Role of cytochrome P-450 in endogenous antipyresis

In previous reports, we (15, 18) and others (29) demonstrated data showing that various inhibitors of cytochrome P-450/epoxygenase augment fever in rats and mice, indicating that the enzyme may be involved in endogenous antipyresis. The aim of this study was to further test the hypothesis that the P-450-dependent epoxygenase pathway of arachidonic acid is part of the homeostatic system to control the height of fever. Sprague-Dawley rats were implanted with biotelemeters to monitor body temperature. Fever was induced by intraperitoneal injection of lipopolysaccharide (LPS; 80 microg/kg). We demonstrate that intraperitoneal administration of P-450 inducers (bezafibrate and dehydroepiandrosterone, 10 and 100 mg/kg) before LPS reduced fever in rats in a dose-dependent manner. In complementary experiments, rats were implanted with brain cannulas in addition to the biotelemeters. Various isomers of epoxyeicosanoids were administered into the lateral ventricle at doses of 0.01 to 10 microg/rat to test their influence on LPS-induced fever in rats. Four of five isomers were antipyretic in a dose-dependent manner. The most potent antipyretic isomers were 11, 12-epoxyeicosatrienoic acid (EET) followed by 14,15-EET, 8,9-EET, and 12(R) hydroxyeicosatetraenoic acid. These data support the hypothesis that the cytochrome P-450/epoxygenase pathway of arachidonate metabolism is part of the endogenous antipyretic system.     

Accumulation of unsaturated lipids in monocytes during early phase pyrogen tolerance

This paper presents data that inspired a new explanation for the mechanism of early phase endotoxin tolerance. Rabbits injected intravenously with LPS from Salmonella abortus developed a two-phase fever (6 h) and monophasic hyperlipidemia of very low density lipoproteins (two consecutive days). If during these days rabbits were injected with the same dose of LPS at 24-h intervals, the second phase of fever disappeared, i.e. early phase pyrogenic tolerance was obtained. This was correlated with a decrease of lipoprotein hyperlipidemia (measured 1.5 h after LPS injection) and an accumulation of lipids rich in double bonds in monocytes (measured 3.5 h after LPS injection). Results showed that the degree of unsaturation of acyl chains (AC) in monocytes (AC/DB, DB=double bonds) is negatively correlated (r=-0.72) with fever response (fever index). The authors maintain that a gradual increase in monocyte membrane fluidity is an adaptation to repeated exposure of monocytes to lipid A and is responsible for the progressive desensitization of monocytes to endotoxin. It is suggested that disorders of this mechanism lead to an accumulation of abnormal quantities of saturated lipids and cholesterol within macrophages, which, as foam cells, are the starting point for atherosclerosis pathology.     

A single amino acid change in the murine leukemia virus capsid gene responsible for the Fv1(nr) phenotype

The nr allele at the mouse Fv1 restriction locus governs resistance to B-tropic and some N-tropic murine leukemia viruses (MLVs). Sequence analysis and site-specific mutagenesis of N-tropic MLVs identified a single amino acid difference responsible for this restriction that is distinct from the site that governs N or B tropism. Viruses with other substitutions at this site were evaluated for altered replication patterns.     

Cooperation of multiple CCR5 coreceptors is required for infections by human immunodeficiency virus type 1

In addition to the primary cell surface receptor CD4, CCR5 or another coreceptor is necessary for infections by human immunodeficiency virus type 1 (HIV-1), yet the mechanisms of coreceptor function and their stoichiometries in the infection pathway remain substantially unknown. To address these issues, we studied the effects of CCR5 concentrations on HIV-1 infections using wild-type CCR5 and two attenuated mutant CCR5s, one with the mutation Y14N at a critical tyrosine sulfation site in the amino terminus and one with the mutation G163R in extracellular loop 2. The Y14N mutation converted a YYT sequence at positions 14 to 16 to an NYT consensus site for N-linked glycosylation, and the mutant protein was shown to be glycosylated at that position. The relationships between HIV-1 infectivity values and CCR5 concentrations took the form of sigmoidal (S-shaped) curves, which were dramatically altered in different ways by these mutations. Both mutations shifted the curves by factors of approximately 30- to 150-fold along the CCR5 concentration axis, consistent with evidence that they reduce affinities of virus for the coreceptor. In addition, the Y14N mutation specifically reduced the maximum efficiencies of infection that could be obtained at saturating CCR5 concentrations. The sigmoidal curves for all R5 HIV-1 isolates were quantitatively consistent with a simple mathematical model, implying that CCR5s reversibly associate with cell surface HIV-1 in a concentration-dependent manner, that approximately four to six CCR5s assemble around the virus to form a complex needed for infection, and that both mutations inhibit assembly of this complex but only the Y14N mutation also significantly reduces its ability to successfully mediate HIV-1 infections. Although several alternative models would be compatible with our data, a common feature of these alternatives is the cooperation of multiple CCR5s in the HIV-1 infection pathway. This cooperativity will need to be considered in future studies to address in detail the mechanism of CCR5-mediated HIV-1 membrane fusion.     

Retinal Nerve Fiber and Optic Disc Morphology in Patients with Human Immunodeficiency Virus Using the Heidelberg Retina Tomography 3

Purpose

To use novel confocal scanning ophthalmoscopy technology to test hypothesis that HIV-seropositive patients without history of retinitis with a history of a low CD4 count are more likely to have damage to their retinal nerve fiber layer (RNFL) when compared to patients with high CD4 count. In addition, we compared optic disc morphologic changes with glaucoma.

Design

Cross-sectional study.

Participants and Controls

171 patients were divided into four groups. The control group consisted of 40 eyes of 20 HIV-seronegative patients. The second group consisted of 80 eyes of 41 HIV-positive patients whose CD4 cell count never dropped below 100 (1.0 x 10⁹/L). The third group consisted of 44 eyes of 26 HIV-positive patients with a history of low CD4 counts <100. Fourth group consisted of 79 eyes of 79 patients with confirmed glaucoma who served as positive controls.

Testing

Confocal scanning laser ophthalmoscopy was performed with the Heidelberg Retina Tomograph (HRT3) and data were analyzed with HRT3, software (Heyex version 1.5.10.0).

Main Outcome Measures

Disc area, cup area, cup volume, rim volume, mean cup depth, maximum cup depth, cup-to-disc ration, mean RNFL thickness, and RNFL cross-sectional area.

Results

Analysis of the global optic nerve and cup parameters showed no difference in disk area among the four groups. There was also no difference in cup, rim volume, mean cup depth, or maximum cup depth among the first three groups but they were all different from glaucoma group. The RNFL was thinner in glaucoma and both HIV-positive groups compared to HIV-seronegative subjects. The cross sectional RNFL area was thinner in both high and low CD4 HIV-positive groups compared to HIV-seronegative group in the nasal and temporal/inferior sectors, respectively. Glaucoma group showed thinning in all sectors.

Conclusions

HIV retinopathy results in retinal nerve fiber layer loss without structural optic nerve supportive tissue change. RNFL damage may occur early in HIV disease by mechanism different than in glaucoma.     

Inactivation of the Sas2 histone acetyltransferase delays senescence driven by telomere dysfunction

Changes in telomere chromatin have been linked to cellular senescence, but the underlying mechanisms and impact on lifespan are unclear. We found that inactivation of the Sas2 histone acetyltransferase delays senescence in Saccharomyces cerevisiae telomerase (tlc1) mutants through a homologous recombination‐dependent mechanism. Sas2 acetylates histone H4 lysine 16 (H4K16), and telomere shortening in tlc1 mutants was accompanied by a selective and Sas2‐dependent increase in subtelomeric H4K16 acetylation. Further, mutation of H4 lysine 16 to arginine, which mimics constitutively deacetylated H4K16, delayed senescence and was epistatic to sas2 deletion, indicating that deacetylated H4K16 mediates the delay caused by sas2 deletion. Sas2 normally prevents the Sir2/3/4 heterochromatin complex from leaving the telomere and spreading to internal euchromatic loci. Senescence was delayed by sir3 deletion, but not sir2 deletion, indicating that senescence delay is mediated by release of Sir3 specifically from the telomere repeats. In contrast, sir4 deletion sped senescence and blocked the delay conferred by sas2 or sir3 deletion. We thus show that manipulation of telomere chromatin modulates senescence caused by telomere shortening.