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Mitochondrial toxicity of metformin and phenformin in human peripheral blood cells assessed by high-resolution respirometry

Piel, Sarah (2013) MOBM11 20131
Degree Projects in Molecular Biology
Abstract
Abstract

Aim: Metformin is an anti-diabetic drug associated with lactic acidosis as a rare side effect which is thought to be due to drug-induced mitochondrial dysfunction in the liver and other tissues. In this study, the mitochondrial toxicity of metformin and its now withdrawn predecessor phenformin was assessed in human peripheral blood cells.
Methods: Platelets and peripheral blood mononuclear cells were isolated and their integrated mitochondrial function was studied in intact and permeabilized state using high-resolution respirometry. Using different concentrations of metformin (0.1 – 100 mM) or phenformin (25-500 μM) the dose- and time-dependent effect on routine respiration, as well as the effect on respiratory states and... (More)
Abstract

Aim: Metformin is an anti-diabetic drug associated with lactic acidosis as a rare side effect which is thought to be due to drug-induced mitochondrial dysfunction in the liver and other tissues. In this study, the mitochondrial toxicity of metformin and its now withdrawn predecessor phenformin was assessed in human peripheral blood cells.
Methods: Platelets and peripheral blood mononuclear cells were isolated and their integrated mitochondrial function was studied in intact and permeabilized state using high-resolution respirometry. Using different concentrations of metformin (0.1 – 100 mM) or phenformin (25-500 μM) the dose- and time-dependent effect on routine respiration, as well as the effect on respiratory states and respiratory function of complex I, II and IV was assessed.
Results: In intact platelets, routine respiration and maximal uncoupled respiration were decreased by 83.27 % and 56.86 % after 60 minutes incubation with 100 mM metformin compared to control. The same dose of metformin caused a drop of 81.22 % in routine respiration during 60 minutes exposure compared to at administration. 10 mM metformin induced a dose-dependent inhibition of complex I-dependent oxidative phosphorylation capacity up to 92.04 % in permeabilized platelets and up to 81.47 % in permeabilized peripheral blood mononuclear cells. A dose of 0.5 mM phenformin caused a 5.32-fold more pronounced complex I inhibition than metformin.
Conclusion: Metformin and phenformin impair mitochondrial function in human peripheral blood cells through inhibition of complex I in a dose- and time-dependent manner. Respirometry of peripheral blood cells may be a suitable assay to predict mitochondrial toxicity of drugs in humans. (Less)
Abstract
Popular science summary

Do metformin and phenformin cause toxicity to mitochondria of human blood cells?

Metformin and phenformin are anti-diabetic drugs associated with lactic acidosis as a rare side effect. This side effect is thought to be due to drug-induced mitochondrial dysfunction. In this project, the mitochondrial toxicity of metformin and phenformin was assessed in human blood cells. It was shown that both drugs impair the function of mitochondria in human blood cells and, that this effect aggravated with time and dose.

Mitochondria produce up to 90 % of the cell’s energy, a process which is called respiration. Metformin and phenformin are anti-diabetic drugs which have been reported to interfere with respiration.... (More)
Popular science summary

Do metformin and phenformin cause toxicity to mitochondria of human blood cells?

Metformin and phenformin are anti-diabetic drugs associated with lactic acidosis as a rare side effect. This side effect is thought to be due to drug-induced mitochondrial dysfunction. In this project, the mitochondrial toxicity of metformin and phenformin was assessed in human blood cells. It was shown that both drugs impair the function of mitochondria in human blood cells and, that this effect aggravated with time and dose.

Mitochondria produce up to 90 % of the cell’s energy, a process which is called respiration. Metformin and phenformin are anti-diabetic drugs which have been reported to interfere with respiration. Metformin is the first choice treatment for Type 2 diabetes, a disease characterized by high glucose levels in the blood due to impaired response to insulin, which is a blood glucose-lowering hormone. Both drugs achieve their anti-diabetic effect by lowering the production of glucose, increasing its uptake into tissues and by increasing the sensitivity to insulin. However, they are associated with lactic acidosis as side effect. Lactic acidosis is a condition where the blood pH is lowered due to accumulation of lactate in the blood. Because of this phenformin has been withdrawn from the market in most countries. Although it is thought that the side effect lactic acidosis is due to drug-induced damage to mitochondria, the exact mechanism remains unresolved. The number of Type 2 diabetes cases and use of metformin is expected to rise in the future. Therefore, the aim of this project was to explore how metformin and phenformin cause toxicity to mitochondria in human blood cells.

Energy production by mitochondria is linked to oxygen consumption. Therefore, the healthiness of mitochondria of human platelets and white blood cells was assessed by measuring their oxygen consumption in response to exposure to metformin and phenformin.

Results

Metformin and phenformin damaged mitochondria of human platelets at complex I, one of the primary centres of the energy production of the cell. The toxic effect was more pronounced with phenformin than with metformin. But for both drugs it aggravated with increasing dose. Further, we were the first to show that metformin causes the same toxic effect to human white blood cells as it does to human platelets. The damage also was found to be caused at complex I and increased with higher doses. Additionally we showed that with prolonged time of exposure to metformin, as it occurs during treatment conditions, the damaging effect on mitochondria in human platelets increased.

In summary, the study demonstrates that metformin and phenformin impair mitochondrial function at complex I in two types of human blood cells, an effect that aggravates with time and dose.


Supervisors: Eskil Elmér, Magnus Hansson
Master´s Degree Project in Pharmacology, 30 ECTS, 2013
Department of Biology, Lund University (Less)
Please use this url to cite or link to this publication:
author
Piel, Sarah
supervisor
organization
course
MOBM11 20131
year
type
H2 - Master's Degree (Two Years)
subject
language
English
id
4254193
date added to LUP
2014-01-24 16:27:35
date last changed
2014-01-24 16:27:35
@misc{4254193,
  abstract     = {Popular science summary

Do metformin and phenformin cause toxicity to mitochondria of human blood cells?

Metformin and phenformin are anti-diabetic drugs associated with lactic acidosis as a rare side effect. This side effect is thought to be due to drug-induced mitochondrial dysfunction. In this project, the mitochondrial toxicity of metformin and phenformin was assessed in human blood cells. It was shown that both drugs impair the function of mitochondria in human blood cells and, that this effect aggravated with time and dose. 

Mitochondria produce up to 90 % of the cell’s energy, a process which is called respiration. Metformin and phenformin are anti-diabetic drugs which have been reported to interfere with respiration. Metformin is the first choice treatment for Type 2 diabetes, a disease characterized by high glucose levels in the blood due to impaired response to insulin, which is a blood glucose-lowering hormone. Both drugs achieve their anti-diabetic effect by lowering the production of glucose, increasing its uptake into tissues and by increasing the sensitivity to insulin. However, they are associated with lactic acidosis as side effect. Lactic acidosis is a condition where the blood pH is lowered due to accumulation of lactate in the blood. Because of this phenformin has been withdrawn from the market in most countries. Although it is thought that the side effect lactic acidosis is due to drug-induced damage to mitochondria, the exact mechanism remains unresolved. The number of Type 2 diabetes cases and use of metformin is expected to rise in the future. Therefore, the aim of this project was to explore how metformin and phenformin cause toxicity to mitochondria in human blood cells. 

Energy production by mitochondria is linked to oxygen consumption. Therefore, the healthiness of mitochondria of human platelets and white blood cells was assessed by measuring their oxygen consumption in response to exposure to metformin and phenformin. 

Results 

Metformin and phenformin damaged mitochondria of human platelets at complex I, one of the primary centres of the energy production of the cell. The toxic effect was more pronounced with phenformin than with metformin. But for both drugs it aggravated with increasing dose. Further, we were the first to show that metformin causes the same toxic effect to human white blood cells as it does to human platelets. The damage also was found to be caused at complex I and increased with higher doses. Additionally we showed that with prolonged time of exposure to metformin, as it occurs during treatment conditions, the damaging effect on mitochondria in human platelets increased. 

In summary, the study demonstrates that metformin and phenformin impair mitochondrial function at complex I in two types of human blood cells, an effect that aggravates with time and dose. 


Supervisors: Eskil Elmér, Magnus Hansson 
Master´s Degree Project in Pharmacology, 30 ECTS, 2013 
Department of Biology, Lund University},
  author       = {Piel, Sarah},
  language     = {eng},
  note         = {Student Paper},
  title        = {Mitochondrial toxicity of metformin and phenformin in human peripheral blood cells assessed by high-resolution respirometry},
  year         = {2013},
}