmu. The relationship between the absorbance and concentration is practically linear over the range 15-65 mug. The range can also be modified for 0-50 mug.