Comparative Fatty Acid Toxicity on Macrophages

Comparative toxicity of fatty acids on a macrophage cell line (J774)

In the present study, the cytotoxicity of palmitic, stearic, oleic, linoleic, arachidonic, docosahexaenoic and eicosapentaenoic acids on a macrophage cell line (J774) was investigated. The induction of toxicity was investigated by changes in cell size, granularity, membrane integrity, DNA fragmentation and phosphatidylserine externalization by using flow cytometry. Fluorescence microscopy was used to determine the type of cell death (Acridine Orange/ethidium bromide assay). The possible mechanisms involved were examined by measuring mitochondrial depolarization, lipid accumulation and PPARγ (peroxisome-proliferator-activated receptor γ ) activation. The results demonstrate that fatty acids induce apoptosis and necrosis of J774 cells. At high concentrations, fatty acids cause macrophage death mainly by necrosis. The cytotoxicity of the fatty acids was not strictly related to the number of double bonds in the molecules: palmitic acid>docosahexaenoic acid>stearic acid=eicosapentaenoic acid=arachidonic acid>oleic acid>linoleic acid. The induction of cell death did not involve PPARγ activation. The mechanisms of fatty acids to induce cell death involved changes in mitochondrial transmembrane potential and intracellular neutral lipid accumulation. Fatty acids poorly incorporated into triacylglycerol had the highest toxicity.

 I could C&P the entire introduction to this paper but don't want to do that, so please go read it.  Summary:

• The FFA/NEFA are generally implicated in having toxic effects in non-adipose tissues, aka lipotoxicity
• Saturated fatty acids tend to be more lipotoxic
• Ectopic (non-adipose) triglyceride storage is somewhat protective but this remains under consideration as metabolites/intermediates of triglycerides (ceramides) are implicated in toxicity.
• Cell death contributes to the inflammatory properties of FA's
• PPAR-ɣ increases reduce inflammatory cytokines like IL's and TNF-α

Macrophage infiltration into adipose tissue in obesity is implicated in the inflammatory state associated with obesity.   It should be noted that this study was in vitro (e.g. culture dish) on a non-human (murine to be exact) derived cell line.   But the elevated NEFA associated with insulin resistance and T2 Diabetes would produce a "toxic" state within adipose tissue leading to macrophage death (and adipocyte death?). 

Cell death types:  

• Apoptosis, aka programmed cell death:  When functioning properly, this is the "natural" death of cells for cellular turnover in tissues, etc.  In cancer, apoptosis is short circuited leading to so-called immortal cells.  Some toxic conditions lead to disruption of the normal signals and pre-mature apoptosis.  
• Necrosis:  Premature cell death due to some - always detrimental - external source.  Necrosis initiates a greater immune response as dead cells must be engulfed and removed, and such cells rupture and "spill" more "stuff" into the surroundings than cells undergoing PCD.

Some exerpts:

In the present study, we evaluated whether the induction of cell death could be a mechanism by which FAs modulate macrophage function. Indeed, treatment with different concentrations of FAs was toxic to the macrophage cell line J774, as assessed by loss of membrane integrity and DNA fragmentation.  In most cases, the lowest concentration that caused loss of membrane integrity was the same that induced DNA fragmentation (Table 3), and the percentages were similar. These findings are indicative that necrosis and apoptosis occurred concomitantly.

... high FA concentrations cause macrophage death mainly by necrosis. This effect was also observed by others after treatment of different cell types, such as melanoma, leukaemia cell lines, lung carcinoma and fibroblasts, with high concentrations of FA [49–51].  The results of both loss of membrane integrity and/or DNA fragmentation shown in the present study suggest the following rank of toxicity on J774 cells: PA>DHA>SA=AA=EPA>OA>LA 

... The relationship between lipid accumulation and apoptosis has been demonstrated through a series of experiments with different cell lines [63–65]. Accumulation of excess FAs into the TAGpool has been postulated to divert these molecules from pathways that lead to toxic effects and, thus, lipid bodies may serve as buffers against lipotoxicity [19]. Treatment with all FAs led to an increase of lipid bodies inside J774 cells (Figure 2B).  Cells treated with non-toxic concentrations of the FAs exhibited higher granularity, indicating accumulation of lipid droplets that was observed by fluorescence microscopy. 

A look at Figure 1 indicates a threshold behavior for the toxic effects.

I have not addressed everything in this article and this post is sort-of half book marking, half just putting this out there as I had not seen a discussion of this nature before.