get news letter from newsletter issue guid

Not directly I don't think, but you could get the newsletter issue first:

var newsletterIssue = IssueInfoProvider.GetIssueInfo(issueGuid, SiteContext.CurrentSiteID);

Then do a GetNewsletterInfo lookup using newsletterIssue.IssueNewsletterID:

var newsletter = NewsletterInfoProvider.GetNewsletterInfo(newsletterIssue.IssueNewsletterID);