Open Journal of Endocrine and Metabolic Diseases, 2013, 3, 1-8
doi:10.4236/ojemd.2013.34A1001 Published Online August 2013 (http://www.scirp.org/journal/ojemd)
Trivalent Chromium Modulates Hexosamine Biosynthesis
Pathway Transcriptional Activation of Cholesterol
Synthesis and Insulin Resistance
Brent A. Penque, Lixuan Tackett, Jeffrey S. Elmendorf
Departments of Cellular and Integrative Physiology and Biochemistry and Molecular Biology, Centers for Diabetes Research, and
Membrane Biosciences, Indiana University School of Medicine, Indianapolis, USA
Received April 23, 2013; revised May 25, 2013; accepted June 26, 2013
Copyright © 2013 Brent A. Penque et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
Trivalent chromium has long been recognized to benefit carbohydrate and lipid metabolism. Given emerging evidence
that suggests chromium improves insulin sensitivity through the maintenance of an optimal level of plasma membrane
(PM) cholesterol, we delineated the role of this micronutrient in attenuating hyperinsulinemia-induced cholesterol bio-
synthesis and insulin resistance. Exposing 3T3-L1 adipocytes to physiological hyperinsulinemia (500 pM 12 h), re-
sulted in a marked impairment in insulin-stimulated glucose transport. Concurrent treatment with chromium in the pi-
colinate form (CrPic, 10 nM 16 h) prevented against glucose transport dysfunction. Insulin signaling was neither im-
paired by hyperinsulinemia nor amplified by chromium to promote this protective action. Instead, it was found that hy-
perinsulinemia promoted an increase in PM cholesterol content that was observed to impair the acute ability of insulin
to stimulate GLUT4 redistribution to the PM. Chromium prevented against the accumulation of PM cholesterol. Mecha-
nistically, hyperinsulinemia promoted increases in O-GlcNAc modification of specificity protein 1 (Sp1), known to
engage a cholesterolgenic response. Subsequent chromatin immunoprecipitation and luciferase assays revealed that hy-
perinsulinemia increased the binding affinity of Sp1 to the promoter region of Hmgcr, encoding 3-hydroxy 3-me-
thyl-glutaryl-CoA reductase (HMGR), as well as HMGR promoter activity. This resulted in gains in mRNA and protein
content of HMGR, with resulting elevations in PM cholesterol content. Moreover, treatment with chromium prevented
this transcriptional response. Together, these data suggest a mechanism whereby CrPic affords glycemic health through
inhibition of a transcriptional cholesterolgenic program detrimental to insulin action.
Keywords: 3T3-L1 Adipocytes; GLUT4; HMG-CoA Reductase; Hyperinsulinemia; Sp1
1. Introduction
Clinical trials have revealed beneficial actions of triva-
lent chromium (Cr3+) on glycemic control [1-3], yet a
mechanism of action remains unknown. In this regard,
data collected in our lab as well as others revealed that
Cr3+ exerts its influence on PM parameters [4-6]. Inter-
estingly, these studies suggested that regulation of glu-
cose transport by Cr3+ may be independent of amplifica-
tion of insulin signaling, as previously described [7]. Ra-
ther, it was found that Cr3+ normalized elevated PM cho-
lesterol levels that impaired glucose transport in 3T3-L1
adipocytes cultured under the diabetic milieu. Exogenous
add back of cholesterol, for instance, blunted the effects
of Cr3+ observed in these insulin-resistant cells. Despite
this association in clonal cells, a basis for alterations in
PM cholesterol content in promoting the development of
insulin resistance remained unclear.
Parallel experiments have since established that nutria-
ent overabundance promotes elevations in membrane cho-
lesterol content in 3T3-L1 adipocytes and L6 myotubes,
as well as in skeletal muscle of C57Bl/6J mice and Zuc-
ker rats [8-12]. These membrane perturbations were ob-
served concomitant with a loss of cortical filamentous-
actin (F-actin) necessary for proper incorporation of the
insulin sensitive glucose transporter GLUT4 into the PM.
Furthermore, increased membrane cholesterol content was
also correlated with diminished glucose disposal rates in
humans [10]. Mechanistically, data revealed increased
glucose flux through the hexosamine biosynthesis path-
way (HBP) promoted elevated O-linked N-acetylgluco-
samine (O-GlcNAc) modification of specificity protein 1
(Sp1), leading to transcriptional activation of HMG-CoA

B. A. PENQUE ET AL.
2
reductase, the rate limiting enzyme in cholesterol syn-
thesis [12]. This culminated in increased PM cholesterol
content that perturbed F-actin structure and impinged
upon insulin action. Inhibition of the HBP or Sp1 binding
to the DNA attenuated hyperinsulinemia-induced PM cho-
lesterol accumulation, F-actin loss, and insulin resistance.
Strikingly, these increases in cholesterol synthesis were
independently found to impair cholesterol efflux process-
es that HBP inhibition also corrected [13].
Based on these studies finding PM stress compromised
insulin action, we hypothesized that Cr3+ may potentially
counter excessive HBP activity thereby inhibiting a tran-
scriptional response leading to dysregulated cholesterol
synthesis. We report herein that Cr3+ protects against hy-
perinsulinemia-induced increases in PM cholesterol con-
tent through inhibition of this pathway. These studies
highlight a novel protective role of this micronutrient on
glucose metabolism entailing the maintenance of optimal
membrane cholesterol content.
2. Materials and Methods
2.1. Cell Culture and Treatments
Murine 3T3L1 adipocytes purchased from Dr. Howard
Green were cultured as described previously [14]. Briefly,
preadipocytes were cultured in Dulbecco’s Modified
Eagle Medium (DMEM) containing 25 mM glucose and
10% bovine calf serum at 37˚C at 10% CO2. Confluent
fibroblasts were induced to differentiate as previously
described [8]. All studies were performed on adipocytes
between 8 and 12 days post initiation of differentiation.
For treatments, cells were left untreated or treated with
CrPic (10 nM, 16 h Nutrition 21) in the presence or ab-
sence of hyperinsulinemia (500 pM, 12 h Sigma) in se-
rum free DMEM. Acute insulin stimulations were per-
formed with a 100 nM dose during the last 5 min for sig-
naling or 30 min for glucose transport analyses.
2.2. Glucose Uptake
Glucose uptake assays were performed as described pre-
viously [12]. Briefly, treated cells were incubated in a
KRPH buffer (136 mM NaCl, 20 mM HEPES, pH 7.4, 5
mM sodium phosphate, pH 7.4, 4.7 mM KCl, 1 mM
MgSO4, 1 mM CaCl2) for 15 min. Cells were then left
unstimulated or stimulated with 100 nM insulin for 30
min and exposed to 50 µM 2-deoxyglucose (2-DG) con-
taining 0.5 µCi 2-[3H] deoxyglucose (Perkin Elmer) in
the absence or presence of 20 µM cytochalasin B. After
10 min, uptake was terminated by aspiration and quen-
ched with the addition of 1.0 ml of 10 µM cytochalasin B.
Cells were solubilized in 0.2 N NaOH and [3H] was mea-
sured by liquid scintillation. Counts were normalized to
total cellular protein, determined by the Bradford method.
2.3. Protein Analyses
Whole cell lysates were prepared following treatments as
previously described [12]. 30 - 50 µg of lysates were
resolved and immunoblotted with antibodies to HMGR
(Millipore), p-Akt (Genscript) Akt2 (Cell Signaling), p-
Akt substrate of 160 kilodaltons (Cell Signaling), and
AS160 (Upstate). Immunoblots were quantitated using a
LI-COR Odyssey infrared imaging system, normalizing
signal intensity to β-actin (Cytoskeleton). For immuno-
precipitation, 1.5 mg of protein and 2 μg of Sp1 antibody
(Santa Cruz) were used as previously described [12].
Eluted immunoprecipitates were then resolved and im-
munoblotted using an RL2 antibody (Thermo Scientific).
2.4. Cholesterol Measurements
For cholesterol measurements, purified PM fractions
were obtained as described [12] and cholesterol content
was assayed using the Amplex Red cholesterol assay kit
(Molecular Probes). Briefly, reconstituted PM pellets
were vigorously mixed with chloroform-methanol (2:1
v/v) for 10 min to extract the cholesterol. The mixture
was then centrifuged at 1000 rpm for 10 min. The lower
phase containing lipids was then evaporated at 100˚C for
10 min. The residue was reconstituted with isopropra-
nol-Triton X solution (10:1 v/v) and 50 µl of sample was
combined with 50 µl of Amplex Red reaction mix and
incubated at 37˚C for 30 min. After incubation, absor-
bance was measured at 600 nm.
2.5. Chromatin Immunoprecipitation
Chromatin immunoprecipitation was performed on treat-
ed adipocytes as described previously [12]. Briefly, adi-
pocytes were fixed with 1% formaldehyde for 10 min.
Cells were then scraped in PBS plus protease inhibitor
cocktail and centrifuged for 2 min at 2000 rpm. The pel-
let was resuspended in 500 µl ChIP lysis buffer (50 mM
Tris pH 8.1, 10 mM EDTA, 1% SDS plus protease in-
hibitor cocktail), sonicated (10 pulses of 30 s on, 30 s
off), and centrifuged at 14,000 rpm at 4˚C for 10 min.
Fragmented chromatin preparations were then diluted
with ChIP dilution buffer (Millipore), and an input sam-
ple was collected. Samples were precleared prior to im-
munoprecipitation with antibodies to Sp1 (Santa Cruz) or
IgG (Millipore) overnight. Eluates were reversed cross-
linked and purified DNA was recovered using the phe-
nol/chloroform method. DNA was subsequently used as
a template for qPCR under the following conditions: 15
min at 95˚C followed by 35 cycles of 15 s at 95˚C, 30 s
at 50˚C, and 34 s at 60˚C. The % input method was used
to quantitate cycle threshold (Ct) values. The sequence of

B. A. PENQUE ET AL. 3
the forward primer was (5’-3’) ACCCGTCA-
TTGGTTGGCTCT and reverse primer (5’-3’) CTCCCT-
AACAACCGCCAACT.
2.6. Plasmids and Luciferase Assays
The proximal promoter sequence of HMGR (−284 to
+36), required for high level expression, was amplified
from mouse genomic DNA using PCR [15,16]. Promoter
fragments were sequenced and cloned into pGL2B luci-
ferase reporter plasmids (Promega, Madison WI). Diffe-
rentiated adipocytes were electroporated (0.16 kV and
960 µF) as previously described [12]. Briefly, cells were
trypsinized and pelleted by centrifugation at 1000 rpm.
Pellets were resuspended in PBS and centrifuged. Pellets
were then resuspended in 0.5 ml PBS. For transfection,
50 µg of HMGR pGL2B and 50 µg of phrlmin TK (Re-
nilla) plasmid were used with a concentration of appro-
ximately 1 × 107 cells/0.5 ml. A single pulse was applied
using a Gene Pulser (Bio-Rad #1652076). The electro-
porated cells were then allowed to recover and plated
into a 24 well plate. Treatments were begun 24 h after
electroporation. After treatments, cells were lysed and
assayed for promoter activity using the dualluciferase re-
porter assay system (Promega, Madison WI). Firefly Lu-
ciferase activities were normalized to Renilla activity to
control for differences in transfection efficiency.
2.7. RNA Analyses
Adipocyte RNA was isolated using an RNeasy mini kit
(Qiagen) according to the manufacturer’s protocols.
RNA was reverse transcribed using a High Capacity
cDNA Reverse Transcription Kit (Applied Biosystems).
Subsequent qPCR reactions were performed under the
following conditions: 15 min at 95˚C followed by 40
cycles of 15 s at 95˚C and 40 s at 60˚C. Ct values were
normalized to 36B4. The ∆∆Ct method was used to de-
termine relative expression levels. The sequence for the
HMGR forward primer was (5’-3’) TGTGGGAA-
CGGTGACACTTA and reverse primer (5’-3’) CTTC-
AAATTTTGGGCACTCA. The sequence of for the
36B4 forward primer was (5’-3’) AAGCGCGTCCT-
GGCATTGTCT and reverse primer (5’-3’) CCGCAGG-
GGCAGCAGTGGT.
2.8. Statistical Analyses
Values presented are means ±SEM. The significance of
difference between means was evaluated by repeated
measures ANOVA. Where a difference was indicated by
ANOVA, a Newman-Keuls post-hoc test was used to
compare differences between groups. Statistical compa-
risons of the fold or percent change of HMGR expression
and Sp1 O-linked glycosylation were performed by two-
tailed Student’s t test analysis. GraphPad Prism 5 soft-
ware was used for all analyses. P < 0.05 was considered
significant.
3. Results
3.1. CrPic Prevents Impaired Glucose Transport
Study first sought to examine the beneficial effects of
CrPic treatment on cells rendered insulin resistant. Low
doses of pathophysiologic hyperinsulinemia, utilized by
many groups to induce insulin resistance [17-20], re-
sulted in a 50% reduction in the ability of a maximal
dose of insulin to stimulate glucose transport into adi-
pocytes (Figure 1). In cells treated with hyperinsuline-
mia in the presence of a low, pharmacologically relevant
dose (10 nM) of CrPic for 16 h [4,6], the acute ability of
insulin to stimulate glucose transport was corrected. Stu-
dies have suggested that a beneficial aspect of CrPic on
glucose transport may entail countering defects in insulin
signaling, thereby improving GLUT4 translocation to the
PM [21-24]. Importantly, cell systems that mimic patho-
physiological hyperinsulinemia, known to promote the
progression/worsening of insulin resistance, and CrPic,
known to improve insulin action, are not associated with
insulin signaling changes [4,6,11,17]. We thus next sought
to verify that insulin signaling was indeed intact under
hyperinsulinemic conditions and that the beneficial effect
of CrPic was not coupled to enhancement in insulin sig-
naling in these cells. Neither hyperinsulinemia, nor CrPic
had any effects on signaling to Akt or its downstream
target, AS160. Combinatorial treatment also did not af-
fect any signaling parameters examined (Figure 2).
0
500
1000
1500
2-DG Transport
(dpm/mg protein/min)
30 ' Ins:-+-+ -+-+
Control 12 h Ins
ns
*
#
16 ' CrPic:-- -- ++++
Figure 1. CrPic improves insulin responsiveness rendered
impaired by hyperinsulinemia. 3T3-L1 adipocytes were
treated with or without 10 nM CrPic for 16 h and 500 pM
insulin for 12 h. After treatments, 3T3-L1 adipocytes were
left unstimulated or stimulated by a maximal dose (100 nM)
of insulin for 30 min to initiate glucose uptake. Values are
mean ± SEM from 4 - 6 independent experiments. *P < 0.05
versus unstimulated control; #P < 0.05 versus all other 30’
insulin groups; ns, non-significant.

B. A. PENQUE ET AL.
4
p-Akt2
Akt2
0.0
0.5
1.0
1.5
A. U. Fluorescense
p-Akt2 / Akt2
30 ' Ins:-+-+-+-+
16 ' CrPic:-- -- ++
Control
++
12 h Ins
ns
****
(a)
B
0.00
0.05
0.10
0.15
0.20
Control 12 h Ins
ns
****
A. U. Fluorescense
p-AS160 / AS160
30 ' Ins:-+-+-+
-+
16 ' CrPic:--- - ++++
(b)
Figure 2. CrPic does not enhance nor does hyperinsuline-
mia impair insulin signaling. After treatments, 3T3-L1 adi-
pocytes were left unstimulated or stimulated by a maximal
dose (100 nM) of insulin for 5 minutes to induce phospho-
rylation of insulin signaling proteins. A, Phosphorylation of
Akt2 (Ser 474) normalized to total Akt2. B, Phosphoryla-
tion of AS160 normalized to total AS160. Values are mean ±
SEM from 4 independent experiments. *P < 0.05 versus res-
pective unstimulated cells; ns, non-significant.
3.2. CrPic Inhibits PM Cholesterol
Accumulation
Studies have demonstrated that hyperinsulinemia pro-
motes increased PM cholesterol, in turn perturbing corti-
cal F-actin necessary for proper GLUT4 incorporation
into the PM [8,9]. Ex vivo examination of skeletal muscle
from insulin-resistant Zucker rats demonstrated that cor-
rection of membrane cholesterol restores actin structure
and insulin sensitivity [9]. It was examined whether
CrPic treatment had beneficial effects on PM cholesterol
levels. PM cholesterol content was elevated by approxi-
mately 50% in adipocytes exposed to hyperinsulinemia
(Figure 3). Importantly, concurrent treatment with CrPic
prevented this gain in cholesterol content.
3.3. CrPic Prevents O-GlcNAcylation of Sp1
Recent findings have established excessive glucose flux
0
100
200
300
CrPic
PM Cholesterol
(g / mg protein)
Control 12 h Ins.
CrPic
--
*
Figure 3. CrPic protects against PM cholesterol accumula-
tion induced by hyperinsulinemia. After treatments, 3T3-L1
adipocytes were lysed and fractionated to prepare purified
PM fractions. Cholesterol content in PM fractions was as-
sessed via Amplex Red, normalized to PM protein content.
Values are mean ± SEM from 5 independent experiments.
*P < 0.05 versus all other groups.
through the HBP in provoking a cholesterolgenic re-
sponse through modification of Sp1 [12]. To test whether
CrPic could be potentiating HBP activity, thereby reduc-
ing a transcriptional response leading to increased PM
cholesterol, the glycosylation status of Sp1 was next exa-
mined. These analyses revealed both a gain in global O-
GlcNAc levels (data not shown) as well as increased O-
GlcNAc of Sp1 induced by hyperinsulinemia (Figure 4).
While CrPic treatment did not alter HBP activity in con-
trol cells, it blunted the effects of hyperinsulinemia in en-
gaging the HBP.
3.4. CrPic Attenuates Sp1 Affinity to and
Activity of the HMGR Promoter
Study next sought to analyze whether CrPic may pro-
mote optimal glucose transport by inhibiting a HBP-in-
duced cholesterolgenic transcriptional response entailing
Sp1. In untreated cells cultured in low or high glucose, a
majority of Sp1 is localized to the nucleus [25], although
some studies suggest O-GlcNAc mediates its nuclear lo-
calization [26,27]. Other data, including our own, suggest
that O-GlcNAc modification may serve to increase Sp1
binding to the promoter region of target genes or prevent
its degradation [12,28,29]. Chromatin immuno-precipi-
tation revealed a significant increase in Sp1 binding affi-
nity to the HMGR promoter induced by hyperinsulinemia,
whereas treatment with CrPic blunted this association
(Figure 5). To discern if CrPic could inhibit activation
the promoter, plasmids containing the coding sequence
(−284 to +36) of HMGR, including 3 Sp1 binding moi-
eties, coupled to luciferase, were electroporated into 3T3-
L1 adipocytes (Figure 6(a)). Luciferase activity was ele-
vated approximately 2 fold by hyperinsulinemia (Figure
6(b)). Consistent with CrPic inhibiting this response,

B. A. PENQUE ET AL. 5
0
50
100
150
200
A. U. Fluor e scen ce
(% change from control)
CrPic
Control 12 h Ins.
CrPic
--
*
IB: RL2
IB: S p 1
IP: S p 1
Figure 4. Hyperinsulinemia provokes and CrPic inhibits
O-GlcNAc of Sp1. After treatments, lysates were immuno-
precipitated with a Sp1 antibody. Eluted samples were sub-
sequently immunoblotted and labeled with an RL2 antibody
to detect O-GlcNAc on Sp1. Values represent the mean ±
SEM from 5 independent experiments. *P < 0.05 versus un-
treated control.
0
2
4
6
8
% Input
CrPic
Control 12 h Ins.
CrPic
--
*
Figure 5. CrPic reduced hyperinsulinemia-induced associa-
tion of Sp1 toward the HMGR promoter. After treatments,
ChIP was performed and primers specific to the Sp1 bind-
ing site in the promoter region of HMGR were used for
amplification of the DNA eluates via qPCR. Ct values from
qPCR were normalized using the fold enrichment method.
Values are mean ± SEM from 3 independent experiments.
*P < 0.05 versus untreated control.
elevations in luciferase activity were not observed in
cells treated with CrPic.
3.5. CrPic Inhibits HMGR Synthesis
It was next examined whether CrPic, through attenuating
Sp1 affinity to the promoter region of HMGR, as well as
(a)
0
100 200 300 400
Relative Luciferase Activity
Control
CrPic
12 h In s
12 h In s + CrPic
*
(b)
Figure 6. Hyperinsulinemia ates and CrPic reduces the
s this enzyme is rate-limiting in the formation of cho-
activ
promoter activity of HMGR. A, the nucleotide sequence of
the minimal HMGR promoter (−284/+38) is shown. The lo-
cation of various sequence motifs that serve as sites of re-
cognition for transcription factors are underlined includ-
ing those for Sp1 (C/EBP, CCAAT/enhancer binding pro-
tein SRE, sterol regulatory element, CRE, cAMP response
element). The +1 indicates the start site of transcription and
the start site of translation is indicated by an asterisk. B,
Hmgcr pGL2B and phrl-minTK constructs were transfected
into 3T3-L1 adipocytes. After transfection, cells were left
untreated or treated with 500 pM insulin and/or 10 nM
CrPic. Cells were then lysed in passive lysis buffer and lu-
ciferase activity was measured, normalized to Renilla. Va-
lues are mean ± SEM from 3 independent experiments. *P <
0.05 versus control.
a
lesterol. Hyperinsulinemia was found to increase HMGR
mRNA by approximately 5 fold, whereas CrPic pre-
vented this alteration (Figure 7(a)). Strikingly, CrPic
treatment also attenuated a 60% gain in protein content
of HMGR that was observed in hyperinsulinemic cells activity of the promoter, could inhibit HMGR synthesis

B. A. PENQUE ET AL.
6
(Figure 7(b)). Together, these data suggest a transcrip-
tional basis for the beneficial effects of CrPic on glucose
transport processes.
4. Discussion
ies provide novel mechanistic insight The current stud
into the established role of CrPic in benefiting glucose
homeostasis. Data support a transcriptional basis for
CrPic action in preventing PM cholesterol accumulation,
which has been previously shown to impinge upon insu-
lin action. While the mechanisms by which CrPic may
precisely inhibit glucose flux through and/or activity of
the HBP were not a focus of this work, study has demon-
strated that CrPic activates AMPK, a known sensor of
0
2
4
6
8
Expression Hmgcr /36B4
(fold of control)
CrPic
Control 12 h Ins.
CrPic
--
*
(a)
0.0
0.1
0.2
0.3
A.U. Fluorescence
(HMG R / Actin)
CrPic
Control 12 h Ins.
CrPic
--
*
HMG R
Ac t in
(b)
Figure 7. CrPic protects agt hyperinsulinemia-induced ains
HMGR synthesis. A, After treatments, RNA was purified,
reverse transcribed, and HMGR mRNA expression levels
were assessed via qPCR and quantitated using the ∆∆ct me-
thod, normalized to 36B4 mRNA expression. B, After treat-
ments HMGR protein content was assessed via western
blotting, normalized to actin. Values are mean ± SEM from
4 - 5 independent experiments. *P < 0.05 versus untreated
control.
low energy status [4,6,13,30,31]. Additionally, it has re-
cently been determined that AMPK can phosphorylate
and inhibit glutamine fructose-6-phosphate amidotrans-
ferase, the rate limiting enzyme in the HBP [32]. In this
regard, CrPic may have pleiotropic effects on cholesterol
synthesis processes through inhibiting both production of
HMGR as well as its activity.
The exact mechanisms whereby this micronutrient
may trigger the activation of AMPK to potentially modu-
late flux through this pathway are thus warranted and
may involve liver kinase B1, calmodulin activated pro-
tein kinase kinases, protein tyrosine phosphatase 2A and/
or alterations in the cellular ATP/AMP ratio through al-
tering mitochondrial complexes [33-36].
With regard to the HBP, approximately 25% of pro-
teins modified by O-GlcNAc are transcription factors
[37]. Sp1 was the primary focus of this work due to re-
cent study suggesting inhibition of Sp1 could protect
against glucose transport dysfunction in adipocytes [12].
Nevertheless, HBP-induced O-GlcNAc on histones has
been demonstrated [38]. Interestingly, this study found
that many metabolic gene products, including HMGR,
were upregulated in response to activation of the HBP.
As HBP-induced modification of proteins is known to
occur in times of nutrient excess, global inhibition of this
pathway by CrPic is of interest as it may have beneficial
metabolic effects extending beyond maintenance of cho-
lesterol synthesis. In this regard, a study has shown that
CrPic or HBP inhibition restores cholesterol efflux ren-
dered impaired by hyperinsulinemia [13]. While the cur-
rent study focused on inhibition of cholesterol synthesis,
CrPic has been documented to be necessary for mainte-
nance or even improve high density lipoprotein levels in
humans given brewer’s yeast [39,40]. Together, these
findings support a mechanism whereby CrPic may bene-
fit glucose metabolism by maintaining optimal PM cho-
lesterol levels needed for appropriate glucose transport
into peripheral tissues.
In terms of human health, our data suggest a novel,
putative mechanism whereby CrPiccould be beneficial to
glucose metabolism through countering PM stress. While
clinical trials suggest a beneficial effect of CrPic in dia-
betics, it may be possible that CrPic treatment has an ef-
fect to counter dysregulation in membrane stress and that
this incremental effect may become impeded later in di-
sease progression when other factors further perturb in-
sulin sensitivity. Alternatively, antihyperglycemic medi-
cations could mask the effects of CrPic, as many are
known to activate AMPK. Further, well-designed longi-
tudinal studies are thus needed in insulin-resistant, non-
diabetic patients to help better characterize the role of
this micronutrient in alleviating insulin resistance. In this
regard, CrPic use may prove beneficial in preventing the
exacerbation of insulin resistance in patient populations

B. A. PENQUE ET AL. 7
through promoting optimal PM fluidity.
5. Acknowledgements
This work was supported b
Institutes of Health (DK082
y grants from the National
773) as well as an In
[1] R. A. Andersoes of Supplemental
Chromium Imlin Variables in In
diana
University School of Medicine Moenkhaus Endowment.
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