HIV-positive people using crystal methamphetamine have lower CD4 cell counts than their HIV-positive counterparts who don’t use the drug, according to new data reported at the fourth IAC Conference on HIV Pathogenesis, Treatment and Prevention (IAS 2007) in Sydney. The study is among the first to show a possible clinically significant effect of methamphetamine use on the health of the immune system in people infected with HIV.
While much has been written about meth use and its association with unsafe sexual activity and HIV transmission, less is known about the effects of the drug on immune function in people already infected with the virus.
Most studies completed to date have been test-tube or rodent experiments. One test-tube study published in 1994 suggested that meth can reduce levels of interleukin-2, a cytokine that promotes immune function in the body and plays a significant role in the immune system's response to HIV infection.
The drug was also shown to decrease the function of CD8 cells, which play a role in the control of HIV replication, particularly during the early stages of infection.
Another study involving retrovirus-infected rats, published in 2002, demonstrated a significant increase in tumor necrosis factor (TNF), an inflammatory cytokine that can negatively affect the immune system's response to HIV and increase viral replication.
While these studies pave the way for further investigation, they do not conclusively answer whether methamphetamine speeds up immune suppression in HIV-infected people.
To explore this further, Jason Barbour, PhD, and his colleagues at the University of California, San Francisco, conducted a pilot study to describe HIV disease parameters associated with the use of the drug.
His group recruited a total of 28 HIV-positive adults, 19 of whom had used meth within 72 hours prior to enrollment (confirmed using a urine drug screen). The remaining nine did not have evidence of recent meth use.
Unfortunately, the study’s poster presentation did not specify if the recent users used the drug chronically or heavily, nor was it clear if those who did not test positive for the drug had a history of use.
The average age at enrollment was 40 years and all of the study subjects were men. Two of the recent meth users and one of the methamphetamine-negative participants were on antiretroviral therapy at the time of joining the study.
Regrettably, the authors did not report the average length of time the volunteers had been infected with HIV prior to joining the study, or if there were any differences between the two groups in this regard.
The recent meth users had a lower average CD4 count compared to the methamphetamine-negative participants: 362 vs. 551 cells respectively. This difference was statistically significant, meaning that it wasn’t likely due to chance.
The recent meth users also tended to have higher viral loads (4.38 log vs. 3.86 log), although this difference was not statistically significant.
Using phenotypic drug resistance testing, Dr. Barbour’s group noted that HIV from the recent meth users was more sensitive to zidovudine (found in Retrovir, Combivir and Trizivir). While the significance of this finding isn’t clear, it possibly reflects a shorter duration of prior antiretroviral therapy use among the methamphetamine-positive participants.
Surprisingly, HIV’s replication capacity—a measure of the virus’s fitness or virulence—was lower in the recent methamphetamine users (83 percent) compared to the methamphetamine-negative volunteers (113 percent).
Three of the methamphetamine-positive patients had dual-tropic virus—a potential indicator of more rapid disease progression—compared to none of the methamphetamine-negative participants.
Running the data through a mathematical model, Dr. Barbour’s group found that recent meth use was the strongest predictor of lower CD4 cell counts in the study.
Additional studies, the study authors conclude, are needed to better understand the possible association between meth use, CD4 cell depletion and other markers of health.
Source:
Barbour J, Philip S, Cohen A, et al. Methamphetamine using HIV-1+ adults have lower CD4+ T cell counts than HIV-1+ adults who do not use methamphetamine [Abstract MOPEB095]. Fourth IAS Conference on HIV Pathogenesis, Treatment and Prevention, Sydney, 2007.
