Earlier than normal ageing in people living with HIV has been debated for many years. The issue emerged when it became clear that HIV-positive people had an increased burden of cardiovascular disease, cancer and other diseases that are associated with ageing in the general population.
Is this increased exposure to co-morbidities due to an accelerated or an accentuated ageing process? Accelerated ageing can be defined as an age-related decline that arises earlier than expected and increases progressively. Accentuated ageing is an increased burden of age-related damage, that will remain static over time.
A study by Davide De Francesco and colleagues in the 1 February issue of AIDS provides at least partial answers to the question. It shows that age advancement was greater in its HIV-positive participants than in a group of HIV-negative counterparts who had similar lifestyles. And, perhaps not that surprisingly, age advancement was also greater in this group of HIV-negative people than in a group of Dutch blood donors (as explained later, individuals who tend to be unusually healthy).
The originality of this study lies not only in its use of blood donors as a comparison group, but also in the use of a novel combination of biomarkers of ageing.
Chronological ageing and biological ageing
Ageing is defined as a time-dependent (chronological) decline of functional capacity and stress resistance, associated with an increased risk of disability, morbidity or mortality. Its rate can significantly differ from one person to another, depending on many factors, from the genetic to the environmental. Chronological age may therefore not be the best way to measure ageing.
Could biomarkers that reflect age-related changes in body function or composition measure this process more accurately and be used to predict the onset of age-related diseases? In other words, could a measurement of “biological age" be more reliable than chronological age?
Many biomarkers have been proposed by scientists to investigate the association between HIV and ageing. However, because combining several biomarkers may measure biological age more reliably than a single one, De Francesco and his team used an algorithm based on ten biomarkers proposed by MARK-AGE, a large scientific project which has identified biomarkers of ageing across a range of physiological systems, among 3200 people from the general population across Europe.
The ten biomarkers had been selected from 400 candidates as the best predictors of chronological age. When used together, they may estimate biological age. The range from levels of complex gene modification mechanisms (cytosine methylation), to lycopene (plant nutrient linked to heart health and protection against cancer) and A2M (Alpha-2 macroglobulin, a coagulation inhibitor).
The investigators looked at associations between the set of ten biomarkers and:
- Sociodemographic factors (age, sex, ethnicity, sexual orientation, education)
- Lifestyle risk factors (self-reported smoking, alcohol consumption and current recreational drug use)
- Chronic viral co-infections – hepatitis B virus (HBV), hepatitis C virus (HCV) and cytomegalovirus (CMV)
- HIV-related parameters (CD4 and CD8 cell-counts; CD4/CD8 ratio; nadir CD4 < 200/mm3; years since HIV diagnosis, and prior AIDS diagnosis)
- Past or current exposure to specific antiretroviral drugs.
Three population samples: why?
As we have seen, the study included three comparison groups:
- HIV-positive people
- HIV-negative people with a similar lifestyle to the HIV-positive people
- Blood donors.
The 134 HIV-positive and 79 HIV-negative people with similar sociodemographic and lifestyle factors were enrolled in the Co-morbidity in Relation to AIDS cohort (COBRA, a European Union funded cohort that evaluates age-associated non-communicable co-morbidities in persons with HIV). They were recruited from HIV outpatient clinics in Amsterdam and sexual health clinics in London, between 2011 and 2014.
All of these participants were 45 years old or older (over 50 in London). HIV-positive participants had to have an undetectable HIV viral load (< 50 copies/ml) for at least 12 months and be taking antiretrovirals.
A number of people were excluded from the study: individuals of any HIV status who suffered from major depression; had specific neurological diseases, previous severe head injury, a history of cerebral infections, excess alcohol intake, severe psychiatric disease, contraindication to MRI scan or lumbar puncture examination; used intravenous injectable drugs (in the past six months) or took recreational drugs daily (except cannabis).
The 35 blood donors from the Dutch national blood bank were age-matched with all the COBRA participants. They had screened negative for HIV, HBV, HCV, syphilis and human T-lymphotropic virus (HTLV) 1 and 2, as required for blood donations in the Netherlands, and had responded to a questionnaire about their general health, sexual health, medication use, sexual risk behaviour and travel, without raising any concerns about health risk factors.
To summarise the complex study, the investigators wanted to compare ageing, by testing an algorithm of biological markers in two groups who were fairly similar except for HIV, and in blood donors, one of the healthiest groups in the Dutch population. (The blood donors have few inflammatory factors such as viral infections.)
Results: participant characteristics
In terms of age (median 56 years), sex (93% male), years of education, smoking and recreational drug use, all COBRA participants were comparable. There were more persons of black African ethnicity among the HIV-positive participants, who generally reported less alcohol consumption than the HIV-negative participants. The blood donor group included a greater proportion of women than the other two. CMV, chronic HBV and HCV were all more frequent among HIV-positive people than in HIV-negative people. But CMV was also more frequent among the non-blood donor HIV-negative individuals than in blood donors.
All HIV-positive participants had a controlled viral load and were taking antiretrovirals (inclusion criteria). Their median CD4 cell count was 618/mm3 and 31% had had a prior AIDS diagnosis. To allow for an analysis of their potential impact on the ageing process, previous or current use of antiretrovirals was reported, including 28% who had previously taken saquinavir.
Results: age advancement
Typically, some biomarkers considered as negative were observed at higher levels in HIV-positive participants. For example, A2M concentrations (measured only in males) were found to be higher in HIV-positive men than in the non-blood donor HIV-negative controls. In contrast, A2M was significantly lower in blood donors than in both COBRA groups.
N-Glycan peak 6, a polymer playing a key role in cell membranes, and generally considered as a favourable marker, was higher in blood donors than in HIV-positive participants, but not higher than in the non-blood donor HIV-negative group.
Consequently, biological age was significantly greater than chronological age by a mean of 13.2 years in HIV-positive participants, and by a mean of 5.5 years in their non-blood donor HIV-negative counterparts. In contrast, biological age was 7 years lower than chronological age in blood donors.
Compared with blood donors, age advancement was greater in both COBRA groups. In addition, in comparison with the non-blood donor HIV-negative participants, greater age advancement was observed among the HIV-positive participants.
Associations and interpretations
No association was found between age advancement and ethnicity, sexual orientation or lifestyle factors. Associations were observed between an increased age advancement and CMV, chronic HBV, CD4 cell count, CD8 cell count and the CD4/CD8 ratio.
Among the HIV-positive participants, the parameters found to be positively correlated to biological age advancement were the time since HIV diagnosis, the duration of anti-HIV treatment and a nadir CD4 cell count below 200/mm3. There were correlations between age advancement and exposure to antiretrovirals, saquinavir in particular, for which each additional year of exposure represented a 1.39 years increase in age advancement.
A multivariable analysis (which controls for other factors that could influence the results) was conducted of all HIV-parameters, antiretroviral exposures, chronic HBV, total CMV IgG antibodies and CD8 T-cell count. It confirmed the significance of associations between age advancement and only:
- Cumulative exposure to saquinavir (+ 1.2 years biological age per each year of exposure)
- Nadir CD4 cell count below 200/mm3 (+ 3 years)
- Chronic HBV (+ 7.4 years)
- Total anti-CMV IgG antibodies (+ 1.9 years per each log IgG level increase).
Interestingly, current or past smoking did not appear to influence age advancement, but the study authors do not exclude the possibility that their markers may not have been specific enough to capture this factor, especially in a cohort where smoking frequency was low (12 cigarettes smoked per day in the COBRA groups).
The authors also highlight that the reasons why they found a significant association between duration of past exposure to saquinavir and advanced ageing are unclear to them. They were surprised to not obtain comparable results with other protease inhibitors, all known to promote vascular ageing through complex phenomena, and even other drugs such as D4T that induce the greatest mitochondrial toxicities. Therefore, these results should be interpreted with caution.
The finding on the role of CMV and HBV co-infections in advanced ageing, even among people on effective antiretroviral therapy, is easier to interpret. The two viruses may be responsible for premature ageing due to their chronic antigenic stimulation, which induces a systemic immune activation. In particular, CMV reactivation and concurrent immune responses to control infection have been known to be associated with ageing and increased morbidity and mortality in both the general population and people living with HIV.
Ageing studies in the future
Davide de Francesco and colleagues state that the use of the MARK-AGE algorithm of biological ageing markers, in these three populations, leads them to conclude that, despite an undetectable viral load while on treatment, persons living with HIV may experience accentuated ageing, rather than accelerated ageing.
They also underline that this age advancement seems to be related to viral co-infections such as CMV and HBV, as well as historic severe immunosuppression and use of particular antiretroviral drugs.
Nevertheless, based on some limitations to their work, such as the exclusion of people with mental disorders from the research, they call for future studies to further clarify “the effect of HIV and its treatment on the natural ageing process and the functional and clinical consequences in the millions of people living with HIV worldwide”.
Separately, the authors of an accompanying commentary call for “more studies assessing novel, integrative biomarkers, which reflect the multisystem nature of aging and its biology, to meaningfully predict an individual’s biologic age”.
de Francesco D et al. Do people living with HIV experience greater age advancement than their HIV-negative counterparts? AIDS 33: 259-268, 2019. (Full text freely available).
Rajasuriar R et al. Integrative biomarkers of biologic aging in HIV. AIDS 33: 345-347, 2019.