Skeletal muscle structural and energetic characteristics in subjects with sickle cell trait, α-thalassemia, or dual hemoglobinopathy

Lower Muscle and Blood Lactate Accumulation in Sickle Cell Trait Carriers in Response to Short High-Intensity Exercise

It remains unclear whether sickle cell trait (SCT) should be considered a risk factor during intense physical activity. By triggering the polymerization-sickling-vaso-occlusion cascade, lactate accumulation-associated acidosis in response to high-intensity exercise is believed to be one of the causes of complications. However, our understanding of lactate metabolism in response to high-intensity exercise in SCT carriers is incomplete. Thirty male SCT carriers (n = 15) and healthy subjects (n = 15) with and without α-thalassemia performed a 2-min high-intensity exercise. Blood and muscle lactate concentrations were measured at exercise completion. Time courses of blood lactate and glucose concentrations were followed during the subsequent recovery. Additional biochemical analyses were performed on biopsies of the vastus lateralis muscle. SCT was associated with lower blood and muscle lactate concentrations in response to the short high-intensity exercise. Compared to controls, the muscle content among SCT carriers of lactate transporter MCT4 and β2-adrenergic receptor were higher and lower, respectively. During recovery, the lactate removal ability was higher in SCT carriers. In the present study, no effect of α-thalassemia was observed. The lower blood and muscle lactate accumulations in SCT carriers may, to some extent, act as protective mechanisms: (i) against exercise-related acidosis and subsequent sickling, that may explain the relatively rare complications observed in exercising SCT carriers; and (ii) against the deleterious effects of intracellular lactate and associated acidosis on muscle function, that might explain the elevated presence of SCT carriers among the best sprinters.

In vivo muscle function and energetics in women with sickle cell anemia or trait: a 31P-magnetic resonance spectroscopy study

Sickle cell anemia (SCA) is a genetic hemoglobinopathy associated with an impaired oxygen delivery to skeletal muscle that could alter ATP production processes and increase intramuscular acidosis. These alterations have been already reported in the Townes mouse model of SCA but the corresponding changes in humans have not been documented. In the present study, we used 31-phosphorus magnetic resonance spectroscopy to investigate in vivo the metabolic changes induced by a moderate-intensity exercise in twelve SCA patients, eight sickle cell trait (SCT) carriers, and twelve controls women. The rest-exercise-recovery protocol disclosed slight differences regarding phosphocreatine (PCr) consumption and lactate accumulation between SCA patients and controls but these differences did not reach a statistical significance. On that basis, the in vivo metabolic changes associated with a moderate-intensity muscle exercise were slightly altered in SCA patients and SCT carriers but within a normal range. The present results strongly support the fact that a moderate-intensity exercise is safe and could be recommended in stable SCA patients and SCT subjects.NEW & NOTEWORTHY The main finding of the present study was that the metabolic changes associated with a moderate-intensity muscle exercise were slightly modified in stable sickle cell anemia patients and sickle cell trait carriers as compared to controls but still in the normal range. The present results strongly support the safety of a moderate-intensity exercise for stable sickle cell anemia patients and sickle cell trait carriers.

How Sickle Cell Disease Impairs Skeletal Muscle Function: Implications in Daily Life

Sickle cell disease (SCD) is the most frequent life-threatening genetic hemoglobinopathy in the world and occurs due to the synthesis of abnormal hemoglobin S (HbS). hemoglobin S-containing red blood cells (RBC) are fragile, leading to hemolysis and anemia, and adhere to the endothelium, leading to hemorheological and hemodynamical disturbances. In its deoxygenated form, HbS may polymerize, leading to sickling of red blood cells and potentially to vasoocclusive crises. Recent findings observed that SCD patients demonstrate significant skeletal muscle remodeling and display reduced muscle functional capacities, contributing to exercise intolerance and poor quality of life. Although acute high-intensity exercise is not recommended for SCD patients because it may increase the risk of sickling, regular moderate-intensity physical activity could have beneficial effects on skeletal muscle and more generally on the well-being of SCD patients. This article reviews the literature regarding the impact of the disease on muscular tissue characteristics and function, as well as the corresponding implications for SCD patients' quality of life.

The role of nitrite in muscle function, susceptibility to contraction injury, and fatigability in sickle cell mice

Sickle cell disease (SCD) patients can have limited exercise capacity and muscle dysfunction characterized by decreased force, atrophy, microvascular abnormalities, fiber distribution changes, and skeletal muscle energetics abnormalities. Growing evidence suggests that in SCD there is alteration in nitric oxide (NO) availability/signaling and that nitrate/nitrite can serve as a NO reservoir and enhance muscle performance. Here, we examined effects of nitrite on muscle strength, exercise capacity, and on contractile properties of fast-(extensor digitorum longus, EDL) and slow-twitch (soleus) muscles in SCD mice. Compared to controls, homozygotes (sickling) had decreased grip strength, impaired wheel running performance, and decreased muscle mass of fast-twitch, but not slow-twitch muscle. Nitrite treatment yielded increases in nitrite plasma levels in controls, heterozygotes, and homozygotes but decreases in muscle nitrite levels in heterozygotes and homozygotes. Regardless of genotype, nitrite yielded increases in grip strength, which were coupled with increases in specific force in EDL, but not in soleus muscle. Further, nitrite increased EDL, but not soleus, fatigability in all genotypes. Conversely, in controls, nitrite decreased, whereas in homozygotes, it increased EDL susceptibility to contraction-induced injury. Interestingly, nitrite yielded no changes in distances ran on the running wheel. These differential effects of nitrite in fast- and slow-twitch muscles suggest that its ergogenic effects would be observed in high-intensity/short exercises as found with grip force increases but no changes on wheel running distances. Further, the differential effects of nitrite in homozygotes and control animals suggests that sickling mice, which have altered NO availability/signaling, handle nitrite differently than do control animals.

Moderate and intense muscular exercises induce marked intramyocellular metabolic acidosis in sickle cell disease mice

Sickle cell disease (SCD) is associated with an impaired oxygen delivery to skeletal muscle that could alter ATP production processes. The present study aimed to determine the effects of sickle hemoglobin (HbS) on muscle pH homeostasis in response to exercise in homozygous (HbSS, n = 9) and heterozygous (HbAS, n = 10) SCD (Townes) mice in comparison to control (HbAA, n = 10) littermates. Magnetic resonance spectroscopy of phosphorus 31 enabled to measure intramuscular pH and phosphocreatine (PCr) concentration during rest-stimulation-recovery protocols at two different intensities. Maximal activity of some enzymes involved in muscle energetics and content of proteins involved in pH regulation were also investigated. HbSS mice presented a more pronounced exercise-induced intramuscular acidosis, whatever the intensity of exercise. Moreover, the depletion of PCr was also exacerbated in HbSS mice in response to intense exercise as compared with both HbAA and HbAS mice ( P < 0.01). While no difference was observed concerning proteins involved in muscle pH regulation, the activity of enolase (a glycolytic enzyme) was higher in both HbSS and HbAS mice as compared with controls ( P < 0.05). Interestingly, HbAS mice presented also metabolic impairments as compared with their control counterparts. This study has identified for the first time an exacerbated exercise-induced intramuscular acidosis in SCD mice.

NEW & NOTEWORTHY The main finding of the present study was that the exercise-induced intramuscular acidosis was systematically more pronounced in sickle cell disease (SCD) mice as compared with their control counterparts. This result is important since it has been demonstrated in vitro that acidosis can trigger hemoglobin polymerization. From that point of view, our results tend to support the idea that high-intensity exercise may increase the risk of hemoglobin polymerization in SCD.

Negative health implications of sickle cell trait in high income countries: from the football field to the laboratory

Worldwide, sickle cell trait is a highly prevalent gene carrier state. While generally a benign condition with a normal life expectancy, it is becoming increasingly clear that the sickle trait is associated with certain adverse outcomes. This article will focus on three of these outcomes, namely exertional rhabdomyolysis and sudden death, chronic renal dysfunction, and venous thromboembolism. In each case, the epidemiological evidence for the association is reviewed, together with the existing data on potential underlying mechanisms. Because newborn screening programmes for sickle cell anaemia also identify those with sickle cell trait, it is imperative that further studies determine what, if any, preventive measures can be taken to reduce the burden of these uncommon but potentially morbid complications in affected individuals.

Differences in lactate exchange and removal abilities between high-level African and Caucasian 400-m track runners

The present study aimed to investigate (1) whether high-level 400-m track runners of different ethnic origin displayed divergent post-run blood lactate concentrations (p400m[La]) and (2) if this discrepancy was based on differences in lactate exchange and removal abilities. Twenty male African (n = 12) and Caucasian (n = 8) runners, paired in terms of personal record, performed (1) an all-out 400-m run to measure p400m[La] at 3, 5 and 7 min into recovery and (2) a 1-min 25.2 km h(-1) running (not maximal but standardized) exercise followed by 90-min passive recovery to determine individual blood lactate recovery curves (IBLRC). IBLRCs were fitted to a bi-exponential time function: [Formula: see text] where γ 1 and γ 2 denote lactate exchange ability between the previously worked muscles and blood, and overall ability for lactate removal, respectively. The quantity of lactate accumulated at the end of the 1-min exercise (Q LaA) was also estimated. Our study showed that after the all-out 400-m run, p400m[La] was lower in African than in Caucasian runners at 3 and 5 min but not at 7 min into recovery. After the standardized exercise, γ 1 and γ 2 were lower (p < 0.01) and Q LaA was higher (p < 0.05) in African than in Caucasian runners. These data suggest that for similar performance levels, ethnicity involves differences in lactate accumulation, exchange and removal.

Effects of regular physical activity on skeletal muscle structural, energetic, and microvascular properties in carriers of sickle cell trait

To assess the effects of regular physical activity on muscle functional characteristics of carriers of sickle cell trait (SCT), 39 untrained (U) and trained (T) hemoglobin (Hb)AA (CON) and SCT subjects (U-CON, n = 12; U-SCT, n = 8; T-CON, n = 10; and T-SCT, n = 9) performed a graded exercise and a time to exhaustion (Tex) test, and were subjected to a muscle biopsy. Maximal power, total work performed during Tex, citrate synthase and cytochrome c oxidase (COX) activities, respiratory chain complexes I and IV content, and capillary density (CD), diameter (COD), and surface area (CSA) were upregulated by the same proportion in T-CON and T-SCT compared with their untrained counterparts. These proportionally similar differences imply that the observed discrepancies between U-SCT and U-CON remained in the trained subjects. Specifically, both CD and COX remained and tended to remain lower, and both COD and CSA remained and tended to remain higher in T-SCT than in T-CON. Besides, carriers of SCT displayed specific adaptations with regular physical activity: creatine kinase activity; complexes II, III, and V content; and type I fiber surface area and capillary tortuosity were lower or unchanged in T-SCT than in U-SCT. In summary, our results show that 1) carriers of SCT adapted almost similarly to CON to regular physical activity for most of the studied muscle characteristics, 2) oxidative potential remains altered in physically active carriers of SCT compared with HbAA counterparts, and 3) the specific remodeling of muscle microvascular network persists in the trained state.

Sickle cell considerations in athletes

This article highlights the exertional-sickling collapse syndrome in athletes with sickle cell trait (SCT). It covers all aspects of this syndrome, including pathophysiology, new research on microcirculatory changes, clinical features, differential diagnosis, prevention, and treatment. Also covered in this article are other clinical concerns for athletes with SCT, including lumbar myonecrosis, splenic infarction, hematuria, hyposthenuria, and venous thromboembolism. The final section offers practical points on athletes with sickling hemoglobinopathies more serious than SCT.