Up to present, there were many studies suggested that propofol could inhibit
immune response in vitro or in vivo. Some of these studies indicated that propofol
showed inhibitory effects on LPS stimulated response but propofol itself would not
have effect on non-stimulated macrophage. On the contrary, some studies suggested that
propofol could enhance inflammation response. And there were also some studies
suggested that propofol could exert inhibitory without LPS stimulation. In addition to
the effects on immune modulations, another controversial issue was the dosage of
propofol for laboratory research, some studies investigated the effects of propofol
within clinical dosages, and however, some used even ten folds of maximal clinical
dosage to study. By the way, many studies used model or mouse cell line to study the
effects of propofol on immune modulations; it might transmit confused information as
propofol exerted on human beings.
In this study, we stood on a compromising position to investigate the effects of
propofol on immune modulations. We used the mouse cells to study the synergistic
effects of propofol and LPS on proinflammatory cytokine production, dosages of propofol were about two and four folds to clinical maximal use (about 6.5 μg/ml). On
the other hand, we considered that propofol used generally in hospital but there were
many situations without intervention of LPS. Thus, we investigate the clinical effects of
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propofol and the effects by propofol itself within the clinical dosages on human cells.
Furthermore, we took an ex vivo assay to clarify the immune modulation effects of
propofol in hospital use.
The first part in this study began with the synergistic effects of propofol and LPS in
mouse immune cells. Our data showed propofol indeed exerted opposite force against LPS stimulation. The mouse-derived spleen cells were induced to secrete TNF-α and
IL-1β, two generally acknowledged proinflammatory cytokines induced by LPS (Fig4
and Fig5). There were many studies about propofol reduced the response stimulated by
LPS. Chu SH et.al suggested that propofol exerts protective effects on the acute lung
injury induced by endotoxin in rats. Chen RM et.al found that propofol had
anti-inflammatory and anti-oxidative effects on LPS-activated macrophages. ELISA revealed that LPS increased macrophage inducible nitric oxide synthase [5], TNF-α,
IL-1β, and IL-6 in both protein and mRNA levels, whereas propofol significantly
reduced the levels of iNOS, TNF-α, IL-1β, and IL-6 at the presence of LPS both in
protein and mRNA levels. In addition, Song HK et.al suggested that propofol allowed
MNCs to retain their cytotoxicity in septic conditions by protecting immune cells from
apoptosis. However, present reports did not expound the mechanisms of propofol
actions. Besides cytokine profiles, in this study we also investigated the transcriptional
regulations which involved in immune modulation of propofol. Here we suggested
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propofol might inhibit the LPS-induced inflammation by two mechanisms. First, propofol could induce the inhibitory cytokine TGF-β but not IL-10 whether in the
presence of LPS or not (Fig6 and Fig7) Second, propofol could suppress the activities of NF-κB and AP-1 (Fig.10) which both were crucial transcription factors involved in
LPS-induced inflammation priming. Interestingly, propofol alone in our experimental conditions did not reduce but promote the activities of NF-κB and AP-1. Thus, we
preliminary exclude the possibility that propofol inhibited the activities of NF-κB and
AP-1 through induced TGF-β. Although we did not provide strong evidences whether
these two mechanisms interact with each other or not, it might another landmark we
could work for.
Through the analysis from mouse splenocyes and cell lines, we found that propofol had potentials to induced TGF-β secretions (Fig.7 and Fig.9). Thus another part of this
study was to make a study of mechanisms and the biological effects of propofol-induced TGF-β in medication. In this study, we first reported that clinical dosages of propofol
not only induced latent TGF-β1 expressions but also conversed to an active form in
human sera (Fig. 12). This effect was accomplished by a two-step mechanism. On one hand, propofol induced endothelial cells to secrete more latent TGF-β1 (Fig. 17); on the
other, propofol induced T lymphocytes (Fig. 14) and monocytes (Fig. 15) to activate the surrounding latent TGF-β1. By TGF-β pathway inhibitor SB431542, the results
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indicated that the propofol-induced TGF-β1 in patient sera mediated the suppression
activities against endocytosis in monocytes (Fig. 20).
Monocytes mediate many responses of the innate immunity. Reducing endocytosis
activity of monocytes-macrophages might have negative influences on antigen uptake,
presentation and immune activation. In addition to endocytosis activity, it is believable that propofol-elicited TGF-β1 could inhibit phagocytosis, the production of the reactive
nitrogen intermediates, TNF-α expression, the common γ-subunit expression and TLR
signaling pathways in monocytes [150, 169, 170]. Thus, the inhibitory activities of
TGF-β1 on monocytes may partake in a key role to suppress inflammatory responses
after clinical administration of the anesthetic propofol.
Two arguments can be made in regards to the propofol effect on the immune
activity. First, propofol could attenuate CD14 expression on the surface of
LPS-stimulated monocytes to reduce inflammatory response [18]. In addition, propofol
also protect endothelial cells against LPS-induced barrier dysfunction by inhibiting NF-κB activation [127]. However, propofol also was shown to reinforce the effects on
the releases of LPS-induced proinflammatory cytokines including TNF-α and
IL-1β [19] which induce/enhance inflammatory responses through NF-κB activation
[171]. Based on our findings, the bioactive TGF-β1 induced by propofol, it might help
to explain the controversial effects of propofol found in previous literature. Studies have
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shown that propofol can increase LPS-stimulated proinflammatory cytokine expression by activating NF-κB pathway; it may be caused by the transient effects of
propofol-induced TGF-β1 on the activation of NF-κB [172]. However, TGF-β1 is a
multifunctional cytokine, reported to decrease the activity of NF-κB with or without
LPS stimulation [173, 174]. Thus, the controversial effects of propofol may be due to the ability of TGF-β1 induction. Propofol can induce the secretion of latent TGF-β1 and
enhance the conversion of latent TGF-β1 into active form. Consequently, the difference
in the dosages, the types of target cells, and the cell-cultured conditions will affect the synergistic effect of propofol-induced TGF-β1 to result in different experimental
outcomes.
The secondary controversial phenomenon is the propofol effect on the activities of immune cell. Although many pro-inflammatory cytokines such as TNF-α which can
increase the activities of granulocytes and monocytes are induced by propofol [15],
propofol treatments in many laboratory studies or clinical observations are believed to
down-regulate the activities of many human immune cells [52], including leukocytes
[46], lymphocytes [175], monocytes [18], macrophages [37] and neutrophils [39]. Our
finding could provide possible explanations to these studies. The propofol-induced latent and active TGF-β1 exerts its antagonistic effect [176-178] with pro-inflammatory
cytokine which are also induced by propofol infusion. Later, sustained propofol in the
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sera may decrease TNF-α production by decreasing the activity of NF-κB. Thus,
sustained propofol will induce endothelial cells to produce latent TGF-β1 and enhance
PBMC to be converted into the active form. Continuous provision of active TGF-β1
shall suppress the activities of TNF-α which amounts are progressively decreasing.
Finally, it will cause the effect of propofol to be suppressive on immunological activities
among surgical or care patients.
Thus, our results in this study should be valued for patients who are using propofol
treatment during medical operations. Their innate immunity would be affected because of propofol-induced active TGF-β1. On the disadvantageous side, these patients should
keep away from opportunistic infections of certain pathogens like Staphylococcus aureus because propofol will suppress patients’ immunity by TGF-β1. Advantageously,
these patients would have a lower opportunity to suffer from endotoxemia- caused death by antagonizing TNF-α effects [13].
In addition to immune regulation, TGF-β1 also plays a crucial role in a range of
biological processes, including regulation of tissue repair, extracellular matrix
accumulation, angiogenesis and fibrosis progression [140, 179]. Evidences indicated that TGF-β pathway involved Smad3 [180] and Smad2 [181] is pivotal in progressive
fibrosis and has effects on the induction of myofibroblasts, enhancement of matrix
synthesis, and inhibition of collagen breakdown. Thus, it should be noted that the
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long-term sedation by propofol in intensive care patients might be at high risk of TGF-β
mediated fibrosis.
In contrast, the propofol-induced TGF-β1 could be considered as a good aspect in
post-operation. It is clear from studies in TGF-β1 deficient mice that TGF-β1 is
necessary for wound healing [148] and also reported acceleration in healing. Such
findings imply that clinical dosages of propofol could promote the recovery of trauma
patients. In fact, propofol anesthesia, as compared to the awaken state, has the potential
of offering a certain degree of protection against neuron damage [182] and burn injury
[58]. Therefore, further studies are needed to investigate the advantages of propofol use
in surgery and intensive care.
In this study, we demonstrated that clinical dosages of propofol induced both human latent and active TGF-β in vivo and the propofol-induced TGF-β1 had the
immunosuppressive activity to monocytes. According to our results, it is worthy to investigate the effects of propofol to induce TGF-β1 in future research. The advanced
results will prevent the side-effects of propofol and strengthen its medical effects for
different patients during medication.
As everyone knows, TGF-β was a multi-function protein involved many biological
regulations. We also found that propofol might have potential to induced IL-8 secretion
from THP-1 (Fig21) although there were no differences within clinical dosage. Because
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both IL-8 and TGF-β were important regulators to enhance the process of wound
healing, propofol might have benefits in wound healing of trauma patients.
In this study, we investigated the effects of clinical dosage propofol on human TGF-β expressions by different types of cells and discovered the biological importance
of propofol-induced TGF-β secretion and conversion ex vivo (Fig22). We provided the
possible reasons that propofol could exert a protect effects and also might be beneficial
to the inflammatory change in sepsis.
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