Establishing a rodent model of long-term consumption of sugar-sweetened beverages

Driescher, Natasha Darne (2014-12)

Thesis (MSc)--Stellenbosch University, 2014.

Thesis

ENGLISH ABSTRACT: Introduction- Cardiovascular complications contribute dramatically to morbidity and mortality incidence amongst individuals who have developed type 2 diabetes (T2D), with myocardial insulin resistance (IR) playing an important role. Poor lifestyle choices and dietary habits such as increased sugar-sweetened beverage (SSB) consumption have emerged as key contributors to the global ‘epidemic’ of obesity, diabetes and heart disease. However, the underlying mechanisms whereby SSBs drive the onset of cardio-metabolic complications remain unclear. For the current study, we hypothesized that long-term SSB consumption will trigger downstream glucose metabolic pathways with physiologically damaging outcomes. Specifically we proposed that increased glucose availability (due to SSB consumption) activates non-oxidative glucose pathways (NOGPs), i.e. polyol pathway, hexosamine biosynthetic pathway (HBP), advanced glycation end-products (AGE), and PKC activation that may in turn contribute to cardio-metabolic complications. Methodology- Male Wistar rats (~200 g) were gavaged daily with 3-5.1 mL of well-known, local SSBs and ASBs for a total period of six months. Dietary behavior and phenotypic changes were monitored on a weekly basis, while systemic (fasted) triglyceride, cholesterol and glucose levels at various time points during the study period. Furthermore, we performed oral glucose tolerance tests (OGTTs) biweekly, and also determined overall weight gain and organ tissue mass. Myocardial NOGPs were evaluated using commercially available kits and by Western blotting techniques. Results- Our data reveal that after six months the different soda groups displayed minimal macroscopic changes, therefore possibly representing a relatively early stage in terms of SSB-mediated cardio-metabolic complications. However, we also found several changes at the biochemical level but with distinct signatures for the Jive® group compared to the Coca Cola® and Coke Light® groups. Here Jive® consumption for six months resulted in early signs of cardiac and skeletal muscle hypertrophy, together with increased liver mass and perturbed adipocyte ultrastructure. We also established that the majority of the myocardial NOGPs were activated that may have contributed to some of the changes already found and that may lead to the onset of future complications. The Coca Cola® and Coke Light® groups exhibited alterations in liver mass and altered adipocyte ultrastructure together with lower glucose clearance after six months suggesting onset of IR. These data also clearly show that the HBP may be a universal pathway that was activated in all of the soda groups, with potential long-term detrimental physiological effects. Conclusion- This study managed to successfully establish a novel in vivo rat model of chronic SSB and artificially sweetened beverage (ASB) consumption. We demonstrated that SSB consumption resulted in minimal macroscopic alterations but that it did trigger variable postprandial excursions together with the induction of several myocardial NOGPs. Thus the current study shows that long-term SSB intake activates potentially detrimental metabolic pathways that may place organisms at risk of developing cardio-metabolic complications despite an apparently “healthy” phenotype.

AFRIKAANSE OPSOMMING: Inleiding- Kardiovaskulêre komplikasies is verantwoordelik vir die bydrae tot morbiditeit en mortaliteit onder individue wat tipe 2 Diabetes ontwikkel het, waar miokardiale insulien weerstanigheid (IW) ‘n belangrike rol speel. Swak lewenstylkeuses en dieetgewoontes soos byvoorbeeld verhoogde suikerversoete drankies (SVDs) inname ‘n ‘n sleutel bydraende faktor vir die wêreld epidemie, vetsugtugheid, Diabetes en hartsiektes. Die onderliggende meganismes waarby SVDs die aanvang van kardio-metaboliese komplikasies aandryf bly steeds onduidelik. Vir die huidige studie is ons hipotese dat langtermyn SVD inname, afstroom glukose metaboliese weë met fisiologies-skadelike effekte sal ontlok met ongewensde uitkomste. Ons stel spesifiek voor dat die verhoogde glukose beskikbaarheid (a.g.v. SVD inname) die nie-oksidatiewe glukose weë (NOGW) aktiveer, i.e. poliolweg, heksosamienbiosintetiese weg (HBP), gevorderde glukeringseindprodukte (GGE), en PKC aktivering wat op sy beurt tot kardiometaboliese komplikasies bydra. Metodologie – Manlike Wistar rotte (~200 g) is daagliks met 3-5.1 mL van ‘n bekende lokale SVD vir ‘n periode van ses maande deur middel van orale toegediening gevoed. Ons het dieetgedrag en fenotipiese veranderinge gemonitor op ‘n weeklikse basis en ook sistemiese (vastende) trigliseried, cholesterol en glukose vlakke op verskeie tydspunte gedurende die ses maande toetsperiode gemonitor. Verder het ons ‘n orale glukose toleransie toets (OGTT) twee-weekliks uitgevoer en ook die algehele gewigstoename en orgaanweefselmassa gemonitor. Miokardiale NOGWs is met behulp van kommersiëel beskikbare toetse en deur middel van Westerse blottegnieke bepaal. Resultate – Ons data het na ses maande aangedui dat daar minimale makroskopiese veranderinge tussen die verskillende soda groepe waargeneem is. Dit kan ‘n relatiewe vroeë stadium, in terme van SSB-gemediëerde kardiometaboliese komplikasies is. Verder het ons verskeie biochemiese veranderinge waargeneem met uitsluitlike kenmerke vir die Jive® groep vergeleke met die Coca Cola® en Coke Light® groepe. Hier het Jive® gebruik vir ses maande in vroeë tekens van kardiale en skeletspierhipertrofie gelei – tesame met verhoogde lewermassa en versteurde adiposietultrastruktuur. Ons het ook vasgestel dat die meerderheid van die miokardiale NOGWs geaktiveer was en dat dit mag bydra tot die veranderinge wat reeds gevind is met die aanvang van toekomstige komplikasies. Die Coca Cola® en Coke Light® groepe het wysigings in lewermassa en adiposietultrastruktuur getoon met laer glukose opruiming na ses maande wat moontlik die aanvang van insulienweerstandigheid kan voorstel. Hierdie data toon duidelik aan dat die HBP ‘n unversiele weg is wat geaktiveer word in al die soda groepe, met potensiële langtermyn newe effekte. Gevolgtrekking – Hierdie studie het daarin geslaag om ‘n sukesvolle nuwe in vivo rot model van ‘n chroniese SSB/ASB inname te vestig. Ons het ook bevind dat die SSB inname ‘n minimale makroskopiese wysigings teweeg bring en dat dit verskeie post prandiale veranderinge tesame met die induksie van verskeie miokardiale NOGWs tot gevolg bring. Dus, het die huidige studie getoon dat langtermyn SSB inname potensiëel skadelike metaboliese weë aktiveer en dat dit individue met verhoogde risiko vir kardiovaskulêre komplikasiese verhoog ten spyte van ‘n gesonde fenotipe.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/95776
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