Role of {\it Mycobacterium avium-intracellulare\/} complex infection in AIDS mortality

Disseminated MAC (dMAC) is the third most prevalent opportunistic infection in AIDS patients. In order to understand the role MAC infection plays in affecting survival of AIDS patients, a cohort of 203 suspected dMAC veterans seen at the Houston Veterans Affairs Medical Center between August 14, 1987 and December 31, 1991 were analyzed. The criteria for suspected dMAC infection was HIV+ men having a CD4+ level $\le$200 cells/mm$\sp3,$ on zidovudine treatment $\ge$1 month and who had any of the following: (a) a confirmed respiratory MAC infection, (b) fever $\ge$101$\sp\circ\rm F$ for $\ge$48 hours, (c) unexplained weight loss of 10 lbs or $\ge$10% BW over 3 months or (d) Hgb $\le$7.5 g/dl or decrease in Hgb $\ge$3.0 g/dl, while on 500-600 mg/day AZT. The study was conducted before the commencement of an effective MAC anti-mycobacterial therapy, so the true course of MAC infection was seen without the confounder of a therapeutic regimen. Kaplan-Meier and Cox regression survival analysis was used to compare 45 MAC culture positive and 118 MAC culture negative veterans. The 1 year survival rate of veterans with documented dMAC infection was 0.37 compared to 0.50 for veterans not acquiring dMAC infection. Significant differences between subgroups were also seen with the variables: PCP prophylaxis, the AIDS indicator disease Candida esophagitis, CD4+ lymphocyte level, CD4 percent lymphocyte level, WBC level, Hgb and Hct levels. Using multivariate modeling, it was determined that PCP prophylaxis (RR = 6.12, CI 2.24-16.68) was a predictor of survival and both CD4% lymphocytes $\le$6.0% (RR = 0.33, CI 0.17-0.68) and WBC level $\le$3000 cells/mm$\sp3$ (RR = 0.60, CI 0.39-0.93) were predictors of mortality. CD4+ level $\le$50 cells/mm$\sp3$ was not a significant predictor of mortality. Although MAC culture status was a significant predictor of mortality in the univariate model, a positive dMAC culture was not a significant predictor of AIDS mortality in the multivariate model. A positive dMAC culture, however, did affect mortality in a stratified analysis when baseline laboratory values were: CD8+ lymphocytes $>$600 cells/mm$\sp3,$ Hgb $>$11.0 g/dl, Hct $>$31.0% and WBC level $>$3000 cells/mm$\sp3.$ ^

Deciphering the C-Type Lectin Receptor Signaling Pathway in Macrophages in Response to Candida albicans

Candida albicans causes opportunistic fungal infections in humans and is a significant cause of mortality and morbidity in immune-compromised individuals. Dectin-2, a C-type lectin receptor, is required for recognition of C. albicans by innate immune cells and is required for initiation of the anti-fungal immune response. We set out to identify components of the intracellular signaling cascade downstream of Dectin-2 activation in macrophages and to understand their importance in mediating the immune response to C. albicans in vivo. Using macrophages derived from Phospholipase-C-gamma 1 and 2 (PLCγ1and PLCγ2) knockout mice, we demonstrate that PLCγ2, but not PLCγ1, is required for activation of NF-κB and MAPK signaling pathways after C. albicans stimulation, resulting in impaired production of pro-inflammatory cytokines and reactive oxygen species. PLCγ2-deficient mice are highly susceptible to infections with C. albicans, indicating the importance of this pathway to the anti-fungal immune response. TAK1 and TRAF6 are critical nodes in NF-κB and MAPK activation downstream of immune surveillance and may be critical to the signaling cascade initiated by C-type lectin receptors in response to C. albicans. Macrophages derived from both TAK1 and TRAF6-deficient mice were unable to activate NF-κB and MAPK and consequently failed to produce inflammatory cytokines characteristic of the response to C. albicans. In this work we have identified PLCγ2, TAK1 and TRAF6 as components of a signaling cascade downstream of C. albicans recognition by C-type lectin receptors and as critical mediators of the anti-fungal immune response. A mechanistic understanding of the host immune response to C. albicans is important for the development of anti-fungal therapeutics and in understanding risk-factors determining susceptibility to C. albicans infection.

The relationship of mutations in alpha- and beta-tubulin to microtubule assembly and anti-mitotic drug resistance

The mechanisms responsible for anti-cancer drug (including Taxol) treatment failure have not been identified. In cell culture model systems, many β-tubulin, but very few α-tubulin, mutations have been associated with resistance to Taxol. To test what, if any, mutations in α-tubulin can cause resistance, we transfected a randomly mutagenized α-tubulin cDNA into Chinese hamster ovary (CHO) cells and isolated drug resistant cell lines. A total of 12 mutations were identified in this way and all of them were confirmed to confer Taxol resistance. Furthermore, all cells expressing mutant α-tubulin had less microtubule polymer. Some cells also had abnormal nuclei and enlarged cell bodies. The data indicate that α-tubulin mutations confer Taxol resistance by disrupting microtubule assembly, a mechanism consistent with a large number of previously described β-tubulin mutations. ^ Because α- and β-tubulin are almost identical in their three dimensional structure, we hypothesized that mutations discovered in one subunit, when introduced into the other, would produce similar effects on microtubule assembly and drug resistance. 9 α- and 2 β-tubulin mutations were tested. The results were complex. Some mutations produced similar changes in microtubule assembly and drug resistance irrespective of the subunit in which they were introduced, but others produced opposite effects. Still one mutation produced resistance when present in one subunit, yet had no effect when present on the other; and one mutation that produced Taxol resistance when present in α-tubulin, resulted in assembly-defective tubulin when it was present in β-tubulin. The results suggest that in most cases, the same amino acid modification in α- and β-tubulin affects the microtubule structure and assembly in a similar way. ^ Finally, we tested whether three β-tubulin mutations found in patient tumors could confer resistance to Taxol by recreating the mutations in a β-tubulin cDNA and transfecting it into CHO cells. We found that all three mutations conferred Taxol resistance, but to different extents. Again, microtubule assembly in the transfectants was disrupted, suggesting that mutations in β-tubulin are a potential problem in cancer therapeutics. ^

Novel Use of Dual Anti-Inflammatory Therapy to Overcome Drug Resistance and Improve Functional Recovery Following Spinal Cord Injury

Over 1.2 million Americans are currently living with a traumatic spinal cord injury (SCI). Despite the need for effective therapies, there are currently no proven effective treatments that can improve recovery of function in SCI patients. Many therapeutic compounds have shown promise in preclinical models of SCI, but all of these have fallen short in clinical trials. P-glycoprotein (Pgp) is an active transporter expressed on capillary endothelial cell membranes at the blood-spinal cord barrier (BSCB). Pgp limits passive diffusion of blood-borne drugs into the CNS, by actively extruding drugs from the endothelial cell membrane. Pgp can become pathologically up-regulated, thus greatly impeding therapeutic drug delivery (‘multidrug resistance’). Importantly, many drugs that have been evaluated for the treatment of SCI are Pgp substrates. We hypothesized that Pgp-mediated drug resistance diminishes the delivery and efficacy of neuroprotective drugs following SCI. We observed a progressive, spatial spread of Pgp overexpression within the injured spinal cord. To assess Pgp function, we examined spinal cord uptake of systemically-delivered riluzole, a drug that is currently being evaluated in clinical trials as an SCI intervention. Blood-to-spinal cord riluzole penetration was reduced following SCI in wild-type but not Pgp-null rats, highlighting a critical role for Pgp in mediating spinal cord drug resistance after injury. Others have shown that pro-inflammatory signaling drives Pgp up-regulation in cancer and epilepsy. We have detected inflammation in both acutely- and chronically-injured spinal cord tissue. We therefore evaluated the ability of the dual COX-/5-LOX inhibitor licofelone to attenuate Pgp-mediated drug resistance following SCI. Licofelone treatment both reduced spinal cord Pgp levels and enhanced spinal cord riluzole bioavailability following SCI. Thus, we propose that licofelone may offer a new combinatorial treatment strategy to enhance spinal cord drug delivery following SCI. Additionally, we assessed the ability of licofelone, riluzole, or both to enhance recovery of locomotor function following SCI. We found that licofelone treatment conferred a significant improvement in hindlimb function that was sustained through the end of the study. In contrast, riluzole did not improve functional outcome. We therefore conclude that licofelone holds promise as a potential neuroprotective intervention for SCI.