Here is how you can do this:
var ps = document.getElementsByTagName('p');
    foreach = Array.prototype.forEach;
foreach.call(ps, function (p) {
    var content = p.innerHTML;
    p.innerHTML = content.replace(/\{(.*?)\}|\((.*?)\)/g, function (m) {
        return '<span style="font-weight: bold;">' + m + '</span>';
    });
});
And of course a fiddle.
For the example you need just pure JavaScript, no additional libraries.
If you don't want to see the brackets in the result you can use:
var ps = document.getElementsByTagName('p');
    foreach = Array.prototype.forEach;
foreach.call(ps, function (p) {
    var content = p.innerHTML;
    p.innerHTML = content.replace(/\((.*?)\)|\{(.*?)\}/g, function (m) {
        return '<span style="font-weight: bold;">' + m.replace(/[\(\)\{\}]/g, '') + '</span>';
    });
});
Fiddle: http://jsfiddle.net/ma47D/4/
Best regards!