Longitudinal Changes in Glucose Metabolism of Denervated Muscle after Complete Peripheral Nerve Injury

Clinical scenarios of unusual FDG uptake in muscle

Glucose is essential for muscle function and its uptake is influenced by aerobic conditions, hormonal regulations, and exercise. 18F-Fluorodeoxyglucose (FDG), a glucose analog used in PET/CT scans, can show incidental uptake in muscles, and thus careful interpretation is required to avoid misdiagnosis. Proper patient preparation and understanding of the clinical scenarios affecting FDG uptake are crucial for accurate PET/CT interpretation, thus ensuring precise diagnoses and avoiding unnecessary interventions. This review emphasizes the need to consider patient-specific factors in evaluating incidental FDG uptake in muscle.

FDG uptake in the cervical muscles after neck dissection: imaging features and postoperative natural course on 18F‑FDG‑PET/CT

PURPOSE

This study aimed to assess the imaging features and postoperative natural course of 18F-fluorodeoxyglucose (FDG) uptake in the cervical muscles after neck dissection.

MATERIALS AND METHODS

This study included 83 patients who underwent preoperative and postoperative 18F-FDG-PET/CT and were diagnosed with head and neck malignancy after neck dissection. Postoperative 18F-FDG-PET/CT was performed within 5 years after neck dissection. Preoperative and postoperative FDG uptake of the trapezius, sternocleidomastoid, scalene, pectoralis major, and deltoid muscles was visually assessed. Increased postoperative uptake was visually defined as higher postoperative FDG uptake than the preoperative one in the corresponding muscle. The maximum standardized uptake value (SUVmax) was measured in cases with increased postoperative uptakes.

RESULTS

Increased postoperative uptakes were observed in 43 patients (52%). The trapezius (31/83, 37%), sternocleidomastoid (19/83, 23%), and scalene (12/83, 14%) muscles were involved, as opposed to the pectoralis major and deltoid muscles were not. Increased postoperative uptakes were observed on the dissected side in all 43 patients. Significant differences between SUVmax estimated from the mixed-effects model and postoperative months were observed in the trapezius muscle (Coefficient (β) = -0.038; 95% confidence interval (CI): [-0.047, -0.028]; p < 0.001) and sternocleidomastoid muscle (β =  -0.015; 95% CI: [-0.029, -0.001]; p = 0.046).

CONCLUSIONS

Increased postoperative uptakes in the cervical muscles were observed on the dissected side in approximately half of the patients after neck dissection. The SUVmax in the trapezius and sternocleidomastoid muscles decreased after surgery over time.

Comparative neuroprotective effects of Cerebrolysin, dexamethasone, and ascorbic acid on sciatic nerve injury model: Behavioral and histopathological study

Background

The majority of the suggested experimental modalities for peripheral nerve injury (PNI) result in varying degrees of recovery in animal models; however, there are not many reliable clinical pharmacological treatment models available. To alleviate PNI complications, research on approaches to accelerate peripheral nerve regeneration is encouraged. Cerebrolysin, dexamethasone, and ascorbic acid (vitamin C) drug models were selected in our study because of their reported curative effects of different mechanisms of action.

Methodology

A total of 40 adult male albino rats were used in this study. Sciatic nerve crush injury was induced in 32 rats, which were divided equally into four groups (model, Cerebrolysin, dexamethasone, and vitamin C groups) and compared to the sham group (n = 8). The sciatic nerve sensory and motor function regeneration after crushing together with gastrocnemius muscle histopathological changes were evaluated by the sciatic function index, the hot plate test, gastrocnemius muscle mass ratio, and immune expression of S100 and apoptosis cascade (BAX, BCL2, and BAX/BCL2 ratio).

Results

Significant improvement of the behavioral status and histopathological assessment scores occurred after the use of Cerebrolysin (as a neurotrophic factor), dexamethasone (as an anti-inflammatory), and vitamin C (as an antioxidant). Despite these seemingly concomitant, robust behavioral and pathological changes, vitamin C appeared to have the best results among the three main outcome measures. There was a positive correlation between motor and sensory improvement and also between behavioral and histopathological changes, boosting the effectiveness, and implication of the sciatic function index as a mirror for changes occurring on the tissue level.

Conclusion

Vitamin C is a promising therapeutic in the treatment of PNI. The sciatic function index (SFI) test is a reliable accurate method for assessing sciatic nerve integrity after both partial disruption and regrowth.

Repetitive transcranial magnetic stimulation regulates neuroinflammation, relieves hyperalgesia and reverses despair-like behaviour in chronic constriction injury rats

Repetitive transcranial magnetic stimulation (rTMS) could effectively relieve the pain and depression in neuropathic pain (NP) patients. However, the specific treatment parameters and exact mechanism are still unclear. Our purpose is to observe the effects of rTMS on pain and despair-like behaviour in chronic constriction injury (CCI) rats and explore its possible mechanism. Thirty-two 8-week-old male Sprague-Dawley rats were randomly divided into four groups: sham operation group (S, n = 8), CCI group (n = 8), 1 Hz-rTMS group (n = 8) and 10 Hz-rTMS group (n = 8). The rTMS was applied to the left dorsal anterior agranular insular (AId) 1 week after the operation, once a day, 5 days/week for 4 consecutive weeks. Mechanical hyperalgesia, despair-like behaviours and sciatic nerve function were used to evaluate the effects of rTMS. Besides, glucose metabolism, the metabotropic glutamate receptors 5 (mGluR5), N-Methyl-D-Aspartic acid receptor type 2B (NMDAR2B), tumour necrosis factor-α (TNF-α), interleukin-6 (Ll-6) and interleukin-1β (Ll-1β) in AId were tested to explore the possible mechanism. Compared with 1 Hz-rTMS, the rats of 10 Hz-rTMS had higher the mechanical hyperalgesia, higher sugar preference and shorter swimming immobility time. Besides, the expressions of mGluR5, NMDAR2B, TNF-α, Ll-1β and Ll-6 both in 1 Hz-rTMS and 10 Hz-rTMS groups were reduced compared with the CCI group; the 10 Hz-rTMS group had a more decrease than that of 1 Hz-rTMS. Furthermore, the [18]F-FDG uptake was lower than that in the 1 Hz-rTMS group. Compared with 1 Hz-rTMS, 10 Hz-rTMS could more effectively relieve mechanical hyperalgesia and reverse despair-like behaviour in rats. The mechanism could be related to regulating mGluR5/NMDAR2B-related inflammatory signalling pathways in the AId.

Insulin Resistance Is Not Sustained Following Denervation in Glycolytic Skeletal Muscle

Denervation rapidly induces insulin resistance (i.e., impairments in insulin-stimulated glucose uptake and signaling proteins) in skeletal muscle. Surprisingly, whether this metabolic derangement is long-lasting is presently not clear. The main goal of this study was to determine if insulin resistance is sustained in both oxidative soleus and glycolytic extensor digitorum longus (EDL) muscles following long-term (28 days) denervation. Mouse hindlimb muscles were denervated via unilateral sciatic nerve resection. Both soleus and EDL muscles atrophied ~40%. Strikingly, while denervation impaired submaximal insulin-stimulated [3H]-2-deoxyglucose uptake ~30% in the soleus, it enhanced submaximal (~120%) and maximal (~160%) insulin-stimulated glucose uptake in the EDL. To assess possible mechanism(s), immunoblots were performed. Denervation did not consistently alter insulin signaling (e.g., p-Akt (Thr308):Akt; p-TBC1D1 [phospho-Akt substrate (PAS)]:TBC1D1; or p-TBC1D4 (PAS):TBC1D4) in either muscle. However, denervation decreased glucose transporter 4 (GLUT4) levels ~65% in the soleus but increased them ~90% in the EDL. To assess the contribution of GLUT4 to the enhanced EDL muscle glucose uptake, muscle-specific GLUT4 knockout mice were examined. Loss of GLUT4 prevented the denervation-induced increase in insulin-stimulated glucose uptake. In conclusion, the denervation results sustained insulin resistance in the soleus but enhanced insulin sensitivity in the EDL due to increased GLUT4 protein levels.

18 F-FDG uptake in denervated muscles of patients with peripheral nerve injury

OBJECTIVE

We aimed to investigate the clinical significance of increased uptake in ¹⁸ F-fluorodeoxyglucose positron emission tomography in patients with peripheral nerve lesions.

METHODS

We selected patients with unilateral peripheral nerve lesions confirmed with electromyography who had undergone ¹⁸ F-fluorodeoxyglucose positron emission tomography covering the lesions. In the denervated muscles and their contralateral corresponding pairs, a mean (SUVmean) and maximum standardized uptake value (SUVmax) were obtained from ¹⁸ F-fluorodeoxyglucose positron emission tomography images. We analyzed the difference in these values between the denervated and normal muscles. The lesion-to-normal ratio of the SUVmean (LNRmean) between each muscle pair was also obtained. Subgroup analysis was performed to find whether these three parameters were related to severity, abundance of abnormal spontaneous activity, and etiology.

RESULTS

Twenty-three patients with 38 denervated muscles were included. Compared to their normal counterparts, the denervated muscles showed significantly higher SUVmax (1.33 ± 0.49 vs. 1.10 ± 0.37, n = 38, P < 0.001) and SUVmean (0.91 ± 0.31 vs. 0.77 ± 0.28, n = 38, P < 0.001). The muscles with severe neuropathy showed significantly higher LNRmean than those with mild neuropathy (1.30 ± 0.36, n = 19 vs. 1.11 ± 0.24, n = 19; P = 0.046), and the muscles with traumatic neuropathy showed significantly higher LNRmean than those with nontraumatic neuropathy (1.32 ± 0.28, n = 13 vs. 1.14 ± 0.33, n = 23; P = 0.015).

INTERPRETATION

Denervated muscles with peripheral nerve injury showed higher uptake than normal muscles in ¹⁸ F-fluorodeoxyglucose positron emission tomography, and this was associated with severity and etiology.

Key Glycolytic Metabolites in Paralyzed Skeletal Muscle Are Altered Seven Days after Spinal Cord Injury in Mice

Spinal cord injury (SCI) results in rapid muscle atrophy and an oxidative-to-glycolytic fiber-type shift. Those with chronic SCI are more at risk for developing insulin resistance and reductions in glucose clearance than able-bodied individuals, but how glucose metabolism is affected after SCI is not well known. An untargeted metabolomics approach was utilized to investigate changes in whole-muscle metabolites at an acute (7-day) and subacute (28-day) time frame after a complete T9 spinal cord transection in 20-week-old female C57BL/6 mice. Two hundred one metabolites were detected in all samples, and 83 had BinBase IDs. A principal components analysis showed the 7-day group as a unique cluster. Further, 36 metabolites were altered after 7- and/or 28-day post-SCI (p values <0.05), with 12 passing further false discovery rate exclusion criteria; of those 12 metabolites, three important glycolytic molecules-glucose and downstream metabolites pyruvic acid and lactic acid-were reduced at 7 days compared to those values in sham and/or 28-day animals. These changes were associated with altered expression of proteins associated with glycolysis, as well as monocarboxylate transporter 4 gene expression. Taken together, our data suggest an acute disruption of skeletal muscle glucose uptake at 7 days post-SCI, which leads to reduced pyruvate and lactate levels. These levels recover by 28 days post-SCI, but a reduction in pyruvate dehydrogenase protein expression at 28 days post-SCI implies disruption in downstream oxidation of glucose.

Ascorbic Acid Facilitates Neural Regeneration After Sciatic Nerve Crush Injury

Ascorbic acid (AA) is an essential micronutrient that has been safely used in the clinic for many years. The present study indicates that AA has an unexpected function in facilitating nerve regeneration. Using a mouse model of sciatic nerve crush injury, we found that AA can significantly accelerate axonal regrowth in the early stage [3 days post-injury (dpi)], a finding that was revealed by immunostaining and Western blotting for antibodies against GAP-43 and SCG10. On day 28 post-injury, histomorphometric assessments demonstrated that AA treatment increased the density, size, and remyelination of regenerated axons in the injured nerve and alleviated myoatrophy in the gastrocnemius. Moreover, the results from various behavioral tests and electrophysiological assays revealed that nerve injury-derived functional defects in motor and sensory behavior as well as in nerve conduction were significantly attenuated by treatment with AA. The potential mechanisms of AA in nerve regeneration were further explored by investigating the effects of AA on three types of cells involved in this process [neurons, Schwann cells (SCs) and macrophages] through a series of experiments. Overall, the data illustrated that AA treatment in cultured dorsal root ganglionic neurons resulted in increased neurite growth and lower expression of RhoA, which is an important inhibitory factor in neural regeneration. In SCs, proliferation, phagocytosis, and neurotrophin expression were all enhanced by AA. Meanwhile, AA treatment also improved proliferation, migration, phagocytosis, and anti-inflammatory polarization in macrophages. In conclusion, this study demonstrated that treatment with AA can promote the morphological and functional recovery of injured peripheral nerves and that this effect is potentially due to AA’s bioeffects on neurons, SCs and macrophages, three of most important types of cells involved in nerve injury and regeneration.

18F-FDG positron emission tomography as a novel diagnostic tool for peripheral nerve injury

BACKGROUND

Glucose hypermetabolism in denervated skeletal muscle suggests the potential for developing a diagnostic tool for peripheral nerve injuries. Herein, we investigated the characteristics and molecular mechanism of this phenomenon.

NEW METHOD

Temporal course of glucose hypermetabolism and development of abnormal spontaneous activities (ASA) through electromyography (EMG) were investigated in rats with complete sciatic nerve injuries. Rats with partial sciatic nerve injuries were used to investigate the relationship between nerve injury severity and change in glucose metabolism. Rapamycin-treated rats were used to study molecular mechanism. Mean lesion-to-normal count ratios (LNR_mean) was calculated as a numeric value of the ¹⁸F-FDG uptake.

RESULTS

Glucose hypermetabolism began 2 days after nerve injury and lasted up to 12 weeks, with the maximum increase at 1 week after denervation (10-fold increase compared to sham-operated muscle; LNR_mean, sham, 1.360 ± 0.452; denervation, 10.340 ± 4.094; n = 5; P < 0.05). The metabolic changes showed similar temporal characteristics to ASA on EMG. The signal intensity of ¹⁸F-FDG uptake in denervated skeletal muscle was strongly related to nerve injury severity in a partial nerve injury model (Pearson correlation coefficient 0.63, P < 0.05). Suppression of mTOR by rapamycin treatment reduced the increase in peak glucose hypermetabolism in muscle denervation.

COMPARISON WITH EXISTING METHOD

Metabolic changes in ¹⁸F-FDG PET scans have a wider time span than abnormalities on EMG after denervation and it is correlated with the severity of nerve injury assessed by NCS.

CONCLUSIONS

¹⁸F-FDG PET may be used to diagnose and evaluate peripheral nerve injuries.

Efect of longitudinally oriented collagen conduit combined with nerve growth factor on nerve regeneration after dog sciatic nerve injury

The research on artificial nerve conduits has become a focus of study in peripheral nerve reconstruction so as a possible replacement for the treatment of autologous nerve grafts in clinics. In this study, we used longitudinally oriented collagen conduit (LOCC) combined with nerve growth factor (NGF) to reconstruct long distance of sciatic nerve defects (35 mm) in adult dog model. The long term follow-up evaluation demonstrated that the LOCC/NGF conduit allowed functional and morphological nerve regeneration at the transection site of the injured sciatic nerve. Furthermore, the functional study confirmed that when NGF was loaded onto LOCC it promoted a better recovery of regenerated axons than LOCC alone. The gastrocnemius muscle mass in the LOCC/NGF group was significantly greater than in the LOCC alone group. The results indicated that when LOCC conduit combined with NGF it would provide a preferential environment for sciatic nerve regeneration. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2131-2139, 2018.