Glutathione and cysteine in HIV-infected hemophiliacs

Prodrug approach for increasing cellular glutathione levels

Reduced glutathione (GSH) is the most abundant non-protein thiol in mammalian cells and the preferred substrate for several enzymes in xenobiotic metabolism and antioxidant defense. It plays an important role in many cellular processes, such as cell differentiation, proliferation and apoptosis. GSH deficiency has been observed in aging and in a wide range of pathologies, including neurodegenerative disorders and cystic fibrosis (CF), as well as in several viral infections. Use of GSH as a therapeutic agent is limited because of its unfavorable biochemical and pharmacokinetic properties. Several reports have provided evidence for the use of GSH prodrugs able to replenish intracellular GSH levels. This review discusses different strategies for increasing GSH levels by supplying reversible bioconjugates able to cross the cellular membrane more easily than GSH and to provide a source of thiols for GSH synthesis.

HIV-dementia, Tat-induced oxidative stress, and antioxidant therapeutic considerations

Oxidative stress is thought to play a role in the onset of dementia. HIV-dementia has recently been demonstrated to be associated with oxidative stress as indexed by increased protein and lipid peroxidation in the brain and cerebrospinal fluid compared to HIV non-demented patients. The HIV protein Tat induces neurotoxicity, and, more recently, Tat was found to induce oxidative stress directly and indirectly. The role of Tat in HIV-dementia and possible therapeutic strategies involving endogenous and exogenous antioxidants are discussed.

Plasma total glutathione concentrations in healthy pediatric and adult subjects

Glutathione, as a free radical scavenger, plays an important role in protecting cells against oxidative damage. Since aging is associated with decreased plasma glutathione levels, we investigated plasma concentrations of total glutathione (including the reduced and oxidized forms, tGSH=GSH+GSSG) and total cysteine in 129 healthy pediatric and adult subjects. Plasma tGSH concentrations were significantly lower in infants than in adults. There were no significant differences in plasma tGSH concentrations between the children and adult group. No significant differences in plasma total cysteine concentrations were found between any pediatric and adult group. We conclude that lower plasma tGSH levels in pediatric subjects may reflect greater oxidative stress during the neonatal and infant period.

Plasma cysteine deficiency and decreased reduction of nitrososulfamethoxazole with HIV infection

The aim of these studies was to determine whether HIV-infected patients have a plasma thiol deficiency and whether this is associated with decreased detoxification of the toxic metabolites of sulfamethoxazole. Reduced, oxidized, protein-bound, and total thiol levels were measured in 33 HIV-positive patients and 33 control subjects by an HPLC method utilizing the fluorescent probe bromobimane. The reduction of sulfamethoxazole hydroxylamine and nitrososulfamethoxazole by plasma and the plasma redox balance in the presence of nitrososulphamethoxazole were also determined by HPLC. Reduced plasma cysteine was significantly (p<0.0001) lower in HIV-positive patients (13.0+/-3.0 microM) when compared with control subjects (16.9+/-3.0 microM). Although there was no difference in oxidized, protein-bound, and total cysteine, the thiol/disulfide ratios were lower in HIV-positive patients. Reduced homocysteine was elevated in patients. Plasma from HIV-positive patients was less able to detoxify nitrososulfamethoxazole than control plasma. These findings show that the disturbance in redox balance in HIV-positive patients may alter metabolic detoxification capacity, and thereby predispose to sulfamethoxazole hypersensitivity.

Plasma total glutathione concentrations in epileptic patients taking anticonvulsants

Glutathione plays an important role in protecting cells against oxidative damage as a free radical scavenger. Since several anticonvulsants have been associated with decreased intrahepatic glutathione levels, we investigated plasma concentrations of total glutathione (including reduced and oxidized forms, tGSH=GSH+GSSG) in 45 epileptic patients taking anticonvulsant drugs. Plasma tGSH concentrations were significantly lower than in controls in patients treated with carbamazepine or phenytoin monotherapy, or with multiple drugs. Plasma tGSH concentrations in patients treated with valproic acid and in patients treated with phenobarbital did not differ significantly from those in controls. In no patient group was a significant correlation evident between duration of treatment or drug concentration and plasma tGSH concentration. No significant differences in plasma total cysteine concentrations were found between any patient group and controls. We conclude that some anticonvulsant drugs can lower plasma tGSH levels, reflecting treatment-related oxidative stress.

Genetic and metabolic control of the mitochondrial transmembrane potential and reactive oxygen intermediate production in HIV disease

Redox mechanims play important roles in replication of human immunodeficiency virus type 1 (HIV-1) and cellular susceptibility to apoptosis signals. Viral replication and accelerated turnover of CD4+ T cells occur throughout a prolonged asymptomatic phase in patients infected by HIV-1. Disease development is associated with steady loss of CD4+ T cells by apoptosis, increased rate of opportunistic infections and lymphoproliferative diseases, disruption of energy metabolism, and generalized wasting. Such pathological states are preceded by: (i) depletion of intracellular antioxidants, glutathione (GSH) and thioredoxin (TRX), (ii) increased reactive oxygen species (ROS) production, and (iii) changes in mitochondrial transmembrane potential (deltapsi(m)). Disruption of deltapsi(m) appears to be the point of no return in the effector phase of apoptosis. Viral proteins Tat, Nef, Vpr, protease, and gp120, have been implicated in initiation and/or intensification of oxidative stress and disruption of deltapsi(m). Redox-sensitive transcription factors, NF-kappaB, AP-1, and p53, support expression of viral genes and proinflammatory lymphokines. ROS regulate apoptosis signaling through Fas, tumor necrosis factor (TNF), and related cell death receptors, as well as the T-cell receptor. Oxidative stress in HIV-infected donors is accompanied by increased glucose utilization both on the cellular and organismal levels. Generation of GSH and TRX from their corresponding oxidized forms is dependent on NADPH provided through the pentose phosphate pathway of glucose metabolism. This article seeks to delineate the genetic and metabolic bases of HIV-induced oxidative stress. Such understanding should lead to development of effective antioxidant therapies in HIV disease.

Management of HIV-infected pregnant patients in malaria-endemic areas: therapeutic and safety considerations in concomitant use of antiretroviral and antimalarial agents

Chemotherapy in pregnancy is an intricate process requiring prudent use of pharmacologic agents. Malarial infection during pregnancy is often fatal, and prophylaxis against the causative parasite necessitates rational therapeutic intervention. Various agents have been used for prophylaxis against malaria during pregnancy, including chloroquine, mefloquine, proguanil, pyrimethamine, and pyrimethamine-sulfadoxine. Use of these agents has been based on a risk-benefit criterion, without appropriate toxicologic or teratologic evaluation. Some of the aforementioned prophylactic agents have been shown to alter glutathione levels and may exacerbate the oxidation-reduction imbalance attendant on HIV infection. HIV-infected patients traveling to or residing in malaria-endemic areas require protection from malarial infection to avoid placing themselves in double jeopardy. Zidovudine (AZT) is recommended for the prevention of vertical transmission of HIV-1 from mother to child. Other agents, such as lamivudine alone or in combination with AZT, nevirapine, or the HIV-1 protease inhibitors, are either being considered or are currently undergoing trials for use in preventing vertical transmission of HIV-1 or managing HIV infection in infants and children. Although the potential for antimalarial agents to cause congenital malformations is low when they are used alone, their ability to cause problems when combined with antiretroviral drugs needs to be evaluated. In developing countries that have high birth rates, a high endemicity of malaria, and alarming rates of new cases of HIV, prophylaxis against both diseases with combination agents during pregnancy is a challenge.

Threonine and methionine are limiting amino acids for protein synthesis in patients with AIDS

This study was conducted to identify the most rate-limiting amino acids for whole-body protein synthesis in acquired immunodeficiency syndrome (AIDS) patients. We postulated that an essential amino acid that would be rate limiting in AIDS should have a low basal plasma concentration and should remain at a low level during amino acid infusion. Seven male AIDS patients (median age 37 y, CD4 cell count: 76 mm-3) without any clinically active opportunistic infection during the month before the experiment were infused intravenously with a complete amino acid-glucose mixture for 2.5 h. Eight healthy volunteers were used as controls. Before the infusion, the concentrations of most free essential amino acids (methionine, threonine, histidine, isoleucine, leucine and tryptophan) were significantly lower (P < 0.05) in AIDS patients than in controls. Most plasma free essential amino acids increased significantly during infusion. However, the absolute increase above basal levels for threonine, valine, lysine, (P < 0.05) and methionine (P < 0.073) was smaller in AIDS patients than in control subjects. Thus, threonine and possibly methionine may be rate limiting for whole-body protein synthesis in AIDS patients, suggesting that there are selective amino acid requirements in patients with AIDS.

Molecular ordering in HIV-induced apoptosis. Oxidative stress, activation of caspases, and cell survival are regulated by transaldolase

Dysregulated apoptosis may underlie the etiology of T cell depletion by human immunodeficiency virus type 1 (HIV-1). We show that HIV-induced apoptosis is preceded by an exponential increase in reactive oxygen intermediates (ROIs) produced in mitochondria. This leads to caspase-3 activation, phosphatidylserine (PS) externalization, and GSH depletion. Since mitochondrial ROI levels are regulated by the supply of NADPH from the pentose phosphate pathway (PPP), the effect of transaldolase (TAL), a key enzyme of PPP, was investigated. Jurkat and H9 human CD4+ T cells were transfected with TAL expression vectors oriented in the sense or antisense direction. TAL overexpression down-regulated glucose-6-phosphate dehydrogenase activities and GSH levels. Alternatively, decreased TAL expression up-regulated glucose-6-phosphate dehydrogenase activities and GSH levels. HIV-induced 1) mitochondrial ROI production, 2) caspase-3 activation, 3) proteolysis of poly(ADP-ribose) polymerase, and 4) PS externalization were accelerated in cells overexpressing TAL. In contrast, suppression of TAL abrogated these four activities. Thus, susceptibility to HIV-induced apoptosis can be regulated by TAL through controlling the balance between mitochondrial ROI production and the metabolic supply of reducing equivalents by the PPP. The dominant effect of TAL expression on oxidative stress, caspase activation, PS externalization, and cell death suggests that this balance plays a pivotal role in HIV-induced apoptosis.