Lesson 18

Question 1

Seak about anicytokine drugs

Answer 1

Anticytokine drugs are new modern drugs, in fact for what concerns inflammatory diseases, groundbreaking solutions have emerged in the form of biopharmaceuticals. These engineered recombinant antibodies and proteins mark a significant step in treating severe inflammation. However, their complex production and high cost often limit their use. Typically, they are reserved for patients not responding well to other therapies, and are administered under expert supervision.

Chronic inflammatory diseases often involve disturbances in glucocorticoid production. Consequently, glucocorticoids play a fundamental role in anti-inflammatory drug therapy, this, as we have seen, is achieved by also repressing the transcription of pro-inflammatory genes like TNF-alpha. These drugs too are able to act on TNF-alpha, which is one of their main targets. The two major classes of anticytokine drugs targeting this factor are:

1. Monoclonal Antibodies (ending in -mab): among which we find momab, which is mouse-produced, at first most monocolonal antibodies were created from mice but thay have the unfortuante effect of stimulating an immune response form our body, so leter on we developed other antibodies like ximab a chimeric, partly mouse, partly human antibody, zumab, a humanized andibody, and mumab which is entirely human. So we have drugs such as Infliximab and Adalimumab.
2. Fusion proteins (ending in -cept): these proteins are formed by a part of an antibody and a part which is similar to a receptor, so they act as soluble receptors for TNF-alpha, preventing its interaction with its own receptor. An example is etanercept.

TNF-alpha’s, produced by macrophages, have an impact on synovial fibroblast activation, promoting cartilage degradation, endothelial cell activation facilitating leukocyte adhesion, and T cell activation. TNF-alfa is present in its soluble form but also bound to the membrane to an enzyme called TACE which isi able to release TNF alpha. Infliximab and adalimumab are able to block the soluble form but also TACE, but the have the side effect of sometimes causing the lysis of the cell, killing it. Instead etanercept is only able to capture the soluble TNF-alfa and prevent the interaction with its receptor. This is the main difference between the action of fusion proteins and monoclonal antibodies. Infliximab sometimes is given in combination with methotrexate, and this combination shows enhanced efficacy compared to individual drugs, offering promising outcomes for patients.

A part from TNF-alpha, another importnat targets for anticytokines drugs is *IL-1. Several antibodies exhibit efficacy in blocking IL-1, each with unique mechanisms, for example we have Anakinra, a recombinant version of IL-1 receptor whcih is able to prevent the binding of IL-1 to the proper receptor and its dimerization and thus and signaling in cells, Secukinumab and Canakinumab which are monoclonal antibodies and Interact with IL-1ß, a critical isoform in the inflammatory response. And Rilonacept, a soluble receptor, adept at sequestering IL-1, hindering its interaction with membrane-bound receptors. During the early stages of the Covid pandemic, evidence pointed to the inflammatory pathogenesis of COVID-19 being tied to a cytokine storm. So, drugs like Anakinra,* targeting proinflammatory cytokines, showed promising results in trials.

Moreover other important targets are **IL-6, IL-12 and IL-23, The firs one is essential for B cell differentiation and immunoglobulin production. Elevated IL-6 levels are implicated in autoimmune and inflammatory conditions; while the latter are cytokines involved in natural killer cell activation and CD4 T-cell differentiation.

There are also drugs Modulating T Cells. A costimulatory signal is required for activation of a T cell response to antigenas, so drugs are able to block this costimulatory signal. An example there is Abatacept, used in rheumatoid arthritis, which prevents costimulatory signals, thereby inhibiting T cell activation.

Then there are compounds Targeting B Cells which induce B cell lysis or prevent B cell activation. Rituximab, for instance, causes B cell lysis. Rituximab is a monoclonal antibody that targets a specific protein on the surface of B cells called CD20. CD20 is involved in the regulation of B-cell activation and differentiation. Rituximab is primarily used in the treatment of certain B-cell malignancies, autoimmune diseases, and conditions characterized by abnormal B-cell activity. The mechanism of action of Rituximab involves several ways:

1. B Cell Depletion: Rituximab primarily acts by binding to CD20, which is expressed on the surface of B cells. This binding triggers an immune response, leading to the destruction of B cells. The exact mechanisms involved in B cell depletion include complement-dependent cytotoxicity (CDC) and antibody-dependent cellular cytotoxicity (ADCC). These processes involve the activation of immune cells (such as natural killer cells) and the complement system, leading to the elimination of B cells from the circulation.
2. Apoptosis Induction: Rituximab can induce programmed cell death, known as apoptosis, in B cells. This occurs after the binding of Rituximab to CD20, initiating intracellular signals that activate pathways leading to apoptosis. This direct induction of apoptosis contributes to the reduction in B-cell populations.
3. Complement Activation: Rituximab can activate the complement system, which is part of the immune system. The complement system can lead to the lysis (rupture) of targeted cells. Rituximab binding to CD20 on B cells triggers the complement cascade, leading to the formation of the membrane attack complex (MAC) and subsequent destruction of B cells.
4. Antibody-Dependent Cellular Phagocytosis (ADCP): In addition to ADCC, Rituximab can also induce antibody-dependent cellular phagocytosis (ADCP). In ADCP, immune cells, such as macrophages, recognize Rituximab-coated B cells and engulf them, contributing to the removal of B cells from the system.

For all these compouns we have to talk about the administration route. Given the large size of these proteins they are mostly are administered via injection, and the frequency of injections varies, ranging from weekly for etanercept to every two months for infliximab. For these novel compounds, approximately 30% of patients may not respond, prompting discontinuation if no therapeutic benefit is observed within 2–4 weeks. Studies suggest that initiating treatment with drugs like infliximab in combination with methotrexate can reduce this failure rate and lead to superior therapeutic outcomes, particularly in rheumatoid disease. Considering the critical role cytokines play, anticytokine or antileukocyte therapy may predispose patients to latent or opportunistic infections. Notably, patients on these therapies may experience side effects such as stomatitis and candida infections.

Question 2

Speak about histamine and antihistamine

Answer 2

In the field of inflammatory processes linked to allergies, histamine is a fundamental inflammatory mediator. This basic amine, derived from histidine through the action of histidine decarboxylase, is a vital component of the parasympathetic system.

Histamine is ubiquitously present but attains high concentrations in tissues in direct contact with the external environment, such as the lungs, skin, and gastrointestinal tract. Primarily found within mast cells and basophils at the cellular level, histamine operates as an autacoid: a locally secreted molecule influencing neighboring cell activity. Not only does histamine play an importnat role in allergic and inflammatory processes, but it also significantly regulates gastric acid secretion, neurotransmission, and immune modulation.

Histamine operates through four distinct receptors (H1-4). For the context of allergic reactions, the focus lies on H1 receptors, as H2 receptors primarily govern gut functions. These receptors are G protein-coupled and vary in G protein coupling.

• H1 receptors: Associated with acute allergic reactions, these Gq-coupled receptors elevate intracellular calcium levels.
• H2 receptors: Coupled with Gs, they regulate gastric acid secretion, predominantly in the gut.
• H3 receptors: Present in neural tissues.
• H4 receptors: Found in hematopoietic cells.

But Histamine’s effects, can givie rise to flare responses observed after an histamine release in the skin during insect bites or allergic reactions, they ofthen include redness and edema. We might have: In the lungs, bronchoconstriction, resembling asthma symptoms. Individuals with asthma exhibit heightened sensitivity to histamine, showcasing variability in responsiveness. Vascular effects including post-capillary dilation, terminal arteriole dilation, and venoconstriction, contributing prominently to redness. Contraction of vascular endothelium and release of serine in tissues lead to edema. Peripheral nerves undergo sensitization, resulting in itch and pain, a cascade triggered by histamine and its ability to induce the release of other mediators.

All these effects are mediated primarily through the H1 histamine receptor.

So, when exposed to allergens, B cells process them, generating IgE on mast cell surfaces. Upon subsequent allergen contact, an IgE-allergen interaction triggers histamine degranulation, initiating inflammatory disorders like allergic rhinitis and acute urticaria. In severe cases, this leads to anaphylaxis, characterized by bronchoconstriction and epiglottal swelling. Anaphylactic shock, a life-threatening condition, ensues upon re-exposure to an allergen, with symptoms like hypotension, bronchoconstriction, and epiglottal swelling. Rapid administration of epinephrine becomes imperative for treatment, countering histamine’s effects.

Antihistamines, particularly H1-antihistamines, offer relief against simple allergies. Recent studies reveal their inverse agonist nature, reducing constitutive receptor activity. Two generations of this compounds exist,

• First Generation: it is characterized by two aromatic rings linked by ethylamine. It is lipidic and neutral at physiological pH, enabling blood-brain barrier (BBB) passage. It acts on both peripheral and central histamine receptors, inducing sedation as a side effect.
• Second Generation: It is structurally similar to the first generation but lacks sedative effects. They remain ionized at physiological pH, precluding BBB passage. These compound work peripherally without central nervous system (CNS) interaction.

While older sedating drugs may find use in promoting sleep, the primary role of antihistamines lies in managing allergic reactions, excluding asthma and anaphylaxis. In these cases, where other mediators are involved, antihistamines alone prove insufficient. For anaphylaxis, epinephrine is the vital intervention, and asthma requires beta agonists.