Free Fatty Acids and Cytokines Induce Pancreatic ß-Cell Apoptosis by Different Mechanisms

Free Fatty Acids and Cytokines Induce Pancreatic ß-Cell Apoptosis by Different Mechanisms

(I've scrubbed the distracting reference numbers from some excerpts of the introduction and I'm also going to try to cite only the information pertinent to T2)

Hypercaloric diets containing large amounts of fat, also called the Western diet, contribute to a major extent to the increasing prevalence of obesity and type 2 diabetes mellitus (T2DM). T2DM is characterized by peripheral insulin resistance, pancreatic ß-cell dysfunction, and decreased ß-cell mass associated with increased rates of ß-cell apoptosis. Elevated levels of circulating free fatty acids (FFAs) contribute to the pathogenesis of T2DM. High concentrations of FFAs lead to both impairment of insulin action and ß-cell dysfunction.  Moreover, FFAs have been shown to cause ß -cell death, mainly by apoptosis. 

Of note, increased adiposity is associated not only with increased FFA release but also with adipocyte secretion of a variety of cytokines and cytokine-like adipokines, such as TNF -α, IL-6, leptin, resistin, and adiponectin. TNF-α has direct cytotoxic effects on pancreatic ß -cells, especially in combination with other cytokines.

Read more »

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.

Fat storage in pancreas and in insulin-sensitive tissues in pathogenesis of type 2 diabetes

Fat storage in pancreas and in insulin-sensitive tissues in pathogenesis of type 2 diabetes

Obesity is associated with increased storage of lipids in nonadipose tissues like skeletal muscle, liver, and pancreatic b cells. These lipids constitute a continuous source of long-chain fatty acyl CoA (LC-CoA) and derived metabolites like diacylglycerol and ceramide, acting as signalling molecules on protein kinases activities (in particular, the family of PKCs), ion channel, gene expression, and protein acylation. In skeletal muscle, the increase in LC-CoA and diacylglycerol translocates and activates specific protein kinase C (PKC) isoforms, which will phosphorylate IRS-1 on serine, preventing its phosphorylation on tyrosine and association with PI3 kinase. This interrupts the insulin signalling pathway leading to the stimulation of glucose transport. In pancreatic b cells, short-term excess of fatty acids or LC-CoA activates PKC and also directly stimulates insulin exocytosis. Longterm exposure to free fatty acids (FFA) leads to an increased basal and blunted glucose-stimulated insulin secretion by affecting gene expression, increase in KATP channel activity, and uncoupling of the mitochondria. In addition, the saturated FFA palmitate increases cell death by apoptosis via increase in ceramide synthesis.

{...} 

In obesity, a situation of excess supply and/or decreased oxidation, fatty acid not only accumulate in adipose cells but also in other tissues like skeletal muscle, liver, and pancreatic b cells. Triglycerides are not harmful as such, but are precursors of signalling molecules like LC-CoA, diacylglycerol, ceramides, acting directly or indirectly in skeletal muscle on insulin signalling and glucose uptake, and in pancreatic b cells, on insulin secretion and cell viability. 

Going to leave this one just "out there" except to say that it ties in with a lot of the other research/studies I've been posting about lately.

Apoptosis - Programmed Cell Death

Here is a link to a website dedicated to Apoptosis/PCD:  Apoptosis Info.com

Apoptosis is the term given when programmed cell death (PCD) occurs in multicellular organisms. Apoptosis is one of the main types of programmed cell death which involves a series of biochemical events leading to specific cell morphology characteristics and ultimately death of cells. Characteristic cell morphology of cells undergoing apoptosis include blebbing, changes to the cell membrane such as loss of membrane asymmetry and attachment, cell shrinkage, nuclear fragmentation, chromatin condensation, and chromosomal DNA fragmentation. Apoptosis differentiates from necrosis as the processes associated with apoptosis in disposal of cellular debris do not damage the organism in apoptosis.

Necrosis is a form of traumatic cell death that results from acute cellular injury. Apoptosis in contrast to necrosis, confers advantages during an organism's life cycle. For instance during the development of the fetus in the mother, the differentiation of fingers and toes occurs because cells between the fingers apoptose with the end result that the digits are separate. Approximately between 50 billion and 70 billion cells die each day due to apoptosis in the average human adult. In a year, this amounts to the proliferation and subsequent destruction of a mass of cells equal to an individual's body weight.

Since the 1990's research has increased substantially in the field of apoptosis. It has been shown that defective apoptotic processes in humans and animals are related to a variety of diseases. Excessive apoptosis causes hypotrophy, such as in ischemic damage, whereas an insufficient amount results in uncontrolled cell proliferation, such as cancer.

A lot of the inflammation and CVD issues associated with metabolic syndrome, diabetes, etc. lead to discussions of premature apoptosis which is how I came across this website and thought I would post it here for future reference.