Immune Cells in Blood Samples from X-ALD Patients May Predict Response to Treatment, Study Says

Immune Cells in Blood Samples from X-ALD Patients May Predict Response to Treatment, Study Says

Immune cells derived from blood samples of people with adrenoleukodystrophy (X-ALD) may help in evaluating their inflammatory status of patients and likely response to treatment, an early study suggests.

The study “Dendrimer–N-Acetyl-L-Cysteine Modulates Monophagocytic Response in Adrenoleukodystrophy,” was published in the journal Annals of Neurology.

In X-ALD, a mutation in the ABCD1 gene leads to a decrease in ALD protein levels, causing a rise in fat molecules known as very long-chain fatty acids (VLCFAs). Patients with X-ALD can develop neurological symptoms in early adulthood, a condition called adrenomyeloneuropathy (AMN; the most common form of the disease), or during childhood where is called childhood cerebral adrenoleukodystrophy (or CALD).

Hematopoietic stem cell transplant (HSCT) is regarded as the only way of stopping ALD from progressing, and is based on the transplanting of hematopoietic stem cells — cells that can form all types of blood cells in the body — from a genetically similar donor (allogeneic), usually a close relative of the patient.

The long-term benefits of this approach are thought to be mediated by donor-derived replacement of immune cells, mainly microglial cells (immune cells of the central nervous system).

A team of researchers at Johns Hopkins’ School of Medicine, with colleagues, assessed how specific immune cells, called monophagocytic cells, acquired from ALD patients react upon exposure to VLCFAs.

Monophagocytic cells came from blood samples taken from four healthy controls, four carriers of the ABCD1 mutation in one allele (for each gene, we carry two alleles), seven patients with AMN, and four with CALD.

Results showed that exposure to VLCFAs significantly increased the release of pro-inflammatory cytokines (signaling molecules), namely tumor necrosis factor alpha (TNFα; by four times) and glutamate in cells derived from CALD patients. Cells from AMN patients also significantly — by two-fold — increased their release of TNFα and glutamate.

As expected, cells derived from healthy individuals or carriers showed no differences upon exposure to VLCFAs, as carriers still have a functional ALD protein.

These findings suggest that a pro-inflammatory response is stronger in CALD and dependent on monophagocytic cells.

Since VLCFAs accumulation causes oxidative stress — when cells fail to control the production of damaging molecules — researchers assessed the level of stress by measuring the levels of glutathione, an antioxidant molecule that prevents this process.

They saw that intracellular levels of glutathione were significantly lower in CALD patient cells, supporting the high levels of stress in their cells.

N-acetyl-L-cysteine, or NAC, is an antioxidant that increases the levels of glutathione. However, previous studies showed that the brain may not be open (permeable) to NAC administration. A modified form of NAC, called dendrimer-NAC (D-NAC), was shown to decrease inflammation in the brain of newborns.

Researchers instead tested the effects of free NAC and D-NAC. After exposure to VLCFAs, treatment with NAC or D-NAC led to a reduction in the release of TNFα and glutamate, but D-NAC was effective at lower doses (30 uM vs 300 uM of free NAC).

The effects of D-NAC were greater on CALD cells than on AMN cells.

“This indicates that D-NAC may be an effective mechanism of arresting neuroinflammation in patients with CALD,” the researchers wrote.

These results show “the differences in immune function of a free VLCFA-stimulated model of ALD, and demonstrate the potential benefit of D-NAC in attenuating an induced proinflammatory response,” the study said.

Regarding tests on patient-derived cells, “ALD phenotypes display unique inflammatory profiles in response to VLCFA stimulation, and therefore ex vivo [lab dish; literally, outside the body] monophagocytic cells may provide a novel test bed for therapeutic agents,” the researchers suggested.