What was Otto Mehoff's seminal discovery regarding lactate, and how was it misinterpreted?

Otto Mehoff quantified glycogen degradation to lactate in frog muscles in an anaerobic environment. His findings led to the incorrect association of lactate production with oxygen lack and fatigue, forming the basis of the 'lactic acidosis' concept.

How does glucose enter a cell and get metabolized to produce ATP?

Glucose enters cells via specific transporters, such as GLUT4 in muscles and fat cells. Once inside, it can be stored as glycogen or enter the glycolytic pathway to be broken down. This process involves splitting a six-carbon glucose molecule into two three-carbon molecules, which can then proceed to form either pyruvate or lactate, ultimately leading to ATP production.

Does lactate enter the mitochondria for ATP production, contrary to traditional beliefs?

Yes, research indicates that lactate is a preferred fuel for mitochondria. A mitochondrial lactate oxidation complex with specific carriers allows lactate to enter the mitochondria, challenging the long-held textbook view that only pyruvate enters for aerobic ATP production.

How does lactate affect fatty acid metabolism?

Lactate can inhibit fatty acid metabolism by blocking the carnitine palmitoyltransferase (CPT1 and CPT2) transporters, which are necessary for fatty acids to enter mitochondria for oxidation. This suggests a competition among substrates, where lactate prioritizes carbohydrate fuel during 'fight or flight' scenarios.

Why do elite athletes and individuals with type 2 diabetes both have high intramyocellular fat, and what's the difference?

Both groups can have high intramyocellular fat. In type 2 diabetes, the fat is static and contributes to insulin resistance. In athletes, it represents a dynamic carbon flux, serving as a readily available fuel source during recovery periods when glycogen stores are low and fat burning is prioritized.

How does lactate affect appetite?

Lactate crosses the blood-brain barrier and acts in the hypothalamus to inhibit appetite. Elevated lactate levels, such as those achieved during intense exercise, can suppress ghrelin secretion, leading to reduced hunger for several hours post-exertion.

What role does lactate play in traumatic brain injury (TBI)?

Lactate is a preferred fuel for injured brains. In TBI, glucose uptake can be suppressed, and lactate, which is highly expressed with transporters in the brain, can become the dominant fuel for neurons, potentially aiding recovery. Clinical trials have explored intravenous lactate for TBI patients.

Is lactate carcinogenic, and what is its relationship with exercise in cancer patients?

Lactate may be carcinogenic, and high lactate production stimulates processes associated with cancer. However, the problem is not lactate accumulation itself but a lack of clearance. Regular exercise increases lactate clearance capacity, potentially reducing the chance for carcinogenesis by removing it.

Why does measuring lactate in sepsis patients need careful interpretation?

High lactate in sepsis is often seen as a sign of anoxia, but it can also be a metabolic response. Additionally, most assays only measure L-lactate, while gut microbes in sepsis can produce neurotoxic D-lactate. Therefore, high L-lactate without severe acidosis might indicate a different underlying issue than previously assumed.

What is enteric glycolysis and its significance in carbohydrate metabolism?

Enteric glycolysis is the process where glucose is rapidly converted to lactate in the gut (enterocytes) immediately after carbohydrate intake, even before blood glucose levels rise significantly. This initial lactate spike suggests the body uses lactate to distribute carbohydrate energy and minimize immediate glucose load.

How does Metformin, a common diabetes drug, interact with lactate metabolism?

Metformin historically has been known to increase lactate levels, which was seen as a potential risk for lactic acidosis due to its inhibition of mitochondrial complex one. However, new interpretations suggest that Metformin may encourage enterocytes to produce lactate, functioning as a beneficial mechanism to deliver carbohydrate energy and not necessarily indicating acidosis.

How does lactate signaling influence gene expression and mitochondrial biogenesis?

Lactate can epigenetically modify gene expression through a process called 'lactylation,' where it covalently binds to histones. This signaling is thought to promote mitochondrial biogenesis and is particularly potent when lactate is produced endogenously during exercise, linking the metabolic signal directly to the physiological adaptations of training.

312 - A masterclass in lactate: metabolic fuel, implications for diseases, and therapeutic potential

Peter Attia MD

Science & Technology4 min read141 min video

Aug 5, 2024|44,926 views|1,009|103

Peter Attia MD Dr. Peter Attia Early Medical The Drive Podcast The Drive Longevity Zone 2

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Key Moments

TL;DR

Lactate, often misunderstood, is a vital metabolic fuel and signaling molecule, not just waste, with implications for disease and therapy.

Key Insights

Lactate, not lactic acid, is produced in the body and acts as a crucial fuel source and signaling molecule for various tissues.

The historical understanding of lactate as solely an anaerobic byproduct leading to acidosis is largely inaccurate.

Lactate plays a critical role as a preferred fuel source, even under aerobic conditions, in tissues like the brain and heart.

Lactate metabolism interacts with glucose and fatty acid metabolism, potentially inhibiting fat oxidation and influencing hormonal signals like appetite suppression.

Exercise significantly enhances lactate clearance capacity and mitochondrial biogenesis, contributing to improved metabolic health and performance.

Dysregulation of lactate metabolism is implicated in diseases like cancer and diabetes, and therapeutic interventions involving lactate are being explored.

REVISITING THE HISTORY OF LACTATE

The historical understanding of lactate, or lactic acid as it was mistakenly called, emerged from Otto Meyerhof's early 20th-century experiments with frog muscles. These studies, conducted in an oxygen-deprived environment, associated lactate accumulation with muscle fatigue and acidity. This led to the long-held belief that lactate was a metabolic waste product of anaerobic glycolysis, directly causing acidosis and fatigue. However, this interpretation overlooked lactate's potential physiological roles and the body's sophisticated regulatory mechanisms, setting the stage for a century of misunderstanding.

LACTATE AS A FUEL AND SIGNALING MOLECULE

Contrary to historical views, lactate is a crucial metabolic fuel and signaling molecule. It's produced in the cytoplasm and can be transported into mitochondria for oxidation, providing ATP in both aerobic and anaerobic conditions. This challenges the traditional textbook model that pyruvate is the sole substrate for mitochondria. Lactate also plays a role in regulating appetite by suppressing ghrelin and can influence gene expression through a process called 'lactation,' potentially impacting mitochondrial biogenesis.

LACTATE METABOLISM AND SUBSTRATE COMPETITION

Lactate metabolism is intertwined with that of glucose and fatty acids. While lactate is a preferred fuel source, it can inhibit fatty acid oxidation by blocking the transport of fatty acids into the mitochondria. This competitive interaction highlights the body's dynamic substrate utilization strategies, particularly during fight-or-flight responses where immediate carbohydrate energy is prioritized over long-term fat stores. Understanding these dynamics is crucial for metabolic health.

LACTATE IN ATHLETIC PERFORMANCE AND TRAINING

Regular exercise, especially endurance training, significantly enhances the body's ability to produce and clear lactate. Trained individuals exhibit increased mitochondrial density and capacity, allowing for more efficient lactate utilization and oxidation. This 'lactate shuttle' system facilitates the transport of lactate between muscle fibers and even to other tissues like the brain and heart, supporting their energy demands. The ability to clear and utilize lactate effectively is a key differentiator in athletic performance.

LACTATE'S ROLE IN DISEASE STATES

The dysregulation of lactate metabolism is implicated in various disease states. In cancer, the 'Warburg effect' describes high lactate production even with sufficient oxygen, suggesting a role beyond ATP production, possibly related to providing cellular building blocks. In type 2 diabetes, elevated resting lactate levels may inhibit beneficial fatty acid oxidation. Furthermore, lactate's presence in conditions like traumatic brain injury (TBI) suggests its potential as a therapeutic fuel to support energy-depleted neurons.

LACTATE AND ACID-BASE BALANCE

The strong historical association between lactate and acidosis is being re-evaluated. While lactate is produced alongside a hydrogen ion, the final step in glycolysis producing lactate is actually alkalizing. Elevated lactate levels do not always correlate with a significant drop in blood pH. This suggests that measurements of lactate alone in conditions like sepsis might be misinterpreted, as the lactate may not always indicate a dangerous acidosis, especially if the pH remains stable. Further research into different lactate 'forms' (L-lactate vs. D-lactate) is also needed.

THERAPEUTIC AND DIAGNOSTIC IMPLICATIONS

THE INTESTINAL AND HEPATIC ROLE IN LACTATE METABOLISM

Recent research highlights the significant, often underestimated, role of the intestines and liver in lactate metabolism. Following glucose intake, lactate spikes rapidly, indicating enteric glycolysis occurring in intestinal cells. The liver then sequesters a large portion of this glucose, gradually releasing it as glucose or other metabolites. This complex interplay between the gut, liver, and peripheral tissues demonstrates a sophisticated system for managing carbohydrate energy, with lactate production serving as an initial, rapid response mechanism.

Mentioned in This Episode

●Organizations

●Concepts

●People Referenced

Common Questions

The body primarily produces lactate, not lactic acid. Lactic acid is lactate with an attached hydrogen ion. Historically, the two were conflated, leading to a long-standing misunderstanding of lactate's role in metabolism.

Topics

Lactic Acid ATP Production Traumatic Brain Injury Sepsis Glucose Disposal

Mentioned in this video

conceptMCTs (Monocarboxylate Transporters)

Proteins responsible for transporting lactate and other monocarboxylates across cell membranes, including into mitochondria.

personRonaldo Bello

World-renowned emergency room physician who advocates for pulmonologists to understand lactate metabolism more like exercise physiologists.

organizationUCLA Neurosurgery

Collaborated on clinical trials to infuse lactate in traumatic brain injury patients, showing promising results.

conceptGLUT4

A glucose transporter protein expressed in muscles and fat cells, whose movement to the cell surface is critical for glucose uptake, often signaled by insulin or muscle contraction.

conceptCorey Cycle

A metabolic pathway in which lactate produced by muscles is transported to the liver, converted to glucose, and then returned to the muscles.

personA.V. Hill

Physiologist, sometimes referred to as the father of physiology or exercise physiology, who shared the Nobel Prize with Otto Mehoff.

conceptGlycogen

The stored form of glucose in animals, primarily in the liver and muscles, serving as a critical energy reserve.

conceptMitochondrial Lactate Oxidation Complex

A complex identified by the speaker that allows lactate to enter mitochondria for oxidation, challenging traditional views of metabolism.

personKen Baldwin

Colleague at UC Irvine who conducted studies on rats exercising, measuring lactate levels in different muscle fibers and blood.

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