Assessing the advantages of 3D bioprinting and 3D spheroids in deciphering the osteoarthritis healing mechanism using human chondrocytes and polarized macrophages.

The molecular niche of an osteoarthritic microenvironment comprises the native chondrocytes, the circulatory immune cells, and their respective inflammatory mediators. Although M2 macrophages infiltrate the joint tissue during osteoarthritis (OA) to initiate cartilage repair, the mechanistic crosstalk that dwells underneath is still unknown. Our study established a co-culture system of human OA chondrocytes and M2 macrophages in 3D spheroids and 3D bioprinted silk-gelatin constructs. It is already well established that Silk fibroin-gelatin bioink supports chondrogenic differentiation due to upregulation of the Wnt/ß-catenin pathway. Additionally, the presence of anti-inflammatory M2 macrophages significantly upregulated the expression of chondrogenic biomarkers (COL-II, ACAN) with an attenuated expression of the chondrocyte hypertrophy (COL-X), chondrocyte dedifferentiation (COL-I) and matrix catabolism (MMP-1 and MMP-13) genes even in the absence of the interleukins. Furthermore, the 3D bioprinted co-culture model displayed an upper hand in stimulating cartilage regeneration and OA inhibition than the spheroid model, underlining the role of silk fibroin-gelatin in encouraging chondrogenesis. Additionally, the 3D bioprinted silk-gelatin constructs further supported the maintenance of stable anti-inflammatory phenotype of M2 macrophage. Thus, the direct interaction between the primary OAC and M2 macrophages in the 3D context, along with the release of the soluble anti-inflammatory factors by the M2 cells, significantly contributed to a better understanding of the molecular mechanisms responsible for immune cell-mediated OA healing.

Bactericidal antibiotic-phytochemical combinations against methicillin resistant Staphylococcus aureus

Methicillin resistant Staphylococcus aureus (MRSA) infection is a global concern nowadays. Due to its multi-drug resistant nature, treatment with conventional antibiotics does not assure desired clinical outcomes. Therefore, there is a need to find new compounds and/or alternative methods to get arsenal against the pathogen. Combination therapies using conventional antibiotics and phytochemicals fulfill both requirements. In this study, the efficacy of different phytochemicals in combination with selected antibiotics was tested against 12 strains of S. aureus (ATCC MRSA 43300, ATCC methicillin sensitive S. aureus or MSSA 29213 and 10 MRSA clinical strains collected from National University Hospital, Singapore). Out of the six phytochemicals used, tannic acid was synergistic with fusidic acid, minocycline, cefotaxime and rifampicin against most of strains tested and additive with ofloxacin and vancomycin. Quercetin showed synergism with minocycline, fusidic acid and rifampicin against most of the strains. Gallic acid ethyl ester showed additivity against all strains in combination with all antibiotics under investigation except with vancomycin where it showed indifference effect. Eugenol, menthone and caffeic acid showed indifference results against all strains in combination with all antibiotics. Interestingly, no antagonism was observed within these interactions. Based on the fractional inhibitory concentration indices, synergistic pairs were further examined by time-kill assays to confirm the accuracy and killing rate of the combinations over time. The two methods concurred with each other with 92% accuracy and the combinatory pairs were effective throughout the 24 hours of assay. The study suggests a possible incorporation of effective phytochemicals in combination therapies for MRSA infections.

Bactericidal antibiotic-phytochemical combinations against methicillin resistant Staphylococcus aureus.

Methicillin resistant Staphylococcus aureus (MRSA) infection is a global concern nowadays. Due to its multi-drug resistant nature, treatment with conventional antibiotics does not assure desired clinical outcomes. Therefore, there is a need to find new compounds and/or alternative methods to get arsenal against the pathogen. Combination therapies using conventional antibiotics and phytochemicals fulfill both requirements. In this study, the efficacy of different phytochemicals in combination with selected antibiotics was tested against 12 strains of S. aureus (ATCC MRSA 43300, ATCC methicillin sensitive S. aureus or MSSA 29213 and 10 MRSA clinical strains collected from National University Hospital, Singapore). Out of the six phytochemicals used, tannic acid was synergistic with fusidic acid, minocycline, cefotaxime and rifampicin against most of strains tested and additive with ofloxacin and vancomycin. Quercetin showed synergism with minocycline, fusidic acid and rifampicin against most of the strains. Gallic acid ethyl ester showed additivity against all strains in combination with all antibiotics under investigation except with vancomycin where it showed indifference effect. Eugenol, menthone and caffeic acid showed indifference results against all strains in combination with all antibiotics. Interestingly, no antagonism was observed within these interactions. Based on the fractional inhibitory concentration indices, synergistic pairs were further examined by time-kill assays to confirm the accuracy and killing rate of the combinations over time. The two methods concurred with each other with 92% accuracy and the combinatory pairs were effective throughout the 24 hours of assay. The study suggests a possible incorporation of effective phytochemicals in combination therapies for MRSA infections.

Maggot metabolites and their combinatory effects with antibiotic on Staphylococcus aureus.

BACKGROUND: Maggot therapy has been in practice for effective debridement, disinfection and healing of chronic wounds. Due to their antiseptic action during wound healing, their metabolites have been investigated in the past for antibacterial activity. They have been particularly useful for treatment of wounds infected with multi-drug resistant Staphylococcus aureus. Antibiotics, on the other hand, can predispose bacteria to develop resistance. Substances that are able to modulate or delay the occurrence of resistance in bacteria are under investigation by many researchers around the world. In the present study, antibacterial activity in excretions/secretions (ES) from maggots of Lucilia cuprina blowfly was demonstrated. The extracts were also screened in combination with antibiotic, ciprofloxacin. METHODS: L. cuprina blowfly maggots were reared for extraction of its metabolites. The ES extracted was screened against S. aureus, alone and in combination with ciprofloxacin, both for short term and long term exposure analysis. A microchannel-based device and system was used for experiments instead of conventional techniques. RESULTS: The original ES had shown partial bacterial growth inhibition. However, in combination with ciprofloxacin, at sub-inhibitory concentrations, certain combinations revealed anti-staphylococcal activity, with bacterial reduction of up to 50%, after 24 hours. The six day study on S. aureus exposed to ES-ciprofloxacin combination suggested a potential delay in development of adaptive resistance as opposed to when ciprofloxacin was used as single agent. CONCLUSIONS: The combination effect of ES and ciprofloxacin at sub-MIC levels showed enhanced antibacterial activity compared to the effect of ES and ciprofloxacin as single agents. Based on the results of ES-ciprofloxacin combinations, a more effective means of treatment for S. aureus can be proposed.