Acid-base balance and cerebrovascular regulation

Delayed Chronic Acidic Postconditioning Improves Poststroke Motor Functional Recovery and Brain Tissue Repair by Activating Proton-Sensing TDAG8

Acidic postconditioning by transient CO2 inhalation applied within minutes after reperfusion has neuroprotective effects in the acute phase of stroke. However, the effects of delayed chronic acidic postconditioning (DCAPC) initiated during the subacute phase of stroke or other acute brain injuries are unknown. Mice received daily DCAPC by inhaling 5%/10%/20% CO2 for various durations (three cycles of 10- or 20-min CO2 inhalation/10-min break) at days 3-7, 7-21, or 3-21 after photothrombotic stroke. Grid-walk, cylinder, and gait tests were used to assess motor function. DCAPC with all CO2 concentrations significantly promoted motor functional recovery, even when DCAPC was delayed for 3-7 days. DCAPC enhanced the puncta density of GAP-43 (a marker of axon growth and regeneration) and synaptophysin (a marker of synaptogenesis) and reduced the amoeboid microglia number, glial scar thickness and mRNA expression of CD16 and CD32 (markers of proinflammatory M1 microglia) compared with those of the stroke group. Cerebral blood flow (CBF) increased in response to DCAPC. Furthermore, the mRNA expression of TDAG8 (a proton-activated G-protein-coupled receptor) was increased during the subacute phase of stroke, while DCAPC effects were blocked by systemic knockout of TDAG8, except for those on CBF. DCAPC reproduced the benefits by re-expressing TDAG8 in the peri-infarct cortex of TDAG8-/- mice infected with HBAAV2/9-CMV-TDAG8-3flag-ZsGreen. Taken together, we first showed that DCAPC promoted functional recovery and brain tissue repair after stroke with a wide therapeutic time window of at least 7 days after stroke. Brain-derived TDAG8 is a direct target of DCAPC that induces neuroreparative effects.

Characterization of Demographic, Clinical, and Laboratory Risk Factors for Stroke in a Tertiary Hospital in Riyadh, Saudi Arabia

Background Stroke is a major cause of death and long-term disability worldwide, with varying incidence and risk factors across different populations. This study aims to analyze demographic, clinical, and laboratory risk factors for stroke among the Saudi Arabian population to enhance the understanding of its behavior and associated mortality. Methods In this retrospective cohort study, we analyzed data from 3586 patients diagnosed with hemorrhagic or non-hemorrhagic stroke at King Fahad Medical City from January 1, 2020, to November 11, 2022. We collected data on demographic variables, past medical history, social history, nationality, and laboratory components. Statistical analyses were performed using IBM SPSS Statistics for Windows, Version 27.0. (Armonk, NY: IBM Corp.), with significance set at p<0.05. Results The study population was predominantly male (57.86%) and within the age group of 51 to 80 years (58.8%). A significant portion of patients were Saudi nationals (99.6%), with hypertension (50.2%) and diabetes (40.4%) being the most common comorbidities. Laboratory abnormalities related to sodium and potassium levels were strongly linked to mortality rates. Notably, ischemic stroke was the most common type across all age groups, except for patients under age 16, where hemorrhagic stroke was more prevalent. Conclusions Our findings reveal significant associations between stroke risk factors and mortality within the Saudi Arabian population, highlighting the impact of hypertension, diabetes, and electrolyte imbalances. The study underscores the need for targeted stroke prevention and management strategies in Saudi Arabia, aligning with global trends to mitigate the burden of this disease.

Designing of multifunctional graphene quantum dot-polyvinyl alcohol-polyglycerol luminescent film for fluorescence detection of pH in sweat

BACKGROUND

Wound infection, skin disease, renal failure, cancer, cystic fibrosis, and other pathologies may induce obvious pH changes in sweat. Thus, tracking skin pH changes can help monitor human health in a convenient manner. Owing to their biocompatibility, easy preparation, and sensitive response to pH changes, graphene quantum dots (GQDs) have received increased attention in the optical detection of pH changes. However, their poor luminescent efficiency under visible light excitation and lack of functional diversification limit their application in skin pH monitoring. Therefore, the development of GQDs with excellent ultraviolet protection ability and antibacterial and luminescence performance is essential.

RESULTS

Folic acid-, histidine-, and serine-functionalized boron-doped graphene quantum dots (FHSB-GQDs) were designed and synthesized via thermal treatment. The resulting FHSB-GQDs exhibit strong yellow fluorescence emission under excitation with 490-nm visible light and sensitive pH responsiveness. The peak fluorescence intensity linearly decreases with increasing pH from 4 to 9. Furthermore, the FHSB-GQDs were integrated with polyvinyl alcohol and polyglycerol to form a luminescent film via hydrogen bond interactions. The film exhibits high transparency, mechanical flexibility, ultraviolet protection ability, and antibacterial activity. The presence of polyvinyl alcohol and polyglycerol restricts the free movement of the FHSB-GQDs and improves fluorescence behavior. The film was successfully applied in an intelligent pH-sensing system for monitoring pH changes in human sweat.

SIGNIFICANCE

The graphene quantum dot-polyvinyl alcohol-polyglycerol luminescent film offers excellent transparency, mechanical flexibility, ultraviolet protection ability, antibacterial activity, and luminescence performance. It was successfully applied in an intelligent pH sensing system for the detection of pH changes in human sweat. This study provides a new strategy for the design and construction of wearable sensing systems for health monitoring, facial masks, and medical dressings.

Activatable Probes for Ratiometric Imaging of Endogenous Biomarkers In Vivo

Dynamic variations in the concentration and abnormal distribution of endogenous biomarkers are strongly associated with multiple physiological and pathological states. Therefore, it is crucial to design imaging systems capable of real-time detection of dynamic changes in biomarkers for the accurate diagnosis and effective treatment of diseases. Recently, ratiometric imaging has emerged as a widely used technique for sensing and imaging of biomarkers due to its advantage of circumventing the limitations inherent to conventional intensity-dependent signal readout methods while also providing built-in self-calibration for signal correction. Here, the recent progress of ratiometric probes and their applications in sensing and imaging of biomarkers are outlined. Ratiometric probes are classified according to their imaging mechanisms, and ratiometric photoacoustic imaging, ratiometric optical imaging including photoluminescence imaging and self-luminescence imaging, ratiometric magnetic resonance imaging, and dual-modal ratiometric imaging are discussed. The applications of ratiometric probes in the sensing and imaging of biomarkers such as pH, reactive oxygen species (ROS), reactive nitrogen species (RNS), glutathione (GSH), gas molecules, enzymes, metal ions, and hypoxia are discussed in detail. Additionally, this Review presents an overview of challenges faced in this field along with future research directions.

Relationship between baseline bicarbonate and 30-day mortality in patients with non-traumatic subarachnoid hemorrhage

Objective

This study aimed to explore the relationship between baseline bicarbonate levels and 30-day mortality in individuals with non-traumatic subarachnoid hemorrhage (SAH).

Methods

Patients with non-traumatic SAH were chosen from the Medical Information Mart for Intensive Care (MIMIC)-IV database. The relationship between baseline bicarbonate and 30-day mortality was examined using Cox regression models. Restricted cubic splines were used to test the hypothesis that there was an association between bicarbonate and mortality. With the use of Kaplan-Meier survival curve analysis, we looked deeper into the validity of these correlations. To find subgroups with differences, interaction tests were utilized.

Results

This retrospective cohort study consisted of 521 participants in total. Bicarbonate had a negative association with death at 30 days (HR = 0.93, 95%CI: 0.88-0.98, p = 0.004). Next, we divided bicarbonate into quartile groups. In comparison to the reference group Q1 (20 mEq/L), groups Q3 (23-25 mEq/L) and Q4 (26 mEq/L) had adjusted HR values of 0.47 (95%CI: 0.27-0.82, p = 0.007) and 0.56 (95%CI: 0.31-0.99, p = 0.047). No definite conclusions can be derived from this study, since there is no obvious curve link between baseline bicarbonate and 30-day mortality. Patients' 30-day mortality increased statistically significantly (p < 0.001, K-M analysis) in patients with low bicarbonate levels. The relationship between bicarbonate and 30-day mortality remained consistent in the stratified analysis, with no observed interactions.

Conclusion

Finally, 30-day mortality was negatively associated with baseline bicarbonate levels. Patients with non-traumatic SAH are more at risk of mortality if their bicarbonate levels are low.

Assessment of Cerebrovascular Reactivity Using CO2 -BOLD MRI: A 15-Year, Single Center Experience

BACKGROUND

Cerebrovascular reactivity (CVR) is a measure of the change in cerebral blood flow (CBF) in response to a vasoactive challenge. It is a useful indicator of the brain's vascular health.

PURPOSE

To evaluate the factors that influence successful and unsuccessful CVR examinations using precise arterial and end-tidal partial pressure of CO2 control during blood oxygen level-dependent (BOLD) MRI.

STUDY TYPE

Retrospective.

SUBJECTS

Patients that underwent a CVR between October 2005 and May 2021 were studied (total of 1162 CVR examinations). The mean (±SD) age was 46.1 (±18.8) years, and 352 patients (43%) were female.

FIELD STRENGTH/SEQUENCE

3 T; T1-weighted images, T2*-weighed two-dimensional gradient-echo sequence with standard echo-planar readout.

ASSESSMENT

Measurements were obtained following precise hypercapnic stimuli using BOLD MRI as a surrogate of CBF. Successful CVR examinations were defined as those where: 1) patients were able to complete CVR testing, and 2) a clinically useful CVR map was generated. Unsuccessful examinations were defined as those where patients were not able to complete the CVR examination or the CVR maps were judged to be unreliable due to, for example, excessive head motion, and poor PET CO2 targeting.

STATISTICAL ANALYSIS

Successful and unsuccessful CVR examinations between hypercapnic stimuli, and between different patterns of stimulus were compared with Chi-Square tests. Interobserver variability was determined by using the intraclass correlation coefficient (P < 0.05 is significant).

RESULTS

In total 1115 CVR tests in 662 patients were included in the final analysis. The success rate of generating CVR maps was 90.8% (1012 of 1115). Among the different hypercapnic stimuli, those containing a step plus a ramp protocol was the most successful (95.18%). Among the unsuccessful examinations (9.23%), most were patient related (89.3%), the most common of which was difficulty breathing.

DATA CONCLUSION

CO2 -BOLD MRI CVR studies are well tolerated with a high success rate.

EVIDENCE LEVEL

4 TECHNICAL EFFICACY: Stage 3.

Relationship between serum bicarbonate levels and the risk of death within 30 days in ICU patients with acute ischemic stroke

Aim

To explore the relationship between baseline bicarbonate levels and their changes with 30-day mortality in patients with acute ischemic stroke who were admitted to the intensive care unit (ICU).

Methods

This cohort study collected the data of 4,048 participants from the Medical Information Mart for Intensive Care (MIMIC)-III and MIMIC-IV databases. Univariate and multivariable Cox proportional risk models were utilized to explore the relationship between bicarbonate T0 and Δbicarbonate with 30-day mortality in patients with acute ischemic stroke. The Kaplan-Meier curves were plotted to measure the 30-day survival probability of patients with acute ischemic stroke.

Results

The median follow-up time was 30 days. At the end of the follow-up, 3,172 patients survived. Bicarbonate T0 ≤ 21 mEq/L [hazard ratio (HR) = 1.24, a 95% confidence interval (CI): 1.02-1.50] or 21 mEq/L < bicarbonate T0 ≤ 23 mEq/L (HR = 1.29, 95%CI: 1.05-1.58) were associated with an increased risk of 30-day mortality in patients with acute ischemic stroke compared with bicarbonate T0 > 26 mEq/L. -2 mEq/L < Δbicarbonate ≤ 0 mEq/L (HR = 1.40, 95%CI: 1.14-1.71), 0 mEq/L < Δbicarbonate ≤ 2 mEq/L (HR = 1.44, 95%CI: 1.17-1.76), and Δbicarbonate >2 mEq/L (HR = 1.40, 95%CI: 1.15-1.71) were correlated with an elevated risk of 30-day mortality in acute ischemic stroke patients. The 30-day survival probability of acute ischemic stroke patients with 21 mEq/L < bicarbonate T0 ≤ 23 mEq/L, 23 mEq/L < bicarbonate T0 ≤ 26 mEq/L, or bicarbonate T0 >26 mEq/L was higher than that of patients with bicarbonate T0 ≤ 21 mEq/L. The 30-day survival probability was greater for patients in the Δbicarbonate ≤ -2 mEq/L group than for those in the Δbicarbonate >2 mEq/L group.

Conclusion

Low baseline bicarbonate levels and decreased bicarbonate levels during the ICU stay were associated with a high risk of 30-day mortality in acute ischemic stroke patients. Special interventions should be offered to those with low baseline and decreased bicarbonate levels during their ICU stay.

Molecular Mechanisms of Obesity-Induced Development of Insulin Resistance and Promotion of Amyloid-β Accumulation: Dietary Therapy Using Weak Organic Acids via Improvement of Lowered Interstitial Fluid pH

Insulin resistance is one of the etiologies of type 2 diabetes mellitus (T2DM) and has been suggested to contribute to the development of Alzheimer's disease by promoting amyloid-β accumulation. Various causes of insulin resistance have been suggested; however, mechanisms of insulin resistance development remain to be elucidated in many respects. Elucidating the mechanisms underlying the development of insulin resistance is one of the key factors in developing methods to prevent the onset of T2DM and Alzheimer's disease. It has been suggested that the body pH environment plays an important role in the control of cellular functions by regulating the action of hormones including insulin and the activity of enzymes and neurons, thereby maintaining homeostatic conditions of the body. This review introduces: (1) Mitochondrial dysfunction through oxidative stress caused by obesity-induced inflammation. (2) Decreased pH of interstitial fluid due to mitochondrial dysfunction. (3) Development of insulin resistance due to diminution of insulin affinity to its receptor caused by the lowered interstitial fluid pH. (4) Accelerated accumulation of amyloid-β due to elevated activities of β- and γ-secretases caused by the lowered interstitial fluid pH. (5) Diet therapies for improving insulin resistance with weak organic acids that act as bases in the body to raise the pH of lowered interstitial fluid and food factors that promote absorption of weak organic acids in the gut.

Cerebral blood flow pulsatility and cerebral artery stiffness acutely decrease during hemodialysis

End-stage kidney disease (ESKD) is associated with increased arterial stiffness and cognitive impairment. Cognitive decline is accelerated in ESKD patients on hemodialysis and may result from repeatedly inappropriate cerebral blood flow (CBF). The aim of this study was to examine the acute effect of hemodialysis on pulsatile components of CBF and their relation to acute changes in arterial stiffness. In eight participants (age: 63 ± 18 years, men: 5), CBF was estimated using middle cerebral artery blood velocity (MCAv) assessed with transcranial Doppler ultrasound before, during, and after a single hemodialysis session. Brachial and central blood pressure, along with estimated aortic stiffness (eAoPWV) were measured using an oscillometric device. Arterial stiffness from heart to MCA was measured as the pulse arrival time (PAT) between electrocardiogram (ECG) and transcranial Doppler ultrasound waveforms (cerebral PAT). During hemodialysis, there was a significant reduction in mean MCAv (-3.2 cm/s, p < 0.001), and systolic MCAv (-13.0 cm/s, p < 0.001). While baseline eAoPWV (9.25 ± 0.80 m/s) did not significantly change during hemodialysis, cerebral PAT increased significantly (+0.027 , p < 0.001) and was associated with reduced pulsatile components of MCAv. This study shows that hemodialysis acutely reduces stiffness of arteries perfusing the brain along with pulsatile components of blood velocity.

Poly β-Cyclodextrin/Quaternary Ammoniated Chitosan Cryogel with a Porous Structure for Effective Hemostasis

Uncontrolled bleeding is one of the most important causes threatening human health, but quick hemostasis remains a challenge. We prepared porous cryogels with poly β-cyclodextrin (Pβ-CD) and quaternary ammoniated chitosan (QCs). Pβ-CD acts as a "water-grabbing agent" to assist QCs' ability to absorb and concentrate blood rapidly. The rat-tail amputation model and liver injury model exhibited that cryogels had excellent hemostatic performance. Moreover, cryogels showed good antibacterial activity and biocompatibility. Therefore, these cryogels can be used as potential hemostatic materials.

Cerebral O2 and CO2 transport in isovolumic haemodilution: Compensation of cerebral delivery of O2 and maintenance of cerebrovascular reactivity to CO2

This study investigated the influence of acute reductions in arterial O₂ content (CaO₂) via isovolumic haemodilution on global cerebral blood flow (gCBF) and cerebrovascular CO₂ reactivity (CVR) in 11 healthy males (age; 28 ± 7 years: body mass index; 23 ± 2 kg/m²). Radial artery and internal jugular vein catheters provided measurement of blood pressure and gases, quantification of cerebral metabolism, cerebral CO₂ washout, and trans-cerebral nitrite exchange (ozone based chemiluminescence). Prior to and following haemodilution, the partial pressure of arterial CO₂ (PaCO₂) was elevated with dynamic end-tidal forcing while gCBF was measured with duplex ultrasound. CVR was determined as the slope of the gCBF response and PaCO₂. Replacement of ∼20% of blood volume with an equal volume of 5% human serum albumin (Alburex® 5%) reduced haemoglobin (13.8 ± 0.8 vs. 11.3 ± 0.6 g/dL; P < 0.001) and CaO₂ (18.9 ± 1.0 vs 15.0 ± 0.8 mL/dL P < 0.001), elevated gCBF (+18 ± 11%; P = 0.002), preserved cerebral oxygen delivery (P = 0.49), and elevated CO₂ washout (+11%; P = 0.01). The net cerebral uptake of nitrite (11.6 ± 14.0 nmol/min; P = 0.027) at baseline was abolished following haemodilution (-3.6 ± 17.9 nmol/min; P = 0.54), perhaps underpinning the conservation of CVR (61.7 ± 19.0 vs. 69.0 ± 19.2 mL/min/mmHg; P = 0.23). These findings demonstrate that the cerebrovascular responses to acute anaemia in healthy humans are sufficient to support the maintenance of CVR.

Physiological Function during Exercise and Environmental Stress in Humans-An Integrative View of Body Systems and Homeostasis

Claude Bernard’s milieu intérieur (internal environment) and the associated concept of homeostasis are fundamental to the understanding of the physiological responses to exercise and environmental stress. Maintenance of cellular homeostasis is thought to happen during exercise through the precise matching of cellular energetic demand and supply, and the production and clearance of metabolic by-products. The mind-boggling number of molecular and cellular pathways and the host of tissues and organ systems involved in the processes sustaining locomotion, however, necessitate an integrative examination of the body’s physiological systems. This integrative approach can be used to identify whether function and cellular homeostasis are maintained or compromised during exercise. In this review, we discuss the responses of the human brain, the lungs, the heart, and the skeletal muscles to the varying physiological demands of exercise and environmental stress. Multiple alterations in physiological function and differential homeostatic adjustments occur when people undertake strenuous exercise with and without thermal stress. These adjustments can include: hyperthermia; hyperventilation; cardiovascular strain with restrictions in brain, muscle, skin and visceral organs blood flow; greater reliance on muscle glycogen and cellular metabolism; alterations in neural activity; and, in some conditions, compromised muscle metabolism and aerobic capacity. Oxygen supply to the human brain is also blunted during intense exercise, but global cerebral metabolism and central neural drive are preserved or enhanced. In contrast to the strain seen during severe exercise and environmental stress, a steady state is maintained when humans exercise at intensities and in environmental conditions that require a small fraction of the functional capacity. The impact of exercise and environmental stress upon whole-body functions and homeostasis therefore depends on the functional needs and differs across organ systems.