Adolescents’ Use of Free Time and Associations with Substance Use from 1991 to 2019

Background: Understanding time trends in risk factors for substance use may contextualize and explain differing time trends in substance use. Methods: We examined data (N = 536,291; grades 8/10/12) from Monitoring the Future, years 1991-2019. Using Latent Profile Analyses, we identified six time use patterns: one for those working at a paid job and the other five defined by levels of socialization (low/high) and engagement in structured activities like sports (engaged/disengaged), with the high social/engaged group split further by levels of unsupervised social activities. We tested associations between time use profiles and past two-week binge drinking as well as past-month alcohol use, cigarette use, cannabis use, other substance use, and vaping. We examined trends and group differences overall and by decade (or for vaping outcomes, year). Results: Prevalence of most substance use outcomes decreased over time among all groups. Cannabis use increased, with the largest increase in the group engaged in paid employment. Vaping substantially increased, with the highest nicotine vaping increase in the high social/engaged group with less supervision and the highest cannabis vaping increase in the highly social but otherwise disengaged group. Substance use was lowest in the low social groups, highest in the high social and employed groups. Conclusions: While alcohol, cigarette, and other substance use have declined for all groups, use remained elevated given high levels of social time, especially with low engagement in structured activities or low supervision, or paid employment. Cannabis use and vaping are increasing across groups, suggesting the need for enhanced public health measures.</p

Contaminant levels (ng/g wt) in the sera of obese JCR rats treated with vehicle (V) or high dose (H) NCM with (E) or without (W) co-exposure to ethanol.

<p>n = 7–8, means ±SEM, 2-way ANOVA with Tukey's post-hoc test.</p>a<p>denotes statistically significant difference between vehicle (V) control and high dose (H) groups at p<0.05.</p><p>Contaminant levels (ng/g wt) in the sera of obese JCR rats treated with vehicle (V) or high dose (H) NCM with (E) or without (W) co-exposure to ethanol.</p

Lipid contents and contaminant levels (ng/g wt) in the liver of obese JCR rats dosed with vehicle or NCM and treated with or without ethanol.

<p><i>n</i> = 7–8, means ± SEM, 2-way ANOVA with Tukey's post-hoc test.</p>a<p>denotes statistically significant difference between vehicle (V) control and high dose (H) groups at p<0.001.</p>b<p>denotes statistically significant difference between OWV and OEV, and between OWH and OEH groups at p<0.001.</p><p>Lipid contents and contaminant levels (ng/g wt) in the liver of obese JCR rats dosed with vehicle or NCM and treated with or without ethanol.</p

Pathways of hepatic cholesterol and Coenzyme Q₁₀ (CoQ10) biosynthesis in liver.

<p>Pathways of hepatic cholesterol and Coenzyme Q₁₀ (CoQ10) biosynthesis in liver.</p

NCM treatment diminishes the activity and expression Complexes IV and V of the respiratory chain, which is associated with increased hepatic CYP2E1 protein levels.

<p><b>A</b>) Measurement of the specific activities of Complex I (NADH:ubiquinone oxidoreductase) and Complex IV (cytochrome C oxidase) in liver homogenate. For Complex I, activities were ascertained by measuring the consumption of NADH. Complex IV activities were determined by measuring the consumption of Cyt C. <i>n</i> = 5, means ±SEM. <b>B</b>) Immunoblot analysis of respiratory complex protein content. Different respiratory complex subunits were detected simultaneously using OXPHOS MitoProfile antibodies. Membranes were then stripped and probed for GAPDH. Blots were quantified using ImageJ software and values were normalized to GAPDH loading control levels. <i>n</i> = 3, means ±SEM. <b>C</b>) Immunoblot analysis of CYP2E1 protein levels. Membranes were stripped and probed for GAPDH. Blots were quantified using ImageJ software and values were normalized to GAPDH loading control levels. <i>n</i> = 3, means ±SEM. Two-way ANOVA with Tukey's post-hoc test. *, or ^# and **** or ^#### denotes P<0.05, P<0.0001 respectively. * denotes statistical comparison between vehicle control (V) and high dose (H) and ^# denotes statistical comparison between water (W) and ethanol (E) treated groups. OWV; obese water vehicle, OWH; obese water high dose, OEV; obese ethanol vehicle, OEH; obese ethanol high dose.</p

NCM exposure increases hepatic creatine kinase activity and total ATPase activity, which is associated with decreases in hepatic ABCA1, CD36, and L-FABP protein expression and circulating levels of cholesterol and triglycerides.

<p><b>A</b>). Measurement of the specific activities of pyruvate kinase, creatine kinase, and total MDR ATPases in liver homogenate. For pyruvate kinase, activities were ascertained by measuring the consumption of NADH. Creatine kinase activities were measured by ADP production. <i>n</i> = 5, means ±SEM. Total MDR ATPases activities were measured using BD Gentest ATPase Assay kit. <b>B</b>) Immunoblot analysis of ABCA1 and ApoB-100 protein levels. Membranes were stripped and probed for GAPDH. Blots were quantified using ImageJ software and values were normalized to GAPDH loading control levels. <i>n</i> = 3, means ±SEM. <b>C</b>) Hepatic CD36 and L-FABP levels were measured using ELISA kits from MyBioSource. <i>n</i> = 6, means±SEM. <b>D</b>) Serum cholesterol and triglycerides levels were measured using the Hitachi Model 917 Multichannel Analyzer. <i>n</i> = 5, means ±SEM. Two-way ANOVA with Tukey's post-hoc test. *, **, and *** denotes P<0.05, 0.01 and 0.001 respectively. * denotes statistical comparison between vehicle control (V) and high dose (H) and ^# denotes statistical comparison between water (W) and ethanol (E) treated groups. OWV; obese water vehicle, OWH; obese water high dose, OEV; obese ethanol vehicle, OEH; obese ethanol high dose.</p

Impact of NCM treatment on liver physiology and fatty acid profile in obese JCR rats treated with or without ethanol.

<p>A) Involvement of mitochondria in hepatic lipid biosynthesis and degradation. <i>1</i>. pyruvate enters into mitochondria and is converted to acetyl-CoA in the matrix. <i>2</i>. Following the synthesis of citric acid it is exported to the cytosol from the matrix and cleaved to reproduce acetyl-CoA. <i>3</i>. Acetyl-CoA is carboxylated and then utilized for the synthesis of fatty acids which then esterify glycerol to produce triglycerides. <i>4</i>. Lipids enter the matrix and are oxidized to acetyl-CoA. <i>5</i>. Acetyl-CoA enters the TCA cycle and produces NADH which then drives oxidative phosphorylation. E: electron transport flavoprotein-ubiquinone oxidoreductase, CTP: citrate transport protein, MCT: monocarboxylate transporter, CACT: carnitine:acyl-carntine transporter. B) Liver weights, <i>n</i> = 8, means ±SEM, and pathological grading of liver hypertrophy. C) Oil red staining of lipid droplets in liver section. D) Total number of lipid vacuoles and quantification of lipid vacuole diameter. Lipid droplets number and diameter were determined using Axion Vision software. <i>n</i> = 6, means ±SEM. E) Hepatic saturated fatty acid, monounsaturated fatty acid, and polyunsaturated fatty acid levels. Fatty acids were extracted and measured by GC-MS. <i>n</i> = 8, means ±SEM. Two-way ANOVA with Tukey's post-hoc test. * denotes statistical comparison between vehicle control (V) and high dose (H) and ^# denotes statistical comparison between water (W) and ethanol (E) treated groups. * or ^#, **, and *** indicate significant difference at p<0.05, 0.02, and 0.001, respectively. OWV; obese water vehicle, OWH; obese water high dose, OEV; obese ethanol vehicle, OEH; obese ethanol high dose.</p

Hepatic adenylate and TCA cycle metabolite levels in obese JCR rats dosed with vehicle or NCM and treated with or without ethanol.

<p><i>n</i> = 7–8, means ±SEM, 2-way ANOVA with Tukey's post-hoc test.</p>a<p>denotes statistical significance at P<0.001 between vehicle (V) control and high dose (H).</p><p>Hepatic adenylate and TCA cycle metabolite levels in obese JCR rats dosed with vehicle or NCM and treated with or without ethanol.</p