The role of the saliva antioxidant barrier to reactive oxygen species with regard to caries development

Figures & data

Figure 1. Antioxidants’ contribution in regulation and mechanism of action of cariogenic bacteria. Response of S. mutans to oxidative stress caused by ROS produced by neutrophils, fibroblasts, and other cells of the oral cavity is accompanied by, e.g. increased response from the bacterial enzymatic systems as intracellular NADH oxidase (Nox) in the SpxA1/ SpxB/ Rex-dependent modulation, and proteins that affect cellular redox status and are involved in the regulation of S. mutans’s metabolism. Antioxidant systems of the host (e.g. salivary GSH, GSSG, TAC) and exogenous factors (e.g. diet and hygienic habits) act in addition to antioxidant systems of bacteria.

Figure 2. Morphological assessment of Streptococcus sp. bacteria. Photograph shows macro- and micromorphology of Streptococcus sp. 1 – S. mutans colonies with characteristic white coloration on the tested medium; 2 – on blood agar (BA); 3 – S. mutans cells in Gram-stained preparation. Photograph 3 taken with an Olympus CX41 microscope, coupled to a CaMedia C5550 camera; 4 – S. mutans cells in a JEOL JSM-35CF SEM.

Figure 3. The percentage share of individual bacterial strains isolated from saliva of children with cavitated ECC, non-cavitated ECC, and children without symptoms of the disease.

Figure 4. (a). Salivary reduced-glutathione levels in all groups with ECC and in the control group. The median and interquartile range (box), and percentile 5–95% range (whiskers) are shown; P-values are given for the comparison of groups with each other (***P < 0.001 post-hoc Mann–Whitney test with Bonferroni correction). Cavitated patients with ECC; non-cavitated patients with ECC; control without lesions. (b). Salivary GSSG levels in all groups with ECC and in the control group. The median and interquartile range (box), and percentile 5–95% range (whiskers) are shown; P-values are given for the comparison of groups with each other (***P < 0.001 post-hoc Mann-–Whitney test with Bonferroni correction). Cavitated patients with ECC; non-cavitated patients with ECC; control without lesions. (c). Salivary TAC levels in all groups with ECC and in the control group. The median and interquartile range (box), and percentile 5–95% range (whiskers) are shown; P-values are given for the comparison of groups with each other (***P < 0.001 post hoc Mann–Whitney test with Bonferroni correction). Cavitated patients with ECC; non-cavitated patients with ECC; control without lesions.

Table 1. Adjusted relationships between reduced glutathione, oxidized glutathione and TAC and salivary bacterial profiles and dental caries progression.

Variables		GSH (mmol/l)	P*	Post hoc **	GSSG (mmol/l)	P*	Post hoc **	GSH/GSSG	P*	Post hoc **	TAC (mmol/l)	P*	Post hoc **
Bacterial profile of saliva	S. mutans (n = 12)	0.289	< 0.001	a	0.197	< 0.001	a	1.43	< 0.001	ab	1.74	< 0.001	a
	L. rhamnosus (n = 25)	0.276		a	0.186		b	1.5		a	1.65		ab
	S. sanguinis (n = 23)	0.255		b	0.173		c	1.44		ab	1.58		b
	S. mitis (n = 12)	0.241		bc	0.168		cd	1.41		bc	1.57		bc
	Others (n = 8)	0.187		c	0.148		d	1.27		c	0.54		c
Disease vs. Control	Non-cavitated group (n = 26)	0.261	< 0.001	a	0.174	< 0.001	a	1.48	< 0.001	ab	1.60	< 0.001	a
	Cavitated group (n = 27)	0.287		b	0.191		b	1.49		a	1.73		b
	Control (n = 27)	0.190		c	0.150		c	1.28		b	0.56		c

Data represent medians. Superscripts a, b, c denote groups differing on Mann–Whitney tests with Bonferroni correction. Groups denoted with the same letter did not show statistically significant differences. GSH – reduced glutathione; GSSG – oxidized glutathione.

*P-value obtained by the Kruskal–Wallis test adjusted for age, gender, frequency of snack eating per week, frequency of soda drinking per week, frequency of sugar drinking per week, and frequency of natural/hybrid/artificial feeding.

**P < 0.05.

Table 2. Relationship between salivary glutathione and TAC levels, and salivary bacterial profiles and dental caries.

Dependent Variables	Relative parameter value	SE	t	P
GSH level in saliva
S. mutans	Reference level
L. rhamnosus	−6.602	3.744	−1.764	0.082
S. sanguinis	−17.905	4.705	−3.805	<0.001
S. mitis	−32.746	5.098	−6.423	<0.001
GSSG level in saliva
S. mutans	Reference level
L. rhamnosus	−10.927	1.354	−8.071	<0.001
S. sanguinis	−14.987	1.702	−8.807	<0.001
S. mitis	−20.247	1.844	−10.981	<0.001
TAC level in saliva
S. mutans	Reference level
L. rhamnosus	−0.013	0.007	−1.81	0.074
S. sanguinis	−0.023	0.009	−2.519	0.014
S. mitis	−0.046	0.01	−4.569	<0.001
GSH level in saliva
Control	Reference level
Non-cavitated	60.462	3.554	17.014	<0.001
Cavitated	74.884	3.447	21.724	<0.001
GSSG level in saliva
Control	Reference level
Non-cavitated	17.073	1.285	13.284	<0.001
Cavitated	31.591	1.247	25.341	<0.001
TAC level in saliva
Control	Reference level
Non-cavitated	1.036	0.007	148.01	<0.001
Cavitated	1.153	0.007	169.9	<0.001

P-value obtained from linear regression model adjusted for age, gender, frequency of snack eating per week, frequency of soda drinking per week, frequency of sugar drinking per week, and frequency of natural/hybrid/artificial feeding.

P-value was acquired using a linear regression model adjusted for age and gender, amount of juices and sodas consumed, and feeding approach.

Figure 5. Scatterplots of the relationship between change in (a) GSH and age, (b) GSSG and age, and (c) TAC and age.