Efficient one-pot transformation of furfural to pentanediol over Cu-modified cobalt-based catalysts.

Pentanediols are substances with significant market potential as the key monomers for advanced polymeric materials. In this study, we successfully achieved directly hydrogenolysis of biomass-based furfural to 1,5-pentanediol with a remarkable yield of 53.4 % using Cu-modified cobalt supported on cerium dioxide catalysts. Through comprehensive characterization techniques, including H2-TPR, NH3-TPD, XPS, EPR and Raman analysis, the study revealed that the introduction of Cu altered the dispersion of Co species, attenuated the interaction between Co species and cerium dioxide, enhanced its reduction extent, and fostered the formation of plentiful cobalt oxide species and oxygen vacancies on the catalyst's surface. The cooperative influence of Cu and Co heightened the selectivity of the hydrogenolysis reaction. This work provides a novel strategy for the development of greener and more efficient catalytic processes based on non-precious metals that for the selective conversion of biomass-derived furfural to high-value pentanediols.

Titanate Nanotubes-Based Heterogeneous Catalyst for Efficient Production of Biomass Derived Chemicals.

The development of efficient heterogeneous catalytic system to convert plentiful biomass to renewable bio-chemicals is urgent need. Titanate nanotubes-based materials obtained from hydrothermal treatment have been reported as low-cost and efficient catalytic materials in chemical syntheses for bio-based chemicals production with interesting catalytic performance. This mini-review expressly revealed the significance and potential of using titanate nanotubes based material as sustainable and environmentally benign solid catalysts/supports for synthesis of various bio-based chemicals, including glycerol-derived solketal, jet fuel range alkanes precursors, biomass-derived esters, aldehydes, aromatic compounds and so on. From the current knowledge on titanate nanotubes-based material via hydrothermal method here summarized, the future lines of research in the field of catalysis/supports for bio-based chemicals production are outlined.

Recent Advances in the Catalytic Hydroconversion of 5-Hydroxymethylfurfural to Valuable Diols.

Biomass, a globally available resource, is a promising alternative feedstock for fossil fuels, especially considering the current energy crisis and pollution. Biomass-derived diols, such as 2,5-bis(hydroxymethyl)furan, 2,5-bis(hydroxymethyl)-tetrahydrofuran, and 1,6-hexanediol, are a significant class of monomers in the polyester industry. Therefore, the catalytic conversion of biomass to valuable diols has received extensive research attention in the field of biomass conversion and is a crucial factor in determining the development of the polyester industry. 5-Hydroxymethylfurfural (HMF) is an important biomass-derived compound with a C6-furanic framework. The hydroconversion of HMF into diols has the advantages of being simple to operate, inexpensive, environmentally friendly, safe, and reliable. Therefore, in the field of diol synthesis, this method is regarded as a promising approach with significant industrialization potential. This review summarizes recent advances in diol formation, discusses the roles of catalysts in the hydroconversion process, highlights the reaction mechanisms associated with the specificities of each active center, and provides an outlook on the challenges and opportunities associated with the research on biomass-derived diol synthesis.

Highly Efficient One-Step Conversion of Fructose to Biofuel 5-Ethoxymethylfurfural Using a UIO-66-SO3H Catalyst.

In this study, a novel sulfonic acid-modified catalyst for MOFs (UIO-66-SO3H) was synthesized using chlorosulfonic acid as a sulfonating reagent and first used as efficient heterogeneous catalysts for the one-pot conversion of fructose into biofuel 5-ethoxymethylfurfural (EMF) in a cosolvent free system. The physicochemical properties of this catalyst were characterized by Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), and powder X-ray diffraction (XRD). The characterization demonstrated that the sulfonic acid group was successfully grafted onto the MOF material and did not cause significant changes to its morphology and structure. Furthermore, the effects of catalyst acid amount, reaction temperature, reaction time, and catalyst dosage on reaction results were investigated. The results showed that the conversion of fructose was 99.7% within 1 h at 140°C, while the EMF yield reached 80.4%. This work provides a viable strategy by application of sulfonic acid-based MOFs for the efficient synthesis of potential liquid fuel EMF from renewable biomass.

Titania Nanotubes-Bonded Sulfamic Acid as an Efficient Heterogeneous Catalyst for the Synthesis of n-Butyl Levulinate.

The titania nanotubes-bonded sulfamic acid (TNTs-NHSO3H) catalyst was designed and successfully fabricated by the post-synthesis modification method. The as-prepared catalyst was characterized by a variety of characterization techniques, including Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, and thermogravimetry-differential thermal gravimetry (TG-DTG). The crystal structure of the TNTs still maintained during the modification process. Although the BET surface area was decreased, the amount of Brønsted acid sites can be efficiently fabricated on the TNTs. The catalytic activity of TNTs-NHSO3H was examined for the synthesis of n-butyl levulinate (BL) from levulinic acid (LA) and furfuryl alcohol (FA). A relatively high selectivity (99.6%) at 99.3% LA conversion was achieved for esterification of levulinic acid owing to the strong Brønsted acidity sites. And also, the TNTs-NHSO3H catalyst exhibited a higher reactivity for alcoholysis of FA and the yield of BL reached 90.4% with 100% FA conversion was obtained under the mild conditions.

Selective Catalytic Isomerization of ß-Pinene Oxide to Perillyl Alcohol Enhanced by Protic Tetraimidazolium Nitrate.

A series of tetraimidazolium salts with different anions was prepared and applied in the isomerization of ß-pinene oxide. After examining the activity of different catalysts, a remarkable enhancement of the selectivity of perillyl alcohol (47 %) was obtained over [PEimi][HNO3 ]4 under mild reaction conditions and using DMSO as the solvent. Furthermore, noncovalent interactions between solvent molecules and the catalyst were found by FT-IR spectroscopy and confirmed by computational chemistry. The homogeneous catalyst showed excellent stability and was reused up to six times without significant loss.

Efficient synthesis of 5-ethoxymethylfurfural from biomass-derived 5-hydroxymethylfurfural over sulfonated organic polymer catalyst.

Herein, we investigated catalytic potential of a functionalized porous organic polymer bearing sulfonic acid groups (PDVTA-SO3H) to the etherification of 5-hydroxymethylfurfural (HMF) to 5-ethoxymethylfurfural (EMF) under solvent-free conditions. The PDVTA-SO3H material was synthesized via post-synthetic sulfonation of the porous co-polymer poly-divinylbenzene-co-triallylamine by chlorosulfonic acid. The physicochemical properties of the PDVTA-SO3H were characterized by FT-IR, SEM, TG-DTG, and N2 adsorption isotherm techniques. PDVTA-SO3H had high specific surface area (591 m2 g-1) and high density of -SO3H group (2.1 mmol g-1). The reaction conditions were optimized via Box-Behnken response surface methodology. Under the optimized conditions, the PDVTA-SO3H catalyst exhibited efficient catalytic activity with 99.8% HMF conversion and 87.5% EMF yield within 30 min at 110 °C. The used PDVTA-SO3H catalyst was readily recovered by filtration and remained active in recycle runs.

[Retracted] Differential miRNAomics of the synovial membrane in knee osteoarthritis induced by bilateral anterior cruciate ligament transection in rats.

Following the publication of the above article, a number of errors were identified in the paper, and after having consulted with the editor of Molecular Medicine Reports, a corrigendum was published last year ("[Corrigendum] Differential miRNAomics of the synovial membrane in knee osteoarthritis induced by bilateral anterior cruciate ligament transection in rats." Zhou J, Zhao Y, Wu G, Lin B, Li Z and Liu X. Mol Med Rep 20: 5363, 2019). However, following publication of the above corrigendum, the paper was re­examined by the authors, and additional errors were identified; therefore, the authors are going to retract this paper from the publication. All the authors agree to this retraction, and apologize to the Editor of Molecular Medicine Reports and to the readership for any inconvenience caused. [the original article was published in Molecular Medicine Reports 18: 4051­4057, 2018; DOI: 10.3892/mmr.2018.9385].

[Corrigendum] Differential miRNAomics of the synovial membrane in knee osteoarthritis induced by bilateral anterior cruciate ligament transection in rats.

Following the publication of the above article, an interested reader drew to our attention that, in Fig. 4A, in which the authors had presented a western blot image depicting protein expression of IL­18, IL­1ß, NLRP3 and ß­actin from synovial tissue lysates from osteoarthritic rats, upon close examination of the figure a striking similarity was noted between the bands shown for the IL­18­ and NLRP3­stained Sham group experiments, although the bands appeared in an inverted position relative to each other. Following an enquiry with the authors, they realized that they had included incorrect data for this figure; an amended version of Fig. 4, showing the correct data for NLRP3, is shown opposite. Secondly, the authors have realized that, at various points throughout the paper, two miRNAs were written incorrectly: Specifically, references to an 'miR­352' should have appeared as miR­532, and 'miR­233' should have been written as miR­223. This error affected the presentation of Fig. 2; therefore, a revised version of this figure, with the miRNAs correctly labelled as miR­532 and miR­223 respectively, is also shown opposite. Furthermore, mi­233 should have been written as miR­223 at the following places in the text: p. 4051, right­hand column (RHC), line 10 ("Furthermore, the miR­223­regulated...); p. 4054, Results section, left­hand column (LHC), third subheading ("miR­223 negatively regulates the expression of NLRP3."); and in the concluding paragraph of the Discussion on p. 4056, LHC, miR­233 should have been written as miR­223 in all five instances where this occurred (lines 4, 7, 8, 9, and 10 of this paragraph). Finally, the second sentence featured in the subsection of the Results section entitled "Expression validation of miRs by RT­qPCR" on p. 4054 contained additional errors. This sentence should have appeared as follows (changed text is highlighted in bold): "The expression of miR­223, ­100, ­345, ­130, ­382, ­9a and 183 were upregulated, whereas miR­377, ­532, ­200b were downregulated with a fold change of ≥1.5, similar to the microarray data (Fig. 2). All the authors agree to the contents of this Corrigendum, and apologize to the Editor of Molecular Medicine Reports and to the readership for any inconvenience caused. [the original article was published in Molecular Medicine Reports 18: 4051­4057, 2018; DOI: 10.3892/mmr.2018.9385].

Electroacupuncture Delays Cartilage Degeneration by Modulating Nuclear Factor-κB Signaling Pathway.

OBJECTIVE: To illustrate the molecular mechanisms underlying the therapeutic effects of electroacupuncture (EA) on knee osteoarthritis (OA). METHODS: Twenty-seven six-month-old New Zealand white rabbits were allocated into three groups in accordance with a random number table: normal group (no surgery-induced OA; without treatment), model group (surgery-induced OA; without treatment) and EA group [surgery-induced OA; received treatment with EA at acupoints Dubi (ST 35) and Neixiyan (EX-LE 5), 30 min twice a day]. After eight consecutive weeks of treatment, the histopathological alterations in cartilage were observed using optical microscopy and transmission electron microscopy, cartilage degeneration was evaluated by modified Mankin's score principles, the synovial fluid concentration of interleukin-1ß (IL-1ß), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α) and matrix metalloproteinase-3 (MMP-3) were evaluated by enzyme-linked immunosorbent assay, and the protein expression levels of IL-1ß, IL-6, TNF-α, MMP-3, IκB kinase-ß (IKK-ß), nuclear factor of α light polypeptide gene enhancer in B-cells inhibitor α (IκB-α) and nuclear factor-κB (NF-κB) p65 were quantified by Western blot analysis. RESULTS: EA treatment significantly improved cartilage structure arrangement and reduced cellular degeneration. The IL-1ß, IL-6, TNF-α and MMP-3 of synovial fluid in the EA-treated group were significantly decreased compared with the model group (all P<0.01). Compared with the model group, the IL-1ß, IL-6, TNF-α, MMP-3, IKK-ß and NF-κB p65 protein expressions in cartilage of EA-treated group were significantly decreased (all P<0.01), whereas IκB-α expression was significantly up-regulated (P<0.01). CONCLUSION: EA treatment may delay cartilage degeneration by down-regulating inflammatory factors through NF-κB signaling pathway, which may, in part, explain its clinical efficacy in the treatment of knee OA.

Selective oxidation of 5-hydroxymethylfurfural into 2,5-diformylfuran over VPO catalysts under atmospheric pressure.

Vanadium phosphate oxide (VPO) heterogeneous catalysts with different V/P molar ratios were prepared and used for selective oxidation of biomass-derived 5-hydroxymethylfurfural (HMF) to produce 2,5-diformylfuran (DFF) in the liquid phase. It was found that the VPO catalyst with V/P molar ratio 0.25 exhibited the best catalytic performance. Then the VPO catalyst was utilized to catalyze the oxidation of HMF in a batch reactor under different conditions, in terms of type of solvent (water and organic), reaction time and temperature. A high DFF yield of 83.6% with HMF conversion of 100% was obtained under atmospheric pressure.

Electroacupuncture inhibits sodium nitroprusside­mediated chondrocyte apoptosis through the mitochondrial pathway.

In China, electroacupuncture (EA) is a therapeutic method that is extensively applied in the clinical treatment of osteoarthritis (OA); however, the underlying molecular mechanism remains unclear. Chondrocyte apoptosis may be observed in cartilage tissue in OA, and is often considered a key target for the treatment of this condition. Therefore, the present study aimed to determine the effects of EA on sodium nitroprusside (SNP)­induced chondrocyte apoptosis. Chondrocytes were obtained from the knee joints of Sprague Dawley rats by type II collagenase digestion. Following microscopic observation and authentication with type II collagen immunohistochemistry, articular cartilage cells were used in subsequent experiments. Using inverted phase contrast microscopy, DAPI staining and flow cytometry, it was revealed that chondrocytes treated with SNP became apoptotic, whereas EA inhibited SNP­induced chondrocyte apoptosis. Subsequently, JC­1 single staining, reverse transcription­quantitative polymerase chain reaction analysis, western blotting, colorimetric assays and immunofluorescence staining were performed for further investigation. The results demonstrated that, when compared with normal chondrocytes, the mitochondrial membrane potential of SNP­treated chondrocytes was markedly lowered, B­cell lymphoma 2 (Bcl­2) expression was reduced, and the expression levels of Bcl­2­associated X protein (Bax), cytochrome c, caspase­9 and caspase­3 were increased. Compared with in SNP­treated chondrocytes, the decrease in the mitochondrial membrane potential of chondrocytes treated with SNP and EA was smaller, Bcl­2 expression was increased, and the expression levels of Bax, cytochrome c, caspase­9 and caspase­3 were decreased following EA intervention. In conclusion, the present study demonstrated that EA modulated the mitochondrial pathway to suppress SNP­mediated chondrocyte apoptosis. Therefore, EA may be of value in the treatment of OA.

Bioinformatics analysis to identify key genes and pathways influencing synovial inflammation in osteoarthritis.

Osteoarthritis (OA) is a chronic arthropathy that occurs in the middle­aged and elderly population. The present study aimed to identify gene signature differences between synovial cells from OA synovial membrane with and without inflammation, and to explain the potential mechanisms involved. The differentially expressed genes (DEGs) between 12 synovial membrane with inflammation and 12 synovial membrane without inflammation from the dataset GSE46750 were identified using the Gene Expression Omnibus 2R. The DEGs were subjected to enrichment analysis, protein­protein interaction (PPI) analysis and module analysis. The analysis results were compared with text­mining results. A total of 174 DEGs were identified. Gene Ontology enrichment results demonstrated that functional molecules encoded by the DEGs primarily had extracellular location, molecular functions predominantly involving 'chemokine activity' and 'cytokine activity', and were associated with biological processes, including 'inflammatory response' and 'immune response'. The Kyoto Encyclopedia of Genes and Genomes results demonstrated that DEGS may function through pathways associated with 'rheumatoid arthritis', 'chemokine signaling pathway', 'complement and coagulation cascades', 'TNF signaling pathway', 'intestinal immune networks for IgA production', 'cytokine­cytokine receptor interaction', 'allograft rejection', 'Toll­like receptor signaling pathway' and 'antigen processing and presentation'. The top 10 hub genes [interleukin (IL)6, IL8, matrix metallopeptidase (MMP)9, colony stimulating factor 1 receptor, FOS proto­oncogene, AP1 transcription factor subunit, insulin­like growth factor 1, TYRO protein tyrosine kinase binding protein, MMP3, cluster of differentiation (CD)14 and CD163] and four gene modules were identified from the PPI network using Cytoscape. In addition, text­mining was used to identify the commonly used drugs and their targets for the treatment of OA. It was initially verified whether the results of the present study were useful for the study of OA treatment targets and pathways. The present study provided insight for the molecular mechanisms of OA synovitis. The hub genes and associated pathways derived from analysis may be targets for OA treatment. IL8 and MMP9, which were validated by text­mining, may be used as molecular targets for the OA treatment, while other hub genes require further validation.

Differential miRNAomics of the synovial membrane in knee osteoarthritis induced by bilateral anterior cruciate ligament transection in rats.

The differential microRNA (miRNA) omics of the synovial membrane were investigated using a rat model of knee osteoarthritis (KOA) induced by bilateral anterior cruciate ligament transection, which produced pathological biomarkers in KOA. Sprague­Dawley rats were randomly divided into two groups; Sham­operated and KOA­operated group. The KOA rats were subjected to bilateral anterior cruciate ligament transection. After 6 weeks, total RNA was extracted from the knee joint synovial membrane of the rats and a microRNA (miR) microarray was performed to identify differentially expressed miRs. Subsequently, the obtained differentially expressed miRs were validated by reverse transcription­quantitative polymerase chain reaction (RT­qPCR) analysis. A total of 24 miRs were identified with alterations ≥1.5­fold in the synovial membrane in the KOA­operated group compared with the sham­operated group, of which 4 miRs (miR­532­5p, ­200b­5p, ­377­3p and ­759­5p) were decreased and 20 miRs (miR­382­3p, ­223­3p, ­100­5p, ­30d­5p, ­183­5p, ­130, ­92b­3p, ­125b­3p, ­151­3p, ­155­3p, 27a­3p, ­146b­3p, ­885­5p, ­352, ­184, ­345­5p, ­30a­5p and ­9a­5p) were increased. Subsequently, RT­qPCR was used to validate the expressions of miR­223, ­100, ­345, ­130, ­382, ­377, ­352, ­200b, ­9a and ­183, which were upregulated by a fold change of ≥1.5 in synovial membranes of KOA rats compared with shams. Furthermore, in vitro miR­223 mimic could suppress the luciferase activity of NACHT, LRR and PYD domains­containing protein 3 (NLRP3) 3' untranslated region by detecting of dual luciferase reporter vector. Additionally, the expression of NLRP3, interleukin (IL)­1ß and IL­18 significantly increased in the synovial membrane of KOA rats. A total of 24 different miRs were determined by comparing the miRNAomics in the synovial membrane of the KOA model rats. Furthermore, the miR­233­regulated NLRP3 inflammasome was implicated in synovial membrane injury, which may be an important mechanism of KOA pathogenesis.

Tackling Osteoarthritic Knee Pain with Electroacupuncture.

Electroacupuncture (EA) has been widely used in pain relief. Clinical evidence has revealed its unique advantages and effectiveness in alleviating pain. Studies on EA and pain relief have revealed that EA displays greater analgesic effects for different types of pain in comparison to manual acupuncture. Here, we reviewed the clinical application and mechanism of EA in treating osteoarthritic knee pain and its influence factors in curative effect.

Glucosamine promotes chondrocyte proliferation via the Wnt/ß­catenin signaling pathway.

The present study investigated the mechanism underlying the effects of glucosamine (GlcN) on the proliferation of chondrocytes isolated from the knee cartilage of Sprague­Dawley rats. Chondrocytes were treated with various concentrations of GlcN or without GlcN. The effects of GlcN on chondrocyte proliferation were determined using reverse transcription­polymerase chain reaction, western blot analysis and immunohistochemistry. The results indicated that GlcN significantly improved chondrocyte viability, accelerated G1/S transition during progression of the cell cycle and promoted the expression of cell cycle regulatory proteins, including cyclin D1, cyclin­dependent kinase (CDK)4 and CDK6, thus indicating that GlcN may promote chondrocyte proliferation. Furthermore, GlcN upregulated the expression levels of Wnt­4, Frizzled­2 and ß­catenin, and downregulated the expression of glycogen synthase kinase­3. GlcN also promoted ß­catenin translocation; ß­catenin is able to activate numerous downstream target genes, including cyclin D1. To determine the role of the Wnt/ß­catenin signaling pathway in chondrocyte proliferation, the Wnt/ß­catenin signaling pathway was inhibited using Dickkopf­1 (DKK­1), after which chondrocytes were treated with GlcN. The results demonstrated that the expression levels of ß­catenin and cyclin D1 were decreased in chondrocytes treated with DKK­1 and GlcN. These results suggested that GlcN may promote chondrocyte proliferation via the Wnt/ß­catenin signaling pathway.

Ultrastructural change of the subchondral bone increases the severity of cartilage damage in osteoporotic osteoarthritis of the knee in rabbits.

Osteoporotic osteoarthritis is a phenotype of osteoarthritis (OA) manifested as fragile and osteoporotic subchondral bone. However, the ultrastructural features of subchondral bone in osteoporosis OA have not been determined. The study was aimed to investigate the ultrastructural dynamic changes of subchondral bone in osteoporotic OA model and how the ultrastructural damage in the subchondral bone caused by osteoporosis deteriorated the cartilage damage in OA. Eighteen rabbits were equally randomized to three groups, including the control, the OA and the osteoporotic OA groups. The structural changes of cartilage were evaluated by HE and safranin-O fast green staining, the Mankin's grading system was used to assess the stage of OA progression. And microstructural or ultrastructural changes in subchondral bone were assessed by micro-computed tomography or by scanning electron microscopy. According to the changes of cartilage histopathology, the OA group was in the early pathological stage of OA while the osteoporotic OA group was in the middle stage of OA based on Mankin's grading system. In addition, the damage of cartilage surface, reduction in the number of chondrocytes and the matrix staining were more increased in the osteoporotic OA group compared to the OA group. Compared to the OA group, the subchondral bone in the microstructure and ultrastructure in the osteoporotic OA group showed more microfracture changes in trabecular bone with more destructions of the tree-like mesh. Moreover, the collagen fibers were random rough with a fewer amount of bone lacunae in subchondral cortical plate in the osteoporotic OA group compared to the OA group. These findings indicated that the subchondral bone ultrastructure in the osteoporotic OA model was characterized by the destruction of the network structure and collagen fibers. The subchondral bone ultrastructural damage caused by osteoporosis may change mechanical properties of the upper cartilage and aggravate OA cartilage. Therefore, early diagnosis and treatment of osteoporosis is of great significance to prevent early OA from further developing osteoporotic OA.

Imidazolyl activated carbon refluxed with ethanediamine as reusable heterogeneous catalysts for Michael addition.

Imidazolyl activated carbon, denoted as AC-N, was prepared via oxidation of AC with HNO3 (AC-O) and then refluxed with ethanediamine under mild conditions. The results showed that the N content of AC-N was 10.3%, and the surface alkali group density of AC-N was 0.96 mmol g-1 from 0.78 mmol g-1 carboxy group of AC-O by Boehm titration. It was revealed that the basic functional groups on the AC-N surface included imidazole and amine groups, from XPS and FT-IR. Evaluated with Michael addition of furfural, the catalytic performance of AC-N showed higher conversion and selectivity than that of commonly used base catalyst such as 2-methylimidazole and KOH. Very remarkably, AC-N showed extraordinary recyclability, in that there was no decline of conversion and selectivity after being recycled 5 times.

Titanate nanotubes-bonded organosulfonic acid as solid acid catalyst for synthesis of butyl levulinate.

In this study, titanate nanotubes-bonded organosulfonic acid (TNTs-SO3H) was prepared and employed as an efficient heterogeneous catalyst for esterification of levulinic acid with n-butanol. Two reaction products pseudo n-butyl levulinate (pseudo-BL) and n-butyl levulinate (BL) were detected by GC-MS. The catalyst showed 86.8% conversion of levulinic acid with 99.7% selectivity towards n-butyl levulinate. TNTs-SO3H exhibited strong acidic sites and high stability even after seven cycles of usage and would be well expected to be a potential candidate for alkyl levulinate production.

Warm sparse-dense wave inhibits cartilage degradation in papain-induced osteoarthritis through the mitogen-activated protein kinase signaling pathway.

Cartilage degradation is an important in the pathogenesis of osteoarthritis (OA). Abnormal activation of the mitogen-activated protein kinase (MAPK) signaling pathway in chondrocytes promotes an inflammatory response, resulting in the release of chondral matrix-degrading enzymes that accelerate the degradation of cartilage. As a non-pharmaceutical and non-invasive physical therapy regimen, warm sparse-dense wave (WSDW) has been successfully used for the treatment of OA. However, it remains unclear whether WSDW inhibits cartilage degradation in OA through the MAPK signaling pathway. The present study investigated the effects of WSDW on papain-induced OA in rat knee joints. Papain-induced OA was established in rats, which were subsequently divided into a model group and three experimental groups that received a WSDW with the following ratios: WSDW=1:1, WSDW=1:2 and WSDW=2:1. After 12 weeks of treatment, cartilage degradation was evaluated by Mankin scoring of paraffin-embedded sections stained with hematoxylin and eosin. The changes in cartilage structure were observed by transmission electron microscopy, and the expressions of RAS, extracellular signal-regulated kinase (ERK), p38 and p53 were measured by reverse transcription-quantitative polymerase chain reaction and western blot analysis. WSDW was demonstrated to improve the arrangement of collagen fibers, inhibit the tidemark replication and delay cartilage degradation in papain-induced OA. The expressions of RAS, ERK, p38 and p53 in the WSDW (1:2) and (2:1) groups were significantly decreased when compared with the model group (P<0.01). Furthermore, amongst the WSDW groups, the inhibitory effects of the WSDW (1:2) group were typically greater than those of the WSDW (1:1) and (2:1) groups. The results indicate that WSDW may inhibit cartilage degradation in papain-induced OA in rat knee joints by regulating the MAPK signaling pathway.