Is serum brain-derived neurotrophic factor related to craving for or use of alcohol, cocaine, or methamphetamine?

Participants

Volunteers were recruited through pamphlets and advertisements placed in local community-based social service agencies providing counseling and addiction treatment. All volunteers had adequate opportunities to ask researchers questions about the study during the consenting process and make an informed decision whether or not to participate. All eligible subjects provided written informed consent to participate in the study and received copies of the consent form and the Certificate of Confidentiality.

Inclusion/exclusion criteria

Eligible participants were 20–60 years old, of all ethnicities, and met current Axis I Diagnostic and Statistical Manual of Mental Disorders-IV (DSM-IV) diagnosis for alcohol, cocaine, or methamphetamine dependence. Subjects were English-speaking and had at least an 8th grade education. Volunteers were excluded if they had any current co-morbid substance dependence other than alcohol, cocaine or methamphetamine. Other exclusion criteria were those who had a brain injury or stroke, mental retardation, dementia, HIV/ AIDS, or those who tested positive for current alcohol or any drug use as demonstrated by a breathalyzer and a 12-panel urine drug screen (Redwood Toxicology Laboratory, Santa Rosa, California). Subjects were required to abstain from food and exercise for three to four hours prior to study participation.

Clinical assessments

Once sociodemographic information was recorded, participants were interviewed using the Mini-International Neuropsychiatric Interview (MINI) to confirm diagnoses and age of onset for lifetime mood and substance use disorders.¹⁸ The MINI is based on Axis I DSM-IV diagnostic criteria and has an acceptable range of reliability for alcohol and drug dependence (a = 0.60 to 0.74) and for psychiatric disorders (a = 0.45−0.59).¹⁸ In addition to its reliability for both substance use and psychiatric disorders, the MINI was used for its brevity (15 minutes) which was more feasible for us to use in our community-based research sample than the time-intensive Structured Clinical Interview for DSM-IV.

The 10-item Cocaine Craving Questionnaire-Brief ¹⁹ was modified to measure subjective alcohol, cocaine and methamphetamine cravings. This instrument measures craving as the lack of control of using, the desire, intention, planning, and anticipation of using to quell withdrawal symptoms.^19,20 This questionnaire is scored using a Likert scale from 1 to 7 with 1 representing ‘strongly disagree’ and 7 being ‘strongly agree’. Scores are additive. The maximum total score indicating severe cravings is 70 while a score of 10 indicates that no craving is present. This craving instrument was used due to its brevity, high internal reliability (α = 0.90) and concurrent validity.¹⁹ In addition, previous studies using this questionnaire found this instrument highly effective in measuring methamphetamine and alcohol cravings.^21,22

Serum BDNF analysis

All testing and sample handling procedures were performed using standard bio-safety techniques and disposal requirements as required by the University of North Texas Health Science Center. Blood specimens were collected only from study participants who satisfied eligibility requirements and tested negative for all drugs and alcohol. Those who had negative toxicology results were allowed to give blood and continue participation in the study. Blood samples were taken between the hours of 9:30 am–10:30 am. Subjects were required to abstain from food or drink for a period of 2–3 hours prior to providing blood samples.

Subjects were placed in a comfortable upright resting position while venous blood samples (30 mL) were drawn from the antecubital vein into Vacutainer^® (BD, Franklin Lakes, NJ) tubes using a butterfly syringe. Blood samples were then centrifuged at 1000 rpm for 5 minutes after collection and serum specimens were stored at −80°C until immunoassays were performed. BDNF was measured according to directions of Promega BDNF Emax Immunoassay System Kit (Promega, Madison, WI, USA). The serum samples were analyzed together in duplicate batch runs to assure an acceptable range of intra-assay coefficient of variation (~7.1%) was obtained. Serum BDNF levels are stated as the mean average with standard deviations reported in picograms per milliliter.

Sociodemographic and substance use variables

There were no significant differences in gender distribution among the three substance groups. However, there was a significant race difference as no African-American subjects used methamphetamines: χ² (6, n = 64) = 19.44; P = 0.003. Age among the three subject groups significantly differed (F_(2,61) = 11.83, P = 0.001). The age difference is reflected in the mean years of use among the substance groups (F_(2,61) = 4.87, P = 0.006). To control for multiple comparisons, Tukey post hoc analyses showed that years of substance use significantly different between alcohol and methamphetamine (P = 0.012) and between alcohol and cocaine (P = 0.009). A near significant trend was noted in the mean number of abstinent days that differed among alcohol, cocaine, and methamphetamine groups (F_(2,61) = 4.50, P = 0.056).

Craving

Table 1 shows a significant difference in the mean craving score among the three substance groups (F_(2,61) = 4.50, P = 0.015). To be more specific, we used Tukey post hoc comparisons and found a significant difference in craving between the alcohol and cocaine groups (P = 0.012). There were no statistical differences in craving between alcohol and methamphetamine (P = 0.756) or between cocaine and methamphetamine groups (P = 0.162). To examine the general effect of demographic and clinical indices on craving we collapsed the substance groups and analyzed mean craving scores according to race, gender, psychiatric disorder and psychotropic medication groups. Table 2 shows no significant demographic or clinical group differences in craving.

Serum BDNF levels, sociodemographic and clinical indices

Table 2 shows that there was no significant influence of race, gender, psychiatric disorder or psychotropic medication on serum BDNF levels. There were no significant gender differences in serum BDNF levels between men and women (F _(1,62) = 3.36, P = 0.071). Serum BDNF levels did not differ significantly among alcohol, cocaine, and methamphetamine groups (F_{(2, 61)} = 1.02, P = 0.366). We analyzed the influence race, gender, psychiatric disorder or psychotropic medication may have had on serum BDNF levels among the substance groups, but there were no significant differences (P ≥ 0.260). The mean serum BDNF level in methamphetamine abusers and the relationship with number of days’ abstinence was not significant (r = −0.503, P = 0.056). Similarly, BDNF levels in alcohol (r = −0.300, P = 0.128) and cocaine (r = −0.185, P = 0.409) abusers were not significantly related to the number of abstinent days. Thus, we collapsed the cocaine and methamphetamine groups and designated this combined sample as the psychostimulant group.

Study limitations and strengths

The sample size in the present study may be small in comparison to some clinical trials. However, our sample is substantially larger than Huang et al¹⁶ who examined BDNF in persons with alcohol dependence (n = 47), Aydemir et al²⁵ who examined serum BDNF in depressed women (n = 20), or Angelluci et al²⁶ who investigated serum BDNF in chronic cocaine and heroin abusers (n = 45). The available data is limited to only a handful of small clinical studies and much of the BDNF research is preclinical rodent studies. Thus, our data clearly augments the existing literature.

Another potential limitation is not having controlled for the duration, frequency of use, and average dose of alcohol or the psychostimulants among our subject population. While we acknowledge the importance and interest of these measures the ability to control for these variables would have been beyond the scope of this study. However, we were able to clarify the state of dependence as our subjects qualified for DSM-IV criteria for dependence which covers a 12-month period. Therefore under the rubric of DSM-IV dependence general frequency is implied for 12 months.

Another limitation of our study is the heterogeneity of our subject population. We did not have a healthy control group to compare BDNF levels to the alcohol and psychostimulant groups. We also did not exclude subjects based on comorbities, endocrine disorders or class of psychiatric medication which are known factors that influence BDNF.^27–30 In doing so, our enrollment goal would have been significantly reduced. Instead, our sample reflects the typical community-based outpatient that clinicians are most likely to encounter. Thus, our study has strong ecological validity producing data that may be helpful to health professionals and case managers.