Effects of wheatgerm agglutinin and aging on the regional brain uptake of HIV-1GP120

Legume Lectins with Different Specificities as Potential Glycan Probes for Pathogenic Enveloped Viruses

Pathogenic enveloped viruses are covered with a glycan shield that provides a dual function: the glycan structures contribute to virus protection as well as host cell recognition. The three classical types of N-glycans, in particular complex glycans, high-mannose glycans, and hybrid glycans, together with some O-glycans, participate in the glycan shield of the Ebola virus, influenza virus, human cytomegalovirus, herpes virus, human immunodeficiency virus, Lassa virus, and MERS-CoV, SARS-CoV, and SARS-CoV-2, which are responsible for respiratory syndromes. The glycans are linked to glycoproteins that occur as metastable prefusion glycoproteins on the surface of infectious virions such as gp120 of HIV, hemagglutinin of influenza, or spike proteins of beta-coronaviruses. Plant lectins with different carbohydrate-binding specificities and, especially, mannose-specific lectins from the Vicieae tribe, such as pea lectin and lentil lectin, can be used as glycan probes for targeting the glycan shield because of their specific interaction with the α1,6-fucosylated core Man3GlcNAc2, which predominantly occurs in complex and hybrid glycans. Other plant lectins with Neu5Ac specificity or GalNAc/T/Tn specificity can also serve as potential glycan probes for the often sialylated complex glycans and truncated O-glycans, respectively, which are abundantly distributed in the glycan shield of enveloped viruses. The biomedical and therapeutical potential of plant lectins as antiviral drugs is discussed.

Role of Oxidative Stress in HIV-1-Associated Neurocognitive Disorder and Protection by Gene Delivery of Antioxidant Enzymes

HIV encephalopathy covers a range of HIV-1-related brain dysfunction. In the Central Nervous System (CNS), it is largely impervious to Highly Active AntiRetroviral Therapy (HAART). As survival with chronic HIV-1 infection improves, the number of people harboring the virus in their CNS increases. Neurodegenerative and neuroinflammatory changes may continue despite the use of HAART. Neurons themselves are rarely infected by HIV-1, but HIV-1 infects resident microglia, periventricular macrophages, leading to increased production of cytokines and to release of HIV-1 proteins, the most likely neurotoxins, among which are the envelope glycoprotein gp120 and HIV-1 trans-acting protein Tat. Gp120 and Tat induce oxidative stress in the brain, leading to neuronal apoptosis/death. We review here the role of oxidative stress in animal models of HIV-1 Associated Neurocognitive Disorder (HAND) and in patients with HAND. Different therapeutic approaches, including clinical trials, have been used to mitigate oxidative stress in HAND. We used SV40 vectors for gene delivery of antioxidant enzymes, Cu/Zn superoxide dismutase (SOD1), or glutathione peroxidase (GPx1) into the rat caudate putamen (CP). Intracerebral injection of SV (SOD1) or SV (GPx1) protects neurons from apoptosis caused by subsequent inoculation of gp120 and Tat at the same location. Vector administration into the lateral ventricle or cisterna magna protects from intra-CP gp120-induced neurotoxicity comparably to intra-CP vector administration. These models should provide a better understanding of the pathogenesis of HIV-1 in the brain as well as offer new therapeutic avenues.

Blood-brain barrier abnormalities caused by HIV-1 gp120: mechanistic and therapeutic implications

The blood-brain barrier (BBB) is compromised in many systemic and CNS diseases, including HIV-1 infection of the brain. We studied BBB disruption caused by HIV-1 envelope glycoprotein 120 (gp120) as a model. Exposure to gp120, whether acute [by direct intra-caudate-putamen (CP) injection] or chronic [using SV(gp120), an experimental model of ongoing production of gp120] disrupted the BBB, and led to leakage of vascular contents. Gp120 was directly toxic to brain endothelial cells. Abnormalities of the BBB reflect the activity of matrix metalloproteinases (MMPs). These target laminin and attack the tight junctions between endothelial cells and BBB basal laminae. MMP-2 and MMP-9 were upregulated following gp120-injection. Gp120 reduced laminin and tight junction proteins. Reactive oxygen species (ROS) activate MMPs. Injecting gp120 induced lipid peroxidation. Gene transfer of antioxidant enzymes protected against gp120-induced BBB abnormalities. NMDA upregulates the proform of MMP-9. Using the NMDA receptor (NMDAR-1) inhibitor, memantine, we observed partial protection from gp120-induced BBB injury. Thus, (1) HIV-envelope gp120 disrupts the BBB; (2) this occurs via lesions in brain microvessels, MMP activation and degradation of vascular basement membrane and vascular tight junctions; (3) NMDAR-1 activation plays a role in this BBB injury; and (4) antioxidant gene delivery as well as NMDAR-1 antagonists may protect the BBB.

Brain endothelial cell-cell junctions: how to "open" the blood brain barrier

The blood-brain barrier (BBB) is a highly specialized structural and biochemical barrier that regulates the entry of blood-borne molecules into brain, and preserves ionic homeostasis within the brain microenvironment. BBB properties are primarily determined by junctional complexes between the cerebral endothelial cells. These complexes are comprised of tight and adherens junctions. Such restrictive angioarchitecture at the BBB reduces paracellular diffusion, while minimal vesicle transport activity in brain endothelial cells limits transcellular transport. Under normal conditions, this largely prevents the extravasation of large and small solutes (unless specific transporters are present) and prevents migration of any type of blood-borne cell. However, this is changed in many pathological conditions. There, BBB disruption (“opening”) can lead to increased paracellular permeability, allowing entry of leukocytes into brain tissue, but also contributing to edema formation. In parallel, there are changes in the endothelial pinocytotic vesicular system resulting in the uptake and transfer of fluid and macromolecules into brain parenchyma. This review highlights the route and possible factors involved in BBB disruption in a variety of neuropathological disorders (e.g. CNS inflammation, Alzheimer’s disease, Parkinson’s disease, epilepsy). It also summarizes proposed signal transduction pathways that may be involved in BBB “opening”.

Blood-brain barrier abnormalities caused by exposure to HIV-1 gp120--protection by gene delivery of antioxidant enzymes

HIV-1 effects on the blood-brain barrier (BBB) structure and function are still poorly understood in animal models based on direct administration of recombinant HIV proteins. We therefore injected HIV-1 envelope glycoprotein, gp120, into rat caudate-putamens (CPs) and examined vascular integrity and function. Gp120 coimmunostained with endothelial cell marker, CD31. It induced apoptosis of endothelial cells in vitro and in vivo. BBB function was assessed by administering Evans Blue (EB) intravenously before injecting gp120. EB leaked near the site of gp120 administration. Within 1h after intra-CP gp120 injection, structures positive for endothelial markers ICAM-1 and RECA-1 were greatly decreased. Vascular density assessed by laminin immunostaining remained decreased 1 month after gp120 injection. RECA-1-positive cells expressed hydroxynonenal, a marker of lipid peroxidation and rSV40-mediated gene delivery of antioxidant enzymes protected the BBB from gp120-related injury. Extravasated IgG accumulated following intra-CP SV(gp120) injection, an experimental model of continuing gp120 exposure. Thus: acute and chronic exposure to gp120 disrupts the BBB; gp120-mediated BBB abnormalities are related to lesions of brain microvessels; and gp120 is directly toxic to brain endothelial cells.

Administration of sesamol improved blood-brain barrier function in streptozotocin-induced diabetic rats

Uncontrolled or poorly controlled blood glucose during diabetes is an important factor in worsened vascular function. While evidence suggests that hyperglycemia-induced oxidative stress plays a prominent role in development of microangiopathy of the retina, kidney, and nerves, the role oxidative stress plays on blood-brain barrier (BBB) function and structure has lagged behind. In this study, a natural antioxidant, sesamol, was administered to streptozotocin (STZ)-induced diabetic rats to examine the role that oxidative stress plays on BBB structure and function. Experiments were conducted at 56 days after STZ injection. Male Sprague-Dawley rats randomly were divided into four treatment groups CON--control; STZ--STZ-induced diabetes; CON + S--control + sesamol; STZ + S--STZ-induced diabetes + sesamol. Functional and structural changes to the BBB were measured by in situ brain perfusion and western blot analysis of changes in tight junction protein expression. Oxidative stress markers were visualized by fluorescent confocal microscopy and assayed by spectrophotometric analysis. Results demonstrated that the increased BBB permeability observed in STZ-induced diabetic rats was attenuated in STZ + S rats to levels observed in CON. Sesamol treatment reduced the negative impact of STZ-induced diabetes on tight junction protein expression in isolated cerebral microvessels. Oxidative stress markers were elevated in STZ as compared to CON. STZ + S displayed an improved antioxidant capacity which led to a reduced expression of superoxide and peroxynitrite and reduced lipid peroxidation. In conclusion, this study showed that sesamol treatment enhanced antioxidant capacity of the diabetic brain and led to decreased perturbation of hyperglycemia-induced changes in BBB structure and function.

NeuroAIDS: characteristics and diagnosis of the neurological complications of AIDS

The neurological complications of AIDS (NeuroAIDS) include neurocognitive impairment and HIV-associated dementia (HAD; also known as AIDS dementia and HIV encephalopathy). HAD is the most significant and devastating central nervous system (CNS) complications associated with HIV infection. Despite recent advances in our knowledge of the clinical features, pathogenesis, and neurobiological aspects of HAD, it remains a formidable scientific and therapeutic challenge. An understanding of the mechanisms of HIV neuroinvasion, CNS proliferation, and HAD pathogenesis provide a basis for the interpretation of the diagnostic features of HAD and its milder form, HIV-associated minor cognitive/motor disorder (MCMD). Current diagnostic strategies are associated with significant limitations, but it is hoped that the use of biomarkers may assist researchers and clinicians in predicting the onset of the disease process and in evaluating the effects of new therapies.

Developmental changes of leptin receptors in cerebral microvessels: unexpected relation to leptin transport

The adipokine leptin participates not only in the regulation of feeding and obesity in adults but also in neonatal development. It crosses the blood-brain barrier (BBB) by receptor-mediated transport. Leptin concentrations in blood differ between neonates and adults. We determined the developmental changes of leptin receptor subtypes in the cerebral microvessels composing the BBB and examined their expected correlation with leptin transport across the BBB. Total RNA was extracted from enriched cerebral microvessels of mice 1, 7, 14, and 60 d of age for real-time RT-PCR analysis of leptin receptor subtypes. In cerebral microvessels from neonates, ObRa, ObRb, ObRc, and ObRe mRNA were all higher than in adults, but ObRd was not detectable. Hypothalamus showed similar age-related changes except for ObRb, which was higher in adults. The homologous receptor gp130 did not show significant age-related changes in either region. Despite the increase of leptin receptors, leptin permeation across the BBB after iv injection was less in the neonates. In situ brain perfusion with blood-free buffer showed no significant difference in the brain uptake of leptin between neonates and adults, indicating an antagonistic role of leptin-binding proteins in the circulation, especially the soluble receptor ObRe. The results are consistent with our previous finding that ObRe antagonizes leptin endocytosis in cultured endothelia and transport from blood to brain in mice. Overall, the developmental changes observed for leptin receptors unexpectedly failed to correlate with the entry of leptin into brain, and this may indicate different functions of the receptors in neonates and adults.

Agrarian diet and diseases of affluence--do evolutionary novel dietary lectins cause leptin resistance?

BACKGROUND

The global pattern of varying prevalence of diseases of affluence, such as obesity, cardiovascular disease and diabetes, suggests that some environmental factor specific to agrarian societies could initiate these diseases.

PRESENTATION OF THE HYPOTHESIS

We propose that a cereal-based diet could be such an environmental factor. Through previous studies in archaeology and molecular evolution we conclude that humans and the human leptin system are not specifically adapted to a cereal-based diet, and that leptin resistance associated with diseases of affluence could be a sign of insufficient adaptation to such a diet. We further propose lectins as a cereal constituent with sufficient properties to cause leptin resistance, either through effects on metabolism central to the proper functions of the leptin system, and/or directly through binding to human leptin or human leptin receptor, thereby affecting the function.

TESTING THE HYPOTHESIS

Dietary interventions should compare effects of agrarian and non-agrarian diets on incidence of diseases of affluence, related risk factors and leptin resistance. A non-significant (p = 0.10) increase of cardiovascular mortality was noted in patients advised to eat more whole-grain cereals. Our lab conducted a study on 24 domestic pigs in which a cereal-free hunter-gatherer diet promoted significantly higher insulin sensitivity, lower diastolic blood pressure and lower C-reactive protein as compared to a cereal-based swine feed. Testing should also evaluate the effects of grass lectins on the leptin system in vivo by diet interventions, and in vitro in various leptin and leptin receptor models. Our group currently conducts such studies.

IMPLICATIONS OF THE HYPOTHESIS

If an agrarian diet initiates diseases of affluence it should be possible to identify the responsible constituents and modify or remove them so as to make an agrarian diet healthier.

Human immunodeficiency virus type 1 transport across the in vitro mouse brain endothelial cell monolayer

Human immunodeficiency virus type 1 (HIV-1) is associated with a neuroinflammatory dementia. Cognitive impairment remains a common complication of late-stage HIV-1 infection. Previous studies have shown that entry of HIV-1 into the central nervous system (CNS) occurs soon after infection. For these reasons, it is important to understand how HIV-1 crosses the BBB. We used primary mouse brain microvessel endothelial cell (MBEC) monolayer models to study interactions between brain endothelial cells and radioactively labeled HIV-1 CL4 (131I-HIV-1), which had been rendered noninfectious with aldithiol, and compared to radioactively labeled bovine serum albumin (131I-BSA or 125I-BSA) and detected HIV-1 on MBEC monolayer with electron microscopic analysis. The permeability of the monolayers to HIV-1 was measured by determining the percent material transported (PMT). Luminal to abluminal PMT of 131I-HIV-1 was 4.65 times greater than that of the much smaller 131I-BSA, showing that the MBEC monolayer is more permeable to HIV-1 than to BSA. Electron microscopy showed that HIV-1 was transported through a trans-cellular pathway from luminal side to basolateral space with some virus associated with the nucleus. Unlabeled HIV-1 did not affect the transport of 131I-HIV-1 or break down the MBEC monolayer. Wheatgerm agglutinin (WGA) increased 131I-HIV-1 penetration across the MBEC monolayer, consistent with absorptive endocytosis as the mechanism for HIV-1 penetration. The enhanced transport of HIV-1 was unidirectional, as the abluminal to luminal PMT of 131I-HIV-1 was not different from that of BSA nor enhanced by WGA. Characterization of the radioactivity transported from the luminal to abluminal chamber on Sepharose 4B-200 columns showed the transported radioactivity represented intact virus. MBEC monolayers preloaded from the luminal surface with 131I-HIV-1 showed most of the virus was retained by the endothelial cells, while the remainder was effluxed mainly to the luminal surface. MBEC monolayers preloaded from the abluminal surface with 131I-HIV-1 retained little virus and most of the virus was effluxed mainly to the abluminal surface. In conclusion, cell-free, intact 131I-HIV-1 crossed brain endothelial cell monolayers unidirectionally in the luminal to abluminal direction through an adsorptive endocytotic pathway. HIV-1 taken up from luminal side by monolayers of brain endothelial cells was mainly released to the luminal side. HIV-1 efflux mechanisms are different from influx mechanisms.

Permeability of the blood–brain barrier to HIV-1 Tat

Infection with human immunodeficiency virus-1 (HIV-1) is associated with dysfunctions of the central nervous system (CNS). HIV-1 induces its effects on the CNS by a variety of mechanisms, including by shedding the neurotoxic viral proteins such as gp120 and Tat. Both HIV-1 and gp120 have been shown to cross the blood-brain barrier (BBB). It is has not been determined, however, whether blood-borne Tat can cross the BBB. Here, we found that Tat crosses the BBB by a nonsaturable mechanism with a unidirectional influx rate of about 0.490 microl/g/min. About 0.126% of an intravenous dose of Tat enters each g of brain. Radioactively labeled albumin injected simultaneously did not cross the BBB. The hypothalamus, occipital cortex, and hippocampus were the regions of the brain most permeable to Tat. Nonsaturable brain-to-blood efflux also occurred, most likely with reabsorption into the blood of the cerebrospinal fluid. In conclusion, we found that Tat crossed the BBB bidirectionally. Such permeability could provide a mechanism by which Tat produced on one side of the BBB could affect neural or immune function on the other side.

Studies on the joint cytotoxicity of Wheat Germ Agglutinin and monensin

Wheat Germ Agglutinin (WGA) cytotoxicity has been studied using two human leukemia cell lines, Molt3 and K562, and human peripheral blood mononuclear cells (PBMC). In spite of similar binding at the cell surface, WGA was found to promote cell death to a different extent in Molt3, K562 and PBMC and to induce different death events leading to apoptosis in Molt3 and either apoptosis and necrosis in K562 cells and PBMC. In Molt3 but not in K562 cells, WGA cytotoxicity could be potentiated 66-200 fold by 50 nM monensin, a carboxylic ionophore that perturbs the intracellular trafficking of endocytosed molecules. Synergism between the cytotoxic activities of WGA and monensin was demonstrated in Molt3 cells by comparing non toxic, or slightly toxic, doses of WGA and monensin alone or in combination. These results show that the cytotoxic effect of WGA is dependent on internalisation events which may differ among the cell lines used. WGA and monensin can enter the human diet being a component of wheat germ and an antibiotic used for zootechnic reasons in the bioindustry, respectively. These data reveal the synergistic effect between two dietary molecules, otherwise per se toxic at much higher concentrations, with possible implications for human and animal health.

HIV-1 envelope glycoprotein 120 increases intercellular adhesion molecule-1 expression by human endothelial cells

Human immunodeficiency virus type 1 (HIV-1) infection is often associated with central nervous system damage and vascular complications. However, the mechanisms of this association are largely unknown. We examined the effect of HIV-1 envelope glycoprotein 120 (gp120) on cell adhesion molecule expression by endothelial cells. We found, for the first time, that both soluble and membrane-bound gp120 could significantly increase the expression of human endothelial intercellular adhesion molecule-1 (ICAM-1) at both mRNA and protein levels, but not vascular cell adhesion molecule-1 and E-selectin. The specificity of gp120-mediated response was demonstrated by blocking experiments using a specific monoclonal antibody against gp120, which successfully abolished the gp120-mediated increase of ICAM-1 expression. Furthermore, there was a significant increase of human monocytic cell line THP-1 adherence onto the gp120-treated endothelial monolayers. This increased cell adhesion was effectively blocked by either anti-gp120 or anti-ICAM antibodies. These findings suggest that HIV-1 gp120-mediated endothelial ICAM-1 expression could be one of the important mechanisms of HIV-1 pathogenesis.