Delayed hypersensitivity to tuberculin in rats: effects of antirheumatic drugs

Hormesis is central to toxicology, pharmacology and risk assessment

This paper summarizes numerous conceptual and experimental advances over the past two decades in the study of hormesis. Hormesis is now generally accepted as a real and reproducible biological phenomenon, being highly generalized and independent of biological model, endpoint measured and chemical class/physical stressor. The quantitative features of the hormetic dose response are generally highly consistent, regardless of the model and mechanism, and represent a quantitative index of biological plasticity at multiple levels of biological organization. The hormetic dose-response model has been demonstrated to make far more accurate predictions of responses in low dose zones than either the threshold or linear at low dose models. Numerous therapeutic agents widely used by humans are based on the hormetic dose response and its low dose stimulatory characteristics. It is expected that as low dose responses come to dominate toxicological research that risk assessment practices will incorporate hormetic concepts in the standard setting process.

Hormetic Dose-Response Relationships in Immunology: Occurrence, Quantitative Features of the Dose Response, Mechanistic Foundations, and Clinical Implications

This article provides an assessment of the occurrence of immune-system-related hormetic-like biphasic dose-response relationships. Such dose-response relationships are extensive, with over 90 different immune response-related endpoints reported, induced by over 70 endogenous agonists, over 100 drugs, and over 40 environmental contaminants. Such hormetic responses were reported in over 30 animal models, over a dozen mammalian and human cell lines. These findings demonstrate that immune-system-related hormetic-like biphasic dose-response relationships are common and highly generalizable according to model, endpoint, and chemical class. The quantitative features of the dose response are generally consistent with previously published examples of hormetic dose responses for other biological endpoints. These findings were generally recognized and explicitly discussed by the original authors, often with consideration given to possible mechanistic foundations as well as numerous clinical implications. Despite the recognition by individual authors of the hormetic nature of these observed responses, the overall widespread nature of immune-related hormetic responses has been only little appreciated, with a general lack of insight into the highly generalizable nature of this phenomenon as well as the complex regulatory networks affecting biological switching mechanisms that result in the hormetic responses.

D-penicillamine in vivo enhances lymphocyte DNA synthesis: role of macrophages

Administration of D-penicillamine (50 mg/kg/day orally) for 4 days increased the uptake of 3H-thymidine (3H-TdR) in unstimulated and concanavalin-A-stimulated unseparated lymph node and spleen cells from Lewis rats. Increased 3H-TdR incorporation was also found in cultures depleted of adherent cells. D-Penicillamine treatment did not increase the incorporation of 3H-TdR in lymph node and spleen cells from rats concomitantly treated with the selective macrophage toxin silica. In contrast, treatment with D-penicillamine during the last 4 days of silica treatment sometimes resulted in a marked decrease in 3H-TdR incorporation. It is suggested that D-penicillamine treatment in vivo is able to enhance the responsiveness of the lymphocytes, dependent on the presence of functionally intact macrophages. The increased response vanished after 2-3 weeks, even with continuous administration of D-penicillamine.

Disease-modifying anti-rheumatic drugs: strategies for screening

Rheumatoid arthritis, a disease of unknown aetiology, has a multifactorial pathogenesis which may result in irreversible connective tissue destruction and loss of joint function. The search for drugs which offer more than symptomatic relief is a long term, largely unachieved aim of many pharmaceutical companies. This review briefly outlines those features of the aetiopathogenesis which appear to offer targets for therapeutic intervention and the structured strategy and test systems that can be used to detect drugs which may be capable of halting disease progression.

Dissociation between antiinflammatory action of tilorone and its interferon inducing activity

A relation between antiinflammatory action of tilorone and its interferon inducing activity was studied in rats. Tilorone (20-100 mg/kg, p.o.) was dose-dependently effective on both carrageenin oedema and passive Arthus, suggesting that the pharmacological property of the compound is different from nonsteroidal antiinflammatory medicaments which were weak inhibitors of passive Arthus. The antiinflammatory action of tilorone had a time-lag and priming with tilorone 24 hrs prior to inflammatory insult was required to demonstrate maximal efficacy. This time course change was similar to that of serum interferon level. In addition, a high correlation was observed between the antiinflammatory activity and the serum interferon level. However, the antiinflammatory action was scarcely affected even if the serum interferon level was remarkably lowered by treatment of an inhibitor of protein biosynthesis, cycloheximide. These findings suggested that the antiinflammatory action of tilorone could be dissociated from its interferon inducing activity.

Drug actions on delayed-type hypersensitivity in rats with developing and established adjuvant arthritis

Rats were sensitized by i.d. injection in the base of the tail with Freund's complete adjuvant (FCA) and were challenged i.d. in the dorsal skin with mycobacterial antigen. The 24 hour dermal delayed-type hypersensitivity (DTH) response increased up to 10 days after FCA injection followed by a decrease by day 15 which coincided with the development of adjuvant arthritis (AA). Drug studies were performed, using a 4-day dosing schedule, on optimal DTH elicited on day 10, suboptimal DTH elicited on day 15, and AA (day 16). Cyclosporine, leflunomide and prednisolone significantly inhibited day 10 DTH and AA with no effect on day 15 DTH. Indomethacin and tiaprofenic acid significantly inhibited AA with no effect on either DTH response. Chloroquine, levamisole, D-penicillamine, diazepam and RU38468 had no significant effect on DTH or AA. These findings suggest a complex temporal relationship between AA, DTH and drug actions.

Pharmacological investigation of acute cellular accumulation in immunological air pouch inflammation

Immunologically-mediated cellular accumulation was measured 24 hours after antigenic challenge using a rat subcutaneous air pouch model. This response was inhibited by treatment with prednisolone, colchicine, anti-thymocyte serum and systemic antigen. In contrast, administration of a range of other pharmacological and clinically active agents had little effect. The profile of inhibitory activity suggested that this response was mainly due to delayed type hypersensitivity with little anaphylactic or Arthus-type component.

Studies of D-penicillamine on strain variability and lymph node cellularity in adjuvant arthritis

Experiments were performed in order to ascertain the action of D-penicillamine (PA) on adjuvant arthritis (AA) in rats and to develop a quantitative evaluation method for PA-like drugs, using Lewis, SD, and Wistar rats. Rats were inoculated in the tail with 0.6 mg of Mycobacterium butyricum suspended in 0.1 ml of liquid paraffin. PA apparently induced enhancement of arthritis only in Lewis rats with a good reproducibility. The enhancing effect of PA was seen when it was administered during the period from day -7 to day -1, from day 0 to day 6, or from day 14 to day 20. In control group of Lewis and Wistar rats, adjuvant caused a rapid increase in the cell number of lymph nodes just after the inoculation, and also a marked increase in spleen cells coinciding with the development of arthritis. In PA-treated Lewis rats, the cell numbers of lymph nodes and spleen significantly surpassed those of control rats. However, PA induced no difference from control in Wistar rats, which were not sensitive to PA treatment during the course of arthritis. These results indicate that AA in Lewis rats is a good model for evaluating the activities of PA-like drugs and that PA may affect lymphocytes in lymph nodes and spleen and induce severer arthritis in Lewis rats.

Prolonged treatment with D-penicillamine: effects on adjuvant arthritis in the rat

The effects of long term D-penicillamine treatment on adjuvant arthritis in the rat were determined in order to establish a possible approach to the laboratory evaluation of anti-rheumatic drugs. Oral pretreatment (1-3 months) followed by continued through-treatment on a daily basis (100 mg/kg p.o.) failed to modify the parameters tested: viz. (a) body weight changes; (b) primary paw lesions; (c) secondary hind paw lesions; (d) secondary forepaw, ear and tail lesions; (e) the number of 'responders'. Autopsy showed no macroscopic abnormalities in the lungs, heart, thymus, liver, spleen, adrenal glands, kidneys and gastro-intestinal tract. These results are discussed in relation to previous findings whereby rat adjuvant arthritis, in addition to other experimental immune reactions, has been suggested as an indicator for D-penicillamine activity.

An unusual profile of activity of a new basic anti-inflammatory drug, timegadine

Timegadine (SR 1368, N-cyclohexyl-N"-4-(2-methylguinolyl)-N'-2-thiazolylguanidine) dose-dependently inhibited carrageenan-, nystatin-, and concanavalin A-induced edema. Detailed studies in adjuvant arthritic rats showed: (a) long dosing regimen with timegadine inhibited primary and secondary lesions, leukocytosis and hyperfibrinogemia, (b) timegadine was significantly active in reducing the severity of the already established disease, (c) a short course of dosing with timegadine at the time of adjuvant injection permanently prevented the development of secondary lesions. The tuberculin hypersensitivity reaction was enhanced by timegadine in both adjuvant arthritic and normal rats. Experimental allergic encephalomyelitis in rats and guinea pigs was not affected. It is concluded that timegadine has a profile or activity which differs from that of known anti-inflammatory drugs.