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Heterogeneous metabolism and toxicity of 4-pentenoate along the dog nephron
1Institut de Génie Biomédical, Université de Montréal, Que., Canada.
Abstract:
4-Pentenoate (4P) is a short-chain fatty acid which causes a complete renal Fanconi syndrome. We have examined the mechanism of 4P toxicity along the nephron after a prolonged (30 min) exposition of isolated renal tubular segments to this agent. In proximal tubules, 4P inhibited the activity of alpha-ketoglutarate dehydrogenase, pyruvate dehydrogenase, and beta-oxidation, but not in thick ascending limb or inner medullary collecting duct tubules in suspension. These proximal effects were accompanied by a marked oxidation of the proximal redox state, with a fall in the tissue respiration and a low content of ATP. The acetyl-CoA content of proximal tubules was simultaneously reduced. Butyrate, acetate, hexanoate or octanoate did not exert these effects. In proximal tubules the metabolism of 4P led to the tissue accumulation of 3-keto-4-pentenoyl-CoA, a known unspecific inhibitor of metabolic oxidation. This metabolite was not detectable in thick ascending limbs which metabolized 4P rapidly. No metabolism of 4P was noted in collecting ducts. We conclude that beta-oxidation probably differs in proximal and thick ascending limb tubules, allowing 4P metabolism to exert a specific toxicity in proximal tubules. A selective proximal defect in energy metabolism probably explains the Fanconi syndrome observed with exposition to 4P.
Insights
4-Pentenoate (4P) causes Fanconi syndrome by inhibiting proximal tubule energy metabolism. This short-chain fatty acid disrupts key enzymes and ATP production, leading to kidney damage.
Area of Science:
- Nephrology
- Biochemistry
- Toxicology
Background:
- 4-Pentenoate (4P) is a short-chain fatty acid linked to renal Fanconi syndrome.
- The precise mechanism of 4P-induced nephrotoxicity remains incompletely understood.
Purpose of the Study:
- To elucidate the specific mechanisms underlying 4-pentenoate toxicity within different segments of the renal tubule.
- To investigate the impact of 4P exposure on cellular energy metabolism and enzyme activity in isolated renal tubules.
Main Methods:
- Isolated renal tubular segments (proximal tubules, thick ascending limb, inner medullary collecting duct) were exposed to 4P for 30 minutes.
- Assays were performed to measure enzyme activities (alpha-ketoglutarate dehydrogenase, pyruvate dehydrogenase, beta-oxidation), ATP content, acetyl-CoA levels, and metabolite accumulation.
- Redox state and tissue respiration were also assessed.
Main Results:
- In proximal tubules, 4P significantly inhibited alpha-ketoglutarate dehydrogenase, pyruvate dehydrogenase, and beta-oxidation.
- 4P exposure led to altered proximal tubule redox state, decreased tissue respiration, reduced ATP content, and lower acetyl-CoA levels.
- Accumulation of 3-keto-4-pentenoyl-CoA, a metabolic inhibitor, was observed in proximal tubules but not in thick ascending limb or collecting duct segments.
- Thick ascending limb tubules rapidly metabolized 4P, and collecting ducts showed no 4P metabolism.
Conclusions:
- 4-Pentenoate exerts specific toxicity in proximal tubules due to differential beta-oxidation pathways compared to thick ascending limb tubules.
- A selective defect in proximal tubule energy metabolism induced by 4P is the likely cause of the observed Fanconi syndrome.