Studies on the possible role of thyroid hormone in altered muscle protein turnover during sepsis

Causal association between thyroid dysfunction and sepsis: a two-sample mendelian randomization study

Background

The causal association between thyroid dysfunction (including hyperthyroidism and hypothyroidism) and sepsis is controversial in previous studies. Therefore, we used Mendelian randomization (MR) to explore the causal association between hyperthyroidism or hypothyroidism and the susceptibility to four distinct subtypes of sepsis (streptococcal sepsis, puerperal sepsis, asthma-associated pneumonia or sepsis, and other sepsis).

Methods

In our research, we conducted two-sample Mendelian randomization (MR) analyses utilizing publicly available genome-wide association studies (GWAS) data from Sakaue et al. and the Finnish database to investigate the potential causal associations between hyperthyroidism, hypothyroidism, and each of the four distinct subtypes of sepsis, in addition to reverse MR analyses of the positive results to examine the existence of reverse causality.

Results

Genetic hypothyroidism was causally related to the development of asthma-associated pneumonia or sepsis (ORIVW: 1.097, 95% CI: 1.024 to 1.174, P = 0.008); hypothyroidism was significantly associated with the development of other sepsis (ORIVW: 1.070, 95% CI: 1.028 to 1.115, P < 0.001). In addition, sensitivity analysis substantiated the robustness of these two MR findings, with no evidence of horizontal pleiotropy observed (P > 0.05). MR Egger regression analysis demonstrated no heterogeneity between instrumental variables (IVs). Inverse MR results confirmed no reverse causality between hypothyroidism and asthma-associated pneumonia or sepsis, or between hypothyroidism and other sepsis. The findings of this study also unveiled that there is no evidence of a causal link between hypothyroidism and the development of streptococcal sepsis or puerperal sepsis. Additionally, the research provided evidence indicating the absence of a causal relationship between hyperthyroidism and streptococcal sepsis, puerperal sepsis, asthma-associated pneumonia or sepsis, and other sepsis.

Conclusions

This study identified a causal link between hypothyroidism and the occurrence of asthma-associated pneumonia or sepsis, and other sepsis, but not with the development of streptococcal sepsis and puerperal sepsis. Moreover, our findings did not reveal any causal association between hyperthyroidism and streptococcal sepsis, puerperal sepsis, asthma-associated pneumonia or sepsis, and other sepsis.

Sloan SN, Stahl G, Johnson K, Goade S, Arnce R. A Retrospective Investigation: Outcome Comparisons Between Septic Patients With and Without Secondary Diagnosis of Hypothyroidism From a Rural Midwest Hospital

Background

Sepsis morbidity and mortality rates have remained high despite recent developments in clinical guidelines aimed to curtail this disease process. Understanding how sepsis interacts with comorbidities and pre-existing disease states is necessary for improving sepsis treatment. Accounting for specific pre-existing conditions in the treatment of sepsis patients may not only improve patient outcomes but also reduce healthcare costs by preventing possible complications. We sought to evaluate whether the presence of hypothyroidism affects outcomes in septic patients.

Methods

In this retrospective observational study, we analyzed the patient dataset from a not-for-profit rural hospital from January 2019 through June 2020. We chose the initial patient sample based on International Classification of Disease (ICD10) codes for sepsis. We then used the ICD10 code for hypothyroidism within that sample to identify the septic patients with hypothyroidism. We did two-sample proportion summary hypothesis tests to identify differences in mortality and 30-day readmission rates.

Results

In our dataset, we had 1,122 patients with sepsis, of whom 225 had hypothyroidism. There was no difference in sepsis outcomes between patients who had hypothyroidism compared to patients who did not have hypothyroidism. Additionally, we did not find sufficient evidence to conclude that the patient’s sex affects sepsis outcomes in hypothyroid patients. 

Conclusion 

Within this Midwest population, the sepsis outcomes were not impacted by having hypothyroidism as a secondary diagnosis. Additionally, there was no sufficient evidence to suggest an impact on sepsis outcomes based on sex, either male or female, when considering concomitant hypothyroidism.

Dexamethasone stimulates store-operated calcium entry and protein degradation in cultured L6 myotubes through a phospholipase A(2)-dependent mechanism

Muscle wasting in various catabolic conditions is at least in part regulated by glucocorticoids. Increased calcium levels have been reported in atrophying muscle. Mechanisms regulating calcium homeostasis in muscle wasting, in particular the role of glucocorticoids, are poorly understood. Here we tested the hypothesis that glucocorticoids increase intracellular calcium concentrations in skeletal muscle and stimulate store-operated calcium entry (SOCE) and that these effects of glucocorticoids may at least in part be responsible for glucocorticoid-induced protein degradation. Treatment of cultured myotubes with dexamethasone, a frequently used in vitro model of muscle wasting, resulted in increased intracellular calcium concentrations determined by fura-2 AM fluorescence measurements. When SOCE was measured by using calcium "add-back" to muscle cells after depletion of intracellular calcium stores, results showed that SOCE was increased 15-25% by dexamethasone and that this response to dexamethasone was inhibited by the store-operated calcium channel blocker BTP2. Dexamethasone treatment stimulated the activity of calcium-independent phospholipase A(2) (iPLA(2)), and dexamethasone-induced increase in SOCE was reduced by the iPLA(2) inhibitor bromoenol lactone (BEL). In additional experiments, treatment of myotubes with the store-operated calcium channel inhibitor gadolinium ion or BEL reduced dexamethasone-induced increase in protein degradation. Taken together, the results suggest that glucocorticoids increase calcium concentrations in myocytes and stimulate iPLA(2)-dependent SOCE and that glucocorticoid-induced muscle protein degradation may at least in part be regulated by increased iPLA(2) activity, SOCE, and cellular calcium levels.

Response of leucine metabolism to hyperinsulinemia in hypothyroid patients before and after thyroxine replacement

We have investigated the effect of hypothyroidism and insulin on protein metabolism in humans. Six hypothyroid patients were studied in a postabsorptive state before and after 5 months of regular treatment for hypothyroidism (153 +/- 17 microg/day of L-T4). The effect of insulin was assessed under hyperinsulinemic euglycemic and eukalemic conditions. Insulin was infused for 140 min at 0.0063 +/- 0.0002 nmol/kg x min. An amino acid infusion was used to blunt insulin-induced hypoaminoacidemia. Whole body protein turnover was measured using L-[1-13C] leucine. When compared to L-T4-induced subclinical thyrotoxic state, hypothyroidism induced a significant decrease (P < 0.05) in leucine endogenous appearance rate (a reflection of proteolysis; 0.89 +/- 0.09 vs. 1.33 +/- 0.05 micromol/kg x min), oxidation (0.19 +/- 0.02 vs. 0.25 +/- 0.03 micromol/kg x min), and nonoxidative disposal (a reflection of protein synthesis; 0.87 +/- 0.11 vs. 1.30 +/- 0.05 micromol/ kg x min). Insulin lowered proteolysis during both the subclinical thyrotoxic and hypothyroid states. Hypothyroidism impaired the antiproteolytic effects of insulin. Thyroid hormones are, therefore, essential for the normal antiproteolytic action of insulin.

Hormonal and metabolic response to operative stress in the neonate

It is evident from this review that newborns, even those born prematurely, are capable of mounting an endocrine and metabolic response to operative stress. Unfortunately, many of the areas for which a relatively well-characterized response exists in adults are poorly documented in neonates. As is the case in adults, the response seems to be primarily catabolic in nature because the combined hormonal changes include an increased release of catabolic hormones such as catecholamines, glucagon, and corticosteroids coupled with a suppression of and peripheral resistance to the effects of the primary anabolic hormone, insulin.

Effect of catabolic hormone infusion on protein turnover and amino acid uptake in skeletal muscle

Increased plasma levels of the catabolic hormones glucagon, epinephrine, and cortisol have been implicated in mediating various metabolic alterations in trauma and sepsis. Their role in altered protein turnover and amino acid transport in skeletal muscle during sepsis, however, is not known. In the current study, rats were infused with a mixture of the catabolic hormones for 16 hours. Control animals were infused with vehicle solution. Protein synthesis and degradation rates were measured in incubated, intact soleus muscles as incorporation of 14C-phenylalanine into protein and release of tyrosine into incubation medium, respectively. Muscle amino acid uptake was determined by measuring the intracellular to extracellular ratio of [3H]-alpha-aminoisobutyric acid after incubation for 2 hours. Infusion of catabolic hormones for 16 hours resulted in elevated plasma glucose and lactate levels, reduced plasma concentrations of most amino acids, and accelerated muscle protein breakdown, similar to previous findings in septic rats. Protein synthesis rates and amino acid uptake in incubated muscles were not significantly different in control and hormone-infused rats. The current study suggests that increased muscle proteolysis in sepsis and severe injury may be mediated in part by catabolic hormones. In contrast, reduced muscle protein synthesis and amino acid uptake are probably signaled by other substances or mechanisms.

Effect of propranolol on nitrogen and energy metabolism in sepsis

Pharmacologic therapy designed to block adrenergic activity or alter hormonal milieu may modulate energy and protein metabolism in stress. The metabolic effects of propranolol (beta adrenergic receptor blocker) in sepsis was investigated in 22 well-nourished rats that underwent superior vena caval cannulation, cecal ligation, and puncture. Animals were randomly assigned to receive either a continuous infusion of 0.7 mg/day of propranolol combined with parenteral nutrition (n = 11) or parenteral nutrition alone (n = 11). Both groups received isocaloric, isonitrogenous, isovolemic, parenteral nutrition post-operatively for 24 hr. Nitrogen balance was better for the propranolol group than for the control group (+743 +/- 84 mg/kg/day versus +300 +/- 63 mg/kg/day, respectively, P less than 0.05). A significant difference between the pharmacologic therapy and control groups was noted for urinary 3-methylhistidine excretion versus control (0.99 +/- 0.08 micrograms/kg/day versus 7.5 +/- 0.37 micrograms/kg/day, respectively, P less than 0.01). Measured energy expenditure was similar for both pharmacologic therapy and control groups (149 +/- 20 kcal/kg/day versus 134 +/- 11 kcal/kg/day, respectively, P = N.S.). No statistically significant difference was demonstrated for 24-hr survival between propranolol and control groups (73 and 64%, respectively). Continuous, low-dose propranolol promotes nitrogen retention and decreases 3-methylhistidine excretion without altering energy expenditure in parenterally fed septic rats.

The effect of sepsis in rats on skeletal muscle protein synthesis in vivo and in periphery and central core of incubated muscle preparations in vitro

Recent studies demonstrated the development of a central, hypoxic core in incubated rat skeletal muscles. The influence of a central core on changes in protein synthesis rate, observed in incubated muscles from septic rats, is not known. In the present study, intact soleus muscles from 40 to 60-g sham-operated control rats and from septic rats (16 hours after cecal ligation and puncture) were incubated in vitro in a flaccid or stretched state. Protein synthesis rate was determined in whole muscle and in the central core and periphery of the muscle by measuring incorporation of 14C-phenylalanine into protein. Protein synthesis rate in vivo was measured with a flooding-dose technique using 3H-phenylalanine. The development of a central, hypoxic core in incubated muscles was assessed histochemically by staining the muscles for alpha-glucan phosphorylase activity. A central core with loss of alpha-glucan phosphorylase activity was noted after incubation for 30 minutes in both control and septic muscles. The protein synthesis rate was lower in the central core than in the periphery of incubated flaccid control muscles. In all other in vitro muscle preparations, however, there were no significant differences in protein synthesis rate among whole muscles, central core and periphery. Protein synthesis rate in septic muscles was reduced to a similar extent, approximately 20%, in vivo and in the different in vitro preparations, both when measured in whole muscle and in the central core or periphery.(ABSTRACT TRUNCATED AT 250 WORDS)