Freestyle lite glucometer

In brief, and as described previously [13 (link)], 80 hand-picked isolated islets were transplanted under the kidney capsule of syngenic C57BL/6 mice with streptozotocin-induced hyperglycaemia. Diabetes was defined as a blood glucose level ≥16 mmol/l on 2 consecutive days following i.v. injection of alloxan (110 mg/kg). Blood glucose levels of non-fasted mice were determined using a FreeStyle Lite glucometer and blood glucose test strips (Abbott Diabetes Care) via tail tipping.

As previously described, animals were fasted overnight before the OGTT [19 (link)]. A bolus of D-glucose solution (5 g per kg BW) was administrated orally by gavage. Blood glucose levels were determined from samples collected from the tail vein (FreeStyle Lite glucometer, Abbott Diabetes Care, Alameda, CA) at 0, 30, 60, and 120 min post-gavage. Collected blood samples were also used to determine circulating insulin levels.

Intraperitoneal glucose tolerance test (IPGTT) and intraperitoneal insulin tolerance test (IPITT) were performed at 22 and 23 weeks of age, respectively. Mice were fasted for 6 h with ad libitum access to water prior to the tests. After measuring baseline blood glucose through the tip of the tail using a FreeStyle Lite glucometer (Abbott Diabetes Care Inc.), a glucose (2 g/kg body weight) or insulin (0.75 U/kg body weight) solution was administered via an intraperitoneal injection. Blood glucose levels were assessed at 15, 30, 45, 60, 90, and 120 min for IPGTT, or at 10, 20, 30, 45, 60, 90, and 120 min for IPITT. Area under the curve (AUC) or area above the curve (AAC) was determined as the total peak area above or below the baseline at t = 0 min using the trapezoid rule. The AAC for IPITT was also calculated for the 0–30 min time range to analyze glucose clearance without the confounding effect of hepatic glucose production.

Following an overnight (~18‐h) fast with free access to water, an IP glucose tolerance test (IPGTT) was performed (2 g/kg; 50% dextrose solution; Sigma) as described previously (Andrikopoulos et al., 2008; Czyzyk et al., 2013). Blood samples were obtained by tail prick at 0 min and 15‐, 30‐, 90‐, and 120‐min post injection and assessed using standard glucose test strips (Freestyle Lite glucometer; Abbott Diabetes Care Inc.). Blood samples were also collected at each timepoint in heparinized capillary tubes, centrifuged and plasma frozen for later analysis. The total area under the curve was calculated using the formula: blood glucose at [(0 + 15 min)*(15 − 0) + (15 + 30 min)*(30 − 15) + (30 + 90 min)*(90 − 30) + (90 + 120 min)*(120 − 90)]/2 (Potteiger et al., 2002). Insulin levels were determined by mouse ultrasensitive ELISA (Alpco). Homeostatic model assessment of insulin resistance (HOMA‐IR) values were calculated using the formula: (fasting blood glucose [mmol/L] × fasting insulin level [mU/L]]/22.5 as previously described (Andrikopoulos et al., 2008).

Glucose and insulin tolerance were measured as previously described^{3 (link)}. In brief, following an 8–12 h fasting period, glucose tolerance was measured by oral challenge with a 2 g/kg bolus of d-glucose (0.5 g/ml). Serum glucose concentrations were measured using the Freestyle Lite glucometer (Abbot) from a skin-prick site adjacent to the most peripheral vein on the ear pinna at 0, 30, 60, 90, and 120 min following administration. Similarly, insulin sensitivity was measured following the SC injection of 0.5 units/kg of regular-acting human recombinant insulin (Humulin-R, Eli Lilly). Glucose concentrations were measured at 0, 25, 50, 75, and 100 min following insulin injection.

Female, outbred Dunkin–Hartley guinea pigs, weighing between 250 and 300 g, were purchased from Charles River Laboratories or inbred Strain-13 guinea pigs were bred at the Colorado State University Laboratory Animal Resources facility, and diabetogenic treatments were initiated at a weight of ∼300 g in guinea pigs of either sex. For collection of serum, guinea pigs were anesthetized via isoflurane inhalation and blood was collected by percutaneous venipuncture of the cranial vena cava. Blood glucose was measured using the Freestyle Lite glucometer (Abbot, Alameda, CA, USA) from a skin-prick site adjacent to the most peripheral vein on the pinna, previously validated against the glucose oxidase enzymatic assay. At the time of euthanasia, guinea pigs were administered 40 mg of ketamine and 0.5 mg of diazepam via intramusclar injection for anesthetic induction. Anesthetized guinea pigs were administered a 750 mg dose of pentobarbital via the IP route for euthanasia. All animal experiments were performed in accordance with the National Research Council's Guide for the Care and Use of Laboratory Animals and were approved by the Animal Care and Usage Committee at Colorado State University under protocol number 10-1990A.