ABSTRACT
The present study examined the relationships among statin use, APOE genotype, and insulin resistance as measured by the homeostasis model assessment of insulin resistance (HOMA-IR) in healthy older adults. APOE epsilon4- (i.e., not having an epsilon4 allele) statin users had higher HOMA-IR values compared with epsilon4+/statin users (p=0.0169), and with non-users who were epsilon4- (p=0.0003) or epsilon4+ (p=0.0006). These results suggest that statin use may modulate insulin levels for individuals without an APOE epsilon4 allele.
Subject(s)
Anticholesteremic Agents/therapeutic use , Apolipoprotein E4/genetics , Hydroxymethylglutaryl-CoA Reductase Inhibitors/therapeutic use , Hypercholesterolemia , Metabolic Syndrome/epidemiology , Aged , Alzheimer Disease/epidemiology , Alzheimer Disease/genetics , Dementia/epidemiology , Dementia/genetics , Diabetes Mellitus/epidemiology , Female , Genotype , Homeostasis , Humans , Hypercholesterolemia/drug therapy , Hypercholesterolemia/epidemiology , Hypercholesterolemia/genetics , Male , PrevalenceABSTRACT
Both insulin alone and the somatostatin analogue octreotide alone facilitate memory in patients with Alzheimer's disease (AD). Since octreotide inhibits endogenous insulin secretion, the cognitive effects of insulin and octreotide may not be independent. This study tested the individual and interactive effects of insulin and octreotide on memory and plasma growth hormone (GH) levels in older adults. Participants were 16 memory-impaired (AD = 7, amnestic mild cognitive impairment = 9; apolipoprotein E [APOE] epsilon4- [no epsilon4 alleles] = 9, epsilon4+ [1-2 epsilon4 alleles] = 7), and 19 cognitively-intact older adults (APOE epsilon4- = 17, epsilon4+ = 1). On separate days, fasting participants received counterbalanced infusions of: 1) insulin (1 mU.kg(-1).min(-1)) and dextrose to maintain euglycemia; 2) octreotide (150 microg/h); 3) insulin, dextrose, and octreotide; or 4) saline. Story recall was the principal endpoint. Insulin alone facilitated delayed recall for epsilon4- patients, relative to epsilon4+ patients (P = 0.0012). Furthermore, epsilon4- patients with higher Mattis Dementia Rating Scale (DRS) scores had greater octreotide-induced memory facilitation (P = 0.0298). For healthy adults, octreotide facilitated memory (P = 0.0122). Unexpectedly, hyperinsulinemia with euglycemia increased GH levels in healthy controls (P = 0.0299). Thus, insulin and octreotide appear to regulate memory in older adults. APOE epsilon4 genotype modulates responses to insulin and octreotide. Finally, insulin may regulate GH levels during euglycemia.
