Six months of voluntary alcohol consumption in male cynomolgus macaques reduces intracortical bone porosity without altering mineralization or mechanical properties

Chronic heavy alcohol consumption is a risk factor for low trauma bone fracture. Using a non-human primate model of voluntary alcohol consumption, we investigated the effects of 6 months of ethanol intake on cortical bone in cynomolgus macaques (Macaca fascicularis). Young adult (6.4 ± 0.1 years old, mean ± SE) male cynomolgus macaques (n = 17) were subjected to a 4-month graded ethanol induction period, followed by voluntary self-administration of water or ethanol (4 % w/v) for 22 h/d, 7 d/wk. for 6 months. Control animals (n = 6) consumed an isocaloric maltose-dextrin solution. Tibial response was evaluated using densitometry, microcomputed tomography, histomorphometry, biomechanical testing, and Raman spectroscopy. Global bone response was evaluated using biochemical markers of bone turnover. Monkeys in the ethanol group consumed an average of 2.3 ± 0.2 g/kg/d ethanol resulting in a blood ethanol concentration of 90 ± 12 mg/dl in longitudinal samples taken 7 h after the daily session began. Ethanol consumption had no effect on tibia length, mass, density, mechanical properties, or mineralization (p > 0.642). However, compared to controls, ethanol intake resulted in a dose-dependent reduction in intracortical bone porosity (Spearman rank correlation = -0.770; p < 0.0001) and compared to baseline, a strong tendency (p = 0.058) for lower plasma CTX, a biochemical marker of global bone resorption. These findings are important because suppressed cortical bone remodeling can result in a decrease in bone quality. In conclusion, intracortical bone porosity was reduced to subnormal values 6 months following initiation of voluntary ethanol consumption but other measures of tibia architecture, mineralization, or mechanics were not altered.

Effects of repeated alcohol abstinence on within-subject prefrontal cortical gene expression in rhesus macaques

Male rhesus monkeys (n = 24) had a biopsy of prefrontal cortical area 46 prior to chronic ethanol self-administration (n = 17) or caloric control (n = 7). Fourteen months of daily self-administration (water vs. 4% alcohol, 22 h access/day termed "open-access") was followed by two cycles of prolonged abstinence (5 weeks) each followed by 3 months of open-access alcohol and a final abstinence followed by necropsy. At necropsy, a biopsy of Area 46, contralateral to the original biopsy, was obtained. Gene expression data (RNA-Seq) were collected comparing biopsy/necropsy samples. Monkeys were categorized by drinking status during the final post-abstinent drinking phase as light (LD), binge (BD), heavy (HD) and very heavy (VHD drinkers). Comparing pre-ethanol to post-abstinent biopsies, four animals that converted from HD to VHD status had significant ontology enrichments in downregulated genes (necropsy minus biopsy n = 286) that included immune response (FDR < 9 × 10-7) and plasma membrane changes (FDR < 1 × 10-7). Genes in the immune response category included IL16 and 18, CCR1, B2M, TLR3, 6 and 7, SP2 and CX3CR1. Upregulated genes (N = 388) were particularly enriched in genes associated with the negative regulation of MAP kinase activity (FDR < 3 × 10-5), including DUSP 1, 4, 5, 6 and 18, SPRY 2, 3, and 4, SPRED2, BMP4 and RGS2. Overall, these data illustrate the power of the NHP model and the within-subject design of genomic changes due to alcohol and suggest new targets for treating severe escalated drinking following repeated alcohol abstinence attempts.

Long-term drinking stability in the open-access self-administration monkey model

The Non-Human Primate (NHP) model for the study of Alcohol Use Disorders (AUD) as developed in our laboratories is critical to our understanding of the pathophysiology of voluntary, chronic, ethanol consumption. Previous work in this model established categories of ethanol consumption that parallel reported categories of human consumption across a spectrum spanning low drinking, binge drinking, heavy drinking, and very heavy drinking, albeit at generally higher daily intakes across categories than documented in people. Original categories assigned to ethanol consumption patterns were established using a limited cohort of rhesus macaques. This study revisits the validity of categorical drinking using an additional 28 monkeys. In addition to finding categorical representations consistent with the original 2014 report, our findings demonstrate that drinking categories remain stable across the observed 12 months of nearly consistent access to ethanol (22 h/day), termed "open access". Animals occupying the two ends of the spectrum, "low" and "very heavy" drinkers, exhibit the largest stability. The findings also indicate a slight escalatory drift over time, with very heavy drinking animals experiencing fatigue near the end of open access.

Ethanol alters the relationship between IGF-1 and bone turnover in male macaques

Insulin-like growth factor 1 (IGF-1) influences bone turnover. Transient decreases in IGF-I levels and/or bioavailability may contribute to the detrimental effects of alcohol on bone. The goals of this non-human primate study were to i) evaluate the 20-h response of bone turnover markers to ethanol consumption and ii) assess how ethanol consumption influences the relationship between IGF-1 and these markers. Osteocalcin (bone formation), carboxyterminal cross-linking telopeptide of type 1 collagen (CTX, bone resorption), IGF-1, and IGF binding protein 1 (IGFBP-1) were measured in plasma from male rhesus macaques (N = 10, 8.4 ± 0.3 years) obtained at 12:00, 16:00, and 06:00 h during two phases: pre-ethanol (alcohol-naïve) and ethanol access. During the ethanol access phase, monkeys consumed 1.5 g/kg/day ethanol (4% w/v) beginning at 10:00 h. Osteocalcin and CTX were lower, and the ratio of osteocalcin to CTX was higher at each time point during ethanol access compared to the pre-ethanol phase. Pre-ethanol marker levels did not vary across time points, but markers varied during ethanol access. IGF-1 levels, but not IGFBP-1 levels, varied during the pre-ethanol phase. In contrast, IGF-1 levels were stable during ethanol access but IGFBP-1 levels varied. There were positive relationships between IGF-1 and turnover markers during the pre-ethanol phase, but not during ethanol access. In conclusion, chronic ethanol consumption reduces levels of bone turnover markers and blocks the normal positive relationship between IGF-1 and turnover markers and alters the normal relationship between IGF-1 and IGFBP-1. These findings support the hypothesis that chronic alcohol consumption leads to growth hormone/IGF-1 resistance.

Impact of putamen inhibition by DREADDs on schedule-induced drinking in rhesus monkeys

The putamen is a nucleus within the sensory-motor striatal network that is involved in automatic, habitual actions. Schedule-induced polydipsia (SIP) is highly automated behavior, reliably occurring under intermediate interval schedules of reinforcement. The effect of putamen inhibition in mediating SIP of water and ethanol (4% w/v) under a Fixed Time 5-min (FT-5 min) schedule for food delivery was tested in 12 rhesus monkeys (6 male, 6 female). Water and ethanol SIP sessions ended after set volumes were consumed. Baseline patterns of SIP intake differed between water and ethanol SIP in volume but not in pattern of drinking. Activation of the designer receptor exclusively activated by designer drug (DREADD: hM4Di) with deschloroclozapine (DCZ; 300 μg/kg, i.m.) administered 30 min prior to the onset of the SIP session, for four consecutive sessions. DCZ administration increased the postpellet drink volume and reduced the time to drink both water and ethanol. Although the effect of DCZ treatment was similar for increasing SIP with either water or ethanol, post-DCZ return to baseline SIP rates of differed, perhaps highlighting the effect of a state dependency with ethanol SIP. Overall, the study shows that targeting the putamen with the inhibitory DREADD produces a reversible, reproducible and reliable increase in adjunctive drinking.

Profiling of extracellular vesicle-bound miRNA to identify candidate biomarkers of chronic alcohol drinking in nonhuman primates

BACKGROUND

Long-term alcohol drinking is associated with numerous health complications including susceptibility to infection, cancer, and organ damage. However, due to the complex nature of human drinking behavior, it has been challenging to identify reliable biomarkers of alcohol drinking behavior prior to signs of overt organ damage. Recently, extracellular vesicle-bound microRNAs (EV-miRNAs) have been found to be consistent biomarkers of conditions that include cancer and liver disease.

METHODS

In this study, we profiled the plasma EV-miRNA content by miRNA-Seq from 80 nonhuman primates after 12 months of voluntary alcohol drinking.

RESULTS

We identified a list of up- and downregulated EV-miRNA candidate biomarkers of heavy drinking and those positively correlated with ethanol dose. We overexpressed these candidate miRNAs in control primary peripheral immune cells to assess their potential functional mechanisms. We found that overexpression of miR-155, miR-154, miR-34c, miR-450a, and miR-204 led to increased production of the inflammatory cytokines TNFα or IL-6 in peripheral blood mononuclear cells after stimulation.

CONCLUSION

This exploratory study identified several EV-miRNAs that could serve as biomarkers of long-term alcohol drinking and provide a mechanism to explain alcohol-induced peripheral inflammation.

Effects of graded increases in ethanol consumption on biochemical markers of bone turnover in young adult male cynomolgus macaques

Chronic heavy alcohol use is often associated with reduced bone mineral density and altered bone turnover. However, the dose response effects of ethanol on bone turnover have not been established. This study examined the effects of graded increases of ethanol consumption on biochemical markers of bone turnover in young adult male cynomolgus macaques (Macaca fascicularis). For this study, 6.6-year-old (95% CI: 6.5, 6.7) male macaques were subjected to three 30-day sessions of increased ethanol intake over a 90-day interval. During the first 30 days, the monkeys drank a predetermined volume of ethanol corresponding to 0.5 g/kg/day, followed by 1.0 g/kg/day and 1.5 g/kg/day. Osteocalcin, a marker of bone formation, and carboxyterminal cross-linking telopeptide of type 1 collagen (CTX), a marker of resorption, were measured during each 30-day session. In addition, the ratio of osteocalcin to CTX was determined as a surrogate measure of global turnover balance. Mean osteocalcin decreased by 2.6 ng/mL (1.8, 3.5) for each one-half unit (0.5 g/kg/day) increase in dose (p < 0.001). Mean CTX decreased by 0.13 ng/mL (0.06, 0.20) for each one-half unit increase in dose (p < 0.001). Furthermore, there was an inverse relationship between dose and the ratio of osteocalcin to CTX, such that the mean ratio decreased by 0.9 (0.3, 1.5) for each one-half unit increase in dose (p = 0.01). In summary, male cynomolgus macaques had decreased blood osteocalcin and CTX, and osteocalcin to CTX ratio during the 90-day interval of graded increases in ethanol consumption, indicative of reduced bone turnover and negative turnover balance, respectively. These findings suggest that over the range ingested, ethanol resulted in a linear decrease in bone turnover. Furthermore, the negative bone turnover balance observed is consistent with reported effects of chronic alcohol intake on the skeleton.

Behavioral Flexibility in Alcohol-Drinking Monkeys: The Morning After

BACKGROUND

Heavy alcohol drinking has aspects of inflexible behavior. This study addressed the consequences of chronic alcohol drinking on cognitive and sensory-motor domains of behavioral flexibility in rhesus monkeys.

METHODS

Behavioral flexibility was assessed in 12 monkeys (n = 9, ethanol [EtOH] drinkers) with a set-shifting visual discrimination procedure before alcohol self-administration and while maintaining consumption of 1.5 g/kg/d EtOH. Task performance was assessed in the morning after ~18 hours of drinking 1.5 g/kg, and 1 hour before the next day's drinking session began. The first 10 set-shifting sessions had the original (preethanol) test parameters and were used to determine retention of preethanol performance. Then, an effect of sensory-motor challenge (60% reduction in the size of the discriminative stimuli) on performance was assessed during 10 additional sessions.

RESULTS

There were no average group-dependent differences in the performance between control and EtOH groups at the preethanol time-point. The daily consumption of 1.5 g/kg/d produced binge alcohol intakes in 7 of 9 monkeys (blood EtOH concentration [BEC ≥ 80 mg/dl]). Chronic daily intakes of 1.5 g/kg had no effect on retention of the task in the sober state. However, when challenged with a reduction in the size of the stimuli, daily 1.5 g/kg EtOH resulted in a decrement in performance due to an increase in the number of errors.

CONCLUSIONS

Rhesus monkeys consuming 1.5 g/kg alcohol daily perform equally as could as control monkeys in retention of a well-learned cognitive task. However, this pattern of daily alcohol intake robustly decreased the ability to flexibly adjust behavior when confronted with novel changes to perceptual stimuli.

Low cognitive flexibility as a risk for heavy alcohol drinking in non-human primates

Chronic alcohol abuse is frequently considered a habitual or inflexible behavior; however, measures of pre-existing cognitive flexibility prior to initiation of alcohol use are usually not available. This study used rhesus monkeys and an attentional set-shifting task to investigate whether pre-existing cognitive flexibility would predict increased risk for heavy alcohol drinking. As previously reported, monkeys were given 30 daily set-shifting sessions prior to alcohol access. These sessions consisted of the same sequence of eight unique visual discriminations (sets) of two objects that varied on two dimensions (shapes and colors). The ratio of errors per trials, session duration, and maximum set reached were primary dependent variables from each session and were used to compose a session performance index (PI) that ranged from a low performance PI of 31 to an optimal performance PI of 247. Here, animals underwent an alcohol induction period followed by 22 weeks of daily (22-h) self-administration sessions with free access to water and alcohol. Based on average daily alcohol intake during 22 weeks of 22-h/day access, the monkeys were categorized as non-heavy (mean = 2.0 ± 0.3 g/kg/day; n = 3) and heavy (mean = 3.3 ± 0.5 g/kg/day; n = 6) drinkers. The two groups diverged in performance on the set-shifting task across the 30 pre-alcohol sessions, and at the end of the pre-alcohol testing, the group average PI was 216 ± 27 and 137 ± 71 for the future non-heavy and heavy drinkers, respectively. The data show that low cognitive flexibility assessed with a set-shifting procedure was predictive of future classification as a heavy alcohol drinker. The data highlight individual differences in both cognitive flexibility and in alcohol self-administration in this population of rhesus monkeys.

Ranking Cognitive Flexibility in a Group Setting of Rhesus Monkeys with a Set-Shifting Procedure

Attentional set-shifting ability is an executive function underling cognitive flexibility in humans and animals. In humans, this function is typically observed during a single experimental session where dimensions of playing cards are used to measure flexibility in the face of changing rules for reinforcement (i.e., the Wisconsin Card Sorting Test (WCST)). In laboratory animals, particularly non-human primates, variants of the WCST involve extensive training and testing on a series of dimensional discriminations, usually in social isolation. In the present study, a novel experimental approach was used to assess attentional set-shifting simultaneously in 12 rhesus monkeys. Specifically, monkeys living in individual cages but in the same room were trained at the same time each day in a set-shifting task in the same housing environment. As opposed to the previous studies, each daily session began with a simple single-dimension discrimination regardless of the animal’s performance on the previous session. A total of eight increasingly difficult, discriminations (sets) were possible in each daily 45 min session. Correct responses were reinforced under a second-order schedule of flavored food pellet delivery, and criteria for completing a set was 12 correct trials out of a running total of 15 trials. Monkeys progressed through the sets at their own pace and abilities. The results demonstrate that all 12 monkeys acquired the simple discrimination (the first set), but individual differences in the ability to progress through all eight sets were apparent. A performance index (PI) that encompassed progression through the sets, errors and session duration was calculated and used to rank each monkey’s performance in relation to each other. Overall, this version of a set-shifting task results in an efficient assessment of reliable differences in cognitive flexibility in a group of monkeys.

Monkey alcohol tissue research resource: banking tissues for alcohol research

BACKGROUND

An estimated 18 million adults in the United States meet the clinical criteria for diagnosis of alcohol abuse or alcoholism, a disorder ranked as the third leading cause of preventable death. In addition to brain pathology, heavy alcohol consumption is comorbid with damage to major organs including heart, lungs, liver, pancreas, and kidneys. Much of what is known about risk for and consequences of heavy consumption derive from rodent or retrospective human studies. The neurobiological effects of chronic intake in rodent studies may not easily translate to humans due to key differences in brain structure and organization between species, including a lack of higher-order cognitive functions, and differences in underlying prefrontal cortical neural structures that characterize the primate brain. Further, rodents do not voluntarily consume large quantities of ethanol (EtOH) and they metabolize it more rapidly than primates.

METHODS

The basis of the Monkey Alcohol Tissue Research Resource (MATRR) is that nonhuman primates, specifically monkeys, show a range of drinking excessive amounts of alcohol (>3.0 g/kg or a 12 drink equivalent per day) over long periods of time (12 to 30 months) with concomitant pathological changes in endocrine, hepatic, and central nervous system (CNS) processes. The patterns and range of alcohol intake that monkeys voluntarily consume parallel what is observed in humans with alcohol use disorders and the longitudinal experimental design spans stages of drinking from the EtOH-naïve state to early exposure through chronic abuse. Age- and sex-matched control animals self-administer an isocaloric solution under identical operant procedures.

RESULTS

The MATRR is a unique postmortem tissue bank that provides CNS and peripheral tissues, and associated bioinformatics from monkeys that self-administer EtOH using a standardized experimental paradigm to the broader alcohol research community.

CONCLUSIONS

This resource provides a translational platform from which we can better understand the disease processes associated with alcoholism.

The effects of age at the onset of drinking to intoxication and chronic ethanol self-administration in male rhesus macaques

RATIONALE

Consumption of alcohol begins during late adolescence in a majority of humans, and the greatest drinking occurs at 18-25 years then decreases with age.

OBJECTIVES

The present study measured the differences in ethanol intake in relation to age at the onset of ethanol access among nonhuman primates to control for self-selection in humans and isolate age effects on heavy drinking.

METHODS

Male rhesus macaques were assigned first access to ethanol during late adolescence (n = 8), young adulthood (n = 8), or early middle age (n = 11). The monkeys were induced to drink ethanol (4 % w/v in water) in increasing doses (water then 0.5, 1.0, 1.5 g/kg ethanol) using a fixed-time (FT) 300-s schedule of food delivery, followed by 22 h/day concurrent access to ethanol and water for 12 months. Age-matched controls consumed isocaloric maltose-dextrin solution yoked to the late adolescents expected to be rapidly maturing (n = 4).

RESULTS

Young adult monkeys had the greatest daily ethanol intake and blood-ethanol concentration (BEC). Only late adolescents escalated their intake (ethanol, not water) during the second compared to the first 6 months of access. On average, plasma testosterone level was consistent with age differences in maturation and tended to increase throughout the experiment more for control than ethanol-drinking adolescent monkeys.

CONCLUSIONS

Young adulthood in nonhuman primates strongly disposes toward heavy drinking, which is independent of sociocultural factors present in humans. Ethanol drinking to intoxication during the critical period of late adolescence is associated with escalation to heavy drinking.

Diurnal pituitary-adrenal activity during schedule-induced polydipsia of water and ethanol in cynomolgus monkeys (Macaca fascicularis)

RATIONALE

Intermittent delivery of an important commodity (e.g., food pellets) generates excessive behaviors as an adjunct to the schedule of reinforcement (adjunctive behaviors) that are hypothesized to be due to conflict between engaging and escaping a situation where reinforcement is delivered, but at suboptimal rates.

OBJECTIVES

This study characterized the endocrine correlates during schedule-induced polydipsia of water and ethanol using a longitudinal approach in non-human primates.

METHODS

Plasma adrenocorticotropic hormone (ACTH) and cortisol were measured in samples from awake cynomolgus monkeys (Macaca fascicularis, 11 adult males) obtained at the onset, mid-day, and offset of their 12-h light cycle. The monkeys were induced to drink water and ethanol (4 % w/v, in water) using a fixed time (FT) 300-s interval schedule of pellet delivery. The induction fluid changed every 30 sessions in the following order: water, 0.5 g/kg ethanol, 1.0 g/kg ethanol, and 1.5 g/kg ethanol. Following induction, ethanol and water were concurrently available for 22 h/day.

RESULTS

The FT 300-s schedule gradually increased ACTH, but not cortisol, during water induction to a plateau sustained throughout ethanol induction in every monkey. Upon termination of the schedule, ACTH decreased to baseline and cortisol below baseline. Diurnal ACTH and cortisol were unrelated to the dose of ethanol, but ACTH rhythm flattened at 0.5 g/kg/day and remained flattened.

CONCLUSIONS

The coincidence of elevated ACTH with the initial experience of drinking to intoxication may have altered the mechanisms involved in the transition to heavy drinking.

Classification of alcohol abuse by plasma protein biomarkers

BACKGROUND

Biochemical diagnostics of ethanol intake would improve alcohol abuse treatment and have applications in clinical trial and public safety settings. Self-reporting of alcohol use has clinical utility but lacks the desired reliability. Previously, proposed single-analyte biochemical tests of alcohol intake suffer from low sensitivity and specificity or examine only acute drinking and have therefore seen limited clinical use.

METHODS

To address this unmet need, plasma protein biomarker discovery and validation were performed with an alcohol self-administering nonhuman primate model system to develop a diagnostic that accurately classifies subjects into nondrinking, nonabusive drinking, and abusive drinking categories.

RESULTS

A 17-plasma protein panel was determined that correctly classifies abusive drinking with 100% sensitivity and also differentiates any level of drinking from alcohol abstinence with 88% accuracy.

CONCLUSIONS

The biomarker panel reflects changes in multiple organ systems and suggests robust changes in the plasma proteome with drinking that might serve as a sensitive and specific diagnostic test. The specific plasma proteins altered with alcohol self-administration might represent indicators of alcohol-induced stress on a variety of organ systems.

Drinking typography established by scheduled induction predicts chronic heavy drinking in a monkey model of ethanol self-administration

BACKGROUND

We have developed an animal model of alcohol self-administration that initially employs schedule-induced polydipsia (SIP) to establish reliable ethanol consumption under open access (22 h/d) conditions with food and water concurrently available. SIP is an adjunctive behavior that is generated by constraining access to an important commodity (e.g., flavored food). The induction schedule and ethanol polydipsia generated under these conditions affords the opportunity to investigate the development of drinking typologies that lead to chronic, excessive alcohol consumption.

METHODS

Adult male cynomolgus monkeys (Macaca fascicularis) were induced to drink water and 4% (w/v in water) ethanol by a Fixed-Time 300 seconds (FT-300 seconds) schedule of banana-flavored pellet delivery. The FT-300 seconds schedule was in effect for 120 consecutive sessions, with daily induction doses increasing from 0.0 to 0.5 g/kg to 1.0 g/kg to 1.5 g/kg every 30 days. Following induction, the monkeys were allowed concurrent access to 4% (w/v) ethanol and water for 22 h/day for 12 months.

RESULTS

Drinking typographies during the induction of drinking 1.5 g/kg ethanol emerged that were highly predictive of the daily ethanol intake over the next 12 months. Specifically, the frequency in which monkeys ingested 1.5 g/kg ethanol without a 5-minute lapse in drinking (defined as a bout of drinking) during induction strongly predicted (correlation 0.91) subsequent ethanol intake over the next 12 months of open access to ethanol. Blood ethanol during induction were highly correlated with intake and with drinking typography and ranged from 100 to 160 mg% when the monkeys drank their 1.5 g/kg dose in a single bout. Forty percent of the population became heavy drinkers (mean daily intakes >3.0 g/kg for 12 months) characterized by frequent "spree" drinking (intakes >4.0 g/kg/d).

CONCLUSION

This model of ethanol self-administration identifies early alcohol drinking typographies (gulping the equivalent of 6 drinks) that evolve into chronic heavy alcohol consumption in primates (drinking the equivalent of 16 to 20 drinks per day). The model may aid in identifying biological risks for establishing harmful alcohol drinking.