Vpliv uživanja beta-glukanov na sestavo črevesne mikrobne flore in na presnovo glukoze in maščob pri osebah z metaboličnim sindromom

Velikonja, Ana (author), Orel, Rok (mentor), Avguštin, Gorazd (comentor)

Izhodišče: Metabolični sindrom (MS) je kompleksna, z življenjskim slogom pogojena bolezen, njena pogostnost pa v razvitem svetu narašča. Gre za sklop metaboličnih motenj, ki so posledica prepleta okoljskih in genetskih dejavnikov. Črevesna mikrobiota je s 1014 bakterijskimi celicami vpletena v fiziologijo gostitelja in zato pomemben element metaboličnih motenj. Prehrana sodi med najpomembnejše dejavnike, ki vplivajo na sestavo črevesne mikrobiote, zato raziskovalci intenzivno preučujejo prehranske učinkovine in diete, s katerimi bi lahko uravnavali sestavo črevesne mikrobiote in posredno izboljšali metabolično stanje pacientov. Med takšne prehranske učinkovine spadajo ječmenovi betaglukani, polisaharidi, ki na podlagi kliničnih raziskav izboljšajo tako lipidni kot glukozni metabolizem. Namen: Namen naše študije je bil ugotoviti, ali uživanje ječmenovih betaglukanov lahko spremeni sestavo črevesne mikrobiote in istočasno izboljša z MS povezane klinične kazalce. Metode: Izvedli smo dvojno slepo, s placebom kontrolirano in randomizirano klinično študijo s preiskovanci z diagnosticiranim MS ali visokim tveganjem za razvoj MS. Preiskovanci so štiri tedne uživali kruh s 6 g dodanih betaglukanov (testna skupina) ali kruh brez dodanih betaglukanov (kontrolna skupina). Pred prehransko intervencijo in ob koncu smo izvedli antropometrične meritve, krvne preiskave maščob, oralni glukoza tolerančni test (OGTT) ter odvzeli vzorce blata za analize sestave črevesne mikrobiote in ugotavljanje vsebnosti kratkoverižnih maščobnih kislin. Stanje inzulinske rezistence smo ovrednotili z modeloma HOMAIR in QUICKI. Koncentracijo kratkoverižnih maščobnih kislin v blatu smo določili s plinsko kromatografijo. Sestavo črevesne mikrobiote smo preučevali s kombinacijo kvalitativnih in kvantitativnih metod, ki so omogočale analizo 16S rRNK molekul: gelsko elektroforezo v gradientu denaturanta (DGGE), verižno reakcijo s polimerazo v realnem času (RT-PCR) in s sekvenciranjem naslednje generacije, pri katerem smo uporabili tehnologijo Illumina Miseq. Rezultati: V študijo je bilo vključenih 43 prostovoljcev z MS oz. visokim tveganjem za razvoj MS. V testni skupini, ki je štiri tedne ob sicer običajni dieti dnevno uživala 6 g ječmenovih betaglukanov, se je značilno znižala koncentracija celokupnega holesterola v krvi in zmanjšal obseg pasu. Vpliva na druge metabolične parametre nam ni uspelo dokazati. Značilno se je spremenila vsebnost kratkoverižnih maščobnih kislin (KMK) v blatu, in sicer v testni skupini s povišanjem vsebnosti propionske kisline. Z analizo sekvenc 16S rRNK smo pokazali, da se po prehranski intervenciji z betaglukani spremeni sestava črevesne mikrobiote. Pri testni skupini smo opazili značilno znižanje tako mikrobne pestrosti kot bogatosti. Poleg tega smo po intervenciji z betaglukani opazili značilen padec v številu sekvenc iz redu Coriobacteriales in tistih, ki pripadajo bakterijskemu redu Clostridiales. Pri preučevanju sestave črevesne mikrobiote pri preiskovancih, ki so bili uvrščeni v testno skupino, smo pred prehransko intervencijo odkrili značilne razlike v sestavi črevesne mikrobiote med tistimi preiskovanci, pri katerih se je koncentracija holesterola značilno znižala (holesterol odzivna skupina), in tistimi, pri katerih se ni. Pri prvih so bile v večjem številu zastopane bakterijske skupine, ki sodijo med t. i. »koristne« bakterije, npr. Bifidobacterium bifidum, Bifidobacterium fecale in Akkermansia municiphila. Sklep: Štiritedensko uživanje betaglukanov je vplivalo na koncentracijo maščob v krvi in spremenilo sestavo črevesne mikrobiote pri preiskovancih z diagnosticiranim MS ali povečanim tveganjem za razvoj MS. Zmanjšanje bogatosti in pestrosti potrjuje, da so betaglukani sposobni spreminjanja sestave črevesne mikrobiote, vendar je odziv na prehransko intervencijo močno odvisen od posameznika. Značilne spremembe posameznih bakterijskih skupin črevesne mikrobiote in povečanje vsebnosti kratkoverižnih maščobnih kislin nakazujejo potencialno ugodne učinke uživanja betaglukanov. S preučevanjem začetne sestave črevesne mikrobiote in opaženimi značilnimi razlikami v njeni sestavi pri holesterol odzivni skupini smo pokazali, da je metabolični odziv na dieto lahko odvisen tudi od specifične sestave črevesne mikrobiote posameznika.

• Language: Slovenian
• Keywords: Metabolični sindrom, betaglukani, holesterol, kratko-verižne maščobne kisline, črevesna mikrobiota, 16S rRNK metagenomska analiza
• Work type: Doctoral dissertation
• Organization: MF - Faculty of Medicine
• Year: 2019
• PID: 20.500.12556/RUL-110452
• COBISS.SI-ID: 301683456
• Publication date in RUL: 15.09.2019

Secondary language

• Language: English
• Title: Impact of consumption of beta-glucans on the intestinal microbiota and glucose and lipid metabolism in a population with metabolic syndrome

Abstract

Background: Metabolic syndrome (MS) is a complex lifestyle disease that is almost exponentially increasing in western world. Gut microbiota is with 1014 bacterial cells involved in certain human physiological processes and is important factor of metabolic disorders. Diet is one of the main elements contributing to gut microbiota composition and one of the possible ways to improve the metabolic status of patients. In recent years many investigations have been performed concerning diets and active components, that could positively control gut microbiota composition and improve metabolic status of patients. Dietary fibres are known to improve glucose and lipid metabolism and modulate gut microbiota composition. Barley beta-glucans have been used to improve cholesterol levels and postprandial glucose response but have been poorly investigated in trials focusing on gut microbiota till now. Aims: The purpose of this study was to investigate if a 4-week dietary intervention with beta-glucans could positively change gut microbiota composition and improve metabolic syndrome parameters at the same time. Methods: Double blind, placebo-controlled and randomised clinical trial was performed with participants with high risk for MS development or with diagnosed MS. Participants consumed bread with 6 g added beta-glucans (test group) or without added beta-glucans (control group). Before and at the end of the trial anthropometric measurements, lipid profile analyses, and oral glucose tolerant test (OGTT) were performed, and faecal samples were retrieved for gut microbiota composition and short-chain fatty acids analyses. HOMAIR in QUICKI indexes were employed for insulin resistance determination. Short-chain fatty acids were extracted from faecal samples and analysed with gas chromatography. Changes in gut microbiota composition were investigated with combination of qualitative and quantitative molecular methods analysing 16S rRNA molecules: denaturing gradient gel electrophoresis (DGGE), real-time polymerase chain reaction (RT-PCR), and the next generation sequencing based on Illumina MiSeq paired end technology. Results: 43 participants with high risk for metabolic syndrome (MS) development or with diagnosed MS successfully finished the trial. Total plasma cholesterol levels decreased in test group, but not in placebo group. Short chain fatty acids composition in faeces significantly changed with increase of propionic acid in the test group. The microbiome analysis showed a decrease in microbial diversity and richness in the test group and a decrease in order Coriobacteriales. Furthermore, a decrease of a single unclassified Clostridiales group was observed. We further examined the differences in the so-called pre-intervention gut microbiota composition within cholesterol responsive and unresponsive group. Interestingly, sequences from several bacterial groups, commonly perceived as health associated, such as Bifidobacterium bifidum, Bifidobacterium fecale and Akkermansia municiphila, were present in higher numbers. Conclusion: Dietary intervention with beta-glucans has showed positive improvements in blood lipid profile and in gut microbiota composition with participants with high risk for MS development or with diagnosed MS. A decrease in richness and diversity of gut microbiota showed that beta-glucans are able to alter gut microbiota composition. However, the response on dietary intervention is individually depended. Changes in abundance of certain bacterial groups and increase of short-chain fatty acids after intervention showed that beta-glucans potentially exert positive effects on gut microbiota composition. Investigating pre-intervention gut microbiota composition with observed changes in gut microbiota composition in cholesterol responsive group, suggests that diet response could be depended on individual gut microbiota composition.

• Keywords: Metabolic syndrome, beta glucans, cholesterol, short chain fatty acids, gut microbiota, 16S rRNA metagenomics