The use of mouthwash is a common complement to oral care. However, the physiological implication of this use, besides of effects on oral hygiene, is poorly known. The research of the gut micro flora and its implications on the host is a very active area of research today. Many important connections between the gut micro flora and obesity and diabetes have been found. These billions of bacteria are part of the immune system, they produce essential vitamins and they make inaccessible polysaccharides more digestible to the host, just to mention a few of their symbiotic roles for the host. A less explored area is the micro flora in the oral cavity. On the back of the tongue, anaerobic bacteria can reduce dietary nitrate to nitrite which then further can be reduced to nitric oxide, NO. NO is important in several important biological functions, e.g. as a signal substance, vasoregulation, mucus production and antibacterial effects. Vegetables as beetroot and spinach are dietary sources with a high nitrate content. Also drinking water and processed meats can be of relevance. Nitrite is added to processed meat for the prevention of botulism but also adds taste and color.   Experiments on humans indicate that mitochondrial efficiency increases after nitrate load, manifested as a decreased oxygen demand during physical exercise. This can also be relevant under conditions where the mitochondrial function is impaired, such as in diabetes and cardiovascular diseases. First a pilot study was made to evaluate the nitrate reducing effect from the antibacterial mouthwash. The mouthwash proved very effective. The concentrations of nitrate and nitrite in saliva was analyzed by HPLC and saliva from the antibacterial treatment showed greatly reduced concentrations of nitrite and high concentrations of nitrate. Saliva from placebo mouthwash showed high concentrations of nitrite and low concentrations of nitrate as expected. To study the importance of oral bacteria on metabolism, we performed a randomized, cross-over double-blinded study with 19 healthy males between 22-43 years. During two separate three-day periods they used an antibacterial and placebo mouthwash, respectively. On the fourth day their basal metabolic rate (BMR) was measured with an indirect calorimetric system. Moreover, samples from saliva, urine and blood were collected but these results are not included in this thesis. An earlier, unpublished study has demonstrated that nitrate administration reduces the basal metabolic rate. Accordingly, our aim was to study potential effects on the basal metabolic rate following reduction of the number of oral bacteria by aid of antibacterial mouthwash. Our hypothesis was that the reduced availability of nitrite would decrease the availability of NO in the body and manifest as an increased basal metabolic rate. The results from indirect calorimetry measurements showed no significant difference between placebo and antibacterial mouthwash, but there may be confounding factors. Further study is needed to assess the potential effects on host metabolism by these bacteria.

The brain is one of the most energetically demanding organs within the human body and is cognitively susceptible to energetic deficits such that the rise in obesity, insulin resistance, and Alzheimer’s disease in recent decades pose a substantial threat to cognitive longevity. The therapeutic efficacy of ketones are well-established in epilepsy and are currently being applied to other disease states. Alzheimer’s disease is characterized by impairments in brain glucose uptake and metabolism in regions relevant to learning, memory, and cognition that progress with the disease. While brain glucose uptake is impaired, ketone uptake is unaltered, potentially enabling ketones to fuel the glucose-deficient brain. Using RNA-seq data acquired from multiple publicly available AD databases, we assessed glycolytic and ketolytic gene expression in post-mortem AD and cognitively normal control brains. Gene expression was normalized to brain region – parietal lobe, cerebellum, temporal cortex, frontal lobe, inferior frontal gyrus, parahippocampal gyrus, superior temporal gyrus – and cell type – neurons, astrocytes, oligodendrocytes, and microglia. We report impairments in glycolytic gene expression in regions of the brain relevant to memory and cognition in neurons and oligodendrocytes, but not ketolytic gene expression in neurons. The data are consistent with previous work and support clinical ketone intervention. The cognitive effects of ketogenic diets remain controversial, especially in healthy adults. To elucidate the effects of a ketogenic diet in healthy mice, C57BL6 mice were placed on a ketone-supplemented ketogenic diet for eight weeks. Recognition memory was assessed in a novel object recognition test and hippocampal bioenergetics were measured using high-resolution respirometry, western blot, and biochemical assays. The diet significantly improved recognition memory and enhanced hippocampal mitochondrial efficiency, measured by ATP production per unit of oxygen consumed, suggesting cognitive validity of the diet in middle-age. Long-term potentiation (LTP), the activity-dependent strengthening of synapses, within the hippocampus, is one of the molecular mechanisms of learning and memory formation. LTP of hippocampal Schaffer-collaterals was quantified in young adult C57BL/6 mice with field electrophysiology following ex vivo brain slice incubation with a β-hydroxybutyrate-rich ACSF. Mice were then placed on the ketone-supplemented diet for four weeks. Behavioral spatial memory was measured in the Morris water maze and Schaffer-collateral LTP was assessed with field electrophysiology. No meaningful changes in LTP and behavioral memory were observed with ketone treatment, suggesting ketogenic interventions may be more applicable in aging and pathologies that display cognitive deficits, rather than in healthy young adults. Together, these studies support the exploration of ketogenic interventions as a potential restorative measure in Alzheimer’s disease and preventative measure in aging, which may be impactful facing the rise of obesity and insulin resistance.

Tout au long de leur vie, les espèces animales vont transformer de l'énergie apportée par l'alimentation en énergie utilisable par la cellule. Cependant, dans l'environnement naturel, l'accès à la ressource alimentaire est souvent limité et dépendant des conditions climatiques. Cette contrainte oblige les espèces sauvages à mettre en place des compromis d'allocation d'énergie permettant de favoriser la survie, la croissance ou la reproduction. Les espèces aviaires représentent de bons modèles pour étudier les adaptations aux contraintes environnementales puisqu'elles ont colonisé la quasi-totalité du globe et notamment les niches écologiques les plus « extrêmes ». Parmi les oiseaux sauvages vivant en conditions défavorables, notre intérêt s'est porté sur le manchot royal (Adptenodytes patagonicus) et plus particulièrement sur son poussin qui, au cours la 1ère année de vie va subir un jeûne hivernal de 4 à 5 mois au cours duquel les nourrissages sont peu fréquents et aléatoires. Ainsi, cette espèce est naturellement adaptée à des conditions thermiques défavorables pouvant être associées à des phases de jeûne alimentaire. Plusieurs travaux ont montré que malgré l'exposition prolongée au froid, la dépense énergétique diminue au cours des phases de jeûne, permettant ainsi d'économiser les réserves énergétiques et de préserver les protéines nécessaires aux fonctions cellulaires. La forte proportion que représente le muscle squelettique lui confère une part importante de la dépense énergétique. Des études ont montré que malgré son implication dans la thermogenèse, l'activité oxydative (consommation d'oxygène) mitochondriale est diminuée au cours du jeûne hivernal. Cependant, ces travaux ont porté uniquement sur l'étude de la capacité oxydative et non sur le couplage entre les oxydations et les phosphorylations (synthèse d'ATP). Ce couplage représente l'efficacité avec laquelle les mitochondries vont produire de l'énergie (ATP) en consommant de l'oxygène. C'est donc un paramètre important dans la gestion des réserves énergétiques. Mes travaux de thèse ont reposé sur l'hypothèse selon laquelle, la plasticité de l'efficacité mitochondriale du muscle squelettique expliquerait en partie les capacités de survie des oiseaux en conditions défavorables, aussi bien lorsque ces derniers sont exposés à une contrainte thermique importante que lorsqu'ils sont soumis à un jeûne prolongé / Throughout their life, wild species face periods of food-deprivation that induce energy tradeoffs between survival, growth and reproduction. These fasting periods occur either when food availability is lacking due to adverse climatic conditions or because individuals are engaged in biological processes that prevent food access. This later reason is particularly well illustrated in the king penguin (Aptenodytes patagonicus), a sea bird that has to moult and reproduce on shore whereas he feed exclusively at sea. Moreover king penguin chicks exhibit exceptional survival capacities during their first year of life when they experience a long period of fast in winter. Thus, this species that lives in sub-Antarctic latitudes, is exposed to environmental and physiological energy constraints during food shortage periods. Since king penguins are endotherms, they need to maintain their body temperature at high level despite variations of ambient temperature. Thus thermoregulation is one of the most expensive process and skeletal muscles account for the greater part of heat production in birds. Several studies showed that despite long term cold exposure, energy expenditure of fasting birds decreases allowing energy savings and especially protein sparing. Since skeletal muscles have high implications in energy expenditure and heat production the question of their implication in energy saving mechanisms arises. During my PhD project I studied skeletal muscle metabolism through mitochondrial efficiency. These sub-cellular organelles are the last effectors of energy transduction from nutrient into ATP, an usable energy for cells. Our hypothesis is based on the flexibility of mitochondrial efficiency as a regulator of energy sparing mechanisms which would explain long term resistance to starvation. My studies were conducted in a wild species, the king penguin chicks, that are naturally acclimated to cold environment and experienced long term fasting stage. To further investigate mitochondrial plasticity in response to energy constraints, I developed several experimental procedures in controlled conditions on a laboratory model (Muscovy ducklings)

Introduction: Recent evidence in isolated mitochondria and permeabilized muscle fibers in ex vivo using simultaneous measurements of O2 consumption and ATP production suggest that mitochondrial efficiency provides an additional mechanism to fine-tune oxidative phosphorylation rate to ATP demand in skeletal muscle. However, in the absence of a direct measurement of both VO2 and ATP synthesis from the same region of the contracting muscle, whether this mechanism plays a role in the skeletal muscle in vivo is still unknown. Purpose: Using a noninvasive approach combining phosphorus and proton magnetic resonance spectroscopy (31P/1H-MRS), the present study aimed to determine skeletal muscle ATP synthesis rate and muscle VO2 during a graded dynamic plantar flexion exercise to determine mitochondrial efficiency in contracting skeletal muscle contraction. Method: To measure mitochondrial efficiency under physiological conditions, we applied a recently developed methodological approach in ex vivo to human gastrocnemius muscle in vivo using 31P/1H-MRS noninvasive techniques. We conducted a series of constant workloads and ischemic protocols to assess oxidative ATP synthesis (ATPox) rate and Myoglobin-derived oxygen consumption (Mb-derived VO2). Specifically, during two separate visits, in 12 healthy, sedentary to recreationally active young male adults, we determined the ATPox rate by measuring the initial phosphocreatine (PCr) resynthesis rate during recovery and Mb-derived VO2 during 30 seconds of occlusion at the end of each given exercise workload. Results: The calculated mean power output during constant load performed by all subjects increased linearly at each incremental workload for both 1H and 31P visits. The mean percent coefficient of variation (CV%) at all exercise workloads (25% of WRmax= 6.0 ± 6.6, 50% of WRmax = 4.5 ± 2.7, 75% of WRmax = 4.9 ± 3.9, 100% = 7.0 ± 4.5) demonstrated high reliability and reproductivity in power output between each visit. The mean concentration of PCr consumption at the steady state remained constant between 25 and 50% of WRmax (28.6 ± 1.7 and 28.2 ± 1.4, respectively) but increased linearly beyond 50% of WRmax (75% = 22.9 ± 1.4 mM and 100%= 18.0 ± 1.4 mM, respectively). Mean intracellular pH was not significantly different between 25 and 50% of submaximal workloads (6.98 ± 0.02 and 6.97 ± 0.02, respectively). Intracellular pH dropped to 6.94 ± 0.02 during the last min of exercise at 75% of WRmax and further decreased at 100% of WRmax, (6.87 ± 0.03). The percentage of Mb oxygenation level and partial pressure of oxygen(PO2) at the steady state exhibited a consistent linear decline with increasing workload. Accordingly, a distinct and strong linear relationship was found between the MbO2 and workload (r2 = 0.71). Similarly, as the exercise workload increased, the ATPox synthesis rate also increased linearly throughout all exercise workloads (r2 = 0.45). In contrast, there was no significant change in Mb-derived VO2 with increased exercise workload averaged over a 30 s (r2 = 0.36) and 10 s time frame (r2 = 0.17). As a result, there was no significant correlation between ATPox synthesis rate and Mb-derived VO2 across exercise intensities. However, at rest, the P/O ratio in the gastrocnemius muscle was 1.95 ± 0.68, consistent with theoretical values and previous studies in mice. Conclusion: Despite the decrease in MbO2 (%), Mb-derived VO2 from both 30 and 10 s averages remained relatively constant during the ischemic protocol, likely due to O2 availability limitation induced by the prolonged occlusion and the slow time-resolution for measuring the dMb signal, which precluded the quantification of mitochondrial efficiency during exercise. However, mitochondrial efficiency calculated at rest was in agreement with previously documented values using other methodologies and thus can provide an additional parameter to more comprehensively evaluate mitochondrial function in vivo.