Learned Immunosuppressive Placebo Response Attenuates Disease Progression in a Rodent Model of Rheumatoid Arthritis

Repeated saline injections reduce the pulmonary allergic inflammatory response in rats by inducing short-term stress

Purpose

Asthma is characterized by pulmonary cell infiltration and hyper-responsiveness of the airways. Short-term stress reduces airway inflammation. Thus, in the present study, we examined the effects of short-term stress induced by repeated treatment with saline injections on the pulmonary allergic inflammatory response in rats.

Methods

Adult male rats were divided into three groups: Naïve group (non-sensitized, challenged, or treated rats), Control group (rats sensitized with ovalbumin (OVA) to induce lung inflammation), and Saline group (rats treated for five days with saline before OVA sensitization). Inhalation challenges were performed one week after the booster with aerosolized OVA. On day 18, the effect of saline injections on total and differential leukocytes in bronchoalveolar lavage (BAL), femoral marrow lavage (FML), and blood was evaluated. The percentage of mucus, serum corticosterone, collagen, cytokines in lung explants, and norepinephrine levels were also measured.

Results

OVA sensitization increased the circulating leukocytes and their migration to the lung, decreasing the bone marrow leukocytes. The repeated saline injections prevented this migration by decreasing the number of leukocytes in BAL and blood in the control group. Cytokine Interleukin-4 (IL-4) was higher in the control group than in the naive and saline groups; cytokines Interleukin-6 (IL-6), Interleukin-10 (IL-10), and tumor necrosis factor-alpha (TNFα) were higher in the control and saline groups than in the naïve group; Interferon gamma (IFNγ) was higher in the saline group than in the naive and control groups; norepinephrine increased in animals sensitized with OVA and was higher only in the saline group relative to the naïve group.

Conclusions

These results suggest that short-term stress could contribute to the anti-allergic airway inflammation effects of a given treatment.

The Effects of Fingolimod (FTY720) on Leukocyte Subset Circulation cannot be Behaviourally Conditioned in Rats

Suppression of immune functions can be elicited by behavioural conditioning using drugs such as cyclosporin A or rapamycin. Nevertheless, little is known about the underlying mechanisms and generalisability of this phenomenon. Against this background, the present study investigated whether the pharmacological properties of fingolimod (FTY720), an immunosuppressive drug widely applied to treat multiple sclerosis, can be conditioned in rats by means of taste-immune associative learning. For this purpose, a conditioned taste avoidance paradigm was used, pairing the presentation of a novel sweet drinking solution (saccharin or sucrose) as conditioned stimulus (CS) with therapeutically effective doses of FTY720 as unconditioned stimulus (US). Subsequent re-exposure to the CS at a later time point revealed that conditioning with FTY720 induced a mild conditioned taste avoidance only when saccharin was employed as CS. However, on an immunological level, neither re-exposure with saccharin nor sucrose altered blood immune cell subsets or splenic cytokine production. Despite the fact that intraperitonally administered FTY720 could be detected in brain regions known to mediate neuro-immune interactions, the present findings show that the physiological action of FTY720 is not inducible by mere taste-immune associative learning. Whether conditioning generalises across all small-molecule drugs with immunosuppressive properties still needs to be investigated with modified paradigms probably using distinct sensory CS. Moreover, these findings emphasize the need to further investigate the underlying mechanisms of conditioned immunomodulation to assess the generalisability and usability of associative learning protocols as supportive therapies in clinical contexts.

Placebo effects in osteoarthritis: implications for treatment and drug development

Osteoarthritis (OA) is the most common form of arthritis worldwide, affecting ~500 million people, yet there are no effective treatments to halt its progression. Without any structure-modifying agents, management of OA focuses on ameliorating pain and improving function. Treatment approaches typically have modest efficacy, and many patients have contraindications to recommended pharmacological treatments. Drug development for OA is hindered by the gradual and progressive nature of the disease and the targeting of established disease in clinical trials. Additionally, new medications for OA cannot receive regulatory approval without demonstrating improvements in both structure (pathological features of OA) and symptoms (reduced pain and/or improved function). In clinical trials, people with OA show high 'placebo responses', which hamper the ability to identify new effective treatments. Placebo responses refer to the individual variability in response to placebos given in the context of clinical trials and other settings. Placebo effects refer specifically to short-lasting improvements in symptoms that occur because of physiological changes. To mitigate the effects of the placebo phenomenon, we must first understand what it is, how it manifests, how to identify placebo responders in OA trials and how these insights can be used to improve clinical trials in OA. Leveraging placebo responses and effects in clinical practice might provide additional avenues to augment symptom management of OA.

[Conditioning of the immune system-Already clinically usable?]

The brain and the immune system permanently exchange information via various neuronal and humoral signaling pathways. This communication network forms the basis for controlling peripheral immune functions via associative learning or conditioning processes. Establishing a learned immune reaction, an immunomodulatory drug that represents the unconditioned stimulus (US) is paired with a new odor or taste stimulus. Re-presentating this previously neutral odor or taste stimulus, its now functions as a conditioned stimulus (CS) and triggers reactions in the immune system similar to those formerly induced by the drug used as US. Using different learning protocols, it was possible to condition immunopharmacological effects in animal disease models, such as lupus erythematosus, contact allergy or rheumatoid arthritis, thereby reducing disease symptoms. Preliminary experimental studies in healthy volunteers and patients confirmed a possible clinical use of learned immune responses with the aim of using associative learning protocols as complementary measures to pharmacological interventions in clinical practice in order to reduce drug doses and thus undesirable drug side effects while maintaining therapeutic efficacy. However, there is still a great need for further research to understand the mechanisms of learned immune responses in preclinical studies and to optimize the associative learning processes for using them in the clinical routine in studies with healthy volunteers and patients.

Taste-immune associative learning amplifies immunopharmacological effects and attenuates disease progression in a rat glioblastoma model

Mechanistic target of rapamycin (mTOR)-signaling is one key driver of glioblastoma (GBM), facilitating tumor growth by promoting the shift to an anti-inflammatory, pro-cancerogenic microenvironment. Even though mTOR inhibitors such as rapamycin (RAPA) have been shown to interfere with GBM disease progression, frequently chaperoned toxic drug side effects urge the need for developing alternative or supportive treatment strategies. Importantly, previous work document that taste-immune associative learning with RAPA may be utilized to induce learned pharmacological placebo responses in the immune system. Against this background, the current study aimed at investigating the potential efficacy of a taste-immune associative learning protocol with RAPA in a syngeneic GBM rat model. Following repeated pairings of a novel gustatory stimulus with injections of RAPA, learned immune-pharmacological effects could be retrieved in GBM-bearing animals when re-exposed to the gustatory stimulus together with administering 10 % amount of the initial drug dose (0.5 mg/kg). These inhibitory effects on tumor growth were accompanied by an up-regulation of central and peripheral pro-inflammatory markers, suggesting that taste-immune associative learning with RAPA promoted the development of a pro-inflammatory anti-tumor microenvironment that attenuated GBM tumor growth to an almost identical outcome as obtained after 100 % (5 mg/kg) RAPA treatment. Together, our results confirm the applicability of taste-immune associative learning with RAPA in animal disease models where mTOR overactivation is one key driver. This proof-of-concept study may also be taken as a role model for implementing learning protocols as alternative or supportive treatment strategy in clinical settings, allowing the reduction of required drug doses and side effects without losing treatment efficacy.

Taste-Associative Learning in Rats: Conditioned Immunosuppression with Cyclosporine A to Study the Neuro-Immune Network

The pharmacological effects of an immunosuppressive drug, such as cyclosporine A (CsA), can be learned and retrieved by humans and animals when applying associative learning paradigms. This principle is based on Pavlovian conditioning, in which repeated presentation of an "unconditioned stimulus" (US; here, the drug CsA) is paired with exposure to a "conditioned stimulus" (CS; here, the novel taste of saccharin). Re-exposure to the CS at a later time leads to an avoidance behavior. Concomitantly, using this paradigm, animals exposed to the CS (saccharin) display immunosuppression, reflected by reduced splenic T-cell proliferation and diminished interleukin-2 and interferon-γ expression and release in ex vivo cultured splenocytes, mimicking the pharmacological effects of the US (CsA). Notably, this paradigm of taste-immune associative learning demonstrates the impressive abilities of the brain to detect and store information about an organism's immunological status and to retrieve this information, thereby modulating immunological functions via endogenous pathways. Moreover, conditioned pharmacological effects, obtained by means of associative learning, have been successfully implemented as controlled drug-dose reduction strategies as a supportive treatment option to optimize pharmacological treatment effects for patients' benefit. However, our knowledge about the underlying neurobiological and immunological mechanisms mediating such learned immunomodulatory effects is still limited. A reliable animal model of taste-immune associative learning can provide novel insights into peripheral and central nervous processes. In this article, we describe protocols that focus on the basic taste-immune associative learning paradigm with CsA and saccharin in rats, where conditioned peripheral immunosuppression is determined in ex vivo cultured splenocytes. The behavioral protocol is reliable and adaptable and may pave the road for future studies using taste-immune associative learning paradigms to gain deeper insight into brain-to-immune-system communication. © 2022 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Taste-immune associative learning with cyclosporine A Basic Protocol 2: Splenocyte isolation and cultivation to study stimulation-induced cytokine production.

Incomplete reminder cues trigger memory reconsolidation and sustain learned immune responses

Peripheral immune responses can be modulated by taste-immune associative learning where the presentation of a sweet taste as conditioned stimulus (CS) is paired with the injection of an immunosuppressive substance as unconditioned stimulus (US). Previous findings demonstrate conditioned immunopharmacological properties of the mechanistic target of rapamycin (mTOR)-inhibitor rapamycin, a drug used to ameliorate neurological diseases and for the prevention of graft rejection. However, conditioned responses gradually weaken over time and eventually disappear following repeated exposure to the CS in the absence of the US. Thus, in order to employ learning paradigms in clinical conditions as supportive immunopharmacological therapy it is important to understand the central and peripheral mechanisms of how learned immune responses can be protected from extinction. Against this background, the present study used a taste-immune learning paradigm with rapamycin as US (5 mg/kg). By applying only 10% (0.5 mg/kg) of the therapeutic dose rapamycin together with the CS (taste stimulus) during eight retrieval trials, conditioned animals still displayed suppressed interleukin-10 production and T cell proliferation in splenocytes as well as diminished activity of the mTOR target protein p70s6k in amygdala tissue samples. Together, these findings indicate that reminder cues in form of only 10% (0.5 mg/kg) of the therapeutic dose rapamycin together with the CS (taste stimulus) at retrieval preserved the memory of conditioned properties of rapamycin, characterizing this approach as a potential supportive tool in peripheral and central pharmacotherapy with the aim to maximize the therapeutic outcome for the patient's benefit.

Treatment with the calcineurin inhibitor and immunosuppressant cyclosporine A impairs sensorimotor gating in Dark Agouti rats

RATIONALE

Calcineurin is a protein regulating cytokine expression in T lymphocytes and calcineurin inhibitors such as cyclosporine A (CsA) are widely used for immunosuppressive therapy. It also plays a functional role in distinct neuronal processes in the central nervous system. Disturbed information processing as seen in neuropsychiatric disorders is reflected by deficient sensorimotor gating, assessed as prepulse inhibition (PPI) of the acoustic startle response (ASR).

OBJECTIVE

Patients who require treatment with immunosuppressive drugs frequently display neuropsychiatric alterations during treatment with calcineurin inhibitors. Importantly, knockout of calcineurin in the forebrain of mice is associated with cognitive impairments and symptoms of schizophrenia-like psychosis as seen after treatment with stimulants.

METHODS

The present study investigated in rats effects of systemic acute and subchronic administration of CsA on sensorimotor gating. Following a single injection with effective doses of CsA, adult healthy male Dark Agouti rats were tested for PPI. For subchronic treatment, rats were injected daily with the same doses of CsA for 1 week before PPI was assessed. Since calcineurin works as a modulator of the dopamine pathway, activity of the enzyme tyrosine hydroxylase was measured in the prefrontal cortex and striatum after accomplishment of the study.

RESULTS

Acute and subchronic treatment with the calcineurin inhibitor CsA disrupted PPI at a dose of 20 mg/kg. Concomitantly, following acute CsA treatment, tyrosine hydroxylase activity was reduced in the prefrontal cortex, which suggests that dopamine synthesis was downregulated, potentially reflecting a stimulatory impact of CsA on this neurotransmitter system.

CONCLUSIONS

The results support experimental and clinical evidence linking impaired calcineurin signaling in the central nervous system to the pathophysiology of neuropsychiatric symptoms. Moreover, these findings suggest that therapy with calcineurin inhibitors may be a risk factor for developing neurobehavioral alterations as observed after the abuse of psychomotor stimulant drugs.

[The learned placebo response in the immune system]

The learned placebo response of the immune system is based on the mutual interaction between the brain and the immune system; both systems continually exchange information via humoral and neural communication pathways. This communication network enables the modification, i.e. suppression or stimulation, of peripheral immune functions by classical or Pavlov's conditioning. The present article provides an overview of the results of recent experimental animal studies, which also document the potential clinical relevance of learned immune responses. Learned immunological responses mediated by classical conditioning have also been demonstrated in humans. The knowledge gained from experimental data and clinical observations paves the way for a potential implementation of learned immune responses as supportive measures to standard immunopharmacological treatment strategies to reduce drug dosage as well as adverse side effects while simultaneously maximizing the therapeutic effect.