The role of lactate in sepsis and COVID-19: Perspective from contracting skeletal muscle metabolism

Lactate Levels and Clearance: Key Predictors of Prognosis for COVID-19 and Non-COVID-19 Septic Shock Patients in the Emergency Department

BACKGROUND

This investigation assesses the prognostic value of lactate levels and their clearance in septic shock patients, particularly emphasizing the comparative analysis between COVID-19 and non-COVID-19 patients in the emergency department. This study aims to elucidate the unique prognostic implications of lactate dynamics in these distinct patient groups, thereby enhancing the management of septic shock.

METHODS

An observational prospective study was conducted, enrolling 114 septic shock patients from the Emergency County Hospital Resita, Romania, categorizing them into COVID-19 and non-COVID-19 groups to examine their initial lactate levels, clearance rates, and their correlation with patient outcomes.

RESULTS

This study identified significant differences in the initial lactate levels and clearance rates between the two groups, indicating higher initial lactate levels and slower clearance rates in COVID-19 patients. Survivors demonstrated significantly lower initial lactate levels (1.5 ± 0.4 mmol/L) and higher lactate clearance rates (33 ± 15%) compared to non-survivors (2.5 ± 0.5 mmol/L and 24 ± 9%, respectively; lactate levels p = 0.001, clearance rates p = 0.002).

CONCLUSIONS

Lactate monitoring, particularly clearance rates, is crucial in the prognostic assessment of septic shock patients. These findings highlight the need for targeted interventions in COVID-19 patients to improve outcomes, underscoring lactate dynamics as a vital component of septic shock management in differing patient populations.

Association of Calf Circumference with Clinical and Biochemical Markers in Older Adults with COVID-19 Admitted at Intensive Care Unit: A Retrospective Cross-Sectional Study

BACKGROUND

COVID-19 is an infectious disease characterized by a severe catabolic and inflammatory state, leading to loss of muscle mass. The assessment of muscle mass can be useful to identify nutritional risk and assist in early management, especially in older adults who have high nutritional risks. The aim of this study was to evaluate the association of calf circumference (CC) with clinical and biochemical markers and mortality in older adults with COVID-19 admitted to the intensive care unit (ICU).

METHODS

A retrospective cross-sectional study was conducted in a public hospital. CC was adjusted for body mass index (BMI), reducing 3, 7, or 12 cm for a BMI of 25-29.9, 30-39.9, and ≥40 kg/m2, respectively, and classified as reduced when <33 cm for women and <34 cm for men. Pearson's correlation between BMI and CC was performed to assess the association between variables. Regression analysis was adjusted for sex, age, and BMI variables. Cox regression was used to assess survival related to CC.

RESULTS

A total of 208 older adults diagnosed with COVID-19 admitted to ICU were included, of which 84% (n = 176) were classified as having reduced CC. These patients were older, with lower BMI, higher nutritional risk, malnourished, and higher concentration of urea and urea-creatinine ratio (UCR) compared with the group with normal CC. There was an association between edematous patients at nutritional risk and malnourished with reduced CC in the Cox regression, either adjusted or not for confounding.

CONCLUSIONS

CC was not associated with severity, biochemical markers, or mortality in older adults with COVID-19 admitted to the ICU, but it was associated with moderately malnourished patients assessed by subjective global assessment (SGA).

Is digit ratio (2D:4D) a biomarker for lactate? Evidence from a cardiopulmonary test on professional male footballers

BACKGROUND

Lactate accumulation is associated with vigorous exercise, cardiovascular disease and a number of cancers. Digit ratio (2D:4D) has also been linked to oxygen metabolism, myocardial infarction and various cancers. Such similarities suggest the possibility that 2D:4D is a biomarker of lactate. Here, we consider the relationship between 2D:4D and lactate during an incremental cardiopulmonary exercise test.

METHOD

The participants were male professional football players. The treadmill test began at a speed of 8 km/h when the first lactate measurement was taken. The speed was increased by 2 km/h every 3.15 min, with measurements at 10, 12, 14 and 16 km/h.

RESULTS

There were 72 Caucasian and 7 Black participants, results are reported for the most numerous group. Lactate levels increased with running speed and were not correlated with age, body size or body composition. Median splits of digit ratios (right, left and right-left 2D:4D [Dr-l]) were calculated. In comparison to the Low ratio group, the High ratio group showed higher lactate levels across speeds. Effect sizes varied from very large to huge (right 2D:4D), large (left 2D:4D) and medium (Dr-l). At the individual level, positive correlations between digit ratios and lactate at the five different speeds varied from large (right 2D:4D), medium (left 2D:4D) and small (Dr-l).

CONCLUSION

There were large positive associations between right 2D:4D and lactate at all running speeds. We discuss our findings in relation to oxygen metabolism and suggest that 2D:4D may be a biomarker for lactate in the wider context of the latter's importance in health and disease.

Glucose turnover at whole-body and skeletal muscle level in response to parenteral nutrition in male patients with alcoholic liver cirrhosis

BACKGROUND & AIMS

Cirrhosis is associated with insulin resistance and impaired glucose tolerance, which may be caused by impairments at different tissue levels (liver, skeletal muscle, and/or beta cell).

METHODS

Here, glucose kinetics at whole-body and skeletal muscle level in patients with cirrhosis (Child-Pugh A and B) were studied during parenteral nutrition using the isotope dilution technique and arteriovenous balance approach across the leg. As opposed to the euglycemic hyperinsulinemic clamp or glucose tolerance tests applied in previous studies, this approach provides a nutrient composition more similar to a normal meal while circumventing any possible portal-systemic shunting, impaired hepatic uptake and incretin effect.

RESULTS

We confirmed the presence of hepatic and peripheral insulin resistance in our patient population. Endogenous glucose production was less suppressed in response to parenteral nutrition. However, glucose uptake in skeletal muscle was increased.

CONCLUSION

Our results suggests that in our study participants with cirrhosis, the hepatic and peripheral insulin resistance is compensated for by increased insulin secretion and thus, increased glucose uptake in muscle. Hereby, glucose homeostasis is maintained.

Gas-exchange deficit and systemic hypoperfusion in COVID-19 and non-COVID-19 young adult patients with pneumonia

BACKGROUND

Lung damage leading to gas-exchange deficit and sepsis leading to systemic hypoperfusion are well-known features of severe pneumonia. Although frequently described in COVID-19, their prognostic impact in COVID-19-related pneumonia versus COVID-19-unrelated pneumonia has never been compared. This study assesses fundamental gas-exchange and hemodynamic parameters and explores their prognostic impact in COVID-19 pneumonia and non-COVID-19 pneumonia.

METHODS

We prospectively evaluated arterial pO2/FiO2, alveolar to arterial O2 gradient, shock index, and serum lactate in 126 COVID-19 pneumonia patients, aged 18-65, presenting to the emergency department with acute, non-hypercapnic respiratory failure. As a control group we identified 1:1 age-, sex-, and pO2/FiO2-matched COVID-19-urelated pneumonia patients. Univariate and multivariable predictors of 30-day survival were identified in both groups.

RESULTS

COVID-19 patients showed lower arterial serum lactate concentration (P<0.001) and shock index (P<0.001) values as compared to non-COVID-19 patients. While we did not observe differences in lactate concentration or in shock index values in deceased vs. surviving COVID-19 patients (P=0.7 and P=0.6, respectively), non-COVID-19 deceased patients showed significantly higher lactate and shock index than non-COVID-19 survivors (P<0.001 and P=0.03). The pO2/FiO2 was the most powerful determinant of survival by Cox regression multivariate analysis in COVID-19 patients (P=0.006), while it was lactate in non-COVID-19 patients (P=0.001).

CONCLUSIONS

As compared to COVID19-unrelated pneumonia, COVID-19 pneumonia outcome seems more strictly correlated to the extent of lung damage, rather than to the systemic circulatory and metabolic derangements typical of sepsis.

Possible Role of Fibrinaloid Microclots in Postural Orthostatic Tachycardia Syndrome (POTS): Focus on Long COVID

Postural orthostatic tachycardia syndrome (POTS) is a common accompaniment of a variety of chronic, inflammatory diseases, including long COVID, as are small, insoluble, 'fibrinaloid' microclots. We here develop the argument, with accompanying evidence, that fibrinaloid microclots, through their ability to block the flow of blood through microcapillaries and thus cause tissue hypoxia, are not simply correlated with but in fact, by preceding it, may be a chief intermediary cause of POTS, in which tachycardia is simply the body's exaggerated 'physiological' response to hypoxia. Similar reasoning accounts for the symptoms bundled under the term 'fatigue'. Amyloids are known to be membrane disruptors, and when their targets are nerve membranes, this can explain neurotoxicity and hence the autonomic nervous system dysfunction that contributes to POTS. Taken together as a system view, we indicate that fibrinaloid microclots can serve to link POTS and fatigue in long COVID in a manner that is at once both mechanistic and explanatory. This has clear implications for the treatment of such diseases.

Role of proprioceptors in chronic musculoskeletal pain

Proprioceptors are non-nociceptive low-threshold mechanoreceptors. However, recent studies have shown that proprioceptors are acid-sensitive and express a variety of proton-sensing ion channels and receptors. Accordingly, although proprioceptors are commonly known as mechanosensing neurons that monitor muscle contraction status and body position, they may have a role in the development of pain associated with tissue acidosis. In clinical practice, proprioception training is beneficial for pain relief. Here we summarize the current evidence to sketch a different role of proprioceptors in 'non-nociceptive pain' with a focus on their acid-sensing properties.

Mitochondrial oxidative stress, mitochondrial ROS storms in long COVID pathogenesis

Significance

This review discusses the coronavirus disease 2019 (COVID-19) pathophysiology in the context of diabetes and intracellular reactions by COVID-19, including mitochondrial oxidative stress storms, mitochondrial ROS storms, and long COVID.

Recent advances

The long COVID is suffered in ~10% of the COVID-19 patients. Even the virus does not exist, the patients suffer the long COVID for even over a year, This disease could be a mitochondria dysregulation disease.

Critical issues

Patients who recover from COVID-19 can develop new or persistent symptoms of multi-organ complications lasting weeks or months, called long COVID. The underlying mechanisms involved in the long COVID is still unclear. Once the symptoms of long COVID persist, they cause significant damage, leading to numerous, persistent symptoms.

Future directions

A comprehensive map of the stages and pathogenetic mechanisms related to long COVID and effective drugs to treat and prevent it are required, which will aid the development of future long COVID treatments and symptom relief.

SEPSIS LEADS TO IMPAIRED MITOCHONDRIAL CALCIUM UPTAKE AND SKELETAL MUSCLE WEAKNESS BY REDUCING THE MICU1:MCU PROTEIN RATIO

ABSTRACT

Purpose: Intensive care unit-acquired weakness (ICUAW) is a severe neuromuscular complication that frequently occurs in patients with sepsis. The precise molecular pathophysiology of mitochondrial calcium uptake 1 (MICU1) and mitochondrial calcium uniporter (MCU) in ICUAW has not been fully elucidated. Here, we speculate that ICUAW is associated with MICU1:MCU protein ratio-mediated mitochondrial calcium ([Ca 2+ ] m ) uptake dysfunction. Methods: Cecal ligation and perforation (CLP) was performed on C57BL/6J mice to induce sepsis. Sham-operated animals were used as controls. Lipopolysaccharide (LPS) (5 μg/mL) was used to induce inflammation in differentiated C2C12 myoblasts. Compound muscle action potential (CMAP) was detected using a biological signal acquisition system. Grip strength was measured using a grip-strength meter. Skeletal muscle inflammatory factors were detected using ELISA kits. The cross-sectional area (CSA) of the tibialis anterior (TA) muscle was detected by hematoxylin and eosin staining. Cytosolic calcium ([Ca 2+ ] c ) levels were measured using Fluo-4 AM. Adeno-associated virus (AAV) was injected into TA muscles for 4 weeks to overexpress MICU1 prophylactically. A lentivirus was used to infect C2C12 cells to increase MICU1 expression prophylactically. Findings: The results suggest that sepsis induces [Ca 2+ ] m uptake disorder by reducing the MICU1:MCU protein ratio, resulting in skeletal muscle weakness and muscle fiber atrophy. However, MICU1 prophylactic overexpression reversed these effects by increasing the MICU1:MCU protein ratio. Conclusions: ICUAW is associated with impaired [Ca 2+ ] m uptake caused by a decreased MICU1:MCU protein ratio. MICU1 overexpression improves sepsis-induced skeletal muscle weakness and atrophy by ameliorating the [Ca 2+ ] m uptake disorder.

Potential biomarker for diagnosis and therapy of sepsis: Lactylation

INTRODUCTION

As a disease that has plagued human health for decades, sepsis has so far had no specific diagnostic or therapeutic indicators. The discovery of lactylation modifications not only uncovered the deep-rooted causes of changing between lactate level and pathophysiology and immunology of sepsis, but also reaffirmed the inevitable link between metabolic reprogramming and epigenetic reprogramming in sepsis. Lactylation modification became a potential marker for diagnosis and guiding the treatment of sepsis.

AIM

In this paper, we will summarize the discovery and regulation of lactylation modifications, discuss the study of lactylation modifications in sepsis, and evaluate their possibility and potential as diagnostic and therapeutic indicators of sepsis.

CONCLUSION

Lactylation modification is directly regulated by glycolysis and lactate, and inhibition of glycolytic pathway-related enzymes can regulate the level of lactylation modification, and more importantly, lactylation modification can act on these enzymes to regulate their functions and feedback regulate the level of glycolysis, this finding provides more ideas for clinical treatment of sepsis. We use "epigenetic modification", "glycolysis", "lactate", "lactylaiton" and "sepsis" as keywords and search the relevant literature through Pubmed and Web of science up to 2023.

Relationship between clinical-epidemiological parameters and outcomes of patients with COVID-19 admitted to the intensive care unit: a report from a Brazilian hospital

Background

People in low-income countries, especially those with low socio-economic conditions, are likelier to test positive for SARS-CoV-2. The unequal conditions of public health systems also increase the infection rate and make early identification and treatment of at-risk patients difficult. Here, we aimed to characterize the epidemiological profile of COVID-19 patients in intensive care and identify laboratory and clinical markers associated with death.

Materials and methods

We conducted an observational, descriptive, and cross-sectional study in a reference hospital for COVID-19 treatment in the Southern Region of Bahia State, in Brazil, to evaluate the epidemiological, clinical, and laboratory characteristics of COVID-19 patients admitted to the intensive care unit (ICU). Additionally, we used the area under the curve (AUC) to classify survivors and non-survivors and a multivariate logistic regression analysis to assess factors associated with death. Data was collected from the hospital databases between April 2020 and July 2021.

Results

The use of bladder catheters (OR 79.30; p < 0.0001) and central venous catheters (OR, 45.12; p < 0.0001) were the main factors associated with death in ICU COVID-19 patients. Additionally, the number of non-survivors increased with age (p < 0.0001) and prolonged ICU stay (p < 0.0001). Besides, SAPS3 presents a higher sensibility (77.9%) and specificity (63.1%) to discriminate between survivors and non-survivor with an AUC of 0.79 (p < 0.0001).

Conclusion

We suggest that multi-laboratory parameters can predict patient prognosis and guide healthcare teams toward more assertive clinical management, better resource allocation, and improved survival of COVID-19 patients admitted to the ICU.

Physiological significance of elevated levels of lactate by exercise training in the brain and body

For the past 200 years, lactate has been regarded as a metabolic waste end product that causes fatigue during exercise. However, lactate production is closely correlated with energy metabolism. The lactate dehydrogenase-catalyzed reaction uses protons to produce lactate, which delays ongoing metabolic acidosis. Of note, lactate production differs depending on exercise intensity and is not limited to muscles. Importantly, controlling physiological effect of lactate may be a solution to alleviating some chronic diseases. Released through exercise, lactate is an important biomarker for fat oxidation in skeletal muscles. During recovery after sustained strenuous exercise, most of the lactate accumulated during exercise is removed by direct oxidation. However, as the muscle respiration rate decreases, lactate becomes a desirable substrate for hepatic glucose synthesis. Furthermore, improvement in brain function by lactate, particularly, through the expression of vascular endothelial growth factor and brain-derived neurotrophic factor, is being increasingly studied. In addition, it is possible to improve stress-related symptoms, such as depression, by regulating the function of hippocampal mitochondria, and with an increasingly aging society, lactate is being investigated as a preventive agent for brain diseases such as Alzheimer's disease. Therefore, the perception that lactate is equivalent to fatigue should no longer exist. This review focuses on the new perception of lactate and how lactate acts extensively in the skeletal muscles, heart, brain, kidney, and liver. Additionally, lactate is now used to confirm exercise performance and should be further studied to assess its impact on exercise training.

Association Between Lactate and 28-Day Mortality in Elderly Patients with Sepsis: Results from MIMIC-IV Database

INTRODUCTION

This study aimed to explore the association of serum lactate with clinical outcomes in elderly patients with sepsis based on data from the MIMIC-IV database.

METHODS

All elderly patients with sepsis (age ≥ 65 years) were included. Different models were constructed for exploring the relationships between lactate and 28-day mortality. A two-segment linear regression model was performed to verify the threshold effects of lactate on clinical outcomes and smooth curve fitting was performed.

RESULTS

A total of 4199 elderly patients with sepsis were included. The 28-day mortality was 32.22% (n = 1395). After adjustment for all potential cofounders, for each 1 mmol/l increment in lactate, the odds ratio (OR) of 28-day mortality was 1.23 (95% CI 1.18-1.28, P < 0.0001). Smooth fitting curves indicated a non-linear positive relationship between lactate and 28-day mortality. The turning point of lactate level was 5.7 mmol/l: at ≤ 5.7 mmol/l, with each 1 mmol/l increment in lactate, the risk of 28-day mortality increased significantly (OR 1.32, 95% CI 1.25-1.38, P < 0.0001); the significantly positive relationship was still present at lactate > 5.7 mmol/l (OR 1.10, 95% CI 1.04-1.18, P = 0.0019). The area under the ROC curve (AUC) of lactate was 0.618 (95% CI 0.599-0.635) and the cutoff value of lactate was 2.4 mmol/l with a sensitivity of 0.483 and a specificity of 0.687.

CONCLUSION

In elderly patients with sepsis, a non-linear positive relationship was discovered between serum lactate and 28-day mortality. Physicians should be alert to lactate assessment at admission and pay more attention to those patients with higher levels of lactate.

Effects of High-Intensity Exercise on Physiological Indicators of Recovery Period by Wearing Face Masks of Elite Athletes

Athletes need to maintain the necessary physical conditioning for sports performance while wearing face masks to reduce the risk of virus transmission during training and competition during the COVID-19 situation. The quantitative and physiological effects of face masks on exercise capacity needs to be reported. The purpose of this study was to evaluate elite athletes to quantify, in detail, the effect of a KF94 face mask on changes in lactic acid during recovery after high-intensity aerobic exercise. Thirteen elite soft tennis athletes were recruited. A crossover design was used to examine the effects of using a disposable KF94 face mask compared with not masking during exercise. The participants completed a shuttle run test experiment two times during a 3-day period, including 5−10 min of warmup according to their personal preferences. The lactic acid concentration at 20 min of recovery after maximum exercise was 5.98 ± 1.53 mM/L without a mask and 7.61 ± 1.85 mM/L with a KF94 mask (p < 0.001). The maximum laps of shuttle run tests were 101.5 ± 22.5 laps without a mask and 94.2 ± 20.2 laps with a KF94 mask (p < 0.001). Intense exercise after wearing quarantine masks reduces the maximum aerobic exercise ability and decreases the ability to recover lactic acid.

The ChoCO-W prospective observational global study: Does COVID-19 increase gangrenous cholecystitis?

BACKGROUND

The incidence of the highly morbid and potentially lethal gangrenous cholecystitis was reportedly increased during the COVID-19 pandemic. The aim of the ChoCO-W study was to compare the clinical findings and outcomes of acute cholecystitis in patients who had COVID-19 disease with those who did not.

METHODS

Data were prospectively collected over 6 months (October 1, 2020, to April 30, 2021) with 1-month follow-up. In October 2020, Delta variant of SARS CoV-2 was isolated for the first time. Demographic and clinical data were analyzed and reported according to the STROBE guidelines. Baseline characteristics and clinical outcomes of patients who had COVID-19 were compared with those who did not.

RESULTS

A total of 2893 patients, from 42 countries, 218 centers, involved, with a median age of 61.3 (SD: 17.39) years were prospectively enrolled in this study; 1481 (51%) patients were males. One hundred and eighty (6.9%) patients were COVID-19 positive, while 2412 (93.1%) were negative. Concomitant preexisting diseases including cardiovascular diseases (p < 0.0001), diabetes (p < 0.0001), and severe chronic obstructive airway disease (p = 0.005) were significantly more frequent in the COVID-19 group. Markers of sepsis severity including ARDS (p < 0.0001), PIPAS score (p < 0.0001), WSES sepsis score (p < 0.0001), qSOFA (p < 0.0001), and Tokyo classification of severity of acute cholecystitis (p < 0.0001) were significantly higher in the COVID-19 group. The COVID-19 group had significantly higher postoperative complications (32.2% compared with 11.7%, p < 0.0001), longer mean hospital stay (13.21 compared with 6.51 days, p < 0.0001), and mortality rate (13.4% compared with 1.7%, p < 0.0001). The incidence of gangrenous cholecystitis was doubled in the COVID-19 group (40.7% compared with 22.3%). The mean wall thickness of the gallbladder was significantly higher in the COVID-19 group [6.32 (SD: 2.44) mm compared with 5.4 (SD: 3.45) mm; p < 0.0001].

CONCLUSIONS

The incidence of gangrenous cholecystitis is higher in COVID patients compared with non-COVID patients admitted to the emergency department with acute cholecystitis. Gangrenous cholecystitis in COVID patients is associated with high-grade Clavien-Dindo postoperative complications, longer hospital stay and higher mortality rate. The open cholecystectomy rate is higher in COVID compared with non -COVID patients. It is recommended to delay the surgical treatment in COVID patients, when it is possible, to decrease morbidity and mortality rates. COVID-19 infection and gangrenous cholecystistis are not absolute contraindications to perform laparoscopic cholecystectomy, in a case by case evaluation, in expert hands.

Plasma Metabolome Alterations Discriminate between COVID-19 and Non-COVID-19 Pneumonia

Pneumonia is a common cause of morbidity and mortality and is most often caused by bacterial pathogens. COVID-19 is characterized by lung infection with potential progressive organ failure. The systemic consequences of both disease on the systemic blood metabolome are not fully understood. The aim of this study was to compare the blood metabolome of both diseases and we hypothesize that plasma metabolomics may help to identify the systemic effects of these diseases. Therefore, we profiled the plasma metabolome of 43 cases of COVID-19 pneumonia, 23 cases of non-COVID-19 pneumonia, and 26 controls using a non-targeted approach. Metabolic alterations differentiating the three groups were detected, with specific metabolic changes distinguishing the two types of pneumonia groups. A comparison of venous and arterial blood plasma samples from the same subjects revealed the distinct metabolic effects of pulmonary pneumonia. In addition, a machine learning signature of four metabolites was predictive of the disease outcome of COVID-19 subjects with an area under the curve (AUC) of 86 ± 10 %. Overall, the results of this study uncover systemic metabolic changes that could be linked to the etiology of COVID-19 pneumonia and non-COVID-19 pneumonia.

Prognostic value of soluble endoglin in patients with septic shock and severe COVID-19

Sepsis is a clinical syndrome characterized by a dysregulated response to infection. It represents a leading cause of mortality in ICU patients worldwide. Although sepsis is in the point of interest of research for several decades, its clinical management and patient survival are improving slowly. Monitoring of the biomarkers and their combinations could help in early diagnosis, estimation of prognosis and patient's stratification and response to the treatment. Circulating soluble endoglin (sEng) is the cleaved extracellular part of transmembrane glycoprotein endoglin. As a biomarker, sEng has been tested in several pathologic conditions where its elevation was associated with endothelial dysfunction. In this study we have tested the ability of sEng to predict mortality and its correlation with other clinical characteristics in the cohort of septic shock patients (n = 37) and patients with severe COVID-19 (n = 40). In patients with COVID-19 sEng did not predict mortality or correlate with markers of organ dysfunction. In contrast, in septic shock the level of sEng was significantly higher in patients with early mortality (p = 0.019; AUC = 0.801). Moreover, sEng levels correlated with signs of circulatory failure (required dose of noradrenalin and lactate levels; p = 0.002 and 0.016, respectively). The predominant clinical problem in patients with COVID-19 was ARDS, and although they often showed signs of other organ dysfunction, circulatory failure was exceptional. This potentially explains the difference between sEng levels in COVID-19 and septic shock. In conclusion, we have confirmed that sEng may reflect the extent of the circulatory failure in septic shock patients and thus could be potentially used for the early identification of patients with the highest degree of endothelial dysfunction who would benefit from endothelium-targeted individualized therapy.

The potential role of ischaemia-reperfusion injury in chronic, relapsing diseases such as rheumatoid arthritis, Long COVID, and ME/CFS: evidence, mechanisms, and therapeutic implications

Ischaemia–reperfusion (I–R) injury, initiated via bursts of reactive oxygen species produced during the reoxygenation phase following hypoxia, is well known in a variety of acute circumstances. We argue here that I–R injury also underpins elements of the pathology of a variety of chronic, inflammatory diseases, including rheumatoid arthritis, ME/CFS and, our chief focus and most proximally, Long COVID. Ischaemia may be initiated via fibrin amyloid microclot blockage of capillaries, for instance as exercise is started; reperfusion is a necessary corollary when it finishes. We rehearse the mechanistic evidence for these occurrences here, in terms of their manifestation as oxidative stress, hyperinflammation, mast cell activation, the production of marker metabolites and related activities. Such microclot-based phenomena can explain both the breathlessness/fatigue and the post-exertional malaise that may be observed in these conditions, as well as many other observables. The recognition of these processes implies, mechanistically, that therapeutic benefit is potentially to be had from antioxidants, from anti-inflammatories, from iron chelators, and via suitable, safe fibrinolytics, and/or anti-clotting agents. We review the considerable existing evidence that is consistent with this, and with the biochemical mechanisms involved.

Cardiovascular Dysfunction in COVID-19: Association Between Endothelial Cell Injury and Lactate

Coronavirus disease 2019 (COVID-19), an infectious respiratory disease propagated by a new virus known as Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2), has resulted in global healthcare crises. Emerging evidence from patients with COVID-19 suggests that endothelial cell damage plays a central role in COVID-19 pathogenesis and could be a major contributor to the severity and mortality of COVID-19. Like other infectious diseases, the pathogenesis of COVID-19 is closely associated with metabolic processes. Lactate, a potential biomarker in COVID-19, has recently been shown to mediate endothelial barrier dysfunction. In this review, we provide an overview of cardiovascular injuries and metabolic alterations caused by SARS-CoV-2 infection. We also propose that lactate plays a potential role in COVID-19-driven endothelial cell injury.

COVID-19, Cation Dysmetabolism, Sialic Acid, CD147, ACE2, Viroporins, Hepcidin and Ferroptosis: A Possible Unifying Hypothesis

Background: iron and calcium dysmetabolism, with hyperferritinemia, hypoferremia, hypocalcemia and anemia have been documented in the majority of COVID-19 patients at later/worse stages. Furthermore, complementary to ACE2, both sialic acid (SA) molecules and CD147 proved relevant host receptors for SARS-CoV-2 entry, which explains the viral attack to multiple types of cells, including erythrocytes, endothelium and neural tissue. Several authors advocated that cell ferroptosis may be the core and final cell degenerative mechanism.

Methods: a literature research was performed in several scientific search engines, such as PubMed Central, Cochrane Library, Chemical Abstract Service. More than 500 articles were retrieved until mid-December 2021, to highlight the available evidence about the investigated issues.

Results: based on COVID-19 literature data, we have highlighted a few pathophysiological mechanisms, associated with virus-based cation dysmetabolism, multi-organ attack, mitochondria degeneration and ferroptosis. Our suggested elucidated pathological sequence is: a) spike protein subunit S1 docking with sialylated membrane glycoproteins/receptors (ACE2, CD147), and S2 subunit fusion with the lipid layer; b) cell membrane morpho-functional changes due to the consequent electro-chemical variations and viroporin action, which induce an altered ion channel function and intracellular cation accumulation; c) additional intracellular iron concentration due to a deregulated hepcidin-ferroportin axis, with higher hepcidin levels. Viral invasion may also affect erythrocytes/erythroid precursors, endothelial cells and macrophages, through SA and CD147 receptors, with relative hemoglobin and iron/calcium dysmetabolism. AB0 blood group, hemochromatosis, or environmental elements may represent possible factors which affect individual susceptibility to COVID-19.    

Conclusions: our literature analysis confirms the combined role of SA molecules, ACE2, CD147, viroporins and hepcidin in determining the cation dysmetabolism and final ferroptosis in the cells infected by SARS-CoV-2. The altered ion channels and electrochemical gradients of the cell membrane have a pivotal role in the virus entry and cell dysmetabolism, with subsequent multi-organ immune-inflammatory degeneration and erythrocyte/hemoglobin alterations.

Activation of Sphingomyelinase-Ceramide-Pathway in COVID-19 Purposes Its Inhibition for Therapeutic Strategies

Effective treatment strategies for severe coronavirus disease (COVID-19) remain scarce. Hydrolysis of membrane-embedded, inert sphingomyelin by stress responsive sphingomyelinases is a hallmark of adaptive responses and cellular repair. As demonstrated in experimental and observational clinical studies, the transient and stress-triggered release of a sphingomyelinase, SMPD1, into circulation and subsequent ceramide generation provides a promising target for FDA-approved drugs. Here, we report the activation of sphingomyelinase-ceramide pathway in 23 intensive care patients with severe COVID-19. We observed an increase of circulating activity of sphingomyelinase with subsequent derangement of sphingolipids in serum lipoproteins and from red blood cells (RBC). Consistent with increased ceramide levels derived from the inert membrane constituent sphingomyelin, increased activity of acid sphingomyelinase (ASM) accurately distinguished the patient cohort undergoing intensive care from healthy controls. Positive correlational analyses with biomarkers of severe clinical phenotype support the concept of an essential pathophysiological role of ASM in the course of SARS-CoV-2 infection as well as of a promising role for functional inhibition with anti-inflammatory agents in SARS-CoV-2 infection as also proposed in independent observational studies. We conclude that large-sized multicenter, interventional trials are now needed to evaluate the potential benefit of functional inhibition of this sphingomyelinase in critically ill patients with COVID-19.

Catabolism of Hydroxyproline in Vertebrates: Physiology, Evolution, Genetic Diseases and New siRNA Approach for Treatment

Hydroxyproline is one of the most prevalent amino acids in animal proteins. It is not a genetically encoded amino acid, but, rather, it is produced by the post-translational modification of proline in collagen, and a few other proteins, by prolyl hydroxylase enzymes. Although this post-translational modification occurs in a limited number of proteins, its biological significance cannot be overestimated. Considering that hydroxyproline cannot be re-incorporated into pro-collagen during translation, it should be catabolized following protein degradation. A cascade of reactions leads to production of two deleterious intermediates: glyoxylate and hydrogen peroxide, which need to be immediately converted. As a result, the enzymes involved in hydroxyproline catabolism are located in specific compartments: mitochondria and peroxisomes. The particular distribution of catabolic enzymes in these compartments, in different species, depends on their dietary habits. Disturbances in hydroxyproline catabolism, due to genetic aberrations, may lead to a severe disease (primary hyperoxaluria), which often impairs kidney function. The basis of this condition is accumulation of glyoxylate and its conversion to oxalate. Since calcium oxalate is insoluble, children with this rare inherited disorder suffer from progressive kidney damage. This condition has been nearly incurable until recently, as significant advances in substrate reduction therapy using small interference RNA led to a breakthrough in primary hyperoxaluria type 1 treatment.

The role of lactate in sepsis and COVID-19: Perspective from contracting skeletal muscle metabolism

NEW FINDINGS

What is the topic of this review? Lactate is considered an important substrate for mitochondria in the muscles, heart and brain during exercise and is the main gluconeogenetic precursor in the liver and kidneys. In this light, we review the (patho)physiology of lactate metabolism in sepsis and coronavirus disease 2019 (COVID-19). What advances does it highlight? Elevated blood lactate is strongly associated with mortality in septic patients. Lactate seems unrelated to tissue hypoxia but is likely to reflect mitochondrial dysfunction and high adrenergic stimulation. Patients with severe COVID-19 exhibit near-normal blood lactate, indicating preserved mitochondrial function, despite a systemic hyperinflammatory state similar to sepsis.

ABSTRACT

In critically ill patients, elevated plasma lactate is often interpreted as a sign of organ hypoperfusion and/or tissue hypoxia. This view on lactate is likely to have been influenced by the pioneering exercise physiologists around 1920. August Krogh identified an oxygen deficit at the onset of exercise that was later related to an oxygen 'debt' and lactate accumulation by A. V. Hill. Lactate is considered to be the main gluconeogenetic precursor in the liver and kidneys during submaximal exercise, but hepatic elimination is attenuated by splanchnic vasoconstriction during high-intensity exercise, causing an exponential increase in blood lactate. With the development of stable isotope tracers, lactate has become established as an important energy source for muscle, brain and heart tissue, where it is used for mitochondrial respiration. Plasma lactate > 4 mM is strongly associated with mortality in septic shock, with no direct link between lactate release and tissue hypoxia. Herein, we provide evidence for mitochondrial dysfunction and adrenergic stimulation as explanations for the sepsis-induced hyperlactataemia. Despite profound hypoxaemia and intense work of breathing, patients with severe coronavirus disease 2019 (COVID-19) rarely exhibit hyperlactataemia (> 2.5 mM), while presenting a systemic hyperinflammatory state much like sepsis. However, lactate dehydrogenase, which controls the formation of lactate, is markedly elevated in plasma and strongly associated with mortality in severe COVID-19. We briefly review the potential mechanisms of the lactate dehydrogenase elevation in COVID-19 and its relationship to lactate metabolism based on mechanisms established in contracting skeletal muscle and the acute respiratory distress syndrome.