- Open Access
Bench-to-bedside review: A possible resolution of the glucose paradox of cerebral ischemia
Critical Care volume 6, Article number: 330 (2002)
The glucose paradox of cerebral ischemia (namely, the aggravation of delayed ischemic neuronal damage by preischemic hyperglycemia) has been promoted as proof that lactic acidosis is a detrimental factor in this brain disorder. Recent studies, both in vitro and in vivo, have demonstrated lactate as an excellent aerobic energy substrate in the brain, and possibly a crucial one immediately postischemia. Moreover, evidence has been presented that refutes the lactic acidosis hypothesis of cerebral ischemia and thus has questioned the traditional explanation given for the glucose paradox. An alternative explanation for the aggravating effect of preischemic hyperglycemia on the postischemic outcome has consequently been offered, according to which glucose loading induces a short-lived elevation in the release of glucocorticoids. When an episode of cerebral ischemia in the rat coincided with glucose-induced elevated levels of corticosterone (CT), the main rodent glucocorticoid, an aggravation of the ischemic outcome was observed. Both the blockade of CT elevation by chemical adrenalectomy with metyrapone or the blockade of CT receptors in the brain with mifepristone (RU486) negated the aggravating effect of preischemic hyperglycemia on the postischemic outcome.
The lactic acidosis hypothesis of cerebral ischemia [1,2,3] postulates that lactic acid accumulates in the brain during an ischemic event and plays a major detrimental role in delayed neuronal damage postischemia. The findings of Myers and Yamaguchi  that glucose administration preischemia significantly aggravates the postischemic outcome have been reproduced numerous times, and have repeatedly been promoted as the validation of the lactic acidosis hypothesis of cerebral ischemia.
The glucose paradox as proof of the validity of this hypothesis is based on the idea that preischemic hyperglycemia leads to elevated lactic acid levels, and thus to aggravation of post-ischemic brain damage. Preventive measures are consequently being practiced in hospitals throughout the world, including the close monitoring and tight control of blood glucose levels [5,6]. Nonetheless, such measures are in disagreement with several facts. First, glucose is the only major aerobic and anaerobic energy substrate in the brain. Second, during cerebral ischemia, glycolytic utilization of glucose is the only metabolic process capable of producing significant levels of ATP until all glucose and glycogen levels are extinguished. Third, during ischemia, lactate is the main product of glycolysis; on reperfusion/reoxygenation, when brain glucose is all but gone, the abundant lactate can easily enter the tricarboxylic acid cycle to maintain ATP production as efficiently as does glucose. Thus, paradoxically, the only process that supplies ATP to the ischemic tissue is viewed as the one responsible for the aggravation of the ischemic damage to this very tissue.
Both in vitro studies [7,8,9,10,11,12,13] and in vivo studies [14,15,16,17,18,19,20,21,22,23,24,25,26,27,28] have shown that preischemic glucose supply is not necessarily harmful, and that it could even be beneficial when provided preischemia. These in vivo findings are considered oddities, however, while in vitro data are not considered to necessarily represent the true in vivo situation. Consequently, when dexa-methasone treatment in stroke patients was found to induce hyperglycemia, Wass et al.  suggested that lactic acidosis, not the steroid itself, is responsible for the exacerbation of ischemic damage frequently observed with dexamethasone treatment. It is important to note, however, that steroids such as dexamethasone are regularly administered postischemia. Postischemic hyperglycemia has been shown not to aggravate postischemic damage [30,31,32]. In contrast, an association between a pronounced systemic stress response, an elevated level of cortisol in the plasma and increased mortality or morbidity has been reported .
The steroid prednisone was shown to inhibit insulin secretion and to elevate blood glucose levels . CT, the rodent equivalent of human cortisol, was shown to depress the release of glucose-induced insulin , while other studies have concluded that hyperglycemia in acute stroke patients represents a stress response [36,37]. Glucocorticoids have been shown to inhibit glucose transport and glutamate uptake in hippocampal astrocytes , to accelerate ATP loss following metabolic insults in neuronal culture , and thus to exacerbate insult-induced declines in energy metabolism . A recent in vitro study was able to demonstrate an aggravation of ischemic damage by CT in vitro .
Until recently, no studies had been conducted to determine whether glucose loading preischemia induces an elevation in blood glucocorticoids (see below). In an unrelated study, Harris et al.  found that glucose challenge in mice elevated CT blood levels sixfold 30 min after glucose injection, which returned to baseline levels 90 min later. Wang et al.  demonstrated that a carbohydrate-rich diet boosted CT blood levels. In contrast, metyrapone (2-methyl-1,2-di-3-pyridyl-1-propanone), a glucocorticoid biosynthesis inhibitor, was shown to reduce ischemic brain injury, possibly by reducing blood CT levels [44,45,46,47].
Preischemic hyperglycemia: detriment or benefit
A recent study in rats is most revealing regarding the role that glucose plays in cerebral ischemia . When rats were made hyperglycemic by glucose loading (2 g/kg, intraperi-toneally) 15–60 min prior to a 7-min episode of cerebral ischemia, a significant increase in the degree of delayed neuronal damage postischemia was found in comparison with control, saline-injected rats (Fig. 1). In contrast, rats loaded with glucose 120–240 min preischemia, although also hyperglycemic at the onset of ischemia, showed a significantly lower degree of delayed neuronal damage postischemia in comparison with control rats. Hippocampal levels of lactate were measured at the end of the ischemic period in rats administered with either saline or glucose preischemia. The lactate levels measured were significantly and equally higher in rats administered glucose either 15 or 120 min preischemia when compared with control, saline-administered rats.
These results contradict, and thus refute, the hypothesis that delayed ischemic neuronal damage is directly correlated with brain lactate levels. Our finding that inhibition of lactate utilization immediately postischemia is detrimental  further refutes the lactic acidosis hypothesis. Thus, in those cases where high brain levels of lactate were detected 30–90 min after the onset of reperfusion [1,50,51,52,53,54,55,56,57,58], lactate probably remained unused due to cell death.
Since neither glucose nor lactate appears to be the damaging factor during cerebral ischemia, we postulated that glucose loading evokes a short-lived (30–60 min) systemic response (hormonal or other) that, when occurring simultaneously with an ischemic episode, is capable of aggravating the degree of delayed neuronal damage postischemia. Allowing this short-lived systemic response to subside (120 min) prior to the onset of the ischemic episode would make apparent the protective effect of glucose on the ischemic brain (Fig. 1). This glucose-induced protection stems from both hyperglycemic supplies of the sugar to sustain anaerobic glycolysis and from the ample supplies of lactate available for oxidation on reperfusion/reoxygenation.
Corticosterone: a systemic factor released in response to glucose administration
Preliminary experiments to test the effects of glucose loading on plasma CT levels revealed a sharp increase in the level of this stress hormone 15–30 min after glucose administration, followed by a return to baseline level 120 min after glucose administration . These changes appear to correlate with the aggravation of neuronal damage by hyperglycemia when induced 15 min preischemia, and by the lack of such aggravation when glucose is administered 120 min preischemia.
These preliminary results support the postulate by which the glucose paradox is an outcome of glucose-induced increase in CT levels that lasts for approximately 60 min (see also ). While the observed changes in plasma CT levels in response to glucose loading do correlate with the post-ischemic outcome, such correlation by itself does not provide the proof that CT is the culprit of the glucose paradox phenomenon. A more direct approach must be taken to demonstrate the complicity of CT. Hence, either blockade of CT biosynthesis, on the one hand, or antagonism of its receptor, on the other, or both, would provide stronger supportive evidence if and when these approaches could abolish the aggravating effect of preischemic hyperglycemia.
Chemical adrenalectomy, using metyrapone, is one way to inhibit CT biosynthesis. Preliminary experiments with metyrapone  support the notion that glucose-induced CT release is the culprit behind the glucose paradox. As can be seen from Figure 1, rats pretreated with metyrapone suffered no aggravation of neuronal damage when administered glucose 15 min preischemia. These rats actually exhibited a degree of ischemic damage that was significantly lower than the damage measured in control, normoglycemic rats. This indicates that, once the aggravating factor (i.e. CT) is removed, glucose can be beneficial even when loaded shortly preischemia. The blood glucose levels of metyrapone-treated, glucose-loaded rats just prior to the ischemic episode were as high as those of untreated rats loaded with glucose.
The second approach, antagonizing CT action at its receptor, was also tested. For that purpose, the glucocorticoid receptor antagonist mifepristone (RU486)  was used. Glucose-loaded rats (15 min preischemia) treated with the antagonist (40 mg/kg, intraperitoneally) 45 min preischemia exhibited a significantly lower degree of postischemic damage than glucose-loaded rats untreated with RU486. The damage was indistinguishable from that measured in control, normo-glycemic rats (unpublished data).
When the findings of the glucose-induced, short-lived increase in CT release and of the abilities of both metyrapone and RU486 to abolish the preischemic hyperglycemia-aggravated postischemic damage are taken together, they unequivocally point at CT as the culprit behind the glucose paradox of cerebral ischemia. The CT hypothesis is consequently being offered to explain this paradox instead of the lactic acidosis hypothesis.
The glucose paradox of cerebral ischemia, the phenomenon of preischemic hyperglycemia-aggravated postischemic outcome, has been blamed on the accumulation of lactate and the intensification of acidosis. This explanation has recently been questioned with several data.
Data have shown that lactate is an excellent aerobic energy substrate in the brain, and a crucial one during recovery from ischemia. It is therefore an unlikely detrimental factor in cerebral ischemia.
Glucose, the only readily available energy substrate in the brain under normoxic conditions, has been shown as the only substrate that could sustain ion homeostasis, at least for a while, during an ischemic episode. Yet, when administered shortly (15–60 min) preischemia, an aggravation of the ischemic outcome is observed. When administered 2–3 hours preischemia, however, despite the presence of hyperglycemic conditions, no aggravation of the outcome was observed. Hence, glucose per se is an unlikely aggravator of ischemic damage.
It has been shown that glucose loading induces a short-lived (~60 min), several-fold increase in CT plasma levels, a stress hormone known to aggravate the outcome of metabolic insults. It has also been shown, however, that pretreatment of rats with metyrapone, an inhibitor of CT biosynthesis, abolished the postischemic aggravating effect of glucose when loaded shortly preischemia. Finally, RU486 (an antagonist of the CT receptor) was also shown to abolish the aggravating effect of glucose loading shortly preischemia.
It is hypothesized that glucose-induced CT release, when occurring shortly preischemia, is the event responsible for the phenomenon known as the glucose paradox of cerebral ischemia. Neither lactate nor glucose per se has anything to do with this phenomenon. Both investigators and clinicians are encouraged to re-examine their notions and clinical practices regarding the roles of glucose in cerebral ischemia (stroke).
CT = corticosterone
RU486 = mifepristone.
Siesjo BK, Nordstrom H-C, Rehncrona S: Metabolic aspects of cerebral hypoxia ischemia. In Tissue Hypoxia and Ischemia. (Edited by: Reivich M, Coburn R, Lahiri S, Chance B). New York: Plenum Press 1977, 261-269.
Siesjo BK: Cell damage in the brain: a speculative synthesis. J Cereb Blood Flow Metab 1981, 1: 155-185.
Siesjo BK: Acidosis and ischemic brain damage. Neurochem Pathol 1988, 9: 31-88.
Myers RE, Yamaguchi S: Nervous system effects of cardiac arrest in monkeys reservation of vision. Arch Neurol 1977, 34: 65-74.
Lanier WL: Glucose management during cardiopulmonary bypass: cardiovascular and neurologic implications. Anesth Analg 1991, 72: 423-427.
Wass CT, Lanier WL: Glucose modulation of ischemic brain injury: review and clinical recommendations. Mayo Clin Proc 1996, 71: 801-812.
Schurr A, West CA, Reid KH, Tseng MT, Reiss SJ, Rigor BM: Increased glucose improves recovery of neuronal function after cerebral hypoxia in vitro. Brain Res 1987, 421: 135-139. 10.1016/0006-8993(87)91283-2
Seo SY, Kim EY, Kim H, Gwag BJ: Neuroprotective effect of high glucose against NMDA, free radical, and oxygen-glucose deprivation through enhanced mitochondrial potentials. J Neurosci 1999, 19: 8849-8855.
Zhu PJ, Kenjevic K: Persistent block of CA1 synaptic function by prolonged hypoxia. Neuroscience 1999, 90: 759-770. 10.1016/S0306-4522(98)00495-3
Tian GF, Baker AJ: Glycolysis prevents anoxia-induced synaptic transmission damage in rat hippocampal slices. J Neurophysiol 2000, 83: 1830-1839.
Yamane K, Yokono K, Okada Y: Anaerobic glycolysis is crucial for the maintenance of neural activity in guinea pig hippocam-pal slices. J Neurosci Methods 2000, 103: 163-171. 10.1016/S0165-0270(00)00312-5
Li X, Yokono K, Okada Y: Phosphofructokinase, a glycolytic regulatory enzyme has a crucial role for maintenance of synaptic activity in guinea pig hippocampal slices. Neurosci Lett 2000, 294: 81-84. 10.1016/S0304-3940(00)01535-4
Ames A III: CNS energy metabolism as related to function. Brain Res Rev 2000, 34: 42-68. 10.1016/S0165-0173(00)00038-2
Ginsberg MD, Prado R, Dietrich WD, Busto R, Watson BD: Hyperglycemia reduces the extent of cerebral infarction in rats. Stroke 1987, 18: 570-574.
Zasslow MA, Pearl RG, Shuer LM, Steinberg GK, Lieberson RE, Larson CP Jr: Hyperglycemia decreases acute neuronal ischemic changes after middle cerebral artery occlusion in cats. Stroke 1989, 20: 519-523.
Kraft LA, Larson CP Jr, Shuer LM: Effect of hyperglycemia on neuronal changes in a rabbit model of focal cerebral ischemia. Stroke 1990, 21: 447-450.
Vannucci RC, Brucklacher RM, Vannucci SJ: The effect of hyperglycemia on cerebral metabolism during hypoxia-ischemia in the immature rat. J Cereb Blood Flow Metab 1996, 16: 1026-1033. 10.1097/00004647-199609000-00028
Schurr A, Payne RS, Tseng MT, Miller JJ, Rigor BM: The glucose paradox in cerebral ischemia: new insights. NY Acad Sci 1999, 893: 386-390.
Tsubota S, Adachi N, Chen J, Yorozuya T, Nagaro T, Arai T: Dexamethasone changes brain monoamine metabolism and aggravates ischemic neuronal damage in rats. Anesthesiology 1999, 90: 515-523. 10.1097/00000542-199902000-00028
Bruno A, Biller J, Adams HP Jr, Clark WR, Woolson RF, Williams LS, Hansen MD: Acute blood glucose level and outcome from ischemic stroke. Neurology 1999, 52: 280-284.
Anderson RE, Tan WK, Martin HS, Meyer FB: Effects of glucose and PaO 2 modulation on cortical intracellular acidosis, NADH redox state, and infarction in the ischemic penumbra. Stroke 1999, 30: 160-170.
Hoxworth JM, Xu K, Zhou Y, Lust D, LaManna J: Cerebral metabolic profile, selective neuron loss, and survival of acute and chronic hyperglycemic rats following cardiac arrest and resuscitation. Brain Res 1999, 821: 467-479. 10.1016/S0006-8993(98)01332-8
Garnier P, Bertrand N, Flamand B, Beley A: Preischemic blood glucose supply to the brain modulates HSP 72 synthesis and neuronal damage in gerbils. Brain Res 1999, 836: 245-255. 10.1016/S0006-8993(99)01711-4
de Crespigny AJ, Rother J, Beaulieu C, Moseley ME: Rapid monitoring of diffusion, DC potential, and blood oxygenation changes during global ischemia. Effects of hypoglycemia, hyperglycemia, and TTX. Stroke 1999, 30: 2212-2222.
Morikawa S, Inubushi T, Ishil H, Nakasu Y: Effects of blood sugar level on rat transient focal brain ischemia consecutively observed by diffusion-weighted EPI and 1 H echo planar spectroscopic imaging. Magnet Reson Med 1999, 42: 895-902. PublisherFullText 10.1002/(SICI)1522-2594(199911)42:5<895::AID-MRM9>3.0.CO;2-R
Kondo F, Kondo Y, Makino H, Ogawa N: Delayed neuronal death in hippocampal CA1 pyramidal neurons after forebrain ischemia in hyperglycemic gerbils: amelioration by indomethacin. Brain Res 2000, 853: 93-98. 10.1016/S0006-8993(99)02256-8
Li PA, Shuaib A, Miyashita H, He O-P, Siesjo BK: Hyperglycemia enhances extracellular glutamate accumulation in rats subjected to forebrain ischemia. Stroke 2000, 31: 183-192.
Rovilas A, Kotsou S: The influence of hyperglycemia on neurological outcome in patients with severe head injury. Neuro-surgery 2000, 46: 335-342.
Wass CT, Scheithauer BW, Bronk JT, Wilson RM, Lanier WL: Insulin treatment of corticosteroid-associated hyperglycemia and its effect on outcome after forebrain ischemia in rats. Anesthesiology 1996, 84: 644-651. 10.1097/00000542-199603000-00020
Hattori H, Wasterlain CG: Posthypoxic glucose supplement reduces hypoxic-ischemic brain damage in the neonatal rat. Ann Neurol 1990, 28: 122-128.
Sheldon RA, Partridge JC, Ferriero DM: Postischemic hyperglycemia is not protective to the neonatal rat brain. Pediatr Res 1992, 32: 489-493.
LeBlance MH, Huang M, Patel D, Smith EE, Devidas M: Glucose given after hypoxic ischemia does not affect brain injury in piglets. Stroke 1994, 25: 1443-1448.
Feibel JH, Hardy PM, Campbell RG, Goldstein MN, Joynt RJ: Prognostic value of the stress response following stroke. J Am Med Assoc 1977, 238: 1374-1376. 10.1001/jama.238.13.1374
Kalhan SC, Adam PAJ: Inhibitory effect of prednisone on insulin secretion in man: model for duplication of blood glucose concentration. J Clin Endocrinol 1975, 41: 600-610.
Billaudel B, Sutter BChJ: Immediate in-vivo effect of corticos-terone on glucose-induced insulin secretion in the rat. J Endocrinol 1982, 95: 315-320.
Woo E, Ma JTC, Robinson JD, Yu YL: Hyperglycemia is a stress response in acute stroke. Stroke 1988, 19: 1359-1364.
O'Neill PA, Davies I, Fullerton KJ, Bennet D: Stress hormone and blood glucose response following acute stroke in the elderly. Stroke 1991, 22: 842-847.
Virgin CE Jr, Ha TP-T, Packan DR, Tombaugh GC, Yang SH, Horner HC, Sapolsky RM: Glucocorticoids inhibit glucose transport and glutamate uptake in hippocampal astrocytes: implications for glucocorticoid neurotoxicity. J Neurochem 1991, 57: 1422-1428.
Lawrence MS, Sapolsky RM: Glucocorticoids accelerate ATP loss following metabolic insults in cultured hippocampal neurons. Brain Res 1994, 646: 303-306. 10.1016/0006-8993(94)90094-9
Yusim A, Ajilore O, Bliss T, Sapolsky RM: Glucocorticoids exacerbate insult-induced declines in metabolism in selectively vulnerable hippocampal cell fields. Brain Res 2000, 870: 109-117. 10.1016/S0006-8993(00)02407-0
Payne RS, Schurr A: Corticosterone-aggravated ischemic neuronal damage in vitro is relieved by vanadate. Neuroreport 2001, 12: 1261-1263. 10.1097/00001756-200105080-00041
Harris SB, Gunion MW, Rosenthal MJ, Walford RL: Serum glucose, glucose tolerance, corticosterone and free fatty acids during aging in energy restricted mice. Mech Ageing Dev 1994, 73: 209-221. 10.1016/0047-6374(94)90053-1
Wang J, Dourmashkin JT, Yun R, Leibowitz SF: Rapid changes in hypothalamic neuropeptide Y produced by carbohydrate-rich meals that enhance corticosterone and glucose levels. Brain Res 1999, 848: 124-136. 10.1016/S0006-8993(99)02040-5
Smith-Swintosky VL, Pettigrew LC, Sapolsky RM, Phares C, Craddock SD, Brooke SM, Mattson M: Metyrapone, an inhibitor of glucocorticoid production, reduces brain injury induced by focal and global ischemia and seizures. J Cereb Blood Flow Metab 1996, 16: 585-598. 10.1097/00004647-199607000-00008
Krugers HJ, Kemper RHA, Korf J, Horst T, Knollema S: Metyrapone reduces rat brain damage and seizures after hypoxia-ischemia: an effect independent of modulation of plasma corticosterone levels? J Cereb Blood Flow Metab 1998, 18: 386-390. 10.1097/00004647-199804000-00006
Krugers HJ, Maslam S, Korf J, Joels M: The corticosterone synthesis inhibitor metyrapone prevents hypoxia/ischemia-induced loss of synaptic function in the rat hippocampus. Stroke 2000, 31: 1162-1172.
Adachi N, Chen J, Liu K, Nagaro T, Arai T: Metyrapone alleviate ischemic damage in the gerbil hippocampus. Eur J Pharmac 1999, 373: 147-152. 10.1016/S0014-2999(99)00294-0
Schurr A, Payne RS, Miller JJ, Tseng MT: Preischemic hyperglycemia-aggravated damage: evidence that lactate utilization is beneficial and glucose-induced corticosterone release is detrimental. J Neurosci Res 2001, 66: 782-789. 10.1002/jnr.10065
Schurr A, Payne RS, Miller JJ, Tseng MT, Rigor BM: Blockade of lactate ransport exacerbates delayed neuronal damage in the a rat model of cerebral ischemia. Brain Res 2001, 895: 268-272. 10.1016/S0006-8993(01)02082-0
Drewes L, Gilboe DD, Betz LA: Metabolic alteration in brain during anoxic-anoxia and subsequent recovery. Arch Neurol 1973, 29: 385-390.
Hossmann K-A, Kleihues P: Reversibility of ischemic brain damage. Arch Neurol 1973, 29: 375-382.
Ljunggren B, Norberg K, Siesjo BK: Influence of tissue acidosis upon restitution of brain energy metabolism following total ischemia. Brain Res 1974, 77: 173-186. 10.1016/0006-8993(74)90782-3
Steen PA, Michenfelder JD, Milde JH: Incomplete versus complete cerebral ischemia: improved outcome with a minimal blood flow. Ann Neurol 1979, 6: 389-398.
Welsh FA, Ginsberg MD, Rieder W, Budd WW: Deleterious effect of glucose pretreatment on recovery from diffuse ischemia in the cat. II. Regional metabolite levels. Stroke 1980, 11: 355-363.
Rehncrona S, Rosen I, Siesjo BK: Brain lactic acidosis and ischemic cell damage: 1. Biochemistry and neurophysiology. J Cereb Blood Flow Metab 1981, 1: 297-311.
Smith M-L, von Hanwehr R, Siesjo BK: Changes in extra-and intracellular pH in the brain during and following ischemia in hyperglycemic and in moderately hypoglycemic rats. J Cereb Blood Flow Metab 1986, 6: 574-583.
Li P-A, Siesjo BK: Role of hyperglycemia-related acidosis in ischaemic brain damage. Acta Physiol Scand 1997, 161: 567-580. 10.1046/j.1365-201X.1997.00264.x
Brian JE Jr: Carbon dioxide and the cerebral circulation. Anesthesiology 1998, 88: 1365-1386. 10.1097/00000542-199805000-00029
Antonawich FJ, Miller G, Rigsby DC, Davis JN: Regulation of ischemic cell death by glucocorticoids and adrenocorticotropic hormone. Neuroscience 1999, 88: 319-325. 10.1016/S0306-4522(98)00213-9
About this article
Cite this article
Schurr, A. Bench-to-bedside review: A possible resolution of the glucose paradox of cerebral ischemia. Crit Care 6, 330 (2002). https://doi.org/10.1186/cc1520
- cerebral ischemia
- neuronal damage