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Nephritogenic ochratoxin A interferes with mitochondrial function and pH homeostasis in immortalized human kidney
S Eder1, A Benesic, R Freudinger
1Physiologisches Institut der Universität Würzburg, Germany.
Abstract:
The ubiquitous nephritogenic and carcinogenic fungal metabolite ochratoxin A (OTA) has been shown to interact with renal cell function at low nanomolar concentrations. This is possibly brought about through changes in cellular pH (pHc) homeostasis and mitochondrial function. We assessed the effect of nanomolar concentrations of OTA on pHc homeostasis and the possible involvement of mitochondria using immortalized human kidney epithelial (IHKE1) cells. Within seconds OTA evoked a decrease of pHc with a threshold concentration of 0.1 nmol/l, followed by a sustained alkalinization. Acidification was the same in bicarbonate and non-bicarbonate Ringer solution. When Ca2+ entry across the plasma membrane was prevented, virtually no OTA-induced pH changes could be observed. Inhibition of Na+/H+-exchange (NHE, Na+-free solution) and H+-ATPase (bafilomycin A1) did not reduce the OTA-induced acidification. By contrast, determination of NHE activity as a function of pHc revealed that OTA stimulates NHE (maximal flux increases) in a Ca2+-dependent manner. OTA exposure did not increase lactic acid production, indicating that anaerobic glycolysis was not enhanced. Inhibiting complexes I, III and IV of the mitochondrial electron transport chain (ETC) with rotenone, antimycin A and CN- prevented the OTA-induced acidification almost completely. Completely inhibiting F1FO-ATPsynthase with oligomycin reduced the effect of OTA by approximately equal 50%. In addition, OTA induced a hyperpolarization of the mitochondrial membrane potential (psim) in a Ca2+-dependent manner. Furthermore, OTA exposure resulted in a mitochondria-dependent increase of the cellular ATP content. We conclude that OTA activates mitochondria and NHE by interfering with cellular Ca2+ homeostasis. Stimulation of mitochondrial metabolism leads to enhanced "proton production". Anaerobic glycolysis is not enhanced.
Insights
Ochratoxin A (OTA) disrupts kidney cell pH and function by affecting calcium levels and mitochondria. This fungal toxin stimulates mitochondrial metabolism and proton production, impacting renal cell health.
Area of Science:
- Toxicology
- Cell Biology
- Renal Physiology
Background:
- Ochratoxin A (OTA) is a fungal metabolite known for kidney toxicity and carcinogenicity.
- Low nanomolar concentrations of OTA affect renal cell function, potentially via cellular pH (pHc) and mitochondrial disruption.
Purpose of the Study:
- To investigate the effects of nanomolar OTA on pHc homeostasis in human kidney epithelial cells.
- To explore the involvement of mitochondria and calcium (Ca2+) in OTA-induced cellular changes.
Main Methods:
- Utilized immortalized human kidney epithelial (IHKE1) cells.
- Measured pHc changes, Ca2+ influx, Na+/H+-exchange (NHE) activity, and mitochondrial function (electron transport chain, membrane potential, ATP production).
- Employed specific inhibitors for NHE, H+-ATPase, and mitochondrial complexes.
Main Results:
- OTA rapidly decreased pHc, followed by alkalinization, dependent on Ca2+ entry.
- OTA stimulated NHE activity in a Ca2+-dependent manner.
- Mitochondrial electron transport chain inhibition prevented OTA-induced acidification; ATP production increased.
- OTA caused mitochondrial membrane hyperpolarization and increased cellular ATP content.
Conclusions:
- OTA activates mitochondria and NHE by disrupting cellular Ca2+ homeostasis.
- Stimulated mitochondrial metabolism leads to increased proton production, contributing to pH changes.
- Anaerobic glycolysis is not enhanced by OTA exposure.