An Oral Adsorbent, AST-120 Protects Against the Progression
of Oxidative Stress by Reducing the Accumulation of Indoxyl
Sulfate in the Systemic Circulation in Renal Failure
and Masaki Otagiri
Received October 11, 2006; accepted January 19, 2007; published online March 27, 2007
Purpose. The effect of AST-120, an oral adsorbent, on oxidative stress in the systemic circulation in
chronic renal failure (CRF) was examined and the potential role of indoxyl sulfate (IS), an uremic toxin
adsorbed by AST-120, in inducing the formation of reactive oxygen species (ROS) in the vascular system
was studied, in vitro and in vivo.
Materials and methods. The level of oxidized albumin, a marker for oxidative stress in the systemic
circulation was determined by HPLC, as previously reported. The mRNA levels of TGF-b
were measured by quantitative RT-PCR. The IS induced ROS generation in cultured human umbilical
vein endothelial cells (HUVECs) was estimated using a ﬂuorescence microplate reader.
Results. An increase in the ratio of oxidized to unoxidized albumin was determined using 5/6
nephrectomized rats (CRF rats) compared to a control group. The ratio was signiﬁcantly reduced in the
group that received AST-120 of 4 weeks, suggesting that AST-120 inhibits oxidative stress in CRF. An
anti-oxidative effect of AST-120 was also observed in CRF rats with a similar renal function. The ratio of
oxidized albumin was correlated with serum IS levels in vivo. The same relationship was also observed in
CRF rats with the continued administration of IS. In addition, IS dramatically increased the generation
of ROS in both a dose- and time- dependent manner in HUVEC, suggesting that accumulated IS may
play an important role in enhancing intravascular oxidative stress.
Conclusion. We propose that AST-120 reduces IS concentrations in the blood that induces ROS
production in endothelial cells, thereby inhibiting the subsequent occurrence of oxidative stress in the
systemic circulation in renal failure.
KEY WORDS: albumin oxidation; AST-120; chronic renal failure; indoxyl sulfate.
Oxidative stress, which involves the production of
excessive levels of reactive oxygen spices (ROS) is closely
related to the progression of renal failure (1). Furthermore,
the management of cardiovascular disease (CVD) is an
important issue in cases of chronic renal failure (CRF)
patients, and oxidative stress has been speculated to greatly
contribute to such onset (2,3). However, the development of
effective treatment methods for reducing oxidative stress has
also been sought on behalf of CRF.
The oral carbonaceous adsorbent, AST-120 (Kremezin
has been used in pre-dialysis, uremic stage renal failure
patients to adsorb biologically active substances, the so-called
uremic toxins, in the circulation that accumulate during CRF,
thereby prolonging the progression of CRF and the interval to
the inception of dialysis (4–7). In nephrectomy animal models,
the administration of AST-120 attenuates the progression of
renal failure without affecting the plasma rennin-angiotensin
system or protein intake and reduces the gene expression of
transforming growth factor-b
), a tissue inhibitor of
metalloproteinease (TIMP-1) and pro-a1(I) collagen in the
kidney (8–10). However, details of the mechanism of
pharmacological action of AST-120 remain unclear.
Indoxyl sulfate (IS), a naturally occurring metabolite of
tryptophan, is considered to be a key target uremic toxin for
AST-120 (11). The toxin is thought to be involved in the
2007 Springer Science + Business Media, LLC
Pharmaceutical Research, Vol. 24, No. 7, July 2007 (
Department of Biopharmaceutics, Graduate School of Pharmaceu-
tical Sciences, Kumamoto University, 5-1 Oe-honmachi,
Kumamoto 862-0973, Japan.
Department of Nephrology, Graduate School of Medical Sciences,
Kumamoto University, Kumamoto 860-8556, Japan.
Department of Pathopharmacology, Graduate School of Pharma-
ceutical Sciences, Kumamoto University, Kumamoto 862-0973,
Department of Pharmacy, Japanese Red Cross, Kumamoto Hospi-
tal, Kumamoto 861-8520, Japan.
To whom correspondence should be addressed. (e-mail: otagirim@
ABBREVIATIONS: CRF, chronic renal failure; CVD, cardiovas-
cular disease; HPLC, high-performance liquid chromatography;
HSA, human serum albumin; HUVEC, human umbilical vein en-
dothelial cell; IS, indoxyl sulfate; OAT, organic anion transporter;
ROS, reactive oxygen spiecies; TGF-b
, transforming growth fac-
; TIMP-1, tissue inhibitor of metalloproteinease.