Thymosin alpha one restores murine T-cell-mediated responses inhibited by in vivo cocaine administration

Historical review of thymosin α 1 in infectious diseases

INTRODUCTION

Thymosin α 1 (Tα1) is a peptidic biological response modifier, which plays a significant role in activating and regulating various cells of the immune system. For the above-mentioned activities it is expected to exert a clinical benefit in the treatment of diseases where the immune system is altered.

AREAS COVERED

Several clinical trials have been carried out with Tα1 for treatment or prevention of many different infectious diseases such as hepatitis B and C, sepsis and Aspergillosis in bone marrow-transplanted patients. Data available on the use of Tα1 in infectious disease as well as a vaccine enhancer will be reviewed to possibly generate new working hypothesis.

EXPERT OPINION

Tα1 has been widely used in thousands of patients. Nevertheless, there are some issues that have not yet been properly addressed (i.e., dose, schedule, combination treatments, end-points to be evaluated in clinical trials). In the most recent clinical trials Tα1 has been used at higher doses than those commonly used in the past showing a direct proportionality between the dose and the effect. The safety profile of Tα1 is excellent and it is virtually devoid of toxicity.

Thymosin α1 continues to show promise as an enhancer for vaccine response

Thymosin α1 (Tα1) is an immune-modulating peptide that can be expected to improve response to vaccinations, as stimulated dendritic cells and T cells can act in concert to increase antibody production along with an improved cytotoxic response from the T cells themselves. Tα1 demonstrated efficacy in preclinical studies; subsequently, it was shown to enhance response to vaccinations in difficult-to-treat populations, including individuals immune suppressed due to age or hemodialysis, and leading to a decrease in later infections. During the 2009 pandemic outbreak of H1N1 influenza, mouse and ferret studies confirmed that the use of higher doses of Tα1 allowed for fewer injections than those used in the previous clinical studies. In addition, a clinical study with Focetria™ MF59-adjuvanted monovalent H1N1 vaccine showed that treatment with Tα1 twice provided an earlier and greater response to the vaccine (P < 0.01).

Potential Role of Thymosin-alpha1 Adjuvant Therapy for Glioblastoma

Glioblastomas are high-grade, malignant CNS neoplasms that are nearly always fatal within 12 months of diagnosis. Immunotherapy using proinflammatory cytokines such as IL-2 or IL-12 may prolong survival with glioblastoma. Thymosin-α1 (Talpha1) is a thymic hormone and immunemodulator that increase IL-2 production and T-cell proliferation. We examined potential therapeutic effects of Talpha1 in experimental in vivo glioblastoma, and characterized Talpha1's anti-tumor effects in vitro. Rar 9L cells (10⁴) were implanted into the right frontal lobe of adult Long Evans rats that were subsequently treated with vehicle, BCNU, Talpha1, or Talpha1+BCNU from postoperative day 6. Talpha1+BCNU significantly lowered tumor burdens, and increased cure rates. In vitro experiments demonstrated that Talpha1 had no direct effect on viability or mitochondrial function, and instead, it increased expression of pro-apoptosis genes, including FasL, FasR and TNFα-R1 (65.89%, 44.08%, and 22.18%, resp.), and increased 9L cell sensitivity to oxidative stress. Moreover, Talpha1 enhanced 9L cell sensitivity to both Granzyme B- and BCNU-mediated killing. The findings suggest that Talpha1 enhances BCNUmediated eradication of glioblastoma in vivo, and that Talpha1 mediates its effects by activating pro-apoptosis mechanisms, rendering neoplastic cells more sensitive to oxidative stress and immune-mediated killing by Granzyme B and chemotherapeutic agents.

The effect of cocaine sensitization on mouse immunoreactivity

Recent studies indicate a role of the immune system in the behavioral effects of cocaine in rodents. In the present study, we attempted to find a correlation between the behavioral changes induced by repeated, intermittent administration of cocaine and some immunological consequences of sensitization to cocaine. Male Albino Swiss mice were treated repeatedly (for 5 days) with cocaine (10 or 15 mg/kg, intraperitoneally, ip). On day 9, they received a challenge dose of cocaine (10 or 15 mg/kg). Acute administration of cocaine increased the locomotor activity of mice. In animals treated repeatedly with the higher dose of cocaine, the locomotor hyperactivity induced by a challenge dose of the psychostimulant (15 mg/kg) was ca. twice as high as that after its first administration; in consequence, evidence for behavioral sensitization was obtained. Immune functions were evaluated by measuring the ability of splenocytes to proliferate and to produce cytokines such as interferon-gamma (IFN-gamma), interleukin (IL)-4 and IL-10. Acute cocaine administration significantly decreased proliferation of splenocytes to concanavalin A (Con A) and increased their ability to produce IFN-gamma. Repeated intermittent treatment with cocaine in a dose of 10 mg/kg significantly decreased the thymus weight and the proliferative response of T cells to a suboptimal dose of Con A. Sensitization with the higher dose of cocaine significantly enhanced IFN-gamma production. These data indicate that cocaine sensitization results in the development of a tolerant state to the cocaine-induced suppression of a thymus dependent T-lymphocyte response. It may be suggested that the cocaine sensitization partly depends on the altered balance of cytokine production, e.g. an increase in IFN-gamma production. Since repeated, intermittent use of cocaine by humans leads to psychoses or craving for this drug, our findings also seem to indicate considerable importance of monitoring and correcting immune changes in the therapy of cocaine addiction.

Increased replication of Sendai virus in morphine-treated epithelial cells: evidence for the involvement of the intracellular levels of glutathione

This paper shows that morphine increases Sendai virus replication in cultured epithelial cells. The effect was maximal when it was added before viral infection. Morphine also reduced the intracellular level of glutathione, namely, the oxidative and most abundant cell thiol. Altered intracellular redox status has recently been proposed as a factor influencing viral infection. Support for this view was provided by our data showing that inhibition of de novo glutathione synthesis, using L-buthionine sulfoximine, increased virus replication. These findings provide the first evidence that morphine increases the susceptibility to virus infection by altering the intracellular levels of glutathione.

Cocaine suppresses fetal immune system

The effects of cocaine are well documented in the CNS; however, recent evidence suggests that cocaine may suppress the immune system. Maternal cocaine use essentially exposes the fetus to a continuous exposure of cocaine. The objective of this study was to investigate the immunomodulatory effects of cocaine and its metabolites on maternal and fetal immune systems. Subjects were recruited from an Investigational Review Board approved protocol, and biologic specimens were collected. For each subject peripheral blood mononuclear cells (PBMCs) were isolated by density gradient. Each PBMC sample was stimulated in separate wells with phytohemagglutinin and phrobol 12-myristate 13-acetate. Samples were radiolabeled and stimulation was measured. Cytokine measurements were made on the serum via ELISA assay techniques. In both the phorbol 12-myrisate 13-acetate and the phytohemagglutinin group, the PBMCs isolated from fetal cord blood in the cocaine-using group had significantly (p < 0.05) decreased responses compared with control subjects. IL 1 and IL 2 concentrations were suppressed in the cocaine-exposed fetal serum compared with controls (p < 0.005 and p < 0.05, respectively). We have shown that in utero cocaine exposure results in a nonspecific suppression of fetal T lymphocyte response. The clinical consequences of prenatal cocaine-induced immunosuppression need to be further explored.

In vivo effects of cocaine on immune cell function

Cocaine use has been shown to increase the risk of HIV infection in humans, and this increased risk cannot be explained by i.v. drug use alone. It is thought that this increased susceptibility may be a result of decreased immune responsiveness in cocaine addicts. Scientists are now using animal models to study the effects of cocaine on immune function in vivo under controlled conditions. Many facets of the immune system are being examined, which include immune cell number and distribution, cellular- and humoral-mediated immunity, cytokine production, and immunocompetence to challenges such as infection and tumor growth. The effects of cocaine on many of these functions are not yet clear. Often there are variations in the response of the immune system to cocaine. Potential confounding factors include variations in dose, duration of treatment, and route of administration of cocaine, as well as variations in assay protocols. In addition, there appear to be species differences in immune responses to cocaine. Although it is clear that more research is necessary to resolve the discrepancies, a sufficient number of trends are starting to emerge. This review will systematically evaluate the reported effects of cocaine on immune cell function in vivo. In addition, the possible mechanisms that may be contributing to the immune modulation observed with cocaine in vivo will be addressed. Further, data will be presented describing the effects of cocaine on the autonomic nervous system and the neuroendocrine system suggesting that inhibition of serotonin uptake may be an important component of the overall effects of cocaine on the immune system.

Tolerance and crosstolerance to the suppressive effects of cocaine and morphine on lymphocyte proliferation

The effects of acute or daily exposure to either cocaine or morphine on lymphocyte proliferative responses and NK cytolytic activity were determined. Two hours following the IV infusion of cocaine (5 mg/kg), blood lymphocyte proliferative responses were found to be suppressed by 75%. Cocaine had no effect on proliferative responses of thymic or splenic lymphocytes or cytolytic activity of splenic NK cells following acute or 5-day repetitive dosing. Similar to the effects of cocaine, morphine (10 mg/kg) administration was also accompanied by a suppressed blood lymphocyte response, which was no longer apparent 8 days following repeated morphine injections. Animals that had received daily injections of either morphine of cocaine were also found to be resistant to the inhibitory effects of a single dose of morphine or cocaine, respectively. These data suggest repeated exposure to either morphine or cocaine results in the development of an apparent crosstolerant state to further suppression of blood lymphocyte proliferative responses by either drug.

Acute infusions of cocaine result in time- and dose-dependent effects on lymphocyte responses and corticosterone secretion in rats

In the present study, we investigated the effect of intravenously (i.v.) administered cocaine on mitogen-induced lymphocyte proliferation and NK cytolytic activity in rats implanted with indwelling jugular cannula. To assess whether the effects of cocaine were accompanied by adrenal gland activation, plasma corticosterone concentrations were also determined. It was found that the i.v. infusion of cocaine resulted in both a time- and dose-dependent decrease in both blood and splenic Con-A-stimulated lymphocyte proliferative responses. Within 60 minutes, blood responses were maximally inhibited by more than 60% with 5 mg/kg cocaine. By 4 h, the suppression of blood lymphocyte responses was no longer significant. In contrast to these findings, there were no significant effects observed with splenic lymphocyte responses until 4 h after drug administration. At this time, cocaine at doses of 5 and 10 mg/kg inhibited splenic proliferative responses by 50 and 75%, respectively. These effects appeared to be selective, since no concurrent decreases in NK cell activity were observed with 5 mg/kg at either 2 or 4 h. Within 30 min, plasma corticosterone concentrations were maximally increased by 10-fold with 5 and 10 mg/kg doses of cocaine. At lower doses of cocaine (1 mg/kg), neither changes in lymphocyte proliferative responses, NK cytolytic activity nor plasma corticosterone levels were apparent. This study demonstrates that a single i.v. infusion of cocaine results in a selective dose- and time-dependent immunosuppression which is preceded by transient increases in circulating levels of corticosterone.

Combined effect of fluconazole and thymosin alpha 1 on systemic candidiasis in mice immunosuppressed by morphine treatments

Treatment of systemic infection with Candida albicans with a combination of an antifungal agent (i.e. fluconazole) and a thymus-derived immunostimulant (i.e. thymosin alpha 1 (T alpha 1)) in mice immunosuppressed by morphine treatments was investigated. In normal mice, fluconazole given after infection with 10(6) C. albicans cells was more effective than in mice treated with morphine. Combination treatment with fluconazole and T alpha 1 prolonged survival and reduced the fungal burden in the kidneys of immunosuppressed mice. We also investigated the influence of this combined treatment on killing properties of polymorphonuclear leucocytes (PMN) and natural killer (NK) cell activity, inhibited by morphine administrations. Treatment with T alpha 1 or fluconazole as single agents promoted a recovery of normal NK cell activity and intracellular killing of C. albicans by PMN, while the combination significantly increased both of these responses, probably through the modulation of lymphokine production. Our data suggest that the additive effect of T alpha 1 and fluconazole is due to a direct antifungal action and activation of the immunocompetence.

Differential effects of short-term or prolonged cocaine exposure on peripheral blood cells in mice

The effects of cocaine on the number of murine peripheral blood cells and on phenotypic expression of lymphocyte subsets were examined using different regimens of drug exposure. Cocaine administered to mice for 7 consecutive days at 1 and 10 mg/kg/day reduced the absolute number of circulating white blood cells and the relative number of cells stained as lymphocytes, polymorphonuclear cells and monocytes. Cocaine did not modify the relative proportion between lymphocytes, polymorphonuclear cells and monocytes. Parallely, there were no changes in the percentage of circulating CD4+ and CD8+ lymphocytes, while the number of natural killer cells increased. In sharp contrast, we didn't observe any significant change in peripheral blood cells after 30 days of consecutive drug administrations.

Effect of synthetic thymic hormones on the cocaine-induced inhibition of the primary immune response in mice

The effects of thymosin alpha 1 (T alpha 1) and thymopentin (TP5) on the cocaine-induced impairment of the primary antibody response to sheep red blood cells (SRBC) was studied. The administration of cocaine from day -4 to the day of immunization (day 0) induced a significant impairment of the response to the T-dependent antigen SRBC, as evaluated on day 5 post-immunization by the Splenocyte-Induced SRBC Hemolysis (SIH) assay. The analysis of the responses to immunogen elicited from each single mouse indicated that, under the experimental conditions used, cocaine acted by exerting more an "all or nothing" effect rather than by modulating the strength of the immune response. Both T alpha 1 and TP5, injected into mice during cocaine administration and for 4 days after, induced a significant recovery of the response to SRBC. Our experiments did not show any great differences in the overall efficacy of the two drugs, although they showed quite a different dose-response effect. The results of the present investigation demonstrated the capability of TP5 and T alpha 1 to reverse the cocaine-induced impairment of the response to SRBC and suggested that the effect of the two peptides may be related to their immunomodulating activities on T-cell functions.

In vitro phencyclidine-induced inhibition of lymphocyte proliferation: prevention by cell activation

The proliferative response of phytohemagglutinin (PHA)- and interleukin 2 (IL-2)-activated murine splenocytes was studied in the presence of phencyclidine (PCP), a potent psychotomimetic drug of abuse. PCP inhibited [3H]-thymidine incorporation in lymphocytes treated with PHA or IL-2. This inhibitory action was dependent upon the drug doses and the time of incubation with the cultures. There was no significant inhibitory activity of PCP when it was added 24 hrs or 48 hrs after mitogenic stimuli. Parallel, a lower inhibitory effect was observed when IL-2 or PHA were simultaneously present in the incubation medium. Moreover, the pretreatment for 18 hrs with IL-2 completely counteracted PCP-induced depression of PHA-stimulated lymphocytes. We suggest that PCP affects some pathway that regulates the activation of resting T cells rather than affecting already cycling cells.