4. Discussion
Our findings showed the effectiveness of the amino acid-enhanced perioperative nutritional therapy using Gln/Arg/HMB products on the short-term outcome and skeletal muscle mass after MIE.
Esophageal cancer surgery is a highly invasive procedure with a high incidence of postoperative complications, which can likely cause increased protein catabolism, inhibition of protein synthesis, nutritional deficiency due to gastrointestinal dysfunction, and skeletal muscle atrophy [
2]. MIE using a thoracoscopy can be expected to improve the short-term outcomes owing to its low invasiveness and reduced risk for complications as compared to the previous open esophagectomy approach [
8,
12,
13,
14]. Various efforts to prevent complications during the perioperative period of patients receiving esophageal cancer surgery have been reported. The use of intraoperative nerve monitoring and ingenuity in mediastinal lymph node dissection are useful to prevent recurrent laryngeal nerve paralysis, and these approaches also resulted in a reduction in the incidence of aspiration pneumonia, respiratory failure, and sputum expectoration disorders [
15,
16]. Additionally, the development of preoperative risk assessment based on the patient’s nutritional status and background diseases, intraoperative evaluation of the blood flow of the reconstructed organs using indocyanine green, and strict blood sugar management in diabetic patients have been reported to be useful in preventing the development anastomotic leakage [
1,
17,
18,
19,
20]. The occurrence of various complications reportedly can lead to an increase in postoperative hospital stay, deterioration in nutritional status, and poor long-term outcomes [
21,
22]. From the viewpoint that the occurrence of disuse syndrome and worsening sarcopenia after surgery considerably impedes the return to daily life and delays the transition to additional cancer therapy, it is strongly desirable to prevent the development of all complications by taking preventive measures [
23,
24]. Contrarily, various studies reported on the positive efforts regarding effective measures to prevent the worsening of secondary sarcopenia after digestive cancer surgery [
25,
26,
27]. Sarcopenia not only affects the quality of life (QOL) and activities of daily living (ADL) of patients with malignant tumors, but also influences the occurrence of various treatment-related adverse events and complications; therefore, sarcopenia should not be ignored to ensure the safety and continuity of cancer treatment [
22].
Patients with esophageal cancer have a high prevalence of malnutrition because of the presence of dysphagia caused by the tumor, along with secondary anorexia and cancer cachexia. Significant weight loss and nutritional deficiencies predispose a patient to an increased risk of complications and protracted admission [
23]. Sarcopenia and frailty from cancer cachexia also affect patient outcomes and recovery [
21,
28]. Hence, it is essential to assess the nutritional status of the patient at diagnosis. The decision to intervene is based on the risk assessment, but nutritional supplementation is known to have a positive effect on the perioperative outcomes [
29,
30].
The mechanisms of progression of postoperative sarcopenia can be broadly summarized into three. The first is the delay or decrease in protein synthesis during postoperative wound healing. Nutrients, including amino acids and carbohydrates, administered to repair damaged tissues are mostly mobilized for tissue repair, and the distribution of nutrients to the skeletal muscles throughout the whole body is relatively reduced, possibly impairing the maintenance of skeletal muscle mass and its quality [
31]. To correct this, the efficient administration of appropriate amino acids to promote protein synthesis is required. The calcium HMB, L-Arg, and L-Gln present in Abound® are speculated to promote wound healing through the synthesis of proteins, such as hydroxyproline, a collagen precursor necessary for epithelialization, and granulation tissue proliferation, fibrosis, and inhibition of proteolysis [
31]. The key enzymes that promote protein synthesis include Gln, vitamins, Arg, branched chain amino acid (BCAA), zinc, phosphorus, and omega-3 fatty acids, which are known to be useful for various pathologies. In a meta-analysis, Zheng et al. have reported the usefulness of Gln administration in terms of cumulative nitrogen balance, infectious complications, and postoperative hospital stay in abdominal surgery [
32]. Arg reportedly promotes protein synthesis and nitric oxide production. Moreover, Arg is thought to be a substrate for nitric oxide, which has a vasodilatory effect, and to play a role in maintaining microcirculation at the site of gastrointestinal anastomosis [
5,
33]. BCAAs are composed of three amino acids (valine, leucine, and isoleucine) with branched side chains [
34], and they are known to have the strongest protein anabolic effect among the essential amino acids [
35,
36]. In liver cirrhosis, protein assimilation does not function properly, especially in a state of leucine deficiency, but BCAA administration is expected to suppress ammonia synthesis and improve the efficiency of nitrogen utilization in the body [
35,
36,
37]. In the treatment of liver cirrhosis patients, the usefulness of BCAA administration and exercise therapy has been reported for sarcopenia [
24,
38,
39]. The importance of nutritional therapy and rehabilitation in the perioperative period of esophageal cancer surgery has also been demonstrated [
25,
27]. Zinc consumption is increased in highly invasive pathological conditions, and it promotes muscle breakdown, causes anemia, and affects the hormones [
40,
41]. ω3 fatty acids are useful in maintaining the nutritional status of patients who had undergone gastrointestinal cancer surgery through their anti-inflammatory effects [
42]. Calcium HMB is a metabolic product of leucine and has the effect of promoting protein synthesis via the mammalian target of rapamycin pathway and inhibiting body protein breakdown via the inhibition of the ubiquitin-proteasome system. The administration of HMB synergistically enhances the metabolic improvement in leucine synthesis in skeletal muscles [
35,
37,
43,
44]. Additionally, HMB promotes wound healing together with Gln, which is an energy substrate for cells involved in wound healing, including macrophages, lymphocytes, and fibroblasts [
6,
31,
45]. Theoretically, our study results suggest that sufficient Gln, Arg, and HMB administration can counteract the inhibitory effect of postoperative protein synthesis.
The second cause of sarcopenia progression is the relative lack of nutrients due to increased inflammation after surgery. Esophageal cancer surgery causes widespread tissue damage, and for some period of time after surgery, exudates are drained out of the body, causing a large amount of protein leakage. The amount of protein lost cannot be replenished by the nutrients administered alone; thus, the body dissolves its own skeletal muscles to mobilize the protein components into the plasma, which is expected to cause considerable atrophy of the skeletal muscles during this period [
3,
4,
21]. It is expected that administering Gln, a material for skeletal muscles, before surgery, prior to protein wasting during this period, may suppress the development of muscle atrophy in the early postoperative phase. Oral Gln administration also enhances immunity, prevents bacterial translocation, and improves the survival rates in patients with severe infections [
5,
45,
46]. The nutritional management guidelines recommend a daily Gln dose of 0.3–0.5 g/kg/day, and the Gln/Arg/HMB combination used in this study contains 14 g of Gln and 14 g of Arg per two packets, which is thought to meet this recommended dose [
6,
45,
47,
48]. Contrarily, Orlila, et al. reported that, in the perioperative nutritional therapy for malnourished patients, the preoperative intravenous administration is more effective in reducing the incidence of postoperative complications and length of stay in the intensive care unit as compared to enteral administration [
49]. Ayala et al. also reported that intravenous Gln administration relieves surgery-related immunosuppression by suppressing interferon (IFN)-γ and interleukin (IL)-4 productions early in response to the overexpression of IFN-γ and IL-4 from T lymphocytes in response to surgical stress [
50,
51]. Unfortunately, intravenous Gln preparations are not approved in Japan; thus, we could not use it. However, enteral administration alone can provide some benefits from systemic distribution via intestinal absorption.
The third reason is that postoperative wound pain, fatigue, and general exhaustion reduce an individual’s ability to perform ADL, which impedes early postoperative rehabilitation. Perioperative nutritional management tailored to the patient’s condition has been reported to promote wound healing and maintain overall health [
6]. According to the European Society of Clinical Nutrition and Metabolism (ESPEN) and American Society for Parenteral and Enteral Nutrition (ASPEN) guidelines, early initiation of enteral nutrition after gastrointestinal cancer surgery is strongly recommended and has become widespread as part of ERAS, but a definitively useful nutritional management method has yet to be established [
52,
53]. Based on the ERAS concept, rehabilitation programs aimed at maintaining ADL throughout the entire perioperative period have become widely practiced in clinical practice [
25,
26,
54,
55]. The contents of ERAS include omission of preoperative intestinal preparation, shortening of the fasting period, oral care, routine postoperative analgesia, early mobilization, and initiation of early postoperative enteral nutrition [
25,
27,
54,
55]. Atrophy of the intestinal mucosa is closely related to Gln deficiency. Gln needs to be sufficiently distributed and utilized by the intestinal epithelium to regenerate the atrophied intestinal mucosa. By preventing mucosal atrophy, bacterial translocation can be suppressed to maintain an individual’s immune function [
46,
56]. Administering sufficient amounts of Gln, together with early enteral nutrition, is an efficient approach that is in line with the concept of ERAS. There have also been reports on the synergistic effect of early rehabilitation and Gln in increasing the skeletal muscle mass, and this is considered a rehabilitation nutritional approach that can be applied to prevent disuse syndrome in various surgical patients [
36,
39,
55]. In our department, we also practice ERAS in the perioperative management of gastrointestinal cancer, including the appropriate use of analgesics, dental intervention, and early enteral nutrition, and the good results of this study are thought to be the overall result of these efforts [
57]. However, from the perspective of preventing postoperative chylothorax, a previously utilized fat-containing enteral nutrition was changed to a fat-free nutritional supplement in the later cases, which may have had an impact. If carbohydrates are administered as enteral nutrition after surgery, there is a concern that they may cause dumping syndrome due to their rapid administration into the intestinal tract; however, our nutritional supplement preparation contains almost no carbohydrates and is mainly composed of amino acids, so it is unlikely to cause rapid blood sugar fluctuations and is theoretically unlikely to cause dumping syndrome. Motoori et al. have reported the usefulness of immunonutrition and synbiotics in perioperative and preoperative chemotherapy for esophageal cancer; they also demonstrated that they contribute to the normalization of the intestinal flora and reduction of chemotherapy-induced adverse events and postoperative complications [
58]. Additionally, Mayanagi et al. have shown that skeletal muscle atrophy caused by preoperative chemotherapy was reduced after surgery [
59]. There have been no reports to date on the usefulness of Gln, Arg, or HMB in preoperative chemotherapy for esophageal cancer, which require further investigation in order to improve the treatment outcomes of patients with esophageal cancer.
In the present study, sarcopenia was defined as having a low PMI, but sarcopenia should be defined using multiple factors, including walking speed, grip strength, upper arm circumference, and body composition analysis through a bioimpedance analysis [
60]. However, the present investigation was a retrospective study, and various parameters related to the definition of sarcopenia were missing and could not be used. Our study subjects were patients who had undergone MIE, and measuring PMA using CT images before and after surgery was possible; thus, for convenience, we used CT image to define sarcopenia. In the present study, the cutoff value for diagnosing sarcopenia based on the iliopsoas muscle area was adopted as an index appropriate for the actual situation of Japanese people, as reported by Hamaguchi et al. [
11].
Our study results showed that the incidence of postoperative pleural effusion and expectoration disorders was significantly lower in the Gln/Arg/HMB group than in the control group. This may be due to the prevention of the development of sarcopenia in the respiratory muscles and maintenance of colloid osmotic pressure as a result of promoting protein synthesis, which is similar to the results of a previous study [
61]. Additionally, from our personal experience, the administration of a Gln/Arg/HMB product to patients with anastomotic leakage after esophageal cancer surgery shortened the recovery period from anastomotic leakage (13.5 ± 14.3 vs. 35.0 ± 17.4 days, P = 0.043) and maintained serum albumin levels on 14th postoperative day (−1.0 ± 0.32 vs. −1.4 ± 0.49 g/dL, P = 0.047), suggesting its usefulness in wound healing and the maintenance of nutritional status (data not shown).
Among the postoperative nutritional indicators, body weight and PMA were significantly higher in the Gln/Arg/HMB group at 1 week and 1 month postoperatively. Only a few studies have reported significant changes in the parameters after the perioperative nutritional intervention [
62,
63]; thus, the results of this study are considered to be very important findings. However, a further study is still needed to determine the detailed impact of this intervention on the nutritional parameters.
The occurrence of complications after esophageal cancer surgery has a great impact on a patient’s long-term prognosis [
64,
65,
66,
67]. It has been suggested that various inflammatory cytokines and chemokines, such as IL-6 and IL-8, not only promote cancer cell proliferation and activation, but also may synergistically promote cancer progression through the suppression of natural killer cell function. The transition of perioperative inflammatory cytokines, which is enhanced in cases with postoperative complications, may be deeply involved in the long-term prognosis [
62,
63,
68]. This highlights the importance of the need for preventing complications.
A limitation of this study is that the historical backgrounds of the two groups differed. It is possible that the postoperative outcome is influenced not only by the nutritional therapy but also by the progress of postoperative management. Additionally, although no apparent adverse events occurred due to the administration of Gln/Arg/HMB product in the cases examined here, diarrhea or abdominal pain may occur depending on the administration dosage and speed, and it is unclear whether the Gln/Arg/HMB product can be administered to all cases. Furthermore, in cases of renal or liver dysfunction, excessive administration of amino acids may lead to the deterioration of renal or liver function; thus, dosage adjustments will be necessary depending on the case. Additionally, it is expected that the administration of Gln/Arg/HMB product can reduce the occurrence of complications, which may ultimately extend the patients’ prognosis, but we were unable to follow up on the long-term outcomes in this study. This is an issue that needs to be investigated in the future.