Insights into the anti-inflammatory and anti-arthritic potential of 3-Acetyl-11-keto-β-Boswellic Acid as a therapeutic approach in Rheumatoid Arthritis

KEYWORDS:

• AKBA
• Rheumatoid arthritis
• NF-κB pathway
• 5-LOX pathway
• Proinflammatory cytokines
• Matrix metalloproteinase enzyme
• Boswellic acid

1. Introduction

Rheumatoid arthritis (RA) is a chronic systemic autoimmune disorder that primarily affects the synovial joint region, if left untreated, it can cause excruciating pain, damage to the joints, and functional impairment [1]. More than 23 million people around the world currently suffer from RA, including 12.6 million Indians [2]. The literature has revealed that the autoimmune inflammatory response that targets the joints and causes chronic inflammation, tissue damage, and joint deformities is the primary factor in the etiology of RA [3]. In RA, the synovial membrane has an inflammatory phenotype and becomes more hypertrophic. These involve the activation and invasion of immune cells into the synovial tissue, primarily macrophages, T cells, and dendritic cells, in addition to B cells, neutrophils, and mast cells. These contribute to the production of chemical mediators and pro-inflammatory cytokines like interleukins (ILs)-1β, IL-6, and tumor necrosis factor (TNF-α) which causes inflammation in the tissue [2].

Pro-inflammatory cytokines were connected in a network in the rheumatoid synovium, with TNF-α at its hub [4]. Additionally, TNF-α may maintain macrophage activation through a positive feedback loop. TNF-α expression is regulated by activating the transcription factor, i.e., nuclear factor kappa B (NF-κB). Thus, increased NF-κB activation, for instance in macrophages, may be in charge of sustaining and amplifying cytokine production, which may be what triggers the pathogenic mechanisms of RA [5]. Also, TNF-α has been shown to promote the expression of matrix metalloproteinases (MMPs) and other catabolic enzymes to damage the extracellular matrix (ECM) that led to cartilage destruction. TNF-α is therefore viewed as a pertinent therapeutic target [6]. There is one crucial inflammatory intermediate called arachidonic acid which is released from membrane phospholipid by the enzyme phospholipase in response to a variety of stressors [7]. Additionally, lipoxygenase (LOX) pathway is involved in the inflammatory actions related to arachidonic acid. Thus, 5-LOX pathway is regarded as a potential target for the development of effective treatment for RA condition [4].

Presently, there are challenges in providing effective treatment for RA as the majority of them are associated with the side effects of gastrointestinal, hepatic, and hematological damage [4]. Therefore, efforts should be focused on developing improved, efficient remedies that have few or no adverse effects [3]. New treatments are now being developed utilizing natural substances after recommendation by the American College of Rheumatology. The majority of RA patients (60–90%) rely on complementary medicines originated from natural origin.

Recently, 3-Acetyl-11-keto-β-boswellic acid (AKBA), a phytoconstituent, explored for the management of moderate-to-severe RA conditions and proved to be a better therapeutic molecule over some conventional synthetic drugs due to their natural origin [8]. AKBA, derived from Boswellia serrata extract, is a white, crystalline powder with a molecular weight of 512.7 g/mol (Figure 1). It is slightly soluble in water and has good solubility in organic solvents such as dimethyl formamide, dimethyl sulfoxide, ethanol, methanol, and acetonitrile. AKBA can donate protons in aqueous solution because of having carboxylic acids (−COOH) or phenolic hydroxyl (−OH) functional groups, which allow it to operate as an acid. In RA condition, it will therefore be in a unionized state with an acidic pH, allowing it to accumulate at the synovial lining of joints and skin tissues. AKBA has been found to be effective owing to their specific mechanism against signaling pathways (5-LOX pathway and NF-κB pathway) and molecular targets (MMPs enzymes and pro-inflammatory cytokines) in RA conditions which is discussed further in this report [9].

Figure 1. Chemical structure of 3-Acetyl-11-keto-β-boswellic acid (AKBA).

2. Signaling pathways and molecular targets modulated by AKBA in rheumatoid arthritis

Indeed, new molecular targets or pathways that may contribute to the onset and progression of RA have been identified. Because of the multifaceted mechanisms of action of AKBA, it can work through various pathways and may provide a comprehensive approach to address the complex inflammation and tissue damage associated with RA as shown in Figure 2.

Figure 2. Diagrammatic illustration of signaling pathways and molecular targets of 3-Acetyl-11-keto-β-boswellic acid (AKBA) in rheumatoid arthritis. Abbreviations: AKBA: 3-Acetyl-11-keto-β-boswellic Acid; NF-κB: nuclear factor kappa B; IL: Interleukin; TNF-α: tumor necrosis factor-alpha; CD4: clusters of differentiation 4; RF: rheumatoid factors; APC: antigen-presenting cells; RANKL: receptor activator of nuclear factor-kappa B ligand; PLA2: phospholipase A2; FLAP: 5-lipoxygenase activating protein; 5-LOX: 5-lipoxygenase; LT (A4, B4, C4, D4, E4): leukotriene (A4, B4, C4, D4, E4).

2.1. 5-lipoxygenase (5-LOX) pathway

Leukotrienes are inflammatory mediators that are produced by the 5-LOX pathway, a biochemical process that contributes to the development of RA [10]. AKBA works by blocking the 5-LOX pathway to combat RA [11]. In this pathway, arachidonic acid is released from membrane phospholipid by the enzyme phospholipase in response to a variety of stimuli. Leukotrienes are produced in large amounts from arachidonic acid because of the 5-LOX enzyme. Leukotrienes play a role in the activation of immune cells and the development of inflammation that can result in tissue damage. Here, AKBA can aid in lowering the generation of pro-inflammatory leukotrienes by blocking the 5-LOX pathway. Therefore, fewer immune cells are being drawn to the affected joints which may lessen RA symptoms and aid in the management of RA [4].

2.2. Nuclear factor-kappa B (NF-κB) pathway

Another signaling pathway that can be targeted in RA is the NF-κB pathway, using AKBA. The NF-κB pathway controls the expression of genes related to immune response, cell survival, persistent inflammation in the synovial joints, and other activities in RA. Inactive NF-κB is typically seen in the cytoplasm coupled to inhibitory proteins. Pro-inflammatory cytokines (including TNF-α), among other stimuli, activate signaling pathways that cause the breakdown of inhibitory proteins, enabling NF-κB to translocate into the nucleus and start the transcription of pro-inflammatory genes [6].

It is thought that AKBA suppresses inflammation by preventing NF-κB from being activated. This can be done by blocking IκB kinase and directing them toward disintegration. AKBA can lessen the expression of pro-inflammatory cytokines, chemokines, and enzymes that fuel the inflammatory process in RA by suppressing the NF-κB pathway. This may result in a decrease in immune cell activation and a reduction in joint inflammation [5].

2.3. Matrix metalloproteinase (MMP) enzymes

Using AKBA to target MMP enzymes is yet another strategy to combat RA. In RA, after activation of immune cells, inflammatory mediators (MMPs) are released as a result of the chronic inflammation that occurs in the synovial joints. The MMPs may break down collagen and proteoglycans found in cartilage and connective tissues [6]. This deterioration of joint tissues led to discomfort, stiffness, and loss of joint function. The ability of AKBA to prevent MMPs activity has been investigated, maybe by interfering with the signaling mechanisms that control their production. Therefore, AKBA can aid in prevention of the cartilage deterioration and other joint tissues by inhibiting MMPs [10].

2.4. Pro-inflammatory cytokines

The key mediators of the inflammatory processes associated with RA include pro-inflammatory cytokines that become an approach to treat RA by utilizing AKBA. The cytokines such as TNF-α, IL-1, and IL-6 are produced in excess when the immune system is dysregulated in RA. An ongoing cycle of inflammation is perpetuated by immune cells, including macrophages and T cells that generate pro-inflammatory cytokines [2]. They cause the synthesis of other inflammatory chemicals to be stimulated and draw more immune cells to the inflamed joints, which causes joint pain, swelling, and tissue degradation [1]. AKBA can inhibit the signaling pathways that control the expression of pro-inflammatory cytokines. This cytokine downregulation can aid in lowering the severity of the inflammatory response in RA. Since AKBA has the capacity to affect a number of inflammatory pathways, including the production of cytokines, it provides a thorough strategy for combating the intricate inflammatory processes associated with the RA condition [4].

3. Current treatments available for RA utilizing AKBA

To develop tailored treatments for RA conditions, it is necessary to put in a lot of effort to accurately identify the distinguishing characteristics and pathogenic pathways of each stage of RA development. Recent findings suggested that utilization of phytoconstituents might be a better choice in the management of RA because of their safety, fewer side or toxic effects, and better efficacy. AKBA has an impact on a number of signaling pathways and molecular targets, including 5-LOX, NF-κB, MMPs, and pro-inflammatory cytokines which are crucial in the emergence of RA condition. There are various studies that have explored the anti-inflammatory and anti-arthritic potential of AKBA mentioned in Table 1.

Table 1. 3-Acetyl-11-keto-β-boswellic acid (AKBA) loaded nanocarrier system for exploring its anti-inflammatory and anti-arthritic potential.

AKBA-loaded nanocarrier system	Route of administration	Activity explored	Significant outcomes	References
Nanogel	Topical	Anti-inflammatory	The results of in-vivo study demonstrated that the AKBA loaded nanogel showed 3-fold faster reduction in edema rate in rats in comparison to free AKBA gel after 12 h of treatment. The outcome of the study indicated the potential of AKBA.	[12]
Free AKBA and Methotrexate (MTX) dispersion	Oral (AKBA) and Intraperitoneal (MTX)	Anti-inflammatory and anti-arthritic	10% AKBA at dose of 20 mg/kg and 40 mg/kg inhibited paw edema of 40.85% and 68.5% in comparison to 2% AKBA (40 mg/kg) and diclofenac (10 mg/kg) respectively. Also, 10% AKBA inhibited paw volume of 63.59% and 59.05% in combination with MTX at 20 and 40 mg/kg respectively in FCA (Freund’s complete adjuvant) induced animal model. These findings proved the anti-inflammatory and anti-arthritic potential of AKBA.	[4]
Poly lactic-co-glycolic acid nanoparticles	Oral	Anti-inflammatory activity	The pharmacokinetic study showed 6-fold increase in oral bioavailability of AKBA in case of AKBA loaded nanoparticles in comparison to free AKBA. The results of in-vivo animal study showed 1.67-fold higher percentage inhibition of edema in case of AKBA loaded nanoparticles than free AKBA after 5 h of treatment to carrageenan induced rat paw edema model. The results suggested that the AKBA is having anti-inflammatory property which makes it a potential candidate for the management of RA.	[13]
Polymeric nanomicelles	Topical	Anti-inflammatory and anti-arthritic	The results of in-vivo carrageenan induced paw edema animal study demonstrated 81.1% inhibition of edema in case of AKBA loaded polymeric nanomicelles gel and 44.1% inhibition in case of free AKBA after 12 h of administration. Additionally, 2-fold higher inhibition of arthritis was achieved by AKBA loaded polymeric nanomicelles gel than free AKBA loaded gel in FCA induced arthritis animal model. The results suggested that the AKBA is having anti-inflammatory and anti-arthritic potential which makes it a drug of choice for the management of RA.	[14]
Nanospanlastics	Topical	NA	The results of ex-vivo study of AKBA-loaded nanospanlastics showed 4-fold improved permeation through the skin in comparison to free AKBA gel. However, these topical formulations can be explored for the carrageenan induced paw edema model and FCA induced arthritis model to explore the anti-inflammatory and anti-arthritic activity of AKBA.	[15]

4. Expert opinion

In the past couple of decades, ample research has been done to study the different pathological signs of RA. However, the target-oriented drug delivery strategy is still lacking. New therapeutic approaches have profoundly changed the course of RA. Based on preclinical research and clinical trials, AKBA has demonstrated pharmacological effect against RA diseased condition. Because of its properties to target multiple pathways, its effectiveness as a treatment for RA get enhanced. AKBA has exhibited positive benefits in RA animal model by altering the activity of numerous molecular targets and signaling pathways that are involved in the development of RA. However, worries about the bioavailability, drug interaction, and pharmacokinetic characteristics of AKBA have significantly slowed down its development into an effective therapeutic molecule for RA. Nevertheless, numerous investigations have been started in this area to overcome the obstacles, but the progress is fairly gradual and requires a lot of attention. To determine its pharmacological effectiveness in RA disease conditions, further investigations in in-vivo research utilizing AKBA in RA-induced animal model are required. Therefore, it is still difficult to develop an animal model that can accurately reflect the condition of RA disease. Models with the highest similarity and the least difference are preferred. The majority of reports on collagen type II-induced arthritis in rats or mice and adjuvant-induced arthritis in rats demonstrated predictability for effectiveness in humans. Additionally, the K/BxN murine model has demonstrated its ability to clarify some of the RA-causing pathways. These models have unquestionably elevated the significance of mechanisms assumed to be significant in the initiation and development of RA disease.

List of abbreviations

AKBA	=	3-Acetyl-11-keto-β-Boswellic Acid
NF-κB	=	Nuclear factor kappa B
IL	=	Interleukin
TNF-α	=	Tumor necrosis factor-alpha
CD4	=	Clusters of differentiation 4
RF	=	Rheumatoid factors
APC	=	Antigen presenting cells
RANKL	=	Receptor activator of nuclear factor-kappa B ligand
PLA2	=	Phospholipase A2
FLAP	=	5-lipoxygenase activating protein
5-LOX	=	5-lipoxygenase
LT (A4, B4, C4, D4, E4)	=	Leukotriene (A4, B4, C4, D4, E4)
K/BxN mice	=	Mice expressing the KRN T cell receptor transgene and the major histocompatibility complex class II molecule Ag7.

Declaration of interest

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

Reviewer disclosures

Peer reviewers on this manuscript have no relevant financial or other relationships to disclose.

Acknowledgments

The authors gratefully acknowledge the Ph.D. fellowship from DST-INSPIRE, Govt. of India [#IF210090].

Additional information

Funding

This paper was not funded.