VACS 2.0 Frailty Index Correlates with Soluble TNF Receptor Levels in Aging Veterans

This study of older HIV-positive Veterans demonstrates that the VACS 2.0 Frailty Index correlates with medication burden and strongly associates with soluble TNF receptor levels, suggesting a potential link between systemic inflammation and frailty that warrants further mechanistic investigation.

The Gist

The Big Picture: Checking the "Wear and Tear" Gauge

Imagine your body is like a classic car. As the car gets older, it naturally shows signs of wear and tear. Sometimes, a car that is 10 years old runs perfectly fine, while another 10-year-old car is constantly breaking down. In medicine, we call this difference frailty. It's not just about how old you are (chronological age); it's about how well your body is actually holding up.

This study looked at a group of older male Veterans (all over 65) to see if they could find a specific "check engine light" in their blood that predicts how frail they are. They used a special scoring system called the VACS 2.0 Frailty Index. Think of this index as a dashboard gauge that calculates a score based on things like your weight, blood counts, and organ function. A higher score means the car is more likely to break down soon.

The Investigation: Looking for the Smoke

The researchers wanted to know: What is actually causing the engine to smoke?

They knew that as we age, our bodies often get a bit "inflamed" (like a low-grade fire burning inside). They also knew our immune system gets tired, similar to a soldier who has been on duty for too long and is now exhausted.

They took blood samples from 30 older Veterans and compared them to a group of younger people (under 50). They looked for two main things:

1. Inflammation markers: Chemicals in the blood that signal the body is under stress.
2. Immune cell "exhaustion": Checking if the body's defense cells (T-cells) looked tired or old.

The Findings: The "TNF" Connection

Here is what they discovered, translated into plain English:

1. The Older Group Was "Louder"
Just like a noisy engine, the older Veterans had much higher levels of certain inflammatory chemicals in their blood compared to the younger group. Specifically, they had high levels of IL-6, IP10, and TNF receptors. Their immune cells also looked more "tired" and "old" (expressing markers like CD57 and PD-1).

2. The Strongest Link: The TNF Receptors
While many things were elevated, the researchers found one specific pair of chemicals that acted like a perfect match for the Frailty Score. These are called Soluble TNF Receptors (sTNFR).

• The Analogy: Imagine the Frailty Score is a report card grade. The researchers found that the sTNF Receptor levels were the single best predictor of that grade. If the sTNF levels were high, the Frailty Score was high. It was a very strong connection, much stronger than just looking at the person's age.

3. The "Medicine Cabinet" Clue
They also noticed that Veterans who were taking a lot of prescription medications (10 or more) tended to have higher Frailty Scores. This makes sense: if you need many different medicines to keep your body running, your body is likely struggling more.

4. The "Unexpected" Group
The researchers divided the Veterans into three groups based on their Frailty Score compared to their age:

• Expected: Their score matched what you'd expect for their age.
• Lower-than-expected: They were surprisingly healthy for their age.
• Higher-than-expected: They were frailer than you'd expect for their age.

The "Higher-than-expected" group was the most interesting. They had the highest levels of those inflammatory chemicals (sTNF receptors) and the most prescriptions.

5. The Survival Story
The researchers looked back at the medical records of these 30 men over several years (up to 2025). They found that the men in the "Higher-than-expected" frailty group were less likely to be alive by the end of the study compared to the other groups. While the group was small, the trend suggested that having a high Frailty Score (and high inflammation) was a sign of a shorter remaining lifespan.

What They Did Not Find

It is important to note what the paper says they didn't find:

• They did not find a strong link between the Frailty Score and IL-6 (another inflammation marker), even though IL-6 was high in the older group. This was surprising because IL-6 is usually blamed for frailty. The researchers suggest their group might have been too small to see this link clearly.
• They did not find that the "Lower-than-expected" group had significantly lower inflammation markers than the "Expected" group. Being "surprisingly healthy" didn't necessarily mean having super-low inflammation; it just meant they didn't have the high levels seen in the frail group.

The Bottom Line

This study suggests that for older Veterans, frailty is closely tied to specific inflammation signals in the blood (specifically sTNF receptors), rather than just the number of years they have lived.

Think of it this way: You can't stop a car from getting older, but if you see a specific type of smoke coming from the engine (high sTNF receptors), you know that particular car is at high risk of breaking down, regardless of its mileage. The researchers conclude that we need to study how these specific chemicals cause frailty so we might one day be able to fix them.

Note: This paper is a preprint, meaning it has not yet been fully reviewed by other scientists, and the authors caution that these results should not yet be used to change medical treatments.

Technical Summary

Technical Summary: VACS 2.0 Frailty Index Correlates with Soluble TNF Receptor Levels in Aging Veterans

Problem Statement
Frailty syndrome, characterized by increased vulnerability and decreased resilience to stressors, is a critical clinical state associated with aging, physiological decline, and increased mortality. While frailty indexes like the VACS 2.0 (Veteran Aging Cohort Study 2.0) have been developed to predict mortality using electronic health records, the biological mechanisms linking frailty to immunosenescence and systemic inflammation remain incompletely understood. Specifically, the association between frailty scores and soluble inflammatory indices, as well as T cell markers of exhaustion and senescence, requires further investigation in aging populations, particularly those without HIV, as the VACS 2.0 index was originally derived from HIV-positive cohorts.

Methodology
The study utilized a cohort of 30 male Veterans aged 65 years and older (mean age 77) recruited from the Northeast Ohio VA Medical Center. A younger control cohort (n=27–39, age ≤50) was included for comparative analysis of immune markers.

• Data Collection: Researchers obtained one-time blood draws (plasma and PBMCs) between 2017–2019. Clinical data, including comorbidities and prescription counts, were extracted from VA Electronic Health Records (EHR) covering a one-year window surrounding the blood draw.
• Frailty Assessment: The VACS 2.0 frailty index was calculated for all participants using the online VACS 2.0 tool. Variables included chronological age, sex, BMI, CD4+ count, HIV-1 RNA viral load (set to zero for this HIV-negative cohort), HCV status (set to "no"), eGFR, hemoglobin, liver enzymes (ALT, AST), platelet count, WBC count, and albumin.
• Immune Profiling:
  • Soluble Indices: Plasma levels of IL-6, IP-10, soluble TNF Receptor I (sTNFRI), and sTNFRII were measured via high-sensitivity ELISA.
  • Cellular Markers: Flow cytometry was performed on PBMCs to assess T cell subsets (naïve, central memory, effector memory, terminal effector memory) based on CD45RA and CD27 expression. Markers of senescence (CD57, KLRG-1) and exhaustion (PD-1, TIGIT) were quantified on CD4+ and CD8+ T cells.
• Statistical Analysis: Correlations between VACS 2.0 scores, age, immune markers, and T cell subsets were assessed using Spearman's correlation with Benjamini-Hochberg adjustment. Participants were stratified into "expected," "higher-than-expected," and "lower-than-expected" frailty categories based on a linear regression of VACS 2.0 score versus chronological age (95% confidence intervals). Survival analysis was conducted using retrospective chart reviews through May 5, 2025.

Key Results

• Immune Elevation in Aging: Compared to the younger cohort, older Veterans exhibited significantly elevated plasma levels of IL-6, IP-10, sTNFRI, and sTNFRII. They also showed higher proportions of T cells expressing senescence (CD57, KLRG-1) and exhaustion (PD-1, TIGIT) markers, alongside a shift from naïve to memory T cell phenotypes.
• Correlation with Frailty: The VACS 2.0 frailty score showed a strong, statistically significant positive correlation with soluble TNF receptor levels (sTNFRI: r=0.743, adj p=0.001; sTNFRII: r=0.781, adj p<0.001). The score also correlated significantly with age (r=0.69) and the number of prescribed medications (r=0.43, p=0.017). Notably, while IL-6 was elevated in the older group, it did not show a statistically significant correlation with the VACS 2.0 score in this specific cohort.
• Stratification by Expected Frailty: When stratifying participants by whether their frailty score was higher, lower, or expected for their age, those with "higher-than-expected" frailty (n=7) demonstrated significantly higher levels of sTNFRI, sTNFRII, and IP-10 compared to those with "expected" frailty. This group also included the majority of patients taking 10 or more prescriptions.
• Survival Outcomes: Over a follow-up period extending to 2025, 11 of the 30 participants died. Patients categorized as having "higher-than-expected" frailty showed a trend toward lower survival probability compared to the other groups, approaching statistical significance (p=0.057).

Significance and Claims
The authors claim that this study provides evidence that soluble inflammatory indices, specifically sTNFRI and sTNFRII, are strongly associated with frailty as measured by the VACS 2.0 index in aging Veterans, potentially more so than chronological age alone. The findings suggest that factors beyond simple aging, such as chronic inflammation ("inflammaging") and polypharmacy, contribute significantly to the frailty phenotype.

The paper posits that the VACS 2.0 index, originally designed for HIV-positive populations, is a valid tool for assessing frailty in HIV-negative older Veterans. Furthermore, the study highlights that patients with frailty scores exceeding what is expected for their age are a distinct subgroup characterized by elevated soluble TNF receptors and higher medication burdens, who may face reduced survival probabilities. The authors conclude that while these soluble indices correlate with frailty, the mechanistic role of sTNF receptors in driving frailty warrants further investigation. The study acknowledges limitations, including a small sample size, a lack of female participants, and limited diversity, which may restrict the generalizability of the findings to the broader population.