Gentamicin과 Tobramycin이 쥐의 신피질 Mitochondria의 산화인산화 과정과 Glutamine 이동에 미치는 영향

Abstract

[한글]

Aminoglycoside항생제 사용시 부작용으로 사람이나 실험동물에 있어서 nephrotoxicity가 나타나는데 이에 대해서는 gentamicin을 이용하여 여러 면에서 연구되어 왔다. 즉 gentamicin을첨가한 동물에서는 근위세뇨관 상피세포에 크고 불규칙한 secondary lysosomes이 많이 나타나고 rough endoplasmic reticulum의 cisternae가 현저히 확장되며 mitochondria가 팽대될 뿐만 아니라(Houghton등, 1976, 1778) 신장의 암모니아 생성 및 gluconeogenesis작용이 억제되고(Kluwe 및 Hoek, 1978) 신피질 조직의 산소소모량이 감소되며 (이 및 박, 1982) mitochondria의 산화인산화작용이 억제되는 것 (Simmons등, 1980)으로 보고되었다. 이러한 사실은 gentamicin nephrotoxicity의 원인중 하나가 mitochondria의 기능을 저해하기 때문임을 암시한다.

신피질 mitochondria는 신세뇨관 세포가 필요로 하는 에너지를 생산할 뿐만 아니라 암모니아를 생성하여 신장의 산염기 평형을 조절하는 중요한 기능을한다.

따라서 본 실험에서는 gentamicin 및 tobramycin이 신피질 mitochondria에 미치는 영향을 생체의 실험으로 조사하였다.

체중 250g 내외의 흰쥐에서 Simpson 및 Adam(1975)의 방법에 따라 신피질 mitochondria를 분리하여 산화인산화작용을 polarographic 및 spectrophotometric 방법으로 측정하였으며 암모니아 생성의 rate-limiting step인 glutamine 이동은 rapid millipore filtration 방법으로 측정하였다. 또한 이들 항생제가 mitochondria의형태변화에 미치는 영향은 산광도(light scattering)로 측정하였다.

이 실험 곁과는 다음과 같다.

1. Gentamicin 및 tobramycin은 신피질 mitochondria의 산광도를 대조군에 비하여 크게 변화시켰는데 tobramycin 고농도군 및 gentamicin 첨가군에서는 산광도가 감소하였으나 tobramycin 저농도군에서는 증가되었다.

2. Gentarnicin 및 tobramycin 첨가로 신피질 mitochondria의 산소소모율과 ATP생성 및 P/O 비율이 감소되었으며 같은 농도에서 gentamicin이 tobramycin보다 더욱 더 억제시켰다.

3. Gentarmicin 및 tobramycin을 고농도로 첨가한 신피질 mitochondria에서 g1utamine이동이 대조군에 비하여 감소되었으나 저농도의 경우 별 영향이 없있다.

이상과 같은 성적으로 미루어 보아 aminoglycoside항생제에 의한 nephrotoxicity의 생성기전의 하나는 신피질 mitochondria가 손상을 받고 산화인산화능 및 glutamine이동능 등이 저하되므로써 나타나며 그 정도는 gentamicin이 tobramycin 보다 더 심하게 유발시킴을 알 수 있었다.

[영문]

Aminoglycoside antibiotics have been reported to induce both nephrotoxicity and ototoxicity in man and experimental animal. Among these toxicities, nephrotoxicity is a prominent side effect of prolonged aminoglycoside antibiotice and it has been studied with gentamicin,.

It was reported that histopathological change and renal dysfunction induced by aminoglycoside antibitics might be due to accumulation of the drugs in proximal tubular epithrlium.

How these antibiotics accumulated in the tissues induce the functional disturbance of kidney is not clear, but gentamicin-induced nephrotoxicity was suggested to be associated with cellular necrosis cauaed by gentamicin which was transported into Iysosomes following pinocytosis across the brush border membrane

and subsquently activating Iysosomal enzymes.

In the gentamicin-treated animals, epithelial cells not only contained increased numbers of large, irregular crtosemes and crtosegresomes but also the cisternae of the rough endoplasmic reticulum were markedly dilated and mitochondria were swollen. Also, it was found that renal ammoniagenesis were reduced, the rate of oxygen consumption of renal cortical tissues and the oxidative phosphorylation of renal mitochondria were reduced.

It is speculated that these findings are due to mitechondrial dysfunction leading to gentamicin nephrotoxicity.

Since mitochondria play central role in cellular energy production and ammonia Production in the renal tubular cella, the effects o( gentamicin and tobramycin on the oxidative phosphorylation of mitochondria isolated from rat renal cortex and glutamine transport across the mitochondrial membrane which is thought to be rate-limiting step in ammonia production mere investigated in this study, Oxygen consumption of isolated mitochondria was measured polarographically(Estabrook, 1967) at 37℃ employing a Clark electrode and total amount of ATP produced was measured by spectrophotometric hexokinase assay(Lampeoht and Trautschold, 1974), Glutamine transport into mitochondria was measured by rapid Millipore filtration method(Goldatein, 1975). Also, the effect of these antibiotics on light scattering

of renal mitochondrial suspension was studied.

The results were summarized as follows :

1. Gentamicin reduced the degree of light scattering of renal mitochondrial suspension in Proportion to its concentration. The same result was found with tobramycin at high concentration. But tobramycin at low concentrations increased the light scattering.

2. Gentamicin and tobramrcin reduced the rate of oxygen consumption, the amount of ATP ayntheaised and P/O ratio. Gentamioin is more potent than tobramycin in reducing both the rate of oxygea consumption and r/0 ratio if equivalent doses are

compared.

3. Glutamine transport into renal cortical mitochondria from incubation medium was inhibited by both gentamicin and tobramrcin at high concentration and was net influenced by these antibiotics at low concentration.

It is speculated from the above findings, that aminoglycoside antibiotics induced morphological and functional changes in the mitochondria, leading to a depression of energy dependent reactions in intermediary metabolism of renal cortical tubular

cells, Also, it is concluded that tobramycin demonstrates a lesser nephrotoxicity than gentamicin.