Malcolm A Traill
Presented 16th June 2012
Lithium, TNF-α, HSPG, Apoptosis and
For the first time, the temporal associations between the biological messengers linking Lithium and tumour cell apoptosis can now be presented.
In an earlier Chapter1 there was an hypothesis explaining how Lithium, through its actions on the Golgi enzyme 3'-phosphoadenosine 5'-phosphate 3'-phosphatase (gPAPP2)3, could modify the production of Heparan's quantity &/or quality, and that this could downgrade the function of a number of receptors for important stimulant cytokines, thereby slowing tumour growth.
Whilst such possibilities still exist, a more powerful explanation can now be added.
There are a number of key points to consider :
1) The timing of events
After Lithium was applied, with a static application, to cells in culture media by Kaufmann et al. (2011)4:
a. The new mRNAs for TNF-α and FasL could be detected at 16 h, indicating that mature TNF-α and FasL were being produced then or would be soon thereafter. Both can, under appropriate conditions, initiate apoptosis of cells,
b. Early apoptosis at 16 h was detected by measurement, using the Roche Cell Death Elisa kit,
c. Cleaved products of poly (ADP-ribose) polymerase[-1] (PARP[-1])5 were weakly detectable at 24 h, strong at 36 h and less strong at 48 h. The general form of the degradation product dynamics, put graphically, is suggested with the brown line in Diagram 1,
d. Apoptosis-associated enzymes, such as Caspases 3, 8 and 10 were not detected until about 36 h. These confirm that the Caspase-associated apoptosis form of cell death is likely to be applicable, and that the full impact was not developed until after about 24 h,
e. Lithium seemed not to cause the release of Cytochrome-c up to 24 h with or without p53,
f. Certain other apoptosis-associated factors (Bax, XiAP and Bid) did not seem to have their expressions changed appreciably,
g. In in vivo tests, using mice inoculated with a mammary tumour, and with a treatment group receiving daily injections of Lithium chloride, the tumours were measured and examined. There seem reduced growth in the lithium-treated group which, when graphed with a logarithmic vertical axis (not shown) indicated that the treated tumour growth was some 52% of the control at the end of the first week, 34.9% at the end of the second week, and 30.6% at the end of the third week. The view expressed was that there was increased apoptosis, but little (if any) detectable reduction in proliferation.
Whilst demonstrating that TNF-α may have an apoptosis-inducing effect, the results can hardly be described as impressive – in accord with the inference drawn from over 60 years of clinical use without any appreciable recognition of a cancer-treating treatment benefit. In particular, tumour stem cells would seem to be untouched; rather like using a lawn mower on weeds, with the blades set slightly higher each day to just below the plant tips; the roots being left unaffected. Forms of chemotherapy, radiotherapy and photodynamic therapy all have this problem.
2) The information highway
With Lithium-induced TNF-α and FasL being produced and released after about 16-24 h, there is a need to consider the cells that receive the assaults. Relevant aspects been made clearer by the work of Chen et al. (2007)6, Juric et al. (2009)7 and Juric et al. (2012)8 :
TNF-α can be a potent inducer of apoptosis, but it can also have either anti-apoptosis or weak apoptosis effects, depending upon the circumstances. The latter effects are overpowered by the more potent effect, if the conditions allow this. For this to happen, there must be special provisions at the TNF-α receptor (TNFR); there need to be particular co-receptors – the matricellular protein CCN1, the Heparan sulphate proteoglycan (HSPG; Syndecan-4), the low density lipoprotein receptor-1 (LRP1) and attachment to integrins αvβ5 & α6β1. TheFasL stimulus pathway is similar, and augments the TNF-α response.
The details need not be discussed here (consult the references); the important point is that there must be a competent HSPG co-receptor for the potent apoptosis pathway to operate, without which, there may be only a weak or absent apoptosis response.
3) Heparan Sulphate & the Golgi
The production of Heparan sulphate in the Golgi is influenced by the gPAPP enzyme, the target for Lithium (in this context). The enzyme is reported to have a Ki of ~0.2 mmol/L of Lithium; meaning that the enzyme is inhibited to 50% effectiveness by 0.2 mmol/L of Lithium – a sensitive enzyme. Just how its inhibition affects the quality/quantity of the Heparan sulphate produced in the Golgi is unclear – but it seems to.
There are a number of unknowns :
a. The relationship of the Lithium level in the serum to that in the cytoplasm in the region of the Golgi. There have been discrepancies in the literature9. All estimates would have been based upon steady-state conditions, not the dynamic rises and falls associated with the treatment discussed here. The relationship in this context can be assumed to be unknown, but there is probably a lag of intra-cytoplasmic levels behind the serum levels. A figure of about 0.5 - 0.6 mmol/L in the serum probably would indicate some inhibition of the gPAPP. Just how much inhibition is required to produce an appreciable change in the Heparan quantity/quality is unknown, but we must assume that it occurs.
b. Newly formed Heparan, contained within HSPG (in the normal state) moves to the cell exterior in some 20 min and has a half life of some 2 - 3 h10, the protein component being degraded first, so the freed Heparan sulphate may still interfere with receptor function.
After the Lithium serum level rises above (say) 0.5-0.6 mmol/L, Heparan affected by the Lithium action on the gPAPP enzyme will show changes in quantity/quality. On reaching the cell surface, it will dilute the normal form for the cell within hours. Other receptor types reliant upon HSPG for co-receptor function (there are a lot) can be expected to be inhibited, probably to varying degrees.
Diagram 1: This attempts to represent, in graphical form, how the Lithium level, HSPG status and apoptosis activity interact over time. The blue line represents the serum Lithium level, and is based upon the figures obtained from patient PC presented in an earlier Chapter11. The red line represents the HSPG effectiveness (quantity/quality). It reflects roughly the inverse of the Lithium level, but with a time lag (a lower level indicates poorer quantity/quality). The brown line represents the degree of apoptosis as deduced from the PARP 86 kDa levels in the Kaufmann et al. (2011) study.
The graph can also show that if another Lithium dose were to be given at ~24 h after the first, the HSPG quantity/quality perturbation to develop then would be expected to block the TNF-α from activating the more potent apoptosis pathway. That would explain the unimpressive anti-cancer effects that have been a feature of Lithium treatments over the last 60 years, and also the weak effects noted by Kaufmann et al. (2011) in their mice experiments.
So, all medical conditions that may be responsive to TNF-α, may benefit from intermittent bolus oral Lithium carbonate, but only on alternate days (or more widely spaced).
Malcolm A Traill
Copyright © MA Traill, June 2012
1MA Traill. Mal's Musings; 2009: 'www.malsmusings.info/index_files/EXPLAINED.htm'
2Abbreviations and further notes may be found in the Glossary, Mal's Musings; 2012 'www.malsmusings.info/index_files/GLOSSARY.htm'
3Frederick JP, Tafari AT et al. Proc Natl Acad Sci USA. 2008; 105(33):11605
4Kaufmann L, Marinescu G et al. Cell Communication Signaling 2011; 9:15
5Chaitanya GV, Steven AJ et al. Cell Communication Signaling 2010; 8:31
6Chen C-C, Young JL et al. EMBO J. 2007; 26:1257
7Juric V, Chen C-C et al. Mol Cell Biol. 2009; 29(12):3266
8Juric V, Chen C-C et al. PloS ONE 2012; 7(2):e31303
9MA Traill, Mal's Musings; 2008'www.malsmusings.info/index_files/LITHIUM.htm'
10Egeberg M, Kjeken R et al. Biochim Biophys Acta. 2001; 1541(3):135
11MA Traill, Mal's Musings; 'www.malsmusings.info/index_files/RENAISSANCE.ht