Acetate metabolism in normal human subjects

Urinary acid-base excretion deciphers high acid load from colonic bicarbonate loss in intestinal failure patients with ileocolonic anastomosis - Guidance for composition of parenteral support

BACKGROUND & AIMS

Acid-base disturbances are common in short bowel (SB) patients due to increased intestinal bicarbonate loss. However, the resulting systemic acid load has not been quantified. Base excess is used to monitor metabolic acid-base disturbances but inadequately reflects the acid load. Our aim was to investigate the systemic acid/base load in SB-patients to obtain quantitative estimates to guide the composition of parenteral support.

METHODS

We calculated total acid load in SB patients by summing 24-h urinary net acid excretion (NAE) and the provision of base equivalents in parenteral support. We then compared differences among anatomical SB-types: jejunostomy (SB-J), jejunocolostomy (SB-JC), and jejunoileostomy (SB-JIC). 47 urine samples from 34 SB patients were analyzed for bicarbonate (HCO3-), ammonium (NH4+), and titratable acid (TA) concentrations. NAE was calculated as (TA + NH4+) - HCO3-. Mixed-effects repeated-measures models were used to statistically examine differences between SB-types and associations with parenteral nutrition and NAE. A healthy cohort served as control.

RESULTS

In comparison to SB-J, SB-JC patients had a 4.1 mmoL/l lower base excess (95% CI: -6.3 to -1.8) and an 84.5 mmol/day higher total acid load (CI: 41.3 to 127.7). There were no significant differences between SB-JIC and SB-J regarding base excess, NAE, or total acid load. Higher amounts of infused acetate, sodium, and chloride, but not the acetate/chloride ratio, were associated with lower NAE and higher base excess.

CONCLUSIONS

Due to increased colonic bicarbonate loss, patients with SB-JC have a ∼4.4-fold higher acid load than healthy controls. The ion transport mechanisms mediating this bicarbonate loss from the remaining colon need further experimental investigation. NAE could be a useful tool to adjust base infusion in SB.

Short-chain fatty acids and insulin sensitivity: a systematic review and meta-analysis

CONTEXT

There is substantial evidence that reduced short-chain fatty acids (SCFAs) in the gut are associated with obesity and type 2 diabetes, although findings from clinical interventions that can increase SCFAs are inconsistent.

OBJECTIVE

This systematic review and meta-analysis aimed to assess the effect of SCFA interventions on fasting glucose, fasting insulin, and homeostatic model assessment of insulin resistance (HOMA-IR).

DATA SOURCES

Relevant articles published up to July 28, 2022, were extracted from PubMed and Embase using the MeSH (Medical Subject Headings) terms of the defined keywords [(short-chain fatty acids) AND (obesity OR diabetes OR insulin sensitivity)] and their synonyms. Data analyses were performed independently by two researchers who used the Cochrane meta-analysis checklist and the PRISMA guidelines.

DATA EXTRACTION

Clinical studies and trials that measured SCFAs and reported glucose homeostasis parameters were included in the analysis. Standardized mean differences (SMDs) with 95%CIs were calculated using a random-effects model in the data extraction tool Review Manager version 5.4 (RevMan 5.4). The risk-of-bias assessment was performed following the Cochrane checklist for randomized and crossover studies.

DATA ANALYSIS

In total, 6040 nonduplicate studies were identified, 23 of which met the defined criteria, reported fasting insulin, fasting glucose, or HOMA-IR values, and reported change in SCFA concentrations post intervention. Meta-analyses of these studies indicated that fasting insulin concentrations were significantly reduced (overall effect: SMD = -0.15; 95%CI = -0.29 to -0.01, P = 0.04) in treatment groups, relative to placebo groups, at the end of the intervention. Studies with a confirmed increase in SCFAs at the end of intervention also had a significant effect on lowering fasting insulin (P = 0.008). Elevated levels of SCFAs, compared with baseline levels, were associated with beneficial effects on HOMA-IR (P < 0.00001). There was no significant change in fasting glucose concentrations.

CONCLUSION

Increased postintervention levels of SCFAs are associated with lower fasting insulin concentrations, offering a beneficial effect on insulin sensitivity.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO registration number CRD42021257248.

Metabolite-based dietary supplementation in human type 1 diabetes is associated with microbiota and immune modulation

BACKGROUND

Short-chain fatty acids (SCFAs) produced by the gut microbiota have beneficial anti-inflammatory and gut homeostasis effects and prevent type 1 diabetes (T1D) in mice. Reduced SCFA production indicates a loss of beneficial bacteria, commonly associated with chronic autoimmune and inflammatory diseases, including T1D and type 2 diabetes. Here, we addressed whether a metabolite-based dietary supplement has an impact on humans with T1D. We conducted a single-arm pilot-and-feasibility trial with high-amylose maize-resistant starch modified with acetate and butyrate (HAMSAB) to assess safety, while monitoring changes in the gut microbiota in alignment with modulation of the immune system status.

RESULTS

HAMSAB supplement was administered for 6 weeks with follow-up at 12 weeks in adults with long-standing T1D. Increased concentrations of SCFA acetate, propionate, and butyrate in stools and plasma were in concert with a shift in the composition and function of the gut microbiota. While glucose control and insulin requirements did not change, subjects with the highest SCFA concentrations exhibited the best glycemic control. Bifidobacterium longum, Bifidobacterium adolescentis, and vitamin B7 production correlated with lower HbA1c and basal insulin requirements. Circulating B and T cells developed a more regulatory phenotype post-intervention.

CONCLUSION

Changes in gut microbiota composition, function, and immune profile following 6 weeks of HAMSAB supplementation were associated with increased SCFAs in stools and plasma. The persistence of these effects suggests that targeting dietary SCFAs may be a mechanism to alter immune profiles, promote immune tolerance, and improve glycemic control for the treatment of T1D.

TRIAL REGISTRATION

ACTRN12618001391268. Registered 20 August 2018, https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=375792 Video Abstract.

Sodium chloride or Plasmalyte-148 evaluation in severe diabetic ketoacidosis (SCOPE-DKA): a cluster, crossover, randomized, controlled trial

PURPOSE

To determine whether treatment with Plasmalyte-148 (PL) compared to sodium chloride 0.9% (SC) results in faster resolution of diabetic ketoacidosis (DKA) and whether the acetate in PL potentiates ketosis.

METHODS

We conducted a cluster, crossover, open-label, randomized, controlled Phase 2 trial at seven hospitals in adults admitted to intensive care unit (ICU) with severe DKA with hospital randomised to PL or SC as fluid therapy. The primary outcome, DKA resolution, was defined as a change in base excess to ≥ - 3 mEq/L at 48 h.

RESULTS

Ninety-three patients were enrolled with 90 patients included in the modified-intention-to-treat population (PL n = 48, SC n = 42). At 48 h, mean fluid administration was 6798 ± 4850 ml vs 6574 ± 3123 ml, median anion gap 6 mEq/L (IQR 5-7) vs 7 mEq/L (IQR 5-7) and median blood ketones 0.3 mmol/L (IQR 0.1-0.5) vs 0.3 (IQR 0.1-0.5) in the PL and SC groups. DKA resolution at 48 h occurred in 96% (PL) and 86% (SC) of patients; odds ratio 3.93 (95% CI 0.73-21.16, p = 0.111). At 24 h, DKA resolution occurred in 69% (PL) and 36% (SC) of patients; odds ratio 4.24 (95% CI 1.68-10.72, p = 0.002). The median ICU and hospital lengths of stay were 49 h (IQR 23-72) vs 55 h (IQR 41-80) and 81 h (IQR 58-137) vs 98 h (IQR 65-195) in the PL and SC groups.

CONCLUSION

Plasmalyte-148, compared to sodium chloride 0.9%, may lead to faster resolution of metabolic acidosis in patients with DKA without an increase in ketosis. These findings need confirmation in a large, Phase 3 trial.

Estimation of the risk of local and systemic effects in infants after ingestion of low-concentrated weak acids from descaling products

INTRODUCTION

The accidental ingestion of diluted household descaling products by infants is a phenomenon that poison control centers regularly encounter. Feeding infants with baby milk prepared with water from electric kettles still containing descaler is a common way of exposure. This study aimed to determine the risks related to ingestion of (diluted) descalers by infants.

METHODS

pH measurements were performed using acetic acid and three different commercially available electric kettle descalers. The pH of different dilutions was measured in the absence or presence of baby milk powder. In addition, an overview was made of pH values of different electric kettle descalers as given by the product information of the manufacturer. Finally, a simple pharmacokinetic (PK) model was used to predict changes in blood pH in infants after ingestion of acetic acid, which is the most commonly used descaler.

RESULTS

Several commercially available electric kettle descalers have a pH <2. Even after diluting such descalers up to 10 times the pH can remain low. The addition of milk powder increases the pH of descalers containing weaker acids, with a pH >1.5, while descalers with stronger acids and pH <1 show little pH increase after the addition of milk powder. Finally, a simple PBPK model for the ingestion of acetic acid predicted that the ingestion of larger amounts of acetic acid (>1000 mg) by an infant could result in relevant changes in blood pH.

CONCLUSIONS

Commercially available electric kettle descaling products may pose a health risk to infants in case of accidental ingestion since the pH of some of these products can be very low, even when diluted 10-times or in the presence of baby milk powder. Oral exposure of infants to the common descaler acetic acid, after accidental preparation of baby milk with cleaning vinegar, will probably not result in serious local effects, but changes in blood pH cannot be excluded when larger amounts of acetic acid are ingested.

Hepatic Arterial Buffer Response in Liver Radioembolization and Potential Use for Improved Cancer Therapy

Simple Summary

Radioembolization of hepatic tumors is performed by injecting ⁹⁰Y or ¹⁶⁶Ho loaded spheres into the hepatic artery. A twofold tumor to normal liver absorbed dose ratio is commonly obtained. In order to improve tumoral cell killing while preserving lobule function, co-injection of arterial vasoconstrictor has been proposed, but without success: the hepatic arterial buffer response quickly inhibits the arterioles vasoconstriction. The aim of the study is to investigate whether it is possible to take benefit from this buffer response, by co-infusing a mesenteric arterial vasodilator in order to dump the hepatic lobules arterial flow. Animal studies evidencing such mechanism are reviewed. Some potential mesenteric vasodilators are identified and their safety profile discussed. A four to sixfold improvement of the tumoral to normal tissue dose ratio is expected, pushing the therapy towards a real curative intention, especially in hepatocellular carcinoma (HCC), more frequent in obese subjects, and where ultra-selective spheres delivery is often not possible.

Abstract

Liver radioembolization is a treatment option for unresectable liver cancers, performed by infusion of ⁹⁰Y or ¹⁶⁶Ho loaded spheres in the hepatic artery. As tumoral cells are mainly perfused via the liver artery unlike hepatic lobules, a twofold tumor to normal liver dose ratio is commonly obtained. To improve tumoral cell killing while preserving lobules, co-infusion of arterial vasoconstrictor has been proposed but with limited success: the hepatic arterial buffer response (HABR) and hepatic vascular escape mechanism hamper the arterioles vasoconstriction. The proposed project aims to take benefit from the HABR by co-infusing a mesenteric arterial vasodilator: the portal flow enhancement inducing the vasoconstriction of the intra sinusoids arterioles barely impacts liver tumors that are mainly fed by novel and anarchic external arterioles. Animal studies were reviewed and dopexamine was identified as a promising safe candidate, reducing by four the hepatic lobules arterial flow. A clinical trial design is proposed. A four to sixfold improvement of the tumoral to normal tissue dose ratio is expected, pushing the therapy towards a real curative intention, especially in HCC where ultra-selective spheres delivery is often not possible.

Metabolism and inflammation: implications for traumatic brain injury therapeutics

INTRODUCTION

Traumatic Brain Injury (TBI) is a leading cause of death and disability in young people, affecting 69 million people annually, worldwide. The initial trauma disrupts brain homeostasis resulting in metabolic dysfunction and an inflammatory cascade, which can then promote further neurodegenerative effects for months or years, as a 'secondary' injury. Effective targeting of the cerebral inflammatory system is challenging due to its complex, pleiotropic nature. Cell metabolism plays a key role in many diseases, and increased disturbance in the TBI metabolic state is associated with poorer patient outcomes. Investigating critical metabolic pathways, and their links to inflammation, can potentially identify supplements which alter the brain's long-term response to TBI and improve recovery. Areas covered: The authors provide an overview of literature on metabolism and inflammation following TBI, and from relevant pre-clinical and clinical studies, propose therapeutic strategies. Expert opinion: There is still no specific active drug treatment for TBI. Changes in metabolic and inflammatory states have been reported after TBI and appear linked. Understanding more about abnormal cerebral metabolism following TBI, and its relationship with cerebral inflammation, will provide essential information for designing therapies, with implications for neurocritical care and for alleviating long-term disability and neurodegeneration in post-TBI patients.

Resuscitation fluid composition affects hepatic inflammation in a murine model of early sepsis

BACKGROUND

Fluid resuscitation is a crucial therapy for sepsis, and the use of balanced fluids and/or isotonic albumin may improve patient survival. We have previously demonstrated that resuscitation with normal saline results in increased hepatic leukocyte recruitment in a murine model of sepsis. Given that clinical formulations of albumin are in saline, our objectives were to develop a novel balanced electrolyte solution specifically for sepsis and to determine if supplementing this solution with albumin would improve the inflammatory response in sepsis.

METHODS

We developed two novel buffered electrolyte solutions that contain different concentrations of acetate and gluconate, named Seplyte L and Seplyte H, and administered these solutions with or without 5% albumin. Normal saline with or without albumin and Ringer's lactate served as controls. Sepsis was induced by cecal ligation and puncture (CLP), and the liver microvasculature was imaged in vivo at 6 h after CLP to quantify leukocyte recruitment. Hepatic cytokine expression and plasma cell-free DNA (cfDNA) concentrations were also measured.

RESULTS

Septic mice receiving either Seplyte fluid showed significant reductions in hepatic post-sinusoidal leukocyte rolling and adhesion compared to normal saline. Hepatic cytokine concentrations varied in response to different concentrations of acetate and gluconate in the novel resuscitation fluids but were unaffected by albumin. All Seplyte fluids significantly increased hepatic TNF-α levels at 6 h compared to control fluids. However, Seplyte H exhibited a similar cytokine profile to the control fluids for all other cytokines, whereas mice given Seplyte L had significantly elevated IL-6, IL-10, KC (CXCL1), and MCP-1 (CCL2). Plasma cfDNA was generally increased during sepsis, but resuscitation fluid composition did not significantly affect cfDNA concentrations.

CONCLUSIONS

Electrolyte concentrations and buffer constituents of resuscitation fluids can modulate hepatic cytokine production and leukocyte recruitment in septic mice, while the effects of albumin are modest during early sepsis. Therefore, crystalloid fluid choice should be an important consideration for resuscitation in sepsis, and the effects of fluid composition on inflammation in other organ systems should be studied to better understand the physiological impact of this vital sepsis therapy.

Blood biochemical changes in pigs after infusion with acetate-buffered or lactate-buffered crystalloid solutions

Perioperative fluid therapy is an important component of many medical procedures with animals. Buffered crystalloid solutions avoid inducing metabolic acidosis, but lactated solutions can elevate blood lactate concentrations and acetated solutions have not been thoroughly investigated using large animals. Here, the authors compare blood biochemical parameters in 20 juvenile pigs after perioperative fluid administration of an acetate-buffered solution (Elo-Mel isoton, EMI) or a lactate-buffered solution (lactated Ringer's solution, LRS). The authors measured blood lactate, glucose and electrolyte concentrations before and after administering the test fluid during surgery. Blood lactate concentration after administration was significantly higher in pigs that received LRS than in pigs that received EMI, but glucose and electrolyte concentrations did not differ significantly between treatment groups before or after administration. These findings suggest that EMI might be a preferable option for perioperative fluid therapy in pigs.

Chloride toxicity in critically ill patients: What's the evidence?

Crystalloids have become the fluid of choice in critically ill patients and in the operating room both for fluid resuscitation and fluid maintenance. Among crystalloids, NaCl 0.9% has been the most widely used fluid. However, emerging evidence suggests that administration of 0.9% saline could be harmful mainly through high chloride content and that the use of fluid with low chloride content may be preferable in major surgery and intensive care patients. Administration of NaCl 0.9% is the leading cause of metabolic hyperchloraemic acidosis in critically ill patients and side effects might target coagulation, renal function, and ultimately increase mortality. More balanced solutions therefore may be used especially when large amount of fluids are administered in high-risk patients. In this review, we discuss physiological background favouring the use of balanced solutions as well as the most recent clinical data regarding the use of crystalloid solutions in critically ill patients and patients undergoing major surgery.

L-Malate's Plasma and Excretion Profile in the Treatment of Moderate and Severe Hemorrhagic Shock in Rats

Introduction. Malate is a standard component in fluid therapy within a wide range of medical applications. To date, there are insufficient data regarding its plasma distribution, renal excretion, and metabolism after infusion. This study aimed to investigate these three aspects in a rat model of moderate and severe hemorrhagic shock (HS). Methods. Male Wistar rats were subjected to HS by dropping the mean arterial blood pressure to 25-30 mmHg (severe) and 40-45 mmHg (moderate), respectively, for 60 minutes. Subsequently, reperfusion with Ringer-saline or a malate containing crystalloid solution (7 mM, 13.6 mM, and 21 mM, resp.) was performed within 30 minutes, followed by an observation period of 150 minutes. Results. In the present experiments, malate rapidly disappeared from the blood, while only 5% of the infused malate was renally excreted. In the resuscitation interval the urinary citrate and succinate amounts significantly increased compared to control. Conclusion. Malate's half-life is between 30 and 60 minutes in both, moderate and severe HS. Thus, even under traumatic conditions malate seems to be subjected to rapid metabolism with participation of the kidneys.

Metabolic profile in right lobe living donor hepatectomy: Comparison of lactated Ringer's solution and normal saline versus acetate based balanced salt solution - a pilot study

BACKGROUND AND AIMS

Lactate levels predict outcomes after hepatectomy. We compared metabolic effects of lactated versus lactate free solutions in living donor hepatectomy.

METHODS

Consecutive right lobe donors (n = 53) were alternatively allotted to lactated Ringer's solution and normal saline (Group L-control) or acetated crystalloid (Sterofundin B Braun^® Group S -study group) in an observational prospective randomised study. The primary outcome measure was lactate level, and secondary outcomes were base excess, bicarbonate, glucose and chloride intra- and post-operatively. Mann-Whitney and Chi-square tests were used for analysis.

RESULTS

The intraoperative, post-operative lactate levels and the time for normalisation were comparable. Group L had significantly lower intraoperative bicarbonate levels (mmol/L) at 6 and 8 h (20.0 ± 2.14 vs. 21.3 ± 1.6, P = 0.0471; 18.68 ± 2.04 vs. 20.39 ± 17, P = 0.002), base excess at 4 and 6 h (mmol/L) (-3.64 ± 2.73 vs. -3.0 ± 1.52, P = 0.031; -6.64 ± 2.76 vs. -4.35 ± 1.7 P = 0.006). The intraoperative chloride levels (mmol/L) were higher in group L at 4 and 8 h (108 ± 5.9 vs. 105.99 ± 2.76, P = 0.0471; 109.51 ± 3.86 vs. 106.93 ± 3.09, P = 0.002). Intraoperative glucose (mg/dL) at 6 h was higher in group L, 160.55 ± 31.52 vs. 145.5 ± 24.29, P = 0.043. The highest post-operative chloride (mmol/L) was higher in Group L (112.3 ± 3.86 vs. 109.81 ± 3.72, P = 0.034). Post-operative base excess and bicarbonate showed an improved profile in Group S (-7.37 ± 2.99 vs. -5.06 ± 1.71 P = 0.001 and 17.79 ± 2.23 vs. 19.68 ± 1.51 P = 0.005).

CONCLUSION

Acetated fluids were associated with higher levels of bicarbonate, lesser base deficit, glucose and chloride but no difference in lactate levels in comparison with Ringer's lactate and normal saline in living donor hepatectomy.

Balanced vs unbalanced crystalloid resuscitation in a near-fatal model of hemorrhagic shock and the effects on renal oxygenation, oxidative stress, and inflammation

BACKGROUND

The aim of the present study was to test the hypothesis that balanced crystalloid resuscitation would be better for the kidney than unbalanced crystalloid resuscitation in a rat hemorrhagic shock model.

METHODS

Male Wistar rats were randomly assigned to four groups (n=6/group): (1) time control; (2) hemorrhagic shock control; (3) hemorrhagic shock followed by unbalanced crystalloid resuscitation (0.9% NaCl); and (4) hemorrhagic shock followed by acetate and gluconate-balanced crystalloid resuscitation (Plasma Lyte). We tested the solutions for their effects on renal hemodynamics and microvascular oxygenation, strong-ion difference, systemic and renal markers of inflammation and oxidative stress including glycocalyx degradation as well as their effects on renal function.

RESULTS

The main findings of our study were that: (1) both the balanced and unbalanced crystalloid solutions successfully restored the blood pressure, but renal blood flow was only recovered by the balanced solution although this did not lead to improved renal microvascular oxygenation; (2) while unbalanced crystalloid resuscitation induced hyperchloremia and worsened metabolic acidosis in hemorrhaged rats, balanced crystalloid resuscitation prevented hyperchloremia, restored the acid-base balance, and preserved the anion gap and strong ion difference in these animals; (3) in addition balanced crystalloid resuscitation significantly improved renal oxygen consumption (increased VO(2), decreased [Formula: see text] ); and (4) however neither balanced nor unbalanced crystalloid resuscitation could normalize systemic inflammation or oxidative stress. Functional immunohistochemistry biomarkers showed improvement in L-FABP in favor of balanced solutions in comparison to the hemorrhagic group although no such benefit was seen for renal tubular injury (measured by NGAL) by giving either unbalanced or balanced solutions.

CONCLUSIONS

Although balanced crystalloid resuscitation seems superior to balanced crystalloid resuscitation in protecting the kidney after hemorrhagic shock and is certainly better than not applying fluid resuscitation, these solutions were not able to correct systemic inflammation or oxidative stress associated with hemorrhagic shock.

Plasma acetate, gluconate and interleukin-6 profiles during and after cardiopulmonary bypass: a comparison of Plasma-Lyte 148 with a bicarbonate-balanced solution

INTRODUCTION

As even small concentrations of acetate in the plasma result in pro-inflammatory and cardiotoxic effects, it has been removed from renal replacement fluids. However, Plasma-Lyte 148 (Plasma-Lyte), an electrolyte replacement solution containing acetate plus gluconate is a common circuit prime for cardio-pulmonary bypass (CPB). No published data exist on the peak plasma acetate and gluconate concentrations resulting from the use of Plasma-Lyte 148 during CPB.

METHODS

Thirty adult patients were systematically allocated 1:1 to CPB prime with either bicarbonate-balanced fluid (24 mmol/L bicarbonate) or Plasma-Lyte 148. Arterial blood acetate, gluconate and interleukin-6 (IL-6) levels were measured immediately before CPB (T1), three minutes after CPB commencement (T2), immediately before CPB separation (T3), and four hours post separation (T4).

RESULTS

Acetate concentrations (normal 0.04 to 0.07 mmol/L) became markedly elevated at T2, where the Plasma-Lyte group (median 3.69, range (2.46 to 8.55)) exceeded the bicarbonate group (0.16 (0.02 to 3.49), P < 0.0005). At T3, levels had declined but the differential pattern remained apparent (Plasma-Lyte 0.35 (0.00 to 1.84) versus bicarbonate 0.17 (0.00 to 0.81)). Normal circulating acetate concentrations were not restored until T4. Similar gluconate concentration profiles and inter-group differences were seen, with a slower T3 decay. IL-6 increased across CPB, peaking at T4, with no clear difference between groups.

CONCLUSIONS

Use of acetate containing prime solutions result in supraphysiological plasma concentrations of acetate. The use of acetate-free prime fluid in CPB significantly reduced but did not eliminate large acetate surges in cardiac surgical patients. Complete elimination of acetate surges would require the use of acetate free bolus fluids and cardioplegia solutions.

TRIAL REGISTRATION

Australia and New Zealand Clinical Trials Register (ANZCTR): ACTRN12610000267055.

Nutritional aspects of post exercise skeletal muscle glycogen synthesis in horses: a comparative review

Carbohydrate (CHO) stored in the form of skeletal muscle glycogen is the main energy source for glycolytic and oxidative ATP production during vigorous exercise in mammals. In man, horse and dog both short-term high intensity and prolonged submaximal exercise deplete muscle glycogen. In horses, however, muscle glycogen synthesis is 2-3-fold slower than in man and rat, even when a diet high in soluble CHO is fed. There appear to be significant differences in CHO and glycogen metabolism between horses and other mammals, and it is becoming increasingly clear that many conclusions drawn from human exercise physiology do not apply to horses. This review aims to provide a comprehensive, comparative summary of the research on muscle glycogen synthesis in horse, man and rodent. Species differences in CHO uptake and utilisation are examined and the issues with feeding high soluble CHO diets to horses are discussed. Alternative feeding strategies, including protein and long and short chain fatty acid supplementation and the importance of rehydration, are explored.

Acid-base effects of a bicarbonate-balanced priming fluid during cardiopulmonary bypass: comparison with Plasma-Lyte 148. A randomised single-blinded study

Fluid-induced metabolic acidosis can be harmful and can complicate cardiopulmonary bypass. In an attempt to prevent this disturbance, we designed a bicarbonate-based crystalloid circuit prime balanced on physico-chemical principles with a strong ion difference of 24 mEq/l and compared its acid-base effects with those of Plasma-Lyte 148, a multiple electrolyte replacement solution containing acetate plus gluconate totalling 50 mEq/l. Twenty patients with normal acid-base status undergoing elective cardiac surgery were randomised 1:1 to a 2 litre prime of either bicarbonate-balanced fluid or Plasma-Lyte 148. With the trial fluid, metabolic acid-base status was normal following bypass initiation (standard base excess 0.1 (1.3) mEq/l, mean, SD), whereas Plasma-Lyte 148 produced a slight metabolic acidosis (standard base excess -2.2 (2.1) mEq/l). Estimated group difference after baseline adjustment was 3.6 mEq/l (95% confidence interval 2.1 to 5.1 mEq/l, P=0.0001). By late bypass, mean standard base excess in both groups was normal (0.8 (2.2) mEq/l vs. -0.8 (1.3) mEq/l, P=0.5). Strong ion gap values were unaltered with the trial fluid, but with Plasma-Lyte 148 increased significantly on bypass initiation (15.2 (2.5) mEq/l vs. 2.5 (1.5) mEq/l, P < 0.0001), remaining elevated in late bypass (8.4 (3.4) mEq/l vs. 5.8 (2.4) mEq/l, P < 0.05). We conclude that a bicarbonate-based crystalloid with a strong ion difference of 24 mEq/l is balanced for cardiopulmonary bypass in patients with normal acid-base status, whereas Plasma-Lyte 148 triggers a surge of unmeasured anions, persisting throughout bypass. These are likely to be gluconate and/or acetate. Whether surges of exogenous anions during bypass can be harmful requires further study.

L-Rhamnose increases serum propionate after long-term supplementation, but lactulose does not raise serum acetate

BACKGROUND

Acute ingestion of the unabsorbed sugar l-rhamnose in humans raises serum propionate, whereas acute ingestion of lactulose raises serum acetate. It is not known whether short-chain fatty acid concentrations in urine and feces reflect those in blood.

OBJECTIVE

The objective was to test the effects of oral l-rhamnose and lactulose for 28 d on acetate and propionate concentrations in serum, urine, and feces.

DESIGN

Eleven subjects ingested 25 g l-rhamnose, lactulose, or d-glucose (control) for 28 d in a partially randomized crossover design. One fecal sample, hourly blood samples, and all urine samples were collected over 12 h on the last day of each phase.

RESULTS

The increase in serum propionate was greater after l-rhamnose than after lactulose (P < 0.05). The effect of lactulose on serum acetate was not significant, but lactulose raised the acetate:propionate ratio compared with d-glucose or l-rhamnose in serum (P < 0.005) and urine (P < 0.02). Flatulence was significantly greater after lactulose and l-rhamnose than after d-glucose (P < 0.0001), an effect that lasted 4 wk with lactulose but only 1 wk with l-rhamnose.

CONCLUSIONS

This study confirmed that l-rhamnose ingestion over 28 d continues to selectively raise serum propionate in humans. Although serum acetate did not increase significantly after lactulose, the serum acetate:propionate ratio was significantly different after l-rhamnose and lactulose, which suggests that these substrates could be used to examine the role of colonic acetate and propionate production in the effect of dietary fiber on lipid metabolism. Changes in the ratio of urinary acetate to propionate reflected those in serum.

Skeletal muscle pyruvate dehydrogenase activity during acetate infusion in humans

Pyruvate dehydrogenase activity (PDHa), acetyl group, and citrate accumulation were examined in human skeletal muscle at rest and during cycling exercise while acetate was infused. Eight subjects received 400 mmol of sodium acetate (Ace) at a constant rate during 20 min of rest, 5 min of cycling at 40% maximal O2 uptake (VO2max) and 15 min of cycling at 80% VO2max. Two weeks later experiments were repeated while 400 mmol of sodium bicarbonate was infused in the control condition (CON). Ace infusion increased muscle acetyl-coenzyme A (acetyl-CoA), citrate, and acetylcarnitine. A decline in resting PDHa during 20 min of Ace infusion (0.37 +/- 0.08 vs. 0.16 +/- 0.03 mmol.min-1.kg wet wt-1) coincided with an elevation in the acetyl-CoA-to-free CoA ratio (acetyl-CoA/CoASH; 0.28 +/- 0.04 to 0.73 +/- 0.14). After 20 min of CON infusion, resting PDHa (0.32 +/- 0.06 mmol.min-1.kg wet wt-1) was similar to PDHa before Ace infusion. During exercise, acetyl-CoA, citrate, and acetyl-CoA/CoASH were further elevated, and the differences that existed at rest were resolved. PDHa increased to the same extent in Ace and CON, in which it was 44-47% transformed after 5 min at 40% VO2max and completely transformed after 15 min at 80% VO2max. At rest PDHa was regulated by variations in acetyl-CoA/CoASH secondary to enhanced acetate metabolism. Conversely, during exercise PDHa regulation appeared independent of variations in acetyl-CoA/CoASH. The resting data are consistent with a central role for PDHa and citrate in the regulation of the glucose-fatty acid cycle in skeletal muscle, as classically proposed. However, in the present study Ace infusion was not effective in perturbing the glucose-fatty acid cycle during exercise.

Effects of acetate on the immune system of mice

The effects of acetate on antibody production and cell-mediated immunity in mice were investigated. Polyclonal antibody responses could be enhanced in vivo by single intraperitoneal administration of acetate (5 mg/mouse) in C57BL/6 mice but not in DBA/2 mice. No enhancement of antibody production by acetate was also induced in athymic C57BL/6 nude mice and carrageenan-pretreated, macrophage-depleted mice. The inoculation of acetate-nonresponder BDF1 mice with T-cells and peritoneal adherent cells derived from acetate-treated C57BL/6 mice resulted in an enhanced antibody response. These results suggest that acetate increases polyclonal antibody responses in vivo by activating indirectly T-cells and macrophages. Acetate administration increased delayed hypersensitivity to pircryl chloride in C57BL/6 mice but not in DBA/2 mice. Allogeneic mixed lymphocyte reaction (MLR) of T-lymphocytes derived from the spleen of acetate-treated C57BL/6 mice was also enhanced. The natural killer (NK) activity and antibody-dependent cell-mediated cytotoxicity (ADCC) were also increased in C57BL/6 mice that were administered acetate. The possible mechanism of the immunopotentiating effect of this chemical is discussed.

Acute cardiovascular and metabolic effects of acetate in men

We studied the potential contribution of acetate to the cardiovascular effects of ethanol in 12 healthy male volunteers. Sodium acetate, or sodium chloride in control experiments, was infused i.v. at the rate of 0.033 mEq/kg/min for 60 min. Left ventricular function was examined by M-mode echocardiography and systolic time intervals during infusion and for 60 min thereafter. Blood acetate rose during infusion from 0.19 +/- 0.02 (mean +/- SEM) to a maximum of 0.99 +/- 0.08 mmol/liter. Changes in serum free fatty acids, glycerol, and ketone bodies indicate that acetate inhibited peripheral lipolysis. The volume of urine excreted during the acetate experiment (305 +/- 37 ml) was significantly larger (p less than 0.01) than during the chloride experiment (181 +/- 21 ml). Left ventricular function did not differ between the experiments during the infusions even though at 45 min heart rate was increased by acetate (7%; p less than 0.01, between infusions). After the infusion period, at 75 min the treatment by acetate increased cardiac output from the baseline by 17% (p less than 0.05, between infusions), and decreased peripheral arterial resistance (19%, p less than 0.05), and diastolic blood pressure (10%, p less than 0.01). Circumferential fiber shortening velocity was increased during the acetate experiment maximally by 7% (p less than 0.01) from the baseline at 120 min. These data indicate that acetate is an arterial vasodilator and a mild diuretic and may slightly improve myocardial performance in the concentrations encountered during ethanol metabolism in men.

The medical and metabolic consequences of administration of sodium acetate

1. The standard total parenteral nutrition, peritoneal dialysis, hemodialysis and many surgical fluids in use today contain 36 to 45 mM D,L-lactate or 2 to 140 mM acetate whereas the normal blood level of D-lactate is 0.02 mM L-lactate 0.5 to 5 mM and acetate 0.1 nM. The reasons for the continued use in patients of such unphysiological concentrations of these anions appear to be historic. 2. Administration of similar concentrations of these anions to the rat causes widespread metabolic disturbances which mimic many of the untoward complications associated with current parenteral and dialysis therapy. Understanding of the mechanisms attendant upon the metabolism of these anions may serve as a guide for designing improved parenteral fluids for human patients. 3. Elevation of blood D-lactate to 5 mM is associated with cerebral dysfunction in human patients. 4. Acetate stimulates the release of the inflammatory leukokine, interleukin-1 from human monocytes. Use of 35 to 45 mM acetate in peritoneal dialysis fluids led to peritoneal fibrosis. Patients exposed to acetate containing hemodialysis fluids have 12-fold elevation in their plasma interleukin-1 levels. 5. Administration of 20 mM sodium acetate to rats leads to a number of metabolic disturbances similar to those seen in human dialysis patients: (a) Acetate elevates blood glucose in the rat and may contribute to the exacerbation of the carbohydrate intolerance seen in uremic patients. (b) Acetate increases the levels of hepatic malonyl CoA, the rate controlling substrate of fatty acid synthesis and may exacerbate the hypertriglyceridemia characteristic of dialysis patients. (c) Acetate administration in the rat leads to a decrease in the cytosolic phosphorylation potential, reduction of the redox state of the free cytosolic NAD couple and paradoxical oxidation of the mitochondrial NAD couple in a pattern analogous to that produced by uncouplers of oxidative phosphorylation and may account in part for the elevation of temperature reported in patients undergoing hemodialysis with acetate. (d) Acetate administration in the rat leads to an increase in intracellular phosphorylated intermediates, adenine nucleotides, inorganic phosphate, inorganic pyrophosphate, calcium and magnesium. On cessation of acetate metabolism, the inorganic phosphate and calcium accumulated intracellularly leave the intracellular space. In patients undergoing hemodialysis, the blood phosphate returns to predialysis levels, within 6 hr after the completion of treatment, leaving significant numbers of patients with chronic hyperphosphatemia and the multiple complications attendant to that state.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetate metabolism and bicarbonate generation during hemodialysis: 10 years of observation

The capacity of chronically hemodialyzed patients to metabolize acetate during conventional hemodialysis was evaluated using a retrospective study in 219 patients dialyzed for up to ten years under similar dialysis conditions. For each patient, and using all available data, a regression line relating the changes of plasma total CO2 during dialysis as a function of the pre-dialysis value was calculated. The intercept of this function indicates the plasma concentration where the losses of bicarbonate in the dialysate is matched by the generation of bicarbonate arising from the metabolism of acetate. This value therefore represents an individual index of the capacity of each patient to metabolize acetate. A value for this index smaller than 18.0 mM was considered abnormal. It was shown that around 10% of chronically hemodialyzed patients are clearly unable to metabolize acetate optimally. This defect is not related to the duration of dialysis, body weight or quality of hemodialysis treatments but is strongly related to sex, 19 of the 22 "acetate intolerant" patients being women. In a prospective study, all the 60 patients of the same population undergoing active dialysis were studied, and this index identified 12 abnormal (11 women, 1 man) patients and 48 normal patients. Plasma acetate measured at the end their dialysis treatments were significantly higher in abnormal than in normal patients. It is concluded: that this index is useful to identify the patients unable to metabolize acetate optimally; that only around 10% of hemodialyzed patients present a severe problem when dialyzed against acetate and should be dialyzed against bicarbonate; that dialysis against acetate does not fully correct the metabolic acidosis even in "normal" patients.

Acetate dialysate versus bicarbonate dialysate: a continuing controversy

The use of bicarbonate dialysate as the buffer during routine dialysis is growing. This discussion reviews several of the comparative trials in which bicarbonate and acetate buffers have been tested. Effects of the two buffers on BP, cardiac function, and pulmonary performance are discussed. Costs of the two systems are also compared. Patients who seem most likely to benefit from bicarbonate dialysate include those with a reduced muscle mass in whom a high sodium dialysate has not prevented hypotension.

Pulmonary gas exchange during hemodialysis and peritoneal dialysis: interaction between respiration and metabolism

This review concerns the alterations in pulmonary gas exchange during hemodialysis and peritoneal dialysis. The occurrence of hypoxemia during hemodialysis has led to numerous studies that now provide sufficient data to explain this complex phenomenon. The role of substrate metabolism during hemodialysis and peritoneal dialysis are explored as it relates to alterations in ventilation. Comparison to similar types of ventilatory changes occurring during total parenteral nutrition are discussed. The effect of peritoneal dialysis on pulmonary function is also described.

Effects of acetate and bicarbonate dialysate in stable chronic dialysis patients

The effects of acetate and bicarbonate dialysate on the biochemical and clinical parameters of 16 stable chronic hemodialysis patients were investigated in a double-blind crossover study. A central delivery system was used for both types of dialysates with identical sodium concentrations (138 mEq/liter) and osmolality in a single-pass dialysate flow. The results indicate that dialysis with bicarbonate leads to significantly less hypoxemia (P less than or equal to 0.001) and hypotensive episodes (P less than or equal to 0.002) than with acetate. Pre- to post-dialysis blood pressure changes were also more marked during acetate dialysis. Older patients with recurrent hypotension on acetate benefit most from bicarbonate dialysate. This group of patients appears to metabolize acetate more slowly and has a significantly lower post-dialysis bicarbonate concentration (P less than or equal to 0.005) than asymptomatic patients during dialysis with acetate dialysate.