A Type 1 Diabetes Genetic Risk Score Predicts Progression of Islet Autoimmunity and Development of Type 1 Diabetes in Individuals at Risk

OBJECTIVE

We tested the ability of a type 1 diabetes (T1D) genetic risk score (GRS) to predict progression of islet autoimmunity and T1D in at-risk individuals.

RESEARCH DESIGN AND METHODS

We studied the 1,244 TrialNet Pathway to Prevention study participants (T1D patients' relatives without diabetes and with one or more positive autoantibodies) who were genotyped with Illumina ImmunoChip (median [range] age at initial autoantibody determination 11.1 years [1.2-51.8], 48% male, 80.5% non-Hispanic white, median follow-up 5.4 years). Of 291 participants with a single positive autoantibody at screening, 157 converted to multiple autoantibody positivity and 55 developed diabetes. Of 953 participants with multiple positive autoantibodies at screening, 419 developed diabetes. We calculated the T1D GRS from 30 T1D-associated single nucleotide polymorphisms. We used multivariable Cox regression models, time-dependent receiver operating characteristic curves, and area under the curve (AUC) measures to evaluate prognostic utility of T1D GRS, age, sex, Diabetes Prevention Trial-Type 1 (DPT-1) Risk Score, positive autoantibody number or type, HLA DR3/DR4-DQ8 status, and race/ethnicity. We used recursive partitioning analyses to identify cut points in continuous variables.

RESULTS

Higher T1D GRS significantly increased the rate of progression to T1D adjusting for DPT-1 Risk Score, age, number of positive autoantibodies, sex, and ethnicity (hazard ratio [HR] 1.29 for a 0.05 increase, 95% CI 1.06-1.6; P = 0.011). Progression to T1D was best predicted by a combined model with GRS, number of positive autoantibodies, DPT-1 Risk Score, and age (7-year time-integrated AUC = 0.79, 5-year AUC = 0.73). Higher GRS was significantly associated with increased progression rate from single to multiple positive autoantibodies after adjusting for age, autoantibody type, ethnicity, and sex (HR 2.27 for GRS >0.295, 95% CI 1.47-3.51; P = 0.0002).

CONCLUSIONS

The T1D GRS independently predicts progression to T1D and improves prediction along T1D stages in autoantibody-positive relatives.

Comparative effects of beta 2-adrenoceptor agonists on intracranial self-stimulation, Sidman avoidance, and motor activity in rats

The effects of beta-adrenoceptor agonists were compared in various operant behavioral tasks, particularly intracranial self-stimulation (ICSS). Clenbuterol, salbutamol, and terbutaline all reduced responding by rats that lever-pressed for low stimulation intensities. The effects of clenbuterol in this test were completely reversed by propranolol, and those of salbutamol were partly reversed. Intermediate doses of clenbuterol and salbutamol slowed the initiation of rewarding brain stimulation in a shuttlebox but had little or no effect on the termination latencies. However, higher doses of both drugs lengthened the termination latencies. Motor activity was reduced at doses that attenuated ICSS responding. Complete tolerance occurred within 4 days to the effects of clenbuterol and salbutamol on lever-pressing ICSS and to the effects of clenbuterol on motor activity. The apparent performance deficits induced by these drugs were overcome by more intense motivation. For example, even at high doses, clenbuterol reduced ICSS lever-pressing only partially when animals bar-pressed for high rather than low stimulation intensities. Furthermore, all three drugs failed to alter Sidman avoidance responding at doses up to 100 times those that attenuated ICSS responding. It is concluded that although beta-adrenoceptor agonists cause apparent sedation in rats, this sedation is limited and shows rapid tolerance.

Avoidance and ICSS behavioral models dissociate TL-99 and 3-PPP from dopamine receptor antagonists

The behavioral effects of the putative dopamine autoreceptor agonists, TL-99 and 3-PPP, were explored in animal procedures that reveal highly characteristic effects of neuroleptics currently in clinical use. Sidman avoidance responding in rats was not altered appreciably by doses up to 10 mg/kg TL-99 or 30 mg/kg 3-PPP. Higher doses of TL-99 attenuated Sidman avoidance performance in squirrel monkeys, although 3-PPP had no effect. Lever pressing for intracranial self-stimulation (ICSS) was attenuated in a dose-related fashion by TL-99 and 3-PPP, with relatively shallow dose-response relationships. A low dose of haloperidol (0.03 mg/kg) partly reversed the effects of 3-PPP (3 mg/kg) on lever pressing ICSS, but not those of TL-99 (3 mg/kg). Yohimbine (3 mg/kg) failed to alter the effects of TL-99 at a dose that abolished the suppressant effect of clonidine on ICSS. Analysis of within-session ICSS response decrement patterns indicated that TL-99 reduced ICSS to a greater extent towards the end of the session than during the first 5 min. No such within-session trend was produced by 3-PPP, suggesting that 3-PPP attenuates ICSS by virtue of a performance deficit. Similar conclusions were reached using a shuttlebox task that involved self-regulation of ICSS duration by rats. Therefore, the clinical profile of neuroleptics is unlikely to be mimicked precisely by 3-PPP or TL-99. Clinical trials of DA autoreceptor agonists for antipsychotic efficacy will indicate whether or not avoidance and ICSS behaviors are relevant to the detection of the intrinsic antipsychotic activity of drugs.

Delayed emergence of antidepressant efficacy following withdrawal in olfactory bulbectomized rats

Repeated antidepressant treatment attenuates the step-down passive avoidance deficit which is induced by olfactory bulbectomy in rats. Using a shuttlebox passive avoidance procedure, the effects of antidepressants were investigated after various drug withdrawal intervals. Imipramine, amitriptyline, doxepin, bupropion and mianserin were effective at 48 and usually 72 hours after withdrawal, but no significant attenuation of the deficit was seen 4 hours after withdrawal from any antidepressant tested. At least 4 to 7 days of imipramine treatment were required for efficacy. A high dose of d-amphetamine (5 mg/kg) produced similar results while tranylcypromine and haloperidol were inactive at all withdrawal intervals tested. The olfactory bulbectomy syndrome may reflect functional serotonin deficiency, which would be ameliorated through antidepressant-induced alterations in serotonin receptor sensitivity.

Differential reversal of various dopamine antagonists by anticholinergics in Sidman avoidance: possible relationship to adrenergic blockade

Various dopamine receptor antagonists have divergent clinical and neurochemical properties. The relative ability of anticholinergics (benztropine and scopolamine) to reverse these drugs was assessed in squirrel monkeys and rats performing a Sidman avoidance task. In monkeys, benztropine markedly attenuated the effects of oxiperomide, metoclopramide, halopemide, tiapride and mezilamine as well as haloperidol. Chlorpromazine and fluphenazine were antagonized to a moderate extent; thioridazine and perlapine were not antagonized; and clozapine was actually potentiated by benztropine. In the rat, benztropine antagonized haloperidol strongly but reversed fluphenazine, thioridazine or clozapine only weakly or not at all. The overall effects of scopolamine in both species were similar to those of benztropine. The dopamine receptor antagonists that were most completely reversed by benztropine were found to inhibit 3H-spiroperidol more strongly than 3H-WB-4101 binding in calf caudate, while the reverse was true for drugs that were antagonized only moderately or not at all by benztropine. These results support a previous suggestion that anticholinergic reversal is less marked against dopamine antagonists with alpha-adrenergic blocking properties. Benztropine reversal of experimental dopamine receptor antagonists in the squirrel monkey Sidman avoidance test may contribute to their preclinical characterization.