Coprisin exerts antibacterial effects by inducing apoptosis-like death inEscherichia coli

Bacterial Apoptosis-Like Death through Accumulation of Reactive Oxygen Species by Quercetin in Escherichia coli

The antimicrobial activity of the natural compounds from plant and food have well discovered since the interest on the beneficial effect of the natural compounds was risen. Quercetin, a flavonoid derived from vegetables, including onions, red leaf lettuces and cherries has been studied for diverse biological characteristics as anti-cancer and anti-microbial activities. The aim of current study is to investigate the specific antibacterial modes of action of quercetin against Escherichia coli. Quercetin decreased the E. coli cell viability and induced the severe damages (oxidative stress, DNA fragmentation) leading to cell death. Reactive oxygen species (ROS) generation was observed during the process, which we confirmed that oxidative stress was the key action of antibacterial activity of quercetin exerting its influence potently. Based on the results of Annexin V and Caspace FITC-VAD-FMK assay, the oxidative damage in E. coli has led to the bacterial apoptosis-like death in E. coli. To sum up, the contribution of ROS generation exerts crucial impact in antibacterial activity of quercetin.

Co-exposure to pentachlorophenol (PCP) and cadmium (Cd) triggers apoptosis-like cell death in Eschericia coli

Pentachlorophenol (PCP) - cadmium (Cd) complex pollution has been identified as a form of persistent soil pollution in south China, exerting detrimental impacts on the indigenous soil bacterial communities. Hence, it is worthwhile to investigate whether and how bacterial populations alter in response to these pollutants. In this study, Escherichia coli was used as a model bacterium. Results showed that PCP exposure caused bacterial cell membrane permeability changes, intracellular ROS elevation, and DNA fragmentation, and triggered apoptosis-like cell death at low exposure concentration and necrosis at high exposure concentration. Cd exposure caused severe oxidative damage and cell necrosis in the tested bacterial strain. The co-exposure to PCP and Cd elevated the ROS level, stimulated the bacterial caspase activity, and induced DNA fragmentation, thereby leading to an apoptosis-like cell death. In conclusion, PCP-Cd complex pollution can cause bacterial population to decrease through apoptosis-like cell death pathway. However, it is worth noting that the subpopulation survives under the complex pollution stress.

Beetroot (Beta vulgaris) Extract against Salmonella Typhimurium via Apoptosis-Like Death and Its Potential for Application in Cooked Pork

Salmonella Typhimurium is a common foodborne pathogen in meat and meat products, causing significant harm and losses to producers and consumers. The aim of this study was to investigate the antibacterial activity and possible mechanisms of beetroot (Beta vulgaris) extract against S. Typhimurium, as well as the application potential in cooked pork. The results suggested beetroot extract could inhibit S. Typhimurium with a minimum inhibitory concentration (MIC) of 20 mg/mL. After treatment with beetroot extract (1 or 2 MIC), S. Typhimurium exhibited the characteristics of apoptotic-like death (ALD), such as membrane depolarization, phosphatidylserine (PS) externalization, caspase-like protein activation, and DNA fragmentation. Further research has shown that the ALD induced by beetroot extract in S. Typhimurium was caused by reactive oxygen species (ROS) consumption, which was different from most natural products. The treatment of cooked pork with beetroot extract could reduce the number of S. Typhimurium, lower pH, defer lipid oxidation, and improve the colour. These results indicate that beetroot extract can inhibit S. Typhimurium through the ALD mechanism and has potential as an antibacterial agent against S. Typhimurium in ready-to-eat meat products.

Recent Progress in the Characterization, Synthesis, Delivery Procedures, Treatment Strategies, and Precision of Antimicrobial Peptides

Infectious diseases are constantly evolving to bypass antibiotics or create resistance against them. There is a piercing alarm for the need to improve the design of new effective antimicrobial agents such as antimicrobial peptides which are less prone to resistance and possess high sensitivity. This would guard public health in combating and overcoming stubborn pathogens and mitigate incurable diseases; however, the emergence of antimicrobial peptides' shortcomings ranging from untimely degradation by enzymes to difficulty in the design against specific targets is a major bottleneck in achieving these objectives. This review is aimed at highlighting the recent progress in antimicrobial peptide development in the area of nanotechnology-based delivery, selectivity indices, synthesis and characterization, their doping and coating, and the shortfall of these approaches. This review will raise awareness of antimicrobial peptides as prospective therapeutic agents in the medical and pharmaceutical industries, such as the sensitive treatment of diseases and their utilization. The knowledge from this development would guide the future design of these novel peptides and allow the development of highly specific, sensitive, and accurate antimicrobial peptides to initiate treatment regimens in patients to enable them to have accommodating lifestyles.

Polyoxometalate K6[P2Mo18O62] Inactivates Escherichia coli O157:H7 by Inducing recA Expression and Apoptosis-like Bacterial Death

Polyoxometalates have emerged as promising bactericidal agents. In the current study, the bactericidal activity of polyoxometalate K₆[P₂Mo₁₈O₆₂] against Escherichia coli (E. coli) O157:H7 and its possible underlying mechanisms were explored. The obtained results demonstrated that K₆[P₂Mo₁₈O₆₂] could effectively kill E. coli O157:H7 at millimolar levels. Moreover, K₆[P₂Mo₁₈O₆₂] treatment also induced significant increases in recA protein expression and further triggered characteristic apoptosis-like bacterial death events such as DNA fragmentation and phosphatidylserine exposure. In conclusion, polyoxometalate K₆[P₂Mo₁₈O₆₂] possesses a desirable antibacterial activity, and induction of bacterial apoptosis-like death might be involved in its underlying bactericidal mechanisms.

Depletion of reactive oxygen species induced by beetroot (Beta vulgaris) extract leads to apoptosis-like death in Cronobacter sakazakii

This research aimed to disclose the antibacterial activity of beetroot extract (Beta vulgaris) against Cronobacter sakazakii and its possible mechanisms. We evaluated its antibacterial activity by measuring the minimum inhibitory concentration (MIC) and time-kill kinetics. We also evaluated the intracellular ATP levels, bacterial apoptosis-like death (ALD), and reactive oxygen species (ROS) levels to reveal the possible antibacterial mechanisms. Our results showed that the MIC of beetroot extract against C. sakazakii was 25 mg/mL and C. sakazakii (approximately 8 log cfu/mL) was completely inhibited after treatment with 2 MIC of beetroot extract for 3 h. Beetroot extract reduced intracellular ATP levels and facilitated characteristics of ALD in C. sakazakii, such as membrane depolarization, increased intracellular Ca²⁺ levels, phosphatidylserine externalization, caspase-like protein activation, and DNA fragmentation. Additionally, and different from most bacterial ALD caused by the accumulation of ROS, beetroot extract reduced the intracellular ROS levels in C. sakazakii. Our experimental data provide a rationale for further research of bacterial ALD and demonstrate that beetroot extract can inhibit C. sakazakii in food processing environments.

Evaluation of the efficacy of the antimicrobial peptide HJH-3 in chickens infected with Salmonella Pullorum

As a promising substitute for antibiotics, increasing attention has been given to the clinical application of antimicrobial peptides (AMPs). In this study, the mode of action of the HJH-3 against Salmonella Pullorum was investigated. The structure and properties of HJH-3 were examined in silico, and minimum inhibitory concentrations (MICs) were determined to evaluate its antimicrobial spectrum. The time-kill kinetics of HJH-3 was determined. The hemolytic activity of HJH-3 was determined by measuring the hemoglobin ultraviolet absorption value, and the cytotoxicity was determined using a CCK-8 kit. The protective effect of HJH-3 on chickens infected with S. Pullorum was evaluated in vivo. The results demonstrated that HJH-3 exhibited strong antibacterial activity against Gram-negative pathogens at MIC values of 1.5625-25 μg/mL and against Gram-positive pathogens at MIC values of 25-50 μg/mL. HJH-3 also showed activity against the Candida albicans (100 μg/mL) and Bacillus subtilis (6.25-12.5 μg/mL). HJH-3 at 100 μg/mL completely killed S. Pullorum after co-incubation for 6 h. Likewise, the hemolysis rate of CRBCs treated with 100 μg/mL HJH-3 (7.31%) was lower than that of CRBCs treated with 100 μg/mL pexiganan (40.43%). Although the hemolysis rate of CRBCs treated with 400 μg/mL HJH-3 was increased to 13.37%, it was much lower than that of 400 μg/mL pexiganan (57.27%). In regards to cytotoxicity, HJH-3 had almost no-effect on the CEF proliferation, pexiganan decreased CEFs proliferation from 56.93 to 31.00% when increasing the concentration from 50 to 200 μg/mL. In a chicken infection model, the results showed that the antibiotic prevention and HJH-3 prevention groups exhibited the best treatment effect, with the chickens being protected from the lethal dose of S. Pullorum, a decreased number of bacteria in the blood and spleen, and less pathological changes in intestinal segments. The prevention of infection by HJH-3 was similar to that by Ampicillin; the effect of treatment after infection was lower than that of treatment before infection, and the survival rate of infected chicks treated with HJH-3 was 70%, which was still higher than that of the infected chickens. These results suggest that HJH-3 has good clinical application potential and can be used as a substitute for antibiotics for the prevention and treatment of S. Pullorum infection.

Physiological changes and growth behavior of Corynebacterium glutamicum cells in biofilm

Biofilm cells are well-known for their increased survival and metabolic capabilities and have been increasingly implemented in industrial and biotechnological processes. Corynebacterium glutamicum is one of the most widely used microorganisms in the fermentation industry. However, C. glutamicum biofilm has been rarely reported and little is known about its cellular basis. Here, the physiological changes and characteristics of C. glutamicum biofilm cells during long-term fermentation were studied for the first time. Results showed that the biofilm cells maintained stable metabolic activity and cell size was enlarged after repeated-batch of fermentation. Cell division was slowed, and chromosome content and cell proliferation efficiency were reduced during long-term fermentation. Compared to free cells, more biofilm cells were stained by the apoptosis indicator dyes Annexin V-FITC and propidium iodide (PI). Overall, these results suggested slow-growing, long-lived cells of C. glutamicum biofilm during fermentation, which could have important industrial implications. This study presents first insights into the physiological changes and growth behavior of C. glutamicum biofilm cell population, which would be valuable for understanding and developing biofilm-based processes.

Enhancement of photodynamic bactericidal activity of curcumin against Pseudomonas Aeruginosa using polymyxin B

BACKGROUND

Pseudomonas aeruginosa (P. aeruginosa) is an emerging opportunistic pathogen, which can cause bacterial skin diseases such as green nail syndrome, interdigital infections and folliculitis. Curcumin-mediated antimicrobial photodynamic therapy (aPDT) has been demonstrated as a promising therapeutic option for the treatment of skin infection though its inactivation of gram-negative bacteria such as P. aeruginosa.

MATERIALS AND METHODS

In the present study, we examined the adjuvant effect of polymyxin B on the antibacterial activity of curcumin-mediated aPDT against P. aeruginosa. P. aeruginosa was treated with curcumin in the presence of 0.1-0.5 mg/L polymyxin B and irradiated by blue LED light (10 J/cm²). Bacterial cultures treated with curcumin alone served as controls. Colony forming units (CFU) were counted and the viability of P. aeruginosa was calculated after aPDT treatment. The possible underlying mechanisms for the enhanced killing effects were also explored.

RESULTS

The killing effects of curcumin-mediated aPDT against P. aeruginosa was significantly enhanced by polymyxin B (over 2-log reductions). Moreover, it was also observed that addition of polymyxin B in the curcumin-mediated aPDT led to the apparent bacterial membrane damage with increased leakage of cytoplasmic contents and extensive DNA and protein degradation.

DISCUSSION

The photodynamic action of curcumin against P. aeruginosa could be significantly enhanced by the FDA-approved drug polymyxin B. Our results highlight the potential of introducing polymyxin B to enhance the effects of aPDT treatment against gram-negative skin infections, in particular, P. aeruginosa.

Investigation of distinct contribution of nitric oxide and each reactive oxygen species in indole-3-propionic-acid-induced apoptosis-like death in Escherichia coli

AIMS

Indole-3-propionic acid (IPA) is a natural product from human microbiota, exhibiting diverse biological activities. The study focused on investigating the antibacterial mode of action(s) triggered by IPA in Escherichia coli. Separate influence of nitric oxide (NO) and each reactive oxygen species, including superoxide anion (O₂^-), hydrogen peroxide (H₂O₂), hydroxyl radical (OH^-), was specifically analyzed throughout the process.

MAIN METHODS

The generation of respective reactive oxygen species (ROS), NO, and ONOO^- was conducted using flow cytometer using different dyes. Further analysis of separate influences was held based on usage of each scavenger: sodium pyruvate, thiourea, tiron, and L-NAME. Oxidative cell damage was observed through the detection of glutathione depletion and lipid peroxidation. DNA fragmentation and membrane depolarization were observed by TUNEL and DiBAC₄(3) staining agent. Finally, Annexin V/PI and FITC-VAD-FMK were applied to detect apoptosis-like death.

KEY FINDINGS

IPA exhibited antibacterial activity in E. coli through the accumulation of ROS, NO, ONOO^-, and DNA damage, eventually leading to apoptosis-like death. NO and O₂^- exerted the most potent influence on oxidative damage of E. coli, whereas H₂O₂ accounts for the least impact. Moreover, the results reveal the major contribution of ONOO^- in IPA-induced apoptosis-like death in E. coli.

SIGNIFICANCE

This is the first study that introduces the antibacterial activity and apoptosis-like death induced by IPA and suggests the possibility of being an alternative for current antibiotics. Furthermore, the distinct influence of each ROS and NO was analyzed to investigate their contribution to oxidative damage leading to bacterial apoptosis-like death.

Apoptosis-like death-inducing property of tachyplesin I in Escherichia coli

 Antimicrobial peptide (AMP) derived from the horseshoe crab, tachyplesin I (KWCFRVCYRGICYRRCR-NH₂ ), displayed the apparent antimicrobial activity with low cytotoxicity, suggesting its efficacy as an attractive agent but still lacks the understandings regarding its mechanism(s). Hence, the study focused on investigating the antibacterial mode of action of tachyplesin I against Escherichia coli. Based on the reactive oxygen species generation displayed in several antimicrobial effects, the detection of superoxide anion and nitric oxide were verified after tachyplesin I treatment. Substantial increment of two molecules was followed by the imbalance in intracellular ion concentration, noticeably magnesium and calcium. The series of stages led to hydroxyl radical generation with reduced glutathione, followed by damage in DNA due to oxidative stress. Eventually, the apoptosis-like death in E. coli was monitored in DNA fragmentation-dependent manner due to the tachyplesin I treatment, verified by membrane depolarization, caspase-like protein activation, and phosphatidylserine exposure. Accordingly, tachyplesin I induces apoptosis-like death in E. coli, suggesting the potential of being a candidate for regulating bacterial infection.

Indole-3-carbinol induces apoptosis-like death in Escherichia coli on different contribution of respective reactive oxygen species

AIMS

Indole-3-carbinol (I3C) is a natural compound derived from brassica vegetables, displaying antibacterial activity. The study aims to elucidate the antibacterial mode of action(s) induced by indole-3-carbionol in Escherichia coli and enhance the understandings on the respective contribution of each reactive oxygen species (ROS), superoxide anion (O₂^-), hydrogen peroxide (H₂O₂), hydroxyl radical (OH^-) during the process.

MAIN METHODS

The antibacterial activity of I3C was assessed through kinetic assay. The generation of ROS was measured by flow cytometer using H₂DCFDA dye, while further analysis of respective contribution was done through application of each scavenger: tiron, thiourea and sodium pyruvate. DNA fragmentation and chromatin condensation were observed by TUNEL and DAPI staining agent. Finally, Annexin V/PI, FITC-VAD-FMK and DiBAC₄(3) was applied for detection of apoptosis-like death.

KEY FINDINGS

I3C exhibited antibacterial activity in E. coli through accumulation of ROS and DNA damage, eventually leading to apoptosis-like death. Contribution of each ROS displayed respective manner, OH^- exerting the most potent influence whereas O₂^- showed least impact.

SIGNIFICANCE

Our study is the first to link I3C to the bacterial apoptosis-like death and displays the potential of this agent as a candidate for potential drugs that could help regulating the E. coli, an opportunistic human pathogen. Moreover, the study focused on investigating the individual contribution of each ROS during the process, trying to enhance the understanding regarding ROS and cellular processes followed by oxidative stress in bacteria.

Silver nanoparticles-induced H2O2 triggers apoptosis-like death and is associated with dinF in Escherichia coli

Silver nanoparticles (AgNPs) are the most widely used nanomaterials as antimicrobial agents. AgNPs have been shown to inhibit the growth of and induce apoptosis-like death in Escherichia coli. However, the precise mechanism of AgNPs-induced apoptosis-like death and association with DNA damage-inducible protein F (dinF), a gene of SOS response, is unknown. Here, AgNPs-contributing depletion of intracellular glutathione levels and deactivation of glutathione peroxidase were shown. This step, indicating disruption of the antioxidant system, resulted in overall oxidative stress. Furthermore, DNA oxidation was accompanied, leading to DNA fragmentation. In addition, AgNPs appeared to induce apoptosis-like death via the SOS response. We used sodium pyruvate - an H₂O₂ quencher - to study the contribution of H₂O₂, which showed attenuation of AgNPs-induced DNA damage, SOS response, and apoptosis-like death. In dinF mutant, the strain showed a higher degree of DNA damage and apoptotic features. In conclusion, AgNPs mediate apoptosis-like cell death by H₂O₂-induced oxidative DNA damage. Furthermore, our result demonstrates that dinF participates in this process, which further supports that AgNPs induces SOS response. Our findings may contribute to expanding the new applications of AgNP-based nanomaterials in biomedical fields.

Interaction of synthetic antimicrobial peptides of the Hylin a1 family with models of eukaryotic structures: Zwitterionic membranes and DNA

Antimicrobial peptides (AMPs) have been appointed as a possible alternative to traditional antibiotics in face of pathogens increasing resistance to conventional drugs. Hylin a1 (IFGAILPLALGALKNLIK), an AMP extracted from the skin secretion of a South American frog, Hypsiboas albopunctatus, was found to show a strong cytotoxicity against bacteria and fungus, but also a considerable hemolytic action. Considering the toxicity of the peptide in eukaryotic cells, this work focuses on investigating the effects of the interaction of the Hylin a1 analogues W⁶Hya1, D⁰W⁶Hya1 and K⁰W⁶Hya1 with models of eukaryotic structures, namely zwitterionic liposomes of dipalmitoyl phosphatidylcholine (DPPC) and calf-thymus DNA (CT DNA). Through intrinsic Trp fluorescence we determined that the peptide affinity for fluid DPPC bilayers follows the decreasing order: D⁰W⁶Hya1 (+2) > W⁶Hya1 (+3) » K⁰W⁶Hya1 (+4). Fluorescence data also indicate that the Trp residue in the more positively charged peptide, K⁰W⁶Hya1, is less deep in the bilayer than the residue in the other two peptides. This finding is supported by differential scanning calorimetry (DSC) data, which shows that both D⁰W⁶Hya1 and W⁶Hya1 disturb DPPC gel-fluid transition slightly more effectively than K⁰W⁶Hya1. DPPC DSC profiles are homogeneously disturbed by the three peptides, probably related to peptide-membrane diffusion. Surprisingly, the peptide that displays the lowest affinity for PC membranes and is located at the more superficial position in the bilayer, K⁰W⁶Hya1, is the most efficient in causing formation of pores on the membrane, as attested by carboxyfluorescein leakage assays. The three peptides were found to interact with CT DNA, with a deep penetration of the Trp residue into hydrophobic pockets of the double helix, as indicated by the significant blue shift on the Trp fluorescence, and the displacement of DNA-bound ethidium bromide by the peptides. The experiments of DNA electrophoresis confirm that Hylin peptides bind DNA in a concentration-dependent manner, inducing complete DNA retardation at the relative AMP/plasmid DNA weight ratio of ~17. These findings could help to better understand the AMPs toxic effects on eukaryotic cells, thus contributing to the design of healthier therapeutic agents.

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AMP Hylin a1 analogues bind to both a model of eukaryotic membrane and DNA.

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The most cationic peptide has lowest affinity to PC vesicle and shallower binding.

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Peptide lower bilayer affinity is related to greater vesicle disruption and leakage.

•AMP hylin a1 analogues deep penetrate into hydrophobic pockets of CT-DNA double helix.

Nitric oxide-inducing Genistein elicits apoptosis-like death via an intense SOS response in Escherichia coli

Increasing prevalence of multidrug-resistant untreatable infections has prompted researchers to trial alternative treatments such as a substitute for traditional antibiotics. This study endeavored to elucidate the antibacterial mechanism(s) of this isoflavone, via analysis of relationship between genistein and Escherichia coli. Furthermore, this investigation analyzed whether genistein generates nitric oxide (NO) in E. coli as NO contributes to cell death. RecA, an essential protein for the bacterial SOS response, was detected through western blot, and the activated caspases decreased without RecA. The results showed that the NO induced by genistein affected the bacterial DNA. Under conditions of acute DNA damage, an SOS response called apoptosis-like death occurred, affecting DNA repair. These results suggested that RecA was bacterial caspase-like protein. In addition, NO was toxic to the bacterial cells and induced dysfunction of the plasma membrane. Thus, membrane depolarization and phosphatidylserine exposure were observed similarly to eukaryotic apoptosis. In conclusion, the combined results demonstrated that the antibacterial mode of action(s) of genistein was a NO-induced apoptosis-like death, and the role of RecA suggested that it contributed to the SOS response of NO defense. KEY POINTS: • Genistein generates nitric oxide in E. coli. • Genistein exhibits intense SOS response in E. coli. • Genistein-induced NO causes apoptosis-like death in E. coli.

Effect of isoquercitrin on membrane dynamics and apoptosis-like death in Escherichia coli

Minimum inhibitory concentration (MIC) is defined as the lowest concentration of a compound that completely inhibits microbial growth. Antibacterial mechanisms of compounds have been investigated at their sub-MICs as well as at their MIC. In this study, the effects of sub-MIC and MIC of isoquercitrin on Escherichia coli were investigated. The antibacterial effect of isoquercitrin was tested using the microdilution method. Sub-MICs of isoquercitrin induced the production of reactive oxygen species and depletion of glutathione. The oxidative effects induced by sub-MICs of isoquercitrin could be prolonged, finally resulting in apoptosis-like death. DNA fragmentation and phosphatidylserine externalization, which are regarded as the hallmarks of apoptosis, were evaluated using the TUNEL assay and Annexin V staining, respectively. Furthermore, isoquercitrin induced the peroxidation of membrane lipids and inner membrane permeabilization at both its sub-MIC and MIC. This suggested membrane damage in response to lipid oxidation. The uptake of membrane impermeable dyes, propidium iodide and calcein, demonstrated that isoquercitrin damaged the cell membrane at concentrations higher than its MIC. Thus, isoquercitrin induced apoptosis-like death and dysregulation of cell membrane dynamics.

Anti-aging effect and gene expression profiling of dung beetle glycosaminoglycan in aged rats

BACKGROUND

This study aimed to evaluate the anti-aging effect of a newly prepared insect-derived compound, dung beetle glycosaminoglycan (GAG), given intraperitoneally to old SD rats as part of their diet for 1 month. Insect GAG administration was found to be related to a reduction in oxidative damage, hepato-cellular biomarker levels, protein carbonyl content, and malondialdehyde concentration. The anti-aging-related molecular genetic mechanisms of dung beetle GAG are not yet fully elucidated.

RESULTS

Catharsius molossus (a type of dung beetle) GAG (CaG) possessed anti-aging activities; it reduced the serum level of creatinine kinase, had aortic vasorelaxant activities and cardioprotective actions, and maintained a normal glucose level in treated rats. Microarray analysis was performed with a rat 30 K cDNA clone set array to identify the gene-expression profiles of 14-month-old SD rats treated with dung beetle glycosaminoglycan 5 mg/kg (CaG5) over a 1-month period, which was done to investigate its anti-aging effect as compared to that of either Bombus ignitus (a type of bumblebee) queen GAG 5 mg/kg (IQG5) or chondroitin sulfate 10 mg/kg. CaG5 and IQG5 had marked anti-inflammatory effects, bringing about inhibition of free fatty acid, uric acid, sGPT, IL-1 beta, and CK values. In addition, anticoagulant and antithrombotic effects were seen: the concentration of factor 1 (fibrinogen) was increased in CaG- treated rat plasma. The CaG5-treated rat group, compared to the control, displayed upregulation of 131 genes, including lipocalin 2 (Lbp) and a serine peptidase inhibitor, Kaszal type3 (Spink3), and 64 downregulated genes, including lysyl oxidase (Lox), serine dehydratase (sds), and retinol saturase (Retsat).

CONCLUSION

Our data suggest that dung beetle glycosaminoglycan may be a helpful treatment for aged rats, which indicates its potential as a therapeutic biomaterial for aging.