1. NQO1, NAD(P)H dependent cytosolic
oxidoreductase, modulates redox status and H2O2
levels in pancreatic β-cells
Delaine M. Zayas-Bazán Burgos1 and Joshua Gray2, Emma Heart3
1
University of Puerto Rico at Cayey; 2US Coast Guard Academy, New London, CT; 3Marine
Biological Laboratory, Woods Hole, MA
Abstract: Diabetes is the illness in which either the β-cells do not secrete enough insulin or secrete
insulin that is not efficient. Type 2 diabetes is marked by a reduction in the ability of beta cells of the
pancreas to secrete insulin. Redox status, defined as the ratio of the reduced-to-oxidized forms of
redox couples (such as NADH-to-NAD+ and NADPH-to-NADP+), plays an important role in overall
cell health and in the in glucose-stimulated insulin secretion (GSIS) from pancreatic β-cells. Here we
have investigated the role of the cytosolic NAD(P)H-dependent oxidoreductase NQO1 on β-cell redox
status and quinone-dependent production of reactive oxygen intermediates (ROI). In both clonal
insulin secreting β-cells (INS-1 832/13) and isolated rodent islets, NQO1 over-expression blunted
quinone-dependent ROI production, while islets from NQO1 knockout mice had enhanced ROI
formation. Furthermore, NQO1 has been found to decrease NAD(P)H-to-NAD(P)+ ratio, consistent
with the NQO1-dependent utilization of NAD(P)H for the intrinsic Plasma Membrane Electron
Transport activity in β-cells. Together, these data show that NQO1 plays an important role in
maintaining proper redox status and maintains insulin secretion in the face of oxidative stress.
endocrine gland that, in most species, arises
Introduction
from ventral and dorsal buds which
Background
subsequently merge to form the pancreas.” This
J
definition has been conserved and further
orgen Jonsson and his team in
detailed to give everyone a better
1994 stated that: “The
understanding of the pancreas. The pancreas
mammalian pancreas is a mixed exocrine and
serves both digestive and endocrine functions

2. and it is composed of two main parts. The first
All of these cells can be directly or
part is known as the Pancreatic Acini and
indirectly linked to many of the metabolism
corresponds to the exocrine area of the
diseases we know. Metabolism can be defined
pancreas. The second main part and our area of
as the essential chemical processes involved in
interest is the endocrine area known as the
converting nutrients into chemical energy and
Islets of Langerhans. The Islets of Langerhans
molecular
are cluster of cells that produce various
maintaining the living system. (Hickman 2007).
hormones. There are five types of cells
These chemical processes include digestion,
composing the Islets of Langerhans and their
acquisition of energy, respiration and synthesis
type dictate the type of hormone they produce,
of molecules and structures. Diabetes mellitus,
release and under what stimuli. The cells and
exocrine
their function are illustrated in the following
pseudocyst among others are diseases that
table.
affect the metabolism by affecting one or
components
pancreatic
for
building
insufficiency
and
and
various steps of the digestion and nutrient
Table 1.1 Islet Composition
absorbance of the organism.
Type of Cell
Function
α cells
Produce Glucagon
In 1990 Lind C et al identified NQO1,
an NAD(P)H-dependent cytosolic
oxidoreductase, was for its ability to reduce
β cells
Produce Insulin
δ cells
Produce Somatosin (Growth
quinones such as menadione. Quinones are a
class of organic compound that could either
hormone-inhibiting Hormone)
be exogenous or endogenous. Haefeli in
2011stated the features of quinones: “quiones
ε cells
Produce Gherlin
PP cells
Produce Pancreatic Polypeptide
feature a quinoid conjugated double-bond

3. system, which is responsible for their
the formation of relatively stable quinols
electrophilic nature”
(hydroquinones), which undergo less redox
cycling due to the greater stability of the
hydroquinone versus the semiquinone and
further detoxification via phase 2
metabolismThis concept is consistent with the
increased susceptibility of the NQO1 knockout
model mouse to high and toxic doses of redox
cycling compounds and xenobiotics evidenced
in 2000 by Joseph and his team. This supports
Figure 1 NQO1 reduces H2O2 production by quinones.
Quinones such as menadione (1) are reduced by NAD(P)H-dependent
oxidoreductase enzymes to either quinols (2) or semiquinols (3).
the protective role of NQO1 against oxidative
stress in a variety of tissues. However, there are
Semiquinols, generated by 1-electron reducation of quinones, are
highly reactive and reduce molecular oxygen to generate reactive
oxygen intermediates (ROIs), while regenerating the parent quinone
no studies on the protective role of NQO1 in
pancreatic islet β-cells, which otherwise
compound (1). Complete 2-electron to the quinol (2), however,
facilitiates further metabolism and elimination of the quinone. NQO1
catalyzes complete 2-electron reduction of quinones to relatively stable
contain relatively low levels of classical
antioxidant enzymes (Tiedge M et al 1997).
quinols, which results in a lower level of ROI production.
Inside the cell, quinones undergo either
one- or two electron NAD(P)H-dependent
reduction: 1-electron reduction leads to the
formation of unstable semiquinones, which can
readily reduce molecular oxygen to superoxide,
regenerating the parent quinone compound via
redox cycling (Fig. 2). In contrast, complete 2
electron reductions mediated by NQO1 lead to
In parallel to its role as a detoxification
enzyme, NQO1 has more recently been
implicated in the regulation of intermediary
metabolism. NQO1 expression is correlated
with fasting insulin levels evidenced in
Palming J et al work in 2007 and an
association between reduced activity of NQO1
due to polymorphism and dysregulated blood

4. glucose levels has been reported in humans
832/13 cells as well as primary rodent islets, we
(Kim 2009). Gaiwkad et al evidenced in 2001
have demonstrated that NQO1 regulates the
NQO1’s role in cellular metabolism with
level of the NAD(P)H/NAD(P)+ ratio, which
studies using global NQO1 knock-out mice,
can explain its effect on the GSIS. Furthermore,
which found that these mice suffer from several
using over-expression or knockout strategies,
metabolic defects, including insulin resistance
we have demonstrated that NQO1 reduces the
in the periphery, and fail to increase insulin
degree of quinone-dependent redox cycling and
output in the face of their insulin resistance in
superoxide production in β-cells, thus acting to
contrast to the normal β-cell compensatory
prevent toxicity under enhanced pro-oxidant
hyperinsulinemic response (Pi 2007). We have
load. We believe that NQO1 reduces oxidative
previously demonstrated that NQO1 regulates
stress in β-cells by lowering quinone-dependent
glucose-stimulated insulin secretion (GSIS) and
H2O2 production, through the complete two
Plasma Membrane Electron Transport (PMET)
electron reduction. We also believe that at the
activity in pancreatic β-cells and our lab
metabolic level NQO1 modulates NAD(P)H-
continues to investigate the mechanisms of this
to-NAD(P)+ ratio in β-cells, as it does in other
pathway.
tissues.
Problem and hypotheses
Materials and Methods
In this study we investigated the role of
In order to conduct the experiments the
NQO1 in β-cell metabolic pathways, namely
first procedures were to over express NQO1 in
the role of NQO1 in modifying the redox
our cell line. This was achieved through the
status. This is one of the key determinants of
infection with the adenovirus that either was an
the β-cell health and a coupling factor in
empty vector, control, or the over expressing
glucose-stimulated insulin secretion (GSIS).
gene. Then the NQO1 activity was measured.
Using both clonal insulin secreting INS-1
Whole cell lysates were prepared by sonication

5. followed by centrifugation at 12 kg for 5 min at
Then the level of released hydrogen peroxide
4 C. Equal concentrations of cell lysate
(H2O2) was quantified using Amplex
protein were tested for NQO1 activity, which
Red/horseradish peroxidase. Fluorescence (540
was quantified by the decrease in absorbance of
excitation, 595 emission) was monitored using
dichlorophenolindophenol (DPI) (600 nm) over
a SpectraMax M5 multi-mode microplate
a period of one minute. The difference in
reader (Molecular Devices, Sunnyvale, CA).
activity in the absence and presence of
This was evaluated with both rodent islets and
dicoumarol (20 µM) are expressed as NQO1
INS-1 832/13 cells. The rodent islets were
activity. Figure 2
isolated from normal mice and the global knock
out utilizing the corresponding procedures.
NQO1 over-expression in INS-1 832/13 cells.
Adenoviral-mediated over-expression resulted
in the increase of NQO1 protein (adapted
Results
from[10]) and enzyme activity, measured as the
The effects of NQO1 over-expression
reduction of DCPIP
(dichlorophenolindophenol)
on menadione-dependent hydrogen peroxide
production in INS-1 832/13 cells were
measured and analyzed (Figure 3). Dicoumarol
(DIC), an inhibitor of NQO1, blocks NQO1
Control
NQO1+
inhibitory action on redox cycling and H2O2
production. On the first column with no
addition of Dicoumarol NQO1’s protection can
be clearly seen. Under high glucose conditions
NQO1 lowers statistically hydrogen peroxide
production. Legend: 3G is 3 mM glucose, 16

6. is 16 mM glucose. Data are means ± SE from 2
NQO1 KO. The levels of hydrogen production
experiments performed in quadruplicate
are clearly lowered by the presence of NQO1.
measurement.*P 0.05 Control vs. NQO1+ .
Figure 3. Effects of NQO1 on H2O2 production in INS-1
Figure 4. Effects of NQO1 on H2O2 production in
rodent islets
832/13 cells
The effects of NQO1 over-expression (panel
A) and knock-down (panel B) on menadionedependent H2O2 production in isolated rodent
islets (Figure 4). The over-expressing islets
came from normal mice and after isolation
were infected with adenovirus. The NQO1
knock-out islets came from the global knockout mice. Data are means ± SE from 2
Lastly in order to evidence the effects of
experiments performed in quadruplicate
NQO1 in the β-cells metabolism the NAD(H)
measurement. *P 0.05 Control vs. NQO1+ or
–to- NAD+ ratio was quantified. NQO1
regulates NADH-to-NAD+ ratio in INS-1

7. 832/13 cells and islets. INS-1 832/13 (A),
Conclusions
infected with control adenovirus (Ad-control)
or NQO1 over-expressing adenovirus (Ad-
All of these results lead to the various
conclusions about NQO1 role in β-cell health
NQO1) or isolated NQO1 Wild Type and
and metabolism. In terms of the health of the βNQO1 Knock-Out islets (B) were exposed to
cell NQO1 protects from oxidant stress,
4mM or 16 mM glucose and NADH and NAD+
therefore enhances β-cell health. In terms of
were measured by LC/MS/MS. Data are means
metabolism NQO1 modulates β-cell redox
± SE from 2-3 experiments performed in
status by lowering the NADH-to-NAD+ ratio as
duplicate measurement.*P 0.05 Ad-control vs.
it does in other tissues such as liver and
Ad-NQO1, and KO vs. WT.
adipose. This effect on redox cycle has a direct
Figure 5. NQO1 mediates redox cylcing
increasing role in glucose metabolism and
glucose stimulated insulin secretion.
Future experiments may include
exploring NQO1’s role in the
physiological state. Under normal
conditions almost every eukaryotic cell
posses the endogenous quinine ubiquinone.
Another great follow-up would be to determine
the role of NOQ1 under glucotoxicity.
Glucotoxicity is high glucose and high fatty
acids.

8. Acknowledgements
Palming J et al (2007) J Clin Endocrinol Metab 92:
2346-52
This project was conducted thanks to
Pi J et al (2007) Diabetes 56, 1783-91.
the collaboration and help of many individuals.
Tiedge M et al (1997) Diabetes 46: 1733-42
This work was supported by the National
Science Foundation through the Biological
Discovery in Woods Hole DBI 1005378, the
American Diabetes Association 7-12-BS-073
and National Institute of Health through both
Dr. Emma Heart’s grant IH R56DK088093,
and through the Research Initiative for
Scientific Enhancement Program in the
University of Puerto Rico at Cayey R25
GM059429. We extend our gratitude towards
the REU directors Dr. Mensinger and Dr.
Malchow.
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Kim D (2009) Korean Diabetes J 33: 24-30
Lind C et al (1990) Method Enzymol, 186:287-301.