Table Of Content(cid:11)-MSH
James M. Lipton1,* and Anna Catania2
1Zengen Inc., 21800 Oxnard Street, Suite 980, Woodland Hills, CA 91367, USA
2Third Division of Internal Medicine, Ospedale Maggiore di Milano IRCCS, Via F. Sforza 35,
20122 Milano, Italy
*corresponding author tel: 818-887-8688, fax: 818-884-5988, e-mail:jlipton@zengen.com
DOI: 10.1006/rwcy.2000.13002.
SUMMARY sequence is part of ACTH; isolation and structural
analysis of (cid:11)-MSH from a number of mammals and
fishes showed a high sequence conservation of the
(cid:11)-Melanocyte-stimulatinghormone((cid:11)-MSH),amela-
molecule during evolution. The importance of the
notropin or melanocortin (ACTH- or (cid:11)-MSH-like)
peptide in the control of inflammation, fever, and
peptide, is known for its neuroimmunomodulatory
microbial invasion was not known for many years
properties. This molecule serves as an endogenous
after the amino acid sequence was described.
mediator in the brain, pituitary, circulation, periph-
eral tissues, and/or between host cells that modulates
the production and actions of proinflammatory
Alternative names
agents. Exogenous (cid:11)-MSH suppresses inflammatory
responsesinanimalmodels.Furthermore,thepeptide
(cid:11)-MSH was originally named for its capacity to
is increased in clinical inflammatory disease in
darken skin color in amphibia. The peptide was sub-
humans, presumably as a natural countermeasure to
sequently called melanotropin. According to the
inflammation. The tridecapeptide (cid:11)-MSH and its
IUPAC-IUB convention, the full name of the hor-
C-terminal tripeptide amino acid sequence KPV ((cid:11)-
mone that covers melanin dispersion is melanocyte-
MSH 11–13) have parallel anti-inflammatory effects
stimulating hormone, abbreviated MSH, and the
in animal models and in in vitro tests on host cells.
trivialnameismelanotropin.Theprefix(cid:11)denotesthe
There is recent evidence that these peptides also have
basic tridecapeptide derived from ACTH (Eberle,
antimicrobial properties that can benefit the host.
1988). The term opiomelanocortins is generally used
for any and all of the peptides derived from the pro-
opiomelanocortin precursor. Melanocortin relates
BACKGROUND only to ACTH/(cid:11)-MSH-derived peptides.
Discovery
Structure
The history of (cid:11)-MSH began with an initial obser-
vation of the influence of the pituitary gland in con- (cid:11)-MSH is derived from the precursor proopiomela-
trol of skin color in amphibia (Eberle, 1988). There nocortin (POMC) (Figure 1). The genetic code for (cid:11)-
were many attempts to identify the amino acid MSH resides in the third exon of the POMC gene
sequence of isolates of highly purified skin-darkening thatalsocontainsthegeneticinformationfor(cid:12)-LPH,
agents.HarrisandLerner(1957)determinedtheamino ACTH, and related peptides. Like other prohor-
acid sequence of porcine (cid:11)-MSH, a tridecapeptide mones, cleavage sites of POMC occur between
with blocked N-terminus and amidated C-terminus. pairs of basic amino acid residues (-Lys-Lys-, -Arg-
Subsequent studies revealed that the (cid:11)-MSH Lys-, -Arg-Arg-, -Lys-Arg-) that are recognized by
CytokineReference Copyright#2000AcademicPress
1384 James M. Lipton and Anna Catania
specific endopeptidases. Two of these enzymes, PC1 Chromosome location
and PC2, are involved in processing POMC peptides.
Their cleavage specificities are distinct: PC1 cleaves
Inhumans,thechromosomesiteforthePOMCgene,
POMC into corticotropin and (cid:12)-lipotropin; PC2
the precursor of (cid:11)-MSH, is 2 P (Zabel et al., 1983).
cleaves POMC into (cid:12)-endorphin and (cid:11)-MSH
(Benjannet et al., 1991). (cid:11)-MSH (1–13) is cleaved
from the ACTH amino acid sequence and therefore Regulatory sites and corresponding
shares the peptide backbone of ACTH (1–13). How-
transcription factors
ever, (cid:11)-MSH lacks the amino acid sequence required
to stimulate adrenal cells. The (cid:11)-MSH peptide is
normally acetylated at the N-terminal and amidated (cid:11)-MSH is derived from the third exon of POMC
at the C-terminal; the predominant form in the DNA. A single gene encodes POMC in humans; this
pituitary is diacetylated. Although the (cid:11)-MSH 6–9 gene is unusual in that it possesses three promoter
amino acid sequence (His PheArgTrp) is considered regions that control transcription: P1, P2, and P3.
the core sequence underlying the melanotropic acti- P2 controls transcription in the normal pituitary
vity of the peptide, it is clear that the 11–13 amino gland; P3 is weakly active in a variety of peripheral
acid sequence (LysPro Val) is especially important in tissues; P1 is the predominant promoter in some
host response functions (Lipton and Catania, 1997). cancers (Kraus et al., 1993).
Main activities and PROTEIN
pathophysiological roles
Sequence
Details of the activities of (cid:11)-MSH peptides are pro-
See Figure 1.
vided in sections below. In brief, the peptides
modulate fever and inflammation and defend against
microbialinvasion.Itisnotablethatininvivotestsin
Description of protein
which the peptides are administered alone in dosage
adequate to influence host responses, there is no
As indicated above, (cid:11)-MSH is a tridecapeptide. It
discernibleinfluenceonnormalphysiology.Extremely
is normally N-acetylated and amidated at the
high dosesare required tolower normaltemperature;
C-terminus.
ithasnotbeenpossibletoreachlethalconcentrations
except by injecting massive amounts into the cerebral
ventricles.Thelatterconcentrationsareunlikelytobe Important homologies
reached even after systemic administration of any
quantity. From the evidence currently in hand, it
(cid:11)-MSH has the same amino acid sequence as the
appears that the peptides exert salutary control over
domain of ACTH from which it is derived. (cid:11)-MSH
host responses, preventing them from reaching dan-
shares the MetGluHisPheArgTrpGly sequence
gerous levels, and they directly kill invading micro-
with (cid:12)-MSH.
organisms.Thattheirinfluencesarepartofanancient
control system is supported by the rises in circulating
peptides during host challenge and in disease. The
proposed role of these peptides in pathophysiology is
that of defender against excessive self-responses and
against direct invasion.
Figure 1 (cid:11)-MSH derivation and amino
acid sequence.
GENE AND GENE REGULATION
Accession numbers
Accession numbers for the human POMC gene, exon
three: J00292, J00293, V0569
(cid:11)-MSH 1385
CELLULAR SOURCES AND Larsson, 1980; Civelli et al., 1982; Gee et al., 1993),
cellsinthedorsolateralhypothalamusdonotstainfor
TISSUE EXPRESSION
other POMC peptides (Guy et al., 1980).
Although evidence from studies of human tissue is
Cellular sources that produce
limited, (cid:11)-MSH is most concentrated in the pituitary
(nanomolar range), whereas it occurs in lower but
Knowledge of (cid:11)-MSH distribution in tissues has substantialconcentrationsinthehypothalamus,locus
changed substantially with development of modern coeruleus, and the substantia innominata (De´sy and
localization techniques. It is now clear that low con- Pelletier, 1978; O’Donohue et al., 1979; Arai et al.,
centrations of (cid:11)-MSH are, or can be, expressed 1986). The highest concentration of immunoreactive
ubiquitously. However, there are distinct regional (cid:11)-MSHwithinthebrainisinthehypothalamus(Arai
differences in that certain cells express the peptide et al., 1986), where the peptide exists mainly in the
constitutively (Table 1). It is remarkable that partic- desacetylated form (Parker et al., 1981); substantial
ularlyhighconcentrationsof(cid:11)-MSHarefoundinthe concentrations also occur in the substantia innomi-
brain and in barrier organs such as skin and gut. nata (Candy et al., 1985). The peptide is likewise
(cid:11)-MSHwas originallyisolated from the parsinter- found in the cerebrospinal fluid (CSF) of monkeys
media of the pituitary gland. Small amounts of the andhumans(Rudmanetal.,1973).HumanCSFalso
peptide are also synthesized by the corticotrophs of contains an anti-(cid:11)-MSH protein (20–40kDa) that
theparsdistalis,especiallyinyounganimals(Usategui binds/neutralizes the peptide (Rudman et al., 1974;
etal.,1976).Immunocytochemicalanalysisofnormal Scimonelli and Eberle, 1987). It may be, because
adult pituitaries for (cid:11)-MSH-containing cells showed (cid:11)-MSH receptors are estimated to be 35–45kDa
that, although there is great interindividual variation proteins (Scimonelli and Eberle, 1987; Mountjoy
in the number of (cid:11)-MSH cells in both the pars inter- etal.,1992),thatthisantagonistissimplyanexcessof
media and pars distalis, the cells are usually more unattached receptors. This would be conceptually
concentrated in the latter site (Coates et al., 1986). similar to the circumstance of soluble cytokine recep-
The number of melanotrophs in the human pituitary tors,suchasthesolubleIL-1andTNFreceptors,that
decreaseswithage;pituitariesofanencephalicsdonot are believed to modulate the actions of the cytokines
contain (cid:11)-MSH cells (Visser and Swabb, 1979). by binding them.
(cid:11)-MSH occurs in widespread regions of the brain Inconsideringtheroleof(cid:11)-MSHinmodulationof
in a distribution that is relatively consistent across host responses, it is appropriate to recognize that the
species(Eberle,1988).Immunoreactivecellbodiesare peptide is located, as stated above, within barriers
concentrated in three regions: first, the arcuate or to invasion and challenge, such as the skin and gut.
infundibularnucleusofthehypothalamus,fromwhich (cid:11)-MSH occurs in the skins of both albino and
fibers project throughout the hypothalamus and into pigmentedratsandinhumanepidermis(Thodyetal.,
the preoptic region, thalamus, midbrain (periaque- 1983); (cid:11)-MSH in rat skin is not of pituitary origin
ductal gray), amygdala, lateral septum, and asso- because it is also present in hypophysectomized
ciated telencephalic structures; second, the nucleus animals(Thodyetal.,1983).Immunoreactive(cid:11)-MSH
tractus solitarius of the brainstem, from which both is found in the mucosal barrier of the gastrointestinal
locally distributed and descending fibers arise; and tract, especially concentrated in the duodenum but
third, the dorsolateral hypothalamus/zona incerta, also found in substantial concentrations in the ileum,
with projections that extend into the dorsal hippo- jejunum, and colon in intact and hypophysectomized
campus and cerebral cortex. Whereas cells in the first rats (Fox and Kraicer, 1981). The nonhypophysial
two regions contain POMC mRNA and POMC originofthepeptidewithinthesebarriersbetweenthe
derivatives such as (cid:12)-endorphin (Bloch et al., 1979; host and the external environment is not proof of
a suppressive host response influence of the local
peptide; however, with evidence of the anticytokine
actions of (cid:11)-MSH described below, the presence of
Table 1 Some cell types that secrete (cid:11)-MSH
thepeptideinthesebarriersisconsistentwithsuchan
influence.
Melanotrophs of pars Eberle, 1988
(cid:11)-MSHalsooccursinotherperipheraltissuessuch
intermedia and pars distalis
astheplacenta(Clarketal.,1978),testes,andovaries
Corticotrophs in humans Eberle, 1988
(Bardin et al., 1987), and the adrenal medulla (Evans
Human melanoma Loir et al., 1997, 1998 et al., 1983). Although in these sites the molecule
Placental cells Kreiger, 1982 might participate in entirely disparate functions, it is
not unreasonable to ask if its role in these peripheral
1386 James M. Lipton and Anna Catania
tissues is also to modulate actions of cytokines pro- acute challenge to the host. An increased plasma (cid:11)-
ducedinthecourseofnormalmetabolismandduring MSH concentration would indicate that the molecule
host challenge and/or to counter microbial invasion. becomes available to influence host reactions taking
Of particular importance, (cid:11)-MSH is produced by placeinwidespreadregionsofthebody.Suchchanges
multiple cell types in response to host challenge in plasma (cid:11)-MSH concentration do occur; they are
(Table 2). Of great importance to understanding the described in a following section.
roleof(cid:11)-MSHinhostresponsesisthevariationinits
concentration in the circulation in disease and in
Eliciting and inhibitory stimuli,
including exogenous and
Table 2 Production of (cid:11)-MSH by cells activated in the
endogenous modulators
host response
Human monocyte/ Rajora et al., 1996 (cid:11)-MSH is induced by proinflammatory agents
macrophages (Table 3) and, in turn, the peptide inhibits the
production of proinflammatory mediators (Table 5).
Murine monocyte/ Star et al., 1995
macrophages It is likely that the latter influence occurs via preven-
tion of activation of nuclear factor (cid:20)B (NF(cid:20)B), as
Lymphocytes Smith and Blalock, 1995
described in the section on In vitro findings. Inhib-
Keratinocytes Chakraboty and Pawelek, 1993
ition of this transcription factor by (cid:11)-MSH results
Murine microglia Delgado et al., 1998 from preservation of I(cid:20)B(cid:11).
Table 3 Examples of (cid:11)-MSH inducers RECEPTOR UTILIZATION
LPS Catania et al., 1998a Thereceptorsthat underliethe effectsof(cid:11)-MSHand
Antigen Taylor and Streilein, 1996 relatedmelanocortinshavebeenidentifiedandcloned.
Five G protein-linked receptors (MC-1R through
LPS + IFN(cid:13) Delgado et al., 1998
MC-5R) are currently recognized. When transfected
PMA Lipton et al., 1999
intocarriercells,thesereceptorsincreaseintracellular
TNF Rajora et al., 1996 cAMP upon stimulation with melanocortin mole-
HIV envelope Catania et al., 1998b cules. The receptors are widely distributed in
glycoprotein gp 120 peripheral tissues and in the brain (Tatro, 1996). All
of the receptors react to (cid:11)-MSH and one subtype,
Table 4 Melanocortin receptor subtypes and loci in host cells and brain
Receptor subtype Loci References
MC-1R Human monocyte/macrophages Rajora et al., 1996
Rodent monocyte/macrophages Star et al., 1995
Human neutrophils Catania et al., 1996
Periaqueductal gray Xia et al., 1995
Whole murine brain Rajora et al., 1997a
MC-2R Adrenal cortex Mountjoy et al., 1992; Cammas et al., 1995
MC-3R Human monocyte/macrophages Taherzadeh et al., 1999
Hypothalamus, septum, thalamus, other Gantz et al., 1993; Roselli-Rehfuss et al., 1993
MC-4R Limbic structures, hypothalamus, Mountjoy et al., 1992; Gantz et al., 1993
hindbrain, spinal cord
MC-5R Human monocyte/macrophages Chhajlani and Wikberg, 1992; Taherzadeh et al., 1999
Human and mouse brains Chhajlani and Wikberg, 1992;
Gantz et al., 1994
(cid:11)-MSH 1387
MC-2R, is believed to be the ACTH receptor. As therefore inhibition of NF(cid:20)(cid:12) activation (Table 6).
indicated in Table 4, there are differences in ligand The (cid:11)-MSH peptides also inhibit PMN migration
specificityofthereceptorsubtypes.Allsubtypeshave (Catania et al., 1995) and they induce anti-
been demonstrated in human cells and several have inflammatory IL-10 (Bhardwaj et al., 1996). (cid:11)-MSH
been isolated from other species. These receptors are peptideslikewiseinhibitHIV-1inchronicallyinfected
the smallest G protein-linked receptors yet described U1 cells and in actively infected monocyte/macro-
and, like the anti-inflammatory effects of the pep- phages (Barcellini et al., 1998).
tides, appear to be highly conserved across species.
That melanocortin peptides characteristically in-
Antimicrobial Activity of (cid:11)-MSH Peptides
crease intracellular cAMP is consistent with evidence
thatincreasesincAMPinhostcellsareassociatedwith (cid:11)-MSH and shorter amino acid sequences derived
anti-inflammatory influences. There is evidence that from it have recently been found to have antimicro-
the IP pathway is also activated in cells transfected bialinfluencesagainsttwomajorrepresentativepath-
3
with MC-3R plasmid vector (Konda et al., 1994). ogens: Staphylococcus aureus and Candida albicans.
(cid:11)-MSH (1–13) and its C-terminal tripeptide (11–13,
KPV) significantly inhibited S. aureus colony forma-
IN VITRO ACTIVITIES tionandreversedtheenhancingeffectofurokinaseon
colony formation. Antimicrobial effects occurred
In vitro findings over a broad range of concentrations, including the
physiological (picomolar) range. Lower concentra-
tions of (cid:11)-MSH peptides likewise reduced viability
The primary effects of (cid:11)-MSH in vitro are inhibi-
and germ tube formation of the yeast C. albicans.
tion of production and action of proinflammatory
The most effective peptides were those bearing the
cytokines (Table 5) and preservation of I(cid:20)(cid:12) and
C-terminal tripeptide of the (cid:11)-MSH sequence, i.e.
(cid:11)-MSH (1–13), (6–13), and (11–13). The (cid:11)-MSH
Table 5 (cid:11)-MSH inhibits production of pro- sequence (4–10), important for melanotropic effects,
inflammatory mediators was also effective but significantly less potent.
ACTH (1–39), the precursor of (cid:11)-MSH, and an
IL-1(cid:12) Catania et al., 1998a, 1998b intermediate sequence of it, ACTH (18–39), which
does not include the (cid:11)-MSH amino acid sequence,
IL-2 Taylor and Streilein, 1996
had no significant candidacidal effects. These anti-
IL-6 Catania et al., 1998a, 1998b
microbialinfluencesof(cid:11)-MSHpeptidesareprobably
IL-8 Lipton et al., 1999 mediated by their induction of cAMP. Indeed, this
TNF(cid:11) Rajora et al., 1997a messenger was significantly augmented in peptide-
treatedyeastandtheadenylylcyclaseinducerforsko-
IFN(cid:13) Lipton and Catania, 1997
linsignificantlyreducedC.albicanscolonyformation.
Neopterin Rajora et al., 1996
Reduced killing of pathogens is a detrimental con-
Nitric oxide Star et al., 1995 sequence of therapy with common anti-inflammatory
drugs and (cid:11)-MSH has potent anti-inflammatory
Table 6 (cid:11)-MSH inhibits NF(cid:20)B activation and I(cid:20)B degradation
Cells/tissue Peptide influence Reference
U-937 cells Inhibited NF(cid:20)B activation/degradation of I(cid:20)B Manna and Aggarwal, 1998
(human lymphoma)
Human glioma in vitro/ Inhibited NF(cid:20)B activation/degradation of I(cid:20)B Ichiyama et al., 1999a
murine brain in vivo
Murine brain in vivo, Inhibited NF(cid:20)B activation/degradation of I(cid:20)B Ichiyama et al., 1999b
systemic peptide
Peripheral NF(cid:20)(cid:12)/ Inhibiton of peripheral activation of Ichiyama et al., 2000a, 2000b
CNS peptide in mouse NF(cid:20)B by systemic peptide
Human glioma Autocrine regulation of NF(cid:20)B activation Ichiyama et al., 1999a
1388 James M. Lipton and Anna Catania
effects. Therefore, it was important to determine potency of the peptide in control of inflammation
whether(cid:11)-MSHinhibitsC.albicanskillingbyhuman and microbial invasion, the most ancient host
neutrophils. (cid:11)-MSH peptides did not reduce killing responses, suggest that the peptide is pivotal in
but rather enhanced it, likely as a consequence of its these functions.
direct antimicrobial activity. The addition of anti-
microbial activity to the established anti-inflamma-
Species differences
tory and antipyretic effects suggest that the peptides
might be useful in treatment of disorders in which
both inflammation and infection occur. To date there are no established differences across
species in host responses to (cid:11)-MSH ligands. The
antipyretic and anti-inflammatory effects of the pep-
Regulatory molecules: Inhibitors
tideshavebeendemonstratedinmice,rats,rabbits,cats,
and enhancers dogs,andsquirrelmonkeys.Theconsistencyisperhaps
notsurprisinggiventheconsistencyacrossspeciesofthe
aminoacidsequencesin(cid:11)-MSHpeptides.
Research on enhancement and inhibition of in vitro
activitiesof(cid:11)-MSHhasbeenlimited.Ingeneral,LPS
and proinflammatory cytokines induce production Knockout mouse phenotypes
and release of the peptide. Any agents that modulate
their stimuli reduce production of the peptide.
There are no (cid:11)-MSH knockout animals to date. This
is in part because the peptide is derived from POMC
Bioassays used and no animals have been produced in which genes
for PC1/PC2 are specifically disrupted. There are
micedeficientintwomelanocortinreceptor subtypes:
(cid:11)-MSH peptides characteristically increase cAMP
MC-1RandMC-4R.ThephenotypeforMC-1Rmice
within those cells that bear melanocortin receptors.
is yellow coat and adult obesity (recessive yellow
Thus, such increases in normal or receptor plasmid
mouse). Recent evidence indicates that (cid:11)-MSH pep-
transfected cells can be used to screen for receptor
tides have anti-inflammatory effects in the MC-1R
ligands, establish antagonists, etc.
knockout animals (Lipton et al., 1999), indicating
that this receptor subtype is not essential for this
function. As with other POMC-derived peptides, it
IN VIVO BIOLOGICAL
appears that related receptor subtypes can and do
ACTIVITIES OF LIGANDS IN participate when one subtype is deleted. Inactivation
ofMC-4Rresultsinmaturity-onsetobesityassociated
ANIMAL MODELS
withhyperphagia,hyperinsulinema,andhyperglycemia
(Huszar et al., 1997). Whether MC-4R knockout
Normal physiological roles
animals have deficient anti-inflammatory response to
(cid:11)-MSH peptides has not been established.
(cid:11)-MSHpeptideshavecleareffectsonpigmentationin
amphibians; the precise role of dermal (cid:11)-MSH in
Transgenic overexpression
human skin pigmentation, if any, remains unclear.
TheACTHpeptideoccursinhigherconcentrationsin
theskin,itactsonsimilarreceptors,anditappearsto At this time no transgenic animals overexpressing
be more potent than (cid:11)-MSH in stimulating melano- (cid:11)-MSHhavebeenproduced.However,inpreparation
genesis. Thody and Graham (1998) suggest that for development of such animals, a plasmid vector
(cid:11)-MSH should not be viewed solely as a pigmentary encoding (cid:11)-MSH and containing enhancers and
peptide since it has many different actions and promoters driving transcriptions of IL-6 and
its primary role in the skin may be to maintain (cid:11)-MSH genes was inserted into human glioma cells
homeostasis. (Ichiyamaet al., 2000a).NF(cid:20)B activationinducedby
The widespread distribution of (cid:11)-MSH and LPS was inhibited in the transfected cells. Western
its receptors make it difficult to link this agent to analysis indicated that this inhibition was linked to
a specific function or functions. It is unlikely that a preservation of I(cid:20)B2 protein. Chloramphenicol ace-
peptide with such a lengthy history has a role in a tyltransferase assay indicated that NF(cid:20)B-dependent
single function such as regulation of coat color or reporter gene was suppressed in glioma cells with
body weight (Hagen et al., 1999). However, the (cid:11)-MSH vector. Fluorescence staining confirmed that
(cid:11)-MSH 1389
these glioma cells express (cid:11)-MSH receptors. The These anti-inflammatory effects are believed to
combined evidence of (cid:11)-MSH receptors, (cid:11)-MSH result from three actions of the peptides:
production,and(cid:11)-MSHproduction-associatedinhib-
itionoftheinflammatoryNF(cid:20)Bpathwaysuggestsan 1. Direct action on host cells
autocrine circuit based on the peptide in these 2. Direct action on host cells within the brain
3. Actions on melanocortin receptors in the brain
transfected cells. These results predict that animals
that overexpress (cid:11)-MSH will have reduced inflam-
Direct Action on Host Cells
matory reactions.
Agouti protein antagonizes the effects of (cid:11)-MSH Although both neutrophils and macrophages are
and other melanocortins. The molecule appears to important in many types of inflammation, there is a
compete with (cid:11)-MSH for the melanocortin receptor tendencytoassociateneutrophilswithacuteordevel-
MC-1R. It is believed that there is a novel signaling oping inflammation and macrophages with longer-
mechanism whereby (cid:11)-MSH and Agouti protein term or chronic inflammatory reactions. Evidence
function as independent ligands, with each inhibiting describedintheinvitrosectionindicatesthat(cid:11)-MSH
the binding of the other and transducing opposing peptidesinhibitneutrophilmigrationinvitro(Catania
signals through a single receptor. It may be that such et al., 1996) This inhibition also occurs in vivo (Chiao
a relation with Agouti protein also occurs with other et al., 1997). Also described in the in vitro section
melanocortin receptor subtypes. That Agouti protein are the effects of (cid:11)-MSH on NF(cid:20)B activation, or
hypersecreting mice have augmented inflammatory inflammatory cytokine production, and related host
responses was indicated by the reactions of the responses. Despite the latter in vitro data, there is no
animals to systemic endotoxin (Lipton et al., 1999). systemic evidence of (cid:11)-MSH peptide influence or
These mice had greater increases in serum IL-6 fol- macrophage counts in in vivo models of chronic
lowing systemic injections of LPS. This increase may inflammation.
occur by virtue of inhibition of endogenous (cid:11)-MSH
at the level of the melanocortin receptor. Direct Action on Host Cells within the Brain
There is substantial evidence, described in the in vitro
section, ofdirectinhibitoryactionsof(cid:11)-MSHpeptides
on inflammatory actions in nonneuronal cells within
Pharmacological effects
the brain, both astrocytes and microglia. The latter
cells share fuctions of inflammatory host cells in the
To date, (cid:11)-MSH peptides have been shown to periphery. There is also evidence that the peptides
modulate inflammation in over 20 animal models modulate CNS inflammation within the living brain.
(Lipton and Catania, 1997). These peptides suppress Such an influence may be very important in view
all in vivo forms of inflammation commonly recog- of the recent evidence that local inflammatory pro-
nized (Table 7). cesses, such as the induction of TNF(cid:11), contribute to
Table 7 Commonly recognized forms of inflammation
Forms of Representative references
inflammation
Acute inflammation Hiltz and Lipton, 1990 (dermal inflammation);
Chiao et al., 1997 (renal inflammation)
Delayed hypersensitivity Hiltz and Lipton, 1990 (dermal inflammation);
Grabbe et al., 1996
Chronic inflammation Ceriani et al., 1994 (arthritis model);
Rajora et al., 1997b (inflammatory bowel disease model)
Systemic inflammation Catania et al., 2000
CNS inflammation Huh et al., 1997 (experimental stroke);
Ichiyama et al., 1999a, 1999b
(generalized CNS inflammation)
1390 James M. Lipton and Anna Catania
Alzheimer’s disease, multiple sclerosis, stroke, and blocks the anti-inflammatory effects of centrally
other CNS disorders. administered (cid:11)-MSH peptides.
(cid:12) -Adrenergic blockers given systemically have a
2
similar effect, indicating that a (cid:12) -receptor is part of
2
the inhibiting circuit. It appears then that normally
Actions on Melanocortin Receptors in the Brain
bothcentralandperipheral(cid:11)-MSHreceptorspartici-
Actions on melanocortin receptors in the brain
pate in modulation of inflammation. Mice with
that activate descending anti-inflammatory neural
inflammation in the hind paw and spinal transection
pathways and thereby modulate peripheral inflam-
do not show an anti-inflammatory effect of central
mation have a very powerful effect which has been
(cid:11)-MSH. However, these same animals with transac-
documented in several animal models (Table 8).
tions show reduced inflammation when (cid:11)-MSH is
The major theory of the mechanism of the given systemically. This result indicates that there are
peripheral anti-inflammatory action of central (cid:11)- at least two pools of (cid:11)-MSH receptors that parti-
MSHpeptidesisderivedfromevidenceofdescending
cipateincontrolofinflammation:onepoolwithinthe
neural pain modulation pathways and concepts of
brain, another in the periphery.
neurogenic inflammation. In brief, inflammation is
normally promoted by neural influences. In the case
Interactions with cytokine network
of an injury at a localized site in the skin of the foot,
for example, neural signals travel in fine fibers to the
dorsalrootsofthespinalcord.Signalsmayascendto The primary conclusions regarding the influence of
the brain to signal pain, but in the case of inflam- (cid:11)-MSH on the cytokine network in vivo is that the
mation, there is a descending train of signals back peptides modulate actions of proinflammatory cyto-
down the terminals that previously transduced sen- kines and/or of production of the cytokines. Central
sory (afferent) information. These now efferent fibers administrationof(cid:11)-MSHantiserumincreasedplasma
release inflammatory agents in the vicinity of the ACTH and corticosterone responses induced by cen-
injury or invasion. These agents, including calci- tral injection of IL-1(cid:12) in rats (Papadopoulos and
tonin gene-related peptide and substance P, increase Wardlaw, 1999).
vascular permeability and induce histamine release, Recent evidence (Huang et al., 1999) indicates that
therebypromotinginflammationinconcertwithlocal systemic injection of LPS suppresses food intake
neutrophils and other host cells. This neurogenic and that (cid:11)-MSH suppresses this cytokine-mediated
inflammation can be inhibited by injections into the effect even further, resulting in even lower intake.
brain ventricles of (cid:11)-MSH peptides. (cid:11)-MSH peptide Nanogram doses of (cid:11)-MSH given centrally block
receptors within the brain (perhaps MC-1R, 3R, 4R, increased nociception induced by central IL-6 (Oka
and 5R) drive descending anti-inflammatory signals etal.,1995).(cid:11)-MSHgiveni.p.tomiceinhibitedPGE
that are believed to inhibit release of the chemical productionbyhippocampaltissueinvivo(Weidenfeld
mediators released from peripheral nerve fibers. The etal.,1995).Central(cid:11)-MSHalsoblockstheimmuno-
main proof of this is that severing the spinal cord suppressiveeffectofcentralIL-1(cid:12)(Weissetal.,1994).
Table 8 Inhibition of peripheral inflammation by central (cid:11)-MSH peptides
Agents/reactions Central peptide Reference
Picryl chloride (cid:11)-MSH 1–13 Lipton et al., 1991
Picryl chloride NDP-(cid:11)-MSH 1–13 Dulaney et al., 1992
IL-1(cid:12) (cid:11)-MSH 1–13/D-Val subs Watanabe et al., 1993
IL-1(cid:12), IL-8, LTB , PAF (cid:11)-MSH 1–13; (cid:11)-MSH 11–13 (IL-1(cid:12)) Ceriani et al., 1994
4
IL-1(cid:12)/(cid:12) -adrenergic blockade or (cid:11)-MSH 1–13 Macaluso et al., 1994
2
spinal transection
Circulating TNF(cid:11) (cid:11)-MSH 1–13 Rajora et al., 1997a
Circulating/lung, liver TNF(cid:11)/NO; (cid:11)-MSH 1–13; antiserum Delgado et al., 2000
lung MPO
Endotoxemia (cid:11)-MSH 1–13 Lipton et al., 1999
(cid:11)-MSH 1391
IL-1(cid:12)-inducedinflammationwasinhibitedby(cid:11)-MSH secretion. Endogenous GABA tonically inhibits
peptide and fragments given systemically or centrally release of (cid:11)-MSH from rat hypothalamic slices
(Watanabeetal.,1993).Migrationofneutrophilsinto (Mabley et al., 1991). Activation of 5-hydroxytrypta-
air pouches injected with IL-1(cid:12) was inhibited by mine (5-HT) receptors stimulates (cid:11)-MSH release and
coadministration of (cid:11)-MSH (Perretti et al., 1993). apomorphine blocks this stimulatory effect, suggest-
Both (cid:11)-MSH (1–13) and 11–13 inhibited anorexia ing that there is a direct antagonism between
caused by central IL-1 (Uehara et al., 1992). (cid:11)-MSH dopaminergic and serotoninergic regulation of (cid:11)-
(1–13) and D-val (11–13) inhibited acute inflamma- MSH release (Carr et al., 1991). Stimulation of (cid:20)
tion in mice caused by IL-1(cid:12), IL-6, and TNF(cid:11) (Hiltz opioid receptors inhibits the activity of intermediate
etal.,1992).Inrabbits,(cid:11)-MSHinhibitedfevercaused lobe tuberohypophysial dopamine neurons and
by IL-6 and TNF(cid:11) (Martin et al., 1991). Ten milli- increases secretion of (cid:11)-MSH from the melanotrophs
grams of (cid:11)-MSH given i.c.v. inhibited IL-1-induced (Manzanares et al., 1990). (cid:12)-Adrenoreceptor activa-
elevations in plasma ACTH and corticosterone and tion causes release of (cid:11)-MSH in response to certain
decreases in NK cell activity (Weiss et al., 1991). stresses,suchasintermittentfootshock(Berkenbosch
Central IL-1 in rats rapidly suppressed cellular et al., 1984).Histaminehasastimulatoryeffecton(cid:11)-
immune responses in peripheral lymphocytes; central MSH secretion, probably through release of epi-
(cid:11)-MSH blocked these effects (Sundar et al., 1989). nephrine(KniggeandWarberg,1991).Corticotropin-
IL-1(cid:12) induced fever, increased production of serum releasing factor (CRF), which plays a major role in
amyloid P, augmentation of circulating neutrophils induction of ACTH secretion, does not seem
were all inhibited by (cid:11)-MSH; the peptide also pre- important in control of (cid:11)-MSH release. PFU 83, a
vented IL-1 induction of corticosterone and depres- rat monoclonal antibody to CRF, did not affect
sion of contact sensitivity (Daynes et al., 1987). resting or ether-induced (cid:11)-MSH secretion (Van Oers
et al., 1989). Also, CRF given in doses that caused a
Endogenous inhibitors and marked increase in plasma ACTH in rabbits did not
promote (cid:11)-MSH release (Catania et al., 1991).
enhancers
The posttranslational processing of POMC, which
PATHOPHYSIOLOGICAL ROLES
yields the mature hormones, includes a number of
steps: glycosylation, phosphorylation, tissue-specific IN NORMAL HUMANS AND
proteolytic cleavage, amidation, and acetylation. DISEASE STATES AND
Some of these posttranslational modifications can be
DIAGNOSTIC UTILITY
regulated by neuronal factors (Lamacz et al., 1991)
(Table1).Forinstance,dopamineinhibitsacetylation
Normal levels and effects
of (cid:11)-MSH and thus reduces secretion of the bio-
logicallyactiveforminthefrog(Lamaczetal.,1991).
Administration of the dopamine antagonist haloper- To evaluate potential use of plasma (cid:11)-MSH
idol to rats resulted in a 4- to 6-fold (time- and dose- concentrations as estimates of disease, the first step
dependent) increase in the concentration of pars was to determine normal values in healthy subjects
intermedia POMC mRNA (Chen et al., 1983). In (Catania et al., 1998a). Plasma concentration of (cid:11)-
contrast, ergocryptine, a dopamine antagonist, MSH (Eurodiagnostica RIA kit, Malmo¨, Sweden) in
decreased POMC mRNA in the rat pars intermedia 234 normal blood donors was 21.30(cid:6)0.63pg/mL
2-to 3-fold(Chenet al., 1983).Stress-induced activa- (mean(cid:6)SE; range 1.5–75.2). There was no difference
tion of (cid:11)-MSH secretion may be due, in part, to between mean concentrations of the peptide in males
decreased activity of tuberohypophysial dopamine and females(P>0.05).To determinewhetherplasma
neurons in the intermediate lobe (Lookingland et al., concentrations of (cid:11)-MSH fluctuate over time, the
1991). Endogenous dopamine inhibits (cid:11)-MSH peptide was measured every 15 minutes over a 180-
release from the rat hypothalamus via D -dopamine minute period in five normal subjects. No major
2
receptors (Tiligada and Wilson, 1989). There appears variationswereobserved(repeatedmeasuresANOVA
to be a feedback circuit between (cid:11)-MSH and onranks:P=0.7).Tolearnwhetherconcentrationsof
dopamine; central (cid:11)-MSH selectively activates (cid:11)-MSH are altered with aging, (cid:11)-MSH in plasma of
tuberoinfundibular dopaminergic neurons, thereby 125 normal elderly subjects (79.63(cid:6)5.8 years, range
inhibiting its own release (Lindley et al., 1990). 66–95) was measured. Mean plasma (cid:11)-MSH in aged
Although the evidence is incomplete, several other subjects was lower than in young controls
neurotransmitters likewise influence (cid:11)-MSH (15.87(cid:6)0.8pg/mL, P<0.001).
1392 James M. Lipton and Anna Catania
(cid:11)-MSH was measured in 106 newborns at delivery cytokines that promote HIV replication in infected
and during the first week of postnatal life. (cid:11)-MSH cellswereallinhibitedby(cid:11)-MSH.Indeed,IL-1,IL-6,
concentration was greater in premature than in full- and TNF(cid:11) were reduced by (cid:11)-MSH in whole blood
term neonates. Plasma (cid:11)-MSH was more elevated in of HIV-positive patients (Catania et al., 1998b).
complicated than in uncomplicated delivery and the Further, recent research in HIV-infected cells shows
peptide significantly decreased 12 hours after birth in that (cid:11)-MSH and its C-terminal tripeptide Lys-Pro-
term newborns (Mauri et al., 1993). Val inhibit HIV-1 replication in chronically infected
promonocyticU1 cells and in acutely infectedhuman
myocytes (Barcellini et al., 1998).
Role in experiments of nature and
disease states Sepsis Syndrome
Although in normal human subjects injected with
Alterationsincirculating(cid:11)-MSHhavebeenobserved endotoxin there was an increase in plasma (cid:11)-MSH
in a number of diseases (Table 9). (Cataniaetal.,1995),duringearlyphasesofnaturally
occurring sepsis syndrome concentrations of the
peptide were reduced (Catania et al., 2000). Plasma
HIV Infection
(cid:11)-MSH returned to normal values in patients who
In research on HIV-infected patients,plasma concen- recovered and remained low in those who died.
trations of (cid:11)-MSH in patients of different CDC Reduction of (cid:11)-MSH is likely to have detrimental
groups were compared. Circulating (cid:11)-MSH was ele- consequences in patients with sepsis syndrome and
vated in plasma of HIV-infected patients of the CDC to contribute to severity of systemic inflammation.
groupsIIIandIV(CataniaandLipton,1993;Catania Consistent with this idea, a negative correlation was
etal.,1994).Furtherresearchonrelationsbetween(cid:11)- found between concentrations of (cid:11)-MSH and TNF(cid:11)
MSHanddiseaseprogressioninHIV-infectedpatients in plasma of septic patients. Although it is possible
showed that greater concentrations of (cid:11)-MSH are thatreduced(cid:11)-MSHandelevatedTNF(cid:11)coexistedin
associated with reduced disease progression. The patients with more severe disease, it may well be that
association between elevated (cid:11)-MSH and reduced reduction in endogenous (cid:11)-MSH promoted TNF(cid:11)
AIDS-related events or death was even more pro- production. Addition of (cid:11)-MSH to LPS-stimulated
nounced in patients with baseline CD4+ T cells whole blood samples of septic patients inhibited pro-
<200/L (Airaghi et al., 1999). This observation was duction of TNF(cid:11) and IL-1 in a concentration-
notsurprisingbecauseproductionofproinflammatory dependent manner.
Table 9 Plasma concentrations of (cid:11)-MSH in human diseases
Condition Comments Reference
HIV infection Increased in plasma of CDC III and IV patients Catania et al., 1993, 1994
HIV infection Reduced disease progression in patients with Airaghi et al., 1999
elevated plasma (cid:11)-MSH concentrations
Rheumatoid arthritis Increased in synovial fluid of patients with Catania et al., 1994
greater inflammation; normal in plasma
Acute myocardial infarction Increased in plasma during AMI in patients Airaghi et al., 1995
(AMI) receiving thrombolytic agents
Multiple sclerosis Increased in patients with greater disability score Catania et al., unpublished results
Sepsis syndrome Reduced in plasma during critical phase of Catania et al., 2000
sepsis syndrome/septic shock
Hemodialysis Increased in plasma Catania et al., unpublished results
Parkinson’s disease Increased in CSF Rainero et al., 1988b
Alzheimer’s disease Reduced in brain tissue Arai et al., 1986;
Rainero et al., 1988a
