Cardiovascular Journal of Africa: Vol 28 No 1 (January/February 2016)

CARDIOVASCULAR JOURNAL OF AFRICA • Volume 28, No 1, January/February 2017

AFRICA

. argued that their result indicates deficient adropin expression

in EPACS patients, and adropin deficiency could be involved in

the development and progression of EPACS. The reason for the

difference in results is unknown.

et al

. measured single-time serum adropin levels in EPACS

patients, while in our study we measured the time courses of

serum and salivary adropin levels in patients and controls.

In our

zero-time samples, serum and saliva adropin values were slightly

(insignificantly) lower in EPACS patients than in controls, and

this could have corresponded to the single-time values measured

by Yu

et al.

The adropin levels then started to increase and

peaked at six hours after EPACS, potentially explaining the

apparent conflict. Also, the mean adropin level is reported to be

significantly lower in certain diseases, including in patients with

late saphenous vein graft occlusion.

Another possibiliy is that

the adropin level was reduced in the baseline blood sample taken

within 30 to 40 minutes of admission to hospital.

Although the glucose level was within normal physiological

limits in the EPACS patients, it was higher than in the controls.

This could have been due to the effect of increased epinephrine

secretion after EPACS, causing glycogenolysis in the liver

and releasing glucose into the blood.

29,30

There was an inverse

relationship between adropin and glucose levels.

10,12,16,17

et al

reported the same glucose levels. Different drugs used to treat

EPACS could also have affected the adropin levels differently.

Here we also assumed that the increased expression of adropin

in saliva and serum could indicate acute cardiac injury caused by

ACS, and could be central to the development of key pathologies

associated with EPACS in humans, but further studies are

needed to resolve the conflict between findings.

Salivary glands are now known to secrete a range of peptides/

proteins involved in regulating endocrinemetabolism.

Therefore,

in this study we also investigated whether the salivary glands

produce adropin. The immunochemical findings indicated that

adropin is one of the most abundant proteins secreted by

human salivary glands, as previously described for peptides such

as irisin,

ghrelin

23,24,31

and hepcidin.

Adropin is synthesised

in the intercalated duct of the parotid, the mucous acinus

of the sublingual, and the striated and interlobular ducts of

the submandibular glands, and is co-localised with irisin,

ghrelin

23,24,31

and hepcidin

in those glands. Its expression has

also been demonstrated in the liver, brain, cerebellum, kidneys,

heart, pancreas and vascular tissues.

The ELISA results in

this study revealed that salivary and serum adropin levels were

substantially higher in EPACS patients than in the controls and

stable CAD patients (0.67–0.8 ng/ml).

The adropin levels in saliva were already elevated and

increasd further at four and six hours after EPACS. The origin

of the high salivary adropin levels is not known but it probably

comes from the plasma after saturation, or a larger amount of

cardiac adropin is secreted by the salivary glands. Because there

is evidence that some of these striated duct proteins are secreted

basally, i.e. into the circulation,

33-35

we concluded that EPACS

induces the synthesis of salivary adropin, and the quantity of

adropin in the saliva could be useful for early management

of EPACS, in conjunction with serum adropin measurement.

This research also showed that blood levels of CK-MB and

CK increased within 30 to 40 minutes (zero time) after EPACS,

peaked at six hours, and started to decrease after 12 hours but

remained higher than control levels, even at 48 hours.

In this study, receiver operating characteristic (ROC) curves

were used to determine the sensitivity and specificity of serum

and saliva adropin levels in EPACS patients. At four hours

after ACS, serum adropin exhibited 91.7% sensitivity and 50%

specificity at a confidence interval of 95% when the cut-off

value was 4.43 ng/ml, while serum troponin I exhibited 100%

sensitivity and 100% specificity at a confidence interval of 95%

when the cut-off value was 0.141 ng/ml. At four hours after

ACS, the saliva adropin concentration had a sensitivity of 91.7%

and a specificity of 57% at a confidence interval of 95% when

the cut-off value was 4.12 ng/ml. At six hours after ACS, the

serum adropin exhibited 91.7% sensitivity and 64% specificity

at a confidence interval of 95% when the cut-off value was 5.37

ng/ml, while serum troponin I exhibited 100% sensitivity and

100% specificity at a confidence interval of 95% when the cut-off

value was 0.226 ng/ml. At six hours after ACS, the saliva adropin

concentration had a sensitivity of 91.7% and a specificity of

57% at a confidence interval of 95% when the cut-off value was

4.24 ng/ml. ROC curve analysis indicated that serum troponin

I and adropin concentrations diagnosed EPACS with over 90%

sensitivity in emergency, cardiology and cardovascular surgery

patients.

Serum and saliva adropin measurements were not as specific

as serum troponin I for diagnosing EPACS. Serum troponin

I was still superior to serum or saliva adropin, even though

there is the advantage of taking a salivary sample, which can

be collected without a venous blood sample. Nevertheless,

serum or saliva adropin could still be useful in diagnosing

EPACS in the future. First-generation ELISA adropin kits,

even from the same company, gave variable results, and there

was even more variability among kits from different companies.

More reproducible and automated adropin measurements could

overcome the current shortfall in specificity, since diagnosis of

EPACS by adropin is highly sensitive.

Our study had other limitations, especially the small number

of patients. Also, this was a single-centre study. The results

should be confirmed in a prospective, multicentre study

involving more patients. Moreover, adropin is expressed in many

tissues, and we did not examine their possible contributions as

potential confounders to our measured saliva and serum adropin

concentrations. Our previous animal studies revealed that liver

and kidney tissue adropin concentrations were considerably

changed by isoproterenol-induced EPACS.

The composition and production of saliva is also variable

(like urine),

and this theoretically makes the quantitative

determination of any substance unreliable. However, there was

a good correlation between the salivary and serum adropin

concentrations in this study. This may have been due to the

added protease inhibitor (aprotinin) before collection of the

biological samples.

Protease inhibitor protects the peptide of

interest (adropin) from degradation.

We also believe that a less

robust correlation in a larger study could be attributed to this

fact.

Conclusions

Despite these limitations, this study provides novel evidence

of a connection between increased saliva/serum adropin levels

and EPACS. The saliva adropin concentration was higher than

the serum adropin level in subjects with and without EPACS.