Pre-analytical and analytical variables affecting the measurement of plasma-derived microparticle tissue factor activity.

INTRODUCTION: Elevated levels of tissue factor positive (TF(+)) microparticles (MPs) are observed in plasma from a variety of patients with an increased risk of thrombosis. We and others have described the measurement of TF activity in MPs isolated from plasma. The aim of this study was to investigate the effects of pre-analytical and analytical variables on TF activity of MPs isolated from blood of healthy volunteers either untreated or treated ex vivo with bacterial lipopolysaccharide. MATERIALS AND METHODS: We evaluated the following parameters: use of different centrifugation speeds to isolate the MPs; comparison of TF activity of MPs isolated from platelet poor plasma versus platelet free plasma; effect of freeze/thaw on MP TF activity; and comparison of the MP TF activity assay with the measurement of TF protein by ELISA or flow cytometry. RESULTS: MPs prepared from platelet poor plasma by centrifugation at 20,000×g or 100,000×g for 15 minutes had similar levels of TF activity. However, significantly less TF activity was found in MPs isolated from platelet free plasma compared with platelet poor plasma. Interestingly, freeze/thawing of the plasma showed donor to donor variation in MP TF activity, with a moderate increase in some individuals. CONCLUSION: TF(+) MPs can be quantitatively isolated from platelet poor or platelet free plasma by centrifugation at 20,000×g for 15 minutes. Measurement of MP TF activity in plasma may be used to detect a prothrombotic state in patients with various diseases.

Development of neuronal sensitivity to toxins in cerebrospinal fluid from HIV-type 1-infected individuals.

HIV infection of the immature nervous system generally results in a rapid progression of neurological disease that cannot easily be explained by the severity of encephalitis, viral burden, systemic immune deficiency, or developmental changes in utero. Rather than the viral infection dictating disease progression, we explored the possibility that immature neurons might be particularly sensitive to toxins secreted in response to HIV. Primary cultures of rat cortical neurons were exposed to toxic cerebrospinal fluid (CSF) from HIV-infected individuals (CSF(tox)) and evaluated for changes in intracellular calcium and cell death. CSF(tox) had no detectable effect on early neurite outgrowth, calcium regulation, or cell death during the first few days in culture. Starting at Day 4, delayed increases in intracellular calcium appeared in response to CSF(tox). The magnitude of the delayed calcium rise and cell death increased with the age of the culture and correlated with the appearance of synaptophysin immunoreactive varicosities. A similar gradual development of sensitivity was seen during exposure of feline neurons to toxins generated by choroid plexus macrophages after exposure to feline immunodeficiency virus. The possibility that toxin sensitivity is dependent on the presence of synaptic activity is consistent with the rapid pathogenesis in the CNS seen during the first postnatal year. Emerging synaptic activity coupled with other factors such as high metabolic demand in the young nervous system may combine to increase the likelihood of calcium overload and neuronal dysfunction in response to HIV-associated toxins.

Destabilization of neuronal calcium homeostasis by factors secreted from choroid plexus macrophage cultures in response to feline immunodeficiency virus.

The choroid plexus contains a major reservoir of macrophages poised for efficient delivery of virus and neurotoxins to the brain after infection by lentiviruses such as human or feline immunodeficiency virus (FIV). However, their contribution to neurotoxicity is poorly understood. Medium from FIV-infected, choroid plexus macrophages applied to cultured feline cortical neurons induced a small acute calcium rise followed by either a delayed calcium deregulation (41%) or swelling and bursting (23%). NMDA glutamate receptor blockade prevented the acute calcium increase and antagonists to the IP(3) receptor, voltage-gated calcium channels and sodium channels suppressed both the acute and late increases. Analysis of intracellular calcium recovery in toxin-treated neurons after a brief exposure to glutamate, revealed a decrease in the rate and extent of recovery. The apparent diverse pharmacological contributions to intracellular calcium destabilization may be due to the ability of macrophage toxins to interfere with recovery of intracellular calcium homeostasis.