https://onlinelibrary.wiley.com/doi/full/10.1002/bies.70181
chatGPT(6AstraMaxPaid):
Blaze and Cluntun’s Lactate Metabolism: Separating Correlation From Causation is a narrative review published in BioEssays in 2026. Its central argument is convincing: lactate concentration alone cannot establish the underlying metabolic mechanism or show that lactate causes harm. Its novelty lies mainly in bringing existing findings together, although some statements are more categorical than the evidence supports.
The paper’s main argument is that lactate is an actively exchanged fuel, a participant in redox regulation, and a regulator of cellular behaviour. The authors organise their discussion around six misconceptions.
| Misconception | The paper’s correction |
|---|---|
| Lactate, lactic acid and lactose are interchangeable | Lactate is chemically distinct from lactose. At physiological pH, more than 99.9% of the lactate/lactic acid pool exists as lactate. |
| Lactate is produced only when oxygen is insufficient | Cells continuously produce lactate under aerobic conditions. Its production helps regenerate NAD+, allowing glycolysis to continue. |
| Lactate is a metabolic dead end | Tissues exchange lactate through the circulation and use its carbon for oxidative metabolism or glucose production. |
| Lactate causes acidosis, fatigue and muscle soreness | The lactate-producing LDH reaction consumes a proton. The authors attribute acidosis primarily to other reactions and delayed soreness to tissue injury and inflammation. |
| Elevated lactate necessarily indicates hypoxia or toxicity | Increased production, altered metabolism, adrenergic stimulation and reduced clearance can all raise blood lactate. |
| Lactate is metabolically passive | Lactate can influence protein function, gene expression and systemic physiology through several mechanisms. |
The strongest conceptual distinction is between concentration and flux, meaning the rate at which material moves through a metabolic pathway. A stable lactate concentration can coexist with rapid production and consumption. Conversely, lactate can accumulate because consumption has fallen, without production increasing.
The same principle applies to location. Blood lactate integrates activity across multiple organs and cannot reliably specify lactate concentrations, reaction directions or mitochondrial activity inside an individual cell.
The paper also describes regulatory functions beyond fuel provision:
- Histone lactylation: addition of lactyl groups to histones can influence gene expression.
- Nonhistone lactylation: modification of proteins such as NBS1 can affect DNA repair and chemotherapy resistance.
- RNA processing: lactylation of NUDT21 can alter alternative polyadenylation, which determines where RNA transcripts acquire their ends. This is distinct from alternative splicing.
- Other signalling mechanisms: the lactate-derived metabolite Lac-Phe influences feeding, while lactate interactions with SENP1 can affect cell division.
The authors therefore recommend combining tracing, targeted interventions and measurements within specific cellular compartments when investigating causation.
The novelty is primarily conceptual and educational. The paper explicitly reports that no new data were generated or analysed.
Lactate shuttling, aerobic lactate production and lactate oxidation are longstanding concepts. Histone lactylation was reported in 2019, while several newer regulatory examples cited here appeared in 2024 and 2025.
Its useful contribution is to connect these findings within a common framework: mistakes arise when researchers confuse concentration with flux, systemic measurements with local conditions, or association with mechanism. Bringing lactylation and RNA processing into this discussion broadens the familiar account of lactate as an energy substrate.
However, it does not establish a new biochemical pathway, quantify the importance of competing mechanisms, or demonstrate that a particular lactate-directed treatment improves outcomes.
My critique is that the review succeeds as a corrective, but needs greater precision in several places.
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Its conclusion overcorrects towards a favourable interpretation of lactate.
The authors appropriately reject the idea that elevated lactate is automatically toxic. However, their concluding portrayal of lactate as part of the solution is broader than their own evidence warrants.
The review itself discusses lactylation promoting chemotherapy resistance and cites work on gliomagenesis. Those examples show that lactate-dependent processes can contribute causally to undesirable outcomes.
The defensible position is that lactate’s effects depend on concentration, location, duration, cell type and the surrounding metabolic state.
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The claim about pain is too broad.
The argument against lactate accumulation causing delayed-onset muscle soreness is persuasive: lactate generally declines well before soreness develops.
That does not exclude lactate from every pain mechanism. Experimental work has shown that lactate enhances acid-sensing ion-channel activity in sensory neurons relevant to ischaemic pain. This does not establish lactate as the cause of ordinary post-exercise soreness, but it limits the paper’s broader claim that lactate does not cause or contribute to pain. (Nature Neuroscience)
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The acidosis discussion needs a fuller account of the system.
The authors are correct that conversion of pyruvate to lactate by LDH consumes a proton. However, the behaviour of that individual reaction does not completely describe cellular or extracellular acid balance.
A fuller explanation would include coupled ATP production and consumption, proton transport, buffering and respiratory carbon dioxide. The discussion of extracellular acidification is particularly incomplete because respiratory CO2 can also generate extracellular acidity, as experimental measurement methods explicitly recognise. (PMC)
The paper successfully challenges a simplistic explanation, but its replacement explanation is also somewhat simplified.
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Mitochondrial fuel use and the location of lactate oxidation need clearer separation.
Detecting lactate-derived carbon in mitochondrial metabolites establishes a contribution to metabolism. By itself, it does not locate the conversion of lactate into pyruvate.
Two possibilities must be distinguished: conversion in the cytosol followed by pyruvate import, and lactate import followed by conversion inside mitochondria. Likewise, detecting a mitochondrial lactate pool does not establish its rate or direction of turnover.
This is a logical limitation of the measurements, rather than evidence that direct mitochondrial lactate oxidation cannot occur. The review acknowledges compartmental uncertainty, but does not consistently preserve this distinction.
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There are identifiable reference errors in the mitochondrial section.
On page 8, the FiLa biosensor finding is attributed to reference 34. That reference describes a different, earlier FRET sensor from 2013; the FiLa study is reference 33.
The mitochondrial-myopathy example is then attributed to reference 33, which is the sensor paper. The relevant myopathy study is Chen and colleagues’ 2023 Science Advances paper, Lactate metabolism is essential in early-onset mitochondrial myopathy, which is absent from the bibliography. (PubMed)
These errors do not invalidate the underlying findings, but they weaken the traceability of an important part of the argument.
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The proposed methods do not automatically resolve causation.
The recommendation to manipulate LDH or lactate transporters is reasonable. However, these interventions also change other variables, including pyruvate availability, redox balance and proton transport. An observed effect cannot automatically be assigned to lactate itself.
Similarly, although the review acknowledges isotopic exchange, its discussion would benefit from more consistently distinguishing exchange from net metabolic flux. Rapid exchange of labelled carbon between pyruvate and lactate can occur without equivalent net lactate production. (PMC)
Stronger causal experiments would combine complementary interventions with controls for pH, substrate availability and redox state, followed by rescue experiments that test the proposed mechanism specifically.
For questions about metabolism and gene regulation, the lactylation discussion is particularly relevant. It establishes additional routes connecting metabolic state to transcription and RNA processing. It does not demonstrate that lactylation substitutes for histone acetylation, or that lactate availability determines nuclear acetyl-CoA supply, splicing fidelity or RNA polymerase II stalling. Those require separate mechanistic tests.