Reduction in the Level of Plasma Mitochondrial DNA in Human Diving, Followed by an Increase in the Event of an Accident

Mitochondrial DNA in Exercise-Mediated Innate Immune Responses

Mitochondria are considered as "the plant of power" with cells for a long time. However, recent researches suggest that mitochondria also take part in innate immune response to a great extent. Remarkably, mtDNA was reported to have immunnostimulatory potential in 2004. Since then, there has been rapid growth in understanding the role of mtDNA in innate immune. The mtDNA is released into cytosol, extracellular environment, or circulating blood through BAK/BAX pore, mPTP, and GSDMD pore upon mitochondrial damage, where it is recognized by PRRs including TLR9, cGAS, and NLRP3, thereby triggering innate immune response. On the other hand, regular exercise has been recognized as an effective intervention strategy for innate immune response. Some studies show that chronic moderate-intensity endurance exercise, resistance training, HIIT, and moderate-intensity acute exercise enhance mitochondrial function by promoting mtDNA transcription and replication, thus blunting the abnormal release of mtDNA and excessive innate immune response. On the contrary, high-intensity acute exercise elicits the opposite effect. Nevertheless, only a very small body of research by far has been performed to illustrate the impact of exercise on mtDNA-driven innate immune response, and an overall review is lacking. In light of these, we summarize the current knowledge on the mechanism mediating the release of mtDNA, the role of mtDNA in innate immune response and the influence of exercise on mtDNA leakage, hoping to pave the way to investigate new diagnostic and therapeutic approaches for immunopathies.

A review of nutritional recommendations for scuba divers

BACKGROUND

Scuba diving is an increasingly popular activity that involves the use of specialized equipment and compressed air to breathe underwater. Scuba divers are subject to the physiological consequences of being immersed in a high-pressure environment, including, but not limited to, increased work of breathing and kinetic energy expenditure, decreased fluid absorption, and alteration of metabolism. Individual response to these environmental stressors may result in a differential risk of decompression sickness, a condition thought to result from excess nitrogen bubbles forming in a diver's tissues. While the mechanisms of decompression sickness are still largely unknown, it has been postulated that this response may further be influenced by the diver's health status. Nutritional intake has direct relevancy to inflammation status and oxidative stress resistance, both of which have been associated with increased decompression stress. While nutritional recommendations have been determined for saturation divers, these recommendations are likely overly robust for recreational divers, considering that the differences in time spent under pressure and the maximum depth could result nonequivalent energetic demands. Specific recommendations for recreational divers remain largely undefined.

METHODS

This narrative review will summarize existing nutritional recommendations and their justification for recreational divers, as well as identify gaps in research regarding connections between nutritional intake and the health and safety of divers.

RESULTS

Following recommendations made by the Institute of Medicine and the Naval Medical Research Institute of Bethesda, recreational divers are advised to consume ~170-210 kJ·kg-1 (40-50 kcal·kg-1) body mass, depending on their workload underwater, in a day consisting of 3 hours' worth of diving above 46 msw. Recommendations for macronutrient distribution for divers are to derive 50% of joules from carbohydrates and less than 30% of joules from fat. Protein consumption is recommended to reach a minimum of 1 g of protein·kg-1 of body mass a day to mitigate loss of appetite while meeting energetic requirements. All divers should take special care to hydrate themselves with an absolute minimum of 500 ml of fluid per hour for any dive longer than 3 hours, with more recent studies finding 0.69 liters of water two hours prior to diving is most effective to minimize bubble loads. While there is evidence that specialized diets may have specific applications in commercial or military diving, they are not advisable for the general recreational diving population considering the often extreme nature of these diets, and the lack of research on their effectiveness on a recreational diving population.

CONCLUSIONS

Established recommendations do not account for changes in temperature, scuba equipment, depth, dive time, work of breathing, breathing gas mix, or individual variation in metabolism. Individual recommendations may be more accurate when accounting for basal metabolic rate and physical activity outside of diving. However, more research is needed to validate these estimates against variation in dive profile and diver demographics.

CO2 Breathing Prior to Simulated Diving Increases Decompression Sickness Risk in a Mouse Model: The Microbiota Trail Is Not Forgotten

Decompression sickness (DCS) with neurological disorders is the leading cause of major diving accidents treated in hyperbaric chambers. Exposure to high levels of CO2 during diving is a safety concern for occupational groups at risk of DCS. However, the effects of prior exposure to CO2 have never been evaluated. The purpose of this study was to evaluate the effect of CO2 breathing prior to a provocative dive on the occurrence of DCS in mice. Fifty mice were exposed to a maximum CO2 concentration of 70 hPa, i.e., 7% at atmospheric pressure, for one hour at atmospheric pressure. Another 50 mice breathing air under similar conditions served as controls. In the AIR group (control), 22 out of 50 mice showed post-dive symptoms compared to 44 out of 50 in the CO2 group (p < 0.001). We found that CO2 breathing is associated with a decrease in body temperature in mice and that CO2 exposure dramatically increases the incidence of DCS (p < 0.001). More unexpectedly, it appears that the lower temperature of the animals even before exposure to the accident-prone protocol leads to an unfavorable prognosis (p = 0.046). This study also suggests that the composition of the microbiota may influence thermogenesis and thus accidentology. Depending on prior exposure, some of the bacterial genera identified in this work could be perceived as beneficial or pathogenic.

Highlighting of the interactions of MYD88 and NFKB1 SNPs in rats resistant to decompression sickness: toward an autoimmune response

Decompression sickness (DCS) with neurological disorders includes an inappropriate inflammatory response which degenerates slowly, even after the disappearance of the bubbles. There is high inter-individual variability in terms of the occurrence of DCS that could have been mastered by the selection and then the breeding of DCS-resistant rats. We hypothesized the selection of single-nucleotide polymorphisms (SNPs) linked to autoimmunity operated upon a generation of a DCS-resistant strain of rats. We used the candidate gene approach and targeted SNPs linked to the signaling cascade that directly regulates inflammation of innate immunity transiting by the Toll-like receptors. Twenty candidate SNPs were investigated in 36 standard rats and 33 DCS-resistant rats. For the first time, we identify a diplotype (i.e., with matched haplotypes)-when coinherited-that strengthens protection against DCS, which is not strictly homozygous and suggests that a certain tolerance may be considered. We deduced an ideal haplotype of six variants from it (MyD88_50-T, _49-A, _97-C coupled to NFKB_85-T, _69-T, _45-T) linked to the resistant phenotype. Four among the six identified variants are located in pre- and/or post-transcriptional areas regulating MyD88 or NFKB1 expression. Because of missense mutations, the other two variants induce a structural change in the NFKB1 protein complex including one damage alteration according to the Missense3D algorithm. In addition to the MyD88/NFKB1 haplotype providing rats with a strong resistance to DCS, this also highlights the importance that the immune response, here linked to the genetic heritage, can have in the development of DCS and offer a new perspective for therapeutic strategies.

Cecal Metabolomic Fingerprint of Unscathed Rats: Does It Reflect the Good Response to a Provocative Decompression?

On one side, decompression sickness (DCS) with neurological disorders lead to a reshuffle of the cecal metabolome of rats. On the other side, there is also a specific and different metabolomic signature in the cecum of a strain of DCS-resistant rats, that are not exposed to hyperbaric protocol. We decide to study a conventional strain of rats that resist to an accident-provoking hyperbaric exposure, and we hypothesize that the metabolomic signature put forward may correspond to a physiological response adapted to the stress induced by diving. The aim is to verify and characterize whether the cecal compounds of rats resistant to the provocative dive have a cecal metabolomic signature different from those who do not dive. 35 asymptomatic diver rats are selected to be compared to 21 rats non-exposed to the hyperbaric protocol. Because our aim is essentially to study the differences in the cecal metabolome associated with the hyperbaric exposure, about half of the rats are fed soy and the other half of maize in order to better rule out the effect of the diet itself. Lower levels of IL-1β and glutathione peroxidase (GPX) activity are registered in blood of diving rats. No blood cell mobilization is noted. Conventional and ChemRICH approaches help the metabolomic interpretation of the 185 chemical compounds analyzed in the cecal content. Statistical analysis show a panel of 102 compounds diet related. 19 are in common with the hyperbaric protocol effect. Expression of 25 compounds has changed in the cecal metabolome of rats resistant to the provocative dive suggesting an alteration of biliary acids metabolism, most likely through actions on gut microbiota. There seem to be also weak changes in allocations dedicated to various energy pathways, including hormonal reshuffle. Some of the metabolites may also have a role in regulating inflammation, while some may be consumed for the benefit of oxidative stress management.

Circulating cell-free mitochondrial DNA in brain health and disease: A systematic review and meta-analysis

OBJECTIVES

Circulating cell-free mitochondrial DNA (ccf-mtDNA) are detectable fragments of mtDNA released from the cell as a result of mitochondrial dysfunction or apoptosis. The brain is one of the most energy demanding organs in the human body, and many neuropsychiatric and non-psychiatric neurological diseases have mitochondrial dysfunction associated with disease pathophysiology. Thus, we aimed to assess ccf-mtDNA as a potential biomarker for brain diseases.

METHODS

We conducted a systematic review and meta-analyses of studies that examined peripheral and/or cerebrospinal fluid (CSF) ccf-mtDNA relevant to neuropsychiatric conditions, which we define as disorders of affect, behaviour and mood, and non-psychiatric neurological diseases, which consist of neurological diseases not related to psychiatry including neurodegenerative diseases.

RESULTS

The results of the sensitivity analysis investigating the levels of peripheral ccf-mtDNA in neuropsychiatric studies showed no significant difference between cases and controls (Z = 1.57; p = 0.12), whereas the results of the sensitivity analysis investigating the levels of CSF ccf-mtDNA in non-psychiatric neurological diseases showed a decreasing trend in cases compared with controls (Z = 2.32; p = 0.02). Interestingly, the results indicate an overall mitochondrial stress associated mainly with non-psychiatric neurological diseases.

CONCLUSIONS

Our study supports the involvement of mitochondrial stress, here defined as ccf-mtDNA, in brain diseases and encourage further investigation of ccf-mtDNA among patients with brain diseases.

Mitochondrial DNA and Exercise: Implications for Health and Injuries in Sports

Recently, several studies have highlighted the tight connection between mitochondria and physical activity. Mitochondrial functions are important in high-demanding metabolic activities, such as endurance sports. Moreover, regular training positively affects metabolic health by increasing mitochondrial oxidative capacity and regulating glucose metabolism. Exercise could have multiple effects, also on the mitochondrial DNA (mtDNA) and vice versa; some studies have investigated how mtDNA polymorphisms can affect the performance of general athletes and mtDNA haplogroups seem to be related to the performance of elite endurance athletes. Along with several stimuli, including pathogens, stress, trauma, and reactive oxygen species, acute and intense exercise also seem to be responsible for mtDNA release into the cytoplasm and extracellular space, leading to the activation of the innate immune response. In addition, several sports are characterized by a higher frequency of injuries, including cranial trauma, associated with neurological consequences. However, with regular exercise, circulating cell-free mtDNA levels are kept low, perhaps promoting cf-mtDNA removal, acting as a protective factor against inflammation.

Evidence of a hormonal reshuffle in the cecal metabolome fingerprint of a strain of rats resistant to decompression sickness

On one side, decompression sickness (DCS) with neurological disorders lead to a reshuffle of the fecal metabolome from rat caecum. On the other side, there is high inter-individual variability in terms of occurrence of DCS. One could wonder whether the fecal metabolome could be linked to the DCS-susceptibility. We decided to study male and female rats selected for their resistance to decompression sickness, and we hypothesize a strong impregnation concerning the fecal metabolome. The aim is to verify whether the rats resistant to the accident have a fecal metabolomic signature different from the stem generations sensitive to DCS. 39 DCS-resistant animals (21 females and 18 males), aged 14 weeks, were compared to 18 age-matched standard Wistar rats (10 females and 8 males), i.e., the same as those we used for the founding stock. Conventional and ChemRICH approaches helped the metabolomic interpretation of the 226 chemical compounds analyzed in the cecal content. Statistical analysis shows a panel of 81 compounds whose expression had changed following the selection of rats based on their resistance to DCS. 63 compounds are sex related. 39 are in common. This study shows the spectral fingerprint of the fecal metabolome from the caecum of a strain of rats resistant to decompression sickness. This study also confirms a difference linked to sex in the metabolome of non-selected rats, which disappear with selective breeding. Results suggest hormonal and energetic reshuffle, including steroids sugars or antibiotic compounds, whether in the host or in the microbial community.

Demonstration by Infra-Red Imaging of a Temperature Control Defect in a Decompression Sickness Model Testing Minocycline

The prevention, prognosis and resolution of decompression sickness (DCS) are not satisfactory. The etiology of DCS has highlighted thrombotic and inflammatory phenomena that could cause severe neurological disorders or even death. Given the immunomodulatory effects described for minocycline, an antibiotic in widespread use, we have decided to explore its effects in an experimental model for decompression sickness. 40 control mice (Ctrl) and 40 mice treated orally with 90 mg/kg of minocycline (MINO) were subjected to a protocol in a hyperbaric chamber, compressed with air. The purpose was to mimic a scuba dive to a depth of 90 msw and its pathogenic decompression phase. Clinical examinations and blood counts were conducted after the return to the surface. For the first time they were completed by a simple infrared (IR) imaging technique in order to assess feasibility and its clinical advantage in differentiating the sick mice (DCS) from the healthy mice (NoDCS). In this tudy, exposure to the hyperbaric protocol provoked a reduction in the number of circulating leukocytes. DCS in mice, manifesting itself by paralysis or convulsion for example, is also associated with a fall in platelets count. Cold areas ( < 25°C) were detected by IR in the hind paws and tail with significant differences (p < 0.05) between DCS and NoDCS. Severe hypothermia was also shown in the DCS mice. The ROC analysis of the thermograms has made it possible to determine that an average tail temperature below 27.5°C allows us to consider the animals to be suffering from DCS (OR = 8; AUC = 0.754, p = 0.0018). Minocycline modulates blood analysis and it seems to limit the mobilization of monocytes and granulocytes after the provocative dive. While a higher proportion of mice treated with minocycline experienced DCS symptoms, there is no significant difference. The infrared imaging has made it possible to show severe hypothermia. It suggests an modification of thermregulation in DCS animals. Surveillance by infrared camera is fast and it can aid the prognosis in the case of decompression sickness in mice.

Static Metabolic Bubbles as Precursors of Vascular Gas Emboli During Divers' Decompression: A Hypothesis Explaining Bubbling Variability

Introduction

The risk for decompression sickness (DCS) after hyperbaric exposures (such as SCUBA diving) has been linked to the presence and quantity of vascular gas emboli (VGE) after surfacing from the dive. These VGE can be semi-quantified by ultrasound Doppler and quantified via precordial echocardiography. However, for an identical dive, VGE monitoring of divers shows variations related to individual susceptibility, and, for a same diver, dive-to-dive variations which may be influenced by pre-dive pre-conditioning. These variations are not explained by currently used algorithms. In this paper, we present a new hypothesis: individual metabolic processes, through the oxygen window (OW) or Inherent Unsaturation of tissues, modulate the presence and volume of static metabolic bubbles (SMB) that in turn act as precursors of circulating VGE after a dive.

Methods

We derive a coherent system of assumptions to describe static gas bubbles, located on the vessel endothelium at hydrophobic sites, that would be activated during decompression and become the source of VGE. We first refer to the OW and show that it creates a local tissue unsaturation that can generate and stabilize static gas phases in the diver at the surface. We then use Non-extensive thermodynamics to derive an equilibrium equation that avoids any geometrical description. The final equation links the SMB volume directly to the metabolism.

Results and Discussion

Our model introduces a stable population of small gas pockets of an intermediate size between the nanobubbles nucleating on the active sites and the VGE detected in the venous blood. The resulting equation, when checked against our own previously published data and the relevant scientific literature, supports both individual variation and the induced differences observed in pre-conditioning experiments. It also explains the variability in VGE counts based on age, fitness, type and frequency of physical activities. Finally, it fits into the general scheme of the arterial bubble assumption for the description of the DCS risk.

Conclusion

Metabolism characterization of the pre-dive SMB population opens new possibilities for decompression algorithms by considering the diver's individual susceptibility and recent history (life style, exercise) to predict the level of VGE during and after decompression.