IMMUNOSUPPRESSIVE EFFECT OF MISOPROSTOL: A NEW SYNTHETIC PROSTAGLANDIN E1ANALOGUE

The immunomodulatory actions of E-type prostaglandins

Prostaglandins (PGs) have been recognised as modulators of immune responses. This has been proved by both in vitro studies and from observations in animals and humans. Administration of prostaglandins for therapeutic purposes, however, has been hampered by their limited bioavailability and their pleiotropic effects, with resultant toxicological profile. Despite this, some success has been demonstrated in the clinic for the control of graft rejection, especially when used as part of a broader immunosuppressant regimen. Full realisation of the therapeutic potential of prostaglandins will depend on a better understanding of their mechanism of action at the cellular level. Recently, it has been appreciated that prostaglandins do not merely inhibit T-cell function, but appear to modulate the profile of lymphocyte sub-populations through regulation of cytokine synthesis and release. Recent efforts have also begun to focus on identifying prostaglandin receptor subtypes important for immune regulation and offer a means, together with targeted delivery, of utilising the immunosuppressant/anti-inflammatory effects of E-type prostaglandins in a safe and effective manner.

COX-2 Inhibitors at The 8th International Conference of the Inflammation Research Association

An intensive search is underway for novel selective inhibitors of cyclo-oxygenase (COX)-2. These compounds promise to be potent anti-inflammatory agents with little gastrointestinal intolerance. Meloxicam, with some selectivity for COX-2, is already marketed, and at least two companies are carrying out clinical studies with selective inhibitors. A variety of potential successor compounds were presented at the 8th International Conference of the Inflammation Research Association (IRA) in Hershey, PA on 27-31 October 1996.

The immunosuppressive potential of misoprostol--efficacy and variability

Existing evidence on the immunosuppressive efficacy of prostaglandin E (PGE) and its analogues in vivo is conflicting. We investigated the effect of misoprostol, an orally available PGE1 analogue, on T-cell proliferation, Th cell-derived cytokine production, and phagocytosis in healthy volunteers. All participants (n=20) received increasing doses of misoprostol (0-400 microg). Blood was drawn before and after intake. Misoprostol intake caused a time- and dose-dependent reduction of anti-CD3-stimulated cell proliferation. Whereas the synthesis of Th1 cytokines (IL-2 and IFN-gamma) was dose-dependently reduced, IL-10 expression was increased at lower misoprostol doses. Concerning IL-4 expression, we observed an increased IL-4 production in males, but a decreased IL-4 production in females. Misoprostol intake also reduced phagocytosis activity in a dose-dependent manner. At least in part our results explain the immunosuppressive effects of misoprostol observed in vivo. The considerable interindividual variability as well as gender-specific differences seem to account for the variability of clinical study results.

Misoprostol therapeutics revisited

Misoprostol, a prostaglandin E1 analog, is a racemate of four stereoisomers. On administration it rapidly de-esterifies to its active form, misoprostolic acid. Misoprostolic acid is 85% albumin bound and has a half-life of approximately 30 minutes. It is excreted in urine as inactive metabolites. No significant drug interactions have been reported. Besides its gastrointestinal protective and uterotonic activities, misoprostol regulates various immunologic cascades. It inhibits platelet-activating factor and leukocyte adherence, and modulates adhesion molecule expression. It protects against gut irradiation injury, experimental gastric cancer, enteropathy, and constipation. It improves nutrient absorption in cystic fibrosis. Misoprostol has utility in acetaminophen and ethanol hepatotoxicity, hepatitis, and fibrosis. It is effective in asthmatics and aspirin-sensitive asthmatic and allergic patients. It lowers cholesterol and severity of peripheral vascular diseases, prolongs survival of cardiac and kidney transplantation, synergizes cyclosporine, and protects against cyclosporine-induced renal damage. It works against drug-induced renal damage, interstitial cystitis, lupus nephritis, and hepatorenal syndrome. It is useful in periodontal disease and dental repair. Misoprostol enhances glycosoaminoglycan synthesis in cartilage after injury. It prevents ultraviolet-induced cataracts and reduces intraocular pressure in glaucoma and ocular hypertension. It synergizes antiinflammatory and analgesic effects of diclofenac or colchicine and has been administered to treat trigeminal neuralgic pain. It reduces chemotherapy-induced hair loss and recovery time from burn injury, and is effective in treating sepsis, multiple sclerosis, and pancreatitis.

Effect of FK 506 and lipo prostaglandin E1 on heart allograft survival in rats

FK 506 (FK) has a strong immunosuppressive effect, but a low-grade, dose-dependent nephrotoxicity and diabetogenicity, which means that reducing the dose of FK is of considerable interest. Lipo-prostaglandin E1 (LPGE1) is a preparation of PGE1 that has potent immunosuppressive properties, and its duration of action is longer than that of ordinary PGE1. The purpose of this study was to investigate whether LPGE1 can enhance the immunosuppressive effect of FK. Heterotopic cardiac transplantations to the neck vessels were performed, and recipient rats were treated with intramuscular injections of FK and LPGE1 once daily for 10 days. All grafts without any treatment were rejected within 14 days. In comparison, the FK doses of 0.07, 0.2 and 1.0 mg/kg/day for 10 days significantly increased the long-term graft survival (>100 days) to 8%, 44% and 100%, respectively. The addition of LPGE1 to the first two dosages caused a further significant increase in the graft survival, to 18% and 80%, respectively, when compared with the control. LPGE1 appears to enhance the immunosuppressive effect of FK.

Factors influencing the outcome of donor marrow transplantation in adults from less than ideal donors: experience from two Australian centres

BACKGROUND

This paper reports the results of 78 marrow transplants in two Australian hospitals between 1991 and 1996, using unrelated (n = 54) or mismatched related (n = 24) donors. Twenty-six patients received granulocyte-macrophage colony stimulating factor (GM-CSF) post-transplant as part of a phase II study. Fifty-four patients (74%) had advanced disease.

AIMS

To identify factors associated with a superior outcome post-transplant, to evaluate the effect of GM-CSF on engraftment and other transplant parameters, and to compare the overall results with those of published series.

METHODS

Review of patient records, a Medline search of the relevant literature and appropriate statistical analysis.

RESULTS

The probability of overall survival and event-free survival (EFS) at three years was 35 +/- 6% and 22 +/- 6% respectively. Pre-transplant factors significantly associated with an inferior EFS were advanced disease, poorer performance status and age > 30 years. The EFS in patients with standard risk disease was 51 +/- 13% versus 10 +/- 5% in patients with advanced disease, p < 0.0001. Severe acute graft-versus-host disease was also associated with a poorer outcome. Neutrophil engraftment was faster in patients who received GM-CSF but there was no difference in any other transplant parameters.

CONCLUSIONS

These results are consistent with reported series elsewhere and suggest that an extended family or unrelated donor transplant should generally be limited to patients with a good performance status and early phase but otherwise incurable haematological disease.

Randomized trial of misoprostol in patients with chronic renal transplant rejection

Chronic vascular rejection is a major cause of long-term graft failure after renal transplantation. We investigated the effect of the addition of misoprostol (200 micrograms four times daily) to standard immunosuppressive therapy on the outcome of chronic rejection in a double-blind, placebo-controlled trial. Patients had to fulfill predefined histological and clinical criteria. After an entry of 40 patients into the study (22 misoprostol, 18 placebo), the inclusion of additional patients was terminated because of a high incidence of withdrawal due to adverse effects. Of the patients who used their study medication for at least 3 months (16 misoprostol, 15 placebo), graft function deteriorated in all but 5 misoprostol-treated and all but 2 placebo-treated patients. There was no difference in dialysis-free survival. Withdrawal because of adverse effects (mainly gastrointestinal complaints) occurred in 3 cases in the placebo group and in 11 cases in the misoprostol group (P < 0.05). In conclusion, we found no evidence for a beneficial effect of misoprostol on the course of chronic renal allograft rejection, while use of the drug was accompanied by a high incidence of side effects.

Defective signal transduction via T-cell receptor-CD3 structure in T cells from rheumatoid arthritis patients

T cells from patients with active RA are known to produce low levels of IL-2 and proliferate poorly in response to various mitogenic stimuli. The present work shows that cross-linking of CD3 antigen on patients' T-cell surface induces two- to threefold lower Ca2+ response than in T cells from age-matched controls. Immunofluorescence studies indicate that the attenuated signal may be due to the suppressed expression of CD3 and/or CD45 molecules on patients' T cells. In the majority of the patients, the level of CD45 expression is reduced by 60%-70% as compared with that in the control T cells. Therefore, the poor mitogenic response of patient cells is apparently due to a defect in early stages of signal transduction through the T-cell receptor (TCR-CD3).

Misoprostol: new frontiers; benefits beyond the gastrointestinal tract

Recent findings suggest that the protective role that misoprostol exerts in the gastrointestinal tract against nonsteroidal anti-inflammatory drug (NSAID) damage may be extended to a variety of other tissues and other noxious stimuli including those mediated by molecules such as interleukin 1 (IL-1), tumor necrosis factor (TNF), and endotoxin. The protective effects of misoprostol outside the gastrointestinal tract may involve prevention of triggering activities that would otherwise initiate a sequence of tissue damaging events. If this capacity of misoprostol to maintain homeostasis in a variety of settings is recognized, a cohesive pattern of action emerges. Numerous studies have shown that misoprostol is likely to act as a regulator within various cascades of immunological regulatory events. The in vitro and in vivo experimental data described in this paper suggest that the events which trigger episodes of pain and inflammation may be controllable by the administration of misoprostol. Mitigation of adverse effects of certain NSAIDs on renal function and cartilage metabolism has also been observed. Demonstration of this latter phenomenon in the clinical setting will greatly benefit the patient if it is shown to modify the arthritis disease process. The therapeutic applications of misoprostol beyond the gastrointestinal tract appear to be among the most interesting of therapeutic advances offered by any class of compound in the next decade. Because of the inflammatory and pain processes associated with arthritis disease progression, particular emphasis and confirmation through further clinical study should be placed on the potential effect of misoprostol on chondroprotection and synergy with NSAIDs.

Relationship between blood transfusion and tumour behaviour

Blood transfusion results in significant alterations in some parameters of immune function. Because some human cancers appear to stimulate immune responses and may be influenced by host immunity, the possibility arises that transfusion could alter the behaviour of tumours. Experimental studies indicate that allogeneic transfusion can directly alter tumour growth in some circumstances, but at present studies of human cancers do not provide evidence of a causal association between transfusion and tumour growth.

Prevention of acute graft rejection by the prostaglandin E1 analogue misoprostol in renal-transplant recipients treated with cyclosporine and prednisone

Prostaglandins of the E series have been shown to have immunosuppressive properties. To study the effects of the prostaglandin E1 analogue misoprostol on renal function and graft rejection after transplantation, we conducted a randomized, double-blind, placebo-controlled trial in 77 renal-allograft recipients. The subjects received misoprostol (200 micrograms four times daily by mouth; n = 38) or placebo (n = 39) for the first 12 weeks after transplantation, in addition to standard immunosuppression with cyclosporine and prednisone. They were then observed for an additional four weeks after the drug or placebo was discontinued. Treatment with misoprostol was associated with a significant improvement in renal function as judged by the mean (+/- SEM) serum creatinine concentration (128 +/- 7 vs. 158 +/- 11 mumol per liter after 12 weeks; P = 0.03) and creatinine clearance (84 +/- 6 vs. 69 +/- 5 ml per minute per 1.73 m2 of body-surface area; P = 0.05). There was a significant reduction in the incidence of acute rejection in the group treated with misoprostol as compared with the placebo group (10 of 38 vs. 20 of 39; P = 0.02), and there was less need for rehospitalization after transplantation (4 +/- 1 days with misoprostol vs. 10 +/- 2 days for placebo; P = 0.03). Although blood levels of cyclosporine did not differ significantly between the groups, they tended to be higher in the misoprostol group, as did the incidence of acute nephrotoxicity due to cyclosporine (13 of 38 vs. 8 of 39). Infectious complications tended to be fewer in the misoprostol-treated group (14 of 38 vs. 21 of 39). We conclude that misoprostol improves renal function and safely reduces the incidence of acute rejection in renal-transplant recipients treated concurrently with cyclosporine and prednisone.