Gary W. Pace

The role of oxidative stress in HIV disease

Evidence has accumulated suggesting that HIV-infected patients are under chronic oxidative stress. Perturbations to the antioxidant defense system, including changes in levels of ascorbic acid, tocopherols, carotenoids, selenium, superoxide dismutase, and glutathione, have been observed in various tissues of these patients. Elevated serum levels of hydroperoxides and malondialdehyde also have been noted and are indicative of oxidative stress during HIV infection. Indications of oxidative stress are observed in asymptomatic HIV-infected patients early in the course of the disease. Oxidative stress may contribute to several aspects of HIV disease pathogenesis, including viral replication, inflammatory response, decreased immune cell proliferation, loss of immune function, apoptosis, chronic weight loss, and increased sensitivity to drug toxicities. Glutathione may play a role in these processes, and thus, agents that replete glutathione may offer a promising treatment for HIV-infected patients. Clinical studies are underway to evaluate the efficacy of the glutathione-repleting agents, L-2-oxothiazolidine-4-carboxylic acid (OTC) and N-acetylcysteine (NAC), in HIV-infected patients.

Rapid Expansion from Supercritical to Aqueous Solution to Produce Submicron Suspensions of Water‐Insoluble Drugs

Stable suspensions of submicron particles of cyclosporine, a water‐insoluble drug, have been produced by rapid expansion from supercritical to aqueous solution (RESAS). To minimize growth of the cyclosporine particles, which would otherwise occur in the free jet expansion, the solution was sprayed into an aqueous Tween‐80 (Polysorbate‐80) solution. Steric stabilization by the surfactant impedes particle growth and agglomeration. The particles were an order of magnitude smaller than those produced by RESS into air without the surfactant solution. Concentrations as high as 38 mg/mL for 400−700 nm particles were achieved in a 5.0% (w/w) Tween‐80 solution.

Phospholipid-stabilized nanoparticles of cyclosporine A by rapid expansion from supercritical to aqueous solution.

The purpose of this research was to form stable suspensions of submicron particles of cyclosporine A, a water-insoluble drug, by rapid expansion from supercritical to aqueous solution (RESAS). A solution of cyclosporine A in CO2 was expanded into an aqueous solution containing phospholipid vesicles mixed with nonionic surfactants to provide stabilization against particle growth resulting from collisions in the expanding jet. The products were evaluated by measuring drug loading with high performance liquid chromatography (HPLC), particle sizing by dynamic light scattering (DLS), and particle morphology by transmission electron microscopy (TEM) and x-ray diffraction. The ability of the surfactant molecules to orient at the surface of the particles and provide steric stabilization could be manipulated by changing process variables including temperature and suspension concentration. Suspensions with high payloads (up to 54 mg/mL) could be achieved with a mean diameter of 500 nm and particle size distribution ranging from 40 to 920 nm. This size range is several hundred nanometers smaller than that produced by RESAS for particles stabilized by Tween 80 alone. The high drug payloads (≈10 times greater than the equilibrium solubility), the small particle sizes, and the long-term stability make this process attractive for development.

Development of a novel glutathione repleting agent, L-2-oxothiazolidine-4-carboxylic acid (Procysteine®)

A number of disease states are associated with episodes of acute or chronic oxidative stress, including Acute Respiratory Distress Syndrome (ARDS) and Human Immunodeficiency Virus (HIV) infection. Under conditions of oxidative stress, glutathione, a central component of the bodys antioxidant defence system, is often depleted and damage to cells and tissues from reactive oxygen species can result. Therapies which replete glutathione may prevent or alleviate such damage. Several approaches to glutathione repletion are under investigation including delivering glutathione in an esterified form and increasing the supply of cysteine, which limits glutathione synthesis. L-2-oxothiazolidine-4-carboxylic acid (OTC), a cysteine prodrug, is metabolised to cysteine intracellularly, where glutathione synthesis occurs. Extensive preclinical research has demonstrated that OTC increases glutathione levels in animal models in which glutathione was depleted by oxidative stress or chemical means. In toxicology studies, Pro...