Modulation of human T lymphocyte functions by isoprinosine

Inosine Acedoben Dimepranol promotes an early and sustained increase in the natural killer cell component of circulating lymphocytes: A clinical trial supporting anti-viral indications

Inosine Acedoben Dimepranol (IAD), licensed for the treatment of cell-mediated immune deficiencies associated with viral infections, has been reported to impact a variety of immune parameters both in vitro and in vivo. Here we report the results from a clinical trial where multiple lymphocyte subsets - CD19+ B cells, CD3+ T cells, CD4+ T-helper cells, FoxP3^hi/CD25^hi/CD127^lo regulatory T cells (Tregs), CD3-/CD56+ NK cells, and CD3+/CD56+ NKT cells - were, together with serum immunoglobulins and IgG subclasses, followed during 14days of IAD administration to ten healthy volunteers; these selected from 27 individuals pre-screened in vitro for their capacity to respond to IAD as gauged by increases in the percentage of Treg and/or NKT cells arising in PHA-stimulated cultures. While a transient spike and dip in Treg and T-helper fractions, respectively, was noted, the outstanding consequence of IAD administration (1g po, qds) was an early and durable rise in NK cells. For half the cohort, NK cells increased as a percentage of total peripheral blood lymphocytes within 1.5h of receiving drug. By Day 5, all but one of the volunteers displayed higher NK cell percentages, such elevation - effectively a doubling or greater - being maintained at termination of study. The IAD-induced populations were as replete in Granzyme A and Perforin as basal NK cells. The novel finding of IAD boosting phenotypically competent NK numbers in healthy individuals supports the drug's indicated benefit in conditions associated with viral infection and reinforces the potential for uplift where immune performance may be compromised.

The efficacy of a new single post-exposure treatment of rabies in mice without vaccination

Local application of rabies immune serum and isoprinosine, an immunomodulator with antiviral activity was effective in mice infected with a sylvatic rabies virus. In this way, a single medical or veterinary treatment is only required, which is particularly important for developing but also for developed countries. The importance of using a post-exposure potency test to monitor rabies vaccines is emphasized. The same principle could be applied to other emerging viral infections of humans (for example, human immunodeficiency virus infection) and animals, for which no effective vaccines are available at this moment.

Effect of isoprinosine on IL-2, IFN-gamma and IL-4 production in vivo and in vitro

The effects of an immunopotentiating drug, isoprinosine, on the splenocytes of BALB/c mice to produce cytokines were investigated. Isoprinosine enhanced IL-2 production, upregulating the expression of IL-2 receptor in vitro. It also significantly increased the IFN-gamma secretion and decreased the IL-4 production in vivo. The significance of these findings in terms of immune regulation is discussed.

Inosine pranobex in the treatment of HIV infection: a review

Inosine pranobex (InPx) could prove a valuable and innovative approach to the treatment of HIV-infected patients, since InPx administration has been shown in two multicenter trials to effectively delay the progression of HIV infection to overt AIDS. However, further studies are strongly required to optimize both the dosage of inosine pranobex and the administration schedules. Furthermore, clinical trials evaluating combination therapy of HIV infection with both InPx and zidovudine should ultimately provide an important advance in the management of HIV-infected patients. Our finding that concomitantly administered InPx to zidovudine-receiving patients increased the plasma levels of zidovudine as well as prolonged zidovudine mean half-life during InPx treatment suggests several potential advantages of the combination treatment with both InPx and zidovudine, such as a need for lower zidovudine dosage and a longer interval period between administering zidovudine to obtain sustained plasma levels as well as a potential to enhance residue immune function resulting from inosine pranobex treatment.

Effect of isoprinosine on lymphocyte proliferation and natural killer cell activity following thermal injury

The effect of in vivo administration of Isoprinosine (ISO) on, i) the proliferation of splenic lymphocytes in response to the T-cell mitogen, concanavalin-A (Con-A) and, ii) the natural killer (NK) cell cytotoxicity was studied following a full skin thickness burn injury in a rat model. Administration of ISO (100 mg/kg body wt/day) twice daily, resulted in significant augmentation of the proliferative responses of lymphocytes compared to non-treated burned animals, at 7 days post injury. However, it did not effect the lymphoproliferation at 14 days post injury, the time period at which a complete suppression of lymphocyte proliferation was observed in burned non-treated animals. Also, the proliferation of lymphocytes from normal nonburned animals was not affected by treatment with ISO. ISO treatment of the burned animals resulted in a significant increase in the NK cytotoxicity compared to non-treated burned animals. As with Con-A responses, ISO administered to control nonburned animals did not have any effect on NK cell cytotoxicity. Our studies thus indicate that ISO can be a potential immunomodulator of suppressed immune function following thermal injury, particularly in patients whose lymphocyte responses to T cell mitogen Con-A are not completely suppressed.

Pharmacologic immunoenhancement in the elderly: in vitro effects of isoprinosine

The loss of immune competence that occurs with aging may be responsible for increased morbidity and mortality in elderly individuals. Pharmacologic modulation of the immune response might reverse the immunologic aberrations associated with aging. We, therefore, investigated the effects of isoprinosine, an immunoenhancing drug, on selected in vitro immune responses in elderly subjects. Subjects studied were 65 years of age or older, and all had chronic diseases. We chose this population since they were at greatest risk for morbid events. Isoprinosine significantly enhanced mitogen-stimulated mononuclear cell proliferation, did not affect unstimulated cell growth, and needed to be present for the entire culture period for maximum effect. Isoprinosine is a potent in vitro immunoenhancing agent in aged humans.

Inosine pranobex. A preliminary review of its pharmacodynamic and pharmacokinetic properties, and therapeutic efficacy

Inosine pranobex is a synthetic compound formed from the p-acetamido benzoate salt of N-N dimethylamino-2-propanol and inosine in a 3:1 molar ratio. It has been reported to exert antiviral and antitumour activities in vivo which are secondary to an immunomodulating effect, and early results suggest beneficial clinical effects in several diseases and infections including mucocutaneous Herpes simplex infections, subacute sclerosing panencephalitis, genital warts, influenza, zoster, and type B viral hepatitis, as well as in homosexual men with persistent generalised lymphadenopathy. However, many of the studies have been preliminary in nature and deficient in design or in the reporting of their results. One must therefore conclude that while inosine pranobex may prove to be a valuable and innovative therapy for a number of diseases and infections for which no satisfactory therapy exist, further long term well controlled studies in larger numbers of patients are required before definitive conclusions about the efficacy of inosine pranobex in these disorders will be possible.

The selectivity of isoprinosine, NPT 15392, avridine and cyclophosphamide on multiple immune responses in rats

Multiple concomitant immune responses were assessed in individual rats following treatment with the immunoenhancing drugs, isoprinosine (5 or 50 mg/kg), NPT 15392 (0.1 or 1.0 mg/kg) and avridine (1 or 25 mg/kg), or the immunosuppressant, cyclophosphamide (75 mg/kg). Immune responses assessed in each rat were specific antibody synthesis, delayed-type hypersensitivity (DTH), natural killer cell (NKC) cytotoxicity and production of three immunoregulatory cytokines, interleukin 1 (IL1), interleukin 2 (IL2) and prostaglandin E2 (PGE2). Spleen and thymus weights and numbers of splenocytes and resident peritoneal cells were also recorded. Rats treated with isoprinosine had dose-related, significant increases in spleen weights and DTH reactions. Rats treated with NPT 15392 had significantly enhanced DTH reactions at the 0.1 mg/kg dose. Rats treated with the 25 mg/kg dose of avridine had significantly increased spleen weights, DTH reactions and NKC cytotoxicity. The effect of avridine treatment on DTH reactions and IL1 and IL2 production was inverse to the dose administered, while the NKC response was directly related to the dose. Thymus weights, antibody production and PGE2 synthesis were not significantly altered in rats treated with isoprinosine, NPT 15392 or avridine. Cyclophosphamide-treated rats had significantly reduced spleen and thymus weights, antibody synthesis, DTH reactions, NKC cytotoxicity and IL2 production, but IL1 and PGE2 synthesis were significantly elevated. It can be concluded that isoprinosine, NPT 15392 and avridine act as general immunostimulants in the rat, with avridine having the greatest effect under these experimental conditions. It also appears that these drugs are differentially immunoselective in the rat and this effect is at least partially related to the dose administered. These results could be of significance in the selective therapeutic manipulation of different arms of the immune system. Also, enhanced production of PGE2 following cyclophosphamide treatment may contribute to the immunosuppressive effects of this drug.

Immunosenescence. Clinical and pharmacologic considerations

The effect of aging on the immune response is highly variable. Many individuals appear to maintain adequate immunologic function throughout life, whereas others have severely depressed immunologic responses accounting for disease activity. Both cellular- and humoral-mediated responses may be abnormal in the elderly. Aberrant function of immunoregulatory cells, effector T cells, and antibody-producing B cells contribute to poor immunity in the aged. Immunoenhancement in the elderly by pharmacologic agents appears promising. Several agents have been demonstrated to improve immune responses when administered to aging animals and humans. Although these studies are encouraging, it is not known if enhancement of immune responses in the elderly will be associated with clinical benefits. This issue must still be examined.

The experimental and clinical use of immune-modulating drugs in the prophylaxis and treatment of infections

Therapeutic agents capable of stimulating immune responses could be of great value in the prophylaxis and treatment of infectious diseases. Three classes of compounds, each representing a separate approach to the goal of immune stimulation, are discussed with respect to recent experimental and clinical findings. The action of microbial structures and their derivatives can be understood on the basis of "acquired cellular immunity", a phenomenon first described in connection with infections by mycobacteria and other intracellular organisms. In contrast, there is hardly a common denominator for synthetic compounds which are currently used as immune-stimulatory agents. Substances which influence purine metabolism in lymphocytes on the one hand and histamine H2 blockers such as cimetidine on the other hand seem to represent the most promising developments in this field to date. Products of immune cells such as transfer factor and lymphokines form the third and possibly most important group of immune-stimulating agents. Current experimental and clinical trends in this field are briefly described. It is suggested that the delineation of the mechanism of action of lymphokines will open the door to the identification or synthesis of artificial agonists and antagonists as has been the case in the pharmacology of the endocrine and nervous systems.

Effects of isoprinosine in animal models of depressed T-cell function

Isoprinosine--a new drug possessing immunostimulating properties--was investigated for its ability to influence cell-mediated immune responsiveness in animal models of deficient T-cell function. In vitro isoprinosine strongly increased T-cell mitogenesis in spleen cells from normal rats, with only modest increases in B-cell mitogenesis and no effects on unstimulated cells. In vivo isoprinosine (50 mg kg-1 day-1 orally) had no effects on spleen cell responsiveness when administered to normal rats for 4 or 14 days. However, when the same dose of isoprinosine was administered to rats immunosuppressed with cyclophosphamide (5 mg kg-1 day-1 orally) a partial restoration of T-cell mitogenesis was observed after 14 days of treatment. In rats with adjuvant arthritis treated with isoprinosine for 14 days, depressed T-cell responsiveness was completely restored to the level of the nonarthritic animals. The involvement of different cell types in the observed effects of isoprinosine was further studied in arthritic rats. Removal of monocytes/macrophages from the cell suspensions prior to culture did not affect the increased T-cell response in isoprinosine-treated rats, suggesting a direct stimulatory effect of isoprinosine on T-cell functions. T-suppressor cell function, impaired in arthritic rats, was not restored by treatment with isoprinosine. These results suggest that isoprinosine may exert selective effects on specific T-cell subsets, a finding that may increase the therapeutic interest of the drug.

Immunopotentiation of impaired lymphocyte functions in vitro by isoprinosine in prodromal subjects and AIDS patients

Immunomodulative actions of isoprinosine were tested in 100 prodromal homosexual males and 23 patients who have been diagnosed with AIDS. All subjects showed reduced T helper cells although T suppressor cell counts were normal. Proliferative responses, particularly T cell-dependent B cell function, were severely impaired in prodromal and AIDS subjects. Upon co-cultivation of their lymphocytes with isoprinosine, significant upward modulation, and in some cases, normalization, of lymphocyte functions as monitored by PHA- and PWM-induced blastogenesis was achieved in prodromal subjects. Similar degrees of modulation but not normalization of lymphocyte functions were observed in patients with severe symptoms of AIDS.

Inosine biosynthesis in transfer RNA: a postulated role in immune regulation

A hypothesis is put forth describing a role in immune regulation for inosine biosynthesis in the anticodon of tRNA. The enzymatic insertion of hypoxanthine into the tRNA wobble base position is predicted to be a control point for the translation of proteins and peptides required for normal immune function. The substrate for inosine biosynthesis in tRNA, hypoxanthine, is an intermediate in the purine catabolic pathway, and defects in this pathway are associated with inherited immunodeficiency diseases. Therefore, a role for aberrant inosine biosynthesis in tRNA is postulated in causing the immunodeficient conditions, and it may be a relevant molecular defect in leukemia as well.

The experimental and clinical use of immune-modulating drugs in the prophylaxis and treatment of infections

Therapeutic agents capable of stimulating immune responses could be of great value in the prophylaxis and treatment of infectious diseases. Three classes of compounds, each representing a separate approach to the goal of immune stimulation, are discussed with respect to recent experimental and clinical findings. The action of microbial structures and their derivatives can be understood on the basis of "acquired cellular immunity", a phenomenon first described in connection with infections by mycobacteria and other intracellular organisms. In contrast, there is hardly a common denominator for synthetic compounds which are currently used as immune-stimulatory agents. Substances which influence purine metabolism in lymphocytes on the one hand and histamine H2 blockers such as cimetidine on the other hand seem to represent the most promising developments in this field to date. Products of immune cells such as transfer factor and lymphokines form the third and possibly most important group of immune-stimulating agents. Current experimental and clinical trends in this field are briefly described. It is suggested that the delineation of the mechanism of action of lymphokines will open the door to the identification or synthesis of artificial agonists and antagonists as has been the case in the pharmacology of the endocrine and nervous systems.