Butanediol induced ketosis increases tolerance to hypoxia in the mouse

Exogenous ketosis increases blood and muscle oxygenation but not performance during exercise in hypoxia

Available evidence indicates that elevated blood ketones are associated with improved hypoxic tolerance in rodents. From this perspective, we hypothesized that exogenous ketosis by oral intake of the ketone ester (R)-3-hydroxybutyl (R)-3-hydroxybutyrate (KE) may induce beneficial physiological effects during prolonged exercise in acute hypoxia. As we recently demonstrated KE to deplete blood bicarbonate, which per se may alter the physiological response to hypoxia, we evaluated the effect of KE both in the presence and absence of bicarbonate intake (BIC). Fourteen highly trained male cyclists performed a simulated cycling race (RACE) consisting of 3-h intermittent cycling (IMT_180') followed by a 15-min time-trial (TT_15') and an all-out sprint at 175% of lactate threshold (SPRINT). During RACE, fraction of inspired oxygen ([Formula: see text]) was gradually decreased from 18.6% to 14.5%. Before and during RACE, participants received either 1) 75 g of ketone ester (KE), 2) 300 mg/kg body mass bicarbonate (BIC), 3) KE + BIC, or 4) a control drink in addition to 60 g of carbohydrates/h in a randomized, crossover design. KE counteracted the hypoxia-induced drop in blood ([Formula: see text]) and muscle oxygenation by ∼3%. In contrast, BIC decreased [Formula: see text] by ∼2% without impacting muscle oxygenation. Performance during TT_15' and SPRINT were similar between all conditions. In conclusion, KE slightly elevated the degree of blood and muscle oxygenation during prolonged exercise in moderate hypoxia without impacting exercise performance. Our data warrant to further investigate the potential of exogenous ketosis to improve muscular and cerebral oxygenation status, and exercise tolerance in extreme hypoxia.

A Metabolic Intervention for Improving Human Cognitive Performance During Hypoxia

BACKGROUND: During hypoxia an operators cognitive performance may decline. This decline is linked to altered brain metabolism, resulting in decreased adenosine triphosphate (ATP) production. Ketone bodies are an alternative substrate to glucose for brain metabolic requirements; previous studies have shown that the presence of elevated ketone bodies in the blood maintains brain ATP levels and reduces cerebral glycolysis during hypoxia. Thus, ketones may be a strategy to mitigate cognitive decline in hypoxia. Ketone ester (KE) consumption allows rapid elevation of blood ketone levels; therefore, we investigated the effects of consuming a KE drink on cognitive performance during hypoxia. Here, we report results of a pilot study.METHODS: There were 11 subjects who completed a cognitive performance test battery under conditions of normoxia and hypoxia following consumption of a KE drink and a placebo control drink.RESULTS: Significant hypoxia effects (O₂ saturation minimum was found to range between 63 and 88 in subjects) were found for blink duration (Ph2 0.665) and blink rate (Ph2 0.626), indicating that the hypoxia condition was associated with longer blink durations and lower blink rates. Significant hypoxia effects were likewise observed for a code substitution task (Ph2 0.487), indicating that performance on the task was significantly disrupted by the hypoxia stressor. KE consumption had a significant effect on blink duration (Ph2 0.270) and the code substitution task (Ph2 0.309).DISCUSSION: These finding suggest that some effects of acute hypoxia can be mitigated by nutritional ketosis.Coleman K, Phillips J, Sciarini M, Stubbs B, Jackson O, Kernagis D. A metabolic intervention for improving human cognitive performance during hypoxia. Aerosp Med Hum Perform. 2021; 92(7):556562.

Systematic Review - Neuroprotection of ketosis in acute injury of the mammalian central nervous system: A meta-analysis

To evaluate the neuroprotection exerted by ketosis against acute damage of the mammalian central nervous system (CNS). Search engines were interrogated to identify experimental studies comparing the mitigating effect of ketosis (intervention) versus non-ketosis (control) on acute CNS damage. Primary endpoint was a reduction in mortality. Secondary endpoints were a reduction in neuronal damage and dysfunction, and an 'aggregated advantage' (composite of all primary and secondary endpoints). Hedges' g was the effect measure. Subgroup analyses evaluated the modulatory effect of age, insult type, and injury site. Meta-regression evaluated timing, type, and magnitude of intervention as predictors of neuroprotection. The selected publications were 49 experimental murine studies (period 1979-2020). The intervention reduced mortality (g 2.45, SE 0.48, p < .01), neuronal damage (g 1.96, SE 0.23, p < .01) and dysfunction (g 0.99, SE 0.10, p < .01). Reduction of mortality was particularly pronounced in the adult subgroup (g 2.71, SE 0.57, p < .01). The aggregated advantage of ketosis was stronger in the pediatric (g 3.98, SE 0.71, p < .01), brain (g 1.96, SE 0.18, p < .01), and ischemic insult (g 2.20, SE 0.23, p < .01) subgroups. Only the magnitude of intervention was a predictor of neuroprotection (g 0.07, SE 0.03, p 0.01 per every mmol/L increase in ketone levels). Ketosis exerts a potent neuroprotection against acute damage to the mammalian CNS in terms of reduction of mortality, of neuronal damage and dysfunction. Hematic levels of ketones are directly proportional to the effect size of neuroprotection.

Toxicological evaluation of the ketogenic ester bis hexanoyl (R)-1,3-butanediol: Subchronic toxicity in Sprague Dawley rats

Bis-hexanoyl (R)-1,3-butanediol (BH-BD) is novel ketone ester undergoing development as a food ingredient to achieve nutritional ketosis in humans. Male and female Crl:CD(SD) rats were administered BH-BD twice daily at 9000, 12,000 or 15,000 mg/kg/day, by oral gavage in a 90-day toxicity study with 28-day recovery period; and an interim 28-day phase. Test substance-related early deaths occurred in four females at 15,000 mg/kg/day. A dose-dependent increase in acute transient postdose (1-3 h) observations of incoordination at ≥12,000 mg/kg/day and decreased activity at all dose levels were noted in both sexes. Postdose observations were likely associated with peak ketonemia and were considered adverse at 15,000 mg/kg/day. These daily observations decreased over the study without any persistent effects, as determined during weekly pre-dose observations. Adverse histopathological changes included ulceration/erosion in non-glandular stomach at ≥ 12,000 mg/k/day and in glandular stomach at 15,000 mg/kg/day. These histopathological findings were not noted after 28-days of recovery. Due to unlikely human relevance of the rat non-glandular stomach effects for BH-BD and test substance-related mortality at 15,000 mg/kg/day, the no-observed-adverse-effect level (NOAEL) for subchronic toxicity of BH-BD was determined to be 12,000 mg/kg/day.

Regional cerebral effects of ketone body infusion with 3-hydroxybutyrate in humans: Reduced glucose uptake, unchanged oxygen consumption and increased blood flow by positron emission tomography. A randomized, controlled trial

Ketone bodies are neuroprotective in neurological disorders such as epilepsy. We randomly studied nine healthy human subjects twice—with and without continuous infusion of 3-hydroxybutyrate–to define potential underlying mechanisms, assessed regionally (parietal, occipital, temporal, cortical grey, and frontal) by PET scan. During 3-hydroxybutyrate infusions concentrations increased to 5.5±0.4 mmol/l and cerebral glucose utilisation decreased 14%, oxygen consumption remained unchanged, and cerebral blood flow increased 30%. We conclude that acute 3-hydroxybutyrate infusion reduces cerebral glucose uptake and increases cerebral blood flow in all measured brain regions, without detectable effects on cerebral oxygen uptake though oxygen extraction decreased. Increased oxygen supply concomitant with unchanged oxygen utilisation may contribute to the neuroprotective effects of ketone bodies.

Hair curvature: a natural dialectic and review

Although hair forms (straight, curly, wavy, etc.) are present in apparently infinite variations, each fibre can be reduced to a finite sequence of tandem segments of just three types: straight, bent/curly, or twisted. Hair forms can thus be regarded as resulting from genetic pathways that induce, reverse or modulate these basic curvature modes. However, physical interconversions between twists and curls demonstrate that strict one-to-one correspondences between them and their genetic causes do not exist. Current hair-curvature theories do not distinguish between bending and twisting mechanisms. We here introduce a multiple papillary centres (MPC) model which is particularly suitable to explain twisting. The model combines previously known features of hair cross-sectional morphology with partially/completely separated dermal papillae within single follicles, and requires such papillae to induce differential growth rates of hair cortical material in their immediate neighbourhoods. The MPC model can further help to explain other, poorly understood, aspects of hair growth and morphology. Separate bending and twisting mechanisms would be preferentially affected at the major or minor ellipsoidal sides of fibres, respectively, and together they exhaust the possibilities for influencing hair-form phenotypes. As such they suggest dialectic for hair-curvature development. We define a natural-dialectic (ND) which could take advantage of speculative aspects of dialectic, but would verify its input data and results by experimental methods. We use this as a top-down approach to first define routes by which hair bending or twisting may be brought about and then review evidence in support of such routes. In particular we consider the wingless (Wnt) and mammalian target of rapamycin (mTOR) pathways as paradigm pathways for molecular hair bending and twisting mechanisms, respectively. In addition to the Wnt canonical pathway, the Wnt/Ca(2+) and planar cell polarity (PCP) pathways, and others, can explain many alternatives and specific variations of hair bending phenotypes. Mechanisms for hair papilla budding or its division by bisection or fission can explain MPC formation. Epithelial-to-mesenchymal (EMT) and mesenchymal-to-epithelial (MET) transitions, acting in collaboration with epithelial-mesenchymal communications are also considered as mechanisms affecting hair growth and its bending and twisting. These may be treated as sub-mechanisms of an overall development from neural-crest stem cell (NCSC) lineages to differentiated hair follicle (HF) cell types, thus providing a unified framework for hair growth and development.

Strain differences in response to acute hypoxia: CD-1 versus C57BL/6J mice

Some mammals respond to hypoxia by lowering metabolic demand for oxygen and others by maximizing efficiency of oxygen usage: the former strategy is generally held to be the more effective. We describe within the same species one outbred strain (CD-1) that lowers demand and another inbred strain (C57BL/6J) that maximizes oxygen efficiency to markedly extend hypoxic tolerance. Unanesthetized adult male mice ( Mus musculus, CD-1 and C57BL/6J) between 20 and 35 g were used. Sham-conditioned (SC) C57BL/6J mice survived severe hypoxia (4.5% O2, balance N2) roughly twice as long as SC CD-1 mice (median 211 and 93.5 s, respectively; P < 0.0001). Following acute hypoxic conditioning (HC), C57BL/6J mice survived subsequent hypoxia 10 times longer than HC CD-1 mice (median 2,198 and 238 s respectively; P < 0.0001). Therefore, C57BL/6J mice are both naturally more tolerant to hypoxia and show a greater increase in hypoxic tolerance in response to hypoxic conditioning. Indirect calorimetry indicates that CD-1 mice lower mass-specific oxygen consumption (V̇′o2 in ml O2·kg−1·min−1) and carbon dioxide production (V̇′co2 in ml CO2·kg−1·min−1) in response to HC ( P = 0.002 and P < 0.0001, respectively), but C57BL/6J mice maintain V̇′o2 and V̇′co2 after HC. Respiratory exchange ratio and fluorometric assay of plasma ketones suggest that C57BL/6J mice rapidly switch to ketone metabolism, a more efficient substrate, while CD-1 mice reduce overall metabolic activity. We conclude that under severe hypoxia in mice, switching fuel, possibly to ketones, while maintaining V̇′o2, may confer a greater survival advantage than simply lowering demand.

Acute and conditioned hypoxic tolerance augmented by endothelial nitric oxide synthase inhibition in mice

To identify a possible role for nitric oxide (NO) in acute hypoxic tolerance (HT) we measured hypoxic survival time (HST), effect of hypoxic conditioning (HC), and survival following hypoxic conditioning while blocking or mimicking the action of nitric oxide synthase (NOS). To inhibit NOS, CD-1 mice were given supplemental endogenous NOS inhibitor asymmetrical dimethylarginine (ADMA) or a synthetic NOS inhibitor N(omega)-nitro-L-arginine (L-NNA), both of which nonselectively inhibit three of the isoforms of NOS [inducible (iNOS), neuronal (nNOS), and endothelial NOS (eNOS)]. ADMA (10 mg/kg i.p.) or saline vehicle was given 5 min before HST testing. L-NNA was given orally at 1 g/l in drinking water with tap water as the control for 48 h before testing. Both ADMA and L-NNA significantly increased HST and augmented the HC effect on HST. Neither the nNOS selective inhibitor 7-nitroindazole (7-NI) nor the iNOS selective inhibitor N-{[3-(aminomethyl)phenyl]methyl}-enthanimidamide (1400W) had a statistically significant effect on HST or HT. The NO donor, 3-morpholinosydnoeimine, when given alone did not significantly decrease HT, but it did mitigate the increased HT effect of L-NNA. These data confirm that acute hypoxic conditioning increases HT and that NOS inhibition by endogenous (ADMA) and a synthetic NOS inhibitor (L-NNA) further increases HT, whereas iNOS and nNOS inhibition does not, suggesting that it is the inhibition of eNOS that mediates enhancement of HT.

Fuel metabolism in starvation

This article, which is partly biographical and partly scientific, summarizes a life in academic medicine. It relates my progress from benchside to bedside and then to academic and research administration, and concludes with the teaching of human biology to college undergraduates. My experience as an intern (anno 1953) treating a youngster in diabetic ketoacidosis underscored our ignorance of the controls in human fuel metabolism. Circulating free fatty acids were then unknown, insulin could not be measured in biologic fluids, and beta-hydroxybutyric acid, which was difficult to measure, was considered by many a metabolic poison. The central role of insulin and the metabolism of free fatty acids, glycerol, glucose, lactate, and pyruvate, combined with indirect calorimetry, needed characterization in a near-steady state, namely prolonged starvation. This is the main topic of this chapter. Due to its use by brain, D-beta-hydroxybutyric acid not only has permitted man to survive prolonged starvation, but also may have therapeutic potential owing to its greater efficiency in providing cellular energy in ischemic states such as stroke, myocardial insufficiency, neonatal stress, genetic mitochondrial problems, and physical fatigue.

D-beta-hydroxybutyrate is neuroprotective against hypoxia in serum-free hippocampal primary cultures

Hypoxia decreased survival of cultured rat primary hippocampal neurons in a time dependent manner. Addition of 4 mM Na D-beta-hydroxybutyrate (bHB), a ketone body, protected the cells for 2 hr and maintained the increase in survival compared to that of controls for up to 6 hr. Trypan blue exclusion indicated that acute cell death was reduced markedly after 2-hr exposure to hypoxia in the bHB-treated group. The presence of bHB also decreased the number of neurons exhibiting condensed nuclei visualized by propidium iodide, indicative of apoptosis. The mitochondrial transmembrane potential (Em/c) was maintained for up to 2 hr exposure to hypoxia in the bHB-treated group, whereas the potential in the control group was decreased. Furthermore, cytochrome C release, caspase-3 activation, and poly (ADP-ribose) polymerase (PARP) cleavage were decreased in the bHB-treated group for the first 2 hr of exposure. These findings indicate that ketone bodies may be a candidate for widening the therapeutic window before thrombolytic therapy and at the same time decreasing apoptotic damage in the ischemic penumbra.

The effects of a butanediol treatment on acute focal cerebral ischemia assessed by quantitative diffusion and T2 MR imaging

Increased water T2 values indicates the presence of vasogenic edema. Decreased apparent diffusion coefficient (ADC) maps reveal ischemic areas displaying cytotoxic edema. ADC and T2 abnormalities spread through the middle cerebral artery (MCA) territory up to 24 h after middle cerebral artery occlusion (MCAO). Also, it was found that ADC and T2 contours closely match at 3.5 and 24 h. Since butanediol reduces vasogenic edema and improves energy status in various models of ischemia, we used these two techniques to investigate putative improvements in cytotoxic and vasogenic edema after permanent MCAO performed on rats. Rats were given no treatment (n = 8), or a treatment with 25 mmol/kg intraperitoneal (i.p.) butanediol (n = 5), 30 min before and 2.5 h after MCAO. Quantitative ADC and T2 maps of brain water were obtained, from which the volumes presenting abnormalities were calculated at various time points up to 24 h. Effects of butanediol on the ADC and T2 values in these areas were determined. Butanediol reduced neither the ADC volume nor the initial ADC decline. However, it reduced T2 volumes by 32% at 3.5 h and 15% at 24 h (p < 0.05), and reduced T2 increase in the striatum at 3.5 h post-MCAO. Therefore, our results show for the first time that a pharmacological agent such as butanediol can delay the development of vasogenic edema but does not limit the development of vasogenic edema but does not limit the development of cytotoxic edema. ADC imaging detects areas of severe metabolic disturbance but not moderately ischemic peripheral areas where butanediol is presumed to be more efficacious.

The neurologic implications of diabetic hyperglycemia during surgical procedures at increased risk for brain ischemia

The neurologic implications of diabetic hyperglycemia depend on whether the ischemic insult is permanent or temporary. Laboratory studies show that following permanent focal ischemia, a situation analogous to stroke, diabetic hyperglycemia is protective in the penumbral region, whereas it may slightly increase infarct size. In addition, clinical studies cannot unequivocally attribute poor outcome in diabetic stroke patients to hyperglycemia. Thus, both laboratory and clinical studies have been unable to define a cause and effect relationship between diabetic hyperglycemia and neurologic outcome following stroke. On the other hand, diabetic hyperglycemia is an important determinant of neurologic outcome following temporary focal ischemia (analogous to temporary occlusion of a cerebral vessel) and global ischemia (analogous to circulatory arrest). Based on laboratory studies, aggressive insulin-based blood glucose management with the goal of euglycemia is imperative prior to temporary ischemia. However, intraoperative ischemic events are overwhelmingly of a permanent focal nature, and the neurologic implications of diabetic hyperglycemia for the vast majority of surgical procedures at increased risk for brain ischemia are minimal. It is only in circumstances where temporary focal or global ischemia are used as part of the surgical procedure that aggressive insulin-based blood glucose management is warranted.

Evaluation of a carbohydrate-free diet for patients with severe head injury

Hyperglycemia, which may be caused or exacerbated by conventional diets, may worsen the neurological outcome from severe head injury, especially if secondary ischemic insults occur. The purpose of this study was to evaluate an experimental diet intended to replace systemic caloric and protein requirements without producing hyperglycemia. In initial studies in the laboratory, 5 experimental diets were employed in a middle cerebral artery temporary occlusion model. The effects of the diets on blood biochemistry and on infarction volume were compared in fasted animals and in animals fed a control diet. Animals fed the experimental diets had a significantly lower preischemia blood glucose concentration, a higher blood concentration of ketone bodies, and a smaller infarct volume than the animals fed a control diet. One diet chosen from the laboratory study was then evaluated in a clinical study as a randomized, open-label trial. Twenty severely head-injured patients were randomly assigned to be fed the experimental diet, EN-9305, or the control diet, Osmolyte HN, for the first 2 weeks after injury. Both treatment groups had similar blood glucose concentrations, averaging 6.33 +/- 0.21 mumol/mL (114 +/- 4 mg/dL), on day 1 prior to starting the assigned diet. Blood glucose concentration increased in the control diet group to a peak of 8.37 +/- 0.94 mumol/mL (151 +/- 17 mg/dL) on day 7 as the infusion rate of the diet was increased to the final rate. In the experimental diet group, the blood glucose concentration remained unchanged from fasting levels as the diet was advanced. Blood lactate concentration was lower, and blood ketone body concentrations were higher in the patients fed the experimental diet. Urinary nitrogen balance was better in the experimental diet group, but measures of visceral protein sparing, including serum albumin, plasma retinol binding protein, and total lymphocyte count, were not significantly different in the 2 treatment groups. Measures of cerebral anaerobic metabolism, including CSF lactate concentration and cerebral lactate production, were not significantly different in the 2 treatment groups. These studies suggest that a carbohydrate-free diet such as EN-9305 might have advantages for patients with severe head injury by replacing systemic caloric and protein requirements without producing hyperglycemia.

Effect of D- and L-1,3-butanediol isomers on glycolytic and citric acid cycle intermediates in the rat brain

DL-1,3-butanediol (DL-BD) is an ethanol dimer which affords cerebral protection in various experimental models of hypoxia and ischemia but its mechanism of action is unknown. DL-BD is a ketogenic alcohol and it has been proposed that its protective effect was accomplished through cerebral utilization of ketone bodies. Since DL-BD is a racemic, its metabolic effects could be due to D, L or both isomers. The effects of equimolar doses of DL-, D- and L-BD (25 mmol/Kg) on cerebral metabolism were studied by measuring the cortical levels of the main glycolytic (glycogen, glucose, glucose 6-phosphate, fructose 1,6-diphosphate, pyruvate and lactate) and citric acid cycle (citrate, alpha-ketoglutarate and L-malate) intermediates. The two BD isomers exerted different effects on cerebral metabolism. Unlike L-BD, D- and DL-BD treatments resulted in a slight (+10%) but significant increase in citrate level whereas L-BD treatment led to significant reduction in pyruvate (-12%) and lactate (-24%) levels. These effects were apparently not linked to hyperketonemia, since DL-BHB treatment, which mimicked hyperketonemia induced by DL-BD, had no effect on cerebral metabolites but might be due to intracerebral metabolism of BD.

Diabetic chronic hyperglycemia and cerebral pH recovery following global ischemia in dogs

BACKGROUND AND PURPOSE

We determined the effect of chronic hyperglycemia associated with diabetes on recovery of cerebral pH after global incomplete cerebral ischemia.

METHODS

31P magnetic resonance spectra and cerebral blood flow (radiolabeled microspheres) were measured in three groups of dogs: (1) chronic hyperglycemic diabetes (pancreatectomy followed by blood glucose > 10 mmol/L for 3 months; n = 8); (2) acute hyperglycemia during ischemia and reperfusion in nondiabetic dogs (n = 8); and (3) normoglycemic controls (n = 8). Incomplete ischemia was produced for 20 minutes by ventricular fluid infusion followed by 3 hours of reperfusion.

RESULTS

Cerebral blood flow was reduced to approximately 5 mL/min per 100 g in all groups during ischemia with individual values ranging from 1 to 11 mL/min per 100 g. Blood flow returned to preischemic values by 30 minutes of reperfusion in the normoglycemia group but remained elevated during reperfusion in the acute hyperglycemia and diabetes groups. Cerebral pH at the end of ischemia was lower in acute hyperglycemia (5.94 +/- 0.05; +/- SE) and diabetes (5.97 +/- 0.08) groups than in the normoglycemia group (6.27 +/- 0.02). However, recovery of pH through 90 minutes of reperfusion in the normoglycemia (7.08 +/- 0.05) and diabetes (7.00 +/- 0.04) groups was significantly greater than in the acute hyperglycemia group (6.74 +/- 0.11). Persistent acidosis in the acute hyperglycemia group was associated with a delayed reduction of cerebral oxygen consumption and high-energy phosphates and with greater cortical water content and impairment of somatosensory evoked potentials compared with the diabetes group.

CONCLUSIONS

This study shows that cerebral pH recovery after global incomplete ischemia is improved in chronic hyperglycemia compared with acute hyperglycemia, despite similar decreases in blood flow and pH during ischemia and similar levels of blood flow and glucose levels during ischemia and reperfusion. In addition, cerebral pH recovery in chronic hyperglycemic dogs was not different from that in normoglycemic controls. These results suggest that an adaptation occurs with chronic hyperglycemia that improves recovery of cerebral pH during reperfusion and that is associated with better maintenance of energy metabolism and evoked potentials and with less edema over 3 hours of reperfusion compared with acute hyperglycemia.

Effect of 1,3-butanediol on cerebral energy metabolism. Comparison with beta-hydroxybutyrate

Previous studies have shown that 1,3-butanediol (BD) has beneficial effects in experimental models of hypoxia or ischemia but the mechanism by which it exerts its protective effects remains unknown. BD is converted in the body to beta-hydroxybutyrate (BHB) and it has been proposed that its effects were linked to its ketogenic effect. The effects of BD (25 and 50 mmol/kg) on cerebral energy metabolism of rats were studied by measuring the cerebral level of energy metabolites and by evaluating the cerebral metabolic rate according to the Lowry's method. BD induced an increase in [cortical glucose]/[plasma glucose] ratio which was associated with a decrease in lactate level and an increase in glucose and glycogen stores. In contrast, BHB treatment which mimicked hyperketonemia equivalent to BD did not modify cerebral glycolysis metabolites. Calculation of the energy reserve flux after decapitation showed that BD did not reduce the cerebral metabolic rate excluding a protective effect due to a depressant, barbiturate-like, action. These results suggest that BD induces a reduction of cerebral glycolytic rate. However, the effect is not linked to hyperketonemia but might be due to intracerebral conversion of BD to BHB.

Changes in extracellular and rat brain tissue concentrations of D-beta-hydroxybutyrate after 1,3-butanediol treatment

1,3-Butanediol (BD) treatment was previously shown to produce a dose-related increase of the plasma levels of D-beta-hydroxybutyrate (BHB) and to protect brain tissue against hypoxia and ischemia. The purpose of this study was to test whether BD-induced hyperketonemia was associated with changes in brain extracellular and tissue concentrations of BHB. Changes in extracellular levels of BHB were continuously monitored in anesthetized rats before and after intraperitoneal injection of BD (25 mmol/kg), using intracerebral microdialysis coupled to online analysis of BHB in the dialysate. Cortical tissue concentrations of BHB were determined in control and BD-treated rats (25 and 50 mmol/kg, i.p.) after freezing of the brain in situ. Butanediol produced a rapid increase in dialysate levels of BHB, with a linear relationship between dialysate and plasma BHB concentrations (r = 0.81, p < 0.001). In contrast, and although brain tissue levels of BHB were markedly increased after BD treatment, they were not related to the plasma concentration of BHB. Our results suggest that BHB produced from BD did not accumulate in brain and that BD protects against hypoxia or ischemia by increasing brain BHB availability.

Role of endogenous opioid peptides in the acute adaptation to hypoxia

A non-lethal, hypoxic conditioning stimulus has been shown by Rising and D'Alecy to increase hypoxic survival time in mice. To determine if endogenous opioids alter the hypoxic conditioning-induced increase in hypoxic survival time, we administered naloxone (0.1, 1.0 mg/kg i.p.) or saline (0.3 ml i.p.) 5 min prior to conditioning. Sixty percent of the mice received the hypoxic conditioning stimulus consisting of three sequential hypoxic exposures (4.5% oxygen balance nitrogen for 1.5, 2 and 2.5 min) separated by 5 min of room air. The remaining mice did not receive hypoxic conditioning but instead remained in room air for this time. All mice were tested for hypoxic survival by first exposing them to 20 s of 8.5% oxygen balance nitrogen followed by exposure to 4.5% oxygen balance nitrogen. The hypoxic survival time was recorded as the time from the onset of the 4.5% oxygen to the cessation of spontaneous ventilation. Naloxone (1 mg/kg) completely blocked the adaptation to hypoxia induced by hypoxic conditioning (P = 0.003). Morphine (1, 5, 10 and 20 mg/kg) had no effect on hypoxic adaptation; however, 50 mg/kg morphine decreased the adaptation induced by conditioning (P less than 0.0001) possibly due to high dose toxicity. These data suggest that endogenous opioids are involved in the protective adaptation to hypoxia induced by prior exposure to non-lethal hypoxia.

Ischemic brain damage is not ameliorated by 1,3-butanediol in hyperglycemic rats

BACKGROUND AND PURPOSE

Treatment with the ketone body precursor 1,3-butanediol has been suggested to ameliorate hypoxic/ischemic brain damage. Butanediol could provide an alternative energy substrate for the brain, thereby decreasing the amount of glycolytically produced lactate. Hyperglycemia aggravates brain damage after brain ischemia and causes fatal postischemic seizures, probably by increasing the production of lactate and decreasing the pH. We studied whether butanediol treatment altered the adverse consequences following ischemia complicated by hyperglycemia.

METHODS

Hyperglycemic adult male rats were given 25 or 50 mmol.kg-1 body wt butanediol intravenously 30 minutes before 10 minutes of transient forebrain ischemia. Morphological evaluation was performed following perfusion-fixation after 15 hours of recovery. Blood concentrations of beta-hydroxybutyrate, acetoacetate, glucose, and lactate and brain tissue concentrations of energy metabolites were measured before and after ischemia.

RESULTS

Blood levels of ketone bodies increased in the butanediol-treated rats. Ischemia decreased the blood levels of acetoacetate but increased the levels of beta-hydroxybutyrate by a similar amount, resulting in unchanged high levels of total ketone bodies in the animals that received butanediol. Brain tissue levels of glucose, energy metabolites, and lactate showed no difference between butanediol- and saline-treated rats. Furthermore, compared with saline-treated animals butanediol-treated rats showed no decrease in brain damage and no attenuation in the development of postischemic seizures.

CONCLUSIONS

The ketone body precursor 1,3-butanediol offers no protective effect in transient forebrain ischemia complicated by hyperglycemia.

Beneficial effect of 1,3-butanediol on cerebral energy metabolism and edema following brain embolization in rats

We assessed the effect of 1,3-butanediol on cerebral energy metabolism and edema after inducing multifocal brain infarcts in 108 rats by the intracarotid injection of 50-microns carbonized microspheres. An ethanol dimer that induces systemic ketosis, 25 mmol/kg i.p. butanediol was injected every 3 hours to produce a sustained increase in the plasma level of beta-hydroxybutyrate. Treatment significantly attenuated ischemia-induced metabolic changes by increasing the concentrations of phosphocreatine, adenosine triphosphate, and glycogen and by reducing the concentrations of pyruvate and lactate. Lactate concentration 2, 6, and 12 hours after embolization decreased by 13%, 44%, and 46%, respectively. Brain water content increased from 78.63% in six unembolized rats to 80.93% in 12 saline-treated and 79.57% in seven butanediol-treated rats 12 hours after embolization. (p less than 0.05). The decrease in water content was associated with significant decreases in the concentrations of sodium and chloride. The antiedema effect of butanediol could not be explained by an osmotic mechanism since equimolar doses of urea or ethanol were ineffective. Our results support the hypothesis that the beneficial effect of butanediol is mediated through cerebral utilization of ketone bodies arising from butanediol metabolism, reducing the rate of glycolysis and the deleterious accumulation of lactic acid during ischemia.

Beta-hydroxybutyrate and response to hypoxia in the ground squirrel, Spermophilus tridecimlineatus

1. Previous studies have suggested that elevated ketone levels are associated with increased survival time in rodents exposed to hypoxia. In this study the association between whole blood BHB (beta-hydroxybutyrate) and hypoxic survival time was investigated in hibernating and non-hibernating ground squirrels and in rats. 2. Non-hibernating ground squirrels and rats were exposed to hypoxia (4.5% O2). One hundred per cent of ground squirrels survived 1 hr of hypoxia vs 20% of rats. 3. Ketone levels were significantly higher in ground squirrels than rats during hypoxia, and rats surviving the longest had the highest ketone levels. 4. When hibernation was induced in ground squirrels there was a significant increase in beta-hydroxy-butyrate from 0.45 to 1.6 mM (P = 0.0005). 5. Ground squirrel heart mitochondrial respiratory control ratios and ATP synthesis rates indicated no preferential ketone utilization which might suggest a possible extramitochondrial role of BHB during hypoxia. 6. We conclude that elevated blood BHB levels are associated with increased hypoxic survival and they may have evolved in response to life-threatening hypoxia as experienced during hibernation.

Hypoxia-induced increases in hypoxic tolerance augmented by beta-hydroxybutyrate in mice

A standard murine model was used to determine whether acute pretreatment exposures to hypoxia could alter ultimate hypoxic survival time. Adult male albino mice (Mus musculus) weighing 25-30 g were subjected to three pretreatment hypoxic exposures (4.5% O2, balance N2) of increasing duration (90, 120, and 150 seconds) with 300 seconds of normoxia between each pretreatment exposure and before testing of hypoxic survival time. Acute pretreatment exposures to hypoxia significantly increased mean +/- SEM hypoxic survival time from 108 +/- 4 to 403 +/- 42 seconds. Mean +/- SEM blood glucose concentrations increased significantly from 201 +/- 19 to 397 +/- 10 mg/dl immediately after hypoxic pretreatment. A significant increase in mean +/- SEM blood ketone concentrations, from 0.15 +/- 0.01 to 0.40 +/- 0.08 mM, was detected in the blood 1,800 seconds but not 300 seconds after hypoxic pretreatment. However, pretreatment with exogenous glucose or ketones alone, to mimic the blood levels seen after hypoxic pretreatment, failed to increase hypoxic survival time. In contrast, mice pretreated with hypoxic exposures plus the exogenous substrate beta-hydroxybutyrate had an increased mean +/- SEM hypoxic survival time of 749 +/- 48 seconds and a decreased body temperature. Stepwise Cox regression analyses with body temperature as a fixed covariate suggest that this decrease in body temperature has a partial role in, but can not fully account for, the increased hypoxic survival time. These data suggest that sequential exposures to hypoxia induce metabolic changes that protect against the lethal effects of hypoxia, perhaps by altering substrate mobilization and utilization and/or by inducing a hypometabolic hypothermia.

Protective action of 1,3-butanediol in cerebral ischemia. A neurologic, histologic, and metabolic study

1,3-Butanediol (BD) is converted in the body to beta-hydroxybutyrate, and previous studies have shown that hyperketonemia had beneficial effects in experimental models of generalized hypoxia. The aim of this study was to determine if BD would reduce brain damage following cerebral ischemia. A transient forebrain ischemia of 30-min duration was induced by the four-vessel occlusion technique in control and BD-treated rats (25 mmol/kg, i.p.; 30 min prior to ischemia). BD treatment led to significant improvement of neurologic deficit during the 72-h recovery period and reduced neuronal damage in the striatum and cortex but not in the CA1 sector of the hippocampus. Evaluation of cerebral energy metabolism before and at the end of the ischemic period showed that the treatment did not change the preischemic glycolytic and energy metabolite levels but attenuated the ischemia-induced metabolic alterations. It increased energy charge, phosphocreatine, and glucose levels, and reduced lactate accumulation. The decrease in brain lactate concentration might account for the beneficial effects of BD by minimizing the neuropathological consequences of lactic acidosis.