Structural and functional impairments of skeletal muscle in patients with [PASC], 2023, Colosio et al.

[SNT Gatchaman]

Structural and functional impairments of skeletal muscle in patients with post-acute sequelae of SARS-CoV-2 infection
Marta Colosio ; Lorenza Brocca ; Marco Gatti ; Marianna Neri ; Emanuela Crea ; Francesca Cadile ; Monica Canepari ; Maria Antonietta Pellegrino ; Biagio Polla ; Simone Porcelli ; Roberto Bottinelli

Background: Following acute COVID-19, a substantial proportion of patients showed symptoms and sequelae for several months, namely the post-acute sequelae of COVID-19 (PASC) syndrome. Major phenomena are exercise intolerance, muscle weakness and fatigue. We aimed to investigate the physiopathology of exercise intolerance in patients with PASC syndrome by structural and functional analyses of skeletal muscle.

Methods: At least 3 months after infection, non-hospitalized patients with PASC (n=11,ys:54±11; PASC) and patients without long-term symptoms (n=12,ys:49±9; CTRL) visited the laboratory on four non-consecutive days. Spirometry, lung diffusion capacity and quality of life were assessed at rest. Cardiopulmonary incremental exercise test was performed. Oxygen consumption (VO2) kinetics were determined by moderate-intensity exercises. Muscle oxidative capacity (k) was assessed by near-infrared spectroscopy. Histochemical analysis, O2 flux (JO2) by high-resolution respirometry, and quantification of key molecular markers of mitochondrial biogenesis and dynamics were performed in vastus lateralis biopsies.

Results: Pulmonary and cardiac functions were within normal range in all patients. VO2peak was lower in PASC than CTRL (24.7±5.0vs32.9±7.4mL*min-1*kg-1, respectively, P<.05). VO2 kinetics was slower in PASC than CTRL (41±12vs30±9s-1, P<.05). k was lower in PASC than CTRL (1.54±0.49vs2.07±0.51min-1, P<.05). Citrate synthase, PGC1alfa and JO2 for mitochondrial complex II were significantly lower in PASC vs CTRL (all P<.05).

Conclusion: In our cohort of patients with PASC, we showed limited exercise tolerance mainly due to "peripheral" determinants. Substantial reductions were observed for biomarkers of mitochondrial function, content, and biogenesis. PASC syndrome appears to negatively impact skeletal muscle function, although the disease is an heterogenous condition.

Link | PDF (Journal of Applied Physiology) Paywall

 

[SNT Gatchaman]

Small numbers.

Although correlation does not allow establishment of cause-and-effect, we also found NIRS data were significantly correlated with exercise tolerance, suggesting a potential role of skeletal muscle impairments in determining exercise intolerance in patients with PASC. [...] muscle oxidative capacity estimated in-vivo by NIRS through intermittent arterial occlusions protocol resulted in significantly lower k values in PASC [...] similar to those observed in patients with chronic heart failure or chronic obstructive pulmonary disease.

the speed of adjustment of oxidative metabolism during transitions to moderate-intensity exercise (O2 kinetics), was utilized as a noninvasive evaluation tool for elucidating intramuscular oxidative metabolism impairments and provided further evidences about the contributing factors to exercise intolerance. Results showed significantly slower tau (τ) in PASC

Mitochondrial function assessed by High-Resolution Respirometry revealed lower JO 2 in the ETS condition of complex II and complex I and II together in PASC [...] In such conditions, complexes are uncoupled with ATP production and express the maximal oxidative capacity of the system. Thus, lower values of O2 fluxes in PASC, compared to CTRL, suggest skeletal muscle fibers of PASC are forced to rely more on glycolysis, leading to early fatigue.

results confirm preliminary data observed in one COVID-19 patient immediately after infection)and suggest that altered mitochondrial function might be a phenomenon that occurs early after infection and lasts long after recovery. Similar results were obtained by our group in healthy subjects after 21 days of bed rest

Pro-fission protein levels (pDRP1(Ser616), and FIS1) were higher whereas pro-fusion OPA1 protein levels were lower in PASC. [...] confirm previous hypotheses suggesting a pro-fission shift in mitochondrial dynamics when a condition of altered mitochondrial function was present. [...] speculate that PASC, compared to CTRL, presented more damaged mitochondria.

 

[SNT Gatchaman]

It has been argued by [...] that deconditioning could be responsible for diminished exercise tolerance in patients with PASC. Following bed rest, which serves as a major model of human disuse, muscle fiber atrophy, lower O2peak , lower PGC1α expression, and impaired mitochondrial function, specifically submaximal concentration of ADP, were found. These findings mirror observations of patients with PASC in the present study.

However [...] several findings support the idea that deconditioning is unlikely to be a major determinant of mitochondrial dysfunction in our patients

First, IPAQ data from PASC suggest they didn’t change the amount of physical activity performed during everyday life. Subject assessments revealed that activity levels appeared similar between the weeks before the infection and during the period when patients were tested.

(Good to see patient reports being listened to here.)

Secondly, it was not possible to observe a classic impairment in the cardiovascular response to exercise which usually characterizes deconditioning. Indeed, the HR vs. O2 and CO vs. O2 relationships in PASC were not different from those observed in healthy subjects.

Finally, the notion that inactivity was not the primary cause of the impairments observed in PASC is also supported by ex-vivo analyses. A shift from slow to fast muscle phenotype, which can generally be observed in cases of disuse, was not evident

 

[Arnie Pye]

I always wonder which meaning of "functional" is being used in research papers because doctors often don't use the word in the same way that normal/ordinary people do. And I know doctors create that confusion in patients deliberately which I think is appalling.

 

[Hutan]

University of Pavia and University of Milan. We've been seeing a few Long Covid studies from Italy.

As SNT says, only 11 people with Long covid, non-hospitalised, which is probably too small to find many issues, given that they didn't even stratify on the presence or absence of PEM.

54 years +- 11 years, so, quite old on average. I think age can serve to confound ME/CFS symptoms somewhat - eventually even healthy people probably start to look a bit like a person with ME/CFS. The controls were a bit younger (49 years +- 9 years). I don't know what the +-'s are in Table 1 (actual range, 95%, SD, SE?) - I couldn't find it stated in the table, in the caption or the text. (I found it in methodology - ranges are SDs unless otherwise stated.)

Gender mix: 50% women in controls; 64% women in PASC.

A pretty extensive range of investigations were done.

 

[Sean]

the speed of adjustment of oxidative metabolism during transitions to moderate-intensity exercise (O2 kinetics)

That is an interesting angle.

 

[Hutan]

70% of PASC reported fatigue.

I'm plodding my way through these findings incredibly slowly today.

IPAQ score was not different between CTRL and 441 PASC both before infection (1797 ± 450 MET-min/week and 1527 ± 407 MET-min/week, 442 respectively) and at the time of examination (1680 ± 443 MET-min/week and 1515 ± 414 MET-443 min/week, respectively).

That's the Physical Activity Questionnaire results. Not much difference between the controls and PASC, even after PASC onset. I wouldn't necessarily be so trusting of what people report about their physical activity, but I guess we can assume that the PASC people were, on average, not abnormally active or underactive before illness onset, and that the PASC people didn't curl up in bed, desperately afraid of any sort of exertion after illness onset. I think we can also assume that the PASC people were relatively mildly affected.

There was a big drop in average reported physical activity in both the controls and PASC after the Covid-19 infection. So, I wonder if all of the controls were as symptom free as they might have thought. Or perhaps it is harder to overestimate's one physical activity when you are thinking about last week, rather than 9 months ago.

Lung function wasn't remarkably different between groups and suggested both groups had very good lung function.

CPET - Part 1

Main pulmonary, cardiovascular and metabolic data are presented in Table 2. ሶO2peak values, normalized per body mass, were higher in CTRL than PASC (32.9 ± 7.4 vs 24.7 ± 5.0 mL* min- 1*kg-1, respectively; P = 0.01). Peak values of [La]b (9.02 ± 1.72 vs 8.13 ± 1.02 mmol*L-1) and RPE (18 ± 1 vs 18 ± 2) were not different between CTRL and PASC. HRpeak was 99 ± 6 % and 96 ± 12 % of predicted in CTRL and PASC, respectively. GET was not different among groups, occurring at 75 ± 7 % of ሶO2peak and 64 ± 9 % of Wpeak in both groups. Δ[HHbMb]peak data, expressed as % of values obtained during prolonged ischemia, were significantly lower in PASC (Table 1).

VO2max were higher in the controls (32.9) than in the PASC (24.7). That's not surprising.

[La]b - that's lactate, sampled from a warmed ear lobe, sampled at rest and up to 7 minutes after exercise. The values weren't statistically different. I think that's important to note. A lot of people talk about lactate levels being part of ME/CFS, but I think that's based on the feeling of heaviness. I think the evidence for blood lactate levels being abnormal in people with ME/CFS is very weak.

RPE - that's perceived exertion at the end of the exertion, the same in two groups.

Peak Heart rate as a percentage of predicted HRpeak - 99% in CTRL, 96% PASC

GET - no, not that GET. It's Gas Exchange Threshold. It's the same as the ventilatory threshold and roughly the same as the anaerobic threshold. Here it was calculated using the slope method. It's expressed here as a percentage of VO2max and of work rate. They found that both numbers were the same in the two groups. So, that's a bit different to what has often been reported in ME/CFS, which is that the ventilatory threshold occurs at a lower workrate. However, this was just one day of tests, and participants were told not to do strenuous exercise for 48 hours before the test. (I do find it a bit surprising that both groups would not only have the same GET expressed as a percentage of both V02max and of work rate, with the exact same standard deviations. I think they might have not reported that accurately.)

Δ[HHbMb]peak data, expressed as % of values obtained during prolonged ischemia, were significantly lower in PASC

Here's an interesting difference. From Table 2: 61%+-13 for CTRL; 45%+-9 for PASC.
The measure relates to the relative concentrations of de-oxygenated haemoglobin and myoglobin and oxygenated haemoglobin and myoglobin in an outer thigh muscle. The measure is the peak muscle deoxygenation during the exercise test, expressed as a percentage of a value obtained by essentially constricting blood supply at rest for a few minutes until the de-oxygenated/oxygenated ratio reached a plateau. So, this value is regarded as a measure of skeletal muscle oxygen extraction.

This seems like a useful measure - it's not invasive. It's measured using light. The PASC people had less muscle oxygenation. There's no individual data, but there does look to be good separation of the mean values for the two groups, and the standard deviations are tight.

I want to see this measure done in lots of ME/CFS and LC studies. To me, it explains a lot of my symptoms. I've said before, my symptoms are a lot like what it's like when doing things at high altitude. And the tendency for numbness, and pins and needles, in limbs; the lack of coordination with repeated muscle use. And that makes sense if oxygen isn't making it into tissues.

 

[Hutan]

I've made a thread to discuss what I think is that important finding of the reduced oxygen extraction in the people with Long covid:
Muscle oxygenation [as assessed by NIRS - Near Infra-Red Spectroscopy]

 

[SNT Gatchaman]

Note if it was truly paywalled originally, it's not now. PDF here.

 

[SNT Gatchaman]

Letter to the editor, includes —

A second limitation is that mood disorders following severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection were not considered to be a cause of exercise intolerance or at least contributor to reduced exercise performance. It would have been useful to apply some of the depression scores, such as the patient health questionnaire-9 (PHQ-9), the Hamilton depression scale (HDS), or Becks depression inventory (BDI), to confirm or rule out depression as a trigger for exercise intolerance.

A third limitation is that central nervous system (CNS) causes of exercise intolerance were not considered and not evaluated. Since SARS-CoV-2 infections are often complicated by CNS disease, such as stroke, bleeding, venous sinus thrombosis, encephalitis, meningitis, acute disseminated encephalomyelitis (ADEM), AHLE, AHNE, ANE, multiple sclerosis, neuromyelitis optica, or MOG-disease, and others (2), it is crucial to assess whether there was clinically manifest or subclinical CNS involvement during the SARS-CoV-2 infection that triggered PASC and therefore could contribute to exercise intolerance three months later.

Since many patients receive sedatives, anxiolytics, antidepressants, hypnotics, and neuroleptics against psychiatric consequences of a SARS-CoV-2 infection, it is imperative that the current medication is provided for all 11 patients. In addition to psychotropic drugs, there are also numerous other medications that can be responsible for exercise intolerance, such as immunosuppressants and immunomodulatory agents, steroids, antiepileptics, and antibiotics.

In summary, the interesting study carries some weaknesses that may confound the results. Before generalizing conclusions are drawn, the objections should be taken into account and the sensible aim of the study should be reassessed.

 

[SNT Gatchaman]

Author reply, includes —

In our study, we recruited eleven (n = 11) nonhospitalized patients with PASC and twelve (n = 12) patients without long-term symptoms (CTRL). All participants were tested several months (8 ± 2) after acute infection. Pulmonary and cardiac functions were within normal range in all patients. In PASC, the cardiopulmonary exercise test combined with some functional biomarkers related to muscle oxidative metabolism showed a limited exercise tolerance mainly due to “peripheral” determinants, and a muscle biopsy suggested a major impairment at the skeletal muscle level, showing impaired mitochondrial function and reduced markers of mitochondrial biogenesis.

As highlighted in the limitations section, we are aware that PASC syndrome is a highly heterogeneous condition, and other organs’ dysfunction may contribute to limited exercise tolerance. In our study, inclusion and exclusion criteria were purposely highly selective to reduce the influence of confounding factors on our results. Many patients who underwent moderate/severe consequences in the acute phase of the SARS-CoV-2 infection, as well as patients with a history of anemia; relevant preexisting cardiac, respiratory, or musculoskeletal comorbidities; use of respiratory assist device; hospitalization; and glucocorticoid therapy, were excluded.

No patients had a history of central nervous system diseases, clinical manifestations of peripheral nervous system alterations, or other potential causes of exercise intolerance, as highlighted in Table 1 of our study, reporting comorbidities, concomitant medication, and laboratory results of PASC and CTRL. In addition, mood disorders were not present in our patients with PASC because an average value of 1.5 on a score of 5 was present in the anxiety/depression dimension of the 5Q-5D-5L questionnaire. Thus, in our cohort of patients, exercise intolerance was mainly associated with impairments in skeletal muscle function. In our opinion, the finding that skeletal muscle impairment per se can be the major determinant of PASC syndrome in a homogeneous cohort of patients selected to rule out potential confounding factors is a strength of our study, although we know that muscle alterations alone cannot explain such a complex phenomenon in all cohorts of patients with PASC.

Thus, we thank Dr. Finsterer and Dr. Scorza for extending the conversation, and appreciate the attention given to our work. However, we believe that impaired skeletal muscle function and alterations in mitochondrial function and mitochondrial dynamics were major determinants of limited exercise capacity in the cohort of recruited patients with PASC.