A structural basis for the acute effects of HIV protease inhibitors on GLUT4 intrinsic activity

Emerging roles of senolytics/senomorphics in HIV-related co-morbidities

Human immunodeficiency virus (HIV) is known to cause cellular senescence and inflammation among infected individuals. While the traditional antiretroviral therapies (ART) have allowed the once fatal infection to be managed effectively, the quality of life of HIV patients on prolonged ART use is still inferior. Most of these individuals suffer from life-threatening comorbidities like chronic obstructive pulmonary disease (COPD), pulmonary arterial hypertension (PAH), and diabetes, to name a few. Interestingly, cellular senescence is known to play a critical role in the pathophysiology of these comorbidities as well. It is therefore important to understand the role of cellular senescence in the disease progression and co-morbidity development in HIV-infected individuals. In this respect, use of senolytic/senomorphic drugs as combination therapy with ART would be beneficial for HIV patients. This review provides a critical analysis of the current literature to determine the potential and efficacy of using senolytics/senotherapeutics in managing HIV infection, latency, and associated co-morbidities in humans. The various classes of senolytics have been studied in detail to focus on their potential to combat against HIV infections and associated pathologies with advancing age.

WNKs regulate mouse behavior and alter central nervous system glucose uptake and insulin signaling

Certain areas of the brain involved in episodic memory and behavior, such as the hippocampus, express high levels of insulin receptors and glucose transporter-4 (GLUT4) and are responsive to insulin. Insulin and neuronal glucose metabolism improve cognitive functions and regulate mood in humans. Insulin-dependent GLUT4 trafficking has been extensively studied in muscle and adipose tissue, but little work has demonstrated either how it is controlled in insulin-responsive brain regions or its mechanistic connection to cognitive functions. In this study, we demonstrate that inhibition of WNK (With-No-lysine (K)) kinases improves learning and memory in mice. Neuronal inhibition of WNK enhances in vivo hippocampal glucose uptake. Inhibition of WNK enhances insulin signaling output and insulin-dependent GLUT4 trafficking to the plasma membrane in mice primary neuronal cultures and hippocampal slices. Therefore, we propose that the extent of neuronal WNK kinase activity has an important influence on learning, memory and anxiety-related behaviors, in part, by modulation of neuronal insulin signaling.

HIV-Associated Hypertension: Risks, Mechanisms, and Knowledge Gaps

HIV type 1 (HIV-1) is the causative agent of AIDS. Since the start of the epidemic, HIV/AIDS has been responsible for ≈40 million deaths. Additionally, an estimated 39 million people are currently infected with the virus. HIV-1 primarily infects immune cells, such as CD4+ (cluster of differentiation 4+) T lymphocytes (T cells), and as a consequence, the number of CD4+ T cells progressively declines in people living with HIV. Within a span of ≈10 years, HIV-1 infection leads to the systemic failure of the immune system and progression to AIDS. Fortunately, potent antiviral therapy effectively controls HIV-1 infection and prevents AIDS-related deaths. The efficacy of the current antiviral therapy regimens has transformed the outcome of HIV/AIDS from a death sentence to a chronic disease with a prolonged lifespan of people living with HIV. However, antiviral therapy is not curative, is challenged by virus resistance, can be toxic, and, most importantly, requires lifelong adherence. Furthermore, the improved lifespan has resulted in an increased incidence of non-AIDS-related morbidities in people living with HIV including cardiovascular diseases, renal disease, liver disease, bone disease, cancer, and neurological conditions. In this review, we summarize the current state of knowledge of the cardiovascular comorbidities associated with HIV-1 infection, with a particular focus on hypertension. We also discuss the potential mechanisms known to drive HIV-1-associated hypertension and the knowledge gaps in our understanding of this comorbid condition. Finally, we suggest several directions of future research to better understand the factors, pathways, and mechanisms underlying HIV-1-associated hypertension in the post-antiviral therapy era.

Machine learning-guided design of potent darunavir analogs targeting HIV-1 proteases: A computational approach for antiretroviral drug discovery

In the pursuit of novel antiretroviral therapies for human immunodeficiency virus type-1 (HIV-1) proteases (PRs), recent improvements in drug discovery have embraced machine learning (ML) techniques to guide the design process. This study employs ensemble learning models to identify crucial substructures as significant features for drug development. Using molecular docking techniques, a collection of 160 darunavir (DRV) analogs was designed based on these key substructures and subsequently screened using molecular docking techniques. Chemical structures with high fitness scores were selected, combined, and one-dimensional (1D) screening based on beyond Lipinski's rule of five (bRo5) and ADME (absorption, distribution, metabolism, and excretion) prediction implemented in the Combined Analog generator Tool (CAT) program. A total of 473 screened analogs were subjected to docking analysis through convolutional neural networks scoring function against both the wild-type (WT) and 12 major mutated PRs. DRV analogs with negative changes in binding free energy (ΔΔ G bind ) compared to DRV could be categorized into four attractive groups based on their interactions with the majority of vital PRs. The analysis of interaction profiles revealed that potent designed analogs, targeting both WT and mutant PRs, exhibited interactions with common key amino acid residues. This observation further confirms that the ML model-guided approach effectively identified the substructures that play a crucial role in potent analogs. It is expected to function as a powerful computational tool, offering valuable guidance in the identification of chemical substructures for synthesis and subsequent experimental testing.

Adipose Tissue Dysfunction and Energy Balance Paradigms in People Living With HIV

Over the past 4 decades, the clinical care of people living with HIV (PLWH) evolved from treatment of acute opportunistic infections to the management of chronic, noncommunicable comorbidities. Concurrently, our understanding of adipose tissue function matured to acknowledge its important endocrine contributions to energy balance. PLWH experience changes in the mass and composition of adipose tissue depots before and after initiating antiretroviral therapy, including regional loss (lipoatrophy), gain (lipohypertrophy), or mixed lipodystrophy. These conditions may coexist with generalized obesity in PLWH and reflect disturbances of energy balance regulation caused by HIV persistence and antiretroviral therapy drugs. Adipocyte hypertrophy characterizes visceral and subcutaneous adipose tissue depot expansion, as well as ectopic lipid deposition that occurs diffusely in the liver, skeletal muscle, and heart. PLWH with excess visceral adipose tissue exhibit adipokine dysregulation coupled with increased insulin resistance, heightening their risk for cardiovascular disease above that of the HIV-negative population. However, conventional therapies are ineffective for the management of cardiometabolic risk in this patient population. Although the knowledge of complex cardiometabolic comorbidities in PLWH continues to expand, significant knowledge gaps remain. Ongoing studies aimed at understanding interorgan communication and energy balance provide insights into metabolic observations in PLWH and reveal potential therapeutic targets. Our review focuses on current knowledge and recent advances in HIV-associated adipose tissue dysfunction, highlights emerging adipokine paradigms, and describes critical mechanistic and clinical insights.

Co-administration of rimonabant prevents glucose intolerance in Sprague-Dawley rats treated chronically with lopinavir/ritonavir and zidovudine: an experimental study design

Introduction

treatment of HIV infection with Protease Inhibitors (PIs) and Nucleoside Reverse Transcriptase Inhibitors (NRTIs) can lead to insulin resistance and changes in body fat distribution. Overactivity of the endogenous cannabinoid system produces similar disturbances in metabolic syndrome within the general population. However, Cannabinoid receptor type 1 antagonism, in both human and animal studies, reverses many of these biochemical and physical derangements observed in the metabolic syndrome.

Methods

using an experimental study design, fifteen adult male Sprague-Dawley rats housed under standard conditions were randomized into three groups; Control, combined Anti-Retroviral Therapy (cART) only and cART + rimonabant. Drugs were administered daily by oral gavage for four weeks. After four weeks, insulin tolerance tests were conducted, the rats were euthanised and fat depots were excised and weighed. Experimental data were analysed using STATA 16.0 with the significance level set at p<0.05. The Shapiro-Wilk test determined normalcy. In cases of significance, post hoc analysis was performed by either the Dunn test or the Tukey HSD test.

Results

Sprague Dawley rats treated with cART + rimonabant demonstrated better insulin sensitivity (p = 0.0239) and lower body weight (p = 0.044) than rats treated with cART alone. They had leaner body composition with 58% less adiposity than cART-only rats.

Conclusion

the study results suggest a role for the endogenous cannabinoid system in cART induced metabolic derangements and physical changes. Future studies can directly assay ECS activity in cART associated metabolic syndrome.

Loss of brain energy metabolism control as a driver for memory impairment upon insulin resistance

The pathophysiological mechanisms intersecting metabolic and neurodegenerative disorders include insulin resistance, which has a strong involvement of environmental factors. Besides central regulation of whole-body homeostasis, insulin in the central nervous system controls molecular signalling that is critical for cognitive performance, namely signalling through pathways that modulate synaptic transmission and plasticity, and metabolism in neurons and astrocytes. This review provides an overview on how insulin signalling in the brain might regulate brain energy metabolism, and further identified molecular mechanisms by which brain insulin resistance might impair synaptic fuelling, and lead to cognitive deterioration.

HIV Protease Inhibitors and Insulin Sensitivity: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Background: Protease inhibitors (PIs) are believed to affect insulin sensitivity. We aimed to analyze the effect of PIs on insulin sensitivity and the onset of diabetes mellitus (DM) in patients with HIV. Methodology: We searched PubMed, Google Scholar, ClinicalTrals.gov, and the WHO International Clinical Trials Registry Platform till November 2020 for randomized controlled trials (RCTs) that studied the effects of PIs on insulin sensitivity and DM in patients with HIV. We followed the PRISMA and PICOS frameworks to develop the search strategy. We used the random-effects meta-analysis model to estimate the mean difference (MD), standardized mean difference (SMD), and risk ratios for our outcomes, using Stata 14 software. Results: We included nine RCTs that enrolled 1,000 participants, with their ages ranging from 18 to 69 years. The parameters and investigations used in the studies to determine insulin sensitivity were glucose disposal rates, hyperglycemia, and mean glucose uptake. The majority of results showed an association between PIs and insulin sensitivity. The pooled analysis showed no statistically significant difference in insulin sensitivity with atazanavir, whether the study was performed on healthy individuals for a short term or long term in combination with other drugs like tenofovir or emtricitabine [SMD = 0.375, 95% CI (0.035, 0.714)]. The analysis showed reduced glucose disposal rates and hence reduced insulin sensitivity with lopinavir (heterogeneity chi-squared = 0.68, I-squared [variation in SMD attributable to heterogeneity] = 0.0%, p = 0.031). The heterogeneity with chi-squared was substantial (61-80%), while with I-squared was not significant (0-40%), p = 0.031). Less adverse events were observed with atazanavir than with lopinavir [RR = 0.987, 95% CI (0.849, 1.124)]. Darunavir and indinavir did not demonstrate any significant changes in insulin sensitivity. Most of the studies were found to have a low risk of bias. Conclusions: There are significant variations in the effects of PIs on insulin sensitivity and onsets of DM. Atazanavir, fosamprenavir, and darunavir did not demonstrate any significant changes in insulin sensitivity, compared to the rest of the group. There is a need to assess the benefits of PIs against the long-term risk of impaired insulin sensitivity. All patients newly diagnosed with HIV should have DM investigations before the start of ARVs and routinely. RCTs should focus on sub-Saharan Africa as the region is worst affected by HIV, but limited studies have been documented.

GluT4: A central player in hippocampal memory and brain insulin resistance

Insulin is now well-established as playing multiple roles within the brain, and specifically as regulating hippocampal cognitive processes and metabolism. Impairments to insulin signaling, such as those seen in type 2 diabetes and Alzheimer's disease, are associated with brain hypometabolism and cognitive impairment, but the mechanisms of insulin's central effects are not determined. Several lines of research converge to suggest that the insulin-responsive glucose transporter GluT4 plays a central role in hippocampal memory processes, and that reduced activation of this transporter may underpin the cognitive impairments seen as a consequence of insulin resistance.

Xenbase: Facilitating the Use of Xenopus to Model Human Disease

At a fundamental level most genes, signaling pathways, biological functions and organ systems are highly conserved between man and all vertebrate species. Leveraging this conservation, researchers are increasingly using the experimental advantages of the amphibian Xenopus to model human disease. The online Xenopus resource, Xenbase, enables human disease modeling by curating the Xenopus literature published in PubMed and integrating these Xenopus data with orthologous human genes, anatomy, and more recently with links to the Online Mendelian Inheritance in Man resource (OMIM) and the Human Disease Ontology (DO). Here we review how Xenbase supports disease modeling and report on a meta-analysis of the published Xenopus research providing an overview of the different types of diseases being modeled in Xenopus and the variety of experimental approaches being used. Text mining of over 50,000 Xenopus research articles imported into Xenbase from PubMed identified approximately 1,000 putative disease- modeling articles. These articles were manually assessed and annotated with disease ontologies, which were then used to classify papers based on disease type. We found that Xenopus is being used to study a diverse array of disease with three main experimental approaches: cell-free egg extracts to study fundamental aspects of cellular and molecular biology, oocytes to study ion transport and channel physiology and embryo experiments focused on congenital diseases. We integrated these data into Xenbase Disease Pages to allow easy navigation to disease information on external databases. Results of this analysis will equip Xenopus researchers with a suite of experimental approaches available to model or dissect a pathological process. Ideally clinicians and basic researchers will use this information to foster collaborations necessary to interrogate the development and treatment of human diseases.

Insulin regulates GLUT4 in the ventromedial hypothalamus to restore the sympathoadrenal response to hypoglycemia in diabetic rats

It is proposed that the impaired counterregulatory response (CRR) to hypoglycemia in insulin-deficient diabetes may be due to chronic brain insulin deficiency. To test this hypothesis, streptozotocin-induced diabetic Sprague-Dawley rats were infused with insulin (3 mU/day) or artificial cerebrospinal fluid (aCSF) bilaterally into the ventromedial hypothalamus (VMH) for 2 wk and compared with nondiabetic rats. Rats underwent hyperinsulinemic (50 mU·kg^-1·min^-1)-hypoglycemic (~45 mg/dl) clamps. Diabetic rats demonstrated an impaired CRR to hypoglycemia, noted by a high glucose infusion rate and blunted epinephrine and glucagon responses. The defective sympathoadrenal response was restored by chronic infusion of insulin into the VMH. Diabetic rats had decreased VMH Akt phosphorylation and decreased VMH glucose transporter 4 (GLUT4) content, which was also restored by chronic infusion of insulin into the VMH. Separate experiments in nondiabetic rats in which GLUT4 translocation into the VMH was inhibited with an infusion of indinavir were notable for an impaired CRR to hypoglycemia, indicated by increased glucose infusion rate and diminished epinephrine and glucagon responses. Results suggest that, in this model of diabetes, VMH insulin deficiency impairs the sympathoadrenal response to hypoglycemia and that chronic infusion of insulin into the VMH is sufficient to normalize the sympathoadrenal response to hypoglycemia via restoration of GLUT4 expression in the VMH.

Targeting ulcerative colitis by suppressing glucose uptake with ritonavir

Glucose is the preferred source of energy in activated inflammatory cells. Glucose uptake into the cell is ensured by a family of glucose uptake transporters (GLUTs), which have been identified as off-target molecules of the HIV protease inhibitor ritonavir. In this study, we examined the effect of ritonavir on inflammation in vitro and in vivo. Peripheral blood mononuclear cells (PBMCs) were activated with anti-CD3 in the presence or absence of ritonavir and analyzed by flow cytometric analysis. Frequencies of CD4+ cells were significantly affected by ritonavir (CD69+ P=3E-05; CD134 P=4E-06; CD25+ P=E-07; central memory P=0.02; effector P=6E-03; effector memory P=6E-05). To corroborate that inflammation has a metabolic effect in vivo, a mouse model was used that is based on immunocompromised NOD-scid IL-2Rγ^null mice reconstituted with PBMCs from patients with ulcerative colitis (UC). Inflammation had a significant effect on amino acid (AA) levels (Glu P=1E-07, Asp P=1E-04). Principal component analysis (PCA) discriminated between unchallenged and challenged groups. Finally, the efficacy of ritonavir was tested in the same mouse model. Dependent variables were clinical and histological scores, frequencies of human leukocytes isolated from spleen and colon, and levels of AA in sera of mice. Mice benefited from treatment with ritonavir as indicated by significantly decreased colon (P=7E-04) and histological (P=1E-04) scores, frequencies of M2 monocytes (CD14+ CD163; P=0.02), and Glu levels (P=2E-05). PCA discriminated between control and challenged groups (P=0.026). Thus, inhibition of glucose uptake might be a promising therapeutic intervention point for active UC.

Summary: Insights into immuno-metabolism open up new avenues for therapeutic intervention. The study presented here suggests that inhibition of glucose suppresses inflammation in a mouse model of ulcerative colitis.

The Impact of Weight Gain During HIV Treatment on Risk of Pre-diabetes, Diabetes Mellitus, Cardiovascular Disease, and Mortality

Since the introduction of combined antiretroviral therapy (cART) and more effective treatments for AIDS, there has been a dramatic shift from the weight loss and wasting that characterised HIV/AIDS (and still does in countries where cART is not readily available or is initiated late) to healthy weight, or even overweight and obesity at rates mirroring those seen in the general population. These trends are attributable to several factors, including the "return to health" weight gain with reversal of the catabolic effects of HIV-infection following cART-initiation, strategies for earlier cART-initiation in the course of HIV-infection which have prevented many people living with HIV-infection from developing wasting, in addition to exposure to the modern obesogenic environment. Older cART regimens were associated with increased risk of body fat partitioning disorders (lipodystrophy) and cardiometabolic complications including atherothrombotic cardiovascular disease (CVD) and diabetes mellitus. Whilst cART now avoids those medications implicated in causing lipodystrophy, long-term cardiometabolic data on more modern cART regimens are lacking. Longitudinal studies show increased rates of incident CVD and diabetes mellitus with weight gain in treated HIV-infection. Abdominal fat gain, weight gain, and rising body mass index (BMI) in the short-term during HIV treatment was found to increase incident diabetes risk. Rising BMI was associated with increased risk of incident CVD, however the relationship varied depending on pre-cART BMI category. In contrast, a protective association with mortality is evident, predominantly in the underweight and in resource-poor settings, where weight gain reflects access to cART and virological suppression. The question of how to best evaluate, manage (and perhaps constrain) weight gain during HIV treatment is of clinical relevance, especially in the current climate of increasingly widespread cART use, rising overweight, and obesity prevalence and growing metabolic and cardiovascular disease burden in people living with HIV-infection. Large prospective studies to further characterise the relationship between weight gain during HIV treatment and risk of diabetes, CVD and mortality are required.

Insulin modulates hippocampally-mediated spatial working memory via glucose transporter-4

The insulin-regulated glucose transporter, GluT4, is a key molecule in peripheral insulin signaling. Although GluT4 is abundantly expressed in neurons of specific brain regions such as the hippocampus, the functional role of neuronal GluT4 is unclear. Here, we used pharmacological inhibition of GluT4-mediated glucose uptake to determine whether GluT4 mediates insulin-mediated glucose uptake in the hippocampus. Consistent with previous reports, we found that glucose utilization increased in the dorsal hippocampus of male rats during spontaneous alternation (SA), a hippocampally-mediated spatial working memory task. We previously showed that insulin signaling within the hippocampus is required for processing this task, and that administration of exogenous insulin enhances performance. At baseline levels of hippocampal insulin, inhibition of GluT4-mediated glucose uptake did not affect SA performance. However, inhibition of an upstream regulator of GluT4, Akt, did impair SA performance. Conversely, when a memory-enhancing dose of insulin was delivered to the hippocampus prior to SA-testing, inhibition of GluT4-mediated glucose transport prevented cognitive enhancement. These data suggest that baseline hippocampal cognitive processing does not require functional hippocampal GluT4, but that cognitive enhancement by supra-baseline insulin does. Consistent with these findings, we found that in neuronal cell culture, insulin increases glucose utilization in a GluT4-dependent manner. Collectively, these data demonstrate a key role for GluT4 in transducing the procognitive effects of elevated hippocampal insulin.

Novel Roles for the Insulin-Regulated Glucose Transporter-4 in Hippocampally Dependent Memory

The insulin-regulated glucose transporter-4 (GluT4) is critical for insulin- and contractile-mediated glucose uptake in skeletal muscle. GluT4 is also expressed in some hippocampal neurons, but its functional role in the brain is unclear. Several established molecular modulators of memory processing regulate hippocampal GluT4 trafficking and hippocampal memory formation is limited by both glucose metabolism and insulin signaling. Therefore, we hypothesized that hippocampal GluT4 might be involved in memory processes. Here, we show that, in male rats, hippocampal GluT4 translocates to the plasma membrane after memory training and that acute, selective intrahippocampal inhibition of GluT4-mediated glucose transport impaired memory acquisition, but not memory retrieval. Other studies have shown that prolonged systemic GluT4 blockade causes insulin resistance. Unexpectedly, we found that prolonged hippocampal blockade of glucose transport through GluT4-upregulated markers of hippocampal insulin signaling prevented task-associated depletion of hippocampal glucose and enhanced both working and short-term memory while also impairing long-term memory. These effects were accompanied by increased expression of hippocampal AMPA GluR1 subunits and the neuronal GluT3, but decreased expression of hippocampal brain-derived neurotrophic factor, consistent with impaired ability to form long-term memories. Our findings are the first to show the cognitive impact of brain GluT4 modulation. They identify GluT4 as a key regulator of hippocampal memory processing and also suggest differential regulation of GluT4 in the hippocampus from that in peripheral tissues.

SIGNIFICANCE STATEMENT

The role of insulin-regulated glucose transporter-4 (GluT4) in the brain is unclear. In the current study, we demonstrate that GluT4 is a critical component of hippocampal memory processes. Memory training increased hippocampal GluT4 translocation and memory acquisition was impaired by GluT4 blockade. Unexpectedly, whereas long-term inhibition of GluT4 impaired long-term memory, short-term memory was enhanced. These data further our understanding of the molecular mechanisms of memory and have particular significance for type 2 diabetes (in which GluT4 activity in the periphery is impaired) and Alzheimer's disease (which is linked to impaired brain insulin signaling and for which type 2 diabetes is a key risk factor). Both diseases cause marked impairment of hippocampal memory linked to hippocampal hypometabolism, suggesting the possibility that brain GluT4 dysregulation may be one cause of cognitive impairment in these disease states.

Development of GLUT4-selective antagonists for multiple myeloma therapy

Cancer cells consume more glucose to fuel metabolic programs fundamental to sustaining their survival, growth and proliferation. Among the fourteen SLC2A family members, GLUTs 1 and 4 are high-affinity glucose transporters. GLUT4 (SLC2A4) is highly expressed in muscle and adipose tissue. Basally retained within the cell, GLUT4 traffics to the plasma membrane (PM) in response to insulin and exercise-stimulation. The plasma cell malignancy multiple myeloma (MM) exhibits increased constitutive expression of GLUT4 on the PM, co-opting use of GLUT4 for survival and proliferation. GLUT4 inhibition by knockdown or treatment with the FDA-approved HIV protease inhibitor ritonavir leads to cytostatic and/or cytotoxic and chemosensitizing effects in tumor cells both in vitro and in vivo. We recently reported our generation of GLUT4 homology models and virtual high-throughput screening (vHTS) to identify multiple series of novel GLUT4 antagonists. In this report, we describe our initial hit-to-lead optimization to synthesize new analogs with improved potency and selectivity for GLUT4, and the biological characterization of these compounds in a variety of assays. We show that our lead compound (compound 20) decreases glucose uptake and cell proliferation as well as inhibits the expression of pro-survival MCL-1 in MM similar to the effect observed via knockdown of GLUT4 expression. Compound 20 is also effective at chemosensitizing multiple myeloma cell lines and patient samples to venetoclax, dexamethasone and melphalan. In sum, we report development of selective GLUT4 inhibitors lacking inhibitory activity against GLUT1 and GLUT8. We show that selective pharmacological inhibition of GLUT4 is feasible and this may represent a novel strategy for the treatment and chemosensitization of multiple myeloma to standard therapeutics.

Regulation of GLUT4 activity in myotubes by 3-O-methyl-d-glucose

The rate of glucose influx to skeletal muscles is determined primarily by the number of functional units of glucose transporter-4 (GLUT4) in the myotube plasma membrane. The abundance of GLUT4 in the plasma membrane is tightly regulated by insulin or contractile activity, which employ distinct pathways to translocate GLUT4-rich vesicles from intracellular compartments. Various studies have indicated that GLUT4 intrinsic activity is also regulated by conformational changes and/or interactions with membrane components and intracellular proteins in the vicinity of the plasma membrane. Here we show that the non-metabolizable glucose analog 3-O-methyl-d-glucose (MeGlc) augmented the rate of hexose transport into myotubes by increasing GLUT4 intrinsic activity without altering the content of the transporter in the plasma membrane. This effect was not a consequence of ATP depletion or hyperosmolar stress and did not involve Akt/PKB or AMPK signal transduction pathways. MeGlc reduced the inhibitory potency (increased K_i) of indinavir, a selective inhibitor of GLUT4, in a dose-dependent manner. Kinetic analyses indicate that MeGlc induced changes in GLUT4 or GLUT4 complexes within the plasma membrane, which enhanced the hexose transport activity and reduced the potency of indinavir inhibition. Finally, we present a simple kinetic analysis for screening and discovering low molecular weight compounds that augment GLUT4 activity.

Brain GLUT4 Knockout Mice Have Impaired Glucose Tolerance, Decreased Insulin Sensitivity, and Impaired Hypoglycemic Counterregulation

GLUT4 in muscle and adipose tissue is important in maintaining glucose homeostasis. However, the role of insulin-responsive GLUT4 in the central nervous system has not been well characterized. To assess its importance, a selective knockout of brain GLUT4 (BG4KO) was generated by crossing Nestin-Cre mice with GLUT4-floxed mice. BG4KO mice had a 99% reduction in GLUT4 protein expression throughout the brain. Despite normal feeding and fasting glycemia, BG4KO mice were glucose intolerant, demonstrated hepatic insulin resistance, and had reduced glucose uptake in the brain. In response to hypoglycemia, BG4KO mice had impaired glucose sensing, noted by impaired epinephrine and glucagon responses and impaired c-fos activation in the hypothalamic paraventricular nucleus. Moreover, in vitro glucose sensing of glucose-inhibitory neurons from the ventromedial hypothalamus was impaired in BG4KO mice. In summary, BG4KO mice are glucose intolerant, insulin resistant, and have impaired glucose sensing, indicating a critical role for brain GLUT4 in sensing and responding to changes in blood glucose.

SLC2A8 (GLUT8) is a mammalian trehalose transporter required for trehalose-induced autophagy

Trehalose is a disaccharide demonstrated to mitigate disease burden in multiple murine neurodegenerative models. We recently revealed that trehalose rapidly induces hepatic autophagy and abrogates hepatic steatosis by inhibiting hexose transport via the SLC2A family of facilitative transporters. Prior studies, however, postulate that intracellular trehalose is sufficient to induce cellular autophagy. The objective of the current study was to identify the means by which trehalose accesses the hepatocyte cytoplasm, and define the distal signaling mechanisms by which trehalose induces autophagy. We provide gas chromatographic/mass spectrometric, fluorescence microscopic and radiolabeled uptake evidence that trehalose traverses the plasma membrane via SLC2A8 (GLUT8), a homolog of the trehalose transporter-1 (Tret1). Moreover, GLUT8-deficient hepatocytes and GLUT8-deficient mice exposed to trehalose resisted trehalose-induced AMP-activated protein kinase (AMPK) phosphorylation and autophagic induction in vitro and in vivo. Although trehalose profoundly attenuated mTORC1 signaling, trehalose-induced mTORC1 suppression was insufficient to activate autophagy in the absence of AMPK or GLUT8. Strikingly, transient, heterologous Tret1 overexpression reconstituted autophagic flux and AMPK signaling defects in GLUT8-deficient hepatocyte cultures. Together, these data suggest that cytoplasmic trehalose access is carrier-mediated, and that GLUT8 is a mammalian trehalose transporter required for hepatocyte trehalose-induced autophagy and signal transduction.

The neuroenergetics of stress hormones in the hippocampus and implications for memory

Acute stress causes rapid release of norepinephrine (NE) and glucocorticoids (GCs), both of which bind to hippocampal receptors. This release continues, at varying concentrations, for several hours following the stressful event, and has powerful effects on hippocampally-dependent memory that generally promote acquisition and consolidation while impairing retrieval. Several studies have characterized the brain's energy usage both at baseline and during memory processing, but there are few data on energy requirements of memory processes under stressful conditions. Because memory is enhanced by emotional arousal such as during stress, it is likely that molecular memory processes under these conditions differ from those under non-stressful conditions that do not activate the hypothalamic-pituitary-adrenal (HPA) axis. Mobilization of peripheral and central energy stores during stress may increase hippocampal glucose metabolism that enhances salience and detail to facilitate memory enhancement. Several pathways activated by the HPA axis affect neural energy supply and metabolism, and may also prevent detrimental damage associated with chronic stress. We hypothesize that alterations in hippocampal metabolism during stress are key to understanding the effects of stress hormones on hippocampally-dependent memory formation. Second, we suggest that the effects of stress on hippocampal metabolism are bi-directional: within minutes, NE promotes glucose metabolism, while hours into the stress response GCs act to suppress metabolism. These bi-directional effects of NE and GCs on glucose metabolism may occur at least in part through direct modulation of glucose transporter-4. In contrast, chronic stress and prolonged elevation of hippocampal GCs cause chronically suppressed glucose metabolism, excitotoxicity and subsequent memory deficits.

HIV protease inhibitors: a review of molecular selectivity and toxicity

Highly active antiretroviral therapy (HAART) is recognized as the most effective treatment method for AIDS, and protease inhibitors play a very important role in HAART. However, poor bioavailability and unbearable toxicity are their common disadvantages. Thus, the development of safer and potentially promising protease inhibitors is eagerly needed. In this review, we introduced the chemical characteristics and associated side effects of HIV protease inhibitors, as well as the possible off-target mechanisms causing the side effects. From the chemical structures of HIV protease inhibitors and their possible off-target molecules, we could obtain hints for optimizing the molecular selectivity of the inhibitors, to provide help in the design of new compounds with enhanced bioavailability and reduced side effects.

In Silico Modeling-based Identification of Glucose Transporter 4 (GLUT4)-selective Inhibitors for Cancer Therapy

Tumor cells rely on elevated glucose consumption and metabolism for survival and proliferation. Glucose transporters mediating glucose entry are key proximal rate-limiting checkpoints. Unlike GLUT1 that is highly expressed in cancer and more ubiquitously expressed in normal tissues, GLUT4 exhibits more limited normal expression profiles. We have previously determined that insulin-responsive GLUT4 is constitutively localized on the plasma membrane of myeloma cells. Consequently, suppression of GLUT4 or inhibition of glucose transport with the HIV protease inhibitor ritonavir elicited growth arrest and/or apoptosis in multiple myeloma. GLUT4 inhibition also caused sensitization to metformin in multiple myeloma and chronic lymphocytic leukemia and a number of solid tumors suggesting the broader therapeutic utility of targeting GLUT4. This study sought to identify selective inhibitors of GLUT4 to develop a more potent cancer chemotherapeutic with fewer potential off-target effects. Recently, the crystal structure of GLUT1 in an inward open conformation was reported. Although this is an important achievement, a full understanding of the structural biology of facilitative glucose transport remains elusive. To date, there is no three-dimensional structure for GLUT4. We have generated a homology model for GLUT4 that we utilized to screen for drug-like compounds from a library of 18 million compounds. Despite 68% homology between GLUT1 and GLUT4, our virtual screen identified two potent compounds that were shown to target GLUT4 preferentially over GLUT1 and block glucose transport. Our results strongly bolster the utility of developing GLUT4-selective inhibitors as anti-cancer therapeutics.

Targeting the metabolic plasticity of multiple myeloma with FDA-approved ritonavir and metformin

PURPOSE

We have previously demonstrated that ritonavir targeting of glycolysis is growth inhibitory and cytotoxic in a subset of multiple myeloma cells. In this study, our objective was to investigate the metabolic basis of resistance to ritonavir and to determine the utility of cotreatment with the mitochondrial complex I inhibitor metformin to target compensatory metabolism.

EXPERIMENTAL DESIGN

We determined combination indices for ritonavir and metformin, impact on myeloma cell lines, patient samples, and myeloma xenograft growth. Additional evaluation in breast, melanoma, and ovarian cancer cell lines was also performed. Signaling connected to suppression of the prosurvival BCL-2 family member MCL-1 was evaluated in multiple myeloma cell lines and tumor lysates. Reliance on oxidative metabolism was determined by evaluation of oxygen consumption, and dependence on glutamine was assessed by estimation of viability upon metabolite withdrawal in the context of specific metabolic perturbations.

RESULTS

Ritonavir-treated multiple myeloma cells exhibited increased reliance on glutamine metabolism. Ritonavir sensitized multiple myeloma cells to metformin, effectively eliciting cytotoxicity both in vitro and in an in vivo xenograft model of multiple myeloma and in breast, ovarian, and melanoma cancer cell lines. Ritonavir and metformin effectively suppressed AKT and mTORC1 phosphorylation and prosurvival BCL-2 family member MCL-1 expression in multiple myeloma cell lines in vitro and in vivo.

CONCLUSIONS

FDA-approved ritonavir and metformin effectively target multiple myeloma cell metabolism to elicit cytotoxicity in multiple myeloma. Our studies warrant further investigation into repurposing ritonavir and metformin to target the metabolic plasticity of myeloma to more broadly target myeloma heterogeneity and prevent the reemergence of chemoresistant aggressive multiple myeloma.

Diabetes and HIV

The co-existence of diabetes mellitus and HIV infection poses significant challenges for both patient and physician. This article reviews the clinical problems, the implications for treatment plans and potential confusions that can arise when managing patients who have both conditions.

Isoform-selective inhibition of facilitative glucose transporters: elucidation of the molecular mechanism of HIV protease inhibitor binding

Pharmacologic HIV protease inhibitors (PIs) and structurally related oligopeptides are known to reversibly bind and inactivate the insulin-responsive facilitative glucose transporter 4 (GLUT4). Several PIs exhibit isoform selectivity with little effect on GLUT1. The ability to target individual GLUT isoforms in an acute and reversible manner provides novel means both to investigate the contribution of individual GLUTs to health and disease and to develop targeted treatment of glucose-dependent diseases. To determine the molecular basis of transport inhibition, a series of chimeric proteins containing transmembrane and cytosolic domains from GLUT1 and GLUT4 and/or point mutations were generated and expressed in HEK293 cells. Structural integrity was confirmed via measurement of N-[2-[2-[2-[(N-biotinylcaproylamino)ethoxy)ethoxyl]-4-[2-(trifluoromethyl)-3H-diazirin-3-yl]benzoyl]-1,3-bis(mannopyranosyl-4-yloxy)-2-propylamine (ATB-BMPA) labeling of the chimeric proteins in low density microsome fractions isolated from stably transfected 293 cells. Functional integrity was assessed via measurement of zero-trans 2-deoxyglucose (2-DOG) uptake. ATB-BMPA labeling studies and 2-DOG uptake revealed that transmembrane helices 1 and 5 contain amino acid residues that influence inhibitor access to the transporter binding domain. Substitution of Thr-30 and His-160 in GLUT1 to the corresponding positions in GLUT4 is sufficient to completely transform GLUT1 into GLUT4 with respect to indinavir inhibition of 2-DOG uptake and ATB-BMPA binding. These data provide a structural basis for the selectivity of PIs toward GLUT4 over GLUT1 that can be used in ongoing novel drug design.

HIV protease inhibitors and onset of cardiovascular diseases: a central role for oxidative stress and dysregulation of the ubiquitin-proteasome system

The successful roll-out of highly active antiretroviral therapy (HAART) has extended life expectancy and enhanced the overall well-being of HIV-positive individuals. There are, however, increased concerns regarding HAART-mediated metabolic derangements and its potential risk for cardiovascular diseases (CVD) in the long-term. Here certain classes of antiretroviral drugs such as the HIV protease inhibitors (PIs) are strongly implicated in this process. This article largely focuses on the direct PI-linked development of cardio-metabolic complications, and reviews the inter-linked roles of oxidative stress and the ubiquitin-proteasome system (UPS) as key mediators driving this process. It is proposed that PIs trigger reactive oxygen species (ROS) production that leads to serious downstream consequences such as cell death, impaired mitochondrial function, and UPS dysregulation. Moreover, we advocate that HIV PIs may also directly lower myocardial UPS function. The attenuation of cardiac UPS can initiate transcriptional changes that contribute to perturbed lipid metabolism, thereby fueling a pro-atherogenic milieu. It may also directly alter ionic channels and interfere with electrical signaling in the myocardium. Therefore HIV PI-induced ROS together with a dysfunctional UPS elicit detrimental effects on the cardiovascular system that will eventually result in the onset of heart diseases. Thus while HIV PIs substantially improve life expectancy and quality of life in HIV-positive patients, its longer-term side-effects on the cardiovascular system should lead to a) greater clinical awareness regarding its benefit-harm paradigm, and b) the development and evaluation of novel co-treatment strategies.

Endoproteolytic cleavage of TUG protein regulates GLUT4 glucose transporter translocation

To promote glucose uptake into fat and muscle cells, insulin causes the translocation of GLUT4 glucose transporters from intracellular vesicles to the cell surface. Previous data support a model in which TUG traps GLUT4-containing vesicles and tethers them intracellularly in unstimulated cells and in which insulin mobilizes this pool of vesicles by releasing this tether. Here we show that TUG undergoes site-specific endoproteolytic cleavage, which separates a GLUT4-binding, N-terminal region of TUG from a C-terminal region previously suggested to bind an intracellular anchor. Cleavage is accelerated by insulin stimulation in 3T3-L1 adipocytes and is highly dependent upon adipocyte differentiation. The N-terminal TUG cleavage product has properties of a novel 18-kDa ubiquitin-like modifier, which we call TUGUL. The C-terminal product is observed at the expected size of 42 kDa and also as a 54-kDa form that is released from membranes into the cytosol. In transfected cells, intact TUG links GLUT4 to PIST and also binds Golgin-160 through its C-terminal region. PIST is an effector of TC10α, a GTPase previously shown to transmit an insulin signal required for GLUT4 translocation, and we show using RNAi that TC10α is required for TUG proteolytic processing. Finally, we demonstrate that a cleavage-resistant form of TUG does not support highly insulin-responsive GLUT4 translocation or glucose uptake in 3T3-L1 adipocytes. Together with previous results, these data support a model whereby insulin stimulates TUG cleavage to liberate GLUT4 storage vesicles from the Golgi matrix, which promotes GLUT4 translocation to the cell surface and enhances glucose uptake.

Dyslipidemia in HIV-infected individuals

Metabolic complications continue to play a major role in the management of HIV infection. Dyslipidemia associated with HIV infection and with the use of combined antiretroviral therapy includes elevations in triglycerides, reduced high-density cholesterol, and variable increases in low-density and total cholesterol. The association between dyslipidemia and specific antiretroviral agents has been underscored. Multiple pathogenic mechanisms by which HIV and antiretroviral agents lead to dyslipidemia have been hypothesized, but they are still controversial. The potential clinical and pathological consequences of HIV-associated hyperlipidemia are not completely known, but several studies reported an increased risk of coronary artery disease in HIV-positive individuals receiving combined antiretroviral therapy. HIV-infected persons who have hyperlipidemia should be managed similarly to those without HIV infection in accordance with the National Cholesterol Education Program. Life style changes are the primary target. Statins and fibrates and/or modification in antiretroviral therapy are possible approaches to this problem.

HIV protease inhibitors act as competitive inhibitors of the cytoplasmic glucose binding site of GLUTs with differing affinities for GLUT1 and GLUT4

The clinical use of several first generation HIV protease inhibitors (PIs) is associated with the development of insulin resistance. Indinavir has been shown to act as a potent reversible noncompetitive inhibitor of zero-trans glucose influx via direct interaction with the insulin responsive facilitative glucose transporter GLUT4. Newer drugs within this class have differing effects on insulin sensitivity in treated patients. GLUTs are known to contain two distinct glucose-binding sites that are located on opposite sides of the lipid bilayer. To determine whether interference with the cytoplasmic glucose binding site is responsible for differential effects of PIs on glucose transport, intact intracellular membrane vesicles containing GLUT1 and GLUT4, which have an inverted transporter orientation relative to the plasma membrane, were isolated from 3T3-L1 adipocytes. The binding of biotinylated ATB-BMPA, a membrane impermeable bis-mannose containing photolabel, was determined in the presence of indinavir, ritonavir, atazanavir, tipranavir, and cytochalasin b. Zero-trans 2-deoxyglucose transport was measured in both 3T3-L1 fibroblasts and primary rat adipocytes acutely exposed to these compounds. PI inhibition of glucose transport correlated strongly with the PI inhibition of ATB-BMPA/transporter binding. At therapeutically relevant concentrations, ritonavir was not selective for GLUT4 over GLUT1. Indinavir was found to act as a competitive inhibitor of the cytoplasmic glucose binding site of GLUT4 with a K_I of 8.2 µM. These data establish biotinylated ATB-BMPA as an effective probe to quantify accessibility of the endofacial glucose-binding site in GLUTs and reveal that the ability of PIs to block this site differs among drugs within this class. This provides mechanistic insight into the basis for the clinical variation in drug-related metabolic toxicity.

Molecular mechanisms for insulin resistance in treated HIV-infection

Identification and characterization of the molecular mechanisms contributing to the high incidence of insulin resistance in HIV infected patients treated with combined antiretroviral therapy remains a critically important goal in the quest to improve the safety of antiretroviral treatment regimens. The use of in vitro model systems together with the investigation of drug-mediated effects on glucose homeostasis in animals and healthy human volunteers has provided important insight into the contribution of individual drugs to insulin resistance and affected cellular pathways. HIV protease inhibitor mediated blockade of glucose transport and nucleoside reverse transcriptase inhibitor mediated mitochondrial toxicity have been well characterized. Together with growing understanding of mediators of insulin resistance in non-HIV metabolic syndrome, additional cellular effects including the induction of endoplasmic reticulum and oxidative stress, altered adipocytokine secretion, and lipotoxicity have been integrated into this developing picture. Further elucidation of these mechanisms provides potential for the continued development of safer antiviral drugs and targeted treatment of insulin resistance in affected patients.

Disease registries on the nationwide health information network

BACKGROUND

Donation by individuals of their protected health information (PHI) for evidence-based research potentially benefits all individuals with disease through improved understandings of disease patterns. In the future, a better understanding of how disease features combine into unique patterns of disease will generate new disease classifications, supporting greater specificity in health management techniques. However, without large numbers of people who donate their PHI to disease registries designed for research, it is difficult for researchers to discover the existence of complex patterns or to create more specific evidence-based management techniques. In order to identify new opportunities in disease registry design, an analysis of the current stage of maturity of the newly created U.S. Nationwide Health Information Network (NwHIN) related to large-scale consumer donation of PHI is presented.

METHODS

Utilizing a use-case analysis methodology, the consumer-centric designs of the policies and technologies created for the NwHIN were examined for the potential to support consumer donations of PHI to research.

RESULTS

The NwHIN design has placed the enforcement point for the policy-based release of PHI over the Internet into a specialized gateway accessible to consumer authorization. However, current NwHIN policies leave the final decision regarding release of PHI for research to the health care providers rather than to the consumers themselves.

CONCLUSIONS

Should disease registries designed for research be established on the NwHIN, consumers might then directly authorize the donation of their PHI to these disease registries. However, under current NwHIN policies, consumer authorization does not guarantee release of PHI by health providers.

GS-8374, a novel HIV protease inhibitor, does not alter glucose homeostasis in cultured adipocytes or in a healthy-rodent model system

Adverse effects induced by HIV protease inhibitors (PIs) are a significant factor in limiting their clinical success. PIs directly contribute to peripheral insulin resistance and alterations in lipid metabolism. GS-8374 is a novel PI with potent antiretroviral activity and a favorable resistance profile. Here we report on the potential of GS-8374 to adversely affect glucose and lipid homeostasis. Acute effects of GS-8374 and control PIs on glucose uptake and lipid accumulation were assessed in vitro in mouse OP9 and primary human adipocytes, respectively. GS-8374 and atazanavir showed no effect on insulin-stimulated deoxyglucose uptake, whereas ritonavir and lopinavir caused significant reductions. Similarly, in vitro lipid accumulation was not significantly affected in adipocytes treated with either GS-8374 or atazanavir. In euglycemic-hyperinsulinemic clamp experiments performed in rats during acute infusion of therapeutic levels of PIs, sustained serum GS-8374 levels of 8 μM had no effect on peripheral glucose disposal (similar to the findings for atazanavir). Comparable serum levels of lopinavir and ritonavir produced acute 19% and 53% reductions in in vivo glucose disposal, respectively. In conclusion, similar to atazanavir, but unlike ritonavir and lopinavir, GS-8374 neither affects insulin-stimulated glucose uptake in adipocytes in culture nor acutely alters peripheral glucose disposal in a rodent model system. These results dissociate the antiretroviral activity of GS-8374 from adverse effects on insulin sensitivity observed with some of the first-generation PIs and provide further support for the use of these experimental systems in the preclinical evaluation of novel PIs.

Insulin-like growth factor-I-forkhead box O transcription factor 3a counteracts high glucose/tumor necrosis factor-α-mediated neuronal damage: implications for human immunodeficiency virus encephalitis

In HIV patients, antiretroviral medications trigger metabolic abnormalities, including insulin resistance. In addition, the inflammatory cytokine tumor necrosis factor-α (TNFα), which is elevated in human immunodeficiency virus encephalitis (HIVE), also induces insulin resistance and inflicts neuronal damage in vitro. In differentiated PC12 cells and rat cortical neurons, high glucose (HG; 25 mM) triggers reactive oxygen species (ROS) accumulation, contributing to the retraction of neuronal processes, with only a minimal involvement of neuronal apoptosis. In the presence of TNFα, HG-treated neurons undergo massive apoptosis. Because mammalian homolog of the Forkhead family of transcription factors, Forkhead box O transcription factor 3a (FOXO3a), controls ROS metabolism, we asked whether FOXO3a could affect the fate of differentiated neurons in the paradigm of HIVE. We observed FOXO3a nuclear translocation in HG-treated neuronal cultures, accompanied by partial loss of mitochondrial potential and gradual retraction of neuronal processes. Addition of TNFα to HG-treated neurons increased expression of the FOXO-dependent proapoptotic gene Bim, which resulted in extensive apoptotic death. Insulin-like growth factor-I (IGF-I) significantly lowered intracellular ROS, which was accompanied by IGF-I-mediated FOXO3a nuclear export and decrease in its transcriptional activity. The clinical relevance of these findings is supported by detection of nuclear FOXO3a in TUNEL-positive cortical neurons from HIVE, especially in brain areas characterized by elevated TNFα.

Effects of the HIV protease inhibitor ritonavir on GLUT4 knock-out mice

HIV protease inhibitors acutely block glucose transporters (GLUTs) in vitro, and this may contribute to altered glucose homeostasis in vivo. However, several GLUT-independent mechanisms have been postulated. To determine the contribution of GLUT blockade to protease inhibitor-mediated glucose dysregulation, the effects of ritonavir were investigated in mice lacking the insulin-sensitive glucose transporter GLUT4 (G4KO). G4KO and control C57BL/6J mice were administered ritonavir or vehicle at the start of an intraperitoneal glucose tolerance test and during hyperinsulinemic-euglycemic clamps. G4KO mice exhibited elevated fasting blood glucose compared with C57BL/6J mice. Ritonavir impaired glucose tolerance in control mice but did not exacerbate glucose intolerance in G4KO mice. Similarly, ritonavir reduced peripheral insulin sensitivity in control mice but not in G4KO mice. Serum insulin levels were reduced in vivo in ritonavir-treated mice. Ritonavir reduced serum leptin levels in C57BL/6J mice but had no effect on serum adiponectin. No change in these adipokines was observed following ritonavir treatment of G4KO mice. These data confirm that a primary effect of ritonavir on peripheral glucose disposal is mediated through direct inhibition of GLUT4 activity in vivo. The ability of GLUT4 blockade to contribute to derangements in the other molecular pathways that influence insulin sensitivity remains to be determined.

HIV protease inhibitors and insulin resistance: lessons from in-vitro, rodent and healthy human volunteer models

PURPOSE OF REVIEW

Although the use of HIV protease inhibitors is linked to the development of insulin resistance and other metabolic changes that greatly increase the risk for cardiovascular disease, the molecular mechanisms responsible remain incompletely understood. This review summarizes recent advances that have been made in understanding the relative contributions of individual protease inhibitors to both acute and chronic insulin resistance together with newly identified cellular mediators.

RECENT FINDINGS

Individual protease inhibitors, alone and in combination, have differing propensities to induce insulin resistance, reflecting relative differences in both affinities for identified molecular targets and pharmacokinetic profiles. Several of the most recent protease inhibitors approved for clinical use or in development appear to be less likely to induce insulin resistance. In addition to direct effects on glucose transporter-4 activity, induction of oxidative stress, proteosome inhibition, alteration of adipokine levels, and changes in suppressors of cytokine signaling-1 have been implicated.

SUMMARY

A better understanding of the propensity of individual HIV protease inhibitors to produce insulin resistance will allow the tailoring of individual treatment plans based upon overall risk for diabetes. The elucidation of the molecular mechanisms for alterations in glucose homeostasis will facilitate the development of newer generations of HIV protease inhibitors that maintain their clinical efficacy without contributing to the development of diabetes mellitus and other proatherogenic effects.

Serum retinol-binding protein 4 correlates with obesity, insulin resistance, and dyslipidemia in HIV-infected subjects receiving highly active antiretroviral therapy

Highly active antiretroviral therapy (HAART) contributes to the development of metabolic complications including dyslipidemia, insulin resistance (IR), and lipodystrophy (LD). Recent studies reported that retinol-binding protein 4 (RBP4) is associated with IR, dyslipidemia, and obesity in non-HIV-infected populations. The aim of this study was to evaluate the associations between RBP4 and LD or metabolic abnormalities in HIV-infected subjects receiving HAART. We performed a cross-sectional study with 113 HIV-infected subjects receiving HAART for more than 6 months. Body composition and abdominal fat were measured by bioelectrical impedance analysis and ultrasonography, and fasting serum RBP4 was measured by enzyme-linked immunosorbent assay. Retinol-binding protein 4 levels in subjects with LD were similar to those without LD (P = .839). Retinol-binding protein 4 had significantly positive correlations with waist circumference (r = 0.298, P = .002), waist-to-hip ratio (r = 0.336, P = .001), body mass index (r = 0.310, P = .002), total body fat mass (r = 0.323, P = .001), total cholesterol (r = 0.188, P = .048), log (triglyceride) (r = 0.269, P = .004), and log (homeostasis model assessment of IR) (r = 0.207, P = .036), and negative correlations with quantitative insulin sensitivity check index (r = -0.209, P = .034) after adjustment for age and sex. In stepwise multivariate linear regression analysis, waist-to-hip ratio was the most significant independent predictor of increased RBP4 (standardized beta = .351, P = .001). These results suggest that serum RBP4 is associated with obesity, IR, and dyslipidemia in HIV-infected subjects receiving HAART.

Acipimox, an inhibitor of lipolysis, attenuates atherogenesis in LDLR-null mice treated with HIV protease inhibitor ritonavir

OBJECTIVE

The advent of HIV protease inhibitors has greatly extended the life span of AIDS patients. With an aging HIV(+) population, the cardiometabolic side effects of these drugs are becoming increasingly important clinical concerns. The purpose of this study was to test the hypothesis that inhibition of adipose lipolysis will retard atherogenic lesion development induced by the antiviral protease inhibitors.

METHODS AND RESULTS

LDLR-null mice receiving ritonavir were compared with those receiving ritonavir plus lipolysis inhibitor acipimox or vehicle alone to determine how acipimox would affect ritonavir-induced atherogenesis. Intermittent high-fat high-cholesterol diet was used to facilitate optimal atheromatous lesion development. Drug effects were assessed as changes in aortic lesion score, plasma lipid and lipoprotein profile, body fat mass, and insulin-induced suppression of plasma fatty acid concentrations. Ritonavir increased aortic lesions, in association with decreased body fat mass, impaired antilipolysis action of insulin, and increased proatherogenic plasma lipoproteins. All these adverse effects were attenuated by cotreatment with acipimox.

CONCLUSIONS

Our results provide the first direct evidence that supports the hypothesis that dysregulation of adipose lipolysis is an important contributor to the proatherogenic role of selected HIV protease inhibitors.

Trends in the European HIV/AIDS epidemic: a perspective from Italy

The HIV/AIDS epidemic represents one of the major public-health challenges in present days. Despite the relevant improvement in the prognosis of HIV disease following the introduction of highly active antiretroviral therapy (HAART), numerous new challenges are progressively emerging as patient characteristics evolve. In this article, we give an insight into more actual topics in the HIV/AIDS epidemic in Italy and Europe, including recent epidemiological trends, emerging drug resistance and non-B-subtype circulation, the lights and shadows of HAART and the potential of HARRT to reduce sexual transmission of HIV.

Effects of switching from lopinavir/ritonavir to atazanavir/ritonavir on muscle glucose uptake and visceral fat in HIV-infected patients

OBJECTIVE

To determine the effects of switching from lopinavir/ritonavir (LPV/r) to atazanavir/ritonavir (ATV/r) on muscle glucose uptake, glucose homeostasis, lipids, and body composition.

METHODS

Fifteen HIV-infected men and women on a regimen containing LPV/r and with evidence of hyperinsulinemia and/or dyslipidemia were randomized to continue LPV/r or to switch to ATV/r (ATV 300 mg and ritonavir 100 mg daily) for 6 months. The primary endpoint was change in thigh muscle glucose uptake as measured by positron emission tomography. Secondary endpoints included abdominal visceral adipose tissue, fasting lipids, and safety parameters. The difference over time between treatment groups (treatment effect of ATV/r relative to LPV/r) was determined by repeated measures ANCOVA.

RESULTS

After 6 months, anterior thigh muscle glucose uptake increased significantly (treatment effect +18.2 +/- 5.9 micromol/kg per min, ATV/r vs. LPV/r, P = 0.035), and visceral adipose tissue area decreased significantly in individuals who switched to ATV/r (treatment effect -31 +/- 11 cm, ATV/r vs. LPV/r, P = 0.047). Switching to ATV/r significantly decreased triglyceride (treatment effect -182 +/- 64 mg/dl, ATV/r vs. LPV/r, P = 0.02) and total cholesterol (treatment effect -23 +/- 8 mg/dl, ATV/r vs. LPV/r, P = 0.01), whereas high-density lipoprotein and low-density lipoprotein did not change significantly. Fasting glucose also decreased significantly following switch to ATV/r (treatment effect -15 +/- 4 mg/dl, ATV/r vs. LPV/r, P = 0.002).

CONCLUSION

Switching from LPV/r to ATV/r significantly increases glucose uptake by muscle, decreases abdominal visceral adipose tissue, improves lipid parameters, and decreases fasting glucose over 6 months.

Prevalence and pathogenesis of diabetes mellitus in HIV-1 infection treated with combined antiretroviral therapy

Combined antiretroviral therapy (cART) in the treatment of HIV-1 infection confers significant survival benefit and, by immunoreconstitution, has altered the natural history of this life-threatening disease. Metabolic complications of cART include hyperlipidemia, insulin resistance, and lipodystrophy, with resultant increases in risk for type 2 diabetes and cardiovascular disease. These diseases will present new challenges in the management of HIV infection. This article reviews the prevalence of diabetes mellitus and its antecedents in HIV-infected patients treated with cART. It also reviews the current understanding of mechanisms involved in the pathogenesis of type 2 diabetes in cART considering insulin resistance and insulin secretion, both requisites for the development of type 2 diabetes mellitus.

Protease inhibitors used in the treatment of HIV+ induce beta-cell apoptosis via the mitochondrial pathway and compromise insulin secretion

Inclusion of HIV protease inhibitors (PIs) in the treatment of people living with HIV+ has markedly decreased mortality but also increased the incidence of metabolic abnormalities, causes of which are not well understood. Here, we report that insulinopenia is exacerbated when Zucker fa/fa rats are exposed to a PI for 7 wk, suggesting that chronic PI exposure adversely affects pancreatic islet beta-cell function. In support of this possibility, we find increased apoptosis, as reflected by TUNEL fluorescence analyses, and reduced insulin-secretory capacity in insulinoma cells and human pancreatic islet cells after in vitro exposures (48-96 h) to clinically relevant PIs (ritonavir, lopinavir, atazanavir, or tipranavir). Furthermore, pancreatic islets isolated from rats administered an HIV-PI for 3 wk exhibit greater cell death than islets isolated from vehicle-administered rats. The higher incidence of HIV-PI-induced cell death was associated with cleavage and, hence, activation of caspase-3 and poly(ADP)-ribose polymerase but not with activation of phospho-pancreatic endoplasmic reticulum (ER) kinase or induction of ER stress apoptotic factor C/EBP homologous protein. Exposure to the HIV-PIs, however, led to activation of mitochondria-associated caspase-9, caused a loss in mitochondrial membrane potential, and promoted the release of cytochrome c, suggesting that HIV-PIs currently in clinically use can induce beta-cell apoptosis by activating the mitochondrial apoptotic pathway. These findings therefore highlight the importance of considering beta-cell viability and function when assessing loss of glycemic control and the course of development of diabetes in HIV+ subjects receiving a protease inhibitor.

Diabetes mellitus, preexisting coronary heart disease, and the risk of subsequent coronary heart disease events in patients infected with human immunodeficiency virus: the Data Collection on Adverse Events of Anti-HIV Drugs (D:A:D Study)

BACKGROUND

Although guidelines in individuals not infected with the human immunodeficiency virus (HIV) consider diabetes mellitus (DM) to be a coronary heart disease (CHD) equivalent, there is little information on its association with CHD in those infected with HIV. We investigated the impact of DM and preexisting CHD on the development of a new CHD episode among 33,347 HIV-infected individuals in the Data Collection on Adverse Events of Anti-HIV Drugs (D:A:D Study).

METHODS AND RESULTS

Over 159,971 person-years, 698 CHD events occurred. After adjustment for gender, age, cohort, HIV transmission, ethnicity, family history of CHD, smoking, and calendar year, the rate of a CHD episode was 7.52 times higher (Poisson regression, 95% CI 6.02 to 9.39, P=0.0001) in those with preexisting CHD than in those without preexisting CHD, but it was only 2.41 times higher (95% CI 1.91 to 3.05, P=0.0001) in those with preexisting DM compared with those without DM. No statistical interactions were apparent between either diagnosis and sex; although older people with DM had an increased CHD rate compared with younger people, older people with preexisting CHD had a lower event rate. A statistically significant interaction between preexisting DM and CHD (P=0.003) suggested that the CHD rate in those with preexisting CHD and DM is lower than expected on the basis of the main effects alone.

CONCLUSIONS

DM and preexisting CHD are both important risk factors for CHD events in HIV-infected individuals. There is a need for targeted interventions to reduce the risk of CHD in both high-risk groups of HIV-infected individuals.

The role of protease inhibitors in the pathogenesis of HIV-associated lipodystrophy: cellular mechanisms and clinical implications

Metabolic complications associated with HIV infection and treatment frequently present as a relative lack of peripheral adipose tissue associated with dyslipidemia and insulin resistance. In this review we explain the connection between abnormalities of intermediary metabolism, observed either in vitro or in vivo, and this group of metabolic effects. We review molecular mechanisms by which the HIV protease inhibitor (PI) class of drugs may affect the normal stimulatory effect of insulin on glucose and fat storage. We then propose that both chronic inflammation from HIV infection and treatment with some drugs in this class trigger cellular homeostatic stress responses with adverse effects on intermediary metabolism. The physiologic outcome is such that total adipocyte storage capacity is decreased, and the remaining adipocytes resist further fat storage. The excess circulating and dietary lipid metabolites, normally "absorbed" by adipose tissue, are deposited ectopically in lean (muscle and liver) tissue, where they impair insulin action. This process leads to a pathologic cycle of lipotoxicity and lipoatrophy and a clinical phenotype of body fat distribution with elevated waist-to-hip ratio similar to the metabolic syndrome.

Hierarchical modeling gave plausible estimates of associations between metabolic syndrome and components of antiretroviral therapy

OBJECTIVE

Hierarchical modeling has been proposed as a solution to the multiple exposure problem. We estimate associations between metabolic syndrome and different components of antiretroviral therapy using both conventional and hierarchical models.

STUDY DESIGN AND SETTING

We use discrete time survival analysis to estimate the association between metabolic syndrome and cumulative exposure to 16 antiretrovirals from four drug classes. We fit a hierarchical model where the drug class provides a prior model of the association between metabolic syndrome and exposure to each antiretroviral.

RESULTS

One thousand two hundred and eighteen patients were followed for a median of 27 months, with 242 cases of metabolic syndrome (20%) at a rate of 7.5 cases per 100 patient years. Metabolic syndrome was more likely to develop in patients exposed to stavudine, but was less likely to develop in those exposed to atazanavir. The estimate for exposure to atazanavir increased from hazard ratio of 0.06 per 6 months' use in the conventional model to 0.37 in the hierarchical model (or from 0.57 to 0.81 when using spline-based covariate adjustment).

CONCLUSION

These results are consistent with trials that show the disadvantage of stavudine and advantage of atazanavir relative to other drugs in their respective classes. The hierarchical model gave more plausible results than the equivalent conventional model.

Therapy insight: Body-shape changes and metabolic complications associated with HIV and highly active antiretroviral therapy

Increasingly effective therapies for HIV infection are now available. These treatments, referred to collectively as highly active antiretroviral therapy, comprise various combinations of anti-HIV drugs from different drug classes. Recently, a range of metabolic complications have emerged as important toxicities in treated patients. Complications present as abnormalities of body-fat mass distribution in association with an often significant dyslipidemia and glucose homeostasis dysregulation. The body-shape changes, manifesting as peripheral lipoatrophy or central lipohypertrophy, can have a negative impact on quality of life and consequently on adherence to treatment. The combination of central lipohypertrophy, dyslipidemia and insulin resistance is associated with accelerated rates of atherosclerosis and other potentially significant long-term effects. The pathogenesis of these effects is complex and is still being actively investigated. Possible contributing factors relate to host characteristics, HIV viral parameters and specific effects of anti-HIV drugs on adipose-tissue biology and on intermediary metabolism. Management of these complications involves manipulation of the anti-HIV drugs using an understanding of their particular effects on lipid and glucose metabolism, in association with standard therapeutic interventions. Individualized approaches, taking into consideration quality-of-life issues, and assessment of potential cardiovascular risks, are now an important component of effective care of HIV-infected patients.

Zidovudine/lamivudine contributes to insulin resistance within 3 months of starting combination antiretroviral therapy

BACKGROUND

Patients with antiretroviral therapy (ART)-associated lipodystrophy frequently have disturbances in glucose metabolism associated with insulin resistance. It is not known whether changes in body composition are necessary for the development of these disturbances in ART-naive patients starting treatment with different combination ART regimens.

METHODS

Glucose metabolism and body composition were assessed before and after 3 months of ART in a prospective randomized clinical trial of HIV-1-positive ART-naive men taking lopinavir/ritonavir within either a nucleoside reverse transcriptase inhibitor (NRTI)-containing regimen (zidovudine/lamivudine; n = 11) or a NRTI-sparing regimen (nevirapine; n = 9). Glucose disposal, glucose production and lipolysis were measured after an overnight fast and during a hyperinsulinaemic-euglycaemic clamp using stable isotopes. Body composition was assessed by computed tomography and dual-energy X-ray absorptiometry.

RESULTS

In the NRTI-containing group, body composition did not change significantly in 3 months; insulin-mediated glucose disposal decreased significantly (25%; P < 0.001); and fasting glycerol turnover increased (22%; P < 0.005). Hyperinsulinaemia suppressed glycerol turnover equally before and after treatment. The disturbances in glucose metabolism were not accompanied by changes in adiponectin or other glucoregulatory hormones. In contrast, glucose metabolism did not change in the NRTI-sparing arm. Glucose disposal significantly differed over time between the arms (P < 0.01).

CONCLUSIONS

Treatment for 3 months with a NRTI-containing, but not a NRTI-sparing, regimen resulted in a 25% decrease in insulin-mediated glucose disposal and a 22% increase in fasting lipolysis. In the absence of discernable changes in body composition, NRTI may directly affect glucose metabolism, the mechanism by which remains to be elucidated.