I'm a little new here and haven't yet gotten the hang of all the nuances of this site, so please excuse my butting in here like this.
I'd created another thread this week about my experiences with B6 deficiency an the relationship to heme and sphingolipid production and immune function. I was asked to copy what I posted there into this discussion, so here goes... I'll look forward to hearing if you all think this might be important in light of Naviaux's findings...
This describes PLP (P5P or B6) and it's importance in sphingolipids and immune function.
http://www.folk.uib.no/mfapu/Pages/papers pdf/2013/paul_2013_nr_71-239.pdf
I extracted this from the PDF:
PLP-dependent metabolism of sphingolipids
Reduced availability of PLP is associated with reduction
in several components ofthe immune response, includ-
ing significant decreases in lymphocyte numbers, espe-
cially T-helper cells and IL-2 production in humans.6
Lymphocytes isolated from vitamin B6-deficient subjects
also show reduction of lymphoproliferative responses to
mitogens that activate both T and B cells when grown in
a culture medium containing adequate concentration of
PLP.6 This has been attributed to the lower numbers of
T-helper cells in the lymphocyte population from vitamin
B6-deficient subjects. Maturation and egress of lympho-
cytes, especially T-cells, from thymus and lymph nodes
relies on the gradient of sphingosine-1-phosphate (S1P).
PLP-dependent enzymes play a major role in the synthe-
sis and breakdown of S1P, which is a potent metabolite
that regulates inflammation and immune response pro-
cesses such as cell growth, survival, differentiation, lym-
phocyte trafficking, vascular integrity, and cytokine
and chemokine production.58,59 PLP is required for the
activity of serine palmitoyl transferase that catalyzes the
condensation of serine and palmitoyl CoA into 3-keto-
dihydrosphingosine, which is then converted to S1P
in a series of reactions.58–60 PLP is also a cofactor for
sphingosine-1-phosphate lyase, which irreversibly cleaves
S1P to regulate its concentration.58,59,61 A gradient of S1P
is required for lymphocyte egress from thymus and
peripheral lymphoid organs, which is maintained by S1P
lyase.62 Administration of vitamin B6 antagonist 4’ deoxy-
pyridoxine interferes with the S1P gradient, results in
accumulation of mature lymphocytes in the thymus, and
depletes B- and T-lymphocytes from lymph causing lym-
phopenia.62 These conditions can be reversed by provid-
ing excess vitamin B6 in the diet.62 During inflammation,
S1P concentration increases in the inflamed peripheral
tissues,63 which functions as a chemoattractant for the
inflammatory cells.
One of the intermediate products during the synthe-
sis of S1P from 3-keto-dihydrosphingosine is ceramide,
which plays an important role in inflammatory processes.
Ceramide functions as a second messenger mediating the
effects of tumor necrosis factor-a and interferon-g on
programmed cell death and regulating senescence.64,65 An
increase in cellular ceramide concentration is observed in
cystic fibrosis, experimental autoimmune encephalomy-
elitis, and diet-induced insulin resistance, all of which are
marked by chronic inflammation.66–68 The importance of
ceramide in these diseases is demonstrated by the fact
that manipulation of ceramide concentration via inhibi-
tion of serine palmitoyl transferase or mutation of sph-
ingomyelinase, reverses the pathology of the disease.66–68
Ceramide-1-phosphate, which is derived from ceramide,
activates mast cells that mediate inflammation.69
Thus, it is possible that is a higher demand exists for
PLP during inflammation due to the role of PLP in the
synthesis of S1P and ceramide, and maintenance of S1P
gradient.