Study of the Effect of Naltrexone on Cerebral Blood Flow and Hypoglycemia in Type 1 Diabetes Mellitus
Phase: PHASE1
Conditions: Type 1 Diabetes, Hypoglycemia Unawareness
Sponsor: University of Minnesota

NCT01053078 
Naltrexone and Hypoglycemia in Type 1 Diabetes 
Protocol Approval Date: August 17th, 2012
PI: Elizabeth Seaquist, MD

Hypoglycemia unawareness is a limiting factor in the treatment of type 1 diabetes and is a very 
difficult problem to reverse.  Using positron emission tomography (PET), Dunn et al have recently 
demonstrated that patients with type 1 diabetes and hypoglycemia unawareness display a brain 
activation pattern during hypoglycemia that resembles the activation pattern seen following the 
administration of an addictive substance such as cocaine (1). In this response, the amygdala and 
hypothalamic regions associated with stress were less activated and the ventral striatum region 
associated with motivation and the lateral orbitofrontal cortex region associated with reward were not 
activated as strongly during hypoglycemia in the unaware compared to the aware subjects. These 
observations raise the question of whether one reason hypoglycemia unawareness is so difficult to 
reverse is that it is rewarding and not perceived as a stress to the patient, much like the response an 
addict has to a drug upon which he has grown dependent.  If so, therapies applied to the treatment of 
addictions might provide a novel approach to the treatment of hypoglycemia unawareness in type 1 
diabetes.  One such therapy could be the orally administered non-addicting opioid antagonist 
naltrexone that has been shown to be effective in the treatment of many addictions (2-4). 
 
The long-term goal of this project is to test the hypothesis that naltrexone therapy in subjects with 
type 1 diabetes and hypoglycemia unawareness will: 
• reduce the number of hypoglycemic events (defined as number of episodes of hypoglycemia 
that require the assistance of another to recognize/treat and as minutes during which blood 
glucose is < 70 mg/dl as measured by continuous glucose monitoring, both over a 7 day 
period),  
• improve recognition of hypoglycemia during experimental conditions, and  
• reduce activation in the ventral striatum and lateral orbitofrontal cortex and increase activation 
in the amygdala and hypothalamus during hypoglycemia.   
 
In this application, we describe a pilot study to determine if this treatment is of any benefit in treating 
hypoglycemia unawareness and to collect the observations necessary to develop a full-scale clinical 
trial of sufficient power to address our hypothesis.  Our specific aim is to perform a randomized 
double blind trial of four weeks of naltrexone or placebo therapy in twenty subjects with type 1 
diabetes and hypoglycemia unawareness and compare the outcome measures collected before 
treatment with those collected at the end of the treatment period. 
 
Background and significance 
Hypoglycemia unawareness is a limiting factor in the treatment of type 1 diabetes.  Lack of 
awareness of hypoglycemia increases the risk for severe hypoglycemia, coma, and death during 
insulin therapy (5) and fear of hypoglycemia may prevent patients from optimally controlling their 
blood sugars, thereby increasing their risk for the development of diabetes complications.  Strict 
avoidance of hypoglycemia has been known to partially restore awareness of hypoglycemia (6), 
however it is very difficult to achieve.  Using PET, Dunn et al (1) have reported an increase in glucose 
uptake (a measure of activation) in brain regions associated with motivation (ventral striatum) and 
reward perception (lateral orbitofrontal cortex) and decreased activation of stress related regions 
(amygdala) during hypoglycemia in hypoglycemia unaware subjects with type 1 diabetes relative to 
hypoglycemia aware subjects with type 1 diabetes.   This activation pattern resembles that seen in 
response to substances with addictive potential (7, 8), raising the question of whether one of the 
reasons that hypoglycemia unawareness is so difficult to reverse is that it is rewarding and not 
perceived as a stress to the patient.     

 
Naltrexone, which can be delivered orally, has been shown to be safe and efficacious in the treatment 
of various addictive disorders such as alcoholism (4), opiate addiction (2) and pathological gambling 
(3). The drug binds primarily to the µ opioid receptor and is believed to block the binding of beta-
endorphins released from the nucleus accumbens and ventral tegmental areas upon exposure to an 
addicting drug like alcohol.  This blockade in turn ultimately affects downstream activation in regions 
associated with reward and craving (9).  Naltrexone is approved by the Food and Drug Administration 
for treatment of alcoholism at a dose of up to 50 mg a day for an indefinite period of time but has 
been used in higher doses to treat pathological gambling (10). Efficacy in reducing alcohol cravings 
increases with treatment periods longer than 60 days, but were reduced by approximately half after 
30 days of treatment (4).  The drug has a black box warning about hepatotoxicity at doses above 50 
mg/day, but in otherwise healthy out-patients, doses up to 200 mg a day were well tolerated and 
associated with normal liver function tests for more than a year (11).  
 
During hypoglycemia, intravenous administration of the µ opioid receptor antagonist naloxone 
enhances the epinephrine and cortisol secretory responses during hypoglycemia in both normal 
controls and in patients with type 1 diabetes (12).  More recently, naloxone infusion during an episode 
of hypoglycemia prevented the development of hypoglycemia associated autonomic failure in normal 
controls (13).  These observations suggest that a m opioid receptor antagonist might be of benefit in 
the treatment of hypoglycemia unawareness through a direct effect on cerebral glucose sensing 
and/or the coordinated counterregulatory response even if it does not prove to have an effect on the 
activation of centers involved in motivation and reward.   
 
Preliminary Data 
Our research group is very experienced in all aspects of the methodology required to complete this 
project.  We have a long track record of successfully recruiting subjects to participate in complicated 
metabolic studies (14-19).  In recent years, our work has focused on subjects with type 1 diabetes 
(20, 21), many with hypoglycemia unawareness, and we have developed a registry of such subjects 
interested in participating in future studies.  We also are skilled in the performance of clinical trials, 
having participated in the ACCORD trial since 1999 (22). 
 
Most relevant to this application is our experience performing hypoglycemic clamp studies while brain 
activation is studied using magnetic resonance techniques.  In our laboratory, we have used 
continuous arterial spin labeling (CASL) to identify brain regions that are activated in response to 
insulin-induced hypoglycemia in healthy human subjects (23).  Five men and five women (age 29 ± 
10 yrs, BMI 23.3 ± 2.1 kg/m2, mean ± SD) participated in this study. CASL images were acquired at 
euglycemia (99±5 mg/dl ) and again during hypoglycemia (52 ± 3 mg/d;) using 2D GE-EPI (labeling 
time=2500 ms, resolution =2x2x3mm, 100 label/control pairs).  In whole brain analysis, increases in 
regional cerebral blood flow, a measure of neuronal activation, were noted during hypoglycemia 
relative to euglycemia bilaterally in the medial thalamus, anterior cingulate, and posterior cingulate 
using BrainVoyager software, as has also been demonstrated by Teves et al using PET (TEVES 
PNAS 2004).   These increases coincided with the peak responses in counterregulatory hormones 
(glucagon = 110 ± 41 pg/ml, epinephrine = 519 ± 273 pg/ml, norepinephrine = 405 ±124 pg/ml), 
providing evidence that activation of these brain regions is involved in the counterregulatory response 
to hypoglycemia.  Focused region of interest analysis of specific regions such as the hypothalamus or 
amygdala was not performed in this study, but will be performed in the proposed project. 

 
Research Design and Methods: 
This study will be a randomized double blind placebo controlled trial involving 20 subjects with type 1 
diabetes and hypoglycemia unawareness.  Since the time necessary for the effect of naltrexone on 
our outcome variables to washout after a treatment period is unknown, each subject will serve as 
their own control and differences between the changes in the outcome measures will be evaluated 
between groups.  The study design is depicted in the figure below.   
 
Subjects 
Subjects between the ages 18 and 65 years of age will be recruited for participation from the 
University of Minnesota Endocrine Clinic and a registry of volunteers maintained by the investigators.  
Type 1 diabetes will be defined on clinical grounds.  To be categorized as experiencing hypoglycemia 
unawareness, subjects must first report at the time of initial contact an inability to recognize at least 
some blood glucose values less than 50 mg/dl during the prior 3 months.  At the time of the screening 
visit, subjects must then be defined as having hypoglycemia unawareness on a Cox questionnaire 
(24). Exclusion criteria will include concomitant use of acetaminophen, aspirin or ibuprofen (all may 
increase risk of naltrexone induced liver dysfunction), history of drug or alcohol abuse, current 
diagnosis or history of psychiatric illness, history of liver disease wiwth elevations in ALT/AST, history 
of renal insufficiency/failure (creatinine >1.5 mg/dL), pregnancy or breastfeeding, history of seizure or 
cardiac disease (both of which will increase risk of hypoglycemic clamp), history of stroke, head 
injury, or other chronic CNS disease, and presence of any characteristics that would preclude 
placement in the magnet (weight > 300 lbs, presence of metallic implants, etc.). 
 
Experimental protocol 
The screening visit will occur within two weeks of day zero, which will be the day of the first 
hypoglycemia study.  At the screening visit, informed consent will be obtained and a standardized 
form will be used to insure subjects meet inclusion/exclusion criteria.  Baseline labs for creatinine, 
ALT, AST, hemoglobin A1c, and CPK will be obtained.  The subject will be educated in the use of the 
continuous glucose monitor and sent home with sufficient supplies to collect data for the seven days  
before the clamp study on day zero.  During this period, subjects will also check their blood glucose 
before each of three meals and at bedtime and record the values as well as note any episodes in 
which another person was required to recognize and/or treat hypoglycemia.  The continuous glucose 
monitor display will be blinded to the subject so that it does not influence their diabetes management. 
 
Subjects will be admitted to the research center the afternoon before the hypoglycemic clamp study 
on day zero.  They will be allowed to take their short acting insulin or a bolus via their pump with their 
evening meal, but their evening dose of long-acting insulin or their pump will be held after 6 PM.  
Blood glucose values will then be monitored every 1-2 hours and an intravenous infusion of insulin 
and/or glucose will be provided to maintain blood sugars between 100-150 mg/dl.  Subjects will not 
be given additional food after their evening meal until the end of the hypoglycemic clamp on day zero. 
 
On the morning of the study, subjects will be transferred to the Center for Magnetic Resonance 
Research. After their arrival, they will be prepared for clamp study by the placement of one 
intravenous catheter into one vein in each antecubital fossa for the later infusion of glucose, insulin, 
and potassium.  A third intravenous catheter will be placed retrograde into a vein in the distal leg for 
later blood sampling.  Baseline blood samples for glucose, glucagon, catecholamines, cortisol, and 

growth hormone will then be collected no sooner than 30 minutes after catheter placement.  At time 0 
a constant infusion of insulin will be started at 2.0 mU/kg/min and the subject will be placed into the 
magnet. Plasma glucose be initially maintained at euglycemia (~100 mg/dl) while the baseline scan is 
done.  Plasma glucose will than be reduced to 50 mg/dl and maintained at this level of glycemia for 
approximately thirty minutes. During the final 15 minutes subjects will be asked to quantitate their 
symptoms using a standardized method (25).   Blood samples will be obtained every five minutes for 
measurement of plasma glucose concentration on a nearby analox machine and every twenty 
minutes for  later measurement of glucagon, catecholamines, cortisol, and growth hormone.   
 
Cerebral blood flow will measured 
on a Siemens 3 Tesla magnet when 
the subject is euglycemic and again 
during the final 15 minutes of the 
hypoglycemic period.   A T1 
mapping technique will be used in 
which a RARE sequence with etl=8 
echoes and an echo spacing of 7 
ms with center-out k-space sampling 
(effective TE = 7 msec) is employed.  
CBF contrast will be achieved using 
FAIR (26)with a 12 msec long HS8 
inversion pulse to generate a 6.6 Hz 
inversion bandwidth above a peak 
B1 of 500 Hz. A T1-image will be 
calculated at steady state from three 
acquired images on a pixel by pixel 
basis, as previously described (27).  
 
Cerebral blood flow maps will be calculated according to: 
 
 
 
where λ (ml/g) denotes the brain-blood partition coefficient of water, T1 (s) is the longitudinal 
relaxation time of tissue water, a is the efficiency of arterial spin labeling, and S0 and ST are signal 
intensities of control and arterial spin labeled images, respectively. Differences in whole brain 
cerebral blood flow measured during hypoglycemia and euglycemia will be determined for each 
subject.  The perfusion images will then be transformed into Talairach space using the anatomic 
images and differences between individual regions of interest (such as amydgala, ventral striatum, 
lateral orbitofrontal cortex, and hypothalamus) during hypoglycemia and euglycemia will be 
determined for each subject.  Dr. Silvia Mangia from the Center for Magnetic Resonance Research 
will be responsible for the collection and processing of the data collected using the 3 T magnet. 
 
At the completion of the clamp study, subjects will be removed from the magnet, the insulin infusion 
will be discontinued,glucose will be given to achieve euglycemia, and subjects will be fed a meal. 
Randomization will then be done  and subjects will be sent home with their assigned treatment.  An 
Study design.  CGMS= continuous glucose monitoring; 
BG=blood glucose; CASL = continuous arterial spin labeling; 
hypo= hypoglycemic; safety labs = ALT, AST, Cr, CPK 

Investigational New Drug (IND ) approval for the use of this medication for this study has already 
been obtained from the Food and Drug Administration.  The investigational pharmacy at the 
University of Minnesota Medical Center will insure that the naltrexone and placebo tablets are 
identical in appearance and will maintain the log of the treatment assignment.  Only the study 
pharmacist will have access to this log until the study is completed.  The dose of the drug will be 
titrated up over 10 days (25 mg daily x 5 days, then 50 mg daily x 5 days, then 50 mg BID x 18 days). 
Subjects will be asked to avoid use of acetaminophen, non-steroidal anti-inflammatory medications 
and alcohol while taking naltrexone.  At 14 ± 1 days, subjects will return to provide blood for 
measurement of ALT, AST, CPK, and creatinine.  Drug will be stopped in subjects who experience an 
increase that exceeds two times the upper limit of normal for ALT, AST, or CPK  or have a rise in their 
creatinine to 2.0 mg/dl or above in men or 1.5 mg/dl or above in women.   
 
At the 14 day visit, subjects will be reminded to wear the continuous glucose monitor for the seven 
days before the next hypoglycemic clamp study and will be sent home with sufficient supplies to do 
so.  On the night before the clamp study, they will be readmitted to the research center for 
preparation as outlined above.  Repeat samples for ALT, AST, CPK, and creatinine will also be 
collected.  On the day of the study, subjects will take their final dose of naltrexone/placebo and be 
transported to the Center for Magnetic Resonance Reserch to repeat the clamp study with 
measurement of cerebral blood flow described above. 
 
Statistical analysis 
This is a pilot study in which a sample size of 20 (10 subjects to receive placebo and 10 subjects to 
receive naltrexone) was arbitrarily selected to determine how large a sample size will be necessary to 
determine if naltrexone has an effect on our outcome measures.  Each subject will serve as his/her 
own control and changes in the outcome variables (number of hypoglycemic events defined as 
number of episodes of hypoglycemia that require the assistance of another to recognize/treat and as 
minutes during which blood glucose is < 70 mg/dl as measured by continuous glucose monitoring, 
both over a 7 day period); symptom scores collected during hypoglycemia’ and differences in regional 
blood flow noted between the euglycemic and hypoglycemic conditions for each study), will be 
compared between pre-treatment and end of treatment periods using Student’s t-test with correction 
for repeated measures.  Dr. Lynn Eberly from the Department of Biostatistics at the University of 
MInnesota will assist in the statistical analyses.  
 
Anticipated problems/potential solutions 
The most significant problem we may encounter is that our treatment outcomes will be unaffected by 
naltrexone treatment. Originally, we intended to focus on the effect of naltrexone on cerebral blood 
flow as a measure of regional activation during hypoglycemia, but since we are unaware of data that 
demonstrate naltrexone alters brain activation patterns in addicts, we have broadened our outcome 
measures to include more clinically relevant information such as frequency of hypoglycemia and 
symptom scores during controlled hypoglycemia.    We are hopeful that naltrexone will have an effect 
on at least one of the outcome variables and will use the data collected from this pilot to design a 
larger study.   
 
 
 

1. 
Dunn JT, Cranston I, Marsden PK, Amiel SA, Reed LJ. Attenuation of amydgala and frontal 
cortical responses to low blood glucose concentration in asymptomatic hypoglycemia in type 1 
diabetes: a new player in hypoglycemia unawareness? Diabetes 2007;56(11):2766-73. 
2. 
Cornish JW, Metzger D, Woody GE, et al. Naltrexone pharmacotherapy for opioid dependent 
federal probationers. J Subst Abuse Treat 1997;14(6):529-34. 
3. 
Grant JE, Kim SW. Effectiveness of pharmacotherapy for pathological gambling: a chart 
review. Ann Clin Psychiatry 2002;14(3):155-61. 
4. 
Sinclair JD. Evidence about the use of naltrexone and for different ways of using it in the 
treatment of alcoholism. Alcohol Alcohol 2001;36(1):2-10. 
5. 
Cryer PE. Mechanisms of hypoglycemia-associated autonomic failure and its component 
syndromes in diabetes. Diabetes 2005;54(12):3592-601. 
6. 
Fanelli C, Pampanelli S, Epifano L, et al. Long-term recovery from unawareness, deficient 
counterregulation and lack of cognitive dysfunction during hypoglycaemia, following institution of 
rational, intensive insulin therapy in IDDM. Diabetologia 1994;37(12):1265-76. 
7. 
Breiter HC, Gollub RL, Weisskoff RM, et al. Acute effects of cocaine on human brain activity 
and emotion. Neuron 1997;19(3):591-611. 
8. 
Kalivas PW, Volkow ND. The neural basis of addiction: a pathology of motivation and choice. 
Am J Psychiatry 2005;162(8):1403-13. 
9. 
Kim C, Seidel KW, Begier EA, Kwok YS. Diabetes and depot medroxyprogesterone 
contraception in Navajo women. Arch Intern Med 2001;161(14):1766-71. 
10. 
Kim SW, Grant JE, Yoon G, Williams KA, Remmel RP. Safety of high-dose naltrexone 
treatment: hepatic transaminase profiles among outpatients. Clin Neuropharmacol 2006;29(2):77-9. 
11. 
Caprio S, Gerety G, Tamborlane WV, et al. Opiate blockade enhances hypoglycemic 
counterregulation in normal and insulin-dependent diabetic subjects. Am J Physiol 1991;260(6 Pt 
1):E852-8. 
12. 
Leu j. Opioid receptor blockade during antecedent hypoglycemia prevents hypoglycemia 
associated autonomic failure in humans. Diabetes 2008;57(Supplement 1):20. 
13. 
Gruetter R, Seaquist ER, Kim S, Ugurbil K. Localized in vivo 13C-NMR of glutamate 
metabolism in the human brain: initial results at 4 tesla. Dev Neurosci 1998;20(4-5):380-8. 
14. 
Gruetter R, Ugurbil K, Seaquist ER. Steady-state cerebral glucose concentrations and 
transport in the human brain. J Neurochem 1998;70(1):397-408. 
15. 
Oz G, Seaquist ER, Kumar A, et al. Human brain glycogen content and metabolism: 
implications on its role in brain energy metabolism. Am J Physiol Endocrinol Metab 
2007;292(3):E946-51. 
16. 
Seaquist ER, Damberg GS, Tkac I, Gruetter R. The effect of insulin on in vivo cerebral glucose 
concentrations and rates of glucose transport/metabolism in humans. Diabetes 2001;50(10):2203-9. 
17. 
Seaquist ER, Pyzdrowski K, Moran A, Teuscher AU, Robertson RP. Insulin-mediated and 
glucose-mediated glucose uptake following hemipancreatectomy in healthy human donors. 
Diabetologia 1994;37(10):1036-43. 
18. 
Seaquist ER, Robertson RP. Effects of hemipancreatectomy on pancreatic alpha and beta cell 
function in healthy human donors. J Clin Invest 1992;89(6):1761-6. 
19. 
Criego A, Kumar A, Tran N, Tkac I, Gruetter R, Seaquist ER. Brain glucose concentrations in 
patients with type 1 diabetes and hypoglycemia unawareness. Journal of Neuroscience Research 
2005;79:42-7. 

20. 
Kodl CT, Franc DT, Rao JP, et al. Diffusion tensor imaging identifies deficits in white matter 
microstructure in subjects with type 1 diabetes that correlate with reduced neurocognitive function. 
Diabetes 2008;57(11):3083-9. 
21. 
Effect of intensive blood-glucose control with metformin on complications in overweight 
patients with type 2 diabetes (UKPDS 34). UK Prospective Diabetes Study (UKPDS) Group. Lancet 
1998;352(9131):854-65. 
22. 
Rao J, Auerback E, Ugurbil K, Seaquist ER. Detection of Regional Cerebral Blood Flow 
Changes during Hypoglycemia Using Continuous Arterial Spin Labeling 
. Diabetes 2006;57(Supplement 1):20. 
23. 
Clarke WL, Cox DJ, Gonder-Frederick LA, Julian D, Schlundt D, Polonsky W. Reduced 
awareness of hypoglycemia in adults with IDDM. A prospective study of hypoglycemic frequency and 
associated symptoms. Diabetes Care 1995;18(4):517-22. 
24. 
Towler DA, Havlin CE, Craft S, Cryer P. Mechanism of awareness of hypoglycemia. 
Perception of neurogenic (predominantly cholinergic) rather than neuroglycopenic symptoms. 
Diabetes 1993;42(12):1791-8. 
25. 
Kim SG. Quantification of relative cerebral blood flow change by flow-sensitive alternating 
inversion recovery (FAIR) technique: application to functional mapping. Magn Reson Med 
1995;34(3):293-301. 
26. 
Gruetter R, Boesch C, Martin E, Wuthrich K. A method for rapid evaluation of saturation factors 
in in vivo surface coil NMR spectroscopy using B1-insensitive pulse cycles. NMR Biomed 
1990;3(6):265-71.