G K Suraishkumar

Titanium dioxide nanoparticles (TiO2 NPs) find applications in our day-to-day life because of unique physicochemical properties. Their release into the aquatic environment poses a possible risk to the organisms. However, the continuing exposure of NPs might reduce their bioavailability to marine organisms owing to aggregation and sedimentation in the aqueous systems thus significantly reducing their toxic impact. In this regard, the present study investigates the effect of continuous exposure of TiO2 NPs to marine microalgae Chlorella sp. under UV-A irradiation through “tanks in series” mode of experiments. In a three-cycle experiment, concentration of TiO2 NPs in the first cycle was fixed at 62.6 μM, and the interacted nanoparticles was subsequently exposed to fresh batches of algae in the next two cycles. After the interaction, the NPs underwent severe aggregation (mean hydrodynamic diameter 3000 ± 18.2 nm after cycle I) leading to gravitational settling in the medium and thus decreased bioavailability. The aggregation can be attributed to interactions between the particles themselves (homo-aggregation) further aggravated by the presence of the algal cells (hetero-aggregation). Cellular viability after cycle I was found to be only 24.2 ± 2.5%, and it was enhanced to 96.5 ± 2.8% after the cycle III in the course of continuous exposure. The results were validated with estimation of oxidative stress markers such as intracellular ROS (total ROS, superoxide and hydroxyl radicals) and LPO after each cycle of exposure. The continuing decrease in the EPS across the cycles further confirmed the diminishing toxicity of the NPs.

We report for the first time that the endogenous, pseudo-steady-state, specific intracellular levels of the hydroxyl radical (si-OH) oscillate in an ultradian fashion (model system: the microalga, Chlorella vulgaris), and also characterize the various rhythm parameters. The ultradian rhythm in the endogenous levels of the si-OH occurred with an approximately 6 h period in the daily cycle of light and darkness. Further, we expected that the rhythm reset to a shorter period could rapidly switch the cellular redox states that could favor lipid accumulation. We reset the endogenous rhythm through entrainment with UVA radiation, and generated two new ultradian rhythms with periods of approximately 2.97 h and 3.8 h in the light phase and dark phase, respectively. The reset increased the window of maximum lipid accumulation from 6 h to 12 h concomitant with the onset of the ultradian rhythms. Further, the saturated fatty acid content increased approximately to 80% of total lipid content, corresponding to the peak maxima of the hydroxyl radical levels in the reset rhythm.

Human skull bone is a three-layered structure with a compliant viscoelastic cancellous bone layer sandwiched between elastic compact layers. The objective of the work was to check whether the skull bone is innately optimized with respect to the various geometrical and material parameters and to find out the parameters with which they are optimized. The effect of varying the thickness of layers and short time modulus of the interlayer are studied for optimality using finite element analysis of the skull subjected to low-velocity impact. Results show that they are optimized to meet different objectives. © Woodhead Publishing Ltd.

Development of colon adenocarcinoma (COAD) metastasis involves several mediators including fluid shear stress (FSS), intracellular ROS levels, and non-coding RNAs. In our present study, we identified and investigated the role of regulatory non-coding RNA molecules specifically involved in COAD metastasis and their association with FSS and ROS. Interactions between the mRNAs associated with FSS and ROS, the corresponding microRNAs (miRNAs), long noncoding RNAs (lncRNAs) and circular RNAs (circRNAs) in COAD metastasis were used to generate the mRNA-miRNA-lncRNA-circRNA network. Experimental validation of the identified RNA hubs using quantitative real-time PCR demonstrated a direct effect of the FSS on their expression levels in cancer cells. FSS resulted in the downregulation of HMGA1 and RAN, as well as the upregulation of HSP90AA1, PMAIP1 and BIRC5. Application of shear stress also led to downregulation of hsa-miR-26b-5p and hsa-miR-34a-5p levels in HCT116 cells. Further, functional enrichment and survival analysis of the significant miRNAs, as well as the OncoPrint and the survival analyses of the selected mRNAs were performed. Subsequently, their functional role was also corroborated with existing literature. Ten significant miRNA hubs were identified, out of which hsa-miR-17-5p and hsa-miR-20a-5p were found to interact with lncRNA (CCAT2) while hsa-miR-335 was found to interact with four circRNAs. Fifteen significant miRNAs were identified in 10 different modules suggesting their importance in FSS and ROS-mediated COAD metastasis. Finally, 10 miRNAs and 3 mRNAs associated with FSS and/or ROS were identified as significant overall survival markers; 33 mRNAs were also identified as metastasis-free survival markers whereas 15 mRNAs showed > 10% gene alterations in TCGA-COAD data and may serve as promising therapeutic biomarkers in the COAD metastasis.

An oncogenic transformation has been associated with different factors such as unhealthy lifestyle and diet, exposure to harmful environmental conditions and infectious agents. These extrinsic and intrinsic carcinogens can be detrimental to cellular, genetic, and epigenetic functions of the cell, leading to abnormal cell growth and division. However, a significant hallmark of cancer cell metabolism is elevated intracellular reactive oxygen species (ROS) level. The increased ROS levels are known to promote cell proliferation, cell-to-cell adhesion, and motility, as well as angiogenesis in tumors. On the other hand, many cancer therapeutics exert their cytotoxic effects on cancer cells by mediating excess intracellular ROS generation, thus implicating a dual role of ROS in tumorigenesis and cancer cell death. Constraint-based modeling (CBM) and genome-scale metabolic models (GSMMs) have been widely used to study diverse biological systems at the metabolic level as well as to understand human diseases better. For instance, reprogrammed metabolism is central to sustaining growth and proliferation in transformed cells and hence needs to be modeled. For this purpose, a constraint-based reconstruction and analysis (COBRA) modeling strategy has been used to analyze cancer-specific metabolism and phenotypes, using context-specific metabolic models. Context-specific GSMMs have also proven advantageous in uncovering potential therapeutic targets. However, unlike numerous experimental studies that have already established the relevance of ROS in cancer, a CBM approach has not considered the role of ROS generation in understanding complex cancer metabolism thus far. This work discusses the significance of CBM in studying the scope of ROS in cancer and in devising novel cancer therapeutics.

The onset of colorectal cancer (CRC) is often attributed to gut bacterial dysbiosis, and thus gut microbiota are highly relevant in devising treatment strategies. Certain gut microbes, like Enterococcus spp., exhibit remarkable anti-neoplastic and probiotic properties, which can aid in silver nanoparticle (AgNPs) induced reactive oxygen species (ROS)-based CRC treatment. However, the effects of AgNPs on gut microbial metabolism have not been reported thus far. In this study, a detailed systems-level understanding of ROS metabolism in Enterococcus durans (E. durans), a representative gut microbe, was gained using constraint-based modeling, wherein, the critical association between ROS and folate metabolism was established. Experimental studies involving low AgNP concentration treatment of E. durans cultures confirmed these modeling predictions (an increased extracellular folate concentration by 52%, at the 9th h of microbial growth, was observed). Besides, the computational studies established various metabolic pathways involving amino acids, energy metabolites, nucleotides, and SCFAs as the key players in elevating folate levels on ROS exposure. The anti-cancer potential of E. durans was also studied through MTT analysis of HCT 116 cells treated with microbial culture (AgNP treated) supernatant. A decrease in cell viability by 19% implicated the role of microbial metabolites (primarily folate) in causing cell death. The genome-scale modeling approach was then extended to extensively model CRC metabolism, as well as CRC–E. durans interactions in the context of CRC treatment, using tissue-specific metabolic models of CRC and healthy colon. These findings on further validation can facilitate the development of robust and effective cancer therapy.

Liquid phase oxygen supply strategy (LPOS), in which hydrogen peroxide (H2O2) is used to supply oxygen to the bioreactor, leads to low cell productivity despite high specific productivities of relevant metabolites. We hypothesized that high H2O2 concentrations in the feed-zone led to local cell death, which in turn, lead to lower cell productivity. To test the hypothesis, a mathematical model was developed. Bacillus subtilis 168 was used as the model system in this study. The model simulations of cell concentrations in the bioreactor-zone were verified with the experimental results. The feed-zone H2O2 concentrations remained 12-14 times higher than bulk bioreactor concentrations. The high local concentrations are expected to cause local cell killing, which explains the decrease in overall cell production by 50% at 300 rpm compared to conventional cultivation. Further, among the four different feed strategies studied using the model, dissolved oxygen (DO) controlled H2O2 feed strategy caused least local cell killing and improved overall cell production by 34%. © 2007 Springer-Verlag.

Continuous increase in the usage of ZnO nanoparticles in commercial products has exacerbated the risk of release of these particles into the aquatic environment with possible harmful effects on the biota. In the current study, cytotoxic effects of two types of ZnO nanoparticles, having different initial effective diameters in filtered and sterilized lake water medium [487.5±2.55nm for ZnO-1 NPs and 616.2±38.5nm for ZnO-2 NPs] were evaluated towards a dominant freshwater algal isolate Scenedesmus obliquus in UV-C, visible and dark conditions at three exposure concentrations: 0.25, 0.5 and 1mg/L. The toxic effects were found to be strongly dependent on the initial hydrodynamic particle size in the medium, the exposure concentrations and the irradiation conditions. The loss in viability, LDH release and ROS generation were significantly enhanced in the case of the smaller sized ZnO-1 NPs than in the case of ZnO-2 NPs under comparable test conditions. The toxicity of both types of ZnO NPs was considerably elevated under UV-C irradiation in comparison to that in dark and visible light conditions, the effects being more enhanced in case of ZnO-1 NPs. The size dependent dissolution of the ZnO NPs in the test medium and possible toxicity due to the released Zn2+ ions was also noted. The surface adsorption of the nanoparticles was substantiated by scanning electron microscopy. The internalization/uptake of the NPs by the algal cells was confirmed by fluorescence microscopy, transmission electron microscopy, and elemental analyses.

In the previous chapter, we discussed the principle of mass balance and saw how it can be used in terms of mass or mass rates, to analyse, design and operate biosystems over a wide length scale, i.e. from a cell to a bioprocess. In this chapter, let us look at a concept that is central to many engineering disciplines, and especially to biological engineering, namely, flux. A flux of a quantity is defined as the amount of that quantity that is transported per unit time across a unit area that is perpendicular to the direction of transport. Thus, mass flux is defined as the amount of mass transported per unit time across a unit area that is perpendicular to the direction of mass transport.

Microbial cement production based on microbially induced calcium carbonate precipitation (MICP) is a technology with high potential but is economically limited. Lower medium costs are expected to improve the economic attractiveness of microbial cement production. We report the effect of an important medium parameter, the carbon-to-nitrogen (C/N) ratio (2, 5, 10, 15, and 20) on the intracellular urease activity (IUA) of ureolytic bacteria, Sporosarcina pasteurii (ATCC 11859) through experiments and analysis of a relevant genome-scale metabolic model (GSMM). A positive correlation was observed between IUA and C/N ratio until an optimal C/N ratio of 15. At a C/N ratio of 15, the IUA was 29.5 U/(g dry-cell-weight). Further, the ammonium (nitrogen waste) generation decreased by 7.7-fold at the optimal C/N ratio of 15 compared to that at 2, which is environmentally significant. Despite the decrease in initial urea concentration with an increasing C/N ratio, no decline in the biomass was observed, which is advantageous. Analysis of the GSMM provided the insights that the optimal C/N ratio of 15 also ensures an efficient bio-mineralization process and that increasing the ratio beyond 15 may negatively impact bio-mineralization. The results will be of significance while selecting a low-cost medium for field-scale MICP applications.