SUNScholar - Browsing by Author "Engelbrecht, Anna-Mart"

Browsing by Author "Engelbrecht, Anna-Mart"

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Amino acid starvation sensitizes resistant breast cancer to doxorubicin-induced cell death
(Frontiers Media, 2020) Thomas, Mark; Davis, Tanja Andrea; Nell, Theo; Sishi, Balindiwe J. N. (Jennifer Nonkosazana); Engelbrecht, Anna-Mart
Many clinical trials are beginning to assess the effectiveness of compounds known to regulate autophagy in patients receiving anti-cancer chemotherapy. However, autophagy inhibition, through exogenous inhibitors, or activation, through starvation, has revealed conflicting roles in cancer management and chemotherapeutic outcome. This study aimed to assess the effect of amino acid starvation on doxorubicin-treated breast cancer cells by assessing the roles of autophagy and apoptosis. An in vitro breast cancer model consisting of the normal breast epithelial MCF12A and the metastatic breast cancer MDAMB231 cells was used. Apoptotic and autophagic parameters were assessed following doxorubicin treatments, alone or in combination with bafilomycin, ATG5 siRNA or amino acid starvation. Inhibition of autophagy, through ATG5 siRNA or bafilomycin treatment, increased caspase activity and intracellular doxorubicin concentrations in MCF12A and MDAMB231 cells during doxorubicin treatment. While amino acid starvation increased autophagic activity and decreased caspase activity and intracellular doxorubicin concentrations in MCF12A cells, no changes in autophagic parameters or caspase activity were observed in MDAMB231 cells. Our in vivo data showed that 24 h protein starvation during high dose doxorubicin treatment resulted in increased survival of tumor-bearing GFP-LC3 mice. Results from this study suggest that short term starvation during doxorubicin chemotherapy may be a realistic avenue for adjuvant therapy, especially with regards to the protection of non-cancerous cells. More research is however, needed to fully understand the regulation of autophagic flux during starvation.
Bcl‑2 confers survival in cisplatin treated cervical cancer cells: circumventing cisplatin dose‑dependent toxicity and resistance
(BioMed Central, 2015-10) Leisching, Gina; Loos, Benjamin; Botha, Matthys; Engelbrecht, Anna-Mart
Background: Cisplatin is the main chemotherapeutic drug for the treatment of cervical cancers, however resistance to cisplatin is increasingly common and therefore has limited the efficacy and use of this drug in the clinic. Dosedependent toxicity poses an additional challenge since patients suffer long-term and often permanent side-effects after treatment. Bcl-2 up-regulation has been implicated in the resistance to cisplatin in a variety of cancer cell lines, however its role in cervical cancer is confounding. Methods: A low, non-cytotoxic concentration of cisplatin was used in the treatment of HeLa and CaSki cells. Bcl-2 expression was determined through Western blotting and immunocytochemistry before and after treatment with cisplatin. To assess the reliance of the cervical cancer cells on Bcl-2 in the presence of cisplatin, Bcl-2 knock-down was achieved through RNA interference, where after apoptosis was assessed through PARP cleavage (Western blotting), Caspase activity (Caspase-Glo©) and PI inclusion analysis (Flow cytometry). Finally, pre-malignant and malignant cervical tissue was analysed for the presence of Bcl-2 through Western blotting and immunofluorescence. Results: Cervical cancer cells upregulate Bcl-2 when treated with a non-cytotoxic concentration of cisplatin, which when silenced, effectively enhanced cisplatin sensitivity, and therefore significantly induced apoptosis. Analysis of the expression profile of Bcl-2 in cervical tissue revealed its up-regulation in cervical carcinoma, which agrees with results obtained from the in vitro data. Conclusions: Our data strongly suggest that utilising a lower dose of cisplatin is feasible when combined with Bcl-2 silencing as an adjuvant treatment, thereby improving both the dose-dependent toxicity, as well as cervical cancer resistance.
Chemoresistance : intricate interplay between breast tumor cells and adipocytes in the tumor microenvironment
(Frontiers Media, 2018-12-11) Mentoor, Ilze; Engelbrecht, Anna-Mart; Van Jaarsveld, Paul J.; Nell, Theo A.; Vella, Veronica
Excess adipose tissue is a hallmark of an overweight and/or obese state as well as a primary risk factor for breast cancer development and progression. In an overweight/obese state adipose tissue becomes dysfunctional due to rapid hypertrophy, hyperplasia, and immune cell infiltration which is associated with sustained low-grade inflammation originating from dysfunctional adipokine synthesis. Evidence also supports the role of excess adipose tissue (overweight/obesity) as a casual factor for the development of chemotherapeutic drug resistance. Obesity-mediated effects/modifications may contribute to chemotherapeutic drug resistance by altering drug pharmacokinetics, inducing chronic inflammation, as well as altering tumor-associated adipocyte adipokine secretion. Adipocytes in the breast tumor microenvironment enhance breast tumor cell survival and decrease the efficacy of chemotherapeutic agents, resulting in chemotherapeutic resistance. A well-know chemotherapeutic agent, doxorubicin, has shown to negatively impact adipose tissue homeostasis, affecting adipose tissue/adipocyte functionality and storage. Here, it is implied that doxorubicin disrupts adipose tissue homeostasis affecting the functionality of adipose tissue/adipocytes. Although evidence on the effects of doxorubicin on adipose tissue/adipocytes under obesogenic conditions are lacking, this narrative review explores the potential role of obesity in breast cancer progression and treatment resistance with inflammation as an underlying mechanism.
A combination of an antimitotic and a bromodomain 4 inhibitor synergistically inhibits the metastatic MDA-MB-231 breast cancer cell line
(Hindawi Publishing, 2019-12-11) Mqoco, Thandi; Stander, Andre; Engelbrecht, Anna-Mart; Joubert, Anna M.
Current chemotherapeutic agents have many side effects and are toxic to normal cells, providing impetus to identify agents that can effectively eliminate tumorigenic cells without damaging healthy cells. The aim of this study was to examine whether combining a novel BRD4 inhibitor, ITH-47, with the antimitotic estradiol analogue, ESE-15-ol, would have a synergistic effect on inhibiting the growth of two different breast cancer cell lines in vitro. Our docking and molecular dynamics studies showed that compared to JQ1, ITH-47 showed a similar binding mode with hydrogen bonds forming between the ligand nitrogens of the pyrazole, ASN99, and water of the BRD4 protein. Data from cell growth studies revealed that the GI50 of ITH-47 and ESE-15-ol after 48 hours of exposure was determined to be 15 μM and 70 nM, respectively, in metastatic MDA-MB-231 breast cancer cells. In tumorigenic MCF-7 breast cancer cells, the GI50 of ITH-47 and ESE-15-ol was 75 μM and 60 nM, respectively, after 48 hours of exposure. Furthermore, the combination of 7.5 μM and 14 nM of ITH-47 and ESE-15-ol, respectively, resulted in 50% growth inhibition of MDA-MB-231 cells resulting in a synergistic combination index (CI) of 0.7. Flow cytometry studies revealed that, compared to the control, combination-treated MDA-MB-231 cells had significantly more cells present in the sub-G1 phase and the combination treatment induced apoptosis in the MDA-MB-231 cells. Compared to vehicle-treated cells, the combination-treated cells showed decreased levels of the BRD4, as well as c-Myc protein after 48 hours of exposure. In combination, the selective BRD4 inhibitor, ITH-47, and ESE-15-ol synergistically inhibited the growth of MDA-MB-231 breast cancer cells, but not of the MCF-7 cell line. This study provides evidence that resistance to BRD4 inhibitors may be overcome by combining inhibitors with other compounds, which may have treatment potential for hormone-independent breast cancers.
Commentary on : "A common origin for immunity and digestion"
(Frontiers Media, 2015-05) Van Niekerk, Gustav; Engelbrecht, Anna-Mart
No abstract
Decreased efficacy of doxorubicin corresponds with modifications in lipid metabolism markers and fatty acid profiles in breast tumors from obese vs. lean mice
(Frontiers Media, 2018-03-17) Mentoor, Ilze; Nell, Theo A.; Emjedi, Zaakiyah; Van Jaarsveld, Paul J.; De Jager, Louis; Engelbrecht, Anna-Mart; Sotgia, Federica
Breast cancer cells modulate lipid and fatty acid metabolism to sustain proliferation. The role of adipocytes in cancer treatment efficacy remains, however, to be fully elucidated. We investigated whether diet-induced obesity (DIO) affects the efficacy of doxorubicin treatment in a breast tumor-bearing mouse model. Female C57BL6 mice were fed a high fat or low fat diet for the full duration of the study (12 weeks). After 8 weeks, mice were inoculated with E0771 triple-negative breast cancer cells in the fourth mammary gland to develop breast tumor allographs. Tumor-bearing mice received either vehicle (Hank's balanced salt solution) or doxorubicin (chemotherapy). Plasma inflammatory markers, tumor, and mammary adipose tissue fatty acid composition, as well as protein expression of lipid metabolism markers were determined. The high fat diet (HFD) attenuated the treatment efficacy of doxorubicin. Both leptin and resistin concentrations were significantly increased in the HFD group treated with doxorubicin. Suppressed lipogenesis (decreased stearoyl CoA-desaturase-1) and lipolysis (decreased hormone-sensitive lipase) were observed in mammary adipose tissue of the DIO animals, whereas increased expression was observed in the tumor tissue of doxorubicin treated HFD mice. Obesogenic conditions induced altered tissue fatty acid (FA) compositions, which reduced doxorubicin's treatment efficacy. In mammary adipose tissue breast cancer cells suppressed the storage of FAs, thereby increasing the availability of free FAs and favored inflammation under obesogenic conditions.
Domesticating cancer : an evolutionary strategy in the war on cancer
(Frontiers Media, 2017) Van Niekerk, Gustav; Nell, Theo A.; Engelbrecht, Anna-Mart
Since cancer shares the same molecular machinery as the host, most therapeutic interventions that aim to target cancer would inadvertently also adversely affect the host. In addition, cancer continuously evolves, streamlining its host-derived genome for a new single-celled existence. In particular, short-term clinical success observed with most antineoplastic therapies directly relate to the fact that cancer is constantly evolving. However, the clonal evolution of cancer occasionally also render cancer cells uniquely susceptible to therapeutic interventions, as is exemplified by the clinical relevance of synthetic lethality. Synthetic lethality describes a situation where the simultaneous loss of function in two genes results in lethality, but where a loss of function in either single gene is tolerated. This observation suggests that the evolution of cancer, usually seen as a major clinical challenge, may also afford a key opportunity in lowering on-target toxicities accosted with chemotherapy. As an example, by subjecting cancer to specific selection regimes, cancer can in effect be placed on evolutionary trajectories leading to the development of “targetable” phenotypes such as synthetic lethal interactions. However, such a selection regime would have to overcome a range of obstacles such as on-target toxicity and the selection of an evolvable trait. Since the majority of cancer evolution manifests as a loss of function, we suggest that the induction of auxotrophic phenotypes (i.e., where an organism lose the ability to synthesize specific organic compounds required for growth and thus become dependent on it from dietary sources) may represent an attractive therapeutic option. As an example, animals can obtain vitamin C either by de novo synthesis or from their diet. However, since the maintenance of synthetic pathways is costly, such pathways are often lost if no longer necessary, resulting in the organism being auxotrophic toward the dietary compound. Similarly, increasing the maintenance cost of a redundant pathway in cancer cells is likely to select for clones that have lost such a redundant pathway. Inhibition of a pathway, while supporting the activity of a compensating pathway, may thus induce auxotrophism in cancer cells but not in genomic stable host cells.
The effect of dietary red palm oil on the functional recovery of the ischaemic/reperfused isolated rat heart : the involvement of the PI3-Kinase signaling pathway
(BioMed Central, 2009-05) Engelbrecht, Anna-Mart; Odendaal, Louise; Du Toit, Eugene F.; Kupai, Krisztina; Czont, Tamas; Ferdinandy, Peter; Van Rooyen, Jacques
We have previously shown that dietary red palm oil (RPO) supplementation improves functional recovery in hearts subjected to ischaemia/reperfusion-induced injury. Unfortunately, the cellular and molecular mechanisms responsible for this phenomenon are still poorly understood and no knowledge exists regarding the effects of RPO supplementation on the phosphoinositide 3-kinase (PI3-K) signaling pathway and apoptosis during ischaemia/reperfusion injury. Therefore, the aims of the present study were three fold: (i) to establish the effect of RPO on the functional recovery of the heart after ischaemia/reperfuion injury; (ii) to determine the effect of the PI3-K pathway in RPO-induced protection with the aid of an inhibitor (wortmannin); and (iii) to evaluate apoptosis in our model. Wistar rats were fed a standard rat chow control diet or a control diet plus 7 g RPO/kg for six weeks. Hearts were excised and mounted on a Langendorff perfusion apparatus. Mechanical function was measured after a 25 min period of total global ischaemia followed by 30 minutes of reperfusion. Hearts subjected to the same conditions were freeze-clamped for biochemical analysis at 10 min during reperfusion to determine the involvement of the PI3-Kinase signaling pathway and apoptosis in our model. Dietary RPO supplementation significantly increased % rate pressure product recovery during reperfusion (71.0 ± 6.3% in control vs 92.36 ± 4.489% in RPO; p < 0.05). The % rate pressure product recovery was significantly reduced when wortmannin was added during perfusion (92.36 ± 4.489% in the RPO group vs 75.21 ± 5.26% in RPO + Wm). RPO + Wm also significantly attenuated PI3-K induction compared with the RPO group (59.2 ± 2.8 pixels in RPO vs 37.9 ± 3.4 pixels in RPO + Wm). We have also demonstrated that PI3-K inhibition induced PARP cleavage (marker of apoptosis) in the hearts during ischaemia/reperfusion injury and that RPO supplementation counteracted this effect.
Enhanced therapeutic efficacy in cancer patients by short-term fasting : the autophagy connection
(Frontiers Media, 2016) Van Niekerk, Gustav; Hattingh, Suzel M.; Engelbrecht, Anna-Mart
Preclinical studies suggest that fasting prior to chemotherapy may be an effective strategy to protect patients against the adverse effects of chemo-toxicity. Fasting may also sensitize cancer cells to chemotherapy. It is further suggested that fasting may similarly augment the efficacy of oncolytic viral therapy. The primary mechanism mediating these beneficial effects is thought to relate to the fact that fasting results in a decrease of circulating growth factors. In turn, such fasting cues would prompt normal cells to redirect energy toward cell maintenance and repair processes, rather than growth and proliferation. However, fasting is also known to upregulate autophagy, an evolutionarily conserved catabolic process that is upregulated in response to various cell stressors. Here, we review a number of mechanisms by which fasting-induced autophagy may have an impact on both chemo-tolerance and chemo-sensitization. First, fasting may exert a protective effect by mobilizing autophagic components prior to chemo-induction. In turn, the autophagic apparatus can be repurposed for removing cellular components damaged by chemotherapy. Autophagy also plays a key role in epitope expression as well as in modulating inflammation. Chemo-sensitization resulting from fasting may in fact be an effect of enhanced immune surveillance as a result of better autophagy-dependent epitope processing. Finally, autophagy is involved in host defense against viruses, and aspects of the autophagic process are also often targets for viral subversion. Consequently, altering autophagic flux by fasting may alter viral infectivity. These observations suggest that fasting-induced autophagy may have an impact on therapeutic efficacy in various oncological contexts.
Hyperglycaemia in critically ill patients : the immune system’s sweet tooth
(BioMed Central, 2017) Van Niekerk, Gustav; Davis, Tanja Andrea; Engelbrecht, Anna-Mart
There is an ongoing debate regarding the efficacy of glycaemic control in critically ill patients. Here we briefly highlight the key function of elevated glucose in critically ill patients, namely, to enable elevation of aerobic glycolysis in rapidly dividing cells. In particular, aerobic glycolysis provides metabolic intermediates necessary for expansion of biomass in immune cells and promotion of tissue repair. Furthermore, we emphasise that insulin may inhibit autophagy, a cell survival process used in the bulk degradation of cellular debris and damaged organelles. These observations provide a rational basis for tolerating elevated glucose levels in certain critically ill patients.
Insulin as an immunomodulatory hormone
(Elsevier, 2019) Van Niekerk, Gustav; Christowitz, Claudia; Conradie, Daleen; Engelbrecht, Anna-Mart
Insulin plays an indispensable role in the management of hyperglycaemia that arises in a variety of settings, including Type I and II diabetes, gestational diabetes, as well as is in hyperglycaemia following a severe inflammatory insult. However, insulin receptors are also expressed on a range of cells that are not canonically implicated in glucose homeostasis. This includes immune cells, where the anti-inflammatory effects of insulin have been repeatedly reported. However, recent findings have also implicated a more involved role for insulin in shaping the immune response during an infection. This includes the ability of insulin to modulate immune cell differentiation and polarisation as well as the modulation of effector functions such as biocidal ROS production. Finally, inflammatory mediators can through both direct and indirect mechanisms also regulate serum insulin levels, suggesting that insulin may be co-opted by the immune system during an infection to direct immunological operations. Collectively, these observations implicate insulin as a bona fide immune-modulating hormone and suggest that a better understanding of insulin’s immunological function may aid in optimising insulin therapy in a range of clinical settings.
Investigation into the intracellular mechanisms whereby long-chain fatty acids protect the heart in ischaemia/reperfusion
(Stellenbosch : Stellenbosch University, 2005-03) Engelbrecht, Anna-Mart; Lochner, Amanda; Page, Carine; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Biomedical Sciences. Medical Physiology.
ENGLISH ABSTRACT: Although there is evidence for a protective role of long-chain polyunsaturated fatty acids (PUFAs) in cardiovascular disease, their mechanism of action as well as their participation in intracellular signalling processes remain to be elucidated. Therefore the aims of this study were twofold: (i) to characterize the roles of the mitogen-activated protein kinases (MAPKs) and protein kinase B (PKB/Akt) in ischaemia/reperfusion-induced apoptosis of neonatal cardiomyocytes and (ii) to establish whether long-chain PUFAs protect the heart via manipulation of these kinases. Rat neonatal ventricular myocytes exposed to simulated ischaemia and reperfusion (Sl/R) were used to characterize the role(s) of extracellular signalregulated kinase (ERK), p38 and c-Jun NH2-terminal protein kinase (JNK), as well as PKB/Akt in apoptosis. The effects of an omega-3 fatty acid (eicosapentaenoic acid - EPA) and an omega-6 fatty acid (arachidonic acid - ARA) on the response of neonatal rat cardiomyocytes to Sl/R with regard to the above parameters were determined. Exposure of the myocytes to SI (energy depletion induced by KCN and 2- deoxy-D-glucose) reduced cell viability, as measured by the 3-[4,5- dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) assay, and stimulated apoptosis (increased caspase-3 activation and poly(ADP-ribose) polymerase (PARP) cleavage). However, morphological evidence of increased apoptosis (Hoechst 33342 staining) occurred only after reperfusion. A rapid activation of p38 and PKB/Akt Ser473 occurred during SI, while significant activation of ERK and JNK was observed during reperfusion only. Myocytes pre-treated with SB203580, a p38-inhibitor, displayed a significant increase in cell viability and attenuation of apoptosis during Sl/R, while SP600125, a specific JNK inhibitor, significantly increased both caspase-3 activation and the apoptotic index. However, PD98059, an ERK inhibitor, was without effect. Wortmannin, a PI3-kinase inhibitor, reduced PKB/Akt Thr308 but not Ser473 phosphorylation during Sl/R and caused a significant increase in Although there is evidence for a protective role of long-chain polyunsaturated fatty acids (PUFAs) in cardiovascular disease, their mechanism of action as well as their participation in intracellular signalling processes remain to be elucidated. Therefore the aims of this study were twofold: (i) to characterize the roles of the mitogen-activated protein kinases (MAPKs) and protein kinase B (PKB/Akt) in ischaemia/reperfusion-induced apoptosis of neonatal cardiomyocytes and (ii) to establish whether long-chain PUFAs protect the heart via manipulation of these kinases. Rat neonatal ventricular myocytes exposed to simulated ischaemia and reperfusion (Sl/R) were used to characterize the role(s) of extracellular signalregulated kinase (ERK), p38 and c-Jun NH2-terminal protein kinase (JNK), as well as PKB/Akt in apoptosis. The effects of an omega-3 fatty acid (eicosapentaenoic acid - EPA) and an omega-6 fatty acid (arachidonic acid - ARA) on the response of neonatal rat cardiomyocytes to Sl/R with regard to the above parameters were determined. Exposure of the myocytes to SI (energy depletion induced by KCN and 2- deoxy-D-glucose) reduced cell viability, as measured by the 3-[4,5- dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) assay, and stimulated apoptosis (increased caspase-3 activation and poly(ADP-ribose) polymerase (PARP) cleavage). However, morphological evidence of increased apoptosis (Hoechst 33342 staining) occurred only after reperfusion. A rapid activation of p38 and PKB/Akt Ser473 occurred during SI, while significant activation of ERK and JNK was observed during reperfusion only. Myocytes pre-treated with SB203580, a p38-inhibitor, displayed a significant increase in cell viability and attenuation of apoptosis during Sl/R, while SP600125, a specific JNK inhibitor, significantly increased both caspase-3 activation and the apoptotic index. However, PD98059, an ERK inhibitor, was without effect. Wortmannin, a PI3-kinase inhibitor, reduced PKB/Akt Thr308 but not Ser473 phosphorylation during Sl/R and caused a significant increase in Although there is evidence for a protective role of long-chain polyunsaturated fatty acids (PUFAs) in cardiovascular disease, their mechanism of action as well as their participation in intracellular signalling processes remain to be elucidated. Therefore the aims of this study were twofold: (i) to characterize the roles of the mitogen-activated protein kinases (MAPKs) and protein kinase B (PKB/Akt) in ischaemia/reperfusion-induced apoptosis of neonatal cardiomyocytes and (ii) to establish whether long-chain PUFAs protect the heart via manipulation of these kinases. Rat neonatal ventricular myocytes exposed to simulated ischaemia and reperfusion (Sl/R) were used to characterize the role(s) of extracellular signalregulated kinase (ERK), p38 and c-Jun NH2-terminal protein kinase (JNK), as well as PKB/Akt in apoptosis. The effects of an omega-3 fatty acid (eicosapentaenoic acid - EPA) and an omega-6 fatty acid (arachidonic acid - ARA) on the response of neonatal rat cardiomyocytes to Sl/R with regard to the above parameters were determined. Exposure of the myocytes to SI (energy depletion induced by KCN and 2- deoxy-D-glucose) reduced cell viability, as measured by the 3-[4,5- dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) assay, and stimulated apoptosis (increased caspase-3 activation and poly(ADP-ribose) polymerase (PARP) cleavage). However, morphological evidence of increased apoptosis (Hoechst 33342 staining) occurred only after reperfusion. A rapid activation of p38 and PKB/Akt Ser473 occurred during SI, while significant activation of ERK and JNK was observed during reperfusion only. Myocytes pre-treated with SB203580, a p38-inhibitor, displayed a significant increase in cell viability and attenuation of apoptosis during Sl/R, while SP600125, a specific JNK inhibitor, significantly increased both caspase-3 activation and the apoptotic index. However, PD98059, an ERK inhibitor, was without effect. Wortmannin, a PI3-kinase inhibitor, reduced PKB/Akt Thr308 but not Ser473 phosphorylation during Sl/R and caused a significant increase in PARP cleavage during reperfusion, but had no effect on caspase-3 activation or the apoptotic index. EPA and ARA (20 jiM, present before and after SI) significantly reduced caspase-3 activation, PARP-cleavage and the apoptotic index during reperfusion. This was associated with increased ERK- and decreased p38 phosphorylation. Vanadate (a tyrosine phosphatase inhibitor), but not okadaic acid (a serine-threonine phosphatase inhibitor), significantly reduced ARAinduced inhibition of p38 phosphorylation, suggesting involvement of tyrosine phosphatases during Sl/R. MKP-1, a dual-specificity phosphatase, was targeted and a significant induction of MKP-1 by ARA and EPA was observed. An in vitro dephosphorylation assay confirmed that this phosphatase might be responsible for the inhibition of p38 activation. It was also demonstrated that the protective actions of ARA are PI3-K dependent. The results suggest that p38 has a pro-apoptotic role while JNK phosphorylation is protective and that these kinases act via caspase-3 to prevent or promote cell survival in response to SI/R-induced injury. It was demonstrated for the first time that EPA and ARA protect neonatal cardiac myocytes from ischaemia/reperfusion-induced apoptosis through induction of a dual-specific phosphatase, MKP-1, causing dephosphorylation of the proapoptotic kinase, p38. These beneficial effects of ARA and EPA were also reflected by improvement in functional recovery during ischaemia/reperfusion of the isolated perfused rat heart model.
Mechanisms of doxorubicin-induced drug resistance and drug resistant tumour growth in a murine breast tumour model
(BMC (part of Springer Nature), 2019-08-01) Christowitz, Claudia; Davis, Tanja Andrea; Isaacs, Ashwin; Van Niekerk, Gustav; Hattingh, Suzel; Engelbrecht, Anna-Mart
Background: Doxorubicin is currently the most effective chemotherapeutic drug used to treat breast cancer. It has, however, been shown that doxorubicin can induce drug resistance resulting in poor patient prognosis and survival. Studies reported that the interaction between signalling pathways can promote drug resistance through the induction of proliferation, cell cycle progression and prevention of apoptosis. The aim of this study was therefore to determine the effects of doxorubicin on apoptosis signalling, autophagy, the mitogen-activated protein kinase (MAPK)- and phosphoinositide 3-kinase (PI3K)/Akt signalling pathway, cell cycle control, and regulators of the epithelial-mesenchymal transition (EMT) process in murine breast cancer tumours. Methods: A tumour-bearing mouse model was established by injecting murine E0771 breast cancer cells, suspended in Hank’s Balances Salt Solution and Corning® Matrigel® Basement Membrane Matrix, into female C57BL/ 6 mice. Fourty-seven mice were randomly divided into three groups, namely tumour control (received Hank’s Balances Salt Solution), low dose doxorubicin (received total of 6 mg/ml doxorubicin) and high dose doxorubicin (received total of 15 mg/ml doxorubicin) groups. A higher tumour growth rate was, however, observed in doxorubicin-treated mice compared to the untreated controls. We therefore compared the expression levels of markers involved in cell death and survival signalling pathways, by means of western blotting and fluorescencebased immunohistochemistry. Results: Doxorubicin failed to induce cell death, by means of apoptosis or autophagy, and cell cycle arrest, indicating the occurrence of drug resistance and uncontrolled proliferation. Activation of the MAPK/ extracellularsignal- regulated kinase (ERK) pathway contributed to the resistance observed in treated mice, while no significant changes were found with the PI3K/Akt pathway and other MAPK pathways. Significant changes were also observed in cell cycle p21 and DNA replication minichromosome maintenance 2 proteins. No significant changes in EMT markers were observed after doxorubicin treatment. Conclusions: Our results suggest that doxorubicin-induced drug resistance and tumour growth can occur through the adaptive role of the MAPK/ERK pathway in an effort to protect tumour cells. Previous studies have shown that the efficacy of doxorubicin can be improved by inhibition of the ERK signalling pathway and thereby treatment failure can be overcome.
Nutritional support in sepsis : when less may be more
(BMC (part of Springer Nature), 2020-02-14) Van Niekerk, Gustav; Meaker, Charne; Engelbrecht, Anna-Mart
Despite sound basis to suspect that aggressive and early administration of nutritional support may hold therapeutic benefits during sepsis, recommendations for nutritional support have been somewhat underwhelming. Current guidelines (ESPEN and ASPEN) recognise a lack of clear evidence demonstrating the beneficial effect of nutritional support during sepsis, raising the question: why, given the perceived low efficacy of nutritionals support, are there no high-quality clinical trials on the efficacy of permissive underfeeding in sepsis? Here, we review clinically relevant beneficial effects of permissive underfeeding, motivating the urgent need to investigate the clinical benefits of delaying nutritional support during sepsis.
The paracrine effects of fibroblasts on Doxorubicin-treated breast cancer cells
(Elsevier, 2019) Carla, Fourie; Davis, Tanja; Kriel, Jurgen; Engelbrecht, Anna-Mart
Breast cancer is frequently diagnosed in women and poses a major health problem throughout the world. Currently, the unresponsiveness of cancer cells to chemotherapeutics is a major concern. During chemotherapeutic treatment with Doxorubicin, neighbouring cells in the tumor microenvironment are also damaged. Depending on the concentration of Doxorubicin, apoptotic or senescent fibroblasts in the tumor microenvironment can then secrete a variety of bioactive molecules which promote tumor growth, metastasis and drug resistance. Mouse embryonic fibroblasts (MEFs) were treated with Doxorubicin to induce apoptosis and senescence respectively. Conditioned media was collected from the MEFs and was used to assess the paracrine effects between fibroblasts and E0771 murine breast cancer cells. Senescent fibroblasts significantly increased cell viability in E0771 cells following Doxorubicin treatment by activating Akt and ERK. Autophagy contributed to cancer cell death and not to treatment resistance in breast cancer cells. Our results highlight the complexity of the tumor microenvironment where chemotherapeutic agents such as Doxorubicin can induce significant changes fibroblasts which can affect tumor growth via the secretion of paracrine factors. Here we have demonstrated that those secreted paracrine factors enhance breast cancer growth and induce therapeutic resistance through the evasion of apoptotic cell death.
The role of bile acids in nutritional support
(BioMed Central, 2018-09-30) Van Niekerk, Gustav; Davis, Tanja Andrea; De Villiers, Willem; Engelbrecht, Anna-Mart
Abstract: Nutritional support continues to receive much attention as a possible intervention to prevent loss of lean tissue mass, promote recovery and re-establish proper immune function in critical care patients. Yet there remains much controversy regarding the clinical efficacy of such interventions. In addition to the direct effect of nutrition in terms of micro- and macronutrient content, nutritional formulations may exert an effect via the physiological response to feeding. Here, we highlight the key role of postprandial reabsorbed bile acids in attenuating both the inflammatory response and autophagy. These observations suggest that not all patients would benefit from aggressive nutritional support.
The secret of dying well : the many faces of cell death and its relevance for treating diseases of our time
(Stellenbosch : Stellenbosch University, 2014-03) Engelbrecht, Anna-Mart
Anna-Mart Engelbrecht is currently professor in the Department of Physiological Sciences at Stellenbosch University. She was born in Pretoria, grew up in the Western Cape and matriculated from DF Malan High School in Bellville. She completed a BScHons in Physiology at Stellenbosch University, a MMedSc at the University of the Free State and was awarded her PhD by Stellenbosch University in 2005. She received several prestigious awards which include the Dean’s and Senate’s Medals as well as the Gencor Bronze Medal from the University of the Free State, the Marie Curie Scholarship of the European Union and the Rector’s Award for Excellence in Research from Stellenbosch University. Twelve MSc and four PhD students completed their studies under her supervision; she currently serves as supervisor and co-supervisor for ten PhD students. She serves on the editorial board of the International Journal of Biomedical Sciences and regularly referees for international journals which include Molecular and Cellular Biochemistry, Pharmacological Research, Apoptosis, Cancer Letters, European Journal of Clinical Investigation and Physiological Research. She has published 32 peer-reviewed research articles and seven book chapters and presented invited lectures at national and international conferences. She established the Disease Signalling Group (DSG-CANCER), which investigates metabolic pathways in cancer cells and protective mechanisms in chemotherapy-induced damage to the heart. She is married to Natie Engelbrecht and is mother to their sixteen-year-old daughter, Retha.
Serum amyloid A and inflammasome activation : a link to breast cancer progression?
(Elsevier, 2020-10-27) Fourie, Carla; Shridas, Preetha; Davis, Tanja; de Villiers, Willem J. S.; Engelbrecht, Anna-Mart
Breast cancer is the most frequently diagnosed cancer in women globally. Although there have been many significant advances made in the diagnosis and treatment of breast cancer, numerous unresolved challenges remain, which include prevention, early diagnosis, metastasis and recurrence. The role of inflammation in cancer development is well established and is believed to be one of the leading hallmarks of cancer progression. Recently, the role of the inflammasome, a cytosolic multiprotein complex, has received attention in different cancers. By contributing to the activation of inflammatory cytokines the inflammasome intensifies the inflammatory cascade. The inflammasome can be activated through several pathways, which include the binding of pattern associated molecular patterns (PAMPs) and damage associated molecular patterns (DAMPs) to toll-like receptors (TLRs). Serum amyloid A (SAA), a non-specific acute-phase protein, can function as an endogenous DAMP by binding to pattern recognition receptors like TLRs on both breast cancer cells and cancer associated fibroblasts (CAFs). SAA can thus stimulate the production of IL-1β, thereby creating a favourable inflammatory environment to support tumour growth. The aim of this review is to highlight the possible role of SAA as an endogenous DAMP in the tumour microenvironment (TME) thereby promoting breast cancer growth through the activation of the NLRP3 inflammasome.
Serum amyloid A binds to fibrin(ogen), promoting fibrin amyloid formation
(Nature Research (part of Springer Nature), 2019-02-28) Page, Martin J.; Thomson, Greig J. A.; Nunes, J. Massimo; Engelbrecht, Anna-Mart; Nell, Theo A.; De Villiers, Willem J. S.; De Beer, Maria C.; Engelbrecht, Lize; Kell, Douglas B.; Pretorius, Etheresia
Complex associations exist between inflammation and thrombosis, with the inflammatory state tending to promote coagulation. Fibrinogen, an acute phase protein, has been shown to interact with the amyloidogenic ß-amyloid protein of Alzheimer’s disease. However, little is known about the association between fibrinogen and serum amyloid A (SAA), a highly fibrillogenic protein that is one of the most dramatically changing acute phase reactants in the circulation. To study the role of SAA in coagulation and thrombosis, in vitro experiments were performed where purified human SAA, in concentrations resembling a modest acute phase response, was added to platelet-poor plasma (PPP) and whole blood (WB), as well as purified and fluorescently labelled fibrinogen. Results from thromboelastography (TEG) suggest that SAA causes atypical coagulation with a fibrin(ogen)-mediated increase in coagulation, but a decreased platelet/fibrin(ogen) interaction. In WB scanning electron microscopy analysis, SAA mediated red blood cell (RBC) agglutination, platelet activation and clumping, but not platelet spreading. Following clot formation in PPP, the presence of SAA increased amyloid formation of fibrin(ogen) as determined both with auto-fluorescence and with fluorogenic amyloid markers, under confocal microcopy. SAA also binds to fibrinogen, as determined with a fluorescent-labelled SAA antibody and correlative light electron microscopy (CLEM). The data presented here indicate that SAA can affect coagulation by inducing amyloid formation in fibrin(ogen), as well as by propelling platelets to a more prothrombotic state. The discovery of these multiple and complex effects of SAA on coagulation invite further mechanistic analyses.
Sickness-associated anorexia : mother nature’s idea of immunonutrition?
(Hindawi Publishing Corporation, 2016) Van Niekerk, Gustav; Isaacs, Ashwin W.; Nell, Theo A.; Engelbrecht, Anna-Mart
During an infection, expansion of immune cells, assembly of antibodies, and the induction of a febrile response collectively place continual metabolic strain on the host. These considerations also provide a rationale for nutritional support in critically ill patients. Yet, results from clinical and preclinical studies indicate that aggressive nutritional support does not always benefit patients and may occasionally be detrimental. Moreover, both vertebrates and invertebrates exhibit a decrease in appetite during an infection, indicating that such sickness-associated anorexia (SAA) is evolutionarily conserved. It also suggests that SAA performs a vital function during an infection. We review evidence signifying that SAA may present a mechanism by which autophagic flux is upregulated systemically. A decrease in serum amino acids during an infection promotes autophagy not only in immune cells, but also in nonimmune cells. Similarly, bile acids reabsorbed postprandially inhibit hepatic autophagy by binding to farnesoid X receptors, indicating that SAA may be an attempt to conserve autophagy. In addition, augmented autophagic responses may play a critical role in clearing pathogens (xenophagy), in the presentation of epitopes in nonprovisional antigen presenting cells and the removal of damaged proteins and organelles. Collectively, these observations suggest that some patients might benefit from permissive underfeeding.

Browsing by Author "Engelbrecht, Anna-Mart"

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