Effect of ketone bodies on glucose production and utilization in the miniature pig

Effect of exogenous and endogenous ketones on respiratory exchange ratio and glucose metabolism in healthy subjects

This study examined the effect of exogenous ketone bodies (KB) on oxygen consumption (V̇o2), carbon dioxide production (V̇co2), and glucose metabolism. The data were compared with the effects of endogenous ketonemia during both, a ketogenic diet or fasting. Eight healthy individuals [24.1 ± 2.5 yr, body mass index (BMI) 24.3 ± 3.1 kg/m2] participated in a crossover intervention study and were studied in a whole-room indirect calorimeter (WRIC) to assess macronutrient oxidation following four 24-h interventions: isocaloric controlled mixed diet (ISO), ISO supplemented with ketone salts (38.7 g of β-hydroxybutyrate/day, EXO), isocaloric ketogenic diet (KETO), and total fasting (FAST). A physical activity level of 1.65 was obtained. In addition to plasma KB, 24-h C-peptide and KB excretion rates in the urine and postprandial glucose and insulin levels were measured. Although 24-h KB excretion increased in response to KETO and FAST, there was a modest increase in response to EXO only (P < 0.05). When compared with ISO, V̇o2 significantly increased in KETO (P < 0.01) and EXO (P < 0.001), whereas there was no difference in FAST. V̇co2 increased in EXO but decreased in KETO (both P < 0.01) and FAST (P < 0.001), resulting in 24-h respiratory exchange ratios (RER) of 0.828 ± 0.024 (ISO) and 0.811 ± 0.024 (EXO) (P < 0.05). In response to EXO there were no differences in basal and postprandial glucose and insulin levels, as well as in insulin sensitivity. When compared with ISO, EXO, and KETO, FAST increased homeostatic model assessment β-cell function (HOMA-B) (all P < 0.05). In conclusion, at energy balance exogenous ketone salts decreased respiratory exchange ratio without affecting glucose tolerance.NEW & NOTEWORTHY Our findings revealed that during isocaloric nutrition, additional exogenous ketone salts increased V̇o2 and V̇co2 while lowering the respiratory exchange ratio (RER). Ketone salts had no effect on postprandial glucose metabolism.

Acute ketone supplementation in the absence of muscle glycogen utilization: Insights from McArdle disease

BACKGROUND & AIMS

Ketone supplementation is gaining popularity. Yet, its effects on exercise performance when muscle glycogen cannot be used remain to be determined. McArdle disease can provide insight into this question, as these patients are unable to obtain energy from muscle glycogen, presenting a severely impaired physical capacity. We therefore aimed to assess the effects of acute ketone supplementation in the absence of muscle glycogen utilization (McArdle disease).

METHODS

In a randomized cross-over design, patients with an inherited block in muscle glycogen breakdown (i.e., McArdle disease, n = 8) and healthy controls (n = 7) underwent a submaximal (constant-load) test that was followed by a maximal ramp test, after the ingestion of a placebo or an exogenous ketone ester supplement (30 g of D-beta hydroxybutyrate/D 1,3 butanediol monoester). Patients were also assessed after carbohydrate (75 g) ingestion, which is currently considered best clinical practice in McArdle disease.

RESULTS

Ketone supplementation induced ketosis in all participants (blood [ketones] = 3.7 ± 0.9 mM) and modified some gas-exchange responses (notably increasing respiratory exchange ratio, especially in patients). Patients showed an impaired exercise capacity (-65 % peak power output (PPO) compared to controls, p < 0.001) and ketone supplementation resulted in a further impairment (-11.6 % vs. placebo, p = 0.001), with no effects in controls (p = 0.268). In patients, carbohydrate supplementation resulted in a higher PPO compared to ketones (+21.5 %, p = 0.001) and a similar response was observed vs. placebo (+12.6 %, p = 0.057).

CONCLUSIONS

In individuals who cannot utilize muscle glycogen but have a preserved ability to oxidize blood-borne glucose and fat (McArdle disease), acute ketone supplementation impairs exercise capacity, whereas carbohydrate ingestion exerts the opposite, beneficial effect.

Dialysis as a Novel Adjuvant Treatment for Malignant Cancers

Simple Summary

There is a clear need for new cancer therapies as many cancers have a very short long-term survival rate. For most advanced cancers, therapy resistance limits the benefit of any single-agent chemotherapy, radiotherapy, or immunotherapy. Cancer cells show a greater dependence on glucose and glutamine as fuel than healthy cells do. In this article, we propose using 4- to 8-h dialysis treatments to change the blood composition, i.e., lowering glucose and glutamine levels, and elevating ketone levels—thereby disrupting major metabolic pathways important for cancer cell survival. The dialysis’ impact on cancer cells include not only metabolic effects, but also redox balance, immunological, and epigenetic effects. These pleiotropic effects could potentially enhance the effectiveness of traditional cancer treatments, such as radiotherapies, chemotherapies, and immunotherapies—resulting in improved outcomes and longer survival rates for cancer patients.

Abstract

Cancer metabolism is characterized by an increased utilization of fermentable fuels, such as glucose and glutamine, which support cancer cell survival by increasing resistance to both oxidative stress and the inherent immune system in humans. Dialysis has the power to shift the patient from a state dependent on glucose and glutamine to a ketogenic condition (KC) combined with low glutamine levels—thereby forcing ATP production through the Krebs cycle. By the force of dialysis, the cancer cells will be deprived of their preferred fermentable fuels, disrupting major metabolic pathways important for the ability of the cancer cells to survive. Dialysis has the potential to reduce glucose levels below physiological levels, concurrently increase blood ketone body levels and reduce glutamine levels, which may further reinforce the impact of the KC. Importantly, ketones also induce epigenetic changes imposed by histone deacetylates (HDAC) activity (Class I and Class IIa) known to play an important role in cancer metabolism. Thus, dialysis could be an impactful and safe adjuvant treatment, sensitizing cancer cells to traditional cancer treatments (TCTs), potentially making these significantly more efficient.

Glucagon, cyclic AMP, and hepatic glucose mobilization: A half‐century of uncertainty

For at least 50 years, the prevailing view has been that the adenylate cyclase (AC)/cyclic AMP (cAMP)/protein kinase A pathway is the predominant signal mediating the hepatic glucose‐mobilizing actions of glucagon. A wealth of evidence, however, supports the alternative, that the operative signal most of the time is the phospholipase C (PLC)/inositol‐phosphate (IP3)/calcium/calmodulin pathway. The evidence can be summarized as follows: (1) The consensus threshold glucagon concentration for activating AC ex vivo is 100 pM, but the statistical hepatic portal plasma glucagon concentration range, measured by RIA, is between 28 and 60 pM; (2) Within that physiological concentration range, glucagon stimulates the PLC/IP3 pathway and robustly increases glucose output without affecting the AC/cAMP pathway; (3) Activation of a latent, amplified AC/cAMP pathway at concentrations below 60 pM is very unlikely; and (4) Activation of the PLC/IP3 pathway at physiological concentrations produces intracellular effects that are similar to those produced by activation of the AC/cAMP pathway at concentrations above 100 pM, including elevated intracellular calcium and altered activities and expressions of key enzymes involved in glycogenolysis, gluconeogenesis, and glycogen synthesis. Under metabolically stressful conditions, as in the early neonate or exercising adult, plasma glucagon concentrations often exceed 100 pM, recruiting the AC/cAMP pathway and enhancing the activation of PLC/IP3 pathway to boost glucose output, adaptively meeting the elevated systemic glucose demand. Whether the AC/cAMP pathway is consistently activated in starvation or diabetes is not clear. Because the importance of glucagon in the pathogenesis of diabetes is becoming increasingly evident, it is even more urgent now to resolve lingering uncertainties and definitively establish glucagon’s true mechanism of glycemia regulation in health and disease.

Exogenous d ‐β‐hydroxybutyrate lowers blood glucose in part by decreasing the availability of L‐alanine for gluconeogenesis

Background

Interventions that induce ketosis simultaneously lower blood glucose and the explanation for this phenomenon is unknown. Additionally, the glucose‐lowering effect of acute ketosis is greater in people with type 2 diabetes (T2D). On the contrary, L‐alanine is a gluconeogenic substrate secreted by skeletal muscle at higher levels in people with T2D and infusing of ketones lower circulating L‐alanine blood levels. In this study, we sought to determine whether supplementation with L‐alanine would attenuate the glucose‐lowering effect of exogenous ketosis using a ketone ester (KE).

Methods

This crossover study involved 10 healthy human volunteers who fasted for 24 h prior to the ingestion of 25 g of d‐β‐hydroxybutyrate (βHB) in the form of a KE drink (ΔG^®) on two separate visits. During one of the visits, participants additionally ingested 2 g of L‐alanine to see whether L‐alanine supplementation would attenuate the glucose‐lowering effect of the KE drink. Blood L‐alanine, L‐glutamine, glucose, βHB, free fatty acids (FFA), lactate and C‐peptide were measured for 120 min after ingestion of the KE, with or without L‐alanine.

Findings

The KE drinks elevated blood βHB concentrations from negligible levels to 4.52 ± 1.23 mmol/L, lowered glucose from 4.97 ± SD 0.39 to 3.77 ± SD 0.40 mmol/L, and lowered and L‐alanine from 0.56 ± SD 0.88 to 0.41 ± SD 0.91 mmol/L. L‐alanine in the KE drink elevated blood L‐Alanine by 0.68 ± SD 0.15 mmol/L, but had no significant effect on blood βHB, L‐glutamine, FFA, lactate, nor C‐peptide concentrations. By contrast, L‐alanine supplementation significantly attenuated the ketosis‐induced drop in glucose from 28% ± SD 8% to 16% ± SD 7% (p < .01).

Conclusions

The glucose‐lowering effect of acutely elevated βHB is partially due to βHB decreasing L‐alanine availability as a substrate for gluconeogenesis.

The Therapeutic Potential and Limitations of Ketones in Traumatic Brain Injury

Traumatic brain injury (TBI) represents a significant health crisis. To date, no FDA approved pharmacotherapies are available to prevent the neurological deficits caused by TBI. As an alternative to pharmacotherapy treatment of TBI, ketones could be used as a metabolically based therapeutic strategy. Ketones can help combat post-traumatic cerebral energy deficits while also reducing inflammation, oxidative stress, and neurodegeneration. Experimental models of TBI suggest that administering ketones to TBI patients may provide significant benefits to improve recovery. However, studies evaluating the effectiveness of ketones in human TBI are limited. Unanswered questions remain about age- and sex-dependent factors, the optimal timing and duration of ketone supplementation, and the optimal levels of circulating and cerebral ketones. Further research and improvements in metabolic monitoring technology are also needed to determine if ketone supplementation can improve TBI recovery outcomes in humans.

Exogenous ketosis in patients with type 2 diabetes: Safety, tolerability and effect on glycaemic control

Introduction

Ketogenic diets have shown to improve glycaemic control in patients with type 2 diabetes. This study investigated the safety, tolerability, and effects on glycaemic control in patients with type 2 diabetes of an exogenous ketone monoester (KE) capable of inducing fasting‐like elevations in serum β‐hydroxybutyrate (βHB) without the need for caloric or carbohydrate restriction.

Methods

Twenty one participants (14 men and 7 women, aged 45 ± 11 years) with insulin‐independent type 2 diabetes, and unchanged hypoglycaemic medication for the previous 6 months, were recruited for this non‐randomised interventional study. Participants wore intermittent scanning glucose monitors (IS‐GM) for a total of 6 weeks and were given 25 ml of KE 3 times daily for 4 weeks. Serum electrolytes, acid‐base status, and βHB concentrations were measured weekly and cardiovascular risk markers were measured before and after the intervention. The primary endpoints were safety and tolerability, with the secondary endpoint being glycaemic control.

Results

The 21 participants consumed a total of 1,588 drinks (39.7 litres) of KE over the course of the intervention. Adverse reactions were mild and infrequent, including mild nausea, headache, and gastric discomfort following fewer than 0.5% of the drinks. Serum electrolyte concentrations, acid‐base status, and renal function remained normal throughout the study. Compared to baseline, exogenous ketosis induced a significant decrease in all glycaemic control markers, including fructosamine (335 ± 60 μmol/L to 290 ± 49 μmol/L, p < .01), HbA1c (61 ± 10 mmol/mol to 55 ± 9 mmol/mol [7.7 ± 0.9% to 7.2 ± 0.9%], p < .01), mean daily glucose (7.8 ± 1.4 mM to 7.4 ± 1.3 mM [140 ± 23 mg/dl to 133 ± 25 mg/dl], p < .01) and time in range (67 ± 11% to 69 ± 10%, p < .01).

Conclusions

Constant ketone monoester consumption over 1 month was safe, well tolerated, and improved glycaemic control in patients with type 2 diabetes.

This study involved a month of closely supervised exogenous ketosis using a ketone monoester. Additionally, it involved six weeks of continuous glucose monitorization to compare glucose control before, during and after exogenous ketosis. Exogenous ketosis was safe, well‐tolerated and improved glucose control.

Acute Nutritional Ketosis and Its Implications for Plasma Glucose and Glucoregulatory Peptides in Adults with Prediabetes: A Crossover Placebo-Controlled Randomized Trial

BACKGROUND

The potential of a ketone monoester (β-hydroxybutyrate; KEβHB) supplement to rapidly mimic a state of nutritional ketosis offers a new therapeutic possibility for diabetes prevention and management. While KEβHB supplementation has a glucose-lowering effect in adults with obesity, its impact on glucose control in other insulin-resistant states is unknown.

OBJECTIVES

The primary objective was to investigate the effect of KEβHB-supplemented drink on plasma glucose in adults with prediabetes. The secondary objective was to determine its impact on plasma glucoregulatory peptides.

METHODS

This randomized controlled trial [called CETUS (Cross-over randomizEd Trial of β-hydroxybUtyrate in prediabeteS)] included 18 adults [67% men, mean age = 55 y, mean BMI (kg/m2) = 28.4] with prediabetes (glycated hemoglobin between 5.7% and 6.4% and/or fasting plasma glucose between 100 and 125 mg/dL). Participants were randomly assigned to receive KEβHB-supplemented and placebo drinks in a crossover sequence (washout period of 7-10 d between the drinks). Blood samples were collected from 0 to 150 min, at intervals of 30 min. Paired-samples t tests were used to investigate the change in the outcome variables [β-hydroxybutyrate (βHB), glucose, and glucoregulatory peptides] after both drinks. Repeated measures analyses were conducted to determine the change in concentrations of the prespecified outcomes over time.

RESULTS

Blood βHB concentrations increased to 3.5 mmol/L within 30 minutes after KEβHB supplementation. Plasma glucose AUC was significantly lower after KEβHB supplementation than after the placebo [mean difference (95% CI): -59 (-85.3, -32.3) mmol/L × min]. Compared with the placebo, KEβHB supplementation led to significantly greater AUCs for plasma insulin [0.237 (0.044, 0.429) nmol/L × min], C-peptide [0.259 (0.114, 0.403) nmol/L × min], and glucose-dependent insulinotropic peptide [0.243 (0.085, 0.401) nmol/L × min], with no significant differences in the AUCs for amylin, glucagon, and glucagon-like peptide 1.

CONCLUSIONS

Ingestion of the KEβHB-supplemented drink acutely increased the blood βHB concentrations and lowered the plasma glucose concentrations in adults with prediabetes. Further research is needed to investigate the dynamics of repeated ingestions of a KEβHB supplement by individuals with prediabetes, with a view to preventing new-onset diabetes. This trial was registered at www.clinicaltrials.gov as NCT03889210.

Oral 3-hydroxybutyrate ingestion decreases endogenous glucose production, lipolysis, and hormone-sensitive lipase phosphorylation in adipose tissue in men: a human randomized, controlled, crossover trial

AIMS

To test whether oral administration of D/L-3-hydroxybutyrate as a sodium salt inhibits lipolysis and intracellular lipid signalling, in particular, hormone-sensitive lipase, and whether D/L-3-hydroxybutyrate alters endogenous glucose production.

METHODS

We studied six young men in a randomized, controlled, crossover study after ingestion of Na-D/L-3-hydroxybutyrate (hyperketotic condition) or saline (placebo control). We quantified lipolysis and endogenous glucose production using [9,10-³ H]-palmitate and [3-3H]glucose tracers, and adipose tissue biopsies were collected to investigate key lipolytic enzymes.

RESULTS

After ingestion, D/L-3-hydroxybutyrate increased by more than 2.5 mmol/l, free fatty acid concentrations decreased by >70%, and palmitate rate of appearance was halved. Protein kinase A phosphorylation of perilipin was reduced and hormone-sensitive lipase 660 phosphorylation in adipose tissue biopsies was 70-80% decreased in the hyperketotic condition and unchanged in the control. Compared to the control, endogenous glucose production was reduced by close to 20% (P<0.05) after 3-hydroxybutyrate ingestion.

CONCLUSION

We conclude that oral D/L-Na-3-hydroxybutyrate increases D/L-3-hydroxybutyrate concentrations within half an hour, decreases free fatty acid concentrations, lowers lipolysis and endogenous glucose production, and dephosphorylates hormone-sensitive lipase. Collectively these phenomena may be viewed as an orchestrated feedback loop, controlling endogenous glucose production, lipolysis and ketogenesis. Such effects would be beneficial in insulin-resistant states. (www.clinicaltrials.gov ID number: NCT02917252).

Comparing the Efficacy and Safety of Low-Carbohydrate Diets with Low-Fat Diets for Type 2 Diabetes Mellitus Patients: A Systematic Review and Meta-Analysis of Randomized Clinical Trials

INTRODUCTION

To compare the efficacy of low-carbohydrate diets (LCDs) with low-fat diets (LFDs) in body weight and glycemic control for type 2 diabetes mellitus (T2DM) patients, and their cardiovascular and renal safety.

METHODS

We searched PubMed, Ovid, Embase databases, Cochrane Central Register of Controlled Trials (CENTRAL), and ClinicalTrials.gov from inception to April, 2021. Randomized controlled trials (RCTs) which lasted more than 3 months were included. The primary outcomes are the mean change from baseline in glycated haemoglobin (HbA1c) and body weight loss. Secondary outcomes included mean difference in lipid parameters, blood pressures, and serum creatinine.

RESULTS

Totally, 12 RCTs met inclusion criteria representing 761 patients. Compared with LFDs, treatment with LCDs achieved significant reduced HbA1c by 0.35% (95% CI: -0.45, -0.24; P < 0.00001). LCDs appeared to be more beneficial in decreasing body weight than LFDs (WMD = -2.99 kg; 95% CI: -4.36, -1.63; P < 0.0001), especially in the subgroup that used VLCDs (WMD = -9.49 kg; 95% CI: -12.88, -6.09, P < 0.00001). For cardiovascular risk factors, the LCD interventions significantly reduced TG concentration (WMD: -0.20 mmol/l; 95% CI: -0.31, -0.10; P = 0.0001) and increased HDL-C concentration (WMD: 0.09 mmol/l; 95% CI: 0.05,0.13; P < 0.00001). Subgroup analyses demonstrated that the difference in HbA1c, TG, and HDL-C between two dietary restrictions respectively lasted up to 1.5 and 2 years, whereas the beneficial effects of body weight loss diminished over time and disappeared after 2 years. LCDs were not associated with decreased level of TC or LDL-C, neither SBP nor DBP in comparison with LFDs. Moreover, no significant difference in serum creatinine could be found among such two diet interventions.

CONCLUSIONS

LCDs are superior to LFDs for T2DM patients in improving HbA1c and reducing body weight, with a rewarding effect of some cardiovascular risk factors in a longer-term diabetes management. However, available data are insufficient to evaluate the association between diet interventions and renal safety. Future larger longer-term follow-up clinical trials are needed to provide more evidence about the sustainable effects and safety of LCDs compared with LFDs.

Why a d-β-hydroxybutyrate monoester?

Much of the world's prominent and burdensome chronic diseases, such as diabetes, Alzheimer's, and heart disease, are caused by impaired metabolism. By acting as both an efficient fuel and a powerful signalling molecule, the natural ketone body, d-β-hydroxybutyrate (βHB), may help circumvent the metabolic malfunctions that aggravate some diseases. Historically, dietary interventions that elevate βHB production by the liver, such as high-fat diets and partial starvation, have been used to treat chronic disease with varying degrees of success, owing to the potential downsides of such diets. The recent development of an ingestible βHB monoester provides a new tool to quickly and accurately raise blood ketone concentration, opening a myriad of potential health applications. The βHB monoester is a salt-free βHB precursor that yields only the biologically active d-isoform of the metabolite, the pharmacokinetics of which have been studied, as has safety for human consumption in athletes and healthy volunteers. This review describes fundamental concepts of endogenous and exogenous ketone body metabolism, the differences between the βHB monoester and other exogenous ketones and summarises the disease-specific biochemical and physiological rationales behind its clinical use in diabetes, neurodegenerative diseases, heart failure, sepsis related muscle atrophy, migraine, and epilepsy. We also address the limitations of using the βHB monoester as an adjunctive nutritional therapy and areas of uncertainty that could guide future research.

Cardiac ketone body metabolism

The ketone bodies, d-β-hydroxybutyrate and acetoacetate, are soluble 4-carbon compounds derived principally from fatty acids, that can be metabolised by many oxidative tissues, including heart, in carbohydrate-depleted conditions as glucose-sparing energy substrates. They also have important signalling functions, acting through G-protein coupled receptors and histone deacetylases to regulate metabolism and gene expression including that associated with anti-oxidant activity. Their concentration, and hence availability, increases in diabetes mellitus and heart failure. Whilst known to be substrates for ATP production, especially in starvation, their role(s) in the heart, and in heart disease, is uncertain. Recent evidence, reviewed here, indicates that increased ketone body metabolism is a feature of heart failure, and is accompanied by other changes in substrate selection. Whether the change in myocardial ketone body metabolism is adaptive or maladaptive is unknown, but it offers the possibility of using exogenous ketones to treat the failing heart.

Ketone body therapy with D/L-β-hydroxybutyric acid solution in severe MADD

Objectives

Multiple acyl-CoA dehydrogenase deficiency (MADD) is a severe inborn disorder of mitochondrial fatty acid oxidation. The only treatment option for MADD is the use of exogenous ketone bodies, like sodium β-hydroxybutyrate (NaβHB). However, the use of ketone body salts leads to a high intake of accompanying minerals, which can lead to additional side effects. The use of mineral-free formulations could improve tolerability.

Methods

In this report, the use of a βHB acid (βHBA) in a patient with MADD is described. The production of D/L-βHBA was carried out using ion exchange chromatography (IEX) and using a precipitation method. During two inpatient treatment intervals, the tolerability as well as clinical and metabolic effects were monitored. D-βHB in serum, blood gas analysis, and standard blood measurements (like minerals) were used as control parameters.

Results

Production of D/L-βHBA using the precipitation method was more effective than using IEX. The tube feed solution used had a minimum pH of 3.5. Capillary D-βHB measurements were between 0.1 and 0.4 mmol/L and venous were at 0.1 mmol/L or below. Minerals and serum pH were within the normal range. During application of D/L-βHBA, gastrointestinal discomfort occurred and no clinical improvement was observed.

Conclusions

The use of D/L-βHBA in the therapy of severe MADD could be a good addition to the use of classical ketone body salts. The observed gastrointestinal side effects were of a mild nature and could not be specifically attributed to the D/L-βHBA treatment. In short-term application, no clinical benefit and no substantial increase of D-βHB in serum were noted. No tendency towards acidosis or alkalosis was observed during the entire period of treatment.

Exogenous Ketone Bodies as Promising Neuroprotective Agents for Developmental Brain Injury

Ketone bodies are a promising area of neuroprotection research that may be ideally suited to the injured newborn. During normal development, the human infant is in significant ketosis for at least the first week of life. Ketone uptake and metabolism is upregulated in the both the fetus and neonate, with ketone bodies providing at least 10% of cerebral metabolic energy requirements, as well as being the preferred precursors for the synthesis of fatty acids and cholesterol. At the same time, ketone bodies have been shown to have multiple neuroprotective effects, including being anticonvulsant, decreasing oxidative stress and inflammation, and epigenetically upregulating the production of neurotrophic factors. While ketogenic diets and exogenous ketosis are largely being investigated in the setting of adult brain injury, the adaptation of the neonate to ketosis suggests that developmental brain injury may be the area most suited to the use of ketones for neuroprotection. Here, we describe the mechanisms by which ketone bodies exert their neuroprotective effects, and how these may translate to benefits within each of the phases of neonatal asphyxial brain injury.

Role of ketone signaling in the hepatic response to fasting

Ketosis is a metabolic adaptation to fasting, nonalcoholic fatty liver disease (NAFLD), and prolonged exercise. β-OH butyrate acts as a transcriptional regulator and at G protein-coupled receptors to modulate cellular signaling pathways in a hormone-like manner. While physiological ketosis is often adaptive, chronic hyperketonemia may contribute to the metabolic dysfunction of NAFLD. To understand how β-OH butyrate signaling affects hepatic metabolism, we compared the hepatic fasting response in control and 3-hydroxy-3-methylglutaryl-CoA synthase II (HMGCS2) knockdown mice that are unable to elevate β-OH butyrate production. To establish that rescue of ketone metabolic/endocrine signaling would restore the normal hepatic fasting response, we gave intraperitoneal injections of β-OH butyrate (5.7 mmol/kg) to HMGCS2 knockdown and control mice every 2 h for the final 9 h of a 16-h fast. In hypoketonemic, HMGCS2 knockdown mice, fasting more robustly increased mRNA expression of uncoupling protein 2 (UCP2), a protein critical for supporting fatty acid oxidation and ketogenesis. In turn, exogenous β-OH butyrate administration to HMGCS2 knockdown mice decreased fasting UCP2 mRNA expression to that observed in control mice. Also supporting feedback at the transcriptional level, β-OH butyrate lowered the fasting-induced expression of HMGCS2 mRNA in control mice. β-OH butyrate also regulates the glycemic response to fasting. The fast-induced fall in serum glucose was absent in HMGCS2 knockdown mice but was restored by β-OH butyrate administration. These data propose that endogenous β-OH butyrate signaling transcriptionally regulates hepatic fatty acid oxidation and ketogenesis, while modulating glucose tolerance. NEW & NOTEWORTHY Ketogenesis regulates whole body glucose metabolism and β-OH butyrate produced by the liver feeds back to inhibit hepatic β-oxidation and ketogenesis during fasting.

Long-term ketone body therapy of severe multiple acyl-CoA dehydrogenase deficiency: A case report

OBJECTIVES

Multiple acyl-CoA dehydrogenase deficiency (MADD) is the most severe disorder of mitochondrial fatty acid β-oxidation. Treatment of this disorder is difficult because the functional loss of the electron transfer flavoprotein makes energy supply from fatty acids impossible. Acetyl-CoA, provided by exogenous ketone bodies such as NaßHB, is the only treatment option in severe cases. Short-term therapy attempts have shown positive results. To our knowledge, no reports exist concerning long-term application of ketone body salts in patients with severe MADD.

METHODS

This case report is a detailed retrospective metabolic analysis of a boy with severe MADD. Treatment with sodium β-hydroxybutyrate (NaβHB) started 8 d after birth using gradually increasing doses. In the initial phase, metabolic and acid-base parameters were checked multiple times a day. After 8 y of standardized therapy with 16 g NaβHB, substitution with calcium β-hydroxybutyrate (CaβHB) was attempted. In addition to the β-hydroxybutyrate (βHB) supplementation, continuous adjustments were made to the child's nutrition to provide necessary nutrients.

RESULTS

Treatment with βHB salts leads to adverse effects like gastrointestinal discomfort and alkalosis. Measured concentrations of βHB were predominantly at 0.1 mmol/L or below detectable concentration. Nutritional therapy based on amino acid and acylcarnitine profiles is a necessary part of the therapy in MADD.

CONCLUSIONS

Therapy with NaβHB is lifesaving in cases of severe MADD but can have significant adverse effects. Supplementation with CaβHB led to gastrointestinal discomfort and had no additional positive clinical effect. The determined tolerable dose of βHB salt for long-term therapy was not high enough for a notable increase of βHB concentrations in blood.

Prior ingestion of exogenous ketone monoester attenuates the glycaemic response to an oral glucose tolerance test in healthy young individuals

KEY POINTS

The recent development of exogenous ketone supplements allows direct testing of the metabolic effects of elevated blood ketones without the confounding influence of widespread changes experienced with ketogenic diets or prolonged fasting. In the present study, we determined the effect of (R)-3-hydroxybutyl (R)-3-hydroxybutyrate ketone monoester on the glycaemic response and insulin sensitivity index during a 2 h oral glucose tolerance test (OGTT) in humans. The results obtained show that consuming a ketone monoester supplement 30 min prior to an OGTT reduced the glycaemic response and markers of insulin sensitivity without affecting insulin secretion. The findings of the present study provides evidence that ketone supplements could have therapeutic potential for future application as a glucose-lowering nutritional supplement.

ABSTRACT

The main objectives of the present study were: (i) to determine whether acute ingestion of ketone monoester (K_me ); (R)-3-hydroxybutyl (R)-3-hydroxybutyrate impacts plasma glucose levels during a standardized oral glucose tolerance test (OGTT) and (ii) to compare changes in insulin concentrations and estimates of insulin sensitivity after acute K_me supplementation. Twenty healthy participants (n = 10 males/females) aged between 18 and 35 years took part in a randomized cross-over study. After an overnight fast, participants consumed a K_me supplement (ΔG®; TΔS Ltd, UK, Oxford, UK; 0.45 ml kg^-1 body weight) or placebo (water) 30 min before completing a 75 g OGTT. Blood samples were collected every 15-30 min over 2.5 h. The participants and study personnel performing the laboratory analyses were blinded to the study condition. K_me acutely raised blood d-beta-hydroxybutyrate (β-OHB) to 3.2 ± 0.6 mm within 30 min with levels remaining elevated throughout the entire OGTT. Compared to placebo, K_me significantly decreased the glucose area under the curve (AUC; -17%, P = 0.001), non-esterified fatty acid AUC (-44%, P < 0.001) and C-peptide incremental AUC (P = 0.005), at the same time as improving oral glucose insulin sensitivity index by ∼11% (P = 0.001). In conclusion, a K_me supplement that acutely increased β-OHB levels up to ∼3 mm attenuated the glycaemic response to an OGTT in healthy humans. The reduction in glycaemic response did not appear to be driven by an increase in insulin secretion, although it was accompanied by improved markers of insulin sensitivity. These results suggest that ketone monoester supplements could have therapeutic potential in the management and prevention of metabolic diseases.

Efficacy of low carbohydrate diet for type 2 diabetes mellitus management: A systematic review and meta-analysis of randomized controlled trials

AIMS

The objective of this systematic review and meta-analysis is to assess the efficacy of Low Carbohydrate Diet (LCD) compared with a normal or high carbohydrate diet in patients with type 2 diabetes.

METHODS

We searched MEDLINE, EMBASE, and Cochrane Library database for randomized controlled trials. Researches which reported the change in weight loss, blood glucose, and blood lipid levels were included.

RESULTS

A total of 9 studies with 734 patients with diabetes were included. Pooled results suggested that LCD had a significantly effect on HbA1c level (WMD: -0.44; 95% CI: -0.61, -0.26; P=0.00). For cardiovascular risk factors, the LCD intervention significantly reduced triglycerides concentration (WMD: -0.33; 95% CI: -0.45, -0.21; P=0.00) and increased HDL cholesterol concentration (WMD: 0.07; 95% CI: 0.03, 0.11; P=0.00). But the LCD was not associated with decreased level of total cholesterol and LDL cholesterol. Subgroup analyses indicated that short term intervention of LCD was effective for weight loss (WMD: -1.18; 95% CI: -2.32, -0.04; P=0.04).

CONCLUSIONS

The results suggested a beneficial effect of LCD intervention on glucose control in patients with type 2 diabetes. The LCD intervention also had a positive effect on triglycerides and HDL cholesterol concentrations, but without significant effect on long term weight loss.

Hypercarnivory and the brain: protein requirements of cats reconsidered

The domestic hypercarnivores cat and mink have a higher protein requirement than other domestic mammals. This has been attributed to adaptation to a hypercarnivorous diet and subsequent loss of the ability to downregulate amino acid catabolism. A quantitative analysis of brain glucose requirements reveals that in cats on their natural diet, a significant proportion of protein must be diverted into gluconeogenesis to supply the brain. According to the model presented here, the high protein requirement of the domestic cat is the result of routing of amino acids into gluconeogenesis to supply the needs of the brain and other glucose-requiring tissues, resulting in oxidation of amino acid in excess of the rate predicted for a non-hypercarnivorous mammal of the same size. Thus, cats and other small hypercarnivores do not have a high protein requirement per se, but a high endogenous glucose demand that is met by obligatory amino acid-based gluconeogenesis. It is predicted that for hypercarnivorous mammals with the same degree of encephalisation, endogenous nitrogen losses increase with decreasing metabolic mass as a result of the allometric relationships of brain mass and brain metabolic rate with body mass, possibly imposing a lower limit for body mass in hypercarnivorous mammals.

{beta}-Hydroxybutyrate inhibits insulin-mediated glucose transport in mouse oxidative muscle

Blood ketone body levels increase during starvation and untreated diabetes. Here we tested the hypothesis that ketone bodies directly inhibit insulin action in skeletal muscle. We investigated the effect of d,l-beta-hydroxybutyrate (BOH; the major ketone body in vivo) on insulin-mediated glucose uptake (2-deoxyglucose) in isolated mouse soleus (oxidative) and extensor digitorum longus (EDL; glycolytic) muscle. BOH inhibited insulin-mediated glucose uptake in soleus (but not in EDL) muscle in a time- and concentration-dependent manner. Following 19.5 h of exposure to 5 mM BOH, insulin-mediated (20 mU/ml) glucose uptake was inhibited by approximately 90% (substantial inhibition was also observed in 3-O-methylglucose transport). The inhibitory effect of BOH was reproduced with d- but not l-BOH. BOH did not significantly affect hypoxia- or AICAR-mediated (activates AMP-dependent protein kinase) glucose uptake. The BOH effect did not require the presence/utilization of glucose since it was also seen when glucose in the medium was substituted with pyruvate. To determine whether the BOH effect was mediated by oxidative stress, an exogenous antioxidant (1 mM tempol) was used; however, tempol did not reverse the BOH effect on insulin action. BOH did not alter the levels of total tissue GLUT4 protein or insulin-mediated tyrosine phosphorylation of the insulin receptor and insulin receptor substrate-1 but blocked insulin-mediated phosphorylation of protein kinase B by approximately 50%. These data demonstrate that BOH inhibits insulin-mediated glucose transport in oxidative muscle by inhibiting insulin signaling. Thus ketone bodies may be potent diabetogenic agents in vivo.

Pregnancy impairs ketone body disposal in late gestating ewes: Implications for onset of pregnancy toxaemia

The impact of pregnancy on ketone body disposal during a hyperketonaemic clamp was examined by tracer isotope dilution techniques in seven 12 h fasted sheep in three reproductive states, in the dry non-gestating period, late in gestation and during early lactation. After a sampling period of 60 min under basal conditions a DL-BHB racemate solution was continuously infused intravenously for 3 h at rates of 14.3-24.3 micromol/(kg min) to elevate the D-BHB concentration in blood plasma to values between 5 and 7 mmol/l. Two separate experiments were carried out with the same sheep in each of the three reproductive states. During pregnancy three ewes were pregnant with a single lamb and four ewes carried twins. Maximal D-BHB turnover rates fell significantly in late gestation by 26% relative to early lactation and by 22% when compared with the dry non-pregnant state. Reduction of maximal D-BHB disposal rate during late gestation was accompanied by a significant 297% (p<0.005) and a non-significant 49% increase in the basal BHB concentration in blood, a non-significant 10% and 4% decrease in the rate constant of D-BHB turnover and a non-significant 24% and 13% rise in the incremented increase of D-BHB concentration per unit D-BHB infusion, relative to the dry and the lactating period, respectively. Induction of hyperketonaemia significantly lowered NEFA and glycerol concentrations in blood by 67% and 57%, respectively, compared to the pre-infusional concentrations. The magnitude of this effect was the same in all reproductive states and was explained as a direct antilipolytic action of D-BHB on adipose tissue. It is concluded that the reduced ability of the late gestating ewe to utilize D-BHB promotes hyperketonaemia. Since hyperketonaemia exerts several adverse effects, e.g. on energy balance and glucose metabolism it appears that the impairment of ketone bodies disposal in late pregnancy facilitates development of pregnancy toxaemia, especially in ewes carrying twins.

Hyperketonemia Impairs Glucose Metabolism in Pregnant and Nonpregnant Ewes

The present study was undertaken to test the hypothesis that high ketone body concentrations suppress endogenous production of glucose and in pregnant sheep facilitate development of pregnancy toxemia. Rates of endogenous glucose production [mmol.min(-1)], and rate constants of glucose turnover [min(-1)] were measured in seven 12-h fasted sheep in the presence of normo- and hyperketonemia by use of D-2-[(3)H]-glucose. The measurements were carried out in the same sheep during the nonpregnant nonlactating state, during late pregnancy (10 +/- 7 d antepartum) and during lactation (19 +/- 6 d postpartum). Hyperketonemia (5 to 7 mmol.L(-1)), similar to that present in spontaneous ovine pregnancy toxemia, was induced by continuous intravenous 4-h infusions of DL-beta-hydroxybutyrate (DL-BHB). Glucose turnover [mmol.min(-1)] in the same 7 nonpregnant nonlactating, late pregnant, and lactating sheep was significantly greater during normoketonemia (0.80, 1.16, 1.76) than during hyperketonemia (0.66, 0.92, 1.16, respectively). The rate constants of glucose turnover were not altered by elevation of the BHB concentration. The results demonstrated that high BHB concentrations significantly suppressed endogenous glucose production but showed no effect on glucose utilization. The suppressive effect of hyperketonemia on hepatic glucose production resulted in a significant reduction of plasma glucose concentration and was qualitatively the same in all three reproductive states. The results indicate that hyperketonemia, which is regularly present in late twin pregnant hypoglycemic sheep contributes significantly to the reduction of available glucose. This effect of hyperketonemia may invoke sustained hypoglycemia and may render the ewe into a vicious cycle that probably makes the animal refractory to treatment in most cases.

Bioavailability of starch and postprandial changes in splanchnic glucose metabolism in pigs

Changes in splanchnic metabolism in pigs were assessed after meals containing slowly or rapidly digested starch. The pigs were fed a mixed meal containing a "slow" native (n = 5) or a "rapid" pregelatinized (n = 5) cornstarch naturally enriched with [(13)C]glucose. Absorption of [(13)C]glucose was monitored by the arteriovenous difference technique, and infusion of D-[6, 6-(2)H(2)]glucose in the jugular vein was used to calculate the systemic appearance of [(13)C]glucose. Arteriovenous balance data obtained during a 12-h study period showed that the fraction of ingested glucose equivalent appearing as glucose in the portal vein was 49.7 +/- 7.2% for the slow starch and 48.2 +/- 7.5% for the rapid starch (P = 0.86). These values, corrected for the gut extraction of circulating [(13)C]glucose, became 66.4 +/- 5.6 and 65. 3 +/- 5.6%, respectively (P = 0.35). Isotope dilution data indicated that systemic appearance of exogenous [(13)C]glucose represented 62. 9 +/- 7.6 and 67.4 +/- 3.0% of the oral load for slow and rapid starch, respectively (P = 0.68). Arterial glucose utilization by the gut increased from 7.3 +/- 0.9 micromol x kg(-1) x min(-1) before the meal to 8.5 +/- 1.6 micromol x kg(-1) x min(-1) during absorption, independently of the nature of the starch. Thus splanchnic glucose metabolism was unaffected by the nature of starch ingested.

The effect of starvation on leucine, alanine and glucose metabolism in obese subjects

The relationship between changes in ketone concentrations and leucine metabolism (seven obese subjects), glucose and alanine metabolism (seven obese subjects) was investigated using radioisotopic techniques after 12 h, 60 h and 2 weeks starvation. Leucine metabolism was also measured in five lean subjects after 12 h and 60 h starvation. In the obese subjects leucine concentration increased after 60 h starvation and leucine metabolic clearance rate, glucose and alanine concentration decreased (P < 0.05). Glucose and alanine production rate (Ra) decreased after 2 weeks (P < 0.05) but there was no change in leucine Ra after 60 h or 2 weeks. In the lean subjects leucine concentration, production rate and oxidation rate were increased after 60 h (P < 0.005, P < 0.05, P < 0.05). Ketone concentration was inversely related to alanine Ra (r = -0.51, P < 0.02) but was not related to measurements of protein metabolism in the obese subjects. This study demonstrates that the effect of short-term starvation on protein metabolism differs in lean and obese subjects. The decrease in glucose Ra during long-term starvation may be in part due to a decreased supply of alanine for gluconeogenesis.

Reduced metabolic efficiency in patients with Crohn's disease

Malnutrition is frequently seen in patients with inflammatory bowel disease, and parenteral or enteral nutrition is considered essential in this patient group. However, many patients with Crohn's disease have difficulties in gaining weight in response to overfeeding, suggesting reduced energy retention. Substrate utilization and nutrient balances as well as changes in body composition were followed in 10 patients with Crohn's disease immediately in the course of remission on low-dose steroid treatment, during an eight-day period of continuous enteral nutrition at constant (protocol 1:1.5-fold basal energy expenditure) and increasing (protocol 2:0.5- to 2.0-fold basal energy expenditure) nutrient supply. Energy, substrate, and nitrogen balances all became positive in response to overfeeding. However, fat was predominantly oxidized at an infusion rate of 1.2 g/kg body wt/day, whereas carbohydrates and proteins were effectively stored. A positive energy balance was reached at an energy infusion rate exceeding 31 kcal/kg body wt/day and corresponding substrate supplies of 1.6, 1.7, and 1.1 g/kg body wt/day for carbohydrates, fat, and protein, respectively. Nitrogen balance normalized at a supply of 0.14 g/kg body wt/day, which also reduced myofibrillar protein breakdown. Considering the relative contributions made by these nutrients in the diets, an accumulation of carbohydrates and protein but a depletion in fat became evident from nutrient balances. In fact, body weight increased by 0.12 kg/day, which was explained by an increased extracellular (+0.18 kg/day) and body cell mass (+0.04 kg/day) at reduced fat mass (-0.10 kg/day). Concomitantly, plasma T3 and insulin secretion both increased, whereas sympathetic nervous system activity decreased with overfeeding. This is contrary to data observed in healthy subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of different lipid substrates on glucose metabolism in normal postabsorptive humans

We investigated the effects on glucose metabolism of the infusion of either long-chain triglycerides (LCT), a mixture of long-chain and medium-chain triglycerides (MCT/LCT), D-beta-hydroxybutyrate (D-beta-OHB), or saline in normal postabsorptive subjects. Plasma insulin, C-peptide, and glucagon concentrations were unchanged in all groups. LCT and MCT/LCT infusions increased levels of plasma free fatty acids (FFA) compared with those of the saline group, whereas D-beta-OHB decreased them. Plasma ketone body concentrations were higher during the D-beta-OHB and triglyceride infusions than during the saline test. Glucose concentrations and appearance (Ra) and disappearance (Rd) rates were not modified during saline infusion. Glucose levels decreased only in the D-beta-OHB and MCT/LCT groups (P < .05), whereas they were unchanged during LCT infusion. Glucose Ra decreased slightly by 15% to 17% in LCT, MCT/LCT, and D-beta-OHB groups (P < .05 v saline). Glucose Rd decreased by 14% to 16% in each lipid-infusion group (P < .05 v saline). Glucose clearance rates decreased by 14% only in the LCT group (P < .001). Glucose oxidation rates did not change significantly during the lipid substrate infusions compared with saline infusion. In conclusion, (1) the effects of fatty acids on glucose metabolism appear to depend on the fatty acid chain length, since only LCT infusion significantly impaired glucose utilization; and (2) in subjects with normal endocrine pancreas function, we found no adverse effects of a short-term increase in lipid substrate availability on glucose production rate and concentration.

Mechanism of insulin resistance associated with liver cirrhosis

Insulin-induced glucose metabolism was investigated in 26 patients with biopsy-proven liver cirrhosis and 10 control subjects. Two glucose clamp protocols together with continuous indirect calorimetry were performed to examine whether reduced rates of glucose oxidation and/or nonoxidative glucose metabolism explain insulin resistance in liver cirrhosis. Using a 4-hour, two-step protocol (0-2 hours, plasma glucose 5.2 mmol/L, plasma insulin 92 mU/L to test the half-maximum response; 2-4 hours, hyperglycemia 10.0 mmol/L, plasma insulin 442 mU/L to test the maximum cellular glucose disposal) liver cirrhosis reduced glucose disposal to 45% and 60% of control values, respectively. Simultaneously, insulin-induced increases in glucose oxidation, plasma lactate levels, and lipogenesis were normal, whereas nonoxidative glucose metabolism was reduced (-82% and -47% of controls, respectively). To determine whether reduced nonoxidative glucose metabolism was caused by reduced glucose disposal, glucose disposal was "matched" to normal values in a subgroup of cirrhotic patients. Nonoxidative glucose metabolism values were normal, but plasma lactate concentrations disproportionally increased (+96%) after "matching" glucose disposal. Insulin resistance was independent of the etiology of the cirrhosis, the biochemical parameters of parenchymal cell damage and liver function, and the clinical and nutritional state of the patients. It is concluded that liver cirrhosis impairs insulin sensitivity and maximum cellular glucose disposal. Reduced glucose disposal is caused by defective glucose storage. Insulin resistance is independent of the etiology of liver cirrhosis and of the clinical and nutritional state of the patient.

Thermic effect of epinephrine: a role for endogenous insulin

The contribution of the basal insulin concentration to the metabolic response to epinephrine was measured in eight, postabsorptive, healthy volunteers before and during epinephrine (0.05 micrograms/kg fat-free mass [FFM] x min) and somatostatin (500 micrograms/h) infusion with and without insulin (0.1 mU/kg body weight [BW] x min) replacement. At basal plasma insulin concentrations, epinephrine increased oxygen consumption, heart rate, heart work, hepatic glucose production, glycogen breakdown in liver and muscle, and glucose oxidation, and the arterial plasma concentrations of glucose, lactate, and free fatty acids. Similar effects were observed during hypoinsulinemia, but epinephrine's actions on oxygen consumption and plasma concentrations of free fatty acids were disproportionally enhanced. We conclude that epinephrine-induced thermogenesis is partially inhibited by basal plasma insulin concentrations.

Energy expenditure and substrate oxidation in patients with cirrhosis: the impact of cause, clinical staging and nutritional state

Many clinicians subjectively feel that cirrhotic patients frequently have clinical signs of hypermetabolism. However, it is unknown whether hypermetabolism is a constant feature of chronic liver disease, corresponds to liver destruction and repair or is of prognostic value. This article is about resting energy expenditure and substrate oxidation rates in 123 patients with biopsy-proven cirrhosis differing with respect to cause, duration of the disease, biochemical parameters of parenchymal cell damage, cholestasis, liver function, number of complications, clinical staging and nutritional state. Resting energy expenditure varied between 1,090 and 2,300 kcal/day and differed from the predicted values in 70% of the patients. Resting energy expenditure was closely related to fat-free mass, and 52% of the variability could be explained by fat-free mass, age and sex. Of all the patients, 18% were hypermetabolic and 31% were hypometabolic. Hypermetabolism showed no strict association with the cause of cirrhosis, the duration of the disease, liver function, cholestasis, cell damage, clinical staging, blood hemoglobin, plasma thyroid hormone levels or human leukocyte antigens. An increased resting energy expenditure was associated with significant losses of muscle, body cell mass and extracellular mass at unchanged body fat, whereas fat and fat-free mass were increased in hypometabolic patients when compared with normometabolic patients. Lipid oxidation was increased, but glucose oxidation was reduced in nearly all patients with cirrhosis. This was most pronounced at advanced stages of liver disease. Although similar with respect to liver function and clinical staging, 76.2% of hypermetabolic patients had transplants within the observation period, compared with only 16.7% and 8.1% in the normometabolic group and hypometabolic group, respectively. Posttransplantation mortality was independent of pretransplantation resting energy expenditure, but it increased significantly in patients with losses in body cell mass. In conclusion, hypermetabolism is not a constant feature of cirrhosis and results more from extrahepatic than from hepatic factors. It may cause malnutrition and contributes to the clinical outcome of patients with chronic liver disease.

Uptake of beta-hydroxybutyrate in perfused hindquarter of starved and diabetic rats

To elucidate the peripheral ketone body uptake and the role of insulin in regulating peripheral ketone body utilization in starvation and diabetes mellitus, uptake of beta-hydroxybutyrate (BOHB) was investigated in the perfused hindquarter of starved (72 hour) or streptozotocin-induced (65 mg/kg, intraperitoneally) diabetic rats. Blood concentration of BOHB was significantly higher in diabetic (1,380 +/- 250 mumol/L) and starved (1,229 +/- 245 mumol/L) rats than in controls (104 +/- 8 mumol/L). The hindquarter was perfused with synthetic medium at a flow rate of 0.5 mL/g muscle weight/min. BOHB was added to the medium at a concentration of 0.1, 0.5, 2, or 10 mmol/L, and insulin was added at a concentration of 20, 100, or 500 microU/mL. In the hindquarter perfused with 0.1, 0.5, 2, or 10 mmol/L BOHB, fractional uptake of BOHB in the absence or presence of insulin was significantly lower in diabetic and starved rats than in controls. The addition of 100 or 500 microU/mL insulin significantly increased BOHB uptake in the perfused hindquarter of control rats; however, insulin addition did not significantly increase BOHB uptake in the perfused hindquarter of starved and diabetic rats. These results suggest that BOHB uptake is markedly reduced in the perfused hindquarter of starved and diabetic rats, and that physiological dose of insulin stimulates BOHB uptake in control rats, but not in starved and diabetic rats.

The independent effect of ketone bodies on forearm glucose metabolism in normal man

Ketone bodies and non-esterified fatty acids (NEFA) inhibit insulin stimulated glucose uptake in muscle in-vitro. In man the infusion of ketone bodies lowers plasma NEFA levels thus confounding the interpretation of individual effects. The aim of this study was to examine the effect of ketone bodies on insulin mediated forearm glucose metabolism independent of the changes in the plasma NEFA levels. Seven healthy men received sodium 3-hydroxybutyrate (15 mumol kg-1 min-1) or sodium bicarbonate (control) for 240 min. Heparin (0.2 U kg-1 min-1) and insulin (0.01 U kg-1 h-1) were infused for 90 min (pre-clamp), followed by insulin alone (0.025 U kg-1 h-1) and euglycaemia was maintained (clamp). Plasma NEFA levels and rates of forearm NEFA uptake (+23 +/- 14 and +49 +/- 21 [mean +/- SEM] nmol 100 ml forearm [FA]-1 min-1) were comparable during the pre-clamp periods, and were suppressed equally during hyperinsulinaemia. Sodium 3-hydroxybutyrate infusion raised the blood ketone body levels from 70 +/- 4 mumol/l to a plateau of 450 +/- 30 mumol/l, while control levels declined from baseline (ketone body vs control; P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Energy expenditure and substrate metabolism in ethanol-induced liver cirrhosis

Energy expenditure and substrate metabolism were investigated in 10 patients with alcoholic liver cirrhosis (EtOH-Ci) and 10 healthy controls (C). Resting metabolic rate (RMR) varied from 1,269 to 2,467 kcal/day in C and from 1,228 to 2,098 kcal/day in EtOH-Ci. RMR was significantly related to fat-free mass (FFM) in both groups, but EtOH-Ci decreased FFM and increased RMR when expressed per kilogram FFM (+33%). Glucose intolerance, hyperinsulinemia, and a decreased C-peptide-to-insulin ratio were observed in EtOH-Ci after a test meal. Concomitantly, nonoxidative glucose metabolism was reduced in association with normal increases in glucose oxidation. EtOH-Ci reduced insulin sensitivity (-59%) and maximal insulin-dependent glucose disposal (-40%) during a sequential two-step glucose clamp protocol (phase 1: 1 mU.kg body wt-1.min-1 insulin infusion rate + euglycemia; phase 2: 4 mU.kg body wt-1.min-1 insulin infusion rate + 165 mg/dl plasma glucose concentration). This was explained by reduced glucose storage (-99%, -51%) in association with normal responses in glucose oxidation rate, plasma lactate concentration, lipid oxidation rate, and rate of lipogenesis. Defective glucose storage was independent of reduced FFM. EtOH-Ci increased glucose-induced thermogenesis by 57%. We conclude that increased resting metabolic rate, enhanced thermogenesis, defective glucose storage, and normal glucose oxidation together result in increased energy needs and favor negative energy balance in patients with alcoholic cirrhosis.

Effects of ketone bodies on carbohydrate metabolism in non-insulin-dependent (type II) diabetes mellitus

The ability of ketone bodies to suppress elevated hepatic glucose output was investigated in eight postabsorptive subjects with non-insulin-dependent diabetes mellitus (NIDDM). Infusion of sodium acetoacetate alone (20 mumols/kg/min) for 3 hours increased total serum ketones (beta-hydroxybutyrate and acetoacetate) to approximately 6 mmol/L, but did not reduce plasma glucose (14.0 +/- 0.8 to 12.3 +/- 0.9 mmol/L) or isotopically determined hepatic glucose output (17.5 +/- 1.4 to 12.7 +/- 1.0 mumols/kg/min) more than saline alone. Plasma C-peptide concentrations were unchanged, while serum glucagon increased from 131 +/- 13 to 169 +/- 24 ng/mL (P less than .015) and free fatty acids were suppressed by 43% (0.35 +/- 0.08 to 0.20 +/- 0.06 mmol/L, P less than .025). When sodium acetoacetate was infused with somatostatin (0.10 micrograms/kg/min) to suppress glucagon and insulin secretion, the decrease in both plasma glucose (13.3 +/- 0.9 to 10.2 +/- 0.7 mmol/L) and hepatic glucose output (17.2 +/- 1.6 to 9.4 +/- 0.6 mumols/kg/min) was greater than either acetoacetate or somatostatin infusion alone. Infusion of equimolar amounts of sodium bicarbonate had no effect on glucose metabolism. In conclusion, these results demonstrate that ketone bodies can directly suppress elevated hepatic glucose output in NIDDM independent of changes in insulin secretion, but only when the concomitant stimulation of glucagon secretion is prevented. Ketone bodies also suppress adipose tissue lipolysis in the absence of changes in plasma insulin and may serve to regulate their own production.

Thyroid hormone action on lipid metabolism in humans: a role for endogenous insulin

The effects of moderate hyperthyroidism on lipid metabolism were investigated in six healthy subjects before and after thyroxine treatment (300 micrograms/d). T4-treatment increased basal metabolic rate (+8%) and glucose oxidation (+87%), without affecting lipid oxidation, plasma free fatty acids, glycerol, and beta-hydroxybutyrate. During euthyroidism, a hypoinsulinaemic-euglycaemic 150-minute clamp protocol increased energy expenditure (+3%), lipid oxidation (+42%), plasma free fatty acids (+254%), glycerol (+232%), and beta-hydroxybutyrate (+343%), but decreased glucose oxidation (-20%). Similar effects were observed after T4-treatment, but hyperthyroidism induced disproportionate increases in energy expenditure (+7%), plasma glycerol (+310%), and ketone body levels (+436%). We conclude that moderate hyperthyroidism enhances hypoinsulinemia-induced increases in lipolysis, free fatty acid recycling, and ketogenesis without affecting lipid oxidation. Thus basal insulin may camouflage some of thyroid hormone action on lipid metabolism.

Evidence that hyperglycaemia per se does not inhibit hepatic glucose production in man

The effect of hyperglycaemia on hepatic glucose production (Ra) was investigated in nine healthy men using sequential clamp protocols during somatostatin infusion and euglycaemia (0-150 min), at plasma glucose levels of 165 mg x dl-1 (9.2 mM, 150-270 min) and during insulin infusion (1.0 mU x kg-1 x min-1, 270-360 min) in study 1 or during hypo-insulinaemia and plasma glucose levels of 220 mg x dl-1 (12.2 mM; 270-390 min) in study 2. Somatostatin decreased Ra and glucose disposal rate (Rd) but increased plasma free fatty acids (FFA) and lipid oxidation during euglycaemia. Increasing plasma glucose to 165 mg x dl-1 (9.2 mM) and hypo-insulinaemia increased Rd, but no suppressive effects on Ra, plasma FFA and lipid oxidation were observed. By contrast hyperinsulinaemia (study 1), as well as a further increase in plasma glucose (study 2), both decreased Ra. However, more pronounced hyperglycaemia increased insulin secretion despite somatostatin resulting in a fall in plasma FFA and lipid oxidation. Our data questions the accepted dogma that hyperglycaemia inhibits Ra independently of insulin action.

Hypocalcemia reduces rate of disappearance of glucose from plasma

The influence of hypocalcemia on glucose disposal from plasma was studied in 4.5 to 24 kg weaned, fasted, calcitriol deficient piglets, which suffered from type I inherited pseudo vitamin D deficiency rickets. The plasma glucose concentration of the piglets was clamped to 40% above its preinfusional level by a continuous intravenous infusion of glucose. This suppressed hepatic glucose production. Since the clamped plasma glucose concentration was below its renal threshold, the rate of steady state glucose infusion served as an estimate for glucose disposal from plasma. It was found that hypocalcemia, generated either by calcitriol deficiency or by continuous EDTA infusions, reduced glucose disposal from plasma by 56-76% compared to normocalcemic control piglets. It was suggested that the effect was not compounded by plasma phosphate, calcitriol or insulin. It was further suggested that hypocalcemia depressed the rate of glucose utilization.

Effects of sodium bicarbonate on nitrogen metabolism and ketone bodies during very low energy protein diets in obese subjects

This study evaluated the effects of oral sodium bicarbonate (NaHCO3) supplementation on ammonium (NH4+) nitrogen (N) and urea N excretion and on ketone bodies during the metabolic acidosis of a very low energy protein diet. Ten healthy obese female subjects (BMI, 38.4 +/- 1.5 kg/m2;weight, 100 +/- 4 kg) were given a 1.72 MJ (412 kcal) all protein (16.8 g N) liquid formula, 16 mmol KCl and a multivitamin-mineral supplement daily for 4 weeks. In addition, the five subjects in group 1 received 60 mmol Na+ daily as sodium chloride (NaCl) for 3 weeks and as NaHCO3 during week 4. The subjects in group 2 were given 40 mmol/d NaHCO3 during the first week, 60 mmol/d during weeks 2 and 3, and 60 mmol/d NaCl during week 4. Nitrogen balance was achieved in both groups by the end of week 3. The subjects in group 1 at week 2 showed an increase in blood [H+] of 0.41 +/- 0.06 x 10(-8) mol/L and a decrease in blood bicarbonate from 26.0 +/- 0.8 to 23.8 +/- 1.2 mmol/L. The subsequent NaHCO3 curtailed NH4+ N excretion by one half, without significant change in ketone body levels or excretion. Administration of NaHCO3 from the start of the diet to the subjects in group 2 prevented both the metabolic acidosis and the increase in NH4+ N excretion and attenuated the increase in blood and urine 3-hydroxybutyrate. When NaCl replaced NaHCO3 during week 4, ammonium N excretion doubled. Urea N excretion was comparable in both groups and was unaffected by bicarbonate.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of free fatty acids and ketone bodies on in vivo non-insulin-mediated glucose utilization and production in humans

The current study was undertaken to examine the effect of an acute elevation of serum levels of free fatty acids (FFA) and ketone bodies (KB) on non-insulin-mediated glucose uptake (NIMGU) in humans. The study group consisted of 11 healthy men, mean age (+/- SD) 30 (+/- 7) years and mean weight (+/- SD) 72 (+/- 7) kg. To examine the effects of FFA levels on NIMGU and insulin-mediated glucose uptake (IMGU), glucose uptake was measured isotopically (3H-3-glucose) in six subjects on four separate days during saline infusion or lipid + heparin infusion with concomitant infusions of somatostatin (SHIF, 0.16 micrograms/kg/min) with or without insulin infusion (40 mU/m2/min) while the serum glucose level was clamped at approximately 11 mmol/L. To examine the effect of KB on NIMGU, saline or sodium acetoacetate (20 mumol/kg/min) was infused in five subjects on separate days during SRIF-induced insulinopenia while the serum glucose level was clamped sequentially at euglycemia and at approximately 11 mmol/L. During insulinopenia basal FFA levels rose twofold during saline infusion and sixfold during infusion of lipid + heparin. Rates of NIMGU were 2.49 +/- 0.27 v 2.41 +/- 0.14 mg/kg/min during saline and lipid infusion, respectively (P = NS). Rates of IMGU were decreased by 55% during lipid + heparin infusion. During insulinopenia basal beta-hydroxybutyrate (BOB) levels rose twofold during saline and approximately 11-fold during sodium acetoacetate infusion. Rates of NIMGU were unchanged by the sodium acetoacetate infusion at euglycemia and hyperglycemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Energy expenditure in children with type I diabetes: evidence for increased thermogenesis

The aim of the study was to assess whether increased energy expenditure causes the negative energy balance (tissue catabolism) commonly seen in children with insulin dependent (type I) diabetes. Resting metabolic rate and thermogenesis induced by adrenaline were measured in five healthy children and 14 children with type I diabetes who were all free of clinical signs of late complications of diabetes mellitus but differed in their degree of glycaemic control (in eight glycated haemoglobin concentration was less than 10% and in the six others greater than or equal to 10%). When compared with the control subjects children with type I diabetes had normal resting metabolic rates but their urinary nitrogen excretion was significantly raised (11.5 (SD 5.4) mg/min in those with glycated haemoglobin concentration less than 10%, 11.6 (5.2) mg/min in those with concentration greater than or equal to 10% v 5.4 (3.0) mg/min in control subjects). During the infusion of adrenaline the diabetic children showed a threefold and sustained increase in thermogenesis and disproportionate increases in the work done by the heart, in lipid oxidation rate, and in plasma concentrations of glucose, free fatty acids, and ketone bodies. The increased thermogenic effect of adrenaline did not correlate with the degree of glycaemic control. Increased thermogenesis may explain the tissue wasting commonly seen in children with type I diabetes during intercurrent stress.

Glucoregulatory function of thyroid hormones: role of pancreatic hormones

Glucose metabolism was investigated in humans before and 14 days after 300 micrograms L-thyroxine (T4)/day using a sequential clamp protocol during short-term somatostatin infusion (500 micrograms/h, 0-6 h) at euglycemia (0-2.5 h), at 165 mg/dl (2.5-6 h), and during insulin infusion (1.0 mU.kg-1.min-1, 4.5-6 h). T4 treatment increased plasma T4 (+96%) and 3,5,3'-triiodothyronine (T3, +50%), energy expenditure (+8%), glucose turnover (+32%), and glucose oxidation (Glucox +87%) but decreased thyroid-stimulating hormone (-96%) and nonoxidative glucose metabolism (Glucnonox, -30%) at unchanged lipid oxidation (Lipox). During somatostatin and euglycemia glucose production (Ra, -67%) and disposal (Rd, -28%) both decreased in euthyroid subjects but remained at -22% and -5%, respectively, after T4 treatment. Glucox (control, -20%; +T4, -25%) fell and Lipox increased (control, +42%; +T4, +45%) in both groups, whereas Glucnonox decreased before (-36%) but increased after T4 (+57%). During somatostatin infusion and hyperglycemia Rd (control, +144%; +T4, +84%) and Glucnonox (control, +326%; +T4, +233%) increased, whereas Glucox and Lipox remained unchanged. Insulin further increased Rd (+76%), Glucox (+155%), and Glucnonox (+50%) but decreased Ra (-43%) and Lipox (-43%). All these effects were enhanced by T4 (Rd, +38%; Glucox, +45%; Glucnonox, +35%; Ra, +40%; Lipox, +11%). Our data provide evidence that, in humans, T3 stimulates Ra and Rd, which is in part independent of pancreatic hormones.

Effect of beta-hydroxybutyrate on whole-body leucine kinetics and fractional mixed skeletal muscle protein synthesis in humans

Because intravenous infusion of beta-hydroxybutyrate (beta-OHB) has been reported to decrease urinary nitrogen excretion, we investigated in vivo metabolism of leucine, an essential amino acid, using L-[1-13C]leucine as a tracer during beta-OHB infusion. Leucine flux during beta-OHB infusion did not differ from leucine flux during normal saline infusion in nine normal subjects, whereas leucine oxidation decreased 18-41% (mean = 30%) from 18.1 +/- 1.1 mumol.kg-1.h-1 (P less than 0.01), and incorporation of leucine into skeletal muscle protein increased 5-17% (mean = 10%) from 0.048 + 0.003%/h (P less than 0.02). Since blood pH during beta-OHB infusion was higher than the pH during saline infusion, we performed separate experiments to study the effect of increased blood pH on leucine kinetics by infusing sodium bicarbonate intravenously. Blood pH during sodium bicarbonate infusion was similar to that observed during the beta-OHB infusion, but bicarbonate infusion had no effect on leucine flux or leucine oxidation. We conclude that beta-OHB decreases leucine oxidation and promotes protein synthesis in human beings.

Glucoregulatory function of glucagon in hypo-, eu- and hyperthyroid miniature pigs

The glucoregulatory function of glucagon was investigated in hypo-, eu- and hyperthyroid miniature pigs. Infusion glucagon, (3 ng x kg body weight-1.min-1) transiently increased blood glucose (p less than 0.01) and hepatic glucose production (p less than 0.01) in euthyroidism, but was without effect in hyperthyroidism. Infusing glucagon plus somatostatin (2 ng x kg body weight-1.min-1 and 0.2 microgram x kg body weight-1.min-1) transiently increased blood glucose (delta 3.0 to 4.3 mmol/l) and hepatic glucose production (delta 3.3 to 7.7 mumol x kg body weight-1.min-1) in all thyroid states, the effect was less pronounced in hyperthyroid pigs. By contrast, hypoglucagonaemia (74 to 107 pg/ml) at basal insulin (28 to 35 microU/ml) provoked hypoglycaemia (1.4 to 2.2 mmol/l) and a fall in glucose production (delta 4.7 to 8.3 mumol x kg body weight-1.min-1), which was independent of the thyroid state; the effect was most pronounced in hyperthyroidism (p less than 0.01). Hepatic glycogen content, arterial gluconeogenic precursor concentrations as well as the glycaemic response (delta 0.60 mmol/l) to alanine infusion (23 mumol x kg body weight-1.min-1) were all unaffected by hyperthyroidism. We conclude that moderate experimental hyperthyroidism reduces glucagon action due to reduced glycogen mobilisation. This may in part result from increased insulin sensitivity.