Abdominal normothermic regional perfusion in controlled donation after circulatory determination of death liver transplantation: Outcomes and risk factors for graft loss.

Postmortem normothermic regional perfusion (NRP) is a rising preservation strategy in controlled donation after circulatory determination of death (cDCD). Herein, we present results for cDCD liver transplants performed in Spain 2012-2019, with outcomes evaluated through December 31, 2020. Results were analyzed retrospectively and according to recovery technique (abdominal NRP [A-NRP] or standard rapid recovery [SRR]). During the study period, 545 cDCD liver transplants were performed with A-NRP and 258 with SRR. Median donor age was 59 years (interquartile range 49-67 years). Adjusted risk estimates were improved with A-NRP for overall biliary complications (OR 0.300, 95% CI 0.197-0.459, p < .001), ischemic type biliary lesions (OR 0.112, 95% CI 0.042-0.299, p < .001), graft loss (HR 0.371, 95% CI 0.267-0.516, p < .001), and patient death (HR 0.540, 95% CI 0.373-0.781, p = .001). Cold ischemia time (HR 1.004, 95% CI 1.001-1.007, p = .021) and re-transplantation indication (HR 9.552, 95% CI 3.519-25.930, p < .001) were significant independent predictors for graft loss among cDCD livers with A-NRP. While use of A-NRP helps overcome traditional limitations in cDCD liver transplantation, opportunity for improvement remains for cases with prolonged cold ischemia and/or technically complex recipients, indicating a potential role for complimentary ex situ perfusion preservation techniques.

Artificial intelligence and liver transplantation: Looking for the best donor-recipient pairing.

Decision-making based on artificial intelligence (AI) methodology is increasingly present in all areas of modern medicine. In recent years, models based on deep-learning have begun to be used in organ transplantation. Taking into account the huge number of factors and variables involved in donor-recipient (D-R) matching, AI models may be well suited to improve organ allocation. AI-based models should provide two solutions: complement decision-making with current metrics based on logistic regression and improve their predictability. Hundreds of classifiers could be used to address this problem. However, not all of them are really useful for D-R pairing. Basically, in the decision to assign a given donor to a candidate in waiting list, a multitude of variables are handled, including donor, recipient, logistic and perioperative variables. Of these last two, some of them can be inferred indirectly from the team's previous experience. Two groups of AI models have been used in the D-R matching: artificial neural networks (ANN) and random forest (RF). The former mimics the functional architecture of neurons, with input layers and output layers. The algorithms can be uni- or multi-objective. In general, ANNs can be used with large databases, where their generalizability is improved. However, they are models that are very sensitive to the quality of the databases and, in essence, they are black-box models in which all variables are important. Unfortunately, these models do not allow to know safely the weight of each variable. On the other hand, RF builds decision trees and works well with small cohorts. In addition, they can select top variables as with logistic regression. However, they are not useful with large databases, due to the extreme number of decision trees that they would generate, making them impractical. Both ANN and RF allow a successful donor allocation in over 80% of D-R pairing, a number much higher than that obtained with the best statistical metrics such as model for end-stage liver disease, balance of risk score, and survival outcomes following liver transplantation scores. Many barriers need to be overcome before these deep-learning-based models can be included for D-R matching. The main one of them is the resistance of the clinicians to leave their own decision to autonomous computational models.

Expert Consensus Guidelines on Minimally Invasive Donor Hepatectomy for Living Donor Liver Transplantation From Innovation to Implementation: A Joint Initiative From the International Laparoscopic Liver Society (ILLS) and the Asian-Pacific Hepato-Pancreato-Biliary Association (A-PHPBA).

OBJECTIVE: The Expert Consensus Guidelines initiative on MIDH for LDLT was organized with the goal of safe implementation and development of these complex techniques with donor safety as the main priority. BACKGROUND: Following the development of minimally invasive liver surgery, techniques of MIDH were developed with the aim of reducing the short- and long-term consequences of the procedure on liver donors. These techniques, although increasingly performed, lack clinical guidelines. METHODS: A group of 12 international MIDH experts, 1 research coordinator, and 8 junior faculty was assembled. Comprehensive literature search was made and studies classified using the SIGN method. Based on literature review and experts opinions, tentative recommendations were made by experts subgroups and submitted to the whole experts group using on-line Delphi Rounds with the goal of obtaining >90% Consensus. Pre-conference meeting formulated final recommendations that were presented during the plenary conference held in Seoul on September 7, 2019 in front of a Validation Committee composed of LDLT experts not practicing MIDH and an international audience. RESULTS: Eighteen Clinical Questions were addressed resulting in 44 recommendations. All recommendations reached at least a 90% consensus among experts and were afterward endorsed by the validation committee. CONCLUSIONS: The Expert Consensus on MIDH has produced a set of clinical guidelines based on available evidence and clinical expertise. These guidelines are presented for a safe implementation and development of MIDH in LDLT Centers with the goal of optimizing donor safety, donor care, and recipient outcomes.

Interaction between tacrolimus, MELD score and acute kidney injury after liver transplantation. Analysis on a large contemporary bicenter meld-era series.

BACKGROUND: Acute kidney injury (AKI) after liver transplantation (LT) is a common problem with complex management. The aims were to analyze the profile of AKI-RIFLE categories in the post-transplant setting of a wide multicentre cohort of patients in the MELD era and to specifically determine the effect of tacrolimus-based (TACRO) immunosuppressive regimes on the development of AKI. METHODS: A retrospective analysis of 550 (2007-2012) consecutive patients transplanted at Reina Sofia, Cordoba, and King's College Hospital, London, was performed. Inclusion criterion was to have CNI as part of initial immunosuppression immediately after LT. RESULTS: After exclusion criteria, a total of 477 patients were analyzed. Incidence of AKI within the first 2 weeks after LT was 65.8% (AKI-Risk), 41.3% (AKI-Injury), and 12.3% (AKI-Failure). The development of any type of AKI had no impact on short- and/or long-term survival up to 3 years after the transplant. Moreover, AKI was almost universal in the early post-transplant period and TACRO trough concentrations during the first 2 weeks after the transplant were not predictors of AKI in none of its categories in the multivariate analyses. CONCLUSIONS: Low-TACRO-based regimes were not as useful as expected in the prevention of AKI when analyzed in the context of a large contemporary LT series.

A systematic review and meta-analysis comparing the short- and long-term outcomes for laparoscopic and open liver resections for liver metastases from colorectal cancer.

BACKGROUND: The laparoscopic approach to liver resection has experienced exponential growth in recent years. However, evidence-based guidelines are needed for its safe future progression. The main aim of our study was to perform a systematic review and meta-analysis comparing the short- and long-term outcomes of laparoscopic and open liver resections for colorectal liver metastases (CRLM). METHODS: To identify all the comparative manuscripts between laparoscopic and open liver resections for CRLM, all published English language studies with more than ten cases were screened. In addition to the primary meta-analysis, 3 specific subgroup analyses were performed on patients undergoing minor-only, major-only and synchronous resections. The quality of the studies was assessed using the Scottish Intercollegiate Guidelines Network (SIGN) methodology and Newcastle-Ottawa Score. RESULTS: From the initial 194 manuscripts identified, 21 were meta-analysed, including results from the first randomized trial comparing open and laparoscopic resections of CRLM. Five of these were specific to patients undergoing a synchronous resection (399 cases), while six focused on minor (3 series including 226 cases) and major (3 series including 135 cases) resections, respectively. Thirteen manuscripts compared 2543 cases but could not be assigned to any of the above sub-analyses, so were analysed independently. The majority of short-term outcomes were favourable to the laparoscopic approach with equivalent rates of negative resection margins. No differences were observed between the approaches in overall or disease-free survival at 1, 3 or 5 years. CONCLUSION: Laparoscopic liver resection for CRLM offers improved short-term outcomes with comparable long-term outcomes when compared to open approach.

Artificial intelligence and organ transplantation: challenges and expectations.

PURPOSE OF REVIEW: Classifiers based on artificial intelligence have emerged in all areas of medicine. Although very subtle, many decisions in organ transplantation can now be addressed in a more concisely manner with the support of these classifiers. RECENT FINDINGS: Any aspect of organ transplantation (image processing, prediction of results, diagnostic proposals, therapeutic algorithms or precision treatments) consists of a set of input variables and a set of output variables. Artificial intelligence classifiers differ in the way they establish relationships between the input variables, how they select the data groups to train patterns and how they are able to predict the possible options of the output variables. There are hundreds of classifiers to achieve this goal. The most appropriate classifiers to address the different aspects of organ transplantation are Artificial Neural Networks, Decision Tree classifiers, Random Forest, and Naïve Bayes classification models. There are hundreds of examples of the usefulness of artificial intelligence in organ transplantation, especially in image processing, organ allocation, D-R matching, precision pathology, real-time immunosuppression, transplant oncology, and predictive analysis. SUMMARY: In the coming years, clinical transplant experts will increasingly use Deep Learning-based models to support their decisions, specially in those cases where subjectivity is common.

Machine-learning algorithms for predicting results in liver transplantation: the problem of donor-recipient matching.

PURPOSE OF REVIEW: Classifiers based on artificial intelligence can be useful to solve decision problems related to the inclusion or removal of possible liver transplant candidates, and assisting in the heterogeneous field of donor-recipient (D-R) matching. RECENT FINDINGS: Artificial intelligence models can show a great advantage by being able to handle a multitude of variables, be objective and help in cases of similar probabilities. In the field of liver transplantation, the most commonly used classifiers have been artificial neural networks (ANNs) and random forest classifiers. ANNs are excellent tools for finding patterns which are far too complex for a clinician and are capable of generating near-perfect predictions on the data on which they are fit, yielding excellent prediction capabilities reaching 95% for 3 months graft survival. On the other hand, RF can overcome ANNs in some of their limitations, mainly because of the lack of information on the variables they provide. Random forest algorithms may allow for improved confidence with the use of marginal organs and better outcome after transplantation. SUMMARY: ANNs and random forest can handle a multitude of structured and unstructured parameters, and establish non explicit relationships among risk factors of clinical relevance.

Normothermic regional perfusion vs. super-rapid recovery in controlled donation after circulatory death liver transplantation.

BACKGROUND & AIMS: Although there is increasing interest in its use, definitive evidence demonstrating a benefit for postmortem normothermic regional perfusion (NRP) in controlled donation after circulatory death (cDCD) liver transplantation is lacking. The aim of this study was to compare results of cDCD liver transplants performed with postmortem NRP vs. super-rapid recovery (SRR), the current standard for cDCD. METHODS: This was an observational cohort study including all cDCD liver transplants performed in Spain between June 2012 and December 2016, with follow-up ending in December 2017. Each donor hospital determined whether organ recovery was performed using NRP or SRR. The propensity scores technique based on the inverse probability of treatment weighting (IPTW) was used to balance covariates across study groups; logistic and Cox regression models were used for binary and time-to-event outcomes. RESULTS: During the study period, there were 95 cDCD liver transplants performed with postmortem NRP and 117 with SRR. The median donor age was 56 years (interquartile range 45-65 years). After IPTW analysis, baseline covariates were balanced, with all absolute standardised differences <0.15. IPTW-adjusted risks were significantly improved among NRP livers for overall biliary complications (odds ratio 0.14; 95% CI 0.06-0.35, p <0.001), ischaemic type biliary lesions (odds ratio 0.11; 95% CI 0.02-0.57; p = 0.008), and graft loss (hazard ratio 0.39; 95% CI 0.20-0.78; p = 0.008). CONCLUSIONS: The use of postmortem NRP in cDCD liver transplantation appears to reduce postoperative biliary complications, ischaemic type biliary lesions and graft loss, and allows for the transplantation of livers even from cDCD donors of advanced age. LAY SUMMARY: This is a propensity-matched nationwide observational cohort study performed using livers recovered from donors undergoing cardiac arrest provoked by the intentional withdrawal of life support (controlled donation after circulatory death, cDCD). Approximately half of the livers were recovered after a period of postmortem in situ normothermic regional perfusion, which restored warm oxygenated blood to the abdominal organs, whereas the remainder were recovered after rapid preservation with a cold solution. The study results suggest that the use of postmortem normothermic regional perfusion helps reduce rates of post-transplant biliary complications and graft loss and allows for the successful transplantation of livers from older cDCD donors.

A Systematic Review and Meta-Analysis Comparing the Short- and Long-Term Outcomes for Laparoscopic and Open Liver Resections for Hepatocellular Carcinoma: Updated Results from the European Guidelines Meeting on Laparoscopic Liver Surgery, Southampton, UK, 2017.

BACKGROUND: The laparoscopic approach to liver resection has experienced exponential growth in recent years; however, its application is still under debate and objective, evidence-based guidelines for its safe future progression are needed. OBJECTIVE: The aim of this study was to perform a systematic review and meta-analysis comparing the short- and long-term outcomes of laparoscopic and open liver resections for hepatocellular carcinoma (HCC). METHODS: To identify all the comparative manuscripts reporting on laparoscopic and open liver resection for HCC, all published English-language studies with more than 10 cases were screened. In addition to the primary meta-analysis, four specific subgroup analyses were performed on patients with Child-Pugh A cirrhosis, resections for solitary tumors, and those undergoing minor and major resections. The quality of the studies was assessed using the Scottish Intercollegiate Guidelines Network (SIGN) methodology and the Newcastle-Ottawa Scale. RESULTS: From the initial 361 manuscripts, 28 were included in the meta-analysis. Five of these 28 manuscripts were specific to patients with Child-Pugh A cirrhosis (321 cases), 11 focused on solitary tumors (1003 cases), 16 focused on minor resections (1286 cases), and 3 focused on major resections (164 cases). Three manuscripts compared 1079 cases but could not be assigned to any of the above subanalyses. In general terms, short-term outcomes were favorable when using a laparoscopic approach, especially in minor resections. The only advantage seen with an open approach was reduced operative time during major liver resections. No differences in long-term outcomes were observed between the approaches. CONCLUSIONS: Laparoscopic liver resection for HCC is feasible and offers improved short-term outcomes, with comparable long-term outcomes as the open approach.

The Southampton Consensus Guidelines for Laparoscopic Liver Surgery: From Indication to Implementation.

OBJECTIVE: The European Guidelines Meeting on Laparoscopic Liver Surgery was held in Southampton on February 10 and 11, 2017 with the aim of presenting and validating clinical practice guidelines for laparoscopic liver surgery. BACKGROUND: The exponential growth of laparoscopic liver surgery in recent years mandates the development of clinical practice guidelines to direct the speciality's continued safe progression and dissemination. METHODS: A unique approach to the development of clinical guidelines was adopted. Three well-validated methods were integrated: the Scottish Intercollegiate Guidelines Network methodology for the assessment of evidence and development of guideline statements; the Delphi method of establishing expert consensus, and the AGREE II-GRS Instrument for the assessment of the methodological quality and external validation of the final statements. RESULTS: Along with the committee chairman, 22 European experts; 7 junior experts and an independent validation committee of 11 international surgeons produced 67 guideline statements for the safe progression and dissemination of laparoscopic liver surgery. Each of the statements reached at least a 95% consensus among the experts and were endorsed by the independent validation committee. CONCLUSION: The European Guidelines Meeting for Laparoscopic Liver Surgery has produced a set of clinical practice guidelines that have been independently validated for the safe development and progression of laparoscopic liver surgery. The Southampton Guidelines have amalgamated the available evidence and a wealth of experts' knowledge taking in consideration the relevant stakeholders' opinions and complying with the international methodology standards.

Validation of artificial neural networks as a methodology for donor-recipient matching for liver transplantation.

In 2014, we reported a model for donor-recipient (D-R) matching in liver transplantation (LT) based on artificial neural networks (ANNs) from a Spanish multicenter study (Model for Allocation of Donor and Recipient in España [MADR-E]). The aim is to test the ANN-based methodology in a different European health care system in order to validate it. An ANN model was designed using a cohort of patients from King's College Hospital (KCH; n = 822). The ANN was trained and tested using KCH pairs for both 3- and 12-month survival models. End points were probability of graft survival (correct classification rate [CCR]) and nonsurvival (minimum sensitivity [MS]). The final model is a rule-based system for facilitating the decision about the most appropriate D-R matching. Models designed for KCH had excellent prediction capabilities for both 3 months (CCR-area under the curve [AUC] = 0.94; MS-AUC = 0.94) and 12 months (CCR-AUC = 0.78; MS-AUC = 0.82), almost 15% higher than the best obtained by other known scores such as Model for End-Stage Liver Disease and balance of risk. Moreover, these results improve the previously reported ones in the multicentric MADR-E database. In conclusion, the use of ANN for D-R matching in LT in other health care systems achieved excellent prediction capabilities supporting the validation of these tools. It should be considered as the most advanced, objective, and useful tool to date for the management of waiting lists. Liver Transplantation 24 192-203 2018 AASLD.

Preliminary results from the use of intraoperative real-time biliary oxygen monitoring in liver transplantation.

BACKGROUND AND AIMS: Biliary anastomosis is a frequent area of complications after liver transplantation (LT) and a potential area of "microangiopathy". The concept of a "marginal bile duct" is unexplored. The main aim was to make a preliminary evaluation of the utility of an innovative real-time oxygen microtension (pO2mt) testing device for the assessment of bile duct viability during LT and to correlate these pO2mt values with microvascular tissue quality by histopathology and outcomes. PATIENTS AND METHODS: Observational prospective cohort study with 23 patients. Oxygen microtension measurements were made placing a micropO2 probe in different areas of recipient and donor's bile duct intraoperative. RESULTS: Mean pO2mt in the graft bile duct at the level of the anastomosis 103.82 (31-157) mm Hg, being 121.52 (55-174) mm Hg 1.5 cm proximal to the hilar plate (P < 0.001). Mean pO2mt in the recipient's bile duct was 117.87 (62-185) mm Hg, while a value of 137.30 (81-198) mm Hg was observed 1.5 cm distal to the anastomosis (P < 0.001). Cystic duct resection (12 cases) was also related with higher pO2mt values at anastomosis [117.8 (93-157) vs 88.54 (31-124) mm Hg] and distal to anastomosis [135.6 (111-174) vs 106.2 (55-133) mm Hg; P < 0.001]. Patients with 1-, 3-, and 12-month biliary complications had significantly lower pO2mt in the intraoperative measurements. CONCLUSION: Our preliminary results show that distal borders of donor and recipient bile ducts may be low-vascularized areas. Tissue pO2mt is significantly higher in areas close to the hilar plate and to the duodenum in donor and recipient's sides, respectively. Bile duct injury and biliary complications are associated with worse tissue pO2mt.

VI consensus document by the Spanish Liver Transplantation Society. / VI documento de consenso de la sociedad española de trasplante hepático (SETH).

The goal of the Spanish Liver Transplantation Society (La Sociedad Española de Trasplante Hepático) is to promote and create consensus documents about current topics in liver transplantation with a multidisciplinary approach. To this end, on October 20, 2016, the 6th Consensus Document Meeting was held, with the participation of experts from the 24 authorized Spanish liver transplantation programs. This Edition discusses the following subjects, whose summary is offered below: 1) limits of simultaneous liver-kidney transplantation; 2) limits of elective liver re-transplantation; and 3) liver transplantation after resection and hepatocellular carcinoma with factors for a poor prognosis. The consensus conclusions for each of these topics is provided below.

Comparative Short-term Benefits of Laparoscopic Liver Resection: 9000 Cases and Climbing.

OBJECTIVE: To perform a systematic review of worldwide literature on laparoscopic liver resections (LLR) and compare short-term outcomes against open liver resections (OLR) by meta-analyses. SUMMARY BACKGROUND DATA: There are no updated pooled data since 2009 about the current status and short-term outcomes of LLR worldwide. PATIENTS AND METHODS: All English language publications on LLR were screened. Descriptive worldwide data and short-term outcomes were obtained. Separate analyses were performed for minor-only and major-only resection series, and series in which minor/major resections were not differentiated. Apparent case duplications were excluded. RESULTS: A set of 463 published manuscripts were reviewed. One hundred seventy-nine single-center series were identified that accounted for 9527 LLR cases worldwide. Minor-only, major-only, and combined major-minor series were 61, 18, and 100, respectively, including 32, 8, and 43 comparative series, respectively. Of the total 9527 LLR cases reported, 6190 (65%) were for malignancy and 3337 (35%) were for benign indications. There were 37 deaths reported (mortality rate = 0.4%). From the meta-analysis comparing case-matched LLR to OLR (N = 2900 cases), there was no increased mortality and significantly less complications, transfusions, blood loss, and hospital stay observed in LLR vs OLR. CONCLUSIONS: This is the largest review of LLR available to date with over 9000 cases published. It confirms growing safety when performed in selected patients and by trained surgeons, and suggests that LLR may offer improved patient short-term outcomes compared with OLR. Improved levels of evidence, standardized reporting of outcomes, and assuring proper training are the next challenges of laparoscopic liver surgery.

Lack of agreement for defining 'clinical suspicion of rejection' in liver transplantation: a model to select candidates for liver biopsy.

The gold standard to diagnose acute cellular rejection (ACR) after liver transplantation (LT) is histological evaluation, but there is no consensus to select patients for liver biopsy. We aimed to evaluate the agreement among clinicians to select candidates for liver biopsy early after LT. From a protocol biopsy population (n = 690), we randomly selected 100 LT patients in whom the biopsy was taken 7-10 days after LT. The clinical information between LT and protocol biopsy was given to nine clinicians from three transplant centres who decided whether a liver biopsy was needed. The agreement among clinicians to select candidates for liver biopsy was poor: κ = 0.06-0.62, being κ < 0.40 in 76% of comparisons. The concordance between indication for liver biopsy and moderate-severe ACR in the protocol biopsy was κ < 0.30 in all cases. A multivariate model based on the product age-by-MELD (OR = 0.81; P = 0.013), delta eosinophils (OR = 1.5; P = 0.002) and mean tacrolimus trough concentrations <6 ng/ml within the prior 4 days (OR = 11.4; P = 0.047) had an AUROC = 0.84 to diagnose moderate-severe histological ACR. In conclusion, the agreement among clinicians to select patients for liver biopsy is very poor. If further validated the proposed model would provide an objective method to select candidates for liver biopsy after LT.

[V Consensus Meeting of the Spanish Society for Liver Transplant on high-risk recipients, immunosupression scenarios and management of hepatocarcinoma on the transplant waiting list]. / V Reunión de Consenso de la Sociedad Española de Trasplante Hepático sobre receptores de riesgo elevado, escenarios actuales de inmunosupresión y manejo del hepatocarcinoma en espera de trasplante.

With the aim to promote the elaboration of consensus documents on state of the art topics in liver transplantation with multidisciplinary management, the Spanish Society for Liver Transplantation (SETH) organized the V Consensus Meeting with the participation of experts from all the Spanish liver transplant programs. In this edition, the following topics were revised, and we present the summary: 1. High-risk receptors; 2. Immunosuppression scenarios; and 3. Management of the patient with hepatocarcinoma in the waiting list.

V Consensus Meeting of the Spanish Society for Liver Transplant on high-risk recipients, immunosupression scenarios and management of hepatocarcinoma on the transplant waiting list.

With the aim to promote the elaboration of consensus documents on state of the art topics in liver transplantation with multidisciplinary management, the Spanish Society for Liver Transplantation (SETH) organized the V Consensus Meeting with the participation of experts from all the Spanish liver transplant programs. In this edition, the following topics were revised, and we present the summary: 1. High-risk receptors; 2. Immunosuppression scenarios; and 3. Management of the patient with hepatocarcinoma in the waiting list.

Effects of N-acetylcysteine on isolated mouse skeletal muscle: contractile properties, temperature dependence, and metabolism.

The effects of the general antioxidant N-acetylcysteine (NAC) on muscle function and metabolism were examined. Isolated paired mouse extensor digitorum longus muscles were studied in the absence or presence of 20 mM NAC. Muscles were electrically stimulated to perform 100 isometric tetanic contractions (300 ms duration) at frequencies resulting in ∼85% of maximal force (70-150 Hz at 25-40 °C). NAC did not significantly affect peak force in the unfatigued state at any temperature but significantly slowed tetanic force development in a temperature-dependent fashion (e.g., time to 50% of peak tension averaged 35 ± 2 ms [control] and 37 ± 1 ms [NAC] at 25 °C vs. 21 ± 1 ms [control] and 52 ± 6 ms [NAC, P < 0.01] at 40 °C). During repeated contractions, NAC maximally enhanced peak force by the fifth tetanus at all temperatures (by ∼30%). Thereafter, the effect of NAC disappeared rapidly at high temperatures (35-40 °C) and more slowly at the lower temperatures (25-30 °C). At all temperatures, the enhancing effect of NAC on peak force was associated with a slowing of relaxation. NAC did not significantly affect myosin light chain phosphorylation at rest or after five contractions (∼50% increase vs. rest). After five tetani, lactate and inorganic phosphate increased about 20-fold and 2-fold, respectively, both in control and NAC-treated muscles. Interestingly, after five tetani, the increase in glucose 6-P was ∼2-fold greater, whereas the increase in malate was inhibited by ∼75% with NAC vs. control, illustrating the metabolic effects of NAC. NAC slightly decreased the maximum shortening velocity in early fatigue (five to seven repeated tetani). These data demonstrate that the antioxidant NAC transiently enhances muscle force generation by a mechanism that is independent of changes in myosin light chain phosphorylation and inorganic phosphate. The slowing of relaxation suggests that NAC enhances isometric force by facilitating fusion (i.e., delaying force decline between pulses). The initial slowing of tension development and subsequent slowing of relaxation suggest that NAC would result in impaired performance during a high-intensity dynamic exercise.