Role of fatty acid uptake and fatty acid β-oxidation in mediating insulin resistance in heart and skeletal muscle

Fatty acids are a major fuel source used to sustain contractile function in heart and oxidative skeletal muscle. To meet the energy demands of these muscles, the uptake and β-oxidation of fatty acids must be coordinately regulated in order to ensure an adequate, but not excessive, supply for mitochondrial β-oxidation. However, imbalance between fatty acid uptake and β-oxidation has the potential to contribute to muscle insulin resistance. The action of insulin is initiated by binding to its receptor and activation of the intrinsic protein tyrosine kinase activity of the receptor, resulting in the initiation of an intracellular signaling cascade that eventually leads to insulin-mediated alterations in a number of cellular processes, including an increase in glucose transport. Accumulation of fatty acids and lipid metabolites (such as long chain acyl CoA, diacylglycerol, triacylglycerol, and/or ceramide) can lead to alterations in this insulin signaling pathway. An imbalance between fatty acid uptake and oxidation is believed to be responsible for this lipid accumulation, and is thought to be a major cause of insulin resistance in obesity and diabetes, due to lipid accumulation and inhibition of one or more steps in the insulin-signaling cascade. As a result, decreasing muscle fatty acid uptake can improve insulin sensitivity. However, the potential role of increasing fatty acid β-oxidation in the heart or skeletal muscle in order to prevent cytoplasmic lipid accumulation and decrease insulin resistance is controversial. While increased fatty acid β-oxidation may lower cytoplasmic lipid accumulation, increasing fatty acid β-oxidation can decrease muscle glucose metabolism, and incomplete fatty acid oxidation has the potential to also contribute to insulin resistance. In this review, we discuss the proposed mechanisms by which alterations in fatty acid uptake and oxidation contribute to insulin resistance, and how targeting fatty acid uptake and oxidation is a potential therapeutic approach to treat insulin resistance.     

Elevation of IL-6 in the allergic asthmatic airway is independent of inflammation but associates with loss of central airway function

Background

Asthma is a chronic inflammatory disease of the airway that is characterized by a Th2-type of immune response with increasing evidence for involvement of Th17 cells. The role of IL-6 in promoting effector T cell subsets suggest that IL-6 may play a functional role in asthma. Classically IL-6 has been viewed as an inflammatory marker, along with TNFα and IL-1β, rather than as regulatory cytokine.

Objective

To investigate the potential relationship between IL-6 and other proinflammatory cytokines, Th2/Th17 cytokines and lung function in allergic asthma, and thus evaluate the potential role of IL-6 in this disease.

Methods

Cytokine levels in induced sputum and lung function were measured in 16 healthy control and 18 mild-moderate allergic asthmatic subjects.

Results

The levels of the proinflammatory biomarkers TNFα and IL-1β were not different between the control and asthmatic group. In contrast, IL-6 levels were specifically elevated in asthmatic subjects compared with healthy controls (p < 0.01). Hierarchical regression analysis in the total study cohort indicates that the relationship between asthma and lung function could be mediated by IL-6. Among Th2 cytokines only IL-13 (p < 0.05) was also elevated in the asthmatic group, and positively correlated with IL-6 levels (r_S = 0.53, p < 0.05).

Conclusions

In mild-moderate asthma, IL-6 dissociates from other proinflammatory biomarkers, but correlates with IL-13 levels. Furthermore, IL-6 may contribute to impaired lung function in allergic asthma.     

Stabilization of HIV-1 gp120-CD4 Receptor Complex through Targeted Interchain Disulfide Exchange

HIV-1 enters cells via interaction between the trimeric envelope (Env) glycoprotein gp120/gp41 and the host cell surface receptor molecule CD4. The requirement of CD4 for viral entry has rationalized the development of recombinant CD4-based proteins as competitive viral attachment inhibitors and immunotherapeutic agents. In this study, we describe a novel recombinant CD4 protein designed to bind gp120 through a targeted disulfide-exchange mechanism. According to structural models of the gp120-CD4 receptor complex, substitution of Ser⁶⁰ on the CD4 domain 1 α-helix with Cys positions a thiol in proximity of the gp120 V1/V2 loop disulfide (Cys¹²⁶–Cys¹⁹⁶), satisfying the stereochemical and geometric conditions for redox exchange between CD4 Cys⁶⁰ and gp120 Cys¹²⁶, and the consequent formation of an interchain disulfide bond. In this study, we provide experimental evidence for this effect by describing the expression, purification, refolding, receptor binding and antiviral activity analysis of a recombinant two-domain CD4 variant containing the S60C mutation (2dCD4-S60C). We show that 2dCD4-S60C binds HIV-1 gp120 with a significantly higher affinity than wild-type protein under conditions that facilitate disulfide exchange and that this translates into a corresponding increase in the efficacy of CD4-mediated viral entry inhibition. We propose that targeted redox exchange between conserved gp120 disulfides and nucleophilic moieties positioned strategically on CD4 (or CD4-like scaffolds) conceptualizes a new strategy in the development of high affinity HIV-1 Env ligands, with important implications for therapy and vaccine development. More generally, this chalcogen substitution approach provides a general means of stabilizing receptor-ligand complexes where the structural and biophysical conditions for disulfide exchange are satisfied.     

In Situ Fluorescence Imaging of Myelination

We describe a novel fluorescent dye, 3-(4-aminophenyl)-2H-chromen-2-one (termed case myelin compound or CMC), that can be used for in situ fluorescent imaging of myelin in the vertebrate nervous system. When administered via intravenous injection into the tail vein, CMC selectively stained large bundles of myelinated fibers in both the central nervous system (CNS) and the peripheral nervous system (PNS). In the CNS, CMC readily entered the brain and selectively localized in myelinated regions such as the corpus callosum and cerebellum. CMC also selectively stained myelinated nerves in the PNS. The staining patterns of CMC in a hypermyelinated mouse model were consistent with immunohistochemical staining. Similar to immunohistochemical staining, CMC selectively bound to myelin sheaths present in the white matter tracts. Unlike CMC, conventional antibody staining for myelin basic protein also stained oligodendrocyte cytoplasm in the striatum as well as granule layers in the cerebellum. In vivo application of CMC was also demonstrated by fluorescence imaging of myelinated nerves in the PNS. (J Histochem Cytochem 58:611–621, 2010)     

Semen protects CD4+ target cells from HIV infection but promotes the preferential transmission of R5 tropic HIV

Sexual intercourse is the major means of HIV transmission, yet the impact of semen on HIV infection of CD4(+) T cells remains unclear. To resolve this conundrum, we measured CD4(+) target cell infection with X4 tropic HIV IIIB and HC4 and R5 tropic HIV BaL and SF162 after incubation with centrifuged seminal plasma (SP) from HIV-negative donors and assessed the impact of SP on critical determinants of target cell susceptibility to HIV infection. We found that SP potently protects CD4(+) T cells from infection with X4 and R5 tropic HIV in a dose- and time-dependent manner. SP caused a diminution in CD4(+) T cell surface expression of the HIVR CD4 and enhanced surface expression of the HIV coreceptor CCR5. Consequently, SP protected CD4(+) T cells from infection with R5 tropic HIV less potently than it protected CD4(+) T cells from infection with X4 tropic HIV. SP also reduced CD4(+) T cell activation and proliferation, and the magnitude of SP-mediated suppression of target cell CD4 expression, activation, and proliferation correlated closely with the magnitude of the protection of CD4(+) T cells from infection with HIV. Taken together, these data show that semen protects CD4(+) T cells from HIV infection by restricting critical determinants of CD4(+) target cell susceptibility to HIV infection. Further, semen contributes to the selective transmission of R5 tropic HIV to CD4(+) target cells.     

A prospective study of aspirin use and the risk of gastrointestinal bleeding in men

Background and Aims

Data regarding the influence of dose and duration of aspirin use on risk of gastrointestinal bleeding are conflicting.

Methods

We conducted a prospective cohort study of 32,989 men enrolled in the Health Professionals Follow-up Study (HPFS) in 1994 who provided biennial aspirin data. We estimated relative risk of major gastrointestinal bleeding requiring hospitalization or a blood transfusion.

Results

During 14 years of follow-up, 707 men reported an episode of major gastrointestinal bleeding over 377,231 person-years. After adjusting for risk factors, regular aspirin use (≥2 times/week) had a multivariate relative risk (RR) of gastrointestinal bleeding of 1.32 (95% confidence interval [CI], 1.12–1.55) compared to non-regular use. The association was particularly evident for upper gastrointestinal bleeding (multivariate RR, 1.49; 95% CI, 1.16–1.92). Compared to men who denied any aspirin use, multivariate RRs of upper gastrointestinal bleeding were 1.05 (95% CI 0.71–1.52) for men who used 0.5–1.5 standard tablets/week, 1.31 (95% CI 0.88–1.95) for 2–5 aspirin/week, 1.63 (95% CI, 1.15–2.32) for 6–14 aspirin/week and 2.40 (95% CI, 1.10–5.22) for >14 aspirin/week (P_trend<0.001). The relative risk also appeared to be dose-dependent among short-term users <5 years; P_trend<.001) and long-term users (≥5 years; P_trend = 0.015). In contrast, after controlling for dose, increasing duration of use did not appear to be associated with risk (P_trend = 0.749).

Conclusions

Regular aspirin use increases the risk of gastrointestinal bleeding, especially from the upper tract. However, risk of bleeding appears to be more strongly related to dose than to duration of use. Risk of bleeding should be minimized by using the lowest effective dose among short-term and long-term aspirin users.     

Estimating the Impact of Plasma HIV-1 RNA Reductions on Heterosexual HIV-1 Transmission Risk

Background

The risk of sexual transmission of HIV-1 is strongly associated with the level of HIV-1 RNA in plasma making reduction in HIV-1 plasma levels an important target for HIV-1 prevention interventions. A quantitative understanding of the relationship of plasma HIV-1 RNA and HIV-1 transmission risk could help predict the impact of candidate HIV-1 prevention interventions that operate by reducing plasma HIV-1 levels, such as antiretroviral therapy (ART), therapeutic vaccines, and other non-ART interventions.

Methodology/Principal Findings

We use prospective data collected from 2004 to 2008 in East and Southern African HIV-1 serodiscordant couples to model the relationship of plasma HIV-1 RNA levels and heterosexual transmission risk with confirmation of HIV-1 transmission events by HIV-1 sequencing. The model is based on follow-up of 3381 HIV-1 serodiscordant couples over 5017 person-years encompassing 108 genetically-linked HIV-1 transmission events. HIV-1 transmission risk was 2.27 per 100 person-years with a log-linear relationship to log₁₀ plasma HIV-1 RNA. The model predicts that a decrease in average plasma HIV-1 RNA of 0.74 log₁₀ copies/mL (95% CI 0.60 to 0.97) reduces heterosexual transmission risk by 50%, regardless of the average starting plasma HIV-1 level in the population and independent of other HIV-1-related population characteristics. In a simulated population with a similar plasma HIV-1 RNA distribution the model estimates that 90% of overall HIV-1 infections averted by a 0.74 copies/mL reduction in plasma HIV-1 RNA could be achieved by targeting this reduction to the 58% of the cohort with plasma HIV-1 levels ≥4 log₁₀ copies/mL.

Conclusions/Significance

This log-linear model of plasma HIV-1 levels and risk of sexual HIV-1 transmission may help estimate the impact on HIV-1 transmission and infections averted from candidate interventions that reduce plasma HIV-1 RNA levels.