Nutritional aspects of prehabilitation in adults with cirrhosis awaiting liver transplant

Malnutrition, sarcopenia (low muscle mass), and physical frailty have gained increasing recognition in candidates for liver transplant (LT) as these conditions can impact postoperative functional capacity. Multidimensional prehabilitation programs have been proposed as a safe intervention in adults awaiting LT but the nutritional pillar of prehabilitation has been understudied. This review summarizes the nutritional recommendations for prehabilitation for individuals with cirrhosis awaiting LT. Three major aspects of nutritional prehabilitation are discussed: (1) Assess: Evaluate nutritional status and assess for malnutrition, sarcopenia, and frailty to guide the nutritional prehabilitation intervention intensity, increasing across universal, targeted, and specialist levels; (2) Intervene: Prescribe a nutritional prehabilitation intervention to meet established nutrition guidelines in cirrhosis with a targeted focus on improving nutritional status and muscle health; (3) Reassess: Follow-up based on the required intensity of nutritional care with as needed intervention adjustment. Topics covered in the review include nutritional care levels for prehabilitation, energy prescriptions across body mass index strata, detailed considerations around protein intake (amount, distribution, and quality), carbohydrate and fat intake, other nutritional considerations, and the potential role of dietary supplements and nutraceuticals. Future research is warranted to more accurately evaluate energy needs, evaluate emerging dietary supplementation strategies, and establish the role of nutraceuticals alongside food-based interventions. While the general principles of nutritional prehabilitation are ready for immediate application, future large-scale randomized controlled trials in this space will help to quantify the benefit that can be gained by transitioning the LT approach from passive "transplant waitlist time" to active "transplant preparation time."

Telehealth-Delivered Program and Accompanying Patients to Enhance the Clinical Condition of Patients Throughout a Liver Transplant: Protocol for a Mixed Methods Study

BACKGROUND

Liver transplantation (LT) is indicated in patients with severe acute or chronic liver failure for which no other therapy is available. With the increasing number of LTs in recent years, liver centers worldwide must manage their patients according to their clinical situation and the expected waiting time for transplantation. The LT clinic at the Centre hospitalier de l'Université de Montréal (CHUM) is developing a new health care model across the entire continuum of pre-, peri-, and posttransplant care that features patient monitoring by an interdisciplinary team, including an accompanying patient; a digital platform to host a clinical plan; a learning program; and data collection from connected objects.

OBJECTIVE

This study aims to (1) evaluate the outcomes following the implementation of a patient platform with connected devices and an accompanying patient, (2) identify implementation barriers and facilitators, (3) describe service outcomes in terms of health outcomes and the rates and nature of contact with the accompanying patient, (4) describe patient outcomes, and (5) assess the intervention's cost-effectiveness.

METHODS

Six types of participants will be included in the study: (1) patients who received transplants and reached 1 year after transplantation before September 2023 (historical cohort or control group), (2) patients who will receive an LT between December 2023 and November 2024 (prospective cohort/intervention group), (3) relatives of those patients, (4) accompanying patients who have received an LT and are interested in supporting patients who will receive an LT, (5) health care professionals, and (6) decision makers. To describe the study sample and collect data to achieve all the objectives, a series of validated questionnaires, accompanying patient logbooks, transcripts of interviews and focus groups, and clinical indicators will be collected throughout the study.

RESULTS

In total, 5 (steering, education, clinical-technological, nurse prescription, and accompanying patient) working committees have been established for the study. Recruitment of patients is expected to start in November 2023. All questionnaires and technological platforms have been prepared, and the clinicians, stakeholders, and accompanying patient personnel have been recruited.

CONCLUSIONS

The implementation of this model in the trajectory of LT recipients at the CHUM may allow for better monitoring and health of patients undergoing transplantation, ultimately reducing the average length of hospital stay and promoting better use of medical resources. In the event of positive results, this model could be transposed to all transplant units at the CHUM and across Quebec (potentially affecting 888 patients per year) but could also be applied more widely to the monitoring of patients with other chronic diseases. The lessons learned from this project will be shared with decision makers and will serve as a model for other initiatives involving accompanying patients, connected objects, or digital platforms.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

PRR1-10.2196/54440.

IL-6 Trans-Signaling Is Increased in Diabetes, Impacted by Glucolipotoxicity, and Associated With Liver Stiffness and Fibrosis in Fatty Liver Disease

Many people living with diabetes also have nonalcoholic fatty liver disease (NAFLD). Interleukin-6 (IL-6) is involved in both diseases, interacting with both membrane-bound (classical) and circulating (trans-signaling) soluble receptors. We investigated whether secretion of IL-6 trans-signaling coreceptors are altered in NAFLD by diabetes and whether this might associate with the severity of fatty liver disease. Secretion patterns were investigated with use of human hepatocyte, stellate, and monocyte cell lines. Associations with liver pathology were investigated in two patient cohorts: 1) biopsy-confirmed steatohepatitis and 2) class 3 obesity. We found that exposure of stellate cells to high glucose and palmitate increased IL-6 and soluble gp130 (sgp130) secretion. In line with this, plasma sgp130 in both patient cohorts positively correlated with HbA1c, and subjects with diabetes had higher circulating levels of IL-6 and trans-signaling coreceptors. Plasma sgp130 strongly correlated with liver stiffness and was significantly increased in subjects with F4 fibrosis stage. Monocyte activation was associated with reduced sIL-6R secretion. These data suggest that hyperglycemia and hyperlipidemia can directly impact IL-6 trans-signaling and that this may be linked to enhanced severity of NAFLD in patients with concomitant diabetes.

ARTICLE HIGHLIGHTS

IL-6 and its circulating coreceptor sgp130 are increased in people with fatty liver disease and steatohepatitis. High glucose and lipids stimulated IL-6 and sgp130 secretion from hepatic stellate cells. sgp130 levels correlated with HbA1c, and diabetes concurrent with steatohepatitis further increased circulating levels of all IL-6 trans-signaling mediators. Circulating sgp130 positively correlated with liver stiffness and hepatic fibrosis. Metabolic stress to liver associated with fatty liver disease might shift the balance of IL-6 classical versus trans-signaling, promoting liver fibrosis that is accelerated by diabetes.

Nutritional education strategies for patients with cirrhosis: A narrative review

BACKGROUND

Patients with cirrhosis suffer from many complications, including malnutrition, which must be managed promptly and effectively by the healthcare team. Educating patients about their medical condition, the risk of malnutrition and other complications of cirrhosis, could contribute to optimal nutritional status, quality of life and general health.

OBJECTIVE

This review provides an overview of the literature on a variety of nutritional education strategies used with patients suffering from cirrhosis. This review also identifies barriers and facilitators which impact the adherence in using these strategies.

PATIENT INVOLVEMENT

A patient-partner contributed to this review by providing insights on different issues and concerns that patients with cirrhosis might ask themselves regarding nutritional education strategies. The patient-partner was also involved in the overall revision of the review.

METHODS

Articles published between the years 2000-2023 focusing on nutritional education strategies in patients living with cirrhosis were identified using Google Scholar and PubMed and were screened for inclusion in the study. All selected studies were intervention studies. A quality assessment of the included studies was conducted using the Mixed Methods Appraisal Tool (MMAT).

RESULTS

Only a few nutritional education strategies in patients with cirrhosis were documented in the literature. The strategies ranged from using traditional printed materials to advanced technologies. These strategies may prove beneficial in complementing routine interventions provided by health professionals, such as registered dietitians, in their clinical practice.

DISCUSSION

This narrative review clearly highlights the need for further research to elaborate and evaluate nutritional education strategies for people living with cirrhosis.

PRACTICAL VALUE

Elaborating and evaluating educational strategies in nutrition for patients living with cirrhosis will be an adjuvant to health professionals and dietitians in their clinical practice by providing them, and the patients, with targeted education resources.

Nutritional Strategies to Manage Malnutrition and Sarcopenia following Liver Transplantation: A Narrative Review

Persisting or newly developed malnutrition and sarcopenia after liver transplant (LT) are correlated with adverse health outcomes. This narrative review aims to examine the literature regarding nutrition strategies to manage malnutrition and sarcopenia after LT. The secondary aims are to provide an overview of the effect of nutrition strategies on the incidence of infections, hospital length of stay (LOS), acute cellular rejection (ACR), and mortality after LT. Four databases were searched. A total of 25 studies, mostly of mid-high quality, were included. Six studies found a beneficial effect on nutritional parameters using branched-chain amino acids (BCAA), immunomodulating diet (IMD), or enteral nutrition (EN) whereas two studies using beta-hydroxy-beta-methylbutyrate (HMB) found a beneficial effect on muscle mass and function. Fourteen studies using pre- or pro-biotics, IMD, and EN were effective in lowering infection and six studies using IMD, BCAA or HMB reported reduced hospital LOS. Finally, four studies using HMB and vitamin D were effective in reducing ACR and one study reported reduced mortality using vitamin D after LT. In conclusion, nutritional intervention after LT has different beneficial effects on malnutrition, sarcopenia, and other advert outcomes. Additional large and well-constructed RCTs using validated tools to assess nutritional status and sarcopenia are warranted to ensure more robust conclusions.

Renal dysfunction independently predicts muscle mass loss in patients following liver transplantation

BACKGROUND: Liver transplantation (LT) is the only curative treatment for cirrhosis. However, the presence of complications can impact outcomes following LT. Sarcopenia, or muscle mass loss, is highly prevalent in patients with cirrhosis and is associated with longer hospitalization stays and a higher infection rate post-surgery. We aimed to identify patients at higher risk of early sarcopenia post-LT. METHODS: This retrospective study included 79 cirrhotic patients who underwent LT. Muscle mass was evaluated using the third lumbar spine vertebra skeletal muscle mass index (SMI) and sarcopenia was defined using established cut-off values. Computerized tomography (CT) scans performed within six-month peri-operative period (three months pre- and post-LT) were included in the study. Complications and comorbidities were collected and correlated to SMI post-LT and predictive models for SMI post-LT were constructed. RESULTS: The overall prevalence of sarcopenia was 46% and 62% before and after LT, respectively. Newly developed sarcopenia was found in 42% of patients. Post-LT sarcopenia was associated with longer hospital stays (54±37 vs 29±10 days, p = 0.002), higher number of infection (3±1 vs 1±2, p = 0.027), and greater number of complications (5±2 vs 3±2, p <0.001) compared to absence of sarcopenia. Multivariate analyses showed that the SMI post-LT was independently associated with pre-LT renal function markers, the glomerular filtration rate (GFR) and creatinine (Model 1, GFR: β = 0.33; 95% CI = 0.04–0.17; p = 0.003; Model 2, Creatinine: β = –0.29; 95% CI = –0.10 to –0.02; p = 0.009). CONCLUSIONS: The present study highlights the potential role of renal dysfunction in the development and persistence of sarcopenia after LT.

Bile-duct ligation renders the brain susceptible to hypotension-induced neuronal degeneration: Implications of ammonia

Hepatic encephalopathy (HE) is a debilitating neurological complication of cirrhosis. By definition, HE is considered a reversible disorder, and therefore HE should resolve following liver transplantation (LT). However, persisting neurological complications are observed in as many as 47% of LT recipients. LT is an invasive surgical procedure accompanied by various perioperative factors such as blood loss and hypotension which could influence outcomes post-LT. We hypothesize that minimal HE (MHE) renders the brain frail and susceptible to hypotension-induced neuronal cell death. Six-week bile duct-ligated (BDL) rats with MHE and respective SHAM-controls were used. Several degrees of hypotension (mean arterial pressure of 30, 60 and 90 mm Hg) were induced via blood withdrawal from the femoral artery and maintained for 120 min. Brains were collected for neuronal cell count and apoptotic analysis. In a separate group, BDL rats were treated for MHE with the ammonia-lowering strategy ornithine phenylacetate (OP; MNK-6105), administered orally (1 g/kg) for 3 weeks before induction of hypotension. Hypotension 30 and 60 mm Hg (not 90 mm Hg) significantly decreased neuronal marker expression (NeuN) and cresyl violet staining in the frontal cortex compared to respective hypotensive SHAM-operated controls as well as non-hypotensive BDL rats. Neuronal degeneration was associated with an increase in cleaved caspase-3, suggesting the mechanism of cell death was apoptotic. OP treatment attenuated hyperammonaemia, improved anxiety and activity, and protected the brain against hypotension-induced neuronal cell death. Our findings demonstrate that rats with chronic liver disease and MHE are more susceptible to hypotension-induced neuronal cell degeneration. This highlights MHE at the time of LT is a risk factor for poor neurological outcome post-transplant and that treating for MHE pre-LT might reduce this risk.

Progressive resistance training prevents loss of muscle mass and strength in bile duct-ligated rats

BACKGROUND

Loss of muscle mass and strength is common in cirrhosis and increases the risk of hyperammonaemia and hepatic encephalopathy. Resistance training optimizes muscle mass and strength in several chronic diseases. However, the beneficial effects of resistance training in cirrhosis remain to be investigated. Bile duct-ligated (BDL) rats develop chronic liver disease, hyperammonaemia, reduced muscle mass and strength. Our aim was to test the effects of resistance training on muscle mass, function and ammonia metabolism in BDL-rats.

METHODS

A group of BDL-rats underwent a progressive resistance training programme and a group of non-exercise BDL-rats served as controls. Resistance training comprised of ladder climbing with a progressive increase in carrying weights attached to the tail. Training was performed 5 days a week during 4 weeks. Muscle strength and body composition were assessed using grip strength and EchoMRI. Weight and circumference of the gastrocnemius muscle (normalized to bodyweight), plasma ammonia and glutamine synthetase protein expression and activity were assessed.

RESULTS

BDL + exercise rats had significantly larger gastrocnemius circumference compared to non-exercise BDL-rats: ratio 0.082 vs 0.075 (P < 0.05). Gastrocnemius muscle weight was higher in exercisers than controls: 0.006 vs 0.005 (P < 0.05). A tendency towards a lower plasma ammonia in the exercise group compared to controls was observed (P = 0.10). There were no differences in lean body mass, GS protein expression and activity between the groups.

CONCLUSION

Resistance training in rats with chronic liver disease beneficially effects muscle mass and strength. The effects were followed by non-significant reduction in blood ammonia; however, a tendency was observed.

Role of Exercise in the Management of Hepatic Encephalopathy: Experience From Animal and Human Studies

Sarcopenia and malnutrition are common features in patients with hepatic encephalopathy. Ammonia, a factor implicated in the pathophysiology of hepatic encephalopathy, may be cleared by the muscle via the enzyme glutamine synthetase when the liver function is impaired. Hence, optimizing muscle mass in patients suffering from hepatic encephalopathy is a potential strategy to decrease ammonia levels. Exercise could be an efficient therapeutic approach to optimize muscle mass and therefore potentially reduce the risk of hepatic encephalopathy in patients with chronic liver disease. This review reports the current evidence regarding exercise and hepatic encephalopathy from animal and human studies. After defining concepts such as frailty, sarcopenia, and malnutrition, the present knowledge regarding exercise as potential therapy in cirrhotic patients with or without hepatic encephalopathy is discussed. Recommendations and future aspects are also considered.

Brain edema: a valid endpoint for measuring hepatic encephalopathy?

Hepatic encephalopathy (HE) is a major complication of liver failure/disease which frequently develops during the progression of end-stage liver disease. This metabolic neuropsychiatric syndrome involves a spectrum of symptoms, including cognition impairment, attention deficits and motor dysfunction which eventually can progress to coma and death. Pathologically, HE is characterized by swelling of the astrocytes which consequently leads to brain edema, a common feature found in patients with acute liver failure (ALF) as well as in cirrhotic patients suffering from HE. The pathogenic factors involved in the onset of astrocyte swelling and brain edema in HE are unresolved. However, the role of astrocyte swelling/brain edema in the development of HE remains ambiguous and therefore measuring brain edema as an endpoint to evaluate HE is questioned. The following review will determine the effect of astrocyte swelling and brain edema on neurological function, discuss the various possible techniques to measure brain edema and lastly to propose a number of neurobehavioral tests to evaluate HE.

Reprint of: Nutrition in the Management of Cirrhosis and its Neurological Complications

Malnutrition is a common feature of chronic liver diseases that is often associated with a poor prognosis including worsening of clinical outcome, neuropsychiatric complications as well as outcome following liver transplantation. Nutritional assessment in patients with cirrhosis is challenging owing to confounding factors related to liver failure. The objectives of nutritional intervention in cirrhotic patients are the support of liver regeneration, the prevention or correction of specific nutritional deficiencies and the prevention and/or treatment of the complications of liver disease per se and of liver transplantation. Nutritional recommendations target the optimal supply of adequate substrates related to requirements linked to energy, protein, carbohydrates, lipids, vitamins and minerals. Some issues relating to malnutrition in chronic liver disease remain to be addressed including the development of an appropriate well-validated nutritional assessment tool, the identification of mechanistic targets or therapy for sarcopenia, the development of nutritional recommendations for obese cirrhotic patients and liver-transplant recipients and the elucidation of the roles of vitamin A hepatotoxicity, as well as the impact of deficiencies in riboflavin and zinc on clinical outcomes. Early identification and treatment of malnutrition in chronic liver disease has the potential to lead to better disease outcome as well as prevention of the complications of chronic liver disease and improved transplant outcomes.

Nutrition in the management of cirrhosis and its neurological complications

Malnutrition is a common feature of chronic liver diseases that is often associated with a poor prognosis including worsening of clinical outcome, neuropsychiatric complications as well as outcome following liver transplantation. Nutritional assessment in patients with cirrhosis is challenging owing to confounding factors related to liver failure. The objectives of nutritional intervention in cirrhotic patients are the support of liver regeneration, the prevention or correction of specific nutritional deficiencies and the prevention and/or treatment of the complications of liver disease per se and of liver transplantation. Nutritional recommendations target the optimal supply of adequate substrates related to requirements linked to energy, protein, carbohydrates, lipids, vitamins and minerals. Some issues relating to malnutrition in chronic liver disease remain to be addressed including the development of an appropriate well-validated nutritional assessment tool, the identification of mechanistic targets or therapy for sarcopenia, the development of nutritional recommendations for obese cirrhotic patients and liver-transplant recipients and the elucidation of the roles of vitamin A hepatotoxicity, as well as the impact of deficiencies in riboflavin and zinc on clinical outcomes. Early identification and treatment of malnutrition in chronic liver disease has the potential to lead to better disease outcome as well as prevention of the complications of chronic liver disease and improved transplant outcomes.

Liver-brain proinflammatory signalling in acute liver failure: role in the pathogenesis of hepatic encephalopathy and brain edema

A robust neuroinflammatory response characterized by microglial activation and increased brain production of pro-inflammatory cytokines is common in acute liver failure (ALF). Mechanisms proposed to explain the neuroinflammatory response in ALF include direct effects of systemically-derived proinflammatory cytokines and the effects of brain lactate accumulation on pro-inflammatory cytokine release from activated microglia. Cell culture studies reveal a positive synergistic effect of ammonia and pro-inflammatory cytokines on the expression of proteins involved in glutamate homeostasis and in oxidative/nitrosative stress. Proinflammatory cytokines have the capacity to alter blood-brain barrier (BBB) integrity and preliminary studies suggest that the presence of infection in ALF results in rupture of the BBB and vasogenic brain edema. Treatments currently under investigation that are effective in prevention of encephalopathy and brain edema in ALF which are aimed at reduction of neuroinflammation in ALF include mild hypothermia, albumin dialysis systems, N-acetyl cysteine and the antibiotic minocycline with potent anti-inflammatory actions that are distinct from its anti-microbial properties.

N-acetylcysteine attenuates cerebral complications of non-acetaminophen-induced acute liver failure in mice: antioxidant and anti-inflammatory mechanisms

N-acetylcysteine (NAC) is an effective antidote to treat acetaminophen (APAP)-induced acute liver failure (ALF). NAC is hepatoprotective and prevents the neurological complications of ALF, namely hepatic encephalopathy and brain edema. The protective effect of NAC and its mechanisms of action in ALF due to other toxins, however, are still controversial. In the present study, we investigated the effects of NAC in relation to liver pathology, hepatic and cerebral glutathione, plasma ammonia concentrations, progression of encephalopathy, cerebral edema, and plasma proinflammatory cytokines in mice with ALF resulting from azoxymethane (AOM) hepatotoxicity, a well characterized model of toxic liver injury. Male C57BL/6 mice were treated with AOM (100 microg/g; i.p.) or saline and sacrificed at coma stage of encephalopathy in parallel with AOM mice administered NAC (1.2 g/kg; i.p.). AOM administration led to hepatic damage, significant increase in plasma transaminase activity, decreased hepatic glutathione levels and brain GSH/GSSG ratios as well as increased expression of plasma proinflammatory cytokines. NAC treatment of AOM mice led to reduced hepatic damage and improvement in neurological function, normalization of brain and hepatic glutathione levels as well as selective attenuation in expression of plasma proinflammatory cytokines. These findings demonstrate that the beneficial effects of NAC in experimental non-APAP-induced ALF involves both antioxidant and anti-inflammatory mechanisms.

Antioxidant and anti-inflammatory effects of mild hypothermia in the attenuation of liver injury due to azoxymethane toxicity in the mouse

Previous studies have demonstrated protective effects of mild hypothermia following acetaminophen (APAP)-induced acute liver failure (ALF). However, effects of this treatment in ALF due to other toxins have not yet been fully investigated. In the present study, the effects of mild hypothermia in relation to liver pathology, hepatic and cerebral glutathione, plasma ammonia concentrations, progression of encephalopathy, cerebral edema, and plasma proinflammatory cytokines were assessed in mice with ALF resulting from azoxymethane (AOM) hepatotoxicity, a well characterized model of toxic liver injury. Male C57BL/6 mice were treated with AOM (100 microg/g; i.p.) or saline and sacrificed at coma stages of encephalopathy in parallel with AOM mice maintained mildly hypothermic (35 degrees C). AOM treatment led to hepatic damage, significant increase in plasma transaminase activity, decreased hepatic glutathione levels, and brain GSH/GSSG ratios as well as selective increases in expression of plasma proinflammatory cytokines. Mild hypothermia resulted in reduced hepatic damage, improvement in neurological function, normalization of glutathione levels, and selective attenuation in expression of circulating proinflammatory cytokines. These findings demonstrate that the beneficial effects of mild hypothermia in experimental AOM-induced ALF involve both antioxidant and anti-inflammatory mechanisms.

IL-1 or TNF receptor gene deletion delays onset of encephalopathy and attenuates brain edema in experimental acute liver failure

Previous reports suggested that brain-derived proinflammatory cytokines are involved in the pathogenesis of hepatic encephalopathy (HE) and brain edema in acute liver failure (ALF). To further address this issue, expression of interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) mRNAs were measured in the brains of mice with acute liver failure resulting from exposure to azoxymethane. In addition, time to severe encephalopathy (coma) was assessed in mice lacking genes coding for interferon-gamma, the tumor necrosis factor receptor-1 or the interleukin-1 type 1 receptor. Interleukin-1beta, tumor necrosis factor-alpha and interferon-gamma expression were quantified using RT-PCR. Significant increases in interleukin-1beta and tumor necrosis factor-alpha mRNA were observed in the frontal cortex of azoxymethane-treated wild-type mice at coma stages of encephalopathy. Interferon-gamma, however, could not be detected in the brains of these animals. Onset of severe encephalopathy (coma) and brain edema in ALF mice were significantly delayed in interleukin-1 type 1 receptor or tumor necrosis factor receptor-1 knockout mice. Deletion of the interferon-gamma gene, on the other hand, had no significative effect on the neurological status or brain water content of acute liver failure mice. These results demonstrate that toxic liver injury resulting from exposure to azoxymethane is associated with selective induction of proinflammatory cytokines in the brain and that deletion of tumor necrosis factor receptor-1 or interlukin-1 type 1 receptor delays the onset of coma and brain edema in this model of acute liver failure. These findings further support a role for selective brain-derived cytokines in the pathogenesis of the cerebral complications in acute liver failure and suggest that anti-inflammatory strategies could be beneficial in their prevention.

Comparison of two rat models of cerebral ischemia under hyperglycemic conditions

Hyperglycemia worsens outcome of stroke either in the clinical setting or in animal models. In the present study, two focal cerebral ischemia models, permanent middle cerebral artery occlusion (MCAO, 3-4 h) and reversible MCAO (1 h ischemia + 3 h reperfusion), under hyperglycemic conditions were compared. Using 2,3,5-triphenyltetrazolium chloride staining to define viable tissue, this resulted in the infarction area being confined primarily to the cerebral cortex in the permanent MCAO group, while it extended to the subcortical area in the reversible MCAO group, and the lesion areas were respectively 27.7 +/- 5.3% and 46.8 +/- 12.0% of the ipsilateral hemisphere (P = 0.012). Hyperglycemia accelerated the cerebral damage compared to normoglycemia and ascorbic acid pre-treatment maintained tissue viability during the acute phase of hyperglycemic MCAO. In conclusion, hyperglycemia combined with either of the two MCAO models resulted in rapid infarction associated with increased oxidative stress. The hyperglycemic models are suitable for pharmaceutical therapeutic studies of antioxidant efficacy.

Increased oxidative stress during hyperglycemic cerebral ischemia

In this review, we summarize the role of hyperglycemia during cerebral ischemia. Hyperglycemia occurring during experimental and clinical stroke has been associated with increased cerebral damage. Increased oxidative stress resulting from hyperglycemia is believed to contribute to the exacerbated damage. More specifically, superoxide, nitric oxide and peroxynitrite are believed to play an important role in cerebral damage. This also involves increased recruitment of various blood cells to the ischemic zone that contribute to inflammation. We present data from our group and others that demonstrate that free radical production is increased during hyperglycemic stroke in rodents. Recent data suggest that inflammation is an important component of ischemic damage under both normo- and hyperglycemic conditions. We summarize numerous studies that indicate that a variety of antioxidant (inhibition of free radical production, scavenging of free radicals and increasing free radical degradation) and anti-inflammatory strategies decrease cerebral infarction. Finally, we compare the success of some of these strategies in clinical trials compared to the animal models.

Dehydroascorbic acid normalizes several markers of oxidative stress and inflammation in acute hyperglycemic focal cerebral ischemia in the rat

We investigated the effect of dehydroascorbic acid (DHA), the oxidized form of vitamin C which is a superoxide scavenger, on manganese superoxide dismutase (MnSOD), copper-zinc SOD (CuZnSOD), cyclooxygenase-2 (COX-2) and interleukin-1beta (IL-1beta) expression in a rat model of focal cerebral ischemia under normo- and hyperglycemic conditions. Edema formation was also assessed. MnSOD, CuZnSOD, COX-2 and IL-1beta mRNA and protein expression were studied 3 h post-ischemia. No changes were observed in MnSOD and CuZnSOD mRNA expression among the groups. COX-2 and IL-1beta mRNA expression were upregulated by ischemia but were not influenced by the glycemic state. At the protein level, hyperglycemic cerebral ischemia increased MnSOD and CuZnSOD [Bémeur, C., Ste-Marie, L., Desjardins, P., Butterworth, R.F., Vachon, L., Montgomery, J., Hazell, A.S., 2004a. Expression of superoxide dismutase in hyperglycemic focal cerebral ischemia in the rat. Neurochem. Int. 45, 1167-1174] and IL-1beta expression compared to normoglycemic ischemia. COX-2 protein expression was also significantly higher following hyperglycemic ischemia compared to hyperglycemic shams. DHA administration did not change the pattern of COX-2 or IL-1beta mRNA expression, but normalized the increased protein expression following hyperglycemic ischemia. DHA administration also normalized MnSOD and CuZnSOD protein expression to the levels observed in normoglycemic ischemic animals. Edema formation was significantly reduced by DHA administration in hyperglycemic ischemic animals. The DHA-induced post-transcriptional normalization of MnSOD, CuZnSOD, COX-2 and IL-1beta levels and the decreased edema formation suggest that hyperglycemia accelerates superoxide formation and the inflammatory response, thus contributing to early damage in hyperglycemic stroke and strategies to scavenge superoxide should be an important therapeutic avenue.

Expression of superoxide dismutase in hyperglycemic focal cerebral ischemia in the rat

This study investigated the possibility that hyperglycemia induces early expression of various superoxide dismutases (SOD) and nitric oxide synthases (NOS) following focal cerebral ischemia in the rat. MnSOD, CuZnSOD, nNOS and eNOS mRNA and protein expression were examined 3 h after permanent middle cerebral artery occlusion under acute hyperglycemic or normoglycemic conditions. 2,3,5-triphenyltetrazolium chloride (TTC) treatment post-mortem revealed a significant area at risk of infarction following ischemia in hyperglycemic compared to normoglycemic rats. Although no changes in MnSOD, CuZnSOD, nNOS and eNOS mRNA expression were detected, Western blots of ischemic cortex revealed an increase in MnSOD and CuZnSOD protein expression in hyperglycemic compared to normoglycemic rats. Pre-treatment of hyperglycemic rats with the NOS inhibitors L-nitroarginine methyl ester (L-NAME) and 7-nitroindazole (7-NI) or dehydroascorbic acid (DHA), a superoxide scavenger, significantly reduced the TTC delineated zone. The hyperglycemia-induced post-transcriptional upregulation of MnSOD and CuZnSOD levels suggest a response to increased superoxide production which, in the presence of increased nitric oxide production, may play a major role in the increased risk of damage following hyperglycemic stroke.

Decreased β-actin mRNA expression in hyperglycemic focal cerebral ischemia in the rat

beta-Actin is often used as a housekeeping gene when performing reverse transcription-polymerase chain reaction (RT-PCR) analysis for cerebral ischemia models. In the present study, we tested two different control genes used for RT-PCR experiments, beta-actin and porphobilinogen deaminase (PBG-D), in a rat model of focal cerebral ischemia under normo- or hyperglycemic conditions. A three-vessel occlusion model with permanent middle cerebral artery occlusion was used in the rat. beta-Actin mRNA expression was decreased in hyperglycemic ischemic rats compared to normoglycemic ischemic animals 3 h post-ischemia. beta-Actin protein content was unchanged. As for PBG-D, its mRNA expression remained constant throughout the groups. Our data thus show that, following focal cerebral ischemia in hyperglycemic conditions, beta-actin is an unsuitable housekeeping gene whereas PBG-D is more appropriate. This study clearly demonstrates the importance of selecting a stable housekeeping gene when performing RT-PCR experiments.

Immunohistochemical detection of inducible nitric oxide synthase, nitrotyrosine and manganese superoxide dismutase following hyperglycemic focal cerebral ischemia

We have characterized the temporal changes in iNOS, MnSOD and nitrotyrosine immune reactivity in a rat model of permanent middle cerebral artery occlusion under acute hyperglycemic or normoglycemic conditions followed by either 3- or 24-h recovery. We found that the macroscopic labeling pattern for all three antibodies colocalized with the ischemic core and penumbra which was determined by cresyl violet histological evaluation in adjacent sections. Hyperglycemia induced prior to ischemia resulted in earlier infarction which correlated with increased immunoreactivity for iNOS, MnSOD and nitrotyrosine. In the penumbral region of the frontal cortex, labeling of specific cell structures was largely limited to cortical neurons near the corpus callosum and was apparent earlier in the hyperglycemic rats. Increased polymorphonuclear leukocyte adhesion in blood vessels was observed at 24 h in the hyperglycemic group. At both of the recovery times studied, we observed only minor vascular staining for nitrotyrosine and none for iNOS. Our results are consistent with hyperglycemia resulting in an early and concomitant increase in both superoxide and nitric oxide production which can lead to peroxynitrite formation that then nitrates tyrosine residues. It would appear that hyperglycemic ischemia contributes to the early induction of key enzymes involved in nitric oxide bioavailability.

Hydroxyl radical production in the cortex and striatum in a rat model of focal cerebral ischemia

BACKGROUND

Increases in hydroxyl radical production have been used as evidence of oxidative stress in cerebral ischemia/ reperfusion. Ischemia can also induce increased dopamine release from the striatum that may contribute to hydroxyl radical formation. We have compared hydroxyl radical production in the cortex and striatum as an index of oxidative stress in a rat model of focal cerebral ischemia with cortical infarction.

METHODS

Using a three vessel occlusion model of focal cerebral ischemia combined with bilateral microdialysis, hydroxylation of 4-hydroxybenzoate (4HB) was continuously monitored in both hemispheres in either the lateral striatum or frontoparietal cortex. The ischemia protocol consisted of one hour equilibration, 30 min of three vessel occlusion, then release of the contralateral common carotid artery (CCA) for 2.5 h.

RESULTS

Induction of ischemia resulted in a 30-fold increase in dopamine release in the lateral striatum. Compared to the nonischemic striatum, the ratio of the hydroxylation product 3,4-dihydroxybenzoate (34DHB) to 4HB (trapping agent) in the ipsilateral striatum increased significantly 30 min after ischemia induction. In contrast, during the 30 min of three vessel occlusion there was no increase in the ratio in the cortex. Following the release of the contralateral CCA, the ratio from the ischemic cortex increased significantly compared to sham-operated animals. However, under all circumstances, the 34DHB/4HB ratio was greater in the striatum than in the cortex.

CONCLUSION

The increase in the 34DHB/4HB ratio in the lateral striatum coincides with the increased dopamine release suggesting a role for dopamine oxidation in the increased production of hydroxyl radicals. The significant increase in the ratio from the ischemic cortex compared to that from the sham-operated animals is consistent with increased oxidative stress induced by ischemia. However, the lower 34DHB/4HB ratio in the cortex which does not receive dopaminergic innervation compared to the striatum suggests a different mechanism for hydroxyl radical production. Such an alternate mechanism may represent a more toxic oxidative insult that contributes to infarction.

Local striatal infusion of MPP+ does not result in increased hydroxylation after systemic administration of 4-hydroxybenzoate

In vivo bilateral microdialysis in the rat striatum was used to investigate hydroxyl radical formation under basal conditions and after intrastriatal administration of the neurotoxin, 1-methyl-4-phenylpyridinium (MPP+). After a short equilibration period, 4-hydroxybenzoate (4HBZ), which scavenges hydroxyl radicals to produce 3,4-dihydroxybenzoate (34DHB), was injected intraperitoneally 15 min before infusion of MPP+. To evaluate the enzymatic contribution to hydroxyl radical formation, two other series of microdialyses were performed following administration of monoamine oxidase B inhibitors, either 1-deprenyl (selegiline) or MDL 72,974A [(E)-2-(4-fluorophenethyl)-3-fluoroallylamine hydrochloride]. Microdialysate samples were analyzed by high-performance liquid chromatography for catecholamines, 3,4-dihydroxyphenylacetate (DOPAC), homovanillate (HVA), along with the hydroxyl radical adduct, 34DHB and its precursor, 4HBZ. MPP+ administration resulted in a massive release of dopamine along with a decrease in DOPAC and HVA in all three groups. A striking effect in all three groups was noted in which MPP+ resulted in a decrease in interstitial 4HBZ to < 50% of the non-MPP+ -treated side. In absolute terms, the amount of 34DHB produced was low but similar in all three groups, even after unilateral MPP+ infusion. When 34DHB was normalized to 4HBZ release to account for differences in precursor availability, there were no significant differences in the 34DHB/4HBZ ratios either with or without MAO inhibitor treatment or after local MPP+ infusion. Systemic 4HBZ administration appears to result predominantly in intra-cellular sampling of hydroxyl radicals which produces different results from local infusion of trapping agents such as salicylate.