Geraniol-mediated osteoarthritis improvement by down-regulating PI3K/Akt/NF-κB and MAPK signals: In vivo and in vitro studies

Highlights

• Geraniol inhibited IL-1β-induced inflammatory response in vitro.

• Geraniol inhibited IL-1β-induced ECM degradation in vitro.

• Geraniol inhibited PI3K/Akt/NF-κB and MAPK signaling in chondrocytes induced by IL-1β.

• The application of geraniol can improve osteoarthritis in mice.

Abstract

Osteoarthritis (OA) is a degenerative disease that has received increasing attention among the elderly. Its clinical manifestation is primarily long-term joint pain. Evidence for the pharmacological effects of geraniol in various diseases is accumulating. However, whether geraniol has a therapeutic effect against OA remains to be determined. In this study, we discussed the anti-inflammatory effects of geraniol in IL-1β-induced chondrocytes and the anti-cartilage degradation effects in a mouse model of destabilization of the medial meniscus (DMM). In cell experiments, we found that the treatment of geraniol inhibited the expression of IL-1β-induced PGE2, NO, COX-2, iNOS, TNF-α and IL-6 by western blot, qRT-PCR and immunofluorescence staining. Besides, geraniol inhibited the expression of MMP-9 and ADAMTS-5, and reversed the degradation of aggrecan and type II collagen. Mechanistically, we revealed that geraniol suppressed IL-1β-stimulated PI3K/Akt/NF-κB and MAPK activation. Importantly, we have found in animal experiments that oral treatment of geraniol was beneficial in protecting articular cartilage from degradation. Overall, these data indicated that geraniol may have the potential to be developed as an effective treatment for OA.

Introduction

Osteoarthritis (OA) is one of the most common orthopedic diseases that causes patients to become incapacitated and disabled. This is also one of the main reasons for the increasing economic burden on households and the country [1]. According to the investigation report, the prevalence rate of knee OA has started to increase sharply in both male and female patients. Besides, a large number of studies have shown that the risk factors for knee osteoarthritis are closely related to age, obesity, gender and living conditions [2]. The essence of OA is a chronic inflammatory immune response. The main pathological manifestation is degenerative changes of knee cartilage involving subchondral bone, synovium and other structures. In addition, pain is the most prominent clinical symptom of OA [3], [4], [5]. Although many scholars devoted to the study of the pathogenesis of OA, the research on OA has not made breakthrough progress due to the complexity of its pathogenesis [6]. Previous studies have shown that many inflammatory mediators were involved in the progression of OA, especially the increase of intraarticular interleukin-1β (IL-1β) and the interaction between this molecule and its receptor IL-1RI, which played an important role in the pathogenesis of OA [7], [8]. Studies reported that stimulation of IL-1β also increased the expression of prostaglandin E2 (PGE2), cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS), and induced the large-scale expression of matrix metalloproteinase-3 (MMP-3), matrix metalloproteinase-13 (MMP-13) and thrombospondin motifs (ADMATs) in chondrocytes [9].

Nuclear factor κB (NF-κB), a transcription factor of the Rel family, participates in the regulation of gene transcription related to immune response, inflammatory response and cell differentiation. The stimulation of the pro-inflammatory factors IL-1β, TNF-α and LPS causes the NF-κB signaling pathway to be activated. Phosphorylated NF-κB is transferred to the nucleus and binds to target genes, thus affecting various biological processes [10], [11]. Moreover, phosphatidylinsitol-3-kinase (PI3K) and protein kinase B (Akt) are involved in the regulation of downstream factors through various pathways. For example, AKT degrades IκB by activating IκB kinase, which causes nuclear translocation of NF-κB [12], [13]. Some scholars have found that activation of the PI3K/Akt pathway could exacerbate cartilage degeneration by promoting chondrocytes to secrete MMPs [14]. Another interesting example was that the inhibitory effect of allicin on the PI3K/Akt pathway in chondrocytes was favorable for down-regulating COX-2 expression and retaining type II collagen content [15]. Furthermore, mitogen-activated protein kinase (MAPK) in eukaryotic cells is a group of serine/threonine kinases, which is mainly composed of stress-activated protein kinases/c-Jun N-terminal kinases (JNKs), extracellular signal-regulated kinases (ERKs) and p38 kinases. Some studies have shown that MAPKs played an important role in cartilage biology. IL-1β could activate MAPK signal pathway in mouse chondrocytes and trigger inflammatory response [16], [17].

Geraniol is a natural acyclic monoterpene alcohol prepared from a variety of plant-based essential oils, including lemongrass, rose, ginger, lavender, coriander, among others [18]. In addition, geraniol has a wide range of uses. For example, it can be used as a fruit-flavored food additive, and can also be made into an ester flavor [19]. It is worth noting that geraniol has a wide range of biological and pharmacological properties, such as antitumor, antibacterial, anti-inflammatory and antioxidant activities [18], [21], [22]. For example, geraniol exhibited anti-inflammatory activity by down-regulating the expression levels of COX-2, PGE2 and iNOS in RAW 264.7 macrophages induced by lipopolysaccharide [23]. In mouse ulcerative colitis induced by dextran sulphate sodium (DSS), geraniol reduced inflammatory response and oxidative stress by inhibiting activation of the NF-κB pathway [24]. In rat models of traumatic spinal cord injury, geraniol has also been reported to inhibit inflammatory response, oxidative stress and apoptosis by regulating NF-κB and p38 MAPK [25]. Furthermore, geraniol acted on the AKT signaling pathway to induce cancer cell apoptosis [26], [27]. Although there are some reports on the anti-inflammatory effects of geraniol, it is still to be determined whether geraniol exerts anti-inflammatory effects in OA. In this study, we sought to determine whether geraniol has anti-inflammatory effects on IL-1β-induced mouse chondrocytes and DMM-induced mouse models, and whether this is mediated by MAPK or PI3K/Akt/NF-κB signaling pathways.